Toluene disproportionation reaction with hydrogen Y zeolite catalysts

Abstract

Toluene disproportionation reaction was cerried out in a fixed bed reactor packed with hydrogen Y zeolite catalysts. The effects of operating conditions, such as, the reaction temperature, hydrogen mole ratio, and regenerated catalysts, on xylene selectivity and catalytic activity were experimentally investigated. Hydrogen Y zeolite was obtained by ion exchange of sodium Y zeolite that was synthesized with an aqueous sodium aluminosilicate mixture of the following oxide mole rations. $$Na_2O/SiO_2 =0.3$$ $$SiO_2/Al_2O_3 = 9$$ $H_2O/Na_2O=40$$ The X-ray diffraction pattern of synthetic Y zeolite showed high crystallinity. At a relatively high temperature, the conversion was close to equilibrium conversion. The deactivation of the catalyst was severe at higher temperature, and not significant below the temperature of 408$^\circ$C. Increased hydrogen mole ratio in feed mixture resulted in the slow deactivation rate. Regenerated catalyst also showed slow deactivation rate. Deactivation tendency decreased with the repetition of catalyst regeneration. The selectivity of xylene over benzene increased as the deactivation proceeded. The selectivity range between 0.6 and 2 were obtained above the temperature of 400$^\circ$C, and between 1.1 and 5 below the temperature of 380$^\circ$C. The reaction rates were measured within the range of negligible diffusion intrusion and under the isothermal piston flow assumption. The slow deactivation region of temperature was adoped. A reaction mechanism was assumed to be the second order Langmuir-Hinshelwood mechanism. The calculated values of the activation energy and the heat of adsorption were 5.1 and 5.5 Kcal/mole respectively in the temperature range of 356-400$^\circ$C.