Title

Studies of oxidative dehydrogenation of ethylbenzene to styrene over manganese oxide octahedral molecular sieve (OMS) materials, and, Synthesis of ZK-5 zeolite using novel synthetic methods

Date of Completion

January 2001

Keywords

Chemistry, Inorganic

Degree

Ph.D.

Abstract

Dehydrogenation of ethylbenzene by a catalytic thermal process is a major industrial method for producing styrene. However, there are two major drawbacks in this process, (1) high reaction temperature, and (2) low yields. A great deal of research has concentrated on the oxidative dehydrogenation of ethylbenzene to styrene. Manganese oxide octahedral molecular sieve (OMS) materials have been found to be unique for the oxidative dehydrogenation of different hydrocarbons. As an extension of this work, OMS materials and a series of OMS materials doped with first row transition metal cations, and other divalentions (M) were synthesized, characterized, and studied in the oxidative dehydrogenation of ethylbenzene to styrene in a gas phase reaction. The results showed that at 400°C [M] OMS-2 materials show higher conversions, which ranged from 49% to 81%, while [M]-OMS-1 materials have higher selectivity for styrene, which ranged from 15% to 81%. [Cu]-OMS-2 has the highest conversion and [Mg]-OMS-1 has the highest selectivity to styrene. ^ ZK-5 zeolite with a window size of 3.9 x 3.9 Å is one of a few small pore-size zeolites, and is a highly selective and active catalyst for synthesizing methylamines in thermal catalytic reactions of ammonia and methanol. ZK-5 zeolites are currently synthesized using hydrothermal methods that require a relatively long period of time (>96 h) as well as high temperatures (>100°C). In this research, two alternative synthetic routes were explored for the synthesis of Cs, K-ZK-5 zeolite, which include seeding and microwave heating methods. In order to increase the atomic ratio of Si/Al in ZK-5 zeolite samples, TMAOH was used to partially replace KOH during the synthesis process. The results have shown that (1) the seeding can significantly shorten the synthesis time from conventional hydrothermal synthetic routes, (2) the microwave can reduce the synthesis time even more dramatically, (3) use of TMAOH agent can increase the atomic ratio of Si/Al in ZK-5 zeolite samples to some extent, and (4) both the amount of water content used and the sequence in which water is introduced are critical factors for Cs, K-ZK-5 zeolite synthesis. ^