Comparative study on fuel characteristics and pyrolysis kinetics of corn residue-based hydrochar produced via microwave hydrothermal carbonization

Heating performances of corn straw particle with/without SiC particle in a microwave chamber

The amount of biomass production each year is huge, and microwave-assisted pyrolysis of biomass to obtain biogas, bio-oil, and biochar is a promising method. In this study, silicon carbide (SiC) was selected as the microwave absorber, and the effects of microwave power (400, 450, 500, 550 and 600 W), reactor chamber volume (100, 150, 200, 250, and 300 W), and the mass ratio of SiC and corn straw (0, 0.25, 0.5, 0.75, and 1) on the heating performances of corn straw particles were investigated and presented in this study. When the microwave power increased from 400 to 600 W, the average heating rate of corn straw particles increased from 23.06 ℃ /min to 101.46 ℃ /min, and that of mixture particles of corn straw and SiC increased from 87.00 ℃ /min to 236.88 ℃/min. When the reactor chamber volume increased from 100 to 300 mL, the average heating rate of corn straw particles decreased from 38.21 ℃/min to 22.54 ℃/min, and that of mixture particles of corn straw and SiC decreased from 98.84 ℃/min to 76.01 ℃/min. When the mass ratio of SiC and corn straw increased from 0 to 1, the average heating rate of mixture particles of corn straw and SiC increased from 101.46 ℃/min to 236.88 ℃/min. Some formulae with R2 values ranged from 0.971 to 0.998 were proposed to determine the transient temperatures of corn straw particles and mixture particles of corn straw and SiC.

Liquid-solid ratio during hydrothermal carbonization affects hydrochar application potential in soil: Based on characteristics comparison and economic benefit analysis

Returning straw-like agricultural waste to the field by converting it into hydrochar through hydrothermal carbonization (HTC) is an important way to realize resource utilization of waste, soil improvement, and carbon sequestration. However, the large-scale HTC is highly limited by the large water consumption and waste liquid pollution. Here, we propose strategies to optimize the liquid-solid ratio (LSR) of HTC, and comprehensively evaluate the stability, soil application potential, and economic benefits of corn stover-based hydrochar under different LSRs. The results showed that the total amount of dissolved organic carbon of hydrochars increased by 55.0% as LSR reducing from 10:1 to 2:1, while the element content, thermal stability, carbon fixation potential, specific surface area, pore volume, and functional group type were not obviously affected. The specific surface area and pore volume of hydrochar decreased by 61.8% and 70.9% as LSR reduced to 1:1, due to incomplete carbonization. According to the gray relation, hydrochar derived at LSR of 10:1 and followed by 2:1 showed greatest relation degree of 0.80 and 0.70, respectively, indicating better soil application potential. However, reducing LSR from 10:1 to 2:1 made the income of single process production increased from -388 to 968 ¥, and the wastewater generation decreased by 80%. Considering the large-scale application of HTC in fields for farmland improvement and environmental remediation, the comprehensive advantages of optimized LSR will be further highlighted.

Hydrothermal carbonization of cow dung with human urine as a solvent for hydrochar: An experimental and kinetic study

Hydrothermal carbonization (HTC) is the most cost-effective, environmentally friendly, and efficient physicochemical and biochemical process for converting biomass to products with added value. The objective and novelty of this work is to produce and investigate the qualities of hydrochar fuel (as a solid fuel) from cow manure using human urine as a solvent in order to find a suitable replacement for conventional fuel (i.e., coal). HTC based studies were conducted in batch, at three different reaction temperatures (180 °C, 200 °C, and 220 °C) and two different reaction periods (2 and 4 h). For kinetic analysis and reaction mechanism of the combustion behavior of the produced hydrochar, the model free kinetic methods and the z-master plot were used. From the model free kinetics methods, it was observed that the resultant optimum average activation energy and pre-exponential factor for the produced hydrochar at 180 °C and 2 h reaction period (HTC_180_2) were ∼120 kJ/mol and ∼5.59 × 10²⁵ sec^-1, respectively. In addition, the little variation between ΔE_α and ΔH_α (∼10 kJ/mol) suggests that the combustion of produced hydrochar (HTC_180_2) occurred with minimal energy use. Furthermore, the hydrochar exhibited its highest heating value at 200 °C for 4 h (HTC_200_4) which was 1.44 times higher than the raw dung (13.4 MJ/kg) due to the HTC process. The produced hydrochar demonstrated a significant improvement compared to the conventional solvent, i.e. water.

Effects of microwave and plastic content on the sulfur migration during co-pyrolysis of biomass and plastic

In order to reduce the risks of sulfur-containing contaminants present in biofuels, the effects of microwave and content of hydrogen donor on the cracking of C-S bonds and the migration of sulfur were studied by co-pyrolysis of biomass and plastic. The synergistic mechanism of microwave and hydrogen donor was explored from the perspective of deducing the evolution of sulfur-containing compounds based on microwave thermogravimetric analysis. By combining temperature-weight curves, it was found that microwaves and hydrogen radicals promoted the cracking of sulfur-containing compounds and increased the mass loss of biomass during pyrolysis. The mixing ratio of hydrogen donor (plastic) was the key parameter resulting in the removal of sulfur from oil. By adjusting the mixing ratio, the yield of co-pyrolyzed oil was three times higher than that of cow dung pyrolysis alone and the relative removal rate of sulfur reached 73.67%. The relative content of sulfur in the oil was reduced by 73.77% due to the escape of sulfur-containing gases (H₂S, COS and C₂H₅SH) and the formation of sulfate crystals in the char. Microwave selectively heated sulfur-containing organics and hydrogen radicals stimulated the breaking of C-S bonds, which improved the cracking efficiency of the oil. This breaking will provide a theoretical and technological reference for the environmentally friendly treatment of biomass and biofuels.

Insight into derivative Weibull mixture model in describing simulated distributed activation energy model and distillers dried grains with solubles pyrolysis processes

The kinetics of biomass pyrolysis is fundamental for exploring its mechanisms and optimizing its processes, which is helpful for designing its systems. The derivative Weibull mixture model was proposed for kinetic description of the simulated distribution energy model (DAEM) processes and distillers dried grains with solubles (DDGS) pyrolysis processes. The conversion rate data of these processes at different heating rates could be accurately described by the derivative Weibull mixture model. Moreover, the proposed model could effectively smooth the noises contained in the experimental conversion rate data of DDGS pyrolysis. The derivative Weibull mixture model separated DDGS pyrolysis reactions into several individual processes, and provided some data required for further isoconversional kinetic analysis. The predicted curves from the derivative Weibull mixture model allowed us to obtain the effective activation energies of DDGS pyrolysis, which varied significantly from 170 to 330 kJ mol^-1 in the conversion range between 0.1 and 0.9.