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Study on the Influence of Imidization Degree of Poly (styrene-co-octadecyl maleimide) as Flow Improver in the Waxy Crude Oils with Asphaltenes Kun Cao, Qing-jun Zhu, Xiang-xia Wei, and Zhen Yao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/ef501281u • Publication Date (Web): 05 Jan 2015 Downloaded from http://pubs.acs.org on January 7, 2015

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Study on the Influence of Imidization Degree of Poly(styrene-co-octadecyl maleimide) as Flow Improver in the Waxy Crude Oils with Asphaltenes Kun Cao a, b, Qing-jun Zhu b, Xiang-xia Wei b, Zhen Yao b * a

State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, CHINA b

Institute of Polymerization and Polymer Engineering, Department of Chemical Engineering, Zhejiang University, Hangzhou 310027, CHINA

*

Corresponding Author’s E-mail: [email protected]

Abstract: A series of poly(styrene-co-octadecyl maleimide) with various imidization degrees as the flow improvers for the model waxy oils with asphaltenes were prepared through the reaction between octadecyl amine and poly(styrene-co-maleic anhydride) (SMA) with random and alterative structure. With a small amount of the designed flow improvers, the wax crystals became fewer, smaller and more dispersed in the oils, asphaltene particles were better dispersed, and the crystallization temperature and the yield stress were reduced considerably. Moreover, it had been found that the performance of the resultant flow improvers for the bituminous paraffin oils is significantly affected by the imidization degree and maleic anhydride content, which are evaluated in terms of the polarity. Keywords: poly(styrene-co-octadecyl maleimide); poly(styrene-co-maleic anhydride); imidization degree; waxy oil with asphaltenes; crystallization; rheological behavior

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1. Introduction The waxes and asphaltenes with high molecular weight in the crude oils are detrimental to the transportation and processing due to their solubility decreasing drastically with a depress in temperature, forming the stable crystals and particles.1 This problem is very well-known within the petroleum industry and becomes increasingly worse, with the ongoing trend to deep water developments and the steady increase in global energy demand. Moreover, wax can crystallize through pipelines or storage, resulting an increase in oil viscosity by several orders of magnitude and causing flow assurance risk in crude oil production. At present, mechanical, thermal and chemical treatments, especially pour point depressant (PPD) treatment,2-8 are widely used in the transportation of waxy crude oils. The pour point depressants (alternatively known as flow improvers or crystal modifiers)9 are polymeric compounds constituted by a hydrocarbon chain which provides the interaction between the additive and paraffin.10 On the other hand, the asphaltenes are the heaviest, most aromatic components of crude oils, commonly defined on the basis of solubility as a complex mixture of molecular species that can be soluble in aromatic solvents such as toluene or benzene but insoluble in hydrocarbon solvents like pentane and heptane.11 The tendency to precipitate from the change of pressure and temperature during oil production, transportation, storage, and the refining causes heavy losses to the oil industry all around the world. Therefore, it is desirable to prevent or reduce the deposition of asphaltenes, and the use of chemical additives has been highly recommended in recent


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years. Chang and Fogler12 used alkyl benzene-derived amphiphiles as the asphaltene stabilizers and concluded that the asphaltene stabilization was primarily controlled by the polarity and the length of alkyl tail. Additionally, they13 investigated the mechanism of stabilizing asphaltenes with a conclusion that the amphiphiles such as p-alkylphenol amphiphiles and p-alkylbenzenesulfonic acid could stabilize the asphaltenes by forming acid-base interactions. Chávez-Miyauchi14 found that aromatic polyisobutylene succinimides, using as viscosity reducers for Mexican heavy crude oil, interacted with the asphaltene aggregates by π-π stacking, hydrogen-bond formation, and acid-base interactions. Studies by Hashmi et al.15 indicated that the polymeric dispersant reduced both the size and polydispersity of the asphaltene particles. Through vapor pressure osmometry experiments and simulation results, Barcenas16 revealed that the efficiency of asphaltene flocculation inhibitors is directly related to the absorbing ability on the surface of the asphaltenes. Many other researchers used polycardanol and sulfonated polystyrene,17 p-alkyl phenol,18 vegetable oils,19 4-n-octyl-benzoic acid and linear alkyl benzene sulfonic acid20 as the asphaltene dispersants to mitigate the deposition problem. According to the literature mentioned above, it may be concluded that the polarity moiety such as -OH and -COOH can interact with the asphaltenes and benefit their dispersion. A handful of studies had used the model oils with asphaltenes to estimate whether the presence of the asphaltenes affected the waxy oils. Oliveira et al.21 found that the addition of asphaltenes did not change the wax appearance temperature (WAT) but reduced the pour point of the wax solution. Kriz22 realized that the


