DD234799B5 - Process for the regeneration and reactivation of palladium carrier catalysts - Google Patents

Description

Field of application of the invention

The invention relates to a process for the regeneration and reactivation of palladium-supported catalysts, which are preferably used for selective hydrogenation and whose activity and selectivity reduced mainly by carbonaceous deposits, by chemisorptive blocking or chemical changes of the active surface and / or by sintering of the active component or has largely been lost.

Characteristic of the known technical solutions

Palladium-supported catalysts, like heterogeneous catalysts in general, undergo gradual deactivation in the course of their commercial use. In the case of selective hydrogenation is often associated with a decrease in the selectivity of the hydrogenation process. The causes of this deterioration of the catalytic properties and, of course, the effectiveness of the catalysts are to be found in

physical changes of the catalysts, an important and frequent effect in this connection is the sintering of the finely dispersed catalyst metal;

- An accumulation of deposits on the catalyst surface, which come from the product stream or from catalytic or non-catalytic side reactions in the reactor;

- The poisoning and / or the chemical change of the catalyst which in turn leads in many cases to detectable physical changes of the active component of the catalyst.

As soon as the activity and selectivity of the catalyst no longer meet the minimum technical-economic requirements, it must be replaced by new or regenerated or reactivated. Since a catalyst change is usually associated with considerable costs, there is great interest in efficient regeneration or reactivation process to extend the life of the catalysts while high efficiency of the processes carried out with them. Regeneration generally refers to the gentle removal of carbonaceous deposits from the catalyst surface. In addition to the normally necessary regeneration, the reactivation also includes further subsequent chemical or physical measures coupled with the regeneration step. By them, the properties of the catalyst which are essential for a specific type of catalytic conversion and undergo an undesired change in the course of catalyst use are restored to a state which at least largely restores its original activity and selectivity. Since both the state of the spent catalyst and the desired properties of the regenerated or reactivated catalyst and, of course, the possibilities for its regeneration or reactivation by the chemical processes to be catalyzed and the prevailing conditions and by the properties of the catalyst are determined , the known regeneration and reactivation generally refer not only to certain types of catalysts, but also to certain applications of these catalysts. For the regeneration of hydrogenation catalysts containing metals of the 8th group of the PSE, the processes DE 2 029 370 and US Pat. No. 3,591,522 describe a process in which the spent catalyst is first washed with an organic liquid at temperatures up to 473 K and subsequently is treated with hydrogen at temperatures between 473 and 773 K. A distillate oil wash, followed by a steam treatment at 477 to 700 customer about 1.37 MPa in a combustion phase with air in a third stage is proposed in DE 2 029 370. According to DE 2 028 208, spent catalysts containing palladium or platinum group metals on an α-Al ₂ O _{3 support} and used for the selective hydrogenation of Сд hydrocarbon mixtures by washing with water, heating in the vapor stream at 613 to 728 K and subsequent burning of the organic deposits at 798 to 813 K regenerated by the addition of air. More generally, in the known regeneration processes for palladium-containing supported catalysts (which are preferably used for selective hydrogenation processes), the temperature on burning in the oxygen-containing gas stream to values between about 773 K (eg WO 81/03 288, DE 2 849 026 and DE 1 112 729) and about 873 K (DD 152 674 and DE 2 365 233) limited. At temperatures above 723 to 773 K usually occurs with increasing treatment temperature and time increasing, largely irreversible loss of hydrogenation activity. For example, DC Manly and FJ Rice, jun. (J. Physic. Chem. 68 [1964], 420-421) that the activity of palladium / Al ₂ O _{3 supported} catalysts in Benzenhydrierung after treatment at 723 K in air and in an oxygen atmosphere largely irreversible to 80 and 36, respectively % of the initial value decreases. A major cause of the decrease in activity generally observed in the tempering of finely dispersed metals is the sintering of the palladium crystallites, as, inter alia, I. Furuoya and T. Shirasaki (Bull Japan, Petrol Inst., Ed [1971] 1, 78-83). In accordance with this, it is found in DE 2 913 209 and DE 3 021 371 that the average palladium crystal size of 3.0 and / or 723 K and 1 173 K in the air flow is determined by calcination of palladium supported catalysts for two hours. 3.5 nm to 8.0 to 8.5 nm increases. Analogous effects are also observed when calcining in an inert or hydrogen-containing gas atmosphere.

In accordance with these facts, the control and limitation of the temperature during burning and in the thermal treatment of palladium hydrogenation catalysts has generally received much attention. As measures in this connection it is proposed to limit the oxygen content in the regeneration gas relatively strongly (eg DE 2 315 930 and DE 3 240 208), the heat capacity of the regeneration gas stream by addition of water vapor (eg DD 68 689, SU 589 013 and US Pat. No. 4,038,209) or carbon dioxide (EP 0 071 397) and / or to carry out technological measures, such as the use of heat exchangers.

However, in many cases sufficient reactivation of the catalysts by the measures and methods described no longer or not at all achieved, because irreversible changes in the catalyst inevitably occur in its technical use and possibly already carried out regenerations to a greater or lesser extent , have accumulated too much or because the catalyst suffers from extreme physical and chemical changes due to comparatively extreme operating conditions or abnormal operating situations, which can not be sufficiently corrected with the usual regeneration methods. In order to be able to continue to use such catalysts, a number of reactivation methods are proposed. These processes generally include, as far as necessary, the preceding or simultaneous regenerative removal of the carbonaceous deposits from the catalyst surface and are intended to combine the altered physical, chemical and thus catalytic properties essential to a particular application of a catalyst due to the restoration of a sufficiently high level of effectiveness.

