DE1443364B2 - Process for the preparation of p-xylene - Google Patents

Description

3 4

absorbed, higher molecular hydrocarbons mainly from fresh isobutane, which becomes isobutylene

Containing oil is dehydrated through line 22, while the recycled

Column 23 out, which works so that the C ₃ - and dimers is converted into xylene at the same time, are

C ₄ hydrocarbons from the absorption oil over the preferred working temperatures

Head and the lean oil by 5 between 538 and 584 ° C and low pressures of

the line 20 to the absorption device 19 back - about 12 cm Hg abs. down to atmospheric pressure

to be led. The column 23 can therefore under such (760 mm Hg).

Conditions are operated that hydrocyclization takes place with isooctane or material materials that boil significantly above the original diisobutylene as fresh feed for the production of the lent boiling point of the absorption oil, as io of aromatics consisting mainly of p-xylene, vapor are released overhead. Somewhat less stringent conditions, matic absorption oils with a boiling range can be used. The best overall results about 80-205 ^° C are used. Borrowed high conversions without excessive pro-die overhead flows from the debutanizing column producing coke and light hydrocarbon gases

16 and column 23, in which C ₃ and C ₄ carbons 15 will prevail at temperatures between about 510 and hydrogen are obtained through lines 565 ° C, preferably between 524 and 552 ° C.

17 or 24 to a propylene separation column 25 Although atmospheric or even slightly increased pressures can be used to separate a pressure through line 26, it is advantageous to remove overhead fraction which, even here, is substantially below atmospheric pressure from propylene Q-hydrocarbons 20 work, so that there is more in the by-products, is operated, while the non-converted ₄ -olefins are present instead of paraffins. The vaporized isobutane, essentially produced from isobutane and isobutene in this process, and the existing soil material through line 27 to the iC ₄ olefins can optionally be recovered dimerization in a suitable reaction vessel 28 and separately or directly combined as such. «5 with the fresh Cg charge for dehydrocyclization

In the reaction vessel 28, each can be returned for the dimerization. The presence of sation of isobutenes known to suitable methods of recycled isobutylene can be used to some extent. So z. B. suppress the cleavage of the C ₈ charge through line 27; and introduced hydrocarbon streams at moderate temperatures, some of the iC ₄ paraffins and olefins temperatures and pressures and high space velocities can be converted directly into xylene, the speeds being converted into xylene via a fixed bed of silica clay The following earth catalyst can be carried out. Typical process reactions in the dehydrocyclization vessel takes place: use temperatures from 149 to 205 ⁰ C, pressures

from 21 to 56 kg / cm ² at hourly space velocity ^ r «j.; h

dities from about 3 to 10. Other known prostitutes 35 i; ru ^ ru j_5h sationverfahren use a phosphoric acid
or sulfuric acid catalyst at moderate temperatures to achieve high yields of the desired properties. specified pressure worked, so dimers, avoiding _{excessively severe conditions, the rate of charging the C 8} alcohols, which prevents excessive production of dimethyl hydrogen from 0.2 to 2.0 vol. Feed / vol. of the hexene or 2,3,4- and 2,2,3-trimethylpentene catalyst / hour. and is expediently chosen to accelerate. The dimerization product of 2,4,4-trimethylpentene-1 and that at the temperature and pressure used is rich in 2,4,4-trimethylpentene-2 and a little triose containing at least 50% and preferably higher conversion butylenes, such as the development of the C ₈ loading is achieved. If the already stated, through line 12 to the dehydrated 45 iC ₄ hydrocarbons - returned as paraffins, olefins or dration system 10. Mixtures of the same - returned, so can

The bottoms fraction from the debutanizing column 16, at generally the same temperatures and pressures, consists essentially of ^ hydrocarbons, as if only a fresh one which is rich in aromatics is used. These are in the. Cg charge is used, the entire coal column 29 for the separation of up to about 105 ⁰ C 50 hydrogen space velocity should, however, be set corresponding or slightly higher boiling hydrocarbons as accordingly that working conditions for an overhead vapor fractionated, but briefly below at least 50% conversion of the C ₈ boiling point of toluene (about 110 ⁰ C) remaining hydrogen can be achieved.

will. Mainly composed of unconverted An important feature of the present invention

