IE69323B1 - Oxychlorination process and fluidisable charge - Google Patents

Abstract

Process for the oxychlorination of a hydrocarbon to form a chlorinated hydrocarbon, in which the hydrocarbon, a gas containing oxygen and gaseous hydrochloric acid pass over a fluidisable charge comprising a mixture of an oxychlorination catalyst and of particles of at least one catalytically and chemically inert solid substance, characterised in that a solution or a suspension of a copper compound is added to the fluidised charge.

Description

The present invention relates to an oxychlorination process and to a fluidisable charge suitable for use therein. This process is especially applicable to the production of 1,2-dichloroethane. 1,2-Dichloroethane (D 12) is a product manufactured Industrially on a scale of several million tons per annum, which, on pyrolysis, gives vinyl chloride monomer (VCM) and hydrochloric acid (HCl). VCM is polymerised to poly(vinyl chloride) (or PVC), a commonly employed plastic material. The HCl obtained on pyrolysis is separated from the VCM and is then brought into contact with ethylene and oxygen in the presence of a catalyst to give D 12; this is the oxychlorination reaction. This reaction is very general and can be carried out with the majority of hydrocarbons.

Oxychlorination has been described in many patents, in particular in FR-A-2,063,365, FR-A-2,260,551, FR-A20 2,213,259 and FR-A-2,125,748. The catalyst generally consists of a copper salt deposited on alumina powder. European Patent Application No. 58,644 describes the t preparation of a catalyst by pouring a solution of cupric chloride into a fluidised bed of alumina powder at a maximum temperature of 50°C. This operation is followed by drying with hot air in a fluidised bed without exceeding 140°C.

European Patent Application No. 29,143 describes the preparation of an oxychlorination catalyst consisting in mixing, in a fluidised bed during an oxychlorination reaction, the catalyst which has already been prepared, that * is to say alumina powder containing a copper compound, and a bare support, that is to say alumina powder not containing any copper compound. Addition of the bare support to a fluidised bed during an oxychlorination reaction, originally charged with catalyst, is also described.

This method is presented as having the advantage of avoiding the adhesion (or agglomeration) of catalyst particles during the operation. This application describes a migration of the copper compound from the alumina containing the copper towards the bare support.

It is quite clear that the result of this method is a reduction in the copper content of the catalyst, since the quantity of support is increased without copper being added. This application clearly presents the fact that the result: suppression or reduction of adhesion is not linked only with the reduction in the quantity of copper but also with the migration of a copper compound from the alumina containing the copper compound towards the bare support. This application also describes a means of preparing a catalyst in situ by % charging the reactor with a bare support, fluidising it with fi the reaction gases and adding solid cupric chloride thereto.

This means is presented as a substitute for the conventional preparation of the catalyst by impregnation outside the reactor. However, this preparation is suggested only on the laboratory scale; in fact, this method of * preparation is not industrial, because at the beginning of this preparation the fluidised bed does not contain any proper catalyst, that is a copper compound on a support; there is therefore no oxychlorination reaction. It is necessary to heat and , if heating is applied while no catalyst exists, at the exit of the fluidised bed there is an explosive region, since there is no reaction and therefore no conversion.

European Patent Application No. 119,933 also describes an oxychlorination catalyst according to the same principle as above, that is to say copper impregnating an alumina powder but not having the disadvantage of adhering because, it is said in this application, there is less copper on the surface than inside the catalyst particles.

All this prior art concerns oxychlorination fluidised beds employing a homogeneous catalyst, that is to say powders in which all the particles are impregnated with copper. There are also oxychlorination fluidised beds employing a heterogeneous catalyst, that is to say powders consisting of a mixture of / alumina pa-rt idea impregnated with copper as above and inert particles such as silicious sand. These catalysts I are described in FR-A-2,242,143, the content of which is incorporated in the present application. These heterogeneous catalysts do not exhibit the disadvantage of adhesion of the homogeneous catalysts but, on the other hand, have the disadvantage of forming a self-abrasive mixture; the sand particles * cause wear of the alumina particles. Copper-rich fines are removed and new catalyst must be added to compensate.

An improvement to these "heterogeneous oxychlorination catalysts has now been found, which makes it possible to keep their performance constant over time.

To avoid confusion with the usual terms of θ homogeneous catalysis and heterogeneous catalysis and to remain consistent with the terms used in FR-A-2,242,143, the heterogeneous oxychlorination catalysts will be called a fluidisable charge or fluidisable catalytic charge.

