Experimental Investigation of Fe3O4-Chitosan Nanocomposite as a Nano-Demulsifier for Water in Crude Oil Separation
Zahra Hasanshahi
1
(
NanoChemical Eng. Dep., Faculty of Advanced Technologies, Shiraz University
)
Payam Parvasi
2
(
Department of Chemical, Petroleum and Gas Engineering, Shiraz University of Technology
)
Mohamad Mahdi Zerafat
3
(
Faculty of Advanced Technologies, Nano Chemical Engineering Department, Shiraz University, Shiraz, Iran
)
Samad Sabbaghi
4
(
Nano Chem. Eng. Dep.
Faculty of Advanced Technologies
Shiraz University
)
Keywords:
Abstract :
Experimental Investigation of Fe3O4-Chitosan Nanocomposite as a Nano-Demulsifier for Water in Crude Oil Separation
Abstract
Nowadays chemical and electrostatic demulsification techniques are typically used to separate water-in-crude-oil emulsions. The need to improve demulsification techniques has led to the use of various additives among which nanoparticles have emerged as a novel alternative. Most of the exploited crude oils exist in an emulsion state, where may cause serious problems during processing. Chemical demulsifiers, bottle tests, and electrostatic desalters are commonly used to separate water from crude oil emulsions but there are some issues involved with these methods. Therefore, using new technologies like nanotechnology can help improve the desalting process. First, Fe3O4 and Fe3O4-chitosan nanocomposite were synthesized via co-precipitation method. Fe3O4-chitosan nanoparticles were characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The results showed that ultrafine Fe3O4 nanoparticles were prepared and coated by chitosan. In this study, Fe3O4 and Fe3O4-chitosan nanocomposite were utilized to improve emulsion destabilization. The effect of different parameters on the separation performance was studied and the best conditions were determined. The results showed that the application of certain nanostructures in crude oil emulsions improves the performance of demulsification up to 86% and decreases the amount of demulsifier consumption in the desalting process.
Keywords: Crude oil; Demulsifier; Magnetic Nanoparticles; Fe3O4-chitosan Nanocomposite
1. Introduction
Crude oil is mainly produced in the form of stable water-in-oil emulsions [1]. Water droplets in the crude oil flowing through transportation lines and refinery processing equipment entail certain standards to prevent corrosion and catalyst deactivation as a result of high-temperature hydrolysis of water producing an acidic environment. Another reason for corrosion is the inclusion of salts such as MgCl2, NaCl and CaCl2 in the emulsified water which makes demulsification necessary as an inevitable part of primary crude oil processing. The water content of crude oil is often < 50 % with a salt content of ~ 400-200000 ppm, bringing about serious problems during crude oil refining. The aim of desalting is generally the reduction of water content down to 10 lb per barrel (10 PTB) [2]. Besides, the emulsified oil-in-water waste is an environmental pollutant, which needs to be discharged to the environment with standard properties [3].
Interfacially-active materials either naturally present in crude oil [4] (asphaltenes, resins and solid particles like clays and waxes) or intentionally added for enhanced oil recovery purposes (surfactant flooding, ASP flooding, etc.) lead to the stabilization of water-in-oil and oil-in-water emulsions by forming active and resilient interfacial layers [1,3]. Asphaltenes are micro-colloidal suspensions in crude oil with a ~ 3 nm diameter, resulting in the stabilization of emulsions through interaction with resins (Pickering emulsions) [5]. Studies show that suspended solids prevent the thinning of film layer by enhancing its resilience. However, inorganic salts are believed to reduce emulsion stability [6].
Various parameters such as water content [7], emulsifier type and concentration [8], mixing rate, temperature [7], viscosity of the continuous phase and surface tension [7] play role in emulsion stability. Electrical and steric stabilization mechanisms are also considered to be effective in emulsion stability [9].
Several techniques have been proposed for emulsion breaking such as flotation [10], chemical coagulation [11], chemical-electrochemical demulsification [12], membrane separation [13], microwave demulsification [14,15], membrane separation [16,17], thermal demuslification, hydro-cyclone separation [18], ultra-sonication [19] and nano-enhanced demulsification [20]. Among these, chemical demulsification is considered as the most prevalent desalting technique currently applied. Demulsifiers possess complicated and harmful components for the environment and researchers have investigated their replacement with more efficient and/or less harmful alternatives. Currently, many chemical demulsifiers are available [21] competitive characters of which include simple, fast oil-water separation, eco-friendliness, and cost-effectiveness.
