Method for removing micropollutants, and use of modified carbon adsorbent

Abstract

Modified carbon adsorbents for use in removal of per- and polyfluoroalkyl substances (PFAS). In a method for removing PFAS from a fluid, the fluid is treated with a carbon adsorbent, which comprises a modified carbon5 adsorbent, which is modified with at least one amphiphilic substance comprising quaternary amine surfactants functionality and having a carbon chain length of C10 - C14.

Description

[0001] METHOD FOR REMOVING MICROPOLLUTANTS, AND USE OF MODIFIED CARBON ADSORBENT

[0002] Field of the invention

[0003] The present invention relates to a method for removing per- and polyfluoroalkyl substances (PFAS) from a fluid according to the independent claim presented below. Further, the invention relates to use of modified carbon adsorbents in removal of per- and polyfluoroalkyl substances.

[0004] Background of the invention

[0005] Chemically and thermally stable per- and polyfluoroalkyl substances, also called PFAS, have become a global concern due to their persistence and widespread contamination of environment. PFAS are resistant to degradation by sunlight, microbes, or heat. Once released, they can remain in soils, water, and sediments for decades or longer. Many PFAS, especially shortchain types, are highly soluble and mobile, allowing them to travel readily through groundwater and surface waters and reach drinking water sources.

[0006] Activated carbon adsorbents are typically used in removal of micropollutants in water treatment. In addition, non-activated porous carbon adsorbents, such as chars, have been used for contaminant removal. The porous carbon adsorbents show good removal performance of many micropollutants. However, they are rather inefficient in removing certain type of harmful micropollutants, such as small sized PFAS.

[0007] Summary of the Invention

[0008] It is an object of the present invention to reduce or even eliminate the above- mentioned problems appearing in prior art.

[0009] It is an object of the present invention to provide a novel efficient method for removing chemically and thermally stable per- and polyfluoroalkyl substances (PFAS) from a fluid. It is an object of the present invention to provide surface modified porous carbon adsorbents for PFAS removal. Especially, an object of the invention is to provide a modified porous carbon adsorbents for use in water treatment in removal of per- and polyfluoroalkyl substances (PFAS).

[0010] In order to achieve among others, the objects presented above, the invention is characterized by what is presented in the characterizing parts of the enclosed independent claims.

[0011] The embodiments and advantages mentioned in this text relate, where applicable, both to the product, the method as well as to the uses according to the invention, even though it is not always specifically mentioned.

[0012] Typical method according to the present invention for removing per- and polyfluoroalkyl substances (PFAS) from a fluid, comprises treating the fluid with a carbon adsorbent, which comprises a modified carbon adsorbent, which is modified with at least one amphiphilic substance comprising quaternary amine functionality and having a carbon chain length of C10 - C14.

[0013] According to the present invention, a modified carbon adsorbent is used in removal of per- and polyfluoroalkyl substances (PFAS) from a fluid. The modified carbon adsorbent according to the present invention comprises a carbon material which is modified with one or a mixture of two or more amphiphilic substances comprising quaternary amine functionalities and having a carbon chain length of C10 - C14. Modified carbon adsorbent according to the present invention can be used in water treatment in removal of per- and polyfluoroalkyl substances (PFAS) from water. According to the present invention, water treatment may comprise a treatment of water, water body and / or wastewater. Water treatment may comprise drinking water treatment or treatment of wastewaters, such as municipal wastewaters, industrial wastewaters or wastewater sludges. Modified carbon adsorbent according to the present invention is found to be an efficient adsorbent for removal of chemically and thermally stable per- and polyfluoroalkyl substances (PFAS), but the modified carbon adsorbent of the present invention can also be used for removal of other micropollutants, particularly hydrophobic and anionic compounds. Brief description of the Figures

[0014] Figure 1 presents PFAS adsorption efficiency of modified carbon adsorbents according to the present invention, prepared according to Examples 1 - 4.

[0015] Figure 2 presents an impact of amphiphilic substance carbon chain length on the PFAS adsorption efficiency of the modified carbon adsorbents.

