Patent Description:
The hydrochlorination of acetylene to produce VCM as the precursor to polyvinyl chloride (PVC) is currently a large scale industrial process, particularly in coal rich areas such as China and in areas rich in natural gas through natural gas to acetylene routes. Over <NUM> million tonnes of VCM are produced annually through acetylene hydrochlorination with the vast majority utilising mercuric chloride (HgCl<NUM>) catalysts supported on activated carbon. The mercury catalyst poses significant environmental concerns due to volatile HgCl<NUM> subliming from the catalyst bed, up to <NUM> Hg/tonne VCM production. Due to the environmental impact of this process, the recently ratified Minamata convention dictates that all new VCM plants must use mercury free catalysts and in the near future all existing industrial plants must switch to mercury free alternatives. This has revived the commercial interest in using gold and other metals as a catalyst for this reaction.

It is known from <CIT>) that Au-containing catalysts prepared by wet impregnation of a mixture of HAuCl<NUM> / aqua regia are active for the conversion of acetylene to VCM. The catalysts are believed to include gold particles having a metallic gold core and a shell of higher oxidation state species, including Au(I) and Au(III) which are believed to be the active species for the hydrochlorination reaction.

<CIT>) describes a development of catalysts based on HAuCl<NUM> by including a sulphur-containing ligand such as thiosulphate. It is thought that the sulphur-containing ligand forms a complex with the Au atoms thereby stabilizing Au(I) and Au(lll) which are the active species in the hydrochlorination reaction.

A further development of the above catalysts is described in <CIT>), in which an inorganic oxide, hydroxide, oxo-salt or oxo-acid is included in order to improve the resistance of the catalyst towards carbon nanotube formation.

VCM catalysts comprising a complex of gold with a thiosulphate ligand on a carbon support have been commercialised by Johnson Matthey under the brand PRICAT™ MFC. While these catalysts have been a commercial success, the very high initial activity of these catalysts in the extremely exothermic acetylene hydrochlorination reaction needs to be carefully optimised for a specific system. If the catalyst activity is too high initially then local hot spots may be formed in the catalyst bed which can cause deactivation. There is a need for alternative catalysts which have a more stable activity profile and which are less prone to initial overheating. The present invention addresses this problem.

The present inventors have found that catalysts with stable activity profiles which are less prone to initial overheating can be prepared by modifying the production method described in <CIT> and <CIT>. The methods exemplified in these references involve the formation of an aqueous impregnation solution containing a complex of gold with a sulphur-containing ligand which is applied onto a carbon support. The inventors have surprisingly found that the initial activity of the catalyst can be reduced by replacing the aqueous solvent of the impregnation solution with an organic solvent or a mixture of organic solvent and aqueous solvent. Without wishing to be bound by theory, this change is thought to alter wetting between the catalyst and the impregnation solution, which alters the dispersion of gold complex on the support.

In a first aspect the invention relates to a method of manufacturing a hydrochlorination catalyst, comprising the steps of:.

wherein the ligand is of Formula (I)
<CHM>
wherein.

<CIT> describes a method of producing hydrochlorination catalysts by combining gold, an organic solvent and a support material. In the examples of this reference catalysts are prepared by impregnating a solution of HAuCl<NUM>·<NUM><NUM>O in an organic solvent. An advantage of this method is that no ligand is required. The method according to the first aspect is similar to the method in <CIT>, but requires that impregnation is carried out using an impregnation solution containing a ligand in addition to the source of gold.

In a second aspect the invention relates to a catalyst comprising a complex of gold and a ligand of Formula (I)
<CHM>
wherein.

It is not yet fully understood whether catalysts comprising gold and a ligand of Formula I are coordination complexes (e.g. of formula Au[ligand]<NUM>-xClx where x = <NUM> to <NUM>) or adducts (e.g. [AuCl<NUM>]·ligand). It is possible that this varies depending on the choice of ligand. As used herein, the term "complex" covers both possibilities. For the avoidance of doubt, the oxidation state of Au within the complex may be +<NUM> or +<NUM>.

It is known that complexes of copper and nitrogen-containing ligands can be used as catalysts in the conversion of acetylene to VCM. <CIT> and <CIT> describe a method for producing a copper-based catalyst for the production of vinyl chloride. The method involves a step of impregnating a carbon support with an impregnation solution containing copper chloride and various additives, which may be nitrogen-containing ligands. <CIT> describes a comparative example, prepared by combining a solution of CuCl<NUM>. <NUM><NUM>O and N-methyl pyrrolidone (NMP) with activated carbon followed by drying and treatment with hydrogen chloride gas. To the inventors' best knowledge, analogous complexes of gold and NMP have not previously been described.

