Luận văn thạc sĩ Kỹ thuật hóa học: Polymer coated on magnetic nanoparticles orienting in enhanced oil recovery application

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY --- NGO TRUNG KIEN POLYMER COATED ON MAGNETIC NANOPARTICLES ORIENTING IN ENHANCED OIL RECOVERY... Name of theme: Polymer coated on magnetic na

Introduction

The world energy consumption will grow by 56% between 2010 and 2040, from 524 quadrillion British thermal units (Btu) to 820 quadrillion Btu [1] Renewable resource cannot meet this growth so oil is still an important energy resource in the future Only 15-30% of the original oil in place (OOIP) is obtained by primary and secondary recovery methods because of the compressibility of fluids and initial pressure of the reservoir While in Vietnam, many major oil fields in Vietnam, such as White Tiger, Dragon, and Dawn, have passed the peak harvesting period and their production is rapidly declining It still remains large amounts of trapped oil in reservoirs; therefore, enhanced oil recovery (EOR) method should be carried out

Nanoparticles (NPs) have been studied for a variety of applications as polymer composites [2], drug delivery [3-8], solar cells [9-12], lipase immobilization [13], metal ion removing [14], imaging [6, 15, 16], and EOR [17] NPs show that they can stabilize foams and emulsions or change the wettability of rock The dispersibility of NPs can be improved by attaching polymers to the nanoparticles surface, creating polymer-coated nanoparticles (PNPs) PNPs have interested properties as additives and interfacial active materials and more recently they have been studied for EOR because they can use as mobility control agents and for wettability alteration Magnetic nanoparticles (MNPs) inherits the outstanding properties of NPs; in addition, they can be easily recovered and reused because of magnetic property and crude oil absorbed on MNPs can isolated when applying the external magnetic field But the surface MNPs need to be modified for migration through porous media, dispersibility in brine and injectable capacity into a reservoir

And polymer-coated nanoparticles (PNPs) were considered as an additives and interfacial active materials for EOR because of their properties in controlling mobility and alternating wettability between liquid surface and solid surface

Nowadays, pollution environment is an urgent and global problem To face with this problem, it needs to utilize the waste sources to produce new products A source of solid waste red mud with the main content of Fe from groundwater treating plants that may contribute to soil and groundwater pollution was used to provide the iron source for synthesis of MNPs in this thesis Besides, a surfactant also needs to be prepared for evaluation oil recovery capacity

Nonylphenoxy polyethoxycarboxylate (NPC) with the structure of hydrophilic group (carboxylate) and hydrophobic tail group separated by ethoxylate (EO) groups helps to liberate the residual oil in enhanced oil recovery application through reducing the interfacial tension between oil and brine This thesis will evaluate the thermal and chemical stability of the mixture PMNPs and NPC in harshness environment that simulates the White Tiger reservoir

This work has been done with 2 related papers including (1) Facile procedure to synthesize ankylphenoxy polyethoxycarboxylate surfactants and investigate the properties for enhanced oil recovery application published in Vietnam Journal Chemistry, and (2) Synthesis of polymer- coated magnetic nanoparticles from red mud waste for enhanced oil recovery in offshore reservoir published in Journal of Electronic Materials – Springer.

Literature Review

Enhanced oil recovery (EOR)

2.1.1 Introduction to Enhanced Oil Recovery

According to the method of production or the time at which hydrocarbons are obtained, there are three terms: primary oil recovery, secondary oil recovery, and tertiary (enhanced) oil recovery Primary oil recovery describes the production of hydrocarbons under the natural driving mechanisms present in the reservoir without supplementary help from injected fluids such as gas or water Secondary oil recovery refers to the additional recovery resulting from the conventional methods of water injection and immiscible gas injection Tertiary (enhanced) oil recovery is the additional recovery over and above what could be recovered by secondary recovery methods Various methods of enhanced oil recovery (EOR) are essentially designed to recover oil, commonly described as residual oil, left in the reservoir after both primary and secondary recovery methods have been exploited to their respective economic limits The concept of the three recovery categories is illustrated in Figure 2.1

2.1.2 Mechanism of enhanced oil recovery

Improved oil recovery (IOR) is a general term that implies improving oil recovery by any means (operational strategies, such as infill drilling, horizontal wells, and improve vertical and areal sweep) Enhanced oil recovery (EOR) is more specific in concept and it can be considered as a subset of IOR EOR implies the process of enhancing oil recovery by reducing oil saturation below the residual oil saturation “S or ” The target of EOR varies considerably by different types of hydrocarbons Figure 2.2 shows the fluid saturations and the target of EOR for typical light and heavy oil reservoirs and tar sand For light oil reservoir, EOR is usually applicable after secondary recovery operations with an EOR target of approximately 45% original oil in place

(OOIP) Heavy oils and tar sands respond poorly to primary and secondary recovery methods, and the bulk of the production from these types of reservoirs come from EOR methods

Figure 2.1: Oil recovery categories Figure 2.2: Target for different crude oil systems

The magnitude of the reduction and mobilization of residual oil saturation “S or ” by an EOR process is controlled by two major factors, they are:

The capillary number is defined as the ratio of viscous force to interfacial tension force, or

Where μ = viscosity of the displacing fluid σ = interfacial tension (IFT) between the displacing fluid and the displaced fluid (oil) v = Darcy velocityθ = the contact angle

 = porosity k 0 = effective permeability of the displaced fluid Δp/L = pressure gradient

Figure 2.3: Effect of N c on residual oil saturation Figure 2.3 is a schematic representation of the capillary number and the ratio of residual oil saturation (after conduction of an EOR process to residual oil saturation before the EOR process) The illustration shows the reduction in the residual oil saturation with the increase in the capillary number It is clear that the capillary number can be increased by:

- Increasing the pressure gradient Δp/L - Increasing the viscosity of the displacing fluid - Increasing displacing fluid viscosity μ

- Decreasing the interfacial tension between the injection fluid and displaced fluid It is easy to understand that the capillary number cannot be practically increased 1000 times by the first two ways It is known that the interfacial tension between a surfactant solution and oil can be reduced from 20 to 30 to the order of 10 -3 mN/m In other words, by adding surfactants, the capillary number can be practically increased by more than 1000 times Due to the low IFT, oil droplets can flow more easily through pore throats because of reduced capillary trapping The oil droplets move forward and merge with the oil down the stream to form an oil bank

Another important concept in understanding the displacing mechanism of an EOR process is the mobility ratio “M” The mobility ratio is defined as the ratio of the displacing fluid mobility to that of the displaced fluid, or:

Where “k” is the effective permeability and “μ” is the viscosity The mobility ratio influences the microscopic (pore-level) and macroscopic (areal and vertical sweep) displacement efficiencies

A value of M > 1 is considered unfavorable because it indicates that the displacing fluid flows more readily than the displaced fluid (oil) This unfavorable condition can cause channeling and bypassing of residual oil Improvement in mobility ratio can be achieved by increasing the viscosity of the injection fluid, polymer flood

All EOR methods that have been developed are designed to increase the capillary number In general, EOR technologies can be broadly grouped into the following four categories:

- Thermal - Chemical - Miscible - Others Each of the four categories contains an assortment of injection schemes and a different variety of injection fluids, as summarized in Figure 2.4:

Figure 2.4: Enhanced oil recovery methods

Thermal Chemical Flood Miscible Others

Cyclic steam stimulation Steam flooding Steam-assisted gravity drainage

Forward combustion Reverse combustion Wet combustion

Magnetic nanoparticles (MNPs)

Magnetic nanoparticles (MNPs) are of great interest for researchers from a wide range of disciplines, including magnetic fluids, catalysis, biotechnology/biomedicine, magnetic resonance imaging, data storage, and environmental remediation Recently they are also being studied for enhanced oil recovery field [18] While a number of suitable methods have been developed for the synthesis of MNPs of various different compositions, successful application of such MNPs in the areas listed above is highly dependent on the stability of the particles under a range of different conditions In most of the envisaged applications, the particles perform best when the size of the NPs is below a critical value, which is dependent on the material but is typically around 10-20 nm However, an unavoidable problem associated with particles in this size range is their intrinsic instability over longer periods of time Such small particles tend to form agglomerates to reduce the energy associated with the high surface area to volume ratio of the nanosized particles Moreover, naked metallic NPs are chemically highly active, and are easily oxidized in air, resulting generally in loss of magnetism and dispersibility For many applications it is thus crucial to develop protection strategies to chemically stabilize the naked MNPs against degradation during or after the synthesis These strategies include grafting or coating with organic species, including surfactants or polymers, or coating with an inorganic layer, such as silica or carbon

MNPs have been synthesized with a number of different compositions and phases, including iron oxide, such as Fe3O4 and γ-Fe2O3, pure metals such as Fe and Co, spinel-type ferromagnets such as MgFe2O4, MnFe2O4 and CoFe2O4 as well as alloys such as CoPt3 and FePt Several popular methods include co-precipitation, thermal decomposition and/or reduction, micelle synthesis, hydrothermal synthesis

