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Selection of Filter Media for Steady-State Bed Coalescers Radmila M. Šećerov Sokolović,*,† Dragan D. Govedarica,† and Dunja S. Sokolović‡ †

Faculty of Technology, University of Novi Sad, Bulevar cara Lazara 1, 21000 Novi Sad, Serbia Faculty of Technical Sciences, University of Novi Sad, Trg Dositeja Obradovica 6, 21000 Novi Sad, Serbia

‡

ABSTRACT: In petrochemical industries oil-in-water dispersion separation is important due to economic, ecological, and safety reasons. If the coalescer is a part of the central unit for wastewater treatment, then it is able to separate oil with different properties in time. Designing such a coalescer is complicated even when this is based on experimental results. This work contributes to the design strategy of the coalescer for the separation of oil of different quality. In this work four different polymeric fibers were tested for separation of model dispersions encompassing four mineral oils of different properties. Experiments were carried out over a wide range of oil properties, bed permeability, and fluid velocities. Selection of filter media was made on the basis of 80 experiments. Contour diagrams which give the dependence of bed permeability, the properties of oil, and the critical fluid velocity enable reliable and easy selection of filter material for steady-state bed coalescence. porosity.18−20 In such a bed the more appropriate term would be the fiber network of the empty space rather than the pore network term. Evidently, what determines the bed geometry is still not sufficiently defined, and therefore researchers rarely give the conditions under which the bed is packed. In the period from 1997 to the present Šećerov Sokolović and colleagues have published a series of studies presenting their experimental results of steady-state fiber bed coalescence that are interconnected and that form the basis for setting up a part of the procedures for the design and optimization of coalescers. They deal with dilute, relatively unstable emulsions corresponding to oily water. Oil drops flow through the highly porous bed with the size smaller than the pore size in all experiments. In these circumstances capture of the drops involves all the known mechanisms such as interception, sedimentation, hydrodynamic retardation, London−van der Walls attraction, and Brownian diffusion, etc. Šećerov Sokolović et al. have been studying the effect of working conditions of the steady-state bed coalescence on one bed material, polyurethane, PU, and one naphthenic-based mineral oil.21 The authors have decided that in future studies they should continue to operate in a wide range of fluid velocity until the effluent oil concentration does not begin to grow exponentially. Due to elasticity polymer fibers are compressible. Thanks to this, bed properties could be widely varied and the bulk density could be changed over a broad range. Because it was shown that the changes in bed permeability cause the change of critical velocity (working velocity) in the interval of 50−100%, the permeability could be considered as a crucial factor for equipment size and therefore capital cost.22 The effect of different polymeric fibers on steady-state bed coalescence was investigated in the next paper.23 Three polymeric low-energy smooth geometrically similar fiber beds

1. INTRODUCTION Although more powerful experimental techniques and more complex software for simulating is nowadays available, it seems that we have not significantly contributed to solving the task of designing steady-state bed coalescers. Expensive and relatively complicated experiments are still required in order to define all design parameters for the coalescer application. One of the main causes for this could be a lack of understanding of surface phenomena that most probably play an important, and even the dominant role. Hence, it must be recognized that a significant number of researchers are working on a better understanding of these effects, such as the surface energy, its roughness, and wettability.1−9 In the near future these results will certainly show the effects of solving the problem for designing bed coalescers. In steady-state bed coalescence bed material needs to provide the necessary conditions for merging of a small droplet to larger ones, enabling easy separation by gravity settling in the effluent stream. In porous beds only relatively unstable emulsions can reach a steady-state regime because they could form saturated liquid, a capillary-conducted fluid, flowing through the bed connected channels.10−12 On the capillary-conducted fluid surface the coalescence of incoming droplets occurs, and from this surface larger globules are detached and separated after leaving the porous bed. The quantity of the capillary-conducted phase in pores is predominantly determined by bed geometry and the intensity of hydrodynamic and adhesion forces.13,14 The pressure drop through the bed is significantly determined by the saturated amount of oil in it. The most reliable indication that the steady-state has been reached is when no change in the pressure drop is detected with time.15−17 Most of the researchers are studying the coalescence in a bed of fibers that additionally complicates better understanding of the system. The fiber bed, although extensively used in practice, is not enough known as a phenomenon and has no satisfactory mathematical models. The structure of the fiber bed is completely different from the structure of the granular bed. This bed can provide the conditions for the fluid flow even when the solid amount is 2% assuring the 98% bed © 2014 American Chemical Society

