Peptizing Effect of the Native Heavy Resin Fraction ... - ACS Publications

Jan 30, 2018 - ... (dm) and the average height of the stack of aromatic sheets (Lc) as well as the decrease of the average diameter of the aromatic sh...
0 downloads 0 Views 2MB Size
Download PDF
Article Cite This: Energy Fuels 2018, 32, 3380−3390

pubs.acs.org/EF

Peptizing Effect of the Native Heavy Resin Fraction on Asphaltenes He Liu, Zhaoxian Liu, Aijun Guo,* Kun Chen, Shengnan Sun, and Zongxian Wang State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering, China University of Petroleum (East China), 66 Changjiang West Road, Qingdao Economic Development Zone, Qingdao, Shandong 266580, China S Supporting Information *

ABSTRACT: C7-asphaltenes and the heavy resin fraction (HRe, i.e., the fraction insoluble in n-pentane but soluble in nheptane) were separated from two typical heavy residues. The role of HRe in asphaltene aggregation was mainly explored. First, the effect of HRe on the size of asphaltene aggregates in heptol solvents was studied by dynamic light scattering. The average aggregate size of asphaltenes upon the increase of the resin concentration shows that HRe could inhibit asphaltene aggregation more efficiently than the light resin fraction (LRe, i.e., the polar fraction from C5-maltenes by adsorption chromatography). However, an obvious size increase of asphaltene aggregates is observed when HRe exceeds some concentration. This can be tentatively attributed to the prior adsorption and penetration of resins in the less polar asphaltenes, followed by the reaggregation of the remaining asphaltenes due to their more aromatic and polar nature. Then the thermodynamics of the asphaltene phase behavior in solutions with the addition of resins were discussed in terms of the molar Gibbs free energy (Δg) based on the Flory−Huggins polymer theory. HRe is more inclined to act as the dispersed phase and could effectively orient the Δg of asphaltene solutions. Moreover, adsorption isotherms of resins on asphaltene solids were obtained, and the adsorption equilibrium constant (KAR) was then calculated. HRe presents a much higher KAR with asphaltenes than LRe. These results indicate that the more aromatic and polar resin fraction, HRe, could serve as a highly efficient peptizing agent for asphaltene stabilization. Through X-ray diffraction analysis, it is found that the aromatic stacking of asphaltenes can be effectively disrupted by peptization of HRe, thus leading to the increase of the layer distance between aromatic sheets (dm) and the average height of the stack of aromatic sheets (Lc) as well as the decrease of the average diameter of the aromatic sheet (La). by alkyl side chains,10−12 with the inclusion of abundant heteroatoms (N, O, and S) and metals (mainly Ni and V).13−15 The asphaltene molecules have been proposed to be either “continent” or “archipelago”, or both structure models coexist.16 These molecules could self-associate due to the intermolecular or intramolecular interactions (e.g., dipole− dipole interaction, charge-transfer interaction, hydrogen bonding).17 A variety of techniques, such as small-angle neutron scattering (SANS), 1 8 small-angle X-ray scattering (SAXS),16,19−21 dynamic light scattering (DLS),22−24 vapor pressure osmometry (VPO),25 nanofiltration,25 Rayleigh scattering,25 and X-ray diffraction (XRD),10−12 have validated the existence of asphaltene aggregates in solutions and solids at different length scales.26,27 In contrast to asphaltenes, resins have fewer aromatic rings with longer alkyl chains and less abundant polar moieties (mainly carbonyl, amine, pyrrole, and indole derivatives). Traditionally, it is believed that the aggregation behavior of asphaltenes could be altered by the presence of resins to some extent. However, the essential role of resins is controversial.9,28 Indeed, resins as well as the distinction between asphaltenes and resins are poorly identified.7,29 In addition to the polar fraction separated by adsorption through the formal SARA (saturate, aromatic, resin, and asphaltene) method,7 the fraction insoluble in n-pentane but soluble in n-heptane (i.e., C5−C7 fraction) separated by solubility has been taken as resins by some researchers.30 The viewpoints relevant to the role of

1. INTRODUCTION With the depletion of conventional oil resources, heavy oil has attracted great attention in the global energy supplies.1 Heavy oil is generally characterized by a substantial amount of asphaltenes. The stability of asphaltenes is susceptible to the fluctuation of the external surroundings and intrinsic molecular structures.2−4 Hence, asphaltenes are extremely prone to precipitate and pose detrimental hazards to exploitation, transportation, and upgrading processes of heavy oil,5,6 such as well-head blocking, pipeline clogging, and coke deposition. As heavy oil gradually becomes very inferior, these problems relevant to asphaltene precipitation are even worse. Therefore, preliminary studies on the stability issue of asphaltenes would be beneficial to prevent asphaltene precipitation more efficiently and have always been hot spots in both the upstream and downstream petroleum research fields. Despite the fact that asphaltenes have been focused on extensively for decades, the definition of asphaltenes still remains debatable.7 In terms of solubility class, asphaltenes are generally defined as the fraction of heavy oil that is insoluble in n-alkanes but soluble in benzene and toluene.8 The method to separate asphaltenes is still not standardized and remains subject to the preferences of the standards organizations of different countries.9 In general petroleum research, n-pentane and n-heptane are the widely advocated solvents in the laboratory to separate C5-asphaltenes and C7-asphaltenes, respectively. The asphaltene fraction composes the dispersed phase in the colloidal system of heavy oil, while the maltenes are the continuous phase. At the molecular level, asphaltenes mainly consist of condensed polyaromatic structures attached © 2018 American Chemical Society

