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1 New Catalysts and New Processes in the Industrial Alkylation of Aromatics Giuseppe Bellussi*, Carlo Perego, Patrizia Ingallina EniTecnologie S.p.A., Via F. Maritano, San Donato Milanese MI, Italy 1. Introduction The alkylation of aromatic hydrocarbons with olefins is applied on a large scale in the chemical industry [1]. Consider that about 7% of the 29.3million tons accounting the world benzene demand in 1999, were expected to be consumed by acid catalyzed alkylation with ethylene and propylene, 53 and 17% respectively, for the production of ethylbenzene and cumene. Analogously, p- diisopropylbenzene, C 1 -C 14 linear alkylbenzenes, cymene, p-ethyltoluene and 4-t-butyltoluene are also important chemical intermediates obtained by acid alkylation of benzene or toluene aromatic ring. Finally, other chemical intermediates, such as 5-(o-tolyl)-pentene-2, isobutylbenzene and t- amylbenzene, are produced by side-chain alkylation of aromatics, catalyzed by base [2-3]. In many industrial processes these alkylations are still performed with catalysts showing drawbacks. Often such catalysts are strong mineral acids or Lewis acids (e.g.: HF, H 2 SO 4, and AlCl 3 ), which are highly toxic and corrosive. They are dangerous to handle and to transport as they corrode storage and disposal containers. Often, the products need to be separated from the acid with a difficult and energy consuming process. Finally, it occurs frequently that these acids are neutralized at the end of the reaction and therefore the correspondent salts have to be disposed. Similar problems arise when free bases are used as catalysts. In order to avoid these problems many efforts have been devoted to the search of solid acid and base catalysts more selective, safe, environmentally friendly, regenerable, reusable and which have not to be destroyed after reaction. The aim of this contribution is to summarize some examples of new industrial processes based on the aforementioned solid catalysts. 2. Alkylation of benzene to produce ethylbenzene In the traditional process, developed since 193s, the alkylation is performed reacting benzene and ethylene in the presence of a Friedel-Crafts catalyst (i.e. AlCl 3 -HCl) at mild conditions (T = 16 C). + single step (alkylation + transalkylation) low benzene/ethylene mild conditions (16 C;.7 Mpa; B/E =2.5) - corrosion acidic waste chlorinated impurities Figure 1. Pros and cons in the alkylation of benzene with ethylene catalyzed by AlCl 3. The advantages and the main problems concerning AlCl 3 technology are summarized in Figure 1. Starting from the mid-196s, different zeolite-based catalysts were extensively evaluated in benzene

2 alkylation with ethylene [4]. The first industrial application of a zeolite catalyst occurred in 1976 by Mobil-Badger. The process, commercialized since 198, uses the ZSM-5 zeolite as catalyst and operates above 4 C at 13-2 atm. At this conditions the feedstock is in gas phase. Later improvements were obtained introducing a) the liquid-phase alkylation and b) a separate step of transalkylation. The liquid phase has the advantage of a better thermal control and longer catalysts life which allow the off site catalyst regeneration and therefore an easier control of pollution. To do this it was necessary to move from medium pore zeolites like ZSM-5 to large pore such as Beta and Y [5-7]. In Figure 2 some results are reported about benzene alkylation with ethylene in the liquid phase [8]. The experiments were performed in plug flow fixed bed reactors at the conditions indicated. The catalyst samples used were a Beta zeolite having a SiO2/Al2O3 molar ratio around 28 and the ultra stable Y zeolite TSZ 33 HUA. The major remarks are the following: Beta zeolite produces more diethylbenzene and triethylbenzene than Y type zeolites, but the latter produces much more heavier by products, such as di phenyls and others Selectivity (%) 6 4 EB/Benzene (DEB+TEB)/Benzene EB/Ethylene (EB+DEB+TEB)/Ethylene Heavies/Benzene 1 Selectivity (%) 2.5 Beta USY T= 17 C; P = 3.5 Mpa ; B/E = 5; Conv C2 = 1% Figure 2. Benzene alkylation with ethylene catalyzed by zeolites. Therefore, considering the possibility to transalkylate the di and triethylbenzene, the overall selectivity to useful products is higher for zeolite Beta than for Y. The use of zeolite Beta as alkylation catalyst was independently claimed by EniChem in Europe and by Chevron researchers in USA. 6 5 T =18 C, P = 4.5 M Pa, B/E =4.5 Si/Al = 14 g/gcat/min Si/Al = 17.5 Si/Al = 112; Si/B= 4 Si/Al = 35 1 Si/Al = 41; Si/B= Si/(Al+B) Figure 3. Alkylation of benzene with ethylene catalyzed by Beta zeolite. Effect of catalyst composition.

