Abstract
Six sodium para-dimethyl alkylbenzene sulfonates (PDABS, abbr. p-S12-5, p-S14-5, p-S16-5, p-S18-5, p-S16-6 and p-S16-8, respectively) have been synthesized. The structures and the purities of the products have also been confirmed by 1H-NMR and mass spectrometry. Crude oil and its equivalent alkanes were chosen as oil phases. The effect of the NaOH concentration on the interfacial tension (IFT) of PDABS was investigated by using a spinning drop tensiometer. The results showed that, in a certain range of NaOH concentrations, p-S14-5, p-S16-5 and p-S18-5 produced ultra-low IFT (∼10−3 mN m−1). NaOH was roughly similar to NaCl in aqueous solutions in terms of its effect on interfacial concentration and arrangement of PDABS at the interface. With the increase in the concentration of NaOH, the electric double layer of hydrophilic groups in PDABS was compressed to become smaller and the electrostatic interactions between hydrophilic groups weakened, which resulted in an increase in interfacial concentration of PDABS. Continuing to increase the concentration of NaOH, the electrical double layer was further compressed; water molecules could incorporate into the interface through loose hydrophilic groups. Therefore, these two aspects of variations caused IFT to display the trend of decreasing and then increasing with increase of NaOH concentration. However, at higher NaOH concentrations, PDABS molecules were driven into the oil phase by the salting out effect, and this process resulted in a decrease of IFT for water-soluble p-S12-5 and p-S14-5. For oil soluble p-S18-5, this process had little effect on the effective distribution in the oil phase. The effective distribution of PDABS in the oil phase played an important role in stabilizing the interface and reducing IFT. There was no clear evidence that NaOH reduced the IFT between oil and water by showing a synergistic effect between PDABS and active species formed in situ with acidic components in the crude oil.
Highlights
In 1926, Harkins discovered the ultra-low interfacial phenomenon in the study of the interfacial tension (IFT) of the benzene/ water system, induced by sodium oleic acid
For a system of normal paraffin and PDABS aqueous solution, the use of NaOH as an electrolyte changes the ionic strength of the aqueous phase, and changes the size of the electrical double layer of PDABS polar groups, to in turn in uence the IFT
The increase of NaOH concentration results in compression of the electrical double layer, which is bene cial to increasing the interfacial concentration of PDABS, such that IFT decreases gradually
Summary
In 1926, Harkins discovered the ultra-low interfacial phenomenon in the study of the interfacial tension (IFT) of the benzene/ water system, induced by sodium oleic acid. E-mail: zhougd@ jlu.edu.cn improved the corresponding experimental equipment, and the relevant theories were veri ed by experiments.[2,3] In these studies, the model proposed by Vonnegut was modi ed by different numerical expressions, to make it easier to adapt to different conditions and environments To this day, the spinning drop tensiometer continues to be used to measure processes characterized by low IFT. Generation of ULIFT is one of the most effective ways to increase Nc: only under ULIFT can a large amount of residual oil in porous rock be ejected.[4] Alkyl benzene sulfonates (ABS) can produce ULIFT and are used as effective surfactants for chemical ooding.[5] in actual production processes, due to the complex composition of industrial products,[6,7] the lack of basic research on the interfacial performance of ABS and other factors results in some problems: for. The in uence of NaOH concentration on IFT of the oil/water phase was determined by the spinning drop method, producing results of great signi cance for further clarifying the role of NaOH in reducing IFT of oil/ABS solutions
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