Production of oligosaccharides and sugars from rye straw: a kinetic approach

Following the biorefinery philosophy, the non-isothermal autohydrolysis of rye straw (an agroindustrial byproduct) was carried out to obtain liquors containing substituted xylooligosaccharides and solids enriched in cellulose (suitable as substrates for further enzymatic hydrolysis). The effects of temperature (in the range 185-220 degrees C) on the composition of solids and liquid phases were evaluated, and kinetic models were developed. When operation was carried out at 208 degrees C, 69.2% of the initial xylan was converted into xylooligosaccharides, leading to reaction liquors containing up to 22.4 g oligosaccharides/L. The effects of treatments on the DP of the target products and on their substituents were also measured. At 208 degrees C, the percentages of XOS having DP2-4, DP5-6 and DP>6 were 24.8%, 22.4% and 54.8%, respectively. Under selected conditions, the molar ratio Xyl:Ac:UA of the oligomers was 10:1.54:0.50. Finally, when the solid was subjected to enzymatic hydrolysis, 70.6% of cellulose and 63.8% of xylan were saccharified after 48 h.