Investigation into a Pour Point Depressant for ... - ACS Publications

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Investigation into a Pour Point Depressant for Shengli Crude Oil Long Fang, Xiaodong Zhang,* Jinhai Ma, and Botao Zhang College of Chemical Engineering and Environmental, Qingdao University, Qingdao 266071, People’s Republic of China ABSTRACT: A new-style pour point depressant (PPD) for crude oil was prepared by mixing the aminated copolymer and the composite commercial ethylene−vinyl acetate copolymers (EVA) in fixed proportion. The aminated copolymer was synthesized by amination of terpolymer copolymerized with monomers octadecyl acrylate, maleic anhydride, and vinyl acetate. Moreover, the aminated copolymer was characterized by Fourier transform infrared (FTIR) spectroscopy, 1H nuclear magnetic resonance (1H NMR), and gel permeation chromatography (GPC). The interaction between components of the crude oil and the PPD was investigated by FTIR, differential scanning calorimetry (DSC), and cross-polarized light microscopy. The results showed that the PPD could form asphaltene−PPD−resin agglomerates. The new agglomerates became the efficient nucleator of the crude oil beneficiated with PPD. They changed the process of wax crystallization and greatly depressed the pour point of the crude oil.

1. INTRODUCTION With the development of economy and society, the need of crude oil increases day by day. However, the presence of paraffin waxes in crude oil represents serious problems to production, transportation, and refinement.1 At low temperature, waxes separate from the crude oil and deposit on the wall of pipelines, which may block the pipelines and reduce the fluidity of the crude oil. Pour point is the temperature at which the crude oil is just able to flow and below which there is a complete absence of flow in it.2 The flow assurance has become a major technical and economic issue.3 Special attention has been given to wax crystallization, and several techniques have been developed to solve the problem caused by the deposition of wax to facilitate pipeline transportation and increase the production of crude oil. Chemical additives (which are referred to as pour point depressants, PPDs), flow improvers, paraffin inhibitors,4 or wax crystal modifiers are widely used to overcome the problem worldwide.5 The most extensively used flow improvers for crude oils are ethylene−vinyl acetate copolymer,6,7 the alkyl ester of unsaturated carboxylic acid−olefin copolymer,8 and the maleic anhydride alkyl ester of unsaturated carboxylic acid copolymer.9−11 These additives functioned by one or more of several postulated mechanisms, viz, nucleation, adsorption, cocrystallization, and improved wax solubility, which result in the formation of smaller wax crystals with more-regular shapes.12 The development of the PPD involves major difficulties, because of the complex composition of the crude oil. There is a complicated interaction of crude oil fractions. The wax, asphaltene, and resin contents in the crude oil have a significant impact in assessing their cold flow properties. El-Gamal et al.9 demonstrated that asphaltenes and resins had profound effects on the solubility of n-paraffins. The wax and asphaltenes govern the ultimate crystal structure. Murgich et al.13 proposed that the asphaltenes were considered to be insoluble colloidal solids that are peptized by adsorbed resin molecules in their surface. In addition, many theoretical and experimental studies have been put forward to explain the interaction between components of the crude oil and the PPD.14−19 Radulscu et al.20 reported that, in the case of crude oil, many other components, such as © 2012 American Chemical Society

asphaltenes and resin, in addition to wax, were present, which affected the performance and behavior of the additive. Yi and Zhang19 found that the performance of the flow improver was dependent on the asphaltene content. However, the interaction between components of the crude oil and the PPD is still not completely understood.21 Many PPDs have been reported in the past several years, but most of them have been focused on improving the fluidity of the crude oil whose pour point is less than 40 °C.1,2,6−9,16,18,22,23 In the present work, a combined PPD for crude oil whose pour point was 43 °C from Shengli oil field (Dongying, PRC) was synthesized and characterized. In addition, an attempt had been made to investigate the action mechanism of the PPD, using differential scanning calorimetry (DSC) and infrared (IR) spectroscopy.

