The gas response of common flammable gases, including methane, carbon monoxide and hydrogen can be tested for determining of gases adsorption on each type of activated carbon. For full descriptions, please refer to the following link address: https://www.nature.com/articles/s41598-017-08074-y

Due to its high degree of micro porosity, one gram of activated carbon has a surface area in excess of 3,000 m2 (32,000 sq ft), as determined by gas adsorption. An activation level sufficient for useful application may be attained solely from high surface area. Because of its high surface area, activated carbon has the ability to selectively adsorb and retain certain types of molecules on the internal surfaces of tiny pores and interstices of its granules. The selectivity and capacity for adsorption depend on the method of carbon production or activation, and can be very high for removal of agents and chlorinated hydrocarbons.

Further chemical treatment often enhances adsorption properties.

Surface area of a powdered solid adsorbent depends upon its particle size. Smaller the particle size, greater is its surface area.

1. An increase in the pressure of the adsorbate gas increases the extent of adsorption.

2. At low temperature, the extent of adsorption increases rapidly with pressure.

Factors affecting the extent of adsorption

1. The extent to which adsorption will happen on a solid surface depends on the following factors:

The adsorption of the gas depends on the nature of the adsorbent. A gas can be adsorbed on different absorbent surfaces in different amounts. For example: Hydrogen is weakly adsorbed on the alumina surface whereas it is strongly adsorbed on the nickel surface under certain conditions.

When we increase the surface area of the adsorbent there is increase in the adsorption of gases. This is because when we increase the surface area there is more number of adsorbing sites. So finely divided solids and some porous substances are good adsorbents.

In general, if a gas is more liquefiable it will be more easily adsorbed. For example: Gases like NH3, HCl, Cl2, CO2, which can be liquefied easily are more readily adsorbed on the solids surface rather than permanent gases like O2, H2, etc.

Heat of adsorption can be defined as the energy liberated when 1 g mol of a gas is liberated on a solid surface. When the temperature is increased the kinetic energy of the gas molecules also increases which results in more number of collisions between the molecules and the surface.

On the solid surface there are fixed number of adsorption sites where gas molecules can be adsorbed. Initially when the pressure is increased the rate of adsorption increases due to increase in the gas molecules striking on the surface. Thus increase in the pressure increases the rate of adsorption linearly. But after sometime, it will reach a point when pressure has no effect on the rate of adsorption as the number of adsorption sites is fixed and no more adsorption can happen in those sites. Hence at that point, the extent of adsorption will be independent of the pressure.

7. Temperature

We know that adsorption decreases with increase of temperature and vice versa. For example, one gram of charcoal adsorbs about 10 cm3 of N2 at 273 K, 20 cm3 at 244 K and 45 cm3 at 195 K. the decrease of adsorption with increase of temperature is explained below:

Like any other equilibrium, adsorption is a process involving a true equilibrium. The two opposing processes involved are condensation i.e. adsorption of the gas molecules on the surface of the solid and evaporation i.e. desorption of the gas molecules from the surface of the solid into the gaseous phase.

Olugbenga

Remember about capillary condensation phenomenon. If it takes place the capacity changes a lot.

Regards

G