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well-dispersed asphaltenes (0.01 wt%) strongly increased the yield stress and WAT of the waxy crude oils. However, Venkatesan et al.23 pointed out that the addition of asphaltenes in small proportions (~0.1 wt%) significantly depressed the gelation temperature as well as the yield stress of the waxy system. In the meantime, Tinsley et al.24 observed a drastically decrease in precipitation temperature and yield stress of the waxy oils, with the aliphatic nature of asphaltenes as an important determination. Also, Alcazar-Vara25 showed that the asphaltenes dramatically depressed the pour point temperature of the model system, and the more aromatic asphaltenes decreased viscosity more significantly. The different and contradictory results reported may be due to the varied chemical nature of the asphaltenes studied.24 Motivated to improve the flowability of the crude oils at low temperature, the novel flow improvers were prepared through the synthesis and modification of poly(styrene-co-maleic anhydride) with octadecyl amine, obtaining products named poly(styrene-co-maleimide) with various imidization degrees in our previous studies.26 It had been demonstrated that the imidization degree of the prepared compounds had considerable effects on their performance as a flow improver in the model waxy oils with C24 as the paraffin. A higher degree of imidization promoted the flowability of the waxy oils. However, it is well known that the crude oils are complex mixture containing waxes, asphaltenes, resins etc. According to the documents mentioned, the addition of asphaltenes has significant influence on the crystallization and rheological behavior of the model waxy oils and the performance of the flow improvers. In the present investigation, the main aim is to evaluate the


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influence of imidization degree of poly(styrene-co-maleimide) in the model waxy oils with the asphaltenes. A series of well-defined copolymers of styrene and maleic anhydride were synthesized, followed by modification using octadecyl amine to various imidization degrees. 2. Experimental Section 2.1 Materials Styrene (St, 99 wt%), purchased from Sinopharm Chemical Reagent, was washed with 10 wt % NaOH aqueous solution, dehydrated with anhydrous CaCl2, and distilled in vacuum with zeolite before being used. Maleic Anhydride (MAh, 99 wt%), provided by Aladdin Industrial Corporation, was recrystalized in anhydrous chloroform. Octadecyl Amine (ODA, 90 wt%) and n-Tetracosane (C24H50, 99 wt%) were obtained from Acros. n-Decane was purchased from Aladdin. NaOH (96 wt%), CaCl2 (96 wt%) and all other solvents (99 wt%) including chloroform (CHCl3), anhydrous methanol, tetrahydrofuran (THF), ethyl benzene (EB), xylene(60 wt% m-xylene, 25 wt% p-xylene and 15 wt% o-xylene) and methyl ethyl ketone were provided by Sinopharm Chemical Reagent were used without further purification. PEPDTA(1-phenylethyl phenyldithioacetate) as RAFT agent was synthesized according to our previous work.27 2.2 Preparation 2.2.1 Copolymerization Synthesis of Alternate Copolymers of Styrene and Maleic anhydride ((alt) SMA) 27


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Copolymerization of styrene and maleic anhydride was carried out in a three-neck round-bottom flask fitted with a condenser, a mechanical stirrer, and a thermometer. St, MAh, and PEPDTA as RAFT agent were dissolved in methyl ethyl ketone at the molar ratio of 100 : 100 : 1. The weight fraction of monomers was 40% and the reaction was carried out at 75 oC under nitrogen atmosphere for a certain period of time. The solution was poured into 10-fold excess of anhydrous methanol followed by centrifugation to obtain the raw product. The solid product was dissolved in THF and precipitated in anhydrous methanol alternatively for two more times to obtain the pure products. Finally, the purified polymers were dried in vacuum at 60 oC for 24 hours. Synthesis of Styrene-Maleic anhydride Random Copolymer ((ran) SMA) Copolymerization of St and MAh was carried out in the same aforementioned apparatus using methyl ethyl ketone as the solvent. In order to obtain (ran)SMAs with different MAh contents, the MAh in methyl ethyl ketone solution was added dropwise in various speeds. St and RAFT agent, PEPDTA, were mixed at the molar ratio of 300 : 1. The copolymerization was carried out at 110 oC using thermal-initiation within a certain period of time. The products were obtained and purified using the same procedure above. 2.2.2 Modification of Styrene-Maleic anhydride Copolymers Synthesis of Poly(styrene-co-octadecyl maleamic acid) (SNODMA) In order to ensure MAh groups reacted completely, both (ran)SMA and (alt)SMA were mixed with ODA at the molar ratio of 1 : 1.5 between MAh and amine.


