Regeneration of polymeric cyclodextrin adsorbents

Abstract

A method for removing PFAS from a cationic CDP adsorbent having adsorbed PFAS is provided. The method includes contacting a volume of the cationic CDP adsorbent with a regeneration medium and separating the cationic CDP adsorbent from the regeneration medium. The present disclosure is particularly directed to regeneration media and regeneration conditions suitable for removing adsorbed PFAS from CDP adsorbents, such as the cationic CDP adsorbents of the present disclosure. In various embodiments, the present disclosure is directed to methods for concentrating adsorbed PFAS after removal from a CDP adsorbent, such as the cationic CDP adsorbents of the present disclosure.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 479,611, filed January 12, 2023, which is incorporated herein by reference in its entirety. [Background technology]

[0002] A new class of aryl-bridged cyclodextrin polymers (CDPs) has been identified that exhibit rapid adsorption properties for polyfluoroalkyl and perfluoroalkyl substances (PFASs), such as those described in U.S. Patent Nos. 9,624,314 and 11,155,646, each of which is incorporated herein by reference for all purposes. To be commercially useful for treating PFAS-contaminated waste streams, such CDP adsorbents must not only adsorb PFASs with rapid kinetics and high adsorption capacity, but also readily release PFASs with a high level of efficiency and under suitable regeneration conditions. That is, substantially all adsorbed PFASs should be removed from the CDP adsorbent during regeneration, recovering, to the greatest extent possible, the original PFAS adsorption properties of the CDP adsorbent and enabling separation of PFAS waste for safe disposal. Typically, regeneration is achieved using a regeneration medium capable of overcoming the adsorption mechanism by which PFASs bind to the CDP. Ideally, such a regeneration medium should be relatively non-toxic and rapidly regenerate the CDP adsorbent using a minimal volume of regeneration medium. However, suitable regeneration media and conditions will depend on the specific properties of the CDP and PFAS. The present invention, in various embodiments, provides particularly effective regeneration media and conditions that are commercially advantageous for regenerating CDP adsorbents containing adsorbed PFASs. Summary of the Invention

[0003] The present disclosure is particularly directed to regeneration media and conditions suitable for removing adsorbed PFAS from CDP adsorbents, such as the cationic CDP adsorbents of the present disclosure. In various embodiments, the present disclosure is directed to methods for concentrating adsorbed PFAS after removal from a CDP adsorbent, e.g., a cationic CDP adsorbent of the present disclosure. The concentrated PFAS provided by the methods of the present disclosure may be in solid or liquid form. In various embodiments, the cationic CDP adsorbents of the present disclosure containing adsorbed PFAS are treated with a mixture of about 0.5:1 (v / v) to about 10:0 (v / v) alcohol:water (in some embodiments, ethanol:water, or pure ethanol), and, optionally, an alkali metal or alkaline earth metal or ammonium (NH4 + The CDP adsorbent is contacted with a regeneration medium comprising a salt selected from the group consisting of hydrochloride, nitrate, sulfate, phosphate, formate, acetate, or hydroxide of the CDP adsorbent. In some embodiments, the regeneration medium is an ethanol solution containing 50% (v / v) ethanol:water, 95% (v / v) ethanol:water, or pure ethanol. In many embodiments, the CDP adsorbent (e.g., a cationic CDP adsorbent) is loaded into a packed-bed vessel. The regeneration process can be carried out in upflow, downflow, or batch mode, as described herein. When the regeneration process is carried out in upflow mode, the flow can be linear or circular, as described herein, and the flow rate can be characterized by a bed expansion rate, which can be in the range of about 5% to about 100%. When the regeneration process is carried out in downflow mode, the empty bed contact time is in the range of about 1 minute to about 120 minutes. When the regeneration process is carried out in batch mode, the contact time between the regeneration medium and the CDP adsorbent (e.g., a cationic CDP adsorbent) can be in the range of about 10 minutes to about 24 hours. After the contacting, the regeneration medium and the cationic CDP adsorbent are separated, thereby transferring at least about 50% of the adsorbed PFAS to the regeneration medium. The PFAS containing regeneration medium can then be further processed, for example, optionally by further concentrating the PFAS, and finally, the PFAS can be subjected to a suitable PFAS destruction process or alternatively disposed of. [Brief explanation of the drawings]

[0004] [Figure 1] FIG. 1 is a schematic diagram of one embodiment of a remediation process for DEXSORB+ to produce PFAS-rich solid waste. [Figure 2] FIG. 2 is a schematic diagram of one embodiment of a regeneration process for DEXSORB+ to produce concentrated liquid waste containing PFAS. [Figure 3] Figures 3a-d show the regeneration efficiencies of various PFAS compounds for DEXSORB+TFN regenerated with 1 mg / mL NHOAc (Fig. 3a), NHHCO (Fig. 3b), CaCl (Fig. 3c), or NaCl (Fig. 3d) dissolved in methanol. [Figure 4] Figure 4a-b: Inlet PFAS concentrations (Figure 4a) and total recoveries of various PFAS compounds (Figure 4b) for DEXSORB+TFN regenerated with a 2:1 (v / v) ethanol:water mixture containing 0.5 g / L K2SO4. [Figure 5] Figure 5: Total PFAS recoveries from batch and column regeneration experiments using methanol and ethanol amended with 2 g / L NH4OAc. [Figure 6] Figure 6: Comparison of total PFAS recoveries from batch regeneration experiments between methanol, ethanol, and isopropanol, each amended with 2 g / L NH4OAc. [Figure 7] Figure 7: Comparison of total PFAS recoveries from batch regeneration experiments between the following regeneration media: ethanol (190 proof, no salt added), a 2:1 (v / v) ethanol:water mixture amended with 0.5 g / L K2SO4 (equivalent to 63% ethanol by volume), and a 1:1 (v / v) ethanol:water mixture amended with 1 g / L K2SO4 (equivalent to 48% ethanol by volume). [Figure 8] Figure 8: Evaluation of other salt, acid, and base additives in a 2:1 (v / v) ethanol:water mixture and comparison of total PFAS recoveries from batch regeneration experiments. [Figure 9]Figure 9: Comparison of total PFAS recoveries from evaluation of other salt, acid, and base additives in ethanol and batch regeneration experiments. [Figure 10] Figure 10: Comparison of total PFAS recoveries at 21 °C and 35 °C between ethanol and a 2:1 (v / v) ethanol:water mixture amended with 0.5 g / L K-2SO4 from a batch regeneration experiment. DETAILED DESCRIPTION OF THE INVENTION

[0005] It is known in the art that adsorption mechanisms for the removal or separation of various adsorbates from a particular matrix vary based on the specific chemical properties of the adsorbent and adsorbate. These adsorption mechanisms depend on interactions between the adsorbent and adsorbate, including, but not limited to, hydrophobic interactions, van der Waals forces, pi-pi stacking, hydrogen bonding, electrostatic interactions, ion exchange, and the like. These interactions can be further influenced by the properties of the matrix containing the adsorbate (e.g., other components dissolved or dispersed in an aqueous solution of PFAS) due to competitive adsorption. For example, Deng et al. (Water Research 2010, 44, 5188-5195) found that dissolved anions, such as sulfate and anionic hexavalent chromium complexes, interfered with the adsorption of perfluorooctane sulfonate (PFOS) to an anion exchange resin.

