PERFORATEDIPLATE LIQUID-LIQUID EXTRACTION TOWERS

P = crushing probability, dimensionless = probability of crack propagation, dimensionless P, Po P,’ = probabilities of collision, dimensionless = plastic work a t crack propagation, g.-cm./sq. cm. PL P,,,Po’= probabilities of stress and structure of material, S

= =

AS

=

S

= = =

r1, r2

U

u, UO

=

uOp

=

X

=

= X, = YI,Y Z = Y =

Downloaded by UNIV OF MASSACHUSETTS AMHERST on September 14, 2015 | http://pubs.acs.org Publication Date: April 1, 1968 | doi: 10.1021/i260026a002

20

dimensionless radii of curvature of two bodies a t impact point, cm. specific surface of particles, sq. cm./g. specific surface increment, sq. cm./g. crushing efficiency, dimensionless velocity of particle a t impact, cm./sec. crack velocity, cm./sec. sound velocity, cm./sec. optimal impact velocity, m./sec. particle size, cm. diameter of minimum particle of product, cm. diameter of particles before crushing, cm. moduli of elasticity, g./sq. cm. or million lb./sq. in. cumulative undersize fraction, dimensionless

GREEKLETTERS a = constant = specific surface energy, g.-cm./sq. cm. Y

Ir V I , ~2

= viscosity of air, g./cm. sec. = Poisson’s ratios of two bodies, dimensionless

density of particle, g./cc. breaking strength of particle, g./sq. cm. urnax = maximum stress produced within material, g./sq. cm. # = separation number, dimensionless PP Q,,

= =

literature Cited

Charles, R. J., M i n . Eng. 9, 80 (1957). Cremer, H. W., Davies, T., “Chemical Engineering Practice,” Vol. 2, P.93, Butterworths. London. 1956. Gilman,.f. J., 2. Appl. Phys. 27, 1262 (1956). Gilvarry, J. J., J . Appl. Phys. 32, 391 (1961). Griffith, A. A,, Trans. Roy. Soc. (London) 221, 163 (1921). Piret, E. L., et al., Chem. Eng. Progr. 45, 506 (1949). Rumpf, H., Chem. Ing. Tech. 31, 323 (1959). Schuhmann, R., Inst. Mining Met., Petrol. Engrs., Tech. Publ. 1 1 8 9 (1940). Tanaka, T., IND.ENC.CHEM.PROCESS DESIGN DEVELOP. 5 , 353 (1966). RECEIVED for review December 27, 1966 ACCEPTEDSeptember 21, 1967

PERFORATEDIPLATE LIQUID-LIQUID EXTRACTION TOWERS Effect of Plate Spacing in the Methyl Isobutyl Ketone-Butyric Acid-Water System R. KRISHNA M U R T Y AND C. VENKATA RAO Department of Chemical Engineering, College of Engineering, Andhra University, Waltair, India

The effect of plate spacing on the mass transfer rates in perforated-plate liquid-liquid extraction towers was studied for 6-, 1 1 -Iand 23-inch spacings in a 4.8-inch i.d. glass tower with the same net height of extraction. The system studied was methyl isobutyl ketone-butyric acid-waterl butyric acid being extracted from the dispersed ketone to the continuous water phase. The mass transfer data are interpreted in terms of over-all mass transfer coefficients, heights of transfer units, and plate efficiencies. Over-all HTU data are satisfactorily correlated with Colburn’s equations. Experimental efficiency data obtained using the equation of Garner et al. (1 953) were compared with data calculated according to Treybal’s correlation; the latter are much higher. Hence, Treybal’s correlation as modified by Krishna Murty was used, which resulted in better agreement between the experimental and calculated efficiency data.

IQuID-liquid extraction has in recent years assumed major industrial significance as a means of separating the components of a solution. Perforated-plate extraction towers are widely employed in petroleum refining and other industries, mainly because of the high order of extraction efficiencies encountered in this type of tower. T h e effect of the physical properties of the solvents on the column behavior and the 166

l&EC PROCESS DESIGN A N D DEVELOPMENT

effect of changing the solute and solvent on the mass transfer coefficients and plate efficiencies were not investigated, in detail, by the earlier workers. Hence, to study these effects, an extensive program of work was undertaken in these laboratories. The present work deals with the effect of plate spacing on mass transfer rates for extraction of butyric acid from the dispersed methyl isobutyl ketone to continuous water phase.


