ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
Processing Variables in Solvent Extraction Towers HARVEY J. VOGT' AND CHRISTIE J. GEANKOPLIS Department of Chemical Engineering, Ohio Stafe Universify, Columbus
E
FFECT of processing variables on the mechanism of diffusion in the liquid state is of importance in understanding the performance of countercurrent extraction spray columns. In recent years much has been published concerning the specific effect of these variables, such as bubble sizes, nozzle design, column design, and flow rates. Much of the published data is somewhat limited in its use since very little has been done to coordinate all these variables in the form of generalized correlations which hold for any combination of conditions for spray towers. Various investigatms (11, 15, 1 7 ) studied the amount of extraction from individual drops in spray towers. Coulson and Skinner ( 3 ) studied the mass transfer inside individual drops and found considerable circulation of liquid inside these drops. Johnson and Bliss (9) and Hayworth and Treybal ( 8 ) studied nozzle design and drop sizes. Minard and Johnmn (22) studied limiting flows and holdup in spray extraction towers. Blanding and Elgin (93) found that end design was critical, particularly at high flow rates. Newman 1
Present address, Columbia-Southern Chemical Co., Corpus Christi, Tex.
n l
IO, Ohio
( 1 4 ) , Gier and Hougen (Y), Kreager and Geankoplis (IO),and Geankoplis (4)stated that there is recirculation of the continuous phase and this may be the cause of the end effect a t the continuous phase inlet. Using a movable internal sampling tube, Geankoplis and Hixson ( 6 ) determined concentration gradients in the continuous phase of a spray tower and found inlet effects a t the continuous phase entrance. Others (6, 7 . 1 0 ) found similar effects with different systems and towers. Kreager and Geankoplis ( 10) systematically varied tower height and found an increase in over-all ( H . T U )OR with an increme in column height for spray towers A t high column heights the (H.T.U.)ow approaches a constant value as the end effect becomes decreasingly important They experimentally determined the effect of flow rates, tower height, and concentration on over-all ( H . T . U . ) ~ and W correlatctl t,he data in one equation with an average deviat>ionof =t5% Their d a h were obtained only for extraction from the continuous to the dispersed phase. Kandi and Viswariathan ( 1 5 ) also found an increase in H.T.U. with an increase in column height. The present investigation continues the xork of Kreager and Geankoplis (10) on spray towers usiiig the same system, methyl isobutyl ketone-propionic acid-water. The effects of column height., flow rates, and concentrations on extraction in the o p posite direction-Le., from the dispersed phase methyl isobutyl ketone to the continuous water phase-were studied. The effect of using a different solute, formic acid in place of propionic acid was also studied. Several investigators (2, 9, 12) studied the novel spray tower end design of Blanding and Elgin (2) which gave high flooding velocities. No one has compared the extraction performance of this tower with other more common spray tower column designs. Therefore such a column was investigated and this comparkon W H S made. Studies Include Tower Height and End Design Effects
Figure 1 is the process flow diagram for the extraction spray tower. The tower and containers were glass and most of the tubing was saran The stoppers a t the ends of the tower and the flexible tubing were neoprene The equipment was similar to that used and described in detail by Kreager and Geankoplis (10).
Figure 1.
Process Flow Diagram of Extraction Tower
September 1954
The methyl isobutyl ketone phase and the water phase were siphoned from the 5-gallon bottles, A , into constant head tanka B from which they overflowed into C. The flow of the continuous water phase was controlled by needle valve E and entered the tower a t nozzle G. The ketone, controlled a t E', was always the dispersed phase and entered the tower through nozzle F . The interface was held a t the tip of nozzle G by loop H . The outlet ketone and water streams were collected in K , and rates of flow were measured by suddenly transferring the flows t o the 500-ml. graduates, L. A glass, movable sampling tube, described by others (6, 6, 10) consisted of a 5-mm. glass tube, P,and extended into the extraction section. By means of suction a t U a sample of the descending
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
1763
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
Table I. Over-all Transfer Data Run No.
Column Temp., Height, ' C. Ft.
