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Cite This: Energy Fuels 2017, 31, 13198−13214

Characterization of the Solid Residue and the Liquid Extract Separated by Propane-Induced Crude Oil Fractionation Marcia Cristina Khalil de Oliveira,* Humberto Lopes, Carmen da Silva Teixeira, Luiz Silvino Chinelatto Jr, Gaspar Gonzalez,† and Rodrigo Altoé‡ PETROBRAS/CENPES, Cidade Universitária, Av. Horácio Macedo, 950, Rio de Janeiro 21941-915, Brazil ABSTRACT: Following a previously reported experimental procedure, a heavy petroleum sample was fractionated by mixing a predefined volume of oil with liquid propane above its saturation pressure at different propane/oil ratios. The separated fractions, considered two mutually saturated liquid phases in equilibrium at p and T separation conditions, were denominated solid residue and liquid extract and were characterized by chemical and spectroscopic methods including elemental compositional and SARA analyses, FTIR, and NMR. The results show that the amount yielded or produced increases for the solid residue and decreases for the liquid extract as the propane/oil ratio increases and that the four SARA components are present in both fractions, independently of the propane/oil ratio used in the fractionation process. The data also indicate that polar components are present in the liquid extract even at the highest dilutions that correspond to rather low solubility parameters. Complementary results show that after the flocculation process and the subsequent liberation of propane, the solid residue and the liquid extract were easily recombined with minimal losses by remixing both fractions. Physical and chemical analysis indicated that the recombined and the original oil presented similar characteristics in terms of API gravity, SARA, elemental composition, FTIR, and NMR, but substantial differences in their rheological behavior. The similarity between original and recombined oil is also evidenced by 1H DOSY NMR that shows that sets of aggregates are present in the spectra for both oil samples.

1. INTRODUCTION In 1837, Boussingault denominated asphaltenes a fraction separated from the distillation residue of some bitumen samples characterized for being soluble in turpentine and insoluble in alcohol1 and for containing, besides hydrocarbons, appreciable amounts of oxygen. Nearly 80 years later, Nellensteyn2 suggested that because asphaltenes constitute the essential part of the asphaltic residue, the problem of the chemical characterization of this residue would resolve itself into a study of these asphaltenes. Since then, significant efforts have been invested in asphaltenes characterization;3−5 nevertheless, important knowledge has been achieved only in recent years. Until very recently, asphaltenes were identified as a crude oil fraction composed of polar high molecular weight molecules6,7 capable of self-associating above a critical concentration following a similar pattern described for surfactants in aqueous solutions.8,9 Resins, although considered essential for micelles formation and crude oil stability, were regarded as a different fraction.10,11 Yen et al. in an extensive experimental work initiated around 1960 concluded that the asphaltenes fraction consisted of amphiphilic molecules of limited molecular mass susceptible to self-associate to form aggregates containing around 5−6 molecules, which, in turn, would be capable of associating to form clusters, crystallites, or larger particles.12 More recent studies developed mainly by Mullins and coworkers13−16 using advanced experimental techniques corroborated Yen’s conclusions. Although it might be considered that the structure and properties of the asphaltenes have been clarified to some extent,17 these advances have not resulted in models to describe the asphaltenes phase behavior in production operations nor in advancements to elucidate the role of asphaltenes in heavy oil high viscosity. Along this period, © 2017 American Chemical Society

the focus has been primarily oriented to separate, purify, and characterize the asphaltenes fraction to infer some information on the structure and phase behavior of the original crude oil.18,19 New concepts for the characterization of crude oil and its fractions that involve reviewing previous paradigms have been introduced in recent years. The theory of compositional continuity that postulates that petroleum composition is continuous with respect to molecular weight, chemical structure, polarity, and the presence of heteroatoms, which was introduced between the late 1980s and early 1990s,20 has recently been confirmed in detailed experimental studies conducted at Florida State University.21 Furthermore, it is also now accepted that asphaltenes molecular weight does not exceed 750−1000 Da,22 although McKenna et al., based on atmospheric pressure photo ionization Fourier transform ion cyclotron resonance mass spectrometry, fix the limit at 2000 D. Yarranton et al.23 have confirmed that asphaltenes effectively associate to form different types of aggregates, depending on their functional groups, concentration, and temperature, and Gonzalez measured the electrokinetic and aggregation of asphaltenes and resins.24 Complementary results however indicate that the concept of critical aggregation concentration does not apply to these complex, multicomponent systems in nonaqueous solvents.25 The role of resins as dispersants for the asphaltenes26 and the discontinuity between these two fractions have also been revised.27 This new set of evidence provides an important contribution to redefine crude oil and its fractions Received: July 6, 2017 Revised: November 16, 2017 Published: November 16, 2017 13198

DOI: 10.1021/acs.energyfuels.7b01949 Energy Fuels 2017, 31, 13198−13214

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Energy & Fuels

processes. Qiao et al.39 suggested extending the SARA analyses by including an asphaltenes fractionation steps based on the extraction of the interfacial active components adsorbed at the interfaces. The authors review results that confirm that the more surface active asphaltenes components effectively accumulate at the interfaces, and for the case of the oil− water interface suggest some hypothetical structures for the subfractions responsible for the formation and stabilization of water-in-oil emulsions. The studies have commonly been carried out at ambient p and T conditions, although in recent years attention has been focused on the investigation of the effect of pressure and temperatures to assess the role of carbon dioxide in crude oil stability.40 Our group at PETROBRAS Research Center recently initiated an experimental work oriented toward the characterization of crude oil using a different approach. Experimental facilities for petroleum fractionation and recombination using condensed gases under controlled conditions were developed, and procedures for the characterization of crude and crude oil fractions at high p and T were established. Our fractionation unit permits the injection of predefined volumes of oil and liquefied gas at high pressures and temperatures to get crude oil/gas homogeneous mixtures. Both pressure and temperature and the gas/oil ratio determine the solubility parameter prevailing in the mixing cell during the fractionation process. In a first report,41 the solution behavior of the solid and liquid phases separated by liquid propane in the fractionation process was examined and compared to the asphaltenes and other crude oil components. In a subsequent article,42 a commercially available high-pressure high-temperature compact flocculation device was used to identify the precipitation onset of model system consisting of solutions of asphaltenes, dissolved in toluene or in mixtures of hydrocarbons and dead oil samples titrated with propane or n-heptane, at 25 bar and 56 °C. The main objectives of this Article are to characterize by physical and chemical methods the solid and liquid fractions separated from a heavy petroleum sample at different crude oil/ propane ratios and high p and T conditions and compare these results with the data for the corresponding the crude oil and asphaltenes fraction. For this purpose, the compositional analyses of the oil sample and its fractions are obtained by SARA analyses and Fourier transformed infrared spectroscopy and elemental analyses. Complementary chemical structural parameter such as aromaticity, linear alkane average chain length, average number of carbons per alkyl side chain in alkyl substituted aromatic hydrocarbons, aggregates formation, and aggregates size obtained nuclear magnetic resonance and diffusion-ordered nuclear magnetic resonance are also used for this characterization. In this regard, the characterization results included in this Article complement the previous results on the phase behavior of the solid residue and liquid extract.