Extraction Equipment

T h e extraction equipment for dispersion of the lighter phase, ketone, consists mainly of the extraction tower and the accessories to maintain steady flow of the continuous and dispersed phases in the tower. T h e tower is built up with borosilicate glass sections and perforated plates, attached with downcomers op a Dexion angle frame, using six 1/4-inch diameter threaded mild steel tie rods and nuts. T h e important accessories include three 30-gallon storage tanks, two motor-centrifugal pump sets, two rotameters, a n inverted Utube and atmospheric vent to maintain the principal interface, connecting pipelines, control valves, and neoprene rubber rings, used as the packing material (between the glass sections and the copper plates). The tower design, in general, follows the lines of earlier investigations with necessary modifications to suit the present problem. I t is described in detail by Krishna Murty (1965). A schematic diagram of the perforated-plate extraction equipment is shown in Figure 1. T h e connecting lines, perforated plates, and storage drums are made of copper, which is not appreciably attacked by the dilute solutions of butyric acid used in the tower. T h e essential dimensions of the perforated-plate tower are presented in Table I.

Table 1.

Essential Dimensions of Tower

Tower Inside diameter Effective tower height Glass sections Inside diameter Wall thickness Height Plates Thickness Perforation diameter No. of holes per plate (drilled at circular pitch of ' / z inch) Total perforation area

4 . 8 inches 55 inches

4 . 8 inches '/a inch 6, 9, 11, and 23 inches '/a '/lo

54 0.001151 sq. ft., 0.9157y0 of tower cross section 6, 11, 23 inches 8 €or 6-inch spacing 5 for 11-inch spacing 3 for 23-inch spacing '/s-inch thick neoprene rubber sheet

Plate spacing No. of plates in tower Packing material Down pipes Outside diameter Inside diameter Inside cross-sectional area

Materials

1 inch 0.875 inch 0.004175 sq. ft. or 3.33oJ, of tower cross section 5.25 inches for 6-inch spacing 9.75 inches for 11-inch spacing 19.00 inches for 23-inch spacing 8.00 inches for 9-inch height disengaging glass section Same as down pipes

Length of pipe ..

Methyl Isobutyl Ketone. T h e physical properties of the methyl isobutyl ketone, supplied by the Burmah-Shell Oil Co:, a t 30' C. were density, 50.12 pounds per cu. foot; viscosity, 0.515 centipose; boiling point a t 760 mm. of Hg, 115.9' C.; interfacial tension of the methyl isobutyl ketonebutyric acid-water system with about 0.004 pound mole of butyric acid per cu. foot of ketone-acid solution used in the tower, 9.8 dynes per cm. T h e density and viscosity of the ketone-acid solution used in the tower were experimentally found to be the same as those of pure ketone.

inch inch

Connecting pipe lines

C

c

T .,

7 L

I

Figure 1. Schematic flow diagram of perforated-plate extraction equipment for rising solvent drops T,.

W a t e r storage tank

Tai. Tank for inlet solvent

Tla. Tank for outlet solvent A. Feed pumps B. C. D. E.

F. G.

H. 1. 1.

Bypass valves Flow-control valves Rotor calibraton valves Rotameters Principol interface control valve Atmospheric vent Extraction column Perforated plates Drain pipe valve

VOL 7

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167

Water. Andhra University tap water, which is fairly neutral, was used throughout the experimental work. For this water a t 30’ C., density = 62.43 pound per cu. foot; viscosity = 0.8 centipose. The density and viscosity of wateracid solutions used in the tower were experimentally found to be the same as those of pure water. Butyric Acid. Butyric acid, Naarden Co., was 99.8% pure by chemical analysis.

Similar equations can be written for the ketone phase. Overall average plate efficiencies were evaluated using Equation 4 of Garner et al. (1953) and Equation 5 given below.

