Underutilization of bubble column reactors due to desorption

Abstract

The occurrence of undesirable desorption of a gaseous reactant due to its supersaturation in the liquid phase is investigated for slow gas—liquid reactions in tall bubble columns within the framework of a modified axial dispersion model. The model accounts for axial dispersion in the gas and liquid phases and change in volume of the gas phase due to absorption of the gaseous reactant and prevailing static head of the liquid phase. For both cocurrent and countercurrent flow operations and for arbitrary kinetics, it is established analytically that such desorption occurs solely due to significant pressure variation in the reactor. Necessary and sufficient conditions for the restriction of such desorption to the top portion of the reactor are also obtained in the regions of interest for bubble column operation. Numerical illustrations are provided for two commonly encountered situations: (a) imperfectly mixed gas and liquid phases, and (b) an unmixed gas phase with a well-mixed liquid phase. The roles of various system parameters in the occurrence and elimination of desorption and the penalties imposed by it on reactor volume and power requirements for the desired gas phase and liquid phase conversions are examined.