Regeneration of polymeric cyclodextrin adsorbents

Abstract

A method for removing PFAS from a cationic CDP sorbent having adsorbed PFAS is provided. The method includes contacting a volume of a cationic CDP sorbent with a regeneration medium, and separating the cationic CDP sorbent from the regeneration medium.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 479,611, filed on January 12, 2023, which is hereby incorporated by reference in its entirety. Background Art

[0003] A new class of aromatic cross-linked cyclodextrin polymers (CDPs) has been identified that exhibit rapid adsorption properties for polyfluoroalkyl and perfluoroalkyl substances (PFASs), such as those described in US Pat. No. 9,624,314 and US Pat. No. 11,155,646, the contents of each of which are hereby incorporated by reference for all purposes. To be commercially viable 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 high efficiency under appropriate regeneration conditions. Specifically, during regeneration, substantially all adsorbed PFASs should be removed from the CDP adsorbent, restoring the original PFAS adsorption properties of the CDP adsorbent to the greatest extent possible and enabling sequestration of PFAS waste for safe disposal. Regeneration is typically achieved using a regeneration medium that can overcome the adsorption mechanism of PFAS binding to the CDP. Ideally, such a regeneration medium should be relatively nontoxic, and the CDP adsorbent should be rapidly regenerated using a minimal volume of regeneration medium. However, the appropriate regeneration medium and regeneration conditions depend on the specific properties of the CDP and PFAS. In various embodiments, the present invention provides particularly effective regeneration media and regeneration conditions that are commercially advantageous for regenerating CDP adsorbents containing adsorbed PFAS. Summary of the Invention

[0004] The present disclosure relates, inter alia, 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 relates to methods for concentrating adsorbed PFAS after removal from a CDP adsorbent, such as the cationic CDP adsorbents of the present disclosure. The concentrated PFAS provided by the methods of the present disclosure can be in the form of a solid or a liquid. In various embodiments, the cationic CDP adsorbent of the present disclosure containing adsorbed PFAS is contacted with a regeneration medium comprising an alcohol:water (in some embodiments, ethanol:water or pure ethanol) in a ratio of about 0.5:1 (v / v) to about 10:0 (v / v), and optionally a salt selected from the group consisting of an alkali metal or alkaline earth or ammonium (NH4 ＋) chlorides, nitrates, sulfates, phosphates, formate, acetates, or hydroxides. 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. As described herein, the regeneration process can be operated in upflow mode, downflow mode, or batch mode. As described herein, when the regeneration process is operated in upflow mode, the flow can be linear or circular, and the flow rate can be characterized by the bed expansion ratio, which can range from about 5% to about 100%. When the regeneration process is operated in downflow mode, the empty bed contact time ranges from about 1 minute to about 120 minutes. When the regeneration process is operated in batch mode, the contact time between the regeneration medium and the CDP adsorbent (e.g., a cationic CDP adsorbent) can range from about 10 minutes to about 24 hours. Following the contact, the regeneration medium is separated from the cationic CDP adsorbent, thereby transferring at least about 50% of the adsorbed PFAS to the regeneration medium. The PFAS containing regeneration media may then be further processed, for example, by optionally further concentrating the PFAS and ultimately subjecting the PFAS to a suitable PFAS destruction process or alternatively disposed of. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 : Schematic diagram of one embodiment of the regeneration process of DEXSORB+ to generate PFAS-laden solid waste.

[0006] Figure 2 : Schematic diagram of one embodiment of the regeneration process of DEXSORB+ to generate concentrated liquid waste containing PFAS.

[0007] Figure 3a -d: For the reaction with 1 mg / mL NH4OAc ( Figure 3a )、NH4HCO2( Figure 3b )、CaCl2( Figure 3c ) or NaCl ( Figure 3d ) Regenerated DEXSORB+TFN, regeneration efficiency of various PFAS compounds.

[0008] Figure 4a -b: For DEXSORB+TFN regenerated with a 2:1 (v / v) ethanol:water mixture containing 0.5 g / L K2SO4, various PFAS compounds ( Figure 4a ) inlet PFAS concentration ( Figure 4b ) and overall recovery percentage.

[0009] Figure 5: Total PFAS recoveries from batch and column regeneration experiments with methanol and ethanol modified with 2 g / L NH4OAc.

[0010] Figure 6 : Comparison of total PFAS recovery in batch regeneration experiments between methanol, ethanol, and isopropanol, each modified with 2 g / L NH4OAc.

[0011] Figure 7 Comparison of total PFAS recoveries in batch regeneration experiments between regeneration media including ethanol (190 proof, no salt added), a 2:1 (v / v) ethanol:water mixture modified with 0.5 g / L K2SO4 (corresponding to 63 vol% ethanol), and a 1:1 (v / v) ethanol:water mixture modified with 1 g / L K2SO4 (corresponding to 48 vol% ethanol).

[0012] Figure 8 : Other salt, acid, and base additives were evaluated in a 2:1 (v / v) ethanol:water mixture and compared for total PFAS recoveries from batch regeneration experiments.

[0013] Figure 9 : Evaluate other salt, acid, and base additives in ethanol and compare the total PFAS recoveries from batch regeneration experiments.

