Temperature sensitivity of CO2-triggered switchable surfactants with acetamidine group

Abstract

In this study, a series of CO2-switchable acetamidines surfactants with different hydrophobic tail groups were synthesized using N, N-dimethylacetamide dimethyl acetal and different aliphatic amines. The conductivity assessment demonstrated the exceptional CO2-switchable performance of these surfactants. It was believed this switchability mainly resulted from the activity of acetamidine groups which could react with CO2 to form the amphiphilic acetamidine carbonate. For this reason, the protonation during CO2 bubbling of acetamidine surfactants with longer hydrophobic tail was more likely to occur at higher temperature due to the improved solubility. It was also found that acetamidines containing shorter hydrophobic tail tend to be more temperature-insensitive in the protonation process. However, as for the deprotonation process (N2 bubbling), the as-formed acetamidines bicarbonates with short hydrophobic tails displayed evident temperature sensitivity, and thus higher temperature favored the regeneration of acetamidines. Additionally, the acetamidine bicarbonates with longer hydrophobic tails showed remarkable surface activity in the hexadecane/water emulsion than those with shorter hydrophobic tails. Furthermore, higher temperature and longer standing time accelerated the N2-triggered demulsification and the recovery of oil phase. The temperature sensitivity could allow these acetamidines to be deployed in CO2-triggered enhanced oil recovery (EOR).