CN105198047B - A kind of Electrochemical hydriding processing method of fluorinated aromatic hydrocarbon pollutant effluents - Google Patents

Abstract

The invention discloses an electrochemical hydrogenation treatment method for wastewater polluted by fluorinated aromatic hydrocarbons. The method comprises: adding a supporting electrolyte to the wastewater polluted by fluorinated aromatic hydrocarbons to obtain electrolytic catholyte; , The electrolysis reaction is carried out in a diaphragm electrolyzer with a chemically inert conductive material as the anode. During the electrolysis process, the pH of the electrolytic catholyte is controlled at 1-6, the temperature is 0-50°C, and the current density is 0.1-10A/dm ² ; the electrolysis reaction is over Finally, the complete hydrogenation of fluorine substituents and aromatic rings in fluorinated aromatic hydrocarbons is realized; the reaction of the present invention can be carried out at normal temperature and pressure and in a water system without organic solvents, and can achieve high current density (1-5A/dm ² ) and high efficiency High-concentration (1-50mmol/L) fluorinated aromatics wastewater can be treated efficiently, and the complete conversion of fluorinated aromatics can be realized. The complete hydrogenation rate of fluorine substituents and aromatic rings is greater than 95%, and the yield of fluorine ions is greater than 95%.

Description

A kind of electrochemical hydrogenation treatment method of fluorinated aromatic hydrocarbon polluted wastewater

(1) Technical field

The invention relates to an electrochemical hydrogenation treatment method for fluorinated aromatic hydrocarbon polluted wastewater, in particular to an electrochemical complete hydrogenation method for fluorine substituents and aromatic rings of fluorinated aromatic hydrocarbon pollutants in wastewater.

(2) Background technology

Fluorinated aromatic hydrocarbons are widely used as important intermediates and raw materials in the manufacture of modern pesticides and medicines. In 1994, the global output of fluorinated aromatic hydrocarbons was 10,000 tons; in 2000, its global output increased to 35,000 tons; in 2013, 30-40% of the world’s pesticides and 25% of pharmaceuticals were fluorine-containing organic substances, of which sales Three of the top 5 medicines are fluorinated organics. The rapid increase in the production of fluorinated aromatic hydrocarbons comes from the optimization of the molecular properties of its fluorine atoms, which generally have better stability and biopharmaceutical efficacy.

Due to the rapid increase in global production and the stability of fluorinated aromatic hydrocarbons in the natural environment, they have become potential environmental pollutants. Due to the high stability of fluorinated aromatic hydrocarbons, conventional biological treatment methods and advanced oxidation technologies are often used to treat wastewater polluted by them with low efficiency. Therefore, it is very necessary to develop efficient methods for the degradation of fluorinated aromatic hydrocarbon pollutants. At present, a variety of oxidation techniques have been proven to be effective in degrading fluorinated aromatics, including hydrogen peroxide oxidation catalyzed by bisiron phthalocyanine [J.Am.Chem.Soc.2013,261(15),463-469] , chloroperoxidase catalytic oxidation [Biotechnol.Lett.2007,29:45–49], titanium dioxide photocatalytic oxidation [Chem.Eng.J.2007,128,51–57] and electrochemical oxidation [J. Phys. Chem. C 2011, 115, 3888–3898]. Although these oxidation methods can oxidize fluorinated aromatics to carbon dioxide and fluoride ions, they have the risk of poor reaction selectivity and may produce highly toxic unknown intermediates and highly stable fluorine-containing products.

Compared with the oxidation method, although the hydrogenation reduction method cannot achieve complete mineralization, it has the advantages of complete defluorination and high reaction selectivity. The biodegradability of the fully hydrodefluorinated product will be greatly improved, and it can be recovered as a chemical raw material, and can also be completely degraded by conventional biochemical treatment methods. Highly chemoselective methods for complete hydrodefluorination of fluorinated aromatics include: using soluble ruthenium-palladium bimetallic complexes [Na.Commun.2013,4,1-7] or carbon-supported platinum [Adv.Synth.Catal.2012, 354,777-782]’s catalytic hydrogenation method can selectively hydrogenate the carbon-fluorine bonds on fluorinated aromatics to generate fluoride ions and fluorine-free aromatics; photocatalytic hydrogenation method catalyzed by phenyl cations [Green Chem.,2009,11,942– 945] Selective hydrogenation and defluorination of monofluoroaromatics containing electron-pushing groups; NaBH4 _- promoted electrochemical reduction method [Tetrahedron Lett., 2015, 56, 1520-1523] can selectively hydrogenate fluorocarbons of fluoroaromatics bond to generate fluorine-free aromatic hydrocarbons. Unfortunately, these methods require relatively harsh reaction conditions (such as the use of toxic organic solvents or the need for high temperature and pressure, etc.), so they are not suitable for the actual treatment of fluorinated aromatic hydrocarbon-contaminated wastewater.

