Article pubs.acs.org/EF
Three-Dimensional Scheme of Supercritical Carbon Dioxide Extraction of Heavy Hydrocarbon Mixture in (Pressure; Temperature; Recovery) Coordinates Svetlana Rudyk*,†,‡ and Pavel Spirov‡ †
Department of Petroleum Engineering and Applied Geophyscis, Norwegian University of Science and Technology, S.P. Andersens vej 15a, 7491 Trondheim, Norway ‡ Section of Chemical Engineering, Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, Campus Esbjerg, Denmark, 6700 Esbjerg, Niels Bohr vej 8 ABSTRACT: A heavy hydrocarbon mixture represented by C17−C31 carbon groups was investigated to determine extraction recoveries by supercritical carbon dioxide in the ranges of 12−65 MPa for pressure and 50−90 °C for temperature. The purpose of the study was to obtain a three-dimensional scheme of the SC−CO2/heavy hydrocarbon mixture system in pressure− temperature−recovery coordinates, which allows the prediction and numerical modeling of phase behavior. At lower temperatures, high recoveries were attained at lower pressures. The highest recovery of 93% was obtained at 70 °C and 56 MPa. The recoveries greater than 65% were determined at the breakover points where the pressure increased by 7 MPa with a temperature increase of 10 °C. The phase envelope, 3D scheme, and the equations describing the boundaries of the system are presented.
1. INTRODUCTION Mixtures of petroleum hydrocarbons of natural and synthetic origin such as crude, light, heavy, fuel, motor, and lubricating oils represent the variety of compositions. Although the interaction of supercritical carbon dioxide (SC−CO2) with light oils has been broadly studied,1,2 fewer investigations have been performed regarding its ability to extract and transport heavy hydrocarbon mixtures, including refinery stock, for various uses. Heavy hydrocarbon mixtures (HHM) may be considered as thickeners or viscosifiers for liquid carbon dioxide in order to increase the productivity of fracture formations in well fracturing. For such applications, the effects of thickeners themselves should be investigated because the thickening agent can precipitate in the formation upon depressurization and mitigate the increased productivity.3 On the contrary, due to its ability to precipitate, slurry was suggested to form a barrier to fluid flow around a treatment area in a subsurface formation. A fluid comprising liquefied wax having a solidification temperature that is greater than the temperature of the formation is injected and solidifies to form a barrier.4 For such application, carbon dioxide may be used as a medium for wax transportation into the formation. Several patents and publications describe the removal of lubricants from metal5 or molded surfaces6,7 by SC−CO2. It was implemented for cleaning sludge from the bottom of oil tanks8 and refinery stock9 from water, dust, and sand. The experimental data on the interaction of heavy hydrocarbons with SC−CO2 may additionally present a certain theoretical, practical, or technological interest for enhanced oil recovery, the removal of paraffin wax from tubing, oil flow in piping, the formation of gas hydrates, or the development of heavy oil and tar sands. SC−CO2 is a well-known strong solvent possessing liquidlike density and gas-like mass-transfer properties with an affinity for polar solutes and nonpolar compounds such as alkanes. To © XXXX American Chemical Society
determine the phase behavior of CO2/oil systems, experimental investigations are performed through either batch or continuous contacting of oil by an SC fluid.1 The overall perspective of the phase boundaries is usually represented by solubility or pressure/composition (P−x) diagrams (where x is a molar or mass fraction of the species) obtained using highpressure view cells. The CO2/oil phase behavior10 demonstrates a variety of phases such as vapor (V) and liquid (L), two coexisting liquids (LL), or two liquids and a gas (VLL); also, solid or semisolid asphaltenes may precipitate. Diverse changes in coloration, turbidity, and other characteristics, visually observed in refs 10 and 11 under conditions in which multiple phases were generated, reflect even more complicated phase behavior than represented by the diagrams. Flow systems comprising slim tubes and high pressure extractors vary in design, size, and operational