Sulfur Dioxide-Ethanol-Water Pulping of Hardwoods

The Tennessee Valley Authority (TVA) has developed a two-stage process to separately convert hemicellulose and cellulose to sugars leaving behind a high-lignin solid residue. Research at The University of Alabama has led to a proposed three-stage process utilizing sulfur dioxide to remove hemicellulose, followed by organosolv delignification to remove lignin and the remaining hemicellulose, then acid hydrolysis of the cellulose to glucose. The purpose of the work presented in this paper was to determine whether the sulfonation and delignification steps could be successfully combined. This would result in a simpler process with improved yield of glucose. Pulping of hardwoods in a sulfur dioxide-ethanol-water system has been shown to give a 50 to 52 percent yield of solid residue with a lignin content of approximately 7%.These results offer improvements to the TVA process in several ways. Removal of the lignin from the lignocellulose matrix would allow more efficient acid hydrolysis of cellulose and the use of less severe conditions. Delignification also serves to increase yields from enzymatic hydrolysis. Use of an organosolv to remove lignin prior to condensation reactions from acid hydrolysis would produce a lignin product which is more reactive and has higher commercial potential. The results of this work have shown the feasibility of combining the University process with the TVA process while maintaining a two-stage process.