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The Electrodynamic Contactor for Extraction
Solvent Extraction 1990, T. Sekine (Editor) © 1992 Elsevier Science Publishers B.V. All rights reserved
1417
THE ELECTRODYNAMIC CONTACTOR FOR EXTRACTION Kenneth W. Warren and J.J. Byeseda NATCO, P.O. Box 1710, Tulsa, OK 74101
USA
ABSTRACT Electrostatic fields are commonly used to coalesce fine water droplets in oilcontinuous emulsions. Soluble salts are removed from the organic phase by first mixing the hydrocarbon with fresh water. The resulting mixture of finely dispersed water drops is then separated using high voltage electrostatic energy. Several stages of mixing and separation (using multiple vessels) may be required in order to achieve the desired mass transfer efficiency. The Electrodynamic Contactor uses electrostatic energy for both mixing and separation of the phases. Countercurrent flow of the aqueous and organic phases enables the attainment of the equivalent of several theoretical stages within one vessel. Data generated in the removal of soluble salts from crude petroleum may be applied in the design of other two-phase solvent extraction processes. INTRODUCTION The removal of soluble of salts from petroleum is a special case of liquid/liquid extraction utilizing intimate contact followed by phase separation to achieve mass transfer from the feed stream to a second stream consisting of an immiscible phase. It differs from conventional two phase liquid extraction in that the feed stream is a heterogeneous dispersion rather than a solution, and the material to be extracted consists primarily of liquid dispersed in the feed rather than solutes. There are sufficient parallels between petroleum desalting and normal solvent extraction processes to enable one to readily utilize developments in one field as steps to process improvements in the other. Any extraction process may be divided into three steps: (1) Intimate contact between the two immiscible phases, (2) Coalescence or growth of the drops of the dispersed phase, and (3) Separation of the phases, usually by sedimentation. Contact is most often secured by a variety of mechanically driven mixing schemes followed by retention time to allow gravity induced phase separation. Coalescence is the agglomeration of drops of the dispersed phase to a size sufficient for removal by sedimentation. It is a multistage process consisting of coagulation, a chemical process in which the surface forces stabilizing the dispersion are reduced to allow droplet collisions to occur, and flocculation in which drops combine into larger drops. It is essential to note that droplet growth cannot proceed until the stabilizing forces are small enough to permit drop collisions. Flocculation may also be promoted chemically, although the introduction of additional chemical species in a closed loop process may be undesirable. Therefore, electroflocculation produced by the application of electric fields to the dispersion is to be preferred as long as operating considerations permit the maintenance of organic phase continuous dispersions.
1418
Sedimentation in a solvent extraction process relies upon retention time within a quiescent zone to allow the flocculated drops to settle out of the continuous phase. This is accomplished in the settler section of a typical mixer/settler. Although elevated temperatures can aid sedimentation by reducing the continuous phase viscosity and often increasing the density differential between the two phases, the range of available temperatures in a conventional mixer/settler is limited. The sedimentation velocity is given by the following: (1.36)(10- 6 )g^ ( P t v - P o )
v
where
V = Sedimentation Velocity (m sec"1) p w = Specific Gravity of Dispersed Phase p 0 = Specific Gravity of Continuous Phase
(1)
g = Gravitation Constant r = Drop Radius (m) rj = Viscosity (centipoise)
The importance of the drop size, differential density, and viscosity are readily apparent. Although augmentation of the gravitational field is possible, due to operational constraints, this approach is of limited application.
