DE2731669A1 - METHOD FOR ISOMERIZING ALKYLAROMATIC HYDROCARBONS - Google Patents

Description

Deutsche Bank AG Munich

Account No. 41-55 2 55 Postal check account: Munich 2196 93-803

PATENT LAWYERS DIPT-ING. H. VON SCHUMANN DIPL.-ING. W. D. OEDEKOVEN

-S-

8 Munich 22, Widenmayentrafie S

Telegram address: Protector Munich

Telephone 089-2212 73

July 13, 1977 6 / Ha

COMPAGNIE FRANCiISE BE RAFFINAGE S.A., Paris, France

Process for the isomerization of alkyl aromatic hydrocarbons

Addendum to patent ... (patent application P 24 55 375-1)

The main patent ... (patent application P 24 55 375.1) has catalysts for the treatment of hydrocarbons with The subject of hydrogen is a carrier containing acidic sites and bound halogen from a refractory, mineral oxide, furthermore the following metals in free or bound form:

a) 0.02 to 2, preferably 0.10 to 0.70% by weight, based on the total weight of the catalyst, of at least one Platinum group metal;

b) 0.02 to 2, preferably 0.02 to 0.60 wt .- #, based on the total catalyst weight, at least one Group of metals: zircon, titanium and tungsten; and

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c) 0.02 to 2, preferably 0.05 to 1% by weight, based on on total catalyst weight, tin.

The support of these catalysts preferably has

a specific surface area greater than 15 m / g. The carrier can for example consist of aluminum oxide or alumina with a specific surface between 100 and 350 m / g. It also has a specific fora volume greater than 0.1 cnr / g.

The main patent ... (patent application P 24- 55 375.1) also relates to a process for the preparation of these catalysts and their use in hydroforming of hydrocarbon batches.

The first additional patent ... (patent application P 26 15 066.3) forms the subject of the main patent ... (patent application P 24 55 375.1) through the use of the catalysts according to the main patent ... (patent application P 24 55 375 · 1) for aromatization of hydrocarbon batches or for the isomerization of alkyl aromatic hydrocarbon batches. When using the catalysts according to the main patent ... (patent application P 24 55 375 · 1) for the isomerization of alkyl aromatic ti cal hydrocarbons, a halogen content of the catalyst between about 1 and 2 % is advantageous. The halogen is preferably chlorine.

Further work on the use of these catalysts for isomerization has found that the process for isomerization, as described in the documents of the additional patent ... (patent application P 26 15 066.3) is of particular interest if it is done in at least two successive procedural steps

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is carried out.

The object of the invention is to provide the process for isomerizing alkyl! Aromatic hydrocarbons according to the Additional patent ... (patent application P 26 15 066.3) to improve.

According to the invention, this is achieved by a process for isomerizing a hydrocarbon charge in which the hydrocarbon charge is hydrogen in at least two successive process steps and a catalyst in at least one of these process steps according to the main patent ... (patent application P 24 55 375 · Ό is exposed.

In the further explanation of the invention, it will be explained with regard to the successive method steps can be described as comprising only a single reactor each. However, this is not a limitation to be understood, because the process can also be carried out in two successive process steps each of which comprises two reactors. These can be connected in parallel or in series for each process step. For the same reason, only two successive process steps will be described. It should be noted, however, that the method according to the invention can also be carried out with a larger number of method steps.

The temperature and pressure conditions can be identical in both successive process steps. Nevertheless, it has been found that excellent results are obtained under these conditions are different in both procedural steps.

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In each of the two process steps, these conditions can vary within the following ranges:

Molar ratio of hydrogen / hydrocarbons: about 3 to 15 »preferably 8 to 10;

Temperature: generally less than about 550 ° C and greater than about 250 ° C;

Pressure: about 3 to 40 bar.

The total hourly volume throughput based on the total volume of those present in all reactors Catalysts, can vary between 0.4 and 4, preferably between 1 and 2.5.