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With CHCl3 as the solvent, the reaction was carried out under nitrogen atmosphere in a flask reactor at 30 oC for 2 hours. The purification process was similar to the ones described above. The purified products ((ran)SNODMA and (alt)SNODMA) were dried in vacuum at 40 oC for 24 hours. Synthesis of Poly(styrene-co-octadecyl maleimide) (SNODMI) The SNODMI as a flow improver was obtained through imidization reaction of SNODMA in ethyl benzene solution heated at 135 oC under a nitrogen atmosphere. Based on our previous knowledge of the imidization reaction,26,28,29 the degree of imidization was controlled through collecting the sample at specified time interval. Then the flow improvers with various imidization degree were obtained after the aforementioned purification process. The reaction scheme is presented in Scheme 1. Scheme 1 2.3 Polymer Characterization The average molecular weight and its distribution of (ran)SMA-1, (ran)SMA-2 and (alt)SMA-3 were determined by size exclusion chromatography (SEC). A Waters 1525/2414 SEC equipped with refractive index detector and ultraviolet detector was used. The mobile phase was tetrahydrofuran with the flow rate set at 1 mL/min and the temperature set at 30 oC. Polymer samples were dissolved in tetrahydrofuran and the concentration was around 5.0-10.0 mg/mL with polystyrene used as the standard. The MAh content in the resultant poly(styrene-co-maleic anhydride) was determined by the conductance titration method in our previous work.28 The imidization degrees were determined by Fourier transition infrared (FT-IR)


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spectrometry (Thermo Nicolet 5700).26 The FT-IR method has been widely applied for quantitatively analyzing imidization degree in many previous publications.30-34 In our previous publication28, the imidization degree was characterized by both FTIR and conductance titration method. The results determined by both methods were in good agreement. FTIR was also used to characterize similar structure of an imidization process with both ring-opening and ring-closing reaction.35 The sequence structure of synthesized SMA has been determined by 13C-NMR in our previous research27.Only the chemical shift representing MSM are found in the spectrum for alternative SMA, which validates the alternating structure. In the spectrum for random SMA, chemical shifts for MSM, SSM, and MSS triad can all be observed, and MSS and SSM triad are predominant rather than MSM triad. Hence, the random structure can be verified.

2.4 Preparation of the Model Waxy Oils with Asphaltenes As theoretical study of the flow improvers is the focus herein, the simple model crude oil, which is widely used in other publications4,24,36,37, is chosen for the fundamental investigation instead of the extremely complex real crude oils. The asphaltenes were isolated from the crude oils by precipitation with n-heptane.24 The 1 g given crude oil was transferred into a glass flask which 40 mL n-heptane (analytical grade) was added. The solution was then kept under stirring for 1 hour at room temperature and then let stand overnight before vacuum-filtering through membrane. Finally, the filtrate was collected and dried in vacuum. The


