Application of Biological Enzymes in Purification of Sulfate Lignin from Broad leaved Wood

Abstract

Sulfate pulping is a chemical pulping method that uses alkaline solution to cook plant fiber raw materials, and the black liquor produced by this method contains a large amount of organic compounds such as lignin and sugars. Lignin is a renewable natural polymer compound with great development and utilization value. Black liquor has a complex composition, in which lignin will combine with various organic compounds through chemical bonds or other forces, which is not conducive to its further modification and utilization. Therefore, how to maximize the purity of lignin is of great significance for lignin development research. In this project, one of the lignin purification methods, enzymatic hydrolysis, was mainly investigated, using biological enzymes to hydrolyze off the sugars connected to lignin, together with H+ to efficiently break the LCC bond on the lignin structure, thus improving its purity, and analyzing and comparing the purification effect of this method with that of the traditional acid precipitation method from different perspectives, to prove its applicability. The main purpose of this project is to compare the advantages and disadvantages of different treatments for the purification of lignin by exploring the optimal conditions and dosage of alkali-resistant cellulase and xylanase, and by applying the characterization means of ion chromatography for the determination of sugar content, Fourier infrared spectroscopy for the determination of the change of functional groups, permeation gel chromatography for the determination of molecular weight size, and UV spectrophotometry for the determination of UV absorbance strength and weakness. The results showed that the cellulase dosage of 100 U/L and the reaction at pH=9 and 45 ℃ for 80 min was optimal, and the xylanase dosage of 100 U/L and the reaction at pH=9 and 40 ℃ for 100 min was the best; moreover, it was found that the biological enzyme could better destroy the structure of LCC after characterization, and the carbohydrates therein were degraded into monosaccharides, such as xylose, which greatly improved the purity of lignin; the purity of lignin obtained from the purification of black liquor using cellulase and xylanase was approximate, 93.8% and 92.9%, respectively, which were higher than that of 86.6% in the traditional acid precipitation method.