Received: January 17, 2018 Published: January 30, 2018 3380

DOI: 10.1021/acs.energyfuels.8b00208 Energy Fuels 2018, 32, 3380−3390

Article

Energy & Fuels

Figure 1. Separation scheme of asphaltenes and resin subfractions from feed residues. The aromatics, light resins, heavy resins, and asphaltenes from VNVR are labeled as VNAr, VNLRe, VNHRe, and VNAs, respectively. The corresponding fractions from OSVR are labeled as OSAr, OSLRe, OSHRe, and OSAs, respectively.

resins in asphaltene aggregation could be colored by the definition and fractionation methodology, as asserted by Zhao et al.31,32 It is well-known that the resin sample collected from SARA fractionation, where the adsorption process is inevitable, usually suffers the loss of the most polar molecules due to irreversible adsorption on the adsorbent. This phenomenon could be much worse for the separation of resins from C7maltenes than that from C5-maltenes. In contrast, the loss can be avoided if the resin sample is prepared by solubility. Hence, this work utilizes the C7-asphaltenes as default asphaltenes, the C5−C7 fraction as the heavy resin fraction (HRe), and the polar fraction from C5-maltenes by SARA as the light resin fraction (LRe). A lot of studies on the influence of resins separated by adsorption on C7-asphaltene stability have been carried out.28,33−35 The UV−vis measurements showed that resins with amphiphilic nature and high surface activity could adsorb on asphaltene aggregates through charge transfer or hydrogenbonding attractive forces.33,36 In analogy with the interaction mechanism between model amphiphiles and asphaltenes, a steric stabilization layer could be formed due to the repulsion caused by aliphatic side chains.37,38 Consequently, the produced asphaltene lyophilic colloids can be readily dispersed by the continuous phase. However, León et al.39,40 observed adsorption isotherms of resins on asphaltenes different from those of model amphiphiles. To explain this phenomenon, they proposed that the adsorbed resin layer could further penetrate into the bulk asphaltenes, break the microporous structures, and help them to diffuse in the continuous phase. The native resins with lower adsorbed amount but higher penetration power could exhibit a comparable effectiveness as asphaltene stabilizers with model amphiphiles.40 The penetration ability was correlated with the solubility of internal polyaromatic rings through a molecular thermodynamic approach, as studied by Rogel.41 Using the SANS42,43 and DLS33 techniques, the decrease of the asphaltene aggregate size and aggregation rate with the addition of resins was evidenced. Therefore, resins could reduce the molecular weight and increase the solubility of asphaltenes, which has been reported by Gawrys et al.42 These findings indicate that resins are effective at both dissolving the larger flocs into noninteracting aggregates and solubilizing the individual asphaltene aggregates.44

On the other hand, there are some observations supporting the incapability of resins to stabilize asphaltenes or even contribute to asphaltene destabilization. By isothermal microcalorimetry, Marques et al.36 found that resins and asphaltenes interacted only by weak van der Waals forces. This interaction could not prevent the flocculation and precipitation of asphaltenes. Goual and Firoozabadi45 first reported the behavior that the mass of asphaltene precipitate increased with resins added. Pereira et al.8 ascribed these contradictions to the self-interaction of resin molecules and put forward the repulsion/adhesion alternative model. In this model, the adsorbed layer of resins with strong self-interaction could promote the attraction and collision of asphaltenes. Nevertheless, there is no consistency in whether this resin fraction could aggregate.46 In regard to the resins separated by solubility (i.e., HRe), their role in asphaltene stability has been reported sporadically. From the SAXS measurements,47 the C7-maltenes showed a great q dependence and a high intensity, indicating the presence of large aggregates. Nevertheless, the C5-maltenes presented a weak q-dependent signal characteristic of a solvent behavior. Thereby, Eyssautier et al.48 proposed that C5-asphaltenes were best represented as a dispersed phase. The aggregated structures present in C7-maltenes while absent in C5-maltenes have also been verified by freeze-fracture replication transmission electron microscopy.30 Accordingly, Li et al.17,30 pointed out that a part of the polar and heavier resins could constitute the dispersed phase and contribute a lot to the formation of colloidal asphaltene−resin clusters. Many researchers have increasingly inclined to pay great attention to the mesoscale aggregate structure of C5-asphaltenes. On the basis of the detailed molecular weight and diffusion data of C7asphaltenes and C5-asphaltenes, Yarranton et al.25 speculated that many of the additional components in HRe were still likely nonassociated. The asphaltenes might self-associate into a different size distribution upon the impact of these components. Zhao et al.31 have quantitatively evaluated the mass fraction of resins in C5-asphaltene-rich aggregates in nanofiltered oils at low temperatures. This further confirms that HRe could interact with asphaltenes and participate in the aggregation process. In spite of these ongoing studies addressing the importance of HRe on asphaltene aggregation, 3381