and asphaltenes in particular. It indicates that the discontinuities observed for the polar fractions, such as asphaltenes and resins, are caused by aggregation of its components and that the asphaltenes nanoclusters rather than monomers represent the insoluble components.28 The standard analytical procedures used at present29,30 characterize crude oil in terms of saturates, aromatics, resins, and asphaltenes (SARA analyses) and include both solvent precipitation and adsorption procedures. In a first step, asphaltenes are separated and quantified by precipitation by n-heptane, n-hexane, or n-pentane, and in a second step saturates, aromatics, and resins are obtained by adsorption on a porous adsorbent bed of clays or silica gel followed by elution with an appropriate solvent or solvent mixtures. In more recent studies,31,32 a method for crude oils fractionation into SARA components based on NIR spectroscopy was developed and tested. According to the authors, the method performs well for various types of crudes and condensates. This alternative seems interesting for being less intrusive than the SARA fractionation procedure involving precipitation, adsorption and subsequent elution, and solvent evaporation. Crude oil fractionation has been used to develop characterization and classification procedures for petroleum samples and, in a more limited extent, to investigate the composition and structure of crude oil fractions. As previously mentioned, the asphaltenes fraction has been extensively studied, and important aspects of its composition,19 structure,14 and aggregation behavior23 and molar mass have been described for this fraction. Other SARA fractions have received less attention, and the approach has been to further fractionate the oil separating subfractions with different specificities or functionalities. Spiecker et al.33 separated the asphaltenes by precipitation from toluene−n-heptane mixtures and identify the least soluble subfraction as the one containing most of the polar components that may cause emulsion stability and related flow assurance problems. Ö estlund et al.34 prepared asphaltenes subfraction by precipitation from methylene chloride−npentane mixtures and observed that the subfractions presented differences in aromaticity, solubility, and stability and that the subfractions with the larger average molar mass and higher aromaticity presented the stronger tendency to flocculate. Buenrostro-Gonzalez et al.35 characterized the asphaltenes and resins fractions of Mexican crudes presenting asphaltenes deposition problems. The resins fraction was split into two subfractions presenting different polarities by open column chromatography using silica gel and a sequence of solvent with increasing polarity. FTIR characterization shows that both subfractions presented differences in their group of band with some bands predominating in the less polar resins fraction. Rudzinski et al.36 separated the sulfur-containing compounds from the saturates and aromatic SARA fractions of a Maya crude oil sample by adsorption onto copper and palladium impregnated silica gel and subsequent elution and characterized these compounds by elemental analyses, FTIR, and 1H and 13C NMR. More recently,37,38 the molecular structure of a Turkish heavy crude oil and its SARA components have been characterized using elemental analysis, FTIR, and 1H NMR spectroscopy. The authors determined the average molar mass of the crude oil SARA components using gel permeation chromatography for asphaltenes and electron spray ionization− mass spectroscopy (ESI−MS) for saturates, aromatics, and resins and suggest hypothetical molecular structures for these fractions aiming to subsidize crude oil upgrading during refinery

2. EXPERIMENTAL SECTION 2.1. Materials. A heavy crude oil sample (12.7° API gravity) was supplied by PETROBRAS S/A. Reagent grade toluene, n-heptane (C7), and cyclohexane were purchased from Vetec Quı ́mica Fina Ltd., Rio de Janeiro, Brazil. All chemicals were used without further purification. Propane (C3) was obtained from White Martins, and it was maintained at room temperature in 45 kg cylinders. Chromium(III) acetylacetonate (∼98%), chloroform-D (D, 99.8%), and tetrachloroethylene (≥99%) were obtained from Merck, Cambridge Isotope Laboratories, and Sigma-Aldrich, respectively, and used without further purification. 13199


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Energy & Fuels 2.2. Methods. 2.2.1. Asphaltenes Precipitation Onset. The asphaltenes precipitation onset of the petroleum sample was measured by titration of 25 g of the oil with n-heptane at ambient conditions as described elsewhere.43 The precipitation onset was also measured at 40 bar and 68 °C using the FT5 flocculation titrimeter (PSL Systemtechnik GmbH, Clausthal-Zellerfeld, Germany), following the procedure described in a previous publication.42 The crude oil sample was too dark and exceeded the equipment detection level, and it was diluted to 50 wt % with cyclohexane prior to titration. The asphaltenes precipitation onset was identified as the ratio between the milliliters of titrant and the mass of oil at the point of minimum absorbance at ambient conditions or maximum translucence at high p and T conditions. 2.2.2. Crude Oil Fractionation at Different Oil to Propane Ratios. As was previously mentioned, a crude oil fractionation and recombination unit was designed and set up to characterize the crude oil phase separation. The device allows splitting crude oil samples into two phases identified as a solid or semisolid residue and a liquid extract. Through the addition of a condensed nonsolvent liquefied gas to the crude oil, a two-phase mixture that represents two liquid phases, in equilibrium at the p and T separating conditions, is obtained. The denser phase is rich in solute (i.e., the crude oil colloidal material), and the lighter one corresponding to a dilute solution contains most of the solvent.44 Subsequent to gas withdrawal, these two phases are identified as a solid residue (SR) and a liquid extract (LE), in this text. The operational range of the device is temperatures up to 110 °C and pressures up to 413 bar. After the unit installation and commissioning, around 40 preliminary tests were carried out to optimize its performance and define the most efficient experimental procedures to ensure p and T sharp control and to avoid propane vaporization during the tests. In addition, efficient methods to measure and control the volumes of condensate mixed to the oil samples were developed, and the mode of procedure to collect the solid residue was defined. Considering that this approach was meant to characterize the two mutually saturated phases produced by the fractionation process, no efforts to purify or subfractionate the fractions were bestowed. Once this preliminary stage was fulfilled, samples of heavy crude oil were fractionated at different oil/propane ratios of 1/1.9, 1/4, 1/6, and 1/10. The equipment also permits the recombination of the original oil by remixing the solid residue and the liquid extract with minimal losses under controlled p and T conditions. After the flocculation process and the subsequent liberation of propane, the high p and high T conditions were restored and the solid and liquid fractions mixed and submitted to gentle agitation for 24 h. Following this period, the system was restored to ambient condition. Physical and chemical analysis indicated that the recombined and the original oil presented similar characteristics in terms of SARA, elemental composition, FTIR, and NMR but substantial differences in their rheological behavior.45 2.2.3. Separation of Asphaltenes and Resins Fractions. The asphaltenes extraction was carried out using two alternative procedures. In the case of crude oil, the asphaltenes were separated by a laboratory procedure similar to the IP-143 standard method. For the solid residue, approximately 15 g of solids was mixed with 5 mL of toluene and left to dissolve under mild agitation overnight. One liter of n-heptane was then added to this solution and left to precipitate under moderate agitation for 24 h. The precipitated solids were separated by filtration under vacuum using 45 μm filter membranes and Soxhlet extracted with n-heptane up to complete removal of the n-heptanesoluble material present in the sample. The resins used in this study were separated by the following procedure: the n-heptane filtrate recovered from the asphaltenes precipitation step and the n-heptane used to extract the soluble components that coprecipitate with the asphaltenes were mixed at the end of the process. The solvent was then removed by evaporation in a vacuum rotary evaporator. This solid corresponds to C7-soluble resins and differs from the solids identified as resins by the SARA analyses. 2.2.4. Density Analysis. The relative densities (water, 20 °C) of crude oil and the liquid extracts were measured at 20 °C (±0.001 °C)

using a digital densimeter (Anton Paar DMA 5000) with an accuracy of 5 × 10−6 g/m3. The density of the solid residue, ρs, was obtained using eq 1.46

