DD298353A5 - METHOD FOR REGENERATING CALIUM-PROMOTED DEHYDRATION CATALYSTS - Google Patents

Abstract

The invention relates to a process for the regeneration of potassium-promoted dehydrogenation catalysts based on iron oxide for the synthesis of styrene from ethylbenzene, which have a potassium deficit with increasing duration of use. The process involves the simultaneous supply of steam and a liquid solution of a potassium ion compound to the catalyst in the reactor in a defined manner. Anschlieszend followed by a temperature treatment of the catalyst with interrupted steam supply. The process leads to an increased catalytic long-term stability of the catalyst {water vapor; regeneration; Dehydrogenation catalyst, containing iron oxide; styrene; Langzeitstabilitaet; Kaliumpromotierung; Potassium ion solution; Additional potassium; Potassium deficit balance; tempering}

Description

Characteristic of known technical solutions

The catalytic dehydrogenation of ethylbenzene to styrene is a well-known large-scale process for the production of monomers for the plastics industry. In this case, usually a mixture of ethylbenzene and steam is passed over a catalyst.

From the large number of possible catalysts, those based on potassium-promoted iron oxides proved to be particularly suitable. It is generally believed that the alkali compounds, especially the potassium compounds, are both the catalytic! Catalyst performance parameters also improve catalytically by catalyzing a reaction between the water vapor and the unwanted catalyst-poisoning carbonaceous intermediates.

Although the catalyst is auto-regenerative over a longer period of time, periodic regeneration becomes necessary, i. h., Water vapor is preferably passed over the catalyst as sole feed component for a short period of time. By the formation of uii.rr the reaction conditions volatile potassium chloride it comes with increasing use of the catalyst to an increasing potassium depletion (DE-AS 1181694 and DE-AS 1618244), especially in the upper part of the catalyst bed, with negative effects on its catalytic) performance parameters and long-term stability. The harmful chloride passes as a trace impurity with the feedstock ethylbenzene (DE-AS 1618244) and / or with the water vapor on the catalyst. There are some suggestions in the pamphlet literature for the prevention of alkali losses or for the recovery of the original alkali concentrations in situ in the catalyst. The proposed use of catalysts with very high levels of alkali metal compounds (DE-AS 1181694) should be particularly detrimental to their physical properties in addition to the negative impact ujt catalytic activity. Especially due to the increased moisture sensitivity of these catalysts, a decrease in their mechanical strength is observed. According to DE-AS 1618244 it is considered to remove the chloride in the ethylbenzene by a chloride-adsorbing precursor and / or an extraction upstream of the reactor. For this purpose, however, a high expenditure on equipment is necessary, and it can not be ruled out that the chloride contained in the feedstock reaches the catalyst after saturation of the precoat.

To avoid larger alkali metal losses of the catalyst with its increasing duration of use is proposed in the patent literature (DE-PS 863342 and DF-AS 1181694) its occasional refreshment by the addition of alkali metal compounds. The addition of alkali metal can be carried out, for example, together with the steam used in the dehydrogenation process in the form of potassium carbonate (DE-PS 863342).

There is evidence in the document DE-AS 1181694 for an addition of potassium compounds after a refreshment of the catalyst with steam.

The suggestions in the literature do not suggest a preferential reallocation of the most potassium-depleted top layer of the catalyst bed, which is the largest contributor to overall sales. Due to the danger of an approximately even distribution or even a disproportionate potassium enrichment in the lower part of the catalyst bed, which has a lower potassium deficit compared to the fresh catalyst, et can lead to throughput-limiting soiling and blockages of subsequent equipment parts and / or to a partial deactivation of the catalyst. Furthermore, there is the risk of an increase in throughput limiting pressure loss over the catalyst bed by a partial formation of a "solid" composite between multiple catalyst strands in the application of the three patents mentioned above.

The listed regeneration methods do not reveal all the effectiveness reserves of the dehydrogenation process, especially with regard to achieving high performance parameters of the catalysts over a longer service life (long-term stability).

Object of the invention

The invention is based on the objective to substantially prolong the effective use of styrene catalysts in Rohrbündeldehydrierungsreaktoren and to enable the desired favorable material and energy economy of the dehydrogenation over a longer period of time compared to previously known solutions.

