A STUDY OF THE MECHANISM OF LIQUID — LIQUID
EXTRACTION FROM FORMING DROPS IN

A STAGNANT CONTINUOUS PHASE

BY

Yuash Pete Jacob

A THESIS

Submitted to
Nfichigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Chemical Engineering

1961

ABSTRACT
A STUDY OF THE MECHANISM OF LIQUID - LIQUID

EXTRACTION FROM FORMING DROPS IN
A STAGNANT CONTINUOUS PHASE

by Yuash Pete Jacdb

This thesis is concerned with a study of the mechanism of
liquid-liquid extraction from single drops forming in a stagnant
continuous phase. Photographic absorption photometry was used to
determine the amount of solute transferred at any instant during
formation.

The system consisted of the solute picric acid with
toluene as the dispersed phase and distilled water as the continuous
phase. water and toluene were mutually saturated. With this system
most of the mass transfer resistance was in the continuous phase.

Experimental data were Obtained from motion picture films
of the drop. The optical density of the film was related to the
amount of solute extracted.

Extraction during drop formation was determined by two
methods: by optical density measurements directly through the image
of the forming drop, and by drawing the drop into the nozzle before
break-off and taking optical density measurements through the image
of the residual picric acid. The second method was used to check
the results of the first.

ii

Yuash Pete Jacdb

In a range of drop formation time of 0.2 to 10 seconds, per cent
extraction across the interface was 0.1 to 0.2 during drop formation.
From 0 to 12 second formation times, mass transfer to the bulk of the
continuous phase was essentially zero. Above the 12 second formation
time some extracted material moved into the bulk of the continuous
phase and remained.behind when the drop rose.

Runs at six different formation rates showed that the rate of
mass transfer increased with an increase in the formation rate.

The per cent extraction was higher during the early life of a
drop.

For a fixed volume, per cent extraction decreased as formation
time decreased at long formation times. At shorter times, this phe-
nomenon was reversed.

An attempt was made to determine the effect of rate of mass
transfer on liquid-drop coalescence time after rising to the main

water-toluene interface. However, in most cases coalescence was

practically instantaneous.

 

iii

To

DO'I'I‘IE

iv

ACKNOWIEDGI~IENTS

The author expresses his appreciation to Dr. Richard A. Zeleny,
Department of Chemical Engineering, Michigan State University, for his
cooperation in conducting this investigation, suggesting the system
studied, and guidance throughout this work.

Appreciation also is extended to: Mr. William Clippinger,
Chemical Engineering Shop Manager, for his help in constructing parts
of the equipment; Mr. Samuel T. Bass and Mr. Jamshid Soulati, Depart-
ment of Agricultural Biochemistry, for instruction in film development
and optical measurement; and colleagues, mr. George Rusin and

Mr. Purushottom Patel, for their help in construction of the apparatus.

TABLE OF CONTENTS

Page
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . 1
LITERATURE SURVEY . . . . . . . . . . . . . . . . . . h
THEORY . . . . . . . . . . . . . . . . . . . . . . . . 10

METHODS OF DETERMINING THE AMOUNT OF EXTRACTION
DURING DROP FORMATION . . . . . . . . . . . . . . . 22

APPARATUS . . . . . . . . . . . . . . . . . . . . . . 27
EXPERIMENTAL PROCEDURE . . . . . . . . . . . . . . . . 35
SUMMARY OF RESULTS . . . . . . . . . . . . . . . . . . 39
DISCUSSION OF RESULTS . . . . . . . . . . . . . . . . #5
CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . 50
APPENDIX . . . . . . . . . . . . . . . . . . . . . . . 52
A. Sample Calculations . . . . . . . . . . . . . 52
B. Method of Analysis . . . . . . . . . . . . . 70
C. Date . . . . . . . . . . . . . . . . . . . . 7h

BImlIm’RAPHY O O O O O O O O O O O O O O O O O O O O O 96

vi

INTRODUCTION

Liquid-liquid extraction consists of the contacting of two
immiscible liquid phases in order to transfer a solute from one phase
to the other phase. The contacting devices usually disperse one phase
in the form of droplets. Therefore, solute transfer occurs during the
periods of drop formation, drop rise or fall, and drop coalescence.

This thesis is concerned with the mechanism of extraction
during drop formation. The amount of a colored solute extracted at
any time during drop formation.was determined by the aid of photo-
graphic absorption photometry. To determine the amount of the
absorbing substance in the light path, photographic films were used
as calibrated responders to a light beam incident upon and transmitted

by the absorbing substance, at the wave length range of 3800 to 55000 .

The absorbing substance was picric acid, which was introduced
into the beam of light in two ways and photographed in each case: in
an absorption cell with a solution of known concentration; in a column
while picric acid was transferred from a toluene drop into a continuous
water phase.

One of the advantages of working with the picric acid-toluene-
water system was that very small amounts of picric acid in the water
phase blocked out more light than large amounts of picric acid in the
toluene phase. For example, in a cell of the same thickness, a
solution of 0.09 grams of picric acid per liter of water produced the

same density on the film as a solution of 100 grams of picric acid per

liter of toluene. Therefore, a small amount of picric acid transferred
from a toluene drop into the water adjacent to the drop surface blocked
out extra light and produced a higher density on the film than the toluene-
picric acid drop would produce by itself.

The density produced on the film was related to the amount of
picric acid present in the path of the light beam passing through each
solution. Therefore, from a plot of film density versus concentration
it was possible to determine the concentration if the density produced
on the film due to the solution was known.

This investigation is the continuation of work done by
Tambo (22), with modifications in the light source, drop forming
device, experimental procedure, and methods of calculation. Tambo
Obtained movies of the transfer of picric acid from a toluene drop
into the stagnant water phase. The films showed that the extracted
picric acid surrounded the drop and stayed adjacent to the drop sur-
face, and that more than 0.1% of the total solute in the drop was
extracted during coalescence. He attempted to determine the amount
of picric acid extracted during drop formation by measurement of
optical density around the edges of the drop profile through the image
of the extracted material. This method was not successful because the
extracted acid appeared as a very thin layer around the drop, and it
was difficult to distinguish between the extracted material and the
profile of the drop itself. Also, refraction at the extreme edges of
the drop profile influenced the readings in this region.

In the present work the amount of extracted picric acid was deter-

mined by two methods: by forming a drop, drawing it back into the nozzle

before break-off, and Obtaining film densities through the image of the
picric acid that was left behind; by obtaining film density measurements
directly through the image of the drop and determining the amount of
picric acid extracted per unit area of drop surface and thus the total

amount surrounding the drop.

LITERATURE SURVEY

Previous Work 93_Extraction in Drop Systems

 

 

 

Among the early investigators on mass transfer from single drops
into a continuous liquid phase are Sherwood, Evans, and Longcor (21) who
transferred acetic acid from benzenezmd methyl isobutyl ketone drops into
water. Using different column heights, they plotted the amount of un-
extracted solute versus column height. Intersection of this line with
the coordinate at zero column height showed a #0 to ks per cent extraction
during drop formation; comparison between experimental and theoretical
amounts transferred indicated that drops had internal circulation. Later,
West and co-workers (2%) attempted to duplicate Sherwood's work on the
acetic acidébenzene-water system, and Obtained approximately 1% to 20
per cent extraction. The discrepancy between the results of these in-
vestigations was attributed to contamination of the acetic acid4benzene
solution by the Tygon tubing feed line (25).

Licht and Conway (1%) studied solute transfer in spray towers
in which acetic acid was transferred from water drops into methyl iso-
butyl ketone. By using different column heights and extrapolating to
zero height they found eight per cent extraction during drop formation,
and postulated that the difference between their result and Sherwood's
result might have been due to the direction of solute transfer.

During the work of the investigators (1h, 21, 2h, 25) on aqueous

extraction of acetic acid from benzene or isobutyl ketone system, the

results Obtained during drop formation varied from 8 to #5 per cent solute
extracted. The variation in these results motivated Licht and Pansing (15)
to make a study of solute transfer from single drops by studying each stage
separately. They showed that, in general, straight line extrapolation of
the fraction of solute not extracted versus column height was not valid
down to zero height. Licht and Pansing also derived an expression relating
fraction extracted, formation time, and molecular diffusivity in the con-
tinuous phase. They assumed a negligible transfer resistance inside the
drop, transport by molecular diffusion outside the drop, and a plane area

for transfer equivalent to the area of a sphere.

Hal
where,

E2 = fraction solute extracted
Dc = molecular diffusivity in the continuous phase
t = formation time

6'
H = distribution coefficient (-2.4— )

c
d = drop diameter

Cd = solute concentration in the dispersed phase

C = solute concentration in the continuous phase

Garner and Hale (h) derived the following formula for the over-

all mass transfer coefficient during drop formation.

4
M- K’ HACA'E (2)
0
where,
M. = total material transferred during the growth
of the drop
K = owxhall mass transfer coefficient (a constant)

A = surface area of the drop at time t
tf = formation time
AC = concentration driving force

For a feed rate of V cm3/sec, the area at time t is given by,
1 2L
3 3
2477-11)
[I 1y27 7f (3)
Substituting Equation 3 into Equation 2,

M=0.( KI} é AC (1+)

In order to determine coefficients for the formation and the rise periods,
a total time of (tr + 0.6tf) was used in Equation h where tr is the time
of rise through the water phase.

