GB1598687A - Chelating resins - Google Patents

Description

(54) CHELATING RESINS (71) We, DIA-PROSIM LIMITED (formerly known as Diamond Shamrock (Polymers) Limited), a British Company, of Emerson House, Albert Street, Eccles, Manchester, formerly of 632/652 London Road, Middlesex TW7 4EZ, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: Ion-exchange resins are known. In recent years, interest has been growing in ion-exchangers whose functional groups are potentially chelate-forming. Such exchangers are prepared by anchoring complexing agents on crosslinked organic polymers.

Styrene-divinylbenzene copolymer resins containing iminodiacetic acid groups [-N(CH2COOH)2] are known and have a high affinity for heavy metals. Materials such as iminodiacetic acid are capable of forming chelate compounds by coordination with metals and the application or resins containing these groups has now been extended to various fields such as analytical chemistry and the extraction of heavy metal ions in hydrometallurgy or in effluent treatment.

It appears that practically all commercially available ion-exchange chelating resins are based on the idea of using iminodiacetate groups to achieve a structure similar to that of ethylenediaminetetraacetic acid (EDTA). The presence and arrangement of the two carboxyl groups and the tertiary nitrogen atom results in a resin which exhibits a strong preference for copper, nickel, zinc, iron and other heavy metal cations over such cations as sodium, potassium and calcium. The equilibrium selectivities of the resin for metal cations are very similar to those of iminodiacetic acid.

Condensation polymers have frequently been employed in the preparation of chelating resins. With the development of styrene-based ion-exchangers, a significant advance was made. Most of the presently available commerical chelating resins are prepared by the chloromethylation of crosslinked polystyrene beads, and the subsequent treatment with either iminodiaceto-nitrile followed by acid hydrolysis, or by reacting the chloromethyl groups with ammonia and subsequently with chloroacetic acid.

Polystyrene-based chelating resins, although they have been successfully used in many applications involving the removal of heavy metals, suffer from some disadvantages common to all resins based on styrene-divinylbenzene copolymers. It is known that these resins, and particularly the type of resins known as gel resins, i.e. resins without macropores, do not stand up to high osmotic and mechanical forces because of their brittleness. Under such conditions they disintegrate, causing a large pressure drop in column applications. This disadvantage is particularly noticable where chelating resins, owing to the particular method by which they are applied and regenerated, exist, in a single cycle, in three different ionic forms, each of different swellability. These three forms are the sodium form, the metal form and the hydrogen form. Therefore each cycle involves large changes in resin volume and large osmotic forces operate inside the resin particles.

Another disadvantage of chelating resins based on polystyrene is that their preparation is difficult and lengthy, invariably involving the synthesis of an intermediate containing chloromethyl groups. This intermediate compound is prepared by reacting the styrenebased polymer, in spherical form, with chloromethyl methyl ether (CME) at elevated temperatures. However, CME contains an impurity, bis-chloromethyl ether, which is a hazard to health. Further, the chlorine atoms of chloromethyl groups are highly reactive and, in reaction with ammonia which is one of the routes by which chelating resins are prepared, tertiary amine groups are formed together with quaternary ammonium groups which cannot react further to produce the corresponding iminoacetic or iminodiacetic acid groups. Thus not only the total amount of the metal complexing groups is decreased but also ion-exchange sites are introduced into the resin which may adversely influence the performance of the resin.

Acrylic and methacrylic acid and their esters have been used in the manufacture of ion-exchange resins, and commerical resins containing carboxylic groups are available.

These resins are very tough and they do not disintegrate even under exceptionally high osmotic or mechanical forces.

Recently, anionic resins similar to the cross-linked acrylate-carboxylic structures have been prepared for both weak and strong base ion-exchange resins. These resins are produced very simply by reacting an acrylic or methacrylic acid ester or acrylonitrile-crosslinked polymer with a polyamine containing at least one primary amine group. The copolymer particles are treated with the polyamine and, in the case of a strong base ion-exchange resin, a subsequent quaternisation with a suitable methylating agent is carried out. Again, these resins show exceptional toughness and resistance to breakdown.

