AIDS FOR THE ANALYST ~
High Vacuum Laboratory
Still for the Organic
Evaporative
Harold E. Zaugg and John Shavel, Jr.], Chicago, 111.
Abbott Laboratories, North
great influence of the surface properties of a liquid on its Tevaporative behavior has been emphasized by Hickman HE
($, 5 ) . Many an organic chemist, attempting to distill a crude plilegmatic liquid in a pot-type molecular still only to have it i)ump and foul the condenser, has been the victim of a torpid surface. l17ith the advent of the falling-film and centrifugal molecular stills ( 4 ) , the chemist has won a measure of deliverance irom the plague of torpidity, hut with even the simplest stills ( 9 ) , the worker, requiring distillation of less than 50 grams of material, must either use carrier oils or face serious mechanical loss of product. Unfortunately, the semimicro falling-film molecular still developed by Brrgrr (2) is not readily adaptable to use o n n much larger scale.
J
E
R
hb--,
Inside A is a rotating barrel, B , a glass cylinder (155 mm. long, 70 mm. in outside diameter) closed off square a t one end and having a constricted opening a t the other. The opening, L (35 mm. in diameter), is formed by flanging the end of the cylinder in and back and a heavy bead is fused on the lip of the aperture The middle (60 to 65 mm.) of B is blown out to an external diameter of 74 mm. This expansion provides a shallow well for the thermocouple and promotes accumulation of the last portion of distilland a t a point where it will be heated most efficiently. The square shoulder of the closed end of B should also be blown out to an external diameter of 72 to 73 mm. in order to facilitate cementing of B to a spindle, E . E consists of a solid brass cylindrical shaft (64 nim. long, 19.5 mm. in outside diameter) attached on center to a shallow cylindrical cup (15 mm. wide, 75.5 nim. in outside diameter, 73.5 mm. in inside diameter), in which B is placed and fastened with litharge cement deposited in the annular space, D . E is secured to a bearing assembly by insertion into and tightening of a brass screw chuck, &’ (20 mm. in inside diameter), which extends about 35 to 37 mm. out from the face of the bearing, S,to v,-hich it is fastened. Also in one piece with the chuck but on the other side of the bearing is a split brass block, P , 31 to 32 mm. square and extending about 40 mm. back of the bearing face. The end of P is cut out to accommodate an Alnico magnet, 0 (51 mni. long and 19 mm. square in cross-section, obtained from the Arthur H. Thomas Co., West Washington Square, Philadelphia 5, Pa.). A seescrew piercing P transversely to the split is tightened to hold the magnet securely in place. The chuck and magnet assembly, 0, P, M , is sweated into a double-row ball bearing, Ai (Fafnir, No. 5206W-C1, 62 nim. in outside diameter, 30.5 mm. in inside diameter, and 23.5 nim. wide). Before use, this bearing must be laped to the point where it will turn easily with only a light oil such as di-n-butyl phthalate or di-%ethyl heup1 phthalate (Octoil) as a lubricant.
-I --T
F
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I
l?
Figure 1
The piebent papei desciilws an evaporative still, which, although more elaborate than the pot still, is less complex than the usual moving thin-film still and is suitable for distillation of quantities in the 5 to 50-gram rang?. I t has given satisfactor) hervice f o i 2 years xith a variety of crude organic liquids. In principle, it resembles the equilibrium still described by Hickman and Trevoy ( 6 ) , in that both involve the use of a barrrl rotating on a ho1i7ontal axis nith an external magnrtic drive.