2. EXPERIMENTAL SECTION 2.1. Materials. Acrylic acid, maleic anhydride, p-toluenesulfonic acid, vinyl acetate, toluene, methanol octadecanol, dodecylamine, dibenzoyl peroxide, and hydroquinol were of laboratory-grade chemicals from Sinopharm Chemical Regent Co., Ltd. The commercial ethylene−vinyl acetate copolymers, EVA (26-4.5) and EVA (28-25), were supplied by Hanwha Chemical Corporation, EVA (28-6) were supplied by Mitsui Chemicals, Inc. Shengli crude oil was selected to evaluate the efficiency of PPD. The physical characteristics of Shengli crude oil are listed in Table 1. 2.2. Asphaltene Content, Resin Content, and Wax Content of Shengli Crude Oil. Waxes were isolated from crude oils and quantified according to UOP Method 46-85. Asphaltenes were isolated using the IP 143 procedure using nheptane, and deasphalted crude oil was obtained. Resins were isolated using the method adopted by the literature.15 Meanwhile, the deasphalted and deresinated crude oil was Received: Revised: Accepted: Published: 11605

April 19, 2012 August 21, 2012 August 24, 2012 August 24, 2012 dx.doi.org/10.1021/ie301018r | Ind. Eng. Chem. Res. 2012, 51, 11605−11612

Industrial & Engineering Chemistry Research

Article

Table 1. Physical Characteristics of Shengli Crude Oil component of the crude oil (wt %) density @ 50 °C (g cm−3)

pour point (°C)

viscosity @ 50 °C (mPa s)

asphaltene

resin

wax

0.872

43

430

2.63

24.59

18.25

g of the combined PPD that had a solute content of 10% was added to 50 g of Shengli crude oil. The pour point of the additive treated crude oil was determined using tehmethod described by ASTM Standard D-97. 2.6. Rheological Measurement. The rheological properties of virgin and additive-treated crude oil were evaluated at different temperatures using a Brookfield viscometer. The oil specimen was heated to 90 °C while stirring, and then cooled to the measurement temperature at a cooling rate of 1 °C/min. The specimen was kept at that temperature for 5 min, and then the viscosity measurement was started. The viscosity was measured at a shear rate of 20 s−1. 2.7. Microscopy Studies. A cross-polarized light microscope was used to study the wax crystal structure in virgin and additive-treated crude oil at room temperature. 2.8. Differential Scanning Calorimetery (DSC). The DSC thermograms of the crude oil with and without PPD were recorded on a thermal analyzer operating in the liquid-nitrogen subambient mode. The transition temperatures and the enthalpies were determined by the computer during the heating cycle at a scanning rate of 5 °C/min and a range from ∼100 °C to 0 °C.

also prepared. The asphaltene prepared was added to the deasphalted and deresinated crude oil. The mixture then was heated to 80 °C and stir well to blend. The deresinated crude oil was obtained. All of the organic solvents were analyticalreagent grade. 2.3. Preparation of the Pour Point Depressant (PPD). The octadecanol and the acrylic acid were added (1.25:1, molar ratio) in a round-bottom flask connected to a Dean and Stark apparatus, as well as p-toluenesulfonic acid (1% by wt) as a catalyst and hydroquinol (0.5 wt %) as a polymerization inhibitor. The melt esterification was carried out until the calculated amount of water was separated. After completion of the reaction, the catalyst, inhibitor, and unreacted materials were removed by washing first with 5% sodium hydroxide (NaOH) solution and then with excess distilled water, and the pure octadecyl acrylate was obtained. In a 250-mL four-necked round flask fitted with a mechanical stirrer, a condenser, a temperature controller, and a nitrogencontrolled inlet valve, the octadecyl acrylate, maleic anhydride, and vinyl acetate were added (7:2:1 mol ratio) under nitrogen atmosphere using benzoyl peroxide as an initiator and toluene as a solvent at 82−86 °C for 3 h with constant stirring. The dodecylamine then was added to react with the resulted terpolymers when the temperature of reaction system was ∼60 °C. The p-toluenesulfonic acid was used as a catalyst. Water was separated using a Dean and Stark apparatus. The time of amination was ∼4 h. Purification of the polymeric products was undertaken by cooling the reaction mixture, precipitating from toluene in excess methanol while stirring, then filtering and vacuum drying. The prepared additive was named MAVA. A blend of three different commercial types of ethylene− vinyl acetate copolymer (EVA) was added to the beaker: EVA(26-4.5), EVA(28-6), and EVA(28-25). The mass ratio of EVA(26-4.5) to EVA(28-6) to EVA(28-25) was 2:2:1. The mixture of EVA then was compounded with MAVA at an optimal mass ratio (3:1). After some toluene was added, the mixture was dissolved with vigorous stirring. The combined pour point depressant (PPD) for high-pour-point crude oil was obtained, whose solute content was 10%. 2.4. Characterization of the Products. The chemical structure of the prepared polymer (MAVA) was studied by means of infrared (IR) spectroscopy using Thermo Nicolet IR spectrophotometer model IR 460 and 1H NMR spectrum using Varian-300A spectrometer. The components in the crude oil were confirmed by IR spectroscopy. In particular, the asphaltene and the resin were mixed at a ratio of 1:9.35 (composition ratio of the crude oil, by weight) in carbon tetrachloride (CCl4) and the solvent was removed under vacuum. Moreover, a PPD was added to the mixture of asphaltene and the resin in a ratio of 1:100 (by weight) in CCl4 and the solvent was removed under vacuum. The weight-average molecular weight (Mw) of the prepared polymer (MAVA) was determined used in gel permeation chromatography (GPC) (Waters Model 1515). 2.5. The Evaluating Test of Pour Point. The Shengli crude oil was used to test the activities of the above PPD additives. The PPD dosage was 400 ppm, which means that 0.2