Diisobutylene together with slightly higher liquid 55 is the use of a special catalyst. Existing overhead fraction of polymer is, like ij-alumina, which is the total or main specified, returned through line 13 to the dehydrogenation part of the carrier for the active catalyst compo vessel 10. The bottoms fraction from the component constitutes, is prepared by heating / S-Alumina column 29 is fed through line 31 to _a: trihydrate (Bayerite) led to temperatures between about fractionator 32, prepared in which Toluene 60 316 and 760 ⁰ C. Alumina / S-trihydrate and lower-boiling hydrocarbons obtained as vapor by various known processes can be withdrawn overhead in line 33, one of which is in the hydrolysis of aluminum ■ whereby at 34 the aromatic C ₈ hydrocarbonate with Ammonium hydroxide. Other substances that contain 95% or more p-xylene, whereby processes are carried out under the regulated aging of the rest consists almost exclusively of isomers, 65 aluminum hydroxide gels. / 5-alumina trihydrate can be obtained in prak. 'purely form (more than 97%) is now in the

Available for the korn trade carried out in the reaction vessel 10; Mixed unrelated people are still in the trade Dehydration, with the fresh charge being made of hydrated clay at 75% or more

5 6

j8-alumina trihydrate together with ά-trihydrate (Gibb- commercial alumina - /? - trihydrate (more than 96%

sit) or with a-monohydrate (boehmite) or with bayerite) was thoroughly mixed with watery two. The calcination (dehydration) of the riger nitric acid using 0.09 Gea trihydrates provides the typical y-form of alumina, parts by weight of nitric acid (specific weight 1.42) and which was previously known as "activated alumina". In the case of 5 0.108 parts by weight of water, based on the weight of calcining alumina hydrate mixtures, the / J-tri of alumina trihydrates are mixed. After standing over hydrate with these α-hydrates contained, the acidic mixture is formed overnight through a nozzle corresponding calcined, extruded from η- and γ-alumina and the emerging material into existing product. The cut in the process of the Erfin tablets of 2.4 mm thickness. The catalyst used in tablet dung is prepared, io th have been dried at 116 ° C and in the air by placing a dehydrated alumina support that is dehydrated at about 427 to 483 ° C (surface area of hydrated, at least 60% and preferably 367 m ² / g) . The dehydrated tablets were then impregnated with clay containing more than 75% /? - trihydrate to adjust the surface area for 2 hours when it was obtained. The dehydrated clay is subjected to a steam treatment at 483 ° C and is subjected to a further heat treatment (surface 170 to 190 m ² / g).

threw the surface to about 100 to 300 m ² / g These aftertreated tablets were through

adjust, and then with chromic acid or an immersion in a chromic acid solution among other things decomposable, soluble chromium compound to turn 11 solution per kilogram of tablets intake of 15 to 25% Cr ₂ O ₃ , based on the impregnated. The chromic acid solution was prepared, \ weight of the finished catalyst, impregnated; the 20 by adding CrO ₃ in water to a solution with an impregnated product is then dried and spec. Weight of 1.420 (15.6 / 15.6 ° C) dissolved the calcined. The calcined chromium-alumina catalyst contained about 550 g of CrO ₃ per liter of solution and in the gate has a surface area of about 50 to 150 m ² / g · also solid sodium hydroxide was dissolved, so that

In the process of the invention, such 41.8 g NaOH per liter will be present. After 2 hours of catalysts, preferably at least 0.6%, prior to immersion, the excess liquid, preferably 0.8 to 1.5 percent by weight of alkali metal, was decanted off from the tablets containing the drained tablets ions, calculated as Na ₂ O; ie the potassium compound, dried in the air at 121 ° C and then used for 4 hours, in the same molecular proportions at 760 ° C in an atmosphere of 20% water vapor, would be heat-treated in the weight and 80% air. According to the analysis, a range of at least 0.9% K ₂ O, preferably 1.2%, the finished tablets contained 1.09% by weight to 2.3 K ₂ O, based on the weight of the catalyst, Na ₂ O.

include. Commercially available hydrated, whole or The catalyst tablets were roughly as follows

Alumina composition consisting mainly of / 5-trihydrate:
Preparations vary in their alkali metal content from
less than about 0.1% Na ₂ O to generally about 35
0.6% Na ₂ O. To incorporate additional alkali metal percentages by weight

