|Ref.||Type of material(s)||System configuration and operation conditions||Relevant results and observations|
|||Prosopis juliflora (PJF)||The experiment was performed to examine how (i) microwave power, (ii) susceptor, (iii) particle size, and (iv) Feed:Susceptor ratio effects on the yields of bio-oil, gas, and char, composition of bio-oil. By altering 5 different industrial wastes as microwave susceptors, (i.e., graphite, char, aluminum, silicon carbide, and fly ash)||Maximum bio-oil was realized using fly ash of 40 wt % with a heating value of 26 MJ kg−1 at a microwave power of 560 W, particle size of 2–4 mm, and Feed:Susceptor ratio of 100:1. The bio-oil analysis showed mixtures of phenolic, aromatic hydrocarbons, cyclopentanones, carboxylic acids, ketones, and furan derivatives. In addition, it demonstrates that the yield and quality of bio-oil are dependent on key parameters such as microwave power, biomass particle size/composition, and type of susceptor|
|||Larch||Experiment was carried out using a fundamentally designed scalable microwave system maximize pyrolysis oil yield and quality.||The results suggested that with controllable sample size, the liquid product yield is comparable to conventional pyrolysis and can be achieved at an energy input around 600 kWh/t. Similarly, quality of the liquid is significantly improved compared to conventional pyrolysis. This is because of the advantage the very rapid heating and quenching that can be achieved with MAP.|
|||Corn cob, corn stover, saw dust and rice straw||The experimental materials were used without any pre-treatment and at standard microwave experimental conditions; also, MgCl2 as a catalyst||
The pyrolysis of corn cob and corn cob plus catalyst gave the highest bio-oil yield up to 42.1 and 40% (wt), respectively.|
Higher HHV of 22.38 MJ/kg of bio-oil from corn cob was due to the presence of ethyl ether and 2-bromo-butane with a relative proportion of 15.63 and 4.60%, respectively.
In addition, GC–MS analysis of corn cob-based bio-oil showed the presence of ethyl ether, phenol, aliphatic hydrocarbons, furfural, furan derivatives, and acids in major proportions.
|||Palm kernel shell||Catalytic fixed-bed and microwave pyrolysis of palm kernel shell using activated carbon (AC) and lignite char (LC) as catalysts and microwave receptors are investigated.||The authors report addition of catalyst increased the bio-oil yield, but decreased the selectivity of phenol in fixed-bed. The highest concentration of phenol in bio-oil of 64.58% (area) and total phenolics concentration of 71.24% were obtained at 500 °C using activated carbon.|
|||Oil palm empty fruit bunch pellets||Experiment was carried out in a multimode microwave system with 2.45 GHz frequency with and without the MW absorber, activated carbon.||The ratio of feed to absorber did influence the temperature profiles of the EFB pellets and also pyrolysis products such as bio-oil, char, and gas. The highest bio-oil yield of about 21 wt.% was obtained with 25% MW absorber. The bio-oil consisted of phenolic compounds of about 60–70 area% as detected by GC-MS and confirmed by FT-IR analysis.|
|||Chlorella sp. strain and Nannochloropsis strain||Experiment was done in the presence of a microwave absorbent SiC and catalyst HZSM-5||Results for Chlorella at temperature of 550 °C without catalyst were the optimal conditions that resulted in a maximum bio-oil yield of 57 wt%. On the other hand, optimal condition for Nannochloropsis at temperature of 500 °C with 0.5 of catalyst ratio was achieved. Resulting in a maximum bio-oil yield of 59 wt.%.|
|||Process design––to do without susceptors||Presented a multidisciplinary design methodology for a microwave fluidized bed system that was based on processing raw biomass without the need for added microwave susceptors.||The authors found that a minimum power density of 54 MW m−3 was necessary to reach temperatures of 400 °C for particles with an average size of 600 μm at the minimum fluidization velocity (0.38 ms−1). The microwave fluidized bed system was shown to be effective in enabling pyrolysis while limiting heterogeneity and thermal runaway effects.|
