阅读说明：本技术 一种钯催化的电化学脱氯处理二氯甲烷的方法 (Method for treating dichloromethane through electrochemical dechlorination under catalysis of palladium ) 是由 刘奇 倪建国 章晶晓 徐颖华 于 2020-04-03 设计创作，主要内容包括：本发明公开一种钯催化的电化学脱氯处理二氯甲烷的方法。本发明以酸性溶液为反应介质,二氯甲烷加入到酸性溶液构成电解反应液,作为阴极液；以碱性水溶液为阳极液；以活性炭负载立方体钯纳米颗粒作为阴极催化剂,加入到阴极液中；以泡沫玻碳为阴极集流体,在阳极液中化学惰性导电材料或涂覆贵金属氧化物的钛金属为阳极置于电解槽中进行电化学反应。其中所述的阴极液在反应过程中,pH保持在1～5。本发明实现利用电化学法将二氯甲烷高选择性(≥90％)的转化成甲烷,有利于回收。本发明采用活性炭负载立方体钯纳米颗粒作为催化剂,在本发明特定体系中能够显著提高电解反应液的催化活性。(The invention discloses a method for treating dichloromethane by electrochemical dechlorination under the catalysis of palladium. The method takes an acidic solution as a reaction medium, and dichloromethane is added into the acidic solution to form an electrolytic reaction liquid as a catholyte; taking an alkaline aqueous solution as an anolyte; adding activated carbon-supported cubic palladium nanoparticles serving as a cathode catalyst into catholyte; the foamed glassy carbon is taken as a cathode current collector, and a chemically inert conductive material or a titanium metal coated with noble metal oxide in an anolyte is taken as an anode and is placed in an electrolytic bath for electrochemical reaction. Wherein the pH of the catholyte is kept between 1 and 5 in the reaction process. The invention realizes the conversion of dichloromethane into methane with high selectivity (more than or equal to 90 percent) by an electrochemical method, and is favorable for recovery. According to the invention, the activated carbon loaded cubic palladium nanoparticles are used as the catalyst, and the catalytic activity of the electrolytic reaction solution can be obviously improved in a specific system of the invention.)

1. A method for electrochemical dechlorination treatment of dichloromethane by palladium catalysis is characterized in that an acid solution is taken as a reaction medium, dichloromethane is added into the acid solution to form an electrolytic reaction solution which is taken as a catholyte; taking an alkaline aqueous solution as an anolyte; adding palladium-carbon particles serving as a cathode catalyst into the catholyte; taking foamed glassy carbon as a cathode current collector, taking a chemically inert conductive material or a titanium metal coated with a noble metal oxide in an anolyte as an anode, and placing the anode in an electrolytic bath for electrochemical reaction; wherein the pH of the catholyte is kept between 1 and 5 in the reaction process; the palladium carbon particles are activated carbon loaded cubic palladium nanoparticles; the current density of the electrochemical reaction is 1-6A/dm²The electrolytic reaction temperature is-10 to 80 ℃;

the acid solution is prepared by mixing a solvent and a supporting electrolyte, wherein the content of the supporting electrolyte in an electrolytic reaction solution is 0.05-0.5 mol/L, the supporting electrolyte is a salt capable of dissolving in the acid solution, the solvent is a mixed solvent of water and other protonic organic solvents, and the content of the protonic organic solvents in the electrolytic reaction solution is 20-90 wt%.

2. The method according to claim 1, wherein the palladium content in the activated carbon-supported cubic palladium nanoparticles is 1 to 10 wt%.

3. The method according to any one of claims 1 to 2, wherein the activated carbon-supported cubic palladium nanoparticles are prepared by the following method:

step 1: preparation of cubic Palladium nanoparticles (Pd NC)

Adding polyvinylpyrrolidone, ascorbic acid, KCl, NaBr and water into a reaction container, heating to 70-90 ℃ and keeping for a certain time; rapidly adding Na₂PdCl₄Stirring the aqueous solution for a certain time, and finishing the reaction to obtain a colloidal solution containing Pd NC;

step 2: pretreatment of activated carbon

Adding activated carbon into a nitric acid aqueous solution with a certain concentration, and magnetically stirring for a certain time at 100 ℃; after the treatment is finished, washing the activated carbon by using a large amount of deionized water until the pH value of the solution is 5-6; carrying out suction filtration, drying and grinding to obtain pretreated activated carbon;

and step 3: preparation of activated carbon loaded Pd NC (Pd NC/C)

Taking the colloidal solution containing Pd NC prepared in the step 1, diluting with deionized water, adding the pretreated activated carbon in the step 2, ultrasonically dispersing for a certain time, and finally placing on a magnetic stirrer to stir for a certain time; and carrying out suction filtration, drying and grinding to obtain PdNC/C.

4. The method according to any one of claims 1-2, wherein 50-200 mg of palladium on carbon particles are added per 100m of L catholyte.

