Adsorption-Enhanced Glucan Oligomer Production from Cellulose Hydrolysis over Hyper-Cross-Linked Polymer in Molten Salt Hydrate

Abstract

Selective saccharification of cellulose into glucose is a critical step for utilization of lignocellulosic biomass. Molten salt hydrates (MSHs) have shown promising performance in selectively converting cellulose into glucose because of the high solubility of cellulose in the solvent. However, the separation of formed glucose from the MSHs is still a grand challenge. To address this issue, we developed a two-step process, where crystalline cellulose is hydrolyzed into short-chain glucan oligomers in MSHs followed by separation and subsequent hydrolysis of the formed oligomers into glucose under mild conditions. The two-step method provides an easy separation for glucan oligomers from the MSHs without sacrificing the selectivity to glucose. Application of the method for crystalline cellulose is, however, limited to a relatively low concentration, 26.2 mg/mL, because of the formation of byproducts in the MSH that facilitate oligomers degradation. In this work, reactive adsorption was employed to in situ remove the byproducts formed during cellulose hydrolysis in the MSH. It was found that hyper-cross-linked polymer (HCP) made from the polymerization of 4-vinylbenzyl chloride and divinylbenzene can selectively adsorb 5-hydroxymethylfurfural (5-HMF) and levulinic acid (LA) while showing negligible sugar adsorption in both water and the MSH. With the reactive adsorption approach, byproducts including 5-HMF and LA were removed from the reaction media under reaction conditions, and their negative effects on oligomer degradation were inhibited. In the presence of the HCP, the obtained glucan oligomer concentration was enhanced from less than 54.2 to 247.1 mg mL–1 when the weight ratio of cellulose was increased to MSH from 1:60 to 1:4, exhibiting an oligomer yield of 69.5%. The HCP can be effectively separated from the reaction media by filtration and regenerated by oxidation with hydrogen peroxide. Application of reactive adsorption with HCP for cellulose hydrolysis in the MSH provides a promising method to produce glucan oligomers and glucose with an improved yield and efficiency.

Enhanced production and separation of short-chain glucan oligomers from corn stover in an unacidified LiBr molten salt hydrate via pre-extraction of hemicellulose

“…However, the acetic acid concentration increased simultaneously with the decrease in mass ratio. The high concentration of acetic acid effectively facilitated the degradation of glucan oligomers into glucose, 5-HMF and possibly humins, 49 resulting in a limited glucan oligomer concentration in the hydrolysate. Additionally, the result in Fig.…”

“…25 The acetic acid generated from hemicellulose hydrolysis, therefore, can potentially promote the cellulose degradation rate, resulting in a rapid conversion of the produced glucan oligomers to glucose and possibly to 5-hydroxymethylfurfural. 26 Due to these reasons, the direct conversion of raw lignocellulose into glucan oligomers in the MSH often shows a low selectivity compared to crystalline cellulose. To address this issue, we developed a new process to improve the glucan oligomer yield.…”

Research advancement in molten salt-mediated thermochemical upcycling of biomass waste

“…However, the separation of glucose from the MSHs is still a significant challenge. Liu et al 59 developed a two-step process to convert crystalline cellulose into short-chain glucan oligomers in MSHs, which is followed by the separation and subsequent hydrolysis of the formed oligomers into glucose under mild conditions. This provided an easy separation for glucan oligomers from the MSHs without sacrificing the selectivity to glucose.…”

“…For the glucan oligomer production, the separation of MSHs ( e.g. , LiBr) and glucan oligomers can be achieved by physical adsorption using various materials such as HCP 59 and amorphous carbon black. 62 As shown in Fig.…”

Numerical Studies on Cellulose Hydrolysis in Organic–Liquid–Solid Phase Systems with a Liquid Membrane Catalysis Model

“…In addition, the preparation of HMF from cellulose is complicated by multitudes of side reactions, and the conversion rate of the raw material is generally low . Therefore, an optimized reaction system is essential for the efficient conversion of cellulose to HMF. − …”