A method for removing ultra-short chain perfluorinated compounds from water

Abstract

The present invention discloses a method for removing ultra-short chain perfluoro compounds in water, the method comprising the following steps: determining the concentrations of long-chain, short-chain and ultra-short chain perfluoro compounds in a target water body, selecting Beta zeolites with different silicon-aluminum ratios according to the concentration ratios of perfluoro compounds with different chain lengths, and using the selected Beta zeolites to cyclically adsorb ultra-short chain perfluoro compounds. The present invention is based on the Beta zeolite hydroxyl cycle mechanism, and realizes the adsorption-regeneration cycle process of ultra-short chain perfluoro compounds in a reagent-free and low-cost manner, while not affecting the treatment capacity of perfluoro compounds with other chain lengths, and significantly improving the removal efficiency of ultra-short chain perfluoro compounds. The method of the present invention can efficiently remove ultra-short chain perfluoro compounds in drinking water and slightly polluted water bodies, which is of great significance to ensuring water quality safety.

Description

Technical Field

[0001] The invention relates to a method for removing perfluorinated compounds in water, in particular to a method for removing ultra-short-chain perfluorinated compounds in water. Background Art

[0002] Perfluorinated compounds are a class of fluorinated organic compounds in which some or all of the hydrogen atoms attached to the alkyl carbon chain are replaced by fluorine. Due to their remarkable thermal and chemical stability, they are widely used in industrial and commercial fields. In recent years, the high persistence, mobility and bioaccumulation characteristics of perfluorinated compounds have led to strong concerns that their use has exceeded the limits that the environment can bear. The 2009 and 2017 Stockholm Conventions banned the production and use of long-chain perfluorinated compounds (chain length > 7, i.e., perfluorooctanoic acid and perfluorooctane sulfonic acid). However, in order to make up for the shortage of long-chain perfluorinated compounds, ultra-short chain (chain length: 1-3) and short chain (chain length: 4-7) homologues have been produced and used in large quantities as substitutes, resulting in their continuous accumulation in the environment and gradually becoming the main type of pollution. In particular, the most hydrophilic ultra-short chain perfluorinated compounds have gradually shown their high mobility and high accumulation in different actual water bodies. Related studies have shown that ultra-short-chain perfluorinated compounds are widely detected in drinking water and slightly polluted water bodies (such as river water and groundwater), accounting for more than 80% of the total perfluorinated compound concentration. Therefore, developing effective means to remove ultra-short-chain perfluorinated compounds in water bodies is of great significance to solving the global perfluorinated compound pollution crisis and ensuring drinking water safety.

[0003] Activated carbon adsorption process is recommended for the treatment of perfluorinated compounds in water bodies. However, this process is generally considered to be effective only for long-chain perfluorinated compounds. Due to the significant shortening of the carbon fluorine chain, ultra-short-chain perfluorinated compounds have the characteristics of small molecular weight and high hydrophilicity, and can easily escape the treatment of conventional adsorption processes. In recent years, a variety of new adsorbent materials have been proposed for the removal of perfluorinated compounds with shorter chain lengths. For example, Chinese patent CN106220786A discloses a bifunctional monomer molecular imprinting polymer for selective adsorption and removal of PFOA and PFOS, but the perfluorinated compounds specifically removed by the polymer are long-chain perfluorinated compounds (carbon chain length: 8), and its effectiveness for ultra-short-chain perfluorinated compounds (carbon chain length: 1-3) needs to be further verified. Similarly, Chinese patent CN116143221A discloses the removal of short-chain perfluorinated compounds (chain length: 4-6) by restricted water-modified activated carbon, and does not disclose how to effectively remove ultra-short-chain perfluorinated compounds. In addition, the current adsorbent materials lack effective regeneration methods, which can easily cause secondary pollution of perfluorinated compounds. Therefore, in response to the persistent pollution crisis of ultra-short-chain perfluorinated compounds in water bodies, it is urgent to develop a new adsorption-regeneration process that can effectively capture hydrophilic small molecules and is easy to regenerate. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method for removing ultra-short-chain perfluorinated compounds from water, so as to solve the problem that the existing adsorption technology is difficult to adsorb and remove ultra-short-chain perfluorinated compounds and lacks regeneration means.