ρs =

ws 1 ρo

−

1 − ws ρl

(1)

in which ws is the solid mass fraction in the original oil and ρo and ρl are, respectively, the oil and liquid extract densities in g/cm3. 2.2.5. SARA Analyses. The separation of the saturates, aromatic, resins, and asphaltenes fractions (SARA Analyses) was carried out using a modified version of the thin layer chromatography-flame ionization detection (TLC-FID) method. In this procedure, asphaltenes are separated and quantified by the IP-143 standard procedure. Another portion of the same petroleum sample is separated by microdistillation into a 260 °C fraction. Supercritical fluid chromatography using carbon disulfide separates the 260 °C fraction is fractionated by TLC-FID into the heavier saturates (S2), aromatics (A2), and the polar compounds (P). S1+S2 correspond to the saturates, A1+A2 to the aromatics, and the polar compounds minus the asphaltenes to the resins. 2.2.6. Elemental Compositional Analysis. The crude oil and the crude oil fractions were analyzed for C, H, N, O, and S content. C, H, S, and N were quantified by combustion followed by chromatography using a ThemoFinningan model EA 1 CHNS analyzer. The oxygen content was determined by difference and therefore is subject to a higher error than the other elements. 2.2.7. Fourier Transformed Infrared Spectroscopy (FTIR). The FTIR spectra for the crude oil, asphaltenes, the liquid extracts, and the solid residues were recorded using an Excalibur 3100 Varian spectrometer in the 400−4000 cm−1 region, in the transmission mode with a resolution of 4 cm−1. Spectra were averaged from the accumulation of 20 scans. The solid samples were analyzed as standard KBr pellets prepared mixing the solid residue with a known amount of KBr in an agate mortar and pressing the mixture into a pellet in a stained steel die. In the case of the liquid extract, the analyses were carried out on films obtained by the addition of drops of the sample on clean KBr windows pellet followed by evaporation to dryness. The data gathering was performed using the Origin version 8.1 SR2 software, and the spectra were normalized with respect to the strongest peak at 2924 cm−1 corresponding to C−H stretching. 2.2.8. Nuclear Magnetic Resonance (NMR) Measurements. Solution-state 13C NMR spectra were recorded at 7.05 T on an Agilent INOVA NMR spectrometer, operating at 75.4 MHz, using a 10 mm broad band probe. Samples were dissolved at 20 wt % in 0.05 M chromium(III) acetylacetonate (as the relaxation agent) in chloroform-D (CDCl3). All experiments were performed at 50 °C, at which temperature the samples appeared to be well-dissolved but were nearly saturated. The following experimental conditions were used: 20.0 kHz spectral width, 9.4 μs (90°) rf pulses, 1.3 s acquisition time, 6 s pulse delay, and 5000 scans were accumulated. The nuclear Overhauser enhancement was suppressed by operating the spectrometer in the “inverse-gating” mode where the broad band protondecoupling was turned on only during acquisition periods. Solutionstate 1H NMR spectra were recorded at 9.40 T on an Agilent 400MR spectrometer, operating at 399.8 MHz, using a 5 mm direct detection probe. Samples were dissolved at 5 wt % in CDCl3:tetrachloroethylene (1:1). All experiments were carried out at 27 °C. The following experimental conditions were used: 6.4 kHz spectral width, 7.9 μs (45°) rf pulses, 2.05 s acquisition time, 1 s pulse delay, and 128 scans were accumulated. 2.2.9. 1H Diffusion-Ordered Spectroscopy NMR. For the DOSY experiments, samples were dissolved at 8 wt % in toluene-d8 (D, 99.5%). The experiments were recorded at 7.05 T on an Agilent INOVA NMR spectrometer operating at 299.8 MHz, equipped with a Performa II gradient pulse amplifier, using a 5 mm direct detection probe, generating a 60 G cm−1 field strength. The D oneshot sequence was employed to measure the self-diffusion of the aggregates, using 25 13200


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Figure 1. Asphaltenes precipitation for the cyclohexane/crude oil mixture by the addition of propane at 40 bar and 68 °C. The precipitation onset is identified as the dilution in mL C3/g of oil at the first translucence maximum.

Table 1. Solubility Parameter for the Various Solvents, the Crude Oil Sample, and at the Asphaltenes Precipitation Onset Values at Ambient Conditions and at 40 bar and 68 °C

a

compound

test conditions

C7

CyC6

solubility parameter (MPa1/2)

ambient 40 bar, 68 °C

15.20 13.90

16.75 16.65

C3

crude oil

oil/CyC6 mix

at the onset

12.40

20.30 20.95

18.55

16.40 15.60a

Adopted from data at 56 °C and 50 bar; ref 56.

linear steps from 0 to 60 G cm−1. The gradients were calibrated according to the manufacturer, using the HOD/D2O (99%) standard solution at 25 °C. In the D Oneshot sequence, the gradient pulse duration (δ) ranged between 1.5 and 2.5 ms and the diffusion delay (Δ) varied between 0.1 and 0.3 s. The spectra were acquired at 25 °C with a relaxation delay of 10 s and pulse duration of 15.8 μs (90°).

As reported in previous publications,48,49 the solubility parameter for crude oil and model systems at the asphaltenes precipitation onset may be calculated from the actual onset values obtained from the titration diagrams. Details of the procedure were given elsewhere,41 and a brief description is given here. According to Hirschberg,50 crude oil may be regarded as a two-component solution containing asphaltenes, considered a pseudocomponent, as the solute and the rest of the oil fractions, also considered a single pseudocomponent, as the solvent. Within this approach, crude oil−hydrocarbon mixtures would correspond to a three-component system, whose volume fraction average solubility parameter would be given by

3. RESULTS 3.1. Asphaltenes Precipitation Onset. The chemical and physical properties of the petroleum sample reported in a previous publication41 characterize the samples as heavy oil,47 and the precipitation onset, 3.3 mL C7/g of oil at ambient conditions, indicates that the sample is stable in relation to asphaltenes precipitation.48 Figure 1 shows that the precipitation onset of the crude oil diluted to 50 wt % with cyclohexane at 40 bar and 68 °C is 1.1 mL C3/g of oil obtained using the PSL FT5 Flocculation Tester. In this case, the trace of the translucence−dilution curve presents more than one maximum. Results reported earlier42 for other crude oil samples at different temperatures and pressure presented similar profiles, and, considering that asphaltenes is the only crude oil fraction prone to precipitate by dilution with low-molecular-weight alkanes, the asphaltenes precipitation onset was identified as the dilution corresponding to the first translucence maximum. The secondary peaks in Figure 1 were preliminarily attributed to the particle growing and agglomeration process that would induce changes in light intensity registered by the FT5 probe in which both the incident and the transmitted radiation are broad-band white light.