Co-precipitation is a facile and convenient way to synthesize iron oxides (either Fe 3 O 4 or γ-Fe2O3) from aqueous Fe 2+ /Fe 3+ salt solutions by the addition of a base under inert atmosphere at room temperature or at elevated temperature The size, shape, and composition of the MNPs very much depends on the type of salts used (e.g chlorides, sulfates, nitrates), the Fe 2+ /Fe 3+ ratio, the reaction temperature, the pH value and ionic strength of the media

Recently, significant advances in preparing monodisperse MNPs, of different sizes, have been made by the use of organic additives as stabilization and/or reducing agents For example, MNPs with sizes of 4-10 nm can be stabilized in an aqueous solution of 1wt% polyvinyl alcohol (PVA) The effect of organic ions on the formation of metal oxides or oxyhydroxides can be rationalized by two competing mechanisms Chelation of the metal ions can prevent nucleation and lead to the formation of larger particles because the number of nuclei formed is small and the system is dominated by particle growth On the other hand, the adsorption of additives on the nuclei and the growing crystals may inhibit the growth of the particles, which favors the formation of small units

Monodisperse magnetic nanocrystals with smaller size can essentially be synthesized through the thermal decomposition of organometallic compounds in high-boiling organic solvents containing stabilizing surfactants The organometallic precursors include metal acetylacetonates [M(acc)n], (M = Fe, Mn, Co, Ni, Cr; n = 2 or 3, aac = acetylacetonates), metal cupferronates [M x Cupx] (M = metal ion; Cup = N-nitrosophenylhydroxylamine, C6H5N(NO)O - ), or carbonyl Fatty acids, oleic acid and hexadecylamine are often used as surfactants In principle, the ratios of the starting reagents including organometallic compounds, surfactant, and solvent are the decisive parameters for the control of the size and morphology of MNPs The reaction temperature, reaction time, as well as aging period may also be crucial for the precise control of size and morphology

A microemulsion is a thermodynamically stable isotropic dispersion of two immiscible liquids, where the microdomain of either or both liquid is stabilized by an interfacial film of surfactant molecules In water-in-oil microemulsions, the aqueous phase is dispersed as microdroplets (typically 1-50 nm in diameter) surrounded by a monolayer of surfactant molecules in the continuous hydrocarbon phase The size of the reverse micelle is determined by the molar ratio of water to surfactant By mixing two identical water-in-oil microemulsions containing the desired reactants, the microdroplets will continuously collide, coalesce, and break again, and finally a precipitate forms in the micelles By the addition of solvent such as acetone or ethanol to the microemulsions, the precipitate can be extracted by filtering or centrifuging the mixture In this sense, a microemulsion can be used as a nanoreactor for the formation of NPs

Using the microemulsion technique, metallic cobalt, cobalt/platinum alloys, and gold-coated cobalt/platinum NPs have been synthesized in reverse micelles of cetyltrimethylammonium bromide (CTAB), using 1-butanol as the co-surfactant and octane as the oil phase

Under hydrothermal conditions a broad range of nanostructured material can be formed Li et al reported a generalized hydrothermal method for synthesizing a variety of different nanocrystals by a liquid-solid-solution reaction The system consists of metal linoleate (solid), an ethanol-linoleic acid liquid phase, and a water-ethanol solution at different reaction temperature under hydrothermal conditions [19] As illustrated in Figure 2.5, this strategy is based on a general phase transfer and separation mechanism occurring at the interfaces of the liquid, solid, and solution phases present during the synthesis As an example, Fe 3 O 4 and CoFe 2 O 4 NPs can be prepared in very uniform sized of about 9 and 12 nm, respectively (Figure 2.5)

The advantages and disadvantages of the four above-mentioned synthetic methods are briefly summarized in Table 2.1 In terms of simplicity of the synthesis, co-precipitation is the preferred route In terms of size and morphology control of the NPs, thermal decomposition seems the best method developed to date As an alternative microemulsions can also be used to synthesize monodispersed NPs with various morphologies However, this method requires a large amount of solvent Hydrothermal synthesis is a relatively little explored method for the synthesis of MNPs, although it allows the synthesis of high-quality NPs To date, MNPs prepared from co- precipitation and thermal decomposition are the best studied, they can be prepared on a large scale

Table 2.1: Summary comparison of the synthetic methods

Co-precipitation Very simple, ambient conditions

20-90 Minutes Water Needed, added during or after reaction

Figure 2.5: Left: TEM images of magnetic and dielectric nanocrystals: Fe 3 O 4 (9.1±0.8 nm;

Fe 2+ :Fe 3+ , 1:2; 160 o C), CoFe 2 O4 (11.5±0.6 nm; Co 2+ :Fe 2+ , 1:2, 180 o C), BaTiO 3 (16.8±1.7 nm; 180 o C), TiO 2 (4.3±0.2 nm; 180 o C) Right: The liquid-solid-solution (LSS) phase- transfer synthetic strategy [19]

Although there have been many significant developments in the synthesis of MNPs, maintaining the stability of these particles for a long time without agglomeration or precipitation is an important issue All the protection strategies result in MNPs as a core-shell structure, that is, the naked MNPs as a core is coated by a shell, isolating the core against the environment The applied coating strategies can roughly be divided into two major groups: coating with organic shells, including surfactant and polymers, or coating with inorganic components, including silica, carbon, precious metals (such as Ag, Au) or oxides which can be created by gentle oxidation of the outer shell of the NPs, or additionally deposited such as Y 2 O 3 But in the scope of this thesis, it is focused on coating with polymer

Surfactants or polymers are often employed to passivate the surface of the NPs during or after the synthesis to avoid agglomeration In general, electrostatic repulsion or steric repulsion can be

Chapter 2: Literature review used to disperse NPs and keep them in a stable colloidal state Surfactants or polymers can be chemically anchored or physically adsorbed on MNPs to form a single or double layer, which creates repulsive (mainly as steric repulsion) forces to balance the magnetic and the van der Waals attractive forces acting on the NPs Thus by steric repulsion, the MNPs are stabilized in suspension Polymer containing functional group, such as carboxylic acid, phosphates, and sulfates can bind to the surface of magnetite Suitable polymers for coating include poly(pyrrole), poly(aniline), poly(alkylcyanoacrylates), poly(methylidende malonate), and polyesters, such as poly(lactic acid), poly(glycolic acid), poly(ε-caprolactone), and their copolymers.

The physical chemistry properties of polymer coated nanoparticles orienting in EOR

In EOR, mobility ratio is the mobility of the injected displacing fluid to that of the oil being displaced Good mobility control is obtained when the viscosity of the injected fluid is higher than the viscosity of the oil in the reservoir This can be attained through generation of foams and emulsions, which can form in the presence of surfactant or NPs Unlike surfactants, NPs have the advantage that they can irreversibly adsorb to a liquid-liquid or gas-liquid interface, forming very stable foams and emulsions Bare NPs may be too hydrophobic or hydrophilic for stabilizing an interface so PNPs can be tailored for a specific interface and application

Using surfactant-coated nanoparticles (SNPs) and PNPs for stabilizing foam and emulsion

SNPs are prepared by blending surfactants and NPs Surfactant can form a monolayer on the NP surface, creating more hydrophobic particles Figure 2.6 shows a schematic representation of surfactant adsorption onto a NPs and examples of foams and emulsions stabilized by SNPs This adsorption is confirmed through contact angle measurement, adsorption isotherms of surfactants on NPs, zeta potential measurements and dispersion stability measurements as a function of concentration of surfactant and NPs

Figure 2.6: (a) Form as viscous fluid is a dispersion of air in water and each air droplet is surrounded by SNPs; (b) Cryo-SEM image of a foam with NPs closed packed; (c) schematic representation of the effect of concentration ratio of NP and surfactant [20]

The relative concentration of surfactant and NPs affect to the properties of SNPs, the rheology of foams and emulsions formed by SNPs Another role of the surfactant in this process is to lower the interfacial tension and form an initial dispersion of air/water or oil/water in case of foam or emulsion, respectively Once this dispersion is formed due to shear and a decreased amount of interfacial tension, the stability of foam/emulsion is augmented by adsorption of NPs at the interface Similar to surfactant-coated nanoparticles, PNPs can be used to stabilize foams and emulsions because they can decrease the interfacial tension of oil and water and air, which can lead to more stable emulsion PNPs can reduce interfacial tension (IFT) from 25 to 1 mN/m

By comparison, surfactant additives can lead to much greater reductions in oil-water IFT, down to 0.001 mN/m and below Therefore, the reduction in oil-water IFT is modest compared with suitably chosen surfactant additives In addition to surface energy, entropy is important to the interfacial properties of PNPs Polymers can exhibit conformational change that influence the thermodynamics of PNPs adsorption at the fluid-fluid interface

Surfactant and PNPs for mobility control

Foams and/or emulsion formation are not only relying on increasing the viscosity of the displacing fluid and the recovery of oil but also through CT scans, an increased pressure drop across the core, and effluent analysis