[0006] These underlying adsorption mechanisms ultimately govern the strength of the adsorbate-adsorbent interaction, which in turn determines the ease and effectiveness of the desorption process, i.e., adsorbate recovery and regeneration of spent adsorbent. Another important factor for effective desorption is the solubility of the adsorbate in the regeneration medium.

[0007] Therefore, suitable regeneration conditions depend on the specific chemical characteristics of the adsorbent and adsorbate, which affect the adsorption mechanism specific to that particular adsorbent and adsorbate. Furthermore, regeneration efficiency is affected by the solubility characteristics of the adsorbent in the regeneration medium. Therefore, the parameters controlling regeneration efficiency cannot be easily extrapolated from regeneration conditions found to be useful for other adsorbents and adsorbates. For example, Deng et al. found that two structurally very similar acrylic anion exchange resins containing adsorbed PFOS, IRA958 and IRA67, nevertheless exhibited very distinct regeneration characteristics with the same regeneration medium.

[0008] Regeneration of PFAS adsorbents is complicated by the fact that PFAS are a category of poly- and perfluoroalkylated compounds that encompass a wide variety of different chemical and structural features, including various alkyl chain lengths, linear and branched structures, and chemicals with different head groups. Each of these chemical and structural features influences adsorption strength, so regeneration of adsorbents containing adsorbed PFAS requires carefully tuned regeneration conditions.

[0009] The efficiency of PFAS desorption from the adsorbent (i.e., recovery efficiency) is important to the design and ultimate cost of removing PFAS from a fluid stream (e.g., PFAS-contaminated water). Higher recovery efficiency of PFAS after regeneration reduces the amount of residual PFAS remaining on the adsorbent, thus allowing for its reuse with a higher PFAS adsorption capacity for the regenerated adsorbent. Higher regeneration efficiency is crucial because it allows for more reuse cycles for a given adsorbent batch before replacement with a new adsorbent is necessary. Higher recovery efficiency also minimizes the volume of regenerated medium required per regeneration cycle, which provides for a higher concentration of PFAS in the spent regenerated medium. Such higher PFAS concentrations minimize subsequent processing costs, including the cost and difficulty of recycling the regenerated medium, the size and selection of unit operations for handling the PFAS-containing regenerated medium (e.g., separation and / or concentration of the regenerated medium from PFAS by membrane or distillation processes), and the ultimate cost of disposing of or destroying the isolated PFAS obtained from regeneration.

[0010] CDP adsorbents, as described herein, are particularly effective for removing PFAS from aqueous mixtures, for example. CDP adsorbents can be regenerated by using a regeneration medium that can easily disrupt the host-guest complex between the cyclodextrin and the adsorbent, e.g., PFAS. DEXSORB+, a class of cationic CDP adsorbents described in US Pat. No. 11,001,645 (the contents of which are incorporated herein by reference for all purposes), has been demonstrated to effectively remove PFAS from water. However, desorption of PFAS from cyclodextrin-based adsorbents has not been extensively investigated. Methanol and ethanol, as well as aqueous methanol or ethanol solutions, have been proposed as suitable regeneration media (e.g., US Pat. No. 9,624,314), and methanol has been demonstrated to desorb bisphenol A (BPA) from used cyclodextrin-based adsorbents (Alsbaiee et al., Nature 2016, 529, 190-194). However, the CDP used in these references was not cationic. Furthermore, these references did not consider or describe complete PFAS desorption from the spent adsorbent to enable safe reuse of the regenerated adsorbent. Furthermore, these researchers did not consider the safety of the selected regeneration medium or the regeneration efficiency (e.g., complete regeneration with the smallest amount of regeneration medium possible for practical and cost-effective disposal of spent regeneration medium containing PFAS waste).

[0011] Other researchers (Du et al., Journal of Hazardous Materials 2014, 274, 443-454; Nickelsen and Woodard, US 10,287,185; James et al., US 2020 / 0306726) have studied the removal of certain PFAS compounds (PFOS; perfluorooctanoic acid, PFOA) from non-cyclodextrin-based adsorbents (such as activated carbon, anion exchange resins, silica, zeolites, montmorillonite clay, hydrotalcite, and chitosan) and found that regeneration efficiencies varied significantly depending on the adsorbent chemistry and regeneration medium used. Therefore, identifying suitable regeneration media and conditions requires careful consideration of several factors, including, inter alia, the chemical composition of the adsorbent (e.g., DEXSORB+ and similar cationic cyclodextrin-based adsorbents described herein), the chemical composition of the adsorbate (e.g., PFAS), the kinetics and completeness of adsorbate desorption during regeneration, safety (toxicity, flammability, etc.), and the suitability of the regeneration media for further processing to isolate the adsorbate. Notably, neither Du et al., Nickelsen and Woodard, nor James et al. evaluated the regeneration of PFAS from CDP or cationic CDP adsorbents.

[0012] The CDP adsorbent of the present invention, in certain embodiments, is a cationic aryl-bridged CDP as described in U.S. Pat. No. 1,155,646, the contents of which are incorporated herein by reference for all purposes. In certain embodiments, the cationic CDP of the present disclosure is a β-cyclodextrin crosslinked with tetrafluoroterephthalonitrile (TFN), which is further modified by reaction with a cationic group (e.g., choline chloride), a β-cyclodextrin crosslinked with an isocyanate (e.g., toluene diisocyanate (TDI), 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, and mixtures thereof, and / or one or more other polyisocyanates such as methylene diphenyl diisocyanate (MDI), 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, polymeric MDI, and mixtures thereof), or a β-cyclodextrin crosslinked with an activated form of a carboxylic acid, such as an acid chloride or ester (e.g., terephthaloyl chloride, or dimethyl terephthalate). Crosslinked β-cyclodextrin, which optionally contains cationic groups (e.g., ammonium or tetraalkylammonium groups). Certain CDP adsorbents described herein are polymers prepared from the specific cyclodextrins and aryl bridged monomers described above, including, but not limited to, α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin, or synthetic cyclodextrins having 3 to 20 glucose units, including 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 glucose units (including any range therebetween), can be used to prepare the cationic CDP adsorbents of the present disclosure.

[0013] Suitable crosslinking groups are aromatic (or heteroaromatic) compounds having two or more functional groups capable of reacting with the hydroxyl groups of cyclodextrin, such as aryl fluorides, isocyanates, carboxylic acids (or any activated form of a carboxylic acid, such as an acid halide (including an acid chloride) or an ester). TFN is a specific embodiment of a suitable aryl fluoride, TDI, MDI, and polymeric MDI are specific embodiments of a suitable isocyanate, and terephthaloyl chloride is a specific embodiment of a suitable activated acid chloride. Other suitable monomers may also be incorporated into the CDP adsorbents of the present invention to modify the adsorption properties of the resulting CDP. In certain embodiments, the CDPs of the present disclosure are modified with compounds having cationic functional groups or functional groups that can be converted to cationic groups. For example, β-cyclodextrin can be polymerized in the presence of TFN, a base (e.g., KCO), and choline chloride to provide a crosslinked polymer containing aryl bridges bearing ethyltrimethylammonium groups (DEXSORB + TFN). In another example, β-cyclodextrin can be polymerized in the presence of a diisocyanate (e.g., TDI and / or MDI) and choline chloride to provide a crosslinked polymer containing aryl bridges bearing ethyltrimethylammonium groups (DEXSORB + TDI or DEXSORB + MDI). In other embodiments, the CDP itself can be treated post-synthetically to incorporate cationic groups. For example, when β-cyclodextrin reacts with a diisocyanate (e.g., TDI and / or MDI), under suitable conditions, some of the isocyanate groups can hydrolyze to form carbamic acids, which can decompose to amines. The resulting amine groups can be quaternized to form cationic ammonium groups on the polymer.

