distilation.pptx
- 1. DISTILLATION Ms. Sneha Anil Pachore Dept. of Pharmaceutics Asst. Professor Indira College of Pharmacy, Pune
- 2. DISTILLATION It is an unit operation which involves separation of a vaporizable component from a multi-component system and subsequent condensation of vapors. OR Also defined as separation of the components of a liquid mixture by a process involving vaporization and subsequent condensation. OR It is defined as the separation of the components of a liquid mixture by a process involving vaporization and subsequent condensation at another place. OR Distillation is the process of converting liquid into its vapours by heating and reconverting it again into liquid by condensing the vapours. The product obtained from the condensation of vapours is known as distillate or condensate. Container which collects the distillate is known as receiver. It results in essentially complete separation (nearly pure components).
- 3. The individual molecules within the liquid are continuously in motion A small Percentage of these molecules attain enough kinetic energy to leave the liquid phase This exerts an opposing pressure on the atmosphere above the solution known as the vapor pressure, P When enough energy, in the form of heat, is imparted to the solution the vapor pressure becomes equal to the atmospheric pressure and the liquid begins to boil The vapor obtained from a boiling liquid, once cooled, will re-condense to a liquid known as the distillate The complete process is called a distillation
- 4. Applications Separation of volatile oils Purification of organic solvents Manufacture of official preparations Refining of petroleum products Recovery of solvents Quality control methods Separation of drugs obtained from plant and animal sources Purification of drugs obtained from chemical process
- 7. CLASSIFICATION OF DISTILLATION METHOD Simple distillation Flash distillation Fractional distillation Distillation under reduced pressure Steam distillation Molecular distillation
- 8. SIMPLE DISTILLATION Simple distillation is process of converting a single constituent from a liquid into its vapour ,transferring the vapour to another place and condensing it again into liquid. Principle : Liquid boils when its vapour pressure is equal to atmospheric pressure. Simple distillation is conducted at its boiling point. The heat is supplied to the liquid so that it boils. The resulting vapour is transferred to different place and condensed. If the liquid of interest is volatile and remaining components are non-volatile then simple distillation is useful means of purification and separation.
- 9. CONSTRUCTION: It consist of distillation flask with a side arm slopping downward which is connected to condenser. The condensed vapours are collected in the flask called receiver. The whole apparatus is made of glass. The condenser is connected to receiver flask using adapter .
- 11. WORKING The distillation flask is filled one half to two third of its volume with liquid to be distilled. Add small pieces of porcelain to avoid bumping. A thermometer is inserted . The contents are heated gradually .the liquid begins to boil after some time. The vapour begins to rise up and passes down the side arm into condenser. The vapour is condensed and collected into the receiver.
- 12. USE : Used to prepare distilled water and water for injection. Used to prepare aromatic water. Used to separate non-volatile solids from volatile liquids.
- 13. FLASH DISTILLATION Flash distillation is defined as process in which entire liquid mixture is suddenly vaporized(flash) by passing the feed from high pressure zone to low pressure zone. It is also known as equilibrium distillation. Principle : When hot liquid mixture is allowed to enter from a high pressure into low pressure ,the entire liquid mixture is suddenly vaporized. This process is known as flash vaporization. During this process chamber where vaporization occurs gets cooled . The individual vapour phase molecules of high boiling fraction get condensed, while low boiling fraction remains as vapour.
- 14. CONT.. This process requires certain amount of time. Therefore ,the liquid and vapour are kept in intimate contact until equilibrium is achieved. Then liquid fraction is collected separately and separated vapour is further allowed to condense.
- 15. CONSTRUCTION It consist of pump which is connected to feed reservoir. Pump pumps the feed (liquid mixture which is to be separated) under high pressure into pipe which passes through the heating chamber. The heating chamber contains suitable heating mechanism. The other end of the pipe is directly introduced into the vapour liquid separator through reducing valve. The liquid outlet is provided at the bottom and vapour outlet is provided at the top of the separator.
- 17. WORKING : The feed is pumped through a heater at a certain pressure. The liquid get heated, which enter the vapour liquid separator through pressure reducing valve. Due to drop in pressure ,the hot liquid flashes, which further enhances the vaporisation process. The sudden vaporisation induces cooling. The individual vapour phase molecule of high boiling fraction gets condensed, while low boiling fraction remains as vapour. The mixture is allowed for a sufficient time ,so that vapour and liquid portions separate and achieve equilibrium. The vapour is separated through a pipe from above and liquid is collected from bottom of the separator.
- 18. DISTILLATION UNDER REDUCED PRESSURE ( VACUUM DISTILLATION) Distillation under reduced pressure may be defined as distillation process in which the liquid is distilled at temperature lower than its boiling point by the application of vacuum. Vacuum pumps, suction pumps etc. Are used to reduce the pressure on the liquid surface. Principle : Liquid boils when vapour pressure is equal to atmospheric pressure . If the external pressure is reduced by applying vacuum ,the boiling point of liquid decreases. Therefore , the liquid boils at lower temperature.
