Effect of SiO2 Nanoparticles on Wax Crystallization and Flow Behavior

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Effect of SiO2 Nanoparticles on Wax Crystallization and Flow Behavior of Model Crude Oil Xin Song,† Hongyao Yin,† Yujun Feng,*,† Sheng Zhang,‡ and Yong Wang‡ †

Polymer Research Institute, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065, People’s Republic of China ‡ Shengli Oilfield Shengli Chemicals Co. Ltd., Dongying 257055, People’s Republic of China

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S Supporting Information *

ABSTRACT: In oil industry, wax deposition is one of the frequently encountered problems that causes severe issues during the production, storage, and transportation of crude oil. Recently, it is found that addition of nanohybrids to crude oil is an effective method to solve this problem. However, the mechanism of how nanoparticles affect the wax crystallization and rheological behavior of crude oil has not been clearly understood. Here we reported the influence of SiO2 nanoparticles on crystallization and rheological behavior of model oils with and without asphaltene and resin. It was demonstrated that the wax appearance temperature increased upon the addition of SiO2 nanoparticles of model oil without asphaltenes and resin, while the rheological behavior was less affected. When in the presence of asphaltenes and resin, the amount of wax crystals, wax appearance temperature, and rheological parameter of model oils were found to decrease while SiO2 nanofluid was added, resulting in the improvement of flowability.

products, and impeding the restart of flow after prolonged shutdown.10 To overcome such problems, both physical and chemical methods have been developed so far.6,11,12 Heating transportation technology is a kind of simple and effective physical technology, but it will consume a great deal of energy and time, resulting in a sharp increase of the cost.13 On the contrary, chemical approaches, particularly the addition of pour-point depressant (PPD), are usually cost-effective and timesaving as the chemical additives can change the structure and morphology of wax crystals, and make the wax hard to form a rigid threedimensional network at ambient or even lower temperature.6,12,14−16 Up to now, a variety of PPDs have been synthesized and investigated to improve the flowability of crude oil by many research groups.5,17−20 Nonetheless, the PPD technique also has some drawbacks. The prominent difficulty is the lack of general applicability; that is, particular PPDs are suited to specific kinds of crude oils,13 which greatly limits their wide range of applications. As a consequence, development of a novel PPD technique with extensive applicability is highly desirable. Recently, Zhang and co-workers13,21,22 developed a new PPD based on nanohybrid materials to decrease the pour point and viscosity of waxy crude oil. It was found that both the pour point and apparent viscosity of waxy crude oil were obviously decreased upon addition of the nanohybrid PPD, and the longterm stability of this nanohybrid PPD was superior to that of

1. INTRODUCTION Crude oil has become one of the most important substances consumed by humans since it is used as a dominant source of energy for industry and also provides the raw materials for the petrochemical plants to produce polymers, plastics, and many other products.1 Crude oil is a complicated fluid that mainly contains paraffins, asphaltenes, resins, and other light hydrocarbons, which in return confers its complex nature that causes various problems in the production, storage, transportation, and processing.2,3 Wax deposition is one of the problems that are often encountered. Generally, the long-chain paraffins are dissolved with balanced state in the crude oil at higher temperature.4 However, with temperature decreasing, the paraffins gradually crystallize as an interlocking network increasing the viscosity of the oil,5 which brings many troubles for oil exploitation, especially for the offshore deep-sea wells where the temperature at the sea bed can be as low as 4 °C.6 In addition to temperature, asphaltenes and resins are another nonneglectable factor influencing wax deposition. In a higher temperature range, asphaltenes are dispersed as nanosized particles in crude oil whereas they transform to become aggregation with temperature decreasing.7,8 Garcı ́a8 reported that the aggregated asphaltene could serve as nucleator for wax crystallization which would increase the wax appearance temperature (WAT) in oil. Roenningsen and co-workers9 also found that asphaltenes and resins can modify the morphology and surface characteristics of wax crystals and, therefore, their tendency to interact. Wax deposition causes reduction in production, in terms of maintenance and removal of deposits already formed, raising the cost of producing and transporting oil © 2016 American Chemical Society

Received: Revised: Accepted: Published: 6563

March 2, 2016 May 18, 2016 May 20, 2016 May 20, 2016 DOI: 10.1021/acs.iecr.6b00836 Ind. Eng. Chem. Res. 2016, 55, 6563−6568

