A COMPARATIVE STUDY OF LOW-MOLECULAR-WEIGHT PRODUCTS EXTRACTED FROM WHEAT STRAW USING ETHANOL AND DIMETHYL CARBONATE

Abstract

Supercritical extraction is a promising method for the preparation of lignocellulosic raw material for subse-quent biochemical processing. This paper presents a comparative analysis of low-molecular-weight prod-ucts extracted from wheat straw in a batch-type autoclave at a temperature of 285С for 10 min. Ethanol and dimethyl carbonate were used as solvents, since these compounds are known to be similar in terms of their dissolution ability but different in terms of their alkylating properties. It is found that wheat straw ex-traction using dimethyl carbonate demonstrates a high level of efficiency. Compared to ethanolysis, a greater extract yield characterized by a high content of hexanol-soluble compounds was obtained. These compounds predominantly included methyl esters of carboxylic acids. On the other hand, lignin fragmentation products were dominated by veratrous-type compounds. A mechanism is proposed for obtaining low-molecular lignin fragmentation products under the conditions of supercritical extraction, which is based on the processes of a radical cleavage of alkyl aryl ester bonds and C-C bonds in the side radical, as well as on the reactions of dehydration, esterification and re-esterification. When this mechanism is applied under the conditions of supercritical ethanolysis, it additionally involves the reactions of hydrogenation and keto-enol rearrangement with the formation of ketones.