This is achieved in the known methods in principle by the fact that at least a partial transfer of fixed on the support surface and sintered or chemically modified particles of the active component in soluble or liquefiable under the respective conditions salts and subsequent careful decomposition and / or reduction in substantially

analogous to the catalyst preparation, a redistribution and reformulation of the active component or of the active centers and, associated therewith, a reactivation of the supported palladium catalyst. The treatments are also known as follows:

- Halogens, in particular with chlorine (eg DD 71 985, DE 1 243 156, DE 1 542 257 and DE 1 920 805) or halogen compounds, in particular with chlorine compounds, if appropriate in the presence of oxidants or oxygen (eg. DD 93 534, DD 120 589, DE 1 243 156, DE 1 920 806, DE 1 935 478 and DE 2 947 634);

Nitric acid or nitrogen oxides, if appropriate in the presence of hydrogen chloride, oxygen or other oxidizing agents (for example DD 119 138, DD 125 189, DE 1 667 086 and DE 2 513 125);

EDTA or its sodium salts (US Pat. No. 3,148,750);

- A sulfidation agent and subsequently with hydrogen at temperatures of 473 to 873 K (DE 2,819,382).

From selective hydrogenation catalysts, the halogen must be removed after reactivation. In general, this is done by washing the reduced catalysts with water.

Significant shortcomings of the known reactivation are that they almost without exception require considerable technological effort with up to 5 and more stages of the process, that they are reliant on either relatively expensive and / or very aggressive and hazardous chemicals and that by using halogens, halogen compounds or Sulfur compounds carried out reactivation in the case of the catalysts used for selective hydrogenation processes generally leads to undesirable side effects or additionally require a relatively high cost to the greatest extent possible removal of the halogens from the reactivated catalysts.

Object of the invention

The aim of the invention is a powerful for used palladium-supported catalysts, the safety requirements according to non-hazardous simple regeneration and reactivation.

Explanation of the essence of the invention

The object of the invention is to develop a technologically simple and in the art as far as possible by conventional means feasible process for the regeneration and reactivation of palladium-supported catalysts, which allows to safely remove carbonaceous deposits from the surface of spent catalysts from a safety point of view, a To achieve redistribution of the active component and restore the optimal catalytic properties for the particular application of the catalyst without undesirable side effects.

In a first step, the process of regenerating and reactivating palladium-supported catalysts, optionally containing further modifying components, is achieved by thermal treatment in an oxygen-containing atmosphere in a multi-stage process Catalysts in the temperature range from 423 to 723 K as long as in a oxidizing substances largely free gas stream containing less than 0.1 vol .-% oxygen, treated until no organic components are discharged, and in a second stage the gas stream 0, 1 to at least 20 vol.% Oxygen are added, wherein the oxygen content in the regeneration gas is gradually increased to the extent that the temperature in the catalyst layer does not exceed 850 K, and the treatment in the second stage with the at least 20 vol.% Oxygen-containing gas stream is carried out for up to 15 hours, and according to the invention a third treatment stage is connected, in which the catalysts in a largely free of oxidizable materials gas atmosphere containing 15 to 100 vol .-% oxygen, treated at temperatures between 773 and 1 373 K up to 48 hours and then cooled and optionally reduced.

It is favorable if in the 1st stage the gas quantity related to the catalyst volume is in the range between 100 and 2500 v / vh, preferably 200 to 1000 v / vh, as regeneration gas nitrogen, water vapor or a mixture thereof or one of Pollutant-free combustion gas mixture, in particular a nitrogen-steam mixture with a vapor content of at least 50 vol .-% or pure steam is used and when the temperature is in the range of 640 to 675 K. In the 2nd stage, the same amount of gas is used. Here, the treatment is carried out at temperatures between 720 and 850 K, wherein at the beginning of the gas stream 2 to 5 vol .-% oxygen are added. In the third stage, the gas stream preferably contains from 20 to 100% by volume of oxygen, and the amount of gas applied to the volume of the catalyst is conveniently from 10 to 1000 v / vh.

It is advantageous if the treatment in the 3rd stage at temperatures between 873 and 1173 K over a period of up to 24 hours, in particular 0.5 to 12 hours with air, an air-oxygen mixture or pure oxygen at temperatures between preferably 1 073 and 1 150 K is performed.

Advantageously, the treatment in the third stage is carried out at temperatures above 1 150 K at an oxygen partial pressure of at least 0.1 MPa and in a substantially static gas atmosphere.

It is favorable if, in carrying out the process, the heating rate in the stages does not exceed 100 K / h (preferably 50 K / h) and the cooling rate does not exceed 150 K / h (preferably 75 K / h) and if at temperatures in the catalyst bed of is heated under 425 K, preferably in the absence of condensable amounts of water vapor in the regeneration gas, treated or cooled.

The process is conveniently carried out in a packed bed with direct passage of Regeneriergasstromes. Advantageously, the process is carried out at comparatively low content of the spent catalysts on carbonaceous or oxidizable deposits in a flat, not more than 20 cm (in particular 10 cm) high, moving or stationary bed with substantially sweeping gas stream, the implementation of the method in a rotary kiln is particularly preferred and in this case the individual process steps are passed through the oven in sequence when passing through the catalyst.

