GB2040950A - Phosphorus-containing Ampholytic Polymers - Google Patents

Abstract

Ampholyte polymers are obtained by treating weakly-basic ionic polymers, e.g. a cross-linked aminated polymer of styrene, with (a) formaldehyde and (b) a salt of hypophosphorus acid under acidic conditions.

Description

SPECIFICATION Process for Producing Polyampholytes The present invention relates to selective ionites and, in particular, to a process for producing polyampholytes.

We have discovered that a polyampholyte having a high capacity and having good kinetic properties can be produced by treating a low-basic ionite with formaldehyde and with a salt of hypophosphorous acid.

Thus, the present invention consists in a process for producing a polyampholyte, which comprises treating a low-basic ionite with formaldehyde and with a salt of hypophosphorous acid under acidic conditions.

We prefer that the low-basic ionite is an aminated cross-linked chloromethylated polymer of styrene, preferably a copolymer of styrene and, for example, divinylbenzene, diisopropenylbenzene, divinylpyridine or diethylene glycol dimethacrylate.

The formaldehyde may be provided by any convenient source, and we prefer the use of formalin, such as 3537% commercial formalin. Alternatively, paraformaldehyde may be used, but in this case a slightly higher reaction temperature may be required in order to cause decomposition to formaldehyde.

The treatment with the salt of hypophosphoric acid is preferably carried out at a pH below 3, and sulphuric acid, hydrochloric acid, nitric acid or phosphoric acid may be added to achieve this pH. Also, treatment is preferably carried out at a temperature of 1400C or less, more preferably 1000C or less.

The higher temperatures are more useful when paraformaldehyde is used as the source of formaldeyde.

Polyampholytes produced by the process of the invention have a high capacity with respect to tungsten, such as from 500 to 900 mg/g. This can be achieved over a wide range of hydrogen ion concentrations. Also, the new polyampholyte has good kinetic properties and maximum sorption under static conditions is reached within from three to five hours. This means that the capacity of a sorption apparatus can be increased. Furthermore, complete desorption of tungsten ions from a polyampholyte having a residual capacity of 0.5 to 0.7% can be achieved by use of a weak solution of ammonia.

The process of the invention preferably starts with a commercially produced low-basic ionite since this has satisfactory physico-chemical and operating properties. This ionite is preferably a crosslinked chloromethylated copolymer of styrene that has been aminated with, for example, an aliphatic amine, ammonia or a polyamine. The ionite may be produced by methods already known for the synthesis of ion-exchange materials, such as suspension copolymerization to produce a copolymer of styrene and divinylbenzene, diisopropenylbenzene, divinylpyridine or diethylene glycol dimethacrylate.

This results in a three-dimensional cross-linked copolymer in the form of spherical granules which are non-fusible and insoluble in water and inorganic solvents. This copolymer is then subjected to chloromethylation, as follows.

This product is then aminated, preferably with a primary or secondary aliphatic amine or polyamine to produce a copolymer having primary and secondary amino groups.

wherein R1 is hydrogen and s2 is hydrogen, -(CH2)-0H or or(CH2)nNH2 (in which n is from 2 to 6, preferably either 2 or 6). Alternatively, R1 and R2 may both be-[(CH2)NH-]rn (CH2)2NH2 (in which m is O or a positive integer).

This aminated cross-linked chloromethylated copolymer of styrene is then treated with formalin (or other source of formaldehyde), and with a salt of hypophosphorous acid in an acidic medium, such as hydrochloric acid, Preferred salts of hypophosphorous acid include sodium hypophosphite, calcium hypophosphite and barium hypophosphite. In the presence of an acid such as a mineral acid, an equilibrium involving these salts is established: VI MeH2P02+H+H3P02+Me+ It can be seen from this formula that hypophosphorous acid, which is necessary for the main reaction, is produced directly in situ.

As mentioned above, interaction of the low-basic ionites with formalin or other source of formaldehyde together with hypophosphorous acid is conducted in an acidic medium, and preferably at a temperature of 1 400C or less, more preferably 1 000C or less. Where paraformaldehyde (CH20)x is used as the source of formaldehyde the temperature should be sufficiently high to cause decomposition to formaldehyde in the acidic medium. The temperature may need to be as high as 1 400C when paraformaldehyde is used in a high-boiling organic solvent.

The functional group of the resulting polyampholyte can, in general, be represented by the following formula:

In this formula R is hydrogen, an alkyl group, -(CH2)20H or t(CH2)2NHim (CH2)2NH2 (in which m is O or a positive integer).

The presence of a polar hydroxymethyl group attached to the phosphorus atom increases the acidity of the hypophosphorous acid moiety and enlarges the range of pH within which the polyampholyte will complex satisfactorily. Also, this polar group enhances the hydrophilic nature of the polymer, and this facilitates penetration of water plus dissolved substances into the granules of the ionite, thereby improving the kinetics of sorption and desorption.

If desired, the structure of the product of the process of the invention may be determined by ultimate analysis, by consideration of acid-base properties, or by IR spectroscopy.

The invention is further illustrated by the following examples.

