ACETYLENE IN THE PRESENCE OF A CATALYTIC SYSTEM CONSISTING OF AT LEAST ONE IONIC LIQUID

The present invention relates to a catalytic system which is particularly useful in a process for manufacturing vinyl chloride by hydrochlorination of acetylene. The present invention also relates to such process.

The manufacture of vinyl chloride by reaction between acetylene and 5 hydrogen chloride is conventionally carried out in the gas phase, in a fixed-bed

reactor, in the presence of a heterogeneous solid catalyst based on mercury chloride on a support. Mainly for reasons of toxicity, there is currently an

increasing interest in catalytic systems with decreased mercury content or which are free of mercury compounds.

0 Various catalysts intended to replace the current catalysts in gas-phase

processes have been developed.

For example, unexamined Japanese Patent Application 52/136104 describes a process of hydrochlorinating acetylene in the gas phase in the

presence of a fixed catalyst bed composed of noble metal halides deposited on5 active carbon. To date however, the lifetime of such alternative catalysts

intended for gas-phase processes remains much shorter than that of catalysts based on mercury compounds.

Furthermore, in the literature there are some examples of hydrochlorinating acetylene in the presence of a liquid catalytic medium.

0 German Patent 709.000 describes a process for preparing vinyl halides by

bringing acetylene into contact, at high temperatures, with a molten mass of hydrohalide salts of organic bases containing a standard catalyst. Aliphatic, aromatic or heterocyclic amines and mixtures thereof are envisaged as organic bases.

5 Inventor's certificate SU 237116 describes the use of an aqueous acid

solution containing 46 wt % of cuprous chloride and from 14 to 16 wt % of a methylamine, dimethylamine or trimethylamine hydrochloride.

European Patent Application EP-A-0 340 416 discloses a process for preparing vinyl chloride by reaction of acetylene with hydrogen chloride in the0 presence of a palladium compound as catalyst in a solvent composed of an

aliphatic or cycloaliphatic amide, at a temperature above room temperature. Although it allows high yields to be obtained, this process has, however, some significant drawbacks: it has emerged that, under the reaction conditions, the liquid catalyst system gradually degrades, forming blackish products of carbonaceous appearance. In addition, in the presence of hydrogen chloride, the amide is converted to a hydrochloride, the melting point of which is generally much higher than room temperature. N-Methylpyrrolidone hydrochloride, for example, is only liquid above 80°C. In practice, this may cause serious implementation problems, problems linked to agglomeration of the catalytic medium during reactor shutdowns or blocking of the lines at the coldest points of the installation. The entire reactor and also the lines in which the reaction medium flows must then be continuously kept at a temperature above the melting point of the hydrochloride.

These various problems seemed to have been solved thanks to the catalytic hydrochlorination systems described in European Patent Applications

EP 0 519 548-A1 and EP 0 525 843-A1 and which comprise at least one group VIII metal compound and either an amine hydrochloride, the melting point of which is less than or equal to 25°C, or a fatty amine hydrochloride comprising more that 8 carbon atoms, the melting point of which is above 25°C and an organic solvent chosen from aliphatic, cycloaliphatic and aromatic hydrocarbons and mixtures thereof. Nevertheless, the catalyst systems that are described therein, especially those of which the group VIII metal compound is

platinum (II) chloride or palladium (II) chloride, are not completely satisfactory when considering the performances that they enable to be achieved in terms of productivity of the vinyl chloride produced by hydrochlorination of acetylene and in terms of long term stability.

WO 2008/77868 discloses a catalytic hydrochlorination system comprising at least one amine hydrochloride and at least one group VIII metal compound selected from the group composed of mixtures of a platinum (IV) compound with Sn(II) chloride, mixtures of a platinum (II) compound with

triphenylphosphine oxide and mixtures of a palladium (II) compound with triphenylphosphine. These catalytic systems show an improved productivity compared to the systems as described in European patent applications

EP-A 0519548 and EP- A 0525843.

Finally, patent application CN 101716528 discloses catalytic systems for production of vinyl chloride by the hydrochlorination of acetylene comprising an imidazolium-based ionic liquid with chloride, bromide, hexafluorophosphate or tetrafluorophosphate ion as anion and one or more of gold, platinum, palladium, tin, mercury, copper or rhodium chlorides.

