Estimation of transition concentration of aqueous mixtures of single and binary electrolytes for bubble coalescence inhibition

Abstract

A bubble column was investigated in which a swarm of air bubbles was dispersed in aqueous electrolyte (NaCl, MgSO4·7H2O, CaCl2·2H2O, and Na2SO4) solutions. In the present work, study of coalescence inhibition has been targeted by applying gas holdup enhancement and surface tension gradient approaches for aqueous solutions in single and binary mixtures (CaCl2·2H2O + NaCl and Na2SO4 + NaCl) of electrolytes. Transition concentrations of a series of coalescence inhibiting inorganic electrolytes were determined. A qualitative comparison of these electrolytes revealed that strong electrolytes (Na2SO4, and CaCl2·2H2O) yield gas holdup enhancement ≥ 60% whereas moderate electrolytes (NaCl and MgSO4·7H2O) give gas holdup enhancement values ≤ 46%. It has been also found that the values of transition concentration for different electrolytes are of the same order in most of the cases and in line with those reported in the literature. Inhibition of bubble coalescence was also analyzed in terms of the parameter $$ C\left( {{\text{d}}\sigma /{\text{d}}C} \right)^{2} $$ . The large value of the parameter $$ ({\text{d}}\sigma /{\text{d}}C)^{2} $$ indicates that the electrolyte will inhibit bubble coalescence, and a smaller value indicates moderate effect on bubble coalescence. Surface elasticity values at transition concentration of various electrolytes were also determined. It was found that the surface elasticity values at transition concentration were in the order CaCl2·2H2O > MgSO4·7H2O > Na2SO4 > NaCl. Surface elasticity for binary electrolytes was also estimated at their transition concentrations. The values were found in the order CaCl2·2H2O + NaCl > Na2SO4 + NaCl. Furthermore, analysis of variance was employed to estimate significance of the parameters.