PARMA N. VASHIST ROBERT B. BECKMANN
ANNUAL REVIEW
review of the liquid-liquid extraction literaThistureyear’s . . ’ . is primarily concerned with the significant de-
Liquid-Liquid Extraction While dynamics and simulation of extraction processes are receiving increasing attention, physical-chemical principles are being comparatively neglected
0
velopments that have appeared in the process and equipment literature during 1966 and 1967. The Annual Review in 1966 (7A) siinilarly covered the process and eqiripinent area of liquid-liquid rxtraction for the previous two-year period, 1964 and 1965. Last year’s review (27A) was priiiiarily concerned with the more fundamental aspcctsof the liquid-liquid mass tranderoperation The years 1766-67 can best be classed as a n active period, yet not dynamic, writh regard to process, equiprnent, and systems areas of liquid-liquid extraction Foreign researchers continue to contribute a inajor share of the developments and progress although equipiiient innovations siill seeiii the primary preserve of Ainerican researchers General reviews and iiiiproved calrulational methods have not rcccivcd as much compreheiisive attentioii as in previous years, and backniixing, dynamic behavior, and simulation continue to be favorite topics Orgaiiophosphates and ainines continue to receive the most attention for inorganic extractions, sulfoxide5 and sulfaniides seein to be favorites of the inoinent for research on hydrocdrbon separations The fundamental aspccts of the physical-organic principles underlying solvent extrartivii recrived surprisingly meager attention The conventional mixer-settler extractor types and the packed-, spray-, and plate-type columns (with and without internal aqitation) continue to receive considerable research emphasis Some new and intriguing equipment modifirations have been reported and these should stimulate future activity
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General Reviews
LI
Both foieign and Anierican authors have been active in reviewing various aspects of processes and equipment relevant to the field of liquid-liquid extraction. The value of these reviews to the enginecr working in the field
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: z $, F
‘ 32 E
$ Loborafory mixer-setfler extractton unit
of liquid-liquid extraction, whcthcr i t be in plant operations or research and developnient, is increasing each year. With the ever-increasing impact of the technical literature explosion they afford the opportunity of contact and appraisal with rrcent developments that would be inipossiblc on an individual basis. Even a review of reviews can be neither exhaustive nor complete-and this review is no exception It can only hope to serve as a guide to further initiative on the part of the reader through the selective prerentation of what are conwdcred to be the more significant contributions. The value of general reviews and presentations should not be overlooked, even if they are used only as refreshers Scheibel ( 7 4 A ) has contributed an excellent section on liquid-liquid extraction to the 2nd Edition of the KirkVOL. 6 0
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Othmer “Encyclopedia of Chemical Technology.” The discussion of diffusional separation methods by Shacter, Von Halle, and Hoglund (77A) in this same treatise is also excellent refresher material. Klaus Hoppe and coworkers (8A) give a very brief review of the recent advances in the theoretical aspects of liquid-liquid extraction; as might be expected with such a brief presentation, it is not comprehensive in coverage, although the reference list is extensive. Schrodt (75A) gives a good presentation of the concepts of unsteady-state processing as applied to many types of mass transfer operations, including extraction. Brounshtein and Zheleznyak (3A) have published an excellent treatise on the physicochemical principles relating to liquid-liquid extraction. Extraction equipment reviews have received increased attention during the past two years. Akell (7A) presents the salient features of solvent extractors generally available in the United States. Both stagewise and differential extractors are discussed, along with a brief presentation of advantages and disadvantages. Reman (73A) covers, briefly, equipment history both outside and within the U.S.A. and also reviews modern extraction equipment and applications outside the U.S.A. Delzenne (4A) similarly reviews the more commonly used types of liquid-liquid extraction equipment such as packed and spray columns, perforated plate and cascade-type columns, mechanically agitated and pulsed columns, and centrifugal extractors. Berkerovskii (2A) and coworkers limit their review to the application, design, and construction of unidirectional, two-phase contactors. A very extensive review of industrial extraction processes and the apparatus used is that of Gel’perin and Pebalk (6A). The review of Misek (77A) is generally limited to rotating disk contactors and their field of application along with the calculational procedures necessary; that of McEwen (7OA) is primarily concerned with the so-called high efficiency types of extractors. Fleetwood (5A) limits his review to the field of application and the principles involved when using the “Craig”-type apparatus. A good review is given by Jackson (9A) of industrial problems in the field of drop formation and coalescence and of the experimental studies which have been carried out with single and multiple orifices, mechanically