Slow-mode induced pulsing in trickle-bed reactors at elevated temperature



Periodic operation, as a process intensification measure for trickle beds, is still tepidly greeted by industry despite numerous benefits underlined in the literature. This state of aloofness is partly ascribed to the paucity of experimental data acquired under elevated temperature and pressure, which, in practice, most catalytic reactions are subjected to. Currently, the hydrodynamics of trickle bed periodic operation at elevated temperature and pressure remains by and large an uncharted territory. This study specifically approaches from a hydrodynamic perspective the pros and cons of slow-mode induced pulsing for Newtonian and non-Newtonian power-law liquids at elevated temperature and moderate pressure. Four morphological features of the liquid holdup periodic pattern were analyzed: shock wave breakthrough, shock wave decay times, shock wave plateau, and shock wave breakthrough amplitude. The shock wave decay and breakthrough times were found to shorten, while correspondingly the shock wave plateau to lengthen, with increasing pressure and temperature. Conversely, the breakthrough amplitude of the shock wave underwent palpable collapse the higher the temperature (and/or pressure). The collapse of the bursting pulses with increasing temperatures and pressures was the result of the reduction of base and pulse liquid holdup levels, delivery of liquid cargo from pulse to baseline flow, and occurrence of dispersive hydrodynamic effects with a tendency to flatten the pulses. Qualitatively, similar effects of temperature and pressure were equally observed whether Newtonian or non-Newtonian liquids were used. The less sensational contrasts prevailing between base and pulse holdups might question the opportunity for implementing induced pulsing strategies in high-temperature, high-pressure tall trickle beds. © 2006 American Institute of Chemical Engineers AIChE J, 2006