For the various deficiencies of the above-mentioned various methods, McNeill's research group has developed the catalytic hydrogenation method [Environ.Sci.Technol.2012,46,10199-10205; Environ.Sci.Technol.2013,47, 6545-6553], this method can realize the complete hydrogenation of fluorobenzene fluorine substituent and benzene ring under normal temperature and pressure and in aqueous medium. The main disadvantage of this method is that a large amount of hydrogen needs to be introduced during the reaction process, and there is a high risk of explosion when treating low-concentration fluorinated aromatic hydrocarbon polluted wastewater.

(3) Contents of the invention

The purpose of the present invention is to provide an electrochemical hydrogenation treatment method for fluorinated aromatic hydrocarbon polluted wastewater. A small amount of electrolyte is added to waste water polluted by fluorinated aromatic hydrocarbons as catholyte, and the catholyte is electrolyzed in a diaphragm electrolyzer with rhodium-modified conductive material as cathode and chemically inert conductive material as anode. The fluorine substituents and aromatic rings of fluorinated aromatic hydrocarbon pollutants in wastewater can be completely hydrogenated to achieve biochemical improvement and toxicity reduction of wastewater; if necessary, fully hydrogenated compounds in wastewater can also be used by traditional methods (adsorption, extraction, etc.) Recycled as chemical raw materials. The present invention can not only solve the problems of poor reaction selectivity, harsh reaction conditions, and massive use of explosive hydrogen in existing waste water treatment technologies for fluoroaromatic pollutants, but also can treat them with high current density (1-5 A/dm ² ) and high efficiency High concentration (1-50 mmol/L) fluorinated aromatic hydrocarbon wastewater.

The technical scheme adopted in the present invention is:

The invention provides a method for electrochemical hydrogenation treatment of waste water polluted by fluorinated aromatic hydrocarbons. The method is as follows: in the waste water polluted by fluorinated aromatic hydrocarbons shown in formula (I), a supporting electrolyte is added to obtain electrolytic catholyte; The modified conductive material is used as the cathode, and the electrolysis reaction is carried out in a diaphragm electrolyzer with the chemically inert conductive material as the anode. During the electrolysis process, the pH of the electrolytic catholyte is controlled at 1-6, the temperature is 0-50°C, and the current density is 0.1-10A/ dm ² ; After the electrolysis reaction finishes, obtain the catholyte containing the compound shown in formula (II), realize the complete hydrogenation of fluorine substituting group and aromatic ring in the fluorinated arene shown in formula (I); Formula (II) in described catholyte The shown compounds can be recovered as chemical raw materials by traditional methods (such as adsorption, extraction, etc.), and the catholyte can also be directly degraded by conventional biochemical treatment methods;

In formula (I), R is C or N; X is H, CH ₃ , OH, OCH ₃ , OCH ₂ COOH, NH ₂ , F, CF ₃ , CN, COOH, and n is a positive integer between 1 and 5 one;

In formula (II), R and X are the same as formula (I).

The concentration of fluoroaromatics represented by formula (I) in the waste water of the present invention is 0.01-50 mmol/L, preferably 1-50 mmol/L.

Further, the fluoroaromatic pollutants represented by the formula (I) in the wastewater are one of the following or a mixture of two or more in any proportion: fluorobenzene, fluorotoluene, fluorophenol, fluoroanisole, fluoro Phenoxyacetic acid, fluoroaniline, fluorotrifluorotoluene, fluorobenzonitrile, fluorobenzoic acid, and fluoropyridine.

