Advanced Ethanol Production with Acetic Acid Fermentation from Lignocellulosics

A novel process of bioethanol production from lignocellulosics was developed by acetic acid fermentation followed by hydrogenolysis of acetic acid to ethanol. This process includes a two-step hot-compressed water treatment of lignocellulosics to C6 and C5 sugars, decomposed products and lignin-derived compounds. In the subsequent fermentation, most of these products are to be anaerobically fermented into acetic acid in form of sodium acetate by free and/or immobilized co-culturing system (Clostridium thermocellum and C. thennoaceticum) by batch or fed-batch fermenter with pH controlled by NaOH or Ca(OH)(2) to be 6.5-7.0. The obtained acetate aqueous solution was then converted and concentrated into acetic acid up to 200 g/L by bipolar membrane electrodialysis. The acetic acid was then converted to bioethanol without emitting CO2 via hydrogenolysis with Lewis acid-supported catalyst (Ru-Sn/TiO2). To evaluate a potential of this process, it was compared with the conventional alcoholic fermentation process, and found that, although conventional process can produce only 200-300 L bioethanol from one dried ton of Japanese cedar, this process can produce double in amount. In addition, energy recovery is higher than the conventional process, with CO2 emission unit (kg/GJ) being lower. Consequently, this process can be promising to reduce CO2 so as to mitigate environmental loading.