types of distillation

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Presentation Transcript

Simple distillation: 

Simple distillation Principle- Also known as differential distillation -differences in volatilities and vapour pressures of the components in the mixture. Liquid boils when its vapour pressure is equal to atmospheric pressure. Heat is supplied to the liquid so that it boils Vapour condensed.

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Construction- Flask- to Condenser Receiver flask Adaptor Procedure- Liquid to be distilled is filled into the flask to one half. Bumbing avoided by adding small pieces porcelling The contents are heated begain to boil and vapourbegains to up and passes down the side arm into the condenser. The vapour is condensed and collected into the receiver.

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Application Used for prepartion of distilled water and water for injection. Voltile and aromatic waters are prepared. Organic solvents are purified. Non volatile solids are separated from volatile liquids.

Flash distillation: 

Flash distillation Flash distillation defined as a process in which the entire liquid mixture is suddently vapourized by passing the feed from a high pressure zone to a low pressure zone. During this process the chamber gets cooled. The individual vapour phase molecules of high boiling fraction get condensed while low boiling fraction remains as vapour. This process requires some time until equilibrium achived Liquid fraction collected separtley and vapour allwded to condesnce.

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Construction PUMP- to pump feed into the heating chamber. FEED RESERVIOUR Heating chamber Vapour- liquid separtor Vapour outlet Liquid outlet Pressure reducing valve

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Working Feed is pumped through a heater at cetain pressure. Liquid gets heated which enters the vapour liquid separator through pressure reducing valve. Due to drop in pressure, hot liquid vaporization induces cooling. High bp liquid get condensed and low bp liquid remains as vapor form. The mixture is allowed for a sufficient time so that vapor and liquid portions separate and achieve equilibrium

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The vapour above and liquid from bottom It could be continuous process. USES- Separating components are boil at different temps. Widely used for petroleum industry for refining crude oil.

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Advantages Continuous process Multicompoents system Disdavantges Not effective in separting components of comparable volatility. Effeciency is low becoz nearly pure components are required.

fractional distillation: 

fractional distillation Fractional distillation 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 known as rectification becoz part of vapour is condensed and returned to a liquid

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PRINCIPLE- When a liquid mixture is distilled ; partial condensation of the vapour is allowded to occur in a fractionating column. The heat evolved from the condensation of the vapour is employed to boil out new vapours from the succeding steps. A portion of the previously evolved vapors is condensed and acts as the heat receiver for the fresh condensing vapours . This condensed vapours which are returned in the individual steps are called reflux This method is known as rectification.

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CONSTURCTION- Still or reboiler- to generate vapours. Rectifying or fractionating column- -provision is made to supply heat to athe bottam of column Top of column condenser provided

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Column- used to bring liquid- vapor into contact so that vapor tends to vaporize the low bp constituents from the liquid. The liquid stream tends to condense the high bp constituents from the vapour. BUBBLE CAP PLATE COLUMN Column – divided into sections by series of horizontal plates. SIEVE PLATE COLUMN Series of horizontal perforated plates assembled at a definite intervals in a cylindrical colummn.`

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WORKING heat the mixture of two or more substances (liquids) with different boiling points to a high temperature. Heating is usually done with high pressure steam to temperatures of about 1112 degrees Fahrenheit / 600 degrees Celsius. The mixture boils , forming vapor (gases); most substances go into the vapor phase.

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The vapor enters the bottom of a long column ( fractional distillation column ) that is filled with trays or plates. The trays have many holes or bubble caps (like a loosened cap on a soda bottle) in them to allow the vapor to pass through. They increase the contact time between the vapor and the liquids in the column and help to collect liquids that form at various heights in the column. There is a temperature difference across the column (hot at the bottom, cool at the top). The vapor rises in the column. As the vapor rises through the trays in the column, it cools .

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When a substance in the vapor reaches a height where the temperature of the column is equal to that substance's boiling point, it will condense to form a liquid. (The substance with the lowest boiling point will condense at the highest point in the column; substances with higher boiling points will condense lower in the column.). The trays collect the various liquid fractions. The collected liquid fractions may pass to condensers, which cool them further, and then go to storage tanks, or they may go to other areas for further chemical processing Fractional distillation is useful for separating a mixture of substances with narrow differences in boiling points, and is the most important step in the refining process.

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Uses Used for the separtion of miscible liquids such as acetone and water, chloroform and benzene. Disadvantges To separte miscible liquids which form azeotropic mixtures.

