Fundamentals of Biomass Pretreatment by Fractionation

Abstract

With the rise in global energy demand and environmental concerns about the use of fossil fuels, the need for rapid development of alternative fuels from sustainable, non-food sources is now well acknowledged. The effective utilization of low-cost high-volume agricultural and forest biomass for the production of transportation fuels and bio-based materials will play a vital role in addressing this concern [1]. The processing of lignocellulosic biomass, especially from mixed agricultural and forest sources with varying composition, is currently significantly more challenging than the bioconversion of corn starch or cane sugar to ethanol [1,2]. This is due to the inherent recalcitrance of lignocellulosic biomass to enzymatic and microbial deconstruction, imparted by the partly crystalline nature of cellulose and its close association with hemicellulose and lignin in the plant cell wall [2,3]. Pretreatments that convert raw lignocellulosic biomass to a form amenable to enzymatic degradation are therefore an integral step in the production of bioethanol from this material [4]. Chemical or thermochemical pretreatments act to reduce biomass recalcitrance in various ways. These include hemicellulose removal or degradation, lignin modification and/or delignification, reduction in crystallinity and degree of polymerization of cellulose, and increasing pore volume. Biomass pretreatments are an active focus of industrial and academic research efforts, and various strategies have been developed.Among commonly studied pretreatments, organosolv pretreatment, in which an aqueous organic solvent mixture is used as the pretreatment medium, results in the fractionation of the major biomass components, cellulose, lignin, and hemicellulose into three process streams [5,6]. Cellulose and lignin are recovered as separate solid streams, while hemicelluloses and sugar degradation products such as furfural and hydroxymethylfurfural (HMF) are released as a water-soluble fraction. The combination of ethanol as the solvent and Aqueous Pretreatment of Plant Biomass for Biological and Chemical Conversion to Fuels and Chemicals, First Edition. Edited by Charles E. Wyman.

Pretreatment of Lignocellulosic Materials as Substrates for Fermentation Processes

“…Thus, the development of efficient technologies is still a challenge in the field [ 61 ]. The research into novel methods of biomass pretreatment, including e.g., non-ionizing and ionizing radiation, pulsed-electric field, high pressure, ultrasounds, supercritical solvents, organosolv or application of deep eutectic solvents is additionally justified because the pretreatment step accounts for up to 40% of total costs of biomass processing towards biofuels or value-added products [ 56 , 62 , 63 , 64 , 65 ].…”

Organosolv Fractionation of Softwood Biomass for Biofuel and Biorefinery Applications

“…Organosolv involves the cooking of lignocellulosic biomass in a mixture of water with an organic solvent that leads to the deconstruction of both lignin and hemicellulose and its dissolution in the cooking liquor [28]. The lignin is typically retrieved as a precipitate by dilution of the liquor with water.…”

Bioreactor design for enzymatic hydrolysis of biomass under the biorefinery concept

“…Pretreatment facilitates the access to biomass by reducing the crystallinity of cellulose, increasing the pore size and surface area of cellulose, modifying the lignin structure, and totally or partially solubilizing hemicellulose. A diversity of pretreatment methods has been developed, including physical, physicochemical, chemical and biological processes [2,12,[22][23][24].…”

“…Equation 22is an empirical expression obtained by Hikita et al [154] for gas hold up in aqueous non-electrolyte solutions. In another study on bubble column bioreactors, Sada et al [155] proposed to include the gas-liquid density ratio (ρ ρ / g l ) on the mathematical expression previously reported by Akita et al [156] for the gas hold up calculation (see equations (23) and (24)). On the other hand, equation (25) correlates the gas hold up with the riser gas velocity (U Lr ) in a gas-lift bioreactor [157].…”