NA = In

[

driving force a t base terminal driving force a t top terminal ln

Experimental

Equilibrium Data. T h e equilibrium distribution of butyric acid in methyl isobutyl ketone and water to a maximum concentration of 0.005516 pound mole per cu. foot of solution in the ketone phase was studied a t 30’ C. using the chemicals specified above. The data obtained are represented by the equation,


Cm = 6.078 C,

[

I/

slope of operating line slope of equilibrium line

EA = (A!rA/actual number of stages) X 100

]

(4) (5)

Also, the efficiency data were evaluated from Treybal’s correlation (1963) given by Equation 6 and Treybal’s correlation as modified by Krishna Murty (1965b), given by Equation 7.

(1)

T h e mass transfer runs were taken a t 30’ f 2’ C.; the effect of this temperature change on the equilibrium distribution data was negligible. Tower Operation. In the present studies, as the direction of mass transfer is from ketone to water, the solute is added to the solvent to prepare the feed solution. As MIBK and water are partially soluble in each other, before the run is started both the phases are mutually saturated by adding the necessary quantities and stirring well. Butyric acid is then added to the ketone phase, to make up the concentration to about 0.004 pound mole per cu. foot of solution, mixed well by stirring, and then used for the runs. Water, being heavier, is admitted a t the top of the tower through its rotameter, whereas ketone, being lighter, is admitted a t the bottom of the toiver through its rotameter. The principal interface is adjusted by means of the fine control valve (Figure 1, F ) to be a t the middle of the top disengaging section, so that the required height of extraction is attained. The height of extraction is measured from the tip of the solvent inlet pipe in the bottom disengaging section to the principal interface in the top disengaging section. Preliminary experiments have shown that steady-state concentration gradients are set up only when the column contents are displaced a t least four times, and hence the column was operated under these steady conditions, which took 20 to 30 minutes or even more, depending on the flow rates. Inlet and outlet solvent and outlet water samples were taken a t two or three fixed intervals and tested for constancy in the titer values. Fresh water was used for every run. Butyric acid concentration in the inlet and outlet streams was determined by titrating a known volume with 0.lX sodium hydroxide solution, using phenolphthalein as indicator. Calculations. The material balance was checked for all the runs and only those i n which the error was within =t10% were presented for evaluating mass transfer data and the rest were rejected. The error is expressed as ( N , - hr,)lOO/AV~v. ( K * a ) ’ sand (HTU)’s are calculated from Equations 2 and 3 as suggested by Elgin and Browning (1935, 1936); as in the present work, the concentrations used are low, and the solutions are dilute.

The variables studied, with the results obtained, are presented in Table 11. The ranges of typical factors pertaining to the work are presented in Table 111.

Discussion of Results

Effect of Flow Rates. With the object of studying the effect of flow rates on the mass transfer coefficients, both the ketone and water phase flow rates were varied over a wide range, as shown in Table 111, and were 90% of the flooding rates. T h e effect is shown by plotting (K,,a) us. V,, V,, as the us. V ,, in Figure 3 for a parameter in Figure 2 and (&,.a) representative set of data. It is evident from Figure 3 that (K,,a)’s increased markedly with increase in the dispersed phase flow rate. This is due to the increase in the number of drops, which resulted in the increased interfacial area of contact and also to vigorous turbulence inside the column. From Figure 2, it is evident that a t a particular dispersed phase flow rate, (K,,.a)’sare almost constant, with minor variations, indicating little dependency on the continuous phase flow rate and thus corroborating the observations of Colburn and Welsh (1942) ; the number of drops is not as much increased with increase in the continuous phase flow rate as with increase in the dispersed phase

Table II.

Details of Variables Studied

Hole diameter, inch. 54 holes per plate. Height of extraction, 55 inches. Dispersed phase, MIBK. Direction of extraction, MIBK to water Plate Spacing, Inches

in Tower

6

8

(HTU),, = 0

11

5

(HTU),,

23

3

(HTU),, = 0

h’o. of

Plates

Results of H T U Correlation

=

(“-) 0 + 11.25 (:%) + 12.08 (”-) dcm 4- 10.83 dCm

(2) (2) (2)

V,, Ft./Hr. 34.4 to 119.3

Table 111. Ranges of Typical Factors of Work Extraction Factor, (dCwldCm)( V w I V m ) ( H T W o w , Ft. 0,0809 to 0.7417 1.152 t o 7 . 5 1 3

V,, Ft./Hr. 26.46 to 69.99

8.0

P

301

.

