Figure 3.11 below shows arithmetic graphs of some typical isotherm shapes (McCabe, 1993). Linear isotherm indicates the amount of adsorbed is proportional to the concentration in fluid. Favourable process is achieved when the isotherms are convex upward because a relatively high solid loading can be obtained at low concentration in the fluid. The isotherm for this favourable adsorption process is Langmuir Isotherm. The assumption made when deriving the Langmuir isotherm is that the process happens at uniform surface. However this relation only works well for gases that a weakly adsorbed (McCabe, 1993).