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C: Surfaces, Interfaces, Porous Materials, and Catalysis

Computational and Experimental Investigations of the Role of Water and Alcohols in the Desorption of Heterocyclic Aromatic Compounds from Kaolinite in Toluene Mateus R. Lage, Gustave Kenne Dedzo, Stanislav R. Stoyanov, WenJuan Huang, Sergey Gusarov, José Walkimar de M. Carneiro, Christian Detellier, and Andriy Kovalenko J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b12655 • Publication Date (Web): 19 Apr 2018 Downloaded from http://pubs.acs.org on April 19, 2018

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The Journal of Physical Chemistry

Computational and Experimental Investigations of the Role of Water and Alcohols in the Desorption of Heterocyclic Aromatic Compounds from Kaolinite in Toluene Mateus R. Lage,a,b,c,d,* Gustave K. Dedzo,e,f,i* Stanislav R. Stoyanov,g,h,a,b,* WenJuan Huang,a,b Sergey Gusarov,a,b José Walkimar de M. Carneiro,d Christian Detellier,e,f Andriy Kovalenkoa,b,* a

National Institute for Nanotechnology, Edmonton AB, Canada T6G 2M9; bDepartment

of Mechanical Engineering, University of Alberta, Edmonton AB, Canada T6G 2G3; c

Federal University of Maranhão, Campus Balsas, Rua José Leão 484, Centro, Balsas

MA, Brazil 65800-000;

d

Department of Inorganic Chemistry, Fluminense Federal

University, Outeiro de São João Batista, s/n, Centro, Niteroi RJ, Brazil 24020-141; e

Department of Chemistry and Biomolecular Sciences, University of Ottawa, 10 Marie-

Curie, Ottawa ON, Canada K1N 6N5; fCentre for Catalysis Research and Innovation, University of Ottawa, Ottawa ON, Canada K1N 6N5; gNatural Resources Canada, CanmetENERGY in Devon, 1 Oil Patch Drive, Devon AB, Canada T9G 1A8; h

Department of Chemical and Materials Engineering, University of Alberta, 9211 - 116

Street NW, Edmonton AB, Canada T6G 1H9. iLaboratory of Analytical Chemistry, Faculty of Science, University of Yaounde I, B.P. 812, Yaoundé, Cameroon. * Corresponding Authors. E-mail: [email protected]; [email protected]; [email protected]; [email protected]

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Abstract Non-aqueous extraction is an attractive alternative to the currently employed warm water process for extraction of bitumen from oil sands, as it could use less energy and water. Hydroxylated cosolvents, such as alcohols, that compete for the adsorptive clay surfaces and help release bitumen components could help improve bitumen recovery. The water naturally present in oil sand also affects oil-mineral interactions. Electronic structure methods and the statistical-mechanical 3D-RISM-KH molecular theory of solvation as well as experimental desorption measurements are employed to study the effects of water and aliphatic alcohol cosolvents in toluene solvent on the desorption of fused pyridinic heterocycles (ArN) from kaolinite. The geometries of phenanthridine and acridine (representative of pyridinic heterocycles of petroleum asphaltenes) adsorbed on the kaolinite clay surface are optimized in periodic boundary conditions using density functional theory. The 3D-RISM-KH method is employed to calculate the solvation free energy and potential of mean force for adsorption of the heterocycles on kaolinite in pure and alcohol-containing toluene. The potentials of mean force show that the adsorption of the fused pyridines on kaolinite is stronger in pure toluene than in toluene mixed with aliphatic alcohol. Analysis of the mechanism of desorption of phenanthridine and acridine from kaolinite in toluene containing alcohol reveals that the alcohol stabilizes both the pyridinic moiety and kaolinite platelet by hydrogen bonding, thus disrupting the ArN…HO-Al(kaolinite) hydrogen bond. A mechanism for retention of toluene on kaolinite is also highlighted. Experimental studies of the desorption of fused pyridines from an ArN-kaolinite aggregate show that in water-saturated toluene the rate of desorption of the phenanthridine from kaolinite is twice as high as that in dry toluene. The experimental and computational results show that water and aliphatic alcohols in 2 ACS Paragon Plus Environment

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toluene help desorb pyridinic heterocycles from kaolinite, a clay mineral abundant in the oil sands. The presented insights are valuable for understanding the molecule-clay interactions in solution and relevant to improving the non-aqueous extraction of bitumen from oil sand.



