DE1231387B - Process for rendering acetylenes harmless in carbon-oxide- and hydrogen-rich, sulfur-free gases - Google Patents

Description

Process for rendering acetylenes harmless in carbon dioxide and hydrogen-rich, sulfur-free gases The synthesis gases for pressure synthesis of ammonia, methanol, hydrocarbons or their oxygen-containing derivatives are made from the gases that occur during the degassing or gasification of solid fuels, or obtained from the product gases of oil or natural gas fission.

Depending on their origin, the raw synthesis gases contain different ones Impurities in varying concentrations, for example organic sulfur compounds and hydrogen sulfide, carbon dioxide, ammonia, highly unsaturated, resin-forming ones Hydrocarbons and the lower gaseous hydrocarbons, which are the initial members the paraffin series, the olefin series and the acetylene series.

For the production of pure hydrogen or pure mixtures of hydrogen with nitrogen or carbon oxide from the raw synthesis gas, a large part of the Impurities are practically completely eliminated, primarily through washing processes. These are in particular the acidic gas components hydrogen sulfide, carbon dioxide, Hydrogen cyanide and the vapors of organic compounds.

The lower saturated and unsaturated hydrocarbons, e.g. B. methane, ethane, ethylene, propylene, acetylene and its homologues, interfere with many Syntheses are not, but are often undesirable as dietary fiber. These associated gases are eliminated by liquefaction in a low-temperature gas separation process. acetylene and its homologues are fixed under the conditions of cryogenic decomposition. Because they are very easily decomposed, they are extremely dangerous in this state.

In gas mixtures that have a sufficient concentration of ethylene, the low-temperature decomposition does not lead to the excretion of solid acetylenes, because these dissolve in the liquid ethylene. This is the case as long as the ratio of ethylene to acetylene in the gas is around 100: 1 .

Because of the comparatively high solubility of the acetylenes in water, this ratio is often established during the preceding gas cleaning with aqueous absorption solutions. For example, solid acetylenes will not be separated out during the low-temperature decomposition of coke oven gas if hydrogen sulfide and carbon dioxide have previously been separated from the crude gas by means of a pressurized water scrubber. So much acetylenes go into solution that the ratio of 100: 1 of ethylene to acetylene is reached in the pre-cleaned gas.

In synthesis gases produced by splitting oils or natural gases this ratio of ethylene to acetylene is usually not given or achievable.

This is especially true if the splitting into synthesis gas is a Acetylene production is linked and in the cleavage to a high acetylene concentration is being worked towards.

The acetylene is converted from such fission gases by means of selective solvents, e.g. B. acetone, dimethylforinamide, N-methylpyrrolidone or the like. Washed out to a residual concentration below 0.5 percent by volume. The gas pre-cleaned in this way then mainly consists of hydrogen, carbon oxide, methane and nitrogen and also contains small amounts of lower hydrocarbons.

For the production of pure synthesis gases for ammonia or methanol synthesis the gas, usually under the same pressure as in the previous gas scrubbing, subjected to cryogenic decomposition. To make the acetylene contained in the gas harmless To do this, some procedures are in use, which are based on the fact that in the pre-cleaned Gas prior to cryogenic decomposition the acetylenes on a platinum group metal containing hydrogenation catalyst is selectively hydrogenated to ethylene.

The hydrogenation on such catalysts is only possible with low carbon or free gases, because the catalytic activity of the platinum metals is poisoned by carbon oxide. This poisoning can be stopped by carrying out the hydrogenation above 280.degree . Then, however, carbon oxide is already hydrogenated to methane, 3 mol of hydrogen being consumed for 1 mol of carbon oxide. This high hydrogen consumption represents a heavy economic burden on this process. This also applies to highly active hydrogenation catalysts which are - insufficiently selective - for the acetylenes, for example for the anhydrous silver silicates and for catalysts containing silver containing palladium.

With less aktivenHydrierungskatalysatoren with a carrier substance alumina-based and cobalt, molybdenum or tungsten as the active components must be used at such high temperatures that a methanation occurs by the hydrogenation of carbon monoxide in the complete hydrogenation of the acetylenes, in turn, a considerable Means loss of hydrogen.

