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Chemical and physical properties of algal methyl ester biodiesel containing varying levels of methyl eicosapentaenoate and methyl docosahexaenoate
Abstract
Microalgae are currently receiving strong consideration as an advanced biofuel feedstock because of their theoretically high yield (gal/acre/year) in comparison to terrestrial vegetable oil feedstocks. Microalgal lipids can be readily converted into a variety of biofuels including fatty acid methyl esters (i.e. biodiesel) via transesterification or alkanes via hydroprocessing. In contrast to paraffinic fuels whose properties can be tailored for a specific application, the properties of algal methyl ester biodiesel are directly related to the fatty acid composition of the algal lipids. Several microalgae species that are suitable for large scale cultivation such as those in the genus Nannochloropsis produce lipids that contain long chain-polyunsaturated fatty acids (LC-PUFA) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These constituents have high value as co-products but are problematic in terms of biodiesel properties such as ignition quality and oxidative stability. The objective of this study was to examine the effect of varying levels of EPA and DHA on algal methyl ester fuel properties. Oxidative stability, Cetane Number, density, viscosity, bulk modulus, cloud point and cold filter plugging point were measured for algal methyl esters produced from various microalgae feedstocks as well as model algal methyl ester compounds formulated to match the fatty acid composition of Nannochloropsis sp., Nannochloropsis oculata and Isochrysis galbana subjected to varying levels of removal of EPA and DHA. The results suggest that removal of 50 to 80% of the LC-PUFA from Nannochloropsis-based methyl esters would be sufficient for meeting existing specifications for oxidative stability. However, higher levels of LC-PUFA removal from Nannochloropsis-based methyl esters would be required to produce fuels with acceptable Cetane Number. The removal of EPA and DHA was shown to have a detrimental effect on cold flow properties since the algal methyl esters are also high in fully saturated fatty acid content.
... Biodiesel derived from microalgae such as Nannochloropsis salina, Spirulina platensis, and Scenedesmus exhibits different stability and viscosity profiles [101]. Generally, higher viscosity correlates with species rich in long-chain polyunsaturated fatty acids (LC-PUFAs), such as eicosapentaenoic acid and docosahexaenoic acid [102]. Spirulina platensis, with a high palmitic acid content, tends to have poor cold properties but remains within acceptable viscosity ranges at standard temperatures. ...
... As an example, among the 15 algae species [98], Nannochloris sp. had the highest kinematic viscosity, measuring 3.73 mm 2 /s. This variability is attributed to the lipid composition, particularly the presence of long-chain polyunsaturated fatty acids (LC-PUFAs) like eicosapentaenoic acid and docosahexaenoic acid [102]. Importantly, the removal of 50 to 80% of LC-PUFAs from Nannochloropsis-based methyl esters can bring the viscosity within current specifications, enhancing oxidative stability [102]. ...
... This variability is attributed to the lipid composition, particularly the presence of long-chain polyunsaturated fatty acids (LC-PUFAs) like eicosapentaenoic acid and docosahexaenoic acid [102]. Importantly, the removal of 50 to 80% of LC-PUFAs from Nannochloropsis-based methyl esters can bring the viscosity within current specifications, enhancing oxidative stability [102]. ...
Microalgae represent a valuable renewable resource for biofuel production due to their high lipid content, rapid growth rates, and non-competition with food resources. Both freshwater species like Chlorella and marine species such as Dunaliella, Tetraselmis, and Nannochloropsis are among the most commonly utilized candidates. This review provides a comprehensive overview of current cultivation and harvesting methodologies for microalgae in the context of biofuel production, emphasizing sustainable aviation fuel and biohydrogen. It synthesizes recent findings, technological advancements, and practical implementations to enhance the productive and economic viability of microalgae-based biofuels, highlighting their potential as a sustainable renewable energy source. Among the biofuels, sustainable aviation fuel and biohydrogen stand out as significant contributors to reducing greenhouse gas emissions. Technologies such as the oil-to-jet process and Fischer–Tropsch synthesis are being optimized to convert algal lipids into high-quality fuels. Biohydrogen offers several advantages, including the potential for negative CO2 emissions and compatibility with existing hydrogen infrastructure. Despite the challenges associated with the high costs of cultivation and processing, advances in biotechnological methods and process engineering promise to overcome these barriers. This review highlights the importance of continued research and development to maximize the potential of microalgal biofuels in achieving sustainable energy goals and contributing to global efforts in mitigating climate change.
... The figure shows that there are always two allylic sites whenever there are one or more double bonds and one fewer bis-allylic site than the numbers of double bonds present. 111 The reaction of bis-allylic and allylic sites with oxygen occurs through the autoxidation mechanism with the classical radical chain reaction steps of initiation, propagation and termination. 111 In the initiation step, a hydrogen atom from an allylic site or bis-allylic site is removed, which results in a radical site that subsequently reacts directly with molecular oxygen to form a peroxy radical. ...
... 111 The reaction of bis-allylic and allylic sites with oxygen occurs through the autoxidation mechanism with the classical radical chain reaction steps of initiation, propagation and termination. 111 In the initiation step, a hydrogen atom from an allylic site or bis-allylic site is removed, which results in a radical site that subsequently reacts directly with molecular oxygen to form a peroxy radical. The peroxy radical site then abstracts a hydrogen atom from a nearby C-H bond; thereby an additional reactive site is produced which is susceptible to oxygen addition. ...
... 112,113 Because of this attribute, small amounts of highly unsaturated fatty acids containing bis-allylic carbon atoms have been observed to have a disproportionately significant effect on C-H bond oxidative stability. 111 Moser 114 has conducted experiments in which several fatty acid alkyl esters were subjected to accelerated methods of oxidation, including EN 14112 (the Rancimat method) and pressurized differential scanning calorimetry (PDSC). With respect to PDSC, a correlation was found in which the oxidation onset temperatures of saturated fatty acid esters increased with decreasing molecular weight (R 2 = 0.7328). ...
... For the use of biodiesel as a fuel there are also feedstock restrictions defined by EN14214 [50]. These restrictions limit the amounts of FAME from linolenic acid and from acids containing more than four double bonds to 12% and 1%, respectively [50]. ...
... For the use of biodiesel as a fuel there are also feedstock restrictions defined by EN14214 [50]. These restrictions limit the amounts of FAME from linolenic acid and from acids containing more than four double bonds to 12% and 1%, respectively [50]. When comparing the FAME profile obtained in this work, it can be concluded that the amount of FAME from linolenic acid does not fulfill the criterion. ...
... When comparing the FAME profile obtained in this work, it can be concluded that the amount of FAME from linolenic acid does not fulfill the criterion. It has been proposed that in such case the biodiesel should be hydrogenated, which, however, decreases the cold flow properties [50]. In addition, it is known that for current motors FAME can be blended due to its oxygen content and its energy content is lower than that of diesel, being 38 MJ/kg and 43 MJ/kg, respectively [51]. ...
... The figure shows that there are always two allylic sites whenever there are one or more double bonds and one fewer bis-allylic site than the numbers of double bonds present. 111 The reaction of bis-allylic and allylic sites with oxygen occurs through the autoxidation mechanism with the classical radical chain reaction steps of initiation, propagation and termination. 111 In the initiation step, a hydrogen atom from an allylic site or bis-allylic site is removed, which results in a radical site that subsequently reacts directly with molecular oxygen to form a peroxy radical. ...
... 111 The reaction of bis-allylic and allylic sites with oxygen occurs through the autoxidation mechanism with the classical radical chain reaction steps of initiation, propagation and termination. 111 In the initiation step, a hydrogen atom from an allylic site or bis-allylic site is removed, which results in a radical site that subsequently reacts directly with molecular oxygen to form a peroxy radical. The peroxy radical site then abstracts a hydrogen atom from a nearby C-H bond; thereby an additional reactive site is produced which is susceptible to oxygen addition. ...
... 112,113 Because of this attribute, small amounts of highly unsaturated fatty acids containing bis-allylic carbon atoms have been observed to have a disproportionately significant effect on C-H bond oxidative stability. 111 Moser 114 has conducted experiments in which several fatty acid alkyl esters were subjected to accelerated methods of oxidation, including EN 14112 (the Rancimat method) and pressurized differential scanning calorimetry (PDSC). With respect to PDSC, a correlation was found in which the oxidation onset temperatures of saturated fatty acid esters increased with decreasing molecular weight (R 2 = 0.7328). ...
Biodiesel is a renewable fuel that is suitable for both stationary and automotive engines. It consists of fatty acid methyl esters and fatty acid ethyl esters when vegetable oils are transesterified with methanol and ethanol respectively. The structural configuration and properties of individual fatty acid methyl esters can significantly influence the biodiesel properties. The purpose of the present work is to review the effects of the properties and the structural configurations of fatty acid methyl esters on various biodiesel properties. The structural configuration includes the molecular structure, the chain length, the saturated or unsaturated nature, the degree of unsaturation and the position of double bonds. Important properties of fatty acid methyl esters are reviewed, and a large number of data consisting of their reported values are given. The viscosity, the cetane number, the heat of combustion, the density, the bulk modulus and compressibility, the iodine value, the oxidative stability, the low-temperature properties, the boiling point, the lubricity, the saponification value, the surface tension, the specific heat, the latent heat of vaporization and the flash point are reviewed in the present study. The reported mathematical equations for estimating the properties of fatty acid compounds and biodiesel are presented. A few studies that recommend enrichment of a particular fatty acid (or acids) which is possible through genetic modification to improve the overall biodiesel properties are also cited. The contribution of a particular fatty acid (or acids) favours some properties while it has an undesirable effect on other properties. Hence the specification of one particular fatty acid profile to improve all the properties of biodiesel is not possible. Considering the low-temperature properties and the oxidative stability, a combination of both saturated fatty acids and unsaturated fatty acids is necessary. Therefore, it is important to decide whether a biodiesel should contain a larger amount of saturated fatty acid esters or unsaturated fatty acid esters in order to obtain better fuel properties. The inherent genetic modification of the fatty acid profile could be the best possibility for addressing several fuel property issues simultaneously.
... It is well understood that the fatty acid composition (carbon chain length and degree of unsaturation) of microalgal has a major effect on biodiesel properties. The most important characteristics affected by the level of unsaturation are oxidative stability, ignition quality and cold flow properties (Bucy et al., 2012). ...
... There is a significant level of EPA + DHA (2.8%) in P. tricornutum and slightly higher proportion of EPA (2.6%) in red algae P. cruentum. Considering the health benefits associated to the consumption of EPA and DHA, particularly in the prevention of cardiovascular diseases and cognitive development (Bucy et al., 2012), these marine microalgae have an enormous potential for application in health food product development. ...
... Therefore, research is now deviated towards the usage of renewable (CO 2 , sunlight, wastewater, etc.), cheap and reliable resources, which are more promising and economically viable (Venkata Mohan et al. 2014b). Environmental sustainability and economic feasibility are the two main motivations that microalgal biofuel production is gaining acceptance when compared to other agro-and terrestrialbased fuels (Harrison et al. 2012). ...
... The production of glycerol and mono-alkyl fatty acid esters by the reaction of alcohol with triglycerides is called the process of transesterification Harrison et al. 2012). There are different types of transesterification, namely, direct (Sathish and Sims 2012), acidcatalyzed (Zhang et al. 2003), base-catalyzed (Vargha and Truter 2005) and enzyme-catalyzed transesterification (Bisen et al. 2010). ...
The perpetual increase in the environmental pollution and the diminution of fossil fuels are forcing mankind towards the usage of sustainable and eco-friendly technologies to build a green and global future. Similarly, increase in human population is eventually resulting in the discharge of huge quantities of waste that need serious attention. If the waste is managed aptly, the negatively valued waste would absolutely result in the generation of a definite value-added product. A multifaceted approach is needed to alleviate the energy crisis in an interdisciplinary way by integrating waste remediation towards bioenergy generation. Diverse forms of energy, viz. biohydrogen, bioelectricity, biodiesel and bioplastics could be produced by utilizing waste/wastewater as substrate by the catalytic action of bacteria. The inherent potential of the diverse bacteria present in waste-water can be effectively exploited for the generation of bioenergy along with the recovery of value-added products in a green and integrated approach. In this context, sustainable, green and eco-friendly technologies were described in this chapter to exploit the potential of waste/wastewater in the framework of biorefinery.
... Concerns over high atmospheric greenhouse gas levels and issues associated with fossil fuel extraction are among the incentives for developing alternative energy resources [1]. Biofuels, produced from a wide range of feedstocks, have the potential to reduce greenhouse gas emissions [2][3][4]. In particular, the use of microalgae as a feedstock has received a high level of interest in recent years [5,6]. ...
