Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Patent
1995-08-15
1997-09-02
Siegel, Alan
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
570225, C07C 1710
Patent
active
056634650
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for improving the efficiency of the oxychlorination of ethane to vinyl chloride monomer (VCM). The increase in efficiency is obtained by recycling the by-products of the reaction.
Most commercial processes for the production of VCM utilise ethylene and chlorine as the raw materials. Ethylene is in general chlorinated by contact with chlorine and a catalyst in liquid 1,2-dichloroethane. The dichloroethane is subsequently dehydrochlorinated at an elevated temperature to yield VCM and hydrogen chloride.
The use of ethylene as a starting material is a significant factor in the cost of producing VCM. In general, significant reductions in this cost can only be achieved by economies of scale since established processes are operating at close to maximum efficiency.
A further disadvantage of the use of ethylene is that the dehydrochlorination of the 1,2-dichloroethane intermediate yields hydrogen chloride. Disposal thereof is usually achieved by catalytic oxychlorination with ethylene in a further processing step to yield more 1,2-dichloroethane.
An alternative, known method for the production of VCM involves the use of ethane. The use of alternative hydrocarbon raw materials, of which ethane is the primary candidate, immediately addresses the issue of the cost of ethylene by substituting it with a cheaper alternative. Additionally, the chemistry of VCM production using alternative hydrocarbons may hold advantages. For example, VCM production can be achieved in a single step.
Three chemical approaches are known for the conversion of ethane to VCM. These are gas phase chlorination, catalysed oxidation and oxychlorination. Of these, a process based on oxychlorination is the most attractive: products+H.sub.2 O.
The chlorine source may be Cl.sub.2, HCl or a chlorinated hydrocarbon. Where HCl is the source, the opportunity arises to utilise one of the intermediate products of VCM production from ethylene.
The production of VCM from ethane has not enjoyed commercial success. A number of attempts have been made, but the processes used have suffered from a number of drawbacks which, while inconvenient in a laboratory, become unacceptable when the process is applied on an industrial scale.
In our copending U.K. Patent Application No. 9318501.5, filed contemporaneously herewith, we describe an oxychlorination catalyst and a set of reaction conditions which are suitable for the operation of an ethane oxychlorination process on an industrial scale. Furthermore, in our copending U.K. Patent Application No. 9318507.2, also filed contemporaneously herewith, we describe a method for increasing the selectivity of the oxychlorination reaction to VCM.
However, this selectivity can never be absolute. In our copending U.K. Patent Application No. 9318501.5, the generation of by-products is carefully assessed, and even under the most favourable conditions large amounts of chlorinated hydrocarbons other than VCM are produced.
A major attraction of the use of ethane for the production of VCM is the cost advantage of the raw material. In order for this cost advantage to be maintained, it is important to eliminate the sources of inefficiency in the reaction process. Therefore, there is a requirement for a method for recovering the by-products of the reaction. Since these by-products cannot be disposed of by direct sales, it would be advantageous to be able to derive a useful saleable product thereform at the minimum cost.
In the prior art, the generation of chlorinated by-products of the oxychlorination reaction is largely ignored.
For example, in GB 1256245 (Princeton Chemical Research, Inc.) "other chlorinated materials" are produced at a level of about one tenth of the yield of vinyl chloride. There is no suggestion in GB 1256245 as to how such by-products should be dealt with. However, it can be seen that they constitute an appreciable fraction of the total yield of the reaction.
U.S. Pat. No. 3,879,481 (Lummus Co.) acknowledges the production of chlorinated by-products in the form of chlorinated
REFERENCES:
patent: 3879481 (1975-04-01), Sze et al.
patent: 3937744 (1976-02-01), Riegel
Clegg Ian Michael
Hardman Ray
EVC Technology AG
Siegel Alan
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