Article

Industrial & Engineering Chemistry Research Table 1. Main Composition of the Crude Oil Used in This Work light fraction (wt %)

wax (wt %)

aliphatic

aromatic

C17−18

C19−20

C21−23

C24−26

C27−30

C31−33

C34−36

C37−40

asphaltene and resin (wt %)

28.96

20.78

5.39

5.13

6.94

6.43

6.58

2.25

1.00

0.63

15.91

dried at 25 °C in a vacuum oven for 24 h to afford asphaltene. Second, the n-heptane solutions were combined and evaporated under vacuum, and then the resulting solution was precipitated with acetic ester to afford resins. Finally, asphaltene that was wellmixed with resins and stored in a desiccator to ensure that the resin/asphaltene ratio is identical to the real ratio of Shengli crude oil. Preparation of Model Oils. Four kinds of model oils with different contents of asphaltene and resin were prepared. All of these model oils have the same content of paraffins with crude oil from Shengli Oilfield, and their final composition was given in Table 2.

conventional ethylene-vinyl acetate copolymer PPD. It seems that introduction of nanohybrids may open a new way to improve oil flowability since nanoparticles have a number of unique properties such as the large surface area to volume ratio, high adsorption affinity, and good dispersion ability, to name just a few.23 However, the details of the nanohybrid materials as well as the mechanism were not investigated in their work. Later, Mohammadi and co-workers24 studied the impacts of TiO2, SiO2, and ZrO2 nanoparticles on asphaltene stability of crude oil at different pH regions. It was observed that the nanofluids could not act as asphaltene precipitant in strongly acidic conditions, and moreover, they may play as a dispersant, enhancing the stability of the asphaltene. More recently, Nassar and coworkers25,26 analyzed the effect of the chemical nature of nanoparticles on asphaltene adsorption. The authors demonstrated that nanoparticles could adsorb the asphaltene quickly and then disperse and stabilize asphaltene. Despite this progress, the mechanism for nanoparticles affecting the wax crystallization and flow behavior of crude oil is still unclear. Thus, this study aims at revealing the influence of nanoparticles on wax crystallization and flow behavior of oils with and without asphaltene and resin. To this end, first of all, model oils containing paraffins, different contents of asphaltene and resin (from 0 to 25 wt %), and other components were prepared in this work. Moreover, the SiO2 nanoparticle was used in this study as it is not only a kind of typical nanoparticle but also cost-effective and environmentally friendly. The WAT, crystal morphology, and rheological behaviors of the model oils were examined by differential scanning calorimeter, polarizing microscope, and rotation rheometer.

Table 2. Composition of the Synthetic Model Oilsa sample

n-C10 (wt %)

toluene (wt %)

asphaltene and resin (wt %)

MO-1 MO-2 MO-3 MO-4

38.22 34.15 28.96 23.67

27.43 24.50 20.78 16.98

0.00 7.00 15.91 25.00

a

The concentration of n-C17, n-C20, n-C23, n-C26, n-C28, n-C32, n-C36, and n-C38 was fixed at 5.39, 5.13, 6.94, 6.43, 6.58, 2.25, 1.00, and 0.62 wt %, respectively, in all samples.

Model oil without asphaltene and resin (MO-1) was prepared by dissolving paraffins in decane and toluene, and then stirred at 80 °C for 3 h. Model oils with asphaltene and resin (MO-2, MO3, and MO-4) were prepared in two steps. First, the mixture of asphaltene and resin was dissolved in toluene, and paraffins were dissolved in decane; then, both of the solutions were sonicated at 80 °C for 1 h. Second, the above two solutions were mixed at 85 °C and stirred for 3 h. Preparation of SiO2 Nanofluid. The content of SiO2 nanoparticles was fixed at 1 wt %. To prepare nanofluid, a mound of SiO2 nanoparticles was added to xylene and stirred at 25 °C for 3 h, followed by sonication for 3 h. The mean particle diameter of aggregated particles was determined by Malvern Zetasizer Nano ZS (Malvern Instruments Ltd.). The particle size distribution curve of SiO2 nanoparticles dispersed in xylene is shown in Figure 1. The mean particle diameter of SiO2 nanoparticles dispersed in xylene is 197.3 nm.

