Synthesis and Evaluation of Grafted EVAL as Pour Point Depressant

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Synthesis and Evaluation of Grafted EVAL as Pour Point Depressant for Waxy Crude Oil yongwen Ren, Long Fang, Zhaojun Chen, Hui Du, and Xiaodong Zhang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b01169 • Publication Date (Web): 08 Jun 2018 Downloaded from http://pubs.acs.org on June 8, 2018

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Industrial & Engineering Chemistry Research

Synthesis and Evaluation of Grafted EVAL as Pour Point Depressant for Waxy Crude Oil Yongwen Ren,‡ Long Fang,‡ Zhaojun Chen, Hui Du, and Xiaodong Zhang* College of Chemistry and Chemical Engineering, Qingdao University, Qingdao 266071, China ABSTRACT Alcoholized ethylene–vinyl acetate copolymer (EVAL) was chemically modified by grafting n-alkyl acrylates with different alkyl chain lengths. The grafted EVAL was characterized through Fourier transform infrared (FTIR) spectroscopy, 1H and 13

C nuclear magnetic resonance (NMR) spectroscopy, and element analysis. The

effect of grafted EVAL on wax crystallization process of crude oil was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results showed that the length of alkyl side-chain in grafted EVAL largely influenced the efficiency of grafted EVAL. Grafted EVAL with side-chain length of C16 could reduce the pour point of Shengli (SL) crude oil by 11 °C, and that with side-chain length of C18 could reduce the pour point of Jianghan (JH) crude oil by 14.5 °C. The introduction of alkyl side-chain could improve wax solubility and promote grafted EVAL to adsorb and cocrystallize with wax molecules, which obviously decreased the wax precipitation amount and changed the wax crystallization process. 1. INTRODUCTION Wax separated from crude oil is the mixture of hydrocarbon chains mainly in the

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range of C20 to C40.1-3 Wax can crystallize as an interlocking network structure at room temperature, thereby leading to the higher pour point and the weaker flowability of crude oil.4-5 Pour point depressant (PPD) which is comprised of polar moiety and nonpolar main chain, has been widely employed to improve the low-temperature flowability of crude oil.6-8 The polar moiety can decrease wax crystal size and provide electrostatic repulsion force to wax crystals, whereas the nonpolar main chain is responsible for adsorbing and cocrystallizing with wax molecules.9-11 In addition, it has been recognized that the introduction of alkyl side-chains can further enhance the effectiveness of PPD in reducing the pour point of crude oil.12-14 Ren et al.15 found that the short alkyl side-chains could largely improve the efficacy of poly (maleic anhydride–methacrylate) by cocrystallizing with wax molecules. Xu et al.16 revealed that the long alkyl side-chains of poly (maleic alkylamide–α–octadecene) could stabilize crude oil by offering steric effects to wax crystals. Particularly, it should be mentioned that the alkyl side-chain length is a key factor to influencing PPD effectiveness, and the length should match with the average carbon number (Cav) of wax.17-19 Some literatures20-21 proposed that the alkyl side-chain length should be a little lower than the wax Cav based on experimental results and theoretical calculations. But other studies15,22 confirmed that, when the side-chain length of PPD was same with the wax Cav, PPD was more efficient and obviously inhibited the wax crystallization process. Therefore, it can be concluded that the correlation between the most effective side-chain length of PPD and average carbon number of wax is still not


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clear. Previous studies10 revealed that alcoholized ethylene–vinyl acetate copolymer (EVAL) was more efficient than EVA to promote the flowability of crude oil. In this work, EVAL was further modified by grafting n-alkyl acrylates with different alkyl chain lengths. The performances of grafted EVALs in reducing the pour points of Shengli (SL) and Jianghan (JH) crude oils were evaluated. Additionally, an attempt had been made to study the relation between alkyl side-chain length of grafted EVAL and Cav of wax, by means of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). 2. EXPERIMENTAL SECTION 2.1. Materials. The chemicals, n-heptane, toluene, methanol, lauryl acrylate, tetradecyl acrylate, hexadecyl acrylate, octadecyl acrylate, eicosyl acrylate, and docosyl acrylate were purchased from Sinopharm Chemical Reagent Co., Ltd. The alcoholized ethylene-vinyl acetate copolymer (EVAL) with alcoholysis degree of 90.94 mol % was obtained from our previous studies.10 The Shengli (SL) and Jianghan (JH) crude oils were provided by SL and JH oil fields of China, respectively. Before testing, the crude oil samples were firstly heated to 90 °C for 4 h to eliminate the thermal and shearing history.23 2.2. Analysis of Crude Oil Composition. The densities of crude oils were measured by the standard ISO 3675-1998.24 Asphaltene was extracted on the base of IP Procedure No.143 using n-heptane as a precipitant.25 Resin was separated according to the literature.26 Wax was isolated in accordance with UOP Method 46-85.27 The



