Reaction cellulose hydrolysis

Reactions of this type are quite popular and widely used to introduce hydrophilic and ionogenic groups into linear polymers as well as directly into polymer networks. These reactions include hydrolysis (PAAm, PAAc and their analogs from PAN, PVA from poly (vinyl acetate), oxyethylation and oxymethylation of starch and cellulose, sulfurization, and other reactions. These processes are of industrial importance, well studied and widely reviewed. 

A product which contains about 2.5 ethoxy groups (47—48%) is thermoplastic and is suitable for commercial and military uses its sp gr is 1.07—1.18, nD 1.47 and softening point 240—45°. It can be prepd in a laboratory, by slowly adding (with stirring) to the pulped filter paper (suspended in 44% aq NaOH so In maintained at 100°) an excess of ethyl chloride (usually 6 moles per one mole of cellulose) and allowing to stand for a while Note In order to obviate to some extent the side reactions of hydrolysis, the procedure is conducted in the presence of large amount of NaCl... 

Processes need to be developed to expose LHC for effective penetration of chemicals that promote separation of LHC or which render cellulose accessible by swelling. These processes can have many objectives (1) to get at cellulose (2) to remove hemicellulose from the reaction site before cellulose hydrolysis (3) to remove lignin from the site and (4) to bring penetrating or hydrolysis agents into effective contact with cellulose. 

Figure 15.6 Reaction scheme for modeling cellulose hydrolysis [17],...

A mathematical model has also been proposed for evaluating cellulase preparations. Sattler et al.209 describe a relationship between hydrolysis extent, reaction time, and enzyme concentration. This procedure permits the effectiveness of different enzymes and of different pretreatment methods to be ranked. This method examines cellulose hydrolysis data collected from hyperbolic functions of substrate concentration versus cellulase enzyme concentration at various timed incubations. The model is based on a double reciprocal plot of the relationship... 

Although the volume of foam was increased by limited proteolysis, the stabilities of the foams, defined as the time required for one half of the weight of the foam to drain from the foam as free liquid, were greatly decreased by this same limited proteolysis. Presumably the increased initial polypeptide concentration in the hydrolysates favors more air incorporation. However, the polypeptides apparently do not have the surface activity required to give a stable foam. The decrease in foam stability becomes evident in the first 30 min of the enzyme reaction. Further hydrolysis results in peptides which lack the ability to stabilize the air cells of the foam. Thus a limited hydrolysis may be advantageous for utilizing whey proteins in foams since the specific volumes of the foams were increased 25% by such treatment. The decrease in foam stability which results from limited hydrolysis can be compensated for by adding stabilizers such as carboxymethyl cellulose (19,27). 

Microwave-assisted polycondensation reactions in ILs have also allowed the enhanced synthesis of polyamides and polyurethanes the comparison between microwave synthesis conditions in ILs with conventional heating methods and conventional organic solvents has also been addressed [92, 93]. Pretreatment methods combining microwave irradiation and ILs for cellulose dissolution and modification have been also proposed [94, 95]. Microwave irradiation can enhance the solubility of cellulose in ILs and decrease the degree of polymerization of regenerated cellulose after IL dissolution, which can be beneficial for improving cellulose hydrolysis [95]. 

Most simple oligosaccharides are quantitatively hydrolyzed by boiling dilute acid. Cellulose by contrast is hydrolyzed very slowly, and even on extended hydrolysis at higher temperatures, the maximum yield of recoverable sugar is very low. This was explained by Luers ( ) who showed the cellulose hydrolysis in dilute acid involves consecutive first-order reactions of somewhat similar rates for the production and the decomposition of sugar. This observation formed the basis for the development of the Scholler percolation process. This process, which involves removal of sugar from the digester as it is formed, resulted in twice the yield obtainable by batch hydrolysis. 

Figure I shows the maximum yield of "B" and the residual "A" in consecutive first-order reactions A C for various ratios of ki k2 kr. Parameters for cellulose hydrolysis were determined by Saeman (4) and redetermined by Kirby j. It might be noted that despite analytical and experimental problems, the general model has been repeatedly confirmed.

As mentioned earlier, the most important issue in cellulose hydrolysis is sohd acid operation in water. Cellulose is insoluble in water, but soluble in some ionic Hquids such as l-butyl-3-methyHmidazolium chloride (BMIMCl). The use of ionic hquids thus affords a good accessibihty to dissolved cehulose for conversion at active sites of sohd add catalysts. Amberlyst resins in ionic hquids could effectively depolymerize cellulose (microcrystaUine cehulose and a-cehulose) into ceUo-ohgomers under mild reaction conditions (373 K, <5 h) [147]. 

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