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Modified Beta Zeolites for Alkylation of Benzene Using Batch andContinuous Fixed-bed Reactors

Genoveva Buelna 1, Tina M. Nenoff 1, Mutlu Kartin 1, Steven M. Thornberg 2, IonC. Abraham 2, Deborah E. Hunka 21 Chem and Bio Technologies Department; 2 Chemical and Biological Sensing,Imaging and Analysis Department. Sandia National Laboratories, Albuquerque,

NM 87185 USA.

IntroductionAlkylation reactions are significant in industry as many important

commercial alkyl aromatics are produced worldwide. Among these alkylationreactions is the alkylation of benzene with propylene, which produces cumene, a

petrochemical commodity produced in large quantities for use in the manufactureof phenol and acetone [1, 2]. Conventionally, cumene is manufactured usingAlCl 3 or phosphoric acid catalysts. However, corrosion and environmental

problems arising from these conventional catalysts have impelled the use of solidacids such as zeolite-based catalysts [3, 4]. Several medium to large pore zeolitesare highly effective catalysts for the reaction of alkylation of benzene to producecumene, but suffer from rapid deactivation of the zeolite catalysts [5, 6]. In the

present work, the activity of several modified H +-beta zeolites was studied in a batch reactor and the life span of the catalyst was tested in a fixed-bed reactor.

Results and DiscussionBenzene alkylation reactions were tested in a batch reactor at 175-250C,

with 7:1 benzene:propylene molar ratio, using modified H +-beta catalysts.Baseline H +-beta catalysts (Si/Al 2=25) were loaded with 1 wt.% of either Pt, La,Ga, or Ce. Platinumimpregnated beta zeolite was prepared by mixing betazeolite with a solution of hexachloroplatinic acid. The other catalysts were

prepared by ion exchange of the beta zeolite with aqueous solutions of lanthanumchloride, gallium nitrate and cerium chloride, respectively. In addition, carbonizedsamples were prepared by exposing (at temperature) the beta zeolite to a gaseousmixture of hydrocarbons. The catalytic activity of the modified catalysts wastested and compared with that of the unmodified H +-beta zeolite.

Our early results in the batch reactor indicated that catalysts modified withPt, Ga, and n-pentane were the most promising. These samples showed highselectivity on par with the unmodified baseline sample. The lifespan of these threecatalysts in the cumene reaction was tested over extended periods of time (8 hcontinuous operation) using a stainless steel fixed-bed reactor at 225C, with 7:1

benzene:propylene molar ratio and WHSV propylene = 1.6/h.

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Preliminary results on the cumene yield and relative selectivity of thesamples showed that all the samples deactivate with time (i.e. the unmodified betacatalyst reached a plateau at about 25% of the initial conversion after 6 h). Initialcumene yield of the studied samples, measured after 1 h of reaction, ranked in anorder as follows: beta-Ga > beta unmodified > beta carbonized > beta-Pt. Thisorder was kept for the first three hours of reaction. Following this initial period,catalysts decayed at different rates, and after 7 hrs of reaction, the cumeneconversion reached a plateau in all the samples with cumene yields in the order:

beta-Ga > beta-Pt > beta unmodified > beta carbonized. The strong loss incatalytic activity with increasing reaction time results from blocking of the zeolite

pores by coke formation, which is affected by the introduction of metals [6-8].

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US DOE under Contract DE-AC04-94- AL85000.

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