2. RESOLUTION OF EMULSIONS BY ELECTRIC FIELDS 2.1 AC Fields Design considerations for solvent extraction systems assume that a properly coagulated mixture is to be processed. Therefore, design emphasis is placed on the flocculation and sedimentation device. The oldest commercially applied electroflocculation technology utilizes the application of high voltage alternating current (AC) fields to the water-in-oil emulsion. Due to the dipolar nature of the water molecules, these molecules tend to align themselves with an electrical field. As the molecules within a drop become aligned with the field, the drop itself becomes distorted into an ellipsoidal shape. A collection of such drops consists of ellipsoids aligned with the field such that the charged end of one drop is adjacent to the oppositely charged end of its neighbor. An electrical attraction thus arises between adjacent drops. The attractive force between adjacent drops of equal size may be ex pressed as follows: p
_ 24e0eE*r*
(2)
(d+2r)4
where
F = Electrostatic Force between Drops (N) e 0 = Permittivity of Free Space e = Dielectric Constant of Continuous Phase d = Interdrop Distance (m)
Although this force is significant, particularly at close range, it rises and falls with the oscillating AC field and reverses itself at a rate twice that of the frequency of the applied
1419
field.1 Thus there is little opportunity for drop movement, and coalescence is limited to drops which are very close together. AC flocculation is particularly effective in assisting condensation of the hindered settling zone which develops at the oil/water interface as large water drops settle but are unable to penetrate the interfacial surface. An additional benefit realized as a result of the oscillatory deformation of the dispersed drops is the rupture of stabilizing films of suspended solids, semisoluble organic fractions, and other debris which collect at the drop surface and hinder interaction between drops which would otherwise coalesce.2 2.2 DC Fields The use of direct current (DC) fields in electroflocculation has several beneficial effects. The dispersed water drops still experience the attraction expressed in Equation (2), but in a steady, unidirectional field, attraction results in migration. Therefore, coalescence effects dependent on drop proximity are greatly enhanced. Migration ultimately results in movement of drops to one of the electrodes where they assume a net charge of the same polarity as the contacted electrode. In an array of oppositely charged electrodes, the charged drops are then accelerated toward an oppositely charged electrode. This results in drops of opposite charge flowing counter-current to each other with a large in crease in electrically induced flocculation. A problem encountered in any metal/electrolyte system in the presence of an electrical current is corrosion. In an AC system, the rapid directional change in the current results in reversal of the electrolytic reactions before diffusion of the reaction products away from the electrolytic cell makes these reactions irreversible. In a DC system, the electrolytic reactions are continuous, and corrosion of the metallic components can become a serious problem. 2.3 Combination AC/DC Fields The benefits of both AC and DC fields can be obtained by an electrical arrangement which places a DC field across adjacent electrodes constructed of corrosion resistant material while maintaining an AC field between these electrodes and electrical ground. (Figure 1) 3 4 The containment vessel and the water layer are maintained at ground potential, so the corrosion inhibiting effects of the AC field are found at the vessel wall, and the AC field induced F | g u r e 1 D u a | P o l a r i t y TM C o a l e s c e r condensation of the hindered settling zone occurs at the oil/water interface. Between the electrodes, the DC induced migration of water droplets and enhanced electroflocculation result in greater droplet growth.
1420 3. DROP SIZE CONTROL BY THE ELECTRIC FIELD It has been recognized that an equilibrium drop size is reached in an electroflocculation device which is dependent upon field strength with smaller drops occurring at higher field strength.5 Examination of Equation (2) also indicates that electroflocculation of small drops requires a high electric field gradient in order to achieve significant coalescence. Thus the field strength necessary to reduce the remnant water content of an organic stream may produce an equilibrium drop size not well suited to sedimentation. There are two approaches for avoiding this compromise. One is time varying control of field strength 6, and the other is control of field strength over a segment of the treating space.7,8 In the first, the field strength is subjected to a periodic variation which coalesces small droplets in a strong field, and then allows drop growth in a declining field. Since the drops are settling as this occurs, the small droplets which settle slowly are subjected to repeated cycles while large drops fall out of the affected zone during periods of low field strength. In the second case, the treating zone field strength is varied along its vertical axis by using resistive electrodes to generate the field.9 Again, the larger drops migrate downward into the zone of lower field strength which results in further growth. In practice, both methods may be applied simultaneously.10 Just as declining field strength can enhance drop growth, increasing field strength can produce drop dispersion or electrostatic mixing. 