Process for minimizing corrosion and coking in an ethylene dichloride plant

摘要

A process is disclosed for the economical operation of a commercial ethylene dichloride (EDC) cracking furnace which typically is prone to coking of the tubes through which the EDC is flowed. The EDC cracking furnace is found to be critically sensitive to the presence of trace amounts, 30 ppm or more of FeCl.sub.3 and/or 20 ppm or more of free chlorine, which cause coking of the tubes of the furnace. The coking of the tubes is minimized by maintaining less than 30 ppm by weight of FeCl. sub.3 or less than 20 ppm of free chlorine in the EDC feed to the EDC furnace. In the particular instance where EDC is produced at least in part in a high temperature direct chlorination ("boiling") reactor constructed from mild steel, this goal requires that the chlorine content of the effluent from the boiling reactor be controlled so as not to exceed 20 ppm. But this is to be done without using more than a 2% by weight excess of ethylene over the stoichiometric amount required to produce the EDC in the boiling reactor. The goal is met by controlling the pressure drop and contact time through a polishing reactor, provided the operation of the boiling reactor is also controlled. The requirements are met with a packed bed of catalyst support having a geometry such that the outer surface area per unit volume of packed catalyst is less than 7. 8 cm.sup.2 /ml and the catalyst support has a wall thickness of from about 2.5 mm to about 6.5 mm. The polishing reactor removes the FeCl.sub. 3 which may be present and also allows the conversion of at least 90% of the free chlorine in the chlorine-rich EDC (100 ppm to about 3000 ppm Cl. sub.2). This results in continuous operation of the EDC furnace for much longer periods than is normal without the use of a polishing reactor.