regimes.1,12 Recovery at a particular pressure is determined from displacement or extraction experiments followed by the collecting and measuring of the displaced/extracted hydrocarbon samples in dynamic, static, or combination modes. For hydrocarbons in the C5-through-C30 range, smaller molecules are extracted more efficiently by dense CO2; large molecules are extracted less efficiently, regardless of whether they are paraffinic, naphthenic, or aromatic.13 As molecular weight increases for alkanes larger than n-C12, the solubility of the hydrocarbons in CO2 decreases. Chartier et al.6 had shown that C17H36 and supercritical carbon dioxide were miscible completely under pressure higher than 20 MPa. When he compared the miscibility of different hydrocarbon fractions, the Received: January 23, 2013 Revised: August 28, 2013
A
dx.doi.org/10.1021/ef401008e | Energy Fuels XXXX, XXX, XXX−XXX
Energy & Fuels
Article
mass concentration of C32H66 was observed to be about 18 times lower at 20 MPa than the mass concentration of C19H40. The above-mentioned observations led to the conclusion that high pressures are required to achieve miscibility between heavy hydrocarbons and dense carbon dioxide. A patent by Faggian and Ligabue9 describes the separation of a liquid phase from a solid residual fraction from refinery sludges with a consistency from semisolid to fluid, using carbon dioxide at the preferred temperature 45−90 °C and 15−35 MPa of pressure. Another patent by Reich et al.5 represents a process for separating solid particles from used rolling oil by supercritical CO2 at the optimal temperature of 40 °C and a pressure of 31 MPa. Kim et al.7 reported about more than 90 wt % of paraffin extraction from a metal surface at 25 MPa of pressure and temperatures of 65−75 °C. It is well-known that the recovery of oil increases as pressure rises and decreases with a temperature increase.2 In the case of solid or semisolid hydrocarbon mixtures, the temperature must be sufficient to ensure melting of the entire mixture. To investigate the influence of the thermodynamic conditions on the recovery of the heavy hydrocarbon mixture, the serial extraction tests were performed in a broad range of pressures from 12 to 65 MPa and temperatures from 50 to 90 °C in order to obtain the three-dimensional scheme of the SC−CO2/HHM system. This allows the determination of the optimal conditions for effective extraction and predicting the phase behavior of the system at greater pressures and temperatures.
Figure 1. Scheme of extractor. (1) Inlet valve. (2) Pipe connecting the inlet valve with extractor. (3) Extractor. (4) Outlet valve. (5) Test tube in the vessel with cold water for cooling.
Table 1. Summary of Experimental Results
2. EXPERIMENTAL SECTION
temperature [°C] pressure [MPa]
2.1. Materials. The 99.9% pure carbon dioxide was supplied by Strandmøllen A/S, Denmark. Haldor Topsøe A/S, Denmark, provided a heavy hydrocarbon mixture originating from the North Sea oil obtained as a result of hydrocracking for experimental study. The density of the mixture was 0.8396 g/cm3 (D 4052 test14). According to D 6591 test, the mixture contained 11.64 wt % aromatics, (8.77 wt % 1 ring, 1.31 wt % 2 rings, and 1.56 wt % 3+ rings). The melting temperature is >30 °C; the boiling temperature is >290 °C. 2.2. Experimental Procedure. A supercritical extractor, Spe-ed SFE shown in Figure 1, was used for the experiment.15 For each test, 42 ± 0.5 g of a heavy hydrocarbon mixture was put into an extractor (3) of 100 mL volume. Caps with holes (3) on both sides covered the extractor. The bottom hole is used for the injection of CO2 from the gas balloon regulated by the inlet valve (1) and connected by the pipe (2) to the extractor. The injection of gas at known pressure occurs during a specific interval of time. After this time, the outlet valve (4) is opened to start the collection of the extracted sample. The extracted hydrocarbon mixture moves up along a pipe of 0.3 mm diameter to the collection module where it is collected into test tubes. The test tubes are set in a vessel with cold water for cooling the extracted samples (5). When the test is finished, the extractor (3) is removed for cleaning. Thereafter, the next portion of the heavy hydrocarbon mixture of the mentioned weight is placed in it. The samples collected in the test tubes after extractions were weighed. The recovery (R) was calculated as a ratio of the extracted amount to the initial amount (42 g) of the heavy hydrocarbon mixture in percent. The results are summarized in Table 1. The collected samples and remnants in the extractor were visually examined, and the observed specific features such as freezing, bubbling, or foaming were recorded. 