Distillation

Full Distillation technique where you find about various terminologies, its principle in which raolt's law and henry's law, assembly, classification. Distillation apparatus with their principle, advantages and disadvantages and detailed abour steam distillation and azeotropic distillation.

1. Distillation Prepared by, Nilam Kaushikbhai Mistry 2 nd Semester, M.Pharm - PCH Pharmaceutical Process Chemistry Enrollment No: 190821212003 1

2. Contents: Introduction Terminology Principle Distillation assembly Classification Steam distillation Azeotropic distillation Application 2

3. Introduction: Distillation is a separation of a two or more components of a liquid mixtures by process of partial vaporization and subsequent condensation to recover two or more of the components in a nearly pure state.(1) OR Distillation is the process of separating the components or substances from a liquid mixture by selective boiling and condensation.(2) 3

4. History(3,4) The earliest evidence of distillation comes from a terracotta distillation apparatus dating to 3000 BC in the Indus valley of Pakistan. Distillation was known to be used by the Babylonians of Mesopotamia around 1200BC. Initially, distillation is believed to have been used to make perfumes. The Arab chemist Al-Kindi distilled alcohol in 9th century Iraq. Distillation of alcoholic beverages appears common in Italy and China starting in the 12th century. 4

5. Still of Democritos, also called the alembic of Synesios, which originally meant kettle, in which water was boiled , fourth century A distillation plant in Damascus consisting of multiple units for producing rose water, thirteenth century. This apparatus was originated from the Alexandrian philosophy schools in the first centuries AD 100 to 900, which overlaps with the Arabian period (AD 700 to 1600). The apparatus consists of four elements: (1)head (helmet dalembicum), (2)receiver (vessel drecaptaculum), (3)still (4) sand bath or water bath on a tripod. 5

6. Terminology(5) Binary mixture : When two liquids mixed together, they may be miscible with each other in all proportion, such miscible liquid are known as binary mixtures of liquid. Example: 1. Ethanol + Water 2. Acetone + Water Ideal Solution : The one in which there is no change in the properties of components other than dilution, when they mixed to form a solution. Properties: 1. Total volume of solution is equal to sum of volume of each component. 2. No heat absorbed and evolved. 3. No change in reaction in-between. 4. Follow Raoult’s law Example: Benzene and toluene 6

7. Real Solution : Most system shows varying degree of deviation from raoult’s law, depending on nature of liquids and temperature. These solution are known as real solutions. Properties: 1. Heat may absorbed or evolved 2. Chemical reaction occur in-between 3. Don’t follow raoult’s law Example: Acetone and Chloroform Volatility : any substance in solution may be defined as the equilibrium partial pressure of substance in vapour phase divided by the mole fraction of substance in the solution. Example: substance A in a liquid mixture has partial pressure PA and its concentration in the mixture is XA on mole fraction scale. Volatility of compo. A = Partial vapour pressure of A Mole fraction XA of A in solution VA = PA/XA The volatility of a material in the pure state is equal to the vapour pressure of the material. 7

8. Relative volatility( α ) : Consider a liquid mixture containing two component A and B, In such case, the volatility of one component is expressed in terms of second as below, α = Volatility of compo. A(VA) Volatility of compo. B(VB) Vapour pressure : The pressure exerted by vapor in thermodynamic equilibrium( transformation of matter and energy in systems as they approach equilibrium) with its condensed phases (solid or liquid) at a given temperature in a closed system. Azeotropic mixture : Mixture of special composition given minimum OR maximum boiling point respectively. 8

9. Principle(1,6) The principles are referred by VAPOR–LIQUID EQUILIBRIUM DIAGRAM . The diagram relates to a binary mixture containing components P and Q. The lower curve gives the composition of the liquid boiling at various temperatures whilst the upper curve gives the composition of the vapor in equilibrium with the boiling liquid. Points x and y, therefore, give the boiling points of the individual components P and Q, respectively. For example, point A shows that at X degrees the vapor has a composition of approximately 90% P, whilst point B shows that the boiling liquid with which it is in equilibrium has a composition of approximately 80% P. In a continuous distillation process, such as occurs in a distillation column, liquid of composition C (90% Q, 10% P) vaporizes to vapor of composition D, which condenses to liquid of composition E. Subsequently, liquid E becomes vapor F and liquid G (composition: 50% Q, 50% P). This continuous process of vaporization and condensation occurs in the distillation column until a volatile fraction leaves the top of the column and is removed from the process by being collected in the collection flask. At the same time the liquid in the distillation flask becomes progressively more concentrated in the involatile component. 9