3 It has also evidenced that the zeolite composition is very important with respect to the catalytic behavior [8]. In fact, increasing the Si/Al ratio results in a decrease of the catalytic activity (Figure 3). The same trend is observed when aluminum is partially replaced by boron. Another important feature of zeolite Beta is the particle size [8]. Increasing the zeolite particle size produces a decrease in catalytic activity (Figure 4). T=18 C, P=4.5 Mpa; benzene/ethylene=4.5 ethylene conversion (%) contact time * 1 (min) >1 µm ~.7 µm ~.2µm Figure 4. Alkylation of benzene with ethylene catalysed by Beta zeolite. Effect of particle size. Both these last behaviors evidence that beside the structure also the composition and the morphology of a zeolite catalyst are important with respect to the performances. According to the above results EniChem has been developing a new EB process based on a zeolite Beta having a proper composition and morphology. The process has been scaled up till to a pilot plant unit having a reactor volume of 6 liters. Recently, Mobil researchers reported that zeolite MCM-22 shows good performance in the liquid phase alkylation of benzene with ethylene. Cheng et al. [9] demonstrated that MCM-22 shows a catalytic activity which is comparable (with lower deactivation rate) to USY and around 2.4 times Ethylene conversion Ethylation selectivity DEB/EB TEB/EB Selectivity (%) 1 Selectivity (%) Si/Al: 12.5 Si/Al: 21.5 Si/Al: 3 Si/Al: 15 alk : 3.8h alk : 9h alk : 3.3h alk :.4h K alk K alk K alk K alk 4 2 MCM-22 Beta USY-1 USY-2 T= 22 C; P = 3.44 Mpa ; B/E = 4 Figure 5. Alkylation of benzene with ethylene. Comparison of various zeolites.

4 less than zeolite Beta (Figure 5). On the other hand, MCM-22 is much more selective, being the formation of diethylbenzenes (DEBs) significantly lower than with USY or Beta. This results in larger ethylation selectivity. Few conclusions can be drawn on EB technology development: Of around 7 EB units operating in the world, 24% are still based on AlCl 3 -HCl. The other are based on zeolite catalysts: 4% in the gas phase and 36% in the liquid phase; The most promising zeolites for liquid-phase operation are MCM-22 and Beta; Beside the zeolite structure, zeolite composition and morphology are very critical in the alkylation catalyst formulation. 3. Alkylation of benzene to produce cumene The alkylation of benzene with propylene gives cumene, a very important petrochemical commodity used for the production of phenol and acetone. The cumene capacity in the world is about 8 millions tons/year distributed over about 4 plants. For cumene production the most widespread process is the UOP one. The catalyst for such a process is phosphoric acid supported on silica kieselgur. Only few plants are based on the Monsanto technology, which uses aluminum tri-chloride as catalyst. Both processes have problems of corrosion, waste treatment (AlCl 3 ) and exhaust catalyst disposal (SPA) (Figure 6). Monsanto UOP Temperature ( C) ( C) Pressure (atm) Phase liquid liquid Catalyst AlCl AlCl 3 3 SPA SPA Status few few installations most widespread Problems corrosion, waste disposal, product contamination corrosion, dust formation, wastes Figure 6. Alkylation of benzene with propylene. Traditional industrial processes. The problems evidenced account for the efforts devoted to the research of new catalysts more efficient, safe and environmental friendly. Starting from the mid-196s different zeolite catalysts has been extensively evaluated in the alkylation of benzene with propylene in gas-phase [1]. Significant performance increases were obtained by performing the alkylation in liquid-phase. Therefore large pore zeolites were preferred. However, only in 1992 the first commercial process was announced by Dow-Kellog, followed by Mobil, Cdtech, Enichem and UOP [11-14]. Then in 1996, Mobil, Enichem and UOP have carried out the start-ups of industrial runs. The zeolites claimed for the new process (Beta, Y, mordenite, ERB-1 and MCM-22), besides ZSM- 5 and ZSM-12, were compared in catalytic tests performed in a continuous fixed bed microreactor in the liquid-phase (Figure 7) [15]. It is evident that ZSM-5 is the less active. Besides it deactivates

