Relationships between cellulosic biomass particle size and enzymatic hydrolysis sugar yield: Analysis of inconsistent reports in the literature

doi:10.1016/j.renene.2013.04.012

Renewable Energy

Volume 60, December 2013, Pages 127-136

https://doi.org/10.1016/j.renene.2013.04.012 Get rights and content

Highlights

•
We summarize reported relationships between biomass particle size and sugar yield.
•
We summarize experimental conditions and results on this topic.
•
We analyze the inconsistent relationships from five perspectives.
•
Several hypotheses are formulated based on what is reviewed.
•
Future research is proposed to test these hypotheses.

Abstract

Cellulosic ethanol made from cellulosic biomass is a promising alternative to petroleum-based transportation fuels. Enzymatic hydrolysis is a crucial step in cellulosic ethanol production. In order to better understand the mechanisms of enzymatic hydrolysis, relationships between cellulosic biomass particle size and enzymatic hydrolysis sugar yield have been studied extensively. However, the literature contains inconsistent reports. This paper presents an analysis of the inconsistent reports on the relationships in the literature. It discusses the differences in the reported experiments from five perspectives (biomass category, particle size definition, sugar yield definition, biomass treatment procedure, and particle size level). It also proposes future research activities that can provide further understanding of the relationships.

Introduction

During the last three decades, consumption of petroleum-based liquid transportation fuels (including gasoline, diesel, and jet fuels) in the U.S. has increased by more than 30% [1]. These fuels account for about 70% of total petroleum consumption in the U.S. [1]. In 2010, more than 3 billion liters of petroleum were consumed in the U.S. every day, and over 60% of them were imported [1]. Also, the price of petroleum in the U.S. has almost doubled during the last ten years [1]. In addition, use of petroleum-based fuels contributes to accumulation of greenhouse gas (GHG) in the atmosphere [2]. Therefore, it is critically important to explore alternatives to petroleum-based liquid transportation fuels [3], [4], [5]. One such alternative is cellulosic ethanol.

An essential step in cellulosic ethanol production is enzymatic hydrolysis which converts cellulose into soluble sugars. A high sugar yield in enzymatic hydrolysis is crucial to the cost-effectiveness of cellulosic ethanol production. Several characteristics of cellulosic biomass have been identified as key factors affecting sugar yield in enzymatic hydrolysis, including biomass particle size, degree of polymerization, crystallinity, and accessible surface area [6], [7], [8], [9], [10]. In order to understand the mechanisms of enzymatic hydrolysis and to increase sugar yield in enzymatic hydrolysis, many studies have been done to investigate the relationships between cellulosic biomass particle size and enzymatic hydrolysis sugar yield. However, three different relationships have been reported: negative (smaller particle size produces higher sugar yield), neutral (particle size has no effects on sugar yield), and positive (larger particle size produces higher sugar yield).

This paper, for the first time, presents an analysis of the inconsistent reports on the relationships. It discusses the differences in the reported experiments from five perspectives (biomass category, particle size definition, sugar yield definition, biomass treatment procedure, and particle size level). It also proposes future research activities that can provide further understanding of the relationships.

Section snippets

Two categories of cellulosic biomass

The cellulosic biomass used to investigate relationships between particle size and sugar yield can be classified into two categories: pure cellulose and lignocellulosic biomass. As summarized in Fig. 1 and Table 1,when pure cellulose was used, negative relationships were reported in a majority of the related studies. When lignocellulosic biomass was used, three different relationships were reported by different researchers.

Shewale and Sadana [15] reported a neutral relationship between particle

Two definitions of particle size

Two definitions of particle size (sieve size versus screen size) were used in reported experiments. As summarized in Fig. 4 and Table 2,when sieve size was used, consistent (positive) relationships were reported. When screen size was used, three different relationships were reported.

Fig. 5 illustrates two definitions of particle size used in the literature. For one definition, different sieve sizes were used in milling to control particle size (one sieve size was used for one particle size).

