Semimicro Molecular Still
'
IRVING A. BREGER, Massachusetts Institute of Technology, Cambridge, Mass.
N THE course of studies dealing with the effects of radioactivity ou organic compounds ($, 4, 7, 8) the quantity of conversion product available for identification has generally been limited to less than 100 mg. Within the past two years, however, advances in the design of cyclotron bombardment chambers (3) have made larger yields possible, so that a t present up to 5 grams may be obtained for identification by chemical and physical means. During a recent study of the effects of deuterons on cyclohexanecarboxylic acid (t),4 ml. of a viscous, yellow, highly Euorescent, nonsaponifiable oil were obtained as one of the major conversion products. Attempts to vacuum-distill 1 ml. of this material under a pressure of 1 mm. of mercury in a jacketed, helical fractionating column were unsuccessful, 8s the liquid decomposed and darkened on continued heating. It seemed advisable, therefore, t o turn t o short-path distillation 8s a means of separating theliquid into its Components. Among the smallscale molecular stillsreportedin theliterature, those designed by Matchett and Levine (6)and Wolluer, Matchett, and Levine (9) require continuous heating of charge. On the other hand, the falling film still designed by Quackenbush and Steenhock (6) operates ou a relatively large scale, as i t depends upon a pump for recycling the charge. In order to eliminate thermal decomposition due t o prolonged heating, a vertical still (Figure l), both ends of which were nearly identical, was designed for use with'falling film flash distillation. Recycling of charge is carried out by rotation of the still about the lead to the vacuum system. Distilland placed in one end is allowed to fall through the still into the other end. After removal of distillate, the still is turned through 180" and the proeess is then repeated. I n this way i t is possible t o separate less Lhau 5 ml. of liquid into a requisite number of fractions
EXPERIMENTAL
The still was used in an effort to separate the components of the nonsaponifiable oil obtained from the bombardment of cyclohexanecarboxylic acid. A 4-gram charge of the oil was subjected to molecular distillation by the procedure described above, and
CONSTRUCTION
The distillation surface, J (Figure 21, is a 28 X 180 mm. section of Pyrex tubing, on the inner surface of which a spiral of 1-mm. platinum wire is closely wound so as to give 10 turns a t a pitch of approximately 15". The ends of the still are identical, with the exception of joint 0. Condensation takes place on 3-mm. Pyrex water condenser G, concentric with the distilling surface and extending through both ends of the still. A small cup, Q (Figure 3), on each end of the condenser serves to deflect condensate out of the still proper and into collecting bulb R or D. Nondistilled liquid is colleoted in trough L, from which i t can be coucentrated into bulb P or A far redistillation at a higher temperature. A Nichrome beating element, If,current to whichis regulated by a variable transformer, surrounds the distilling surface, J , and enables operation a t different temperatures. Temperature measurement is by means of a copperconstantan thermocouple, one junction of which is inserted between the still m d heating jacket. Pressure is measured by a Mc gage connected t o the apparatus &mm. tube F. T h e . entire systt evacuated tbroug h 28-mm. tube 1. Semimicro Moleeul, dry ice-acetone trap, mercury d Still sion pump, and Hyvrtc fore-pump. All dimensions in mm,
980
'igure 2. Semimioro M o l e o u l a r tilII in Position for Sample Intro-
duction a n d Degassing
V O L U M E 20, NO. 10, O C T O B E R 1 9 4 8
981
ny . Original Oil Fraction 1 Fraction 2 Fraction 3 Residue Dieyelohexyl ketone (1)
1.4985 1.4111 1.4822 1.4875 1.5018
1.4851/14'
dZo n.g8o
0.035 0.943 0.98T O:'%
Distillation Temperature, 0
c.
(;I 50 ..,...
......