[0016] Figure 3 presents PFAS adsorption efficiency of modified carbon adsorbents according to the present invention, prepared according to Examples 1 , 5 and 6.

[0017] Figure 4 presents PFAS adsorption efficiency of modified carbon adsorbents according to the present invention, prepared according to Example 7.

[0018] Figure 5 presents PFAS adsorption efficiency of modified carbon adsorbents according to the present invention, prepared according to Example 8.

[0019] Detailed description of the invention

[0020] A modified carbon adsorbent according to the present invention is surface modified whereby the modified carbon adsorbent provides an efficient removal of PFAS. Modified carbon adsorbent according to the present invention is modified with at least one amphiphilic substance comprising quarternary amine functionality and having a carbon chain length of C10 - C14. In an embodiment of the present invention the modified carbon adsorbent is modified with a mixture of two or more amphiphilic substances comprising quarternary amine functionalities and having a carbon chain length of C10 - C14. In a method according to the present invention, a modified carbon adsorbent modified with one or a mixture of two or more amphiphilic substances comprising quarternary amine functionalities and having a carbon chain length of C10 - C14, is used in removal of PFAS.

[0021] A modified carbon adsorbent according to the present invention is modified by using at least one amphiphilic substance comprising quarternary amine functionality. According to an embodiment of the present invention, an amphiphilic substance comprises quaternary ammonium cation. In one preferred embodiment of the present invention amphiphilic substance comprises quaternary ammonium cation and hydrophobic moiety or moieties. In an exemplary embodiment according to the present invention, an amphiphilic substance comprises a linear quaternary amine surfactant with a hydrophobic alkyl chain with a chain length of C10 - C14. In an exemplary embodiment according to the present invention, an amphiphilic substance may comprise decyltrimethylammonium halide, octyltrimethylammonium halide, dodecyltrimethylammonium halide and / or tetradecylmethlyammonium halide. According to an embodiment of the present invention, the amphiphilic substance is selected from a group consisting of decyltrimethylammonium chloride or bromide, octyltrimethylammonium chloride or bromide, dodecyltrimethylammonium chloride or bromide, tetradecyltrimethylammonium chloride or bromide, and any combination thereof.

[0022] According to an embodiment of the present invention, a modified carbon adsorbent comprises 0.1 - 20 weight-% of the amphiphilic substance or substances comprising quarternary amine functionalities and having a carbon chain length of C10 - C14, preferably a modified carbon adsorbent comprises 1 - 10 weight-%, and more preferably 1 - 5 weight-% of the amphiphilic substance or substances comprising quarternary amine functionalities and having a carbon chain length of C10 - C14, calculated from dry total weight of the modified carbon adsorbent.

[0023] According to an embodiment of the present invention, the carbon adsorbent used in a method of the invention may further comprise an unmodified carbon adsorbent. The carbon adsorbent can thus be a mixture of a modified carbon adsorbent according to the present invention and an unmodified carbon adsorbent. In an embodiment of the present invention, the carbon adsorbent may comprise 5 - 100 weight-% of the modified carbon adsorbent, calculated from the weight of the carbon adsorbent. In an embodiment of the present invention, a carbon adsorbent may comprise a mixture of modified carbon absorbent(s) with 5 - 95 weight-% fraction and an unmodified carbon adsorbent with 5 - 95 weight-% fraction.

[0024] In the present invention, a modified carbon adsorbent or an unmodified carbon adsorbent can be activated or non-activated carbon adsorbent. According to the present invention, a modified carbon adsorbent or unmodified carbon adsorbent may comprise activated carbon material, nanocarbon material and / or carbon char adsorbent. In an embodiment according to the present invention a modified carbon adsorbent or unmodified carbon adsorbent can be activated carbon material, nanocarbon material and / or carbon char adsorbent with high surface area and micro- mesoporosity. In an embodiment according to the present invention a modified carbon adsorbent or unmodified carbon adsorbent comprises activated carbon material, nanocarbon material and / or carbon char adsorbent, which has a specific surface area of > 100 m2 / g, typically in a range of 100 - 2000 m2 / g and pore volume of 0.1-0.95 cc / g. Specific surface area and pore size distributions can be determined with BET surface analyzer using gas sorption (e.g. N2, CO2 or Ar), and the SSA / porosities can be calculated e.g. with adsorption based on Brunaeur-Emmett-Teller (BET) theory, density functional theory (DFT) or variations of these.