2.3. Chromatographic Analysis. The sample of crude heavy hydrocarbon mixture used in the experiment and the samples extracted at 50 °C at 30, 40, and 56 MPa were analyzed by gas chromatography−mass spectrometry (GC-MS). To prepare the samples for chromatographic analysis, 0.5 mL of HHM was diluted with 1.5 mL of n-pentane. The GC-MS system consisted of a GC−CP3800 gas chromatograph and a MS-ION TRAP 2000 mass
50
60
70
80
90
0.06
0.04
recovery [%] 12.4 15 17.7 20 22.5 25 27.7 30 32.5 35 37 37.5 40 42 42.5 45 47.5 50 52 56 60 65
0.23 1.55 2.87 6.28 10.19 8.92 10.39 9.17 10.97 13.28 77.52 81.74 81.75
0.09
0.07
0.29
0.28
2.71
2.65
2.61
4.32
3.18
2.9
3.70
4.60
8.18
6.03
86.00 45.77 76.67
34.75 71.10 73.67 84.57
9.23 80.14
88.43 81.83
88.79 89.57
93.66 81.48
0.45
6.74
1.01 1.60 2.40 3.68
6.57 7.60 8.77
4.70 10.78 10.98 48.89 79.27
11.40
8.72 35.93 81.02
spectrometer with the VF-5s30Mx0.25MM capillary column from Varian (Middelburg, The Netherlands). Helium was used as the carrier gas at a pressure of 20 psi. The MS was operated in electron ionization mode. The temperature was 300 °C. The mass range was from m/z 50 to m/z 600 in scan mode. The total run time was 45 min. The identification of compounds was made by comparison with mass spectra reported in the NIST library. The composition of the crude heavy hydrocarbon mixture is presented via the GC-MS total ion current chromatogram in Figure 2. B
dx.doi.org/10.1021/ef401008e | Energy Fuels XXXX, XXX, XXX−XXX
Energy & Fuels
Article
3.2. Experimental Results. The experimental results of the current study were plotted in Figure 3 as pressure, P (MPa),
Figure 2. Chromatogram of the sample of the experimental heavy hydrocarbon mixture.
The chromatogram shows the presence of eluted single carbon number (SCN) groups from C17 to C31 forming a fold shape of an unresolved hump, with the C25 carbon group at the top of the fold.
3. RESULTS AND DISCUSSION 3.1. Optimization of the Operating Conditions. The extraction recovery, among other factors, also depends on the duration of the interaction of hydrocarbons with carbon dioxide required to achieve equilibrium. After this time, at particular pressures and temperatures, no significant changes in the volume of the extracted sample would occur. Besides that, it is desirable to set the interaction time so that it is short enough to make the method cost-effective. The equipment can function in either static, dynamic, or combination mode. In the static mode, before collection of the extracted oil, the inlet valve is closed to prevent any further gas injection. In the combination mode, the inlet valve is not closed after interactions in the static mode. The continuously injected gas carries the extracted product into the collection module in the dynamic mode. This also implies that the interaction between gas and hydrocarbons continues during the period of collection. To determine the optimum time and operating mode, the tests were conducted during different periods in static and combination modes at several pressure values. The temperature throughout the tests was kept at 50 °C. The static mode was tested using 20 and 40 min of interaction at 45 MPa followed by 15 min for the collection time. Recovery in both cases was calculated as 5%. In the combination mode, several tests were conducted at 30 and 45 MPa during different periods of interaction in the static mode followed by 15 min in the dynamic mode. At 30 MPa, during 20 and 40 min of interaction, the recovery was 4%; at 45 MPa, during 40, 30, and 20 min of interaction, the recovery was calculated as 72%, 71%, and 72%, respectively. Recovery in the combination mode was much higher than in the static mode. It was also noted that 20 min of interaction in the static mode followed by 15 min of dynamic mode was sufficient, because no substantial change in recovery was measured for longer periods. As a result, this regime was selected for further experiments.