carbon number distribution of wax was analyzed according to ASTM D-544228 by an Agilent 6890 gas chromatograph (Agilent Technologies, Santa Clara, CA), fitted with an Agilent DB-5 fused silica capillary column (30 m × 0.25 mm × 0.25 µm). Based on the method, the mixed solution of nC16, nC20, nC26 nC28, nC30 and cyclohexane was used as the standard sample, and the nC16 was employed as the internal standard for the determination. The operating conditions were as follows: The column was procedurally raised from 50 °C to 300 °C at a heating rate of 6 °C/min, the injector and detector temperatures of 320 °C and 340 °C, with helium as a carrier gas at a constant flow of 1.5 mL/min, and the injection volume was 1 µL.29 The average carbon number (Cav) of waxes were calculated according to the literature as follows:30 max

Cav = (1) =min

where n is the carbon number, and φn represents the mass fraction of components of wax (wt %). 2.3. Synthesis of the Grafted EVALs. Grafted EVALs were prepared by free-radical polymerization of EVAL with n-alkyl acrylates under a nitrogen atmosphere, using dibenzoyl peroxide (BPO) as an initiator and toluene as a solvent. Firstly, EVAL and n-alkyl acrylates (mass ratio = 2:1) were added to a 250-mL four-neck round-bottom flask and were mixed at 60 °C. BPO was added after the reactants completely dissolved. Then the reaction mixture was heated to 90 °C gradually and maintained for 3 h with continuous stirring. The purified grafted EVALs were obtained by adding moderate methanol to the reaction mixture, filtering, washing with methanol, and vacuum drying at 60 °C. The reaction equation is presented in Scheme 1. According


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to the carbon number of alkyl chain in n-alkyl acrylate, corresponding grafted EVALs were named EVAL-g-12, EVAL-g-14, EVAL-g-16, EVAL-g-18, EVAL-g-20, and EVAL-g-22, respectively. The pour point depressants (PPDs) for waxy crude oil were obtained by dissolving them in toluene with a solute content of 10 wt %.

Scheme 1. Synthetic routine for grafted EVALs. 2.4. Characterization of Grafted EVALs. The structure of grafted EVAL was characterized with Fourier transform infrared (FTIR) spectroscopy using Thermo Nicolet IR spectrophotometer model IR 460, 1H nuclear magnetic resonance (NMR) spectroscopy through a Varian-300A spectrometer, and

13

C NMR spectroscopy by a

Bruker Avance III HD 400MHz spectrometer. The carbon and hydrogen contents of EVAL and grafted EVALs were obtained by an element analyzer (Vario Macro cube, Elementar Corp., Germany), and the oxygen contents were generated by subtraction method. The grafting yield (G) of grafted EVAL defined as the mass fraction of graft monomer in grafted EVAL was calculated using the equation:31 M WO2 WO2 G (wt %) = × 100 % (2) M2 where M1 and M2 are the relative molecular mass of graft monomer and oxygen, WO2 and WO2 denote the oxygen contents in grafted EVAL and EVAL, respectively. 2.5. Measurement of Pour Point. The pour points of treated and untreated crude oil



were determined by ASTM Standard D-97.25 All the determinations were repeated for three times, and the pour point values were averaged. Based on the measured results, the standard error was confirmed to be within 1 °C. 2.6. Viscosity Measurement. The viscosities of the oil samples were performed according to SY/T 0520-2008, through the 40 mm diameter 2° cone and plate geometry of a HAAKE VT550 viscometer, fitted with a HAAKE C25P cooling bath.32 The oil sample (20 mL) was preheated to 90 °C to make the wax crystal melt completely, and then cooled to the test temperature and equilibrated for 5 min, at a shear rate of 60 rpm and a cooling rate of 5 °C/min. All the viscosity values were measured three times and were averaged to ensure the reproducibility. 2.7. Differential Scanning Calorimetry (DSC). The DSC 822 (Swiss METTLER TOLEDO Ltd.) was employed to investigate the crystallization process of treated and untreated crude oil. Each sample was initially heated to 90 °C for 5 min, and then cooled to 0 °C at a cooling rate of 5 °C/min. In order to ensure the reproducibility of the determination, all DSC curves were performed in duplicate. Meanwhile, the crystallization enthalpy of wax was calculated according to SY/T 0545-2012 by integrating the wax exothermic peak.33 2.8. Polarized Optical Microscopy (POM). A POM (Nikon OPTIPHOT2-POL, Nikon Corp., Japan) equipped with an automatic camera and a Linkam PE60 Peltier thermal stage (Linkam Scientific Instruments Ltd., U.K.) was used to record the microscopy images of oil samples during cooling process. All samples were preheated to 90 °C for 5 min, and then cooled to the test temperature with a cooling rate of


