Experimental Determination of k-Values and Compositional Analysis

Article pubs.acs.org/jced

Experimental Determination of k‑Values and Compositional Analysis of Liquid Phases in the Liquid−Liquid Equilibrium Study of (Athabasca Bitumen + Ethane) Systems Mohammad Kariznovi, Hossein Nourozieh, and Jalal Abedi* Department of Chemical & Petroleum Engineering, University of Calgary, Calgary, Canada ABSTRACT: Phase behavior properties of (bitumen + solvent) systems have a significant effect on surface upgrading methods and are necessary for the recovery of bitumen from reservoir. In this study, the phase partitioning and component distribution between phases as well as phase properties at equilibrium condition for the (Athabasca bitumen + ethane) system at room temperature were experimentally evaluated. The experiments were conducted using a designed pressure− volume−temperature (PVT) apparatus to obtain liquid−liquid equilibrium properties as well as extraction yield for (bitumen + solvent) systems. In addition, the equilibrium k-value for each component present in the mixture at equilibrium condition was calculated on the basis of compositional analysis of liquid phases and available correlations for the molecular weight of heavy components. The impact of pressure and solvent to bitumen ratio on the boiling point curves and compositional analysis of flashed off liquids as well as equilibrium k-values were evaluated. Finally, the molecular weight of flashed off liquid phase samples were estimated on the basis of molecular weight and compositional analysis of liquids.

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INTRODUCTION The production of heavy oil and bitumen has been increased as the production of the conventional light and medium crude declined. Different recovery methods for the production of heavy oil and bitumen have been invented and patented.1−3 The performance of these techniques depends on the interaction between the solvent and the bitumen and to the corresponding change in physical properties of bitumen, especially the reduction of viscosity. Thus, the phase behavior of (heavy oil + solvent) mixtures and their properties are key elements for the design and development of heavy oil recovery processes, and knowledge in this area makes the selection of appropriate diluents or the selection of suitable separation techniques easier for any application. The study of liquid−liquid separation and the partitioning of components in the (bitumen + solvent) systems was carried out elsewhere.4−12 A few experimental studies considered the phase behavior of the (bitumen + ethane) systems.9,12−18 Among these studies, only Rose12 reported some supercritical extraction data for (Peace River bitumen + ethane) systems. However, no experimental data for the liquid−liquid equilibrium (LLE) or for the extraction of bitumen with ethane at ambient temperature as well as partitioning of components within the phases have been reported. Our previous studies indicated that, in the case of LLE, two phases, solvent-enriched and bitumen-enriched, exist at equilibrium conditions.19,20 The former is mostly composed of solvent and some light components extracted from the bitumen phase. The latter mainly consists of heavy components of bitumen, like asphaltene, that cannot be extracted by solvent. In our previous study, the LLE of the (Athabasca bitumen + ethane) system at the average temperature of 294.8 K was © XXXX American Chemical Society

conducted at three pressures, (5 to 9) MPa, and four different overall ethane concentrations.20 The physical properties of phases such as solubility, viscosity, density, and volume of each liquid phase were measured during the experiments and the impact of pressure and solvent to bitumen ratio on these properties were evaluated. However, no compositional analysis in terms of component distribution and partitioning between two phases has been reported. In this study, the phase partitioning and component distribution between phases at equilibrium condition for the (Athabasca bitumen + ethane) system at room temperature were evaluated. Thus, the flashed-off liquid samples taken from the phases (solvent-enriched and bitumen-enriched phases) in the LLE experiments were subjected to compositional analyses to obtain carbon number distributions up to C100. In addition, the k-value for each component present in the mixture at equilibrium condition was calculated on the basis of compositional analysis of liquid phases and available correlations for the molecular weight of heavy components. The impact of pressure and solvent to bitumen ratio on the boiling point curves and compositional analysis of flashed-off liquids as well as equilibrium k-values were evaluated. Finally, the molecular weight of flashed off liquid phase samples was estimated on the basis of molecular weight and compositional analysis of liquids. Received: February 20, 2013 Accepted: April 17, 2013

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dx.doi.org/10.1021/je4001735 | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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EXPERIMENTAL SECTION Chemicals. The ethane (0.99 purity, grade 2) used in these measurements was supplied by Praxair. The bitumen was provided from the Athabasca field, and its measured density at ambient temperature (298 K) is 1002 kg·m−3. Table 1 summarizes the

