DE69721226T2 - Process for the electrochemical degradation of organic pollutants - Google Patents

Description

background the invention

The invention relates to a method for the electrochemical degradation of organic pollutants to carbon dioxide.

That industrial chemicals, production waste and other unwanted Chemicals in water and pesticides in soils and crops has convinced the public that the burden a problem of great importance due to synthetic organic molecules is.

U.S. Patent No. 5,545,799 a process for the chemical degradation of toxic organic compounds using hydrogen peroxide as an oxidizing agent in the preselected temperature and pH ranges, e.g. B. about 50 ° C up to about 90 ° C, pH starting at about 1 to about 2 and about 5 during oxidation reached about 8, and then the degradation of the oxidation product of the original toxic organic compound over at an alkaline pH to be led, z. B. at a maximum final pH of about 11.

Japanese Patent No. 07265862 A2 discloses a device for the oxidative degradation of organic substances in water using electrolysis. The device contains one electrolysis tank with anode plates and cathode plates (made of graphite), with activated carbon is filled between two electrodes. The electrolysis is carried out with the addition of iron salt and hydrogen peroxide carried into the wastewater, that is to be electrolyzed at low voltage and high current flow.

With regard to an ideal procedure To break down organic pollutants you have to deal with the following aspects Dedicate in depth: 1) Efficiency of organic pollutant degradation to carbon dioxide and inorganic substances without increasing the Waste volume, formation of new toxins and / or, biosynthesis more durable Products. 2) Gentle, simple and safe control conditions the cleaning process the environment. 3) Versatile process that uses all kinds of organic Pollutants for economic reasons with the same device can be treated. For these reasons there is an urgent desire to create a beneficial one industrial process for the degradation of organic pollutants.

Summary the invention

Object of the present invention is the provision of a novel electrochemical process Breaking down organic pollutants to carbon dioxide is easy, safe is economical and does not require any post-treatment of the waste.

The present invention provides a method of degrading an organic compound selected from aliphatic hydrocarbons, aromatic hydrocarbons, halogenated aliphatic compounds, halogenated aromatic Compounds, aliphatic oxo compounds, aromatic oxo compounds, nitrogen-containing aliphatic compounds, nitrogen-containing aromatic Compounds, sulfur-containing aliphatic compounds and sulfur-containing aromatic compounds, ready for carbon dioxide, that labeled is through the steps: (a) presenting the organic compound in an acidic aqueous solution, so that a reaction solution is formed with a pH below 7; and (b) electrolyzing the reaction solution in an electrolytic system with an Ag / AgCl reference electrode and a working electrode, which is a graphite-containing electrode acts in the presence of an oxygen-containing gas and at one Reduction potential between –0.1 V and -1.0 V (based on the reference electrode) or a reduction current, the more negative than -10 mA (related to the working electrode).

The present invention provides a process for the electrochemical degradation of organic pollutants ready as follows:

• 1) halogenated aromatics: for example 2,4,6-trichlorophenol, Pentachlorophenol, 2,3,4,5-tetrachlorobiphenyl, other polychlorinated Biphenyls (PCBs), dioxins and others.
• 2) halogenated aliphatics: for example 1,2-dichloroethane, Polyvinyl chloride (PVC), lindane, aldrin and others.
• 3) Aliphatic and aromatic 0xo compounds, including aldehydes, Ketones, phenols, alcohols, ethers, amides, carboxylic acids (and their esters): for example 2-nitrophenol, 4-hydroxybenzoic acid, 1-chlorocresol, 4-chloroanisole, phthalates, maleic acids, acetic acids, fatty acids, chloromethyl methyl ether, N, N-dimethylformamide (DMF), ethylene glycol, rormalin, 2-butanone (MEK) , 2- (2-thiazolylazo) -p-cresol and others.
• 4) Aliphatic and aromatic hydrocarbons: for example Heptane, polyethylene, benzene, toluene, naphthalene, polycyclic aromatic Hydrocarbons (PAHs) and others.
• 5) Nitrogen-containing organic compounds: for example Aniline, 4-aminophenol, benzidine, pyridine, acetonitrile, nitrobenzene, 2-nitrobenzoic acid, 2- (2-thiazolylazo) -p-cresol, paraquat and other.
• 6) Sulfur-containing compounds: for example dimethyl sulfoxide (DMSO), dimethyl sulfide, thiophenol, toluenesulfonic acid, 2- (2-thiazolylazo) -p-cresol and other.

