In our previous papers [1-3], the stability of cellular foam generated from nonionic, anionic, cationic and amphoteric surfactant aqueous solutions was investigated for the purpose of foam breakage in chemical reactors and bioreactors. From the results, it was found that the cellular foam formed from anionic surfactant aqueous solution was the most stable one. In the present study, the growth and collapse process of cellular foam formed on a perforated plate in a standard bubble column was observed using three kinds of anionic surfactant aqueous solutions under the addition of ethanol. As a result, the cellular foam is found to become unstable with increasing concentration of ethanol. Further, to evaluate the stability of cellular foam, the critical film thickness at the time of the burst of the cellular foam is estimated by using the uniform film model of film drainage in the Plateau border to describe the rate of thinning of a film proposed by Hartland and Barber [4] and Barber and Hartland [5]. The critical film thickness increases with ethanol concentration. Moreover, the critical film thickness is correlated in terms of capillary number, HLB (Hydrophile-Lipophile-Balance) value and mass fraction of ethanol.

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