DE1064496B - Process for the dehydrogenation of hydrocarbons - Google Patents

Description

Process for the dehydrogenation of hydrocarbons It is general known to carry out aromatization reactions with hydrocarbons or saturated To convert compounds into unsaturated, with the overall effect a dehydration the starting materials takes place.

In individual cases, the corresponding reaction in the direct one-step process Procedure possible, e.g. B. the production of acetylene from methane. These procedures however, leave many technical ones because of poor yield or high energy consumption Wishes open.

The reason for this is that at temperatures at which z. B. by means of catalysts the reaction C2H6 = C2H4 + H2 without significant side reactions is feasible, only very low hydrogen pressures due to the equilibrium position can be achieved.

Trapping of the hydrogen formed in the process was generally possible the prior art can not be carried out so that the main reaction product (e.g. ethylene) is retained. Therefore one had to work at temperatures where the hydrogen pressure is already quite high. With a few exceptions apart from (e.g. the formation of diphenyl from benzene), large parts of the too expected reaction product further decomposed.

It is known from literature that even with some alkaline earth metals the dehydrogenation of paraffins by the mechanism of metal hydride formation as was found impossible, with the exception of temperatures so low that the degree of conversion is totally inadequate. In contrast to this statement, it was found that the alkaline earth metals are very suitable as dehydrating agents when at temperatures Work is carried out above about 500 ° C., the metal being in solid form.

The present invention relates to a process for dehydration of hydrocarbons by heating them in the presence of hydride-forming metals, that is that the reaction at temperatures above about 5000 C in the presence of solid alkaline earth metal. In this way, the cleavage of Hydrogen - even if it is only in extremely small concentrations in terms of equilibrium can occur - in a very simple way and avoiding all the side reactions, that would bring about the use of chlorine or oxygen. The dehydration reaction can e.g. B. be carried out over metallic calcium, which in calcium hydride passes, 2CH4 + Ca = C2H6 + CaH2 C2H0 + Ca = C2H6 + CaH2.

The ongoing reaction is exothermic.

The calcium hydride formed during the reaction can be used in a simple, well-known manner Way regenerated by supplying heat to calcium metal with the formation of hydrogen will. The calcium or calcium hydride can advantageously be in the granulated form, as occurs in carbide hydrogenation.

In addition to calcium, other similar hydride-forming alkaline earth metals, such as barium or strontium, can be used.

Because most of the hydrocarbons to be produced are on their part can also split off hydrogen are the optimal ones for each individual case Specify reaction conditions individually. The following examples provide a guide.

A standing stainless steel tube with a diameter of 57 mm serves as the reaction vessel. which is electrically heated from the outside over a length of 800 mm. Store in it on a sieve 600 g of granulated calcium metal, which by dehydrating 650 / oigem Calcium hydride was obtained in vacuo. The hydrocarbons to be converted are in gaseous form from the bottom up through the calcium, whereby the reaction temperature is measured inside the solid filling. The reaction process is ongoing Analyzes of the exhaust gas followed with the help of the UR absorption. In a single test with fresh calcium metal in each case about 1 m3 of gas over the course of 3 to 6 hours implemented.

Example 1 It becomes 960% ethane (remainder: CH4 and H2) with increasing Temperatures and changing flow rates prevailed. Below no reaction worth mentioning is observed at 5000C. Be at 500 to 6000 C. Quantities of 1 to 3 l / h of ethane are dehydrated to ethylene without side reactions, while the C2 H6 excess remains unchanged. At temperatures higher than 6000 C this will be Ethylene partly further changed, so that at flow velocities of less than 50l / h the ethylene content of the exhaust gas is no longer proportional to the decrease in the content of ethane grows, but also acetylene and soot are formed. At higher flow velocities (from 100 to 400 l / h), however, the side reactions do not occur. An almost complete one Conversion to C2 H4 is achieved at 7500 C and 200 standard l / h of gas passage.

Example 2 About 900% propane (remainder propylene, ethane, butane, Isobutylene) with increasing temperatures and changing flow velocities enforced. Propylene formation begins measurably at 5000 C after a gas passage of 30 Nl / h to become; the propylene content of the exhaust gas initially increases with changing temperature up to 6000 C in order to continue together with the propane content in favor of cracking products, like ethylene and acetylene.

Propylene is formed at higher flow rates such as 200 lih on the other hand measurable without side reactions at 5500 C, strong at 6500 C and at 7500 C almost completely, while cracking at 200 Nl / h only takes place above 7800 ° C. Granulated strontium metal can be used in place of granulated calcium metal with equal success can be used.

Example 3 Argon is saturated with pure cyclohexane vapor at 200.degree. The gas becomes with increasing temperature and changing flow velocities enforced. Benzene formation is observed regardless of the flow rate at temperatures above 5000 C. They run at flow velocities below 50 llh side reactions, such as the formation of ethylene and acetylene, in to a considerable extent. These side reactions are almost completely suppressed Temperatures between 550 and 6000 C with flow speeds of 200 to 400 llh. Only at even higher temperatures do they form at this gas velocity apart from benzene, there are also ethylene, acetylene and butadiene.

Claims (1)

PATENT CLAIM: Process for the dehydrogenation of hydrocarbons by heating them in the presence of hydride-forming metals, characterized in that that the reaction at temperatures above about 5000 C in the presence of solid alkaline earth metal he follows. ~~~~~~~~~ Publications considered: German Patent No. 559 735; U.S. Patent Nos. 1,945,960, 2728712.