Figure 2.7 shows the CT-scan of different cross sections of a Boise sandstone core after flooding with brine and CO2, both with and without PEG-coated silica NPs The difference in these two experiments is only the presence or absence of PNP and the same core has been scanned at the same injected pore volume of CO 2 Large regions of the core are bypassed due to viscous fingering (Figure 2.7a) when no PNP added, while the CT-scan results show greater sweep efficiency in the presence of PNP (Figure 2.7b),

Figure 2.7: CT-scan of the cross section of a core flooded with CO 2 and (a) 2% NaBr brine and (b) 2% NaBr brine and 5% PEG-coated silica nanoparticles; pure brine and CO 2 are illustrated with red and blue, respectively The scan is taken after 0.25 pore volume of CO 2 injected and each slice is 1 cm apart longitudinally [21]

One practical challenge in the application of foam and emulsions from PNPs is the energy needed for foam and emulsion formation There is a threshold shear rate needed for NPs to start generating foams and emulsions This threshold injection flow may be much greater than the practical injection rates in reservoirs Pregeneration of foams and emulsions outside the reservoir before injection increases the cost and difficult of injection into reservoir

A type of polymeric nanoparticles with commercial name BrightWater was the first successfully field-tested nanoparticles to increase the sweep efficiency in an actual oil reservoir

(Salema field, Campos Basin, Brazil) [22] BrightWater is a polymeric nanoparticle that hydrolyzes at a specific temperature and expands to many times its original volume By blocking the pores in the high-permeability regions of reservoir, the injected flow will be directed toward low-permeability zones of the reservoir, which may have been previously untouched

Figure 2.8: Schematic and SEM image of BrightWater polymeric NPs The particles expand at elevated temperatures, diverting flow to low permeability regions [22]

Figure 2.8 illustrates the basic idea behind the application of these polymeric nanoparticles, which can lead to significant increase in oil recovery Although BrightWater is not a PNP, its successful implementation provides guidelines for the design of PNPs and demonstrates that PNPs do have potential for use in EOR

2.3.2 The surface wettability alteration property

Oil can be extracted easily from water-wet rock than from oil-wet rock, and one approach to improve oil recovery is through changing the wettability of the reservoir rock from oil-wet towards water-wet A surface is called water-wet if the water contact angle is < 90 o and oil-wet if the water contact angle is >90 o

Mechanisms of surface wettability alteration by PNPs

Surface and interfacial energies determine whether a surface is water-wet or oil-wet A spreading coefficient S of water on a solid in contact with both oil and water can be defined in terms of the IFTs between each phase in following equation:

Where γ O/S , γ W/S, and γO/W are the interfacial energies between oil/solid, water/solid, and oil/water Reducing the oil-water interfacial tension results in an increase in S and a more water- wet surface “Rollup” is a well-known mechanism for removal of oily soils from solid surfaces by wettability alteration using surfactants

However, in a fluid containing nanoparticles or spherical surfactant micelles, phenomena are observed that may not be fully explained through the previously known mechanisms The underlying mechanism that can explain for this unusual interfacial behavior is related to the size of NPs Adjacent to the wedge-shape inner contact line, the NPs can form ordered structures, as shown in Figure 2.9

Experimental

Chemical and materials

Table 3.1: Chemical and materials using for experiments

No Name of chemical/material

For synthesis of MNPs, PMNPs

2 Fluoride acid HF Liquid China

3 Sodium hydroxide NaOH Solid Germany (Merck)

4 Nitric acid HNO 3 Liquid China

5 Chloride acid HCl Liquid China

6 Iron (III) nitrate Fe(NO3)3 Solid Merck - Germany

8 Iron (II) chloride FeCl 2 Solid Merck –

9 Sodium dodecyl sulfate SDS Solid China

10 Ammonium hydroxide NH4OH Liquid/ 30% China

11 Absolute ethanol C2H5OH Liquid China

12 Oleic acid C 17 H 33 COOH Liquid China

14 2-acrylamido-2- methylpropane AMPS Solid USA (Sigma-

15 Methyl methacrylate MMA Liquid USA (Sigma-

16 Ammonium persulfate (NH4)2S2O8 Solid China

For synthesis and analysis of nonylphenoxy polyethoxy carboxylate (NPC) surfactant

2 Chloroacetic acid ClCH2COOH Solid Germany (Merck)

3 Acetone CH3COCH3 Liquid China

4 Sodium hydroxide NaOH Solid Germany (Merck)

Hyamine 1622 (Trade name) Liquid USA (Sigma-

Basic Red 2, Cotton Red, Gossypimine, Safranin T, Safranin Y or A (Trade name)

Liquid, the ingredient as Table

Lab (preparing as brine in White Tiger reservoir)

Liquid, the properties as Table

White Tiger Oligocene oilfield of Vietnam

4 Absolute ethanol C2H5OH Liquid China

Table 3.2: The ingredient and properties of brine

Cl - SO4 2- pH Density, kg/l

Table 3.3: The properties of crude oil at White Tiger reservoir [32]

The n-paraffin content 27% in weight

Equipments, instrument, software

No Using for Equipment/Instrument Condition in thesis Equipment’s origin

For synthesis, characterization and evaluation of MNPs, PMNPs

1 Stirring Mechanical stirrer Maximum 900 rpm USA

3 Measuring viscosity Brookfield DV-III Ultra - USA

5 Measuring pH pH Accument Research

Annealing at high temperature, high pressure

Decanting MNPs from the mixture

X-ray Diffraction (XRD) Two theta from 20 to 70 o Bruker –

Measuring the contents of red mud

Energy-dispersive X-ray Spectroscopy (EDS)

Analyzing the solid sample USA

Fourier transform infrared spectroscopy (FT-IR)

Evaluating thermal stability in solid state

Thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC)

The temperature is from 30 to 800 o C with a heating rate of 10 o C/min, under dynamic flow of nitrogen using differential scanning calorimeter (DSC)

Field emission scanning electron microscope (FE- SEM) and transmission

Disperse material in brine water Japan

Chapter 3: Experimental dispersibility electron microscope (TEM),

Software for finding the appropriate condition for polymerization reaction/plotting the graphs

1 Microsoft Office Excel 2007 for calculating in orthogonal planning level 2 Microsoft -

2 Matlab 2012 for plotting 3D response surface Mathwork -

3 Orgin 8.0 for plotting XRD patterns, FT-IR spectra USA

4 Endnote X7 for citing the references USA

5 ChemBio Draw Ultra 12.0 for drawing chemical formulas USA

6 Google scholar for find the reference documents USA

Synthesis of PMNPs

3.3.1 Preparing FeCl 2 and FeCl 3 from red mud

Red mud source was taken from Saigon Ground Water Company Limited (SAGROWA CO

LTD) The mass percentage of elements in red mud was analyzed according to Energy-dispersive X-ray spectroscopy (EDS) method The result analysis was showed in Figure 3.1 and Table 3.5

Figure 3.1: The compounds in red mud via analyzing EDS method

Table 3.5: The mass percentage of compounds in red mud

According to the above table and solubility chart, the compounds existing in red mud are oxide compounds such as SiO2, Al2O3, FeO, Fe2O3; carbonate compounds such as Al2(CO3)3, CaCO3, FeCO3, and phosphate compounds such as AlPO4, Ca3(PO4)2 First, the red mud was dissolve in concentrated HCl to eliminate the insoluble compounds The reactions happen as follows:

Al2O3 + 6HCl → 2AlCl3 + 3H2O FeO + 2HCl → FeCl2 + H2O Fe2O3 + 6HCl → 2FeCl3 + 3H2O Al 2 (CO 3 ) 3 + HCl  AlCl 3 + H 2 O + CO 2 CaCO 3 + HCl  CaCl 2 + H 2 O + CO 2 FeCO3 + HCl  FeCl2 + H2O + CO2

Ca 3 (PO 4 ) 2 + HCl  CaCl2 + H 3 PO 4 The insoluble compound (SiO 2 ) was removed after reaction The obtained solution includes AlCl 3 , FeCl 2 , FeCl 3 , CaCl 2

After that, mount of redundant NaOH was added into above solution to dissolve completely precipitate Al(OH)3 and obtained Fe(OH)2, Fe(OH)3 The oxygen was pumped into solution to obtained only Fe(OH)3 The reactions happen as follows:

AlCl3 + 3NaOH → Al(OH)3 + 3H2O Al(OH)3 + NaOH → NaAlO2 + 2H2O FeCl2 + 2NaOH → Fe(OH)2 + 2NaCl 4Fe(OH)2 + O2 + 2H2O 4Fe(OH)3

2FeCl3 + 6NaOH  2Fe(OH)3 + 6NaCl A part of Fe(OH)3 was dissolve into N2H4 to obtained Fe(OH)2

4Fe(OH)3 + N2H4  4Fe(OH)2 + N2 + 4H2O FeCl2 and FeCl3 salts were obtained by adding HCl into Fe(OH)2 and Fe(OH)3

