Purity vinyl chloride

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. 

High purity vinyl chloride is produced in an overall yield of 80 mol% based on ethane. The feed can contain ethane, ethylene, mixed ethylene-chlorination products, and HCl in various mixtures, and can thereby allow recovery of values from such materials. The flow sheet for the simultaneous chlorination, oxidation, and dehydrochlorination for producing vinyl chloride by the Transcat process is shown in Figure 3. 

The solution to be nebulized is usually pumped to the nebulizer using a peristaltic pump, unlike for FAAS, where the solution uptake is by free aspiration. The solution is pumped through polymeric tubing [usually poly(vinyl chloride)] and also connecting tubing (usually Teflon) to the nebulizer. Both of these materials can be manufactured to a high degree of purity, hence contamination is minimized. The solution is pumped at a rate of 1 -2 ml min, which is much slower than the 5-10 ml min uptake rate for FAAS. This tends to favour the formation of fewer but smaller droplets, which results in less noise but a lower overall sample transport efficiency. 

In Fig. II the effect of plasticizer is shown for the system poly(vinyl chloride)/tricresyl phosphate. Water also affects the conductivity considerably but its precise function is by no means clear particularly at low moisture contents (135). The presence of ionic impurities causes increased conductivity but the effect of organic impurities is less apparent. For instance, the addition of plasticizers of differing purity to poly-... 

Materials. The purity and analysis of isobutene, methyl chloride, and aluminum chloride have been described (16). Ethyl chloride gas (U.S.P. grade, 99.99% minimum purity, Matheson Co.) was further purified by scrubbing through Molecular Sieves (5A, Linde Co.) and BaO, and distillation into the dry box. Vinyl chloride (99.9% minimum purity, Matheson Co.) was distilled into the box, cooled to —78° C., and filtered cold until free from solid matter. Propane gas (instrument grade and natural grade, Matheson Co.) was passed over Molecular Sieves and then condensed into the box. 

Antoni and Langstrom have recently reported the synthesis of carbon-11 labelled vinyl cyanides from H CN. This provides useful synthons because vinyl chlorides can undergo Michael additions to give a wide variety of carbon-11 labelled compounds. The carbon-11 labelled vinyl and cinnamyl cyanides have been prepared in 35% yield and greater than 99% radiochemical purity in 3 minutes by reacting CN with the appropriate bromide in the presence of a palladium catalyst and 18-crown-6 ether in acetonitrile (equation 71). 

Vinyl halides. The method of Normant et al. (6, 270) for preparation of vinylcopper compounds can be used to obtain vinyl halides. Reaction of 1 with iodine gives vinyl iodides directly, but this reaction when extended to Bf2 or CI2 gives mainly dimers. The desired vinyl chlorides and bromides canTte obtained with NCS or NBS in fair to good yields. The replacement occurs with retention of initial stereochemistry. The American group also stresses the importance of the purity of the copper salt and uses House s cuprous bromide complex with dimethyl sulfide (6, 270). 

From the point of view of the polymerization process, bulk (mass) polymerization produces the purest PVC because only initiators and vinyl chloride are used in the process. Bulk polymerization is capable to yield 99.9% pure polymer. In suspension polymerization, a suspending agent is added in addition to initiator, which decreases the purity of suspension PVC to about 99.8%. Microsuspension polymer contains emulsifier and its piuity can be approximately 98.8%. Emulsion polymer may contain more emulsifier and initiator rests and its purity can be estimated as 98%. All these results are quite good for commercial product and PVC can be considered as a relatively pure polymer. More admixtures are usually introduced on the compounding stage from various contaminations and brought together with additives. 

PN-92/Z-04208.10 Air purity protection - Tests for phthalic acid esters - Determination of dibutyl phthalate vapors in permanent residence area air by gas ehromatography with sample enrichment PN-93/Z-04231.02 Air purity protection - Tests for content of harmful substances emitted during plastics processing - Determination of acetone, benzene, toluene, ethylbenzene 2-ethylhexanol, dibutyl phthalate and di-(2-ethylhexyl) phthalate in work places in the mixture emitted during poly(vinyl chloride) processing by gas chromatography... 

