Mass transfer equipmentMass transfer equipment are used mainly for separation of constituents of a mixture. Few others are also used as mixers. Separation of a desirable species from a mixture depends upon the nature of mixture. DistillationDistillation separates the components of liquid mixture due to difference in vapour pressureVapour pressure. Gas absorptionGas absorption is used to separate component from gaseous mixtures using different solubility. Packed and tray towers used for mass-transfer operations were discussed. Equilibrium relationship, pressure drop, and mass-transfer coefficients in process design of packed and tray columns were discussed. Methodology for process design of distillation and gas absorption in these towers were presented and illustrated through examples using numerical solutions using spreadsheets and graphical methods. Estimation of dew and bubble-point temperatures and FUG method for estimation of number of ideal plates for multi-component mixtures were discussed and illustrated..