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Biodiesel Current Technology: Ultrasonic Process a Realistic Industrial Application

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Biodiesel is briefly defined as a renewable fuel derived from vegetable oils or animal fats. Similarly, the American Society of Testing and Materials (ASTM) defines biodiesel as monoalkyl long-chain fatty acids esters derived from fatty renewable inputs, such as vegetable oils or animal fats. The term “bio” refers to its origin from biomass related resources, in contrast to the traditional fosil-derived diesel, while the term “diesel” refers to its use on engines; as a fuel, biodiesel is typically used as a blend with regular diesel. To date, biodiesel is well recognized as the best fuel substitute in diesel engines because its raw materials are renewable, and it is biodegradable and more environmentally friendly; biodiesel probably has better efficiency than gasoline and exhibits great potential for compression-ignition engines. Resumen: Tecnología de ultrasonido para la obtención de biodiesel a partir de aceite de Jatropha curcas, la cual permite producir biocombustible limpio en tiempos cortos respecto a la producción tradicional con catalizadores básicos en reacciones homogéneas.
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Chapter 7
Biodiesel Current Technology: Ultrasonic Process a
Realistic Industrial Application
Mario Nieves-Soto, Oscar M. Hernández-Calderón,
Carlos Alberto Guerrero-Fajardo,
Marco Antonio Sánchez-Castillo,
Tomás Viveros-García and
Ignacio Contreras-Andrade
Additional information is available at the end of the chapter
http://dx.doi.org/10.5772/ 52384
1. Introduction
Biodiesel is briefly defined as a renewable fuel derived from vegetable oils or animal fats.
Similarly, the American Society of Testing and Materials (ASTM) defines biodiesel as mono‐
alkyl long-chain fatty acids esters derived from fatty renewable inputs, such as vegetable
oils or animal fats. The term “bio” refers to its origin from biomass related resources, in con‐
trast to the traditional fosil-derived diesel, while the term “diesel” refers to its use on en‐
gines; as a fuel, biodiesel is typically used as a blend with regular diesel. To date, biodiesel is
well recognized as the best fuel substitute in diesel engines because its raw materials are re‐
newable, and it is biodegradable and more environmentally friendly; biodiesel probably has
better efficiency than gasoline and exhibits great potential for compression-ignition engines.
Biodiesel was mainly produced from soybean, rapeseed and palm oils, although social and
economic considerations have turned attention to second generation biomass raw materials
such as Jatropha curcasoil [1]. It is well known that biodiesel competitiveness has to be im‐
proved, as to compare to curcas oil diesel, to spread out its consumption. Two routes are
suggested to overcome this problem; one is related to get cheap raw materials (i.e., triglycer‐
ides, nonedible vegetable oils, animal fats and wasted oils), and other one is to reduce proc‐
essing cost; notoriously both issues are interrelated [1]. The raw material origin is of great
relevance because it determines the final biodiesel properties and also the type of process to
be used. It is importance to notice that low-cost raw materials usually contain significant
© 2013 Nieves-Soto et al.; licensee InTech. This is an open access article distributed under the terms of the
Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits
unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
amounts of free fatty acids (FFA), which lead to a complex and more expensive final proc‐
ess, e.g. the catalyst depletion is accelerated, the purification costs are increase, and the yield
in alkali-catalyzed transesterification is decreased.In the other hand, processing costs could
be reduced through simplified operations and eliminating decreased. On the other hand,
waste streams. There are several current biodiesel technologies that tried to overcome the
issues just indicated. For instance, some plants in Europe produce biodiesel by transesterifi‐
cation using supercritical methanol without any catalyst. In this case, the reaction is very
fast (less than 5 min) and the catalyst absence decreases downstream purification costs.
However, the reaction requires very high temperature (350–400 ºC) and pressure (100–250
atm) which, in turn, increases the capital and safety costs. Another suggested alternative is
the use of heterogeneous catalysts that can be separated more easily from reaction products,
and required less harsh reaction conditions than the supercritical methanol process. Howev‐
er, these technologies are still far to produce low cost biodiesel, even if they overcome some
problems of the conventional process. In this scenario, new technologies are still required
for the transformation of second and third generation biomass raw materials, as well as re‐
sidual biomass, in sustainable production of biodiesel.
To this respect, recently, an increasing number of applications of ultrasonic processes(US) in
chemical transformations have made sonochemistry an attractive area of research and devel‐
opment [13]. The main benefit of US is to enhance chemical reactivity by providing enough
energy through out the cavitation phenomenon. The bubble implosions generated in this
phenomenon provide sufficient energy to break chemical bonds. Thus, the application of US
can completely change the reaction pathways as well as the reaction yield and selectivity.
Importantly, the main benefits that can be pointed out from the application of US are the
reaction rate increase and the use of less severe operating conditions, as well as shorten in‐
duction periods and reduction of reagents amount. An interesting extension of US is the
possibility to apply it for the transesterification of vegetable oils to produce biodiesel. Typi‐
cally, this reaction is kinetically slow and shows mass transfer limitations. Thus, cavitation
phenomenon of the US could provide the activation energy required in the reaction as well
as the conditions (i.e., mechanical energy) to improve the reaction mixing. In this way, US
could provide technical an economic advantage for biodiesel production, as compared to
conventional transesterification processes.
In this chapter we report the advantageous application of US for biodiesel lab scale produc‐
tion from Jatropha curcas oil (JCO). This proposal is in agreement with the search of opti‐
mized, sustainable biodiesel production. The chapter briefly describes the basics of current
biodiesel technologies and, in more detail, the fundamentals and benefits provided by sono‐
chemistry to alkaline transesterification process (“sonotransesterification” process). In addi‐
tion, the experimental setup used for sonotranseterification and the main results to date are
also discussed. In general, sonotranseterification shows a significant improve when applied
to biodiesel production from JCO; when using a 4.5:1 molar ratio of alcohol/JOC, 25 ºC, at‐
mospheric pressure and 60% of amplitude, yields up to 98% are obtained. Finally, these re‐
sults are compared to more conventional processes such as supercritical methanol and
heterogeneous catalysis for the same raw material. Results are discussed in terms of the ad‐
Biodiesel - Feedstocks, Production and Applications
178
vantages/disadvantages of reaction operating conditions, energy demand and process time.
Notoriously, sonotransesterification shows significant benefits as compare to conventional
technologies, which could be further improved as the process be optimized.
