Continuous Separation Process of Water-in-Crude Oil Emulsion by Simultaneous Application of an Electrical Field Combined with a Novel Absorbent Based on Functionalised PolyHIPE Polymer

During the extraction process of crude oil, the removal of water from a high stability water-in-crude oil emulsions is life-threatening for the production of a profitable product. However, several technologies of separation exist today, e.g. stripping columns, centrifugal separators, coalescence separators, vacuum distillation systems and gravity separators, almost all of these approaches are not able to completely remove water from water-in-crude oil emulsions besides their high cost. In this study, the preparation of a high internal phase emulsion (HIPE) was achieved on a laboratory scale. Subsequently, it was polymerized and sulphonated to produce a hydrophilic macroporous polyHIPE polymer (PHP) called silane (vinyl trimethoxy silane) PHP with a relatively high surface area of 104 m 2/g. It demonstrates high water absorption capability in addition to its ability to remove surface active substances such as Mg, Ca, Na and Cl, from crude oil which cause crude oil emulsification. The rates of demulsification of water-in-crude oil emulsions were examined in high AC field under various emulsion inlet flow rates from 100 ml/min to 1500 ml/min and different applied voltages from 1-5 kV (equivalent to 14-69 kV/m) by using a model of an electrostatic separator combined with silane PHP as absorber. It was found that the best separation efficiency was 91% with applied voltage of 5 kV and emulsion inlet flow rate of 100 ml/min. When the spent silane PHP was reused in the demulsification process under similar conditions, a separation efficiency of up to 73% was achieved. Also, it was noticed that the separation efficiency was increased This work is licensed under a Creative Commons Attribution 4.0 International License. Journal of Petroleum Research and Studies PISSN: 2220-5381 EISSN: 2710-1096 Open Access No. 33, December 2021, pp.91-113 92 with the increase in applied voltage and reduction in the inlet flow rate of emulsion. Moreover, the original or spent silane PHP were able to remove the undesired metals present in the crude oil.

worse by the existence of contaminants like chloride. Moreover, the production of off-specification crude oil, failure of separation equipment in the units of the gas-oil separation, poisoning of catalysts, increase in the use of demulsifier(s), losses of production and increase in viscosity of crude oil in the transportation pipeline also necessitate further funds and cost of operations [1,2]. The deposition of organics in processing equipment, inadvertently requires accommodating an increased volume from the presence of water to produce crude oil to conform with specifications.
Therefore, due to these challenges, the crude oil emulsions are considered undesirable and the breaking of crude oil emulsions process of great importance and feasibility for crude oil producers. To be efficient, the content of water after demulsification process should be lower than 0.5% -3.0%.
Among the various demulsification methods, (e.g., sedimentation technique, thermal breaking methods, and centrifugation technique), the method of electrostatic demulsification is one of the simplest and more efficient demulsification methods [3,4]. The process of electrostatic demulsification is basically based on the coalescence of water droplets and their precipitation. Although, the electrostatic approach has a comparatively large implementation, the electrical coalescence technique is known unwell due to electrical phenomena of interfacial polarization and hydrodynamic complexity. In general, the droplets coalescence includes three stages: (i) motion and approach of droplets because of the force of electrostatic; (ii) breakdown of the film detaching the droplets; (iii) collapse of the film and droplets coalescence. The effect of electrostatics is mainly connected to the first stage, that is, an increased the droplets motion rate in the electric field [5].
When applying an electric field, the droplets of water are polarized by the stimulated dipole. The fields of AC stimulate an oscillating motion of the droplets and the droplets of water convert into an ellipsoid, which leads to reduce the space between the droplets. It can be observed from the distribution lines of electric field that the intensity of the lines of field is increased between two adjacent droplets ( Figure 1).
The electrical potential gradient of the two droplets is proportional to the attractive force since the attractive force is proportional to the voltage gradient. Thus, the dense lines of the electrical field in Fig. 1 means the attractive force and gradient V surfaces permit the droplets to spread on the surface because of a small contact angle which breaks up the droplet and water absorbs into the PHP; (iii) the water is absorbed inside the particle and not freed back into the emulsion [6]. The high ability of water uptake and high surface area is crucial to remove as much water as possible. Practically, both DC and AC fields can achieve an effective demulsification process.
In DC fields, the electrophoretic droplet motion enhances the probability of coalescence, whilst in AC fields, the larger motion is essential to achieve greatest coalescence in bulk fluids [7]. Consequently, to attain an ideal continuous demulsification process, it is preferable to apply AC field, as it is more appropriate.
The parameters which are considered to have an impact on kinetics of demulsification are (emulsion properties) interfacial tension, density, viscosity, surfactant concentration in oil phase, water droplet size, holdup, electrolyte concentration in water phase, frequency [8,9]; (operating conditions) degree of mixing, shape, voltage, distance between the electrodes and temperature. In this research, a continuous electrostatic separator has been built, in which variable inlet flow rates of water-in-crude oil emulsion and AC voltages have been used to determine the demulsification rates. This study aims to develop a continuous non-chemical demulsification method to enhance the efficiency of water separation process. Moreover, the removal of surface-active species from high stability water-in-crude oil emulsions depend on the use of a novel absorbent material is silane-PHP, combined with an electrostatic technique. It is an alternate method to the commonly used demulsification approach by adding chemicals, which leads to the formation of undesirable complex substances in addition to its high cost.

