GB2156379A - Alkylation of aromatic hydrocarbons - Google Patents

Abstract

This invention relates to a process for the alkylation of aromatic hydrocarbons in the presence of tectometallosilicates e.g. zeolites of the TON-1 type. The alkylating agent is an aliphatic compound capable of supplying the alkyl group under the reaction conditions e.g. 200-800 DEG C and 0.1-20 bar pressure. The process is capable of producing products rich in the para-substituted alkylaromatic isomer.

Description

SPECIFICATION Alkylation of aromatic hydrocarbons The present invention relates to a process for the alkylation of aromatic hydrocarbons in the presence of tectometallosilicates, such as zeolites.

Zeolites are well known natural and synthetic compositions. Many of them have been demonstrated to have catalytic properties for various types of hydrocarbon and related reactions. Zeolites can be defines as ordered porous crystalline aluminosilicates having a framework structure sufficiently open to accommodate at least water molecules. Such structures generally contain a regular array of small voids interconnected by channels or pores. The dimensions of the voids and channels can range from those of a water molecule to those of quite large molecules. For a given framework structure, the dimensions of the voids and channels are limited to a small number of values, which can vary from structure to structure.

Thus these structures are capable of absorbing molecules of certain dimensions while rejecting those of dimensions larger than a critical value which varies with structure. This had led to zeolites being used as molecular sieves. Zeolites belong to a class of materials that can be termed tectoaluminosilicates which comprise (in addition to zeolites) felspars and felspathoids. Zeolites have a framework structure consisting of a rigid regular three dimensional network of SO4 and Al04 tetrahedra in which the tetrahedra are cross-linked by sharing the oxygen atoms. All oxygen atoms are shared, thus the ratio of total aluminium and silicon atoms to oxygen atoms is 1:2.The inclusion of aluminium in the framework leads to a net negative charge which is balanced by the inclusion in the crystal of an electrochemical equivalence of cations, for example alkali metal, alkaline earth metal, hydrogen or ammonium cations or mixtures thereof. This can be expressed by a formula in which the ratio of Al to the number of the various cations such as Ca/2, Sr/2, Na, K, Li or generally M/n (where n is the formal oxidation state of the cation) is equal to unity. Additionally in zeolites, but not in felspars and some felspathoids, the framework is sufficiently open to accommodate water molecules as well as cations. This enables these cations to be exchanged in their entirety or partially by other cations using ion-exchange techniques in a conventional manner.

These materials can exhibit specific affinities for specific cations and can thus be used as selective ionexchangers. By means of ion-exchange, it is possible to vary the size of the pores in a given crystalline zeolite material, modifying its molecular sieve properties. Also be means of ion-exchange the catalytic properties of these materials can be altered. In addition to the framework and charge-compensating cations, zeolites can contain other materials such as water and organic molecules, (hydrated) salts and oxides of e.g. Na, Al and Si introduced during synthesis, or formed or added during subsequent treatments.

Zeolites are best characterised according to framework structure type, i.e. on the topology of the framework, irrespective of composition, distribution of different tetrahedral atoms, cell dimensions and symmetry. A code consisting of three capital letters has been adopted for each known structure type following the recommendations by IUPAC on zeolite nomenclature ("Chemical Nomenclature, and Formulation of compositions, of Synthetic and Natural Zeolites, "IUPAC yellow booklet, 1978) and a compilation of 38 known zeolite structure types has been published by The Structure Commission of the International Zeolite Association ("Atlas of Zeolite Structure Types",by Meier, W.M. and Olsen, D.H.

(1978), distributed by Polycrystal Book Service, Pittsburgh, Pa, USA). In addition to the groups classified by known structure type, there is a further group of crystalline zeolite materials whose X-ray diffraction patterns, sorption, ion-exchange and related properties indicate that they do not have known structure types but appear to have new, as yet undetermined structure types. An example of such a material is the novel porous crystalline aluminosilicate designated Theta-l and described in our published European patent specification No. 0057049.

Zeolites (and other tectoaluminosilicates) belong to a larger class of materials that can be termed tectometallosilicates which can be defined in the same way as tectoaluminosilicates except that the aluminium is replaced by a range of elements, which includes, it is claimed, Ti, Zr, V, Cr, Mo, Mn, Fe, Co, Rh, Ni, Zn, B, Al, Ga, Ge, Sn, As and Sb, but in some cases the claimed materials have not been well characterised. In some cases (where the element has the same formal oxidation state as Si i.e. +4) the resultant framework is electroneutral and the resultant materials resemble crystalline silicas. In other cases there is a resultant framework negative charge which must be compensated by cations as in tectoaluminosilicates. In some cases the materials have porous frameworks like those of zeolites or porous crystalline silicas which they therefore resemble.