Demulsifiers are expected to be adsorbed at the oil-water interface to break the stable water-oil interface. This breakdown occurs by replacing emulsion stabilizers which alter surface properties such as interfacial tension, mechanical strength, elasticity, and interfacial film thickness, resulting in enhanced coalescence. Most demulsifiers are non-ionic surfactants with the main components as polypropylene oxide (PPO) as the hydrophobic part and polyethylene oxide (PEO) groups as the hydrophilic part. Alkylphenol ethers, fatty amides, fatty esters and ethoxylated phenols are also used for demulsification.
Recently, new technologies have been successfully studied and tested in laboratory for demulsification of water-in-oil emulsions such as microwave and ultrasonic technologies. In the presence of a microwave field, emulsion temperature is increased resulting in the reduction of viscosity and zeta potential of the water-oil suspension. Microwave radiation causes molecular rotation. So, electrical double bonds between water and oil molecules are destroyed resulting in the reduction of zeta potential and increasing gravitational separation efficiency. Also, in the ultrasonic field, primary and secondary acoustic forces are applied to water emulsions. Due to primary acoustic forces, water droplets move to the pressure nodes of standing ultrasonic wave. Further coalescence of droplets is based on secondary inter-droplet acoustic forces [22, 23].
Khajehesamedini et al. (2018) designed an ultrasound transducer to reduce the consumption of chemical demulsifiers. They examined the effect of ultrasonic radiation time, ultrasonic intensity, and the water content. The results showed that by choosing the appropriate field time duration and intensity, the use of chemical suspensions can be reduced up to 50%. They also proposed a population balance model for the interpretation of experimental data and the proposed model was in good agreement with the experimental results [24].
Another novel technology is the use of nanoparticles [25-29]. Various nanoparticles are proposed as alternative additives for the improvement of demulsifier performance. Nanoparticles can accumulate at the water-oil interfaces, leading to the improvement of demulsification efficiency. Among suggested nanoparticles, magnetic nanoparticles (MNPs) can be regained by an external magnetic field and reused [30]. Magnetic core-shell structures are generally used using magnetite (Fe3O4) as the magnetic core due to its low cytotoxicity and biocompatibility modified by various active materials (surfactants or polymers) to improve dispersion characters [30, 31]. Magnetic nanoparticles are synthesized by different techniques such as the co-precipitation and thermal decomposition [32, 33], microemulsion, hydrothermal technique and sono-chemical synthesis [34]. Various magnetic core-shell structures are proposed and utilized for demulsification improvement. Peng et al. (2012) reported a magnetic demulsifier, ethyl cellulose-grafted nano-Fe3O4, to separate water droplets from heavy naphtha and diluted bitumen bulks. Lemos et al. [31] synthesized a magnetic amphiphilic composite to remove biodiesel droplets from water. Li et al. [3] used magnetite nanoparticles to enhance the performance of a polyether polyol demulsifier for separating oil in water emulsion. In other study, single-layer oleic acid-coated magnetite (Fe3O4-OA) nanoparticles have been synthesized and tested for demulsificaion of cyclohexane-in-water nano-emulsions (CH-NEs) [35]. These nanoparticles were used for removing oil nano-emulsions from water while evaluating the technical feasibility of a magnetic demulsifier for treatment of extracted crude oil and oily wastewater from oilfields. Nikkhah et al. (2015), suggested nano-titania as an improved chemical demulsifier for water-in-oil emulsions. In their study, sol-gel method was used to synthesize nano-titania particles. The results show that this demulsifier can improve demulsification efficiency by 90 % besides reducing the time taken for water and salt separation [36].
These studies reveal the potential of interfacially-active MNPs in water-oil multiphase separation. However, detailed properties of the protective film around water particles are essential for understanding the mechanisms involved, besides the fundamental knowledge of the chemistry of interacting active components in crude oil. In this study, Fe3O4-chitosan nanocomposite particles are synthesized and their ability to destabilize water-in-oil emulsions is investigated. Based on the literature review performed, this material has not been investigated previously as crude oil demulsification agent.
2. Experimental
2.1. Materials and Methods
FeCl2.4H2O, FeCl3.6H2O (Merck; with > 98% purity) as Fe sources and chitosan as polymer stabilizer were used without further purification. Also, HCl and NaOH for pH adjustment were supplied by Merck Co.
