Catalysts aromatics alkylation

Future Developments. The most recent advance in detergent alkylation is the development of a soHd catalyst system. UOP and Compania Espanola de Petroleos SA (CEPSA) have disclosed the joint development of a fixed-bed heterogeneous aromatic alkylation catalyst system for the production of LAB. Petresa, a subsidiary of CEPSA, has announced plans for the constmction of a 75,000 t/yr LAB plant in Quebec, Canada, that will use the UOP / -paraffin dehydrogenation process and the new fixed-bed alkylation process (85). 

Polynuclear Aromatics. The alkylation of polynuclear aromatics with olefins and olefin-producing reagents is effected by acid catalysts. The alkylated products are more compHcated than are those produced by the alkylation of benzene because polynuclear aromatics have more than one position for substitution. For instance, the alkylation of naphthalene [91-20-3] with methanol over mordenite and Y-type zeoHtes at 400—450°C produces 1-methylnaphthalene [90-12-0] and 2-methylnaphthalene at a 2-/1- ratio of about 1.8. The selectivity to 2-methylnaphthalene [91-57-6] is increased by applying a ZSM-5 catalyst to give a 2-/1- ratio of about 8 (102). 

Over the years, improvements in aromatic alkylation technology have come in the form of both improved catalysts and improved processes. This trend is expected to continue into the future. 

Catalysts. Nearly aU. of the industrially significant aromatic alkylation processes of the past have been carried out in the Hquid phase with unsupported acid catalysts. For example, AlCl HF have been used commercially for at least one of the benzene alkylation processes to produce ethylbenzene (104), cumene (105), and detergent alkylates (80). Exceptions to this historical trend have been the use of a supported boron trifluoride for the production of ethylbenzene and of a soHd phosphoric acid (SPA) catalyst for the production of cumene (59,106). 

The use of MSA as catalyst to prepare 2-alkylphenols and 2,6-dialk5lphenol has been described (407). MSA has also been used as an aromatic alkylation agent (408). 

Upon calcination the template is removed and the zeolite s well-defined pores are available for adsorption and catalysis. Particularly challenging is the field of electrophilic aromatic substitution. Here often non-regenerable metal chlorides serve as the catalyst in present industrial practice. Zeolites are about to take over the job and in fact are doing so for aromatic alkylation. 

Zeoliltes seem particularly suited to take over the job and in fact are doing so already for aromatic alkylation. Thus in ethylbenzene manufacture (from benzene and ethene) modern processes apply zeolites (H-ZSM-5, H-Y) as the catalyst, substituting conventional processes based on AICI3 or BF3-on-alumina catalysis. Substantial waste reductions are achieved. 

Among the wide variety of organic reactions in which zeolites have been employed as catalysts, may be emphasized the transformations of aromatic hydrocarbons of importance in petrochemistry, and in the synthesis of intermediates for pharmaceutical or fragrance products.5 In particular, Friede 1-Crafts acylation and alkylation over zeolites have been widely used for the synthesis of fine chemicals.6 Insights into the mechanism of aromatic acylation over zeolites have been disclosed.7 The production of ethylbenzene from benzene and ethylene, catalyzed by HZSM-5 zeolite and developed by the Mobil-Badger Company, was the first commercialized industrial process for aromatic alkylation over zeolites.8 Other typical examples of zeolite-mediated Friedel-Crafts reactions are the regioselective formation of p-xylene by alkylation of toluene with methanol over HZSM-5,9 or the regioselective p-acylation of toluene with acetic anhydride over HBEA zeolites.10 In both transformations, the p-isomers are obtained in nearly quantitative yield. 

Following are several commercially available fluoromonomers (1-4) that contain functional groups and have been utilized to make polymeric membranes for ion separations6"9 or as catalysts for aromatic alkylation and acylation reactions.1011 They are also convenient starting precursors, allowing for further functionalization reactions. 

There are several means to maximize the yield in the desired monoalkylation product high aromatic/alkylation agent ratio, association of a transalkylation unit to the alkylation unit, and use of a shape selective zeolite as catalyst. 

Cumene was originally produced with SPA- [57], then FAU- or BEA-based catalysts, and most recently MWW. While most industrial processes use MWW-based catalysts [58], Dow and KeUog co-developed a dealuminated MOR based process called 3-DDM [59]. With each new process generation, conversion and selectivity to cumene has increased. These processes and the chemistry behind them are covered in Section 15.4. As the use of zeoHtes for alkylation reactions in industry increased, so did the study of the reaction and how the zeoHte topology affects the mechanism and selectivity to products, so that now many zeotypes are tested for aromatic alkylation as a way of figuring out a new structure s reaction pattern. Therefore, many zeotypes have been used to catalyze aromatic alkylation (Tables 12.9-12.11). 

Tellurium tetrachloride as reagent for the conversion of alcohols into alkyl chlorides and as a Lewis acid catalyst for aromatic alkylation... 

Hydrogen fluoride also is used as a catalyst in alkylation of aromatic compounds and for dimerization of isobutene. Other catalytic applications are in isomerization, polymerization, and dehydration reactions. Other uses are in... 

