Investigation on the Performance of a Block Polyether Demulsifier

Aug 21, 2017 - School of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu, Sichuan 610500, People's Republic of China. ‡ ...
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Investigation the Performance of a Block Polyether Demulsifier Based on Polysiloxane for the Treatment of Aged Oil Lili Ma, Yanbang Chen, Yucheng Liu, Mingyan Chen, Bing Yang, Bo Zhang, and Yue Ding Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b00694 • Publication Date (Web): 21 Aug 2017 Downloaded from http://pubs.acs.org on August 24, 2017

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Investigation the Performance of a Block Polyether

2

Demulsifier Based on Polysiloxane for the Treatment of

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Aged Oil

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Lili Ma,† Yanbang Chen,† Yucheng Liu,*,† Mingyan Chen,† Bing Yang†

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Bo Zhang,‡ and Yue Ding†

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†School of Chemistry and Chemical Engineering, Southwest Petroleum University,

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Chengdu 610500, China

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‡Petroleum Sale Company of Chongqing Chuyu Co. Ltd., Chongqing 401326, China

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ABSTRACT: Using a silicone demulsifier is an efficient approach in the treatment of

11

environmental pollution caused by aged oil. A new type of silicone demulsifier was

12

prepared in this work by following a two-step synthesis method based on SP169

13

(octadecanol block polyether) and AE16 (monoamine fat alkyl block polyether).

14

Reaction conditions, such as reaction time, temperature, and so on, were optimized for

15

the synthesis of poly(ether ester) intermediates and silicone demulsifier. Both the 1H

16

NMR and IR spectra confirmed the successful preparation of poly(ether ester)

17

intermediates from acrylic acid based on the presence of the C=C and C=O bonds

18

provided, indicating the successful modification of the silicone demulsifier by the

19

polysiloxane and poly(ether ester) intermediates. The thermal degradation interval of

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the silicone demulsifier is 325°C–390°C according to thermogravimetric analysis. In

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addition, the diffusion and adsorption of the silicone demulsifier, which were 1

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measured by Quartz Crystal Microbalance with Dissipation, indicated that the silicone

2

demulsifier forms a compact and uniform adsorbed layer, which contributed to the

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demulsification. The dehydration rate was 86.87% when the poly(ether ester) ratio,

4

silicone demulsifier dosage, demulsification temperature and time were 2:1, 150 mg/L,

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65°C, and 1.5 h, respectively, during the demulsification tests. The silicone

6

demulsifier has a great potential application in oil/water separations of aged oil.

7

INTRODUCTION

8

Due to the increasingly serious environmental pollution caused by aged oil,

9

oil/water separation is considered an important procedure that has attracted research

10

interest in aged oil treatment.1,2 Higher viscosity and stronger electrical conductivity

11

make water drops disperse and stabilize in aged oil,3–6 and the stable emulsions

12

include W/O, O/W, W/O/W and O/W/O, which are mainly divided according to the

13

presence of a continuous phase. The treatment method is different for each kind of

14

petroleum emulsion. Traditional treatments of oil/water separation, such as flotation,

15

gravity separation, and coagulation, usually yield relatively low separation

16

efficiencies and high energy costs.7,8 In comparison with these methods, chemical

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demulsification is one of the most effective and convenient methods,9–11 and its

18

efficiency depends on demulsifier performance.12

19

In previous studies, the demulsifier examined is either ionic or non-ionic.13

20

Studies have shown the superiority of the performance of the non-ionic demulsifier

21

compared with the ionic type, based on the high hydrophilicity of the former. A 2

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non-ionic demulsifier mainly includes polyether types, such as alcohol amine block

2

polyether, 14 alkyl phenolic resin block polyether, 15 phenol amine resin block

3

polyether,

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accelerate water drop sedimentation,17 favors interphase destabilization,20 and has

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better dehydration effect.18 A structurally branched demulsifier absorbing onto the

6

interface can reduce the interfacial viscosity and interfacial tension as well as play a

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positive role in the oil–water interface. 19 However, a recent theoretical study

8

indicated that the number of demulsifier branches makes the diffusion of the

9

demulsifier through the crude oil more difficult.20 Therefore, demulsifier diffusivity

10

16

and modified block polyether. Branched polyether demulsifiers

and adsorptivity are still open to new research.

11

Meanwhile, because of its hydrophobic silica component, the polysiloxane

12

demulsifier is considered superior over other demulsifiers in the treatment of oil–

13

water emulsion.

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siloxane-based demulsifier to handle a simulative crude oil emulsion, and reported

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dehydration rate (99.6%).22 However, the one-step synthesis method often produces

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H2 gas, which is flammable and combustible.22 In consideration of experimental safety,

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the two-step synthesis method has become more popular in the synthesis of organic

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silicon demulsifier.

