Energy, fuels, and chemicals 5111 



A typical example of a concentrated-acid process is the Rheinau-Bergius 

 process which was used by Germany in World War II to produce yeast from 

 hydrolyzed sugars. In stage one, fuming hydrochloric acid (up to 41 percent) is 

 used to degrade cellulose mostly to lower oligomers at ambient temperatures. In 

 the second stage, the acid is diluted with water and heated to yield monomeric 

 sugars. In the Rheinau-Udic process, a modification of the earlier procedure, 

 prehydrolysis is carried out with a 32 percent acid solution and the main hydroly- 

 sis uses 41 percent hydrochloric acid. The hydrochloric acid is recovered by 

 vacuum distillation. The hydrolyzate is post-hydrolyzed, filtered, decolorized, 

 and passed through an ion-exchange column, before cyrstallization of the glu- 

 cose. Reportedly, 22 kg of crystalline glucose can be obtained per 100 kg of 

 wood (Wenzl 1970). See section 28-33 and figures 28-45 and 28-46 for an 

 economic analysis of a concentrated-acid process. 



The use of hydrogen chloride gas, rather than concentrated hydrochloric acid, 

 is the basis of several proposed processes (Titchener 1976). In the Japanese 

 Noguchi-Chisso process, wood is first prehydrolyzed to remove hemicellu- 

 loses. The residue is heated with a 5 percent hydrochloric acid solution and 

 cooled. Gaseous hydrogen chloride is then administered; the temperature is kept 

 below 10°C. Next, the temperature is raised to 40°C for hydrolysis to lower 

 oligomers. The hydrogen chloride is recovered by blowing hot air through the 

 hydrolyzate. Post-hydrolysis at 100°C with 3 percent hydrochloric acid yields 

 glucose. In this step, acid is removed by vacuum distillation. The advantages of 

 this system are the simplicity of acid recovery, fewer corrosion problems, and 

 more highly concentrated sugar solutions. 



In the Hokkaido process, first prehydrolysis is carried out with steam or 

 dilute sulfuric acid at temperatures up to 185°C. A furfural yield of 65 to 75 kg 

 per ton of dry wood is obtained from dehydration of the pentose in the reactor. 

 The prehydrolysis residue is then dried, powdered, and treated with 80 percent 

 sulfuric acid for about 30 seconds. The reaction mixture is immediately washed 

 with water and filtered. Acid is recovered by use of ion-exchange resins. The 

 hydrolyzate, which still contains dilute sulfuric acid, is post-hydrolyzed by 

 heating at 100°C. Yield of crystalline glucose is about 280-290 kg/metric ton of 

 dry wood (Bliss and Blake 1977). 



A recently developed technique that employs anhydrous hydrogen fluoride 

 splits cellulose rapidly at 0°C with high yields (Chemical and Engineering News 

 1982). 



ENZYMATIC HYDROLYSIS IN NATURE 



The ligno-cellulosic matrix which comprises wood presents a formidable 

 barrier to most enzyme systems. For example, anaerobic bacterial production of 

 methane from slurried wood and bark (visualize marsh gas formation) is slow, 

 and yields are low. Wood degradation by white and brown rotting fungi is also 

 slow and selective. 



Even termites are selective in their eating habits (table 11-6), do not eat all the 

 wood and bark, and metabolize only part of what they do eat. The termite system 