... Many species of microalgae are capable of accumulating high levels (N 50% w/w) of lipids, which can be extracted and converted to biodiesel, green diesel, or green jet fuel [2,6,7]. Compared with terrestrial plants, the advantages of using microalgae as a potential source of fuels include the ability to use non-fertile land [8], the higher growth rates of microalgae, higher productivity per unit land area, lower requirements for fresh water, and the fact that microalgal cultivations would not divert food supplies [6]. ...
The primary focus of research and development toward algal biofuels has been the production of fuel from the lipid fraction, with the non-lipid biomass used for production of biogas, electricity, animal feed, or fertilizer. Since the non-lipid fraction comprises approximately half of the algal biomass, the development of processes to produce additional liquid fuel or higher value products is of interest. We evaluated several hydrolysis methods for the deconstruction of cell wall carbohydrates in residual algal biomass. The hydrolysate, which contains the released sugars, can be used as a fermentation feedstock. For all methods, hydrolysis rates and yields of released sugars were measured. The effects of temperature, acid concentration, and biomass loading on acid hydrolysis were studied. Combined severity factors, indicators of treatment intensities, were evaluated for their correlation to the hydrolysis outcome. An optimal enzyme mixture, which released sugars with an acceptable yield and rate, was found. The ability of the resulting hydrolysates to support the growth of an industrial yeast strain was tested and the levels of common fermentation inhibitors were examined. Of the conditions tested, the highest yield of released sugar (243.2 mg/g biomass) was obtained with a one-step sulfuric acid process with 10% acid concentration at 90 °C for 5 h, while the maximum sugar release rate was obtained with 10% hydrochloric acid under the same conditions. This is the first process for conversion of residual algal biomass that does not require pretreatment and that results in a hydrolysate on which yeast can be grown with no added nutrients. Adapting a biorefinery concept by conversion of algal residue to value-added products may improve the process economics.
... One major difference between algal methyl esters and most common vegetable oil derived FAME is that some algal lipids contain a substantial quantity of long chain polyunsaturated fatty acids. The chain polyunsaturated fatty acids are better than fatty acid methyl esters in terms of fuel properties, including cetane number, oxidation stability and cold flow properties [11,12]. ...
... Various methods are applied for extracting microalgae, including supercritical extraction, ultrasonic extraction, microwave extraction, high-pressure homogenizer extraction, hydrothermal liquefaction and solvent extraction [10][11][12][13][14][15][16][17][18][19]. Nevertheless, a large amount of solvent is necessary for traditional oil extraction, which causes environmental pollution increases costs, and consumes much energy in the extraction process [13,14]. ...
... Despite several advantages of microalgal biodiesel, it faces many economic and technical issues (Mata et al., 2010). Although microalgae-derived lipids can be converted to methyl esters and alkanes for use in spark-ignition engines, compression ignition engines, and aircraft gas turbine engines, the suitability of algal biodiesel, however, depends on the fatty acid (FA) composition (Bucy et al., 2012). The FAME composition of biodiesel determines several properties of the biofuel, such as viscosity, oxidative stability, calorific value (CV), cetane number (CN), saponification value (SV), iodine value (IV), degree of unsaturation (DU), cold filter plugging point (CFPP) and long-chain saturation factor (LCSF), (Kalayasiri et al., 1996, Ramos et al., 2009. ...
In the current study, biodiesel properties of fatty acid methyl ester (FAME) derived from fats of four gamma-irradiated mutants (Cl801, Cl802 Cl803 & Cl804) and wild type (ClWT) of Chlorella sp. KM504965 were determined and compared with American Society for Testing and Materials (ASTM), European Norm (EN) and Indian standards (IS). Maximum concentration of saturated fatty acids (62.69%), monounsaturated fatty acids (36.29%) and polyunsaturated fatty acids (15.49%) recorded in ClWT, Cl801 and Cl803 respectively. The kinematic viscosity of Cl801 (4.88 mm2s-1), Cl802 (4.90 mm2s-1), Cl803 (4.73 mm2s-1), Cl804 (4.88 mm2s-1) and ClWT (4.92 mm2s-1) fits with ASTM, EN and IS. The density of Cl801 (0.83 gcm-3), Cl802 (0.84 gcm-3), Cl803 (0.78 gcm-3), Cl804 (0.80 gcm-3) and ClWT (0.81 gcm-3) was slightly lower than the standard limits (0.86 – 0.90 gcm-3). The high heating value of Cl801 (37.62 MJKg-1), Cl802 (38.15 MJKg-1), Cl803 (34.93 MJKg-1), Cl804 (36.44 MJKg-1) and ClWT (36.99 MJKg-1) were in accordance with ASTM standards. The iodine value was 47.38 mgI2 100g-1 (Cl801), 52.18 mgI2 100g-1 (Cl802), 50.87 mgI2100g-1 (Cl803), 47.04 mgI2100g-1 (Cl804), and 27.45 mgI2100g-1 (ClWT). The oxidative stability was 10.78 h (Cl801), 6.60 h (Cl802), 6.44 h (Cl803), 9.06 h (Cl804) and 39.83 h (ClWT). The cetane number of Cl801 (63.3), Cl802 (61.80), Cl803 (62.16), Cl804 (64.99) and ClWT (68.7) was greater than the standard values (61 to 65). It is concluded that the biodiesel from mutants could comply IS, ASTM, and EN and equivalent with biodiesel from vegetable oil.
... To evaluate the biodiesel derived from algae, different aspects must be considered: Variable fatty acid composition of the algal oil is subjected to transesterification process. Higher percentages of saturated fatty acid methyl esters refer to higher both oxidative stability and cetane number but at the same time have poor cold flow characteristics, as reported by Harrison et al. [9]. On the other hand, higher percentages of unsaturation in the fatty acid profile design better cold flow properties but lower oxidative stability and cetane number. ...
... Additional benefits of using microalgae feedstock include their faster growth rates and higher production of biomass relative to other omega-rich plants and crops [24]. Microalgal production systems do not compete arable land space for agricultural activities, and freshwater resources are not required if marine or brackish species are preferred [25]. ...
Chlorococcum novae-angliae is a terrestrial green microalgae species with remarkable potential to synthesize omega-3 (ω-3) and omega-6 (ω-6) fatty acids. In this study, Chlorococcum novae-angliae has been subjected to varying growth conditions (light, nitrogen, salinity, and temperature) to investigate the accumulation of ω-3 and ω-6 fatty acids. Among tested growth conditions, eicosapentaenoic acid, α-linoleic acid, γ-linoleic acid, and arachidonic acid were enhanced by nitrogen limitation. Significant increases were observed in concentration of linoleic acid, an essential precursor molecule for the production ω-6 fatty acids under decreased nitrogen concentrations. Despite the lowest biomass growth, monounsaturated fatty acids and docosahexaenoic acid were increased by 14.4% and 8.7% under low light intensities, respectively. Meanwhile, the highest concentrations of palmitic acid (C16:0), stearic acid (C18:0), and oleic acid (18:1cis-9) were also detected under nitrogen limitation. Total lowest fatty acid concentrations were obtained under increased salinity while low temperature conditions heavily inhibited cellular growth.
... Beyond short-chain (C 8 -C 18 ) fatty acids, microalgae also synthetize a group of essential fatty acids, the polyunsaturated fatty acids (PUFAs), such as omega-3 (ω3) and omega-6 (ω6). Linoleic acid (LA, 18:2 ω6) and α-linolenic acid (ALA, 18:3 ω3), are precursors for the long-chain (C 20 -C 22 ) PUFA (LC-PUFA) of the ω6 group and of the ω3 group (KHOZIN-GOLDBERG et al., 2011;BUCY et al., 2012). In general, the LC-PUFA biosynthesis pathways (Figure 2.7) in the endoplasmic reticulum are initiated by Δ12 desaturation of the chloroplast-derived oleic acid (OA, 18:1 Δ9 , ω9), producing LA (18 :2 Δ9,12 , ω6). ...
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... Thomson et al., (2015) observed that at 60 °C, the oil and alcohol formed a homogeneous phase resulting in a faster completion of the reaction. The optimum temperature for algal oil transesterification was found to be 60°C and the maximum conversion of algal oil to methyl ester was achieved at 98.79% (Bucy et al., 2012) ...
Simarouba glauca belongs to family simarubaceae, commonly known as "The Paradise Tree" or "King Oil Seed Tree", is a versatile multipurpose evergreen tree having a height of 7-15 m with tap root system. It is mainly found distributed throughout coastal South Florida. In India, it is mainly found in Andhra Pradesh, Karnataka, Tamil Nadu etc. It has the potentiality to produce 2000-2500 kg seed/ha/year. It can grow well in marginal lands and wastelands with degraded soils and therefore considered as a major forest tree. The oil content of the seed is 60-65 %. In the present study biodiesel was prepared from the crude oil of Simarouba glauca by transesterification with methanol in the presence of NaOH as a catalyst. The reaction parameters such as catalyst concentration, methanol to oil molar ratio, temperature, reaction time and rate of mixing were optimized for the production of Simarouba oil methyl ester. The yield of methyl esters from Simarouba oil under the optimal condition was 93.6 %.
... It is well documented that a wide range of microalgae species such as Chlorella minutissima, Chlorella vulgaris have been used for biodiesel production [101][102][103]. In addition, transesterification can reduce the viscosity of FAME for biodiesel production from algae [104]. Fig. 5 illustrates the steps of transesterification of microalgae for biodiesel production which are cultivation, harvesting, lipid extraction, and transesterification. [105]. ...
Biodiesel has privileges than conventional diesel fuel because of its low toxicity, renewability, and eco-friendly properties. Biodiesel is produced from various edible and non-edible sources via transesterification process. Non-edible sources such as waste cooking oil (WCO), algal oil, non-edible vegetable oil, and waste animal oil are commonly used to produce biodiesel due to their low cost and no dependency on the food chain. The production process is influenced by several factors such as reaction temperature and time, alcohol to oil molar ratio, and catalyst type and concentration. The analyses of economic aspects of biodiesel production are crucial to reduce the cost of biodiesel production by finding alternatives to available technologies, catalyst, and feedstock. Moreover, the biodiesel production cost is affected by factors such as the type of raw material, by-product selling price, operation and labor cost, the catalyst, and the reaction type. Besides, crude glycerol is a major by-product of biodiesel production with yields ranging between 8% and 10%. Crude glycerol could be used as a beneficial material to produce biopolymers, hydrogen, ethanol, and fuel additive through pyrolysis and gasification processes. Therefore, this review focuses on the recent finding in transesterification of non-edible sources for bio-diesel production as well as its economic aspects, fuel properties, and by-products applications. Finally, the economic aspects and process optimization of biodiesel production should be considered as important factors in order to enhance the economic sustainability of biodiesel production.
... Oxidative stability is a key factor in the process of storage of methyl ester biodiesel. The oxidative stability of FAME declines with increasing levels of unsaturation; therefore, limitation of their proportion in the final oil product is advisable [20,36]. ...
In recent years, there has been growing interest in the biomass of unicellular algae as a source of valuable metabolites. The main limitations in the commercial application of microbial biomass are associated with the costs of production thereof. Maize silage is one of the main substrates used in biogas plants in Europe. The effects of sterilized agricultural liquid digestate (LD) from methane fermentation of maize silage on the growth rates, macro and micronutrient removal efficiency, lipid content, and fatty acid profile in Auxenochlorella protothecoides were investigated. The results indicate that A. prothecoides can proliferate and accumulate lipids with simultaneous reduction of nutrients in the 1:20 diluted liquid digestate. The rate of nitrogen and phosphorus removal from the liquid digestate was 79.45% and 78.4%, respectively. Cells growing in diluted liquid digestate exhibited the maximum lipid content, i.e., 44.65%. The fatty acid profile of A. prothecoides shows a decrease in the content of linolenic acid by 20.87% and an increase in oleic acid by 32.16% in the LD, compared with the control. The liquid digestate changed the content of monounsaturated fatty acids and polyunsaturated fatty acids. The cells of A. protothecoides growing in the liquid digestate were characterized by lower PUFA content and higher MUFA levels.
... At the same time, it faces many hurdles including social, political, economic and technical issues [10]. Besides, microalgae-derived lipids can be converted to methyl esters and alkanes for use in sparkignition engines, compression ignition engines and aircraft gas turbine engines, yet the suitability of microalgal biodiesel eventually depends on the composition of the fatty acid (FA) [11]. ...
The sustainability of microalgal biodiesel industries depends not only on the development of a low-cost production system but also on the selection of the species used to produce commercially acceptable biodiesel. Therefore, estimation of biodiesel properties is a vital aspect of the microalgal biodiesel production process. Only if the properties of biodiesel comply with the American Society for Testing and Materials (ASTM) and European Norms (EN) biodiesel standards can it be commercialized and used as an alternative source of fuel. In the current study two microalgal species, Chlamydomonas sp. BTA 9032 and Chlorella sp. BTA 9031, were grown using Blue-green 11 medium substituted with 40% cheese whey permeate under mixotrophic conditions, and their biodiesel properties were estimated empirically using equations available in the literature. The biodiesel properties estimated were viscosity, oxidative stability, calorific value, cetane number, iodine value, saponification value, degree of unsaturation, cold filter plugging point and long-chain saturation factor. The biodiesel properties of Chlamydomonas sp. BTA 9032 were observed to meet biodiesel standards ASTM D 6751-08 and EN 14214, and were comparable with previously reported values for biodiesel feedstocks such as jatropha, Chlorella minutissima, and Chlorella vulgaris.