Figure 3. Close-Up of Distillate Removal Cup
the fractions listed in Table I were collected. The first fraction recorded was low boiling and escaped from the still into the dry ice-acetone trap, from which i t wm recoyvered. As shown in Table I, the physical properties of fractions 2 and 3 indicated portion of the oil was probably dicyclohexyl
Figure 5. Infrared Spectra of Fraetions Obtained by Molecular Distillation of Nonsaponifiahle Oil From beuteron Bombardment of Cyolohexaneear. borylie Acid
T o obtain further information regarding the distilled material each fraction was submitted for infrared analysis, using a PerkinElmer instrument. The spectra. thus ohtained.(Figure 5) showed strong absorption in the carbonyl region (1700 to 1750 cm.-') and offered further evidence for dicyclohexyl ketone. Because all the spectra were obtained under the same conditions using a k e d cell, variations of the fractions in the regions of 1080, 1140, 1350, and 1750 cm-1 indicated that this still is capable of separating and concentrating the components of a heavy oil. CONCLUSIONS
A semimicro molecular still has been designed which employe the falling film principle t o eliminate continuous heating of the samp le. and makes possible recycling of the sample without use o f a pbump. By means of an experimental run i t has been demonstr& :d that this apparatus can be used for the fractionation of .. small quwtities of heat-sensitive oils a t low temperatures. ~~
ACKNOWLEDGMENT
Sincere appreciation is extended to Clark Goodman of the Massachusetts Institute of Technology, physics department, for his suggestions regarding this work. Appreciation is also extended t o Virginia L. Burton for rtssistance with the experimental work, and to Earle C. Farmer for the infrared curves. The assistance of Walter Ennis, Massachusetts Institute of Technology, physics department glass blower, is acknowledged. LITERATURE CITED
emimiero Molecular ,tanding Position
Still in
(1) Anderson, L. C., and Gooding, C. M.. J . Am. Chm.SOC., 57,999 (1935). ('2) Breger. I. A,, and Burton, Y. L., Ibid.. 68,1639 (1946). (3) Honig. R. E., Rea. Sci. Inslmments, 18.389 (1947)
ANALYTICAL CHEMISTRY
982 (4) Honig, R. E., Science, 104,27 (1946).
( 6 ) Matchett, J. R., and Levine, J., IND.ENQ.CHEM.,ANAL.ED.,15, 296 (1943). (6)Quackenbush, F.W., and Steenbock, H., Zbid., 15,468 (1943). ( 7 ) Sheppard, C. W., and Burton, V. L., J . Am. Chem. Soc., 68,1636 (1946). (8) Sheppard, C. W., and Whitehead, W. L., Bull. Am. Assoc. PB trolevrn Geol., 30,32 (1946).
H. J., Matchett, J. R., end Levine, J., IND. ENO. CHEM.,ANAL.ED., 16,629(1944).
(9) Wollner,
RECEIVEDOctober 6, 1947. Contribution from American Petroleum Institute Research Projeot 43C loosted s t *he Massachusetts Institute o! Technology; W. L. Whitehead, duwtor; Clark Goodman, physical director.
Simple Electronic Reflux Ratio Timer HERBERT E. FISHER Shawinigan Chemicals, L t d . , Shawinigan Fulls, Quebec, Canadn
N THE course of the past few years, the increasing popularity
this time, analogous to Ry,). As the negative voltage, stored b? CI, on the control grid of VI biases the beam power section to cutoff, Ry1 drops out and remains open until the charge on C1 has leaked off through R1R2. The time interval during which Ryl is energized is controlled by the setting of R1 and, with the constants given, ma>-be varied over a period of 4 to 60 seconds When the negative charge has leaked off the control grid of VL, Ryl pulls in once more and the cycle is repeated. Vl thus delivers a repetitive pulse (through contacts Sl of Ry,) at a constant, controllable rate. The action of V2, triggered by the pulse from VI,is strictly analo gous, except that theoutput circuit doesnot pulse The constants given in theschematic diagram re sult in a deliverv period of 1to 5 seconds, variable b r Rs. VI and Vg are interlocked through contacts St of Ry,to prevent Vi from pulsing unless V2 has completed its timing cycle. The output of ITp(through Ry2)is delivered to X1X2,an ordinary duplex receptacle with one of