The design and construction of a five inch centrifugal molecular still

Molecular distillation is that process of free transfer of molecules under high vacuum from an evaporator to a condenser, where the distance of travel is within the limits of the mean free path of the vapor molecules in the residual gas. Under these conditions, distillations can be made at temperatures 100 to 150°C. lower than ordinary distillations.

Many of the so-called "undistillables“ can be distilled under conditions existing in the molecular distillation process. The natural fats and waxes, sugar derivatives, petroleum residues, plastics, and plasticizers now fall within the scope of molecular distillation.

The use of the molecular distillation process is now limited by the high costs involved. Thermal efficiency is low, only 2% of the total input heat is utilized for distillation. The separating powers of molecular stills are low, never more than that of one ”theoretical plate“. Only those materials that can bear the high process costs are now being produced commercially, the production of vitamins being the most prominent.

Considerable work has been done relative to the development of molecular stills. Advancement to the present day centrifugal stills has been accomplished relatively recently. Many problems are yet unsolved. Much work must be done before molecular distillation can be placed on a level with other methods of distillation. An increase in thermal efficiency, an increase in separating powers, a decrease in film thickness, and a lowering of the costs of the process are necessary.

The purpose of this investigation was to design and construct a five inch centrifugal molecular still. Four interchangeable rotors were employed, each of different thickness, different diameter, and having a different angle of inclination. The effect of angle of inclination on film thickness can then be studied. Although no data has been published relative to still performance of five inch commercial stills, data obtained from the operation of the still constructed in this investigation can be compared when such data is published.