Effective Interactions and Adsorption of Heterocyclic Aromatic Hydrocarbons in Kaolinite Organic Solutions Studied by 3D-RISM-KH Molecular Theory of Solvation

Abstract

We employ the molecular theory of solvation also known as the three-dimensional reference interaction site model with the Kovalenko−Hirata closure relation (3D-RISM-KH) to study adsorption of several heterocyclic aromatic hydrocarbons (acridine, benzothiophene, carbazole, dibenzothiophene, indole, and phenanthridine), which are intended to represent bitumen fragments on the surfaces of a single-sheet kaolinite nanoparticle in cyclohexane and toluene solvents. In addition to adsorption, we also examine solvent-mediated effective interactions between two kaolinite nanoparticles in organic and aqueous solutions. The proposed adsorption model serves as a simple prototype of suspensions formed during nonaqueous extraction of bitumen from oil sands of the Athabasca Basin. Using the proposed computational approach, excess adsorption isotherms of bitumen fragments on two different faces of kaolinite were calculated and compared in cyclohexane and toluene solvents at several temperatures. Almost all the studied molecules show strong preference for adsorption on the octahedral aluminum hydroxide surface of kaolinite. While adsorption of the molecules on the tetrahedral silicon oxide surface is weaker, it is still significant compared to the octahedral surface and for some of the studied molecules adsorption appears to be stronger than for the octahedral surface. Due to the better surface and bulk solvation properties of toluene, the adsorption of the bitumen fragments in toluene is weaker than in cyclohexane. Potentials of mean force between kaolinite nanoplatelets in cyclohexane at several temperatures were calculated using the 3D-RISM-KH molecular theory of solvation. Evaluation of effective interactions by conventional molecular simulation techniques generally requires costly free energy integration and therefore is usually avoided by adopting simple and often unrealistic semiempirical effective potentials. On the other hand, the 3D-RISM-KH molecular theory of solvation offers a fully atomistic description with all-atom force fields and notable performance advantages over molecular simulations. Obtained in this way potentials of mean force in organic solvents exhibit complex oscillating behavior and generally possess deeper main minima and smaller aggregation barriers than the corresponding potentials in aqueous solution.

Computational Evaluation of Mg–Salen Compounds as Subsurface Fluid Tracers: Molecular Dynamics Simulations in Toluene–Water Mixtures and Clay Mineral Nanopores

“…In contrast, the Mg–pyrid 2+ compounds almost exclusively bind to the siloxane surface under the same constraints. This result is consistent with recent experiments , and FF modeling − of bitumen fragments in kaolinite nanopores containing organic solvent, in which the hydrophilic bitumen compounds preferentially adsorb to the gibbsite surface via hydrogen bonding.…”

Challenges in developing polymer flocculants to improve bitumen quality in non-aqueous extraction processes: an experimental study

“…This phenomenon has been demonstrated in simulations of kaolinite platelets in water, toluene, and cyclohexane. Stronger short-range attractive forces are present in cyclohexane and toluene than in water (Hlushak et al 2016;Hlushak and Kovalenko 2017). These FBRM results demonstrate that the chord length distribution can be measured under experimental conditions that consist of a dark 10 wt% bitumen solution.…”

Understanding the Liquid States of Cyclic Hydrocarbons Containing N, O, and S Atoms via the 3D-RISM-KH Molecular Solvation Theory

“…Development of force field parameters for saturated ring systems is a non-trivial task. We have first-hand experience of difficulties in obtaining physically meaningful solvent susceptibility functions using available force field parameters for cyclic molecules [ 63 , 64 ]. The performances of the UFF parameters with the MP2/cc-pVTZ level atomic charges for RISM-KH provided reasonable results, in comparison to available experimental results.…”