A mechanistic model of fast pyrolysis of glucose-based carbohydrates to predict bio-oil composition

Abstract

Bio-oil obtained from fast pyrolysis of biomass has the potential to be upgraded to renewable, drop-in fuel intermediates. The quality of bio-oil produced is critical to downstream process development and is determined by a number of factors like reaction timescale, extent of primary and secondary reactions, and the presence of minerals. In this work, we provide a mechanistic understanding of the various competing reactions in fast pyrolysis of cellulose and other glucose-based carbohydrates through a unified microkinetic model. The model incorporates the reactions of the cellulose chain and of the glucose intermediate to form a variety of bio-oil components, which are confirmed by either experiments or theoretical calculations reported in the literature. The majority of the Arrhenius rate parameters were based on existing studies, while a small number were fitted to match the experimental product distribution over a wide range of temperatures. The model yields of all the major primary fast pyrolysis products, viz., levoglucosan, formic acid, glycolaldehyde, 5-hydroxymethyl furfural, furfural and char, match reasonably well with the experimental data over the temperature range of 400-550 C. The model predicted that the time required for complete conversion corresponds to 2.5-3 s. Net rate analysis identified key pathways to levoglucosan via either mid-chain initiation, or depropagation and end-chain initiation that were dominant over the timescales of 0-100 ms and 100-1000 ms, respectively, at 500 C. Unlike the existing lumped kinetic models, our model provides a detailed picture of levoglucosan formation that involves mid-chain glycosidic bond cleavage followed by unzipping of levoglucosan from the chain ends. The model, utilizing the same set of rate coefficients, was able to predict the dominant products of fast pyrolysis of maltohexaose, cellobiose and glucose that also are in good agreement with experimental data. The initial chain length of cellulose was found to have a profound effect on the product yields for chain lengths shorter than 50, while it had no effect on the total reaction time.

Pyrolysis characteristic of kenaf studied with separated tissues, alkali pulp, and alkali lignin

“…The pathways for the formation of cyclic monomers, such as furans, anhydrous sugars, and cyclopentanones, from carbohydrate polymers are as yet unknown, but the pathways for the formation of low-molecular-weight products from glucose have been reported in detail by Vinu et al (2012). The pyrolysis products obtained from the alkali pulp were formed via more Table 5.…”

Biomass Pyrolysis Kinetics: A Review of Molecular-Scale Modeling Contributions

“…Much of the research efforts have focused on the structural and chemical properties of cellulose due to its widespread use in construction (wood) and industrial applications. And, while there is an extensive body of literature, leading back to a number of pivotal publications (Shafizadeh and Fu, 1973, Broido and Nelson, 1975, Antal Jr et al, 1980; yet, few comprehensive review papers on cellulose pyrolysis have been written (Anital Jr, 1982;Antal Jr and Varhegyi, 1995;Vinu and Broadbelt, 2012;Lede, 2012;and Burnham, Zhou and Broadbelt, 2015) in the past four decades or more of focused research. Notably, the paper by Vinu and Broadbelt, 2012, is technically not a review, but is summative in regard to its effort to bring together the state of knowledge on pyrolysis kinetic mechanisms for glucose-based carbohydrates including cellulose.…”

“…And, while there is an extensive body of literature, leading back to a number of pivotal publications (Shafizadeh and Fu, 1973, Broido and Nelson, 1975, Antal Jr et al, 1980; yet, few comprehensive review papers on cellulose pyrolysis have been written (Anital Jr, 1982;Antal Jr and Varhegyi, 1995;Vinu and Broadbelt, 2012;Lede, 2012;and Burnham, Zhou and Broadbelt, 2015) in the past four decades or more of focused research. Notably, the paper by Vinu and Broadbelt, 2012, is technically not a review, but is summative in regard to its effort to bring together the state of knowledge on pyrolysis kinetic mechanisms for glucose-based carbohydrates including cellulose. Since 2000, however, pyrolysis of whole biomass, cellulose and lignin has been a fastmoving field of research, spawning extensive reviews, every 10 months (inclusive of the recent papers by Vinu and Broadbelt, 2012, Lede, 2012and and Burnham, Zhou and Broadbelt, 2015 on the average in an effort to inform the research community and keep-up with the pace of advances.…”

“…Notably, the paper by Vinu and Broadbelt, 2012, is technically not a review, but is summative in regard to its effort to bring together the state of knowledge on pyrolysis kinetic mechanisms for glucose-based carbohydrates including cellulose. Since 2000, however, pyrolysis of whole biomass, cellulose and lignin has been a fastmoving field of research, spawning extensive reviews, every 10 months (inclusive of the recent papers by Vinu and Broadbelt, 2012, Lede, 2012and and Burnham, Zhou and Broadbelt, 2015 on the average in an effort to inform the research community and keep-up with the pace of advances. In addition to the earlier reviews on cellulose already mentioned, the following papers, listed chronologically, chronical the advances made in the 15 year period from 2000 to 2015 (Anital Jr, 1985;Sinha, et al, 2000;Bridgwater and Peacocke, 2000;Amen-Chen, Pakdel and Roy, 2001;Czernick and Bridgwater, 2004;Reale, et al, 2004;Branca, Albano and Di Blasi, 2005;Mohan, Pittman and Steele, 2006;Prakash and Karunanithi, 2008;Venderbosch and Prins, 2010;Slutter, et al, 2010;White, Catallo and Legendre, 2011;Pandey and Kim, 2011;Bridgwater, 2012;and Shen, et al, 2015).…”

Formation of Methoxybenzenes from Cellulose in the Presence of Tetramethylammonium Hydroxide by Pyrolysis

“…Fundamentally, the cellulose pyrolysis products are formed via a free radical mechanism. 41,42 First of all, to form a benzene ring, a glucose unit has to be transformed to a cyclohexane ring. A cyclohexane ring can be formed by cleavage of the ether linkage between C1 and C5 of a glucose unit and following rearrangement to Hydroxybenzene (phenol) can be formed from the THCH unit by rearrangement including two hydroxyl groups and loss of a water molecule as shown in Scheme 2.…”