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Huge π-conjugated system of carbon nanotubes (CNTs) endows the two-dimensional carbon-based nanomaterials with special affinity towards aromatic organic compounds such as asphaltenes. Based on the special bonding structure, functional CNTs was designed and used for demulsification of crude oil/water emulsion and the treatment of emulsified oily wastewater in our previous study. Despite the macro bottle tests and micro-scale polarizing microscope were used to observe the separation process, the nanoscale or molecular scale demulsification mechanism was still not well understood. Therefore, molecular dynamics (MD) simulations were carried out to study the adsorption and separation behaviors of crude oil/water emulsion on the CNT surface. It was interesting to found that the oil and water was gradiently separated on the CNT surface due to their different spreading velocity resulted from the different affinity and interaction energy between various molecules (water, heptane and asphaltenes) and the CNT material. The demulsification mechanism of CNT was put forward as follows: when oil droplets approach the CNT surface, the water molecules rapidly spread and flow over the CNT surface, while the saturates slowly spread along CNT surface and the molecules with π-conjugated system (such as asphaltenes) were restricted due to their strong interaction with the CNT material. Because of their enormous difference of spreading velocity and time on CNT surface, the oil molecules were stayed and accumulated on CNT surface and thereby separated from the water molecules. The results obtained in this work provides a deep insight into the oil-water separation behaviors when using carbon-based nanomaterials to demulsify the crude oil-water emulsion and the treatment emulsified oily wastewater. [ABSTRACT FROM AUTHOR]

Rapid separation of emulsified oil from oily wastewater is one of the most serious challenges faced in the petroleum industry. In this study, a rapid and efficient demulsifier, functionalized multiwalled carbon nanotubes (F-MWCNTs), was prepared and used to separate the emulsified oil from oily wastewater. Demulsification test showed that the oil removal efficiency could attain as high as 99.8% at an optimal condition within a few minutes. The micro-morphology of the oil–water mixture before and after demulsification was observed using a polarizing microscope. It was found that the fine oil droplets experienced a rapid coalescence to form oil phase floating on the water surface. Mechanism of the demulsification process was discussed. The introduction of the functional groups (such as ‒OH and ‒COOH) on the surfaces of F-MWCNTs enable them good amphiphilicity and therefore easily arriving at the oil/water interface to destroy the interfacial protective film mainly composed of asphaltenes and resins. The findings in this work showed that the F-MWCNT is an efficient nanomaterial to remove emulsified oil from the oily wastewater and might have wide application prospects in the petroleum industry. [ABSTRACT FROM AUTHOR]