THE EFFECT OF ELECTROLYTES ON BUBBLE COALESCENCE AND GAS HOLDUP IN BUBBLE-COLUMN REACTORS

The purpose of this work was to link the coalescence behaviour of bubb les in aqueous electrolyte solutions with the character of gas-liquid beds generated in bubble column reactors and with corresponding values of bubble bed voidage. The experimental programme, performed with the set of nine inorganic salts, included determination of the bubble coa lescence frequency in a coalescence cell and measurement of gas holdup in a sieve tray bubble column reactor of 0.14 m I.D. Values of the tr ansition concentration, corresponding to the switch from the complete coalescence to virtually total coalescence suppression, were evaluated for all electrolytes studied from respective concentration dependence s of bubble coalescence frequency and the gas holdup values were measu red in solutions of respective electrolytes on both sides of these tra nsition concentrations. The absolute increase of bubble bed voidage du e to the presence of electrolytes was found to be independent of the t ype of electrolyte and varied only with the mode of primary gas disper sion. The appropriate limiting dependences of bubble bed voidage on su perficial gas velocity, corresponding to respective bubbling regimes w ere, for all electrolytes studied, achieved at concentrations close to the transition concentrations of respective electrolytes, while furth er increase of salt concentration had an almost negligible effect on g as holdup values. The influence of electrolytes on the character of bu bble beds and on appropriate values of bubble bed voidage was very str ong in the homogeneous and transition bubbling regimes, while in heter ogeneous bubble beds, it was largely overshadowed by the predominant e ffect of macro-scale turbulence.