J
I
APPARATUS
Figure 2
Of the two modifications of the “rotating barrel” still illustrated in Figures 1 and 2, the former is the more generally useful. I t consists of an outer cylindrical glass jacket, A (about 270 nim. long, 84 mm. in outPide diameter, and 80 mm. in inside diameter), open a t one end. The open end is flanged out to a diameter of 112 to 115 mm., T , and ground to planarity. Near the top of the flanged end of A is sealed an outlet, C (80 to 90 mm. long, 28 nim. in outside diameter, 21 mm. in inside diameter), terminated by the ball half of a standard (35,’25) spherical joint to facilitate connection to the vacuum system. The bottom of jacket A is ahaped in the form of a trough, F , I--shaped in cross section and sloping downward into a distillate delivery tube, G, consisting of a standard-taper (19/38) ground-glass joint with a drip-tip 25 nini. in length leading into a fraction cutter, H. S e a r the top of the closed hemispherical end of A is sealed the socket of a standard (18/9) ball joint, J . A4thermocouple well, K (5 mm. in outside diameter, extending 180 mm. from the ground surfaces of the joint), is attached by means of a ring seal to the ball half of the joint. At a point some 20 mm. from the closed end of K , the tube is bent to parallel the surface of B when in operating pouition ~~
1
Present address, Warner-Cliilcott R e s m i c h Laboratories N e w York 11,
N Y
Bearing S is anchored to a stepped cylindrical brass housing, R. The first step of this housing consists of a ground flange (111 to 113 mni. in outside diameter, 80 mm. in inside diamet,er) propoi’tioned to match the ground-glass flange, T . il brass ring, S (80 mm. in outside diameter, 59 mm. in inside diameter), recesved inside this flange, overlaps N . Fastening S to R by means of four screws holds the bearing securely in its recess, which in turn forms the second step (82 mm. in outside diameter, 62 mm. in inside diameter) of the housing. The outside of t’his step also provides a convenient location on which to wind several turns of a removable copper coil, &, to be used whenever the housing must be cooled. The last step (62.5 mm. in outside diameter, 57.5 mm. in inside diameter) of the housing accommodates the magnet, 0, and, when in operation, serves as a convenient’ point for clamping R in place (see Figure 3). For obvious reasons the internal magnet, 0 . should be positioned as close as possible to the inside wall of I< without touching it. The wall itself (ea. 2.5 mm. thick) should not be made too thick a t this point. The entire movable assemb1)is rotated by means of an external magnet, 0, identical with thc one inside. This magnet is clamped by any suitable means to a variable speed shaft (50 to 100 r.p.m.) and, during operntion, is placed 3~ close as possible to the rnd of R.
1999
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ANALYTICAL CHEMISTRY
In the modification of the still shown in Firrure 2, Darts B. C ~~~
~~
~~~~
~
o i a standard (50/30) &heri&l joint is sealed. The socket, U,of this joint is built into a oneniece condenser, V-fraction cutter.
be adjusted to a reflux Gosition if by distilland.
% is accidentally contamidated
OPERATION
Kodak Co.) with 0;toil-S as the'working fluid. A cold trap is located between the diffusion pump and the still. All tubing linking the various units of the assembly is of the size of outlet C (28 mm. in outside diameter, 24 mm. in inside diameter) and length and number of bends in these connections have been kept to a minimum. Vacuum-measuring devices include Pirani gages between the forepump and the diffusion pump (to measure f o r e pressure) and between the cold trap and the still (to measnre working pressure) in addition to s McLeod gage (reading to 10mm.) tapped into the system between the cold trap and the diffusion pump.
200' t o 260' C. a t a rate of 23 grams per hour (MeLeod gage pressure, 0.3 to 0.5 micron; barrel speed, 80 to 90 r.p.m.). In the authors' experience, distillation of coconut oil in the laboratory Mnch centrifugal molecular still (1)takes place in the mnge 200" to 250". To be snre, the distilland in the centrifugal still is subjected to heat only during the time i t is in contact with the rotor, whereas in the present design heating is continuous. This difference is obviously of great significance in the distillation of large quantities of material, but, except for extremely labile substances, becomes less important as the batch size is reduced and the time required for a distillation is diminished. Indeed, no perceptible darkening of the distilland was encountered during a %hour distillation of cooonut oil. Table I. Distillation of Solution" of 30 Mole % Di-2-ethylhexyl P h t h a l a t e in Di-tethylhexyl Sebacate in A p p a r a t u s of Figure l6 Fraction 1
2 3 4d
Weight, Grams
Time for Collection. Min.
EHPC,
Mole %
ma:
10.37 8.00 8.87 9.11
1.4681 1.4615 1.4535 1.4496
57.7
43 44 65
59.5 15.1 2.5
n
'(I
4.25 4.13 4.00
1.21 1.19
1.12
" 36.35 grams, n2i 1.4584. b Distilland temperature remained oonstant at 140°' working pressure (MoLeod) varied between 0.2 and 0.3 mioron; barrel'rotation. 80 to YO '.P.'". . 0 Computed from Trevoy's (10) table. d Residue. Weight calculated by difference
Figure 3 The assembly of the still itseli, with the heating lamps and aluminum shields removed, is shown in Figure 3. The outer jacket. A , is fixed horizontally by clamping a t C. Thebarrelunit.