... The amount of esters in the sample before Rancimat analysis is calculated to exceed 85% of the total composition which sits well with the FTIR analysis of the samples which show a spectral library match of 88% with various methyl esters. The characteristic methyl esters of oleic acid and linoleic acid together compose 68% of the sample, which is common in the FAME obtained from microbial TAGs (Bucy et al. 2012;Ramos et al. 2009;Stefania et al. 2003). ...
Microbial-derived biodiesel was tested on a lab scale CI diesel engine for carrying out exhaust emission and performance characteristics. The performance, emission, and combustion characteristics of a single cylinder four stroke fixed compression ratio engine when fueled with microbial bio-diesel and its 10–30% blends with diesel (on a volume basis) were investigated and compared with conventional diesel. The bio-diesel was obtained from microbes which were grown by combining distillery spent wash with lignocellulosic hydrolysate at nutrient deprived conditions. The microbes consumed the wastes and converted the high strength waste water into lipids, which were trans-esterified to form bio-diesel. Testing of microbial bio-diesel blends with ordinary diesel at different loading pressures and the emission characteristics were compared. Results indicate that with increasing of the blends, reduction of HC and CO emissions were observed, whilst brake thermal efficiency maxed out at 20% blending. Further increase of blends showed a tendency of increasing of both emissions in the exhaust stream. The Brake Specific Fuel consumption was observed to decline with blending until 20% and then increased. The nitrogen oxide emissions, however, were found to increase with increasing blend ratios and reached a maximum at 20% blend. The escalation of HC, CO, CO2, and NOx emissions was also observed at higher blending ratios and higher engine loads. The performance studies were able to show that out of the three blends of biodiesel, 20% biodiesel blend was able to deliver the best of reduced hydrocarbon and carbon monoxide emissions, whilst also delivering the highest Brake thermal efficiency and the lowest Brake Specific Fuel consumption.
... The persistent trend towards depletion of non-renewable petroleum sources and the climate change associated with the combustion of fossil fuels are important issues to be dealt with on a global scale. In the framework of emergent technologies [1], increasing focus is being placed on renewable and sustainable sources of energy such as oleaginous microalgae which synthesize and accumulate substantial amounts of neutral lipids, mainly as triacylglycerols (TAG) [2], making them potential cell factories for the production of biodiesel [3][4][5][6][7][8][9][10][11]. ...
The use of microalgae as triacylglycerides (TAG) feedstock for biodiesel is a widely researched field in the development of new technologies. In order to underpin the potential of microalgal biodiesel as a possible substitute in the biofuel industry, more detailed data is therefore required on these aspects. This study assesses the growth, TAG accumulation, kinetics of dissolved nutrients and the quality of biodiesel and its blends from the marine diatom Navicula cincta grown in a photobioreactor, using seawater enriched with nutrients and soil extract. Acid-catalyst transesterification was tested for biodiesel production. This species presented during nutrient depletion: 1) a total lipid content of 49.7% of ash-free dry weight (AFDW) with neutral lipid (mainly TAG) as the dominant fraction (ca. 81.5% of total lipids), and 2) favourable fatty acids for biodiesel, such as palmitic acid (28%) and palmitoleic acid (46%). The yield of biodiesel (B100) derived from diatom N. cincta (B NC) and analysed by Gas Chromatography was 97.6% of FAME, being the FAME composition similar to the fatty acid profile of N. cincta neutral lipids. The fuel properties (including FAME percentage, cetane number, heat of combustion, color and sulfur content) of diatom blends prepared with petrodiesel in a 7% (B7 NC) and 10% (B10 NC) vol ratio were evaluated using a PetroSpec (PAC) and compared with commercial soybean blends (B7 S and B10 S). B7 and B10 derived from N. cincta met the requirements of ASTM D6751 and presented improved cetane numbers (50.2 and 51.6, respectively) with respect to soybean blends. Furthermore, biodiesel derived from the studied species showed the lowest sulfur content (0.0056% w/w). The rapid accumulation of neutral lipids in response to natural nutrient deficiency in N. cincta and its capacity of autoflocculate are good selling points for the use of this microalga in the biofuel industry.
... The amount of esters in the sample before Rancimat analysis is calculated to exceed 85% of the total composition which sits well with the FTIR analysis of the samples which show a spectral library match of 88% with various methyl esters. The characteristic methyl esters of oleic acid and linoleic acid together compose 68% of the sample, which is common in the FAME obtained from microbial TAGs (Bucy et al. 2012;Ramos et al. 2009;Stefania et al. 2003). ...
Biodiesel and single cell oils obtained from oleaginous yeasts grown in industrial waste are attractive alternatives to the conventional fuels. However, there are only few articles dealing with the stability of the microbial biofuels. Hence, this study aimed at characterizing the storage time of biodiesels using Rancimat methods. The microbial oil and the biodiesel obtained from microbial oil have been characterized with storage stability due to various oxidizing and thermal damage. Here, the microbial fuels were subject to Rancimat analysis and found to have high thermal-oxidative stability of 18 and 8.78 h for biodiesel and oil, respectively. The storage stability resulting from storage conditions was extrapolated for biodiesel and oil and has been found to be 1.62 and 0.54 years, respectively. The infrared spectroscopic analysis reveals the degree of oxidation found after the induction time was reached and shows the characteristic peaks for degradation products. Gas chromatography revealed the compounds that were responsible for the stability as well as the amount of degradation products left.
... Biofuels produced from a wide range of raw materials have the potential to reduce GHG emissions (Bucy et al. 2012). In particular, the use of microalgae as a feedstock has been highlighted in recent years (Zhu and Ketola 2012). ...
Microalgae are photosynthetic microorganisms that are capable of converting carbon dioxide, nutrients, and solar energy into biomass and oxygen. In addition, microalgae have high photosynthetic rates, do not require potable water and arable land for cultivation, and can use liquid and gaseous effluents as nutrients for growth. The biochemical composition of microalgae can be manipulated by changing the cultivation conditions and environmental stresses. Thus, these microorganisms can be induced to produce biomass that is rich in biocompounds of commercial importance. The microalgal biomass can be converted into biofuels and high value-added bioproducts. Thus, microalgae have potential uses as renewable raw materials and could provide promising materials for the development of biorefineries. In this context, this chapter examines microalgae within a biorefinery concept and describes the advantages of using microalgae, culture conditions, biocompounds from biomass and the potential for converting them into biofuel and bioproducts.
... Absence of such poly unsatuK. A. Salam et al. rated methyl esters has been shown to improve oxidation stability [25]. According to standard EN 14214, polyunsaturated fatty acid methyl ester (≥4 double bonds) should be ≤1%, while linolenic acid (an 18 carbon chain fatty acid methyl ester with 3-double bonds) should be ≤12%. ...
... The fatty acid profile of Nannochloropsis species has previously been determined to be satisfactory for biodiesel production, but may suffer from poor oxidative stability due to high concentrations of poly-unsaturated fatty acids (PUFAs) [70,71], so it is preferable to utilise nutrient starved biomass to decrease the proportion of these components in the final oil. Fig. 3. Nannochloropsis sp. ...
Microalgal biotechnology has yielded a range of products for different consumer markets, but large scale production for bulk commodities is limited by the cost and environmental impact of production. Nutrient requirements for large-scale production contribute significantly to the cost and environmental impact of microalgal biomass production and should subsequently be addressed by more careful sourcing of nutrients. This study assessed the use of nitrogen and phosphorus contained in effluents from anaerobic digestion of food waste to cultivate the marine microalga Nannochloropsis sp. With suitable dilution, effluent could replace 100% of nitrogen demands and 16% of required phosphorus, without significant impacts on growth or biomass productivity. Additional phosphorus requirements could be decreased by increasing the N:P molar ratio of the media from 16:1 to 32:1. Nannochloropsis sp. accumulated lipid up to 50% of dry weight under N-stress, with significant increases in the content of saturated and mono-unsaturated fatty acids. Using empirical data generated in this study, the cost and environmental impact of nitrogen and phosphorus supply was assessed versus the use of fertilizers for biomass and biodiesel production. Nutrient requirements predicted by the Redfield Ratio overestimating impacts by as much as 140% compared to empirical data. By utilising residual nutrients and optimising nutrient supply, the cost and environmental impact of nitrogen and phosphorus were decreased by > 90% versus the use of artificial fertilizers. This study demonstrates the importance of using empirical data for process evaluation and how anaerobic digestate effluent derived nutrients can contribute to the sustainability of algal biomass production.
... Trans-esterification is the chemical conversion of the oil into fatty acid methyl esters (biodiesel). The viscosity of vegetable oil is also reduced through the process of trans-esterification, therefore it is widely used [24]. ...
Pakistan has a strong potential of biodiesel production if the available feedstock resources are used sustainably
and implementable policies are made in appropriate direction. To meet the energy demands and to find
alternative and non-conventional resources of energy different challenges like research and development,
infrastructure development, decentralized type of power delivery system, commercialization, market development,
education and outreach programs, public awareness, monitoring, subsidies, government participation,
technology transfer and evaluation must be considered and a comprehensive policy must also be made to
systematically control and integrate them at national level. Pakistan is enriched with a wide variety of feed
stocks which can be used for biodiesel production. Pakistan has an enormous potential of biodiesel production
from jatropha, plants seed oil and microalgae which needs more consideration and practical applications.
Harvesting the potential of microalgae for biodiesel production in Pakistan can be helpful to make it selfsufficient for energy demands. Pakistan is also facing several challenges like climate change, lack of financial resources, state of art technology and absence of appropriate government policies, which limit the
commercialization of biodiesel. Although Government of Pakistan has established different institutions to
promote and develop alternative energy technologies and to achieve 10% share of bioenergy in the energy sector
by 2020, but still the targets are to be achieved on practical grounds. In this article, we have reviewed the
potential of biodiesel in Pakistan, feed stocks, biodiesel production process, barriers and future developments.
Future policies on biofuels, trends, recommendations, and the implication of existing policies are also discussed with research and developments goals for the promotion of biodiesel in Pakistan.
... Several methods can be used to extract lipids from microalgae, including supercritical extraction, ultrasonic extraction, microwave extraction, high-pressure homogenizer extraction, hydrothermal liquefaction, and solvent extraction (Bligh and Dyer, 1959;Friedrich and Pryde 1984;Chao et al. 1993;Converti et al. 2009;Bucy et al. 2012;Iqbal and Theegala 2013;Toor et al. 2013;Reddy et al. 2014). However, high quantities of solvent are necessary, which may lead to environmental pollution and increase costs as well as energy consumption during the process (Xu et al. 2006). ...
Alternative biofuel sources, such as biodiesel, produced from nontoxic, biodegradable, and renewable materials are currently attracting great interest given the growing global energy demand. Microalgae are an exceptional biofuel source due to their potential for generating significant quantities of biomass and oil and for combining their production with environmental technologies such as wastewater treatment. Technologies for producing biodiesel from microalgae have been widely studied, especially increasing the lipid content in the cell, strain selection, lipid extraction, and transesterification methods and innovations that use wet biomass for extraction, which reduces the environmental impact and production cost. These aspects are explored in this chapter to identify the different production methods and technologies under development for expanding biodiesel production from microalgae.
... The use of solvent extraction requires extra energy input to recover the solvents and it has the potential to contaminate the algae solids, thereby restricting options for their end use . In recent years newer methods have been reported applying additional processes to enhance the extraction such as supercritical extraction, ultrasonic extraction, microwave extraction, high-pressure homogenizer extraction, hydrothermal liquefaction and solvent extraction (Iqbal and Theegala, 2013;Reddy et al., 2014;Bucy et al., 2012;Toor et al., 2013;Reddy et al., 2013). A brief review of the various extraction methods is given by Ranjith Kumar et al. (2015). ...