In Table I below, the conditions are summarized under which each process step is preferred is carried out, for only two process steps.

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Table I.

Operating conditions
First
Process step Operating conditions Hourly
volume
throughput
(partial) 1 to 4 Second
Process step Molars
relationship
hydrogen 3 to 15 1 to 6 Hydrocarbon
fabrics 3 to 15 temperature 100 to 450,
preferably
240 to 450 ° C 300 to 550,!
preferably
350 to 500 ° C pressure 10 to 40,
preferably
20 to 35 bar 3 to 30,
preferably
10 to 25 bar

It was found that the effectiveness of the catalysts according to the main patent ... (patent application F 24 55 375 · 1) is improved in the isomerization of alkylaromatic hydrocarbons when proceeding according to the process according to the invention with the conditions given above will.

This process, which is carried out in two process steps, is particularly applicable when hydrocarbon batches are loaded under the conditions set out above.

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containing mostly hydrocarbons with 8 carbon atoms, with the aim of increasing the yield of paraxylenes by converting other hydrocarbons present in the feed. This method is particularly advantageous for batches containing about 5 to 50 % ethylbenzene.

The catalysts used can have the same or a different composition in the two process steps. In the first step of the process, the halogen content is generally the Chlorine content of the catalyst greater than that of the catalyst used in the second process step, if the conditions in the two process steps correspond to the table given above. Indeed it is the equilibrium between water contained in the charge added to the reactor and chlorine depends on these conditions.

Apart from the chlorine content, the composition of the catalysts can vary as a result of the type of active metals or promoters applied to the support. if the process for isomerization is carried out, for example, only in two process steps, so it can the first reactor have a catalytic composition in which only platinum is present as metal, and the second a catalytic composition that corresponds to the main patent (patent application P 24 55 375-1). Likewise can the following combinations of catalysts can be used:

In the first reactor a catalyst according to FR-PS 2 031 984, which contains a metal of the platinum group and tin as active metals. Likewise, in the

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In the first reactor a catalyst may be present which comprises at least one platinum group metal on a support from a refractory oxide, optionally with one or more promoters to improve any property of the catalyst (life, activity, stability, inhibition of cracking sites, etc.)

In the second reactor a catalyst according to the main patent ... (patent application P 24- 55 375.1).

Ke different catalysts can each be used in either of the two process steps. For example, the catalyst according to the main patent ... (patent application P 24 55 375 · Ό can be provided for the first, the second or for all process steps. However, it has been found that it is particularly interesting to use this catalyst, especially in the second process step, if two process steps are used to carry out the isomerization process, Good results are obtained with a catalyst composition of platinum / aluminum oxide in the first process step and platinum + tin + zirconium / aluminum oxide in the second process step.

Composition of platinum / aluminum oxide in the first reactor can, without the result changing significantly, replaced by the composition of platinum + tin on aluminum oxide, as explained above. The halogen content, that is to say generally chlorine, in the catalysts provided for the various process steps is present, will change from one process step to another, as indicated above, due to

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the differences between the reaction conditions of these process steps. The halogen content is accordingly preferably between 1 and 2 % in each process step. The halogen content of the catalyst for the first process step is, however, higher than that of the second process step, the difference fluctuating between, for example, about 0.05 and 0.50%, based on the catalyst weight.

The purpose of the halogen is known, is the carrier of a refractory oxide a certain Aci dität to impart. Other elements which have this property can likewise be added to the various catalyst compositions which are intended for the individual process steps. Thus, additions of silicon in a ratio of about 0.1 to 2%, based on the total weight of the catalyst, to the catalyst compositions mentioned have proven successful.

