WO2008061938A2

WO2008061938A2 - Method for the dehydrogenation of hydrocarbons, entailing dehydrogenation and oxidation steps

Info

Publication number: WO2008061938A2
Application number: PCT/EP2007/062445
Authority: WO
Inventors: Christophe Houssin; Gerald Vorberg; Christian Walsdorff
Original assignee: Basf Se
Priority date: 2006-11-20
Filing date: 2007-11-16
Publication date: 2008-05-29
Also published as: WO2008061938A3; CA2668032A1; KR20090082216A; EP2094628A2

Abstract

The invention relates to a method for producing styrene by the dehydrogenation of ethyl benzene, comprising steps (i) to (iii): (i) in a first dehydrogenation step, a gas mixture containing ethyl benzene and optionally water vapour is brought into contact with a first dehydrogenation catalyst A, producing a reaction gas containing ethyl benzene, styrene and hydrogen, (ii) in an oxidation step, the reaction gas obtained in the first dehydrogenation step is brought into contact with oxygen in the presence of an oxidation catalyst, whereby the hydrogen is at least partially burnt, (iii) in a second dehydrogenation step, the reaction gas obtained in the oxidation step is brought into contact with a second dehydrogenation catalyst B, which is characterised in that the molar ratio of hydrogen to ethyl benzene in the reaction gas obtained according to the first dehydrogenation step is greater than 0.4.

Description

Process for dehydrogenating hydrocarbons comprising dehydrogenation and oxidation steps

description

The present invention relates to an improved process for the production of styrene by dehydrogenation of ethylbenzene.

The production of styrene by dehydrogenation of ethylbenzene is usually carried out by mixing ethylbenzene with steam and introducing this mixture into a fixed bed reactor equipped with dehydrogenation catalysts. Since the dehydrogenation reaction of ethylbenzene is endothermic, the temperature decreases with the progress of the reaction and thus slows the reaction rate. In addition, as the reaction proceeds, the content of hydrogen increases, and a high content of hydrogen adversely affects the dehydrogenation reaction and further slows the reaction rate as the reaction progresses.

To solve this problem, it has gone over to mix the product mixture of the dehydrogenation process with oxygen, to pass into a packed with oxidation catalysts fixed bed reactor and to selectively burn the hydrogen. Subsequently, the reaction gas obtained is in turn introduced into a fixed bed reactor equipped with dehydrogenation catalysts and further reacted.

Thus, after the oxidation step, a gas mixture having a reduced amount of hydrogen is obtained, which further has a high temperature by the combustion reaction, so that the subsequent dehydrogenation process can be carried out at a high reaction rate.

Consequently, dehydrogenation processes, which are divided into several stages and see between the individual stages of oxidation processes, ultimately leading to a very high conversion of ethylbenzene.

In addition to the advantages described, the dehydrogenation processes with combined oxidation step unfortunately have some drawbacks. A disadvantage of these methods lies in the fact that after a longer operation time, the styrene yield, especially in the first dehydrogenation reactor, drops significantly.

In EP-A 1 229 011 this problem is solved, in which hydrogen is fed to the reaction mixture leaving the oxidation step. It is described that the molar ratio of hydrogen to Sytrol when entering the second dehydrogenation reactor is advantageously between 0.9 and 1.3. Furthermore, it is recommended in EP-A 1 229 01 1 to use a styrene catalyst with a reduced potassium catalysis rate in the inlet area of the second dehydrogenation step. In the case that different Dehydrierkatalysa- If the less active catalyst is used upstream and the comparatively more active catalyst downstream.

A disadvantage of the solution of EP-A 1 229 01 1 is that due to the increased amount of hydrogen in the second dehydrogenation step, the conversion in this step is adversely affected.

Another problem with the described dehydrogenation process with combined oxidation is that in addition to hydrogen, the product styrene and the starting material ethylbenzene are burned in the oxidation step, so that on the one hand the yield of styrene is adversely affected and on the other the desired energy input from the hydrogen combustion lower fails.

