Stabilization of CO2-foams in brine by reducing drainage and coarsening using alkyldimethylamine oxides as surfactants.

[Display omitted] • Alkylamine oxides stabilized CO 2 -in-brine foams at low concentrations (0.1–1 wt%) • Foam stabilization was enhanced by intermolecular hydrogen bonding due to low pH. • Long alkyl chains (C 14) and salt promoted formation of large surfactant aggregates. • High protonation degree and bulk viscosity significantly increased the CO 2 -foam half-life. • CO 2 -foam coarsening followed a linear rate of bubble growth, faster than for N 2 -foam. Producing CO 2 -foams in saline environments can be a great challenge in many industrial applications, since fast gas diffusion and reduction of electrical double layer promote fast coarsening and coalescence of bubbles. Amine oxides are zwitterionic surfactants that have been shown to improve foam stability by intermolecular hydrogen bonding, but have not been investigated for CO 2 -foams yet. This paper reports a study on the use of commercial alkyldimethylamine oxides (C x DAO) as foaming agents in brine for CO 2 -foams, based on the interactions present at the low pH imposed by the dissolution of the CO 2 and the presence of salts. Despite the presence of salt and CO 2 increased the protonation degree of amine oxide molecules, favoring hydrogen bonding, a significant improvement in foam stability was only observed when using the long chain surfactant (C 14 DAO). This behavior was attributed to the synergy between increased attractive hydrophobic interactions of alkyl chains and reduced repulsion among ionic surfactant heads, which led to formation of large surfactant aggregates in bulk, as demonstrated by the significant increase in viscosity of the aqueous phase. There was also a decrease in foam drainage and coarsening rates for the foams using C 14 DAO in brine, compared to results in deionized water, suggesting that formation of hydrogen bonds is not enough to arrest the destabilization in CO 2- foams. Moreover, the linear rate of bubble growth obtained for these foams (∝ t) was higher than that reported for N 2 – or air-foams (∝ t 1/2), likely due to the high solubility of CO 2 in the aqueous phase, which accelerated the coarsening phenomena. The results of this work offer insight on the future design of foaming formulations for stabilizing CO 2- foams in applications that require the use of high salinity brines, such as carbon sequestration and oil recovery. [ABSTRACT FROM AUTHOR]