Oxychlorination of ethylene in two stage fixed-bed reactor

Details Oxychlorination of ethylene in two stage fixed-bed reactor Oxychlorination of ethylene in two stage fixed-bed reactor

1997-10-22

1998-11-24

Siegel, Alan

Organic compounds -- part of the class 532-570 series

Organic compounds

Halogen containing

C07C 1715

Patent

active

058410090

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/1B96/00159 filed Feb. 1, 1995.
The present invention relates to the oxychlorination of ethylene in a fixed bed reactor system which consists of a single reactor, to produce chlorinated hydrocarbons, particularly 1,2-dichloroethane (EDC).
It is well known that hydrocarbons such as ethylene may be chlorinated by reacting them with hydrogen chloride and gases containing elemental oxygen, particularly air or oxygen enriched air, in the presence of a catalyst at elevated temperatures and pressures in order to produce chlorinated hydrocarbons such as EDC. The reaction may be carried out with two different reactor technologies. The first is fluid bed reactor technology wherein a gaseous mixture of reactants is contacted with a fluidizable catalyst powder. The second is fixed bed reactor technology, in which the gaseous reactants flow over a fixed catalyst inside the reactor.
Fluid bed reactors have a number of drawbacks, such as potential stickiness of the catalyst powder, unsteady operation, poor selectivity owing to the gas and catalyst solids back mixing in the reactor, loss of heat transfer owing to fouling of the cooler bundle and limits in reagent velocity imposed by the need to avoid catalyst loss by elutriation from the reactor.
Fixed bed reactor technology has been developed in order to overcome these problems (see U.S. Pat. No. 3,892,816 and U.S. Pat. No. 4,123,467).
Although the fixed bed reactor overcomes many of the problems incurred with the fluid bed reactor system, a number of new problems have been encountered. A major problem is the difficulty, in the fixed bed reactor, of transferring the heat developed by the exothermic oxychlorination reaction away from the reactor to prevent overheating. For this reason, all the necessary reagents may not be fed in the correct stoichiometric ratio to the reactor. Moreover, because it can be unsafe to have an oxygen concentration of above 8% in the mixture feeding the reactor, for flammability reasons, the reaction is carried out in two or more subsequent stages (usually three) such that the ethylene is introduced into the first reactor while the HCl and oxygen feeds are split between the reactors. Unreacted ethylene plus some inert gases are recycled back to the first reactor.
In a further attempt to reduce the incidence of hot spots and the like, it is known to alter the activity profile of the catalyst within a fixed bed reactor such that the activity increases in the direction of flow. For example, see European patent application 0146925. However, in the prior art, even when a profiled catalyst is used it has been deemed necessary to use a multi-reactor system.
The three-reactor systems of the prior art have a number of disadvantages. For example, because the contact time decreases from the first to the third stage, the partial pressure of the reagents is also decreased. This means that the three reactors have to be operated at different temperatures, requiring separate cooling jackets. Moreover, in spite of these precautions, the productivity of each reactor is different. This is particularly notable in the third reactor, where productivity is about 50% of that in the first reactor.
Furthermore, as a result of the high pressure drop which occurs across the whole catalytic bed system in three reactors, the recycling of vent gases necessitates an elevated energy consumption.
Moreover, it is self-evident that setting up and maintaining a three reactor system is more costly that a system involving a single or twin reactors.
We have now developed a new process for the catalytic oxychlorination of ethylene which makes use of a twin reactor system. Owing to a particular catalytic loading scheme, the same EDC productivity as a three reactor system can be maintained, which means that total productivity, with respect to the volume of catalysis involved, is 50% greater than that achievable in a three reactor system.
According to a first aspect of the invention, we provide a method for the oxychlorination of ethylene to produce 1,2-d

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