Demulsification of water in oil emulsion by surface modified SiO2 nanoparticle

Journal Pre-proof Demulsification of water in oil emulsion by surface modified SiO2 nanoparticle Soheila Javadian, S. Morteza Sadrpoor PII:

S0920-4105(19)30968-4

DOI:

https://doi.org/10.1016/j.petrol.2019.106547

Reference:

PETROL 106547

To appear in:

Journal of Petroleum Science and Engineering

Received Date: 27 April 2019 Revised Date:

4 September 2019

Accepted Date: 29 September 2019

Please cite this article as: Javadian, S., Sadrpoor, S.M., Demulsification of water in oil emulsion by surface modified SiO2 nanoparticle, Journal of Petroleum Science and Engineering (2019), doi: https:// doi.org/10.1016/j.petrol.2019.106547. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.

1

Demulsification of water in oil emulsion by surface

2

modified SiO2 nanoparticle

3

Soheila Javadian*, S. Morteza Sadrpoor

4

Department of Physical Chemistry, Faculty of Basic Science, Tarbiat Modares University,

5

P.O. Box 14115-175Tehran, I.R. of Iran

6

7

Abstract

8

In the present study, SiO2 nanoparticles (NP) were used for dehydration of crude oil.

9

Also, in order to enhance the hydrophobicity and hydrophilicity of the nanoparticles,

10

they were functionalized respectively with oleic acid (OA) and sodium dodecyl

11

benzene

12

employed

13

Nanodemulsifiers were characterized with scanning electron microscopy (SEM), field-

14

emission

15

(BET),

16

thermogravimetric analysis (TGA), and zeta potential. Additionally, the performance of

17

nanodemulsifiers was evaluated with bottle test. The results of bottle test revealed that

sulfonate to

synthesis

scanning X-ray

(SDBS)

surfactant.

GO-SiO2

electron

nanocomposite

microscopy

diffraction (XRD),

Furthermore, as

(FESEM),

Fourier-transform

1

graphene a

oxide

superhydrophilic

(GO)

demulsifier.

Brunauer–Emmett–Teller infrared

was

spectroscopy

method (FT-IR),

1

GO-SiO2 nanocomposite has the best performance among all nanodemulsifiers and

2

dehydration of crude oil was completed during 90 min (while dehydration of crude oil

3

with SiO2 nanoparticle was done at 110 min). Moreover, the effects of temperature and

4

salt were surveyed and the results demonstrated that both factors influence the stability

5

of water in oil emulsion. The outcomes of the interfacial tension (IFT) at the water

6

/crude oil interface displayed GO-SiO2 nanocomposite has interface active property

7

and can decrease IFT from 14.38 mN.m-1 to 2.44 mN.m-1.

8

Keyword: demulsification, SiO2 surface modification, water in oil emulsion

9

Introduction

10

The crude oil extracted from reservoirs is usually accompanied by the water droplets

11

in the form of a waste emulsion (Delgado-Linares et al., 2016; Feng et al., 2011; Jiang

12

et al., 2010; Silva et al., 2013). The formation of a stable emulsion of water in crude oil

13

(w/o) is related to asphaltene and resin that are known as natural surface active

14

materials (Gafonova and Yarranton, 2001; Ligiero et al., 2017). These materials build a

15

film around water droplets that inhibit coalescence of them which results in a stable

16

emulsion of water in oil medium (Chang et al., 2018; Gafonova and Yarranton, 2001).

17

Asphaltenes can establish a complex plexus by connecting together which play an

18

essential role in the formation of the mentioned film (Czarnecki et al., 2012; Li et al.,

19

2002; Tchoukov et al., 2014).

20

This harmful emulsion (w/o emulsion) is the cause of catalyst poisoning and

21

corrosion in pipes and pumps, therefore the water droplets should be removed before

22

entering to petrochemical industries (Atta et al., 2018; Fan et al., 2018; Santos et al.,

2

1

2015; Shi et al., 2017). Today, various demulsification methods such as chemical,

2

physical (as essential methods), and biological are used to eliminate such harmful

3

emulsions. The physical methods including electrical, thermal, etc. are not used alone

4

but they are utilized in a conjunction with other methods (Tubuke Mwakasala et al.,

5

2016; Zolfaghari et al., 2016). Between these methods, chemical demulsifiers are cost-

6

effective and more popular (Biniaz et al., 2016; Tubuke Mwakasala et al., 2016;

7

Zolfaghari et al., 2016). Nanoparticles as chemical demulsifiers have high surface area

8

and surface charge which enhance their ability to adsorb the asphaltene on their

9

surfaces (Franco et al., 2013; Nassar et al., 2014, 2012; Shayan and Mirzayi, 2015).