The electrolytic process can be carried out in a three-electrode system comprising a working electrode, a reference electrode and an auxiliary electrode. The working electrode can be a graphite electrode or a modified graphite electrode, selected from a nontronite-coated graphite electrode and one with Ruthenium oxide pyrochlore modified electrode.

To increase the solubility of organic pollutants in the reaction solution as well as the rate of the degradation reaction, water is preferred or water mixed with small amounts of an organic solvent, as a solvent for the Reaction used. The organic solvents can be such be such as acetonitrile, acetone, N, N-dimethylformamide (DMF), dimethyl sulfoxide and other. of these, acetonitrile is preferably used.

The reaction temperature is generally at 5 to 80 ° C, preferably at ambient temperature. The speed of dismantling increases with increasing temperature. If the temperature is too high, becomes a low efficiency for the degradation more volatile observed organic substances. If the temperature is too low, so the efficiency of the degradation due to the reduction in solubility of organic compounds in aqueous solvents and due to Decrease in the rate of degradation reaction low.

The response time will vary depending on the different types of organic compounds and the reaction conditions varifiert. The longer the more complete the degradation reaction is the reaction time. is If the response time is too short, the response is insufficient, causing the efficiency of the degradation is reduced. On the other hand the response time too long, takes the ratio of sales per unit of time off so this is not usable.

The reaction solution is generally reduced to one acidic pH adjusted, preferably pH 0.5 to 6. The speed the degradation reaction is increased acidity the reaction solution increased. Therefore the acidity is particularly preferred to one pH adjusted to 1. The reaction solution is generally with inorganic acids like sulfuric acid, Hydrochloric acid, Nitric acid, Phosphoric acid, perchloric and others to the one you want pH adjusted, particularly preferably with hydrochloric acid. on the other hand acts as an inorganic acid in the reaction solution also like a carrier electrolyte. Others can usually also be used to increase the rate of degradation Carrier electrolytes used such as sodium chloride, potassium chloride, etc. are added to the reaction solution become.

For sequential oxidative degradation organic pollutants the oxidizing agents electrochemically through the reduction of oxygen Generated simultaneously and continuously under electrolysis conditions without others Reagents (e.g. hydrogen peroxide, ozone or other common oxidizing agents) and catalysts (e.g. Fe, Cu, Ni or other metal complexes) be added. The efficiency of the degradation can indeed be increased from oxidizing agents and / or metal catalysts to electrolyzed solution be increased, but this is less economical, uncertain and requires post-treatment of the waste. In contrast to that a process that uses oxygen as a source of the oxidant becomes, safer, more economical, easier and produces no secondary waste, in particular with the appropriate mode of operation. To maintain efficiency the dismantling process must the electrolysis reaction constantly Oxygen or air as the main source of the oxidant the reaction solution be pearled.

In the oxidative degradation of organic pollutants the electrolysis reaction is carried out in a three-electrode system Conditions of a constant reduction potential in the range from -0.1 to -1.0 V (against Ag / AgCl). If the reduction potential is too low, the efficiency of the obtained drops Degradation reaction and the reaction time increases. On the other hand, if the reduction potential is excessive, can Water and other chemicals (e.g. sulfate) accumulate in the reaction vessel participate in the electrolysis reaction, so that the efficiency of the degradation reaction impaired becomes. For example, water can be oxidized to oxygen at the anode at -1.0V and this oxygen can be reused as an oxidant source become. In the electrochemical degradation process, a constant Reduction current as well as a constant reduction potential used become. Will be a higher one Reduction current is used, so a higher efficiency of the degradation reaction receive. In this invention, a constant reduction current maintained below 2 A, preferably 100 mA to 1 A. Each after the ohmic voltage drop associated with the electrolysis process the electrolysis reaction is applied with or without voltage equalization become.