δ ̅ = δaϕa + δoϕo + δ hϕh

(2)

where the subindexes a, o, and h denote asphaltenes, oil, and hydrocarbon, respectively. At the precipitation onset, the asphaltenes volume fraction is, in most cases, negligible as compared to the volume fractions of the oil and the hydrocarbon, and eq 2 reduces to eq 3. δonset = δoϕo + δ hϕh ̅

(3)

The term δ̅onset in previous equation represents the solvent medium solubility parameter at the asphaltenes precipitation onset. According to various authors,51,52 this parameter is the same independently of the asphaltenes being dissolved in crude oil, crude oil blends, or in any other mixture containing noncomplexing solvents. On the basis of previous studies,42,53 a value of 16.4 MPa1/2 has been adopted for this parameter54,55 at ambient p and T conditions. Introducing this value in eq 3, and 13201


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Energy & Fuels using the n-heptane solubility parameter (Table 1) and the density data for the oils reported in Table 3, the calculated solubility parameter for the oil sample was 20.3 MPa1/2. The use of eq 3 at higher pressures and temperatures requires the knowledge of the hydrocarbons solubility parameter and an estimation of δ̅onset at these p and T conditions. The propane solubility parameter at 40 bar and 68 °C was evaluated following the usual simplified method starting from eq 456 where ΔvH is the molar enthalpy of vaporization, ν is the molar volume, R is the gas constant, and T is the absolute temperature. ⎛ Δ H − RT ⎞1/2 ⎟ δ≅⎜ v ⎝ ⎠ ν

The four petroleum−propane mixtures present solubility parameters lower than 15.6 MPa1/2, the value adopted for asphaltenes precipitation onset at 40 bar and 68 °C in the previous section. The solubility parameter for the first mixture, corresponding to an oil/C3 dilution ratio of 1/1.9, is 15.3 MPa 1/2, somewhat smaller but relatively close to the precipitation onset. The second mixture with dilution 1/4 presents a 1.5 δ units below the precipitation onset. For the subsequent mixtures including the fractionation using supercritical propane (43 bar and 97 °C), there are larger differences between the onset and the mixture solubility parameter. The standard methods for asphaltenes preparation by precipitation with C7 at room temperature and pressure use dilutions that never exceed a reduction of one solubility parameter unit in the oil/heptane mixture. Hence, from this point of view, the present fractionation process represents a more rigorous experimental condition. The yield corresponding to the solid residue increases while the liquid extract decreases with dilution, and concomitant to the extraction, the liquid extract becomes less viscous (Table 3) and, as exhibited in Figure 2, fades from dark brown to a yellowish color, suggesting a reduction of the polycyclic aromatic hydrocarbons, responsible for the crude oil characteristic dark color.61 The solid residue is a very viscous and sticky material, characteristic of concentrated slurries, pastes, and coagulated dispersions. A small additional pressure was necessary to extrude the solids through the collection line. As illustrated in Figure 3, in the process of recovering the solid residue, some material remains adhered in the mixing cell and in the interior of the lines and valves. These solids cannot be completely recovered from the equipment without the addition of solvents, and are considered to account for the appreciable losses observed in the fractionation process. Thus, although there may be other minor losses inherent to the experimental procedure, it was assumed that the test losses corresponded to these remnant solids, and the column for the percent of total solids in Table 2 represents the percent the solid residue increased by the percent of losses. 3.3. Crude Oil Fractionations Characterization. SARA Analyses. The composition in terms of SARA analysis was obtained for the crude oil, solid residues, and liquid extracts at various crude oil/propane dilution ratios. With this information and the respective yields, the percentages for saturates, aromatics, resins, and asphaltenes in the whole oil were calculated for the solid and the liquid fractions; these results together with the density and the viscosity at 50 °C are presented in Table 3. The results indicate that the four SARA components are present in both fractions, solid and liquid, independent of the petroleum to propane ratio used in the fractionation process. As expected, saturated and aromatics predominate in the liquid extract and resins and asphaltenes concentrate in the solid residue, notwithstanding being also present in the liquid extract in appreciable amounts. This distribution determines that the solids residue density is higher than the crude oil density but lower than 1.2 g/cm3, the value often reported for asphaltenes,62 making it evident that, even at low dilutions ratios, there is partition of lighter components into the heavier phase. The concentration of total polar components and asphaltenes, in particular, in the fractions increases in relation to their value in the oil, due most likely to the association tendency of these species. Table 3 also shows that the density and composition in terms of SARA analyses of

(4)

The National Institute of Standards and Technology (NIST) Chemistry WebBook57 data source reports a value of 19.2 kJ mol−1 for the propane enthalpy of vaporization, at the 329−369 K (56−96 °C) temperature interval. This value and the molar volume calculated by the Peng−Robinson equation58,59 using the University of Cambridge computational program for solving cubic equations of state provide a value of 12.4 MPa1/2 for the propane solubility parameter. A similar procedure, with 32.7 kJ mol−1 for the enthalpy of vaporization,57 conduced to 16.65 MPa1/2 for the solubility parameter of cyclohexane (CyC6) at 40 bar and 68 °C. The value of δ̅onset probably changes with pressure and temperature, and it will probably be necessary to determine its value for each set of experimental conditions. Hartman et al.42 through the titration of asphaltenes solutions in toluene with propane at 56 °C and 50 bar obtained a value of 15.6 MPa1/2 for δ̅onset. Although the temperature is somewhat smaller and the pressure somewhat higher than those we have used in our experiments, we adopted this value because the effect of both variables will probably compensate for practical purposes.60 Using this value for δ̅onset and the precipitation onset reported in Figure 1, the solubility parameter for the 50/50 cyclohexane petroleum mixture was obtained (18.55 MPa1/2), and, from this, a value of 20.95 MPa1/2 for the solubility parameter of petroleum sample, at 40 bar and 68 °C. From these data, the crude oil asphaltenes precipitation onset was estimated to be 1.67 mL C3/g of oil. The results are summarized in Table 1. 3.2. Crude Oil Fractionation at Different Oil/Propane Ratios. The crude oil sample was fractionated at different oil/ propane ratios. The solubility parameter for the mixtures, calculated with eq 3, the fractionation yields for both solid residue and the liquid extract, and the estimated losses for each test are shown in Table 2. Table 2. Solubility Parameter, Yields for the Solid Residue and the Liquid Extract, and the Losses, for Four Fractionation Tests at Different Crude Oil/Propane Ratios and at Supercritical Conditions yield (wt %) composition oil/C3 ratio in vol

dm (MPa1/2)

SR

LE

losses

total solids (wt %)

1/1.9 1/4 1/6 1/10 1/10 (supercritical)

15.3 14.1 13.6 12.8 7.6

28.6 33.1 33.8 34.4 44.6

67.6 58.6 59.7 59.1 50.8

3.8 8.3 6.5 6.5 4.6

32.4 41.4 40.3 40.9 49.2 13202


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Table 3. Density, Viscosity, and SARA Components (as wt % of the Original Petroleum Sample) for the Whole Petroleum and Its Solid Residues and Liquid Extracts Obtained at Various Oil/Propane Dilution solid residue dilution ratio density °API viscosity at 50 °C (cP) saturates aromatics resins asphaltenes total resins + asphaltenes

1/1.9 1.0659

1.3 8.1 12.0 11.3 32.7 23.3

1/4 1.0419

1.0 12.0 19.0 9.5 41.5 28.5

1/6 1.0573

liquid extract 1/10 1.0628

1/1.9 0.9456 17.49 1500

0.9 14.3 11.0 14.7 40.9 25.7

23.6 26.0 17.7 0.3 67.6 18.0

0.5 10.1 18.1 11.7 40.4 29.8

1/4 0.9397 18.40 210.0 23.0 22.2 13.1 0.3 58.6 13.4

1/6 0.9362 18.98 70.0 23.4 21.7 14.3 0.3 59.7 14.6

crude oil

recomb. oil

1/10 0.9322 19.80 60.0

0.9815 12.70 1700

from 1/10 0.9789 12.51 900

23.5 27.1 8.0 0.5 59.1 8.5

32.6 33.1 30.9 3.3 99.9 34.2

31.4 33.5 31.4 3.8 100 35.2

Figure 2. Aspect of the liquid extract separated by fractionation at different crude oil/propane ratios.