The object of the present invention was therefore to show a more efficient process for the production of styrene, which overcomes the disadvantages of the prior art.

A process for the preparation of Sytrol by dehydrogenation of ethylbenzene has been discovered, which ensures a high styrene yield even after a long service life, comprising steps (i) to (iii):

(i) contacting a gas mixture containing ethylbenzene and optionally steam in a first dehydrogenation step with a first dehydrogenation catalyst A to form a reaction gas comprising ethylbenzene, styrene and hydrogen; (ii) contacting the from the first dehydrogenation step reaction gas obtained in an oxidation step with oxygen in the presence of a Oxidati- onskatalysators, wherein at least partially the hydrogen is burned, (iii) contacting the reaction gas obtained from the oxidation step in a second dehydrogenation step with a second dehydrogenation catalyst B, characterized in that the molar ratio of hydrogen to ethylbenzene in the reaction gas obtained after the first dehydrogenation step is greater than 0.4.

Advantageously, the molar ratio of hydrogen to ethylbenzene after the first step (i) is greater than 0.45, preferably greater than 0.5, in particular greater than 0.55.

The high molar ratio of hydrogen to ethylbenzene compared to the prior art can be achieved by using a very active dehydrogenation catalyst in the first dehydrogenation step (i). However, the high molar ratio can also be achieved by additional supply of hydrogen before the oxidation step. For example, the hydrogen is supplied at the end of the first dehydrogenation step, between the first dehydrogenation step and the oxidation step and / or at the beginning of the oxidation step.

Preferably, the molar ratio is achieved by the use of a very active dehydrogenation catalyst in the first dehydrogenation step (i).

The prior art generally distinguishes between very active and very selective dehydrogenation catalysts. Very active dehydrogenation catalysts can advantageously be operated at a low reaction temperature as very selective dehydrogenation catalysts. This high activity is generally achieved at the expense of selectivity. By contrast, very selective dehydrogenation catalysts require comparatively higher reaction temperatures. The higher selectivity is generally achieved at the expense of activity.

The value of the "activity" is determined by the molar conversion of ethylbenzene. The value of "selectivity" is determined by the molar conversion of ethylbenzene to styrene.

The performance of catalysts is given, for example, in the form of a "temperature parameter" and a "selectivity parameter". In the present invention, the temperature parameter is understood to mean the temperature at which a catalyst reaches a conversion of ethylbenzene of 65%, the selectivity parameter describing the selectivity achieved at this temperature. Accordingly, the temperature parameter is the lower, the more active the respective catalyst is. The selectivity parameter is the higher the higher the selectivity.

Very active as well as very selective dehydrogenation catalysts are generally known to the person skilled in the art. The dehydrogenation catalysts are generally iron oxide-containing catalysts, as described, for example, in DE-A 101 54 718. As iron oxides, it is possible to use all iron oxides known to the person skilled in the art.

In order to influence the catalyst activity / catalyst selectivity, the dehydrogenation catalyst usually has other components in addition to the iron oxide. The manner of increasing the activity or selectivity is generally known to the person skilled in the art and described, for example, in WO 2004/769 on pages 8 to 10 and pages 14 to 15. Other known components are, for example, lanthanides, in particular cerium; Molybdenum, copper and / or chromium; Alkali metals, in particular potassium and / or cesium; Alkaline earth metals, in particular magnesium and / or calcium around; or optionally further component, in particular manganese, zinc, titanium, vanadium and / or tungsten.

For example, high activity, high selectivity dehydrogenation catalysts may differ in one or more component aspects, such as the source, choice, and amount of single or multiple dopant components. However, the dehydrogenation catalysts may also differ in their surface structure, for example in the BET surface area, in the pore size or in the pore volume.

Advantageously, the average pore diameter of the more selective catalyst is greater than the average pore diameter of the more active catalyst.

Advantageously, the dehydrogenation in the first step (i) to be used dehydrogenation catalyst has a temperature parameter 570 to 655 ° C, preferably 580-645 ° C, in particular 605-640 ⁰ C.

