EDC is made by the chlorination of ethylene via one of two processes: direct chlorination using pure chlorine and ethylene; or oxychlorination in which ethylene reacts with chlorine in hydrogen chloride. Many EDC/VCM plants employ a combination of chlorination and oxychlorination to consume the hydrogen chloride by-product from the cracking of EDC to VCM.
Direct chlorination is performed in the liquid phase where liquid chlorine and pure ethylene are reacted in the presence of ferric chloride, although other catalysts have been suggested. The reaction can be carried out at either low (20-70oC) or high (100-150oC) temperatures. The low temperature process has the advantage of low by-product formation but requires more energy to recover the EDC. The high temperature process utilises the heat of reaction in the distillation of the EDC, leading to considerable energy savings.
In the oxychlorination process, pure ethylene and hydrogen chloride, mixed with oxygen, are reacted at 200-300oC and 4-6 bar in the presence of a catalyst, usually cupric chloride. The reaction takes place in either a fixed bed or fluid bed reactor, the latter being preferred as it is easier to control the temperature. The oxychlorination unit can use air or pure oxygen but the oxygen-based route is favoured on environmental and efficiency grounds.
A new high temperature direct chlorination process that claims to have significantly higher yields and purity has been developed by VinTec, the technology licensing subsidiary of German PVC producer Vinnolit. In the direct chlorination EDC is produced by chlorination of ethylene in liquid EDC phase in one reactor. Conventional direct chlorination processes operate with FeCl3 as catalyst, leading to a variety of highly chlorinated by-products.
The new Vinnolit catalyst is an inorganic complex, which enhances the velocity of chlorine-addition to ethylene. This positive effect is achieved over a wide temperature range. The catalyst may be charged to the reactor before start-up or during normal operations. There is no catalyst consumption in normal operation hence a refill is not required. The catalyst can be used in a liquid-loop-reactor as well as in a boiling reactor. The EDC thus produced has a quality which permits the direct feed to the EDC cracker without distillation.
It has been tested on a 3000 tonnes/year pilot plant in Gendorf, Germany. The first commercial application of the process was in a 250,000 tonnes/year plant at LVM's Tessenderlo, Belgium site, which came on-stream in 2006.
Ethylene dichloride
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Ethylene dichloride
Uses and Outlook
With about 95% of ethylene dichloride (EDC) being used in the manufacture of vinyl chloride monomer (VCM), nearly all of which goes into polyvinyl chloride (PVC), EDC supply/demand balances are influenced by the PVC market. In addition, many EDC plants are integrated with VCM production.
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