Under the direct chlorination method, ethylene and chlorine (obtained from electrolysis of salt) react within a catalyst-containing reactor to form the intermediate material EDC. EDC is then thermally cracked to yield VCM at a few hundred °C. When the hydrogen chloride obtained as by-product from the above method reacts with ethylene in the presence of catalyst and air (or oxygen), EDC is obtained again. This is called the oxychlorination process. When EDC from the oxychlorination process is dehydrated and then thermally cracked (together with the EDC from the direct chlorination process), VCM is obtained. These two methods are usually combined at the major VCM plants in Western Europe.