Figure 3. Recovery curves at all pressures and temperatures. Five isotherms are shown superimposed. The solid circles represent recovery values higher than 30%. The quadrates designate recovery values less than 20%.
versus recovery, R (%). They are also shown in a threedimensional scheme in Figure 4 to help to view the entire system16 in the range of measured pressures and temperatures. Upon extraction, the samples differed by color, temperature, the character of flow, and other specific features, signifying the complex phase behavior of the system. From the observations of the isotherms, it may be deduced that they are similar to the
Figure 4. Three D model of the experimental results in pressure− temperature−recovery coordinates. Dashed lines are mere interpolations between F points and D points. C
dx.doi.org/10.1021/ef401008e | Energy Fuels XXXX, XXX, XXX−XXX
Energy & Fuels
Article
phase diagram of the binary system,12,17,18 schematically shown in Figure 5, which crude oil also matches. In the current study,
extraction under the conditions of DB segments differed substantially. At 80 °C/60 MPa and 90 °C/65 MPa, the sluggish flow of dark brown liquid with bubbles was observed. At 50, 60, and 70 °C, and pressures lower than 56 MPa, the liquid flowed smoothly with a dark yellow color. Starting from 56 MPa at 50 and 60 °C, the collected liquids were boiling with tiny bubbles. At 70 °C and 56 MPa, where the highest extraction recovery of 93 wt % was attained, the extracted sample was foam-like and retained a porous structure upon cooling. Recent investigations, including those in refs 20 and 21, have reported the similar supercritical carbon dioxide foaming of many substances. We presumed that boiling with a large amount of gas bubbles and foaming of the samples upon extraction observed at all temperatures and pressures above 56 MPa compared to clear liquid at the lower pressures would show that the heavy hydrocarbon mixture was oversaturated with dense carbon dioxide. If the volume of dissolved gas is too big, the viscous liquid starts boiling or foaming upon release. All of the observed features, such as breaking points, high recoveries, and boiling or foaming of the extracted samples, enabled us to presume that miscibility of the CO2/HHM was achieved at D points. The samples of heavy hydrocarbon mixtures were frozen not only under the AF path conditions but at 50 °C and 47.5 MPa. The tests under the mentioned conditions were repeated four times; recovery varied from 16 to 22 g. The average value of four tests of 20 g was plotted. The heavy hydrocarbon mixture freezing at that point can be explained as a result of the interaction of the solvent and solute, which are subjected to the influence of pressure and temperature differently; this is accompanied by the breaking and creating of new bonds between molecules. Such effects are common for the methane− water system where the breaking of bonds has a cooling effect when the gas hydrates are forming.22 It is worth mentioning that freezing was also detected below certain temperatures in similar experiments with bitumen of tar sand and paraffin wax from well tubing. Projection of the FD plane in a pressure−temperature plot is shown in Figure 6. An increase of pressure (P) at increasing temperature (T) is estimated in eq 1 along the D line and by in 2 along the F line:
Figure 5. Schematic pressure−composition diagram of a binary mixture at constant temperature. In the current study, liquid L1 is carbon dioxide enriched with hydrocarbons, liquid L2 is hydrocarbons enriched with carbon dioxide, and V is a vapor phase.
