WO2013026720A1

WO2013026720A1 - Process for the manufacture of 1,2 - dichloroethane (dce)

Info

Publication number: WO2013026720A1
Application number: PCT/EP2012/065720
Authority: WO
Inventors: Uwe Rodemerck; David Linke; Michel Strebelle
Original assignee: Solvay Sa
Priority date: 2011-08-25
Filing date: 2012-08-10
Publication date: 2013-02-28
Also published as: AR087662A1

Abstract

Process for the manufacture of 1,2-dichloroethane (DCE), said process comprising : - the hydrothermal treatment of a mixture of catalytic oxide precursors comprising Mo, V and W in order to manufacture a catalyst for oxydehydrogenation (ODH) reactions; - an ODH step of ethane to ethylene; - a subsequent (oxy)chlorination step of the ethylene so obtained.

Description

PROCESS FOR THE MANUFACTURE OF 1 ,2 - DICHLOROETHANE (DCE)

The present invention relates to a process for the manufacture of a catalyst, to an oxydehydrogenation (ODH) process using such a catalyst, to a process for the manufacture of 1 ,2-dichloroethane (DCE), to a process for the manufacture of vinyl chloride (VC) and to a process for the manufacture of polyvinyl chloride (PVC).

DCE is usually prepared by oxychlorination of ethylene using hydrogen chloride (HCl) and a source of oxygen or by direct chlorination of ethylene using chlorine. The dehydrochlorination of DCE by pyro lysis thus results in the production of VC with release of HCl. The oxychlorination and chlorination are generally carried out in parallel and the HCl produced in the pyro lysis is used in the oxychlorination.

To date, ethylene which is more than 99.8 % pure is normally used for the manufacture of DCE. This very high purity ethylene is obtained via the thermal cracking of various petroleum products, followed by numerous complex and expensive separation operations in order to isolate the ethylene from the other products of the cracking and to obtain a product of very high purity.

Given the high cost linked to the production of ethylene of such high purity, and also the advantage that there could be in envisaging a process for the manufacture of VC by DCE in favourable regions that lack accessible ethylene capacities, various processes for the manufacture of DCE using ethylene having a purity of less than 99.8 % have been envisaged. These processes have the advantage of reducing the costs by simplifying the course of separating the products resulting from cracking of petroleum products and by thus abandoning complex separations which are of no benefit for the manufacture of DCE.

Thus, various processes for the manufacture of DCE starting from ethylene having a purity of less than 99.8 % produced by simplified cracking of ethane have been envisaged.

Processes in which VC is obtained by oxychlorination of ethane and not of ethylene are also known. Such processes have not found an industrial application up till now given that as they are conducted at high temperatures, they result in a mediocre selectivity with loss of the reactants used and costs for separating and destroying the by-products and they are also characterized by problems of behaviour of the material in a corrosive oxychlorination medium. Finally, problems linked to the behaviour of the catalysts used owing to the gradual vaporization of their constituents and also linked to the deposition of these constituents on the cold surface of the exchanger bundle are usually encountered.

The processes described respectively in patent applications

WO 2008/00693, WO 2008/000702 and WO 2008/000705 in the name of the Applicant aim at solving the above mentioned problems and use impure ethylene coming from the catalytic oxydehydrogenation (ODH) of ethane either used as such, or pre-treated by absorption/desorption steps.

In these applications, mention is made of catalysts based on Vanadium (V), with the preference to mixed oxides comprising V, and more precisely : to mixed oxides containing both Mo and V, W and V or Mo, W and V.

The Applicant has now found that the last category (mixed oxides based on

Mo, W and V) are the most effective ones. They namely offer a high selectivity to ethylene and a low selectivity to COx.

Such catalysts, and their use in the ODH of ethane to ethylene are known for instance from US 4,250,346. In this patent, said catalysts are merely listed among others (namely examples 46 and 58 in a list of 58 examples) and they were obtained by merely drying a solution of catalytic precursors comprising Mo, V and W at atmospheric pressure.

However, the Applicant found out that surprisingly, such catalysts, when obtained by a process comprising a hydrothermal treatment step, are much more active in ODH reactions, especially in the ODH of ethane in ethylene and that they are especially useful if said ethylene is used to manufacture DCE by (oxy)chlorination i.e by chlorination and/or oxychlorination. Hence, in a first aspect, the present invention relates to a process for the manufacture of a catalyst for ODH reactions, said process comprising the hydrothermal treatment of a mixture of catalytic oxide precursors comprising Mo, V and W.

