Kinetic analysis for the isomerization of cellobiose to cellobiulose in subcritical aqueous ethanol

The isomerization of cellobiose to cellobiulose, and other degradation reactions of cellobiose were investigated in subcritical aqueous ethanol with concentrations of ethanol ranging from 0 to 60% (w/w) and at temperatures ranging from 170 to 200 °C. The maximum yield of cellobiulose (ca. 40%) was obtained from the treatment of cellobiose in 60% (w/w) aqueous ethanol at 190 °C. Glucose and fructose were also detected as byproducts. The concentration-time integral method was employed to analyze the rate constants for the isomerization and degradation processes. The rate constant of cellobiose isomerization to cellobiulose was greater than those of the degradation reactions under all experimental conditions, and it increased significantly with treatment temperature and ethanol concentration. However, the use of higher temperatures and ethanol concentrations was restricted due to decomposition of the saccharides and the low solubility of cellobiose, respectively. The effect of initial feed concentration (0.5–5.5% w/w) was also studied. The maximum productivity of cellobiulose, 54.1 kg/(h m3-reactor), was accomplished at a feed concentration of 5.5% (w/w) in 20% (w/w) subcritical aqueous ethanol. [Display omitted] •The isomerization of cellobiose was promoted by increasing temperature and ethanol concentration.•Increasing in a higher range of temperature and ethanol concentration were limited by the decomposition and solubility.