ANS:C - absorption

Absorption is a separation process in which one or more components of a gas mixture are transferred from the gas phase into a liquid phase. It involves the selective dissolution of certain components of the gas mixture into a liquid solvent. Absorption is commonly used in various industries for gas purification, pollutant removal, and gas recovery processes. Here's how absorption typically works:

1. Contacting Phase:
   • Absorption occurs when the gas phase (the feed gas) comes into contact with a liquid phase (the absorbent or solvent) in a contacting device such as a packed column, tray column, or absorption tower.
   • The gas and liquid phases are brought into intimate contact to facilitate mass transfer between them. This is usually achieved by passing the gas stream through the liquid phase, allowing the components to dissolve into the solvent.
2. Selective Solubility:
   • The absorption process relies on the differential solubility of the components in the gas mixture in the liquid solvent. Certain components of the gas mixture have higher solubility in the liquid phase compared to others.
   • The solvent is chosen based on its ability to selectively absorb the desired component(s) from the gas stream while leaving the undesired components in the gas phase.
3. Mass Transfer:
   • As the gas mixture comes into contact with the liquid solvent, the desired component(s) are transferred from the gas phase into the liquid phase by dissolution.
   • The rate of mass transfer is influenced by factors such as the concentration gradient between the gas and liquid phases, the solubility of the components, and the contact time between the phases.
4. Separation:
   • After absorption, the gas stream exits the absorption column or tower with reduced concentrations of the absorbed component(s).
   • The liquid phase, now containing the absorbed component(s), is typically collected at the bottom of the column and may undergo further processing to recover the absorbed component(s) or to regenerate the solvent for reuse.
5. Applications:
   • Absorption is used in various industrial applications, including:
     • Gas purification: Removal of impurities, such as CO2, H2S, or ammonia, from natural gas or syngas.
     • Pollutant control: Removal of harmful gases, such as SO2 or NOx, from industrial emissions.
     • Gas recovery: Recovery of valuable gases, such as hydrogen or methane, from process streams or waste gases.

In summary, absorption is a separation process that involves the transfer of components from a gas phase into a liquid phase, based on differences in solubility. It is a widely used technique for gas purification, pollutant control, and gas recovery in various industrial processes.