[0014] Figure 10 : Total PFAS recoveries were compared in ethanol and a 2:1 (v / v) ethanol:water mixture modified with 0.5 g / L K2SO4 at 21°C and 35°C in batch regeneration experiments. DETAILED DESCRIPTION

[0015] It is known in the art that the adsorption mechanisms used to remove or separate various adsorbates from a given matrix vary based on the specific chemical properties of the adsorbent and adsorbate. These adsorption mechanisms rely on interactions between the adsorbent and the adsorbate, including but not limited to hydrophobic interactions, van der Waals forces, pi-pi stacking, hydrogen bonding, electrostatic interactions, ion exchange, and others. Due to competitive adsorption, these interactions can be further influenced by the properties of the matrix containing the adsorbate (e.g., other components dissolved or dispersed in the PFAS aqueous solution). 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 sulfonic acid (PFOS) onto anion exchange resins.

[0016] These underlying adsorption mechanisms ultimately control the strength of the adsorbate-adsorbent interaction, which in turn determines the ease and effectiveness of the desorption process (i.e., recovery of the adsorbate and regeneration of the spent adsorbent).Another key factor for effective desorption is the solubility of the adsorbate in the regeneration medium.

[0017] Therefore, appropriate regeneration conditions depend on the specific chemical properties of the adsorbent and adsorbate, which influence the adsorption mechanism specific to that particular adsorbent and adsorbate. Furthermore, regeneration efficiency is influenced by the solubility properties of the adsorbate in the regeneration medium. Consequently, the parameters governing regeneration efficiency cannot be easily extrapolated from regeneration conditions found to be effective for other adsorbents and adsorbates. For example, Deng et al. found that two structurally very similar acrylic anion exchange resins, IRA958 and IRA67, exhibited distinct regeneration characteristics when exposed to the same regeneration medium, containing adsorbed PFOS.

[0018] Regeneration of adsorbents for PFAS is complicated by the fact that PFAS are a class of polyfluoroalkylated and perfluoroalkylated compounds that encompass a wide range of different chemical and structural features, including varying alkyl chain lengths, linear and branched structures, and different head group chemistries. Because each of these chemical and structural features influences adsorption strength, regeneration of adsorbents containing adsorbed PFAS requires carefully tailored regeneration conditions.

[0019] The PFAS desorption efficiency (i.e., recovery efficiency) of an adsorbent is crucial to the design and ultimate cost of PFAS removal from fluid streams (e.g., PFAS-contaminated water). Higher PFAS recovery efficiency after regeneration reduces the amount of residual PFAS remaining on the adsorbent and, therefore, enables its reuse at the higher PFAS adsorption capacity of the regenerated adsorbent. Higher regeneration efficiency is important because higher PFAS recovery efficiency allows for more reuse cycles of a given batch of adsorbent before it needs to be replaced with fresh adsorbent. Higher recovery efficiency also minimizes the volume of regeneration media required for each regeneration cycle, which provides higher PFAS concentrations in the spent regeneration media. Such higher PFAS concentrations minimize subsequent processing costs, including the cost and difficulty of recycling the regeneration media, the size and selection of unit operations for processing PFAS-containing regeneration media (e.g., separating and / or concentrating the regeneration media from PFAS via membrane or distillation processes), and the ultimate cost of disposing of or destroying the separated PFAS obtained through regeneration.

[0020] As described herein, CDP adsorbents are particularly effective at removing PFAS from, for example, aqueous mixtures. CDP adsorbents can be regenerated using a regeneration medium that readily disrupts the host-guest complex between the cyclodextrin and the adsorbate (e.g., PFAS). DEXSORB+, a type of cationic CDP adsorbent described in US Pat. No. 11,001,645 (the contents of which are hereby incorporated by reference for all purposes), has been shown to effectively remove PFAS from water. However, the desorption of PFAS from cyclodextrin-based adsorbents has not been extensively explored. Methanol and ethanol, as well as aqueous methanol or aqueous ethanol solutions, have been suggested as suitable regeneration media (e.g., US Pat. No. 9,624,314), and methanol has been demonstrated for desorption of bisphenol A (BPA) from spent cyclodextrin-based adsorbents (Alsbaiee et al., Nature 2016, 529, 190-194). However, the CDPs used in these references are not cationic. Furthermore, these references do not consider or describe the complete desorption of PFAS from spent adsorbents to enable safe reuse of the regenerated adsorbent. Additionally, these workers do not consider the safety of the selected regeneration media or the efficiency of regeneration (e.g., using the minimum amount of regeneration media possible to achieve practical and cost-effective disposal of spent regeneration media containing PFAS waste).

[0021] 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 efficiency of regeneration media for the removal of specific PFAS compounds (PFOS; perfluorooctanoic acid, PFOA) from various non-cyclodextrin-based adsorbents (activated carbon, anion exchange resins, silica, zeolites, montmorillonite clay, hydrotalcite, chitosan, etc.) and found that regeneration efficiency varies significantly depending on the chemical nature of the adsorbent and the regeneration media used. Therefore, identifying an appropriate regeneration medium and regeneration conditions requires careful consideration of multiple factors: in particular, 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 integrity of the adsorbate desorption during regeneration, the safety of the regeneration medium (toxicity, flammability, etc.), and the suitability of the regeneration medium for additional processes to separate the adsorbate. Notably, neither Du et al., Nickelsen and Woodard, nor James et al. evaluated the regeneration of PFAS from CDP adsorbents or cationic CDP adsorbents.

