Fibrous Coalescer for the Treatment of Hydrometallurgical Oil

Article pubs.acs.org/IECR

Fibrous Coalescer for the Treatment of Hydrometallurgical Oil Dispersions Dan Hu,†,‡ Lei Li,† Yanxiang Li,† and Chuanfang Yang*,† †

Key Laboratory of Green Process & Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, P. R. China ‡ University of Chinese Academy of Sciences, Beijing 100049, P. R. China ABSTRACT: Coalescence separation of oil dispersions of various hydrometallurgical extractants and solvents was studied using in-house-developed fibrous media that showed good separation performance toward four out of six common extraction reagents suspended in water as small oil droplets. The separation was affected by oil/ water interfacial tension and their density difference. Further, using kerosene as the model oil, the separation was performed on a flatsheet bench to investigate the effect of other factors including the media thickness, influent oil concentration, and media face velocity. Media with larger thickness resulted in better separation and, correspondingly, higher pressure drop. The influent oil concentration and media face velocity were mutual constraints to the separation efficiency. When the oil concentration was low, the time-weighted average separation efficiency stayed the same or increased with the velocity; when it was high, the opposite trend prevailed.

1. INTRODUCTION Fibrous coalescers are commonly used for separating dispersed emulsions because of their good performance and convenient operation.1 The coalescence separation efficiency is affected by the properties of coalescence media including the media structure, thickness, surface energy, pore size, and porosity. It is also affected by engineering parameters such as the flow rate, inflow direction, influent droplet size, and concentration, as well as the media surface area and surface wettability by the dispersed phase. A fibrous coalescence medium is typically made from randomly packed fibers of the same or different kind. Sokolović et al.2 designed a coalescer using packed fibers for the separation of various oil dispersions. They tested four polymeric fiber beds, namely, polyurethane (PU), two kinds of poly(ethylene terephthalate), and polypropylene (PP) constructed with different bed permeabilities, and concluded that a PU bed was the most reliable coalescer for a wide range of oily wastewater treatments. Chase et al.3 investigated the coalescence filtration performance of a water-in-oil dispersion using composite filter media prepared with a blend of electrospun PP fibers and microglass (MG) fibers. They found that the amount and fiber diameter of the electrospun PP fibers in the blend significantly affected the separation efficiency and pressure drop. In another work, they made multilayered media with varying amounts of hydrophilic MG fibers and hydrophobic PP or polyester fibers in an attempt to improve the media performance for coalescence separation.4 These kinds of fibrous media were also discussed by Agarwal et al.,1 who found that vertically oriented gradient media, with increasing fiber size and permeability from the influent to the effluent and with fibers preferably wetted by the dispersed © XXXX American Chemical Society

phase, were the most favorable design for the effective separation of liquid−liquid dispersions. There are cases where chemical or other treatment is applied directly to the fibers or to the packed fibrous beds. Yang et al.5,6 carried out research by self-assembling nano-SiO2 particles and applying chemical treatment afterward to a commercial stainless steel felt. The treated material showed superhydrophobicity and good coalescence separation efficiency for oil-in-water emulsions. Krasinski and Wierzba7 constructed coalescence materials with multilayers of meltblown PP fine fibers and found that a properly designed media surface structure aided by nanosuspension treatment could lead to a good separation efficiency of the water-in-oil emulsions and relatively low pressure drop. The effect of the surface energy of the fibers on the coalescence performance was also studied by many investigators. Despite some discrepancies in the literature, the prevailing conclusion was that, to achieve high efficiency of separation, the surface of the fibers had to be preferably wetted by the dispersed phase.8,9 It is common in coalescence separation that the droplets to be separated are typically smaller than the average pore size of the media,9−11 which is different from size-exclusion-based membrane separation.12,13 However, the droplet capture efficiency normally increases with decreasing pore size, and the total coalescence separation efficiency thus increases accordingly.9 Yang et al.5 made an effort to discriminate the effect of the media surface wettability and pore size on coalescence separation. They concluded that the less Received: Revised: Accepted: Published: A