DOI: 10.1021/acs.energyfuels.8b00208 Energy Fuels 2018, 32, 3380−3390

Article

Energy & Fuels Table 1. Chemical Analysis Results of Fractions from VNVR and OSVRa content/wt % [H]/wt % [C]/wt % [N]/wt % [S]/wt % [O]b/wt % H/C atomic ratio fA* c f N* d f P* e (HAU/CA)* f RA* g R N* h

VNAr

VNLRe

VNHRe

VNAs

OSAr

OSLRe

OSHRe

OSAs

43.52 10.65 84.16 0.27 4.92 0.00 1.52 0.312 0.253 0.435 0.748 2.53 2.46

23.92 9.73 84.17 1.22 4.88 0.00 1.39 0.383 0.184 0.433 0.601 4.45 2.78

4.62 8.85 82.22 1.52 4.66 2.75 1.29 0.437 0.204 0.359 0.583 4.81 2.86

19.05 7.32 81.77 2.01 5.50 3.40 1.08 0.549 0.192 0.259 0.414 10.83 4.25

42.20 10.73 84.10 0.20 4.96 0.01 1.53 0.307 0.231 0.461 0.737 2.67 2.38

23.67 9.84 81.54 1.12 4.68 2.82 1.45 0.364 0.238 0.397 0.687 3.51 2.63

5.93 9.33 82.0 1.11 5.92 1.64 1.37 0.417 0.254 0.329 0.663 4.09 2.81

18.05 7.89 81.68 1.20 7.04 2.10 1.16 0.497 0.201 0.302 0.481 7.69 3.65

a

An asterisk indicates the parameter for each structural unit. bCalculated by the subtraction method. cAromaticity. dNaphthenic carbon ratio. Paraffinic carbon ratio. fCondensation degree of aromatic rings. gAromatic ring number. hNaphthenic ring number.

e

Nicolet Nexus IR spectrometer from Thermo Nicolet Co. LRe was coated as a film on a KBr wafer, while HRe and asphaltenes were finely ground with KBr powder and tableted. 2.3. Particle Size Analysis of Asphaltenes. The particle size analysis of asphaltenes was performed using DLS on a Malvern Zetasizer Nano zs at 25 °C. According to Rastegari et al.,51 an asphaltene concentration in the narrow range of 0.05−0.1 mg/mL favors an accurate particle size measurement. Therefore, a series of solutions of 0.08 mg/mL asphaltenes in n-heptane/toluene (so-called “heptol” mixture) with volume ratios of 60:40, 40:60, 20:80, and 0:100 were prepared. Subsequently, different amounts of resins were added to the asphaltene solution to ensure the resin concentration varied from 0.008 to 0.072 mg/mL. All the solutions were completely mixed in volumetric flasks and left for 5−8 h to ensure adequate dissolution. The particle size distributions in these solutions were then monitored by the DLS method. 2.4. Adsorption Isotherms of Resin Subfractions on Asphaltenes. Measurement of the adsorption isotherms was referenced from previous papers.39,40 Specifically, a series of solutions of resin subfractions in n-heptane at concentrations ranging from 0.02 to 1 mg/mL were prepared. A 10 mL aliquot was added to 10 mg of asphaltenes in a flask and the resulting mixture ultrasonically stirred for 12 h in a thermostatic bath at 25 °C. After reaching equilibrium, the slurry was centrifuged for 30 min at a speed of 8000 r/min. The absorbance of the supernatant at 400 nm was measured by UV−vis spectrometry on a Varian Cary 50 spectrophotometer to evaluate the equilibrium concentration of resins. The amount of adsorbed resins is calculated from the depleted amount in the mass balance. 2.5. XRD Analysis of Asphaltenes. Asphaltenes and HRe were ground to fine powders separately. Then a certain amount of black asphaltene powder and dark-brown resin powder was weighed accurately. The proportion of asphaltenes and HRe was the same as that in the feed residue shown in Table 1. Finally, the asphaltene and resin powders were mixed and ground until the color was uniform to ensure the homogeneity of the mixtures. XRD patterns of asphaltenes, HRe, n-pentane insolubles, and the mechanical mixture of asphaltenes and HRe were recorded on a Panalytical X’Pert Pro MPD diffractometer using Cu Kα radiation (λ = 1.5418 Å). The operation temperature was 25 °C, and the scanning angle 2θ was 0.017°. The XRD patterns were deconvoluted and analyzed as reported by previous researchers10−12 to obtain different crystallite parameters, including the layer distance between aromatic sheets (dm), the layer distance between aliphatic chains and naphthenic sheets (dγ), the average height of the stack of aromatic sheets (Lc), and the average diameter of the aromatic sheet (La).

the essential effect of HRe on asphaltene stability still remains obscure and needs to be further clarified. This could also benefit the understanding of the distinction between resins and asphaltenes to some degree. In the present work, asphaltenes and two resin subfractions (HRe and LRe) were separated from heavy residues. The role of HRe in the stability of asphaltenes was mainly explored. The effect of HRe on the average aggregate size of asphaltenes in heptol solvents was investigated using DLS. The thermodynamics of the asphaltene phase behavior in solutions with the addition of resins were then discussed in terms of the molar Gibbs free energy based on the Flory−Huggins polymer theory. Moreover, adsorption isotherms of resins on asphaltene solids were obtained, and the adsorption equilibrium constant was calculated. Finally, the change of the macrostructures of asphaltenes caused by the peptizing effect of HRe was monitored by XRD analysis.

