Reactions of butylbenzene isomers on zeolite HBeta: Methanol-to-olefins hydrocarbon pool chemistry and secondary reactions of olefins

The reactions of h-butylbenzene, isobutylbenzene, sec-butylbenzene, and tert-butylbenzene on zeolite HBeta (SiO2/Al2O3 = 150) were studied at 350 degreesC using a pulse reactor with GC-MS analysis of product gases. Similar experiments also probed the reactions of butylbenzene isomers with excesses of methanol- C-13. The reactions of tert-butylbenzene were also explored as. a function of zeolite acid site density and reactant loading. In the absence of secondary reactions such as oligomerization and cracking, olefin product selectivity is governed by the detailed structure of alkyl side chains; for example, tert- and isobutylbenzene each yielded isobutene, but sec- and n-butylbenzene each gave equilibrium mixtures of 1-butene and cis- and trans-2butene. The rate of butene elimination from the benzene rings increased with the degree of branching on the carbon (x to the aromatic ring as well as the extent of in situ ring methylation by co-fed methanol. In the presence of methanol-C-13, isomerization between 2-butene and isobutene did not occur through a direct pathway; rather skeletal isomerization was observed after chain growth to C-7 or higher olefins followed by cracking. Coking reactions formed volatile alkanes through a mechanism that conserved the carbon skeleton of the precursor olefin. These studies relate to the hydrocarbon pool mechanism of methanol-olefin catalysis (MTO), as well as secondary reactions in MTO chemistry.