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11. Raoult’s Law(6,8): It express a quantitative relationship between the concentration and vapour pressure . It states that partial vapour pressure of each volatile constituent is equal to vapour pressure of the pure constituent multiplied by its mole fraction in the solution at a given temperature. Suppose Homogeneous mixture of liquid A and B Partial vapour pressure of component A in mixture PA = P ̊ A * XA… 1 Mole fraction of A in solution = XA Vapour pressure of A in pure state = P ̊ A Partial vapour pressure of component B in mixture PB = P ̊ B * XB Mole fraction of B in solution XB = (1 – XA) Vapour pressure of B in pure state = P ̊ B Total vapour pressure of mixture PT = PA + PB PT = P ̊ A * XA + P ̊ B * XB 11

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13. In addition as per Dalton's law PA = YA * PT Molecular fraction of A in vapour = YA YA = PA = PA PA +PB PT = P ̊A * XA = P ̊A * XA P ̊A * XA + P ̊B * XB PT YB = P ̊B * XB PT Now , YA + YB =1 P ̊A * XA + P ̊B (1 – XA) = 1 PT PT XA= PT - P ̊B P ̊A - P ̊B 13

14. Limitation of Raoult’s law For some pairs of liquids this law holds quite well for all concentrations, e.g.. Pentane and heptane, benzene and chlorobenzene. In other cases such as hydrochloric acid and water, alcohol and water it doesn’t hold at all. It applies only to mixtures in which the components are very similar chemically and the molecules of the two substance do not interact in any way. Raoult’s law applies to many systems which states that is applies to the solvent(pure component) and is only valid to short range of compositions and composition rich in solvent(dilute solvent). 14

15. POSITIVE DEVIATION In some liquids systems, the total vapour pressure is greater than the sum of the partial pressures of the individual component Example: benzene and ethanol Differ in their polarity, length of hydrocarbon chain and degree of association. NEGATIVE DEVIATION In some liquids systems, the total vapour pressure is lower than the sum of the partial pressures of the individual component Example: chloroform and acetone Due to hydrogen bonding, salt formation and hydration. 15

16. Henry’s law(1,9) It is states that the partial pressure of liquid (solute) mixed in large amount of solvent is proportional to its mole fraction in the solution. PA α XA Partial pressure of component A over liquid mixture PA = HXA…. 2 Mole fraction of A = XA Henry’s law constant = H Now, Compare Raoult’s law 1 equation and Henry’s law 2 equation YA = PA OR H * XA PT PT YA= H’XA Where H’ = H PT Also written as H = c pA Where c = concentration in a liquid as pound mols per cubic foot pA = partial pressure of the solute in atmospheres. 16

17. Distillation Assembly(1) 17

18. STILL : It is a vaporizing chamber and used to place the material to be distilled. The still is heated by a suitable means of vaporization of the volatile constituents. On laboratory scale RBF ( round bottom flask ) made of glass are used so that the progress of the distillation can be noticed. A condenser is attached to the still using appropriate joints. A trap is inserted between distillation flask and condenser. 18

19. CONDENSER : Used to condense the vapor. It is kept cold by circulating water/air through jacket. TYPES Single surface condensers Straight tube Bulb type Spiral Coiled type Double surface condensers Multi – tubular condensers 19

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21. RECEIVER: It is used to collect distillate. It may be simple flask. It immersed in ice-bath to minimize loss of volatile matter. Florentine receivers are used for the separation of oil and water. TYPES: Type-1 : For separation of oil heavier than water. Type-2 : For separation of oil lighter than water 21

22. RECEIVERS 22

23. Classification(1,10): Simple distillation Flash distillation Vacuum distillation Molecular distillation Fractional distillation Destructive distillation Compression distillation Steam distillation Aezotropic distillation 23