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5 °C/min and equilibrated for 5 min.10 Each micrograph was investigated in duplicate to guarantee the reproducibility.34 3. RESULTS AND DISCUSSION 3.1 Physical Properties and Component Analysis of Crude Oil Samples. The physical characteristics and compositions of Shengli (SL) and Jianghan (JH) crude oils are listed in Table 1. It was found that each crude oil contained less asphaltenes, whereas the contents of resins and liquid oils were relatively higher. Furthermore, the wax contents and the pour point of SL crude oil were higher than that of JH crude oil. Table 1. Physical Characteristics and Composition of SL and JH Crude Oil crude oil

pour point (°C)

viscosity @ 50 °C (mPa·s)

density @ 20 °C (g·cm-3)

asphaltene

resin

wax

liquid oil

SL

43.0

430.0

0.890

2.69

31.37

13.09

52.75

JH

34.0

147.0

0.802

1.65

46.06

7.87

44.42

component of the crude oil (wt %)

The carbon number distributions of wax extracted from SL and JH crude oils are shown in Figure 1. It was observed that the wax carbon numbers of SL and JH crude oils were in the range of C17 to C32 and C18 to C38, respectively. Furthermore, the average carbon number (Cav) of wax extracted from SL and JH crude oils were 24.3 and 28.3, respectively.

Figure 1. Carbon number distribution of wax extracted from SL and JH crude oils.



3.2. Characterization of Grafted EVALs. The infrared spectra of EVAL and EVAL-g-18 were given in Figure 2. It could been found that these two spectra were almost same, which might be because the lower grafting yield of EVAL-g-18.

Figure 2. Infrared spectra of EVAL and EVAL-g-18. The 1H NMR spectra of EVAL and EVAL-g-18 and their assignments are given in Figure 3. The 1H NMR spectra of grafted EVALs are almost the same, thus there takes EVAL-g-18 for an example. It could be seen that the peak area ratio of the H in the methine (δ = 4.85) to the H in hydroxyl (δ = 3.58 and δ = 3.67) was 5.34 for EVAL (see Figure 3a), whereas it was 4.82 for EVAL-g-18 (see Figure 3b). The results indicated that a part of octadecyl acrylates were grafted onto EVAL by replacing the H atoms in methine.

Figure 3. 1H NMR spectra of (a) EVAL and (b) EVAL-g-18.


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The 13C NMR spectra of EVAL and EVAL-g-18 and their assignments are given in Figure 4. It could be observed from Figure 4b that the chemical shift of tertiary carbon atom linked to the hydroxy group appeared at 75.21 ppm. Futhermore, the chemical shift of carbon atoms in octadecyl acrylate also could be observed. The results further confirmed that the octadecyl acrylate was grafted onto EVAL by replacing the H atoms in the methine.

Figure 4. 13C NMR spectra of (a) EVAL and (b) EVAL-g-18. The contents of carbon (C), hydrogen (H), and oxygen (O) and the grafting yields of grafted EVALs are listed in Table 2. It was found that, for the same kind of graft monomer, the grafting yield of grafted EVAL was improved with the increase of BPO amount. Additionally, under the same BPO amount, the grafting yield of grafted



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EVAL was decreased with the increase of alkyl chain length of n-alkyl acrylate. Table 2. Element Compositions and Grafting Yields of Grafted EVALs PPD

BPO (wt %) H [wt %] C [wt %] O [wt %]

EVAL EVAL-g-12

EVAL-g-14

EVAL-g-16

EVAL-g-18

EVAL-g-20

EVAL-g-22

1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3

13.330 13.148 13.037 12.972 13.175 13.147 13.121 13.167 13.162 13.066 13.168 13.125 13.075 13.171 13.119 13.073 13.133 13.118 13.101