The present invention provides a process for the oxychlorination of a hydrocarbon to a chlorinated hydrocarbon, which comprises passing the hydrocarbon, a gas containing oxygen and gaseous hydrochloric acid over a fluidisable charge comprising a mixture of an oxychlorination catalyst and inert particles of at least one catalytically and chemically inert solid substance, wherein a solution or suspension of a copper compound is added to ·Ί the fluidised charge.

The present invention also provides a fluidisable charge capable of being employed in an oxychlorination reactor, which comprises a mixture of (i) an oxychlorination catalyst and (ii) particles of at least one catalytically and chemically inert solid substance to which a solution or suspension of a copper compound has been added.

The invention is therefore a composition which can be employed as an oxychlorination catalyst, which comprises a mixture of an oxychlorination catalyst and of particles of at least one catalytically and chemically inert solid substance to which a solution or suspension of a copper compound has been added.

The hydrocarbon may, for example, be a mixture of hydrocarbons chosen from CJ-C20 aliphatic hydrocarbons, cycloaliphatic hydrocarbons up to Cj2 and aromatic hydrocarbons containing up to 4 condensed benzene nuclei, and their chlorinated substitution derivatives. They may be chosen, for example, from methane, ethane, propane, ethylene and propylene. The invention is particularly useful in the case of ethylene. The gas containing oxygen may quite simply be air but air which is depleted or enriched in oxygen may also be employed.

The oxychlorination catalyst which can be employed in the invention may be any oxychlorination catalyst capable of being employed per se without mixing with a catalytically and chemically inert substance. Powders based essentially on alumina having a particle size of from 20 to 200 μτα and surface area of from 90 to 450 m2/g, preferably from 30 to 90 μπι and from 250 to 400 m2/g, are advantageously employed.

These powders are impregnated with copper or a copper salt in a quantity which may, for example, provide up to 10% and preferably from 3 to 10% by weight of copper relative to the finished catalyst.

As the catalytically and chemically inert substance acting as a diluent (but in no case as a. catalyst support) there may be mentioned, especially, glass or silica ballotini, alpha alumina and, preferably, siliceous sand which is found in the natural state and whose particle size distribution is adapted to the requirements of the fluidisation.

The particle size distribution of the actual catalyst, on the one hand, and that of the catalytically and chemically inert substance, on the other hand, are chosen so that the diameter and the particle size range of the mixture are favourable for satisfactory fluidisation.

The size of the inert particles is advantageously from 20 to 200 pun.

The amount of inert substance may vary within wide limits. The amount is advantageously from 1 to 20 times by weight of the amount of the catalyst.

The objective of the oxychlorination is essentially to employ hydrochloric acid as a source of chlorine. The quantity of oxygen and of hydrocarbon is therefore adjusted to obtain the chlorinated hydrocarbon approximately stoichiometrically by consuming as much HCl and hydrocarbon as possible.

During the operation of an oxychlorination fluidised bed a drop in activity is found, reflected in a lack of conversion of the hydrocarbon.

This drop is due to catalyst wear. This wear, which results in a drop in activity, is accompanied by a physical loss by entrainment with the gases at the exit of the fluidised bed and an imperfect, efficiency of the separation between the entrained catalyst and the gases. This separation is made difficult by the conversion of a part of the catalyst into dust because of attrition. The reduction in the quantity of catalyst and the decrease in its activity are generally compensated by additions of new catalyst. We have surprisingly found that this drop in activity can be compensated by adding a solution or suspension of a copper compound to the fluidised bed. Among the copper compounds, the chloride and the oxychloride may, for example, be employed. It is preferred to employ cupric chloride.

The solution can be, for example, a suspension if its concentration is high or if the copper compound is slightly soluble.

The solution of the copper compound may be, for example, an aqueous solution. This solution or suspension may be added to the oxychlorination reactor continuously or noncontinuously, but during the operation of the oxychlorination. It may, for example, be introduced via a spraying nozzle.

The quantity of copper to be introduced in solution or suspension form is a function of the performance which is t required. The operation may be repeated as many times as necessary. In addition to this solution or suspension of a copper compound it is also possible to add powdered copper, a powdered copper compound or new catalyst containing copper.

The copper or a powdered copper compound may be in the form of a catalyst which is very rich in copper. Very rich in copper means that its content, expressed as copper as a weight percentage of the finished catalyst, is higher than that of the catalyst in operation in the fluidised charge. This value is advantageously at least 1.2 times and preferably from 1.5 to 3 times that of the catalyst in operation in the fluidised charge.