Some peculiarities of the thermal and thermooxidative decomposition of polyvinyl chloride depend on the conditions of its production. Thus, it is known that samples of the polymer produced by initiating the polymerization of vinyl chloride with ultraviolet irradiation possess higher stability in comparison with samples produced in polymerization under the action of chemical agents [26, 27]. Reversibility of the process of dehydrochlorination in the decomposition of samples of polyvinyl chloride produced by the latex method is noted, while in the process of decomposition of suspension polymer, the phenomenon of reversibilily is not observed [21]. It has been shown that the rate of dehydrochlorination of the latex polymer is significantly higher than that of the suspension polymer under the same conditions [21]. It has been established that the polymerization of vinyl chloride in the presence of oxygen leads to the formation of unstable peroxide groups, which can initiate decomposition of the polymer [28, 29]. It is noted that an extremely substantial influence on the stability of polyvinyl chloride is exerted by the purity of the monomer, as well as the presence of impurities of metals of variable valence [28]. 

Vinyl chloride is available for commercial and industrial use in various grades having much the same composition from one producer to another. It typically has a minimum purity of 99.9 mole percent in the liquid phase. 

Polymerization conditions I mmole of initiator per mole of vinyl chloride reaction temperature as indicated polymerization by bulk technique under nitrogen of high purity. 

TLC has been used in the study of many homopolymers polystyrene, poly(methyl methacrylate), poly(ethylene oxide), polyisoprene, poly(vinyl acetate), poly(vinyl chloride) and polybutadiene. Their molecular weight, molecular-weight distributions, microstructure (stereo-regularity, isomerism and the content of polar end groups), isotope composition and branching have been studied. For copolymer characterisation (e.g. purity and compositional inhomogeneity), random copolymers such as styrene-methacrylate, and block copolymers such as styrene-butadiene, styrene-methyl methacrylate and styrene-ethylene oxide have been separated. A good review article on polymers... 

The solid polymer bodies of PTFE and polyimide (obtained from E. I. Dupont Co.) used in these studies were research grade materials. The polymer forming gaseous monomer vinyl chloride, was 99.95 percent in purity as was the ethyl chloride. 

The direct chlorination of ethylene usually is run in the liquid phase and is catalyzed with ferric chloride. High-purity ethylene normally is used to avoid product purification problems. The cracking (pyrolysis) of EDC to vinyl chloride typically is carried out at temperatures of 430 to 530°C over a catalyst. The hot gases are quenched and distilled to remove HCl and then VCM. The unconverted EDC is returned to the EDC purification train. The oxychlorination step is the heart of the process and has two major variables, the type of reactor and the oxidant. The reactor may be either a fixed bed or a fluidized bed, and the oxidant is either air or oxygen. The temperature is in the range of 225 to 275" C with a copper chloride-impregnated catalyst. 

Extract the aqueous phase with six 250-m portions of methylene chloride wash the solid cake with three of the portions prior to their use on the solution. Dry the combined extracts over 40 g of anhydrous magnesium sulfate and inhibit with 0.5 g of hydroquinone. Remove the drying agent by filtration and strip the methylene chloride by distillation at atmospheric pressure remove final traces of this solvent by stripping at 20 mm pressure and room temperature. Then separate the mixture of crude vinyl isomers by distillation at reduced pressure. By heating to a pot temperature of 90°C, the 2-methyl-5-vinyltetrazole is conveniently and almost completely removed at 1.0 mm pressure. A well cooled condenser and a receiver chilled in an ice-water bath are needed to prevent loss of the condensate. The weight of once distilled 2-isomer is 89.9 g the index of refraction at 25°C is 1.4814, corresponding to a purity of 97.2 percent. The corrected yield amounts to... 

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