Different definitions of sugar yield

Three different definitions of sugar yield (glucose/pre-hydrolysis cellulose ratio, glucose/pre-hydrolysis biomass ratio, and glucose/pre-pretreatment cellulose ratio) were used in reported studies. Fig. 10 describes the sequence of four processes (size reduction, pelleting, pretreatment, and hydrolysis) in cellulosic ethanol production. The glucose/pre-hydrolysis cellulose ratio represents the ratio (weight/weight) of glucose in post-hydrolysis solution to cellulose in pre-hydrolysis biomass.

Two procedures of treatment

Two procedures of treatment were used in reported studies – one with pretreatment and the other without. As shown in Fig. 12 and Table 6, when pretreatment was not applied, consistent negative relationships were reported. When pretreatment was applied, three different relationships were reported. When biomass was pretreated by ammonia fiber explosion (AFEX) [19], hot water [21], sodium carbonate [24], sodium chlorite [22], and steam explosion [18], negative relationships were reported. When

Different levels of particle size

Particle sizes used in most studies can be classified into two levels: micron level (particle sizes were smaller than 1 mm) and millimeter level (particle sizes were larger than 1 mm). As shown in Fig. 13 and Table 7, when micron-level particle sizes were used, negative relationships were reported by most studies. When millimeter-level particle sizes were used, two different relationships were reported.

Concluding remarks

It is of both academic and practical importance to know the relationships between cellulosic biomass particle size and enzymatic hydrolysis sugar yield. The literature contains inconsistent reports on this relationship. Some say that smaller particles produce higher sugar yield, some say that larger particles produce higher sugar yield, and some say that particle size does not affect sugar yield.

It is desirable to understand why such inconsistence exists. Looking at relevant publications from

Competing interests

The author(s) declare that they have no competing interests.

Acknowledgments

This study is supported financially by NSF award CMMI-0970112.

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ReviewRelationships between cellulosic biomass particle size and enzymatic hydrolysis sugar yield: Analysis of inconsistent reports in the literature

Highlights

Abstract

Introduction

Section snippets

Two categories of cellulosic biomass

Two definitions of particle size

Different definitions of sugar yield

Two procedures of treatment

Different levels of particle size

Concluding remarks

Competing interests

Acknowledgments

Renew Energ

Renew Energ

Renew Energy

Renew Energy

Carbohydrate Polym

Bioresour Technol

Bioresour Technol

Process Biochem

Bioresour Technol

Chem Eng Sci

Biomass Bioenergy

Enzyme Microb Technol

Biomass Bioenergy

Bioresour Technol

Bioresour Technol

Bioresour Technol

Bioresour Technol

Enzyme Microb Technol

Short-term energy outlook

The role of biomass in America's energy future: framing the analysis

Biofuels Bioprod Biorefin

The energy independence and security act of 2007

Influence of feedstock particle size on lignocellulose conversion – a review

Appl Biochem Biotechnol

Factors affecting cellulose hydrolysis and the potential of enzyme recycle to enhance the efficiency of an integrated wood to ethanol process

Biotechnol Bioeng

Substrate and enzyme characteristics that limit cellulose hydrolysis

Biotechnol Progr

The use of adsorbed cellulase in the continuous conversion of cellulose to glucose

J. Polym. Sci.

Effect of structural and physico-chemical features of cellulosic substrates on the efficiency of enzymatic hydrolysis

Appl Biochem Biotechnol

Rationale for particle size effect on rates of enzymatic saccharification of microcrystalline cellulose

J Food Biochem

Enzymatic hydrolysis of cellulosic materials by Sclerotium rolfsii culture filtrate for sugar production

Can J Microbiol

Effect of particle size based separation of milled corn stover on AFEX pretreatment and enzymatic digestibility

Biotechnol Bioeng

The effect of particle size on hydrolysis reaction rates and rheological properties in cellulosic slurries

Appl Biochem Biotechnol

Microscopic examination of changes of plant cell structure in corn stover due to hot water pretreatment and enzymatic hydrolysis

Biotechnol Bioeng

Review
Relationships between cellulosic biomass particle size and enzymatic hydrolysis sugar yield: Analysis of inconsistent reports in the literature