10

Therefore, adding nanoparticles to crude oil is a suitable choice for the destruction of

11

the film around water droplets and destabilization of w/o emulsion.

12 13

Feng et al (Fang-Hui and Hong, 2008) in 2008 synthesized new demulsifiers by adding SiO2

14

(NP) nanoparticle to TA1031 demulsifier with a different mass ratio. The results showed that, a

15

new demulsifier in the mass ratio of 1Np:10 TA1031 can dehydrated oil with an efficiency of

16

around 97%. Peng and coworkers (Peng et al., 2012) prepared Fe3O4@SiO2 for separation water

17

from crude oil. Chen and his team (Chen et al., 2015) coated Fe3O4 with SiO2 and, they then

18

functionalized Fe3O4@SiO2 with KH-1231 (commercial demulsifier). The results of the

19

demulsification test represented that the magnetic demulsifier separated water from oil, about

20

94%. Yegya et al (Yegya Raman and Aichele, 2018) was indicated partially hydrophobic SiO2

21

nanoparticle can unstable w/o emulsion stabled with surfactant. Huang with coworkers (Huang et

22

al., 2019) used nanotubes/SiO2 nanomaterial (CNTs/SiO2) for unstable w/o emulsion. Ghanadkar

23

et al (G.E. Ghanadkar et al, 2015) prepared SiO2 with poly vinyl alcohol (PVA), the results of

3

1

the bottle test show the efficiency of nanodemulsifier is 40%. Li and his team (Li et al., 2014)

2

synthesized Fe3O4@SiO2 and then functionalized the magnetic nanoparticle with 5010 industrial

3

demulsifier for demulsification of oil in water (o/w) emulsion.

4

Environmentally friendly (Spataru et al., 2016; Zhang et al., 2013) and cost-effective

5

SiO2 nanoparticles were utilized in this study. Having an active surface and high

6

surface area, SiO2 nanoparticles can adsorb asphaltene particles efficiently, which this

7

in turn leads to the removal of the rigid film around water droplets. In addition, for the

8

first time to the best of our knowledge, the separation of water from w/o emulsion by

9

SiO2 nanoparticles modified with different surfactants, has been questioned. Also, to

10

provide a demulsifier with a very high surface area and high activity, GO-SiO2

11

nanocomposite was synthesized. The effect of salt on the demulsification efficiency of

12

nanoparticles has been less considered, so this paper studies the effect of sodium

13

chloride and calcium chloride on the performance of nanodemulsifiers.

14

Materials and methods

15

2.1 Materials

16

All the chemical materials were used as shown in Table 1. Also, dead crude oil was prepared

17

from reservoirs in the southern region of Iran.

18

2.2 Methods

19

2.2.1 Preparation of W/O emulsion

20

Distilled water slowly (within few seconds) was added to crude oil (proportion 2:3

21

V/V) and the mixture was stirred (model, Wise-Stire MS-MP8) for 110 minutes at

22

1100 rpm. The formed emulsion was stable over several days.

23

4

1

2.2.2 Demulsification test

2

The bottle test is a common method for evaluation of oil dehydration by different

3

demulsifiers. Stable w/o emulsion was introduced to graded bottles (at 298K), then the

4

nanodemulsifier was added to the bottles. The amount of separated water was recorded

5

(at the concentration in which nanodemulsifier was separated completely from water,

6

or at the time that the performance of the nanodemulsifier did not improve anymore

7

over time) and the efficiency of nanodemulsifiers was calculated from the equation 1,

8

where ܸ௦ and ܸ଴ are the volume of separated water and initial water, respectively.

9

error of the bottle test results is within plus or minus 3 percent. ‫ܧ‬% = the

optical

microscope

ܸ௦ × 100 ܸ଴

(Olympus

-

The

‫ݍܧ‬. 1

10

Further,

BH2)

was

used

for

evaluation

of

11

demulsification mechanism of silica nanoparticle. Also, Image j software was used for

12

measuring the size of water droplets.

13

2.2.3 Functionalized silica nanoparticle

14

2.2.3.1 SiO2@OA

15

SiO2@OA preparation was performed according to the method reported by Zhu (Li

16

and Zhu, 2003). Frist, oleic acid was dissolved in n-hexane, then silica nanoparticle

17

was added to the solution so that the weight ratio of OA to nanoparticle was 1:2. The

18

solution was heated to 60°C under sonicated for a few minutes, then it was stirred for 4

19

hours at the same temperature. The solution was centrifuged and precipitate was

20

washed several times with a mixture of water and ethanol. The precipitate was placed

21

in an oven for 24 hours at 80°C.