Flow Rate, Cu. Ft.,'(Hr.) (Sq.Ft.) LK Lir-
so,
~i~~ nispersed phase Nozzle
Over-all Acid Transfer Rate Deviation, Lb.-Mole/Hr. ~ ' 1 0 3 N W - X K Sv NK Nay. .?ray.
1 2 3
24 30 24
3.0 3.0 3.0
28 48,~ 28, R
Column A , Propionic 40.3 6 38.2 10 39.6 6
Acid 3.05 4.36 2.12
3.03 4.23 2 07
3.04 4.30 2.10
0.7 3.0 2.4
4A 6
24 27 24
3.0 3.0 3.0
29.9 49.6 31 . O
Column A, Formic Acid 39.3 6 3.41 39.1 10 5.30 40.0 6 2.29
3.63 3 . 69 2 34
3.52 3 00 2.32
-0 3 -7.1 -2.2
7 8 9 10 11 12.4 15
24 25 24 27 26 27 30
2.0 2.0 2.0 1.0 1. 0 1.0 1.0
29.3 48.0 28. F, 30.0 48.2 29.2 29 5
Column A, Propionic 40.5 6 38.7 10 39.3 6 40.3 6 39.5 10 39.0 6 19.6 6
Acid 2.34 3.67 1.75 1.89 2.59 1 21 1.43
2.48 3.60 1.04 2 02 2.63 1 17 1.22
2.41 3.64 3.70 1 Oh 2.61 1.21 1.4;
-6.8
13 149
31 26
1 0 1. 0
29.6 29.2
Column A, Formic Acid 39.0 6 2.10 6 1 33 39 4
2.16 1 41
2.13 1 37
-2.7
20.1 28.9 48.7 29.0 29.5 48.8 20.6 28.9 30 3 31.1
Column B, Propionic Acid 38.5 4 7 21 39.4 6 9.99 38.5 10 13.29 39.7 6 8.53 39.6 6 3 70 40.0 10 5.15 39.9 6 2.58 39.9 6 2.90 38.7 6 10.16 39.2 6 1.40
7 56 10.72 12,31 6.74 3.84 5,26 2.51 2.94 10.60 1 40
7.39 10.36 12.80 6.63 3.77 5.20 2.51 2.92 10,38 1.13
29.5 28.R 49 7 29.8 19 6
Column A , Propionic Acid 6 0.97 39.5 38.8 6 1.36 39.9 10 1.92 39.7 6 2.52 39.9 4 2.54
0.95 1 31 1.94 2.64
0.96
5
18.4 19 20 21 24 25 26a 27e 28a 29 a
25 26 23 25 28 31 22 21 21 23
30 5
26 25 25 25 25
316 32n 33a 34" 6
3.0
3.0
3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 0.5 0.5 0.5 0.5
0.5
2
2.67
D a t a of Rishop ( I ) .
continuous water phase waa slowly withdrawn at P into sample flask T. The vertical position of the sampler was adjusted by securing B in scale S. Extraction Towers and Nozzles. Details of the two basic glass extraction towers, column A and column B, are shovin in Figure 2. Tower A, employed by Kreager and Geankoplis ( I O ) , was 1.41 inches in inside diameter and had a flared settling section at the bottom. The dispersed phase nozzle was placed a t the bottom of the flare so that t,he annual area open to flow equaled the tower crom-sectional area. Three columns of this type were used which differed only in the length of the nliddle extraction section between the bottom nozzle tip and the top interface. The continuous phase inlet nozzle x a s the same as that used by Kreager arid associates ( 1 0 ) and consisted of four tips, each 0.159 inch in diameter. Tower B (Figure 2) had an inside diameter of 1.52 inches. The continuous phase entered through three 7-mm. glass tubes inserted in stoppers a t the top of the tower. The liquid flowed down into the annular space! up over the weir, and down into the ton-er as the continuous phase. The interface level was held 1 inch above the circular weir. This tower was similar to that of Blanding and Elgin ( 2 ) : which gave very high flooding rates. The dispersed phase nozzle is not shown but was identical to that used by Kreager and Geankoplis (IO). I n this nozzle the number of tips was varied directly with the flow to give the same bubble size regardless of the dispersed phase flow. The baffle plate inside the nozzle gave good liquid distribution to the tips (IO). Procedure. The direction of extraction was from the continuous water phase to the dispersed methyl isobutyl ketone phase in mme runs and in the reverse direction in others. When the 1764
1.34 1.93 2.58 2.60
1.9 6.2 -6.6 --1. d
5.8 -6.2
-3.6
7
-4
--
-7
1
,
I
-3.2 -3.7 -1.9 2.8 -1.4 -4 3 -4 2 2.6 3 7 -1.0 -4.7 -3.0
