Celluloses degradation

Solution Process. With the exception of fibrous triacetate, practically all cellulose acetate is manufactured by a solution process using sulfuric acid catalyst with acetic anhydride in an acetic acid solvent. An excellent description of this process is given (85). In the process (Fig. 8), cellulose (ca 400 kg) is treated with ca 1200 kg acetic anhydride in 1600 kg acetic acid solvent and 28—40 kg sulfuric acid (7—10% based on cellulose) as catalyst. During the exothermic reaction, the temperature is controlled at 40—45°C to minimize cellulose degradation. After the reaction solution becomes clear and fiber-free and the desired viscosity has been achieved, sufficient aqueous acetic acid (60—70% acid) is added to destroy the excess anhydride and provide 10—15% free water for hydrolysis. At this point, the sulfuric acid catalyst may be partially neutralized with calcium, magnesium, or sodium salts for better control of product molecular weight. 

An example of cellulose degradation initiated by hydrogen ions and water is shown below (Scheme 4). 

Recently, we have shown that non-isothermal chemiluminescence measurements for oxidized cellulose provide the same rate constants of cellulose degradation as may be measured from experiments on the decay of polymerization degree determined by viscometry. This may be also taken as indirect evidence that the light emission is somehow linked with the scission of polymer chains [29]. 

Most often, the rates for feedstock destruction in anaerobic digestion systems are based upon biogas production or reduction of total solids (TS) or volatile solids (VS) added to the system. Available data for analyses conducted on the specific polymers in the anaerobic digester feed are summarized in Table II. The information indicates a rapid rate of hydrolysis for hemicellulose and lipids. The rates and extent of cellulose degradation vary dramatically and are different with respect to the MSW feedstock based on the source and processing of the paper and cardboard products (42). Rates for protein hydrolysis are particularly difficult to accurately determine due the biotransformation of feed protein into microbial biomass, which is representative of protein in the effluent of the anaerobic digestion system. 

The titers of cellulase activities found in anaerobic digesters, when compared to the few other "hydrolytic environments" for which analytical data are available, are strikingly low. Table III shows such values for filter paper and carboxymethyl cellulose degrading activities. This evidence seems to indicate that the cellulose degrading enzymes in ... 

Figure 2. Comparisons of cellulose degradation of the MSW feedstock with specific cellulase enzyme activities in sludge from 7 CSTR digesters operated under different retention times and various conditions of nutrient limitation.

RunUnococcus albus and Ruminococcus flavefadens. These bacteria are important cellulose-degraders found in the rumen of cattle and sheep (2). Most isolated strains ferment cellulose and xylan and all ferment cellobiose. Fermentation of glucose and some other carbohydrates depends on the particular strain. R flavefadens and B. succinogenes can ferment the highly ordered crystalline cellulosic su trates but R albus cannot. No evidence has been found for extracellular cellulase production by R albus, but Ohmiya et al. purified cellobiosidase from this culture 17). Laboratory growth of R albus has been conducted at pH 7.0 and 37 C. 

Lamed, R. Bayer, E.A. In Biochemistry and Genetics of Cellulose Degradation Academic Press New York, NY, 1988 pp 101-106. 

Biely, P. Defaye, J. Abstracts FEMS Symp. Biochemistry and Genetics of Cellulose Degradation, Paris, 1987 p 98. 

In an inciteful discussion of insect-microbe relationships, Jones (10) postulated that insect-microbial associations, known to involve catabolic (e.g. cellulose-degrading) and anabolic (e.g. biosynthesis of vitamins, sterols, and amino acids) processes necessary to the survival of the host, could also include detoxification abilities. Most investigations in this area have been limited (11). Nevertheless, some studies indicate detoxification of terpenoids (12,... 

Aubert, J.-P. Beguin, P. Millet, J., Eds. Biochemistry and Genetics of Cellulose Degradation FEMS Symp. No. 43 Academic Press San Diego, 1988. 

Figure 1. Possible interactions between micro-organisms during cellulose degradation. Source Reproduced with permission from Ref. 11. 1985, L. A. Harrison.

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