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Distillation- Theory, Types of distillation

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Distillation:

Distillation Basic Principles and methodology of simple distillation, Flash distillation, fractional distillation, distillation under reduced pressure steam distillation & molecular distillation 1 Dr V P Sonar RCPIPER, Shirpur

Slide 2:

Distillation: Separation of the components of liquid mixture by a process involving vaporization and subsequent condensation. 2 step process, Converting a liquid into vapor phase Transferring the vapor to another place and recovering the liquid by condensation. Feed liquid – distillant Condensed liquid- distillate or condensate 2 Dr V P Sonar RCPIPER, Shirpur

Application s of Distillation:

Application s of Distillation Separation of volatile oil Purification of organic solvent Manufacturing of official preparation e.g Aromatic spirit of ammonia, WFI Refining of petroleum products Recovery of solids QC methods- Determination of alcohol content in elixir Separation of drug form plant and animal sources Purification of drug obtained from chemical process 3 Dr V P Sonar RCPIPER, Shirpur

Simple Distillation:

Simple Distillation It is a process of converting a single constituent from a liquid or mixture into its vapor, transferring the vapor to another place and recovering the liquid by condensing the vapor, by allowing it to come in contact with cold surface. This process known as differential distillation, as distillation is based on difference in volatilities and vapor pressure of the component in mixture 4 Dr V P Sonar RCPIPER, Shirpur

Classification :

Classification Simple Distillation Flash Distillation Fractional Azeotropic and Extractive Distillation under reduced pressure Steam Molecular Destructive Compression 5 Dr V P Sonar RCPIPER, Shirpur

Slide 7:

Principle- Liquid boils when its vapor pressure is equal to atmospheric pressure. Simple distillation is conducted at its boiling point. Higher the relative volatility of a liquid, better is the separation by simple distillation. Heat is supplied to boil the liquid. Resulted vapor is transferred to a different place and condensed. If the liquid of interest is volatile and the other one is nonvolatile then Simple distillation is useful means of purification and separation. 7 Dr V P Sonar RCPIPER, Shirpur

Slide 8:

Laboratory Scale apparatus for distillation It consist of a distillation flask with a side arm sloping downwards. Condenser is fitted into the side arm by means of cork. Condenser is usually water condenser i.e jacketed for circulation of water. The condenser is connected to a receiver flask using an adapter. On lab scale whole apparatus is made of glass Liquid to be distilled is filled into the flask to one half to two-third of its volume. Bumping is avoided by adding small pieces of porcelain or porous pot. 8 Dr V P Sonar RCPIPER, Shirpur

Slide 9:

A thermometer is inserted into the cork and fixed to the flask. The thermometer bulb must be just below the level of the side arm. Water is circulated through the jacket of the condenser The contents are heated gradually. The liquid begins to boil after some time. Vapor begin to rise up and passes down the side arm into the condenser. Vapor is condensed and collected in receiver. Flame is adjusted so that distillate is collected 1-2 drop per second. 9 Dr V P Sonar RCPIPER, Shirpur

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Large scale Equipment for simple distillation A simple still is used for large scale distillation. It is made up of stainless steel, copper or any other suitable material. A still of this kind has limited heating surface and functions properly with volatile solvents, but is not useful for concentrating liquid. Specially designed stills suitable for particular product or group of product is used. An observation window is there to see the progress of distillation and level of the content 11 Dr V P Sonar RCPIPER, Shirpur

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Still is connected to a condenser and then to a receiver. Still is heated with steam. A steam inlet is provided at the bottom and an outlet for removing condensed steam. Working- Same as simple distillation Application Preparation of distilled water Preparation of Volatile and aromatic water Purification of organic solvents Spirit of nitrous ether, aromatic spirit of ammonia Separation of nonvolatile from volatile component 12 Dr V P Sonar RCPIPER, Shirpur

2. Flash Distillation:

2. Flash Distillation It s defined as a process in which the entire liquid mixture is suddenly vaporized by passing the feed from high pressure zone to low pressure zone. It is also known as equilibrium distillation i.e. separation is achieved when liquid and vapor phase are in equilibrium. This method is frequently carried out as a continuous process and does not involve rectification. 13 Dr V P Sonar RCPIPER, Shirpur

Slide 14:

The  boiling  point of a substance is the temperature at which the vapor pressure of the  liquid  equals the pressure surrounding the  liquid  and the  liquid  changes into a vapor. ... A  liquid  at  high  pressure has a  higher boiling  point than when that  liquid  is at atmospheric pressure. Liquid boils when vapor pressure is equal to atmospheric pressure, i.e., pressure on its surface. If the external pressure is reduced, the boiling point of the liquid decreases and liquid boils at lower temperature 14 Dr V P Sonar RCPIPER, Shirpur

