Ethyl xylosides formation in SEW (AVAP®) fractionation of sugarcane straw; implications for ethanol and xylose recovery.

High solvent recovery and monomeric sugar yield are essential for a viable biochemical conversion technology. The SO2-ethanol-water (SEW) or AVAP® process has great potential to produce easily fermentable pulp fibers and sugars dissolved in the spent liquor stream. The SEW fractionation process is evaluated for delignification, xylan removal and potential reactions between ethanol and sugarcane straw (SCS) carbohydrates. α-ethyl-xyloside (aEX) and β-ethyl-xyloside (bEX) formed by reaction of ethanol with xylose are quantified. The fractionation experiments are carried out at 135°C, 145°C, and 155°C for 20-120 min at fixed liquor composition (SO2/EtOH/H2O = 12:44:44, w/w) and liquor to feedstock ratio (4 l kg-1). The results are interpreted in terms of combined severity factor (CSF). Maximum ethyl xylosides (EX, or sum of aEX and bEX) and monomeric xylose concentrations are observed at CSF of 2.4 ± 0.1. The maximum amount of EX in spent liquor accounts for nearly 1.4% of EtOH (feedstock basis). The implications for downstream recovery of EtOH and sugars from the spent liquor are discussed. [ABSTRACT FROM AUTHOR]