August 18, 2016 October 23, 2016 October 25, 2016 October 25, 2016 DOI: 10.1021/acs.iecr.6b03160 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research

octyl/decylamine (N235), (2-ethylhexyl)phosphonic acid mono(2-ethylhexyl) acrylate (P507), and diisooctyl phosphate (P204). In addition, the separation was conducted by using inhouse-developed fibrous media, which led to the findings that the separation was affected not only by the water and oil density difference but also more so by the oil/water interfacial tension. On top of it, the effects of process parameters (i.e., media thickness, media face velocity, and influent oil concentration) on the separation efficiency were investigated by a flatsheet bench, and mutual constraints of the influent oil concentration and media face velocity were discovered. The research provides some new insights and perspectives of using filter media coalescence technology for wastewater treatment in hydrometallurgy processes.

amphiphobic surface was preferred to leverage the separation, but in general, the surface should have a moderate wettability by the dispersed phase for both small droplet capture and effective release of the grown droplets. The droplet residence time in the filter media is another important factor that affects the coalescence efficiency. It is a strong function of the bed length, media face velocity, and media wettability by the droplet. Some researchers11,14,15 think the bed should have an optimal length for best operation, while some others16 have confirmed that a longer bed depth gives a better separation efficiency. Sokolović et al.17 looked into such an effect, targeting steady-state bed coalescence. They concluded that a critical bed length for effective separation depends on several system properties involving the fluid-flow mode, bed permeability, and inlet oil concentration. Researchers1,18 also found that, with increasing media face velocity, the separation efficiency of coalescence decreases and the pressure drop across the media increases, leading to a reduction in the filtration quality factor (a ratio of the efficiency and pressure drop) as a result. The property of influent emulsion is the third factor that determines the oily water treatment efficiency, especially in practical applications where it often varies. In most of the studies,2,3,8,17−21 the dispersed oil droplets are usually larger than 10 μm and the influent concentration ranges from 500 to 10000 mg/L. However, Sokolović et al.19 developed a bed coalescer that was less sensitive to the inlet oil concentration and water quality. The influence of flow orientation, which can be categorized mostly into horizontal and radial, was also investigated by some researchers.1,22 Agarwal et al.1 discovered that it did not affect the separation efficiency but did affect the pressure drop and therefore the filtration quality factor. Horizontal flow gave a lower pressure drop compared to radial flow. Sokolović et al.22 came to the conclusion that bed coalescers with horizontal flow were more efficient than those with vertical flow, and for vertical flow, upflow operation was the least efficient at high fluid velocity, while no significant difference was present at low velocity between horizontal and vertical flow. In solvent extraction hydrometallurgy processes, raffinate containing a certain amount of solvent is discharged to a wastewater station for further treatment. The solvent, consisting of either the diluent or the extractant and sometimes both in a dispersed form, needs to be removed to a certain extent to facilitate the subsequent treatment to minimize water chemical oxygen demand for discharge. Oftentimes, it also needs to recover the lost solvent for economical reasons. Separation of these dispersed emulsions is challenging because of the emulsifying effect of the extractant itself, which enhances the stability of the emulsions. Conventional treatment methods include absorption, air flotation, coagulation, and coalescence. Coalescence separation has its own advantages over other techniques. However, making an effective filter media type of coalescence material for extractant-containing oil dispersion separation and recovery is not straightforward and barely reported, regardless of the many engineering studies using commercially available media for process control that are not necessarily aimed at hydrometallurgical solvent handling in wastewater. Therefore, in contrast to other work for oil/water emulsion separation using coalescence technology, in this paper, we focused on the separation of six common solvents used in solvent extraction processes, namely, sulfonated kerosene (SK), primary amine (N1923 and LK-N21), tri-n-

