Patent GB-767924-A (GB)
Title: Improvements in or relating to the manufacture of carboxyalkyl cellulose ether salts
IPC: C08B11/20
Filed: 1954-03-01
Abstract: Fibrous water-soluble salts of carboxyalkyl cellulose ethers are converted into free-flowing granular powders by agitating a loose fibrous mass comprising a water-soluble salt of a carboxyalkyl cellulose ether moist with an aqueous alcohol miscible with water in all proportions and containing water and alcohol in such proportions that the mass would normally dry to a loose fibrous product at a temperature below 100 DEG  C., simultaneously introducing thereto a dispersed stream of aqueous liquid comprising water, an aqueous salt solution or an alcohol containing not more than 15 per cent of watermiscible alcohol, or wet or saturated steam, until the amount of water introduced is sufficient to form, with the aqueous alcohol present in the mass, a powerful solvent for the watersoluble salt of the carboxyalkyl cellulose ether, the solvent containing at least 67.5 per cent by weight of water, maintaining the total liquid content of the mass below 4 parts by weight based on the dry weight of the salt, continuing agitation until the fibrous structure of the mass is substantially destroyed and the salt is converted into a mass of separate gel particles, discontinuing agitation while the mass is still substantially in this form and before the particles coalesce into doughy masses, and drying the gel particles thus formed to obtain a free-flowing substantially granular powder.  In an example 160 parts by weight of a loose mass of crude sodium carboxymethylcellulose fibres, containing 100 parts of the crude ether, 51 parts of isopropyl alcohol and 9 parts of water, are stirred and tumbled in a mixer while 100 parts of water are sprayed on to the mass as a fine mist or spray from pressure nozzles in about 3 minutes.  Agitation of the mass is continued for about 5 minutes to convert the sodium carboxymethyl cellulose into a mass of separate gel particles, which is then discharged into sufficient 99 per cent methanol to reduce the water content of the liquid in the mass from about 68 to about 25 per cent.  The gel particles are separated from the liquid by centrifuging and dried at about 70 DEG  C. to a volatile content below about 5 per cent to form a freeflowing granular powder which can be pulverized and screened.  In another example fibrous sodium carboxymethyl hydroxyethyl cellulose moist with aqueous methanol is similarly converted into a dry powder. Fibrous water-soluble salts of carboxyalkyl cellulose ethers which may be converted into powders include the alkali-metal or ammonium salts of carboxymethyl, carboxyethyl-, carboxypropyl-, carboxymethyl hydroxyethyl- and carboxyethyl hydroxyethyl celluloses.  The cellulose ether salts may be in the crude form still containing by-product salts or may have been purified.  The alcohol may be methyl, ethyl, propyl, isopropyl or tertiary butyl alcohol.  The powerful solvent for the salt is preferably displaced from the gel particles with an aqueous alcohol, miscible with water in all proportions and containing less than 40 per cent of water by weight, prior to drying the gel particles.  The proportion of aqueous alcohol initially mixed with the salt may be about 0.5 to 1.5, preferably about 0.75 to 1.25, parts by weight, based on the salt, the aqueous alcohol containing not more than 40 per cent of water by weight. Specifications 683,627 and 767,923 and U.S.A. Specification 2,618,632 are referred to.