Production of ethanol from lignocellulosic materials

In the bioconversion of lignocellulosic materials to ethanol, the cost of the raw material and the cost of the enzymes have been identified as the major costs for the product. In addition, many lignocellulosic materials contain considerable amounts of five-carbon sugars which are not easily fermented to ethanol. The possibility of improving the cost-intensive steps was investigated.

The steam pre-treatment of a fast-growing species of Salix (Q082) was optimized with respect to treatment time and temperature, to give the best glucose yield after enzymatic hydrolysis. It was found that the semi-continuous production of cellulolytic enzymes with Trichoderem reesei Rutgers C30 in an aqueous two-phase system (an extractive fermentation system) increased the amount of recoverable enzyme activity compared with a batch process. It was also found that the enzyme consumption in the hydrolysis of cellulolytic materials, in filter paper units (FPU) g−1 reducing sugars (RS), could be considerably reduced by recirculating the cellulolytic enzymes in an aqueous two-phase system combined with an ultra-filtration unit. For the fermentation of pentoses, it was found that the combination of the commercial enzyme glucose isomerase and regular bakers' yeast, Saccharomyces cerevisiae, was superior to xylose fermenting yeasts. Yields and productivities comparable to those obtained in hexose fermentation could be achieved.