2. EXPERIMENTS 2.1. Materials. The fibers used to prepare the filter media are glass wool (diameter 0.6 μm; Shenyang Dongxiang Glass Fiber Co. Ltd.), glass fiber (diameter 7 μm and length 6 mm; Taishan Fiberglass Inc.), and cellulose fiber [diameter 11 μm and length 6 mm; Lenzing Fibers (Hong Kong) Ltd.]. Cetyltrimethylammonium bromide (CTAB) and cyclohexanone were purchased from Sinopharm Chemical Reagent Co. Ltd. Ethanol and SK were purchased from Beijing Chemical Works. Aromatic thermoplastic polyurethane (TPU) resin was obtained from Taiwan Sheen Soon Co. Ltd. N1923, N235, P507, and P204 were provided by the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. The primary amine LK-N21, a mixture of C16−C20 primary amines with a −NH2 molar concentration of 3.15 mol/L, was homemade.23 All reagents were used without further purification unless otherwise indicated. 2.2. Preparation of Fibrous Media. A total of 3 g mixture of glass wool, glass fiber, and cellulose fiber based on a mass ratio of 2:1:1 were mixed and uniformly dispersed in 500 mL of water. The dispersion was then transferred to a hand-sheet former originally filled with 10 L of water, stirred for remixing with a homogenizer for 10 min, and finally filtered through a fine copper screen by simply draining off the water to obtain a wet filter medium. The medium of 200 mm diameter was then removed from the porous support and put on a plate dryer to dry at 80 °C for 2 h. The dried medium was then cut into a 140 mm × 140 mm square, fully immersed in a resin solution (10% TPU in cyclohexanone) for 2 s, lifted up to drain the residual solvent, and then ventilation-dried in a fume hood for 30 min to remove the solvent. The material impregnated with a partially solidified resin was next put into an emulsification bath containing 3 L of ethanol and 3 g of CTAB, and then mechanical stirring was applied for 3 h at 480 rpm. The treated medium was later picked up from the bath and air-dried with ventilation. For different emulsion separation tests, the medium was cut into many round pieces with 25 mm diameter. They were used as either a single layer or multiple layers, the properties of which are shown in Table 1. 2.3. Oil-in-Water Emulsion Separation. The properties of the extractants and the diluent used as the oils are listed in Table 2. To make an emulsion, 500 mg/L oil was added to water. The mixture was then preemulsified at 10000 rpm by a homogenizer (Shinetek Instruments Co. Ltd.) for 5 min. The experimental setup for conducting the small-scale separation is depicted in Figure 1, where a peristaltic pump was used to deliver the emulsion at a constant flow rate (30 mL/min) to the filter medium for separation. The preemulsified emulsion was B

DOI: 10.1021/acs.iecr.6b03160 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research Table 1. Physical Properties of the Prepared Filter Media material one layer two layers three layers

thickness (μm)

basis weight (g/m2)

porosity (%)

pore size (μm) [average size]

500 1000

155 315

93 89

3.7−11.8 [5.8] 2.4−9.0 [3.9]

1500

461

87

1.8−8.8 [3.3]

under continuous stirring at 600 rpm during the whole separation experiment. A separating funnel was used to collect the filtrate from the filter holder mounted with two layers of the round filter medium stacked together (diameter 25 mm; effective area 285 mm2); the thickness of each layer was 0.5 mm. The flux of the fluid flow was calculated to be 6350 L/m2· h (media face velocity 11 cm/min) at a pressure drop typically smaller than 5 kPa. For each filtration, 100 mL of emulsion was pumped through the filter medium, and four consecutive filtration tests were conducted in series. 2.4. Equipment and Operating Procedure. SK was used as the typical oil in coalescence filtration experiments using a flatsheet test bench, shown in Figure 2. Emulsions of 500 mL with different oil concentrations were preemulsified as described earlier and then moved to the large storage tank of the bench (Figure 2a) for dilution to the target oil concentration (100−500 mg/L). The diluted emulsion was circulated and remixed by the centrifugal pump for 4 h for emulsion stabilization and then pumped to the flatsheet media holder at a media face velocity of 0.05−0.2 m/min for separation. The structure of the media holder is shown in Figure 2b. It consists of two parts, a base and a cover, which form a flatsheet coalescer when combined with a filter medium inserted in between. The holder was mounted vertically, and the emulsion was delivered from the bottom of the cover holder, passing first through the stainless steel mesh for flow

Figure 1. Small-scale separation test setup.

