Analysis of the System Water-Benzene-Methyl Ethyl Ketone By Means of a High Frequency Oscillator PHILIP W. WEST, THOMAS ROBICHAUX, A M I T. S. BURKJULTEK Coates Chemical Laboratory, Louisiana State University, Baton Rouge, La.
A study showed that the system water-benzene-methyl ethyl ketone can be successfully analyzed by means of a high frequency oscillator. Only 25 ml. of sample are required and the analysis takes only 5 minutes of the operator's time. The method is sufficiently accurate for most plant control requirements. The present study provides a useful method of analyzing an important mixture and suggests the applicability of direct measurements on binary and ternary systems through the use of high frequency oscillators.
T
HE high frequency oscillator built and reported by West, Burkhalter, and Broussard (6) for use in chemical analysis has shown real promise, especially in applications to quantitative organic analysis. The instrument consists essentially of two oscillators, the outputs of ~ h i c hare beaten in a mixer tube. The output of this tube in turn contains the difference frequency (beat frequency) of the two, which is then measured by suitable means, Insertion of a chemical system into the tank circuit coil of one of the osc.illatois causes a measurable change of frequency, 15 hich is a function of the composition of the system. Through use of working curves, the instrument is readily adapted to quantitative analyses of binary systems and can he used also for the analysis of certain ternary systems. Construction of high frequency oscillators for analytical applications has been repoited by other workers (1-6). I n these, the principles of operation have been different, and the instruments have been used for titrimetric work or determination of physical properties such it3 dielectric contents. The instrument used in this work was built and used for the broader type of analysis employing direct concentration measurement. In the problem under discussion the mixture benzene-methyl ethyl ketone-water M as selected for investigation because the system is of industrial iniportance and because the beat frequency characterizing each of the components is sufficiently different from the other two to give a system suitable for study by means of the high frequency oscillator. Standard curves \\ere prepared for the change of beat frequency versus cornposition of solution, the constancy of these curves was tested, and their applicability -as checked by performing determinations using them. It was found necessary t o preparr the curves holding the concentration of one of the components constant a t certain specified valuea R hile the other t'ir o components were varied. A series of known concentrations of nater n as selected to give lime values, thus providing for a faniilv of curves, each member of n hich a as for a known constant n ater compoqition. All that was then necessary for an analysis of an unknon n solution was to determine the concentration of watei present, so as to establish the curve to be used. Then 1iy determining the beat frequency change r+tahlishrd by the ternary solution, the composition of the two rt.nixininy components could be read dirrctl! tiom the plot. I n determining the conccntration of the water p i c v n t , it was oliserved that the difference between the beat frequency- change caused when the IT ster was present in the solution and the heat frequency change caused iyhen the water was absent ( A B F C ) M A S a function of the amount of water and independent of the ratio of benzene to methyl ethyl ketone. This led to the preparation of a standard curve of ABFC versus percentage water. The constancy and validity of this curve had then to be proved. The water was removed hy drying the solution over a suitable desiccating agent. The above procedure and the results obtained indicated the
feasibility of using the new instrument in analyses of this and other similar systems. APPARATUS AND MATERIALS
A block diagram of the analyzer is shown in Figure 1. The instrument consists of two separate oscillators which are of the inductance-capacitance type and operate in the high radiofrequency range. The outputs of these two oscillators are fed into a mixer tube where, by proper filtering, the difference of frequency is obtained. This difference (or beat frequency) is the output of the instrument which is measured. The measuring device consists of a cathode ray oscilloscope and an audio-frey e n c y oscillator which is matched to the output frequency of t e instrument. The insertion of a solution in a special cell into the tank coil of the working oscillator causes a change in the characteristics of this oscillator and thus a change in its frequency. The new beat frequency is measured. This beat frequency change (or BFC) is usually proportional to the composition of the system introduced into the coil. The instrument readings can easily be made with a precision of *lo cycles per second and a t i 5 cycles per second with more careful work. REFERENCZ OSCILLATOR
+
WORKING OSCILLATOR
DETECTOR
AMPLIFIER
METER
Figure 1. Block Diagram of Ileterodyne Analyzer
The standard solutions were prepared on a weight percentage basis. The components were: methyl ethyl ketone, Eastman Kodak, distilled over either anhydrous calcium chloride or calcium oxide, boiling range i9.5-80.0" C. ; benzene, Eimer and Amend, C.P. reagent, boiling range i9.5-80.3" C., and Merck reagent grade, boiling range 79.5-81.0" C.; and water, stock distilled. DATA
I n the preparation of the family of curves, preliminary investigation indicated that for the present study, plotting the curves a t intervals of 1.5% water would give sufficient data to determine the usefulness of the proposed scheme of analysis. The accuracy of the scheme is dependent upon the magnitude of the interval between the curves, regardless of the components of the system. Investigation showed that the range from 0 to 5.0% water would sufficiently cover the range of solubility of water in the other two components. Figure 2 includes plots of beat frequency change versus percentage benzene in mixtures of benzene, methyl ethyl ketone,
1625
and water. After the curvtls were draun, check points were run a t 31.6% benzene t o test the accuracy of drawing. This gave the resulta shown in Table I. At benzene concentrations above 3l.6yethe water roniponent of the 5.Oye water series had separated. The results obtained show that the accuracy of the scheme is dependent upon the drawing of the standard curves. This is t o be expected and indicates that the points for the curves should be run rather close together.
