Fundamentals of Biomass Pretreatment at Low pH

Trajano, Heather L.; Wyman, Charles E.

doi:10.1002/9780470975831.ch6

Cited by 32 publications

(34 citation statements)

References 119 publications

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“…Low pH pretreatments have been extensively studied, and dilute acid-pretreated samples have shown high enzyme digestibility. However, the primary disadvantages of acid pretreatment are the generation of inhibitors to enzymes and yeasts, and the requirement of corrosion-resistant reactors [ 29 ].…”

Section: One-step Pretreatmentmentioning

confidence: 99%

Promise of combined hydrothermal/chemical and mechanical refining for pretreatment of woody and herbaceous biomass

Kim

Dien

2016

Biotechnol Biofuels

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Production of advanced biofuels from woody and herbaceous feedstocks is moving into commercialization. Biomass needs to be pretreated to overcome the physicochemical properties of biomass that hinder enzyme accessibility, impeding the conversion of the plant cell walls to fermentable sugars. Pretreatment also remains one of the most costly unit operations in the process and among the most critical because it is the source of chemicals that inhibit enzymes and microorganisms and largely determines enzyme loading and sugar yields. Pretreatments are categorized into hydrothermal (aqueous)/chemical, physical, and biological pretreatments, and the mechanistic details of which are briefly outlined in this review. To leverage the synergistic effects of different pretreatment methods, conducting two or more pretreatments consecutively has gained attention. Especially, combining hydrothermal/chemical pretreatment and mechanical refining, a type of physical pretreatment, has the potential to be applied to an industrial plant. Here, the effects of the combined pretreatment (combined hydrothermal/chemical pretreatment and mechanical refining) on energy consumption, physical structure, sugar yields, and enzyme dosage are summarized.

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Section: One-step Pretreatmentmentioning

confidence: 99%

Promise of combined hydrothermal/chemical and mechanical refining for pretreatment of woody and herbaceous biomass

Kim

Dien

2016

Biotechnol Biofuels

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“…Prehydrolysis, which is also referred to as ’pretreatment’, refers to the reaction pathway to remove hemicelluloses from lignocellulosic material during the production of high-purity dissolving pulps or biofuels [ 3 , 5 , 6 ]. Here, an acid catalyzes the breakdown of long hemicellulose chains to form shorter chain oligomers and sugar monomers in the presence of water or steam.…”

Section: Introductionmentioning

confidence: 99%

“…Hemicellulose is hydrolyzed into mostly soluble sugars during prehydrolysis, while during torrefaction, it is degraded, depending on process temperature, into volatile organic compounds including CO 2 and CO, and char [ 9 ]. Prehydrolysis is typically performed by treating biomass at 140–180 °C with either water/steam (autohydrolysis) or dilute acid solutions [ 6 ]. Autohydrolysis is an industrially practiced step in dissolving pulp production, and both autohydrolysis and dilute-acid hydrolysis are considered viable pretreatment options in the production of lignocellulosic ethanol.…”

Section: Introductionmentioning

confidence: 99%

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

Kapu

Yuan

Chang

et al. 2016

Biotechnol Biofuels

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BackgroundDuring 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.ResultsThe 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.ConclusionsThe 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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“…Although kinetic models have become more elegant, their applicability to diverse feedstocks and reactor configurations over broad ranges of process conditions is still limited . The complexity of hemicellulose and wall chemistry of different feedstocks/species is a major contributing factor in this regard, and many inventive steps undertaken to improve models of feedstocks such as corn stover have not been adopted for bamboo and softwoods.…”

Section: Kinetic Models Of Hemicellulose Hydrolysismentioning

confidence: 99%

Review of hemicellulose hydrolysis in softwoods and bamboo

Kapu

Trajano

2014

Biofuels Bioprod Bioref

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Hydrolysis to remove hemicellulose and/or generate saccharides is an integral unit operation for the production of chemicals, fuels, and materials from lignocellulosic biomass. Softwoods and bamboo are both widely available but comparatively understudied feedstocks. This paper fi rst reviews the unique hemicellulose chemistry of these feedstocks and the fundamental mechanism of polysaccharide hydrolysis. The infl uence of temperature, time, acid concentration, particle size, and reactor confi guration on water-only hydrolysis, or autohydrolysis, and dilute acid hydrolysis are summarized. The composition, molecular weight, and yields of saccharides and degradation products generated during hydrolysis are presented. Finally, the types, strengths, and weaknesses of current hemicellulose hydrolysis kinetic models are reviewed.

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Fundamentals of Biomass Pretreatment at Low pH

Cited by 32 publications

References 119 publications

Promise of combined hydrothermal/chemical and mechanical refining for pretreatment of woody and herbaceous biomass

Promise of combined hydrothermal/chemical and mechanical refining for pretreatment of woody and herbaceous biomass

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

Review of hemicellulose hydrolysis in softwoods and bamboo

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