For example, if the catalyst in operation in the fluidised charge contains from 3.5 to 7% by weight of copper, catalyst additions may be made containing approximately 12 % by weight of copper. It is considered that this content of 12 %, expressed as copper, is very rich in copper. It is an unusual value, because the process of obtaining it is much more complicated L than in the case of the usual values of 3 to 8%.

The advantage of the invention, when compared with the traditional operation which consists in compensating the drop in activity and the decrease in the quantity of catalyst only by additions of new catalyst. Is steadier running, activity surges are avoided, and the improvement is more durable.

The following Examples further illustrate the invention.

EXAMPLE 1 1) Test No. Is reference to normal running conditions (not in accordance with the invention).

In a reactor 3 m in diameter, producing 25 tons/h of 1,2-dichloroethane, the operating conditions are the Temperature: Pressure; Residence time: Catalyst system: concentration of 6 (22 tons). The alumina has a surface area of 357 m2/g, a mean diameter of 53 μα, a pore volume of 33 cm3/100 g and a packing density of 1,192 kg/m3. The silica is a Fontainebleau sand (pure silica) with a mean diameter of 50 μα and having a diameter range of from 20 to 300 μιη. See the results obtained in Table I below. 2) Test No. 2 in accordance with the invention: with additions of a solution of cupric chloride following: 245 to 250 *C bars to 30 s tons of alumina impregnated at a % of coDDer icatalvst) olus silica Same conditions as in test No. 1 with, in ( addition, additions o£ a solution of cupric chloride.

Noncontinuous additions are made, corresponding to metal copper quantities of 50 to 200 kg. The results are given in Table I below: TABLE I _H£1_ c2h, (mole mole) -Qa- c2h4 (mole mole) Υβ (Ό Degree of conversion of HCl xD« (Ό Degree of conversion into D12 R C2H4 (X) Degree of conversion into chlorinated products VENT (volume X) Cat. consumption (g/t D12) Cu wt. X of the bed Cu consumption (g/t D12) C2H4 co2 CO °2 Test I 1.97 0.68 99.5 95.5 96.8 0.42 1.20 0.60 5 250 1 to 1.2 0 Test II 1.99 0.63 99 96 97.3 0.30 1.00 0.65 4.25 120 2.5 to 3 2i * The catalyst consumption reflects the additions of catalyst which are identical with the catalyst forming the initial catalytic system (catalyst + silica) - The copper consumption is a consumption of cupric chloride in solution, expressed as copper.

The catalyst consumption and consumption of f cupric chloride solution, expressed in grams per ton of A D 12 manufactured, are shown in Table I. The additions of catalyst and of cupric chloride solution are made to obtain uniform operating conditions.

Claims (11)

1. A process for the oxychlorination of a hydrocarbon to a chlorinated hydrocarbon, which comprises passing the hydrocarbon, a gas containing oxygen and gaseous hydrochloric acid over a fluidisable charge comprising a mixture of an oxychlorination catalyst and inert particles of at least one catalytically and chemically inert solid substance, wherein a solution or suspension of a copper compound is added to the fluidised charge.

2. A process according to Claim 1, wherein the hydrocarbon is ethylene.

3. A process according to Claim 1 or 2, wherein the inert particles are present in an amount of from 1 to 20 times by weight of the amount of catalyst.

4. A process according to any one of Claims 1 to 3, wherein the copper compound is cupric chloride.

5. A process according to any one of Claims l to 4, wherein powdered copper or a powdered copper compound is also added to the fluidised charge.

6. A process according to Claim 1 substantially as described in Example 1 Test No. 2.

7. A fluidisable charge capable of being employed in an oxychlorination reactor, which comprises a mixture of (i) an oxychlorination catalyst and (ii) particles of at least one catalytically and chemically inert solid substance to which a solution or suspension of a copper compound has been added.

8. A fluidisable charge according to Claim 7, wherein the inert particles are present in an amount of from 1 to 20 times by weight of the amount of catalyst.

9. A fluidisable charge according to Claim 7 or 5 8, wherein the copper compound is cupric chloride.

10. A fluidisable charge according to any one of Claims 7 to 9, which also comprises powdered copper or a powdered copper compound.

11. A fluidisable charge according to Claim 7 10 substantially as described in Example l Test No. 2.