EP2596836B1

EP2596836B1 - Method for decomposing a halogenated organic compound

Info

Publication number: EP2596836B1
Application number: EP20110190293
Authority: EP
Inventors: Inas Muen AlNashef; Saeed Mohammed Al-Zahrani
Original assignee: King Saud University
Current assignee: King Saud University
Priority date: 2011-11-23
Filing date: 2011-11-23
Publication date: 2014-03-05
Anticipated expiration: 2031-11-23
Also published as: EP2596836A1

Description

The present invention relates to a method for decomposing a halogenated organic compound.
A deep eutectic solvent (DES) is a type of ionic solvent with special properties composed of a mixture of compounds which form an eutectic with a melting point much lower than either of the individual components. DESs are useful as solvents, as electrolytes and as catalysts. Although DESs have many common characteristics with ionic liquids, they are considered as different type of solvents. Ionic liquids are composed entirely from ions while DESs have both ions and neutral molecules. In addition, ionic liquids are synthesized by chemical reactions while DESs are prepared by mixing and heating only. The first generation of eutectic solvents was based on mixtures of quaternary ammonium salts with hydrogen bond donors such as amines and carboxylic acids. Compared to ionic liquids they share many characteristics but are ionic compounds and not ionic mixtures, deep eutectic solvents are cheaper to make, much less toxic and sometimes biodegradable. The major advantages of the approach used for the synthesis of DESs is that common, non-toxic components can be used and that they are easy to make by just mixing two compounds with gentle heating and subsequent cooling to room temperature.
WO 02/26701 relates to a method for the synthesis of DES by the mixing of one amine salt, such as choline chloride, with an organic compound capable of forming hydrogen bond with the ion of the amine salt, such as urea.
WO 00/56700 relates to a method for the synthesis of deep eutectic solvents formed by mixing a quaternary ammonium compound or a mixture of two or more thereof with a halide of zinc, tin or iron or a mixture of two or more thereof.
The publication of M.A. Kareem et al., J. Chem. Eng. Data 2010, 55, 4632-4637 relates to DESs successfully prepared by mixing phosphonium salts with different hydrogen bond donors.
US 7,763,768 discloses the use of a deep eutectic solvent comprising a quaternary ammonium salt and different hydrogen bond donors as a solvent for the preparation of hydrogen peroxide.
Although industry is making strides in reducing the usage of chlorinated solvents, a survey shows that approximately 341,000 kg of trichlorethylene, perchloroethylene, trichloroacetylene, and other chlorinated solvents are used per year in part by dry cleaning, critical cleaning, paint stripping, and similar operations. Additional significant volumes of chlorinated hazardous wastes exist in landfills, brownfields and other contaminated sites. Polyhalogenated aromatic hydrocarbons represent a major environmental problem. These materials represent components that are animal carcinogens and can cause birth defects. The continual release into the ecosystem has a deleterious effect on animal life.
In recent years, with the global emphasis on the reduction of the huge stockpile of chemical warfare agents, the art has been confronted with the problem of safely destroying and disposing of a variety of obsolescent chemical warfare agents e.g. mustard gas and Lewisite. Large quantities of chemical warfare agents are contained in a wide spectrum of munitions ranging from tactical ordnance to ballistic missiles, while equally large quantities are found in storage vessels with capacities ranging from a few grams to several tons. Therefore, the problem of treatment and disposal is severely complicated not only due to the extreme toxicity of infinitesimal quantities of these agents but also by the need to simplify their recovery and to minimize the number of transfer and handling steps.
Thermal oxidation is a standard method of destroying hazardous chemicals. Destructive oxidation is done in high-efficiency thermal incinerators or in cement kilns but the potential for emission of dioxins makes regulations on these operations very strict.
Sugimoto et al., Sci. Technol. 1988, 22, 1182, relates to polyhalogenated aromatic hydrocarbons, by example PCBs and hexachlorobenzene and its rapid degradation by the superoxide ions in dimethylformamide to carbonate and halide ions. The efficient desctruction of such materials is accomplished via the in situ electrolytic reduction of dioxygen to generate the superoxide ion which reacts with the polyaromatics by nucleophilic substitution.
US 7,812,211 relates to a process for the destruction of small to large quantities of halo-genated hydrocarbons using superoxide ions in ammonium salt based deep eutectic solvents.
It is an object of the present invention to provide a method for decomposing halogenated organic compounds which overcomes the drawbacks of the prior art. Particularly, a method shall be provided in which the halogenated organic compound is decomposed by the reaction with superoxide ions in a non-ammonium salt based deep eutectic solvent. By using non-ammonium salt based deep eutectic solvents an efficient decomposition of compounds which exhibit poor solubility in ammonium salt based deep eutectic solvents shall be enabled.
The first object is achieved by a method for decomposing a halogenated organic compound comprising the steps:

a) providing at least one deep eutectic solvent comprising:
- aa) at least one compound (I) of the general formula
  
