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Insight into the evolution of the proton concentration during autohydrolysis and dilute-acid hydrolysis of hemicellulose

BACKGROUND: During pretreatment, hemicellulose is removed from biomass via proton-catalyzed hydrolysis to produce soluble poly- and mono-saccharides. Many kinetic models have been proposed but the dependence of rate on proton concentration is not well-defined; autohydrolysis and dilute-acid hydrolys...

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Autores principales: Kapu, Nuwan Sella, Yuan, Zhaoyang, Chang, Xue Feng, Beatson, Rodger, Martinez, D. Mark, Trajano, Heather L.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: BioMed Central 2016
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5073983/
https://www.ncbi.nlm.nih.gov/pubmed/27790287
http://dx.doi.org/10.1186/s13068-016-0619-6
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author Kapu, Nuwan Sella
Yuan, Zhaoyang
Chang, Xue Feng
Beatson, Rodger
Martinez, D. Mark
Trajano, Heather L.
author_facet Kapu, Nuwan Sella
Yuan, Zhaoyang
Chang, Xue Feng
Beatson, Rodger
Martinez, D. Mark
Trajano, Heather L.
author_sort Kapu, Nuwan Sella
collection PubMed
description BACKGROUND: During pretreatment, hemicellulose is removed from biomass via proton-catalyzed hydrolysis to produce soluble poly- and mono-saccharides. Many kinetic models have been proposed but the dependence of rate on proton concentration is not well-defined; autohydrolysis and dilute-acid hydrolysis models apply very different treatments despite having similar chemistries. In this work, evolution of proton concentration is examined during both autohydrolysis and dilute-acid hydrolysis of hemicellulose from green bamboo. An approximate mathematical model, or “toy model”, to describe proton concentration based upon conservation of mass and charge during deacetylation and ash neutralization coupled with a number of competing equilibria, was derived. The model was qualitatively compared to experiments where pH was measured as a function of time, temperature, and initial acid level. Proton evolution was also examined at room temperature to decouple the effect of ash neutralization from deacetylation. RESULTS: The toy model predicts the existence of a steady-state proton concentration dictated by equilibrium constants, initial acetyl groups, and initial added acid. At room temperature, it was found that pH remains essentially constant both at low initial pH and autohydrolysis conditions. Acid is likely in excess of the neutralization potential of the ash, in the former case, and the kinetics of neutralization become exceedingly small in the latter case due to the low proton concentration. Finally, when the hydrolysis reaction proceeded at elevated temperatures, one case of non-monotonic behavior in which the pH initially increased, and then decreased at longer times, was found. This is likely due to the difference in rates between neutralization and deacetylation. CONCLUSIONS: The model and experimental work demonstrate that the evolution of proton concentration during hydrolysis follows complex behavior that depends upon the acetyl group and ash content of biomass, initial acid levels and temperature. In the limit of excess added acid, pH varies very weakly with time. Below this limit, complex schemes are found primarily related to the selectivity of deacetylation in comparison to neutralization. These findings indicate that a more rigorous approach to models of hemicellulose hydrolysis is needed. Improved models will lead to more efficient acid utilization and facilitate process scale-up.
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spelling pubmed-50739832016-10-27 Insight into the evolution of the proton concentration during autohydrolysis and dilute-acid hydrolysis of hemicellulose Kapu, Nuwan Sella Yuan, Zhaoyang Chang, Xue Feng Beatson, Rodger Martinez, D. Mark Trajano, Heather L. Biotechnol Biofuels Research BACKGROUND: During pretreatment, hemicellulose is removed from biomass via proton-catalyzed hydrolysis to produce soluble poly- and mono-saccharides. Many kinetic models have been proposed but the dependence of rate on proton concentration is not well-defined; autohydrolysis and dilute-acid hydrolysis models apply very different treatments despite having similar chemistries. In this work, evolution of proton concentration is examined during both autohydrolysis and dilute-acid hydrolysis of hemicellulose from green bamboo. An approximate mathematical model, or “toy model”, to describe proton concentration based upon conservation of mass and charge during deacetylation and ash neutralization coupled with a number of competing equilibria, was derived. The model was qualitatively compared to experiments where pH was measured as a function of time, temperature, and initial acid level. Proton evolution was also examined at room temperature to decouple the effect of ash neutralization from deacetylation. RESULTS: The toy model predicts the existence of a steady-state proton concentration dictated by equilibrium constants, initial acetyl groups, and initial added acid. At room temperature, it was found that pH remains essentially constant both at low initial pH and autohydrolysis conditions. Acid is likely in excess of the neutralization potential of the ash, in the former case, and the kinetics of neutralization become exceedingly small in the latter case due to the low proton concentration. Finally, when the hydrolysis reaction proceeded at elevated temperatures, one case of non-monotonic behavior in which the pH initially increased, and then decreased at longer times, was found. This is likely due to the difference in rates between neutralization and deacetylation. CONCLUSIONS: The model and experimental work demonstrate that the evolution of proton concentration during hydrolysis follows complex behavior that depends upon the acetyl group and ash content of biomass, initial acid levels and temperature. In the limit of excess added acid, pH varies very weakly with time. Below this limit, complex schemes are found primarily related to the selectivity of deacetylation in comparison to neutralization. These findings indicate that a more rigorous approach to models of hemicellulose hydrolysis is needed. Improved models will lead to more efficient acid utilization and facilitate process scale-up. BioMed Central 2016-10-21 /pmc/articles/PMC5073983/ /pubmed/27790287 http://dx.doi.org/10.1186/s13068-016-0619-6 Text en © The Author(s) 2016 Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
spellingShingle Research
Kapu, Nuwan Sella
Yuan, Zhaoyang
Chang, Xue Feng
Beatson, Rodger
Martinez, D. Mark
Trajano, Heather L.
Insight into the evolution of the proton concentration during autohydrolysis and dilute-acid hydrolysis of hemicellulose
title Insight into the evolution of the proton concentration during autohydrolysis and dilute-acid hydrolysis of hemicellulose
title_full Insight into the evolution of the proton concentration during autohydrolysis and dilute-acid hydrolysis of hemicellulose
title_fullStr Insight into the evolution of the proton concentration during autohydrolysis and dilute-acid hydrolysis of hemicellulose
title_full_unstemmed Insight into the evolution of the proton concentration during autohydrolysis and dilute-acid hydrolysis of hemicellulose
title_short Insight into the evolution of the proton concentration during autohydrolysis and dilute-acid hydrolysis of hemicellulose
title_sort insight into the evolution of the proton concentration during autohydrolysis and dilute-acid hydrolysis of hemicellulose
topic Research
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5073983/
https://www.ncbi.nlm.nih.gov/pubmed/27790287
http://dx.doi.org/10.1186/s13068-016-0619-6
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