11,12,13 Several mechanisms con tribute to this effect, (a) Increasing migration velocity at high field strength leads to increased hydrodynamic shear resulting in drop deformation and division, (b) If the field strength is oscillating at a frequency near the resonant frequency of the drops, unstable oscillations resulting in drop shatter are produced. 14-15'16 (c) Drop charge of sufficient magnitude has been shown to produce electrostatic instability leading to drop shattering. It should be noted in each of these mechanisms that the forces leading to dispersion are largely confined to the dispersed phase with minimum power expenditure on movement of the continuous phase. The resonant frequency technique, called the Emulsion Phase Contactor, is now being commercially developed for solvent extraction applications. 4. APPLICATION DATA 4.1 Salt Extraction from Petroleum Electrostatic mixing in which the voltage is periodically modulated between dispersion voltage and coalescing voltage has been applied in the extraction of soluble salts from petroleum. Performance in such a system consists of two factors: mass transfer and phase separation. These factors are shown for a light petroleum (specific gravity 0.845), similar to the diluents in commercial hydrometallurgical installations, in Figures 2 and 3. Figure 2 illustrates the mass transfer of soluble salts from the petroleum to the aqueous phase. Note that two parallel commercial installations are included. The average inlet salt concentration is 56.1 ppm while the average outlet concentrations are 2.69 ppm for Unit #1 and 2.20 ppm for Unit #2. Salt was analyzed as soluble chloride and reported as equivalent sodium chloride. In each case, the outlet values approach the limits of analytical accuracy for the methods used (titrimetry). Phase separation performance is shown in Figure 3. Inlet water concentration was
1421
effectively five percent since that was the amount of water added. Unit #1 had an average effluent water content of 0.06% while Unit # 2 had an average of 0.11%. Phase separation efficiencies were 98.8% for Unit #1 and 97.8% for Unit #2. These data represent a single physical contact stage operated at a flux of between 1.2 and 1.5 gpm ft"1.
- #2 Outlet Salt
I
■W-s^ 30 Days
4.2 Extraction of Organic Acid Figure 2 Salt Extraction Performance Data from Oak Ridge National Laboratory using the #2 Outlet Water #1 Outlet Water resonant frequency technique17 have d e m o n s t r a t e d the effectiveness of the electrostatic contactor as compared to JjO.6 \ conventional techniques. Data Jl for the transfer of acetic acid " jl 1ii1 1 \ between water and methyl 11 A /1 !'; isobutyl ketone in the Emulsion I \ Ai / I „J Phase Contactor were i'\A \ \ /MJ /\ V*S^ ' compared with published mass transfer data on this system in a Days York-Scheibel column and a Figure 3 Phase Separation Performance Podbielniak centrifugal contactor. The Emulsion Phase Contactor produced 1.71 theoretical stages per centimeter of column compared to 0.10 stages per cm for the York-Scheibel column and 0.17 stages per cm for the Podbielniak.
iH '! k
jihc±
4.3 Removal of Water from Alcohol/Ketone/Ester Solvent Samples of a solvent used in a wash process in an ester plant consisting of a blend of oxygenated organic compounds were tested for susceptibility to electrostatic phase separation. The samples were saturated with the aqueous phase in a blender and allowed to settle. The resulting emulsion contained 1.1% aqueous phase in the form of a fine haze after settling. Electrostatic treatment of these emulsions consistently produced phase separation with an organic phase containing less than 0.1% by weight of water. 4.4 Removal of Water from Lanthanide Extraction Solvent Samples of a solvent from a lanthanide extraction operation using an aliphatic organic acid in a kerosene diluent were also tested for phase separation by electrostatic fields. Water was added to the samples as received to a concentration of 10%. After agitation, the samples were subjected to electrostatic separation. The water content dropped
1422