Use of modified aluminosilicates for the alkylation of aromatics is known. In particular, the use of MFItype aluminosilicates in such processes is described for instance in US Patent Nos. 4100215 and 4238630 and GB 1574523. However, in each of these cases the MFI-type aluminosilicate has to be modified by the introduction of other species such as inorganic oxides in order to obtain a high selectivity to para-substituted alkyl aromatics.

Generally, the formation of ortho- and meta-substituted aromatics over un-modified MFI-type aluminosilicates has to be suppressed by appropriately modifying the aluminosilicate.

Theta-l-type aluminosilicates, as described in our European Patent Publication NO. 0057049 are expected to have similar catalytic properties to MFI-type aluminosilicates because of very similar physicochemical properties. MFI- and Theta-l-type aluminosilicates can be prepared with very similar Si02:AI203 ratios and with near identical shape-selective sorption characteristics. For example, they both adsorb and desorb xylenes. They both can be prepared from very similar starting gels (inciuding the same template such as diethanolamine) subjected to identical digestion parameters, see for example our European Patent Publication No 0057049.Thus it could be reasonably expected that alkylation of aromatic hydrocarbons over an un-modified hydrogen-form of Theta-l aluminosilicate should lead to a mixture of alkyl aromatics if exposed to conditions under which the un-modified hydrogen-form of MFI-type aluminosilicate leads to the formation of such mixed alkyl aromatics.

Surprisingly, it has now been found that hydrogen-form Theta-l type aluminosilicates and other tectometallo- silicates of similar structure can, without further modification, alkylate aromatic hydrocarbons selectively to p-alkyl substituted aromatic hydrocarbons.

Accordingly, the present invention is a process for the alkylation of an aromatic hydrocarbon with an aliphatic compound capable of supplying the alkyl group under the reaction conditions in the presence of a tectometallosilicate at an elevated temperature characterised in that the tectometallosilicate has the following composition in terms of the mole ratios of the oxides:

wherein M is at least one cation having a valence n, m is the valency of the metal X in the metal oxide, X is one or more of the metals selected from Al, Ga, Zn, Fe, Cr and B, x is at least 10, y/x is from 0 to 5, Q is a template used in the synthesis of the tectometallosilicate and z/x is 0-20, and the tectometallosilicate in its organo-free hydrogen-form has an X-ray diffraction pattern substantially as set forth in Table A of this specification.

Thus the tectometallosilicates used in the present invention have a Theta-l-type structure as described in our European Patent Specification No. 0057049.

By the term "organic-free hydrogen form" is meant here and throughout this specification that the tectometallosilicate has been rendered substantially free of organic material introduced during synthesis or subsequent treatments, and the cation M is hydrogen. The tectometallosilicates prepared from organic bases contain organics as synthesised and these can suitably be removed by calcination in air. The tectometallo- siiicates prepared from ammonia do not contain organics as synthesised. Therefore, in such a case, an organics removal step such as calcination in air is not essential.

The H20 content "y" of the tectometallosilicate is the water of hydration and will depend, within the ratios set out above, upon the conditions under which it is dried, calcined, subjected to further aqueous treatments or combinations thereof after synthesis. The H2O content "y" does not include water which may be notionally present when the cation M is hydrogen.

The 'template' is a chemical agent, e.g. an organic or inorganic base which encourages crystallisation to proceed towards a particular framework structure or structures.

The content "z" of template "0" in the tectometallo- silicate will also depend upon the conditions under which it is washed, calcined or subjected to further aqueous treatments or combinations thereof after synthesis, and also on the synthesis parameters of the gallosilicate, particularly the proportion of 0 present in the original hydrogel. The molar ratio of the template 0 to silica, i.e. zlx is preferably 0-5 in the tectometallosilicate as synthesised. The template content is usually highest for the "parent" tectometallosilicate. Complete removal of the template, if present, is usually only possible by thermal or oxidative degradation or both.

By the "parent" tectometallosilicate is meant throughout this specification the product of synthesis and washing and optionally drying.