More specifically, the present invention concerns a process for the manufacture of 1 ,2-dichloroethane (DCE)a catalyst for oxydehydrogenation (ODH) reactions, said process comprising :

- the hydrothermal treatment of a mixture of catalytic oxide precursors

comprising Mo, V and W in order to manufacture a catalyst for

oxydehydrogenation (ODH) reactions ; - an ODH step of ethane to ethylene ;

- a subsequent (oxy)chlorination step of the ethylene so obtained.

In other words, the present invention concerns a process for the

manufacture of 1 ,2-dichloroethane (DCE), said process comprising an ODH step of ethane to ethylene and a subsequent (oxy)chlorination step of the ethylene so obtained, wherein during the ODH step, a catalyst is used which has been obtained by the hydrothermal treatment of a mixture of catalytic oxide precursors comprising Mo, V and W.

By "catalytic oxide precursors" are meant chemical compounds which after a thermal treatment and optionally, a calcination step, constitute a mixed oxide of Mo, V and W which is active in the catalysis of ODH reactions.

By "hydrothermal treatment" is meant a treatment of the catalytic precursors in solution in water at a temperature above 100°C and under pressure. Preferably, the treatment temperature is from 100 to 300°C, more preferably from 120 to 250°C and even more preferably : from 150 to 200°C and the pressure is preferably the one corresponding to the liquid- vapor equilibrium conditions at the given temperature (which, considering the chemical medium, is a little less than the one given in wide available tables for pure water).

Hence, the catalytic oxide precursors used must be at least partially water soluble under the treatment conditions. They may either be organic compounds of Mo, V and W (like organic acids or salts thereof) or inorganic compounds of said elements (like oxides, hydroxides, sulphates, nitrates, chlorides...), as long as they are at least partially water soluble (i.e. as long as they can dissolve in a concentration allowing to get the required concentration in the final catalyst). Also, to the extent possible, the selected compounds of the various elements preferably are mutually soluble.

Preferably, each catalytic oxide precursor is introduced in the mixture to be treated already as an aqueous solution thereof.

The molybdenum is preferably introduced into solution in the form of ammonium salts thereof such as ammonium paramo lybdate, and organic acid salts of molybdenum such as acetates, oxalates, mandelates and glycolates.

Other water soluble molybdenum compounds which may be used are partially water soluble molybdenum oxides, molybdic acid, and the chlorides of molybdenum.

The vanadium is preferably introduced into solution in the form of ammonium salts thereof such as ammonium meta- vanadate and ammonium decavanadate, and organic acid salts of vanadium such as acetates, oxalates and tartrates. Other water soluble vanadium compounds which may be used are partially water soluble vanadium oxides, and the sulfates of vanadium.

The tungsten is preferably introduced into solution in the form of ammonium salts such as ammonium paratungstate. Other water soluble tungsten compounds which may be used are the tungstic acids.

The mixture treated by the process according to the invention

advantageously contains, in addition to the oxide precursors comprising Mo, V and W, at least one oxide precursor of at least one other element such as, for example Cr, Mn, Nb, Ta, Te, Ti, P, Sb, Bi, Zr, Ni, Ce, Al or Ca. Oxide precursors of Te and/or Ti are preferred, especially when said catalyst is intended for the ODH of ethane in ethylene (see below). P and/or Nb oxide precursors may also be added.

It is worth noting that catalysts containing Mo, V and W, and additionally, at least one element selected from Te, Ti, P and Nb, but in a total amount of these element(s) of less than 0.1 expressed in atomic fraction of metals, are believed to be novel an inventive i.e. to be active catalysts in ODH reactions namely of ethane to ethylene. Hence, the present invention also relates to such catalysts independently of the way they are obtained. However, such catalysts obtained by the process described above and including a hydrothermal treatment, are preferred.

Preferred catalyst compositions are those containing (expressed in atomic fraction of metals) 0.35 to 0.5 Mo, 0.1 to 0.3 W and 0.2 to 0.35 V. Even more preferred are those containing additionally Te and/or Ti (preferably both) but in a total atomic fraction of less than 0.1.

Generally, not all the precursors in solution are precipitated at the end of the hydrothermal treatment so that a chemical analysis may be required in order to know the exact chemical composition of the catalyst. Techniques like

ICP-OES (Inductively Coupled Plasma - Optical Emission Spectroscopy) analysis or XRF (X-Ray Fluorescence) analysis may be used in that regard.

Hence, to obtain the above preferred composition, the mixture preferably comprises the following atomic fractions of metals : 0.3 to 0.6 Mo, 0.05 to 0.3 W, 0.1 to 0.4 V (preferably about 0.32 V) and optionally, less than 0.1 Te and/or Ti and/or P and/or Nb. Preferably, said mixture comprises an atomic fraction o f Te and Ti o f at least 0.01.

