Still for Flash or Molecular Distillation MARVIN H. GOLD’ The Visking Corporation, Chicago 38, Ill. The distillate is collected in a receiver directly below the condenser and the residue flows off to the side into another receiver. No provision has been made for continuous recycling. However, as little or no material remains in contact with the hot evaporator, there is little danger in admitting air immediately and pouring the residual distilland back into the dropping funnel for recycling.
GREAT deal of work has been done on the development I n this quest for distillation equipment to operate under high vacuum, the obvious has been somewhat overlooked and relegated to an obscure position. The fact remains that a great many organic substances have a reasonably low boiling point a t pressures produced by the ordinary vacuum pump or water aspirator. However, they may be heat-sensitive to long exposures to the temperatures needed for their distillation in the usual diqtillation apparatus. An ideal approach
A of molecular stills.
CONSTRUCTION OF APPARATUS
The critical part of the apparatus is the capillary ring shown at d in Figure 1. The taper selected for this joint is a f 50/50.
About 5 mm. are cut or ground off the end of the inner member. \Then section L is sealed into position, the bottom flare makes a capillary opening or ring with the bottom of the inner joint, F , and with the face of the outer member of the joint. This step is a critical operation and both capillaries should be of the order of 0.5 mm. An exaggerated illustration of the capillary ring is shown in the upper right-hand corner of Figure 1. The dropping funnel, D, has a volume of 300 ml. It is connected by means of the ground joint, E ( T 14/35) and supported by the pressure equalizer tube, connected a t G and H (18/9 spherical joints). L,which forms the capillary ring, is a section of Pyrex 30 X 100 mm. sealed in a t M with thickness of glass a t the flare about the same as the remainder of the tube. The condenser, B, is 16 X 540 mm. sealed into the head a t S and is equipped for an inlet and outlet for the cooling medium. The evaporator, C, is a Pyrex tube 45 X 450 mm. which has a B 50/50 outer joint sealed to the top. At the bottom it is connected through an annulus to inner joints I and J (7 24/40) for distilland and distillate, respectively. The outer joint, K ( f 24/ 40), leads directly to the vacuum source. The evaporator is heated by a jacket containing sixteen 30-cm. (12-inch) vertical strands of N o . 24 Chrome1 wire. A 360’ thermometer is mounted in contact with the evaporator wall and the temperature is controlled by means of a variable transformer. The joints are all lubricated with a suitable grease. Dow-Corning high vacuum silicone lubricant has been found ade uate, but some slight contamination may always be expected a t &e heated joint, A . OPERATION OF THE STILL
The material to be distilled is placed in D and the system is evacuated through K . When the desired vacuum is reached the distilland is allowed to flow down into the evaporator. As i t reaches the capillary ring it flows around it, making a bed of liquid several millimeters deep. When sufficient hydrostatic head has been developed, the liquid flows down the side of the evaporator in a thin film or a number of fine streams, depending upon the ability of the liquid to wet the glass. Sufficient degassing occurs in one or two passes. Then the evaporator is heated to the desired temperature and the material distilled.
Figure 1
then is to carry out such distillations with a minimum exposure of the distilland in the heated portion of the apparatus. The “falling film” type of apparatus fulfills the above requirements adequately and frequently without going to the extreme of using a high vacuum. The apparatus described here is designed for general purpose use in the organic chemical laboratory. The author makes no claim as to the efficiency or effectiveness as compared to the present commercial stills. However, it is an inexpensive, simple, and compact laboratory apparatus which requires no special skill in its operation. Quackenbush and Steenbock ( I ) have surveyed the subject rather thoroughly. The apparatus used in this laboratory is modeled after some of their suggestions, but the design has been somewhat simplified and all moving parts have been eliminated. The present apparatus uses a capillary ring to spread the distilland over the evaporating surface. In the case of viscous materials the flow is aided by having the heating jacket project above the capillary ring. The distilland then flows down over the heated evaporating surface and flash or molecularly distills (depending upon the pressures used) over to the inner condenser. 1
Figure 2
Present address, Aerojet Engineering Corp., Azusa, Calif.
636
Long-chain aliphatic acid chlorides are notably difficult to distill. They eliminate large volumes of hydrogen chloride and give low yields upon distillation in the ordinary Claisen-type
V O L U M E 2 1 , NO. 5, M A Y 1 9 4 9
637
in the design and construction of this apparatus, and Leonard J. Druker of the Visking Corporation for his numerous tests of the design under laboratory conditions.
apparatus. Using the falling film method described here, compounds such as stearoyl chloride and sebacyl chloride have been rapidly distilled to give clear water-white products at 1 to 5 mm.
LITERATURE CITED ACKNOWLEDGMENT
(1) Quackenbush, F. W., and Steenhock, Harry, IND.ENG. CHEM., ANAL.ED.,15, 468 (1943).
The author gratefully acknowledges the aid of H. S. Martin of the H. S. Martin Glass Company, Evanston, Ill., for assistance
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Vacuum-Jacketed Vapor Dividing Reflux Head W. R. DOTY California Research Corporation, Richmond, Calif.
HE advantages of the vapor dividing head over the more T c o m o n liquid dividinghead have beensummarieed by Collins and Lante ( 1 ) as follows: 1. There is less product leakage at total reflux. 2. The moving partrts are more accessible. 3. The reflux ratios are closer t o the "off-on" ratio of the timer. 4. There is no leakage of reflux to take off during flooding.
In the commercially available head (Glass Engineering Labo- . ratories, Belmont, Calif.) described by Collins and Lantz these advantages are compromised by the fact that the single solenoid operated valve in its ''product-on" position closes the throat of the reflux condenser. As s result of this construction the valve
traps some liquid in the condenser and when the valve changes t o the "product-off" position some of this liquid is transferred t o the product line. I n operation a t high reflux ratios this characteristic causes a reduction in the reflux ratio. The head described below overcomes the above difficulties by employing two separate single-acting valves, one of which closes the reflux condenser while the other opens the product line and vice versa. The liquid reflux, therefore, never comes in contact with the product take-off valve and only saturated vapor passes the latter. The condenser is integral with the head, and access to the valves is provided through two 14/35 standard-taper ground joints. As these are not exposed to appreciable quantities of liquid, they cause no trouble due to sticking or leaking.
TOP VlEH
GLASS VACUUM JACt ilAPOR DIVIDIN(
1 /r N-
'E VIEW
U
re
mamma raper valve sleeve removable for regrinding. redaoing, or cIs&ing valve
D. Bulge to sumort solenoid
E. F. G. H. I.
Prodnot take-off line Thermometer m pyrometer point well Refiux valve detail Reflux aondenser Liquid s e d to allow reflux run-hack while valve LS
dosed
SCALE IN
INCHES
c1 O
FRONT VIEW
re Beat, finely ground L..
-
FIGURE I.
I
E
Vacuum=nd/orlight vapor trLke-off Preseuree quaiisingline with reUux oondenser for oondenilation of light prod uot "spore L. T o atandard deaign produi;t coder and cut taker 8:od/or receiver M. Tubulatia8nS for Silvering &"C I evsouating N. Standard tawr to fit datillal;ion ColUmn P . Erpansioin bellows R . ReRurvab e seat, finely ground J. R.
Figure 2