21

A past study synthesized a dihydrogen

polydimethyl

19

In recent years, the influence of hydrophobic silica on demulsification effect has

20

become easily recognizable.21 For the polysiloxane-modified polyether demulsifier, a

21

hydrophilic polyether block can improve water solubility, and the hydrophobic 3

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polysiloxane segment can reduce surface tension. Therefore, the modified polyether

2

demulsifier can strengthen the interaction of the oil–water interface. Furthermore,

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hydrophobic silica has a wetting feature, which changes the position of a natural

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emulsifier; hence, the oil-water interface breaks, and oil and water separate.23 Past

5

studies attempted to better understand demulsifier action by studying such a

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mechanism based on molecular structure. 24 – 27 The molecular structure of the

7

demulsifier is tetrahedral with the Si atom in the center and two methyl groups

8

standing on the plane formed by the Si and O atoms. Given that the Si-C bond is

9

longer than the C-H bond of methyl, the demulsifier is more hydrophobic. Moreover,

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the rotary H atom with the methyl group occupies more space and increases the

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distance between two silanes. Therefore, intermolecular surface tension is lower, the

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properties of diffusion and adsorption are better, and the dehydration effect is more

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pronounced.28–31 Demulsifier efficiency depends on its adsorption on the oil–water or

14

droplet surface.32 For this reason, investigating demulsifier adsorption is necessary.

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In this work, silicone demulsifier was prepared through a two-step synthesis

16

method. The poly(ether ester) intermediates were first manufactured by adding C=C

17

bond based on the SP169 (Octadecanol block polyether) and AE16 (Monoamine

18

aliphatic alkyl block polyether), before connecting the intermediate to polysiloxane.

19

Moreover, demulsification performance was determined through a standard bottle-test.

20

Quartz Crystal Microbalance with Dissipation (QCM-D) measured the adsorption and

21

diffusion performance, and the fitting of |∆D/∆F| certified the adsorption performance. 4

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The results of this study can help broaden the method of solving the oil–water

2

separation problem.

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EXPERIMENTAL SECTION

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Materials

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The polysiloxane ((CH3)3SiO[(CH3)2SiO]cSiO[(CH3)HSiO]dSi(CH3)3) with 0.18%

6

hydrogen content was purchased from Zhejiang Chuangji Organic Silicon Material

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Co., Ltd (Zhejiang, China). SP169 (Octadecanol block polyether, M=1870) and AE16

8

(Monoamine aliphatic alkyl block polyether, M=2091) were purchased from Hubei

9

Jinxin J Dolor Chemicals (Hubei, China), and acrylic acid and other chemicals were

10

supplied by Kelong Chemical Reagent Factory (Chengdu, China). All reagents in this

11

work were pure. Aged oil was obtained from the Liuhua Oilfield of CNOOC (China

12

National Offshore Oil Corporation) and was identified as W/O type through staining.

13

Only 2.87% water was separated in 8000 r/min and 20 min. The characteristics of

14

aged oil are listed in Table 1.

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Synthesis of the Silicone Demulsifier

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Synthesis of the Poly(ether ester) Intermediates. The poly(ether ester)

17

intermediates were synthesized through the esterification reaction of acrylic acid and

18

SP169 or AE16 under a catalyst and polymerization inhibitor, as described in Scheme

19

1(a) and Scheme 1(b). SP169 or AE16 and acrylic acid were placed in a mouth flask,

20

to which p-Toluenesulfonic acid and hydroquinol were added to serve as the catalyst

21

and inhibitor, respectively. The mixture was heated for 6 h at 130°C. Next, 5

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dichloromethane was added to dissolve the mixture after cooling down to room

2

temperature. At the same time, the mixture was added with 0.05 M NaOH to adjust

3

pH to neutral, and the bottom layer was separated. Poly(ether ester) intermediates

4

were successfully obtained after removing excess dichloromethane by rotary

5

evaporator. The reaction conversion rate is defined as the esterification rate (Section

6

1.1, Supporting Information).