[0025] Activated carbon is a form of carbon that has been physically or chemically processed to increase its porosity and surface area available for adsorption and chemical reactions. According to an embodiment of the present invention, a modified carbon adsorbent or unmodified carbon adsorbent comprises or consists of activated carbon material. The activated carbon material may be powdered activated carbon, pelletized activated carbon and / or granular activated carbon. Powdered activated carbon is a finely ground form of activated carbon. Typically, powdered activated carbon particles have an average particle size of below 200 pm, preferably in a range of 0.1 - 100 pm. Granular or pelletized activated carbon has typically an average particle size in a range of 0.2 - 5 mm, preferably between 0.5 - 3 mm. A specific surface area of activated carbon is typically at least 500 m2 / g.

[0026] According to an embodiment of the present invention, an activated carbon material comprises microporous, macroporous and / or mesoporous activated carbon material. In an embodiment according to the present invention, an amount of a fraction consisting of meso- or macropores having a diameter > 2 nm, is at least 40%, preferably at least 50% from total pore volume in the mesoporous activated carbon material. In an embodiment according to the present invention a modified carbon adsorbent or unmodified carbon adsorbent may comprise or consist of a carbon char adsorbent, such as biochar and / or charcoal. According to an embodiment of the present invention, a carbon adsorbent or unmodified carbon adsorbent may also comprise or consist of nanocarbon material, such as powdered nanocarbon material, granulated nanocarbon material and / or pelletized nanocarbon material.

[0027] According to an exemplary embodiment, a modified carbon adsorbent used in a method according to the present invention is produced by the following method

[0028] - obtaining a solution, which comprises an amphiphilic substance comprising quaternary amine functionality and having a carbon chain length of C10 - C14,

[0029] - dissolving a carbon adsorbent to the solution to obtain a carbon slurry, and

[0030] - mixing the carbon slurry for at least 15 minutes, typically at least 5 hours at a temperature of 20 - 80 °C for complete impregnation and obtaining a modified carbon adsorbent, and

[0031] - optionally filtrating the modified carbon adsorbent and drying and milling of the modified carbon adsorbent.

[0032] The amphiphilic substance comprising quaternary amine functionality and having a carbon chain length of C10 - C14 can be dissolved in an aqueous solution, an aqueous alcohol solution or aqueous salt solution and carbon adsorbent is added to this solution for obtaining a modified carbon adsorbent.

[0033] According to an embodiment of the present invention, a method for removing PFAS comprises treating a fluid, such as water by adding the carbon adsorbent to the fluid, which carbon adsorbent comprises at least a modified carbon adsorbent, which is modified with one or a mixture of two or more amphiphilic substance comprising quaternary amine surfactants functionality and having a carbon chain length of C10 - C14.

[0034] According to an embodiment of the present invention, a carbon adsorbent comprising a modified carbon adsorbent can be added directly to a fluid to be treated, such as water, water body and / or wastewater to be treated. A carbon adsorbent comprising a modified carbon adsorbent can be added to the fluid as a slurry or as dried product, optionally carbon adsorbent is used as dried and milled product. After reaction time, the PFAS filled carbon adsorbent is filtrated from the solution.

[0035] In another embodiment of the present invention a fluid to be treated, such as water is treated by passing the fluid through a filter, a fluidised bed reactor and / or a column comprising a modified carbon adsorbent. The modified carbon adsorbent is typically used as dried or moist product. Moist carbon adsorbent refers to carbon adsorbent, which is filtrated after impregnation with the amphiphilic substance, but not dried. In an embodiment of the present invention, a concentration of PFAS is monitored before and after the treatment with the carbon adsorbent according to the present invention to evaluate the removal levels of PFAS from the treated fluid, such as water.