The method of preparation of the dehydrogenation catalysts is likewise generally known to the person skilled in the art and described, for example, in WO 2004/769 on pages 10 to 12. The dehydrogenation catalysts are usually used in the form of solid cylinders, star strands or gear-shaped strands, as described for example in EP-A 1 027 928 or EP-A 423 694.

The principle underlying the process according to the invention of using a combined dehydrogenation process comprising dehydrogenation and oxidation steps is generally known and is described, for example, in US Pat. No. 4,565,898 or in US Pat. No. 4,599,471.

The dehydrogenation reaction can be carried out by all methods known to those skilled in the art, for example as described in WO 2005/97715, page 5, lines 17 to 35.

The inlet temperature into the first dehydrogenation reactor is thus advantageously at 570-655 ° C, preferably 580-645 ° C, in particular 605-640 ⁰ C.

The ethylbenzene fed to the first dehydrogenation step is advantageously mixed with water vapor. The molar ratio of water vapor to ethylbenzene is usually between 1 and 15, preferably between 1 and 10.

Generally, in this method, two or more dehydrogenation steps are connected in series. Optionally, some dehydrogenation steps may be parallel. There is an oxidant at least between two dehydrogenation steps. tion step, advantageously there is an oxidation step at least between the first and the second dehydrogenation step. Advantageously, there is an oxidation step between every two dehydrogenation steps. The process according to the invention preferably has three dehydrogenation steps, an oxidation step being integrated between the first and the second dehydrogenation step and optionally an oxidation step between the second and the third dehydrogenation step.

For example, fixed bed reactors or radial reactors can be used as dehydrogenation reactors or as oxidation reactors.

Advantageously, the stages (ii) and (iii) and, if appropriate, further combined oxidation and dehydrogenation steps are combined in one reactor each. Advantageously, the catalysts are arranged so that the reaction gas flows through first the oxidation catalysts and then the dehydrogenation catalysts. Preference is given to using radial flow reactors in which the catalyst beds of oxidation and dehydrogenation catalysts are arranged concentrically with one another and optionally separated from one another by cylindrical sieves. The oxidation catalyst is then used as the inner of the two concentrically arranged approximately hollow cylindrical beds. The volume ratio of the beds of oxidation catalyst and dehydrogenation catalyst per reactor is generally 0.1: 1 to 1: 1, preferably 0.15: 1 to 0.6: 1, in particular 0.2: 1 to 0.4: 1.

Optionally, after step (i), the first dehydrogenation step, there is a potassium trap well known to those skilled in the art.

Furthermore, the oxidation process can be carried out by all methods known to the person skilled in the art, for example as described in WO 2005/97715, page 4, lines 1 to 15 and page 5, line 37 to page 6, line 5.

Advantageously, in addition to oxygen and, if appropriate, water vapor, nitrogen is also added to the reaction gas from stage (i). The molar ratio of oxygen to nitrogen is advantageously less than 25%.

Oxidation catalysts which can be used are all oxidation catalysts known to the person skilled in the art, for example noble metal catalysts as in WO

2005/97715 on page 2, line 10 to page 3, line 4 or in EP-A 826 418 described.

Advantageously, a catalyst is used as the oxidation catalyst, which, supported on substantially α-alumina, 0.01 to 0.1 wt .-% of platinum and 0.01 to 0.1 wt .-% tin, based on the total weight of the catalyst contains. The oxidation catalysts can be prepared by all preparation processes known to those skilled in the art, as described, for example, in WO 2005/97715, in EP-A 826 418 or in US Pat. No. 6,280,608. Advantageously, the application of the active components of the catalyst by impregnation.

The hydrogen selectivity in the oxidation reaction is advantageously greater than 70%, preferably greater than 80%, in particular greater than 85%, measured at the beginning of the two to three-year runtime of the process according to the invention.

Advantageously, the reaction temperature is when it enters the second dehydrogenation step (step iii) 580 to 655 ° C, preferably 590-650 ⁰ C, in particular 610-645 ° C.

