DE1284403B - Process for the production of palladium-heavy metal-alumina catalysts for the removal of acetylenes and diolefins from gas mixtures predominantly containing monoolefins by selective hydrogenation - Google Patents

Description

Because of their high reactivity, acetylenes and diolefins hydrogenate more easily than olefins which have only a single double bond.

The selective hydrogenation of acetylenes contained in olefin gas mixtures and diolefins are generally carried out in the presence of an active catalyst. In this method, however, the amount of hydrogen to be added must be accurate kept within strictly defined limits and regulated accordingly. In such a selective hydrogenation one encounters in general, if only minor ones Amounts of acetylenes and diolefins are present as impurities in the gas, to great difficulty. This is especially true when considering the acetylenes and Diolefine wants to hydrogenate almost completely without noticeably changing the olefin content of the gases to belittle. In the manufacture of gases used as an intermediate for organic Syntheses are to be used, this is of the utmost importance. It is Z. B. known that high ethylene-containing gas mixtures for the production of polyethylene no more than about 0.025% acetylenes and diolefins, such as acetylene, methylacetylene, Propadiene or other low molecular weight diolefins as impurities, may contain. In the newer polymerization processes, the cleaned Gases containing olefins do not contain more than 0.0100 /, acetylenes and diolefins.

It is already known from the German patent specification 1 171 901, that there are significantly more effective catalysts for the selective hydrogenation of acetylenes and diolefins can be obtained by applying palladium to an alumina support. With the help of these catalysts acetylenes and diolefins can be converted into predominantly monoolefins containing gas mixtures are completely hydrogenated. This hydrogenation takes place with a perfectly usable speed, so that these catalysts at find technical hydrogenation use.

It should be emphasized that these catalysts for long-term Use under the general procedural conditions remain active. Although these Catalysts for the purification of olefin gas streams are extremely suitable and prove to be excellent under most conditions, however found that the activity of these catalysts under the given conditions goes beyond the desired level. With all known technical processes for selective hydrogenation, an excess must exceed the stoichiometric amount of hydrogen can be used so that the acetylenes and diolefins are reduced to olefins will. If very active catalysts are used, the excess hydrogen will be used up by reducing the olefins to saturated hydrocarbons, so that the olefin content of the gas stream is undesirably reduced. if if small amounts of hydrogen can be used, the temperature increases will be smaller and you can therefore control the process better. Furthermore, with a Reducing the amounts of hydrogen required significantly reduces the desired olefins larger quantities. A selective hydrogenation of acetylenes and diolefins To achieve this, but without further hydrogenating the monoolefins, one must therefore Use catalyst that has the advantages of the German patent 1,171 901 has the catalyst described, but also less activity in the hydrogenation of monoolefins. The hydrogenation is said to be proportionate run at low temperatures and a small excess of hydrogen, and that The finished product should not exceed a few parts acetylenes and diolefins per million included, but the monoolefin content of the mixture is not affected may be.

From the German Auslegeschrift 1 052 979 there are still catalysts for the removal of acetylene from a gas mixture predominantly containing ethylene known by selective hydrogenation. The active ingredients of this catalyst consist of 60 to 99 parts by weight of palladium and 40 to 1 parts by weight from one of the elements copper, silver or gold. With the help of this catalyst will not only the acetylene, but also a smaller proportion of ethylene hydrogenated to ethane, d. that is, its selectivity is too low.

The invention relates to a process for the production of palladium-heavy metal-alumina catalysts for the removal of acetylenes and diolefins from predominantly monoolefins Gas mixtures by selective hydrogenation, the fired carrier with palladium and optionally heavy metal salts are impregnated and calcined and wherein the pore volume of the support is not more than 0.4 g / cm3, the diameter of the Pores no larger than 800Â and the metal mainly on the surface layer of the carrier is deposited.

The method is characterized in that the carrier with impregnated in such amounts of palladium and chromium salts that the (for the metals calculated) content of palladium 0.026 to 0.09 percent by weight and of chromium 0.01 to 0.09 percent by weight, based on the total amount of the catalyst and the atomic ratio between palladium and chromium is less than 1: 1.

Preferably, the carrier is with a palladium chloride and a Chromic anhydride solution impregnated.

