DSpace at VNU: Synthesis of Polymer-Coated Magnetic Nanoparticles from Red Mud Waste for Enhanced Oil Recovery in Offshore Reservoirs

Then, MNPs are encapsulated by a copolymer of me-thyl methacrylate and 2-acrylamido-2-meme-thyl-1-propanesulfonate via oleic acid linker.. Fe3O4þ 4H2O: ð2Þ Synthesis of Oleic Acid-Coated

Synthesis of Polymer-Coated Magnetic Nanoparticles from Red Mud Waste for Enhanced Oil Recovery in Offshore Reservoirs

T.P NGUYEN,1,2,5U.T.P LE,3K.T NGO,1,3K.D PHAM,1and L.X DINH4 1.—Institute of Applied Materials Science, 1 Mac Dinh Chi Street, District 1, Ho Chi Minh City, Vietnam 2.—Duy Tan University, K7/25 Quang Trung Street, District Hai Chau, Da Nang, Vietnam 3.—Ho Chi Minh City University of Technology, 268 Ly Thuong Kiet Street, District 10,

Ho Chi Minh City, Vietnam 4.—Institute of Materials Sciences, 18 Hoang Quoc Viet, Cau Giay District, Ha Noi, Vietnam 5.—e-mail: phuongtungng@gmail.com

Buried red mud waste from groundwater refineries can cause pollution The aim of this paper is to utilize this mud for the synthesis of Fe3O4 magnetic nanoparticles (MNPs) Then, MNPs are encapsulated by a copolymer of me-thyl methacrylate and 2-acrylamido-2-meme-thyl-1-propanesulfonate via oleic acid linker MNPs are prepared by a controlled co-precipitation method in the presence of a dispersant and surface-modified agents to achieve a high hydrophobic or hydrophilic surface Mini-emulsion polymerization was con-ducted to construct a core–shell structure with MNPs as core and the copolymer as shell The core–shell structure of the obtained particles enables them to disperse well in brine and to stabilize at high-temperature environ-ments The chemical structures and morphology of this nanocomposite were investigated by Fourier transform infrared spectroscopy, transmission elec-tron microscopy, and field emission scanning elecelec-tron microscopy The ther-mal stability of the nanocomposite was evaluated via a thermogravimetric analysis method for the solid state and an annealing experiment for the liquid state The nanocomposite is about 14 nm, disperses well in brine and is thermally stable in the solid state The blends of synthesized nanocomposite and carboxylate surfactant effectively reduced the interfacial tension between crude oil and brine, and remained thermally stable after 31 days annealed at 100°C Therefore, a nanofluid of copolymer/magnetic nanocomposite can be applied as an enhanced oil recovery agent for harsh environments in offshore reservoirs

Key words: Red mud waste, mini-emulsion polymerization, magnetic

nanoparticles, core–shell, enhanced oil recovery, offshore

INTRODUCTION Global energy demand is expected to increase by

2–3% annually in the coming decades, and the

increase is predicted to rise by 50% after 20 years.1

Satisfying this demand is the main challenge for the

oil and gas industry With the era of easily

acces-sible and produced oil coming to an end and the

increasing difficulty of finding new resources, the

traditional oil and gas industry has been directed to

extract more resources from existing oil fields [enhanced oil recovery (EOR)] and from the fields exposed to extremely harsh environments by using new technologies and solutions Thus, the EOR field

is important and urgent in the petroleum industry The typical oil recovery efficiency of 30–40% should

be increased to 60–80%.2Recovery of secondary oil, which is trapped in the pores of reservoir solids, needs a more sophisticated approach Therefore, improved reservoir mapping and advanced produc-tion methods are necessary Nanotechnology has recently received considerable attention from the petroleum industry, and a decade’s worth of (Received December 18, 2015; accepted April 1, 2016;

published online April 29, 2016)