5

1

2.2.3.2 SiO2@SDBS

2

The surface of SiO2 was modified by SDBS surfactant thoroughly as Jiyan reported

3

(Liu et al., 2010). SDBS was mixed with NP in distilled water with 1.6% mass ratio of

4

the nanoparticle. The solution was subjected to ultrasonic treatment for 18 min. After

5

that, it was centrifuged and the white precipitate was separated. The precipitate was

6

washed multiple times with distilled water and was dried in an oven.

7

2.2.3.3 GO

8

The synthesis method of graphene oxide (GO) is taken from a previous study

9

(Javadian et al., 2017). Preparation of acidic mixture was done with Potassium

10

permanganate (KMnO4) which was dissolved in the mixture of Phosphoric acid

11

(H3PO4) and Sulphuric acid (H2SO4) in 0.5 L distilled water. Then graphite powder

12

(100 mg) was added to the prepared acidic mixture and was stirred for a few minutes.

13

For simultaneous oxidization, the mixture was put under the ultrasonic irradiation for

14

an hour. Finally, 120 ml distilled water was added slowly to the solution, followed by a

15

vacuum filtration and was washed several times with water and H2O2 for removal of

16

ions and acids. The nanosheets were stored in the mixture of water and alcohol.

17

2.2.3.4 GO- SiO2

18

GO-SiO2 was prepared according to the procedure described by Gao (Kou and Gao,

19

2011). Briefly, 50 mg of GO was dispersed in ethanol-water solution for 30 min. Then

20

pH of the solution was adjusted about 9 by adding the ammonia solution. Then 0.5 ml

21

of tetraethyl orthosilicate (TEOS) was added to a solution and sonicated for 30 min,

22

again. The solution was stirred with a magnetic stirrer for 24 hours at room

6

1

temperature. Finally, suspension of GO-SiO2 was centrifuged and washed several times

2

with ethanol.

3

2.2.4 Characterization

4

Morphology of SiO2 nanoparticle and GO-SiO2 nanocomposite was characterized by

5

both scanning electron microscope (SEM, first the powder of SiO2 nanoparticle coated

6

with gold (Au) then for imaging of the coated powder was used of SEM- TESCAN

7

Vega model instrument) and field-emission scanning electron microscopy (FESEM-

8

MIRA3TESCAN-XMU).

9

Malvern zeta sizer (model nano-zs). The nanodemulsifiers were dispersed in toluene

10

and then 400 µl of the dispersion was introduced into the instrument. In order to study

11

the surface coating of the composition, the Fourier-transform infrared spectroscopy (in

12

order to make KBr pellet the nanodemulsifiers mixed with the powder KBr then the

13

pellet of samples introduce to FTIR-Nicolet 100) and thermo gravimetric analysis

14

(TGA- Netzsch - TGA 209 F1) was used (all samples were heated in the N2 atmosphere

15

from 24°C to 800°C at a heating rate of 10°C/min). The surface area of nanoparticles

16

was

17

method. The crystal size of nanodemulsifiers with X-ray diffraction (XRD- Philips

18

X'Pert MPD) with Co kά radiation (λ=0.1789 nm).

calculated

Zeta

by using

potential

of

nanodemulsifiers

Brunauer_Emmett_Teller

(BET-

was

measured

micromeritics

TriStar

with

II)

19

2.2.5 Interfacial tension measurement

20

The water/Oil interfacial tension (IFT) was measured in the presence and absence of

21

the

nanodemulsifiers

22

activity

23

demulsification with oil and compared with IFT of distilled water/crude oil.

of

by

ring

nanodemulsifier

tensiometer was

(KRUSS

evaluated

7

by

K12)

IFT

of

method. water

The

interfacial

separated

after

1

2.2.6 Total acid number determination

2

The total acid number (TAN) value of crude oil was measured as the amount of

3

potassium hydroxide (KOH) in milligrams that is needed to neutralize the total acids in

4

one gram of crude oil. To calculate the TAN of crude oil, the KOH solution (0.005 M)

5

was used to neutralize total acidic constituents pesent in crude oil. The titrations were

6

performed (3 times) in the mixture of toluene, isopropanol, distllid water (volumetric

7

proportion 500:495:5), and in the present of indicator (Phenolphthalein).

8

2.2.7 Viscosity measurement

9

15 ml of the crude oil introduce to viscosity instrument (Cambridge Electromagnetic

10

Viscometer, SPSL 440 model) for determination of the viscosity of crude oil at 298K. The result

11

of the measurement of crude oil viscosity is shown in table 2.

