Vinyl chloride purification

Vinyl chloride can be completely oxidized to CO2 and HCl using potassium permanganate [7722-64-7] in an aqueous solution at pH 10. This reaction can be used for wastewater purification, as can ozonolysis, peroxide oxidation, and uv irradiation (42). The aqueous phase oxidation of vinyl chloride with chlorine yields chloroacetaldehyde (43). 

Chlorinated by-products of ethylene oxychlorination typically include 1,1,2-trichloroethane chloral [75-87-6] (trichloroacetaldehyde) trichloroethylene [7901-6]-, 1,1-dichloroethane cis- and /n j -l,2-dichloroethylenes [156-59-2 and 156-60-5]-, 1,1-dichloroethylene [75-35-4] (vinyhdene chloride) 2-chloroethanol [107-07-3]-, ethyl chloride vinyl chloride mono-, di-, tri-, and tetrachloromethanes (methyl chloride [74-87-3], methylene chloride [75-09-2], chloroform, and carbon tetrachloride [56-23-5])-, and higher boiling compounds. The production of these compounds should be minimized to lower raw material costs, lessen the task of EDC purification, prevent fouling in the pyrolysis reactor, and minimize by-product handling and disposal. Of particular concern is chloral, because it polymerizes in the presence of strong acids. Chloral must be removed to prevent the formation of soflds which can foul and clog operating lines and controls (78). 

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. 

Alternatives to oxychlorination have also been proposed as part of a balanced VCM plant. In the past, many vinyl chloride manufacturers used a balanced ethylene—acetylene process for a brief period prior to the commercialization of oxychlorination technology. Addition of HCl to acetylene was used instead of ethylene oxychlorination to consume the HCl made in EDC pyrolysis. Since the 1950s, the relative costs of ethylene and acetylene have made this route economically unattractive. Another alternative is HCl oxidation to chlorine, which can subsequently be used in dkect chlorination (131). The SheU-Deacon (132), Kel-Chlor (133), and MT-Chlor (134) processes, as well as a process recently developed at the University of Southern California (135) are among the available commercial HCl oxidation technologies. Each has had very limited industrial appHcation, perhaps because the equiHbrium reaction is incomplete and the mixture of HCl, O2, CI2, and water presents very challenging separation, purification, and handling requkements. HCl oxidation does not compare favorably with oxychlorination because it also requkes twice the dkect chlorination capacity for a balanced vinyl chloride plant. Consequently, it is doubtful that it will ever displace oxychlorination in the production of vinyl chloride by the balanced ethylene process. 

The gases from the reactor are then cooled and subjected to a caustic wash to remove unreacted hydrogen chloride. This is then followed by a methanol wash to remove water introduced during the caustic wash. A final purification to remove aldehydes and ethylidene dichloride, formed during side reactions, is then carried out by low-temperature fractionation. The resulting pure vinyl chloride is then stored under nitrogen in a stainless steel tank. 

In the production of polyvinyl chloride by the emulsion process, the percentages of catalyst, wetting agent, initiator, and solvent all affect the properties of the resultant polymer. They must be carefully metered into the reaction vessel. The vinyl chloride used must also be very pure. Either the scope must specify that the purchased raw material shall meet certain specifications, or some purification equipment must be installed so that the required quality can be obtained. 

Improvement teams, Six-Sigma, 21 174 Impurities. See also Contaminants Metal ion impurities Purification caustic soda in removing, 22 832 in limestone, 15 33, 34t, 40 in magnesium, 15 342-343 in manganese ore, 15 542—545 in metal, 16 130 in MOCVD growth, 22 157 removal in vinyl chloride manufacture, 25 641, 642... 

Thermal dehydrochlorination of 1,2-dichloroethane188-190 272 273 takes place at temperatures above 450°C and at pressures about 25-30 atm. A gas-phase free-radical chain reaction with chlorine radical as the chain-transfer agent is operative. Careful purification of 1,2-dichloroethane is required to get high-purity vinyl chloride. Numerous byproducts and coke are produced in the process. The amount of these increases with increasing conversion and temperature. Conversion levels, therefore, are kept at about 50-60%. Vinyl chloride selectivities in the range of 93-96% are usually achieved. 

Latex Preparation Analysis. Deionized water was used for the aqueous phase in the polymerization and commercial grade vinyl chloride monomer (99.9% pure) was used without further purification. The emulsifier was a salt of a sulfated fatty alcohol, and the emulsifier solution for metering was prepared to have 0.15 mol/L in water. The initiator system was a water soluble redox system. 

Sodium hydroxide has many different uses in the chemical industry. Considerable amounts are used in the manufacture of paper and to make sodium hypochlorite for use in disinfectants and bleaches. Chlorine is also used to produce vinyl chloride, the starting material for the manufacture of polyvinyl chloride (PVC), and in water purification. Hydrochloric acid may be prepared by the direct reaction of chlorine and hydrogen gas or by the reaction of sodium chloride and sulfuric acid. It is used as a chlorinating agent for metals and organic compounds. 

Although they have not experienced Substantial industrial development, processes have also been developed to produce an ethylene/acetykse mixture of a suitable composition directly, and by the type (c) scheme, to perform the rest of the operations to produce vinyl chloride, without separation or purification of the components of the stream produced. These techniques have been proposed by SBA and especially Kureha. This type of method, which uses a dilute gas mixture, avoids costly fractionation of acetylene and ethylene, replacing them by the easier fractionation of vinyl chloride and ethylene dichloride. 

Purification of crude vinyl chloride produced by cracking and hydrochlorination, including the lowering to about 5 ppm of the butadiene content by means ofliquid/liquid countercurrent contact with hydrochloric arid, separation by distillation of the light products returned to hydrochlorination, followed by neutralization with dilute caustic soda, scrubbing with water, drying on molecular sieves, and finally the removal of heavy compounds by distillation. 

Another procedure involves the dehydration of N(2-hydroxyethyl)carbazole [405,406], which is obtained by the reaction of potassium carbazole with ethylene oxide or 2-chloroethanol. Dehydrochlorination of N(2-chloroethyl)carbazole was reported to be a convenient laboratory scale method [407,408]. Several other methods, such as direct vinylation with ethylene catalyzed by PdCl2 [409] or with vinyl chloride [410] and some transvinylation reactions, have been reported. Although a variety of purification techniques have been developed [404], complete elimination of impurities from NVK prepared from coal tar seems to be impossible. NVK from coal tar contains substantial amounts of sulfur compounds as well as a variety of condensed aromatic impurities... 

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