DD229112A1 - PROCESS FOR THE PREPARATION OF CHLORINE METHANE DERIVATIVES - Google Patents

Abstract

The invention relates to a method of thermal chlorination of methane in the gas phase for the preparation of the four chloromethanes. The task is to reduce the starting temperature, to improve the course of the reaction and to significantly increase the chlorine conversion with adiabatic Reaktionsfuehrung. According to the invention, large amounts of carbon monoxide are admixed with the reaction gas mixture. In the presence of a catalyst starts at 50C, a reaction. It is formed phosgene. The catalyst used is activated carbon. Once 250C has been achieved by this strongly exothermic reaction, the thermal chlorination of methane begins in parallel. By appropriate addition of chlorine, a final temperature of 550C can be achieved. At these high temperatures, phosgene is decomposed, whereby chlorine is attached to methane and carbon monoxide is released.

Description

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Process for the preparation of chlorinated methane derivatives

Field of application of the invention

The invention relates to a method of thermal chlorination of methane in the gas phase for the preparation of the four Ghlormethane mono-, di-, tri- and tetrachloromethane.

Characteristic of the known technical solutions

It is known to produce the chloromethanes by thermal chlorination of methane. 9, pp. 405, - Kirk Othmer, Encyclopedia of Chemical Technology, See, Edith, 1963, Vol.5, pp. 100 ff - McKetta Encyclopedia of Chemical Processing and Design, Vol. 8 p. 236 ff.). Most single-stage adiabatically operating reactors are used, their capacity in relative

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may fluctuate narrow limits. The thermal stability of the reaction depends strongly on the flow conditions in the reactor. »Reactors with strong backmixing are thermally more stable than reactors with a rather ideal plug flow. The backmixing, however, causes an increased attack of higher chlorinated chloromethanes in relation to low chlorinated methanes, so more and more is transferred to flow tubes. In addition to the flow conditions in the reactor, the ratio of chlorine to ethane also has a major influence on the product distribution. Substituting a lot of methane, so you get relatively larger proportions of higher chlorinated chloromethanes. Therefore, it is operated with low methane conversions, separates · the reacted methane from the reaction gas mixture and brings it together with the methyl chloride intended for further chlorination and again with Prischmethan to the reaction. This recycling of methane causes high operating costs. The reaction in the flow tube is generally performed adiabatically. The reactants are preheated to 250 to 300 ⁰ C, mixed with chlorine and react within a few seconds. This causes a steep rise in temperature. Cooling in the reaction phase by heat removal is hardly possible. At the top, the reaction temperature is limited to about 500-600 ⁰ C, otherwise a thermal decomposition (soot formation) begins. To reduce the circulation measures to increase the methane conversion and to reduce the attack of higher chlorinated chlorinated hydrocarbons are taken.

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Measures to increase the methane conversion are:

- Lowering the starting temperature of the reaction

- Cooling by feeding inerts

The lowering of the starting temperature is possible by radiation, which has not yet been introduced on an industrial scale.

Another possibility is the introduction of substances that provide chlorine radicals in the range just below the starting temperature. A well-known example is the addition or deliberate accumulation of phosgene in the reaction process (DE-OS 1 936 940). The elimination of the phosgene is not satisfactorily solved, so that the quality of the chlorination products is poor. The feeding of inert to lower the reaction end temperature has been widely used. The feeding of liquid chloroform and carbon tetrachloride causes due to the high heat of vaporization of these components considerable absorption of heat of reaction. Yon disadvantage is the subsequent separation of these two components and the possible partial i "" y chlorination of chloroform

(..} As an inert cooling medium, water or aqueous HCl is also recommended, and if the hydrogen chloride is washed out with water anyway, there is no additional effort to separate the inert substances adversely affected.

All these disadvantages have brought with it that methods of inert feed for receiving a portion of the heat of reaction have not introduced on a large scale.

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Object of the invention

The aim of the invention is to improve the process of thermal chlorination of methane and weiterzuchlorierenden chloromethanes by increasing the chlorine conversion.

Explanation of the essence of the invention

The invention has for its object to lower the starting temperature, to improve the course of the reaction and to increase the chlorine conversion in adiabatic reaction regime significantly. According to the invention the object has been achieved in that a mixture of methane, chlorinated methane derivatives, chlorine and carbon monoxide in the presence of an active carbon catalyst is reacted. The activated carbon is activated with ammonium silicofluoride. With activated carbon as a catalyst, the reaction starts at 50 ^° C. to form phosgene. This formation of phosgene is highly exothermic and the reaction gas mixture heats up by a few hundred degrees Celsius.

