DE1198809B - Process for the removal of acetylenes and diolefins from gas mixtures mainly containing monoolefins by selective hydrogenation - Google Patents

Description

Process for removing acetylenes and diolefins from predominantly Gas mixtures containing monoolefins by selective hydrogenation because of their large size Reactivity, acetylenes and diolefins can be hydrogenated more easily as olefins that have only a single double bond. The selective hydrogenation of acetylenes and diolefins contained in olefin gas mixtures is generally carried out in the presence of an active catalyst. However, this method must the amount of hydrogen to be added exactly within strictly defined limits be held and regulated accordingly. With such a selective hydrogenation One generally comes across, if only small amounts of acetylenes and diolefins when impurities are present in the gas, there is great difficulty. This is true especially if you want to hydrogenate the acetylenes and diolefins almost completely, without noticeably reducing the olefin content of the gases. In the preparation of of gases that are to be used as an intermediate product for organic syntheses, this is of the utmost importance. It is Z. B. known that high ethylene content Gas mixtures for the manufacture of polyethylene not exceeding approximately 0.025 Ωlots Acetylenes and diolefins such as acetylene, methylacetylene, propadiene or other diolefins may contain low molecular weight impurities. With the newer ones Polymerization processes must not exceed the purified olefin-containing gases 0.010 ° / 00 contain acetylenes and diolefins. It is already from the German patent specification 1 171901 known that there are significantly more effective catalysts for selective hydrogenation from acetylenes and diolefins can be obtained by placing palladium on an alumina carrier brings up.

With the help of these catalysts acetylenes and diolefins in predominantly Gas mixtures containing monoolefins are completely hydrogenated. This hydrogenation runs at a perfectly usable speed, so these catalysts find use in the technical hydrogenation process. It should be emphasized that these catalysts with long-term use under the general process conditions stay active. Although these catalysts for the purification of olefin gas streams are extremely suitable and perform well under most conditions proven, however, it has been found that the activity of these catalysts under goes beyond the desired level under the given conditions. With all known Technical processes for selective hydrogenation must include the stoichiometric amount Excessive excess of hydrogen can be used to prevent the acetylenes and diolefins be reduced to olefins. When using very active catalysts the excess hydrogen becomes saturated by reducing the olefins Hydrocarbons used up, so that undesirably the olefin content of the Gas flow is reduced. If you can use smaller amounts of hydrogen, in this way, the temperature rises less, and the process can therefore be used control better. Furthermore, there would be a reduction in the amounts of hydrogen required the desired olefins are obtained in significantly larger quantities. To be selective To achieve hydrogenation of the acetylenes and diolefins, but without the monoolefins further to hydrogenate, one must therefore use a catalyst that takes advantage of the in German Patent 1171 901 has the catalyst described but also has a lower activity in the hydrogenation of monoolefins. The hydrogenation should take place at relatively low temperatures and at a low temperature Excess hydrogen will run off, and the finished product should be no more than a few Parts of acetylenes and diolefins per million contain, however, the monoolefin content of the mixture must not be impaired.

The invention relates to a method for removing acetylenes and diolefins from gas mixtures containing predominantly monoolefins by selective Hydrogenation at elevated temperatures and optionally under pressure in the presence a palladium-heavy metal-alumina catalyst, the pore volume of the support is not more than 0.4 g / cm3, the diameter of the pores is not greater than 800 Ä and the metal is mainly deposited on the surface layer of the support which is characterized in that the catalyst is 0.027 to 0.09 Contains percent by weight palladium and 0.01 to 0.09 percent by weight chromium.

The catalyst used according to the invention has on the one hand a low activity in the hydrogenation of monoolefins, but has a high effect in the hydrogenation of acetylenes and diolefins. Is the one applied to clay Palladium-chromium catalyst for the selective hydrogenation of predominantly monoolefins containing gas mixtures used, the acetylenes and diolefins in proportion Contain small amounts and an excess of hydrogen (with the existing Hydrogen amount the theoretically determined amount of hydrogen that you need to reduce the acetylenes and diolefins required to form olefins exceeds), then observed one that this excess of hydrogen is not completely used up in the hydrogenation which significantly increases the performance of the selective hydrogenation process.

