Catalyst, process for catalyst manufacture and process for catalytic

oxidative dehydrogenation

This application claims priority to European application No. 11194574.7 filed on December 20, 2011, the whole content of this application being incorporated herein by reference for all purposes.

The present invention relates to a catalyst, a process for the manufacture of said catalyst and a process for catalytic oxidative dehydrogenation using said catalyst.

Lower alkenes, such as ethene and propene, are important starting materials for the production of petrochemicals and fine chemicals. Presently, ethene can be industrially obtained from thermal steam cracking of ethane which does not involve catalysis translating to an expensive high temperature production process with limited energy efficiency and frequent production interruption. The process is strongly endothermic and has to be performed at temperatures around and above 800°C. Furthermore, several products are formed (various saturated and unsaturated hydrocarbons) leading to the necessity of a complex separation of product streams. Severe coke formation additionally leads to further problems, as the heat transfer from the heat source to the reacting medium is deteriorated. Thus, a selective burning of the coke is necessary in regular intervals. An additional problem is that nitrous oxides (NOx) are formed due to the very high reaction temperatures in the external burners.

Alternatives for the production of lower alkenes are catalytic processes, one of which being the catalytic dehydrogenation of lower alkanes. However, the dehydrogenation ^' s thermodynamic constraints lead to unfavorable low alkane conversion. Furthermore, coking is a major problem of the process which causes rapid catalyst deactivation.

Another catalytic process for the production of lower alkenes is oxidative dehydrogenation (ODH) of lower alkanes. ODH is exothermic and can be operated at temperatures <650°C, which can reduce the required energy input. Involving catalysis, specifically in ODH of ethane, could thus yield a highly energy efficient process with long continuous plant operation and a very narrow product spectrum. The reaction forms mainly ethene and water as products provided suitable stable catalysts with ideal selectivity are available for ODH of ethane. Hence, the process is in principle suitable to selectively produce ethene without complex separation of the products, as water can be condensed out of the product stream.

Catalysts that can activate ethane effectively, while maintaining high ethene selectivity are highly desirable. Several classes of catalysts have been reported in the literature for ODH of alkanes. The most common catalysts for ODH of ethane are reducible metal oxides, i.e. MoVNb mixed oxides. Those catalysts mainly produce ethene, but their activity decreases when catalyst poisons are present in the feed streams of the process.

Supported alkali metal oxide catalysts belong to another class of catalysts active for ODH, particularly also for ODH of ethane. Activity and selectivity could be improved doping these catalysts with secondary chloride salts.

Furthermore, the activity could be improved by doping the support with Dy203 (Gaab, S.; Find, J.; Mueller, T. E.; Lercher, J. A., Kinetics and mechanism of the oxidative dehydrogenation of ethane over Li/Dy/Mg/0/(Cl) mixed oxide catalysts. Top. Catal. 2007, 46, 101; Conway, S. J.; Wang, D. J.; Lunsford, J. H., Selective oxidation of methane and ethane over Li+-MgO-Cl- catalysts promoted with metal oxides. Applied Catalysis A: General 1991, 79, LI).

Catalysts with binary combinations of LiCl and an alkali (sodium or potassium) chloride or an earth alkali (strontium or barium) chloride on

Dy203/MgO supports were also tested in ODH of ethane. Catalysts containing additional alkali (sodium or potassium) or alkaline earth metal (strontium or barium) chlorides besides LiCl exhibited a high selectivity to ethene once reaction temperatures exceed the melting point of the salt combinations, however, at lower activity for ODH of ethane as compared to the case when only LiCl was deposited on the support (Tope, B.; Zhu, Y.; Lercher, J. A. Oxidative dehydrogenation of ethane over Dy203/MgO supported LiCl containing eutectic chloride catalysts. Catalysis Today 2007, 123, 1 1).

To meet the industrial needs of lower alkenes, i.e. C2-C4-alkenes, particularly ethene and propene, there is a demand for new catalysts applicable in ODH. Improvements are desired in various aspects of the catalysts, such as e.g. activity, selectivity, stability of the catalyst, applicability under certain reaction conditions, e.g. resilience against catalyst poisons being present, ease of manufacturing etc.

The present invention thus provides as a first aspect a new catalyst as defined in the claims. It has surprisingly been found that the catalyst according to the present invention resolves aforementioned and other problems. In particular, the present invention provides a new catalyst that is active and selective in ODH, particularly in ODH of ethane to ethane. The new catalyst, e.g., enables the production of ethene even with selectivities up to 97% with still high conversion levels.

