Economics vinyl chloride monomer process

Telescope the Process by Combining Stages. This has been done successfully in the conversion of propylene to acrylonitrile by direct ammoxidation rather than oxidation to acrolein followed by reaction with ammonia in a separate stage, as was described in the earlier patent literature. The oxychlorination of ethylene and HC1 directly to vinyl chloride monomer is another good example of the telescoping of stages to yield an economic process. 

World-wide consumption of PVC [poly(vinyl chloride)] has increased dramatically in the past few years. It has now exceeded 8 billion lbs annually. The production of VCM (vinyl chloride monomer) has also been expanded to meet the PVC demand. Future trends for VCM and PVC pro-ductions for the next five years can be forecast on the basis of the raw materials sources, the different process techniques in manufacturing VCM and PVC, and their relative economics, technical merits, and limitations. VCM will be produced principally through the ethylene route by fluid-bed oxyhydrochlorination of ethylene and thermal cracking of ethylene dichloride. PVC will be produced by various processes resulting in more specialized PVC varieties tailored for specific end markets and new processing technologies. 

Vinyl chloride monomer (VCM) is one of the leading chemicals used mainly for manufacturing polyvinyl chloride (PVC). The PVC worldwide production capacity in 2005 was of about 35 million tons per year, with an annual growth of about 3%, placed after polyolefines but before styrene polymers. In the 1990s the largest plant in the USA had a capacity of about 635 ktons [1], but today there are several plants over one million tons. At this scale even incremental improvements in technology have a significant economic impact. Computer simulation, process optimization and advanced computer-control techniques play a determinant role. 

Then, in the 1970s, a number of poly(vinyl chloride) producers were completely surprised when it was found that long-term (20-year) exposure to vinyl chloride could cause rare forms of tumors.22 After the discovery that vinyl chloride was a carcinogen, venting was not permissible. Containment and recovery of the monomer was mandatory. As a result, some older processes and manufacturing facilities could not be economically modified to incorporate containment, and as a result such operations were discontinued. This case is but one example of the impact that necessary and regulated environmental controls can have on manufacturing processes and operations. 

Plastics waste can also serve as a source of chemical raw materials. The potential possibilities are considerable, here, since about 25%-30% of plastics consumed are thrown away as waste each year. The following process has proved to be useful hydrolyzable plastics are first hydrolyzed to their monomers below about 200° C the monomers are fractionally distilled off. Then, the poly(vinyl chloride) in the mixture is dehalogenated to poly(olefins) at about 350° C. The residues are then pyrolyzed at about 600-800° C in a sand-fluidized bed. The product fractions are very dependent on the composition of the pyrolyzed material. Generally, however, up to 40% fractions of the economically desirable aromatics are obtained by this high-temperature pyrolysis, and, indeed, when additional steam is blown into the system to reduce carbon char formation. Alternatively, what is known as a low-temperature pyrolysis can be carried out at about 400° C in poly(ethylene) wax as reaction medium. In this case, readily volatile oils of high olefin content are obtained together with waxes and carbon black. 

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