Propene, adsorption alkylation

Vapor-phase alkylation of benzene by ethene and propene over HY, LaY, and REHY has been studied in a tubular flow reactor. Transient data were obtained. The observed rate of reaction passes through a maximum with time, which results from build-up of product concentration in the zeolite pores coupled with catalyst deactivation. The rate decay is related to aromatic olefin ratio temperature, and olefin type. The observed rate fits a model involving desorption of product from the zeolite crystallites into the gas phase as a rate-limiting step. The activation energy for the desorption term is 16.5 heal/mole, approximately equivalent to the heat of adsorption of ethylbenzene. For low molecular weight alkylates intracrystalline diffusion limitations do not exist. 

Most processes for separating individual species from petroleum involve use of refined engineering methods, with distillation and selective adsorption the most important. Once separated, however, most materials then undergo chemical conversion into more desirable products. Alkylation involving propene and butenes yields C6 to C8 hydrocarbons for high-octane gasoline. Propylene becomes polypropylene, propylamine, or propylene glycol and ethers. 

H-beta zeolite proved to be an active and selective catalyst for alkylation of benzene with propene. In situ spectroscopic methods were applied to follow the formation and the evolution of surface intermediates and products,. It was found that when benzene is taken alone on the zeolite surface, its adsorption is reversible up to 473 K. On the contrary propene undergoes to several transformations even at 295 K. Isopropylbenzene behaves as propene, giving the same intermediates and products by decomposition at higher temperatures. Isopropyl cations formed upon chemisorption of propene on Broensted acid sites are the key intermediates for the alkylation reaction and are responsible for the faster deactivation via unsaturated caibenium ions formation. 

As the surface species generated upon adsorption of alkylaromatics can be detected spectroscopically [20], their formation, i.e. from propene and benzene, should be followed as well. According to our knowledge no data have been published on the spectroscopic characterization of cumene formation on H-beta zeolite, despite the recent large interest in alkylation catalysts [21]. In this work, we report the results of UV-VIS-IR spectroscopic... 

Adsorption of 0.5 Torr propene was also studied alone with time at 453 K, in order to simulate the reaction conditions generally cited for the alkylation of benzene with propene [21]. 

There are few reports of alkene-deuterium reactions on bimetallic catalysts, but those few contain some points of interest. On very dilute solutions of nickel in copper (as foil), the only product of the reaction with ethene was ethene-di it is not clear whether the scarcity of deuterium atoms close to the presumably isolated nickels inhibits ethane formation, so that alkyl reversal is the only option, or whether (as with nickel film, see above) the exchange occurs by dissociative adsorption of the ethene. Problems also arise in the use of bimetallic powders containing copper plus either nickel, palladium or platinum. Activation energies for the exchange of propene were similar to those for the pure metals (33-43 kJ mol ) and rates were faster than for copper, but the distribution of deuterium atoms in the propene-di clearly resembled that shown by copper. It was suggested that the active centre comprised atoms of both kinds. On Cu/ZnO, the reaction of ethene with deuterium gave only ethane-d2. as hydrogens in the hydroxylated zinc oxide surface did not participate by reverse spillover. ... 

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