Coke and Byproduct Formation during 1,2-Dichloroethane Pyrolysis in a Laboratory Tubular Reactor

A laboratory quartz tube reactor apparatus was used to study coke and byproduct formation in 1,2-dichloroethane, also known as ethylene dichloride (EDC), pyrolysis. The effects of metal coupons, feed purity, and temperature on the amount of coke deposited and exit gas-phase compositions were analyzed. Coke formation on nickel, chromium, iron, and stainless steel metal coupons was investigated by scanning electron microscopy/energy-dispersive X-ray spectroscopy and ion-coupled plasma atomic adsorption spectroscopy. Based on scanning electron micrographs, different metals have little effect on the nature of coke formed, and it appears that coke is formed by tar droplet formation in the gas phase with subsequent impingement on surfaces. FeCl 2 formation and migration along the reactor accompanied coke formation on the metal coupons. It was determined that the presence of metals coupons increases EDC conversion as well as coke formation. Two distinct types of coke are formed: hard coke is formed in the hot zone of the reactor and soft coke is formed at the exit. Increases in reaction temperature, CCl 4 in the feed, and presence of FeCl 2 all increase both types of coke formation, but hard coke in particular. A total of 0.3 wt % Cl 2 in the feed resulted in 60% EDC conversion at 380 °C. This also reduced by more then half the total amount of hard coke formed, as compared to the lowest amount of hard coke formed by all other runs, but increased the total byproduct formation. EDC feed obtained from a commercial vinyl chloride monomer manufacturing plant produced 28% EDC conversion at 480 °C and large amounts of coke. Chloroprene was the only chemical species that strongly correlated with total coke formation.