Multipurpose Solvent Extractor V. M. Bhuchar and A. K. Agrawal National Physical Laboratory, New Delhi- 72, India
During the preparation and purification of analogs of sulfone-phthalein indicators ( I ) under investigation here, a multipurpose extractor was required which could not only extract these hydrophillic indicators from the solid condensation products, but also from their aqueous solution using more dense or less dense solvents. For each function, different individual extractors have been described by Morrison and Freiser (2). They are useful when a small amount of substance is to be handled but, for general preparative work, some other adaptation was called for. Soxhlet extraction apparatus ( 3 ) has been found useful for a long time for batch extraction of solids by liquids, but the extractor of the following design (Figure 1) was adapted for the purification of indicators to chromatographic purity. With this adaptation, one could siphon off the solvent extract into the boiling flask, while the starting solution could be held back in the extractor. The solvent could be then distilled back into the extractor for repeated extraction by the same solvent. It could thus combine the functions of a separating funnel and soxhlet apparatus and perform the multipurpose extraction described below. Procedures. Extraction by a More Dense Solvent. This apparatus (Figure 1) can be used not only for batch extraction from a solid by liquid, but also for extraction of a solute of interest by a solvent from a non-miscible less dense solution. The siphoning of the more dense solvent can be stopped a t will by turning the stopcock (S) a t right angles to the vapor-lead-tubes (V1 and V2) so that the solvent vapors do not pass through the vapor-lead-tube but exert a back pressure in the siphon tube. This stops the siphoning. The less dense solution can thus be retained in the extractor for renewed extraction, while the more dense extract is transferred to the boiling flask. With the provision of the three-way glass or P T F E stopcock (S) (Figure 2) one could divert the entire vapor through the vapor-lead-tube (Vl) and perform the distribution extraction between the two liquids at the boiling point of the recycling extracting solvent. Thorough mixing takes place by the passage of the vapor. The effective liquid-liquid surface can thus be increased without the provision of a separate mechanical or magnetic stirrer. Turning the stopcock (S)toward the vapor-lead-tube arm (V2) diverts the vapors to the condenser to liquify and return to the extraction chamber. When the chamber has filled to the point before siphoning occurs; the stopcock is turned from V1 gradually toward V2 until the back pressure in the siphon tube due to incoming vapors balances the pressure due to the liquid head in the extraction chamber. The two liquids remain undisturbed and this allows them to separate. When they have separated to a point somewhat above the siphon exit (E), the entire vapor is diverted to (V2) and the condensor. This is continued until siphoning takes place. When siphoning of the extract is almost complete, the stopcock (S)is again turned quickly to the closed position. The back pressure due to the incoming vapor in the siphon tube prevents further siphoning. Another cycle of extraction is then repeated. The three-way T-bore, glass, or P T F E plug of the stopcock (S)has been provided with one passage between V1 and V2. The diameter of the passage is equal to or greater than the diameter of the siphon tube. The two extremity 360
holes of this passage are aligned a t an angle away from the line connecting V1 and V2 such that the minimum distance between the centers of these extremity holes is not less than the diameter of one of the vapor lead-tubes (Figure 2d(ii)). In other words, this passage is formed a t a chord to the circle of the plug a t the level of the vapor lead tubes V1 and V2, and the length of the chord is greater than the diameter of the vapor lead tube. This permits one to adjust the volumes through V1 of the hot vapor and through V2 of the warm condensate, to varying proportions as the plug is turned in the barrel. The temperature of the extraction can thus be adjusted. If however, the channel is symmetrically drilled in the plug around the diameter, the distribution of the vapors to V1 and V2 is always equal. Then the temperature of the extraction cannot be controlled to the desired extent. Extraction with a Less Dense Solvent. In case the partition extraction is to be carried out by an immiscible less dense solvent (e.g., benzene) from an aqueous solution, one fixes the siphon arm (D) to the exit of the siphon (E). Then the siphoning automaticaliy takes place only to the partition surface of the two liquids and little manipulation is necessary. The phase boundary may be adjusted to the height of the siphon arm or vice versa. Proportionating the Vapors between VI and V2. The proportion of vapors led through V2, to the condensor and through V1, into the liquid contained in the extractor, can be easily calculated. If it is assumed that there is no influence of the gravity on the vapors, and the resistance offered by increasing liquid column during extraction has little effect, and because the lead-tubes are of the same diameter, the volume of vapors passing to V1 and V2 will be proportional to the area of the segment of the circular end of the plug-channel open to each of these, respectively. The results of the vapors’ proportion given below were calculated ( 4 ) by drawing a 5-mm diameter channel bored into a 20-mm