The conversion of biomass to ethanol has become a new focus of interest, due to increasing costs of petrol refinery. Pure ethanol may be used as additive for fuel motors, blends from 3 - 85% are feasible. However, in conventional processes, the final purification step of ethanol (99.9%) from aqueous low concentrated fermentation sludge requires sophisticated distillation steps including membranes /molecular sieving technologies and others. Consequently, few bio-ethanol production technologies (Arkenol [1] and BCI/ Organosolv [2]) are industrially applicable. One of the main drawbacks was the need of organic acids for the catalysed hydrolysis of the cellulose/hemicellulose chains to the intermediate sugar molecules (glucose, xylose). Up to the recent times, this process was not competitive with petrol-based processes, except in some regions with unique rural conditions [3]. Process alternatives, based on the enzyme catalyzed conversion have been intensively investigated during the past decades (BPI /Logen[4]). A process configuration of this type consists of at least four major steps: pre-treatment of raw material, including chip size reduction, sieving, (enzymatic) hydrolysis of hemicelluloses and cellulose; fermentation using a suitable yeast strain; and ethanol refining. One of the most studied alternative methods for cellulose/ hemi-cellulose hydrolysis is the hot water pre-treatment [5]. In the temperature range above 100°C and at pressure conditions above the temperature-affiliated vapour pressure, the hemicellulose is hydrolysed and the cellulose is made more accessible to biological attack. In the next step, cellulose may be hydrolysed by means of adapted enzymes (cellulase). Due to its low lignin content compared to other biological waste products, milled and defatted rice bran (27% cellulose, 37% hemicellulose, 5% lignin) is an interesting representative of the group of lignocellulose biomass. Rice bran production is in the range of 40 megatons/year [6], defatted rice bran is mainly used as nutritional additive for cattle feed. The super-critical extraction of rice bran and the purification of the high value compounds of the extracted rice bran oil is not scope of this work, we refer to Danielski et al. [7], as well as the poster communication in this meeting.
展开▼