  R¹R²R³R⁴P⁺X^-
  
  and/or
  
  R¹R²R³S⁺X^-; and
- bb) at least one compound (II) selected from a metal halide and/or a metal halide hydrate;
  wherein R¹, R². R³ and R⁴ are independently selected from H, substituted or unsubstituted, linear or branched alkyl, alkoxy, cycloalkyl, aryl or alkaryl or
  wherein two of R¹, R², R³ or R⁴ are an optionally substituted alkylene group, preferably a C₄-C₁₀ alkylene group;
  X is halogen;
  the metal in compound (1I) is independently selected from Li, Mg, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Sn, Pb, Bi, La or Ce, preferably Zn, Sn or Fe, or mixtures thereof; and
  the molar ratio of compound (I) to compound (II) is in a range from 1:1 to 1:5;
b) dissolving the halogenated organic compound in the deep eutectic solvent;
c) maintaining the solution obtained in step b) in a temperature range from 15°C to 100°C; and
d) adding molecular oxygen to the solution obtained in step c) and electrochemically generating superoxide ions from the molecular oxygen and/or adding at least one alkali superoxide and/or at least one alkaline earth metal superoxide to the solution obtained in step c).

In a preferred embodiment R¹, R², R³ and R⁴ are independently selected from substituted or unsubstituted, linear or branched C₁-C₁₈ alkyl, C₁-C₁₀ alkoxy, C₆-C₁₀ cycloalkyl, C₆-C₁₂ aryl or C₇-C₁₂ alkaryl.
Preferably, X is chlorine or bromine, more preferably chlorine.
Even preferred, the halogenated organic compound contains at least one chlorine atom.
In a further preferred embodiment, the halogenated organic compound is a chemical warfare agent, more preferably sulfur mustard gas, nitrogen mustard gas Lewisite or derivatives thereof.
Preferably, the halogenated organic compound is a halogenated hydrocarbon, more preferably halogenated aromatic hydrocarbon, halogenated polyaromatic hydrocarbon, halogenated aliphatic hydrocarbon and/or halogenated cycloaliphatic hydrocarbon.
Even preferred, the molar ratio of compound (I) to compound (II) is 1:2.
In a preferred embodiment, the electrochemical generating takes place in a membrane electrochemical reactor.
Preferably the deep eutectic solvent has a freezing point of up to 100°C.
Surprisingly, it was found that superoxide ions can be generated by the reduction of molecular oxygen in a deep eutectic solvent according to step a) of the inventive method without the use of an additional supporting electrolyte.
Further, it was surprisingly found that superoxide ions can be provided in the DES according to step a) of the inventive method by preferably dissolving alkali superoxides or alkaline earth metal superoxides in the DES without the addition of any other chemicals, such as crown ethers. It was also found that the solubility of alkali superoxides or alkaline earth metal superoxides in phosphonium based DESs is significant higher than in ammonium based DESs.
The method of the present invention provides the opportunity to decompose small to large quantities of hazardous chemicals at ambient conditions without producing any toxic byproducts.
Further, it was found that the method of the present invention can be carried out in a fast, cost-effective, easy manner to substantially completely decompose the hazardous chemicals.
Additional features and advantages of the present invention will become apparent in the following detailed description and on the basis of examples with reference to the drawings, wherein

Fig. 1 shows a GC chromatogram of sulfur mustard before being processed according to the inventive method.
Fig. 2 shows a mass spectrum of the peak of Fig. 1; and
Fig. 3 shows a GC chromatogram of sulfur mustard after being processed according to the inventive method.

