Vinyl chloride production from acetylene

If desired, the hydrochloric acid can be obtained via cracking of ethylene dichloride. The oxychlorination process freed vinyl chloride production from the economics of a more costly raw material, acetylene. Deliberate acetylene manufacture is energy intensive and relatively expensive. By-product acetylene from gas cracking is less expensive, but it has not been available in sufficient supply for the large, approximately billion-pound-per-year plus, vinyl chloride production units. 

Vinyl chloride was first discovered in the early 1800s. It was made from the reaction of dichloroethane and alcoholic potash. Later it was discovered that vinyl chloride polymerized spontaneously on prolonged exposure to sunlight, and studies of the white solid product, polyvinyl chloride, were carried out and published in 1872. In 1912, a commercial process for vinyl chloride produced from acetylene and hydrochloric acid with a mercuric chloride catalyst was patented in Germany and assigned to Chem-ische Fabrik Griesheim-Electron. By 1930, vinyl chloride was being produced as a commercial product based on this process 117,18]. 

By-products from EDC pyrolysis typically include acetjiene, ethylene, methyl chloride, ethyl chloride, 1,3-butadiene, vinylacetylene, benzene, chloroprene, vinyUdene chloride, 1,1-dichloroethane, chloroform, carbon tetrachloride, 1,1,1-trichloroethane [71-55-6] and other chlorinated hydrocarbons (78). Most of these impurities remain with the unconverted EDC, and are subsequendy removed in EDC purification as light and heavy ends. The lightest compounds, ethylene and acetylene, are taken off with the HCl and end up in the oxychlorination reactor feed. The acetylene can be selectively hydrogenated to ethylene. The compounds that have boiling points near that of vinyl chloride, ie, methyl chloride and 1,3-butadiene, will codistiU with the vinyl chloride product. Chlorine or carbon tetrachloride addition to the pyrolysis reactor feed has been used to suppress methyl chloride formation, whereas 1,3-butadiene, which interferes with PVC polymerization, can be removed by treatment with chlorine or HCl, or by selective hydrogenation. 

Acetylene is usually thought of as a coke-derived product via calcium carbide. But acetylene, used for vinyl resins manufacture, has been made by partial oxidation of natural gas methane for over a year now in a major installation in Texas, which is now being expanded (6). Moreover, another Gulf Coast plant now under construction will also produce acetylene from natural gas, utilizing this product for acrylonitrile as well as vinyl chloride production (28). These moves represent a momentous advance, pointing to the future entry of natural gas to an even greater degree into aliphatic syntheses. 

A competing process produces vinyl chloride from acetylene, which also can be derived from petroleum feed stocks but is usually made from calcium carbide. It has been estimated (17) that 45% of current production of vinyl chloride is from ethylene, the remainder from acetylene. 

Ethene and ethane account for 80% of the mass of the hydrocarbons identified as products. Trace amounts of methane and acetylene are also produced (Orth and Gillham, 1996). The reduction of PCE forms cis-1,2-dichloroethylene (DCE), frans-l,2-DCE, 1,1-DCE, vinyl chloride, ethylene, dichloroacetylene, acetylene, ethene, ethane, chloroacetylene, methane, and several alkenes ranging from C3 to C6. The trace amounts of dichloro-ethylene and vinyl chloride formed during the reduction of PCE and TCE are further reduced (Burris et al., 1995). Reaction rates vary with substrate, chemical, and microbiological conditions. Selected f1/2 values are provided in Table 13.3. 

One of the oldest applications of activated carbon as catalyst carrier is at the production of a HgCk supported catalyst. The HgCh content is about 10 %. This catalyst is used for the production of vinyl chloride monomer from HCl (in the vapour phase) and acetylene... 

We described the production of vinyl chloride first firom acetylene and then firom ethylene to illustrate an important point about industrial organic chemistry. The aim is to produce a desired chemical from readily available and inexpensive starting materials by reactions in which by-products can be recycled. All chemical companies now support this objective to minimize both costs and production of materials that require disposal or can harm the environment. 

The principal chemical markets for acetylene at present are its uses in the preparation of vinyl chloride, vinyl acetate, and 1,4-butanediol. Polymers from these monomers reach the consumer in the form of surface coatings (paints, films, sheets, or textiles), containers, pipe, electrical wire insulation, adhesives, and many other products which total biUions of kg. The acetylene routes to these monomers were once dominant but have been largely displaced by newer processes based on olefinic starting materials. 

At one time, the only commercial route to 2-chloro-1,3-butadiene (chloroprene), the monomer for neoprene, was from acetylene (see Elastomers, synthetic). In the United States, Du Pont operated two plants in which acetylene was dimeri2ed to vinylacetylene with a cuprous chloride catalyst and the vinyl-acetylene reacted with hydrogen chloride to give 2-chloro-1,3-butadiene. This process was replaced in 1970 with a butadiene-based process in which butadiene is chlorinated and dehydrochlorinated to yield the desired product (see Chlorocarbonsandchlorohydrocarbons). 

