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Chapter 7
Plausible Locus for Large Paraffinic Compounds in the Boduszynski Continuous Composition Petroleum Model Lante A. Carbognani Ortega* Catalysis and Adsorption for Fuels and Energy, University of Calgary, Calgary, Alberta T2N 1N4, Canada *E-mail:
[email protected].
Literature presenting evidence on the existence of petroleum large molecular weight paraffinic compounds spanning the C90-C215 carbon atoms is reviewed. The use of conventional handling and characterization techniques of the oil samples could lead to inadequate or misleading information. High temperature liquid chromatography isolation and characterization techniques and the use of soft ionization mass spectrometry techniques were shown mandatory for their analysis. Both positive and negative properties over petroleum fractions provided by such hydrocarbons were identified. A plausible locus within the Boduszynski continuous molecular composition petroleum model is advanced.
Introduction The existence of large molecular mass paraffinic compounds was known decades ago, mostly related to oil field deposits. Alkanes in the vicinity of C57 (i.e., carbon atoms/molecule) were reported (1). One seminal article published in 1985 by Dr. Boduszynski reported on the existence of large cycloparaffins (“naphthenes” ) spanning up to C90, as illustrated in Figure 1 (2). Adoption of soft mass spectrometry ionization techniques such as Field Ionization Mass Spectrometry (FIMS) and Field Desorption Mass Spectrometry (FDMS) allowed for the detection of these compounds that otherwise were routinely fragmented when analyzed with the standard high energy electron impact ionization techniques, widely followed by most researchers at that time. Two important © 2018 American Chemical Society
Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
concepts were advanced in this article (2): 1) The inadequate and/or misleading information provided by average structures of hydrocarbon complex mixtures; 2) The continuous distillation patterns determined for petroleum components, where distillation properties were influenced by the weak and strong intermolecular forces affecting molecules (London, dipole-dipole, dipole-induced dipole and H-bonding).
Figure 1. FIMS analysis of the 1150-1369°F saturates fraction isolated from Kern River Petroleum. Reproduced with permission from reference (2). Copyright 1985 American Chemical Society. Alkane mixtures are indistinctly identified like “paraffins”, “saturates” and “waxes” in the oil-related literature, the latter term describing large isomers able to crystallize under ambient conditions. Paraffins interact only via weak intermolecular forces (London) and thus, are the largest compounds present in a defined distillation cut that comprises additional low Molecular Weight (MW) polar, acidic and basic compounds. The preceding aspects were thoroughly covered in the well-known monograph on heavy petroleum fractions published by Drs. Altgelt and Boduszynski in 1993 (3).
Recently Published Evidence Supporting the Existence of Large MW Alkanes in Petroleum As mentioned in the previous section, FDMS proved to be a key analytical technique for the characterization of large MW paraffins, a fact recognized by authors studying the nature of waxes (4), and sludges containing high MW alkanes (boiling points above 1,250°F) (5). Results presented by Musser and Kilpatrick suggested the possible existence of paraffins spanning the C70-C215 174 Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
range (i.e.,~1,000-3,000 a.m.u.), as illustrated in Figure 2 (4). Thomson et al. showed the existence of alkanes spanning up to C62 (Z series +2) together with monocycloalkyl (Z series +0, up to C62) and monoaromatic waxes (Z series -6, up to C81) within 1,250°F+ waxy sludges isolated from the USA Strategic Petroleum Reserve (US-SPR) (5). These results are deemed interesting because the later discussion in this chapter will point out that mixtures of these hydrocarbon families often occur within waxy paraffinic deposits. Figure 3 illustrates the findings reported by Thomson et. al. (5)
Figure 2. FDMS Spectrum for San Joaquin Valley waxes, showing microcrystalline character. Reproduced with permission from reference (4). Copyright 1998 American Chemical Society.