agitated systems, and columns. Some general reviews relating to the chemistry and physicochemical principles of the solvent extraction process have also appeared. I n addition to the aforementioned book by Brounshtein and Zheleznyak (3A), Sharma (78A) reviews the coupling of chemical reaction with solvent extraction and points out the need for detailed considerations under such circumstances. Topchiev (20A) is primarily concerned with reviewing computational procedures and principles involved when molecular complexes or aggregates are involved in the extraction process; the presentation is quite extensive. The physical and organic chemical aspects relevant to metal ion and metal chelate separations by solvent extraction are reported by Peppard ( I Z A ) , Sinegribova and Yagodin (79A), and Schweitzer and Van Willis (76A). 44
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
General Calculation Procedures
General calculation methods are always of interest to those working in the field of liquid-liquid extraction. The necessity for the coupling of the mass transfer relationships with those of hydrodynamics under general conditions, which are not easy to define-not to mention the complicating geometric equipment factors-creates the need for calculation and design procedures that afford a realistic approach to the actual physical phenomena taking place. Graphical and/or analytical procedures to determine the number of equilibrium stages, extraction factors, or over-all separation factors continue to receive a modest amount of attention. Tierney and Bruno (25B) give an excellent presentation of the advantages of iterative methods for the determination of the number of stages required for multiphase separation processes involving heat and/or mass transfer, and Gal and Kikolic (70B) use the method of continuous variations to analyze the extraction process variable when mixed solvents are employed. Hrubisek (74B) is primarily concerned with the selection of the optimal separation process when two or more fractions are to be produced from a multicomponent mixture. Chen (5B)presents a simplified equation, also a generalized chart, to determine the number of stages needed for distillation, absorption, extraction, or leaching. The utility of the equation presented is quite limited, due to the assumptions necessary for application. Fi1ippos’yants (9B) and Hartland ( 7 7B) both present calculation methods specific to the determination of the number of equilibrium stages required for liquid-liquid extraction separation; the former presents his method in nomogram form, while the latter’s is a more general mathematical presentation relating to extraction factors, separation factors, phase flow rates, and stage configuration. Bulatov and coworkers (3B, 4B) present an interesting modification of the well known triangular diagram method for computing the number of actual stages required for a liquid-liquid extraction separation by incorporating the kinetics of the transfer rate in each stage. Optimization of the two-phase contacting-separation problem is the subject of the articles by Jackson (75B), Chien ( 7 B ) , Ditter and Luck (8B), and two articles by Hartland (72B, 73B). Jackson describes the basic timedependent behavior of such systems to establish the optimal conditions for start-up and control, and Hartland’s works are concerned with the optimization of countercurrent and crosscurrent flow patterns. Chien’s work is concerned with optimizing product recycle in a crosscurrent system, while that of Ditter and Luck is concerned with countercurrent column operation.
Parma N . Vashist is a Graduate Research Assistant and Robert B. Beckmann is Professor in the Department of Chemical Engineering, University of Maryland, College Park, M d . Professor Beckmann is also Dean of the College of Engineering at the University of Maryland. AUTHORS
TABLE I . Metal Extruded
METAL EXTRACTION SYSTEMS AND PROCESSES Feed Soln. Type
Silver, gold
Chloride solns.
Indium
Acid solns.
Nickel, cobalt
HC1 and CaCh solns.
Cobalt
Ferrous nickel matte
Zirconium Vanadium
Nitrate solns. Aq. solns. with Fez+
Alkaline earths
Aq. s o h . (NHaOH)
P r and Nd Americium and europium Transplutonium ions
Nitrate s o h . Amine-acetic acid c om p 1exes Nitrate solns.
Thorium and cerium
Nitrate s o h .
TABLE II.
Solvent and References Diesel oils (26C), tributylphosphates (76C) Organophosphates ( K ) , namyl and n-octyl alcohols (3C) CvCe tertiary amines in kerosine (75C) Air-silica (analogy to liquid extraction) (E) Tribu t ylp hospha te (33C) O r anophosphorus compounds P73C) Trifluoroacetone deriv. in methvlisobutylketone (7C) Tribu tylphosphate ( 2 4 2 Xylenes (7QC) Tertiary and quaternary amines ( 7 4 2 ) Various organic solvents (7C)
HYDROCARBON EXTRACTION SYSTEMS AND PROCESSES
Extraction Product Aromatics Aromatics
Feed Type
Solvent and References
270-440'F gas oil Hydrocarbon mixtures
Furfural (3QC) Alkylformamide deriv. (37C), esters (30C), dimethylsulfoxide or dimethylformamide (4C, IOC, 28C 29C) aqueous solutions IZ$O. 6imethvl...... ~~~~. formamide aLd heptane (27C) aq. s o h . of N-methylpyrrokdinoic acid (72C) Diethylene glycol with ultrasonics (ZC) Methyl ethyl ketone-benzenenaphtha (5C) Sulfuric acid (77C) Furfural with a ketone or ketones (25C) Propylene carbonate (40C) ~
Aromatics
Hydrocarbon mixture
Dewaxing
Waxy lube oil
Isobutylene Selected hydrocarbon fractions Phenols
Hydrocarbon mixture Lube oil fraction
2,6-XyIenols
Hydrocarbons or aq. soh. Crude xylenols
Cyclopentadiene
