GB2052554A - Production of aromatic hydrocarbons - Google Patents

Abstract

Hydrocarbon conversion, especially beneficial conversion of ethylbenzene in a mixed xylenes- ethylbenzene feedstock, by contacting the feedstock in the liquid or vapour phase with a catalyst comprising a zeolite, for example zeolite FU-1,and in the presence of an inert gaseous diluent, for example nitrogen. In the preferred embodiment of the process, ethylbenzene destruction is influenced to proceed in the direction of cracking (to benzene and ethylene) rather than disproportionation/ transalkylation (which lead to benzene and less useful products such as diethylbenzenes, ethylxylenes and ethyltoluene).

Description

SPECIFICATION Production of Aromatic Hydrocarbons This invention relates to a process for the production of aromatic hydrocarbons and particularly to the production of C8 alkylaromatic hydrocarbons.

According to the present invention a hydrocarbon conversion process comprises contacting a feed of an alkylbenzene or a mixture of alkylbenzenes in the liquid or vapour phase with a catalyst comprising a crystalline aluminosilicate zeolite and in the presence of an inert gaseous diluent.

The isomerisation of alkylbenzene hydrocarbons, especially xylenes, is a well known and widely practised process. The process may be operated in the vapour or liquid phase and with a wide variety of catalysts. In recent years catalysts comprising crystalline aluminosilicate zeolites have been proposed for use in xylenes isomerisation. Among the zeolites so proposed have been the "ZSM" series of zeolites, for example the ZSM-5 family and the ZSM-2 1 family.

The ZSM-5 family of zeolites includes those known as ZSM-5, ZSM-8, ZSM-1 1 and ZSM-1 2. A general description of the family is available in US Patent No. 3,775,501 and the above members are more particularly described in the following patent specifications: ZSM-5 : USP No. 3,702,886 and UK Patent No. 1,161,974 ZSM-8 : UK Patent No. 1,334,243 ZSM-1 1:UK Patent No. 1,365,317 ZSM-1 2: UK Patent No. 1,365,317 Typically, the ZSM-5 family of zeolites can be defined by the following characteristics: SiO2/Al2O3 mole ratio 5 to 100 port size 6 to 6.5A (corresponding to rings of 10 SiO4 and Al04 tetrahedra) in addition to their characteristic X-ray diffraction patterns which are set out in the appropriate patent specifications listed above.

Another family of zeolites includes those known as ZSM-35 and ZSM-38. A general description of the family is available in US Patent No. 4,046,859 and the above members are more particularly described in the following patent specifications: ZSM-35 USP No.4,046,245 ZSM-38 USP No. 4,046,859 'Methods of preparation of the "ZSM" zeolites are described in the patent specifications listed above and in other specifications.

Another zeolite which has been proposed for use in alkylbenzene isomerisation is zeolite FU-1, whose preparation and use as a catalyst are described in our UK Patent application Ni.1,563,346.

The crystallographic structure of FU-1 is shown to be unique by its X-ray diffraction pattern, which includes the following characteristic lines: TABLE 1

d(A) 100 I/Io d(A) 100 I/Io 9.51 31 4.48 6 8.35 8 4.35 13 6.92 28 4.07 19 6.61 9 4.00 9.4 6.26 9 3.89 13 5.25 16 3.73 28 4.61 63 3.68 3 3.44 100 These lines were measured on the sodium/tetramethylammonium (TMA) form of FU1 but we find that the pattern of the hydrogen form, as exemplified by the corresponding material from which all the TMA and all but 300 ppm w/w of Na2O has been removed differs negligibly from the above pattern.

The diffraction peaks observed are very broad suggesting that FU-1, at least as so far produced, occurs in small crystallites typically 100 to 500 Angstrom units (A) in diameter.

The crystalline structure of FU-1, as shown by electron microscope examination, can consist of very thin sheets of angularly interlocking platelets typically 50 to 400 A thick and are agglomerated into packs of total thickness in the range 0.1 to 10 microns.

