Alkylphosphonium-functionalized ion exchange resins

Abstract

Provided are ion exchange resins comprising an insoluble matrix having functional groups bonded thereto, the functional groups comprising a quaternary alkylphosphonium salt represented by the formula: - P(R1R2R3)+ X- wherein X- is an anionic counterion; and R1, R2 and R3 are independently acyclic hydrocarbon groups having a carbon chain length of C4 to C18. Systems for PFAS removal from water and methods of PFAS removal from water are also provided.

Description

[0001] ALKYLPHOSPHONIUM-FUNCTIONALIZED ION EXCHANGE RESINS

[0002] BACKGROUND

[0003] Water used in homes and by industries, i.e., wastewater, commonly needs to be treated before if can be safely released back to the environment. Wastewater treatment can involve a variety of physical, chemical, and biological processes and is a common form of pollution control.

[0004] Due to increasing demands on water supplies, there is a need for improvement in the efficiency and effectiveness of wastewater treatment methods and systems.

[0005] SUMMARY

[0006] In one aspect, provided are ion exchange resins comprising an insoluble matrix having functional groups bonded thereto, the functional groups comprising a quaternary alkylphosphonium salt represented by the formula:

[0007] - P(RIR2R3)+X- wherein

[0008] X" is an anionic counterion; and

[0009] Ri, R2and R3 are independently acyclic hydrocarbon groups having a carbon chain length Of C4 tO C18.

[0010] In another aspect, provided are systems for the removal of PFAS from water, the system comprising: a vessel containing an ion exchange resin, the ion exchange resin comprising an insoluble matrix having functional groups bonded thereto, the functional groups comprising a quaternary alkylphosphonium salt represented by the formula:

[0011] - P(RIR2R3)+X- wherein

[0012] X- is an anionic counterion; and

[0013] Ri, R2and R3 are independently acyclic hydrocarbon groups having a carbon chain length of C4 to Cis; an inlet for directing a flow of water into the vessel to thereby contact the ion exchange resin; and an outlet for directing a flow of water out of the vessel.

[0014] In another aspect, provided are methods for removal of PFAS from water, the process comprising: exposing an aqueous solution including a PFAS to an ion exchange resin the ion exchange resin comprising an insoluble matrix having functional groups bonded thereto, the functional groups comprising a quaternary alkylphosphonium salt represented by the formula: - P(RIR2R3)+X- wherein

[0015] X- is an anionic counterion; and

[0016] Ri, R2and R3 are independently acyclic hydrocarbon groups having a carbon chain length Of C4 tO C18.

[0017] As used herein: the term “fully saturated” refers to an organic group including only carbon-carbon single bonds; the term “partially saturated” refers to an organic group including at least one double or triple carbon-carbon bond; the term “PFAS” refers to per- and polyfluoroalkyl substances , such as, for example perfluorooctanoic acid (“PFOA”), perfluorooctane sulfonic acid (“PFOS”), perfluoropropionic acid (“PFPA”), perfluorobutyric acid (“PFBA”), trifluoroacetic acid (“TFA”), and perfluorobutane sulfonic acid (“PFBS”); the term “substituted” refers to a hydrocarbon group wherein at least one hydrogen atom is replaced by a non-hydrogen atom or group (e.g. halide, ethyl, phenyl); the term “unsubstituted” refers to a hydrocarbon group wherein no hydrogen atom is replaced by a non-hydrogen atom or group.

[0018] Features and advantages of the present disclosure will be further understood upon consideration of the detailed description as well as the appended claims.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is schematic of a system including an alkylphosphonium-functionalized ion-exchange resin according to the present disclosure.

[0021] FIG. 2 shows PFPA isotherms of trialkyphosponium and trialkylammonium functionalized PS resins.

[0022] FIG. 3 shows TFA isotherms of trialkyphosponium and trialkylammonium functionalized PS resins.

[0023] Repeated use of reference characters in the specification and drawings is intended to represent the same or analogous features or elements of the disclosure. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the disclosure. The figures may not be drawn to scale. DETAILED DESCRIPTION

[0024] Removal of per- and polyfluoroalkyl substances ("PF AS") from water is an increasingly important aspect of wastewater treatment. One method of PFAS removal is extraction via ion exchange resins. By passing the PF AS-contaminated water through a bed of appropriately functionalized ion exchange resin, target PFAS molecules can be removed from a wastewater stream. However, because each PFAS is unique and different resins have different affinities for a given molecule, there is an ongoing need for the development of novel resins to effectively remove specific PFAS from wastewater streams.

