RESEARCH ARTICLE

Synthesis of poly(maleic acid alkylamide-co-α-olefin-co-styrene) and their effect on flow ability of oils

Jingjing XU1, Jun XU (✉)1, Jie SUN2, Shili XING1, Li LI1, Xuhong GUO1

1 State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China2 Institute of Chemical Materials, China Academy of Engineering Physics, Sichuan 621900, China

© Higher Education Press and Springer-Verlag Berlin Heidelberg 2010

Abstract To improve the flow ability of crude oil withhigh content of aromatic asphaltenes, new comb-typecopolymers of poly(maleic anhydride-co-α-olefin-co-styrene) (MASCs) with different ratios of maleic anhydride(MA) to styrene were designed and synthesized. 1H NMRand FTIR spectra were used to characterize the chemicalstructure of the copolymers. The effect of copolymers onthe flow ability of model waxy oil and crude oil werestudied by rheological method and polarizing lightmicroscopy. Upon the addition of MASCs, the yieldstresses of oils were decreased by 1 to 3 orders ofmagnitude, and the morphology of paraffin crystals werereduced and changed from plates to needles.

Keywords comb-polymers, styrene, paraffin, crystalliza-tion, flow ability

1 Introduction

Crude oil is a complex mixture that consists of paraffins,aromatic hydrocarbons, resins, and asphaltenes. At hightemperatures (70°C–150°C), crude oils behave as fluidwith low viscosity. However, as the temperature declines,the solubility of long chain paraffins and asphaltenesdecreases sharply. The long chain paraffins and asphalteneswill precipitate and deposit at the pipe walls, reducing oilflow and even blocking the pipeline [1]. The problembecomes more serious for offshore deep-sea wells, wherethe temperature at the sea bed can be 4°C or lower [2,3]. Tosolve this problem, heating and mechanical pigging arealways applied in the petroleum industry [4]. However,these methods consume a lot of energy and are

uneconomic. Using the chemical additives to alleviate orsolve the wax deposition problem becomes a better choiceand an important method that has absorbed intensiveresearch interests recently.Several kinds of comb-type polymer additives, such as

poly(ethylene-butene) (PEB) and poly(maleic anhydride-co-α-olefin) (MAC), have been reported to be effective inimproving the cold flow ability of waxy oils [5–8]. In thiswork, new comb-type copolymers of poly(maleic acidalkylamide-co-α-olefin-co-styrene) (MASC) with differentratios of maleic anhydride (MA) to styrene were designedand synthesized. The introduction of styrene will lead to abetter interaction with asphaltenes that contain aromaticsubstance. 1H NMR and FTIR spectra were used tocharacterize the chemical structure of the MASC copoly-mers. The effect of copolymers on the cold flow ability ofmodel waxy oil and crude oil were studied by rheologicalmethod.

2 Experiment

2.1 Chemicals and sample preparation

Decane (anhydrous, > 99%), hexatriacontane(C36,> 98%), maleic anhydride (99%), α-octadecene(95%), benzoyl peroxide (99%), o-xylene (98%), andoctadecylamine (97%) were purchased from Alfa-Easercompany and used as obtained. Styrene (90%), purchasedfrom Shanghai Lingfeng Medicine Company, was washedby 5%NaOH aqueous solution for 3 times, then washed byexcess distilled water until the pH reached 7, and finallydried by anhydrous Na2SO4.The model waxy oil was prepared by dissolving

hexatriacontane (C36) in decane with concentrations of4 wt-%. The number in MASC0.5, MASC0.75, and

Received March 10, 2010; accepted May 8, 2010

E-mail: wiselyxj@126.com

Front. Chem. Sci. Eng. 2011, 5(1): 74–78DOI 10.1007/s11705-010-0542-5

MASC1.0 means that the molar ratio of styrene to maleicanhydride is 0.5, 0.75, and 1.0, respectively.

2.2 Synthesis of MASC

Poly(maleic anhydride-co-α-olefin-co-styrene) wassynthesized by α-octadecene, maleic anhydride, andstyrene in o-xylene by free-radical polymerization, usingbenzoyl peroxide as initiator (Scheme 1(a)). By amidationwith excess long chain n-amines, the comb-type terpoly-mers (MASC) were obtained (Scheme 1(b)).The terpolymers were precipitated in methanol, washed

by distilled water after filtration, and then dried by freezedrying. The chemical structure of terpolymer wasconfirmed by 1H NMR and FTIR spectroscopy. Themolecular weight of terpolymers with different ratios ofmaleic anhydride (MA) to styrene was determined by GPCwith THF as solvent (Table 1).

2.3 Instruments

1H NMR spectra were recorded on a Bruker DRX500

spectrometer for samples dissolved in deuterated acetone.FTIR spectra were recorded on Magna-IR550 (Nicolet,America). Wax crystal morphologies were observed usinga Nikon COOLPIX P5100 inverted microscope (ShanghaiChangfang 59XA). The molecular weights and molecularweight distributions were determined by GPC (DIONEXUltimate 3000) using poly(styrene) samples as standards.The yield stress measurements were performed on a

Physica MCR101 controlled stress rheometer with a 25mm parallel plate. Oil samples were heated to 70°C, kept atthis temperature for 5 min to erase their thermal history,and then cooled to the experimental test temperature at arate of ca. 10°C/min. Both the model waxy oil and crudeoil tests were made at 0°C. After allowing the samples toanneal at constant temperature with no stress for 5 min,stress was applied and incrementally increased every 10 s(100 stress increments per decade), and the viscosity wasmeasured. The yield stress (τy) is defined as the stressbelow which no flow occurs. An operational definition ofthe yield stress is adopted as the stress at the transitionbetween the creep and liquid-like viscosity regimes, wherethe yield stress can be identified as the stress for which the

Scheme 1 Synthesis of (a) poly(maleic anhydride-co-α-olefin-co-styrene) and (b) poly(maleic acid alkylamide-co-α-olefin-co-styrene amide).

