Multiscale Modeling of Mass Transfer and Adsorption in Liquid–Liquid Dispersions. 2. Application to Calcium Naphthenate Precipitation in Oils Containing Mono- and Tetracarboxylic Acids

Kovalchuk, Karina; Riccardi, Enrico; Grimes, Brian A.

doi:10.1021/ie501296t

Cited by 5 publications

(13 citation statements)

References 36 publications

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“…This means that when the two metal ions (Ca 2+ , Mg 2+ ) present in a solution, most likely Ca 2+ will be able to diffuse faster to any available COO -groups, especially for tetracarboxylic acids adsorbed at an oil-water interface where transport dynamics 7,8 should affect the selectivity.…”

Section: Fig 5: Helmholtz Free Energy E Int Curves Of the Metal Imentioning

confidence: 99%

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Ab Initio Molecular Dynamics Study on the Interactions between Carboxylate Ions and Metal Ions in Water

et al. 2015

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The interaction between a carboxylate anion (deprotonated propanoic acid) and the divalent Mg(2+), Ca(2+), Sr(2+), Ba(2+) metal ions is studied via ab initio molecular dynamics. The main focus of the study is the selectivity of the carboxylate-metal ion interaction in aqueous solution. The interaction is modeled by explicitly accounting for the solvent molecules on a DFT level. The hydration energies of the metal ions along with their diffusion and mobility coefficients are determined and a trend correlated with their ionic radius is found. Subsequently, a series of 16 constrained molecular dynamics simulations for every ion is performed, and the interaction free energy is obtained from thermodynamic integration of the forces between the metal ion and the carboxylate ion. The results indicate that the magnesium ion interacts most strongly with the carboxylate, followed by calcium, strontium, and barium. Because the interaction free energy is not enough to explain the selectivity of the reaction observed experimentally, more detailed analysis is performed on the simulation trajectories to understand the steric changes in the reaction complex during dissociation. The solvent dynamics appear to play an important role during the dissociation of the complex and also in the observed selectivity behavior of the divalent ions.

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Section: Fig 5: Helmholtz Free Energy E Int Curves Of the Metal Imentioning

confidence: 99%

“…8, the results presented in the previous sections are schematically summarized in an attempt to explain the specific ion selectivity. It should be noted that the scaling in the figure does not represent the true values and it is made just for clarity of illustration.…”

mentioning

confidence: 99%

Ab Initio Molecular Dynamics Study on the Interactions between Carboxylate Ions and Metal Ions in Water

et al. 2015

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“…The results suggested similar behavior of the two TAs as a function of the increasing interfacial concentration, where 50% of the TA molecules are cross-linked when the interfacial coverage is around 70%. The fractional conversion increases nonlinearly with an increase of the surface coverage but does not demonstrate the sigmoidal shape assumed by Kovalchuk et al 12 Thus, the f p (Γ TA ) calculated in this work should be employed in the process model of Kovalchuk et al 12 to properly characterize the cross-linking mechanism in the multiscale framework. Analysis of the intra-and intermolecular cross-linked sites demonstrated that the intramolecular sites are dominating and are increasing linearly with an increase of the surface concentration.…”

Section: ■ Conclusionmentioning

confidence: 71%

“…An important constituent function in this multiscale approach is the fractional conversion [f p (Γ TA )] of TAs to calcium naphthenate precipitates as a function of the interfacial concentration of TAs. Because the functionality of the fractional conversion is not known, Kovalchuk et al 12 assumed f p (Γ TA ) to have a sigmoidal shape.…”

Section: ■ Introductionmentioning

confidence: 99%

“…The extent of cross-linking is dependent on the interfacial concentration of the TAs, Γ TA . Consequently, a multiscale framework , employing MD simulations and continuum modeling has been developed for liquid–liquid dispersions to predict Γ TA on the process scale, which could provide quantitative results for the mass of calcium naphthenate precipitates produced per unit process volume. An important constituent function in this multiscale approach is the fractional conversion [ f p (Γ TA )] of TAs to calcium naphthenate precipitates as a function of the interfacial concentration of TAs.…”

Section: Introductionmentioning

confidence: 99%

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Coarse-Grained Interface Surfactant Density Maps for Calculation of the Fractional Conversion of Tetrameric Carboxylic Acids to Calcium Naphthenate Precipitates

Mehandzhiyski

Grimes

2016

Ind. Eng. Chem. Res.