extraction was to be performed from the ketone t,o the wat,er, the spent Ireton(. was brought to the desired normality with fornlic or propionic acid, depending on which solute was to be used If the ketone i w s to contain no w l u i ~ ~ , the spent ketone from previous run* was regenerated by washing with 2.\. sodium hydroxide solution and twicv with distilled water. The water concentration was adjusted by addition of the concentrated acid. After the flow rates and the interface level had been correctly set, steadystate conditions in the tower were att'ained after the tower contents hati changed four to five times. In obtsining internal samples of the conhuous phase, the sample line was first, purged and then a sample wais slowly taken in another bottle. Sample rates lr-ere l ~ s s than 2.5% of the continuous phase floiv rate. Inlet and outlet samples of both phases were taken Peveral t>imesduring the run and composited. Rates were also measured several times and averages used. The methyl isobutyl ketone used WBL: technical grade and wvas obt,ained from the Carbide & Carbon Chemicals Corp. Chemically pure formic and propionic acid and distilled water were also u ~ c d in all runs. The acid concentration was determined by duplicate titrations with O . I N sodium hydioxide using suitable end point blanks. Ethvl alcohol was added to the organic phase befoie titration.
Performance Comparison Shows Greater Extraction Efficiencyof Specially Designed Tower
By using the same calculation proccdures of others ( 5 , 6 , IO) for dilute solutions, the follovring equations were employed f o i the over-all tower:
.Y = K,va V a C ~ l m
(11 ( 2I
Eyuations 1 and 2 can also be used t,o calculate maM transfer coefficients for short sect,ions of the tower. Thip has bmrl diucussed in detail ( 6 , 6 , I O ) . The expcrimental spray towcr ( h t a are given in Tablcs I, 11, and 111. The actual calculations were performed in the usual manner and are identical to thom which have been described in tietail ( 5 , 6, IO). The over-all Kwn and (H.T.V.)olv values are givtrii in Table 11. The equilibrium data for the propionic acid solute were obtained from Johnson and Bliss (9) and data for the formic acid solute from Vogt and Geankoph (16). Internal (H.T.U.)ow and End Effects. The experirnentul C,, values (Table 111)obtained from internal sampling wort plottoti, as in Figures 4, 5, 9 to 11, and smoothed values a-ere used to calculate the internal (H.T.U.jow for short internal t o w r sections given in Table IV. The internal concentrations in t'he dispersed ketone phase were obtained by material balances assuming no recirculation of the continuous phase. The average ( € I , T , l ~ , ) ~ , l ~ values in Table IV were obtained by neglecting the end effect-: at both ends. End effects were determined graphically by employing the same methods of others (6: 6, I Q ) and are reportecl in Table 11.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 9
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT Material Balances. I n removing internal samples, approxiniately 2.5% or less of the continuous phase was removed. The average deviation of the over-all material balances for all runs is 4%, and the mLYimum is 7.7%. The effect on calculations of over-all mass transfer coefficients should be minor. It has been shown ( 5 , 6, IO) that internal sampling has a negligible effcct on the mass transfer in the tower.
r W A T E R INLET
Table
111.
Run No.
Internal Samples of Acid in Water at Points Inside Tower Concn. of Acid in Water Phase, Lb.-Moles/Cu. Ft. X 103, a t Distance from T o p Interface, Inches 2 5 6 8 10 12 18 30
1
2
3 4'4 5 6 7
8
T e'
9 10 11
5.42C 8.30 3.62c 26.22 24.29 16.55 5.30e 793 3.92e
6.%d
10.20 4.49d 22.20 19.06 14.69
... ,..
