3224 Chapter 26 



molded products and adhesives that are used in automobile and appliance 

 manufacture. 



Today, nearly all phenol is made from cummene, a petrochemical, but var- 

 ious hydrogenolysis techniques also can produce phenols from lignin. Re- 

 portedly, yields in the neighborhood of 40 percent of monomeric phenol 

 derivatives have been obtained in pilot-plant experiments (National Research 

 Council 1976). However, hydrodealkylation of the mixture of phenol deriva- 

 tives to a high yield of phenol is not a proven process. 



Other potential uses for the hydrolysis products of pine site hardwoods in- 

 clude the production of Torula yeast, a protein supplement (Herrick and Hergert 

 1977). Unlike fermentation to ethanol, which utilizes only the hexose sugars, 

 both hexose and pentose sugars, certain sugar acids, and carbohydrate fragments 

 can be used to grow the yeast. A reagent such as Raney Nickel or a hydrogena- 

 tion catalyst can reduce xylose and glucose to xylitol and sorbitol, their corre- 

 sponding sugar alcohols. Hydrolysis lignin can be used as a soil conditioner, 

 filler for resins and rubber, depressant in ore floatation, decay-retardant in 

 fabrics, a binding agent for particle and hardboard, and a grinding aid for 

 Portland cement (Hoyt and Goheen 1971). In the Soviet Union, much of the 

 hydrolysis lignin is burned as fuel. However, the high moisture content must be 

 removed first. In one process, the lignin is dried to 12-18 percent moisture 

 content with hot flue gases and then pressed into briquettes. It has also been 

 suggested that hydrolysis lignin be used as a source of activated carbon (National 

 Research Council 1976). 



WOOD HYDROLYSIS PROCESSES 



Hemicelluloses are readily hydrolyzable under mild acidic conditions; cellu- 

 lose, on the other hand, is much more difficult to hydrolyze because of its 

 crystalline organization and stable structure. Efficient production of sugars from 

 whole-wood hydrolysis must take into account this difference or a competing 

 reaction in which sugars are destroyed can occur (Harris 1975). 



There are a number of potential wood hydrolysis processes (Oshima 1965, 

 Wenzl 1970, Titchener 1976; Bliss and Blake 1977, Karlivan 1980). The proc- 

 esses use hydrochloric acid, sulfuric acid, or enzymes (table 26-14). The acid- 

 catalyzed processes can be further divided into those using dilute or concentrated 

 acids. Hyrolysis with dilute acids is carried out in a single stage at elevated 

 temperature and pressure. Concentrated-acid processes are generally conducted 

 in two stages, a prehydrolysis and a main hydrolysis stage that is kept near 

 ambient temperature. 



Dilute acid processes are typified by the Scholler-Tornesh process which 

 uses 0.5 percent sulfuric acid to complete hydrolysis in one stage at elevated 

 temperature and pressure. Dilute acid is percolated through wood chips or 

 sawdust followed by a charge of steam. The short hydrolysis time does not 

 completely hydrolyze the cellulose, so the acid-steam percolation is repeated up 

 to 12 times. The dilute sulfuric acid in the hydrolyzate is neutralized by calcium 

 carbonate to form calcium sulfate (CaS04) which is removed by filtration. The 



