Effect of Heteroaromatic Pendants in Comb Copolymers on Paraffin

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Effect of Heteroaromatic Pendants in Comb Copolymers on Paraffin Crystallization and Cold Flow Ability of Crude Oil Hanqing Zhao, Jun Xu, Tao Li, Tongshuai Wang, Xiaoming Wei, Jie Wang, Yisheng Xu, Li Li, and Xuhong Guo Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b00451 • Publication Date (Web): 08 Jun 2016 Downloaded from http://pubs.acs.org on June 9, 2016

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Effect of Heteroaromatic Pendants in Comb

2

Copolymers on Paraffin Crystallization and Cold

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Flow Ability of Crude Oil

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Hanqing Zhao1, Jun Xu1*, Tao Li1, Tongshuai Wang1, Xiaoming Wei2, Jie Wang1,

6

Yisheng Xu1, Li Li1, Xuhong Guo1,3*

7 8 9

1

State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China

10 11

2

Petrochina Liaohe Oilfield Company, Panjin 124010, China

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3

Engineering Research Center of Materials Chemical Engineering of Xinjiang

13

Bingtuan, Shihezi University, Xinjiang 832000, PR China

14 15 16 17 18 19

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

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or [email protected] (Xuhong Guo)

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ACS Paragon Plus Environment

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1

Abstract

2

Adding comb copolymers as chemical additives is considered an effective and

3

convenient method to improve the cold flow ability of crude oils. To improve the

4

effectiveness of comb copolymers on the flow ability modification for crude oils with

5

asphaltenes, poly(maleic acid amide-α-octadecene) with benzimidazolyl pendants

6

(MACB) were designed and synthesized. Compared with reported comb maleic

7

anhydride copolymers (MAC) with octadecyl (MACO) or phenyl (MACP) pendants,

8

MACB with heteroaromatic pendants are more efficient in reducing the yield stress of

9

both model oil and Liaohe crude oil as revealed by rheological measurements, in

10

modifying the morphology of wax crystals as observed by polarizing light microscope

11

(PLM), in lowering the wax appearance temperature (WAT) and quantity of wax

12

precipitation as determined by differential scanning calorimetry (DSC), and in

13

decreasing the crystallinity of paraffins as measured by X-ray diffraction (XRD). The

14

benzimidazolyl pendants in MACB can provide both hydrogen banding by amino

15

groups and - stacking by benzyl group with asphaltenes in crude oil, which

16

improves the interactions with asphaltens and thus the effectiveness in modification

17

the cold flow ability of crude oils.

18 19

Key words: Crude oil, flow ability, comb copolymer, heteroaromatic pendant

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1. Introduction

2

Paraffin deposition and asphaltene flocculation may induce a series of risks on

3

crude oil production and petroleum transportation/storage industry [1]. It is known

4

that, crude oil is a complex mixture of aromatics fraction, paraffins, asphaltenes, and

5

resins [2]. When the temperature is below the wax appearance temperature (WAT),

6

paraffin will precipitate and form a three-dimensional network structure [3, 4]. In

7

addition, it was found that asphaltenes also significantly influence the flow behavior

8

of crude oil [5-7]. Upon cooling crude oil, asphaltenes will aggregate, which provides

9

sites for crosslinking and builds complex wax-asphaltenes mixture to damage the flow

10

ability of crude oils [4, 8, 9]. It is dangerous when the pipelines are blocked by the

11

precipitation, and enormous amount of wastage are taken every year.

12

To solve this problem, chemical additives (also called wax crystal inhibitor, pour

13

point depressant, or cold flow improver) have been applied widely in petroleum

14

industry [10-17]. Under the effect of additives, paraffin crystallization process is

15

disturbed and then the flow ability of crude oil is improved. So far, several theories

16

have been widely adopted to explain the working mechanism of flow improvers such

17

as adsorption, co-crystallization, nucleation, and wax solubility enhancement [18, 19].

18

Nonetheless, it is believed that the mechanism is still controversial and researchers are

19

continually exploring that [20-25].

