Toluene disproportionation reaction in a packed-bed reactor with acid-treated natural zeolite catalysts

Abstract

As a study for toluene disproportionation reaction to benzene and xylene, the properties of natural zeolite mined in Kuryongpo, Kyungsang-Namdo and its property changes after acid treatment, the effects of the operating conditions on toluene conversion and selectivity in a packed-bed reactor, and the reaction mechanism and kinetics were investigated. The chemical composition analysis and X-ray diffraction spectrum of the original zeolite sample showed that the sample contained 30 - 40\% of the mordenite structure, and other impurities such as clinoptiolite, quartz, feldspar, and amorphous clavs. The surface area measured by nitrogen adsorption in the BET system was 75$M^2$/gr for original sample and increased to a maximum value of 320 $M^2$/gr after treatment with 2N hydrochloric acid solution. This results from the rearrangement of the pore structure and the enlargement of the pore openings by decationization and extraction of aluminum and other impurities. The sample treated with higher acid concentration caused the collapse of the structure which was observed from the X-ray diffration spectrum. Toluene conversion for toluene disproportionation reaction in a packed-bed reactor reached a maximum value at 2N acid treated catalyst because of strong acidities on catalyst surface and enough pore size for reactants and products to diffuse. The deactivation rate of such a catalyst that treated with 1 - 3N hydrochloric acid solution was much faster than with other concentration because of coke deposition by the strong acid sites. The selectivity of xylene over benzene decreased with increasing acid concentration indicating increased Lewis acid-sites on the catalyst surface which correspond to cracking rather than isomerization. The reaction was carried out at various operating conditions to study the catalytic acti ity and optimum reaction conditions. Large catalyst to feed rate ratio which means longer contact time resulted in higher conversion, but the selectivity ...