Coulson and Skinner (3), in their study of the mechanism of liquid-
liquid extraction across stationary and moving interfaces, determined the
amount of mass transfer during drop formation and rise. They transferred
benzoic acid and propionic acid from water to benzene drops and measured
the solute transferred when a drop was formed and then ejected from the
system. Figure 1 is a sketch of the device that was used in these

experiments.

 

 

 

 

 

Propionic
benzene Acid-water
dr
H ~38 two-way cock

from f

benzene

reservoir 0E

ee-‘e L___~——¢p.t0 collecting burette

Figure l

When the two-way cock was opened, benzene flowed from a small
reservoir through a needle valve to form a drop at the end of the glass
nozzle (A). A side tube (B) was sealed just below the tip of the nozzle
and led to a collecting burette. Upon closing the two-way cook, the flow
of benzene to the nozzle was stopped and the hydrostatic head in the
column pushed the drop through the side tube. After a number of drops
were formed, ejected, and collected, the sample was analyzed. It was
found that: mass transfer during formation was almost independent of
the formation time for a range of 1/2 to 1 second; the over-all transfer
coefficient, K, based on the average area exposed during drop formation
decreased with an increase in time of formation, but was independent of
the drop size; smaller drops approached more closely to equilibrium be-
cause of the increased area of interface per unit volume.

Gregory (11) used an apparatus similar to that of Coulson and
Skinner, but modified the design and experimental procedure. Systems
were selected in which the distribution coefficient strongly favored
the continuous phase so that resistance to mass transfer in the dis-
persed phase could be measured. Transfer was from the dispersed phase
to the continuous phase. Data from the smallest drops showed that
per cent extraction decreased as formation time decreased until a for-
mation time was reached at which per cent extraction began to increase
in spite of the shorter time. This was explained by the spread of
turbulence from the jet of incoming fresh liquid.

The following are several different mechanisms of mass transfer
during drop formation which were discussed and compared to the eXperimental

data by Gregory:

l. Turbulence throughout the whole drop may be so
great that the bulk concentration of dispersed
phase is the same as the interface concentration,
and there is no dispersed phase resistance.

2. Mass transfer may take place by molecular or
eddy diffusion throughout the entire forming drop
with the fresh liquid entering at the center and
pushing the older portions of the liquid uniformly
and without mixing toward the surface.

3. Mass transfer may take place by diffusion through-
out the entire forming drop with the entering liquid
distributing itself uniformly so that none of the
older liquid is displaced from its position relative
to the surface.

A. Circulation within the drop may cause constant re-
newal of the elements of liquid next to the surface.
bass transfer is by diffusion within these surface
elements, which, in turn, mix with the bulk.

5. The film theory mechanism depends on the presence
of a resistance which consists of a laminar film
next to the interface and an inner turbulent film.
The film must be thin enough so that any change in
the quantity of solute present in the film is neg-
ligible compared to the change undergone by the
bulk.

When the drop phase was lighter than the continuous phase the

data was best correlated by the following equation, obtained from film

theory. 02
_.. ,_/
fl = 3.751 (M) A ( )
v A flfl 5
where,

7rd:

V - = jet velocity at the orifice of the
gynf nozzle, cm/sec

d = drop diameter, cm

D = moiecular diffusivity in the dispersed phase,
cm /sec

Kd = mass transfer coefficient in the dispersed

phase, cm/sec

An = cross sectional area of nozzle, cm2

tf = time of formation of the drop, sec

’fi9= density in dispersed phase, gm/cm3

‘/Q = viscosity in dispersed phase, gm/cm-sec

This equation was valid only when the following condition was fulfilled:

‘ D
A: >/-52 JT (6)
,c
When relation 6 was not satisfied, mass transfer by Mechanism 2 best
described the experimental result.
Other attempts to study the mechanism of extraction from single
drops have been made by Christenson and Terjesen (2), Garner and
Skelland (5, 6, 7, 8), Treybal (23), and Johnson and Hamielec (13).
Investigations on liquid drop coalescence have been made by
Gillespie and Rideal (10), Nielson et a1 (17), Linton and Sutherland (l6),

and Charles and Mason (1).

10

THEORY

I. Extraction in the Picric Aeid-Toluene-Water System

The picric acid-toluene-water system was chosen because the
extracted material could be determined photographically and, unlike
most dyes, picric acid was not colloidal in water or toluene solutions
(25).

Distribution coefficient data plotted in Figure 2 show that
picric acid strongly favors the toluene phase at high concentrations.
Therefore it was expected that the resistance to mass transfer in the
toluene phase would be negligible compared to the resistance in the
water phase.

The fact that picric acid has a more intense color in water
than in toluene indicates that it exists in a different molecular form
in each phase (20). Transition from one form to the other at the
interface may result in an interfacial resistance to mass transfer.
However this resistance was considered to be negligible.

In the stagnant continuous water phase, mass transfer prObably
occurs primarily by molecular diffusion. Therefore the expression
developed by Licht and Pansing (15) should be applicable to the system

studied. From Equation 1 the per cent extraction was given by

VD‘ 1‘ m

va

% extraction = 2.3h

11

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NH

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12

where
Dc = Eolecular6dif£usivity in the continuous phase,
.9 x 10 cm /sec
t = formation time, seconds
H = distribution coefficient, 10
V = drop volume, cm3

Substituting the values of Dc and H into Equation 7,

% extraction = 6.12 x 10'.2 -L—%i—— (8)
V 3

Equation 8 was compared to the results of this investigation.

II. Photographic Absorption Photometry

Photographic absorption photometry involves photography
of a beam of light after its attenuation by an absorbing medium.
Application of this technique requires a suitable light source,
an absorption cell for introducing the specimen into the beam of
light, and photographic films.

In this study the absorbing substance was picric acid in
water and toluene solutions. The optical density of a photographic
film of these solutions depended upon the amount of picric acid in
the path of the light beam and on which of the two solvents was used.
When the optical density of a film of a solution of known concentration
was equal to the density of a film of unknown concentration, the fol-

lowing equation was used to relate the solution concentrations.

A.
K CS L = K C dfl (9)

13

where,

K = extinction coefficient, a constant dependent
upon the phase

CS = known concentration in a standard cell of
thickness L

C = unknown concentration in a cell of thickness
L. The concentration may be a function of the
solution depth.
In the following derivation of Equation 9 a light energy balance was
made about a volume increment of thickness AA. in the path of a light
beam that passed through a cell. The cross sectional area of a light
beam that fell on a fixed film area varied with the cell thickness. In

the following sketch, I equals light intensity, A equals cross sectional

area, and 1 equals distance along the cell depth.

 

All 13

r ‘——

 

 

 

 

 

Energy balance:

(Energy in) - (Energy out) = Energy absorbed in volume.A.A1.
Since intensity equals light energy per unit area,

(IA)? = input at positiong

(IA), + AL = output at position £4» A9.
According to Beer's and Lambert's Laws of absorption, the light absorbed
at a particular light wave length is proportional to the amount of
picric acid in volume A.Ai. and the light intensity.

K I (C A AA ) = Energy absorbed

where

K equals the proportionality constant.

lh

Combining these terms,

(IA)! - (110/ = K c I A A9 (10)

«A?

Dividing by A1 and taking the limit as AQ __...o,

 

- KCdi (11)

Integrating from zero to L gives

 

 

 

A
*fA/CJQ
5,13”- 6’ 0 (12)
/b.
For a standard cell of concentration CS,
—-K L-o
1f == 12/9, .a C; ( ) (l )
AS‘ A, " 3
For a solution of unknown concentration
1
1:1. A. ‘5 “C4”
A ”L C (11+)

Equations 13 and 1h are equal when the optical densities on the film pro-

duced by I and IL are equal.

L S

Therefore

1
KQL= ”COM (9)

0

If the solution of unknown concentration consists of only one

phase which is the same as the standard cell phase,

feta” (9.)
1.

 

C: - Cflyerage-

15

Applying Equation 9 to water and toluene phases in series,

t I.
K..an =K~f, 'c...u + K, I. 6,40 (15>

where w refers to the water phase of thickness L1 and t to the toluene
phase of thickness (L - L1).

In the extraction of picric acid from toluene drops, the con-
centration in the drop was approximately constant and equal to the
initial concentration. Thickness (L-Ll) equaled the drop diameter at
the position of optical density measurement. In this case Equation 15
was solved for I" Cw‘” by the following procedure. From

Equation 9,

L
Icy/11 =—. Ct(L-L)=C“, L (16)
L

where,

a concentration of a standard toluene cell
that will block out as much light as the
toluene drop.

C'st

By applying Equation 9 to standard solutions of toluene and water,

/ I
Kt 41. L 3 (to CSUOL (17)

where,

0'8", 2 concentration of a standard water solution
that will block out as much light as the
standard toluene solution of concentration

C'Bt.

Combining Equations 15, 16, and 17 and solving,

ll
I /\
(amass-L’— Laud!) =7.,_(C‘”—C"“’)L ,1 (18)

I

16

where,

C = average concentration in the water phase
of thickness L1 (this includes the water
phase in front and in back of the toluene
drop)-

W ave

The derivation of Equations 9 and 18 depended upon Beer's
and Lambert's Laws of light absorption. These laws apply to solutions
of picric acid in water and toluene over a narrow wave length range.
This is illustrated by the straight line plots of solution optical
density versus concentration at fixed wave lengths in Figures 3 and
h. A plot of the water concentration from Figure 3 versus toluene
concentration of the same solution optical density from Figure A will
result in a straight line as predicted by Equation 17.