Surprisingly, it was furthermore found that the catalyst of the present invention is not poisoned by catalyst poisons such as chlorinated hydrocarbons, particularly 1,2-dichloroethane. While, e.g., 1 ,2-dichloroethane is known to notably deteriorate the catalytic performance of several catalysts of the literature, no deactivation occurs for the catalyst of the present invention, but catalytic activity is even boosted. The novel catalysts are thus suitable for ODH processes, wherein a chlorine containing hydrocarbon is present in the gas phase contacting the catalyst during the process. The chlorine containing hydrocarbon is particularly 1,2-dichloroethane (DCE) and more specifically, DCE coming from a gas stream recycled in a DCE manufacturing process including an ODH step of ethane to ethene.

The catalyst of the first aspect of the present invention comprises a mixture of 3 or more different chlorides, which are selected from alkali chlorides and/or earth alkali chlorides, on a support which is not inert and comprises an oxide of a metal different from Al and Zn.

By the terms "not inert" is meant that said support participates to

(promotes) chemical reactions, preferably ODH reactions, and preferably ODH of ethane in ethylene. In that case, supports promoting the dissociation of oxygen molecules into atomic oxygen are preferred.

In one embodiment, the catalyst of the present invention comprises a mixture of 3 or more different chlorides selected from alkali chlorides.

Preferably, the catalyst of the present invention comprises LiCl, eventually LiCl and RbCl, or LiCl and CsCl.

In one embodiment, the catalyst of the present invention comprises a mixture of 4 or more different chlorides, which are selected from alkali chlorides and/or earth alkali chlorides, on a support.

In one embodiment, the catalyst of the present invention comprises a mixture of 4 or more different chlorides selected from alkali chlorides. A catalyst according to a preferred embodiment of the invention comprises LiCl, and eventually also KC1, NaCl and RbCl. Preferably, the present invention relates to a catalyst which comprises no transition metal, more preferably: which comprises no member of the group consisting of molybdenum, nickel, tin, zinc, cobalt, platinum, and aluminum. In the present invention the term member refers to the member in its elemental state as well as to any compound containing the member. The catalyst of the present invention can be for example a catalyst, which does not comprise elemental platinum and which does not comprise a platinum containing compound, such as PtCl ₂ . In another embodiment, the present invention relates to a catalyst, wherein the catalyst comprises no member of the group consisting of molybdenum, nickel, tin, zinc, cobalt, platinum, and aluminum. In another embodiment, the present invention relates to a catalyst, wherein the catalyst comprises no member of the group consisting of molybdenum, nickel, tin, zinc, cobalt, platinum, aluminum, copper and manganese. In another embodiment, the catalyst of the present invention relates to a catalyst, wherein the catalyst comprises no member of the group consisting of platinum and aluminum. In still another embodiment, the catalyst comprises no copper.

Preferably, the catalyst of the present invention comprises a eutectic mixture of at least 3, or 4, or more different chlorides, which are selected from alkali chlorides and/or earth alkali chlorides, on the support. Preferred catalysts according to the present invention thus are e.g. catalysts comprising a eutectic mixture of LiCl and KC1 and RbCl and CsCl, LiCl and KC1 and CsCl, LiCl and RbCl and CsCl, LiCl and KC1 and NaCl and RbCl, LiCl and CsCl and SrCl ₂ , LiCl and NaCl and RbCl, LiCl and NaCl and CsCl, LiCl and KC1 and BaCl ₂ , or LiCl and KC1 and NaCl on a support. In certain embodiments, catalysts of the present invention, therefore comprise a eutectic mixture of LiCl(0.555) and

KC1(0.187) and RbCl(0.014) and CsCl(0.243), LiCl(0.575) and KC1(0.133) and CsCl(0.292), LiCl(0.565) and RbCl(0.285) and CsCl(0.055), LiCl(0.504) and KC1(0.183) and NaCl(0.080) and RbCl(0.233), LiCl(0.582) and CsCl(0.398) and SrC12(0.02), LiCl(0.566) and NaCl(0.024) and RbCl(0.41), LiCl(0.581) and NaCl(0.017) and CsCl(0.403), LiCl(0.580) and KC1(0.400) and BaCl ₂ (0.060) , or LiCl(0.403) and KC1(0.240) and NaCl(0.330) on a support, whereby the number in brackets indicates the mole fraction of the respective salt (e.g. LiCl) in each of the described eutectic mixtures (e.g. LiCl and KC1 and RbCl) which are deposited on a support.

By "eutectic mixture" should be understood that the chlorides of the mixture should be present in the ratio at which the mixture solidifies at a lower temperature than any other composition (at a certain pressure). The presence of other salts, oxides... besides the chlorides forming a eutectic mixture together, should however not be excluded from the scope of the invention. The same applies to mixtures where the ratio is different from the eutectic ratio, especially if when heating them, a molten phase with the eutectic composition would form besides a solid phase.

