Isomerization of Xylenes (a Review)

The review deals with catalysts for isomerization of the C-8 aromatic fraction with the aim of obtaining valuable petrochemical products: o- and p-xylenes required for the subsequent synthesis of phthalic anhydride, dimethyl terephthalate, and terephthalic acid. Mono- and bimolecular mechanisms of xylene isomerization and ethylbenzene transformation pathways (isomerization, dealkylation, disproportionation, transalkylation, and hydrogenation) on various catalysts are discussed. Catalysts containing zeolites of structural types MFI, MTW, MOR, TUN, NES, CON, and BEA and composite materials based on zeolites and ordered mesoporous aluminosilicates (МСМ-41, МСМ-48) are considered. The effect that the structural and acid properties of support and the kind of the metal component and promoters exert on the course of the main and side reactions occurring in the course of isomerization of xylenes is demonstrated. Data on key commercial processes and catalysts are systematized.