To determine the efficiency the electrochemical degradation of organic pollutants to carbon dioxide becomes the gaseous Trapped the product of the electrolysis reaction with an aqueous solution of 0.1 N NaOH, so that one can assume that the Carbon dioxide is converted into carbonate ion. For one specific reaction time will be a certain amount of barium chloride dihydrate into the container with the given aqueous sodium hydroxide solution, so that a white precipitate of barium carbonate forms. After filtering and drying the Weighed barium carbonate precipitate. After that, the yield of carbon dioxide determined and the efficiency for the electrochemical degradation of organic pollutants on the Determined the basis of this yield.

Short description of the drawings

1 Fig. 4 is an exploded view of an electrolytic device according to the present invention; and

2 shows an electrolytic system according to the present invention.

Detailed description of the preferred embodiment

If you look at 1 , the electrolytic system according to the present invention generally comprises an electrolytic cell 10 , two graphite working electrodes 20 , an auxiliary electrode 30 and a reference electrode 40 ,

The graphite working electrodes 20 can be made of unmodified or modified graphite. The reference electrode 40 can be Ag / AgCl, Hg / Hg ₂ SO ₄ , etc. The auxiliary electrode 30 can one around an air pipe 50 wound platinum electrode. The air pipe 50 is with a porous ceramic element 51 provided by a gas (oxygen or air) of the electrolytic cell 10 is fed. The electrolytic cell 10 has an upper opening 11 that with a stopper 60 is sealed from silicone rubber, and an outlet opening on one side 12 to deflate the air.

If you look at 2 , the reaction solution (organic compound in acid solution) into the electrolytic cell 10 poured oxygen from an oxygen bottle 70 is through the air tube 50 the electrolytic cell 10 fed and an electrochemical analyzer 80 (for example HA-151) for regulating the electrodes and for applying a reduction potential to the graphite working electrodes 20 put into operation. A reduction potential is applied to the graphite working electrodes 20 applied, the organic compound is decomposed and carbon dioxide is generated, which in the three-necked flask 90 is directed. The three-necked flask 90 contains an alkaline solution to collect the carbon dioxide, for example 0.1 M NaOH. The aqueous barium chloride solution then becomes the alkaline solution in the three-necked flask 90 given, which leads to the formation of a barium carbonate precipitate, from which the yield of carbon dioxide is determined.

The invention is illustrated by the following examples described, which, however, are in no way restrictive. In all examples are the yields of carbon dioxide are represented by values based on the number of moles of carbon in organic compounds based.

example 1

77.4 mg (0.56 mmol) of 4-hydroxybenzoic acid in 70 ml deionized. Water was introduced and the mixture was with an aqueous 6th N HCl solution adjusted to pH 1 to add an approximately 8 mM reaction solution result. This solution was transferred to a self-made electrochemical cell. Two Graphite electrodes formed the working electrode. The potential was kept constant at –0.3 V against Ag / AgCl without voltage equalization. While the electrolysis at ambient temperature was continuously initiated oxygen gas, and the gaseous Product carbon dioxide was trapped with 80 ml of an aqueous 0.1 N NaOH solution. After the reaction solution After being electrolyzed for 9 hours, 960 mg of barium chloride dihydrate was added into the container with the given aqueous NaOH solution, and the mixture was stirred for 20 minutes, giving a white, crystalline Precipitation occurred. After suction, the precipitate was also Washed water and then dried in the oven at 102 ° C for 3 hours 599 mg of barium carbonate were obtained, which is a yield of carbon dioxide of 77%.