Catalysts comprising a eutectic mixture of LiCl and RbCl and BaCl ₂ or LiCl and NaCl and RbCl are e.g. preferred embodiments of the catalyst of the present invention. In ODH of ethane, high ethane conversion levels are achieved and ethene selectivities above 90% can be obtained using these catalysts. A catalyst comprising a eutectic mixture of LiCl and KC1 and NaCl and RbCl is another preferred embodiment of the catalyst of the present invention. Such catalyst enables the production of ethene with a selectivity of more than 95% at a conversion level around 40%> at 550°C.

In a preferred embodiment the catalyst of the present invention is a catalyst, wherein 3, or 4, or more different chlorides, which are selected from alkali chlorides and/or earth alkali chlorides, are comprised in a shell on the support which builds a core. The catalyst thus exhibits a core-shell structure, wherein the shell constitutes a coating on the support. The core is thus covered partially or preferably entirely by the shell. When the core is entirely covered by the shell, the shell is also termed to be a "closed shell" in the present invention.

In one embodiment, the catalyst of the present invention is a catalyst, wherein 3, or 4, or more different chlorides, which are selected from alkali chlorides and/or earth alkali chlorides, are comprised in or form a closed shell on the support which builds a core. Preferably, the catalyst comprises LiCl, KC1, NaCl and RbCl in this embodiment.

Preferably, the shell of the catalyst of the present invention consists of the above mentioned chlorides.

The catalyst of the present invention, which may exhibit a core-shell structure, has for example a particle size from 100 nm to 100 μιη.

In one embodiment of the present invention, the eutectic mixture of at least 3, or 4, or more different chlorides, which are selected from alkali chlorides and/or earth alkali chlorides, has a melting point lower than 360°C whereas in another embodiment it has a melting point lower than 330°C, and in yet another embodiment it has a melting point lower than 300°C. Melting of the salts comprised in the shell may also by accompanied by spreading of the molten salts on the support, thus forming a closed shell. A low melting point helps to the full coverage of the oxide core, thus leading to high selectivity.

The support of any of the afore described catalysts comprises a metal oxide, said metal being different from Al and Zn. It has namely been found that the oxides of these metals are inert i.e. do not participate to ODH reactions.

Preferably, the support comprises MgO, Zr0 ₂ , Si0 ₂ and/or Ti0 ₂ , more preferably MgO, Zr0 ₂ or Ti0 ₂ , MgO being more preferred. It can also be advantageous that the support is doped with a lanthanide metal oxide (i.e. contains a small amount of lanthanide metal oxide in its lattice), preferably dysprosium oxide, lanthanum oxide, neodymium oxide, samarium oxide, cerium oxide and/or holmium oxide. Oxides of lanthanum, neodymium, samarium and cerium are cheaper than those of dysprosium and holmium, but the latter perform slightly better. The lanthanide metal oxide is then preferably present in an amount that is sufficient to substantially increase e.g. the ethene yield in a process for ODH of ethane when compared with the yield that can be achieved with a catalyst comprising no lanthanide metal oxide in the support. A preferred catalyst of the invention is thus for instance a catalyst, wherein the support comprises MgO and is doped with a lanthanide metal oxide. The atomic ratio of Mg and the lanthanide metal comprised in the doped catalyst can be between 500: 1 and 5:1, preferably between 200: 1 and 25: 1 or more preferably between 100: 1 and 30: 1. Most preferably it is about 50: 1.

In one embodiment, the catalyst of the present invention is a catalyst, wherein the support does not comprise aluminum. In an even more preferred embodiment, the support consist essentially of (i.e. is "pure" except for less than 5wt% impurities preferably less than 2wt% and even more preferably, less than lwt %) MgO eventually doped with a lanthanide oxide.

The support preferably has a mean particle size (average diameter preferably before calcination, the case being) comprised between 1 and 500 μιη, more preferably between 10 and 100 μιη and even more preferably, 20 and 60 μιη.

The support preferably has a BET surface (preferably before calcination, the case being) comprised between 10 and 500 m ² /g, more preferably between 50 and 150 and even more preferably, 80 and 120 m ² /g.

The support preferably has a pore volume (preferably before calcination, the case being) comprised between 0.01 and 5 cm ³ /g, more preferably between 0.1 and 1 and even more preferably, 0.2 and 0.4 cm ³ /g. In one embodiment, the catalyst of the present invention does not comprise chlorides other than alkali and/or earth alkali chlorides.

The total chloride concentration in the catalyst of the present invention can e.g be 1-50 wt-%, preferably 10-30 wt-% and most preferably about 20 wt-% each based on the weight of the support. In a preferred embodiment of the present invention the total chloride concentration in the catalyst is thus 10- 30 wt-%) based on the weight of the support preferably consisting of (eventually doped) MgO.