12

2.2.8 Saturate, aromatic, resin, and, asphaltene fractions measurement

13

The SARA (Saturate, Aromatic, Resin and Asphaltene) analysis of crude oil was performed

14

with ASTM D-2007 method. The result of the SARA analysis is shown in table 2.

15

3. Results and discussion

16

3.1 Characterization

17

The size and morphology of SiO2 are given in Fig1-a. The SEM image of SiO2 is

18

depicting the spherical shape of nanoparticles as well as representing the size of silica

19

particles which is below 100 nm. The FESEM image of GO-SiO2 nanocomposite

20

displays the formation of silica nanoparticle on the surface of GO (Fig1-b). The XRD

21

spectra of nanoparticles are given in Fig.2. The existence of a broad peak between 20-

22

30 in Fig.2-a (for all samples) agrees with standard XRD pattern of silica (Musić et al.,

23

2011) , also position of a sharp peak and a broad peak in Fig.2-b are related to (001)

8

1

peak of GO and silica, respectively (Cui et al., 2011; Jabbar et al., 2017; Johra et al.,

2

2014). The crystal size of the nanoparticles is calculated with Scherrer equation (Eq.2)

3

that is shown in table 3. ‫=ܦ‬

4

݇ߣ . 2 ߚܿ‫߆ݏ݋‬

Where D is the crystal size of the nanoparticle, λ is X-ray wavelength (λ=0.1789 is the dimensionless Scherrer constant that is usually equal to 0.9, " expresses

5

nm),

6

full width at half maximum (radian), and Θ is related to the position of the peak

7

(degree).

8

Fig.3 shows FT-IR spectra of nanodemulsifiers. Peaks at 467 and 801 cm-1 are

9

attributed to Si-O (Bazmandegan-Shamili et al., 2018; İşçi et al., 2006) and the peak at

10

1098 cm-1 is attributed to Si-O-Si bond (Fig.3-a) (Bazmandegan-Shamili et al., 2018;

11

Feifel and Lisdat, 2011) Also, the peak at 3430 cm-1 is related to OH and Si-O-H

12

groups (Ma et al., 2013). Obviously, the peaks in Fig.3b-c are because of the core of

13

SiO2@OA and SiO2@SDBS which have the same silica nanoparticle. Also, peaks at

14

1187 and 1647 cm-1 in Fig.3-b represent the existence of S=O and C=C groups

15

(Bouraada et al., 2016; Nersasian and Johnson, 1965), and the one at 1870 cm-1 is

16

ascribed to a combination bond of the C=C aromatic ring (Upmanyu et al., 2011) on

17

the surface of nanoparticle that conforms with the structure of

18

at 1745, 2925 and 2857 cm-1 are related to C=O of carboxylic acid and CH2 groups of

19

OA respectively (Chen et al., 2018; Jalili et al., 2016; Zhang et al., 2006) that prove

20

that the functionalization of the nanoparticle with OA has successfully been performed.

21

The peaks at 458, 802 and 1090 cm-1 in Fig3-d is an evidence of the successful

22

synthesis of GO-SiO2 nanoomposite, and

SDBS. In Fig.3-c peaks

peaks at 1632 and 1720 cm-1 are attributed to

9

1

the stretching of C=C bond and C=O carbonyl stretching, respectively (Fig.3-d)

2

(Alsharaeh et al., 2014; Yang et al., 2012) .

3

The values of zeta potential indicate that the zeta potential of SiO2 increases by the

4

modification of its

5

carboxylic and sulfonate groups in OA and SDBS surfactants respectively,

6

ether

7

nanodemulsifiers are shown in table 3. SiO2 has a high specific surface area (152.4

8

m2.g-1) and its surface area decreased when it was coated by OA and SDBS surfactants.

9

The reduction of the surface area of the nanoparticles resulted from coating by

10

surfactant was reported in several papers (bo Zhong et al., 2012; Lankoff et al., 2012;

11

Ma et al., 2010; Spataru et al., 2016). GO-SiO2

12

specific surface area (292.7 m2.g-1) in comparison to SiO2 alone thanks to

13

specific area of GO (Ma et al., 2017). The results of BET-BJH method reveal that all

14

the nanodemulsifiers show IV-type isotherm

15

indicate mesopore structures of them (Fig.4) (Sing, 1985). Also, SiO2, SiO2@SDBS,

16

and SiO2@OA show H3-type hysteresis loop and GO-SiO2 shows H2-type hysteresis

17

loop

18

nanoparticles with H3-type hysteresis loop and ink bottle pores shape in the structure

19

of nanocomposite (Lowell et al., 2012; Sing, 1985).

