J Polym Res (2015) 22:219 DOI 10.1007/s10965-015-0837-9
ORIGINAL PAPER
Iron oxide-based polymeric magnetic microspheres with a core shell structure: from controlled synthesis to demulsification applications Nisar Ali 1 & Zhang Baoliang 1 & Hepeng Zhang 1 & Wajed Zaman 2 & Sarmad Ali 1 & Zafar Ali 1 & Wei Li 1 & Qiuyu Zhang 1,3
Received: 22 May 2015 / Accepted: 10 September 2015 # Springer Science+Business Media Dordrecht 2015
Abstract In this paper, iron oxide poly(methylmethacrylateacrylicacid-divinylbenzene) Fe3O4@P(MMA-AA-DVB) magnetic core shell microspheres with chemical bonds between the inorganic core and the polymer shell in a narrow particle size were designed and synthesized. The surface morphology and magnetic properties of the magnetic Fe3O4@P(MMA-AA-DVB) nanoparticles formed were characterized using a laser particle size analyzer, transmission electron microscopy, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and thermogravimetric analysis. Fourier transform infrared spectrometer analysis indicates the presence of carboxylic group -COOH and Fe3O4 in the final Fe3O4@P(MMA-AA-DVB) core shell microspheres. The Fe3O4@P(MMA-AA-DVB) core shell microspheres possessed a characteristic of paramagnetic with the saturation magnetization value of about 7 to 9 emu/g determined by vibrating sample magnetometer (VSM). The experimental results show that Fe3O4@P(MMA-AA-DVB) magnetic core shell microspheres exhibit model interfacially active and demulsification properties. The results showed that the microspheres exhibited excellent magnetic and demulsification properties and can be recycled to use again.
* Qiuyu Zhang
[email protected] 1
Key Laboratory of Applied Physics and Chemistry in Space of Ministry of Education, School of Science, Northwestern Polytechnical University, Xi’an 710072, China
2
School of material science, Northwestern Polytechnical University, Xi’an 710072, China
3
School of Science, Northwestern Polytechnical University, Xi’an 710072, China
Keywords Core shell magnetic materials . Interfacial properties . Emulsion . Demulsification . Composite microspheres
Introduction Magnetic nanoparticles represent a potential class of materials that has varied applications, such as in magnetic resonance imaging and magnetic separation [1, 2]. Magnetic polymer microspheres constitute of advanced nano- or microsize composites, composed of a polymer and a magnetic inorganic material, and exhibit the dual characteristics of both. The magnetic material with super paramagnetic properties enables the particles to be convenient and quickly separated from a reacting solution for reuse in a magnetic field without resorting to high cost high energy operations such as centrifugation and filtration [3, 4]. Magnetic polymer particles, especially those encapsulating magnetite (Fe3O4), have attracted considerable research interest due to their broad potential applications, such as target drug delivery, hyperthermia therapy, separation or purification, and catalysis [5–7]. Magnetic separation is comparatively rapid and easy, cost effective, and highly efficient [8]. To integrate and/or modulate the functionality of Fe3O4 nanoparticles, the fabrication of versatile core shell magnetic composite nanoparticles by modifying polymer materials physically or chemically on the surface of Fe3O4 nanoparticles has been developed in recent years [9, 10]. Xu et al. demonstrated an effective method for synthesizing magnetic polymer submicrospheres with controllable size and shape and desirable interfacial chemical functionalities by surfactant-free seeded emulsion polymerization with Fe3O4 nanoparticles as the seeds [11]. Core shell nanoparticles have a core made of a material coated with another material on top of it. In