It is also preferred to have a Mo/W atomic fractions ratio of 2 to 10. The process according to the first aspect of the invention preferably comprises, after the hydrothermal treatment step of the aqueous mixture, during which solids have crystallized/precipitated from a liquid aqueous medium, a step of separating these solids from said liquid aqueous medium. This may be done by any known technique like filtering, centrifuging...

These solids which have precipitated generally comprise at least one crystal phase diluted in an amorphous matrix. This invention includes also processes where a solid is introduced in the crystallization stage or just after to obtain a supported catalyst. This allows an improved mechanical stability and a better efficiency of the active components from an accessibility point of view.

After separation from the aqueous medium, the solids are preferably calcined. By "calcination" is meant heating to a high temperature but below the melting or fusing point, causing loss of moisture, reduction or oxidation, and formation of desired crystal phases. Typically, calcination occurs at a temperature above 100°C, generally above 200°C and even, above 300°C.

It has been found that surprisingly, a calcination at a lower temperature (typically : below 500°C, preferably below 450°C and even more preferably : below 400°C) gives better results than a calcination at a higher temperature (typically : above 800°C or even : above 600°C) although higher temperatures are generally recommended in literature as they enhance the formation of the above mentioned crystal phase(s) which are believed to be at the origin of the catalytic activity of the catalysts. The duration of calcination is typically in the range of hours, namely : generally from 1 to 15h, preferably from 2 to lOh, even more preferably from 4 to 6h.

Also, a calcination in the presence of an oxidant gas like air, seems to give better results that a calcination in the presence of an inert gas like Argon.

Following said calcination, a thermal activation step (generally in an inert atmosphere or under vacuum, and at a temperature of at least 600°C may be applied if required and as known in the art.

According to a second aspect, the present invention concerns a process for the catalytic oxydehydrogenation (ODH) of ethane to ethylene using the catalyst obtained as described above.

The term "catalytic oxydehydrogenation (ODH)", also known as catalytic oxidative dehydrogenation, is understood to mean, in the frame of that aspect of the invention, a partial oxidation of ethane by oxygen in the presence of the above mentioned catalyst. In this process, a stream of ethane is converted to a gas mixture containing ethylene, unconverted ethane, water and secondary constituents. Said stream of ethane may or may not be chemically pure. The stream of ethane used may contain up to 70 vol % of other gases such as methane, hydrogen, ethylene, oxygen, nitrogen, carbon oxides and even, chlorinated substances like DCE (see below).

The stream of ethane used advantageously contains at least 80 vol %, preferably at least 90 vol %, particularly preferably at least 95 vol % and more particularly preferably at least 98 vol % of ethane. If necessary, the ethane may be separated from the secondary compounds having a higher boiling point in any known device, for example by absorption, extraction, diffusion or distillation.

According to this aspect of the invention, ODH may take place either at a temperature above 650°C up to 800°C, below the range of thermal cracking temperatures, or at a temperature less than or equal to 650°C.

The pressure at which ODH is carried out is advantageously at least 1, preferably at least 1.5 and particularly preferably at least 2 bar absolute. It is preferably at most 30 bar, advantageously at most 16, even more preferably at most 11 and particularly preferably at most 6 bar absolute. Rising pressure is generally advantageous in terms of productivity.

The oxygen used in the ODH may be "pure" (as commercially available : see below) oxygen or a gas containing oxygen with other inert gases, such as for example air. Preferably, oxygen is used. Thus, it is possible to use a very pure source of oxygen containing at least 99 vol % of oxygen but also a source of oxygen containing less than 99 vol % of oxygen. In the latter case, the oxygen used advantageously contains more than 90 vol % and preferably more than 95 vol % of oxygen. A source of oxygen containing from 95 to 99 vol % of oxygen is particularly preferred.

The amount of oxygen introduced, based on the amount of ethane, is advantageously from 0.001 to 1 mol/mol, preferably from 0.005 to 0.5 mol/mol and particularly preferably from 0.05 to 0.3 mol/mol.

ODH may be carried out in any known device. Advantageously, ODH is carried out in one reactor or a series of reactors of fixed bed type having one or more beds, between which a thermal conditioning step may be carried out, or in one reactor or a series of reactors of fluid bed type, preferably adiabatic or with temperature control using an auxiliary fluid inside the reactor (multitubular reactor or heat exchanger immersed in the catalytic bed) or outside the reactor. The reactants may be previously mixed before introduction into the reaction zone. One or more reactants may also be added differently, for example between the beds of a multi-bed reactor. The reactor may be equipped with preheating means and with any means necessary to control the reaction temperature. A cross exchanger advantageously enables the heat of the products formed to be recovered to reheat the incoming products.

