US3629351A - Catalytic rearrangement of alkyl aromatics - Google Patents

Abstract

IN THE CATALYTIC REARRANGEMENT OF ALKYL AROMATICS OVER A CATALYST OF A HYDROGENATING COMPONENT OR AN ALKALICATION DEFICIENT ZEOLITE, THE FEEDSTOCK CONTAINS LESS THAN 0.5% WT., PREFERABLY LESS THAN 0.1% WT. OF NON-AROMATIC HYDROCARBONS SO THAT THE CATALYST ACTIVITY IS INCREASED. THE PREFERRD ZEOLITE IS DECATIONISED MORDENITE AND THE PREFERRED HYDROGENATING COMPONENT A GROUP VIII METAL E.G. NICKEL ADDED BY ION-EXCHANGE. THE OPERATING CONDITIONS MAY BE 300-525*C., 0-1500 P.S.I.G., 0.1-10 V./V./HR. 1,000-15,000 S.C.F. H2/B. PARAFFINS WERE FOUND TO BE A PERMANENT AND NAPHTHENES A TEMPORARY POISION FOR THE CATALYST.

Description

United States Patent 3,629,351 CATALYTIC REARRANGEMENT 0F ALKYL AROMATICS Martin Frederick Olive, Lightwater, and Geoffrey Dovey,

Shepperton, England, assignors to The British Petroleum Company Limited, London, England No Drawing. Filed Dec. 16, 1969, Ser. No. 885,627 Claims priority, application Great Britain, Jan. 15, 1969, 2,405/ 69 Int. Cl. C07c 3/00, 15/08 US. Cl. 260-672 T 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the catalytic rearrangement of alkyl aromatics over zeolite catalysts.

Various rearrangements of alkyl aromatics are known to be possible and to be catalysed by acidic catalysts, particularly disproportionation (e.g. the conversion of toluene to benzene and xylenes) but also isomerisation (e.g. the alteration of the proportions of xylene isomers in a mixture) and transalkylation (e.g. the interaction of xylenes and toluene to give tri-methyl benzenes and benzene). It is also known that certain zeolites will catalyse these reactions.

It has now been found that the presence of non-aromatic hydrocarbons in an alkyl aromatic feedstock has a marked effect on the activity of zeolite catalysts. Alkyl aromatics are obtained on a commercial scale by separation from hydrocarbon mixtures containing them, particularly by the solvent extraction of catalytic reformates and steam cracker gasolines which have been hydrogenated to convert olefins to paraffins. In such commercial separations small amounts of non-aromatic hydrocarbons can and do appear in the alkyl aromatic portion, but it has now been found that these non-aromatics should be kept to a minimum.

According to the present invention therefore a process for the catalytic rearrangement of alkyl aromatics comprises contacting an alkyl aromatic feedstock having a non-aromatic hydrocarbon content of less than 0.5 wt. at elevated temperature and pressure and in the presence of hydrogen with a catalyst comprising an alkali metal cation deficient zeolite having pores of at least 6 A. and a hydrogenating component selected from the metals of Groups I-B, V-A, VI-A, VIIA and VIII of the Periodic Table according to Mendeleeff.

Preferably the non-aromatic hydrocarbon content of the feedstock is less than 0 .1% Wt. The non-aromatic hydrocarbons normally present in commercial alkyl-aromatic feedstocks are paraffins and naphthenes but olefins may also be present. It has been found that paraflins are more deleterious than naphthenes since parafiins appear to deactivate the catalyst permanently. Naphthenes lower the catalyst activity if present but the activity is at least partially restored when the naphthenes are removed. The content of non hydrocarbon components e.g. sulphur compounds is also preferably less than 0.1% wt.

ice

The feedstocks having the above mentioned low nonaromatic hydrocarbon content may be produced in any known manner. As indicated above the most common method of producing alkyl aromatics of high purity is by the extraction of alkyl aromatics from hydrocarbon mixtures containing them using a selective solvent for the aromatics. Various commercially available solvent extraction processes exist, the most common solvents being alkylene glycols, sulpholanes, N-alkyl pyrrolidones and furfural. The term solvent extraction is to be understood as including extractive distillation. As is also known, the operating conditions for such processes e.g. temperature, temperature gradient in the extraction column and solvent: hydrocarbon ratio can be varied to control the yield and purity of the aromatics produced. Samples from a commerical solvent extraction process have, for example, been analysed and found to have a purity of 99.95% wt., so there is no problem, in practice, of reaching the levels specified above. Other methods of producing the feedstocks required, which may be used in combination with solvent extraction if desired are distillation, and molecular sieve extraction.