The selective oxidation of the higher acetylenes with excess oxygen on metal sulfide catalysts is not applicable. You should still be sulphurous Gas are made, so before the acetylene production, 'and the acetylene yield would considerably diminish.

It has now been found that acetylene and its homologues can be hydrogenated in hydrogen sulfide-free, in hydrogen and carbon oxide-rich gases under normal or elevated pressure without any conversion of carbon oxide into methane, if the gas still containing acetylene at temperatures between 150 and 300 ° C., preferably at 220 to 260'C, is passed through a catalyst containing silver on a support of aluminum or iron-containing magnesium silicate, with a loading of a maximum of 25 Nm3 acetylene per cubic meter of catalyst and hour (space velocity h-1). At 10 atmospheres pressure, a loading of 10 Nm2 acetylene per cubic meter of catalyst and hour is selected for complete conversion of the acetylenes , but at a pressure of -40 atmospheres a loading of 25 Nm3 acetylene per cubic meter of catalyst and hour.

With this catalyst loading, the concentration of acetylene and its homologues in the treated gas is reduced to 0.0005 %, and this small amount goes into solution in the comparatively large amount of ethylene during a low-temperature decomposition.

. The silver-containing catalysts for carrying out the selective acetylene hydrogenation according to the invention contain less than 0.501, for example 0.1 to 0.2 percent by weight of metallic silver.

. These catalysts remain effective for a long time under the conditions mentioned above and, if their activity decreases, they can be regenerated to their original activity by careful oxidation.

The following example may serve to explain the invention further to serve.

A sulfur-free cracked gas with the composition Volwn percent Co, ..................... 3.5 C2H. .................... 0.25 C1H4 .................... 0.30 CO ...................... 27.00 02 ....................... 0.05 H. ........... ........ ... 61.9 CH4 .................... 5.0 N .............. ... 2.0 was passed at 250 ° C and 11 atm over a magnesium silicate catalyst with 0.250 /, metallic silver at a load of 4000 Nm3 cracked gas per cubic meter of catalyst and hour, which, based on the acetylene content of 0.25 percent by volume in this cracked gas, a catalyst load of 10 Nm3 acetylene per cubic meter of catalyst and hour.

The gas treated in this way still contained 0.000020 / 0 acetylene. One There was hardly any increase in methane in the treated gas.

The same gas was passed under similar conditions over a nickel catalyst with 200% nickel on a silica gel-alumina support or over palladium catalysts with 0.01 to 2.5 percent by weight of palladium on a silica gel-alumina support. Such catalysts have heretofore been used for acetylene hydrogenation. Both cataly-. When the acetylenes were fully hydrogenated, catalysts caused a considerable conversion of carbon monoxide to methane.

Since according to the methanation reaction Co + 3 H, = C'H4 + H, 0 1 volume of carbon oxide consumes 3 volumes of hydrogen, the hydrogen content in the treated gas decreases by 3 volumes per part by volume of hydrogenated carbon oxide, which leads to considerable reductions in the hydrogen yield, like the following Table shows. Catalyst hydrogenation temperature acetylene conversion carbon oxide conversion. Hydrogen yield 1 oc %% Volurnprozent Pd .................. 220 100 1 to 2 93.8 to 95.3 Ni .................. 260 to 28 () 100 4 to 5 76 to 81 Ag ................. 240 to 260 100 0 100

Claims (1)

Patent claim: A process for rendering harmless of acetylenes in carbonic oxide and the hydrogen-rich, sulfur-free gases, which are to become methanol or ammonia synthesis gas, the Tieftemperaturzerlegang subjected for the purpose of further processing, by selective catalytic hybrid of the acetylenes drierung over silver-containing catalysts, characterized in that the gases under pressure at temperatures between 150 and 300'C with a silver-containing catalyst which contains less than 0.5 percent by weight of silver on a support of natural or synthetic aluminum, magnesium or iron silicate, with a loading of the catalyst with a maximum of 25 Nm3 Acetylene are brought into contact per cubic meter of catalyst and hour, and that, if necessary, the catalyst is regenerated by treatment with an oxygen-nitrogen mixture containing 1 to 2 percent by volume of oxygen at temperatures of 450 to 500 ° C. Considered publications: German Auslegeschriften No. 1052 979, 1066 192.