the composition of the liquid L1 is carbon dioxide enriched with hydrocarbons. Liquid L2 is hydrocarbons enriched with carbon dioxide, and V is the vapor phase. The specific segments in the curves of the experimental isotherms were denoted by capital letters similar to Figure 5. At first, recoveries at all the temperatures were less than 20% at pressures increasing from A points to F breakover points, where the graphs changed abruptly; they then reached values above 65% at D breakup points with a further increase to B points. Recovery along the vapor-like AF root improved because of a gradual increase in the pressure-dependent density of carbon dioxide. The AF segments at all of the isotherms starting from 60 °C were concentrated very close to each other, implying that the recovery did not depend on temperature. The samples extracted at the conditions of AF segments were bright yellow in color, and often frozen, even at 90 °C, indicating that the interaction was endothermic and more energy was required than provided by heating, which led to the freezing of the extracts. Recoveries along the AF segment are greater at greater boiling temperatures, as shown in ref 19. Because the boiling point of HHM is very high, the temperature has no noticeable effect on the recovery under the mentioned conditions. At 50 °C and 25−35 MPa, the samples in the collection tubes were a white, foamy, boiling liquid. With temperature increases, the pressures at F points also increased as the solvent properties of SC−CO2 worsened. Under the conditions matching the FD segments, the samples were extracted at 60, 80, and 90 °C. The flows of liquid upon extraction were smooth at all temperatures; bubbles were observed at 90 °C. High recoveries above 65 wt % were achieved beginning from D points at 37.5 MPa and 50 °C, 42 MPa and 60 °C, 47.5 MPa and 70 °C, 60 MPa and 80 °C, and 65 MPa and 90 °C. Some of the features of the samples upon
P = 0.7·T + 2.5, R2 = 0.99
(1)
P = 0.52·T + 9.5, R2 = 0.98
(2)
As temperature increases by 10 °C, the pressure increases by 5.2 MPa at F points and by 7 MPa at D points. Regression coefficients calculated for both D and F lines are very close to 1. This proved that the experiment was performed with high precision. It also showed that all of the deviations from the trend lines that mainly occurred under the conditions of DB segments were not occasional and arose due to changes in the physical properties of the species. The extraction along the AFDB path separates the investigated system from many systems of crude oil with supercritical carbon dioxide that follow the ADB path, which can be found elsewhere.1,2,12,17,18,23 The ADB path is typical for the SC−CO2 extraction of light hydrocarbons, especially from the porous matrix,2,24,25 probably because the process is analogous to some extent with drainage/imbibition of capillary curve analysis.26 The most distinguishable characteristic of the investigated system is an abrupt increase from F to D points, showing a D
dx.doi.org/10.1021/ef401008e | Energy Fuels XXXX, XXX, XXX−XXX
Energy & Fuels
Article
with increasing temperatures. The HHM density is similar to the density of crude oil, while their viscosities and microstructures are very different. Temperature differently affects interacting species. Vaporization, which depends on boiling temperature, may mitigate extraction of the liquid phase, but it does not seem to have great significance with HHM compared to the above-mentioned crude oil. The vapor fraction calculated as the difference between the initial and collected amount of HHM at 70−90 °C in the entire pressure range was 10% on average, which is less than that of the crude oil. Nevertheless, as the slope of FD planes becomes less sharp with temperature increases, it could be presumed that at higher temperatures HHM is less viscous, which enables SC−CO2 diffusion into the mixture. However, high temperature affects the carbon dioxide to the extent that the effect from reduced viscosity of HHM is negated, requiring the additional pressure to achieve D points. This is consistent with the general theory of interaction of carbon dioxide with crude oil, where miscibility is attained at higher pressures as the temperature rises.1 Because the measurements are not possible in a closed extractor, it could be only speculated