The catalyst used for ODH may or may not be supported. In the case where it is supported, the support which may possibly be used includes silica, alumina, titanium oxide, silicon carbide, zirconia and mixtures thereof such as mixed oxides.

The catalyst used for ODH is advantageously resistant to DCE. In that regard, the presence of Te and/or Ti (especially both) in the catalyst is preferred.

The catalyst used may be placed on a bed or in tubes or outside of those tubes so that a temperature control may be obtained by a fluid surrounding these tubes or running through them.

ODH of the stream of ethane gives a gas mixture containing ethylene, unconverted ethane, water and secondary constituents. The secondary constituents may be carbon monoxide, carbon dioxide, hydrogen, various oxygen-containing compounds such as, for example, acetic acid or aldehydes, nitrogen, methane, oxygen, and optionally organic compounds comprising at least 3 carbon atoms.

According to a first variant, ODH takes place at a temperature above 650°C up to 800°C.

According to a second variant of the process according to the invention, ODH takes place at a temperature less than or equal to 650°C.

Advantageously, ODH then takes place at a temperature less than or equal to 600°C, preferably less than or equal to 550°C, particularly preferably less than or equal to 500°C, more particularly preferably less than or equal to 450°C and most particularly preferably less than or equal to 400°C. A temperature between 200 and 400°C is particularly advantageous.

In this case, the process according to the invention has the advantage of generating very small amounts of hydrogen responsible for many drawbacks, namely :

- oxygen consumption and heat generation owed to its combustion, which limits the capacity of the reactors ; and - explosion danger with some of the gas streams of the DCE manufacturing processes described below.

This second variant has the advantage that the ODH reaction generally does not generate troublesome amounts of heavy compounds having a number of carbon atoms greater than or equal to 3, such as for example propylene and olefins with a molecular weight higher than that of propylene. Such compounds and also their chlorinated derivatives are strong inhibitors of the pyrolysis of DCE in VC and hence, could jeopardize the use of the ethylene for making DCE. The second variant of the process according to the invention is hence preferred to the first.

According to a third aspect, the present invention concerns a process for the manufacture of 1 ,2-dichloroethane (DCE) comprising an ODH step of ethane to ethylene as described above, and a subsequent oxychlorination step of ethylene. In this aspect of the invention, it may be advantageous to recycle part of the products derived from the oxychlorination, to the ODH step.

In a first 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 ethylene, unconverted ethane, water and secondary constituents ;

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

c) after an optional additional purification step, the dry gas mixture is then conveyed to a chlorination reactor supplied with a flow of chlorine so that at least 10 % of the ethylene 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 ethylene 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 above mentioned patent application

WO 2008/000705 to the Applicant, the content of which is incorporated by reference in the present application.

In a second 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

c) after an optional additional purification step, said dry 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 ethylene containing some of the ethylene (fraction A) and into a fraction Fl ;

d) fraction A is conveyed to a chlorination reactor in which most of the ethylene 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 ethylene (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 ethylene 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 above mentioned patent application WO 2008/000702 to the Applicant, the content of which is incorporated by reference in the present application.

In a third 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

c) after an optional additional purification step, said dry 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 ethylene containing some of the ethylene (fraction A) and into a fraction Fl ; d) fraction A is conveyed to a chlorination reactor Rl in which most of the ethylene 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 ethylene fraction depleted of the compounds that are lighter than ethylene (fraction C) which is conveyed to a chlorination reactor R2, the stream of products derived from this reactor being added to the dry 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 ethylene (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 ;

g) fraction B is conveyed to an oxychlorination reactor in which most of the ethylene 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

Such a process is described in the above mentioned 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), it has been observed that the ODH step according to the invention is not detrimentally influenced by residual amounts of DCE and CO in said stream.

The DCE obtained by (oxy)chlorination of ethylene as described above may then be converted into VC. 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 pyro lysis 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 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 ethylene) 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 ethylene. 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 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 by-products 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.

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 ethylene 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. The second variant of the process according to the invention, according to which the ODH takes place at temperatures less than or equal to 650°C, has the advantage of generating very small amounts of hydrogen, responsible for numerous drawbacks.

Some aspects of the present invention will now be described in light of the

Examples below, which are only used for the purpose of better explaining the benefits of some embodiments of the invention and not of limiting the scope thereof.

Catalyst preparation

Hydrothermal synthesis

The catalysts were prepared in small-scale autoclaves (50 ml, Parr) heated in a metal-block thermostat.

