Phase space trajectories of protonated and deprotonated mono-and tetracarboxylic acid surfactants at an oil/ water interface are obtained from molecular dynamics (MD) simulations and are employed to calculate the interfacial area of the molecules as a parameter for a molecular mixed monolayer model. Three simple methods, based on the available volume at the interface and the solvent accessible area, are applied to calculate the interfacial molecular areas from the MD trajectories. Experimental equilibrium interfacial tension (IFT) data for single component systems are employed with the calculated interfacial molecular areas to fully parametrize the model in order to predict the equilibrium IFT data for mixed solutions of mono-and tetraacids. The agreement between experiment and theory is found to be good. The methodology demonstrated here provides a tool to evaluate the effect of the bulk concentration and composition of various model crude oil surfactant compounds on their interfacial concentrations and composition upon the initial formation of a monolayer at a water/oil interface. In part 2 (Kovalchuk, K.; Riccardi, E.; Grimes, B. A. Multiscale Modeling of Mass Transfer and Adsorption in Liquid−Liquid Dispersions. 2. Application to Calcium Naphthenate Precipitation in Oils Containing Mono-and Tetracarboxylic Acids. Ind. Eng. Chem. Res. 2014,
A dynamic multicomponent mass transport model is constructed and solved to determine the interfacial composition and bulk phase concentrations of surfactant mixtures containing a synthetic tetracarboxylic acid (BP10) and decanoic acid (DA) for water droplets dispersed in oil. The transport model employs a molecular mixed monolayer adsorption model that was parametrized by MD simulation and interfacial tension experiments in part 1 [Kovalchuk, K.; Riccardi, E.; Grimes, B. A. Ind. Eng. Chem. Res. 2014, ]. The model accounts for oil−water partitioning, the pH determined dissociation state of the acids, and micelle formation in the water phase. Since the interfacial concentration of tetracarboxylic acids in crude oil emulsions is hypothesized to influence the extent of fouling by calcium naphthenate precipitation, trends for the amount of calcium naphthenate precipitate formed in the system can be predicted as a function of the water volume fraction for various BP10:DA concentration ratios and drop sizes. The model provides an experimentally testable prediction that could support the hypothesis that calcium naphthenate precipitation is an interfacial reaction and have implications on petrochemical and engineering based inhibition strategies. The modeling framework outlined in parts 1 and 2 of this work is well-suited to studying interfacial phenomena in well-defined model systems employing a library of synthetic and purified indigenous crude oil surfactants.
The interfacial properties of three succinic surfactants (PIBSA) with different hydrophilic end groups and sorbitan monooleate (SMO) in water-in-oil emulsions of the liquid explosive type were studied. The aqueous phase contained 40% of ammonium nitrate (AN). The trend in equilibrium interfacial tension was found to be PIBSA-MEA > PIBSA-UREA > PIBSA-MEA/ SMO mixture > PIBSA-IMIDE > SMO, where MEA, UREA, IMIDE are amid/amide, urethane and imide end groups, respectively. The same trend was observed for the interfacial elastic modulus. The FTIR study revealed interactions between surfactant head groups and an AN solution. The interactions depend on the polarity of head groups determined by their chemical structure. The packing efficiency of the surfactants under study is also influenced by the chemical structure of head groups. Attempts to model the conformation of the surfactants at the interface were made. The investigation of mixed interfacial cover (PIBSA-MEA/SMO) showed that SMO remained at the interface reducing the interfacial tension at the W/O interface. It was also demonstrated that variation of the nature of head groups influences the rheological properties of emulsions. Bulk elasticity and yielding correlate with interfacial interaction characteristics.
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