The chemical composition of FU1 is as follows:- 0.6 to 1.4 R2O.Al2O3. over 5 SiO2.0 to 40 H2O where R is a monovalent cation or 1/n of a cation of valency n and H2O is water of hydration additional to water notionally present when R is H.

The number of molecules of SiO2 is more typically at least 10, for example 1 5 to 300 and FU1 appears to be most readily formed in a state of high purity when the number of molecules of SiO2 is in the range 15 to 45, preferably 1 5 to 30. It is believed to be unusual to have hydrophobic properties at such a low SiO2 level. The upper limit for SiO2 in the FU1 structure is not yet known.

The use of zeolites in processes for isomerising xylenes is well-known and the use of zeolite FU--l,for example, as a catalyst for xylenes isomerisation is described in our UK Patent Application number 1,563,346. As is well known, the aim in xylenes isomerisation is to increase the para-xylene content of the feedstock at the expense of other isomers since para-xylene is by far the most valuable of the xylene isomers. As can be seen from the description in our UK Patent Application number 1,563,346, the use of zeolite FU1 as catalyst in the isomerisation of feedstocks comprising mainly xylenes with only small amounts of ethylbenzene leads to a useful increase in para-xylene content.

Hitherto, much of the mixed xylenes feedstock available in many parts of the world has contained relatively small amounts of ethylbenzene but it is anticipated that in the future such feedstocks will become somewhat scarce and that resort will have to be made to feedstocks containing rather larger amounts of etbylbenzene, say up to about 25% ethylbenzene. Although ethylbenzene has its uses, for example as a feedstock in styrene manufacture, operators of xylenes plants tend to prefer to convert it into other useful products. A certain amount may be convertible into xylenes or undergo cracking to benzene and d ethylene. A third possibility is disproportionation/transalkylation to benzene and diethylbenzenes although in a mixed ethylbenzene/xylenes feedstock this would also lead to the formation of ethylxylenes and ethyltoluene, thus wasting useful xylenes.Thermodynamic predictions suggest that at about 5000 C, ethylbenzene should be converted in approximately equal amounts by cracking and by disproportionation/transalkylation.

We have now found that the destruction of ethylbenzene can be influenced to proceeed in the direction of cracking rather than disproportionation/transalkylation.

Accordingly, a preferred form of the present invention is a process for the beneficial conversion of ethylbenzene which comprises contacting a feedstock comprising ethylbenzene at elevated temperature with a catalyst comprising a zeolite and in the presence of an inert gaseous diluent.

Preferably the feedstock is a mixed xylenes-ethylbenzene feedstock, for example one containing ethylbenzene in an amount of about 6% to about 25% by weight. Preferably at least part of the xylenes content of the feedstock is isomerised during the process of the invention.

Preferably the catalyst comprises a zeolite selected from zeolite FU-1, a zeolite of the ZSM-5 family, ZSM-35 or ZSM-38.

The inert gas must be one which does not react detrimentally under the process conditions with either the reactants or the reaction products or the catalyst. Particularly preferred as the inert gas is nitrogen but other inert gases, for example helium, argon and hydrogen are also suitable. The use of hydrogen as a reactant in xylenes hydroisomerisation is well known but in the process of the present invention the hydrogen, if used, is inert. Xylenes hydroisomerisation is effected in the presence of hydrogen and of a catalyst comprising a hydrogenation component, for example platinum on a suitable support. In the process of this invention, such hydrogenation components must be absent from the catalyst if hydrogen is to be used as the inert gas.

Preferred operating conditions for the process of this invention include a temperature in the range 300 to 8000 C, more preferably in the range 350 to 5500C, a reaction pressure in the range 1 to 100 Bar, more preferably in the range 1 to 60 Bar, a weight hourly space velocity (weight of feedstock comprising alkylbenzene per unit weight of catalyst per hour) in the range 1 to 50, more preferably in the range 1 to 10 and a volume ratio of inert gas to alkylbenzene feedstock in the range 1 to 10, more preferably in the range 2 to 8.

The invention will now be described further with reference to the following examples.