rapidly to between 0.05 and 0.1% and continued to drop to trace quantities within five minutes. 5. CONCLUSIONS Electrostatic processes have proved their merit in phase separation and mass transfer in liquid/liquid extraction systems in both pilot and commercial scale installations. Although phase separation is the more commercially advanced application, rapid developments in electrostatically enhanced mass transfer promise great benefits to solvent extraction operators in the form of more compact equipment, reduced energy requirements, higher purity products, and the increased environmental safeguards inherent in closed systems. 6. REFERENCES 1. Burris, D. R.: "Dual Polarity Oil Dehydration," Petroleum Engineer International (August 1977). 2. Brown, A. H. and Hanson, C: "The Effect of Oscillating Electric Fields on the Coalescence of Liquid Drops," Chem. Enq. Sci. 23, 841 (1968). 3. Prestridge, F. L: "Electric Treater," U. S. Pat. 3,772,180. 4. Prestridge, F. L: "Process for Electrical Coalescing of Water," U. S. Pat. 3.847.775. 5. Bailes, P. J.: "Solvent Extraction in an Electrostatic Field," l&EC Process Design and Development 20, 564-570 (July 1981). 6. Prestridge, F. L, Schuetz, A. A., and Wheeler, H. L: "Voltage Control System for an Electrostatic Oil Treater," U. S. Pat. 4,400,253. 7. Prestridge, F. L: "Method and Apparatus for Separation of Fluids with an Electric Field," U. S. Pat. 4.126.537. 8. Prestridge, F. L. and Longwell, R. L: "Separation of Emulsions with an Electric Field," U. S. Pat. 4.308.127. 9. Prestridge, F. L. and Johnson, B. C : "Distributed Charge Composite Electrodes and Desalting System," U. S. Pat. 4.702.815. 10. Warren, K. W. and Prestridge, F. L: "Crude Oil Desalting by Counterflow Electrostatic Mixing," National Petroleum Refiners Association 1988 Annual Meeting, AM-88-78, San Antonio, Texas (March 1988). 11. Warren, K. W. and Prestridge, F. L: "Apparatus for Application of Electrostatic Fields to Mixing and Separating Fluids," U. S. Pat. 4.161.439. 12. Warren, K. W. and Prestridge, F. L: "Process for Application of Electrostatic Fields to Mixing and Separating Fluids," U. S. Pat. 4.204.934. 13. Johnson, B. C. and Prestridge, F. L: "Electrostatic Mixer/Separator" U. S. Pat. 4.606.801. 14. Basaran, O. A. and Scriven, L E.: "Axisymmetric Shapes and Stability of Isolated Charged Drops," Phvs. Fluids A 5, 795-798 (May 1989). 15. Basaran, O. A. and Scriven, L. E.: "Axisymmetric Shapes and Stability of Charged Drops in an External Electric Field," Phvs. Fluids A 5, 799-809 (May 1989). 16. Scott, T. C. and Wham, R. M.: "Surface Area Generation and Droplet Size Control in Solvent Extraction Systems Utilizing High Intensity Electric Fields," U. S. Pat. 4.767.515. 17. Scott, T. C. and Wham, R. M.: "An Electrically Driven Multistage Countercurrent Solvent Extraction Device: The Emulsion Phase Contactor," Industrial and Engineering Chemistry Research 28, 94 (1989).
1417
THE ELECTRODYNAMIC CONTACTOR FOR EXTRACTION Kenneth W. Warren and J.J. Byeseda NATCO, P.O. Box 1710, Tulsa, OK 74101
USA
ABSTRACT Electrostatic fields are commonly used to coalesce fine water droplets in oilcontinuous emulsions. Soluble salts are removed from the organic phase by first mixing the hydrocarbon with fresh water. The resulting mixture of finely dispersed water drops is then separated using high voltage electrostatic energy. Several stages of mixing and separation (using multiple vessels) may be required in order to achieve the desired mass transfer efficiency. The Electrodynamic Contactor uses electrostatic energy for both mixing and separation of the phases. Countercurrent flow of the aqueous and organic phases enables the attainment of the equivalent of several theoretical stages within one vessel. Data generated in the removal of soluble salts from crude petroleum may be applied in the design of other two-phase solvent extraction processes. INTRODUCTION The removal of soluble of salts from petroleum is a special case of liquid/liquid extraction utilizing intimate contact followed by phase separation to achieve mass transfer from the feed stream to a second stream consisting of an immiscible phase. It differs from conventional two phase liquid extraction in that the feed stream is a heterogeneous dispersion rather than a solution, and the material to be extracted consists primarily of liquid dispersed in the feed rather than solutes. There are sufficient parallels between petroleum desalting and normal solvent extraction processes to enable one to readily utilize developments in one field as steps to process improvements in the other. Any extraction process may be divided into three steps: (1) Intimate contact between the two immiscible phases, (2) Coalescence or growth of the drops of the dispersed phase, and (3) Separation of the phases, usually by sedimentation. Contact is most often secured by a variety of mechanically driven mixing schemes followed by retention time to allow gravity induced phase separation. Coalescence is the agglomeration of drops of the dispersed phase to a size sufficient for removal by sedimentation. It is a multistage process consisting of coagulation, a chemical process in which the surface forces stabilizing the dispersion are reduced to allow droplet collisions to occur, and flocculation in which drops combine into larger drops. It is essential to note that droplet growth cannot proceed until the stabilizing forces are small enough to permit drop collisions. Flocculation may also be promoted chemically, although the introduction of additional chemical species in a closed loop process may be undesirable. Therefore, electroflocculation produced by the application of electric fields to the dispersion is to be preferred as long as operating considerations permit the maintenance of organic phase continuous dispersions.