The aqueous paste of the Cr ₂ O ₃ 20

_{Alumina Al 2} O ₃ (~ 100% η) 78.9 used by grains or tablets

hydrates with sodium bentonite or sodium hydroxide Na ₂ O 1.1

be mixed in such quantities that in the finished 40
Catalyst the desired alkali metal content is present. Sodium or other alkali metals can also be introduced into the tableted material simultaneously with the solution used for the chromium impregnation under the conditions given below via a catalyst obtained according to a). The desired amount of Na ₂ O can be determined by the action of different ratios of isobutane / adding a small amount of sodium dichromate to diisobutylene in the feed. The chromic acid supplied or the chromic acid solution results are given in the table below which can be partially neutralized by sodium hydroxide:

will. It is believed that the presence of these experiments shows that a miracle specified amount of alkali metal in catalyst 50 is a well-balanced product at molar ratios Selectivity of the catalyst for the dehydrons from isobutane to diisobutylene from 2: 1 to 3: 1 cyclizations improved while acid catalysis is achieved; about equilibrium conditions sated side reactions including isomerisa- achieved when the molar ratio of isobutane to isotion, Polymerization and carbon-carbon butylene in the feed ranges from 2 to 4. Cleavage will be reduced. 55 In the illustrated embodiment of the present

When using isooctane (2,2,4-trimethyl- the invention, the diisobutylene became the reaction pentane) only in the dehydrocyclization under the vessel, in which also the dehydration of iso conditions of the process described, butane is carried out, recycled. Given higher yields of p-xylene achieved than in the case of, separate reaction vessels for the Diisobutylene or mixtures of diisobutylene and 60 dehydrogenation of isobutane and the cyclization of Isooctane. Diisobutylene may be provided, the latter with something

■ ^; less severe conditions including lower temperature and higher, closer to atmospheric

Example of pressure lying pressure works. At a

■ 65 such processes would all isobutylene, which at 28

(Fig. 1) is not polymerized, with the not

e) The isobutane, which is preferably converted in the process of the invention, to the dehydrogenation vessel The catalyst used was prepared as follows. returned. .

Tabel

Approach no. 3 j 4

Temp .; ⁰ C

Pressure; mm Hg

Space velocity *)

Mole ratio of isobutane to
Diisobutylene

565
400
200

0.9

565 400 300

565 400 400

1.9

594
400
400

594
120
800

6.4

Data based on isobutane and diisobutylene weight percent of feed

Conversion 74.2

Selectivity 80.3

■ Isobutylene and p-xylene

Yield / pass

59.6

66.7 85.8 57.2

62.4 83.3 52

Data related to isobutane -> p-xylene

Weight percent of the charge

Conversion 37.8

Selectivity 61.6

Yield / pass 23.3

*) Steam volume per hour per catalyst volume.

26.7 64.4 17.2

23.9 56.6 13.5 74.8
77.9
57.8

29.4
42.2
12.4

44.3
79.9

35.4

16.8
47
7.9

594 120 400

60.7 76.9 46.7

25.4 44.9 11.4

1 sheet of drawings

Claims (1)