Explanation of the essence of the invention The invention is based on the object, an improved process for the regeneration of kaliumpromotierten Iron oxide based dehydrogenation catalysts for the synthesis of styrenes from ethylbenzene Operating have a potassium deficiency, in situ in a heated tube bundle reactor by adding an aqueous solution

To develop e .ner Kaliurti'onenverbindung that due to the positive effect on the catalytic performance parameters leads to a higher long-term stability of the catalyst and allows the accumulation of the applied potassium ion compound in the upper layer of the catalyst bed.

The technical problem is solved according to the invention by the addition of the potassium ion solution at a temperature which

between the average tube bundle temperature during the dehydrogenation reaction and a maximum of 30 Kelvin higher

Temperature is selected, with a potassium ion content of 0.6 mol / l to 4.0 mol / l with the simultaneous addition of water vapor

in such an amount that a mass ratio of added potassium ionone to water vapor of 1:60 to 1:14 sets, wherein a mass ratio of supplied potassium ions to the catalyst in the reactor of 1: 115 to 1:22 is maintained and after the potassium ion supply followed by a one to two-hour treatment of the catalyst at a temperature 30 to 40 Kelvin higher compared to the average tube bundle temperature with interrupted water supply and before its gradual further loading with water vapor and ethylbenzene.

It is surprising that in the selected process parameters, a preferred fixation of the supplied potassium in the

upper part of the catalyst bed, which otherwise has the largest potassium deficit takes place.

Particularly suitable was a temperature depending on the duration of use of the catalyst. When choosing the potassium compound must be noted that the corresponding anion or its decomposition products not

act as catalyst poisons. Potassium hydroxide and potassium carbonate proved to be particularly favorable.

The selected mass ratio of added potassium ions to water vapor of 1:60 to 1:14 ensures compliance

the other process parameters surprisingly in addition to an optimal regeneration of the catalyst (i.a. partially

Reoxidation dos iron oxide and elimination of carbon and potassium deposits) the desired fixation

the potassium ions predominantly in the upper part of the catalyst bed.

The amount of potassium ions supplied depends on the duration of use and the extent involved Potassium depletion of the catalyst. The choice of the mass ratio of added potassium ions to that in the reactor

located catalyst from the range of 1: 115 to 1:22 takes into account the achieved catalytic

Performance parameters. The regeneration process closes after the supply of potassium ions for one to two hours of temperature treatment of the Catalyst at a 30 to 40 Kelvin higher temperature compared to the average tube bundle temperature during the Dehydrogenation reaction at the interruption of the steam supply. Surprisingly, this succeeds Temperature treatment, compared to the prior art, the predominant fixation of the supplied Potassium ions in the upper part of the catalyst bed and optimal formation of the catalyst. After regeneration, the stepwise loading of the catalyst with steam and ethylbenzene follows. Advantageously, you start with steam. The time intervals between two regenerations depend on the achieved catalytic performance parameters (sales

and selectivity) and the differential pressure over the reactor length. An exact zehliche specification is not possible due to the often fluctuating in terms of the chloride content quality of the feedstock. According to experience, the

Regeneration but done several times in a year of operation of the catalyst. The regeneration process is for all potassium-promoted dehydrogenation catalysts based on iron oxide

applicable.

The surprisingly found fixation of the supplied potassium ions predominantly in the potassium-depleted most

top layer of catalyst bed, which makes the largest contribution to total sales, while avoiding extensive

Deposits in the plant parts subsequent to the reactor and the simultaneous optimal regeneration effect by Water vapor affects the otherwise observed dramatic decrease in catalytic performance parameters with increasing Duration of use of the catalyst while maintaining a high Ethylbenzendurchsatzes contrary. The main advantages

of the method thus exist due to the high long-term stability of the regenerated catalyst in a considerable

Increase in the yield of styrene over its entire service life, combined with very good material and energy economics

the dehydration process.

