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![Schematic diagram of temperature distribution, heat transfer, and mass transfer in the conventional heating and microwave heating [9].](profile/Yaning-Zhang-6/publication/318242308/figure/fig1/AS:513201864482816@1499368267301/Schematic-diagram-of-temperature-distribution-heat-transfer-and-mass-transfer-in-the.png)
Schematic diagram of temperature distribution, heat transfer, and mass transfer in the conventional heating and microwave heating [9].
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![Figure 2. Schematic diagram of a typical MAP set‐up [37]. (1) microwave...](profile/Yaning-Zhang-6/publication/318242308/figure/fig2/AS:513201865072640@1499368267374/Schematic-diagram-of-a-typical-MAP-set-up-37-1-microwave-control-panel-2_Q320.jpg)
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Context 1
... conventional electrical heating methods, heat is transferred from high-temperature gas to the fuel particle surface through convection mechanism and it is then further transferred from the outside surface to the inside core through conduc- tion mechanism. A temperature gradient from outside to inside of the feedstock particle is formed because of the poor thermal conductivity of the feedstock material, and the released volatile diffuses from the inside core to the outside surface through a higher temperature region (Figure 1). For the microwave heating method, microwave penetrates the feedstock particle and microwave energy is transformed into heat inside the particle. ...
Context 2
... of the heat loss effect of particle surface, heat constantly accumulates inside the feedstock and is transferred outwards. A temperature gradient from inside to outside of feedstock particle is formed also because of the poor thermal conductivity of the feedstock material, and the released volatile diffuses from the inside core to the outside surface through a lower tem- perature region (Figure 1). ...
Context 3
... the reaction catalysts are used in microwave-assisted pyrolysis, the heating rates and pyrolysis temperatures would be increased due to the microwave absorbance of the reaction catalysts. Figure 10 shows the temperature profiles of a biomass feedstock under microwave heating with and without reaction catalysts. When the biomass feedstock was heated by a 450 Table 15. ...
Context 4
... third way is to place the reaction catalyst at the outlet of the connection tube in the quartz reactor, where the vapors exit the quartz reactor. Figure 11 shows a typical experimental setup for this catalytic fast microwave-assisted pyrolysis (cfMAP). As regard to this set-up, reaction [51,84]. ...
Context 5
... regard to this pyrolysis, the temperature of the reaction catalyst (cata- lytic temperature) cannot be easily varied or controlled, the fourth way is to place the reac- tion catalyst outside the reaction volume and thus comes the term "ex situ" catalytic fast microwave-assisted pyrolysis. Figure 12 shows a typical experimental setup of the "ex situ" catalytic fast microwave-assisted pyrolysis (cfMAP). Compared with the "in situ" catalytic fast microwave-assisted pyrolysis, an extra electrical heater (11) (also means more energy) is required to vary and control the catalytic temperatures for more precise upgrading and refining of the bio-oil. ...
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Citations
... While a number of reports on bio-oil production used microwave-assisted pyrolysis without inert gas, the optimization of this method is rarely explored, especially for microalgae without inert gas (Aladin et al., 2021(Aladin et al., , 2018Zhang et al., 2017). Evaluating the correlation between process parameters and their interactions can optimize complex production statistically (Kumar et al., 2022;Wakatuntu et al., 2023). ...
... The bio-oil produced from pyrolysis has received some attention as a potential fuel, but its varied composition is causing many problems. L. Qiang et al. [23] state that over 300 organic compounds can be found in this bio-oil which depends on the diverse range of biomass feedstock available [24]. This means that each pyrolysis oil from different resources must be analysed and treated accordingly to meet the property requirements of engine fuel. ...
Lignocellulosic and waste materials, such as sewage sludge, can be broken down into its useful constituents and converted into fuel for engines. This paper investigates microwave pyrolysis to decompose biomass into H2 and CO (syngas), which may be catalysed in the Fischer–Tropsch (F-T) process to liquid biofuels. Using microwave radiation as the heat source for pyrolysis proves to yield large quantities of gas with higher concentrations of H2 and CO compared to conventional heating methods. This is largely due to the energy transfer mechanism of microwaves. Pyrolysis parameters such as temperature (which increases with input power), feedstock type, microwave absorber, and biomass moisture content influence syngas yield. Several papers reviewed for this study showed differing optimal conditions for microwave pyrolysis, all being heavily dependent on the biomass used and its composition. However, all researchers agreed on the thermal efficiency of microwave heating and how its material-selective nature can increase syngas yield. Compared to diesel fuels (while processing a similar efficiency and a higher cetane number), FT fuels and specifically pyrolysis may yield the benefit of reduced nitric oxides (NOx), particulate matter (PM), unburnt hydrocarbons (HC) and carbon monoxide (CO) emissions.