5 Propylene conversion (%) Beta ZSM-5 USY Mordenite ERB-1/MCM22 ZSM-12 T= 15 C; P = 3.5 Mpa; B/P= 7; WHSV = 3 h -1 Fig. 7. Alkylation of benzene with propylene. Effect of the zeolite on propylene conversion. quickly. All the other samples show a significant activity. Among the large pore zeolites USY shows a slightly lower activity. Concerning the by-product formation (Figure 8), ZSM-5 and ZSM-12 produce the lowest amount of DIPBs [15]. However, with respect to Beta, the amounts of n-propylbenzene and propylene oligomers are significantly higher. Mordenite and USY produce less n-propylbenzene than zeolite Beta but almost two and three times the amount of DIPBs. Taking into account that during transalkylation of DIPBs a further amount n-propylbenzene is formed, the overall amount of the latter is lower for Beta zeolite. Hence the zeolite Beta shows the best performances. Few conclusions can be drawn on cumene technology development: Among 4 units in the world, 11 cumene plants are in operation with zeolite catalysts. The most promising zeolites for liquid phase operation are Beta and MCM-22. EniChem has developed a new zeolite catalyst, based on zeolite Beta, having the following features: high product yield and quality; long catalyst life (> 4 years) 4% of capacity increase. DIPBs/Cumene (g/kg) 3 DIPBs npbz 25 oligomers/2 2 ppm Beta MOR ERB-1/MCM22 USY ZSM-12 ZSM-5 Figure 8. Alkylation of benzene with propylene. Effect of the zeolite on the by-products formation.

6 4. Alkylation of toluene to produce cymene m-cymene and p-cymene are intermediates for the production of m- and p-cresol, by oxidation and acid cleavage. Some commercial units are operating with an installed capacity of around 4 kton/y. The alkylation produces a mixture of cymene isomers. The optimum isomer distribution requires a low o-cymene content, since o-cymene is difficult to oxidize and it inhibits the oxidation of the other isomers. AlCl 3 -HCl SPA ortho para meta ortho para meta T = 6-8 C T= 155 C Figure 9. Alkylation of toluene with propylene. Effect of the catalyst on the product distribution. As for cumene, two catalytic technologies are applied for the production of cymene, based on AlCl 3 -HCl and on SPA (Figure 9). Using AlCl 3 -HCl an isomer ratio close to the equilibrium one is obtained. After oxidation to cymene hydroperoxide, the excess of o-cymene is recycled to the alkylation step, so that the o-cymene content can again be lowered through isomerization on AlCl 3. SPA process differs from AlCl 3 process for the isomer distribution obtainable, which is far from the equilibrium one. The process has a separation unit (Cymex), based on a 13X molecular sieve, for the separation of m- and p- isomers, which allow the production of the pure corresponding cresols. The o- isomer is then transferred to an isomerization step. The isopropylation of toluene with propylene or isopropanol has been largely studied using different zeolite catalysts [16-18]. Also amorphous silica-aluminas with controlled porosity have been considered for the liquid phase alkylation of toluene with propylene. Mesoporous MSA and MCM-41 show alkylation activities larger than the microporous ERS-8 and comparable with zeolite Beta at 18 C (Figure 1). T= 18 C, P=3.9 Mpa, Toluene/Propylene=7 (mol) wt % 1 Cymenes Polyalkylates oligomers/1 ppm Beta MSA MCM-41 ERS-8 Figure 1. Alkylation of toluene with propylene catalyzed by zeolites or amorphous silica aluminas.

