Ethanol production by fermentation of pentoses and hexoses from cellulosic materials

The search for renewable raw materials to replace fossile fuel has directed research towards the utilization of various cellulosic materials. Cellulosic plant materials consist of three main components: cellulose, hemicellulose, and lignin. In order to develop an economically feasible process, it is necessary to utilize all these materials. Cellulose and hemicellulose can be decomposed either by enzymatic or acid hydrolysis to yield sugars. In the case of both hardwoods and annual plants the main part of the hemicellulose consists of pentosans yielding xylose on hydrolysis (Table 1). The hydrolysate thus contains mainly glucose and xylose which must be fermented to ethanol in order to obtain a combustible motor fuel. Glucose can easily be fermented by conventional yeasts or by some bacteria, e.g., Zymo-monas, but xylose presents a more difficult problem. Recently, there has been much interest in this field and the results are promising although no commercial process is available as of yet.