[0005] Technical solution: A method for removing ultra-short-chain perfluorinated compounds in water according to the present invention comprises the following steps:

[0006] (1) Determine the concentrations of long-chain perfluorinated compounds, short-chain perfluorinated compounds, and ultra-short-chain perfluorinated compounds in the target water body;

[0007] (2) selecting Beta zeolites with different silicon-aluminum ratios according to the ratio of long-chain perfluorinated compound concentration / (short-chain perfluorinated compound concentration+ultra-short-chain perfluorinated compound concentration) and the ratio of short-chain perfluorinated compound concentration / ultra-short-chain perfluorinated compound concentration;

[0008] (3) Use the selected Beta zeolite for cyclic adsorption to remove ultra-short-chain perfluorinated compounds from the target water body.

[0009] The present invention is based on the Beta zeolite hydroxyl cycle mechanism to achieve simultaneous adsorption-regeneration cycle of ultra-short chain perfluorinated compounds in water, thereby achieving efficient treatment capabilities while breaking the "permanent cycle" of perfluorinated compounds in the environment.

[0010] Preferably, the carbon chain length of the long-chain perfluorinated compound is C 8 -C 12 The carbon chain length of the short-chain perfluorinated compound is C 4 -C 7 The carbon chain length of the ultra-short chain perfluorinated compound is C 1 -C 3 .

[0011] Preferably, in step (2), the method for selecting Beta zeolites with different silicon-aluminum ratios is:

[0012] When the concentration of long-chain perfluorinated compounds in the target water body / (concentration of short-chain perfluorinated compounds + concentration of ultra-short-chain perfluorinated compounds) is ≥1.5, Beta zeolite with a silicon-aluminum ratio of >600 is selected;

[0013] When the concentration of long-chain perfluorinated compounds / (concentration of short-chain perfluorinated compounds + concentration of ultra-short-chain perfluorinated compounds) of the target water body is less than 1.5 and the concentration of short-chain perfluorinated compounds / concentration of ultra-short-chain perfluorinated compounds is greater than or equal to 0.9, select Beta zeolite with a silicon-aluminum ratio of 200-600;

[0014] When the long-chain perfluorochemical concentration / (short-chain perfluorochemical concentration+ultra-short-chain perfluorochemical concentration) of the target water body is less than 1.5 and the short-chain perfluorochemical concentration / ultra-short-chain perfluorochemical concentration is less than 0.9, Beta zeolite with a silicon-aluminum ratio of 150-200 is selected.

[0015] After a lot of theoretical exploration and experimental research, the present invention has determined the competitive factors of long-chain, short-chain and ultra-short-chain perfluorinated compounds in the Beta zeolite adsorption process. In the initial application stage, by establishing the Beta zeolite silicon-aluminum ratio selection scheme, the specific adsorption capacity of Beta zeolite for ultra-short-chain perfluorinated compounds is significantly improved without affecting the removal efficiency of other chain length perfluorinated compounds, reducing the negative impact of the competitive adsorption effect.

[0016] Preferably, in step (3), the method for cyclically adsorbing ultra-short-chain perfluorinated compounds on Beta zeolite comprises the following steps:

[0017] (1) calcining Beta zeolite, and then filling Beta zeolite with water vapor to adsorb ultra-short chain perfluorinated compounds in target water bodies;

[0018] (2) The Beta zeolite adsorbing the ultra-short-chain perfluorinated compound is re-calcined, and step (1) is repeated for cyclic adsorption treatment.