80.257 79.803 79.710 79.615 79.851 79.710 79.577 79.917 79.792 79.722 79.968 79.891 79.801 80.017 79.949 79.869 80.096 80.001 79.897

6.413 7.049 7.253 7.413 6.974 7.143 7.302 6.916 7.046 7.212 6.864 6.984 7.124 6.812 6.932 7.058 6.771 6.881 7.002

grafting yield (wt %) 9.55 12.62 15.03 9.41 12.25 14.92 9.32 11.73 14.81 9.15 11.58 14.42 8.79 11.44 14.22 8.51 11.13 14.01

3.3. Performances of Grafted EVALs. The influences of EVAL and grafted EVALs on pour points of SL and JH crude oils are compared in Figure 5. For SL crude oil (see Figure 5a), under the same alkyl chain length of n-alkyl acrylate, grafted EVAL showed better performance in reducing pour point when the BPO amount was 2 wt %. The pour point depression of crude oil treated with EVAL-g-16 (BPO amount = 2 wt %) was 11 °C, which was 4 °C larger than that of crude oil treated with EVAL (7 °C). For JH crude oil (see Figure 5b), the optimal BPO amount also was 2 wt %, whereas the optimal side-chain length of grafted EVAL was C18. The pour point depression of crude oil treated with EVAL-g-18 (BPO amount = 2 wt %) was 14.5 °C, ACS Paragon Plus Environment

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which was 3.5 °C larger than that of crude oil treated with EVAL (11 °C). Therefore, it could be concluded that grafted EVAL with side-chain lengths of C16 and C18 were more effective for SL crude oil (wax Cav = 24.3) and JH crude oil (wax Cav = 28.3), respectively.

Figure 5. Performances of EVAL and grafted EVALs for (a) SL crude oil and (b) JH crude oil (additive dosage = 1000 ppm). The effects of EVAL-g-16 and EVAL-g-18 dosages on decreasing the pour point of SL and JH crude oils are illustrated in Figure 6. The pour point depressions of SL and JH crude oils were improved obviously with the increase of the dosage. But when the dosage exceeded 1000 ppm, the pour point depression decreased a little for SL crude oil, and that maintained unchanged for JH crude oil. Therefore, 1000 ppm was



the optimal dosage both for SL and JH crude oils in terms of economy and efficiency, and was adopted in all following experiments.

Figure 6. Effects of EVAL-g-16 and EVAL-g-18 (2 wt % BPO) dosages on pour points of SL and JH crude oils. 3.4. Viscosities. The viscosities of treated and untreated SL and JH crude oils during the cooling process are given in Figure 7. It could be seen from Figure 7a that the viscosities of all samples increased gradually with the decrease of temperature. For SL crude oil, at the same temperature, the viscosity value of crude oil treated with EVAL-g-16 was the lowest among all crude oil samples. Moreover, EVAL-g-16 also was more efficient in depressing the temperature of abnormal point that the viscosity increased dramatically. But for JH crude oil, EVAL-g-18 showed best performance in reducing viscosity and abnormal point temperature (see Figure 7b).


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Figure 7. Viscosity–temperature curves of (a) SL crude oil and (b) JH crude oil untreated and treated with EVAL and grafted EVALs (2 wt % BPO). 3.5. Studies by Differential Scanning Calorimetry (DSC). Figure 8 gives DSC curves of SL and JH crude oils untreated and treated with EVAL and grafted EVALs during the cooling process. It was found from Figure 8a that SL crude oil exhibited two exothermic peaks, attributed to the precipitation of asphaltene–resin agglomeration (ARA) and the wax crystallization, respectively.27 Meanwhile, it also could be observed that the agglomeration appearance temperature (AAT) in crude oil treated with EVAL was about 2 °C lower than that in crude oil. This was because EVAL could interact with ARA to form a new agglomeration structure (the new nucleators of wax crystal), which could change the wax crystallization process.10,25,27



Furthermore, as given in Figure 8b, the AATs in crude oils treated with grafted EVALs were further reduced by about 1 °C compared with that in crude oil treated with EVAL. This indicated that the alkyl side-chains in grafted EVALs could promote the newly formed agglomerations to dissolve in waxes and liquid oils due to Van der Waals forces.35-37 In addition, it still could be observed from Figure 8a that the wax appearance temperature (WAT) of crude oil was decreased by about 2 °C after the treatment of EVAL. Moreover, the WATs of crude oils treated with grafted EVALs were further decreased compared with that of crude oil treated with EVAL (see Figure 8b). The results indicated that grafted EVALs were more efficient than EVAL to alter the wax crystallization process. Similarly, for JH crude oil (see Figure 8c,d), it also could be found that grafted EVALs had better performance than EVAL in decreasing the AAT and the WAT.

