Influences of the Molecular Weight and Its Distribution of Poly(styrene

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Influences of the Molecular Weight and its Distribution of Poly(styrenealt-octadecyl maleimide) as a Flow Improver for Crude Oils Kun Cao, Qing-jun Zhu, Xiangxia Wei, Yun-fei Yu, and Zhen Yao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b02946 • Publication Date (Web): 01 Mar 2016 Downloaded from http://pubs.acs.org on March 1, 2016

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Effects of the (alt)SNODMIs with different molecular weight and its distribution as the flow improver on rheological behavior and crystallization temperature for the model waxy oils with or without asphaltenes 271x197mm (300 x 300 DPI)

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Influences of the Molecular Weight and its Distribution of Poly(styrene-alt-octadecyl maleimide) as a Flow Improver for Crude Oils Kun Cao a, b, Qing-jun Zhu b, Xiang-xia Wei b,#, Yun-fei Yu 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, Zhejiang University, Hangzhou 310027, CHINA

*

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

Abstract: A series of poly(styrene-alt-octadecyl maleimide)s ((alt)SNODMIs) with different molecular weights and molecular weight distributions were obtained through the reaction of octadecyl amine and poly(styrene-alt-maleic anhydride), which were synthesized using controlled free radical polymerization. The (alt)SNODMIs were assessed as flow improvers in two types of model waxy oils: one that was free of asphaltenes and one that contained asphaltenes. A differential scanning calorimeter, a polarizing microscope with a hot stage, and a rotational rheometer with parallel plate geometry were employed to characterize the crystallization temperature, the morphologies of the wax crystals and asphaltene particles, and the rheological behavior, respectively. The results indicate that the molecular weight and its distribution significantly affect the performance of the flow improver. In both model waxy oils, (alt)SNODMIs with a medium molecular weight achieved optimal effectiveness in #

Ms. Wei’s present address: Department of Materials Science and Engineering, National University of Singapore, 117574, Singapore


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decreasing the crystallization temperature, improving the morphology, and reducing the yield stress and viscosity. Moreover, (alt)SNODMIs with a narrower molecular weight distribution are more effective in the model waxy oil without asphaltenes, whereas the opposite result is found in the model waxy oil with asphaltenes. Keywords: Poly(styrene-alt-octadecyl maleimide); Molecular Weight; Molecular Weight Distribution; Flow Improver; Waxy Oil; Asphaltene.

1. Introduction Crude oil, which is a complex mixture of hydrocarbons, is primarily composed of waxes, asphaltenes, and resins.1 The waxes in crude oil are generally present in the form of crystallized “house-of-cards” type structures,2 in which orthorhombic wax crystals overlap and interlock with each other. Such structures lead to cold flow problems, which typically cause pipeline blockages. Moreover, the flocculation and deposition of asphaltenes from crude oil, primarily due to their solubility limits,3 also represent significant technical and economic issues. In addition, asphaltenes have also been reported to play an important role in the crystallization of waxes.4,5 To date, various methods,6-9 including heating, dilution with light oils, emulsion, and magnetic field processing, have been proposed to address the aforementioned problems. Each of these methods has its own drawbacks and also presents other undesired challenges, such as high energy consumption and costs, geological restrictions, and post-processing difficulties. Alternatively, pretreating crude oils with various flow improvers should be an economically viable method for tuning the crystallization and rheological properties of gelled crude oil.


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Various types of properly designed polymeric flow improvers are commercially available, e.g.,

poly(ethylene-co-vinyl

acetate)

(EVA),10

poly(ethylene-butene)

(PEB),11

polymethacrylates,12,13 and modified maleic anhydride copolymers.14-18 Many investigations of these flow improvers have frequently incorporated maleic anhydride as the functional co-monomer due to its versatility in the grafting of side chains. In general, the molecular structure of the flow improver is known to significantly influence its effectiveness as a flow improver. For polymeric flow improvers, various types and compositions of (co)monomers and grafted alkyl chain lengths have been extensively studied to determine their influence in improving the cold flow properties of crude oils.19 In contrast, the effects of the molecular weight (MW) and molecular weight distribution (MWD) on the effectiveness of flow improvers have not been extensively assessed. In the literatures, several preliminary investigations indicated that MW and MWD should play a fundamental role in the performance as a flow improver for crude oils.20-21 Chanda et al.22 reported that polybehenyl acrylate with a lower molecular weight exhibited better efficacy as a flow improver for asphaltene-rich crude oils. Similarly, El-Gamal et al.23 showed that prepared acrylate/methacrylate polymer additives with a lower range of molecular weights achieved the optimum effectiveness for waxy crude oils. Moreover, Ahmed et al.24,25 synthesized polymeric additives for lube oil and reported that decreasing the molecular weight increased the efficiency as pour point depressants. However, Kuzmic et al.26 prepared polymeric additives of alkyl acrylate with styrene, acrylic acid and 1-vinyl-2-pyrrolidone for crude oils from Croatian oil fields and concluded that additives with molecular weights below 20000 Da were not efficient. Taraneh27 reported that ethylene-vinyl acetate copolymer, as a flow


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improver with a higher molecular weight, was the better additive for crude oils with low asphaltene contents. In addition, El-Gamal et al.