Example 1 Into a flask provided with a stirrer and a reflux condenser were placed 0.5 moles (80 g) of a chloromethylated copolymer of styrene and divinylbenzene that had been aminated with ethylenediamine. Then, 1 500 ml of formalin followed by 2 moles of calcium hypophosphite and 2 moles of concentrated hydrochloric acid were added. The flask was then stirred for from 1 to 2 hours and the reaction mixture was then heated to a temperature from 90 to 95 C and maintained at this temperature for 1 5 hours.

The resulting polyampholyte was washed with water until the washings were weakly acidic.

Washing was then continued with a 3% solution of alkali, again with water, then with a 3% solution of hydrochloric acid, and finally with water until all chloride ions had disappeared. The phosphorus content was then equal to 7.1%.

The polyampholyte had a capacity with respect to W032- of from 450 to 500 mg/g and its capacity with respect of CU2+ was 60 mg/g. The desorption with three volumes of a solution of ammonia (based on the volume of polyampholyte) was 96%, and the residual capacity was 0.5%.

Example 2 Into a similar flask to that used in Example 1 were placed 0.01 moles (2.4 g) of polyvinylbenzylamine that had been produced by aminating a macroporous chloromethylated copolymer of styrene and divinylbenzene by means of hexamethylenetetramine. Also, 20 ml of a 37% solution of formalin and later 0.06 moles (5.6 g) of sodium hypophosphite and 0.06 moles of concentrated hydrochloric acid were added. The reaction mixture was heated to 900C and maintained at this temperature for 20 hours. The resulting polyampholyte was washed as in Example 1.

The phosphorus content of the polyampholyte was 10.2%, its sorption capacity relative to WO2- was 800 mg/g, and its residual capacity was as in Example 1.

Example 3 Into a flask similar to that used in Example 1 were placed 350 ml of a 37% solution of formalin, 0.3 moles of barium hypophosphite and 0.3 moles of concentrated hydrochloric acid, followed by 0.05 moles (1 2.5 g) of a chloromethylated copolymer of styrene and diethylene glycol dimethacrylate that had been aminated with monoethanolamine. The reaction mixture was stirred for from 1 to 2 hours without heating, and the temperature was then raised to 90 to 950C and maintained at this temperature for 1 5 hours. The resulting polyampholyte was washed as in Example 1.

The amount of phosphorus in the resulting polyampholyte was 6.8%, its sorption capacity relative to WO2- was 420 mg/g, and its residual capacity was 0.7%.

Example 4 Into a flask similar to that used in Example 1 were placed 50 g of a chloromethylated copolymer of styrene and diisopropenylbenzene which had been aminated by means of ethylenediamine. Then 1 500 ml of a 37% solution of formalin were added, and the reaction mixture was maintained at room temperature for 1 5 hours. Then, 1 76 g of sodium hypophosphite were added and the mixture acidified to a pH of below 3. The reaction mixture was again kept at room temperature with stirring, then heated to 900C and maintained at this temperature for 1 5 hours. The resulting polyampholyte was successively washed with water until the washings were weakly acidic, then washed with a 5% solution of sulphuric acid, and finally with water.

The amount of phosphorus in the resulting polyampholyte was 7.1%, its capacity relative to W03- at pH 5.2 was 450 mg/g, and its capacity at pH 6 was 900 mg/g.

Claims (15)

Claims

1. A process for producing a polyampholyte, which comprises treating a low-basic ionite with formaldehyde and with a salt of hypophosphorous acid under acid conditions.

2. A process according to Claim 1, in which the low-basic ionite is a cross-linked aminated polymer of styrene.

3. A process according to Claim 2, in which the aminated polymer contains primary and secondary amino groups.

4. A process according to Claim 2 or Claim 3, in which the polymer is a copolymer of styrene and one or more other monomers.

5. A process according to Claim 4, in which the copolymer is a copolymer of styrene and one or more of divinylbenzene, diisopropenylbenzene, divinylpyridine and diethylene glycol dimethacrylate.

6. A process according to any one of Claims 2 to 5, in which the polymer is produced by: crosslinking a polymer; chloromethylating the cross-linked polymer, and aminating the chloromethylated polymer.

7. A process according to any one of the preceding claims, in which treatment with formaldehyde is carried out by use of formalin.

8. A process according to Claim 7, in which the formalin is 35 to 37% commercial formalin.

9. A process according to any one of the preceding claims, in which treatment with formaldehyde is carried out by use of paraformaldehyde at a temperature sufficient to cause production of formaldehyde.

10. A process according to any one of the preceding claims, in which treatment with a salt of hypophosphorous acid is carried out at a pH below 3.

11. A process according to any one of the preceding claims, in which treatment under acidic conditions is carried out in the presence of sulphuric acid, hydrochloric acid, nitric acid, or phosphoric acid.

12. A process according to any one of the preceding claims, in which treatment is carried out at a temperature of 1 400C or less.

13. A process according to Claim 12, in which treatment is carried out at a temperature of 1 000C or less.

14. A process according to Claim 1, substantially as herein described with reference to the foregoing examples.

15. A polyampholyte when produced by a process according to any one of the preceding claims.