Bioconversion of Lignocellulose into Bioethanol: Process Intensification and Mechanism Research

Abstract

Biofuels produced from lignocellulosic biomass can significantly reduce the energy dependency on fossil fuels and the resulting effects on environment. In this respect, cellulosic ethanol as an alternative fuel has the potential to become a viable energy source in the near future. Over the past few decades, tremendous effort has been undertaken to make cellulosic ethanol cost competitive with conventional fossil fuels. The pretreatment step is always necessary to deconstruct the recalcitrant structures and to make cellulose more accessible to enzymes. A large number of pretreatment technologies involving physical, chemical, biological, and combined approaches have been developed and tested at the pilot scale. Furthermore, various strategies and methods, including multi-enzyme complex, non-catalytic additives, enzyme recycling, high solids operation, design of novel bioreactors, and strain improvement have also been implemented to improve the efficiency of subsequent enzymatic hydrolysis and fermentation. These technologies provide significant opportunities for lower total cost, thus making large-scale production of cellulosic ethanol possible. Meanwhile, many researchers have focused on the key factors that limit cellulose hydrolysis, and analyzing the reaction mechanisms of cellulase. This review describes the most recent advances on process intensification and mechanism research of pretreatment, enzymatic hydrolysis, and fermentation during the production of cellulosic ethanol.

A Two-Step Conversion of Corn Stover into Furfural and Levulinic Acid in a Water/Gamma-Valerolactone System

“…In recent years, increasing awareness of the need to decrease the environmental footprint of society has resulted in great enthusiasm for utilizing biomass, which is a sustainable alternative source of carbon that could feasibly meet the increasing demands for biofuels and bio-chemicals in the future (Huang et al 2011;Dutta and Pal 2014;Ioelovich 2015). To that end, extensive research has been focused on the effective conversion of lignocellulosic biomass into fuels and chemicals (Cherubini 2010;Zu et al 2014;Zhang et al 2015;Maity 2015).…”

Cellulase Recycling after High-Solids Simultaneous Saccharification and Fermentation of Combined Pretreated Corncob

“…Second-generation bioethanol produced from lignocellulosic materials presents a good potential alternative to -exhaustible fossil fuels because of its renewability, low environmental impact, and limited employment of food crops (Huang et al, 2011). Since corncob has a wide distribution and high bulk density for bioethanol production, its collection and transport are highly convenient (Liu et al, 2010).…”

“…We previously evaluated a combined pretreatment with dilute sulfuric acid-sodium hydroxide (Zhang et al, 2010b) to increase the relative amount of cellulose and improve the digestibility of corncob during high-solids ethanol fermentation. Although efforts from many researchers and enzyme companies have focused on increasing the production efficiency and specific activity of enzymes, enzyme recycling and reuse is a more practical strategy to reduce enzyme cost (Huang et al, 2011). Several recycling strategies, such as β-glucosidase immobilization (Tu et al, 2006;Wang et al, 2009), enzyme ultrafiltration (Qi et al, , 2012, and enzyme re-adsorption (Tu and Saddler, 2010), have been applied in lignocellulosic hydrolysis.…”

Immobilization of cellulase on modified mesoporous silica shows improved thermal stability and reusability

“…The growing demand for energy and diminishing fossil fuel reserves have stimulated tremendous interest in finding alternative renewable energy sources (Huang et al, 2011). Over the past few decades, a large number of research efforts have focused on the cellulose, because cellulose is the most abundant renewable biomass in the world, and it can be converted into biofuels, such as ethanol after cellulose is degraded to sugar (Huang et al, 2011).…”

“…Over the past few decades, a large number of research efforts have focused on the cellulose, because cellulose is the most abundant renewable biomass in the world, and it can be converted into biofuels, such as ethanol after cellulose is degraded to sugar (Huang et al, 2011). Many methods have been used for the degradation of cellulosic materials to sugars, such as acidolysis (Li et al, 2010), alkaline hydrolysis (Carrillo et al, 2005) and enzymatic hydrolysis (Park et al, 2002).…”