AdsorptionAdsorption

What is Adsorption?What is Adsorption?

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

Example: Silica gel, Activated carbon, Example: Silica gel, Activated carbon, Alumina, Zeolites and molecular sieves, Alumina, Zeolites and molecular sieves, Polymers.Polymers.

Factors affecting the processFactors affecting the process

The physical and chemical properties The physical and chemical properties of the gas or vapor (of the gas or vapor (adsorbateadsorbate).).

The temperature at which the The temperature at which the process occurs.process occurs.

The properties of the The properties of the adsorbentadsorbent..

The adsorption isotherm or The adsorption isotherm or equilibrium adsorption data.equilibrium adsorption data.

Physical and chemical Physical and chemical adsorptionadsorption

Physical adsorption occurs when Physical adsorption occurs when the bonding forces are dispersion the bonding forces are dispersion and coulombic type.and coulombic type.

The amount of heat released during this The amount of heat released during this process is equal to the heat of condensation.process is equal to the heat of condensation.

Chemical adsorption occurs when Chemical adsorption occurs when there is sharing of electrons there is sharing of electrons between adsorbent and adsorbate.between adsorbent and adsorbate.

The amount of heat released during this The amount of heat released during this process is equal to the heat of reaction.process is equal to the heat of reaction.

Single-component Monolayer Single-component Monolayer modelsmodels

The following two isotherms are more The following two isotherms are more commonly used:commonly used:

1. Langmuir equation: q1. Langmuir equation: qAA = (QKC = (QKCAA/ 1+KC/ 1+KCAA))

qqAA= equilibrium uptake of adsorbate= equilibrium uptake of adsorbate

Q = weight of adsorbateQ = weight of adsorbate

CCAA= concentration of adsorbate A = concentration of adsorbate A

K = constantK = constant

2. Freundlich equation: q2. Freundlich equation: qAA = K(C = K(CAA))1/n1/n

qqAA= equilibrium uptake of adsorbate= equilibrium uptake of adsorbate

CCAA= concentration of adsorbate A = concentration of adsorbate A

K, n = constants K, n = constants

Single compartment multilayer Single compartment multilayer modelsmodels

The following model is most The following model is most commonly referred to:commonly referred to:

BET equation: BET equation:

P/V(PP/V(Pss – P) = 1/V – P) = 1/VmmC + ((C-1)P)/(CVC + ((C-1)P)/(CVmmPPss))

V= Volume adsorbedV= Volume adsorbed

PPss= saturation pressure= saturation pressure

P = pressure at which “V” is adsorbedP = pressure at which “V” is adsorbed

VVmm= volume occupied in a monolayer= volume occupied in a monolayer

C = a constantC = a constant

Multicomponent modelsMulticomponent models

Such a model is employede when the Such a model is employede when the adsornber is to remove two or more adsornber is to remove two or more pollutants.pollutants.

Markham and Benton model: The equation for an n Markham and Benton model: The equation for an n component systemcomponent system

qqii = Q = QiiKKiiPPii/(1+/(1+∑KjPj) (for j=1 to n)

Pii= partial pressure of component i= partial pressure of component i

QQii = amount adsorbed for component I = amount adsorbed for component I

KKii= a constant.= a constant.Total quantity adsorbed

qT = ∑qii= = ∑QjKjPj/(1+ ∑KjPj)

(for i and j from 1 to n)