Figure 3. Aspect of the material derived from the solid residue adhered to the unit lines (a) and (b) and at the interior of the mixing cell. (c) Mixing cell.

Table 4. Elemental Analyses for the Solid Residue and Liquid Extract Separated at the Dilutions of 1/1.9 and 1/10, the Whole Oil, and the Resins and Asphaltenes Components concentration (wt %) fraction

solid residue

liquid extract

dilution at fractionation:

1/1.9

1/10

1/1.9

1/10

element N S C H H/C (molar)

1.1 2.8 84.9 10.0 1.41

1.1 0.4 82.9 10.2 1.48

0.3 2.2 85.9 11.8 1.65

0.3 0.3 86.4 12.1 1.68

13203

resins

asphaltenes

crude oil

0.8 1.0 88.1 11.5 1.57

2.1 1.2 83.3 8.2 1.18

0.6 0.3 85.9 12.6 1.75


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Figure 4. FTIR spectra for the solid residue (blue line), the liquid extract (red line), and the original heavy crude oil sample (black line) at 4000− 500 cm−1 (A) and 2000−500 cm−1 (B).

Asphaltenes present comparatively high levels of N and S and the lowest H/C atomic ratio. This is characteristic of this fraction and results from the presence of condensed aromatic hydrocarbons that are selectively separated by the extraction procedure. The methods, IP-143 or ASTM-2007, for instance, involve precipitation with an excess of n-heptane or n-pentane followed by successive Soxhlet extractions with the precipitating hydrocarbon for washing and purification purposes and subsequent recovery of the asphaltenes by redissolution in toluene and evaporation to dryness. Fourier Transform Infrared Spectroscopy. Infrared spectroscopy has been extensively used to characterize the chemical structure and functionalities of asphaltenes molecules. The most important bands and peaks have been identified and assigned to different hydrocarbon structures or functional groups.63−65 The use of the FTIR spectra was limited to identify in the solid residue or the liquid extract, together with the elemental analysis, the presence of polar and functional

the recombined and the original oil are very similar. Conversely, the dynamic viscosity is significantly different. Elemental Compositional Analyses. Table 4 presents the elemental analysis and the H/C atomic ratio for the liquid extract and solid residue at the dilutions of 1/1.9 and 1/10 and for the crude oil and its asphaltenes and resins SARA components. In the fractions separated by the process described in this work, the heteroatoms accumulate in the solid residue, but they are still present in the liquid extract even at a petroleum/propane dilution of 1/10 that corresponds to three solubility parameter units below the asphaltenes precipitation onset. This is evidence that the fractionation process does not concentrate the condensed polyaromatic species solely in the solid residue, but that there is a partition of these species in the two phases. The H/C molar ratio that represents an estimation of the fraction aromaticity is lower for the solid residue than for the whole oil and the liquid extract. 13204


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Figure 5. Identification of the bands corresponding to functional groups in the crude oil sample and its fractions. (A) Crude oil, red line; asphaltenes, black line. (B) Solid residue, blue line; liquid extract, red line.

corresponding to one hydrogen on ring (24) predominates in the extract. The peaks at 1378 (15) and 1460 cm−1 (13) correspond to symmetric and asymmetric deformation vibration of aliphatic −CH3 groups, and the bands at 1603 cm−1 (12) corresponding to CC stretching are present in the three spectra but predominate in the residue. The spectra also show intense absorption bands corresponding to aliphatic C−H axial stretching, between 2923 and 2852 cm−1 with two absorption bands at 2865 and 2927 cm−1, a band around 2855 cm−1 ascribed to methylene linking or methyl-substituted aromatic rings,67 and a shoulder at 2957 cm−1, as shown in the inset of Figure 4A. Focusing on the functional groups and heteroatoms, Figure 5 shows the FTIR spectra for the crude oil and asphaltenes samples. Various bands ascribed to N, O, and S containing structures have been identified in the 1000−1750 cm−1 region for crude oil and asphaltenes, and some of these have been detected in the solid residue and liquid extract. As shown in Figure 5A, these bands predominate and are more evident in

groups using the assignments described in the literature. This information and the SARA analyses would provide a qualitative compositional description of these fractions. The FTIR spectra for the solid residue (SR), the liquid extract (LE), and the corresponding whole crude oil (PP) are shown in Figure 4. The three spectra in Figure 4A show no noticeable differences and follow the pattern described for other samples of crude oil or fractions such as asphaltenes and resins in which bands corresponding to the hydrocarbon groups predominate.48 However, as shown in Figure 4B and its inset, there are some subtle differences in the weak absorption bands in the region between 900 and 700 cm−1 characteristic of out-of-plane bending vibration of C−H bonds on aromatic rings, detailed by Islas-Flores et al.66 The band around 750 cm−1 (27 and 28) ascribed to four H’s adjacent on the ring predominates in the solid residue and is relatively weak in the whole oil, whereas in the extract the band around 807 cm−1 (25) ascribed to two H bending modes on the ring is more prominent. The band 13205


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Energy & Fuels the asphaltenes fraction. Only the band at 1707 cm−1 ascribed to the O-containing group in the form of carboxylic acids and amides68 predominates in the oil. The band at 1257 cm−1 shows the presence of N as aril-derivatives,69 and the bands at 1215, 1090, and 1030 cm−1 are ascribed, respectively, to SO groups, aryl-S, and C2SO, evidence of S-containing functional groups.70 Figure 5B shows that the band at 1707 cm−1 is present in the solid residue and predominates in the liquid extract. The band between 1590 and 1612 cm−1 is ascribed to aromatic carboxylic acids and H-bonded ketones and quinones71 but, as mentioned previously, containing also some contribution from the band at 1603 cm−1 characteristic of the stretching vibration of the carbon−carbon bonds in aromatic systems, is also present in the solid residue and the liquid extract. The small band for arylN at 1257−1261 cm−1 is observed in the liquid extract but is absent in the solid residue. The bands in the 1215−1030 cm−1 region reveal the presence of S-containing groups in both fractions. Some poorly resolved bands that form a small bumping area in the 3100−3600 cm−1 region are also observed in Figure 4A for the whole oil, and its fractions. This band has been ascribed to the presence of aromatic CH groups merged together with N- and O-containing groups. Bands at 3460 and 3480 cm−1 ascribed to pyrrole72 and hydrogen-bonded pyrrolic groups73 and a broad band centered at 3469 cm−1 corresponding to carbazole-type compounds74 have been identified. These peaks also were not discriminated in this study. Some qualitative or semiquantitative information may be obtained from the FTIR spectra. Equation 5 shows the ratio between the intensities of the peaks at 1603 and at 1460 cm−1, which corresponds to the ratio between the CC aromatic groups and the aliphatic C−H groups and provides some qualitative indication of the aromaticity of the crude oil or its fractions. The intensities at 1603 and 1460 cm−1 in eq 5 may be easily identified as the highs of peaks 12 and 13, respectively, in Figures 4B and 5A. R1 =