Abstract: The prospects of producing carbon-neutral biofuels from microalgae appear bright because of their
unique features such as high CO2-sequestering capability and ability to grow in wastewater/seawater/brackish water and high-lipid productivity. Extraction of lipids from microalgae/algae is still considered a challenging process due to the difficulties faced during extraction. The commercial production of microalgae biofuels including biodiesel is still not feasible due to the low biomass concentration and costly downstream processes. This study reports the solvent effectiveness of methyl ester (biodiesel) for microalgal lipid extraction together with microwave irradiation. Two co-solvent systems, BD20 (20% Methyl Ester and 80% Ethanol) and BD40 (40% Methyl Ester and 60% Ethanol) were experimented at time intervals of 5, 10 and 15 min, by Microwave-Assisted Extraction at 100 Watts. Microwave irradiation led to disruption of the algal cell walls which facilitated lipid extraction. Results were compared to another system, Chloroform 33% and Ethanol 67% by Microwave-Assisted Extraction as well as conventional Soxhlet extraction as the control. The results obtained from the experiment shows that BD40 has the highest lipid yield for all time intervals compared to BD20, Chloroform + Ethanol. When compared to the control, all of the samples that were extracted with the microwave had a higher lipid yield than Soxhlet Extraction.
Keywords: Co-solvent, lipid extraction, methyl ester, microalgae, microwave irradiation
... EN 14214 recommends that the maximum contents of linolenic acid methyl ester should not be more than 12 % (m/m) while polyunsaturated methyl esters (with four or more double bonds) should not be more than 1 % (m/m) [54]. Probable solution to reduce PUFAs include addition of fuel additive containing 0.03 % tert-butyl hydroquinone (TBHQ) [55] or harvesting of microalgae using ozone floatation [56] . ...
Microalgae has large scale cultivation history particularly in aquaculture, pigments and nutraceutical production. Despite the advantages of microalgal oil as feedstock for biodiesel production, algal biodiesel is still at laboratory scale due to technical challenges required to be overcome to make it economical and sustainable. Indeed, complete drying of microalgae is energy intensive and significantly increases the cost of algae pre-treatment. In situ transesterification is more water tolerant due to excess methanol to oil molar ratio required by such production route. However, the need to remove unreacted methanol (>94% of it) from the product streams certainly requires distillation heat load which increases the operating cost. This article reviews the key process variables affecting efficiency of in situ transesterification. These include alcohol to oil molar ratio, moisture, stirring rate, reaction time, temperature, microalgal cell wall and catalyst type. Potential solutions of improving the efficiency/economy are discussed. Overall, an integrated approach of in situ dimethyl ether (DME) production along with the desired biodiesel synthesis during in situ transesterification would substantially reduce the volume of unreacted methanol thereby reduces operating cost. Use of resulting microalgal residue for biogas (methane) production can provide energy for biomass production/separation from the dilute algae˗water mixture. Use of bio˗digestate as nutrients for supporting microalgal growth is among the probable solutions suggested for reducing the production cost of in situ transesterification.
... Others have noted the challenges associated with examining the fuel properties of algal biodiesel due to the small experimental quantities that are generally produced compared to the larger amounts required for each individual test [15]. For this reason, many of the reports describing algal biodiesel fuel properties are incomplete with algal biodiesel blended with petrodiesel to complete the fuel testing [16] or have relied on predictions [17] and simulations such as using a mixture of biodiesel from vegetable oil and fish oil to model algal biodiesel fuel properties [18]. ...
Results from the comprehensive fuel testing according to American Society for Testing and Materials International (ASTM) standards of an alkenone-free and decolorized biodiesel produced from the industrially grown marine microalgae Isochrysis sp. are presented. Fatty acid methyl ester (FAME) profiles of the non-decolorized and subsequently decolorized biodiesel fuels were nearly identical, yet the fuel properties were remarkably different. Significant positive impacts on the cetane number, kinematic viscosity, and lubricity were observed, indicating a potential deleterious effect of pigments like chlorophylls and pheophytins on these fuel properties. The decolorization process using montmorillonite K10 gave on average 90% mass recovery, and allowed for an otherwise unobtainable cloud point determination. Oxidative stability of the decolorized Isochrysis biodiesel remained well below the minimum prescribed in biodiesel standards due to elevated content of highly polyunsaturated fatty acids, however other values were in the range of those prescribed in the ASTM standards. Overall, decolorization improved the fuel properties of biodiesel from Isochrysis and may provide a path toward improved biodiesel fuels from other algal species.
... Calculated CP and PP of microalgal oils[37][38][39][40][41][42][43][44][45][46][47][48][49]. ...
... The degree of saturation and the chain length of the fatty acids are known to affect the biodiesel properties such as oxidation stability, cetane number, the iodine value [3,37]. According to the American Society for Testing and Materials (ASTM D6751) biodiesel standard and the European Union (EU) biodiesel standard (EN 14214), good quality biodiesel should have a high oxidation stability, high cetane number and low iodine value [38]. It is known that in biodiesel, both low amounts of polyunsaturated fatty acids and high oleic acid content improve oxidation stability, whereas high amounts of fully saturated fatty acids (e.g., palmitic and stearic) result in high cetane number and low iodine value [36,37]. ...
In this study, a mixed microalgal culture grown in secondarily treated domestic wastewater effluent was investigated for biodiesel production using in situ transesterification method with conventional heating. The total lipid content of the mixed culture was found as 26.2 % ± 0.6 by weight of dry biomass, and 74 % of the lipids were contributed by total glycerides. In situ transesterification with conventional heating process under acidic conditions produced higher biodiesel yield with chloroform as the co-solvent (82.1 % ± 3.9) compared to hexane (55.3 % ± 3.9) under the same reaction conditions. The gas chromatography analysis showed that FAME composition was mainly composed of palmitic, palmitoleic, stearic, oleic, linoleic and linolenic acid methyl esters., and thus the mixed microalgal culture fed by domestic wastewaters has had comparable biodiesel conversion yields and FAME composition to mono-culture and pure cultures fed by synthetic culture media. Hence, this study showed that secondarily treated domestic wastewater could potentially be a suitable and sustainable medium for microalgae grown to be used as biodiesel feedstock.
... The conventional method for biodiesel production from alga begins with lipid extraction using organic solvents followed by transesterification of extract (Kasim et al., 2010). Various methods are applied for extracting microalgae, including supercritical extraction, ultrasonic extraction, microwave extraction, high-pressure homogenizer extraction, hydrothermal liquefaction and solvent extraction (Iqbal and Theegala, 2013;Reddy et al., 2013Reddy et al., , 2014Bucy et al., 2012;Toor et al., 2013). Nevertheless, a large amount of solvent is necessary for traditional oil extraction, which causes environmental pollution, increases costs and consumes much energy in the extraction process. ...
Microalgae can provide solutions to the twin challenges of energy security and environmental pollution. They can capture carbon dioxide in the flue gas thereby reducing greenhouse gas and also producing algal biomass, which can be converted into biofuel. The present study evaluated the effects on growth and lipid content of
Nannochloropsis sp., under reduced nitrogen content and enrichment with sodium carbonate/bicarbonate derived from flue gas. Studies have been conducted to identify and develop efficient lipid induction techniques in microalgae, such as nutrients stress (e.g., nitrogen and/or phosphorus starvation), osmotic stress,
radiation, pH, temperature, heavy metals and other chemicals. Our results showed that the total lipid productivity of Nannochloropsis sp. cultures aerated with five different CO2 levels (1, 10, 15, 20 and 25% CO2) had the highest lipid level of 18.93 mg LG1 dayG1 for the 15% CO2. The growth using soluble carbonates was
slightly better than when using only CO2 gas as carbon source. The 20% flue gas solution gave maximum yield of dry biomass of 0.55 g, while the maximum yield of dry biomass for 15% dissolved CO2 gas was around 0.44 g. In terms of nitrogen level; the concentration of nitrogen at 0.882 mM gave the best growth and biomass
amount. Those with lower nitrogen had their growth and biomass reduced by almost 5 times. Lipid productivity increased when exposing the culture to nitrogen starvation condition. The 100% N cultures (0.882 mM) yielded the lowest lipid productivity, while the 25% N cultures (0.353 mM) showed the highest productivity of lipid. The cells that grew in the lowest nitrogen content showed slightly more than twice the productivity of oil production compared with the one with 100% N cultures. This work has described the favorable conditions for lipid production by Nannochloropsis sp. in respect to CO2 gas, soluble carbonates and different nitrogen concentrations.
Key words: Lipid content, biodiesel, flue gas, CO2 mitigation, Nannochloropsis sp.
... The CN is a dimensionless descriptor of the ignition quality of a diesel fuel; it is a prime indicator of biodiesel quality [19,35]. The carbon chain length and the number of double bonds in a hydrocarbon both have an effect on the CN [36]. ...
... These highly unsaturated species would have important implications with respect to biodiesel properties, such as the IV, CN and oxidation stability. Bucy et al. [40] further investigated the properties of algal-oil derived methyl ester biodiesel, noting the high content of these long chain polyunsaturated fatty acids (LC-PUFA) often present in microalgae species that are suitable for large scale cultivation for biodiesel production. These constituents are problematic in terms of oxidation stability, as well as other properties such as Cetane number. ...
Oxidation Stability is one of the most important properties of fatty acid alkyl esters (biodiesel fuel) and primarily affects the stability of biodiesel during extended storage. Degradation by oxidation yields products that may compromise fuel properties, impair fuel quality and engine performance. In Europe, standardization and fuel quality assurance are crucial factors for biodiesel market acceptance, and storage stability is one of the main quality criteria. An overview of researches into biodiesel oxidation stability is presented in an attempt to convey the significance of this important property of biodiesel fuel. Aspects covered include: significance of biodiesel oxidation stability, oxidation chemistry, methods used for characterization of stability, factors known to influence stability, and consequences of biodiesel oxidation for diesel engines. The purpose of this work was to review the findings from some of the key prior research efforts available in the literature and to identify aspects of biodiesel oxidation stability in need of further study.
The global energy demand is expected to rise due to improved living standards, population growth, and urbanization. It underscores the need to explore alternative energy sources. Biodiesel, derived from renewable feedstock, is considered a promising solution to meet future energy needs while addressing concerns about dwindling fossil fuel reserves and environmental issues. Microalgal oils are identified as third-generation feedstock for biofuels production due to their advantages over conventional edible crops and non-edible oils, which face limitations in availability and yield. Microalgal oils are particularly significant because edible oils serve as food sources, and non-edible oil resources have slow growth rate as well as less oil yields. For biodiesel derived from any feedstock, meeting specific physical and chemical properties to comply with biodiesel standards. Therefore, thoroughly examining the conversion process from microalgal oil to biodiesel is necessary. This study explores various aspects of microalgal oils as biodiesel feedstock, including different microalgal species and their oil content, technologies used for biodiesel production from microalgal oils and biomass, and biodiesel standards and characterization across other countries. Techno-economics and Life Cycle Assessment are applied in this study to evaluate the economic viability and environmental impact of microalgae-based processes, addressing challenges such as data availability, uncertainty, and stakeholder engagement. This review highlights a significant opportunity to produce biodiesel from microalgal feedstock, which could contribute to future biodiesel production and provide a sustainable alternative to conventional diesel fuels.
Technology has developed tremendously in the last few decades and the quality of lifestyle is improving day by day. Most of the gadgets, we are using nowadays, runs on electric power which are unique just because of its easy transmission through a pair of thin wires. On the other hand, 1.5 billion people in the world have no access to electricity (UNDP 2016). Underdeveloped countries are involved in solving this growing demand. An attempt might be taken soon to give them a minimum access to electricity. For this an alternative arrangement, research and development, and technological innovation are very much important.
The effects of mixing pure vegetable oils with diesel fuels and using them in diesel engines were explored in this study. Due to its great production, Chorella protactes, a microalgae species, was employed as a vegetable oil. First, pure microalgae oil was combined with 5% (DSYK-5) and 10% (DSYK-10) diesel reference fuel (RDF) by volume for this experiment. The resulting blended fuels and diesel reference fuel were put to the test in a four-cylinder, four-stroke diesel engine at 1500 rpm and various loads. With the use of pure oil, the results showed a 4.64 percent rise in specific fuel consumption (SFC). CO emissions reduced by 9.05 percent on average when DSYK-5 fuel was used, while CO emissions increased when DSYK-10 fuel was used. HC emissions reduced by 4.6 percent on average when blended fuels were used, whereas NOx emissions increased by 3.13 percent on average. CO2 emissions were comparable to RDF fuel when DSYK-5 fuel was used. When comparing RDF fuel to DSYK-10 fuel, fewer CO2 emissions were found. Average gas temperatures, cumulative heat releases, and cylinder pressure values all reduced as the pure oil ratio in the mixture ratio increased.
