IL102636A - Gelled material compositions and their preparation - Google Patents

Description

Gelled material compositions and their preparation YEDA RESEARCH AND DEVELOPMENT COMPANY LIMITED »"y2 m«n Ί η» man y"T» The inventors ;- 1. Gideon LEVIN 1M ντλ .1 2. Lev BROMBERG aa a a!? .2 C:- 85526 FIELD OF INVENTION The invention is in the field of organic synthetic polymers and relates specifically to gelled materials and beads prepared therefrom as well as to a method and a process for their preparation. These gelled materials and beads are characterized, inter alia, by high stability in contact with water solutions of inorganic salts and may be used in ion-exchange processes.

LIST OF REFERENCES: 1. A. Warshawsky in "Ion Exchange and Solvent Extraction", Eds. A.

Marinsky and Y. Marcus, Marcel Dekken, New York, Vol. 8, Chap. 3, p. 230. 2. H. Small, /. Inorg Nucl. Chem. (1961), 18, 232. 3. D. Oktavec, J. Stefanec, B. Silec, V. Konecmy and J. Garaj, Collection Czechoslov. Chem. Commun. " (1977), 44, 2487.

I.S. Levin, V.V. Sergeeva, V.A. Tarasova et al., Zh. Neorg. Khim. (1973), 18, 1643.

BACKGROUND AND PRIOR ART Resins containing extractants have been used in analytical, hydrometallurgical and water processes. These impregnated resins have been prepared by two different general approaches (1): i) Physical impregnation on a selected polymeric carrier, thus providing a solvent-impregnated resin, ii) Polymerization or copolymerization of two or more monomers containing a cross-linking agent in the presence of an extractant, thus providing a gel.

A variety of different types of gels that contain specific extractants are known and these can be classified as follows (1): 1. Gel-type resins from copolymerization of certain monomers. 2. Modified gel type resins, obtained by polymerization in an inert solvent. In cases where the solvent dissolves the monomer and solvates the polymer, telogenated polymers are produced, whereas when the polymer precipitates out, macroporous structures are obtained. 3. Swelled, cross-linked polymers or copolymers. Here the cross- linking agents are long-chain spacers instead of the conventional divinyl-benzene. These polymers have the ability to swell and Small (2) suggested that this property be utilized to incorporate extractant into the gel polymer.

Gelled materials are very attractive materials for use in exchange processes in general and ion-exchange processes in particular. The efficacy of such gels is due to the fact that with such materials the exchange process takes place nearly in the entire volume of the gel, while in conventional exchangers the exchange process takes place only on a surface of the polymeric support due to slow diffusion of ions through the bulk.

However, all the above known gel-type materials have a relatively low chemical and physical stability and thus suffer from high extractant losses. Also, the technologies for their preparation are complicated and expensive. In addition, preparation of stable and homogeneous beads from known gelled materials is difficult and relatively expensive.

There is thus a need for a new approach leading to cheap, improved gelled materials with high chemical and physical stability, high exchange capabilities and which are suitable for preparation of beads.

OBJECTS OF THE INVENTION It is thus the object of the present invention to provide gelled materials comprising a chemically modified organic synthetic polymer and an extractant which overcome most of the above drawbacks of known gelled materials, and methods for their preparation.

It is a further object of the present invention to provide stable and homogeneous beads for use in ion-exchange operations comprising a chemically modified organic polymer and specific extractant, and a process for the preparation thereof.

SUMMARY OF THE INVENTION The invention is based on the finding that a simple specific chemical modification of polymers having a halogen atom in their backbone, e.g. polyvinyl chloride (PVC), such polymers to be referred to hereinafter as "halopolymers", increases the compatibility between the polymer and some specific extractant and is capable of forming together therewith stable gelled materials. It was found that only when the group used to modify the halopolymer is identical with or chemically closely related to the specific extractant, the halopolymer and the extractant become - 4 - 102636/2 compatible and form a stable gelled material. The gelled materials so obtained were found useful for preparing beads for ion-exchange processes.

The term "specific extractant" used herein denotes a substance having a selective affinity to a desired ion or molecule and thereby being capable of selectively extracting such ion or molecule from mixtures in which it is contained.