The following examples serve to further illustrate the invention, both for the case at which the catalysts according to the main patent ... (patent application P 24 55 375.1) aur in both process steps They are used as in the case in which these catalysts are only used in the last process step.

example 1

The isomerization of a batch of alkyl aromatic hydrocarbons of the following composition is carried out as indicated above:

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1.07 % 2731669 t 71.42 % Toluene: 27.45 % Ethylbenzene: 1.44% y para-XyΙοί: 68.67 % \ meta-xylene: 1.31% y ortho-xylene:

This reaction aims to achieve a maximum yield of para-XyIo1. The compositions of the used Catalysts are as follows:

Catalyst according to the main patent ... (patent application P 24 55 375.1) - A -

Platinum: 0.35% by weight

Tin: 0.20 wt%

Zircon: 0.15% by weight

Comparative catalyst -B platinum: 0.35% by weight

The supports for these catalysts are aluminum oxides with the following conventional properties:

specific surface: 185 m / g

Pore volume: 0.48 cm / g

ο mean pore radius: 40 A

The chlorine content of the catalysts is given in Table II below and is obtained by adding 184 p.p.m. Chlorine in the form of dichloro-propane to the non-anhydrous, alkylaromatic hydrocarbon charge to compensate for the dechlorination by the moisture of the batch kept exactly constant. A certain number of experiments are carried out, the conditions of which are in the Table II are shown.

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Table II

Experimental
number «Η 475 ⁰ C 1, C3 1.59 2 3 •1 5 G 7th 475 1.25 1.01 1.56 e 9 10 Il 12th
3 Deployed
catalyst Λ 15th
boron 17c: n ³ lOcnf Λ A. Λ Λ Λ D. 15th 10 lOcn ³ 27cm ³ B. B. B. D. 1 Number of ver
driving steps
temperature 2 1.25 1 1 1 1 1 2 1 1 1 1 447.5 pressure 1. 2.
step 10 475 475 420 ** 420 ** 417.5 .1. 2.
Step. 475 475 420 ** • * .2C ** 22.5 Total V.V.H. 35O ⁰ C .20 15th 30th 15th 22.5
* 350 30th 15th 30th 15th 1.25 Molars
relationship
Kp / batch, 30th 1.25 1.25 1.25 1.25 1.25 30th 1.25 1.25 1.25 1.25 10 Chlorine content of
Catalyst 10 10 10 10 10 10 10 10 10 i, 45 catalyst
volume 1.59 1, S9 1.59 1.59 1.59 1.45 1.45 1.4 * 1.45 27c., ³ 27cn ³ 27crr. ³ 27cm ³ 27crr, ³ 17cn \ ³ 27C.T ³ 27cm ³ 27cm ³ 27cm ³

the total V.V.H. (hourly volume throughput) is the V.V.H. based on the Total volume of the catalyst.

the temperature of 420 °. C was chosen instead of that of 350 ° C because at the latter temperature, most of the effluent at 15 to 30 bar due to ^ of the thermodynamic equilibrium is not composed of aromatics. For the comparison is therefore more suitable at 420 ° C.

The results of these various tests are shown in Table III. In this table are given :

the weight yields of the various products in the effluent;

the total yield R ^ of hydrocarbons with 8 carbon atoms in %;

the ratio R ^ = entered xylenes

Xylenes in the effluent;

Conversion of ethylbenzene (CEB) in%.

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Table ill.

