Improvements relating to ion-exchange processes

In an anion-exchange process anions are removed from an aqueous liquid also containing organic impurities by treatment of the liquid with a macroporous TBCS (tert.-butylcatechol sulphonic acid) - satisfactory anion - exchange resin containing strongly basic groups. The strongly-basic resins include those which owe their ion-exchange properties to quaternary ammonium, guanidinium, tertiary sulphonium or tertiary phosphonium groups. Some resins have both strongly basic and weakly basic groups, an example being a chlormethylated cross-linked polystyrene aminated with dimethylamine. TBCS-satisfactory is directly associated with the presence of the strongly basic groups and presents a problem whenever the resin contains any considerable proportion, say 20%, of such groups and a liquid containing organic matter is under treatment or when the resin is used for removing silica. Macroporous resins suitable for use in the process of the invention can be prepared by copolymerizing a compound having one polymerizable double bond, for example a mono-vinyl compound such as styrene, with a high proportion of a compound having two or more polymerizable double bonds, for example a divinyl compound such as divinyl benzene, as a cross-linking agent, in the presence of a solvent. Anion-exchange groups are then introduced into the polymer in known manner, for example, by chlormethylating the polymer and then aminating the product to introduce quaternary ammonium groups. The polymerization is preferably performed using the technique of suspension polymerization. In order to produce a TBCS-satisfactory macroporous resin it is important that the proportion of cross-linking agent should be high. In the manufacture of microporous resins it is wellknown that the proportion of the cross-linking agent is commonly from 2-10%, but in the resins used according to the invention the proportion should in general be at least 25% and preferably 30% or more. In addition, to ensure adequate macroporosity, the normal process of suspension polymerization employed in the manufacture of microporous resins must be varied. This variation involves, as indicated above, the presence of a solvent for the monomers. This solvent, e.g. hexane, may be a precipitant for the polymer, as described in Specification 849,122. Again the solvent for the monomer mixture may also be a swelling-agent for the copolymer. Suitable solvents that are also such swelling agents are toluene and xylene. When a small proportion