The present invention also relates to the use of a catalyst as described above, in a catalytic reaction in conditions such that the mixture of chlorides is molten. A particularly preferred embodiment of that use is one wherein said catalyst exhibits a core-shell structure and wherein the molten chlorides mixture is a eutectic mixture which constitutes or forms part of a closed shell on the support which builds a core (the former embodiment being preferred).

The catalyst of the present invention can be prepared by putting the support in a bath of the chloride mixture in molten state. Such a method is however limited to monolithic supports (as opposed to those in particulate form).

Alternatively, the catalyst of the present invention can be prepared by impregnating the support in an aqueous phase, or by simply milling the support and the chloride together.

The catalyst of the present invention can be prepared in analogy to the methods as known by the skilled person by preparing a dispersion of the support materials in an aqueous phase and adding the metal nitrates as precursors (termed "nitrate method" for the purpose of the present invention) and HCI/NH ₄ CI as chloride source, followed by evaporative separation from water, drying and calcination for 12 h at 650°C-700°C in synthetic air. However, this process has several disadvantages. The use of HC1 can cause HC1 losses while adding it to the synthesis mixture. This can cause wrong metal -chloride ratios during the further production of the catalysts.

Hence, as a further aspect, the present invention also relates to a novel process for the manufacture of a catalyst of the present invention (as described above). The process is described in the claims. The invention thus relates to a process for the manufacture of a catalyst of the present invention, said process comprising (a) mixing at least 3, or 4, or more different chlorides, which are selected from alkali chlorides and/or earth alkali chlorides with an aqueous dispersion of support material(s),

(b) separating the water from the mixture, and

(c) calcining the residue obtained after separation from water.

For the purpose of the present invention, the novel process is also termed "chloride method" herein.

The catalyst prepared according to the above described method e.g. shows high ethene selectivities. The new process can also benefit from more exact metal/chloride ratios than obtained with the previously known process.

Additional sources of chloride in the process for manufacture can be avoided, which is particularly beneficial for large scale industrial applications, e.g. in order to simplify the manufacturing process.

The mixing can for instance take place at room temperature (20-25°) or at an elevated temperature from 50 to 150 °C, such as e.g. 80°C and the mixing time can be e.g. from 0.5 to 10 h, preferably between 1 to 5 h. Usually, it is sufficient to mix for 2 h, or even less. From an industrial point of view, this time can be adjusted to the minimum required.

In step (b) of the process of the second aspect of the present invention, the water is separated from the mixture obtained in step (a). This is usually done by evaporating the water from the mixture. For instance, evaporation of the water is conducted under reduced pressure and at elevated temperatures. In one embodiment of the present invention, the water is e.g. evaporated under reduced pressure at 50°C and the obtained residue is then dried, e.g. at an elevated temperature (e.g. 120°C) for several hours (e.g. 12 h).

The process of the present invention can also optionally include a calcination step to enable a better distribution of the chloride phase over the support. Preferably, the calcination step takes place at a temperature above the melting point of the (preferably eutectic) chloride mixture. A temperature above 500 °C, or even above 600°C is preferred. Good results have been obtained at a temperature of about 650°C. In this case, the duration of calcination is typically in the range of hours, namely generally from 4 to 24 h, more preferably from 10 to 15 h. It can further be advantageous to conduct calcination in a stream of air. In some embodiments, the residue obtained from step (b) is crushed and/or sieved before calcining or after calcining or before and after calcining. Calcining is furthermore preferably conducted at 400-800°C, more preferably at 550- 650 °C. Most preferred is calcination at about 650°C, preferably over several hours.

In the process for manufacture of a catalyst of the present invention, preferably no precursors are used i.e. no HC1 and no NH ₄ C1 are used, and preferably also, no nitrate(s) are used but instead: the metal/alkali chlorides are used directly for impregnating the support.

Catalysts obtained by the novel process of the present invention are preferred catalysts of the present invention.

According to another aspect, the present invention concerns a process for catalytic oxidative dehydrogenation (ODH) as described in the claims. The present invention thus relates to a process for catalytic ODH using a catalyst of the present invention. In a preferred embodiment, the present invention relates to a process for catalytic oxidative dehydrogenation of C2-C4 alkanes, particularly ethane and propane using a catalyst of the present invention.

A particularly preferred embodiment of the process of the present invention is a process for catalytic ODH of ethane to ethene using a catalyst of the present invention. The term catalytic oxidative dehydrogenation of ethane, is understood to mean a partial oxidation of ethane by oxygen in the presence of the above mentioned catalyst.

The process for catalytic ODH, particularly of ethane to ethene, may take place either at a temperature above 650°C and below the range of thermal cracking temperatures, or at a temperature less than or equal to 650°C. It is preferred that the process for catalytic ODH, particularly of ethane to ethene, using a catalyst of the present invention takes place at temperatures of less than or equal to 650°C. Lower reaction temperatures are desired, as unselective side reactions (radical-based total oxidation of hydrocarbons) can be suppressed.