Examples

Quality of used chemicals and general proceedings

The used halogenated compounds were obtained from different sources, e.g. Sigma-Aldrich, Acros. The stated purity of most of the used substrates was ≥ 99. The deep eutectic solvents were obtained from Scionix, UK. All chemicals were used without further purification.
Sulfur mustard (SM) and nitrogen mustard (HN1) were synthesized in our labs using methods reported in the literature. GC/MS and HPLC analysis showed that the purity of said compounds was ≥ 99%.
The conductivity of the used DES is in a range of 1-20 mS/cm.
For decomposition experiments using an electrochemically generated superoxide ion, a membrane electrochemical reactor was used. The cathode and anode compartments were made of Plexiglas with appropriate openings to accommodate the electrodes and to load and unload solutions. Proton exchange membranes of different thicknesses were used as a separator between the cathode and anode compartment. The membranes were soaked in a boiling 5M NaOH solution for 2-3 h to get rid of H⁺ and then in boiling distilled water for about 1 h. The membrane was soaked with DES for 24 h before being used. The anode and cathode compartments were made of Plexiglas. The outside frames of the reactor were made of either Plexiglas for clear visualization of the reactor contents or from metallic alloy with proper grooves to accommodate electrical heating elements. Silicon rubber gaskets were used for leak prevention. A reticulated vitreous carbon or Pt mesh was used as a working electrode. The cathode chamber containing DES (≈20 mL) was purged with argon for 20 min. The catholyte was first pre-electrolyzed until the background current fell to ≈ 1 mA. Then a weighed amount of the substrate to be destroyed was added to the DES and the solution was stirred with a magnet stirrer for several hours. A sample from the solution was then analyzed using HPLC to be sure that the substrate is totally dissolved in the DES. Oxygen was bubbled through the solution during the electrolysis period. Agitation of the catholyte was achieved by using a magnetic stirrer and through bubbling of oxygen. After electrolysis, diethyl ether was used to extract the products and the remaining reactant from the DES. A sample of the extract was then analyzed using HPLC and GC/MS.
A gas-sampling bag had been used for the collection of evolved gaseous products from the reactor. The gaseous products and the sample drawn from the reaction mixture were analyzed for the identification of volatile and non-volatile products monitored by GC/MS. The results were compared with authentic samples. The gaseous contents in the sampling bags were analyzed as such by GC/MS using gas tight syringe, the analysis results showed the formation of SO₂, NO₂, and chlorine which were matched with spectral library. These gases may be readily contained and prevented from escaping to the atmosphere.
Using HPLC and GC/MS no peaks were detected for the hazardous chemical or any known degradation product. Calibration of mustard gases using authentic compounds showed that both GC and HPLC are capable of detecting mustard gas down to 100 ppm. This means that the destruction of mustard gases was ≥ 99.9 %. Electro-spray ionization spectrometry confirmed the presence of bicarbonate ion.
In a further embodiment, the superoxide ions can be generated by dissolving Group 1 (alkali metals) or Group 2 (alkaline earth metals) superoxides, e.g. potassium superoxide in DES without the need to use any additional chemicals which are usually used to enhance the solubility of these metal superoxides in aprotic solvents, e.g. crown ethers. In addition, increasing the temperature to about 50°C increased the solubility of said superoxides drastically. The presence and stability of the superoxide ion in the tested DES were checked using UV-vis spectrophotometer.
A weighed amount of the selected hazardous chemical was added to about 10 g of DES. The solution was mixed vigorously. After enough time, a sample from the solution was withdrawn and analyzed using HPLC and the resulting peak was compared to the peak of the corresponding pure chemical. Then small weighed amounts of the metal superoxide, e.g. potassium superoxide, were added to the solution under vigorous mixing. Samples were then taken and analyzed using HPLC until no peak for the hazardous chemical is detected. The solution was then extracted using a proper solvent, e.g. diethyl ether, and the sample was analyzed using GC/MS. No peaks were detected for the hazardous chemical or any known degradation products. Samples from the solution before extraction by ether were dissolved in water and analyzed using electro-spray ionization mass spectrometer. KCl and K₂SO₄ or KNO₃ salts were formed, as confirmed by electro-spray ionization mass spectrometry. Electro-spray ionization mass spectrometry confirmed also the presence of the bicarbonate anion in some cases. During the reaction, samples of the gases evolved from the reaction were collected using gas sampling bags. The samples were then analyzed using GC/MS. No gaseous products, other than water vapor, were detected.

EXAMPLES

Example 1

About 0.01 g of sulfur mustard gas was added to about 10 g of the DES synthesized by mixing methyltriphenylphosphonium bromide with zinc chloride in the molar ratio of 1:2. The solution was stirred using a magnetic stirrer until all the added SM was dissolved. A sample of the solution was taken and dissolved in acetonitrile and then analyzed using HPLC. Small amounts of potassium superoxide were added carefully to the solution under vigorous stirring. Samples from the solution were taken at different intervals and dissolved in acetonitrile and then analyzed using HPLC. The height of the peak of the SM decreased as the added potassium superoxide increased. When the peak of the SM disappeared, the solution was extracted using diethyl ether, evaporated under vacuum and then dissolved in acetonitrile. The sample was then analyzed using GC/MS. No peaks were detected for mustard gas or any known degradation products. Samples from the solution before extraction by ether were dissolved in water and analyzed using electro-spray ionization mass spectrometer. KCl and K₂SO₄ salts were formed, as confirmed by electro-spray mass spectrometry, Electro-spray ionization mass spectrometry confirmed also the presence of the bicarbonate anion. During the reaction, samples of the gases evolved from the reaction were collected using gas sampling bags. The samples were then analyzed using GC/MS. No gaseous products other than water vapor were detected. Fig. 1 shows a GC chromatogram of the sulfur mustard before being processed according to the inventive method. Fig. 2 shows a mass spectrum of the peak of Fig. 1, and Fig. 3 shows a GC chromatogram of the sulfur mustard after being processed according to the inventive method. As can be taken, no sulfur mustard can be detected.