dry helium and ethane to remove any contaminants. Then, the entire system was evacuated with a vacuum pump. After cleaning, bitumen was charged into the equilibrium cell using the two pumps. The mass of bitumen in the equilibrium cell was calculated with measuring the volume and density of bitumen at a constant temperature and pressure. The required amount of ethane to have a specific solvent-to-bitumen ratio was then charged into the cell. To measure the properties of equilibrium phases at a desired condition, the experimental temperature and pressure were set. To attain the equilibrium condition for the system under study, the rocking mechanism was used. During the mixing, the equilibrium cell was kept at constant pressure with the pump. The change in the total injected volume of water to keep a constant pressure in the equilibrium cell indicated the equilibrium condition. Prior to the displacement of the equilibrium phases, the equilibrium cell was kept in vertical position to obtain phase separation. Then, the equilibrium phases were passed through the density meter and viscometer at a constant pressure and temperature. The uncertainty of measurements for the pressure was ± 10 kPa. The change in the density and viscosity during the phase sampling indicated a phase boundary. The volume of each phase at equilibrium condition was measured with the Quizix pumps. One or two samples from each phase were collected from the sampling port for solubility measurements and compositional analysis. To measure the composition of ethane in the collected samples, the samples were flashed at atmospheric conditions. The volume of the evolved ethane was measured by a gasometer (Chandler Engineering, model 2331) with an accuracy of 0.2 % of the reading. The composition of ethane in each sample was then obtained from the volume and density of the evolved ethane at atmospheric pressure. The evolved gas and liquid residue was analyzed by gas chromatography (GC) and simulated distillation (SimDis), respectively.

Table 1. Chemical Sample Specifications chemical name

source

CAS No.

initial purity (fraction)

purification method

ethane bitumen

Praxair Athabasca Field

74-84-0

0.99 mol

none none

chemical sample specifications. The compositional analysis of the raw bitumen was obtained with the standard test method ASTM D7169 and is presented in Table 2. Table 2. Compositional Analysis of Athabasca Bitumen; w, Weight Fraction of Components in Bitumen component

102w

C1 to C10 C11 to C20 C21 to C30 C31 to C40 C41 to C50 C51 to C60 C61 to C70 C71 to C80 C81 to C90 C91 to C100 C100+

0.36 12.47 18.94 12.78 8.03 6.61 6.70 6.40 5.06 3.89 18.76

Apparatus. The details of the experimental setup have been described elsewhere.19,21 It consists of two feeding cells, an equilibrium cell, four sampling cells, a density meter, a viscometer, and two Quizix pumps. The equilibrium and sampling cells, the density meter, and the viscometer were placed in a temperaturecontrolled Blue M oven. The temperature in the oven was controlled within ± 0.1 K. The two pumps control the system pressure. The rocking mechanism of the equilibrium cell with a free rolling ball accelerates the process of the mixing. The volume of the equilibrium cell is about 900 cm3, which provides enough volume of each equilibrium phase for the phase detection, the thermo-physical properties measurement, and any further analyses. The density meter and viscometer were used for phase detection, and they were installed in series to improve the phase detection. The density meter was Anton Paar density measuring cell equipped with a DMA HPM external high pressure unit calibrated with water and nitrogen. The Cambridge viscometer was used to measure the viscosity of the fluids in the range (0.2 to 10,000) mPa·s. The viscometer was calibrated by the factory, and the measured viscosities were evaluated with the reported values for standard fluids and pure hydrocarbons. The piston-style viscometer uses two magnetic coils within a stainless steel sensor and a magnetic piston inside the pipe line. The piston is forced magnetically back and forth within a predetermined distance. The fluid sample surrounds the piston and, depending on the viscosity, the piston’s round trip travel time is measured at constant force exerted. The time required to complete a two way cycle is an accurate measure of viscosity. Procedure. Before any experiment, the system was cleaned with toluene. The lines and cells were successively flushed with

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RESULTS AND DISCUSSIONS Thermo-physical Properties of Bitumen. The density and viscosity were measured at the temperatures up to 448 K by an Anton Paar density measuring cell and a Cambridge viscometer, respectively. The pressure was kept at 1.12 MPa, and the temperature range of (319 to 447) K was considered for density and viscosity measurements. The measured densities were fitted with the following correlation, ρB /( kg·m−3) = [− 0.5981T /K + 1180.5]

(1)

where ρB is the bitumen density and T is temperature. The average absolute deviation (AAD) (AAD = [1/N]∑|ρcalcd − ρexptl|) for this correlation is 0.8. The measured densities and correlated values are plotted in Figure 1. As the figure shows, the density of bitumen linearly reduces with temperature, and the measured data are well correlated with eq 1. The bitumen viscosity data were also fitted with a linear double logarithm model.22 The fitted correlation is log(log(μB /mPa·s)) = a log(T /K) + b

(2)

where μB is the bitumen viscosity and T is temperature. The constants for eq 2 are summarized in Table 3 along with the coefficients fitted by other authors for Athabasca bitumen. Figure 2 shows the measured and the correlated density values as a function temperature for Athabasca bitumen used in this study. As depicted B