[0022] The CDP adsorbent of the present invention is, in a specific embodiment, a cationic, aromatic cross-linked CDP as described in US 11,155,646, the contents of which are hereby incorporated by reference for all purposes. In specific embodiments, the cationic CDPs disclosed herein include: β-cyclodextrin crosslinked with tetrafluoroterephthalonitrile (TFN), which is further modified by reaction with a cationic group (e.g., choline chloride); β-cyclodextrin crosslinked with an isocyanate (e.g., toluene diisocyanate (TDI), including 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 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), which is optionally modified with a cationic group, such as an ammonium group or a tetraalkylammonium group. The specific CDP adsorbents described herein are not limited to polymers prepared from the specific cyclodextrins described above and aromatic crosslinking monomers. That is, any cyclodextrin described in US Pat. No. 11,155,646, including α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin, or a synthetic cyclodextrin having 3-20 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 all ranges therebetween) can be used to prepare the cationic CDP adsorbent of the present disclosure.

[0023] 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 carboxylic acids, such as acyl halides (including acyl chlorides) or esters). TFN is a specific example of a suitable aryl fluoride; TDI, MDI, and polymeric MDI are specific examples of suitable isocyanates; and terephthaloyl chloride is a specific example of a suitable activated acyl 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 bearing cationic functional groups or functional groups that can be converted to cationic functional groups. For example, β-cyclodextrin can be polymerized in the presence of TFN, a base (e.g., K2CO3), and choline chloride to provide a crosslinked polymer containing aryl crosslinks 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 aromatic crosslinks bearing ethyltrimethylammonium groups (DEXSORB+TDI or DEXSORB+MDI). In other embodiments, CDP itself can be treated post-synthesis to incorporate cationic groups. For example, when β-cyclodextrin reacts with a diisocyanate (e.g., TDI and / or MDI), under appropriate conditions, some of the isocyanate groups can hydrolyze to form carbamic acid, which can decompose into amines. The resulting amine groups can be quaternized to form cationic ammonium groups on the polymer.

[0024] The CDP adsorbents described herein can be used to adsorb PFAS from various mixtures, including water streams contaminated with PFAS (groundwater, drinking water, wastewater, etc.). PFAS can include a variety of polyfluorinated and perfluorinated compounds, including perfluorobutyric 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), perfluorotetradecanoic acid (PFTeA), perfluoropropane sulfonic acid (PFPrS), perfluorobutane sulfonic acid (PFBS), perfluoropentane sulfonic acid (PFPeS), perfluorohexane sulfonic acid (PFHxS), Perfluoroheptanesulfonic acid (PFHpS), perfluorooctanesulfonic acid (PFOS), perfluorononanesulfonic acid (PFNS), perfluorodecanesulfonic acid (PFDS), perfluorododecanesulfonic acid (PFDoS), 4:2 fluorotelomer sulfonate (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), perfluorooctanesulfonamide (PFOSA), perfluorodecanesulfonate Perfluorooctanesulfonamide (FDSA), N-ethylperfluorooctane-1-sulfonamide (NEtFOSA), N-methylperfluorooctane-1-sulfonamide (NMeFOSA), perfluorooctanesulfonamidoacetic acid (FOSAA), N-ethylperfluorooctanesulfonamidoacetic acid (NEtFOSAA), N-methylperfluorooctanesulfonamidoacetic acid (NMeFOSAA), N-methylperfluorooctanesulfonamidoethanol (NMeFOSE), N-ethylperfluorooctanesulfonamidoethanol (NEtFOSE), hexafluoropropylene oxide dimer acid (HFPO-DA), 4,8-dioxa-3H-perfluorononanoate (ADONA ), perfluoro-3-methoxypropionic acid (PFMPA), perfluoro-4-methoxybutyric acid (PFMBA), perfluoro-3,6-dioxaheptanoic acid (NFDHA), 9-chlorohexafluoro-3-oxanone-1-sulfonic acid (9Cl-PF3ONS), 11-chloroticosyl-3-oxanonane-1-sulfonic acid (11CL-PF3OUdS), perfluoro(2-ethoxyethane)sulfonic acid (PFEESA), perfluoro-4-ethylcyclohexanesulfonic acid (PFECHS), 8-chloroperfluoro-1-octanesulfonic acid (8Cl-PFOS), 3-perfluoropropylpropionic acid (3:3FTCA), 2H,2H,3H,3H-perfluorooctanoic acid (5:3FTCA), 3-perfluoroheptylpropionic 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-dimethylaminoprop-1-yl)perfluoro-1-hexanesulfonamide (N-AP-FHxSA), and combinations thereof.

[0025] The regeneration medium that can be used to efficiently regenerate 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 alcohol:water volume ratio of the aqueous alcohol mixture can be in the range of about 0.5:1 to about 10:0, for example, 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 between any of these ratios. In a specific embodiment, the alcohol is ethanol. In other specific embodiments, the alcohol is methanol. In still other specific embodiments, the alcohol is propanol (eg, isopropanol).

[0026] In other embodiments, the amount of alcohol in the suitable regeneration medium can be expressed as the volume percent (% (v / v)) of alcohol in water (when present). For example, a suitable regeneration medium can 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) volume percent alcohol, including any range between any of these values. In a specific embodiment, the alcohol is ethanol. In other specific embodiments, the alcohol is methanol. In still other specific embodiments, the alcohol is propanol (e.g., isopropanol).

