Aqueous ionic liquids and deep eutectic solvents for cellulosic biomass pretreatment and saccharification

Abstract

Ionic liquids (ILs) have proven effective solvents for pretreating lignocellulose, leading to the fast saccharification of cellulose and hemicellulose. However, the high current cost of most ILs remains a major barrier to commercializing this recent approach at a practical scale. As a strategic detour, aqueous solutions of ILs are also being explored as less costly alternatives to neat ILs for cellulose pretreatment. However, limited studies on a few select IL systems are known and there remains no systematic survey of various ILs, eluding an in-depth understanding of pretreatment mechanisms afforded by aqueous IL systems. As a step toward filling this gap, this study presents results for Avicel cellulose pretreatment by neat and aqueous solutions (1.0 and 2.0 M) of 20 different ILs and three deep eutectic solvents, correlating enzymatic hydrolysis rates of pretreated cellulose with various IL properties such as hydrogen-bond basicity, polarity, Hofmeister ranking, and hydrophobicity. The pretreatment efficiencies of neat ILs may be loosely correlated to the hydrogen-bond basicity of the constituent anion and IL polarity; however, the pretreatment efficacies for aqueous ILs are more complicated and cannot be simply related to any single IL property. Several aqueous IL systems have been identified as effective alternatives to neat ILs in lignocellulose pretreatment. In particular, this study reveals that aqueous solutions of 1-butyl-3-methylimidazolium methanesulfonate ([BMIM][MeSO3]) are effective for pretreating switchgrass (Panicum virgatum), resulting in fast saccharification of both cellulose and hemicellulose. An integrated analysis afforded by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and cellulase adsorption isotherm of lignocellulose samples is further used to deliver a more complete view of the structural changes attending aqueous IL pretreatment.

Thermal and mechanical properties of chitosan nanocomposites with cellulose modified in ionic liquids

“…Despite the fact that the mechanism of cellulose dissolution with ionic liquid remains disputable, some ionic liquids, favorably imidazole-based, are used to produce nanometric cellulose. Moreover, it was proved that aqueous ionic liquid is as well or even more effective in terms of nanometric cellulose production than dehydrated ones [12,13]. Time and temperature of ionic liquid treatment were also found to be of critical importance [14].…”

Efficient Cleavage of Lignin–Carbohydrate Complexes and Ultrafast Extraction of Lignin Oligomers from Wood Biomass by Microwave‐Assisted Treatment with Deep Eutectic Solvent

“…With these characteristics, DESs have been widely utilized in many fields,33, 34, 35, 36, 37 such as metal processing33 and synthesis media or templates 34, 35. DESs also have effects on delignification and can be used in the extraction of bioactives38, 39 and biomass refinery 40, 41, 42, 43, 44, 45, 46, 47. Francisco et al.…”

Doubly ionic hydrogen bond interactions within the choline chloride–urea deep eutectic solvent

“…There is a large amount of literature relating to the history and evolution of our understanding of H-bonding. 1 The notion that H-bonds, X δ --H δ + ⋅⋅⋅Y δ -, only form when X and Y are highly electronegative 25 elements (e.g. N, O, F, Cl), or that these interactions are exclusively electrostatic in origin, has long been dispelled.…”

“…As such, the number of studies focussing on the applications of DESs is steadily increasing and diversifying, application fields include catalysis, synthesis, novel materials preparation, separations, drug solubilisation, electrodeposition and 20 pretreatment of biomass. 21,25,26 Within DESs H-bonding is of significant importance. For example, the complexed anion is proposed to form via H-bond interactions between the anion and the organic, H-bond donating, complexing agent.…”