3226 



Chapter 26 



yield of sugar on a weight basis is around 40-50 percent for softwoods (Titchener 

 1976; Bliss and Blake 1977). 



The Madison process is a continuous-flow variation of the Scholler-Tornesh 

 process. A continuous flow of reagent removes the hydrolyzate to a cool zone to 

 reduce sugar degradation. Total saccharification time is about one-fourth of that 

 required in the Scholler-Tornesh process, thus lowering the production cost. 

 Hardwoods yield about 35 percent fermentable sugars and 20 percent pentoses 

 on a weight basis (Titchener 1976; Herrick and Hergert 1977). 



In the NYU process (fig. 26-39) sawdust is fed into the barrel of a twin-screw 

 plastics extruder (fig. 18-280a). In the barrel the sawdust is heated to about 

 230°C and water is removed. As the water is removed, the material becomes 

 very dense, forming a plug that allows pressures of about 500 psi to be generated 

 in the forward sections of the barrel. As the screws convey the material toward 

 the front of the barrel, their shearing action breaks up the sawdust particles 

 making the cellulose more accessible to the chemical reaction that will convert it 

 to glucose. Just before the material is expelled from the extruder barrel, a weak 

 solution (1 .0 to 1.5 percent) of sulfuric acid is injected into it. Contact times in 

 this continuous hydrolysis method are short, e.g., 5 to 25 seconds. Output of the 

 extruder is a mud-like material containing glucose, unconverted cellulose, de- 

 composition products from the hemicellulose fraction, and degraded lignin. 

 After separation, a liquor containing 8 to 10 percent glucose is available for 

 fermentation to ethanol. Pilot-plant work has achieved 50 to 55 percent conver- 

 sion of cellulose to glucose, but the process developers feel that 80 to 90 percent 

 conversion will be possible ultimately (Chemical Engineering 1981). 



CELLULOSIC MATERIAL 

 (SHREDDED PAPER, SAWDUST, ETC.) 



SCREW FEEDER 



SULFURIC ACID 

 SOLUTION 



STEAM SUPPLY 



TWIN SCREW EXTRUDER 



PRESSURE INDICATOR 



Figure 26-39. — NYU process for converting cellulose in lignocellulosic material to glu- 

 cose. (Drawing after Chemical Engineering 1981.) 