Received: November 28, 2013 Accepted: January 20, 2014 Published: January 20, 2014 2484

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Table 1. Physical Characteristics of Oil Samples sample

A

A1

A4

P1

density at 20 °C, kg/m3 viscosity at 40 °C, mPa s neutral no., mg of KOH/L pour point, °C interfacial tension, mN/m surf tension, mN/m emulsivity, vol % dielectric constant mean mol weight, kg/mol fraction, °C

915.5 43.350 1.42 −42 18.8 26.56 99.92 0.1612 410 150−550

918.9 168.904 1.71 −3 30.5 27.72 70.00 0.1905 520 315−550

905.9 9.183 1.13 −56 33.8 28.91 56.25 0.1334 150 330−390

879.0 10.316 0.13 +3 32.4 30.16 54.17 0.0645 300 320−415

results may be simplified and how to distinguish which bed material gives the best separation efficiency in function of dispersed oil properties and bed geometry.

were investigated over a wide range of bed permeability, from 5.39 to 0.18 × 10−9 m2. Unexpectedly large differences in critical velocity were obtained, from 45 to 65 m/h. On that basis, the question arises as to how to select filter media for efficient separation of oil droplets from water. The most frequent type of bed orientation for liquid−liquid separation is vertically down that was probably taken from deep bed filtration. When comparing experimental results, many researchers have neglected fluid flow orientation. Šećerov Sokolović et al showed that such an approach is not acceptable.24 They experimentally proved that separation efficiency of steady-state bed coalescence is highly influenced by the flow mode. The effect of the flow mode is dominantly determined by the range of fluid velocity. At high fluid velocity, horizontal flow bed coalescers are more efficient than vertical configurations, whereas at low velocities, no significant difference is detected. Increasing the operating velocity, the size and weight of the coalescer is reduced. These facts are of particular interest in ships and oil platforms where the load and space is drastically limited. Bed length is one of the most important design variables in bed coalescence.25−27 Šećerov Sokolović et al. investigated the effect of bed length on the steady-state coalescence of oil-inwater emulsion over all three flow modes. The presence of a minimal bed length, the critical bed length, in steady-state bed coalescence was established. This value depends on several system properties: flow mode, bed permeability, inlet oil concentration, and the nature of the filter media, etc. Bed coalescers can be installed in the industry to perform separation of oil in two different situations. One is to separate one oil during its lifetime and the other one with the task to separate different oils with time. The same oil is separated by the coalescer in the oil field, oil platform, and on ships. These coalescers can be designed on the basis of experiments on model emulsions of these oils, and therefore the optimal conditions for the work can be selected. In oil refineries and petrochemical industries, coalescers, as part of a central unit for wastewater treatment are in the situation to separate oils of different quality over time. The coalescer design for such circumstances, in our opinion, is the most complex. The scope of this work is to develop methodology for the selection of filter material for separation of oils with a broad range of properties from water using steady-state bed coalescence to obtain maximum fluid velocity. All of the parameters that were adopted in our previously published studies, such as the range of operating velocities, bed length, fluid flow orientation, and the range of bed permeability, are respected in the experiments which are the subject of this work. This work will show how the analysis of a large number of