When carrying out the process according to the invention, it was found that even in those cases where the known oxidizing regeneration processes do not or no longer lead to the desired success, a virtually complete reactivation of the spent catalysts is achieved. Associated with this is also the restoration of the selectivity originally achieved with these catalysts in the hydrogenation process. The degree of reactivation achieved is decisively determined by the conditions selected in the third stage of the process according to the invention, in particular by the treatment temperature, the treatment time and the oxygen content or oxygen partial pressure of the gas atmosphere present. To achieve a clear and sufficiently rapid reactivation effect, the regeneration gas in this stage should have an oxygen content of at least 10% by volume or an oxygen partial pressure of at least 0.01 MPa and a treatment temperature above 700 K should be selected. Oxygen contents of at least 15% by volume and treatment temperatures of at least 800 ° C. are particularly effective. With increasing temperature and treatment time and / or with increasing oxygen content or partial pressure, the rate and / or the degree of reactivation which can be achieved are increased.

For the characterization of the original catalysts, the catalysts used after their use and the catalysts regenerated and reactivated by the use of the process according to the invention were used u. a. the gas phase hydrogenation of ethyne in the presence of ethene and the liquid phase hydrogenation of propyne and propadiene in the presence of propene. In addition, the so-called F values - the ratio between the number of exposed and the total number of palladium atoms present - were determined by means of a CO chemisorption method according to the pulse flow method for characterizing the palladium dispersity. This method determines the CO chemisorption capacity of the investigated catalyst sample at 273 K. For this purpose, depending on the palladium content, 0.5 to 5 g of catalyst initially pretreated at 393 K in a hydrogen stream reducing, then after adjusting the measurement temperature of 273 K in the hydrogen stream (2 l / h) 5 pulses of 0.4 ml of CO introduced and the СО amount not chemisorbed by the palladium surface atoms of the catalyst sample is determined katharometrisch at the output. On the basis of the chemisorbed СО amount and the palladium content of the sample, the F value is calculated assuming that one СО molecule is chemisorbed per palladium surface atom. The values thus determined are well suited as a relative measure of the dispersity of palladium present in the respective catalyst. The actual absolute values, however, are consistently higher, since the СО molecules on the palladium surface atoms can always be adsorbed in addition to the simplistic underlying linear in a bridge-like, 2 surface metal atoms per adsorbate molecule. The ratio between linear and bridge-shaped adsorption can z. B. by IR spectroscopic methods or comparative studies to determine the metal surface can be determined. The test results available in this regard show that the surface palladium atom / CO ratio is substantially constant for a particular type of catalyst, typically between about 1.5 for palladium-supported catalysts and 2, i. H. virtually pure bridge-shaped adsorption SOCO, for palladium black catalysts (see, for example, E.-G. Schlosse: Chemie-lng.-Technik 39 [1967] 7, 409-414).

The fact that a considerable increase in the hydrogenation activity is achieved with the process according to the invention, although treatment temperatures are used, for example, between 1,000 and about 1,200 K in the third stage, is extremely surprising. On the basis of the known fact that finely dispersed metals, in particular finely dispersed palladium, generally sinter rapidly at temperatures above about 800 K with increasing temperature, the increase, which has been demonstrated parallel to the increase in activity as a result of the process according to the invention, at such high treatment temperatures the palladium dispersity completely unexpected. Thus, the F-values increase up to about six times the value determined in the case of the spent catalysts and thus again reach the dispersity ranges present in the original catalysts.

Obviously, there is a close correlation between the increase in the hydrogenation activity and the palladium dispersity of the catalysts regenerated and reactivated according to the invention. But this does not rule out that further, activity and selectivity-enhancing factors, such. B. the preferred embodiment of certain, for selective hydrogenation particularly advantageous activity centers, crystallite surfaces and / or particle size distributions are brought by the inventive method to action.

In an expedient embodiment of the method according to the invention, in the 1st and 2nd stage, a gas quantity of 100 to 2500 v / vh, in particular 200 to 100 v / vh, based on the volume of the spent catalyst is used. As regeneration gas, all gases or gas mixtures are suitable, which at temperatures up to about 900 K to the catalyst components and also in the 1st stage compared to the carbonaceous deposits and in the 2nd stage in the presence of a palladium catalyst to molecular oxygen practically inert are. As a rule, it is favorable to use the same regeneration gas in both stages. The Austreibphase is terminated after setting the specified conditions, if no appreciable amounts of organic matter condense more when cooling the exhaust stream or the resulting aqueous condensate remains clear.

In the 2nd stage, as the H / C ratio of the deposits still present in the catalyst decreases, higher treatment temperatures are preferred, and the amounts of air added to the regeneration gas stream at the beginning of the burning-off phase increase. The higher the carbon residue content of the catalyst, the lower the oxygen content chosen. Moreover, it is usually favorable initially to choose a relatively low burning temperature and then to increase it in the course of the burning phase together with the oxygen content of the regeneration gas. For monitoring and control and to determine the end of the burning phase, it is expedient to determine the CO ₂ content in the exhaust gas from time to time. Moreover, at a comparatively low oxygen content in the gas atmosphere, relatively low treatment temperatures and / or longer treatment times and at relatively high treatment temperatures, a comparatively low gas throughput or a virtually static gas atmosphere and / or a high oxygen content or partial pressure in the gas atmosphere are advantageous. The pressure is expediently not chosen to be significantly higher in the process according to the invention than is necessary for overcoming the pressure loss in the treatment device when carrying out the process under the selected conditions, in particular for the respective gas throughput. If only a gas with a relatively low oxygen content is available for carrying out the process in the third stage, the increase in pressure offers advantages, since in this way a shortening of the treatment time and / or an increase in the