Figure 3. FDMS spectrum of >1250°F wax from Cavern B. Reproduced with permission from reference (5). Copyright 1989 American Chemical Society. 175 Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
The advent of commercial High Temperature Gas Chromatography (HTGC) at the beginning of the 1990s, allowed researchers to apply the technique to the study of waxy deposits. Thomson et al. reported the existence of waxy components larger than C100 within the >600°C fraction isolated from one US-SPR storage cavern, as presented in Figure 4 (6). HTGC was widely applied by other research groups during the 1990s decade to study waxy solid deposits (7–10). Paraffinic compounds up to C70 were reported in these studies. The use of unheated autosamplers despite temperature programmable cold on-column injectors for sample introduction into the GC was described, is believed by the author of the present chapter as the reason precluding the detection of larger MW components. The preceding practice induced losses of large paraffinic compounds which adhered to the walls of vials and/or syringe tips since warm and diluted conditions were not carefully maintained. One interesting feature of waxy solid deposits studied in these articles is the existence of bimodal and even multimodal compound distributions (7–10), feature also observed by the author when relying on High Temperature Size Exclusion Chromatography (HT-SEC) of solid deposits retrieved from paraffinic oil storage tanks (11). One further important aspect described by Biao et al. pertains to the use of hot xylene for extraction of large MW waxes (9). The preceding discussion emphasises the importance of high temperature as a fundamental parameter for isolation and analysis of large petroleum paraffinic compounds.
Figure 4. HTGC chromatogram of a > 600°F wax from Cavern B sludge. *C100 appended over the chromatogram based on the reported data. Reproduced with permission from reference (6). Copyright 1992 Wiley-VCH Verlag GmbH & Co. KGaA. Researchers from India provided an important body of information over solid sludges sampled from the bottom of paraffinic oils storage tanks in the 1990s decade (12–15). Combined separation/spectroscopy techniques like distillation, solvent precipitation, chromatographic separation, solvent extraction, urea adduction, simulated distillation, elemental analysis, and Nuclear Magnetic Resonance spectroscopy (NMR) were used by these authors to study the nature 176 Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
of the studied solids. A summary of the most important results for the aims of the present article ensues: -
-
-
Paraffinic components spanning the C70-C125 carbon range were described, the largest showing melting points above 90°C High proportions of n-alkanes (60-90 wt%) were determined in selected studied fractions via urea adduction Cycloalkane and aromatic waxy components were observed present in the waxy solids. Concomitant hydrogen deficiencies were determined within these fractions Combined presence of naphtheno-aromatic structures (i.e., hydrogen deficient compounds) plus the high complexation capacity of urea adduction, indicate the possibility that molecules long alkyl appendages were included within urea host helices, leaving outside their non-linear moieties Bimodal and even trimodal wax distributions were observed in some of the studied cases
The preceding results are considered important because in the experience of the author of the present article, these coincide in many aspects with results gathered for paraffinic solids studied in relation to oil production and storage operations within the Eastern and Maracaibo basins in Venezuela, during the 1990s. These will be addressed in the next section.
Large MW Saturates Isolation via High Temperature Liquid Chromatography (HTLC) and Characterization via High Temperature Size Exclusion Chromatography (HT-SEC) A systematic study of oilfield solid deposits indicated the necessity of developing isolation techniques that guarantee samples integrity, i.e., achieve complete recovery of hydrocarbon components (16). High temperatures were determined necessary for waxy deposits, which often showed high melting temperature ranges spanning the 90-100ºC, thus requiring solvents like i-octane or xylene for their complete extraction. The final protocol set up for complete solid wax recovery from field deposits was reported by Garcia (17), comprising sequential Soxhlet extraction with solvents of increasing boiling temperatures: I) CHCl3/MeOH:95/5 vol., II) toluene/2-propanol:95/5 vol., III) xylene/n-butanol:95/5 vol. After wax extraction was achieved, further separation of the saturates fraction from other co-extracted components was accomplished by applying HTLC separation (18). Paraffinic compounds, i.e., alkane soluble saturates fractions were not retained on the column packing and were observed with refractive index detectors as one single initial band eluting from the column with apolar solvents like n-heptane or i-octane. The key for successful isolation of saturates was to be able to dissolve/disperse waxy components in hot solvents to avoid wax crystals to grow and adhere to any surface contacting them (vials, pipettes, syringes…). A rule of thumb for success was to visually observe the 177 Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
absence of cloudiness in the prepared sample solutions. On-column deposition of dissolved samples in hot solvent was carried out over medium-pressure columns packed with different type of adsorbents, as described in detail elsewhere (18). Complete recovery of paraffins was thus achieved by guaranteeing high MW alkanes elution in hot liquid media, i.e., they were not allowed to crystallize under the combined effects of dilution and high temperature. Figure 5 illustrates successful complete isolation of paraffinic fractions carried out under increasing temperatures, up to 90ºC.