2.2. Preparation of water in crude oil emulsion
Crude oil was supplied by the GACHSARAN oil field with an industrial chemical demulsifier (FD 7250). Characterization of crude oil is given in Table 1. Water-in-oil emulsions were prepared by adding 5 Vol. % and 10 Vol. % water to crude oil at 50ºC and mixed perfectly. The prepared emulsions were stable for about a week without significant phase separation.
Table 1
2.3. Preparation of the Fe3O4-Chitosan Nanocomposite
Fe3O4 nanoparticles were synthesized by the co-precipitation technique using FeCl2 and FeCl3 as Fe sources. 2 mmol of FeCl3.6H2O and 1 mmol of FeCl2.4H2O were dissolved in 100 ml HCl at pH = 2 until a homogeneous solution was obtained. Chemical precipitation was induced by gradual addition of a 0.5 mM NaOH solution to the mixture. Vigorous mixing for 30 min at 80 0C was necessary for precipitation. Centrifugation was used to separate the precipitates. Then, they were washed with water and ethanol so that side products and impurities were removed. The final product was kept in the oven and dried at 60 0C [37].
In order to produce Chitosan coating on the as-synthesized particles, a 0.01 V/V acetic acid solution was prepared (1 cc acetic acid in 100 cc water) and then 1 g of chitosan was added and dissolved. 1 g of the as-synthesized Fe3O4 nanoparticles were dispersed in 100 ml distilled water using ultrasonication and vigorously mixed at 50 0C. The Chitosan solution was added during a 30 min period. Then magnetic separation was applied to collect the final product, washed with ethanol and water and finally dried in an oven at 500C. The procedure for the synthesis of Fe3O4 nanoparticles is summarized in Figure 1.
Figure 1
2.4. Bottle Test Procedure
Bottle test was employed to evaluate the performance of the as-synthesized nanocomposite particles for demulsification. In the first step, crude oil and freshwater (5 vol. % and 10 vol. %) were mixed perfectly with an electric mixer to dissolve more salt crystals in the added water, and the process water from oil separation is performed with a higher efficiency. Then, the industrial demulsifier was added via a micro-syringe and nanoparticles were added through sonication during 5 minutes. After performing the above steps, the sample was shacked and poured in a graduated cylinder. Then the graduated cylinder was placed in an electric oven and heated to 70°C. Eventually, after 12 hours the demulsification efficiency (DE) was calculated by the following equation:
| (1) |
Where, V is the the separated water volume and V0 the initial water volume [17].
2.4.1. Preparation of samples
Bottle test was performed on four different samples. Namely: (1) a sample with 80 ppm of demulsifier (the standard demulsifier concentration in desalting units) named blank80;
(2) A sample with 40 ppm chemical demulsifier named blank40. Both samples were considered as reference samples and were prepared without addition of nanocomposite particles. (3, 4) Two other samples containing Fe3O4 and Fe3O4-chitosan, with equal proportions of NP and blank40.
3. Results and Discussion
3.1. Particle Size Analysis (PSA)
Figure 2 shows the PSA of Fe3O4 nanoparticles and Fe3O4-chitosan nanocomposite using HORIBA LB-550 equipment. Fe3O4 nanoparticles show a narrow PSD with an average value of 5 nm in diameter which was enhanced to ~ 90 nm upon coating by chitosan. TEM results from a previous study performed by the authors reveal that the as-produced nanoparticles have a single magnetite nanoparticle covered by a chitosan shell configuration [38]; thus the difference between the graphs can be attributed to the thickness of the chitosan shell.
Figure 2-a
Figure 2-b
3.2. FTIR Analysis
To realize the binding, FTIR spectra of chitosan-coated Fe3O4 nanocomposite is examined as shown in Fig. 3. The Fe-O peak can be observed at the 580 cm-1 wavelength which is prevalent for other mineral bonds also and observed in other studies in the same range [39]. Other peaks are also observed in the FTIR for Chitosan which confirms the coating of Fe3O4 with chitosan. The wide peak at 3600 cm-1 is attributed to the stretching vibration of the amine (–NH2) and hydroxyl (–OH) groups. The absorption bands at 1883 cm-1 1586 cm-1 are attributed to –C–O stretching of primary alcoholic group in chitosan. These peaks indicate the Fe bond to the NH2 group of chitosan [32]. The results indicate that chitosan was coated on Fe3O4 nanoparticles successfully. Due to the negative surface charge of iron oxide an affinity exists toward chitosan and coating can occur by the electrostatic interaction [39].
