Dichloroethane pyrolysis

Using the technique of differential calorimetry, Kapralova has found evidence that, the initiation and termination of chains in 1,2-dichloroethane pyrolysis occurs on the reaction vessel walls instead of in the homogeneous gas phase. It has also beenproposed - that the inhibitory effect of propene may be associated with its absorption on the vessel walls causing a reduction in the rate of the initiation of chains on the surface. The mechanism of chain initiation and the action of inhibitors and sensitisers in 1,2-dichloroethane pyrolysis have been further discussed in papers by Kapralova and Semenov > Kitabatake and Onouchi and Smolyan . 

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. 

Pyrolysis. Pyrolysis of 1,2-dichloroethane in the temperature range of 340—515°C gives vinyl chloride, hydrogen chloride, and traces of acetylene (1,18) and 2-chlorobutadiene. Reaction rate is accelerated by chlorine (19), bromine, bromotrichloromethane, carbon tetrachloride (20), and other free-radical generators. Catalytic dehydrochlorination of 1,2-dichloroethane on activated alumina (3), metal carbonate, and sulfate salts (5) has been reported, and lasers have been used to initiate the cracking reaction, although not at a low enough temperature to show economic benefits. 

The results of low-temperature matrix-isolation studies with 6 [41a] are quite consistent with the photochemical formation of cyclo-Cif, via 1,2-diketene intermediates [59] and subsequent loss of six CO molecules. When 6 was irradiated at A > 338 nm in a glass of 1,2-dichloroethane at 15 K, the strong cyclobut-3-ene-1,2-dione C=0 band at 1792 cm in the FT-IR spectrum disappeared quickly and a strong new band at 2115 cm appeared, which was assigned to 1,2-diketene substructures. Irradiation at A > 280 nm led to a gradual decrease in the intensity of the ketene absorption at 2115 cm and to the appearance of a weak new band at 2138 cm which was assigned to the CO molecules extruded photo-chemically from the 1,2-diketene intermediates. Attempts to isolate cyclo-Cig preparatively by flash vacuum pyrolysis of 6 or low-temperature photolysis of 6 in 2-methyltetrahydrofuran in NMR tubes at liquid-nitrogen temperature have not been successful. 

In the manufacture of vinyl chloride (VC) by the pyrolysis of dichloroethane (DCE), the reactor conversion is limited to 55 per cent to reduce carbon formation, which fouls the reactor tubes. 

The HC1 from the pyrolysis step is recycled to the oxyhydrochlorination step. The flow of ethylene to the chlorination and oxyhydrochlorination reactors is adjusted so that the production of HC1 is in balance with the requirement. The conversion in the pyrolysis reactor is limited to 55 per cent, and the unreacted dichloroethane (DCE) separated and recycled. 

Vinyl chloride (VC) is manufactured by the pyrolysis of l,2,dichloroethane (DCE). The reaction is endothermic. The flow-rates to produce 5000 kg/h at 55 per cent conversion are shown in the diagram (see Example 2.13). 

Direct-fired reactors for example, the pyrolysis of dichloroethane to form vinyl chloride. 

Demonstration of the technical feasibility of producing mixtures of acetylene and ethylene by pyrolysis of hydrocarbons (Wulff process or Kureha process) has led to the manufacture of vinyl chloride from such mixtures. The acetylene component reacts selectively with hydrogen chloride to form vinyl chloride, the residual ethylene is converted to dichloroethane, and the latter is cracked to vinyl chloride, with the resulting hydrogen chloride being recycled. However, this type of process has not achieved the industrial importance of the all-ethylene type of process. 

Example 4.28 Assessment of separation section of vinyl chloride monomer (VCM) plant VCM is produced by the pyrolysis of 1,2-dichloroethane (EDC) at 483°C and 26.5 atm with a conversion of 55%. The pure EDC is fed to the reactor with a flow rate of 909.1 kmol/h. The feed is at21°Cand26.5 atm. The reactor outlet is cooled to 47.6°C. The first column operates at 25 atm with 15 stages. The feed is introduced at stage 8. The top product is anhydrous... 