In this study, the performance and emission characteristics of produced biodiesel from Dunaliella tertiolecta microalgae are investigated for the first time. To achieve reliable results, all production stages including cultivation, harvesting, oil extraction, and transesterification are executed in the current study. The cetane number and heating value of the produced biodiesel from Dunaliella tertiolecta microalgae were 54 and 40.2 MJ kg⁻¹, respectively. The results of emission analysis showed that the use of B10 and B20 biofuels emitted less CO, HC, and NOx pollutants than diesel fuel (the average reductions of CO, HC, and NOx emissions for B10 are 9.21%, 7.32%, and 2.89%, and for B20 are 23.54%, 18.28%, and 6.97%, respectively); however, these biofuels resulted in more O2 and CO2 relative to the pure diesel fuel (the average increments of O2 and CO2 emissions for B10 are 1.55% and 1.33%, and for B20 are 3.46% and 5.43%, respectively). Also, the engine output power with B20 fuel decreased averagely 2.64%, and the BSFC increased 3.46% compared to pure diesel fuel. The results demonstrate the considerable capability of Dunaliella tertiolecta microalgae to be the source of a clean fuel.
The increased demand and price of petroleum diesel along with its limited reservation and emitted harmful substances have made the world confronted. Biodiesel as an alternative to petroleum diesel offers immediate potential to meet these concerns. It provides several technical benefits over diesel such as reduced emission, high flash point, and improved cetane number. However, the oxidative nature of biodiesel is found to be one of the major problems which limits its commercial usage and sustainability. Molecular reactions in biodiesel and their susceptibility to oxidation are important to understand but only limited information is available in this regard. The present study aims to investigate the biodiesel molecular changes upon exposure of metal surface. The tests were conducted by immersing copper coupons in palm biodiesel at ambient temperature (25–27 ˚C) for various immersion time, viz., 200 h, 600 h, 1200 h, 2880 h. Density, total acid number and composition of biodiesel before and after immersion tests were determined by density meter, TAN analyzer and gas chromatography mass spectroscopy analysis. Date obtained from different tests are analyzed and compared to explore the possible degradation mechanism of biodiesel molecules. Results show that the key components of biodiesel include methyl stearate (9.94%), palmitate (38.64%), oleate (34.29%) and linoleate (6.92%). Upon exposure of copper for 2880 h, the concentrations of these molecules are changed to 10.14%, 33.78%, 31.34% and 1.09% respectively. Such changes in composition cause alteration in fuel properties and thus, hinders its sustainability. The possible reaction mechanisms have been discussed in detail with the help of obtained data and relevant literatures.
Pollution is one of the major tricky issues in the world due to the negative impact of vehicle population and industrialization. Transport sector is still struggling to control the pollution in spite of making many initiatives to keep it in control. Researchers have successfully claimed that biodiesel could be a possible solution due to its closed carbon cycle. In this scenario, microalgal biodiesel has the potential resource to reduce the vehicle pollution as an alternative fuel source. In this work, microalgae cultivated in open raceway ponds in optimized composite media were harvested with low cost filters, dried and oil extracted using solvent method. Two step conversion processes was employed to convert algal oil into biodiesel using optimized process parameters. Naturally available sea shell was used as the catalyst in the transesterification process. A new comprehensive bioreactor was designed and fabricated for oil extraction, esterification, transesterification and distillation process to produce 10 l of biodiesel in a batch. The biodiesel was then tested in the internal combustion (IC) engine test rig for various blends to analyse the performance and emission at different compression ratios (CRs). The brake thermal efficiency (BTE) of 27.42% at specific fuel consumption (SFC) of 0.225 kg/kWh was obtained for B30 blend at CR of 19. The emission characteristics were also found to be low at CR 19, which is the rated CR of the engine for diesel fuel.
ACKNOWLEDGMENT First, I thank Allah for granting me this development opportunity by conducting a master's degree in environmental engineering at a reputable university as the American University in Cairo (AUC). Moreover, I thank Alexandria University for accommodating me in its biology lab during the early stage of my research and provide me with resources and materials to set up the initial cultivation phase for my research. I want to thank also my company (BP) for offering me an education assistantship without which I would not be able to pay for my master's degree. Also, I want to thank my line manager Ahmed El Sherbiny who encouraged me to join the environmental program in the AUC and facilitated me all resources to progress with my master's degree. I am also thankful to my academic supervisors Prof. Salah El-Hagar, Dr. Ahmed El-Gendy, and Prof. Eman Mohamed Fakhry for guiding more over my research course. Prof. Salah has always provided support, and guidance, and helped me a lot in managing my efforts to stay on track and follow the research plan. Assoc. Prof. Ahmed El-Gendy has helped me to reveal new potentials in myself and guided me to overcome the challenges I encountered through my research and encouraged me to expand my research to cover broader scope in microalgae research. Prof. Eman Mohamed Fakhry gave me the throttle to start my research and empowered me with academic knowledge to set up my experiments. I want to thank also Assoc. Prof. Hala Mohamed Taha (researcher at hydrobiology, Marine Division, National Institute of Oceanography & Fisheries), and Eng. Ahmed Saad from the environmental lab in the AUC for educating me the required lab skills to conduct my research. Last but not least, I am grateful to my family who incurred my absence through those years and supported me to complete my master's degree. II ABSTRACT Investigating alternatives for fossil fuels have always been an area of interest for scientist around the globe. The decline in the oil & gas stock along with the increasing demand for energy that accompanies the increase in population has created the need for an alternative energy solution. From the renewable energy solution, microalgae stand out as a very promising source for biofuel production due to its high lipid content. However, the production of biofuel from microalgae is still of a high cost compared to production of the same amount from fossil fuels. The unfeasibility commercial production for biofuel from microalgae goes back to the high cost in the cultivation process, mainly supply the cultivation medium with nutrients, extraction process, and transesterification process. This research aimed to reduce the cultivation process cost by investigating the substitution of required nutrients in the synthetic Woods Hole MBL (MBL) medium by those available in wastewater streams. Chlorella vulgaris was selected for this research for its high biomass productivity and its ability for adaptation in various media. Different cultivation conditions were tested to reach to growth rate close to which was recorded from the cultivation on synthetic medium (MBL). The research reached to the conclusion that a mixture between synthetic medium (MBL) and non-sterilized agriculture wastewater under indirect sunlight (16:8 light to dark cycle) achieved a growth rate close to the growth rate from cultivation on a pure synthetic medium (MBL). Regarding total lipids, The non-sterilizer agriculture wastewater and MBL mixture achieved the highest results after fourteen cultivation days. Both growth rates and total lipid results prove that a mixture between agriculture wastewater and synthetic medium (MBL) can be utilized as a substitution for the pure MBL medium. This substitution will support the objective of reducing the total cost for producing biofuel from microalgae. III
Microalgae biodiesel has captured the attention as a clean renewable fuel for diesel engines due to their positive characterizations such as high productivity, fast growing rate and their ability to convert CO2 to fuel. This work investigates the use of microalgae biodiesel from Chlorella Protothecoides (MCP-B) as alternative fuel for Compression Ignitions (CI) engines. Engine performance and emissions along with the fuel properties of the MCP-B100, MCP-B50, and MCP-B20 were evaluated and compared with petroleum diesel (PD). Analysis of variance statistical test (ANOVA) was conducted to evaluate the significance of the differences between the parameters means. The results showed that MCP-B100 produces less emission compared to PD. Statistically significant differences were found in the engine brake power, torque, BSFC, exhaust gas temperature, CO, O2 and NOx when MCP-B100 and its blends were used compare to PD. MCP-B100 showed a reduction of 7, 4.9, 6.1, 28, 4.2 and 7.4% in brake power, torque, exhaust gas temperature, CO, CO2 and NOx, respectively. Contrarily, the use of MCP-B100 resulted in an increase of 10.2 and 15.8% in BSFC and O2, respectively compared to PD.
The biodiesel industry has undergone stable growth over the past decade. The biodiesel production process is relatively complex and rather expensive relative to the production of mineral diesel, and thus to retain production shares and expand the industry, there is a growing demand for changes related to the search for new raw materials and advanced technologies. Microalgae have attracted considerable attention as a potential biodiesel raw material. This article presents an overview of possible applications of one new form of technology, the so-called in situ technology for simultaneous oil extraction and transesterification. The article also describes ways of applying this technological tool for biodiesel production from microalgae oil.
Microalgae are responsible for more than half of the world’s primary production of oxygen. They are the simplest and most abundant form of plant life on the earth (Energy from algae (Technical Summary. Scott Maden, 2010). These photosynthetic organisms are categorized under third generation biofuels and are known to have high oil and biomass yields, can be cultivated with wastewater, do not need arable land for cultivation, do not compete with common food resources and very efficiently use water and nutrients for growth (Hannon et al., Biofuels 1:763–784, 2010). There are various routes of metabolism which microalgae have adopted for their growth and survival viz., autotrophic, heterotrophic and mixotrophic. They are capable of shifting their metabolism in response to changes in the environmental conditions (Devi et al., J Renew Energy 43:276–283, 2012). Algal cultivation for biodiesel production is considered more amenable a technology than the cultivation of oil crops (Chisti, Biotechnol Adv 25:294–306, 2007) because the yields of algae-derived oils are much higher (Abou-Shanab et al., J Power Energy Eng 1:4–6, 2010). Autotrophically algae gain energy through light by fixing atmospheric CO2 (Devi and Venkata Mohan, Bioresour Technol 112:116–123, 2012). However, low biomass yields, requirement of cultivation systems with large surface area and shallow depth for better access of light are some of the disadvantages associated with autotrophic mode of nutrition. In the absence of light, the photosynthetic process gets suppressed and algae gain energy from alternative organic processes using heterotrophic pathways that convert sugar into lipids (Perez-Garcia et al., J Phycol 46:800–812, 2010). This pathway leads to significantly denser biomass, facilitating greater lipid yields.
In recentyears,theenergyforthedevelopmentofworldeconomydependsentirelyonfossilfuelswhich
are notonlyrapidlydepletingbutarealsocausingenvironmentaldegradation.Thissituationhas
attractedtheattentionofworld’s countriestodevelopalternativebiofuelsasasubstituteofpetroleum
fuels. Biodiesel,thealkylestersofvegetableoils,isbeinggiventoppriorityforitsproductionfromedible,
non-edible andmicroalgaloilsasfeedstocksandhaspropertiesalmostsimilartodieselexceptoxidation
stability andcold flow propertiesthatmayrendertheuseofbiodieselforengineoperationdifficult.
In thisstudy,theeffortsaremadetoclassifydifferent oilsonthebasisofoxidationstabilityindex(OSI),
so thatonecanselecttheoilswithhighOSIfortheproductionofbiodieselwhichdonotrequireadditivesto
enhance thefuelstabilityandthebiodieselqualitywouldremainunchangedfortheperiodofOSIandbefore
that, thefuelisexpectedtobeentirelyutilizedforengineoperation.BasedonAmericanSocietyforTesting
andMaterials(ASTM)D-6751andEuropeanEN-14214standardforOSI,theoilsareclassified intothreemain
categoriesnamelybest,moderateandpooroils.Asperthisclassifications, 19non-edibleand19microalgal
oils arefoundasthebest,9nonedibleand7microalgaloilsasmoderateand13non-edibleand6microalgal
oils aspooroils.AsperavailabilityandOSI,thebestoilscanberecommendedfortheproductionofbiodiesel
whichcanbedirectlyusedforenginewithoutanyqualityproblem.Thisclassification wouldhelpthe
biodieselproducers/industriestoselectoilsthatcanbeconvertedtobiodieselrequiringnoadditives.While
the biodieselsfromotheroilcategorieswouldrequirestabilisationusingantioxidantsandwouldbe
relativelycostlierthanthebiodieselfromthebestoils
Waste/wastewater signifies a potential renewable feedstock to generate various forms of bioenergy aside from the remediation process by regulating the biological process. Bioenergy has gained significant attention as a sustainable and futuristic alternative to fossil fuels. Using waste for bioenergy through its remediation has instigated considerable interest and has further opened a new avenue for the use of renewable and inexhaustible energy sources. This chapter attempts to cohesively outline various routes of possible value addition from waste remediation in concurrence with contemporary research. Biohydrogen, bioelectricity (through the microbial fuel cell), algae-based biodiesel, and bioplastics production in the context of waste/wastewater treatment are covered.
Biodiesel, defined as the monoalkyl esters of vegetable oils and animal fats, can be derived from other triacylglycerol-containing feedstocks. Algae are being considered for this purpose due to their claimed high production potential. However, there are no comprehensive reports regarding the fuel properties of biodiesel obtained from algal oils. Algal oils, with examples of some exceptions also mentioned here, often contain significant amounts of saturated and highly polyunsaturated (≥4 double bonds) fatty acid chains which influence fuel properties of the resulting biodiesel. In this connection, the relevant fuel properties of biodiesel from algal oils and the important fuel properties of highly polyunsaturated fatty acid methyl esters as they would occur in many biodiesel fuels obtained from algal oils, have not yet been reported. To fill this gap, in the present work for the first time two neat highly polyunsaturated fatty acid methyl esters with more than three double bonds, methyl 5(Z),8(Z),11(Z),14(Z)-eicosatetraenoate (C20:4) and methyl 4(Z),7(Z),10(Z),13(Z),16(Z),19(Z)-docosahexaenoate (C22:6), were investigated. The cetane numbers were determined as 29.6 for C20:4 and 24.4 for C22:6. Kinematic viscosity values were observed as 3.11 mm2/s for C20:4 and 2.97 mm2/s for C22:6, while oxidative stability values were below 0.1 h for both by the Rancimat test while densities were above 0.9 g/cm3. Two polyunsaturated C20 methyl esters, methyl 11(Z),14(Z)-eicosadienoate and 11(Z),14(Z),17(Z)-eicosatrienoate, were also studied for kinematic viscosity, density, and oxidative stability to expand the database on these properties of C20 compounds and provide additional data to predict the properties of other highly polyunsaturated fatty acid methyl esters. Properties of biodiesel from algal oils are predicted with cetane numbers expected in the low to upper 40s and kinematic viscosity between 3 and 4 mm2/s for most algal biodiesel.
