Effect of Spacer Length between Phenyl Pendant and Backbone in

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Effect of Spacer Length between Phenyl Pendant and Backbone in Comb Copolymers on Flow Ability of Waxy Oil with Asphaltenes Tao Li, Jun Xu, Run Zou, Hejian Jiang, Junyou Wang, Li Li, Martien Abraham Cohen Stuart, Robert K Prud'homme, and Xuhong Guo Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b02904 • Publication Date (Web): 18 Oct 2017 Downloaded from http://pubs.acs.org on October 19, 2017

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Industrial & Engineering Chemistry Research

Effect of Spacer Length between Phenyl Pendant and Backbone in Comb Copolymers on Flow Ability of Waxy Oil with Asphaltenes Tao Li1, Jun Xu1*, Run Zou1, Hejian Jiang1, Junyou Wang1, Li Li1, Martien A. Cohen Stuart1, Robert K. Prud’homme2, Xuhong Guo1,3*

1

State Key Laboratory of Chemical Engineering, East China University of Science

and Technology, Shanghai 200237, China 2

Department of Chemical Engineering and Princeton Materials Institute, Princeton

University, Princeton, New Jersey 08544, USA 3

Engineering Research Center of Materials Chemical Engineering of Xinjiang

Bingtuan, Shihezi University, Xinjiang 832000, PR China

*To whom correspondence should be addressed. E-mail: [email protected] (Jun Xu) or [email protected] (Xuhong Guo)

ACS Paragon Plus Environment


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Abstract Waxy crude oil containing large amounts of paraffins often results in various difficulties in extraction and transportation especially at low temperature. Comb-type copolymers with phenyl pendants were found to be able to improve the flow-ability of waxy oils effectively. To investigate the influence of spacer length between phenyl pendant and polymer backbone in comb copolymers on the flow-ability of waxy oil, poly(α-octadecene -comaleic acid phenyl alkyl amide)s with various spacer length were synthesized by modification of poly(α-octadecene -comaleic anhydride) with aniline

(AMAC),

phenethylamine

(EMAC),

phentermine

(BMAC)

and

phenyl-undecanoicamide (UMAC), respectively. Their effects on the morphology and crystallization of model and crude oils were observed by polarized light microscopy and DSC. The flow-ability of both oils in the presence of copolymers were studied by means of rheology, including measuring yield stress, viscosity and thixotropic properties. It is found that the spacer length remarkably affects the rheology and wax crystallization behaviors for both oils. Copolymer with longer spacer can provide better flexibility of phenyl pendants to disperse asphaltenes more effectively, and the long spacer can co-crystallize with long chain paraffins.

Keywords: waxy crude oil, paraffin crystallization, asphaltene aggregation, flow ability.


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1. Introduction Crude oil is a significant and fundamental source of energy. As oil consumption plays an important role in economic growth nowadays, there are continuous demands for crude oil worldwide. However, crude oil and its abundant derivative products are composed of a wide range of complex hydrocarbons, among which long chain paraffin waxes and polar asphaltenes are mainly responsible for some serious problems from production, transportation and refinement in oil industry.1-3 Especially, paraffin waxes constitute up to 35% of the total mixture in some crude oils.4, 5 In the world petroleum reserves, waxy crude oils occupy about 20% of nonconventional oils at present.

Over 80% of crude oils exploited are waxy crude

oil in China. Waxy crude oil with a high content of waxes normally shows a high wax appearance temperature (WAT), high viscosity, and follows non-Newtonian flow behaviors. Below the WAT, wax begins to precipitate and crystallize, and then forms the “house-of-card” network,6 thereby entrapping the remaining liquid oil in cake-like structure.7 As the temperature further decreases and approaches the pour point, crude oil may gelate completely and block the entire pipeline during the transportation, which usually leads to the cease of flow.8 Therefore, improvement of flow-ability of crude oil during transportation at low temperature becomes very important in technology and economy.9 Plenty methods including thermal treatment, mechanical method and chemical additives are available to improve the flow-ability of crude oils.10 The best solution is treating the crude oil with wax inhibitors or PPD additives.11-14 Various types of polymers were investigated to assure the cold flow-ability of waxy oils, including ethylene-vinyl acetate copolymer (EVA),15, 16 ethylene-butene copolymers (PE-PEB),17-19 alkyl esters of poly(styrene-maleic anhydride) derivatives,



