Effect of Gas and Liquid Superficial Velocities on the Performance of Monolithic Reactors

Abstract

The effect of gas and liquid velocities on the rate of hydrogenation of α-methyl styrene (AMS) in a monolithic reactor has been investigated at different washcoat loadings. The catalyst used was 0.5 wt % Pd/Al2O3. To cover a wide range of velocities, reaction studies were conducted in multichannel as well as single-channel monolith blocks. The liquid channel velocity was varied from 0.5 cm/s to 22 cm/s, and the gas channel velocity was varied from 1.2 cm/s to 22 cm/s. To study the effect of internal diffusional resistance, the washcoat thickness was varied from 11 μm to 62 μm. Under these operating conditions, both external mass-transfer and internal diffusional resistance affected the rate of reaction. At low liquid velocities (<2 cm/s), the measured rate of reaction was not significantly affected by the gas velocity, whereas at high liquid velocities, the measured reaction rate passed through a maximum with increasing gas velocity. The highest reaction rates were obtained for gas and liquid velocities in the range of 5−10 cm/s. At higher liquid velocities (>10 cm/s), the rate of reaction decreased with liquid velocity, most probably because of the increase in liquid slug length and film thickness around the gas bubble. The overall effectiveness factor of the monolith catalyst was determined from the measured rate of reaction and the published intrinsic kinetics. Using the approximation of Gottifredi et al. for nonlinear kinetics [Gottifredi et al. Chem. Eng. Sci. 1981, 36, 313−317], the internal effectiveness factor and overall mass-transfer coefficient were determined. The overall mass-transfer coefficients determined from the reaction-rate data have been compared with the values calculated using the available correlations.