2. Biodiesel
Biodiesel is obtained by transesterification reaction, also known as alcoholysis; in this reac‐
tion, vegetable oils (preferably non-edible oils) or animal fats are reacted with a significant
excess of alcohol (methanol or ethanol), in the presence of a catalyst (homogeneous, hetero‐
geneous or enzymatic), to form fatty acid alkyl esters (FAME) and glycerol, a valuable by-
product for industry [2]. In a conventional biodiesel process (CBP), the alcohol-FAME phase
is separated and the alcohol excess is recycled (Figure 1). Next, esters undergo a purification
process, consisting of water washing, dry vacuum and subsequent filtering. In this process,
importantly, the oil used as raw material must be cleaned and its FFA content must belower
than 0.5wt%; otherwise, a pretreatment of the raw material must be carried out. Then, the oil
is typically mixed with the alcohol in a 6:1 molar ratio, and 1 to 3% homogeneous catalyst
(KOH or NaOH) is added to the reaction mixture. Reactants, including the catalyst, must be
anhydrous to avoid soap formation. The reaction is then stirred for 40 to 60 minutes, at tem‐
perature between 50 and 60 °C, afterward the reaction is completed [2].
Figure 1. Flow diagram of conventional alkaline homogeneous process for biodiesel production [2].
The overall transesterification chemistry involves an exchange between the alcohol groups
(i.e., methanol or ethanol) and glycerol, at given reaction conditions, to produce methyl or
ethyl fatty acidsesters (Figure 2). Each fatty acid molecule has the same chemistry configura‐
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tion [3] and it only differs from other molecules for the carbon chain length or its unsatura‐
tion number, which leads to produce FAME with different properties that, in turn, impact
the final biodiesel characteristics such as melting point, oxidation stability, etc. This is the
reason why the raw material quality is suggested to be the key point for the biodiesel proc‐
ess. Figure 2 also shows the well-accepte dreaction pathway. From the thermodynamic point
of view, triglycerides and methanol are well-accepted reaction pathway unable to react at
room temperature and atmospheric pressure (i.e., 25ºC and 1 atm, respectively) because of
the extremely low solubility of the alcohol into the oil; for this reason, catalysis plays an im‐
portant role for the alcoholysis reaction to take place.
Figure 2. Well-generalized transesterification pathway [3].
Literature [1-4] describes that the first reaction step is the formation of an alkoxide ion (RO)
through proton transfer from the alcohol. Actually, when homogeneous Brönsted basic cata‐
lysts (i.e., NaOH, KOH, Na2CO3) are interacts with the alcohol, the following reaction occurs:
KOH + CH3OH CH3O-+K(OH )H+(1)
This alkoxide group then attacks the carbonyl carbon atom of the triglyceride molecule to
form a tetrahedral intermediate ion (step 2); therefore, an alkoxide (NaOCH3, KOCH3) is of‐
ten directly used as catalyst. This intermediate ion rearranges to generate a diglyceride ion
Biodiesel - Feedstocks, Production and Applications
180
and alkyl ester molecule (step 3). Next, the diglyceride ion reacts with the protonated base
catalyst, which generates a diglyceride molecule and returns the base catalyst to its initial
state (step 4). The resulting diglyceride is then ready to react with another alcohol molecule,
there by maintaining the catalytic cycle until all the glyceride molecules have been complete
converted to biodiesel at 60-80 ºC (Figure 2).
The conventional process (based on homogenous catalysts) has associated several problems,
which makes it more expensive when compared to fosil-derived diesel, e.g. raw materials
pretreatment and process and cost issues. If raw materials are taken into account, fat and
oils cannot directly be used when large amounts of FFA are present. As previously indicat‐
ed, when alkaline homogeneous catalysts are used, FFA should be less than 0.5 w/w% to
avoid high soap formation. Moreover, expensive refinery steps are associated to separate the
catalyst and the methanol/biodiesel/glycerol mixture. Generally, water is used to remove al‐
kaline catalysts but this stage makes the overall process less important from environmental
point of view. Other relevant issues such as reaction time, mass transfer limitations, opti‐
mized set of operating conditions (temperature, pressure, alcohol: oil ratio), determine the
economic success of biodiesel production. Regarding the reactor technology, continuous bio‐
diesel process (CBP), especially when equipped with tubular reactors, are always preferred
as compared to batch processes. Obviously, this is due to the fact that CBP allow the proc‐
essing of higher amounts of raw material. However, always that CBP is selected it should be
considered the need to incorporate a centrifuge process for glycerol/biodiesel separation,
which has a considerable increase in the processing cost. Therefore, an optimum conven‐
tional biodiesel process should be conducted at room temperature, atmosphere pressure,
avoid water for homogeneous catalysts recovering, and use a low cost glycerol/biodiesel co‐
alescence unit; importantly, the process should reached oil yields over 98%.
Table 1 shows some a comparison of current biodiesel technologies; it is evident from this
table that there is a direct connection between complexity and process cost and the quality
of final product. As outlined above, conventional process capital cost is low, but processing
cost is high because of long reaction time, and separation and purification issues, among
others. Regarding the supercritical methanol process, it seems simple and delivers high pu‐
rity product but, also, capital and operating cost are too high because they are related to se‐
vere process conditions. With respect to the use of heterogeneous catalyst, it certainly
improves the products separation and purification but, again, this technology is still far to
be asuitable economic option because of the high temperature and long reaction time still
required for the process. Moreover, another issue to overcome is the design of solid catalysts
with appropriate acid sites configuration to improve yield and selectivity, and to decrease
catalyst deactivation in hydrous conditions. On the other hand, the US process is less ex‐
tended and its advantages have not totally documented. However, it could be postulated
that the thousands of bubbles formed during the cavitation phenomenon of the US facili‐
tates the formation of a methanol-KOH/oil microemulsion at high temperature, which dras‐
tically decreases mass transfer limitations. In this scenario, the transesterification reaction
could be carried out within a few seconds, at room temperature (at the "bulk") and atmos‐
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pheric pressure, thus helping to decrease the process cost. The next section of this chapter
describes the basic principles of ultrasound applied to transesterification reaction.
Variable Homogeneous
Catalysis
Heterogeneous
Catalysis
Enzymatic
Catalysis Non Catalytic SMP2
Reaction time 0.5-4h 0.5-5.5h 1-8h 120-240s
Operation conditions 0.1 MPa,
30-65 ºC
0.1-5 MPa,
30-200 ºC
0.1 Mpa,
35-40 ºC
>25Mpa,
>239.4 ºC
Catalyst Acid/base Metal oxides o carbonates Lipase Non
Free fatty acid Soap formation Esters Esters Esters
Water Interfere No interfere No interfere Act as catalyst to the
process
Yield Normal Low to normal Low to normal High
Purification Difficult Easy Easy Very easy
Downstream Water Non Non Non
Glycerol purity Low Low to normal Normal High
Process Complex Normal Simple Simple
Capital cost Low Medium High Very high
Operation cost High High Normal High
Table 1. Comparison of current biodisel technologies for processing biodisel1 . Source: [9]. 2 SMP: Supercritical
methanol process
3. Principle of Ultrasonic Process
Traditionally, sound is a subject studied in physics and it is not a well-met topic in a
chemistry course and, so, is somewhat unfamiliar to practicing chemists. However, sono‐
chemistry, which is defined as the use of sound to promote or enhance chemical reac‐
tions, has recently received much attention in several chemical reactions concerning
sustainability process [5].
