Atkins M. P.

Gregory R.

Westlake D. J.

English

University of Szeged

- THE USE OF LAYERED CLAYS FOR THE PRODUCTION OF PETROCHEMICALS D.J. Westlake, M.P. Atkins, R. Gregory BP Research Centre, Sunbury-Upon-Thames, Middlesex, England ABSTRACT Some exchanged Wyoming montmorlllonlte clays are effective catalysts for the alkylatlon of benzene with propene or ethylene in the liquid phase. Under these conditions the clay catalysts give equilibrium product distributions. In contrast zeolites are generally poor catalysts and do not give equilibrium product distribution under these mild conditions. INTRODUCTION The alkylatlon of benzene by propene and ethylene is widely practised in the petrochemical industry. Cumene has been manufactured on a large scale for more than 40 years, firstly as a high octane component for aviation gasoline and subsequently as an intermediate for the production of phenol. Ethylbenzene is also manufactured on a large scale as a precursor for the production of styrene. Acidic catalysts are used in the production of both cumene and ethylbenzene. The former is generally manufactured using a supported phosphoric acid catalyst in a fixed bed reactor with the reactants in the liquid phase although aluminium chloride and sulphuric acid catalysts have also been used (1,2). Ethylbenzene is generally produced using either aluminium chloride as catalyst with the reactants in the liquid phase or with a zeolite catalyst and the reactants in the vapour phase (3,4). There has recently been considerable interest in the application of layered montmorlllonlte clays as acidic catalysts so it seemed reasonable to examine these materials for the alkylatlon of benzene. Montmorlllonlte clays possess both Lewis and Br^nsted acid sites which are responsible for the diverse catalytic activity of these materials eg in ether formation from alcohols and alkenes, olefin hydration, ester formation from carboxylic acids and alkenes and many other reactions (5, 6,7). 301 The detailed structure of montmorillonlte minerals is still the subject of debate although it is generally agreed that they are formed from an octahedrally coordinated alumina sheet sandwiched between two tetrahedrally coordinated silicate sheets. The layers carry an overall negative charge which may arise from isomorphous substitution of Al3+ by Fe2+ or Mg2+ in the octahedral sheet and to a lesser extent of Si4+ by in the tetrahedral sheet. These negative charges on the layers are balanced by hydrated cations, usually Na+ or in the naturally occuring state, which are situated in the interlamellar space and which can be readily ion-exchanged. By suitable choice of cation the acidity and polarisation of coordinated water and other molecules in the interlamellar environment can be varied. The Bronsted acidity of the cation-exchanged clays can be accounted for by dissociation of coordinated water in the interlamellar space, M(H20)xn+ 5==^|M(0H)(H20)x_1](n-1)+ + H+ and Lewis acidity may arise from dehydroxylation of the framework hydroxyl groups, Si OH A1 heat .Si > \ 0 0 0 In this paper the performance of montmorillonlte clays is compared with zeolite catalysts for the alkylation of benzene with propene and ethylene. The generally accepted mechanism for aromatic alkylation is IT1" R-CH = CH9 RCH-CH, ® C % \ J / R C + H 0 where R = alkyl or H. 302 Further alkylation of the alkylated product can be reduced, If desired, by the use of large benzene:olefin reactant ratios. Alternatively, lower ratios can be used in commercial processes provided the catalyst chosen is also effective for transalkylatlon reactions such as R R ¿ 1 + 0 2 ® R since the unwanted polyalkyl-benzenes can be separated and recycled with fresh feed. EXPERIMENTAL Catalyst Preparation. Hydrogen and aluminium exchanged Wyoming montmorillonites were prepared by methods described previously (6,7). The zeolite catalysts were either synthesised by known methods or were commercial samples and converted to the hydrogen form by calcination of the ammonium form. The amorphous aluminosllicate (85.5% S102) was obtained from Strem Chemicals Incorporated. Apparatus• Alkylation experiments with both