TABLE OF CONTENTS The starting materials for commercial polyvinyl chloride (PVC) production are ethylene and chlorine. Ethylene is derived from a cracking process involving feedstock based on oil or natural gas hydrocarbons, such as ethane, propane, or butane. The process involves catalysis at high temperatures and pressures to produce ethylene and other co-products, such as propylene and butadiene. The ethylene is further processed to separate it from the co-products.
Chlorine is manufactured industrially, in the manufacture of caustic soda, by the cell electrolysis of salt water (saturated brine). Approximately 35% of Europe s chlorine production goes into PVC production. Three different electrolysis processes are currently in use (www.eurochlor.org):
Mercury cell which uses a mercury cathode ( ) along the cell bottom and titanium anodes (+) located above. The application of a direct electrical current liberates chlorine at the anode with sodium dissolving into the mercury cathode to form an amalgam. In a separate reactor, the amalgam reacts with water to produce hydrogen and caustic soda solution (50%). This regenerates the mercury, which is returned to the electrolytic cell. The process is very energy intensive and appropriate measures are necessary to protect the workforce and the environment from the effects of mercury. The current emission standard, of a maximum 2 g per tonne of capacity installed, is being met by treatment of the spent brine before discharge. However, the industry has been criticised for its poor environmental performance in the past on mercury discharge. This process was the first to...