7 However MSA and MCM-41 give a lower cymenes selectivity than zeolite Beta, because of the larger formation of polyalkylates. This can be due to both the presence of large pores and the low transalkylation activity, in agreement with the low Brønsted acidity of this amorphous silicaaluminas. Amorphous silica aluminas however produce less propylene oligomers. The distribution of cymene isomers obtained with MCM-41, MSA and ERS-8 is far from the equilibrium. Para and ortho prevail on meta. Increasing the contact time a slight increase of meta is evidenced. This behavior indicates the low isomerization activity of the amorphous silica-aluminas with respect to zeolites like Beta. With the latter increasing the contact time allows to obtain the equilibrium composition (Figure 11). 1 8 % 6 MSA Beta Equilibrium contact time (h) ortho para meta Figure 11. Alkylation of toluene with propylene. Effect of contact time. In the alkylation of toluene with propylene, large pore zeolites and mesoporous silica aluminas show different behavior. Large pore zeolites show high isomerization activity, as well as AlCl 3. Amorphous mesoporous silica aluminas (e.g. MCM-41 and MSA) behave very similarly to SPA. Zeolite Beta is the best candidate to substitute AlCl 3 in cymene production while mesoporous silica aluminas are good substitutes of SPA. 5. Conclusions For the aromatic alkylations accounting the largest productions, new solid catalysts and new processes conforming the environmental and safety concerns are currently available. Various solid catalysts based on different zeolites have been developed for the production of ethylbenzene and cumene up to the industrial scale. The data available do not allow to easily ascertaining which the best catalyst is. However, to our knowledge, it seems that the structure BEA is the most suitable for cumene synthesis, while MWW is the most suitable for EB synthesis. The new technologies operate in the liquid phase and showed to be very rewarding as far as the productivity and stability are concerned, so that a complete substitution of AlCl 3 and H 3 PO 4 with solid acid catalysts is expected by 21. As far as cymene is concerned, a green solution based on a solid acid catalyst is also available, although the industrial stage has not been demonstrated so far. Beta zeolite and mesoporous alumina oxides are in this case the best catalysts ever tested, depending on the isomer composition desired. The new deal towards processes environmentally benign, which has just been inaugurated with the recognition of the qualities of some solid catalysts, is expected to be further reinforced by the

8 validation of other tools now available. Structured catalysts that leads to smaller, cleaner and more energy efficient technology (i.e.: process intensification), the use of ionic solvents, the exploitation of new substrates, are only some of the new directions that should be performed in order to improve the sustainability of the alkylation processes. 6. References [1] H. G. Franck and J.W. Stadelhofer, Industrial Aromatic Chemistry, Springer-Verlag, Berlin Heidelberg (1988). [2] J. S. Beck and W. O. Haag, Handbook of Heterogeneous Catalysis, G. Ertl, H. Knoezinger, J. Weitkamp (Eds.), VCH, Weinheim (1997), [3] K. Tanabe and W. F. Hoelderich, Appl. Catal. A: General 181 (1999) 399. [4] P. B. Venuto, L. A. Hamilton, P. S. Landis and J. J. Wise, J. Catal., 5 (1966) 81. [5] C. G. Wight, U.S. Pat. 4,169,111 to Union Oil Company of California (1979). [6] R. A.Innes, S. I. Zones and G. J. Nacamuli US to Chevron USA Inc. (199). [7] F. Cavani, V. Arrigoni and G. Bellussi EP A1 to Eniricerche, EniChem, Snamprogetti (1991). [8] G. Bellussi, G. Pazzuconi, C. Perego, G. Girotti and G. Terzoni, J. Catal., 157 (1995) 227. [9] J. C. Cheng, T. F. Degnan, J. S. Beck, Y.Y. Huang, M. Kalyanaraman, J. A. Kowalasky, C. A. Loehr and D. N. Mazzone, in Science and Technology in Catalysis 1998, Kodansha Ltd. (1999) 53. [1] Kr. M. Minachev, Ya. I. Isakov, V. I. Garanin, L. I. Piguzova, V. I. Bogomolov and A. S.Vitukina, Neftekhimiya 5 (1965) 676. [11] G. R. Meima, CATTECH, June 1998, 5. [12] J. C. Cheng, A. S. Fung, D. J. Klocke, S. L. Lawton, D. L. Lissy, W. J. Roth, C. M. Smith and D. E. Walsh, U.S. Pat., 5,453,554 to Mobil Oil Corp. (1995). [13] M. F. Bentham, G. J. Gajda, R. H. Jensen and H. A. Zinnen, in Proceedings of the DGMK- Conference, Catalysis on Solid Acids and Bases, Berlin, Germany, March 14-15, 1996, Edited by J. Weitkamp and B. Lücke, (1996) 155. [14] C. Perego, S. Amarilli, G. Bellussi, O. Cappellazzo and G. Girotti, Proceedings of the 12 th International Zeolite Conference, Edited by M.M.J. Treacy et al., Materials Research Society, Warrendale, Pennsylvania (1999), Vol. 1, 575. [15] C. Perego, S. Amarilli, R. Millini, G. Bellussi, G. Girotti and G. Terzoni, Microporous Mater., 6 (1996) 395. [16] D. Fraenkel and M. Levy, J. Catal., 118 (1989) 1. [17] K. S. N. Reddy, B.. Rao and P. V. Shiralkar, Appl. Catal., A: 121 (1995) 191. [18] C. Perego, S. Amarilli, A. Carati, C. Flego, G. Pazzuconi, C. Rizzo and G. Bellussi, Microporous and Mesoporous Materials 27 (1999) 345.