Patent GB-860695-A (GB)
Title: Improvements relating to ion-exchange processes
Inventor: KRESSMAN THEODORE ROGER ERNEST
IPC: B01J41/14
Filed: 1958-07-09
Abstract: 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 of cross-linking agent is used a polymer results that is virtually indistinguishable from a conventional one made in the absence of solvent or precipitant. As the proportion of cross-linking agent reaches a certain level that depends upon the proportion of solvent or precipitant used, the transition from microporosity to macroporosity takes place fairly rapidly.  In the case of a copolymer of styrene and divinyl benzene made with a solvent, there should be at least 45% solvent (based on the total mixture) when the divinyl benzene amounts to 25% of the monomer mixture.  With 33% divinyl benzene in the monomer mixture the minimum solvent is 35% of the total mixture. With 55% divinyl benzene the minimum solvent is 30%, and remains 30% as the divinyl benzene is increased.  There should not be more than 80% solvent in the total mixture in any event.  As the proportion of solvent increases, so should the proportion of catalyst increase in order to effect polymerization.  By way of example a macroporous anion-exchange resin was prepared as follows : 10 gms. azobisisobutyronitrile was dissolved in a mixture of 150 c.c. styrene, 250 c.c. of a commercial divinyl benzene concentrate containing 50% divinyl benzene and 50% ethyl styrene and 800 c.c. of toluene.  The solution was stirred up with water containing a suspension stabilizer (0.1% polyvinyl alcohol) so as to form globules of particle size about 14 to 52 mesh. The whole was heated to about 75 DEG  C. with continuous stirring for 18-24 hours, after which time polymerization was substantially complete and the globules had become converted to solid spheres.  A solution of 1 gm. t-butyl catechol in 100 c.c. toluene was then added and the stirring continued for a further 1 hour.  Finally the toluene was removed by distillation and the toluene-free polymer beads filtered off from the water and dried at 100 DEG  C. The dried beads were swollen in 1.5 litres ethylene dichloride and a mixture of 940 gms. chlormethyl ether containing 350 gms. powdered anhydrous aluminium chloride was then added.  The whole was warmed to 60-65 DEG C. for 12 hours, then poured into an excess of water and the beads filtered off and washed with water.  They were then covered with 2 litres of 25% aqueous trimethylamine solution and left in the cold for 12 hours.  The resulting aminated beads were filtered off and washed with dilute HCl and then with water.  The hydrocarbon polymer before the introduction of the ion-exchange groups was found to have 77% of its pore volume in the form of macropores.ALSO:Anions are removed from tap-water which usually contains small amounts of organic impurities by treatment with a macroporous T.B.C.S. (tert. butylcatechol sulphonic acid) satisfactory anion-exchange resin containing strongly basic groups.  T.B.C.S. (tertiary butyleatechol sulphonic Acid satisfactory is directly associated with the presence of strongly basic groups and presents a problem when the resin contains more than 20% of such groups where silica or organic matter is present in the liquid to be treated and to produce a T.B.C.S. satisfactory resin the proportion of cross-linking should be high. Specification 849,122 is referred to.