[0025] For example, PFAS materials including four or fewer carbon atoms (e.g., sodium pentafluoropropionic acid, trifluoroacetic acid, heptafluorobutyric acid, trifluoromethanesulfonic acid, nonafluorobutanesulfonic acid) are often more difficult to remove from aqueous solutions than longer- chain PFAS materials. Thus, resins with a higher affinity for these small-chain compounds may provide advantages when compared to the currently available resins used for ion exchange wastewater treatment.

[0026] Functionalized polystyrene ("PS") resins including ammonium groups are known and used to remove small-chain PFAS from wastewater streams, with tributyl ammonium functionalized PS being the most effective resin for short-chain PFAS removal. Synthesis of resins such as these is typically accomplished by displacement between an amine nucleophile and a chloromethylene group appended to the polystyrene polymer backbone. Though direct functionalization of the polystyrene beyond C4 tertiary amines has proved to be impractical, at least in part due to low ammonium functional group formation as a result of decreased reactivity of the amine with the chloromethylene residue of the resin, it was surprisingly determined that phosphonium-functionalized PS resins, wherein the phosphonium functional groups are comprised of acyclic alkyl chains greater than four carbons in length (e.g., trihexylphosphine, trioctylphosphine), provide materials with a higher PFAS affinity than that of the tributylammonium- functionalized resin.

[0027] Provided in the present disclosure are ion exchange resins including an insoluble matrix having functional groups bonded thereto, where the functional groups comprise a quaternary alkylphosphonium salt represented by the formula:

[0028] - P(RIR2R3)+X- wherein X" is an anionic counterion and Ri, R2 and R3 are independently acyclic hydrocarbon groups having a carbon chain length of C4 to Cis. The acyclic hydrocarbon groups can be normal or branched. The acyclic hydrocarbon groups may be fully saturated or partially saturated. The acyclic hydrocarbon groups may be substituted or unsubstituted. Any of the hydrocarbon groups may optionally include a heteroatom (e.g., O, N, S) in the hydrocarbon chain. In some embodiments, Ri, R2 and R3 are the same. In some embodiments, Ri, R2 and R3 are independently acyclic hydrocarbon groups having a carbon chain length of G, to Cs. In some embodiments, the insoluble matrix is selected from the group consisting of a polymer, a gel, a clay, a diatomaceous earth, and combinations thereof. In some preferred embodiments, the polymer comprises polystyrene. In some embodiments, the anionic counterion is selected from the group consisting of a halide (e.g., chloride, bromide, iodide), an inorganic and ionic oxide (e.g., sulfate, nitrate), an organic anion (e.g., acetate), and combinations thereof.

[0029] One or more ion exchange resins may be useful in embodiments of the present disclosure. Such ion exchange resins typically include an insoluble matrix, substrate, or support structure. In some embodiments, the support structure is in the form of small, spherical beads having an average diameter ranging from about 1 mm to about 2 mm. In some embodiments, the support structure is a polymeric substrate, where the surface of the polymeric substrate includes sites that trap and release ions. In some embodiments, the ion exchange resins useful in the present invention may be based on one or more polymeric materials which may or may not be crosslinked. In some embodiments, the substrates are based on styrene that has been crosslinked with a cross-linker such as divinyl benzene, for example. Crosslinked polymeric substrates may also be porous, and a crosslinked substrate will tend to be hard and not malleable. Polymeric substrates that are not crosslinked can be softer and more malleable than a crosslinked substrate and can have a gel-like consistency, depending on the material used.

[0030] In some embodiments, the ion exchange resin can comprise a matrix material in the form of non- spherical particles. In still other embodiments, the matrix can comprise a material that is more amorphous or gel-like such as silica gel, diatomaceous earth, clay, or the like.

[0031] In still other embodiments, the ion exchange resin of the present disclosure is a ‘difunctional’ resin comprising two or more different quaternary alkylphosphonium groups. For example, a single ion exchange resin may comprise the quaternary amine groups +P(C6HI3)3 and +P(CsHi7)3.

[0032] Ion exchange resins suitable for use in embodiments of the present disclosure may be prepared by the chemical modification of resins known to those of ordinary skill in the relevant arts. In one embodiment, a suitable ion exchange resin is prepared by the reaction of a chloromethylated styrene bead (or other electrophilic group-containing resin) with a tertiary phosphine such as, for example, trihexylphosphine or trioctlyphosphine in a polar aprotic solvent such as 1,4-dioxane. The reaction of the tertiary phosphine and the chloromethylated styrene bead is represented by Scheme 1, where Ri, R2, and R3 are as previously described.