2. EXPERIMENTAL SECTION 2.1. Experimental Setup of the Coalescer and Operating Conditions. The experiments were performed on a horizontal laboratory-scale bed coalescer, described in detail in our previous paper,21 operating in a steady-state regime. Diluted and relatively unstable model emulsion prepared using four different mineral oils were separated on four different waste polymeric materials. A fiber bed of polyurethane (designated as PU), two qualities of poly(ethylene terephthalate) (designated as BA1 and PE, respectively), and polypropylene (PP) were tested. Four mineral oils containing no additives were as follows: Vojvodinian crude oil (A), its two vacuum distillation fractions (A1, A4), and a high paraffinic blended petroleum product (P1). The inlet oil concentration (500 mg/L), working temperature (20 °C), and bed length (5 cm) were constant in all experiments. The experiments were carried out in the velocity range of 19−80 m/h, and the selected velocity was kept constant for 1 h. The experiments were performed in a broad range of bed permeability ((0.18−5.39) × 10−9 m2) and bed porosity (0.85−0.97). A steady-state regime was achieved by preoiling the bed. Model oily water was continuously stirred with a stainless steel impeller in order to ensure a mean droplet diameter of about 10 μm. In order to measure the effluent oil concentration, a composite sample consisting of three individual samples, taken after 45 min at 5 min intervals, was analyzed in each experiment. Oil concentration was measured using a ThermoNicolet 5700 FTIR spectrometer. 2.2. Properties of Dispersed Oils. As the dispersed phase four oils were selected having a wide range of property values, such as density from 880 to 920 kg/m3, viscosity from 9 to 170 mPa s, interfacial tension from 18 to 34 mN/m, dielectric constant from 0.06 to 0.20, the neutralization number from 0.10 to 1.70 mg KOH/l, emulsivity from 54 to 100%, and molecular weight from 150 to 520 kg/kmol (Table 1). It should be noted that all four investigated oils originate from naphthenic-based mineral oils. All four oils have a defined content of polar compounds which is evident from the values of the neutralization number and dielectric constant. The mentioned oil properties were characterized by the following methods and techniques: Viscosity was determined according to ISO 3104, and density according to ISO 3675. Mean molecular weight was determined by standard test 2485

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method ASTM D 2502-67. Surface tension was measured using a stalagmometer. Interfacial tension measurements were done according the du Noüy ring method. The pour point of oils was determined according to ISO 3016 standard method. The neutralization number was determined by titration. Dielectric constant was measured using Baur DPA 75. Emulsivity was estimated using a centrifuge technique28 and the following expression:

En =

VIV100 VUV

(1)

2.3. Properties of the Bed. The bed was formed using fibers of PU, or BA1, or PE, or PP. All chosen bed materials are waste materials. The PU fibers were obtained by cutting waste blocks in the furniture industry, while those of BA1 were obtained by cutting the parts of thermomaterial used for stuffing jackets. The PE fibers are waste in cutting filter media for kitchen aspirators, and PP fibers are waste in carpet production. Some important properties of filter media are given in Table 2. The bed permeability was calculated from the

Figure 1. Dependence of effluent oil concentration on fluid velocity for fiber bed PU over K01 for all investigated oils.

Table 2. Characteristics of the Fiber Bed Materials sample 3

density, kg/m melting point, °C dielectric constant crit surf tension, mN/m

PU

BA1

PE

PP

1200 310.8 3.4 23

1400 254.3 2.3 31

1400 250.7 2.3 31

900 168.60 1.5 30.5

measured pressure drop across the bed for tap water, and the data were complied with Darcy’s law. The bed porosity was measured by the weighing method. The microstructure, size and surface morphology of the fibers were characterized by scanning electron microscopy.

Figure 2. Dependence of effluent oil concentration on fluid velocity for fiber bed PP over K01 for all investigated oils.

