Numerous findings have indicated that the distance between the evaporator and condenser of the molecular still is not as critical, as far as mean free-path design criteria are concerned, as formerly believed. It had been recommended that studies be made on the present apparatus at Virginia Polytechnic Institute to determine exactly how critical this factor is.

The purpose of this investigation was to study the effect of condenser temperature and location on the molecular distillation characteristics of stearic acid, and from this study, determine this relationship of condenser temperature and location to be used in centrifugal molecular still operation.

This investigation was accomplished using a magnetically driven centrifugal molecular still with a five-inch rotor and employing the following operating conditions: operating pressure, 24 ± 2 microns of mercury, absolute; feed rate, 60 to 65 milliliters per minute; rotor speed, 1000 ± 50 revolutions per minute; feed-residue temperature differential, 24 ± 1 degrees centigrade; condenser water temperature, 25, 35, and 45 degrees centigrade; condenser locations, 3/4 2-1/2, and 5-3/8 inches from the evaporator; and number of passes of the feed over the rotor per fraction, one.

lt was concluded from this investigation that if the Iocation of the condenser did not exceed a mean free-path multiple of three, that the location of the condenser had no effect on the elimination maximum of stearic acid, and the elimination maximum was increased approximately one degree centigrade for every four degrees centigrade decrease in condenser temperature. The elimination maximum was not affected by condenser temperature when the condenser was located in a position with a mean free path multiple of six.