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Acidic anions of ionic liquids have been demonstrated as efficient catalysts for the cleavage of the β-O-4 ether linkage prevalent in the lignin superstructure. Through the use of lignin model compounds with varying functionality and by monitoring reaction kinetics, a full mechanistic investigation into the hydrolysis of the β-O-4 linkage in acidic ionic liquid solutions is reported. Hammett acidities are reported for different 1-butyl-3-methylimidazolium hydrogen sulfate [C4C1im][HSO4] ionic liquid systems with varying acid and water concentrations and were correlated to substrate reactivity. Results show that the rate of ether cleavage increases with an increase in acidity and the initial dehydration of the model compound is the rate-determining step of the reaction. The Eyring activation parameters of the reaction in hydrogen sulfate ionic liquids with a variety of cations are reported, indicating a consistent E1 dehydration mechanism. Hydrogen bonding in protic ionic liquids was shown to significantly influence anion–cation interactions, consequently altering the solvation of the protonated starting material and therefore the overall rate of reaction. Comparison of reaction rates in these ionic liquids with results within aqueous or aqueous/organic media indicate that the ionic liquids facilitate more rapid cleavage of the β-O-4 ether linkage even under less acidic conditions. All the reported results give a complete overview of both the mechanistic and solvation effects of acidic ionic liquids on lignin model compounds and provide scope for the appropriate selection and design of ionic liquids for lignin processing. [ABSTRACT FROM AUTHOR]

Ionic liquids are of great interest as potential solvents/catalysts for the production of fuels and chemicals from lignocellulosic biomass. Attention has focused particularly on the pretreatment of lignocellulose to make the cellulose more accessible to enzymatic hydrolysis. Any biomass processing requires a reduction in the size of the harvested biomass by chipping and/or grinding to make it more amenable to chemical and biological treatments. This paper demonstrates that significant energy savings can be achieved in the grinding of pine wood chips when the ionic liquid is added before the grinding operation. We show that this is due to the lubricating properties of the ionic liquids and not to physico-chemical modifications of the biomass. A brief impregnation of the chipped biomass results in higher savings than a longer treatment. [ABSTRACT FROM AUTHOR]

Ground lignocellulosic biomass (Miscanthus giganteus, pine (Pinus sylvestris) and willow (Salix viminalis)) was pretreated with ionic liquid–water mixtures of 1-butyl-3-methylimidazolium methyl sulfate and 1-butyl-3-methylimidazolium hydrogen sulfate. A solid fraction enriched in cellulose was recovered, which was subjected to enzymatic hydrolysis. Up to 90% of the glucose and 25% of the hemicellulose contained in the original biomass were released by the combined ionic liquid pretreatment and the enzymatic hydrolysis. After the pretreatment, the ionic liquid liquor contained the majority of the lignin and the hemicellulose. The lignin portion was partially precipitated from the liquor upon dilution with water. The amount of hemicellulose monomers in the ionic liquid liquor and their conversion into furfurals was also examined. The performance of ionic liquid–water mixtures containing 1,3-dialkylimidazolium ionic liquids with acetate, methanesulfonate, trifluoromethanesulfonate and chloride anions was investigated. The applicability of the ionic liquid 1-butylimidazolium hydrogensulfate for lignocellulose pretreatment was also examined. It was found that ionic liquid liquors containing methyl sulfate, hydrogen sulfate and methanesulfonate anions were most effective in terms of lignin/cellulose fractionation and enhancement of cellulose digestibility. [ABSTRACT FROM AUTHOR]