It is known that an acoustic wave is a propagation of pressure oscillation in a given medi‐
um (gas, liquid or solid), with the velocity of sound producing both the rarefication and
compression phases. Figure 3 shows that sound waves are often disclosed as a series of
vertical lines or shaded colors, where line separation or color depth represent the intensi‐
ty or amplitude of the sine wave; the pitch of the sound depends upon the frequency of
the wave. According to the sound spectrum, an ultrasonic wave is an acoustic wave whose
frequency is above 20 kHz, which is not audible to human. Hence, when a liquid is irra‐
diated by a strong ultrasonic wave, the pressure at some regions in the liquid becomes
Biodiesel - Feedstocks, Production and Applications
182
negative (expansion) because the acoustic amplitude of the wave is larger than the ambi‐
ent pressure. Therefore, if the pressure wave propagating through a liquid has enough
intensity, formation of vapor bubbles may occur because the gas dissolved in the liquid
can no longer be kept dissolved, because the gas solubility is proportional to the pres‐
sure; this is known as the cavitation phenomenon [11].
Figure 3. Sound waves interaction with a liquid medium [13]. The bubble growth due to the expansion-compression
cycles resulting in the formation of localized “hot spots”.
The bubbles formed in the cavitation phenomenon grow from nuclei, over many acoustic
cycles, through an elastic process [10]. During the expansion cycle an inflow occurs into the
bubble, due to the gradient in gas concentration of the fluid shell surrounding the bubble.
As the gas diffusion rate into the bubble is proportional to the concentration gradient of dis‐
solved gas, the net inflow of gas into the bubble is essentially higher during the expansion
process. Then, when acoustic bubbles reach a critical size range they undergo a violent col‐
lapse. There are three at least theories to explain the chemical effects arising from the col‐
lapse of cavitation bubbles:
1. electrical theory,
2. plasma discharge theory and
3. super-critical theory.
Another approach is the “hot spot” theory. This theory suggests that bubbles growth is al‐
most adiabatic up to the collapse. At this point, the gas in the bubble core is rapidly com‐
pressed (life time in the order of nanoseconds); hence, temperature of thousands of degrees
and pressure of more than hundreds of atmospheres can be locally generated; this is the
“hot spot” condition. It is noteworthy that, in addition to the extreme conditions of the “hot
spot”, a secondary region formed by a thin layer of the liquid surrounding the collapsed
bubble, it is also transiently heated, although to a lesser extent; this thin layer is about 200
nm in thickness and may reach a temperature of 1726 ºC [11], see a simplified scheme of the
“hot spot” model is shown in Figure 4.
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Figure 4. Hot-Spot model in the cavitation process [11].
The physicochemical properties of the solvent and solute, and also the gas in the bubble,
have notorious effects on the cavitation phenomenon. Therefore, the sonochemical process
is very complicated; it is more frequently influenced by the solvent because cavities are
spontaneously formed with solvents having high vapor pressure, low viscosity, and low
surface tension. Consequently, as liquid must overcome intermolecular forces to form bub‐
bles, poor cavitation efficiency is obtained when solvents with low vapor pressure, high
viscosity, surface tension and density are used. Nevertheless, these kinds of solvents have
higher threshold for cavitation but more harsh conditions once cavitation begins; this might
help in some chemical reactions [12]. On the other hand, there are several gas phase prop‐
erties that affect sonochemical cavities, Adewuyi [13] recently reported that heat capacity
ratio (also known as polytropic ratio, γ), thermal conductivity and solubility are the most
important gas properties. γ is involved with the amount of heat released and, hence, af‐
fect the final temperature and pressure produced in the adiabatic compression, according
to the following equations [14, 15]:
Tmax =T0
Pa(γ- 1)
Pv(2)
Pmax =Pv
Pa(γ- 1)
Pv
γ
γ-1 (3)
Where T0= bulk medium temperature, Pv= pressure in the bubble when bubble size is maxi‐
mum or vapor pressure of the solution, Pa= acoustic pressure in the bubble at the moment of
collapse.
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184
Thus, a gas with high thermal conductivity improves the heat transfer from collapsed bub‐
bles to the liquid; this means that it reduces the temperature achieved in an implosion. The
solubility of the gas in the liquid is also relevant. The more soluble the gas, the more likely it
is to diffuse into the cavitation bubble. Soluble gases should originate the formation of larger
number of cavitation nuclei and extensive bubble collapse, because these gases are readily
forced back to the liquid phase. Therefore, a decrease of the bulk liquid temperature increas‐
es the rate of sonochemical reaction, unlike most chemical reaction systems. This is reasona‐
ble because the amount of dissolved gas increases and the vapor pressure of the liquid
decreases and, then, less vapor diffuses into the bubble thus cushioning the cavitational col‐
lapse; in this condition the implosion more violent.
4. Sonochemical transesterification reaction
There are many aspects that make different the sonochemical and conventional chemical re‐
actions. As already mentioned, the “hot spot” is a suitable concept to explain experimental
results in many environmental sonochemistry reactions. This theory considers that reactive
species and huge heat are produced from bubble cavitation; each bubble created from the
interaction of the ultrasonic wave with the liquid is assumed to be a well-defined micro‐
rreactor [13]. Actually, according to the “hot spot” model there are three reactive zones:
1. a huge hot gas core,
2. a gas-liquid interface of approximately 200 nm, and
3. the bulk of the liquid media.
This model is frequently used in aqueous reactions, where solvent or substrate suffer homo‐
lytic (symmetrically) bond breakage to produce reactive species, and it assumes that free
radicals may be in all the reactive zones. However, this model does not necessarily corre‐
spond to the thermodynamic reality of the transesterification reaction, because the system is
constituted mainly of triglycerides (TG), small amount of FFA, KOH and methanol. Again,
the methanol/oil phase is immiscible creating very large mass diffusional problems. But, in
general, the energy generated by the US process produces free radicals, which are very reac‐
tive, and a significant amount of heat that improves mass transfer among phases [4]. This
combined effect of very reactive species and intimate contact between phases could certainly
improve the transesterification reaction rate. In this section, some ideas that further explain
experimental results obtained in our laboratories are also discussed.
Figure 5 shows the sono transesterification model, which is an adaptation of Adewuyi´s
model [13], constrained as follows.
1. Water hydrolysis is not considered as reactive species source because anhydrous condi‐
tions should be achieved for biodiesel processing; from our experience with JCO (FFA
<1.5-5%), soap formation is not promoted.
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2. Relative humidity of air is also dismissed; so, air is dissolved in the methanol and oil
phases.
3. The supercritical theory recently proposed by Hua et al. [16] regarding to the transient
supercritical water (373 ºC, 22.1 MPa) at the bubble-solution interface is also discarded,
because under these conductions the interphase would be considered as a supercritical
methanol microrreactor, and then the use of catalyst would become censer.
However, from our lab experience the sonication of methanol/oil mixture without alkaline
catalysts does not produce FAME.