'

%

( H T L l ) o m , Ft. 7.76 to 16.89

4.751 to 47.9

/I 7

1

I "

20

60

40

80

100

120


"W

Figure 2. Variation of K,,.a with Vu, V, as parameter for 23-inch spacing V,, Ft./Hr.

55.25 40.51 26.46

0 2

0

0 0

40

04

06

08

0

02

04

06

08

7 Figure 4. Variation of (HTU),, with extraction factor, (dCw/dCm)(Vw/Vm)

7'0

02

0

20

40

60

Leff. 6-inch plate spacing Right. 1 1 -inch plate spacing

80

Vm Figure 3.

Variation of K,,.u with

8.0

V, for 23-inch spacing

7.0 -

flow rate. Hence, there is little increase in the contact area A trend of plots similar to that and litrle change in (K,,.a)'s. in Figures 2 and 3 is also observed when (Kom.a)'s are plotted (not shown) against one flow rate, and the other is kept constant. Effect of Plate Spacing. In view of the advantages of (HTU)'s over ( K .a)'s for the analysis of mass wansfer data, the results are also expressed in terms of the over-all (HTU)'s based on both the continuous and dispersed phases. T h e effect of plate spacing on mass transfer rates is shown in Figures 4 and 5 , where (HTU),, is plotted against the extraction factor for 6-, 11-, and 23-inch spacings. T h e extraction factor is defined by Treybal (1951) as ( ~ C E / ~ C R ) ( V E / V R ) , which in the present case becomes (dC,/dC,)(V,/V,). I n general, (HTU),, varies over a considerably greater range (HTU),, has therefore been chosen than does (HTU),,. to show the effect of varying the extraction factor on the values of (HTU)'s as in Figures 4 and 5. The data in these figures are represented by straight lines passing through the origin and with the slopes 10.83, 11.25, and 12.08 for 6-, 11-, and 23-inch spacings, respectively. From these values, it can be observed that for a given extraction factor, the (HTU),, value is higher for higher plate spacing, and so (K.a) is lower. Many authors (hloulton and Walkey, 1944;

6.0 -

23"

0

0.2

c

0.4

0.6

0.8

Figure 5. Variation of (HTU),, with extraction factor, (dC,/dC,) (Vw/Vm),for 23-inch spacing VOL. 7 NO. 2

A P R I L 1968

169


Mayfield and Church, 1952; Nandi and Ghosh, 1950; Pyle et al., 1950; Treybal and Dumoulin, 1942) have observed that decreased plate spacing resulted in improved rates of mass transfer and the present results are in conformity with their observations. T h e increase in (K.u)’s with 6-inch plate spacing over those with 11- and 23-inch spacings is due solely to the increase in the number of redispersions of the drops, taking advantage of more end effects a t the same net height of the column; this increase is obtained by the use of more plates (eight for 6-inch, five for 11-inch, and three for 23-inch spacings) in the lower plate spacing. Hence, for the same net height of the column, even though the 6-inch plate spacing gave higher mass transfer coefficients than 11- and 23-inch spacings, the operational cost increased, because of increase in the number of plates from three to five to eight with decrease in plate spacing. Hence, in judging the over-all performance of the column economic factors must be taken into consideration. Heights of Transfer Units. The individual film coefficients are more fundamental in nature than the over-all, and since the effect of flow rates can be better analyzed in terms of the film coefficients, their magnitudes are of considerable importance. The best method of resolving the over-all (HTU)’s into individual film values appeared to be the empirical treatment of the data by Colburn’s (1939) H T U method and the data are accordingly correlated by Equations 8 and 9 as shown in Figures 4 and 5.

