Cellulose processes, practical

THPC—Amide Process. The THPC—amide process is the first practical process based on THPC. It consists of a combination of THPC, TMM, and urea. In this process, there is the potential of polymer formation by THPC, melamine, and urea. There may also be some limited cross-linking between cellulose and the TMM system. The formulation also includes triethanolamine [102-71-6J, an acid scavenger, which slows polymerization at room temperature. Urea and triethanolamine react with the hydrochloric acid produced in the polymerization reaction, thus preventing acid damage to the fabric. This finish with suitable add-on passes the standard vertical flame test after repeated laundering (80). 

Reverse Osmosis. This was the first membrane-based separation process to be commercialized on a significant scale. The breakthrough discovery that made reverse osmosis (qv) possible was the development of the Loeb-Sourirajan asymmetric cellulose acetate membrane. This membrane made desalination by reverse osmosis practical within a few years commercial plants were installed. The total worldwide market for reverse osmosis membrane modules is about 200 million /yr, spHt approximately between 25% hoUow-ftber and 75% spiral-wound modules. The general trend of the industry is toward spiral-wound modules for this appHcation, and the market share of the hoUow-ftber products is gradually falling (72). 

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. 

In a number of recent publications (1, 2) microcrystailine cellulose dispersions (MCC) have been used as models to study different aspects of the papermaking process, especially with regard to its stability. One of the central points in the well established DLVO theory of colloidal stability is the critical coagulation concentration (CCC). In practice, it represents the minimum salt concentration that causes rapid coagulation of a dispersion and is an intimate part of the theoretical framework of the DLVO theory (3). Kratohvil et al (A) have studied this aspect of the DLVO theory with MCC and given values for the CCC for many salts, cationic... 

The major chemical processes of membrane deteriorations are hydrolysis and oxidation. Cellulose acetate is most stable at the level of around pH 4.7, and at the pHs lower or higher than that value, membrane hydrolysis is accelerated. In practical applications of cellulose acetate membranes, feed water pH is usually controlled between 5 to 6. But it is Impossible to control the pH of demineralized pure water for electronic and pharmaceutical uses, i.e. for ultrapure water polishing. In such cases feed water pH 7 should be supplied to cellulose acetate material. Studies of membrane behaviour under such conditions will give good information for estimating the membrane life. 

Alcohol recovery from the fermentation brews was less than complete in most cases, which may be attributable to less than ideal conditions. The best yields, 60 to 97% of theory, were obtained with sugars obtained by hydrolysis of cellulosic residues of the autohydrolysis-extraction process. Unextracted pulps, or the hemicellulose solutions, gave poor ethanol formation, which suggests inhibition. In the calculation of material and energy balances which follows, we have assumed 95% yields of ethanol from wood sugars, which is readily achieved in industrial practice and which we believe to be achievable with our wood sugars as well. 

Direct Oxidation. Direct oxidation of petroleum hydrocarbons has been practiced on a small scale since 1926 methanol, formaldehyde, and acetaldehyde are produced. A much larger project (29) began operating in 1945. The main product of the latter operation is acetic acid, used for the manufacture of cellulose acetate rayon. The oxidation process consists of mixing air with a butane-propane mixture and passing the compressed mixture over a catalyst in a tubular reaction furnace. The product mixture includes acetaldehyde, formaldehyde, acetone, propyl and butyl alcohols, methyl ethyl ketone, and propylene oxide and glycols. The acetaldehyde is oxidized to acetic acid in a separate plant. Thus the products of this operation are the same as those (or their derivatives) produced by olefin hydration and other aliphatic syntheses. 

Later experiments were carried out with a nitrocellulose stabilization process that consisted in treating a partially purified nitrocotton in an ammonia bath (e.g. Reeves and Giddens [12]). This was based on the supposition that ammonia was capable of neutralizing accurately adds contained in the interior of nitrocellulose fibres. However, this method has not been adopted in practice, since it was feared that the sulpho groups attached to cellulose in the form of mixed esters would undergo only partial hydrolysis in the presence of ammonia and later spontaneous hydrolysis of these substituents in the finished (stabilized) product might reduce its stability. 

Up to the present, continuous processes for the cellulose nitration have not been introducted in practice. 

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