Figure 5. Chromatographic elution of waxes from Attapulgus clay packed columns, carried out at different temperatures. n-heptane used for 25, 45 and 75 ºC; i-octane for 90ºC elution.
Interesting behavior of “waxes” isolated from commercial asphalt used in paving operations was observed when applying HTLC separation (19). It was found that these “waxes” comprised compounds bearing naphtheno-aromatic moieties linked to alkyl functionalities (19). The presence of these functionalities on the studied waxes provided them with intermediate polarity properties, between those for pure alkanes and pure aromatics, thus leading these fractions to elute within ranges in-between those typical for saturates/aromatics (19). The preceding findings suggest that complex waxy mixtures like those existing in solid field deposits and also in distillation vacuum residua, often include different hydrocarbon types like mentioned before in the discussion related to Figure 3 (cycloparaffinic waxes) and in relation to waxy tank bottoms gathered in India’s facilities (naphtheno and aromatic-alkanic waxes, addressed in the previous section) (12–15). 178 Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
Setting up high temperatures for handling very large paraffinic components was shown in the preceding discussion to be mandatory for avoiding losses during their isolation and purification. HT-SEC was then developed with the purpose of characterizing large alkane mixtures (20). High resolution silica columns (80Å pores) eluted with hot toluene delivered with highly accurate syringe pumps and very stable-very sensitive evaporative type detectors, allowed the analysis of large wax components. Elution examples for n-paraffin standards, one asphalt paraffinic fraction and a commercial polyethylene wax (“Polywax 655”) routinely used for calibration of high temperature simulated distillation (21), are presented in Figure 6. The included chromatograms visually show the presence of large paraffinic components in the asphalt fractions, reaching up to 113 °C / molecule. The Polywax 655 displays components within the 20-79 carbon atoms, which is the most abundant range observed in ASTM D7169 simulated distillation chromatograms (21); low abundance C79-C110 components normally observed in GC (21), precluded their detection by HT-SEC, indicating this technique to be less sensitive than HTGC for minor components of complex mixtures.
Figure 6. HT-SEC chromatograms for selected samples. *Numbers identified n-paraffins used for calibration purposes. Cn: show the carbon numbers determined at the described elution points. Saturates fractions from different samples were isolated via HTLC as described before (18). Fractions from a paraffinic oil (M12S) were isolated under varying temperatures from a column packed with Attapulgus clay and, further characterized via HT-SEC. Figure 7 presents the HT-SEC results achieved. The whole sample does not show saturates larger than C60, possibly by their inherent low concentration, as discussed before. Interesting is the fact that with a temperature increase for the HTLC isolation step (i.e., 45 and 75ºC) larger components sequentially appeared, reaching up to C157 at 75ºC. Existence of large waxy hydrocarbons reaching limits beyond those published by others (about C90-C120) (2, 5, 6, 12–15), was thus demonstrated with these HT-SEC 179 Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
examples, agreeing with a previous report that suggests the existence of large alkanes spanning a range from C70 to about C215, as determined via FDMS (4). Appearance of small components at the highest tested temperature of 90 ºC (Figure 7), initially was difficult to explain; however, further studies confirmed this finding and provided a plausible explanation for the phenomenon, as discussed in the ensuing paragraph.
