Enhanced ethanol production from enzymatically treated steam-exploded ricestraw using extractive fermentation

Alcohol fermentation of an enzymatic hydrolyzate of exploded rice straw was studied experimentally. Rice straw was treated under variable conditions, such as steam pressure and steaming time. The exploded rice straw was separ ated into water-soluble material, methanol-soluble lignin, Klason lignin, a nd a mixture of cellulose and a low molecular weight substance. The effects of steam explosion on the characteristics of the exploded rice straw were clarified from the point of view of the amounts of extractive components. S team explosion was found to be effective for the delignification of rice st raw and for increasing its susceptibility to enzyme hydrolysis and alcohol fermentation. The polysaccharides (cellulose and hemicellulose) in the rice straw treated at a steam pressure of 3.5 MPa with a steaming time of 2 min were hydrolyzed almost completely into monosaccharides, (ie glucose and xy lose) by a mixture of Trichoderma viride cellulase (Meicelase) and Aspergil lus aculeatus cellulase (Acucelase). The enzymatic hydrolyzate of exploded rice straw was converted into ethanol efficiently by Pichia stipitis and th e ethanol yield from sugar was about 86%(w/w) of the theoretical value. The ethanol concentration in a membrane bioreactor coupled with a pervaporatio n system reached 50 gdm(-3) and was about five times higher than that in th e culture broth. The energy efficiency (ratio of combustion energy of ethan ol produced to energy for steam explosion) reached a maximum value at a pre ssure of 3.5 MPa for 2 min. (C) 2001 Society of Chemical Industry.