ethylene and propene were carried out in stainless steel autoclaves in the normal manner. The autoclaves were heated to the reaction temperature, held for 2.5 hours, and allowed to cool overnight. Continuous experiments were carried out with a premixed feed under pressure in a small continuous unit whose schematic flow diagram has been described previously (6). Analysis. All reaction products were analysed by capillary gas chromatography using calibration factors derived from authentic standards. RESULTS AND DISCUSSION Cumene. The performance of Wyoming montmorillonlte clay catalysts is compared with that of a range of zeolite and other catalysts for the alkylation of benzene with propene in Table 1. In these batch reactions the H"1" and exchanged Wyoming montmorillonlte clays gave complete conversion of propene at 150°C with the former giving virtually the same product over the temperature range 125° to 230°C. In contrast none of the other catalysts examined gave more than 65% propene conversion at 150°C. The best result was obtained with the commercial amorphous aluminosllicate and the worst with the large pore size zeollte-Y. 303 TABLE 1 FORMATION OF CUMENE FROM BENZENE AND PROPENE Reaction Propene Product Distribution Catalyst Temp Conversion °C % Benzene Cumene DIPB3 (MoleZ) (MoleZ) (Mole%) ff^-Montmorillonite 125 100 84.4 14.7 0.9 ff*"-Montmorillonite 150 100 84.3 14.7 1.0 ff^-Montmorillonite 230 100 84.3 14.7 1.0 A13+-Montmorillonite 150 100 85.6 13.9 0.6 H-Y Zeolite 150 5 99.3 0.7 tr H-Mordenite 150 20 97.8 2.0 0.2 H-MFI 150 25 96.7 3.3 tr Aluminosilicate 150 65 90.5 8.9 0.6 Reactants:- Benzene 120g, Propene lOg, Catalyst 5g, 0^:03 = 6:1 a) DIPB = di-isopropylbenzene In a second series of experiments the catalysts were compared for the reaction of benzene, propene and meta-di-isopropylbenzene (DIPB) in order to determine how much, if any, of the DIPB was transalkylated to give additional cumene (Table 2). Only ff^-Montmorillonite gave any significant conversion of DIPB under these conditions. The best result with the remaining catalysts was obtained with zeolite-Y whilst the TABLE 2 FORMATION OF CUMENE FROM BENZENE, PROPENE AND DIPBa Temp DIPB (Prod) Product Distribution Catalyst °C DIPB (React) Benzene (MoleZ) Cumene (MoleZ) DIPB3 (MoleZ) ff^-Montmorillonite 230 0.6 72.6 24.7 2.7 H-Y Zeolite 230 0.9 93.9 2.1 4.0 H-MFI 230 1.3 90.2 5.6 4.1 H-MFI 270 1.1 85.3 9.7 4.9 Aluminosilicate 230 1.1 83.5 11.7 4.8 Reactants:- Benzene 120g, Propene 12g, meta-DIPB 12g, Catalyst 5g a) DIPB = di-isopropylbenzene 50 r o 3 TJ o Q. c a o 2. 25 Cumenè C6 : C3 Mole ratio Figure 1. Calculated thermodynamic (solid lines) and experimental (plotted points) product distributions for the formation of cumene. TABLE 3 CONTINUOUS PRODUCTION OF CUMENE Catalyst Temperature (°C) Pressure (bar). LHSV (h_1) Feed (Mole %) benzene Propylene DIPB C6:C3 Product (Mole %) Benzene Cumene DIPB H^-Montmorillonite 190 30 2 . 1 82 15 2.1 5:1 79 + 1 18 ±.1 2.3 + .25 3 0 5 others gave a net production of DIPB. Thus, with the exception of the ff1" -Montmorillonite catalysed reaction, the initial DIPB behaves as an inert diluent in these systems. The reaction product distribution with the Wyoming montmorillonite catalyst in both sets of experiments is close to the calculated thermodynamic equilibrium. In Figure 1 the calculated and experimentally observed product distributions are plotted for a wide range of initial benzene and C3~alkyl fragment compositions. The experimental points were obtained from reactions using various combinations of propene, benzene and DIPB as the initial reactants and the calculated equilibrium compositions show little variation with temperature over the range 120° to 230°C which is in agreement with the experimental results in Table 1. The performance of the IT1"- Montmorillonite was also examined in the continuous production of cumene using a feed comprising benzene, propene, and DIPB. The product composition shown in Table 3 remained constant over a test period of 50 hours on stream at constant temperature and LHSV. The product composition was also close to the calculated thermodynamic value shown in Figure 1 