Vacuum and infra-red radiation solvent evaporation

#This invention relates to solvent evaporators, and in particular to laboratory scale rotary evaporators.

#Current laboratory practice makes use of the popularly named "rotary evaporator" to either concentrate or remove solvents such as alcohol, acetone, water, and so on, from various samples. The solvents to be concentrated or removed are typically placed in a pear shaped PYREX (a registered trademark of Corning Glass Works) flask which is then connected to a motor which will cause the flask to be rotated. Means are provided for connecting the flask to a source of vacuum which usually includes a means for condensing the evaporating solvents as well as a vacuum pump, and the flask is usually placed in a water bath which can be temperature controlled with thermostatically controlled heating. Under these conditions of flask rotation and vacuum the solvents are evaporated efficiently while frothing and bumping that often accompanies a vacuum distillation is suppressed to various degrees. Both batch and continuous process rotary evaporations of this type are described in U.S. Pat. No. 2,797,747 and U.S. Pat. No. 2,865,445.

#While the above mentioned devices have proven to be generally satisfactory, there are problems inherent to their design which has been addressed by U.S. Pat. Nos. 4,790,911 and 4,913,777. In these two patents a solvent evaporator is disclosed which does away with the necessity for rotating the solvent flask by placing a magnetically driven cylinder within the flask. A rotatable magnet exterior to the flask causes the cylinder within the flask to rotate in synchrony, thereby developing a thin solvent film on both the exterior and interior of the cylinder, providing for efficient solvent evaporation, and frothing and bumping control, when a vacuum and thermostatically controlled heating is applied to the solvent container. A conventional heated water bath can be used to expedite solvent evaporation, or, since the solvent container is stationary, hot plates or heating mantles can be used as a source of thermostatically controlled heating. While the above described stationary evaporator can eliminate the cumbersome and expensive water bath heating methods usually employed, ordinary conductive heaters provide slower evaporation rates in comparison to the standard water bath. To overcome this, the instant invention makes use of infra-red heating to provide comparable solvent removal efficiencies to water bath procedures without the use of a water bath, while at the same time maintaining the simplicity of operation of the stationary solvent evaporator.

#FIG. 1 is a partially sectional view of a first version of the solvent evaporator, showing the solvent container in tilted position.

#FIG. 1A is a perspective view of the solvent evaporator of FIG. 1, with the solvent container shown in phantom and the control box shown partially broken away to show one version of the product temperature display and control.

#FIG. 2 is a partially sectional view of a second version of the solvent evaporator, showing a solvent container having a well area in place adjacent the base of the container.

#Referring now to the drawings wherein like structures having the same function are referred to with like numerals, in FIG. 1 a version of the solvent evaporator 10 in accordance with the present invention is shown. A control box 12, which can be made out of a variety of materials and in this example steel being the preferred material, houses a motor 14, the motor having a circular shaped 8 pole ceramic magnet 16 attached to it. A laterally extending portion of the control box contains an infra-red radiation emitting heater 18. The heater 18 contains metal resistance elements 20 encased in a ceramic blanket 21. During operation infra-red radiation 82 is efficiently transmitted through a flat VYCOR (a registered trademark of Corning Glass Works) plate 22. The infra-red heater is conventional, and well known to the art. For the purpose of laboratory scale evaporations, e.g. 50 ml. to 1 liter, maximum power is 600 watts at 110 volts, A.C. Maximum watts/square inch is 40, and the infra-red wavelength range in microns is 2.6 to 6.0. Infra-red heaters of this type are available from Manostat Corporation, 518 Eighth Ave., N.Y., N.Y. 10018. Controls within the control box include an on/off switch 26 for the entire apparatus, an analog indicator knob 24 to activate the motor 14 and regulate the rotation of the first magnet 16, and a heat knob 28 to turn on the infra-red heater 18 and to set a high limit temperature on the LED temperature diplay/set point panel 86. These electrical and electronic switches and controls are all interconnected electrically in a conventional manner as shown in the drawings, and all are conventional and well known to the art.

#The flat upper surface of the laterally extending portion of the control box has a stand 30 for supporting a solvent container. The stand provides a slope of approximately 15 degrees from the horizontal surface of the VYCOR top plate 22 on the infra-red heater, from that portion of the stand which is nearest to the first magnet 16, to the end of the stand 30 which is farthest away from this magnet, the full length of the stand being directly over the VYCOR top plate.

#Solvent container 32 is placed directly on the stand 30. The embodiment of the solvent container 32 shown in FIGS. 1 and 4 is a cylindrical PYREX container having a substantially flat, fully closed base portion and an open top. Prior to being placed on the stand 30, the container 32 has the cylinder 36 together with second magnet 38 placed within it, and then the solvent 44 to be evaporated is placed within the container 32. The open top of the container is then sealed with a vacuum tight closure such as the closure 34 illustrated in FIG. 1. This closure is fabricated in TEFLON, having a VITON (a registered trademark of E.I. du Pont de Nemours) O ring around its circumference in order to provide the vacuum tight seal. Openings within this closure (74, 76, and 77--FIG. 4) are for the connection of a PYREX vapor transport tube 46, containing vapor conduit 48, a TEFLON plug 52 to seal the opening 74 for additional solvent entry into the container, and for the insertion of a stainless steel (or TEFLON coated) temperature probe 54 within the container.