The cation present in the tectometallosilicate used to catalyse the alkylation is most preferably hydrogen though the hydrogen ion may be replaced using conventional ion exchange techniques either wholly or partially by other cations e.g. metal cations without adversely affecting the selectivity to parasubstituted isomers.

The organic-free hydrogen-form of the tectometallosilicate may be produced by known methods such as exchange with hydrogen ions or with ammonium cations followed by one or more calcinations or a combination of the two followed by one or more calcination stages, if the tectometallosilicate still contained ammonium ions.

The metal X in the metal oxide XO2 is preferably Al, Ga, Zn or Cr. In the tectometailosilicate the molar ratio of silica to metal Xis preferably from 20:1 to 500:1.

The tectometallosilicates according to the present invention have in their organic-free hydrogen form an X-ray diffraction pattern shown in Table A below. The specific values in the Table were determined using copper K-alpha radiation and a computer step scan.

The peak heights, I, and their position as a function of 2-theta, where theta is the Bragg angle, were read from the spectrometer output. From this output the relative intensities 100 x ills, where Ia is the intensity of the strongest peak, and d the interplanar spacing in A, corresponding to the recorded peaks were calculated.

It will be understood by those skilled in the art that the X-ray diffraction pattern of tectometallosilicates may vary in the values of I/I, and the d-spacing depending for example upon whether the sample being examined is calcined or uncalcined, upon the temperature of calcination, upon the nature of the cation present in the tectometallosilicate, the mole ratio of silica to metal oxide, and the particle size of the tectometallosilicate.

The tectometallosilicate is suitably produced by mixing a source of silica, a source of gallia, a source of alkali metal(s), water and an organic or inorganic nitrogen containing base until a homogeneous gel is formed and crystallising the gel at a temperature above 70"C.

The tectometallosilicate may be used as such or bound in a suitable binder to improve its active life.

TABLE A 2-theta d-spacing Relative Intensity (degrees) (Angstroms) 100 x l/lo 8.06 t 0.2 11.25 - 10.70 50 to 100 10.06 + 0.2 9.01 - 8.63 5 to 30 12.69 + 0.2 7.09 - 6.87 10 to 30 16.28 + 0.2 5.51 - 5.38 5 to 15 19.40 j 0.2 4.62 - 4.53 5 to 15 20.26 + 0.2 4.43 - 4.34 50 to 100 24.11 t0.2 3.72- 3.66 50to100 24.52 + 0.2 3.66 - 3.60 30 to 90 25.65 t 0.2 3.50 - 3.45 15 to 45 scanned up to 2 theta = 32 The aliphatic compound capable of supplying the alkyl group under the reaction conditions may be represented by the formula RX, wherein R is a saturated alkyl group or an unsaturated alkylene group having 1-20 carbon atoms and X is selected from the groups H, -OH, OR" -CHO, -CO.R1, -COOH, -COOR, and a halogen atom such that R, is an alkyl group having 1-20 carbon atoms and is the same as or different from R. A mixture of aliphatic compounds represented by the formula RX may also be used for alkylation.

Specific examples of such compounds include ethylene, propylene, methanol, ethanol, propanol, butanol, dimethyl ether, diethyl ether and derivatives thereof, acetone, methylethylketone, diethyl ketone, acetic acid, propionic acid, butyric acid and esters thereof, and methyl and ethyl chlorides.

The aromatic hydrocarbons which can be alkylated may already carry lower alkyl substituents such as C,-C4 alkyl groups.

The alkylation reaction is suitably carried out from 200-800 C preferably from 300-700"C.

The alkylation reaction may be carried out at reduced or elevated pressure, suitably from 0.1-20 bar pressure, preferably from 0.5-10 bar pressure.

The liquid hourly space velocity (LHSV) of the feedstock over the tectometallosilicate is suitably in the range of 0.01-1000 per hour.

The products of the a\kylation reaction are principally alkyl aromatics which are rich in the para-substituted isomer.

The present invention is further illustrated with reference to the following Examples.

EXAMPLES A. Catalyst Preparation Theta-1 tectometallosilicate was synthesised as described in our European Patent Publication No.

0057049.