[0036] In an embodiment of the present invention, water is treated by passing it through a filter, a fluidised bed reactor and / or a column comprising a mixture of modified carbon absorbent with 5-95 weight-% fraction and an unmodified carbon adsorbent with 5-95 weight-% fraction.

[0037] According to an embodiment of the present invention a carbon adsorbent comprising a modified carbon adsorbent used as a filler material in a filter, a column or the like can be re-activated by passing an aqueous solution comprising one or a mixture of two or more amphiphilic substances in certain time intervals through the filter, the fluidised bed reactor and / or the column.

[0038] A method according to an embodiment of the present invention for treating water, water body and / or wastewater for removing PFAS comprises

[0039] - adding carbon adsorbent comprising a modified carbon adsorbent to water, water body and / or wastewater to be treated, and / or

[0040] - guiding water, water body and / or wastewater to be treated through a filter, a fluidised bed reactor and / or a column, which comprises carbon adsorbent comprising a modified carbon adsorbent according to the present invention. EXPERIMENTAL

[0041] The following examples show typical processes for preparation of surface modified carbon adsorbents according to the present invention and their use in removal of per- and polyfluoroalkyl substances (PFAS) from water.

[0042] Example 1

[0043] 0.05 g of dodecyltrimethylammonium chloride (carbon chain length of C12) as an amphiphilic substance is dissolved in 49 g of deionized (DI) water. After dissolution, 0.95 g of powdered activated carbon (micro- and mesoporous powdered activated carbon with average particle size of 15 - 25 pm and specific surface area (by BET method) of about 1000 m2 / g, pore volume of about 0.6 cc / g) is added. The powdered activated carbon (PAC) slurry is mixed overnight at room temperature. The PAC slurry comprises 5 weight-% of the amphiphilic substance, calculated from the dry total weight of carbon adsorbent. The solids carbon adsorbent concentration (amphiphilic substance + PAC) in water is 2 weight-%.

[0044] Example 2

[0045] The modified powdered activated carbon slurry is prepared as in Example 1 , with the exception that decyltrimethylammonium chloride (carbon chain length of C10) is used as an amphiphilic substance instead of dodecyltrimethylammonium chloride.

[0046] Example 3

[0047] The modified powdered activated carbon slurry is prepared as in Example 1 , with the exception that tetradecyltrimethylammonium chloride (carbon chain length of C14 is used as an amphiphilic substance instead of dodecyltrimethylammonium chloride.

[0048] Example 4

[0049] The modified powdered activated carbon slurry is prepared as in Example 1 , with the exception that hexadecyltrimethylammonium chloride (carbon chain length of C16) surfactant is used as an amphiphilic substance instead of dodecyltrimethylammonium chloride.

[0050] Example 5

[0051] The modified powdered activated carbon slurry is prepared as in Example 1 , with the exception that 0.02 g of dodecyltrimethylammonium chloride (carbon chain length of C12) is used as an amphiphilic substance instead of 0.05 g of dodecyltrimethylammonium chloride. The PAC slurry comprises 2 weight-% of the amphiphilic substance, calculated from the dry total weight of carbon adsorbent.

[0052] Example 6

[0053] The modified powdered activated carbon slurry is prepared as in Example 1 , with the exception 0.1 g of dodecyltrimethylammonium chloride (carbon chain length of C12) is used as an amphiphilic substance instead of 0.05 g of dodecyltrimethylammonium chloride. The PAC slurry comprises 10 weight-% of the amphiphilic substance from the dry total weight of carbon adsorbent.

[0054] PFAS adsorption tests relating to Examples 1-6

[0055] Per- and polyfluoroalkyl substances (PFAS) adsorption performance of the modified powdered activated carbon slurries produced in the Examples 1-7 were tested in batch tests. The aqueous mixture of the modified powdered activated carbon adsorbent is dosed as a slurry to surface water sample. Analysed PFAS compounds are listed in Table 1. The listed PFAS compounds were quantified from the surface water before and after the sorption tests with LC-MS / MS (method CEN / TS 15968) using external laboratory. Detection limit, i.e. the lowest concentration of the analyte that can be reliably detected in the analysis, was 0.01 pg / L.