The catalyst used in the present invention can be various Ways are made; z. B. you can the alumina carrier with a solution that Contains palladium and chromium compounds, splashes, or the alumina carrier can be immersed in this solution. Any process that allows the alumina carrier To attach a solution of the active, catalytic substances is to manufacture of the catalysts used according to the invention are suitable. The palladium and also The chromium compound can be in the form of a single or two separate solutions can be applied to the carrier in any order. When soaking the Alumina support should be noted that the finished catalyst body according to the invention about 0.027 to 0.09 percent by weight palladium and 0.01 to 0.09 percent by weight Should contain chromium, the atomic ratio of palladium to chromium being preferred should be less than 1: 1.

No protection is sought for the manufacture of the catalyst.

The combination of the catalytically active metals, chromium and palladium on the alumina carrier leads to a reduction in the activity of the in general highly effective palladium in hydrogenation and at the same time a balanced one Operation of the catalyst, causing poisoning and a consequent one Reduced activity can be prevented.

The catalyst reaches temperatures of 38 to 205 C and at Pressing 50 to 500 atu is its greatest effectiveness. The preferred space velocity is between 200 and 2000 parts by volume of gas per part by volume of catalyst and hour, the gas stream to be treated being charged with the catalyst as it flows into the Have the reaction vessel a temperature of approximately 16 C and a pressure of 1 atm should. The amount of hydrogen to be used is at least 1.2 times, preferably 4 times that required for the hydrogenation of acetylenes and diolefins, calculated Lot. The following examples are intended to illustrate the invention.

Example 1 221 of a 0.05 molar palladium chloride solution and 221 of a 0.1 molar chromic anhydride solution (CrO3) were mixed well with one another and sprayed onto 400 kg of clay carrier tablets. Before being sprayed on, the clay carrier tablets were fired at a temperature of 550 ° C. for 8 hours. The spraying was carried out in a rotating drum so that the clay tablets were completely coated with the solution on their entire surface. The coated clay tablets were then fired again at a temperature of 550 ° C. for 8 hours. The tablets contained 0.033 percent by weight palladium and 0.036 percent by weight chromium. The catalyst bodies produced in this way were then compared with catalyst bodies which had been produced by the process described in German Patent 1171 901. The comparison tablets contained 0.046 percent by weight palladium and no chromium and were prepared by treating alumina tablets with 44 l of a 0.05 molar palladium chloride solution using the immersion or spray-on methods described here. The two catalysts were then procedurally applied in the same reaction vessels and under the same conditions. The reaction vessel was charged with 25 cm 3 of catalyst and heated to a temperature of 52 to 121 ° C. and then started up at a pressure of 350 atm. The space velocity was 1000 parts by volume of gas per part by volume of catalyst and hour. The gas flow used for the experiment was the following starting composition: propadiene ........................ 1% methylacetylene --- 1 0 / o propylene .......... ............... 80% propane ........................... 1.5% hydrogen ................ 2.5 to 7.0 01o methane ................... 9.5 to 14, 0% The molar ratio between hydrogen and the more highly unsaturated hydrocarbons (propadiene and methylacetylene) was about 2: 1. The following results were obtained: Table I A. 0.046% Pd on A1203 C; 3H4 H2- Tempe- H2 / C3H4 Loss loss temperature ° C Molar ratio%% 66 3.5 0.003 0 52 3.5 0.008 0.2 93 3.5 0.010 0 121 3.5 0.025 0 B. 0.033% Pd and 0.036% Cr on A1203 G6 3.5 0.005 0.8 93 3.5 0.004 0.015 121 i 3.5 0.001 0.0065 Table 1 shows that the palladium-chromium catalyst (B) has a significantly higher selectivity than the palladium catalyst (A) within the temperature limits of 66 ° C. to 121 ° C. This is due to the low level of (B) Loss of allylene (C3H4) can be seen and is also confirmed by the very moderate loss of hydrogen.

It can also be seen from Tables I A and I B that the palladium catalyst has too great an activity without the addition of chromium, because at a temperature of 66 ° C the existing hydrogen becomes perfect used up. Self in those cases where the H2: C2H4 ratio is 3.5, all of the hydrogen used up without the existing methylacetylene and propadiene completely or removed to a satisfactory degree.

Example 2 In a further experiment with those described in Example 1 Catalysts were now comparative tests at temperatures from 66 to 121 "C and the same gas flow was carried out, but with a smaller molar ratio used from hydrogen to allylene. The results are given in the table.