20

At present, various kinds of chemical additives are commonly applied, such as

21

ethylene butane copolymers (PE-PEB) [11, 26], ethylene and vinyl acetate (EVA)

22

[12], and alkyl esters of styrene-maleic anhydride derivatives [13, 27-29]. Polar and 3


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1

nonpolar pendants can be found along their backbone structure, which may play

2

different

3

anhydride-α-octadecene) copolymers (MAC) with various pendants such as octadecyl

4

(MACO) or phenyl (MACP) ones were found to be effective in improving the flow

5

ability of waxy crude oils [33-36]. It seems that the structure of copolymers can

6

significantly affect their effectiveness and working mechanism [30, 32, 35, 36].

7

However, the influences of pendant structure in MAC on their modification effect for

8

oil flow ability have not been studied systematically.

roles

[30-32].

In

our

previous

work,

comb-type

poly(maleic

9

In the present work, a novel MAC derivate with benzimidazolyl pendants

10

(MACB) was designed and synthesized. As comparison, MAC with octadecyl

11

(MACO) and phenyl pendants (MACP) were prepared to study the effect of pendants

12

on the interactions between copolymers with paraffin and asphaltenes in crude oils

13

(Figure 1). Change of paraffin crystal structure and crystallization thermodynamics

14

under the effect of MACB were observed by polarizing light microscope (PLM),

15

X-ray diffraction (XRD), and differential scanning calorimetry (DSC).

16 17 18

2. Experimental Section

19

2.1 Materials and Oil Samples

20

Decane (anhydrous, 99%), hexatriacontane (97%), methylnaphthalene (97%),

21

α-octadecene (95%), benzoyl peroxide (99%), octadecylamine (97%), aniline (99%)

22

and 2-aminobenzimidazole (98%) were purchased from Alfa Inc. and used as received. 4


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Maleic anhydride (99%), o-xylene (98%), and dimethyl formamide (97%) were

2

purchased from the Shanghai National Chemical Reagent Company.

3

Model oil (MO) used in the present work was prepared by the dissolving

4

hexatriacontane (C36) in decane, and mixed with asphaltenes pre-dissolved in methyl

5

naphthalene. The concentration of C36 and asphaltenes are controlled at 10 wt% and

6

1 wt%, respectively. The crude oil sample (CO) was from Liaohe oil field, which

7

contains 30 wt% of paraffins and 10 wt% of asphaltenes with a pour point of 60 oC.

8

To extract the asphaltene, Liaohe heavy crude oil was dispersed in n-heptane for 24 h.

9

The precipitated asphaltenes were filtered out, dried at 30 C under vacuum, and then

10

stored in dark place.

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2.2 Synthesis of MACB

13

All the comb copolymer additives (Figure 1) were based on poly(maleic

14

anhydride-co-α-octadecylene) which was copolymerized by octadecylene and maleic

15

anhydride in o-xylene at 115 C for 2.5 h with benzoyl peroxide as initiator. Then,

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2-aminobenzimidazole with different molar ratios to maleic anhydride were fed in and

17

reacted at 75 ºC for 12 h. Both reaction steps were carried out under nitrogen. The

18

products were precipitated from the solvent by excess methanol, filtrated, washed

19

with hot water for three times to remove unreacted amides, and dried by vacuum

20

drying. The synthesis of MACO and MACP was reported in our previous papers [11,

21

13].

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2.3 1H NMR Spectra and GPC 1

H NMR spectra of MACO, MACP and MACB were recorded on a BRUKER

3

AVANCE 500 spectrometer operating at 500 MHz with deuterated chloroform or

4

dimethyl sulfoxide as solvent. The molecular weight and molecular-weight

5

distribution of the comb copolymers were measured by gel permeation

6

chromatography (GPC, Dionex UltiMate 3000) with THF as mobile phase using

7

polystyrene samples as standards.

8 9 10 11 12 13 14

Figure 1. Synthesis approach of MACB and molecular structures of (a) MACO, (b)

15

MACP, and (c) MACB copolymers.

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2.4 Rheology and Yield Stress

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The rheological measurements were performed using a Physica MCR501 (Anton

19

Paar GmbH, Austria) rheometer equipped with 25 mm parallel plate geometry. The

20

yield stress is defined as the stress below which no flow occurs [30, 33]. The

21

temperature of the plate surface was controlled by a Peltier plate with an error-limit of

22

0.2 ºC. Gap was set at 1 mm during all of the measurements. Liquid samples were

6


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placed in a measuring cell mounted on top of the lower Peltier plate. A hood was used

2

to prevent the vaporization of solvent.

