Single stage distillation involves a continuous process where a liquid mixture is partially vaporized, while multistage distillation is typically used for seawater distillation with multiple stages of flashing and condensation to produce fresh water. Flash distillation is a single stage equilibrium process, whereas differential distillation is a batch process with a column for multiple equilibrium stages, allowing vapors to enrich and condense as distillate. Simple steam distillation uses steam to lower boiling points for separating temperature-sensitive materials.

1. 1. Briefly state the difference between single stage and multistage distillation. (i.e. you can solve
this question with an aid of the schematic diagram)
2. Briefly describe the equilibrium or flash distillation, simple batch or differential distillation,
and simple steam distillation.
Solution
1.SINGLE STAGE DISTILLATION :A single-stage continuous operation where a liquid
mixture is partially vaporized: the vapour produced and the residual liquid are in equilibrium,
which are then separated and removed. The feed is preheated before entering the separator. As
such, part of the feed may be vaporized. The heated mixture then flows through a pressure-
reducing valve to the separator. In the separator, separation between the vapour and liquid takes
place.
Multistage distillation : Method used for sea water distillation. The heated seawater flows to the
first stage, where it flashes upon entry. During flashing, some of the water vapour (steam) is
removed from seawater. The flashed vapour is then condensed on the outside of the tubes
carrying seawater feed to the brine heater.condensed steam is withdrawn as fresh water. The
unflashed portion of seawater now contains more salts, and is send to the second stage for further
flashing. The second stage is operated at a pressure lower than the first stage in order to lower
the boiling point of seawater.
At the second stage, more water vapour (steam) is flashed off, and is again recovered as fresh
water by condensing on the tubes carry seawater feed to the first stage. The remaining seawater
is then send to the third stage, at a lower pressure than the second stage, for more separation.
2.Flash distillation :It is also called single stage equilibrium explained above..
Differential distillation :Batch distillation is an unsteady state operation. It is usually carried out
in a batch still to which a column equivalent to a number of equilibrium stages is attached. As in
the case of simple distillation, a fixed quantity of liquid is originally charged to the batch still.
During distillation, the vapour passes upward through the column. The whole column is an
enriching section. The vapour is condensed into liquid at the top of the column. Part of the liquid
is returned to the column as reflux, and the remainder withdrawn as distillate. Nothing is added
or withdrawn from the still until the run is completed.

2. Simple steam distillation : Steam distillation is a separation process used to purify or isolate
temperature sensitive materials, like natural aromatic compounds. Steam or water is added to the
distillation apparatus, lowering the boiling points of the compounds. The goal is to heat and
separate the components at temperatures below their decomposition point.