2. EXPERIMENTAL SECTION 2.1. Materials. Heptane (AR), ethyl acetate (AR), and toluene (AR) were purchased from Kelong Chemical Reagent Factory; decane (RG) was obtained from Adamas. Heptadecane (C17, 99%), eicosane (C20, 99%), tricosane (C23, 99%), octacosane (C28, 99%), and dotriacontane (C32, 97%) were purchased from Acros; hexacosane (C26, 99%) and hexatriacontane (C36, 97%) were purchased from TCI. Octatriacontane (C38, 98%) was purchased from Aldrich. The above paraffins were used as received. The hydrophobic fumed silica (SiO2) nanoparticles used were supplied from Waker Chemie AG under the trade name HDK H18. They were produced by treating hydrophilic fumed silica nanoparticles with polydimethylsiloxy, and had a specific surface area 170−230 m2 g−1 and average primary particle size 12 nm. Crude oil was provided by Shengli Oilfield Branch Company of Sinopec, and its composition is given in Table 1. 2.2. Sample Preparation. Preparation of Asphaltene and Resin. Asphaltene and resin were extracted from Shengli Oilfield crude oil according to previously reported method that employs n-heptane and acetic ester as solvents.26,27 First of all, crude oil was mixed with n-heptane at a volume ratio of 1:40. Then, the mixture was sonicated at 25 °C for 1 h and further stirred at 300 rpm for 12 h, followed by filtration with 8 μm Whatman filter paper. The resulting solid was extracted in a Soxhlet apparatus with n-heptane to remove the remaining impurities, and then

Figure 1. Particle size distribution curve obtained for SiO2 nanoparticles dispersed in xylene. 6564

DOI: 10.1021/acs.iecr.6b00836 Ind. Eng. Chem. Res. 2016, 55, 6563−6568

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Industrial & Engineering Chemistry Research Preparation of Model Oils with SiO2 Nanoparticles. A 0.2 g portion of the above SiO2 nanofluid was added to 20 g of MO-1, MO-2, MO-3, and MO-4, respectively, and then stirred at 80 °C for 3 h. 2.3. Characterization. Differential Scanning Calorimetry (DSC). To investigate the interactions of SiO2 nanoparticles with wax crystals in model oils, thermal analysis via DSC was conducted to determine the wax appearance temperature (WAT) of the oil samples. DSC analysis was conducted on a TA-Q200 differential scanning calorimeter (TA Instruments Inc.) in the temperature range from 85 to −20 °C at a cooling rate of 5 °C min−1. Polarized Optical Microscopy. The polarized optical microscope (POM) system used for the determination of wax crystal size and shape microscopy (POM) observation was a LECICA DM2500P microscope equipped with a Pixelink CCD/CMOS camera. Samples were initially heated to 80 °C for 5 min to remove thermal history, and then were cooled to 25 °C at a rate of 5 °C min−1. The microscopic studies were carried out at 25 °C to observe the size and shape of the wax crystals. Rheological Measurement. The rheological measurements of the model oils were carried out on an Anton Paar rotational rheometer (MCR302) equipped with CC27 (ISO3219) concentric cylinder system and thermostated cooling system for temperature control. For a better repeatability of rheological measurements, the model oils were preheated for at least 1 h at 80 °C to remove their thermal history and then loaded on the rheometer to start the tests. Afterward, shearing 5 min at 90 °C in a constant shear rate 30 s−1 then changed the test conditions such as decreased temperature from 90 to 14 °C with a cooling rate 0.5 °C min−1 and testing the viscosity−temperature curve.

of WAT is presented in Figure S5, and the standard deviations obtained are less than 0.3 °C. It can be observed that the WAT of model oil without asphaltene and resin is only 30.2 °C; however, it significantly increases together with the broadening of the phase transition peak after introduction of asphaltene and resin. Moreover, with the concentration of asphaltene and resin increasing, the phase transition peak of model oil becomes broader, and the WAT moves to a higher temperature. For instance, the WAT of MO-2 with 7 wt % asphaltene and resin is 40.4 °C, which is 10.2 °C higher than that of MO-1 without asphaltene and resin, whereas it achieves 49.2 °C for MO-4 that contains 25 wt % asphaltene and resin. It can be explained from two aspects: first of all, the solvent content decreases with the rise of asphaltene and resin concentration, which leads to the reduction of wax solubility; second, as proposed by Garcı ́a et al.,8 flocculated asphaltene and resin act as crystal nucleus and change the process of wax crystallization which increases the WAT of model oils. With the increase of asphaltene and resin concentration, the number and the size of flocculated asphaltene increase, thus resulting in the wax crystallizing at higher temperature. An additional microscopic investigation was used to gain a better understanding of action mechanism between the model oils and asphaltene and resin. The variation in the morphology and structure of wax crystals of model oils with different concentrations of asphaltene and resin at 25 °C are shown in Figure 3. The wax crystal morphology of model oil (MO-1)