These equations indicate that plots of (HTU),, against mVc/VD or (HTU)oD against (Vo/mVc) should result in straight lines and that the slope and intercept values of such a plot are as significant as the film (HTU)’s. This type of correlation is limited in its application, since the following three conditions should be satisfied to obtain true film values: The equilibrium line should be straight-i.e., m = dCc/dCD = a constant. T h e operating line should be straight, which means that the volumetric rate of each phase is constant throughout the tower, as for dilute solutions. The individual film IHTU)’s should be constants and independent of phase flow rates. Experimental investigations of Colburn and Welsh (1942) and Laddha and Smith (1950) clearly indicate the dependence of film (HTU)’s o n the flow rate ratio. I n spite of these limitations, Row et al. (1941), Treybal and Dumoulin (1942), Morello and Beckman (1950), and several others have applied these equations to resolve the over-all (HTU)’s into individual (HTU)’s. I n using Equations 8 and 9, the limitation that the individual (HTU)’s must be independent of both the phase flow rates is no doubt violated. But, with the lack of any other precise method, this has been used, and the individual (HTU)’s resulting from this plot may be regarded as indicative of the magnitude of film resistances only and not the actual film values. The results indicate that these equations represent the data fairly well, as only straight lines are obtained on plotting (HTU),, against (dC,/dC,) ( V,/V,) in Figures 4 and 5. Thus, it is clear that the intercepts-i.e., the probable (HTU),’s-are zero, while the slopes-Le., the probable (HTU),’s-are positive and varied as 10.83, 11.25, and 12.08 for 6-, 11-, and 23-inch spacings, respectively. Such zero or nearly zero values, which are indicative of the continuous 170

I & E C PROCESS D E S I G N A N D D E V E L O P M E N T

50

t

I

\

*

401 ‘i 01 0

1

,

1

,

,

,

I

0.1

0.2

0.3

0.4

0.5

0.6

0.7

(

3

(%)($) Figure 6. Variation of E A with extraction factor, (dC,/ dC,l(V,/VJ Plate Spacing, Inches

0

6 11 23

0

0

phase film (HTU)’s, were previously obtained by several authors (Allerton et al., 1943; Morello and Beckmann, 1950; Row et al., 1941; Treybal and Dumoulin, 1942) and hence the present results are in conformity with those of the earlier authors. Plate Esciencies. T h e average over-all plate efficiency data, EA, are plotted against the extraction factor, (dC,/dC,) (V,/V,), as shown in Figure 6 for all the plate spacings, which reveals that larger plate spacing results in higher efficiencies. This fact can also be observed from Figure 7, where EA is plotted against the plate spacing a t representative values of (dC,/dC,)(V,/V,). Figure 7 shows not only that EAincreases with plate spacing but also that the variation is linear. The perforated-plate tower corresponds to short multiple spray columns arranged one over the other in a vertical fashion. Hence, the tower acted more as a spray-type extractor than a mixer-settler type, and the increased efficiency a t higher spacings is due almost wholly to increased height of droplet travel. For any particular set of flow rates, the height of droplet travel is greater in the case of larger than of smaller plate spacing, because the number of plates and the total thickness of layers beneath the plates (height of extraction being the same in all cases) are less. The increase in efficiencies for the 23-inch spacing is nearly twofold.

I

4

Figure 7.

8

I

I

I

12 16 20 P L A T E SPACING INCHES

Variation of

EA

0

1

28

with plate spacing

Extraction Factor

0 0

I

24

0.1397

0.401 1 0.6088

60

/-Y:X

.

plots are considered only as empirical constants, indicative of the individual film (HTU)’s and not as true film values. Treybal’s correlation (1963) for the plate efficiency data is not very satisfactory for the present experimental results and hence a suitably modified correlation of Treybal (Krishna Murty, 1965a), was used, which resulted in better agreement between the experimental and newly calculated data.

