Vinyl chloride monomer production

Abstract

 This invention relates to a process for producing vinyl chloride monomer by pyrolysing a mixture of 1,2-dichloroethane and the isomer 1,1-dichloroethane. It has been found that mixtures containing between 0.1 and 10% by weight of the 1,1-isomer improves the yield of the monomer otherwise obtainable by using the 1,2-isomer alone.

Description

[0001] The present invention relates to a process for the preparation of vinyl chloride by the dehydrochlorination of mixtures of isomeric dichloroethanes.

[0002] It is known that vinyl chloride can be produced by the pyrolytic dehydrochlorination of 1,2-dichloroethane. The process involves the passing of 1,2-dichloroethane through a small diameter reaction tube in which it is heated to elevated temperatures to bring about the dehydrochlorination thereof. In contrast to this, it has not hitherto been possible to convert the isomeric 1,1-dichloroethane, which is a by-product of the pyrolysis of 1,2-dichlorethane, into vinyl chloride in economic yields. Published data indicate that 1,1-dichloroethane pyrolyses very much more slowly than 1,2-dichloroethane and hence it has always been considered desirable to separate the two isomers prior to pyrolysis.

[0003] It has now been found that mixtures of these isomers can be pyrolysed without impairing the quality or yield of vinyl chloride monomer produced by regulating the concentration of the two isomers in the mixture being pyrolysed.

[0004] Accordingly the present invention is a process for producing vinyl chloride comprising pyrolysing at elevated temperature 1,2-dichloroethane mixed with between 0.1 and 10% by weight of 1,1-dichloroethane.

[0005] The above reaction may be carried out in conventional tubular reactors as normally employed for the pyrolysis of 1,2-dichloroethane. The pyrolysis of mixtures of 1,1-dichloroethane and 1,2-dichloroethane in the specified range of concentrations significantly increases the conversion of 1,1-dichloroethane from about 20% (for the pure isomey) to above 90% (when present in the isomeric mixtures). Both below and above this range the conversion of the 1,2-isomer is depressed relatively. The amount of the 1,1-dichloroethane in the isomeric mixture being pyrolysed is preferably between 1 and 8%. The 1,1-isomer may be mixed with the pyrolysis feed prior to the introduction thereof into the reaction zone. Alternatively it may be incorporated in the pyrolysis feed in the reaction zone itself at the time of pyrolysis.

[0006] The pyrolysis of the isomeric mixtures may be carried out in packed or unpacked tubular reactors. Where packed reactors are used they may suitably be packed with ceramic spheres.

[0007] The pyrolysis of the isomeric mixture of dichloroethanes according to the present invention is suitably carried out at a temperature of between 450° and 550°C, preferably between 500° and 535°_C.

[0008] The pyrolysis of the isomeric mixture of dichloroethanes may be carried out at sub-atmospheric, atmospheric or super-atmospheric pressures. It is, however, preferred to use super-atmospheric pressure, preferably below 500 psig.

[0009] The pyrolysis of the isomeric mixture of dichloroethanes may be carried out in a continuous manner.

[0010] The advantages of the present invention are illustrated with reference to the.following Examples.

EXAMPLES

[0011] The apparatus, run at atmospheric pressure, consisted of feed reservoir, metering pump, vaporiser, cracker tube, coolers, organic product receiver, hydrogen chloride scrubbing column, scrub liquor reservoir and wet gas meter. There was also a nitrogen diluent/ carrier feed applied to the vaporiser inlet.

[0012] Feedstocks comprising pure 1,2-dichloroethane (1,2-EDC), 1,2-dichloroethane with up to 10 per cent by weight of 1,1-dichloroethane (1,1-DCE) and also pure (98.2% by weight) 1,1-DCE were pyrolysed at a peak temperature of 500°C and a contact time of 4.5 seconds under conditions found to give a 50 per cent by weight conversion of pure 1,2-dichloroetliane.

[0013] Analysis of feedstock, organic condensate, scrub liquor and vent gas were used to calculate the conversions tabulated below.

Claims

1. A process for producing vinyl chloride comprising pyrolysing at elevated temperature 1,2-dichloroethane mixed with between 0.1 and 10% by weight of 1,1-dichloroethane.

2. A process according to claim 1 wherein the amount of 1,1-diehloroethane in the isomeric mixture being pyrolysed is between 1 and 8% by weight.

3. A process according to claim 1 or claim 2 wherein the pyrolysis of the isomeric mixture of dichloroethanes is carried out at a temperature between 450°C and 550°C

4. A process according to claim 3 wherein the pyrolysis of the isomeric mixture of dichloroethanes is carried out at a temperature between 500 and 535°C.

5. A process according to any of the preceding claims wherein the pyrolysis of the isomeric mixture of dichloroethanes is carried out at superatmospheric pressures.

6. A process according to claim 5 wherein the superatmospheric pressure is below 500 psig.

7. A process according to any of the preceding claims wherein the pyrolysis of the isomeric mixture of dichloroethanes is carried out in a continuous manner.

8. A process for producing vinyl chloride according to claim 1 as hereinbefore described with reference to the Examples.

9. Vinyl chloride whenever produced by a process according to any of the preceding claims.