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phase at equilibrium condition. As the table shows, the solventenriched phase (L1), that is, the light liquid phase, has a much higher ethane concentration than the bitumen-enriched phase (L2). This is because the solvent-enriched phase mainly comprises the liquid ethane and light components, while the bitumenenriched phase is mostly composed of heavy components, in which the solubilities of ethane are much lower than those of ethane in the light components. As the results show, with increasing overall ethane concentration, the density of the solvent-enriched phase decreases; whereas, the density of the bitumen-enriched phase increases. The viscosity of the bitumen-enriched phase increases with increasing the pressure and overall ethane concentration. Thus, the increase in pressure or overall ethane concentration results in higher extraction of light components from the bitumen. This leads to an increase in the fraction of heavier components in the bitumen-enriched phase compared to the raw bitumen. The effect of pressure and solvent to bitumen ratio on the extraction of light components from bitumen was studied and is summarized in Table 5. The apparatus used in this study is batch for the bitumen and solvent. Solvent contacted the whole bitumen and extracted light fractions. As the table shows, the extraction yields increase with the pressure at a constant temperature and at a constant overall ethane concentration. For example, at constant overall ethane weight fraction of 0.6, the extraction yield increases from an average of 0.110 weight fraction to 0.155 with increasing the pressure from (5 to 9) MPa. In addition, at a constant overall ethane weight fraction of 0.4, the increase in pressure from (5 to 9) MPa almost doubles the extraction yield. The experimental results also indicate that the extraction yield increases with increasing overall ethane concentration. The maximum extraction yield is obtained at the highest ethane weight fraction. For example, at 9 MPa, the extraction yield increases from 0.101 weight fraction to 0.384 when the overall ethane concentration is increased from (0.4 to 0.9) weight fraction. The effect of overall ethane concentration on the extraction yield is more significant at low pressure (5 MPa) compared to high pressure (9 MPa). The increase in the overall ethane concentration from (0.4 to 0.6) weight fraction leads to the increase in the extraction yield that is more than double at the pressure of 5 MPa while this value would be 1.5 for a constant pressure of 9 MPa. Compositional Analyses of Extracts and Residues. The bitumen and flashed-off liquid samples (solvent-enriched and bitumen-enriched phases) from LLE experiments were subjected to compositional analyses to obtain carbon number distributions up to C100. Thus, the impacts of pressure and solvent to bitumen ratio on the phase partitioning are evaluated from the chemical analysis. The compositional analysis was done on the basis of standard test method, ASTM D7169.24 This provides useful information and knowledge of the amount of residue by the determination of the distribution of boiling points in petroleum fractions, vacuum residues, and crude oils. The distribution of the boiling points and the intervals of cut points in residues and crude oils were determined with a hightemperature GC. An external standard method was used to determine the amount of residue (or sample recovery). In fact, this method relies on the applicability of SimDis to the oil samples that cannot completely be distilled with the chromatographic system. Using this standard method, the elution of components and their

Figure 1. Experimental (□) and correlated (―) density ρ of Athabasca bitumen as a function of temperature T.

Table 3. Coefficients of Double Logarithm Viscosity Model (eq 2); a, b, Correlation Constants; T, Temperature 23

Svrcek and Mehrotra Badamchi-Zadeh et al.23 this study a

a

b

T/K

MARDa

−3.70015 −3.70015 −3.83894

9.90602 9.87056 10.2485

323 to 403 377 to 420 319 to 447

15 5 15

MARD = 100· |μcalcd − μexptl|/μexptl

Figure 2. Experimental (□) and correlated (―) viscosity μ of Athabasca bitumen viscosity as a function of temperature T.

in the figure, the viscosity of bitumen dramatically decreases with temperature. The variation of bitumen viscosity with temperature is nonlinear in the semilog plot. The maximum absolute relative deviation (MARD) of our model from experimental data is 15 % comparing to Svrcek and Mehrotra23 and Badamchi-Zadeh et al.23 which are 15 % and 5 %, respectively. However, our model covers a wider range of temperature compared to Svrcek and Mehrotra23 and Badamchi-Zadeh et al.23 models. Liquid−Liquid Equilibrium. The measured data indicated that at the average temperature of 294.8 K and at the pressures (5 to 9) MPa, only liquid−liquid equilibrium exists for (Athabasca bitumen + ethane) systems at the ethane overall weight fraction of 0.2 or higher. Table 4 summarizes the ethane solubility, phase density, phase viscosity, and the volume of each C



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Table 4. LLE Properties for (Athabasca Bitumen + Ethane) Systems at Ambient Temperatures;20 P, Pressure; T, Temperature; wf, Weight Fraction of Ethane in Feed; ρ, Densities; μ, Viscosity of Bitumen-Enriched Phase; V1·V2−1, Liquid 1 to Liquid 2 Volume Ratioa ρ/(kg·m−3)