In the extraction experiments the light filter did not suf-
ficiently restrict the wave length range so that Beer's and Lambert's
Laws were not strictly applicable. This was illustrated by the plot
of water concentration versus toluene concentration at the same film
optical density, Figure 5. Since solutions of equal film densities
have equal solution optical densities, a straight line should have
resulted. However, the error introduced by use of Equations 9 and
18 was not greater than the experimental error in the film optical
density measurements. This fact was determined experimentally by
Obtaining film optical density measurements from a cell of three
compartments of thickness L1, L2, and L3 with known concentrations
Cl, C2, and C3, and determining the numerical value of Cave of
Equation 9 or 18 directly from the optical density - concentration
curve which is for standard solutions in a cell of thickness

L a L1 + L2 + L3. Using the numerical value of Cave in Equation 9

Solution - optical density

1.0

0.8

O
0‘

O
b

0.21

O

 

 

 

 

 

Data obtained
from
Spectrophotometer
I
i—————
L L l
0' 0.4 0.8 1.2

 

 

 

 

 

 

Grams of picric acid per liter of water

Figure 3 - Graph of solution - optical denaity veraua
concentration at 4800

17

A for a one centimeter cell.

Solution 9 optical density

1.0

O
Q

C
0‘

0.4

 

 

 

 

 

 

 

 

 

 

 

 

I

Data Obtained

' from
apectrophotometer

I
r ,
l I 1 1 J 1 7
40 80 120

Grams of picric acid per liter of toluene

Figure 4 - Graph of solution-optical denaity veraua
concentration at 4500°A for a one c-.ce11.

18

Grams of picric acid per liter of toluene

100

80

60

40

20

19

 

 

 

 

 

 

 

 

 

 

 

1 4 1 1 '
0 0.02 ' ' 0.04 . 0.06 ' 0.07
Grama of picric acid per liter of water,

Figure 5 - Plot of water concentration veraua toluene concentration
at the same film density. '

 

20

the concentration of the solution in the first compartment was determined
and compared to the actual value in that compartment. For the case where
both water and toluene phases were present the concentration 03w corres-
ponding to the measured optical density was substituted in Equation 18

and solved for C

ware ’

The value of CM“ was compared to the actual value
of the concentration in the first compartment. The results of a number
of experiments are presented in Table I and sample calculations are given
in Appendix A. The calculated and actual concentrations agree within

experimental error.

21

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22

METHODS OF DETERMINING THE AMOUNT OF EXTRACTION
DURING DROP FORMATION

I. Method of Calculation of the Amount of Extracted Picric Acid from
Density Measurements Directly Through the Image of the Drop

The extracted picric acid was determined from density measurements
through the image of the drop. As an illustration consider the drop in
Figure 6. The shaded area around the drop represents the extracted acid
which surrounded the entire surface of the
drop as a thin film. Symmetry was assumed
about the vertical axis of the drop. Since
the amount of extracted acid was always less
than 0.3 per cent, the concentration in the

drop was approximately constant and uniform

 

 

 

 

throughout the drop. Therefore, Equations
Figure 6
15 through 18 can be used to determine the

average water phase concentration in front and in back of the drop.

L. I
ism _(c..—c...)z.
L. L.

l I

(18)

 

W ave

where

Csw = concentration corresponding to each density
measurement along the vertical axis of the
drop (08" was determined from the density
measurement and the density-concentration
calibration curve for the water phase).

Céw = concentration of a water cell of thickness
L (the column thickness) which blocks out
as much light as the toluene drop of

23

concentration Ct and thickness equal to the
drop diameter at the position of density
measurement. In order to determine C'sw’ the
value of C'st was first determined from
Equation 16,

c’ = (L —LI) Ct
St L
where L-Ll equals the drop diameter. Using
the film density equivalent to C'st from the
density--toluene concentration curve, and
applying it to the density-water concentration
curve, the value of C'8w was obtained.

c'w'ave = the average concentration in the water phase at
the position of density measurement. It includes
extracted acid'both in front and in back of the
drop (L1 = L-drop diameter).

The area of film density measurement was equivalent to an area AX AX
in the extractor as shown in Figure 6. Therefore the acid in the
volume element L1 AX AX was Ci" ave L1 AX AX; Since the extracted acid

was present in a thin layer around the drop, the total amount of acid

around the drop in height AX'was,

"D
<3“,n / I
are L, AYCJx'ET Q~¢€WDAT a

I

0

The group ( Exéaxe L141 AX) equals the amount of extracted acid either
in front or in back of the drop over area AX AK, and D is the drop
diameter at each point of density measurement. The amount of acid over
the_entire drop was given by

H
Hef—g-ijtrmdy <19)
0’

/

where H is the height along the vertical axis and C' is given by

w ave
Equation 18.
Since light refraction or reflection due to the shape of the

drop would influence the film density measurements, this effect was

2h

investigated experimentally. Film density measurements of drops in
equilibrium with the continuous phase were obtained. The measured
densities agreed with values calculated from Equation 9. The results
are presented in Table II and sample calculations are given in
Appendix A.

During the experiments conducted on the effect of light re-
fraction, the effects of camera focusing and distance of the camera
from the column were also studied. The camera was focused at the
center of a stationary drop. Photographs were obtained by moving the
camera without refocusing. Film density measurements through the
center of the drop showed that the density did not vary with camera
position. Thus any error in density readings caused by inaccurate
camera focusing were negligible.

II. Method of Calculation of the Amount of Picric Acid Left Behind
in water Phase When Drop was Withdrawn into the Nozzle

When the drop was withdrawn into the nozzle, the extracted
acid was left behind in the water phase. The image of the extracted
acid on the negative or on a photographic plate appeared as an irregu-
lar geometric shape as shown in Photograph ll and sketched in Figure 7.
The total amount of acid in the image was calculated from optical
density measurements over areas AX.AX which accounted for the acid in

volume L AX AX: Therefore,

A = L Cave dx dy, (20)
where
A = total amount of extracted acid
L = column thickness or depth in the L direction in

Figure 2.

25

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0wm0.0 m:m0.0 m:
0wa0.0 m:H0.0 m:

 

 

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among one no omuaH one nwsousa apnoaunseeez anemone Haoepmo - HH mmm<a

26

Cave = Average concentration in volume L AX Ad:
The numerical value of Cave was determined
directly from the optical density-concentration
calibration plot and optical density measurement.
The integral in Equation 20 covers the entire area of the image, and was

determined by first integrating along the X-axis with Al equal to the

slit length of the densitometer. values

0f fcave dx were obtained by graphical
integration. These values were added in

the Y direction and multiplied by L to

 

 

 

give A, the total amount of extracted

 

acid.
Drop volumes were determined by graphical integration of the

following equation which was derived by Tambo (22).

” 2
V=fLYDJh <21)
.11

where,
V = volume of the drop
D = diameter of the drop as a function of H
H = height along the vertical axis of the drop.

The linear velocity of the Jet entering the drop was determined by divid-

ing the volumetric flow rate by the cross sectional area of the nozzle.

27

APPARATUS

The apparatus, illustrated in Figures 8 through ll, consisted of
a vertical extraction column, a water tank and pump, a drop feeder device,
a light source, absorption cells, light filters, and a camera mounted on
an adjustable platform.

The extractor was fabricated from four brass plates 30 inches
long and 3/8 inch thick, soldered together to form a column with a square
inside cross section one inch on a side. Grooved openings were cut into
the front and back sides of the extractor to accommodate two l/h inch
thick plate glass windows one inch wide by eighteen inches long. The
‘windows were held in place with epoxy resin with the inner surfaces of
the windows 1.25 inches apart.

Piping was arranged so that distilled water saturated with toluene
could be pumped from the storage tank to the bottom of the column. The
column outlets at the top and bottom led to a drain.

Toluene-picric acid drops were formed at the end of a glass
capillary which was joined to a 20-gage hypodermic needle with epoxy-
resin (insoluble in water or toluene). A rubber stopper around the
needle enabled the capillary to be inserted into the extractor from a
side-hole. The needle was bent so the glass nozzle was vertical when
inserted in the extractor. The inside diameter of the nozzle tip was
0.037 inches, and the outside diameter was 0.072 inches. A one milliliter
syringe (A) held in place by platform (B) was used to form the drop. A

spindle (C) placed behind the syringe plunger controlled the rate of drop

28

 

 

 

 

”II” ”0"".
:2:::n:..

I" |

 

i'H'IH'
N nu.-

 

 

 

water
inlet

 

 

 

quick
closing
valve

to
drain

electric motor

 

 

 

dis «lled
EEer

 

 

 

 

filter

 

 

 

 

1F

 

 

 

 

A.- Syringe

B - Platform

0 - Spindle

D - Spindle Arm

Nhnua1.Advancer

- thal Spring
- Graduated Bar

Micrometer-type Screw

 

Figure 8 _ DIAGRAM OF THE APPARATUS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

tiger-m9 - Extractor Detail

 

30

formation. An arm (D) soldered to the spindle at a 90-degree angle was
placed in the grooves of a micrometer-type screw. When the screw was
turned, the arm, spindle, and plunger all moved parallel to the screw
axis. The screw was turned by‘a combination of pulleys, cone sheaves,
sash cord belts, and a gear reducer that was connected to a l/50 horse-
power variable speed electric motor. This arrangement provided drop
formation times ranging from 0.2 to 25 seconds.