3500 3 100.
2700
2 2300 In
6.
Table I.
&) 0.5 2.0 3.5
Comparison of Predicted and Observed Beat Frequency Change Values Observed BFC 2410 2510 2655
BFC from Plot 2400 2500 2640
Difference
Table 11. HIO 0.5 3.5 5.0
Benzene 0.0 10.72 0.0 10.40 20.62 10.24
1/17/50 3055 2865 3210 8010 2800 3100
Beat Frequency Change 3/1/50 4/1/50 3055 3055 .. 2855 3220 3230 3025 3015 2790 2810 3100 3100
-
1100
Reproducibility of Measurements %
1500
+++151010
To check the reproducibility of the curves, and t o ascertain the effects of room temperature and humidity on the characteristics of the instrument, a number of points were rerun on different days when atmospheric conditions were changed. I n the cases cited, the points were run on new samples each time a check was made, From the results shown in Table I1 it was apparent that atmospheric conditions had no significant effect on the instrument and that the curves were easily reproduced, provided that the samples were themostated t o the operating temperature of the working coil (36' C. for the instrument used). Thus, the constancy of the curves throughout normal changes of operating conditions waa proved.
%
i
ANALYTICAL CHEMISTRY
1626
__ Ar.
700
0.5 % 2.0 % v = 3.5 % o = 5.0 S. 0 = b
I
a
I
I
I
H20 H20
H20 H20
I
/
I
I
I
This ensured complete renioval of the adter from the system, As the calcium chloride removed the water, it separate fluid layer was formed below the niethyl ethyl ketone-benzene solution. I n removing a sample for determining the a B F C , care had to be taken not t o include any of this in the sample. The curve of ABFC versus percentage ivater is shown in Figure 3. To prove the reproducibility of the curve, several checks on the values of a B F C ' s were made ovei a period of time. The results shown in Table 111 give satiifactory evidence that t h e
3055 2860 3220 3015 2800 3100
240 2 IO
Attention was then turned to the preparation of the standard curve of ABFC versus percentage water shown in Figure 3. The plot was obtained by determining the bent frequency changes of standard solutions of knorvn M ntvr caoricentration. Then the solutions Mere allovred t o d r j over a de8iccant for approximately 30 minutea and the new heat frequency changes of the dried solutions were determined. By subtracting the latter value from the former, a ABFC was obtained and was plotted against percentage of water originally present. A d r j ing agent was sought which could be obtained readily and cheaply and would have no effect on the system other than t o absorb all the B ater. Calcium chloride was the only efficient desiccant found. In order t o prove that it removed all the water from the solution while not otherwise affecting the mixture, the beat frequency changes of methyl ethyl ketone in benzene were determined, a a t e r was added, and calcium chloride n a s placed in contact with the solutions. -4fter equilibrium tlm reached, the beat frequency changes of these solutions %ere redetermined and found to be the same as those of the original solutions. This indicated that the calcium chloride was removing all the water present and not otherwise affecting the solutions. Effects of varying amounts and types of this reagent were studied and it was observed t h a t calcium chloride dried in an oven a t approximately 110" C. for about 12 hours before use was sufficiently active for its role in the determination. The amount of reagent used varied from 3 to 5 grams for each 50 ml. of solution. Enough was added to the solution t o have lumps remaining on the bottom of the vessel after the absorption waa complete.
I80 7 150 V
W
J*
'120
i m aY
g- 90 60 30
0 2.0 4.0 % WATER ( B Y WEIGHT)
Figure 3.
Table 111. %
Ha0 0.0 0.5 2.0 3.5 5.0
6.0
Beat Frequency Change v s . Per Cent Water
Reproducibility of Working Curve for Water Determinations ABFC 2
1
0
0
40 125 215 260
45 105 210 265
3 0 45 130 210 265
4 0 50 125 190 260
AT..
0 45 125 210 260
V O L U M E 2 3 , N O . 11, N O V E M B E R 1 9 5 1 Table I \ .
4nalyses of K n o w n Samples"
A round BFC RFC H20 Benzene 11th 1 2830 215 3 7 I9 7 76 6 2830 215 3 7 19 7 i6 6 2780 160 2 6 19 6 77 9 2. 2280 130 2 . 0 41.4 n6.6 2280 120 1 9 41.0 57.1 2285 125 2.0 41.3 56.8 3. 2205 105 1.6 42.3 56.1 ?i 2200 100 1.5 42.7 g . 0 57.2p; AIE:R 3 2200 100 1.5 42.7 9.1.8 4 2195 8.5 1.3 42.0 36.7 4. 0.411,/c 1 1 ~ 0 4; 2 . 6 7 , H a 1 2140 50 0.7 43.4 35,Q 2 2135 40 0.5 43.0 33.5 .i7 , 4 73 81E K 3 2135 45 0.6 43.1 j6.3 4 2130 35 0.4 43.2 56.4 .i.O.O5%II20; 40 0% R z 1 2160 10