...
12A
15 13 14A
TO 14"
18.4 19 20 21 24 25 26 27 28 29 31 32 " 2.5-inch point. 6.5-inch point. c 18.5-inch point. d 29.5-inch point. e 20-inch uoint. 13-inch pbint. Q 1.5-inch point. h 3.5-inch point.
i
3',2', I ' OR 0.5'
la:& 15.95 9.39 11.84 5.55 8.19 3 73 5 22 14.50 1 91
15'15 10.34 fi.20
7.72 6.82 10.00 4 , x 4.14 9 80 2 , s
Over-all Performance. The over-all (H.T.U.)om d a h obtained from runs in towers A and B for extraction from water to ketone are plotted in Figure 3 V C ~ ' S U Sthe ratio of disperRd tu continuous WATER flow rate. T h t plots show that column B is more efficient and SETTLING SECTION the over-all (H.T.U.)ow of t o m r A4is about 25% greater for :L tower height, of 3 feet. The slopes of both lines are about thc same, or (II.T.C.)ovis proportional to ( L ~ / L w ) - " a 7 . For the reverse citraction (ketone to water), runs 24, 25, 26. and 29 for column B were compared wit'h similar runs of columri COLUMN A COLUMN B A. The over-all (H.T.C.)om of column A was, on the average, Figure 2. Extraction Columns 16% greater than for B. The average results for extraction from water t'o lretoiie 01'in the reverse direction show that the (H.T.U.)om for t o u t r A is about' 20% greater than'for tower I3. Table 11. Over-all Mass Transfer Data and End Effects This difference in efficiency is only for a Acid Concn., Over-all Transfer End Effects in Terms %foot column and may be different at Lb.-Moles/Cu. Ft. x 108 Coefficient_ of Fictitious cw different tower heights. Run (H.T.U.)ows - Height- Ft. -___C K KO In Out In Out Kwaa ft. 2; z; Inspection of Table I1 and the data of 1 0 lj,O9 29 18 19.41 10.78 3 i4 , . .... Kreager and Geankoplis ( I O ) shows that 2 0 10.52 2K40 21.40 17.75 2.1.5 .. Zh, the fictitious height, of column equiv3 0 4.45 21 26 14.57 10.10 3.92 ,. .. .. .. 4.4 29.74 21.82 0 11.19 11.5C 3 40 0 ' is 0 alent to the continuous phase inlet 5 30.33 17.81 0 10.54 10.73 2 34 n 28 0 6 20.18 14.89 0 f3.97 9.12 4 39 0.38 0 effect, is approximately 50% greater for 7 0 5 33 29.73 21.91 11 17 3 , ti3 .. .. .. .. .. .. column A compared to tower B. This 8 0 8.74 30.30 23.38 19.90 1.9.5 9 0 4.11 20 88 15.56 11.05 3.66 . . . means that column A has a greater entl 10 0 4 32 30 30 24.16 16.96 2 , RR , . . . 11 n G.Od 30 43 2%5,.40 22 0 2 I 78 , . . . effect. In most cases Zb is negligible, 12A 0 2.93 14.79 16.10 14.39 2.71 The average (H.T.U.jOw with both entl 1R n 0 72 29 7 3 25.00 13.70 1 43 .. .. . .. 13 30.16 25.10 0 0 73 10.32 3 78 l'i8 0 effects eliminated (Table IV) is about 14'4 20.18 10.911 0 4.45 9.86 3 oq 1.84 0 1RA 29.78 14.8-1 0 2R.98 13.18 2 02 0 72 -0.22 40% greater for column A than for 19 29.92 $3.70 0 29..57 22.40 1.76 0.66 -0.13 column B when compared at the same 20 30.04 454 0 21.76 33.00 1.17 0.58 0 21 2 0 . 4 5 1 . 3 4 0 18 52 19.57 2 03 0 47 0 . 1 3 flow rates. 24 0 1.45 29 43 19 00 11.88 3 33 .. .... 25 0 10.20 30.33 21 7.5 18.84 2.12 .. .... Since the internal (1I.T.U.)OW is less for 26 0 5.15 19.40 12.08 13.00 3.00 .... column B, this means the concentration 27 9.64 3 86 0 8 09 19.60 2.04 0.67 -0.18 28 29.90 o.oi n 27.71 21.92 1 77 O.4B 70.19 gradient of this tower is steeper than for 24 0 2.82 10 12 0.38 13.21 2.86 ,... tower A. This may indicate more 30 0 2.26 20.30 17.35 21.00 1 89 .. .... 