Cellulose Pretreatments: Technology and Techniques

The lignocellulosic materials represent the largest reservoir of potentially fermentable carbohydrates on earth. It is estimated that approximately 50 billion tons of cellulose and hemicelluloses are produced annually worldwide by photosynthesis. This renewable resource provides us with fuel, feed and fiber and could become the basis of a much larger fermentation industry if a number of technical problems were solved. A major obstacle to increased lignocellulose utilization is the chemically unreactive nature of cellulose, particularly its resistance to hydrolysis. To this end, a number of pretreatments have been devised to increase the yields of hydrolysis sugars from cellulose. While a few of these pretreatments have been developed to the point where they can be called technologies, most are still at the stage of laboratory techniques, hence the title of this review. Unfortunately, many of the pretreatment methods summarized here have not been studied or reported in such a way as to permit valid comparisons between different pretreatments. This review is therefore not as conclusive as was hoped when this work was begun. We suggest some possible standards for performing and reporting pretreatment research at the end of the review.