Microwave‐assisted torrefaction and pyrolysis of rice straw pellets for bioenergy

Abstract

The highlights of this study involve the use of microwave heating for torrefaction and pyrolysis of pelletized rice straw for the generation of high‐quality bio‐char pellets, and thorough energy assessment of the process. The effects of microwave power and final temperature on the product yields and their quality were thoroughly assessed. At 600 W power, the bio‐char yield followed the trend: 33.7 wt.% (800°C) < 35.5 wt.% (600°C) < 55.6 wt.% (300°C). Bio‐char yield was unaffected by microwave power at the final temperature of 300°C. High yield of moisture (23.5 wt.%) with a minimal amount of bio‐oil (10.5 wt.%) and gases (10.7 wt.%) were obtained at 600 W and 300°C. The major functional groups in the bio‐oil were phenols (∼40%), cyclic oxygenates (∼16%), furan derivatives (∼20%) and aliphatic oxygenates (16%). Bio‐char obtained from torrefaction at 600 W and 300°C possessed a calorific value of 17.2 MJ/kg with limiting oxygen index of 36.7%, and power generation potential of 4.8 kWh/kg. Overall, microwave‐assisted torrefaction is shown to be a promising process intensification strategy to derive high‐quality bio‐char in a short time of 5–10 min with high process efficiency (51–56%) and comparable biomass conversion efficiency (∼83%) with respect to conventional pyrolysis.

Lignin Catalytic Depolymerization for Guaiacols and Alkylphenols over Co–Zr/Sepiolite under Supercritical Ethanol

“…The elemental contents of carbon, hydrogen, oxygen, nitrogen, and sulfur in both lignin and liquid products were determined by employing a Vario EL III elemental analyzer (Germany). The higher heating value (HHV) was obtained according to Dulong’s formula: HHV (MJ/kg) = 0.3491 × C + 1.1783 × H + 0.1005 × S – 0.1034 × O – 0.0151 × N – 0.0211 × ash …”

“…The higher heating value (HHV) was obtained according to Dulong's formula: HHV (MJ/kg) = 0.3491 × C + 1.1783 × H + 0.1005 × S − 0.1034 × O − 0.0151 × N − 0.0211 × ash. 10 The gas chromatography−mass spectrometry (GC-MS) technique was utilized to analyze both the liquid and model conversion products. A Thermo Scientific ISQ 7000 MS detector from the USA and a TG-5SILMS capillary column (30 m × 0.25 mm × 0.25 μm) were used.…”

“…4−8 In recent years, on the strength of the structural characteristics of lignin, it has been extensively demonstrated that lignin catalytic depolymerization (LCD) for liquid fuels and cooperative production of phenolic monomers is one of the promising methods for highly efficient utilization of lignin. 9,10 However, it had been found that the produced highly reactive intermediates during the LCD process underwent an irreversible condensation reaction and formed abundant coke, which restricts the advancement of LCD technology. 11,12 It has been demonstrated that LCD under a special solvent system and a reducing atmosphere could inhibit coke and increase the HHV (higher heating value) of liquid products and the selectivities of different monomers.…”

“…Lignin, as one of the abundant natural renewable resources, has been extensively researched in the field of fabricating aromatic products, biodegradable materials, and liquid fuels due to the specificity of its composition and structure. − It has been found that lignin consists of coumarin (H), mustard alcohol (S), and pineal (G) groups, which are randomly connected by C–C/C–O bonds (4-O-5, α-O-4, β-O-4, β–β, β-1, etc.) to form natural aromatic polymer compounds with complex three-dimensional networks. − In recent years, on the strength of the structural characteristics of lignin, it has been extensively demonstrated that lignin catalytic depolymerization (LCD) for liquid fuels and cooperative production of phenolic monomers is one of the promising methods for highly efficient utilization of lignin. , …”

A comprehensive comparative study on the energy application of chars produced from different biomass feedstocks via hydrothermal conversion, pyrolysis, and torrefaction

“…Comparative studies of pyrolysis, torrefaction and hydrothermal tend to focus on one material, such as olive tree prunings [68], Miscanthus giganteus [69], straw [70,71], or mushroom compost waste [72][73][74]. There are numerous studies which explore pyrolysis and hydrothermal processing [75], torrefaction and hydrothermal processing [31,[76][77][78][79][80], and pyrolysis and torrefaction [81,82] but, again, these tend to focus on single biomass feedstocks and there are no comparative seaweed-based studies of all three thermal treatments, despite numerous individual studies [83]. Studies indicate that the preferred processing route varies with feedstock, thus comparing studies is difficult due to variations in equipment, processing conditions and limiting studies to single feedstocks or single types of feedstocks.…”