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applications of core shell, nanoparticles have major advantages over simple nanoparticles, leading to the improvement of properties such as (i) less cytotoxicity, (ii) increased dispersibility, and (iii) increased thermal and chemical stability [12]. Many polymerization techniques have been developed to prepare magnetic/polymer composite particles, such as conventional emulsion, soap-free emulsion, atomic transfer radical, mini-emulsion, and inverse emulsion [13]. The most frequently used approaches are physical/chemical adsorption, self-assembly, and surface coating of desired materials. [14–16] Most recently, research focus has been shifted to the synthesis of interfacially active magnetic nanoparticles (MNPs). The interfacial activity of magnetic composite nanoparticles allows them to assemble at the liquid/liquid interface [17]. Recently, there has been increasing interest in the use of magnetic particles to stabilize emulsions by so-called Pickering emulsion stabilization [18]. In many industrial applications, it is highly desirable to destabilize stable multiphase emulsions [19]. Here we have reported a novel and easy technique for the encapsulation of Fe3O4 nanoparticles via facile precipitation polymerization, and the monodispersed core shell (Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres were obtained with higher effective content of magnetite. Also, the prepared microspheres are interfacially active and magnetically responsive and are able to attach emulsified water droplets in an emulsion, leading to quick separation due to the magnetic response of the external magnetic field. The particle size and shell thickness can be readily tuned in a wide range by using different amounts of monomers. Our material gives a new route for demulsification in the petroleum industry because of controlled movement and enhanced coalescence of stable water droplets, aiming at a rapid and effective phase separation by an external magnetic field.
Experimental Materials Two different heavy crude oil samples were provided by Yang Chang oil field in Gansu province, China. Ferric chloride (FeCl3 ·6H2O), sodium acetate(NaAc), trisodium citrate (Na3Cit), and acrylic acid (AA) were purchased from Fu Chen Chemical Reagent, Tianjin, China. Divinylbenzene(DVB) and methylmethacrylate (MMA) were purchased from Fu Yu Chemical Reagent Co., Ltd., Tianjin, China. Ethylene glycol (EG) was purchased from Jin Shan Hua Shi Chengdu Chemical. Azobisisobutyronitrile (AIBN) was obtained from Sinopharm Chemical Reagent Co.,Ltd., Shanghai, China. All the chemicals used for synthesis were of analytical grade.
Preparation and surface modification of Fe3O4 microspheres Fe 3 O 4 magnetic nanoparticles were prepared by a solvothermal reduction method with some modifications [20]. The mixture of FeCl3, polyethylene glycol, sodium acetate, and sodium citrate was dispersed in different amounts (Table 1) in ethylene glycol (66.7 mL) under ultrasonic irradiation and vigorous magnetic stirring for 40 min until the FeCl3 ·6H2O was dissolved completely. The dispersion was then sealed in a Teflon-lined, stainless-steel autoclave, heated to 200 °C for 10 h, and then carefully cooled to room temperature. The black product was washed with deionized water three times and finally dried under vacuum at 50 °C to constant weight. For surface modification of Fe3O4 nanoparticles, the condensation reaction between the carboxylic groups on the surface of the Fe3O4 nanoparticles and allylamine was used to introduce vinyl groups. Briefly, Fe 3 O 4 nanoparticles (0.6 g), ammonia solution (2 to 3 drops), γ-methacryloyloxypropyltrimethoxysilane KH570 (2 mL) were mixed in ketone (80 mL) and then stirred at 50 °C for 12 h. The modified Fe3O4 nanoparticles were extensively washed with ethanol and then dried under vacuum at 50 °C. Synthesis and assembly of Fe3O4@P(MMA-AA-DVB) magnetic composite core-shell microspheres The distillation precipitation polymerization DPP was used w i t h s o m e m o d i f i c a t i o n s f o r t h e p re p a r a ti o n o f Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres. In a 250-mL, three-necked flask equipped with a mechanical stirrer, a reflux condenser, Fe3O4 magnetic nanoparticles, MMA, AA, DVB, and a radical initiator AIBN were mixed in different amounts (Table 2) with acetonitrile (80 mL). The flask was submerged in a water bath, and the reaction mixture was heated from ambient temperature to boiling state under stirring at 150 rpm, and maintained for 2 h. During the reaction, the bath temperature was set at 87 °C, higher than the boiling point of the reaction mixture to ensure violent boiling of the polymerization system. Then the solvent was distilled off the reaction system, and the reaction was stopped after 40 mL of acetonitrile was distilled from the reaction system within 2 h. After polymerization, the resulting Table 1 Data for the synthesis of Fe3O4 nanoparticles with different particle size Sample No.