[0027] In some embodiments, it is useful to include dissolved salts in the regeneration medium to increase the efficiency of removing adsorbed PFAS from a CDP adsorbent of the present disclosure (eg, DEXSORB+ or other cationic CDP adsorbents as disclosed herein). The salt content of the regeneration medium can be in the concentration range of about 0.1 g / L to about 50 g / L, including 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 2.1 g / L, about 2.2 g / L, about 2.3 g / L, about 2.4 g / L, about 2.5 g / L, about 2.6 g / L, about 2.7 g / L, about 2.8 g / L, about 2.9 g / L, about 3 g / L, about 3.1 g / L, about 3.2 g / L, about 3.3 g / L, about 3.4 g / L, about 3.5 g / L, about 3.6 g / L, about 3.7 g / L, about 3.8 g / L, about 3.9 g / L, about 4 g / L, about 4.1 g / L, about 4.2 g / L, about 4.3 g / L, about 4.4 g / L, about 4.5 g / L, about 4.6 g / L, about 4.7 g / L, about 4.8 g / L, about 4.9 g / L, about 5 g / L, about 5.1 g / L, about 5.2 g / L, about 5.3 g / L, about 5.4 g / L, about 5.5 g / L, about 5.6 g / L, about 5.7 g / L, about 5.8 g / L, about 5.9 g / L, about 6 g / L, about 6.1 g / L, about 6.2 g / L, about 6.3 g / L, about 6.4 g / L, about 6.5 g / L, about 6.6 g / L, about 6.7 g / L, about 6.8 g / L, about 6.9 g / L, about 7 g / L, about 7.1 g / L, about 7.2 g / L, about 7.3 g / L, about 7.4 g / L, about 7.5 g / L, about 7.6 g / L, about 7.7 g / L, about 7.8 g / L, about 7.9 g / L, about 8 g / L, about 8.1 g / L, about 8.2 g / L, about 8.3 g / L, about 8.4 g / L, about 8.5 g / L, about 8.6 g / L, about 8.7 g / L, about 8.8 g / L, about 8.9 g / L, about 9 g / L, about 9.1 g / L, about 9.2 g / L, about 9.3 g / L, about 9.4 g / L, about 9.5 g / L, about 9.6 g / L, about 9.7 g / L, about 9.8 g / L, about 9.9 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, 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 all ranges between any of these values. Alternatively, the amount of dissolved salts in the regeneration medium can be expressed as a weight percentage (wt. %). Suitable weight percentages of any salt 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.%, about 2.1 wt.%, about 2.2 wt.%, about 2.3 wt.%, about 2.4 wt.%, about 2.5 wt.%, about 2.6 wt.%, about 2.7 wt.%, about 2.8 wt.%, about 2.9 wt.%, about 3 wt.%, about 3.1 wt.%, about 3.2 wt.%, about 3.3 wt.%, about 3.4 wt.%, about 3.5 wt.%, about 3.6 wt.%, about 3.7 wt.%, about 3.8 wt.%, about 3.9 wt.%, about 4 wt.%, 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 wt.%, or about 6 wt.%, including all ranges between any of these values. As described above, the salt-containing regeneration medium 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.

[0028] Suitable salts include alkali metals (e.g., Li ＋ 、Na ＋ , K ＋ or Cs ＋ ) or alkaline earth metals or ammonium (NH4 ＋ ) chloride, nitrate, sulfate, phosphate, format, acetate, hydroxide, or a combination thereof. In certain embodiments, the salt comprises sodium sulfate (Na2SO4), potassium sulfate (K2SO4), cesium sulfate (Cs2SO4), ammonium acetate (NH4OAc), ammonium hydroxide (NH4OH), ammonium formate (NH4HCO2), lithium chloride (LiCl), sodium chloride (NaCl), or potassium hydroxide (KOH). In a specific embodiment, the regeneration medium comprises a 2:1 (v / v) ethanol:water mixture containing approximately 0.5 g / L K2SO4.

[0029] In other specific embodiments, the regeneration medium comprises a mixture of ethanol and water (in any ratio as described herein) and further comprises LiCl. In a specific embodiment, the regeneration medium comprises a mixture of ethanol and water (in any ratio as described herein) and further comprises LiCl at a concentration of about 4 g / L. In still other specific embodiments, the regeneration medium comprises a mixture of ethanol and water (in any ratio as described herein) and further comprises KOH. In a specific embodiment, the regeneration medium comprises a mixture of ethanol and water (in any ratio as 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 a specific embodiment, the regeneration medium comprises ethanol that is substantially free of water and substantially free of added salt. In yet other embodiments, the regeneration medium comprises 95% (v / v) ethanol (and 5% (v / v) water, i.e., an azeotropic composition of ethanol and water), optionally containing 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 as described herein, the ratio of ethanol:water (v / v) is in the range of about 2:1 to about 10:0.

[0030] The cationic CDP adsorbents described herein can be used to remove PFAS from aqueous liquids by contacting the cationic CDP adsorbent with a PFAS-contaminated aqueous liquid using equipment and methods known in the chemical and environmental engineering arts. For example, a cationic CDP adsorbent (e.g., DEXSORB+) can be loaded into a packed bed vessel equipped with at least one inlet and outlet, whereby a PFAS-contaminated aqueous liquid can 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 relevant process parameters can be appropriately adjusted to allow PFAS to be removed 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 the PFAS-contaminated liquid, 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 adsorbed PFAS can be achieved by contacting the cationic CDP adsorbent bed with a regeneration medium as described herein using methods known in the art. This process is performed in a Figure 1 and Figure 2 In display.

