Question

Define Electrodialysis (ED), draw a schematic diagram of the process, and determine the main characteristics of ion exchange membranes to be used. What are the process limitations in ED systems? then differentiate between dialysis and osmosis phenomena.

Answer 1

Electodialysis is a process used to transport salt ions from one solution through ion-exchange membranes to another solution under the influence of an applied electric potential difference. Characteristics of ion-exchange membrane:

1. Semi-rigidity for ease of handling

2. Low electrical resistance

3. Insolubility in aqueous solutions

4. Availability to use above 46°C

5. Availability in different sizes and configurations

6. Long life expectancy

7.Resistance to change in pH from 2 to 9

Limitations:

1. Inherent limitation of working best at removing low molecular weight ionic components from a feed stream.

2. Becomes less economical when extremely low salt concentrations in the product are required and with sparingly conductive feeds.

3. Require feed pretreatment to remove species that coat, precipitate onto, or otherwise "foul" the surface of the ion exchange membranes.

Difference between Dialysis and Osmosis

Dialysis	Osmosis
1. Involves separation of smaller molecules against the larger molecules through a permeable membrane.	1. Passing of water molecules from a low pressure to a high pressure across a semipermeable membrane.
2. Emphasizes what type of solute, such as salt, glucose, protein, fats, etc. will be allowed to pass through the membrane.	2. Only allowing that amount of solvent that will be allowed across the semipermeable membrane.
3.Used in the field of medicine in helping patients with renal failure excrete their body wastes.	3. Used in the field of biochemistry and pharmacology