31 0 3.23 29.50 25.30 20.40 1.90 countercurrent actioti or less cocurrent 32 0 4.44 29.00 20.00 30.30 1.32 .. .. .. . .. 33 19.55 13.70 0 8.15 33.00 1.20 .. .... act'ion for tower B. This seeme t o be 34 30.28 24.41 0 12.50 19.80 2.02 .. .... borne out by the fact#that the end eKect a Lb.-nioles per (hr.)(cu. ft.)(lb.-moles/cn. ft.). of tower B is smaller. It has been stated ( 4 , 7 , 10, 1 4 ) that the end effect may be
rn
I
September 1954
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1'165
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT due to cocurrent flow or mixing of the continuous phase. Yet it is likely that the Zb and the concentration gradient are tied together so that lower concentration gradients give greater end effects. More experimental data are needed concerning these questions. Internal Performance. The concentration gradients of towers A and B are compared in Figure 4 for the extraction from water t o lrctone a t various inlet water concentrations. The curves fihorv that both towers have the same absolute amount of extraction performed a t the inlet. The concentration gradient is considerably steeper for tower B. The same trends are evident if the data a t different ketone rates are plotted.
IO
Z = 3.0'
I
PROPIONIC A C I D LK ' 2 9
@COLUMN A OCOLUMN B TOP IO 20 30 BTM. DISTANCE FROM IVNTERFACE, INCHES
INLET C 30 x 1 5 3
0
d 0 2 0 X IOJ @
A
IO
x
10-3
0.5
TOP
IO 20 30 BTM. D I S T A N C E FROM INTERFACE, INCHES
Figure 4. Effect of Type of Tower on Concentration Gradient
PROPIONIC AC,ID 2 * 3.0
Figure 5. Effect of Type of Tower on Concentration Gradient with Reverse Extraction
Table IV. Internal (H.T.U.)om for Short Column Sections
+ Figure 3.
0.6
0.8
2
1.0
"I(' LW Effect of Column End Design on Over-all (H.T.U.)ow
The explanation of the differences in towe and conflict,ing. In tower B there should he less turbulence and, hence, less recirculation because of the weir overflow entrance. However, a flow pat'tern may be established whereby the liquid in tower B overflows the vieir and by-passes partially down the Fides of the wall, missing contact with the rising bubbles. Rough preliminary calculations shoiv that decreases in densit'y of the downcoming water phase of 1% could conceivably set up a maximum recirculation velocity of about 1 foot per second. Recirculation increases velocit'ies or turbulence and increases mass transfer coefficients. Yet, recirculation decreases countercurrent action or the driving force, ACT. In the reverse extraction from ketone t o water there should be a reverse density yradient aiding countercurrent action. In Figure 5 data are plotted for the reverse direction of extraction (from ketone to water). The lines of all runs of both towers are approximately parallel. This also t,ies in n-ith the fact that' for reverse extraction the average internal (H.T.U.)owwith end effects eliminated is about the same for both types of towers. Since the over-all (H.T.C.)ovof tower A was shown previously to be greater, the end effects of tower B must be larger for reverse extract'ion. I t is difficult to determine the end effects in reverse extraction (Figure 5 j,but they are appreciable. Direction of Extraction Has Signincan1 Effect on Mass Transfer Coefficients
