Reactions of Butylbenzene Isomers on Zeolite HBeta:  Methanol-to-Olefins Hydrocarbon Pool Chemistry and Secondary Reactions of Olefins

Abstract

The reactions of n-butylbenzene, isobutylbenzene, sec-butylbenzene, and tert-butylbenzene on zeolite HBeta (SiO 2 /Al 2 O 3 ) 150) were studied at 350°C using a pulse reactor with GC-MS analysis of product gases. Similar experiments also probed the reactions of butylbenzene isomers with excesses of methanol-13 C. 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-2-butene. The rate of butene elimination from the benzene rings increased with the degree of branching on the carbon R to the aromatic ring as well as the extent of in situ ring methylation by co-fed methanol. In the presence of methanol-13 C, 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.

The Effect of Acid Strength on the Conversion of Methanol to Olefins Over Acidic Microporous Catalysts with the CHA Topology

“…[9][10][11][12][13]. Several independent studies have concluded that methylbenzenes and their protonated analogues are main pool constituents in various catalysts (H-SAPO-34, H-ZSM-5, H-Beta) [7,[14][15][16][17][18][19][20][21][22][23][24][25][26], and further that the number of methyl groups on the main methylbenzene intermediate is limited by topology [9,14,23,[27][28][29]. It has recently been shown that the higher methyl benzenes in wide-pore zeolite H-Beta give a high selectivity to propene and butene, while the lower methyl benzene analogues in H-ZSM-5 give a high selectivity to ethene and propene [27][28][29].…”

Selectivity control through fundamental mechanistic insight in the conversion of methanol to hydrocarbons over zeolites

“…The mechanism explains formation of alkenes through an indirect route rather than direct coupling of methanol molecules. Detailed studies on the identity and activity of the hydrocarbon pool species have shown that polymethylbenzenes (methylated benzene molecules) act as the main reaction centers for the MTH reaction [9,[15][16][17][18][19][20]. Unlike Dessau's mechanism, light alkene formation including ethene from the hydrocarbon pool species is well documented and there is general consensus about the importance of the hydrocarbon pool mechanism over a limited number of materials studied so far [15][16][17][18][19].…”

High Propylene Selectivity in Methanol-to-olefin Reaction over H-ZSM-5 Catalyst Treated with Phosphoric Acid

“…Many researchers have concentrated on converting methanol to hydrocarbons such as methanol to gasoline (MTG), methanol to hydrocarbons (MTH) and MTO using zeolitic catalysts such as ZSM-5 1)～3) , zeolite Beta 4), 5) , and SAPO-34 6)～8) , and the reaction paths of MTO and MTG processes over zeolitic catalysts have been reported 9) . Silicoaluminophosphate SAPO-34 (pore size ca.…”