20

SiO2@SDBS and SiO2 nanoparticle (Fig.5-a), also a comparison between the TGA

21

curves of SiO2 nanoparticle and SiO2@OA indicates in fig.5-b. The weights loss before

22

200°C are related to the physically adsorbed water (for all samples). The TGA curve of

1

and

upon

surface. The reason

carboxylic

IUPAC

groups,

categories,

in

the

that

for this observation

structure

exhibit

International Union of Pure and Applied Chemistry

10

of

GO.

The

is the existence of

surface

as well as area

of

nanocomposite has a higher the high

based on the IUPAC1 categories that

slit-shaped

pores

in

structures

of

Fig.5 shows the TGA curves of

1

SiO2@SDBS is conforming to the TGA decomposition pattern of SDBS in some

2

studies (Wei et al., 2005). The mass lost about 360°C in SiO2@OA nanodemulsifiers

3

attributed to the decomposition of oleic acid (Grisorio et al., 2016). The change in zeta

4

potential, specific surfaces area, and the change of the TGA curves of coated

5

nanodemulsifier compare to SiO2 are proofs for a successful surface modification of

6

the silica nanoparticle.

7

3.2 Demulsification test

8

To evaluate the demulsification ability of the nanodemulsifiers a set of bottle tests

9

were conducted. The results (in Fig.6) depict that SiO2 nanoparticle and GO-SiO2

10

separate water from crude oil completely at 110 and 90 min, respectively (More details

11

of dehydration oil vs. time is found in Fig.1 in supporting information, S1), but

12

SiO2@OA and SiO2@SDBS separate water by a much lower efficiency of respectively

13

around 37.5% and 84%,. The optimum concentration of both GO-SiO2 and SiO2@OA

14

is 300 ppm while that of SiO2 and SiO2@SDBS is found to be 500 and 400 ppm,

15

respectively.

16

Due to injection of hydrophilic SiO2 nanoparticles in hydrophobic crude oil medium,

17

silica nanoparticles have a tendency to migrate to the water-oil interface because of

18

hydrophilicity property which this in turn depletes asphaltene molecules from the film

19

surrounding water droplets, that eventually causes water droplets coalescence together.

20

In addition, the hydroxyl groups on the nanoparticles can form hydrogen bonding with

21

asphaltenes present in the film which this bonding finally flocculate the emulsion

22

droplets (Yegya Raman and Aichele, 2018). Fig.7 pictured the w/o emulsion before

23

and after injection of the SiO2 nanodemulsifier, the water drops of emulsion were

11

1

growth remarkably after injection of SiO2 that indicate the nanoparticle can adsorb to

2

water/oil interface during the demulsification process and destroyed the films around

3

water droplets and make w/o emulsion unstable. This argument is in agreement with

4

some studies used in this method (Fang et al., 2017; Ali et al., 2015).

5

Owing to the hydrophobic alkyl chains present in its structure, the SiO2@OA

6

nanodemulsifier has a less affinity to migrating to the water/crude oil interface.

7

Besides, the steric repulsion between the alkyl chains and the asphaltene molecules

8

present

9

compared

in

the to

film, that

makes

of

the

demulsification

SiO2 nanoparticle.

performance

Moreover,

of

functionalizing

SiO2@OA of

wore

the

SiO2

10

nanoparticle with SDBS, However, hydrogen bonding between sulfonate group and

11

asphaltene causes instability of water droplets but it makes SiO2 more hydrophilic,

12

which this consequently causes entrapping a more fraction of the functionalized-

13

nanodemulsifiers

14

adsorption in the water/crude oil interface.

15

decreased as compared to SiO2 nanoparticle, decrease of interface superposition of

16

demulsifier property due to increase of hydrophilicity has been proposed by Raman

17

(Yegya Raman and Aichele, 2018). Also, limited adsorption of SDBS in high

18

concentration

19

molecules (as anionic surfactant) adsorbed in interface (Sun et al., 2002).

20

demonstrate that GO-SiO2 nano-composite has the best performance between the

21

nanodemulsifiers (both less concentration and a higher rate of demulsification). Better

22

performance of GO-SiO2 is due to the presence of aromatic rings in the structure of GO

23

that interact with asphaltene in the film. Juan Liu and coworkers in two separate reports

in

(500

the

ppm),

aqueous

may be

phase

due

(relative

silica

nanoparticle)

instead

of

Therefore, water separated by SiO2@SDBS

to

12

electrostatic

repulsion

between

SDBS

The results

1

by using theoretical calculation, have shown graphene oxide and asphaltene can have

2

Π-Π interaction (Liu et al., 2017, 2015). And also, because of this high aromaticity of

3

the demulsifiers, they can diffuse in crude oil much better, and this in turn raises the

4

rate of demulsification (Kang et al., 2018; Zhang et al., 2017). Moreover, the functional

5

groups (such as ether and carboxylic groups) in the structure of GO cause the GO-SiO2

6

to have stronger penetrability at the interface; thus GO-SiO2 is more effective as a

7

demulsifier (Xu et al., 2016; Zhang et al., 2005). It should be noted the OH groups of

8

silica nanoparticles present on GO surface can react with asphaltene in the film and

9

unstable

emulsion (Yegya

Raman

and

Aichele,

2018).

