DE882985C - Process for carrying out catalytic reactions, in particular for the production of hydrocyanic acid - Google Patents

Description

Process for carrying out catalytic reactions, in particular for the production of hydrocyanic acid when carrying out catalytic reactions is it is known per se, numerous small contact carriers in the form of balls, shards, Filling rings, small gas-permeable tubes, asbestos fibers and the like, which are on all sides are impregnated with contact substance or soaked in contact solution, in looser To accommodate bulk in a reaction space and this whole space from the outside to heat or to cool. One has already experienced exothermic, relatively low ones Hydrogenation processes working at high temperatures, the caking of known powder trying to avoid wire-shaped catalysts by making contact applied to slightly larger wall surfaces.

The new process refers specifically to the catalytic, endothermic ongoing production of hydrocyanic acid from ammonia and hydrocarbons. These Implementation, e.g. B. from N H3 and C H4, in the presence of catalysts such as platinum, is known per se. It is also known to produce hydrogen cyanide from ammonia and hydrocarbons in the presence of oxygen, the reaction mechanism meanwhile is different and the reaction proceeds via the formation of nitrogen oxides. These have the latter procedure also the disadvantage that the valuable Hydrogen is burned into water and thus is lost, the presence of Water leads to losses and in many cases interferes with further processing makes noticeable.

The procedure refers to the one mentioned in the first place above Reaction of the reaction of ammonia with hydrocarbons, which is represented by the, equation NH3 -f- C H4 = H C N -f- 3H2 can be characterized. Instead of methane you can other hydrocarbons are also used. For the. Mentioned reaction are already numerous catalysts, metals, metal alloys, nitrides, oxides, etc. The like. Has been proposed without this method entering the technology have found. This was partly because the sales were or were unsatisfactory Decomposition of ammonia or hydrocarbons occurred, the quantitative output and durability of the catalysts left something to be desired, etc. more so. that the Yields remained unsatisfied. In addition, as a result of the endothermic Due to the nature of the above reaction, the catalysts had to be heated, the special requirements for heat transfer, corrosion resistance, durability and the like of the catalyst. All of these drawbacks come with the introduction of the Process in large-scale technology has been prevented so far.

This is where the invention comes in. It was found that while avoiding the aforementioned disadvantages, hydrocyanic acid in a surprisingly simple manner and hydrogen through the catalytic conversion of ammonia-hydrocarbon mixtures let win if you ammonia and hydrocarbon, z. B. methane-containing 'Gas mixtures, at elevated temperatures by means of see. known platinum catalysts converts, which are located on preferably ceramic carriers, those on the one Side the heat is supplied, while the other side with the contact in shape a coating, an impregnation or the like. is provided.

Instead of self-supporting, metallic catalyst surfaces, foils, -weave or the like and also in place of powder or granular, oxydbz.w. Nitride-containing compositions are formed according to the invention with two surfaces used, with the platinum catalysts applied to only one of its surfaces while the other (opposite) surface is at least at reaction temperature or is heated above. This not only makes it possible to use the catalyst itself before .the action of the heating medium, z. B.. Hot flame gases, and thus against corrosion to protect, whereby the durability is significantly increased, but it is at the same time also possible to use such catalytically active metals, metal alloys or the like in Form of a coating, an impregnation or the like. To use that in itself only have a low shelf life. So z. B. according to the invention from a pipe ceramic material, e.g. B. Silimanitröhr, on the inner wall with an impregnation coating made of platinum and this tube from the outside to inner wall temperatures between 9.5o and i3oo ° heated. Instead of ceramic tubes, suitable tubes can of course also be used Metal pipes are used, e.g. B. Tubes made of nickel-chromium alloys, which on their Provide the inner or outer surface with a catalytically active coating and are heated from the outside or inside. The embodiments of the method `can of course also be changed accordingly, and instead of pipes any other reaction spaces, e.g. B. those of oval, triangular or polygonal, star-shaped cross-section can be used. To increase the inner surface., it is also possible to have the tubes impregnated with catalyst substance with packing on the inside to be filled in, which in turn is impregnated on its surface with metals of the platinum group or are covered, e.g. B. impregnated ceramic rods, granular masses or the like. to be filled into the impregnated catalyst tubes.