Example 2

The same procedure used in Example 1 was repeated except that the superoxide ion was generated electrochemically by the electrochemical reduction of oxygen dissolved in the DES using a membrane electrochemical reactor. The working, reference, and counter electrodes were reticulated carbon, Ag/AgCl, and Pt mesh, respectively.

Example 3

The same procedure used in Example 1 was repeated except that the used DES is synthesized by mixing methyltriphenylphosphonium bromide with nickel nitrate hexahydrate in the molar ratio of 1:2.

Example 4

About 0.01 g of nitrogen mustard gas (HN1) was added to about 10 g of the DES synthesized by mixing methyltriphenylphosphonium bromide with zinc nitrate hexahydrate in the molar ratio of 1:2. The solution was stirred using a magnetic stirrer until all the added NMG is dissolved. A sample of the solution was taken and dissolved in methanol and then analyzed using HPLC. Small amounts of potassium superoxide were added carefully to the solution under vigorous stirring. Samples from the solution were taken at different intervals and dissolved in methanol and then analyzed using HPLC. When the peak of HN1 disappeared, the solution was extracted using diethyl ether, evaporated under vacuum and then dissolved in methanol. The sample was then analyzed using GC/MS. Samples from the solution before extraction by ether were dissolved in water and analyzed using electro-spray ionization mass spectrometer. KCl and KNO₃ salts were formed, as confirmed by electro-spray mass spectrometry. Electro-spray ionization mass spectrometry confirmed also the presence of the bicarbonate anion. During the reaction samples of the gases evolved from the reaction were collected using gas sampling bags. No gaseous products, other than water vapor, were detected.
The results of examples 2-4 are as for example 1. No hazardous chemical could be detected after processing according to the present invention.
The features disclosed in the foregoing description, the claims and the accompanying drawing may, both separately and in any combination thereof, be material for realizing the invention in diverse forms thereof.

Claims

Method for decomposing a halogenated organic compound comprising the steps
a) providing at least one deep eutectic solvent comprising:
aa) at least one compound (I) of the general formula

R¹R²R³R⁴P⁺X^-

and/or

R¹R²R³S⁺X^-; and

bb) at least one compound (II) selected from a
metal halide and/or a metal halide hydrate;
wherein R¹, R², R³ and R⁴ are independently selected from H, substituted or unsubstituted, linear or branched alkyl, alkoxy, cycloalkyl, aryl or alkaryl or wherein two of R¹, R², R³ or R⁴ are an optionally substituted alkylene group, preferably a C₄-C₁₀ alkylene group;
X is halogen;
the metal in compound (II) is independently selected from Li, Mg, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Sn, Pb, Bi, La or Ce, preferably Zn, Sn or Fe, or mixtures thereof; and
the molar ratio of compound (I) to compound (II) is in a range from 1:1 to 1:5;

b) dissolving the halogenated organic compound in the deep eutectic solvent;

c) maintaining the solution obtained in step b) in a temperature range from 15°C to 100°C; and

d) adding molecular oxygen to the solution obtained in step c) and electrochemically generating superoxide ions from the molecular oxygen and/or adding at least one alkali superoxide and/or at least one alkaline earth metal superoxide to the solution obtained in step c).
Method according to claim 1, wherein R¹, R², R³ and R⁴ are independently selected from substituted or unsubstituted, linear or branched C₁-C₁₈ alkyl, C₁-C₁₀ alkoxy, C₆-C₁₀ cycloalkyl, C₆-C₁₂ aryl or C₇-C₁₂ alkaryl.
Method according to claim 1 or 2, wherein X is chlorine or bromine, preferably chlorine.
Method according to any of the preceding claims, wherein the halogenated organic compound contains at least one chlorine atom.
Method according to any of the preceding claims, wherein the halogenated organic compound is a chemical warfare agent, preferably sulfur mustard gas, nitrogen mustard gas Lewisite or derivatives thereof.
Method according to any of the preceding claims, wherein the halogenated organic compound is a halogenated hydrocarbon, preferably halogenated aromatic hydrocarbon, halogenated polyaromatic hydrocarbon, halogenated cycloaliphatic hydrocarbon and/or halogenated aliphatic hydrocarbon.
Method according to any of the preceding claims, wherein the molar ratio of compound (I) to compound (II) is 1:2.
Method according to any of the preceding claims, wherein the electrochemical generating takes place in a membrane electrochemical reactor.
Method according to any of the preceding claims, wherein the deep eutectic solvent has a freezing point of up to 100°C.