Selection criteria for solvent in gas absorption :
While selecting a particular solvent for absorption operation, the following properties of the solvent are considered :
1. Gas solubility :
The solubility of a solute gas in a solvent should be high, i.e., the solvent should have a high capacity for dissolving the desired solute gas so that the less amount of the solvent will be required for a given absorption duty. In general, for good solubility, a solvent of chemical nature similar to that of the solute to be absorbed must be searched out and used.
The solvent selected should have a high solubility for the solute to be absorbed.
2. Volatility :
As the gas leaving an absorption unit is generally saturated with the solvent, there will be a loss of the solvent with the gas leaving the unit operation. Hence, to minimise the solvent loss (in the gas leaving), the solvent should be less volatile, i.e., it should have a low vapour pressure under given operating conditions.
3. Corrosive nature :
The solvent should not be corrosive (as far as possible) towards common materials of construction so that the construction material for an absorption equipment will not be too expensive.
4. Viscosity :
The solvent should have a low viscosity for rapid absorption rates, low pumping cost and better heat transfer. The solvent should be non-viscous.
5. Cost and availability :
The solvent should be cheap and readily available. Losses are less costly with the cheap solvent.
6. Miscellaneous :
The solvent should be non-toxic, non-flammable, non-foaming, and chemically stable from a handling and storage point of view.