Figure 6 is a plot of over-all (H.T.U.)oTv versu? L K / L w for reverse extraction (ketone to mater). The elopes of the lines are the same as those found by Kreager and Geankoplis ( 1 0 ) for extraction from water to ketone, Hence, the direction of extraction does not alter the effect of the flow rates. 1766
Ft., %Foot Coluinnl for Length of Section, Inches R ~ ~(H.T.U.)on', ~ , KO. 2-10 10-20 20-30 30-36 Average 1 5.20 3.23 4.13 30.1 4.14 2 2.39 2.50 2.87 7.27 2.72 3 4.90 4.43 6.08 6.90 5.14 4A 4.20 6.41 2.37 8.62 4.35 2.91 4.14 1.96 5 5.26 3.00 6 6.11 8.35 4.17 6.21 9 87 18.4 3.60 5.62 2.69 10.7 3.96 2.00 2.31 1.74 19 3 44 2 .02 1.34 1.42 1.31 20 1.36 1.28 2.08 21 2.38 4.08 2.75 2.40 24 3.63 5.43 5.20 11.4 4.75 25 3.32 3.03 10.2 2.74 3.03 4.675 26 3.26s 5.03 3.91b 3.95 27 2.85" 3.91C 7.23 2.386 3.04 28 2.19b 2.42c 1.54= 6.00 2.06 29 3.82c 4.286 3.44Q 3.56 3 8.5 R~~ NO.
7 8
Q
R~~ NO.
10 11
12A 15 13 14.4
R~~
No. 31 32
c
(H.T,U.)om, Ft., 2-Foot Column, for Length of Section, Inches 2-6 4.25 1.93 6.51
6-12 4.72 2.49 6.16
12-20 7.23 4.60 7.10
20-24 99.0 7.65 11.3
~ v e r i g e 5.41 2 0-1 6 39
(H.T.C.)ow, Ft,., 1-Foot Column, ____ for Length of Section, Inches ~
2-5 5.19 3.18 4.95 3.56 12.3 14.2
5-8 9.07 5.62 7.67 8.52 13.1 15.3
8-12 16.0 12.7 49.2 47.0 14.2 16 2
A4verape 7 13 4 10
6 6 12 14
32 04
7 8
(H.T.U.)ow, Ft., 0.5-Foot Column, for Length of_ Section, Inches _ ~.~~ ~ 1.5-3.5 12.7 14.0
3.5-6 39.4 26.0
Average
12.9 14.0
Section length 2--6 inches. Secrion length 6-18 inches. Section length 18-30 inches.
The gcrieralized correlations relating over-all (H.T.17.)o~, flow rates, tower height, and direction of extraction at all concentrations are shown in Figure 7 for the system methyl isobutyl ketone-propionic acid-water . Reverse extraction from the ketone t o the water gives (H.T.U.)om values that are an avciage of 52% greater than for straight extraction from water to kotonc. Visual observation shon-s that when extraction is from the k(4one bubbles t o the water the bubbles tend to flatten out and coalcscc.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol, 46, No. 9
ENGINEERING. DESIGN. AND PROCESS DEVELOPMENT 110% greater than values from propionic acid runs. There are insufficient data for definite conclusions, but indications are that the extraction with formic acid gives much higher (H.T.U.)op values and is much less dependent on over-all tower height. In Figure 9 internal concentration plots for formic and propionic acids in a %foot column are shown. The formic acid runs show the typical end effects. The average 2; of formic acid for the runs in the plot and for those a t 1-foot height (not shown) is about one third to one half as large as it is for propionic acid.