FeCl3 (g)
NaCit (g)
NaAc (g)
01 02 03
2.69 2.69 2.69
0.48 0.68 0.84
4.33 4.33 4.33
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Table 2 Data for the synthesis of Fe3O4@P(MMA-AA-DVB) core shell microspheres with different core shell thickness Sample No.
Fe3O4 (g)
MMA (g)
AA (g)
DVB (g)
AIBN (mg)
01 02 03
0.05 0.05 0.05
0.06 0.34 0.68
0.09 0.16 0. 32
0.30 0.16 1.00
0.015 0.50 0.02
Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres were thoroughly washed with deionized water and ethanol. The final product was vacuum dried at room temperature. Emulsion preparation Stable emulsion was prepared from provided heavy crude oil (Table 3) as an oil phase (continuous phase) and distilled water as the water phase (dispersed phase). In a 500-mL beaker, crude oil and distilled water were mixed with continuous stirring at 25 °C and 2000 rpm until the two phases became completely homogeneous. These emulsions were then put at rest for 24 h at ambient temperature in order to achieve equilibrium. Different ratios (vol:vol) of emulsions were prepared, i.e., 3:7, 4:6, and 5:5.
Characterization Transmission electron microscopy TEM (JEOL JEM-3010 electron microscope) at an accelerating voltage of 200 kV was used to investigate the surface morphology of the prepared Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres. LS-13320 (Beckman Coulter) laser diffraction particle size analyzer was used to measure diameter and particle size distribution of the Fe3O4 magnetic nanoparticles and Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres. Fourier transform infrared spectra (FT-IR) were obtained using a Bruker Tensor 27 FTIR spectrometer over a potassium bromide pellet in the range of 4000 to 400 cm−1 in the reluctance mode. For thermal stability, TGA data were obtained at a heating rate of 10 K/min under a nitrogen atmosphere using a TA Instruments TGA-Q50. The mass change was detected at temperatures ranging from 50 to 800 °C [21]. The magnetic properties of the samples were studied in the dried state using a vibrating sample magnetometer(9600 VSM, BOJ Electronics, Inc., Troy, MI, USA) at room temperature. The crystalline structure of the inorganic part of the Fe3O4@P(MMA-AADVB) core shell microspheres was studied using an X-ray diffractometer (XRD-6000, Shimadzu Corporation). The JCPD Card XRD instruments were set for Cu K α (λ = 0.15406 nm) radiation at40 kV and 40 mA.
Demulsification The prepared magnetic composite demulsifiers were used in different amounts, i.e., 400, 600, 800 ppm, for 10 mL of prepared emulsion. The mixture was then placed on the external magnet in a water bath and heated to 80 °C for another 6 h. The amount of water separated was immediately measured at room temperature. Recycling Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres were reused many times for demulsification during the recycle test. The particles once used for demulsification were separated using an external magnet and washed with absolute ethanol and deionized water and dried by vacuum freeze drying. The resulting core shell microspheres were then used for the demulsification test again, which was considered as first recycle. Table 3
Physical parameters of crude oil samples
Sample No.
