DE887041C - Process for the catalytic dehydrogenation of gaseous hydrocarbons - Google Patents

Description

Process for the catalytic dehydrogenation of gaseous hydrocarbons -To avoid the supply of heat through the wall of the reaction vessel and the with it Associated difficulties are encountered in the thermal treatment of carbon dioxide and hydrocarbon derivatives, e.g. B. in the splitting hydrogenation of oils or in the elimination of water from alcohols, the starting materials have already been proposed before placing in the reaction vessel to heat so high that, another Heat supply is no longer necessary during the implementation. To .this way of working make it easier, the reaction vessel and the starting materials have already been subdivided or the products of each level before entering the first or the next Stage the necessary heat is supplied.

This type of heat supply has so far been limited to processing limited to those substances that cause moderate heating above the reaction temperature is harmless. So passed z. B. no concerns, alcohols such as ethyl alcohol, which should be dehydrogenated at about 25o to 2-8o ° _ in the presence of catalysts, to be heated to about 300 ° before introduction into the reaction vessel and so the proportionate bring in a small amount of heat necessary for this implementation.

Surprisingly, it has now been found that dehydration of gaseous hydrocarbons; .the considerably larger amounts of heat consumed using the mentioned. Temperature regulation is possible. All experiences with the dehydrogenation of gaseous hydrocarbons which show that .these substances in the presence of good dehydrogenation catalysts at 500 ° to a great extent so strongly decompose; that the catalyst .by carbon deposition is very weakened, had to discourage the use of less sensitive raw materials or if lower temperatures are used, a proven heat supply should be used. Against all expectations it has now been shown that gaseous hydrocarbons, e.g. B. Butane, which is to be dehydrated at about Soo to 54o °, without the When the catalyst hits, disruptive side reactions occur to about 58o ° Let it preheat, which gives the opportunity to do what is necessary for the first stage bring a considerable amount of heat into the reaction vessel.

It was even more surprising that it is also permissible for the Dehydration of such carbon. products resulting from hydrogen that are rich in Olefins are, before they are introduced into the second and further dehydrogenation stages again to a temperature lying above the reaction temperature, e.g. B. to 58o °, to heat up without '.the contained in the mixtures to be heated, very implementable Unsaturated hydrocarbons change in an undesirable way. in the On the contrary, it was even found that the yield of olefins is .these Working method increased.

The temperatures at which the starting materials oller the products of the individual stages have to be heated up in order to obtain the necessary heat for the respective stage can be easily determined by preliminary tests. The residence time the gases in the heating devices are adjusted so that there are no reactions can occur to a significant extent. It amounts to z. B. in the implementation of Butane to butylene about 3 seconds or less.

The 'dehydrogenation is carried out in two or more reaction vessels connected in series: The starting materials or the materials to be introduced into the next step are supplied with as much heat as is required for the reaction to be carried out in the relevant stage. first again 'attributed vleic i Henden gases after suitable heating in the same vessel, and using a vessel so for every two reaction stages.

The process is particularly suitable for the dehydration of saturated Hydrocarbons finite 2 to 4 carbon atoms in the molecule. As catalysts the usual dehydrogenation catalysts are used. Leaves its effectiveness after a long time After use, they are revived in a known manner, e.g. B. by guiding of oxygen mixed with inert gases to dissipate the heat of combustion : can be, through the reaction chambers, which are expediently connected in parallel.

Example i With three vertically arranged, one behind the other Quartz tubes with a clear width of 50 mm, the upper one, from an electric heating device Surrounded parts serve as a preheater, while their lower parts, through a separate heating is only heated to such an extent that no heat loss occurs, Containing the catalyst, 400 liters of n-butane are passed per hour. As a catalyst serves chunky active clay that has been impregnated with potassium dichromate solution and contains 5 parts by weight of chromium oxide (Cr2 03) for every 100 parts by weight of aluminum oxide. Each quartz tube contains zoo cc. Of this catalyst and layered pottery shards.

The butane is heated to about 58o ° in the upper part of the first pipe, then flows through the catalyst zone and cools down to the reaction temperature, about 53o °, from. With a content of 6.41 / o butylene, the gas then enters the second Tube after it has been reheated to 586 °. Of the. Process will then repeated in the same way in the third tube. Contain the escaping gases behind the second pipe r2.2% and behind the third pipe 1911 / o butylene. All in all --5 "/ o of the butane used are converted, of which 0/0 to butylene. Examples With four iron vessels connected in series, -6oo mm high and 5oo mm Diameter inside with. ceramic material up to a clear width of 300 mm are lined and also well insulated on the outside and each of which has 15 liters of catalytic converter Contains 25 cbm of n-butane per hour. In front of each oven is a gas-heated preheater in which the butane is brought to the desired temperature is heated. Lumpy active alumina with chromic acid serves as the catalyst and potassium bichroinate was impregnated and preheated to 500 °. The finished catalyst contains 8 parts Cr for every 100 parts ale Ö3. 02 and 2 parts K2 O.

The temperatures of the gases are when they enter the four reaction vessels in sequence 564 °, 568 °, 578 ° and 58q. °, the outlet temperatures 48q. °, 5i2 °, 520 ° and 527 °. The most favorable reaction temperature is around 50 to 5400. That Gas contains after the first stage 13.8, after the further stages 16.9,: 2o; 2 and 23.2 "/ o butylene. On the whole, 32% of the butane was converted, of which about 20% to butylene.

After 7 hours of operation, the deposited on the catalyst Carbon burned away by passing a mixture of air and nitrogen over it. This shows that the amount of carbon deposited is only 1.4 percent by weight, based on butylene produced. If you work in a familiar Way without preheating the butane and the intermediate gases above the reaction temperature, whereby the necessary heat is supplied through the wall of the reaction vessel, amounts to the amount of carbon deposited under otherwise identical conditions 2.6 percent by weight, based on butylene produced.

Claims (1)

PATENT CLAIM: Process for the catalytic dehydrogenation of gaseous Hydrocarbons, characterized in that the reaction in two or more series-connected reaction vessels takes place and the starting materials before the entry into the first stage or the entire products of each stage before Entry into the next following by heating above the reaction temperature for the necessary heat is supplied to each stage. Printed publications: British Patent No. 51636o; French patent specification No. 863651.