distribution and then through the medium and exiting from the upper port of the base holder, as illustrated in Figure 2a. The effluent samples were collected periodically using a separating funnel after the fluid was discharged at the exit port for 30 s to remove the coalesced oil. The lower part of the sample in the funnel was taken for oil content analysis. Stacked filter media (effective area 156.25 cm2) with differing thicknesses were tested, and a small storage tank was used to collect the filtrate. Water samples from the sampling port of this tank were also analyzed for oil content after the experiment to double check the time-weighted average separation efficiency calculated using the instant efficiency−time curves. The two flow paths, one in a closed loop and the other with an open end, as shown in Figure 2a, were run at the same time, ensuring unchanged stability of the feed emulsion for the continuous single-pass separation tests. A pressure gauge was used to monitor the pressure drop across the filter media. 2.5. Characterization. The media were characterized by scanning electron microscopy (SEM; Hitachi UHR FE-SEM SU8020 microscope), along with energy-dispersive X-ray spectroscopy (EDS). The pore-size distribution of the media

Table 2. Chemical Structures and Physical Properties of the Solvents Studied

a

S.T. = surface tension. bI.T. = interfacial tension of oil and water. C


Article


Figure 2. Flowchart of a flatsheet test bench (a) and the breakup parts of the media holder (b).

Figure 3. SEM images of the pristine media (a) and the as-prepared media (b). Insets are images with higher magnification, showing the features of an individual fiber. D


Article

Industrial & Engineering Chemistry Research was measured by a Quantachrome Porometer 3G pore-size analyzer. The droplet size of the emulsions was observed with an optical microscope (6XB-PC, Shanghai Optical Instrument Factory), and the droplet size distribution by number was measured using Nano Measure 1.2 software. The influent droplet size of all of the oils investigated ranged from 1 to 10 μm with an average of 2.5 μm. An oil content analyzer (Oil 460 Infrared photometer made by Beijing China Invent Instrument Tech. Co. Ltd.) was used to measure the oil concentration. The quantitative oil/water separation efficiency (E) was calculated using the concentration of the filtrate (Cf) and that of the influent emulsion (C0) with the following equation: E (%) =

C0 − Cf × 100% C0

(1)

3. RESULTS AND DISCUSSION 3.1. Physical Properties of Filter Media. The media were prepared based on the concept proposed in our past publications.24,25 The physical properties including the media thickness, basis weight, pore size, and porosity are listed in Table 1. The microstructures of the pristine and treated media are shown in Figure 3, where many polymer resin particles on the fiber surfaces can be identified on the treated media, which is a characteristic of the resin emulsification process for media treatment.24 The media obtained can be wetted well by both water and oil in air with a wetting angle of 0°. However, oil wetting of the media underwater is different from that in air, which favors coalescence separation, as discussed previously.24,25 The pore size of the media constructed with one to three layers of the as-prepared material was measured. Layer stacking causes a multimode pore-size distribution with reduced average pore size. This is typical for nonwoven materials, which always have defects in terms of the pore shape, pore distribution across the thickness, tortuosity, and so on. Stacking these kinds of materials together will offset the defects and narrow down the average pore size and size distribution.26 The smallest average pore size is 3.3 μm for the three-layer medium, while the largest average is 5.8 μm for a single layer. Both are greater than the average size of the emulsion. 3.2. Emulsified Organic Solvent Separation. Five solvent extractants and one diluent with a wide range of properties were investigated. Their properties are shown in Table 2. For each solvent, the inlet emulsion concentration was controlled at 500 mg/L. The coalescence experiment was conducted to each emulsion four times in a row, and for each experiment, 100 mL of emulsion was filtered, with the separation efficiency independently determined. This was to exclude the possibility of oil sorption being the main separation mechanism. The separating funnel shown in Figure 1 allowed for easy collection of the uncontaminated filtrate for oil content analysis to calculate the separation efficiency. As shown in Figure 4, the medium could separate emulsions containing SK, N1923, N235, and LK-N21 efficiently, with separation efficiencies being over 90%. Particularly, for SK, the average efficiency of the four consecutive tests is 96.1%, with the first test being 96.6% and the second one 99.7%. However, the separation of a P507- and P204-containing emulsion is not as satisfactory, with respective efficiencies being 80% and 60% only. This result indicates that the medium performs better for alkaline extractants than for acidic extractants. From the properties and structures of alkaline and acidic extractants, as

Figure 4. Separation efficiency of LK-N21/water, N1923/water, N235/water, P507/water, P204/water, and SK/water emulsions using the as-prepared two-layer media for four consecutive filtrations at a flow rate of 30 mL/min (100 mL of emulsion was filtered each time).

