CELF pretreatment of corn stover boosts ethanol titers and yields from high solids SSF with low enzyme loadings

Abstract

† The authors declare no conflict of interest. Electronic Supplementary Information (ESI) available: Ethanol yields from the SSF of CELF pretreated corn stover at enzyme loading of 5 mg-protein g-glucan-in-RCS -1 , component mass balance from the SSF of DA pretreated corn stover at enzyme loadings of 15 mg-protein gglucan-in-RCS -1 , cell viability of SSF flasks with CELF pretreated corn stover at an enzyme loading of 2 mg-protein g-glucan-in-RCS -1 . See A major challenge to economically produce ethanol from lignocellulosic biomass is to achieve industrially relevant ethanol titers (> 50 g L -1 ) to control operating and capital costs for downstream ethanol operations while maintaining high ethanol yields. However, due to reduced fermentation effectiveness at high biomass solids loadings, excessive amounts of enzymes are typically required to obtain reasonable ethanol titers, thereby trading off reduced operating and capital costs with high enzyme costs. In this study, we applied our newly developed Co-Solvent Enhanced Lignocellulosic Fractionation (CELF) pretreatment to produce highly digestible glucan-rich solids from corn stover. Simultaneous saccharification and fermentation (SSF) was then applied to pretreated solids from CELF at 15.5 wt% solids loadings (corresponding to 11 wt% glucan loadings) in modified shake flasks to achieve an ethanol titer of 58.8 g L -1 at 89.2% yield with an enzyme loading of 15 mg-protein g-glucan-in-raw-corn-stover -1 (-RCS) -1 in only 5 days. By comparison, SSF of corn stover solids from dilute acid pretreatment at 18.3 wt% solids loading (or 10 wt% glucan loadings) only achieved an ethanol titer and yield of 47.8 g L -1 and 73.0%, respectively, despite needing longer fermentation times (~20 days) and an additional 18 h of prehydrolysis at 50°C. Remarkably, although longer fermentation times were required at more economical enzyme loadings of 5 and 2 mg-protein g-glucan-in-RCS -1 , high solids SSF of CELF pretreated corn stover realized final ethanol titers consistently above 50 g L -1 and yields over 80%.

Heterogeneous Catalyst Design Principles for the Conversion of Lignin into High‐Value Commodity Fuels and Chemicals

“…The combination of solvents with dilute concentrations of acid or bases is used to promote the glycolysis or scission of bonds for facile separation of lignin from cellulose and hemicellulose. There are many different chemical methods that utilize solvents, such as the Klason, Kraft, organosolv, and cosolvent‐enhanced lignocellulosic fractionation (CELF) strategies . Each of these isolation techniques utilize solvents with either acids or bases to give unique isolated lignin feedstocks.…”

“…The lignin is precipitated out and has a higher purity and less structural changes than that of acid and base pretreated lignin . The CELF method uses THF with dilute acid to remove lignin and solubilize biomass from hardwoods and corn stover . This method is able to recover over 90 % of lignin from maple wood and keep the lignin in a relatively unaltered and pristine form.…”

Strategies for structuring diverse emulsion systems by using wood lignocellulose-derived stabilizers

“…To release and recover individual com-ponents, wood biomass is commonly subjected to pretreatment, which can take the form of mechanical milling, extrusion, acid, alkaline, or organosolv treatments, oxidation, ionic liquids, or hot water extraction. [35][36][37][38] Green biomass treatment methods include deep eutectic solvents, steam explosion, supercritical fluids, and microbial degradation, and emerging lignocellulose pretreatment methods include microwave irradiation, ultrasound, gamma radiation, electron beam irradiation, pulsed-electric field, high hydrostatic pressure, and high pressure homogenization. 39 Also, we recently presented centrifugation as a solvent-free method of separating lignin-and hemicellulose-rich fractions in softwood extracts.…”

Bioethanol from Lignocellulosic Biomass

“…In SSF, the yeast so quickly consumes the glucose released by cellulase enzymes that sugar concentrations remain low enough to not substantially affect enzyme action [121]. In addition, ethanol produced by the yeast has a much lower impact on enzymatic hydrolysis than glucose and cellobiose [96,120,122].…”

“…However, removing lignin from an ethanol organosolv stream typically involves dilution with water that hurts downstream processing and economics. Compared to other solvents, tetrahydrofuran (THF) offers several important attributes including high volatility that facilitates recycle, the ability to be made from furfural that can be a pretreatment byproduct, and lignin recovery by dilution, evaporation, or extraction [121,145,146].…”