Fe(OH)2 + 2HCl  FeCl2 + 2H2O 2Fe(OH)3 + 6HCl  2FeCl3 + 3H2O

MNPs were synthesized using the combined method of co-precipitation and mini-emulsion under the presence of SDS as surfactant 40 mL of FeCl 2 0.625M and 40mL of FeCl 3 1.25M from preparing Section 3.3.1 were put in a 250 mL three-neck round-bottom flask, which was equipped with a mechanical stirrer under inert gas (nitrogen) Meanwhile, 1 g of SDS was dissolved into 20 mL of deoxygenated distilled water, which was poured into three-neck round- bottom flask through a funnel The mixture was stirred vigorously with the speed of 900 rounds per minute (rpm) and heated gradually to 80 °C MNPs was also synthesized from FeCl2 and

Fe(NO3)3 (Merck Company) to compare with MNPs synthesizing from red mud, and MNPs counted as reference

Subsequently, 32.85g of NH4OH 25% in weight (about 45 mL) was poured into the solution with the adding speed of 0.5 mL/minute Black precipitate appeared during the reaction Time for adding NH 4 OH completely was 1.5 hours and continued to keep in another 0.5 hour The precipitates were decanted by using super magnet and washed three times with 50 mL of distilled water, 1 time with 50 mol of ethanol, and 1 time with 50 mL of water The pH of decantation solution was tested with pH paper The washing process stops when the pH of solution is 7 In case of pH still be larger than 7, the process will be repeated The washed material was dried at 50 o C in vacuum environment for 12 hours The mass of magnetic nanoparticles (MNPs) after drying was 4.3547g The relevant chemical reaction can be expressed as follows:

Figure 3.2: Process of synthesis of iron oxide nanoparticles (MNPs)

The crystallized structure MNPs are confirmed through X-Ray Diffraction pattern (XRD) while chemical functional group are determined by Fourier Transfer Infrared (FT-IR) Vibrating Sample method (VSM) give us the magnetic property of MNPs The size of material can be determined via Transmission Electronic Microscope (TEM), Scanning Electronic Microscope (SEM) Thermo Gravimetric Analysis (TGA) shows the thermal stability of obtained materials

3.3.3 Synthesis of PMNPs from OMNPs

There are two stages when synthesizing PMNPs

Oleic acid is linked onto MNPs surface via ester reaction between OH- (on MNPs surface) and COOH- (of oleic acid) This obtained material is called OMNPs

• Speed of adding NH4OH: 0.5mL/min 1 g SDS

45mL NH4OH 40mL FeCl2 0.625M 40 mL FeCl3 1.25M

Figure 3.3: Synthesis of MNPs via oleate linker

The detail synthesis process as follows:

MNPs (4.3547g) were dispersed into 50 mL of deoxygenated distilled water with the aid of an ultrasound bath in 1 hour After that, the MNPs was decanted with supermagnet and transferred to 250 mL three-neck round-bottom flask Then, 50 mL of hexane using as solvent was added the flask The mixture was vigorous stirred with the speed of 250 rpm and simultaneously heated until to 60 °C Oleic acid (4g or about 4.5 mL) was poured into the mixture The temperature of reaction was raised to 80 o C, and was carried out for 2 hours

Afterward, the mixture was cooled to room temperature

Firstly, the obtained mixture was decanted by using super magnet Secondly, the obtained material was washed and decanted 3 times with 50 mL of ethanol The washing process stops if the color of decantation solution is transparent The process will be repeated on the contrary to assure that the redundant oleic was removed completely out of the MNPs’ surface Finally, the material was dried at 50 o C in vacuum environment for 12 hours This material was called OMNPs with the mass of 5.0950 g OMNPs are confirmed through FT-IR spectra

Figure 3.4: Process of synthesis of OMNPs

The above OMNPs are copolymerized in mini-emulsion environment with 2-acrylamido-2- methylpropane sulfonate (AMPS) and methyl methacrylate (MMA) This obtained material is called PMNPs The nature is the additional polymerized reaction between the double bond of oleic acid with AMPS and MMA with the assistance of radical initiator (NH4)2S2O8

50 mL distilled H 2 O • Stirring speed: 250 rpm

Figure 3.5: Synthesis of PMNPs from OMNPs

The detail synthesis process as follows:

OMNPs (5.0950 g) were added to 250 mL three-neck round-bottom flask containing 40 mL of distilled H2O 0.0035 mol of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and 0.0035 mol methyl methacrylate (MMA) were fulfilled with water in 50 mL volumetric flask Both of two flasks were stirred mildly for 30 minutes After that, pouring the solution of 50mL volumetric flask into 250 mL three-necked round bottom flask The mixture was sonicated and stirred with the speed of 100 rpm for 1.5 h at room temperature

Meanwhile, dissolving 1 g of ammonium persulfate (NH4)2S2O8 was put into the 50 mL beaker containing 10 mL of distilled H2O, then 0.5g SDS was added into this solution with the assistance of ultrasound for 1 h with vigorous stirring

Next, pouring the solution in beaker into the flask by using a dropping funnel with the adding speed of 0.5mL/min The mixture was stirred, heated gradually to T°C with the assistance of ultrasound for t hours

Finally, the obtained mixture was decanted by using super magnet and washed 3 times with 50 mL of ethanol The washing process stops if the color of decantation solution is transparent

The process will be repeated on the contrary to assure that the redundant polymer is eliminated fully the obtained materials This material was called PMNPs and transferred to vacuum oven at 50 o C for 12 hours PMNPs are confirmed through FT-IR spectra

Figure 3.6: The synthesis process of PMNPs from OMNPs

The total procedure to synthesize PMNPs from red mud can be illustrated in Figure 3.7

Dissolving Fulfill with water to 50mL

Figure 3.7: The illustration of synthesis of PMNPs from red mud

There are many parameters affecting on the reaction such as the stirring speed, ultrasound time, temperature and time for polymerization but the significant parameter are temperature T and reaction time t The polymerization is optimized base on the percentage of copolymer coated on OMNPs via experimental planning And the model using in this thesis is Orthogonal planning level 2 [33] x 100%

Temperature was investigated from 60 to 80 o C, and the time for polymerization varied from 6 to 8 hours The different conditions according to temperature and reaction time were summarized as following table:

Table 3.6: The different conditions for polymerization

No The number of experiments Temperature of reaction

9 experiments with varied conditions including temperature and time for reaction

10 3 experiments at the center to calculate reappear variance sth: (n)

Table 3.7: The parameters of orthogonal planning level 2

The number experiment at the center (n0) 1

The number of additional experiments at the center to calculate reappear variance s th : (n)

Table 3.8: Value and variable range of affecting parameters

To facilitate for calculating experimental coefficients of mathematic model and conducting data processing, it is needed to transfer to dimensionless coding value, with upper value and lower value of +1 and -1; average value x 0 j = 0 (at the corner of coordinate)

 with j = 1, 2 The regression equation of experimental planning orthogonal level 2 has the general form as follows:

Table 3.9: Matrix for orthogonal planning level 2 for polymerization

Obtained value after calculating the percentage of copolymer coated on OMNPs for every reaction

After finding the optimum condition for polymerization, the reaction was carried out with this condition and compared with the calculated results.

Synthesis of Nonylphenoxy carboxylate surfactant

The nonylphenoxy polyethoxy carboxylate (NPC) surfactant was prepared by carboxymethylation method [34] Firstly, 0.05 mol nonylphenoxy polyethoxy alcohol (NPA) was

Chapter 3: Experimental put into a three-neck flask, 0.2 mol of pulverized sodium hydroxide was added partially and stirred (250 rpm) for 4 hours at T temperature Secondly, 0.1 mol of chloroacetic acid was dissolved in 50 mL acetone as solvent and added this solution to flask, the mixture was stirred (350 rpm) for 1 hour at 30 o C and another 4 hours at 50 o C Finally, the mixture was filtrated to remove the solid (redundant NaOH, created NaCl), the NPC surfactant was obtained by removing acetone solvent The reaction equation is as following:

RONa + ClCH2COOH + NaOH Acetone o

Figure 3.8: The procedure for synthesis of NPC surfactant

3.4.2 Determination the yield of reactions and characterize the NPC surfactant

The yield of reactions was also the mass percentage of anionic surfactant (NPC) in final products Therefore, it can be calculated based on two phase titration (water/chloroform) with cationic reagent (Hyamine 1622) and cationic dye (Safranine O) as indicator The sample was

0.05 mol NPA 0.2 mol pulverized NaOH

Solid dissolved in a suitable solvent (distilled water) and titrated with cationic reagent Cationic dye will form a complex with anionic surfactant at the beginning of titration, which will be extracted into chloroform layer The cationic reagent replaces cationic dye in the chloroform layer and the cationic dye moves into the aqueous layer at the end of titration The endpoint obtained when both layers are the same color

The structure of starting alcohol and obtained surfactant were characterized by Fourier transform infrared spectroscopy (FT-IR spectrometer Brucker Equinox 55 in the range of 4000- 400 cm -1 )

3.4.3 Investigating the effect of temperature on carboxymethylation reactions

To investigate the effect of temperature on the carboxymethylation reactions, it is needed to vary T from 30 to 110 o C and kept other conditions in the same.