Example 2

The procedure of Example 1 was followed repeated, except that this Potential at -0.1 V was held. 368 mg of barium carbonate were obtained, and the yield of carbon dioxide was 48%.

example 3

The procedure of Example 1 was followed repeated, except that this bubbled gas was air rather than oxygen gas. There were Obtained 746 mg of barium carbonate, and the yield of carbon dioxide was 97%.

example 4

The procedure of Example 1 was repeated except that an aqueous 18 NH ₂ SO ₄ solution was used in place of the aqueous 6 N HCl solution to adjust the pH to 1. 243 mg of barium carbonate were obtained and the yield of carbon dioxide was 31%.

example 5

The procedure of Example 4 was followed repeated, except that 410 mg sodium chloride to the reaction solution were given. 419 mg of barium carbonate were obtained, and the The yield of carbon dioxide was 54%.

example 6

The procedure of Example 1 was followed repeated, except that this Potential under voltage equalization was kept at -0.6 V. There were Obtained 130 mg of barium carbonate, and the yield of carbon dioxide was 17%.

example 7

The procedure of Example 6 was followed repeated, except that the Reaction was carried out at pH 0.5 instead of pH 1. There were 343 mg Obtained barium carbonate, and the yield of carbon dioxide was 44%.

example 8th

The procedure of Example 1 was followed repeated, except that this Potential was kept at -1.0 V under voltage equalization. There were 702 mg of barium carbonate are obtained, and the yield of carbon dioxide was 91%.

example 9

The procedure of example 1 was repeated except that there was a switch from constant potential to constant current, which was maintained at -800 mA with voltage equalization, and the pH was adjusted to 0.5 with 12 N HCl solution. 492 mg of barium carbonate was obtained and the yield of carbon dioxide was 64%.

example 10

111 mg (0.56 mmol) of 2,4,6-trichlorophenol suspended in 70 ml of deionized water and the mixture was with an aqueous 6th N HCl solution adjusted to pH 1 to add an approximately 8 mM reaction solution result. This solution was transferred to a self-made electrochemical cell. Two Graphite electrodes formed the working electrode. The potential was kept constant at -0.8 V with voltage equalization. During the Electrolysis at ambient temperature was continuously initiated oxygen gas, and the gaseous Product carbon dioxide was trapped with 68 ml of an aqueous 0.1 N NaOH solution. After the reaction solution After being electrolyzed for 9 hours, 821 mg of barium chloride dihydrate into the container with the given aqueous NaOH solution, and the mixture was stirred for 20 minutes, giving a white, crystalline Precipitation occurred. After suction, the precipitate was washed with water washed and then dried in the oven at 102 ° C for 3 hours, whereby 332 mg of barium carbonate were obtained, which corresponds to a yield of carbon dioxide 50% corresponded.

example 11

The procedure of Example 9 was followed repeated, except that two Nontronite-coated graphite electrodes are used as working electrodes were. 528 mg of barium carbonate were obtained, and the yield of carbon dioxide was 80%.

example 12

52.5 ml of deionized water were added with a solution of 111 mg (0.56 mmol) 2,4,6-trichlorophenol in 17.5 ml acetonitrile were added, and the mixture was adjusted to pH with an aqueous 6N HCl solution 1 set to an approximate 8 mM reaction solution to surrender. This solution was transferred to a self-made electrochemical cell. Two Graphite electrodes formed the working electrode. The potential was kept constant at –0.3 V without voltage equalization. During the Electrolysis at ambient temperature was continuously initiated oxygen gas, and the gaseous Product carbon dioxide was trapped with 470 ml of an aqueous 0.1 N NaOH solution. After the reaction solution After being electrolyzed for 2 hours, 5.74 g of barium chloride dihydrate was obtained into the container with the added aqueous NaOH solution, and the mixture was Stirred for 20 minutes, being a white, crystalline precipitate was obtained. After suction, the precipitate washed with water and then dried in the oven at 102 ° C for 3 h, being 875 mg of barium carbonate were obtained, a yield of obtained Carbon dioxide corresponded to 132% (acetonitrile was also broken down).