°API gravity
Total water%
Asphalt Content wt %
01 02
36.05 26.56
3.40 12.0
04.10 14.00
Results and discussions The synthesis of Fe3O4 was carried out in a solvothermal system by modifying reduction reactions between FeCl3 and ethylene glycol. A TEM image of Fe3O4 nanoparticles is presented in Fig. 1a, c, and e and size distribution in Fig. 1b, d, and f, which demonstrates that the Fe3O4 nanoparticles exhibit a spherical and narrow particle size distribution. Both the literature [22, 23] and our own experiment reveals that ethylene glycol plays an important role in Fe3O4 formation. Ethylene glycol has a strong ability as a reducing agent with a relatively high boiling point [24] and has been widely used to provide monodisperse Fe3O4 nanoparticles. The size and shape of the Fe 3 O 4 nanoparticles was controlled by using different amounts of trisodium citrate (Na3Cit) [25]. Na3Cit has a strong affinity to Fe+3 ions, which favors the attachment of citrate groups on the surface of the magnetite nanoparticles, and prevents them from aggregating into a single large particle. When the initial Na3Cit concentration is increased from 0.48 to 0.84 g, the size of the obtained Fe3O4 particles decreases from 250 nm to about 30 nm. Fig. 1a, b, c, d, e, and f, indicating that the higher Na3Cit concentration can yield magnetite particles with smaller size [26]. Inorganic nanoparticles have high surface polarity and show the problem of low dispersion stability in organic
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Fig. 1 TEM images (a, c, and e) showing magnetic nanoparticles and (b, d, and f) are particle size distribution
solvents. This problem was overcome by treating the surface of inorganic nanoparticles with some good organic compounds. Recently, the considering encapsulation of inorganic nanoparticles in a polymer matrix from a colloidal aspect is of high importance in various application domains [27]. Generally, the encapsulation of inorganic (Fe3O4) nanoparticles in a
polymer matrix leads to phase separation due to the incompatibility between organic and inorganic materials [22]. To increase the compatibility to magnetite (Fe3O4) with the polymer matrix and to increase the dispersion homogeneity further morphological investigations of Fe3O4@P(MMAAA-DVB), magnetic composite core shell microspheres were
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created on the coated nanoparticle formulations after growing a polymer layer. This depends on the nature of the functional groups present on the surface of Fe3O4 nanoparticles. The TEM images of Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres are shown in Fig. 2a, c, and e and particle size distribution in Fig. 2b, d, and f, which demonstrate that Fe3O4@P(MMA-AA-DVB) has a spherical morphology with good monodispersity. For core shell structure, Fe3O4 microspheres were dispersed in a solvent, and with an increase in temperature, the precipitation polymerization of MMA, AA, and DVB takes place on the surface of the Fe3O4 nanoparticles. We assume the binding mechanism of P(MMA-AA-DVB) onto the magnetite surface of magnetic nanoparticles is through precipitation polymerization. A possible explanation for the surface polymerization is given as follows. The C=C double bonds present on the surface of magnetic nanoparticles can copolymerize with the active oligomers developed in the polymerization system. Also, carboxylic groups on the surface of the magnetic nanoparticles can form hydrogen bonds with the carboxyl of monomers, such as MMA or AA, leading to adsorbed surface C=C double bonds that may function similar to those preliminarily fixed on the surface via covalent coupling. Thus, a continuous P(MMA-AA-DVB) polymer layer would be formed on the surface of Fe3O4 nanoparticles. For the design and preparation of any core shell structure, the shell thickness should be readily controlled to meet different requirements. As for the methods for constructing core shell particles, the thickness of polymer shells is tailored mainly by changing the monomer dosage. We can likewise control the thickness of the P(MMA-AA-DVB) layer coated on the Fe3O4 by changing the amount of monomer added in the polymerization system, quite similar to the DPP method reported previously [28–30]. By increasing the amount of monomers (Table 2), the polymer graft percentage of the resulting F3O4@P(MMA-AA-DVB) particles increased gradually from 4.4 to 20.2 %, and 40 %, respectively. The thickness of the P(MMA-AA-DVB) shells increased from ~10 to finally~50 nm, as shown in Fig. 2a, c, and e. All of the resulting magnetic composite microspheres show selfassembly behavior with a definite core shell structure and show nearly as monodisperse as the original magnetic nanoparticle seeds. Figure 3a explains the FT-IR spectra of bear magnetic microspheres and (b) surface modified magnetic microspheres. There is main strong peak centered at 560 cm−1 in the case of FT-IR spectra (a), which indicates the presence of an iron oxide (FeO) component in the magnetic medium. This finding demonstrates that the prepared nanoparticles are iron oxide in the sample. In the FT-IR spectra (b), there is a medium peak at about 2925 cm−1 , which proves the attachment of vinyl groups and confirms the surface modification of the magnetic nanoparticles. This method for coupling of the carbon–carbon
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double bond (C=C) to the magnetite surface is simple and will not result in the decrease of the magnetic content in the modified microspheres. The presence of -COOH groups on the surface of the core shell magnetic composite microspheres is confirmed by FT/IR spectra shown in Fig. 3c. The main carboxyl band centered at 1670.90 cm − 1 (C = O) and 1452.77 cm−1 (C–O), 904.68 cm−1 (OH), 1601.32 cm−1 (phenyl ring) indicates the presence of COOH groups on the surfaces of the microspheres. The characteristic medium absorption peaks at 2923 cm−1 and very small peak at 2852 cm−1 in Fig. 3c can be attributed to the symmetric and antisymmetric stretching vibrations of -C–H in methyl and methylene of P(MMA-AA-DVB), which exists in the outer shell of magnetic composite microspheres. There is a large absorption band centered at 3400 cm−1, the typical resonance frequency for –OH functional group of moisture (water) in the sample. The Fe3O4 strong absorbing peak at 564.15 cm−1 confirms that these magnetic microspheres are located mainly in the interior part. The locations of the wave number are almost same for the nonmagnetic microspheres and the magnetic part, which suggests that the polymer coating is probably mainly mechanically and physically formed and not chemically bonded on the surface of the microspheres [31]. Otherwise, the vibration absorbing bands will disappear, shift, or be transferred. XRD study was done to investigate the structure of Fe3O4 magnetic microspheres (Fig. 4a), surface modified Fe3O4 (Fig. 4b), and Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres (Fig. 4c). Figure 4 displays six characteristic diffraction peaks (2θ=30.21°, 35.61°, 43.31°, 53.81°, 57.3,1° and 63.01°) corresponding to the (220), (311), (400), (422), (511), and (440) reflections of inverse spinel Fe3O4 can be observed clearly in all three curves (Fig. 4a, b, and c). From the figure it can be observed clearly that peaks appeared in the XRD pattern of Fe3O4@P(MMAAA-DVB) magnetic composite core shell microspheres, owing to Fe3O4 nanoparticles. The enhancive diffraction peaks agree well with inverse spinel Fe3O4 (JCPD 19–0629) showing that the XRD patterns of the synthesized Fe3O4@P(MMA-AA-DVB) matched well with those of the pure magnetite (Fe3O4). No other peaks have been detected in the XRD pattern, indicating the high purity of the Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres. Therefore, the magnetic part of the magnetic core shell microspheres is Fe3O4. The synthesized Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres shows proper core shell structure with superior magnetic properties with a saturation magnetizationvalue of about 9.00 emu/g (Figs. 3, 4, and 5). Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres in 0.007 g samples were used for VSM analysis (Fig. 5). Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres have the ability to produce a magnetic
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particle Size/um Fig. 2 TEM images (a, c, and e) showing Fe3O4@P(MMA-AA-DVB) core shell microspheres, while (b, d, and f) are particale size distribution
field with a low mass and should be stable against the external effects that would demagnetize the field [32]. In addition, no
