Effect of Pressure and Hot Vapor Residence Time on the Fast Pyrolysis of Biomass: Experiments and Modeling

Abstract

Pyrolysis of acid-leached bagasse (515 °C) and pinewood (485 °C) has been carried out in the pressure range from 5 × 10 −3 to 100 kPa in a screen-heater, designed for nearly isothermal operation and rapid quenching of reaction products. At the lowest pressure, i.e., by maximizing the escape rate of products away from the hot reaction zone, 73% of the poly-C 6 -sugars in bagasse were recovered in the liquid product as C 6 -anhydrosugars (C 6 aS) with degree of polymerization between 1 and 6 (DP 1 to DP 6 ). A mathematical model, including reactions and mass transfer, was able to predict the measured decrease in the total yield of C 6 aS and the shift to lighter C 6 aS in the DP-distribution as a function of increasing pressure. The effect of the hot vapor residence time on the DP-distribution of the C 6 aS was investigated by pyrolyzing pinewood in a fluidized bed. At identical pressure (50 kPa) and temperature (485 °C) the total yield of C 6 aS was the same for the screen-heater and fluidized bed while the DP-distribution shifted to DP 1 as a result of the higher hot vapor residence time in the fluidized bed, which could be described by assuming first order kinetics for all possible cracking reactions of C 6 aS in the vapor phase.

Advances in Multiscale Modeling of Lignocellulosic Biomass

“…This approach has been further advanced by Anca-Couce an co-workers − who have made improvements to the model and successfully employed it in simulations of biomass pyrolysis and combustion . Further work has been done to account for the presence and qualities of partially degraded biopolymer fragments in pyrolysis oil, but more work is needed as discussed by Terrell et al…”

“…This approach has been further advanced by Anca-Couce an co-workers 236−238 who have made improvements to the model and successfully employed it in simulations of biomass pyrolysis 204 and combustion. 239 Further work has been done to account for the presence and qualities of partially degraded biopolymer fragments in pyrolysis oil, 240 but more work is needed as discussed by Terrell et al 241 The coupling of simulation results across scales is a strategy that has also demonstrated utility in predicting the outcome of thermochemical conversion processes based on a combination of biomass feedstock characteristics and reactor operating conditions. A recent study used the results of a fluidized bed reactor simulation to provide residence time distributions employed in particle-scale ensemble calculations of pyrolytic conversion.…”

Vacuum Pyrolysis of Hybrid Poplar Milled Wood Lignin with Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry Analysis of Feedstock and Products for the Elucidation of Reaction Mechanisms

“…The first one proposes that oligomers result from the recombination of monomeric lignin pyrolysis products. , The second hypothesis considers that pyrolytic lignin is produced from the degradation of primary lignin oligomeric products. − Experimental evidence shows that during lignin pyrolysis, the starting material undergoes swelling, softening, and/or melting at low temperature (<∼200 °C), dehydration and side-chain reactions at intermediate temperature (∼200–500 °C), and aromatic substituent conversion with polycyclic rearrangement at high temperature (>∼500 °C). , From a microkinetic modeling perspective, Yanez et al report that major reaction families include ether cleavage, demethoxylation, demethanation, decarboxylation, deacylation, dealkylation, aliphatic C–C cleavage, methoxyl isomerization, oxidation, hydrogen addition, and char formation . The nonreactive vaporization of low-molecular-weight oligomers has also been recently highlighted as an important occurrence during lignin pyrolysis processes. ,− In this mass-transport-driven phenomenon, oligomeric species with sufficiently low devolatilization temperature (conceptually similar to the normal boiling point) are capable of evaporating/sublimating directly from the reaction front with a limited extent of actual reactions having taken place. , The effect of pressure on the production of oligomeric lignin products is still poorly understood. Using empirical methods applied to hypothetical molecular structures, it is possible to estimate vaporization curves from the Clausius–Clapeyron equation, thereby suggesting the molecular sizes capable of evaporating at a given pyrolysis temperature .…”

“…44,46−48 In this mass-transport-driven phenomenon, oligomeric species with sufficiently low devolatilization temperature (conceptually similar to the normal boiling point) are capable of evaporating/sublimating directly from the reaction front with a limited extent of actual reactions having taken place. 44,49 The effect of pressure on the production of oligomeric lignin products is still poorly understood. Using empirical methods applied to hypothetical molecular structures, it is possible to estimate vaporization curves from the Clausius−Clapeyron equation, thereby suggesting the molecular sizes capable of evaporating at a given pyrolysis temperature.…”

Techno-Economical Evaluation of Bio-Oil Production via Biomass Fast Pyrolysis Process: A Review

“…Many research articles have been published on optimizing bio-oil production from various biomass using a fast pyrolysis process under different operating conditions (Chen et al, 2019;Nzihou et al, 2019;Marathe et al, 2020). On the other hand, there is a lack of information on economic analysis comparison on fast pyrolysis process to make it commercially stable.…”