[0019] In the adsorption stage, the pore size adaptation effect of Beta zeolite is used to make the inner surface of the crystal and the restricted water molecules generate strong van der Waals forces and hydrogen bonds to the CF chains and hydrophilic functional groups of ultra-short-chain perfluorinated compounds, respectively, thereby achieving specific strong adsorption behavior. In the regeneration stage, high-temperature calcination is used to remove the zeolite hydroxyl groups while promoting the desorption and degradation of ultra-short-chain perfluorinated compounds, thus forming a synchronous adsorption-regeneration cycle of ultra-short-chain perfluorinated compounds.

[0020] Preferably, the Beta zeolite is calcined at 700-900° C. in an air atmosphere for 4-8 hours.

[0021] Preferably, the method of filling Beta zeolite with water vapor is: placing the calcined Beta zeolite in a closed room temperature environment with a humidity of 60-70% for water vapor diffusion for 2-6 hours, then increasing the humidity to 90-100% for water vapor diffusion for 36-48 hours, and finally placing the zeolite in water with a volume ratio of 1:0.5-1 and letting it stand for 12-18 hours.

[0022] Preferably, the method of using Beta zeolite to adsorb ultra-short-chain perfluorinated compounds in the target water body is: filling the Beta zeolite filled with water vapor into an adsorption column, and discharging the target water body after pretreatment through the adsorption layer of the adsorption column, and controlling the empty bed residence time to be 10-30 minutes; when the total perfluorinated compound concentration in the effluent water reaches 80% of the influent water, re-calcining the Beta zeolite.

[0023] Preferably, the concentration of dissolved organic matter in the target water body after pretreatment is ≤10 mg / L, the turbidity is ≤10 NTU, and the concentration of total perfluorinated compounds is <10 μg / L.

[0024] Preferably, the total perfluorochemical concentration is the sum of the long-chain perfluorochemical concentration, the short-chain perfluorochemical concentration and the ultra-short-chain perfluorochemical concentration.

[0025] Preferably, the target water body includes at least one of slightly polluted water and drinking water.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0027] (1) The present invention can achieve the cyclic and efficient removal of ultra-short-chain perfluorinated compounds in water by Beta zeolite, breaking its "permanent cycle" while ensuring the safety of drinking water.

[0028] (2) The present invention significantly improves the specific adsorption capacity of Beta zeolite for ultra-short chain perfluorinated compounds without affecting the removal efficiency of perfluorinated compounds with other chain lengths, thereby reducing the negative impact of the competitive adsorption effect.

[0029] (3) The scheme of the present invention is a reagent-free, low-cost technical method. During the application process, only water and heat are used as material modification media, and there is no risk of secondary pollution. Compared with other existing processes, the scheme of the present invention has obvious cost-effectiveness advantages and is more valuable for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0032] Example 1: The target water body in this example is the tap water of a certain household, and its basic water quality characteristics are as follows: average pH value is 7.1, average dissolved organic matter concentration is 0.9 mg / L, average permanganate index is 2.1 mg / L, average nitrite concentration is 0.2 mg / L, and average turbidity is 0.5 NTU. Perfluorinated compounds with different chain lengths are added to the reactor inlet water to simulate contaminated drinking water, and the concentrations after addition are: C 1 -C 3 The average total concentration of perfluorinated compounds was 1032 ng / L. 4 -C 7 The average total concentration of perfluorinated compounds was 752 ng / L. 8 -C 12 The average total concentration of perfluorinated compounds was 420 ng / L.

[0033] According to the method of the present invention, the water from the household tap is treated, and the specific steps are as follows: Figure 1 As shown:

[0034] (1) Determine the long chain (C 8 -C 12 ) perfluorinated compound concentration, short chain (C 4 -C 7 ) Perfluorinated compound concentration and ultrashort chain (C 1 -C 3 ) perfluorinated compound concentrations, which were 1032 ng / L, 752 ng / L, and 420 ng / L, respectively, denoted as C 长链 , C 短链 and C 超短链 ;