According to the present invention, a chelating resin having monomeric units of the formula

wherein A is hydrogen or methyl; R is hydrogen, C16 alkyl or CH2COOZ; X is an alkylene chain of from one to 12 carbon atoms optionally interspersed with oxygen atoms or NH or NCH2COOZ groups; and Z is hydrogen, an alkali metal or ammonium; is prepared in the form of beads by a process which comprises (a) preparing a copolymer, in the form of beads, by reacting an acrylate ester, a methacrylate ester, acrylonitrile or methacrylonitrile with a cross-linking agent; (b) reacting the copolymer with a polyamine of the formula H2N-X'-NHR' II wherein X' is alkylene of 1 or 12 carbon atoms optionally interspersed with oxygen atoms or NH groups and R' is hydrogen or C1 -6 alkyl, provided that water is present when an acrylonitrile or methacrylonitrile copolymer is used, thereby replacing a proportion of the esterified carboxyl or nitrile side chains of the copolymer by groups of the formula -CO-NH-X'-NHR' wherein X' and R' are as defined above; and (c) reacting the product of step (b) with an alkali metal chloroacetate.

If an acrylate or methacrylate ester is used in the first step of the process of this invention it will usually be the methyl or the ethyl ester, but higher esters of acrylic or methacrylic acid such as the propyl, isopropyl or butyl ester or any higher paraffinic or cycloparaffinic ester can also be used. Suitable cross-linking agents for use in the preparation of such copolymers are known and are usually di-ethylenically unsaturated compounds. Divinylbenzene is the preferred agent but other suitable compounds which can be used include trivinylbenzene, alkyldivinylbenzenes having up to 4 methyl or ethyl groups, ethylene glycol dimethacrylate and divinyl ketone. The concentration of crosslinking agent is suitably from 1 to 20%, the lower concentrations being suitable for gel resins and the upper concentrations for macroporous resins.

In the second step of the process of the invention, the copolymer is reacted with a polyamine, of formula II, which contains one or two primary amino groups and which may contain secondary amino groups. This ammonolysis reaction is preferably carried out in such a way that the copolymer beads are suspended in the polyamine and, if desired, a suitable solvent and are heated for a predetermined period of time under normal or increased pressure. When an acrylonitrile or methacrylonitrile copolymer is used, water and, if desired, catalytic quantities of a strong acid must also be added. The polyamine is preferably symmetrical if R' is hydrogen (which is preferred). Thus X' is usually of formula III or, preferably, of formula IV (CH2)rnD'(CH2)nD'(CH2)rn III (CH2)mD'(CH2)m IV wherein D' is a valence bond, -0- or -NH- and m and n are each one, 2, 3, or 4. The preferred polyamines for use in the ammonolysis reaction are ethylenediamine, 1,3propylenediamine, diethylenetriamine, dipropylenetriamine and 4,7-dioxadecan-1 ,10- diamine. The most preferred polyamine is diethylenetriamine.

the the last step of the process of the invention, the primary and/or secondary amine groups in the side chains of the cross-linked subsituted copolymer are reacted under suitable conditions with an alkali metal chloroacetate, e.g. sodium chloroacetate.

Depending on the amount of, say, sodium chloroacetate which is used, the primary amine groups of the side chain react to give iminodiacetate or aminoacetate groups (V and VI) and any secondary amine groups which are present give iminoacetate groups (VII): -N(CH2COONa)2 -NHCH2COONa N- CH2COONa V VI VII The group of formula V is directly capable of complexing metals while those of formula VI and VII might have to rely on a suitable steric configuration for true complexing to occur.

Preferably sufficient chloroacetate is used to convert all primary amine groups to iminodiacetate group (V) rather than aminoacetategroups (VI).

All the primary and any secondary amine groups in the side chain can be reacted with chloroacetate molecules to introduce a large number of iminoacetic or iminodiacetic acid groups per monomeric unit in the resin, and the capacity of the resultant resin for heavy metals (which can be expressed as milliequivalents of the metal per 1 gram dry resin) is very high in comparison with conventional chelating resins.

For the acetylation, the basic form of the substituted crosslinked polyamide is suspended in a strong solution of sodium chloroacetate and reacted at room or elevated temperature for from 2 to 15 hours, during which a solution of sodium hydroxide is added at a rate such that the pH of the system is maintained between 8 and 9. On preparation, the chelating resin is washed with water and is ready for use.