example 13

The procedure of Example 12 was repeated, except that 149 mg pentachlorophenol instead of 2,4,6-trichlorophenol treated were. 368 mg of barium carbonate were obtained, and the yield of carbon dioxide was 56%.

example 14

The procedure of Example 1 was followed repeated, except that 600 mg acetic acid instead of 4-hydroxybenzoic acid were treated. The concentration in the reaction was approximately 0.143 M; and 400 ml of an aqueous 0.1 N NaOH solution were used to collect the carbon dioxide. After the reaction solution 9 h long had been electrolyzed, 4.89 g of barium chloride dihydrate into the container with the given aqueous NaOH solution, 2.21 g of barium carbonate precipitate using the same work-up procedure were obtained as described in Example 1. The yield of carbon dioxide was 56%.

example 15

The procedure of Example 1 was followed repeated, except that 72 mg treated with naphthalene instead of 4-hydroxybenzoic acid and 115 ml of one aqueous 0.1 N NaOH solution were used to capture the carbon dioxide. After the reaction solution 9 h long had been electrolyzed, 1.368 g of barium chloride dihydrate into the container with the given aqueous NaOH solution, taking 500 mg of barium carbonate precipitate following the same work-up procedure as described in Example 1 were obtained. The yield of carbon dioxide was 45%.

example 16

The procedure of Example 1 was followed repeated, except that 25th mg treated 2,3,4,5-tetrachlorobiphenyl instead of 4-hydroxybenzoic acid were. The concentration in the reaction was approximately 1.22 mM, and 45 ml of an aqueous 0.05 N NaOH solution were used to collect the carbon dioxide. After the reaction solution 72 H. long had been electrolyzed, 251 mg of barium chloride dihydrate into the container with the given aqueous NaOH solution, where 124 mg barium carbonate according to the same work-up procedure were obtained as described in Example 1. The yield at Carbon dioxide was 61%.

example 17

The procedure of Example 1 was followed repeated, except that 89 mg treated with p-chloroanisole instead of 4-hydroxybenzoic acid and 80 ml of an aqueous 0.1 N NaOH solution were used to capture the carbon dioxide. After the reaction solution 9 h long had been electrolyzed, 0.96 g of barium chloride dihydrate into the receptacle with the given aqueous NaOH solution, where 190 mg barium carbonate according to the same processing were obtained as described in Example 1. The yield at Carbon dioxide was 25%.

example 18

The procedure of Example 1 was followed repeated, except that 52 mg of aniline instead of 4-hydroxybenzoic acid and 68 ml of one aqueous 0.1 N NaOH solution were used to collect the carbon dioxide. After the reaction solution 9 h long had been electrolyzed, 0.821 g of barium chloride dihydrate into the container with the given aqueous NaOH solution, where 241 mg barium carbonate according to the same work-up procedure as described in Example 1 were obtained. The yield of carbon dioxide was 36%.

Example 19

The procedure of Example 1 was repeated except that 500 mg of dimethyl sulfoxide was treated in place of 4-hydroxybenzoic acid. The concentration in the reaction was approximately 91 mM, and 100 ml of a 0.1N NaOH aqueous solution was used to collect the carbon dioxide. After the reaction solution was electrolyzed for 9 hours, 3.12 g of barium chloride dihydrate was added to the trap with the NaOH aqueous solution, 215 mg of barium carbonate by the same working-up procedure as in Example 1 described. The carbon dioxide yield was 9%.

example 20

The procedure of. Example 19 was repeated, except that the Reaction time was 43 h instead of 9 h, and 100 ml of an aqueous 0.1 N NaOH solution were used to capture the carbon dioxide. There were 3,048 g of barium carbonate was obtained, and the yield of carbon dioxide was 75%.

