Article pubs.acs.org/EF
Study of the Influence of Imidization Degree of Poly(styrene-co-octadecyl maleimide) as Waxy Crude Oil Flow Improvers Kun Cao,†,‡ Xiang-xia Wei,‡ Ben-ju Li,‡ Jiang-shan Zhang,‡ and Zhen Yao*,‡ †
State Key Laboratory of Chemical Engineering, Zhejiang University, Hangzhou 310027, China Institute of Polymerization and Polymer Engineering, Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China
‡
ABSTRACT: A series of flow improvers (FIs) were synthesized through the reaction between poly(styrene-co-maleic anhydride) with octadecyl amine. Fourier transform infrared spectra confirmed that these FIs had different degrees of imidization, which indicated that the fraction of the maleamic acid group and maleimide group in the FIs could be changed. These FIs were applied to the model waxy oil with C24 as the paraffin. A differential scanning calorimeter, polarizing microscope with a hot stage, and rotation rheometer with parallel plate geometry were employed to characterize the crystallization temperature, crystal morphology, and rheological behaviors, respectively. The results indicated that adding a little bit of the FIs can significantly reduce the crystallization temperature, the number and size of waxy crystals, and the yield stress of the model oil. Moreover, it has been found that the degree of imidization has considerable effects on the performance of the FIs. The FIs with a higher degree of imidization are more effective. This effect is attributed to the difference in the polarity between the maleamic acid group and the maleimide group.
1. INTRODUCTION Wax deposition on the cold wall of crude oil pipelines, which hinders flow and can lead to blocking pipelines, is a severe problem for the oil industry, especially in frigid places or in deep ocean water.1−3 Adding polymer additives, named as the flow improvers (FIs), viscosity reducing agents, and also pour point depressants is effective to prevent wax deposition.4−6 According to their chain structure, FIs can be divided into various types: the polymers with a flexible main chain and short side chains, such as poly(ethylene-co-vinyl acetate) (EVA)7−9 and poly(ethylene-co-butene) (PEB);10−12 the polymers with long nonpolar side chains, such as polyoctadecyl acrylate,13 polytetradecyl/hexadecyl/octadecyl methacrylate, 14 poly(octadecene-co-octadecyl maleamic acid),15 poly(ethyl vinyl ether-co-docosanyl maleamic acid),16 poly(N,N-diallyl-N-octadecylamine-alt-(maleic acid),17 and poly(vinyl acetate-codocosanyl fumarate);18 and the polymers with nonpolar side chains, polar groups, and aromatic groups, such as dodecylphenolic resin,19 poly(alkyl acrylate-acrylic acid),20 poly(alkyl acrylate-acrylic acid-styrene),20 poly(alkyl acrylate-acrylic acid1-vinyl-2-pyrrolidone),20 and poly(alkylacrylate-styrene-1-vinyl2-pyrrolidone),20 which are designed for the crude oil with both paraffins and asphaltene to prevent wax deposition and asphaltene aggregation. Maleic anhydride (MAH) copolymers are commonly used as the precursor for synthesis of FIs. Alkyl side chains are introduced through the reaction between the MAH group and amines. These FIs have been proven efficient for model waxy oil and/or heavy crude oil.1,16,21−28 In these works, FIs were assumed to have either maleamic acid or a diamide structure, as shown in Scheme 1. However, studies on the kinetics of reaction between MAH and amines showed that not only amidification (ringopening reaction) happens but also imidization (ring-closing © 2012 American Chemical Society
Scheme 1. Structures of the Existing Poly(styrene-maleic anhydrate amide) and/or Poly(maleic acid alkylamide-co-α-olefin-co-styrene)16,21−27
reaction) occurs.29−31 The FIs produced from the reaction between MAH and amines are expected to have both the maleamic Received: August 13, 2012 Revised: October 23, 2012 Published: October 24, 2012 640
dx.doi.org/10.1021/ef301336n | Energy Fuels 2013, 27, 640−645
Energy & Fuels
Article