[0031] In various embodiments, the operating temperature of the regeneration process can vary from ambient temperature (e.g., approximately 20°C) to a temperature at which the regeneration medium remains below its boiling point (e.g., slightly below the boiling point of the alcohol or aqueous alcohol present in the regeneration medium). When the alcohol forms an azeotrope with, for example, water, one skilled in the art will recognize that the minimum boiling point can be lower than the boiling point of the alcohol. Additionally, since the boiling point of the regeneration medium can vary based on atmospheric pressure and the amount of any dissolved salts that may be present, the maximum suitable regeneration temperature at which the regeneration medium remains below its minimum boiling point can vary accordingly. In most embodiments, the regeneration process is performed 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 ranges between any of these values.

[0032] In some embodiments, the regeneration process can be operated in an upflow mode, where the regeneration medium flow flows from the bottom to the top of the packed bed vessel. In alternative embodiments, the regeneration process can be operated in a downflow mode, where the regeneration medium flow flows 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 adsorbed PFAS only once, or "annular," meaning that the regeneration medium is recirculated multiple times (2, 3, or more times) through the CDP adsorbent containing adsorbed PFAS. In a "linear" flow setup, the regeneration medium that passes through the vessel containing the spent CDP adsorbent can be collected for concentration, or it can be directed to other vessels containing spent CDP adsorbent and then collected for concentration. In a "annular" flow setup, the regeneration medium is recirculated multiple times through the same vessel containing the spent CDP adsorbent, and the regeneration medium is collected for concentration. This recirculation process can be repeated for multiple rounds, starting with fresh regeneration medium in each round.

[0033] When the process is operated in downflow mode, the flow rate of the regeneration medium can be determined based on the desired empty bed contact time (EBCT), which in various embodiments will be 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 ranges between any of these values. EBCT refers to the amount of time required for the regeneration 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, ie, the volume of the cationic CDP adsorbent.

[0034] When the process is operated in upflow mode, the flow rate can be determined based on the desired bed expansion ratio, which in various embodiments will be in 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 ranges between any of these values. In specific embodiments, the bed expansion ratio is in the range of about 30-50%. Proper adjustment of the bed expansion ratio is important to ensure that the majority of the particles are suspended during upflow and to minimize particle loss. The term "bed expansion ratio" refers to the increase in bed length occupied by the CDP adsorbent in the vessel during upflow regeneration.

[0035] Generally, sufficient regeneration media should be used to allow complete or nearly complete removal of PFAS from the cationic CDP adsorbent. Efficient removal of PFAS from cationic CDP adsorbents is highly advantageous for a number of reasons.

[0036] In other embodiments, the regeneration process can be carried out in a "batch" mode, wherein the cationic CDP adsorbent containing adsorbed PFAS is mixed with a regeneration medium (e.g., any regeneration medium described herein) for a suitable contact period (e.g., about 10 minutes to 24 hours, including 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, 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 ranges between any of these values), and then removed from contact with the regeneration medium by suitable means (decanting, filtration, etc.).

[0037] Removing all or nearly all PFAS during the regeneration process provides a regenerated cationic CDP adsorbent having the same or nearly the same PFAS adsorption properties as the original adsorbent, i.e., a high adsorption capacity and rapid adsorption kinetics for PFAS. The speed and efficiency with which the regenerated media removes adsorbed PFAS are also important. Using a regenerated media that rapidly removes adsorbed PFAS in a relatively small volume is advantageous because the recovered PFAS obtained by the regeneration process are present in higher concentrations in the spent regenerated media.

[0038] One way to describe the effectiveness of a regeneration media in removing PFAS is to use the numerical value of the bed volume of regeneration media required to remove all or substantially all PFAS from a 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 in the vessel with a sufficient void space ratio, which in various embodiments will be 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 ranges between any of these values. In specific embodiments, the void space ratio is in the range of about 30-50%. The term "void space ratio" refers to the volume fraction of the empty headspace in the entire vessel after filling with the CDP adsorbent. A regeneration media that can regenerate an adsorbent with a lower "bed volume" is more effective than another regeneration media that requires a higher value of bed volume to desorb the same level of PFAS from the adsorbent under the same conditions. In various embodiments, the numerical value of the bed volume will be in the range of about 1-20, 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 ranges between any of these values. In specific embodiments, the numerical value of the bed volume is in the range of about 1-10. More efficient regeneration media, such as the regeneration media described herein for desorbing PFAS from the cationic CDP adsorbents disclosed herein, reduces the bed volume of regeneration media required to achieve regeneration of the adsorbent, which results in higher concentrations of desorbed PFAS in the spent regeneration media. 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. Figure 1 and Figure 2 Higher PFAS concentrations can also be beneficial if PFAS must be further concentrated before destruction.

[0039] Additionally, more efficient regeneration media that can regenerate cationic CDP adsorbents using less bed volume typically desorb PFAS faster, which shortens the time required for regeneration. This can be highly beneficial for the overall PFAS removal process because it allows for faster turnaround times for recycling regenerated adsorbents for reuse.

[0040] 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 of these. These additional concentrated solutions can contain (i) a mixture of solvents initially present in the regeneration medium, and in the case of a solvent mixture, the ratios of the solvents can be the same as those initially present in the regeneration medium, or can be present in ratios different from those initially present in the regeneration medium, (ii) an aqueous solution provided after substantial removal of the alcohol, or (iii) a solid that is substantially free of solvent. These processes not only provide more concentrated PFAS solutions, but are also advantageous because the volume of recovered PFAS is smaller and can therefore be more efficiently destroyed or disposed of, and also allow for the recovery and reuse of the regeneration solvent.

