What is Molecular distillation?

Molecular distillation is a special liquid liquid separation technology, operating under extremely high vacuum.He is according to,the molecular motion of a different material has different mean free path of the physical characteristics and achieve the purpose of separation,and the liquid at a temperature below the boiling point will be the separation,and is especially suitable for the separation of high boiling point,heat sensitive and easily oxide system.Because of its boiling point distillation temperature is lower than the material,distillation pressure reduction,heating time is short, high characteristics and high degree of separation,which can greatly reduce the separation cost of high boiling point material,excellent protection of sensitive material quality.The molecular distillation technology is used for the purification of natural health care products and functional oils, etc. it can get rid of the shackles of chemical treatment,and it can keep the pure natural properties.

Molecular distillation technology, as a kind of high boiling point, heat sensitive materials for effective separation method,since the 1930s,has got more and more attention all over the world.On the Japanese,British,United States, Germany,and the Soviet Union have designed and manufactured a number of molecular distillation device for concentrated vitamin A,but the application is also very narrow,the development is slow.In spite of this,people have been in constant importance of the development of the new liquid – liquid separation technology,the separation device continue to improve and perfect,the application areas continue to explore and expand,which has been the new patents and new applications. Especially since the end of 80 “s,the molecular distillation technology has been developed rapidly since the people” s favor of natural substances and the trend of natural distillation.

Basic Principles of Molecular Distillation

According to the principle of thermodynamics shows that, under certain temperature and pressure of the molecular mean free path L=0.707K*T/(πd2P), in D for effective molecular diameter; P for molecular space in which the pressure; T for the molecular environment temperature; K is the Boltzmann constant (Fu and Chen, 1979).

By the molecular mean free path of the movement of the formula, we can see that different kinds of molecules, because of the difference of the effective diameter of the molecule, the mean free path is different, that is, different kinds of escaping from the molecular level not and other molecular collision of flight distance is not the same. Light molecular mean free path, small molecular mean free path, if in away from the liquid surface is smaller than the mean free path of molecular light rather than heavy molecular mean free path set a condensing surface, making molecular light falling on the condensing surface chant condensation, and heavy molecules reach the condensing surface and return to the original level, so as to realize the mixture separation.

Molecular Distillation Features

The typical molecular distillation unit consists of two kinds of centrifugal and rotary film blowing, and the rotating film – type molecular distillation device includes a variable – layer jacket, a condenser and a rotating scraper system.When the material is distilled, the material enters the rotating distributor continuously, and the centrifugal force is swung onto the heating wall, and the film is evenly distributed on the inner wall and downwards flowing.. This unique structure has obvious advantages:

1.The relative volatility of the mixture was explained by the relative volatility of the mixture, and the relative volatility of molecular distillation wasαm=p1/p2(M1/M2)0.5,And conventional distillation of volatile alpha =p1/p2,The p1/p2 is the ratio of the vapor pressure of light recombination in a certain circumstance, the molecular weight of M1 for the light component, and the molecular weight of M2 for the reorganization.

2.Low pressure distillation, condensation and evaporation was very close to the surface and materials by steam must not throttle to the condensing surface, operating pressure can reach 0.01 mbar.

3.Evaporating temperature is low, in the molecular distillation device, the separation of mixtures is due to the different kinds of escaping from the molecular level the mean free path of different nature to achieve, does not need to be boiling, so molecular distillation is operating at a very low boiling point temperature.

4.Heating time is short, the mixed liquid is like a thin film thickness (much less than 1 mm), almost equal to the evaporation surface and the heating surface area, makes the material along the heated surface leave and evaporate quickly, very short residence time, about tens of seconds.

5.Low energy consumption, blows the membrane design almost no products remain in the inner wall of the heating, can avoid the clogging phenomenon; fast steam condensed, compact structure, small vacuum pump can meet the requirements of vacuum, reduce energy consumption; rapid replacement of material, does not produce mixture; therefore, molecular distillation, especially for those with ordinary distillation product loss, poor quality material.

The Function of Molecular Distillation

Molecular distillation can be widely applied to various aspects of the national economy,especially suitable for the separation of high boiling point,heat sensitive and easily oxidized materials,such as separation and purification of fatty acids; distillation separation of natural and synthetic paraffin products; separation purification Jiao Shawan cod liver oil (ene); production of high concentration of monoglyceride;monomer MDI,TDI and two yuan of fatty acid separation polyurethane material;extraction of natural products VE;free fatty acid separation of oil products in special silicone oil; purification; separation of a small amount of solvent in natural extracts;application in polymer manufacturing; alkylpolyglucosides  carotene purification;solation and purification;separation of hydrocarbons in petrochemical industry, purification of organic intermediates,antioxidant, lecithin;plastics industry by purification of plasticizer;refined emulsifier in food industry and purification of functional oil refining industry of traditional Chinese medicine;pharmaceutical intermediates;natural essential oil in the perfume industry decolorization,deodorization,improve purity etc..The summer and the purpose of the summer to give some practical examples to illustrate.