The invention thus provides a gelled material composition suitable for the performance of exchange processes, comprising a specific extractant being a member selected from the group consisting of di(2— ethylhexyl)dithiophosphoric acid and di(2-ethylhexyl) phosphoric acid, an organic solvent and a modified halopolymer substituted with a radical of a substance compatible with said specific extractant.

If desired, the composition may comprise also an amount of unmodified halopolymer.

The term "compatible" as used herein means that the substance from which the said radical used to modify said halopolymer is derived, is identical with the specific extractant used, is a derivative or a salt thereof or is a compound which is physically compatible with said specific extractant, in that they have similar solubility properties. The stipulated compatibility is thus either chemical or physical and may also be a combination of both.

An example of a specific extractant is di(2-ethylhexyl)dithio-phosphoric acid and examples of modifying substances compatible therewith are the alkali salts of dialkyldithiocarbamate or of dialkyldithiophosphoric acid wherein the alkyl moiety has at least 5 carbon atoms, e.g. the alkali salts of dioctyldithiocarbamate and diisooctyldithiophosphoric acid.

The starting halopolymer used in accordance with the present invention for making said modified halopolymer may, for example, be a halogenated polyvinyl such as polyvinyl chloride; halogenated derivatives of any of polyolefin; polyvinylacetate; polystyrene; polyacrylate; polyacrylamide; and the like. A preferred starting polymer is polyvinyl chloride, further examples being a copolymer of vinylchloride with any of vinylacetate, acrylonitrile, vinyl alcohol, an acrylate, acrylamide and others.

The invention also provides a method for preparing a gelled material composition of the kind specified above characterized in that a halopolymer is modified by reaction with a substance compatible with said specific extractant, the modified halopolymer so obtained is admixed with said specific extractant and the resulting mixture is dissolved in an organic solvent.

If desired, the organic solvent may be heated in order to obtain an homogeneous solution.

Examples of organic solvents which may be used in accordance with the invention are dioxane, tetrahydrofuran (THF), dimethyl-sulfoxide (DMSO) and dimethylformamide (DMF).

By another aspect the invention provides beads for use in ion-exchange processes comprising at least one gelled material composition of the kind specified above.

By a further aspect of the invention, there is provided a process for the preparation of such beads, comprising dripping a gelled material composition of the kind specified into an aqueous surfactant solution, filtering off the solution and drying the beads so obtained, if desired under vacuum.

Particularly good results are obtained when the organic solvent in the gelled material composition from which the beads are prepared is dioxane.

Suitable surfactants for use in the above process are those selected from the group consisting of polyethyleneglycol, polyvinylacetate, or a copolymer of polyethylene glycol terminated by substituted phenols, a preferred surfactant being an aqueous solution of 4% (v/v of) polyethyleneglycol having a molecular weight of about 4,000.

By yet another aspect the invention provides as novel products a PVC based polymer selected from the group consisting of dioctyldithio- carbamate-substituted PVC; diisooctyldithiophosphate-substituted PVC and di (2-ethylhexyl) dithiophosphate-substituted PVC.

The gelled materials and the beads prepared according to the present invention have the advantage of being chemically and physically stable and they profess only relatively low losses of extractant even when in the course of an ion-exchange operation a very aggressive eluent of extremely low pH is used. The beads have good ion-exchange capabilities and, in addition, it was found that the beads prepared according to the present invention are round and homogeneous - a characteristic which generally is difficult to obtain.

The method of preparing a gelled material and the process of making beads therefrom, both as taught by the present invention, are simple and inexpensive. The starting halopolymer may be polyvinyl chloride, a cheap and well known polymer, which may be modified by a simple, one step nucleophilic reaction.