Jingjing XU et al. Synthesis of poly(maleic acid alkylamide-co-α-olefin-co-styrene) 75

derivative is a maximum [6]. The initial applied stress waschosen well below the stress at which creep began.

3 Results and discussion

3.1 Characterization of MASC

Figure 1 shows the 1H NMR spectrum of MASC sampleafter purification. The resonance peaks of protons inphenyl group ( –C6H5) of styrene unit, –CH of maleicanhydride unit, and –CH3 of octadecene unit can be foundat 7.2, 3.5, and 0.89 ppm, respectively. In Fig. 2, thestretching of the carbonyl group (C = O) from maleicanhydride unit at 1720 cm–1 can be found in the FTIRspectrum. The characteristic absorptions of the styreneappear at 1613 and 705 cm–1.The solubilities of the new copolymer MASC in various

solvents are compared with those of the possible homo-polymer and dipolymers: polystyrene, poly(maleic anhy-

dride-styrene), and poly(maleic anhydride-co-olefin).MASC does not dissolve in cyclohexane, while poly(maleic anhydride-styrene) and polystyrene do. MASCalso shows different solubility from poly(maleic anhy-dride-co-olefin) in ethyl acetate.The new copolymer was also confirmed by comparing

its melting point with other copolymers using the meltingpoint apparatus. The melting point of the new copolymerMASC is between 125°C – 130°C, which is higher thanpoly(maleic anhydride-co-olefin) (85°C – 90°C) but ismuch lower than poly(maleic anhydride-styrene) (200°C –210°C). Therefore, we consider that the obtained copoly-mer MASC should be a random terpolymer of maleicanhydride, α-olefin, and styrene.

3.2 Effect of MASCs on the model oil and crude oil

As shown in Fig. 3, the yield stress of model waxy oil andcrude oil decreased significantly upon the addition of0.1 wt-% MASC0.5. Upon the addition of 0.1%MASC0.5, the yield stress of crude oil with asphaltenereduced from 1.2 to 0.2 Pa.The relative yield stress is defined as the ratio of the

yield stress with and without MASC. With the increase ofthe concentration of MASCs from 0 to 100 ppm, the yieldstress of the model waxy oil decreased significantly.However, further increase of the MASC concentration to200 ppm results in the enhancement of the yield stress of

Fig. 1 1H NMR spectrum of MASC

Table 1 The molecular weight of MASCs measured by GPC

sample molecular weights /(kg$mol–1)

MASC0.5 16.9

MASC0.75 24.4

MASC1.0 21.9

76 Front. Chem. Sci. Eng. 2011, 5(1): 74–78

model waxy oil due to the “bridge effect” of extrapolymers [3]. Obviously, 100 ppm (0.10 wt-%) of MASCsis the best concentration for the reduction of yield stress ofmodel waxy oil (Fig. 4).Comparing the effect of MASC0.5, MASC0.75, and

MASC1.0, the copolymer with less styrene shows a betterresult to reduce the yield stress of model waxy oil, andMASCs containing more styrene units show a better resultof reducing the yield stress of crude oil with asphaltenesmainly consisted of aromatic components (Fig. 5) due toenhanced interactions between styrene and asphaltenes.

3.3 Effect of MASCs on the morphology of paraffin crystal

With the addition of 0.10% MASCs, the crystal of modelwaxy oil became smaller, and the shapes changedsignificantly from large plate-like crystals to small pieces(Fig. 6). The reduced size of waxy crystals may contributeto the reduction of yield stresses and the improvement ofcold flow ability.

4 Conclusions

Novel comb-type poly(maleic acid alkylamide-co-α-ole-fin-co-styrene)s (MASCs) were synthesized successfullyby free-radical copolymerization. They significantlyreduce the yield stress and improve the cold flow abilityof model waxy oil and crude oil at low temperature. Formodel waxy oil without asphaltenes, the MASCs with lessstyrene units show a better result to reduce the yield stressand the crystal size as observed by optical microscope. Forcrude oil with asphaltenes, MASCs with more styreneunits work better due to the enhanced interactions witharomatic component in asphaltenes.

Fig. 2 FTIR spectrum of MASC

Fig. 3 Yield stresses of model waxy oil and crude oil with andwithout MASC0.5

Fig. 4 Effect of the concentration of MASCs on the yield stressof model waxy oil

Fig. 5 Effect of MASCs on the yield stress of model waxy oil andmix oil

Jingjing XU et al. Synthesis of poly(maleic acid alkylamide-co-α-olefin-co-styrene) 77

Acknowledgements Financial support by the Science Foundation for theExcellent Youth Scholars of East China University of Science andTechnology is gratefully acknowledged.

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Fig. 6 Optical micrographs of crystals from 4 wt-% hexatriacontane (C36). (a) C36; (b) C36+ 0.1% MASC0.5; (c) C36+ 0.1%MASC0.75; (d) C36+ 0.1% MACSC1.0

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