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and copolymers of α-olefins and maleic anhydride or acrylic acid modified by esterification and admidation.4, 5, 12, 20 It has been revealed that the chemical structure, especially appropriate polar and nonpolar groups in the polymers, played an essential role in improving oil flow ability.21 Asphaltenes are important component of waxy oils which contain abundant aromatic groups in structure and have been proved influencing the oil rheological behavior.22-27 Aggregation of asphaltenes would reduce the flow-ability of crude oil.4 In our previous work,28 maleic anhydride copolymers with phenyl, naphthalene pendants were found capable of reducing the WAT and decreasing the yield stress of waxy crude oils containing asphaltenes. The copolymer with phenyl pendant exhibits an excellent performance on the oil flow improvement. Inspired by the fact that the aliphatic spacers between functional groups affect assembly behavior significantly, we highly expect that the spacers between copolymer backbone and aromatic pendants should have impact on the interactions between phenyl pendants and asphaltenes.29, 30

Figure 1. Structure of maleic anhydride derivatives. (a) Aniline graft on poly(α-olefin -comaleic anhydride) (AMAC); (b) Phenylethylamine graft on poly(α-olefin -comaleic anhydride), (EMAC); (c) Phentermine graft on poly(α-olefin -comaleic anhydride) (BMAC); (d) Phenyl-undecanoicamide graft on poly(α-olefin -comaleic anhydride) (UMAC).


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In the present work, four kinds of poly(α-octadecene -comaleic acid phenyl alkyl amide)s with varying spacer length between the copolymer backbone and phenyl pendants were synthesized (Figure 1). Model oil, consisting of paraffins and asphaltenes, was prepared to mimic waxy crude oil with asphaltenes. Rheology, polarized light microscope (PLM) and differential scanning calorimetry (DSC) were employed to investigate the impact of copolymers on the flow-properties and crystallization

behavior

of

model

oil

and

Liaohe

waxy

crude

oil.

A

plausiblemechanism was proposed to explain the influence of spacer length on the assembly of the prepared copolymers with paraffins and asphaltenes in waxy oils.

2. Experimental 2.1 Materials Aniline

(97%),

phenylethylamine

(98%),

phentermine

(97%),

1-methylnaphthalene (97%), decane (99%), maleic anhydride (99%), α-octadecene (90%), benzoyl peroxide (99%) and o-xylene (98%) were bought from Acros company and used without further purification. Paraffins (No. p100928 and No. p100934) were supplied by Aladdin Company. The melting point of paraffin (No. p100928) is ranging from 52~54 °C and the other (No.p100934) is ranging from 60~62 °C. Crude Oil was provided free by Petroleum Liaohe oilfield Company with a density of 0.8676 g/cm3, freezing point of 54 °C, and viscosity of 7.2 mPa.s (at 70 °C). The paraffin and asphaltenes content are 38.5% and 15.6% by weight, respectively.



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2.2 Synthesis of copolymers Radical polymerization was employed to prepare comb copolymers in this paper. In the first step, poly(α-olefin -comaleic anhydride) was prepared by copolymerization of a-olefin and maleic anhydride at 120 °C in nitrogen atmosphere for 1.5 hours, which was initiated by 0.1% benzoyl peroxide in solvent of o-xylene. In the second step, aniline, phenylethylamine, phentermine and phenyl-undecanoicamide (Figure S2) were individually fed into above copolymer solution under reflux for 15 hours in o-xylene. Phenyl-undecanoicamide was synthesized in three steps.31, 32 The detailed synthesis procedure including protection of the amino group of undecyline, peptide coupling with aniline and deprotection of the amine function which depicted in Figure 2, as well as the 1H NMR spectrum of phenyl-undecanoicamide (Figure S2) was shown in the supporting information.

Figure 2. The process reaction equations of synthesis of phenyl-undecanoicamide.

The copolymers were precipitated by excess methanol and filtration. Final products were obtained after a vacuum drying for 12 hours. The synthesized


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copolymers were characterized by 1H NMR spectra, which were performed by a Bruker Avance 500 spectrometer at 500 MHz using a solvent of deuterated chloroform.

2.3 Preparation of model oil By dissolving 30% of mixed paraffins in decane and 20% of asphaltene in 1-methylnaphthalene, the model oils were prepared by mixing them.5 Asphaltenes used in this paper were isolated from Liaohe oil deposit in n-heptane.22, 23 The mixed paraffins are a 50/50 blend of two commercial paraffin waxes. The carbon-number distribution ranging from C16-C37 in the purchased waxes is similar to the waxes isolated from Liaohe oil, which has been measured in our previous work.28

2.4 Rheological measurements All the rheological experiments were performed on the MCR501 rheometer (Anton-Paar Physical, Austria). Due to high viscosity of crude oil, 25 mm parallel plate geometry has been employed to characterize the rheological behaviors of crude oil, while

the 50 mm one used to characterize the model oil.