reaction, as in Scheme 3, samples were collected at specified time intervals to obtain polymers with various degrees of imidization. The samples were purified using the same procedure for SODMA. Characterization. The fractions of the maleic anhydride(MAH), maleamic acid, and maleimide in the obtained FIs were determined by Fourier transition infrared (FT-IR) spectrometry (Thermo Nicolet 5700). 2.3. Preparation and Characterization of Model Waxy Oil Samples. Model waxy oil was prepared by dissolving 4 wt % C24 in decane. The FIs with different degrees of imidization were dissolved in this model waxy oil with a given 0.1 wt % concentration. The crystallization temperature (Tc) and melting temperature (Tm) were obtained by a TA-Q200 differential scanning calorimeter (DSC). The scanning rate was 10 °C/min, and the scanning range was from −25 to 50 °C. The instrument calibration was checked by an indium standard before tests. The morphology was observed by a Nikon Eclipse E600POL polarizing microscope equipped with an automatic camera and an ED600 hot stage. Model waxy oil samples were poured in a liquid sample cell with a cover glass and quenched from room temperature to −5 °C, and the morphology of crystals in decane was observed at this temperature. The yield stress measurement was performed on a Thermo HAAKE RS6000 rheometer with parallel plate geometry under shock stress scan mode. The scanning frequency was fixed at 0.318 Hz. The samples were initially heated to 70 °C to erase their thermal history. After the samples were heated, the temperature was immediately decreased to −20 °C to precipitate the wax and form a solid-like gel. The stress was continuously increased from 0.1 to 1000 Pa.
acid and the maleimide groups. To the best of our knowledge, there is no public report on the effect of imidization degree on the performance of FIs. In this work, a series of FIs were synthesized through the reaction between poly(styrene-co-maleic anhydride) with octadecyl amine. On the basis of our previous knowledge of imidization kinetics,30,31 the degree of imidization was controlled in order to investigate its effects on the crystallization temperature, crystal morphology, and rheological behaviors of model waxy oils.
2. EXPERIMENTAL SECTION 2.1. Materials. SMA1000P, SMA2000P, and SMAEF40 were obtained from Sartomor Company, and their characterization data are summarized in Table 1. n-Octadecyl amine (ODA), n-decane, and
Table 1. Poly(styrene-co-maleic anhydride) (SMA) Used in This Work samples
MAH content (mol %)
Mn
polydispersity
SMA1000P SMA2000P SMAEF40
45.7 37.9 23.6
1800 2200 3300
1.69 2.07 2.34
n-tetracosane were purchased from Acro. Chloroform (CHCl3), anhydrous methanol, tetrahydrofuran (THF), and ethyl benzene (EB) were provided by Sinopharm Chemical Reagent, and all materials were used without further purification. 2.2. Synthesis and Characterization of Flow Improvers. Synthesis of Poly(styrene-co-octadecyl maleamic acid) (SODMA). To ensure SMA with an MAH group reacted completely, as in Scheme 2, SMA and ODA were mixed at the molar ratio of 1:1.5 between maleic anhydride and amine. With CHCl3 as the solvent, the reaction was carried out under a nitrogen atmosphere in a flask reactor at 30 °C for 2 h. The crude products were precipitated in anhydrous methanol and alternately dissolved with THF and precipitated with methanol three times. The purified products were dried in vacuum at 40 °C for 24 h. Synthesis of Poly(styrene-co-octadecyl maleimide) (SODMI). SODMA was heated at 135 °C for 48 h with EB as the solvent under a nitrogen atmosphere. During the process of the ring-closing
3. RESULTS AND DISCUSSION 3.1. Degree of Imidization. As shown in Figure 1, the characteristic absorption peaks of SMA at 1860 and 1780 cm−1 (CO stretching bands in the MAH group) completely disappeared, especially for the strong latter in the spectrum for SODMA, while the peak of amide at 1610 cm−1 (CO in amide group) appeared and the peak at 2926 cm−1 (for −CH2 unit in the alkyl chain) obviously strengthened after the ringopening reaction of SMA with ODA, which indicated that the ring-opening reaction was completed. After the ring-closing reaction at high temperature, the peak of amide at 1610 cm−1
Scheme 2. Amidification (Ring-Opening Reaction)
Scheme 3. Imidization (Ring-Closing Reaction)
641
dx.doi.org/10.1021/ef301336n | Energy Fuels 2013, 27, 640−645
Energy & Fuels
Article
Table 3. Summary of Relative DSC Characterization flow improvers 0.1% SODMI 0.05% POMBa
effect on various temps
application system 4 wt % C24 in decane Changqing waxy crude oil 4 wt % C36 in decane diesel fuel jet fuel
0.5% MACb 0.12% EVAPc 250 mg/L POSF-3741 lube oil 0.5% AMd 0.15% C18FVAe viscous oil and residual oil 10 wt % wax in 1% CEf and T801g isooctane
Figure 1. FTIR spectra of SMA1000P, SODMA1000P, and SODMI1000P with various degrees of imidization.
