Deactivation of NaY in Aniline Alkylation with Methanol: Accumulation Kinetics, Composition, and Localization of Coke Deposits

This study investigates the kinetics of deactivation of a commercial NaY zeolite catalyst in alkylation of aniline with methanol due to coke deposition. In order to identify the accumulation trend, composition, and localization of coke deposits, a series of zeolite catalyst samples differing in reactor residence time were obtained. The catalysts and the accumulated coke deposits were characterized by X-ray fluorescence analysis, X-ray powder diffraction, TGA/DTA, SEM, low-temperature nitrogen adsorption, ²⁷Al and ¹³C MAS NMR, NH₃-TPD, and GC/MS. The coke species deposited on the catalyst during the reaction were found to mostly consist of long-chain aliphatic compounds (mainly alkanes) and heterocyclic aromatics. Both the TGA and GC/MS data showed that the relative content of aliphatic compounds increased with the progress of the catalyst deactivation. Moreover, the variation in the zeolite’s interplanar distances (measured by XRD) showed that the aliphatics were mainly localized in the zeolite pores.