Adsorption of Indole on Kaolinite in Nonaqueous Media: Organoclay Preparation and Characterization, and 3D-RISM-KH Molecular Theory of Solvation Investigation

Abstract

Current oil sand mining operations in the Athabasca basin are predominantly aqueous-based. Extracts containing large amounts of fines lead to the formation of stable organoclay suspensions in froths giving lower yields and greater tailing wastes and making the development of more efficient extraction methods desirable from both economical and environmental perspectives. We examine an indolekaolinite system as a model for these oil fines and their resistance to washing in nonaqueous solvents. The prepared organoclays show indole loading exclusively on the external surface of the clay. Micron-scaled vermicular structures, similar to natural kaolinite, are observed. Their formation is believed to be driven by strong adsorbate− adsorbate interactions. Indole is the primary adsorbate, as solvent adsorption is shown to be minimal based on both experimental and computational results. Isotherms are constructed and parameters calculated from linear regression analysis fitted to the Brunauer−Emmett−Teller equation. Monolayer quantities calculated match well to the theoretical amount calculated from surface areas measurements. Washing the organoclays with both toluene and isopropanol results in a 50% decrease of loaded organic material, leaving a monolayer equivalent of organic matter. The statistical-mechanical 3D-RISM-KH molecular theory of solvation is employed to perform full sampling of solvent orientations around a kaolinite platelet and gain insights into the preferred orientation and adsorption thermodynamics of indole on kaolinite in toluene and heptane solvents. In its preferred orientation, indole is hydrogen-bonded to one or two O atoms at the aluminum hydroxide surface of kaolinite. The calculated solvation free energy and potential of mean force for adsorption of indole and solvents on kaolinite in solution yield the increasing adsorption strength order of heptane < toluene < indole on the aluminum hydroxide surface. Multilayer adsorption profiles are predicted based on the integrated three-dimensional distribution functions of indole, toluene, and heptane.

Molecule–Surface Recognition between Heterocyclic Aromatic Compounds and Kaolinite in Toluene Investigated by Molecular Theory of Solvation and Thermodynamic and Kinetic Experiments

“…The g γ (r) density distribution isosurfaces yield predictions of the preferred adsorption configurations, as shown for indole. 31 The isosurfaces of g γ (r) calculated using the 3D-RISM-KH theory suggest a set of statistically probable solvent arrangements and orientations that are more realistic for solvent in liquid phase at room temperature than, for example, an optimized geometry. 52 Moreover, based on g γ (r), we evaluate the binding capacity and affinity of HAC based on the strongest-bonded sites of HAC molecules on kaolinite.…”

“…30 Recently, we reported the preparation, characterization, and computational investigation of indole−kaolinite organoclays formed by hydrogen bonding recognition interactions in the presence of toluene and heptane solvents. 31 The two major computational modeling approaches employed to study molecule−kaolinite interactions are molecular simulations and electronic structure calculations. Molecule−kaolinite interactions, such as water adsorption, 32,33 and intercalation of small organic molecules, including dimethyl sulfoxide, formamide, and methanol, 34 have been studied using molecular simulations.…”

Solvation Thermodynamics of Organic Molecules by the Molecular Integral Equation Theory: Approaching Chemical Accuracy

“…Moreover, the theory is not limited to bulk water solutions and it can be generalized to many different pure and mixed solvent systems. [171][172][173] RISM theory has been used to study a wide-variety of physicochemical phenomena: the surface- …”

“…172,312 In these studies the 3D RISM/KH method was used to predict the adsorption configuration and thermodynamics from the 3D site density distribution functions and total SFE, respectively, for adsorption of HAC and solvents (toluene and heptane) on kaolinite. The results were used to interpret spectrophotometric measurements and experimentally determined adsorption isotherms.…”

Adsorption of Bitumen Model Compounds on Kaolinite in Liquid and Supercritical Carbon Dioxide Solvents: A Study by Periodic Density Functional Theory and Molecular Theory of Solvation

“…Nonbonding parameters and partial charges for the kaolinite atoms are adopted from the CLAYFF general force field developed by Cygan et al 71 For the bitumen model compounds, we use the nonbonded parameters σ and ε from the OPLS all-atom force field 87,88 and atomic charges calculated using the MOPAC2012 computational chemistry software, 89 as in our previous studies. 68,69 ■ RESULTS AND DISCUSSION DFT in PBC Calculations. The PW91/DNP method implemented in the DMol 3 software was used to fully optimize the geometries of the bitumen model compounds on kaolinite.…”