Epilogue

Abstract

Numerous and complex factors need be taken into account in economically assessing processes for hydrolytic utilization of cellulose. Cellulose hydrolysis must compete with hydrolysis of starch from grain crops. While lignocellulosic residues are abundant, their distributions are diffused; the availability of commercially viable collection systems for them is limited. Of all crops, corn is a primary source of starch because its supply is ample, its cost is relatively low, and commerically viable systems are on hand for storing and transporting it over long distances. Cellulosic biomass, approximately at US $ 30 per dry ton currently, is far cheaper than corn approximately at US $ 100 per dry ton. Nevertheless, it is very difficult for most naturally occurring organisms to hydrolyze cellulose due to the inaccessible nature of cellulose crystallites. Consequently, a tradeoff exists between the low raw material cost and high investment cost for cellulose hydrolysis. To enhance hydrolyzability, a cellulosic biomass need be subjected to a variety of pretreat-ments; however, this increases the cost of processing.