Come as a ceramic carrier substance for the catalyst impregnation all z. B. alumina and / or silica and optionally other ingredients containing refractory compositions into consideration, which are still at the reaction temperature not and especially above. i3oo. to 1q.00 ° begin to soften and have as smooth a surface as possible. Such materials are, besides the approximately at 1700 ° softening sillimanite, z. B. baked soapstone, hard porcelain, Pythagoras mass and the like

The method according to the invention has the particular advantage of using platinum itself or platinum compounds as a coating, impregnation or the like on shaping, catalytic carrier substances for the conversion of ammonia-hydrocarbon mixtures to be able to use hydrogen cyanide. If you wanted to use platinum for this purpose up to now, so the poor durability and the softness of the metal made themselves disadvantageous noticeable; in addition, the platinum had to be used in greater amounts by weight and im generally be surrounded on the outside by a protective tube, by the heated outer wall the heat had to be transferred to the platinum foil. Through the. bad contact The heat transfer between the protective tube and the platinum was hindered. That The method according to the invention therefore not only has the advantage of being catalytic at all Metals with less adhesion, such as B. Platinum, also use in continuous operation to be able to, but also in small quantities and because of the intimate contact with special good heat transfer from the externally heated carrier substance to the catalyst surface.

Another embodiment of the invention consists in the metals To use platinum groups that contain ruthenium in the active catalyst substance, preferably in amounts above 5%, and ceramic surfaces with this catalyst substance to bedeci, -eu or to be impregnated. This achieves a high level of durability and yield. One uses z. B. platinum rufhenium with contents of 5 to 2oo / o rufhenium. With or without the presence of ruthenium. Other platinum metals can also be used, z. B. iridium or rhodium. The use of other additives is also possible, e.g. B. from Rhen.Jum, or from metals of the i. Group of the Periodic Table, in particular z. B. Copper.

The reaction temperature is between 95o and 50 °, in particular between 100 and 1200 °; Temperatures of 1050 to 115o °, measured optically on the inner pipe wall, are preferably used in pipes through which the reaction mixture flows. The ammonia-klethane mixture has approximately the composition i: i, but deviations upwards and downwards are permissible. This causes z. B. an excess of N H3 increases the conversion of metal, so that the use of preferably small excesses of N H always comes into consideration if a corresponding increase in the i \ 'H3 content in the reaction mixture is permissible.

One uses z. B. ceramic tubes impregnated with catalysts of 15 to So mm light, r width and adjusts the gas mixture so that 0.3 to 2.01 / 1i C H4 and the same amount of NH3 are introduced per nuadratzentimeter catalyst surface. A preferred gas velocity for this tube is 0.5 to 1.5-2 1 / h CH4. Instead of a pipe, a large number of pipes connected in parallel or in series, all of which. flowed through and / or washed around or alternately flowed through and washed around, can be used, for. B. also concentrically nested tubes, of which the outer on the inside and the inner on the outside is covered or impregnated with a catalytically active substance, so that a catalytically active annular space is created, which both from the outside and the inside (through the inner tube) can be heated. In a similar way, other O_uerschnittsformen, z. B. od completely or partially flattened tubes, bags. Like. Use. Here, too, the interior space can still be filled with catalyst substance, with the individual surfaces optionally also being able to be covered or impregnated with various catalyst substances or the type of catalyst changing in the direction of flow.

The surfaces covered or impregnated with catalyst, e.g. B. tube walls are subjected to activation prior adjustment of the overall continuous operation desired working conditions at the same or higher temperature. This is done by initially passing a gas mixture almost free or poor in hydrocarbons over the contact surfaces until the hydrocarbon conversion is satisfactorily high, then increasing the hydrocarbon concentration while avoiding carbon deposition and this new gas mixture again until a sufficiently high one is reached Sales over the. Contact g; ° is conducted, then again .the hydrocarbon concentration is increased, etc., until the desired mixing ratio is achieved. of the starting gas or by the fact that the hydrocarbon concentration is increased gradually and continuously from low starting values while avoiding carbon deposition.

During the activation period, which is for example 1 to 2 days (sometimes takes longer, the initially unsatisfactory hydrocarbon conversions will be always higher and finally reach values between 9o and iooo / o. The procedure can also be designed in such a way that the fresh gas mixture is less Amount of oxygen, air or the like. Is added, so that by a partial inner Combustion the external heating is supported. The oxygen or air is added but in such a limited amount that at least one mole of hydrogen per mole of hydrocyanic acid preserved. The oxygen acts primarily as an energy carrier, and the reaction does not proceed via the formation of nitrogen oxides. This additional Internal combustion can also be achieved by: adding special combustible gases to the Starting mixture can be effected, whereby at least the heat requirement of the reaction is partially covered, e.g. B. by adding some hydrogen and oxygen.

The nitrogen yields in the process according to the invention are very high good and are above 95%, e.g. B. at 96%.

The method is not limited to the aforementioned embodiments, - but also refers to all embodiments in which shaping carrier substances on the one hand with metals of the platinum group of the periodic table of the elements in the form of a coating, an impregnation or the like. Are covered and on the other Side through. Heat supply can be heated.