The initial plunger position was adjusted by a horizontal
cylinder (E) which was screwed into the base of the feeder, and the
spindle slid through the cylinder.

The arm (D) pressed against a flat metal-spring (F) while
moving forward under a rigid, adjustable, graduated bar (G). When
the arm (D) moved a linear preset distance (which would form one drop)
and reached the end of bar (G), the spring (F) pushed the arm up, freed
it from the grooves of the micrometer screw and thus stopped the advance-
ment of the plunger.

Three 20-watt blue fluorescent tubes each 1 1/2 inches in diameter
and 23 inches long served as light source. Blue tubes were used be-
cause they produced a high light intensity in the desired 3800 to
5500°A wave length range (26). The tubes were placed vertically with
their axes forming an isosceles triangle with sides of about 1 5/8,

1 5/8, and 3 inches. The bulb at the tip of the triangle was 7/8 inch
from the column.

During the preliminary experiments, the light source was operated
on 60 cycle current. The film densities of a number of frames taken from
one solution varied t 8 units or more. A plot of per cent transmission

versus number of frames showed an almost sinusoidal variation in readings.

31

This was caused by the nonuniform light output resulting from the cyclic
variation in 60-cycle current. The nonuniform light output could have
been also due to the "flicker" (per cent deviation from mean light out-
put) of the fluorescent lamp, which is particularly higher for blue
fluorescent tubes (9). To diminish the nonuniformity of light output,
the light source was operated on a lOOO-cycle circuit.

The arrangements for 1000 cycle circuit are illustrated in
Figure 10. The bulb fixture carried a 60-cycle ballast (0.38A, 118V)
in series with each bulb. The ballasts limit the current and raise or
lower the circuit voltage to provide the wattage required by the lamp.
In order to operate the bulbs at a frequency of 1000 cycles and voltage
of about 110 volts, rheostats of l36-ohm resistance were connected in
parallel to the ballast of each bulb.

The 1000 cycle alternating current was produced by a three-
phase induction-motor and generator combination with a syncronous
speed of 3h50 R.P.M. The combination was connected to two electrical
systems: A D. C. source or field exciter connected to the generator
and an A. C. system connected to the motor.

The D. C. source was produced by connecting a llO-volt A. C.
line through a variable voltage transformer (powerstat) and a 60-
cycle rectifier to convert the alternating current to direct current.

The hho-volt, 60-cycle.A. C. motor was on the same shaft as
the 220-volt, lO35-cycle A. 0. generator. The two were General Electric
models 5K79BCh and SLYGGAIB, respectively.

Photographs of standard solutions were taken through standard
cells. The cells were positioned on a wood column which replaced the

extractor. The standard cells shown in Figure 11 had the same cross

 

 

Glow-Switch

Starter
O
p 0

Three 20 watt blue
fluorescent tubes

i
r17

0..

Q Q Q C ea c 1 e e e

 

 

T
A
.0.o.e.e.o.e.e.e.e

 

 

 

 

 

 

l—BTUI’TIU“TOCO

 

 

Rheostat

136 ohm -\\\\‘ m

Ballast

 

   

 

 

no - nj volts

 

 

 

 

 

 

 

 

 

 

 

d
1000 cycle
A.C.
60 Cycle Rectifier
a. v... a a _ I
Ac "’1“ 17* IN I Y T
60 Cycle
Powerstet
8
no Volts AC Main :3,
O
2&3
Start and .3
Stop Switch ““
8
‘ Mom, 60 Cycle 230/220 Volts
AC Mbtor {a r 1035 Cycle
3150 R.P.M. “ A-C Generator
31+50 R.P.M.
a _ \ Q

 

 

 

 

Figure 10 - Diagram of the light source.

33

 

 

 

‘b——— /;.37'

 

 

"—W|

I
1
8

L:

 

 

 

 

 

 

 

 

Top View

 

iiHHHHHHHHmi

J
.

lilllllllL

a
.

 

 

nu...i!-l_n.

 

 

 

 

["|

 

Li-_-__.J._.... ....JL

 

 

 

 

 

 

[III V '

 

 

 

Side View

Front View

STANDARD CELL DETAIL

Figure 11

 

 

3h

section as the extractor, and a height of three inches. The bottom was
closed and the top open; the glass windows were 1 3/h inches high.

A rectangular glass cell (glass thickness 0.0365 inches) was
positioned inside the standard cell to separate one layer of a solution
from the rest of the cell contents when this arrangement was desired.

Pictures of the drops and standard solutions were taken at 32
frames per second at f/3.5 opening by a 16-millimeter CINE-Kbdak Special
movie camera. The film used was 16-millimeter, Flux-X reversal safety
film (type 7276) made by Eastman Kodak Company. Kodak Wratten Filter

Number 3h was placed between the camera and the column.

35

EXPERIMENTAL PROCEDURE

Standard Cell Pictures

 

The wooden column used to hold a standard cell was positioned
and leveled in front of the light source. A standard cell containing
distilled water was placed in the column, with a pin located at the
center of the cell. The camera was clamped to the adjustable platform
and was focused on the pin. Standard solutions of water-picric acid
and toluene-picric acid were placed in the cell and pictures were taken

for at least one second for each cell.

Movies of Forming Drops

 

After the syringe was filled with the toluene-picric acid
solution, the glass capillary section was connected to the syringe.
Care was taken to avoid air bubbles in the syringe. The needle section
was then inserted into the column and the rubber stopper was tightened
in the side-hole with the capillary in a vertical position at the center
of the column. The body of the syringe was tightened in the saddle-
type platform so the plunger was lined up with the moveable spindle.
Using the manual advancer, the plunger was pushed forward until the
solution in the syringe reached a point about 3/h inch from the tip of
the capillary. Next the plunger was held against the manual advancer
while the spindle was pushed forward to reach the plunger. The arm of
the spindle was positioned under the graduated bar at a point five

millimeters from the end of the bar. The inlet valve to the column was

36

opened until the continuous phase reached above the capillary tip, and
then the valve was closed. Finally, the electric motor was turned on
and the spindle pushed the plunger forward. After the spindle traveled
the preset distance of five millimeters, one air bubble ani one toluene
drop had been formed, and the spindle arm was automatically released
from the micrometer screw. The movie camera was started as soon as the
air-toluene interface began moving. After pictures of one drop were
obtained, the column was flushed and rinsed with distilled water and
the same operation was repeated. All the experiments were conducted at
room temperature with water and toluene phases at 25 122°C.

When a drop was withdrawn into the capillary, the manual advancer
was pushed forward until the air bubble in the capillary was almost
ready to detach. The spindle arm was held manually against the micrometer
screw until the drop reached the desired size. Then the plunger was
pulled back to the manual advancer. By this procedure only the drop

itself was withdrawn.

Movies 2: Coalescing Drops

 

Experiments were conducted to study the effect of rate of mass
transfer on stability of the drop at the tolueneewater interface. The
operation for drop formation was the same as for the regular drops except
that before forming a drop, pure toluene was placed on top of the water
above the capillary nozzle to form an interface. The interface was free
of air bubbles and dirt which could promote coalescence. In order to
prevent the drops at the interface from moving toward the sidewalls, the
interface was shaped slightly concave downward by injecting additional

water after the toluene was added. The level of the interface was

 

37

maintained 1/8 inch above the forming dr0p to eliminate extraction during
the drop rise. M0vies of the drops were taken with different rates of

formation.

Film Processing and.Recording on the Densitometer

 

 

The 16-millimeter Plux-X reversal type movie film was developed
to a negative stage for five minutes in Eastman Kbdak DK-60A Developer.
Each roll of film contained.both the standard solutions and the drop,
so both were processed under the same conditions.

The negative film was enlarged and developed to a positive stage
on k" X 10" Kodak No. 33 photographic plates. The desired frames of the
negative film were cut out in small rectangular sizes and placed between
two clear glass plates in a rectangular area of 7/8 X 2 1/8 inches. A
A" X 10" black cardboard with an opening at the center was placed on
top of the glass plates, leaving the area of the films open for exposure.
The glass plates with the films between were placed on a Wollensak 135-
millimeter enlarger, and projected to a magnification of about five times.
The enlarger lens opening was at f/32, and the exposure times ranged from
eight to ten seconds. The plates were processed as follows: developed in
D-ll Kbdak Developer for eight minutes, rinsed in 5% acetic acid solution
for 40 seconds, fixed in Kbdak acid fixer for 15 minutes, washed in 8
running water for 20 minutes, rinsed in distilled water, and dried.

Optical density measurements along the axis of the drop were
Obtained.by first placing a piece of graph paper on the densitometer
screen along the slit length. By this arrangement it was possible to
move the plate holder one slit length at a time. Readings were taken for
each position along the vertical axis of the drop. The densitometer pro-

jected the drop from the plate to the screen with a magnification of 10

38

times, so that it was possible to move the plateholder and thus the frame
containing the drop to the desired position along the vertical axis.

The diameters of a drop along its vertical axis were determined
by projecting the plate on a graph paper to a magnification of 10 times.

In order to Obtain optical densities across the image of the
extracted material in the water phase, the recorder and synchronous
motor drive were used to plot transmission values versus distance
automatically. From the rate of plate movement and the recorder graph
movement the distance along the image corresponding to optical density

at each point was found and plotted versus concentration at that point.