2. EXPERIMENTAL SECTION 2.1. Sample Preparation. Vacuum residue with a boiling point higher than 500 °C from Venezuelan heavy oil (VNVR) and that from Canadian oil sand bitumen (OSVR) were used as the feedstocks. Asphaltenes and resins were obtained from these residues by solvent extraction followed by alumina chromatographic separation. The scheme is shown in Figure 1. In brief, the residue was initially mixed with 40 mL of n-pentane and 1 mL of toluene per gram of sample. The mixture was refluxed for 4 h, left for 24 h, and filtered through a 1−3 μm filter paper. The filter cake was washed with n-pentane to remove the soluble materials. The obtained n-pentane insolubles were then extracted with n-heptane and toluene sequentially to recover heavy resins and asphaltenes, respectively. The n-pentane solubles were further fractionated into saturates (Sa), aromatics (Ar), and light resins on an alumina chromatographic column with a water content of 5 wt % eluted by sequential solvents with increasing polarity. The asphaltene and resin samples were dried under vacuum at 60 °C for about 5 h and stored under nitrogen to prevent oxidation. 2.2. Characterization of Resin Subfractions and Asphaltenes. The elemental composition was determined using a Vario EL III elemental analyzer from Elementar Co. The 1H NMR spectrum was recorded on a Bruker av500 NMR spectrometer using deuterated chloroform as the solvent and tetramethylsilane as the internal standard. On the basis of the above analysis, the average molecular parameters of each structural unit for different fractions were calculated by the modified Brown−Ladner method.49,50 The detailed calculation process is described in the Supporting Information. The main properties of these fractions are shown in Table 1. Fourier transform infrared (FTIR) spectrometry analysis was conducted on a 3382

DOI: 10.1021/acs.energyfuels.8b00208 Energy Fuels 2018, 32, 3380−3390

Article

Energy & Fuels

3. RESULTS AND DISCUSSION 3.1. Structural Characterization of Resin Subfractions and Asphaltenes. Table 1 shows the elemental compositions and the average molecular parameters of each structural unit for different fractions from VNVR and OSVR. The H/C atomic ratio decreases with increasing solubility of the fractions, which correlates well with the increasing aromaticity ( fA*) and aromatic ring number (RA*).52 This indicates that the insoluble fraction is more abundant with aromatic structures than the soluble portion. Moreover, the fraction with lower solubility presents a much lower (HAU/CA)*, suggesting the inherent aromatic structures are more condensed. The strong π−π conjugation of these highly aromatic sheets could be greatly responsible for the aggregation behavior of the least soluble fraction (i.e., asphaltenes).17,25 Also, the value of f P* decreases when the fraction becomes heavier. It is generally believed that the paraffinic side chains attached to the aromatic moiety could hinder the asphaltene aggregation due to the steric repulsion.37 Since asphaltenes are relatively deficient in paraffinic structures, it can be inferred that the steric stabilization layer for asphaltene dispersion is not selfsufficient and could be supplied by resins to maintain the stability. Furthermore, each fraction of VNVR seems to be a little more aromatic and heavier than the corresponding fraction of OSVR. In addition, the heteroatom contents show that the heavier fraction tends to be more polar and functionalized. Figure 2 displays the FTIR spectra of different fractions from VNVR and OSVR. The peak at 3030 cm−1 is ascribed to the stretching vibration of phenyl C−H bonds, and peaks at 874, 800, and 756 cm−1 represent the substitution to the aromatic rings. The bands at 2800−2900 and 1370−1465 cm−1 can be assigned to the stretching and bending modes of aliphatic C−H bonds, respectively. This evidence of aromatic and aliphatic structures is noticeable in the spectra of all fractions. Compared with aromatics, resin subfractions and asphaltenes also show a broad band at 3100−3700 cm−1 assigned to an O−H or a N−H bond and a relatively weak band at 1000−1250 cm−1 attributed to a C−O or C−N bond. This results from the small amount of nitrogen and oxygen ( 0). This is consistent with the presence of the threshold volume ratio of n-heptane for the asphaltene aggregation observed by SAXS and DLS.56 As discussed in the previous section, for 0.08 mg/mL asphaltene solutions, aggregation of asphaltenes arose in heptol with a solubility parameter of 17.08 (J/mL)0.5. Meanwhile, the sharp growth of asphaltene aggregates occurred in heptol with a 3386

DOI: 10.1021/acs.energyfuels.8b00208 Energy Fuels 2018, 32, 3380−3390

Article

Energy & Fuels

Figure 8. Δga−r of mixed asphaltene−resin solutions with the volume fraction of resins at different partition ratios of resins into the dispersed phase and continuous phase.