102w

a

P/MPa

T/K

feed

L1

L2

pure ethane

L1

L2

μ/(mPa·s)

(V1·V2−1)/(m3·m−3)

5.09 5.08 5.05 7.08 9.08 9.08 9.04 9.05

295.9 294.8 294.7 294.7 294.6 294.3 294.7 294.3

20 40 60 40 40 60 80 90

91.4 92.9 87.7 84.5 89.0 93.1 96.0

17.9 15.7 14.5 16.6 16.6 15.5 13.1 11.6

350 355 355 376 390 390 389 390

399 397 385 425 448 431 414 404

854 864 878 862 859 881 906 931

45.5 64.8 115 67.2 64.4 146 491 1908

0.150 1.112 3.322 1.113 1.112 3.072 10.779 32.019

u(T) = 0.1 K, u(P) = 0.01 MPa, u(w) = 0.005, uc(ρ) = 0.5 kg·m−3, and uc(μ) = 0.05 μ.

Table 5. Extraction Yield EY (in weight fraction) for (Athabasca Bitumen + Ethane) Systems at Ambient Temperatures; P, Pressure; T, Temperature; wf, Weight Fraction of Ethane in Feed.a

a

P/MPa

T/K

102wf

102EY

5.09 5.08 5.05 7.08 9.08 9.08 9.04 9.05

295.9 294.8 294.7 294.7 294.6 294.3 294.7 294.3

20 40 60 40 40 60 80 90

2.9 4.8 11.0 7.9 10.1 15.5 27.7 38.4

u(T) = 0.1 K, u(P) = 0.01 MPa, and u(EY) = 0.05EY.

boiling point distribution at the temperatures up to 720 °C was determined. At this temperature, the component n-C100 is eluted.24 The chemical analysis and carbon number distribution of raw bitumen is illustrated in Figure 3. As depicted in this figure, no

Figure 4. Boiling point curves (temperature T versus weight fraction distilled wD) for raw bitumen and flashed-off equilibrium phases: ▲, raw bitumen; ○, solvent-enriched phase (L1) at 5 MPa and a constant overall ethane weight fraction of 0.4; Δ, solvent-enriched phase (L1) at 9 MPa and a constant overall ethane weight fraction of 0.4; □, solventenriched phase (L1) at 9 MPa and a constant overall ethane weight fraction of 0.9; +, bitumen-enriched phase (L2) at 5 MPa and a constant overall ethane weight fraction of 0.4.

pressure of 5 MPa and at a constant overall ethane weight fraction of 0.4 are compared, it is found that the bitumenenriched phase (L2) has a much higher boiling point curve than the solvent-enriched phase (L1). This shows that ethane has extracted light components from bitumen. The hydrocarbons with heavier molecular weights have higher boiling points. Therefore, the bitumen-enriched phase is much heavier than the solvent-enriched phase and it contains heavy components such as asphaltenes and resins. As anticipated from Figure 4, the boiling point curves of raw bitumen and of the bitumenenriched phase (L2) are similar, which shows that the boiling point curve of bitumen is a function of heavier components than of light components. Figure 4 also demonstrates the impact of pressure and the impact of the change in the overall ethane concentration on the boiling point distribution of the solvent-enriched phases. As presented in Table 5, increasing the pressure raises the amount of bitumen that was extracted into the solvent-enriched phase. The ability of ethane to extract more components increases with the pressure, and this is due to the increased attractive forces between the solute and solvent that result from higher solvent densities. Comparing the boiling point curves of the

Figure 3. Compositional analysis (□) and carbon number distribution (▲) for Athabasca bitumen determined by simulated distillation (SimDis); component weight fraction w, cumulative weight fraction wc, carbon number CN.

component lighter than carbon number C8 exists in the bitumen, and about 19 wt % of bitumen is composed of components heavier than C100+. Figure 4 shows the boiling point curve for the flashed-off phase samples and for raw bitumen. If the flashed-off liquid samples taken from two equilibrium phases at a constant D



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Figure 5. Compositional analysis (component weight fraction w) for raw bitumen (black) and two flashed-off equilibrium phases (solvent-enriched phase, red, and bitumen-enriched phase, blue) at 5 MPa and a constant overall ethane weight fraction of 0.4: CN, carbon number.

