This invention relates to heterogeneous ion exchange resins of a cross-linked polymer and a halo-substituted olefin.
Ion exchange resins are normally solid materials which generally carry exchangeable ions. Due to their ability to exchange ions in a liquid without substantial alteration of the solid resin's structure, they are widely employed in recovery processes such as the recovery of uranium and in waste treatment to remove undesirable components from water.
Generally, effective ion exchange resins are substantially insoluble but swellable to a limited degree in water and are resistant to physical deterioration such as excessive spalling and shattering. Moreover, in many applications, particularly up-flow column operations, often encountered in uranium recovery and sugar processing, the resin advantageously has a sufficiently high density to assure efficient removal of the valuable ionic ingredients from the ion containing liquid, which is generally a thick slurry, without entrainment loss of the resin.
Conventionally, ion exchange resins are prepared by (1) haloalkylating a copolymer of a monovinylidene aromatic such as styrene and a cross-linking agent which is generally a polyvinylidene aromatic such as divinylbenzene in the presence of a Friedel-Crafts catalyst and (2) attaching ion active exchange groups to the halogenated product. For example, an anion exchange resin is prepared by aminating the haloalkylated polymer. See, Ion Exchange by F. Helfferich, published in 1962 by McGraw-Hill Book Company, New York. Unfortunately, these anion exchange resins, without modification, possess relatively low densities.
Ion exchange resins having increased density are known in the art. For example, U.S. Pat. Nos. 2,769,788 and 2,809,943 disclose higher density ion exchange resins prepared by incorporating inert, finely divided solid materials of a high density, i.e., 2.5 g/cc or higher, into copolymer beads of the monovinylidene and polyvinylidene aromatic compounds. Unfortunately, these ion exchange resin beads exhibit excessive spalling and surface irregularities. Moreover, such beads have a low mechanical stability and have a tendency to break and spall when employed in a continuous operation.
To increase the mechanical stability of high density ion exchange resin beads, German Patent Application No. 2,218,126 teaches higher density resins can be prepared by using a nonionic substituted styrene, such as monochlorostyrene, as the monovinylidene aromatic compound. Unfortunately, halogenated non-ionic substituted styrenes are relatively expensive and of limited availability.
In view of the stated deficiencies of the known ion exchange resins having increased density and the methods for their preparation, it remains highly desirable to provide an improved heavy density ion exchange resin.