Figure 8. DSC curves of SL and JH crude oil untreated and treated with EVAL and grafted EVALs (2 wt % BPO).


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The wax crystallization enthalpy (△Hwc) can be used to determine the wax precipitation amount.33 △Hwc values of SL and JH crude oils untreated and treated with EVAL as well as grafted EVALs are presented in Figure 9. It was found that all the △Hwc values of SL and JH crude oils were reduced after the treatment with grafted EVALs. Furthermore, for SL crude oil, the lowest △Hwc value was observed after the EVAL-g-16 treating, whereas for JH crude oil, it could be obtained after the EVAL-g-18 treating. The results confirmed that grafted EVALs could improve wax solubility and decrease wax precipitation amount. This was because the existences of alkyl side-chains with proper length, could promote the intermolecular intermiscibility between grafted EVALs and wax molecules.38-39

Figure 9.Wax crystallization enthalpy (△Hwc) of untreated and treated crude oil samples. 3.6. Process of Wax Crystallization. Polarized optical microscopy (POM) images of SL crude oil untreated and treated with EVAL as well as grafted EVALs during the cooling process are exhibited in Figure 10. As shown in Figure 10a1, plenty of irregular wax crystals formed at 45 °C in crude oil, thus a lot of liquid oils were wrapped by the irregular wax crystals. But for crude oils treated with EVAL and



EVAL-g-16, fewer wax crystals appeared at the same temperature of 45 °C (see Figure 10a2,a3). This revealed that EVAL-g-16 could improve wax solubility, which was well in line with the previous DSC studies. Additionally, it also could be seen from Figure 10a2,a3 that the wax crystal shapes were more regular (spherical crystal). Furthermore, the wax crystals formed in crude oil treated with EVAL-g-16 were much bigger than that formed in crude oil treated with EVAL, indicated that EVAL-g-16 could adsorb more wax molecules due to the existences of alkyl side-chains. When the temperature dropped to the pour point of crude oil (43 °C), the wax crystals in crude oil formed a compact and strong network structure (see Figure 10b1). But for crude oil treated with EVAL (see Figure 10b2), the network structure was much looser at its pour point temperature (36 °C), which was in accordance with our previous studies.10 However, as given in Figure 10b3, relatively few wax crystals appeared at 36 °C in crude oil treated with EVAL-g-16, which further proved that

Figure 10. Polarized optical microscopy images of SL crude oil untreated and treated with EVAL and grafted EVALs (2 wt % BPO).


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EVAL-g-16 could improve wax solubility and change the wax crystallization process. From this point of view, it was one of the reason that EVAL-g-16 could reduce the pour point of crude oil to a great extent. Additionally, the network structures formed in crude oils treated with EVAL-g-14, EVAL-g-16, and EVAL-g-18 were thicker than that formed in crude oil treated with EVAL at corresponding pour point temperatures, and that formed in crude oil treated with EVAL-g-16 was thickest (see Figure 10c1,c2,c3). It was recognized that the new formed agglomeration with alkyl side-chain, contributed to adsorbing more wax molecules and cocrystallizing with wax molecules. Correspondingly, there existed fewer irregular wax crystals formed by wax itself, which tended to wrap a large quantity of liquid oils.27,38 Therefore, more liquid oils were released in crude oil treated with EVAL-g-16. This was another reason that EVAL-g-16 could evidently decrease the pour point and promote the low-temperature flowability of crude oil. The wax crystallization processes of treated and untreated crude oil were further illustrated in Figure 11. It had been well known that the crude oil at higher temperature was a more stable disperse system, which was based on the micelle of asphaltenes solvated by resins (asphaltene-resin agglomeration (ARA)) as the dispersed phase, and waxes, part of resins as well as liquid oils as the dispersed medium.10,27,40 The ARA usually worked as the inherent nucleator of wax crystal in crude oil.10 However, the grafted EVAL with proper alkyl side-chain could interact with ARA to form a new agglomeration structure (the new nucleator of wax crystal). The new formed nucleator could adsorb more wax molecules and cocrystallize with



wax molecules, which led to forming plenty of regular wax crystals. Therefore, the liquid oils were released, and the pour point was also reduced.

