Dr Saad Al-Shahrani 1. Phase Creation: Use ESA (heat or depressurize) 2. Phase Addition: Use MSA (add solvent, liquid absorbent) 3. Barrier Separation:

Dr Saad Al-Shahrani

1. Phase Creation: Use ESA (heat or depressurize)

2. Phase Addition: Use MSA (add solvent, liquid absorbent)

3. Barrier Separation: Use membrane (semipermeable membrane)

4. Solid Agent separations: Use particles (reaction, absorbent film, direct absorption, chromatography)

5. Separation by gradient: Use electric field, magnetic field, gravity (Hall effect, electrophoresis, mass spec)

There are five separation techniques used in the separation processes:

Introduction to Separation processes

ChE 334: Separation Processes

Dr Saad Al-Shahrani


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.


Dr Saad Al-Shahrani

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)

PhaseCreation

Feed

Phase 1

Phase 2

(M.S.A)

M.S.A

PhaseAddition



Dr Saad Al-Shahrani

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.

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:

1. Need for an additional separator to recover the MSA for recycle.

2. Need for MSA makeup.

3. Possible contamination of the product with the MSA.

4. More difficult design procedures.


Dr Saad Al-ShahraniChE 334: Separation Processes

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.


Dr Saad Al-ShahraniChE 334: Separation Processes

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.

1. Partial condensation or vaporization:

Dr Saad Al-Shahrani

Liq.

Or vap.

Coolingor heating

( When the feed mixture includes species that differ

widely in their tendency to vaporize and condense)

liquid

Initial or feed phase

vapor or Liquid

Created phase

vapor or Liquid

Separating AgentHeat transfer

(ESA)

e.g : Recovery of H2 and N2 from NH3 by partial condensation and high pressure phase separation.



Vapor

Dr Saad Al-Shahrani

2. Flash vaporization

vapor

liquid


Liquid

Created phase

vapor

Separating Agent

Pressure reduction

e.g : Recovery of water from sea water (Desalination).

Liquid

pressurereduction

Drum



( By reducing the pressure of the feed with a valve)

Dr Saad Al-Shahrani

3. Distillation

V/L

L

L


Vapor and / or Liquid

Created phase

Vapor and liquid

Separating Agent

Heat transfer (ESA)

e.g : Purification of styrene.



(When volatility differences among species in the feed are not sufficiently large)

Dr Saad Al-Shahrani

4. Extractive DistillationInitial or feed phase

Created phase

Vapor and liquid

Separating Agent

Liquid solvent(MSA) and heat transfer (ESA)

e.g : Separation of acetone and methanol.

L

V/L

L

MSA

Vapor and/or liquid



(When volatility differences between species to be separated are so small as to necessitate more than about 100 trays in a distillation operation)

Dr Saad Al-Shahrani

5. Liquid – liquid extractionInitial or feed phase

liquid

Created phase

liquid

Separating Agent

Liquid solvent(MSA)

e.g : Recovery of aromatics.

L

L

MSA

L



(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)

(One solvent or two solvents)

Dr Saad Al-Shahrani

6. AbsorptionInitial or feed phase

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.

LV

MSA

V



(If the feed is all vapor and the stripping section of the column is not needed to achieve the desired separation)

Dr Saad Al-Shahrani

7. DryingInitial or feed phase

Liquid and often solid

Created phase

vapor

Separating Agent

Gas (MSA) and or/ heat transfer (ESA)

L / S

Feed

(MSA) + (MSA)V V

S

Phase created

(hot gas)

e.g : Removal of water from polyvinylchloride with hot air in a fluid-bed dryer.



(involves removal of a liquid from a solid by vaporization of the liquid)

Dr Saad Al-Shahrani

Basic Description of operations

8. StrippingInitial or feed phase

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.

L

L

MSA

V


(A liquid mixture is separated, generally at elevated temperature and ambient pressure, by contacting liquid feed with a stripping agent)

Dr Saad Al-Shahrani

9. Reflux stripping (steam distillation)


Vapor and/ or liquid

Created phase

Vapor and liquid

Separating Agent

e.g : Separation of products from delayed coking.

L

MSA

V/L

L / V

MSA

Stripping vapor (MSA)and heat transfer (ESA)



(If contacting trays are also needed above the feed tray in order to achieve the desired separation)

Dr Saad Al-Shahrani

10.Re-Boiled strippingInitial or feed phase

liquid

Created phase

vapor

Separating Agent

Heat transfer(ESA)

e.g : Recovery of amine absorbent.

L

L

V



(If the bottoms product from a stripper is thermally stable, it may be reboiled without using an MSA)

Documents

Dr Saad Al-Shahrani 1. Phase Creation: Use ESA (heat or depressurize) 2. Phase Addition: Use MSA (add solvent, liquid absorbent) 3. Barrier Separation: