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Adsorption

Adsorption. What is Adsorption?. Adsorption is the transfer of a material from one liquid or gaseous state to a surface. The substance that is transferred to the surafce is the adsorbate . The material on which the adsorbate deposits is the adsorbent .

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Adsorption

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  1. Adsorption

  2. What is Adsorption? • Adsorption is the transfer of a material from one liquid or gaseous state to a surface. • The substance that is transferred to the surafce is the adsorbate. • The material on which the adsorbate deposits is the adsorbent. • Example: Silica gel, Activated carbon, Alumina, Zeolites and molecular sieves, Polymers.

  3. Factors affecting the process • The physical and chemical properties of the gas or vapor (adsorbate). • The temperature at which the process occurs. • The properties of the adsorbent. • The adsorption isotherm or equilibrium adsorption data.

  4. Physical and chemical adsorption • Physical adsorption occurs when the bonding forces are dispersion and coulombic type. • The amount of heat released during this process is equal to the heat of condensation. • Chemical adsorption occurs when there is sharing of electrons between adsorbent and adsorbate. • The amount of heat released during this process is equal to the heat of reaction.

  5. Single-component Monolayer models • The following two isotherms are more commonly used: 1. Langmuir equation: qA = (QKCA/ 1+KCA) qA= equilibrium uptake of adsorbate Q = weight of adsorbate CA= concentration of adsorbate A K = constant 2. Freundlich equation: qA = K(CA)1/n qA= equilibrium uptake of adsorbate CA= concentration of adsorbate A K, n = constants

  6. Single compartment multilayer models • The following model is most commonly referred to: • BET equation: P/V(Ps – P) = 1/VmC + ((C-1)P)/(CVmPs) V= Volume adsorbed Ps= saturation pressure P = pressure at which “V” is adsorbed Vm= volume occupied in a monolayer C = a constant

  7. Multicomponent models • Such a model is employede when the adsornber is to remove two or more pollutants. • Markham and Benton model: The equation for an n component system qi = QiKiPi/(1+∑KjPj)(for j=1 to n) Pi= partial pressure of component i Qi = amount adsorbed for component I Ki= a constant. • Total quantity adsorbed qT = ∑qi= ∑QjKjPj/(1+ ∑KjPj) (for i and j from 1 to n)

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