The last above-mentioned catalytic systems present the disadvantages of requiring either an amine hydrochloride or an ionic liquid and at least one metal compound which increases the costs of the catalytic systems. Problems linked with deactivation of the metal can also occurred in such catalytic systems.

Accordingly it was an object of the instant invention to provide a catalytic system, in particular for hydrochlorination reactions and more particularly for the hydrochlorination of acetylene, which is as simple and cheap as possible, which do not encounter problems linked to deactivation of metal and which allows very good performance. Another object of the invention was a process for synthesizing vinyl chloride by hydrochlorination of acetylene in the presence of such a catalytic system which does not degrade under the reaction conditions and which makes it possible to achieve very good productivity towards vinyl chloride. Unlike systems based on mercury compounds, the catalytic system according to the invention furthermore has the advantage of not having toxicity problems linked to these compounds and of avoiding the vaporization of metal salts in the installation.

The invention therefore relates to a catalytic system, more particularly a catalytic system for the hydrochlorination of acetylene, as defined in claim 11.

Preferred embodiments of the catalytic system in accordance with the instant invention are set forth in the claims dependent on claim 11 and the more detailed description hereinafter.

Another aspect of the instant invention relates to a process for

manufacturing vinyl chloride through the hydrochlorination of acetylene in the presence of a catalytic system as defined in claim 1 and the claims dependent on claim 1 and in the more detailed description hereinafter.

The catalytic system according to the instant invention consists essentially of at least one ionic liquid comprising at least one non-protonated cation and at least one anion selected from chloride and methanesulfonate.

The expression "consisting essentially of is understood to mean, in the present description, that besides the at least one ionic liquid as defined, the catalytic system according to the invention may comprise additional

component(s), preferably in small amount, that do not have an effect on the catalytic properties of the catalytic system; in other words that do not have a catalytic effect on the reaction during which the catalytic system is used. Among such additional component(s) may be cited ionic liquid(s) other than the ionic liquid(s) defined above, added for example to decrease the viscosity of the catalytic system. Preferably, the catalytic system according to the invention does not comprise any metal.

Preferably, the catalytic system according to the invention consists of at least one ionic liquid comprising at least one non-protonated cation and at least one anion selected from chloride and methanesulfonate.

The expression "consists of is understood to mean, in the present description, that the catalytic system consists solely of the at least one ionic liquid as defined above.

Ionic liquids are in principle salts in the liquid state while ordinary liquids, such as e.g. water and gasoline are predominantly made of electronically neutral molecules. Ionic liquids are advantageously made of ions.

It may be generally said that any salt melting without decomposition will usually yield an ionic liquid. Many salts, however, melt at high temperatures, much higher than the temperatures used in catalytic processes. For the purposes of the instant invention the term ionic liquid shall refer to a system being liquid at temperature used in the process in which the catalytic system is used.

Preferred ionic liquids for the purposes of the instant invention are those which are liquid at temperatures of 150°C or less, more preferably at temperatures of 100°C or less even more preferably at temperatures of 80°C or less. Most preferred are ionic liquids which are in the liquid state at room temperature or even below. Furthermore, preferred ionic liquids are those which have a very low vapor pressure and a very low flammability and which show a good electrical conductivity.

The ionic liquid which advantageously functions as reaction medium, is preferably selected so that it is largely inert toward the substances participating in the reaction and has preferably a solvent capability for the products and intermediates formed in the reaction.

In the present description, the expression "at least one ionic liquid" is understood to mean one or more than one ionic liquid.

Preferably, the catalytic system consists essentially of one ionic liquid as defined above.

In the remainder of the text, the expression "ionic liquid" used in the singular or plural should be understood as denoting one or more than one ionic liquid, except where denoted otherwise. The ionic liquids according to the invention comprise at least one non- protonated cation and at least one anion selected from chloride and

methanesulfonate.

In the present description, the expression "at least one non-protonated cation" is understood to mean one or more than one non-protonated cation.

Preferably, the ionic liquid comprises one non-protonated cation.

In the remainder of the text, the expression "non-protonated cation" used in the singular or plural should be understood as denoting one or more than one non-protonated cation, except where denoted otherwise.

The term non-protonated cations as used herein for the purpose of the instant invention shall mean cations which do not carry free hydrogen atom(s) at the atom(s) to which the positive charge of the cation is allocated.