3. RESULT AND DISCUSSION 3.1. Characterization of the Chemical Structures and Evaluation of MAVA. Figure 1 shows the IR spectrum of

Figure 1. Infrared (IR) spectrum of MAVA.

MAVA. In Figure 1, the characteristic N−H absorption peak at 3449 cm−1, the characteristic CO strong absorption peak of octadecyl methacrylate at 1735 cm−1, and the characteristic CO absorption peak of acylamino at 1627 cm−1 were observed. The characteristic stretching vibration peak of anhydride at 1760 and 1830 cm−1 disappeared almost completely. Figure 2 shows the 1H NMR spectrum of MAVA. Table 2 lists the 1H NMR spectra assignments for MAVA. As seen in Figure 2, Figure 3, and Table 2, it was confirmed that the octadecyl acrylate, maleic anhydride, and 11606

dx.doi.org/10.1021/ie301018r | Ind. Eng. Chem. Res. 2012, 51, 11605−11612


Article

Figure 2. 1H NMR spectrum of MAVA.

Table 2. 1H NMR Spectra Assignments for MAVA MAVA 1H δ

position

4.0 3.6 3.5 2.7 2.4 1.6 1.3 0.9

6.7 10 3.4 2 11 1 8 9

Figure 4. Effect of PPD dosage on the pour point.

Table 3. Pour Points of Crude Oil and the Prepared Oil before/after Additives Beneficiationa pour point (°C) sample crude oil deasphaltened crude oil deresinated crude oil deasphaltened and deresinated crude oil

vinyl acetate had copolymerized and the copolymer had reacted with the dodecylamine. The weight average molecular weight of MAVA was 41080 g/mol. 3.2. Pour Point of the Treated Crude Oil and the Influence of the Constituents on the Pour Point. Figure 4 shows the pour point depressing effect of the prepared PPD. The PPD could lower the pour point by 11 °C at a dosage of 400 ppm. However, when the dosages are higher than 400 ppm, the pour point reduction remains the same and it was not economically advisible. The crude oil was usually composed of fluid oil at normal temperature, crystal wax, resin, and asphaltene. Table 3 shows that when the asphaltene was separated from the oil, the pour point was depressed by 2 °C, and when the asphaltene and resin were both separated from the crude oil, the pour point was depressed by 4 °C. However, it was contrary to the results of Chanda et al.16 They indicated that asphaltenes act as natural flow improvers for Dikom and Kathaluni crude oil. When PPD dosages of 400 ppm were respectively added to the crude oil, the deasphaltened crude oil, the deresinated crude oil, and the deasphaltened and deresinated crude oil, the pour points of the above crude oils could be depressed by 11 °C, 6

a

pour point (°C)

added PPD

added EVA

added MAVA

43 41 41 39

32 35 38 38

38

38

The entire additive concentration was 400 ppm.