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chemical structure of asphaltene was determined by Fourier transition infrared (FT-IR) spectrometry (Thermo Nicolet 5700). The element composition analysis of carbon, hydrogen and nitrogen was performed by using 5E-CHN2000 Elemental Analyzer. The content of sulfur was determined by 5E-IRSII Infrared Sulfur Analyzer. To obtain the model waxy oils with asphaltenes, the asphaltenes in xylene (99 wt%) blends were prepared firstly. The second step was the blending of the asphaltenes in xylene mixture with the C24H50 (Acros, 99 wt%) in n-decane (Aladdin, 99 wt%) solution to achieve the same concentration in all samples—the model system was the mixture composed of 4 wt% C24H50, 66 wt% n-decane, and 30 wt% of asphaltene-xylene blends. It was observed that concentration larger than 0.1 wt% promoted asphaltene precipitation in the waxy model systems.25 Therefore, the asphaltene concentration in the total mixture was 0.1 wt%. Moreover, the resultant flow improvers with different imidization degrees were dissolved in this model oil with given 0.1 wt% concentration. To ensure the same initial thermal history for all samples, the high-temperature pretreatment was found as the only possible solution.22 The model oils should be heated to 70 oC for 1 hour then slowly cooled down to room temperature before used. 2.5 Characterization of the Model Waxy Oils with Asphaltenes Differential Scanning Calorimetry (DSC) Crystallization temperatures (Tc) of the model samples were obtained by differential scanning calorimeter (TA-Q200) with following temperature profile: (1)


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The sample was heated at 10 oC/min to 70 oC to dissolve the solid phase completely and to remove any thermal history; (2) The sample was cooled from 70 oC to -20 oC at 10 oC/min. The instrument calibration was checked by an indium standard. Cross-Polarized Microscopy Polarized light microscopy is probably the most common technique to observe wax crystals.38 The polarizing microscope (Nikon Eclipse E600POL) equipped with an automatic camera and ED600 temperature-control stage was used to obtain the morphology of the model oils. Drops of the model oil samples were added to a liquid sample cell with glass cover and cooled from room temperature to the observing temperature, which was -5 oC and maintained for 30 min to assure the stable particles and aggregate size before the morphology was observed. Rheological Behaviors Thermo HAAKE RS6000 rheometer with parallel plate geometry was used to measure the rheological behavior of the model samples. A 20 mm parallel plate with a 1 mm gap was employed. The Peltier plate used for temperature control was cooled from room temperature to testing temperature, which was -20 oC and held constant for testing. Each sample was then dropped slowly on the plate and maintained under no stress for 20 min to precipitate the wax and form a solid-like gel completely prior to testing. The scanning frequency was fixed at 0.318 Hz, and the stress was continuously increased from 0.1 Pa to 1000 Pa. 3. Results and Discussion 3.1 Structure of the resultant flow improvers


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Three kinds of styrene-maleic anhydride copolymers have been synthesized through RAFT polymerization, which all possess a quite narrow ploydispersity with Mw/Mn less than 1.3. The MAh molar content of (alt)SMA is 45.1% and close to the strictly alternating SMA , which manifests an alternating sequence structure. The (ran)SMA has lower MAh molar content and a random sequence structure. The imidization degrees of modified SMAs vary from 50% to 100%. The specific characteristics such as molecular weight, molecular weight distribution, MAh content and imidization degree of SMA copolymers used in this research were summarized in Table 1. Table 1 3.2 Characterization of the extracted Asphaltenes The FTIR spectrum for the resulting asphaltenes was shown in Figure 1. The characteristic peaks are similar to many previous studies,12,21,39 and the details are as following: the strong and broad band at 3411 cm-1 corresponds to OH and NH groups, which suggest that the asphaltenes are likely to form hydrogen bonds; sharp peaks for absorption of CH2 symmetric and asymmetric stretching bands locate at 2851 and 2918 cm-1; absorption peak at 1602 cm-1 illustrates the asphaltenes contain a significant portion of aromatics and/or C=C bonds, and the peak at 3052 cm-1 ( aromatic CH stretching) also strengthen this opinion; peaks at 1457 and 1372 cm-1 corresponding to the CH3 asymmetric and symmetric stretching; and signal around 750 cm-1 character the vibration of four hydrogen atoms adjacent to an aromatic ring.


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Furthermore, the elemental composition analysis showed the obtained asphaltenes had 79.31 wt % C, 8.18 wt % H, 1.47 wt % N and 3.74 wt % S. Figure 1 3.3 Crystallization Temperature Both crystallization temperature and melting temperature can be applied to assess the effectiveness of the flow improver for crude oils. The detrimental pipeline blockage caused by wax crystallization and deposition often occurs with the temperature decreasing of the crude oils in practice. Therefore, instead of melting temperature, crystallization temperature is used herein as we intend to find out the effects of flow improvers under cold conditions. In addition, it is quite common to investigate the effectiveness of flow improvers in terms of crystallization temperature in previous publications.40-43 An understanding of crystallization behavior of the crude oils is critical to manage wax deposition during oil production, transportation, and end-use applications. Figure 2 showed the crystallization temperature for the model oils (containing 0.1 wt% asphaltenes) with and without the addition of 0.1 wt% flow improvers, which had various degrees of imidization derived from (ran)SMA-1 (14.5% MAh fraction). First of all, with comparison to our previous model waxy oils, the presence of asphaltene-xylene mixture decreases the crystallization temperature from 0.6 oC to -2.2 oC. Moreover, it was found that adding 1000 ppm flow improver can significantly reduce the crystallization temperature of the model samples. The depression in crystallization temperature reaches maximum when the imidization


