In order to investigate the effect of thermal stability of alkanolamide on oil/water interfacial tensions (IFT), lauric diethanolamide (LDEA) was synthesized. The effects of temperature and standing time on the composition and oil/water IFT was studied in detail. The results showed that the changes in composition and oil/water IFT at the same conditions were essentially in agreement. The best standing temperature range was from 30 to 60 °C with a standing time of more than 10 days. The inherent cause of thermal stability on oil/water IFT was revealed through structure characterization and composition analysis with FTIR spectrometry and GC–MS spectrometry. It was found that the composition's change of mixed LDEA systems disturbed the hydrophilic‐lipophilic balance, which influenced the ability to reduce the interfacial tension.
In order to investigate the high interfacial activity and fair oil phase adaptability of alkanolamide, "1:1" type lauric acid diethanolamide impurities (LDEA) were synthesized and purified by the column chromatography method to obtain dodecanoic acid diethanolamide (C 12 DEA), ester mixture, etc. The exact structures of these compounds were further confirmed by IR, gas chromatogrph with mass spectroscopy (GC-MS), and NMR. The influence of each component on the interfacial tension of oil/water (IFT) was studied by systematic quantitative analysis. The results showed that (i) the strength of each system to reduce oil/water IFT is C 12 DEA /DEA ≈ LDEA > C 12 DEA/DEA/ ESTER > C 12 DEA/NaOH > C 12 DEA > C 12 DEA/ESTER > DEA. This indicates that LDEA contributes to the reduction of the oil/water IFT and the enhanced adaptability of crude oil in this order: DEA > > ESTER; (ii) when the IFT of the LDEA/DEA system reached an ultralow value, the minimum content of DEA in the system was 1%, and the maximum ester content was less than 5% when the LDEA/DEA/ ESTER system reached the ultralow IFT; (iii) the possible mechanism of effect of LDEA components on the IFT and oil phase adaptability was proposed as the synergistic process among the hydrogen bonding, alkali effect, and interface self-assembly of molecules in the interfacial layer. The contribution of these three factors were hydrogen bonding > alkali effect > interface self-assembly.
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