Dongfang Liu,Yuxin Suo,Jihe Zhao,Peiyao Zhu,Jiang Tan,Baogang Wang,Hongsheng Lu
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.
Honghong Li,Qian Li,Jingcheng Hao,Zhenghe Xu,Dejun Sun
We prepared a CO 2 responsive emulsion by using switchable hydrophobic tertiary amine, N , N -dimethylcyclohexylamine (DMCHA). DMCHA exhibits little miscibility with water in the absence of CO 2 , but shows a complete miscibility with water in the presence of CO 2 . DMCHA converts to water-soluble bicarbonate salts upon treatment with CO 2 , which could induce the ionic strength increase of aqueous phase. Together with paraffin oil, DMCHA was used to prepare CO 2 responsive O/W emulsions with a conventional surfactant, sodium dodecyl benzene sulfonate (SDBS), as the emulsifier. Emulsions containing DMCHA in paraffin oil were more stable than those without DMCHA, as a result of electrostatic interactions between a small fraction of protonated DMCHA and SDBS, confirmed by surface tension and 1 H NMR measurements. However, when exposed to CO 2 most of the paraffin oil and water separate from the emulsion with formation of a middle phase microemulsion. More significantly, DMCHA could be separated from the lower water phase upon removal of CO 2 and recycled.
Ionic liquid surfactants (ILSs) show great potential for forming wormlike micelles (WLMs) due to their tunable molecular structures. However, their economic and environmental sustainability remains challenging. In this study, a fully recyclable PS-DMCHA ILSs was synthesized from a 1:1 molar mixture of palmitic acid (PA) and stearic acid (SA) (denoted PS) with N, N -dimethylcyclohexylamine (DMCHA). The HOMO, LUMO and molecular electrostatic potential were calculated by Dmol 3 with PBE functional. The formation of WLMs was confirmed through surface tension measurements, rheological analysis, and Cryo-TEM imaging. The recyclability of PS and DMCHA was validated using FTIR, 1 H NMR and molecular dynamics simulation. Results revealed that electrostatic interactions and proton transfer drive the formation of ILSs. The long carbon chain of PS contributes to the low surface tension of the ionic liquid system. The combination of PA and SA enables the formation of an ionic liquid at room temperature. When the concentration of ILSs exceeded 6.31 wt%, a wormlike network was formed. Under acidic conditions (pH<4), PS was fully precipitated from the viscoelastic fluids as a solid and separated out, while DMCHA was recovered under basic conditions (pH>12). This study offers valuable insights into enhancing both the economic and environmental feasibility of WLMs as recyclable fracturing fluid systems.
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