Molecular distillation is a distillation process done under high vacuum. The very short distance the vapor travels before condensing ensures minimal to no loss due to surface hold-up of the vapor and is an immediate release from vapor to condenser surface. This distillation process is classified as short path distillation and is also referred to as molecular distillation due to the minimal vapor/liquid interface. The technique and equipment are typically used to purify substances with low volatility and/or temperature sensitivity.
Molecular distillation is a time-tested method. First developed before the start of the Second World War, it was used to distill natural products which were highly sensitive to heat, such as vitamins. The process was invented in the United States by Dr. Kenneth Hickman.
This process is considered the safest means of separation for purifying thermally unstable substances with other related compounds that have elevated boiling point and low volatility. Molecular distillation is unique as it allows low(er) operating temperature, as a result of the vacuum within the distillation space. The equipment capability also results in shorter residence time within the molecular evaporator zone.
Theoretically, molecular distillation is used to separate mixtures that form azeotrope or have close boiling point. Further developments in the field of molecular distillation took place in the later 20th Century, which give birth to gentler distillation conditions at higher temperatures. These developments allow for reduced operating pressures and consequently lower boiling temperatures, enabling separation of products which would otherwise be destroyed or damaged in conventional vacuum distillation processes.
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