[0056] The PFAS adsorption performance of 2 weight-% powder activated carbon (PAC) slurry without the modification with an amphiphilic substance is used as a reference. The reference PAC slurry is prepared similarly as the surface modified samples by mixing PAC overnight with deionized water before dosing to the adsorption test. In the adsorption tests, sorption time: 22 h, solid adsorbent dosage: 0.025 g / L.

[0057] Table 1 .

[0058] Example 7

[0059] 0.75 g of dodecyltrimethylammonium chloride (carbon chain length of C12) as an amphiphilic substance is dissolved in 45 g of deionized (DI) water. After dissolution, 4.25 g of mesoporous pyrolysis carbon product (fraction of mesopores is about 85%; pore volume about 0.2 cc / g) is added. The mixture of the amphiphilic substance and mesoporous pyrolysis carbon product is mixed overnight in rotational mixer. The obtained surface modified carbon adsorbent is filtered with GFA filter and dried at 50 °C overnight before dosing to PFAS adsorption test. The obtained modified carbon adsorbent comprises 15 weight-% of the amphiphilic substance, calculated from the dry total weight of modified carbon adsorbent, assuming complete impregnation and no amphiphilic substance loss during filtration.

[0060] PFAS are analysed as described above in relating to Examples 1- 6. PFAS adsorption performance of mesoporous pyrolysis carbon product without surface modification with an amphiphilic substance is used as reference. The unmodified adsorbent is dosed directly as product to the treated water. In the adsorption test, Sorption time: 22 h, adsorbent dosage: 0.2 g / L.

[0061] Example 8

[0062] 5 g of dodecyltrimethylammonium chloride (carbon chain length of C12) as an amphiphilic substance is dissolved in 900 g of DI water. After dissolution, 95 g of granular activated carbon (GAC: 8x30 mesh size, iodine number of about 1000 mg / g, specific surface area (by BET method) of about 1000 m2 / g) is added. The mixture of amphiphilic substance and GAC are mixed overnight in rotational mixer. The surface modified adsorbent is filtered with GFA filter and dried at 50 °C overnight. The dried surface modified adsorbent is filled to an adsorption column and the PFAS concentrations in treated water are monitored regularly to evaluate the PFAS removal performance of the sample. The obtained modified GAC adsorbent comprises 5 weight-% of the amphiphilic substance, calculated from the dry total weight of carbon adsorbent, assuming complete impregnation and no amphiphilic substance loss during filtration. For comparison, PFAS adsorption efficiency of GAC without surface modification is monitored.

[0063] Adsorption column filled with adsorbent (60 grams) is treated with PFAS spiked tap water. 150 ng / L of five PFAS (PFBS, PFPeA, PFOS, PFOA, PFNA, PFDA) were used for waiter spiking (total PFAS concentration being 750 ng / L). Flow rate of 40 ml / min was used. The water samples were taken for PFAS analyses before water treatment and weekly from the adsorbent treated effluent.

[0064] Results

[0065] Figure 1 shows the results of adsorption tests, when using the modified powdered activated carbon (PAC) adsorbents according to Examples 1 - 4. In Figure 1 , the average PFAS adsorption capacity (AVG removal-%): PAC slurry = 45%, PAC+C10 = 82%, PAC + C12 = 88%, PAC + C14 = 86%, PAC + C16 = 70%. The results are calculated as the average removal of all detected PFAS according to Equations: where PFAS removal-% is the removal percentage of single PFAS compound, PFASatter treatment is the PFAS concentration after adsorption treatment, PFASinitiai is the initial PFAS concentration of the surface water, AVG removal-% is the average removal percentage of all PFAS compounds detected in water, n is the number of PFAS compounds found from the water.

[0066] As shown in Figure 1 , the modified PAC absorbents according to the present invention perform better for PFAS removal as compared to PAC alone.

[0067] Figure 2 shows an impact of amphiphilic substance carbon chain length on the PFAS adsorption efficiency. The modified PAC adsorbents are prepared according to Examples 1 - 4.

