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Content •

Introduction

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Principle

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Construction

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Working

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Type of SPDU

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Factor affecting SPDU

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Advantage and Disadvantage

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Application

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Application of Vitamin E acetate

Introduction

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Short path distillation is a technique by which heat sensitive chemicals can be distilled efficiently.

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Short path distillation is usually performed under vacuum at a pressure less than 0.001 mbar

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It is a process in which distillation apparatus consist of condenser and evaporator fitted in a single unit.

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The distance between evaporator and condenser surface is only of few centimeters.

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Hence it provides lowest distillation temperature and short residence time.

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Thus reduces possibility of thermal degradation of product.

Principle The principle of short path distillation can be understood from the figure below:

Construction It contain many things such as 1. Residue Discharge 2. Heater jacket 3. Roller wiper 4. Space under vacuum 5. Internal condenser 6. Feed 7. Geared motor 8. Heating medium inlet 9. Heating medium outlet 10. Exhaust 11. Cooling medium inlet 12. Cooling medium outlet 13. Distillate discharge

Working 1. Feed is continuously fed at top through a rotating distributor plate. 2. Distributor is rotated using motor. 3. Distributor plate distributes feed uniformly on the heat transfer surface. 4. Feed flows down on heat transfer surface by gravity and gets heated. 5. Heat required can be provided by thermic fluid, steam or hot water. 6. This heat causes partial vaporization of feed. 7. Vapor travel through the distillation gap to condenser surface where heat is removed by cooling coils. 8. Cooling medium can be cooling water, chilled water, oil or brine.

Types of short path distillation units.

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There are mainly two types of short path distillation units based on force used for distribution of liquid feed: 1. Falling film short path distillation unit; which uses gravitational force to allow the liquid to be distributed as a thin film on a vertical vaporizer surface . 2. Centrifugal short path distillation unit; which uses centrifugal force generated by rotor to promote the formation of thin film.

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The separation principle of both type of distillation unit is same

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There is also a third kind of short path distillation unit based on working; 1. Reactive short path distillation unit; which is a combination of reactor and a short path distillation unit 2. Reactive short path distillation can be of both; falling film or centrifugal unit type.

Factors affecting short path distillation •

The parameters affecting the molecular diffusion are feed and condensation temperature, feed rate, pressure and concentration of feed.

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With increase in temperature and decrease in pressure, the separation increases.

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By increasing the temperature, product purity increases but its yield decreases.

It is called molecular distillation when •

If distance travelled by vapor molecules from the vaporization surface to surface of internal condenser is less than mean free path of molecule between two successive collision then SPDU is called molecular distillation.

Difference Short path Distillation High purity. Temperature variation is less.

Vacuum distillation Less purity. Vast temperature variation.

Denature doesn't take place.

Denature take place .

Advantages and Disadvantages

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Advantages – Can be used for thermally sensitive substances. – Components with high boiling points can be distilled easily due to high vacuum. – There is minimum pressure drop in the system due to short distance between vaporizer and condenser unit. – It requires relatively less maintenance. – High purity of end products is obtained. – Disadvantages ─ high vacuum is required for carrying out distillation. ─ High operating cost.

Application •

Separation of fat soluble vitamins.

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Grape seed oil decaffeination

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Separation of fatty acids from vegetable oil.

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Increasing citral concentration in lemongrass oil.

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Removing phthalates from sweet orange oil.

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Separation of waxes, fats and natural oils.

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For fish oils, petroleum residues, solvent removals.

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In fractionation of milk fat.

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For enrichment of carotene.

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For recovery of polyphenols, tocopherols and sterols from deodorizer distillate.

1. For separation of vitamin E •

Use for synthesis of vitamin E as well as natural vitamin E.

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In 100kg crude vitamin E acetate it contain 78.75kg pure vitamin E acetate. 13.73 kg residue and 7.5kg low boiling impurities.

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Pure vitamin E obtain as light yellow pure oil.

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Deodorizer distillate of edible oil is source of natural vitamin E.

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It concentration varies from 3-10% by mass in distillate of soybean oil depending upon operating condition of deodorizer.

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Concentration upto 40% by mass can be carried out in SPDU.

Distillation of vitamin E acetate

2. Short path distillation for recovery of Polyphenols from deodorizer distillate

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Polyphenols are identified as the natural compounds which impart antioxidant property and thus improve shelf life.