When

comparing

10

demulsification performance of GO-SiO2 nanocomposite and SiO2 nanoparticles, it is

11

noteworthy that the performance of GO-SiO2 at high concentrations slightly decreased,

12

due to the formation of GO-film at the interface (Fang et al., 2016) and also the

13

capability of aggregation behavior between demulsifiers at high concentration (Hazrati

14

et

15

concentrations below 2% w/w cannot stabilize emulsion (Binks et al., 2007) (whereas

16

maximum concentration used in this work is about 0.05% w/w). Moreover, silica is a

17

good emulsifier for o/w emulsion (Yan et al., 2001), therefore, it is considered as a

18

weak emulsifier for

19

performance of the nanoparticle in the size of 500 ppm.

al.,

2018).

However,

w/o

studies

emulsion

on

silica

thus

indicate

there is no

that

SiO2

nanoparticles

observable decline in

at

the

20

The performance of different modified silica nanoparticle is shown in table 4 (in various

21

works). It has to be noted that the crude oil which is used in each work and the process of

22

stabilization is different. Therefore, this table is only a collection of different results for different

13

1

modified SiO2 nanoparticle, and any conclusions about the highest effectiveness of the

2

nanoparticles in the separation of water from oil are incorrect.

3

3.3 . Temperature effect

4

To investigate the effect of temperature on demulsification, a set of bottle tests were

5

done in 50°C and 75°C for optimal concentration of the nanodemulsifiers (other

6

conditions were the same). Table 5 shows the results of demulsification for the three

7

different temperatures. A direct relationship can be drawn between the temperature and

8

the rate of demulsification for the all nanodemulsifiers. This observation is especially

9

bold for GO-SiO2 nanocomposite where the dehydration time decreases from 90 to 16

10

min by temperature increasing from 25°C to 75°C. Demulsification time decreases (for

11

all nanodemulsifiers) by increasing the temperature. To understand this observation, it

12

can be argued that, temperature increasing results in the viscosity of the crude oil to be

13

decreased and also increasing the extent of water droplets’ movement (Al-Sabagh et

14

al., 2011; Alsabagh et al., 2016; Farrokhi et al., 2017) . Both of these factors cause the

15

diffusion of water droplets toward another to be more effective. In addition, the

16

Brownian movement of the nanodemulsifiers is higher when

17

increased, so the nanodemulsifiers migrate to water/oil interface more easily (Bi et al.,

18

2017; Fang et al., 2017) . Thus the demulsification temperature is an important factor

19

influencing the rate of dehydration of crude oil. The positive effect of temperature

20

increase on the demulsification performance, has been reported in several papers (Al-

21

Sabagh et al., 2015; Fang et al., 2017; Rajak et al., 2016; Yi et al., 2017).

22

3.4 Salt effect

14

the temperature is

1

For assessing the salt effect on the dehydration of the crude oil, sodium chloride

2

(NaCl) and calcium chloride (CaCl2) salts were chosen. All the steps of the emulsion

3

preparation were the same as before, except that the salt solution of 2000 ppm was

4

used instead of distilled water. The results of the bottle test for the optimum

5

concentration

6

demulsification increased by adding NaCl to the water phase (table 6). The droplets

7

size distribution (DSD) was demonstrated to be increased as a result of adding salt

8

(table 7). The increase of the DSD value leads to a reduction in the viscosity of the

9

emulsions (Fortuny et al., 2007) thus the water droplets diffuse more easily and hence

10

the stability of the emulsions decreases, also the increasing of the value of DSD causes

11

the smaller droplets to redeposit onto the larger ones, which are more stable

12

thermodynamically (Ostwald ripening)(Maia Filho et al., 2012; Rosen and Kunjappu,

13

2012). Therefore, the DSD increasing results in a reduction of emulsion stability and

14

also improvement of the performance of all the nanodemulsifiers. In spite of the

15

observation that the DSD value of water droplets was larger in the presence of CaCl2

16

solution compared to that when NaCl solution was used, (table 7) but the performance

17

of some of the nanodemulsifiers did not improved (table 6). This phenomenon can be

