DE1210800B - Process for the production of vinyl chloride by thermal cleavage of dichloroethane - Google Patents

Description

Process for the production of vinyl chloride by thermal cracking of dichloroethane It is known thermally from dichloroethane with cleavage of hydrogen chloride to produce vinyl chloride. With this procedure, the undesirable occurs Formation of carbon on. Most of the carbon is deposited in the reactor as a hard, firm crust, which very quickly leads to clogging and downtime of the reactor leads.

In addition, the yields of vinyl chloride are naturally also reduced. The carbon deposition increases with the cracking temperature. On the other On the other hand, the conversion also increases with increasing temperature. Because of the increasing However, carbon deposition does not succeed in the reaction with the desired carry out high sales.

In order to avoid these disadvantages, other known methods proposed to carry out the thermal cleavage using catalysts, in order to keep the required gap temperatures as low as possible and at the same time higher Generate sales. The catalysts used are preferably chlorides of the alkaline earth metals, of magnesium and zinc on carriers such as charcoal, aluminum oxide or silica gel. Conversions are achieved at cracking temperatures between approximately 300 and 500 ° C from about 50 to 700 / o (U.S. Patent 2,875,255, German Patent 1,095 269). Working with catalysts has the disadvantage that they are relatively quick become ineffective and need to be renewed. Even small amounts of soot Deposits on the catalyst surface quickly make the catalyst inactive.

In the process described in U.S. Patent 2,378,859 the dichloroethane smaller amounts of halogens or halogen-releasing compounds added. You can thereby the conversion in the thermal cleavage of dichloroethane, which is below 300/0 at 500 "C without the addition of halogen, by adding 0.5 percent by weight Increase chlorine at a temperature of 370 "C to about 700 / o.

To simplify the condensation and work-up of the cleavage products and to facilitate has been proposed in another known method, carry out the thermal cleavage under increased pressure, the reaction components condense and distill under this pressure. Up to a pressure of 20 Atü, the conversion should not be adversely affected. To the unwanted To reduce the formation of soot, however, the conversion should not be driven above 66% (German patent specification 857 957).

In another known work-up process, the under Pressure formed fission gases relaxed, which liquefied at lower temperatures Components are distilled, the hydrogen chloride optionally through beforehand a water wash can be removed (German Patent 899 191).

According to the German patent specification 1 135451 one can Pressure of 2.5 atü and at temperatures between 160 and 350 "C in the presence of catalysts, such as barium chloride on activated carbon or aluminum silicate, with practically no formation of Soot and decomposition products work when the partial pressure of the vinyl chloride is 0.5 does not exceed atü; however, it does not succeed in this way of working, high conversions apply.

According to the previously known methods, it has not yet been possible to Dichloroethane at high sales without significant formation of by-products, in particular Carbon, which then leads to the occurrence of serious malfunctions, thermally columns.

A process for the preparation of vinyl chloride has now been carried out found thermal cleavage of dichloroethane, which is characterized in that dichloroethane at pressures between 3 and 20 ata in the presence of 0.5 to 2 percent by weight Halogen or halogen-releasing compounds at temperatures between 500 and 620 "C heated.

Suitable halogens are chlorine, bromine, iodine. In particular, however, one will use the technically easily accessible chlorine.

Halogen-releasing compounds are understood to mean sulfuryl chloride, Thionyl chloride, hexachloroethane, carbon tetrachloride, perchlorethylene, where one will give preference to the chlorine compounds.

Chlorinated hydrocarbons with more than 2 carbon atoms are used because of avoid the by-products that then occur.

The addition of halogen is expediently 0.5 to 1.0 percent by weight Halogen or the corresponding amount of halogen-releasing compound, but are even even smaller amounts, e.g. B. - 0.1 percent by weight, effective. Up to one addition of 2 percent by weight is a clear increase in conversion with increasing amount of halogen detectable. In addition, since the conversion is then already over 90 »/ 0, no longer aim to increase significantly.

Higher additions have the disadvantage that they prevent the formation of more highly chlorinated substances - Favor secondary products.

