1. Separation (Mass Transfer) Unit Ops

2. Components are separated using a semipermeable membrane
1. Membrane Separation
Components are separated using a semipermeable membrane

3. Function of a membrane separator
Separate a stream based upon phase or properties
Prevent two phases from mixing
Control concentration

4. Types of membranes Porous Membranes:
Separation based on size and diffusivity
Nonporous Membrane:
Separation based on diffusivity

5. Components are separated using a semipermeable membrane.
The permeate passes through the membrane
The retentate does not pass through the membrane
Common uses include: hemodialysis, desalination of brackish water, and sterilization of food and drugs

6. Example flow diagrams of multiple separators
In parallel
In series

7. Visualization of a spiral-wound membrane

8. Useful calculations
Separation factor: A measure of relative diffusibility through membrane
Cut: The fraction of feed which permeates through the membrane

9. 2. Gas Absorption/Stripping
Components are separated by contacting different phases

10. Components are separated by contacting different phases
Gas absorption occurs when components of a gas are removed through contact with a liquid
Stripping occurs when components of a liquid are removed through contact with a gas
An example of absorption: the removal of ammonia from air using water
An example of stripping: the removal of VOCs (volatile organic compounds) in wastewater

11. Absorption and stripping are done in packed columns
Absorption and stripping are done in packed columns. The columns are filled with ‘packing’ that promotes contact between the vapor and liquid streams and facilitates mass transfer

12. Absorption/Stripping Graphical Procedure
Plot the equilibrium curve and operating lines
Count the theoretical number of stages required
Find total height of packing can be found using HETP correlation info and number of theoretical stages
Algebraic Solution of Equilibrium Stage Problems: The Kremser Equation (accessed Feb 3, 2020).

13. Absorption/Stripping Kremser Method
Provides convenient algebraic solution for several separations cases
Convert both equilibrium and operating information into linear format
Can solve for # stages using Kremser equation
(accessed Feb 3, 2020).
Algebraic Solution of Equilibrium Stage Problems: The Kremser Equation (accessed Feb 3, 2020).

14. 3. Distillation
A mixture of two or more species enters a vertical column to be purified, and separated via boiling point.

15. Distillation Columns The column is made of consecutive stacked trays
The feed enters the column at one or more designated tray(s)
There are holes in the trays to allow for the vapor to bubble up through the tray

16. Distillation Columns Continued
Volatility
The boiling points of the components are exploited to determine the optimal temperature for the column.
Phases
Due to the temperature of the column, the components reach different phases. The vapor rises as the liquid falls down the column
Interactions
As the two components interact more with each other, they exchange energy as they travel in opposite directions within the column. This results in desired purities.

17. Distillation Column Design
Reflux Ratio: The ratio of fluid put back into the column to distillate product removed.
Reboiler Concentration
Number of Stages
Feed Stage