- 19. CONSTUCTION It consist of double neck distillation flask known as claisen flask . In one of the necks of the claisen flask ,a thermometer is fitted. The second neck a capillary tube is fitted which prevents bumping of the heating liquid. The claisen flask is connected to a receiver through a condenser. Vacuum pump is attached through a adapter to the receiver.
- 21. WORKING The liquid to be distilled is filled one half to two third volume of flask. Small pieces of porcelain are added to the liquid for facilitating distillation and prevent bumping. The capillary tube and thermometer are kept in place in the flask. The required vacuum is applied. The contents are heated gradually. The temperature rises and liquid gets vaporised rapidly due to vacuum. The vapour passes through condenser. The condensate is collected in the receiver.
- 22. STEAM DISTILLATION Steam distillation is method of distillation carried with aid of steam and is used for separation of high-boiling substances from non-volatile impurities. High boiling liquids cannot be purified by simple distillation, since constituents in the mixture tends to decompose at higher temperature. In such cases ,steam distillation is employed. Steam distillation is used for the separation of immiscible liquids.
- 23. PRINCIPLE A mixture of immiscible liquids begins to boils when the sum of their vapour pressure is equal to the atmospheric pressure. In consider the mixture water and turpentine, mixture boils below boiling point of pure water, though the turpentine boils at much higher temperature than that of water. For example ,boiling point of turpentine is about 160尊c . But when it is mixed with water and heated ,the mixture boils at about 95.6尊 c. At this temperature ,the vapour pressure of water is 647mmhg and that of turpentine is 113 mm Hg. The sum of vapour pressure is 760 mmHg which normal atmospheric pressure. Thus, high boiling substances may be distilled at temperature much below its boiling point.
- 24. CONSTRUCTION It consist of metallic steam can fitted with cork having two holes. Through one of the holes, a long tube is passed so as to reach almost the bottom of steam generator. This tube acts as safety tube, so that in case the pressure inside the steam generator becomes too much ,water will be forced out of it and the pressure will be relieved.
- 25. CONT.. When steam starts coming out from the safety tube , it indicate that the steam can is almost empty. Through another hole, the bent tube is passed. The other end of bent tube is connected to the flask containing non-aqueous liquid. This tube should reach almost bottom of the flask. Through other hole ,a delivery tube is inserted which connects the flask and the condenser. The condenser connected to receiver flask using adapter.
- 27. WORKING The non-aqueous liquid is placed in the flask. Quantity of water is added to it. Steam can is filled with water. The steam generator and flask are heated simultaneously ,so that uniform flow of steam passes through boiling mixture. This mixture gets heated. The steam carries the volatile oil and passes into condenser, which is cooled by cold water. The condensed immiscible liquid is collected into receiver. Distillation is continued until all non-aqueous liquid has been distilled. In receiver ,water and organic liquid form two separate layers ,which can be easily separated using separating funnel.
- 28. FRACTIONAL DISTILLATION Fractional distillation is process in which vaporisation of liquid mixture gives rise to mixture of constituents from which desired one is separated in pure form. This method is also known as rectification, bcz a part of the vapour is collected and returned as liquid. This method is used to separate miscible volatile liquids ,whose boiling points are close, by means of a fractionating column. In fractional distillation the vapour must pass through fractionating column in which partial condensation of vapour is allowed to occur. The condensation takes place in the fractionating column ,so that a part of the condensing vapour returns to the still.
- 29. PRINCIPLE : When a liquid mixture is distilled ,the partial condensation of the vapour is allowed to occur in fractionating column. In the column ,ascending vapour from the still is allowed to come in contact with the condensing vapour returning to the still. By condensing the vapour and reheating the liquid repeatedly, equilibrium between liquid and vapour is set up at each stage, which ultimately results in the separation of a more volatile component.
- 30. CONSTRUCTION A laboratory scale fractional distillation unit consist of : A source of heat Distillation flask A fractionating column A thermometer A condenser A receiver.
- 32. WORKING The mixture to be distilled is fed to boiler and heated usually by steam. The liquid mixture is put into a distillation flask along with a few pieces of porcelain to avoid bumping. Then fractionating column is fitted over the mouth of flask. Heat the mixture . As mixture boils ,vapour rises up the column. The vapour condenses on the glass plateforms known as tray, insides the fractionating column, and runs back down into the liquid below. This is known as refluxing the distillate.
- 33. CONT.. Only the most volatile fraction of the vapours remains in gaseous form all the way to the top of the column. This fraction passes into condenser ,which cools it down to a liquid ,and this liquid is collected in the receiver.
- 34. THEORY According to principle of colligative properties ,when a substance is dissolved in a liquid ,the vapour pressure of solvent is lowered. When two miscible liquids are mixed ,each may be considered as a solution of one in the other. The vapour pressure of each component is lowered. The pressure excreted by each one is known as partial pressure.