that the sharp increase from F to D points occurred because of the combined effect of pressure and temperature and the particularities of the microstructure and composition of HHM. 3.3. Chromatographic Analysis. The investigations of SC−CO2 extraction of crude oil from different places of origination2,15 have shown that the recovery and composition of hydrocarbons are closely related. It was even found2 that the hydrocarbon composition of extracts was similar at different temperatures if recoveries were equal. Because of the high viscosity of HHM, GC-MS TIC analysis of the extracted samples was only performed for three pressures at 50 °C. The comparison of the extracts with the original HHM was made in order to determine whether the selective fractionation of the HHM occurs as with a crude oil owing to pressure change or whether the composition of the HHM remains unchanged because pressure controls only the magnitude of recovery. The areas of unresolved humps and the peak heights of hydrocarbons up to C26 did not differ substantially in any of the chromatograms. The chromatogram of the sample extracted at 56 MPa coincided with the chromatogram of the original HHM. Although starting from C28, the SCN group peaks were poorly eluted; it was observed that the peak heights of SCN groups from C27 change from almost noneluted at 30 MPa to a maximum at 56 MPa, demonstrating the greater extraction of heavier SCN groups under increasing pressure. The comparison of the fractions extracted under the conditions of different segments of the recovery graph has shown that SC−CO2 possesses selective fractionation: the higher-boiling hydrocarbons were extracted at the highest pressure. However, the temperature of the chromatograph is lower than the boiling temperature of the high-boiling fractions. To determine a more detailed composition of the HHM by means of chromatographic analysis is not possible, which requires additional investigations. After cooling, the extracted samples were solid, implying that the water, if present, was removed during the extraction process. The water content in the initial samples was not determined, however. Once the general type of phase behavior is identified,31 the prediction regarding the phase behavior and extraction recovery under increasing pressure and temperature or verification of the numerical modeling can be made. Many differences in
Figure 6. Pressure−temperature plot. D line and F line are drawn as interpolation between D and F points at all the temperatures. The region above the D line indicates miscibility conditions of the heavy hydrocarbon mixture and SC−CO2. Recovery above the D line is higher than 65%. Recovery below the F line is less than 20%.
rapid increase in solubility. The pressure difference between F and D points gradually increased from 2 to 8 MPa at 50−90 °C. Similar slopes, although less sharp, were observed in our experiments15,27,28 carried out using North Sea crude oil from different oilfields at various temperatures. The pressure difference between F and D points was above 15 MPa, signifying the slow increase of solubility and higher pressures of miscibility conditions. Although the experimental study of two types of North Sea crude oil at 20−60 MPa (unpublished data) was not very detailed (40−70 °C) at the interval between pressure values of 10 or 20 MPa, the observations suggested that the temperature increase might cause oil vaporization up to 60%; as a result, the recovery curves were very dependent on the type of oil. Such a pronounced effect of temperature as with HHM was not observed. The same clear and streamlined 3D scheme was not obtained for the crude oils, although the general conclusion suggested that while the FD plane of the HHM was uplifting, it was declining for crude oil due to the decreasing yield of the liquid phase at higher temperatures. Regardless of the opinion that a much higher pressure can be expected for miscibility of heavy hydrocarbons with SC−CO2 than the light oil, in the current study, the opposite effect was observed, as supercritical carbon dioxide and heavy hydrocarbons were miscible at comparatively moderate thermodynamic conditions; this can be attributed to the effect of higher viscosity of HHM. A similar phenomenon was observed by Chen et al.,29 who found that some olefins with higher