[0068] Figure 3 shows the results of adsorption tests, when using the modified powdered activated carbon (PAC) adsorbents according to Examples 1 , 5 and 6, i.e. an amount of dodecyltrimethylammonium chloride (C12) is varied in the carbon absorbent materials. In Figure 3, the average PFAS adsorption capacity (AVG removal-%): PAC slurry = 45%, PAC+C12 2 wt-% = 98%, PAC + C12 5 wt-% = 88%, PAC + C12 10 wt-% = 100%. The modified PAC absorbents according to the present invention perform better for PFAS removal as compared to PAC alone.

[0069] Figures 4 presents PFAS adsorption performances of adsorbent samples prepared according to Example 7. In Figure 4, the average PFAS adsorption capacity (AVG removal-%): mesoporous carbon (reference) = 35%, Mesoporous carbon + C12 = 74%. The modified mesoporous carbon absorbent according to the present invention perform significantly better compared to the untreated mesoporous carbon absorbent. Figure 5 presents PFAS adsorption performance (as PFAS average removal, %) of modified GAC adsorbent sample prepared according to Example 8 and unmodified GAC adsorbents in column adsorption test. Modified GAC adsorbent according to the present invention provides an improved PFAS removal.

Claims

Claims1 . A method for removing per- and polyfluoroalkyl substances (PFAS) from a fluid, characterized in that the method comprises treating the fluid with a carbon adsorbent, which comprises a modified carbon adsorbent, which is modified with at least one amphiphilic substance comprising quaternary amine surfactants functionality and having a carbon chain length of C10 - C14.

2. The method according to claim 1 , characterized in that the modified carbon adsorbent is modified with a mixture of two or more amphiphilic substances comprising quarternary amine functionalities and having a carbon chain length of C10 - C14.

3. The method according to claim 1 or 2, characterized in that the modified carbon adsorbent comprises 0.1 - 20 weight-%, preferably 1 - 10 weight-% and more preferably 1 - 5 weight-% of the amphiphilic substance, calculated from dry total weight of the modified carbon adsorbent.

4. The method according to any one of the preceding claims, characterized in that the amphiphilic substance comprises decyltrimethylammonium halide, octyltrimethylammonium halide, dodecyltrimethylammonium halide, tetradecyltrimethylammonium halide and any combination thereof.

5. The method according to any one of the preceding claims, characterized in that the carbon adsorbent further comprises an unmodified carbon adsorbent.

6. The method according to any one of the preceding claims, characterized in that the carbon adsorbent comprises 5 - 100 weight-% of the modified carbon adsorbent, calculated from the weight of the carbon adsorbent.

7. The method according to any one of the preceding claims, characterized in that the modified carbon adsorbent or the unmodified carbon adsorbent comprises activated carbon material, nanocarbon material and / or carbon char adsorbent.

8. The method according to any one of the preceding claims, characterized in that the modified carbon absorbent or the unmodified carbon adsorbent comprises powdered activated carbon, pelletized activated carbon and / or granular activated carbon.

9. The method according to claim 7 or 8, characterized in that the activated carbon material comprises microporous, macroporous and / or mesoporous activated carbon material.

10. The method according to claim 9, characterized in that an amount of a fraction consisting of meso- or macropores having a diameter > 2 nm, is at least 40%, preferably at least 50% from total pore volume in the activated carbon material.11 . The method according to any one of the preceding claims, characterized in that the fluid is treated by adding the carbon adsorbent to the fluid.

12. The method according to any one of the preceding claims, characterized in that the fluid is treated with the carbon adsorbent by passing the fluid through a filter, a fluidised bed reactor and / or a column comprising the carbon adsorbent.

13. The method according to any one of the preceding claims, characterized in that the fluid comprises water, water body and / or wastewater.

14. Use of a modified carbon adsorbent in removal of per- and polyfluoroalkyl substances (PFAS) compounds from a fluid, wherein the modified carbon adsorbent is modified with at least one amphiphilic substance comprising quaternary amine functionality and having a carbon chain length of C10 - C14.

15. Use according to claim 14, characterized in that the fluid comprises water, water body and / or wastewater.

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