Reflecting the shortages of petroleum with rising prices and of foods in relation to world population growth, an increasing attention has been paid to the potential uses of lignocellulosic materials for chemicals, foods, and fuels in the future.
Steam explosion is one of the effective pretreatment for enhancing the enzymatic susceptibility of hardwoods and for fractionating the components, hemicellulose, lignin, and cellulose leading to total utilization of wood components. Depending on starting material, 10-20% hemicellulose with contents of xylose residue up to 80% can be recovered as mono-and oligosaccharides by extraction of the steam-exloded fiber materials with water. These fragments are good substrates for chemical, biochemical, or microbial processes. The purified fragments mainly consisting of xylose and xylooligosaccharides can be used as food additives as it is and/or after hydrogenation. Xylose and xylitol can also be produced from the extracts. About two thirds of the original lignin can be isolated from the residual fiber material by subsequent extraction with dilute alkali and/or organic solvents. The lignins are quite reactive and can be used as chemical feedstocks. The lignins are converterd to carbon fibers or adhesives by modification with phenolysis. The residual fiber material containig 10-20% lignin is hydrolysed with cellulose giving glucose which is fermented to alkohol or single cell protein. As the cellulose of steam-exploded fiber materials is susceptible to enzymatic hydrolysis in spite of the presence of lignin, the fiber material can be used as roughage for ruminants.
Numerous invesitigators have examined the process for total utilization of wood components by steam explosion pretreatment. This paper intends to summarize these recent studies.