Based on these two diagrams, which are shown, it is obvious that the value of the critical velocity is different for all materials used for the separation of oil with different properties. In the realized experimental program for each material there are five diagrams and therefore 20 all together. The influence of bed permeability on the oil separation cannot be distinguished in these diagrams. If the dependence of the effluent oil concentration on the fluid velocity and bed permeability is presented in three-dimensional (3D) diagrams, then the diagram only applies to one oil and one bed material. These diagrams are shown in Figures 3 and 4. In Figure 3 the values of the effluent oil concentration in dependence of the bed permeability and fluid velocity of oil P1 and PU bed material are presented, while Figure 4 gives an equivalent form of dependence for oil P1, but for the bed material BA1. The

3. RESULTS AND DISCUSSION 3.1. Introduction. Since many plants are related to the treatment of oily wastewater in the petroleum industry, the chemical and physical characteristics of the dispersed phase in wastewater change in a wide range of values. In order to successfully complete the selection of filter materials for coalescer work, an extensive experimental program was defined. The experiments were carried out by testing the efficiency of four fiber polymer materials during the separation of four different oils, with the variation of five bed permeabilities thus changing the geometry, as well as fluid velocity. In this way a large amount of data was collected (80 experiments including 500 points) that additionally complicated the data comparison. 3.2. Selection of the Dependent Variables. The basic form of the diagram that is necessary for the analysis of the results is the diagram dependence of the effluent oil concentration on fluid velocity. Each experiment was carried out until the critical velocity was obtained above which there is a significant breakthrough of the oil phase. Therefore, the shape of the curves in all of our experiments is exponential, as shown in Figures 1 and 2.21 The dependence of the effluent oil concentration and fluid velocity is presented in Figures 1 and 2 including all investigated oils using only one bed material, out of four tested, and one bed permeability out of five tested. These diagrams are required, in our studies, to determine the critical fluid velocity value. As already mentioned, we defined that the critical fluid velocity is the value at which the effluent oil concentration reaches a value of 15 mg/L.21−24,15,29−31

Figure 3. Three-dimensional diagram representing the interdependence of effluent oil concentration, bed permeability, and fluid velocity for fiber bed PU and oil P1. 2486

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all four diagrams, it is still not clear what material should be selected for the separation of any oil. 3.3. Selection of the Independent Variables. Bed permeability has a significant influence on the coalescence; therefore the two-diemensional (2D) diagrams on which these values are placed on the X-axis are suitable. In 3D diagrams, where bed permeability is one of the independent variables, it is difficult to perceive numerical values of the critical velocity for each experimental point, while these values are very visible on 2D diagrams. In the analysis of our results there are two sets of 2D diagrams. One diagram set refers to just an oil, Figure 7, where each curve represents a filter material, whereas the other diagram set refers to the filter materials where each curve represents one oil, Figure 8. From Figure 7 it can be noticed that the A1 oil is successfully separated with a high value of the critical velocity of PU and BA1 materials at the highest values of bed permeability, whereas in these conditions the separation of this oil for PE and PP materials was carried out at very low values of critical velocity. Considering that these values are in the 3D diagrams divided in four diagrams, it is difficult to distinguish the mentioned observations. If we look at the same type of diagram for oil P1, Figure 8, it can be concluded that the critical velocity value for this oil is highly dependent on the bed permeability, but that all the materials are equally successful at the highest bed permeability. In Figure 9 the diagram of dependence of the critical velocity and bed permeability of PU material is presented for all oils. From the mentioned diagram it is obvious that, for this material, the highest bed permeability realizes the maximum value of critical velocity. Unfortunately, in our circumstances it is not possible to create 3D diagrams on which some of the relevant material properties will exist as an independent variable. Only a small number of material properties were available from literature for our studies, such as the dielectric constant and critical surface tension. Two out of four investigated materials had the same dielectric constant; three had the same critical surface tension, while all materials showed different separation efficiency for the investigated oils. Taking all into consideration, as an independent variable, we used bed permeability and the selected properties of the oil phase. 3.4. Selection of the Diagram Type. In the two previous sections the opportunities for presenting analysis of the results using 2D and 3D diagrams were illustrated with varying combinations of dependent and independent variables. In our

Figure 4. Three-dimensional diagram representing the interdependence of effluent oil concentration, bed permeability, and fluid velocity for fiber bed BA1 and oil P1.