[0041] Recovery or regeneration efficiency is defined as the mass percentage of adsorbed PFAS that is recovered (i.e., desorbed) from the spent adsorbent after regeneration. A higher recovery efficiency is advantageous because it increases the number of adsorption / desorption cycles that a given volume of cationic CDP adsorbent can undergo, and thus enables the adsorbent to be reused multiple times. The regeneration media of the present disclosure provide recovery efficiencies of about 50% to about 95% or more, 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 ranges between any of these values.

[0042] All documents referenced herein, including especially patents, patent applications, patent publications, and journal references, are incorporated by reference in their entirety for all purposes.

[0043] Examples

[0044] Material

[0045] Methanol - Fisher Chemical, HPLC grade; Ethanol - Spectrum, 190 proof, reagent grade; Isopropyl alcohol - Optima, LC / MS grade; Deionized (DI) water - obtained from a Milli-Q system; Tap water - obtained from the Chicago city water supply; Ammonium acetate (NH4OAc) - Fisher Chemical, crystallization / HPLC grade; Ammonium hydroxide (NH4OH), 30.0% w / w, certified ACS+ 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+ grade; Lithium chloride (LiCl) - Sigma-Aldrich. Aldrich), reagent grade +; sodium chloride (NaCl) - Sigma-Aldrich, ACS reagent grade; sodium sulfate (Na2SO4) - Sigma-Aldrich, ACS reagent grade; potassium hydroxide (KOH) - Fisher Chemical, flake, industrial grade; potassium sulfate (K2SO4) - Sigma-Aldrich, BioUltra grade.

[0046] Example 1: Regeneration of PFAS-loaded Cationic CDP Adsorbent from DI Water

[0047] To evaluate various salts for regeneration of DEXSORB+TFN, empty 6 mL polypropylene solid-phase extraction (SPE) cartridges were loaded with 50 mg of DEXSORB+TFN. The cartridges were cleaned and conditioned by passing through 10 mL of methanol modified with 1 mg / mL ammonium acetate (NH4OAc), ammonium formate (NH4HCO2), calcium chloride (CaCl2), or sodium chloride (NaCl), followed by 10 mL of deionized water using gentle 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 using gentle vacuum at a flow rate of approximately 5 mL / min. Adsorbed PFASs were recovered by passing 10 mL of methanol modified with 1 mg / mL of each of the salts listed above through the DEXSORB+TFN bed and collected in a 15 mL centrifuge tube. Aliquots of the eluent were fortified with mass-labeled internal standards and analyzed using LC-MS / MS (Thermo Scientific Q-Exactive Hybrid Quadrupole Orbitrap) to determine the amount of recovered PFASs. As shown in Figure 3, the overall regeneration efficiency is in the range of 86-105%.

[0048] Example 2: Regeneration of PFAS-Loaded Cationic CDP Adsorbent from RO Concentrate of Drinking Water

[0049] Prior to regeneration, a rapid small-scale column test (RSSCT) experiment was performed in which 0.3 g (0.72 mL) of DEXSORB+TFN was loaded onto an HPLC column (Restek, ID = 4.6 mm) and 7.63 gallons of PFAS-contaminated reverse osmosis (RO) concentrate, with an initial total PFAS concentration exceeding 3,000 ng / L, was passed through the column at a flow rate of 1.38 mL / min. The mass of PFAS on the DEXSORB+TFN was calculated by integrating the difference between the initial (column inlet) and residual (column outlet) PFAS concentrations and then multiplying by the total volume of water passed through the column.

[0050] A regeneration experiment was subsequently performed using the same DEXSORB+TFN column from the RSSCT experiment. The regeneration medium was a 2:1 (v / v) ethanol:water mixture modified with 0.5 g / L K₂SO₄ to obtain a saturated solution. A total of 73 mL of regeneration medium was passed through the DEXSORB+TFN column at a flow rate of 0.5 mL / min at ambient temperature (approximately 20°C) and pressure (approximately 1 bar) over several cycles to maximize the use of the regeneration medium. The mass of PFAS recovered from the PFAS-loaded DEXSORB+TFN was calculated based on the volume of regeneration medium and the PFAS concentration. A mass balance model was developed based on PFAS adsorption during RSSCT and PFAS desorption during regeneration. As shown in Figure 4, the regeneration efficiency for all PFAS in solution combined was 92%.

[0051] Example 3-9: Regeneration of PFAS-Loaded Cationic CDP Adsorbent from RO Concentrate of Surface Water

[0052] Material

[0053] The spent DEXSORB+TFN adsorbent used in this set of examples was obtained from a field test column of surface water RO concentrate treated with a total PFAS concentration of approximately 350 ng / L. Over 200,000 gallons of RO concentrate were passed through the column over a nine-month period. The primary PFAS species in the RO concentrate influent were PFOS, PFOA, PFHxS, and PFBS. After completing the initial testing, the DEXSORB+TFN adsorbent was removed from the column, air-dried, and used in further regeneration experiments. The regeneration efficiency of the spent DEXSORB+TFN adsorbent was evaluated in batch and column experiments.