shown in Table 2, it can be seen that the acidic extractants have lower interfacial tension of oil and water than the alkaline extractants, which makes separation more difficult because lower interfacial tension is indicative of more stable emulsions. In addition, the densities of P507 and P204 are higher than those of other extractants and close to that of water, which also contributes significantly to the difficulty of separation. The separation of SK is the easiest because the interfacial tension is the highest and the density difference is also among the largest. The polarity of the organic compound should also play a role because it determines the solubility of oil in water, indirectly related to the lowering of the interfacial tension, which gives rise to separation difficulties through coalescence. 3.3. Coalescence Filtration on the Flatsheet Bench. Here, we took SK as the target oil to investigate the effect of the influent oil concentration, media face velocity, and media thickness on the separation performance of the obtained media. SK is the most common and largely consumed diluent in industrial extraction processes, the recovery of which is therefore strongly desired. Coalescence filtration of its emulsion was performed on the flatsheet test bench consisting of a flat media holder (media size 14 cm × 14 cm; effective area 156.25 cm2), two storage tanks, a centrifugal pump, two flowmeters, and a pressure gauge (Figure 2a). 3.3.1. Saturation of Medium with SK. Oil holdup due to adhesion and capillary forces happens in the initial stage of coalescence separation before steady state is established. To know how much oil is needed to saturate the medium is necessary to exclude its contribution to the steady-state operation efficiency. To do so, medium fragments with the same mass were put into 150 mL of SK-in-water emulsions of 100, 200, and 500 mg/L contained in separate bottles. These bottles were then shaken for 12 h to reach medium oil saturation equilibrium before the fragments were separated out. The emulsions used were then analyzed to determine the remaining SK concentration to calculate the saturation capacity, and the result is shown in Figure 5. The amount of oil adsorbed from the emulsion to the medium is far less than that for pure oil saturation because of the existence of water, which also gets sucked into the material. However, the oil saturation capacity indeed varies with the initial emulsion concentration. According E


Article


in the system are mainly from the tap water used, the rusts from the pipelines in our test system, as well as a small amount of gel formed by oil degradation. Optical microscopy and SEM−EDS were used to analyze the surface of the medium used after the separation experiment. Scattered colorization of the media surface was identified, as shown in Figure 7a, where the black spots were the contamination collected by the material that could not be easily discovered by SEM (Figure 7b). The EDS result in Table 3 shows the existence of iron and zinc in the medium used, an indication of the rust in the test system due to the use of cast-iron valves and pipe connectors. The adverse effect of the particles on coalescence filters includes two aspects that are typically not reversible. The first one causes plugging of the apertures and an increase of the differential pressure; the second one changes the surface properties of the material, resulting in a reduction of the coalescence filtration efficiency. Overall, the time-weighted average separation efficiencies of the three media with increasing thicknesses are 94.3%, 94.3%, and 97.0%, respectively, and the corresponding terminal pressure drops are 0.030, 0.040, and 0.043 MPa, much lower than those of the microfiltration membranes. It is also noticed that the efficiency for the two-layer medium is slightly lower (94.3%) than the average of the consecutive filtration tests in small scale (96.1%). 3.3.3. Effect of the Media Face Velocity. The effect of the media face velocity (m/min) on the oil removal efficiency and pressure drop using a two-layer medium at different influent oil concentrations is shown in Figures 8−10. For all of the influent concentrations studied, the pressure drop increases with an increase in the velocity, but the separation efficiency varies differently. For a low oil concentration of 100 mg/L, the separation efficiency is not affected much by the velocity. However, the pressure drop at 0.2 m/min is much higher, as illustrated in Figure 8b. When the oil concentration is changed to 200 mg/L, the separation efficiency at 0.2 m/min becomes higher than the case with lower velocities except the last data point, and the trend of the pressure drop becomes normal (Figure 9). The time-weighted average efficiencies at 0.05, 0.1, and 0.2 m/min are 93.6%, 94.3%, and 94.8%, respectively. When the oil concentration is further increased to 500 mg/L, the separation efficiency falls dramatically at a face velocity of 0.2 m/min, and a moderate decline also happens at lower

Figure 5. SK saturation capacity (bar) by the media and the maximum time for adhesion saturation under different media face velocities (scattered data points).