7

Synthesis of the Silicone Demulsifier. Silicone demulsifier synthesis was

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performed by the hydrosilation addition reaction of SP169 poly(ether ester) and AE16

9

poly(ether ester) mixture with polysiloxane under 40 mg/L chloroplatinic

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acid/isopropanol catalyst in toluene solvent,33 as described in Scheme 1(c). When the

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temperature reached 90°C after 2 h, SP169 poly(ether ester) and AE16 poly(ether

12

ester) were added. The entire reflux was kept for 5 h. When the mixture solution

13

cooled to 55°C, toluene was removed through distillation to obtain a yellow liquid

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product. The percent conversion of the hydrosilation addition reaction is defined as

15

the ratio of consumed Si-H to the initial Si-H of the polysiloxane (Section 1.2,

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Supporting Information). CH 3 C 18H 37

(a) 17

CH 3

O (CHCH 2O)m (CH 2CH 2O)n (CHCH 2O)p H + CH 2 CH 3

Catalyst Retarder

C 18H 37

CH 3

CHCOOH

O

O (CHCH 2O)m (CH 2CH 2O)n (CHCH 2O)p CCH

CH 2 + H 2O

CH 3

R N

(CHCH 2O)a (CH 2CH 2O)b H + CH 2

CHCOOH

R

(b) 18

Catalyst Retarder R: C16-C 18

CH 3

R N

O

(CHCH 2O)a (CH 2CH 2O)b

CCH

R

6

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CH 2 + H 2O

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CH3 CH3

CH3

C18H37

CH3

CH3

CH3

Si O

(SiO)c (SiO)d Si CH3 +

CH3

CH3

O CH3

R

O

O

H

CH3

CH3

CH3

Si O

(SiO)c (SiO)x (SiO)y Si CH3

CH3

CH3

N

CH3

(CHCH2O)m (CH2CH2O)n (CHCH2O)p CCH CH2

(CHCH2O)a (CH2CH2O)b CCH CH2

R

(c) Catalyst

CH3

CH3

CH3

CH3 CH3

R

CH2CH2C (OCH2CH2)b (OCH2CH)a N O

R

CH3

CH2CH2C (OCH2CH)p (OCH2CH2)n (OCH2CH)m O O

1

CH3

H37C18

CH3

2

Scheme 1. Synthetic principle of (a) SP169 poly(ether ester), (b) AE16 poly(ether

3

ester) and (c) silicone demulsifier.

4

Characterization of the Poly(ether ester) Intermediates and the

5

Silicone Demulsifier

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The NMR characterizations of SP169 poly(ether ester), AE16 poly(ether ester)

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and silicone demulsifier were carried out on a Bruker Avance II-400 MHz NMR

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spectrometer with CH3OD as the solvent. Fourier transform infrared (FTIR) spectra

9

were recorded on a WQF-520 spectrometer (Beijing Rayleigh analytical instruments

10

co. LTD). Surface tension of silicone demulsifier in toluene/ethanol (75/25 v%)

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solutions were determined by XZD-SP (Beijing Harke) at 25°C. Thermal transition

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behaviors were investigated by a Thermal Gravimetric Analyzer (TGA) system

13

(METILER TOLEDO), with a scanning rate of 10°C min-1.

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Demulsification Test

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Demulsification effectiveness was evaluated by bottle-test. Demulsifier was

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added into 50 g aged oil in centrifuge tube (50 mL). The mixture was shaken by an

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electric vibrating machine (shake 30 s every 20 min). Through the centrifugal (8000 7

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r/min, 20 min) and layered, the water separated was taken out by pipette and

2

transferred into a cylinder to read the volume. The dehydration rate Φ from the aged

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oil sample is calculated by the formula Φ=

v ×100% (1) v0

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where V0 is the original water volume before the bottle test (Table 1), and V is the

5

water volume after demulsification. Neatness of the oil–water interface should also be

6

recorded to evaluate the demulsifier performance.

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Measurement of Demulsifier Adsorption Performance

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QCM-D is a rising technology, in which a quartz crystal generates an inverse

9

piezoelectric effect to study the adsorption, desorption, and so on. During quartz

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crystal vibration, the change of the sensor resonant frequency (∆F) is related to the

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total mass of the vibrating quartz crystal. The relation is directed towards the rigid

12

adsorbed layer. The definitions is given by ∆m = -C

∆F (2) n

13

where C is the quartz vibrator constant at 17.7 ng/cm2·Hz; ∆F is the vibrational

14

frequency change of the quartz crystal; n is the number of vibrational frequency times,

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which can be 1, 3, 5, 7, 9, or 11; and ∆m is the mass change of the adsorbed layer.

16 17

The dissipation factor (∆D) reflecting the viscoelasticity of an adsorbed layer is defined in Equation (3 ∆D =

18

Elost (3) 2πEstored

where Elost is the dissipated energy, and Estored is the stored energy in one cycling 8

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vibration.