Advantageoulsy, the non-protonated cation is selected from

- quaternary ammonium cations which can be represented by the general formula [ R ¹ R ² R ³ R] ⁺ ,

phosphonium cations which can be represented by the general formula

[PR ¹ R ² R ³ R] ⁺ , and

cations comprising five or six-membered heterocycles which have at least

- pyrrolidinium cations of the general formula (III)

wherein radicals R and R ¹ to R ⁹ may, independently from one another, with the proviso that the radical carried by the atom(s) to which the positive charge of the cation is allocated is not hydrogen, each be hydrogen, an optionally substituted saturated or insaturated Ci-Cis alkyl group (preferably an optionally substituted saturated or insaturated Ci-Ci ₆ alkyl group and more preferably an optionally substituted saturated or insaturated C1-C14 alkyl group), an optionally substituted saturated or insaturated C ₂ -C18 alkyl group with the carbon chain interrupted by one oxygen atom or an optionally substituted C ₆ -Ci ₂ aryl group.

Preferably, the non-protonated cation is selected from quaternary ammonium cations, phosphonium cations, imidazolium cations, pyridinium cations and pyrrolidinium cations.

More preferably, the non-protonated cation is selected from phosphonium cations, imidazolium cations, pyridinium cations and pyrrolidinium cations.

Most preferably, the non-protonated cation is selected from phosphonium cations and imidazolium cations.

Catalytic systems where the non-protonated cation is selected from phosphonium cations and pyrrolidinium cations are new and give good results within the frame of the invention.

Examples of quaternary ammonium cations are tributylmethylammonium, butyltrimethylammonium, octyltrimethylammonium, tetramethylammonium, tetraethylammonium, tetrabutylammonium, methyltrioctylammonium,

2-hydroxyethyltrimethylammonium and diethylmethyl(2- methoxyethyl)ammonium.

Examples of phosphonium cations are triisobutylmethylphosphonium, tributylmethylphosphonium, ethyltributylphosphonium, tetrabutylphosphonium, tetraoctylphosphonium, tributyltetradecylphosphonium,

trihexyltetradecylphosphonium and benzyltriphenylphosphonium.

Examples of imidazolium cations are 1,3-dimethylimidazolium, l-ethyl-3- methylimidazolium, l-butyl-3 -methylimidazolium, l-pentyl-3- methylimidazolium, l-hexyl-3 -methylimidazolium, l-decyl-3- methylimidazolium, l-dodecyl-3 -methylimidazolium, l-tetradecyl-3- methylimidazolium, l-hexadecyl-3 -methylimidazolium, l-(2-hydroxyethyl)-3- methylimidazolium, l-Allyl-3 -methylimidazolium, l-benzyl-3- methylimidazolium, l-phenylpropyl-3 -methylimidazolium, 1,3- diethylimidazolium, l-butyl-3 -ethylimidazolium, l-methyl-3- propylimidazolium, l-methyl-3-octylimidazolium, l-methyl-3- octadecylimidazolium, l,3-dibutyl-2-methylimidazolium, l,3-didecyl-2- methylimidazolium, l-(2-hydroxyethyl)-3-methylimidazolium, l-ethyl-2,3- dimethylimidazolium, l-propyl-2,3-dimethylimidazolium, l-butyl-2,3- dimethylimidazolium, l-butyl-3,4-dimethylimidazolium, l-hexyl-2,3- dimethylimidazolium, l-hexadecyl-2,3-dimethylimidazolium,

1,2,3-trimethylimidazolium, 1,3,4-trimethylimidazolium, l-butyl-3- ethylimidazolium, 1,3-dibutylimidazolium, l-methyl-3-octylimidazolium, l-butyl-3,4,5-trimethylimidazolium and 1,3,4,5-tetramethylimidazolium.

