Process for separating mixtures of substances of low volatility

A process for substantially separating the components of mixtures of substances at least one of which is of low volatility, while the other is of low or no volatility by using a compressed gas under supercritical conditions, and an entrainer adapted to increase the concentration of said mixtures of substances in the gaseous phase as well as the separation factor between the components to be separated, comprising in combination, feeding such mixture and said entrainer into a first distillation zone, passing said compressed gas upward through said distillation zone, effecting the separation and downward travel of the first component mixed with entrainer, to the bottom of said first distillation zone;

• passing from the top of said first distillation zone, the compressed gas, entrainer and second component to a point at most as high as the center of a second distillation zone, passing said compressed gas, entrainer and second component upward past a condensing zone at the top of said second distillation zone condensing part of said entrainer so it will travel downward in countercurrent to the compressed gas whereby to substantially free the same from the second component, and to pass to the bottom of said second distillation zone;
• recycling the compressed gas from the top of the second distillation zone to the bottom of the first distillation zone, recycling part of the bottom product of said second distillation zone to the top of said first distillation zone, whereby to effect substantial separation of said components in the absence of any substantial pressure decrease and the consequent need for recompression.