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Here, |∆D/∆F| reflects the loose level of adsorbed layer structure 34 –36 and

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expresses the adsorption and diffusion abilities of the demulsifier in the oil–water

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interface. Hence, the aged oil and demulsifier were diluted to 0.25% and 1.0 wt% in

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toluene, respectively. The quartz crystal was prepared by the UV-light and the mixed

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liquor was mixed with 25 v% ammonium hydroxide and 30 v% H2O2. The flow

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velocity and vibrational frequency were set to 80 µL/min and 5, respectively. Aged

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oil and silicone demulsifier were sent to the quartz crystal in sequential order for

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analysis.

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RESULTS AND DISCUSSION

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Factors Affecting Esterification Reaction

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Effect of Temperature on the Reaction. At temperatures below 125°C, the

13

esterification rate of SP169 increases with temperature due to the greater molecular

14

thermal motions (Figure S1(a), Supporting Information). However, when the

15

temperature exceeds 125°C, side reactions may occur, and the product undergoes

16

carbonization. p-Toluenesulfonic acid and acrylic acid can also partially gasify when

17

the temperature approaches their boiling points of about 140°C, thereby reducing the

18

contact opportunity of acrylic acid and SP169 and the catalytic activity of

19

p-toluenesulfonic acid. Therefore, given that the esterification rate of SP169 decreases

20

with temperatures above 125°C, the optimal temperature of SP169 esterification

21

reaction is 125°C. The same trend is also observable in the esterification of AE16, the 9

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optimal temperature for which is 130°C. Such difference in optimal temperature arises

2

from the different molecular structures and molecular weights of SP169 and AE16.

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Effect of time on the reaction. SP169 and AE16 esterification rates rise with the

4

extension of the reaction (Figure S1(b), Supporting Information). The esterification

5

rates of SP169 and AE16 at 7 h are 89.4% and 86.3%, respectively. After 7 h, the

6

increasing trends of SP169 and AE16 esterification rate become minimal. Hence, the

7

reaction time for both SP169 and AE16 was set at 7 h.

8

Effect of the carboxyl to hydroxyl ratio on reaction. Carboxyl to hydroxyl

9

ratio is yet another esterification parameter (Figure S1(c), Supporting Information),

10

with the reaction rate rising continually with increasing acrylic acid. When the ratio is

11

1.5:1, the esterification rates of SP169 and AE16 are 91.5% and 89.4%, respectively.

12

When the ratio exceeds 1.5:1, the increasing trend is not obvious at the expense of the

13

possible auto-agglutination of acrylic acid and the enlargement of viscosity of the

14

product. Therefore, the optimal n(Carboxyl)/(Hydroxyl) ratio in both esterification

15

reactions of SP169 and AE16 is 1.5:1.

16

Effect of the catalyst dosage on reaction. The quantity of a catalyst is an

17

important factor of esterification rate (Figure S1(d), Supporting Information). The

18

esterification of SP169 and AE16 first increased with catalyst dosage before

19

decreasing. The rate of SP169 at 2.0% catalytic dosage is is 94.0% and that of AE16

20

at 2.5% catalytic dosage is 93.0%. This difference possibly arises from the branched

21

structure of AE16, which requires more catalytic activity. When the catalytic amount 10

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is above 3.0%, the esterification rates of both SP169 and AE16 are lower, because the

2

increase of catalyst strengthens the hydroxyl activity of polyether chain endings, thus

3

inducing the condensation polymerization of the raw material. Hence, the optimal

4

catalyst dosages for SP169 and AE16 esterification are 2.0% and 2.5%, respectively.

5

Effect of the polymerization inhibitor dosage on reaction. As shown in Figure

6

S1(e) (Supporting Information), the esterification rate of SP169 rises with the

7

increasing quantity of polymerization inhibitor. On the one hand, when the

8

polymerization inhibitor is 0.6%, the esterification rate is 94.0%, and the rising

9

tendency becomes gradual. On the other hand, the polymerization inhibitor for the

10

esterification of AE16 reaches 0.8%. When the polymerization inhibitor is below

11

0.6%, the auto-agglutination of acrylic acid could take place, thus reducing the

12

activity of the carboxyl moiety. If the polymerization inhibitor is above 0.6%, the

13

esterification reaction reaches the limit of the raw material. To save the raw material,

14

the optimal dosages of the polymerization inhibitor for the esterification reactions of

15

SP169 and AE16 are set at 0.6% and 0.8%, respectively.

