Molecular distillation is a type of
short-path vacuum distillation
Vacuum distillation is distillation performed under reduced pressure, which allows the purification of compounds not readily distilled at ambient pressures or simply to save time or energy. This technique separates compounds based on differences i ...
, characterized by an extremely low vacuum pressure, 0.01
torr or below, which is performed using a molecular still. It is a process of separation, purification and concentration of natural products, complex and thermally sensitive molecules for example vitamins and polyunsaturated fatty acids. This process is characterized by short term exposure of the distillate liquid to high temperatures in
high vacuum (around mmHg) in the distillation column and a small distance between the evaporator and the condenser around 2 cm.
[http://www.nt.ntnu.no/users/skoge/prost/proceedings/distillation06/CD-proceedings/paper062.pdf ] In molecular distillation, fluids are in the
free molecular flow
Free molecular flow describes the fluid dynamics of gas where the mean free path of the molecules is larger than the size of the chamber or of the object under test. For tubes/objects of the size of several cm, this means pressures well below 10− ...
regime, i.e. the
mean free path of molecules is comparable to the size of the equipment. The gaseous phase no longer exerts significant pressure on the substance to be evaporated, and consequently, rate of evaporation no longer depends on pressure. The motion of molecules is in the line of sight, because they do not form a continuous gas anymore. Thus, a short path between the hot surface and the cold surface is necessary, typically by suspending a hot plate covered with a film of feed next to a cold plate with a line of sight in between.
This process has the advantages of avoiding the problem of toxicity that occurs in techniques that use solvents as the separating agent, and also of minimizing losses due to thermal decomposition. and can be used in a continuous feed process to harvest distillate without having to break vacuum.
Molecular distillation is used industrially for purification of oils. It is also used to enrich
borage oil Borage seed oil is derived from the seeds of the plant, '' Borago officinalis'' (borage).[Borage]
at ...
in
γ-linolenic acid (GLA) and also to recover
tocopherols from deodorizer distillate of soybean oil (DDSO).
Molecular stills were historically used by
Wallace Carothers
Wallace Hume Carothers (; April 27, 1896 – April 29, 1937) was an American chemist, inventor and the leader of organic chemistry at DuPont, who was credited with the invention of nylon.
Carothers was a group leader at the DuPont Experiment ...
in the synthesis of larger
polymers, as a reaction product, water, interfered with polymerization by undoing the reaction via hydrolysis, but the water could be removed by the molecular still.
[pg113, ''Enough for One Lifetime: Wallace Carothers, Inventor of Nylon'', Hermes 1996]
"Du Pont Strikes Pay Dirt at Purity Hall: Groundbreaking studies by Wallace Carothers paved the way for the development of nylon and neoprene."
''Today's Chemist''
See also
*
Fragrance extraction
Fragrance extraction refers to the separation process of aromatic compounds from raw materials, using methods such as distillation, solvent extraction, expression, sieving, or enfleurage. The results of the extracts are either essential oils, ...
References
{{Separation processes
Distillation
Separation processes
Laboratory techniques