1. (i) A solution was prepared from a mixture of sodium aluminate (12.6g), sodium hydroxide (6.65g) and water (140g). Diethanolamine (DEA, 180g) was melted and added to the solution and the resultant solution "X" was stirred and maintained at room temperature. 500g of a commercial silica sol., 'Ludox AS40' (Reg. Trade Mark) which contains 40% by weight of silica, was further diluted with (354g) water to form solution "Y". Thereafter solution Y was added dropwise to solution X over a period of 15 minutes with vigorous stirring.Stirring was continued for a further 20 minutes and then the resultant gell which had the composition: 2.64 NA2O : 35 (DEA) : Awl203: 68.0 Six2: 890 H2O was transferred to an oven and crystallised with agitation at 175"C for 48 hours in a revolving stainless steel pressure vessel. The product was filtered, washed and dried at 90"C.

(ii) The dried product was transferred to an oven and heated to 550"C over 4 hours the maintained at 550"C for 60 hours then cooled. The calcined product was then refluxed in 10 volume per cent aqueous nitric acid for 2.5 hours, filtered, washed then refluxed in 0.67 M aqueous ammonium nitrate for 4 hours.

In both refluxes the solution: zeolite weight ratio was 6:1. The product was filtered, washed, dried at 90"C then transferred to an oven, heated to 550"C over 4 hours, maintained at 550"C for 16 hours then cooled.

The X-ray powder diffraction pattern of the resultant material is shown in Table 1 and shows the product to be good crystalline Theta-1. The resultant material was mixed with twice its weight of Ludox AS40 and just sufficient distilled water to wet the mixture. The resulting slurry was dried at 90"C and the resultant cake was broken and sieved to 12 to 30 mesh BSS.

TABLE 1 2-theta d Relative Intensity (degrees) (Angstroms) I/lo (%) 8.15 10.85 100 10.15 8.72 17 12.77 6.93 17 16.35 5.42 10 19.41 4.57 11 20.34 4.37 84 24.19 3.68 88 24.63 3.61 54 25.72 3.46 28 35.59 2.52 21 Scanned up to 2-theta = 36 and l/l,% = 10 or more B. Theta-1 tectometailosilicate was synthesised as described in our European Patent Publication No.

0104800.

(i)A solution was prepared from a mixture of sodium aluminate (15g), and sodium hydroxide (7.8g) in water (120g).

Aqueous ammonia solution (700g containing 25% w/w ammonia) was added to the solution and the resultant solution "B"was stirred for 5 minutes at room temperature.

600g of a commercial silica gel Ludox AS 40 (Regd. Trade Mark), which contains 40% by weight of silica was added to solution B, over 10 minutes with vigorous stirring and stirring was continued for a further 20 minutes. The resultant gel of composition 2.70Na20:85(NH4)20: Al203:66.3Si02:842H20 was transferred to a stainless steel pressure vessel and crystallised with agitation at 170"C for 48 hours. The product was filtered, washed and dried at 90"C. It was found by X-ray diffraction, to be very good crystalline Theta-1.

(ii) The product was converted to the hydrogen form using the procedure described above in A(ii).

However the catalyst was bound as follows: the zeolite powder was pressed into pellets which were broken and sieved to 12 to 30 mesh BSS (no amorphous silica was added).

C. Comparative Test (i)ZSM-5 type zeolite with Si02/AI203 = 70 molar was synthesised according to USP 3702 886. The X-ray diffraction patterns of the product was typical of that of ZSM-5 zeolite.

(ii) the product was converted to the hydrogen form and a catalyst was prepared as described in B(ii) above.

Examples 1 to 4 and Comparative Test Each of the catalysts prepared as in paragraphs A, B and C above respectively were loaded into a reactor and a mixture of toluene and methanol (2:1 molar ratio) was passed at an LHSV of 1 hour-1 and various temperatures. Table 2 shows products obtained from catalysts A and B at various temperatures.

Table 3 shows a comparison of the products in the present invention and a comparative catalyst C at 600"C.

Examples 5 and 6 A mixture of benzene and methanol (2:1 molar ratio) was passed over catalyst A at 1 hourq LHSV and temperature of 550"C and 600"C. The products of the reaction are shown in Table 4.

Table 2 Alkylation of Toluene with Methanol LHSV = 1 hr'l Feed 2 moles Toluene:1 mole Methanol

Examples 1 2 3 4 Catalyst B A B A Temperature C 450 550 600 650 Product wt% wt% wt% wtZ Benzene j 0.0 0.7 0.2 1.2 Toluene 81.4 70.8 75.4 67.3 p-Xylene 8.0 (0.53) 10.2 (0.45) 12.0 (0.57) 12.1 (0.43) m-Xylene 3.3 (0.22) 6.5 (0.29) 3.9 (0.19) 8.4 (0.30) o-Xylene 3.7 (0.25) 6.0 (0.26) 5.1 (0.24) 7.4 (0.26) Polymethyl ) 3.6 1 4.0 3.4 3.3 benzene and) higher ) Figures in brackets show the proportions of the specific isomers in the total xylene yield.

