The optimization of dilute acid hydrolysis of cotton stalk in xylose production.

Cotton stalk, a lignocellulosic waste material, is composed of xylose that can be used as a raw material for production of xylitol, a high-value product. There is a growing interest in the use of lignocellulosic wastes for conversion into various chemicals because of their low cost and the fact that they are renewable and abundant. The objective of the study was to determine the effects of H(2)SO(4) concentration, temperature, and reaction time on the production of sugars (xylose, glucose, and arabinose) and on the reaction by-products (furfural and acetic acid). Response surface methodology was used to optimize the hydrolysis process in order to obtain high xylose yield and selectivity. The optimum reaction temperature, reaction time, and acid concentration were 140 °C, 15 min, and 6%, respectively. Under these conditions, xylose yield and selectivity were found to be 47.88% and 2.26 g g(-1), respectively.

Production of xylooligosaccharides by controlled acid hydrolysis of lignocellulosic materials.

Different agricultural wastes, namely tobacco stalk (TS), cotton stalk (CS), sunflower stalk (SS), and wheat straw (WS), were used for the production of xylooligosaccharide (XO). XO production was performed by acid hydrolysis of xylan, which was obtained by alkali extraction from these agricultural wastes. The major component of these agricultural wastes was determined as cellulose (30-42%), followed by xylan (20%) and lignin (20-27%). Xylans from these wastes had mainly xylose (85-96%) with small amount of glucose, while wheat straw xylan contained also arabinose. The best xylan conversion into XOs was achieved with 0.25M H(2)SO(4) with 30-min reaction time. Under these conditions, the XO yield was between 8% and 13%. The yield of XOs depends on both acid concentration and hydrolysis time, but the yield of monosaccharide depends on the structure and composition of xylan besides acid concentration and the time. The more branched xylan, WSX, gave the highest monosaccharide ( approximately 16%) and furfural ( approximately 49mg/100g xylan) yield. This research showed that all xylans from selected agricultural wastes generated XOs with similar profiles, and these oligosaccharides could be used as functional food ingredients or soluble substrates for xylanases.