GB767923A - Improvements in or relating to manufacture of water-soluble salts of carboxyalkyl cellulose ethers - Google Patents

Abstract

Fibrous water-soluble salts of carboxyalkyl cellulose ethers are converted into free-flowing substantially granular powders by (1) agitating a loose fibrous mass comprising a water-soluble salt of the ether moist with an aqueous watermiscible alcohol and containing water and alcohol in such proportions that the mass would normally dry to a loose fibrous product, (2) simultaneously introducing thereto a dispersed stream of an aqueous liquid comprising water, an aqueous salt solution or an aqueous alcohol containing more than 40 per cent of water by weight, or live saturated steam, the proportion of aqueous liquid or steam introduced into the fibrous mass being sufficient to form with the aqueous alcohol already present in the mass a liquid containing a sufficiently high proportion of water to cause incipient gelation at the surfaces of the fibres but insufficient to destroy substantially the fibrous character of the mass, (3) displacing the aqueous alcohol in the mass, after the introduction of the aqueous liquid or condensed steam, with a mixture of a water-miscible alcohol and water containing less than 40 per cent by weight of water, (4) substantially drying the thus-treated mass, and (5) mechanically comminuting the substantially dried product. The water-soluble salts of the ethers may include any of the alkali-metal or ammonium salts of carboxymethyl-, carboxyethyl- or carboxy-propyl-celluloses and the carboxyalkyl cellulose ether may contain hydroxyalkyl substituent groups such as hydroxyethyl. The cellulose ether is preferably in the form of the crude product still containing by-product salts such as sodium chloride and sodium glycolate. These may be washed out of the crude product, after the treatment of the latter with an aqueous liquid or steam, by means of the alcoholic liquid containing less than 40 per cent of water. The alcohol used in the process may be methanol, ethanol, propanol, isopropanol, or tertiary butanol. In an example 128 parts by weight of moist sodium carboxymethyl cellulose, which has been purified by washing with 85 per cent methanol and contains 82.1 parts of sodium carboxymethyl cellulose and 45.9 parts of aqueous methanol containing 6.9 parts of water, is sprayed while agitated with 41 parts of water, and the mixture is reslurried in 99 per cent methanol, centrifuged, dried to a volatile content of below 5 per cent and pulverized to a fine powder. Specifications 683,627 and 767,924 are referred to.