Pretreatment of Corn Stover by Levulinic Acid-Based Protic Ionic Liquids for Enhanced Enzymatic Hydrolysis

Abstract

Economically competitive and sustainable dissolution pretreatment technology is in high demand due to the remarkable achievement in the pretreatment of lignocellulose using ionic liquids (ILs) for enhanced enzymatic hydrolysis. Herein, levulinic acid (Lev), a well-known bio-based platform chemical derived from carbohydrates, in conjunction with a series of organic superbases, was used as a raw chemical to prepare a new class of protic ILs (PILs). The findings indicated that the obtained PILs exhibited a good solubility of up to 10 wt % toward corn stover-based lignocellulose at 140 °C in 40 mins, based on which a facile and efficient dissolution pretreatment technology was developed for enhanced enzymatic hydrolysis of corn stover. The facile dissolution and regeneration of corn stover resulted in significant changes in the composition and physical−chemical structures. These changes led to significantly enhanced enzymatic hydrolysis behavior of the pretreated sample with total reducing sugar and glucose yields of 0.8 and 0.49 g/g within 48 h under optimal conditions, respectively. The Kamlet−Taft solvent parameters of the PILs were systematically evaluated, and the interaction between the lignocellulose and PILs was studied by 13 C NMR, indicating that the satisfactory performance of PILs was benefited from the higher ß parameter value and the stronger interactions, particularly the existence of the extra hydrogen-bond interaction from the potential keto−enol tautomerism of the ketone groups in levulinate anions. The compositional and physicochemical changes in the lignocellulose were systematically evaluated to achieve an in-depth understanding of the dissolution activation mechanism using various characterization techniques. The findings also showed that 44.3% of lignin could be fractionated during the facile dissolution and regeneration process, together with a transformation of the crystalline structure of cellulose I to cellulose II and of the packed morphology to a porous one. The structure of the fractionated lignin was also characterized for a better understanding of the fractionation process. The study demonstrated a new sustainable dissolution pretreatment technology for enhanced enzymatic hydrolysis, which can provide significant insights into the design of new solvents for biomass dissolution and processing.

Lignin-grafting alternative copolymer of 3,4-dihydrocoumarin and epoxides as an active and flexible ingredient in sunscreen

“…S7-S10, † indicating a clear reaction between lignin and DHC or the epoxides individually under identical conditions. 31 P NMR was identified as a powerful tool to evaluate the various types of hydroxyl groups distributed in lignin, 49 which will provide direct evidence of the two initiating process shown in Scheme 1, as both will result in the transformation of different types of hydroxyl groups (Fig. S11 †).…”

“…Details of the tests are shown in ESI Text S1. † 49 The total degree of polymerization (DP) of DHC and SO alternating copolymer fragments was determined with eqn (1) according to a previous publication: 39…”

“…The molar ratio of DHC, epoxides and DBU can be quantitatively used according to the whole hydroxyl group content in EHL, which can be evaluated by 31 P NMR. 49 The protocol was optimized by selecting styrene oxide associated with DHC to prepare EHL-g-P(DHC-alt-SO) under various conditions (Table 1). It was found that the conversion of DHC reached 73.83% and 81.52% at 120 °C and 140 °C, respectively, compared to 57.00% at 100 °C, indicating that increasing temperature could favor the reaction (Table 1, entries LD5S5-1, LD5S5-2, LD5S5-3).…”

Rapid fractionation of corn stover by microwave-assisted protic ionic liquid [TEA][HSO4] for fermentative acetone–butanol–ethanol production

“…To date, various researches have been conducted on the decomposition of different types of lignocelluloses by the protic ILs. For instance, Chen et al suggested to fractionate corn stover by [DBNH][Lev], and a reducing sugars yield of 0.80 g g −1 pulp was obtained [ 18 ]. Semerci et al analyzed the capacities of various proton ionic liquids to the fractionation of lignocelluloses, among which, the highest glucose yield of 92% was obtained using [TEA][HSO 4 ] [ 19 ].…”

Eco-Friendly Catalytic Synthesis of Top Value Chemicals from Valorization of Cellulose Waste

“…Lignocellulosic biomass is considered as the most abundant source of renewable carbon on Earth, with an estimated annual production of 2·10 11 tons, mainly represented by residues from forestry and agriculture [ 1 ]. Given its nature as a renewable resource, lignocellulosic biomass is considered as a promising alternative to fossil sources to obtain chemicals [ 2 , 3 , 4 ] and biofuels [ 5 , 6 ]. Through an acid-catalyzed dehydration process, it is possible to convert the carbohydrate component of biomass (cellulose, hemicellulose, and related subunits such as glucose, xylose, galactose, arabinose, etc.)…”