Figure 5. Transesterification cavitation model
The model depicted in Figure 5 assumes that a homogeneous methanol/oil macroemulsion is
formed by mechanical mixing. It is very important to note that prior to the sonolysis, the
methoxide ion produced, unreacted KOH, and methanol coexist inside the microemulsion.
Once that the sound-macroemulsion interaction begins, cavitation is performed with vapor of
methanol-KOH and air gas inside the bubbles, carrying out the dissociation reactions of the
vapor and gas constituents; then, after several cycles of rarefication and compression, the
implosion takes a place involving a significant rate of heat and mass transfer. The surround‐
ing liquid quickly quenches a short-lived, localized entity exposed to high temperature
(4226-4726 ºC) and pressure (over 1000 atm). Quenching occurs in few microseconds [17] and
very fast cooling rates (about 1010ºC−1). This process has a profound influence on the physi‐
cal properties of interface (microemulsion), where the transesterification reaction is spontane‐
ously carried out, at local temperatures ca. 2000 K, without any diffusional problems.
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186
As already mentioned, TG transesterification by basic catalysis consists of three consecutive,
reversible reactions (Figure 2). In the reaction sequence, TG is converted stepwise to digly‐
ceride, to monoglyceride and, finally, to glycerol, accompanied with the liberation of an es‐
ter at each step. The reaction mechanism of TG transesterification shown in Figure 6
indicates that in the catalyst-TG interaction the key step is the nucleophilic attack of the alk‐
oxide ion, originating a different reaction chemical. The conventional transesterification
process has been associated to a mass-transfer controlled regime occurring at the beginning
of reaction. In addition, as the reaction proceeds and ester products act as emulsifiers, two
rate-limiting steps change over time. One step is kinetically controlled and it is characterized
by a sudden surge in product formation; the second step is reached once equilibrium is
found near the reaction completion [19]. Importantly, in the sono transesterification model
showed in Figure 5, neither mass transfer nor kinetic reaction are rate-limiting steps, but
rather the chemical equilibrium.
Figure 6. Homogeneous based-catalyzed reaction mechanism for triglyceride (TG) transesterification: methoxide ion
form by dissociation of potassium hydroxide into methanol and it is encapsulated into TG-methoxidemicroemulsion,
then: (1) CH3O-attacks nucleophilically to carbonyl group on TG, which leads to the tetrahedral intermediate forma‐
tion; (2) intermediate breakdown; (3) regeneration of CH 3O- active species. These steps are repeated twice to com‐
plete TG transesterification, according to Loreto et al. [18].
5. Comparison of experimental biodiesel processing technologies from
Jatropha curcas
5.1. Why Jatropha curcas?
Current feedstock for biodiesel production plants derive from a great biomass variety, includ‐
ing first generation biomass raw materials such as vegetable oils (e.g., soybean, cottonseed,
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palm, peanut, rapeseed/canola, sunflower, safflower and coconut oils), animal fats (usually
tallow) as well as spent or waste oils (e.g., used frying oils). But, given the fact that the use of
vegetable oils has been strongly questioned, the use of second- and third-generation bio‐
mass feedstock is continuously growing. Among the raw materials coming from nonedible
crops for humans, a key issue is their availability near to the biodiesel production plant. In
this scenario, our research group is interested to use Jatropha curcas oil as feedstock. Jatropha
curcas L. (JC) is a stress-tolerant ruderal, drought-resistant, oil-bearing small tree, which is well
adapted to tropical, semi-arid regions and marginal sites. JC propagates easily and can be
established quickly in a wide variety of soils with different agroclimatic conditions and does
not put pressure on fertile agricultural land or natural ecosystems. In addition, JC is charac‐
terized for a short gestation period, low seed cost and, importantly, for the multiple uses that
may have different parts of the plant [20, 21]. JC has received a lot of attention as a source of
renewable energy, because its seeds contain 27–40% nonedible oil with a high quality of fatty
acid profile (Table 2), which can be easily converted into biodiesel that meets American and
European Standards (Table 3).
Fatty acid Systematic name Structure wt %
Lauric acid Dodecanoic acid C12 -
Mysteric acid Tetradcanoic acid C14 0-0.1
Palmitic acid Hexadecanoic acid C16 14.1- 15.3
Palmitolileic acid Cis-9-hexadecanoic acid C16:1 0-1.3
Stearic acid Octadecanoic acid C18 3.7-9.8
Oleic acid Cis-9-Octadecanic acid C18:1 34.3-45.8
Linoleic acid Cis-9-cis-12-Octadecanoic acid C18:2 29-44.2
Linolenic acid Cis-6-cis-9-cis-12-Octadecanoic acid C18:3 0-0.3
Arachidice acid Ecosanoic acid C20 0-0.3
Behenic acid Docosanoic acid C22 0-0.22
Gadoleic acid C24 14
Saturated - - 21.1
Unsaturated - - 78.9
Table 2. Fatty acids profile of Jatropha curcas oil [22]
In terms of availability, JC easily grows in Norwest Mexico, where our lab is located. For
this reason, we set a research project to evaluate the potential of the local JC variety as
source of renewable energy (i.e., biodiesel production). Notoriously, we also seek the utiliza‐
tion of valuable byproducts or residues of the conversion of JC oil to biodiesel; for instance,
fruit husk and seed shell may lead to production of energetic pellets, part of the harvested
seed shell may be used to produce humic acid, a biofertilizer; from the seed kernel, not only
oil and subsequently biodiesel may be produced, but also protein flour for poultry, sheep,
Biodiesel - Feedstocks, Production and Applications
188
shrimp and tilapia (Figure 7). Once that biodiesel is produced a significant amount of glyc‐
erol become available, and we look for the production of high-added value chemical derive
from glycerol catalytic conversion. Results presented hereby concern to biodiesel produc‐
tion, in particular the development of alternative strategies to improve the efficiency of the
transesterification reaction and to decrease the overall processing cost. In this way, the pro‐
posed integrated approach clearly contributes for the development of sustainable biomass
conversion processes.
Parameter JC
Biodiesel Diesel USA ASTM Europe EN
Density at 15ºC (g mL-1) 0.91 0.85 0.88 0.8-0.9
Kinematicviscosityat 40°C (mm2s-1) 3.43 2-8 1.9 - 6 3.5 - 5
Cetane number 52 47.5 "/47 >51
FAME content (%) >99 0 - > 96.5
Sulfur (ppm) 0 <5 <15 < 10
Flash point (ºC) 186 >61.5 >93 >101
Acid number (mgKOHg-1)Depend of
process
0.5 0.5
Table 3. USA and Europe international standards for biodiesel [23].
Figure 7. Productive chain for non-toxic JC research project in Norwest Mexico [23].