flashed-off phase samples taken from the solvent-enriched phases at two different pressures (5 and 9) MPa and at a constant overall ethane concentration (0.4 weight fraction) shows that although two samples have the same initial boiling points, the final boiling points are different. The difference between the end points for the boiling point curves indicates that there is a greater amount of heavier hydrocarbons extracted at the higher pressure. The effect of increasing the amount of solvent in the equilibrium cell on the boiling point curves of the flashed-off phase samples taken from the solvent-enriched phases is also evaluated at a constant pressure of 9 MPa in Figure 4. The components in the solvent-enriched phase at higher overall ethane concentration are heavier. This is in agreement with the maximum extraction yield that was obtained at the highest ethane concentration (Table 5). Figure 5 illustrates the fraction of each carbon number in the flashed-off phase samples taken from the solvent-enriched and the bitumen-enriched phases in LLE condition at 5 MPa and at a constant overall ethane weight fraction of 0.4 as well as the fraction of each carbon number in the raw bitumen. As the figure indicates, the solvent-enriched phase is composed of components with carbon numbers C8 up to C70 and mainly containing components between C12 to C35. The composition of raw bitumen and that of the bitumen-enriched phases are close to each other. However, the raw bitumen has higher light components compared to the bitumen-enriched phase. The C100+ for raw bitumen and for the flashed-off liquid sample taken from the bitumen-enriched phase at 5 MPa and at a constant overall ethane weight fraction of 0.4 are 0.188 and 0.199, respectively. This is due to the nature of the solvent, ethane, that extracts the saturated fraction more than the aromatic and resin fractions. The studies by Schmitt and Reid25 and by Moradinia and Teja26 showed the solubilities of the normal n-alkanes in supercritical fluids such as ethane are higher than that of other classes of hydrocarbons (e.g., aromatics). Figure 6 shows the carbon number distribution for the flashedoff liquid phase samples and raw bitumen. As depicted in this figure, the extraction of the heavier hydrocarbon components into the solvent-enriched phase increases when the pressure or overall ethane concentration increases. The carbon number distribution of the flashed-off phase samples taken from the bitumen-enriched phase presented in Figure 6 also highlights this behavior. The bitumen-enriched phases are depleted from the light hydrocarbon components and become heavier with an increase in the pressure or overall ethane concentration. Figures 7 and 8 demonstrate the weight fraction of components in the solvent-enriched and the bitumen-enriched phases, respectively.

Figure 6. Carbon number distribution for raw bitumen and flashed-off equilibrium phases: wc, cumulative weight fraction; CN, carbon number; ▲, raw bitumen; △, solvent-enriched phase (L1) at 5 MPa and a constant overall ethane weight fraction of 0.4; □, solventenriched phase (L1) at 9 MPa and a constant overall ethane weight fraction of 0.4; ○, solvent-enriched phase (L1) at 9 MPa and a constant overall ethane weight fraction of 0.9; +, bitumen-enriched phase (L2) at 5 MPa and a constant overall ethane weight fraction of 0.4; × , bitumen-enriched phase (L2) at 9 MPa and a constant overall ethane weight fraction of 0.4; ◊, bitumen-enriched phase (L2) at 9 MPa and a constant overall ethane weight fraction of 0.9.

As anticipated from Figure 7, the extracted oil is composed of a high fraction of light components at a low operating pressure while the product can be richer in intermediate components by increasing the system pressure. The weight fraction of the light components decreases with pressure due to an increase in the fraction of heavier components. Thus, the characteristics and properties of the extracted oil can be controlled by the pressure. From Figure 8, it is found that the bitumen-enriched phase (L2) becomes leaner in light components with an increase in the pressure. The C100+ fraction of the flashed-off phases (L2) increases from 0.199 to 0.207 when the pressure changes from (5 to 9) MPa at a constant overall ethane concentration of 0.4 weight fraction. Figure 7 also shows that the increase in the overall ethane concentration will shift the distribution of components toward the intermediate hydrocarbons. Thus, a higher fraction of intermediate components are extracted at the overall ethane concentration of 0.9 weight fraction compared to that of 0.4 weight fraction at a constant E



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Figure 7. Compositional analysis (component weight fraction w) for raw bitumen (black) and flashed-off solvent-enriched phases (blue, red, and green): CN, carbon number; blue, 5 MPa and a constant ethane overall weight fraction of 0.4; red, 9 MPa and a constant ethane overall weight fraction of 0.4; green, 9 MPa and a constant ethane overall weight fraction of 0.9.

