Processes forming Gas, Tar, and Coke in Cellulose Gasification from Gas-Phase Reactions of Levoglucosan as Intermediate

Understanding cellulose pyrolysis via ab initio deep learning potential field

Comprehensive and dynamic studies of cellulose pyrolysis reaction mechanisms are crucial in designing experiments and processes with enhanced safety, efficiency, and sustainability. The details of the pyrolysis mechanism are not readily available from experiments but can be better described via molecular dynamics (MD) simulations. However, the large size of cellulose molecules challenges accurate ab initio MD simulations, while existing reactive force field parameters lack precision. In this work, precise ab initio deep learning potentials field (DPLF) are developed and applied in MD simulations to facilitate the study of cellulose pyrolysis mechanisms. The formation mechanism and production rate of both valuable and greenhouse products from cellulose at temperatures larger than 1073 K are comprehensively described. This study underscores the critical role of advanced simulation techniques, particularly DLPF, in achieving efficient and accurate understanding of cellulose pyrolysis mechanisms, thus promoting wider industrial applications.

Sludge pyrolysis integrated biomass gasification to promote syngas: Comparison of different biomass

The sludge pyrolysis and biomass gasification (SPBG) integrated process has been demonstrated to promote hydrogen-rich gas generation from the two solid waste materials by interaction, however, the effect of biomass species is unclear. Six agriculture and forestry biomass were chosen to participate SPBG in the current study to monitor the roles of biomass on product evolution. The results revealed that SPBG has promoted the syngas for all the biomass samples with the gas yields increased by 10.30 %-38.90 %, while the H2 yields increased by 17.31 %-81.40 %. By statistical analysis, it can be concluded that H2 was mainly derived from the gasification reaction of the biomass char and water in the sludge volatile, followed by the cracking of tar, while H elements released from biomass were mainly transformed into CH4 and C2Hy. The syngas composition verified a lot for SPBG experiments with different biomasses. Cellulose intensifies the production of CO through CO bonds cracking on char, while hemicellulose intensifies the production of CH4 through tar polymerization. Therefore, biomass with higher concentrations of cellulose and hemicellulose exhibited improved performance in gas production.

Quantification of Cellulose Pyrolyzates via a Tube Reactor and a Pyrolyzer-Gas Chromatograph/Flame Ionization Detector-Based System

Pyrolysis of cellulose primarily produces 1,6-anhydro-β-d-glucopyranose (levoglucosan), which easily repolymerizes to form coke precursors in the heating zone of a pyrolysis reactor. This hinders the investigation of primary pyrolysis products as well as the elucidation of cellulose pyrolysis mechanisms, particularly because of the significant buildup of coke during slow pyrolysis. The present study discusses the applicability of a pyrolysis-gas chromatography/flame ionization detection (Py-GC/FID) system using naphthalene as the internal standard, with the aim of substantially improving the quantification of pyrolyzates during the slow pyrolysis of cellulose. This method achieved quantification of levoglucosan with a yield that was 14 times higher than that obtained from offline pyrolysis in a simple tube reactor. The high yield recovery of levoglucosan was attributed to the suppression of levoglucosan repolymerization in the Py-GC/FID system, owing to the rapid escape of levoglucosan from the heating zone, low concentration of levoglucosan in the gas phase, and rapid quenching of levoglucosan. Therefore, this method facilitated the improved quantification of primary pyrolysis products during the slow pyrolysis of cellulose, which can be beneficial for understanding the primary pyrolysis reaction mechanisms. This method can potentially be applied to other polymeric materials that produce reactive pyrolyzates.

Carbonization of cellulose cell wall evaluated with ultraviolet microscopy

This is the first study of cellulose carbonization in the interior of cell walls.

Gas-Phase Reactions of Glyceraldehyde and 1,3-Dihydroxyacetone as Models for Levoglucosan Conversion during Biomass Gasification

Levoglucosan, the major intermediate in wood gasification, is decomposed selectively to C1/C2 fragments at 550-600 °C. Kinetic analyses suggest that radical chain mechanisms with the involvement of short-lived carbonyl intermediates explain the lower production of larger fragments. To address this hypothesis, the gas-phase reactivities of glyceraldehyde (Gald), 1,3-dihydroxyacetone (DHA), and glycerol, as simple C3 model compounds, were compared at 400-800 °C under N2 flow at residence times of 0.9-1.4 s. Retro-aldol fragmentation and dehydration proceeded for the pyrolysis of Gald/DHA at 400 °C, far below the 600 °C decomposition point of glycerol. Pyrolysis of Gald/DHA generated exclusively syngas (CO and H2). On the basis of the results of theoretical calculations, the effects of carbonyl intermediates on reactivity were explained by postulating uni- and bimolecular reactions, although the bimolecular reactions became less effective at elevated temperatures.