The method of vapor-phase hydrodechlorination of carbon tetrachloride

 

(57) Abstract:

During hydrodechlorination in the gas phase carbon tetrachloride is used, the catalyst is platinum on aluminum oxide, which process the reaction mixture with the addition of 0.5 - 1.5 vol.% water vapor for 2 to 5 h at 60 - 120oC. After this treatment, by varying the concentration added to the reaction mixture of water vapor (up to 1 vol.%) direct the process of the priority obtaining or chloroform, or chloroform and chlorohydrocarbons, containing two carbon atoms. Thus alter the activity of the catalyst and the ratio of the reaction products. table 2.

The invention relates to a method of carrying out catalytic processes, in particular to a method of changing the activity and selectivity of catalysts in the hydrodechlorination of carbon tetrachloride in the vapor phase.

It is known (F. H. Weiss et al., J. Catal., 1971, V 22, p. 345, U.S. patent 3579596) that when the hydrogenation of carbon tetrachloride with hydrogen at 70 - 180oC on the catalyst is platinum on alumina" the main products are chloroform and methane:

CCl4+ H2= CHCl3+ HCl

CCl4+ 4H2= CH4+ 4HCl

Most proximity which is Yes way described in the patent (U.S. patent 5097081). According to this patent, to modify the activity and selectivity of the hydrodechlorination of carbon tetrachloride, the reaction is carried out in the presence of oxygen or oxygen-containing gas (in the above examples used the air). As catalysts are encouraged to apply noble metals or metals of subgroups of copper deposited on the aluminum oxide or titanium (in the examples used in the catalyst of 0.5 wt.% Pt on alumina). From the data presented in the examples of the patent, additives air in quantities of up to 4.5 vol.% in the original gas-vapor mixture of hydrogen with carbon tetrachloride (molar ratio of these substances about 8) leads to an increase in activity (characterized by the conversion and the performance of the catalyst and reduce the selectivity of the formation of perchloroethylene and hexachlorethane. After cessation of air activity of the catalyst decreased and the selectivity of education chlorohydrocarbons C2grew from less than 1% to .8%.

The disadvantages of this method include the need to add oxygen (or air) to the stream containing hydrogen, the result of which can form explosive with the R fails if necessary to carry out the process in the direction of the predominant obtain chlorohydrocarbons C2.

The objective of the invention is such a method of conducting the process in which the catalyst activity and the ratio of the reaction products can be varied within wide limits, in particular to achieve preferential receipt of chlorohydrocarbons C2and to avoid the disadvantages of the prototype associated with mixing of streams containing hydrogen and oxygen.

The above objective is achieved by treatment for 2 to 5 h at 60 - 120oWith catalyst reaction mixture containing 0.5 to 1.5 vol.% water vapour.

The catalyst was prepared by the following method.

The carrier of active alumina with a specific surface area of 210 sq m on g is used in the form of extrudates with a length of 3 to 5 mm and a diameter of 3 mm at the Beginning of 43.3 g of this carrier was progulivali in air at a temperature of 500oWith, then soaked in water holding capacity of 34.4 ml of an aqueous solution hloristovodorodnykh acid containing 0.037 g Pt/ml Impregnated granules kept in a closed container for 3 days, then dried at 130oC for 4 h Then the sample was reduced by hydrogen for 4 h at 460 - 480oC. the thus Prepared catalyst was not in contact with getcatalog used a glass U-shaped tube with a diameter of 5 mm Catalyst loading in all experiments was 0,93 g

The nature of the influence of water vapor on the reaction of hydrodechlorination of carbon tetrachloride illustrate the examples below.

Example 1 (for comparison). The reactor was loaded catalyst and at a temperature of 80oC it was filed 0,6 IO vapor of carbon tetrachloride and 4.2 nl of hydrogen per hour.

Under these conditions, the conversion of carbon tetrachloride 0,08 when the molar izbirateljnostj education chloroform, methane and chlorohydrocarbons C2(mainly trichloroethane) of 0.65, respectively, 0,098 and 0.25.

Example 2. In the reaction mixture of example 1 at 80oC for 5 h was added to 0.05 nl of water vapor per hour (which corresponds to its concentration in the initial mixture of 1,1 vol.%).

Continued experience, stopping the flow of water vapor. Within 5 h, the conversion was in the range of 0.49 - 0,515 when izbirateljnostj on the above products 0,82 - 0,835, 0,15 - 0,17 and 0.008 - 0.01 respectively.

Newly added to the source gas-vapor mixture of 0.05 nl of water vapor per hour. Within 5 hours the conversion was varied in the range of 0.066 - 0,071 and selectivity of 0.42 to 0.44, 0,041 - 0,047 and 0,53 is 0.55, respectively.

Again pricolo of 0.005, respectively.

These examples show that the treatment with water vapor added to the source gas-vapor mixture supplied to the newly restored catalyst, leads to a significant change in its properties in the hydrodechlorination of carbon tetrachloride, namely, in the absence of water vapor treated in this way the sample is more active and selective in relation to the formation of chloroform and methane than newly restored, and in the presence of steam at almost the same activity more selective in terms of education hydrocarbon, C2.

Further examples illustrate the effect of pre-processing newly restored sample of catalyst and holding it then hydrodechlorination of carbon tetrachloride on process performance. In all these examples (which presents part of the results of the study) after treatment of the catalyst the reaction mixture of 0.6 nl/h CCl44.2 nl/h of hydrogen) with the addition of water vapor under the conditions shown in table. 1, at first for 5 h, the reaction was carried out in the absence of water vapor in the source gas mixture, and then 5 h in the presence (PL. 2). < / BR>
1. Weiss, F. H., Gambhir, B. S., Leon, R. B. J. Catal. 22, 345, (1971).

2. US Patent N 3579596

3. US Patent N n

The method of vapor-phase hydrodechlorination of carbon tetrachloride in the presence of a catalyst of platinum on alumina" at 40 - 180oC, wherein the catalyst is treated with the reaction mixture with the addition of 0.5 - 1.5 vol.% water vapor at 60 - 120oC for 2 to 5 h, and then the process is carried out at concentrations of water vapor up to 1 vol.%.

 

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