ι Trial number 1 2 3 4th 5 G 7th Q 9 10 11 12th Total yield in
Weight % 97 97 97 97 97 97 93 92.3 93.3 97 97 Light hydrocarbons * 0.91 4.09 1.03 2.2C 0.04 2.11 3.62 OK, 2o 2.73 2.60 0.70 1.86 benzene 0.66 2.79 1.54 - - 1, G6 1.30 - 2.80 - - toluene 4.04 3,:; ü 4.70 1.14 1.27 1.96 7.93 9.15 11.67 1.64 1.90 3, OO ι Cg paraffins ·· 2.04 26.70 2, G2 70, CG 22, Ü9 23.47 4.52 11.13 1.85 40.67 13, Eq ) 6.19 « ι ethylbenzene 12.63 5.22 15.66 1.67 10, 5G 6.60 9.07 6.32 13.01 4.14 16, Κ 12.03 I. C. , para-xylene 10.3C 12.9G 16.60 5.10 13, G4 14.67 13.55 12.93 12.96 9.53 11.20 14.11 * I meta-xylene 39.97 23, 3Ü 30.94 11.30 35.34 32.30 32.93 20.96 35.45 21.47 44 - 36.73 C.
O J ortho-xylene 17, OC 12.16 15.09 4.64 11.9u 13.50 16.51 12.45 11.49 0.56 9.20 12, £ 0 IS
< 'Heavy hydrocarbons
* · · · 0.40 0.4 H. 0.59 0.12 0.24 0.37 0.57 0.99 0.50 0.21 0.14 O,? 2 R 1 00.9 50.7 86.3 22.8 71.7 07.2 74.9 60.7 73.7 43.7 CjO, 5 75.7 R 2. · '"· ^.: 1.07 0.75 0.99 0.29 C, C6 O, Ü5 0.91 0.76 0.84 0.55 0.90 0, D9 CEB 54 81 42.9 93.9 61.5 76.0 64 76.8 49.4 IN THE B 40.9 55.7

Hydrocarbons with a maximum of 7 carbon atoms, with the exception of benzene and toluene Paraffin and cycloparaffin hydrocarbons with 8 carbon atoms Hydrocarbons with at least 9 carbon atoms.

CO

cn "CD CD

The results obtained and shown in this table require some explanation:

1) In a single process step, the best result with the composition Pt-Sn-Zr in a Pressure of 15 bar and 475 ° C obtained (test no. 3 cf. the values of the para-xylene yield, the ratio B 2 and the yield B 1).

2) By comparing tests 3 and 1 it becomes clear that in two process steps:

the overall yield B 1 is greater, the ratio B 2 is the same, and the yield of para-xylene is considerably increased.

It is therefore more interesting to work with two process steps than with a single process step, to increase paraxylene production.

3) In a single process step, the best result is achieved with the composition with platinum at 22.5 bar and 447.5 ° C (test no. 12 - cf. the para-xylene yield ).

4) By comparing experiments no. 12 and 7, It is clear that working with two procedural steps (experiment no. 7) is profitable because it results in the Yield of para-xylene is increased. While with the composition Pt-Sn-Zr according to the main patent ... (patent application P 24 55 375.1) the extent of para-xylene production is low, the over-

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J.! ·,; ■■ *: · DIfIO

In the course of the first to the second process step, the profit to be recorded in the Pail of the compositions Pt Sn-Zr to be very interesting.

Example 2

This example involves isomerization of a hydrocarbon feed containing essentially metaxylene and ethylbenzene carried out with an almost constant composition. According to the invention, the isomerization takes place in two reactors, under the following conditions:

First reactor:

Pressure: 20 bar

Temperature: 280 ° C

25 cm ^ catalyst with 0.35 wt .-% platinum and

1.6% by weight of chlorine on aluminum oxide;

Second reactor:

Pressure: 15 bar

Temperature: fluctuating between 490 and 530 ° C 15 cnr catalyst (carrier: aluminum oxide), its composition in the various, carried out Experiments (Experiment Nos. 13 to 18, see Table IV below) varied.

The total hourly volume throughput is 1.5 »and the molar ratio of hydrogen / hydrocarbon 7.5 · The hydrocarbon charge is still dichloro-propane added, in the ratio of 180 p.p.m./200 p. p.m. of water present in the batch. At the beginning of the reaction the catalysts contained in the reactors are subjected to a reducing treatment with hydrogen (at 20 bar)

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subjected at 500 C within 2 h.

The catalysts used in the second reactor are identified in Table IV below.