|||Corn stalk biomass briquettes||It was carried out in a developed microwave reactor supplied with 2.45 GHz frequency using 3 kW power generators.||The highest bio-oil, biochar, and gas yield of 19.6, 41.1, and 54.0% was achieved at different process condition. Quality wise, the biochar exhibited good heating value (32 MJ/kg) than bio-oil (2.47 MJ/kg).|
|||Rice straw, rice husk, corn stover, sugarcane bagasse, sugarcane peel, waste coffee grounds, and bamboo leaves||Use empirical equation to predict the various product yields. Also applied energy return on investment.||Solid, liquid, and gas yields were in the ranges of 18–22, 40–48, and 30–40 wt%, respectively. The primary components of the gas product were H2 (18–25 vol%), CH4 (6–8 vol%), CO (51–59 vol%), and CO2 (10–14 vol%), and the rest undetermined part was only 3–5 vol%. The energy return on investment of microwave pyrolysis can be approximately 3.56, so the technique proofs can be economically feasible.|
|||Used cooking oil||Pyrolysis was designed in order to create contact with a bed of microwave absorbents heated by microwave radiation. Different materials were used in the reaction bed, including particulate carbon, activated carbon, and mesoporous aluminosilicate.||
The use of particulate and activated carbon as the reaction bed provided a fast heating rate and extensive cracking capacity to pyrolyze the used oil, thus showing favorable features that could lead to short process time and less energy usage.|
Thus, it resulted in a production of a high yield of a biofuel product (up to 73 wt%) in 35 min. Additionally, the biofuel showed a composition dominated by light C5–C20 aliphatic hydrocarbons with low amounts of oxygenated compounds (≤11%). In particular, the oil product obtained from activated carbon bed showed low nitrogen content and was free of carboxylic acid and sulfur.
|||Malaysian oil palm shell, empty fruit bunch, rice husk, and coconut shell and wood sawdust||The dielectric properties were measured from room temperature to ~700 °C and at six different frequencies (397, 912, 1429, 1948, 2466, and 2986 MHz) using a cavity perturbation method.||The dielectric properties recorded a fallen in the drying region (24–200 °C) which is due to removal of moisture, and further, it decreased in the pyrolysis region (200–450 °C) that is due to decomposition or removal of volatile matter. Still, dielectric properties increased drastically beyond temperature 450 °C. Minimum MW absorption was attained in temperature range of 300–400 °C. Biochar which was formed after the pyrolysis process, showed high loss tangent as compared to the original biomass, signifying it as a suitable material for MW absorber and catalyst applications.|
|||Tire powders||Experiment was carried out under standard microwave pyrolysis with special attention to the yields, and composition over time was studied||At the end of the pyrolysis, 43% of the solid residues, 45% of the oils, and 12% of the pyrolysis gases were obtained.|
|||Softwood, hardwood, and herbaceous biomass||In this paper, these were processed by microwave-assisted acidolysis to produce high-quality lignin.||The lignin from the softwood was isolated largely intact in the solid residue after acidolysis. For example, a 10-min treatment, microwave-assisted acidolysis produced a lignin with a purity of 93% and yield of 82%, superior to other conventional separation methods reported in literature.|
|||Corn stover and scum||Fast microwave-assisted catalytic co-pyrolysis for the production of bio-oil was carried out with CaO and HZSM-5 as the catalyst. The aim of the study was to carry out investigations on the effects of reaction temperature, CaO/HZSM-5 ratio, and corn stover/scum ratio on co-pyrolysis product fractional yields and selectivity. A constant ratio of corn stover: scum: CaO: HZSM-5 = 1:1:1:1 was used in carrying the experiment.||Overall, the results showed that co-pyrolysis temperature of 550 °C gave the maximum bio-oil and aromatic yields. Mixed CaO and HZSM-5 catalyst with the weight ratio of 1:4 increased the aromatic feedstock yield to 35.77 wt.% which was 17% higher than that with HZSM-5 alone. Scum as the hydrogen donor, showed a significant synergistic effect with corn stover to promote the production of bio-oil and aromatic hydrocarbons. The maximum yield of aromatic hydrocarbons (29.3 wt.%) were obtained when the optimal corn stover to scum ratio was 1:2.|