asphaltenes and resins, a completely new system would be formed, as shown in Figure 5. In this system, part of the asphaltenes (mainly A1) and a small amount of resins constitute the dispersed phase, while part of the asphaltenes (mainly A2) with the protection of resins and solvents can be regarded as the continuous phase. It can be suspected that the molar Gibbs free energy of this new mixing solution would subsequently be changed by the addition of more resins. This needs to be further studied in the future. 3.4. Adsorption Equilibrium of Resins on Asphaltene Solids. To further investigate the interaction between asphaltenes and resins, the adsorption isotherms of resin subfractions on asphaltene solids were measured and are shown in Figure 9. The isotherms of HRe display a continuous rise in the amount of adsorbed resins on asphaltenes. According to León et al.,39 this can be well interpreted using the penetration theory of the solute in the microporous structure of asphaltenes. Both the amount of HRe adsorbed onto asphaltenes and the increasing rate appear to be much higher than those of LRe. This further proves that HRe shows a higher ability for adsorption and penetration in asphaltenes than LRe. A plateau seems to appear in the isotherms of LRe at low concentrations. This might indicate the formation of a multilayer of LRe on asphaltenes because of the low penetration ability.40,70 The multilayer of LRe would lead to the size increase of asphaltene aggregates shown in Figure 4. The equilibrium constants for adsorption of resin subfractions on asphaltenes (KAR) are then calculated on the basis of the Langmuir adsorption isotherms:71 [ReS] KAR [Re] = m[As] KAR [Re] + 1

(14)

[ReT] = [ReS] + [Re]

(15)

Figure 9. Adsorption isotherms for resin subfractions on asphaltenes from feed residues. (a) VNVR, (b) OSVR.

the adsorption isotherm can be expressed as the following equation: [As] 1 1 = + + Δδ [ReS] KAR [Re] 1

(16)

The variation of [As]/[ReS] is then plotted as a function of 1/[Re], as shown in Figure 10. The good linear correlation indicates that the adsorption of resins on asphaltenes could be analyzed by the Langmuir adsorption model. The calculated KAR results are listed in Table 2. They show that KAR for adsorption of OSHRe on OSAs is approximately 2 times that for adsorption of OSLRe. The KAR for adsorption of VNHRe on VNAs can be 4.6 times that for adsorption of VNLRe. The quantitative data confirm that HRe presents much stronger peptizing ability than LRe. Furthermore, KAR for VNHRe− VNAs seems to be higher than that for OSBHRe−OSBAs, suggesting that VNHRe is more efficient for maintaining asphaltene stability than OSHRe. 3.5. Change of the Macrostructures of Asphaltenes Caused by the Peptizing Effect of HRe by XRD Analysis. The change of the macrostructures of asphaltenes caused by the peptizing effect of HRe was probed by XRD analysis. The XRD

where [As] is the asphaltene concentration, [ReS] is the equilibrium concentration of resin subfractions adsorbed on asphaltenes, [Re] is the concentration of resin subfractions in the continuous phase, [ReT] is the total concentration of resin subfractions, and m is defined as the ideal concentration of resin subfractions for complete adsorption on asphaltenes. If m is assumed to be unity and the deviation factor Δδ is introduced, 3387

DOI: 10.1021/acs.energyfuels.8b00208 Energy Fuels 2018, 32, 3380−3390

Article

Energy & Fuels

characterized by the graphene band around 26° and the γ band around 19°, which can be assigned to the stacking of aromatic molecules and packing of saturated structures, respectively. The graphene band is used to estimate the layer distance between aromatic sheets (dm) and the average height of the stack of aromatic sheets (Lc), while the γ band is used to estimate the layer distance between aliphatic chains and naphthenic sheets (dγ).10−12 A relatively weak 10 band at about 43° can also be observed, which reveals the average diameter of the aromatic sheet (La).72 In contrast, HRe shows no graphene band, indicating the aromatic stacking of resin molecules is relatively weak and beyond the detection limit of XRD since X-ray experiments are more sensitive to the aromatic-rich regions.44 This is compatible with the suggestion of Lima et al.73 from conformation of resin dimers by a computational study. The previous comparison of SAXS measurements47 for C5-maltenes and C7-maltenes showed that HRe could possess the selfassociation ability. Hence, the self-association of HRe could possibly be attributed to the hydrogen-bonding or van der Waals forces due to the incorporation of heteroatoms in molecules. The XRD patterns are then deconvoluted in to calculate the crystallite parameters.72 The deconvoluted curves for the mixture of HRe and asphaltenes are displayed in Figure 11 as an example. The crystallite parameters of different asphaltenes are listed in Table 3. The data in Table 3 show that dm and dγ for the original asphaltenes from feed residues are around 3.500 and 4.380 Å, respectively. The two parameters present a very slight increase when HRe is mechanically mixed with asphaltenes. When asphaltenes are peptized with HRe (i.e., npentane insolubles), the layer distance between aromatic sheets as well as that between saturated sheets is further increased. This phenomenon could be further proved by transmission electron microscopy (TEM) in that C5-asphaltenes present a larger mean interlayer spacing than C7-asphaltenes in the work of Zhang et al.74 Meanwhile, the value of Lc for asphaltenes peptized with HRe increases obviously. For OSAs, it has increased from 41.9 to 46.7 Å. It seems that asphaltenes are swollen in the presence of HRe, which could be attributed to the adsorption and penetration of HRe into asphaltene macromolecules.40 Moreover, the average diameter of aromatic sheets (La) has correspondingly decreased. Hence, it can be concluded that the aromatic stacking of asphaltenes can be effectively disrupted by the peptizing effect of HRe.74

Figure 10. [As]/[ReS] as a function of 1/[Re] for adsorption of OSHRe on OSAs.