To reveal factors which influence activities of acid-base catalysts in alkylation and isomerization is the challenge to activity in this field. Q he greatest amount of work has been done in connection with the effect of para-selectivity, which is observed in alkylation of aromatic hydrocarbons on ZSM-5 type zeolites [1]. This effect has been explained by a number of authors either by the influence of diffusion factors [2,3] or by the isomerizing activity of the external surface of zeolite crystals [4]. In refs. [5,6] and especially in ref.[7] the para-selective effect of ZSM-5 type zeolites is shown to be due to decreasing their isomerizing activity becaiase of the decrease in the concentration of strong protic centres as a result of modifiers introduced. Para-selective effect is related to the action of chemical factors. However, in... 

Explore the use of ionic liquids as catalysts for aromatic alkylation reactions ... 

The catalytic cracking of four major classes of hydrocarbons is surveyed in terms of gas composition to provide a basic pattern of mode of decomposition. This pattern is correlated with the acid-catalyzed low temperature reverse reactions of olefin polymerization and aromatic alkylation. The Whitmore carbonium ion mechanism is introduced and supported by thermochemical data, and is then applied to provide a common basis for the primary and secondary reactions encountered in catalytic cracking and for acid-catalyzed polymerization and alkylation reactions. Experimental work on the acidity of the cracking catalyst and the nature of carbonium ions is cited. The formation of liquid products in catalytic cracking is reviewed briefly and the properties of the gasoline are correlated with the over-all reaction mechanics. 

Inflates of aluminum, gallium and boron, which are readily available by the reaction of the corresponding chlorides with triflic acid, are effective Friedel-Crafts catalysts for alkylation and acylation of aromatic compounds [119, 120] Thus alkylation of toluene with various alkyl halides in the presence of these catalysts proceeds rapidly at room temperature 111 methylene chloride or ni-tromethane Favorable properties of the Inflates in comparison with the correspond 1 ng fluorides or chlorides are considerably decreased volatility and higher catalytic activity [120]... 

The products formed in these reactions are very sensitive to the functionality on the carbenoid. A study of Schechter and coworkers132 using 2-diazo-1,3-indandione (152) nicely illustrates this point. The resulting carbenoid would be expected to be more electrophilic than the one generated from alkyl diazoacetate and consequently ihodium(II) acetate could be used as catalyst. The alkylation products (153) were formed in high yields without any evidence of cycloheptatrienes (Scheme 33). As can be seen in the case for anisole, the reaction was much more selective than the rhodium(II)-catalyzed decomposition of ethyl diazoacetate (Scheme 31), resulting in the exclusive formation of the para product. Application of this alkylation process to the synthesis of a novel p-quinodimethane has been reported.133 Similar alkylation products were formed when dimethyl diazomalonate was decomposed in the presence of aromatic systems, but as these earlier studies134 were carried out either photochemically or by copper catalysis, side reactions also occurred, as can be seen in the reaction with toluene (equation 36). 

Another important development is chiral titanocene catalyst using 203 as the catalyst precursor225. The (R, R)-(EBTK)Ti(OR)2 (203) is proposed to generate the active catalyst species, (R, R)-(EBTHI)TiH , upon reaction with n-BuLi (2 equivalents) and polymethyl-hydrosiloxane (PMHS). This chiral Ti-catalyst system is highly efficient for the reactions of aromatic alkyl ketones achieving >90% ee in many cases. In sharp contrast to this, only 24% ee is obtained for the reaction of cyclohexyl methyl ketones. However, the reaction of cyclohexen-l-yl methyl ketone achieved 85-90% ee. Thus, it is extremely important for this chiral Ti-catalyst to have a 7r-system to be effective. 

Although boron trifluoride has been known for a long time as a catalyst for alkylation reactions, it did not become commercially important until larger quantities of aromatic alkylates were required by industry as raw materials for synthetic fibers, rubber, and plastics. As the petrochemical industry finds new uses for these aromatic alkylates, the use of BF3 catalyst is expected to expand greatly. Cumene, diispropylbenzene, and ethylbenzene are among the important alkylates which can be produced by this catalyst. 

The transport and adsorption properties of hydrocarbons on microporous zeolites have been of practical interest due to the important properties of zeolites as shape-selective adsorbents and catalysts. The system of benzene adsorbed on synthetic faujasite-type zeolites has been thoroughly studied because benzene is an ideal probe molecule and the related role of aromatics in zeolitic catalysts for alkylation and cracking reactions. For instance, its mobility and thermodynamic properties have been studied by conventional diffusion 1-6) and adsorption 7-9) techniques. Moreover, the adsorbate-zeolite interactions and related motion and location of the adsorbate molecules within the zeolite cavities have been investigated by theoretical calculations 10-15) and by various spectroscopic methods such as UV (16, 17), IR 17-23), neutron 24-27), Raman 28), and NMR 29-39). 

It has been shown that single ring aromatic alkylation reactions such as benzene to ethylbenzene take place primarily within the 12- ring (12-MR) system, and that the 10-ring (10-MR) system contributes little to the ethylbenzene reaction. A key feature of MCM-22 is its ability to operate stably at low benzene-to-ethylene ratios with minimal production of polyethylbenzenes (PEBs) or ethylene oligomers. The excellent ethylbenzene selectivity of the MCM-22 catalyst is likely due to confinement effects within this 12-MR pore system and to the very facile desorption... 

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