Zeolites ethylbenzene/cumene production

Alkylation over the MWW Zeolite. The MWW (or MCM-22) zeolite developed by Mobil as catalyst for ethylbenzene and cumene production deserves particular attention. Indeed, this zeolite presents unique structural features (Figure 12.5). Its structure is constituted of three independent pore systems " large supercages (inner diameter of 7.1 A dehned by a 12-member-ring [12-MR], height 18.2 A) each connected to six others through 10-MR apertures... 

Small quantities of methanol and ethanol are sometimes added to the C3S in pipelines to protect against freezing because of hydrate formation. Although the beta zeolite catalyst is tolerant of these alcohols, removing them from the feed by a water wash may still be desirable to achieve the lowest possible levels of EB or cymene in the cumene product. Cymene is formed by the alkylation of toluene with propylene. The toluene may already be present as an impurity in the benzene feed, or it may be formed in the alkylation reactor from methanol and benzene. Ethylbenzene is primarily formed from ethylene impurities in the propylene feed. However, similar to cymene, EB can also be formed from ethanol. 

Alkylation of Aromatics with Liquid Catalysts. Forty years ago, ethylbenzene, cumene, and dodecyl benzenes were produced by alkylation reactions of benzene with liquid catalysts. Although some production processes still involve these catalysts, solid catalysts such as zeolites are now often the preferred catalysts. Olefins are generally employed for commercial alkylation reactions. The chemistry discussed next will involve liquid catalysts that are protonic acids or Friedel-Crafts catalysts. 

The aromatics alkylation with olefins is a well-known technology, especially in the case of ethylbenzene (a Mobil-Badger process [109]) and cumene production [110], Ethylbenzene synthesis can be catalyzed by diverse modified HZSM-5, BEA, rare-earth Y, and MCM-22 zeohtes. In most cases, the selectivity is pretty high (99%), but the process must be carried out at a large excess of benzene and the conversion of the latter typically does not exceed 20-25% at 400°C and WHSV= 3 h . For cumene production, a few commercial processes have been developed by CD-Tech (Y zeolite), Lummus-Unocal (Y zeolite), Enichem (H-BEA), Mobil-Raytheon (MCM-22), Dow Chemical (dealuminated mordenite (MOR)), and UOP (a Q-Max process with MgSAPO-31). 

In the manufacture of ethylbenzene and cumene, the cost of benzene feedstock is a major factor in the overall economics. Thus, it is critical to have efficient technology for the alkylation of benzene. Zeolitic catalysts have the advantages of achieving higher purity and higher yield of product relative to aluminum chloride and SPA catalysts. Table 4.10 compares purities and yields and also shows the breakdown of impurities for both ethylbenzene and cumene. In both cases, extremely high purities can be achieved, 99.96 and 99.97%, respectively. The product yields are also extremely high, 99.6% and 99.7%. 

An important industrial application of CD is the alkylation of benzene with ethylene or propylene to produce ethylbenzene or cumene, respectively, using acidic ion-exchange resins such as Amberlyst or zeolites operating at 130-5065 kPa and 80-500°C. Cumene is a chemical intermediate for the production of phenol, acetone, and alpha-methyl styrene, which are used to produce resins and solvents. Ethylbenzene is an intermediate for styrene, an important monomer for polymers. Alkylation of benzene could also be used to reduce the carcinogenic benzene content of gasoline. 

Besides the production of cumene and ethylbenzene, there are a number of recent reports on the production of linear alkylbenzene, precursors to detergents, via the alkylation of benzene with C6-C18 olefins. One process uses suspension CD and essentially 100% conversion of olefin at low temperatures of 90-100°C was obtained. An HF-treated mordenite used in the alkylation of benzene and C10-C14 olefins was foimd to give a 74-84% selectivity to linear alkylbenzene containing 80% 2-phenyl isomer. A new patent on the alkylation of aromatic hydrocarbons such as benzene and cumene with straight-chain C6-C20 olefins on acidic catalyst such as zeolites or fluorine-treated zeolite catalyst packed in a Katamax-type packing was granted. A patent application on the manufacture of xylenes from reformate by RD also appeared and higher than equilibrium amounts of para-xylene were claimed. 

Two catalysts have emerged as commercially viable. The Mobil—Badger ethylbenzene process, which has been in commercial use since 1980, employs a zeolite catalyst and operates in the gas phase. A liquid-phase ethylbenzene process joindy licensed by Lummus and UOP uses a Y-type Zeolite catalyst developed by Unocal. This liquid-phase process was commercialized in 1990. The same Y-type ZeoUte catalyst used for the production of ethylbenzene is being offered for the production of cumene but has not yet been commercialized. 

Side Chain Aikyiation ofAikyiaromatiCS. Alkylation of alkylbenzenes with alkenes or alcohols over base catalysts yield the products alkylated at the side chain, while ring-alkylation proceeds over acidic catalysts. To abstract a proton from the alkyl groups, strongly basic catalysts are required. The pKa values of toluene and cumene are 35 and 37, respectively. In the vapor-phase reaction of toluene with methanol, alkali ion-exchanged zeolites, especially, RbX and CsX give ethylbenzene and styrene as products, while acidic zeollites afford xylenes (52). 

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