Figure 11. Illustration for wax crystallization process of treated and untreated crude oil. 4. CONCLUSIONS A series of grafted EVALs with various alkyl side-chain lengths were prepared by grafting n-alkyl acrylates and characterized with Fourier transform infrared (FTIR) spectroscopy, 1H and

13

C nuclear magnetic resonance (NMR) spectroscopy, and

element analysis. The alkyl side-chain length was a significant factor affecting the efficacy of grafted EVAL in reducing the pour point of crude oil. The side-chain lengths of C16 and C18 in grafted EVALs were optimal towards Shengli (SL) and Jianghan (JH) crude oils respectively, which reduced the pour points of corresponding crude oil by 11 °C and 14.5 °C. The introduction of the alkyl side-chain contributed to improving wax solubility and prompting grafted EVAL to adsorb and cocrystallize with wax molecules. As a result, grafted EVAL obviously decreased the wax precipitation amount and changed the wax crystallization process of crude oil. AUTHOR INFORMATION Corresponding Author


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*E-mail:

[email protected].

Tel.:

+86-532-85955589.

Fax:

+86-532-85950518. Author Contributions ‡ These authors contributed equally to this work. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS The work is financially supported by the Project of Shandong Province Higher Educational Science and Technology Program (J15LC19). REFERENCES (1) Huang, H.; Larter, S. R.; Love, G. D., Analysis of wax hydrocarbons in petroleum source rocks from the Damintun depression, eastern China, using high temperature gas chromatography. Org. Geochem. 2003, 34, 1673–1687. (2) Jung, K. M.; Chun, B. H.; Park, S. H.; Lee, C. H.; Kim, S. H., Synthesis of methacrylate copolymers and their effects as pour point depressants for lubricant oil. J. Appl. Polym. Sci. 2015, 120, 2579–2586. (3) Soldi, R. A.; Oliveira, A. R. S.; Barbosa, R. V.; César-Oliveira, M. A. F., Polymethacrylates: pour point depressants in diesel oil. Eur. Polym. J. 2007, 43, 3671–3678. (4) Wang, F.; Li, P.; Mei, Z.; Mi, J., Auto- and Forced-Ignition temperatures of diffusion flames obtained through the steady RANS modeling. Energy Fuels 2013, 28, 666–677.



(5) Nassar, N. N.; Betancur, S.; Acevedo, S.; Franco, C. A.; Cortés, F. B., Development of a population balance model to describe the influence of shear and nanoparticles on the aggregation and fragmentation of asphaltene aggregates. Ind. Eng. Chem. Res. 2015, 54, 8201–8211. (6) Zhao, Z.; Xue, Y.; Xu, G.; Zhou, J.; Lian, X.; Liu, P.; Chen, D.; Han, S.; Lin, H., Effect of the nano-hybrid pour point depressants on the cold flow properties of diesel fuel. Fuel 2017, 193, 65–71. (7) He, C.; Ding, Y.; Chen, J.; Wang, F.; Gao, C.; Zhang, S.; Yang, M., Influence of the nano-hybrid pour point depressant on flow properties of waxy crude oil. Fuel 2016, 167, 40–48. (8) Cao, K.; Zhu, Q.; Wei, X.; Zhen, Y., Study on the influence of the imidization degree of poly (styrene-co-octadecyl maleimide) as a flow improver in waxy crude oils with asphaltenes. Energy Fuels 2015, 29, 993−1000. (9) Zhang, J.; Zhang, M.; Wan, J.; Li, W., Theoretical study of the prohibited mechanism for ethylene/vinyl acetate co-polymers to the wax crystal growth. J. Phys. Chem. B 2008, 112, 36–43. (10) Ren, Y.; Chen, Z.; Du, H.; Fang, L.; Zhang, X., Preparation and evaluation of modified ethylene-vinyl acetate copolymer as pour point depressant and flow improver for Jianghan crude oil. Ind. Eng. Chem. Res. 2017, 56, 11161–11166. (11) Wu, C.; Zhang, J. L.; Li, W.; Wu, N., Molecular dynamics simulation guiding the improvement of EVA-type pour point depressant. Fuel 2005, 84, 2039–2047. (12) Adeyanju, O. A.; Oyekunle, L. O., Influence of long chain acrylate ester


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For Table of Contents Only


Synthesis and Evaluation of Grafted EVAL as Pour Point Depressant

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