Synthesis and Physicochemical Properties of CO2-switchable Gemini Surfactants

Abstract

Conventional surfactants have excellent performance but not easily recycled and sustainable. The CO2/N2 switchable Gemini surfactants can be reused while maintaining performance and can also effectively utilize greenhouse gas CO2, thereby reducing carbon emissions. In our work, three tertiary amines N, N'-dimethyl N, N'-dialkyl ethylenediamine with different hydrophobic chain lengths (CnDEs, n = 12, 14, and 16) were fabricated by a two-step process using alkyl bromide, ethylenediamine, formic acid, and formaldehyde as raw materials. Structures of intermediates and end products were characterized by FTIR and 1H NMR. The Gemini surfactants such as N,N′-dimethyl N,N′-bis (dodecane, tetradecane, and hexadecane) alkylethylenediamine bicarbonates (CnDBs, n = 12, 14, and 16) were generated by the synthetic corresponding tertiary amines after bubbling CO2. After bubbling N2, the bicarbonate surfactants were converted into tertiary amine non-surfactants again. The reversibility of the switching of three surfactants was verified by measuring the changes in surface tension, zeta potential, particle size distribution, and foaming volume before and after CO2/N2 bubbled into the tertiary amine solutions. The physicochemical properties of CnDBs were studied by thermogravimetric analysis, surface tension measurement, cation content measurement, and dissipative particle dynamics (DPD). The results demonstrated that the synthesized CO2/N2 switchable Gemini surfactants had excellent reversibility and reproducibility. The application properties indicated that the Gemini surfactants could reduce interfacial tension of oil/water to ultra-low value; possessed good cation conversion rate and decent foaming properties. Furthermore, the surfactant performances were verified through DPD simulation experiments. With the industrialization of synthetic technology, the costs of CO2/N2 switchable Gemini surfactants will effectively decrease. Storage and utilization of considerable quantities carbon dioxide promote our green low-carbon life, which are conducive to the achievement of the national strategic goal of China's carbon peak in 2035 and carbon neutralization in 2050.