Process for the alkaline saponification of crosslinked acrylonitrile bead polymers
View Patent ↗The alkaline saponification of acrylonitrile bead polymers provides weakly acidic cation exchangers with little intrinsic color and with reduced residual nitrogen content if the saponification is begun at a temperature T 1 of from 70 to 120° C. and, once a degree of saponification of at least 65% has been reached, is completed at a temperature T 2 of from 120 to 180° C.
1. A process for preparing a weakly acidic cation exchanger comprising saponifying crosslinked acrylonitrile bead polymers using an alkaline saponifier, beginning the saponifying at a temperature T 1 of from 70 to 120° C. and, once a degree of saponification of at least 65% has been reached, completing the saponifying at a temperature T 2 of from 120 to 180° C., T 2 being higher than T 1 by at least 10° C.
2. The process as claimed in claim 1 , wherein the alkaline saponifier is fed at the temperature T 1 into an aqueous suspension of the acrylonitrile polymer.
3. The process as claimed in claim 1 , wherein the acrylonitrile bead polymer has been crosslinked using a crosslinking agent selected from the group consisting of divinyl ethers and polyvinyl ethers.
4. The process as claimed in claim 3 , wherein the crosslinking agent is selected from the group consisting of compounds of the formula (I):
where
R is a member selected from the group consisting of C n H 2n , (C m H 2m —O) p —C m H 2m , and CH 2 —C 6 H 4 —CH 2 , wherein n≧2, m=from 2 to 8, and p≧1.
5. The process as claimed in claim 1 , wherein the saponifying at the temperature T 1 is controlled optically, and a change in the color of the bead polymers from red to white or colorless indicates that the degree of saponification of at least 65% has been reached.