[0014] The CDP adsorbents described herein are useful for adsorbing PFAS from various mixtures, including PFAS-contaminated water streams (groundwater, drinking water, wastewater, etc.). PFAS can include various polyfluorinated and perfluorinated compounds, including perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnA), perfluorododecanoic acid (PFDoA), perfluorotridecanoic acid (PFTrDA), and perfluoropentanoic acid (PFTrDA). Fluorotetradecanoic acid (PFTeA), perfluoropropanesulfonic acid (PFPrS), perfluorobutanesulfonic acid (PFBS), perfluoropentanesulfonic acid (PFPeS), perfluorohexanesulfonic acid (PFHxS), perfluoroheptanesulfonic acid (PFHpS), perfluorooctane sulfonic acid (PFOS), perfluorononanesulfonic acid (PFNS), perfluorodecanesulfonic acid (PFDS), perfluorododecanesulfonic acid (PFDoS), 4:2 fluorotelomersulfonic acid Perfluorohexanesulfonate (4:2FTS), 6:2 fluorotelomer sulfonate (6:2FTS), 8:2 fluorotelomer sulfonate (8:2FTS), 10:2 fluorotelomer sulfonate (10:2FTS), perfluorobutanesulfonamide (FBSA), N-methylperfluorobutanesulfonamide (MeFBSA), perfluorohexanesulfonamide (FHxSA), perfluorooctane sulfonamide (PFOSA), perfluorodecanesulfonamide (FDSA), N-ethylperfluorohexanesulfonamide (FDSA), Perfluorooctane-1-sulfonamide (NEtFOSA), N-methylperfluorooctane-1-sulfonamide (NMeFOSA), perfluorooctane sulfonamidoacetic acid (FOSAA), N-ethylperfluorooctane sulfonamidoacetic acid (NEtFOSAA), N-methylperfluorooctane sulfonamidoacetic acid (NMeFOSAA), N-methylperfluorooctane sulfonamidoethanol (NMeFOSE), N-ethylperfluorooctane sulfonamidoethanol (NEtFOSE),Hexafluoropropylene oxide dimer acid (HFPO-DA), 4,8-dioxa-3H-perfluorononanoate (ADONA), perfluoro-3-methoxypropanoic acid (PFMPA), perfluoro-4-methoxybutanoic acid (PFMBA), perfluoro-3,6-dioxaheptanoic acid (NFDHA), 9-chlorohexadecafluoro-3-oxanone-1-sulfonic acid (9Cl-PF3ONS), 11-chloroeicosafluoro-3-oxanonane-1-sulfonic acid (11CL-PF3OUdS), perfluoro(2-ethoxyethane)sulfonic acid (PFEESA), perfluoro-4-ethylcyclohexanesulfonic acid (PFECHS), 8-chloroperfluoro-1-octanesulfonic acid (8C l-PFOS), 3-perfluoropropylpropanoic acid (3:3FTCA), 2H,2H,3H,3H-perfluorooctanoic acid (5:3FTCA), 3-perfluoroheptylpropanoic acid (7:3FTCA), 2H-perfluoro-2-dodecenoic acid (FDUEA), 2H-perfluoro-2-decenoic acid (FOUEA), bis(perfluorohexyl)phosphinic acid (6:6PFPi), (heptadecafluorooctyl)(tridecafluorohexyl)phosphinic acid (6:8PFPi), bis(perfluorooctyl)phosphinic acid (8:8PFPi), N-(3-dimethylaminopropan-1-yl)perfluoro-1-hexanesulfonamide (N-AP-FHxSA), and combinations thereof.

[0015] A regeneration medium useful for efficiently regenerating the PFAS-contaminated cationic CDP adsorbent of the present disclosure comprises an alcohol, optionally an aqueous alcohol. Suitable alcohols include methanol, ethanol, and propanol (e.g., isopropanol). The aqueous alcohol mixture can have a volumetric alcohol:water ratio ranging from about 0.5:1 to about 10:0, such as about 0.5:1, about 0.6:1, about 0.7:1, about 0.8:1, about 0.9:1, about 1:1, about 1.5:1, about 2:1, about 2.5:1, about 3:1, about 3.5:1, about 4:1, about 4.5:1, about 5:1, about 5.5:1, about 6:1, about 6.5:1, about 7:1, about 7.5:1, about 8:1, about 8.5:1, about 9:1, or about 10:0 (including any range therebetween). In a specific embodiment, the alcohol is ethanol. In other particular embodiments, the alcohol is methanol. In yet other particular embodiments, the alcohol is propanol (e.g., isopropanol).

[0016] In other embodiments, the amount of alcohol in a suitable regeneration medium can be expressed as a volume percentage (% v / v) of alcohol in water (if present). For example, a suitable regeneration medium may contain about 40% v / v, about 45% v / v, about 50% v / v, about 55% v / v, about 60% v / v, about 65% v / v, about 70% v / v, about 75% v / v, about 80% v / v, about 85% v / v, about 90% v / v, about 95% v / v, or about 100% v / v (including any range therebetween). In certain embodiments, the alcohol is ethanol. In other certain embodiments, the alcohol is methanol. In yet other certain embodiments, the alcohol is propanol (e.g., isopropanol).

