**2.1.2 Adsorption**

It refers to the process by which molecules of a substance, such as a gas or a liquid, collect on the surface of a solid. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid (Tondeur & Teng, 2008). It could be physical or chemical. In physical adsorption processes, gas molecules adhere to the surface of the solid adsorbent as a result of the molecules attraction force (Van der Walls Forces). Chemical adsorption involves a chemical reaction. Usually, adsorbents are 12 µm to 120 µm high porosity solid grains, inert to the treated fluid. The most used adsorbents for CO2 are activated charcoal, silica gel, zeolites and synthetic resins.

### **2.1.3 Condensation**

It is the process of converting a gas into a liquid by reducing temperature and/or increasing pressure. Condensation occurs when partial pressure of the substance in the gas is lower than the vapor pressure of the pure substance at a given temperature.