°C, 3 °C, and 1 °C, respectively. Results indicate that the PPD displayed a good effect on the high-pour-point crude oil. In addition, the resin and the asphaltene had a synergistic interaction on the PPD reducing the pour point of the crude oil. 3.3. IR Spectroscopy Analysis of Components in the Crude Oil. IR spectra of components in the crude oil and the prepared PPD are given in Figure 5. From a comparison of Figures 5a, 5b, and 5c, it was seen that the absorption peak area ratio of C−H (2910 cm−1) to aromatic ring (1571 cm−1 and 1637 cm−1) changed. The CH stretching band intensities of the mixture of asphaltene and resin obviously decreased. The variations in the spectra were due to the interactions of the asphaltene and the resin. In the crude oil, asphaltenes have a natural tendency to self-associate24 or coalesce to form large asphaltene particles, while resins gathered around an alreadyformed asphaltene particle. Asphaltenes and resins had a mutual intrinsic effect on the stability of molecular self-assembling and formed asphaltene−resin micellar association.25

Figure 3. Molecular formula of MAVA. 11607



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Figure 5. IR spectrum of components in the crude oil and the prepared PPD.

(shift to smaller frequency) of the A−H stretching vibration upon hydrogen bond formation.26 Therefore, it is due to intermolecular hydrogen bonding. It was concluded that the PPD, asphaltene, and resin formed complex agglomerates by hydrogen bonding interactions.

Compared to Figures 5c, 5d, and 5e, when PPD was added to the sample mixtures of asphaltene and resin, it was observed that the −OH or −NH stretching vibration moved from 3447 cm−1 to 3421 cm−1. The basis for the experimental detection of a conventional hydrogen bond is the red shift of the frequency 11608



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Figure 6. Differential scanning calorimetry (DSC) curves of some components (separated oil, and crude oil beneficiated with and without PPD).

ened and deresinated crude oil, and the deasphaltened crude oil. It was observed that they had only one exothermic peak, which was attributable to wax crystallization. From the three figures, their wax appearance temperature (WAT) and their peak temperature of wax crystallization (WPT) could be obtained. The WAT values of the three samples were basically equal, which was 46.1, 46.3, and 46.9 °C, separately. However, their WPT values were different, which were, respectively, 42.0, 32.6, and 33.2 °C. The WPT is the temperature at which the wax crystallization rate reaches its maximum. The WPT of the deasphaltened and deresinated crude oil and the deasphaltened crude oil were markedly lower than that of the pure wax. According to the difference of WPT, it was concluded that the liquid oil retarded the wax crystallization. Figures 6d and 6e gave the DSC thermogram of the virgin crude oil and the crude oil beneficiated with 400 ppm PPD. Each curve also had two exothermic peaks. The first exothermic peak temperature of the virgin crude oil was 56.9 °C. It was obviously lower than that of the deresinated crude oil (63.7 °C; see Figure 6f). This exothermic peak was due to the precipitation of asphaltene. Some scholars27−30 thought that the exothermic heat effect was attributed to the interactions between the n-alkanes and the asphaltene aliphatic chains. However, in our experiment, we thought that the interactions between the resin and the asphaltene made the precipitation of

Figure 7. Entire viscosity−temperature comparison curves between undoped and doped crude oil.

3.4. Differential Scanning Calorimetry (DSC). Figures 6a, 6b, and 6c respectively gave the DSC thermograms of the temperature-reducing process of the pure wax, the deasphalt11609



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Figure 8. Polarized microscopy images of (a) virgin crude oil and (b) crude oil beneficiated with PPD (PPD concentration = 400 ppm).

