Effect of Electrolytes on Bubble Coalescence in Columns Observed with Visualization Techniques

Abstract

Bubble coalescence and the effect of electrolytes on this phenomenon have been previously studied. This interfacial phenomenon has attracted attention for reactor design/operation and enhanced oil recovery. Predicting bubble coalescence may help prevent low yields in reactors and predict crude oil recovery. Because of the importance of bubble coalescence, the objectives of this work were to improve the accuracy of measuring the percentage of coalescing bubbles and to observe the interfacial gas-liquid behavior. An experimental setup was designed and constructed. Bubble interactions were monitored with a visualization setup. The percentage of air bubble coalescence was 100% in distilled water, about 50% in 0.1 M sodium chloride (NaCl) aqueous solution, and 0% in 0.145 M NaCl aqueous solution. A reduction of the contact gas-liquid area was observed in distillate water. The volume of the resulting bubble was the sum of the original bubble volumes. Repulsion of bubbles was observed in NaCl solutions exceeding 0.07 M. The percentage of bubble coalescence diminishes as the concentration of NaCl chloride increases. High-speed video recording is an accurate technique to measure the percentage of bubble coalescence, and represents an important advance in gas-liquid interfacial studies.

Inhibition of bubble coalescence: Effects of salt concentration and speed of approach

“…Examples include observation of freely rising bubbles in vertical columns with two bubbles rising sideby-side [11][12][13], and a bubble rising to approach the liquid surface [14][15][16][17][18][19][20][21][22] (in this case the air phase above the liquid surface can be considered as an infinitely-large bubble). Some studies have used a bubble contacting device where pairs of bubbles are formed from two adjacent or two directly opposed nozzles [23][24][25][26][27][28][29][30][31][32][33][34][35]. In these studies, coalescence characteristics were examined with bubbles approaching each other at relatively high speeds, i.e.…”

“…Most studies in bubble coalescence deal with the effects of factors such as surfactants [11,12,14,18,20,28,30,32,38,[41][42][43]47,48,[51][52][53], electrolytes [3][4][5][8][9][10]20,21,25,29,[32][33][34][35]38,43,46,[54][55][56][57][58][59][60][61], their concentrations [4,5,11,12,14,20,25,[28][29][30]…”

“…All these models define the transition concentration to be proportional to (dc/dc) À2 , also known as the Marangoni factor. From that time on most experimental works focused not only on the effect of electrolyte on coalescence [33,59] but also on determining transition concentrations for different electrolytes [4,5,9,32,34,35,46,61,68,69]. Almost all these studies show that coalescence occurs easily in pure water and that with increasing concentrations of added electrolytes there is a transition to coalescence inhibition.…”

Rate of Bubble Coalescence following Quasi-Static Approach: Screening and Neutralization of the Electric Double Layer

“…Air-bubble coalescence is frequently encountered in nature as well as in industry12345678910111213141516171819202122232425262728293031323334353637. In some cases, rapid coalescence is preferred, e.g.…”

“…This phenomenon has been widely discussed10111213141516171819202122232425262728293031323334353637, since it appears to be in qualitative contradiction to the DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory38, which describes the stability of colloidal particles in a medium, by calculating the combined effects of van der Waals (vdW) attraction and electric double layer (EDL) repulsion between the particles. It predicts accelerated bubble coalescence in aqueous solutions of electrolytes compared with purified water.…”