Treatment temperature and thus an improvement in the effectiveness of the process is possible. Oxygen partial pressures above 0.1 MPa are particularly advantageous at very high treatment temperatures or are required at temperatures above about 1200 K to achieve the reactivation of the catalysts or the redispersion of palladium. If the treatment temperature at oxygen partial pressures below 0.1 MPa exceeds this limit, the reactivating and redispersing effect is largely or completely lost, and the sintering of the palladium, which starts with a further increase in temperature, finally leads to a further deactivation of the catalyst. As the oxygen partial pressure in the gas atmosphere is increased above 0.1 MPa, this limit is shifted to higher temperatures. Accordingly, in carrying out the process according to the invention in the third stage, treatment temperatures above 1 200 K are possible, but usually not expedient for economic reasons. The reduction of the catalysts thermally treated in the presence of oxygen is carried out, if necessary, according to the invention preferably with hydrazine, hydrogen or hydrogen-containing gas mixtures. In an expedient embodiment of the method according to the invention, the treated catalyst according to its water absorption capacity with an aqueous, max. 20%, in particular max. Soaked 10% hydrazine hydrate solution, in this way at temperatures between 283 and 373 K within max. Reduced for 60 minutes and finally dried at 373 to 393 K. Another advantageous variant of the process according to the invention is the reduction with hydrogen or a hydrogen-containing gas mixture at temperatures below 500 K. This hydrogen reduction preferably takes place immediately in the apparatus for regeneration and reactivation or after the replacement of the treated catalyst in the reactor in situ, at pressures of at least 0.1 MPa and a reducing gas amount of at least 50 v / vh, preferably at least 100 v / vh, based on the catalyst volume. In situ, the reduction is preferably carried out at the start-up of the reactor, at temperatures, pressures and gas flow rates substantially in accordance with the conditions employed in the subsequent catalytic process.

The apparatus for carrying out the method according to the invention consists essentially of the required Gasmeß- and -mischeinrichtungen, at least one preheater or a burner chamber equipped with Temperaturmeßstellen regeneration furnace or reactor and usually downstream apparatuses for cooling the exhaust gas and for the deposition of therein contained condensable components. Conveniently, the waste heat for heating the condensable components contained therein. Advantageously, the waste heat for heating the regeneration gas or the regeneration gas is used for cooling the exhaust gases with. In principle, an at least partial circulation of the regeneration gas in the individual stages is possible.

The heat supply and cooling takes place with the aid of the regeneration gas and / or via the furnace or reactor wall. In a preferred embodiment of the process according to the invention, the regeneration and reactivation of the catalysts take place in a packed bed with direct passage of gas fixedly arranged on a gas-permeable, temperature-resistant and oxidation-resistant carrying device.

Another variant of the method according to the invention, which is particularly advantageous if the Kiuäi consumed bodies contain only small amounts of carbonaceous deposits from the outset or can be largely removed by regeneration in situ prior to the expansion of the catalysts, represents the reactivation of in a shallow , moving or stationary layer arranged catalyst in a virtually static gas atmosphere or in a substantially sweeping this gas flow. Well suited for this are rotary tube or muffle furnace. The bed height of the catalyst can be made larger in the case of a moving catalyst layer than in the stationary arrangement. It should not exceed 20 cm, in particular 10 cm. In a rotary kiln, the inventive method is preferably carried out so that the individual stages in a furnace passage of the catalyst are passed through successively, the devices used are suitably equipped with suitable internals (baffles, turning plates and the like.), Which are for a constant mixing and good Transport the bulk material in the oven.

The process according to the invention is suitable for the regeneration and reactivation of optionally promoted palladium supported catalysts whose constituents, in particular their support materials, are sufficiently heat-resistant and undergo no undesired reactions under the process conditions and / or undergo unfavorable changes. It is preferably used for the regeneration and reactivation of spent catalysts which are used for selective hydrogenation and in addition to palladium and optionally other metals or their compounds contain a carrier material consisting mainly of alumina.

The process according to the invention for the regeneration and reactivation of spent palladium-supported catalysts has a number of significant advantages over the previously known regeneration or reactivation processes. So z. B. allows the effective and in terms of the desired catalytic properties also targeted reactivation of supported palladium catalysts, which could no longer be achieved with conventional methods or so far not at all. Very advantageous in this context is that with the aid of the method according to the invention in the course of application and / or previous regenerations occurred by conventional methods sintering of the active component can be reversed and quite obviously in addition to the redispersion and a favorable for selective hydrogenation surface structure of palladium is reached or trained. Not insignificant is, especially from a practical point of view, that with comparatively simple technical means and without the use of particularly aggressive or dangerous or expensive chemicals is achieved that no adverse side effects occur in terms of subsequent reuse, for example, by lower hydrogenation or enhanced Formation of undesirable by-products the effectiveness of the catalytic processes carried out with the regenerated and reactivated catalysts u. U. can significantly affect and that on the desired level beyond chemical attack on the catalyst material is practically not observed in total.

The inventive method allows much longer catalyst life without compromising their catalytic efficiency and thus improves the economy considerably in their technical application. In addition, it leads to a better utilization of the catalyst material, in particular of the palladium contained therein or further possibly present value components.

Without question, it is also an advantage of the method according to the invention that it can be made very environmentally friendly with simple and technically proven means.

embodiment example 1

A catalyst containing 0.034 mass% Pd and 0.018 mass% Cu on a tablet-shaped ac-Al ₂ O _{3 support} with a specific surface area of 8.3 m ² / g, the hydrogenation activity after several years of technical use for selective Hydrogenation of ethyne in a C ₂ fraction in an adiabatic packed bed reactor by conventional oxidative process is no longer sufficiently regenerated and the 15.6 wt .-% carbon and a total of 17.4 wt .-% at temperatures up to 1 373 K volatile or contains burnable components in the presence of oxygen, is regenerated and reactivated. The regeneration and reactivation takes place in a shell-side heatable tube furnace with direct gas passage through the catalyst bed. The pilot plant is completed by an upstream steam superheater and preheater as well as a downstream cooler and separator. In the oven 500 ml of the spent catalyst are installed. The pressure in the apparatus is only so much above normal pressure as is necessary to overcome the flow resistance.