Examples of pyridinium cations are 1 -methylpyridinium,

1-ethylpyridinium, 1-propylpyridinium, 1-butylpyridinium, 1-hexylpyridinium, 1 -octyl pyridinium, 1 ,2-dimethylpyridinium, 2-ethyl- 1 -methylpyridinium, 1 -butyl-2-methylpyridinium, 1 -butyl-3 -methylpyridinium, 1 -butyl-4- methylpyridinium, 1 -hexyl-3 -methylpyridinium, 1 -hexyl-4-methylpyridinium, 1 -butyl-2-ethylpyridinium, 1 -butyl-3 -ethylpyridinium, 4-methyl- 1 - octylpyridinium, l-butyl-2-ethyl-6-methylpyridinium, 2-ethyl- 1,6- dimethylpyridinium, 1 -butyl-3, 4-dimethylpyridinium and 1 -butyl-3, 5- dimethylpyridinium.

Examples of pyrrolidinium cations are 1, 1-dimethylpyrrolidinium, 1-ethyl- 1-methylpyrrolidinium, l-ethyl-3-methylpyrrolidinium, 1 -butyl- 1- methylpyrrolidinium, 1-hexyl-l -methyl pyrrolidinium, 1 -octyl- 1- methylpyrrolidinium, 1 -butyl- 1-ethylpyrrolidinium and 1 -methyl- 1- propylpyrrolidinium.

In the present description, the expression "at least one anion" is understood to mean one or more than one anion.

Preferably, the ionic liquid comprises one anion.

In the remainder of the text, the expression "anion" used in the singular or plural should be understood as denoting one or more than one anion, except where denoted otherwise.

The at least one anion is selected from chloride and methanesulfonate. The catalytic system according to the invention consists essentially of at least one ionic liquid comprising at least one non-protonated cation and at least one anion selected from chloride and methanesulfonate with the preferences listed above for the non-protonated cation and for the anion.

Preferably, the ionic liquid is selected from quaternary ammonium chlorides, quaternary ammonium methanesulfonates, phosphonium chlorides, phosphonium methanesulfonates, imidazolium chlorides, imidazolium methanesulfonates, pyridinium chlorides, pyridinium methanesulfonates, pyrrolidinium chlorides and pyrrolidinium methanesulfonates.

Catalytic systems wherein the ionic liquid is selected from quaternary ammonium methanesulfonates, phosphonium chlorides, phosphonium methanesulfonates, imidazolium methanesulfonates, pyridinium

methanesulfonates, pyrrolidinium chlorides and pyrrolidinium

methanesulfonates, are new and give good results within the frame of the invention.

More preferably, the ionic liquid is selected from phosphonium chlorides, phosphonium methanesulfonates, imidazolium chlorides, imidazolium methanesulfonates, pyridinium chlorides, pyridinium methanesulfonates, pyrrolidinium chlorides and pyrrolidinium methanesulfonates.

Most preferably, the ionic liquid is selected from phosphonium chlorides, phosphonium methanesulfonates, imidazolium chlorides and imidazolium methanesulfonates.

Catalytic systems wherein the ionic liquid is selected from phosphonium chlorides and imidazolium methanesulfonates are new and give good results within the frame of the invention.

Particularly preferred ionic liquids are those used in the working examples hereinafter i.e. l-butyl-3-methylimidazolium chloride,

trihexyltetradecylphosphonium chloride, 1 -ethyl-3 -methylimidazolium methanesulfonate, l-methyl-3-octylimidazolium chloride, 1 -Ethyl-3 - methylimidazolium chloride and l-benzyl-3 -methylimidazolium chloride.

Catalytic systems wherein the ionic liquid is

trihexyltetradecylphosphonium chloride or 1 -ethyl-3 -methylimidazolium methanesulfonate are new and give good results within the frame of the invention.

The same is true for catalytic systems wherein the ionic liquid is selected from l-methyl-3-octylimidazolium chloride, 1 -Ethyl-3 - methylimidazolium chloride and l-Benzyl-3 -methylimidazolium chloride

Those particularly preferred ionic liquids are e.g. commercially available from Iolitec GmbH or from BASF SE.

Methods for the manufacture of suitable ionic liquids are known to the skilled man and thus a detailed description is not necessary here.

The catalytic system in accordance with the instant invention may be used in the liquid phase or be deposited on a solid support such as a silica, alumina, silica alumina, cordierite, mullite or activated carbon (to name only a few suitable support materials), up to the limit of the pore volume and the available surface of the support. The support can have any shape known for such support materials, including but not limited to honeycombs and extrudates or the like.