- 35. GENERAL METHODS FOR FRACTIONAL DISTILLATION Consider , mixture of two miscible liquid A and B containing 20% of A and 80% B. Liquid A (more volatile component ) is having a lower boiling point than B (less volatile component). These liquids do not produce constant boiling point mixture. The boiling point composition curve of this mixture shown in fig. 1) When boiling point of the mixture is reached ,the vapour composition curves are drawn as shown by lowest pair of curves. These curves indicates that vapour contains 60% of A.
- 37. CONT.. 2) when this vapour is condensed ,the resulting liquid is again heated to boiling point, this vapour gives the composition containing 90% of A. 3)This vapour impinging on a cool surface and gets condensed. This fraction is revaporised by heating to its boiling point. This boiling point curve of this distillate indicates 98% of A. 4) This fraction of vapour impinges on cooling surface. This gives fourth pair of curve. Now this vapour contains higher (more than 98%)proportion of A. 5)The vapour moves to condenser at the top of the column and gets condensed.
- 38. CONT.. Thus ,repetition of these processes yield pure A . Once a low boiling point fraction has passed over ,distillation should be stopped. The liquid available in the still is pure B. It can be collected as such.
- 39. AZEOTROPIC SOLUTION Azeotropic solution ( constant boiling point) cannot be completely separated by fractional distillation, because either vapour or the liquid in the still has mixture of components. The principle of azeotropic distillation lies in addition of a new substance to the mixture so as to increases relative volatility of one of the two key components and thus making separation relatively easy. Azeotropic distillation is a distillation method in which azeotropic mixture is broken by the addition of third substance, which form a new azeotrope with one of the component.
- 40. ADVANTAGE It is easy to use. It is highly effective and efficient. Disadvantages It can be expensive. it can contribute to environmental pollution. It cannot be used to separate miscible liquids which forms azeotropic mixture
- 41. MOLECULAR DISTILLATION Molecular distillation is defined as a distillation process in which each molecule in the vapour phase travels mean free path and gets condensed individually without intermolecular collisions on application of vacuum. This is also called as evaporative distillation or short path distillation. Mean free path is the distance travelled by the molecules in straight line without any collision.
- 42. PRINCIPLE The substances to be distilled have very low vapour pressure . Example are viscous liquids ,oils ,greases, waxy materials and high molecular weight substances. These boils at very high temperature . In order to decrease boiling point of the liquid , high vacuum must be applied. At very low pressure ,the distance between evaporative surface and the condenser is approximately equal to the mean free path of the vapour molecules. Molecules leaving the surface of the liquid are more likely hit the condenser surface than to collide with other molecule.
- 43. TWO TYPES OF MOLECULAR DISTILLATION Falling film or wiped film molecular still Centrifugal molecular still Falling film molecular still Principle : In this method, vapourisation occurs from liquid film flowing down a heated surface under high vacuum. The vapour travels a short distance and strike the condenser nearby. Each molecule is condensed individually. The distillate is subsequently collected.
- 44. CONSTRUCTION The wall of the vessel are provided with suitable means of heating (jacket). Wipers are provided adjacent to the vessel wall. Wipers are connected to rotating head through rotor. The condenser are arranged very close to the wall . Vacuum pump is connected to large diameter pipe at the centre of the vessel. Provisions are made for collecting distillate and the undistilled liquid residue at the bottom.
- 46. WORKING The 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 inlet of the vessel. As a liquid flows down the walls,it is spread to form a film by wipers . Wipers are moving at the rate of 3 meter per second. The surface is already heated which causes the liquid film to evaporate immediately. The vapour (molecules) travels its mean free path and strikes the condenser. The condensate is collected into a vessel. The residue is collected from bottom of the vessel .
- 47. CENTRIFUGAL MOLECULAR STILL Principle : Liquid feed is introduced into vessel,which rotate at very high speed (centrifugal action). This centrifugal force spread the liquid feed as thin film. Due to heating, vapourisation occurs from film of liquid on the sides of the vessel. The molecules of vapour travel a short distance and gets condensed on the adjacent condenser. Each molecule condensed individually. Distillate is subsequently collected.
- 48. CONSTRUCTION It consist of bucket shaped vessel having diameter of about 1 t0 1.5 meter. It is rotated with high speed using a motor. Radiant heaters are provided externally to heat the fluid in the bucket. Condenser are closely arranged to evaporating surface. Vacuum pump is connected to entire vessel at the top. Provision are made for introducing the feed into centre of the bucket , for receiving the product .
- 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 the rotating bucket ,liquid moves outward over the surface of the vessel and forms a film. Since , radiant heaters heat the surface, the liquid evaporates directly from the film. The vapour travels its mean free path and strikes the condenser. The condensate is collected into another vessel.