Figure 8. Compositional analysis (component weight fraction w) for raw bitumen (black) and flashed-off bitumen-enriched phases (blue, red, and green): CN, carbon number; blue, 5 MPa and a constant ethane overall weight fraction of 0.4; red, 9 MPa and a constant ethane overall weight fraction of 0.4; green, 9 MPa and a constant ethane overall weight fraction of 0.9.

where xLj,i is the mole fraction of component i in equilibrium phase j. Thus, on the basis of experiments, the equilibrium k-values for different components present in a mixture are obtained and directly applied into reservoir simulation software. There are some experimental equilibrium k-values reported in the literature for a (bitumen + light hydrocarbon gases) mixture at vapor−liquid equilibrium conditions. However, no data for liquid−liquid equilibrium k-values or distribution of components in different phases using generated k-values were reported. The compositional analysis of liquid phases combined with the available correlations for molecular weight distribution enable the determination of equilibrium k-values for all components present in the mixture. The following correlation for molecular weight of components Cn, n ≥ 10 was applied to calculate equilibrium k-values,27

pressure of 9 MPa. This occurs because of the complete depletion of the bitumen-enriched phase from light components. Figure 8 clearly shows this behavior as the bitumen-enriched phase (L2) at the overall ethane concentration of 0.9 weight fraction containing no components lighter than C22. Thus, it can be concluded that the overall ethane concentration controls the cumulative extraction. The complete extraction of components with carbon numbers C8 to C21 can be attained with increasing the overall ethane concentration in the mixture. The C100+ fractions of two flashed-off phases (L2) are 0.207 and 0.297 for 0.4 and 0.9 overall ethane weight fractions, respectively. Equilibrium k-Values and Molecular Weight. The experimental solubility and density data for binary systems of (bitumen + solvent) systems provide an appropriate thermodynamic and phase behavior model for reservoir simulation software. An approach for the thermodynamic modeling and equilibrium calculation rather than using equation of state is direct application of experimental k-values. The k-value is represented by k and is defined as the ratio of the mole fraction of a component in the solvent-enriched phase to its corresponding value in the bitumen-enriched phase,

k=

⎡ 6.97996 − ln(1080 − Tb/K) ⎤3/2 MW = ⎢ ⎥ ⎣ ⎦ 0.01964

where Tb is the boiling temperature. For components with n ≤ 10, the molecular weight was taken from Riazi.27 The calculated equilibrium k-values for different components are summarized in Table 6. As the table shows, the trends discussed in previous sections are also observed in the equilibrium k-values. As pressure or overall ethane concentration increases, the extraction yield

x L1, i x L2, i

(4)

(3) F



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Table 6. Correlated Molecular Weight MW and Measured k-Values for Components at Equilibrium Conditions: P, pressure; wf, Weight Fraction of Ethane in Feed component

MW

wf = 0.4 and P/MPa = 5



component

C2 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C30 C31 C32 C33 C34 C35 C36 C37 C38 C39 C40 C41 C42 C43 C44 C45 C46 C47 C48 C49 C50 C51 C52

30.07 84 95 107 121 136 149 163 176 191 207 221 237 249 261 275 289 303 317 331 345 359 373 387 400 415 429 443 457 471 485 499 513 528 542 556 570 584 599 614 629 641 656 670 684 698 713 727

1.284 ∞ ∞ 0.062 0.032 0.086 0.134 0.229 0.168 0.173 0.153 0.126 0.119 0.101 0.088 0.075 0.065 0.057 0.050 0.044 0.039 0.035 0.031 0.028 0.024 0.022 0.020 0.018 0.016 0.014 0.013 0.011 0.010 0.009 0.008 0.006 0.007 0.007 0.004 0.003 0.004 0.004 0.004 0.004 0.004 0.003 0.002 0.001

1.240 ∞ ∞ 0.902 0.072 0.138 1.192 0.379 0.298 0.288 0.272 0.232 0.224 0.193 0.170 0.152 0.134 0.120 0.110 0.100 0.091 0.084 0.078 0.072 0.066 0.061 0.057 0.053 0.049 0.046 0.044 0.041 0.039 0.036 0.033 0.030 0.030 0.027 0.025 0.023 0.024 0.021 0.021 0.019 0.017 0.017 0.017 0.014

1.258 ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ 0.407 0.147 0.091 0.059 0.045 0.036 0.032 0.027 0.023 0.019 0.016 0.014 0.013 0.011 0.010 0.009 0.008 0.007 0.006 0.006 0.005 0.005 0.004 0.004 0.004 0.003 0.003 0.002 0.002 0.002 0.002 0.002

C53 C54 C55 C56 C57 C58 C59 C60 C61 C62 C63 C64 C65 C66 C67 C68 C69 C70 C71 C72 C73 C74 C75 C76 C77 C78 C79 C80 C81 C82 C83 C84 C85 C86 C87 C88 C89 C90 C91 C92 C93 C94 C95 C96 C97 C98 C99 C100

MW




0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

0.012 0.012 0.011 0.011 0.009 0.006 0.005 0.005 0.006 0.006 0.005 0.005 0.005 0.004 0.004 0.005 0.003 0.002 0.001 0.001 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