[0054] Batch regeneration procedure

[0055] Spent PFAS-laden DEXSORB+TFN was sampled from a bulk container into 1 L high-density polyethylene (HDPE) bottles. The sampled adsorbent in the bottles was thoroughly mixed before use in batch and column regeneration experiments. For batch experiments, 50 mL polypropylene (PP) conical 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 rotating drum at 40 rpm for two hours at ambient temperature. After two hours, the tubes were centrifuged at 4,800 rpm for 10 minutes. 5 mL of supernatant from each tube was poured into a plastic scintillation vial. The remaining supernatant was discarded as waste. This process was repeated for a total of five cycles. After all five cycles were completed, the tubes were dried at 60°C overnight under a stream of hot air and then dried under vacuum. The final dry mass of the regenerated adsorbent was recorded. PFAS concentrations in the spent regeneration medium were measured and analyzed according to the methods outlined in Examples 1 and 2, respectively. All experiments were performed in duplicate.

[0056] Column regeneration procedure

[0057] Column testing was performed using a liquid chromatography column consisting of a borosilicate glass cylinder and PEEK endpieces. The columns were set up in parallel on two ring stands with clamps. Each column was prepared as follows: the column base was capped and sealed, then the column was filled with loosely packed glass wool. Finally, spent DEXSORB+TFN adsorbent was added to a height of 30 cm, corresponding to approximately 70 g of wet adsorbent. After allowing the column to settle and filling it with water, the final adsorbent height 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 the outlet nozzle attached. 300 mL of the regeneration medium tested was poured into a 500 mL HDPE bottle. The bottle cap was equipped with two drilled holes to accommodate tubing, and both inlet and outlet tubing (Masterflex L / S high-performance precision tubing, L15) were inserted into the cap 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 and the pump line was primed until the regeneration medium reached the vicinity of the column, with the flow rate set to 20 mL / min. The design parameters are summarized in Table 1.

[0058] Table 1

[0059]

[0060] During the first regeneration cycle, carefully monitor bed expansion to prevent contact between the top of the adsorbent bed and the outlet filter. A bed expansion of 20-30% was consistently observed with upflow backwash of DEXSORB+TFN particles. Gently tap any visible large bubbles (>3 mm in diameter) in the column with a rubber mallet until they dissipate. Stop the cycle after two hours of backwashing. Slightly elevate the outlet tubing from the top of the column in an HDPE bottle until it is no longer submerged, and set the drive to downflow mode. Start a downflow cycle at the same flow rate (20 mL / min) to purge the regeneration medium from the column. Upon completion, stop the pump and exchange the 500 mL HDPE bottle with a new one containing 300 mL of fresh regeneration medium. Repeat backwashing of the adsorbent in the same column until five regeneration cycles have been completed, with a total regeneration medium volume of 1500 mL, corresponding to a total of 6.1 bed volumes.

[0061] Procedure for determining PFAS loading in used sorbents

[0062] A PFAS extraction method was developed to determine the identity and amount of PFAS adsorbed on the spent adsorbent and to calculate PFAS recovery during the regeneration cycle. A 25 mL sample of spent DEXSORB+TFN pellets was oven-dried overnight at 60°C under a stream of hot air and then pulverized in a pulverizer. 2.0 (± 0.05) g of dry adsorbent was added to a 50 mL PP conical centrifuge tube. These samples were prepared in duplicate. A methanol eluate solution modified with 10 g / L NH4OAc was then prepared and PFASs were extracted following the same protocol described above for the batch regeneration procedure. The supernatant solution was collected, diluted, and analyzed by LC-MS / MS according to the procedure outlined in Example 1.

[0063] Example 3

[0064] Figure 5 The data compared regeneration efficiency in batch and column tests using methanol and ethanol modified with 2 g / L NH4OAc as regeneration media according to the above procedure. Both regeneration media demonstrated high total PFAS recoveries (>94 mass %) from the spent adsorbent. These results demonstrate that chemical regeneration of spent DEXSORB+TFN is effective in both batch and column operations, and that batch experiments can serve as a suitable proxy for column regeneration performance.

[0065] Example 4

[0066] Batch regeneration experiments were performed to compare the regeneration efficiency of alcohol solvents including methanol, ethanol and isopropanol. The regeneration medium was prepared by modifying each solvent with 2 g / L NH4OAc. Figure 6The results shown in indicate that both regeneration media containing methanol and ethanol outperformed the regeneration medium containing isopropanol. For large-scale operations, ethanol would be a particularly useful regeneration solvent compared to the more hazardous nature of methanol for safety and handling.

[0067] Example 5

[0068] These experiments were performed after a batch regeneration procedure to evaluate the effect of the ethanol content and salt concentration of the regeneration medium on the regeneration efficiency. Three regeneration media were tested: (1) ethanol without added salt, (2) a 2:1 (v / v) ethanol:water mixture modified with 0.5 g / L K2SO4, corresponding to 63 vol% ethanol, and (3) a 1:1 (v / v) ethanol:water mixture modified with 1 g / L K2SO4, corresponding to 48 vol% ethanol. It was observed that the concentration of K2SO4 was close to its saturation limit in both solutions. K2SO4 is insoluble in ethanol. As Figure 7 As shown, ethanol alone was found to be more effective in desorbing PFAS than a 1:1 (v / v) ethanol:water mixture modified with 1 g / L K2SO4 (53 ± 1% vs. 24 ± 1% total PFAS recovery) and was equally effective as a 2:1 (v / v) ethanol:water mixture modified 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 crucial for achieving high regeneration efficiency and also suggest that the hydrophobic interaction-based adsorption mechanism plays an important role in PFAS adsorption in DEXSORB+TFN.