... Conversely, increasing the microwave power from 0.9 kW to 1.2 kW led to a 37% higher bio-oil yield. The increased bio-oil production can be attributed to the moisture content and elevated heating rates during pyrolysis, facilitating the formation of condensable gases [11,24,25]. However, excessive temperatures beyond the optimal range for bio-oil generation caused thermal breakdown, resulting in a reduced bio-oil yield [11,20]. ...
... In contrast, a minor degradation of O-H (cellulose) was detected at 0.9 kW. Notably, a significant variation was observed in the range of 700 to 1800 cm −1 due to the dehydration of hemicellulose (C=O) and lignin groups (C-O-C), resulting in the loss of aliphatic C-H, C-O-C, and olefinic C=C compounds [24]. vated heating rates during pyrolysis, facilitating the formation of conde [11,24,25]. ...
... Notably, a significant variation was observed in the range of 700 to 1800 cm −1 due to the dehydration of hemicellulose (C=O) and lignin groups (C-O-C), resulting in the loss of aliphatic C-H, C-O-C, and olefinic C=C compounds [24]. vated heating rates during pyrolysis, facilitating the formation of conde [11,24,25]. However, excessive temperatures beyond the optimal range for b tion caused thermal breakdown, resulting in a reduced bio-oil yield [11,20]. T enon was observed at 1.5 kW. ...
The significant quantities of food waste that require disposal have a high environmental impact, and the depletion of non-renewable fuel sources has heightened the need to investigate sustainable and efficient methods of biomass conversion into energy. This research focuses on utilising pumpkin peel as a feedstock for energy recovery through microwave pyrolysis under different operating conditions. The study demonstrated that a higher biochar yield (11 wt%) was achieved at 0.9 kW. However, results revealed that superior quality biochar was obtained at 1.2 kW, characterized by high carbon content (70.33%), low oxygen content (23%), and significant pore formation in the carbon surface area. Optimal operating conditions, such as 1.2 kW, resulted in superior quality biochar and higher bio-oil generation. The pumpkin peel demonstrated the potential for CO2 (carbon dioxide) sequestration, with a rate of 14.29 g CO2 eq/kg. The research findings contribute to the exploration of sustainable solutions for biomass conversion and emphasize the importance of utilizing food waste for energy production while mitigating environmental impacts.
... It decreases the time it takes for pyrolysis reactions to start. Additionally, the process uses a less energy [108]. In fast pyrolysis, higher temperatures generally result in a higher output of H 2, but the catalyst could cause an even greater increase. ...
... Fu et al. reported the microwave heating performances of highdensity polyethylene [19], low-density polyethylene [20] and polyethylene terephthalate [21] in fixed bed reactor, the results showed that the heating rate of plastics was between 2.0 and 4.9 • C/min. The low microwave heating rate is due to that materials being categorized into insulators (penetrated by microwaves without any energy losses), conductors (reflect microwaves) and absorbents (absorb the microwave energy and convert it into heat) [22], the ability of materials to absorb microwave energy depends on the dielectric constant [23]. And the plastics is one kind of insulators, its microwave absorption capacity is very poor, which greatly limits the microwave heating of plastic materials. ...
... These were due to the fact that AC generally has higher microwave absorbability (tanδ = 0.62) than plastic waste (tanδ = 0.0001-0.0004) [56]. ...