The catalyst prepared according to the invention on the one hand has 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 according to the invention can be prepared in various ways will; z. B. one can the alumina carrier with a solution containing palladium and chromium compounds contains, splash, or the clay carrier can be immersed in this solution.

Any method that allows the alumina carrier with a solution To attach the active, catalytic substances is to the production of the invention catalysts used. The palladium and also the Chromium compound can be in the form of a single or two separate solutions in can be applied to the carrier in any order. When soaking the It should be noted that, according to the invention, the finished catalysts are 0.026 contain up to 0.09 percent by weight palladium and 0.01 to 0.09 percent by weight chromium should, the atomic ratio of palladium to chromium being less than 1: 1 target. The combination of the catalytically active metals, chromium and palladium the alumina carrier leads to a reduction in the activity of the in general the hydrogenation of highly effective palladium and at the same time to a balanced 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 atm is most effective. 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 Lot. The following examples are intended to illustrate the invention.

Example 1 221 of a 0.05 molar palladium chloride solution and 22 1 a 0.1 molar chromic anhydride solution (CrO3) were mixed well with one another and sprayed onto 400 kg clay carrier tablets. Before spraying, the Clay tablets burned for 8 hours at a temperature of 550 ° C. The splash was carried out in a rotating drum so that the clay tablets on their entire Surface were completely covered with the solution.

Then the coated clay tablets were again for 8 hours Fired at a temperature of 550 ° C. The tablets contained 0.033 percent by weight Palladium and 0.036 weight percent chromium.

COMPARATIVE EXPERIMENT 1 The catalyst bodies produced according to Example 1 were then compared with catalyst bodies which had been produced according to the process described in German Patent 1,171,901. The comparison tablets contained 0.046 percent by weight palladium and no chromium and were prepared by treating alumina tablets with 441 of a 0.05 molar palladium chloride solution using the immersion or spray-on methods described here. The two catalysts were then tested 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 atmospheres. The space velocity was 1000 parts by volume of gas per part by volume of catalyst per hour. The gas stream used for the experiment had the following initial composition: Propadiene ................. 1% methyl acetylene ............... 1 ° / o propylene .................. 80% propane ..................... 1.5% Hydrogen 25 5 to 7, 0 ° / O methane ....................... 9.5 to 14,% The molar ratio between hydrogen and the more unsaturated hydrocarbons (Propadiene and methyl acetylene) was about 2: 1. The following results were obtained: Table I. Temperature H2: C3H4 C3H4 loss H2 loss ° C (molar ratio) (A) -0.046% Pd on Al203 66 3.5 0.003%% 0% 52 3.5 0.008% 0.2% 93 3.5 0.010% 0% 121 3.5 0.025% 00/0 (B) - 0.033% Pd and 0.036% Cr on A1203 66 3.5 0.005 0 / o 0.8 0 / o 93 3.5 0.0040 / 0.015% 121 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 to 121 ° C.

This can be seen in (B) from the slight loss of propadiene (C3H4) and is also confirmed by the very modest loss of hydrogen.

It can also be seen from Table I, (A) and (B) that the Palladium catalyst without added chromium has too great an activity, because with one At a temperature of 66 ° C, the available hydrogen is completely used up. Self in those cases where the H2: C3H4 ratio is 3.5, all of the hydrogen will be used up without the existing methylacetylene and propadiene completely or removed to a satisfactory degree.

Comparative experiment 2 In a further experiment with those in the example 1 described catalysts were now comparative tests at temperatures carried out from 66 to 121 ° C, and it was the same gas stream, but with a smaller molar ratio of hydrogen to propadiene is used. The results are given in Table II.

Table II temperature H2: C3H4 C3H4 loss H3 @ loss ° C # (molar ratio) (A) -0.046% Pd on Al203 66 2 0.0174% 0% 93 2 0.0514% 00 /, (B) - 0.0330 / 0 Pd and 0.0360 / 0 Cr on Al2O3 66 2 0.00180 / 0 0.0844% 93 2 0.0011% 0.0061% 121 2 0.0081% should 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 some of the olefins present were hydrogenated by the palladium-chromium catalyst, which suggests a selective hydrogenation. This is clearly evident from the relatively large loss of hydrogen.

