Recent updates on different methods of pretreatment of lignocellulosic feedstocks: a review

Abstract

Lignocellulosic feedstock materials are the most abundant renewable bioresource material available on earth. It is primarily composed of cellulose, hemicellulose, and lignin, which are strongly associated with each other. Pretreatment processes are mainly involved in effective separation of these complex interlinked fractions and increase the accessibility of each individual component, thereby becoming an essential step in a broad range of applications particularly for biomass valorization. However, a major hurdle is the removal of sturdy and rugged lignin component which is highly resistant to solubilization and is also a major inhibitor for hydrolysis of cellulose and hemicellulose. Moreover, other factors such as lignin content, crystalline, and rigid nature of cellulose, production of post-pretreatment inhibitory products and size of feed stock particle limit the digestibility of lignocellulosic biomass. This has led to extensive research in the development of various pretreatment processes. The major pretreatment methods include physical, chemical, and biological approaches. The selection of pretreatment process depends exclusively on the application. As compared to the conventional single pretreatment process, integrated processes combining two or more pretreatment techniques is beneficial in reducing the number of process operational steps besides minimizing the production of undesirable inhibitors. However, an extensive research is still required for the development of new and more efficient pretreatment processes for lignocellulosic feedstocks yielding promising results.

Comparison and Optimization of Saccharification Conditions of Alkaline Pre-Treated Triticale Straw for Acid and Enzymatic Hydrolysis Followed by Ethanol Fermentation

“…The results (Table 2) indicate that an increase in the concentration of NaOH causes an increase in the biomass loss of 37%, 49%, and 52%, respectively, for catalyst concentrations of 1%, 6%, and 11%. A similar dependence was obtained in [12,37,38]. The research results indicate that the use of 1% NaOH already significantly lowers the lignin content.…”

Kinetic Modelling and Experimental Studies for the Effects of Fe2+ Ions on Xylan Hydrolysis with Dilute-Acid Pretreatment and Subsequent Enzymatic Hydrolysis

“…However, hydrolysis of lignocellulosic biomass into fermentable monosaccharides remains a challenging task due to the notorious biomass recalcitrance [7]. Pretreatment of lignocellulosic biomass with dilute mineral acids under mild conditions has been found to effectively separate and break down hemicellulose, modify the lignin network and increase cellulose accessibility [8,9]. Overall, the technology of dilute-acid pretreatment is being actively studied and applied; in 2017 alone, a number of papers have been published in the field of dilute-acid pretreatment of biomass [10][11][12][13][14][15][16][17][18].…”

Pretreatment Conditions for Hydrolysates from Unbleached Pulp Waste for Ethanol Fermentation with Xylose-fermenting Yeast, <i>Candida intermedia</i> 4-6-4T2

“…Hydrolysis of hemicelluloses is essential and removal of lignin is desirable to dissolve the cellulosic fiber structures and increase enzyme accessibility as well as enzyme hydrolysis activity. Typical pretreatments include hot water, steam explosion, acid or alkali explosion, and ammonia fiber expansion, all of which have specific advantages and disadvantages 1), 2) . Acid or alkali explosion requires lower processing temperatures than steam explosion but the acid/alkali must be neutralized before the enzymatic hydrolysis and fermentation processes 1), 2) .…”

“…Typical pretreatments include hot water, steam explosion, acid or alkali explosion, and ammonia fiber expansion, all of which have specific advantages and disadvantages 1), 2) . Acid or alkali explosion requires lower processing temperatures than steam explosion but the acid/alkali must be neutralized before the enzymatic hydrolysis and fermentation processes 1), 2) . Unbleached pulp waste is a type of uncommercialized substrate obtained in the process of preparing cellulose, and is a relatively pure cellulosic material which could be easily saccharified by steam explosion pretreatment followed by enzymatic hydrolysis due to the low concentration of lignin.…”