The starting solutions were dosed by a synthesis robot (Zinsser Sophas) to the autoclaves inlays (made of PTFE or glass). The solutions of the different elements used for hydrothermal preparation route are listed in Table 1 below.

Table 1

Element Precursor Concentration in solution g(element)/L

Zr ZrO(N03)2*9H20 24.25

Ca Ca(N03)2 37.73

Ta Tantalum oxalate 133.37

Ni Ni(N03)2 31.85

Al A1(N03)3 24.16

Ce Ce(N03)3 119.8

Mo (NH4)6Mo7024 55.16

Bi Bi(N03)3 91.63

V VOS04 108.35

Sb Sb203 / tartric acid 10.54

W (NH4)6H2W12041 *6H20 176.85

P (NH4)2HP04 49.67

Te Te(OH)6 50.9

Nb Ammonium Niobium Oxalate 41.58

Ti (NH4)2TiO(C204)2*H20 13.3

The autoclaves were closed, purged three times with Argon and put into the cold metal-block thermostat.

Then the autoclaves were heated to 180°C and hold for 44 h at this temperature while stirring the mixture by a magnetic stirrer. After cooling down the autoclaves were opened and the mixtures were filtered, washed with small amount of bidistilled water and dried for 12 hours at 120°C.

The solids then were calcined in air at 350°C for 5 hours (heating ramp 2°C/min). As indicated in Table 2 below, some solids were also calcined at higher temperature (650°C) in Argon.

Table 2

Preparation

ChanCat.

Nominal catalyst composition method / nel system

calcination

1 MoV Mo0.5V0.5 hydrothermal,

350°C, air

2 MoV Mo0.4V0.6 hydrothermal,

350°C. air

3 MoV Mo0.6V0.4 hydrothermal,

350°C. air

4 MoVX Mo0.49Zr0.02V0.49 hydrothermal,

350°C. air

5 MoVX Mo0.487Sb0.003Ta0.003Zr0.02V0.487 hydrothermal,

350°C. air

6 MoVX Mo0.497Sb0.003Ta0.003V0.497 hydrothermal,

350°C. air

7 MoVX Mo0.6Nb0.073Te0.1V0.227 hydrothermal,

350°C. air

8 MoVX Mo0.6Nb0.073Te0.1V0.227 hydrothermal,

650°C, Ar

9 MoVX Mo0.54Bi0.02Nb0.06Ni0.04V0.34 hydrothermal,

350°C. air

10 MoVX Mo0.56Bi0.02Nb0.06V0.36 hydrothermal,

350°C. air

11 MoVX Mo0.56Nb0.06Ni0.04V0.34 hydrothermal,

350°C. air

12 MoVX Mo0.6Ca0.01Nb0.05Sb0.01V0.33 hydrothermal,

350°C. air

13 MoVX Mo0.58A10.06Ta0.09V0.27 hydrothermal,

350°C. air

14 MoVX Mo0.62Ta0.09V0.29 hydrothermal,

350°C. air

15 MoVX Mo0.64A10.06V0.3 hydrothermal,

350°C. air

16 MoVX Mo0.49Sb0.02V0.49 hydrothermal,

350°C. air

17 wv W0.5V0.5 hydrothermal,

350°C. air

18 wv W0.4V0.6 hydrothermal,

350°C. air

19 wv W0.6V0.4 hydrothermal,

350°C. air

20 wv W0.485Nb0.03V0.485 hydrothermal,

350°C. air

21 wv W0.485Ta0.03V0.485 hydrothermal,

350°C. air Preparation

ChanCat.