Introduction Alternative sources of petroleum are abundant and economically important.1 The depletion of conventional oil fields and the structural and compositional complexity of heavy petroleum are driving fundamental changes in the modern oil industry worldwide. Oil is being derived increasingly from alternative sources such as oil sand and shale oil.2 The oil sand deposits in the Athabasca region of western Canada along with those in Venezuela and the conventional petroleum deposits in Saudi Arabia are the largest hydrocarbon deposits in the world.1,3 Oil sands are a mixture of bitumen, sand, clays, and water.1,4,5 Bitumen, a very heavy petroleum, contains large amounts of S, N, O, Ni, and V that according to the supramolecular assembly model6 contribute substantially to asphaltene aggregation, a major effect responsible for bitumen’s distinct physical properties.1 The strong adsorption affinity of bitumen towards the lamellar clay kaolinite, a typical and adsorbent constituent of oil sand, poses challenges for bitumen extraction.1,4,5 Due to the complexity of bitumen, representative models have been developed to facilitate studies of its chemical and physical behavior.4,5 Considering that the main interactions that make bitumen distinct from conventional oil arise from the presence of heteroatoms, model heterocyclic compounds can be used to represent certain aspects of the chemical behavior and properties of bitumen.7 Therefore, studies on the interaction of mineral clays, such as kaolinite, with heterocycles can provide important insights into bitumen-clay interactions so as to help improve the existing bitumen extraction technologies.7,8 There is a renewed interest in non-aqueous extraction of bitumen from oil sands, as highlighted in a recent review on this theme,9 due to the high water and energy usage 4 ACS Paragon Plus Environment

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associated with the currently used hot water-based process and the challenges of tailings remediation. Several approaches for extraction of bitumen using ionic liquids at nearambient conditions,10 critical and supercritical CO2,11 and organic solvents,12,13 have been tested at small scale.5,14 Despite encouraging results, non-aqueous extraction has not yet been used commercially for bitumen mainly due to poor solvent recovery.5 Solvent retention in tailings is a major challenge to the large-scale implementation of nonaqueous extraction processes.9 Improved understanding of the mechanism of the complex bitumen-clay-solvent interactions is key to the sustainable development of this abundant natural resource.15 Kaolinite is a 1:1 phyllosilicate composed of a tetrahedral silicon oxide sheet coupled with an octahedral aluminum hydroxide sheet.16,17 Layers of kaolinite stack together due to numerous hydrogen bonds between the silicon dioxide and aluminum hydroxide surfaces from adjacent kaolinite layers.17,18 These multiple bonds restrict the access of molecules to the interlayer of kaolinite to the extent that only a few molecules and salts can intercalate in a single step.19,20 Employing a melt intercalation approach, we have prepared a number of grafted19,21 and intercalated kaolinite composites.19,22 Kaolinite adsorbs a wide variety of compounds on its surfaces and is widely used as adsorbent for environmental decontamination.23,24 Removal of compounds from kaolinite surfaces can be very challenging and requires extensive investigation,25,26 as for example, in the predominantly kaolinite and illite organoclays4 of the Athabasca oil sands, which are hydrophobic in nature due to adsorbed bitumen components.27,28 Polar groups of heavy oil components adsorb on the hydrophilic surface of aluminum hydroxide of kaolinite by forming hydrogen bonds and partially coat the clay particles 5 ACS Paragon Plus Environment


with bitumen, a behavior that makes bitumen distinct from conventional crude.29 In water-wet oil sands, such as these found in Canada’s Athabasca River basin, the water is naturally present in thin films30 that facilitate extraction using the hot water process and also influence non-aqueous processes.31 Methanol and ethanol entrainers are found to enhance the solvent power and polarity of fluids, such as liquid and supercritical CO2, in enhanced oil recovery.32 The mechanism of action of alcohols as cosolvents33 and the role of water in bitumen recovery from oil sands require further investigation. Computational studies on the interactions of kaolinite with organic molecules and water have been mainly based in classical force field and density functional theory (DFT) methods. Molecular dynamics simulations have been employed to study the intercalation in, and adsorption of small organic molecules on kaolinite.34,35,36 The simulations show that thin films of water adsorb more strongly on kaolinite than layers of n-heptane and pyridine.36 Recently, the adsorption of decane, decanoic acid, and decanamine, on kaolinite has been investigated using classical molecular dynamics.37 Classical DFT methods cannot account for dispersion interactions, such as intermolecular interactions involving aliphatic and aromatic hydrocarbons and some molecule-mineral interactions. An approach to address this shortcoming is the implementation of dispersion corrections to DFT. The exchange hole dipole moment dispersion model38 with periodic boundary conditions has been employed to study the adsorption of aromatic, aliphatic, and polar molecules on kaolinite.39 The results show that polar molecules, such as pyridine and isopropanol, form hydrogen bonds with the aluminum hydroxide surface, whereas the adsorption configuration on the silicon oxide surface is non-specific, similar to that of hydrocarbons.39 For a more thorough description of materials structure and properties, it 6 ACS Paragon Plus Environment