Table IV

attempt 13th 14 y 0 , 35 15th ! 16 17th '18 y catalyst (Ver (Ver 0 , 20 UBB
2. reactor The same) - Platinum-
salary
(Wt%) 0.35 1 , 69 0.34 0.38 0.37 0.36 Tin content
(Wt%) - 0.21 0.22 0.22 0.20 Zircon
salary
(Wt%) - 0 0.15 0.14 0.15 0.79 Chlorine content
(Wt%) 1.66 27 , 26 1.80 1.68 1.73 1.67 Batch
Content of
(in% by weight): 2 , 11 - toluene 0 68 , 82 0.03 0.07 0.18 0 - ethylbenzene 27.56 1 , 81 27.45 27.38 27.47 27.56 - para-xylene 2.30 72 , 74 2.09 2.10 2.29 2.30 - meta-xylene 68.07 62.42 62.64 63.91 68.07 - ortho-xylene 2.07 8.01 7.81 6.15 2.07 - xylenes
all in all 72.44 72.52 72.55
I. 72.35 72.44!
i I

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to '

Tables V to X below show the results obtained in each case by experiments 13 to 18 shown again.

It is especially the relationship

R a para-xylene in the effluent

Paraxylene in the effluent + losses

specified, whereby the losses due to benzene, toluene, light hydrocarbons (with a maximum of 7 carbon atoms, Except for benzene and toluene) and heavy hydrocarbons (with at least 9 carbon atoms) are formed.

R represents the yield of para-xylene based on the batch used, if the hydrocarbons with 8 Carbon atoms after the separation of the para-xylene and the losses are fed back into the circuit.

Hit C _EB , the conversion of ethylbenzene is called.

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Table V

Trial 13

I.
I.
I. Temperature of the 2nd
Reactor (° C) . 490 ι 500 ι 510 ι 520 ι 530 Weight yield Light products ι 0.91 ! 1.16 i 1.05 ! 1.43 ! 1.74 benzene «1.05 t 1.11 ι 1.29 ι 1.52 toluene t 1.80 I 2.28 ! 3.16 ι 3.70
t ! 4.24 ι; saturated
Hydrocarbons
with 8 carbon atoms - • 7.11
ι ι 4.44
:
ι
t t 3.10
I.
I. ι
ι 2.17 ι i
ι 1.42
ι ΐ Ethylbenzene ι
1 t
ι 15.60 ι
I 1 15.58 ι i 16.58 ι
ι 15.25 ι 16.01 I.
I. para-xylene ι ι 16.73 ι
ι ! I.
17.05 yrs
ι 16.43!
ι I.
16.81 ι
I. 16.32? ^: ; meta-xylene ι I.
39.14 j I.
39.38 j 39.28 ι ι
38.30 ι 37.78 ι ortho-xylene ι i
14.96 ι 15.46 i 14.83! 15.67 · April 15 •, Heavy products ι 0.31 ι 0.43 ι 0.66 ι 0.90 ι 0.70 t ι R t 0.829: 0.776 ι 0.733 » 0.697 ι 0.666 t ⁰ EB. J 43.4! 43.5: 39.8 ι 44.6 ι 41.9 [
r

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Table VI Trial

Temperature of

2. Reactor (° C)

Weight yield 490

500

510

520

530

Light products benzene

toluene

saturated hydrocarbons with 8 carbon atoms

Ethylbenzene para-xylene meta-xylene ortho-xylene

Heavy products 0.50

0.76

0.9 **

13.37

17.62

40.38

16.88

0.22

0.50

0.42

1.17

3.37

16, O4

17.52

40.64

16.78

0.3 * »

