Hot Water Pretreatment of Lignocellulosic Biomass: An Effective and Environmentally Friendly Approach to Enhance Biofuel Production

Abstract

Hot water pretreatment without usage of chemicals is a particularly attractive approach for pretreatment of lignocellulosic biomass due to its fewer safety and environmental concerns as well as relatively low cost. However, a prohibitive amount of sugar degradation products limits the efficiency of such pretreatment, and excessive water consumption accompanied with the over-diluted sugar streams still impedes the implementation of this pretreatment to be an economically viable pathway. These limitations are associated with the scant attention of water-biomass interaction mechanism and engineering aspects regarding kinetic modeling and reactor configurations. This review aims at investigating those critical factors in terms of chemistry and engineering fundamentals in order to understand the correct axiomatic approaches needed to advance this technology. Various reactor configurations and kinetic models are evaluated to explore optimization strategies toward application.

Characterization of Value-Added Non-Carbohydrate Compounds Solubilized during Acidic Hot Water Flowthrough Pretreatment of Poplar Wood

“…Apart from aromatic compounds, 18.7% HMF selectivity was obtained at a flow rate of 10 mL/min, indicating that the precursor of HMF, i.e., glucose, was susceptible to dehydration if exposed in hot water for a relative long retention time because of the lower flow rate. This corresponds with previous studies (Yan et al 2016a), which reported that glucose degraded rapidly once hydrolyzed from cellulose in hot water conditions. …”

“…AHWF benefits from the acidic characteristic of water because of its dissociation into hydronium ions at high temperatures (e.g., 240 °C), which enhances the degradation of lignocellulosic biomass into sugar and non-carbohydrate compounds (Yan et al 2016a). To evaluate the impact of acidity on the selectivity of non-carbohydrate products, 0.05% (w/w) and 0.1% (w/w) H2SO4 were added into the hot water flowthrough system.…”

“…Some preliminary attempts, such as adding high concentrations of sodium hydroxide (Silva et al 2009), calcium salts (Silva et al 2009), and copper salts (Fache et al 2016) to produce specific non-carbohydrate compounds from lignocellulosic biomass (e.g., vanillin, syringaldehyde) have been carried out, but high chemical consumption makes these strategies less competitive. By reviewing the intrinsic kinetics of hot water pretreatment (Yan et al 2016a), the authors realized that optimizing and tailoring reaction parameters (e.g., temperature) and reactor operational parameters (e.g., flow rate) can likely achieve the same goal to selectively produce these non-carbohydrate structures with much less chemical usage. However, there exists a large knowledge gap on how to optimize the reaction parameters and the key reaction mechanisms.…”

Single-step microwave-assisted hot water extraction of hemicelluloses from selected lignocellulosic materials – A biorefinery approach

“…The intercalation of hemicelluloses into cellulose microfibrils and their interlinkage with lignin is another important factor for such recalcitrance (Bond et al, 2013;Yang et al, 2011). Thus, aside from loosening up the structural rigidity of celluloses and breaking up the lignin shield, the removal of hemicelluloses from the lignocellulosic matrix forms an essential part of biomass pretreatment for enhanced cellulose digestibility (Yan et al, 2016;Hayashi and Kaida, 2011).…”

Influence of Operating Parameters on Biomass Conversion under Sub‐ and Supercritical Water Conditions

“…Under conditions close to the critical point, water has several interesting properties. Among them are low viscosity and high solubility of organic substances, close to those in organic solvents, which make subcritical water an excellent medium for homogenous, rapid, and efficient reactions , , . Water in the critical region is still as polar as acetone .…”