difference of the separation efficiency of these two materials for oil P1 is obvious. There are 16 diagrams of this kind. If the dependent variable was the critical velocity instead of the effluent oil concentration, this empty space could be filled with some other variable, for example the property of the oil phase. In this way we form a diagram that would include all investigated oils, not just one. Our previous studies gave a major review of such analyses.29,31−34 In these analyses, the question was opened as to what would be the most relevant property of the oil phase to monitor the separation efficiency using bed coalescence. Based on multivariate statistical analysis method,31 we gave an answer. The most important properties of the oil phase through which successful monitoring of the process steady-state bed coalescence can be achieved are as follows: viscosity, interfacial tension, emulsivity, and dielectric constant. The 3D diagrams are shown in Figure 5 giving the dependence of the critical velocity change, the bed permeability, and the investigated oil viscosity for materials PU, a, and BA1, b. In Figure 6 are 3D diagrams of the dependence of the critical velocity, bed permeability, and the investigated oil viscosity for materials PE, a, and PP, b. The form of the dependence of the critical velocity, bed permeability, and oil viscosity for all of the investigated materials is similar. With viscosity and bed permeability increases, the critical velocity also increases, but with a different intensity for different filter materials. Based on these diagrams, it is clear that the PU achieves a significantly higher value of the critical velocity for the separation of oil with high viscosity and at high bed permeability. Although all of the available data are included in

Figure 5. Three-dimensional diagram representing the interdependence of critical velocity, oil viscosity, and bed permeability for fiber beds (a) PU and (b) BA1. 2487

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Figure 6. Three-dimensional diagram representing the interdependence of critical velocity, oil viscosity, and bed permeability for fiber beds (a) PE and (b) PP.

Figure 7. Dependence of critical velocity on bed permeability for oil A1 using all investigated fiber beds.

Figure 9. Dependence of critical velocity on bed permeability for fiber bed PU and all investigated oils.

mentioned, according to our analysis, the most important features of the oil phase through which one can successfully monitor the bed coalescence process are as follows: viscosity, interfacial tension, emulsivity, and dielectric constant. For the contour diagrams for efficient comparison of polymer materials, emulsivity was selected for this study. Emulsivity is defined as the characteristic of oil related to water and shows the water amount left behind after the mixing and separation process.28 This feature shows the tendency of oil to form water-in-oil emulsion. Interfacial tension of the oil phase shows affinity of the oil phase to form an oil-in-water emulsion. This means that with the increase of emulsivity the interfacial tension decreases, Table 1. The mentioned feature proved to be the best in describing the influence of natural emulsifiers that are present in our investigated oils.35 The y-axes of the contour diagrams represent the bed permeability, whereas the curves are related to isocritical velocity. Contour diagrams are given in Figure 10 for fiber bed PU (a) and fiber bed BA1 (b), as well as in Figure 11 for fiber materials PE and PP, respectively. The following conclusions can be made from the contour diagrams. Materials PU and BA1 have a big area with high values of critical velocity that exceed 50 m/h for the highest bed permeability and the whole range of oil emulsivity. It has already been pointed out that high bed permeability is best suited for the separation of a number of oils. This phenomenon can be explained as follows. In the pores of the bed at steady-state bed coalescence, the capillary-

Figure 8. Dependence of critical velocity on bed permeability for oil P1 using all investigated fiber beds.

work, Govedarica et al.,31 a new type of contour diagram was presented. Such diagrams allow simultaneous analysis of the effects of the bed geometry, the nature of the dispersed oil phase, and the nature of the filter medium. The curves of the constant critical velocity were derived from the 3D plots by the projection into the XY plane. These velocities we named isocritical velocity. With this technique the total implemented experimental program (80 experiments) was included in the four diagrams. On the horizontal axis of the diagram the selected properties of the oil were placed. As already 2488

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Figure 10. Contour diagrams representing the interdependence of isocritical velocity, dispersed oil emulsivity, and bed permeability: (a) PU and (b) BA1 fiber beds.