Biologically produced fuels are considered potential and viable alternatives to meet the world's fuel requirements. In this context, algal-based oil is of significant importance due to its renewable and carbon-neutral nature. Biosynthesis of triglycerides by utilizing CO2 (by biofixation) or wastewater under stress conditions via photoautotrophic, heterotrophic (photo/dark), or mixotrophic mechanisms enumerates the potential of microalgae for generation of renewable biodiesel. In addition to the algal cultivation, the conversion of the accumulated lipids to biodiesel is gaining considerable interest. Though there exist some constraints, the process of harnessing biofuel from microalgae is both economically viable and environmentally sustainable compared to the other oil-producing terrestrial crops.This chapter explores biofuel production using microalgae. Concerted efforts are made in this chapter to discuss the biochemistry pertaining to algal lipid synthesis, nutritional modes of algae, cultivation systems used for algal oil production, and the cascade of steps involved, from biomass cultivation to transesterification of the fuel. The ability of microalgae to capture CO2 and its survivability in wastewater is also elaborated in the context of lipid synthesis.
In this report, we present a compilation of reported cetane numbers for pure chemical compounds. The compiled database contains cetane values for 299 pure compounds, including 156 hydrocarbons and 143 oxygenates. Cetane number is a relative ranking of fuels based on the amount of time between fuel injection and ignition. The cetane number is typically measured either in a combustion bomb or in a single-cylinder research engine. This report includes cetane values from several different measurement techniques - each of which has associated uncertainties. Additionally, many of the reported values are determined by measuring blending cetane numbers, which introduces significant error. In many cases, the measurement technique is not reported nor is there any discussion about the purity of the compounds. Nonetheless, the data in this report represent the best pure compound cetane number values available from the literature as of August 2004.
The objectives of this work were to identify a practical accelerated oxidative stability test method and to define a reasonable, data-based, stability minimum requirement. The biodiesel (B100) samples show a broad distribution of stability on accelerated tests, with EN14112 induction time results ranging from less than 1 h to as much as 12 h and ASTM D2274 total insolubles ranging from less than 1 mg/100 mL to nearly 18 mg/100 mL. The accelerated test data indicate that if the B100 stability is above roughly a 3 h induction time, blends prepared from that B100 appear to be stable on the induction time and D2274 tests. The D4625 long-term storage results for B100 indicate that most biodiesel samples, regardless of initial induction time, will begin to oxidize immediately during storage. If induction time is near or below the 3 h limit, the B100 will most likely go out of specification for either stability or acid value within 4 months (4 weeks on the D4625 test). Even B100 with induction times longer than 7 h will be out of specification for oxidation stability at only 4 months, although these samples may not have shown a significant increase in acidity or in deposit formation. The 3 h B100 induction time limit appears to be adequate to prevent oxidative degradation for B5 blends in storage for up to 12 months and B20 blends for up to 4 months. The results indicate that B100 stability is the main factor that affects the stability of B5 and B20 blends, independent of diesel fuel aromatic content, sulfur level, or stability. Synthetic antioxidants were highly effective at preventing acid and insoluble formation during storage.
During storage and use, vegetable oil-derived industrial products such as biodiesel and biodegradable lubricants can be subjected
to conditions that promote oxidation of their unsaturated components. The materials arising during oxidation and subsequent
degradation can seriously impair the quality and performance of such products. Therefore, oxidative stability is a significant
issue facing these vegetable oil-derived products, and enhanced understanding of the influence of various components of vegetable
oils and storage parameters is necessary. In this work, the oil stability index (OSI) was used for assessing oxidation of
monoalkyl esters of FA by varying several parameters. Neat fatty compounds and prepared mixtures thereof were studied for
assessing the influence of compound structure and concentration. Small amounts of more highly unsaturated compounds had a
disproportionately strong effect on oxidative stability. The recently developed concept of bis-allylic equivalents correlated
more closely than the iodine value with the OSI times of mixtures of fatty esters. The OSI times of free acids were shorter
than those of the corresponding alkyl esters. The presence of copper, iron, and nickel also reduced oxidative stability, but
their effect was less than the presence of more highly unsaturated fatty compounds. Of these metals, copper had the strongest
catalytic effect on OSI time. OSI may be an alternative to long-term storage tests for determining the influence of extraneous
materials such as metals on oxidative stability.
Interest in algae as a feedstock for biofuel production has risen in recent years, due to projections that algae can produce
lipids (oil) at a rate significantly higher than agriculture-based feedstocks. Current research and development of enclosed
photobioreactors for commercial-scale algal oil production is directed towards pushing the upper limit of productivity beyond
that of open ponds. So far, most of this development is in a prototype stage, so working production metrics for a commercial-scale
algal biofuel system are still unknown, and projections are largely based on small-scale experimental data. Given this research
climate, a methodical analysis of a maximum algal oil production rate from a theoretical perspective will be useful to the
emerging industry for understanding the upper limits that will bound the production capabilities of new designs. This paper
presents a theoretical approach to calculating an absolute upper limit to algal production based on physical laws and assumptions
of perfect efficiencies. In addition, it presents a best case approach that represents an optimistic target for production
based on realistic efficiencies and is calculated for six global sites. The theoretical maximum was found to be 354,000L·ha−1·year−1 (38,000gal·ac−1·year−1) of unrefined oil, while the best cases examined in this report range from 40,700–53,200L·ha−1·year−1 (4,350–5,700gal·ac−1·year−1) of unrefined oil.
KeywordsAlgae-Biofuels-Theoretical yield-Oil production-Second-generation feedstock
Microalgae provide various potential advantages for biofuel production when compared with 'traditional' crops. Specifically, large-scale microalgal culture need not compete for arable land, while in theory their productivity is greater. In consequence, there has been resurgence in interest and a proliferation of algae fuel projects. However, while on a theoretical basis, microalgae may produce between 10- and 100-fold more oil per acre, such capacities have not been validated on a commercial scale. We critically review current designs of algal culture facilities, including photobioreactors and open ponds, with regards to photosynthetic productivity and associated biomass and oil production and include an analysis of alternative approaches using models, balancing space needs, productivity and biomass concentrations, together with nutrient requirements. In the light of the current interest in synthetic genomics and genetic modifications, we also evaluate the options for potential metabolic engineering of the lipid biosynthesis pathways of microalgae. We conclude that although significant literature exists on microalgal growth and biochemistry, significantly more work needs to be undertaken to understand and potentially manipulate algal lipid metabolism. Furthermore, with regards to chemical upgrading of algal lipids and biomass, we describe alternative fuel synthesis routes, and discuss and evaluate the application of catalysts traditionally used for plant oils. Simulations that incorporate financial elements, along with fluid dynamics and algae growth models, are likely to be increasingly useful for predicting reactor design efficiency and life cycle analysis to determine the viability of the various options for large-scale culture. The greatest potential for cost reduction and increased yields most probably lies within closed or hybrid closed-open production systems.
Studies conducted since the late 1970s have estimated the net energy value (NEV) of corn ethanol. However, variations in data and assumptions used among the studies have resulted in a wide range of estimates. This study identifies the factors causing this wide variation and develops a more consistent estimate. We conclude that the NEV of corn ethanol has been rising over time due to technological advances in ethanol conversion and increased efficiency in farm production. We show that corn ethanol is energy efficient as indicated by an energy output:input ratio of 1.34.
Biofuels demand is unquestionable in order to reduce gaseous emissions (fossil CO(2), nitrogen and sulfur oxides) and their purported greenhouse, climatic changes and global warming effects, to face the frequent oil supply crises, as a way to help non-fossil fuel producer countries to reduce energy dependence, contributing to security of supply, promoting environmental sustainability and meeting the EU target of at least of 10% biofuels in the transport sector by 2020. Biodiesel is usually produced from oleaginous crops, such as rapeseed, soybean, sunflower and palm. However, the use of microalgae can be a suitable alternative feedstock for next generation biofuels because certain species contain high amounts of oil, which could be extracted, processed and refined into transportation fuels, using currently available technology; they have fast growth rate, permit the use of non-arable land and non-potable water, use far less water and do not displace food crops cultures; their production is not seasonal and they can be harvested daily. The screening of microalgae (Chlorella vulgaris, Spirulina maxima, Nannochloropsis sp., Neochloris oleabundans, Scenedesmus obliquus and Dunaliella tertiolecta) was done in order to choose the best one(s), in terms of quantity and quality as oil source for biofuel production. Neochloris oleabundans (fresh water microalga) and Nannochloropsis sp. (marine microalga) proved to be suitable as raw materials for biofuel production, due to their high oil content (29.0 and 28.7%, respectively). Both microalgae, when grown under nitrogen shortage, show a great increase (approximately 50%) in oil quantity. If the purpose is to produce biodiesel only from one species, Scenedesmus obliquus presents the most adequate fatty acid profile, namely in terms of linolenic and other polyunsaturated fatty acids. However, the microalgae Neochloris oleabundans, Nannochloropsis sp. and Dunaliella tertiolecta can also be used if associated with other microalgal oils and/or vegetable oils.
Human skin fibroblasts can convert arachidonic acid to 14- and 16-carbon polyunsaturated fatty acid products by peroxisomal beta-oxidation. The purpose of this study was to determine whether similar products are formed from eicosapentaenoic acid (EPA) and whether EPA and arachidonic acid compete for utilization by this oxidative pathway. Three radiolabeled metabolites with shorter retention times than EPA on reverse-phase high-performance liquid chromatography accumulated in the medium during incubation of fibroblasts with [5,6,8,9,11,12,14,15,17,18-3H] EPA ([3H]EPA). These metabolites, which were not formed from [1-14C]EPA and were not detected in the cells, were identified as tetradecatrienoic acid (14:3n-3), hexadecatetraenoic acid (16:4n-3), and octadecatetraenoic acid (18:4n-3). The most abundant product under all of the conditions tested was 16:4n-3. [3H]EPA was converted to 16:4n-3 and 14:3n-3 by fibroblasts deficient in mitochondrial long-chain acyl CoA dehydrogenase, but not by Zellweger syndrome or acyl CoA oxidase mutants that are deficient in peroxisomal beta-oxidation. Competition studies indicated that 16:4n-3 formation from 5 microM [3H]EPA was reduced by 60% when 10 microM arachidonic acid was added, but the conversion of [3H]arachidonic acid to its chain-shortened products was not decreased by the addition of 10 microM EPA. These findings demonstrate that as in the case of arachidonic acid, chain-shortened polyunsaturated fatty acid products accumulate when EPA undergoes peroxisomal beta-oxidation. While EPA does not reduce arachidonic acid utilization by this pathway, it is possible that some biological actions of EPA may be mediated by the formation of the corresponding EPA products, 16:4n-3 and 14:3n-3.
This study describes the effect of different types of biodiesel (fatty acid methyl esters, FAME) on the oxidative stability of low and ultra low sulfur automotive diesel fuels. Eight different samples of FAME were employed to create blends of 2, 3, 4, 5, 7, and 10% v/v with four different types of diesel fuels. The samples were analyzed using the modified Rancimat method (EN 15751). The aim of this paper was to evaluate the impact of biodiesel source material and biodiesel concentration in diesel fuel, on the oxidation stability of the final blend. Moreover, the effect of sulfur content and the presence of cracked stocks in the base diesel fuel, on the oxidation stability of the final blends were also investigated.