[0035] (2) According to C 长链 / (C 短链 +C 超短链 )=0.24<1.5 and C 短链 / C 超短链 =0.73<0.9, Beta zeolite with a silicon-aluminum ratio of 150 is selected;

[0036] (3) Using Beta zeolite with a silicon-aluminum ratio of 150 to circulate and remove ultra-short-chain perfluorinated compounds in the water from the household tap, the specific steps are as follows:

[0037] (a) Beta zeolite was calcined at 900 °C in air atmosphere for 8 h to remove surface hydroxyl groups;

[0038] (b) placing the calcined Beta zeolite in a closed room temperature environment with a humidity of 60% to 70% for water vapor diffusion for 6 hours, then increasing the humidity to 90% to 100% for water vapor diffusion for 48 hours, and finally placing the zeolite in water with a volume ratio of 1:1 for 18 hours;

[0039] (c) The water vapor-filled Beta zeolite is loaded into the adsorption column to adsorb the ultra-short-chain perfluorinated compounds in the tap water. Since the concentration of dissolved organic matter in the tap water is 0.9mg / L<10mg / L, the turbidity is 0.5<10, and the total perfluorinated compound concentration is 2.2μg / L<10μg / L, no pretreatment is required. The tap water is discharged after passing through the adsorption layer, and the empty bed residence time is controlled to be 30min; when the perfluorinated compound concentration in the tap water reaches 80% of the inlet water, the Beta zeolite is re-calcined in an air atmosphere at 900℃ for 8h to achieve regeneration and hydroxyl cycle.

[0040] Table 1 Treatment effect of adsorption column in Example 1

[0041]

[0042] The water volume treated by the method of the present invention, and the average concentrations of ultra-short chain, short chain, long chain and total perfluorinated compounds in the effluent are shown in Table 1. The activated carbon control group replaces the Beta zeolite in the adsorption column with activated carbon, and the operation mode is the same as the Beta zeolite adsorption column. The method of the present invention can treat 52000BV of water, and the average concentration of ultra-short chain perfluorinated compounds in the effluent is 325ng / L, the average concentration of short chain perfluorinated compounds is 137ng / L, the average concentration of long chain perfluorinated compounds is 22ng / L, and the average concentration of total perfluorinated compounds is 484ng / L, which meets the EU's health limit for the concentration of perfluorinated compounds in drinking water (total perfluorinated compound concentration <500ng / L). Compared with the traditional activated carbon adsorption process (treatment water volume 6800BV, total perfluorinated compound concentration 669ng / L), the method of the present invention significantly improves the removal efficiency of ultra-short chain perfluorinated compounds without affecting the treatment capacity of perfluorinated compounds of other chain lengths, and has obvious advantages.

[0043] Embodiment 2: It is basically the same as Embodiment 1, except that:

[0044] In this example, the Beta zeolite regenerated in Example 1 was used to repeat steps (b) and (c) to cyclically adsorb and remove the ultra-short-chain perfluorinated compounds in the tap water of the household, and the cyclic use was performed twice in total.

[0045] Table 2 Treatment effect of adsorption column in Example 2

[0046]

[0047] After two cycles, the amount of water treated by the present invention and the average concentration of perfluorinated compounds in the effluent are shown in Table 2. In the two cycles, the amount of water treated decreased by about 5%, the concentration of perfluorinated compounds in the effluent did not change, and the total perfluorinated compound concentration still met the EU health standard for the concentration of perfluorinated compounds in drinking water. This shows that the method of the present invention has good recycling performance, and breaks the "permanent cycle" of perfluorinated compounds in the environment while reducing the process operation cost.

[0048] Example 3: The target water body of this example is a surface river water, and its basic water quality characteristics are: average pH value of 7.8, average dissolved organic matter concentration of 9.7 mg / L, average turbidity of 12 NTU, average COD of 23.1 mg / L, and average nitrite concentration of 0.7 mg / L. Perfluorinated compounds of different chain lengths were added to the reactor inlet water to simulate contaminated drinking water, and the concentrations after addition were: C 1 -C 3 The average total concentration of perfluorinated compounds was 694 ng / L. 4 -C 7 The average total concentration of perfluorinated compounds was 831 ng / L. 8 -C 12The average total concentration of perfluorinated compounds was 221 ng / L.