In a third aspect the invention relates to a process for the catalytic hydrochlorination of a substrate containing an alkyne unit, wherein the reaction is carried out in the presence of a catalyst according to the second aspect, or a catalyst produced by or producible by a method according to the first aspect.

The process is particularly suitable when acetylene is used as the substrate, to produce VCM. The conversion of acetylene to VCM is preferably carried out in the gas phase.

Herein all % relate to percentages by weight of the total catalyst, unless otherwise stated.

According to a first aspect of the invention, there is provided a method of manufacturing a hydrochlorination catalyst comprising the steps of:.

It is thought that in step (i) a complex is formed between the gold and the ligand. It is preferred that the impregnation solution is prepared by adding the ligand to a solution containing the source of gold and the solvent. However, it is also possible to add the source of gold to a solution containing the ligand and the solvent. It is also expected that the catalyst could be prepared by treating the support sequentially with the source of gold followed by the ligand, or vice versa.

The source of gold is typically a gold salt which is able to form a complex with the ligand. A preferred source of gold is HAuCl<NUM>, either as a solid (e.g. HAuCl<NUM>·<NUM><NUM>O) or as a solution (e.g. HAuCl<NUM> in HCl/water).

The solvent comprises an organic solvent which comprises or consists of acetone. The presence of an organic solvent in the impregnation solution is thought to alter wetting between the impregnation solution and the support, leading to improved dispersion of gold in comparison to when an aqueous solution of gold complex is used as the impregnation solution.

In some embodiments the solvent consists of acetone. This may be preferable where both the source of gold and the ligand are soluble in acetone.

In some embodiments the solvent comprises a mixture of an organic solvent and an aqueous solvent. This may be necessary where one of the source of gold or ligand are poorly soluble in the organic solvent. For example, where the source of gold is soluble in organic solvent but the ligand is poorly soluble in organic solvent, the ligand may be dissolved in aqueous solvent and then added to the solution of gold in organic solvent.

Suitable organic solvents are described in <CIT>, the contents of which are incorporated herein by reference.

In some embodiments it is preferred that the organic solvent has an ET(<NUM>) polarity ≤ <NUM>, such as ≤ <NUM>, ≤ <NUM> or ≤ <NUM>. ET(<NUM>) polarity is measured by the method described in <NPL>. Where the solvent comprises a mixture of organic solvents, or is a mixture of organic solvent(s) and water, the ET(<NUM>) polarity refers to the solvent as a whole.

In some embodiments it is preferred that the organic solvent has a boiling point of ≤ <NUM> at <NUM> atm, such as ≤ <NUM> or ≤ <NUM>.

The molar equivalents of ligand of Formula (I) added relative to gold is preferably from <NUM> : <NUM> to <NUM> : <NUM>, such as from <NUM> : <NUM> to <NUM> : <NUM>. Including more than <NUM> equivalents of ligand does not appear to have a detriment to the catalyst performance but is unfavoured on cost grounds. Using <NUM> molar equivalents of ligand is generally sufficient to fully complex the gold.

In step (ii) the support is impregnated with the impregnation solution formed in step (i). Impregnation techniques will be well known to those skilled in the art.

In step (iii) the catalyst is dried to remove the organic solvent. Drying techniques will be well known to those skilled in the art. A typical procedure involves heating the catalyst at a temperature of ≥ <NUM> for a period of <NUM> hours or more. A stream of gas may be used to help remove the organic solvent. It will be appreciated that the temperature and duration of drying will differ depending on the scale at which the preparation is carried out.

The invention also relates to catalysts comprising a complex of gold and a ligand of Formula (I)
<CHM>
wherein.

It is preferred that X is O. The use of ligands in which X is S tend to have lower activities compared to when X is O.

In one embodiment R is a C1 to C10 hydrocarbon group including one or more heteroatoms selected from halogen (F, Cl, Br, I), oxygen (e.g. OH) or nitrogen (e.g. NH<NUM>), e.g. a C1 to C6 hydrocarbon group. For example a C1-C6 hydrocarbyl group or a C1-C3 hydrocarbyl group, in each case including one or more heteroatoms selected from halogen (F, Cl, Br, I), oxygen (e.g. OH) or nitrogen (e.g. NH<NUM>). The presence of heteroatoms in group R may be beneficial to improve the solubility of the ligand in a high polarity solvent.