A pressure of 5 to 7 ata has been found to be particularly useful, but higher pressures or lower pressures up to 3 ata can also be used will. However, you will not increase the pressure above 20 ata because of the achieved high turnover practically no turnover increases can be achieved: The applied Temperatures are generally between 500 and 620 "C, preferably between 520 and 550 "C.

The thermal cleavage is carried out in a manner known per se Tubular reactors with small tube cross-sections, expediently used-tubes with a diameter of 10 to 40, preferably 15 to 20 mm. The flow rate is kept so that the residence time is 1 to 3, preferably 1.5 to 2.5 seconds, is, The halogens or the halogen-releasing compounds are dichloroethane added before introduction into the reactor. Working up the reaction mixture generally takes place by condensation of the chlorinated hydrocarbons. The im HCl gas remaining portion is washed out with dichloroethane or a washing oil won.

The resulting reaction gases are practically free of soot and contain a maximum of 1.5 percent by weight of by-products, consisting primarily of 1,1,2-trichloroethane and trans-1,2-dichloroethylene exist and by addition of chlorine to already formed Vinyl chloride or acetylene are formed. However, they do not interfere with the work-up of the reaction gases and can be easily removed therefrom. With the fractionated Distillation z. B. they remain in the wake.

In the procedure according to the invention, even when used higher gap temperatures, e.g. B.

580 "C, the deposition of carbon is practically completely avoided. After several weeks of operation, sales of 900 / o are on the inner pipe wall of the reactor only a very thin carbon coating less than 1 mm thick was detectable. While in the known procedure, which is only carried out under increased pressure the reaction gases contain significant amounts of soot, which is deposited in cyclones must be, the reaction gases are practically soot-free in the present process.

Example 1 By an electrically heated tubular reactor from a Pipe of 30 m length and 14 mm diameter are per hour 62.5 kg dichloroethane steam, to which 0.5 percent by weight of chlorine is added when entering the furnace be put under a pressure of 5 ata at 535 "C. The residence time is about 1.6 seconds.

The reaction gases leaving the furnace become 35.3 per hour kg of vinyl chloride, 21.0 kg of hydrogen chloride and 0.5 kg of a mixture which predominate consists of 1,1,2-trichloroethane and 1,2-dichloroethylene. 5.7 kg dichloroethane are recovered unchanged hourly, corresponding to a conversion of 910 / o, based on the dichloroethane used. After 72 hours of operation, it is connected Cyclone barely detectable soot.

If the thermal cleavage is carried out in the same way without the addition of chlorine through, 30.1 kg of vinyl chloride, 17.7 kg of hydrogen chloride and 0.3 kg of the chlorinated hydrocarbons mentioned. Pass 14.4 kg of dichloroethane the furnace unchanged, corresponding to a conversion of 77O / o.

After a 10-hour test, a downstream Cyclone deposited about 0.8 kg of soot.

Example 2 Under the conditions described in Example 1 are hourly 62.5kg hand dichloro vapor passed through the furnace after before entry 1.0 weight percent chlorine was added to the reactor.

With a single pass, 62.5 kg of dichloroethane are produced every hour 36.6 kg of vinyl chloride, 0.9 kg of said chlorinated hydrocarbons and 21.9 kg of hydrogen chloride. About 3.1 kg of dichloroethane pass through the oven unchanged, corresponding to a conversion of 95O / o, based on the dichloroethane used.

Soot cannot be detected in the cyclone after 75 hours of operation will.

Claims (4)

Claims: 1. Process for the production of vinyl chloride by thermal cleavage of dichloroethane, characterized by the fact that dichloroethane at pressures between 3 and 20 ata in the presence of 0.5 to 2 percent by weight of halogen or halogen-releasing compounds are heated to temperatures between 500 and 620 "C. 2. The method according to claim 1, characterized in that the thermal cleavage takes place in the presence of 0.5 to 2 percent by weight of chlorine. 3. The method according to claim 1 and 2, characterized in that the thermal cleavage is carried out at a pressure of 3 to 7 ata. 4. The method according to claim 1 and 3, characterized in that the Residence time in the reactor is 1 to 3 seconds. Considered publications: German Patent Specifications No. 1,135,451, 1,095,269, 899191, 857957; U.S. Patent Nos. 2,875,255, 2724006, 2378859.