example 21

The procedure of Example 1 was followed repeated, except that 94 mg of 2-nitrobenzoic acid instead of 4-hydroxybenzoic acid were treated, and the potential was kept at -0.8 V under voltage equalization has been. 625 mg of barium carbonate were obtained, and the yield of carbon dioxide was 81%.

example 22

The procedure of Example 20 was repeated except that 44 mg of pyridine was treated instead of 2-nitrobenzoic acid, 56 ml of a 0.1N NaOH aqueous solution was used to capture the carbon dioxide, and 684 mg of barium chloride dihydrate to form the white barium carbonate - Precipitation was added. Following the same refurbishment process as in the example 20 429 mg of barium carbonate were described and the yield of carbon dioxide was 78%.

example 23

The procedure of example 1 was repeated except that 36 mg of polyvinyl chloride powder was suspended in the reaction solution instead of 4-hydroxybenzoic acid and 23 ml of an aqueous 0.1 N NaOH solution was used to capture the carbon dioxide. After the reaction solution was electrolyzed for 18 hours, 12 mg of unreacted polyvinyl chloride suspended in the reaction solution was recovered, and 274 mg of barium chloride dihydrate was added to the catch vessel with the aqueous NaOH solution to form the white barium carbonate precipitate. 118 mg of barium carbonate was obtained by the same work-up procedure as described in Example 1 and the yield of carbon dioxide was 80%.

example 24

The procedure of Example 8 was followed repeated, except that this electrolytic system with a graphite auxiliary electrode instead operated with a platinum auxiliary electrode and the pH with a 12 N HCl solution 1 was set. 422 mg of barium carbonate were obtained, and the yield of carbon dioxide was 55%.

According to the present invention, many can Types of organic pollutants can be broken down electrochemically to carbon dioxide simply, safely, economically and without the formation of secondary waste.

Claims (10)

Organic compound degradation method selected from aliphatic hydrocarbons, aromatic hydrocarbons, halogenated aliphatic compounds, halogenated aromatic Compounds, aliphatic oxo compounds, aromatic oxo compounds, nitrogen-containing aliphatic compounds, nitrogen-containing aromatic compounds, sulfur-containing aliphatic compounds and sulfur-containing aromatic compounds, to carbon dioxide through the steps: (a) Presentation of the organic compound in an acidic aqueous solution, so that a reaction solution is formed with a pH below 7; and (b) Electrolyzing the reaction solution in an electrolytic system with an Ag / AgCl reference electrode and a working electrode, which is a graphite one Acts in the presence of an oxygen-containing gas and at a reduction potential between –0.1 V and –1.0 V (based on the reference electrode) or a reduction current that is more negative than -10 mA (based on the working electrode) is. The method of claim 1, wherein the graphite-containing electrode a graphite electrode or a modified graphite electrode is selected from a nontronite coated graphite electrode or one with ruthenium oxide pyrochior modified electrode. The method of claim 1, wherein the acidic solution is an inorganic acid solution, and the inorganic acid selected is from hydrochloric acid, Sulfuric acid, Nitric acid, phosphoric acid and perchloric acid. The method of claim 1, wherein the pH of the reaction solution at 0.5 to 6.0. The method of claim 1, wherein the oxygen-containing gas is oxygen gas or is air. The method of claim 1, wherein the acidic solution is a acidic aqueous solution. The method of claim 6, wherein the acidic aqueous solution is further a miscible organic solvent comprises that selected is made of methanol, ethanol, propanol, acetone, 2-butanone, acetonitrile, N, N-dimethylformamide and dimethyl sulfoxide. The method of claim 1, wherein the reaction solution of the another a carrier electrolyte comprises the selected is made of sodium chloride and potassium chloride. The method of claim 1, wherein it is the halogenated aromatic compound around 2,4,6-trichlorophenol, pentachlorophenol, Dioxins, 2,3,4,5-tetrachlorobiphenyl or polyvinyl chloride. The method of claim 1, wherein the electrolytic system a three-electrode system comprising the reference electrode is a Auxiliary electrode and the working electrode.