Enzymatic separation and purification of saccharides from wheat straw machine pulp black liquor

Abstract

In recent years, the concept of biomass refining has opened up a new way for the efficient utilization of biomass resources, and the application prospect of biomass conversion into high value-added products is very broad. With the development of biomass refining technology for pulping and paper making, the high value utilization of hemicellulose in black liquor has attracted extensive attention. In the process of using hemicellulose in black liquor to produce high value-added products, lignin and furfural in black liquor will hinder its utilization. In order to realize the separation, purification and high value utilization of sugar substances in black liquor, this paper takes wheat straw machine pulping black liquor as the research object, using calcium hydroxide, resin, activated carbon and laccase to purify the black liquor, while removing lignin and other impurities, as far as possible to reduce the loss of xylose. Then, xylanase was used for hydrolysis and directed degradation of black liquor to produce xylo-oligosaccharide, in order to provide a certain theoretical basis and technical support for the high-value utilization of black liquor. Firstly, calcium hydroxide combined with ion exchange resin was used to treat wheat straw machine pulp black liquor to remove impurities such as lignin and furfural. The effects of calcium hydroxide and resin dosage on each component of black liquor were investigated. The results showed that calcium hydroxide and resin treatment could effectively remove impurities such as lignin, furfural and 5-HMF in black liquor. The optimal dosage of calcium hydroxide was 0.6 wt%, and the removal rates of lignin, furfural and 5-HMF in black liquor were 27.53%, 40.23% and 31.56%, respectively, and the loss rate of xylose was 7.26%. On the basis of D301 resin treatment, 67.85% of the lignin was removed. Then laccase combined with xylanase was used to treat the purified black liquor to improve the removal rate of lignin and prepare xylo-oligosaccharide by enzymolysis. Finally, the black liquor was further purified by activated carbon adsorption. When the laccase dosage was 2 U/g, the xylanase dosage was 2 U/g, the temperature was 50℃, the pH5.5 and the time was 4 h, the lignin removal rate was increased by 19.62%, and the xylooligosaccharide content was increased by 52.25%. The optimal condition was 0.4wt % activated carbon, and the lignin removal rate was 20.07% and the loss rate of xylose was 6.45%.