DE1013636B - Process for the catalytic production of hydrocyanic acid and hydrogen from mixtures of hydrocarbon and ammonia - Google Patents

Description

Process for the catalytic production of hydrogen cyanide and hydrogen from mixtures of hydrocarbons _. and ammonia die-. Invention relates to a. Process for the production of hydrocyanic acid by converting hydrocarbons, in particular methane, with ammonia, .an catalysts of the platinum metal group. she -references- mainly to the representation of hydrocyanic acid - in - absence of Oxygen.

This so-called direct process in ceramic reaction tubes is known at temperatures. to carry out between 900 and 1300 °, using as catalysts for the endothermic direct reaction, metals of the platinum group, preferably -Pure platinum, can be used. It is also known - the - as. Catalysts used platinum metals directly on the inner wall of the tubes or on ceramic Carrier, for example made of molded bodies containing clay and / or silica To apply silicates, soapstone, hard porcelain, Pythagoras mass and the like. -It However, it has been shown that such catalysts require a long start-up time - up to they work with a consistently high throughput yield and with the full amount of methane, for which the respective apparatus is designed, can be loaded. The disturbances when the process starts up, there are in particular increased soot formation, which can quickly clog the equipment; and in an insufficient one Methane conversion, which is noticeable in an excessively high methane content of the exhaust gas. It is therefore necessary to interrupt the operation frequently, the soot deposits to remove by burning and to reform the catalyst. - -As below will be shown on the basis of an example, these formation times for platinum catalysts 250 to 400 hours - before the catalyst can be fully loaded and a consistently high throughput yield is obtained.

These phenomena are particularly detrimental when the The reaction space is divided into a large number of individual tubes, in which the formation runs at different speeds, so that the slowest forming pipe determines the speed for the entire apparatus. The addition of other platinum metals to platinum has so far not produced any significant improvements in this regard.

It has now been found that these difficulties can be eliminated and the formation of hydrocyanic acid from volatile hydrocarbons, in particular methane and ammonia, in a short time. Start-up times that are less than a tenth of the hitherto required can be carried out with high gas admission and throughput yield if platinum metal catalysts are used which, in addition to one or more metals of the platinum group, also contain aluminum, magnesium or elements of the lanthanides, individually or in groups in the form of their nitrides. Although there are already known catalysts which consist essentially of aluminum with z. B. consist of about 1 % platinum, but in these the aluminum is essentially in the form of aluminum oxide, and such catalysts have so far been used almost exclusively for catalytic cracking processes. Finally, a number of oxidic catalysts have also been proposed for the Andrussow process.

In contrast, the catalysts according to the invention are, however, as already stated, to those whose additives are essentially in the form of nitrides.

The amount of the elements mentioned in the catalysts can be calculated as metal content, up to 90 at percent. It is best to use catalysts to use the 50 to 80 at percent aluminum and / or magnesium or elements of lanthanides in metallic form as nitride or as easily converted into nitrides Connection included.

A catalyst has proven particularly useful for the process of the invention, which contains aluminum, essentially in the form of nitride. The aluminum content should here expediently up to 50 percent by weight and advantageously 20 to 35 percent by weight be.

However, the process of the invention is not based on catalysts Platinum and aluminum or other of the elements mentioned are limited, rather can the platinum metal component also in addition to platinum in a manner known per se nor the Metals containing rhodium, iridium, palladium or ruthenium individually or in groups. For example, the method results according to the invention a highly effective catalyst composition with 60% platinum, 8% ruthenium and 32 "/, aluminum, the latter being at least about 60% as aluminum nitride should be present.

The .Verfahren der- invention is particularly advantageous in itself carried out in a known manner using ceramic tubes as the reaction space, especially of such pipes, which consist mainly of aluminum oxide. One proceeds appropriately so that the z. B. aluminum-containing platinum metal catalyst applied as a practically coherent coating layer on the inside of these pipes is, so that the conversion between methane and ammonia as large as possible, catalytic Wall area is available, which also has the direct influence of external heating is exposed.

Even with a different arrangement of the catalytic converter, for example on supports or moldings, can be satisfactory by the process of the invention Achieve success if the catalyst is made of platinum metals and the elements mentioned, in particular aluminum, in the form of nitride or such easily formed compounds consists.

Finally, it is also possible to use the catalyst in the form of ribbons and wires, nets or the like. More or less free-standing and self-supporting in to arrange the reaction spaces.

If the catalyst is used as a coating on the inner wall of the Reaction space or is applied to support or packing, one proceeds advantageously so that the tubes or the carrier with z. B. aluminum-containing solutions of platinum hydrochloric acid, if necessary several times, are impregnated. For the adhesive strength of the coatings it has proven to be beneficial, between the catalyst layer and the support to insert a layer of an easily reducible ruthenium salt - with that Application of a ruthenium salt layer is assumed to be known per se, whose Ruthenium when carrying out the process as a result of the high reaction temperatures can later migrate more or less into the actual catalyst layer.

In addition to the deposition of the catalyst coating from easily decomposable or easily reducible, dissolved compounds can be used to carry out the process According to the invention, the coating is also deposited on the support from the vapor phase by, for example, placing a flame against the surface to be coated of platinum carbonyl halide, which is a volatile compound of aluminum, contains about aluminum chloride, or another of the elements mentioned, wherein hydrogen or carbon oxide can also be added to the flame-forming mixture. By appropriate movement of the flame and the carrier, the Deposition of the aluminum-containing platinum coating evenly and firmly adhering the entire surface to be coated takes place, as is the case with impregnation from the solution the treatment can be repeated one or more times in order to to achieve the desired layer thicknesses. The conversion of aluminum into nitride can then be done before or during use.

