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fractional distillation, molecular distillation


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Distillation Presented by Miss. Argade P. A Assistant Professor SHREE SANTKRUPA COLLEGE OF PHARMACY, GHOGAON .


FLASH DISTILLATION Principle: Hot liquid is allowed to enter from a high pressure to low pressure zone. Mixture is vapourised . V apour phase molecule of high boiling fraction get condensed, while low boiling fraction remains as vapour . Equilibrium is achieved.

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Uses: Petroleum industry for refining crude oil. Advantages: Continuous process. Disadvantages : Not suitable for two Component system. Fig no.1 Flash distillation


FRACTIONAL DISTILLATION Principle: Liquid mixture is distilled, condensation of the vapour occur in the fractionating column. ascending vapour from the still is come in contact with the condensing vapour returning to the still. condensing the vapour and reheating the liquid repeatedly. Equilibrium is achieved between liquid and vapour .

Fig no. 2 Assembly of apparatus for fractional distillation (laboratory scale):

Fig no. 2 Assembly of apparatus for fractional distillation (laboratory scale)

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Working: Two miscible liquid A and B containing 20% of A and 80% B. A have low B.P than B.P These liquid do not produce Constant boiling point. Fig no. 3 Fractional distillation apparatus for large scale

Fractionating column:

Fractionating column Packed column Plate column


DISTILLATION UNDER REDUCED PRESSURE Liquid is distilled at a temperature lower than it’s boiling point by the application of vaccum . Applications: Preventing degradation of active constituents. Changing physical form.

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Fig no.6 Distillation under reduced pressure (Laboratory scale)

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Procedure : Liquid distilled is filled ½ to 2/3 volume. Capillary tube, thermometer Kept in place in the flask. ↑ Temperature, liquid vapourised . Vapour pass through the Condenser. Condensate is collected into the receiver Fig no.7 Distillation under reduced pressure (industrial scale).


MOLECULAR DISTILLATION Principle : Substances to be distilled have very low vapour pressures. Boils at very high temperature. ↓B.P of the liquids then high vaccum is applied. At low pressure, the distance between evaporating surface and condenser is equal to mean free path of the vapour molecule .

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Applications: Refining of fixed oils. Vitamin A seperated From fish liver oil. Purification of Chemicals such as tricresyl phosphate, Dibutyl pthalate and dimethyl pthalate . Fig no.8 Molecular distillation


References: Sharp , K.A., Nichollis , A., Fine, R.F. and Honig , B (1991 ).  Science ,  252 , 106. Anderson , R. and Prausnitz , J.M. (1961).  AIChE J .,  7 , 97. Barton , A.F. (1983).  Handbook of Solubility Parameters and other Cohesion Parameters , CRC Press, Florida. Garner , F.H. and Ellis, R.M. (1951).  Trans. Inst. Chem. Eng. ,  29 Anderson , R., Cambio , R. and Prausnitz , J.M. (1962).  AIChE J . ,  8 , 67.

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