24. 1. SIMPLE DISTILLATION: Principle : liquid boils when its vapour pressure is equal to atmospheric pressure. Is conducted at its BP. The higher the relative volatility of a liquid, the better is the separation by these distillation. Heat is supplied to liquid so that it boils. The resulting vapour is transferred to different place and condensed. Application : Used for preparation of distilled water and water injection. Volatile and aromatic waters are prepared. Organic solvents are purified. Non volatile solids are separated from volatile liquids. 24

25. 2. FLASH DISTILLATION: 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 which is known as flash vaporization . During these chamber gets cooled. The individual vapour phase molecules of high boiling fraction get condensed, while low boiling fraction remains as vapour. Application : Used for separating components, which boil at widely different temperatures. Used in petroleum industry for refining crude oil. 25

26. 3. VACCUME DISTILLATION: Principle : Liquid boils when vapour pressure is equal to atmospheric pressure, i.e., pressure on its surface. If the external pressure is reduced by applying vacuum, the boiling point of liquid is lowered. This principle is illustrated using an example of water. The net result is the increase in rate of mass transferred into vapour Application : Preventing degradation of active constituents Enzymes – malt extract, pancreatin Vitamins – thiamine, ascorbic acid Glycosides – anthraquinones 26

27. 4. MOLECULAR DISTILLATION : Principle: The substance to be distilled have very low vapour pressure. E.g., viscous liquids, oils, greases, waxy materials and high molecular weight substances. The pressure exerted by vapors above the liquid is much lower. At very low pressure, the distance between the evaporating surface and the condenser is approximately equal to the mean free path of the vapour molecules. Application : Used in the refining of mixed oils. Free fatty acids are distilled at 100 ̊C. Vitamin A is separated from fish liver oil. 27

28. 5.FRACTIONAL DISTILLATION: Principle: When a liquid mixture is distilled, the partial condensation of the vapour is allowed to occur in a fractionating column. In the column, ascending vapour from the still is allowed to come in contact with the condensing vapour returning to the still. This results in enrichment of the vapour with the more volatile component. Application: Used for the separation of volatile miscible liquids with near BP such as a 1. Acetone and water. 2. Chloroform and benzene 28

29. Distillation is decomposition product of constituents of the organic matter burnet in absence of air. Not used in lab practice but very useful in industrial process to obtain valuable product from wood, coal and animal matter. It involve the heating of dry organic matter in suitable vessel in absence of air, until all volatile substances are driven off. The distillate is the decomposition product of constituents. Wood distillation industry and coal caronation industry provides many useful fuel material with the method. 6. DESTRUCTIVE DISTILLATION: 29

30. Compression distillation method was developed to meet the need of navy and army for fresh water from sea-water. Product obtained is quite pure and pyrogen-free, there for it meets the requirement of Pharmaceutical industry. Its economical from the standpoint of consumption of fuel and water. The feed water is heated in an evaporator for boiling then a vapour gets separate and conveyed to compressor which raises its temperature to about 118 ̊ C It than flows to the steam chest where its condensed on the outer surface of tube. During condensation, heat is released which is allowed for heating of fresh feed in the tube. 7.COMPRESSION DISTILLATION: 30

31. STEAM DISTILLATION: 31

32. Steam distillation of volatile oils (1) 32

33. Steam distillation is method of distillation carried out with aid of steam. It is used to separate.. - high boiling substance from non-volatile impurities. - separate immiscible liquids. Examples: Boiling point of turpentine = 160 ̊ C Boiling point of water + turpentine mixture = 95.6 ̊ C At these temperature vapour pressure of Water = 86.245 kPa Turpentine = 15.06 kPa Sum of vapour pressure = 101.31 kPa Which is normal atmospheric Pressure and thus high boiling liquid may be distilled with water at a temperature much below its BP. 33

34. Principle : A mixture of immiscible liquid begins to boil when sum of their vapour pressure is equal to atmospheric pressure. In case of mixture of water and turpentine, mixture boils below the BP of pure water, though turpentine boils at a much higher temperature than that of water. Application : Used to separate immiscible liquids. E.g., water + toluene To extract volatile oils like clove, anise and eucalyptus oils Purification of essential oils like a almond oil. Camphor is distilled by these method. Aromatic water are prepared. Recovery of aniline from the reducer charge. 34