39

SUMMARY OF RESULTS

The experimental results are summarized in Table III, and
plotted in Figure 12 as amount extracted versus time for each
individual set of drops. Drop volume versus formation time is
plotted in Figure 13.

The drops were not completely spherical in shape. As re-
ported by Poutanan and J0hnson (19), before break-off each drop
had an elongated neck by which it was attached to the capillary.

The results of one experiment in which a drop was with-
drawn into the capillary is presented in Table IV.

Photographs of Drop Sets 53 and 56 appear on the follow-

ing page-

 

.1

0.250 sec 0.325 see

no

0.500 sec

0.625 sec

 

DROP 53 DURING FORMATION

Photographs 1 - h

h.0 sec

 

»~—_._

6.0 sec

3'? I i I?

8.0 sec 9.1 sec

 

_‘
‘— ______

DROP 56 DURING FORMATION
Photographs 5 - 9

No mass transfer into bulk of the continuous phase below 12
second formation time.

 

 

. J.

Photograph 10
Typical drop, formation
time over 12 seconds
Extracted picric acid
diffusing into bulk of
the continuous phase.

 

 

Photograph ll
Extracted picric acid re-
maining in the continuous
phase after the drop has
been withdrawn into the
capillary.

Ml

TABLE III - Experimental Results

 

 

 

Jet
Drop Set Formation Volume Amount Extrac ed Velocity
and No. Time, Sec. cm3 grams x 10 cm/sec
52-1 0.0625 0.00380 1.650 15.1
2 0.1250 0.0098u 1.7A2 15.1
3 0.1875 0.018h8 2.163 15.1
h 0. 2810 0. 01960 3. 790 15 .1
53-1 0.125 0.008h5 1.268 10.52
2 0.250 0.01868 1.726 10.52
3 0.375 0.02790 2.075 10 52
h 0.500 0.03h80 2.032 10 52
5 0.625 0.0A570 3.100 10.52
35-1 0.h68 0.01950 1.93 6.65
2 0.780 0.0h065 1.79 6.65
3 1.h06 0.066u0 3.29 6.65
n 1.625 0.07h60 h.02 6.65
37-1 1.00 0.01717 2.h30 3.22
2 1.56 0.03365 2.825 3.22
3 2.03 0.0h370 3.9u0 3.22
h 2.50 0.05210 n.020 3.22
5 2.9a 0.06600 5.89u 3.22
38-1 2.00 0.03130 3.22 2.30
2 3.00 0.0h500 h.05 2.30
3 n.00 0.06h10 5.95 2.30
h 5.01 0.08200 6.95 2.30
56-1 2.0 0.0168 1.83 1.22
2 h.0 0.0292 2.88 1.22
3 6.0 0.0513 h.h2 1.22
h 8.0 0.070h 5.98 1.22
5 9.1 0.0726 7.27 1.22

A2

TABLE IV - Results of Drop 60 Before and After it
was Withdrawn into the Capillary

Time at which drop was withdrawn . . . . . . . . . . . . . 5.62 seconds

Drop volume . . . . . . . . . . . . . . . . . . . . . . . 0.0259 cm3
Time it took to withdraw the drop . . . . . . . . . . . . 3.36 seconds
Amount of acid extracted during 5.62 seconds . . . . . . . 3.2M x 10'6

-6
Amount of acid left behind after drop was withdrawn . . . h.86 x 10

gm

gm

43

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MS

DISCUSSION OF RESULTS

Three methods were used to compare the results with the theo-
retical equation given in the theory section as,

% extraction = 6.12 x 10.2 ‘Ii—1:T_' (8)

‘V‘3
In the derivation it was assumed that mass transfer resistance inside
the drop was negligible and that transport outside the drop occurred
primarily by molecular diffusion. The per cent extraction from
Equation 8 was 0.3 per cent for a drop of 0.082 cm3 volume formed in
five seconds. The experimental value was only 0.08 per cent. If the
molecular diffusion assumption was not valid, transport by convection
in the continuous phase would have increased the per cent extraction
and the experimental value would be greater than the calculated value.
Since the reverse was true, the assumption of negligible resistance
inside the drop was not valid despite the 10 to 1 distribution ratio
favoring the dispersed phase.

Inspection of Equation 8 shows that a log-log plot of per
cent extraction versus time, for drops of a fixed volume, should
result in a straight line of slope 0.5. However, the experimental
data plotted in Figure 1h show that a curve exhibiting a minimum
per cent extraction was obtained. A similar result was found by
Gregory (11) with systems in which the dispersed phase resistance

controlled the extraction rate. His results are included in Figure 1h

for comparison. At formation times less than one second, apparently

; 2

' Per cent extracted 2 10

Per cent extracted

 

46

 

 

 

 

 

60
l' TVV‘Vi .‘ fl”
Curve RAP is from Gregory's (11) , ’
results for acetic acid - carbon
tetrachloride - water system.

30 ,

 

I
20 .1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1 .
0.2 0.3 0.4 0.5 0.7 1.0 2.0 . 3.0 4.0 5.0

4.11

 

 

 

 

 

 

 

 

 

Formation time, see
Figure 14 - Per cent extracted versus formation time.

“7

the dispersed phase transfer coefficient increased rapidly due to the
increase in formation rate.
Equation 8 was solved for the amount extracted as a function of

the rate of formaticn and time,

2/3 t7/6

amount extracted = 0.67 b (22)

Figure 15 is a log-10g plot of amount of acid extracted versus time, for
a constant formation rate. Inspection of Equation 22 shows that,

for a constant value of U, a log-log plot of amount extracted versus
time should result in a straight line of slope 1.17. It was found that
the slope increased as the formation rate decreased. At the slowest
formation rate of 8.h5 x 10"2 cm3/sec, the exponent of t was 0.95
compared to the theoretical value of 1.17. At lower formation rates,
transport by molecular diffusion within the drop would increase in
importance. In addition if the continuous phase resistance was negli-
gible, an equation of the form of Equation 22 would be applicable. There-
fore, it was expected that the time exponent would approach 1.17 at low
formation rates.

The per cent of solute extracted was higher during the early life
of each drop.

Inspection of the photographs of Drop Set 53 shows that in drops
of less than one second formation time, extraction took place mostly
around the bottom half of the drop. This is illustrated by the increase
in darkness near the bottom of the drops. For drops that formed at a
slower rate, extraction was uniform all around the drop. This was
prdbably due to the increase in mass transfer coefficient inside the

drop near the capillary tip at high formation rates.

6

Alannt extracted, gm 2 10

10

48

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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// ”I r'
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0T6? 7 /
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0.1 0.2 0.3 0.6 1.0 2.0
. ' /| V
l/
333' , 3315‘ 5:2 m;
.L___ -
. I [ ° 52
3,01» " 53
/ 0.95 x A 35
0 37
V O 38
a 56
1‘ ’ 2 4 t L 5 I in 2'0

Figure 15 - Plot of amount extracted versus. drop formation

tor-nation time, sec

tine in accordance with Equation 22.

 

1+9

Figure 12 of the results is a plot of the amount extracted versus
drop formation time with formation rate as a parameter. At a fixed for-
mation time the amount of extraction was lower for drops that formed at
a slower rate.

When drops were formed in less than 12 seconds, none of the
extracted acid was left behind as the drop broke away and rose. There-
fore, in these experiments, transfer to the bulk of the continuous phase
did not occur. This effect has not been previously reported in the
literature.

Table IV of the results presents the amount of extraction from
Drop 60 which was withdrawn into the capillary. The variation Obtained
in the amount of extraction by two methods, namely by taking optical
density measurements directly through the image of the drop and by taking
optical density measurements through the image of the extracted material,
was due to: extra mass transfer during the time it took to draw the
drop into the capillary and possible higher mass transfer from the
unsteady motion of the plunger when withdrawing the drop manually.

Sufficient data on coalescence of the drops was not Obtained;
however, from the few experiments conducted, coalescence of the drops
at the toluene-water-interface seemed to be instantaneous. The ex-
'periments conducted with drops forming at different rates of formation
revealed that higher rates of mass transfer decrease the stability of
the drops at the interface, as reported by Charles and Mason (1h) for
other systems. In the preliminary investigations it was found that
for picric acid-water-toluene system , the coalescence was not complete;
that is, the primary drop was succeeded by a smaller secondary drop of

the dispersed phase.

50

CONCLUSIONS

 

It was possible to study the mechanism, rate, and amount of
extraction at any time during drop formation period by photographic
absorption photometry.

For the system picric acid-toluene-water, with toluene as the
dispersed phase, and for drop formation times below 12 seconds, mass
transfer to the continuous phase was essentially zero, and extraction
across the interface was about 0.1 per cent.

The per cent of picric acid extracted was higher during the
early life of a drop.

For a fixed drop volume, per cent_extraction decreased as
formation time decreased at long formation times. At shorter times,
this phenomenon was.reversed.

The rate of mass transfer increased with increase in the
formation rate.

For drops with high rates of formation, extraction took
place mostly around the bottom half of the drop. For slow rates
of formation, extracted material was more uniformly distributed
all around the drop.

The dispersed phase resistance was important and not at all
negligible.

The coalescence of drops at the water-toluene interface was
instantaneous in most cases, but it was not complete; that is, the
primary drop was succeeded bya smaller secondary drop of the dispersed

jphase.

