Comparative study of lignin characteristics from wheat straw obtained by soda-AQ and kraft pretreatment and effect on the following enzymatic hydrolysis process. (May 2016) - Yang, Haitao
Graphical abstract: Highlights: Characteristics of lignin after kraft or soda-AQ pretreatment was compared. Quantitative information of different substructures in the lignin was obtained. Lignin was more degraded during kraft pretreatment than soda-AQ pretreatment. More cellulose was converted to glucose in the wheat straw after kraft pretreatment. LCC played a role in the enzymatic hydrolysis of lignocellulosic material. Abstract: To understand the structural changes of lignin after soda-AQ and kraft pretreatment, milled straw lignin, black liquor lignin and residual lignin extracted from wheat straw were characterized by FT-IR, UV, GPC and NMR. The results showed that the main lignin linkages were β -aryl ether substructures ( β -O-4′), followed by phenylcoumaran ( β -5′) and resinol ( β - β ′) substructures, while minor content of spirodienone ( β -1′), dibenzodioxocin (5-5′) and α, β -diaryl ether linkages were detected as well. After pretreatment, most lignin inter-units and lignin-carbohydrate complex (LCC) linkages were degraded and dissolved in black liquor, with minor amount left in residual pretreated biomass. In addition, through quantitative 13 C and 2D-HSQC NMR spectral analysis, lignin and LCC were found to be more degraded after kraft pretreatment than soda-AQ pretreatment. Furthermore, the subsequent enzymatic hydrolysis results showed that more cellulose in wheat straw was converted to glucose after kraft pretreatment, indicating that LCC linkages were important in the enzymatic hydrolysis process.