Figure 7. HT-SEC chromatograms for M12S paraffinic oil and its separated fractions by HTLC carried out at 25ºC, 45ºC, 75ºC, and 90ºC. HT-SEC carried out with toluene eluent @ 60°C. Waxy components from the tank bottom sludge produced from the same oil described above (M12B deposit originating from the M12S oil) were further separated via HTLC using columns packed with different adsorbents. Figure 180 Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
8 presents the HT-SEC results achieved for fractions isolated from silica or asphaltenes packed columns. Three interesting features were shown with these examples: I) HTLC isolation under increasing temperatures sequentially provided larger components identified via HT-SEC, II) Small components appeared at the largest tested temperature of 90 ºC, III) Multimodal compound distributions as determined via HT-SEC, were observed in all studied cases. Elution of small components at the largest evaluated temperature (90ºC) is believed to have occurred because these were able to enter the porous space of packed adsorbents (Attapulgus clay, silica gel or asphaltenes), being then trapped by the largest components that solidified when the sample was deposited over the adsorbent, before starting the HTLC elution process. When the larger solid components finally eluted under high-temperature regimes, the smaller compounds were then able to exit the pores of the packings. The results discussed in the present section are evidence of the existence of paraffinic fractions spanning the C90-C215 range, the upper limit inferred from published results from other authors via FDMS (4). The ensuing section will address some ideas on the possible implications derived from the existence of such large paraffins in oils.
Figure 8. HT-SEC chromatograms for M12B waxy deposit and its separated fractions by HTLC carried out from silica gel or Orinoco Asphaltenes packed columns. HTLC carried out at 25ºC, 45ºC, 75ºC, and 90ºC. HT-SEC carried out with toluene eluent @ 60°C. 181 Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
Implications Derived from the Existence of Large MW Paraffins in Oils Understanding and assessing the amount and nature of large MW paraffinic compounds is of paramount importance as they impact the properties of some oil fractions. Three possible consequences are believed derive from the presence of large paraffins in petroleum:
I)
Positive effects: one example presented in a study case where the paraffinic waxes isolated from Boscan asphalt (see Figure 6), were spiked over asphalts from this as well as other crudes, showing improved performance for the doped materials, i.e., better elasticity and resistance to cracking under low set up temperatures (22). II) Negative effects: since large MW paraffinic compounds solidify when temperatures attain lower values than their crystallization ranges. Solid deposition in storage tanks and pipelines flow disruption have been discussed in this regard (5–7, 11–17, 19, 20). III) Feasible effects derived from the resulting properties of wax-asphaltenes composite materials. The field of wax-asphaltenes composite materials has received the attention of many authors in the past decades (10, 23–27). Thermal maturation differences of occluded-protected paraffins versus adsorbed materials more prone to maturation have been recently addressed in the open literature (28–31). Cycloparaffins like steranes and hopanes are among the biomarker molecules studied in the preceding studies (28–31). Surprising enhanced solubilities have been reported for wax-asphaltene composite solids (23, 24) implying that many aspects of these composite materials are worth studying in greater detail. Example of increased asphaltenes solubility provided by waxes is presented in Figure 9. Highly “insoluble asphaltenes” having 0.9 H/C atomic ratio and 0.65 carbon aromaticity were observed to improve solubility when admixed with waxy alkanes in the example presented, providing values beyond those calculated based on the solubilities for the pure blended components.
Locus of Large MW Alkanes within the Boduszynski Continuous Molecular Petroleum Model The preceding discussion from the article is evidence of the existence of large paraffinic compounds in petroleum oils. As predicted long time ago by Boduszynski (2, 3), these are the largest compounds within defined distillation cuts, because they are mostly affected by the weakest London forces, thus requiring large carbon backbones that made thus possible the existence of noticeable intermolecular interactions by a large number of atoms present. One fundamental property allowing their isolation either from solid deposits or from distillation residua is their low solubility parameter (they appear as the alkane 182 Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
soluble “saturates” fraction in HTLC). A C90-C215 spanned carbon range was discussed in the preceding section of this article, based on published reports (2, 4, 6, 14, 18, 20). Presence of unsaturation (H-deficiency) due to naphtheno and aromatic moieties was determined by different authors in waxy deposits (2, 5, 12, 19). Long alkane moieties (urea adductables) were also reported (14, 15). It is the belief of this author that the field of large petroleum paraffinic compounds and very large molecular mass alkanes has rarely been addressed in the past since the mandatory high temperatures and diluted ranges required for handling these compounds have been neglected. Figure 10 suggests a plausible locus for such compounds within the Boduszynski continuous molecular model of petroleum.