The catalyst is first heated in a nitrogen stream of 200 l / h, but as soon as the temperature in the bed has reached 433 K, 240 g / h of superheated steam are added to the nitrogen. The substantially linear heating rate is 50 K / h. The catalyst is then treated at a temperature between 670 and 675 K until no more organic phase in the separator from the cooled to about 298 K exhaust gas and the condensate remains clear. A total of 68.5 ml of an oily liquid separated connection to this first treatment stage, the temperature is increased within 40 minutes to 723 K and then the Regeneriergasstrom air is added in the second treatment stage. It starts with 10 l / h of air. Then, as soon as the exothermicity of the running in the catalyst bed oxidation reactions has subsided as far as possible, the amount of air gradually increased gradually to the same principle to 20, 50, 100, 250 and finally to 500 l / h. At the same time, after increasing the air volume to 50,100 and 250 l / h, the temperature in the furnace is raised to 738,748 or 773 K, and after increasing the air volume to 250 l / h the steam supply or to 500 l / h the nitrogen supply is turned off. The adiabatic temperature increase measured in the catalyst bed as a result of the oxygen supply is not significantly higher than 15 K in any of the steps. Even when the air volume is increased to 100 l / h, no exothermal effect can be observed. The end of the burn-off phase is determined by the analytical monitoring of the CO ₂ content in the exhaust gas stream. This treatment is followed by removal of a catalyst sample from the oven to a third treatment stage. In this first the air is replaced by oxygen. The oxygen flow is adjusted to 200 l / h and then the furnace temperature is raised to 1 123 K at a mean heating rate of 75 K / h and the catalyst is treated for 2 hours at this temperature. Cooling to room temperature is carried out in an oxygen stream. Before removal, the catalyst is purged with nitrogen for a further 30 minutes. The reduction of the catalyst takes place in situ with hydrogen at 473 K. The catalysts are characterized by determining the F value as a measure of the palladium disperity and by the gas-phase hydrogenation of ethyne in a laboratory apparatus. For F-value determination, the CO chemisorption capacity of the catalyst is determined at 273 K by a pulse flow method. Depending on the palladium content, 0.5 to 5 g of the catalyst are initially pretreated for reduction at 393 K in a hydrogen stream of 2 l / h for 1.5 hours, then, as soon as the measurement temperature of 273 K has been set, 5 pulses of 0.4 ml of CO are introduced and the amount of SiO 2 not chemisorbed by the palladium surface atoms is determined katharometrically at the outlet of the apparatus. Based on the chemisorbed СО amount and the palladium content of the catalyst sample, assuming that one СО molecule is chemisorbed per palladium surface atom, the F value-the ratio of exposed to the total number of palladium atoms-is calculated. The catalytic characterization of the catalysts is carried out in a laboratory flow-through reactor by hydrogenation of the ethyne in the gas phase at a pressure of 0.981 MPa. The test gas used contains 2% by volume of ethyne, 4% by volume of hydrogen, 0.28% by volume of propane and the balance argon. 2 g of catalyst in the form of chippings with a grain size between 1.0 and 1.25 mm are installed per test. The catalytic test is carried out with a pilot gas volume of 5 l / h and usually at reactor temperatures of 343 to 373 K. If the reduction takes place in situ, the catalyst sample is treated for 1 hour at 473 K with 10 l / h of hydrogen before the catalytic test , To assess the activity and selectivity of the catalyst, the ethinol content and the amount of ethane formed are determined by known gas chromatographic methods after the reactor, wherein the selectivity, S, is defined herein and in the following as additionally related to the reacted alkyne or alkadiene resulting (S with a positive sign, ie, alkene gain) or hydrogenated alkene amount (S with a negative sign, ie, alkene loss). The determined F-values and the most important catalytic test results, including the variable test conditions, are summarized in Table 1. For comparison, the tables also contain the analogously determined data for the original catalyst, the spent catalyst and the oxidatively regenerated catalyst removed after the second treatment stage. The results show that in this catalyst also a very careful removal of the carbonaceous deposits from the catalyst surface, despite increased reaction temperatures, does not lead to a sufficient regeneration of its hydrogenation activity, because in the technical implementation of such selective hydrogenation Ethinrestgehalte <2 ppm are usually required. Obviously, this decrease in activity is not least caused by the sintering of palladium that has occurred. The results also make it clear that the use of the process according to the invention substantially restores the original state of the catalyst, which is characterized by high activity and selectivity.

Example 2

A technical catalyst comprising 0.92 mass% Pd, 0.08 mass% Ag and 3.5 mass% Ni in bound form on an a-Al ₂ O _{3 support} with a specific surface area of 11 contains m ² / g, which is used for the selective hydrogenation of propyne and propadiene in liquid C ₃ fractions in the trickle phase and which is extremely coked and damaged due to a malfunction, so that by a conventional oxidative regeneration its activity and selectivity not again can be prepared is regenerated and reactivated in the apparatus described in Example 1.