Demulsification of water-in-crude Oil Emulsion
All the past studies on demulsification under electrostatic force or demulsifier separately have been experimented in batch condition [4,8]. While on continuous electrostatic demulsification a little research was reported [10,11]. In this work, a continuous non-chemical demulsification method has been conducted by using a sulphonated silane-PHP as absorber combined with an electrostatic technique. This approach is like real-world process in order to increase the efficiency of the process of water separation and removal of the surface-active materials from water-in-crude oil emulsions of high stability. PolyHIPEs polymer, are a macroporous material with a highly porous interconnected monolithic structure. They consist of a well-defined, open-cell and uniform macrostructure with low dry density of around 0.1 gm/cm 3 [12,13]. PHPs have numerous pretty features like a high ability for the disposal of metal ions through an ion exchange mechanism as well as the capacity to adsorb the toxins of organics due to the hydrophobic and hydrophilic domains on the porous structure walls [14,15]. Moreover, the technique of electrostatic used has the suitable features to fulfill the aim of this research like low consumption of power owing to the low current usage during dispersion [16]. Furthermore, this technique does not risk the mechanical faults since it is independent of moving parts. Over and above, it has the capacity to be combined with various techniques such as, centrifugal separation, hydro cyclones, chemical emulsification, etc. to improve affirmative synergy for removal of water [17,18]. This can be attained by creating the dispersed (water) phase droplets coalescence, which are stable by the indigenous surface-active materials existence in the emulsion such as oxides, phosphate, organic carboxylates, asphaltenes and the like [19,20], and gathering them in the silane-PHP absorber. The relative effect of the conditions on demulsification have been studied and found a significant increase in efficiency of separation because of the synergistic impact.

Preparation of silane PHP
The procedure used to prepare the silane HIPE is reported by numerous researchers [21,22] and is demonstrated in Figure 2. The aqueous phase was pumped into the oil phase in the reactor with continuous mixing to produce silane HIPE. The operation time and mixing time were 10 minutes and 50 minutes, respectively. Then, the produced silane HIPE has been transported into 50 ml polypropylene containers with an inside diameter of 2.6 cm.
These small containers were then placed in an oven of polymerization at 60 °C for 8 hours.
After polymerisation, the containers were removed from the oven, and then the silane PHP blocks were removed from the containers and cut into small discs by a sharp blade. After that, silane PHP discs were washed to eliminate the impurities from the pores and channels of the micro-porous structure and dried to remove the water of washing. Finally, the silane PHP surface was sulphonated using sulfuric acid to convert it from hydrophobic to hydrophilic. Then, all the produced samples were evaluated in terms of surface area and ability to absorb water using Brunauer-Emmett-Teller (BET) method and water uptake test, respectively. It was found that the optimal PHP silane sample was 30% silane as it achieved a surface area of 104 m 2 /g and a high-water absorption capacity. Subsequently, they were processed and sieved to change them into granules with sizes ranging from 490 to 720 µm to use them as absorber in the separation experiments.

Preparation the emulsion of water-in-crude oil
Different volumes of aqueous and crude oil phases were utilized to prepare water-incrude emulsions. The aqueous phase was prepared by adding three kinds of salts (anhydrous powder forms), namely 0.6 g/l CaCl 2 , 5.0 g/l MgCl 2 and 28.1 g/l NaCl, to deionized water to mimic seawater. No artificial surfactants were added to stabilize the emulsions because of the natural surfactants and impurities that were already present in crude oil (i.e. resins, asphaltenes, wax, nitrogen, sulfur, oxygen, and some other elements mostly metals like vanadium, iron, nickel, copper etc.) and a density of 1.038 g/l was achieved.
A 40% (equivalent to 640 ml) aqueous phase was added into the 60 % (equivalent 960 ml) crude oil to prepare water-in-crude emulsions. Crude oil was placed in a container and mixed by a magnetic stirrer (Hiedolph instruments RZR 2052, Germany). Aqueous phase was added slowly into crude oil. Mixing was continued to compose the complete 40% water-in-crude oil emulsion (% by volume). The water-in-crude oil emulsion collected up to 1.6 L for continuous demulsification.    To determine the pore size range of silane PHP, its microscope images were analyzed using ImageJ software. The pore sizes range was found to be 5.0 µm to 180 µm, which is consistent with the pore size range reported in previous studies (4.0 µm to 190 µm [21].