16

Characteristic Properties of Poly(ether ester) Intermediates

17

IR and 1H NMR of SP169 Poly(ether ester). As shown in Figure 1(a), the band

18

at 3492 cm−1 indicates the stretching of –OH at the end of the molecule, and those at

19

2950, 2923, and 2857 cm−1 can be ascribed to -CH3, -CH2, and C-H stretching,

20

respectively. Moreover, the bands at 1456, 1377, and 728 cm−1 denote the bending of

21

-CH3, -CH2, and C-H, respectively. The band at 1090 cm−1 refers to asymmetrical 11

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C-O-C stretching, and that at 1042 cm−1 represents C-C stretching. The IR spectrum

2

indicates that SP169 has a common functional group characteristic with the polyether

3

type demulsifier. In contrast to that of SP169, the intensity of -OH stretching in SP169

4

poly(ether ester) is weaker at 3492 cm−1, and C=O and C=C stretching appear at 1726

5

and 1635 cm−1, respectively. Therefore, esterification reaction can successfully

6

produce the SP169 poly(ether ester).

7

Figure 1(b) and Table 2 show the 1H NMR results. As can be seen, the ester

8

group and C=C are grafted to the molecular skeleton of SP169. Due to the excess

9

carboxyl, the hydroxyl group was consumed completely, thus leaving a little carboxyl

10

group and indicating the successful synthesis of SP169 poly(ether ester).

(a)

11

12

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(b)

1 2

Figure 1. (a) IR spectrum and (b) 1H NMR and proton assignment of the SP169

3

poly(ether ester).

4

IR and 1H NMR of AE16 Poly(ether ester). As shown in Figure 2(a), the bands

5

at 3482, 2943, 2920, and 1167 cm−1 can be ascribed to the stretching of -OH, -CH3,

6

-CH2-, C-H, and C-N, respectively, and those at 1455, 1383, and 732 cm−1 indicate the

7

bending of -CH3, -CH2- and C-H, respectively. The band at 1103 cm−1 relates to

8

asymmetrical C-O-C stretching, whereas that at 1046 cm−1 refers to C-C stretching.

9

IR spectrum of AE16 shows that the compound contains hydroxyl, ether group, and

10

carbon and nitrogen groups. In contrast, the intensity of -OH stretching in AE16

11

poly(ether ester) is weaker than that of AE16, and the stretching of C=O and C=C

12

bonds in the former appears at 1765 and 1670 cm−1, respectively. Hence, the

13

esterification reaction successfully produces the AE16 poly(ether ester).

14

Figure 2(b) and Table 3 show the 1H NMR results. As can be seen, the ester

15

group and C=C are grafted to the molecular skeleton of AE16, thus demonstrating the 13

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successful synthesis of AE16 poly(ether ester).

(a)

2

(b)

3 4

Figure 2 (a) Infrared spectrum and (b) 1H NMR and proton assignment of AE16

5

poly(ether ester).

6

Factors Affecting Hydrosilation Reaction

7

Temperature, time, amount of catalyst, and Si-H to C=C bond ratio can affect the

8

hydrosilation reaction. All conditions are optimized in this study (Figure S2 (a), (b),

9

(c), (d), Supporting Information). The conversion rate is 90.8% when the temperature, 14

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reaction time, catalytic amount, and Si-H to C=C bond ratio are set to 90°C, 6 h, 35

2

µg/g, and 1:1.2, respectively.

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Characteristic of the silicone demulsifier

4

Infrared Spectrogram and 1H NMR of Silicone Demulsifier. The mechanism

5

of silicon hydrogen addition reaction can be explained through free radical and

6

coordination addition. The electronegativities of Si and H are 1.8 and 2.1, respectively.

7

The negative Si-H can add to the unsaturated bonds to generate stable Si-C bonds, as

8

in the case of introducing acrylate to the main polysiloxane chain.37,38

9

Figure 3(a) shows the IR spectra of the silicone demulsifiers. In comparison with

10

polysiloxane, Si-H stretching, Si-H bending, and C=C stretching bands of the silicone

11

demulsifier disappear in the 2166, 888/843, 1635, and 1670 cm−1 regions, respectively,

12

thus suggesting the consumption of Si-H in the reaction. Bands at 2855 and 724 cm−1

13

can be ascribed to C-H stretching and -CH2 bending, respectively. Peaks at 1733, 1174,

14

1100, and 1043 cm−1 indicate the stretching of C=O, C-N, C-O-C, C-C, respectively.

15

Hence, the IR spectra demonstrated the grafting of SP169 poly(ether ester) and AE16

16

poly(ether ester) to the polysiloxane skeleton. However, the band at 3465 cm−1

17

ascribed to -OH stretching is not consumed during esterification. IR peaks at 2958,

18

1264, 1042–1097, and 762 cm−1 refer to C-H stretching in -CH3, Si-H stretching,

19

Si-O-Si stretching, and Si-H bending, respectively, thus confirming the identity of the

20

target product as the silicone demulsifier. As shown in Figure 3(b) and Figure 3(c) as

21

well as in Table 4, the 1H NMR of the silicone demulsifier shows that all Si-H protons

22

disappear in δ = 4.70 ppm, and the peak of C=C appears weakly in δ = 6.19 and 6.38

23

ppm out of the superfluousness of C=C. The proton peaks of Si-CH2, CH2-O, and

24

CH-O also appear in δ = 0.43, 4.14/4.18, and 4.22 ppm, respectively. 15

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(a)

1

(b)

2 CH3

CH3

CH3

CH3

CH3

CH3

Si O

(SiO)c (SiO)x (SiO)y Si CH3 10 11 12 13 CH3 CH3 8 9 CH2 (CH2)13-15 CH2 CH3 1 CH2CH2C (OCH2CH2)b (OCH2CH)a-1 (OCH2CH) N CH2 (CH2)13-15 CH2 CH3 O CH3 CH3 6 CH2CH2C (OCH2CH)p (OCH2CH2)n (OCH2CH)m O CH2 (CH2)15 CH2 CH3 2 3 O 4 CH 7 CH

CH3

(c)

3

3

3

5

4

Figure 3. Comparison of the (a) IR spectra of silicone demulsifier and raw material,

5

(b) 1H NMR and (c) proton assignment of the silicone demulsifier. 16

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1

Surface Tension Measurement. The critical micelle concentration (CMC) of the

2

silicone demulsifier can be determined by surface tension measurement (Figure 4).

3

The CMC of all silicone demulsifiers under different proportions of SP169 polyether

4

and AE16 polyether is about 150 mg/L. The silicone demulsifier obtains the lowest

5

surface tension when AE16 polyether/SP169 polyether ratio is 2:1. AE16 poly(ether

6

ester) has more alkyl chains than SP169 poly(ether ester); thus, the former possesses a

7

stronger ability to reduce surface tension. When the proportion exceeds 2:1 (AE16

8

polyether: SP169 polyether), the ability to reduce the surface tension declines, which

9

may be due to the fact that the proportions of the hydrophilic and lipophilic groups

10

balance out to a certain extent. However, more tests are needed.

11 12

Figure 4. Surface tension of silicone demulsifier with different ratios of AE16

13

poly(ether ester) and SP169 poly(ether ester).

14

Thermal Analysis of the Silicone Demulsifier. Figure 5 describes the thermal

15

stability of the silicone demulsifier. The interval of thermal degradation of the silicone

16

demulsifier was 325°C–390°C. The temperature at 350°C can be considered as the 17

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1

average thermal degradation temperature of the silicone demulsifier. Consequently,

2

the silicone demulsifier would be useful in high-temperature reservoirs, which could

3

broaden its application sphere.

4 5 6

Figure 5. Thermograms of the silicone demulsifier (q=10°/min).

Adsorption Performance of the Silicone Demulsifier by QCM-D

7

The demulsifier changes the drainability of the oil–water interfacial film.39 A

8

demulsifier fills the vacant position of the oil–water interface in the emulsion to

9

prevent the migration of the natural emulsifier. As a result, the interfacial tension

10

between two drops lower, and the interfacial film drainability strengthens. In addition,

11

the drainability relates to the gradient of interfacial tension, which depends on the

12

adsorbability and diffusivity of the demulsifier in the oil-water interface.40

13 14

Figure 6 shows the diffusion and adsorption performance of the demulsifier measured by QCM-D.

18

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(a)

1

(b)

2 3

Figure 6.(a) Frequency change of quartz and (b) dissipation factor change of quartz

4

with different adsorbed demulsifiers.

5

As shown the Figure 6(a), ∆F has two phases. In the first phase, the adsorption of

6

aged oil onto the piezoid surface changes ∆F and ∆D. The second phase entails the

7

adsorption of the demulsifier onto the surface of the aged oil. The two-phase result

8

indicates that a greater amount of silicone demulsifier could absorb onto the surface of

9

aged oil, thus making its adsorption performance superior to that of SP169 and AE16.

10

Meanwhile, ∆D reflects the intensity and viscoelasticity of adsorbed aged oil layer 19

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1

treated by silicone demulsifier. Figure 6(b) shows that the silicone demulsifier causes

2

the largest change of ∆D with the same amounts of silicone demulsifier, SP169, and

3

AE16.

4 5

To further study the loose extant of the adsorbed layer, the ∆D/∆F curves for the second phase of different demulsifiers were investigated (Figure 7).

(a)

(b)

(c)

(d)

6

7 8

Figure 7. ∆D-∆F curve of the adsorbed layer of (a) SP169, (b) AE16, (c) silicone

9

demulsifier and (d) comparison of the ∆D-∆F slopes of SP169, AE16, and the silicone

10

demulsifier.