Nominal catalyst composition method / nel system

calcination

22 MoWVX Mo0.355W0.21Ce0.02Ni0.02P0.02Ta0.02Te0.025Ti0.02V hydrothermal,

0.31 350°C. air

23 MoWVX Mo0.37W0.22P0.02Ta0.025Te0.025Ti0.02V0.32 hydrothermal,

350°C. air

24 MoWVX Mo0.373W0.22Ce0.02P0.02Te0.025Ti0.02V0.322 hydrothermal,

350°C. air

25 MoWVX Mo0.373W0.22Ni0.02P0.02Te0.025Ti0.02V0.322 hydrothermal,

350°C. air

26 MoWVX Mo0.385W0.225P0.02Te0.025Ti0.02V0.325 hydrothermal,

350°C. air

27 MoWVX Mo0.39W0.23Te0.026Ti0.02V0.334 hydrothermal,

350°C. air

28 MoWVX Mo0.39W0.23P0.02Te0.026V0.334 hydrothermal,

350°C. air

29 MoWVX Mo0.4W0.23Te0.03V0.34 hydrothermal,

350°C. air

30 MoWVX Mo0.355W0.21Ce0.02Ni0.02P0.02Ta0.02Te0.025Ti0.02V hydrothermal,

0.31 650°C, Ar

31 MoWVX Mo0.37W0.22P0.02Ta0.025Te0.025Ti0.02V0.32 hydrothermal,

650°C, Ar

32 MoWVX Mo0.373W0.22Ce0.02P0.02Te0.025Ti0.02V0.322 hydrothermal,

650°C, Ar

33 MoWVX Mo0.373W0.22Ni0.02P0.02Te0.025Ti0.02V0.322 hydrothermal,

650°C, Ar

34 MoWVX Mo0.385W0.225P0.02Te0.025Ti0.02V0.325 hydrothermal,

650°C, Ar

35 MoWVX Mo0.39W0.23Te0.026Ti0.02V0.334 hydrothermal,

650°C, Ar

36 MoWVX Mo0.39W0.23P0.02Te0.026V0.334 hydrothermal,

650°C, Ar

37 MoWVX Mo0.4W0.23Te0.03V0.34 hydrothermal,

650°C, Ar

38 MoWVX Mo0.4W0.24Nb0.025V0.335 hydrothermal,

350°C. air

39 MoWVX Mo0.53W0.15Sb0.03V0.29 hydrothermal,

350°C. air

40 MoWVX Mo0.52W0.15Bi0.01Sb0.03Ti0.01V0.28 hydrothermal,

350°C. air

41 MoWVX Mo0.53W0.15Sb0.03Ti0.01V0.28 hydrothermal,

350°C. air

42 MoWVX Mo0.53W0.15Bi0.01Sb0.03V0.28 hydrothermal,

350°C. air

43 MoWVX Mo0.53W0.17V0.28 hydrothermal,

350°C. air

44 MoWVX Mo0.558W0.2Nb0.001Ta0.001V0.24 hydrothermal,

350°C. air

45 MoWVX Mo0.537W0.18Nb0.003V0.28 hydrothermal,

350°C. air

46 MoWVX Mo0.56W0.2V0.24 hydrothermal,

350°C. air

47 Ni Ni0.62Ta0.38 slurry, 350°C.

air

48 Ni Nb0.38Ni0.62 slurry, 350°C. Preparation

ChanCat.

Nominal catalyst composition method / nel system

calcination air

49 Ni Nb0.28Ni0.62Ta0.1 slurry, 350°C.

air

50 Thorsteinson MolV0.25Nb0.125Ox slurry, 400°C air

Lit for 50 : Thorsteinson et al. J.Catal. 52 (1978) 116.

The catalysts were crushed and sieved after calcination ; for the catalytic tests a particle size fraction from 0.315 mm to 0.710 mm was used.

Slurry route

The catalyst were prepared and calcined according to US 4,250,346 mentioned before (conditions of Example 34).

Spray drying

The catalyst were prepared by preparing the solutions as described above for the hydrothermal synthesis and the mixtures obtained were dried using a standard laboratory spray drier with fixed nozzles.

Catalyst performance tests

These tests were conducted in a stainless steel (SS316) reactor comprising 50 parallel fixed-bed reactors (called "channels" in the tables and figures attached) having a diameter of 4.8 mm, each containing 0.3 g of catalyst.

The catalysts listed in Table 2 were tested at a temperature of 305°C and a pressure of 1 bara (bar absolute), under a gas flow of 8 Nml/min in each channel, with a gas feed of the following molar composition : 65 % ethane, 15 % oxygen and 0.5 % DCE or 2 % CO the case being, the balance being N2.

The results obtained are shown in Table 3 below and Figure 1 (comparison of Ethylene Yield (Y) with and without DCE in the feed) and Figure 2

(comparison of Ethylene Yield (Y) with and without CO in the feed) attached.

Table 3

As can be seen there from, catalysts containing the 3 elements (Mo, W and V) and obtained by hydrothermal synthesis according to the invention generally perform the best, especially in the presence of DCE, and they are virtually inert towards CO. Their performances are even improved by the presence of both Te and Ti.

The catalysts listed in Table 4 below were tested in similar conditions than those of Table 2, except for the pressure which may sometimes be different if and when indicated in the results of Figures 3 to 7 attached.