Cs hydrocarbons
Phenylmethane ( N a O H s o h ) (38C) N- or 0-heterocyclics (37C)
Backmixing, dynamic behavior, and the general characteristic phenomenon of fluid mixing in extraction apparatus continue to receive much attention in an effort to further the design and/or operational understanding of the basic characteristics of multiphase contacting systems. Apelblat and Faraggi (7B) and Chernyshev (6B) discuss the mathematical developments necessary to simulate the dynamics of extraction apparatus. Landau and Prochazka and their coworkers (78B, ZOB, 27B, 23B, 24B) continue to be among the most active in this field. Their works are excellent and most comprehensive and should be referred to by all interested in backmixing phenomena and the related effect on efficiency. Their works cover the range from mathematical formulation to experimental determination and design to allow for backmixing effects. Rod (22B) presents the equations for calculating the limiting influence of backmixing and forward mixing on mass transfer in polydisperse flow systems. Some general design procedures and criteria for various types of extraction systems are presented by Kostelnik and Tesar (77B), Mercea and coworkers (79B), Bobikov (ZB), and Kavetskii et al. (76B). Kostelnik and Tesar relate their experimental determination of stage efficien-
cies to observations on plant scale units, and Mercea and coworkers use the approach-to-equilibrium concept to discuss column performance. Kavetskii and coworkers and Bobikov discuss general design considerations with longitudinal mixing; Bobikov also discusses incorporation of kinetic factors in ionic systems. Ziolkowski (26B) offers a good review of various calculation methods generally used for the design or performance evaluation of extraction columns. Extraction Systems and Processes
Most of the reported work on liquid-liquid extraction processes and systems centered around inorganic metal extractions or processes related to petroleum refining and hydrocarbon separation. As noted in previous reviews, most of the work centered on the resolution of specific problems relevant to unique separation problems. No particularly comprehensive types of presentation were noted during 1966-67. Selective literature references relating to the removal of specific metals or purification of metal ion solutions are shown in Table I. The purification of specific petroleum fractions and particularly the production of pure aromatic compounds continue to receive the major share of research attention. Dimethylsulfoxides and dimethylformamides seem to be particularly interesting solvents. Selected hydrocarbon extraction systems and processes reported in 1966-67 are illustrated in Table 11; many of the authors cited list additional valuable references. The thermodynamic and the physical-organic chemistry aspects of the appropriate solvent selection for inorganic liquid-liquid separation processes have received a moderate amount of attention, but the subject is yet in need of a comprehensive and collective appraisal and treatment. Grieger and Eckert ( 1 7C) present the design considerations when considering mixed solvents for liquid-liquid extraction. They use a thermodynamic approach based on the Gibbs-Duhem equation to illustrate the improvements possible through the suitable selection of the third component. Takashima and coworkers (34C) discuss the carbon tetrachloride extraction of halogens and inorganic species of the basis of ionic strengths and reaction potentials. Shevchuk and coworkers (25C) and Scibona and coworkers (22C) are concerned with amine solvent extractions, the former dealing with permanganato removal from dilute sulfuric acid solutions and the latter with halogen acid removal from aqueous solutions. Munson (2OC) correlates the selectivity parameters of fluorochemical solvents for hydrocarbon extractions. The separation factor is correlated in terms of a selectivity parameter, which is a function of the latent heats of vaporization of the components, the mole fraction of the solvent in the solvent phase, and the temperature. Boyadzhiev (6C) uses a turbulent-flow extraction system to evaluate the transfer characteristics of the carbon tetrachloride extraction of iodine from aqueous solutions. Martin (78C) recommends a polar solvent (such as aqueous methanol) for the extraction of fatty acid monoVOL. 6 0
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glycerides from mixed mono-, di-, and triglycerides. T h e Texaco Development Corp. (35C) has patented a high temperature process for the extraction of water from brines, such as sea water, using aliphatic, alicyclic, and aromatic hydrocarbons with Cs-C20 alcohols or C6-C12 ketones, in admixture, as the solvent. Waddington (36C) has patented a double solvent process that accomplishes extraction and solvent regeneration through the use of two individual solvents. The principles are illustrated to be applicable to the recovery of tar acids from carbolic oils and the separation of paraffins from hydrocarbon-type mixtures. Centrifugal Extractors