35. Construction : Metallic still can fitted with cork having two holes. Safety tube inserted up to bottom through one hole to maintain pressure in side steam can, more over when steam comes out from safety tube indicates that can is empty. Through other hole band tube is passed and other end of this tube is dipped. Flask and condenser is connected with delivery tube. Condenser is connected is receiver with help of adopter. 35

36. Working : Metallic steam can fitted with cock having two holes. Safety tube inserted up to bottom through one hole to maintain pressure in side stem can, more over when steam comes out from safety tube indicates that can is empty. Through other hole band tube is passed and other end of this tube is connected to flask containing non-aqueous liquid in which tube is dipped. Flask and condenser is connected with delivery tube. Condenser is connected to receiver with help of adopter. Provision are made to heat both steam and flask separately 36

37. Advantages : Steam distillation is used for thermo labile material as higher BP component boil below 100 C Disadvantages : Product is mixture of water and non-aqueous liquid, cannot separate completely. Limitation : Not suitable when two immiscible liquids react with each other. 37

38. Azeotropic distillation(5) 38

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40. Azeotropic distillation : Its volatility characteristics are always such that it forms one or more azeotropes, usually of the minimum boiling type, with the components of the system called azeotropic distillation. An entrainer that forms a heterogeneous azeotrope with one of the original component is advantageous because the recovery of the azeotrope former requires less equipment. Example: Use of benzene for dehydrating ethanol-water mixture. 40

41. A continuous azeotropic distillation unit for dehydrating alcohol-water azeotrope is shown in figure. The azeotrope is fed to column A. the required quantity of benzene is added to the feed. The vapour from column A, which approaches the ternary azeotrope in composition, when cooled to atmospheric temperature separates into a benzene phase and a water phase . These are separated in a decanter. The benzene phase is returned to the main column as a reflux and to serve as the entrainer and the water phase is fed to column B in which the benzene is recovered as the ternary azeotrope which is returned to column A. Aqueous alcohol from the base of column B is fed to a column C. The overhead from this column, which is 96 % alcohol, is recycled to the main column for dehydration, and practically pure water is discarded from the base of the column. Anhydrous alcohol is taken out as the residue from the main column A. since benzene is cycled continuously back to column A. Trichloroethylene, BP 87.2 ̊ C can be employed as the entrainer instead of benzene. 41

42. Dehydration of 96% alcohol to absolute alcohol by azeotropic distillation with benzene. 42

43. Application(1,3) Separation of volatile oils. Separation of drugs from plant and animal source. Purification of organic solvent. Manufacture of official preparations. Quality control methods. Refining of petroleum products. Recovery of solvents. Purification of drugs obtained from chemical process. Production of gasoline, distilled water, xylene, alcohol, paraffin. Gas like nitrogen, oxygen, and argon are distilled from air. For making food flavorings Used in perfume industries 43

44. Reference: Girish.K.Jani , H.G.Jani et al., Pharmaceutics -1 by B.S.Shah prakashan, page no: 243-364. Roger Ruan, Yaning Zhang, and Paul Chen et al., Biofuel: introduction, biochemical(2019), page no: 3-43. Anne marie helmenstine et al.,chemistry journal (2019) page no: 1- 5 Norbert Kockmann et al., history of distilation chemistry (2014), page no: 1-10 K. Sambhumurthy et al.,Pharmaceutical engineering by new age international limited, publishers, page no: 126-172 J.D.Green, encylopedia of anlytical science (2005), page no: 281-285. Ahmead.Y et al., Science and technology in islam (2001),page no: 65-69. J.F.Richardson, J.H.Harker et al., chemical engineering series vol -2 (2002), page no: 542-655. A.Kayode Cokar et al., chemistry journal vol -2 (2010), page no: 1-268. Wilfred l.F. Armando et al., 7 th edition chemistry (2013), page no: 1-70. 44

45. 11. Zeki Berk Professor et al., by food process engineering and technology 2 nd edition (2013), page no : 329-352. 12. Sue Clarke et al., by essential chemistry for aromatheraphy 2 nd edition (2008) , page no: 79-93. 13. Kasture et al., pharmaceutical engineering , B.S.Shah prakashan, page no :79-95. 45

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