APPENDIX

51

52

APPENDIX A

SAMPLE CALCULATIONS

I. Sample Calculation of the Concentration of Different layers of
Solutions as Presented in Table I

Table I presents data obtained from a cell containing different

solutions in each compartment of the standard cell.

Sample Calculation for Runs 2g and 72

 

Calculated concentrations were determined from Figures 16 and 17

and Equation 9;

(940,4: aquI+ k/s €40 hf]; C3“ (9)

where,

=L1+L2+L3.

For water phase, the values of Kg were constant and equal. Integrating

Equation 9,
1 _
9n» = .15. (ClLl + CQLQ + C3L3) (23)

2213.11.51.29.

L1 = 0.h985 inches cl = 0.01h5 gm/L

L2 = 0.1880 inches 02 = 0.0000 gm/L

L3 = 0.h985 inches 03 = 0.01h5 gm/L

L = 1.2500 inches measured optical density = 0.15

Optical density

1.6

53

2.0

 

 

1.2

 

0.8

 

0"

 

    

 

 

 

 

l T l :I I i-
-0 0.02' 0.04 0.06
Grass of picric acid per liter of water

Figure 16 - Plot of optical density on the place versus concen-
tration of the standard. solutions (calibration curve
for Drops 35, 37, and 38).

 

Optical density

2.0

1.6

1.2

54

 

 

 

 

 

 

 

 

 

l

.l

 

20

o .

40

Grass of picric acid per liter of toluene

Figure 17 - Plot,ef optical density on the plate versus
concentration of the standard solutions

60

(calibration curve for grape 35, 37, and 38).

 

55

The thickness of two glass pieces separating the compartments was 0.073
inches. Light absorption due to the glass was assumed zero. From
Figure 16 for a measured density of 0.15,

CSW = 0.0113 cm/L

Substitution of Csw and L = Ll + L2 + L3 + 0.073 in Equation 23 gives

01 = c3 = 0.01h1 gm/L.

sushi.
L1 = L3 = 0.367 inches 03 = C1 = 0.0325 gm/L water phase
L2 = 0.hh3 inches C2 = 109 gm/liter of toluene
L = 1.25 inches measured density = 1.62

Thickness of the glass separating the compartments was
0.073 inches.

In this case Equation 23 becomes

KuLCsw = K£11101 + K£14202 + KwL3C3 (2“)
Then by application of Equation 9 to toluene phase,

C't = C2L2 = 109 x 0.hh3 = 38.62 gm/L in toluene phase
L 1.25

 

From Figure 19 a plot of concentration in the toluene phase

versus optical density for a concentration of 38.62 gm/L, d = 1.065.

In turn from Figure 18 a plot of concentration in the water phase
versus optical density - the water phase concentration equivalent to
an optical density of 1.065 for a cell 1.25 inches thidk was

C'w = 0.0516 gm/L.

Therefore,

KuC'wL = KtC'tL = K2C2L2

Optical density

2.0

1.6

1.2

0.8

56

 

 

 

 

 

 

 

 

 

 

l 1 J L l L l

 

0.04 0.08.

, Grams of picric acid per liter of water
Figure 18 - Plot of optical density on the plate versus
concentration of standard solutions.

0.1;

 

Optical density

57

2.0..

 

 

1.6

 

1.2

 

 

 

 

 

 

 

 

 

 

1 l l

0 ‘ 20 40 ’ 6O
era-s ef picric acid per liter ef toluene ‘

Figure 19 - Plot of optical density on the plate versus ,
concentration of the standard solutions.

 

58

Kw (0.0516) (1.25) = K2C2L2

From the measured density at 1.62 and the water calibration curve,

Figure 18, csw = 0.0706. substituting into Equation 2h,
0.0706 x 1.25 = 0.367 x 01 + 0.0516 x 1.25 + 0.367 x C3
Since C1 = C3,

C1 = 0.032u gm/L
This figure was compared to the actual value of 0.0325 gm/L.
II. Sample Calculation of the Optical Density for Drops at Equilibrium
with Continuous Phase as Presented in Table II
The expected optical density through drops at equilibrium was
calculated by a method similar to that of the previous section for
Runs 75 through 80. Distance L2, the drop diameter, equaled the

thickness of the toluene phase.

For Drop £3,

C1 = C3 0.01h5 gm/L in water phase

02 0.016 gm/L in toluene phase

At a point where the drop thickness was 1.57 mm on the image,
L = (1.57 x 0.0531) = 0.0835 inches, where 0.0531 equaled inches in
the extractor per mm of the image.

From Equation 16,

 

C't = 0212 = 0.016 x 0.0835 = 10.7 x 10-4 sm/L
L 1.25 in toluene phase

From Figure 17,

Optical density = 6.h x 10"6 for C't (by interpolation)

59

From Figure 16,

-6
C'w = 7'5 x 10 gm/L for optical density of 6.h x 10‘6
(by interpolation)

 

Therefore,
KtCtL2 = KwC'wL
Substituting into Equation 2h,
Csw = (L-LQ) C1 + C'UL
L

(1.25-0.0835) x 0.01u5 + 7.5 x 10-6 x 1,25
1.25

 

0.0135 gm/L in water phase

From Figure 16 for a concentration of 0.0135 gm/L the optical density was

0.195.

III. Calculation of the Amount of Extraction when Optical Density
Measurements were made Directly Through the Drops

Sample Calculation for Drop 1 of Set 23

 

The amount of extraction was determined from Equation 25.

 

f/
I
2 1000 (25)
40
where,
.A = total amount of extraction, grams
D = thickness of the drop at each point of trans-

mission measurement, cm

L = effective depth of the extractor or standard
cell (L = 1.25 inches x 2.5h cm/in = 3.175 cm)

= concentration in water phase corresponding to
the transmission read at each point of the drop,

sm/L

C'SW = concentration in water phase which gives the
same transmission as a concentration CS in
toluene phase, gm/L (where cat = Ct~D/L)

60

H = position of diameter and transmission
measurement along the vertical axis of
the drop, cm

1000 = conversion from liters to cm3
2 = a factor taking into account that AC =

Csw ' C'sw is twice the actual value.

Conversion factor from the plate to actual size in the extractor was

equal to 1.35 (to convert from the plate to actual size in the extractor

multiply by 1.35).

From Drop 1 of Set 53 the values for one/point of optical

density measurement are:

L . . . . . . . . . . . . . . . . . . . . . . . . 3.175 cm
H, on the plate . . . . . . . . . . . . . . . . . 0.1 mm

D, on the plate . . . . . . . . . . . . . . . . . 0.6 mm

(The values of H and D were converted into cm in the extractor by multi-
plying by 0-135-)

T, per cent transmission . . . . . . . . . . . . 20%
Csw: for a transmission of 20% (or d = log .JL.
a 0.699) from Figure 21 . . . . . . . . . . 9'80. 0.0307 gm/L

Ct . . . . . . . °.} . . . . . . . . . . . . . . 109 gm/L

cat = 21:13.. - 01;- (0.135 D plate)

 

L L
= 109 gm/L x £9'§.§7§':$51—Cm = . . . . . . 2.78 gm/L

C'sw, for a concentration Cst = 2.78 gm/L
from Figure 22, d = 0.16.and in turn from
Figure 21 for an optical density of 0.16 . . . . 0.0108 gm/L

__ _ , /
AC - Csw - C'8w — 0.0307 - 0.0108 . . . . . . . . 0.0199 gm/L

Optical density

2.0

 

1.6

 

1.2

 

0.8

 

 

 

 

 

l

 

 

 

O 0.02 g
. Grass of picric acid per liter of water
Figure 21 - Plot of optical density on the plate versus
concentration of standard solutions (calibra-
tidn curve for Drops 52, 53, and 56).

0.04

0.06

61

Optical density

2.0

 

1.6

62

 

1.2 7

 

 

0.8 .

 

0.4

 

 

 

 

0 1 1 I I

 

 

0 20 ' 40 6O
Grams of picric acid per liter of toluene
Figure 22 - Plot of optical density on the plate versus
conchntration-of-standard solutions (calibra-
tion curve for Drops 52, S3, and 56).

63

substituting into Equation 25,
' If

2 ac -
(0.135) (“2”) 3.175 x 10
o

3

A x 3.1M x D“dh (25a)

or,

:>
n

//
9.08 x 10'5 .L D so dh (25b)

For the first point of optical density measurement,

D AC = 0.6 x 0.0199

3

=11. 911 X 10- gm-mm/L

Equation 25b was evaluated graphically by plotting values of D.AC versus

1

H in Figure 20a- The area under the curve was 0.1M x 10' gm-mme/L.

Total extracted acid,'A a 9.08:: 10'5 x 0.11; x 10'1

= 1.27 x 10"6 gm

The drop volumes were determined by the following equation:
H .2
v-/,ln .41. (21>
6>

position along the vertical axis of the drop, cm

where,

RI!
ll

U
ll

diameter of the drop at position H, cm

V = volume of the drop, cm3

Since the values of H and.D were in millimeters on the plate,
the right side of Equation 21 was multiplied by the conversion factor

(0.135)3 (gem in extractor)3 to obtain the actual volume. Then,
mm on plate 7 .