The literature on centrifugal extractors continues to be dominated by Russian and European workers. Berestovoi and coworkers ( 7 0 , 2 0 ) report on a compound centrifugal mixer-settler, the mixer and rotor of the centrifuge being on a common shaft. Their final correlation indicates a dependence of the mass transfer coefficient on the volume flow rate of both phases, on the speed of the rotor, on the density of feed phase, on the viscosities of both phases, and on the interfacial tension. Goncharenko and coworkers (60,70) describe a new horizontal mixer-settler centrifugal extractor with stirrers and give an equation for the width of the mixing zone. Konovalov and coworkers (80) improve the centrifugal extractor by equipping the extraction chambers of the rotor with a spray device for feeding the heavy phase on the surface of the light phase. Doyle and coworkers ( 4 0 ) offer an adjustable centrifugal countercurrent distributor in which the rotating drum carries interchangeable partitions with various patterns of perforations. I n another apparatus ( 3 0 ) , they suggest that detachable disks would permit a more efficient distribution of the liquid phases. Podbielniak (90) uses stationary, external, annular chambers connected with the extraction zone through a rotating passage for feeding and removing both heavy and light phases from a centrifugal liquid-liquid contactor. A rotary seal between the annular and the rotating member maintains the unit leakproof. Dresser Industries, Inc. (50),modify the centrifugal contactors having axially extending rotors by providing two consecutive contacting chambers mounted side by side on the shaft, so constructed and interconnected that different conditions can be maintained in the two chambers. This permits high efficiency contacting to be carried out without the disadvantage of a large diameter rotor. Centrally Agitated Columns
There have been relatively few really new significant equipment developments in the field of centrally agitated columns during 1966-67. Most of the efforts have been directed toward improvement or modification and/or the hydrodynamic and mass transfer characterization of existing types of units. A high efficiency extractor of new design, for the extraction of aromatic hydrocarbons, is offered by Sokov 46
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
and Putilova (QE).This improves the settling zone of the Reman rotating-disk contactor at the column walls and in the chambers between two adjacent stator rings at maximum peripheral speeds. The new RDEB-1 extractor has no stator rings, but the rotating disks are of two sizes; the larger ones are perforated and carry out mixing at the walls of the apparatus while settling takes place in the center at the minimum peripheral speed. This gives greater efficiencies at lower speeds and an almost fourfold increase in productive capacity when compared to the Reman RDC. A correlation for holdup is given. F. Hoffmann-La Roche and Co. ( 2 E ) have patented an apparatus which offers an improvement on the internals of a n R D C to provide for more positive, directed liquid flows to reduce backmixing and axial diffusion. Metallgesellschaft A.-G. (6E) offers an extraction tower containing chambers located on top of one another; a central vertical shaft passes through the entire length of the tower with pump vanes attached in each separation chamber. Zirnmer (7OE) achieves higher efficiency in a liquidliquid extraction column with mixer fittings by superimposing a horizontal rotational movement on the motion of the fittings which reciprocate axially via the driving member. I t results in a helical motion to make possible different residence times for the phases in the column by varying the angle of inclination of the blades. Kagan and coworkers (4E)present a correlation for the dispersed-phase holdup in an R D C column in terms of the volume fraction of the dispersed phase holdup, x , the volume flow ratio of the dispersed and continuous phases, b, the droplet settling velocity, u,, and the linear velocity of the continuous phase, u,: b -
x
1 += 0.23 1--x
The equation given by Sokov and Putilova ( 9 E ) for the volume fraction holdup, x , of the dispersed phase for their RDEB-1 extractor is :
where V , and V , are the flow rates of dispersed and continuous phases, respectively, and V , is a characteristic rate. Kagan and coworkers ( 5 E ) use a comparative study of mixer-settler type units and R D C extraction columns in a caprolactam plant to illustrate the superiority of R D C columns over mixer-settler extraction units for this type of separation. Interesting operating and design data are also presented. Nakamura and Hiratsuka (8E) compare the performance of a Rieman-type column with a column having radially supported arc plates with a 60' angle at the center, fixed at the rotating axis. Gel'perin and coworkers (3E) compare the conventional R D C extraction column with a modified form of the Scheibel column and with a modified form of the Oldshue-Rushton extraction column.
Miyauchi and coworkers (7E) offer a single correlation for evaluating the effect of longitudinal dispersion in R D C and Mixco extraction columns ; their correlation covers impeller Reynolds numbers from 3.5 x lo3 to 1.0 X 106, and column diameters from 4.1 to 218 cm. Bibaud and Treybal ( ? E )correlate axial mixing in terms of an eddy axial diffusivity and other variables for both phases in a countercurrent impeller-agitated extractor of the Oldshue-Rushton design. Mixer-Settler Extractors