Slide 15:

Principle- When a hot liquid mixture is allowed to enter from a high pressure zone into a low pressure zone, the entire liquid mixture is suddenly vaporized: Flash vaporization During this process the chamber gets cooled. The individual vapor phase molecules of high boiling fraction get condensed, while low boiling fraction remains as vapor. This process takes some time. Therefore the liquid and vapor is kept in intimate contact until equilibrium is achieved 15 Dr V P Sonar RCPIPER, Shirpur

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The liquid fraction is collected separately. The vapor is separated from the liquid and further allowed to condense. 16 Dr V P Sonar RCPIPER, Shirpur

Slide 17:

Construction It consist of a pump, which is connected to a feed reservoir. Pump helps in pumping the feed into the heating chamber which contains a suitable heating mechanism. The other end of the pipe is directly introduced into the vapor liquid separator through a reducing valve. The vapor outlet is provided at the top of the separator and liquid outlet is provided at the bottom. 17 Dr V P Sonar RCPIPER, Shirpur

Slide 18:

Working- The feed is pumped through a heater at a certain pressure. The liquid gets heated, which enters the vapor- liquid separator through a presure reducing valve. Due to drop in pressure, the hot liquid flashes, which further enhance the vaporization process. The sudden vaporization induces cooling. The individual phase molecule of high boiling fraction gets condensed, while low boiling fraction remains as vapor. 18 Dr V P Sonar RCPIPER, Shirpur

Slide 19:

This process takes some time. Therefore the liquid and vapor is kept in intimate contact until equilibrium is achieved. The vapor is separated through a pipe from above and liquid is collected from the bottom of the separator. By continuous feeding into still it is possible to obtain continuous flash distillation. The operating condition can be adjusted in such a way that amount of feed exactly equals to amount of material removed. Therefore vapor and liquid concentration at any point remain constant. 19 Dr V P Sonar RCPIPER, Shirpur

Slide 20:

Uses- Separation of components which boils at widely different temperature In petroleum industry for refining crude oil Advaantages - Continuous process. Use to obtain multi-component system of narrow boiling range Disadvantages- Not suitable for comparable volatile compounds, not suitable for 2 component system. Not efficient when nearly pure components are required. 20 Dr V P Sonar RCPIPER, Shirpur

3. Distillation under reduced Reduced pressure:

3. Distillation under reduced Reduced pressure Distillation process in which the liquid is distilled at a temperature lower than its boiling point by the application of vacuum. Vacuum or suction pumps are used to reduce the pressure on the liquid surface Principle- Liquid boils when vapor pressure is equal to atmospheric pressure, i.e., pressure on its surface. If the external pressure is reduced, the boiling point of the liquid decreases and liquid boils at lower temperature 21 Dr V P Sonar RCPIPER, Shirpur

Slide 22:

Water boils at 100°C at an atmospheric pressure of 101.31 kPa (760mmHg). At 40°C vapor pressure of water is approximately 9.33 kPa (70mmHg). If external pressure is reduced to 9.33kPa, water will boil at 40°C. The net result will be increase the rate of mass transfer. 22 Dr V P Sonar RCPIPER, Shirpur

Assembly of apparatus :

Assembly of apparatus 23 Dr V P Sonar RCPIPER, Shirpur

Slide 24:

Assembly of apparatus (Lab scale) - It consist of double neck distillation flask known as claisen flask. Thick walled glass apparatus with interchangeable standard glass joints are used for vacuum distillation. In one of the necks of the claisen flask, a thermometer is fitted. The second neck prevents splashing of the violently agitated liquid. Bumping occurs readily during vacuum distillation, a small capillary is placed to prevent bumping. 24 Dr V P Sonar RCPIPER, Shirpur

Slide 25:

The capillary tube is dipped in boiling liquid, so that a stream of air bubble is drawn out. Water bath or oil bath is used for heating. Claisen flask is connected to receiver through condenser. Vacuum pump is attached through an adapter to the receiver. A small manometer is inserted between the pump and receiver. Procedure- Refer C V Subrahmanyam Page no 223 25 Dr V P Sonar RCPIPER, Shirpur

Slide 27:

Assembly of apparatus (Industrial scale) It consist of vacuum jacketed still made of SS, copper or any other material which can withstand high vacuum. An observation window is provided to check the progress of distillation and level of liquid content. Still is fitted with drainpipe at the bottom and an air vent. Still is connected to condenser. A vacuum gauge is connected. Thermometer is provided in still Procedure- Refer C V Subrahmanyam P. No- 224 27 Dr V P Sonar RCPIPER, Shirpur

Slide 28:

Applications- Useful in preventing degradation of active constituents. Eg . Enzymes, vitamins, glycosides, alkaloids, tannins Extraction and concentration needs temp below 55°C Changing physical form- Removal of solvent under reduced pressure produces light porous mass rather a dense and compact residue. Disadvantages- In vacuum distillation persistent foaming occurs Not suitable for the preparation of semisolid or solid extract 28 Dr V P Sonar RCPIPER, Shirpur

4. Steam Distillation:

4. Steam Distillation Distillation is carried out with the aid of steam. It is used for the separation of high boiling substances Suitable for high boiling liquid which get decomposed at higher temperature. Suitable for Substance which are insoluble in water and not decomposed by heat. Used for separation of immiscible liquids It is also a type of differential distillation 29 Dr V P Sonar RCPIPER, Shirpur

Slide 30:

Principle- A mixture of immiscible liquid begins to boil when the sum of their vapor pressure is equal to atmospheric pressure. In case of a mixture of water and turpentine the mixture boils below the boiling point of water. BP of turpentine- 160°C, but when it is mixed with water and heated, the mixture boils at 95°C. At this temp vapor pressure of water = 86.245kPa (647mmHg) and Vapor pressure of turpentine = 15.06 kPa (113 mmHg) 86.245kPa + 15 kPa = 101.31kPa (760mmHg) = Atmospheric pressure 30 Dr V P Sonar RCPIPER, Shirpur

Slide 31:

High boiling substances may be boiled at low temperature. Application- Separation of immiscible liquids eg . Toluene & Water Extraction of volatile oil eg . Clove, anise, eucalyptus Purification of liquid with high boiling points eg Almond oil Distillation of camphor Preparation of aromatic water 31 Dr V P Sonar RCPIPER, Shirpur

Slide 32:

32 Assembly of steam Distillation- Laboratory Scale Dr V P Sonar RCPIPER, Shirpur

Slide 33:

33 Assembly of steam Distillation- Industrial Scale Dr V P Sonar RCPIPER, Shirpur

Slide 34:

Assembly / Construction- It consist of a metallic steam can fitted with a cork having two holes. A long tube is passed through one hole so as to reach the bottom of steam generator. This tube is act as safety tube, in case the pressure inside the steam generator becomes too much, water will be forced out of it and pressure will be relieved. When steam starts coming out of the safety tube, it indicates that steam can is empty. Through another hole , a bent tube is passed, other end of this tube is connected to flask containing non aqueous liquid. This tube reaches to the bottom of flask 34 Dr V P Sonar RCPIPER, Shirpur

Slide 35:

Through the other hole of the rubber bung, a delivery tube is inserted which connects the flask and the condenser. The condenser is connected to a receiver flask using an adaptor. Provision are made to heat to heat the steam can and flask. Procedure- Non- aq liquid is placed in the flask. A small quantity of water is added to it. Steam can is filled with water. The steam generator and the flask are heated simultaneously, so that a uniform flow of steam passes through the boiling mixture. 35 Dr V P Sonar RCPIPER, Shirpur

Slide 36:

The mixture gets heated. The steam carries the volatile oil and passes into condenser, which is gets cooled by water passing through condenser. The condensed immiscible liquid is collected into the receiver. Distillation is continued until non-aqueous liquid has been distilled. In the receiver water and organic liquid form two separate layers which can be easily separated using separating flask. 36 Dr V P Sonar RCPIPER, Shirpur

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Advantages- Volatile oils can be separated at lower temperature in steam distillation, without any decomposition and loss of aroma. Less volatile substance can be distilled satisfactorily Disadvantages- It is not suitable when immiscible liquid and water reacts with each other 37 Dr V P Sonar RCPIPER, Shirpur

5.Molecular distillation:

5.Molecular distillation It is a process in which each molecule in the vapor phase travels mean free path and gets condensed individually without intermolecular collision on application of vacuum. This is also called as evaporative distillation or short path distillation. Principle - The substance to be distilled have very low vapor pressure. E,g - viscous liquid, oils, greases, waxy material. These boils at very high temperature. 38 Dr V P Sonar RCPIPER, Shirpur

Slide 39:

Boiling point of such material can be decrease by applying high vacuum. The vapor pressure above the liquid is much lower than that of the saturated vapor in equilibrium. At very low pressure the distance between the evaporating surface and the condenser is approximately equal to the mean free path of the vapor molecule. Molecule leaving the surface of the liquid are more likely hit the condenser than to collide with other molecules. 39 Dr V P Sonar RCPIPER, Shirpur

Slide 40:

Application- Purification of chemicals e.g Tricresyl phosphate, Dibutyl phthalate and dimethyl phthalate. Refining of fixed oil Separation of Vitamin A and E from fish liver oil Separation of free fatty acid, steroids, triglycerides. 40 Dr V P Sonar RCPIPER, Shirpur

Slide 41:

Theory – Mean free path of a molecule- average distance through which a molecule can move without coming into collision with another. λ - Mean path length, m η – viscocity , Pa.s p- vapor pressure, kPa ρ - Density, kg/m 3 41 Dr V P Sonar RCPIPER, Shirpur

Slide 42:

The evaporating surface must be close to the condensing surface. This ensures the molecule to come in contact with the condenser as soon as they leave the evaporating surface. For this reason this process is known as short distillation Molecular collision should be minimized because they change the direction path of molecule. i.e intermolecular distance should be fairly high. It can be achieved under high vacuum. The liquid surface must be as large as possible so that vapor is evolved from the surface only .(Evaporative Distillation) 42 Dr V P Sonar RCPIPER, Shirpur

Slide 43:

6.1- Falling film molecular still or wiped film molecular still Principle- In this method vaporization occurs from a film of liquid flowing down a heated surface under high vacuum. The vapor molecule travels short distance and strikes the condenser nearby. Each molecule is condensed individually. The distillate is subsequently collected. Capacity- 1000 liter per hour 43 Dr V P Sonar RCPIPER, Shirpur

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44 Dr V P Sonar RCPIPER, Shirpur

Slide 45:

Construction- It consist of a vessel of one meter in diameter. Walls are provided with suitable means of heating (jacket). Wipes are adjacent to the vessel wall Wipers are connected to a rotating head through a rotor. Condensers are arranged very close to the wall (evaporating surface) Vacuum pump is connected to a large diameter pipe at the centre of the vessel. Provision are made for collecting the distillate and the undistilled liquid residue at the bottom. 45 Dr V P Sonar RCPIPER, Shirpur

Slide 46:

Working- Vessel is heated by suitable means. Vacuum is applied at the centre of the vessel and wipers are allowed to rotate. The feed is entered through the inlet of the vessel. As the liquid flows down the walls, it is spread to form a film by PTFE wipers which are moving at rate of 3 meter per second. The velocity of film is 1.5 meter per second. Since the surface is already heated, the liquid film evaporates directly. The vapor molecule travels its mean free path and strikes the condenser. The condensate is collected into a vessel and recirculated . 46 Dr V P Sonar RCPIPER, Shirpur

Slide 47:

6.2 Centrifugal Molecular Still Principle - Liquid feed is introduced into a vessel, which is rotated at very high speed (centrifugal action). On account of heating, vaporization occurs from a film of liquid on the sides of the vessel. The vapor molecules travel a short distance and gets condensed on the adjacent condenser. Each molecule is condensed individually. The distillate is collected subsequently. 47 Dr V P Sonar RCPIPER, Shirpur

Slide 48:

Construction- it consist of a bucket shaped vessel having a diameter of about 1-1.5meter. It is rotated at high speed using a motor. Radiant heaters are provided externally to heat the fluid in the bucket. Condensers are arranged very close to the evaporating surface. Vacuum pump is connected to the entire vessel at the top. Provision are made for introducing the feed into the centre of the bucket, for receiving the product and residue for recirculation. 48 Dr V P Sonar RCPIPER, Shirpur

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49 Dr V P Sonar RCPIPER, Shirpur

Slide 50:

Working- Vacuum is applied at the centre of the vessel. The bucket shaped vessel is allowed to rotate at high speed. The feed is introduced from the centre of the vessel. Due to centrifugal action of rotating bucket, liquid moves outward over the surface of the vessel and forms a film. Since the radiant heaters heat the surface, the liquid evaporates directly from the film. The vapor molecule travels its mean free path and strikes the condenser. The condensate is collected into another vessel. The residue is collected from the bottom of the vessel and re-circulated through feed port. 50 Dr V P Sonar RCPIPER, Shirpur

Slide 51:

6.FRACTIONAL DISTILLATION It is process in which vaporization of liquid mixture gives rise to a mixture of constituents from which the desired one is separated in pure form. This method is also known as rectification , because part of the vapor is condensed and returned as a liquids. This method is use to separate miscible volatile liquids, whose boiling points are close, by means of fractionating column. Vapor passes through fractionating column in which partial condensation of vapor is allowed to occur. 51 Dr V P Sonar RCPIPER, Shirpur

Slide 52:

Condensation takes place in the fractionating column, so that a part of condensing vapor returns to still Principle- It is a mass transfer process involving counter current diffusion of the component at each equilibrium stage. When liquid mixture is heated, the partial condensation of the vapor is allowed to occur in fractionating column. In the column ascending vapor from still is allowed to come in contact with the condensing vapor returning to the still. This results in enrichment of the vapor with more volatile component. 52 Dr V P Sonar RCPIPER, Shirpur

Slide 53:

Condensation of the vapor and reheating the liquid repeatedly sets up the equilibrium between liquid and vapor, which ultimately results in separation of more volatile component. Boiling point Curve- for a mixture In fractional distillation repeated vaporization and condensation process is involved simultaneously, therefore the composition of liquid and vapor phase changes continuously. Boiling point composition curve are helpful in predicting whether the separation is possible or not. These are helpful in designing the equipment for fractional distillation. 53 Dr V P Sonar RCPIPER, Shirpur

Slide 54:

Mixture of liquid A and B are prepared in different proportions and their boiling points are determined Boiling points are plotted on y axis against composition of the mixture. Upper curve represents the vapor phase composition Lower curve represents the liquid phase composition The different areas corresponds to the existence of liquid, vapor and liquid plus vapor The curves represents the equilibrium condition , therefore they are helpful in drawing the conclusion regarding the composition at any given temperature. 54 Dr V P Sonar RCPIPER, Shirpur

Slide 55:

Fractional Distillation- type I Miscible liquid For ideal solution 55 Dr V P Sonar RCPIPER, Shirpur

Slide 56:

Fractional distillation is always suitable for a system when the boiling point of the mixture is always intermediate between those of pure components. There is neither maximum nor minimum in the composition curves .These system is known as zeotropic mixture E.g Benzene and toluene, CCl 4 and Cyclohexane , Water and Methanol 56 Dr V P Sonar RCPIPER, Shirpur

Slide 57:

Fractional Distillation- Azeotropic Mixture 57 Dr V P Sonar RCPIPER, Shirpur

Slide 58:

Many liquid mixture cannot be separated completely by simple distillation, as their volatilities are nearly equal. Such mixture is known as azeotropic / constant boiling mixture: in which distills unchanged at constant temperature. E.g Chloroform and acetone, pyridine and acetic acid, water and nitric acid Azeotropic mixture has lower boiling point than that of the component with least boiling. At the minimum boiling point temperature, the liquid composition remains constant and is equal to the vapor composition 58 Dr V P Sonar RCPIPER, Shirpur

Fractionating column:

Fractionating column In fractional distillation special type of still heads are required to achieve repetitive condensation and re- vaporisation . It is a long vertical tube in which vapor passes upward and gets partially condensed. The condensate flows down the column and returned eventually to the flask It offers a large cooling surface for vapor to condense An obstruction to the ascending vapor allows easy condensation. The obstruction also retards the downward flow of liquid, which is high boiling component. 63 Dr V P Sonar RCPIPER, Shirpur

Slide 64:

64 Packed column- Some form of packing is used in the column to affect the necessary liquid vapor contact. Packing may consist of single turn helices (spiral) of wires or glass, glass rings, glass beads, SS rings Long fractionating column is required when the boiling points are close together. Packing must be uniform to obtain proper channels E.g Widmerr column Dr V P Sonar RCPIPER, Shirpur

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66 Dr V P Sonar RCPIPER, Shirpur

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Efficiency of Fractionating column- Length Reflux ratio- Amt of liquid returning through column/ Amt collected into the receiver. Heat input- heat must be controlled so that liquid passes over at a rate of one drop per 2-3 seconds Column Temperature Experimental condition- large amt of liquid should be continuously return through column, Thorough mixing of liquid and vapor, large active surface of contact between liquid and vapor 67 Dr V P Sonar RCPIPER, Shirpur

Slide 68:

Type of Distillation Synonym Application Simple Differential Flash equilibrium Fractional Rectification Steam Differential Under Reduced Pressure vacuum Molecular Short path/ Evaporative 68 Dr V P Sonar RCPIPER, Shirpur

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