[0033] Scheme 1: Those skilled in the relevant arts will appreciate that resins within the scope of the present disclosure can comprise matrix materials other than styrene. Suitable matrix materials include without limitation polymers, gels, clays, diatomaceous earth and combinations of two or more of the foregoing. In some embodiments, a suitable polymer matrix is polystyrene. In some embodiments, a suitable gel matrix is silica gel.

[0034] Referring now to the drawings, FIG. 1 schematically illustrates an ion exchange system 10 for the removal of PFAS from water, according to the present disclosure. The system 10 includes a flow- through vessel 12 which can be provided in any of a variety of configurations. In the depicted embodiment, the vessel 12 is cylindrical column having an ion exchange bed 14 comprised of ion exchange resin contained within the vessel 12. The ion exchange resins within the bed 14 are those described herein. An inlet 16 at a first end of the vessel 12 allows for the introduction of untreated water into the vessel 12. The water is pumped into the vessel 12 through the inlet 16 and through the ion exchange bed 14. PFAS and other contaminants in the water stream are removed from the water by the ion exchange mechanism provided by the resins in the ion exchange bed 14. Treated water is directed out of the vessel 12 through an outlet valve 18 at the opposite end of the vessel from the inlet 16.

[0035] In all embodiments, untreated water comprising PFAS is exposed to an ion exchange resin for a sufficient period of time to have the PFAS within the untreated water be adsorbed onto the resins in an ion exchange process that substitutes the PFAS for another anion such as chloride, for example. Exposing the untreated water to the resins can be accomplished in any manner. In a process incorporating the ion exchange system 10 of FIG. 1, an ion exchange bed is provided within a vessel that includes in inlet valve and an outlet valve. Untreated water is directed into the vessel through the inlet valve and through the ion exchange bed where PFAS are removed. The thus treated water comprises a lowered level of PFAS and exits the vessel through the outlet valve. The flow may be directed from the outlet valve to another treatment station for further reduction of PFAS or for removal or treatment to remove or neutralize other impurities.

[0036] In other embodiments, an amount of untreated water can be placed within a vessel along with an adequate amount of ion exchange resin. The amount of resin within the vessel is typically selected to provide adequate ion exchange capacity to adsorb an expected loading of PFAS. The vessel can be shaken or the contents stirred or agitated in some manner so that the PFAS are adequately adsorbed onto the resins and the ion exchange process is completed. The water and resin may then be separated (e.g., by centrifuging, filtering and / or decanting) to yield a volume of treated water.

[0037] Objects and advantages of this disclosure are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure. EXAMPLES

[0038] Unless otherwise noted, all parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, and all reagents used in the examples were obtained, or are available, from general chemical suppliers or may be synthesized by conventional methods. The following abbreviations are used in this section: mL=milliliter, min=minutes, h=hours, g=gram, mol=mole, mmol=millimole, °C = degrees Celcius.

[0039] Table 1. Materials Used in Examples Preparative Example 1 (PE-1). Preparation of tributylphosphonium functionalized polystyrene resin.

[0040] Resin (1.0 g) was placed in a 25 mL thick-walled flask with tributyllphosphine (1.0 g, 4.9 mmol) and 1,4-dioxane (5 mL, 58.57 mmol) and heated to 90°C for 48 h. The reaction was cooled to room temperature, filtered, washed with about 100 mL H2O followed by 100 mL MeOH, then dried in an oven at 90°C for two days. The material was characterized by IR.

[0041] Preparative Example 2 (PE-2). Preparation of trihexylphosphonium functionalized polystyrene resin.

[0042] Resin (1.0 g) was placed in a 25 mL thick-walled flask with trihexylphosphine (1.30 g, 4.5 mmol) and 1,4-dioxane (5 mL, 58.57 mmol) and heated to 90°C for 48 h. The reaction was cooled to room temperature, filtered, washed with about 100 mL H2O followed by 100 mL MeOH, then dried in an oven at 90°C for two days. The material was characterized by IR.

[0043] Preparative Example 3 (PE-3). Preparation of trioctylphosphonium functionalized polystyrene resin.