Methane behaves practically inert in the initial phase and thus dampens the reaction process. Once the starting temperature of the thermal chlorination of methane is reached, about 250 ⁰ C - 300 ⁰ C, both reactions run in parallel ·. It has been found that it is advantageous if the proportion of carbon monoxide is sufficient only for the formation of phosgene until the starting temperature of the thermal chlorination of methane is reached.

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It has been found that above 450 ⁰ C Biosgen noticeably, decomposed. The released chlorine reacts with methane. It forms a balance! Phosgene out to carbon monoxide. At temperatures around 550 ⁰ C, the! Phosgene is almost completely decomposed and the released chlorine is attached to methane or to its chlorine derivatives. The rearrangement of chlorine extends slightly endothermic, so that large amounts of phosgene can be reacted with virtually no influence on the temperature-j temperature of the reaction mixture C ") can. A final temperature of at least 550 ⁰ C.

ν is adjusted by the addition of chlorine to the exothermic reaction of methane chlorination. The released carbon monoxide can be recycled together with the unreacted methane. • Losses of carbon monoxide are compensated by adding fresh methane.

embodiment

The invention will be explained in more detail in the following two examples.

¹ ^ Example 1

The reactor is tubular and lined with an acid-proof material. Its lower part is filled with activated carbon activated with ammonium silicofluoride. The gas flow rate is 600 Hm ^ / h. The gas has the following composition (in Vol. JS): 53 % methane, 21 % CH ₃ Cl, 22 % chlorine, 3.5 % CO, 0.5 % inert.

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The ratio COtCl ₂ : (CH ₃ + CH ₃ Gl) is 0.16: 1: 3.36. Methane and monochloromethane are preheated so that after the mixture with chlorine and carbon monoxide, a temperature of 190 ⁰ C is obtained at reactor inlet. The reaction starts very fast. laugh about 2 see. Residence time will leave the catalyst layer. It is usually already reached a temperature of 560 ⁰ C. Above the catalyst layer is a long, slender reaction section which corresponds to the conventional thermal chlorination reactor. The reaction pressure is 0.3 MPa. The total residence time is 4 see.

The gas coming out of the reactor has the following composition: 43.5% methane, 21 % CH ₃ Cl, 7.8 % CH ₂ Cl ₂ , 1.7 % GEQIy 0.2 % CCl ₄ , 21.6 % HCl, 3 , 2 % CO, 1% inert.

Example 2

The reactor and the catalyst are identical to Example 1. Bs are enforced 600 in / h gas. The input gas mixture has the following composition (in% by volume): 4 % , 5 % methane, 19 % CH ₃ Cl, 24.5%, chlorine,

8.5 % CO, 0.5% inert.

The ratio CO: Cl ₂ : (CH ₃ CH ₃ Cl) gives: 0.345: 1: 2.71.

Methane and monochloroethane are preheated so that after the mixture with chlorine and carbon monoxide, a temperature of 100 ⁰ C is obtained. At this temperature, the gas enters the reactor.

In the lower catalyst-filled part of the reactor, the reaction starts very quickly. Hach about 2 see. Residence time will leave the catalyst layer. It is usually a reaction temperature

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reached from 560C. In the upper part of the reactor, which contains no catalyst, the reaction gas mixture may optionally react. The reaction pressure is 0.3 MPa and the residence time is 4 seconds.

The gas coming out of the reactor has the following composition: 37 % methane, 19% CH ₃ Cl, 8.3% CH ₂ Cl ₂ , 2.2 % CHCl ₃ , 0.35 % CCl ₄ , 24.5 % HCl, 7 , 3% CO, 1.35 % inert.

Claims (4)

 pe © · o / - 8 - 2613 invention claim 1. A process for the preparation of chlorinated methane derivatives by thermal chlorination of methane in the gas phase, characterized in that methane, chlorinated methane derivatives, carbon monoxide and chlorine at temperatures of 50 ⁰ C to 300 ⁰ C are reacted in the presence of a catalyst and the reaction up to, a final temperature of at least 550 C is performed. 2. The method according to item!, Characterized in that activated carbon is used as the catalyst, which is activated with ammonium silicofluoride. 3. The method according to item 1 and 2, characterized in that the molar ratio of CO: CIp: (CH. + CH ^ Cl) is between 0.03: 1: 4.0 to 0.4: 1: 2.4. 4. Process according to items 1 to 3 », characterized in that the unreacted carbon monoxide is circulated with methane and chloromethane to be chlorinated.