Figure 3
3.3. XRD Analysis
Figure 4 shows the XRD pattern for Fe3O4-chitosan nanocomposite. As expected, six peaks are observed at (220), (311), (040), (422), (511), and (440) which are also confirmed by other synthesis results in the literature [40].
The peak before 2Ө = 200 indicates that Fe3O4 nanoparticles were successfully coated by amorphous chitosan.
Figure 4
3.4. Parameters affecting the demulsification efficiency
Demulsification efficiency is related to many parameters such as adding freshwater, settling time, temperature, nanoparticle dose and mixing time. The main parameters have been studied in this paper.
3.4.1. Freshwater injection
Bottle tests were performed with 5% and 10% water injection to similar samples to investigate the effect of water addition on the demulsification efficiency. The results (Figure 5) show that when 10 wt. % freshwater is added, demulsification performance is not enhanced by the addition of NPs, although demulsifier consumption is reduced by 50%. So, it is affordable to use 5 wt. % freshwater to achieve the highest efficiency.
Figure 5
3.4.2. Effect of Settling Time
The effect of settling time on desalting efficiency is shown in Figure 6. It is observed that demulsification efficiency is increased by increasing the contact time. Although, the efficiency does not clearly change after 12 h. As can be seen in the figure, Fe3O4-chitosan nanoparticles have been able to increase the separation efficiency of chemical demulsifier by 15% compared to Fe3O4 nanoparticles.
Figure 6
3.4.3. Effect of Mixing Time
Mixing time is varied in the 0-7 min range and according to the results, if other parameters are kept constant, 3 min of vigorous mixing can result in the highest demulsification efficiency. Shorter mixing periods are insufficient to stabilize the water-oil mixture. Longer mixing times lead to very stable emulsions which are hard to separate (Figure 7). Also, longer mixing times usually causes breakage of water and form smaller droplets, which is not desirable in the crude oil desalting process.
Figure 7
3.4.4. Effect of Nanoparticle Dosage
The effect of NP dose is shown in Figure 8. This figure shows that there is an optimum value when adding NP at 0.004 wt. %. At higher NP contents, NP interactions are increased which reduce their interfacial activity, leading to lower demulsification efficiencies.
Figure 8
Figure 9 shows demulsification efficiency at the best conditions by the bottle test method. According to this figure, addition of nanocomposite particles results in a 10 % enhancement of the demulsifier efficiency by reducing the demulsifier consumption up to 50%.
Figure 9
3.5. Electrostatic Separation
In this study, the electrostatic desalination pilot was used to check the accuracy of the bottle test results under crude oil desalting plant operating conditions. As shown in Figure 10, the system consists of two grid electrodes. The upper electrode is an earth electrode while the lower one is a high voltage grid electrode. The distance between the electrodes and device voltage can be adjusted so that the electric field can be set based on the emulsion type.
In the electrostatic test, a certain volume of crude oil is poured into a beaker and heated by a plate magnetic stirrer. Then, nano-particle, chemical demulsifier and freshwater were added respectively and perfectly mixed with the emulsion. Afterward, an electrical field of 1000 v/cm was applied to the produced mixture for 20 min. Finally, the height of separated water was measured to calculate the DE (%).
Figure 10
According to Figure 11, the results indicate a significant increase in the demulsification efficiency which is higher in case of Fe3O4-chitosan nanoparticles. The electric current affects the surface tension and weakens the stable layer around droplets and causes coalescence. As can be seen in this figure, the efficiency of the desalting process with the new Fe3O4-chitosan demulsifier is increased by 15% compared to the conventional operating conditions.
Figure 11
3.7. Interfacial tension
Interfacial tension was measured for the demulsifier as well as after the addition of NP to the Fe3O4-chitosan. Pendant drop technique is used in this regard. The results demonstrate that the reduction of interfacial tension due to NP addition (22.53 mN/m) is almost equal to the industrial demulsifier (23.18 mN/m).
4. Conclusions
Bottle tests and electrostatic equipment were used to investigate the effect of magnetic Fe3O4 NPs and Fe3O4-chitosan nanocomposite on the oil desalting efficiency. NPs were synthesized and used at various concentrations. The as-produced nanocomposite exhibits a higher performance due to chitosan hydrophobicity. According to the bottle test, 5% water is added to crude oil along with 40 ppm injection of the commercial demulsifier as well as the addition of 0.004 wt% NPs provide the highest performance. At similar conditions, it was observed that the electrostatic test with an electric field of 1000 v/cm and 20 min residence time led to a significant improvement in the separation performance.
Funding Information
The authors declare that they have no conflict of interest.
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