Production of aromatics from hydrocarbon feedstock

This invention relates to the aromatization of methane rich hydrocarbon feedstock by contact with a gallium loaded zeolite containing a Group VIIB metal or metal compound as catalyst. The preferred metal is rhenium. The reaction proceeds at a temperature between 600.degree.-800.degree. C. in the absence of oxygen. The reaction products are useful as gasoline blending components.

The present invention relates to a process for producing liquids rich in 
aromatic hydrocarbons from a hydrocarbon feedstock containing a major 
proportion of methane. 
Hitherto synthetic routes to producing aromatics from open chain 
hydrocarbons have started from feedstocks which have at least two carbon 
atoms. Such feedstocks are initially dimerised or oligomerised and the 
dimerised or oligomerised product is subsequently cyclised over a variety 
of catalysts at temperatures in the region of 500.degree.-600.degree. C. 
Such processes are described for example in our British Pat. Nos. 1507778 
and 1561590. According to the British Pat. No. 1561590 a gallium catalyst 
supported on an aluminosilicate in which the ratio of silica to alumina is 
between 20:1 and 70:1 is used. 
It has now been found that aromatics may be produced from hydrocarbon 
feedstocks containing less than two carbon atoms. 
Accordingly, the present invention is a process for producing liquids rich 
in aromatic hydrocarbons comprising bringing into contact at a temperature 
between 600.degree. C. and 800.degree. C. a hydrocarbon feedstock 
containing a major proportion of methane with a catalyst composition 
comprising an aluminosilicate having silica to alumina in a molar ratio of 
at least 5:1, said aluminosilicate being loaded with (i) gallium or a 
compound thereof and (ii) a metal or a compound thereof from Group VIIB of 
the Periodic Table. 
The term "Periodic Table" referred to herein refers to the table appearing 
at pages 448 and 449 of the Handbook of Chemistry and Physics, Ed. 
Hodgman, C. D. et al and published by The Chemical Rubber Publishing 
Company, Cleveland, Ohio, USA (44th Edition), 1963. 
The hydrocarbon feedstock has at least 50% w/w, preferably at least 70% w/w 
of methane and may be admixed with C.sub.2 hydrocarbons. The C.sub.2 
hydrocarbon in the feedstock, if any, may be ethane, ethylene or mixtures 
thereof. The feedstock may contain in addition other open chain 
hydrocarbons containing between 3 and 8 carbon atoms as coreactants. 
Specific examples of such additional coreactants are propane, propylene, 
n-butane, isobutane, n-butenes and isobutene. 
The aluminosilicate in the catalyst composition may be suitably zeolites 
e.g. those having an MFI type structure (cf. "Chemical Nomenclature, and 
Formulation of Compositions, of Synthetic and Natural Zeolites," IU 
yellow booklet, 1978, and zeolite structure types published by The 
Structure Commission of the International Zeolite Association entitled 
"Atlas of Zeolite Structure Types", by Meier, W. M. and Olsen, D. H. 
(1978), distributed by Polycrystal Book Service, Pittsburgh, Pa, USA). The 
zeolites suitably have a silica to alumina ratio from 20:1 to 200:1 and 
may be represented by the general formula M.sub.2/n O.Al.sub.2 
O.sub.3.ySiO.sub.2 zH.sub.2 O wherein M is a cation which is a positively 
charged ion selected from a metal ion or an organic ion of valence n and a 
proton, y is an integer greater than 5 and z is from 0 to 40. The metal 
cation, M, is preferably an alkali metal or alkaline earth metal ion, 
preferably sodium or potassium ions. The organic cations may be 
represented by the formula R.sup.1 R.sup.2 R.sup.3 R.sup.4 N.sup.+ or by 
an ion derived from the amine R.sup.1 R.sup.2 R.sup.3 N, the diamine 
R.sup.1 R.sup.2 N(CH.sub.2).sub.x NR.sup.3 R.sup.4 or pyrrolidine where 
R.sup.1 R.sup.2 R.sup.3 and R.sup.4 may be H, CH.sub.3, C.sub.2 H.sub.5, 
C.sub.3 H.sub.7, C.sub.4 H.sub.9 or --CH.sub.2 CH.sub.2 OH and x equals 2, 
3, 4, 5 or 6. A typical example of an MFI zeolite is ZSM-5 although other 
zeolites, for example ZSM-8, ZSM-11, ZSM-12 and ZSM-35 may also be used. 
These zeolites are extensively described in a number of publications 
including U.S. Pat. No. 3,970,544 (Mobil). These zeolites are usually 
produced from a silica source, an alumina source, an alkali metal 
hydroxide and a nitrogen containing base as template. The 
nitrogen-containing base may be organic such as an alkanolamine, for 
example, diethanolamine or, inorganic e.g. ammonia. Zeolites made in this 
manner are described in our published European Patent Application Nos. 
0002899, 0002900 and 0030811. Zeolites derived by the process of No. 
EP-A-30811 are preferred. 
The gallium or gallium compound in the catalyst composition may be gallium 
oxide or it may be present as gallium ions if the cations in the 
aluminosilicate have been exchanged for gallium ions. Methods of loading 
zeolites with a gallium compound are well known and is published for 
instance in our No. EP-A-24930. The gallium ion or compound loaded zeolite 
may be reduced to metallic gallium during subsequent reduction treatment, 
if any, prior to contact with the feedstock. 
Similarly, a metal or a compound thereof from Group VIIB of the Periodic 
Table may be incorporated into the catalyst composition by impregnation or 
ion-exchange. Specifically, the preferred metal is rhenium which may be 
present in the catalyst composition as the oxide, as an ion or as the 
reduced metal. The metals, oxides or ions may be suitably provided from a 
solution e.g. aqueous solution, of the respective metal salt such as for 
instance rhenium trichloride or ammonium perrhenate which may be 
subsequently oxidised or reduced prior to contact with the feedstock. 
Alternatively the gallium loaded zeolite may be intimately mixed with a 
Group VIIB metal compound. 
The aluminosilicate may be loaded with the compounds of gallium and the 
Group VIIB metal in either order or a mixture of the two compounds may be 
used for simultaneous loading of the aluminosilicate. It is preferable to 
load the aluminosilicate with the Group VIIB metal compound prior to the 
addition of the gallium compound. 
Whichever method of catalyst preparation is used, the amount of gallium 
present in the catalyst compositions may vary for instance from 0.05 to 
10% by weight of the total aluminosilicate in the catalyst composition. 
The gallium exchanged or impregnated zeolite thus obtained may be combined 
with a porous matrix, e.g. silica or alumina or other inorganic 
compositions to improve the mechanical strength of the catalyst. 
The amount of Group VIIB metal present in the catalyst composition is 
suitably from 0.05 to 10%, preferably from 0.1 to 1.0% w/w of the total 
composition. 
The catalyst composition may be activated prior to contact with the 
hydrocarbon feedstock. The activation may be carried out by heating the 
catalyst at a temperature from 400.degree. C. to 650.degree. C., 
preferably from 500.degree. C. to 600.degree. C. Activation may be carried 
out in an atmosphere of hydrogen, air, steam or a gas inert under the 
reaction conditions such as nitrogen but preferably in an atmosphere 
containing hydrogen. The activation may be carried out in the reactor 
itself prior to the reaction. The catalyst composition is suitably used in 
a fixed bed, a moving bed or a fluidised bed. 
The hydrocarbon feedstock is thereafter contacted in the vapour phase with 
the catalyst composition at a temperature from 600.degree. to 800.degree. 
C. preferably from 650.degree. to 775.degree. C. in the absence of oxygen. 
The reaction is suitably carried out at a pressure of 1-10 bar, preferably 
from 3-7 bar absolute. The weight hourly space velocity (WHSV) is suitably 
from 0.1-10, preferably from 0.5-5.0. Any unreacted methane recovered from 
the reaction products may be recycled to the aromatisation reaction. 
The reaction products are useful as gasoline blending components.