DESCRIPTION OF THE DRAWINGS In the following Examples the preparation of gelled materials and beads therefrom as well as results achieved with beads prepared in accordance with the present invention will be described with reference to the annexed drawings in which: Fig. 1 is a graph showing the elution of Ag+, Cd2* and Pb2+ by different eluents from a column packed with beads prepared according to Example 4 herein and loaded with these cations; Fig. 2 is a graph showing the elution of Fe3+ and Hg2* by different eluents from a column of beads prepared according to Example 4 herein, and loaded with these cations; Fig. 3 is a scanning electron microscopy (SEM) picture of a bead prepared according to Example 6; Fig. 4 is an output curve obtained by the displacement of K+ by Ni2+ and Zn2+ in aqueous solution from a column packed with beads prepared according to Example 6 and which was first treated with a saturated aqueous solution of KN03; Fig. 5 is a graph showing the elution of Ag* and Pb2+ by different eluents from a column packed with beads prepared according to Example 6 and loaded with these cations; and Fig. 6 is a graph showing the recovery of Ag+ cations from an AgN03 solution in deionized water (curve A) and from Kodak Co. developer waste solution (curve B) using beads prepared according to Example 6, with the use of different eluents.

Example 1: Preparation of a chemically modified polymer: A dioctyldithiocarbamate-substituted polymer Dioctyldithiocarbamate (DODTC) which is used as a nucleo-philic agent in the reaction with polyvinyl chloride (PVC) to produce the modified polymer containing the DODTC group, was first prepared by reacting the sodium salt of dioctylamine with carbon disulfide according to the general procedure given in ref. 3. Then one mol of PVC (43 grade, Frutarom, Israel) was dissolved in 750 cm3 of dried dimethylformamide (DMF) until a transparent solution was obtained. Then a solution of 0.4 mol of DODTC sodium salt in 200 cm3 of DMF was added to the above solution. The obtained solution was heated to 45 °C under stream of nitrogen for several hours. Samples were withdrawn from the reaction mixture at various intervals and dissolved in methanol and precipitated therefrom. The polymer was washed with water and methanol to remove the unreacted DODTC and the remaining sodium salt, and dried under vacuum at room temperature. Sulfur (S, /w%) and chlorine (Cl,w/w%) elemental analysis as a function of the reaction time are given in Table 1: TABLE 1 The relation between the reaction time and the sulfur w/w content (%S), and chlorine w/w content (%C1) of dioctyldithiocarbamate-substituted PVC.

Sample Time, min %S %C1 0 0 0.00 56.80 1 90 4.85 42.45 2 180 5.52 38.75 3 270 6.12 36.64 4 345 7.06 34.72 5 2 days 8.59 28.18 Complete substitution (calculated) 18.65 6.00 Example 2: Preparation of a chemically modified polymer; A di(2- ethylhexyDdithiophosphate-suhstituted PVC Di(2-ethylhexyl)dithiophosphoric acid was synthesized and purified according to ref. 4. The sodium salt of di(2-ethylhexyl)dithio-phosphoric acid was prepared by the reaction- of 0.019 mol of NaH with 0.02 mol of di(2-ethylhexyl)dithiophosphoric acid.

The modification of the polymer was carried out in the following way: 0.06 Mol of PVC (43 grade, Frutarom, Israel), was mixed with 25 cm3 of dried DMF until a transparent solution was obtained. To this solution there was added 0.02 mol of the sodium salt of di(2-ethylhexyl) dithiophosphoric acid dissolved in 35 cm3 of DMF. The mixture was heated to 45°C under nitrogen. The polymer was washed with water and methanol to remove the unreacted di(2-ethylhexyl)dithiophosphoric acid and the remaining sodium salt, and dried under vacuum at room temperature. Samples were withdrawn from the reaction mixture, at various intervals, dissolved and precipitated therein in methanol. Elemental analysis of one of the polymer fractions showed: S=4.1%, Cl=42.1%.

Example 3: The effect of the nature of the substituting group in the polymer on the formation of gelled material with diQ-ethylhexyl) dithiophosphoric acid To verify the effect of the relationship between the nature of the substituting group on the polymer backbone and the specific extractant on stability of the gels obtained, a series of clear solutions of THF containing the investigated polymers and di(2-ethylhexyl)dithiophoshoric acid were prepared. It was found that PVC, polyvinyl acetate, diethyl-dithiocarbamate-substituted PVC and dibenzyldithiocarbamate-substituted PVC do not form a gel with di(2-ethylhexyl) dithiophosphoric acid. Only the modified polymer of Examples 1 and 2 were found to form stable gel material with di(2-ethylhexyl) dithiophosphoric acid. These results demonstrate that the substituents on the polymer backbone should be compatible with the specific extractant used in the preparation of the gel.

