Introduction

  • In absorption (also called gas absorption, gas scrubbing, or gas washing), there is a transfer of one or more species from the gas phase to a liquid solvent. The species transferred to the liquid phase are referred to as solutes or absorbate.

  • The operation of removing the absorbed solute from the solvent is called stripping.

  • Absorption is used to separate gas mixtures, remove impurities, or recover valuable chemicals.

  • The solvent may be a physical solvent — where there is no chemical reaction of solute with the solvent, or a chemical solvent — where solute reacts with the solvent.

  • Water is the most common solvent used in absorption.

  • Absorption is the chief method for controlling industrial air pollution.

  • Most absorption processes aim at separation of acidic impurities from mixed gas streams. These acidic impurities include \(\ce{CO2}, \ce{H2S}, \ce{SO2}\), and organic sulfur compounds. The most important of these are \(\ce{CO2}\) and \(\ce{H2S}\), which occur at concentrations of 5–50%.