[0069] Example 6

[0070] 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: Na2SO4 (0.5 g / L), NaCl (0.65 g / L), LiCl (4 g / L), and Cs2SO4 (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 NH4OH (0.5 g / L) and KOH (0.76 g / L), with concentrations adjusted to achieve the same molar amount of hydroxide ions between the two solutions. All regeneration media were tested following a batch regeneration procedure. The results are summarized in Figure 8 Regeneration with both NH4OH and KOH solutions showed high efficiencies (102% and 96%, respectively). Regeneration media with high salt concentrations of LiCl also showed near-quantitative regeneration efficiencies (99%).

[0071] Example 7

[0072] The PFAS recovery efficiency of the following additives was evaluated using only ethanol as the regeneration solvent: 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 molarity was equal to that of KOH. All regeneration media were tested following a batch regeneration procedure. The results are summarized in Figure 9 Ethanol with HCl (0.5 g / L) showed lower PFAS recovery performance compared to the other solutions. When the LiCl concentration in ethanol was reduced from 4 g / L to 2 g / L, the recovery efficiency also decreased. A LiCl concentration of 4 g / L appeared to be equally effective in both a 2:1 (v / v) ethanol:water mixture and ethanol.

[0073] Example 8

[0074] 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 modified with 0.5 g / L K2SO4. Two batch experiments were performed in which the first set of samples was tumbled at ambient temperature (21°C) using a benchtop roller and the second set of samples was tumbled in an incubated roller set at 40°C. The incubated samples always reached a uniform internal temperature of 35°C. A batch regeneration procedure was followed for all experiments. As desorption conditions are more favorable at higher temperatures, increasing the temperature of both regeneration media resulted in an increase in total PFAS recoveries as expected ( Figure 10 It was found that in the case of a 2:1 (v / v) ethanol:water mixture modified with 0.5 g / L K2SO4, the net increase in recovery efficiency was greater than that in salt-free ethanol.

[0075] Example 9

[0076] The experiment was 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. This concentration process can be tailored to provide a liquid waste with a high PFAS concentration after partial solvent removal or a solid waste loaded with PFAS after complete solvent removal. The concentration step can be achieved by membrane filtration, distillation, or evaporation, or a combination of these.

[0077] A simple distillation apparatus consisting of a hot plate and crucible, a 1 L round-bottom flask, a still head connected to a condensing column (110 mm condenser length), and a 500 mL round-bottom collection flask was used. Distillation was performed under slight vacuum. Spent regeneration medium was generated from spent DEXSORB+TFN following a column regeneration procedure involving five regeneration cycles with a 2:1 (v / v) ethanol:water mixture modified with 0.5 g / L K₂SO₄. A 300 mL aliquot from this spent regeneration medium was distilled. After heating at 70°C under slight vacuum for less than 3 hours, approximately 185 mL of distillate was collected, indicating that nearly all of the ethanol in the solution had been removed. This concentration process produced an aqueous solution with a PFAS concentration approximately 2.6 times that of the original spent regeneration medium.

[0078] To isolate the solid form of PFAS, distillation was further continued at high temperature (100°C) under vacuum. The remaining portion of the spent regeneration medium (115 mL) was collected as distillate, and a solid mixture containing PFAS was obtained in a flask. This process was repeated for the remaining four treatment cycles (4 × 300 mL) until complete distillation was achieved, resulting in a total of approximately 0.78 g of solid. It was estimated that K2SO4 accounted for the majority of the solid mixture (approximately 0.75 g). The solid mixture was reconstituted in methanol and analyzed for PFAS, which showed a total of approximately 1 mg of PFAS.

Claims

1. A method for removing PFAS from a cationic CDP adsorbent having adsorbed PFAS, The method comprises 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, At least about 50% of the total amount of PFAS thus adsorbed is removed from the cationic CDP adsorbent and enters the regeneration medium.

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

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

0.

6. 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 method according to any one of claims 1 to 7, wherein the regeneration medium comprises a salt selected from the group consisting of an alkali metal or alkaline earth metal or ammonium (NH4 + ) chlorides, nitrates, sulfates, phosphates, formates, acetates, hydroxides, and combinations thereof.

9. The method according to any one of claims 1 to 8, wherein the regeneration medium comprises a salt selected from the group consisting of: K2SO4, NaCl, LiCl and KOH.

10. The method of any one of claims 1 to 9, wherein the amount of salt in the regeneration medium is in the range of about 0.01 wt.% to about 6 wt.%.

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 0.5 g / L K2SO4.

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

18. The method according to any one of claims 1 to 17, wherein the cationic CDP adsorbent is prepared by polymerizing β-cyclodextrin and a compound carrying a cationic functional group with: (a) Tetrafluoroterephthalonitrile; or (b) toluene diisocyanate; or (c) Methylene diphenyl diisocyanate.

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

20. The method according to claim 19, wherein the compound carrying a cationic functional group is choline chloride.

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

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. The method of claim 22, wherein the regeneration medium has a flow rate that provides a bed expansion ratio in the range of about 30% to about 50%.

24. The method of any one of claims 1 to 21, wherein the method is performed in batch mode and the contact period of the cationic CDP adsorbent with adsorbed PFAS with the regeneration medium is in the range of about 10 minutes to about 24 hours.

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 the PFAS removed from the cationic CDP adsorbent is further concentrated to increase the concentration of PFAS.

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. The method of any one of claims 25 or 26, wherein the concentrated PFAS is in the form of a liquid.

28. The method of any one of claims 25 or 26, wherein the concentrated PFAS is in the form of a solid.

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