Example 4: Preparation of beads comprising dioctyldithiocarbamate-substituted PVC and di(2-ethylhexyl) dithiophosphoric acid.

A mixture of dioctyldithiocarbamate-substituted PVC (S=4.9%, Cl=42.5%), PVC and di(2-ethylhexyl) dithiophosphoric acid in a weight ratio of 1.0: 2.3: 3.4, was stirred in 10 gr of dioxane at 40°C until a transparent viscous polymeric solution was obtained. The solution was dripped by means of a syringe and a needle into a 4% v/v solution of the surfactant polyethyleneglycol (Mw - 4,000) in deionized water under stirring in a coagulation bath whereupon coagulation took place. The resulting beads were filtered and dried under vacuum. Sulfur and chlorine elemental analysis of the dried beads showed: S=7.7 and Cl=29.5%.

Example 5: The performance of beads prepared according to Example 4.

To evaluate the performance of beads prepared according to the present invention a series of ion-exchanges columns were prepared using the beads prepared according to Example 4.

Each column consisted of a polyethylene tube having an internal diameter 4.5 mm and closed at the end by the three-way stopcock connected to the syringe. Weighted amounts of beads (0.2-0.3 g) were transferred in small increments to the columns and pressed gently with a flat-ended rod in order to obtain a uniform packing of the beads in the column. The resin bed height in the packed columns was set to about 33-35 mm. Beads were then pretreated with 1M H2S04 and rinsed with distilled water. Metal ion concentrations in the eluents were monitored with a Perkin Elmer Model 5100 PC atomic absorption spectrophotometer and pH values were measured with the aid of a Cornin Model 240 pH-meter.

First, aqueous solutions of silver nitrate, lead acetate and cadmium acetate having concentrations of about 100 ppm each were passed through one of the packed columns. Then the column was rinsed with 3 bed volumes of distilled water. All three cations, which form strong neutral or anionic complexes with the gelled material of the beads, were stripped off selectively from the column by changing the constituents of the eluent solutions.

Fig. 1 shows the selective elution of these metal ions by eluents containing proper complexing anions. Using 1M H2S04 saturated with thiourea only Ag+ was stripped off the column (see peak following arrow in Fig. 1) while 9M HQ was used to strip off the column the Cd2+ cation (see peak following arrow 2). Pb2+ was selectively stripped off the column by 0.13M sodium salt of ethylenediaminetetracetic acid (see peak following arrow 3). Each time before the eluent was changed each column was rinsed with 5-10 ml of distilled water.

This experiment clearly demonstrates the selectivity of the separation of microamounts of these metal ions and demonstrates the potential application of beads according to the invention in extraction chromatography for analytical purposes.

The effect of the weight ratio of the constituents of the beads on the performance of the beads in ion extraction chromatography was verified by repeating the above experiment with beads prepared similarly as in Example 4 with, however, a different weight ratio of the modified polymer, PVC and di(2-ethylhexyl) dithiophosphoric acid, which in this case was 1.0: 10.2: 9.0.

Using another packed column, the beads were loaded with Fe+3 and Hg+2 ion by passing through the column water solutions containing Fe(N03)3 and Hg(N03)2 of 100 ppm each and the results are shown in Fig. 2. Fe+3 ion was stripped off the column by using 1 M oxalate (the peak following arrow 1). At this stage no Hg 2+ was stripped off the column and only after the addition of 1M H2S04 saturated with thiourea the Hg2* was strip off the column (peak following arrow 2).

This experiment demonstrates that good elution selectivity is retained even when the weight ratio between the three major constituents of gelled material in the beads is very different.

Example 6; Preparation of beads comprising di(2-ethylhexyn dithiophosphate-substituted PVC and di (2-ethylhexyDdithiophosphoric acid.