Evaluation thermal and chemical stability of PMNPs

The thermal and chemical stability of PMNPs in solution were studied via annealing experiment Namely, diluting NPC surfactant (obtained from Section 3.4) in brine to obtain concentration of 1000 ppm PMNPs were dispersed in brine to obtain concentration of 1000 ppm The appropriate PMNPs solutions were added to appropriate NPC solution to obtain PMNPs/surfactant mixture with desired ratios Next, putting these mixtures into the heat- resistant ampoules, at the same time, the inert gas (nitrogen) was pumped into these ampoules to remove the oxygen dissolving in the solution This was done to prevent the degradation of solution from oxidation reaction happening during the annealing experiments Then the ampoules were put into the oven with temperature of 120 o C Observing the transparency and measuring the interfacial tension of mixtures before annealing every 7 days After 31 days, the PMNPs will be decanted and washed with ethanol for measuring FT-IR to evaluate their chemical stability

Table 3.10: Appearance of mixtures PMNPs-NPC surfactant by the time

No The mass ratio of mixture

PMNPs-NPC surfactant Appearance of mixtures by the time

Observing the appearance every 7 days and record the result

Table 3.11: Interfacial tensiometer (IFT) of mixtures PMNPs-NPC surfactant by the time

No The mass ratio of mixture

PMNPs-NPC surfactant IFT of mixtures by the time

Measuring IFT the mixtures and record the result every 7 days

Evaluation the wettability alteration of PMNPs and mixture PMNPs-NPC surfactants

The wettability of PMNPs and PMNPs-NPC surfactant was evaluated through measurement contact angle between surfaces of rock’s slice and oil drop in the solution that need to be investigated

Slices of rock were put into the crude oil that was taken from White Tiger Oligocene oilfield of Vietnam Then they were annealed at 120 o C for a month After that, they were taken and preparing for contact angle experiments There are 4 solutions need to be studied comprising brine (1), PMNPs solution (2), NPC surfactant solution (3), mixture of PMNPs and NPC surfactant (4).

Evaluation the reusing capacity of PMNPs

The PMNPs after annealing experiment were collected from a super magnet They were washed and decanted 3 times with absolute ethanol Then these nanoparticles were reused for evaluation thermal and chemical stability Moreover, their appearances were also observed after the reusing.

Results and Discussion

Characterization of MNPs and PMNPs

4.1.1 XRD patterns of MNPs from red mud and MNPs reference

Figure 4.1 showed XRD patterns of the obtained materials The Joint Committee on Powder

Diffraction Society (JCPDS) was used to index the peaks of XRD Six characteristic peaks at 30.2 o , 35.5 o , 43.3 o , 53.7 o , 57.2 o , and 62.9 o were corresponded to the (220), (311), (400), (422), (511) and (440) crystal planes of a pure Fe3O4 according to JCPDS 79-0417 Therefore MNPs were synthesized successfully A correct particle size is required in MNPs preparation to ensure its dispersion 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 size depending on the reaction medium

Figure 4.1: XRD pattern of MNPs

The crystal structure of the obtained material was characterized by X-ray Diffraction (XRD) Siemens D5000 The patterns with the Cu Kα radiation (λ = 1.54051 Å) were recorded in the region of 2θ range 20 o to 70 o the average crystallite size can be calculated from the Scherrer equation [35]

 Where D is the average crystallite size of the particles, K is a shape factor (~ 0.9), λ is the wavelength of the incident X-ray (λ = 1.54051 Å = 0.15405 nm), B indicates the full width at half maximum intensity of the peak in radian, and θ corresponds to the diffraction angle

According to Scherrer equation (1) with B = 0.69 o = 0.012043 radian, θ = 17.75 o = 0.3098 radian, the average crystallite size of sample was 12 nm

4.1.2 VSM of MNPs and PMNPs

Ma gn et iza tio n (e mu /g )

Figure 4.2: VSM of MNP and PMNPs

Figure 4.2 showed the obtained magnetization curve of MNPs and PMNPs by VSM at 25 o C

The saturation magnetization of MNPs and PMNPs were 52 emu/g and 49.1 emu/g in respectively This result reflected the successful of synthesizing the magnetic materials The saturation magnetization of PMNPs was not much less than MNPs Therefore, PMNPs was still keeping the good properties of magnetic materials to apply in enhanced oil recovery

Nonfunctionalized MNPs surface was modified by reaction with oleic acid to enhance the probability of core–shell structure performance further 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

4.1.3 FT-IR of MNPs, OMNPs and PMNPs

The presence of oleic acid on the MNPs surface was confirmed through FT-IR (Figure 4.3)

The band at 587 cm −1 , corresponding to the vibration of the Fe–O bonds in the Fe3O4 structure, was observed While the bands at 1438 and 1518 cm −1 were clearly recognized and attributed to the asymmetric and symmetric stretching vibrations of the –COO– functional group The stretching vibration of C=O at 1710 cm −1 was clearly detected The bands at 2862 and 2923 cm −1 were observed according to the stretch modes of –CH2– and –CH3 of oleic acid This result indicates that the layer of oleic acid was successfully coated on the MNP surface The results corresponded well with other previous data [36]

Figure 4.3: FT-IR spectrum of MNPs, oleic acid and OMNPs Figure 4.4 shows that the presence of co-polymer AMPS-MMA on the OMNP surface was confirmed through FT-IR The band at 582 cm −1 that belongs to the Fe–O bond in the Fe 3 O 4 structure was still observed While the bands at 659, 1099, 1250, and 3200–3500 cm −1 from the FT-IR spectrum were assigned to S-O, C–S, S=O, and –NH– stretching vibrations, respectively, indicating that the AMPS structure Moreover, the vibration of CH 3 , CH 2 , and –COONa group in MMA was clearly observed at 1389–2956, 1502, and 1567–1385 cm−1 In addition, the absorption bands at 1747 and 1196 cm −1 correspond to carbonyl (C=O) and asymmetric C–O–C stretching vibrations, indicating that oleic acid coated onto the MNPs’ surface Thus, the FT-IR

Chapter 4: Results and Discussion spectra exhibited all the component signals in the core–shell structure of co-polymer AMPS- MMA

Figure 4.4: FT-IR spectra of (a) OMNPs, (b) Copolymer MMA-AMPS, and (c) PMNPs

4.1.4 TGA for OMNPs–MMA–co-AMPS

Thermal stability of PMNPs and copolymer MMA-AMPS was investigated using a thermo gravimetric analysis (TGA), and the resultant thermo diagram is presented in Figure 4.5 and Figure 4.6

The thermo diagram of PMNPs shows four steps The first weight-loss process at a temperature range of 30–185 °C is associated with the loss of adsorbed water that constitutes 10–

15% of the weight of PMNPs The second weight-loss process lies at the temperature range of 185–335 °C that can be attributed to the loss of loosely bonded polymer matrix This weight-loss process is 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 Figure 4.5 shows a thermo diagram of unfilled copolymer At 350 o C, copolymer lost about half of its mass, and the final degradation happens at 400 o C, or in 100 o C lower than in the case of PMNPs nanocomposite (500 o C)

Figure 4.5: TGA patterns of copolymer MMA-AMPS

Figure 4.6: TGA patterns of PMNPs

TGA spectra showed that the copolymer AMPS-MMA lost 90% weight in total because of the loss of loosely bonded polymer matrix, while PMNPs only lost 9.43 % in total It is assumed

Chapter 4: Results and Discussion that the mass of MNPs was no change during thermo gravimetric analysis The main loss was from the degradation of copolymer From there, the mass percentage of copolymer coated on MNPs was estimated about 10.5% This result is not much different from experimental result

This confirmed again that copolymer coated on MNPs surface

4.1.5 TEM images of MNPs and PMNPs

Figure 4.8: TEM image of PMNPs

According to the TEM images, the average size of MNPs was 12 nm, while the average size of PMNPs was 16 nm This result together with FT-IR spectra showed that the copolymer MMA-AMPS coated successfully on MNPs surface The dispersibility of PMNPs was better than MNPs, there was no agglomeration between nanoparticles This could be contributed by polymer AMPS that links to MNPs and change their property from inert to hydrophilic Besides, co-polymer played roles as steric inhibition agents and created electrostatic repulsion between among PMNPs

4.1.6 Result of optimization the reaction of copolymer coated on MNPs

Table 4.1: Matrix for orthogonal planning level 2 for polymerization

Real variable Encoding variable Objective function,

Reappeared variance was determined according to 3 additional experiment at the center:

The coefficients of regression equation and the their error were calculated as follows: b0 = 8.65; b1 = 0.69; b2 = 1.23; b12 = -0.89; b11 = -2.57; b22 = 1.25 sb0 = 0.13; sb1 = 0.16; sb2 = 0.16; sb12 = 0.20; sb11 = 0.28; sb22 = 0.28 The meaning of coefficients in regression equation were verified according to Student Standard

 j j j b t b s t0 = 65.77; t1 = 4,3034; t2 = 7.61; t12 = 4.50; t11 = 9.20; t22 = 4.49 Look up t p (f 2 ) in Microsoft Office Excel, where f 2 = n – 1 = 3 – 1, p =0.05 was chosen The t p (f 2 ) value was fought as follows: t 0,05 (2) = 4.302