The conductive material in the rhodium-modified conductive material of the cathode in the present invention is one of the following materials or one of the following materials modified by conductive polymer: nickel, copper, silver, titanium, graphite, carbon fiber felt or carbon-containing conductive plastic. The conductive polymer is polypyrrole, and the polypyrrole is prepared by anodic oxidation of 0.01-0.1 mol/L pyrrole monomer in 0.5 mol/L sulfuric acid aqueous solution. The mass loading of the rhodium metal is 0.1-10 g/m ² conductive material, preferably 0.5-5 g/m ² , most preferably 2 g/m ² . The shape of the cathode is plate, rod, wire, mesh, mesh, foam, wool or sheet, preferably expanded mesh. The cathode of the present invention is preferably rhodium-modified nickel foam (2g Rh/m ² ), rhodium-modified copper foam (2g Rh/m ² ), rhodium-modified extended silver screen (2g Rh/m ² ), rhodium-modified titanium mesh ( 2g Rh/m ² ), rhodium-modified graphite plate containing polypyrrole (2g Rh/m ² ), rhodium-modified carbon-containing conductive plastic plate (2g Rh/m ² ), rhodium-modified graphite plate (2g Rh/m ² ), More preferably the cathode is a rhodium-modified carbon fiber felt (2 g Rh/m ² ).

The technique of modifying rhodium on the conductive material of the present invention is well known, such as active metals such as nickel, copper, silver can modify rhodium with chemical replacement method or electrodeposition method; Titanium, graphite, carbon fiber material, conductive plastic or modified conductive polymer The above conductive material can be modified with rhodium by electrodeposition.

Further, the concentration of the supporting electrolyte in the electrolysis catholyte is 1-100 mmol/L, preferably 5 mmol/L.

The anode in the present invention is not a key factor, and can be any chemically inert conductive material or alloy, such as platinum, graphite, conductive plastic, and the like. The anode can also consist of a conductive coating applied to another material, for example: a noble metal oxide such as ruthenium oxide applied to titanium metal. The shape of the anode may be in the form of a plate, a rod, a wire, a mesh, a mesh, a foam, a fleece or a sheet, preferably an expanded mesh. Most preferably the anode is titanium platinized mesh.

The electrolysis reaction described in the present invention can be carried out batchwise or in a continuous or semi-continuous manner. The electrolyzer can be a stirred tank containing electrodes or a flow electrolyzer of any conventional design. The electrolyzer is a diaphragm electrolyzer. Available diaphragm materials include various anion or cation exchange membranes, porous Teflon, asbestos or glass, preferably perfluorosulfonic acid cationic membrane as the diaphragm of the electrolyzer.

While the evolution of oxygen is preferred as the anodic reaction, many other anodic reactions can be used, including the evolution of molecular chlorine and bromine or the production of carbon dioxide through the oxidation of protective species such as formate or oxalate or through organic Oxidation of reactants to form valuable by-products. For example, 1mol/L sulfuric acid or hydrochloric acid aqueous solution can be used as the anolyte of the present invention; 1mol/L sodium hydroxide aqueous solution can also be used as the anolyte of the present invention.

During the electrolysis reaction process of the present invention, the current density changes according to the concentration of fluorinated aromatic hydrocarbons in the catholyte. Usually, the suitable electrolysis cathode current density is 0.1-10A/dm ² , preferably 1-5A/dm ² . The pH of the electrolytic reaction solution of the present invention is controlled at 1-6, preferably 2.5-3.5 during the reaction process; temperature is not a key factor, but considering the convenience of control, the suitable temperature is 0-50°C, preferably 20-30°C.

The present invention performs the desired electrolytic reduction by techniques generally known in the art. Generally, in wastewater polluted by fluorinated aromatic hydrocarbons, a certain amount of supporting electrolyte and pH regulator are added as catholyte, which is passed through a diaphragm electrolyzer with a rhodium-modified conductive material as the cathode and a chemically inert conductive material as the anode. Sufficient current is applied until the desired degree of reduction is obtained. After the electrolysis reaction is over, traditional techniques (such as adsorption, extraction, etc.) can be used to recover the electrolysis products in the catholyte, or traditional biochemical treatment methods can be used to directly treat the electrolytically treated wastewater.

