Charles R. Begeman
General Motors Research Laboratories Warren, Michigan
Simple Evaporator for Heat Sensitive Compounds
The need for complete removal of eluting solvents from labile chromatographic fractions led to the fabrication of the simple evaporation apparatus here described. Essentially it is a device for: increasing the available liquid surface from which volatile molecules can escape, increasing the flow of heat to the evaporating surface, and providing for operation a t a reduced pressure to facilitate the vaporization of solvents a t relatively low temperatures. I n these respects it is similar to flask rotating devices recently described in the literature1-6 or available commercially. The novel features of this device are the use of an inexpensive windshield-wiper motor to provide an oscillatory rotational force, and the e l i i n a tion of rotating vacuum seals. The device is inherently explosion-proof because it operates from the laboratory vacuum system. The apparatus is illustrated in the photograph. The automohile-type windshield-wiper motor is mounted on a '/,-in. thick steel plate using the motor mounting holes provided. A '/s-in. thick brass gear having 80 teeth (pitch diameter 2'/2 in.) is mounted on a stub shaft attached to the steel plate directly opposite the end of the motor shaft. A pin in the hub of this gear connects with the crank supplied on the end of the motor shaft. A second gear, which has 32 teeth, is attached to a 6-in. long, S/8-in.diameter stainless steel tube a t a point approximately l'/z in. from the upper end. This tube rotates in 11/%in. long bronze bearing which is pressed into the steel plate. A small collar on the tube a t the lower end of the bearing keeps the tube in position. An early version used a simple mhber stopper a t the lower end of the tube for attaching Erlenmeyer flasks. In later units the rubber stopper was replaced by a stainless steel 24/40 standard taper male joint soldered on the tube. A '/.-in. wide groove located 3/,6 in. from the larger end of the standard taper is machined to a diameter of a/r in. for a size 14 O-ring. The upper end of the metal tube is connected through the usual dry ice
or liquid air traps to a vacuum pump via elastic tubing. Rubber or plastic tubing permit flask rotation of 300' or more virtually without hindrance. In some operations the use of a trap immediately above the evaporation flask has been helpful, especially for liquids that froth excessively. A glass trap which rotates with the flask is shown also in the photograph. The vacuum motor shaft operates through a sector of approximately 120". Using the gears described, the resultant flask rotation is 300°, which has proved to be very satisfactory for distributing a film of liquid on the surface of the evaporation flask.
A 6-in. long by '/%-in.diameter steel rod is fastened to the mounting plate a t a right angle to the axis of rotation and parallel to a line connecting the gear centers. This arrangement allows the entire assembly to be supported in a regular laboratory rod clamp and permits selecting or changing the axis of rotation (with respect to horizontal) a t any time. This feature has proved to be especially convenient. The application of heat to the flask, if required, is accomplished in the usual manner: i.e., by rotatiug the flask in a water bath or by means of a heat lamp. The apparatus can be constructed a t a very nominal cost since no rotating seal is used. For the rubber stopper model no precision machining is required. The vacuum motor operates directly off the laboratory vacuum line. The largest single material item is the vacuum motor which can be purchased for approximately $8.75.
CRAIG,L. C., GREGORY, J. D., AND HAUBMANN, W., Anal. Chem., 22,1462 (1950). PARTRIDGE, S. M., J . S& Instr., 28, 28 (1951). VOLK,E., Anal. Chrm.,27, 1207 (1955). ' GREEF,F.,AND LARSEN,C., J. CAEM.EDUC.,33, 556 (1956). ARNETT. E. A,. J. CHEM.EDUC..37.247 (1960).
+
+
+
Volume 40, Number 8, August 1963
/
427