A mixture of di(2-ethylhexyl)dithiophosphate-substituted PVC, PVC and di(2-ethylhexyl)dithiophosphoric acid in a weight ratio of 1.0: 0.9: 1.1 was stirred in dioxane at 40°C until a transparent solution was obtained. The weight percent of dioxane in the solution was about 83%. Then the viscous polymeric solution was dripped by means of a syringe and a needle into a 4% v/v surfactant (polyethyleneglycol, « 4,000) solution in deionized water under stirring in a coagulation bath whereupon coagulation occurred. Then the coagulation solution was filtered off and the beads so obtained were dried under vacuum. Sulfur and chlorine elemental analysis of the content of the dried beads showed: S=7.0% and Cl=32.9%. A scanning electron microscopy picture of a bead prepared according to the above procedure is shown in Fig. 3. This cross-cut picture of the bead taken on a SEM Philips Model 505 microscope having a MicroScan Tracor energy dispersive spectroscopy attachment shows the essentially round shape of the bead which has a diameter of about 1mm.

Blank material without any polymer modification was prepared by mixing 0.22 g PVC and 0.22 g of di(2-ethylhexyl) dithiophosphoric acid in 5 g dioxane at 40°C making beads from this material in the manner described above. The elemental analysis of these beads showed: S-8.6% and Cl=33.65%.

Example 7: Performance of beads prepared according to Example 6.

To evaluate the performance, beads prepared according to Example 6 were packed into columns by the procedure described in Example 5.

In a series of experiments by which water solutions of different metal ions were eluted from the columns sequentially, the displacement of metal cations by each other were found to be in excellent agreement with their respective adsorption affinities. For example, Ag+ which forms very stable complexes with the beads containing di(2-ethylhexyl) dithiophos-phoric acid did replace all other metal ions investigated. Ni2* and Zn2+ were able to displace K+ from a column that was loaded on by passing through the column a saturated solution of KN03. A solution of N^CH^COO^ and Zn(CH3COO)2 was run following the KN03 solution and the results of this experiment are shown in Fig. 4.

Similar experiments were conducted with other cations and the sequence of displacement of the various metal cations investigated was found to be in the following order: Ag+ » Hg2* > Pb2+> Fe3+> Cd2+> Ni2+> Zn2+» K+.

These metal ion exchange experiments were also performed using beads prepared from the blank materials which contained only unmodified PVC and di(2-ethylhexyl) dithiophosphoric acid. In the course of the experiment these beads soon lost the described shape forming fibrilles, and almost entirely lost their ion exchange capacity after the first extraction- stripping cycle. In contrast, the cation exchange columns packed with beads prepared according to Example 6 retained their selective ion-exchange capacity during 20 and more extraction-stripping cycles. After an initial decrease of ion-exchange capacity of about 20-30% during the first 5-10 cycles their ion-exchange capacity reached an equilibrium. The CI and S . content of the beads after 25 cycles was found to be: S=3- 5% and Cl=42.3-47.5%.

In a separate experiment a column was loaded with Ag+ and Pb2* by passing through the column solutions of AgN03 and Pb(CH3COO)2 having concentrations of about 100 ppm each. Then two eluent solutions, one of 1M H2S04 saturated with thiourea and the other of 0.13M sodium ethylenediaminetetracetic acid were passed through the column sequentially. The results are shown in Fig. 5. As can be seen, Ag+ was stripped off from the column by eluting with 1M H2S04 saturated with thiourea (peak following arrow 1) and the Pb2+ cation was stripped off by elution with 0.13M EDTA solution. These results show that also these beads have high metal ions selectivity and may thus also be used for analytical purposes.

In further experiments the recovery of silver cations from aqueous solutions by means of columns packed with beads prepared according to Example 6 was monitored. Fig. 6 demonstrates the performance of the column in the extraction of silver cations from a solution of AgN03 in deionized water (curve A) and from a filtered waste solution containing AgN03 (curve B). The waste solution was obtained from the photographic process using a photofinisher of Kodak Co. (curve 2) and contained 1.4mM AgN03, 1.3 M Na^Oj and lOmM NaBr.

Fig. 6 also demonstrates the selectivity of the stripping off of the Ag+ cations from these beads. No elution of Ag+ occurred with 1.3M Na2S203 solution (flat part following arrow 1). By contrast, fast elution took place with a 1M H2S04 and 9M HC1 (peak following arrow 2).

These experiments demonstrate that the beads prepared according to the present invention are very stable and have a very high cation selectivity. Very aggressive eluents such as 1M H2S04 and 9M HC1 may be used and the beads may be used repeatedly without a significant reduction in their ion-exchange capability. The blank experiments do prove unequivocally that the nature of the gels and beads according to the present invention is responsible for the superior ion-exchange performance.

These above experiments also show that ion-exchange capacity and selectivity of the gels and beads according to the invention is manifested within a wide range of weight ratio between the three major components thereof.

Claims (20)

- 16 - 102636/2 CLAIMS:

1. A gelled material composition suitable for the performance of exchange processes, comprising a specific extractant being a member selected from the group consisting of di(2-ethylhexyl)dithiophosphoric acid and di(2-ethylhexyl) phosphoric acid, an organic solvent and a modified halopolymer substituted with a radical of a substance compatible with said specific extractant.

2. A gelled material composition according to Claim 1, wherein said substance compatible with said specific extractant, is a member selected from the group consisting of alkali salts of dialkyldithiocarbamates and dialkyldithiophosphoric acid in which the alkyl moiety has at least five carbon atoms.

3. A gelled material composition according to Claim 1 or 2, wherein said halopolymer is selected from the group consisting of a halogenated derivative of any of polyolefin, polyvinyl, polyvinylacetate, polystyrene, polyacrylate, and polyacrylamide.

4. A gelled material composition according to Claim 1 or 2, wherein said halopolymer is a copolymer of vinylchloride.

5. A gelled material composition according to Claim 1 or 2, wherein said halopolymer is polyvinyl chloride.

6. A process of preparing a gelled material composition according to any one of Claims 1 to 5, characterized in that a starting halopolymer is modified by reaction with a substance compatible with said specific extractant, the modified halopolymer so obtained is admixed with said specific extractant and the resulting mixture is dissolved in an organic solvent.

7. A process according to Claim 6, wherein an amount of unmodified halopolymer is incorporated in the said resulting mixture. - 17 - 102636/2

8. A process according to Claim 6 or 7, wherein the starting halopolymer is selected from the group consisting of a halogenated derivative of any of polyolefin, polyvinyl, polyvinylacetate, polystyrene, polyacrylate, and polyacrylamide.

9. A process according to any one of Claims 6 to 8, wherein the starting halopolymer is polyvinyl chloride or a vinylchloride copolymer.

10. A process according to any one of Claims 6 to 9, wherein the organic solvent is heated.

11. A process according to any one of Claims 6 to 10, wherein the organic solvent is a member of the group of dioxane, tetrahydrofuran, dimethylsulfoxide and dimethylformamide.

12. Beads for use in ion-exchange processes, comprising at least one gelled material composition according to any one of Claims 1 to 5.

13. A process for the preparation of beads according to Claim 12, comprising dripping at least one gelled material composition according to any one of Claims 1 to 5 into an aqueous surfactant solution, filtering off the aqueous solution and drying the beads so obtained.

14. A process according to Claim 13, wherein the organic solvent in said gelled material composition is dioxane.

15. A process according to Claim 13 or 14, wherein the beads are dried under vacuum.

16. A process according to any one of Claims 13 to 15, wherein the surfactant is a polyethylene glycol.

17. A process according to Claim 16, wherein the surfactant is a polyethylene glycol having a molecule weight of about 4,000.

18. A process according to Claim 17, wherein said surfactant is used in the form of a 4% v/v aqueous solution. - 18 - 102636/2

19. A process according to any one of Claims 13 to 15, wherein the surfactant is a copolymer of polyethylene glycol terminated by a substituted phenol group.

20. As novel product, a member of the group consisting of dioctyl-dithiocarbamate-substituted polyvinyl chloride; diisooctyldithiophosphate-substituted polyvinyl chloride and di(2-ethylhexyl) dithiophosphate-substituted polyvinyl chloride. 85526-2-aaims-MC/be/30.10.1995