1418
Sedimentation in a solvent extraction process relies upon retention time within a quiescent zone to allow the flocculated drops to settle out of the continuous phase. This is accomplished in the settler section of a typical mixer/settler. Although elevated temperatures can aid sedimentation by reducing the continuous phase viscosity and often increasing the density differential between the two phases, the range of available temperatures in a conventional mixer/settler is limited. The sedimentation velocity is given by the following: (1.36)(10- 6 )g^ ( P t v - P o )
v
where
V = Sedimentation Velocity (m sec"1) p w = Specific Gravity of Dispersed Phase p 0 = Specific Gravity of Continuous Phase
(1)
g = Gravitation Constant r = Drop Radius (m) rj = Viscosity (centipoise)
The importance of the drop size, differential density, and viscosity are readily apparent. Although augmentation of the gravitational field is possible, due to operational constraints, this approach is of limited application.
2. RESOLUTION OF EMULSIONS BY ELECTRIC FIELDS 2.1 AC Fields Design considerations for solvent extraction systems assume that a properly coagulated mixture is to be processed. Therefore, design emphasis is placed on the flocculation and sedimentation device. The oldest commercially applied electroflocculation technology utilizes the application of high voltage alternating current (AC) fields to the water-in-oil emulsion. Due to the dipolar nature of the water molecules, these molecules tend to align themselves with an electrical field. As the molecules within a drop become aligned with the field, the drop itself becomes distorted into an ellipsoidal shape. A collection of such drops consists of ellipsoids aligned with the field such that the charged end of one drop is adjacent to the oppositely charged end of its neighbor. An electrical attraction thus arises between adjacent drops. The attractive force between adjacent drops of equal size may be ex pressed as follows: p
_ 24e0eE*r*
(2)
(d+2r)4
where
F = Electrostatic Force between Drops (N) e 0 = Permittivity of Free Space e = Dielectric Constant of Continuous Phase d = Interdrop Distance (m)
Although this force is significant, particularly at close range, it rises and falls with the oscillating AC field and reverses itself at a rate twice that of the frequency of the applied
1419
field.1 Thus there is little opportunity for drop movement, and coalescence is limited to drops which are very close together. AC flocculation is particularly effective in assisting condensation of the hindered settling zone which develops at the oil/water interface as large water drops settle but are unable to penetrate the interfacial surface. An additional benefit realized as a result of the oscillatory deformation of the dispersed drops is the rupture of stabilizing films of suspended solids, semisoluble organic fractions, and other debris which collect at the drop surface and hinder interaction between drops which would otherwise coalesce.2 2.2 DC Fields The use of direct current (DC) fields in electroflocculation has several beneficial effects. The dispersed water drops still experience the attraction expressed in Equation (2), but in a steady, unidirectional field, attraction results in migration. Therefore, coalescence effects dependent on drop proximity are greatly enhanced. Migration ultimately results in movement of drops to one of the electrodes where they assume a net charge of the same polarity as the contacted electrode. In an array of oppositely charged electrodes, the charged drops are then accelerated toward an oppositely charged electrode. This results in drops of opposite charge flowing counter-current to each other with a large in crease in electrically induced flocculation. A problem encountered in any metal/electrolyte system in the presence of an electrical current is corrosion. In an AC system, the rapid directional change in the current results in reversal of the electrolytic reactions before diffusion of the reaction products away from the electrolytic cell makes these reactions irreversible. In a DC system, the electrolytic reactions are continuous, and corrosion of the metallic components can become a serious problem. 2.3 Combination AC/DC Fields The benefits of both AC and DC fields can be obtained by an electrical arrangement which places a DC field across adjacent electrodes constructed of corrosion resistant material while maintaining an AC field between these electrodes and electrical ground. (Figure 1) 3 4 The containment vessel and the water layer are maintained at ground potential, so the corrosion inhibiting effects of the AC field are found at the vessel wall, and the AC field induced F | g u r e 1 D u a | P o l a r i t y TM C o a l e s c e r condensation of the hindered settling zone occurs at the oil/water interface. Between the electrodes, the DC induced migration of water droplets and enhanced electroflocculation result in greater droplet growth.