The present invention also concerns a process for catalytic ODH wherein a chlorine containing hydrocarbon is present in the gas phase contacting the catalyst during the process. In one embodiment, the present invention thus also relates to a process for catalytic ODH, preferably of ethane to ethene, using a catalyst of the present invention, in which 1 ,2-dichloroethane (DCE) is present in the gas phase contacting the catalyst during the process, in particular in an amount up to 1000 ppm. It is namely so that some processes for manufacturing DCE from ethene integrate a step of making at least part of said ethene by ODH of ethane and include a step of recycling at least part of the unconverted ethane which is separated from the DCE, to the ODH stage. Hence, according to another aspect, the present invention concerns a process for the manufacture of 1 ,2-dichloroethane (DCE) comprising an ODH step of ethane to ethene as described above, a subsequent chrorination and/or oxychlorination step of the ethene and preferably, a recycling step of the unconverted ethane to the ODH step.

In a first sub-embodiment, the invention thus relates to a process for the manufacture of DCE starting from a stream of ethane according to which:

(a) the stream of ethane is subjected to an ODH step as described above

producing a gas mixture containing ethene, unconverted ethane, water and secondary constituents;

(b) said gas mixture is optionally washed and dried thus producing a dried gas mixture;

(c) after an optional additional purification step, the dried mixture is then

conveyed to a chlorination reactor supplied with a flow of chlorine so that at least 10% of the ethene is converted to 1 ,2-dichloroethane;

(d) the 1 ,2-dichloroethane formed in the chlorination reactor is optionally

isolated from the stream of products derived from the chlorination reactor;

(e) the stream of products derived from the chlorination reactor, from which the 1,2-dichloroethane has optionally been extracted, is conveyed to an oxychlorination reactor in which the majority of the balance of ethene is converted to 1,2-dichloroethane, after optionally having subjected the latter to an absorption/desorption step e'), during which the 1,2-dichloroethane formed in the chlorination reactor is optionally extracted if it has not previously been extracted;

(f) the 1,2-dichloroethane formed in the oxychlorination reactor is isolated from the stream of products derived from the oxychlorination reactor and is optionally added to the 1 ,2-dichloroethane formed in the chlorination reactor; (g) the stream of products derived from the oxychlorination reactor, from which the 1 ,2-dichloroethane has been extracted, optionally containing an additional stream of ethane previously introduced in one of steps b) to f), is optionally recycled to step a) after having been optionally purged of gases and/or after an optional additional treatment in order to eliminate the chlorinated products contained therein.

Such a process is described in the patent application WO 2008/000705 to the Applicant, the content of which is incorporated by reference in the present application. In a second sub-embodiment, the invention relates to a process for the manufacture of DCE starting from a stream of ethane according to which:

(a) the stream of ethane is subjected to an ODH step as described above

producing a gas mixture containing ethene, unconverted ethane, water and secondary constituents;

(b) said gas mixture is optionally washed and dried thus producing a dried gas mixture;

(c) after an optional additional purification step, said dried gas mixture is

subjected to an absorption Al which consists of separating said gas mixture into a fraction enriched with the compounds that are lighter than ethene containing some of the ethene (fraction A) and into a fraction Fl;

(d) fraction A is conveyed to a chlorination reactor in which most of the ethene present in fraction A is converted to 1 ,2-dichloroethane and optionally the

1 ,2-dichloroethane obtained is separated from the stream of products derived from the chlorination reactor;

(e) optionally the stream of products derived from the chlorination reactor, from which the 1 ,2-dichloroethane has optionally been extracted, is subjected to an absorption A2 which consists of separating said stream into a fraction enriched with ethane F2 which is then conveyed back to fraction Fl, and into a fraction enriched with compounds that are lighter than ethane F2';

(f) fraction Fl , optionally containing fraction F2 recovered in step e) of

absorption A2, is subjected to a desorption D which consists of separating fraction Fl into a fraction enriched with ethene (fraction B) and into a fraction F3, optionally containing the 1 ,2-dichloroethane formed in the chlorination reactor then extracted if it has not been extracted previously, which is recycled to at least one of the absorption steps, optionally after an additional treatment intended to reduce the concentration of compounds that are heavier than ethane in fraction F3;

(g) fraction B is conveyed to an oxychlorination reactor in which most of the ethene present in fraction B is converted into 1 ,2-dichloroethane, the

1 ,2-dichloroethane obtained is separated from the stream of products derived from the oxychlorination reactor and is optionally added to the

1 ,2-dichloroethane formed in the chlorination reactor; and the stream of products derived from the oxychlorination reactor, from which the 1 ,2- dichloroethane has been extracted, optionally containing an additional stream of ethane previously introduced in one of steps b) to g), is optionally recycled to step a) after having been optionally purged of gases and/or after an optional additional treatment in order to eliminate the chlorinated products contained therein.