Table 3 Alkylation of Toluene with Methanol LHSV = 1 hr'l Feed 2 moles Toluene:l mole Methanol 6000C

Catalyst C C B Comparative Comparative Example 3 Test Test Time on Stream 0.25 3 1 hr hr Product wt% wt% wt% Benzene 28.1 1.5 0.2 Toluene 42.6 75.2 75.4 p-Xylene 4.2 (0.23) 10.2 (0.49) 12.0 (0.57) m-Xylene 9.3 (0.51) 7.4 (0.36) 3.9 (0.19) o-Xylene 4.8 (0.26) 3.1 (0.15) 5.1 (0.24) Polymethyl 10.7 2.6 3.4 benzene and higher Figures in brackets show the proportions of the specific isomers in the total xylene yield.

Table 4 Alkylation of Benzene with Methanol LHSV = 1.0 her 1 2 mole Benzene:lmole Methanol

Example 5 6 Catalyst A A Temperature "C 550 600 Products wt% wt% Benzene 46.1 53.0 Toluene 35.5 34.2 p-Xylene 6.5 (0.47) 3.5 (0.41) m-Xylene 3.7 (0.27) 2.2 (0.26) o-Xylene 3.4 (0.26) 2.8 (0.33) Polymethyl 4.7 4.1 benzene and higher Figures in brackets show the proportions of the specific isomers in the total xylene yield.

From the above data it can be seen that for similar conversion rates, the catalysts used in the process of the present invention give rise to a higher amount of the para-isomer in the product than that in the comparative tests. Moreover, the higher yield is achieved over a shorter reaction time (cf. Comparative Test using Catalyst C over 3 hours on stream with Example 3, Table 3). In addition the make of benzene is less with Theta-1.

Claims (10)

1. A process for the alkylation of an aromatic hydrocarbon with an aliphatic compound capable of supplying the alkyl group under the reaction conditions in the presence of a tectometallosilicate at an elevated temperature characterised in that the tectometallosilicate has the following composition in terms of the mole ratios of the oxides:

wherein M is at least one cation having a valence n, m is the valency of the metal X in the metal oxide, X is one or more of the metals selected from Al, Ga, Zn, Fe, Cr and B, x is at least 10, y/x is from 0 to 5, Q is a template used in the synthesis of the tectometallosilicate and z/x is 0-20, and the tectometallosilicate in its organo- free hydrogen-form has an X-ray diffraction pattern substantially as set forth in Table A of this specification.

2. A process according to claim 1 wherein the cation in the tectometallosilicate is hydrogen.

3. A process according to claim 1 or 2 wherein the molar ratio of silicon to metal X in the tectometallosilicate is from 20:1 to 500:1.

4. A process according to any one of the preceding claims wherein the aliphatic compound capable of supplying the alkyl group under the reaction condition is represented by the formula RX, wherein R is a saturated alkyl group or an unsaturated alkylene group having 1-20 carbon atoms and X is selected from the groups H, -OH, OR1, -CHO, -CO.R1, -COOH, -COOR, and a haolgen atom such that R, is an alkyl group having 1-20 carbon atoms and is the same as or different from R.

5. A process according to claim 4 wherein the aliphatic compound capable of supplying the alkyl groups is selected from ethylene, propylene, methanol, ethanol, propanol, butanol, dimethyl ether, diethyl ether and derivatives thereof, acetone, methylethylketone, diethyl ketone, acetic acid, propionic acid, butyric acid and esters thereof, and methyl and ethyl chlorides.

6. A process according to any one of the preceding claims wherein the alkylation reaction is carried out from 200-8000C.

7. A process according to any one of the preceding claims wherein the alkylation reaction is carried out at a pressure of 0.1-20 bar.

8. A process according to any one of the preceding claims wherein the liquid hourly space velocity of the feedstock over the tectometallosilicate is in the range of 0.1-1000 per hour.

9. A process for the alkylation of aromatics according to any one of the preceding claims whereby the reaction product is rich in the para-substituted alkyl aromatic isomer.

10. A process for the alkylation of aromatics as claimed in claim 1 and as hereinbefore described with reference to the Examples.