In one embodiment R is a C1 to C10 hydrocarbyl group consisting of C and H atoms only, e.g. a C1 to C6 hydrocarbyl group. For example a C1-C6 hydrocarbyl group or a C1-C3 hydrocarbyl group. The absence of heteroatoms in group R may be beneficial to improve the solubility of the ligand in a low polarity solvent.

It is preferred that R is H or Me, preferably R is Me. The use of ligands in which R is H tend to have lower activities compared to when R is Me.

Preferred ligands are N-methyl-<NUM>-pyrrolidone (NMP) and N-methyl-<NUM>-piperidone. These ligands show equivalent or better acetylene conversion than a comparative catalyst comprising a gold thiosulphate complex. NMP is a particularly preferred ligand.

For the avoidance of doubt, NMP has the following structure:
<CHM>.

The role of the ligand is to stabilise Au in the Au(I) or Au(III) oxidation state. The method of the present invention makes it possible to produce catalysts having a high dispersion of Au and a high proportion of Au(I) and Au(III) species, which are believed to be the active species for hydrochlorination.

The loading of Au is a trade-off between the cost of Au and the activity of the catalyst. A typical Au content for the catalyst is typically from <NUM> to <NUM> wt%, based on the weight of catalyst as a whole. Typically the loading of Au will be from <NUM> to <NUM> wt%, such as from <NUM> to <NUM> wt%, such as from <NUM> to <NUM> wt%.

In some embodiments, in addition to Au the catalyst may include one or more promoter metals. The presence of a promoter metal may improve the activity of the catalyst and/or help to maintain the activity of the catalyst over time. Suitable promoters include Group <NUM> and Group <NUM> metals, as well as cobalt, copper, lanthanum and cerium.

Any known catalyst support may be used to make the catalyst of the invention. Typical metal oxide supports such as alumina, silica, zeolite, silica-alumina, titania or zirconia and composites thereof may be used. It is preferred that the support is a carbon support. The carbon may be derived from natural sources (e.g. peat, wood, coal, graphitic) or may be a synthetic carbon. The carbon is preferably an activated carbon, activated for example by steam, acid, or otherwise chemically activated.

The support may be in the form of a powder, granules or shaped particles. Examples of shaped particles include spheres, tablets, cylinders, multi-lobed cylinders (e.g. trilobes), rings, miniliths etc. or a massive catalyst unit such as a monolith. Alternatively, the catalyst in the form of a powder may be included in a coating formulation and coated onto a reactor wall or shaped substrate such as a monolith. One preferred form of catalyst support comprises a plurality of shaped units in the form of cylinders, spheres or lobed cylinders each having a diameter of <NUM> - <NUM>, or, more preferably a diameter in the range <NUM> - <NUM>. In the case of a cross-section shape having a non-uniform diameter, such as a lobed cylinder, the diameter is an average diameter. Cylinders and trilobes are particularly preferred shapes of support.

It is envisaged that the catalysts of the present invention will be useful in any chemical process where gold containing catalysts are known to find utility. The catalysts are particularly suitable for hydrochlorination of compounds containing an alkyne moiety, especially for the conversion of acetylene to VCM.

The conversion of acetylene to VCM is typically carried out at elevated temperature, usually between about <NUM> and <NUM>. The reaction temperature is a balance between conversion and economics of running the reactor at higher temperatures. Furthermore, at temperatures significantly above <NUM> coking can become significant. Surprisingly, catalysts comprising a ligand of Formula (I) are active at lower temperatures than existing Au-based catalysts.

The HCI and acetylene are preferably premixed, and also preferably pre-heated to the reaction temperature. Normally HCI is present in excess of the amount required for the stoichiometric reaction. The catalyst may be present in the reactor in the form of a fixed bed of catalyst particles arranged such that the feed gases are passed over or through the catalyst bed. Alternative reactor arrangements may be used, including fluidised beds or other moving bed arrangements. The catalyst may alternatively be provided in the form of a monolith or coated on the wall of a reactor vessel. The catalyst bed may be provided with means to regulate the temperature to avoid overheating due to the exothermic reaction, or to raise the temperature, if required. It may be preferred to treat the catalyst with HCl before use in the process. This treatment is typically carried out by flowing HCI over the catalyst for a period of at least an hour at a temperature of at least <NUM>, more especially > <NUM>. This pre-treatment may take place in the reactor by operating with a flow of HCI without the acetylene, at a suitable temperature.