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is important to bring together different techniques and levels of description.40 In a comparative study of the adsorption of aromatic bitumen model compounds on chabazite, we have highlighted the distinct insights obtained using hybrid quantum mechanics / molecular mechanics and DFT methods in periodic boundary conditions.41 Accurate modeling of solvation is very important to understand the adsorption of molecules on mineral surfaces in the presence of solvents. An important method for solvation modeling in complex molecular nanosystems is the three-dimensional reference interaction site model theory of solvation with the Kovalenko and Hirata closure relation (3D-RISM-KH).42,43,44,45 The 3D-RISM-KH molecular theory of solvation has been employed to study the multilayer adsorption of indole on kaolinite in toluene and heptane solvents7 and the molecular recognition interaction between heterocycles and kaolinite in toluene,8 as well as the effect of acrylate and styrene additives on the stacking of kaolinite nanoplatelets in aqueous solutions.46 The optimal temperature and pressure conditions for the desorption of bitumen components from kaolinite in liquid and supercritical CO2 solvent have been explored using the 3D-RISM-KH approach.47 The effects of trace amounts of water and temperature on asphaltene aggregation in organic media have been elucidated.48,49 The solvation structure and thermodynamics of ionic liquids50 and electrolyte solutions,42 gelation,51 self-assembly of supramolecular rosette nanotubes,52 cellulose aggregation in hydrothermal treatment conditions,53 and the hierarchy of supramolecular interactions in plant cell walls have also been investigated.54,55 In the present work, the experimental desorption of acridine and phenanthridine is studied in the presence of controlled amounts of water and aliphatic alcohols in toluene at ambient temperature. Moreover, the effective adsorption interactions of these asphaltene 7 ACS Paragon Plus Environment


model compounds with kaolinite in toluene solvent containing water and alcohol cosolvents are investigated computationally using the 3D-RISM-KH method. The experimental and computational results are discussed in the light of the fundamental chemical interactions so as to help understand the role of water and the effect of hydroxylated cosolvents in the extraction of bitumen from oil sands in non-aqueous media. 2. Experimental and Computational Models and Methods Materials and chemicals. The heterocyclic compounds acridine (97%) and phenanthridine (98%) were purchased from Aldrich. Toluene (99.9%) was purchased from Fisher Scientific. Well-crystallized kaolinite (KGa-1b, Georgia) was obtained from the Source Clays Repository of the Clay Minerals Society (Purdue University, West Lafayette, Indiana, USA). The clay fraction with grain size less than 2 µm was collected by sedimentation and used without pretreatment. Preparation of kaolinite-heterocycle composites. The kaolinite-adsorbate composites were prepared under the same experimental condition used for the monolayer formation measurements (initial heterocycle concentration of 0.003 mol L-1) in toluene solvent, as described previously.8 Typically, 5 g kaolinite was dispersed in a 0.5 L solution of 3x103

M heterocycle in toluene and stirred for 5 hours. The mixture was centrifuged and the

supernatant removed and analyzed by UV-Vis spectrophotometry. The absorption wavelengths used for quantification were 358 nm for acridine and 345 nm for phenanthridine. Calibration curves obtained at these wavelengths from standard solutions were used to convert absorbance of solutions to concentration and thus determine the amount loaded on clay.


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Desorption experiments. For desorption experiments, a 20 mg sample of freshly prepared dry kaolinite-adsorbate composite was dispersed in 2 mL of toluene containing a hydroxylated compound (water or alcohol) at controlled concentration. After 5 hours of stirring the mixture was centrifuged and the concentration of the supernatant determined by the method described above. Desorption percentages (%D) were then calculated using the following equation:

%D =

Cs *V *100 nk

(1)

where Cs (mol·L-1) is the equilibrium concentration of a heterocycle in solution after desorption, V (L) is the volume of the desorption solution, and nk (mol) is the amount of heterocycle loaded on kaolinite before desorption. 3D-RISM-KH molecular theory of solvation overview. The 3D-RISM-KH theory37-42 represents the solvation structure of a crystal layer in terms of 3D spatial maps that give the probability density of finding solvent site γ at 3D space position r around the solute crystal. The probability density is determined by the average number density ργ in the solution bulk times the 3D distribution function gγ(r) of solvent site γ, ργgγ(r). The 3D site distribution functions of solvent are calculated using the 3D-RISM integral equation42,43,44

hγ (r) = ∑ ∫ dr' cα (r − r' ) χαγ (r ' ) ,

(2)

α

where hγ(r) is the 3D total correlation function of solvent site γ related to the 3D site distribution function by gγ(r) = hγ(r) + 1 and cγ(r) is the 3D direct correlation function; the 9 ACS Paragon Plus Environment


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site-site susceptibility of pure solvent χαγ(r) is an input to the 3D-RISM calculation; the indices α and γ enumerate all sites on all sorts of solvent species. The 3D-RISM integral equation (2) is coupled with the Kovalenko-Hirata (KH) closure relation42,43,44 exp (d γ (r)) for d γ (r) ≤ 0 g γ (r ) =  for d γ (r ) > 0  1 + d γ (r )

d γ (r ) = −

u γ (r ) k BT

and

(3)

+ hγ (r ) − c γ (r ) ,

where uγ(r) is the 3D interaction potential between the whole solute and solvent site γ specified by a molecular force field, and kBT is the Boltzmann constant times the solution temperature. The KH closure (3) combines in a nontrivial way the mean spherical approximation (MSA) and hypernetted chain (HNC) approximation. The MSA is applied to the spatial regions of solvent density enrichment (gγ(r)>1), such as association peaks, and the HNC is applied to regions of solvent density depletion (gγ(r)

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