Synthesis And Properties Of Imidazoline Type CO ₂ 2 Switching Surfactants

In practical application, surfactant should be separated from the system or lose surface activity after completing their function. Switchable surfactants, which can undergo fully reversible interconversions between active and inactive forms through chemistry or electro-chemistry method, could be used to address this problem in a satisfactory way. Actually, the system based on switchable surfactant can realize the separation of oil and water on demand. There are several triggers based on addition of acids, bases, oxidants or reductants, electro-chemistry, etc. However, they still have several drawbacks because the nature of the triggers can limit the practical viability of switchable surfactants, while the recycled carbon dioxide is environmental benign and inexpensive. However, the synthetic root of long chain amidine is very difficult. Therefore, it is important to develop a novel kind of CO2switchable surfactants based on amidine group.In the present study, decanoic, dodecanoic, tetradecanoic acids and N-(2-hydroxyethyl) ethyl en ediamine were employed to synthesize the2-alkyl-l-hydroxyethylimidazolines, which reacted with CO2to produce the bicarbonates cationic surfactants:2-alkyl-1-hydroxyethyl imidazolinium. The optimal reaction conditions of2-alkyl-l-hydroxyethylimidazolines were studied as follows:xylene as solvent, n (acid):n(amine)=1:1.2, the amidation reaction time is4h, and the temperature is140℃, while the recyclization reaction time is4h, and the temperature is220℃. IR and ’H-NMR were used to characteristic the molecular structure of the products, which showed that the compounds met the anticipative requirements. Additionally, decanoic. dodecanoic, tetradecanoic acids and triethylenetetramine were employed to synthesize (1’,2’-ethylene)-1-bis (2-alkylimidazoline) and the bicarbonates.The properties of the amidine switchable surfactants were evaluated in this paper, including the surface tension, cation content, thermogravimetric analysis, etc. Additionally, the measurements of electrical conductivity, Zeta potential, particle size analysis, emulsifying-demulsification and foam on-off reversibility were conducted to verify the switchablity of CO2/N2trigger. The results showed that,2-alkyl-1-hydroxyethylimidazolinium bicarbonates cationic surfactants can remarkably reduce the surface tension. The cation contents (active substance) of the amidinuims bicarbonates surfactants were more than80%.2-alkyl-l-hydroxyethylimidazolinium bicarbonates cationic surfactants was reduced to amidine, CO2and H2O about60℃.The conductivity of2-alkyl-1-hydroxyethylimidazolines in water sustained rise with CO2addition, and then gradually decreased with bubbling N2. Zeta potential of HEAls in aqueous solution increased after bubbling of CO2, and then decreased upon N2addition. The dynamic light scattering experiment proved the particle size of amidine in aqueous solution decrease after bubbling CO2and then increase again by bubbling N2. In emulsification experiments, the bicarbonate surfactants can emulsify the dodecane and water, then demulsify easily after N2addition. However, the emulsion of heavy oil and water stabilized by the imidazolinium cannot be broken, this may because imidazoline could be hydrolyzed to amideand due the endogenous surfactans in heavy oil, which is surface-active and can also emulsify water and alkane.We also investigate the probability that2-dodecyl-1-hydroxyethylimidazolinium used as foaming agent which can be switchable controlled.2b is the long chain alkyl imidazolinium based on hydroxyl, have good solubility and foam ability which can generate stable foam in20-80℃, and thus dissipated rapidly upon exposure to N2or air after foam drainage.