3. RESULTS AND DISCUSSION 3.1. Wax Crystallization and Rheological Behavior of Model Oils with Different Content of Asphaltene and Resin. As our goal is to study the influence of SiO2 nanoparticles on crystallization and flowability of model oils, their originally corresponding properties were first investigated for the purpose of comparison. Wax appearance temperature (WAT), which is defined as the temperature at which the crystallization first begins to appear in oils, is a key parameter to examine the wax crystallization, while according to DSC analysis, it is the onset temperature at which the curve deviates from the baseline. Figure 2 gives the DSC cooling curves of model oils with different concentration of asphaltene and resin, and the corresponding WAT is shown in Figure S1. The repeatability of measurements

Figure 3. Photomicrographs of model oils: (a) MO-1, which does not contain asphaltene and resin; (b) MO-2, which has 7.00 wt % asphaltene and resin; (c) MO-3, which has 15.91 wt % asphaltene and resin; (d) MO-4, which has 25.00 wt % asphaltene and resin.

without asphaltene and resin shows platelet-like growth. However, it changes from platelet-like to almost spherical, and the size also experiences a decrease after introduction of asphaltene and resin. Furthermore, with the increase of asphaltene and resin content in model oils, from 7.00 to 25.00 wt %, both the size and number of wax crystals experience an obvious increase. The changes of the wax crystals with the increase of asphaltene and resin concentration appear compatible with previous observations;8,28 namely, the presence of asphaltene and resin in the system would provide multiple nucleation sites for wax crystals and impede the formation of large crystals. As a result, with the asphaltene and resin concentration rising, both the number and the size of flocculated asphaltene increase, giving rise to the increase in the size and number of wax crystals, which is beneficial to the formation of wax crystals network.

Figure 2. DSC cooling curves of model oils with different concentration of asphaltene and resin. 6565

DOI: 10.1021/acs.iecr.6b00836 Ind. Eng. Chem. Res. 2016, 55, 6563−6568

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Industrial & Engineering Chemistry Research

enough solids in the solution to build a stable network even under shearing. Thus, this indicates that, after the addition of asphaltene and resin, more solids in solution are needed to build a stable network under shearing and eventually to turn the oil to gel. This effect is caused by the interference of the asphaltene− wax agglomerates and the rest of the waxes during a structure spatial arrangement.29 Therefore, the wax crystal cannot be built properly, and the structure buildup is delayed. The effect of asphaltene and resin on wax crystallization and flow behavior of model oils was investigated in this part. It is found that the WAT moves to a higher temperature, the phase transition peak becomes broader, and the flowability becomes poorer with the increase of asphaltene and resin concentration for model oils. On the basis of the above analysis, the variations originate from the change of wax crystal morphology from platelet-like to almost spherical after introduction of asphaltene and resin which act as crystal nucleus and then change the process of wax crystallization during the wax crystallization process. 3.2. Effect of SiO2 Nanoparticles on Crystallization and Rheological Behavior of Model Oils with and without Asphaltene and Resin. To investigate the effect of SiO2 nanoparticles on crystallization and rheological behavior of model oils with and without asphaltene and resin, MO-1 and MO-3 were selected to study. While MO-1 does not have asphaltene and resin, MO-3 contains 15.91 wt % asphaltene and resin. Figure 6 gives the thermal response of model oils before and after addition of SiO2 nanoparticles. It can be seen that the WAT

Paraffins can crystallize out from crude oil and interlock to form a three-dimensional network to increase the viscosity of the oil, thus impeding the flow and causing the blockage of a pipeline.5 The crystallization habits of paraffins influence flow rheological behaviors to a large extent; hence, the rheological behaviors of these model oils were studied by Anton Paar rotational rheometer. It is well-known that cooling temperature adversely affects the flow property of crude oil in such a way that it alters their rheological behavior to a non-Newtonian character. The inflection point is the temperature at which the viscosity increases sharply, meaning that rheological behavior of crude oil changes into non-Newtonian character. The viscosity−temperature relationships for model oils with asphaltene and resin in various amounts are presented in Figure 4, and the