EXAMPLE i A sillimanite tube with a clear width of 13 mm, which after completion of the impregnation with hot, concentrated platinum chloride solution contained a uniform impregnation layer of 10 g of platinum, was heated to a dark red heat to remove the last traces of chlorine while passing hydrogen through it. The tube prepared in this way was then provided with an electrical heating coil over a length of 1 m and heated to a temperature of 100 ° and activated. A gas mixture of doo 1 / h methane and .loo 1 / 1i ammonia was allowed to enter this catalyst tube from below, so that a gas mixture of over 19 m3 was processed per day. The gas velocity was adjusted so that (based on the unit of the catalyst surface area) 0.95 to i 1 C H4 / cm2 catalyst area and the same amount of ammonia were introduced every hour. The reaction temperature was kept at 100 °. At the upper end of the tube, a mixed gas escaped the following composition: 352, 1/11 HCN, 10791 / h H2, 32.41 / h H3 N, 48, o C 1/11 H4.

It could therefore be done with this simple apparatus and with only 8.5 mg hydrogen cyanide per day with more than 5 kg hydrogen cyanide-N produce. The yield of hydrocyanic acid, based on the converted ammonia, was 96%, based on the converted methane, practically 100%.

EXAMPLES In a vessel built in the manner of a steam boiler with boiler tubes, 60 to 70 sillimanite tubes with an internal width of 23 mm were installed, each individual tube of which was impregnated with platinum in a manner similar to Example 1 and contained 20 to 2.5 g of platinum. The length of these tubes which could be heated was 2.3 m. The tube bundle was heated to a reaction temperature of 10 ° to 120 °, measured on the inner wall, by means of a gas furnace. A gas mixture of 13.0 to 180 mg / h of an undiluted methane-ammonia gas mixture with a mixing ratio of i: i was introduced into the tube bundle. The flow rate was measured so that 0.7 to 0.85 1/11 methane or ammonia were penetrated per square centimeter of catalyst surface. The apparatus thus allowed around 170 to 240o mg N H3 per day, -d. You to process almost 43 to 1.9 t of NH3.

The gas mixture withdrawn from the apparatus had the following composition, for example: 67.3 mg / h HCN, 2o7.2 mg / h H2, 7.48 mg / h C H41 3.94 m3 / 11 N -H3.

Around 1 to 1.3 t of hydrogen cyanide was thus produced in the apparatus per day. This was 9.5.1% of the converted ammonia and practically 100% of the converted Methane as, hydrocyanic acid obtained, while the ammonia conversion 94 to 96% and the methane conversion 90% were ..

The performance of the apparatus described increases with higher. , Gas velocity without impairment of the NH3 yield 1.3 to 1.5 times, so that for production of i t hydrocyanic acid-N per day 4o to 45 of the pipes of the specified. Kind of sufficient.

The apparatus described was operated without preheating the gases. If the gas is preheated separately or if the gas enters, leave it at elevated temperatures achieve significantly higher performance while: on the other hand, through transition the number of pipes required for larger pipe diameters and lengths to a fraction of that mentioned in the example above. can.

Claims (6)

PATENT CLAIMS: "i. Process for carrying out catalytic conversions, especially for the production of hydrocyanic acid, with applied to supports or walls Catalysts, characterized in that ammonia and hydrocarbons, z. B. methane-containing gas mixtures to hydrocyanic acid by means of platinum catalysts known per se converts, which are located on preferably ceramic carriers, those on the one Side the heat is supplied, while the other side with the platinum contact in Form of a coating, an impregnation or the like. is provided. 2. Procedure. after Claim i, characterized in that the active catalyst substance is further Platinum metals, such as rhodium and / or iridium and / or ruthenium, contain and themselves is on one side of a support containing two surfaces, its opposite catalyst-free side is heated. 3. The method according to claim i and 2, characterized in that. to the mentioned, on the unheated Side of the carrier located elements of the platinum group metals of the i. group , of the Periodic Table of the Elements, especially copper. 4th Method according to Claims 1 to 3, characterized in that refractory, ceramic Tube on its inner or outer surface with catalyst substance in preferably fine distribution are covered and flowed through by the gas mixture to be converted or washed around and heated on their outer or inner surface. 5. Procedure according to claims i to 4, characterized in that when using fresh catalysts initially a gas mixture free or poor in hydrocarbons over the Contact surface is passed until the hydrocarbon conversion is satisfactorily high, that then the hydrocarbon concentration while avoiding carbon deposition increased and this new gas mixture again until it reaches a .sufficiently high Sales are directed through the contact; then the hydrocarbon concentration again is increased etc.,. until the achievement. the desired mix ratio .The starting gases or by the fact that the hydrocarbon concentration of low Starting values continuously increasing while avoiding carbon separation is increased. 6. The method according to claim i to 5, characterized in that ceramic tubes impregnated with catalysts of 15 to 8o mm clearance are used and that 'per square centimeter of catalyst surface 0.3 to 21 / h methane and the same amount of ammonia in the order of magnitude be initiated. Cited pamphlets: German Patent Nos. 4566, 119279, 317 979, 354 a12; USA .. Patent No. 1,043,580.