0.85

0.80

1.56

2.20

16.20

17.62

40.47

16.88

0.42

0.76 t 0, 93 0.87 «I. 1 1 2.07 • 2, 67 1.20 ι 0, 7 *

15.93

17.8O

40.30

17.28

0.81

16.31

17.6O

39.78

17.08

0.80

'EB 0.879

0.878

41.2

0.846

40.6

0.798

41.6

0.762

40.2

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Table VII Experiment 15

Temperature of the 2nd reactor ( ⁰ C) weight yield 500

310

520

530

Light products benzene toluene

saturated hydrocarbons with 6 carbon atoms

Ethylbenzene

j para-xylene i

meta-xylene

j ortho-xylene

Heavy products 0.58

0.85
7.62

16.23

39.20
15.69
0.35

0.68 0.45 1.15 3.98

17.02

16.51

40, 18

16.78

O.25

0.77 O.61

1.59 2.62

16.8O 16.62 40.30

17.29 0.4 ol

0.98 1.06 2.12 2.58

16.56 16.79

17.01

0.74

'EB O.9O2

40.9

0.867

38.0

0.832

38.8

0.774

39.7

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Table VIII

attempt

Temperature of

2. Heaktors (C)

Weight yield

ι 510

520

530

Light products

j benzene

t toluene

saturated
j hydrocarbons
it with 8 carbon atoms

Ethylbenzene

para-xylene

meta-xylene

ortho-xylene

Heavy products

0.51 ι 0.76

j t

0.91 t 1.13

8.69: 6.37

ζ t 1

15.54: 16.02

ζ 16.31 to 6.49

38.35 8.95

16.49 ii6.95

0.23: 0.35 ζ 0.64 0.45 1.41 3.78

17.49 16.43 39.60 16.92 0.29

0.57 0.78 1.41 2.92

17.76

16.51 39.72 16.98

0.35

0.84 0.70 1.78 2.33

17.67

16.73

39.41

17.14

0.40

^C EB

ok, 9O8 jO, 881 ζ

43.2 »41.5 y 0.855 36.6

tO

, 842 35.1

0.818 35.4

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Table IX

273 IbbiJ

attempt

Temperature of

2. Reactor (° C) weight yield

490 500

310

320

530

j Light products
I.

t benzene

“Toluene

saturated
Hydrocarbons with 8 carbon atoms

Ethylbenzene
para-xylene
meta-xylene
ortho-xylene
Heavy products

0.45

1.02 8.57

15.68 16.32

38.51

16.28

O, 18 0.63 ι 0.86

t 0.46

t 1.26: 1.59

5.82 »4.20

16.13 t i6, in

16.74 1 16.84 ι

39.20: 39.33 ι

16.85 1 17.01

0.39 1 0.30 t

0.85 0.94 2.28 2.65

15.59 17.33 39.33 17.50 0.54

0.96 1.09

2.73 1.88

15.65 I f

17.23 j 39.09 t

17.45 j

0.7 ^

'ED

0.908 42.9

0.880 »0.84p t t

41.3: 40.3 χ

0.790 43.2

0.757 I 43.0

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Table X

Attempt 18

Temperature of
_t 2nd reactor (° C)

, Weight yield

490

500

510

520

530

ι Light products

benzene

: Toluene

Hydrocarbons
with 8 carbon atoms

: Ethylbenzene

t para-xylene

meta-xylene

ortho-xylene

ι Heavy products

t -----—————

0.56

0.96

6.08

15.56

17.32

39.14

16.99

0.38

0.9 '*

0.30

1.25

4.43

15.83

39.29

17.27

0.24

0.93

0.67

1.70

2.53

16.20

17.58

39.64

17.48

0.27

0.86

0.76

1.98

1.71

16.18

17.68

39.86

17.49

0.49

0.92: ι

0.92:

2.54 t 0.99 χ

15.95 t

17.68: t

39.41 t

17.63: 0.93 χ

0.769 42.1 t

£ B

0.901

0.865

43.5: 42.6

0.831

4i, 2

0.812

41.3

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_ 27 3IbB y

17-

Given the results in these tables can be concluded that the process according to the invention in the isomerization of aromatic hydrocarbons having 8 carbon atoms, is very effective. It is particularly advantageous with respect to a method in which only platinum is used as a catalyst. The comparison with a platinum-tin composition provided in the second reactor is in favor of the platinum + tin + zirconium compositions for experiments 15 and 16, the results for experiments 17-18 and 14 being exactly the same.