Yield Stress At first, model oils s were heated to 70 oC. After keeping for 30 minutes at this temperature, they were cooled to 35 oC with a rate of 10 oC/min. The waxy crude oils were warmed up to 80 oC, and then lowered the temperature to 50 oC at a rate of 10 oC/min after maintaining the temperature of 80 oC for 30 minutes. When the temperature are invariant, the shear stress was increased logarithmically



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from 0.01 Pa to 1000 Pa during the measurement. The final results were recorded in the average values of three parallel tests. Viscosity as a Function of Temperature Viscosities of oil at various temperatures were determined from 70 °C to 45 °C in 1°C/min by keeping a constant shear rate of 10 s-1. Above the WAT, crude oil gives the Newtonian behaviors. But below the WAT, the wax with high molecular weight will precipitate from liquid components, form the gel and show non-Newtonian behaviors. The Arrhenius equation can describe the correlation between viscosity and temperature when the temperature is higher than the WAT.20

ln(η) = ln(A) +

Ea ×T R

(1)

where η is the viscosity of flowing fluid, which can be determined by rheometer. As a constant, A relies on the flowing entropy of activation. The activation energy of flowing fluid Ea reflects the internal friction of fluid molecules. The gas constant R is 8.314 J/mol·K. Hysteresis Loop The strength of waxy gel can be detected by thixotropic property by measuring the hysteresis loop. The area of hysteresis loop reflects the structural strength in value. Fluid with a small area means weak structural strength which shows good flow-ability. The model oil was initially heated to 70 oC, and cooled to 35 oC with a cooling rate of 10 oC/min. The crude oil was loaded to the coaxial cylinder sensor system after heating to 80 °C, and cooled to 50 °C at a cooling rate of 1 °C/min. The shear rate was increased in 2 s-1/s linearly and reduced in a same rate, as shown in eq. 2:


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 R × t;  R × (2t1 − t );

γ& = 

0 ≤ t ≤ t1 t1 ≤ t ≤ 2t1

(2)

Here ߛ represents the shear rate (s-1), R the altering rate of shear rate (2 s-1/s), t the testing time, and t1 equals to 10 min which is the increased time of shearing.

2.5 Polarized Light Microscope A LEIKA DM2500P Polarized Light Microscope (PLM) equipped with cross-polarization optics and fluorescence module (with excitation wavelength λ = 440-460) was employed to observe the morphology of crystals. The temperature was controlled by a Linkam THMS 600 cold/hot stage. Pictures were recorded by a LEIKA MC120 CCD camera with HD resolution. A very small amount of oil sample were put on a glass slide to observe at 20 °C. The scale bar was set by LAS Version 4.5.0 (Leica Microsystems Limited, Switzerland), and the statistical analyses of shape and size were operated by ImageJ 1.51j8 (National Institutes of Health, USA).

2.6 Differential Scanning Calorimetry Paraffin crystallization was measured via TA Q2000 Differential scanning calorimetry (DSC) apparatus equipped with refrigerated cooling system 90 from TA Instruments (USA). The calibration of enthalpies and temperatures were performed by using indium and cyclohexane standards. In order to remove the thermal history, samples were kept at 80 °C for half an hour. Using a cooling rate of 10 °C/min, model oil was cooled from 80 to -20 °C and crude oil from 80 to 0 °C. TA Instruments Universal Analysis 2000 software was used to analyze the enthalpy and WAT of



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transitions.

3. Results and Discussion 3.1 Characterization of copolymers Aniline graft on poly(α-olefin -comaleic anhydride)s (AMAC) were synthesized as

described

in

our

previous

work.10

Following

the

similar

procedure,

phenylethylamine graft on poly(α-olefin -comaleic anhydride)s (EMAC), phentermine graft on poly(α-olefin -comaleic anhydride)s (BMAC) and phenyl-undecanoicamide graft on poly(α-olefin -comaleic anhydride)s (UMAC) were prepared and characterized using 1H NMR spectra. Based on integration area of proton peaks from benzyl A(C5H6) and methyl groups A(CH3) in 1H NMR spectra, the amidation ratio (f) representing the number of amine groups reacted with maleic anhydride group in polymers was calculated by eq 3, which should be between 0 and 2. f= 1

A(C 6 H 5 )/5 A(CH3)/3

(3)

H NMR spectra of AMAC, EMAC, BMAC and UMAC were displayed in the

Figure 3. The peaks at 0.9, 1.5 and 2.0 ppm are assigned respectively to the protons in CH3, CH2 and CH in α-octadecene unit. Those peaks around 6.9~7.7 ppm come from the protons in the phenyl pendants. The amidation ratios of these copolymers were listed in Table 1.


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Table 1. The feeding ratio of monomers and corresponding amidation ratio of AMAC, EMAC, BMAC and UMAC Copolymer

Feeding ratio (maleic

Amidation ratio (f)

anhydride/amine) AMAC1.0

1:1

0.58

AMAC2.0

1:2

0.83

EMAC1.0

1:1

0.67

EMAC2.0

1:2

1.01

BMAC1.0

1:1

0.57

BMAC2.0

1:2

1.04

UMAC1.0

1:1

0.47

UMAC2.0

1:2

0.83

It is worth of noting that the peak areas (at 1.5~3.5 ppm) of protons in CH2 group can reflect the length of spacer in copolymers, although the peak areas contributed by three parts: (1) the spacer group between phenyl group and backbone, (2) hexadecyl group from octadecene and (3) CH2 on backbone, while only the first part is different. The 1H-NMR spectra confirm that AMAC, EMAC, BMAC and UMAC were synthesized successfully.



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Figure 3. 1H NMR spectra of (a) AMAC, (b) EMAC, (c) BMAC and (d) UMAC (500 MHz, CD3Cl, 298.2 K).

3.2 Rheological Properties Yield stress. Impact of copolymers on the yield stress of model oil and crude oil is shown in Table 2. The yield stresses of all oils reduced significantly in the presence of copolymers. Upon increasing copolymer concentration, the yield stresses of both


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model oil and crude oil reduced. Among these copolymers, the sequence of performance in reducing yield stress is UMAC > BMAC > EMAC > AMAC, which seems to indicate that the copolymer with longer spacer can disperse asphaltenes more effectively.10 Phenyl pendant has been proved possessing good interactions with asphaltenes by means of π-π attraction.10 However, if phenyl pendant is too close to the backbone of copolymers, it loses flexibility to form optimized π-π interaction with asphaltenes. Therefore, UMAC, which possesses the longest spacer, shows the best performance on declining the yield stress of both oils. The trends of copolymer performance in both oils are quite similar.

Table 2. Effect of copolymer concentration on yield stresses of model oil and crude oil Yield Stress (Pa) Concentration (%) AMAC

EMAC

BMAC

UMAC

0

355

355

355

355

Model

0.1

169

148

129

99

Oil

0.3

148

129

112

84

0.5

112

175

57

58

0

448

448

448

448

Crude

0.1

188

177

141

121

Oil

0.3

145

122

92

78

0.5

110

100

79

58



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Viscosity. The change of model oil viscosity in the absence and presence of copolymers with temperature during cooling was demonstrated in Figure 4a. During cooling, the critical temperature corresponding to the sharp increase of viscosity for model oil with and without AMAC, EMAC, BMAC and UMAC is 42.5, 40.0, 37.0, 37.5 and 35.0 oC, respectively. Apparently, the viscosity and the critical temperature reduced upon increasing spacer length in copolymer (Figure 4a).

Figure 4. Viscosity as a function of temperature for (a) model oil and (b) crude oil with 0.5% of AMAC, EMAC, BMAC and UMAC.

As shown in Figure 4b, there is no abrupt viscosity increase for Liaohe waxy crude oil with and without copolymers during cooling. Interestingly, the viscosity in the presence of copolymers with longer spacer was also lower than that with shorter spacer at an identical temperature. In addition, the sequence of performance by copolymers is also identical to that found in model oil, which also reflects that long spacer benefits for the interactions between the phenyl pendants and asphaltenes.


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Thixotropic Property. The ability to restart the crude oil transformation in pipelines is often investigated through their thixotropic properties, which represents the strength of structure and recovering ability of waxy gel.11 Here, the hysteresis loop, as one of the crucial thixotropic behaviors, was measured for both oils (Figure 5).

Figure 5. The hysteresis loops of model oil (a) and crude oil (b) with and without copolymers at the concentration of 0.5%.