The reactions involved in the electrochemical hydrogenation treatment method of fluorinated aromatics polluted wastewater of the present invention (taking fluorophenol as example):

(1) Cathode reaction:

(2) Anode reaction:

(n+3)H ₂ O-(2n+6)e ^- →(n+3)/2O ₂ ⁺ (2n+6)H ⁺

(3) Total reaction:

The beneficial effects of the present invention are mainly reflected in: (1) the reaction can be carried out at normal temperature and pressure and in an organic solvent-free water system; (2) no highly explosive hydrogen is used in the reaction process; (3) fluorinated aromatic hydrocarbons in waste water are polluted The fluorine substituent and aromatic ring of the compound can be selectively hydrogenated, which can greatly improve the biodegradability of wastewater and reduce the toxicity of wastewater; (4) can be treated with high current density (1～5A/dm ² ) and high efficiency High-concentration (1-50mmol/L) fluorinated aromatics wastewater can realize the complete conversion of fluorinated aromatics, the complete hydrogenation rate of fluorine substituents and aromatic rings is greater than 95%, and the yield of fluorine ions is greater than 95%.

(4) Specific implementation methods

The present invention is further described below in conjunction with specific embodiment, but protection scope of the present invention is not limited thereto:

The preparation method of the cathode material described in the embodiment of the present invention refers to [Colloid.Surf.B: Biointerfaces2014, 261, 121, 444-450; Analytica Chimica Acta 2009, 632, 63-68].

Embodiment 1 Electrochemical hydrogenation treatment of p-fluorophenol polluted wastewater

1000mL aqueous solution of 5mmol/L p-fluorophenol+5mmol/L sodium sulfate+5mmol/L sodium chloride was used as catholyte; 1mol/L sulfuric acid aqueous solution was used as anolyte. Rhodium-modified carbon fiber felt (2g Rh/m ² ) is used as the cathode, the platinum-plated titanium mesh is used as the anode, the diaphragm plate frame tank is used as the electrolytic reactor, and the perfluorosulfonic acid membrane is used as the diaphragm.

During the electrolysis process, the temperature is controlled at 20-25°C, the current density is controlled at 3A/dm ² , and the pH of the catholyte is controlled at 2.5-3.5. Stop the electrolysis after feeding 8F/mol 4-fluorophenol electricity. After the electrolysis, the catholyte (30mL) was transferred to the split funnel, and the catholyte was extracted three times with 30mL dichloromethane; after the extraction, the three extracts were combined, and then passed through a solid containing 5g of anhydrous sodium sulfate. Use a funnel to remove residual water; finally, use a volumetric flask to adjust the volume to 500 mL for gas chromatography analysis. Another 5 mL of catholyte was diluted 20 times with deionized water, and then analyzed by ion chromatography. The analysis results of gas chromatography and ion chromatography showed that the yield of cyclohexanone was 46%, the yield of cyclohexanol was 53%, and the yield of fluoride ion was 100%.

The gas chromatography analysis conditions are: HP-INNOWAX (30m x 320μm x 0.5μm) is the separation column; the detector is FID; the hydrogen flow rate is 30mL/min; the oven temperature is 75-230°C; the heating rate is 15°C/min.

Ion chromatography conditions: IonPac AS 19 anion exchange column (4×250mm) is the separation column; elution gradient program: 0→5min (10mM KOH), 5→20Min (10→40mM KOH); flow rate: 1mL/Min; The instrument model is: DionexICS-2000).

Embodiment 2-Example 29 Electrochemical Hydrogenation Treatment of Wastewater Contaminated by Different Fluorinated Aromatic Hydrocarbons

Embodiment 2 to Embodiment 29 were carried out according to the experimental parameters in Table 1, and the rest of the operations were the same as in Embodiment 1.

Table 1 Embodiment 2～Example 29 Experimental conditions and results

Examples 30 to 37 use different rhodium-modified cathodes for electrochemical hydrogenation treatment of p-fluorophenol polluted wastewater

Embodiment 30 to Embodiment 37 were carried out according to the experimental parameters in Table 2, and the rest of the operations were the same as in Embodiment 1.

Table 2 embodiment 30～embodiment 37 experimental conditions and result ^a

^a 1mol/L sodium hydroxide aqueous solution is the anolyte; the ruthenium-plated titanium mesh is the anode.

Comparative example 1～comparative example 8 uses the p-fluorophenol polluted waste water electrochemical hydrogenation treatment of the matrix cathode that does not modify rhodium

Comparative Example 1 to Comparative Example 8 were carried out according to the experimental parameters in Table 3, and the rest of the operations were the same as in Example 1.