Ó2016 The Minerals, Metals & Materials Society

3801

rock phases and alternate the contact angle NPs can

also be absorbed by the surfactants in the surfactant

medium Therefore, given the effect of packing, the

local surface/capillary pressure is reduced and

conse-quently increases the oil displacement efficiency

MNPs surface-modified by different agents have

been actively studied for biomedical

applica-tions,12–14 and investigation of their potential use

in oil exploration, especially EOR, has recently

started.15,16 Compared with SiO2NPs, besides the

common advantages of nanoscale materials, MNPs

can also be easily recovered and reused because of

their magnetic responsivity Sanders et al.16 used

magnetic shell cross-linked knedel-like

nanoparti-cles in a contaminated aqueous environment to

remove hydrophobic contaminants Once loaded,

crude oil-absorbed nanoparticles were easily

iso-lated through introducing an external magnetic

field The surface of MNPs requires modification to

function as an EOR agent The surrounding

poly-mer layer enables the particles to disperse in

injected brine, become compatible with oil and be

stable at high temperatures, and resist adsorption

on the surface of the reservoir rock

To date, many major oil fields in Vietnam, such as

White Tiger, Dragon, and Dawn, have passed their

peak harvesting period and their production is

rapidly declining; thus, EOR measures should be

considered, including the use of NPs.17,18 To focus

on the use of modified MNPs in nanofluids as EOR

agents, MNPs must be fabricated at an affordable

cost Red mud waste from groundwater refinery

stations is currently being buried and becomes a

source of solid waste that may contribute to soil and

groundwater pollution Therefore, this work used

red mud as raw material to synthesize

polymer-coated MNPs and to evaluate its nanofluid system

as an EOR potential agent for offshore

high-tem-perature reservoirs in Vietnam

EXPERIMENTAL Materials

Methyl methacrylate (MMA), sodium

2-acry-lamido-2-methyl-propanesulfonate (AMPS), ferrous

chloride tetrahydrate (FeCl Æ4H O), oleic acid

Preparation of Ferric Salts from Red Mud Source Red mud (12 g) was dissolved in a 400-ml beaker containing 200 ml distilled H2O A calculated amount of HCl (30 ml) was then added The reaction mix was stirred vigorously at room temperature for

30 min Then, the solution was filtered, and the filtrate, which was ferric salt (FeCl3), was obtained The filtrate was used for the synthesis of iron oxide nanoparticles (MNPs) The relevant chemical reac-tion can be expressed as follows (Eq.1):

Fe OHð Þ3þ HCl ! FeCl3þ H2O: ð1Þ

Synthesis of Fe3O4Magnetic Nanoparticles (MNPs) MNPs were synthesized using the combined method of co-precipitation and microemulsion in the presence of SDS as surfactant FeCl3 (0.5 M,

100 ml) and FeCl2 (0.5 M, 50 ml) (molar ratio 2:1) were premixed in a 500-ml three-necked round-bottom flask, which was equipped with a mechan-ical stirrer, under nitrogen atmosphere Meanwhile,

1 g of SDS was dissolved into 50 ml of deoxygenated distilled water, which was poured into the mixture

of Fe3+and Fe2+through a funnel The mixture was then heated gradually to 80°C and maintained at this temperature for 1 h Subsequently, 45 ml of

NH4OH (30%) was poured drop by drop (1 drop/s) into the solution Black nanoparticles were precip-itated After the reaction, the mixture was stirred vigorously for another 2 h; the nanoparticles were isolated by centrifugation and washed three times with 20 ml of ethanol by magnetic decantation until the pH was neutral The relevant chemical reaction can be expressed as follows (Eq.2):

Fe2þþ 2Fe3þþ 8OH! Fe3O4þ 4H2O: ð2Þ

Synthesis of Oleic Acid-Coated MNPs (OMNPs) MNPs (3 g) were dispersed into 50 ml of deoxy-genated distilled water with the aid of an

simultaneously at 60°C with vigorous stirring for

1 h Oleic acid (1.5 ml) was added into the

disper-sion and was vigorously stirred with a mechanical

stirrer for 2 h at 80°C Afterward, the mixture was

cooled to room temperature and centrifuged

(1000 rpm) for 30 min The obtained precipitates

(OMNPs, 4.52 g) were washed three times with

20 ml of ethanol–distilled water solution

(volumet-ric ratio 1:1) to remove the excess amount of oleic

acid

Synthesis of OMNPs Encapsulated by Copolymer of

MMA and AMPS (OMNPs-MMA-co-AMPS)

OMNPs (4.52 g) were added to a three-necked

round-bottom flask containing 50 ml of distilled

H2O and 40 ml of AMPS–MMA mixture (molar ratio 1:1) The mixture was then sonicated and stirred vigorously for 2 h at room temperature

(NH4)2S2O8 was dissolved in 10 ml of distilled

H2O, and surfactant SDS was added This initial solution was sonicated for 1 h with vigorous stirring and then poured into the above solution by using a dropping funnel The obtained polymerization mix-ture was stirred, heated gradually to 75°C, and then maintained at this temperature for 1.5 h without ultrasonics Afterward, the solution was sonicated for another 2 h at ambient condition The final product was dried in an oven at 50°C overnight to

Fig 1 Synthesized procedure for OMNPs-MMA-co-AMPS.

