Today, vinyl chloride is almost exclusively manufactured by thermal cleavage (dehydrochlorination) of 1,2-dichloroethane (EDC). The feedstock for the thermolysis can be obtained from two routes:
1. By the older method, addition of chlorine to
2. By the more modcrn process, oxychlorination of ethylene with hydrogen chloride and O₂ or air.

To 1:

Ethylene chlorination gencrally takes place in the liquid phase in a bubble-column reactor using the rcaction product EDC as reaction medium with dissolved FeCl₃, CuCl₂, or SbCl₃ as catalyst at 40-70°C and 4-5 bar:

The addition of chlorine probably takes place according to an electrophilic ionic mechanism in which the catalyst causes polarization of the chlorine molecule, thereby facilitating an electrophilic attack.

Selectivity to 1,2-dichlorocthane can reach 98% (based on C₂H₄) and 99% (based on Cl₂).

The chlorination of clhylcnc can also be carried out in the gas phase at 90-130°C. Formation of 1,2-dichlorocthane probably results from a radical chain mechanism, initiated by chlorine radicals formed at the reactor surface by homolysis of chlorine molecules.

To 2:

The oxychlorination of ethylene is generally conducted in the gas phase. When ethylene is reacted with anhydrous HCl and air or oxygen at 220-240 °C and 2-4 bar, it is converted into EDC and H₂O:

Supported CuCl₂ serves as catalyst. The supports often contain activators and stabilizers such as chlorides of the rare earths and alkali metals. No free chlorine is formed under the reaction conditions; CuCl₂ is the chlorinating agent which is subsequently regenerated with air and HCl through the intermediate oxychloride. This is similar to the oxychlorination of benzene to chlorobenzene. Catalysts of this type, which are employed for example by Distillers and Shell, allow EDC selectivities of about 96% to be attained. The ethylene conversion is almost quantitative when a slight excess of HCl and air is used.

In the USA in 1964, Goodrich, Dow, and Monsanto were among the first firms to operate an industrial oxychlorination process. Today, numerous other firms have developed their own processes based on a similar principle.

There is a basic difference in the process operation which affects the heat removal from this strongly exothermic reaction. Ethyl Corp., Goodrich, Mitsui Toatsu Chemicals, Monsanto, Scientific Design (based on the Monsanto process), and RhBne-Poulenc use a fluidized-bed reactor, while the other manufacturers employ a fixed-bed reactor. Another method to limit the local development of heat is the use of catalysts diluted with inert materials.

Besides the gas-phase processes for oxychlorination, Kellogg has developed a method involving an aqueous CuCl₂ solution acidified with hydrochloric acid. Ethylene can be converted into 1,2-dichloroethane by oxychlorination with 7-25% conversion and 96% selectivity at 170-185 °C and 12-18 bar. The advantages of this modification lie with the use of aqueous hydrochloric acid and good heat removal by H₂O evaporation. However, considerable corrosion problems arise from the handling of the hot aqueous hydrochloric acid.

The further conversion of 1,2-dichloroethane to vinyl chloride used to be carried out in the liquid phase with alkali. Today, gasphase dehydrochlorination is used exclusively:

The endothermic cleavage of EDC is conducted at 500-600°C and 25 - 35 bar at high flow rates in tubes made of special steels (Ni, Cr) with high heat resistance. This is a thermal reaction that proceeds by a radical chain mechanism. In many cases, carbon tetrachloride is added in small amounts as an initiator. More important is the purity of the EDC used (> 99.5%), since impurities can easily inhibit the thermolysis (radical trapping). Catalytic cracking at 300-400°C on pumice (SiO₂, Al₂O₃, alkalis) or on charcoal, impregnated with BaCl₂ or ZnCl₂, has not found more widespread application due to the limited life of the catalysts.

Conversion of EDC in thermal cracking amounts to 50-60% with a selectivity to vinyl chloride of greater than 98% (based on EDC). The reaction mixture is directly quenched with cold EDC, releasing gaseous hydrogen chloride. After separation of the vinyl chloride by distillation, the EDC is fed back to the dehydro-chlorination step.

Modern industrial processes for the manufacture of vinyl chloride are characterized by an extensive and thus very conomical integration of the above-mentioned partial steps of ethylene-chlorine addition, EDC thermolysis, and ethylene oxychlorination. In this integrated operation, chlorine is introduced to the process by addition to ethylene, and hydrogen chloride from the thermolysis is used in the oxychlorination.