Dehydrochlorination, of 1,2-dichloroethane

Dichloroethane, an important intermediate for vinyl chloride production, is produced by catalytic chlorination of ethylene in either vapor or Hquid phase or by oxychlorination of ethylene. Thermal dehydrochlorination of 1,2-dichloroethane produces vinyl chloride and coproduct hydrogen chloride. Hydrogen chloride is commonly recycled to an oxychlorination unit to produce 1,2-dichloroethane or is processed into sales-grade anhydrous or aqueous hydrogen chloride. 

Dehydrochlorination of 1,1,2-trichloroethane at 500°C in the presence of a copper catalyst gives a different product, ie, cis- and /n7 j -l,2-dichloroethylene. Addition of small amounts of a chlorinating agent, such as chlorine, promotes radical dehydrochlorination in the gas phase through a disproportionation mechanism that results in loss of hydrogen chloride and formation of a double bond. The dehydrochlorination of 1,2-dichloroethane in the presence of chlorine, as shown in equations 19 and 20, is a typical example. 

Oxychlorination. This is an important process for the production of 1,2-dichloroethane which is mainly produced as an intermediate for the production of vinyl chloride. The reaction consists of combining hydrogen chloride, ethylene, and oxygen (air) in the presence of a cupric chloride catalyst to produce 1,2-dichloroethane (eq. 24). The hydrogen chloride produced from thermal dehydrochlorination of 1,2-dichloroethane to produce vinyl chloride (eq. 25) is usually recycled back to the oxychlorination reactor. The oxychlorination process has been reviewed (31). 

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. 

Sotowa, C., Kawabuchi, Y. and Mochida, I., Catalytic dehydrochlorination of 1,2-dichloroethane over pyridine deposited pitch-based active carbon fiber, Chem. Lett., 1996, (11), 967 968. 

Schneider M, Wolfrum J. 1986. Mechanisms of by-product formation in the dehydrochlorination of 1,2-dichloroethane Ber Bunsen Ges Phys Chem 90 1058-1062. 

Vinyl chloride monomer, the basic building block of polyvinylchloride (PVC), is commercially manufactured by dehydrochlorination of 1,2-dichloroethane. The modern process for producing 1,2-dichloroethane involves oxychlorination of ethylene in a fluidized bed catalytic reactor ... 

Dehydrochlorination of 1,1,2-trichloroethane [25323-89-1] produces vinyHdene chloride (1,1-dichloroethylene). Addition of hydrogen chloride to vinyHdene chloride in the presence of a Lewis acid, such as ferric chloride, generates 1,1,1-trichloroethane. Thermal chlorination of 1,2-dichloroethane is one route to commercial production of trichloroethylene and tetrachloroethylene. 

Oxychl orin ation of ethylene has become the second important process for 1,2-dichloroethane. The process is usually incorporated into an integrated vinyl chloride plant in which hydrogen chloride, recovered from the dehydrochlorination or cracking of 1,2-dichloroethane to vinyl chloride, is recycled to an oxychl orin a tion unit. The hydrogen chloride by-product is used as the chlorine source in the chlorination of ethylene in the presence of oxygen and copper chloride catalyst ... 

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. 

Systematic investigations on the performance of cement-containing catalytic systems with various chemical and phase compositions in the reaction of 1,2-dichloroethane dehydrochlorination with forming vinyl chloride... 

Fig. 2. The conversion of 1,2-dichloroethane in the dehydrochlorination reaction at various catalysts as a function of temperature, t = 8 s 1- galyumin (Sspec = 130 m2/g), 2- galyumin with a dopant of copper (8 wt % in terms of CuO) 3- CsCl/silica gel.

When the addition of chlorine to ethylene is carried out in the vapor phase and in the presence of metal contact agents, higher proportions of 1,2-dichloroethane are obtained. Equimolecular proportions of chlorine and ethylene reacting at 80-100°C in the presence of copper or iron give about 90-95 per cent of the theoretical yield of dichloroethane. The reactions may be carried out in tubes that are packed with shavings or particles of the preferred metal. When small amounts of dichloroethane are recirculated to the reaction zone, the exit gases can be scrubbed more easily. In many plants, the concurrent formation of polychloroethanes is considered desirable, for such compounds are subsequently submitted to dehydrochlorination and yield desired chloroolefins. 

Currently around lOOOkton/year of numerous other C2-based building blocks are utilized. Some of the vital examples are acetic acid, dichloroethane (formed by the chlorination of ethane), vinylchloride (formed by the dehydrochlorination of dichloroethane), ethylene oxide (oxidation of ethylene), and ethylenediamine (reaction of 1,2-dichloroethane and ammonia Jong, 2012). 

The formation of 1,2-dichloroethane from ethane and ethylene is described in patents issued to National Distillers (11) and I.C.I. (12), respectively. Englin et at. (13) report the formation of vinyl chloride from chloroalkanes using catalysts containing melts of cuprous and cupric chloride. The details of the mechanism and kinetics of many of these reactions are still unresolved. It appears, though, that copper chloride can function effectively as a catalyst for chlorination and dehydrochlorination as well as being able to participate in os chlorination reactions. 