28

showed that poly-α-olefin with a higher

molecular weight exhibited good performance as a pour point depressant for gas oil. Regarding the influence of the molecular weight distribution, El-Gamal et al.25 demonstrated that the performance of acrylate-methacrylate copolymer for waxy crude oils was enhanced by increasing the molecular weight distribution and that poly-α-olefin with a broad weight distribution was more efficient as a pour point depressant for gas oil. In contrast, Chanda et al.22 determined that polybehenyl acrylate with a narrow molecular weight distribution was a better flow improver for asphaltene-rich crude oils. The possible reason for this contradictory phenomenon is that the performance of a polymeric flow improver is dependent on both the structure of the flow improver and the oil composition.29 It was subsequently reported that the performance of a flow improver is also related to the wax and asphaltene composition in the crude oil, which requires various molecular characteristics, such as molecular weight, molecular weight distribution and composition of the flow improver, to optimally promote the flow properties of crude oil.20,27 Further investigations are thus required to thoroughly comprehend the interaction between the structure of the polymeric flow improver and crude oil and to establish proper guidelines for obtaining a more efficient flow improver. Based on our previous studies on effects of the imidization degree and the sequence structure of poly(styrene-co-octadecyl maleimide) ((alt)SNODMI) as a flow improver,30,31 a series of (alt)SNODMIs with various number-average molecular weights and molecular weight distributions were synthesized and applied in two types of model waxy oils: one that was free


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of asphaltenes and one that contained asphaltenes. To comprehensively understand the influences of the molecular weight and molecular weight distribution on the performance of the flow improver, the crystallization temperature, the morphology and the rheological properties of the above two types of model waxy oils were thoroughly evaluated. 2. Experimental

2.1 Materials

Styrene (St, 99 wt%) was provided by the Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) and was redistilled under vacuum prior to use. Maleic anhydride (MAh, 99 wt%) was provided by Aladdin Industrial Corporation and was recrystallized in anhydrous chloroform. 1-Phenylethyl phenyldithioacetate (PEPDTA) was prepared in-house as a RAFT agent.31,32 All other reagents were used as received. Chloroform, anhydrous methanol, tetrahydrofuran (THF), 2-butanone, ethyl benzene, and n-heptane, which were of analytical grade (99 wt%), along with xylene (60 wt% m-xylene, 25 wt% p-xylene, and 15 wt% o-xylene) were all purchased from the Sinopharm Chemical Reagent Co., Ltd.. n-Decane (C10, 99 wt%) was obtained from Aladdin. n-Octadecyl amine (ODA, 90 wt%) and n-tetracosane (C24, 99 wt%) were purchased from Acros. The asphaltenes were isolated from crude oil provided by the Shanghai Research Institute of Petrochemical Technology. The extraction of asphaltenes followed a modification of ASTM D2007-03 method. 40 mL of n-heptane, which was used as a precipitant, was thoroughly mixed with 1 g of the crude oil. The precipitated asphaltenes were collected via filtration and washed until colorless. The characterization of the chemical structure of the asphaltenes was described in detail in our previous publication.31


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2.2 Synthesis and Characterization of Flow Improvers

Synthesis of Poly(styrene-alt-maleic anhydride) ((alt)SMA) Poly(styrene-alt-maleic anhydride)s ((alt)SMAs) with different molecular weights and a narrow

molecular

weight

distribution

were

synthesized

using

the

reversible

addition-fragmentation chain transfer (RAFT) polymerization technique with PEPDTA as the RAFT agent at 75 °C under an inert nitrogen (N2) atmosphere. St, MAh, and PEPDTA were reacted at a molar ratio of 100:100:1. According to the studied kinetics,32 the copolymerization was performed for a certain period of time, and then the reaction solution was poured into anhydrous methanol to obtain (alt)SMAs with various molecular weights. The solid product was then re-dissolved in THF and re-precipitated in anhydrous methanol, and this process was repeated twice. Finally, the purified polymers were dried in a vacuum oven at 60 °C for 24 hours. Synthesis of Poly(styrene-alt-octadecyl maleamic acid) ((alt)SNODMA) Using chloroform as the solvent, (alt)SMA and ODA at a molar ratio of 1:1.5 reacted under an inert nitrogen (N2) atmosphere at 30 °C for 2 hours. The purification process was the same as above, and the product was dried in a vacuum oven at 40 °C for 24 hours. Synthesis of Poly(styrene-alt-octadecyl maleimide) ((alt)SNODMI) The imidization of (alt)SNODMA in ethyl benzene was performed at 135 °C for 36 hours under an inert nitrogen (N2) atmosphere to ensure complete imidization. The purification process was the same as above, and the product was dried in a vacuum oven at 40 °C for 24 hours. Structure Characterization


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The number-average molecular weights (Mn) and molecular weight distributions (MWDs) of the resulting (alt)SMAs were characterized using a size-exclusion chromatography instrument (PL GPC 50 plus) equipped with a refractive index detector, a light scattering detector, and a viscosity detector at 30 °C. Tetrahydrofuran (THF) was used as the mobile phase at a flow rate of 1 mL/min. Polystyrene was used as the standard. The results are presented in Table 1. The molar content of MAh in the resultant (alt)SMAs was determined using the conductance titration method described in our previous work.33 The chemical structure of (alt)SNODMI was characterized using a Fourier transform infrared (FTIR) spectrometer (Thermo Nicolet 5700), and the details of the spectral analysis are available in our previous work.30 Herein, the complete amidation of the MAh group of (alt)SMA and the imidization of the amide group of (alt)SNODMA were confirmed via FTIR characterization.