Preferred feedstocks contain C7-C15 alkyl aromatics, particularly C -C alkyl aromatics, and more particularly, toluene. However alkyl derivatives of naphthalene having 1 to 5 carbon atoms in alkyl side chains may also be treated. The feedstock may be a single alkyl aromatic or mixtures thereof.

The preferred reaction is disproportionation. Since disproportionation, transalkylation and isomerisation are all believed to be carbonium ion reactions more than one reaction may occur in any given system. The broad ranges of conditions and preferred conditions tending to give disproportionation are set out in Table 1 below.

Pressure, p.s.i.g 0-1, 500 Space velocity, v./v./hr 0.1-10 1, 000-15, 000

0. 5-4 Hydrogen gas rate, s.c.t./b 4, 000-12, 500

There may also be some dealkylation. However, it is believed that dealkylation proceeds via a different mechanism from rearrangement reaction and is not likely to be markedly affected by the content of non-aromatic hydrocarbons in the feedstock.

The zeolite used in the catalyst is preferably mordenite, although other zeolites with pores greater than 6 A. may be used if desired e.g. faujasite or Zeolite Y and Zeolite L. In their normal form zeolites have a rigid network of aluminum, silicon and oxygen atoms together with metal cations which are interchangeable. In freshly prepared synthetic zeolites or natural Zeolites these are usually alkali metal cations. These alkali metal cations can be exchanged for other metal cations e.g. Group 11 metal cations or for hydrogen or ammonium cations and the term alkali-metal cation deficient zeolite as used in this specification preferably means a zeolite with an alkali metal content of less than 2% wt, more particularly less than 1.0% wt.

The alkali metal cations normally present may be replaced for example by Group II metal cations e.g. calcium or magnesium or by rare earth metal ions but preferably a decationised zeolite is used. Decationised zeolites are sometimes referred to as hydrogen zeolites, it being assumed that the ion balance is maintained by hydrogen ions. Decationisation can be achieved by exchange of the alkali metal cations with ammonium ions followed by heating at e.g. 250600 C. to drive off the ammonia.

With this method of decationisation alkali metal contents can be reduced to less than 0.5% wt. An alternative method is treatment with an acid to decationise the zeolite directly. Suitable acids are hydrochloric or sulphuric acid. A combination of ammonium and acid treatment in either order may also be used. Both ammonium and acid treatment have been found to give active catalysts and it appears that the most important factor in activity is the residual alkali metal cation content, which is preferably as low as possible. In general it has been found that ammonium treatment gives the lowest residual metal cation content.

Desirably the zeolite has a SiO :Al O ratio of at least 3 :1 since the higher the ratio the more stable is the zeolite to decationisation and to acids. If the acid treatment uses strong acid of from 5-50% wt. strength, preferably wt. strength, an additional effect is obtained, particularly with the preferred Zeolite, mordenite, in that aluminium is removed from the crystal lattice with a consequent increase in the silicazalumina ratio. With mordenite, for example, the normal silicazalumina ratio of 9-1111 can be substantially increased (SiO :Al O- ratios of as high as 90:1 have been reported) without alteration of the physical characteristics of the zeolite.

After either form of decationisation the zeolite is desirably washed to remove excess acid or ammonium exchange solution and is heated to 250600 C.

The hydrogenating component is preferably a Group VIII metal, for example an iron group metal, particularly 4 water at ambient temperature and then dried for 4 hours at 110 C.

The finished catalyst had the following analysis Ni0.77% wt.

Si-40.0% wt.

SiO :Al O ratio-41.52% Wt. Na0.69% Wt.

Surface area-408 m. g. Pore volume0.22 ml./ g.

The catalyst, after calcination in air at 500 C. for 3 hours and reduction in hydrogen at 450 C. for 2 hours, was used to disproportionate toluene in an extended run The toluene feedstock was obtained from a commercial solvent extraction plant. Small changes in the feedstocks and operating conditions produced variations in the parafiin and naphthene contents. Variations in such contents were also obtained by the addition of parafiins and naphthenes to the feedstock. The effect of these variations on catalyst activity was assessed during the run and the recobalt or nickel, or a platinum group metal, particularly sults are show in Table 2 below.