Table 4

channel Code composition / molar content Preparation

Mo W V Nb Ta Te Ti P Fe

1 C01 0.378 0.219 0.318 0.045 0.020 0.020 hydrothermal

2 C02 0.547 0.050 0.318 0.045 0.020 0.020 hydrothermal

3 C03 0.587 0.010 0.318 0.045 0.020 0.020 hydrothermal

4 C04 0.597 0.318 0.045 0.020 0.020 hydrothermal

5 C05 0.348 0.204 0.318 0.090 0.020 0.020 hydrothermal

6 C06 0.363 0.209 0.318 0.045 0.045 0.020 hydrothermal

7 C07 0.338 0.189 0.318 0.090 0.045 0.020 hydrothermal

8 C08 0.517 0.010 0.318 0.090 0.045 0.020 hydrothermal

9 C09 0.363 0.204 0.318 0.030 0.045 0.020 0.020 hydrothermal

10 C10 0.517 0.050 0.318 0.030 0.045 0.020 0.020 hydrothermal channel Code composition / molar content Preparation

Mo W V Nb Ta Te Ti P Fe

1 1 C1 1 0.363 0.204 0.318 0.030 0.045 0.020 0.020 hydrothermal

12 C12 0.517 0.050 0.318 0.030 0.045 0.020 0.020 hydrothermal

13 D01 0.388 0.229 0.318 0.045 0.020 hydrothermal

14 D02 0.567 0.050 0.318 0.045 0.020 hydrothermal

15 D03 0.607 0.010 0.318 0.045 0.020 hydrothermal

16 D04 0.617 0.318 0.045 0.020 hydrothermal

17 D05 0.229 0.388 0.318 0.045 0.020 hydrothermal

18 D06 0.363 0.209 0.318 0.090 0.020 hydrothermal

19 D07 0.373 0.219 0.318 0.045 0.045 hydrothermal

20 D08 0.348 0.199 0.318 0.090 0.045 hydrothermal

21 D09 0.547 0.318 0.090 0.045 hydrothermal

22 D10 0.373 0.214 0.318 0.030 0.045 0.020 hydrothermal

23 D1 1 0.537 0.050 0.318 0.030 0.045 0.020 hydrothermal

24 D12 0.373 0.214 0.318 0.030 0.045 0.020 hydrothermal

25 D13 0.537 0.050 0.318 0.030 0.045 0.020 hydrothermal

26 E01 0.378 0.229 0.318 0.045 0.020 0.010 hydrothermal

27 E02 0.378 0.229 0.318 0.045 0.020 0.010 hydrothermal

28 F01 0.431 0.198 0.290 0.057 0.024 slurry

29 F02 0.567 0.050 0.318 0.045 0.020 slurry

30 F03 0.607 0.010 0.318 0.045 0.020 slurry

31 F04 0.617 0.318 0.045 0.020 slurry

32 F05 0.229 0.388 0.318 0.045 0.020 slurry

33 F06 0.373 0.214 0.318 0.030 0.045 0.020 slurry

34 F07 0.537 0.050 0.318 0.030 0.045 0.020 slurry

35 F08 0.373 0.214 0.318 0.030 0.045 0.020 slurry

36 F09 0.537 0.050 0.318 0.030 0.045 0.020 slurry

37 G01 0.415 0.229 0.279 0.055 0.023 slurry

38 G02 0.449 0.165 0.302 0.059 0.025 slurry

39 G03 0.407 0.187 0.329 0.054 0.023 slurry

40 G04 0.458 0.210 0.246 0.061 0.025 slurry

41 G05 0.426 0.196 0.287 0.068 0.024 slurry

42 G06 0.434 0.199 0.292 0.046 0.029 slurry

43 G07 0.433 0.199 0.291 0.057 0.019 slurry

44 H01 0.424 0.162 0.297 0.057 0.030 0.030 slurry

45 H02 0.587 0.010 0.318 0.045 0.020 0.020 slurry

46 H03 0.597 0.318 0.045 0.020 0.020 slurry

47 101 0.431 0.198 0.290 0.057 0.024 spray dried

48 I02 0.431 0.198 0.290 0.057 0.024 spray dried

49 103 0.424 0.162 0.297 0.057 0.030 0.030 spray dried

50 104 0.424 0.162 0.297 0.057 0.030 0.030 spray dried

Figure 3 (tests with DCE in the feed) shows that the conversion of ethane (X) is negligible (less than 1 %) with catalysts obtained by the slurry route or spray dried, while catalysts according to the invention can reach conversions above 25 % (see namely the samples coded C01 to C03, C06, C10-D02, D05, D07, D10-E02).

A Mo/W ratio of about 2 to 10 seems to give the best results (see Figures 4 and 5 respectively obtained by reactions at a temperature of 290°C and 305°C). The preferred catalysts identified in Figure 3 seem to also give high conversion (X(ethane)) under pressure and in the presence of DCE (see Figure 6 obtained at a reaction temperature of 305°C).