embodiments

The experiments were carried out in a laboratory-scale integral flow-through reactor. The reaction tube, in which the catalyst is located on a sieve plate, is electrically heated and the temperature in the catalyst bed is determined with the aid of a jacket thermocouple. By means of an electronic controller and a further jacket thermocouple, the temperature control of the reactor takes place. The metered addition of the ethylbenzene and water by-products is carried out separately from storage vessels via two micro-metering pumps. The reactants are evaporated and heated to the respective reactor inlet temperature after intensive mixing. The Reaktoi vorlassende gaseous reaction product is condensed, the liquid phase separated from gaseous by-products and separated via a separating vessel into an organic and an aqueous phase. At regular intervals carried out a volumetric measurement and a gas chromatographic analysis of the gaseous waste products and the organic liquid phase. From the data, conversion (percentage of converted ethylbenzene) and selectivity to styrene (%... Of the conversion of ethylbenzene to styrene) can be calculated. The catalyst bed has a volume of 120 ml, the load of the catalyst is 0.21 ethylbenzene catalyst) × h and the catalyst temperature 580 ° C. The mass ratio of ethylbenzene to water vapor is 1: 1.2 in the experiments. The duration of the catalyst cake comprises about 100 hours. In Table 1, the determined catalytic performance characteristics and the potassium contents of two freshly prepared catalysts are compared with those of the respective catalyst developed from a technical reactor after different operating times, which has a potassium depletion. The results in Table 1 document the dramatic decrease in catalytic performance characteristics with increasing service life and the associated increased potassium depletion of the catalysts

 The two freshly prepared catalysts have the following chemical composition (% by weight):

Catalyst 1

87.8% iron oxide (calculated as Fe ₂ O ₃ ) 7.7% potassium (calculated as K ₂ O) 2.8% calcium (calculated as CaO) 1.7% copper (calculated as CuO)

Catalyst 2

87.1% iron oxide (calculated as Fe ₂ O ₃ ) 1.4% chromium (calculated as Cr ₂ O ₃ ) 9.5% potassium (calculated as K ₂ O) 2.0% calcium (calculated as CaO).

To characterize the potassium distribution above the catalyst bed height after regeneration, it was divided into approximately four equal parts after completion of the catalytic test. Table 1 lists the determined potassium contents of the catalyst strands from the upper or lower layer and the amount of potassium in the aqueous phase of the condensate at the reactor outlet.

Example 1 (according to the invention)

In this example, for the regeneration at 59O ⁰ C of the old catalysts 1 and 2, which have a potassium ion content (in mass fraction in%) of 4.1 and 2.7% (calculated as K ₂ O), potassium hydroxide solution with a potassium ion content of 2.1 mol / l, a mass ratio of added potassium ions to water vapor of 1:42, and a mass ratio of potassium ion added to the catalyst in the reactor of 1:95. This was followed by a two-hour temperature treatment of the catalysts at 620 ⁰ C and interrupted steam supply before their stepwise loading at 58O ⁰ C with steam and ethylbenzene to determine the resulting catalytic performance characteristics. The results in Table 1 confirm that the preferred fixation of the η potassium to be conducted in the upper part of the catalyst bed leads to a significant improvement in the catalytic performance characteristics of the catalysts.

Example 2 (not according to the invention)

In this example, the regeneration of the two used catalysts based on the conditions selected in Example 1 was carried out only with steam (addition amount and rate of addition according to Example 1). The improvement of the catalytic performance characteristics is only slight compared to Example 1.

Example 3 (according to the invention)

The spent catalyst 2 was carried out at 61O ⁰ C with potassium hydroxide solution (potassium ion content: 3.9 mol / l) is regenerated, wherein a mass ratio of added potassium ions to water vapor of 1:60, a mass ratio of fed potassium ions to the present in the reactor catalyst 1:22 and a temperature of 62O ⁰ C were used for a one-hour 9 temperature treatment. In addition to an improvement in the catalytic performance characteristics determined at 580 ^° C., an increase in the potassium content in the lower part of the catalyst bed and the potassium amount in the aqueous phase of the condensate are observed.

Example 4 (not according to the invention)

Compared to Example 3, the regeneration temperature of the used catalyst 2 was reduced to 54O ⁰ C, and there was no heat treatment. In addition to the approximate uniform distribution of the supplied potassium above the catalyst layer height, a significant increase in the amount of potassium in the aqueous phase of the condensate is observed.