refs
Tc decrease 3.6 °C Tc decrease 2 °C
this work 25
Tc decrease 1.03 °C Tc decrease 0.95 °C Tc decrease 1.7 °C
26 32 33
Tc decrease 3.66 °C 34 Tm decrease 1.95 °C 35 Tm decrease 5.5 °C
36, 37
a
POMB: derivative of octadecyl acrylate−maleic anhydride copolymer. MAC: poly(maleic alkylamide-co-α-olefin). cEVAP: copolymer of ethylene, vinyl acetate, and propylene. dAM: methacrylic acid ester− maleic anhydride copolymers. eC18FVA: copolymers of n-dioctadecyl fumarate with vinyl acetate. fCE: polyalkyl methacrylate. gT801: alkyl naphthalene copolymer. Tc = crystallization temprature, Tm = melting temprature. b
Figure 2. DSC cooling curves for model waxy oil containing 0.1 wt % FIs with various degrees of imidization derived from SMA1000P with 45.7% MAH fraction.
was weaken and even almost completely disappeared, and the characteristic absorption peaks of SODMI at 1700 cm−1 (CO in maleimide unit) and 1277 cm−1 (annular peak in maleimide unit) appeared, which confirmed that the amide group turned into the imide group. FTIR spectra were used here to characterize the reaction degree of imidization. It has been proven in good agreement with the results determined by conductance titration methods in our previous work.30 The characteristic peaks of the phenyl group at 700 cm−1 did not change during the reaction of amidification and imidization. Therefore, the absorbance at 700 cm−1 was chosen as the inner standard before and after the reactions. The fraction of the SODMA converted to SODMI was calculated using the ratio between the area of peaks at 1700 and 700 cm−1. Samples with various degrees of imidization used in this work are summarized in Table 2. 3.2. Crystallization Temperature. Figure 2 presents the DSC cooling curves for model waxy oils containing 0.1 wt % FIs with various degrees of imidization derived from SMA1000P, in which the MAH mole fraction was 45.7%. It
Figure 3. DSC cooling curves for model waxy oil containing 0.1 wt % FIs with various degrees of imidization derived from SMA2000P with 37.9% MAH fraction.
was found that adding a few FIs can reduce the crystallization temperature of model waxy oil. The decrease in crystallization temperature becomes significant when the imidization degree of given FIs is increased. Using the FIs with 100% degree of imidization derived from SMA1000P, the decrease in crystallization temperature is 3.6 °C, and we summarize the relative DSC characterization in this research area in Table 3.32−37 It can be found that the crystallization temperature depression is comparable to that of other works. In Figures 3 and 4, the same trend was found for FIs derived from SMA2000P and SMAEF40, which possessed 37.9 and 23.6 mol % MAH, respectively. Figure 5 further demonstrates the influence of imidization degree and alkyl side group fraction. The FIs derived from SMA with a higher MAH content have
Table 2. Resulting SODMIs with Various Degrees of Imidization precursor SMA MAH content/mol % reaction time/h imidization degree/mol %
FI-1
FI-2
FI-3
FI-4
FI-5
FI-6
FI-7
FI-8
FI-9
1000P 45.7 17.7 85
1000P 45.7 19.1 91
1000P 45.7 21.1 100
2000P 37.9 17.0 84
2000P 37.9 18.4 90
2000P 37.9 20.6 100
EF40 23.6 19.5 85
EF40 23.6 20.8 90
EF40 23.6 23.5 100
642
dx.doi.org/10.1021/ef301336n | Energy Fuels 2013, 27, 640−645
Energy & Fuels
Article
Figure 4. DSC cooling curves for model waxy oil containing 0.1 wt % FIs with various degrees of imidization derived from SMAEF40 with 23.6% MAH fraction. Figure 7. Crystallization morphology of model waxy oil containing 0.1 wt % FIs with various degrees of imidization derived from SMA2000P with 37.9% MAH fraction.