5. The method according to any one of claims 1 to 4, wherein the content of methylene chloride in the electrolytic reaction solution is 0.01 to 1 mol/L.

6. The method according to any one of claims 1 to 4, wherein the supporting electrolyte is a salt of a cation which is a lithium ion or an ammonium ion and an anion which is a chloride ion or a perchlorate ion.

7. The process according to any one of claims 1 to 4, wherein the protic organic solvent is a mixture of a C1-C4 organic alcohol and acetic acid.

8. The method of any one of claims 1 to 4, wherein the aqueous alkaline solution is L iOH or NaOH.

9. The method according to any one of claims 1 to 4, wherein the electrolysis temperature is 10 to 35 ℃.

10. A method according to any one of claims 1 to 4, wherein the membrane of the cell is a perfluorosulphonic acid cation membrane.

Technical Field

The invention belongs to the technical field of electrochemical dechlorination, relates to a dechlorination method for chlorine-containing Volatile Organic Compounds (VOCs), and particularly relates to a method for dechlorinating dichloromethane through electrochemical catalysis of palladium.

Background

Chlorine-containing VOCs can pose serious threats to human health and the global ecological environment. Such as: at present, chlorine-containing VOCs (volatile organic compounds) such as chloroethenes, chloromethanes and the like which are widely used have a 'three-cause' effect; the refrigerant freon (chlorofluoroalkane) which is used in large quantity generates serious damage to the ozone layer in the atmosphere stratosphere; research on the Martyn Chipperfield topic group at the university of british showed: dichloromethane is also an ozone depleting substance, and the recovery process of the Antarctic ozone layer is slowed down for 5-30 years due to the continuous increase of global dichloromethane emission [ Nat Commun 8,15962(2017) ]. The exploration of an effective treatment method for the chlorine-containing VOCs has become one of the urgent problems in the environmental protection field of all countries in the world. The toxicity of the chlorine-containing VOCs is mainly caused by the introduction of chlorine elements, and chlorine atoms have higher electronegativity, so that the difficulty of electrophilic reaction is increased along with the increase of chlorine substituents, and the degradability of the chlorine-containing VOCs is greatly reduced. If the chlorine atoms in the chlorine-containing VOCs are removed, the generated chlorine-free product can be recycled as a raw material or used as a green fuel. Therefore, the research on the efficient dechlorination method of the chlorine-containing VOCs has important application value.

Research by the group of professors of Armando Gennaro, italy, has found that electrochemical dechlorination processes can be used for the dechlorination of chlorine-containing VOCs: both tetrachloromethane and trichloromethane can be completely dechlorinated on a copper electrode in DMF solvent [ applied catalysis B: Environmental 126 (2012): 347-354 ], the main product being methane; both trichloroethylene and dichloroethylene can be completely dechlorinated to ethylene and ethane [ Applied Catalysis B: Environmental 126 (2012): 355-. Research conducted by the group of professors of Sandra Rondinini, Italy has found that on silver electrodes in acetonitrile solvent, trichloromethane and dichloromethane can also be completely dechlorinated to methane [ Electrochimica acta 49(2004) 4035-4046 ]. The two methods have the defects that solvents DMF and acetonitrile have high toxicity and easily cause secondary pollution; the conductivity of the catholyte is poor, and the cell pressure is high; poor selectivity of the dechlorination reaction results in products that are not unique and are not conducive to recovery, for example, the yield of methane produced by dechlorination of tetrachloromethane and trichloromethane on a copper electrode is up to less than 80% [ Applied Catalysis B: Environmental 126(2012) -. Therefore, technical measures for realizing dechlorination of dichloromethane with high selectivity under the condition of adopting a green solvent system are needed.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a method for treating dichloromethane through palladium-catalyzed electrochemical dechlorination.

The technical scheme adopted by the method for treating dichloromethane by electrochemical dechlorination under the catalysis of palladium is as follows:

adding dichloromethane into an acidic solution serving as a reaction medium to form an electrolytic reaction solution serving as a catholyte; taking an alkaline aqueous solution as an anolyte; adding palladium-carbon particles serving as a cathode catalyst into the catholyte; the foamed glassy carbon is taken as a cathode current collector, and a chemically inert conductive material or a titanium metal coated with noble metal oxide in an anolyte is taken as an anode and is placed in an electrolytic bath for electrochemical reaction. Wherein the pH of the catholyte is kept between 1 and 5 in the reaction process.

The acid solution is prepared by mixing an acid solvent and a supporting electrolyte, wherein the content of the supporting electrolyte in the electrolytic reaction solution is 0.05-0.5 mol/L.

The supporting electrolyte is a salt which can be dissolved in the acidic solvent, specifically a salt consisting of cations and anions, wherein the cations are lithium ions or ammonium ions, and the anions are chloride ions or perchlorate ions.