[0049] According to the method of the present invention, the above-mentioned surface river water is treated, and the specific steps are as follows:

[0050] 1) Determine the long chain (C 8 -C 12 ) perfluorinated compound concentration, short chain (C 4 -C 7 ) Perfluorinated compound concentration and ultrashort chain (C 1 -C 3 ) perfluorinated compound concentrations were 694 ng / L, 831 ng / L, and 221 ng / L, respectively, denoted as C 长链 , C 短链 and C 超短链 ;

[0051] 2) According to C 长链 / (C 短链 +C 超短链 )=0.14<1.5 and C 短链 / C 超短链 =1.20>0.9, Beta zeolite with a silicon-aluminum ratio of 400 is selected;

[0052] 3) Using Beta zeolite with a silicon-aluminum ratio of 400 to circulate and remove ultra-short-chain perfluorinated compounds in the tap water of the household, the specific steps are as follows:

[0053] a) calcining Beta zeolite in air atmosphere at 700°C for 4 h to remove surface hydroxyl groups;

[0054] b) placing the calcined Beta zeolite in a closed room temperature environment with a humidity of 60% to 70% for water vapor diffusion for 2 hours, then increasing the humidity to 90% to 100% for water vapor diffusion for 36 hours, and finally placing the zeolite in water with a volume ratio of 1:0.5 and allowing it to stand for 12 hours;

[0055] c) The Beta zeolite filled with water vapor is filled into the adsorption column to adsorb the ultra-short chain perfluorinated compounds in the surface river water. Since the concentration of dissolved organic matter in the surface river water is 9.7mg / L<10mg / L, the turbidity is 12NTU>10NTU, and the total perfluorinated compound concentration is 1.7μg / L<10μg / L, it is pre-treated by sand filtration. The surface river water is discharged after passing through the adsorption layer, and the empty bed residence time is controlled to be 10min; when the perfluorinated compound concentration of the effluent reaches 80% of the influent, the Beta zeolite is re-calcined in an air atmosphere at 700℃ for 4h to achieve regeneration and hydroxyl cycle.

[0056] Table 3 Treatment effect of adsorption column in Example 3

[0057]

[0058] The water volume treated by the method of the present invention, and the average concentrations of ultra-short chain, short chain, long chain and total perfluorinated compounds in the effluent are shown in Table 3. The activated carbon control group replaces the Beta zeolite in the adsorption column with activated carbon, and the operation mode is the same as the Beta zeolite adsorption column. The method of the present invention can treat 33,000 BV of water, and the average concentration of ultra-short chain perfluorinated compounds in the effluent is 386 ng / L, the average concentration of short chain perfluorinated compounds is 317 ng / L, the average concentration of long chain perfluorinated compounds is 36 ng / L, and the average concentration of total perfluorinated compounds is 739 ng / L. Compared with the traditional activated carbon adsorption process (water treatment volume 5000 BV, total perfluorinated compound concentration 878 ng / L), the method of the present invention significantly improves the removal efficiency of ultra-short chain perfluorinated compounds without affecting the treatment capacity of perfluorinated compounds of other chain lengths, and has obvious advantages.