All regression coefficient are bigger than t 0,05 (2) so no coefficient was eliminated The regression equation was gained as follows:

To check the compatibility between regression equation and experimental, it needs to calculate residual variance (s du)

The value of Fisher Standard looked up with level of significance p = 0,05 and degrees of freedom: f 1 = N – l = 9 – 6 = 3; f 2 = n – 1 = 3 – 1 = 2 was F 1-p (f 1 , f 2 ) = F 1-0,05 (3, 2) = F 0,95 (3, 2)

= 19,15 (Look up F 0,95 (3, 2) from Microsoft Office Excel)

F < F 1-p (f 1 , f 2 ) therefore the regression equation is compatible with experimental

The encoding variable was shifted to real variable, where: 1 T 70 2 t 7 x ; x t 7

Therefore, regression equation with the real variables as follows:

        From this equation, The response surface of % copolymer coated on MNPs according to temperature (T) and reaction time (t) was plotted as Figure 4.9 The graph was plotted by Matlab software with the command as follows

]; mesh(X,Y,Z) grid on title ('Response surface of copolymer coated on OMNPs reaction') xlabel('Time of reaction, h');ylabel('Temperature of reaction, o C');zlabel('%copolymer coated on OMNPs');

Notes: X presents for reaction time (t), Y presents for temperature of reaction (T) and Z presents for the mass percentage of copolymer coated on MNPs (%mcopo)

Figure 4.9: Response surface of mass percentage of copolymer MMA-AMPS coated on

To optimize the mass percentage of copolymer coated on MNPs, The maximum value of function %mco-po withT[60;80] and t[6;8] was fought by taking partial derivative and solving two equations to find T and t at the extremum position

With: co po co po

%mco-po(T, t) were calculated at boundary position and extremum position as follows:

%m co-po (80; 8) = 9.24 % From the above calculation, the optimum condition for polymerization in the investigating range was 70.22 o C and the time for reaction was 8 hours The mass percentage of copolymer coated on MNPs was 12%

The polymerization was carried out at 71 o C and 8 hours to compare with the calculated result

And the mass percentage of copolymer coated on MNPs was 12.17% This result was conformity with the calculated result.

Synthesis of Nonylphenoxy carboxylate (NPC) surfactant

4.2.1 Investigating the effect of temperature on carboxymethylation reactions

Figure 4.10 showed that the highest yield of reaction was 51% at 90 o C through a facile procedure when comparing previous reported procedures [34, 37, 38] about the conditions, the time The effect of temperature on the yield of reaction is according to quaternary function or sine function To understand this relation, it needs be more researched on the kinetic as well as the mechanism of reaction But in this thesis, the lower or the higher temperature was not good for reaction and the reaction at 50 o C is not much more different than the reaction at 90 o C because the difference about the yield of reaction is only 3 % [39]

Figure 4.10: Yield of reactions at various temperatures

Y ie ld of r ea ct ion , %

4.2.2 FT-IR spectroscopy of NPC surfactant

Figure 4.11 (e) shows that the peak at ~3400 cm -1 corresponded to O-H stretch Because the product is the mixture of NPA and NPC (mass percentage of NPC is 51 %), the peak still existed when comparing starting NPA (a) While the peak at ~1740 cm -1 corresponded to C=O in carboxylic acid This can be demonstrated that ClCH 2 COOH was still on the product but in small content As the Figure 4.11, the peak at ~1600 cm -1 was C=O stretch in carboxylate salt (c) and it also appeared in NPC product (e) Combination with the result of two phase titration to determine the mass percentage of anion surfactant (NPC) showed that the NPC surfactant was synthesized successfully

(a) NPC (b) Acetone (c) ClCH 2 COONa (d) ClCH 2 COOH (e) NPA

Figure 4.11: FT-IR spectroscopy of NPA, NPC and other substances in the reaction.

Evaluation thermostability of the mixtures PMNPs-NPC

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, not as surfactant solutions, cannot reduce IFT

As shown in Table 4.3 and Figure 4.12, a slight synergistic effect resulting in IFT reduction appeared in the mixture of 200 ppm magnetic nanocomposite and 800 ppm surfactant During

Chapter 4: Results and Discussion the aging period, the IFT of all the tested samples with nanocomposite increased, which is similar to surfactant solution (Sample 1) This finding can be explained by the presence of alkyl phenol polyethoxy alcohol (NP-9), a nonionic surfactant–precursor of synthesized alkyl phenolpolyethoxy carboxylate in a mass ratio of 50:50

Figure 4.12: (a) The color of MNPs solution (a) before applying super magnet and (b) after applying super magnet

Table 4.2: Interfacial tensiometer of mixtures PMNPs-NPC surfactant by the time

No The mass ratio of mixture

31 days 0 Brine (using as reference) 19.1401 19.1402 19.1401 19.1403 19.1401

Table 4.3: Appearance of mixtures PMNPs-NPC surfactant by the time

The mass ratio of mixture PMNPs-NPC surfactant

Disperse well No change in color

Disperse well No change in color

Disperse well No change in color

Still disperse well No change in color

Disperse well No change in color

Disperse well No change in color

Disperse well No change in color

Still disperse well No change in color

Disperse well No change in color

Disperse well No change in color

Disperse well No change in color

Still disperse well No change in color

5 600-400 Disperse Disperse Disperse Disperse Still

Chapter 4: Results and Discussion well well

No change in color well No change in color well No change in color disperse well No change in color

Disperse well No change in color

Disperse well No change in color

Disperse well No change in color

Disperse well No change in color

Disperse well No change in color

Disperse well No change in color

Disperse well No change in color

Disperse well No change in color

The data of thermal stability of mixture PMNPs-NPC surfactants was plotted as Figure 4.13, where X axis was plotted as log 2 scale to show easily the IFT of the mass ratios especially with the presence of NPC surfactant in the mixtures

The graphs showed that PMNPs can reduce slightly the interfacial tension between brine and oil from 19.1401 to 17.6737 dyne/cm The mixture with the presence of NPC surfactants reduces strongly the IFT of mixture The mixture with ratio PMNPs-NPC of 200-800 even reduce the IFT lower than NPC surfactant (mass ratio 1000-0) This value was 0.7899 in comparison with 0.8554 of NPC solution The surface energy and entropy is important to the interfacial properties of PMNPs The layer copolymer coated on MNPs can exhibit conformational change that influence the fluid-fluid interface so this properties supports for reducing the IFT of mixture when combination with the appropriate mass ratio Especially, this ratio also showed that the chemical and thermal stability of solution after a long time annealing in the harshness environment that simulating the reservoir condition The IFT tends stable when comparing with other mass ratios as showing in Figure 4.13

IF T o f mi xt u re s, d yn e /cm

Figure 4.13: Thermal stability of mixture PMNPs-NPC surfactants by time

Chemical stability of PMNPs was evaluated by FT-IR spectra before annealing and after 31 days annealing days

Figure 4.14: FT-IR spectra of PMNPs before and after annealing experiment

The PMNPs after annealing 31 days were washed with absolute ethanol to eliminate completely carboxylate acid adsorbing on their surface FT-IR spectra (Figure 4.14) pointed out that the functional group of co-polymer still existed such as S=O, S-O, C-S, and –NH- stretching vibration for AMPS structure; -COONa vibrations in MMA as well as C=O and asymmetric C- O-C stretching vibrations of oleic acid coated on MNPs

There was no much different between the spectra shape of PMNPs before and after contacting with brine at high temperature (120 o C) and high salinity (13‰) In high salinity environment with the presence of divalent ions can also affect the stability of MNPs, but the co- polymer coated on MNPs provided both providing steric inhibition and electrostatic repulsion to optimize the stabilization the nanoparticle This prevented PMNPs from agglomeration and degradation after a long time withstanding Moreover, NPC surfactant also contributed as heat resistant film covering PMNPs and keeping them out of directive contacting with high temperature and high salinity.

Evaluation the wettability alteration of PMNPs and mixture PMNPs-NPC surfactants

Figure 4.15: The picture of oil drop in brine environment

Figure 4.16: The picture of oil drop in solution PMNPs 1000 ppm

Figure 4.17: The picture of oil drop in solution NPC surfactant 1000 ppm

Figure 4.18: The picture of oil drop in mixture PMNPs-NPC with mass ratio 200-800 in respective

The contact angle was 66 o and the value was small than 90 o This result pointed out that the surface of rock’s slice was hydrophobic, and the oil drop spread on the surface of rock This created the difficult to withdraw the oil out of the reservoir if only using traditional method (water injection into the reservoir) When the environment was PMNPs 1000ppm, the contact angle was 70 o , it is clear there have the change the wettability of rock surface when having presence of magnetic nanoparticles This change can be explained by the chocking of nanoparticles into the boundary where contacting oil and rock surface as Figure 4.19 The surface of PMNPs was hydrophilic and also hydrophobic because of contribution of two polymer AMPS (hydrophilic) and MMA (hydrophobic) When contacting with the rock surface, the hydrophobic surface of PMNPs helps them to approach the rock surface and chocking the boundary between oil and solid surface This leads to change the contact angle of oil drop, and they will tend to remove easier out of the rock surface However, the change of contact angle was not much to remove completely oil drop It is need to combination with a surfactant

Figure 4.19: The mechanism of PMNPs for wettability alternation of rock surface in reservoir

When the environment was solution of NPC surfactant, the contact angle changed significantly from 67 o to 141 o And the mixture PMNPs-NPC with mass ratio of 200-800 even changed the contact angle to 144 o This value showed that the potentiality of combination to enhance oil recovery.