When it is used in the liquid phase, the catalytic system may be diluted by an organic solvent. The choice of the nature of the organic solvent then included in the catalytic system according to the invention especially depends on the requirement that it be inert with respect to the reactants under the reaction conditions, that it be miscible or not with the ionic liquid and on the desire that it forms with this ionic liquid a medium, the viscosity of which is lower than that of the ionic liquid alone.

Preferably, however, the ionic liquid serves itself as a solvent so that no further solvent is necessary.

The catalytic system according to the invention can be used for any reaction on an alkyne i.e. compound in which two carbons are linked by a triple bond. Among such alkynes can be cited acetylene, propyne also called methylacetylene, dimethylacetylene dicarboxylate, 1,4-butynediol as well as propargylic compounds. The reaction can be a hydrohalogenation, in particular a hydrochlorination (with hydrogen chloride), a hydroiodination (with hydrogen iodide), a hydrofluorination (with hydrogen fluoride) or a hydrobromination (with hydrogen bromide), or a reaction with phosphorous acid.

The catalytic system in accordance with the instant invention is particularly useful for the hydrochlorination of acetylene.

In the present description, the term "acetylene" has to be understood as acetylene or mixtures comprising acetylene which can, in addition to acetylene, comprise other components, e.g. ethylene or other unsaturated hydrocarbons which may be by-products of acetylene synthesis. The origin of such mixtures of different unsaturated compounds can be any known source of reaction mixtures as they may be obtained in the course of the known synthesis methods for acetylene. Mixtures comprising less than 50 % of acetylene can be used.

Preferably however, the term "acetylene" refers to mixtures comprising at least 90 % of acetylene and more preferably 100 % of acetylene.

Acetylene is mainly manufactured by the partial combustion of methane or appears as a side product in the ethylene stream from cracking of hydrocarbons.

Another method for the manufacture of acetylene is the hydrolysis of calcium carbide CaC ₂ + 2H ₂ 0→ Ca(OH) ₂ + C ₂ H ₂

which requires extremely high temperatures of approximately 2000°C, necessitating the use of an electric furnace or the like.

Mixtures comprising acetylene and ethylene may be used directly as such, i.e. without the necessity to separate the components as the reactivity of acetylene vs. ethylene enables the hydrochlorination of acetylene to be carried out first with separation of the vinyl chloride obtained and the subsequent use of ethylene. This ethylene can be chlorinated to produce 1,2-dichoroethane for a combined process for the manufacture of vinyl chloride monomer. The pyrolysis of the 1,2-dichloroethane can produce the hydrogen chloride for the first reaction with acetylene.

Therefore the present invention also relates to a process for manufacturing vinyl chloride by reaction of acetylene with hydrogen chloride

(hydrochlorination) in the presence of a catalytic system in accordance with the instant invention.

The definitions and preferences defined above for the catalytic system according to the invention apply for the process for manufacturing vinyl chloride according to the invention.

The process according to the invention can advantageously be carried out at a temperature in the range of from room temperature to 220°C. At higher temperatures, the catalytic system has a tendency to degrade. The preferred reaction temperature, that is to say that offering the best compromise between productivity, yield and stability of the catalytic medium, is greater than or equal to about 40°C. The best results are obtained at temperatures greater than or equal to about 50°C with a more particular preference for temperatures greater than or equal to about 80°C and a most particular preference for temperatures greater than or equal to about 120°C. Preferably, the reaction temperature does not exceed about 200°C. A reaction temperature of about 40°C to about 200°C is most particularly preferred. In certain cases a reaction temperature not exceeding 170°C has proven advantageous.

The process according to the invention is advantageously carried out at atmospheric pressure or at higher pressures compatible with the safety regulations for handling acetylene. Usually the pressure will not exceed 5 MPa, preferably it will not exceed 2.5 MPa acetylene partial pressure.

The process for manufacturing vinyl chloride by hydrochlorination of acetylene according to the invention is advantageously carried out by bringing the gaseous reactants - acetylene and hydrogen chloride - into contact with the catalytic system, in any suitable reactor.

The process according to the invention may be carried out conventionally in any equipment promoting gas-liquid exchange, such as a plate column, a flooded packed column or a flooded non-packed column. Another embodiment of the process enabling good exchange of matter between the liquid and gas phases consists of the use of a countercurrent reactor, optionally of the sparged packed-bed type, the liquid catalytic system flowing over the packing, countercurrently to the gaseous flow of reactants.