I
IOC
COLUMN A
0.4
0.6
COLUMN
\
PROPIONIC ACID
l
I
l
A
PROPIONIC A C I D
I e
1.0
0.8
LK 'LW
Figure 6. Effect of Flow Rates on Overall (H.T.U.)orr. with Reverse Extraction
?--, Y
By using the methods of Kreager and Geankoplis (fO),the following equation was derived from both curves: (H.T.U.)ow = b ( L ~ / L w ) - 0 3(1.50)-""
(3)
2
I
0.61 0.4)
0
I
I
0.5
1.0
I
I
2 .o
1.5
2.5
I/Z
where b = 2.13 for extraction from water to ketone and 3.24 for extraction from ketone to water. The data for extraction from ketone to water deviate from the equation on the average of =k5.0% and the maximum deviation is 12.301,. For extraction from water to ketone the average deviation is 1 5 . 0 %and the maximum 18.4%. This equation differs slightly from that of Kreager and Geankoplis (10)because two additional data points were obtained for this curve and the two lines were drawn parallel. In Figure 8 the same data are plotted versus l/Zinstead of Z to give straight lines. This plot or Equation 3 can probably be used with some confidence for extrapolation t o heights greater than 3 feet. Extrapolatlone to heights less than 0.5 foot should be made with caution. Formic Acid Solute. The five runs made by extracting formic acid from water to ketone are not shown, but they were compared with propionic acid extraction plotted on Figure 7 . Runs were made a t only 1 and 3 feet, The runs with formic acid a t 3 feet gave (H.T.U.)ow values about 40% greater and a t 1 foot about
Figure 8.
Correlation of Operating Variables for Over-all Tower
INLET Cw=30.0 COLUMN A
FOR
FORMIC A C I D
5 I
PROPIONIC
x 10-3
,
I
ACID
1
I 'I!he (H.T.U.)OW with inlet effects eliminated is considerably greater for the formic compared to the propionic acid. Tower Height and Concentration Gradients. Figures 10 and 11 are plots of internal concentration in the continuous water phase versus distance from the top interface for different overall tower heights and extraction from ketone to water. For the same tower heights but different inlet ketone concentrations, the curves in Figures 10 and 11 are approximately parallel.
e-&--------
COLUMN A
0.8
0.61 0.41 0.4
INLET 0
cK =
IO
I
0.6
x
10-3 TO 30
x IO+
I
K R E A G E R , G E A N K O P L I S [IO)
oa ID
2
,
I
4
I
,
6
,
/
,
810
z Figure
7. Correlation of
September 1954
Operating Variables for Over-all Tower
Design Method Using Data from a Single Run I s Proposed
Inspection of Figures 10 and 11 shows t,hat the outlet concentrations in the continuous water phase of runs for 2, 1, and 0.5
INDUSTRIAL AND ENGINEERING CHEMISTRY
1767
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT feet fall close to the 3-foot concentration curve. This means that if the internal concentration gradient is experimentally determined for only one tall height, the over-all (H.T.U.)on. can be piedicted a t any tower height in the following way. The outlet
effective height of extraction section of tower. ft. fictitious height Of column cquivalent t o continuouh phase inlet effect, ft. = fictitious height of column equivalent t o dispersed phasc, 2; inlet effect. ft. (H.T.U.)ow = over-all height of transfer unit based on phase TI', ft. K n a = over-all extraction coeffirient based on phase TV, 1b.moles per (hr.)(csu. ft.)(lb.-moies/cu. ft.) LI: = flow rate of phase K , cu. ft./ hr.)(sq. i t . ) LW = flow rate of phase W, cu. ft.& )(sq. ft.) N = amount of solute t r a n s f e r r e d , 1 b . moles/ hr .VK = amount of solutc transferred in phase IC, 1b.-moles/hr. N w = amouut of solute transferred in phasc W, 1b.-moles/hr. V = effeclive volume of extraction column, cu. ft. Z
= =
z;
5-
4-
.
7 -
6m
0
5
x L V
Subscripts 1,2 refer to ends of t'ower or section of t,ower K refers to ketone phase W refers t,o rvater phase
LK' 29
m
COLUMN A
-3
I
INLET CKz20X10
'I
2 X
I
PROPIONIC ACID LK = 29
V
COLUMN A INLET CK:30X10
I
l
/
I
TOP
INCHES
IO
20
constant depending on direction of extraction
= cross-sectional area of column, sq.
ft.