Claims

1. A method for removing ultra-short-chain perfluorinated compounds in water, characterized in that: The steps include: (1) Determine the concentrations of long-chain perfluorinated compounds, short-chain perfluorinated compounds and ultra-short-chain perfluorinated compounds in the target water bodies respectively; (2) Selecting Beta zeolites with different silicon-aluminum ratios according to the ratio of long-chain perfluorinated compound concentration / (short-chain perfluorinated compound concentration + ultra-short-chain perfluorinated compound concentration) and the ratio of short-chain perfluorinated compound concentration / ultra-short-chain perfluorinated compound concentration; (3) Using selected Beta zeolite for cyclic adsorption to remove ultra-short-chain perfluorinated compounds from target water bodies; The carbon chain length of the long-chain perfluorinated compound is C8-C 12 , the carbon chain length of the short-chain perfluorinated compound is C4-C7, and the carbon chain length of the ultra-short-chain perfluorinated compound is C1-C3; In step (2), the method for selecting Beta zeolites with different silicon-aluminum ratios is: When the concentration of long-chain perfluorinated compounds / (concentration of short-chain perfluorinated compounds + concentration of ultra-short-chain perfluorinated compounds) in the target water body is ≥1.5, Beta zeolite with a silicon-aluminum ratio of >600 is selected; When the concentration of long-chain perfluorinated compounds / (concentration of short-chain perfluorinated compounds + concentration of ultra-short-chain perfluorinated compounds) of the target water body is <1.5 and the concentration of short-chain perfluorinated compounds / concentration of ultra-short-chain perfluorinated compounds is ≥0.9, select Beta zeolite with a silicon-aluminum ratio of 200-600; When the long-chain perfluorinated compound concentration / (short-chain perfluorinated compound concentration + ultra-short-chain perfluorinated compound concentration) of the target water body is <1.5 and the short-chain perfluorinated compound concentration / ultra-short-chain perfluorinated compound concentration is <0.9, Beta zeolite with a silicon-aluminum ratio of 150-200 is selected.

2. The method for removing ultra-short chain perfluorinated compounds in water according to claim 1, characterized in that: In step (3), the method for cyclically adsorbing ultra-short-chain perfluorinated compounds on Beta zeolite comprises the following steps: (1) calcining Beta zeolite, and then filling Beta zeolite with water vapor to adsorb ultra-short chain perfluorinated compounds in the target water body; (2) The Beta zeolite adsorbing the ultra-short-chain perfluorinated compound is re-calcined and step (1) is repeated for cyclic adsorption treatment.

3. The method for removing ultra-short chain perfluorinated compounds in water according to claim 2, characterized in that: In step (1), the Beta zeolite is calcined at 700-900° C. in an air atmosphere for 4-8 h.

4. The method for removing ultra-short chain perfluorinated compounds in water according to claim 2, characterized in that: In step (1), the method of filling Beta zeolite with water vapor is as follows: placing the calcined Beta zeolite in a closed room temperature environment with a humidity of 60-70% for water vapor diffusion for 2-6 hours, then increasing the humidity to 90-100% for water vapor diffusion for 36-48 hours, and finally placing the zeolite in water with a volume ratio of 1:0.5-1 and allowing it to stand for 12-18 hours.

5. The method for removing ultra-short-chain perfluorinated compounds in water according to claim 2, characterized in that: In step (1), the method for adsorbing ultra-short-chain perfluorinated compounds in the target water body by Beta zeolite is as follows: the Beta zeolite filled with water vapor is filled into an adsorption column, the target water body is pretreated and then flows through the adsorption layer of the adsorption column and then discharged, and the empty bed residence time is controlled to be 10-30 minutes; when the total perfluorinated compound concentration in the effluent water reaches 80% of the influent water, the Beta zeolite is re-calcined.

6. The method for removing ultra-short-chain perfluorinated compounds in water according to claim 5, characterized in that: The dissolved organic matter concentration in the target water body after the pretreatment is ≤10 mg / L, the turbidity is ≤10 NTU, and the total perfluorinated compound concentration is <10 μg / L.

7. The method for removing ultra-short chain perfluorinated compounds in water according to claim 5, characterized in that: The total perfluorinated compound concentration is the sum of the long-chain perfluorinated compound concentration, the short-chain perfluorinated compound concentration and the ultra-short-chain perfluorinated compound concentration.

8. The method for removing ultra-short-chain perfluorinated compounds in water according to claim 1, characterized in that: The target water body includes at least one of slightly polluted water and drinking water.

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