This column is based on “Ethylene Dichloride from Ethylene and Chlorine,” a report published by Intratec. It can be found at: www.intratec.us/analysis/edc-e11a.
Ethylene dichloride (also known as 1,2-dichloroethane, as well as EDC and DCE) is by far the most widely produced chlorinated hydrocarbon. The vast majority (~95%) of EDC is employed in the manufacture of vinyl chloride monomer (VCM), which is in turn mostly used as the starting material for the plastic polyvinyl chloride (PVC). EDC can also be used as an intermediate in the production of chlorinated solvents, such as trichloroethylene, ethylene amines, vinylidene chloride and trichloroethane.
The following describes a process for EDC production from ethylene and chlorine. Figure 1 presents a simplified flow diagram of the process.
Direct chlorination. In the direct chlorination step, chlorine and ethylene are fed to a high-temperature chlorination (HTC) reactor filled with liquid EDC as the reaction medium. Heat from the highly exothermic reaction is removed by boiling off EDC, and by the circulation of EDC, which is recycled from the product column downstream. Ferric chloride (FeCl 3) is used as a catalyst. About 99% of the ethylene and almost 100% of chlorine are converted, with high selectivity, to EDC. Unavoidable side reactions generate polychlorinated compounds as byproducts (mainly 1,1,2-trichloroethane). Among the byproducts, those with boiling points higher than EDC are primarily withdrawn from the bottom of the reactor as a liquid stream. The gaseous effluent from the chlorination unit, containing the EDC product, is routed to the purification steps downstream.
Product column. In this area, the gaseous effluent, rich in EDC, is passed through a heat exchanger, where it generates steam while being partially condensed by boiler feedwater. The EDC-rich stream is then fed to a distillation column, where it is purified by separating residual byproducts. The stream withdrawn from the column overhead is then cooled in a cooling water condenser, yielding a liquid stream composed of EDC 99.5 wt.%, which is pumped to the EDC tank. Non-condensed gases — mainly ethylene, nitrogen, chlorine, HCl and residual water and EDC — are then passed through a second condenser using refrigerant fluid. After this second condensation step, uncondensed gases are routed to an incinerator located outside battery limits. The column bottom product composed of EDC and polychlorinated compounds is recycled to the direct chlorination reactor. Part of this stream is purged to avoid the buildup of impurities.
EDC tank. The EDC product is stored in intermediate tanks before it is directed to storage facilities located outside battery limits.
Ethylene dichloride production routes are primarily based on the chlorination of ethylene: direct chlorination by chlorine or oxychlorination by hydrogen chloride. Figure 2 presents these two different pathways for EDC production.
The total operating cost (raw materials, utilities, fixed costs and depreciation costs) estimated to produce EDC was about $510 per ton of EDC in the second quarter of 2014. The analysis was based on a plant constructed in the U.S. with capacity to produce 500,000 metric tons per year of EDC.
Edited by Scott Jenkins
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