asphaltene shift to lower temperature, through comparison of Figure 6d with Figure 6f. The resin could form asphaltene− resin micellar associations with the asphaltene. Studies31 have also shown that the flocculated asphaltenes provide nucleation sites for the crystallization of waxes. More precisely, the asphaltene−resin micellar association worked as nucleation sites in the first stage of crystallization process. It was the inherent nucleator for wax crystals in the crude oil. They promoted steric interference among the paraffin molecules, which caused the formation of a weaker and less-stable wax crystal network.32 In addition, because large numbers of fluid oil were wrapped in the network structure, the amount of liquid oil which could disperse the wax in the crude oil relatively decreased. As a result, the crude oil tended to lose fluidity. As shown in Table 3, the pour point of the deasphaltened and deresinated crude oil was 4 °C less than that of the crude oil. When the asphaltene and the resin were separated from the oil, the influence of the association structure in wax crystallization was eliminated. The quantity of liquid oil wrapped decreased. Moreover, the quantity of liquid oil relatively increased. Therefore, the fluidity of the crude oil was improved and the pour point of the crude oil was depressed. The first exothermic peak temperature of the doped crude oil was 49.8 °C in Figure 6e. After a PPD was added to the crude oil, it reduced the precipitation temperature of the asphaltene further. This was in agreement with the results obtained by Garcia.́ 33 PPD could inhibit precipitation and flocculation of asphaltene. The WAT and WPT values of the undoped crude oil were 46.9 and 32.4 °C, respectively, and those of doped crude oil were 46.7 and 25.9 °C, respectively. Although the PPD did not change the WAT value of the crude oil, it significantly decreased the WPT value. In addition, the enthalpy change of wax crystallization in the crude oil was measured through the DSC curve of the undoped and doped crude oil. The crystallization enthalpy was used for the determination of the amount of precipitated wax versus temperature.34 That of the undoped crude oil is 41.80 J/g and that of the doped crude oil is 38.94 J/g. This observation means that the PPD has little effect on the total amount of wax that would completely precipitate.35

Combined with the IR spectroscopy analysis results, it was concluded that PPD, asphaltene, and resin formed a new agglomerate structure. It provided nucleation sites for wax crystallization instead of an asphaltene−resin association structure. The new agglomerate structures of asphaltene− PPD−resin became development centers of wax crystal. It became an efficient nucleator of the wax crystal in the additivetreated crude oil. The agglomerate structure of asphaltene− PPD−resin could change the process of wax crystallization in the crude oil. In addition, it was difficult to form big wax blocks. So the pour point of the crude oil is greatly depressed. On the other hand, Table 3 showed that PPD had little effect on the deasphaltened and deresinated crude oil. It also proved our conclusion. 3.5. Rheological Studies. A PPD dosage of 400 ppm was inserted into additive-treated crude oil. From Figure 7, it could be seen that, when temperatures exceeded ∼55.0 °C, the viscosity of the crude oil beneficiated with and without PPD were, respectively, lower and almost the same. With the decrease of the temperature, the viscosity of the crude oil increased gradually. At temperatures below 46.9 °C (WAT), the viscosity of the crude oil started to increase quickly. However, at temperatures below 46.7 °C (WAT) and above 38.0 °C, the viscosity of the crude oil beneficiated with PPD increases less. When the temperature decreased to 38.0 °C, the viscosity of the crude oil added PPD rose rapidly. This indicated that the addition of a PPD could obviously improve the low-temperature flow properties of crude oil. 3.6. Comparison of Structures of Wax Crystals. Figure 8a shows that the structure of the wax crystal is not compact and there is relatively more liquid oil (black area). While in Figure 8b, the structure of the wax crystal is compact and there is relatively less liquid oil. It suggested that the original association structures were changed by the action of PPD with asphaltene and resin. The PPD made the structure of the wax crystal compact by changing the process of wax crystallization; thus, the quantity of liquid oil wrapped decreased. Subsequently, the quantity of liquid oil that could disperse the wax crystal relatively increased. The wax crystal had difficulty in forming a three-dimensional network structure, and the low11610



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temperature flow properties of the treated oil was improved. Thus, the pour point of the doped crude oil was reduced.