1.Single Lipid

Monoglyceride is widely used in the food industry emulsifier and proper molecular distillation technology is a typical example of that process study reported a lot, the whole process research, also has simple molecular distillation process research (Azelag and Zwierzykowski 1983). The most common method of manufacture is hardening oleic oil solution generation of so-called low content of products containing 40-50% monoglyceride and 7% glycerol and 35% diglyceride, and the rest of the unreacted triglyceride, through molecular distillation purification after, monoglyceride content in more than 90% and by-product glycerol and triglycerides can reuse, the result is almost all of the triglyceride into monoglyceride.

2.Vitamin E

Molecular distillation can be used for the production of synthetic vitamin E and natural vitamin E, the final step in the synthesis of vitamin E is in the form of acetate, containing 10% low boiling point by-products and approximately 2% resinous residue, after two stage molecular distillation, pale yellow, oily vitamin E products.Natural vitamin e found in vegetable oils in the removal of odor process as part of the fatty acids are presented, together, enriched in deodorizer distillate were, the concentration can reach more than 1%, by molecular distillation can be concentrated to 50%, even more than 70%.


Carotene is a kind of vitamin, as a kind of additives widely used in food, now more and more to the use of natural carotene instead of synthetic carotene, commonly used concentration is more than 25%.To from the red palm oil (carotene content of 0.07%) for the extraction of carotenoids and general machining process is palm oil after methyl esterification by molecular distillation steam to methyl, whole process needs three-step molecular distillation, products containing carotene can reach 40%.

4.ω-3 Fatty Acid Ester in Fish Oil

Due to the fish oil containing ω-3 fatty acid glycerol ester, so eat more fish on the heart is good, but due to the constraints, the risk of heart disease is difficult to directly obtain fish nutrition, food containing high concentration of the fatty acid ester capsule is a effective method.Because of the good effect of EPA and DHA containing 5-6 double bond, high temperature and easy polymerization and failure.


The fatty acid amide, such as 16~20 carbon atoms,is commonly used as the emulsifier and dispersant in the textile industry,and the corresponding acid and amine reactions are derived from the reaction.Although the high product quality index (especially the chrominance) requirements, but low yield, such as quality of 98.5%, rate of not more than 88%, and the use of molecular distillation rate is up to 94%, can reduce 50% of the waste.

6. Two Polylactic Acid

Two polylactic acid is the basic raw materials of polyester,the reaction mixture containing single acid, two – acid and oligomer, need to be further refined to meet certain requirements of the product. According to reports, the current domestic and international production are used the method of molecular distillation, the Xing Ming Yang (Yang, Guo Helu, 1993) of dimer acid molecular distillation process research, Guangzhou light industry research also of dimer acid molecular distillation process were a large number of studies, scale from small test, try to 1000 tons / year industrial trial production run, with satisfactory results, can be more than 95%, light yellow color, consistent with the theoretical value of dimer acid, reaching the quality standard of similar products abroad.


Glucose and C8~12 fatty alcohol under catalytic conditions was obtained by the reaction of alkyl polyglycosides, obtained after the reaction is a mixture mainly not reaction of sugar, alcohol, single Chungan, glycol glycoside, multi alcohol glycosides and other product requirements single glycosides, glycosides, glycosides to maintain a certain proportion, does not contain sugar and alcohol. Therefore, it is necessary to refined, using conventional distillation may make the product deterioration of. Distillation kettle bottom coking and four molecular distillation can get qualified products, reach the level of foreign products of the same quality.

8.Purification of Capsanthin

Capsicum red pigment containing 1% to 2% of the solvent, after two stage molecular distillation processing, products dissolved residual amount < 2.0 * 10-6, meet the quality requirements (Erdweg, 1983); in addition,also can realize the effective separation of capsaicin and pigment,containing capsaicin 10% general pepper supercritical extract, by molecular distillation treatment, allicin content can rise to 25% or more.

9.Purification of Natural Essential Oil

Strong spices like volatile substances, high heat sensitivity and its common process is deodorization, decolorization and purification, generally using the three-step molecular distillation, first grade deoxidation, second level off odor or purification, the third stage bleaching or purification. Such as rose oil after molecular distillation, can solve the smell is not good, color depth and wax content of higher, so that the added value greatly improved.

Above is a typical example of the application of molecular distillation, in addition, but also can be used in many fields, such as asphalt manufacturing, silicon oil reuse, high carbon alcohol refining, sucrose ester preparation, synthetic fragrances of refining. The molecular distillation applied research laboratories were a large number of experiments and have rich experience and fruitful results, at present in mainland China has 1000 tons / year of erucic acid amide, 1500 tons / year of dimer acid, 3000 tons / year single glucoside ester, 500 tons / year of alkyl polyglycosides etc. dozens of sets of equipment in operation, with great economic benefits.


The application of molecular distillation can make the product quality,system stability,maintenance time short,energy consumption is low,and can be used in the traditional process of technology improvement and new process development. Although the molecular distillation equipment is higher than the ordinary distillation equipment in the price,but todays vacuum technology to stabilize the system, high output.High efficiency and reduction of the workers can reduce the cost of distillation,and the extent of the reduction is far more than the cost of the equipment.With the development of engineering technology and application development,the application of molecular distillation will become more and more popular.

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