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degree of given flow improver is 100%. For instance, when adding the flow improver with 100% degree of imidization derived from (ran)SMA-1 in model oil (sample-4), the decrease in crystallization temperature is almost 2 oC. The same trend could be obtained from the Figures 3 and 4, which examine the presence of flow improvers with various imidization degrees derived from (ran)SMA-2 and (alt)SMA-3, which possessed 26.0% and 45.1% MAh fraction, respectively. The decrease in crystallization temperature for the model samples further demonstrate the conclusion—the higher imidization degree, the lower crystallization temperature for the model waxy oils with asphaltenes. Interestingly, the result is consistent with our previous work.26 Figures 2, 3 and 4 3.4 Morphology Optical microscopy provides a static image of the solids formed in the model oils after they have grown into a stable size. Effect of imidization degree upon the morphology of model waxy oils with the asphaltenes was shown in Figure 5. It had been found that the asphaltenes aggregate heavily, and this phenomenon can illustrate the rheological behavior in the following section. Figure 5(a)~(d) examined the morphology of the model oils doped with flow improvers (derived from (ran)SMA-1, 14.5% MAh fraction) with different imidization degree. As seen from Figure 5(a), the addition of flow improver with 50% imidization degree can disperse the asphaltene particles (shown as small block dots), and the wax crystals become smaller in size and more dispersed than the samples


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without flow improver. With the imidization degree increasing to 72%, as shown in Figure 5(b), it is obvious that both the needle-like wax crystals and asphaltenes particles become more dispersed in the oils than before. When the imidization degree of flow improver continues to increase, the wax crystals further become smaller and more dispersed. However, the asphaltene particles become larger even flocculate as shown in Figure 5(d). That is to say, the optimal imidization degree for dispersing the asphaltene particles is about 72% for flow improvers derived from precursor (ran)SMA-1 with 14.5% MAh fraction. Furthermore, crystallization morphology of the model oils containing flow improvers derived from (ran)SMA-2 and (alt)SMA-3 was also shown in Figure 5. Consistent with the results above, it could be seen that the addition of flow improvers decreases the number and size of wax crystals more significant with the imidization degree increasing. However, there are an optimal imidization degree for dispersing the asphaltene particles, corresponding to 82% and 87% imidization degree as seen from Figure 5(g) and Figure 5(k), respectively. Therefore, the presence of asphaltenes in the model systems changes the performance of flow improvers. The flow improvers with polar moiety such as COOH and NH are likely to form hydrogen bonds with the asphaltenes containing OH and NH groups, which can benefit the dispersion of asphaltenes. However, when the imidization degree of flow improvers is too low, there are too many polar moieties which do not benefit non-polar wax. When the imidization degree increases too high, the asphaltenes deposit heavily due to the reduction of interaction with polar moiety from the flow


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improvers, even though the waxes are dispersed better. Thus, we concluded that the flow improvers with suitable imidization degree may interact with the asphaltenes sufficiently and co-crystalize with wax very well simultaneously. Figure 5 3.5 Rheology The rheological parameters of petroleum fluids are very important for all processes where these fluids are transferred from one place to another, such as the production processes of hydrocarbon reservoirs and the processes of petroleum refining.44 Among them, the yield stress, relative yield stress and relative viscosity are often used. The wax gels can fail in two different ways as illustrated in previous reference45. In the first case, the viscosity undergoes a continuous transition from a viscous creeping flow plateau at low stress to diminished liquid-like viscosities with increasing stress. The yield stress can be defined as the stress for which the derivative—d lnη/d lnτ reaches maximum. In the second case, creep is followed by catastrophic failure of the gel to a low viscosity fluid. After failure of the gel, the recovery of the high plateau viscosity is diminished and the high to low viscosity transition is shifted to lower values of the stress as a result of the breakdown of the wax crystal network. In this case, the yield stress is defined as the ﬁnal stress measured before sample failure. The rheological behavior of our samples followed the same trend as the second case. In this work, yield stress (τy) is defined as the stress applied prior to the model oil gel failure, which agrees with the “flow stress”