In order to make this comparison easier, the curves are shown in the single figure of the accompanying drawing, which, as a function of the temperature T, are the values of the ratio R for each of those used in experiments 13 to 18 Reproduce catalyst combinations.

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L e r s e i t e

Claims (15)

Claims (1. h / experienced in the isomerization of alkyl aromatic hydrocarbons, in which the hydrocarbon charge is hydrogen and a catalyst according to the patent ... (patent application P 24 55 375-1) with a carrier containing acidic sites and 0.4 to 2% by weight of bound halogen a refractory, mineral oxide is exposed, which catalyst is in free or bound form and each based on the total weight of the catalyst a) 0.02 to 2, preferably 0.10 to 0.70% by weight of at least one metal from the platinum group; b) 0.02 to 2, preferably 0.02 to 0.60% by weight of at least one metal from the group: zirconium, titanium and tungsten; and c) 0.02 to 2, preferably 0.05 to 1% by weight of tin contains, characterized by at least two successive process steps, wherein the hydrocarbon charge in at least one of these steps the hydrogen and the catalyst according to the patent ... (Patent application P 24 55 375 · Ό is suspended. 2. The method according to claim 1, characterized in that the following operating conditions during of the procedural steps are applied: Pressure: 3 to 40 bar,
Temperature: 250 to 550 ° C, 273166a molar ratio of hydrogen / hydrocarbons: 3 to 15, Total hourly volume throughput, "based on the liquid state: 0.5 to 4, preferably 1 to 2.5. 3. The method according to claim 1 or 2, characterized in that that two process steps are used, with the following operating conditions for the first process step: Pressure: 10 to 40, preferably 20 to 35 bar, temperature: 100 to 450, preferably 250 to 450 ° C, hourly volume throughput, based on the liquid state: 1 to 4, molar ratio of hydrogen / hydrocarbons: 3 to 15. 4. The method according to any one of claims 1 to 3 »characterized in that two process steps are used, with the following operating conditions for the second process step: Pressure: 3 to 30 »preferably 10 to 25 bar, Temperature: 30 to 550, preferably 350 to 500 C, hourly volume throughput, based on the liquid state: 1 to 6, molar ratio of hydrogen / hydrocarbons: 3 to 15. 7098 * 4/0829 273166 ^{1 y} 5. The method according to any one of claims 1 to 4, characterized characterized in that the operating conditions for the two process steps are identical. 6. The method according to any one of claims 1 to 4, characterized in that the operating conditions are different for the two procedural steps. 7 · The method according to any one of claims 1 to 6, characterized gekennzei chnet that the respectively used in the successive process steps Catalysts are identical. 8. The method according to any one of claims 1 to 6, characterized characterized in that the respectively used in the successive process steps Catalysts are different. 9 · The method according to any one of claims 3 to 8, characterized characterized in that the halogen, preferably chlorine content of the catalysts between successive Process steps is different, a catalyst used in the first process step which, based on the total weight of the catalyst, contains about 0.03 to 0.50% by weight more of halogen than that used in the second process step. 10. The method according to any one of claims 1 to 9 »thereby gekennzei chnet that the catalyst according to the patent ... (patent application P 24 55 375.1) at the last Process step is used. 7 0 9 8 8 4/0 0? 11. The method according to any one of claims 3 Ms 10, characterized characterized in that a catalyst is used in the first process step, which only platinum contains as active metal and optionally silicon. 12. The method according to any one of claims 3 to 10, characterized characterized in that a catalyst is used in the first process step, the platinum and tin as active metals and optionally silicon. 13 · Process according to one of the preceding claims, characterized in that the catalyst used in any of the process steps according to patent ... (patent application P 24 55 375 · 1) also contains 0.1 to 2 % silicon. 14. Use of the process according to one of the preceding claims for the isomerization of alkyl! Aromatic hydrocarbons with 8 carbon atoms. 15. Application of the method according to one of claims 1 through 13 for treating alkyl aromatic hydrocarbon charges with about 5 to 35 wt .-% ethylbenzene. 709884/0829