The effect of liquid phase properties on gas holdup in bubble column reactors

Abstract

The effect of liquid phase properties on gas holdup in bubble column reactors was investigated within a large set of gas-liquid systems. Air was used as a gaseous phase in all experiments, liquid phases included distilled water and aqueous solutions of alcohols and electrolytes. Gas holdup values were determined in a sieve tray bubble column 0.15 m i.d. under conditions of stable uniform gas distribution and an attempt was made to relate these data with values of bubble coalescence ratio determined for respective gas-liquid systems in a coalescence cell. Experimental results proved strong influence of solute addition on bubble coalescence reduction and on the increase of gas holdup values in aqueous solutions of both alcohols and electrolytes. An unambiguous dependence was observed between gas holdup data and values of bubble coalescence ratio in alcohols solutions, the effect of coalescence suppression on gas holdup enhancement increased markedly with increasing gas flow rates. An empirical equation was proposed for estimation of lower and upper gas holdup limits in electrolyte solutions within the coalescence suppression region, i.e. at solute concentrations above coalescence transition value.With the exception of concentrated glycerol solutions, homogeneous bubble beds were generated in all gas-liquid systems using the appropriate gas distributing plate. The positive effect of coalescence restraining on gas holdup values was even more significant in homogeneous bubble beds than under conditions of turbulent bubbling regime.