Figure 9. Dissolution of asphaltene / microcrystalline wax:75/25:wt/wt composite material as a function of Toluene solvent eluted volume. Experiments carried out at 25ºC.
Advanced petroleomics techniques now available should be applied to unravel the nature of such large paraffinic compounds (32). Mixtures of multiple paraffin classes (Z: 2, 0, -4, -6,…) (2, 5), plus the observed multimodal nature of waxy mixtures discussed in the preceding sections (11, 12, 18, 20), suggest as a possibility that their large molecular mass can be a consequence of reaction or even n-merization processes, i.e., reactive coupling of smaller paraffinic moieties to produce the large structures detectable and discussed in the preceding. Speculation on the feasible coupling of reactive groups like those present in long alkenones (34), or unsaturated biomolecules like squalene (35), interacting with insaturated cyclic biomarkers like sterenes and hopenes (35), represents an intriguing idea in this regard. 183 Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
Figure 10. Visualization of the heavy end (C20+) from the Petroleum Continuum Model as proposed by Boduszynski. Adapted with permission from reference (33). Copyright 2013 American Chemical Society.
Conclusions High molecular weight paraffinic compounds have been shown to exist in petroleum. Paraffinic compounds spanning the C90-C215 carbon atoms were discussed in these regards. Handling and analysis performed under dilute conditions and high set up temperatures were found to be mandatory for their successful characterization; absence of these conditions has precluded more frequent study of these oil components. Both positive and negative practical effects were discussed in relation to the studied compounds. A plausible locus within the Boduszynski continuous molecular model of petroleum is proposed. However, better understanding deserves further efforts with advanced petrolemic techniques to address the point and unravel their, so far, practically unknown nature.
Acknowledgments The author wishes to acknowledge the support and helpful discussions held with former colleagues working in the areas of asphaltenes, solid deposition and flow-assurance: Drs. A. Izquierdo, O. Leon, M. C. Garcia. J. Espidel, F. Cassani, O. Rivas and Mr. M. Orea. Funding provided by Intevep S.A.-Affiliate of Venezuela’s National Oil Company (PDVSA) during the 1990s, allowed to carry out the experimental part of the described research. Dr. P. Pereira-Almao from the University of Calgary is thanked for the opportunity to keep working in areas related to oil characterization, thus enabling the continuous adventure of getting to know the complex nature of petroleum oils in greater detail. Dr. Maria 184 Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
Josefina Perez-Zurita is acknowledged for helpful suggestions for improving the manuscript. Finally, Dr. M. M. Boduszynski is acknowledged for inspiring published research that gave origin to studies like the one covered in the present chapter.
References 1. 2. 3.
4. 5.
6.
7.
8.
9.
10. 11. 12.
13.