pronounced hysteresis loop was observed. The effective content of magnetite in the final Fe3O4@P(MMA-AA-DVB)
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Fig. 3 FT-IR spectra of (a) bare magnetic microspheres, (b) surface modified magnetic microspheres, (c) Fe3O4@P(MMA-AA-DVB) core shell microspheres
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magnetic composite core shell microspheres is due to the purification of the core shell microspheres with an external magnet to remove the neat polymer microspheres and impurities. The TGA curves are presented in Fig. 6 and demonstrate that the mass of magnetite in the Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres was as high as 40 wt.% after the neat polymer microspheres were completely decomposed at high temperature. It was observed in the TGA curve that Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres show three main weight losses, but this loss in mass is different in all the three samples because of the different amounts of monomers used. The weight loss at about 150 °C and above is because of the evaporation of the adsorbed water or solvent, and between 320 and 370 °C is due to the pyrolysis of the polymer component. Between 370 and 470 °C, the weight loss is attributed to further self condensation of iron hydroxide. This difference is because of the increase in the polymer shell thickness on the surface of magnetite microspheres, hence the need for more heat to be decomposed. Petroleum naphtha and water mixture were used in a test vial in order to study the interfacial properties of Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres (Fig. 7a and b). Fe3O4@P(MMA-AA-DVB) was added to the bottle (a). It was observed that
Fig. 5 Magnetization curve of Fe3O4@P(MMA-AA-DVB) magnetic core shell microspheres
Fe3O4@P(MMA-AA-DVB) microspheres move to the interface quickly. After 30 min it was observed that Fe3O4@P(MMA-AA-DVB) microspheres were completely moved to the petroleum naphtha/water interface without penetrating to the water or naphtha phases as shown in Fig. 7b. It is clear from the experiment that Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres show proper interfacial properties. Different amount in ppm i.e., 400, 600, 800 ppm, of Fe3O 4@P(MMA-AA-DVB) magnetic core shell microspheres was used as showed in Fig. 8a, image (a1, 2, and 3) and the graph (b). The results are shown against 400, 600, and 800 ppm at 80 °C and 6 h for the 10 mL of 6:4 ratio heavy crude oil and water emulsion. During the separation process magnetic core shell microspheres stay at the oil/water interface due to the interfacially active nature. The magnetic properties of Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres play important role in breaking stable emu ls io n. In the cu rren t s tudy c once ntration of Fe 3 O 4 @P(MMA-AA-DVB as high as 800 ppm shows
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Fig. 6 TGA curve of Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres
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excellent demulsification of more than 95 % separation of water in 6 h time. Figures 8c1 and 2 and graph d explain the phenomenon of interfacial activity and demulsification efficiency for different crude oils with different oAPI, i.e., c1 (36.05 °API) and c2 (26.56 °API), respectively. An optimized amount of 800 ppm of the magnetic core shell microspheres were dosed to 10 mL of 7:3 ratio crude oil and water emulsion. It is clear from Fig. 7 c1 that Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres show high coalescence efficiency with 800 ppm at 80 °C in 6 h and show separation from c1 (95 %), but also in the case of c2 (92 %). This is attributed to the added Fe3O4@P(MMA-AA-DVB) magnetic
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Fig. 7 Image (a) showing naphtha and water with Fe3O4@P(MMA-ADVB) and (b) after 30 min
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Fig. 8 Image (a) 1, 2, and 3, showing demulsification efficiency of Fe3O4@P(MMA-AA-DVB) at 400, 600, and 800 ppm and (b) is the graphical representation. Image (c1 and 2) showing demulsification of crude with different oAPI while (d) is the graphical representation
Table 4 Interfacial tension of crude oil and water before and after the addition of Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres Sample No.