2.3 Preparation and Characterization of Model Waxy Oil Samples

It is well known that the efficacy of a flow improver can be affected by the presence of asphaltenes in crude oils. Thus, due to the complex composition of crude oil, for a comprehensive exploration, two types of representative model waxy oils were prepared to conduct a fundamental investigation of the effectiveness of the obtained (alt)SNODMI as a flow improver. One was a model waxy oil without asphaltenes, which was composed of 4 wt% C24 and 96 wt% C10, and the other was a model waxy oil with asphaltenes, which was obtained by blending the asphaltenes in xylene solution with the C24 in C10 solution and was composed of 4 wt% C24, 66 wt% C10, 0.1 wt% asphaltenes and 29.9 wt% xylene. All the


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samples investigated in this work are presented in detail in Table 1. To evaluate the influence of molecular weight in the above two model waxy oils, (alt)SNODMI with a concentration of 0.1 wt% based on the model crude oils should be used as

the

flow

improver.

(alt)SNODMI-A,

(alt)SNODMI-B,

(alt)SNODMI-C

and

(alt)SNODMI-E were selected for the waxy crude oil without asphaltenes, and (alt)SNODMI-B, (alt)SNODMI-C, (alt)SNODMI-D and (alt)SNODMI-E were selected for the waxy crude oil with asphaltenes. Moreover, the effect of the molecular weight distribution was investigated using (alt)SNODMI-B and three types of blends of (alt)SNODMIs with broader MWDs, namely, SNODMI-I, (alt)SNODMI-J and (alt)SNODMI-K; for example, (alt)SNODMI-I (MWD = 1.71) was obtained by blending 33 wt% (alt)SNODMI-A with 67 wt% (alt)SNODMI-C. The details of all the blends are shown in Table 1. Insert Table 1 In addition, a differential scanning calorimeter (TA-Q200), a polarizing microscope (Nikon Eclipse E600POL), and a rotational rheometer (Thermo HAAKE RS6000) were used to determine the crystallization temperature, the morphologies of the wax crystals and asphaltene particles, and the rheological properties of both model waxy oils, respectively. The details of these measurements were the same as those presented in our previous study.33 3. Results and Discussion The effects of the molecular weight and molecular weight distribution are discussed in terms of the crystallization temperature, morphology and rheological properties for two types of typical model waxy oils, i.e., without and with asphaltenes.


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3.1 Effect of Molecular Weight

Crystallization Temperature (Tc) As shown in Figure 1, in the presence of 0.1 wt% (alt)SNODMIs with different molecular weights, the crystallization temperature of the model waxy oil without asphaltenes decreased compared to the sample without the flow improver. According to the results, (alt)SNODMI-B (Mn = 3300 Da) most significantly decreased Tc by approximately 4 °C compared to sample N1, which did not contain a flow improver. However, with further increases or decreases in the molecular weight of the (alt)SNODMIs, a smaller decrease in the crystallization temperature was observed. Therefore, it is concluded that (alt)SNODMI with a medium molecular weight can most efficiently decrease Tc for the model waxy oil without asphaltenes. Insert Figure 1 A similar phenomenon was observed in the model waxy oil with asphaltenes, as shown in Figure 2. It was clear that the addition of (alt)SNODMIs also decreased the crystallization temperature of the model waxy oil with asphaltenes. Among all the selected flow improvers, (alt)SNODMI-C (Mn = 5600 Da) exhibited the best performance. Consistent with the aforementioned results from the investigation of the model waxy oils without asphaltenes, a flow improver with the appropriate medium molecular weight tends to decrease the crystallization temperature of the model waxy oil with asphaltenes to the greatest extent. Insert Figure 2 Morphology It is known that the morphology of wax crystals in crude oils is a crucial aspect in the study


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of flow improvers. Figure 3 shows the morphology of the wax crystals in the model waxy oil without asphaltenes. As shown in Figure 3(a), large wax crystals formed and overlapped with each other in the model waxy oil without asphaltenes that did not contain a flow improver. However, upon the addition of (alt)SNODMIs with various molecular weights as the flow improvers, the size of the wax crystals was greatly reduced, and the crystals appeared to be well dispersed in the matrix. Thus, the tendency of wax crystals to interlock was considerably inhibited with the addition of (alt)SNODMIs. Further comparison among b, c, d and e in Figure 3 revealed that the presence of (alt)SNODMI-B (Mn = 3300 Da) improved the morphology of the wax crystals the most because the crystals were the smallest in size, fewest in number and best dispersed in the matrix. Thus, (alt)SNODMIs with a medium molecular weight were found to be the most effective in improving the morphology of wax crystals. Insert Figure 3 Figure 4 indicates that analogous behavior was achieved by adding various (alt)SNODMIs to the model waxy oil with asphaltenes. By comparing b, c, d and e in Figure 4, the presence of (alt)SNODMI-C (Mn = 5600 Da) was found to provide the greatest benefit in terms of improving the morphologies of the wax crystals and asphaltene particles. As shown in Figure 4(e), as the molecular weight of the flow improver increased, the wax crystals in the matrix increased in size and the asphaltenes aggregated and deposited heavily. Overall, the influence of molecular weight in decreasing the crystallization temperature and improving the morphology should be consistent. Insert Figure 4