3

In the initial state, samples were heated to 70 ºC inside the cell, and kept for 5

4

min to erase their thermal history and then cooled to 10 ºC for MO and 20 ºC for CO

5

at the rate of 10 ºC/min. After keeping the temperature under no stress for 10 min,

6

measurements were carried out with shear rate increasing from 0.01 to 1000 Pa

7

logarithmically. Initially, low shear stress which is below the yield stress was applied

8

resulting in essentially high viscosity. As the stress increased, the curve crept for

9

some time and then failed. Yield stress was recorded at the failure of the stress [27].

10 11

2.5 Polarized Light and Fluorescence Microscope

12

The morphologies of the wax crystals in model oil were observed using a

13

microscope (2500P, LEIKADAM) with a Linkam THMS 600 cold/hot stage and

14

cross-polarization optics and fluorescence module (excitation wave length λ = 390 -

15

410 nm). Before observation, samples were heated to 85 ºC for at least 15 min to

16

remove any thermal and shearing histories. Afterwards, a small amount of solution

17

was loaded on a glass slide (25.4 × 25.4 mm) which was also preheated to 85 ºC, and

18

covered by a cover glass (18 × 18 mm). The plate was cooled from 85 to 10 ºC at a

19

rate of 10 ºC /min, and then kept at 10 ºC for at least 2 hours to confirm the fully

20

growth of paraffin crystals. All samples were observed under both polarized light and

21

fluorescence excitation.

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2.6 Differential Scanning Calorimeter (DSC)

2

Differential Scanning Calorimeter (DSC) of TA2000/MDSC2910 apparatus (TA

3

Instruments) was utilized to examine the crystallization thermodynamics of oil

4

samples. All of the samples were heated to 85 ºC and kept for at least 15 min to

5

eliminate any thermal history. The cooling rate was set at 10 ºC/min from 85 to -10 ºC

6

for MO and 85 to 0 ºC for CO. The enthalpy of crystallization (H) was calculated

7

from DSC peak area integration using TA software (TA Universal Analysis 2000). The

8

wax appearance temperature (WAT) of oil samples was identified from the transitions

9

of peaks using the TA Universal Analysis software.

10 11

2.7 X-ray Diffraction (XRD)

12

One-dimensional images were collected in reflection mode with a Rigaku

13

D/Max-2550v XRD instrument equipped with an evacuated Statton camera. X-rays

14

with a sour wavelength of 0.154 nm were produced with a sealed tube generator with

15

a Cu target and a Huber graphite monochrometer. The scattering patterns were

16

recorded over a range of angles corresponding to 2θ = 5 - 50 ºC. In order to explore

17

the effect of various pendants on the paraffin crystal type, C36 paraffin was chosen

18

and measured in the presence and absence of copolymers.

19 20 21

3. Results and Discussion

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3.1 Structure and Molecular Weight of MACB

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The 1H NMR spectrum of MACB is shown in Figure 2. The peaks at around 0.9,

24

1.5 and 2.0 ppm belong to protons in CH3, CH2, and CH of the α-octadecene

25

monomer unit, respectively. At chemical shift of 6.2, 6.8, and 7.1 ppm, the peaks 8


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come from the protons in the amino and amide groups of 2-aminobenzimidazolyl

2

pendant, while the two peaks at 2.5 and 3.4 ppm belong to the solvent deuterated

3

DMSO. Obviously, the 1H NMR spectrum can confirm the structure of our target

4

MACB (Figure 2).

5 6 7 8 9 10 11 12 13 14

Figure 2. 1H NMR Spectrum of MACB.

15 16

Table 1. Amidation ratio (f) and molecular weight (M n) of copolymers f

M n (Kg/mol)

MACO

0.307

5.88

MACP

0.350

6.07

MACB

0.365

6.34

17 18

The amidation ratio (f) of maleic anhydride group, or the average number of

19

grafted pendant groups can be estimated from the integrated areas of peaks for the

20

protons in 2-aminobenzimidazolyl groups and for those singly linked to the backbone 9


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carbon in each maleic group [27, 30], and is listed in Table 1.

2

The molecular weights of MACO, MACP, and MACB measured by GPC are also

3

shown in Table 1. The amidation ratios of three comb copolymers are controlled to be

4

close in order to compare their performance.