A sample of the catalyst (~ <NUM>) was loaded onto glass wool inside a reactor tube. A feed stream was prepared by combining <NUM>/min C<NUM>H<NUM> (<NUM>% acetylene in Argon), <NUM>/min HCI (<NUM>% HCI in Argon) and <NUM>/min Argon. The temperature of the feed stream was set at <NUM> unless otherwise specified. The acetylene conversion was determined by gas chromatography.

Catalyst E1 was prepared via an impregnation method. Activated carbon (NORIT ROX <NUM>) was initially ground and sieved (<NUM> mesh) to obtain a powder with a particle size < <NUM>. The gold precursor, HAuCl<NUM>·<NUM><NUM>O (solid from Alfa Aesar, <NUM>, assay <NUM>%) was dissolved in dry acetone (<NUM>) and allowed to stir for <NUM> mins. The solution was added drop-wise, with stirring, to the ground, activated, dry carbon powder (<NUM>). The solution was left to stir for <NUM> at room temperature and finally dried under nitrogen at <NUM> for <NUM>.

Examples <NUM> to <NUM> reported in Table <NUM> were prepared by the same method as described for Example <NUM>, modified as follows. The ligand was weighed into a vial. The solution of HAuCl<NUM>·<NUM><NUM>O in acetone was added to the ligand and the resulting solution was used for impregnation of the carbon powder as described in Example <NUM>. The ratio of Au : ligand (mol : mol) was <NUM> : <NUM>, <NUM> : <NUM> or <NUM> : <NUM>. The final Au loading was <NUM> wt%.

Ligands E3-E11 are not according to the present invention.

These catalysts were tested for their acetylene conversion following the general procedure. The results are shown in <FIG>. With the exception of E1 (no ligand), E2-<NUM> (NMP) and E10 (benzyl isothiocyanate) all of the catalysts deactivated during the course of the test.

The role of ligand equivalents for E2-<NUM>, E2-<NUM> and E2-<NUM> is compared in <FIG>. The performance was similar but in general E2-<NUM> > E2-<NUM> > E2-<NUM>.

An overlay of the <NUM>H NMR spectrum of NMP in d<NUM>-acetone and E2-<NUM> prepared in d<NUM>-acetone is shown in <FIG>. All of the peaks associated with NMP are shifted in the complex suggesting that the NMP is coordinated.

The activity of Example E2-<NUM> was tested at temperatures of <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>. The results are shown in <FIG>. Activity increased with increasing temperature. Although the acetylene conversion was highest at <NUM>, the amount of acetylene converted did not correspond to the amount of VCM produced. It is thought that this discrepancy is related to the formation of coke at high temperatures.

The catalysts in Table <NUM> were prepared following the same procedure as Examples <NUM>-<NUM> using <NUM> equivalents of the ligand. The final Au loading was <NUM> wt%.

Ligands E15-E18 are not according to the present invention.

These catalysts were tested for their acetylene conversion following the general procedure. The results are shown in <FIG>. Catalyst E2-<NUM> containing the NMP ligand showed the highest activity of all catalysts and had an activity which was relatively stable over time. Catalyst E12 containing the N-methyl-<NUM>-piperidone ligand also showed good activity which was relatively stable, but slightly less active than E1 containing thiosulphate ligands.

The other catalysts were less active and, in the case of E13 containing <NUM>-pyrrolidinone and E15 containing <NUM>-methylpyrrolidine, showed gradual deactivation from the start.

Catalysts containing <NUM>% Au, in each case as a complex with thiosulphate ligand, were prepared by the following procedure.

Activated carbon (NORIT ROX <NUM>) was ground to a powder and sieved to < <NUM> micron. Ammonium thiosulphate (<NUM>) and CaCl<NUM> (<NUM>) were dissolved in <NUM> demineralized water. An HAuCl<NUM> solution (Johnson Matthey, <NUM> Au, assay <NUM>%) was diluted with <NUM> demineralized water and this solution as added to the ammonium thiosulphate containing solution. The carbon powder (<NUM> dry weight) was impregnated with the gold containing solution by an incipient wetness technique. The impregnated mass was allowed to stand for <NUM> and then dried in air at <NUM> for <NUM> to obtain catalyst E19.

Activated carbon (NORIT ROX <NUM>) ground to a powder and sieved < <NUM> micron). Ammonium thiosulphate (<NUM>) was dissolved in <NUM> demineralized water. An HAuCl<NUM> solution (Johnson Matthey, <NUM> Au, assay <NUM>%) was diluted with <NUM> acetone and this solution as added to the ammonium thiosulphate containing solution. The carbon powder (<NUM> dry weight) was impregnated with the gold containing solution by an incipient wetness technique. The impregnated mass was allowed to stand for <NUM> at room temperature in flowing air and then dried in air at <NUM> for <NUM> to obtain catalyst E20.