E ~Cia&p& Z ita smallest Zep. For distilfation tekperatu& below 150", the u8e of the cooling mil is unnecessary. After the thermocouple well, K,and fraction cutter, € (with I , receivers a t I) have been attached to A , rotation of the external magnet is begun, the fore-pump is started and, 8.8 the still is evacuated, B is centered inside A by proper relative positioning of the two ground flanges. Next, three infrared lamps are clamped radially around A , within 5 mm. of its outside surface, and directed toward the center of B . Because they emit very little light, 250-watt Ruby glass infrared lamps manufactured by the Penetmy Corp., Toledo 5, Ohio, are preferred. Their adaptability to the present task is
For more heat-sensitive substances the still of Figure 2 can be employed. Here, with the approach to conditions present in true molecular still where the distance between the distilling surface and the condenser is comparable to the molecular mean free path of the vapor (b), somewhat lower distillation temperatures are attainable, but usually a t the expense of distillation rate; with every substance distilled to date in the apparatus of Figure 2, the capacity of the condenser, V , is invariably exceeded whenever distillation approaches the rates exemplified in Tables I and 11. Another obvious disadvantage of the still of Figure 2 is the absence of means for measuring the temperature of the distilland, an omission that can be eliminated only a t the sacrifice of considerable simplicity. Table 11. Distillation of Solution' of 50 Mole % Di-2-ethylhexyl Phthalate in Di-2-ethylhexyl Sehacate in the Apparatus of Figure 1' Fraotion
Weight. Grams
1
10.92 8.90 9.60 8.90
2 3 4d
EHP', Mole n ;'
1.4753 1.4107 1.4618 1.4509
70
Time for Distilland Coll~otioo. Temp. Min. SC.
76.6
44
65.7
39
40.2 6.8
77
130-140 140-142 142
1.7
3.96 3.89 3.24
" 1.14 1.12 0.93
38.32 grama, nn< 1.4653. 6
Norking p~essure(McLeod) varied between 0.2 and 0.5 micron: barrel
with it and d t h each other. The top limps me b&h contrded by a single variable transformer, while the bottom one is regulated
and dn b o h sides of the heit lamps. Usually, spec% cooling of the condensing surface of A is unnecessary. If desired, a properly directed fan or blast of air can be employed for this purpose. PERmRMANCE
The highest temperature encountered to date in the utilkation
of the still of Figure 1 has been in the distillation of coconut oil its a test substance. This material could be distilled in the range
Ootoil) and di-2-ethylhexyl sebacate (EHS, Octoil-S) has been studied by Trevoy (IO) as a possible test system for evaluating molecular still efficiencies, 30 and 50 mole % solutions of di-2ethylhexyl phthalate in di-Zethylhexyl sebacate were distilled in the apparatus of Figure 1, with the results summariaed in Tables I and 11. The values for the effective relative volatility ('a)were calculated assuming that the memured mole Yo di-%ethylhexyl phthalate of each fraction represented the composition of a drop of the distillate a t the half-way point in each fraction. The composition of the distilland was then computed for this
V O L U M E 26, NO. 1 2 , D E C E M B E R 1 9 5 4
2001
point and the relative volatility was derived from the expression,
'
'a = where y is the mole fraction of di-2-ethylhexyl 4 1 - Y)' phthalate in the vapor and z is the mole fraction of di-2-ethylhexyl phthalate in the distilland. The calculated plate efficiency, n, is entered in the last column of the tables and was derived from the relationship n = ' C Y / C Y where CY = 3.47, the value determined by Hickman and Trevoy (6, 10) for the relative volatility of a mixture of di-2-ethylhexyl phthalate and di-2-ethylhexyl sebacate projertively distilled in a unit act a t 140' C. The observed values for n , with one exception, are all slightly greater than 1. This divprgence from unity probably represents a measure of slightly prolonged vapor-liquid contact brought about by the constricted opening in the barrel through which the vapors must pass to the condenser. ACKNOW LEDGMEKT
The authors are greatly indebted to C. F. Plummer for technical assistance, to J. H. Beebe and Paul Dolken for aid in the design of metal parts, to Boyer Clauson for the mechanical drawings, and to Richard Crook and Frank Rejc for the photographic work. LITERATURE CITED
Biehler, R. M., Hickman, K. C. D., and Perry, E. S., ANAL. CHEM.,21, 638 (1949). Breger, I. A., Ibid., 20, 980 (1948). Gilson, A. R., Chemistry & I n d u s t r y , 1950, 739. Hickman, K. C. D., Chem. Revs., 34, 51 (1944). Hickman, K. C. D., Znd. E n g . Chem., 44, 1892 (1952). Hickman, K. C. D., and Trevoy, D. J., Ibid., 44, 1903 (1952). Matchett, J. R., and Levine, J., IND.EXG.CHEM.,ANAL.ED., 15, 296 (1943).