to this result, the maximum time needed for the medium to reach oil saturation during the coalescence separation process (media face velocity 0.1 m/min and two stacked layers) was estimated to be 0.9, 2, and 2.2 min for 100, 200, and 500 mg/L emulsions, respectively (Figure 5; scattered data points). Even when the velocity was reduced to 0.05 m/min, the longest possible time to reach medium oil saturation was 4.3 min for the 500 mg/L emulsion. In reality, the time should be shorter because of the shear flow, which tends to minimize the saturation level. That means that, after 4.3 min, steady state of coalescence separation should dominate the process. 3.3.2. Effect of the Media Thickness. The thickness of the media influences the residence time of the dispersed phase inside the media. With increasing thickness, the residence time and oil removal efficiency both increase, and so does the pressure drop, as shown in Figure 6. The separation efficiency differs little between one-layer and two-layer media but improves greatly for the three-layer medium. It is interesting to note that the separation is stable initially but has a sudden drop afterward. This corresponds to a sudden pressure drop increase, which may be a result of filter plugging by excessive adhesion of oil and solid particles in the feed emulsion. Particles

Figure 6. Time-dependent separation efficiency of a SK-in-water emulsion (a) and differential pressure (b) versus media thickness at a media face velocity of 0.1 m/min and an influent oil concentration of 200 mg/L. F


Article


Figure 7. Optical microscopy (a) and SEM (b) images of the contamination collected in the medium after separation and (c) the corresponding elemental mapping of iron elements.

relationship between the media face velocity and influent oil concentration, the coeffect of the two factors on the timeweighted average separation efficiency is plotted in Figure 11. It can be seen that oil removal at a media face velocity of 0.2 m/ min is equal to or better than the case with lower velocities when the influent concentrations are 100 and 200 mg/L. For an influent concentration of 500 mg/L, the separation efficiency at a velocity of 0.05 m/min is the highest. In general, higher influent concentration results in lower separation efficiency. This is coincident with the conclusion drawn from Figures 8−10. To understand why, we can look back at the principle of coalescence separation. Coalescence separation relies on droplet collision and sorption by the coalescence material to increase the droplet size for gravitational sedimentation or flotation. Droplet collision depends on fluid turbulence, which is mainly affected by the velocity at low influent oil concentration in this work. Droplet sorption by the material depends not only on the wettability of the dispersed phase toward the material but also on the media face velocity and feed oil concentration. When the wettability is fixed in the system, the velocity and concentration will determine the oil sorption behavior. A high oil concentration provides more opportunity for oil droplets to contact the material surface to be captured, thus improving sorption. A low velocity permits a longer residence time for droplet sorption, and a high velocity favors droplet collision but only to a certain extent, after which it can cause less capture due to short residence time and oil reentrainment. Therefore, it is reasonable to believe that

Table 3. Element Content of the Medium after Separation and the Original Medium by EDS medium after separation

original medium

element

wt %

atom %

wt %

atom %

C O Si Fe Ca Na Al Zn K

54.13 30.06 3.86 7.49 1.24 0.69 0.68 1.56 0.30

66.53 27.73 2.03 1.98 0.46 0.44 0.37 0.35 0.11

62.23 27.08 5.95

71.56 23.38 2.93

1.98 1.33 0.95

0.68 0.80 0.49

0.47

0.17

velocities, as indicated in Figure 10a. Interestingly, the terminal pressure drop at 0.2 m/min for all of the influent oil concentrations remains almost the same at around 0.05− 0.055 MPa. This further indicates that particle plugging instead of oil clogging of the filter media is likely the main reason for the pressure drop rise during the course of filtration. From these data, we can also conclude that the separation can be conducted at higher media face velocity when the influent oil concentration is low, with a cost of higher pressure drop. When the influent oil concentration is high, a lower media face velocity is preferred for better separation efficiency. 3.3.4. Mutual Constraints of the Media Face Velocity and Influent Oil Concentration. To clearly understand the

Figure 8. Time-dependent separation efficiency of a SK-in-water emulsion (a) and differential pressure (b) as a function of the media face velocity (two-layer medium and influent oil concentration 100 mg/L). G


Article


Figure 9. Time-dependent separation efficiency of a SK-in-water emulsion (a) and differential pressure (b) as a function of the media face velocity (two-layer medium and influent oil concentration 200 mg/L).