1 2 pent feeding; the yield of p-xylene based Claim: on the loading, amounts to a maximum of about 12%. It has now been found that the selective conversion Process for the production of p-xylene by the development of certain aliphatic C ₈ hydrocarbons, dehydrocyclization of 2,4,4-trimethylpentene or 5 using chromium oxide catalysts on 2,2,4-trimethylpentane in the presence of a catalyst and process conditions p -Xylysators from 15 to 25 percent by weight Cr ₂ O ₃ and lol supplies in high yields.
0.6 to 1.5 percent by weight of an alkali oxide. The inventive method of preparation (calculated as Na ₂ O) on alumina as the carrier and of p-xylene by dehydrocyclizing 2,4,4-tri at temperatures of 510 to 594 ° C, characterized in that io methylpentene or 2,2,4-trimethylpentane in counterpart as catalyst presence of a catalyst consisting of 15 to 25 weight percent carrier η-alumina used by dehydra- Cr ₂ O ₃ and 0.6 to 1.5 weight percent of at least 60% of an alkalizing / - trihydrate contained oxide (calculated as Na ₂ O) has been produced on alumina as a carrier, and before and at temperatures of 510 to 594 ° C, impregnation has a surface area of 100 to 300 m ² 15 characterized in that the catalyst carrier ^ clay is possessed, isobutane in the charge in the molar ratio of earth used, which is added by dehydrating a min-2: 1 to 3: 1 and the dehydrocyclization of at least 60% /? - trihydrate-containing alumina has been made absolute at a pressure of 125 to 760 mm Hg and an and before impregnation has a space velocity of 0.2 to 2 volume surface area of 100 to 300 m ² / g, isobutane men liquid per volume of catalyst per hour 20 of the feed in a molar ratio of 2: 1 to 3: 1 is carried out, and the dehydrocyclization is carried out at one pressure of 125 to 760 mm Hg absolute and a space velocity of 0.2 to 2 volumes of liquid per volume of catalyst per hour.
25 The new procedure makes it possible to the easily accessible and relatively cheap isobutane in economical way to convert to p-xylene. Furthermore, a more effective temperature control is possible, since the presence of the isobutane has a dampening effect on the temperature fluctuations that occur during the dehydrocyclization of the C ₈ carbon The present invention relates to dehydrogenation with adiabatic cyclization of 2,4,4-trimethylpentene or 2,2,4-trigens occur. The periodic partial burning methylpentane to p-xylene. of the coke deposited in the catalyst provides one The production of aromatic hydrocarbons 35 part of the heat required in the subsequent endothermic carbon by dehydrocyclization of the corresponding C _{6 -hydrogen conversion.} The Sche and higher hydrocarbons are known. Further ma such a working method is in the known, selected, aliphatic C ₈ -carbons single drawing in the form of a flow diagram of hydrogen for the production of xylenes to aromatic illustrated. sate. So z. B. from n-octane a mixture 40 in the Ausaller shown in the drawing three isomers of xylene together with ethyl implementation of the process of the invention is in Obtain benzene, in which o-xylene predominates. To the dehydration system 10 a fresh charge given the proposed 11 for these dehydrocyclizations, consisting essentially of isobutane and the One of the catalysts is chromium oxide with or without refluxing streams 12 and 13, the diisobutylene contain small amounts of other metal oxides on a carrier 45 and previously unconverted isobutane, made of y-alumina. . . consists. The extracted from the dehydration vessel 10 For the selective production of the desired p-xylene flowing material is fed into a drum or an isomer by dehydrocyclization of acyclic C ₈ - other liquid-vapor separation system 14, hydrocarbons with only very small amounts in which hydrogen and low molecular weight gases of other xylene isomers are in the reaction product 50 (to C ₃ ) are removed at the head, while the products not evaporated from FC Herington and EK R idea 1 in as liquid in line 15 Proc. Roy. Soc, London, A 184, 1955, p. 434, which are deducted. Use of 2,2,4-trimethylpentane as an outlet The liquid products are poured into a debutanic gang material used. Similar processes are conducted sierkolonne 16, which is operated in such a way that a vapor fraction in U.S. Patents 2,785,209 and 2,785,21055 is separated overhead and described by the where isooctane line 17 is withdrawn as the initial feed, which is essentially of (2,2,4-trimethylpentane) or diisobutylene (2,4,4-tri-C ₃ - and C ₄ -hydrocarbons; the non-methylpentene) or mixtures of these evaporated, higher-boiling materials will be used. These patents describe discharged through line 18 in various ways. The overhead gases dene catalysts for this process, whereby a 60 from the vapor separator 14 are passed into an absorption catalyst 5 to 40% (preferably about 12%) tion device 19, after they have reached about chromium oxide on y-alumina, the even smaller amounts 3 , 5 to 14.1 kg / cm ^{2 have been} compressed. Which contains potassium oxide and cerium oxide is preferred. Absorption takes place by means of an aromatic carbon although the aromatics produced in the liquid reaction product of this hydrogen oil, which is introduced through line 20 in the above patents, are introduced into up to 95 to 65 parts of the absorption device; cannot contain 98% p-xylene, the total hydrogen absorbed and low molecular weight conversion of isooctane is no more than about 30% gases (up to C ₂ ) that are not adsorbed become up to about 36% that of a mixed trimethyl head withdrawn through line 21. That the