Table 1

catalyst

F value catalytic test:

Temperature test time K min

inventively 0.19 353 5 Ethan 30 regenerated and 6 Vol .-% 150 reactivated 5 1.02 300 363 <1 0.96 30 <1 0.97 150 <1 1.18 300 by careful 0.08 373 550 1.16 30 Burning off "rain 910 1.16 150 riert "(after 2nd stage) 1 100 1.10 300 consumed (with 0.01 373 16,500 1.05 30 17.6% by mass C) 11000 1.04 150 (for comparison) 11 100 0.21 300 original 0.20 353 2 0.57 30 (for comparison) 3 0.57 150 3 1.09 300 363 <1 0.99 30 <1 0.99 150 <1 1.22 300 373 <1 1.13 30 <1 1.14 150 <1 1.64 300 catalyst 1.58 final concentration 1.57 Selectivity of ethyne Ethenbildung ppm S in% inventively +49.0 regenerated and +52.0 reactivated +51.5 +41.0 +42.0 +42.0 by careful +43.4 Burning off "rain +45.0 riert "(after 2nd stage) +45.0 consumed (with +40.0 17.6% by mass C) +36.7 (for comparison) +36.0 original +45.5 (for comparison) +50.5 +50.5 +39.0 +43.5 +43.0 +18.0 +21.0 +21.5

500 ml of the spent catalyst with a carbon content of 14.3% by mass are introduced into the furnace and, at an average rate of 50 K / h, initially in a stream of nitrogen of 100 l / h from 423 K with a mixture of 100 l Nitrogen and 320 g / h of superheated steam at 673 purchased. Since only relatively small amounts of organic products are produced in the separator at this temperature, the treatment temperature is increased to 723 K. The seepage in the separator remains low with 11ml of liquid organic products.

After the resulting condensate remains clear, 10 l / h of air are initially added to the regeneration gas stream at 723 K. The observed exotherm is low, therefore, the temperature is slowly increased within one hour in steps of 4 to 5 K, until at about 765 K in the furnace a clear exotherm is observed. As soon as it begins to decay, the air quantity is gradually increased to 20, 40, 100, 250 and finally 500 l / h according to the same principle. At the same time, after increasing the air flow to 20, 40 and 100 l / h, the furnace temperature is increased to 783, 803 and 833 K, respectively, to ensure rapid burning off of the carbonaceous deposits from the catalyst surface. In addition, at 250 l / h of air, the nitrogen and at 500 l / h of air, the steam supply is turned off. As soon as analytically no carbon dioxide formation can be detected in the treatment in the pure air stream at 833 K in the exhaust gas, the burning-off phase is terminated.

After removing a catalyst sample from the furnace and replacing the air flow with 250 l / h of oxygen, the furnace temperature is increased to 1 123 K at a rate of 80 K / h and the catalyst is treated at this temperature for 5 hours. The furnace is then cooled to room temperature, the oxygen is replaced by nitrogen and the catalyst is rinsed for one hour in an inert gas stream.

For reduction, the catalyst is soaked at room temperature with 220 ml of a 10% hydrazine hydrate solution. After a reaction time of 15 minutes, the wet catalyst moldings are treated under continuous motion with hot air until they appear superficially dry. The reduction is followed by a five hour drying at 393K. The taken after completion of the 2nd treatment stage catalyst sample is reduced analogously.

To characterize the regenerated and reactivated catalyst, the F value is determined according to the method described in Example 1, and also its activity and selectivity in the hydrogenation of propyne and propadiene in a liquid C ₃ fraction. The catalytic test is carried out in a laboratory reactor operating on the trickle phase principle. In this case, the liquid hydrocarbon mixture trickles from top to bottom in a virtually static or flowing in the same direction hydrogen-containing gas atmosphere through the catalyst bed arranged in the reactor. In the lower container-shaped part of the reactor, the selectively hydrogenated C ₃ -hydrocarbon mixture is removed under controlled conditions. The total pressure in the reactor is set and maintained constant at 1.57 MPa, regardless of the respective reactor temperature and the amount of electrolyte hydrogen supplied by means of nitrogen. 20 ml of catalyst in the form of chippings with a grain size between 1.25 to 2.0 mm are incorporated per test. The other conditions of the catalytic test are

Liquid quantity: 300 g / h of a C 1 -C hydrocarbon technical fraction containing 5.37 mass% of C ₃ H ₄ (propyne and propadiene), 90.88 mass% of propene and 3.75 mass% of propane;

molar H ₂ / C ₃ H ₄ ratio: 1.5: 1

- Reactor temperature: 308 K.

The analysis of the feedstock and of the catalyst at the reactor outlet takes place by means of known gas chromatographic methods. The determined F values and the most important catalytic test results are summarized in Tab. For comparison, the table also contains the analogously determined data for the original catalyst, the spent catalyst, and the oxidatively regenerated catalyst removed after the second treatment stage.

Table 3

catalyst

F value

Trial time minutes

Final concentration C ₃ H ₄ propane

ppm Ma .-%

Selectivity, propene formation S in%

original (for comparison) 0.12 30 150 300 <10 5.79 5.73 5.74 +62.0 + 63.1 +63.0 Consumption (for comparison) <0.01 30 150 300 34 200 35 900 36 500 5.44 5.28 5.23 + 13.1 +13.8 + 13.9 after 2nd treatment step ("regenerated") 0.08 30 150 300 2 530 2 690 2 700 7.18 7.13 7.13 +32.9 +33.8 +33.7 erfindungsge regenerated and reactivated 0.11 30 150 300 10 12 10 5.84 5.61 5.64 +61.1 +65.3 +64.8

Essential for the assessment of these results is the fact that in the technical application C ₃ H ₄ residual levels of less than 100 ppm, not infrequently already required by a maximum of 20 ppm and, of course, the highest possible propene yield is sought. From this aspect, it becomes clear that the spent catalyst, even after removal of the carbonaceous deposits, no longer has the required hydrogenation activity, as shown by the high residual C ₃ H ₄ content, and also has significantly lower selectivity for propene formation compared to the original catalyst. Furthermore, the results summarized in Table 2 show that the high activity and selectivity of the original catalyst is almost completely restored by the regeneration and reactivation of the spent catalyst according to the invention.