Figure 4. Semilogarithmic curves of viscosity versus temperature for model oils with different content of asphaltene and resin.

corresponding inflection points are shown in Figure S2. The repeatability of measurements of inflection point is presented in Figure S6, and the standard deviations obtained were less than 0.9 °C. It can be seen that the infection point and viscosity of model oil ascend with the increase of asphaltene and resin concentration, suggesting the presence of asphaltene and resin increases the viscosity of model oils. These results can be explained by microscopic analysis. The size and number of wax crystals significantly rise with the asphaltene and resin concentration increasing, which is favorable for the formation of a wax crystal network, thus leading to the increase in viscosity and inflection point of model oils. In addition, the inflection point of model oil is observed lower than WAT, and the difference becomes more significant after introducing asphaltene and resin (Figure 5). It is well-known that the appearance of inflection point means that there are already

Figure 6. DSC cooling curves of model oils untreated and treated with SiO2 nanoparticles.

of MO-1 increased about 1.5 °C after being treated with SiO2 nanoparticles. This result is different from the previous report30 that addition of chemical flow improvers can significantly reduce the WAT of the model wax oil which only contains paraffin and solvent. It means that SiO2 nanoparticles may act as crystal nucleus to promote wax crystallization in this case. However, the WAT of MO-3 decreased about 1.7 °C after introduction of SiO2 nanoparticles, which is contrary to the result of MO-1, suggesting SiO2 nanoparticles can reduce the WAT of model oil containing asphaltene and resin. It has been previously demonstrated that the aggregated asphaltene can serve as nucleator for wax crystallization and then increase the WAT of wax in oil. Thus, SiO2 nanoparticles may play a role in dispersing and stabilizing the asphaltene to prevent its aggregation so that the WAT decreases. To gain a better understanding, the microscope study was performed.

Figure 5. Wax appearance temperature and inflection point for model oils with different content of asphaltene and resin. 6566

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Industrial & Engineering Chemistry Research

The viscosity−temperature semilogarithmic curves of MO-1 and MO-3 with and without SiO2 nanoparticles are shown in Figure 9, and the corresponding inflection points are given in

The images of MO-1 and MO-3 in the absence and presence of SiO2 nanoparticles are shown in Figures 7 and 8, respectively.

Figure 9. Semilogarithmic curves of viscosity versus temperature for the model oils untreated and treated with SiO2 nanofluid: (a) MO-1 and (b) MO-3.

Figure 7. Polarized optical microscopy images of MO-1 in the absence (a and c) and presence (b and d) of SiO2 at 25 °C. While the magnification of parts a and b is ×50, the magnification of parts c and d is ×150.

Figure S2. It can be seen that MO-1 with and without SiO2 nanoparticles displays the same inflection point, 29.3 °C, and both viscosity versus temperature semilogarithmic curves are also almost coincident. However, the result for MO-3 is different from that for MO-1, in which the inflection point in the absence of SiO2 nanoparticles is 41.1 °C, whereas it decreases to 39.2 °C in the presence of SiO2 nanoparticles. Namely, the inflection point experiences a drop of 1.9 °C upon addition of the nanoparticle. The above results demonstrate that SiO2 nanoparticles cannot influence the rheological behavior of model oil without asphaltene and resin, whereas they play a positive role in improving the rheological property of model oil in the presence of asphaltene and resin. This interesting phenomenon might be explained as follows: the wax crystal number is decreased significantly after the addition of SiO2 nanoparticles, which inhibits the formation of the wax crystal network to make the model oil from Newtonian fluid into non-Newtonian fluid at lower temperature, thus leading to the decrease on inflection point of model oils. On the basis of the above analysis, it is clear that SiO2 nanoparticles play different roles in wax crystallization of model oils with and without asphaltene and resin, which in return gives rise to the opposite effect on WAT and flowability of model oils. In the absence of asphaltene and resin, the addition of SiO2 nanoparticles acts as a crystal nucleus to promote wax crystallization. However, in the presence of asphaltene and resin, SiO2 nanoparticles adsorb the asphaltene and then disperse and stabilize asphaltene to prevent the aggregation of asphaltene, thus impeding the nucleation effect of asphaltene and resin and finally hindering wax crystallization. The influence of SiO2 on wax crystallization and flowability of Shengli crude oil was also evaluated; the results are in accordance with model oils which contain asphaltene and resin (Figures S7−S9 and Table S1, see Supporting Information for details).

