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

Abstract

Producing CO2-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 CO2-foams yet. This paper reports a study on the use of commercial alkyldimethylamine oxides (CxDAO) as foaming agents in brine for CO2-foams, based on the interactions present at the low pH imposed by the dissolution of the CO2 and the presence of salts. Despite the presence of salt and CO2 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 (C14DAO). 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 C14DAO in brine, compared to results in deionized water, suggesting that formation of hydrogen bonds is not enough to arrest the destabilization in CO2-foams. Moreover, the linear rate of bubble growth obtained for these foams (∝t) was higher than that reported for N2– or air-foams (∝t1/2), likely due to the high solubility of CO2 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 CO2-foams in applications that require the use of high salinity brines, such as carbon sequestration and oil recovery.