DK172880B1 - Process for the treatment of inert residual gases containing ethylene and CO - Google Patents

Description

The present invention relates to a process for treating inert residual gases containing ethylene and CO resulting from the preparation of dichloroethane by oxychlorination of ethylene.

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Industrial processes for the preparation of dichloroethane by the action of oxygen on a mixture of hydrochloric acid and ethylene never lead to a complete reaction, and the gases coming from the oxychlorination reactor always contain unreacted ethylene. This amount of ethylene represents a not insignificant loss and several methods have been developed to reduce this loss by converting the residual ethylene to dichloroethane by means of a supplementary chlorination.

15 In FR patent specification No. 1,421,903, it is disclosed that the gas derived from the oxychlorination is treated after cooling to compensate the resulting dichloroethane in vapor phase with chlorine over an iron-based catalyst. This treatment 20 is carried out at high temperature - from 80 to 250 ° C - which is a disadvantage, since gaseous mixtures containing damp chlorine are highly corrosive, resulting in either the use of expensive construction materials or an increase in maintenance costs. In addition, it is necessary to reheat the gas stream to a sufficiently high temperature to allow the reaction to proceed relatively quickly, resulting in considerable energy consumption.

The same criticism may be directed to FR Patent Nos. 1 575 262 and 30 to DE Patent Application 2 733 502 which, under similar conditions, describe the use of aluminum as a catalyst.

To avoid these drawbacks, it has been proposed to carry out the liquid phase chlorination in a non-reactive solvent. Thus, GB Patent No. 1,364,610 discloses a process in which the residual gases from DK 172880 B1 2, after drying, pass through a reactor 1 which is flowed by a stream of inert liquid, preferably of 1,2-dichloroethane, while introducing chlorine into the sufficient amount to convert a large portion of the remaining ethylene. The chlorination reaction takes place between 35 and 85 ° C in the presence of ferric chloride. However, due to the high degree of dilution of the ethylene in the residual gas, this process requires the use of a very powerful stream of dichloroethane for contact, which leads to 10 reactors with very significant dimensions and thus a costly investment in relation to the expected production of dichloroethane. .

FR patent 491 792 cites a process for the preparation of dichloroethane by reaction between ethylene and chlorine at least 90 ° C in the presence of charcoal or black bone charcoal, without further clarifying the reaction conditions. According to Pascal, Vol. VIII, pp. 768-769, chlorine reacts with CO in the presence of activated carbon 20 to form phosgene, so the technique described in the French patent is not advisable in the treatment of inert residual gases resulting from the production of dichloroethane by the oxychlorination of ethylene - residual gases, which by definition contain CO.

In the process of the present invention, these disadvantages are avoided. This allows conversion of the ethylene residual gases from oxychlorination to 1.2-dichloroethane in excellent yield, and to operate at a sufficiently low temperature, thus reducing the energy costs necessitated by the re-heating of the gas and reducing the risk of corrosion. need to use a very vigorous circulation of the solvent.

DK 172880 B1 3 r

Thus, the invention relates to a method of treatment. of inert residual gases containing ethylene and CO arising from the preparation of dichloroethane by oxychlorination of ethylene by chlorinating in gas phase the residual gas with chlorine in the presence of a catalyst, the process being characterized in that the reaction is carried out at a temperature of 15 - 80 ° C in the presence of a catalyst based on activated charcoal, where the contact time with the catalyst is 0.1 - 10 seconds.

To this end, the ethylene-containing residual chlorine in a molar ratio CL₂ / C₂H * of between 0.5 and 1.5 is added, in particular between 0.8 and 1.1. The mixture thus obtained is passed over a catalyst with a contact time of between 0.1 and 10 seconds, preferably between 0.2 and 5 seconds (the contact time being defined as the ratio of the catalyst volume (ml) to the space velocity (ml / s). The reaction temperature is between 0 and 150 ° C, preferably 20 between 15 and 80 ° C. The catalyst may be, for example, activated carbon or alumina in the form of spheres.

The degree of conversion of ethylene is between 90 and 100%, with the yield of dichloroethane practically quantitative.

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The following examples illustrate the invention. In particular, they have been carried out on residual gases from oxychlorination of ethylene; but any inert residual gas containing ethylene or other unsaturated hydrocarbon may be treated in the same manner to obtain easier recovery of a higher molecular weight product.