the connecting straps divided into two, which enables the timer to operate directly a reflux dividing head activated by two alternately energized magnets. The more common type of single solenoid head may be activated from rece tacle Xt. 1 The single receptacle, which may be connected a t will to either timing interval by the single-pole double-throw sxitch, 8 7 , serves the 3 purpose of initial calibration, or accurate resetting of controls R1 and R3 when an electric stop AC clock is connected to it. Switch Sg may be opened Figure 1. Schematic Diagram to de-energize the output circuit without shutting off the timer. Pilot lights P1 and Pz indiR t . 3-meeohm carbon DO tentiometer Ruz Double-vole double-throw re_ (SsSd. . R;. 250,050-ohm, O.5-6att resistor lay, 1000- 60 4000-ohm coil cate which of the output circuits is connected, VI Vn. 117 L7/M7-GT bubes RI. 1-megohm carbon potentiometer and map be used for stopwatch timing in CaliR4. 50,000-ohm, 0.5-watt resistor Sa,’Sa. Single-pole single-throw toggle brating or checking the device. CI. 4-mfd. paper condenser, 400-volt switches
of magnetically operated heads for distilling columns (Oldershaw, Du Pont, Piros-Glover) has made a flexible, low-cost timer desirable. Earlier controls based on single synchronous clock motors were reliable and cheap, but suffered from the restrictions imposed by simple proportioning of a fixed total period. More elaborate double synchronous clock motors eliminated this difficulty, but required considerable maintenance, usually had a fixed “on” period, and rwre relatively expensive.
3,
Ci. 2 mfd. paper Condenser, 400-volt CI, Cd. 8-mfd. electrolytic condensers, 250volt R y l (5152). Double-pole double-throw relay, 1000- to 4000-ohm coil
S I . Single-pole double-throw toggle switch XIXZ. Duplex receptacle (see text) XI. Single receptacle Pi, P2. 110-volt Ss pllot light@
Recently Thacker and \17alker ( 4 ) described ail electronic timer which met most of the requirements, but had the disadvantage of rather specialized, difficultly obtainable parts. The two-tube electronic timer described below is reliable and flexible and is easily constructed a t very low cost (under $20). The circuit is based on the well-known condenser discharge principle, which has been used, in various forms, for pump control ( 1 , S),spectrographic exposure control (a), and time delay relays. I t consists of two interlocked timing units, one for “off’ or reflux timing, the other for “on” or delivery timing. Both periods may be varied over a wide range by selection of proper resistance and capacitance values. The constants given in Figure 1 serve only as a guide, and may be changed to suit the application of the device. The operation of the timer may be easily understood by considering separately the action of each tube. Khen switch S6 is closed, tube Vl warms up and the beam power section acts as a self-rectifying amplifier, drawing current through relay Ryl and closing its contacts, SI and Sz. The diode rectifier section of VI then applies a negative bias to the control grid of VI beam tetrode through contacts S2 of Ryl and Sa of Ry2 (the latter has closed by
The timer, as described above. has been in u ~ e in the Research Laboratories ’ of Shawinigan Chemicals for the past year, much of the time on 24-hour, 5.5-day-week service. No maintenance or tube replacement has been required during this period. Constancy of timing over 24-hour periods has been better than 1%. ACKNOWLEDGMENTS
The author wishes to acknowledge gratefully the encouragement of K. G. Blaikie, director of the Research Laboratories, Shawinigan Chemicals, Ltd., and to thank Shawinigan Chemicals, r,td., for permission to publish this work. LITERATURE CITED (1, Bechthold, I. C.. ISD. ESG. CHEM., ANAL.ED.,14,429(1942) 12) Gentr5, C. H.R., Newson, D., and Rushman, D. F., J . SOC.C h m
Ind.,66,323 (1947). (3) Taylor, J. I(.and Reid, J. G., IND.ENGCHEM.,ANAL.ED.,18
79 (1946). (4) Thacker. G. O.,and Walker. B. P., J. SOC.Chem. I d . , 65 2.59 (1946).
RECEIYED January 28, 1948