Example 3

A technical catalyst used for the selective hydrogenation of propyne and propadiene in liquid Cj fractions, which contains 0.6% by weight of Pd on a <x-Al ₂ O _{3 support} , is treated by treatment with a hydrogen-containing technical C ₃ - Fraction at temperatures between 613 and 638 K subjected to aging. The catalyst thus deactivated contains 2.55% by mass of C and, in principle, is regenerated and reactivated by the process described in Example 1. The conditions are changed as follows:

In the 1st stage, the heating rate is increased to 80 K / h and the treatment is carried out with 350 l / h of nitrogen without added steam.

In the 2nd stage, the air is supplied in steps 20, 50, 100 and 350 l / h, and after the 2nd and 3rd steps, the furnace temperature is increased to 738 and 735 K, respectively, and after setting an air quantity of 350 l / h turned off the nitrogen supply

In the third stage, the catalyst is treated for 5 hours at 923 K with 100 l / h of a mixture of equal parts of air and oxygen. The reduction and characterization of the regenerated and reactivated catalyst is carried out as described in Example 2. The most important results are summarized in Table 3. The C ₃ fraction used for the hydrogenation experiments contains 5.84 mass% C ₃ H ₁ (propyne and propadiene), 90.58 mass% propene and 3.58 mass% propane. For comparison, the analogously determined data for the original catalyst and the aged catalyst are listed.

Table 3

catalyst F value experiment final concentration propane Selek Time C ₃ H ₄ Wt .-% tivity of minutes ppm propene education 5.48 S in% original 0.09 30 22 5.46 +67.5 (for comparison) 150 24 5.51 +67.8 300 24 7.55 +67.0 aged 0,045 30 4,800 7.46 +25.9 (for comparison) 150 5,150 7.46 +27.1 300 5 100 5.50 +27.2 erfindungsge- 0.09 30 18 5.51 +67.1 regenerated 150 20 5.48 +66.9 and reactivated 300 19 +67.5

These results also make it clear that the use of the process according to the invention not only achieves virtually complete reactivation and redispersion of the palladium but also the recovery of the high selectivity which is reduced by the deactivation or sintering of the active component.

Example 4 to 6

To support the effect achieved in the 3rd treatment stage of the process according to the invention for the regeneration and reactivation of spent palladium supported catalysts, various catalysts are activated or reactivated under varied treatment conditions. For this purpose, 500 ml of the catalyst are incorporated into the apparatus described in Example 1, set a treatment gas flow of 200 l / h and the temperature heated in the catalyst bed at a rate of 75 K / h to the treatment temperature. The treatment is carried out at a pressure which is so much above normal pressure, as is necessary to overcome the flow resistance in the apparatus. After the treatment time is cooled in the treatment gas stream to room temperature, the treatment gas replaced by nitrogen and the catalyst rinsed for at least 30 minutes in a stream of nitrogen. The reduction of the treated catalysts is carried out by characterizing in situ with hydrogen at a maximum of 473 K. The methods used for the characterization of the F-value determination and the selective hydrogenation of ethyne, including the conditions in the reducing pretreatment with hydrogen, described in Example 1.

A summary of the results obtained, including some information on the catalysts and the treatment conditions, is given in Table 4. For comparison, the table also lists the corresponding starting catalyst data obtained in the same way. On the basis of these results, it is particularly clear that in the application of the process according to the invention by the choice of treatment conditions, especially in the 3rd treatment stage, not only the desired degree of reactivation but also in most cases quite remarkable increase in the selectivity in alkene formation in the hydrogenation the alkynes or alkadienes is achieved. This circumstance deserves particular attention, because experience teaches that on the one hand in many selective hydrogenation processes with the deactivation, a deterioration of the selectivity is accompanied and on the other hand usually increasing the activity of a catalyst is associated with a decrease in its selectivity.

Example 7 to 12

In further series of experiments to investigate the influence of the treatment conditions in the third stage of the process according to the invention and the catalyst properties on the obtained palladium redispersing or reactivating effect, various supported palladium catalysts with F values between 0.03 and 0.138 are treated by the process according to the invention , For this purpose, 15 ml of catalyst sample in a provided with a heating jacket

Tube furnace installed, the treatment gas stream adjusted by the Katalysatorschuttung and the catalyst heated at a rate of 75 K / h to the treatment temperature. After the treatment time has elapsed, the catalyst is cooled to room temperature in the treatment gas stream and purged with nitrogen for at least 30 minutes before it is removed (about 5 Hh). To characterize the catalysts treated according to the invention, the F value is determined using the CO chemisorption method described in Example 1. The values determined are summarized in Table 5 together with the required information on the treated catalysts and the respective treatment conditions. For comparison, the analog determined data of the starting catalysts are listed.