Evaluation the reusing capacity of PMNPs

4.5.1 Observing the appearance the solution after being reusing

Table 4.4: Appearance of the MNPs and PMNPs solutions after being reused

STT Fresh First reusing Second reusing Third reusing Fourth reusing

The picture of Table 4.4 showed the stability of MNPs and PMNPs after using Especially, PMNPs solution still dispersed well after fourth using while not happening with MNPs solution

After second using, MNPs tended to agglomeration This happens because of the presence of high salinity and hardness (in White Tiger oil reservoir) and the poor chemical stability of MNPs can lead to aggregation or precipitation through van der Waals and hydrophobic attractions

PMNPs escaped from the agglomeration by providing electrostatic or steric repulsions due to the copolymer layer coated on MNPs surface This experiment showed that PMNPs are a potential candidate for enhanced oil recovery in the harshness reservoir with high temperature, high salinity

4.5.2 IFT and viscosity of MNPs and PMNPs after being reused

Table 4.5: IFT of MNPs and PMNPs after being used

Both MNPs and PMNPs were stable and can be using after refresh The IFT and viscosity of both materials change negligible when being recycle with ethanol This is an advantage of PMNPs when deploying the big scale in industry This can save a lot of money for company and protect environment because of decreasing the natural resources to produce MNPs.

Conclusions & Recommendations

Conclusions

Magnetic nanoparticles (MNPs) were synthesized from red mud of ground water treating plant by co-precipitation in mini-emulsion system with the iron content of 57% in weight The structure of MNPs characterized via XRD method confirmed that obtained material was Fe3O4 with the main peaks at 30.2 o , 35.5 o , 43.3 o , 53.7 o , 57.2 o , and 62.9 o corresponding to the (220), (311), (400), (422), (511) and (440) crystal planes of a pure Fe3O4 according to JCPDS 79-0417

After that, MNPs were coated co-polymer 2-acrylamido-1-propane sulfonic acid (AMPS) and methyl methacrylate (MMA) by polymerization in the presence of sodium dodecyl sulfate (SDS) surfactant and they were called PMNPs The appropriate temperature for polymerization was 70 o C and reaction time was 8 hours through calculation of orthogonal planning level 2 when with the mass percentage of co-polymer coated on MNPs surface about 12%

The saturation magnetization of MNPs and PMNPs were 52 emu/g and 49.1 emu/g in respectively via VSM method The PMNPs materials still had enough magnetization to easily separate after using

FT-IR results pointed out that the vibration of the Fe–O bonds in the Fe3O4 structure presented in both MNPs and PMNPs The other bands reflected oleic’s structure presented in obtained materials such as stretching vibrations of carbonyl (C=O) and asymmetric C–O–C;

AMPS’s structure such as stretching vibrations of S-O, C–S, S=O, and –NH– , the functional group in MMA’s structure as the vibration of CH3, CH2, and –COONa

Thermal stability of PMNPs and copolymer MMA-AMPS was investigated via TGA, the thermal diagram showed that final degradation of copolymer happened at 400 o C while happening at 500 o C for PMNPs This showed the thermal stability of PMNPs when withstanding at higher temperature

The average size of MNPs and PMNPs were 12 and 16 nm according to TEM results Also, the dispersibility of PMNPs was better than MNPs because there was no agglomeration between nanoparticles Copolymer played roles as steric inhibition agents and created electrostatic repulsion between among PMNPs

Moreover, nonylphenol polyethoxy carboxylate (NPC) were synthesized from Nonylphenol polyethoxy alcohol (NPA) by carboxymethylation The NPC obtained product were analyzed by two phase titration and characterized by FT-IR The results pointed out that the highest yield of reaction was 51% at 90 o C when the reactions were carried out from 30 to 110 o C

The mixture PMNPs-NPC with the mass ration 200-800 was thermal and chemical stable after annealing 31 days at 120 o C And this mixture changed significantly the contact angle between brine and oil drop from 66 o to 144 o This leaded to the surface of rock transferred hydrophobic to hydrophilic and the oil could be removed easily when injecting brine into the reservoir PMNPs also showed the reusing capacity after treating with ethanol and decanting with super magnet PMNPs still dispersed well and thermal stable until the fourth using

These results showed that PMNPs are a potential candidate to orient using in enhanced oil recovery areas at the harshness reservoir and contribute to protect environment by utilizing thoroughly the pollution source of red mud from the ground water treating plant.

Recommendations

The polymerization for coated co-polymer AMPS-MMA on MNPs can extend the reaction time from 6 to 12 hours because the graph of orthogonal planning level 2 presented that the mass percentage of copolymer tends increasing when extending the reaction time

The reaction for synthesis of NPC surfactant should be more researched about kinetic as well as the mechanism to raise the yield of reaction

The mixture of PMNPs-NPC with the mass ratio of 200-800 can be used for the nanofluid in enhanced oil recovery model experiments because of the thermal and chemical stability and wettability alternative capacity

List of published papers related to learner

LIST OF PUBLISHED PAPERS RELATED TO LEARNER

1 Nguyen Thi Ly, Ngo Trung Kien, Pham Duy Khanh, Nguyen Phuong Tung, Facile procedure to synthesize ankylphenoxy polyethoxy carboxylate surfactants and survey the properties for enhanced oil recovery application Vietnam Journal of Chemistry, 2015 253(6e1): p 382-387

2 T.P Nguyen, U.T.P Le, K.T Ngo, K.D Pham, L.X Dinh, Synthesis of Polymer-Coated Magnetic Nanoparticles from Red Mud Waste for Enhanced Oil Recovery in Offshore Reservoirs Journal of Electronic Materials, 2016 45(7): p 3801-3808

1 Administration, U.S.E.I., Annual Energy Consumption Projection Report 2013

2 Kumar, S.K., et al., Nanocomposites with polymer grafted nanoparticles

3 Kumari, A., S.K Yadav, and S.C Yadav, Biodegradable polymeric nanoparticles based drug delivery systems Colloids and Surfaces B: Biointerfaces, 2010 75(1): p 1-18

4 Soppimath, K.S., et al., Biodegradable polymeric nanoparticles as drug delivery devices

5 Torchilin, V.P and V.S Trubetskoy, Which polymers can make nanoparticulate drug carriers long-circulating? Advanced drug delivery reviews, 1995 16(2): p 141-155

6 Liong, M., et al., Multifunctional inorganic nanoparticles for imaging, targeting, and drug delivery ACS nano, 2008 2(5): p 889-896

7 Zhang, J and R Misra, Magnetic drug-targeting carrier encapsulated with thermosensitive smart polymer: core–shell nanoparticle carrier and drug release response Acta Biomaterialia, 2007 3(6): p 838-850

8 Qian, F., et al., Chitosan graft copolymer nanoparticles for oral protein drug delivery: preparation and characterization Biomacromolecules, 2006 7(10): p 2722-2727

9 Briseno, A.L., et al., Oligo-and polythiophene/ZnO hybrid nanowire solar cells Nano letters, 2009 10(1): p 334-340

10 Saunders, B.R and M.L Turner, Nanoparticle–polymer photovoltaic cells Advances in colloid and interface science, 2008 138(1): p 1-23

11 Wang, P., et al., Enhance the performance of dye-sensitized solar cells by co-grafting amphiphilic sensitizer and hexadecylmalonic acid on TiO2 nanocrystals The Journal of

12 Zhang, X., et al., A quasi-solid-state dye-sensitized solar cell based on the stable polymer-grafted nanoparticle composite electrolyte Journal of power sources, 2006

13 Yong, Y., et al., Characterization of Candida rugosa lipase immobilized onto magnetic microspheres with hydrophilicity Process Biochemistry, 2008 43(11): p 1179-1185

14 Takafuji, M., et al., Preparation of poly (1-vinylimidazole)-grafted magnetic nanoparticles and their application for removal of metal ions Chemistry of materials,

15 Li, Z and E Ruckenstein, Water-soluble poly (acrylic acid) grafted luminescent silicon nanoparticles and their use as fluorescent biological staining labels Nano Letters, 2004

16 Lu, A.H., E.e.L Salabas, and F Schüth, Magnetic nanoparticles: synthesis, protection, functionalization, and application Angewandte Chemie International Edition, 2007

17 Cocuzza, M., et al., Current and future nanotech applications in the oil industry

American Journal of Applied Sciences, 2012 9(6): p 784-793

18 Yahya, N., et al Cobalt ferrite nanoparticles: an innovative approach for enhanced oil recovery application in Journal of Nano Research 2012 Trans Tech Publ