If
v = 1.93 x 10'.3 f D2 dh (21a)
0

64

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65

Equation 213 was integrated graphically from a plot of D2 versus H.
Figure 20b is a sample plot for Drop 1 of Set 53. The area under the

curve was 11.38 m3. Substituting into Equation 21a,
v = 8.115 x 10-3 cm3

The linear velocity of the Jet entering the drop was determined
by dividing the volumetric flow rate by the cross sectional area of the
nozzle.

Inside diameter of the nozzle at the tip was 0.037 inches.

Then,

cross sectional area -%;—(0.037 in x 2.5M cm/in)2

= 0.069h cm2
Therefore, for Drop 56 with a volumetric flow rate of 8.h5 x 10'2
cm3/sec,
Jet Velocity = 8.h5 x 10'2 cm3/ sec x 1 2
0.069Ecm
= 1.22 cm/sec.

IV. Calculation of the Amount of Extraction when Drops were Drawn
into the Capillary

The amount of acid left behind the drop when drawn into the

capillary was determined by the following equation:

)C
A: C-d"L-dx (26)

where,

A. = amount of picric acid in the volume covered by
the slit along the X axis, grams '

66

C = concentration in grams per cubic centimeters
corresponding to the per cent transmission read

L = depth of standard cell or extractor = 3.175 cm
d' a slit length, cm. The slit length = 0.02 cm on

the plate or 0.02 x 1.5 = 0.30 cm in the extractor
(where 1.5 cm in the extractor = 1.0 cm on the

plate)
X = distance in which picric acid was spread in X
direction.
Then,
A = C . 0.03 . 3.175 dx
or, 0
Jr
A = 0.09525 f 0 dx (26a)
0

Equation 268 was integrated by a plot of X versus concentration
C in gm/L. The values of X were centimeters on the recorder graph.
To convert X to centimeters in the extractor, let

recorder graph movement = N mm/min = 60 mm/min

plate movement = S mm/min = 2.5 mm/min

Then to convert centimeters on the recorder graph to centimeters in

the extractor multiply by ngg- = 1126%_§;2 . Therefore in

X

. 2 IHSOXQS I
O 095 5 x 60 0 C dx

or, X'
5.95 x 1041) 0 dx (26b)

Figure 25 was a plot of X in centimeters on the recorder graph

Equation 26a,

:1>
ll

 

:D
II

versus concentration C in grams per liter. The values of C for each

C, grams of picric acid per liter of water 10

40

 

36

 

 

 

 

32

 

Data from Appendix C
28

 

 

Section II

(slit position 10)

24

 

20

 

16

 

12.

 

 

 

 

 

 

 

 

 

 

0v

 

 

0 2" 4‘ '6 a '10
. x,cm

Figure 23 - Typical plot of data in accordance with
Equation 265.

12

67

68

optical density measurement were read directly from Figure 24. The area
-3

under the curve of ten graphs similar to Figure 23 was 0.817 x 10 gm~cm/L.

Thus, the total amount of acid left behind Drop 60 was,

A . 5.95 x 10'3 x 0.817 x 10'3

. 4.86 x 10'3 grams.

2.0

1.6

H
N

Optical density

0
0
on

0.4

 

 

 

 

 

 

 

 

 

 

0 0.02 0.1

 

l I I

 

 

0.06

Grams of picric acid per liter of water

Figure 24 - Plot of optical density on the plate versus
concentration of standard solutions of picric

acid in water (calibration curve for Drop 60).

l

69

70

APPENDIX B

METHODS OF ANALYSIS AND PREPARATION
OF STANDARD SOLUTIONS

The concentrations of picric acid in water and toluene were
found by titration with a standard base solution to a faint orange
phenolphthalein end point. A Beckman spectrophotometer was used to
determine picric acid concentrations below 0.01 grams per liter.

Due to the different range of concentrations of picric acid in
water and toluene, three standard solutions of sodium hydroxide with
normalities of 0.0029, 0.035, and 0.57 were used. The hydroxide
solutions were standardized against a standard solution of 0.02 N
sulfuric acid.

Picric acid solutions were prepared from reagent grade crystals
and distilled water or reagent grade toluene at room temperature.
Solutions of low concentrations were Obtained by dilution.

Analysis and Sample Calculation of
Water-Picric Acid Solutions

 

 

Fifty milliliters of picric acid-water solution were trans-
ferred with a 50 m1 pipette to a clean 250 ml Erlenmeyer flask. Two
to three drops of phenolphthalein were added and the mixture was ti-
trated against the standard base solution from a 50 ml burette. All
the titrations of picric acid solutions were carried to a faint orange

phenolphthalein end point.

Sample Data

 

Standard base nOlmality, Nb. . .
Volume of picric acid-water solution, Va
Volume of the standard base consumed to8
reach the end point . . . . . . . . . .
Volume of the standard base required for
the blank test on 50 ml distilled water .
Actual volume of the base needed, by
difference, Vb

Then the concentration of the picric acid solution was,

22.26 mi of NaOH Sol. x 0-0029 60- of N90“

71

. 00.0029 N
50.00 ml

. 22.30 m1
. 00.0% ml

. 22.26 m1

1 eq. of picric acid

 

1000 m1 of NaOH Sol.

1 x

 

229.11 gm of picric acid

 

50 m1 of picric acid 1 eq. of picric acid

Analysis and Sample Calculation of
Picric Acid-Toluene Solutions

 

 

Ten milliliter portions of toluene-picric acid solutions were
taken with a 10 ml pipette for titration against standard base solution.

Equal amounts of pure ethyl alcohol were added to the samples before ti-

tration.

Sample Data

 

Standard.base normality, Nb . . . . .
Volume of the neutral ethyl alcohol .
Volume of the picric acid, V3 . . .
Volume of the standard base consumed to
reach the end point, Vb . . .
Normality of the sample solution, N5

me = Q.035.x_16.3 = 0.057

 

1 eqf of NaOH

X

= 0.2965 gm/L

A faint orange change of color was taken as the end point.

00.35 N
10.00 m1
10.00 m1

16.30 ml
2

eq. picric acid

 

10 liter toluene

Concentration of the same solution

0.057 eq. of picric acid X

229.11 gm picric acid

 

 

liter toluene

13.10 grams per liter.

eq. pciric acid

72

The concentrations of picric acid solutions analyzed by titration
'were checked by a plot of solution optical density versus concentration.

Since both the water and toluene solutions Obey Beer's Law, tle plot re-

sulted in a straight line. The refractive index data presented in

Table V and VII were also measured.

73

TABLE V - Index of Refraction of Picric Acid in Water at 23.6°(3

 

 

Concentration, gm/L Refractive Index
0.0000 1.3320
0.078h 1.3320
0.2262 1.3321
0.8860 1.3323
1.6h50 1.3325

12.5000 1.3355

TABLE VI - Index of Refraction of Picric Acid in Toluene at 23.6°c

 

 

Concentration, gm/L Refractive Index
0.00 1.h9h0
12.30 1.h951
23.38 1.h960
3h.60 1.h968

11h.50 1.5037

I.

7h

APPENDIX C

DATA

Data from Optical Density'hbasurements Made Through the Image
of the Drops

position of diameter and transmission measurement
along the vertical axis of the drop image on the
photographic p1ate,mm (transmission values were
obtained starting at the tip of the capillary and
going toward the top of the drop)

1
per cent transmission at position H, d = loglo (~T1-I5-2)
optical density on the photographic plate
diameter of the drop image on the photographic plate, mm

Csw ' C'sw

concentration in the water phase corresponding to the
transmission T, gm/L

concentration in the water phase which blocks out as
much light as the toluene drop of concentration Ct and
thickness DI

DROP 52 - 1

D-AC°103
H,mm fl D,mm gm—mm L
0.0 ---- 0.000 00.00
0.1 28.0 0.060 9.72
0.3 30.0 0.090 10.35
0.5 30.0 0.100 10.20
0.7 29.0 0.115 9.88
0.9 28.0 0.120 10.30
1.1 3h.o 0.115 7.93
1.3 3u.8 0.115 7.h6
1.5 35.0 0.105 8.20
1.7 38.0 0.090 7.7M
1.9 ---- 0.070 -----
2.1 ---- 0.000 00.00

75

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2.3 22.0 2.10 7.76
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20.0 2.10
19.0 2.30
19.0 2.u0
19.5 2.50
19.5 2.50
19.5 2.55
21.0 2.50
22.0 2.48
23.0 2.35
27.0 2.20
31.0 2.00
36.0 1.60
38.0 1.20
---- 0.00
DROP 53 - h
u D,mm
---- 0.00
16.5 0.80
16.0 1.30
16.2 1.70
16.0 2.10
16.0 2.30
16.0 2.u0
17.8 2.60
18.u 2.70
18.u 2.80
19.0 2.80
19.0 2.85
19.0 2.85
19.0 2.70
20.0 2.55
27.5 2.15
29.0 2.10
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---- 0.00

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0.5 18.0 2.00 13.80
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0.9 19.0 2.10 8.6M
1.1 17.2 2.h8 9.90
1.3 18.0 2.50 8.75
1.5 20.0 2.h0 7.20
1.7 22.0 2.30 5.29
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2.3 ---- 1.30 -----
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0.3 17.3 1.96 1h.90
0.5 17.2 2.20 13.20
0.7 16.0 2.60 10.80
0.9 15.8 2.85 8.68
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1.5 15.8 3 15 5.50
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2.5 21.5 2.60 2.3M
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H,mm M D,mm gm-mm/L
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0.3 25.0 1.30 10.90
0.5 22.0 1.70 10.90
0.7 20.0 1.90 11.00
0.9 19.2 2.05 10.65
1.1 18.2 2.20 10.35
1.3 18.0 2.30 9.11
1.5 18.0 2.30 9.11
1.7 20.0 2.20 7.90
1.9 2h.0 2.05 5.3M
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0.5 17.8 1.95 13.10
0.7 16.5 2.20 12.75
0.9 1h.2 2.55 13.50
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1.7 13.8 2.95 10.60
1.9 15.2 2.80 9.38
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2.3 18.5 2.h5 7.10
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DROP 60*