For the experiments described below, on which the effectiveness of the process of the invention using the novel catalysts, for example is shown, a platinum-aluminum catalyst can also be used instead of a platinum-aluminum catalyst Platinum Magnesium can be used.

For this purpose, the reaction tube is filled with a solution of a mixture from platinum chloride and magnesium chloride impregnated several times, whereby the solution of about 5 g platinum content to improve the adhesion and distribution of the components another 0.3 g of polyvinyl alcohol were added. The ratio of platinum chloride and Magnesium chloride in the solution was chosen so that the coating layer after Drying the chlorides and the reduction with hydrogen at temperatures between 600 and 900% contained 20% magnesium metal. A conversion of the magnesium in Nitride by treatment with nitrogenous gases before the start-up of the There is no need for a reaction, as it is under the action of the ammonia used for the synthesis the nitride formation takes place during operation.

The synthesis of hydrocyanic acid was carried out with the catalysts described in a tube consisting essentially of aluminum oxide at a temperature carried out continuously from 1250 °. The reaction gases were fed into the tube from below initiated, with the hourly supplied amount of methane according to the progressive Formation of the catalytic coating applied to the inner wall up to a maximum 30 moles / hour was increased. The maximum output after running in the catalyst was 0.66 kg hydrogen cyanide per hour. Experiments A and B were carried out with a catalytic coating made of pure platinum, while for test C according to the Method of the invention deposited the catalytic coating from a solution that on 5 g of platinum in the form of platinum hydrochloric acid 1.45 g of aluminum contained. The aluminum content was then essentially converted into aluminum nitride.

In tests A and B, in order to avoid an impossibly high content of methane in the exhaust gas, the load on the pipe could only be increased slowly, starting at 13 mol / hour and finally increasing to 30 mol / hour. In between, it was necessary to remove the soot build-up by burning it off frequently and to reform the catalytic converter, which resulted in significant operational interruptions, in which the inevitable cooling and reheating of the ceramic tube was extremely endangered. The course of the formation of the catalyst until a constant high throughput yield is achieved is shown in the table below, which indicates the time after which the pipe could be loaded with the full methane amount of 30 mol / hour without the methane content of the exhaust gas reaches impossibly high values; Furthermore, the compilation shows the total time of the interruptions in operation which were necessary in tests A and B due to the burning off and reforming of the catalyst. Attempt C Trial A Trial B Platinum Operating data platinum platinum aluminum cata- cata- minium- lysator lysator cat- lyser Full methane pollution (30 moles / hour) Hours ............. 230 310 25 constant throughput yield ° / o .................. 83-86 after hours ......... 285> 357 25 Business interruptions (Burning off, forming) Hours ............. 38 48 - The summary shows that in the process according to the invention using aluminum nitride-containing platinum catalysts, the catalyst, in contrast to the known catalysts, starts up within a very short time and can be loaded with the full amount of methane for which the apparatus is designed. Carbon black deposits or fluctuations in yield, which would make burning off or reforming necessary, are completely eliminated in the process of the invention, so that the catalyst is already working properly after 25 hours. In contrast, the start-up times in experiments A and B are more than ten times as long, apart from the fact that the final throughput, which was not achieved in experiment B after 350 hours, was noticeably behind that in experiment C. A constant throughput yield of 86%, already beginning in the 25th hour after the start of the reaction, is proof that the full catalytic effectiveness in the process of the invention not only sets in in incomparably shorter times, but also in absolutely higher yields leads, so that a substantial advance in two respects is achieved by the process using aluminum-containing platinum metal catalysts. It should not go unmentioned that the frequent interruptions in operation, which have hitherto seemed unavoidable, represent an extremely heavy load on the thermally sensitive reaction tubes, so that, according to the method of the invention, by eliminating these interruptions, the service life of the tubes can also be considerably increased.

Claims (7)

PATENT CLAIMS: 1. Process for the production of hydrocyanic acid and hydrogen from hydrocarbons and ammonia on catalysts of the platinum metal group, characterized in that ammonia and hydrocarbon, preferably methane, are passed over catalysts which, in addition to one or more platinum metals, in particular platinum, aluminum and / or Contains magnesium in metallic form or as nitride. 2. The method according to claim 1, characterized in that catalysts, instead of adding aluminum or magnesium, one or more elements containing lanthanides. 3. The method according to claim 1, characterized characterized in that catalysts are used with a content of up to 90 At percent, preferably 50 to 80 at percent, of aluminum and / or magnesium. 4. The method according to claim 1, characterized in that catalysts with 20 to 35 weight percent aluminum can be used, with at least the largest part of aluminum is present as nitride. 5. The method according to claims 1 to 3, characterized characterized in that catalysts are used, their platinum metal component in addition to platinum, rhodium, palladium, iridium and / or, in particular, ruthenium individually or contains more than one. 6. The method according to claims 1 to 4, characterized in that that the catalyst as a practically coherent coating layer on the inside the ceramic reaction tubes, preferably consisting essentially of aluminum oxide, for example from the gas phase, using volatile or thermal or compounds of the platinum metals which are easily chemically decomposable is applied. 7. The method according to claim 6, characterized in that a layer of an easily reducible ruthenium salt is applied to the inner wall of the reaction tube as a base for the catalyst layer. Considered publications: German Patent Nos. 549 055, 820 134, 882 985; USA. Patent Nos. 2 611736, 2611749, 2 631136, 2658028.