Application of Pulsation to Liquid-Liquid Extraction W. A. CHANTRY', R. L. VON BERG,
AND
H. F. WIEGANDT
Cornell Universify, fthoco, N. Y.
Extraction efficiencies in conventional countercurrent columns are often poor. Many designs have been proposed to aid mass transfer by means of agitation. A promising method is that of pulsating the liquid in a column to provide turbulence throughout the column. The results of a detailed study of pulsation in both packed and sieve-plate columns are given. As great as threefold improvement was achieved over conventional operation for the packed column. Efficient performance can be maintained at low feed rates b y pulse action. Only slight reduction in flooding rate was noted. Sieve-plate construction allowed greater capacity but suspended material easily plugged the plates. Sieve plates must have small holes, and the column will not operate without pulsating. Existing packed columns can readily be modified and can be operated conventionally when not pulsated. Emulsion formation may be a problem with some systems
01 N W
0
N E of the requirements for effective liquid-liquid extraction is thorough mixing of the two phases. I n a batch extraction
*
this is easily achieved by agitating the two liquids and then allowing them to settle and separate. By suitable arrangement of mixing vessels and settling tanks it becomes possible to operate stagewise and countercurrently. However, if many repeated extractions are necessary this method is likely t o be cumbersome and expensive. In order to reduce the number of pieces of equipment needed for countercurrent extraction it has become common to use a column, usually a packed column, with counterflow of two liquid streams through it. A large number of variations in the design of countercurrent extraction columns have been summarized in the literature (18, 19). With but few exceptions the energy for mixing the liquids in these columns has been obtained solely from the gravity force resulting from the difference in density between the two phases. The exceptions, all reported within the last few years, have used several different methods for supplying additional energy for added internal agitation. A column with a series of mixers and settling areas was reported by Cornish, Archibald, Murphy, and Evans (8) as early as 1934. The following year, Van Dijck (SO) patented a column in which a set of perforated plates was moved up and down with respect to t,he column to provide agitation. Another apparatus patented (16)was designed to oscillate the entire column. Ney and Lochte ( 1 9 ) and Maycock ( 1 7 ) tried spinner columns consisting of a smooth revolving cylinder in a slender column. There have been several reports (23-95) on the Schiebel-type columns. These columns consist of alternate packed and mixing sections. Each mixing section includes a paddle driven a t high speed from a central shaft. I n some instances the performance of a combined mixing section and a packed section exceeded one theoretical stage. Robinson (2%)patented a similar unit using distribution plates between packed sections. Oldshue and Rushton (10)reported the results of their investigation of a column constructed with mixing sections made from an impellor and vertical baffles separated by perforated compartmenting plates. Gallo and Hartvigsen (11) patented a mixer-settler continuous countercurrent extractor which used sections in which the liquids were mixed with propellers separated by horizontal-tube settling areas. Davis and Hicks ( 9 ) review a number of mixer-settler devices. Present address, Shell Chemical Corp., Martinez, Calif.
June 1955
Recent news items (4,5) inchate continued interest in the development of other mechanical arrangements. The study of the effect of pulsation on liquid-liquid extraction in packed and sieve-plate columns was initiated a t Cornell University in February 1949. Two brief descriptions of this work have appeared in the literature ( 6 , S I ) . Both liquid phases were moved up and down together within the column by connecting a device similar to a reciprocating piston to the bottom of the column. Studies have been made by Goundry and Romero ( I S ) , Marsland and Buckner ( 1 6 ) , Smith and Caplan (28), Rich, Mehler, and Ross (11), Gilbert and Huntress ( 1 2 ) ,and Callahan and Geyh ( 2 ) . The present study (5)was completed in June 1953. I n 1952 an investigation of the effect of pulsation on the operation of a packed extraction column was reported by Feick and Anderson (10). They reported considerable improvement in extraction efficiency with pulsation when extracting benzoic acid or acetic acid from toluene with water. Cohen and Beyer ( 7 ) reported on the effect of pulsation on sieve-plate columns. Extraction devices considered by the Atomic Energy Commission are mentioned by Benedict ( I ) and by Sege and Woodfield (16). The earlier studies at Cornell University had indicated that extraction efficiency could be greatly increased by pulsation. First determined in this study using a packed laboratory column were the best operating conditions of pulse frequency and amplitude for one 3-component system a t a constant feed rate. Then the effect of varied feed rates and effect of pulsation on flooding capacity were established. Preliminary considerations were also given t o variations in the pattern of the pulse stroke. A series of runs was initiated to determine the best operating conditions and attainable efficiencies for a pulsed sieve-plate column.
