GB618251A - Improvements relating to cation-exchange resins - Google Patents

Abstract

In the manufacture of synthetic resinous condensation products having selective exchange properties for cations equivalent to the anions of weak acids, a phenol and/or a tannin is condensed with an aldehyde to form a gel and before or after gel formation, but before the gel is dried the condensation product is heated at a temperature of at least 130 DEG C. and under elevated pressure with carbon dioxide and/or a bicarbonate which decomposes at the temperature employed. The products contain COOH groups. The pressure is of the order of 10 atmospheres, and drying is carried out at 100 DEG -120 DEG C. In examples (1) paraformaldehyde is added to a mixture of Quebracho tannin caustic soda solution and sodium bicarbonate, and the resulting gel is heated in an autoclave at 170 DEG C. with carbon dioxide at 10 atmospheres, and dried at 120 DEG C.; (2) a gel formed by heating resorcinol, sodium hydroxide solution and formalin is broken up and heated in an autoclave with sodium bicarbonate and water at 170 DEG -180 DEG C. and 10 atmospheres, and dried at 120 DEG C.; (3) phenol and Quebracho tannin replace the resorcinol of (2); (4) a viscous mixture obtained by heating resorcinol, sodium hydroxide and formalin is heated at 170 DEG C. with sodium bicarbonate and carbon dioxide introduced at a pressure of 20 atmospheres. After heating for 5 hours the resulting gel is dried at 120 DEG C. The products are prepared for use by washing with hydrochloric acid. The products may be used for removing temporary hardness from water (see Group I).ALSO:A cation exchange resin for removing temporary hardness from water having both permanent and temporary hardness selectively exchanges the cations equivalent to the weak acid anions present in the water. The resins which contain COOH groups are prepared from a phenol and/or a tannin with an aldehyde and carbondioxide and/or a bicarbonate [see Group IV].