Synthesis and evaluation of CO2 responsive surfactants based on dynamic imine bond

In this work, through mixing alkyl primary amines of C_nH_2n+1NH₂ （n=6, HA; n=12, DA; n=18, ODA） and disodium 4-formylbenzene-1, 3-disulfonate (DFD) at 1:1 mol ratio, three novel dynamic imine surfactants (DFD-HA, DFD-DA and DFD-ODA) were synthesized. The imine bond was verified by infrared spectroscopy (IR) and nuclear magnetic resonance (NMR). After preparing the emulsion, DFD-DA exhibited superior stability among the three surfactants at lower concentrations (< 20 mM). Subsequently, an emulsifier system (DFD-DA/LHSB) with excellent interfacial activity and emulsification stability was obtained by blending DFD-DA with lauramidopropyl hydroxy sulfobetaine (LHSB). The system effectively reduced the interfacial tension to the order of 10⁻² mN/m. At a total concentration of 5 g/L and mole ratio (DFD-DA: LHSB = 1:2), the emulsion could be stable for more than 60 days. Contact angle measurements substantiated the superior wettability inversion capability of the system, facilitating the formation of oil-in-water emulsions more effectively. Furthermore, this system possesses remarkable CO₂ responsiveness. After CO₂ injection, the emulsion can be completely demulsified within 45 s in a broad mole ratio range. Changing the relative content of DFD-DA and LHSB can also dynamically regulate the demulsification rate of emulsion. In contrast to previous imine surfactants, the system can achieve full demulsification under higher pH conditions (about 6.0), thereby significantly enhancing the response efficiency and alleviating the equipment corrosion. This discovery provides a new approach to tackling the problems associated with surfactant flooding and heavy oil demulsification, holding important implications for enhancing oil recovery (EOR).