Such a process is described in the patent application WO 2008/000702 to the Applicant, the content of which is incorporated by reference in the present application.

In a third sub-embodiment, the invention relates to a process for the manufacture of 1 ,2-dichloroethane starting from a stream of ethane according to which:

(a) the stream of ethane is subjected to an ODH step as described above

producing a gas mixture containing ethene, unconverted ethane, water and secondary constituents;

(b) said gas mixture is optionally washed and dried thus producing a dried gas mixture;

(c) after an optional additional purification step, said dried gas mixture

comprising the stream of products derived from the chlorination reactor R2 separated in step e) is subjected to an absorption A which consists of separating said gas mixture into a fraction enriched with the compounds that are lighter than ethene containing some of the ethene (fraction A) and into a fraction Fl;

(d) fraction A is conveyed to a chlorination reactor Rl in which most of the ethene present in fraction A is converted into 1 ,2-dichloroethane and the 1 ,2-dichloroethane obtained is separated from the stream of products derived from the chlorination reactor Rl;

(e) fraction Fl is subjected to a desorption Dl which consists of separating fraction Fl into an ethene fraction depleted of the compounds that are lighter than ethene (fraction C) which is conveyed to a chlorination reactor R2, the stream of products derived from this reactor being added to the dried gas mixture subjected to step c) after having optionally extracted the 1 ,2-dichloroethane formed, and into a fraction F2;

(f) fraction F2 is subjected to a desorption D2 which consists of separating fraction F2 into a fraction enriched with ethene (fraction B) and into a fraction F3, optionally containing the 1 ,2-dichloroethane formed in the chlorination reactor R2 then extracted, if it has not previously been extracted, which is recycled to the absorption A, optionally after an additional treatment intended to reduce the concentration, in fraction F3, of the compounds that are heavier than ethane;

fraction B is conveyed to an oxychlorination reactor in which most of the ethene present in fraction B is converted into 1 ,2-dichloroethane, the

1 ,2-dichloroethane obtained is separated from the stream of products derived from the oxychlorination reactor and is optionally added to the 1 ,2-dichloroethane formed in the chlorination reactor Rl and optionally to that formed in the chlorination reactor R2; and the stream of products derived from the oxychlorination reactor, from which the 1 ,2- dichloroethane has been extracted, optionally containing an additional stream of ethane previously introduced in one of steps b) to g), is optionally recycled to step a) after having been optionally purged of gases and/or after an optional additional treatment in order to eliminate the chlorinated products contained therein.

Such a process is described in the patent application WO 2008/000693 to the Applicant, the content of which is incorporated by reference in the present application.

In the case a stream of ethane coming from a process according to any of the embodiments described above is recycled in step a) thereof (either in a continuous, loop process (which is generally the case in an industrial process) or in a batch one), the ODH step according to the invention is not detrimentally influenced by residual amounts of DCE in said stream.

The DCE obtained by (oxy) chlorination of ethene as described above may then be converted into VC (Vinyl Chloride). The invention therefore also relates to a process for the manufacture of VC. Namely, in this process, the 1 ,2- dichloroethane obtained as described above is subjected to a pyrolysis thus producing VC.

The conditions under which the pyrolysis may be carried out are known to a person skilled in the art. This pyrolysis is advantageously achieved by a reaction in the gas phase in a tube furnace. The usual pyrolysis temperatures extend between 400 and 600°C with a preference for the range between 480°C and 540°C. The residence time is advantageously between 1 and 60 seconds with a preference for the range of 5 to 25 seconds. The conversion rate of the DCE is advantageously limited to 45 to 75 % in order to limit the formation of by- products and fouling of the furnace pipes. The following steps make it possible, using any known device, to collect the purified VC and the hydrogen chloride to be upgraded preferably in the oxychlorination. Following purification, the unconverted DCE is advantageously reconveyed to the pyrolysis furnace.

In addition, the invention also relates to a process for the manufacture of PVC (Polyvinyl Chloride) by polymerisation of the VC obtained as described above.

The process for the manufacture of PVC may be a bulk, solution or aqueous dispersion polymerization process, preferably it is an aqueous dispersion polymerization process.

The expression "aqueous dispersion polymerization" is understood to mean radical polymerization in aqueous suspension and also radical

polymerization in aqueous emulsion and polymerization in aqueous

microsuspension.

The expression "radical polymerization in aqueous suspension" is understood to mean any radical polymerization process performed in aqueous medium in the presence of dispersants and oil-soluble radical initiators.

The expression "radical polymerization in aqueous emulsion" is understood to mean any radical polymerization process performed in aqueous medium in the presence of emulsifiers and water-soluble radical initiators.