0.002 0.002 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

742 756 770 785 799 814 828 843 857 872 886 901 915 930 945 959 974 988 1003 1018 1033 1047 1062 1077 1092 1107 1121 1136 1151 1166 1181 1196 1211 1226 1241 1256 1271 1286 1302 1317 1332 1347 1362 1378 1393 1408 1424 1439

molecular weight, and the results are summarized in Table 7. As the table shows, the molecular weight of the solvent-enriched

increases and lighter components mostly partition into the solventenriched phase (L1) and results in infinity value for equilibrium k-value. The value of infinity for a specific component indicates that the component is completely extracted by solvent into the solventenriched phase. Therefore, the component does not exist in the bitumen-enriched phase (L2). On the other hand, the k-value equal to zero means that ethane cannot extract the component and it remains in the bitumen-enriched phase (L2). The molecular weights of the flashed-off liquid samples were also calculated on the basis of component mole fraction and its

Table 7. Molecular Weight of Flashed-off Liquid Phase Samples: P, pressure; wf, Weight Fraction of Ethane in Feed

G

equilibrium condition

L1

L2

wf = 0.4 and P/MPa = 5 wf = 0.4 and P/MPa = 9 wf = 0.9 and P/MPa = 9

259 286 370

541 572 870



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(7) Huang, S. H.; Radosz, M. Phase behavior of reservoir fluids II: Supercritical carbon dioxide and bitumen fractions. Fluid Phase Equilib. 1990, 60 (1−2), 81−98. (8) Deo, M. D.; Hwang, J.; Hanson, F. V. Supercritical fluid extraction of a crude oil, bitumen-derived liquid and bitumen by carbon dioxide and propane. Fuel 1992, 71 (12), 1519−1526. (9) Lim, G. B.; Kry, R. P.; Harker, B. C.; Jha, K. N. Cyclic stimulation of Cold Lake oil sand with supercritical ethane. SPE 30298 presented at SPE International Heavy Oil Symposium, 19−21 June 1995, Calgary, Alberta, Canada. (10) Subramanian, M.; Hanson, F. V. Supercritical fluid extraction of bitumens from Utah oil sands. Fuel Process. Technol. 1998, 55 (1), 35− 53. (11) Han, B.; Yang, G.; Ke, J.; Mao, C.; Yan, H. Phase equilibria of supercritical propane−Fengcheng bitumen system and the density and viscosity of the liquid phase. Fluid Phase Equilib. 1998, 143 (1−2), 205−211. (12) Rose, J. L. Extraction of Peace River Bitumen Using Supercritical Ethane. Ph.D. Thesis, University of Calgary: Calgary, Alberta, 1999. (13) Mehrotra, A. K.; Svrcek, W. Y. Viscosity, density and gas solubility data for oil sand bitumens. Part I: Athabasca bitumen saturated with CO and C2H6. AOSTRA J. Res. 1985, 1 (4), 263−268. (14) Mehrotra, A. K.; Svrcek, W. Y. Viscosity, density and gas solubility data for oil sand bitumens. Part II: Peace River bitumen saturated with N2, CO, CH4, CO2, and C2H6. AOSTRA J. Res. 1985, 1 (4), 269−279. (15) Mehrotra, A. K.; Svrcek, W. Y. Viscosity, density, and gas solubility data for oil sand bitumens. Part III: Wabasca bitumen saturated with N2, CO, CH4, CO2, and C2H6. AOSTRA J. Res. 1985, 2 (2), 83−93. (16) Mehrotra, A. K.; Svrcek, W. Y. Properties of Cold Lake bitumen saturated with pure gases and gas mixtures. Can. J. Chem. Eng. 1988, 66 (4), 656−665. (17) Fu, C. T.; Puttagunta, V. R.; Vilcsak, G. Gas solubility of methane and ethane in Cold Lake bitumen at in situ conditions. J. Can. Pet. Technol. 1988, 27 (4), 79−85. (18) Frauenfeld, T. W. J.; Kissel, G.; Zhou, S. PVT and viscosity measurements for Lloydminster-Aberfeldy and Cold Lake blended oil systems. SPE International Thermal Operations and Heavy Oil Symposium and International Horizontal Well Technology Conference, Calgary, AB, Canada. (19) Nourozieh, H.; Kariznovi, M.; Abedi, J. Phase behavior study of liquid−liquid equilibria in bitumen-solvent mixtures. Presented at the 60th Canadian Chemical Engineering Conference (CSChE2010), Saskatoon, Saskatchewan, Canada, 24−27 October 2010. (20) Nourozieh, H.; Kariznovi, M.; Abedi, J. Physical properties and extraction measurements for athabasca bitumen + light hydrocarbon system: Evaluation of pressure effect, solvent-to-bitumen ratio, and solvent type. J. Chem. Eng. Data 2011, 56 (11), 4261−4267. (21) Kariznovi, M.; Nourozieh, H.; Abedi, J. Experimental apparatus for phase behavior study of solvent-bitumen systems: A critical review and design of a new apparatus. Fuel 2011, 90 (2), 536−546. (22) Khan, M. A. B.; Mehrotra, A. K.; Svrcek, W. Y. Viscosity models for gas-free Athabasca bitumen. J. Can. Pet. Tech. 1984, 27 (4), 47−53. (23) Badamchi-Zadeh, A.; Yarranton, H. W.; Svrcek, W. Y.; Maini, B. B. Phase behaviour and physical property measurements for VAPEX solvents: Part I. Propane and Athabasca bitumen. J. Can. Pet. Technol. 2009, 48 (1), 54−61. (24) ASTM Standard D7169-11, Standard Test Method for Boiling Point Distribution of Samples with Residues Such as Crude Oils and Atmospheric and Vacuum Residues by High Temperature Gas Chromatography. ASTM International: West Conshohocken, PA, DOI: 10.1520/D7169-11, www.astm.org. (25) Schmitt, W. J.; Reid, R. C. The influence of the solvent gas on solubility and selectivity in supercritical extraction. Supercritical Fluid Technology; Elsevier Science, Publishers: Amsterdam, The Netherlands, 123−147.