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5.2. Materials and methods
5.2.1. Physical chemical JC oil characterization
The study used JC from selected elite germoplsms and cultivated in three zones of Sinaloa,
Mexico. The approach used to obtain Jatropha curcas oil (JCO) was the well-established cold
pressing followed by solvent oil extraction. The JCO physicochemical properties studied in
this work included: fatty acid profile, acid index (AI), saponification index (SI), peroxide in‐
dex (PI), and iodine index (II), which were obtained following the methodologies suggested
by the Association of Analytical Communities, AOAC.
The quality criteria for the production of biodiesel are specified in EN 14214. In particular,
method EN 14103 specifies the FAME content, which is used to profile the vegetable or ani‐
mal oil feedstock used in biodiesel production. EN 14103 requires calibration of all FAME
components by relative response to a single compound, methyl heptadecanoate. This re‐
quires the measurement of accurate weights for each sample and the addition of an internal
standard. The FAME range for which the method is intended lies between C14:0 and C24:1.
A modified EN 14103 chromatographic method was used. In this method, FAME analysis
was carried out in a 6890N Agilent Gas Chromatograph (GC), equipped with a capillary
split/splitless injector and a selective 5973 Agilent mass spectrometer detector. A 1 μL split
injection (split ratio 50:1) was made to a Supelco omega wax column (bonded polyethylene
glycol), using 1 mlmin-1of helium into the column as carrier. Samples were injected via an
auto sampler series 7683 also from Agilent technologies. A good resolution and peak shape
was obtained when using the following oven temperature program: The initial temperature,
100 °C was kept for 2 min; then a heating rate of 4 °C min-1 was used to increase the temper‐
ature to 240 °C and, finally, this temperature was kept for 10 min. For identification and cali‐
bration of the individual FAME, the Supelco standard “37 Component FAME Mix” was
used. The response and retention time of each component was experimentally determined.
Then, the calibration was verified by both, the analysis of a calibration-check standard and
the database of mass spectrum reported by the National Institute of Standards and Technol‐
ogy (NIST). Results of analyses were then compared with the certificate of analysis, verify‐
ing the quality of the calibration. The standard preparation for this technique consisted of
the dilution of the FAME standard into 4 mL of n-heptane. The sample preparation was also
quite simple with 100 μL of biodiesel feedstock into 4 mL of n-heptane. Finally, concentra‐
tion reports were based on the area percentage rather than a mass percentage, to simplify
the calculations.
On the other hand, quantitative determination of free and total glycerin in biodiesel (B100)
was also carried out by gas chromatography, followed by a modified methodology pro‐
posed by the ASTM D6584-10aε1.The same Agilent GC system was also used for this analy‐
sis, the only difference being the use of a MS detector. ADB-5 ms column from Agilent
Technologies was used for free and total glycerin analysis, which is equivalent in chromato‐
graphic efficiency and selectivity to that of the MET-Biodiesel capillary column of Sigma Al‐
drich.
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5.2.2. Transesterification procedure
5.2.2.1. Conventional process
Conventional alkaline transesterification was conducted in a 2-necked glass reactor (100 mL,
Aldrich). A homogeneous reaction mixture was obtained by using plate stirrers, and a con‐
stant reaction temperature was kept by using isolated bath vessels equipped with a stainless
steel coils. The reaction temperature was fixed by using of a heater/cooler recirculation iso‐
thermal bath (Fisher Scientific 3016). Figure 8 shows that each reactor was connected to‐
cooled straight glass condenser to avoid alcohol leaks; water at 5ºC from another isothermal
bath (Fisher Scientific 3028) was used as cooling fluid.
Figure 8. Transesterification reaction system for the conventional process
Anhydrous methanol (Sigma-Aldrich, 99.8 %,) and KOH reagent grade (Sigma-Aldrich,
90%) were used for all experiment of this study. The stirrer was fixed at 600 rpm, and the
temperature at 40, 60, 70 or 90 C), a methanol: JCO molar ratio was 3:1 or 6:1. Previous‐
ly to each reaction, methanol and KOH solutions were prepared according to the pro‐
posed molar ratio. Then, the reaction volume was fixed to 50 mL of JCO. After the desired
reaction temperature was reached, a preheated methanol-catalyst solution was added to
start the reaction. Reaction mixture was sampled after 15, 45, 60, 90, and 120 min. These
samples were quenched by a sudden immersion of the sample to a plastic container at 0
C, for 15 min. Then, reaction products were purified according to the methodology suggest‐
ed by Cervantes [24](Figure 9), and the biodiesel yield was determined by means of the
following equation:
Yield =wt B100
wt oil x100 (4)
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5.2.2.2. Heterogeneous process
As reported elsewhere [25], JCO transesterification was also conducted by using ZnO, Al2O3
and ZnO-Al2O3 mixed oxide powders as catalysts. The objective was to compare the hetero‐
geneous catalytic conversion of the same JCO. In this case, the catalytic activity was meas‐
ured in a Parr 4560 stirred tank reactor, operated at 1000 rpm, 250ºC, P= 14.7 atm. A
methanol: JCO molar ratio of 6:1 and a 3 wt% of catalysts (based on JCO weight) were used.
Previously to the reaction, the reactor was uploaded with the 50 ml of JCO, the required
methanol to achieve the 6:1 molar ratio, and 1.36 g of catalyst. Then, the reactor was purged
with nitrogen (Praxair, reagent grade) for 3 min to avoid JCO burning. The reaction time
was 1 h and then the reactor mixture was suddenly cooled to room temperature. The prod‐
uct separation included the following steps.
1. Catalysts removal by means of vacuum filtration.
2. Methanol recovery by using a rotary evaporator at the same condition indicated in Fig‐
ure 9.
3. Glycerol and biodiesel separation by centrifugation, using the same condition indicated
in Figure 9.
At the end, the biodiesel yield was calculated by using equation 4
Figure 9. Biodiesel purification process for a conventional alkaline transesterification process.
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5.2.2.3. Supercritical methanol process
Non-catalytic transesterification process was evaluated by means of the supercritical metha‐
nol reaction. This process was also carried out using the 4560 Parr stirred tank reactor. The
effect of both, methanol: JOC molar ratio (40:1 and 60:1) and temperature (250, 300, and
350ºC) was evaluated using nitrogen as co-solvent. Once the required reagents amounts
were charged to the reactor, the air was vented with nitrogen and the stirrer was fixed at
1000 rpm. Next, the temperature was increased until the desired set point; in this process the
pressure increased but not enough to reach the methanol supercritical point. Therefore, ad‐
ditional nitrogen was loaded to ensure 14 MPa. As an alternative to decrease the drastic op‐
eration conditions N2was used as co-solvent. The reaction took place over 30 min, sampling
the mixture every 5 min through the liquid reactor valve. After the reaction was finished,
the reactor was suddenly cooled to room temperature. The product separation included the
following steps.
1. Methanol recovery by using a rotary evaporator at the same condition indicated in Fig‐
ure 9.
2. Glycerol and biodiesel separation by decantation.
At the end, the biodiesel yield was calculated by using equation 4.