[0044] Resin (1.0 g) was placed in a 25 mL thick-walled flask with trioctylphosphine (1.70 g, 4.5 mmol) and 1,4-dioxane (5 mL, 58.57 mmol) and heated to 90°C for 48 h. The reaction was cooled to room temperature, filtered, washed with ~100 mL H2O followed by 100 mL MeOH, then dried in an oven at 90°C for 2 days. The material was characterized by IR.

[0045] Preparative Example 4 (PE-4). Preparation of tricyclohexylphosphonium functionalized polystyrene resin.

[0046] Resin (1.0 g) was placed in a 25 mL thick-walled flask with tricyclohexylphosphine (1.25 g, 4.5 mmol) and 1,4-dioxane (5 mL, 58.57 mmol) and heated to 90°C for 48 h. Reaction was cooled to room temperature, filtered, washed with ~100 mL H2O followed by 100 mL MeOH, then dried in an oven at 90°C for 2 days. The material was characterized by IR.

[0047] Preparative Example 5 (PE-5). Preparation of triphenylphosphonium functionalized polystyrene resin.

[0048] Resin (1.0 g) was placed in a 25 mL thick-walled flask with triphenylphosphine (1.17 g, 4.5 mmol) and 1,4-dioxane (5 mL, 58.57 mmol) and heated to 90°C for 48 h. Reaction was cooled to room temperature, filtered, washed with ~100 mL H2O followed by 100 mL MeOH, then dried in an oven at 90°C for 2 days. The material was characterized by IR. Comparative Example 1 (CE-1). Preparation of tributylammonium functionalized polystyrene resin.

[0049] Resin (1.0 g) was placed in a 25 mL thick-walled flask with tributylamine (3.8 mL, 16 mmol) and 1,4-dioxane (5 mL, 58.57 mmol) and heated to 90°C for 48 h. Reaction was cooled to room temperature, filtered, washed with ~100 mL H2O followed by 100 mL MeOH, then dried in an oven at 90°C for 2 days. The material was characterized by IR.

[0050] Procedure for PFPA Adsorption Isotherm Experiments:

[0051] TFA solution Preparation:

[0052] A 1000 ppm TFA solution was made by dissolving sodium trifluoroacetate (1.20 g) in DI water (998.80 mL).

[0053] A concentrated synthetic ground water solution (120 ppm NaCl; 120 ppm Na2SC>4; 40 ppm NaNO,: and 900 ppm NaHC’0,) was made by dissolving the appropriate amount of each listed salt in DI water.

[0054] IL solutions of a given concentration of TFA (2.5 ppm; 5 ppm; 10 ppm) were made by combining 500 mL of the synthetic ground water solution and the required amount of 1000 ppm TFA solution and then diluting to volume of IL with DI water. This provided experimental stock solutions used in the TFA isotherm studies.

[0055] PFPA solution preparation:

[0056] A 1000 ppm PFPA solution was made by dissolving sodium pentafluoropropionate (1.14 g) in DI water (998.86 mL).

[0057] A concentrated synthetic ground water solution (120 ppm NaCl; 120 ppm Na2SC>4; 40 ppm NaNO’,: and 900 ppm NaHCO,) was made by dissolving the appropriate amount of each listed salt in DI water.

[0058] IL solutions of a given concentration of PFPA (2.5 ppm; 5 ppm; 10 ppm) were made by combining 500 mL of the synthetic ground water solution and the required amount of 1000 ppm PFPA solution and then diluting to volume of IL with DI water. This provided experimental stock solutions used in the PFPA isotherm studies.

[0059] Isotherm experiments:

[0060] Polypropylene bottles (2oz.) were charged with approximately 50 mg of desired resin and 50 g of the desired PFPA stock solution. The bottles were then sealed and placed on a mechanical shaker for 48h. After removal from the shaker, an aliquiot of the solution was filtered through a 0.45 pm polypropylene syringe filter into a plastic container for LC-MS analysis (>3 mL sample). Samples were diluted 100X and 1000X with 1 / 1 acetonitrile / water prior to analysis which was carried out using the following equipment and settings: Instrument: Agilent 6470 TRIPLE QUAD LCMS MAID 1665

[0061] Column: lonPac AS17-C 2x 250mm (210519005)

[0062] Solvent A: Water with 50 mM ammonium bicarbonate

[0063] Solvent B: Methanol

[0064] Gradient: 80% B hold 1 minute ramp to 50% B at 10 minutes

[0065] Stop Time: 11 minutes

[0066] Post Time: 6 minutes

[0067] Injection: lOmL

[0068] Col. Temp: 40°C

[0069] Flow Rate: 0.3 mL / min

[0070] MS: Negative electrospray

[0071] “Ce” is the concentration in ppm of the analyte in solution at equilibrium as measured by LC-MS. The “qe” value was calculated via the following equation: qe = ((measured PFPA cone, of control in ppm - Ce) * (grams of solution / 1000)) (mg of resin / 1000).