Testing of the catalyst at different temperatures and hydrogen concentrations The catalyst prepared according to Example 1 was under various process conditions Checked for suitability for selective hydrogenation. Gas streams with a high percentage of hydrogen used in relation to propadiene.

The experiments were carried out at temperatures from 66 to 149 ° C.

Table III 0.033% Pd and 0.036% Cr on Al203 Temperature H2: C3H4 C3H4 loss $ H3 @ loss oc (molar ratio) 121 3.8 0.001 <> / <> 0.005% 93 3.8 0.0022% 0.0960 / 0 66 3.8 0.006 <> 1 <>% 0.6% 149 4 0.0007 <> / <>% 0.0051% Example 2 The procedure of Example 1 was repeated, with the difference that instead of 221 of a 0.05 molar palladium chloride solution and instead of 221 of a 0.1 molar chromic anhydride solution, only about 17.3 or 19 l of the respective solution were sprayed onto 400 kg clay carrier tablets. The finished catalyst contained 0.026 percent by weight palladium and 0.031 percent by weight chromium. The catalytic converter 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 2-month endurance test was carried out were the same as in Comparative Experiment 1, but were made the following changes: The flow rate of the gas stream was 800 per hour.

The molar ratio of hydrogen to propadiene was about 1.6 to 2.0.

The inflowing gas contained 0.50/0 propadiene and 1.5% 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 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 Al2O3 Tempe-H2: C3H4 Days rature (mol C3H4 loss loss ° C 2 71 2.0 0.0033% 0.4080% 5 54 1.9 0.00180 / 0 0% 11 54 1.9 0.0032%% 0% 23 54 1.8 0.0009% 0.02170 /. 32 54 1.6 0.0005% 00/0 51 54 1.7 0.00020 / 0 0% 59 54 1.7 0.0002% 0.003001.

Example 3 Using the procedure of Example 1, by using the appropriate amounts of palladium chloride and chromic anhydride solutions Catalysts made containing approximately 0.03 weight percent palladium and 0.03 and 0.06 weight percent chromium contained. The beneficial influence of chromium on the selective hydrogenation of the palladium was determined on the basis of three different series of tests detected using these catalysts. When using 0.06 Percentage by weight of chromium could very strongly inactivate the hydrogenation effect of the Palladium can be observed. The palladium catalysts that did not contain chromium showed reasonably satisfactory results only at temperatures of 60 "C. At higher temperatures the selectivity decreased progressively, and at temperatures from 79 ° C upwards they showed only a very poor effect or no selective effect at all.

The fact that the catalysts contain suitable amounts of chromium a exhibited high selective hydrogenation capacity and insensitive to temperature fluctuations is the particular advantage of these catalysts. The test results over the effects of chromium on palladium are given in Table V. These attempts were carried out under the same conditions as in Example 2.

Table V Temperature H .: C3H4 C3H4 loss H3 loss oc (molar ratio) (A) # 027% 0.027 <> / o Pd on A1203 60 2.0 0.0002% 0.0113% 79 2.0 0.0007% 0.00260 / 0 (B) - 0.0270 / 0 Pd and 0.0300 / 0 Cr on Al2O3 60 2.0 0.0002% 0.0044% 79 2.0 0.00390 / 0 0.0034% (C) - 0.028% Pd and 0.062% Cr on Al2O3 60 2.0 0.0010% 0.0408% 79 2.0 0.0497% 0.0038%

Claims (2)

Claims: 1. Process for the production of palladium heavy metal Alumina support catalysts for the removal of acetylenes and diolefins from mainly Gas mixtures containing monooelfine by selective hydrogenation, the burned Carrier impregnated with palladium and possibly heavy metal salts and calcined and wherein the pore volume of the support is not more than 0.4 g / cm3, the The diameter of the pores is not larger than 800 Å and the palladium is mainly on the surface layer of the Is deposited on the carrier, which is not indicated, that the carrier is impregnated with such amounts of palladium and chromium salts, that the (calculated for the metals) content of palladium 0.026 to 0.09 percent by weight and of chromium 0.01 to 0.09 percent by weight, based on the total amount of the catalyst, and the atomic ratio between palladium and chromium is less than 1: 1. 2. The method according to claim 1, characterized in that the Carrier impregnated with a palladium chloride solution and a chromic anhydride solution.