Dissolution of surfactants in supercritical CO2 with co-solvents

• We use visualized PVT cell and UV spectrometer to measure the solubility of surfactants in CO2.
• The solubility of nonionic and ionic surfactants in CO2 with co-solvents was studied.
• Ethanol and ethylene glycol are good co-solvents to improve surfactant's dissolution in CO2.
• Dissolution of surfactants in CO2 with co-solvents can increase the mixture's viscosity greatly.

The dissolution of surfactant-like compounds in supercritical CO2 in presence of co-solvents was investigated. The solubility measurement was conducted using a visualized PVT cell combined with UV spectrophotometer method at different pressures and 313 K. The viscosity of mixtures of CO2 and co-solvents with or without dissolved surfactants was also measured at similar conditions using a capillary tube rheometer. Nonionic surfactants (N-NP-10c, branched alkylphenol ethoxylates and APG-1214, alkyl polyglucoside) and anionic surfactants (N-NP-15c-H, sulfonated alkylphenol ethoxylates) were studied, which are good CO2 foaming agents. Experimental results showed that increasing pressure and addition of co-solvents could effectively improve solubility of surfactants in supercritical CO2. The addition of ethanol as a co-solvent could increase N-NP-10c's solubility in CO2 from 0.15 g (100 g)−1 to 1.76 g (100 g)−1 (over 11 times). APG-1214 with a mixture of ethanol and ethylene glycol as co-solvents exhibited an immediate dissolution capability in CO2, and its solubility could reach up to 1.99 g (100 g)−1. The solubility of N-NP-15c-H in comparison with APG-1214 was relatively low, only 0.57 g (100 g)−1 was obtained with the same co-solvents and at similar conditions. The addition of ethanol into CO2 could slightly increase its viscosity, while the effect of ethylene glycol and surfactants was much higher than that of ethanol, which indicates that the dissolution of surfactants in CO2 with co-solvents involves complicated interactions between molecules.

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