Distillation is a very important mass transfer operation which is used to separate components based on the difference in boiling points. it is used in refineries to distill crude oil into useful petroleum products. There are two phases liquid and gases. As in distillation all the components are volatile, so all components will be there in liquid and vapour phase, but the more volatile component has lesser boiling point, so has more tendency to be in vapour phase at any temperature, compared to less volatile components. The temperature increases down the column.
At any temperature, a component has a vapor pressure which makes it to go in vapor phase. When vapour and liquid streams at different temperatures (not in equilibrium) are brought in contact, more volatile in the liquid phase will vaporise and less volatile from the vapour phase will condense. So, vapour phase will be enriched with more volatile and liquid phase will be enriched with less volatile components.
Distillation column has two sections: extraction and enriching or stripping and rectifying. Extraction or stripping (bottom section) refers to more volatile component which gets extracted or stripped from less volatile component and get rectified or enriched (top section) at the top.
In distillation of binary mixture let say benzene (x in liquid, yin vapor) and toluene ;
Let at any plate x = 0.3 and y = 0.6; then can benzene be transferred from the liquid to vapour phase, that means low concentration (0.3) to high concentration (0.6). the answer is difference in pressure of benzene in liquid and vapor phases.
the pressure in the liquid phase is calculated through Raoult’s law (pA = xAPv) and vapor phase pressure is calculated by Dalton’s law (pA = yAPT); if the pressure in liquid phase is higher, then the component will go in vapor phase increases till the pressure in vapor phase becomes equal to liquid phase pressure.
In distillation of binary mixture let say benzene (x in liquid, yin vapor) and toluene ;
Let at any plate x = 0.3 and y = 0.6; then can benzene be transferred from the liquid to vapour phase, that means low concentration (0.3) to high concentration (0.6). the answer is difference in pressure of benzene in liquid and vapor phases.
the pressure in the liquid phase is calculated through Raoult’s law (pA = xAPv) and vapor phase pressure is calculated by Dalton’s law (pA = yAPT); if the pressure in liquid phase is higher, then the component will go in vapor phase increases till the pressure in vapor phase becomes equal to liquid phase pressure.