°API gravity
Density of crude oil g/cm
Density of water @ 25 °C (g/cm3)
Interfacial tension of crude oil and water (mN/m)
Interfacial tension of oil and water with Fe3O4@P(MMA-AA-DVB) (mN/m)
01 02
36.05 26.56
0.885 0.901
0.997 0.997
24.55 33.76
21.50 30.10
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Interfacial tension mN/m
35 30
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Interfacial tension without magnetic composite microspheres interfacial tension with microspheres
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Fig. 9 The effect of Fe3O4@P(MMA-AA-DVB) as demulsifiers on interfacial tensions between the heavy crude oil and water
composite core shell microspheres that show high interfacial activity and magnetic responsivity and the tagged water droplets move towards the bottom of the test vial, leading to a rapid separation of water from the oil phase in less than 6 h. The results show rapid separation of water droplets by an external magnet. Such rapid separation implies that these novel particles have potential application as high efficiency demulsifiers in the field of oil and gas industry. Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres have a strong effect on the surface tension of emulsion and interfacial tension of emulsion before and after the demulsification. A ZL3000 automatic interfacial tension meter was used to measure the interfacial tension between crude oil and deionized water. Prior to each measurement, a platinum ring was properly cleaned with flame. Crude oil/water interfacial tension was calculated both in the absence and presence of Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres at 25 °C. Without Fe3O4@P(MMA-AA-DVB) microspheres, the interfacial tension was about 24.55 for sample 01 (36.05 °API) and 33.76 mN/m for sample 02 (26.56 °API), respectively, which decreased to 21.50 mN/m for sample 01 and 30.10 mN/m for sample 02 after the addition of Fe3O4@P(MMA-AA-DVB). Table 4 and Fig. 9 explain the decrease in the interfacial tension before and after the addition of magnetic composite core shell microspheres into crude oil and water interface, which indicate the adsorption of Fe3O4@P(MMA-AA-DVB) to the water/crude oil interface. Table 5 and Fig. 10 explain the surface tension data of emulsion before and after the separation of water which shows a considerable decrease is observed in the
Table 5 Surface tension of crude oil /water emulsion and oil after demulsification
surface tension after the demulsification. This decrease in the surface tension indicates that magnetic composite core shell microspheres comprised of both interfacially active P(MMAAA-DVB) and magnetically responsive iron oxide. Decrease in the interfacial tension and interfacial viscosity increase the demulsification of crude oil and water emulsion [33]. Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres were found to break stable emulsion and have the ability to be reused after the demulsification process. The recycle tests of Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres were performed for five cycles at 80 °C and 6 h. Figure 11a and graph b show the demulsification efficiency after each cycle. Results show that the Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres have constant and excellent demulsification efficiency in the first five cycles with about 95 % removal of emulsified water from the heavy crude oil and water emulsion. Recycling reduces the demulsifier price and economizes its use in the oil and gas industry. Formation and application mechanism Step I: Fig. 12 shows the formation mechanism of the Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres. In the first stage of this process, the Fe3O4 magnetic microspheres were synthesized by solvothermal reduction of FeCl3 with ethylene glycol as both solvent and reducing agent, sodium acetate as an alkali source, and trisodium citrate as an electrostatic stabilizer. For surface modification of Fe3O4 microspheres, the condensation reaction between the carboxylic groups on the surface of the Fe3O4 microspheres and γ-methacryloyloxypropyltrimethoxysilane (KH-570) was used to introduce vinyl groups. The formation of P(MMAAA-DVB) shell on the surface of magnetic microspheres is through precipitation polymerization. A possible explanation of the surface polymerization is as follows. The C=C double bonds present on the surface of magnetic nanoparticle, can copolymerize with the active oligomers developed in the polymerization system. Also, with carboxylic groups on the surface of magnetic microspheres, hydrogen bonds can form with the carboxyl of the monomer such as MMA or AA and lead to adsorbed surface C=C double bonds, which may function similar to those preliminarily fixed on the surface via covalent coupling. Thus, a continuous P(MMA-AA-DVB) polymer layer would be formed on the surface of Fe3O4 microspheres.
Sample No.