Activated carbon (AC) is widely utilized in water treatment, gas adsorption, and purification as well as the protection of environment due to the characteristics of prominent catalytic and adsorbent effect. The heating performances are therefore of significant importance for the further applications. The main objective of this study was therefore to detail the heating performance of activated carbon in microwave field, and the factors affecting the heating performance were also explored. In this study, the heating performance of AC as affected by microwave power (400, 450, 500, 550, and 600 W), feeding load (5, 10, 15, 20, and 25 g), and reactor volume (50, 100, 150, 200, and 250 mL) were detailed and reported. The results showed that when the microwave powers were 400, 450, 500, 550, and 600 W, the temperatures of AC increased to the desired value (about 200 °C) within 90, 85, 70, 60, and 35 s with average heating rates of 2.0, 2.2, 2.8, 3.0, and 5.9 °C/s, respectively. When the feeding loads were 5, 10, 15, 20, and 25 g, the temperatures of AC increased to desired temperature within 40, 70, 60, 50, and 50 s with average heating rates of 4.2, 2.8, 3.1, 3.50, and 3.55 °C/s, respectively. When the reactor volumes were 50, 100, 150, 200, and 250 mL, the temperatures of AC increased to the desired temperature within 25, 60, 70, 70, and 160 s with average heating rates of 7.6, 3.3, 2.8, 2.6, and 1.2 °C/s, respectively. In general, the faster heating rate of activated carbon was achieved at higher microwave power, more feeding load, and smaller reactor volume. Fitting formulae were given to predict the transient temperatures of AC in the microwave field, and the relative errors were in the ranges of −15.4~12.4%, −15.4~13.5% and −18.7~12.4% at different microwave powers, feeding loads, and reactor volumes, respectively.
... Microwave pyrolysis can also help greatly to save energy and increasing the processing time of biomass production while at the same time improving the quality of bio char, bio gas and bio oil. Microwave pyrolysis and bioenergy include the conversion of oil palm, wood, microalgae, corn stover and sewage sludge [11]. Feedstocks do not need pre-treatment processes in microwave-assisted pyrolysis such as drying and grinding as feedstock heating can be driven through this technique. ...
... In addition, decrease in feedstock size is always necessary when using conventional pyrolysis as contrast to microwaveassisted pyrolysis which can use feedstock's original size. Zhang et al. 2017 [11] stated that conventional pyrolysis is highly dependent with the particle size of the feedstock as larger particle size produces low thermal conductivity and heat transfer thus creates a negative impact on the efficiency of bio-oil production. Having the ability to increase the overall heat transfer and high yield of pyrolysis materials, tiny particles in conventional pyrolysis are always favourites given the lengthy pre-treatment process involving testing of biomass feedstock, elimination of moisture and reduction of size. ...
... This is due to the ability of microwave absorbents to absorbs the microwave energy and conveyed it to the poor absorbing material [15]. Although microwave absorbents are great material that would help in increasing the pyrolysis end product especially bio-oil, however, the possibility for the volatile matter to enter secondary reactions where the vapour would break down into non-condensable gases are high due to sudden elevated temperature during the process which could reduce the yielding of bio-oil [11]. Zhang et al. 2017 [11] stated that there are few methods that can be used in mixing the feedstock with microwave absorbent. ...
Bio-oil is one of the potential resources to address the sustainable energy development and environmental issues. Microwave-assisted Rapid Hydrothermal Liquefaction Process is one of the popular techniques that is used to extract bio-oil from biomass. In this paper, the bio-oil has been extracted from Palm Kernel Shells by using microwave-assisted and conventional heating pyrolysis processes. A modified heating mantle apparatus are used to conduct the experiment for extracting the bio-oil. The experiments are conducted by varying the hydrothermal temperature and time for both techniques to achieve the conversion of the bio-oil from the raw material. It is found that the yield of bio-oil for microwave-assisted Rapid Hydrothermal Liquefaction Process at 350°C and 400°C are from 10.70 wt% to 25.60 wt% within hydrothermal time 6, 9 and 12 minutes. The pH value of the bio-oil is acidic with the range from 3 to 4. The calorific value of the bio-oil is varied from 24 to 26 MJ/kg for both conversion methods. Fourier Transform Infrared Spectroscopy (FTIR) result reveals that multiple functional groups (alcohol, aldehydes, carboxylic acid and ketones) are present in the PKS bio-oil.
... The temperature gradually rises from inside to outside in materials, and the temperature gradient is the same as the direction of volatile emission. Above all, microwave heating has the following advantages: (a) uniform heating , (b) fast heating (Zhang et al. 2020;Chen et al. 2022a), (c) selective heating (Zhang et al. 2017a) and (d) energy-saving and efficient heating (Zhang et al. 2017b). Microwave has the penetrability. ...