Effect of inlet flow rate variation
The impact of the flow rate of emulsion on the efficiency of separation was assessed using the optimum sample of silane PHP produced. Experiments of separation were conducted over a high electric field strength ranging from 14 to 69 kV/m (1-5 kV applied along the distance of 0.09 m between the two separated electrodes). The inlet flow rate of the emulsion has been varied from 100 ml/min to 1500 ml/min.
According to the performance of the process of continuous demulsification, the experiment results predicted that the separation efficiency of oil/water was significantly increased when the saline PHP absorber was added to the model of emulsion at a high-voltage electric field. In Figure (

Effect of electric field strength variation
The performance of silane PHP as an adsorber was investigated at various electric field strengths at a constant inlet flow rate of a 100 ml/min emulsion. Compared to the previous outcomes, a noticeable separation (more than 20%) occurs promptly after passage of the emulsion from the electrostatic separator with the presence of silane PHP as shown in Figure (7). However, the voltage value was at a minimal.
While in the absence of silane PHP, no separation was observed under identical operating conditions. In fact, in the absence of silane PHP, the demulsification take places via the electrostatic separator only when the strength of electric field is higher than 28 kV/m (equal to 2 kV). In order to evaluate the elements in the spent silane PHP after the process of demulsification. The spent silane PHP was exposed to Energy Dispersive X-rays (EDX) spectroscopy and the results are summarized in Table (3). The EDX of silane PHP polymer denoted the existence of some more elements, such as Na, Mg, Ca and Cl, which were not present originally in the silane PHP but were joined onto silane PHP from the crude oil. This demonstrates that the silane PHP has capability to adsorb some other elements from the crude oil further to its capability to enhance the capacity of separation during the process of demulsification utilizing electrostatic field. Thus, silane PHP has the further feature attributed to its capacity to remove the metal ions like Mg, Ca, Na and Cl that induce crude oil emulsification by an ion exchange mechanism.  With the aim to verify the elements in the spent silane PHP structure after the process of demulsification, the spent silane PHP has been subjected to EDX spectroscopy. The outcome is presented in Table (4). It can be observed that the spent silane PHP included elements which were not present in the original PHP-I, namely Na, Mg and Ca, that were adsorbed from the crude oil. This shows that the spent silane PHP also has sufficient capacity to remove the undesired elements from the crude oil which cause the crude oil emulsification. Thus, the spent silane PHP also has the ability to remove the existing undesired metals in the crude oil but with lower efficiency than in the original silane PHP. Silane PHP has been analyzed by Environmental Scanning Electron Microscope (SEM). Figure (11, a) displays the SEM micrograph of silane PHP before using it in the separation experiment. While, in Figure (11, b) appearance of spent silane PHP which has been utilized in separation experiments. After finishing the process of demulsification, silane PHP was gathered, dried, and sent to the SEM for analysis to evaluate its capability to remove the surface-active materials. It can be observed that the structure of porous silane PHP partially collapses as an effect of a mechanical stresses produced from pumping of emulsion along with the process of drying and shows a few clogged pores due to the accumulation of surface-active material absorbed by the silane PHP inside the pores.

Conclusion
The process of demulsification in recovery of crude oil was simulated with the electric field strength, the inlet flow rate of the emulsion and silane PHP absorber. A model of water-in-crude oil emulsion has been prepared with 40% of water and addition of certain concentrations of calcium, sodium, and magnesium salts to make it more stable. The size of the water droplets was around 15-60 mm and was stable for around 122 days at room temperature. Using a continuous electrostatic separator combined with original and spent silane PHP, the separation efficiencies of demulsification process of water-in-crude oil emulsion with different inlet flow rate and high AC electric fields were investigated.
The efficiency of water separation increases with the increase in the applied electric field due to generation of an electrostatic force between water droplets which distort along the field direction. The addition of silane PHP absorber to water-in-crude oil emulsion increases the water separation as it helps to accelerate the film collapse around the water droplets as well as in its adsorption of water inside the pores.
The findings from a series of demulsification experiments under various operating conditions reveal that the separation efficiency using the inlet flow rate of 100 ml.min-1 and applied electric field strength of 5 kV with the presence of the original and spent silane PHP were 91% and 73%, respectively. These separation efficiencies are higher than as compared to the separation efficiency in the absence of silane PHP of 56%. This means the original silane PHP achieved a significant separation efficiency, while spent silane PHP attained a satisfactory separation efficiency. Moreover, they achieved a high capacity to remove surface-active materials, such as Mg, Na, Cl and Ca ions, from crude oil which cause the emulsification of crude oil. Finally, it was found that the silane PHP absorber attained sensible results in terms of the water separation efficiency and the ability to remove surface-active species from water-in-crude oil emulsion, but needs some chemical modification to attain more reasonable results for multi-used.