°API gravity
Density of oil g/cm
Density of water @ 25 °C (g/cm3)
Surface tension of emulsion (mN/m)
Surface tension of crude oil after demulsification (mN/m)
01 02
36.05 26.56
0.885 0.901
0.997 0.997
35.40 51.37
22.73 23.00
219
Surface tension of emulsion Surface tension after demulsification
50
surface tension mN/m
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Sample number
Fig. 10 The effect of Fe3O4@P(MMA-AA-DVB) as a demulsifier on surface tension between the heavy crude oil and water
Step II. The structure of P(MMA-AA-DVB) block copolymer bears two types of functional groups: one is the carboxylic group, which is hydrophilic in nature, and the alkyl group, which is hydrophobic in nature. Both of these
hydrophilic and hydrophobic groups make the P(MMAAA-DVB) block copolymer amphiphilic, which move and stay at the oil–water interface. At the interface, Fe3O4@P(MMA-AA-DVB) capture the strong layer of natural surfactants (asphaltenes and resins) and reduce the interfacial viscosity and interfacial tension of the emulsion, which leads to the easy coalescence of emulsified water droplets. The interfacial activity of Fe3O4@P(MMA-AADVB) allows them to attach to the emulsified water droplets in emulsions, while the strong magnetic response of Fe3O4 provides effective separation of the emulsified water droplets at 80 °C and 6 h by an external magnet. The results show that Fe3O4@P(MMA-AA-DVB) remain efficient and chemically stable after each recycling test. Indeed, this is the first report on the synthesis of magnetic composite core shell microspheres with magnetic Fe3O4 and an interfacially active polymer. Thus, Fe3O4@P(MMA-AA-DVB) are anticipated to give a new idea of demulsification in the petroleum industry and engineering practices.
(a)
(b)
1
2
4
3
5
Fig. 11 Image (a) showing the five recycling data of Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres for the demulsification in 10 mL emulsion at 80 °C and 6 h and (b) is the graphical representation
S tep I: Synthesis of M agnetic C ore shell m icrospheres
Fe 3 O 4 + MM A +A A +D V B
Po ly merizatio n
KP S/
O O OHC OH O C
C OH OH O C Magnetite C O OH HO C C O H O CH O O
Step II: Application of Fe3O4@P(MMA-AA-DVB) as demulsif ier Mag
Addition of composite m icrospheres
Mag Mag
Mag
Mag
Ma g
Ma g
Mag
Solvothermal pol yme rizat ion Mag Ma g
Mag
Fe 3O 4 core
O Recy cled Fe 3 O 4 @P(M MA-AA-DVB)
Ma g
Demulsif ication
M ag M ag
M ag Mag
Ma g
c rude oil
M ag
M ag Mag Mag
Fe+ 3 /200 o C/10 h
Mag
Mag
Mag Mag
P(MMA-AA-DVB) shell
Mag
water
External Magnet Fig. 12 Structure and formation mechanism of Fe3O4@P(MMA-AA-DVB) core shell magnetic microspheres
Crude oil af ter seperation of water
J Polym Res (2015) 22:219
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Conclusion
8.
Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres, was designed and synthesized with surface properties and demulsification efficiency by solvothermal process followed by precipitation polymerization methos. The TEM image confirms the growth of interfacially active P(MMA-AA-DVB) polymer on the surface of Fe3O4 magnetite. The magnetic response of Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres was determined by VSM at room temperature. The interfacial activity of Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres allows them to effectively tag the emulsified water droplets in crude oil and water emulsions, while the strong magnetic response of Fe3O4 provides effective separation at 80 °C and 6 h by an external hand magnet. Furthermore, the strong magnetic response of Fe3O4@P(MMA-AADVB) magnetic composite core shell microspheres at the interface enhances the coalescence of emulsified water droplets. Recycling test results show that after recycling, Fe3O4@P(MMA-AA-DVB) magnetic composite core shell microspheres remain efficient and chemically stable up to five cycles. Indeed, this is the first report on the synthesis of magnetic composite core shell microspheres with magnetic Fe3O4 and an interfacially active polymer P(MMA-AA-DVB, which gives a new route to the separation of water from oil/water emulsion in the petroleum industry.
9.
Acknowledgments The authors are grateful for the financial support provided by the National Natural Science Foundation of China (No. 51173146), basic research fund of Northwestern Polytechnical University (3102014JCQ01094, 3102014ZD).
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