Question

Explain the effects of distillation rate, column packing, and column height on fractionation. When is a fractionating column necessary?

Answer 1

An important factor affecting the separation of the compounds is:

Distillation rate number of drops per second. If the distillation is conducted too rapidly, liquid-vapour equilibrium will not be established in the fractionating column, and poor separation of the compounds will result.

An actual number of trays required for a particular separation duty is determined by the efficiency of the plate, and the packings, hence efficiencies are affected by fouling, wear and tear and corrosion, and the rates at which these occur depends on the properties of the liquids being processed. Liquids tend to wet the surface of the packing, and the vapours pass across this wetted surface, where the mass transfer takes place. Differently shaped packings have different surface areas and void space between packings. Both of these factors affect packing performance.

The effectiveness of separation is dependent upon the height and diameter of the column, the ratio of the column's height to diameter, and the material that comprises the distillation column itself. Vapour flow velocity is dependent on column diameter

Substances in a mixture have large differences in boiling points, a simple distillation is adequate to be implemented. No fractionating column is required for use as single distillation cycle is enough to separate the mixture.

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