I(1603 cm−1) I(1460 cm−1)

Figure 6A displays the original spectra for the crude oil and its solid residue and liquid extract, obtained at an oil/propane

(5)

An additional relationship may be obtained from the quotient between the intensity bands at 2927 and 2957 cm−1 corresponding to the symmetric and asymmetric stretching frequencies of the methylene and methyl groups. In eq 6, R represents the ratio of CH2 and CH3, n and m, respectively, and may be calculated using the intensities, I, at the corresponding wavelengths and the constant k = 1.243, which was obtained as the linear correlation for the (nCH2/mCH3) versus I2927/I2957 plot for various alkanes and alkyl aromatic hydrocarbons used as model compounds for this purpose.

(6)

Figure 6. FTIR spectra region 2985−2825 cm−1 for (A) whole (black line) and the corresponding solid residue (1/4) (blue) and liquid extract (red), and representative band deconvolution components for the solid residue (B) and asphaltenes (C) in the range of 2750−3050 cm−1.

The use of eq 6 requires one to deconvolute the overlapping bands in the 2600−3100 cm−1 region into discrete peaks.75 Deconvolution was carried out with the commercial software Origin 8.1 SR2 and involved Lorentzian curve fitting.76 In addition to the intensity bands reported in eq 6, the peaks with wavenumbers at 2890 and 2870 cm−1 corresponding to the symmetric stretching of CH2 and CH3 and the band at 2855 corresponding to an aromatic methyl group were used as guides to improve the resolution of the deconvolution procedure.

dilution of 1/1.9 for the 2985−2825 cm−1 frequency range, and Figure 6B and C shows representative deconvoluted bands for the solid residue and the asphaltenes fraction at the selected wavenumbers and their sum. The deconvoluted spectra shown in Figures 5 and 6 still consist of highly overlapped modes including overtones and combination bands, and their use is limited to a qualitative or semiquantitative analysis.

R=

n(CH 2) I(2927 cm−1) = k m(CH3) I(2957 cm−1)

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higher than whole oil value. The asphaltenes present a much higher aromaticity than the solid residue, and this result may again be ascribed to the exhaustive washings with heptane reflux procedure that concentrate polyaromatic hydrocarbons in the asphaltenes fraction. The parameter R represents the average number of CH2 groups per CH3 in the aliphatic chains; hence it corresponds to an estimation of the length of the methyl terminated aliphatic chains and, to some extent, of the degree of ramification.77 The R and Rm values for the solid residue are higher than those for the whole crude oil and the liquid extract, indicating that, on the average, larger molecules tend to selectively partition into the solid phase. Asphaltenes again present a rather high value for these parameters that, as in previous sections, may be ascribed to the preparation procedure. Characterization by Nuclear Magnetic Resonance (NMR). NMR techniques have been extensively used to determine a series of structural parameters to characterize crude oil and crude oil fractions. They were used in the present study to complement the data gathered in the previous section and, in particular, to characterize the reconstituted oil. The 1H NMR spectra for crude oil and its solid residue and liquid extract are shown in Figure 7. These spectra are normally split into two broad regions or integration domains. The shifts up to 4.0 ppm correspond to the distribution of aliphatic protons and the range of 6.0−9.0 ppm to the aromatic protons. The aliphatic region is further subdivided into three different spectral regions: Hα (from 4.0 to 2.0 ppm) corresponding to protons contained in a saturated carbon in α-position with respect to an aromatic ring, including methyl groups and hydrogens on alpha carbons of other alkyl groups; Hβ (from 2.0 to 1.0 ppm) including protons belonging to CH3, CH2, CH groups in β-position in relation to an aromatic ring; and Hγ ( 10 wt %), structures presenting diffusion coefficient of the order of 0.4 × 10−10 m2 s−1 have 13210


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Energy & Fuels measured D values is not an easy task. An approach to overcome this problem is to compare data from different DOSY experiments, according to their relative diffusion coefficients (Dsample/Dtoluene). Thus, it is reasonable to consider a slightly deviation of lowest D values for the liquid extract (all relative diffusion coefficients are 0.20 only for the liquid extract). This observation suggests the presence of molecules with lower size then observed for the three other samples (or fraction), and the absence of aggregated aromatic molecules for the liquid extract.” The peaks at 7−8 ppm with D between 8 and 11 × 10−10 m2 −1 s and the corresponding set of peaks labeled as g, in the aliphatic region, are also present in the liquid extract 1H DOSY spectrum. It is also evident that the signal for toluene in the aromatic region has been expanded, indicating the presence of nonaggregated aromatic molecules. As mentioned before, after the flocculation process and the subsequent propane flash, the conditions of high p and high T were restored and the solid and liquid fractions mixed and submitted to gentle agitation for 24 h to prepare the recombined oil. Figure 12 shows the 1H DOSY spectrum for the recombined oil. It is interesting to note that this spectrum differs considerably from the spectra for the solid residue and the liquid extract, but in general terms reproduces the structure of the spectrum of the original oil (Figure 9). In the aromatic region, except by the peaks ascribed to reverse micelles, all of the sets of signals were restored, even those that were practically nonexistent in the solid residue or the liquid extract. In the aliphatic region, the sets b, c, d, f, and g that were present in the liquid extract but nonexistent in the solid residue are detected in the recombined oil. The set e that was present in the solid residue and h present only in the original oil were restored. The set i present in recombined oil corresponds to silicon grease impurity. All of the signals in the recombined petroleum spectrum were less compact, expanded or wider in terms of chemical shift and diffusion coefficient when compared to the original oil. This difference that reflects higher polydispersity and reduced stability of the aggregates may probably be responsible for differences in the rheological behavior observed between the original and the recombined oil.85

