Distillation (Pharmaceutics)

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Distillation:

Distillation V V S Narayana Reddy Karri Lecturer Dept of Pharmaceutics JSS College of Pharmacy, Ootacamund ( JSS University, Mysuru ) Rocklands Udhagamandalam.

Introduction:

Introduction Condensing Liquid Liquid Heat Distillation is the process of converting liquid into its vapors by heating and reconverting it again in to liquid by condensing the vapors . The distillation process is carried out in an apparatus which consists of: Still , in which volatile material is boiled Condenser, in which vapors are condensed Receiver, in which distillate is collected 1 2 3

Types of Distillation Process:

Types of Distillation Process Simple Distillation Distillation under reduced pressure Fractional distillation Steam distillation

When Liquid Boils..?:

When Liquid Boils..? General Under Reduced Pressure Mixture of liquids V.P: Vapor pressure, B.P: Boiling point, A.P: Pressure V.P=A.P V.P=A.P B.P is reduced Sum of partial pressure (A+B)=A.P A B

1. Simple Distillation:

1. Simple Distillation It is process of converting a liquid into its vapor in a distillation still , transferring the vapor in to condenser and condensing again in to liquid Apparatus: Distillation flask with a side arm slopping down which is connected to a condenser . The condensed vapors are collected in a flask called receiver. The thermometer is fitted in the distillation flask to note down the temperature, at which the vapors are distilled . Bumping is avoided by adding small piece of porcelain before distillation. Applications

2. Distillation under “reduced pressure”:

2. Distillation under “reduced pressure” Theory: Liquid boils when its vapor pressure is equal to the atmospheric pressure . The boiling point of the liquid may be lowered to the desired temperature by reducing the pressure on its surface . Apparatus: Double-neck Distillation flask ( claisen flask) In one neck thermometer is fitted in second neck a capillary tube is fixed The distillation flask is connected to a condenser. The condensed vapors are collected in a flask called receiver. Vacuum pump is attached to the receiver to attain the desired degree of vacuum Applications: Extracts containing Thermo liable substances

Vacuum Still:

Vacuum Still Vacuum stills are employed for distilling substances under reduced pressure on large scale Construction and working: A vacuum still is made of stainless steel or any other metal which can withstand high vacuum. The still is connected to a condenser. The vacuum is created by means of a vacuum pump. An observation window in the hood is very helpful to the operator to see the progress of distillation and also the level of content of liquid to be distilled. Two receivers are generally attached to the condenser in order to collect the distillate without stopping distillation . Condenser

3. Fractional Distillation (Distillation of miscible liquids):

3. Fractional Distillation (Distillation of miscible liquids) Theory: When a substance is dissolved in liquid, the vapor pressure of the liquid is lowered . When two miscible liquids are mixed together, each will act as solute for the other. So, when a mixture of two such liquids is heated, the vapor pressure of each is lowered. The pressure exerted by each liquid in the mixture is known as partial pressure. The liquid boils when sum of the partial pressures is equal to the atmospheric pressure . Apparatus: Fractionating column is fitted b/w the distillation flask and condenser. Fractionating column is used for continuous separation of two miscible liquids. The distillation flask is connected to a condenser. The condensed vapors are collected in a flask called receiver. The liquid with higher boiling point is condensed first and vapor becomes richer with the liquid having lower boiling point which get condensed later.

4. Steam Distillation (Distillation of immiscible liquids):

4. Steam Distillation (Distillation of immiscible liquids) Theory: When two immiscible liquids are mixed together , The liquid boils when sum of the partial pressures is equal to the atmospheric pressure . So, when a mixture of two such liquids is heated, the vapor pressure of each is lowered. The pressure exerted by each liquid in the mixture is known as partial pressure. Steam Can Apparatus: Consists of ‘steam can’ fitted with a cork having two holes. Through one hole steam is passed through bent tube into the flask containing non-aqueous liquid. The another tube (safety tube) is long and kept almost to the bottom of the steam can. It will remove the excess pressure incase the pressure is too much. The delivery tube carries vapors from the flask is connected to condenser and then condenser is connected to receiver. The distillate is then collected in florentine receiver where oil is completely separated from water.

Florentine Receivers:

Florentine Receivers Type-I Type-II

Purified water I.P Vs. Water for Injection I.P:

Purified water I.P Vs. Water for Injection I.P Purified water I.P Water for Injection I.P Water which is free from volatile and non-volatile impurities Water which is free from volatile and non-volatile impurities, micro-organisms and pyrogens Prepared by distillation, ion-exchange and reverse osmosis process Prepared by distillation of potable water, purified water or distilled water. It contains no added substances It contains no added substances It is liable to contaminate by micro-organisms , hence not been used for preparations meant parenteral administration. It need not to be sterile but it should comply with test for pyrogen . Stored in tightly closed containers Stored in tightly-closed neutral glass containers

Preparation of Purified water I.P and Water for Injection I.P:

Preparation of Purified water I.P and Water for Injection I.P Potable water is used for the preparation of purified water. It contains: Dissolved gases Dissolved salts and solids This can be avoided by By heating the water (The solubility of the gases decreases when temperature increases) A constant level device is attached to the boiler to avoid excessive concentration of salts

Slide 13:

Distillation Unit for Purified Water It consists of boiler which is made of cast iron . It is connected to the condenser tubes through the baffles. Baffles are provided over the top of the condenser tubes to avoid water drops getting mixed with the vapors . The cooling water enters at the bottom of the condenser and is heated by the condensing vapors The flow rate is adjusted in such a way that water gets heated at 90-95 0 C before it enters the boiler. The top of the condenser is open so that gases from the water can escape into the atmosphere .

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