Example 5 (according to the invention) For the regeneration of the old catalyst 2 at 580 ⁰ C came an aqueous solution of potassium carbonate (potassium ion content: 0.6 mol / l)

used, wherein a mass ratio of added potassium ions to water vapor of 1:14, a mass ratio of zugleihrt potassium ions to the catalyst in the reactor of 1: 115 and a one-hour temperature treatment at 61O ⁰ C were chosen. The observed improvement of the catalytic performance characteristics is in comparison to the

Results in Example 3 slightly lower with significant decrease in the amount of potassium in the aqueous phase of the condensate Example 6 (not according to the invention)

In this example, the regeneration of the used catalyst 1 was carried out at 580 ° C with potassium hydroxide (potassium ion content: 8.2 mol / l), wherein a mass ratio of added potassium ions to water vapor of 1: 100, a mass ratio of supplied potassium ions to the catalyst in the reactor vcn 1:18 and a temperature treatment time of 30min at 585 ⁰ C were selected. In addition to the high amount of potassium in the aqueous phase of the condensate and the small improvement in the catalytic performance of the catalyst due to its high potassium content, there is a strong tendency for the formation of aggregates by the catalyst strands previously present individually.

Example 7 (not according to the invention) The regeneration of the old catalyst was carried out at 58O ⁰ C with potassium hydroxide solution (potassium ion content: 0.3 mol / l), wherein a Mass ratio of added potassium ions to water vapor of 1, 10, a mass ratio of supplied potassium ions

to the catalyst in the reactor of 1: 195 and a one-hour temperature treatment at 610 ° C were used.

Example 8 (according to the invention

For the Aitkatalysator 1, which was regenerated according to the conditions selected in Example 1, was carried out in addition to the determination of the catalytic! Performance characteristics after 100 hours even after 700 hours. The inventively regenerated catalyst has a very good long-term catalytic stability.

Table 1: Summary of the results

catalyst at sales selectivity Potassium ion content of lower Amount of potassium in the game in fabric in fabric Catalysts in Layer ¹ » aqueous phase of mengenan- quantity fractions Mass share in% Condensates in mmol teilin% in% upper 7.7 Layer ' ¹ Frischkata 4.1 lysator 1 - 54.3 93.2 7.6 0.4 Altkata 9.5 lysator 1 - 43.1 88.6 4.0 0.2 Frischkata 2.7 lysator 2 - 55.6 9 ^Λ , 5 9.3 0.8 Altkata 4.3 lysator 2 - 40.0 87.1 2.6 3.1 Altkata 2.9 lysator 1 1 47.3 91.8 8.1 1.8 Altkata - lysator 2 1 44.3 90.4 6.7 1.6 Altkata - lysator 1 2 44.0 89.3 - - Altkata 5.2 lysator 2 2 41.9 87.9 - - Altkata 6.6 lysator 2 3 43.8 90.8 11.8 5.2 Altkata 2.8 lysator 2 4 42.1 88.3 7.5 38.9 Altkata 9.2 lysator 2 5 43.5 90.0 5.4 1.3 Altkata 4.2 lysator 1 6 43.7 90.6 10.0 44.1 Altkata 4.4 lysator 1 7 44.9 90.2 5.7 1.0 Altkata lysator 1 8th 46.8 92.1 7.9 2.0

a) calculated as K ₂ O.

Claims (1)

Process for the regeneration of potassium-promoted dehydrogenation catalysts based on iron oxide for the synthesis of styrene from ethylbenzene, which have a potassium deficit with increasing service life, in situ in a heated shell and tube reactor by adding an aqueous Kaüumhydroxid- or potassium carbonate solution together with water vapor, characterized in that the Adding a solution having a potassium ion content of from 0.6 mol / l to 4.0 mol / l at a temperature which is chosen between the average tube temperature during the dehydrogenation reaction and a maximum of 30 Kelvin higher temperature, with simultaneous addition of water vapor in such an amount carried out that sets a mass ratio of added potassium ions to steam of 1: 6 to 1:14, wherein a mass ratio of potassium ions supplied to the catalyst in the reactor is maintained from 1: 115 to 1:22 and after the potassium ion supply a - to two Quantcast treatment of the catalyst anschloßt at a higher by 30 to 40 Kelvin temperature as compared to the central tube bundle temperature at intermittent supply of water vapor and prior to its gradual re-exposure to water vapor and ethylbenzene. Field of application of the invention The invention relates to a process for the regeneration of potassium-promoted iron oxide-based hydrogenation catalysts for the synthesis of styrenes from ethylbenzene, which have a potassium deficiency with increasing duration of use compared to the fresh catalysts.