However, some of them lead to a propylene by- formation above 10 ppm (see Figure 7) which is judged too detrimental if the ethylene is used in VC production, so that finally, the best outperforming catalysts found are those coded C02, C03, CIO, D02 and Dl 1, which all contain Mo, W, V, Te, Ti and optionally, P or Nb.

Claims

C L A I M S

1. Process for the manufacture of 1 ,2-dichloroethane (DCE), said process comprising :

- the hydrothermal treatment of a mixture of catalytic oxide precursors

comprising Mo, V and W in order to manufacture a catalyst for

oxydehydrogenation (ODH) reactions ;

- an ODH step of ethane to ethylene ;

- a subsequent (oxy)chlorination step of the ethylene so obtained.

2. Process for the manufacture of 1 ,2-dichloroethane (DCE), said process comprising an ODH step of ethane to ethylene and a subsequent

(oxy)chlorination step of the ethylene so obtained, wherein during the ODH step, a catalyst is used which has been obtained by the hydrothermal treatment of a mixture of catalytic oxide precursors comprising Mo, V and W.

3. Process according to Claim 1 or 2, in which the mixture comprises the following atomic fractions of metals : 0.3 to 0.6 Mo, 0.05 to 0.3 W, 0.1 to 0.4 V.

4. Process according to the preceding claim, wherein the mixture comprises an atomic fraction of Te and Ti of at least 0.01.

5. Process according to any of the preceding claims, comprising, after the hydrothermal treatment step during which mixed oxides have

crystallized/precipitated out as solids from a liquid aqueous medium, a step of separating the solids from said liquid aqueous medium and a step of calcinating said solids.

6. Process according to the preceding claim, in which the calcinating step takes place in the presence of an oxidant gas.

7. Process according to any of the preceding claims, wherein the catalyst contains at least one element selected from Te, Ti, P and Nb in a total amount of less than 0.1 expressed in atomic fraction of metals.

8. Process according to the preceding claim, wherein the catalyst contains the following atomic fractions of metals : 0.35 to 0.5 Mo, 0.1 to 0.3 W, 0.2 to 0.35 V and less than 0.1 Te and/or Ti.

9. Process according to any of the preceding claims, in which the catalytic ODH takes place at a temperature of less than or equal to 650°C.

10. Process for the manufacture of 1 ,2-dichloroethane (DCE) comprising an ODH step of ethane to ethylene a and a subsequent oxychlorination step of the ethylene so obtained.

1 1. Process according to the preceding claim, comprising recycling part of the products derived from the oxychlorination step to the ODH step.

12. Process according to any of the preceding claims, wherein : a) the stream of ethane is subjected to an ODH step producing a gas mixture containing ethylene, unconverted ethane, water and secondary constituents ; b) said gas mixture is optionally washed and dried thus producing a dry gas mixture ; c) after an optional additional purification step, the dry gas mixture is then conveyed to a chlorination reactor supplied with a flow of chlorine so that at least 10 % of the ethylene 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 ethylene 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.

13. Process according to any of claims 1 to 1 1, wherein : a) the stream of ethane is subjected to an ODH step producing a gas mixture containing ethylene, unconverted ethane, water and secondary constituents ; b) said gas mixture is optionally washed and dried thus producing a dry gas mixture ; c) after an optional additional purification step, said dry 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 ethylene containing some of the ethylene (fraction A) and into a fraction Fl ; d) fraction A is conveyed to a chlorination reactor in which most of the ethylene 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 ethylene (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 ethylene 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.

14. Process according to any of claims 1 to 1 1, wherein : a) the stream of ethane is subjected to an ODH step according to Claim 8 or 9, producing a gas mixture containing ethylene, unconverted ethane, water and secondary constituents ; b) said gas mixture is optionally washed and dried thus producing a dry gas mixture ; c) after an optional additional purification step, said dry 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 ethylene containing some of the ethylene (fraction A) and into a fraction Fl ; d) fraction A is conveyed to a chlorination reactor Rl in which most of the ethylene 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 ethylene fraction depleted of the compounds that are lighter than ethylene (fraction C) which is conveyed to a chlorination reactor R2, the stream of products derived from this reactor being added to the dry 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 ethylene (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 ; g) fraction B is conveyed to an oxychlonnation reactor in which most of the ethylene 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 oxychlonnation 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.

15. Process for the manufacture of vinyl chloride (VC) according to which the 1,2-dichloroethane obtained by a process according to any of the preceding claims is subjected to a pyrolysis thus producing VC.

16. Process for the manufacture of PVC by polymerisation of the VC obtained by a process according to the preceding claim.