Two-step Conversion of Acetic Acid to Bioethanol by Ethyl Esterification and Catalytic Hydrogenolysis

A two-step conversion of acetic acid to ethanol was discussed by ethyl esterification followed by catalytic hydrogenolysis for highly efficient bioethanol production from lignocellulose via acetic acid fermentation. Non-catalytic supercritical ethanol treatment was demonstrated for the esterification of acetic acid, and an appropriate condition was found to be 270 degrees C/20 MPa for ethyl acetate production. Because of the autocatalytic effect of acetic acid, a low ethanol ratio favored a fast reaction rate but diminished the ethyl acetate yield due to the reverse reaction. Therefore, it seems better to employ a water removal method during the esterification reaction for efficient conversion of acetic acid to ethyl acetate with minimal ethanol. For the hydrogenolysis of ethyl acetate, catalytic activities of several Cu-type catalysts were evaluated with a flow-type reactor. The Cu-Zn catalyst was more effective than other Cu-Cr-type ones in the temperature range of 210-270 degrees C, where only small amounts of methane and ethane (0.89 wt% at 270 degrees C upon the fed methyl acetate) were formed as by-products along with ethanol. These findings will help us to design an efficient bioethanol production process from acetic acid by the proposed two-step method.