Studies have shown that the magnitude of pollutant emissions (e.g. NO x and PM) from diesel engines operating on fatty acid methyl esters (i.e. FAME biodiesel) are related to the fatty acid composition of the triglycerides present in the bio feedstock. Specifically, NO x emissions have been shown to increase with increasing levels of unsaturation in the hydrocarbon chain and decrease with increasing carbon chain length; and PM emissions have been shown to decrease with increasing carbon chain length. Little work has been done to date to characterize the pollutant emissions of algae-based FAME, which have far different fatty acid composition than FAME derived from typical vegetable or animal fat feedstocks. Accordingly, the goal of the present study was to characterize the performance and emissions from a diesel engine operating on FAME with fatty acid composition commensurate with that produced from several algal species currently under consideration for wide scale fuel production. Tests were performed on a 2.4 L, 56 HP John Deere 4024T, non-road diesel engine meeting USEPA Tier 2 emissions regulations. The engine was fitted with a unique, low-volume fuel injection system that enabled emissions tests to be conducted with very low volumes of specialty fuel sample. Tests were performed on 9 different fuel blends at 2 different engine loading conditions. Exhaust gas measurements were made using a 5-gas emissions analysis system that includes chemiluminescence measurement of NO, NO 2 and total NO x, flame ionization detection of total hydrocarbons and nondispersive infrared detection of CO and CO 2. An FTIR was used to measure additional hazardous air pollutants such as formaldehyde. Particulate matter was characterized on-line, using an Aerodyne Aerosol Mass Spectrometer (AMS), which is capable of direct measurement of both particle size (50 and 1000 nm) and chemical composition. Smaller PM size distributions (10 to 100 nm) were measured using a Scanning Mobility Particle Sizer. Total PM mass emissions and the ratio of elemental carbon to organic were measured using gravimetric sampling. Results showed that the emissions from the two simulated algal methyl ester formulations were similar to those measured from soy and canola methyl esters with the exception of NO x emissions which were shown to decrease for the simulated algal methyl esters. The decreased NO x emissions from the simulated algal methyl esters were accompanied by a decrease in premixed burn fraction.
Biodiesel is an alternative diesel fuel that is produced from vegetable oils and animal fats. It consists of the monoalkyl esters formed by a catalyzed reaction of the triglycerides in the oil or fat with a simple monohydric alcohol. The reaction conditions generally involve a trade-off between reaction time and temperature as reaction completeness is the most critical fuel quality parameter. Much of the process complexity originates from contaminants in the feedstock, such as water and free fatty acids, or impurities in the final product, such as methanol, free glycerol, and soap. Processes have been developed to produce biodiesel from high free fatty acid feedstocks, such as recycled restaurant grease, animal fats, and soapstock.
Biodiesel, an “alternative” diesel fuel derived from vegetable oils, animals fats or used frying oils, largely consists of the mono-alkyl esters of the fatty acids comprising these feedstocks. One of the major technical issue facing biodiesel is its susceptibility to oxidation upon exposure to oxygen in ambient air. This susceptibility is due to its content of unsaturated fatty acid chains, especially those with bis-allylic methylene moieties. Oxidation of fatty acid chains is a complex process that proceeds by a variety of mechanisms. Besides the presence of air, various other factors influence the oxidation process of biodiesel including presence of light, elevated temperature, extraneous materials such as metals which may be even present in the container material, peroxides, and antioxidants, as well as the size of the surface area between biodiesel and air. Approaches to improving biodiesel oxidative stability include the deliberate addition of antioxidants or modification of the fatty ester profile. This article discusses some factors influencing biodiesel oxidative stability and their interaction. Resulting approaches to improving this property of biodiesel are related to these factors and the corresponding mechanisms.
Biodiesel is an alternative fuel derived from vegetable oils, animal fats and used frying oils. Due to its chemical structure, it is more susceptible to oxidation or autoxidation during long-term storage compared to petroleum diesel fuel. One of the major technical issues regarding the biodiesel blends with diesel fuel is the oxidation stability of the final blend, which is, nowadays, of particularly high concern due to the introduction of ultra low sulphur diesel, in most parts of the EU. This study examined the factors influencing the stability of several biodiesel blends with low and ultra low sulphur automotive diesel fuels. The aim of this paper was to evaluate the impact of biodiesel source material and biodiesel concentration in diesel fuel, on the stability of the final blend. Moreover, the effects of certain characteristics of the base diesels, such as sulphur content and the presence of cracked stocks, on the oxidation stability are discussed.
The term biodiesel means the monoalkyl esters of long-chain fatty acids made from biolipids such as vegetable oils, animal fats, or algae. Chemical reactivity of biodiesel can be divided into oxidative and thermal instability. Many of the biolipids contain polyunsaturated fatty acid chains in that their double bonds have high chemical reactivity. The oxidative and thermal degradation occurs on the double bonds of unsaturated aliphatic carbons chains in biolipids. Oxidation of biodiesel results in the formation of hydroperoxides. The formation of the hydroperoxide follows a well-known peroxidation chain mechanism. The olefinic unsaturated fatty acid oxidation is a multi-step reaction process where primary products (conjugated diene hydroperoxides) decompose and chemically interact with each other to form numerous secondary oxidation products. The oxidative and thermal instability are determined by the amount and configuration of the olefinic unsaturation on the fatty acid chains. The viscosity of biodiesel increases with the increase of thermal degradation degree due to the trans-isomer formation on double bonds. The decomposition of biodiesel and its corresponding fatty acids linearly increases from 293 K to 625 K. The densities of biodiesel fuels decreased linearly with temperatures from 293 K to 575 K. The combustion heat of biodiesel partially decreases with the increase of thermal degradation degree.
Fatty acid methyl esters (FAME) are considered to be promising and prospective alternative fuels for diesel engines. They can be produced from vegetable oils and animal fats by transesterification of triacylglycerols with methanol. This paper presents the results related to the stability of FAME from aging tests of FAME in the period of 7 months. The FAME were prepared from four oil types, which were finally treated, stabilized, and stored in a different way. The results show that lower ester content in freshly prepared FAME, having at the same time a good conversion, is related to degradation of the oil from which the FAME were prepared. The stabilities of FAME samples prepared from old oils and used frying oils are lower than the stability of FAME samples prepared from fresh oils. Insufficient conversion of FAME itself does not have negative influence on its stability. After final distillation treatment, FAME exhibits lower stability when compared with the sample treated in the standard way. However, they are very sensitive to the presence of an antioxidant; the addition of 0.04 wt % of pyrogallol ensures high FAME stability.
This study investigates the impact of various synthetic phenolic antioxidant additives on the oxidation stability of several neat biodiesels, with special emphasis on the stability behavior of diesel/biodiesel blends with the employment of the modified Rancimat method (EN 15751). The performance of antioxidants was evaluated for treating five biodiesels, obtained from different origins, and their blends with a typical automotive ultra-low sulfur diesel. The examined blends were in proportions of 2, 3, 4, 5, 7, and 10% by volume, similar to those that currently penetrate the European fuel market. All biodiesel samples were treated with a constant concentration of 1000 mg/kg of each additive and then blended with diesel fuel. The experimental results revealed that an improvement in oxidation stability could be achieved with all antioxidants tested, while the efficiency of the antioxidants varied depending upon the different types and quality of biodiesel. Among the antioxidants evaluated, butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) displayed the lowest effectiveness in neat methyl esters, whereas their use in biodiesel blends showed a greater stabilizing potential. It was also found that additives that significantly improve the stability of biodiesel may act as pro-oxidants in biodiesel blends.
In this paper, we examine the interaction between the bulk modulus of compressibility of various fuel samples and its effect on fuel injection timing. The fuels considered range from soy oil-derived biodiesel, unrefined soybean oil, and paraffinic solvents to ultralow-sulfur and conventional diesel fuels. Both the impact on injection timing and the variation in the bulk modulus of compressibility are measured. The present work confirms that the higher bulk modulus of compressibility of vegetable oils and their methyl esters leads to advanced injection timing with in-line pump−line−nozzle fuel injection systems. This has been shown in the literature to contribute to the well-documented increase in NOx emissions with the use of biodiesel fuel. An opposite trend, a retarding of injection timing, is observed with paraffinic fuels, because they have a lower bulk modulus of compressibility than conventional diesel fuels. This supports the observation that paraffinic fuels such as Fischer−Tropsch diesel yield lower NOx emissions.
This study aimed to evaluate the influence of different volumes of supplemented carbon dioxide. which is a potential donator of carbon atom, on the fatty acid profile of four microalgae strains (Nannochloropsis sp., Nannochloropsis oculata (Droop) Hibberd. Nannochloris atomus Butcher and Isochrysis sp.) currently used to enrich rotifers fed to marine fish larvae during two different phases of growth (logarithmic and stationary). Half of the microalgae were cultured at a low CO2 concentration (0.5 L/min). corresponding to 1 % the air volume (0.038 L/min per L of culture) and the other half of microalgae were cultured at a high concentration of CO2 (1.1 L/min), corresponding to 2% the air volume (0.086 L/min per L of culture).
The resulting fatty acid profile was species-specific and Nannochloris atomus appeared less suitable for inarine organism feeding because of its high percentage of alpha-linolenic acid which represents the only n-3 PUFA of this alga (28.7%). On the contrary, Isochrysis sp. showed the largest proportions of n-3 PUFA also when maintained in the stationary phase (36.46%). Algae cultures contained higher percentages of n-3 PUFA during the logarithmic phase than in the stationary phase when the proportions of short-chain fatty acids increased. High levels of concentrated CO2 generally increased the content of long chain fatty acids from 17 carbon atoms onwards. The percentages of total n-3 and n-6 were higher than those recorded at low CO2 concentration. Similarly, the n-3/n-6 ratio was higher at the maximum CO2 concentration (logarithmic phase). During stationary phase the difference between the two groups was less apparent than that observed in the logarithmic one. The high CO2 addition exerted a significant and more favorable influence than the low supplementation on the C18:1, C20:0, C20:4n-6, and C22:6n-3 concentrations in both phases, in all four microalgae strains studied.
The lipid profile of seven species of unicellular eukaryotic microalgae grown under controlled conditions was studied with emphasis on the hydrocarbons and the fatty acids as part of a search for oil-producing algae. Green, slow-growing colonies of Botryococcus braunii Kutz contained the highest lipid content of 45% based on the organic weight, with an increase to 55% under nitrogen deficiency and with no effect of sodium chloride stress. Ankistrodesmus sp. Thomas, Dunaliella spp., Isochrysis sp., Nannochloris sp. Thomas, and Nitzschia sp. Chapman contained an average of 25% lipids under nitrogen sufficient conditions. Nitrogen deficiency resulted in significant increase in the lipid content in all species but Dunaliella spp., which produced a higher content of carbohydrates. Significant low amounts of acyclic hydrocarbons were detected only in Botryococcus braunii Kutz and not in the other algae. The major hydrocarbon fractions in nitrogen deficient Botryococcus braunii Kutz, Dunaliella salina Thomas, Isochrysis spp. and Nannochloris sp. Thomas were cyclic and branched polyunsaturated components which were identified as various isoprenoid derivatives. The polar lipid composition of glycolipids and phospholipids of all species investigated was fairly typical of photosynthetic eukaryotic algae. Fatty acid composition was species specific, with changes occurring in the relative amounts of individual acids of cells cultivated under different conditions and growth phases. All species synthesized C14:0, C16.0, C18:1, C18:2 and C18:3 fatty acids; C 16:4 in Ankistrodesmus sp. Thomas; C18:4 and C 22.6 in Isochrysis sp.; C16:2, C16:3 and C20:5 in Nannochloris sp. Thomas; C16:2, C16:3 and C20:5 in Nitzschia sp. Chapman. Nitrogen deficiency and salt stress induced accumulation of C18:1 in all treated species and to a lesser extent in Botryococcus braunii Kutz. The low production of hydrocarbons under optimal growth conditions and the high production of hydrocarbons under limited growth conditions cannot support the notion that microalgae can be utilized as biosolar energy converters for the production of liquid fuel, but point to the availability of a variety of neutral and polar lipid products.
Biodiesel, an alternative to petroleum-derived diesel fuel, is defined as the mono-alkyl esters of vegetable oils and animal fats. Several current issues affecting biodiesel that are briefly discussed include the role of new feedstocks in meeting increased demand for biodiesel and circumventing the food versus fuel issue, biodiesel production, as well as fuel properties and their improvement. © 2010 GovernmentEmployee: U.S. Department of Agriculture, Agricultural Research Service, National Center for Agricultural Utilization Research.
Most common analytical methods in FA chemistry can be categorized as yielding either structure or quality indices. Quality
indices often describe components in fats and oils arising from processing, storage, and naturally occurring, nonfatty materials.
Common structure indices are the iodine value (IV), the saponification value, and the hydroxyl value. Although modern analytical
methods yield more detailed and reliable information, structure indices are still widely used. The IV, which indicates total
unsaturation, has even been included in some standards for industrial products such as biodiesel. However, the IV index is
too general to allow the correlation of physical and chemical properties with FA composition. The IV is treated in a theoretical
fashion regarding biodiesel- and oxidative stability-related issues. That the concept of IV as a structure index is unsatisfactory
is shown by the development of a quaternary composition diagram (QCD). The QCD demonstrates the derivation of a specific IV
from varying FA compositions. Improved correlations are possible among the structure indices. Alternative indices for the
IV are developed. Possible alternatives are the allylic position equivalent (APE) and the bisallylic position equivalent (BAPE)
which better relate structure and amount of common component FA in vegetable oils to observed properties. The APE and BAPE
indices are based on the number of reactive positions in oxidation.