Apparatus The experimental apparatus was arranged as shown in Figure 1. The two columns interchangeable with the auxiliary equipment were each constructed from a 4-foot section of 40-millimeter borosilicate glass tubing. The packed column contained a 27inch section with dumped 1/4-inch porcelain Raschig rings. The rings were 1/4 x 1/4 inch with a '/rz-inch wall. The packing after settling had a dry void fraction of approximately 58%. The sieve-plate column contained 11 plates spaced 3 inches apart and held in place by a central spacer and support rod. Two sets
INDUSTRIAL AND ENGINEERING CHEMISTRY
1153
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT Table 1.
Run
No.
Acid Concentrations, Wt. % Acetic
Feed Flow Rates,
R Ketone Acid af Ex- fi- CU. Ft./Hrfeed 0.2 0.2 0.2 0.2 0.1
0.1 0.1 0.1 0.1 0.1 0.3 0.1 a
Performance of Pulsed Packed Column with Varied Feed Rates
feed 19.5 19.5 19.0 19.0 18.9 18.9 19.0 19.0 19.0 19.0 18.8 18.5
tract 15.0 14.7 10.7 12.0 10.7 14.2 13.8 11.8 11.8 13.0 10.7 12.4
nate 12.2 9.1 3.1 4.6 3.4 12.2 9,4 4.7 5.1 6.9 4.2 5.8
4.33 6.08 11.52 9.70 11.82 4.16 6.41 9.98 8.75 8.57 7.87 9.55
Sq. Ft.
7.68 7.86 7.91 7.68 7.26 7.70 8.20 9.32 6.43 9.06 5.81 8.68
Material Pulse Balance DisAccuracy placeMeasured Cycles/ ment, Wt. Out/ minute mm,b Calcd. Wt. I n 6 0.999 54 54 6 0.997 6 54 0.996 6 54 0.996 29 6 1.000 29 6 0.997 29 6 o.gg9 6 29 0.994 47 5 1 ,002 5 47 0.995 47 0,986 5 5 47 0.997
No.
of Stages 3.11 3.50 4.26 4.15 4.00 2.68 3.28 3.84 3.67 3.68 3.71 4.00
H.E.T.S. Solvent in Inches 8.73 7.75 6.37 6.55 6.81 10.10 8.30 7.08 7.40 7.40 7.35 6.80
Rate Faotorc 0.762 0.865 1.097 1.029 1,108 0.751 0.881 1.040 0.998 0.984 0.962 1.022
Ad-
€I%?.%
Continuous phase.
of column. Solvent rate factor is equal to (actual solvent rate/standard solvent rate)o.*'.
b Measured in unpacked section c
Table II.
Performance of Pulsed Packed Column with Constant Feed Rates Pulse
Run NO.
2b 35 37 4b 10 15 32 39 65 66 67 68 3 b
8 16 25 31 34 40 58 59 60 5b 11 12 33 56 57 13 17 24 28 41 18 19 21 29 27 a b
Feed Flow Acid Concentrations, Wt. yo Acetic Ketone Acid Ex~ ~ f f i CU. Ft./Hr. Ketone tract nate feed feed 9.40 12.4 6.4 0 17.8 6.84 12.5 10.0 19.6 0.1 7.62 17.6 13.0 7.6 0.2 10.15 12.3 5.0 18.2 0.4 9.31 14 .% 6.0 20.4 0.2 8.26 13.8 7.2 19.0 0.4 8.45 20.1 13.3 5.5 0.2 10.01 12.4 4.3 19.1 0.4 9.14 13.4 6.0 20.6 0.3 8.93 13.9 6.1 20.5 0.3 9.42 13.4 5.5 20.5 0.3 8.72 18.9 1 2 . 0 7 . 2 0.3 8.97 15.3 7.8 19.0 2.2 7.70 1 5 . 0 6 . 0 19.2 0.5 8.10 13.3 7.0 18.0 0.9 9.84 1 1 . 9 6 . 8 18.2 0.4 8.37 13.8 6.0 19.9 0.2 6.84 14.4 4.6 19.7 0.1 10.48 12.0 5.2 20.4 0.2 9.19 12.6 5.7 18.5 0.1 9.55 12.4 5.8 18.5 0.1 9.39 12.7 5.5 18.6 0.1 8.54 13.6 5.5 18.7 0.3 9.18 14.2 6.0 19.4 0.2 9.42 14.4 5.4 20.3 0.2 7.66 13.6 7.7 20.1 0.2 8.30 15.6 6.0 22.2 0.1 8.11 15.5 6.1 22.2 0.1 9.42 13.9 5.3 20.3 0.2 8.56 13.6 5.0 19.0 0.6 8.76 14.6 5.0 20.4 0.5 8.29 14.1 5.6 19.2 0.3 9.73 11.7 5.8 20.3 0.2 8.34 14.4 6.8 19.2 0.4 8.34 13.8 4.4 19.2 0.4 7.90 13.4 5,3 18.5 0.3 8.53 13.2 5.2 18.4 0.3 8.29 15.0 4.4 20.8 0.2
Rates, 8s. Ft. Cycles/ Acid'" minute 9.16 17 7.54 17 17 7.30 29 7.85 7.94 29 8.65 29 8.15 29 29 7.85 29 7.95 29 8.45 29 8.10 8.52 29 9.00 47 47 8.05 47 8.10 8.00 47 8.20 47 47 7.57 47 9.30 8.23 47 8.69 47 47 8.60 8.69 78 8.23 78 78 7.85 78 8.60 78 8.35 78 8.16 7.93 88 7.63 88 7.69 88 7.76 88 88 8.49 147 8.27 8.27 147 7.55 147 147 8.89 252 7.37
Displacement, mm. 4.5 7.0 8.0 5.5 5 3.0 9.5 9.0 5.0 10.0 7.5 2.5 5.5 6.0 3.0 1.5 10.0 9.0 6.0 8.5 5.0 7.0 6.0 5.0 5.0 8.5 3.0 7.0 5.5 2.5 2.5 1.5 6.0 3.0 1.5 1.5 2.5 1.0
Material Balance Accuracy Measured Wt. Out/ Calod. Wt. I n