Table 3. Maximum shear stress and integration area deduced from hysteresis loops for model oil and crude oil with and without AMAC, EMAC, BMAC and UMAC Maximum shear stress (Pa)

Area integration ( Pa/(s·ml))

Additive Model Oil

Crude Oil

Model Oil

Crude Oil

121.1

113.5

316.0

377.4

AMAC

92.5

29.8

253.2

106.4

EMAC

38.9

23.9

38.0

94.4

BMAC

24.8

18.0

24.2

68.5

Without Copolymer



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UMAC

19.5

12.3

12.7

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44.1

In the upward curves, a creep formed for both model oil and crude oil when the shear stress increased suddenly at the initial shearing stage. The waxy gels were destroyed and began to flow when the shear strain is beyond the yield point. The maximum shear stress (peak value) can evaluate the flow-ability of oils, which listed in Table 3. The maximum shear stress can reflect the flow ability like the yield stress. As shown in Table 3, the maximum stress reduced upon lengthening spacer between phenyl pendent and main copolymer backbone following the sequence of UMAC > BMAC > EMAC > AMAC. The areas of hysteresis loops are also shown in Table 3. It is found that the integration areas of model and crude oils are reduced by feeding of copolymers, which indicates that these copolymers can decline the resilience of gel structure. The sequence of copolymers reducing the area of hysteresis loop is similar to that of maximum shear stress and yield stress, indicating that copolymers with a long spacer can inhibit the structure recovery of waxy gels and thus improve the flow-ability of oils.

3.3 Morphology


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The morphology and size distribution of long chain paraffin crystals in model oil with and without copolymers were observed and analyzed (Figure 6). The average size and amount of crystals in all samples vary with the type of copolymer.

Figure 6. Polarizing light micrographs of model oil with and without copolymers. (a) Model Oil (MO), (b) MO+ 0.5% AMAC, (c) MO+ 0.5% EMAC, (d) MO+ 0.5% BMAC, (e) MO+ 0.5% UMAC, (f) Data analyzed by ImageJ software.

The crystal size is around 48 µm in model oil. After adding copolymers, the average size reduced to less than 10 µm, and followed the sequence of no copolymer >



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AMAC > EMAC > BMAC > UMAC (Figure 6f). The amount of crystals shows the identical trend (Figure 6f).

Figure 7. Polarizing light micrographs of crude oil with and without copolymers. (a) CO, (b) CO+ 0.5% AMAC, (c) CO+ 0.5% EMAC, (d) CO+ 0.5% BMAC, (e) CO+ 0.5% UMAC (f) Data analyzed by ImageJ software.

The morphology and size distribution of paraffin crystals in crude oil with and without copolymers were also investigated by polarized optical microscopy (Figure 7). In the absence of copolymers, the crystal size in crude oil is about 14 µm. The


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presence of copolymers reduced their average size and amount. As shown in Figure 7f, the size and amount of crystals show the sequence of no copolymer > AMAC > EMAC > BMAC >UMAC, similar to that found in model oil. The similar trend found in model and crude oils indicates that copolymers with long spacer are benefit to the reduction of size and amount of crystals in waxy oils. All of the morphology changed is resulted by the co-crystallizaiton of non-polar long-chain alkyl pendants with paraffins. The dispersed asphaltenes are capable of inhibiting the formation of a wax network further. It can be proved by supporting information which contain the morphology of dispersed situation of asphaltene. (Figure S3) The change of crystal morphology is mainly resulted by the co-crystallizaiton of long-chain alkyl pendants with paraffins. The asphaltenes well-dispersed can also prevent the formation of a wax network and thus reduce the crystal size. The inhibiting effect should be more significant with smaller size of asphaltene aggregates. It was found that the aggregation size of the asphaltenes was reduced upon increasing the length of spacers in polymers (Figure S3). Therefore, the correlation between spacer length and crystal morphology change is reasonable.

3.4 Thermodynamic Behavior The DSC curves of the model oils and crude oils with and without copolymers are displayed in Figure 8. Similar to our previous work10, there are two obvious transitions in the cooling curves for crude oil, but those of model oil only show one



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transition. It is found that both the WAT and the enthalpy of transition for model oil are reduced by adding copolymers following the sequence of no copolymer > AMAC > EMAC > BMAC > UMAC (Figure 8a), which is similar to the rheological and microscopic observations. For crude oil, copolymers reduced the WAT and transition (at around 50 °C) enthalpy with the similar sequence found in model oil (Figure 8b).

Figure 8. (a) DSC thermogram of model oil and (b) crude oil with and without AMAC, EMAC, BMAC, UMAC.