19 Wang, X., et al., A general strategy for nanocrystal synthesis Nature, 2005 437(7055): p 121-124

20 Worthen, A.J., et al., Carbon dioxide‐in‐water foams stabilized with nanoparticles and surfactant acting in synergy AIChE Journal, 2013 59(9): p 3490-3501

21 Aminzadeh-goharrizi, B., et al Effect of Nanoparticles on Flow Alteration During CO2

Injection in SPE Annual Technical Conference and Exhibition 2012 Society of

22 Roussennac, B.D and C Toschi Brightwater trial in Salema Field (Campos Basin,

Brazil) in SPE EUROPEC/EAGE Annual Conference and Exhibition 2010 Society of

23 Liu, K.-L., et al., Dynamic spreading of nanofluids on solids Part II: modeling

24 Ju, B., T Fan, and M Ma, Enhanced oil recovery by flooding with hydrophilic nanoparticles China Particuology, 2006 4(01): p 41-46

25 Ju, B and T Fan, Experimental study and mathematical model of nanoparticle transport in porous media Powder Technology, 2009 192(2): p 195-202

26 Shokrlu, Y.H and T Babadagli Transportation and interaction of nano and micro size metal particles injected to improve thermal recovery of heavy-oil in SPE Annual Technical Conference and Exhibition 2011 Society of Petroleum Engineers

27 Baez, J., et al Stabilization of interfacially-active-nanohybrids/polymer suspensions and transport through porous media in SPE Improved Oil Recovery Symposium 2012

28 Ersenkal, D.A., et al., Impact of dilution on the transport of poly (acrylic acid) supported magnetite nanoparticles in porous media Journal of contaminant hydrology, 2011

29 Miranda, C.R., L.S.d Lara, and B.C Tonetto Stability and mobility of functionalized silica nanoparticles for enhanced oil recovery applications in SPE International Oilfield Nanotechnology Conference and Exhibition 2012 Society of Petroleum Engineers

30 Bagaria, H.G., et al., Stabilization of iron oxide nanoparticles in high sodium and calcium brine at high temperatures with adsorbed sulfonated copolymers Langmuir,

31 Pu, W.-F., et al., Water-Soluble Core–Shell Hyperbranched Polymers for Enhanced Oil

Recovery Industrial & Engineering Chemistry Research, 2015 54(3): p 798-807

32 Dao Thi Hai Ha, H.L., Luong Van Tuyen, Synthesis of additive for reducing the melting temperature of crude oil with more content of parrafin at White Tiger in exploiting and transporting on ester substrate of poly-triethanolamine Petroleum Journal, 2013 5: p

33 Canh, N., Experimental planning 2011, Ho Chi Minh City - Vietnam National

34 Wang, L.-c., et al., Synthesis and Interfacial Activity of Nonyl Phenol Polyoxyethylene

Ether Carboxylate Journal of Dispersion Science and Technology, 2014 35(5): p 641-

35 Cornell, R.M and U Schwertmann, The iron oxides: structure, properties, reactions, occurrences and uses 2006: John Wiley & Sons

36 Nguyen, T.P., et al., Synthesis of Polymer-Coated Magnetic Nanoparticles from Red Mud

Waste for Enhanced Oil Recovery in Offshore Reservoirs Journal of Electronic

37 Sheng, J., Modern chemical enhanced oil recovery: theory and practice 2010: Gulf

38 Lake, L.W., Enhanced oil recovery 1989: Prentice Hall

39 Nguyen Thi Ly, N.T.K., Pham Duy Khanh, Nguyen Phuong Tung, Facile procedure to synthesize ankylphenoxy polyethoxy carboxylate surfactants and survey the properties for enhanced oil recovery application Vietnam Journal of Chemistry, 2015 253(6e1): p

APPENDIX A.1 Pictures of the equipments and instruments

Figure A.1: Ultrasonic machine - Powersonic 603 Hwashin Technology

Figure A.2: Viscosity machine – Brookfield DV-III Ultra, USA

Figure A.3: Drying/Oven – Shellap USA

Figure A.4: Interfacial tensiometer machine – TEMCO Inc Texas, USA

Figure A.5: Contact angle measurement machine – OCA 15EC with software SCA 20

Figure A.6: Transmission electronic microscope (TEM) - TEM JEM1010-JEOL

A.2 Original images in this thesis

Figure A.7: XRD pattern of MNPs from red mud

Figure A.8: XRD pattern of MNPs from red mud

Figure A.9: VSM curve of MNPs

Figure A.10: VSM curve of PMNPs

Figure A.11: IR spectra of NPA

Figure A.12: IR spectra of ClCH 2 COOH

Figure A.13: IR spectra of ClCH2COONa

Figure A.14: IR spectra of acetone

Figure A.15: IR spectra of NPC

Figure A.16: TGA diagram of copolymer AMPS-MMA

Figure A.17: TGA diagram of copolymer PMNPs

Figure A.18: TEM images of MNPs (10 images)

Figure A.19: Images of PMNPs (10 images)

A.3 Microsoft Excel for calculating th optimization the copolymer coated MNPs reaction

The orthogonal planning level 2 with k =1 and n 0 = 1

The number of experiments at the center n 0 n 0 = 1

The number of experiments including 1 experiment N = 9 at the center (2 k +2k+n0) The number of meaningful coefficients of regression equation L= 6 The number of additional experiments at the center to calculate s th n= 3

The core of experimental planning

2k experiments with level ±α, k-1 remaining paramenters

The center of experimental planning, all parameters with level 0

The coefficients in regression equations b 0 b 1 b 2 b 12 b 11 b 22

VERIFY THE COEFFICENT IN REGRESSION EQUATION ACCORDING TO STUDENT STANDARD Reappear variance s 2 th s 2 th s th

N N N ji i j l i i ji i i i i j N j l N jj N ji j l i ji i i i du th x y x x y x y b b b x x x x

   j jl ji th th th b N b N b N ji j l i ji i i i s s s s s s x x x x

NHẬN NHẬN NHẬN NHẬN NHẬN NHẬN

Look up t from TINV function t p (f 2 ) (p = 0,05, f 2 = n-1) 4.30265273

CHECK THE COMPATIBILITY BETWEEN REGRESSION EQUATION AND EXPERIMENTAL s 2 dư 1.103917593

F calculated (s 2 dư /s 2 th ) 7.088511939 F look up , F 1-p (f 1 ,f 2 )

A.5 Matlab 2012 for plotting 3D response surface of copolymer coated MNPs

A.6 ChemBio Draw Ultra 12.0 for drawing chemical formulas

A.7 Endnote X7 for citing the references

A.8 Google scholar for finding the references documents

Full name: Ngo Trung Kien Date of birth: January 1 st , 1991 Place of birth: Hiep Thanh Commune, Bac Lieu District, Bac Lieu Province Address: 15 Tan Trang, Ward 9, Tan Binh District, Ho Chi Minh City

Hard coating Section of Hoya Lens Vietnam Company - 20 Street No 4, Vietnam-Singapore Industrial Park II (VSIP II), Hoa Phu Ward, Thu Dau Mot District, Binh Duong Province (Ext: 225) Telephone: +84 985 8509 33

2009-2014: Got engineer degree on major Chemical Engineering at Ho Chi Minh City University of Technology

2014-2016: Pursued master degree on major Chemical Engineering at Ho Chi Minh City University of Technology

2014-2016: Worked as researcher at Institute of Applied Materials Science

2016-2017: Worked as team leader at Hoya Lens Vietnam

Journal of Elec Materi DOI 10.1007/s11664-016-4513-6

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

T P Nguyen, U T P Le, K T Ngo, K D Pham & L X Dinh

Metals & Materials Society This e-offprint is for personal use only and shall not be self- archived in electronic repositories If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website The link must be accompanied by the following text: "The final publication is available at link.springer.com”.

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

T.P NGUYEN, 1,2,5 U.T.P LE, 3 K.T NGO, 1,3 K.D PHAM, 1 and L.X DINH 4

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 Fe 3 O 4 magnetic nanoparticles (MNPs) Then, MNPs are encapsulated by a copolymer of me- thyl methacrylate and 2-acrylamido-2-methyl-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 electron 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

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% 2 Recovery 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

DOI: 10.1007/s11664-016-4513-6 Ó 2016 The Minerals, Metals & Materials Society

Author's personal copy nanotechnology development is poised to become a reality in the oil field 3,4

Numerous studies that involve EOR in the field of nanotechnology have recently been published SiO 2 nanoparticles (SiO 2 NPs) are commonly used as nano- materials because of their commercial availability A number of studies that focused on EOR from hard nanoparticles (NPs) engineering have been per- formed Li et al., 5–7 Moustafa et al., 8 and McElfresh et al 9,10 reported the possibility of using SiO 2 NPs dispersion fluids as a more robust wettability modifier than the soft ones Hunter et al 11 found that the effects of NPs, especially SiO 2 NPs, on reducing capil- lary pressure can be attributed to the specific attrac- tion of NPs to absorb onto the interfaces of water–oil– 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 SiO 2 NPs, 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.

Methyl methacrylate (MMA), sodium 2-acry- lamido-2-methyl-propanesulfonate (AMPS), ferrous chloride tetrahydrate (FeCl ặ4H O), oleic acid