Jock Radell and J. W. Connolly
Wright Air Development Division Wright-Patterson AFB, Ohio
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Frattionation Technique for Vacuum Distillation
T h e receiver shown in the figure has been found to he of great advantage in operating a fractional distillation under vacuum during which repeated small fractions had to be collected. During the course of a distillation the stopcocks numbered in the figure were in the open (a) or closed (c) condition: 1 o or c, 2 a, 3 a, and 4 c. When the operator wishes to remove a fract,ion,first stopcock 2 is briefly (2 see) closed to suck down the small slug of liquid adhering to the glass above stopcock 1, and then the stopcocks are adjusted as follows: 1 c, 2 a, 3 c, and 4 a. The distilling receiver containing the fraction is removed and replaced witah an empty distilling receiver. An auxiliary vacuum pump is connected to the open tube on the right of stopcock 4. The receiver is evacuat,ed by the auxiliary pump until the characteristic sound of the pump working against an evacuated system is obtained. Then the stopcocks are changed in the following order: 4 c, 3 a , 1 o. The auxiliary pump is removed and the distillation cont,inued. The operation could be simplified by using a three-way stopcock for stopcock 4, which could open the receiver either to the atmosphere or to the auxiliary pump. This technique has been used satisfactorily for the
vacuum distillation of a variety of high-boiling organic compcunds with various columns. Decomposition in the distilling pot has been minimized and pressure readings have remained constant for several fraction changes.
Volume 38, Number 9, September 1961
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