Vinyl chloride monomer

Vinyl Chloride Monomer (VCM) is a colorless organochloride. Vinyl chloride is a gas with a sweet odor. It is highly toxic, flammable, and carcinogenic. It is used to produce the polymer Polyvinyl Chloride (PVC). PVC has the advantage of being utilized in conversion and fabrication processes with great flexibility, such that end products cover a wide range, including pipe and fittings, profiles and tubes, siding, wire and cable, windows, doors, floorings, film and sheet, and bottles. While the most important ultimate end-use markets are commercial, residential, and nonresidential construction, a wide variety of PVC converted products are also utilized in agricultural, electrical (wire and cable), and health care markets.

Manufacturing from ethylene

Most of the vinyl chloride produced nowadays starts with chlorine, ethylene, and air. High purity ethylene dichloride (EDC) is prepared by reacting ethylene and chlorine in the presence of iron(III) chloride as a catalyst. Vinyl chloride plants use recycled HCl to produce more ethylene dichloride via oxychlorination, which entails the reaction of ethylene, oxygen, and hydrogen chloride over a copper(II) chloride catalyst. The reaction is highly exothermic. When heated to 500°C at 15 to 30 bar (225 to 450 psi) ethylene dichloride vapor decomposes to produce vinyl chloride and anhydrous HCl. The thermal cracking reaction is highly endothermic, and is generally carried out in a fired heater. Even though residence time and temperature are carefully controlled, it produces significant quantities of chlorinated hydrocarbon side products. In practice, ethylene dichloride conversion in vinyl chloride is relatively low (50 to 60%). The furnace effluent is immediately quenched with cold ethylene dichloride to stop undesirable side reactions. The resulting vapor-liquid mixture then goes to a purification system. Some processes use an absorber-stripper system to separate hydrochloric acid (HCl) from the chlorinated hydrocarbons, while other processes use a refrigerated continuous distillation system. Very hazardous wastes are generated in the recovery of vinyl chloride. These wastes are burned onsite in thermal oxidizers.

Production from acetylene

Acetylene reacts with anhydrous hydrogen chloride gas over a mercuric chloride catalyst to give vinyl chloride. The reaction is exothermic and highly selective. Product purity and yields are generally very high. This industrial route to vinyl chloride was common before ethylene became widely distributed. When vinyl chloride producers shifted to using the thermal cracking of ethylene dichloride described above, some used byproduct HCl in conjunction with a collocated acetylene-based unit. China still uses this method to produce vinyl chloride due to the large reserves of coal from which acetylene is produced.

GAB Neumann’s process equipment

The vinyl chloride monomer (VCM) manufacturing process involves the recovery (absorption and further processing) of very large amounts of hydrochloric acid therefore the need for usually large corrosion resistant process equipment. Organochloride effluents have to be treated usually through thermal oxidation thus generating more hydrochloric acid.

GAB Neumann supplies annular groove graphite heat exchangers, graphite heaters, graphite coolers, graphite block heat exchangers, graphite absorbers, graphite quenches, graphite columns as well as hydrochloric acid recovery units to the VCM producers.

Associated products:

Impervious graphite annular groove interchangers

Impervious graphite annular groove heavy-duty condensers

Impervious graphite annular groove partial condensers

Impervious graphite block heat exchangers

Quenches

Annular groove isothermal absorbers

Impervious graphite columns

Hydrochloric acid recovery units