LINE

0

vO

20 40 60 80 CALCULATED E F F IC I ENCY ‘10

100

Nomenclature

specific interfacial area, (sq. ft.)/(cu. ft.) of active extractor volume = concentration of solute in liquid, lb. molesjcu. ft. C AC = difference in concentration, lb. mole//cu. ft. = orifice diameter, ft. = experimental average over-all plate efficiency from N A , % = over-all plate efficiency, calculated from correlations, fractional = calculated over-all plate efficiency from Treybal’s correlation, fractional = calculated over-all plate efficiency from author’s correlation, fractional EF = extraction factor, (dC,/dC,) (V,,Wm), dimensionless H = effective height of extraction of column), ft. H,, = plate spacing, ft. (HTU) = height of a transfer unit, ft. (HTL),,, over-all, based on continuous phase ; (HTU)oD, over-all, based on dispersed phase; (HTU),,, over-all, based on methyl isobutyl ketone phase; (HTU),,, over-all, based on water phase ( K . a ) = mass transfer coefficient, lb. mole/(hr.)(cu. ft.) (AC) ; &,a, over-all, based on the water phase; K,,.a, over-all, based on methyl isobutyl ketone phase; KoD.u, over-all, based on dispersed phase; K,,.a, over-all, based on continuous phase flow m = (dC,/dCD), slope of equilibrium line, dimensionless MBE = material balance error, 70, = ( N u - iV,)lOO/NA, MIBK = methyl isobutyl ketone N = rate of solute transfer, lb. mole/hr. = number of theoretical stages as defined by Equation IVA 4 U’ = effective volume of tower, cu. ft. V = superficial velocity in tower, (cu. ft.)/(hr.) (sq. ft. of extractor cross section) = ft./hr. =

U

Figure 8. Experimental and calculated efficiencies for 23-inch spacings 0


0

Treybal Author

,,

But larger plate spacing resulted in lower (K.a)’s. This is not surprising, because a t lower plate spacings the increase in the mass transfer rate is not commensurate with the increase in the number of plates because of several other factors. T h e choice of plate spacing should ultimately be based on economic considerations only. Plate efficiencies are also greatly influenced by the extraction factor, (dC,/dC,) ( V,/V,), increased values being obtained with a decrease in the extraction factor within the range of flow rates studied. As (dC,/dC,) is a constant for the system, any variation in the extraction factor is due only to the variation in the flow rates of either phase, V , and V,. The trend of curves in Figure 6 approximates that of a rectangular hyperbola, as reported by Garner et al. (1953, 1955, 1756). Treybal (1763) gave a n empirical correlation of the over-all plate efficiency data on perforated-plate towers of various authors as given by Equation 6. I n a n attempt to correlate the present experimental data with this equation, it was found that the calculated data are higher than the experimental data in case of all the plate spacings similar to the one shown in Figure 8, for a representative set of data. A modified Treybal’s correlation, based on the studies of diameter variation, represented by Equation 7 , is presented in the literature (Krishna Murty, 1965b), and is believed to be a n improved correlation. Hence, the plate efficiency data are calculated by this modified correlation and are plotted against experimental data in Figure 8 for a representative set of data. This figure reveals a definite improvement in agreement between the experimental and newly calculated efficiency data.

Conclusions

GREEKLETTER U

interfacial tension, lb. mass/sq. hr. = 28700 where U ’ is interfacial tension, dynes/cm.

(0’)

SUBSCRIPTS Av

=

G

average value

D

= continuous phase = dispersed phase

E

=

1.m.

= logarithmic mean = methyl isobutyl ketone phase = raffinate phase

m T h e mass transfer coefficients increased rapidly with increase in the dispersed phase flow rate but remained more or less constant, with minor variations with increase in the continuous phase flow rate. Increased plate spacing resulted in decreased mass transfer coefficients and increased plate efficiencies. The over-all (HTU) data have been satisfactorily correlated with Colburn’s equations (1939), resulting in straight lines. T h e slope and intercept obtained from these

=

R W

1 2

extract phase

water phase top end of tower = bottom end of tower = =

SUPERSCRIPT

*

=

refers to equilibrium VOL. 7

NO. 2

APRIL

1968

171

Acknowledgment

Thanks are due to M. Sanyasi Reddy for his help and cooperation. literature Cited