[0017] In some embodiments, it is useful to include dissolved salts in the regeneration medium to improve the efficiency of removing sorbed PFASs from the CDP adsorbents of the present disclosure (e.g., DEXSORB+ or other cationic CDP adsorbents disclosed herein). The salt content of the regeneration medium can range from about 0.1 g / L to about 50 g / L, including concentrations of about 0.1 g / L, about 0.2 g / L, about 0.3 g / L, about 0.4 g / L, about 0.5 g / L, about 0.6 g / L, about 0.7 g / L, about 0.8 g / L, about 0.9 g / L, about 1 g / L, about 1.1 g / L, about 1.2 g / L, about 1.3 g / L, about 1.4 g / L, about 1.5 g / L, about 1.6 g / L, about 1.7 g / L, about 1.8 g / L, about 1.9 g / L, about 2 g / L, about 3 g / L, about 4 g / L, about 5 g / L, about 6 g / L, about 7 g / L, about 8 g / L, about 9 g / L, about 10 g / L, about 11 g / L, about 12 g / L, about 13 g / L, about 14 g / L, about 15 g / L, about 16 g / L, about 17 g / L, about 18 g / L, about 19 g / L, about 20 g / L, about 21 g / L, about 22 g / L, about 23 g / L, about 24 g / L, about 25 g / L, about 26 g / L, about 27 g / L, about 28 g / L, about 29 g / L, about 30 g / L, about 31 g / L, about 32 g / L, about 33 g / L .1g / L, approximately 2.2g / L, approximately 2.3g / L, approximately 2.4g / L, approximately 2.5g / L, approximately 2.6g / L, approximately 2.7g / L, approximately 2.8g / L, approximately 2.9g / L, approximately 3g / L, approximately 3.1g / L, approximately 3.2g / L, approximately 3.3g / L, approximately 3 .4g / L, approximately 3.5g / L, approximately 3.6g / L, approximately 3.7g / L, approximately 3.8g / L, approximately 3.9g / L, approximately 4g / L, approximately 4.1g / L, approximately 4.2g / L, approximately 4.3g / L, approximately 4.4g / L, approximately 4.5g / L, approximately 4.6g / L, approximately 4 .7g / L, approximately 4.8g / L, approximately 4.9g / L, approximately 5g / L, approximately 5.1g / L, approximately 5.2g / L, approximately 5.3g / L, approximately 5.4g / L, approximately 5.5g / L, approximately 5.6g / L, approximately 5.7g / L, approximately 5.8g / L, approximately 5.9g / L, approximately 6g / L, approximately 6.1g / L, approximately 6.2g / L, approximately 6.3g / L, approximately 6.4g / L, approximately 6.5g / L, approximately 6.6g / L, approximately 6.7g / L, approximately 6.8g / L, approximately 6.9g / L, approximately 7g / L, approximately 7.1g / L, approximately 7.2g / L, approximately 7. 3g / L, approximately 7.4g / L, approximately 7.5g / L, approximately 7.6g / L, approximately 7.7g / L, approximately 7.8g / L, approximately 7.9g / L, approximately 8g / L, approximately 8.1g / L, approximately 8.2g / L, approximately 8.3g / L, approximately 8.4g / L, approximately 8.5g / L, approximately 8. 6g / L, approximately 8.7g / L, approximately 8.8g / L, approximately 8.9g / L, approximately 9g / L, approximately 9.1g / L, approximately 9.2g / L, approximately 9.3g / L, approximately 9.4g / L, approximately 9.5g / L, approximately 9.6g / L, approximately 9.7g / L, approximately 9.8g / L, approximately 9.9g / L, approximately 10g / L, approximately 11g / L, approximately 12g / L, approximately 13g / L, approximately 14g / L, approximately 15g / L, approximately 16g / L, approximately 17g / L, approximately 18g / L, approximately 19g / L, approximately 20g / L, approximately 21g / L, approximately 22g / L, approximately 23g / L, approximately 24g / L, approximately 25g / L, approximately 26g / L, approximately 27g / L, approximately 28g / L, approximately 29g / L, approximately 30g / L, approximately 31g / L , about 32 g / L, about 33 g / L, about 34 g / L, about 35 g / L, about 36 g / L, about 37 g / L, about 38 g / L, about 39 g / L, about 40 g / L, about 41 g / L, about 42 g / L, about 43 g / L, about 44 g / L, about 45 g / L, about 46 g / L, about 47 g / L, about 48 g / L, about 49 g / L, or about 50 g / L (including any range therebetween). Alternatively, the amount of salt dissolved in the regeneration medium can be expressed as weight percent (wt%). Suitable weight percentages of any of the salts disclosed herein in the regeneration medium range from about 0.01 wt.% to about 6 wt.%, including about 0.01 wt.%, about 0.02 wt.%, about 0.03 wt.%, about 0.04 wt.%, about 0.05 wt.%, about 0.06 wt.%, about 0.07 wt.%, about 0.08 wt.%, about 0.09 wt.%, about 0.1 wt.%, about 0.2 wt.%, about 0.3 wt.%, about 0.4 wt.%, about 0.5 wt.%, about 0.6 wt.%, about 0.7 wt.%, about 0.8 wt.%, about 0.9 wt.%, about 1 wt.%, about 1.1 wt.%, about 1.2 wt.%, about 1.3 wt.%, about 1.4 wt.%, about 1.5 wt.%, about 1.6 wt.%, about 1.7 wt.%, about 1.8 wt.%, about 1.9 wt.%, about 2 wt.%, and about 2. 1% by weight, approximately 2.2% by weight, approximately 2.3% by weight, approximately 2.4% by weight, approximately 2.5% by weight, approximately 2.6% by weight, approximately 2.7% by weight, approximately 2.8% by weight, approximately 2.9% by weight, approximately 3% by weight, Approximately 3.1% by weight, approximately 3.2% by weight, approximately 3.3% by weight, approximately 3.4% by weight, approximately 3.5% by weight, approximately 3.6% by weight, approximately 3.7% by weight, approximately 3.8% by weight, approximately 3.9% by weight, approximately 4 weight% Amount %, about 4.1 wt%, about 4.2 wt%, about 4.3 wt%, about 4.4 wt%, about 4.5 wt%, about 4.6 wt%, about 4.7 wt%, about 4.8 wt%, about 4.9 wt%, or about 5 wt%, about 5.1 wt%, about 5.2 wt%, about 5.3 wt%, about 5.4 wt%, about 5.5 wt%, about 5.6 wt%, about 5.7 wt%, about 5.8 wt%, about 5.9% by weight, or about 6% by weight (including any range therebetween). The salt-containing regeneration medium described herein above can include any of the aforementioned alcoholic solutions containing a suitable salt, including aqueous alcoholic solutions containing a suitable salt, and solutions containing essentially only alcohol containing a suitable salt.

[0018] Suitable salts include alkali metal salts (e.g., Li + , Na + , K. + , or Cs + ) or alkaline earth metals or ammonium (NH4 + ), hydrochloride, nitrate, sulfate, phosphate, formate, acetate, hydroxide, or combinations thereof. In certain embodiments, the salt comprises sodium sulfate (NaSO), potassium sulfate (KSO), cesium sulfate (CsSO), ammonium acetate (NHOAc), ammonium hydroxide (NHOH), ammonium formate (NHHCO), lithium chloride (LiCl), sodium chloride (NaCl), or potassium hydroxide (KOH). In certain embodiments, the regeneration medium contains about 0.5 g / L of KSO. 、 Contains 2:1 (v / v) ethanol:water.

[0019] In other specific embodiments, the regeneration medium comprises a mixture of ethanol and water (in any ratio described herein) and further comprises LiCl. In specific embodiments, the regeneration medium comprises a mixture of ethanol and water (in any ratio described herein) and further comprises LiCl at a concentration of about 4 g / L. In yet other specific embodiments, the regeneration medium comprises a mixture of ethanol and water (in any ratio described herein) and further comprises KOH. In specific embodiments, the regeneration medium comprises a mixture of ethanol and water (in any ratio described herein) and further comprises KOH at a concentration of about 0.76 g / L. In yet other specific embodiments, the regeneration medium comprises ethanol that is substantially free of water. In specific embodiments, the regeneration medium comprises ethanol that is substantially free of water and substantially free of added salts. In still other embodiments, the regeneration medium comprises 95% (v / v) ethanol (and 5% (v / v) water, i.e., an azeotropic composition of ethanol and water, and optionally contains a salt as described herein. In yet other specific embodiments, any of the regeneration media described herein (e.g., ethanol:water, or ethanol) further comprises about 0.65 g / L NaCl. In various embodiments described herein, the ethanol:water (v / v) ratio ranges from about 2:1 to about 10:0.