[0072] Results are shown in Tables 2 and 3 below.

[0073] Table 2. PFPA Isotherm Results

[0074] As shown in FIG. 2, the slope of the line calculated for each resin is a measurement of the effectiveness of the resin to adsorb the given analyte (in this case PFPA). The resulting data indicates the most effective material to be the trioctylphophonium-modified resin, which shows an almost fourfold increase when compared to the tributylammonium-modified resin. Table 3. TFA Isotherm Results

[0075] As shown in FIG. 3, the slope of the line calculated for each resin is a measurement of the effectiveness of the resin to adsorb the given analyte (in this case TFA). The resulting data indicates the most effective material to be the trioctylphophonium and trihexylphosphonium modified resins, which show a little more than threefold increase when compared to the tributylammonium modified resin.

[0076] All cited references, patents, and patent applications in the above application for letters patent are herein incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control. The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.

Claims

What is claimed is:

1. An ion exchange resin comprising an insoluble matrix having functional groups bonded thereto, the functional groups comprising a quaternary alkylphosphonium salt represented by the formula:- P(RIR2R3)+X- whereinX" is an anionic counterion; andRi, R2and R3 are independently acyclic hydrocarbon groups having a carbon chain length Of C4 tO C18.

2. The ion exchange resin of claim 1, wherein Ri, R2and R3 are the same.

3. The ion exchange resin of claim 1, wherein Ri, R2and R3 are independently acyclic hydrocarbon groups having a carbon chain length of G, to Cs;4. The ion exchange resin of claim 1, wherein the insoluble matrix is selected from the group consisting of a polymer, a gel, a clay, a diatomaceous earth, and combinations thereof.

5. The ion exchange resin of claim 4, wherein the polymer comprises polystyrene.

6. The ion exchange resin of claim 1, wherein the anionic counterion is selected from the group consisting of a halide, an inorganic and ionic oxide, an organic anion, and combinations thereof.

7. A system for the removal of PFAS from water, the system comprising: a vessel containing an ion exchange resin, the ion exchange resin comprising an insoluble matrix having functional groups bonded thereto, the functional groups comprising a quaternary alkylphosphonium salt represented by the formula:- P(RIR2R3)+X- whereinX- is an anionic counterion; andRi, R2and R3 are independently acyclic hydrocarbon groups having a carbon chain length of C4 to Cis; an inlet for directing a flow of water into the vessel to thereby contact the ion exchange resin; and an outlet for directing a flow of water out of the vessel.

8. The system of claim 7, wherein Ri, R2and R3 are the same.

9. The system of claim 8, wherein Ri, R2and R3 are independently acyclic hydrocarbon groups having a carbon chain length of G, to Cs;10. The system of claim 7, wherein the insoluble matrix is selected from the group consisting of a polymer, a gel, a clay, a diatomaceous earth, and combinations thereof.

11. The system of claim 10, wherein the polymer comprises polystyrene.

12. The system of claim 1, wherein the anion is selected from the group consisting of a halide, an inorganic and ionic oxide, an organic anion, and combinations thereof.

13. A method for removal of PFAS from water, the process comprising: exposing an aqueous solution including a PFAS to an ion exchange resin the ion exchange resin comprising an insoluble matrix having functional groups bonded thereto, the functional groups comprising a quaternary alkylphosphonium salt represented by the formula:- P(RIR2R3)+X- whereinX- is an anionic counterion; andRi, R2and R3 are independently acyclic hydrocarbon groups having a carbon chain length Of C4 tO C18.

14. The method of claim 13, wherein Ri, R2and R3 are the same.

15. The method of claim 13, wherein Ri, R2and R3 are independently linear hydrocarbon groups having a carbon chain length of G, to Cs;16. The method of claim 13, wherein the insoluble matrix is selected from the group consisting of a polymer, a gel, a clay, a diatomaceous earth, and combinations thereof.

17. The method of claim 16, wherein the polymer comprises polystyrene.

18. The method of claim 13, wherein the anionic counterion is selected from the group consisting of a halide, an inorganic and ionic oxide, an organic anion, and combinations thereof.

Images