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Rheological Behavior A thorough understanding of the rheological behavior of crude oils is crucial for overcoming flow and restarting problems, particularly at low temperatures.34 In this work, the rheological behavior of our samples showed that creep should be followed by catastrophic failure of the gel to a low viscosity fluid. In addition, yield stress (τy) is defined as the stress applied before the model oil gel fails, which is identical to the “flow stress” described by Mezger.35,36 The relative yield stress is defined as the ratio of the yield stress obtained with adding the flow improver to that obtained without adding the flow improver. In the model waxy oil without asphaltenes, the effects of (alt)SNODMIs with various molecular weights on the complex viscosity (η*) and yield stress (τy) were examined, as shown in Figure 5. It was observed that the addition of (alt)SNODMI caused a decrease in the complex viscosity and yield stress. Furthermore, the most effective flow improver shown in Figure 5 was still (alt)SNODMI-B with a medium molecular weight (Mn = 3300 Da), which significantly reduced the complex viscosity by nearly one order of magnitude and decreased the yield stress of the model waxy oil without asphaltenes from 217 Pa to 24 Pa. Insert Figure 5 A similar trend of the reduction in the complex viscosity and yield stress for the model waxy oil with asphaltenes was also observed in Figure 6. (alt)SNODMI-C (Mn = 5600 Da) achieved the largest reduction in both complex viscosity and yield stress, showing that the flow improver with a medium molecular weight also functions the best in the presence of asphaltenes. Insert Figure 6


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From the results, it can be inferred that (alt)SNODMIs with an adaptive medium molecular weight are an optimal flow improver for two typical types of model waxy oils. For the model waxy

oil

without

asphaltenes,

this

trend

can

be

interpreted

by

using

the

incorporation-perturbation37 and co-crystallization mechanism, which dictates that the flow improver should first be incorporated into the amorphous wax aggregates when the waxy oils are cooled to near the wax appearance temperature (WAT). The incorporated flow improvers dramatically impede or delay the ordering transition of amorphous wax deposits into crystalline wax deposits, causing a reduction in the crystallization temperature. Moreover, even if during the transition process the flow improvers migrate to the periphery of gradually forming crystalline wax deposits, a portion of the alkyl chains of (alt)SNODMIs will co-crystallize with the waxes in them, while the remaining part will cover the outer surface of them to form a protective layer. The growth of wax crystals into larger crystals can be inhibited, and the interlocking of wax crystals into a three-dimensional structure of wax crystals will be prevented. Therefore, the wax morphology is improved, and both the viscosity and yield stress are decreased. In general, (alt)SNODMIs with low molecular weights can be relatively easier to incorporate into the amorphous wax deposits. However, these low-molecular-weight (alt)SNODMIs may not be large enough to effectively perturb the formation of crystalline wax deposits and may readily co-crystallize with the wax deposits, thus not providing adequate protective layers. As the molecular weight of (alt)SNODMIs increases, the incorporating capacity of (alt)SNODMIs is reduced, whereas their perturbing ability is enhanced. More importantly, (alt)SNODMIs with excessively large MWs are difficult to co-crystallize with crystalline wax deposits and easily migrate out of the


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wax deposits, resulting in inadequate protective layers. In summary, the well-defined flow improver with a medium molecular weight (Mn = 3300 Da) achieves the best flow improving performance through the balance of the ability to incorporate and to perturb along with the appropriate ability to co-crystallize with waxes. For the model waxy oil with asphaltenes, the operating mechanism of the flow improver may be slightly different due to the presence of the asphaltenes. In the literature, it was reported that asphaltenes can concentrate on wax crystals to hinder the formation of large crystals.20 Through the morphological observations, (alt)SNODMI with a medium molecular weight (Mn = 5600 Da) can better disperse the asphaltenes. Therefore, the amount of larger asphaltene aggregates is greatly reduced, whereas the stable smaller asphaltene aggregates are increasingly formed. The greater the number of stable smaller asphaltene aggregates, the more enhanced is the hindrance of wax crystal formation. Moreover, it was found that the optimum medium molecular weight of the flow improver for the model waxy oil with asphaltenes is slightly higher than that (Mn = 3300 Da) of the model waxy oil without asphaltenes. This observation may be attributed to the difference in the flow improver operating mechanism. In the presence of asphaltenes, improving the flow properties is primarily dependent on the dispersion of asphaltenes, and the flow improvers with smaller MWs may not be able to well disperse the asphaltenes.

3.2 Effect of Molecular Weight Distribution

Crystallization Temperature (Tc) Figures 7 and 8 show the influence of the molecular weight distributions of (alt)SNODMIs as


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the flow improver on the crystallization temperature in the two types of model waxy oils. Figure 7 indicates that the flow improver with the narrowest MWD reduced the crystallization temperature by approximately 4°C in the model waxy oil without asphaltenes. Moreover, as the MWD became broader, the ability of the flow improver to reduce Tc in the model waxy oil without asphaltenes was attenuated. In contrast, Figure 8 shows that the flow improver with a broader MWD was advantageous in decreasing the crystallization temperature in the model waxy oil with asphaltenes. Insert Figures 7 and 8 Morphology As shown in Figure 9, the presence of flow improvers with various MWDs could decrease the number of wax crystals and allow them to be better dispersed in the waxy model oil without asphaltenes. However, as shown in Figures 9 (b) to (e), when the MWD became broader, the wax crystals became larger in size and formed in greater numbers. It has been established that a flow improver with a narrower molecular weight distribution can further improve the morphology of wax crystals in the model waxy oil without asphaltenes. The effect of MWD on the morphology of the model waxy oil with asphaltenes is complex, as shown in Figure 10. It was clear that the addition of (alt)SNODMIs could disperse both the wax crystals and asphaltene particles. Consistent with the model waxy oil without asphaltenes, a flow improver with a broader MWD should be detrimental to the improvement in the wax morphology, as manifested by the overlapped large wax crystals observed in Figure 10 (d). However, Figures 10 (c) and (d) show that (alt)SNODMIs with broader MWDs had excellent performances in dispersing the asphaltene particles, which illustrated the following