20 25 30 35 40 45 50 55 60 65 70

Two theta, degree

Synthesized Fe3O4

Fig 2 (a) XRD pattern of MNPs produced from red mud, (b) TEM image of MNPs produced from red mud waste.

synthetic procedure of OMNPs-MMA-co-AMPS is

shown in Fig 1

Characterization of Obtained Compounds

The chemical structure of MNPs, OMNPs and

OMNPs-MMA-co-AMPS, were characterized by

using Fourier transform infrared spectroscopy (FT–

IR) with a Brucker Equinox 55 spectrometer in the

range of 4000–400 cm1 The morphology of the

obtained materials was examined by transmission

electron microscopy (TEM), field emission scanning

electron microscopy (FE-SEM) (JSM 7401F).The size

of the nanocomposite OMNPs-MMA-co-AMPS was

estimated by using FE-SEM Thermo-gravimetric

analysis (TGA) was conducted on both unfilled

poly-mer and polypoly-meric nanocomposite from 30°C to

800°C with a heating rate of 10°C/min under a

dynamic flow of nitrogen by using a differential

scanning calorimeter (DSC; Labsys Evo)

appropriate nanofluid solution to obtain a nanocomposite/surfactant mixture with the de-sired ratios

– Put these mixtures into glass heat-resistant ampoules (ACE), deoxygenating with nitrogen, annealing at temperature of 100°C, observing the transparency and measuring the interfacial tension (IFT) of the mixtures before annealing and after every 7 days

The IFT of the mixtures was measured on a spinning drop interfacial tensiometer model 500 (TEMCO, TX, USA) Crude oil and brine from the White Tiger Oligocene oilfield of Vietnam were used

RESULTS AND DISCUSSION Synthesis of MNPs and Oleic Acid-Coated MNPs (OMNPs)

The x-ray diffraction (XRD) pattern (Fig.2a) showed that the obtained materials had a Fe3O4 structure and that the size of these materials was about 14 nm (Fig.2b) Therefore, MNPs were syn-thesized successfully A correct particle size is required in MNPs preparation to ensure its disper-sion capacity in brine medium while preserving good magnetic properties Ferric salt obtained from red mud waste reacted well in the co-precipitation

to produce MNPs with tailored sizes depending on the reaction medium

The surface of the nonfunctionalized MNPs was modified by reaction with oleic acid to enhance the probability of a core–shell structure performance later in polymerization Oleic acid is known to provide a high affinity with iron oxide through chemical interaction between their –COO– groups and Fe atoms Consequently, the hydrophobic tails

of oleic acid molecules face outward and generate a non-polar shell, therefore warranting stability of MNPs suspension in non-polar solvents during the occurrence of mini-emulsion polymerization The presence of oleic acid on the MNPs surface was confirmed through FT-IR (Fig.3) The bands at

2862 cm1and 2923 cm1were observed according

Wavenumber, cm-1 Fig 3 FT–IR spectra of MNPs, oleic acid and OMNPs.

4000 3600 3200 2800 2400 2000 1600 1200 800 400

Wavenumber, cm -1

(a) OMNPs-MMA-co-AMPS

(b) MMA-co-AMPS

(c) OMNPs

(a)

(b)

(c)

Fig 4 FT–IR spectra comparison of (a) OMNPs, (b)

MMA-co-AMPS, and (c) OMNPs-MMA-co-AMPS.

to the stretch modes of –CH2– and –CH3 of oleic

acid The stretching vibration of C=O at 1710 cm1

was clearly detected, and the bands at 1438 cm1

and 1518 cm1 were clearly recognized and

attrib-uted to the asymmetric and symmetric stretching

vibrations of the –COO– functional group This

result indicates that the layer of oleic acid was

successfully coated onto the MNP surface

Further-more, a band at 587 cm1, corresponding to the

vibration of the Fe–O bonds in the Fe3O4structure,

was observed The results corresponded well with

previous data

Encapsulation of OMNPs by Copolymer of MMA and AMPS

Figure4 shows the presence of the MMA-co-AMPS copolymer on the OMNP surface whch was confirmed through FT-IR The bands at 1250 cm1,

659 cm1, 1099 cm1, and 3200–3500 cm1from the FT-IR spectrum were assigned to S=O, S–O, C–S, and –NH– stretching vibrations, respectively, indi-cating that the AMPS structure compared with the –CH3, –CH2, and –COONa vibrations in MMA was clearly observed at 1389–2956 cm1, 1502 cm1,

Fig 5 FE-SEM images of (a) OMNPs coated on the surface layer of MMA-co-AMPS copolymer (not used SDS) and (b) MMA-co-AMPS copolymer-coated OMNPs in the core–shell structure (used SDS).