Smith, C. C., and Matalon, R., Nature, 165, 613 (1950). Taylor. J. K.. J. Research AVuTatZ.Bur. Standards, 37, 173 (1946). Trevoy, D. J., I n d . E n g . Chem., 44, 1888 (1952).
cluding a cooling coil and bath, thermostatic bath, and viscometer and bath. Ruh, Conklin, and Curran (3) used a threebath arrangement with a bimetallic regulator. Haul and Theron (2) achieved good regulation using a bath surrounded by a cold reservoir with a heater regulated by a platinum resistance controller. The Zeitfuchs bath has only one cold reservoir, and regulation is achieved by intermittent circulation of the bath liquid through this cold reservoir. Only a single controller is required, and the bath can be cooled to the desired temperature rapidly. A schematic drawing of the bath is shown in Figure 1. The bath chamber is a 2.5-gallon, clear Dewar flask (American Thermos Bottle Co., Norwich, Conn., Catalog KO. 63403) insulated a t the top, bottom and partially around the circumference, with space left to view the viscometer tubes. In the bath chamber are a small centrifugal pump and stirrer on a common shaft driven by an induction-type electric motor mounted above the bath chamber. The pump circulates the bath liquid through a cooling coil immersed in an adjacent 1gallon Dewar flask which is filled with an acetone-carbon dioxide coolant. The pump also helps stir the bath. Regulation is achieved by a bimetallic regulator which, operating through a relay, opens and closes a solenoid valve in the line through which the bath liquid goes to the cooling coil. A throttling valve in this line permits rapid cooling of the bath. To operate the viscosity bath, carbon dioxide is placed in the coolant flask, and the throttling valve is opened fully. As the bath approaches the desired temperature the throttling valve is closed until only a small amount of liquid is being circulated and the final adjustment of the regulator is made. -4bout 30 minutes is required to cool the bath from room temperature to -55" C. The acetone in the viscosity bath must be kept reasonably dry or ice will collect in the solenoid valve and prevent it from closing completely. Normally rhanging the acetone weekly is sufficient to prevent this from happening. PERFORMANCE OF BATH
Zeitfuchs l o w Temperature Viscosity Bath Julian F. Johnson, California Research Corp., Richmond, Calif.
4
temperature viscosity bath has been in use for a number of years in these laboratories. It has been very satisfactory because of its simplicity, accuracy, small space requirements, and low initial cost. Similar baths have been described in the literature, but the Zeitfuchs bath is somewhat simpler. The bath of Baldeschwieler and Wlcox ( 1 ) has three parts, in-
-
LOW
The temperature of the bath is measured by a Speedomax recording resistance thermometer based on that designed by Stull (4). The temperature cycles about +0.02" to 0.03' C. about the mean value in a symmetrical manner. The mean temperature stays constant to &0.0lo to 0.02" C. for an hour or longer. The regulator is susceptible to thermal and mechanical shock, and the temperature should be checked after viscometers are inserted or removed. As there is a temperature gradient in the top 2 inches of the bath, viscometers must be located a t least 2 inches below the surface. The simple regulator is used because it is easily adjustable and gives satisfactory regulation. LITERATURE CITED
(1) Baldeschwieler. E. L., and Wilcox, L. Z., IND.ENO.CHEY.,ASAL.
ED.,11,221 (1939). (2) Haul, R. -4.W., arid Theron, J . J., J . Sci. Instr., 28, 236 (1951). (3) Ruh. E. L., Conklin. G. E., and Curran, ,J. E., IND.Exo. CHmi., SAL. ED..17, 451 (1945). ( 4 ) Stull, D. R., Ibid., 18,234 (1946).
Ultraviolet Irradiation for Air-Interrupted Spark Sources J. T. Rozsa and N. A. Grondin, National Spectrographic laboratories, Inc., L
Cleveland, Ohio
ultraviolet irradiation of interrupter gaps [Balz, G., KaiT ser, H., and Koch, P. H., Acta, 2,92-8 (1941)] is prevalent for spectrographic alternating current spark light HE
Spectrochim.
ACETONE COz BATH
il
w 2 k G A L . CLEAR DEWAR
Schematic Drawing of Bath
sources of the feussner type. Simpson [Simpson, S. F., J . O p t . SOC. Amer., 35, 40-2 (1945)l has demonstrated that the synchronization of small induction motors with applied voltage is often difficult because of their sensitivity to phase shifting and periodicity and that irradiation of the interrupted gap improves the uniformity of breakdown time of this gap. No such reasoning would be applicable to the air-interrupted type of inter-