[0020] The cationic CDP adsorbents described herein can be used to remove PFAS from aqueous liquids by contacting the cationic CDP adsorbent with the PFAS-contaminated aqueous liquid using equipment and methodologies known in the chemical and environmental engineering arts. For example, the cationic CDP adsorbent (e.g., DEXSORB+) can be loaded into a packed-bed vessel with at least one inlet and outlet, allowing the PFAS-contaminated aqueous liquid to enter the packed-bed vessel and thereby contact the cationic CDP adsorbent. The size of the packed-bed vessel, the cationic CDP adsorbent loading, the flow rate and residence time of the PFAS-containing liquid, and other related process parameters can be suitably adjusted to enable removal of PFAS from the liquid to an acceptable level. When the cationic CDP adsorbent becomes saturated with PFAS or adsorbs enough PFAS to reduce its effectiveness in removing PFAS from PFAS-contaminated liquids, the adsorbed PFAS must be removed from the cationic CDP adsorbent so that it can be reused (i.e., regenerated). Regeneration of the cationic CDP adsorbent containing the adsorbed PFAS can be achieved by contacting the cationic CDP adsorbent bed with a regeneration medium described herein using methods known in the art. This process is illustrated in Figures 1 and 2.

[0021] In various embodiments, the operating temperature of the regeneration process can vary from ambient temperature (e.g., about 20°C) to a temperature below the boiling point of the regeneration medium, e.g., slightly below the boiling temperature of the alcohol or aqueous alcohol present in the regeneration medium. Those skilled in the art will recognize that if the alcohol, for example, forms an azeotrope with water, the lowest boiling point may be lower than the boiling point of the alcohol. Furthermore, because the boiling point of the regeneration medium can vary depending on atmospheric pressure and the amount of any dissolved salts that may be present, the most suitable regeneration temperature at which the regeneration medium remains below its lowest boiling point can vary accordingly. In most embodiments, the regeneration process is carried out at a temperature ranging from about 10°C to about 100°C, including about 10°C, about 15°C, about 20°C, about 25°C, about 30°C, about 35°C, about 40°C, about 45°C, about 50°C, about 55°C, about 60°C, about 65°C, about 70°C, about 75°C, about 80°C, about 85°C, about 90°C, about 95°C, or about 100°C (including any range therebetween).

[0022] In some embodiments, the regeneration process can be performed in an upflow mode, where the flow of the regeneration medium occurs from the bottom to the top of the packed-bed vessel. In an alternative embodiment, the regeneration process can be performed in a downflow mode, where the flow of the regeneration medium occurs from the top to the bottom of the packed-bed vessel. The flow can also be "linear," meaning that the regeneration medium passes through the CDP adsorbent containing the adsorbed PFAS only once, or "circular," meaning that the regeneration medium recirculates through the CDP adsorbent containing the adsorbed PFAS multiple times (2, 3, or more). In a "linear" flow rate setting, the regeneration medium passing through a vessel containing spent CDP adsorbent can be collected for concentration or directed to another vessel containing spent CDP adsorbent and then collected for concentration. In a "circular" flow rate setting, the regeneration medium is recirculated multiple times through the same vessel containing spent CDP adsorbent, and the regeneration medium is collected for concentration. This recirculation process can be repeated multiple times, starting with fresh regeneration medium each round.

[0023] When the process is run in downflow mode, the flow rate of the regenerating medium can be determined based on the desired empty bed contact time (EBCT), which in various embodiments is in the range of about 1 to 120 minutes for the regeneration process, including about 1 minute, about 2 minutes, about 3 minutes, about 4 minutes, about 5 minutes, about 6 minutes, about 7 minutes, about 8 minutes, about 9 minutes, about 10 minutes, about 15 minutes, about 20 minutes, about 25 minutes, about 30 minutes, about 35 minutes, about 40 minutes, about 45 minutes, about 50 minutes, about 55 minutes, about 60 minutes, about 65 minutes, about 70 minutes, about 75 minutes, about 80 minutes, about 85 minutes, about 90 minutes, about 95 minutes, about 100 minutes, about 105 minutes, about 110 minutes, about 115 minutes, or about 120 minutes (including any range therebetween). EBCT refers to the amount of time required for the regenerating medium to travel through one empty bed volume. The term "empty bed volume" refers to the volume of the packed bed vessel occupied by the cationic CDP adsorbent, i.e., the volume of the cationic CDP adsorbent.

[0024] When the process is run in upflow mode, the flow rate can be determined based on the desired bed expansion rate, which in various embodiments is within the range of about 5-100%, including about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, about 95%, or about 100% (including any range therebetween). In certain embodiments, the bed expansion rate is within the range of about 30-50%. Careful adjustment of the bed expansion rate is important to ensure that the majority of particles are suspended in the upflow and minimize particle loss. The term "bed expansion rate" refers to the increase in bed length occupied by the CDP adsorbent in the vessel during upflow regeneration.

[0025] Generally, sufficient regeneration medium should be used to ensure complete or near-complete removal of PFAS from the cationic CDP adsorbent. Efficient removal of PFAS from the cationic CDP adsorbent is highly advantageous for several reasons.

[0026] In other embodiments, the regeneration process may be carried out in a "batch" mode, in which the cationic CDP adsorbent containing the adsorbed PFAS is contacted with a regeneration medium (e.g., any of the regeneration media described herein) for a suitable contact period (e.g., about 10 minutes to 24 hours, about 10 minutes, about 15 minutes, about 20 minutes, about 25 minutes, about 30 minutes, about 35 minutes, about 40 minutes, about 45 minutes, about 50 minutes, about 55 minutes, about 60 minutes, about 2 hours, about 3 hours, about 4 hours, The regeneration medium is mixed for about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, about 10 hours, about 11 hours, about 12 hours, about 13 hours, about 14 hours, about 15 hours, about 16 hours, about 17 hours, about 18 hours, about 19 hours, about 20 hours, about 21 hours, about 22 hours, about 23 hours, or about 24 hours (including any range therebetween) and then removed from contact with the regeneration medium by suitable means (decanting, filtration, etc.).

[0027] Removing all or nearly all of the PFASs during the regeneration process provides a regenerated cationic CDP adsorbent with PFAS adsorption properties that are the same or nearly the same as the original PFAS adsorbent, i.e., with high PFAS adsorption capacity and rapid adsorption kinetics. The speed and efficiency with which the regenerated media removes adsorbed PFASs are also important. Regenerated media that rapidly remove adsorbed PFASs using a relatively small volume are advantageous in that the recovered PFASs obtained by the regeneration process are present in higher concentrations in the spent regenerated media.

[0028] One way to describe the effectiveness of regeneration media in removing PFASs is the number of bed volumes of regeneration media required to remove all or nearly all PFASs from the cationic CDP adsorbent. The term "bed volume" refers to the empty volume of the entire packed-bed vessel in which regeneration is performed. To allow for bed expansion during upflow regeneration, the CDP adsorbent is packed into the vessel with a sufficient empty space ratio, which in various embodiments is in the range of about 15-60%, including about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, or about 65% (including any range therebetween). In certain embodiments, the empty space ratio is in the range of about 30-50%. The term "empty space ratio" refers to the volume fraction of empty headspace in the entire vessel after packing the CDP adsorbent. A regeneration medium that can regenerate an adsorbent with fewer "bed volumes" is more effective than another regeneration medium that requires more bed volumes under the same conditions to achieve the same level of PFAS desorption from the adsorbent. In various embodiments, the number of bed volumes is in the range of about 1 to 20, including about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 11, about 12, about 13, about 14, about 15, about 16, about 17, about 18, about 19, or about 20 (including any range therebetween). In certain embodiments, the number of bed volumes is in the range of about 1 to 10. More effective regeneration media, such as those described herein, for desorbing PFAS from the cationic CDP adsorbents disclosed herein reduce the bed volume of regeneration medium required to achieve adsorbent regeneration, resulting in a higher concentration of desorbed PFAS in the spent regeneration medium. Such higher concentrations are beneficial because they reduce the volume of PFAS-contaminated liquid that must ultimately be treated to isolate and destroy (i.e., mineralize) the PFAS (Figures 1 and 2). Higher PFAS concentrations are also beneficial in cases where the PFAS must be further concentrated before destruction.

[0029] Furthermore, a more effective regeneration medium capable of regenerating the cationic CDP adsorbent in a smaller bed volume would generally desorb PFASs more quickly and reduce the time required for regeneration, which could be highly beneficial to the overall PFAS removal process by allowing for a faster turnaround time for recycling the regenerated adsorbent for reuse.

[0030] After removing the adsorbed PFAS from the CDP adsorbent using the regeneration methods described herein, the resulting PFAS solution can be further concentrated using methods known in the art, such as membrane filtration, distillation, or evaporation, or a combination thereof. These further concentrated solutions may include (i) a mixture of solvents originally present in the regeneration medium, and in the case of a solvent mixture, the ratio of solvents may be the same as or different from that originally present in the regeneration medium; (ii) an aqueous solution provided after substantial removal of the alcohol; or (iii) a solid essentially free of solvent. These processes are advantageous not only in providing a more concentrated PFAS solution, but also in that the recovered PFAS volume is smaller and therefore can be more efficiently destroyed or disposed of, allowing for the recovery and reuse of the regeneration solvent.

[0031] Recovery or regeneration efficiency is defined as the mass fraction of adsorbed PFAS recovered (i.e., desorbed) from a used adsorbent after regeneration. Higher recovery efficiencies are advantageous because they increase the number of adsorption / desorption cycles a given volume of cationic CDP adsorbent can undergo, thus allowing for multiple reuse of the adsorbent. The regeneration media of the present disclosure provide recovery efficiencies of about 50% to greater than about 95%, including about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, about 95%, about 96%, about 97%, about 98%, about 99%, or about 100%, including any range therebetween.

[0032] All documents referenced herein, including, inter alia, patents, patent applications, patent publications, and journal references, are incorporated by reference in their entirety for all purposes. [Example]

[0033] material Methanol - Fisher Chemical, HPLC grade; Ethanol - Spectrum, 190 proof, reagent grade; Isopropanol - Optima, LC / MS grade; Deionized (DI) water - obtained from a Milli-Q system; Tap water - obtained from the Boston City Water Supply; Ammonium acetate (NH4OAc) - Fisher Chemical, crystalline / HPLC grade; Ammonium hydroxide (NH4OH), 30.0% w / w, certified ACS Plus grade; Ammonium formate (NH4HCO2) - Fisher Chemical, LC / MS grade; Calcium chloride (CaCl2) - Acros, reagent grade; Cesium sulfate (Cs2SO4) - Alfa Aesar, reagent grade; Hydrochloric acid (HCl) - Fisher Chemical, 38.0% w / w, certified ACS Plus grade; Lithium chloride (LiCl) - Sigma Aldrich, ReagentPlus grade; Sodium chloride (NaCl) - Sigma Aldrich, ACS reagent grade; Sodium sulfate (Na2SO4) - Sigma Aldrich, ACS reagent grade; potassium hydroxide (KOH) - Fisher Chemical, flakes, technical grade; potassium sulfate (K2SO4) - Sigma Aldrich, BioUltra grade.

[0034] Example 1: Regeneration of PFAS-containing cationic CDP adsorbent from DI water To evaluate various salts for DEXSORB+TFN regeneration, 50 mg of DEXSORB+TFN was loaded onto 6 mL empty polypropylene solid-phase extraction (SPE) cartridges. The cartridges were cleaned and conditioned by passing 10 mL of methanol amended with 1 mg / mL of either ammonium acetate (NH4OAc), ammonium formate (NH4HCO2), calcium chloride (CaCl2), or sodium chloride (NaCl), followed by 10 mL of deionized water using a light vacuum. A 10 mL sample of deionized water fortified with 1 ppb of each of the 12 PFAS compounds was then passed through each cartridge at a flow rate of approximately 5 mL / min using a light vacuum. The adsorbed PFASs were recovered by passing 10 mL of methanol amended with 1 mg / mL of the various salts listed above through the DEXSORB+TFN bed and collected in a 15 mL centrifuge tube. An aliquot of the eluent was enriched with mass-tagged internal standards and analyzed using LC-MS / MS (Thermo Scientific Q-Exactive Hybrid Quadrupole-Orbitrap) to determine the amount of PFAS recovered. Overall regeneration efficiency was in the range of 86-105%, as shown in Figure 3.

[0035] Example 2: Regeneration of PFAS-containing cationic CDP adsorbents from drinking water RO concentrate A rapid small-scale column test (RSSCT) experiment was conducted in which 0.3 g (0.72 mL) of DEXSORB+TFN was packed onto an HPLC column (Restek, ID = 4.6 mm) before regeneration, and 7.63 gallons of PFAS-contaminated reverse osmosis (RO) concentrate was passed through the column at a flow rate of 1.38 mL / min with an initial total PFAS concentration of >3,000 ng / L. The mass of PFAS on the DEXSORB+TFN was calculated by integrating the difference between the initial (column inlet) and remaining (column outlet) PFAS concentrations, then multiplying by the total volume of water passed through the column.

[0036] Regeneration experiments were then conducted using the same DEXSORB+TFN column as in the RSSCT experiments. The regeneration medium was a 2:1 (v / v) ethanol:water mixture amended with 0.5 g / L K2SO4 to obtain a saturated solution. To maximize the use of the regeneration medium, a total of 73 mL of regeneration medium was passed through the DEXSORB+TFN column at a flow rate of 0.5 mL / min in several circulation cycles at ambient temperature (approximately 20 °C) and pressure (approximately 1 bar). Based on the volume and PFAS concentration of the regeneration medium, the mass of PFAS recovered from the PFAS-containing DEXSORB+TFN was calculated. A mass balance model was established based on PFAS adsorption during RSSCT and PFAS desorption during regeneration. As shown in Figure 4, the regeneration efficiency for all PFAS combinations in solution was 92%.

[0037] Examples 3-9: Regeneration of PFAS-containing cationic CDP adsorbents from surface water RO concentrates material The spent DEXSORB+TFN adsorbent used in this set of examples was obtained from a field pilot column that processed surface water RO concentrate with a total PFAS concentration of approximately 350 ng / L. Over 200,000 gallons of RO concentrate was passed through the column over a nine-month period. The predominant PFAS species in this RO concentrate influent were PFOS, PFOA, PFHxS, and PFBS. Upon completion of the pilot test, the DEXSORB+TFN adsorbent was removed from the column, dried in air, and used for further regeneration experiments. The regeneration efficiency of the spent DEXSORB+TFN adsorbent was evaluated in both batch and column experiments.

