1. Introduction to Separation
processes
There are five separation techniques used in the separation processes:
Phase Creation: Use ESA (heat or depressurize)
Phase Addition: Use MSA (add solvent, liquid absorbent)
Barrier Separation: Use membrane (semipermeable membrane)
Solid Agent separations: Use particles (reaction, absorbent film, direct absorption, chromatography)
Separation by gradient: Use electric field, magnetic field, gravity (Hall effect, electrophoresis, mass spec)
ChE 334: Separation Processes
Dr Saad Al-Shahrani

2. Introduction to Separation
processes
All five techniques relay on the ability to enhance the rate of mass transfer of certain species relative to others to effect a spatial separation of components.
Thus, all separations processes must introduce a thermodynamic driving force to overcome the decrease in the entropy of the system as the components are separated.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

3. Introduction to Separation
processes
Separation by phase creation or addition:
This technique is based on the creation or addition of second phase (vapor, liquid or solid) that is immiscible with the feed phase.
Feed
Phase 1
Phase 2
(E.S.A)
Phase
Creation
Feed
Phase 1
Phase 2
(M.S.A)
M.S.A
Phase
Addition
ChE 334: Separation Processes
Dr Saad Al-Shahrani

4. Separation by Phase Creation or Addition
If the feed mixture is a homogeneous, single-phase solution (gas, liquid or solid), second immiscible phase must be created or added before separation of chemical species can be achieved.
The second phase is created by an energy-separating agent (ESA) or added a mass-separating agent (MSA).
(MSA) → (add solvent, liquid absorbent)
(ESA) → Heat added or heat removed
Other separating agent such as pressure reduction and work transfer.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

5. Separation by Phase Creation or Addition
Separations that use an (ESA) are generally preferred, an (MSA) can make possible a separation that is not feasible with an (ESA).
Disadvantages of the use of an MSA are:
Need for an additional separator to recover the MSA for recycle.
Need for MSA makeup.
Possible contamination of the product with the MSA.
More difficult design procedures.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

6. Separation by Phase Creation or Addition
When two immiscible fluid phases are contacted, intimate mixing of the two phases is important in enhancing mass transfer rates so that the thermodynamic-maximum degree-of-partitioning of species can be approached more rapidly.
After phase contact, the separation operation is completed by employing gravity and/or an enhanced technique, such as centrifugal force, to disengage the two phases.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

7. Separation by Phase Creation or Addition
Partial condensation or vaporization:
( When the feed mixture includes species that differ widely in their tendency to vaporize and condense)
Initial or feed phase
Vapor
vapor or Liquid
Created phase
Liq.
Or vap.
vapor or Liquid
Cooling
or heating
Separating Agent
Heat transfer
(ESA)
liquid
e.g : Recovery of H2 and N2 from NH3 by partial condensation and high pressure phase separation.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

8. Separation by Phase Creation or Addition
Flash vaporization
( By reducing the pressure of the feed with a valve)
Initial or feed phase
Liquid
Liquid
pressure
reduction
Drum
vapor
Created phase
vapor
Separating Agent
Pressure reduction
liquid
e.g : Recovery of water from sea water (Desalination).
ChE 334: Separation Processes
Dr Saad Al-Shahrani

9. Separation by Phase Creation or Addition
Distillation
V/L L
Initial or feed phase
(When volatility differences among species in the feed are not sufficiently large)
Vapor and / or Liquid
Created phase
Vapor and liquid
Separating Agent
Heat transfer (ESA)
e.g : Purification of styrene.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

10. Separation by Phase Creation or Addition
Extractive Distillation
V/L L
MSA
Initial or feed phase
(When volatility differences between species to be separated are so small as to necessitate more than about 100 trays in a distillation operation)
Vapor and/or liquid
Created phase L
Vapor and liquid
Separating Agent
Liquid solvent
(MSA) and heat
transfer (ESA)
e.g : Separation of acetone and methanol.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

11. Separation by Phase Creation or Addition
Liquid – liquid extraction
Initial or feed phase
(when distillation is impractical, especially when the mixture to be separated is temperature-sensitive and/or more than about 100 distillation stages would be required) L
MSA
liquid
Created phase
liquid
Separating Agent
(One solvent or two solvents)
Liquid solvent
(MSA)
e.g : Recovery of aromatics.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

12. Separation by Phase Creation or Addition
Time: 120 h Cinitial=450 mg Sr/Kg of dry clay
Catholyte: H2SO4 Sr extraction= 86.7%
Separation by Phase Creation or Addition
Absorption L V
MSA
Initial or feed phase
(If the feed is all vapor and the stripping section of the column is not needed to achieve the desired separation)
Vapor
Created phase
liquid
Separating Agent
Liquid absorbent
(MSA)
e.g : Separation of CO2 from combustion products by absorption with aqueous solutions of an ethanolamine.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

13. Separation by Phase Creation or Addition
Drying
Initial or feed phase
(involves removal of a liquid from a solid by vaporization of the liquid)
Liquid and often solid
Created phase
vapor
Phase created
Separating Agent
(MSA) + (MSA) V V
Gas (MSA) and or/ heat transfer (ESA)
(hot gas)
L / S
Feed S
e.g : Removal of water from polyvinylchloride with hot air in a fluid-bed dryer.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

14. Basic Description of operations
Stripping
Initial or feed phase L
MSA V
(A liquid mixture is separated, generally at elevated temperature and ambient pressure, by contacting liquid feed with a stripping agent)
liquid
Created phase
vapor
Separating Agent
Stripping vapor
(MSA)
e.g : Stream stripping of naphtha, kerosene, and gas oil side cuts from crude distillation unit to remove light ends.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

15. Separation by Phase Creation or Addition and heat transfer (ESA)
Reflux stripping (steam distillation) L
MSA
V/L
L / V
(If contacting trays are also needed above the feed tray in order to achieve the desired separation)
Initial or feed phase
Vapor and/ or liquid
Created phase
Vapor and liquid
Separating Agent
Stripping vapor (MSA)
and heat transfer (ESA)
e.g : Separation of products from delayed coking.
ChE 334: Separation Processes
Dr Saad Al-Shahrani

16. Separation by Phase Creation or Addition
Re-Boiled stripping L V
Initial or feed phase
(If the bottoms product from a stripper is thermally stable, it may be reboiled without using an MSA)
liquid
Created phase
vapor
Separating Agent
Heat transfer
(ESA)
e.g : Recovery of amine absorbent.
ChE 334: Separation Processes
Dr Saad Al-Shahrani