Figure 11. Contour diagrams representing the interdependence of isocritical velocity, dispersed oil emulsivity, and bed permeability: (a) PE and (b) PP fiber beds.

conducted oil phase is situated. High bed permeability corresponds to a large volume of pores and the drastic reduction of the interstitial velocity. In these circumstances the quantity of capillary-conducted oil inside pores is maximal. This ensures high efficiency of coalescence on its surface. The other two materials, PE and PP, do not have high values of critical velocity at high bed permeability in the whole range of oil emulsivity and only exhibit high critical velocity at oil emulsivity higher than 70%. This indicates that PE and PP materials are sensitive to the change of the nature of the dispersed oil. From this, it could be concluded that materials PU and BA1 are a better choice for the separation of oils with different natures. The selection of one material from the last two remains. If we adopt the operating velocity to be 50 m/h, this aimed goal could be accomplished by both materials for all oils. However the size of the surface over which these materials can provide the mentioned velocity is significantly different. The region of the velocity of 50 m/h for the PU material is dominant also at lower bed permeability and over a wide range of emulsivity, while for the BA1 material this is not the case. Why is this fact important and significant? While working in the field, coalescers are exposed to different situations. It may happen that there is a high content of suspended solids and/or solid particles of oil

below the pour point, especially in the winter. This could temporarily or permanently block the pores, which would cause a decrease in bed permeability. The PU material is not sensitive in such a situation, while the BA1 material is sensitive to it. Considering all of the above, application of PU material provides greater reliability of bed coalescers for a wide range of wastewater quality, not only in terms of the nature of the oil phase but also on the content of suspended solids in the influent.

4. CONCLUSION This work presents a strategy for the selection of fiber filter media for bed coalescer that works in the steady-state regime and has the ability to separate oils of different nature over time. On the basis of experiments in which four polymer materials were investigated for the separation of four different types of mineral oils changing the geometry over the five bed permeability, using contour diagrams, the following conclusions were made. Materials PU and BA1 have big areas with high values of the critical velocity, exceeding 50 m/h in the zone of the highest bed permeability for the full range of natural oils related to their emulsivity. The other two materials, PE and PP, did not exhibit this area in the whole range of oil properties, in 2489