In a flow system, at 200-250 C, phosgene combines with ethene over activated charcoal to give 1,2-dichloroethane, with an activation energy calculated to be 29.6 kj mol [1CI88,ICI89,ICI90]. A small quantity of chloroethene is formed at temperatures as low as 100 C from the simultaneous decarbonylation and dehydrochlorination of the intermediate acid chloride [ICI90] ... 

The dependences shown in Fig. 3 reveal that employing a catalyst with a larger specific surface area with rising temperature would, probably, lead to the deep oxidation of vinyl chloride and, to a lesser extent, of ethylene, resulting in a decrease in the total yield of ethylene and vinyl chloride. A certain increase in the overall yield of COx products, which was observed for catalyst 2, is accompanied with an increase in the total yield of ethylene and vinyl chloride. This suggests that saturated chlorinated hydrocarbons — ethyl chloride and 1,2-dichloroethane — are oxidized predominantly and that the rate of oxidation is lower rate compared to that of the dehydrochlorination of these compounds. 

We can suppose on the strength of the data listed in Table 2 that at the short times-on-stream, the major contribution to the formation of deep oxidation products is made by saturated chlorinated hydrocarbons 1,2 dichloroethane and ethyl chloride. On increasing time-on-stream to more than 6 s, we observed a sharp increase in the yield of deep oxidation products together with the decrease in the yield of vinyl chloride. It is likely that at the longer times-on-stream, the rate of deep oxidation of vinyl chloride would increase and become higher than the rate of dichloroethane dehydrochlorination. Taking into account this fact, we believe that the optimum time-on-stream assuring the best total yield of ethylene and vinyl chloride would be 3—5 s. 

A more complex degradation takes place when this process is applied to PVC. The authors propose that PVC depolymerization under supercritical water conditions proceeds in accordance with a mechanism consisting of four different pathways (i) dehydrochlorination and partial oxidation, (ii) dehydrochlorination and chain scission, (iii) dehydrochlorination and total oxidation, and (iv) hydrochlorination. In the reaction products, high yields of vinyl chloride, 1,1-dichloroethane and 1,2-dichloroethane are detected, especially at short reaction times, whereas longer times favour total oxidation products. 

We recognize from previous discussions in Chapter 2 that 1,1,2-trichloroethane results from the base-catalyzed dehydrochlorination of 1,1,2,2-dichloroethane. From this analysis, however, we observe that there has been a change in the overall oxidation state of the carbon atoms in 1,2-dichloroethylene (0) compared to that of the parent compound (+ 2). We conclude that the formation of 1,2-dichloroethylene results from a process involving the transfer of two electrons. For larger, more complex molecules, we must only consider the atoms directly involved in the reaction process to determine if a change in oxidation state has occurred. 

Via thermal or photochemical chlorination of 1,1-dichloroethane. The latter is produced through a route which starts from ethylene chlorination to produce 1,2-dichloroethane, followed by dehydrochlorination to vinyl chloride followed finally by hydrochlorination to produce 1,1-dichloroethane... 

Chlorine and sodium hydroxide are the main products of the industrial chlor-alkali electrolysis that is described as a process example in Section 6.19. Hydrochloric acid is produced by reaction from the elements H2 and CI2 or by the reaction of chloride salts such as, for example, NaCl or CaCl2, with sulfuric acid. Other important sources of HCl are industrial chlorination processes using CI2 as chlorination agent (e.g., chlorination of benzene to form chlorobenzene and HCl or the chlorination of methane to give chloromethane and HCl) or industrial dehydrochlorination processes (e.g., production of vinyl chloride and HCl from 1,2-dichloroethane). The main uses of hydrochloric acid are addition reactions to unsaturated compounds (by hydrochlorination or oxychlorination), formation of chlorine in the Deacon process, production of chloride salts from amines and other organic bases, dissolution of metals, regeneration of ion exchange resins, and the neutralization of alkaline products. 

An alternate process, rarely used for commercial production, involves the reaction of ethylene with hypochlorous acid to form ethylene chlorohydrin. This chlorohydrin is then dehydrochlorinated with lime to produce ethylene oxide and calcium chloride. Major by-products of this process are 1,2-dichloroethane, bis-(2-chloroethyl) ether, acetaldehyde, trace acetylenes, and other chlorinated hydrocarbons. The reaction product is purified by fractional distillation. 

Chloroethene (vinyl chloride) is made from ethene by a chlorination-dehydrochlorination sequence in which addition of CI2 produces 1,2-dichloroethane. This compound is converted into the desired product by elimination of HCl. 

Another modification of the process can be used to meet the growing demand for 1,1,1-trichloroethane (methylchloroform). In this version, the chlorination of dichloroethane can be directed toward maximum production of 1,1,2-trichloroethane (9). This product when dehydrochlorinated yields vinylidene chloride, a widely used monomer. Hydrochlorination of vinylidene chloride yields 1,1,1-trichloroethane, a solvent of increasing importance. 

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