molecular weight dissolved in propane at lower pressures, despite the well-established fact that within the same group of polyolefins the cloud-point pressure increased with increasing molecular weight. This was explained by the difference in microstructure of the olefins and contribution of the shortchain branchiness in enhanced miscibility with propane. Whether alkanes, aromatics, or naphthenes as well as branched or straight-chain alkanes experience higher extraction by CO2 requires further study at high pressures and temperatures. The properties of HHMs obtained after hydrocracking can differ from the properties of natural HHMs. Solubility theory states that two liquids achieve the highest mutual solubility when their densities become close.30 Solubility of hydrocarbon mixtures with SC−CO2 increases at high pressures as the CO2 density approaches the density of hydrocarbon mixtures, facilitating their extraction, and worsens E
dx.doi.org/10.1021/ef401008e | Energy Fuels XXXX, XXX, XXX−XXX
Energy & Fuels
Article
(14) Drews, A. W. Manual on Hydrocarbon Analysis; ASTM International: Baltimore, MD, 1992; p 648. (15) Rudyk, S.; Spirov, P.; Sogaard, E. Application of GC−MS chromatography for the analysis of the oil fractions extracted by supercritical CO2 at high pressure. Fuel 2013, 106, 139−146. (16) Schneider, G. M. Phase equilibria in fluid mixtures at high pressures. Adv. Chem. Phys. 1970, 17, 1−42. (17) Firoozabadi, A. Thermodynamics of Hydrocarbon Reservoirs; McGraw-Hill: New York, 1999; p 355. (18) Smith, J. M. Introduction to Chemical Engineering Thermodynamics, 6th ed.; McGraw-Hill: Boston, MA, 2001; p 789. (19) Rudyk, S. Determination of saturation pressures using experimental data of modified SC-CO2 extraction of crude oil by consistency test. J. Supercrit. Fluids 2013, 82 (0), 63−71. (20) Bao, J. B.; Liu, T.; Zhao, L.; Barth, D.; Hu, G. H. Supercritical Carbon Dioxide Induced Foaming of Highly Oriented Isotactic Polypropylene. Ind. Eng. Chem. Res. 2011, 50 (23), 13387−13395. (21) Salerno, A.; Di Maio, E.; Iannace, S.; Netti, P. Solid-state supercritical CO2 foaming of PCL and PCL-HA nano-composite: Effect of composition, thermal history and foaming process on foam pore structure. J. Supercrit. Fluids 2011, 58 (1), 158−167. (22) Tavasoli, H.; Feyzi, F.; Dehghani, M. R.; Alavi, F. Prediction of gas hydrate formation condition in the presence of thermodynamic inhibitors with the Elliott−Suresh−Donohue Equation of State. J. Pet. Sci. Eng. 2011, 77 (1), 93−103. (23) Scott, R. L.; van Konynenburg, P. H. Static properties of solutions. Van der Waals and related models for hydrocarbon mixtures. Discuss. Faraday Soc. 1970, 49, 87−97. (24) Librando, V.; Hutzinger, O.; Tringali, G.; Aresta, M. Supercritical fluid extraction of polycyclic aromatic hydrocarbons from marine sediments and soil samples. Chemosphere 2004, 54 (8), 1189−1197. (25) Yang, Y.; Gharaibeh, A.; Hawthorne, S. B.; Miller, D. J. Combined temperature/modifier effects on supercritical CO2 extraction efficiencies of polycyclic aromatic hydrocarbons from environmental samples. Anal. Chem. 1995, 67 (3), 641−646. (26) Bradley, H. B. Petroleum Engineering Handbook. SPE: Richardson, TX, 1987; Vol. 2, p 1640. (27) Spirov, P.; Rudyk, S. Effect of RegenOx Oxidant As a Modifier on Crude Oil Extraction by Supercritical Carbon Dioxide. Energy Fuels 2013, 27 (3), 1492−1498. (28) Rudyk, S.; Hussain, S.; Spirov, P. Supercritical extraction of crude oil by methanol- and ethanol-modified carbon dioxide. J. Supercrit. Fluids 2013, 78, 63−69. (29) Chen, S.-j.; Banaszak, M.; Radosz, M. Phase Behavior of Poly(ethylene-1-butene) in Subcritical and Supercritical Propane: Ethyl Branches Reduce Segment Energy and Enhance Miscibility. Macromolecules 1995, 28 (6), 1812−1817. (30) Hansen, C. M. Hansen Solubility Parameters: A User’s Handbook; CRC Press: Boca Raton, FL, 2000; p 208. (31) Raeissi, S.; Florusse, L.; Peters, C. Scott−van Konynenburg phase diagram of carbon dioxide + alkylimidazolium-based ionic liquids. J. Supercrit. Fluids 2010, 55 (2), 825−832.
characteristics of the extracted samples were observed during the extraction of heavy hydrocarbon mixtures by supercritical carbon dioxide, giving better insight into the actual phase behavior of the system. Those visual observations are useful when planning various applications.