Table 2. Equilibrium Constants for Adsorption of Resin Subfractions on Asphaltenes sample

m

KAR/(mL/mg)

VNLRe−VNAs VNHRe−VNAs OSBLRe−OSBAs OSBHRe−OSBAs

1 1 1 1

0.457 2.091 0.534 1.138

± ± ± ±

0.043 0.135 0.066 0.096

Δδ 1.333 0.348 1.379 −1.744

± ± ± ±

1.344 0.395 1.581 0.761

patterns of asphaltenes, HRe, n-pentane insolubles, and the mechanical mixture of HRe and asphaltenes were obtained and are shown in Figure 11. The profiles of asphaltenes are mainly

■

CONCLUSIONS The role of HRe in asphaltene aggregation was explored in the present work. The aggregate size of asphaltenes upon the increase of the resin concentration measured by DLS shows that HRe could inhibit asphaltene aggregation more efficiently

Figure 11. XRD patterns of asphaltenes, HRe, n-pentane insolubles, and mixture of asphaltenes and HRe from VNVR.

Table 3. Crystallite Parameters for Asphaltenes, HRe, n-Pentane Insolubles, and Mixture of Asphaltenes and HRe sample VNVR

OSVR

asphaltenes HRe n-pentane insolubles mixture of asphaltenes and HRe asphaltenes HRe n-pentane insolubles Mixture of asphaltenes and HRe

dm/Å

dγ/Å

Lc/Å

La/Å

fA

R2

3.507 − 3.541 3.511 3.498 − 3.507 3.503

4.384 − 4.426 4.388 4.373 − 4.383 4.379

40.3 − 41.2 39.0 41.9 − 46.7 41.9

14.9 − 14.1 14.8 14.9 − 14.6 14.6

0.17 − 0.15 0.15 0.16 − 0.13 0.14

0.9991 − 0.9994 0.9994 0.9996 − 0.9993 0.9992

3388

DOI: 10.1021/acs.energyfuels.8b00208 Energy Fuels 2018, 32, 3380−3390

Article

Energy & Fuels

(2) Hajiakbari, N.; Teeraphapkul, P.; Fogler, H. S. Energy Fuels 2014, 28, 909−919. (3) Guzmán, R.; Ancheyta, J.; Trejo, F.; Rodríguez, S. Fuel 2017, 188, 530−543. (4) Rogel, E. Langmuir 2002, 18, 1928−1937. (5) Ghloum, E. F.; Al-Qahtani, M.; Al-Rashid, A. J. Pet. Sci. Eng. 2010, 70, 99−106. (6) Derakhshesh, M.; Eaton, P.; Newman, B.; Hoff, A.; Mitlin, D.; Gray, M. R. Energy Fuels 2013, 27, 1856−1864. (7) Merinogarcia, D.; Shaw, J. M.; Carrier, H.; Yarranton, H.; Goual, L. Energy Fuels 2010, 24, 2175−2177. (8) Pereira, J. C.; López, I.; Salas, R.; Silva, F.; Fernández, C.; Urbina, C.; López, L. C. Energy Fuels 2007, 21, 1317−1321. (9) Speight, J. G. The Chemistry and Technology of Petroleum, 3rd ed., revised and expanded; Marcel Dekker, Inc.: New York, 1999; pp 244− 298. (10) Tanaka, R.; Sato, E.; Hunt, J. E.; Winans, R. E.; Sato, S.; Takanohashi, T. Energy Fuels 2004, 18, 1118−1125. (11) Tanaka, R.; Hunt, J. E.; Winans, R. E.; Thiyagarajan, P.; Sato, S.; Takanohashi, T. Energy Fuels 2003, 17, 127−134. (12) Kayukova, G. P.; Gubaidullin, A. T.; Petrov, S. M.; Romanov, G. V.; Petrukhina, N. N.; Vakhin, A. V. Energy Fuels 2016, 30, 773−783. (13) Speight, J. G.; Moschopedis, S. E. Fuel 1980, 59, 440−442. (14) Cataldo, F.; Garcíahernández, D. A.; Manchado, A. Mon. Not. R. Astron. Soc. 2013, 429, 3025−3039. (15) Cataldo, F.; Angelini, G.; García-Hernández, D. A.; Manchado, A. Spectrochim. Acta, Part A 2013, 111, 68−79. (16) Eyssautier, J.; Levitz, P.; Espinat, D.; Jestin, J.; Gummel, J.; Grillo, I.; Barré, L. J. Phys. Chem. B 2011, 115, 6827−6837. (17) Li, S.; Liu, C.; Que, G.; Liang, W.; Zhu, Y. Fuel 1997, 76, 1459− 1463. (18) Sheu, E. Y. J. Phys.: Condens. Matter 2006, 18, S2485−S2498. (19) Fenistein, D.; Barré, L. Fuel 2001, 80, 283−287. (20) Hurtado, J. L. A.; Chodakowski, M.; Long, B.; Shaw, J. M. Energy Fuels 2011, 25, 5100−5112. (21) Jestin, J.; Barré, L. J. Dispersion Sci. Technol. 2004, 25, 341−347. (22) Hashmi, S. M.; Firoozabadi, A. J. Phys. Chem. B 2010, 114, 15780−15788. (23) Eyssautier, J.; Frot, D.; Barré, L. Langmuir 2012, 28, 11997− 12004. (24) Hashmi, S. M.; Quintiliano, L. A.; Firoozabadi, A. Langmuir 2010, 26, 8021−8029. (25) Yarranton, H. W.; Ortiz, D. P.; Barrera, D. M.; Baydak, E. N.; Barré, L.; Frot, D.; Eyssautier, J.; Zeng, H.; Xu, Z.; Dechaine, G.; Becerra, M.; Shaw, J. M.; McKenna, A. M.; Mapolelo, M. M.; Bohne, C.; Yang, Z.; Oake, J. Energy Fuels 2013, 27, 5083−5106. (26) Maham, Y.; Chodakowski, M. G.; Zhang, X.; Shaw, J. M. Fluid Phase Equilib. 2005, 227, 177−182. (27) Barré, L.; Simon, S.; Palermo, T. Langmuir 2008, 24, 3709− 3717. (28) Sedghi, M.; Goual, L. Energy Fuels 2010, 24, 2275−2280. (29) González, G.; Sousa, M. A.; Lucas, E. F. Energy Fuels 2006, 20, 2544−2551. (30) Li, S.; Liu, C.; Que, G.; Liang, W.; Zhu, Y. Fuel 1996, 75, 1025− 1029. (31) Zhao, B.; Becerra, M.; Shaw, J. M. Energy Fuels 2009, 23, 4431− 4437. (32) Zhao, B.; Shaw, J. M. Energy Fuels 2007, 21, 2795−2804. (33) Anisimov, M. A.; Ganeeva, Y. M.; Gorodetskii, E. E.; Deshabo, V. A.; Kosov, V. I.; Kuryakov, V. N.; Yudin, D. I.; Yudin, I. K. Energy Fuels 2014, 28, 6200−6209. (34) Mclean, J. D.; Kilpatrick, P. K. J. Colloid Interface Sci. 1997, 196, 23−34. (35) Mclean, J. D.; Kilpatrick, P. K. J. Colloid Interface Sci. 1997, 189, 242−253. (36) 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, 1880−1888. (37) Chang, C. L.; Fogler, H. S. Langmuir 1994, 10, 1749−1757.