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(13) Rosenfeld, J. I.; Wasan, D. T. Coalescence of Drops in a LiquidLiquid Dispersion by Passage through a Fibrous Bed. Can. J. Chem. Eng. 1974, 52, 3−10. (14) Hazlett, R. N. Fibrous Bed Coalescence of Water: Steps in the Coalescence Process. Ind. Eng. Chem. Fundam. 1969, 8, 625−632. (15) Spielman, L. A.; Goren, S. L. Model for Predicting Pressure Drop and Filtration Efficiency in Fibrous Media. Environ. Sci. Technol. 1968, 2, 279−287. (16) Austin, D. G.; Jeffreys, G. V. Coalescence Phenomena in LiquidLiquid Systems. J. Chem. Technol. Biotechnol. 1981, 31, 475−488. (17) Bitten, J. F. Coalescence of Water Droplets on Single Fibers. J. Colloid Interface Sci. 1970, 33, 265−271. (18) Šećerov Sokolović, R. M.; Sokolović, S. M. Coalescence in porous bed (Koalescencija u poroznom sloju). Monography; Faculty of Technology, University of Novi Sad: Novi Sad, Serbia, 2000. (19) Šećerov Sokolović, R. M.; Stanimirović, O. P.; Sokolović, S. M. The infulence of fibrous bed bulk density on the bed properties (Uticaj promene nasipne gustine na osobine sloja vlaknastih materijala). Hem. Ind. 2003, 57, 335−340. (20) Jackson, G. W.; James, D. F. Can. J. Chem. Eng. 1986, 64, 364− 374. (21) Šećerov Sokolović, R. M.; Sokolović, S. M.; Đoković, 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. (22) Šećerov Sokolović, R.; Vulić, T. J.; Sokolović, S. M.; Marinković Nedučin, R. P. Effect of Fibrous Bed Permeability on Steady-State Coalescence. Ind. Eng. Chem. Res. 2003, 42, 3098−3102. (23) Šećerov Sokolović, R. M.; Sokolović, S. M. Effect of the Nature of Different Polymeric Fibers on Steady-State Bed Coalescence of an Oil-in-Water Emulsion. Ind. Eng. Chem. Res. 2004, 43, 6490−6495. (24) Šećerov 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. (25) Sareen, S. S.; Rose, P. M.; Gudesen, R. C.; Kintner, R. C. Coalescence in Fibrous Beds. AIChE J. 1966, 12, 1045−1050. (26) 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, A19 (3), 299−319. (27) Šećerov Sokolović, R. M.; Vulić, T.; Sokolović, S. Effect of Bed Length on Steady-State Coalescence of Oil-in-Water Emulsion. Sep. Purif. Technol. 2007, 56, 79−84. (28) Šević, S. Influence of Formation Water on Production and Transport of Petroleum and Natural Gas (Uticaj ležišne vode na proizvodnju i transport nafte i gasa); DIT NIS-Naftagas: Novi Sad, Serbia, 2000, 207−235. (29) Govedarica, D. D. Fiber Bed Coalescence of Mineral Oil (Koalescencija mineralnih ulja u vlaknastom sloju). Ph.D. Dissertation, University of Novi Sad: Novi Sad, Serbia, April 2011 (30) Govedarica, D. D.; Šećerov Sokolović, R. M.; Sokolović, D. S.; Sokolović, S. M. Evaluation of the Separation of Liquid-Liquid Dispersions by Flow through Fiber Beds. Ind. Eng. Chem. Res. 2012, 51, 16085−16091. (31) Govedarica, D.; Šećerov Sokolović, R.; Sokolović, D.; Sokolović, S. A Novel Approach for the Estimation of the Efficiency of SteadyState Fiber Bed Coalescence. Sep. Purif. Technol. 2013, 104, 268−275. (32) Šećerov Sokolović, R. M.; Sokolović, S. M.; Mihajlović, Đ. S. Influence of Oil Properties on Bed Coalescence Efficiency. Sep. Sci. Technol. 1996, 31, 2089−2104. (33) Šećerov Sokolović, R.; Sokolović, S.; Šević, S. Oily Water Treatment Using a New Steady-State Fiber-Bed Coalescer. J. Hazard. Mater. 2009, 162, 410−415. (34) Šećerov Sokolović, R. M.; Govedarica, D. D.; Sokolović, D. S. Separation of Oil-In-Water Emulsion Using Two Coalescers Of Different Geometry. J. Hazard. Mater. 2010, 175, 1001−1006. (35) Sokolović, D. S.; Šećerov Sokolović, R. M.; Sokolović, S. M. Rheology of unstable mineral emulsions (Proučavanje reoloških osobina nestabilnih emulzija mineralnog porekla). Hem. Ind. 2013, 67, 293−301.

this case the high critical velocity is limited to emulsivity higher than 70%. This indicated that PE and PP materials are sensitive to the change of the nature of the dispersed oil phase. On the other hand the PU material is not sensitive to the decrease of bed permeability due to clogging of pores, while the BA1 material is sensitive. We give an advantage to the PU material over the other investigated materials for the separation of oils of different nature. This material shows greater reliability for bed coalescers in a wide range of wastewater quality, not only in terms of the nature of oil phase but also on the content of suspended solids.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +381214853677. Fax: +38121450413. E-mail: radost@ uns.ac.rs. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work was supported by the Ministry of Education and Science of the Republic of Serbia, Grant No. 172022.

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NOMENCLATURE En = dispersed oil emulsivity, vol % K0 = bed permeability, m2 Vk = critical velocity for the effluent oil concentration of 15 mg/L, m/h VIV = free water volume, mL VUV = total water volume, mL

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REFERENCES

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dx.doi.org/10.1021/ie404013e | Ind. Eng. Chem. Res. 2014, 53, 2484−2490