... The temperature of the core in the materials is much higher than that in the outer surface, so that the materials are heat up rapidly (Wang et al. 2020b). What's more, the capability of the materials to absorb microwave determines the capability to heat, which directly affects the thermal efficiency of microwave heating (Zhang et al. 2017a;Zhang et al. 2017b). When some materials with weak capability to absorb microwave, they can be mixed with the microwave absorbents to improve the heat efficiency. ...
In order to seek efficient resource utilization, the carbonization of agricultural and forestry wastes through microwave pyrolysis technology is an important research hotspot to develop value-added products. The main objective is to produce value-added biochar through microwave pyrolysis of peanut shell in this study. The product yields, functional groups, and biochar HHVs caused by pyrolysis temperature (400, 450, 500, 550, and 600 °C), microwave power (350, 450, 550, 650, and 750 W), and residence time (10, 20, 30, 40, and 50 min) were investigated, and the energy recovery efficiencies were evaluated. It was obtained that the biochar yield declined monotonously within the range of 45.3–86.0 wt% with the enhancement of pyrolysis temperature, microwave power, or residence time. The pyrolysis temperature of 400 °C, microwave power of 350 W, and residence time of 10 min generated the maximum biochar yield (86.0 wt%). The value-added biochar was obtained with high HHV (20.15–31.02 MJ/kg) and abundant oxygen-contained functional groups (C–O bonds and C=O bonds). The maximum energy recovery efficiency during the whole process reached 97.96%. The results indicated that the peanut shell could reach high biochar yield through microwave pyrolysis, and potentially be transformed into value-added products with high energy recovery efficiency.
... The moisture in bio-oil comes from two sources; i) water in the biomass or ii) dehydration reactions generated during the microwave pyrolysis process. The water content of the bio-oil impacts the quality and yield of the bio-oil (Zhang et al., 2017b). High moisture content influences the heat transfer distribution during the conversion process. ...
... High moisture content influences the heat transfer distribution during the conversion process. Moreover, water produces large quantities of condensate water in the liquid phase, generating a higher bio-oil J o u r n a l P r e -p r o o f yield, reducing its viscosity, and improving its combustion properties (Jahirul et al., 2012;Nomanbhay et al., 2017;Zhang et al., 2017b). Nonetheless, the high water content in bio-oil contributes to lower heating value, causing ignition delay and reducing combustion rate (Ethaib et al., 2020;Zhang et al., 2017b). ...
... Moreover, water produces large quantities of condensate water in the liquid phase, generating a higher bio-oil J o u r n a l P r e -p r o o f yield, reducing its viscosity, and improving its combustion properties (Jahirul et al., 2012;Nomanbhay et al., 2017;Zhang et al., 2017b). Nonetheless, the high water content in bio-oil contributes to lower heating value, causing ignition delay and reducing combustion rate (Ethaib et al., 2020;Zhang et al., 2017b). ...
The agricultural industry faces a permanent increase in waste generation, which is associated with the fast-growing population. Due to the environmental hazards, there is a paramount demand for generating electricity and value-added products from renewable sources. The selection of the conversion method is crucial to develop an eco-friendly, efficient and economically viable energy application. This manuscript investigates the influencing factors that affect the quality and yield of the biochar, bio-oil and biogas during the microwave pyrolysis process, evaluating the biomass nature and diverse combinations of operating conditions. The by-product yield depends on the intrinsic physicochemical properties of biomass. Feedstock with high lignin content is favourable for biochar production, and the breakdown of cellulose and hemicellulose leads to higher syngas formation. Biomass with high volatile matter concentration promotes the generation of bio-oil and biogas. The pyrolysis system's conditions of input power, microwave heating suspector, vacuum, reaction temperature, and the processing chamber geometry were influence factors for optimising the energy recovery. Increased input power and microwave susceptor addition lead to high heating rates, which were beneficial for biogas production, but the excess pyrolysis temperature induce a reduction of bio-oil yield.
... So, the thermal inertia is extremely low (Zhang et al., 2018). In addition, microwave energy has a certain selectivity to materials, and only some materials with dielectric properties can absorb microwave energy (Zhang et al., 2017). During the MAP process, the use of microwave absorbents will further improve the heating selectivity, so as to achieve high efficiency and energy saving. ...