than LRe. An obvious size increase of asphaltene aggregates is observed when HRe exceeds some concentration. This can be tentatively attributed to the prior adsorption and penetration of resins in the less polar asphaltenes, followed by the reaggregation of the remaining asphaltenes due to their more aromatic and polar nature. The thermodynamics of the asphaltene phase behavior based on the Flory−Huggins polymer theory suggest that HRe is more inclined to act as the dispersed phase and could effectively orient the Δg of asphaltene solutions. HRe presents a much higher adsorption equilibrium constant with asphaltenes than LRe. These results indicate that the more aromatic and polar resin fraction, HRe, could serve as a highly efficient peptizing agent for asphaltene stabilization. XRD analysis shows that the aromatic stacking of asphaltenes could be effectively disrupted by peptization of HRe, leading to the increase of the layer distance between aromatic sheets (dm) and the average height of the stack of aromatic sheets (Lc) as well as the decrease of the average diameter of the aromatic sheet (La).

■

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.8b00208. Complete description of the calculation of the H/C atomic ratio and average molecular parameters by the modified Brown−Ladner method, 1H NMR spectra of different fractions from VNVR (Figure S1), assignments of different types of hydrogen in the 1H NMR spectra (Table S1), and equations for the modified Brown− Ladner method (Table S2) (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*Phone: 086-0532-8698-0607. Fax: 086-0532-8698-1787. Email: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by a project funded by the National Natural Science Foundation of China (Grants 21776313 and U1362101), the China Postdoctoral Science Foundation (Grant 2016M602219), the Provincial Natural Science Foundation of Shandong (Grant ZR2017BB021), the State Key Laboratory of Heavy Oil Processing (Grants SLKZZ2017003 and SLKZZ-2017011), the Qingdao Postdoctoral Applied Research Project (Grant 2016224), the Fundamental Research Funds for the Central Universities (Special Projects, Grant 17CX05016), the PetroChina Innovation Foundation (Grant 2017D-5007-0506), the Key Research and Development Plan of Shandong Province (Grant 2017GGX70108), Shandong Postdoctoral Funded Project (Grant 201702028), and the China National Petroleum Corp. (Grant PRIKY16066). We are grateful to master student UmmulKhairi Ibrahim from Ghana for improving the English of this paper.

■

REFERENCES

(1) Shah, A.; Fishwick, R.; Wood, J.; Leeke, G.; Rigby, S.; Greaves, M. Energy Environ. Sci. 2010, 3, 700−714. 3389

DOI: 10.1021/acs.energyfuels.8b00208 Energy Fuels 2018, 32, 3380−3390

Article

Energy & Fuels

(73) Lima, F. C. D. A.; Alvim, R. D. S.; Miranda, C. R. Energy Fuels 2017, 31, 11743−11754. (74) Zhang, L. L.; Yang, G. H.; Wang, J. Q.; Li, Y.; Li, L.; Yang, C. H. Fuel 2014, 128, 366−372.