11

The |∆D/∆F| reflects the loose extant of the adsorbed layer. The slope of |∆D/∆F|

12

is smaller, and the structure of the adsorbed layer is tighter. Figure 7 shows that the

13

lowest |∆D/∆F| slope belongs to the silicone demulsifier, and the adsorbed silicone

14

demulsifier layer is the tightest; thus, the adsorbability and diffusivity of silicone 20

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demulsifier are greater than those of SP169 and AE16. These excellent characteristics

2

allow the silicone demulsifier to absorb quickly to the opening section of the oil–

3

water surface and form the positive gradient of interfacial tension. Thus, the draining

4

process accelerates and water is effectively separated.

5

Influence

6

Performance

of

the

Operating

Conditions

on

Demulsifier

7

Ratio of Poly(ether ester). The different ratios of poly(ether ester) were

8

investigated during 1 h treatment of 150 mg/L demulsifier at 70°C. As seen in Figure

9

8(a), the dehydration rate of the aged oil rises with increasing AE16 poly(ether ester).

10

When excess AE16 poly(ether ester) is added, the variation tendency of dehydration

11

rate is totally the opposite. This result agrees with the surface tension characteristic of

12

the silicone demulsifier. Hence, the optimal AE16 poly(ether ester) to SP169

13

poly(ether ester) ratio is 2:1.

14

Demulsification Time. Dehydration rate under 150 mg/L demulsifier at 70°C

15

was observed at a AE16 poly(ether ester) to SP169 poly(ether ester) ratio of 2:1. Time

16

influences the demulsification, because the demulsifier absorbs and replaces the

17

emulsifiers like solid impurities and asphaltenes in the oil–water interface. Figure 8(b)

18

shows that the dehydration rate of aged oil improves with increasing demulsification

19

time. Hence, the best demulsification time is 1.5 h.

20

Demulsification Temperature. The change of dehydration with demulsification

21

temperature was recorded when the AE16 poly(ether ester) to SP169 poly(ether ester) 21

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1

ratio was set at 2:1 during 1.5 h demulsification under 150 mg/L dosage.

2

Demulsification temperature can enhance the molecular freedom thermal motion, thus

3

accelerating the diffusion speed of the demulsifier and coalescence of water drop.

4

Meanwhile, temperature reduces the viscosity of the emulsion and the stability of the

5

oil–water interface. As shown in Figure 8(c), the ideal demulsification temperature is

6

65°C.

7

Demulsifier Dosage. Dehydration rate for 1.5 h under 65°C was investigated

8

when the AE16 poly(ether ester) to SP169 poly(ether ester) ratio was set at 2:1. The

9

dosage of the demulsifier influences the demulsification effect. As shown in Figure

10

8(d), the dehydration rate of aged oil is 85.44% at 150 mg/L dosage. However, the

11

maximum dehydration rate is 86.16% at 200 mg/L demulsifier. Any concentration

12

above 200 mg/L will make the demulsifier form micelles, which can affect the

13

demulsification behavior. At the same time, the surface tension of aged oil rises if the

14

demulsifier dosage exceeds 200 mg/L, as illustrated in Figure 8(e). Therefore, the

15

optimal dosage of silicone demulsifier is 150 mg/L.

(b)

(a)

16

22

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(d)

(c)

1 (e)

2 3

Figure 8. Effect of (a) n(AE16 poly(ether ester))/n(SP169 poly(ether ester)), (b)

4

demulsification time, (c) demulsification temperature, (d) demulsifier content on

5

dehydration rate and (e) demulsifier content on interfacial tension.

6

Comparison of the demulsification of SP169, AE16, and the

7

silicone demulsifier

8

As shown in Figure 9, demulsification effect of blank, SP169, AE16, and silicone

9

demulsifier were all evaluated under the 1.5 h, 65 °C, 150 mg/L. The dehydration

10

rates of silicone demulsifier, SP169, and AE16 are 86.87%, 56.72%, and 55.28%,

11

respectively. The dehydration rate of aged oil treated by silicone demulsifier is

12

obviously better than those under SP169 and AE16 treatments. The oil–water

13

interface treated by silicone demulsifier is clearer, and the separated water is pale 23

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1

yellow and almost clear. Hence, the silicone demulsifier is advantageous compared

2

with SP169 and AE16 in the treatment of aged oil from the Liuhua oilfield. The

3

excellent performance of the silicone demulsifier may be related to its better diffusion

4

and adsorption performance. In addition, comparison of other commercial

5

demulsifiers with the silicone demulsifier was also conducted. The aged oil

6

dehydration rate treated by the silicone demulsifier is better than those under

7

commercial demulsifiers (Supporting Information, Page 7, Figure S3).