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rheological behaviors. Insert Figures 9 and 10 Rheological Behavior The decrease in the complex viscosity of the model waxy oil without asphaltenes became less significant when the molecular weight distribution of the (alt)SNODMIs was broader, as shown in Figure 11. Moreover, the yield stress monotonically increased with increasing molecular weight distribution, as shown in Figure 11(b). The results were in complete agreement with the results of the crystallization temperature and morphologies of the wax crystals and asphaltene particles. As shown in Figure 12, for the model waxy oil with asphaltenes, both the complex viscosity and yield stress decreased as the MWD of the (alt)SNODMIs increased. The opposite trend compared with the model waxy oils was attributed to the dispersion of asphaltenes, as shown in Figure 10. Insert Figures 11 and 12 Overall, the influence of the molecular weight distribution is rather different for the two types of model waxy oils, i.e., without and with asphaltenes. For the model waxy oil without asphaltenes, the effectiveness of the flow improver is impaired with increasing MWD, which is attributed to the decrease in the number of the most effective component, (alt)SNODMI-B. However, for the model waxy oil with asphaltenes, the effectiveness of the flow improver is enhanced by increasing MWD and flow improver, with a broader MWD being even better than the most effective flow improver with a narrow MWD. Because asphaltenes are polydisperse, it is hypothesized that the larger asphaltenes can be better stabilized by a flow improver with a high molecular weight, whereas the smaller asphaltenes can be better


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stabilized by a flow improver with a low molecular weight. Consequently, asphaltenes can be more efficiently dispersed by flow improvers with a broader MWD rather than a narrower MWD, thus leading to better flow improving performances. The influence and mechanism of the flow improver on the dispersion of asphaltenes will be further investigated in model waxy oils with various contents of asphaltenes in future research.

4. Conclusions

(alt)SNODMIs, which were demonstrated as flow improvers, were synthesized by modifying (alt)SMAs with various molecular weights. To obtain flow improvers with various molecular weight distributions, (alt)SMODMIs with specific molecular weights were blended. (alt)SNODMIs were applied as flow improvers in two types of model waxy oils, i.e., with and without asphaltenes. (alt)SNODMIs greatly reduced the size of the wax crystals, well dispersed the asphaltene particles, and significantly reduced the crystallization temperature, the yield stress, and the complex viscosity. The molecular weight and molecular weight distribution of the prepared flow improvers were found to play critical roles in defining their effectiveness as flow improvers. For the model waxy oil without asphaltenes, (alt)SNODMI with an appropriate medium molecular weight exhibited the best performance as a flow improver. A similar trend was found in the model waxy oil with asphaltenes. It is disadvantageous for the flow improver applied in the model waxy oil without asphaltenes to have an increased molecular weight distribution of (alt) SNODMIs, whereas the opposite results were found in the model waxy oil with asphaltenes. Acknowledgements


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This study was supported by the National Natural Science Foundation of China (21176217), the Zhejiang Provincial Natural Science Foundation (Y4110134), and the Fundamental Research Funds for the Central Universities (2014FZA4023). The authors thank Dr. Erwin Peng at the National University of Singapore for assistance with editing the manuscript.

The authors declare no competing financial interests.


Page 19 of 36

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Energy & Fuels

References (1) Huang, Z.Y.; Lee, H. S.; Senra, M.; Fogler, H. S. AIChE J. 2011, 57, 2955-2964. (2) Ashbaugh, H. S.; Radulescu, A.; Prud'homme, R. K.; Schwahn, D.; Richter, D.; Fetters, L. J. Macromolecules 2002, 35, 7044-7053. (3) Maqbool, T.; Balgoa, A. T.; Fogler, H. S. Energy Fuels 2009, 23, 3681-3686. (4) Venkatesan, R.; Östlund, J. A.; Chawla, H.; Wattana, P.; Nydén, M.; Fogler, H. S. Energy Fuels 2003, 17, 1630-1640. (5) Alcazar-Vara, L. A.; Garcia-Martinez, J. A.; Buenrostro-Gonzalez, E. Fuel 2012, 93, 200-212. (6) Goncalves, J. L.; Bombard, A. J. F.; Soares, D. A. W.; Alcantara, G. B. Energy Fuels 2010, 24, 3144-3149. (7) Kudaibergenov, S. E.; Didukh, A. G.; Ibraeva, Z. E.; Bimendina, L. A.; Rullens, F.; Devillers, M.; Laschewsky, A. J. Appl. Polym. Sci. 2005, 98, 2101-2108. (8) Maity, S. K.; Ancheyta, J.; Marroquín, G. Energy Fuels 2010, 24, 2809-2816. (9) Hasan, S. W.; Ghannam, M. T.; Esmail, N. Fuel 2010, 89, 1095-1100. (10) Machado, A. L. C.; Lucas, E. F.; González, G. J. Pet. Sci. Eng. 2001, 32, 159-165. (11) Schwahn, D.; Richter, D.; Lin, M.; Fetters, L. J. Macromolecules 2002, 35, 3762-3768. (12) Soldi, R. A.; Oliveira, A. R. S.; Barbosa, R. V.; César-Oliveira, M. A. F. Eur. Polym. J. 2007, 43, 3671-3678. (13) Jung, K. M.; Chun, B. H.; Park, S. H.; Lee, C. H.; Kim, S. H. J. Appl. Polym. Sci. 2011, 120, 2579-2586.