Figure 5. Crystallization temperature of model waxy oil containing 0.1 wt % FIs with various degrees of imidization.
Figure 8. Crystallization morphology of model waxy oil containing 0.1 wt % FIs with various degrees of imidization derived from SMAEF40 with 23.6% MAH fraction.
shape of a round rod. There is also an apparent overlap between crystals. With the addition of FIs, the crystals become fewer and are well-dispersed in the solvent. Furthermore, the size of crystals is reduced considerably, and the shape of crystals is changed to needle-like. The influence is more significant for FIs with a higher degree of imidization. The crystallization morphology of the model waxy oil containing FIs derived from SMA2000P and SMAEF40 is shown in Figures 7 and 8, respectively. It could be seen that adding FIs results in the decrease in the number and size of crystals from waxy oils. Profound effects of the degree of imidization on crystallization morphology are also found in Figures 7 and 8. 3.4. Rheology. The yielding behavior of waxy oils is complex and similar to the deformation and fracture of ductile solids.38 The yield stress (τy) is defined as the stress below which no flow occurs. Here, τy is identified as shown below39
Figure 6. Crystallization morphology of model waxy oil containing 0.1 wt % FIs with various degrees of imidization derived from SMA1000P with 45.7% MAH fraction.
more alkyl side chains, which results in a more significant decrease in crystallization temperature. 3.3. Morphology. Figure 6 shows the crystallization morphology of model waxy oils containing 0.1 wt % FIs with various degrees of imidization derived from SMA1000P. Without the addition of FIs, crystals from model waxy oil are large and in the
τy = −
d(ln η*) d(ln τ )
where η* is the measured viscosity. 643
dx.doi.org/10.1021/ef301336n | Energy Fuels 2013, 27, 640−645
Energy & Fuels
Article
Figure 9. (a) Evolution of viscosity for model waxy oil containing 0.1 wt % FIs with various degrees of imidization derived from SMA1000P with 45.7% MAH fraction. (b) Effect of imidization degree on yield stress.
Figure 10. (a) Evolution of viscosity for model waxy oil containing 0.1 wt % FIs with various degrees of imidization derived from SMA2000P with 37.9% MAH fraction. (b) Effect of imidization degree on yield stress.
Figure 11. (a) Evolution of viscosity for model waxy oil containing 0.1 wt % FIs with various degrees of imidization derived from SMAEF40 with 23.6% MAH fraction. (b) Effect of imidization degree on yield stress.
τy is reached. It demonstrated that adding FIs can reduce τy by about 70 times. Also seen in Figure 9b, the decline in τrelative increases considerably with the increase of imidization degree. Similar phenomena are found for FIs derived from SMA2000P and SMAEF40, as shown in Figures 10 and 11. As all MAH groups in SMA reacted with ODA, the alkyl side chain content in FIs is proportional to the MAH fraction in its SMA precursor. Figure 12 shows that both τy and τrelative are reduced significantly with the increase in the molar fraction of alkyl side chains.