5.2.2.4. Ultrasonic process
The sonotransesterification of JCO was conducted by using a highly efficient Hielscher Ul‐
trasonic processor, model UP200 HS. This equipment was used to generate mechanical vi‐
brations by means of the reversed piezoelectric effect (electric excitation), with frequency of
24 kHz, and a control range of 1 kHz. The vibrations were amplified by the S14 sonotrode
fitted to the horn and formed as a λ
2 vibrators, and transferred via its end face to the JCO.
To optimize the sonotransesterification reaction, the effect acoustic power density (N), soni‐
cation time (or reaction time), and methanol: JCOmolar ratio (MR) were evaluated at room
temperature (25ºC) and ambient pressure (1 atm). Reaction temperature was controlled by
using an isothermal bath (Fisher Scientific 3016). The continuous sonication of the reaction
mixture was conducted using N=105 Wcm-2 and a molar ratio of 6:1, following the approach
described in Figure 9. Reaction time was fixed at 1, 2, 4, 6, 8, 10, 15, 20, 25 or 30 min. Next,
the methanol: JCO molar ratio was evaluated varied to 3:1, 4:1 and 6:1. For the smaller reac‐
tion time and molar ratio, the acoustic power density effect was evaluated at 42, 63, 73.5, 84,
94.5, and 105 Wcm-2. When the best set of parameters was found, an experiment was con‐
ducted again to determine the biodiesel quality.
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5.3. Results and discussions
5.3.1. Physical chemical JC oil characterization
The Jatropha curcas oil obtained from non-toxic, harvested seed in Northwest Mexico, seems
to be an excellent candidate for biodiesel production due to its high quality. Table 4 includes
the basic JCO physicochemical characteristics that back up this quality. The iodine index is a
measurement of the oils unsaturation degree; a higher iodine index corresponds to higher
degree of unsaturation [26], and probably leads to oxidation and viscosity problems. The
JCO iodine index was 28.75 cg I2g-1, which is well below the maximum specified value (120
cg I2 g-1) for biodiesel as indicated in the EN14214 specification. The limitation of unsaturat‐
ed fatty acids is convenient because heating higher unsaturated fatty acids results in poly‐
merization of glycerides, leading to the formation of deposits or to deterioration of the
lubricant [27]. Fuels with this characteristic (e.g Sunflower, soybean and safflower oil) are
also likely candidates to produce thick sludge’s in the sump of the engine, when fuel seeps
down the sides of the cylinder into crankcase [26]. The JCO iodine index could was caused
by the high content of unsaturation fatty acid such as oleic and linoleic acid (Table 5).
Test Parameter1
Appearance Yellowish transparent
Free fatty acid (%) 1.51 ± 0.10
Density at 15ºC (gml-1) 0.92 ± 0.01
Acid index (mg KOH g-1) 3.07 ± 0.12
Saponification index (mg KOH g-1) 180.92 ± 2
Iodine index (cg I2 g-1) 28.75 ±0.1
Peroxide index (meq O2 Kg-1) 18.5 ± 0.7
Table 4. Physical chemical properties of Jatropha curcas Oil. 1 Standard desviation measured from triplicate
determinations.
In on another hand, JCO peroxide index was 18.5 meqg-1, that is higher than the index
recently reported in the literature for crude seed Jatropha oil, 1.93 meqg-1 [26] and 2.5
meqg-1[28]. Despite this high peroxides index, JCO upholds the good quality of biodie‐
sel purposes. The JCO saponification index was 181 mg KOH g-1, which suggested that
JCO was mostly normal triglycerides, and very useful in biodiesel production due to its
low FFA content (1.15wt%). The content of FFA was assessed from the acid index (AI)
measurement, taking into account the composition showed in Table 5. The acid index of
3.07 mg KOH g-1reported in Table 3 was lower than the values reported by other au‐
thors (10 - 14 mg KOH g-1) for crude JCO [29, 30]; this could be attributed to the change
of local environmental conditions where by the Jatropha curcas plant was grown. There‐
fore, acid index becomes a very important parameter to determine the most convenient
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processing route of a given FAME; this means that oils can undergo a pretreatment or
direct transesterification as a function of FFA amount.
Compound Estructure wt %
Palmitic 16:00 23.992
Stearic 18:00 7.224
Oleic 18:01 41.368
Linoleic 18:02 27.186
Table 5. Faty acid composition de Jatropha curcas Oil determine by MS-CG.
The properties of triglyceride and biodiesel are determined by the amounts of each fatty
acid present in the molecules. Chain length and number of double bonds determine the
physical characteristics of both fatty acids and triglycerides [3]. Nevertheless, transesterifica‐
tion does not alter the fatty acid composition of the feedstocks, and this composition plays
an important role in some critical parameters of the biodiesel, as cetane number and cold
flow properties. Therefore, measuring fatty acid profile of JCO was another important target
of this study. These results are shown in Table 5.
Figure 10. Type of fatty acids in Jatropha curcas oil from the Norwest of México
There are three main types of fatty acids that can be present in a triglyceride which is satu‐
rated (Cn:0), monounsaturated (Cn:1) and polyunsaturated with two or three double bonds
(Cn:2,3). Ideally, the vegetable oil should have low saturation and low polyunsaturation,
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that is, be high in monounsaturated fatty acids, as shown in Figure 10. Vegetable oils rich in
polyunsaturated (linoleic and linolenic) acids, such as soybean and sunflower oils [26], usu‐
ally produce methyl ester fuels with poor oxidation stability. In the other hand, vegetable
oils with high degree of unsaturation (Cn:2,3) lead to a product with high freezing point,
poor flow characteristics and may become solid (e.g palm oil) at low temperatures, although
they may perform satisfactorily in hot climates. The main fatty acids in the JCO used in this
study were the oleic, linoleic, palmitic and the stearic fatty acids. The predominant acids
were monounsaturated (41.36%), polyunsaturated (27.18%) and saturated fatty acid
(31.21%) (Figure 10). This result was in agreement with the reported by Akbar [26], although
it was slightly different in terms of saturated and polyunsaturated compounds for the JCO
from Malaysia. Thus, JCO can be classified as oleic–linoleic oil. Compared to others vegeta‐
ble oil JCO had highest oleic acid contain than palm oil, palm kernel, sunflower, coconut,
and soybean oil.
5.3.1. Jatropha curcas oil transesterification
Three current biodiesel technologies were evaluated and compared with the conventional
homogeneous transesterification, using the JCO characterized above. The main objective
was to evaluate the potential advantages of sonotransesterification in terms of operating
conditions, transesterification rate and processing steps and costs.