EXAMPLE 1 A feedstock comprising 25% (by weight) ethylbenzene and 75% m-xylene was passed over a zeolite FU1 catalyst in a glass unit laboratory reactor at 4500C and a WHSV on the feed of 3.6 hr-1.

Nitrogen was simultaneously fed through the reactor and a number of runs were made at various volume ratios of nitrogen: feedstock. The results are summarised in Table 2.

TABLE 2

Nitrogen: Ethyl- Xylenes lost para Ethylbenzene/ benzene by dis- Conversion of xylene in m-xylene destroyed proportionation m-xylene product volume ratio % % % % 1:1 90 18 54 19.5 2:1 89 19 53 19.3 4:1 85 8.3 45 19.2 6:1 81 (0.7)* 36 18.5 10:1 79 (3.7)' 32 18.0 * xylenes made.

From these results it can be seen that large proportions of the ethylbenzene are seiectively removed in the presence of xylenes.

EXAMPLE 2 Three runs were carried out in similar conditions to those used in Example 1. The feedstock having the composition (expressed as % by weight) Benzene 0.05 Toluene 2.18 Nonane 1.49 Ethylbenzene 7.8 Para-xylene 8.72 Meta-xylene 53.64 Ortho-xylene 23.15 Heavy Ends 2.96 (cuts s C10,s) The reaction conditions used in each run and the results obtained (the average of 6-hour runs) are summarised in Table 3.

TABLE 3

Run 1 Run 2 Run 3 Molar ratio of nitrogen:feedstock Nil 6:1 6:1 WHSV(hr-1) 3.6 3.46 4.63 Temperature ( C) 450 450 450 Product analysis (wt%) Benzene 4.01 2.94 2.51 Toluene 14.67 7.37 5.41 Nonane 0.05 0.22 0.34 Ethylbenzene 1.06 1.18 1.74 Para-xylene 16.35 17.83 17.23 Meta-xylene 38.47 44.42 46.57 Ortho-xylene 18.11 20.99 22.06 Heavy ends (C9's and C10's) 7.28 5.10 4.15 Ethylbenzene destroyed (%) 86.5 84.8 77.3 Xylenes lost by disproportionation (%) 14.7 2.7 (0.6)* Proportion of para-xylene in xylene produc (%) 22.4 21.4 20.1 k 5.0 2.3 1.83 S.F. 0.58 0.22 -0.04 Sev 1.39 0.65 0.408 * xylenes made "k" is the pseudo 1st order rate constant for conversion of m-xylene to p-xylene.

"S.F." is a measure of xylene loss by disproportionation xylene isomerisation "Sev"= K WHSV Both Examples 1 and 2 illustrate how the presence of nitrogen helps to reduce very substantially the amount of xylenes lost as ethylbenzene is destroyed.

EXAMPLE 3 A further laboratory experiment was carried out using a catalyst of the ZSM-5 type. The catalyst comprises 1 part ZSM-5 type zeolite and 8 parts alumina and the feedstock had the following composition (% by weight): Benzene 0.07 Toluene 1.88 Nonane 1.22 Ethylbenzene 22.83 Para-xylene 7.85 Meta-xylene 47.35 Ortho-xylene 18.79 The feedstock was passed over the catalyst in a glass unit laboratory reactor at a reactor temperature and pressure of 4000C and 200 psig respectively. Hydrogen was used as the inert diluent at a hydrogen:hydrocarbon volume ratio of 5:1. The run extended over 75 hours during which the weight hourly space velocity on the feed was varied. The results are summarised in Table 4.

