Lewis B. Young

Selective alkylation of toluene with methanol to produce para-Xylene

Abstract Toluene has been alkylated with methanol over ZSM-5-class zeolite catalysts to produce xylenes and water. A near equilibrium mixture containing 24% of the para isomer was usually observed. Production of over 90% para isomer in the xylene product was achieved when the catalyst was modified by impregnation with phosphorus and with boron compounds. para-Xylene selectivity was also enhanced by coking and coating the catalyst surface with heat-stable polymers. A controlled reduction in the effective dimensions of the catalyst pore openings, and/or channels, along with deactivation of acidic surface sites, has been proposed as a mechanism for the selective production of p-xylene.

Shape selective reactions with zeolite catalysts: III. Selectivity in xylene isomerization, toluene-methanol alkylation, and toluene disproportionation over ZSM-5 zeolite catalysts

Abstract Data are presented for para -selective and nonselective formation of xylenes from alkylation of toluene with methanol and toluene disproportionation over ZSM-5 class zeolite catalysts. Possible mechanisms leading to para -selectivity are discussed. Isomerization of the pure xylene isomers has been used as a mechanistic probe. Distinctly different reaction paths (i.e., isomer composition curves) for xylene isomerization have been observed for para -selective in comparison to nonselective catalysts. Reaction paths followed by the para -selective catalysts are probably a consequence of diffusional effects possibly superimposed on the sterically altered intrinsic kinetics, both of which favor formation of the more rapidly diffusing para isomer.

Shape-selective reactions with zeolite catalysts: II. Selective disproportionation of toluene to produce benzene and p-Xylene

Toluene disproportionated to produce benzene and xylenes rich in the para isomer (70–90%) over ZSM-5 zeolites which were modified with phosphorus, boron, or magnesium compounds. A mechanism is proposed where oxides of these elements, present in the zeolites, reduce the dimensions of pore openings and channels sufficiently to favor formation and outward diffusion of p-xylene, the isomer with the smallest minimum dimension. This chemistry has potential for an improved process to prepare benzene and p-xylene from toluene.