In the process according to the invention the molar ratio of the hydrogen chloride to the acetylene introduced into the reactor is advantageously greater than or equal to about 0.5. Preferably, this ratio is greater than or equal to about 0.8. Advantageously, this molar ratio is less than or equal to about 3.

Preferably, the molar ratio of the hydrogen chloride to the acetylene introduced into the reactor is less than or equal to about 1.5.

Good results have been obtained when the hydrogen chloride and the acetylene are used in a molar ratio of about 0.5 to about 3.

The acetylene and the hydrogen chloride may be brought into contact in the reactor or, preferably, mixed prior to being introduced into the reactor.

For the purpose of increasing the amount of acetylene dissolved in the liquid phase, it is also possible to use a process in which only the acetylene is introduced into the reactor in gaseous form, where it reacts with the hydrogen chloride present in the liquid phase in hydrochloride form. The hydrogen chloride can be introduced in any form: dilute gaseous, pure or dissolved in a solvent to be extracted, such as for example an insoluble amine, advantageously then with an intermediate drying operation.

The catalytic system in accordance with the instant invention can be advantageously used in the manufacture of vinyl chloride in the process in accordance with the instant invention.

The present invention also therefore relates to the use of the catalytic system according to the invention for the catalytic hydrochlorination of acetylene to manufacture vinyl chloride.

Compared to prior art catalytic systems the catalytic system in accordance with the instant invention presents the advantages of being a simple and cheap catalytic system which further does not encounter problems linked to

deactivation of metal. It allows also obtaining very good performance in terms of conversion, selectivity and thus also improved productivity and is

characterized by long term stability. Avoiding the use of mercury compounds, the catalytic system according to the invention furthermore has the advantage of not having toxicity problems linked to these compounds.

The following examples are intended to illustrate the invention without however limiting the scope thereof. Examples denoted with letter C are comparative examples whereas other examples describe catalytic systems in accordance with the instant invention.

General procedure for the working examples:

A pyrex reactor having an internal volume of 45 ml, equipped with a double jacket in which a heat transfer oil circulated and a device for introducing reactants composed of a sintered glass nozzle intended to ensure the dispersion of the gases in the liquid medium, was charged with 30 ml of the catalytic system consisting essentially of the respective ionic liquid used as received. The reactor was held at a temperature of 150°C.

The reactants acetylene and HC1 were introduced in a molar ratio of 1 : 1.2 in amounts of 10 Nl/h and 12 Nl/h (measured at 0°C and atmospheric pressure).

The effluents leaving the reactor were analyzed for conversion of acetylene. The selectivity was 100 % in all experiments, i.e. there were no by-products besides the desired product vinyl chloride. Thus, the productivity could be calculated directly from the acetylene conversion.

The ionic liquids tested and indicated in the table which summarizes the catalytic systems tested were the following :

IL1 l-butyl-3-methylimidazolium chloride

IL2 trihexyltetradecylphosphonium chloride

IL3 l-ethyl-3-methylimidazolium methanesulfonate

IL4 l-methyl-3-octylimidazolium chloride

IL5 l-Ethyl-3-methylimidazolium chloride

IL6 l-Benzyl-3-methylimidazolium chloride

IL7 l-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

IL8 butyltrimethylammonium bis(trifluoromethylsulfonyl)imide

IL9 l-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide

IL10 l-ethyl-3-methylimidazolium triflate

IL11 l-butyl-3-methylimidazolium tetrachloroferrate(III)

IL12 l-ethyl-3-methylimidazolium tetrafluoroethyl sulfonate

IL13 triisobutylmethylphosphonium tosylate ILl 4 l-methyl-3-octylimidazolium triflate

ILl 5 trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ILl 6 1 -butyl- 1 -methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ILl 7 l-ethyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide The results of the experiments are given in the following table and/or illustrated on figure 1 which shows the acetylene conversion (%) in function of time (the x-axis shows the time in hour). The number next to the curve corresponds to the number of the example.

Table 1 - Examples 1 to 17

The results of the experiments show that very good conversion was obtained with catalytic systems according to examples 1 to 6 while no conversion was observed with catalytic systems according to comparative examples 7 to 17.