Short Path Molecular Distillation

The Unique Principle Behind a Unique Process

Vacuum DiagramFor those classes of chemical compounds which decompose, polymerize, react or are destroyed by conventional low pressure distillation, efficient commercial high vacuum distillation equipment is available from Myers Vacuum. (Myers Vacuum bought the line from CVC products.)

Myers Vacuum builds laboratory and continuous production units for the distillation of thermally sensitive organic and silicone compounds in a vacuum range of 1 to 80 X 10-3 Torr in the molecular weight range of 150 – 4000.

Low Cost and High Throughput

Low cost per pound and high throughput feed rates may be obtained on groups of compounds which include vitamins, epoxy resins, highly concentrated pure fatty acids, plasticizers, fatty acid nitrogen compounds, and a host of other heat sensitive materials which may require only deoderizing and decolorizing.

The pharmaceutical industry, in its continuing search for purity in high molecular weight intermediates and products, finds the molecular still an invaluable commercial reality in the separations of product from excess reactants and catalysts.

Significant Reduction of Thermal Hazard

High vacuum distillation, which has been termed “molecular” or “short path” distillation, is a safe process tool to separate mixtures of organic or silicon compounds, most of which will not tolerate prolonged heating above 250┬║C without excessive structural change or decomposition.

As opposed to conventional atmospheric and low pressure packed distilling towers that use packing, these high vacuum stills utilize the heat of condensation as a prime body for radiant heat emission to the surface film on the evaporator. The path between evaporator and condenser is totally unobstructed. With short residence time and lower distilling temperatures, thermal hazard to the organic material is greatly reduced.

Greater Fractionation Efficiency

The best approach to a mechanical method of creating a film of fast moving uniform thickness is to feed material to the center of a heated spinning disc. By centrifugal force, the material spreads in a film across the heated disc which intimately faces a large condensing surface. The lighter compound evaporates and condenses in a fraction of a second. The heavier residue which has not evaporated slides off the outer edge of the disc into a concentric residue collector and is discharged.

The degree of separation is a function of the difference in molecular weights of any distilled mixture. The greater the variance in the molecular weights, the purer the distillate. The closer the molecular weights of the mixture, the less efficient is the desired fractionation, resulting in the need for successive runs of the distillate.

Enhanced Purity of Distillate

Vacuum StillPurity of the distillate also depends on the film thickness. Controlled positive pressure on the distill and supply to the heated evaporator surface will provide a uniform film throughout the distillation, and reduce process variables to predictable changes caused only by temperature changes made by the still operator.

The absence of air molecules in the high vacuum still permits most of the distilling molecules to reach the condenser, with relatively few molecules returning to the liquid surface of film on the evaporator. Experiments show that on a broad range of molecular weight materials, a relationship exists between the molecular weight and the distillation temperature of the material.

There is no predictable temperature at which distillation will occur; condensation begins whenever a sufficient temperature differential occurs between evaporator and condenser. Thus there is an infinite number of sets of operating conditions for every feed material. Since pressure is a constant, the only variables are flow rate (which governs film thickness) and evaporator temperature.

 

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