Hydrothermal combined alkali pretreatment for fractionation the xylan from cotton stalk

Hydrothermal combined alkaline method was conducted to improve the yield of xylan from cotton stalk in this study. The extraction process was optimized by single factor and orthogonal experiments. The maximum yield of recovered xylan was 67.75 ± 0.27% obtaining from hydrothermal extraction of 170 ºC, 60 min, 1:10 and alkaline extraction with 4% alkali at 65 ºC for 2 h with S/L of 1:10. The physic-chemical properties of water-soluble xylan (Xwater) and alkali-soluble xylan (Xalkali) were determined by Fourier transform infrared spectroscopy, Gel permeation chromatography, thermogravimetric analysis and 2D nuclear magnetic resonance (2D NMR). The observed xylan was composed of (1→4)-β-d-xylp as main chain, β-glycosidic bond, and 4-O-methyl-α-D-glucuronic acid as branch chain. Xalkali also contains α-L-arabinose side chains. And the molecular weight of Xalkali was higher than that of Xwater, indicating that alkali pretreatment had a positive protective effect on xylan structure compared with hydrothermal pretreatment. The proposed combined pretreatment method has established a reliable xylan separation method, which has high industrial application feasibility.