Azotropic and extractive distillation: 

Azotropic and extractive distillation Azotropic solutions – cannot be completely separated by fractional ditillation Becoz of either the vapour or liquid in the still has a mixture of components. Principle- Azeotropic distillation is a distillation method in which azeotropic mixture is broken by the addition of a third substance which forms a new azeotrope with one of the components.

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3 rd sub added to the mixture so as to increase the relative volatility of one of the two key components thus making separation relatively eazy . 3 rd sub Non volatile compared to components to be separated . 3 rd sub withdrawn at the base of the fractionating columns. Eg azotropic mixture – water and ethyl alcohol – benzene added to break and forms a new azeotrope benzene and ethyl alcohol Furfural added to separate butadiene contain butane and butane

Distillation under reduced pressure: 

Distillation under reduced pressure Distillation under reduced pressure is a process in which the liquid is distilled at a temp lower than its boilng point by the application of vacuum. Liquid boils – Vapour pressure = atmospheric pressure , if atmosphric pressure reduced by applying vaccum the bp of liquid decreases. Thefore liquid boils at lower temp. Mass of vapour formed α vp of evaporting liquid Exteranal pressure

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Construction- Double neck distillation flask- clasian flask One neck –thermomether fixed. Second neck – prevents splashing of violently agitated liquid. To avoid bumbing fine capilllary tube placed Interchangeable standard glass joints Receiver Condenser

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Working- The liquid to be distilled is filled one half to two third volume of the flask. Capillary tube and thermomether place in flask. The required vacuum is applied. The contents are heated gradually The temp reises and liquid gets vaporised rapidly due to vacuum The vapour passes through the condeser . The condensate is collected in the reciver The temp note down would be less than the bp of the liquid.

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Application- Preventing degradation of active constituents Eg vitamins, enzymes,alkaloids, tannins, glycosides Changing physical form. Eg cascara tablets Disadvantages Persistant foming occurs

Molecular distillation: 

Molecular distillation Molecular distillation defined as a distillation in which each molecule in the vapour phase travels mean free path and gets condensed individually without intermolecular collisions on application of vaccum . The evaporting suface must be close to the condesing suface so that the molecules to come in contact with condenser as soon as they leave the evaporting suface so this is also called as evaporative distillation or short path distillation.

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Liquids to be distilled have very low vapour pressures. Eg . Viscous liquids, oils, greases, waxy materials and high molecular weight. To decrease the boiling point of the liquids high vacuum must be applied. The mean free path of a molecule is defined as the average distance though which a molecule move without coming into collision with another. To minimize molecular collisions and to increase intermolecular distance high vacuum is applied. The liquid surface area must be a large possible vapours are formed from surface only not by boilng so this process called as evaporation distillation.

Falling Film molecular still or wiped Film molecular still: 

Falling Film molecular still or wiped Film molecular still Principle- Vaporization occurs from a film of liquid flowing down a heated surface under high vacuum. The vapour travels a short distance and strikes the condenser nearby; molecule is condensed individually. Subsquently distillate is collected.

Slide 37: 

Vessel- Provided with heating jacket Wipers connected to a rotating head through a rotor – allow to rotate. The condensers are arranged very close to the wall Vaccum pump connected to large dia pipe at the center of the vessel. Distilate collecte and undistilled liquid residue at the bottom.

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Working The feed is passed through the inlet of the vessel. As the liquid flows down the walls, it is spread to form a film by PTFE wipers(3 mt/ sec). The vapour travels its mean free path and strikes the condenser. The condensate is collected into the vessel. Undistlled again recycled again.

Centrifugal molecular still: 

Centrifugal molecular still Principle- Liquid feed is introduced into a vessel, rotated at very high speed (centrifugal). On heating, vapourization occurs forming film on ht sides of vessel. The vapour molecules travels a short distance and gets condensed on the adjacent condenser. Each molecule is condensd individully Distillate collected subsequently.

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Construction Bucket shaped vessel Radiant heaters are provided. Condensers arranged closely to evaporating surface Vacuum pump provided. Distillate outlet, feed inlet and nondiatillate to recirculate.

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Working The bucket vessel is allowded to rotate at high speed and vaccum applied at center of the vessel. Due to centrifugal effect liquid moves outward over the suface of the vessel and forms a film. As radiant heaters provided the liquid evaporators directly from the film. The vapour molecules travels its mean free path and strikes the condenser. The condensate collected and residuce recirculated throuhgh feed port .