Figure 10. Time-dependent separation efficiency of a SK-in-water emulsion (a) and differential pressure (b) as a function of the media face velocity (two-layer medium and influent oil concentration 500 mg/L).

droplet collision is the dominant factor for better separation at low influent concentration, which demands higher media face velocity for faster mass transfer; while droplet sorption by the coalescence material is favored by a high influent concentration, under which a lower media face velocity is still preferred not only to increase the total sorption but also to prevent shearinduced early breakthrough to achieve relatively higher separation efficiency.

4. CONCLUSION A coalescence fibrous medium designed in-house with roughened surfaces generated in situ by emulsification of resin polymer binders showed a reasonable performance for separating various extractants and diluent containing oil-inwater emulsions. The average separation efficiency is above 90% for SK, N1923, N235, and LK-N21, 80% for P507, and 60% for P204 in consecutive small-scale filtration tests. The separation of SK-containing emulsions was further performed on a flatsheet test bench to investigate the role of engineering factors. It was found by adjusting the media thickness, a 97% time-weighted separation efficiency could be achieved with minimal pressure drop. Mutual constraints of the media face

Figure 11. Coeffect of the influent concentration and media face velocity on the separation efficiency of a SK-in-water emulsion.

H


Article


(15) Spielman, L. A.; Su, Y. P. Coalescence of Oil-in-Water Suspensions by Flow through Porous Media. Ind. Eng. Chem. Fundam. 1977, 16, 272−282. (16) Fahim, M. A.; Akbar, A. M. Removal of fine oily hazes from wastewater using deep fibrous bed Coalescer. J. Environ. Sci. Health, Part A: Environ. Sci. Eng. 1984, 19, 299−319. (17) Sokolović, R. M. Š.; Vulić, T. J.; Sokolović, S. M. Effect of bed length on steady-state coalescence of oil-in-water emulsion. Sep. Purif. Technol. 2007, 56, 79−84. (18) Lu, H.; Yang, Q.; Liu, S.; Xie, L. S.; Wang, H. L. Effect of fibrous coalescer redispersion on W/O emulsion separation. Sep. Purif. Technol. 2016, 159, 50−56. (19) Šećerov Sokolović, R. M.; Sokolović, S. M.; Šević, S. Oily water treatment using a new steady-state fiber-bed coalescer. J. Hazard. Mater. 2009, 162, 410−415. (20) Secerov Sokolović, R. M.; Sokolović, S. M.; Doković, B. D. Effect of Working Conditions on Bed Coalescence of an Oil-in-Water Emulsion Using a Polyurethane Foam Bed. Ind. Eng. Chem. Res. 1997, 36, 4949−4953. (21) Li, X.; Xu, H.; Liu, J.; Zhang, J.; Li, J.; Gui, Z. Cyclonic state micro-bubble flotation column in oil-in-water emulsion separation. Sep. Purif. Technol. 2016, 165, 101−106. (22) Secerov Sokolović, R. M.; Vulić, T. J.; Sokolović, S. M. Effect of Fluid Flow Orientation on the Coalescence of Oil Droplets in SteadyState Bed Coalescers. Ind. Eng. Chem. Res. 2006, 45, 3891−3895. (23) Ning, P.; Lin, X.; Cao, H.; Zhang, Y. Selective extraction and deep separation of V(V) and Cr(VI) in the leaching solution of chromium-bearing vanadium slag with primary amine LK-N21. Sep. Purif. Technol. 2014, 137, 109−115. (24) Hu, D.; Li, X. Y.; Li, L.; Yang, C. F. Designing high-caliber nonwoven filter mats for coalescence filtration of oil/water emulsions. Sep. Purif. Technol. 2015, 149, 65−73. (25) Hu, D.; Li, L.; Li, Y. X.; Yang, C. F. Restructuring the surface of polyurethane resin enforced filter media to separate surfactant stabilized oil-in-water emulsions via coalescence. Sep. Purif. Technol. 2017, 172, 59−67. (26) Bruil, A.; Van Aken, W. G.; Beugeling, T.; Feijen, J.; Steneker, I.; Huisman, J. G.; Prins, H. K. Asymmetric membrane filters for the removal of leukocytes from blood. J. Biomed. Mater. Res. 1991, 25, 1459−1480.

velocity and influent oil concentration on the separation efficiency were also revealed, which led to the speculation that, at low influent concentration, droplet collision dominates the separation, while at high influent concentration, the low media face velocity is preferred to enhance sorption and avoid droplet reentrainment simultaneously for better separation.

