3222 Chapter 26 



Hemicelluloses are composed of several different polysaccharides (tables 6-3 

 and 6-4). In the pine-site hardwoods the major hemicellulose is an acetylglucur- 

 onoxylan. Hydrolysis of the pine-site hardwood hemicelluloses predominantly 

 yields the pentose sugar xylose. Lesser amount of other constituents will also be 

 released from the hemicelluloses, as follows: arabinose (a pentose sugar); glu- 

 cose, galactose, and mannose (hexose sugars); and glucuronic acid. 



Centrifugation or filtration can also recover an insoluble lignin residue from 

 wood hydrolysis products (Hoyt and Goheen 1971). Called hydrolysis lignin, 

 this material is condensed and contains some unhydrolyzed cellulose residues. 

 Hydrolysis lignin should not be confused with kraft lignin or sulfite lignin, 

 residues from pulping processes (Sarkanen and Ludwig 1971). 



USES FOR HYDROLYSIS PRODUCTS 



The three major products of pine-site hardwood hydrolysis, glucose, xylose, 

 and lignin, potentially can be used in a number of ways. At present, using them 

 to produce ethanol, furfural, and phenol is of much interest (fig. 26-37). 



Ethanol is used as a solvent to manufacture pharmaceuticals and perfume and 

 as an intermediate in organic syntheses. It could be used as a clean burning fuel 

 and can be mixed with gasoline to make gasohol. In the United States, most 

 ethanol is produced by the petrochemical industry from ethylene. 



HARDWOOD 



ACID 

 HYDROLYSIS 



ETHANOL 



FURFURAL 



PHENOL 



Figure 26-37. — Production of ethanol, furfural, and phenol from pine-site hardwoods by 

 hydrolysis. 



Fermentation to produce ethanol is an old, well established process. In one 

 approach that might be taken with a pine-site hardwood hydrolysis mixture, 

 glucose and the other hexose sugars can be selectively fermented to ethanol by 

 saccharomyces yeast; xylose and arabinose are left unchanged, and the xylose 

 can be recovered by crystallization (Herrick and Hergert 1977). 



In the Madison process for obtaining ethanol from wood (fig. 26-38), yield of 

 ethanol ranges from a low of 35 gallons per ton of dry hardwood to a high of 60 

 gallons per ton of softwood; hardwoods have fewer fermentable sugars than 

 softwoods (Baker 1980). 



For economic analyses of ethanol and furfural production from southern 

 hardwoods, see section 28-5 (small-scale), and 28-33 (large-scale). 



The dehydration of pentose sugars such as xylose to furfural is a well known 

 acid-catalyzed reaction that is favored by high temperature and pressure. Current 

 production of furfural in the United States is from pentose-rich residues such as 



