Adsorption

Question 1

What are assumptions of langmuir isotherm? (5)

Answer 1

1. Only one monolayer forms
2. No adsorbate- adsorbate interactions
3. Gaseous molecules behave ideally
4. All sites on surface are equivalent
5. An adsorbed molecule is immobile

Question 2

What are assumptions of BET isotherm? (7)

Answer 2

1. Multiple molecules can be adsorbed to each site
2. No adsorbate- adsorbate interactions
3. Gaseous molecules behave ideally
4. All sites on surface are equivalent
5. An adsorbed molecule is immobile
6. Each adsorbed molecule provides a site for the adsorption of the molecule in the layer above it
7. Molecules in the second and higher layers are assumed to be liquid like

Question 3

What are the advantages (4) and disadvantages (4) of carbon adsportion?

Answer 3

Adv:
High surface area 
Fast kinetics
High adsorption capacity for a wide range of organics
High quality effluent
Dis:
Cost increases with quality
Non selective removal (competition)
Reactivation costs and loss of carbon
Ineffective for hydrophilic substances

Question 4

What are the 3 adsorption kinetics?

Answer 4

Bulk transport - Transfer of adsorbate from bulk fluid to outer surface of the particle occurs by molecular and convective diffusion.
Film Transport - Transport of material through a boundary layer is often referred to as film diffusion.
Intraparticle transport - Transfer of adsorbate from the external surface to the interior of the particles occurs by diffusion.

Question 5

What is physisorption?

Answer 5

Physical adsorption
Van der waals force
Small change in electronic structure of the atom or molecule
Interaction energy is weak

Question 6

What is chemisorption?

Answer 6

Chemical adsorption
Covalent or ionic bonds form
Electronic structure of the atom or molecule changes
Strong binding energy

Question 7

Derive langmuir isotherm

Answer 7

x

Question 8

What are the 4 isotherms?

Answer 8

Linear
Langmuir
BET
Freundlich

Question 9

Factors which affect adsorption extent? (4)

Answer 9

Solubility (molecular size and polarity)
pH
Temperatures
Presence of other adsorbates (Multicomponent adsorption)

Question 10

Factors which affect adsorption on adsorbent? (5)

Answer 10

Surface area
Pore size 
Pore shape
Pore volume
Availability of surface functional groups

Question 11

What is the breakthrough point?

Answer 11

The maximum allowable solute concentration in the effluent fluid.

Question 12

What are mechanistic and apparent rate?

Answer 12

Mech - Chemical kinetics of an elementary reaction

App - Chemical kinetics and physical controlled processes

Question 13

What is adsorption?

Answer 13

A surface phenomenon as opposed to absorption where matter changes to solution phase. Adsorption is a process in which matter is extracted from one phase and concentrated at the surface of a second phase (solid).

Question 14

Explain capillary condensation in mesopores?

Answer 14

Less than 2 um is mono layer
Greater than 10 um is flat surface multilayer
Between 2-10 get multilayer with pore filling and surface tension causing a meniscus and causes hysteresis . Want to decreases Pv less than saturation pressure to achieve desorption

Question 15

Draw hysteresis graph

Answer 15

x