Probing Contaminant Transport to and from Clay Surfaces in Organic Solvents and Water Using Solution Calorimetry

Clays, in tailings, are a significant ongoing environmental concern in the mining and oilsands production industries, and clay rehabilitation following contamination poses challenges episodically. Understanding the fundamentals of clay behavior can lead to better environmental impact mitigation strategies. Systematic calorimetric measurements are shown to provide a framework for parsing the synergistic and antagonistic impacts of trace (i.e., parts per million level) components on the surface compositions of clays. The enthalpy of solution of as-received and “contaminated” clays, in as-received and “contaminated” organic solvents and water, at 60 °C and atmospheric pressure, provides important illustrative examples. Clay contamination included pre-saturation of clays with water and organic liquids. Solvent contamination included the addition of trace water to organic solvents and trace organic liquids to water. Enthalpy of solution outcomes are interpreted using a quantitative mass and energy balance modeling framework that isolates terms for solvent and trace contaminant sorption/desorption and surface energy effects. Underlying surface energies are shown to dominate the energetics of the solvent–clay interaction, and organic liquids as solvents or as trace contaminants are shown to displace water from as-received clay surfaces. This approach can be readily extended to include pH, salts, or other effects and is expected to provide mechanistic and quantitative insights underlying the stability of clays in tailings ponds and the behaviors of clays in diverse industrial and natural environments

On the Applicability of the Regular Solution Theory to Asphaltene + Diluent Mixtures

The similarity of the Hildebrand or Hansen solubility parameter is frequently used in petroleum science as a measure of the compatibility of constituents and for interpreting and correlating properties of asphaltene + diluent mixtures. A partial specific volume at near infinite dilution and enthalpies of solution are sensitive measures of solute–solvent interactions derived from high precision density and calorimetry measurements for dilute mixtures. In this contribution, the partial specific volumes and enthalpies of solution of pyrene and various Athabasca and Maya asphaltenes at near infinite dilution on a mole fraction basis, in decane, toluene, 1-methylnaphthalene, quinoline, anisole, 2,6-lutidine, pyridine, methylene chloride, and tetrahydrofuran are reported over the temperature range of 20–80 °C. At 20 °C, these diluents possess solubility parameters ranging from 15 MPa^0.5 (decane) to 22 MPa^0.5 (quinoline). The properties of pyrene + diluent mixtures are used to illustrate the application and misapplication of the regular solution theory to such mixtures. Thermodynamic measurements, partial specific volume, and enthalpy of solution are shown to be independent of both Hildebrand and Hansen solubility parameter values. These results do not support the use of the solubility parameter or other simple solution thermodynamic concepts to describe asphaltene + diluent mixture behavior. The need for a more detailed description of physiochemical phenomena arising upon mixing asphaltenes with diluents is discussed

Probing the Impact of Asphaltene Contamination on Kaolinite and Illite Clay Behaviors in Water and Organic Solvents: A Calorimetric Study

A detailed understanding of the impacts of trace compounds and asphaltene adsorption on the behavior of clays contributes to the development of production processes for heavy oils and bitumen with lower environmental impacts, to the treatment of tailings from mined bitumen, and to the mitigation of impacts from oil spills in natural environments. Probes, such as solution calorimetry, are sensitive to species transfer to and from clay surfaces and outcomes can be interpreted unambiguously when supplemented with thermogravimetric analysis and scanning electron microscopy measurements. In this study, the effects of asphaltene coating on the enthalpy of solution of kaolinite and illite clays in toluene, <i>n</i>-heptane, and deionized water were investigated at 60 °C and atmospheric pressure. Asphaltene coating increases organic compound sorption but does not impact water sorption vis-à-vis uncoated clay particles or water displacement from clay particles by organic liquids as solvents or as trace contaminants in water. Experimental outcomes are interpreted using a quantitative mass and energy balance model framework that isolates terms for solvent and trace contaminant sorption/desorption and surface energy effects. Mechanistic and quantitative insights underlying the stability of asphaltene-coated clay dispersions in tailings ponds and the behaviors of these clays in diverse industrial and natural environments are discussed

Probing the Role of Water Chemistry on the Behavior of Clays in Process and Natural Environments Using Solution Calorimetry