5 6

3.2 Effect of Copolymers on Rheology

7

Different concentrations of MACO, MACP, and MACB varying from 0.1 wt% to

8

0.5 wt% were added into MO and CO, and their effects on the rheological behaviors

9

of MO and CO were compared (Figure 3 and 4). As shown in Figure 3, the yield

10

stresses of both MO and CO were reduced by addition of comb copolymers. Among

11

them, MACB has the best capability in reducing the yield stress of MO. Upon

12

addition 0.1 wt% MACB, the yield stress is reduced from 121 to 16 Pa with a

13

reduction of 87%. Further increasing the amount of MACB up to 0.5 wt% seems to

14

have less impact on the yield stress of model oil (Figure 3a).

15

16

(a)

17

(b)

18

Figure 3. Yield stresses of (a) MO and (b) CO as a function of copolymer

19

concentration.

20 10


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As shown in Figure 3b, the yield stresses of crude oils were also reduced by

2

addition of all three comb copolymers although the decline was relatively slow

3

compared to model oils upon increasing the dosage of copolymers. At the

4

concentration of 0.5 wt% for MACB, the reduction of yield stress reaches 56%. The

5

ranking of copolymers reducing the yield stress is the same for both MO and CO:

6

MACB > MACP > MACO, which means MACB is most effective to reduce the yield

7

stress.

8

The oil viscosity as a function of temperature upon cooling in absence or

9

presence of 0.5 wt% copolymers are shown in Figure 4a and b. Addition of

10

copolymers can reduce the viscosity of both model oil and crude oil, and the

11

effectiveness sequence is MACB > MACP > MACO.

12 13 14 15 16 17 18

(a)

(b)

19

Figure 4. Viscosity of oils as a function of temperature with and without the dosage

20

of copolymers. (a) Model oil. (b) Crude oil.

21

11


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1

Upon cooling from 65 ºC for model oil and 60 ºC for crude oil, the viscosity

2

exhibited a significant increase. The temperature at this transition point was

3

determined as WAT. Obviously, all comb copolymers can reduce the WAT for both

4

model oil and crude oil. The WAT of model oil is reduced from 52.8 to 47.5 oC and

5

from 51.0 to 45.0 oC for crude oil by the dosage of MACB, which is the largest

6

reduction of WAT among all copolymers. The sequence of effectiveness to reduce the

7

oil viscosity and WAT is similar to the yield stress: MACB > MACP > MACO.

8

It is worth to note that the model and crude oils contain 1 wt% and 10 wt%

9

asphaltenes, respectively. The behavior of asphaltenes in these oils plays a very

10

important role in rheology. Usually, asphaltenes aggregate and generate

11

three-dimensional networks where the paraffin crystals embedded. The rheological

12

results imply that the MACB shows the strongest interaction with asphaltenes which

13

helps to disperse the asphaltenes in the oil.

14 15

3.3 Effect of Copolymers on Paraffin Crystallization

16

Observation by Optical Microscopy. The morphology of paraffin crystals under

17

polarized light in the presence and absence of copolymers is shown in Figure 5. For

18

model oil in absence of any copolymer, paraffin crystalline grains show a spindle

19

shape and densely stacked each other. In the presence of MACO, the shape of paraffin

20

grains changes into needle-like, as shown in Figure 5b. In the presence of MACP and

21

MACB, the shape of grains recovers to spindle shape, as shown in Figure 5c and d.

22

For crude oil, the paraffin crystal is irregular and small. Notably, the amount of

23

paraffin crystals in crude oil is significantly reduced by the addition of copolymers, 12


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showing a ranking of MACO > MACP > MACB.

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Figure 5. Polarized optical micrographs of MO and CO in presence and absence of

20

0.5 wt% copolymers. (a) MO; (b) MO + MACO; (c) MO + MACP; (d) MO + MACB;

21

(e) CO; (f) CO + MACO; (g) CO + MACP; (h) CO + MACB.

22 23

MACO only contains alkyl branches, which are apt to insert into the paraffin

24

crystals by co-crystallization, and disturb their regular arrangement, thus resulting in

25

the changes of grain shape. Differently, the phenyl and benzimidazolyl pendants 13


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cannot insert into the layers of paraffin crystals. Due to this reason, the morphology of

2

paraffin crystals in the presence of MACP or MACB is similar to that without

3

copolymer (spindle shape).