■

AUTHOR INFORMATION

Corresponding Author

*Tel: +86-10-8254-4976. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS

■

REFERENCES

This work was supported by the Chinese Academy of Sciences under the Talented Program and National Natural Science Foundation of China under Grants 21476237 and 21401201, as well as the Major Science and Technology Program for Water Pollution Control and Treatment (Grant 2015ZX07202-013).

(1) Agarwal, S.; von Arnim, V.; Stegmaier, T.; Planck, H.; Agarwal, A. Effect of Fibrous Coalescer Geometry and Operating Conditions on Emulsion Separation. Ind. Eng. Chem. Res. 2013, 52, 13164−13170. (2) Šećerov Sokolović, R. M.; Govedarica, D. D.; Sokolović, D. S. Selection of Filter Media for Steady-State Bed Coalescers. Ind. Eng. Chem. Res. 2014, 53, 2484−2490. (3) Kulkarni, P. S.; Patel, S. U.; Patel, S. U.; Chase, G. G. Coalescence filtration performance of blended microglass and electrospun polypropylene fiber filter media. Sep. Purif. Technol. 2014, 124, 1−8. (4) Kulkarni, P. S.; Patel, S. U.; Chase, G. G. Layered hydrophilic/ hydrophobic fiber media for water-in-oil coalescence. Sep. Purif. Technol. 2012, 85, 157−164. (5) Li, X.; Hu, D.; Cao, L.; Yang, C. Sensitivity of coalescence separation of oil−water emulsions using stainless steel felt enabled by LBL self-assembly and CVD. RSC Adv. 2015, 5, 71345−71354. (6) Li, X.; Hu, D.; Huang, K.; Yang, C. Hierarchical rough surfaces formed by LBL self-assembly for oil−water separation. J. Mater. Chem. A 2014, 2, 11830. (7) Krasinski, A.; Wierzba, P. Removal of Emulsified Water from Diesel Fuel Using Polypropylene Fibrous Media Modified by Ionization during Meltblow Process. Sep. Sci. Technol. 2015, 50, 1541−1547. (8) Sokolović, R. M. Š.; Sokolović, S. M. Effect of the Nature of Different Polymeric Fibers on Steady-State Bed Coalescence of an Oilin-Water Emulsion. Ind. Eng. Chem. Res. 2004, 43, 6490−6495. (9) Bansal, S.; von Arnim, V.; Stegmaier, T.; Planck, H. Effect of fibrous filter properties on the oil-in-water-emulsion separation and filtration performance. J. Hazard. Mater. 2011, 190, 45−50. (10) Speth, H.; Pfennig, A.; Chatterjee, M.; Franken, H. Coalescence of secondary dispersions in fiber beds. Sep. Purif. Technol. 2002, 29, 113−119. (11) Ma, S.; Kang, Y.; Cui, S. Oil and Water Separation Using a Glass Microfiber Coalescing Bed. J. Dispersion Sci. Technol. 2014, 35, 103− 110. (12) Shi, H.; He, Y.; Pan, Y.; Di, H.; Zeng, G.; Zhang, L.; Zhang, C. A modified mussel-inspired method to fabricate TiO2 decorated superhydrophilic PVDF membrane for oil/water separation. J. Membr. Sci. 2016, 506, 60−70. (13) Gao, S.; Sun, J.; Liu, P.; Zhang, F.; Zhang, W.; Yuan, S.; Li, J.; Jin, J. A Robust Polyionized Hydrogel with an Unprecedented Underwater Anti-Crude-Oil-Adhesion Property. Adv. Mater. 2016, 28, 5307−5314. (14) Hazlett, R. N. Fibrous Bed Coalescence of Water. Ind. Eng. Chem. Fundam. 1969, 8, 625. I


Fibrous Coalescer for the Treatment of Hydrometallurgical Oil

Recommend Documents