The relative yield stress is calculated as τrelative =
τy (with FI) τy (without FI)
Evolution of viscosity with increasing stress is shown in Figure 9a for the model waxy oil containing 0.1 wt % FIs with various degrees of imidization derived from SMA1000P. As the stress upon the samples increased, a decrease in η* is observed, indicating that creep occurs. The samples finally yield when the 644
dx.doi.org/10.1021/ef301336n | Energy Fuels 2013, 27, 640−645
Energy & Fuels
Article
(5) Soni, H. P.; Kiranbala; Bharambe, D. P. Energy Fuels 2008, 22, 3930−3938. (6) Castro, L. V.; Vazquez, F. Energy Fuels 2008, 22, 4006−4011. (7) Machado, A. L. C.; Lucas, E. F. J. Appl. Polym. Sci. 2002, 85, 1337−1348. (8) Marie, E.; Chevalier, Y.; Eydoux, F.; Germanaud, L.; Flores, P. J. Colloid Interface Sci. 2005, 290, 406−418. (9) Ashbaugh, H. S.; Guo, X. H.; Schwahn, D.; Prud’homme, R. K.; Richter, D.; Fetters, L. J. Energy Fuels 2005, 19, 138−144. (10) Ashbaugh, H. S.; Radulescu, A.; Prud’homme, R. K.; Schwahn, D.; Richter, D.; Fetters, L. J. Macromolecules. 2002, 35, 7044−7053. (11) Radulescu, A.; Schwahn, D.; Stellbrink, J.; Kentzinger, E.; Heiderich, M.; Richter, D.; Fetters, L. J. Macromolecules 2006, 39, 6142−6151. (12) Guo, X. H.; Pethica, B. A.; Huang, J. S.; Prud’homme, R. K.; Adamson, D. H.; Fetters, L. J. Energy Fuels 2004, 930−937. (13) Jang, Y. H.; Blanco, M.; Creek, J.; Tang, Y. C.; Goddard, W. A. J. Phys. Chem. B 2007, 111, 13173−13179. (14) Soldi, R. A.; Oliveira, A. R. S.; Barbosa, R. V.; Cesar-Oliveira, M. A. F. Eur. Polym. J. 2007, 43, 3671−3678. (15) Guo, X. H.; Herrera-Alonso, M.; Tinsley, L.; Prud’homme, R. K. Abstr. Pap. Am. Chem. Soc. 2005, 230, 2316−2317. (16) Tinsley, J. F.; Prud’homme, R. K.; Guo, X. H.; Adamson, D. H.; Callahan, S.; Amin, D.; Shao, S.; Kriegel, R. M.; Saini, R. Energy Fuels 2007, 21, 1301−1308. (17) 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. (18) Borthakur, A.; Chanda, D.; Choudhury, S. R. D.; Rao, K. V.; Subrahmanyam, B. Energy Fuels 1996, 10, 844−848. (19) Chang, C. L.; Fogler, H. S. Fuel Sci. Technol. Int. 1996, 14, 75−100. (20) Kuzmic, A. E.; Radosevic, M.; Bogdanic, G.; Srica, V.; Vukovic, R. Fuel 2008, 87, 2943−2950. (21) Guo, X. H.; Li, L.; Prud’homme, R. K. Abstr. Pap. Am. Chem. Soc. 2006, 51, 254−256. (22) Abdel-Azim, A.; Nasser, A. M.; Ahmed, N. S.; Kamal, R. S. Pet. Sci. Technol. 2011, 29, 97−107. (23) Tinsley, J. F.; Jahnke, J. P.; Adamson, D. H.; Guo, X. H.; Amin, D.; Kriegel, R.; Saini, R.; Dettman, H. D.; Prud’homme, R. K. Energy Fuels 2009, 23, 2065−2074. (24) Xu, J.; Qian, H. Q.; Xing, S. L.; Li, L.; Guo, X. H. Energy Fuels 2011, 25, 573−579. (25) Wu, Y. M.; Ni, G. D.; Yang, F.; Li, C. X.; Dong, G. L. Energy Fuels 2012, 26, 995−1001. (26) Xu, J.; Zhang, X. Y.; Sun, J.; Li, L.; Guo, X. H. Asia-Pac. J. Chem. Eng. 2009, 4, 551−556. (27) Li, L.; Xu, J.; Tinsley, J.; Adamson, D. H.; Pethica, B. A.; Huang, J. S.; Prud’homme, R. K.; Guo, X. H. AIChE J. 2012. DOI: 10.1002/ aic.12729. (28) Soni, H. P.; Kiranbala; Agrawal, K. S.; Nagar, A.; Bharambe, D. P. Fuel Process. Technol. 