Conventional alkaline transesterification
According to the overall transesterification pathway shown in Figure 1, stoichiometrically,
JCO methanolysis requires three moles of methanol for each mole of oil. Since the transester‐
ification of triglycerides is a reversible reaction, excess methanol shifts the equilibrium to‐
wards the direction of ester formation. As it is evident from Figure 11, the maximum yield
for the conventional alkaline transesterification process (84%) was reached after 15 min reac‐
tion time; afterwards no signification variations were observed. In addition, when the meth‐
anol: JCO molar ratio was increased from 3:1 to 6:1, no major differences were found within
the first 15 min; however, a higher biodiesel yield was observed in the experiment with a 6:1
molar ratio toward the end of the reaction. On the other hand, results shown in table 5 indi‐
cate that temperature effect is not important. These results correspond to the biodiesel yield
evaluated after 15 min. Thus, the higher biodiesel yield was found at 40 °C, and then it de‐
creased to around 73 – 75 % for temperatures between 60 and 90 °C.
Current results of the conventional process disclosed in Figure 11 and Table 6 suggested a
significant improve to the conventional alkaline transesterification process, because the reac‐
tion yield was enhanced at a shorter reaction time (40 min as compared 60 min) and temper‐
ature (40 °C as compared to 60ºC) for industrial application [3]. A shorter reaction time can
be translated to a continuous process with a shorter resident time and then, the possibility to
reduce costs at the reaction stage. However, a higher JCO conversion is needed to ensure a
sustainable process. Moreover, the biodiesel purification process is still a problem because it
implies long times and it is energy demanding.
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Figure 11. Progress of transterification reaction as function of methanol:JCO ratio at 40ºC
Temperature, ºC Yield, %
(At 15 min of reaction time)
40 84.0
60 73.06
70 73.60
90 75.30
Table 6. The effect of temperature on the performance of alkaline transesterification of JCO by conventional process.
Supercritical methanol process
Thus, as an alternative of the problems indicated above, the supercritical methanol process
(SMP), using nitrogen as co-solvent, was conducted. Figure 12 shows that the best set of op‐
erating conditions for this non-catalytic process were: methanol: JCO mol ratio of 40:1 and
350ºC. Under these conditions, a biodiesel yield ca. 60% was obtained. From Figure 13, it can
be observed that after 20 min the equilibrium was reached for the transesterification reaction
for both molar ratios studied: 40:1and 60:1. This is a very promising result if it is compared
with reported for palm [31] and soybean oils [32], where biodiesel yields up to 84% were
obtained under very high pressure, 40 and 35Mpa, respectively.
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Figure 12. Effect of temperature and methanol: JCO molar ratio on the yield of Biodiesel obtained by supercritical
methanol process at 14Mpa and 30 min.
Figure 13. Progress of transterification reaction as function of methanol: JCO ratio at T= 350ºC for supercritical meth‐
anol process
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Importantly, supercritical methanolysis did not require any kind of catalyst, and no pre‐
treatment to remove water or FFA was used in this work. A very simple separation process‐
es evaporation and layer separation were used for biodiesel purification. Our findings
agree with the literature that supercritical process is simpler and faster than conventional al‐
kaline transesterification for biodiesel production. In addition, since wastewater was not in‐
troduced by pretreatment or washing processes, the supercritical process is environmental
friendly. However, to date, high investment and energy cost are still required due to high
temperature and pressure of the supercritical state. Another issue with economic implica‐
tions is the large methanol needed to enhance the forward reaction without catalyst. It could
expected that these costs are comparable to those of the pretreatment and separation process
of the conventional alkaline transesterification process. Clearly, as the methanol demand be
decreased, and the operating conditions be more moderate, the economic feasibility of su‐
percritical methanol process would be possible.
Heterogeneous process
As indicated in the previous section, three heterogeneous powder catalysts, ZnO, Al2O3 and
ZnO- Al2O3 mixed oxides supported on SBA-15 were evaluated for transesterification reac‐
tion. Figure 14 shows our best results to date, when experiments were conducted with a
methanol: JCO molar ratio of 6:1, 250ºC, and 3 wt % of catalyst. Results were collected after 1
h of reaction time. Under these conditions, the equilibrium biodiesel yield (83%) was
reached for the supported Al2O3 catalysts. Importantly, no catalysts deactivation was ob‐
served for at least 10 runs (without regeneration treatment). It is noteworthy that Al2O3is tra‐
ditionally used as support instead of active phase due to its poor catalytic activity for
transesterification [33]. In fact, in our experiments Al2O3 itself showed no more than 5% of
FAME yield, but the it showed a totally different catalytic performance when it was well
dispersed on SBA-15. On the other hand, several supported basic catalysts have also been
reported in the literature -sodium [33] or potassium [34] loaded on a support (normally alu‐
mina), using several precursors and treated at high calcination temperatures (500–600ºC).
The catalysts showed good activities (80-90 % biodiesel yield) at low temperatures (70-90ºC),
but no data were reported about their stability. K2CO3 supported on both MgO and Al2O3
provided good results for rapeseed oil transesterification with methanol at 60–63 ºC, but
K2CO3 leached into the solution.
Meantime, pure ZnO and ZnO supported on Al2O3 have also been reported as good transes‐
terification catalyst. In experiments performed in a packed-bed reactor at 225-230 ºC, 91.4%
and 94.3% of FAME yields were obtained, for 1 and 7 h, respectively [35]; in this case, no Zn
leaching was practically observed (5 ppm). In addition, no data about catalysts has been re‐
ported. In our case, experiments conducted with ZnO and ZnO/Al2O3 showed biodiesel
yields below 75 %. The most promising results found for the Al2O3/SBA15 have to be stud‐
ied in detail to optimize the catalyst formulation.
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Figure 14. Yield of biodiesel of transesterification of JCO with MR=6, and 250ºC, 1 h and 3 wt.% of each heterogene‐
ous catalyst.
Sonotransesterification
Experimental results of JCO sonotransesterification are shown in Figure 15. The first issue
that became evident was that sonotransesterification was much faster than the conventional
alkaline transesterification. Thus, in just 1 minute of reaction time the maximum FAME
yield (ca. 65%) was reached for the experiment conducted with a methanol: JCO molar ratio
of 6:1, an acoustic power density (N) of 105 Wcm-2 and temperature of 25ºC. Moreover, Fig‐
ure 16 shows that for 1 min of reaction time, a reduction of the methanol: JCO molar ratio
from 6:1 to 4:1 increased the biodiesel yield. Under these conditions, a 71 % biodiesel yield
was obtained. Notoriously, the later molar ratio is closer to the stoichiometric one, thus help‐
ing to decrease the excess of alcohol required by the other biodiesel technologies under com‐
parison in this study. These results clearly showed the following advantages for the
sonotransesterification process: a shorter processing time is required, a lower amount of al‐
cohol is required (almost the stoichiometric amount), and the experiment is conducted at
room temperature and atmospheric pressure.
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Figure 15. Effect of the sonication time on the yield of biodiesel by sonotransterification reaction with MR of 6:1,
room temperature, and acoustic power density of 105 Wcm-2.
Figure 16. Effect of the methanol:JCO molar ratio on the yield of biodiesel by sonotransterification reaction at room
temperature,1 min of reaction time, and acoustic power density of 105 Wcm-2.