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During physical refining of rapeseed oil, polyphenols gets separated and concentrates in the distillate along with fatty acids, tocopherols, sterols, etc.

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Thus oil obtained as bottom product is lean in polyphenols and hence lags in antioxidant property.

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So in order to obtain natural antioxidant, deodorizer distillate is treated in short path distillation to separate them from free fatty acids which act as oxidants.

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The effect of various parameters was studied experimentally which is stated as follows: – At 110°C about 43% of the material was evaporated to the distillate phase whereas at 170°C the total distillate yield was approximately 86%. – A separation factor near one is equivalent to an inefficient separation. – Separation efficiency between FFA and tocopherols increases with decrease in evaporation temperature with decrease in distillate rate. – Whereas when experiment were carried out for different feed rates (100-300 mL/h) at 110°C no significant change was observed

Separation of Monoglyceride: Monoglycerides are mono fatty acid esters of glycerol. Mono fatty acid + Glycerol → Monoglyceride + Water Monoglycerides are used as emulsifiers in many of food products. The modern food product technology demands the concentration of monoglyceride more than 90%. It is a heat sensitive product. More than 90% concentration of monoglycerides is achieved by twostage short path distillation

3. Carotene: It is a pro-vitamin which is used as a supplement in many food products. Red palmoil ester contains about 0.06% carotene. Three-stage short path distillation plant is required to increase the concentration up to 40%.

4. Dimeric Fatty Acids: They are basic materials for polyester or alkyd resins. They are produced by dimerisation of oleic acid. After reaction a mixture of monomer, dimer and oligomer fatty acids are formed. The fractionation of this mixture takes place in two or there stage short path distillation plant

5. To recover more middle distillate from the residuum, coming from vacuum distillation unit of refinery, currently vacuum distillation is carried out in conventional distillation equipment in which operating pressure at the base of column or in reboiler is decided by pressure drop in the column. The same operating pressure also decides the certain boiling range of residuum. Currently, considerable amount of middle distillate remains in the residuum. With conventional vacuum distillation unit, one can increase the % recovery of middle distillate by increasing base temperature but the same cannot be permitted because increase in the base temperature above the certain limiting value results in considerable thermal cracking of the residuum. In short path distillation, the same residuum can be boiled or distilled at much lower temperature range. Reduction in operating pressure in SPDU creates the sizeable reduction in boiling temperatures. Hence, with SPDU, it is possible to recover the middle distillate further without causing thermal cracking

6. Oleoresin: Oleoresin is a red colour natural pigment separated from paprika. It is used as a natural colour additive in food products. The oleoresin is extracted by hexane. From the extracted product, which contains 96% oleoresins and 4% hexane (by mass), hexane can be completely removed from oleoresin (down to 10 ppm) by two stage short path distillation

7. Deacidification of Ricebran Oil and Palm Oil: Ricebran oil and palm oil are preferred to be used as cooking mediums because of their high nutritional values. But because of considerable high content of free fatty acids, deacidification by conventional distillation is difficult. With short path distillation, these oils can be gently deacidified to the concentrations of less than 0.1% without loss of nutritional values 8. Separation of Monomers from Prepolymers: Polyurethanes are polymers with different compositions and wide range of characteristics. They are produced by polyadduct-type polycondensation reaction from toluene diisocyanate and polyols. In the first step, so-called prepolymers are formed. These prepolymers still contain a certain amount of non-reacted diisocyanate monomers. It is necessary to reduce monomer content before selling to end manufacturers because these monomers are toxic in nature. It can be reduced by short path distillation

Other application

Oil and Fat Industry •

Separation of free fatty acids from vegetable oil Fractionation of tall oil

Petrochemical Industry •

Fractionation of synthetic and petrochemical waxes to soft-and hard waxes

Chemical Industry •

Separation of long chain acid chlorides from impurities and free acids

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Solvent separation from silicon oils

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Concentration and purification of esters

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Purification of organic esters

Food Industry •

Separation of solvents from flavors

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Concentration of juices or extracts

Pesticides produce •

Purification and refining of pesticides and its intermediate

Polymer Industry •

Purification and concentration of monomers Purification and concentration of polymers Purification of softeners

Painting industry •

Subtractive solvent of polyurethane partial polymer and separation of TDI monomer

Cosmetic industry •

Producing wool alcohols and wool acid of sheep oil Wiping off pesticides of cosmetic substrate