Graves, R. H.; Tuggle, R. Composition of Paraffin Deposits in Oil Field and Lines. Am. Chem. Soc. Prep. Div. Pet. Chem. 1968, 13, 46–52. Boduszynski, M. M. Characterization of “Heavy” Crude Components. Am. Chem. Soc. Prep. Div. Pet. Chem. 1985, 30, 365–382. Altgelt, K. H.; Boduszynski, M. M. Composition and Analysis of Heavy Petroleum Fractions; CRC Press, Taylor and Francis Group: Boca Raton, FL, 1993. Musser, B. J.; Kilkpatrick, P. Molecular Characterization of Wax Isolated from a Variety of Crude Oils. Energy Fuels 1998, 12, 715–725. Thomson, J. S.; Grigsby, R. D.; Doughty, D. A.; Woodward, P. W.; Giles, H. N. Characterization of High-Boiling Sludge Waxes from Underground Crude Oil Storage Reservoirs. Am. Chem. Soc. Prep. Div. Pet. Chem. 1989, 34, 275–281. Thomson, J. S.; Rynaski, A. F. Simulated Distillation of Wax Samples Using Supercriticial Fluid and High Temperature Chromatography. J. High Resol. Chromatogr. 1992, 15, 227–234. Radler de Aquino Neto, F.; Nobrega Cardoso, J.; dos Santos Pereira, A.; Zupo Fernandes, M. C.; Caetano, C. A.; Castro Machado, A. L. Chromatography to Paraffinic Deposits in Petroleum Production Pipelines. J. High Resol. Chromatogr. 1994, 17, 259–263. Wavrek, D. A.; Dahdah, N. F. Characterization of High Molecular Weight Compounds-Implications for Advance-recovery Technologies. Proceedings of the SPE International Symposium on Oilfield Chemistry, San Antonio, TX, Feb. 14−17, 1995 (SPE 28965, pp 207−212). Biao, W.; Lijian, D. Paraffin Characteristics of Waxy Crude Oils in China and the Methods of Paraffin Removal and Inhibition. Proceedings of the International Meeting on Petroleum Engineering, Beijing, PR China, Nov. 14−17, 1995 (SPE 29954, pp 33−48). Thanh, N. X.; Hsieh, M.; Philp, R. P. Waxes and Asphaltenes in crude oils. Org. Geochem. 1999, 30, 119–132. Carbognani, L.; Orea, M.; Fonseca, M. Complex Nature of Separated Phases from Crude Oils. Energy Fuels 1999, 13, 351–358. Agrawal, K. M.; Joshi, G. C. Composition of Hard Waxes Derived from Tank Bottoms in Relation to Their Properties. Fuel Sci. Technol. Int. 1994, 12, 1105–1113. Fazal, S. A.; Zarakpar, S. S.; Joshi, G. C. Studies on Sludge from Storage Tank of Waxy Crude Oil. Part I: Structure and Composition of Distillate Fractions. Fuel Sci. Technol. Int. 1995, 13, 881–893. 185
Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
14. Fazal, S. A.; Zarakpar, S. S.; Joshi, G. C. Studies on Sludge from Storage Tank of Waxy Crude Oil. Part II: Solvent Fractionation. Fuel Sci. Technol. Int. 1995, 13, 1239–1249. 15. Fazal, S. A.; Rai, R.; Joshi, G. C. Characterization of Sludge Waxes form Crude Oil Storage Tanks Handling Offshore Crude. Fuel Sci. Technol. Int. 1997, 15, 755–764. 16. Carbognani, L.; Espidel, J.; Izquierdo, A. In Asphaltenes, and Asphalts, 2; Yen, T. F., Chilingarian G. V., Eds.; Developments in Petroleum Series, 40B; Elsevier Science B.V: New York, 1993; pp 335−362. 17. Garcia, M. C. Paraffin Deposition in Oil Production. Proceedings of the SPE International Symposium on Oilfield Chemistry, Houston, TX, Feb. 13−16, 2001 (SPE 64992, pp 1-7). 18. Carbognani, L.; Orea, M. Studies on Large Crude Oil Alkanes. I: High Temperature Liquid Chromatography. Fuel Sci. Technol. Int. 1999, 17, 165–187. 19. Carbognani, L.; DeLima, L.; Orea, M.; Ehrmann, U. Studies on Large Crude Oil Alkanes. II: Isolation and Characterization of Aromatic Waxes and Waxy Asphaltenes. Fuel Sci. Technol. Int. 2000, 18, 607–634. 