[0038] Batch Playback Procedure The PFAS-containing spent DEXSORB+TFN was sampled from a larger container into a 1 L high-density polyethylene (HDPE) bottle. The sampled adsorbent in the bottle was thoroughly mixed before use in both batch and column regeneration experiments. For batch experiments, 50 mL conical polypropylene (PP) centrifuge tubes were weighed and 10 mL of spent DEXSORB+TFN was added, followed by 20 mL of regeneration medium. The centrifuge tubes were tumbled in a rotary tumbler at 40 rpm for 2 hours at ambient temperature. After 2 hours, the tubes were centrifuged at 4,800 rpm for 10 minutes. 5 mL of supernatant from each tube was decanted into a plastic scintillation vial. The remaining portion of the supernatant was discarded as waste. This process was repeated for a total of five cycles. After completing all five cycles, the tubes were dried overnight at 60°C under a hot air stream and then under vacuum. The final dry mass of the regenerated adsorbent was recorded. PFAS concentrations in the spent reclaimed media were measured and analyzed according to the methods outlined in Examples 1 and 2, respectively. All experiments were performed in duplicate.

[0039] Column regeneration procedure Column testing was performed using a liquid chromatography column consisting of a borosilicate glass barrel and PEEK end pieces. The columns were set up in parallel on two ring stands with clamps. Each column was prepared by capping and sealing the bottom of the column, then packing the column with loosely packed glass wool, and finally adding used DEXSORB+TFN adsorbent to a height of 30 cm, corresponding to approximately 70 g of wet adsorbent. After settling the column with water and capping, the final height of the packed adsorbent was recorded. A felt filter was placed near the top of the column to prevent particle loss during backwashing. Finally, the column was capped and fitted with an outlet nozzle. 300 mL of the regenerated medium to be tested was poured into a 500 mL HDPE bottle. Two drilled holes were made in the bottle lid to hold the tubing, and both the inlet and outlet tubing (Masterflex L / S High-Performance Precision Tubing, L15) were inserted through the lid and attached to the column inlet and outlet. The inlet tubing was then locked into place in the head of a Masterflex L / S standard digital drive pump. The drive was set to upflow mode, the pump line was primed until the regenerant medium reached near the column, and the flow rate was set to 20 mL / min. The design parameters are summarized in Table 1. [Table 1]

[0040] During the first regeneration cycle, bed expansion was carefully monitored to prevent contact between the top of the adsorbent bed and the outlet filter. A consistent bed expansion rate of 20-30% was observed with upflow backwashing with DEXSORB+TFN granules. Visible large air bubbles (>3 mm in diameter) in the column were gently tapped with a rubber mallet until they dissipated. After 2 hours of backwashing, circulation was stopped. The outlet tubing from the top of the column was slightly elevated in the HDPE bottle until it was no longer submerged, and the drive was set to downflow mode. Downflow circulation was initiated at the same flow rate (20 mL / min) to purge the regeneration medium from the column. Upon completion, the pump was stopped, and the 500 mL HDPE bottle was replaced with a new one containing 300 mL of fresh regeneration medium. Adsorbent backwashing was repeated in the same column until five regeneration cycles were completed, for a total regeneration medium volume of 1500 mL, corresponding to a total bed volume of 6.1 mL. Procedure for determining PFAS loading in spent adsorbents

[0041] A PFAS extraction method was developed to determine the identity and amount of PFAS adsorbed to the spent adsorbent and to calculate the PFAS recovery rate during the regeneration cycle. A 25 mL sample of spent DEXSORB+TFN granules was oven-dried overnight at 60°C under a hot air stream and then crushed in a grinder. 2.0 (±0.05) g of dried adsorbent was added to a 50 mL PP conical centrifuge tube. These samples were prepared in duplicate. An elution solution of methanol amended with 10 g / L NHOAc was then prepared, and PFAS were extracted following the same protocol as described above for the batch regeneration procedure. The supernatant solution was collected, diluted, and analyzed via LC-MS / MS according to the procedure outlined in Example 1.

[0042] Example 3 The data in Figure 5 compare the regeneration efficiencies under batch and column tests using methanol and ethanol amended with 2 g / L NHOAc as the regeneration media, following the procedure described above. Both regeneration media demonstrated high total PFAS recovery (>94% by mass) from the spent adsorbent. These results indicate that chemical regeneration of spent DEXSORB+TFN is effective under both batch and column operation, and that batch experiments can be used as a suitable proxy for column regeneration performance.

[0043] Example 4 Batch regeneration experiments were conducted to compare the regeneration efficiency of alcohol solvents, including methanol, ethanol, and isopropanol. The regeneration media were prepared by amending each solvent with 2 g / L of NHOAc. The results, shown in Figure 6, indicate that both methanol- and ethanol-containing regeneration media are superior to isopropanol-containing regeneration media. For large-scale operations, ethanol is a particularly useful regeneration solvent due to the more hazardous nature of methanol for safety and handling.

[0044] Example 5 These experiments were performed according to a batch regeneration procedure to evaluate the effect of the ethanol content and salt concentration of the regeneration medium on regeneration efficiency. Three regeneration media were tested: (1) ethanol without added salt, (2) a 2:1 (v / v) ethanol:water mixture amended with 0.5 g / L K2SO4, equivalent to 63% ethanol by volume, and (3) a 1:1 (v / v) ethanol:water mixture amended with 1 g / L K2SO4, equivalent to 48% ethanol by volume. The K2SO4 concentration was observed to be near its saturation limit in both solutions. K2SO4 is insoluble in ethanol. As shown in Figure 7, ethanol alone was found to be more effective at desorbing PFAS than a 1:1 (v / v) ethanol:water mixture amended with K2SO4 (53 ± 1% vs. 24 ± 1% total PFAS recovery), and equally effective compared to a 2:1 (v / v) ethanol:water mixture amended with 0.5 g / L K2SO4 (53 ± 1% vs. 55 ± 3% total PFAS recovery). These results indicate that a certain amount of ethanol in the regeneration medium is important for obtaining high regeneration efficiency and also suggest that an adsorption mechanism based on hydrophobic interactions plays an important role in PFAS adsorption in DEXSORB+TFN.

[0045] Example 6 Additional salts and bases were evaluated for PFAS recovery efficiency using a 2:1 (v / v) ethanol:water mixture as the regeneration solvent. The following salts were screened: NaSO (0.5 g / L), NaCl (0.65 g / L), LiCl (4 g / L), and CsSO (2 g / L). The concentrations of all salts except LiCl were close to the saturation limit. LiCl is highly soluble in ethanol. The bases screened were NHOH (0.5 g / L) and KOH (0.76 g / L), with concentrations adjusted to ensure the molar amount of hydroxide ions was the same between the two solutions. All regeneration media were tested according to the batch regeneration procedure. The results are summarized in Figure 8. Regeneration using both NHOH and KOH solutions showed high efficiencies (102% and 96%, respectively). Regeneration media with LiCl at high salt concentrations also showed near-quantitative regeneration efficiency (99%).

[0046] Example 7 Using ethanol as the sole regeneration solvent, the following additives were evaluated for PFAS recovery efficiency: HCl (0.5 g / L), LiCl (2 g / L and 4 g / L), and KOH (0.76 g / L). The concentration of HCl was chosen so that its molar concentration was equal to that of KOH. All regeneration media were tested according to the batch regeneration procedure. The results are summarized in Figure 9. Ethanol containing HCl (0.5 g / L) showed lower PFAS recovery performance compared to the other solutions. Recovery efficiency also decreased when the concentration of LiCl was reduced from 4 g / L to 2 g / L in ethanol. A LiCl concentration of 4 g / L appeared to be equally effective in both a 2:1 (v / v) ethanol:water mixture and ethanol.