Catalyst testing was carried out using a fritted reactor tube. <NUM> of SiC was placed on the frit followed by <NUM> of the catalyst. A sample of the catalyst (~ <NUM>) was loaded onto glass wool inside a reactor tube. A feed stream was prepared by combining (<NUM>/min acetylene (<NUM>% acetylene in Argon)) and <NUM>/min HCI (<NUM>% HCI in Argon). The temperature of the feed stream was set at <NUM> unless otherwise specified. The acetylene conversion was determined by gas chromatography. The results are shown in <FIG>.

The catalyst prepared using an aqueous impregnation solution with <NUM>% Au (E19) originally showed ~ <NUM>% conversion and stabilised at ~ <NUM>% conversion. The stable value was ~ <NUM>% of the initial activity.

In contrast, the catalyst prepared using an acetone/water impregnation solution (E20) originally showed ~ <NUM>% conversion and stabilised at ~ <NUM>% conversion. The stable value was ~ <NUM>% of the initial activity. This catalyst showed a much more stable activity profile without high initial activity. This is expected to be advantageous in avoiding local hot-spots on initial activation of the catalyst.

A catalyst containing <NUM>% Au (E21) was prepared following the procedure used to produce E20, except that aqueous solution of ammonium thiosulphate was replaced by a solution of sodium thiocyanate (<NUM>) dissolved in <NUM> acetone. The solution of the HAuCl<NUM> solution was diluted with <NUM> acetone rather than <NUM>. The solutions were mixed together and immediately used to impregnate the carbon powder.

A catalyst containing <NUM>% Au (E22) was prepared following the procedure used to produce E21, except that <NUM> Au as HAuCl<NUM> solution was used instead of <NUM> Au as HAuCl<NUM> solution. aqueous solution of ammonium thiosulphate was replaced by a solution of sodium thiocyanate (<NUM>) dissolved in <NUM> acetone. The solution of the HAuCl<NUM> solution was diluted with <NUM> acetone rather than <NUM>. The solutions were mixed together and immediately used to impregnate the carbon powder.

The results are shown in <FIG>. In each case, the catalyst showed a stable activity profile without an initial spike in catalyst activity. This is expected to be advantageous in avoiding local hot-spots during initial activation of the catalyst.

Acetone (<NUM>) was added to <NUM> of a solution of HAuCl<NUM> (<NUM>% Au) containing <NUM> Au. To this solution was added a solution containing <NUM> molar equivalents of N-methyl pyrrolidine (<NUM>) in <NUM> acetone. The resultant solution was mixed and allowed to react for <NUM>. Thereafter the solution was evaporated under vacuo to give an oily residue. After washing with aliquots of cyclohexane a solid product was obtained and recrystallised from <NUM>-propanol - cyclohexane to yield a crop of fine bright yellow needles in high yield. Needle shaped single crystals suitable for X-ray crystal structure analysis were obtained by slow crystallisation from <NUM>-propanol - cyclohexane.

Elemental analysis calculated for AuC<NUM>Cl<NUM>H<NUM>N<NUM>O<NUM> requires Cl, <NUM>%; C, <NUM>%; H, <NUM>%; N, <NUM>%; found Cl, <NUM>%; C, <NUM>%; H, <NUM>%; N, <NUM>%.

Single crystal structure determination by X-Ray diffraction analysis at <NUM> using radiation with a wavelength of <NUM>Å showed that the material had the following properties: monoclinic, space group P2<NUM>/n, a = <NUM>(<NUM>) Å, b = <NUM>(<NUM>) Å, c = <NUM>(<NUM>) Å, α = <NUM> °, β = <NUM>(<NUM>) °, γ = <NUM> °, Z = <NUM>, crystal dimensions <NUM> x <NUM> x <NUM><NUM>. A total of <NUM> independent reflections were collected.

Claim 1:
A method for the production of a hydrochlorination catalyst, comprising the steps of:
i) preparing an impregnation solution by combining a source of gold and a ligand in a solvent, wherein the solvent comprises an organic solvent which comprises or consists of acetone;
ii) impregnating a support with the impregnation solution from step (i); and
iii) drying the product of step (ii) to obtain the catalyst;
wherein the ligand is of Formula (I)
<CHM>
wherein
X is O or S;
n is <NUM> or <NUM>;
R is H or a C1 to C10 hydrocarbon group optionally including one or more heteroatoms selected from halogen (F, Cl, Br, I), oxygen or nitrogen.