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Despite of the important advantages initially found for the sono transesterification process
in this work, the biodiesel yield had to be increased to make it atractive from the industrial
point of view. To this respect, a more detail study of the acoustic power effect was conduct‐
ed. Figure 17 shows that acoustic sonocation power had a significant effect on yield. For an
N of 64 Wcm-2, coupled with the best set of parameters used in previous experiments, a
FAME yield up to 96% was reached at room temperature. The reason why a higher transes‐
terification rate was obtained with the ultrasonic process was already outlined in the previ‐
ous sections. Briefly, the huge local temperature generated in the “hot spot” formed during
the cavitation phenomenon favors the formation of highly reactive species and promotes
mass transfer. These issues are the key to improve the transesterification reaction rate be‐
cause under the experimental ultrasonic conditions the process is not affected by mass trans‐
fer or by kinetic limitations, but rather by the equilibrium condition.
Figure 17. Effect of the acoustic power density on the yield of biodiesel by sonotransterification reaction with MR of
4:1, room temperature, and one minute of reaction time.
In this scenario, sono transesterification becomes a very attractive process to be implement‐
ed in a continuous industrial process. Thus, results found in Figure 17 were used to con‐
figure a continuous US process with a tubular sonorreactor, using a resident time of 1
min. In this case, a constant yield of 96% was reached. Importantly, the quality of the
biodiesel obtained in this experiment, overcame the quality of biodiesel with internation‐
al standards (Table 7).
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Parameter Value
FAME contenta (%) 98
Density at 15ºC (gml-1) 0.84
Acid index (mgKOHg-1) 0.5
Total glycerin (wt. %) <0.2
Free glycerin (wt. %) <0.02
Table 7. Physical chemical properties of biodiesel obtained by sonotransesterification under continuous process with
optimized conditions operated at room temperature. a after purification process
6. Conclusions
Nowadays, the conversion of non-edible and residual biomass feedstock into biofuels is al‐
ready considered a suitable alternative for the generation of alternative energy sources. In
particular, transesterification of oils and fats is a well-known technology, and the produc‐
tion of biodiesel is continuously growing using second- and third-generation biomass raw
materials. The main technology used in the industrial production of biodiesel is based on
the alkaline transesterification of vegetable oils with methanol. However, the problems re‐
lated with this technology (mainly in operating conditions and product purification) are the
driving force for research in the field of heterogeneous catalysis for biodiesel production
and for the development of non-catalytic process under supercritical fluids. The use of het‐
erogeneous catalysts and supercritical methanol process for transesterification reaction seem
to be attractive for industrial application because theses simpler processes have a beneficial
impact in the process economy. In particular, industry is making great research efforts to
find the optimum catalyst formulation and to decrease the drastic operating conditions of
supercritical methanol process. However, these technologies are still far to be economically
attractive. A more recent alternative is the new ultrasound-assisted method for biodiesel
production, which has to be tested and optimization for this particular application.
In this work, we evaluated and compared the performance of four technologies for the
transesterification of JCO obtained from JC grown in Northwest Mexico: conventional alka‐
line catalyst (KOH), heterogeneous powder catalysts (ZnO, ZnO/Al2O3 and Al2O3/SBA 15),
supercritical methanol and sonotransesterification. Results showed that the ultrasonic meth‐
od has significant advantages as compared to the other three methods. Notoriously, ultraso‐
nication reduced the transesterification reaction time to 1 min at room temperature and
atmospheric pressure, as compared to 1-6 h in conventional processing under more drastic
operating conditions. We suggest that this result could be explained with the proposed so‐
notransesterification cavitational model where by diffusional problems are eliminated. Our
results demonstrated that acoustic power density and methanol: JOCmolratio are the most
sensitive parameters to increase FAME yield for JCO; at the best set of experimental condi‐
tions, the biodiesel yield is higher than that obtained by conventional methods. Importantly,
the ultrasound-assisted method was also effectively used for continuous production of bio‐
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diesel by using a plug flow reactor; the physicochemical properties of the biodiesel pro‐
duced, such as acid value, density, FAME content, total and free glycerin were within the
limits of ASTM and EN standards.
In summary, sonotransesterification is faster and easier to handle than conventional transes‐
terification processes. The sonoreactor is significantly cheaper, and the process works under
safer and less energy demanding conditions (e.g room temperature and ambient pressure).
The major advantages of the current ultrasonic system include operational simplicity, short
reaction time, high conversion and reusability. In summary, ultrasonic irradiation is a faster
alternative that leads to higher product yield, and with the real possibility to benefit the
process economy. Thus, the ultrasonic process discussed in this work established the basis
for the development a sustainable process for biodiesel production, although some issues
are still to be solved; for instance, if water is avoided in the purification process,the overall
process would be even more environmentally friendly.
Acknowledgements
The authors want to thank to FORDECyT for financial support with the project 146409, and
Universidad Autónoma de Sinaloa throughout the PROFAPI project No. 2011/47.
Author details
Mario Nieves-Soto1, Oscar M. Hernández-Calderón2, Carlos Alberto Guerrero-Fajardo3,
Marco Antonio Sánchez-Castillo4, Tomás Viveros-García5 and Ignacio Contreras-Andrade6*
*Address all correspondence to: ica@uas.edu.mx
1 Facultad de Ciencias del Mar, Universidad Autónoma de Sinaloa, Mazatlán, México
2 Facultad de Ciencias Químico Biológicas, Universidad Autónoma de Sinaloa, Culiacán,
México
3 Facultad de Química, Universidad Nacional de Colombia, Bogotá, México
4 Universidad Autónoma de San Luis Potosí, San Luis Potosí, México
5 Departamento de Ingeniería de Procesos e Hidráulica, Universidad Autónoma Metropoli‐
tana-Iztapalapa, México
6 Facultad de Ciencias Químico Biológicas, Universidad Autónoma de Sinaloa, Culiacán,
México
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... Eminent fossil fuel depletion has motivated the search for alternative fuels such as biodiesel, which is obtained from vegetable or raw animal products (Nieves-Soto, et al., 2012). An important question regarding the feasibility of biofuels production is the availability of land to meet the potential demand of biomass as a feedstock. ...
... To this purpose, a physical-chemical characterization J. cinerea seeds oil was carried out to evaluate its composition, toxicity, and oil quality. In addition, its potential as a fuel feedstock was evaluated by performing the transesterification of the J. cinerea oil by using an ultrasonic process following a methodology recently reported (Nieves-Soto et al., 2012). ...
... To this purpose, a highly efficient Hielscher Ultrasonic processor, model UP200S, was used to generate mechanical vibrations by means of the reversed piezoelectric affect (electric excitation) with a frequency of 24 kHz and a control range of 1 kHz. An acoustic power density (N) of 65 Wcm-2 was used, as suggested by Nieves-Soto et al. (2012). The effect of sonication time (reaction time), methanol:oil molar ratio (MOR) and reaction temperature on FAME content were evaluated at ambient pressure, using 0.85 wt. ...
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