Strengths, challenges, and opportunities for hydrothermal pretreatment in lignocellulosic biorefineries

Abstract

Pretreatment prior to or during biological conversion is required to achieve high sugar yields essential to economic production of fuels and chemicals from low cost, abundant lignocellulosic biomass. Aqueous thermochemical pretreatments achieve this performance objective from pretreatment coupled with subsequent enzymatic hydrolysis, but chemical pretreatment can also suffer from additional costs for exotic materials of construction, the need to recover or neutralize the chemicals, introduction of compounds that inhibit downstream operations, and waste disposal, as well as for the chemicals themselves. The simplicity of hydrothermal pretreatment with just hot water offers the potential to greatly improve the cost of the entire conversion process if sugar degradation during pretreatment, production of un-fermentable oligomers, and the amount of expensive enzymes needed to obtain satisfactory yields from hydrothermally pretreated solids can be reduced. Biorefi nery economics would also benefi t if value could be generated from lignin and other components that are currently fated to be burned for power. However, achieving these goals will no doubt require development of advanced hydrothermal pretreatment confi gurations. For example, passing water through a stationary bed of lignocellulosic biomass in a fl owthrough confi guration achieves very high yields of hemicellulose sugars, removes more than 75% of the lignin for potential valorization, and improves sugar release from the pretreated solids with lower enzyme loadings. Unfortunately, the large quantities of water needed to achieve this performance result in very dilute sugars, high energy costs for pretreatment and product recover, and large amounts of oligomers. Thus, improving our understanding of 126

Enhancing Lignocellulosic Biomass Hydrolysis by Hydrothermal Pretreatment, Extraction of Surface Lignin, Wet Milling and Production of Cellulolytic Enzymes

“…Removal of these barriers by various pretreatment and fractionation methods has greatly increased the yields of enzymatic hydrolysis of cellulose, providing sugars that can be exploited by fermentation or chemo‐catalytic processes into various fuels or platform chemicals . On the other hand, efficient fractionation removal of hemicellulose and lignin as well as their recovery is critical for their exploitation, considering that whole biomass valorization is the main goal of the future biorefinery . Finally, the cost of enzyme production still represents a major issue that increases the overall process economics.…”

“…In addition, it allows the recovery of a significant portion of hemicellulose as sugars and/or the respective furans and organic acids (i.e., furfural, HMF, levulinic and formic acids, etc.) and produces a cellulose‐rich solid with increased digestibility by cellulolytic enzymes . The nature of hardwoods (i.e., beech, birch, poplar, etc.)…”

“…[2][3][4][5] On the other hand, efficient fractionation removal of hemicellulose and lignin as well as their recovery is criticalf or their exploitation, considering that whole biomass valorizationi st he main goal of the future biorefinery. [5][6][7][8][9][10][11][12] Finally,t he cost of enzyme production still represents am ajor issue that increases the overall process economics.…”

Techno‐economic analysis of jet‐fuel production from biorefinery waste lignin

“…The former include phenolic resins, epoxies, adhesives, polyolefins, carbon fiber, and PHAs . The latter consists of syringol, guaiacol, BTX (benzene, toluene, and xylene), vanillin, lipids, and jet fuel . Some current and future market and product opportunities are presented in Fig.…”

“…The former include phenolic resins, [13][14][15][16][17][18][19][20] epoxies, [21][22][23] adhesives, [24][25][26] polyolefins, [27][28][29][30][31] carbon fiber, [32][33][34][35] and PHAs. [36][37][38] The latter consists of syringol, guaiacol, 39,40 BTX (benzene, toluene, and xylene), 41,42 vanillin, 43,44 lipids, 45,46 and jet fuel. [47][48][49][50][51][52][53][54][55] Some current and future market and product opportunities are presented in Fig.…”