Home Podcasts THMG102 – Absorbents vs. Adsorbents

THMG102 – Absorbents vs. Adsorbents


In this episode, we learn some very valuable information about the differences between absorbents and adsorbents.

Complete Show Notes

6:30 Introduction to Adsorbents and Absorbents

  • “-sorption” refers to the physical and chemical process by which one substance becomes attached to another

10:00 Adsorption

  • Adsorption refers to the adhesion of the molecules of a gas, liquid, or dissolved substance to a surface
  • To “adsorb” means undergoing or causing a process in which a substance (usually a gas) accumulates on the surface of a solid, forming a thin film that’s often only one molecule thick
  • In other words, the molecular species accumulates at the surface, rather than in the bulk of the solid or liquid
  • It’s important to note that the hazard is only on the outside of the substance
  • One example of this is sand – sand can cling to the outside of something without soaking it in
  • Another example is paint manufacturing – paint has to adhere or stick to the surface it’s designed to cover and does so by bonding to that surface
  • Benefits
    • There’s no chemical change in the substance, so the substance can be recovered
    • We don’t have to worry about heat since there’s no chemical change
    • No nasty by-products to deal with since there’s no reaction

19:20 Absorption

  • The process whereby one material (gas or liquid) is taken into another – happens at an atomic or molecular level where the atoms and molecules of two materials combine
  • When something is absorbed, it either diffuses or dissolves
  • In other words, the molecular species is assimilated throughout the bulk of the solid or liquid
  • One example is the purification of natural gas – in order to remove unwanted hydrogen sulphide (H2S) and carbon dioxide (CO2), the natural gas is passed through a water-based solution of ethanolamine (a viscous liquid) – this resolves the two acidic gasses by making them more soluble and dissolving them

24:30 Main Differences Between Adsorption and Absorption

  • Adsorption
    • One material sticks to the surface of another
    • One material coats the surface of another
    • Related to surface area
    • Involves a process of adhesion
    • Example: mist on a window
  • Absorption
    • Two materials chemically combine
    • One material is taken internally into another
    • Related to volume
    • Involves a process of dissolution or diffusion
    • Example: table salt dissolving into water

32:45 Phenomenon of Adsorbents

  • Heat exchange – endothermic
  • Temperature – favors low temperatures
  • Rate of reaction – steadily increases and reaches equilibrium
  • Concentration – there’s more material at the surface than the inside

35:20 Phenomenon of Absorbents

  • Heat exchange – exothermic
  • Temperature – favors warm temperatures
  • Rate of reaction – uniform
  • Concentration – homogenous

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