increases, while for the liquid extract it decreases with the oil/ propane dilution ratio. Furthermore, the concentration of the polar components and asphaltenes, in particular, increases in the solid residue in relation to their value in the oil. This effect may occur, in part, by transfer of some resins to the asphaltenes fraction and may reflect a higher degree of association of these species in this more concentrated fraction or, alternatively, a preferential partition of the dispersing agents toward the liquid extract. It interesting to note that the four SARA components are present in both fractions, solid and liquid, independently of the petroleum to propane ratio used in the fractionation process. Saturated and aromatics predominate in the liquid extract, and resins and asphaltenes concentrate in the solid residue, notwithstanding being present in detectable amounts in the liquid extract. Elemental analyses can detect N and S in the solid residue, but these elements are also present in the liquid extract even at a petroleum/propane dilution of 1/10 that corresponds to three solubility parameter units below the asphaltenes precipitation onset. The FTIR spectra corroborate these results. Indeed, many of the peaks ascribed to N-, S-, and O-containing structures in crude oil and asphaltenes have been identified in both solid residue and liquid extract. It may be inferred from Figures 4 and 5 that the FTIR spectra for the crude oil, the solid residue, the liquid extract, as well as for the asphaltenes and resins contain basically the same bands, but in different intensity. Thus, to examine more accurately the spectra for these fractions, intensity ratios as those defined by eqs 5 and 6 must preferentially be considered.67 The parameter R1 in Table 5 indicates that the aromatic components tend to partition into the solid residue and that this effect increases as the proportion of propane used for the fractionation is also increased. However, aromatic components are still present in the liquid extract. In terms of aromaticity, the sequence followed by parameter R1 is asphaltenes > solid residue > resins > oil ≈ liquid extract. A similar sequence is observed for the H/C atomic ratio that also represents an estimation of the fractions aromaticity. Table 5 also shows that the values of R and Rm, which reflect the relative abundance of CH2 and CH3 aliphatic groups, follow a sequence similar to that previously shown for R1 except that their value for the liquid extract is lower than that for the whole oil. This sequence indicates that long-chain methyl terminated aliphatic hydrocarbons are not present in significant concentration in the liquid extract. In general terms, it may be inferred from the results discussed so far that the fractionation process does not concentrate, even at high dilution ratios, neither the aromatic components nor the species containing heteroatoms or functional groups solely in the solid residue. These species also partition into the liquid extract. Although the experiments were not planned to test this hypothesis, the results indicate that both the increase of polar components concentration in the solid residue and the corresponding decrease in the liquid extract correlate with the reduction of solubility parameter at the fractionation process. In this context, it may be inferred that the propane-induced fractionation process follows, in an inverse order, the sequence described by Boduszynski for the separation by distillation of petroleum fractions presenting different boiling point and composition.87 Propane reduces the petroleum solubility parameter, and at the precipitation onset separation occurs by flocculation of the petroleum more polar components. As dilution proceeds, the solid residue yield

4. DISCUSSION Although propane is frequently used in refinery processes for commercial deasphaltening of bitumen or other asphaltic material, its use for crude oil fractionation for characterization purposes is rather uncommon in a laboratory scale. The approach presented in this study was to separate the oil into two mutually saturated liquid phases in equilibrium at the separation conditions using liquefied propane as the flocculating solvent. Pressure, temperature, and the propane/oil ratio determine the solubility parameter prevailing in the mixing cell for each fractionation process. Following the colloidal definition of flocculation,86 the denser phase is considered rich in solute (i.e., the crude oil colloidal material in this case) and the lighter one a dilute solution containing most of the solvent. After propane flash, these two phases may be collected separately for characterization or recombined by restoring the system to given p and T separation conditions, followed by agitation and homogenization to obtain a recombined crude oil. The attained results disclose some interesting features on crude oil fractionation and the fractions properties. As shown in Tables 2 and 3, the yield corresponding to the solid residue 13211


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Energy & Fuels increases by the flocculation of other less polar petroleum components, generating liquid extracts progressively depleted of polar fractions. Another aspect that deserves attention is that the values for the semiquantitative parameter H/C, R1, R, and Rm are much higher for the asphaltenes than for the solid residue. This characteristic has been ascribed to that the preparation procedures that involve successive Soxhlet extractions with the precipitating hydrocarbon used for washing and purification purposes end up concentrating polyaromatic hydrocarbons and polar components in the asphaltenes fraction. From a practical point of view, solids separation caused by pressure drop or reservoir fluids blending in field operations may be considered to be better represented by the solid residue than by the asphaltenes prepared and purified according to the standard methods. The NMR results confirm most of the data detailed in previous sections. In fact, the higher content of aromatic compounds in the solid residue derived from the H/C molar ratio and the FTIR R1 parameter is confirmed by the aromaticity factors fa(13C) and fa(1H). Regarding the aliphatic chain length, the NMR esc parameter corroborates that the solid residue contains the longest aliphatic chains as inferred from the FTIR R and Rm parameters. It is also interesting to note that the recombined and the original oil are very similar in terms of density and SARA analyses and that the NMR results presented in Tables 6 and 7, except for the percent of linear alkanes, are also very similar. These similarities are probably due to the fact that neither the fractionation nor the recombination processes modify the overall petroleum composition, and most of the parameters in those tables represent the fluids composition or are composition dependent. The 1H DOSY results reported in Figures 9−12 provide some interesting complementary information. Taking into account studies carried out with model systems,88 a rather complex structure is observed for the whole oil spectrum. In the aromatic region, sets of peaks elongated mainly in the ydirection indicating the predominance of different size aggregates predominate. In the aliphatic region, the structures are less disperse in terms of their particle size and more disperse in relation to their composition. Subsequent to fractionation, only large compact structures are recovered in the solid residue, while in the liquid extract some of the micro and macro-structures of the original oil are still evident. Soxhlet extraction of the solid residue would eliminate, to some extent, amphiphilic molecules acting as dispersing agents, decharacterizing the disperse phase by both enhancing its compactness and reducing its solubility. Another interesting aspect is that recombination of these fractions restores most of the structures observed in the original oil spectrum. The aggregates are expanded in terms of diffusion coefficient and chemical shift, but the spectra are remarkably similar. As reported in Table 3, the most important difference between the original and the recombined oil is the viscosity that drops from 1700 to ca. 900 mPa s. In fact, the rheological behavior of the petroleum samples over in a wide extensive temperature range was modified.85 Two complementary tests for the same crude oil under the same experimental conditions reproduced the slightly higher but still reduced viscosities values of 1020 and 1090 mPa s for the recombined samples. For a heavier oil sample, the viscosity was observed to be reduced from 5400 mPa s in the original oil to 3300 mPa s in the recombined sample. These results indicate that, although

the general features of the original sample were restored, the expanded aggregates represent loose structures with higher polydispersity and reduced stability. Thus, the fractionation/ recombination process has been considered an encouraging starting point to develop technologies and strategies for heavy oil viscosity reduction.

5. CONCLUSIONS The fractionation of a heavy oil sample into a solid residue and a liquid extract showed that fractionation yield and the fractions composition in terms of API density and SARA analyses show a good correlation with the solubility parameter prevailing in the solvent medium. Besides, the four SARA components are present in both fractions, independent of the petroleum to propane ratio used in the fractionation process. Elemental analyses and FTIR spectroscopy results corroborated these findings. In this context, the propane-induced fractionation process follows, in a reverse order, the compositional sequence for the crude oil fractions separated by distillation designed by Boduszynski to depict the continuum composition petroleum model. Asphaltenes present comparatively high levels of N and S and the lowest H/C atomic ratio. In addition, the semiquantitative parameter that characterizes polarity, aromaticity, and molar mass, (R1, R, Rm) present values that are much higher for the asphaltenes than for the solid residue. This difference is considered to be generated by the preparation procedure that involves successive Soxhlet extractions with the precipitating hydrocarbon for washing and purification purposes that certainly concentrate polyaromatic hydrocarbons and polar components in the asphaltenes fraction. The diffusion-ordered 1H NMR spectroscopy confirms the complex structure of the petroleum dispersions in which coexist aggregates with different particle size, degree of polydispersity, and stability. The liquid extract prepared by propane fractionation maintains, in part, the structure of the original oil, while the solid residue presents a relatively simpler and apparently more compact structure. Soxhlet extraction of the solid residue would decharacterize the disperse phase by enhancing its compactness and reducing its solubility. From a practical point of view, the solids separated by depressurization or reservoir fluids mixture in actual field operations is considered to be better represented by the solid residue than by the asphaltenes prepared and purified according to the currently available standard analytical procedures. The oil obtained by recombination of the solid residue and the liquid extract contains most of the structures observed in the original oil. The parameters that characterize both samples (recombined and original oil) and the 1H NMR DOSY spectra are remarkably similar, the most important difference being that the recombined oil viscosity is significantly lower than that of the original oil. This reduction has been ascribed to the polydispersity and reduced stability of the aggregates present in the recombined oil. The fractionation/recombination process is considered an encouraging starting point for the development of technologies and strategies for heavy oil upgrading in terms of viscosity reduction.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. 13212