The expression "polymerization in aqueous microsuspension", also called polymerization in homogenized aqueous dispersion, is understood to mean any radical polymerization process in which oil- soluble initiators are used and an emulsion of monomer droplets is prepared by virtue of a powerful mechanical stirring and the presence of emulsifiers.

In relation to a similarly simplified thermal cracking process, the process according to the invention making use of an ODH step has the advantage of combining an endothermic step (ethane converted into ethene) with an exothermic water production step, of taking place at a moderate temperature and of avoiding having to provide the heat of reaction at a high temperature.

The process according to the invention also has the advantage of making it possible to recycle the stream of products derived from the oxychlorination, from which the DCE has been extracted, to the ODH step, thus ensuring an increased conversion of ethane into ethene. Furthermore, given the moderate temperature of the ODH relative to thermal cracking, even if this recycled stream contains traces of chlorinated organic products such as DCE, their presence does not cause material behaviour and corrosion problems as occur in the case of thermal cracking above 800°C. The presence of chlorinated products may furthermore be advantageous in so far as it allows an increase of the efficiency of the ODH reaction.

The process according to the invention has the advantage of not generating (starting from ethane) compounds comprising at least 3 carbon atoms in troublesome amounts, these compounds generally being responsible for a certain inhibition during the pyrolysis of the DCE. This inhibition is due to the formation of derivatives such as 1 ,2-dichloropropane and monochloropropenes. Their aptitude for forming stable allyl radicals explains their powerful inhibitory effect on the pyrolysis of DCE which is carried out by the radical route. The formation of these by-products containing 3 carbon atoms and heavier byproducts furthermore constitutes an unnecessary consumption of reactants in the oxychlorination and in the chlorination, or generates costs for destroying them. Furthermore, these heavy compounds contribute to the soiling of the columns and evaporators.

The process of the invention also has the advantage of generating less acetic acid compared to prior art processes using catalysts active at a lower temperature.

Since the ODH reaction takes place at a lower temperature than thermal cracking, the process according to the invention is advantageously characterized, in addition, by the fact that the formation of heavy compounds by

oligomerization is much lower.

The process according to the invention making use of an ODH step also has the advantage of allowing a limited conversion by passing to the ODH without having to resort to expensive separations such as those that require an ethene distillation.

Another advantage of the process according to the invention is that it makes it possible to have, on the same industrial site, a completely integrated process ranging from the hydrocarbon source - namely ethane - up to the polymer obtained starting from the monomer manufactured.

While different embodiments of the present invention have been described herein, the present invention is not limited to any specifically described embodiment. Rather any combination of the described features is intended to be encompassed by the present invention.

The present invention will now be described by the following examples which are not intended as being limiting.

Catalyst preparation Chloride method

For the synthesis of catalysts according to the chloride method alkali/earth alkali chlorides were added to a suspension of MgO and Dy ₂ 03 or La ₂ 03 in 100 mL deionized water (masses of starting materials for the catalyst syntheses are given in Table 1). After stirring (stirrer speed: 500 min-1) at 80 °C for 2 h, the water was removed under reduced pressure (-70 mbar) at 50 °C. The obtained solids were dried for 12 h at 120 °C. Subsequently, the precursors were calcined for 12 h in synthetic air (100 mL/min) at 650 °C.

Table 1

MgO Dy203 La203 Li CI RbCI BaCI2 CsCI NaCI KCI SrCI2*6 H20

[g] [g] [g] [g] [g] [g] [g] [g] [g] [g]

Li NaCsCI/MgO-Dy203 6.64 0.6 0.983 2.714 0.04

Li KCsCI/MgO-Dy203 6.64 0.6 0.975 1.966 0.397

LiNa RbCI/MgO-Dy203 6.64 0.6 0.96 1.983 0.056

LiRbCsCI/MgO-Dy203 6.64 0.6 0.958 1.862 0.337

Li Na KRbCI/MgO-Dy203 6.64 0.6 0.855 1.127 0.187 0.546

Li KRbCsCI/MgO-Dy203 6.64 0.6 0.941 0.068 1.636 0.558

Li Na KCI/MgO-Dy203 6.64 0.6 0.729 0.771 0.716

Li KBaCI/MgO-Dy203 6.64 0.6 0.916 0.5 1.193

LiSrCsCI/MgO-Dy203 6.64 0.6 0.987 2.68 0.213 Li NaCsCI/MgO-La203 6.64 0.52 0.983 2.714 0.04