It will be appreciated that, when Xis of formula III or IV, X in the product will be of formula IIIa or IVa, respectively: (CH2)m - D - (CH2)n - D - (CH?)rn IIIa (CH2)m - D - (CH2)rn IVa wherein D is a valence bond, -0- or -NY- and m and n are as defined above, NY being -NH- or, depending on the degree to which the chloroacetate reacts with any such secondary amino group, -N(CH2COOZ) -. The preferred polyamides described above will give rise to products of formula I in which X is -(CH2)2-, -(CH2)3-, - (CH2)2-NY- (CH2)2 - , - (CH2)3 -NY- (CH2)3 - or -(CH2)3-O-(CH2)4-O-(CH2)3-, respectively. X is most preferably -(CH2)2-NY-(CH2)2-.

The novel resins will usually be prepared in a form in which Z is sodium or another alkali metal such as potassium. These products can be converted to those in which Z is hydrogen or ammonium by known procedures. Z is preferably hydrogen or an alkali metal and most preferably hydrogen or sodium.

The products of the invention may have similar molecular weights to commercially available chelating resins and so this value may vary over a very wide range.

The resins of the invention can be put to any of the uses known for chelating resins but are especially useful owing to their good mechanical properties. In addition, the novel resins can be used in the applications described and claimed in copending British Application No. 17984/77 serial No. 1598686.

The following Examples illustrate the invention.

Example 1 Damp crosslinked (3% w/w divinylbenzene) polyethyl acrylate beads of 0.3 to 1.00 mm diameter (200 g) were suspended in 1200 g of diethylenetriamine and heated at 1750C for 20 hours. The water present on the beads and the ethanol formed during the reaction as a by-product were allowed to distil off from the vessel. After cooling, excess amine was filtered off and the resin washed with water. The characteristics of this intermediate were: swelling in water 1.64 g water/g dry resin; dry weight capacity 7.32 meq/g dry resin.

To 796 g of chloroacetic acid dissolved in the minimum of water, 533 g of a 63% w/w solution of sodium hydroxide were added. The temperature was kept below 40"C. and the pH below 9.

To 2000 g of this solution was added 673 g of surface dry resin (approx. 260 g dry resin) and the mix was heated to 100"C. Over 5 hours, 240 g of sodium hydroxide were added dropwise as a 5% w/w solution, the pH being kept below 9. After a further 1 hour at 100"C, the resin was washed with a limited quantity of water.

The resin was tested as follows: A solution containing 1000 ppm Ca and 100 ppm Zn (both as choride salts) was adjusted to a pH of 4.5. This solution was passed through a 10 ml column of the resin (in the sodium form) at the rate of 12 bed volumes per hour and the effluent was collected and analysed.

The run was terminated at 2ppm Zn breakthrough. Regeneration was carried out with N hydrochloric acid at 3 bed volumes per hour. 10 bed volumes gave complete elution.

The resin capacity for zinc in the presence of 10 times excess of calcium ion was 1.44 meq/g dry resin. A commercial chelating resin based on polystyrene structure gave a capacity 1.08 meq/g dry resin under identical experimental conditions.

Example 2 Damp crosslinked (7% w/w divinylbenzene) polyethyl acrylate heads containing 30% v/v n-heptane during their preparation of 0.3 to 1.0 mm diameter (200 g) were suspended in 1000 g diethylenetriamine and heated at 175"C, for 20 hours. The water and n-heptane present and the ethanol formed during the reaction as a by-product were allowed to distil off from the vessel. After cooling, excess amine was filtered off and the resin washed with water. The characteristics of this intermediate were: swelling in water 1.61 g water/g dry resin; dry weight capacity 7.07 meq/g dry resin.

To 682 g sodium chloroacetate, dissolved in 400 ml water, 470 g of surface dry resin (approx. 180 g dry resin) were added, and the mix was heated to 100"C. Over 7 hours 166g sodium hydroxide were added dropwise as a 5% w/v solution in water, the pH being kept below 9. After a further 1 hour at 100"C., the resin was filtered and washed with a limited quantity of water.

The characteristics of this chelating resin were: swelling in water 1.25 g water/ g dry resin; Cu++ capacity (total) 4.70 meq/g. The resin was slightly macroporous.

Example 3 Damp crosslinked (2.5 % w/w divinylbenzene) polyethyl acrylate beads of 0.3 to 1.0 mm diameter (200 g) were suspended in 1000 g ethylenediamine and heated at 117"C for 20 hours. The water present in the beads and the ethanol formed during the reaction as a by-product were allowed to distil off from the vessel. After cooling excess amine was filtered off and the resin washed with water. The characteristics of this intermediate were: swelling in water 2.90 g water/g dry resin; dry weight capacity 5.47 meq/g dry resin.