Energy & Fuels

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(14) Wu, Y. M.; Ni, G. D.; Yang, F.; Li, C. X.; Dong, G. L. Energy Fuels 2012, 26, 995-1001. (15) Guo, X. H.; Li, L.; Prud'homme, R. K. Abstr. Pap. Am. Chem. Soc.2006, 51, 254-256. (16) Xu, J.; Qian, H. Q.; Xing, S. L.; Li, L.; Guo, X. H. Energy Fuels 2011, 25, 573-579. (17) Deshmukh, S.; Bharambe, D. J. Disper. Sci. Technol. 2011, 32, 291-297. (18) Al-Sabagh, A. M.; El-Din, M. R. N.; Morsi, R. E.; Elsabee, M. Z. J. Disper. Sci. Technol. 2009, 30, 420-426. (19) Song, Y. P.; Ren, T. H.; Fu, X. S.; Xu, X. H. Fuel Processing Technology 2005, 86, 641-650 (20) Borthakur, A.; Chanda, D.; Choudhury, S. R. D.; Rao, K. V.; Subrahmanyam, B. Energy Fuels 1996, 10, 844-848. (21) Castro, L. V.; Flores, E. A.; Vazquez, F. Energy Fuels 2011, 25, 539-544. (22) Chanda, D.; Sarmah, A.; Borthakur, A.; Rao, K. V.; Subrahmanyam, B.; Das, H. C. Fuel 1998, 77, 1163-1167. (23) El-Gamal, I. M.; Ghuiba, F. M.; El-Batanoney, M. H.; Gobiel, S. J. Appl. Polym. Sci. 1994, 52, 9-19. (24) Ahmed, N. S.; Nassar, A. M.; Nasser, R. M.; Khattab, A. F.; Abdel-Azim, A. A. A. Pet. Sci. Technol. 2008, 26, 1390-1402. (25) Ahmed, N. S.; Nassar, A. M.; Nasser, R. M.; Khattab, A. F.; Abdel-Azim, A. A. A. J. Disper. Sci. Technol. 2012, 33, 668-675. (26) Kuzmic, A. E.; Radoševic, M.; Bogdanic, G.; Srica, V.; Vukovic, R. Fuel 2008, 87,

2943–2950. (27) Taraneh, J. B.; Rahmatollah, G.; Hassan, A.; Alireza, D. Fuel Process Technol. 2008, 89,


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Energy & Fuels

973-977. (28) El-Gamal, I. M.; Gobiel, S. J. Appl. Polym. Sci. 1996, 61, 1265-1272. (29) El-Gamal, I. M.; Gad, E. A. M.; Faramawi, S. J. Chem. Tech. Biotechnol. 1992, 55, 123-130. (30) Cao, K.; Wei, X. X.; Li, B. J.; Zhang, J. S.; Yao, Z. Energy Fuels. 2013, 27, 640-645. (31) Cao, K.; Zhu, Q. J.; Wei, X. X.; Yao, Z. Energy Fuels. 2015, 29, 993-1000. (32) Yao, Z.; Zhang, J. S.; Chen, M. L.; Li, B. J.; Liu, H. Y.; Cao, K. J. Appl. Polym. Sci. 2011, 121, 1740-1746. (33) Liu, H. Y.; Cao, K.; Huang, Y.; Yao, Z.; Li, B. G.; Hu, G. H. J. Appl. Polym. Sci. 2006, 100, 2744-2749. (34) Pedersen, K. S.; Rønningsen, H. P. Energy Fuels. 2003, 17, 321-328. (35) Mezger, T. G. The Rheology Handbook, 2nd ed.; Vincentz Network: Hannover, 2006; Chapter 8. (36) Ashbaugh, H. S.; Fetters, L. J.; Adamson, D. H.; Prud’homme, R. K. J Rheol. 2002, 46, 763-776. (37) Jang, Y. H.; Blanco, M.; Creek, J.; Tang, Y. C.; Goddard, W. A. J. Phys. Chem. B. 2007, 111, 13173−13179.