phase (L1) as well as the bitumen-enriched phase (L2) increases with the pressure and overall ethane concentration. This is an indirect indication of component distribution within the phases. The overall ethane concentration significantly changes the molecular weight of the samples. It might be due to the complete extraction of light components from the bitumenenriched phase (L2) at high overall ethane concentrations which results in a high molecular weight value for this phase.

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CONCLUSION In this study, the phase partitioning and component distribution between phases as well as phase properties at equilibrium condition for the (Athabasca bitumen + ethane) system at room temperature were experimentally evaluated. The flashed off liquid samples were subjected to compositional analysis and the concentration of each component in different liquid phases were determined. The results indicate that the increase in both pressure and solvent to bitumen ratio raises the extraction yield and the separation of light components from the bitumen-enriched phase. It could be stated that at a constant temperature, as the extraction pressure increases the extraction yields increase and, as a result, a heavier and less volatile hydrocarbon liquid is produced. As pressure or overall ethane concentration increases, the lighter components mostly partition into the solvent-enriched phase and infinity values for equilibrium k-values of light components are obtained.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: 403-220-5594. Address: 2500 University Dr., NW, Calgary, Alberta, T2N 1N4 Canada. Funding

The authors wish to express their appreciation for the financial support of all member companies of the SHARP consortium: Alberta Innovates Energy and Environment Solutions, Chevron Energy Technology Co., Computer Modeling Group Ltd., ConocoPhillips Canada, Devon Canada Co, Dover Operating Co, Foundation CMG, Husky Energy, Japan Canada Oil Sands Limited, Nexen Inc., Laricina Energy Ltd., Natural Sciences and Engineering Research Council of Canada (NSERC-CRD), OSUM Oil Sands Co., PennWest Energy, Statoil Canada Ltd., Suncor Energy, and Total E&P Canada. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Butler, R. M.; Mokrys, I. J. Solvent analogy model of steamassisted gravity drainage. AOSTRA J. Res. 1989, 5 (1), 17−31. (2) Butler, R. M.; Stephens, D. J. The gravity drainage of steamheated oil to parallel horizontal wells. J. Can. Pet. Technol. 1981, 20 (2), 90−96. (3) Butler, R. M.; Mokrys, I. J. A new process (VAPEX) for recovering heavy oils using hot water and hydrocarbon vapour. J. Can. Pet. Technol. 1991, 30 (1), 97−106. (4) Eisenbach, W. O.; Niemann, K.; Gottsch, P. J.; in: Paulaitis, M.E.; Penninger, J.M.L.; Gray, R.D.; Jr., Davidson, P., Chem. Eng. Supercrit. Cond., 1983, Ann Arbor Science, Ann Arbor, MI. (5) Radosz, M.; Cotterman, R. L.; Prausnitz, J. M. Phase equilibria in supercritical propane systems for separation of continuous oil mixtures. Ind. Eng. Chem. Res. 1987, 26 (4), 731−737. (6) Yu, J. M.; Huang, S. H.; Radosz, M. Phase behavior of reservoir fluids: supercritical carbon dioxide and Cold Lake bitumen. Fluid Phase Equilib. 1989, 53, 429−438. H



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(26) Moradinia, I.; Teja, A. S. Solubilities of five solid n-alkanes in supercritical ethane. Supercritical Fluids: Chemical and Engineering Principles and Applications; Squires, T. G., Paulaitis, M. E., Eds.; American Chemical Society: Washington, DC, 1987. (27) Riazi, M. R. Characterization and Properties of Petroleum Fractions, 1st ed.; ASTM International: Philadelphia, PA, 2005.

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Experimental Determination of k-Values and Compositional Analysis

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