Simultaneous production of xylitol and ethanol from cellulosic biomass

Process for the simultaneous production of xylitol and ethanol - Patent 6846657:
1/25/2005
"It has now been found that xylitol and ethanol can be produced simultaneously by using the process of the invention wherein xylose is converted to xylitol, while the majority of the other hexoses present in the raw material are converted to ethanol. Thus the raw material is effectively utilized and two commercially very important products are obtained in a pure form and with a high yield. The process is simple and effective.

The process of the invention is characterized in that the hydrolyzed starting material is fermented with a yeast strain, the ethanol produced is recovered, a chromatographic separation is carried out on the remaining xylitol solution, and pure xylitol is crystallized. Xylose-containing substances are used as starting materials, which in accordance with the invention are fermented with a yeast strain that is capable of converting xylose to xylitol and most hexoses to ethanol. By fermentation, a xylitol-rich solution is obtained wherefrom xylitol is recovered in a simple way. Laborious and complex separation steps (such as the conventional ion exchange, demineralization, precipitations etc.) are not needed, but generally the xylitol can be purified in a single step chromatographically, whereafter it is crystallized to obtain pure xylitol. Ethanol is easy to remove from the fermentation solution for instance by evaporation. Thus the need for separating xylitol from the hexitols and other sugars produced in the hydrolysis and reduction steps is avoided. The hydrolysis performed in accordance with the invention also provides a solution to the problem of using pulp discarded as waste mass, in other processes, and thus in the process of the invention substantially the entire starting material is utilized. "