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 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.

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 on 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.

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.

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 the presence of a palladium compound as catalyst in a solvent composed of an aliphatic or cycloaliphatic amide, at a temperature above ambient 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 ambient 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 in combination with a metal compound.

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 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 10.

Preferred embodiments of the catalytic system in accordance with the instant invention are set forth in the claims dependent on claim 10 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 comprises a) at least one N-alkylated imidazole and

b) optionally at least one compound of at least one metal.

Catalytic systems comprising

a) at least one N-alkylated imidazole and

b) at least one compound of at least one metal chosen from Pd, Pt, Hg, Ru and Os are new and give good results within the frame of the invention, especially if the metal is Pd.

The expression "comprises" is understood to mean, in the present description, that besides the at least one N-alkylated imidazole and the optionally at least one compound of at least one metal, the catalytic system according to the invention may comprise additional component(s) having an effect on the catalytic properties of the catalytic system or not. Among such additional component(s) may be cited ionic liquid(s) added for example to have an effect on the catalytic properties of the catalytic system and/or allow a decrease of the viscosity of the catalytic system.

Preferably, the catalytic system according to the invention consists essentially of

a) at least one N-alkylated imidazole and

b) optionally at least one compound of at least one metal.

The expression "consists essentially of is understood to mean, in the present description, that besides the at least one N-alkylated imidazole and the optionally at least one compound of at least one metal, 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) added for example to decrease the viscosity of the catalytic system.

More preferably, the catalytic system according to the invention consists of a) at least one N-alkylated imidazole and

b) optionally at least one compound of at least one metal.

The expression "consists of is understood to mean, in the present description, that the catalytic system consists solely of the at least one N- alkylated imidazole and the optionally at least one compound of at least one metal.

The catalytic system according to the instant invention comprises as component a) at least one N-alkylated imidazole.

In the present description, the expression "at least one N-alkylated imidazole" is understood to mean one or more than one N-alkylated imidazole.

Preferably, the catalytic system comprises one N-alkylated imidazole.

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

N-alkylated imidazoles according to the invention is advantageously defined by formula (I) here below wherein radicals R ¹ , R ² , R ³ and R ⁴ may, independently from one another, each be hydrogen or an optionally substituted saturated or insaturated Ci-Cis (preferably C1-C14, more preferably C1-C12, most preferably C1-C10 and particularly most preferably Ci-C ₈ ) alkyl group.

Examples of N-alkylated imidazoles are 1-methylimidazole, 1- ethylimidazole, 1-propylimidazole, 1-butylimidazole, 1-pentylimidazole, 1- hexylimidazole, 1-heptylimidazole, 1-octylimidazole, 1-nonylimidazole, 1- decylimidazole, l-methyl-2-octylimidazole, l-ethyl-2-methylimidazole, 1-butyl- 2-methylimidazole, l-hexyl-2-methylimidazole and l-decyl-2-methylimidazole.

Preferably, the N-alkylated imidazole is selected from 1-methylimidazole, 1-ethylimidazole, 1-butylimidazole, 1-hexylimidazole, 1-octylimidazole, 1- decylimidazole, l-methyl-2-octylimidazole, l-ethyl-2-methylimidazole, 1-butyl- 2-methylimidazole, l-hexyl-2-methylimidazole and l-decyl-2-methylimidazole.

More preferably, the N-alkylated imidazole is selected from those used in the working examples hereinafter i.e. 1-methylimidazole, 1-ethylimidazole and 1-butylimidazole. Those most preferred N-alkylated imidazoles are e.g.

commercially available from Aldrich ^® .

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

The catalytic system according to the instant invention comprises as component b) optionally at least one compound of at least one metal.

In the present description, the expression "at least one compound of at least one metal" as used herein includes single metal compounds of one metal as well as mixtures of different compounds of the same metal or mixtures of compounds of different metals or compounds comprising two metals as defined hereinbefore, i.e. the catalytic systems in accordance with the invention may comprise more than one metal respectively metal compounds as defined above.

Preferably, the catalytic system comprises one compound of at least one metal and more preferably one compound of one metal.

In the remainder of the text, the expressions "compound" and "metal" used in the singular or plural should be understood as denoting respectively one or more than one compound and one or more than one metal, except where denoted otherwise.

In the present description, the expression "comprises optionally at least one compound" is understood to mean that such compound is present or not in the catalytic system.

According to a first embodiment according to the invention, the catalytic system according to the instant invention does not comprise component b) i.e. at least one compound of at least one metal.

The definitions and preferences defined above apply also for this first embodiment.

According to a second embodiment according to the invention, the catalytic system according to the instant invention comprises advantageously a) at least one N-alkylated imidazole and

b) at least one compound of at least one metal.

The definitions and preferences defined above apply also for this second embodiment.

The catalytic system according to the invention comprises optionally as component b) at least one compound of at least one metal.

The metal can be any metal. The metal is advantageously chosen from Pd, Pt, Au, Hg, Ru, Os, Ru, Rh and Ir. Preferably, the metal is chosen from Pd, Pt, Au, Hg, Ru and Os.

The catalytic system according to the instant invention comprises therefore preferably

a) at least one N-alkylated imidazole and

b) at least one compound of at least one metal chosen from Pd, Pt, Au, Hg, Ru and Os.