No. of Stages 3.23 3.03 4.70 4.66 4.61 4.18 4.14 4.39 3.75 4.10 4.04 2.90 8.40 6.22 4.88 3.22 3.30 4.15 5.31 4.33 4.00 4.42 5.78 5.90 5.24 3.27 4.52 4.40 4.68 6.23 6.05 6.12 4.10 6.00 6.65 5.92 5.97 8.25
H.E.T.S. in Inches 10.0
9.00 5.78 6.76 5.97 6.54 6.50 6.20 7.25 6.63 6.74 9.40 3.84 5.04 5.61 8.43 8.20 6.55 5.10 6.42 6.80 6.15 5.44 4.67 5.25 8.30 6.00 6.20 5.90 4.40 4.48 4.43 6.60 4.54 4.12 4.60 4.56 3.30
Solvent Rate Factor
Adjusted H.E.T.B. 10.15 8.85 5.43 7.08 6.74 6.33 6.34 6.45 7.29 6.62 6.85 9.26 3.83 4.76 5.40 8.81 8.10 6.45 5.28 6.47 6.96 6.25 5.35 4.71 5.54 7.81 5.82 5.99 6.00 4.33 4.44 4.28 6.77 4.42 4.02 4.38 4.48 3.20
Continuous phase. Runs 1 through 6 were made with packed height of 31.5 inches; packed height in all other runs was 27.2 inches.
of sieve plates were used; one with twenty-four 3/Ba-inchholes and the other with twenty-four j/04-inch holes. Two types of pulsators were used to supply the added agitation. The unit especially designed and used for this project was fundamentally a pair of copper bellows driven by an electric motor through two sets of speed change pulleys and an adjustable cam. Frequencies from 0 to 300 cycles per minute were available a t amplitudes, measured in the unpacked section, ranging from 0 to 10 millimeters. The other pulsator, used to check the results was a proportioning pump with its valves removed and inlet line sealed. The feed tanks were two &gallon carboys. Each feed line included a rotameter and a surge tank which eliminated the effect of the pulse on the feed control. The raffinate was removed through the vented interface-control leg. The solvent feed entered about 1 inch below the packing support or the bottom sieve plate; the pulse line entered 4 inches below this plate. The pulse was transmitted through a mercury-filled U-tube which sealed the column liquids from the pulsator. All of
1154
the lines were of borosilicate glass joined with neoprene tubing on the acid side and polyvinyl alcohol tubing on the solvent side. Two 3-component liquid systems were used in the tests: methyl isobutyl ketone-acetic acid-water and ethyl acetate solvent-acetic acid-water. I n nearly all the runs a 2001, by weight acetic acid solution fn water was extracted by neutral solvent with the water phase continuous and the interface held a t the top of the column. The feed solutions were mutually saturated with respect to water and solvent. The column was allowed to run until the composition of the product streams, as checked periodically by titration with 0.1N sodium hydroxide, remained constant for at least 30 minutes. Then the exit streams were collected for timed intervals and the accumulated volume analyzed. With these data the material balance could be checked for each run. The results were used to calculate the height equivalent to a theoretical stage (H.E.T.S.) for the packed column and the average plate efficiency in the sieve-plate column. The theoreti-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 6
PULSATION AND VIBRATION
+m u
c%
SAMPLE
S4M
Hi
PACKED COLUMN
W Figure
1.
MERCURY T R A P
Layout
of countercurrent apparatus
extraction
cal stages were estimated analytically using the method of Hunter and Nash (14). The equilibrium data for the system methyl isobutyl ketone-acetic acid-water were those reported by Sherwood, Evans, and Longcor ( 8 7 ) . The ethyl acetate solvent was a special solution furnished by the Hercules Powder Co.; and, since no equilibrium data were available, these were determined experimentally and correlated for use in the calculation of theoretical stages.