T h e basic requirement of a liquid-liquid extractor is the contact of two immiscible liquid phases to allow mass transfer to take place and subsequent separation of the phases. Mixer-settler extractors, being the simplest and most versatile form of such equipment, continue to receive considerable research and development interest for better designs and improved operational characteristics. Treybal (ZOF, Z?F) has patented a unique continuous liquid-liquid extractor. This is a vertical stack of horizontal trays, each of which is divided by a vertical partition into a mixing and a settling compartment. Gel’perin and coworkers (5F) describe a horizontal columntype apparatus consisting of mixing and calming sections ; these are separated by slotted baffles and a paddle impeller situated on a common shaft coaxial with the column. Metallgesellschaft A,-G. (15F) has modified a previously patented design to avoid the necessity of removing the air at the time of filling the extractor. Dolgikh and coworkers ( 4 F ) discuss the complete process and a pilot plant extraction apparatus for extracting noble metals from sludges. T h e solvent used is an amineHC1 complex dissolved in kerosine, and the sludge is dissolved in chlorine in the presence of HC1 and NaC1. Sanderson (76F) has patented a unique design incorporating a small-diameter rotating column connected to a vessel of larger diameter. He claims this construction minimizes the entrainment of solvent. CIBA, Ltd. ( 3 F ) , has patented a countercurrent compartmented extractor with agitation accomplished by rotation about an inclined axis. The patents of Schuetze ( I B F ) and Balleyer ( 2 F ) are related to the separation of immiscible binary liquid phases. Gel’perin and coworkers (6F, 7 F ) report interesting work on the mass transfer characteristics and the phase recirculation phenomena in a box-type extractor with a turbine mixer. Gur’yanov and Galeev (9F) report on a vertical column extractor with alternating mixing and calming sections. T h e unique feature is that the central agitator in each mixing section is a two-bladed impeller with one blade having a n angle of inclination greater than 45” and the other less than 4 5 ” ; this imparts a pulsating motion to the fluid travel through the column. Kapacheva and coworkers ( 1 2 F ) review the structural features of pulsed mixer-settler units and recommend a design and scale-up procedure to be used. Lukin and coworkers ( 7 4 F ) offer a generalized dimensionless mass transfer equation for scaling up a mixersettler extractor with centrifugal phase separation from laboratory to larger sizes. Goncharenko and Gotlin-
skaya (BF) give correlations and graphical representations for the extraction rate and intensity of stirring with vane-type stirrers for continuous extractions in a liquidliquid system. Kagan and Kovalev (77F, ?3F) report a n excellent study of the hydrodynamics of flow-type mixers. They observe that a minimum agitation rate is required for the uniform distribution of the dispersed phase for optimum conditions. T h e average droplet diameter is reported to be independent of residence time in the vessel, except when substances which prevent coalescence are present. T h e average diameter of the dispersed phase droplets in batch or continuous flow apparatus is essentially the same. Souhrada et al. (79F) compare and discuss the methods of evaluating the backmixing coefficient and the stage efficiency for stagewise models of countercurrent extraction, using a tracer method. Special reference is made to a vibrating-plate extractor. Halligan (?OF) compares four mathematical models for the prediction of the approach to steady state of a mixer-settler extractor. T h e “hybrid” model, obtained by combining the best features of two of the other models, is recommended for the prediction of the performance characteristics of a tube-type mixer-settler extractor for a certain range of physical properties of the phases. Sawistowskii and Austin (17F) report on the mass transfer rate in a stirred cell unit. Velocity profiles in a cylindrical, flat-bottomed, and baffled agitated vessel in the flow regime near the wall are reported by Askew and Beckmann ( ? F ) . The heat and/or mass transfer characteristics at the wall of an agitated, baffled vessel are generally analogous to the transfer functions predicted from flat-plate, turbulent, boundary-layer flow. Packed, Spray, and Plate Columns
Packed, spray, and plate columns continue to receive a significant amount of research attention, particularly looking toward extraction efficiency by agitation or pulsating effects and/or the use of improved packings or plate designs in the column. Li and Ziegler (24G) review the various theories of axial mixing in extraction columns and report their own results on packed and spray columns. They estimate that neglecting the effect of axial mixing in the design or evaluation of extractors can lead to errors of 30y0in performance calculation. Brounshtein and Shapiro ( I G ) report that backmixing may decrease the efficiency of a pulsed column by as much as 50%. A series of new models has been proposed to explain the dispersion and flow characteristics in packed extraction columns. Otake and coworkers (ZZG, 34G) present two models; one is based on a series-of-tanks concept to describe the flow characteristics in packed beds and to explain longitudinal mixing. I n the other, they offer the premise that longitudinal dispersion is caused by coalescence and redispersion of the droplets. Green and Perry (9G) report a theoretical mathematical model for the longitudinal dispersion mechanism in packed beds. This is of considerable interest because of its applicability VOL. 6 0