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described by Mezger.46 In Reference 46, the limiting value of the linear viscoelastic (LVE) range in terms of the shear stress is the “yield point”, which is preferred to analyze materials and the structure strength. At the crossover point of the storage modulus (G’) and the loss modulus (G’’), the gel character with G’> G’’ changes to a liquid character with G’’ > G’. This point is also called “flow point”, which is preferred to investigate the point at which the internal structure is breaking to such an extent causing the material to flow finally. Therefore, the stress at the “flow point” is identical to the yield stress defined in this work. The rheological behaviors for the samples with 0.1 wt % flow improvers (14.5% MAh fraction) with various imidization degrees were shown in Figure 6. Figure 6(a) reflected the imidization degree on viscosity, and it could be seen that flow improver with 72% imidization degree performs the best in viscosity depression (over one order of magnitude). Furthermore, the effect of imidization degree on the yield stress was shown in Figure 6(b). It demonstrated that adding flow improver with 72% imidization degree can reduce τy by nearly one order of magnitude and presents the best performance, the same as the results for viscosity. The same trend could be found in the Figure 7 and 8. From Figure 7, increasing the imidization degree of flow improver (26.0% MAh) to 82% makes the best performance in decreasing the viscosity and yield stress. Also, the influence of imidization degree of flow improver with 45.1% MAh fraction was shown in Figure 8. Similarly, an appropriate imidization degree (about 87%) does the best in depressing the relative viscosity and


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yield stress of model oils. Meanwhile, the results in rheological behaviors resemble those in morphology. Figure 6, 7and 8 It should be attributed to the polarity, which can be parallel to our previous research.26 In non-polar waxy system, the flow improvers with higher imidization degree have less polarity so that it can be more compatible with n-paraffin and significantly affect the crystallization and rheological behavior of the waxy oils. However, with the addition of asphaltene, the model samples have higher polarity than before. The polarity of flow improvers with suitable imidization degree may have the similar polarity as that of the model waxy oils with the asphaltenes. Compared with (ran)SMA-1 and (ran)SMA-2 with 14.5% and 26.0% MAh fraction respectively, it was found that the imidization degree of flow improvers with the best performance is about 72% and 82%. That is to say, the optimal imidization degree of the flow improvers with larger MAh content is higher. As shown in Scheme 1, the content of MAh is consistent with polar maleamic acid group. To match the polarity of model waxy oils with the asphaltenes, the increase of imidization degree is needed to decrease the polarity of flow improvers. The same trend was found in (alt)SMA-3, of which optimal imidization degree has the highest value of 87%. Thus, it could be concluded that the polarity of flow improvers affects the efficiency of flow improvers. It had been found that the flow impeovers derived from (alt) SMA structure performed much better than the ones obtained from (ran)SMA. A plausible


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explanation should be that (alt)SMA have higher MAh content, which results in more alkyl side chain to interference the crystallization of wax. 4. Conclusions A series of poly(styrene-co-octadecyl maleimide) with different imidization degrees were synthesized and used as flow improvers for the model waxy oils containing asphaltenes. With the addition of the resultant flow improvers, the wax crystals become fewer, smaller and more disperse in the oils, asphaltene particles is better dispersed , the crystallization temperature and the yield stress can be reduced considerably. Moreover, it had been found that the performance of the flow improvers is significantly affected by the imidization degree and maleic anhydride content, which are evaluated in terms of the polarity.

Acknowledgement

This study was supported by the National Natural Science Foundation of China through Project No. 21176217, Zhejiang Provincial Natural Science Foundation through Project No. Y4110134, the Program for Changjiang Scholars and Innovative Research Team in University (No. IRT0942).

