New Method For Isolation of Lignin-Carbohydrate Complexes From Wheat Straw Alkali Black Liquor

A new method of isolation and fraction of lignin-carbohydrate complexes (LCC) from wheat straw black liquor was established. This new method is involved in the solvent extractions, in which free-lignin and carbohydrates are removed, and the subsequent hollow fiber ultrafiltration, in which is efficiently the removals of sodium salts and low molecular weight substances (<1000) from LCC fraction. Three fractions, precipitated LCC, water-soluble LCC and water-insoluble LCC, were obtained with high yield and purity. About 60-65% of lignin in the black liquor is proposed covalently linked to carbohydrates. The enriched-carbohydrate LCCs accounted for at least 80% of the total contents of LCC in the black liquor while the enriched-lignin LCC accounted for only 20%. LCC consists of about 18% of wheat straw mass and is a quite important composition of wheat straw.