Energy & Fuels

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Page 22 of 36

Captions Table 1. Samples of the model waxy oils with various (alt)SNODMIs Figure 1. Effect of (alt)SNODMIs with different molecular weights on the crystallization temperature for the model waxy oil without asphaltenes Figure 2. Effect of (alt)SNODMIs with different molecular weights on the crystallization temperature for the model waxy oil with asphaltenes Figure 3. Effect of (alt)SNODMIs with different molecular weights on the morphology of wax crystals for the model waxy oil without asphaltenes: (a) without flow improver; (b) (alt)SNODMI-A (Mn = 1800 Da); (c) (alt)SNODMI-B (Mn = 3300 Da); (d) (alt)SNODMI-C (Mn = 5600 Da); and (e) (alt)SNODMI-E (Mn = 12100 Da) Figure 4. Effect of (alt)SNODMIs with different molecular weights on the morphology of wax crystals for the model waxy oil with asphaltenes: (a) without flow improver; (b) (alt)SNODMI-B (Mn = 3300 Da); (c) (alt)SNODMI-C (Mn = 5600 Da); (d) (alt)SNODMI-D (Mn = 9000 Da); and (e) (alt)SNODMI-E (Mn = 12100 Da) Figure 5. Effect of (alt)SNODMIs with different molecular weights on the rheological behavior of the model waxy oil without asphaltenes: (a) evolution of viscosity and (b) influence on yield stress and relative yield stress Figure 6. Effect of (alt)SNODMIs with different molecular weights on the rheological behavior of the model waxy oil with asphaltenes: (a) evolution of viscosity and (b) influence on yield stress and relative yield stress Figure 7. Effect of (alt)SNODMIs with different molecular weight distributions on the crystallization temperature for the model waxy oil without asphaltenes Figure 8. Effect of (alt)SNODMIs with different molecular weight distributions on the crystallization temperature for the model waxy oil with asphaltenes Figure 9. Effect of (alt)SNODMIs with different molecular weight distributions on the morphology of wax crystals for the model waxy oil without asphaltenes: (a) without flow improver; (b) (alt)SNODMI-B (Mn = 3300 Da, PDI = 1.26); (c) (alt)SNODMI-I (Mn = 3300 Da, PDI = 1.71); (d) (alt)SNODMI-J (Mn = 3300 Da, PDI = 2.39); and (e) (alt)SNODMI-K (Mn = 3300 Da, PDI = 2.98) Figure 10. Effect of (alt)SNODMIs with different molecular weight distributions on the morphology of wax crystals for the model waxy oil with asphaltenes: (a) without flow improver; (b) (alt)SNODMI-B (Mn = 3300 Da, PDI = 1.26); (c) (alt)SNODMI-I (Mn = 3300 Da, PDI = 1.71); and (d) (alt)SNODMI-J (Mn = 3300 Da, PDI = 2.39) Figure 11. Effect of (alt)SNODMIs with different molecular weight distributions on the rheological behavior of the model waxy oil without asphaltenes: (a) evolution of viscosity and (b) influence on yield stress and relative yield stress Figure 12. Effect of (alt)SNODMIs with different molecular weight distributions on the


Page 23 of 36

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Energy & Fuels

rheological behavior of the model waxy oil with asphaltenes: (a) evolution of viscosity and (b) influence on yield stress and relative yield stress


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

Page 24 of 36

Table 1. Samples of the model waxy oils with various (alt)SNODMIs (alt) SMA (precursor of (alt) SNODMI) Flow improver

Model waxy oil without asphaltenes

Model waxy oil with asphaltenes

Mn (Da)

MWD

MAh Molar Content (%)

None

-

-

-

N1

N2

(alt) SNODMI-A

1800

1.29

45.2

A1

-

(alt) SNODMI-B

3300

1.26

45.1

B1

B2

(alt) SNODMI-C

5600

1.24

46.3

C1

C2

(alt) SNODMI-D

9000

1.29

45.5

-

D2

(alt) SNODMI-E

12100

1.31

46.2

E1

E2

3300

1.71

45.9

I1

I2

3300

2.39

45.4

J1

J2

3300

2.98

45.7

K1

K2

(alt) SNODMI-I (blending 33 wt % A with 67 wt % C)

(alt) SNODMI-J (blending 43 wt % A with 57 wt % D)

(alt) SNODMI-K (blending 46 wt % A with 54 wt % E)

Note: all flow improvers were added at a concentration of 0.1 wt% concentration based on the model waxy oils.


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

Heat Flow / W/g

Page 25 of 36

-2.4

Mn=12100 D a

-2.7

Mn=5600 D a

-3.3

Mn=3300 D a

-2.9

Mn=1800 D a

0.5

-20

-10

0

without flow i mprover

10

20

30

o

Crystalliz ation Temperatu re / C

Figure 1. Effect of (alt)SNODMIs with different molecular weights on the crystallization temperature for the model waxy oil without asphaltenes


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

Heat F low / W/g

Energy & Fuels

-3.7

Mn= 12100 Da

-3.9

Mn= 9000 Da

-4.5

Mn= 5600 Da

-3.7

Mn= 3300 Da

-2.2

-20

-10

Page 26 of 36

0

without flow improv er

10

20

30

o

Crystallization Temperature / C

Figure 2. Effect of (alt)SNODMIs with different molecular weights on the crystallization temperature for the model waxy oil with asphaltenes


Page 27 of 36

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

(a)

(b)

(c)

(d)

(e)

Figure 3. Effect of (alt)SNODMIs with different molecular weights on the morphology of wax crystals for the model waxy oil without asphaltenes: (a) without flow improver; (b) (alt)SNODMI-A (Mn = 1800 Da); (c) (alt)SNODMI-B (Mn = 3300 Da); (d) (alt)SNODMI-C (Mn = 5600 Da); and (e) (alt)SNODMI-E (Mn = 12100 Da)


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

(a)

(b)

(c)

Page 28 of 36

(d)

(e)

Figure 4. Effect of (alt)SNODMIs with different molecular weights on the morphology of wax crystals for the model waxy oil with asphaltenes: (a) without flow improver; (b) (alt)SNODMI-B (Mn = 3300 Da); (c) (alt)SNODMI-C (Mn = 5600 Da); (d) (alt)SNODMI-D (Mn = 9000 Da); and (e) (alt)SNODMI-E (Mn = 12100 Da)


Page 29 of 36

10

10

6

600 t y without flow impr over t y versus Molecular Weight t re la tiv e versus Molecular Weight

5

1

y / Pa

 relative

100

104

*

 / 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

Waxy oil without asphaltenes

10

3

Mn=1800 Da Mn=3300 Da Mn=5600 Da

0.1

Mn=12100 Da

102

10

0

10 1

10  / Pa

10

2

0

2000

4000

(a) Figure 5.