4 5

Observation by DSC. DSC curves of MO and CO in the presence and absence of

6

copolymers during cooling are shown in Figure 6. All the cooling curves of crude oil

7

exhibit two distinct peaks which is probably due to the existence of two groups of

8

crystallizable paraffins whose carbon numbers are significantly different [35]. It is

9

found that addition of copolymers shifts the onset of paraffin crystallization to lower

10

temperature and reduces the enthalpy (area of exothermic peaks) of the transition

11

upon cooling for both MO and CO. These effects follow a ranking of MACB >

12

MACP > MACO, coinciding with the rheological and PLM observations.

13 14 15 16 17 18 19 20

(a)

(b)

21

Figure 6. DSC thermographs of (a) MO and (b) CO in the presence and absence of

22

copolymers during cooling. (Tp is the temperature of exothermic peak.)

23 24

Observation by XRD. Since the broad diffraction peak from asphaltenes will

25

mask most information from long chain paraffin crystals, to avoid the influence of 14


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asphaltenes, model oils without asphaltenes were dried and applied to study the

2

changes of paraffin crystal structure in the presence of copolymers by XRD (Figure 7).

3

Accordingly, fluorescent optical module was utilized to observe the distribution of

4

copolymers in the paraffin crystals.

5 6 7 8 9 10 11 12 13 14

Figure 7. XRD diffractograms and fluorescence micrographs (excitation wavelength

15

λ = 390 – 410 nm) of C36 in absence and presence of copolymers at the concentration

16

of 0.5 wt%.

17 18 19

Particle size of paraffin crystals was estimated according to the Scherrer equation, as shown as eq. 2 [19]:

20 21

Dhkl 

0.89  hkl cos  hkl

(2)

22 23

where Dhkl is the average size of crystals in direction perpendicular to the (hkl) plane

24

of the crystals. 0.89 is the Scherrer constant; λ is the wavelength of X-ray which is

25

0.154 nm here; βhkl is the full width at half maximum (FWHM) and calculated by the 15


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1

Jade 5.0 software; θhkl is the Bragg angle. The crystallinity of wax crystal was

2

calculated by comparing the integration area of crystal peak and amorphous zone

3

using Jade 5.0 software according to the eq. 3:

4 

Xc

5

  

0



0

s 2 I c  s  ds s 2 I  s  ds



Ac A

(3)

6 7

where S = 2sinθ/λ; I(s) is the total coherent scattering intensity; Ic(s) is the coherent

8

scattering intensity of crystal; Ac is the area sum of crystals diffusion peaks; A is the

9

total area of all the peaks, including the diffusion peaks of crystals and amorphous

10

region. XRD parameters and estimated results were listed in Table 2.

11 12

Table 2. XRD parameters of C36 crystals in the presence and absence of copolymers

MO

MO+0.5 wt%MACO MO+0.5 wt%MACP MO+0.5 wt%MACB

2θ (°)

d (Å)

I/I0 (%)

βhkl(°)

Dhkl(nm)

20.93 25.19 40.46 22.25 24.63 40.93 21.00 23.91 40.46 21.04 25.23 40.50

4.24 3.53 2.23 3.99 3.61 2.20 4.23 3.72 2.23 4.22 3.53 2.23

8.26 7.14 100 100 21.70 2.10 19.90 72.33 100 12.06 7.06 100

0.20 0.19 0.18 0.26 0.34 0.29 0.22 0.27 0.25 0.21 0.21 0.22

39.75 43.28 47.04 31.11 23.43 28.66 37.17 29.31 33.36 37.69 37.62 38.95

Crystallinity (%) 65.28

21.85

46.93

56.38

13 14

As shown in Table 2, the crystal size (Dhkl) and crystallinity of C36 are reduced

15

following the trend of MACO > MACP > MACB, which is contrary to the sequence

16

of their effectiveness to improve the flow ability of oils with asphaltenes. It confirms 16


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that the effect of MACB on the rheology and paraffin crystallization of crude oils is

2

based on the interactions with asphaltenes.

3

The distribution of copolymers in C36 crystals is observed through the

4

fluorescence micrographs (Figure 7). Since lack of fluorescent substances, pure C36

5

crystals are invisible under the fluorescent excitation. Amide groups in MACO are

6

visible with blue color. It is found that the blue color is full of all paraffin grains with

7

MACO, which confirms that MACO molecules with only alkyl pendants are able to

8

co-crystallize with C36 and disperse into the paraffin crystal layers.