To 900 g sodium chloroacetate dissolved in 520 ml water, 890 g surface dry resin (approx.

230 g dry resin) were added, and the mix was heated to 100"C. Over 4 hours, 220 g sodium hydroxide were added drop-wise as a 5% w/w solution, the pH being kept below 9. After a further 1 hour at 100"C, the resin was filtered and washed with a limited quantity of water.

The characteristics of this chelating resin were: swelling in water 1.90 g water/g dry resin, Cu++ capacity (total) 5.42 meq/g dry resin.

Example 4 Dry crosslinked polyacrylonitrile beads containing 6% w/w divinylbenzene and 5% w/w isoprene of 0.3 to 1.0 mm diameter (200 g) were suspended in 700 g diethylenetriamine containing 50 g water and heated at 1500C in a pressure vessel for 20 hours. After cooling, excess amine was filtered off and the resin washed with water. The characteristics of this intermediate were: swelling in water 1.12 g water/g dry resin; dry weight capacity 6.46 meq/g dry resin.

To 950 g sodium chloroacetate, dissolved in 600 ml water, 560 g of surface dry resin (approx 270 g dry resin) were added, and the mixture was heated to 100"C. Over 10 hours 231 g sodium hydroxide were added dropwise as a 5% w/v solution in water, the pH being kept below 9. After a further 2 hours at 100"C. the resin was filtered and washed with a limited quantity of water.

The characteristics of this chelating resin were: swelling/water 0.73 g water/g dry resin, Cu++ capacity (total) 3.30 meq/g resin.

Claims (14)

WHAT WE CLAIM IS:

1. A process for preparing, in the form of beads, a chelating resin having monomeric units of the formula

wherein A is hydrogen or methyl; R is hydrogen, C16 alkyl or CH2COOZ; Xis an alkylene chain of one to 12 carbon atoms optionally interspersed with oxygen atoms or NH or NCH2COOZ groups; and Z is hydrogen, an alkali metal or ammonium; the process comprising (a) preparing a copolymer, in the form of beads, by reacting an acrylate ester, a methacrylate ester, acrylonitrile or methacrylonitrile with a cross-linking agent; (b) reacting the copolymer with a polyamine of the formula H2N-X'-NHR' wherein X' is alkylene of 1 to 12 carbon atoms optionally interspersed with oxygen atoms or NH groups and R' is hydrogen or C16 alkyl, provided that water is present when an acrylonitrile or methacrylonitrile copolymer is used, thereby replacing a proportion of the esterified carboxyl or nitrile side chains of the copolymer by groups of the formula -CO-NH-X' -NHR' wherein X' and R' are as defined above; and (c) reacting the product of step (b) with an alkali metal chloroacetate.

2. A process according to claim 1 wherein X' is a group of the formula - (CH2)rnD'(CH2)nD'(CH2)rn wherein D' is a valence bond, -0- or NH and m and n are independently selected from one, 2, 3 and 4.

3. A process according to claim 1 wherein X' is a group of the formula (CH2)rnD'(CH2)rn wherein D' and m are as defined in claim 2.

4. A process according to claim 3 wherein X' is -(CH2)2-, -(CH2)3-, - (CH2)2- NH- -(CH2)2-,-NH-(CH2)3-- or -(CH2)3-O-(CH?)J-O-(CH2)3- .

5. A process according to claim 4 wherein X' is -(CH2)2-NH-(CH2)2-.

6. A process according to any preceding claim wherein R is C1-6 alkyl or CH2COOZ and Z is as defined in claim 1.

7. A process according to claim 6 wherein R is CH2COOZ and Z is as defined in claim 1.

8. A process according to any preceding claim wherein Z is hydrogen or an alkali metal.

9. A process according to claim 8 wherein Z is hydrogen or sodium.

10. A process according to claim 1 substantially as described in Example 1.

11. A process according to claim 1 substantially as described in any of Examples 2 to 4.

12. Beads of chelating resin when prepared by a process according to any preceding claim.

13. Beads of a chelating resin when prepared by a process according to any of claims 8 to 10.

14. A method of chelating a metal which comprises contacting a solution of the metal with beads of a chelating resin according to claim 12 or claim 13.