While good results have been obtained when the metal is chosen among the ones cited above, very good results have been obtained when the metal is chosen from Pd, Ru, Au and Os, particularly very good results have been obtained when the metal is chosen from Pd, Ru and Au and more particularly very good results have been obtained when the metal is chosen from Pd and Ru. The most interesting results have been obtained when metal is Pd.

Preferred Pt(IV) or Pt(II) or Pd(II) compounds are those which can be converted into chlorides of the mentioned metals during the preparation of the catalytic system in accordance with the instant invention. Thus, chlorides, nitrates, acetates, carbonates or oxides of platinum (IV), platinum (II) or palladium (II) may be used. Chlorides and acetates of these metals are nevertheless preferred.

Among the chloride-based compounds of platinum (IV), mention may be made of platinum (IV) chloride and hexachloroplatinic acid or its salts, for example Na ₂ PtCl ₆ , K ₂ PtCl ₆ or Li ₂ PtCl ₆ .

Among the chloride-based compounds of platinum (II), mention may be made of platinum (II) chloride and the platinochlorides of alkali metals or of alkaline-earth metals, such as for example Na ₂ (PtCl ₄ ), K ₂ (PtCl ₄ ), Li ₂ (PtCl ₄ ) and ( H ₄ ) ₂ (PtCl ₄ ).

Among the chloride-based compounds of palladium (II), mention may be made of palladium (II) chloride and the palladochlorides of alkali metals or of alkaline-earth metals, such as for example Na ₂ (PdCl ₄ ), K ₂ (PdCl ₄ ), Li ₂ (PdCl ₄ ) and ( H ₄ ) ₂ (PdCl ₄ ).

Particularly preferably, PtCl ₄ , PtCl ₂ , PdCl ₂ and palladium (II) acetate are chosen as compounds of platinum (IV), platinum (II) and palladium (II) respectively. PtCl ₂ , PdCl ₂ and palladium (II) acetate are most preferred.

Among compounds of Au, Au ³⁺ compounds are preferred and, similarly as in the case of Pd and Pt, those compounds which can be converted into chlorides are preferred. AuCl ₃ is most preferred.

Suitable compounds of Ru, and Os are those of valency 3 and again those compounds which can be converted into chlorides or the chlorides themselves are particularly preferred. RuCl ₃ and OsCl ₃ are respectively most preferred.

Amongst the suitable compounds of Hg, HgCl ₂ may be mentioned.

The content of metal compound in the catalytic system according to the second embodiment, expressed in millimoles per litre of N-alkylated imidazole is advantageously greater than or equal to about 1 mmol/1 and less than or equal to about 1000 mmol/1. The content of metal compounds in the catalytic system according to the second embodiment is advantageously greater than or equal to about 1 mmol/1, preferably greater than or equal to about 5 mmol/1 and particularly preferably greater than or equal to about 10 mmol/1. The content of metal compound in the catalytic system is advantageously less than or equal to about 1000 mmol/1, preferably less than or equal to about 800 mmol/1, particularly preferably less than or equal to about 600 mmol/1, more particularly preferably less than or equal to about 500 mmol/1 and most particularly preferably less than or equal to about 400 mmol/1. Although it is not mandatory, it is however preferable that all the metal compounds included in the catalytic system be in dissolved form.

Generally, the catalytic system in accordance with the second embodiment according to the invention, when used in hydrochlorination reactions with hydrogen chloride is prepared by dissolving or dispersing the desired amount of metal compound in the N-alkylated imidazole, and then saturating this solution with hydrogen chloride. However, it is also possible to first saturate the N- alkylated imidazole with hydrogen chloride then to next introduce the metal compound into the N-alkylated imidazole. Usually, the amount of metal compound used is such that, in the catalytic system, the entire metal compound is in dissolved form. However, it is also possible to use a metal compound in an amount or of a nature such that at least one fraction of this compound is present in the catalytic system in the form of a dispersed solid, without prejudicing the invention.

The catalytic system in accordance with the first and the second

embodiments according to 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 with N-alkylated imidazole and on the desire that it forms with this N-alkylated imidazole a medium, the viscosity of which is lower than that of the N-alkylated imidazole alone.

Preferably, however, the N-alkylated imidazole 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.

The catalytic system in accordance with the instant invention provides a 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 respective solutions comprising the catalytic systems prepared as described hereinafter. 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 N-alkylated imidazole was used as received. When present in the catalytic system, the metal compound indicated was dissolved in the necessary amount in the N-alkylated imidazole used. The amount of metal, unless otherwise indicated, was 22.6 mmol/1 of ionic liquid.

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 N-alkylated imidazole tested and indicated in the table which summarizes the catalytic systems tested were the following:

IM1 1-methylimidazole

IM2 1-butylimidazole

IM3 1-ethylimidazole

The results of the experiments are given in the following table and/or illustrated on figures 1 and 2 which show 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 14

: amount of metal of 22.6 increased to 67.8 mmol/1 during experiment : amount of metal of 354 mmol/1

The results of the experiments show that very good conversion was obtained with catalytic systems according to examples 1 to 14.