Fig 6 TGA patterns of MMA-co-AMPS copolymer.

and 1567–1385 cm1, repectively In addition, the

absorption bands at 1747 cm1 and 1196 cm1

corresponded to carbonyl (C=O) and asymmetric

C–O–C stretching vibrations, repectively, indicating

that oleic acid had been coated onto the MNPs’

surface

Furthermore, the band at 582 cm1 which

belongs to the Fe–O bond in the Fe3O4 structure

was still observed Thus, the FT-IR spectrum

exhib-ited all the component signals in the core–shell

structure of the MMA-co-AMPS copolymer

As shown in Fig 5, the FE-SEM images clearly

show the differences of our OMNPs coated in

MMA-co-AMPS copolymer on the surface layer of latex

particles or in the core–shell structure

TGA for OMNPs-MMA-co-AMPS Thermal stability of the polymer-coated iron oxide nanoparticles and unfilled copolymer MMA-co-AMPS was investigated using a thermogravimetric analyzer, and the resultant thermo-diagrams are presented in Figs.6and7

The thermo-diagram of the nanocomposite for OMNPs-MMA-co-AMPS shows four steps The first weight-loss process in a temperature range of 30– 185°C is associated with the loss of adsorbed water that constitutes 10–15% of the weight of OMNPs-MMA-co-AMPS The second weight-loss process lies

in the temperature range of 185–335°C which can

be attributed to the loss of the loosely bonded polymer matrix This weight-loss process is

Fig 7 TGA pattern of OMNPs-MMA-co-AMPS.

Table I IFT of MNP-copolymer composite/surfactant mixtures in brine aged at 100°C and crude oil

Appearance, IFT (dyne/cm) in time (days)

influenced by the magnetite concentration used for

nanocomposite preparation The third (400–600°C)

step shows the advanced thermal stability of this

nanocomposite to unfilled polymer The fourth (600–

800°C) step is related to iron oxide nanoparticles

Figure6 shows a thermo-diagram of the unfilled

copolymer At 350°C, the copolymer lost about half

of its mass, and the final degradation happened at

400°C, or at 100°C lower than in the case of

polymer-coated MNPs composite (500°C)

Thermostability of the Mixtures

The interfacial tension (IFT) between the solution

of 1000 ppm of MNPs in brine and crude oil was

17.6737 dyne/cm This value was compared with

that of sea water and crude oil of 19.1401 dyne/cm

This result indicates that nanofluids, as surfactant

solutions, cannot reduce IFT

As shown in TableIand Fig.8, a slight

synergis-tic effect resulting in IFT reduction appeared in the

mixture of 200 ppm magnetic nanocomposite and

800 ppm surfactant During the aging period, the IFT of all the tested samples with the nanocompos-ite increased, which is similar to the surfactant solution (Sample 1) This finding can be explained

by the presence of alkylphenolpolyethoxy alcohol (NP-9), a nonionic surfactant precursor of synthe-sized alkylphenolpolyethoxy carboxylate in a ratio

of 50:50 Thermostability of nanocomposites is bet-ter than bare MNPs, which is shown by good dispersion of the system, which we can observe in Fig.9

CONCLUSION

A nanocomposite of MNPs and encapsulated copolymer of MMA and AMPS was sucessfully synthesized in the core–shell structure with advanced properties such as good dispersion, ther-mal stability, and reusing capacity The obtained magnetic nanocomposite exhibited a high potential for implementation as an EOR agent for offshore high temperature reservoirs

ACKNOWLEDGEMENTS

We would like acknowledge Prof Dr N.T.K Thanh (University College London, UK) for her good ideas and other support We also thank Dr Nguyen Hoang Duy (Institute of Applied Materials Science, Vietnam) for his good dicussion of this pa-per

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(a) Before

applying

magnetic field

(b) During applying magnetic field

(c) After applying magnetic field

Fig 8 Thermal stability of mixture copolymer composite/surfactant

mixtures by time.

0.5

1

2

4

8

16

32

Time of aging, days

NC-Surf 0-1000 ppm NC-Surf 200-800 ppm

NC-Surf 400-600 ppm NC-Surf 600-400 ppm

NC-Surf 800-200 ppm NC-Surf 1000-0 ppm

Fig 9 Appearance of nanocomposite/surf brine solutions after

aging for 25 days at 100°C.