Molecular dynamics study of morpholines at water – Carbon dioxide interfaces

Abstract

Abstract Strong international focus on measures aiming to mitigate the emission of carbon dioxide into the atmosphere call for efficient solutions feasible for a wide range of CO2 sources. Low-cost chemicals that are both environmentally friendly and potentially applicable for all stages of carbon dioxide handling, will open new possibilities. Surfactants with affinity towards both water, CO2 and residual hydrocarbons can become a basis for technology that will enable safe long-term storage of carbon dioxide with enhanced hydrocarbon production in carbonate reservoirs. In order to pinpoint surfactant candidates with desired properties, we have performed molecular dynamics simulations of morpholine structures in water/CO2 interfacial systems. Novel surfactant molecules were generated by modifying the structures N-Formyl Morpholine and N-Acetyl Morpholine with hydroxyl and/or ether functional groups. Simulation results revealed that the introduction of simple modifications allowed the morpholines to retain their surfactant ability, while drastically altering their bulk and interfacial affinities in some cases. The formation of surfactant clusters was substantial for all modified surfactants and especially pronounced when a hydroxyl and an ether group were added. When two ether groups were added to NAM, we observed increased solubility and affinity for the carbon dioxide, reduced solubility and clustering in the aqueous phase, and lower interfacial tensions. These characteristics suggest that NAM_OC_COC could be a promising candidate for combined CO2 storage and enhanced hydrocarbon recovery. Results presented in this work clearly demonstrate the potential of our approach of using simple ether and hydroxyl functional groups to tailor the affinity of morpholines for water and carbon dioxide, with our numerical experiments able to achieve effective and fast screening of modifications.