* Example 172880 B1 4 EXAMPLE 1

A gaseous waste stream of 191 l / h derived from oxychlorination of ethylene is treated and the composition of which is as follows: CO 2 2.1% CO 1.2% C 2 H 4 1.2%! HCl 0.1% I CH 2 Cl-CH 2 Cl 0.03% I O 2 6.0% Ϊ N 2 89.37%! 15 with 2.23 l / hour of chlorine in vapor phase (i.e., a molar ratio C1 / C220 of 0.973) at a temperature of 70 ° C over 175 ml of activated charcoal ("Acticarbone AC 40" from CECA S.A.). Thus, the contact time is 2.6 seconds.

"20 Z Under these reaction conditions the conversion rate of" ethylene is 97.5% EXAMPLE 2 7 25

A flow of 600 l / h of the gas waste stream described in Example 1 is treated with 6.9 l / h of chlorine (molar ratio Cl; / C: H 4 = 0.958) at a temperature of 70 ° C over 88 ml of activated charcoal. for a contact time of 0.4 seconds.

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The conversion rate of ethylene is 96%.

EXAMPLE 3 35 600 l / h of a gas stream is treated as described in Ex.

1 with 7.9 l / hr of chlorine (molar ratio Cl 2 / C; H 4 = 1.097) under the same reaction conditions as in Example 2, ie. at a temperature of 70 Ό and over 88 ml of activated charcoal (contact time: 0.4 seconds).

5 The conversion rate of ethylene is 96% as in Example 2. In contrast, after treatment, an excess of chlorine which has not reacted, is found in the gas, ie. 1.02 l / h; but this excess can be easily removed by classical methods.

EXAMPLE 4

180 l / h of a waste gas stream is treated from the oxychlorination of ethylene, the composition of which is as follows: 15 CO * 2.5% CO 1.0% C 2 H 4 1.27% CH 2 6.0%

Nz 89.11% with 2.35 l / h chlorine (molar ratio C12 / C2H4 = 0.984) at a temperature of 20 ° C over 170 ml of activated carbon. Thus, the contact time is 25 seconds.

Under these conditions, the conversion rate of ethylene is 97.5%.

EXAMPLE 5

216 l / h of a waste gas stream having the following composition is treated: 35 CO * 1.9¾ CO 0.8%

MW

C

DK 172880 B1 6 C2H4 0.7% 02 6.0% N2 90.6%

5 with 1.38 l / hour chlorine in vapor phase at a temperature of 50 ° C

over 175 ml of activated charcoal, ie with a contact time of 2.9 seconds.

! Under these reaction conditions, where the chlorine / ethylene molar ratio is only 0.913, the degree of conversion of ethylene is 10 89%.

in Example 6

168 liters per hour of the 15 waste gas stream described in Example 5 are treated with 1.18 liters per hour chlorine (molar ratio C12 / C2H4 * 1.003) at a temperature of 90 ° C over 175 ml of spherical alumina, which provides a contact time of 2.8 seconds.

The conversion rate of ethylene is 97.2%.

In Example 7

189 l / hr of the waste gas stream described in Example 5 is treated with 1.8 l / hr of chlorine (molar ratio C12 / C2H4 «25 1.360) at a temperature of 50 'Cover 175 ml of alumina in the form of spheres, ie. a contact time of 2.5 seconds.

The degree of conversion of ethylene is 100%. You find in the gas after treatment excess chlorine which is not reacted, ie.

0.5 l / hr.

EXAMPLE 8 i

1140 l / h of a waste gas stream is treated from the oxychlorination of ethylene, the composition of which is as follows: t: a Ψ ^ Ψί DK 172880 B1 7 CO 2 1.6% CO 0.7% C 2 H, 0.59% CH 2 Cl -CH 2 Cl 0.11% 5.02 6.0% N 2 91% with 12.6 l / h chlorine (molar ratio Cl 2 / C 2 H, = 1.873) at a temperature of 90 'Cover 175 ml alumina. Thus, the contact time 10 is 0.4 seconds.

The conversion rate of ethylene is 96.6%. The gas is recovered after the treatment of the excess chlorine which has not reacted, ie. 6.1 l / hr.

Claims (2)

A process for treating inert residual gases containing ethylene and CO resulting from the preparation of dichloroethane by oxychlorination of ethylene by chlorinating the residual gas with chlorine in the presence of a catalyst, characterized in that the reaction is carried out at a temperature of 15 - 80 ° C in the presence of an activated charcoal catalyst, with the contact time with the catalyst being 0.1 - 10 seconds. Process according to claim 1, characterized in that the chlorine / unsaturated ethylene molar ratio is 0.5 - 1.5, preferably 0.8 - 1.1. I 1 i