20. Carbognani, L. Fast monitoring of C20-C160 crude oil alkanes by size-exclusion-chromatography-evaporative light scattering detection performed with silica columns. J. Chromatogr. A 1997, 788, 63–73. 21. American Society for Testing and Materials (ASTM). ASTM D7169. Standard Test method for Boiling Point Distribution of Samples with Resid such as Crude Oil and Atmospheric Resids by High Temperature Gas Chromatography; ASTM: West Conshohocken, PA, 2011. 22. Carbognani, L.; Duarte, D.; Rosales, J.; Villalobos, J. Isolation and Characterization of Paraffinic Components from Venezuelan Asphalts. Effects of Paraffin Dopants on Rheological Properties of Some Asphalts. Pet. Sci. Technol. 1998, 16, 1085–1111. 23. Garcia, M. C.; Carbognani, L. Asphaltenes-Paraffins Structural Interactions. Effect on Crude Oil Stability. Energy Fuels 2001, 15, 1021–1027. 24. Carbognani, L.; Rogel, E. Solid Petroleum Asphaltenes Seem Surrounded by Alkyl Layers. Pet. Sci. Technol. 2003, 21, 537–556. 25. Venkatesan, R.; Ostlund, J-A.; Chawa, H.; Wattana, P.; Nyden, M.; Scott Fogler, H. The Effect of Asphaltenes on the Gelation of Waxy Oils. Energy Fuels 2003, 17, 1630–1640. 26. Kriz, P.; Andersen, S. Effects of Asphaltenes on Crude Oil Wax Crystallization. Energy Fuels 2005, 19, 948–953. 27. Mahmoud, R.; Gierycz, P.; Solimando, R.; Rogalski, M. Calorimetric Probing of n-Alkane-Petroleum Asphaltenes Interactions. Energy Fuel 2005, 19, 2474–2479. 28. Chacon-Patino, M. L.; Vesga-Martinez, S. J.; Blanco Tirado, C.; OrregoRuiz, J. A.; Gomez-Escudero, A.; Combariza, M. Y. Exploring Occluded Compounds and Their Interactions with Asphaltene Networks Using HighResolution Mass Spectrometry. Energy Fuel 2016, 30, 4550–4561.
186 Ovalles and Moir; The Boduszynski Continuum: Contributions to the Understanding of the Molecular Composition of Petroleum ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
29. Orea, M.; Ranaudo, M. A.; Lugo, P.; Lopez, M. Retention of Alkane Compounds on Asphaltenes. Insights About the Nature of AsphalteneAlkane Interactions. Energy Fuels 2016, 30, 8098–8113. 30. Snowdon, L. R.; Volkman, J. K.; Zhang, Z.; Tao, G.; Liu, P. The organic geochemistry of asphaltenes and occluded biomarkers. Org. Geochem. 2016, 91, 3–15. 31. Cheng, B.; Zhao, J.; Yang, C.; Tian, Y.; Liao, Z. Geochemical Evolution of Occluded Hydrocarbons inside Geoma-cromolecules: A Review. Energy Fuels 2017, 31, 8823–8832. 32. Rodgers, R. P.; Marshall, A. G. In Asphaltenes, Heavy Oils , and Petroleomics; Mullins, O. C., Sheu, E. Y., Hammami, A., Marshall, A. G., Eds.; Springer Science+Business Media, LLC: New York, 2007; pp 63−93. 33. Podgorski, D. C.; Corilo, Y. E.; Nyadong, L.; Lobodin, V. V.; Bythell, B. J.; Robbins, W. K.; McKenna, A. M.; Marshall, A. G.; Rodgers, R. P. Heavy Petroleum Composition. 5. Compositional and Structural Continuum of Petroleum Revealed. Energy Fuels 2013, 27, 1268–1276. 34. Volkman, J. K.; Eglington, G.; Cromer, E. D. S.; Sargent, J. R. In Advances in Organic Geochemistry; Douglas, A. G., Maxwell, J. R., Eds.; Proceedings of the 9th International Meeting on Organic Geochemistry, New Castle, UK, 1979; Pergamon Press: Oxford, U.K., 1980; pp 219−227. 35. Tissot, B. P.; Welte, D. H. Petroleum Formation and Occurrence; SpringerVerlag: New York, 1978.
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