Table II A. 0.046% Pd on A1203 C3H4- H2- Tempe- H2 / C3H1 Loss loss rature C | Loss | C. Molar ratio%% 66 2 0.0174 0 93 2 0.0514 0 B. 0.0330 / 0 Pd and 0.036% Cr on A1203 66 2 0.0018 0.0844 93 2 0.0011 0.0061 121 2 0.0081 0 As can be seen from Table II A, all of the hydrogen present was consumed by the palladium catalyst, suggesting that all of the olefins present were completely hydrogenated. However, as can be seen from Table II B, only a portion of the olefins present was hydrogenated by the palladium-chromium catalyst, which suggests a selective hydrogenation. This is clearly evident from the relatively large loss of hydrogen.

Example 3 A palladium-chromium catalyst was prepared according to that in Example 1 and under different process conditions tested for suitability for selective hydrogenation. There were gas streams with a high percentage of hydrogen relative to all used. The experiments were carried out at temperatures of 66 to 149 C.

Table III 0.033% Pd and 0.036% Cr on A1203 Tempe- | H2 / C3H4 | C3H4- | H2- rature C loss loss Molar ratio | 121 3.8 .0.001 0.005 93 3.8 0.0022 0.096 66 3.8 0.006 0.6 149 4 0.0007 0.0051 Example 4 A palladium-chromium-alumina support catalyst according to Example 1, which contained 0.026 percent by weight of palladium and 0.031 percent by weight of chromium, was subjected to a service life test. It was found that this catalyst showed no noticeable weakening in terms of activity and selectivity when operated continuously for 2 months.

The procedural conditions under which this two-month endurance test were the same as in the first example except that the following were made Changes made: The gas flow rate was 800 per Hour; the hydrogen to allylene molar ratio was about 1.6 to 2.0; the Incoming gas contained 0.5% propadiene and 1.50 / 0 methylacetylene.

After the catalyst within the first 2 days at a constant Temperature of 71 "C had reached its maximum activity, he was 2 months (60 Days) at a process temperature of 54 "C continuously with the gas stream to be hydrogenated charged, with a loss of more highly unsaturated hydrocarbons in the order of magnitude of less than 0.001% occurred, which did not occur during the entire duration of the experiment changed. The results are given in Table IV. After the end of the experiment the catalyst was almost completely free of carbon deposits.

Table IV 0.026% Pd and 0.031% Cr on Al203 Temp- C3H4- H2- Days rature loss loss ° C molar ratio%% 2 71 2.0 0.0033 0.4080 5 54 1.9 0.0018 0 11 54 1.9 0.0032 0 23 54 1.8 0.0009 0.0217 32 54 1.6 0.0005 0 51 54 1.7 0.0002 0 59 54 1.7 0.0002 0.0030 EXAMPLE 5 The beneficial influence of chromium on the selective hydrogenation of palladium was demonstrated in three different series of tests in which catalysts containing approximately 0.03 percent by weight of palladium and 0 percent by weight, 0.03 percent by weight and 0.06 percent by weight of chromium were used became. When using 0.06 percent by weight of chromium, a very strong inactivation of the hydrogenation effect of the palladium could be observed. The palladium catalysts which did not contain chromium showed reasonably satisfactory results only at temperatures of 600 C. At higher temperatures their selectivity increasingly decreased, and at temperatures of 79 ° C. and above they showed only a very poor or no selective effect.

The fact that the catalysts used according to the invention with suitable amounts of chromium had a high selective hydrogenation ability and against The particular advantage of these catalysts is that they are insensitive to temperature fluctuations. The test results on the effect of chromium on the palladium are given in the table. These experiments were carried out under the same conditions as carried out in example 4.

Table V A. 0.027% Pd on Al203 Temp- C3H4- H2- rature loss loss ° C molar ratio%% 60 2.0 0.0002 0.0113 79 2.0 0.0007 0.0026 B. 0.027% Pd and 0.030% Cr on Al203 60 2.0 0.0002 0.0044 79 2.0 0.0039 0.0034 C. 0.028% Pd and 0.062% Cr on Al203 60 2.0 0.0010 0.0408 79 2.0 0.0497 0.0038

Claims (1)

Claim: Process for removing acetylenes and diolefins from gas mixtures predominantly containing monoolefins by selective hydrogenation at elevated temperatures and optionally under pressure in the presence of a palladium heavy metal - Alumina catalyst, the pore volume of the support not exceeding 0.4 g / cm3 is, the diameter of the pores is not larger than 800 Å, and the metal is mainly deposited on the surface layer of the support, characterized in that the catalyst 0.027 to 0.09 weight percent palladium and 0.01 to 0.09 weight percent Contains chrome. Publications considered: German Auslegeschriften No. 1,095,808, 1,052,979; U.S. Patent No. 2,475,155; French patent specification No. 1 177 764.