SOLVENT FEED RATE CUBIC FEET PER K)UR PER SQUARE FOOT
Figure 2.
Effect of solvent rate on stage height
The method of stage calculetion was accurate to the nearest 0.25 stage, and the material balances were all checked to within 5 % of closing.
Packed Column About 100 experimental runs were made with the packed column, mostly with the system methyl isobutyl ketone-acetic acid-water. The main portion of the study was made with feed
June 1955
rates constant at approximately 60% of the calculated flooding capacity. Several runs were made with these feed rates and no pulsation to determine the H.E.T.S. under conventional conditions. With feed rates of 8 cubic feet per hour per square foot of unpacked area for 20% acetic acid and 9 for methyl isobutyl ketone the H.E.T.S. was 10 inches. I n three series of runs the feed rates were varied t o determine the effect of this variable with pulsation. The data and calculated results of these runs are shown in Table I. The H.E.T.S. calculated for runs 72 through 75 made at a pulse rate of 54 cycles per minute and a 6-mm. displacement and runs 76 through 80 made a t a pulse frequency of 29 cycles per minute and 6-mm. displacement are plotted in Figure 2 as a function of the dispersed-phase flow rate. The results based on runs in which only the solvent feed varied indicate that the H.E.T.S. varies inversely with the volumetric solvent rate raised to the 0.37 power. Using a solvent feed rate of 9 cubic feet per hour for each square foot of cross-sectional area as a standard, the results are also expressed in Table I for the calculated H.E.T.S. values a t this flow rate. This effect of changing the dispersed phase rate is less with pulsation than generally reported for conventional packed columns. Lower stage heights are expected with increased rates as the result of greater turbulence in both phases. With pulsation, the turbulence comes more from external agitation than from the flow of liquids; thus, the effect of the rate change is less.
I
8
Yu
G 7
3
,
0
vi
*
2 6
!
I
H.E.T.S. calculated for runs 59, 81, 82, and 83 corrected for the effect of varying solvent rate as already established, are plotted in Figure 3. The efficiency of the column is shown to be almost independent of the continuous-phase rate when the column is pulsed. The influence of the continuous-phase rate on the holdup in the column as well as the turbulence is reduced to almost nothing with pulsation. The holdup becomes more a function of the up-and-down motion than the flow rates. All the results for the packed column, except those concerned with flooding, have been adjusted t o a constant solvent feed rate of 9 cubic feet per hour per square foot. I n order t o establish how much the efficiency can be improved and how the pulse can best be applied, 38 runs were made at 7 frequencies using a range of amplitudes from 1 to 10 milimeters. One pulsator afid approximately constant feed concentrations and rates were used for all of these runs. The results are shown in Table I1 and Figure 4. As the amplitude is increased a t any one frequency the H.E.T.S. a t first decreases, reaches a minimum, and then increases as the flooding characteristics are approached. When the flooding point has been reached, the column becomes inoperative, and the condition represents a degree of agitation which gives drop sizes too small to coalesce readily. The flooding point under pulse conditions probably varies greatly with the interfacial tension. Different systems and the presence of surface active impurities should be studied in future investigations. The curved lines in Figure 4 are cross-plotted in Figure 5 to show the effect of frequency.
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
1155
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
Figure 4.
Effect of pulse amplitude on stage
There are two effects of the increase in amplitude or frequency which cause an increase in efficiency. The drop size is reduced, slowing their rate of rise and increasing the holdup of the dispersed phase. Therefore, greater interfacial area is available for mass transfer. At the same time, because of the greater turbulence in both phases, the rate of mass transfer to and from the interface increases. Several authors ( 2 7 ) have determined from studies of extraction by single drops that 25 to 60% of the extraction in a spray column takes place during drop formation and coalescence. Observations of the pulsed column in operation indicate there is a large amount of this action, especially when the holdup of the dispersed phase is high. Thus, the increased holdup and turbulence both contribute to the constant formation of fresh interfaces. From Figure 4,the values of the frequency and amplitude necessary to obtain an H.E.T.S. of 7 inches were obtained and plotted in Figure 6. The equation of the line drawn to represent the points is Amplitude = 10000 (Frequency)-*
time. At 252 cycles per minute this product is 17.6 millimeters per minute and a t 47 cycles per minute it is 164.5 millimeters per minute. This indicates that the power required is much larger a t the lower frequency. The average velocity in the column is directly proportional to the product of the amplitude, and frequency and friction losses are greater a t higher velocities. The conclusion drawn is that less power will be required if the combination of the highest frequency and the lowest amplitude that will give the desired results is used. This assumes that there is no regain of energy from a balancing hydraulic leg or similar device. Actually the power requirements, even for a column several feet in diameter, are quite small and more important engineering considerations are those of pump size and the vibrational stresses a t higher frequencies. This may very likely lead to a compromise for the increase in efficiency attained, power height consumed, and the stresses placed on the equipment. The dashed line in Figure 4 describes the limits of operability for the system studied. A similar line through the minima of the curves would represent conditions for maximum efficiency. The facts that have been established are 1. Pulsation does improve the efficiency by as much as 300%. 2. There is an optimum amplitude that may be used with each pulse frequency to obtain the best efficiency improvement.
