Xueqin Li

The thermo-chemical conversion of biomass wastes is a practical approach for the value-added reclamation of bioenergy in large quantities, and pyrolysis plays a core role in this process. In this work, poplar (PR) and cedar (CR) were used as staple wood biomasses to investigate the apparent kinetics of TG/DTG at different heating rates. Secondly, miscellaneous wood chips (MWC), in which PR and CR were mixed in equal proportion, were subjected to comprehensive investigations on their pyrolysis behavior and product evolution in a fixed bed reactor with pyrolysis temperature, catalyst, and the flow rate H₂O steam as influencing factors. The results demonstrated that both PR and CR underwent three consecutive pyrolysis stages, the TG/DTG curves shifted to higher temperatures, and the peak temperature intervals also enhanced as the heating rate increased. The kinetic compensation effect expression and apparent reaction kinetic model of CR and PR pyrolysis were obtained based on the law of mass action and the Arrhenius equation; the reaction kinetic parameter averages of Ea and A of its were almost the same, which were about 72.38 kJ/mol and 72.36 kJ/mol and 1147.11 min⁻¹ and 1144.39 min⁻¹, respectively. The high temperature was beneficial for the promotion of the pyrolysis of biomass, increased pyrolysis gas yield, and reduced tar yield. This process was strengthened in the presence of the catalyst, thus significantly increasing the yield of hydrogen-rich gas to 117.9 mL/g_-biomass. It was observed that H₂O steam was the most effective activator for providing a hydrogen source for the whole reaction process, promoted the reaction to proceed in the opposite direction of H₂O steam participation, and was beneficial to the production of H₂ and other hydrocarbons. In particular, when the flow rate of H₂O steam was 1 mL/min, the gas yield and hydrogen conversion were 76.94% and 15.90%, and the H₂/CO was 2.07. The yields of H₂, CO, and CO₂ in the gas formation were significantly increased to 107.35 mL/g_-biomass, 53.70 mL/g_-biomass, and 99.31 mL/g_-biomass, respectively. Therefore, H₂ was the most dominant species among gas products, followed by C-O bond-containing species, which provides a method for the production of hydrogen-rich gas and also provides ideas for compensating or partially replacing the fossil raw material for hydrogen production.

Torrefaction is an effective method for upgrading biomass. Cedar torrefaction is carried out in a fixed bed reactor at the temperature of 200–300 °C. The structural parameters are obtained from elemental analysis and ¹³C nuclear magnetic resonance (NMR). Thermal degradation behavior of raw and torrefied cedar is monitored by thermogravimetry analysis. The results show that carbon structure varied during torrefaction has a significant effect on thermal degradation of cedar. Some unstable oxygen functional groups, such as C1 of hemicellulose, β-O-4 linked bonds, and amorphous C6 of cellulose, are decomposed at mild torrefaction of torrefied temperature ≤ 200 °C. The temperature of maximum weight loss rate increases from 348 °C of raw cedar to 373 °C of C-200. The amorphous cellulose is partly re-crystallized at moderate torrefaction of torrefied temperature 200–250 °C. The aromaticity of torrefied cedar increases from 0.45 of C-200 to 0.73 of C-250. The covalent bond in the side chain of aromatic rings in cedar was further broken during torrefaction at severe torrefaction of torrefied temperature 250–300 °C. The area percentage of DTG mainly signed at 387 °C of C-300. The proton aromatic carbon increases from 12.35% of C-250 to 21.69% of C-300. These results will further facilitate the utilization of biomass for replacing fossil fuel to drive carbon neutrality.

CO2-assisted co-gasification of binary mixtures of pinewood pellets (PWP) and two kinds of plastics polyethylene-terephthalate (PET) and high-density polyethylene (HDPE) were examined at 800 °C using a fixed bed reactor. Evolutionary behavior and yields of CO, H2, and CmHn were investigated for both individual feedstock and binary mixtures of biomass and plastic. Synergetic effects in co-gasification of mixtures under CO2 atmosphere were analyzed and compared between experimental and calculated results. The results showed that PET and HDPE although had similar behavior in gasification, they provided many different characteristics on blending with solid biomass in CO2-assisted co-gasification. Both PWP–PET mixture and PWP–HDPE mixture showed positive effects on hydrocarbons yield and negative effects on solid yield. For PWP–PET mixture, H2 yield showed no change compared to the calculated value; however, CO yield and CO2 consumption showed negative effects due to the blocked porosity of solid biomass from the softened PET. For PWP–HDPE mixture, H2 yield showed significant enhancement compared to the calculated value, and CO yield showed slight enhancement but a slight reduction in CO2 consumption. It was also observed that the experimental CmHn yields obtained from biomass-plastics mixtures were of higher values than the calculated values. The morphologies of solid residues for PWP, PET, PWP–PET, and PWP–HDPE were analyzed and taken as a supplement to explain the synergetic effects in the co-gasification process. These results provide an insight into energy recovery and waste treatment potential for both biomass and waste plastic using thermochemical conversion.