18

explained as follows: calcium ions (unlike sodium ion) can react with oxygen atoms

19

existing in the GO-SiO2 and SiO2@SDBS nanodemulsifiers (Zhai et al., 2013) so

20

because of this interaction, the performance of these nanodemulsifiers decreases. It is

21

worth noting that with an increase in the ionic strength, the stability of w/o emulsion

22

decreases. This

23

2015; Maaref and Ayatollahi, 2018; Moradi et al., 2010). Further information of water

of

the

nanodemulsifiers

represent

that,

the

efficiency

of

the

result is in compliance with several studies (Hajivand and Vaziri,

15

1

droplets variance and also the pictures of w/o emulsion prepared with salt solution is

2

given in supporting information (S2).

3 4

3.5 Interfacial tension

5

The IFT between water and blank crude oil (without demulsifier) was measured to be

6

14.38(±0.11) mN.m-1. The IFT was also measured after adding SiO2 nanoparticle and

7

GO-SiO2

8

nanocomposite show a higher interfacial activity than SiO2. Actually, SiO2 makes a

9

decrease of 3.93(±0.01) in IFT, while GO-SiO2 nanocomposite reduces it from

10

14.38(±0.11) mN.m-1 to 2.44(±1.0) mN.m-1. The interfacial activity of GO-SiO2 helps

11

its migration to oil/water interface, hence the replacement of GO-SiO2 with the natural

12

surface-active materials present on the surface of water droplets, is taken place in the

13

asphaltene film which this in turn leads to the destruction of the film (Fang-Hui and

14

Hong, 2008; Fang et al., 2017) .

nanocomposite.

According

to

the

results,

it

is

found

that

GO-SiO2

15 16

Conclusion

17

In this study, an environmentally friendly and cost-effective SiO2 nanoparticle for

18

dehydration of crude oil was functionalized. GO-SiO2 nanocomposite shows the best

19

performance compare with bare SiO2 nanoparticles, SiO2@OA, and SiO2@SDBS for

20

demulsification of crude oil. This is because, it has several aromatic rings and chains

21

which aid the nanoparticle to migrate to the water/oil interface more quickly-confirmed

22

by the result of IFT which represent that the nanocomposite reduced IFT between oil

23

and water significantly. Also, it was demonstrated that the salt play role in the

16

1

demulsification performance of nanodemulsifier. With the increase, the ionic strength

2

DSD of the emulsion was increasing, but depends on used the type of salt used,

3

demulsification performance can increase or reduction.

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

17

1

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20 21 22 23 24

27

1 2 3 4

Tables and figures

5 6

Table 1. Provenance and purity of Chemical materials applied Chemical name

Source

Purity %

Sulphuric acid (H2SO4)

Aldrich

99

Phosphoric acid (H3PO4)

Aldrich

99

Tetraethyl orthosilicate

Aldrich

98

Potassium permanganate (KMnO4)

Aldrich

99

isopropanol

Aldrich

99.5

Graphite powder

Aldrich

99

Oleic acid (OA)

Aldrich

99

SiO2 nanoparticle

IS*

98

Sodium dodecyl benzene sulfonate (SDBS)

Aldrich

technical grade

Toluene

Aldrich

99

(TEOS)

7

*Iran Science Company.

8 9 10 11 12 13

28

1 2 3

Table 2. Characterization of crude oil Value API

17.4

TAN (mg KOH/g Oil)

0.29 (±0.03)

Viscosity (at 298K)

37.7 (±0.2) cP

Saturate

61.1%

Aromatic

27.7%

Resin

7.9%

Asphaltene

3.3%

4 5 6

Table 3. Crystal size and surfaces area of nanodemulsifiers. nanoparticles

7

Crystal size (nm)

Specific surface area (BET) (m2.g-1)

t-Plot External Surface Area(m2.g-1)

Zeta potential (mv)

SiO2

1.2

152.4 ±1.8

126.8

-1.9

SiO2@SDBS

1.3

33.0 ±0.8

26.7

-35.0

SiO2@OA

1.3

138.1 ±1.9

132.7

-13.9

GO-SiO2*

12.1

292.7 ±3.8

211.9

-44.2

*Upon (001) peak (actually average height of stacking layers)

8 9 10 11 12

29

1 2 Table 4. The dehydration efficiency of different modified SiO2 nanoparticle.