where the amplitude is in millimeters and the frequency in cycles per minute. The amplitude is approximately proportional to the reciprocal of the frequency squared. The product of the frequency and amplitude a t any of the conditions on the line is a measure of the energy needed to raise the column of liquid per unit
Table Ill.
FREQUENCY CYCLES PER MINUTE
Figure 5.
Performance of Pulsed Packed Column with Constant Feed Rates Using Proportioning Pump Pulse
Run No. 42 43 44 45 46 47 48 49 50 51 52 53 54 55 a
Acid Concentrations, Wt. % Acetic ExRaffifeed tract nate
feed 0.2 0.2 0.1 0.1 0.1 0.2 0.2 0.1 0.1 0.1 0.3 0.2 0.2 0.1
19.6 19.6 19.8 19.2 19.3 19.5 19.4 18.2 18.2 18.1 18.9 20.0 20.0 20.3
Effect of pulse frequency on stage height
14.0 13.9 13.4 13.0 13.2 13.6 13.8 11.4 12.0 12.4 13.2 13.8 14.0 15.2
5.2 5.0 5.7 5.4 4.6 5.2 5.0 6.5 5.1 5.5 4.9 4.2 4.2 3.8
Feed Flow Rates, CU. Ft./Hr. 8s. Ft. Ketone Acida 9.15 9.16 9.19 9.55 9.72 9.35 9.45 9.27 9.29 9.04 9.14 10.20 8.87 8.80
8.71 8.76 8.64 8.46 8.47 8.76 8.83 7.85 7.91 8.77 8.29 8.71 7.69 7.90
Cycles/ minute 55 56 55 80 80 80 80
80
80 135 135 135 135 135
Displacement, mm. 4.0 3.0 2.0 4.0 3.0 2.5 1.5 0.3 0.8 0.8 1.0 1.5 2.0 2.5
Material Balance Accuracy Measured Wt. Out/ Calcd. Wt. In
No. of Stages
H.E.T.S. In Inches
Solvent Rate Factor
Adjusted H.E.T.S.
0.996 0,994 0.996 0.998 0.998 0.997 0.997 1,000 1.000 0.995 0.998 0.998 1,000 0.998
5.61 5.51 4.14 4.32 5.14 5.07 5.62 3.24 4.29 4.45 5.68 5.90 6.20 5.80
4.84 4.92 6.56 6.29 5.28 5.35 4.83 8.39 6.35 6.10 4.78 4.61 4.38 4.70
1.006 1.006 1.007 1.022 1.029 1.014 1.018 1.011 1.012 1.002 1.006 1.047 0.994 0,992
4.87 4.95 6.60 6.43 5.43 5.43 4.91 8.48 6.43 6.11 4.81 4.82 4.35 4.66
Continuous phase.
1156
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 41, No. 6
PULSATION AND VIBRATION
Table IV.
Performance of Pulsed Packed Column with Another System’ malance ICY
it. Out/
E
No.
of Stages
H.E.T.S. In Inches
Solvent is 10% methylene dichloride in ethyl acetate: acid feed is acetic acid in water.
b Continuous phase.
Run flooded-results
estimated.
. Table V.
Performance of Packed Column Near Flooding Point
Acid Concentrations, Wt. % ’ Acetic Ketone Acid RaffiNO. feed feed Extract nate 7.2 19.4 12.0 105 0.2 11.9 6.2 114 0.2 18.1 6.8 12.3 115 0.2 18.1 4.5 19.2 13.6 116 0.4 13.0 4.8 117 0.4 19.4 56 0.1 22.2 15.6 6.0 118 0.4 19.4 13.4 4.6 a Continuous phase. b This run a t highest rate possible without flooding. This run flooded and results are estimated. d This run incomplete-apparent equilibrium is reported. Run
Feed Flow Rates,
cu. Ft./Hr. sq. Ft.
Ketone 8.96 13.92 14.17 14.17 12.60 8.30 12.30
Acida 8.14 12.80 14.40 13.90 14.16 8.35 13.72
Pulse Material Balance DisplaceAccuracy ment, Measured Wt. Out/ mm. Calcd. Wt. I n 0 0.997 0 0 0.999 0 ’ 0 0.998 47 6 47 6 0 : 990 78 3 0.991 78 3 ...