(38) Correra, S.; Cimino, R.; Delbianco, A.; Lockhart, T. Solubility and Phase Behavior of Asphaltenes. In Asphaltenes: Fundamentals and Applications; Sheu, E. Y., Mullins, O. C., Eds.; Plenum Press: New York, 1996; pp 97−130. (39) León, O.; Contreras, E.; Rogel, E.; Dambakli, G.; Acevedo, S.; Carbognani, L.; Espidel, J. Langmuir 2002, 18, 5106−5112. (40) León, O.; Contreras, E.; Rogel, E.; Dambakli, G.; Espidel, J.; Acevedo, S. Energy Fuels 2001, 15, 1028−1032. (41) Rogel, E. Energy Fuels 2008, 22, 3922−3929. (42) Gawrys, K. L.; Spiecker, P. M.; Kilpatrick, P. K. Pet. Sci. Technol. 2003, 21, 461−489. (43) Spiecker, P. M.; Gawrys, K. L.; Trail, C. B.; Kilpatrick, P. K. Colloids Surf., A 2003, 220, 9−27. (44) Bardon, C.; Barre, L.; Espinat, D.; Guille, V.; Li, M. H.; Lambard, J.; Ravey, J. C.; Rosenberg, E.; Zemb, T. Fuel Sci. Technol. Int. 1996, 14, 203−242. (45) Goual, L.; Firoozabadi, A. AIChE J. 2004, 50, 470−479. (46) Mostowfi, F.; Indo, K.; Mullins, O. C.; Mcfarlane, R. Energy Fuels 2009, 23, 1194−1200. (47) Eyssautier, J.; Hénaut, I.; Levitz, P.; Espinat, D.; Barré, L. Energy Fuels 2012, 26, 2696−2704. (48) Eyssautier, J.; Espinat, D.; Gummel, J.; Levitz, P.; Becerra, M.; Shaw, J. M.; Barré, L. Energy Fuels 2012, 26, 2680−2687. (49) Qing, W.; Chunxia, J.; Jianxin, G.; Wenxue, G. Energy Fuels 2016, 30, 2478−2491. (50) Zhang, J.; Tian, Y.; Qiao, Y.; Yang, C.; Shan, H. Energy Fuels 2017, 31, 8072−8086. (51) Rastegari, K.; Svrcek, W. Y.; Yarranton, H. W. Ind. Eng. Chem. Res. 2004, 43, 6861−6870. (52) Spiecker, P. M.; Gawrys, K. L.; Kilpatrick, P. K. J. Colloid Interface Sci. 2003, 267, 178−193. (53) Ferworn, K. A.; Svrcek, W. Y.; Mehrotra, A. K. Ind. Eng. Chem. Res. 1993, 32, 955−959. (54) Fenistein, D.; Barré, L.; Broseta, D.; Espinat, D.; Livet, A.; Roux, J.; Scarsella, M. Langmuir 1998, 14, 1013−1020. (55) Savvidis, T. G.; Fenistein, D.; Barré, L.; Béhar, E. AIChE J. 2001, 47, 206−211. (56) Yudin, I. K.; Nikolaenko, G. L.; Gorodetskii, E. E.; Kosov, V. I.; Melikyan, V. R.; Markhashov, E. L.; Frot, D.; Briolant, Y. J. Pet. Sci. Eng. 1998, 20, 297−301. (57) Fávero, C. V. B.; Maqbool, T.; Hoepfner, M.; Haji-Akbari, N.; Fogler, H. S. Adv. Colloid Interface Sci. 2017, 244, 267−280. (58) Derakhshesh, M.; Bergmann, A.; Gray, M. R. Energy Fuels 2013, 27, 1748−1751. (59) Nikooyeh, K.; Bagheri, S. R.; Shaw, J. M. Energy Fuels 2012, 26, 1756−1766. (60) Sirota, E. B. Pet. Sci. Technol. 1998, 16, 415−431. (61) Acevedo, S.; Guzman, K.; Ocanto, O. Energy Fuels 2010, 24, 1809−1812. (62) Sedghi, M.; Goual, L.; Welch, W.; Kubelka, J. J. Phys. Chem. B 2013, 117, 5765−5776. (63) Aguiar, J. I. S.; Mansur, C. R. E. Fuel 2015, 140, 462−469. (64) Nikooyeh, K.; Shaw, J. M. Energy Fuels 2013, 27, 66−74. (65) Rassamdana, H.; Dabir, B.; Nematy, M.; Farhani, M.; Sahimi, M. AIChE J. 1996, 42, 10−22. (66) Mohammadi, A. H.; Eslamimanesh, A.; Richon, D. Ind. Eng. Chem. Res. 2012, 51, 4041−4055. (67) Zuo, J. Y.; Mullins, O. C.; Freed, D.; Zhang, D. J. Chem. Eng. Data 2010, 55, 2964−2969. (68) Liang, W. Heavy Oil Chemistry; Petroleum University Press: Dongying, China, 2000; pp 194−199. (69) Hoepfner, M. P.; Fogler, H. S. Langmuir 2013, 29, 15423− 15432. (70) Acevedo, S.; Ranaudo, M. A.; Escobar, G.; Gutiérrez, L.; Ortega, P. Fuel 1995, 74, 595−598. (71) Levan, M. D.; Vermeulen, T. J. Phys. Chem. 1981, 85, 3247− 3250. (72) Alhumaidan, F. S.; Hauser, A.; Rana, M. S.; Lababidi, H. M. S.; Behbehani, M. Fuel 2015, 150, 558−564. 3390

DOI: 10.1021/acs.energyfuels.8b00208 Energy Fuels 2018, 32, 3380−3390