Alkylation catalysts rare earth exchanged zeolites

An analysis of the aging process in the alkylation of benzene with ethylene over a rare earth-exchanged X zeolite (REX) (43) provides insight into the physicochemical phenomena operative. In this reaction, a catalyst lifetime of over 792 hours was observed at 204°, benzene ethylene molar ratio of 5, and pressure of 500 psig. Under similar conditions, but at atmospheric pressure, a drastic increase in the rate of catalyst aging was observed, with catalytic activity lasting only 2 to 3 hours. Subsequent mechanistic studies showed that most of the catalyst aging in this reaction could be attributed to complex, temperature-dependent side reactions of ethylene (44,44a). 

An inspection of the industrial use of zeolites as catalysts shows, however, that only a rather limited number of zeolite topologies are currently used in major industrial processes. Among the more important ones are ultrastable Y (USY) (FAU), rare-earth-exchanged faujasite-type (X, Y) (FAU) andZSM-5-type (MFI) zeolites in fluid catalytic cracking (FCC) of oil fractions [4] noble-metal-loaded U SY for hydroisomerization and hydrocracking of naphtha feedstocks [5] mordenite (MOR) and zeolite Omega (MAZ) -based catalysts for C4-C6 alkane isomerization [6] zeolites ZSM-23 (MTT), ZSM-35 (FER), ZSM-5 for selective oil dewaxing [7] ZSM-5, silicalite (MFI), MCM-22 (MWW), Beta-type (BEA) zeolites for aromatics alkylation to yield ethylbenzene, p-xylene. 

Catalytic activity measurements and correlations with surface acidity have been obtained by numerous investigators. The reactions studied most frequently are cracking of cumene or normal paraffins and isomerization reactions both types of reactions proceed by carbonium ion mechanisms. Venuto et al. (219) investigated alkylation reactions over rare earth ion-exchanged X zeolite catalysts (REX). On the basis of product distributions, patterns of substrate reactivity, and deuterium tracer experiments, they concluded that zeolite-catalyzed alkylation proceeded via carbonium ion mechanisms. The reactions that occurred over REX catalysts such as alkylation of benzene/phenol with ethylene, isomerization of o-xylene, and isomerization of paraffins, resulted in product distribu-... 

Faujasites exchanged with rare earth cations, and particularly with La " ", have shown good performance as solid alkylation catalysts, as nicely reported in the pioneering works carried out in the late 1960s by researchers at Mobil Oil (89) and Sun Oil (96), and later on by Weitkamp s group (132,133). This fact is most likely related to the ability of La-FAU zeolites to catalyze hydride transfer reactions. The Bronsted acidity in La-exchanged FAU zeolites can be associated with the protons generated upon hydrolysis of water in the hydrated lanthanum cations when snbjected to thermal activation treatment at temperatures between 60 and 300°C (134-136) ... 

---