Cycles/ minute 0
NO. of
Stages 2.73 3.53 3.69 6.41 4.79 4.52 5.68
H.E,T.S. in Inches 10.00 7.70 7.390 4.25C 5.69b
6.00 4.79d
3. Increasing either frequency or amplitude first improves t,he extraction efficiency until an optimum is reached, then the efficiency is reduced until the column floods. 4. High frequencies and short amplitudes give the largest improvement in efficiency. 5 . Conditions of high frequency and short amplitude consume less power input for the same efficiency improvement than low frequency and greater displacement. Two series of runs were made independently to check these facts. First, the pulsator was replaced with a proportioning pump which gave a sharp up-pulse as compared to the sine wave transmitted from the pulsator. Runs were made at three frequencies-55, 80, and 135 cycles per minute-and displacements from zero to 4 millimeters. Table I11 and Figure 7 show the results. The results agree well with the previous results. The sharper pulse gives no noticeable improvement in efficiency. What the effect of changing the pulse pattern would be in other systems, particularly if there exists a large dirference in viscosity between the two phases, remains to be established. Next, a series of 17 runs was made using another 3-component system, ethyl acetate solvent-acetic acid-water. The density difference between the phases was much lower in these runs so the throughput was reduced. Table IV and Figure 8 show the results. I n all these runs the holdup of the dispersed phase, again the solvent, was quite large, and operation was near the flooding point. I n runs 98 and 99 some of the solvent phase was being carried out with the raffinate and steady-state conditions were not attained. I n general, the shape of the curves in Figure 8 and the magnitude of efficiency improvement agrees quite well wit,h previous results. To conclude the packed column study, several runs were made to determine the effect of pulsation on maximum throughput. The results of these runs are listed in Table V. Run 115 was made at the highest rates possible without flooding the column June 1955
FREQUENCY CYCLES PER MINUTE
Figure 6 . Relation of puke amplitude and frequency for an H.E.T.S. of 7 inches
with no pulsation. The H.E.T.S. for this run was calculated to be 7.39 inches. Run 117 was made a t the highest possible rates without flooding a t a frequency of 47 cycles per minute and an amplitude of 6 millimeters. A total hourly rate per square foot of column cross section of 26.57 cubic feet of liquids were accommodated during this run as compared to 28.57 during run 115. This represents a 6% reduc$ion in maximum throughput when the column is pulsed. For run 118 a t 7 8 cycles per minute the total hourly throughput was 26.02 cubic feet per square foot or equivalent to 8.9% less than the capacity without pulsation. * The reduction in capacity with increased agitation is surprisingly little even though smaller drops are produced in the packing and the holdup increases. The flooding point is defined as the condition a t which the holdup is too large to accommodate increases in either phase rate. Any increase will cause the dis-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1157
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT Table VI.
Performance of a Pulsed Sieve-Plate Column
Acid Concentrations, Wt. % Acetic Feed Flow Rates, Pulse cu.Ft*/Hr*sq* Ft- Cycles/ Amp., Ketone Acid RaffiNo. feed feed Extract nate Ketone Acid5 minute mm. 0.6 9 18.4 13.1 6.2 8.67 8.35 47 2.0 14 20.8 0.1 13.30 47 2.5 6.5 15.8 12.70 22 0.3 19.8 7.6 7.87 13.4 8.25 80 1.5 47 20.1 23 2.1 0.3 7.84 12.2 10.37 1.6 26 0.3 20.2 1.8 8.21 2.0 10.8 14.73 30 0.3 20.3 14.0 2.7 7.55 2.0 11.68 20.6 61 0.2 6.94 11.4 6.9 9.24 5.5 62 0.2 20.7 12.0 7.2 6.0 8.55 8.88 0.2 20.5 63 12.4 8.63 7.5 8.99 3.5 0.2 20.5 64 12.6 7.4 9.06 8.15 2.0 70 0.4 20.4 13.1 2.0 8.0 8.65 8.52 20.5 71 0.3 11.9 9.1 8.25 8.50 3.0 19.0 78 0.1 12.0 7.30 8.33 3.0 9.0 0.4 19.1 84 10.2 7.80 5.0 11.08 3.0 19.1 9.4 4.7 3.0 0.4 7.73 12.82 85 0.3 19.5 9.0 8.30 3.7 13.90 3.0 86 0.3 19.5 13.2 87 12.9 3.0 7.27 15.99 0.2 18.9 7.6 4.0 17.60 4.6 106 8.05 0.4 18.9 8.5 4.0 3.1 107 16.82 8.38 1 9 . 6 4.0 0 . 2 5 . 4 11.9 17.15 108 13.18 19.6 13.6 4.0 0.2 8.6 109 16.67 18.92 1 9 . 1 0 . 4 12.3 4.0 7.3 8.24 110 8.50 19.1 0.4 11.6 6.0 8.6 8.05 8.90 112 18.3 10.4 0.2 9.1 113 6.0 8.27 9.25 19.4 12.4 0.4 6.0 119 10.2 8.74 7.20 19.4 0.4 4.0 6.70 120 2.7 8.1 15.37 Continuous phase. b These runs were made using plates with a/sa-inch holes; remainder used plates with s/winch holes. c Ketone phase was continuous in this run with interface below bottom plate.