Li KCsCI/MgO-La203 6.64 0.52 0.975 1.966 0.397

LiNa RbCI/MgO-La203 6.64 0.52 0.96 1.983 0.056

Li RbCsCI/MgO-La203 6.64 0.52 0.958 1.862 0.337

Li NaKRbCI/MgO-La203 6.64 0.52 0.855 1.127 0.187 0.546

Li KRbCsCI/MgO-La203 6.64 0.52 0.941 0.068 1.636 0.558

Li Na KCI/MgO-La203 6.64 0.52 0.729 0.771 0.716

Li KBaCI/MgO-La203 6.64 0.52 0.916 0.5 1.193

LiSrCsCI/MgO-La203 6.64 0.52 0.987 2.68 0.213

Nitrate method

Catalysts according to the nitrate method were prepared by suspending MgO (6.64 g, 0.166 mol) and Dy ₂ 03 in 100 mL deionized water. Subsequently, alkali/earth alkali nitrate(s), were added to the mixture (masses of starting materials for the catalyst syntheses are given in Table 2). Then, the chloride was introduced by the addition ofNH ₄ Cl (1.02 g, 0.019 mol) and HC1 (37%, 1.57 mL). The atomic ratios of were chosen to obtain eutectic mixtures of the alkali/earth alkali chlorides. The suspensions obtained were stirred (stirring velocity: 500 min-1) at 80 °C for 2 h, before the water was evaporated under reduced pressure (-70 mbar) at 50 °C. Afterwards, the residues were dried for 12 h at 120 °C. Then, the catalyst precursors were calcined for 12 h in synthetic air (100 mL/min) at 650 °C.

Table 2

Catalytic ODH

Experiments were carried out in a continuous- flow fixed-bed reactor system. The educt gas stream was passed through a quartz tube (OD: 6mm; ID: 4 mm) surrounded by the reactor block, a heating coil and insulation material. The quartz tube was packed in the following order: Quartz wool, SiC, 300 mg catalyst (particle size: 300-600 μιη) and 500 mg SiC, SiC, Quartz wool. Silicon carbide was added in order to improve the thermal conductivity and thus avoid hot spots and to minimize temperature differences in the catalyst bed. The reactor was heated with a heating coil. The temperature was measured using a thermocouple attached in-between the two halves of the reactor. Mass flow controllers were utilized to control the flow rates of the gases having passed a filter. By means of valves the gas stream could be fed to the reactor or to the vent. The product gas stream was analyzed by a Maxum edition II Process gas chromatograph (Siemens) equipped with TCD detectors. For the separation of oxygen, carbon monoxide and methane a Molesieve 5 A column was employed. The other hydrocarbons were separated by a HayeSep Q column and a HayeSep T precolumn. A Poraplot Q column was applied for the additional detection of products.

Reactant molar ratio / %: He/0 ₂ /C ₂ H ₆ = 86.0/7.0/7.0 (total flow: 11.52 mL/min,), Pressure: 1 bar

Ethane conversion, ethene yield and ethene selectivity were tested for different catalysts prepared by the nitrate method or chloride method. Test results of the different catalysts in ODH of ethane are shown in Figures 1-6.

Description of the drawings

Figure 1 shows performance (ethane conversion (a), ethene selectivity (b)) of different Dy ₂ 0 ₃ -MgO supported catalysts in ODH of ethane. Catalysts were prepared according to the nitrate method using Dy ₂ 0 ₃ (see Table 2).

Figure 2 shows performance (ethane conversion (a), ethene selectivity (b)) of different Dy ₂ 0 ₃ -MgO supported catalysts in ODH of ethane. Catalysts were prepared according to the nitrate method using Dy ₂ 0 ₃ (see Table 2).

Figure 3 shows performance (ethane conversion (a), ethene selectivity (b)) of different La ₂ 0 ₃ -MgO supported catalysts in ODH of ethane. Catalysts were prepared according to the chloride method using La ₂ 0 ₃ (see Table 1).

Figure 4 shows performance (ethane conversion (a), ethene selectivity (b)) of different Dy ₂ 0 ₃ -MgO supported catalysts in ODH of ethane. Catalysts were prepared according to the chloride method using Dy ₂ 0 ₃ (see Table 1). Figure 5 shows performance (ethane conversion (a), ethene selectivity (b)) of different La ₂ 0 ₃ -MgO supported catalysts in ODH of ethane. Catalysts were prepared according to the chloride method using La ₂ 0 ₃ (see Table 1).

Figure 6 shows performance (ethane conversion (a), ethene selectivity (b)) of different Dy ₂ 0 ₃ -MgO supported catalysts in ODH of ethane. Catalysts were prepared according to the chloride method using Dy ₂ 0 ₃ (see Table 1).

The examples show the high efficiency of the new catalyst. High efficiency of the catalysts is expressed in high ethane conversions and high selectivities (Figures 1-6). While reaching high conversion levels, ethene selectivities above 90% can be obtained. For example, the production of ethene with a selectivity of more than 95% at an ethane conversion above 50% at 600°C is enabled with a catalyst of the present invention.

Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.