Table 3 Comparative Example 1～Comparative Example 8 Experimental conditions and results ^a

^a 1mol/L sodium hydroxide aqueous solution is the anolyte; the ruthenium-plated titanium mesh is the anode.

Claims (9)

1. a kind of Electrochemical hydriding processing method of fluorinated aromatic hydrocarbon pollutant effluents, it is characterised in that described method is：At formula (I) In the waste water of shown fluorinated aromatic hydrocarbon pollution, add supporting electrolyte and obtain electrolysis cathode liquid；In the conductive material modified with rhodium For negative electrode, using chemical inertness conductive material as the diaphragm cell of anode in carry out cell reaction, electrolysis cathode in electrolytic process Liquid pH controls are 1~6, and temperature is 0~50 DEG C, and current density is 0.1~10A/dm²；After cell reaction terminates, acquisition contains formula (II) catholyte of compound shown in, the complete hydrogenation of fluoro substituents and aromatic ring in fluorinated aromatic hydrocarbon shown in formula (I) is realized；The branch Electrolyte is held as one of following or two kinds of arbitrary proportions mixing：Sodium sulphate, sodium chloride；The mass loading amount of rhodium in the negative electrode For 0.1~10g/m²Conductive material；

In formula (I), R is C or N；X is H, CH₃、OH、OCH₃、OCH₂COOH、NH₂、F、CF₃, CN, COOH, n be 1~5 between just One of integer；

The same formulas of R and X (I) in formula (II).

2. the Electrochemical hydriding processing method of fluorinated aromatic hydrocarbon pollutant effluents as claimed in claim 1, it is characterised in that the waste water The concentration of fluorinated aromatic hydrocarbon shown in middle formula (I) is 1~50mmol/L.

3. the Electrochemical hydriding processing method of fluorinated aromatic hydrocarbon pollutant effluents as claimed in claim 1, it is characterised in that the waste water Fluorinated aromatic hydrocarbon shown in middle formula (I) is one of following or two kinds and any of the above ratio mixing：Fluorobenzene, fluorotoluene, fluoro Phenol, fluoro methyl phenyl ethers anisole, fluoro phenoxy acetic acid, Fluoroaniline, fluorobenzotrifluoride, fluoro benzonitrile, fluorinated acid and fluoro Pyridine.

4. the Electrochemical hydriding processing method of fluorinated aromatic hydrocarbon pollutant effluents as claimed in claim 1, it is characterised in that the negative electrode Using conductive material in the conductive material of rhodium modification as one of one of following or conducting polymer modified llowing group of materials：Nickel, copper, Silver, titanium, graphite, carbon fiber felt or carbon containing conductive plastics.

5. the Electrochemical hydriding processing method of fluorinated aromatic hydrocarbon pollutant effluents as claimed in claim 1, it is characterised in that the negative electrode To be one of following：The nickel foam of rhodium modification, the foam copper of rhodium modification, the silver-colored screen cloth of extension of rhodium modification, the titanium net of rhodium modification, rhodium are repaiied The graphite cake containing polypyrrole that the graphite cake of decorations, the carbon fiber felt of rhodium modification, the carbon containing conductive plastic plate or rhodium of rhodium modification are modified.

6. the Electrochemical hydriding processing method of fluorinated aromatic hydrocarbon pollutant effluents as claimed in claim 1, it is characterised in that the support Concentration of the electrolyte in electrolysis cathode liquid is 1~100mmol/L.

7. the Electrochemical hydriding processing method of fluorinated aromatic hydrocarbon pollutant effluents as claimed in claim 1, it is characterised in that the electrolysis During electrolysis cathode liquid pH control be 2.5~3.5, temperature be 20~30 DEG C, current density is 1~5A/dm²。

8. the Electrochemical hydriding processing method of fluorinated aromatic hydrocarbon pollutant effluents as claimed in claim 1, it is characterised in that the anode Platinum guaze is plated for titanium.

9. the Electrochemical hydriding processing method of fluorinated aromatic hydrocarbon pollutant effluents as claimed in claim 1, it is characterised in that the barrier film Electrolytic cell septation is perfluorinated sulfonic acid cationic membrane.