9

However, in the presence of MACP and MACB, the blue color in grains is

10

dispersed mainly on the surface and seems brighter than that in the presence of

11

MACO (Figure 7). This observation supports the hypothesis that the phenyl and

12

benzimidazolyl pendant groups in MACP and MACB cannot co-crystallize with C36

13

and insert into the inner paraffin crystal layer. Since the phenyl and benzimidazole

14

groups also show a blue color under fluorescent excitation [37, 38], the increased

15

concentration of functional groups on the surface leads to the enhanced blue light.

16 17

Possible Working Mechanism of MACB. Based on the experimental results, a

18

possible working mechanism of copolymers with alkyl, phenyl and benzimidazole

19

pendants assembled with long chain paraffins and asphaltenes, the major components

20

of waxy crude oil, is presented as shown in Figure 8.

21

The rheological behaviors of crude oil mainly depend on the structure formed by

22

long chain paraffins and asphaltenes. Upon cooling crude oils with relatively high

23

asphaltene content like Liaohe crude oil, asphaltenes may aggregate and form a

24

three-dimensional network in the interspace of paraffin crystals. In this case, the

25

dispersion of asphaltenes will play an important role. 17


Energy & Fuels

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Figure 8. Possible working mechanism of MACO, MACP and MACB assembly with

18

long chain paraffins and asphaltenes in crude oil.

19 20

In order to effectively disperse asphaltenes, the interactions with them for

21

copolymer additives have to be enhanced. Therefore, MACB with heteroaromatic

22

pendants were designed and synthesized in this work.

23

Due to the abundant polar and aromatic groups in asphaltene structure, the

24

benzimidazolyl pendant in our synthesized MACB can provide both hydrogen

25

bonding by amino groups and - stacking by benzyl group, and improve the 18


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Energy & Fuels

1

interactions with asphaltens. As a result, the asphaltenes will be prevented from

2

aggregation and can help to stabilize paraffin crystals in oils as they have been

3

reported as natural flow improver in oil [2, 4, 8]. Therefore, by increasing the

4

interactions with asphaltenes, MACB show the best performance to improve the flow

5

ability of crude oils upon cooling.

6

At the second place of the three copolymers used in this work, MACP have

7

phenyl pendants which can form - stacking with aromatic groups, thus show

8

stronger interactions with asphalenes than MACO, but weaker compared to MACB.

9

MACO, which possesses only alkyl branches, are able to affect the crystallization of

10

long chain paraffins by co-crystallization, but has less impact on the dispersion of

11

asphaltenes. Therefore, the performance of MACO to improve the cold flow ability of

12

crude oils with relatively high asphaltene content is the worst among the three

13

copolymers.

14 15 16

Conclusion

17

Comb poly(maleic anhydride-co-α-octadecene)s amidated by alkyl amines

18

(MACO), aniline (MACP) and 2-aminobenzimidazole (MACB) were synthesized by

19

free radical copolymerization and amidation reaction. Their structures were

20

characterized by 1H NMR. MACB can reduce the yield stress, the viscosity, and

21

amount of paraffin crystals for both model and crude oils with asphaltenes more

22

effectively compared to MACP and MACO. In general, the sequence of copolymers

23

improving the cold flow ability of crude oils is MACB > MACP > MACO. MACB,

24

which possesses both amino groups and benzyl groups, can form hydrogen bonding

25

and π-π conjugation with the polar and aromatic groups in asphaltenes, respectively. 19


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1

Thus MACB are able to disperse asphaltenes effectively in crude oils and perform the

2

best in decreasing the yield stress and viscosity, and reducing the WAT and wax

3

crystallinity among three copolymers.

4 5 6

Acknowledgement

7

Financial support by National Natural Science Foundation of China (51003028,

8

21004021, 21306049, 21476143 and 51273063), the Fundamental Research Funds for

9

the Central Universities, and 111 Project Grant (B08021) is gratefully acknowledged.

10

The authors also thank Petrochina Liaohe Oilfield Company for affording oil samples

11

and technological supports.

12 13 14

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Effect of Heteroaromatic Pendants in Comb Copolymers on Paraffin

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