3 Type of oil

Demulsifier

Temperature

Water content

(K)

(w/w %)

D.Ca (ppm)

Time

E%

Ref.no

(min)

Crude oil

SiO2-TA1031

338

~ 40

100

120

96.78

20

Crude oil

Fe3O4@SiO2

353

5

15000

60

23.2

61

Crude oil

CNTs/SiO2

343

78

500

60

87.4

33

cyclohexane

Partially hydrophobic SiO2

-

29.96

1000

5

<90

78

Toluene

Fe3O4@SiO2KH1231

-

1

40000

1

94

15

Crude oil

GO-SiO2

298

~ 40

300

90

100

This work

4

a.

demulsifier concentration

5 6 7 8 9 10

30

1 2

Table 5. Dehydration efficiency of the optimum concentration nanodemulsifiers at different

3

temperatures. 25°C

50°C

75°C

nanodemulsifier

E%

Time(min)

E%

Time(min)

E%

Time(min)

SiO2

100

110

100

35

100

19

SiO2@SDBS

84

125

100

42

100

38

SiO2@OA

37.5

960

40

120

53

120

GO-SiO2

100

90

100

30

100

16

4 5 6 7 8

Table 6. Dehydration efficiency of the optimum concentration of nanodemulsifiers at the present

9

of NaCl solution and CaCl2 solution. Distilled water

10

2000 ppm NaCl

2000 ppm CaCl2

nanodemulsifier

E%

Time(min)

E%

Time(min)

E%

Time(min)

SiO2

100

110

100

15

100

7

SiO2@SDBS

84

125

100

30

60

100

SiO2@OA

37.5

960

25*

100

28

100

GO-SiO2

100

90

100

4.5

100

10

*The efficiency of SiO2@OA at 100 min (without salt) lower 10% (figure 1 in S1)

11 12

31

1 2 3

Table 7. Size and variance of the water droplets in the presence of 2000 ppm salt solution Type water

Salt concentration (ppm)

Ionic strength

Size droplet (µm)

D(0.1) (µm)

D(0.5) (µm)

D(0.9) (µm)

D(4,3) (µm)

D.W

0

0

2.27

2.3

4.8

7.8

4.82

Water + NaCl

2000

0.072

2.05

3.3

7.6

12.7

7.84

Water + CaCl2

2000

0.156

1.70

4.4

10.2

16.4

10.28

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

32

a)

b)

1 2

Figure 1. Scanning electron microscopy of SiO2 nanoparticle (a), field-emission scanning electron

3

microscopy (FESEM) of GO-SiO2 nanocomposite (b)

4 5 300

a

b

SiO2@OA SiO2@OA

GO-SiO2 GO-SiO2

400

GO GO

200

Intensity

SiO2@SDBS SiO2@SDBS

Intensity

SiO2 SiO2

200 100

0

0 10

30

50

10

70

30

2Θ

2Θ

6 7

Figure 2. XRD spectra of SiO2, SiO2@SDBS, and SiO2@OA (a), GO and GO-SiO2 (b)

8 9

33

50

1 2

Figure 3. FT-IR spectra of SiO2 (a), SiO2@SDBS (b), SiO2@OA (c), GO-SiO2 (d)

3 4 5 6

34

300

SiO2 SiO2 SiO2@SDBS SiO2@SDBS

Quantity Adsorbed (cm³/g)

250

SiO2@OA SiO2@OA GO-SiO2 GO-SiO2

200

150

100

50

0 0

0.2

0.4

0.6

0.8

1

Relative Pressure (p/p°)

1 2

Figure 4. Nitrogen adsorption - desorption isotherms for SiO2, SiO2@SDBS, SiO2@OA, GO-SiO2

3 4 5

35

100

98

Weight resdue%

Weight residue%

100

96

94

SiO2

60 SiO2 SiO2@OA

SiO2@SDBS

a

b

92 0

80

200

400

600

40

800

0

Temperature(°C)

200

400

600

800

Temperature(°C)

1 2

Figure 5. Thermo gravimetric curve of SiO2 and SiO2@SDBS (a). SiO2 and SiO2@OA (b)

3 4 5 6

36

1

2 3 4

Figure 6. Dehydration efficiency of crude oil by nanodemulsifiers at 298 K. The dehydration times of

the different nanodemulsifiers represented on each plot.

5 6 7 8

9 10

a)

b)

c)

Figure 7. Optical microscope photos of the w/o emulsion: without nanodemulsifier (zero time) (a), 10 minutes (b), and 40 minutes (c) after injection optimum concentration SiO2 nanoparticle at 298 K

11

37

1 2 3

4 5

Graphical Abstract

38

Synthesis of superhydrophilic nanocomposite for demulsification of w/o emulsion. The mechanism of demulsification for different nanodemulsifiers are discussed. The increase in demulsification temperature caused efficiency enhanced. The results of optical microscopy & IFT show SiO2 has high surface active property.