Illustrating that equilibrium is also achieved in continuous reactions with this catalyst and a relatively short contact time. Ethylbenzene. The performance of Wyoming montmorillonite clay catalysts is compared with the H-MFI zeolite for the alkylatlon of benzene with ethylene In Table 4. In these batch reactions at 230°C where benzene is in the liquid phase both the IT1" and Al3+ Wyoming montmorillonite catalysts gave complete conversion of ethylene compared to only 20% with H-MFI. As In the earlier experiments with propene only the Wyoming montmorillonite clay catalysts give product distributions which are close to the calculated thermodynamic equilibrium composition. Thus, at a Cg:C2 ratio of 2.5 :1, the experimentally observed product distribution is ethylbenzene 28.4% and dlethylbenzene 5.5Z compared to 32.4% and 3.8% respectively for the calculated thermodynamic equilibrium. Reaction mechanism and catalytic activity. There would seem to be no reason to suggest that the generally accepted mechanism for the acid catalysed addition of an olefin to an aromatic ring should not be extended to reactions catalysed by Wyoming montmorillonite clay, zeolite, or alumlno8lllcate catalysts. All of these catalysts have acidic sites capable of supplying the necessary proton for formation of the carbonlum ion Intermediate. 306 TABLE 4 FORMATION OF ETHYLBENZENE Ethylene Product Distribution Catalyst Temp Convn °C % Benzene Ethyl- DEBa (Mole%) benzene (Mole%) (Mole%) H^-Montmorilloniteh 230 100 65.1 28 .4 6.4 Al3+-Montmorilloniteh 230 100 66.1 28 .4 5.5 H-MFIb 230 20 92.6 6 .3 tr H*"-Montmorillonitec 250 100 89.6 9 .8 0.6 a) DEB = diethylbenzene b) Reactants:- Benzene 120g, Ethylene to 40bar, Catalyst 5g c) Reactants:- Benzene 120g, Ethylene to 40bar, DEB 12g, Catalyst 5g It Is proposed that the substantial difference in catalytic activity between the clay and zeolite catalysts is due to the ready accessibility of the acidic sites to the reactants in the former case. In liquid phase reactions diffusional constraints for reactants or products will be greatest for catalysts with rigid mlcroporous structures such as zeolites. The expanding layer structure of the Wyoming montmorlllonlte clay catalysts allows access to the lnterlamellar acidic sites with few diffusional constraints and hence these have greater activity. Similarly the acidic sites on the amorphous alumlnosllicate are more accessible than those in the zeolite structure. It is known that zeolite catalysts such as MFI are effective for the vapour-phase alkylatlon and transalkylatlon of benzene and ethylene at 425°C (4). Under these conditions the diffusional constraints would probably be much less significant but collapse of the lnterlamellar space in Wyoming montmorlllonlte would decrease the activity. CONCLUSION It is concluded that Wyoming montmorlllonlte clays are effective catalysts for the alkylatlon of benzene with propene or ethylene in liquid phase reactions to give cumene and ethylbenzene respectively. Under these conditions, these catalysts are also effective for transalkylatlon 307 reactions thereby allowing recycle of unwanted polyalkylated products to extinction in commercial processes. They are also more effective than zeolite catalysts in these liquid phase reactions. ACKNOWLEDGEMENTS We thank the British Petroleum Company pic for permission to publish this paper.. REFERENCES 1. Brayford, D., Encyclopaedia of Chemical Processing and Design, Edited by McKetta, J.J., Dekker 1980, Vol 14. 2. McAllister, S.H., Anderson, J., Ballard, E.F., Chem. Eng. Progress, 1947, 43, 189. 3. MacFarlane, A.C., Oil Gas J,. 1976, 74(6), 99. 4. Hagopian, C.R., Lewis, P.J., McDonald, J.J., Hydroc. Proc., 1983, 62(2), 45. 5. Ballantine, J.A., Purnell, J.H., J. Molec. Catal., 1984, 27, 157. 6. Atkins, M.P., Smith, D.J.H., Westlake, D.J., Clay Miner., 1983, 18, 423. 7. Gregory, R, Smith, D.J.H., Westlake, D.J., Clay Miner., 1983, 18, 431. 308 

The use of layered clays for the production of petrochemicals

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The use of layered clays for the production of petrochemicals

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