Table 4

0.035 6.2

example Catalyst Pd Ma .-% Surface m ² / g carrier Treatment conditions: Temp. Gaszus. Time K Vol .-% h 2 F value 4 0,035 6.2 a-Al ₂ O ₃ 1123 100% O ₂ 0.18 Starting catalyst (for comparison) 6 0.03 5 0,035 6.2 CX-Al ₂ O ₃ 923 air 0.11 Starting catalyst (for comparison) 0.03

Cx-Al ₂ O ₃ 1 123

N ₂ + 70% O ₂

Starting catalyst (for comparison)

catalytic temp. K Test Results: Time Final Concentration min Ethin Ethane ppm Vol.% <1 <1 0.93 0.93 Selectivity of ethene formation, S in% 353 150 300 9 200 9 300 0.54 0.54 +53.5 +53.5 353 150 300 21? 0 0.58 0.B8 + 50.7 +50.5 353 150 300 9 200 9 300 0.54 0.54 +70.0 +70.0 353 150 300 5 4 <1 <1 101 1.00 1, W 1.19 +50.7 +50.5 363 363 150 300 150 300 +49.5 +50.0 +40.5 +40.5

373

150 300

12 800 12 900

+36.1 +35.2

Table 5

Example catalyst

Pd surface

Ma .-% m ² / g

Treatment conditions: Carrier temperature Gas / O, in Vol .-%

0,035

6.5

U-Al ₂ O ₃ 1123 100% O ₂

Starting catalyst (for comparison)

0.60

5.4

α-ΑΙ, Ο,

923 1 123 1 123 1 123 1 123

Air air

N ₂ /50% O ₂ N / 70% O ₂ 100% O ₂

Starting catalyst (for comparison)

1.00

221

Oi-Al ₂ O ₃ 923 air

1 123 air

1123 100% O ₂

Starting catalyst (for comparison)

Table 5 (continued)

Example catalyst

Pd surface

Ma .-% m ² / g

Treatment conditions: carrier temperature

Gas / O ₂ in Vol .-%

0.60 149

Ot Al ₂ O ₃ 923 Air

1 123 air

1123 100% O ₂

Starting catalyst (for comparison)

11 0.60 211 3.6 3.6 3.6 3.6 (for comparison) «-ΑΙ ₂ Ο ₃ 873 100% O ₂ 973 100% O ₂ 1073 100% O ₂ 1173 100% O ₂ starting catalyst (for comparison) 12 0.60 580 3,5 3,5 (for comparison) SiO ₂ 923 air 923 100% O ₂ starting catalyst (for comparison) Time h Gas quantity l / h F value 2 output catalyst 3.5 (for comparison) 0.18 0.03 10 2 2 2 2 Acoustic decoder 3,5 3,5 3,5 3,5 3,5 (for comparison) 0.069 0.065 0.070 0.100 0.126 0.055 10 2 2 starting catalyst 3,5 3,5 3,5 (for comparison) 0.079 0.095 0.136 0.041 10 3.5 2 3.5 2 3.5 starting catalyst (for comparison) 0.056 0.051 0.097 0.049 1 1 1 1 starting catalyst 0.06 0.08 0.19, 30 14 2 2 starting catalyst 0.21 0.24 0.138

Claims (9)

1. A process for the regeneration and reactivation of palladium-supported catalysts, optionally containing further modifying components, by thermal treatment in an oxygen-containing atmosphere in a multi-stage process, wherein in the first stage, the spent catalysts in the temperature range of 423 to 723 K as long as in one of oxidizing substances largely free gas stream containing less than 0.1 vol .-% oxygen, treated until no more organic components are discharged and are added in a second stage the gas stream 0.1 to at least 20 vol .-% oxygen, wherein the oxygen content in the regeneration gas is increased stepwise to the extent that the temperature in the catalyst layer does not exceed 850 K and the treatment in the second stage is carried out with the at least 20 vol.% oxygen-containing gas stream for up to 15 hours, characterized that a third treatment stage angeschl ossen, in which the catalysts in a largely free of oxidizable materials gas atmosphere containing 15 to 100 vol .-% oxygen, further treated at temperatures between 773 and 1 373 K up to 48 hours and then cooled and optionally reduced. 2. The method according to claim 1, characterized in that the gas stream in the third stage contains 20 to 100 vol .-% oxygen and the applied, based on the catalyst volume amount of gas up to 2 500 v / vh, preferably 10 to 1 000 v / vh, is. 3. The method according to claim 1 and 2, characterized in that the treatment is carried out in the third stage at temperatures between 873 and 1 173 K. 4. The method according to claim 1 to 3, characterized in that the treatment in the third stage over a period of a maximum of 24 hours, in particular over a period between 0.5 and 12 hours, takes place. 5. The method according to claim 1 to 4, characterized in that the treatment in the third stage with air, an air-oxygen mixture or pure oxygen at temperatures between 1 073 to 1 150 K is performed. 6. The method according to claim 1 to 4, characterized in that the treatment is carried out in the third stage at temperatures above 1 150 K, at an oxygen partial pressure of at least 0.1 MPa and in a substantially static gas atmosphere. 7. The method according to claim 1 to 6, characterized in that in the implementation of the method, the heating rate in the steps 100 K / h, preferably 50 K / h, and the cooling rate 150 K / h, preferably 75 K / h, does not exceed , And that is heated at temperatures in the catalyst bed of less than 425 K in the absence of condensable amounts of water vapor in the regeneration gas, treated or cooled. 8. The method according to claim 1 to 7, characterized in that the method is carried out in a packed bed with direct passage of the Regenerierstromes. 9. The method according to claim 1 to 7, characterized in that the method at comparatively low content of the spent catalysts of carbonaceous or oxidizable deposits in a flat, not more than 20 cm, in particular at most 10 cm high, moving or stationary bed with substantially überstreichendem Gas stream is carried out, wherein the implementation of the method is particularly preferred in a rotary kiln, and in this case, the individual process steps when passing the catalyst through the furnace are passed in sequence.