diameter plug (corresponding approximately to B 19 plug), and working it inside a barrel which bears two outlet-tubes of 8-mm diameter opposite to each other. The length of the channel a t the level of the lead tubes is bigger than the diameter of the lead tubes. Considering the mid-point “h” of the central line of the channel of the barrel to be shifted, respectively, 2 mm and 3 mm away from the mid point “g” (Figure 2d(i))of the line joining the centers of the extremities of opposite tubes, the proportion of the segment areas of the open portions of the plug channel toward tubes V1 and V2 in different positions of the plug was as follows (Table I). The plug has been rotated clockwise for these calculations. In these drawings, the channel of the plug was considered cylindrical, and the end of the tube fused hexagonally to the barrel. This was done to make the calculations of the segment areas easier. The proportion is expected to be correct within 10% of the values obtained in practice. T o check the proportionating, a glass stopper was fabricated. The plug was bored obliquely with a 3-way channel of 6.4-mm diameter. T o the barrel were fused lead-tubes of 8-mm diameter. The barrel and the plug were fine ground. The diameter of the plug a t the level of the Vl-V2 was 19.5 mm. The shift was calculated to be 2.4 mm from the actual measurement of length of the arc and from the reference
ANALYTICAL CHEMISTRY, VOL. 47, NO. 2 , FEBRUARY 1975
Table I. Calculated Proportions of Areas Open to T w o Openings of t h e Proportionating Stopcock Proportion of open areas towards V I and V2, The plug (20mm dia. ) , c h a n n e l (5mm d i a . ) being open towards tube
shift behveen central points "g;h" being
POSF
tion
"1
"2
2mm
1
Fully open just after closed posit ion Fully open just after closed position Fully open Partially open Fully open just before closing Fully open just before closing
Major portion open
20:16
2 3
3mm
Partially open Half open Half open Minor opening
20:6 20: 10 20:11 20:2
Completely closed
20:Nil
Table 11. Proportions of Open Areas to the Two Openings of a Proportionating Stopcock With a plug (dia. 19.5mm)channel (dia. 6 . 4 m m ) and "0-h" shift (2.4mm), particulars of the open channel b e i n g towards Porltlon
1 2
3
4 5
L' 1
Closed, just opening Partially open Mainly open Open fully, just to close Fully open
"2
W
Proportion of outflowing water from V1:Vz
Open fairly
1:189
Open fully,and just closing Partially open Nearly closed
1:4 2:l 23:2
Closed
10:Nil
table ( 4 ) . The proportionating was checked by the volume of outflowing water from the two outlets when the water was fed through a common inlet from an aspirator. The results are given in Table 11. The volume of the vapors going to the condensor, Le., V2, and into the extracting solvent, i.e. V1, are proportional to the respective open segment areas and would deter-
Figure 1. Pictorial view of the extractor
mine the temperature of extraction. A better variation of vapor proportionating can be obtained, with larger "g-h" shift; but it should be consistent with the ease of fabrication and dimensional requirements. However, in actual practice one could control the temperature of extraction f 5 O C , by keeping a convenient thermometer in the extracting solvent directly or by providing a thermometer well in the body of the extraction chamber. A depression has been provided exactly a t half the volume of the extractor up to the siphon tip. This helps in extraction being carried out between equal volumes of the extractant and the extracted liquid. After n extractions, a t a specified temperature, one could determine the concentration of the solute in the extractant and the extracted liquid and calculate the distribution coefficient under specified conditions or else determine the distribution factor from the half-extraction volume as suggested by Beamish et al. (5).
Table 111. Distribution Factors a n d Half-Extraction Volumes Description of t h e solution being extracted
4 x 10-~,11c r e s o l sulfamphthalein aqueous solution (50 cm') 0. OOZbl iodine solution in 0.LV aq. pot. iodide (50 c m 3 )
0.0965M phenol solution in w a t e r (50 cm3)
Conditions of extraction
Temp. of extn. 55"; each extn. was done by 50 c m 3 of chloroform Temp. of extn. 70"; each extn. was done by 50 om3 of carbon t e t r a c h l o r i d e Temp. of extn. 67"; each extn. was done by 50 c m 3 of benzene Temp. of extn. 55"; e a c h extn. w a s done by 50 c m 3 of chloroform
Half e x t n volume,
Refer t o curve
vO. S Ex
(Fig. 3)
0.35 0.14
100 250
X
1.08
32 2 10
u
0.17
1.06
33
P
1.02
34
not shown
Distribution factor, k
Y
V
A N A L Y T I C A L CHEMISTRY, VOL. 4 7 , NO. 2 , FEBRUARY 1975
361
31
2t
__
__.
FRONT
ELEVATION
(0)
YOE ELEVATON
(b)
SECTDN AT X-X
STOP-COCK SHOWING.
*
t
\
il \\ 'P'
3 2
( I l l ITS COMPLETELY CLOSE0 POSITION
Figure 2. Design of the three-way plug (a) front elevation, (b) side view, (c) section of the Plug at X-X. (d) expanded version of (c) with the plug showing. ( i ) the proportionating of the openings in the barrel. and (ii) in completely closed position
T h e progress of extraction of some aqueous solutions by heavier and lighter immiscible solvents is shown in Figure 3. The corresponding distribution factors ( h ) and half-extraction volumes ( V g . j ~ + ) under specified conditions are given in Table 111. I t may be noticed that with the present apparatus the determination of distribution factor over a wide range can be done with the same ease, whereas the Beamish (5 ) apparatus has been recommended mainlv for k values (favorable extraction) greater than unity.