DoAC°103
Hzmm 5L2. D,mm gm-mm L
0.0 ---- 0.00 00.00
0.1 22.5 1.00 9.80
0.3 21.5 1.60 12.00
0.5 20.0 2.00 13.00
0.7 21.5 2.20 11.00
0.9 21.5 2.30 10.58
1.1 19.0 2.ho 11.00
1.3 19.0 2.10 13.h2
1.5 18.0 2.30 15.28
1.7 21.0 2.20 13.20
1.9 22.0 2.00 11.h0
2.1 2h.0 1.80 10.25
2.3 2h.5 1.30 10.00
2.5 ---- 0.00 00.00

*Calibration data on page 9h
Concentration of drop solution, 102 gm/L
Conversion factor, 1.5 cm in the extractor per cm on the plate

 

 

 

92

 

 

 

 

 

II. Data Obtained for Drop 60 After it was Withdrawn into the Capillary
x = distance along the image of the extracted
acid in X direction (x was measured in
centimeters on the recorder graph)
%T = the values of per cent transmission at
point x, taken from recorder graph paper
Positions 1 through 10 refer to the location of
the densitometer slit with respect to the image
in Y direction.

Position 1 Position 2 Position 3
x,cm % T xzcm % T x,cm EJT
0.00 100 0.00 100 0.00 100
0.20 90 0.50 90 0.35 90
0.30 70 1.00 70 0.50 70
0.h7 50 1.10 50 0.70 50
1.00 30 l.h0 30 1.50 30
1.20 28 1.80 26 2.10 26
1.50 30 2.20 30 2.70 30
1.70 50 2.h0 50 2.90 50
1.75 70 2.60 70 3.50 70
1-95 90 3.h0 90 3.75 90
2.10 100 3.80 100 h.h0 100

Position h Position 5 Position 6
xzcm % T xgcm fJT xgcm %_T
0.00 100 0.00 100 0.00 100
0.20 90 0.35 90 0.20 90
0.h0 70 0.50 70 0.h0 70
0.50 50 0.60 50 0.50 50
1.h0 30 0.80 30 0.75 30
2.20 26 2.20 25 2.503 2h
2.80 30 3.70 30 h.10 30
3.60 50 3.80 50 5.20 50
3-70 70 3.90 70 5.65 70
3.80 90 h.10 90 6.10 90
h.20 100 h.h0 100 6.30 100

Position 7 Position 8

__———. —- ———— _

 

 

 

 

 

x,cm 1LT x,cm E’-_3__‘I‘_
0.00 100 0.00 100
0.50 90 0.30 90
0.80 70 0.70 70
1.00 50 1.10 50
2.30 30 1.70 30
5.00 2h 1.00 2h
7.60 30 6.10 30
8.00 50 6.70 50
8.20 70 7.00 70
8.u0 90 7.70 90
8.50 100 8.h0 100
Position 9 Position 10
xzcm i T x,cm u
0.00 100 0.00 100
0.20 90 0.10 90
0.22 70 0.70 70
0.50 50 1.15 50
1.20 30 2.70 3b
3.00 25 h.10 5O
n.60 30 1.90 70
5.h0 50 5.30 90
5.70 70 5.70 100
6.10 90

6.50 100

9h

III - Optical Density Data of Standard Solutions from Photographic
Plates for a 1.25 inch Absorption Cell

Calibration Data for
Runs 76 Through 80

Calibration Data for
Drops 52, 53, and 56

 

 

 

 

 

 

 

 

 

 

 

 

Cone. of Picric Per Cent Cone. of Picric Per Cent
Acid,gm/L* Transmission Acid, gm/L*' Transmission
0.0000w 100.0 0.0000w 100
0.0050w 90.0 0.01u5w 60
0.0235w h5.0 0.02h2w 3h
0.0325w 28.0 0.03hlw 1h
0.0380w 19.0 0.0528w 3
0.0h78w 11.0
0.072hw 2.2
0.081hw 0.8
0.00t 100.0 0.00t 100.0
7.5ht hh.0 7.5ht 35.5
13.10t 28.0 13.10t 21.0
22.38t 18.0 22.38t 9.5
33.00t 10.5 33.00t h.2
62.30t 1.0 62.3Ot 1.0
Calibration Data for Calibration Data
Drops 35, 37, and 38 for Drop 60
Cone. of Picric Per Cent Cone. of Picric Per Cent
Acid, gm/L* Transmission Acid, gm/L* Transmission
0.0000w 100.0 0.0000w 100
0.0050w 85.5 0.0150w #5
0.0235w 37.0 0.0180w 3n
0.0325w 16.0 0.0225w 21
0.0380w 11.0 0.0300w ll
0.0h78w 5.0 0.0360w 7
0.072hw 0.8 0.0hh8w 3
0.00t 100.0 0.00t 100 O
7.5ht 39.0 9.75t 3u.0
13.10t 21.0 29.h0t 12.0
33 00t 10.5 M6 80t 3.5
62 30t 1.5 76.80t -----

*w refers to water phase

t refers to toluene phase

95

IV - Optical Density Data Obtained from Spectrophotometer for
Picric Acid Solutions as Presented in
Figures 3 and h

Concentration
of Picric Acid
in water, gm/L

 

0.000

0.0208
0.1095
0.8860

12.2500

Per Cent
Transmission

Concentration
of Picric Acid
in Toluene, gm/L

 

 

100.0
98.0
77-5
12.5

h.0

0.00

9-75
29.h0
h6.80
76.8

Per Cent
Transmission

 

100.0
77-5
52-5
37-0

19.0

.u-o u-

 

100

ll.

l2.

13.

1h.

15.

16.

96

BIBLIOGRAPHY

Charles, G. E. and S. 0. Mason, "The Coalescence of Liquid Drops
With Flat L-L Interfaces" (to be published in the Journal 9:
Colloid Science}.

 

Christenson, Boye and S. G. Terjesen, Chemical Engineering Science,

9; 225. 1958-59.

 

Coulson, J. M. and S. J. Skinner, Chemical Engineering Science, 1,

197; 1951-520

 

Garner, F. H. and A R. Hale, Chemical Engineering Scienee, 2,
157. 1953.

 

Garner, F. H. and A. H. P. Skelland, Chemical Engineering Science,

A, 1M8, 1955.

 

 

, Transactions of the Institute of Chemical Engineers,

29, 315. 1951.

, Industrial and Engineering Chemistry, #6, 1255, 195h.

 

 

 

, Industrial and Engineering Chemistry, #8, 51, 1956.

 

General Electric Company, Fluorescent Lamps, Engineerinngata
gn_Lamps and Auxiliary Eguipment, December, 1950.

 

 

Gillespie, T. and Eric K. Rideal, The Faraday Society Transactions,
52. 173. 19560

Gregory, Clarence L., Jr., Eh. D. Thesis, MIT, 1957.

 

Harrison, G. R., R. C. Lord, and J. R. Loofbourow, Praetigal
Spectroscopy, p. 1h3, 1957.

Johnson, A. J. and A. E. Hamielec, American Institute 2:.92291981
Engineers, 6, No. 1, 1&5, 1960.

 

 

Licht, W., Jr. and J. B. Conway, Industrial and Engineering
Chemistry, #2, 1151, 1950.

 

Licht, W., Jr. and William F. Pansing, Industrial and Engineering

Chemistry, A5, 1885, 1953.

 

Linton, M. and K. L° Sutherland, Journal of Colloid Scienig,
11, 391, 19560 "”"“"

 

17.

18.

19.

20.

22.

23.

2h.

25.

26.

97

Nielson, Lawrence E., Robert Wall, and 0. Adams, Journal of Colloid
Science, 13, hhl, 1958.

Perry, John E., Chemical Engineers” Handbook, 3rd ed. (McGraw-Hill,
New York, 19507, p. 715.

 

Poutanen, A. A. and A. I. Johnson, The Canadian Journal 9:_Chemical
Engineering, 38, No. A, 1960, p. 93.

 

 

Seidell, A., Solubilities 9: Organic Compounds, 3rd ed., Vol. 2,
19h1, p. 330.

 

 

Sherwood, T. K., J. E. Evans, and J. V. A. Longcor, Iniustrial
and Engineering Chemistry, 31, llhh, 1939.

 

 

Tambo, William, M. S. Thesis, Michigan State University, 1960.

Treybal, R. E., Liquid Extraction (McGraw Hill, New York, 1951),
p. 381.

 

West, F. B. et al., Industrial and Engineering Chemistry, #3, 23%,
1951.

West, Frank B., A. J. Herrman, A. T. Chong, and L. E. K. Thomas,
Industrial and Engineering Chemistry, 625, Lh, 1952.

 

 

Zeleny, Richard A., M. S. Thesis, Worcester Polytechnic Institute,
June, 195k.

‘1 U

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L

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MICHIGAN STATE UNIVER l

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