The thermal effect Q is the integration of the enthalpy of cold transition from the WAT to a specified temperature. The concentration of wax deposited from oil Cw wt%) is deduced by eq 3. Tw is the given temperature at which Cw is measured, mpre is the weight of deposited wax, mtotal is the weight of wax in oil, and ܳത is 210 J/g.26

cw =

m pre m total

∫ =

WAT

Tw

Q

dQ =

Q Q


(3)

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Figure 9. Amount of wax precipitated in percentage from the model oil (a) and crude oil (b) with and without copolymers.

The amount of wax precipitated in percentage from model oil and crude oil with and without copolymers at various temperatures is displayed in Figure 9. It seems that copolymers reduced the amount of wax precipitated from both model and crude oils. The sequence of wax precipitation weight percentage is AMAC > EMAC > BMAC > UMAC, demonstrating that longer spacer is benefit to inhibiting the precipitation of wax. The reduction on the amount of wax deposited from crude oil is more significant than from model oil in the same temperature range during cooling, which indicates that the copolymers are effective to inhibit the wax precipitation from crude oil than from model oil.

3.5 Proposed Mechanism In Figure 10, the possible mechanism of the copolymers with phenyl pendant and various spacer length to enhance the flow-ability of waxy oils with asphaltenes is



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proposed. The alkyl pendants in copolymer reduce the regularity of paraffin crystal by co-crystallization (Figure 10a). In addition, the phenyl pendants adsorb on the asphaltenes surface to disperse their aggregation.33-38 Those assembly behaviors effectively prevent the formation of a wax network and asphaltene aggregation, and dramatically enhance the cold flow-ability of waxy oils, which has been proved in our previous work10. However, if the spacer between the copolymer backbone and phenyl pendant is too short, large steric hindrance will hinder the phenyl pendant to approach and adsorb on the surface of asphaltenes. In the present work, we demonstrated that copolymer with longer spacer can provide more flexibility and opportunity for phenyl pendants (Figure 10c) to interact with aromatic groups in asphaltenes, to disperse asphaltenes, and inhibit their aggregation. Moreover, more phenyl pendants with long spacer can be adsorbed onto the surface of asphaltene particles by avoiding the steric hindrance of copolymer backbone (Figure 10b). The dispersed asphaltenes can also work as inhibitor to prevent the formation of a wax network (Figure 10e).4 Consequently, the improvement of cold flow-ability of waxy oil containing asphaltenes becomes more pronounced upon increasing the spacer length in copolymer, which has been confirmed by the rheological, microscopic and DSC data.


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Figure 10. The possible mechanism of comb copolymers with phenyl pendant and different spacer lengths to enhance the cold flow-ability of waxy oils containing asphaltenes. (a) Co-crystallization; (b) Asphaltene dispersion; (c) Flexibility of phenyl group with various lengths of spacer; (d) Inhibition from crosslinking of paraffin crystals by dispersed asphaltenes.

4. Conclusions Poly(α-octadecene -comaleic acid phenyl alkyl amide)s with four spacer lengths were synthesized, whose structures were characterized by 1H NMR spectra. These copolymers improved remarkably the cold flow-ability of model oil and Liaohe crude oil. They reduced the yield stress as revealed by rheology, the size and amount



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of paraffins crystals as viewed by optical microscopy, and the wax appearance temperature and enthalpies as determined by DSC. The length of spacer between the copolymer backbone and phenyl pendant is of crucial importance for their performance as cold flow improvers. Copolymer with longer spacer can provide more flexibility and opportunity for phenyl pendants to interact with aromatic groups in asphaltenes, to disperse asphaltenes, and inhibit their aggregation. From all of the measurements, the cold flow-ability of both model and crude oil was improved by copolymers following the similar sequence: UMAC > BMAC > EMAC > AMAC.

5. Associated Content Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: The method of synthesis of UMAC, 1H NMR spectrum of each process product and the morphology of the asphaltene dispersed situation in the model oil. (PDF)

6. Acknowledgement We thank the support financially by National Natural Science and Foundation of China (21476143, 51003028), PetroChina Innovation Foundation (2016D-5007-0211), the Open Project of State Key Laboratory of Shihezi University (2016BTRC004), and 111 Project Grant (B08021). We also highly appreciate Petrochina Liaohe Oilfield


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Company for giving oil samples and technological supports.

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For Table of Contents Only


Effect of Spacer Length between Phenyl Pendant and Backbone in

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