Even though vinyl chloride was discovered in 1835, polyvinyl chloride was not produced until 1912. It is now one of our most common polymers production in 1984 was over 6 billion pounds. The monomer is made by the pyrolysis of 1,2-dichloroethane, formed by chlorination of ethylene. Free radical polymerization follows Markovnikov s rule to give the head-to-tail polymer with high specificity ... 

The quantity of chloroethene generated in this reaction was considered too high to be accounted for solely on the basis of the catalysed pyrolysis of the 1,2-dichloroethane, and the mechanism of the formation of the products can be explained on the basis of the charcoal-catalysed decomposition of the common intermediate chloroformate ... 

Best and Wege59have reported the first total synthesis of Mansonone F and this is described in Scheme 10. Phenol (111)60 was made to react with 2-chloroacetyl-5-methylfuran (112) in dimethylsulfoxide and sodium methoxide to yield (113). Ketalization of (113) followed by catalytic reduction and basic hydrolysis afforded anthranilic acid (114). Diazotization followed by pyrolysis with propene oxide in 1,2-dichloroethane probably yielded aryne (115), which undergoes intramolecular Diels-Alder reaction producing the adduct (116). Deoxygenation and then acid hydrolysis afforded the product (117). This was subjected to Grignard reaction. The resulting tertiary alcohol on nitration yielded the nitro compound (118) which was subjected to reduction and oxidation respectively to obtain (119). It yielded Mansonone F (120) on dehydration. 

Figure 9-3. Technological scheme of production of the vinyl chloride monomer (1) plasma-chemical pyrolysis (2) cleaning from higher unsaturated hydrocarbons (3) hydrochlorination of acetylene (4) chlorination of ethylene (5) thermal pyrolysis of dichloroethane.

The chlorination of etlylene proceeds in liquid dichloroethane in the presence of a catalyst (iron chloride) at a pressure of 5 atm without separation of the pyrolysis gas mixture. The composition of the residual plasma pyrolysis gas mixture after the hquid-phase chlorination is lydrogen (H2) 85.5-90 vol % and methane (CH4) 10-14.5 vol %. This mixture is then apphed as an energy carrier gas for plasma pyrolysis of lydrocarbons in the first stage. Dichloroethane formed in hquid phase then imdergoes thermal pyrolysis in the fifth step of the technology. The pyrolysis of dichloroethane is performed at temperatures of450-550°C and pressures of 7 atm and results in production of vii rl chloride and lydrogen chloride ... 

Products and characteristics of plasma pyrolysis Dichloroethane, rate 8 kg/h Butyl chloride, rate 5.4 kg/h Hexachlorane Organic chlorine mixture, rate 7.2 kg/h... 

Thermal Plasma Pyrolysis of Dichloroethane, Butyl Chloride, Hexachlorane, and Other Organic Chlorine Compounds for Further Synthesis of Vinyl Chloride... 

In reaction (3.5), which oxychlorinates ethylene to produce 1,2-dichloroethane, HCl is the source of chlorine. This highly exothermic reaction achieves a 95% conversion of ethylene to dichloroethane at 250 C in the presence of cupric chloride (CUCI2) catalyst, and is an excellent candidate when the cost of HCl is low. As in reaction path 3, the dichloroethane is cracked to vinyl chloride in a pyrolysis step. This reaction path should be considered also as a solution for design alternative 3. 

Next, the dichloroethane source from the chlorination operation is sent to its sink in the pyrolysis operation, which operates at 500°C. Here only 60% of the dichloroethane is converted to vinyl chloride with a byproduct of HCl, according to reaction (3.4). This conversion is within the 65% conversion claimed in the patent. To satisfy the overall material balance, 158,300 Ib/hr of dichloroethane must produce 100,000 Ib/hr of vinyl chloride and 58,300 Ib/hr of HCl. But a 60% conversion only produces 60,000 Ib/hr of vinyl chloride. The additional dichloroethane needed is computed by mass balance to equal [(1 - 0.6)/0.6] X 158,300 or 105,500 Ib/hr. Its source is a recycle stream from the separation of vinyl chlo-... 

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