Figure 8. Polarized optical microscopy images of MO-3 in the absence (a and c) and presence (b and d) of SiO2 at 25 °C. The magnification of parts a and b is ×50, whereas the magnification of parts c and d is ×150.

From Figure 6, we can find that the wax crystal number of MO-1 increases but the size decreases upon addition of the SiO2 nanoparticles. Nevertheless, the variation for MO-3 is different from MO-1 by viewing Figure 7. One can find that the wax crystal number of MO-3 significantly decreases, but the size becomes a little bigger after the addition of SiO2 nanoparticles. Therefore, the effect of SiO2 nanoparticles on wax crystals of model oils with and without asphaltene and resin is the opposite. It can be explained by the observation that SiO2 nanoparticles are welldispersed in the model oil and easily accessible for any kind of interactions with the paraffins; they will act as a crystal nucleus to promote wax crystallization in the absence of asphaltene and resin, but play a different role in the presence of asphaltene and resin. Nanoparticles have high adsorption affinity and large surface area to volume ratio; thus, asphaltene and resin will be adsorbed on the surface of nanoparticles, and then dispersed and stabilized in oils, so that the aggregation of asphaltene will be prevented. Additionally, the above result has demonstrated that flocculated asphaltenes provide multiple nucleation sites for wax crystals. Therefore, nanoparticles will impede the nucleation effect of asphaltene and resin, and then increase the size and decrease the number of wax crystals, giving rise to lower WAT. The changes in the morphology of wax crystals are in agreement with the result of DSC.

4. CONCLUSIONS In conclusion, the effect of SiO2 nanoparticles on wax crystallization and rheological behavior on model oils with different contents of asphaltene and resin was investigated. The opposite influence of nanohybrids on the properties of model oils in the absence and presence of asphaltene and resin was observed for the first time. It was demonstrated that SiO2 nanoparticles serve as the crystal nucleus to increase the wax crystal number but decrease the wax crystal size so that the WAT rises for the oil 6567