6000

8000

10000 12000 14000

Mo lecular Weigh t / Da

(b)

Effect of (alt)SNODMIs with different molecular weights on the rheological behavior of the

model waxy oil without asphaltenes: (a) evolution of viscosity and (b) influence on yield stress and relative yield stress


Energy & Fuels

1000 t y without flow impr over t y versus Molecular Weight t rel at iv e versus Molecular Weight

5

*

104

1

relative

10

6

y / Pa

10

 / 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 30 of 36

100

0.1

waxy oil with asphaltene

10

3

Mn= 3300 Da Mn= 5600 Da Mn= 9000 Da Mn= 12100 D a

102

0

10

Figure 6.

1

10

10

2

0

2000

4000

6000

8000

0.01 10000 12000 14000

 / Pa

Molecular Weight / Da

(a)

(b)

Effect of (alt)SNODMIs with different molecular weights on the rheological behavior of the

model waxy oil with asphaltenes: (a) evolution of viscosity and (b) influence on yield stress and relative yield stress


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

Heat F low / W/g

Page 31 of 36

-20

-10

-2.0

M n=330 0 Da, PDI= 2.98

-2.6

M n=330 0 Da, PDI= 2.39

-2.9

M n=330 0 Da, PDI= 1.71

-3.3

M n=330 0 Da, PDI= 1.26

0.5

without flow improver

0

10

20

30

o


Figure 7.

Effect of (alt)SNODMIs with different molecular weight distributions on the crystallization

temperature for the model waxy oil without asphaltenes


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

Heat F low / W/g

Energy & Fuels

-20

-10

Page 32 of 36

-4.9

Mn=3300 Da, PDI=2 .39

-4.7

Mn=3300 Da, PDI=1 .71

-3.7

Mn=3300 Da, PDI=1 .26

-2.2

without flow improver

0

10

20

30

o


Figure 8.

Effect of (alt)SNODMIs with different molecular weight distributions on the crystallization

temperature for the model waxy oil with asphaltenes


Page 33 of 36

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

(a)

Figure 9.

(b)

(c)

(d)

(e)

Effect of (alt)SNODMIs with different molecular weight distributions on the morphology of

wax crystals for the model waxy oil without asphaltenes: (a) without flow improver; (b) (alt) SNODMI-B (Mn = 3300 Da, PDI = 1.26); (c) (alt) SNODMI-I (Mn = 3300 Da, PDI = 1.71); (d) (alt) SNODMI-J (Mn = 3300 Da, PDI = 2.39); and (e) (alt) SNODMI-K (Mn = 3300 Da, PDI = 2.98)


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

(a)

(b)

(c)

Page 34 of 36

(d)

Figure 10. Effect of (alt)SNODMIs with different molecular weight distributions on the morphology of wax crystals for the model waxy oil with asphaltenes: (a) without flow improver; (b) (alt)SNODMI-B (Mn = 3300 Da, PDI = 1.26); (c) (alt)SNODMI-I (Mn = 3300 Da, PDI = 1.71); and (d) (alt)SNODMI-J (Mn = 3300 Da, PDI = 2.39)


Page 35 of 36

6

500

10

t y without Flow Improver t y versus Molecul ar Weight Distribution t re la ti ve versus Molecul ar Weight Di stribution

5

10

1

y / Pa

4

*

10

3

10

 relative

100

 / 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

waxy oil without asphaltene Mn=3300 Da, PDI=1.26 Mn=3300 Da, PDI=1.71 Mn=3300 Da, PDI=2.39 Mn=3300 Da, PDI=2.98

0.1

10

2

10

0

10

1

10  / Pa

2

10

1.0

1.5

(a) Figure 11.

2.0

2.5

3.0

3.5

Molecular Weight Distribution

(b)

Effect of (alt)SNODMIs with different molecular weight distributions on the rheological

behavior of the model waxy oil without asphaltenes: (a) evolution of viscosity and (b) influence on yield stress and relative yield stress


Energy & Fuels

6

4

10

3

10

2

1

relative

10

t without Flow Improver y t y versus Molecular Weight Distribution t rel at iv e versus Molecular Weight Distribution

*

10

5

1000

y / Pa

10

 / 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 36 of 36

100

0.1

waxy oil with asphaltenes Mn=3300 Da, PDI=1.26 Mn=3300 Da, PDI=1.71 Mn=3300 Da, PDI=2.39

10

0

Figure 12.

1

10

10

2

10 1.0

1.5

2.0

2.5

 / Pa

Molecular Weight Distribution

(a)

(b)

0.01

Effect of (alt)SNODMIs with different molecular weight distributions on the rheological

behavior of the model waxy oil with asphaltenes: (a) evolution of viscosity and (b) influence on yield stress and relative yield stress


Influences of the Molecular Weight and Its Distribution of Poly(styrene

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