Run
. I
I
I
I
2 3 AMPLITUDE, MILLIMETERS
I
4
Figure 7. Effect of pulse amplitude using a proportioning pump
Material Balance Accuracy Measured Wt. Out/ Calcd. Wt. In
No.
Av. Plate Efficiency,
of Stages 4.95 6.25 3.33 6.20 5.31 7.63 2.41 2.49 2.60 2.70 2.81 2.10 2.24 3.02 2.58 2.65 2.71 2.38 3.04 3.27 3.26 3.00 2.35 1.75 2.08 3.10
%
45.01 56.8b 30.01 56.4b 48.3b 70.0b 21.9 22.6 23.7 24.6 25.5 19.0c 20.3 27.6 23.5 24.1 24.5 21.6 27.6 29.7 29.6 28.2 21.4 15.9 18.9 28.2
poorer plate efficiencies. The highest attainable average plate efficiency was about 30y0. Several series of runs were made to determine the best operating procedure. However, complete coalescence of the dispersed solvent phase below the plates was not attained, and the column never performed effectively with the larger hole size. These results lead to the conclusion that the best operation of a pulsed sieve-plate column is obtained with a combination of high holdup and sufficient turbulence. Plates with smaller holes appear best for both effects. Sufficient frequency and amplitude must be supplied for turbulence and feed rates must be maintained a t a high enough level for sufficient holdup. The column must be operated near the flooding point t o have a coalesced dispersed phase layer a t each plate. Any change in operating characteristic8 will cause the column either to flood or to lose one of the liquid layers.
persed phase to become continuous a t some point in the column. Usually a layer of solvent first appeared below the packing and gradually filled the free area a t the bottom of the column. Sieve-Plate Column
Exploratory runs were made with a pulsed sieve-plate column. The results of these runs appear in Table VI. For these runs, the average plate efficiency obtained by dividing the number of theoretical stages by the number of plates is reported instead of the H.E.T.S. Runs 9, 15, 22, 23, 26, and 30 were made using the sieve plates with twenty-four a/,,inch perforations. These results were unsatisfactory and inconsistent; however, efficiencies as high as 70% were obtained. Corrosion and clogging of the small holes made use of these plates impractical for the solutions used. Two or three plates appeared to flood while others were operating satisfactorily. The pressure drop through the plates was quite high. Considering that numerous additional holes could have been drilled it is obvious from comparative thrpughputs that the allowable capacity for sieve-plate construction is inherently greater than fqr packing. When proper operation was obtained, a layer of solvent phase was held under each plate and only rose in the column on the up-pulse. On the down-pulse a jet of acid phase entered the solvent phase. Effectively, two mixing and settling operations are obtained a t each plate. The balance of the runs made with plates with holes enlarged to a diameter of ‘/e4 inch showed
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36
Figure
I 2 ’
I
I
I
4 6 e AMPLITUDE, MILLIMETERS
IO
8. Effect of pulse amplitude with a different system
No investigation was made of the sieve-piate column under conditions allowing no coalescence of the dispersed phase under the plates. However, many of the runs using the 6/6&-inchholes approached this condition. When the column is operated in this manner the sieve plates serve the same function as packing.
Conclusions Packed Column 1. The application of pulsation to a packed column is a practical method for efficiency improvement. The height of packed
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 6
PULSATION AND VIBRATION section required is reduced as much as three times when the column liquids are pulsed. 2. Optimum operating conditions can be obtained by varying both frequency and amplitude of pulse. 3. Greater efficiency can be obtained with the proper low amplitude a t high frequencies than is possible a t low frequencies. 4. The maximum throughput is reduced slightly ( 5 t o 1 O o J ~ ) when the column is pulsed. 5 . Changes in feed rates have less effect on the efficiency when pulsation is used than with the usual packed column operation. Sieve-Plate Column 1. Average plate efficiencies as high as 70% can be obtained in pulsed sieve-plate columns. 2. High throughput rates compared t o packed column capacity may be used with high efficiency. 3. Smaller perforations are more efficient but more a p t to corrode and clog, and have reduced capacity.