The acidic solvent is a mixed solvent of water and other protonic organic solvents, and the content of the protonic organic solvent in the electrolytic reaction liquid is 20-90 wt%. Wherein the protonic organic solvent is a mixture of C1-C4 organic alcohol and acetic acid, and the C1-C4 organic alcohol is one of methanol, ethanol, n-propanol, isopropanol, n-butanol, etc., preferably ethanol.

The palladium carbon particles are activated carbon supported cubic palladium nanoparticles, and the preferred palladium content is 1-10 wt%.

The preparation method of the activated carbon supported cubic palladium nanoparticle comprises the following steps:

step 1: preparation of cubic Palladium nanoparticles (Pd NC)

Adding 105-210 mg of polyvinylpyrrolidone, 60-120 mg of ascorbic acid, 0-360 mg of KCl, 5-600 mg of NaBr and 8m of L m of water into a reaction vessel, heating to 70-90 ℃ and keeping for 15min, and then rapidly adding 3m of L containing 20-100 mg of Na₂PdCl₄Stirring the aqueous solution for 3 hours, and then finishing the reaction to obtain a colloidal solution containing Pd NC;

step 2: pretreatment of activated carbon

Adding 1g of activated carbon into a nitric acid aqueous solution with the concentration of 165m L being 5-20 wt%, magnetically stirring for 5h at 100 ℃, washing the activated carbon with a large amount of deionized water after the treatment is finished until the pH value of the solution is 5-6, and performing suction filtration, drying and grinding to obtain the pretreated activated carbon.

And step 3: preparation of activated carbon loaded Pd NC (Pd NC/C)

And (3) taking 5m L of the colloidal solution containing Pd NC prepared in the step (1), diluting with 20m L of deionized water, adding 400mg of the pretreated activated carbon in the step (2), ultrasonically dispersing for 30min, finally placing on a magnetic stirrer, stirring for 30min, and performing suction filtration, drying and grinding to obtain the Pd NC/C.

Preferably, 50-200 mg of palladium-carbon particles are added into every 100m of L catholyte.

Preferably, the shape of the cathode current collector may be in the form of a plate, a rod, a wire, a mesh, a net, a foam, a wool, or a sheet, and preferably, a foam.

The current density of the electrochemical reaction is 1-6A/dm²。

In the electrolytic reaction process, the corresponding current density is changed according to the change of the concentration of dichloromethane in an electrolytic reaction liquid, and the content of the dichloromethane in the electrolytic reaction liquid is 0.01-1 mol/L, preferably 0.05-0.5 mol/L.

The alkaline aqueous solution is L iOH aqueous solution or NaOH aqueous solution.

The anode material can be any conductive material that is chemically inert in alkaline aqueous solutions, such as stainless steel, platinum, graphite, carbon, conductive plastics, the anode can also be comprised of a coating applied to another material, such as a noble metal oxide, such as ruthenium oxide, applied to titanium metal, preferably 316L stainless steel as the anode.

The electrolysis reaction temperature is-10 to 80 ℃, and preferably 10 to 35 ℃ in consideration of volatilization of the solvent, solubility of the reactant in the electrolysis reaction solution, and conductivity of the electrolysis reaction solution.

The bath pressure is 11.2-14.1V in the electrolyte process.

The electrolysis reaction according to the invention can be carried out batchwise or in a continuous or semi-continuous manner. The electrolysis cell may be a stirred cell containing electrodes or a flow cell of any conventional design. The electrolytic cell may be a single-chamber cell or a diaphragm cell, preferably a diaphragm cell. Separator materials which can be used are various anion or cation exchange membranes, porous Teflon, asbestos or glass, preferably perfluorosulphonic cation membranes as the diaphragm of the electrolysis cell.

While oxygen evolution as an anodic reaction is preferred, many other anodic reactions can be used. Including the evolution of chlorine and bromine molecules, or the production of carbon dioxide by the oxidation of protective materials such as formate or oxalate or the formation of valuable by-products by the oxidation of organic reactants.

The invention has the following beneficial effects:

(1) the solvent adopted by the method is green and environment-friendly and is convenient to recover;

(2) the catholyte adopted by the method has good conductivity and low pressure of the electrolytic bath;

(3) the invention realizes the conversion of dichloromethane into methane with high selectivity (more than or equal to 90 percent) by an electrochemical method, and is favorable for recovery.

(4) According to the invention, the activated carbon loaded cubic palladium nanoparticles are used as the catalyst, and the catalytic activity of the electrolytic reaction solution can be obviously improved in a specific system of the invention.

Drawings

FIG. 1 is a Transmission Electron Microscope (TEM) photograph of Pd NC;

FIG. 2 is a TEM photograph of Pd NC/C;

FIG. 3 is an H-type electrolytic cell used in the present invention.

Detailed Description

The present invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.