1420 3. DROP SIZE CONTROL BY THE ELECTRIC FIELD It has been recognized that an equilibrium drop size is reached in an electroflocculation device which is dependent upon field strength with smaller drops occurring at higher field strength.5 Examination of Equation (2) also indicates that electroflocculation of small drops requires a high electric field gradient in order to achieve significant coalescence. Thus the field strength necessary to reduce the remnant water content of an organic stream may produce an equilibrium drop size not well suited to sedimentation. There are two approaches for avoiding this compromise. One is time varying control of field strength 6, and the other is control of field strength over a segment of the treating space.7,8 In the first, the field strength is subjected to a periodic variation which coalesces small droplets in a strong field, and then allows drop growth in a declining field. Since the drops are settling as this occurs, the small droplets which settle slowly are subjected to repeated cycles while large drops fall out of the affected zone during periods of low field strength. In the second case, the treating zone field strength is varied along its vertical axis by using resistive electrodes to generate the field.9 Again, the larger drops migrate downward into the zone of lower field strength which results in further growth. In practice, both methods may be applied simultaneously.10 Just as declining field strength can enhance drop growth, increasing field strength can produce drop dispersion or electrostatic mixing. 11,12,13 Several mechanisms con tribute to this effect, (a) Increasing migration velocity at high field strength leads to increased hydrodynamic shear resulting in drop deformation and division, (b) If the field strength is oscillating at a frequency near the resonant frequency of the drops, unstable oscillations resulting in drop shatter are produced. 14-15'16 (c) Drop charge of sufficient magnitude has been shown to produce electrostatic instability leading to drop shattering. It should be noted in each of these mechanisms that the forces leading to dispersion are largely confined to the dispersed phase with minimum power expenditure on movement of the continuous phase. The resonant frequency technique, called the Emulsion Phase Contactor, is now being commercially developed for solvent extraction applications. 4. APPLICATION DATA 4.1 Salt Extraction from Petroleum Electrostatic mixing in which the voltage is periodically modulated between dispersion voltage and coalescing voltage has been applied in the extraction of soluble salts from petroleum. Performance in such a system consists of two factors: mass transfer and phase separation. These factors are shown for a light petroleum (specific gravity 0.845), similar to the diluents in commercial hydrometallurgical installations, in Figures 2 and 3. Figure 2 illustrates the mass transfer of soluble salts from the petroleum to the aqueous phase. Note that two parallel commercial installations are included. The average inlet salt concentration is 56.1 ppm while the average outlet concentrations are 2.69 ppm for Unit #1 and 2.20 ppm for Unit #2. Salt was analyzed as soluble chloride and reported as equivalent sodium chloride. In each case, the outlet values approach the limits of analytical accuracy for the methods used (titrimetry). Phase separation performance is shown in Figure 3. Inlet water concentration was
1421
effectively five percent since that was the amount of water added. Unit #1 had an average effluent water content of 0.06% while Unit # 2 had an average of 0.11%. Phase separation efficiencies were 98.8% for Unit #1 and 97.8% for Unit #2. These data represent a single physical contact stage operated at a flux of between 1.2 and 1.5 gpm ft"1.
- #2 Outlet Salt
I
■W-s^ 30 Days
4.2 Extraction of Organic Acid Figure 2 Salt Extraction Performance Data from Oak Ridge National Laboratory using the #2 Outlet Water #1 Outlet Water resonant frequency technique17 have d e m o n s t r a t e d the effectiveness of the electrostatic contactor as compared to JjO.6 \ conventional techniques. Data Jl for the transfer of acetic acid " jl 1ii1 1 \ between water and methyl 11 A /1 !'; isobutyl ketone in the Emulsion I \ Ai / I „J Phase Contactor were i'\A \ \ /MJ /\ V*S^ ' compared with published mass transfer data on this system in a Days York-Scheibel column and a Figure 3 Phase Separation Performance Podbielniak centrifugal contactor. The Emulsion Phase Contactor produced 1.71 theoretical stages per centimeter of column compared to 0.10 stages per cm for the York-Scheibel column and 0.17 stages per cm for the Podbielniak.