8 9

Figure 9. Comparison of the demulsification of SP169, AE16, and the silicone

10

demulsifier.

11

CONCLUSIONS

12

A structurally branched silicone demulsifier was modified based on SP169 and

13

AE16 in a two-step synthesis method. In the first step, the poly(ether ester)

14

intermediates of SP169 and AE16 were synthesized by esterification. The reaction

15

conditions of SP169 and AE16 esterification were optimized. The esterification rates 24

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of SP169 and AE16 are 95.8% and 94.2%, respectively. The IR and 1HNMR spectra

2

indicate the construction of molecular skeletons and the addition of the C=C bond of

3

acrylic acid to SP169 and AE16. In the second step, the silicone demulsifier was

4

prepared by silicon hydrogenation addition. The conversion rate is 92.3% under

5

optimal conditions. The IR and 1HNMR spectra illustrate the replacement of two

6

poly(ether ester) intermediates by the -H group of polysiloxane.

7

The IR and 1HNMR spectra further reveal the successful synthesis of the silicone

8

demulsifier. The combination of interfacial tension measurements and TGA provides a

9

clue in better understanding demulsifier performance. Meanwhile, the absorption

10

behavior of the silicone demulsifier in the oil–water interface was investigated via

11

QCM-D, with the silicone demulsifier displaying the largest change of ∆F and ∆D.

12

The descending order of |∆D/∆F| reflecting the loose extant of the adsorbed layer is as

13

follows: SP169 > AE16 > silicone demulsifier. The trend shows that the silicone

14

demulsifier could form a compact and homogeneous adsorbed layer, thus showing

15

better performance in aged oil demulsification.

16

Furthermore, when the poly(ether ester) ratio, demulsification time, temperature,

17

and dosage are at 2:1, 1.5 h, 65 °C, and 150 mg/L, the dehydration rate of aged oil

18

reaches 86.87%, thus indicating the potential application of silicone demulsifiers in

19

Liuhua oilfields.

25

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1

Page 26 of 33

Tables Table 1. Characteristics of aged oil. Items

Value

Density (20°C, g/cm3)

952.7

Viscosity (50°C, mPa S)

412

Water content (%)

34.82

Asphaltene (%)

4.63

Colloid (%)

19.45

Solid impurities (%)

2.16

Acid value (mg KOH/g)

5.25

Salt content (mg/L)

417.9

Strength of the interface film (mN/m)

23.9

Zeta potential (mV)

-15.45

2 Table 2. Results of the 1H NMR of SP169 poly(ether ester) Chemical shift (δH)

Functional group

Affiliation

0.98–1.01

-CH3

1H, 5H

1.41–1.47

-CH2-

2H, 3H

4.07, 4.12

CH2-O

4H, 7H

4.20

CH-O

6H

4.61

CH2-OC=O

8H

6.12

CH=CH2

9H

6.35

-CH=CH2

10H

9.30

-COOH

3

26

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1 Table 3. Results of the 1H NMR of AE16 poly(ether ester). Chemical shift (δH)

Functional group

Affiliation

0.97–1.03

-CH3

1H, 5H

1.43, 1.46

-CH2-

2H, 3H

2.20, 2.23

CH2-N, CH-N

4H, 6H

4.12

CH2-O

7H, 9H

4.21

CH-O

8H

4.66

CH2-OC=O

10H

6.18

CH=CH2

11H

6.37

-CH=CH2

12H

9.37

-COOH

2 Table 4. Results of the 1H NMR of the silicone demulsifier. Chemical shift (δH)

Functional group

Affiliation

0.05

Si-CH3

1H

0.43

Si-CH2

2H

1.07

-CH3

5H, 12H

1.43–1.46

-CH2-

10H, 11H

2.22, 2.25

CH2-N, CH-N

9H, 8H

2.36

CH2-COO-

3H

4.14, 4.18

CH2-O

4H, 7H

4.22

CH-O

6H

6.19, 6.38

CH=CH2, -CH=CH2

3

27

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1 2

3

AUTHOR INFORMATION *Corresponding Author; Tel./Fax: +8613551308326, E-mail: [email protected]

ACKNOWLEDGMENTS

4

This study received financial support from the SWPU Pollution Control of Oil

5

and Gas Fields Science and Technology Innovation Youth Team, under Grant No.

6

2013XJZT003.

7

SUPPORTING INFORMATION

8

Section 1. Measurement Method of Conversion Rate. Figures S1 (a), (b), (c), (d),

9

and (e) describe the esterification reaction parameters. Figures S2 (a), (b), (c), and (d)

10

describe the hydrosilation reaction parameters.

11

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