The scarcity of known petroleum reserves will make renewable energy resources more attractive. The most feasible way to meet this growing demand is by utilizing alternative fuels. Biodiesel is defined as the monoalkyl esters of vegetable oils or animal fats. Biodiesel is the best candidate for diesel fuels in diesel engines. The biggest advantage that biodiesel has over gasoline and petroleum diesel is its environmental friendliness. Biodiesel burns similar to petroleum diesel as it concerns regulated pollutants. On the other hand, biodiesel probably has better efficiency than gasoline. One such fuel for compression-ignition engines that exhibit great potential is biodiesel. Diesel fuel can also be replaced by biodiesel made from vegetable oils. Biodiesel is now mainly being produced from soybean, rapeseed and palm oils. The higher heating values (HHVs) of biodiesels are relatively high. The HHVs of biodiesels (39–41 MJ/kg) are slightly lower than that of gasoline (46 MJ/kg), petrodiesel (43 MJ/kg) or petroleum (42 MJ/kg), but higher than coal (32–37 MJ/kg). Biodiesel has over double the price of petrodiesel. The major economic factor to consider for input costs of biodiesel production is the feedstock, which is about 80% of the total operating cost. The high price of biodiesel is in large part due to the high price of the feedstock. Economic benefits of a biodiesel industry would include value added to the feedstock, an increased number of rural manufacturing jobs, an increased income taxes and investments in plant and equipment. The production and utilization of biodiesel is facilitated firstly through the agricultural policy of subsidizing the cultivation of non-food crops. Secondly, biodiesel is exempt from the oil tax. The European Union accounted for nearly 89% of all biodiesel production worldwide in 2005. By 2010, the United States is expected to become the world's largest single biodiesel market, accounting for roughly 18% of world biodiesel consumption, followed by Germany.
This study examined factors impacting the stability of biodiesel (B100) samples collected as part of a 2004 nationwide fuel quality survey in the United States. Biodiesel is significantly less stable than petroleum diesel, so an understanding of the chemical and environmental factors affecting its degradation is required. The survey included samples produced from soy, waste oils, and tallow. The 27 samples were assessed for stability using the ASTM D2274 test for insoluble formation and the OSI method (via Rancimat apparatus) for induction time. Additionally, the samples were characterized for fatty acid make up, relative antioxidant content, metals content, and total glycerin content (free glycerin plus glycerin bound as mono-, di-, and triglycerides). For the samples examined here the polyunsaturated content (or oxidizability) has the largest impact on both increasing insoluble formation and reducing induction time. However, the formation of insolubles is also measurably decreased by increasing relative antioxidant content and increased by increasing total glycerin content. The OSI or Rancimat induction time is also increased by increasing relative antioxidant content, as expected.
Biodiesel consists of long chain fatty acid esters derived from feed stocks such as vegetable oils, animal fats and used frying oil, etc. which may contain more or less unsaturated fatty acids which are prone to oxidation accelerated by exposure to air during storage and at high temperature may yield polymerized compounds. Auto oxidation of biodiesel can cause degradation of fuel quality by affecting the stability parameters. Biodiesel stability includes oxidation, storage and thermal stability. Oxidation instability can led to the formation of oxidation products like aldehydes, alcohols, shorter chain carboxylic acids, insolubles, gum and sediment in the biodiesel. Thermal instability is concerned with the increased rate of oxidation at higher temperature which in turn, increases the weight of oil and fat due to the formation of insolubles. Storage stability is the ability of liquid fuel to resist change in its physical and chemical characteristics brought about by its interaction with its environment and may be affected by interaction with contaminants, light, factors causing sediment formation, changes in color and other changes that reduce the clarity of the fuel. These fuel instabilities give rise to formation of undesirable substances in biodiesel and its blends beyond acceptable quantities as per specifications and when such fuel is used in engine, it impairs the engine performance due to fuel filter plugging, injector fouling, deposit formation in engine combustion chamber and various components of the fuel system.
In this article, the status of fat and oil derived diesel fuels with respect to fuel properties, engine performance, and emissions is reviewed. The fuels considered are primarily the methyl esters of fatty acids derived from a variety of vegetable oils and animal fats, and referred to as biodiesel. The major obstacle to widespread use of biodiesel is the high cost relative to petroleum. Economics of biodiesel production are discussed, and it is concluded that the price of the feedstock fat or oil is the major factor determining biodiesel price.Biodiesel is completely miscible with petroleum diesel fuel, and is generally tested as a blend. The use of biodiesel in neat or blended form has no effect on the energy based engine fuel economy. The lubricity of these fuels is superior to conventional diesel, and this property is imparted to blends at levels above 20 vol%. Emissions of PM can be reduced dramatically through use of biodiesel in engines that are not high lube oil emitters. Emissions of NOx increase significantly for both neat and blended fuels in both two- and four-stroke engines. The increase may be lower in newer, lower NOx emitting four-strokes, but additional data are needed to confirm this conclusion. A discussion of available data on unregulated air toxins is presented, and it is concluded that definitive studies have yet to be performed in this area. A detailed discussion of important biodiesel properties and recommendations for future research is presented. Among the most important recommendations is the need for all future studies to employ biodiesel of well-known composition and purity, and to report detailed analyses. The purity levels necessary for achieving adequate engine endurance, compatibility with coatings and elastomers, cold flow properties, stability, and emissions performance must be better defined.
Sustainable production of renewable energy is being hotly debated globally since it is increasingly understood that first generation biofuels, primarily produced from food crops and mostly oil seeds are limited in their ability to achieve targets for biofuel production, climate change mitigation and economic growth. These concerns have increased the interest in developing second generation biofuels produced from non-food feedstocks such as microalgae, which potentially offer greatest opportunities in the longer term. This paper reviews the current status of microalgae use for biodiesel production, including their cultivation, harvesting, and processing. The microalgae species most used for biodiesel production are presented and their main advantages described in comparison with other available biodiesel feedstocks. The various aspects associated with the design of microalgae production units are described, giving an overview of the current state of development of algae cultivation systems (photo-bioreactors and open ponds). Other potential applications and products from microalgae are also presented such as for biological sequestration of CO2, wastewater treatment, in human health, as food additive, and for aquaculture.
Vegetable oils and their derivatives (especially methyl esters), commonly referred to as "biodiesel," are prominent candidates as alternative diesel fuels. They have advanced from being purely experimental fuels to initial stages of commercialization. They are technically competitive with or offer technical advantages compared to conventional diesel fuel. Besides being a renewable and domestic resource, biodiesel reduces most emissions while engine performance and fuel economy are nearly identical compared to conventional fuels. Several problems. however, remain, which include economics, combustion, some emissions, lube oil contamination, and low-temperature properties. An overview on all aspects of biodiesel is presented.
The aim of this work was the study of the influence of the raw material composition on biodiesel quality, using a transesterification reaction. Thus, ten refined vegetable oils were transesterificated using potassium methoxide as catalyst and standard reaction conditions (reaction time, 1h; weight of catalyst, 1 wt.% of initial oil weight; molar ratio methanol/oil, 6/1; reaction temperature, 60 degrees C). Biodiesel quality was tested according to the standard [UNE-EN 14214, 2003. Automotive fuels. Fatty acid methyl esters (FAME) for diesel engines. Requirements and test methods]. Some critical parameters like oxidation stability, cetane number, iodine value and cold filter plugging point were correlated with the methyl ester composition of each biodiesel, according to two parameters: degree of unsaturation and long chain saturated factor. Finally, a triangular graph based on the composition in monounsaturated, polyunsaturated and saturated methyl esters was built in order to predict the critical parameters of European standard for whatever biodiesel, known its composition.
Thirty microalgal strains were screened in the laboratory for their biomass productivity and lipid content. Four strains (two marine and two freshwater), selected because robust, highly productive and with a relatively high lipid content, were cultivated under nitrogen deprivation in 0.6-L bubbled tubes. Only the two marine microalgae accumulated lipid under such conditions. One of them, the eustigmatophyte Nannochloropsis sp. F&M-M24, which attained 60% lipid content after nitrogen starvation, was grown in a 20-L Flat Alveolar Panel photobioreactor to study the influence of irradiance and nutrient (nitrogen or phosphorus) deprivation on fatty acid accumulation. Fatty acid content increased with high irradiances (up to 32.5% of dry biomass) and following both nitrogen and phosphorus deprivation (up to about 50%). To evaluate its lipid production potential under natural sunlight, the strain was grown outdoors in 110-L Green Wall Panel photobioreactors under nutrient sufficient and deficient conditions. Lipid productivity increased from 117 mg/L/day in nutrient sufficient media (with an average biomass productivity of 0.36 g/L/day and 32% lipid content) to 204 mg/L/day (with an average biomass productivity of 0.30 g/L/day and more than 60% final lipid content) in nitrogen deprived media. In a two-phase cultivation process (a nutrient sufficient phase to produce the inoculum followed by a nitrogen deprived phase to boost lipid synthesis) the oil production potential could be projected to be more than 90 kg per hectare per day. This is the first report of an increase of both lipid content and areal lipid productivity attained through nutrient deprivation in an outdoor algal culture. The experiments showed that this marine eustigmatophyte has the potential for an annual production of 20 tons of lipid per hectare in the Mediterranean climate and of more than 30 tons of lipid per hectare in sunny tropical areas.
Continued use of petroleum sourced fuels is now widely recognized as unsustainable because of depleting supplies and the contribution of these fuels to the accumulation of carbon dioxide in the environment. Renewable, carbon neutral, transport fuels are necessary for environmental and economic sustainability. Biodiesel derived from oil crops is a potential renewable and carbon neutral alternative to petroleum fuels. Unfortunately, biodiesel from oil crops, waste cooking oil and animal fat cannot realistically satisfy even a small fraction of the existing demand for transport fuels. As demonstrated here, microalgae appear to be the only source of renewable biodiesel that is capable of meeting the global demand for transport fuels. Like plants, microalgae use sunlight to produce oils but they do so more efficiently than crop plants. Oil productivity of many microalgae greatly exceeds the oil productivity of the best producing oil crops. Approaches for making microalgal biodiesel economically competitive with petrodiesel are discussed.
Microalgae represent an exceptionally diverse but highly specialized group of micro-organisms adapted to various ecological habitats. Many microalgae have the ability to produce substantial amounts (e.g. 20-50% dry cell weight) of triacylglycerols (TAG) as a storage lipid under photo-oxidative stress or other adverse environmental conditions. Fatty acids, the building blocks for TAGs and all other cellular lipids, are synthesized in the chloroplast using a single set of enzymes, of which acetyl CoA carboxylase (ACCase) is key in regulating fatty acid synthesis rates. However, the expression of genes involved in fatty acid synthesis is poorly understood in microalgae. Synthesis and sequestration of TAG into cytosolic lipid bodies appear to be a protective mechanism by which algal cells cope with stress conditions, but little is known about regulation of TAG formation at the molecular and cellular level. While the concept of using microalgae as an alternative and renewable source of lipid-rich biomass feedstock for biofuels has been explored over the past few decades, a scalable, commercially viable system has yet to emerge. Today, the production of algal oil is primarily confined to high-value specialty oils with nutritional value, rather than commodity oils for biofuel. This review provides a brief summary of the current knowledge on oleaginous algae and their fatty acid and TAG biosynthesis, algal model systems and genomic approaches to a better understanding of TAG production, and a historical perspective and path forward for microalgae-based biofuel research and commercialization.
Triacylglycerols produced by plants are one of the most energy-rich and abundant forms of reduced carbon available from nature. Given their chemical similarities, plant oils represent a logical substitute for conventional diesel, a non-renewable energy source. However, as plant oils are too viscous for use in modern diesel engines, they are converted to fatty acid esters. The resulting fuel is commonly referred to as biodiesel, and offers many advantages over conventional diesel. Chief among these is that biodiesel is derived from renewable sources. In addition, the production and subsequent consumption of biodiesel results in less greenhouse gas emission compared to conventional diesel. However, the widespread adoption of biodiesel faces a number of challenges. The biggest of these is a limited supply of biodiesel feedstocks. Thus, plant oil production needs to be greatly increased for biodiesel to replace a major proportion of the current and future fuel needs of the world. An increased understanding of how plants synthesize fatty acids and triacylglycerols will ultimately allow the development of novel energy crops. For example, knowledge of the regulation of oil synthesis has suggested ways to produce triacylglycerols in abundant non-seed tissues. Additionally, biodiesel has poor cold-temperature performance and low oxidative stability. Improving the fuel characteristics of biodiesel can be achieved by altering the fatty acid composition. In this regard, the generation of transgenic soybean lines with high oleic acid content represents one way in which plant biotechnology has already contributed to the improvement of biodiesel.
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