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to both heat and mass transfer, even though the analysis is derived for single-phase flow. Vignes (49G) offers a mathematical analysis of the various packed-column physical and operational factors on the simultaneous counterflow of the two liquid phases in a packed extraction column. Special attention is given to clogging, holdup of the dispersed phase, and the drop size distribution. He distinguishes three types of holdups-static, free, and semifree-and includes the effects of disturbances due to interface mass transfer on the hydrodynamics of the column. Miller and King (32G) report on axial dispersion studies in liquid flow through packed beds, and Doninger (4G) reports on the dynamic behavior of a packed liquid extraction column. Degaleesan and Ladha (3G) offer generalized dimensionless equations for the transfer from a continuous aqueous phase to a dispersed organic phase, and also in the reverse direction, for packed liquid-liquid extraction columns. A comparative study of distributors with different sizes of nozzles for the dispersed-phase entry into a packed and an unpacked countercurrent liquid-liquid extraction column is reported by Shih and Kraybill (3QG). The initial dispersion is reported to have negligible effect on rate of extraction in the packed column, while the rate of extraction in the unpacked column is observed to increase greatly as the size of the nozzle is decreased. A new distributing apparatus utilizing perforated pipes to inject the dispersed liquid into a vertically flowing fluid in a packed column is described in a Universal Oil Products Co. patent (47G). Kaminskii and Partsakhashvili (77G) report a study on new pzcking types for isotope separation in packed columns. Stage (42G) improves the efficiency of a packed liquidliquid extraction column by subdividing the column into compartments with partitions parallel to the vertical axis, thereby reducing the effective diameter of the column; this permits the use of packings smaller than normal. He further suggests the introduction of an inert gas stream into each compartment for improved contact between the liquid phases. Kroepelin and Beier (27G) also recommend the use of a finely dispersed gas stream to improve the efficiency of packed-, spray-, and plate-type extraction columns. Raff (36G) uses a hydrophobic surface on the column packings to improve column efficiency when the dispersed phase is hydrophobic and the continuous phase is hydrophilic. Grinevich (IOG) has reported wetting coefficients and surface areas for large-size staggered column packings. Chao and Adams (2G) rearrange the Ergun correlation for flow through packed beds and present it in graphical form. Lodh and R a o (2%) report on the effect of plate spacing, hole area, and the plate wetting characteristics on the mass transfer efficiency of a perforated plate column. Shirotsuka and Murakami (4OG) report on the response of a perforated plate column to a variation in the continuous phase feed composition when solute migrates from the continuous phase to the dispersed phase, and Zheleznyak (52G) studied extraction in similar columns, in which the Fourier number (the dimensionless process 48
INDUSTRIAL AND ENGINEERING C H E M I S T R Y
time referred to a column section) changes along the height of the column. Holtzer’s (Xetherlands) patent (14G) modifies a perforated plate column by mounting a “floating plate” on sliding brackets above each stationary mass transfer tray for distillation or for liquid-liquid extraction. The holes in these two trays are shifted in relation to each other. The rising light phase pushes the top tray u p to a predetermined level above the base tray. This arrangement is expected to reduce entrainment, thereby increasing the plate efficiency. Susanov and Novozhilova (44G) claim indisputable advantages for plates with single layer sieves compared with those having double layers. They report on the construction of a number of plates and also on the effect of the operating temperature on the sieve plate efficiency. I n addition, Maksimenko and coworkers (27G) are equally adamant about the advantages of using twin perforation plates, compared to single perforation types, for the phenol refining of lube oils. Kneule and Zelfel (ZOG) have presented a useful design equation for estimating the “dry plate” pressure drop for sieve plates. Their correlation, presented in terms of a dimensionless “tube inlet number,” involves the Reynolds number based on the hole diameter, the plate thickness, the number of perforations, and the distance between them. Letan and Kehart (23G) report local and average holdup and drop size distributions as a function of flow rates in a study of the mechanics of spray column performance. They describe three modes of drop packings-dispersed, restrained, and dense-and also define the flooding in a spray column either as the point of maximum average specific area of the drops (which corresponds to the onset of coalescence in the column) or as the start of rejection of drops from the column proper. Nanda and Sharma (33G) use a combined extractionreaction technique to compute the effective interfacial area for a spray-type extraction column. Subbarao and Venkatarao (43G) have reported on the effect of nozzle spacing and variations in the phase flow rates on the efficiency of mass transfer in a spray extraction tower. T h e values of the mass transfer coefficients increase with increase in flow rate of either of the phases, and the effect of changing the arrangement of nozzles on the distributor plate from square to triangular is reported as negligible. Hughmark (75G) has critically examined the literature data and correlations on liquid-liquid spray column holdup, drop size, and the continuous phase mass transfer coefficient. He concludes that dispersed phase holdups can be reliably predicted and that the continuous phase mass transfer coefficient can only be predicted from single drop data if the viscosity ratio of the continuous to the dispersed phase is less than one. For viscosity ratios >1, interaction effects reduce the coefficient. The effect of pulsations or vibrations on the rate of mass transfer between two immiscible liquid phases in various types of extraction apparatus has received the attention of many research workers during recent years. Tudosc (45G) discusses various systems under this effect and observes that an increase in the frequencies or ampli-