■
CONCLUSION The estimations of the phase transitions based on the comparison with the phase diagram of the binary mixture showed that the heavy hydrocarbon mixture inherited its phase behavior and mimicked its paths. Our experiments showed that recoveries were low in the AF segment along the AFDB path in a wide pressure range at various temperatures, due to which the entire method could be misinterpreted as inefficient; however, the recoveries substantially increased following the FD segment to the region of maximum recoveries of the DB path at pressures lower than required for the crude oil in an identical experiment. The boundaries of freezing conditions, as well as the conditions of greatest recoveries, can be precisely calculated by eq 1 and eq 2, respectively. The influence of the distribution of normal alkanes, branched alkanes, naphthenes, and aromatics on SC−CO2 extraction efficiency should be further investigated.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
REFERENCES
(1) Stalkup, F. I. Miscible Displacement. Henry L. Doherty Memorial Fund of AIME, SPE: Richardson, TX, 1992; Vol. 8, p 204. (2) Al-Marzouqi, A. H.; Zekri, A. Y.; Jobe, B.; Dowaidar, A. Supercritical fluid extraction for the determination of optimum oil recovery conditions. J. Pet. Sci. Eng. 2007, 55 (1), 37−47. (3) Enick, R.; Olsen, D.; Ammer, J.; Schuller, W. Mobility and Conformance Control for CO2 EOR via Thickeners, Foams, and Gels-A Literature Review of 40 Years of Research and Pilot Tests; U. S. Department of Energy: Washington, DC, 2012; p 267. (4) Vinegar, H. J.; Carter, E. E.; Son, J. S.; Bai, T.; Verdian, M. F. K. U.S. Patent No. 7703513 B2. 2010. (5) Reich, R. A.; Kasun, T. J.; Colbert, R. J. U.S. Patent No. 6001245A, 1999. (6) Chartier, T.; Delhomme, E.; Baumard, J. F.; Marteau, P.; Subra, P.; Tufeu, R. Solubility in supercritical carbon dioxide of paraffin waxes used as binders for low-pressure injection molding. Ind. Eng. Chem. Res. 1999, 38 (5), 1904−1910. (7) Kim, Y.; Yoo, K. P.; Lim, J.; Lee, Y. W. Removal of paraffin wax binder from metal injection molded part by supercritical fluids. Sep. Sci. Technol. 2005, 39 (8), 1967−1987. (8) Á vila-Chávez, M. A.; Eustaquio-Rincón, R.; Reza, J.; Trejo, A. Extraction of hydrocarbons from crude oil tank bottom sludges using supercritical ethane. Sep. Sci. Technol. 2007, 42 (10), 2327−2345. (9) Faggian, L.; Ligabue, M. European Patent No. 0314223, 1992. (10) Henry, R.; Metcalfe, R. Multiple-phase generation during carbon dioxide flooding. SPE J. 1983, 23 (4), 595−601. (11) Yellig, W.; Metcalfe, R. Determination and Prediction of CO2 Minimum Miscibility Pressures. J. Pet. Technol. 1980, 32 (1), 160−168. (12) Danesh, A. PVT and Phase Behaviour of Petroleum Reservoir Fluids; Elsevier Science: Amsterdam, The Netherlands, 1998; Vol. 47, p 388. (13) Orr, F. M., Jr.; Silva, M. Effect of Oil Composition on Minimum Miscibility Pressure-Part 2: Correlation. SPE Reservoir Eng. 1987, 2 (4), 479−491. F
dx.doi.org/10.1021/ef401008e | Energy Fuels XXXX, XXX, XXX−XXX