DOI: 10.1021/acs.iecr.6b00836 Ind. Eng. Chem. Res. 2016, 55, 6563−6568

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(12) Yang, F.; Zhao, Y. S.; Sjöblom, J.; Li, C. X.; Paso, K. G. Polymeric Wax Inhibitors and Pour Point Depressants for Waxy Crude Oils: A Critical Review. J. Dispersion Sci. Technol. 2015, 36, 213. (13) Wang, F.; Zhang, D. M.; Ding, Y. F.; Zhang, L. X.; Yang, M. S.; Jiang, B. L.; Zhang, S. M.; Ai, M. Y.; Liu, G. W.; Zhi, S. J.; Huo, L. F.; Ouyang, X.; Li, L. The Effect of Nanohybrid Materials on the Pour-Point and Viscosity Depressing of Waxy Crude Oil. Chin. Sci. Bull. 2011, 56, 14. (14) Martínez-Palou, R.; de Lourdes Mosqueira, M.; Zapata-Rendón, B.; Mar-Juárez, E.; Bernal-Huicochea, C.; de la Cruz Clavel-López, J.; Aburto, J. Transportation of Heavy and Extra-Heavy Crude Oil by Pipeline: A Review. J. Pet. Sci. Eng. 2011, 75, 274. (15) Chanda, D.; Sarmah, A.; Borthakur, A.; Rao, K. V.; Subrahmanyam, B.; Das, H. C. Combined Effect of Asphaltenes and Flow Improvers on the Rheological Behaviour of Indian Waxy Crude Oil. Fuel 1998, 77, 1163. (16) Al-Sabagh, A. M.; Noor El-Din, M. R.; Morsi, R. E.; Elsabee, M. Z. Styrene-Maleic Anhydride Copolymer Esters as Flow Improvers of Waxy Crude Oil. J. Pet. Sci. Eng. 2009, 65, 139. (17) Ercegkuzmic, A.; Radosevic, M.; Bogdanic, G.; Srica, V.; Vukovic, R. Studies on the Influence of Long Chain Acrylic Esters Polymers with Polar Monomers as Crude Oil Flow Improver Additives. Fuel 2008, 87, 2943. (18) Soni, H. P.; Kiranbala; Agrawal, K. S.; Nagar, A.; Bharambe, D. P. Designing Maleic Anhydride-α-Olifin Copolymeric Combs as Wax Crystal Growth Nucleators. Fuel Process. Technol. 2010, 91, 997. (19) Pedersen, K. S.; Rønningsen, H. P. Influence of Wax Inhibitors on Wax Appearance Temperature, Pour Point, and Viscosity of Waxy Crude Oils. Energy Fuels 2003, 17, 321. (20) Borthakur, A.; Chanda, D.; Choudhury, S. R. D.; Rao, K. V.; Subrahmanyam, B. Alkyl Fumarate-Vinyl Acetate Copolymer as Flow Improver for High Waxy Indian Crude Oils. Energy Fuels 1996, 10, 844. (21) Zhang, D. M.; Yang, M. S.; Jiang, B. L. Application of Nanotechnology in Waxy Oil Pipeline Transportation. Oil Gas Storage Transp. 2010, 29, 487. (22) Zhang, D. M.; Jiang, B. L.; Zhang, L. X.; Yang, M. S.; Ding, Y. F.; Zhi, S. J.; Huo, L. F.; Ouyang, X.; Wang, F.; Zhang, S. M.; Li, L. The Influence of Composite Nanometer-Sized Material on Wax Deposit Property of Waxy Crude Oil. Oil Gas Storage Transp. 2011, 30, 249. (23) Perez, J. M. Iron Oxide Nanoparticles: Hidden Talent. Nat. Nanotechnol. 2007, 2, 535. (24) Mohammadi, M.; Akbari, M.; Fakhroueian, Z.; Bahramian, A.; Azin, R.; Arya, S. Inhibition of Asphaltene Precipitation by TiO2, SiO2, and ZrO2 Nanofluids. Energy Fuels 2011, 25, 3150. (25) Hashemi, R.; Nassar, N. N.; Pereira Almao, P. Nanoparticle Technology for Heavy Oil In-Situ Upgrading and Recovery Enhancement: Opportunities and Challenges. Appl. Energy 2014, 133, 374. (26) Franco, C. A.; Nassar, N. N.; Ruiz, M. A.; Pereira-Almao, P.; Cortés, F. B. Nanoparticles for Inhibition of Asphaltenes Damage: Adsorption Study and Displacement Test on Porous Media. Energy Fuels 2013, 27, 2899. (27) Akhlaq, M. S.; Kessel, D.; Dornow, W. Separation and Chemical Characterization of Wetting Crude Oil Compounds. J. Colloid Interface Sci. 1996, 180, 309. (28) Taraneh, J. B.; Rahmatollah, G.; Hassan, A.; Alireza, D. Effect of Wax Inhibitors on Pour Point and Rheological Properties of Iranian Waxy Crude Oil. Fuel Process. Technol. 2008, 89, 973. (29) Kriz, P.; Andersen, S. I. Effect of Asphaltenes on Crude Oil Wax Crystallization. Energy Fuels 2005, 19, 948. (30) Cao, K.; Wei, X. X.; Li, B. J.; Zhang, J. S.; Yao, Z. Study of the Influence of Imidization Degree of Poly(styrene-co-octadecyl maleimide) as Waxy Crude Oil Flow Improvers. Energy Fuels 2013, 27, 640.

without asphaltene and resin, whereas it prevents the aggregation of asphaltene that gives rise to the significant decrease of the wax crystals number and the slight increase of the wax crystal size, leading to the improvement of the flowability of oils with asphaltene and resin. Although the effect of SiO2 nanohybrids to improve the properties of model oils in our case is not as significant as that for the previously reported PPDs, for the first time, it reveals the mechanism of how nanoparticles work on affecting the properties. We hope researchers can benefit from this work to develop highly efficient PPDs based on nanohybirds.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.6b00836. Additional results, Figures S1−S4; reliability and repeatability of experimental data, Figures S5 and S6; the effect of SiO2 nanoparticles on crystallization and rheological properties in crude oil, Figures S7−S9; and Table S1 (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The financial support from the open funding of State Key Laboratory of Polymer Materials Engineering (sklpme2014-206) is greatly acknowledged.

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REFERENCES

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DOI: 10.1021/acs.iecr.6b00836 Ind. Eng. Chem. Res. 2016, 55, 6563−6568