tudes of pulsation improves the mass transfer efficiencies by a factor of 2 to 6 owing to the increased contact at the interface and mixing of the phases which reaches a maximum at a resonance frequency. He recommends the use of uniform-size droplets and operation at the resonance frequency of the droplets for liquid-liquid extraction. Gur’yanov and Galeev (72G) describe a pulsating-mixing extractor consisting of mixing and settling zones in a vertical column and define two regions of operation which enabled them to generalize the performance characteristics. They also give comparative values of HETS (height equivalent to a theoretical stage) and the maximum operational flow rates for various equipment types such as packed columns, sieve columns with inclined trays, rotary disk contactors, and pulsed contactors. Rama-Raju and Jagannadha-Raju (37G) report on an interesting study of the characteristics of the pulse generated by means of a diaphragm in a vertical liquid column. Specifically, they studied the longitudinal and radial variation of the mass transfer coefficient at different frequencies and amplitudes of the diaphragm and with the pulse axial and transverse to the measurement electrodes. St. James and coworkers (76G, 47G) report that the two most significant factors in a pulsed liquid-liquid extraction system are a uniform droplet size and complete atomization of the dispersed phase; they also describe a spray-type pulsed column for liquid-liquid extraction. Groenier et al. ( I 7G) have examined and correlated the literature data on the flow capacity of pulsed perforated plate extraction columns. Zheleznyak (57G, 52G) and Zheleznyak and Brounshtein (53G) offer excellent comparative studies of perforated plate columns with and without pulsation. Wagner and Sausset (50G) have patented a novel pulsed column design using glass tubing to construct perforated plates. Perovskii and Kossykh (35G) interpret the mass transfer characteristics of laboratory-size pulsed glass columns with perforated plates in terms of the phase flow rates, dispersed phase holdup, equilibrium data, and the pulse intensity. A new packing type for pulsed columns, “KRIMZ,” is described by Karpacheva and Zakharov (18G, 19G). The packing is reported suitable for operation with high holdup loadings and for permitting much higher flooding loads than obtainable with other types of packings. They present equations for computing the diameter and height of pulsed columns with special reference to those packed with “KRIMZ” disks. Maksimenko and coworkers (26G-29G) have presented a comprehensive series of comparative evaluations on the effects of pulsations and vibrations on extraction column performance. The pulsing and vibrational effects were evaluated on packed columns, agitated columns, perforated plate columns, and mixed types; they used zone pulsing or vibration or pulsing of the entire column. The pulsed-agitated column is reported more effective than the vibrating plate column. Vdovenko and Kulikov (48G), Evans (7G), Elkins (6G), and Hale (73G) also report on the hydrodynamics and mass transfer characteristics in various types of
pulsed columns. Uhle (46G) uses a rotating valve arrangement to impart the pulse action to an extraction column. Gel’perin and coworkers (8G) and Elenkov et al. (5G) also report mass transfer studies on vibrating plate-type extraction columns. New column designs, intended to improve mass transfer efficiency, are reported by Mehner and Wirth (31G),Rodionov (38G), and Ziehl (54G). The internal construction of plate-type columns is becoming as cluttered as a supermarket; with horizontal, spiral, and vertical baffles, rotating or vibrating actions, and with and without packings--anything to produce a schizophrenic drop for rapid mass transfer followed by an effective tranquilizer for separation. Some of the nonclassifiable equipment innovations reported in the last section of this review further bear this out. Miscellaneous and Laboratory Equipment