Allerton, J., Strom, B. O., Treybal, R. E., Trans. Am. Znst. Chem. Engrs. 39, 361 (1943). Colburn, A. P., Trans. Am. Znst. Chem. Engrs. 35, 211 (1939). Colburn, A. P., Welsh, D. G., Trans. Am. Ztut. Chem. Engrs. 38, 179 (1942). Elgin, ‘J. C.; Browning, F. M., Trans. Am. Znst. Chem. Engrs. 31, 639 (1935); 32, 105 (1936). Garner, F. H., Ellis, S. R. M., Fosbury, D. W., Trans. Znst. Chem. Eners. (London) 31. 348 (1953). Gar&, F. H., Ellis, S. R. M:, Hill, J. W., A.Z.Ch.E. J. 1, 185 11955’1. \----,-


Garner, F. H., Ellis, S. R. M., Hill, J. W., Trans. Znst. Chem. Engrs. (London) 34, 223 (1956). Krishna Murtv. R.. D. Sc. thesis. “Studies on Perforated-Plate Liquid-Liquid Extraction Towers,” Andhra University, Wal-

tair, India, 1965 (copies available from author, Andhra University Library, I.N.S.D.O.C., New Delhi). Krishna, Murty R., unpublished data, 196513. Laddha, G. S., Smith, J. M., Chem. Eng. Progr. 46, 195 (1950). Mayfield, F. D., Church, W. L., Znd. Eng. Chem. 44,2253 (1952). Morello, V. S., Beckmann, R. B., Znd. Eng. Chem. 42, 1078 (1950). Moulton, R. W., Walkey, J. E., Trans. Am. Znst. Chem. Engrs. 40, 695 (1944). Nandi, S. K., Ghosh, S. K., J. Indian Chem. Soc., Znd. News Ed. 13, 93, 103 (1950). Pyle, C., Colburn, A. P., Duffey, H. R., Znd. Eng. Chem. 42, 1042 (1950). Row, S. B., Koffolt, J. H., Withrow, J. R., Trans. Am. Inst. Chem. Engrs. 37, 559 (1941). Treybal, R. E., “Liquid Extraction,” 1st ed., McGraw-Hill New York, 1951. Treybal, R. E., “Liquid Extraction,” 2nd ed., McGraw-Hill New York, 1963. Treybal, R. E., Dumoulin, F. E., Znd. Eng. Chem. 34,709 (1942). RECEIVED for review October 14, 1966 ACCEPTED AUGUST3, 1967

STEADY-STATE SOLVENT EXTRACTION CALCULATIONS FOR CURIUM RECOVERY I . D. EUBANKS’AND J. T. LOWE Savannah River Laboratory, E. Z. du Pont de Nemours @ Co., Aiken, S. C .

29801

A numerical method has been programmed in FORTRAN IV for calculating steady-state phase concentrations in countercurrent liquid-liquid extractors. An integral number of stages, cocurrent mass transfer efficiencies, and compositions of multiple feed streams are included in the input data. Distribution data are represented b y mathematical expressions for the specific process computed. Stage concentrations for as many as seven mutually dependent distributing components can be calculated from a single set of input data. Computed and experimental concentration profiles are compared for flowsheets used to purify curium.

OUNTERCURRENT

solvent extraction is normally used to

C process irradiated nuclear material because a product of high purity is attainable, the process chemicals are relatively stable to ionizing radiation, the quantity of solid radioactive wastes is minimal, and the processing equipment may be operated remotely (Haas, 1961). Stage concentrations in solvent extraction processes are calculated from distribution coefficients and material balance ex1 Present address, Department of Chemistry, Oklahoma State University, Stillwater, Okla. 74074

172

l & E C PROCESS D E S I G N A N D D E V E L O P M E N T

pressions. The concentrations can be determined either numerically (Siddall, 1958) or graphically (Codding et al., 1958). Although the graphical method has been widely accepted for flowsheet design and interpretation, extensive calculations are required to design optimum flowsheets and to establish permissible fluctuations in process variables. If two components influence each other’s distribution, graphical solutions require lengthy trial-and-error procedures (Haas, 1958) ; a numerical method for a computer is therefore preferable. A limited number of previous treatments of similar problems have been reported. Mills (1965) reviewed several programs

PERFORATEDIPLATE LIQUID-LIQUID EXTRACTION TOWERS

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