Clays, due to their specific surface area and electrical charge density, are among the most active minerals in aquifers, oil and gas reservoirs, and tailings ponds. Important problems, such as limited yield of oil recovery during petroleum exploration, involve the interaction of process fluids with minerals which constitute reservoir pore walls. During mine tailings treatment and management, water chemistry impacts the aggregation and settling of clays. Solution calorimetry is a sensitive probe for species transfer to and from clay surfaces, and for the measurement of the effects of water chemistry (temperature, pH, salinity) on clay particle surfaces, in this case, kaolinite, illite, and montmorillonite. In this work, we show that interactions between clays and surrounding water are temperature-independent for all three clay types and that water chemistry has no measurable effect on the surface properties of illite. For kaolinite, water pH does impact surface properties and has a synergistic impact with salinity at high pH. The surface properties of montmorillonite are sensitive to water pH and salinity. These data and observations extend a solution enthalpy modeling framework for clays and contaminated clays in water and liquid hydrocarbons. In the next phases of this work, entropic effects will be addressed so that a quantitative Gibbs free energy modeling framework for the enthalpy of solution of clays can be constructed and linked to clay settlement kinetics

Fickian and Non-Fickian Diffusion in Heavy Oil + Light Hydrocarbon Mixtures

Diffusive mass transfer is expected to play a key role in existing and proposed solvent-added processes for heavy oil production. Composition–distance profiles arising during free diffusion scale as a function of the joint variable (distance/time^<i>n</i>_<i>w</i>). Simple fluids are governed by Fickian diffusion, where <i>n</i>_<i>w</i> = 0.5. For nanostructured fluids, the value of <i>n</i>_<i>w</i> can be as low as <i>n</i>_<i>w</i> = 0.25, known as the single-file limit, but more typically, the value for the exponent falls between these two limits and is composition-dependent. In this work, five published data sets, comprising free diffusion composition profiles for Athabasca bitumen fractions and for Cold Lake bitumen + light hydrocarbons obtained using diverse apparatus, are probed from this perspective. Additional experimental results are provided for Athabasca bitumen + toluene mixtures over the temperature range of 273–313 K, and results from positive and negative control experiments for two well-defined mixtures(0.25 mass fraction carbon nanotubes + polybutene) + toluene, and polybutene + tolueneare also provided. The value of <i>n</i>_<i>w</i> for the negative control experiment remains at 0.50 ± 0.05 over the entire composition range, and for the positive control experiment, the value drops to <i>n</i>_<i>w</i> = 0.30 ± 0.02 at low toluene mass fraction. Although the quality of the diffusion profile data in the data sets analyzed is variable, the values of the exponent <i>n</i>_<i>w</i> are shown to be light-hydrocarbon-dependent and increase from <i>n</i>_<i>w</i> ∼ 0.25 at low light-hydrocarbon mass fraction up to <i>n</i>_<i>w</i> ∼ 0.50 at high light-hydrocarbon mass fraction. Secondary convective effects are also noted in free diffusion experiment outcomes at long times. The industrial applications of these findings are currently being evaluated, but it is clear that the time for light hydrocarbons to penetrate a fixed distance into nano- and micro-structured hydrocarbon resources is greater than the value anticipated for unstructured fluids

Effect of Diluents on the Rheological Properties of Maya Crude Oil

Understanding the rheological properties of mixtures of heavy oil or bitumen and diluents, specifically at low temperatures, is key in designing different processes employed in the production or transportation of these resources reliably and efficiently. The effect of diluents (<i>n</i>-heptane, toluene, and toluene + butanone (50:50 vol %)) on the non-Newtonian behavior of Maya crude oil including shear thinning and thixotropy at temperatures from 258 to 333 K are discussed. Toluene + butanone (50:50 vol %) addition to Maya crude oil induces the greatest reduction in shear thinning behavior irrespective of temperature. Thixotropic properties of mixtures of Maya crude oil and diluent were studied through startup experiments. It was shown that toluene + butanone (50:50 vol %) is the best diluent in moderating the thixotropic effect, whereas <i>n</i>-heptane showed the most pronounced thixotropic effect. It was shown that toluene + butanone (50:50 vol %) is more promising in decreasing oil viscosity in comparison to two other diluents tested. Less of this diluent is required to decrease the viscosity to a certain value, which confirms its potential to be used in the industry as a diluent. The results presented also provide a reliable database for model development and evaluation

Effect of Pressure on the Rheological Properties of Maya Crude Oil

At atmospheric pressure, hydrocarbon resources, such as bitumen and Maya and other heavy oils, have been shown to exhibit non-Newtonian behavior at or below typical ambient temperatures. This work is devoted to investigating the effect of pressure on the non-Newtonian rheological properties of Maya crude oil (a commercial heavy oil blend from Mexico). Measurements were performed from 258 to 333 K, using a stress-controlled rheometer, at pressures up to 150 bar and over a broad range of shear rates. Maya crude oil was shown to be a shear-thinning fluid below 313 K exhibiting thixotropy below 293 K, at atmospheric pressure, in a prior work. At fixed temperature, the magnitude of the non-Newtonian behaviors of Maya crude oil appears to increase with increasing pressure, and shear thinning is shown to persist to higher pressures below 313 K. Boundaries of the non-Newtonian region with respect to temperature, pressure, and viscosity are identified and discussed. The thixotropic behavior of Maya crude oil is also shown to persist at higher pressure, and the recovery of the moduli at rest appears to be faster at elevated pressures than at atmospheric pressure

Phase Behavior and Thermophysical Properties of Peace River Bitumen + Propane Mixtures from 303 K to 393 K

Propane and mixtures including propane as a principal component are among the leading potential candidates for co-injection along with steam for improving the process and environmental efficiency of oil sands bitumen production processes. Phase diagrams and thermophysical property data enable technologies for the development and optimization of such processes. In this work, phase behavior, phase composition, and phase densities of propane + Peace River bitumen mixtures are reported in the temperature range 303 to 393 K at pressures ranging from 1 to 6 MPa. The phase behavior of this pseudobinary mixture can be categorized as Type III according to the van Konynenburg–Scott nomenclature. Pressure–temperature at fixed composition, and pressure–composition at fixed temperature phase diagrams, and pressure–temperature phase projections are presented, along with saturated compositions and densities of the coexisting bitumen-saturated propane liquid (L₁) and propane-saturated bitumen liquid (L₂) phases. Saturated L₁ and L₂ phases are both significantly less dense than liquid water phases at the same temperatures and pressures, and the volumes of mixing, particularly for the L₁ phase, are large and negative. This data set provides a benchmark for process development and process design calculations for ongoing bitumen production and deasphalting applications

Bitumen–Toluene Mutual Diffusion Coefficients Using Microfluidics

In this paper, we present a microfluidic approach to measure liquid solvent diffusivity in Athabasca bitumen. The method has three distinguishing features: (a) a sharp initial condition enabled by the high wettability of the solvent; (b) one-dimensional diffusive transport (in the absence of convection) ensured by microscale confinement; and (c) visible-light-based measurement enabled by the partial transparency of the bitumen at small scales. The method is applied to measure the diffusion of toluene into bitumen by imaging transmitted light profiles over time, and relating intensities to the mass fractions. Plotting toluene mass fraction versus distance/sqrt­(time), results in a tight superposition of all curves (time-dependent mass fractions) demonstrating the diffusion dominated nature of the system and the robustness of the method. The diffusion transport equations were solved and fit to a constant diffusion coefficient as well as a variety of concentration-dependent diffusion coefficient relations found in the literature. For intermediate toluene mass fractions (0.2–0.8), a constant diffusion coefficient of 2.0 × 10^–10 m²/s provides an appropriate representation. However, at low toluene mass fractions (<0.2), significantly reduced diffusive transport is observed, and endpoint analysis indicates diffusion coefficients trending toward 4.3 × 10^–11 m²/s. At high toluene mass fractions (>0.8), the values trend toward 1.5 × 10^–10 m²/s. This microfluidic method provides an inexpensive and rapid mutual diffusion coefficient evaluation, with significantly improved spatial/composition resolution vis-à-vis competing measurement methods

Forced and Diffusive Mass Transfer between Pentane and Athabasca Bitumen Fractions

Forced and diffusive mass transfer between pentane and Athabasca bitumen fractions was investigated at 297 K. Mutual diffusion coefficients were obtained using a free diffusion technique, where time-dependent composition profiles were jointly fit to obtain composition-dependent values. Because the density difference between pentane and Athabasca bitumen is significant, the density gradient was accounted for explicitly in the data analysis. Forced mass-transfer measurements were made by placing a high shear impeller in the pentane-rich phase adjacent to the pentane−feedstock interface. Mass-transfer coefficients were evaluated independently on the basis of the movement of the interface with time and changes in the bulk composition of the well-mixed pentane-rich phase above the interface. Because bitumen fractions are only partially soluble in pentane, the impact of the asymptotic assumptions, complete miscibility and complete immiscibility, on mass-transfer coefficient values obtained was assessed and found to fall within experimental error. The dependence of mass-transfer coefficients upon the shear rate and impeller-interface distance was also evaluated. Mass-transfer rates are shown to range from the diffusion limit at low shear rates and large impeller-interface distances to values consistent with those obtained from pertinent correlations for forced mass transfer under turbulent conditions at higher shear rates. The results suggest that bitumen−pentane mass transfer in reservoirs and surface facilities is likely to be diffusion-limited