TABLE 4

ANALYSIS OF PRODUCTS (%ET) Hours on WHSV Ethyl- Para- Meta- Ortho- Total Heavy line (hr-1) Gas Naphtenes Nonane Benzene Toluene benzene xylene xylene xylene Xylenes Ends 1 5 2.61 0.52 0.08 7.97 3.28 10.76 16.51 38.57 16.33 71.41 3.39 3 5 2.77 0.74 0.08 7.56 3.56 11.78 16.06 37.73 16.02 69.81 3.70 10 5 2.99 0.76 0.08 7.74 3.77 11.36 16.02 34.40 15.83 69.25 4.07 15 5 2.71 0.79 0.08 7.34 3.56 11.82 15.87 37.65 16.08 69.60 4.10 16 15 1.08 0.09 0.84 3.99 2.22 16.34 14.10 41.64 17.48 73.22 2.24 17 15 1.30 0.16 0.82 3.97 2.67 16.86 13.89 40.94 17.17 72.00 2.23 18 10 1.61 0.22 0.65 5.21 2.93 14.72 15.11 39.67 16.75 71.53 3.13 19 10 1.74 0.29 0.64 5.17 2.94 14.95 15.05 39.39 16.62 71.06 3.23 20 5 2.64 0.30 0.48 6.82 3.58 13.31 15.74 37.65 15.93 69.32 3.56 26 5 2.55 0.44 0.46 7.30 3.31 12.19 16.04 37.96 16.09 70.09 3.64 28 5 2.63 0.32 0.456 7.18 3.31 12.27 16.08 38.03 16.11 70.22 3.63 54 5 2.59 0.26 0.48 7.12 3.25 12.47 15.95 38.12 16.20 70.27 3.54 75 5 2.58 0.32 0.48 7.10 3.27 12.41 16.00 38.08 16.14 70.22 3.62

Hours Para-xylene Ethyl-benzene Xylenes Ethyl-benzene on Xylenes in xylene destroyed destroyed destroyed line Lost % product % % % Xylenes destroyed 1 2,58 23,12 52,87 3,49 15,15 3 4,18 23,01 48,40 5,66 8,57 10 4,74 2,13 50,24 6,41 7,84 15 4,39 22,80 48,23 5,93 8,13 Continued 16 0,77 19,26 28,43 1,04 27,34 from 17 1,99 19,29 26,15 2,69 9,72 above 18 2,46 21,123 35,52 3,32 10,70 19 2,93 21,18 34,52 3,96 8,72 20 4,67 22,71 41,70 6,31 6,61 26 3,90 22,88 46,61 5,27 8,84 38 3,77 22,90 46,25 5,10 9,07 54 3,72 22,70 45,38 5,03 9,02 75 3,77 22,79 45,64 5,10 8,95 As can be seen, substantial amounts of ethylbenzene in the feed are destroyed with reiatively low - loss of xylenes. Moreover, in comparing the results at WHSV = 5 hrl it can be seen that the % of ethylbenzene destroyed is substantially constant over the whole length of the run.

Claims (9)

1. A hydrocarbon conversion process which comprises contacting a feed of an alkylbenzene or a mixture of alkylbenzenes in the liquid or vapour phase with a catalyst comprising as crystalline aluminosilicate zeolite and in the presence of an inert gaseous diluent.

2. A process as claimed in claim 1 for the beneficial conversion of ethylbenzene which comprises contacting a feedstock comprising ethylbenzene at elevated temperature with a catalyst comprising a zeolite and in the presence of an inert gaseous diluent.

3. A process as claimed in claim 1 or 2 in which the feedstocl: is a mixed xylenes-ethylbenzene feedstock.

4. A process as claimed in claim 3 in which the ethylbenzene content of the feedstock is in the range of about 6% to 25% by weight.

5. A process as claimed in any one of the preceding claims in which the catalyst comprises a zeolite selected from zeolite FU-1, a zeolite of the ZSM-5 family, ZSM35 5 or ZSM-38.

6. A process as claimed in any one of the preceding claims in which the inert gas is selected from nitrogen, helium, argon and hydrogen.

7. A process as claimed in any one of the preceding claims in which the process operating conditions include a temperature in the range 300 to 8000 C, a reaction pressure in the range 1 to 160 Bar, a weight hourly space velocity in the range 1 to 50 and a volume ratio of inert gas to alkylbenzene feedstock in the range 1 to 10.

8. A process for hydrocarbon conversion substantially as hereinbefore described with reference to any one of Examples 1 to 3.

9. Hydrocarbons whenever produced by a process as claimed in any one of the preceding claims.