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Energy & Fuels

Captions Table 1. Precursor SMA and the resultant SODMI with various imidization degrees as the flow improvers Scheme 1. The imidization processes for obtaining the designed flow improvers Figure 1. FTIR spectrum of the extracted asphaltenes Figure 2. DSC cooling curves for the model waxy oils with 0.1 wt % asphaltenes simultaneously doped 0.1 wt % flow improvers with different imidization degrees derived from (ran)SMA-1 with 14.5% MAh fraction Figure 3. DSC cooling curves for the model waxy oils with 0.1 wt % asphaltenes simultaneously doped 0.1 wt % flow improvers with different imidization degrees derived from (ran)SMA-2 with 26.0% MAh fraction Figure 4. DSC cooling curves for the model waxy oils with 0.1 wt % asphaltenes simultaneously doped 0.1 wt % flow improvers with different imidization degrees derived from (alt)SMA-3 with 45.1% MAh fraction Figure 5. Morphology of the model waxy oils with 0.1 wt % asphaltenes observed at -5 oC after maintained for 30 min. (a)~(d) doped 0.1 wt % flow improvers with different imidization degree derived from precursor (ran)SMA-1 with 14.5% MAh fraction; (e) without flow improvers; (f)~(h) doped 0.1 wt % flow improvers with different imidization degree derived from precursor (ran)SMA-2 with 26.0% MAh fraction; (i)~(l) doped 0.1 wt % flow improvers with different imidization degree derived from precursor (alt)SMA-3 with 45.1% MAh fraction Figure 6. Effects of 0.1 wt % flow improvers (derived from (ran) SMA-1, 14.5% MAh fraction) with different imidization degrees on the rheological behavior tested at -20 oC: (a) evolution of viscosity; (b) the effect of imdization degree on complex viscosity and yield stress Figure 7. Effects of 0.1 wt % flow improvers (derived from (ran) SMA-2, 26.0% MAh fraction) with different imidization degree on the rheological behavior


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

tested at -20 oC: (a) evolution of viscosity; (b) the effect of imdization degree on complex viscosity and yield stress Figure 8. Effects of 0.1 wt % flow improvers (derived from (alt) SMA-3, 45.1% MAh fraction) with different imidization degree on the rheological behavior tested at -20 oC: (a) evolution of viscosity; (b) the effect of imdization degree on complex viscosity and yield stress


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Energy & Fuels

Table 1.

Precursor SMA and the resultant SODMI with various imidization degrees as the flow improvers MAh Molar

Imidization

Content (%)

Degree (%)

1.18

14.5

50

6000

1.18

14.5

72

(ran) SMA-1

6000

1.18

14.5

85

Sample -4

(ran) SMA-1

6000

1.18

14.5

100

Sample -5

(ran) SMA-2

4200

1.27

26.0

61

Sample -6

(ran) SMA-2

4200

1.27

26.0

82

Sample -7

(ran) SMA-2

4200

1.27

26.0

100

Sample -8

(alt) SMA-3

3100

1.23

45.1

63

Sample -9

(alt) SMA-3

3100

1.23

45.1

75

Sample -10

(alt) SMA-3

3100

1.23

45.1

87

Sample -11

(alt) SMA-3

3100

1.23

45.1

100

Samples

Precursor SMA

Mn

Polydispersity

Sample-1

(ran) SMA-1

6000

Sample -2

(ran) SMA-1

Sample -3


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Scheme 1. The imidization processes for obtaining the designed flow improvers


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e x tra c te d a s p h a lte n e s

Transmittance/%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

750 3052 1605

1372

3411 1457

2851 2918

4000

3500

3000

2500

2000

1500

1000

-1

W aven um ber(cm )

Figure 1. FTIR spectrum of the extracted asphaltenes


500

Energy & Fuels

Samples (imidization degree) o

-4.1 C sample-4(100%) o

-3.8 C

Heat Flow

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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sample-3(85%)

o

-3.7 C sample-2(72%) o

-3.6 C

sample-1(50%)

o

-2.2 C

-20

-10

without sample

0

10

20

30

o

Crystallization Temperature / C

Figure 2. DSC cooling curves for the model waxy oils with 0.1 wt % asphaltenes simultaneously doped 0.1 wt % flow improvers with different imidization degrees derived from (ran)SMA-1 with 14.5% MAh fraction