The invention is further illustrated with reference to the following 
Examples. 
In the Examples the following notations have been used: 
##EQU1## 
EXAMPLE 1 
A sample of an MFI type zeolite containing ammonium cations (zeolite 
prepared using ammonia as template according to the general process of our 
published No. EP-A-0030811) was contacted with an aqueous solution of 
ReCl.sub.3. The mixture was dried under vacuum at 130.degree. C. 
The rhenium impregnated zeolite was then contacted with an aqueous solution 
of gallium nitrate and dried under vacuum at 130.degree. C. 
The gallium/rhenium impregnated zeolite was bound in an inert silica matrix 
by mixing with an equal weight of LUDOX AS 40 (Registered Trade Mark) 
colloidal silica to obtain a slurry which was dried at 100.degree. C. to 
give a hard cake which was broken up and sieved to give coarse particles 
which passed through a standard 12 mesh sieve but were retained by a 30 
mesh sieve. This gave a final catalyst composition containing 0.7% w/w Ga 
and 0.4% w/w Re. These compositions were determined by X-ray fluorescence 
spectroscopy. 
6.2 ml of this catalyst composition was taken and then loaded into a 
vertical fixed bed reactor. The catalyst composition was contacted with 
nitrogen and the temperature of the reactor raised to 600.degree. C. over 
45 minutes. 
The catalyst composition was then contacted with H.sub.2 at 600.degree. C. 
for 2 hours prior to testing for methane aromatisation by contacting with 
methane at 700.degree. C., 1 WHSV and 7 bar absolute pressure (CT-9.0 
secs). 
Analysis of the reaction products was carried out using an on-line, dual 
column gas chromatograph (POROPAK QS and OV101 silicone gum rubber 
columns) and the following results were obtained. 
______________________________________ 
CONVERSION SELECTIVITY 
OF TO AROMATICS 
METHANE AROMATICS YIELD 
Wt % Wt % Wt % 
______________________________________ 
4.9 51.6 2.53 
______________________________________ 
EXAMPLE 2 
The catalyst composition was prepared and activated as in Example 1 above 
and tested for aromatisation of methane at 675.degree. C., 1 WHSV and 7 
bar absolute pressure (CT-9.25 secs) as in Example 1 above. 
______________________________________ 
CONVERSION SELECTIVITY 
OF TO AROMATICS 
METHANE AROMATICS YIELD 
Wt % Wt % Wt % 
______________________________________ 
3.6 54.7 2.0 
______________________________________ 
EXAMPLE 3 
The catalyst composition was prepared and activated as in Example 1 above 
and tested for the aromatisation of methane at 750.degree. C., 1 WHSV and 
7 bar absolute pressure (CT 8.6 secs) as described in that Example. 
______________________________________ 
CONVERSION SELECTIVITY 
OF TO AROMATICS 
METHANE AROMATICS YIELD 
Wt % Wt % Wt % 
______________________________________ 
8.3 35.4 2.95 
______________________________________