2010, 91, 997−1004. (29) Hu, G. H.; Lindt, J. T. Polym. Bull. 1992, 29, 357−363. (30) Liu, H. Y.; Cao, K.; Huang, Y.; Yao, Z.; Li, B. G.; Hu, G. H. J. Appl. Polym. Sci. 2006, 100, 2744−2749. (31) Liu, H. Y.; Yao, Z.; Cao, K.; Li, B. G. J. Appl. Polym. Sci. 2010, 116, 2951−2957. (32) Zhang, J. L.; Wu, C. J.; Li, W.; Wang, Y. P.; Han, Z. T. Fuel 2003, 82, 1419−1426. (33) Zabarnick, S.; Widmor, N. Energy Fuels 2001, 15, 1447−1453. (34) Du, T.; Wang, S.; Liu, H.; Song, C.; Nie, Y. Pet. Sci. Technol. 2012, 30, 212−221. (35) Peng, H. Y.; Yang, Y. S.; Qi, G. R. Pet. Sci. Technol. 2002, 20, 65−75. (36) Chen, W. H.; Zhao, Z. C.; Yin, C. Y. Fuel 2010, 89, 1127−1132. (37) Chen, W. H.; Zhang, X. D.; Zhao, Z. C.; Yin, C. Y. Fluid Phase Equilib. 2009, 280, 9−15. (38) Wardhaugh, L. T.; Boger, D. V. J. Rheol. 1991, 35, 1121−1156. (39) Ashbaugh, H. S.; Fetters, L. J.; Adamson, D. H.; Prud’homme, R. K. J. Rheol. 2002, 46, 763−776.
Figure 12. Effect of alkyl side chain content of poly(styrene-cooctadecyl maleimide) on yield stress.
A plausible mechanism has been proposed by studies8,13 to explain the effects of FIs on the crystallization and rheological behavior of waxy oil. It is demonstrated that the alkyl chains in FI molecules cocrystallize with the n-paraffins, inhibiting the formation of platelets and the growth of crystals. In our research, the influence of imidization degree can be attributed to the difference in polarity. Nonpolar paraffins, such as C24, should be less compatible with the polar maleamic acid group than the maleimide group, which has less polarity. Therefore, given FIs with a higher degree of imidization are more effective for the model waxy oil.
4. CONCLUSIONS The designed poly(styrene-co-octadecyl maleimide) with different degrees of imidization were obtained and used as FIs for the model waxy oil. Using these FIs, the wax crystals become fewer and smaller. The crystallization temperature and the yield stress can be reduced by 3.6 °C and 70 times, respectively. Moreover, it has been found that the performance of FIs is significantly affected by the degree of imidization. With the increase in the degree of imidization, more maleamic acid groups are converted into maleimide groups, which promotes the compatibility between nonpolar paraffins and FIs.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This study was supported by the National Natural Science Foundation of China through Project 21176217, Zhejiang Provincial Natural Science Foundation through Project Y4110134, the Program for Changjiang Scholars and Innovative Research Team in University (No. IRT0942), and the Fundamental Research Funds for the Central Universities.
■
REFERENCES
(1) Al-Sabagh, A. M.; El-Din, M. R. N.; Morsi, R. E.; Elsabee, M. Z. J. Pet. Sci. Eng. 2009, 65, 139−146. (2) García, M. D. C.; Orea, M.; Carbognani, L.; Urbina, A. Pet. Sci. Technol. 2001, 19, 189−196. (3) García, M. D. C.; Urbina, A. Pet. Sci. Technol. 2003, 21, 863−878. (4) Castro, L. V.; Flores, E. A.; Vazquez, F. Energy Fuels 2011, 25, 539−544. 645
dx.doi.org/10.1021/ef301336n | Energy Fuels 2013, 27, 640−645