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International Conference: Petroleum Phase Behavior and Fouling; June 13−17, 2012; St. Petersburg Beach, FL, P-36. (26) Marques, L. C. C.; Pereira, J. O.; Bueno, A. D.; Marques, V. S.; Lucas, E. F.; Mansur, C. R. E.; Machado, A. L. C.; González, G. J. Braz. Chem. Soc. 2012, 23 (10), 1880−1888. (27) 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. Energy Fuels 2013, 27 (3), 1268−1276. (28) Boduszynski, M. M.; Mckay, J. F.; Lathan, D. R. Asphaltenes, where are you? Asphalt Paving Technol. 1980, 49, 123−143. (29) ASTM 02007-93: Standard Test Method for Characteristic Groups in Rubber Extender and Processing Oils by the Clay-Gel Adsorption Chromatographic Method. ASTM, 1993. (30) Fan, T.; Buckley, J. S. Energy Fuels 2002, 16, 1571−1575. (31) Aske, N.; Kallevik, H.; Sjoblon, J. Energy Fuels 2001, 15, 1304− 1312. (32) Hannisdal, A.; Hemmingse, P. V.; Sjoblon, J. Ind. Eng. Chem. Res. 2005, 44, 1349−1357. (33) Spiecker, P. M.; Gawrys, K. L.; Kilpatrick, P. K. J. Colloid Interface Sci. 2003, 267, 178−193. (34) Ö stlund, J. N.; Wattana, P.; Nydén, M.; Fogler, H. S. J. Colloid Interface Sci. 2004, 271, 372−380. (35) Buenrostro-Gonzalez, E.; Espinosa-Pena, M.; Andersen, S. I.; Lira-Galeana, C. Pet. Sci. Technol. 2001, 19, 299−316. (36) Rudzinski, W. E.; Aminabhavi, T. M.; Sassman, S.; Watkins, L. M. Energy Fuels 2000, 14 (4), 839−844. (37) Akmaz, S.; Iscan, O.; Gurkayank, M. A.; Yasar, M. Pet. Sci. Technol. 2011, 29, 160−171. (38) Yasar, M.; Akmaz, S.; Gurkaynak, M. A. Pet. Sci. Technol. 2009, 27, 1044−1061. (39) Qiao.; et al. Energy Fuels 2017, 31, 3330−3337. (40) Deo, M.; Parra, M. Energy Fuels 2012, 26, 2672−2679. (41) Altoé, R.; de Oliveira, M. C. K.; Lopes, H. E.; Teixeira, C.; Cirilo, L. C. M.; Lucas, E. F.; Gonzalez, G. Colloids Surf., A 2014, 445, 59−66. (42) Hartman, D.; Lopes, H. E.; Teixeira, C. L. S.; de Oliveira, M. C. K.; Gonzalez, G.; Lucas, E. F.; Spinelli, L. S. Energy Fuels 2016, 30, 3693−3706. (43) Marques, L. C. C.; González, G.; Monteiro, J. B. A Chemical Approach to Prevent Asphaltenes Flocculation in Light Crude Oils: Stateof-the-art; SPE Annual Technical Conference and Exhibition: Houston, TX, 2004; SPE 91019. (44) Gunsberger de Jong, H. G. Crystallizations−Coacervation− Flocculation. In Colloid Science; Kruit, H. R., Ed.; Elsevier Pub. Co.: New York, 1949; Vol. II, Chapter 7, pp 232−258. (45) Oliveira, M. C. K.; Gonzalez, G. Waxy crude oil fractions separation by liquid propane. 18th Petroleum Phase Behavior and Fouling Conference, June 11−15, 2017; Le Havre (Normandie, France). (46) Yarranton, H. W.; Masliyah, J. H. AIChE J. 1996, 42 (12), 3533−3543. (47) Argillier, J. F.; Barre, L.; Brucy, F.; Douranaux, J. L.; Henaut, I.; Bouchard, R. SPE Conference, Porlamar, Venezuela; 2001, SPE 69711. (48) Gonzalez, G.; Sousa, M. A.; Lucas, E. F. Energy Fuels 2006, 20, 2544−2551. (49) Carbonezi, C. A.; Almeida, L. C.; Araujo, B.; Lucas, E. F.; González, G. Energy Fuels 2009, 23 (3), 1249−1252. (50) Hirschberg, A.; DeJong, L. N. J.; Schipper, B. A.; Meijers, J. G. SPEJ, Soc. Pet. Eng. J. 1984, 24, 283−293. (51) Anderson, S. I. Energy Fuels 1999, 13, 315−322. (52) Wiehe, I. A. The oil compatibility model. Symp. Stab. Comp. Fuel Oils Heavy Ends; ACS 217th Nat. Meet. Pet. Chem. Div.: Anaheim, CA, March 21−25, 1999. (53) Sousa, M. A.; Oliveira, G. E.; Lucas, E. F.; Gonzalez, G. Prog. Colloid Polym. Sci. 2004, 128, 61−70. (54) Wiehe, A.; Kennedy, R. J. Energy Fuels 2000, 14, 56−59. (55) Ramos, C. S.; Rolemberg, M. P.; Moura, L. G. M.; Zilio, E. L.; Santos, M. F. P.; Gonzalez, G. J. Pet. Sci. Eng. 2013, 102, 36−40. (56) Hildebrand, J. H.; Scott, R. L. The Solubility of Nonelectrolytes, 3rd ed.; Reinhold Publishing Corp.: New York, 1950; p 424.

Marcia Cristina Khalil de Oliveira: 0000-0001-8820-8567 Present Addresses †

Institute of Macromolecules, Federal University of Rio de Janeiro, Av. Horácio Macedo, 2030, Cidade Universitária, Rio de Janeiro 21941-598, Brazil. ‡ CDTN - Centro de Desenvolvimento da Tecnologia Nuclear, Belo Horizonte, Minas Gerais 31270-901, Brazil. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Sônia Maria Cabral de Menezes and Luiz Alexandre Sacorague (CENPES - Chemical department) for revising the analytical procedures, Elizabeth Lucas (IMA/UFRJ) for laboratory support, Luiz Carlos do Carmo Marques for reading the manuscript, and PETROBRAS for permission to publish this paper.

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