concentration of solute in phase K , 1b.-moles/cu. ft. concentration of solute in phase TY which would be in C*, equilibrium with concentration in opposite phaw, lb~-moles/cu.ft. C W = concentration of solute in phase W , 1b.-moles/cu. ft. Acmlm = 109 mean values of (Cw - c*,)or (c*,- c w ) for t w o terminals of column
1768
Lw ~35.1 INI ET c K = 3 0 . 0
x
10-3
SOLUTE = PROPIONIC ACID COLUMN A
I I I l j
TOP 5 IO BTM. DISTANCE FROM INTERFACE, INCHES
Figure 12. Effect of Ketone Flow Rate on Concentration Gradient with Reverse Extraction Literature Cited (1) Bishop, J. V.,
B.S.thesis in cheniical engineering, Ohio State University, 1952. (2) Blanding, F. H., and Elgin. J. C., Trans. Am. Inut. Chem,. Eng,.~., 38, 305 (1942). (3)
Coulson, J. AI., and Skinner, S. J., J . C h e m E'ng. Sci.,1, 197 (1952).
(4) Geankoplis, C. J., ISD. ENG.CHEM.,44, 2468 (1952). (5) Geankoplis, C. J., and Ilixson, *I.S . ,Ibid., 42, 1141 (1950). (6) Geankoplis, C. J., WellJ, P. I,., and Hawk, E.L.. I b d . , 43, 1848 (1951). (7) Gier, T. E., and
Hougen, J. O., Ibid., 45, 1383 (1953). (8) Hayworth, C. B., and Treybal. It. I:.. Ibid., 42, 1174 (1950). (9) Johnson. H. F., and Bliss, H., T r a u . Am. liaaf. Chern. Engrs., 42,331 ( 1 9 4 6 ) . (10) Kreager, R. AI., and Geankoplis, C. J., J s n . ENG.C m x , 45,
2156 ( 1 9 5 3 ) . (11) T'icht, W., Jr., and Connay. ,J. B.. Ibid.,42, 1151 (1950). (12) Minard. G . >I., and Johnson. A.. I.. Che?i&.Eny. €',on., 48, 6 2 (1952).
= interfacial mea per unit volume of extractor, sq. ft. 'cu. f t . = =
z =1.0'
INCHES
Nomenclature
C'X
1.
Figure 11. Effect of Tower Height on Concentration Gradient with Reverse Extraction
concentrations a t shorter heights can be read from the concentration curve for the tall height and t'he over-all (H.T.U.)orr .~' )ow values calculated. A straight-line plot of ( L K / L ~ ) "(H.T.U. versus 1/Z can be made. This was done for run 3 of Figure 10 in a 3-fOOt tower for extraction from ketone to water and the maximum deviation of the predicted line from the upper experimental line (Figure 8) was 47, at a height of 0.5 foot. The use of data for run 1 of Figure 11 gave similar results. From run 9 (%foot t'ouer) a maximum deviation of 22% was obtained. This is t o be expected, since it is more difficult t,o determine accurat,ely the concentration gradient for small tower heights. Kreager and Geankoplis ( I O ) presented similar concentration plots for different tower heights for extraction from water to ketone. By rning the same method, the ( L K / L ~ ) ~ (H.T.U.)ow .~' versus 1/ Z line was predicted with the concentration gradient of run 1 of their data. Similar results were obtained. Hence, this method can be used for either direction of extraction. I n Figure 12 the effect of ketone flow rate on the concentration gradient is shown for reverse extrnct,ion and tower height of 1 foot. The lines are parallel. Data for other tower heights and also for column B show the same type of parallel lines for different rates.
=
/
30 E
D I S T A N C E F R O M INTERFACE,
Figure 10. Effect of Tower Height on Concentration Gradient with Reverse Extraction
b A
RUN II
j
D I S T A N C E FROM I N T E R FtlCE,
a
-3
Sandi, S.K., and Tisn-anathan. T. It.. Current Sci. (Pndia), 15, 162 (1946). (14) Sewman, A I . L., IND.Ex.CHEM.,44,2.157 ( 1 9 5 2 ) . (15) Sherwood, T. K., Evans, ,J. E., and Longcor, J. V. A,, I / i i d , , 3 1 , (13)
1144 (1839). (16) Vogt, H. J., and Geaiikopliu. C .