Thus, in the first dehydrogenation step (i), it is advantageous to use a catalyst which has a lower temperature parameter (T) than the second dehydrogenation step (iii). Further, in the first dehydrogenation step (i), the catalyst has a lower selectivity parameter (S) compared to the second dehydrogenation step (iii) (TA <TB and SA <SB).

Accordingly, in the second dehydrogenation step (iii), compared with the first dehydrogenation step (i), a catalyst is used which has a higher temperature parameter (T) and a higher selectivity parameter (S) (TA <TB and SA <

Advantageously, the catalyst has in the first dehydrogenation step (i) a temperature parameter on which, preferably at least 5 ° C, more preferably at least 10 ⁰ C, in particular at least 20 ⁰ C is lower by at least 1 ° C than the temperature parameter the catalyst of the second dehydrogenation step (iii).

For example, as dehydrogenation catalysts in the second dehydrogenation step (iii), catalysts may be used which may be partial or complete

Use of secondary catalyst material have been prepared, as described in the international application with the file number PCT / EP2006 / 064178. The term "secondary catalyst material" is understood in the present invention to be used / used / deactivated, optionally treated catalyst material.

Catalysts containing a mixture of 10 to 70 wt .-% ground, optionally calcined at 100 to 1500 ° C secondary catalyst material of a used (de) hydrogenation catalyst containing iron oxide and 30 to 90 wt .-% of the corresponding fresh are advantageously used in the second dehydrogenation step Catalyst material containing iron oxide, wherein the iron oxide of the fresh catalyst material predominantly in the form of hematite or potassium ferrite phases.

If a third or further dehydrogenation step takes place, which does not comprise a combined oxidation step, the reaction mixture is advantageously brought to the desired temperatures via a heat exchanger by means of, for example, superheated steam before entering the third or further dehydrogenation step.

If a third or further combined oxidation and dehydrogenation step takes place, it is optionally possible once again to supply hydrogen to the reaction gas before the oxidation step.

The process according to the invention has the advantage that styrene can be produced with a higher yield. Furthermore, the drop in yield which can be determined over a longer period of the described process can be reduced.

Claims

claims

A process for preparing Sytrol by dehydrogenating ethylbenzene comprising steps (i) to (iii): (i) contacting a gas mixture comprising ethylbenzene and optionally steam in a first dehydrogenation step with a first dehydrogenation catalyst A, wherein a reaction gas comprising ethylbenzene, styrene and hydrogen,

(ii) contacting the reaction gas obtained from the first dehydrogenation step in an oxidation step with oxygen in the presence of an oxidation catalyst, at least partially burning the hydrogen,

(iii) contacting the reaction gas obtained from the oxidation step in a second dehydrogenation step with a second dehydrogenation catalyst B, characterized in that the molar ratio of hydrogen to ethylbenzene in the reaction gas obtained after the first dehydrogenation step (i) is greater than Is 0.4.

2. Process according to claim 1, characterized in that the molar ratio of hydrogen to ethylbenzene in the reaction gas obtained after the first dehydrogenation step (i) is greater than 0.5.

3. The method according to claim 1 or 2, characterized in that the temperature turing parameter of the first dehydrogenation catalyst A is smaller than the temperature parameter of the second dehydrogenation catalyst B.

4. The method according to claims 1 to 3, characterized in that the selectivity parameter of the second dehydrogenation catalyst B is greater than that of the first dehydrogenation catalyst A.

5. Process according to claims 1 to 4, characterized in that the temperature parameter of the first dehydrogenation catalyst A is between 605 and 640 ⁰ C.

6. The method according to claims 1 to 5, characterized in that the catalyst in the first dehydrogenation step (i) has a temperature parameter which is lower by at least 5 ° C than the temperature parameter of the catalyst in the second dehydrogenation step (iii).

7. Process according to claims 1 to 6, characterized in that the hydrogen selectivity of the oxidation catalyst is at least 80%. A method according to claim 1 or 2, characterized in that the reaction gas obtained from the first dehydrogenation step is further brought into contact with additional hydrogen before being introduced into the oxidation step.