[yOsh77]

Hi I'm currently trying to understand the distillation process, I don't get it why when pressure on the overhead condenser is increased, the lighter component in bottom product is increased. How does the pressure affect the components in the process? Please guide me, thanks.

[thelastone]

I'm not sure what you ask but I'll try:

Imagine two vessels, and in the second vessel (the overhead condenser), where all the products with a low boiling point go, suddenly you increase the pressure OR you cool this mix:
What will happen with the boiling point?
The products that are volatile will condense first?
What current then is reintroduced in your first vessel (column)?

[IshaniGupta]

As we increase pressure then tendency to vaporize for any component reduces and hence when increasing the pressure in overhead condenser it decreases then tendency to distill(i.e.vaporize by heating) so the component which has maximum probability of leaving the liquid state i.e. one having maximum volatility 's concentration increases in vapor. 

[Enthalpy]

Less pressure means a lower liquid temperature, which makes the evaporation less probable hence more selective.