iH '! k
jihc±
4.3 Removal of Water from Alcohol/Ketone/Ester Solvent Samples of a solvent used in a wash process in an ester plant consisting of a blend of oxygenated organic compounds were tested for susceptibility to electrostatic phase separation. The samples were saturated with the aqueous phase in a blender and allowed to settle. The resulting emulsion contained 1.1% aqueous phase in the form of a fine haze after settling. Electrostatic treatment of these emulsions consistently produced phase separation with an organic phase containing less than 0.1% by weight of water. 4.4 Removal of Water from Lanthanide Extraction Solvent Samples of a solvent from a lanthanide extraction operation using an aliphatic organic acid in a kerosene diluent were also tested for phase separation by electrostatic fields. Water was added to the samples as received to a concentration of 10%. After agitation, the samples were subjected to electrostatic separation. The water content dropped
1422
rapidly to between 0.05 and 0.1% and continued to drop to trace quantities within five minutes. 5. CONCLUSIONS Electrostatic processes have proved their merit in phase separation and mass transfer in liquid/liquid extraction systems in both pilot and commercial scale installations. Although phase separation is the more commercially advanced application, rapid developments in electrostatically enhanced mass transfer promise great benefits to solvent extraction operators in the form of more compact equipment, reduced energy requirements, higher purity products, and the increased environmental safeguards inherent in closed systems. 6. REFERENCES 1. Burris, D. R.: "Dual Polarity Oil Dehydration," Petroleum Engineer International (August 1977). 2. Brown, A. H. and Hanson, C: "The Effect of Oscillating Electric Fields on the Coalescence of Liquid Drops," Chem. Enq. Sci. 23, 841 (1968). 3. Prestridge, F. L: "Electric Treater," U. S. Pat. 3,772,180. 4. Prestridge, F. L: "Process for Electrical Coalescing of Water," U. S. Pat. 3.847.775. 5. Bailes, P. J.: "Solvent Extraction in an Electrostatic Field," l&EC Process Design and Development 20, 564-570 (July 1981). 6. Prestridge, F. L, Schuetz, A. A., and Wheeler, H. L: "Voltage Control System for an Electrostatic Oil Treater," U. S. Pat. 4,400,253. 7. Prestridge, F. L: "Method and Apparatus for Separation of Fluids with an Electric Field," U. S. Pat. 4.126.537. 8. Prestridge, F. L. and Longwell, R. L: "Separation of Emulsions with an Electric Field," U. S. Pat. 4.308.127. 9. Prestridge, F. L. and Johnson, B. C : "Distributed Charge Composite Electrodes and Desalting System," U. S. Pat. 4.702.815. 10. Warren, K. W. and Prestridge, F. L: "Crude Oil Desalting by Counterflow Electrostatic Mixing," National Petroleum Refiners Association 1988 Annual Meeting, AM-88-78, San Antonio, Texas (March 1988). 11. Warren, K. W. and Prestridge, F. L: "Apparatus for Application of Electrostatic Fields to Mixing and Separating Fluids," U. S. Pat. 4.161.439. 12. Warren, K. W. and Prestridge, F. L: "Process for Application of Electrostatic Fields to Mixing and Separating Fluids," U. S. Pat. 4.204.934. 13. Johnson, B. C. and Prestridge, F. L: "Electrostatic Mixer/Separator" U. S. Pat. 4.606.801. 14. Basaran, O. A. and Scriven, L E.: "Axisymmetric Shapes and Stability of Isolated Charged Drops," Phvs. Fluids A 5, 795-798 (May 1989). 15. Basaran, O. A. and Scriven, L. E.: "Axisymmetric Shapes and Stability of Charged Drops in an External Electric Field," Phvs. Fluids A 5, 799-809 (May 1989). 16. Scott, T. C. and Wham, R. M.: "Surface Area Generation and Droplet Size Control in Solvent Extraction Systems Utilizing High Intensity Electric Fields," U. S. Pat. 4.767.515. 17. Scott, T. C. and Wham, R. M.: "An Electrically Driven Multistage Countercurrent Solvent Extraction Device: The Emulsion Phase Contactor," Industrial and Engineering Chemistry Research 28, 94 (1989).