Page 29 of 34

Samples (imidization degree)

o

-3.9 C sample-7(100%) o

-3.8 C

Heat Flow

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

sample-6(82%) o

-3.7 C sample-5(61%) o

-2.2 C without sample

-20

-10

0

10

20

30

o


Figure 3. DSC cooling curves for the model waxy oils with 0.1 wt % asphaltenes simultaneously doped 0.1 wt % flow improvers with different imidization degrees derived from (ran)SMA-2 with 26.0% MAh fraction


Energy & Fuels

Samples (imidization degree) o

-5.0 C sample-11(100%) o

-4.6 C sample-10(87%)

Heat Flow

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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o

-4.3 C sample-9(75%) o

-4.1 C sample-8(63%) o

-2.2 C

-20

-10

without sample

0

10

20

30

o


Figure 4. DSC cooling curves for the model waxy oils with 0.1 wt % asphaltenes simultaneously doped 0.1 wt % flow improvers with different imidization degrees derived from (alt)SMA-3 with 45.1% MAh fraction


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Energy & Fuels

(a) 50% imidization degree

(e) without samples

(i) 63% imidization degree

(b) 72% imidization degree

(f) 61% imidization degree

(j) 75% imidization degree

(c) 85% imidization degree

(g) 82% imidization degree

(k) 87% imidization degree

(d) 100% imidization degree

(h) 100% imidization degree

(l) 100% imidization degree

Figure 5. Morphology of the model waxy oil with 0.1 wt % asphaltenes observed at -5 oC after maintained for 30 min. (a)~(d) doped 0.1 wt % flow improvers with different imidization degree derived from (ran)SMA-1 with 14.5% MAh fraction; (e) without flow improvers; (f)~(g) doped 0.1 wt % flow improvers with different imidization degree derived from (ran)SMA-2 with 26.0% MAh fraction; (i)~(l) doped 0.1 wt % flow improvers with different imidization degree derived from (alt)SMA-3 with 45.1% MAh fraction


Energy & Fuels

6

10

6

10

4

10

∗

η versus Imidization Degree τ y versus Imidization Degree 5

5

10

10

3

4

104

*

*

10

2

10

waxy oil with asphaltenes 3

10

3

10

sample-1(50%) sample-2(72%) sample-3(85%) sample-4(100%)

2

10

0

10

2

1

10

2

τ /Pa

10

10

40

1

50

(a)

60

70

80

90

100

The Imidization Degree/%

(b)

Figure 6. Effects of 0.1 wt % flow improvers (derived from (ran) SMA-1, 14.5% MAh fraction) with different imidization degrees on the rheological behavior tested at -20 oC: (a) evolution of viscosity; (b) the effect of imdization degree on complex viscosity and yield stress


10 110

τ y /Pa

η /Pa s

10

η /Pa s

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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6

10

6

10

∗

10

4

10

3

10

2

10 110

1

η vers us Imidiza tion Degree τ y v ersus Imidization Degree 5

5

10

4

104

*

10

3

waxy oils with asphaltenes

3

10

10

sample-5(61%) sample-6(82%) sample-7(100%)

2

10

2

10

0

10

1

10

2

τ /Pa

10

50

60

70

80

90

100


(a)

(b)

Figure 7. Effects of 0.1 wt % flow improvers (derived from (ran) SMA-2, 26.0% MAh fraction) with different imidization degree on the rheological behavior tested at -20 oC: (a) evolution of viscosity; (b) the effect of imdization degree on complex viscosity and yield stress


τ y /Pa

η /Pa s

10

*

η /Pa s

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Energy & Fuels

6

6

10

10

4

10

∗

η versus Imidization Degree τ y versus Imidization Degree 5

10

5

10

3

4

104

*

*

10

2

10

waxy oils with asphaltenes 3

10

τ y /Pa

η /Pa s

10

η /Pa s

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 34

3

10

sample-8(63%) sample-9(75%) sample-10(87%) sample-11(100%)

2

10

0

10

2

10 1

10

2

τ /Pa

10

50

1

60

70

80

90

100

10 110


(a)

(b)

Figure 8. Effects of 0.1 wt % flow improvers (derived from (alt) SMA-3, 45.1% MAh fraction) with different imidization degree on the rheological behavior tested at -20 oC: (a) evolution of viscosity; (b) the effect of imdization degree on complex viscosity and yield stress


Study on the Influence of the Imidization Degree of ... - ACS Publications

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