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Modeling molecular interactions on different length scales is often necessary and presents a significant challenge in chemical engineering. In the present study, we apply molecular dynamics (MD) simulations on different tetrameric carboxylic acid (TA) molecules absorbed at a water–oil interface, which tend to form a cross-linked network in the presence of calcium. From the MD simulations, we obtain various spatial probabilities describing the molecular geometries of TAs in the interfacial region. The MD-obtained probability distribution functions are then used to recreate a coarse-grained representation (interface map) of the interfacial density of the TA molecules. The interface maps are created by randomly placing molecules in an interfacial region and calculating the coordinates of the carboxylate groups according to the MD probability functions. By creating a large number of interface maps, we can obtain a better statistical representation of how the molecules are spatially arranged at the interface at different interfacial concentrations. The orientation and distance between the carboxylate groups from different TA molecules is important for the study of the formation of calcium naphthenate precipitates occurring in the petroleum industry. After an interface map has been built, we can assess how many molecules are cross-linked for a given interfacial concentration based on MD-calculated calcium carboxylate binding probabilities. Subsequently, we can obtain the fractional conversion [f p(ΓTA)] of tetrameric acids to cross-linked calcium naphthenate precipitates. The fractional conversion function can then be used in multiscale approaches for further elucidation of the phenomena of calcium naphthenate precipitation.

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Interfacial Shear Rheology of Gels Formed at the Oil/Water Interface by Tetrameric Acid and Calcium Ion: Influence of Tetrameric Acid Structure and Oil Composition

Simon

Subramanian

Gao

et al. 2015

Ind. Eng. Chem. Res.

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The tetrameric acid ARN is present in crude oil and can form deposits that can cause plugging in oil production facilities during oil production in the presence of calcium ions. It has been previously shown that BP-10, a compound designed to mimic the properties of ARN, can form gel at the oil/water interface by reacting with Ca 2+ if the pH is high enough to ionize BP10s carboxylic acid functions. In this study, the BP-10 and ARN are compared. Although BP-10 forms a gel at the interface, ARN creates rather a viscoelastic material perhaps due to the presence of impurities like naphthenic acids in the sample analyzed. The amount of BP-10 required to form a gel at the interface was found to be ca. 0.45−0.76 mg·m −2 . The influence of the presence of asphaltenes on the gel formation has then been studied. It has been found that the gel is weakened in the presence of asphaltenes and G′ is not measurable at high enough concentrations. This inhibition could result from either a competition between ARN and asphaltenes to adsorb at interface or complexation of ARN and asphaltenes in the oil bulk phase. The influence of naphthenic acid (NA) on the gel formation was also studied by considering a commercial mixture of NA from Fluka. It is shown that NA can inhibit the gel formation of ARN or BP-10 at the oil/water interface most likely by acting as a cross-linking termination point agent. Finally, the effect of commercial calcium naphthenate inhibitors on gel strength has been studied. It is found that the inhibitors delay the formation of tetrameric acid gels and reduce their elastic modulus G′. However, results show that the order of inhibitor efficiency depends on the tetrameric acid used (ARN or BP-10). This could be linked to different specific inhibitor/TA interactions between ARN and BP-10. In conclusion, interfacial shear rheology appears to be a promising method to screen calcium naphthenate inhibitor.

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Multiscale Modeling of Mass Transfer and Adsorption in Liquid–Liquid Dispersions. 2. Application to Calcium Naphthenate Precipitation in Oils Containing Mono- and Tetracarboxylic Acids

Cited by 5 publications

References 36 publications

Ab Initio Molecular Dynamics Study on the Interactions between Carboxylate Ions and Metal Ions in Water

Ab Initio Molecular Dynamics Study on the Interactions between Carboxylate Ions and Metal Ions in Water

Coarse-Grained Interface Surfactant Density Maps for Calculation of the Fractional Conversion of Tetrameric Carboxylic Acids to Calcium Naphthenate Precipitates

Interfacial Shear Rheology of Gels Formed at the Oil/Water Interface by Tetrameric Acid and Calcium Ion: Influence of Tetrameric Acid Structure and Oil Composition

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