[0047] Example 8 The effect of temperature on regeneration efficiency was evaluated using two different regeneration media: salt-free ethanol and a 2:1 (v / v) ethanol:water mixture amended with 0.5 g / L K2SO4. Two sets of batch experiments were performed: the first set of samples was tumbled at ambient temperature (21 °C) using a benchtop tumbler, and the second set of samples was tumbled in an incubated tumbler set at 40 °C. The incubated samples consistently reached a uniform internal temperature of 35 °C. All experiments followed the batch regeneration procedure. Increasing the temperature in both regeneration media resulted in an expected increase in total PFAS recovery due to more favorable desorption conditions at higher temperatures (Figure 10). The net increase in recovery efficiency for the 2:1 (v / v) ethanol:water mixture amended with 0.5 g / L K2SO4 was found to be greater than that in salt-free ethanol.

[0048] Example 9 Experiments were designed to test the concentration of spent regeneration media to demonstrate the feasibility of recycling the regeneration solvent and minimizing the amount of PFAS-containing waste for subsequent disposal or treatment. The concentration process can be tailored to result in either a liquid waste with high PFAS concentrations after partial removal of the solvent, or a solid waste rich in PFAS after complete removal of the solvent. The concentration step can be achieved through membrane filtration, distillation, or evaporation, or a combination of these.

[0049] A simple distillation setup was used, consisting of a heat plate and crude product, a 1 L round-bottom boiling flask, a distillation head coupled to a condensation column (110 mm condenser length), and a 500 mL round-bottom collection flask. Distillation was performed under light vacuum. Spent regeneration medium was generated from spent DEXSORB+TFN according to a column regeneration procedure that included five regeneration cycles using a 2:1 (v / v) ethanol:water mixture amended with 0.5 g / L K2SO4. A 300 mL aliquot from this spent regeneration medium was subjected to distillation. After heating at 70 °C under light vacuum for less than 3 hours, approximately 185 mL of distillate was collected, indicating the removal of nearly all of the ethanol in solution. This concentration process yielded an aqueous solution that was approximately 2.6-fold more concentrated in PFAS than the original spent regeneration medium.

[0050] To isolate the PFAS in solid form, the distillation was further continued under vacuum at elevated temperature (100°C). The remaining portion of the spent regeneration medium (115 mL) was collected as distillate, and a solid mixture containing PFAS was obtained in a boiling flask. This process was repeated for the remaining four treatment cycles (4 x 300 mL) until complete distillation was achieved, yielding a total of approximately 0.78 g of solid. K2SO4 was estimated to constitute the majority of the solid mixture (approximately 0.75 g). The solid mixture was reconstituted in methanol and analyzed for PFAS, which revealed a total of approximately 1 mg of PFAS.

Claims

1. 1. A method for removing PFAS from a cationic CDP adsorbent having adsorbed PFAS, comprising: contacting a volume of the cationic CDP adsorbent with a regeneration medium comprising an alcohol, optionally water, and optionally at least one salt; and separating the cationic CDP adsorbent from the regeneration medium; The method, wherein at least about 50% of the total adsorbed PFAS is removed from the cationic CDP adsorbent into the regeneration medium.

2. 2. The method of claim 1, wherein the alcohol is selected from the group consisting of methanol, ethanol, and propanol.

3. The method of claim 1 or 2, wherein the regeneration medium further comprises water.

4. The method according to any one of claims 1 to 3, wherein the alcohol is ethanol.

5. 5. The method according to any one of claims 1 to 4, wherein the volume ratio of alcohol to water in the regeneration medium ranges from about 0.5:1 to about 10:

0.

6. 10. The method of claim 1, wherein the regeneration medium comprises a mixture of alcohol and water in a volume ratio of about 2:

1.

7. The method according to any one of claims 1 to 6, wherein the regeneration medium further comprises a salt.

8. The regeneration medium is an alkali metal or alkaline earth metal or ammonium (NH ４ ＋ 8. The method of claim 1, comprising a salt of the compound selected from the group consisting of hydrochloride, nitrate, sulfate, phosphate, formate, acetate, hydroxide, and combinations thereof.

9. The playback medium is K ２ SO ４ 9. The method of claim 1, wherein the aqueous solution contains a salt selected from the group consisting of NaCl, LiCl, and KOH.

10. 10. The method according to any one of claims 1 to 9, wherein the amount of salt in the regeneration medium ranges from about 0.01% to about 6% by weight.

11. The regeneration medium is about 2:1 (v / v) ethanol:water, and about 0.5 g / L K ２ SO ４ The method according to any one of claims 1 to 10, comprising:

12. 11. The method of any one of claims 1 to 10, wherein the regeneration medium comprises about 2:1 (v / v) ethanol:water and about 0.65 g / L NaCl.

13. 11. The method of any one of claims 1 to 10, wherein the regeneration medium comprises about 2:1 (v / v) ethanol:water and about 4 g / L LiCl.

14. 11. The method of any one of claims 1 to 10, wherein the regeneration medium comprises about 2:1 (v / v) ethanol:water and about 0.76 g / L KOH.

15. 11. The method of any one of claims 1 to 10, wherein the regeneration medium comprises 95% (v / v) ethanol:water and about 4 g / L LiCl.

16. 11. The method of any one of claims 1 to 10, wherein the regeneration medium comprises 95% (v / v) ethanol:water and about 0.76 g / L KOH.

17. 11. The method of any one of claims 1 to 10, wherein the regeneration medium comprises 95% (v / v) ethanol:water, and wherein the regeneration medium is substantially free of salts.

18. The cationic CDP adsorbent comprises β-cyclodextrin and a compound having a cationic functional group, (a) tetrafluoroterephthalonitrile, or (b) toluene diisocyanate, or (c) methylene diphenyl diisocyanate.

19. 20. The method of claim 18, wherein the compound having a cationic functional group comprises a compound having a trimethylammonium group.

20. 20. The method of claim 19, wherein the compound having a cationic functional group is choline chloride.

21. The method according to any one of claims 1 to 20, wherein the method is carried out at a temperature below the boiling point of the regeneration medium.

22. 22. The method of any one of claims 1 to 21, wherein the cationic CDP adsorbent is contained in a packed bed vessel and the regeneration medium flows from the bottom to the top of the packed bed vessel.

23. 23. The method of claim 22, wherein the regenerating medium has a flow rate such that the bed expansion rate ranges from about 30% to about 50%.

24. 22. The method of any one of claims 1 to 21, wherein the method is carried out in a batch mode and the contact period between the cationic CDP adsorbent having adsorbed PFAS and the regeneration medium ranges from about 10 minutes to about 24 hours.

25. 25. The method of any one of claims 1 to 24, wherein after the cationic CDP adsorbent is separated from the regeneration medium, the resulting regeneration medium containing PFAS removed from the cationic CDP adsorbent is further concentrated to increase the concentration of PFAS.

26. 26. The method of claim 25, wherein the PFAS removed from the cationic CDP adsorbent is further concentrated using a method selected from the group consisting of membrane filtration, distillation, evaporation, and combinations thereof.

27. 27. The method of claim 25 or 26, wherein the concentrated PFAS is in liquid form.

28. 27. The method of claim 25 or 26, wherein the concentrated PFAS is in solid form.

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