TABLE 2 Hours on stream 0-699 700-1, 467 1, 468-1, 543 1, 544-1, 654 1, 655-1, 750 1, 751-2, 063 2, 064-2, 133 2, 134

Feedstock percent wt.:

Total parafiins and naphthenes" 1. 43 0.06 1. 43 0. O6 0. 9!) 0. 49 1. 49 0.49 Isa-octane 0. 5 Methyl cyclohexano 1.0 Toluene 98. 47 99. 62 98. 47 90. 02 93. 84 99. 98. 42 99. 35 Other aromatics 0.10 0.32 0.10 0.32 0.17 0.16 0. 09 0. 16 Toluene conversion, percent wt 43 47 43 44. 5 43 43 39. 5 42 Product, percent wt.:

Benzene 19. 4 21. 0 18. 7 18.8 10.1 18. 7 16. 2 17. 0 Xylenes 19. 5 21. 6 20.0 21.2 20.1 20. 6 19.1 20. 4

*The parafiin and naphthene contents were measured by gas-li uid chromatography.

platinum or palladium. It may also be a Group IB metal (i.e. copper, gold, or, particularly, silver). It may be present in an amount from 0.15% wt., particularly 0.5- 2.0% wt., and it is preferably added by ion exchange, thereby taking up at least a part of the alkali metal cation deficiency. It is preferably incorporated into the alkalimetal deficient Zeolite e.g. after decationisation, although it may be incorporated before the heating to drive off ammonia and/or water. Certain of the hydrogenatnig metals, particularly the Group V-A metals (i.e. vanadium, niobium and tantalum) and the Group VI-A metals (i.e. chromium, molybdenum and tungsten) are not readily incorporated into zeolites by ion-exchange and these metals may be present at least partly as impregnated metals. The Group VIIA metals are manganese, masurium and rhenium.

The catalyst may be reduced in a stream of hydrogen at 250-600 C. before use.

The invention is illustrated by the following example.

EXAMPLE A decationised mordenite was prepared by refluxing 150 g. of sodium mordenite with 50 g. of ammonium nitrate in one litre of deionised water for 4 hours. The mordenite was filtered, thoroughly washed with deionised water and dried at 110 C. for 4 hours.

Nickel was exchanged onto the decationised mordenite by refluxing with a solution of 4.75 g. nickel nitrate, Ni(NO 6H O, in 250 m1. deionised water for 18 hours. The resulting catalyst was washed with 6 liters of deionised From the first 4 columns of Table 2 it will be seen that the toluene conversion was markedly affected by the amount of parafiins and naphthenes in the feedstock.

In columns 5 to 8 the relative effect of parafiins and naphthenes was investigated. In column 5, 0.5 wt. of iso octane was added to a feedstock already containing 0.49% wt. of paraflins and naphthenes (giving a total 0.99). As expected the conversion dropped, and it did not increase again when the addition of the iso octane was stopped (column 6). In column 7, 1.0% wt. of methylcyclohexane was added to the same feedstock and again the conversion dropped. However in this instance the activity improved when the addition of the naphthene was stopped (column 8).

We claim;

1. A process for the catalytic rearrangement of alkyl aromatics comprising contacting an alkyl aromatic feedstock having a non-aromatic hydrocarbon content of less than 0.5% wt. at a temperature of from 300 to 525 C. and a pressure of from 0 to 1500 p.s.i.g. and in the presence of hydrogen with a catalyst comprising a zeolite having pores of at least 6 A. and an alkali metal content of less than 2% wt. having incorporated therewith from 0.1 to 5% wt. of a hydrogenating component selected from the metals of Groups IB, V-A, VI-A, VII-A and VIII of the Periodic Table according to Mendeleeff, and maintaining the non-aromatic hydrocarbon content of said feedstock at less than said percent wt. during the contacting operation.

2. A process as claimed in claim 1 wherein the nonaromatic hydrocarbon content of the feedstock is less than 0.1% wt.

3. A process as claimed in claim 1 wherein the feedstock is toluene.

4. A process as claimed in claim 1, wherein the process is carried out at 350 to 500 C. and 150 to 1000 p.s.i.g.

5. A process as claimed in claim 1 wherein the zeolite is mordenite.

6. A process as claimed in claim 1 wherein the zeolite has an alkali metal content of less than 1% Wt.

7. A process as claimed in claim 1 wherein the hydrogenating component is present in an amount of from 0.5 to 2% Wt.

8. A process as claimed in claim 1 wherein the hydrogenating component is nickel.

References Cited UNITED STATES PATENTS Benesi et a1. 260672 Wise 2'60668 Pollitzer 260672 Pollitzer 260672 Pollitzer 260-672 Brandenburg et al. 260672 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,629,351 Dated D c r 21', 1971 Inventor) Martin Frederick Olive and Geoffrey Dovey It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, Line 2 3, I for 'v/v/hr. I read v/v/hr,

Col. 2, Line 47, for "reaction" I I read reactions Col. 3, Line 52, for "hydrogenatnig" read,

hydrogenating Col. 4, Line 5, v Q for "6:77," read 6. 77

Signed and sealed this 13th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTISCHALK Attesting Officer Commissioner of Patents