Effect of Demulsification for Crude Oil-in-Water Emulsion: Comparing CO2 and Organic Acids

Acidic substances (naphthenic acids) were found in crude oil, which provides favorable conditions for the formation of surfactants. N,N-Dimethylcyclohexylamine (DMCHA) can activate the naphthenic acid in the crude oil to form the surfactant by noncovalent bonding. This process has an unusual meaning for the crude oil pipelines transportation by the method of forming a low-viscosity oil-in-water emulsion. At the same time, CO2 can be used as a demulsifier to separate crude oil and water at the end of pipeline transportation because the surfactant has a CO2 stimulus response characteristic. In our study, it was found that crude oil-in-water emulsion can be formed and has very good stability. CO2 has a high demulsification efficiency in emulsions with lower crude oil content. For high oil content conditions, the emulsion cannot be demulsified completely by CO2 Since sulfuric acid, hydrochloric acid, and the like are liquid and corrosive, this is not conducive to its application as a demulsifier in crude oil pipeline transportation. Organic acids in this area have a stronger advantage obviously, so citric acid, oxalic acid, acetic acid, and lactic acid were used as demulsifiers in this article; all of them have good demulsification performance in high crude oil content emulsions, especially citric acid. Meanwhile, DMCHA can be recycled and reused by adding NaOH to the lower aqueous solution after demulsification.