Photochemistry. Vinyl chloride is subject to photodissociation. Photexcitation at 193 nm results in the elimination of HCl molecules and Cl atoms in an approximately 1.1 1 ratio (69). Both vinyUdene ( B2) [2143-69-3] and acetylene have been observed as photolysis products (70), as have H2 molecules (71) and H atoms [12385-13-6] (72). HCl and vinyUdene appear to be formed via a concerted 1,1 elimination from excited vinyl chloride (70). An adiabatic recoil mechanism seems likely for Cl atom elimination (73). As expected from the relative stabiUties of the 1- and 2-chlorovinyl radicals [50663-45-1 and 57095-76-8], H atoms are preferentially produced by detachment from the P carbon (72). Finally, a migration mechanism appears to play a significant role in H2 elimination (71). 

Pyrolysis. Vinyl chloride is more stable than saturated chloroalkanes to thermal pyrolysis, which is why nearly all vinyl chloride made commercially comes from thermal dehydrochlorination of EDC. When vinyl chloride is heated to 450°C, only small amounts of acetylene form. Litde conversion of vinyl chloride occurs, even at 525—575°C, and the main products are chloroprene [126-99-8] and acetylene. The presence of HCl lowers the amount of chloroprene formed. 

The photolysis of chlorodiazirine was investigated in several cases. From chloromethyl-diazirine (232) vinyl chloride was formed as the stable primary product of stabilization of chloromethylcarbene, with acetylene and hydrogen chloride as secondary products. Some 1,1-dichloroethane was assumed to have been formed through a linear diazo compound by reaction with HCl. Added HBr yielded 1-bromo-l-chloroethane (76MI5Q800). 

On November 8, 2000, U.S. EPA listed as hazardous two wastes generated by the chlorinated aliphatics industry.18 The two wastes are wastewater treatment sludges from the production of ethylene dichloride or vinyl chloride monomer (EDC/VCM), and wastewater treatment sludges from the production of vinyl chloride monomer using mercuric chloride catalyst in an acetylene-based process. 

Vinyl chloride, formerly obtained from acetylene, is now produced by the transcatalytic process where chlorination of ethylene, oxychlorination of the by-product hydrogen chloride, and dehydrochlorination occur in a single reactor. 

It is used in reactions where aq HC1 is not suitable, such as production of vinyl chloride from acetylene or of alkyl chlorides from olefins (Ref 2, p 256 Ref 3, p 588-R)... 

Another chlorinated compound which, like vinyl chloride, is used only in its polymeric form, is chloroprene (2-chloro-l,3-butadiene), which is polymerized to make neoprene, first produced in 1940. As far as is known (17) y the monomer is made commercially only from acetylene via addition of hydrochloric acid to monovinylacetylene in the presence of cuprous chloride, but syntheses from butylenes or butadiene have been described. The production of chloroprene exceeded 100,000,000 pounds per year at the wartime peak and has been somewhat lower since then, but in view of the many valuable properties of the neoprene rubber it will continue to be important. 

In addition to the polymer, copolymers of vinyl chloride with other vinyl monomers are important commercial plastics. Copolymers with vinyl acetate, which is produced from acetylene and acetic acid, are widely used in sheeting, surface coating, and filaments, being less brittle and more readily soluble in organic solvents than is pure polyvinyl chloride. Copolymers with acrylonitrile are also of importance for the production of... 

Another major chlorinated hydrocarbon is vinyl chloride. For many years acetylene was the sole raw material for the production of vinyl chloride by a catalytic fixed bed vapor-phase process. This process is characterized by high yields and modest capital investment. Nevertheless, the high relative cost of acetylene provided an incentive to replace it in whole or in part by ethylene. The first step in this direction was the concurrent use of both raw materials. Ethylene was chlorinated to di-chloroethane, and the hydrogen chloride derived from the subsequent dehydrochlorination reacted with acetylene to form additional vinyl chloride. 

Technological advances in the production of the vinyl chloride monomer (VCM) have contributed to the declining price of the polymer. Figure 4 illustrates this statement the price of the vinyl chloride monomer (1) over a period of 20 years is plotted against two curves that represent the annual production of monomer made from two different bases, acetylene and ethylene. The classic acetylene route was the first to be exploited commercially, but its popularity has declined as more processes were developed that could utilize ethylene, a cheaper base. 

Acetylene (Figure 13.1) is widely used as a chemical raw material and fuel for oxyacetylene torches. It was once the principal raw material for the manufacture of vinyl chloride (see reaction 13.2.4), but other synthetic routes are now used. Acetylene is a colorless gas with an odor resembling garlic. Though not notably toxic, it acts as an asphyxiant and narcotic and has been used for anesthesia. Exposure can cause headache, dizziness, and gastric disturbances. Some adverse effects from exposure to acetylene may be due to the presence of impurities in the commercial product. 

Acetylene still is a preferred raw material for some products, but it has been largely replaced by ethylene for many others. Chemicals once produced from acetylene by processes now considered outdated include vinyl chloride, vinyl acetate, acetaldehyde, acrylonitrile, neoprene, and chlorinated solvents. 

The use of acetylene to make vinyl chloride (VCM) is now considered outdated and it is a minor process compared to the production of VCM from ethylene. Only 120 million lb of 16 billion lb VCM was made from acetylene. 

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