As mentioned earlier, there are always equipment innovations which defy logical attempts at classification, and 1966-67 was no exception. Tudosc and Christian (79H) offer a new type of liquidliquid extraction column consisting of an annular space divided into a spiral-shaped volume by means of a continuous, spiral-shaped baffle which is perforated with a large number of orifices. The orifices are placed in rows and provided with small baffles (scoops), turned upward in one row and downward in the following row. This arrangement causes continuous mass transfer along the spiral interface and discontinuous mass transfer through the droplet interfaces. This construction is more complicated than that of packed or spray columns but simpler than many of the plate-type, agitated, or vibrated columns. The authors claim higher efficiencies than for mechanically agitated columns. Signer and Arm (78H) improve this design for operation with multicomponent systems. Mel’nikov (1.223) offers a cylindrical extractor with multiple mixers and concentrically arranged compartments connected by overflows. The annular spaces are similarly agitated and compartmentalized. Watt (27H) similarly proposes an annular cell arrangement, with rotating cells and a split-level arrangement to allow gravity separation. Priorr (75H) modifies the Friedrichs extractor to accommodate operation with low boiling solvent systems. Special-purpose equipment designs are proposed by Konovalov and Semenov (9H) for removal of trace metals from aqueous solutions, by Lerenard and Simon ( I 7H) for the removal of organic pollutants from water, and by Muenzel (14H) to handle highly active radiochemical liquid-liquid separations. Gel’perin and coworkers (613)describe a new horizontal extractor equipped with piston-type pulsing, and Boyadzhiev and Elenkov ( 4 H ) present an operational analysis of a venturi-type extractor. Coleby ( 5 H ) has similarly patented a rotating disktype horizontal extractor, Beau ( 7 H ) an agitated compartmentalized extractor claiming high efficiencies, and Grob and coworkers ( 7 H ) have been primarily concerned with space economy. Laboratory apparatus innovations for process developVOL. 6 0
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ment or equipment simulation have not been particularly active during 1966-67. Only a few items are covered here, principally to serve as a guide for directing the interested researcher’s attention. Belter ( 2 H ) and Belter and Speaker ( 3 H )present methods for laboratory simulation of large-scale extraction systems and are particularly concerned with controlled cycle operations. Labii (IOH) uses a simple test tube-shaped apparatus for multiple solution extractions and process simulation. Wieglieb (22H) has designed a laboratory apparatus for low temperature use with volatile solvents ; the applicability is demonstrated using liquid sulfur dioxide as the solvent for the desulfurization of petroleum stocks. Rodionov and Pavlov (76H)describe a sectionalized laboratory apparatus which uses gas lifts for fluids movement and a throttling device to control the phase separation. Other laboratory modifications were noted by Morgan (73H),Kardasz ( 8 H ) ,and Wallace (2OH). An interesting laboratory drop-forming apparatus having a micrometer screw for adjustment of a square orifice and a micrometer pump for admitting the dispersed phase into a second liquid in a vertical rectangular Schlieren chamber is described by Sehrt (77H). He used this for determining the hydrodynamic relations of rising or falling drops and for schlieren optical observations. REFERENCES General Reviews (1A) Akell, R . B., Chem. Enq. Progr., 62 (9), 50-5 (1966). (2A) Berkerovskii, M. A,, Skoblo, A . I., Aleksandrov, I . A , , and Sheinman, V. I., Khim. i Tekhnol. Tobliu i Masel, 11 (5), 41-46 (1966). (3A) Brounshtein, B. I;, , ~ n dZheleznyak, A. S., “Fiziko Khimicheskie Osnovy Zhidkostnoi Ekstraktsn, Leningrad, Khimiya, 318 pp, 1966. (4A) Delzenne, A , , Ind. Chim. (Paris), 53 (5861, 123-33 (1966). (5A) Fleetwood, J. G., Brit. Med. Bull., 22 (2), 127-31 (1966). (6A) Gel’perin, N. I., and Pebalk, V. L., Teor. Osnovy Khim. Tekhnol., 1 (5), 603~~
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(7A) Harris, D. K . , Vashist, P. N., and Beckmann, R . B., IND.END.CHEM.,5 8 ( l l ) , 97-103 (1966). (8A) Hoppe, Klaus, Kuenne, H., and Bendix H., Chim. Tech. (Berlin), 19 ( l ) , 18-22 (1967). (9A) Jackson, R., Chem. Eng. Progr., 62 (9), 82-8 (1966). (10A) McEwen, C. K . (Q.V.F., Ltd., Stoke-on-Trent, Engl.), Spec. Ind., 21-5 (1966) (winter). (11.4) Misek, Tomas “Rotacni Diskove Extraktory a Jejich Vypocty; Metody a Pochody Chemicke) Technologie, SV. 13,” (Methods andjProcesses of Chemical Technology, Pt. 13), Prague, SNTL, 61 pp, 1964. (12A) Peppard, D. F., Aduan. Inorg. Chem. Rndiochem., 9, 1-80 (1966). (13A) Reman, G . H., Chem. Eng. Progr., 62 ( 9 ) , 56-61 (1966). (14A) Scheibel, E. G., “Kirk-Othmer Encycl. Chem. Tech.,” 2nd ed, Vol. 8, pp 719-75, 1965. (1j A ) Schrodt, V. N., I N D ENC. . CHEM.,59 (G), 58-65 (1967). (16.4) Schweitzer, G . K . , and Van Willis, W., Advan. Anal. Chem. Znstr., 5, 169-219 (1966). (17.4) Shacter J. Von Halle E., and Hoglund, R . L., ”Kirk-Othmer Encycl. Chem.Tech:,” i n d ed, Vol. ?, pp 91-175, (1965). (18.4) Sharma, M . M . , Chem. Age (India), 17 (6), 455-60 (1966). (19A) Sinegriboaa, 0. A , , and Yagodin, G. A,, A t . Energy Rev., 4 ( l ) , 93-106 (1966). (20A) Topchiev, A . V., an:,Solod, V. I., “Raschet Proizvoditel’nosti Vyemochnykh Kompleksov i Agregatov, Moscow, Nedra, 101 pp, 1966. (21A) Vashist, P. N., and Beckmann, R . B., IND. END.CHEM.,59 ( l l ) , 71-9 (1967). G e n e r a l Calculation Procedures (IB) Apelblat, A,, and Faraggi, M., J. Nucl. Energy, Parts A-B, 2 0 (11-12), 953-
69 (1966). (2B) Bobikov, P . I., “Tr. Vses. Xauchn.-Tekhn. Soveshch. Protsessy Zhidkostnoi Ekstraktsii i Khemosorbtsii,” 2nd ed, Leningrad, 90-8 (1964) (Pub. 1966) (Russ.). (3B) Bulatov, S. N., Planovskii, A. PIT., and Dukel’skii, G. Ya., Teor. Osnovy Khim. Tekhnol., 1 ( I ) , 88-93 (1967). (4B) Bulatov, S . N., Planovskii, A. N., and Dukel’skii, G. Ya., ibid. (Z), p p 224-8. (5B) Chen, Ning Hsing, Chem. Eng., 74 (l),93-9 (1967). (6B) Chernyshev, V. N., AatomaEiz. Proizv. Protsessov. (Moscow, Nauka.) Sb. (4),