Gallo, S. G., and Hartvigsen, B. (to Standard Oil Development Co.), U. S. Patent 2,562,783 (July 31, 1951). Gilbert, T. E., and Huntress, A. R., “Pulsation in a Packed Liquid-Liquid Extraction Column,” Senior Project Report, Cornell University, June 1953. Goundry, P. C., and Romero, V. M., “Effect of Agitation on Liquid-Liquid Extraction in a Packed Column,” Senior Project Report, Cornell University, Feb. 1950. Hunter, T. G., and Nash, A. W., J . SOC.Chem. Ind., 53, 95T (1934).
I. G. Farben, British Patent 457,552 (Nov. 25, 1936). Marsland, D. B., and Buckner, L. R., Jr., “Effect of Agitation on Liquid-Liquid Extraction in a Packed Column,” Senior Project Report, Cornell University, June 1951. Maycock, R. L. (to Shell Development Co.), U. S. Patent 2,474,007 (June 21, 1949). Morello, V. S., and Poffenberger, N., IND. ENG.CREM.,42, 1021 (1 950).
Ney, W. O., and Lochte, H. L., Ibid., 33, 825 (1941). Oldshue, J. Y . ,and Rushton, J. H., Chem. Eng.Progr., 48, No. 0, 297 (1952).
Literature Cited
Benedict, iM., IND. ENQ.CEIEM.,45, 2372 (1953). Callahan, E. W., and Geyh, C. A., “Effect of Pulsation on 8 Sieve-Plate Extraction Column,” Senior Project Report. Cornell University, June 1953. Chantry, W. A., “Application of Pulsation to Liquid-Liquid Extraction,” Ph.D. Thesis, Cornell University, June 1953. Chem. Eng.,61, No. 6, 282 (1954). Chem. Eng. News, 32, 350 (1954). Chemical Week, 69, No. 24, 32 (Dec. 15, 1951). Cohen, R. M., and Beyer, G. H., Chem. Eng. Progr., 49, 279 (1953).
Coinish: R. E., Archibald, R. C., Murphy, E. A., and Evans, H. M., IND. ENG.CHEM.,26, 397 (1934). Davis, M. W., Jr., Hicks, T. E., and Vermeulen, T., Chem. Eng. Progr., 50, 188 (1954). Feick, G., and Anderson, H. M., IND.ENG. CHEM.,44, 404 (1952).
Rich, W., Ross, K., and Mehler, G., “Agitation in a LiquidLiquid Extraction Column,” Senior Project Report, Cornell University, June 1952. Robinson, J., U. S. Patent 2,072,382 (March 2, 1937). Scheibel, E. G., Chem. Eng. Progr., 44, 681, 771 (1948). Scheibel, E. G., IND. ENG.CHEM.,42, 1497 (1950). Scheibel, E. G., and Karr, A. E., Ibid., 42, 1043 (1950). Sege, G., and Woodfield, F. M., Chem. Eng. Progr., 50, 396 (1954).
Sherwood, T. K., Evans, J. E., and Longcor, J. V., IND.ENQ. CHEM.,31, 1144 (1939). Smith, H. M., and Caplan, R. H., “Effect of Agitation on LiquidLiquid Extraction in a Sieve-Plate Column,” Senior Project Report, Cornell University, June 1951. Treybal, R. E., IND.ENG.CHEM.,45, 50 (1953). Van Dijck, W. J. D., U. 9. Patent 2,011,186 (August 13, 1935). Von Berg, R. L., and Wiegandt, H. F., Chem. Eng., 59, No. 6, 189 (1952). RBCEIVED for review December 20, 1954.
ACCEPTED March 28, 1956.
Power Requirements for Pulse Generation in Pulse Columns A. CARLETON JEALOUS O a k Ridge Nafional laborafory, O a k Ridge, Tenn.
HOMER
F. JOHNSON
Deparfmenf o f Chemical Engineering, Universify o f Tennessee, Knoxville, Tenn.
The power required to pulse a liquid-liquid extraction column is determined by the static head of the liquid system, the acceleration and deceleration forces on the liquid system, and the friction losses. The theoretical total power that must be applied to the liquid-liquid system b y the pulser i s given by the equation
where the equation for y defines the cyclic motion imparted to the liquid system by the pulse generator. Power input data obtained on a 50-foot pulse column 24 inches in diameter are presented, as well as information on development of the power formula and the means of experimentally evaluating the formula.
T
HE use of pulsed towers in continuous, countercurrent liquidliquid extraction frequently leads to improved performance over conventional types of towers such as the packed tower. The pulse action is provided by aome sort of mechanical pulse generator, usually a reciprocating piston-type unit. Pulsing June 1955
the fluid in the tower has the effect of putting energy into the liquid-liquid system beyond that which is due solely to the action of gravity on the dispersed phase particles. This additional energy probably benefits performance by increasing effective interfacial area as well as increasing turbulence in the system.
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