(13) Murgich, J. Intermolecular forces in aggregates of asphaltenes and resins. Pet. Sci. Technol. 2002, 20 (9−10), 983−997. (14) LeÓ n, O.; Rogel, E.; Espidel, J.; Torres, G. Asphaltenes: structural characterization, self-association, and stability behavior. Energy Fuels 2000, 14 (1), 6−10. (15) Suryanarayana, I.; Rao, K. V.; Duttachaudhury, S. R.; Subrahmanyam, B.; Saikia, B. K. Infrared spectroscopic studies on the interactions of pour point depressants with asphaltene, resin and wax fractions of Bombay high crude. Fuel 1990, 69 (12), 1546−1551. (16) 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 (11), 1163−1167. (17) Kriz, P.; Andersen, S. I. Effect of asphaltenes on crude oil wax crystallization. Energy Fuels 2005, 19 (3), 948−953. (18) Chen, W. H.; Zhao, Z. C.; Yin, C. Y. The interaction of waxes with pour point depressants. Fuel 2010, 89 (5), 1127−1132. (19) Yi, S. Z.; Zhang, J. J. Relationship between waxy crude oil composition and change in the morphology and structure of wax crystals induced by pour-point-depressant beneficiation. Energy Fuels 2011, 25 (4), 1686−1696. (20) Radulescu, A.; Schwahn, D.; Stellbrink, J.; Kentzinger, E.; Heiderich, M.; Richter, D. Wax crystallization from solution in hierarchical morphology templated by random poly(ethylene-cobutene) self-assemblies. Macromolecules 2006, 39 (18), 6142−6151. (21) Li, L.; Guo, X. H.; Adamson, D. H.; Pethica, B. A.; Huang, J. S.; Prud’homme, R. K. Flow improvement of waxy oils by modulating long-chain paraffin crystallization with comb polymers: An observation by X-ray diffraction. Ind. Eng. Chem. Res. 2011, 50 (1), 316−321. (22) 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 (9), 997− 1004. (23) Deshmukh, S.; Bharambe, D. P. Synthesis of polymeric pour point depressants for Nada crude oil (Gujarat, India) and its impact on oil rheology. Fuel Process. Technol. 2008, 89 (3), 227−233. (24) Cosultchi, A.; Bosch, P.; Lara, V. Small-angle X-ray scattering study of oil- and deposit-asphaltene solutions. Colloid Polym. Sci. 2003, 281 (4), 325−330. (25) Ortega-Rodríguez, A.; Cruz, S. A.; Gil-Villegas, A.; GuevaraRodríguez, F.; Lira-Galeana, C. Molecular view of the asphaltene aggregation behavior in asphaltene-resin mixtures. Energy Fuels 2003, 17 (4), 1100−1108. (26) Malla, P.; Marion, D.; Ivanova, E. V.; Muchall, H. M. The hydrogen bonding network in the dimer of syn-N-phenyl-N′sulfinylhydrazine, PhNHNSO. J. Mol. Struct. 2010, 979 (1−3), 101− 107. (27) Tinsley, J. F.; Jahnke, J. P.; Dettman, H. D.; Prud’home, R. K. Waxy gels with asphaltenes, 1: Characterization of precipitation, gelation, yield stress, and morphology. Energy Fuels 2009, 23 (4), 2056−2064. (28) Mahmoud, R.; Gierycz, P.; Solimando, R.; Rogalski, M. Calorimetric probing of n-alkane−petroleum asphaltene interactions. Energy Fuels 2005, 19 (6), 2474−2479. (29) Alcazar-Vara, L. A.; Buenrostro-Gonzalez, E. Experimental study of the influence of solvent and asphaltenes on liquid−solid phase behavior of paraffinic model systems by using DSC and FT-IR techniques. J. Therm. Anal. Calorim. 2011, 107, 1321−1329 (DOI: 10.1007/s10973-011-1592-8). (30) Stachowiak, C.; Viguie, J.-R.; Grolier, J.-P.; Rogalski, M. Effect of n-alkanes on asphaltene structuring in petroleum oils. Langmuir 2005, 21 (11), 4824−4829. (31) Alcázar-Vara, L. A.; García-Martínez, J. A.; Buenrostro-Gonzalez, E. Effect of asphaltenes on equilibrium and rheological properties of waxy model systems. Fuel 2012, 93 (3), 200−212. (32) Ortega-Rodriguez, A.; Duda, Y.; Guevara-Rodriguez, F.; LiraGaleana, C. Stability and aggregation of asphaltenes in asphalteneresin-solvent mixtures. Energy Fuels 2004, 189 (3), 674−681.

4. CONCLUSIONS The additive MAVA was synthesized, and its structure was confirmed by Fourier transform infrared (FTIR) spectroscopy and 1H nuclear magnetic resonance (1H NMR) spectroscopy. When the prepared pour point depressant (PPD) was added in Shengli high-pour-point oil at a dosage of 400 ppm, the pour point of the crude oil was depressed 11 °C. The interaction between asphaltene and resin had an obvious impact on the process of wax crystallization in the crude oil. The PPD, asphaltene, and resin formed the new agglomerates. The agglomerates became the efficient nucleator of the wax crystal in the additive-treated crude oil. They changed the process of wax crystallization and greatly depressed the pour point of the crude oil.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-532-85955589. Fax: +86-532-85950518. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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