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SEPARATION METHODS
Objectives
• Explain the role of separations
operations in industrial chemical
process
• Explain what constitutes the separation
of a chemical mixture and enumerates
general separation techniques
• Explain the use of external fields to
separate chemical mixtures
Introduction
• Early civilization techniques:
– - Extracts metal from ores
– - Perfume from flower
– - Dyes from plant
– - Evaporation of sea water to obtain salt
– - Distill liquor
Introduction
• Chemist – use chromatography to
separate complex mixtures quantitatively
• Chemical engineers – concerned with
the manufacture of chemicals using large
scale separation methods
Chemical Processes
• Conducted:
– Batchwise
– Continuous
– Semi-continuous
Key operations in chemical process
involved:
- Reaction Processes
- Separation Processes
Mechanism of Separation
• Mixture of homogenous phase
• Mixture of two or more immiscible
phases
MEMBRANE
PERMEATE
HYDROGEN
Light
Hydrocarbons
RESIDUE
Sieve
Dryer
Feed
FURNAC
E
COOLING
Caustic Scrubber
LIQUIDS
EXAMPLE: SEPARATION PROCESS
Heavier
Hydrocarbons
Mechanism of Separation
• Mixing of chemical is spontaneous,
increase entropy and randomness.
• Separation of chemicals requires the uses
of energy.
• Separation includes:
– - Separation of component A from mixture in
homogenous phase
– - Separation of component A from mixture in
different phases
Mechanism of Separation
• If two or more immiscible phases exist
mechanical separation is preferable
• E.g: Centrifuge, pressure reduction,
electric/magnetic field
Basic of separation
Types of Separation Process
1) Separation
creation
2) Separation
3) Separation
4) Separation
by phase addition or
of barrier
by solid agent
by external field or gradient
- Centrifugation
- Thermal diffusion
- Electrophoresis
- Electrodialysis
Phase creation process
• Involve the creation of a second phase
that is immiscible with the feed.
• Accomplished by energy or pressure
reduction.
• Suitable for mixture that have tendency
to vaporize.
• E.g: Evaporation, sublimation,
crystallization, distillation.
Phase addition processes
• For separation of homogenous, single phase
mixture, a second immiscible phase must be
developed.
• This is achieved by:
– - Creation of energy separating agent (ESA)
– - Mass separating agent (MSA)
• When 2 immiscible fluid phases are contacted,
intimate mixing of the 2 phases is important in
enhancing mass transfer rates.
• After phase contact, employing gravity and/or
enhanced techniques completed the
separation process.
Cont’
• Disadvantages of MSA:
- Need additional separator to recover
MSA
- Need for MSA make up
- Possible contamination of the product
- More difficult design procedure
• Eg: Extractive distillation, liquid-liquid
extraction, leaching
Separation by Barrier
• Includes the use of microporous and
nonporous membrane as semipermeable
barriers
• Membrane are fabricated from polymer,
natural fiber, ceramic, metal etc.
• Microporous membrane – separation occur
at different diffusion rate
• Nonporous – separation based on the
solubility
Cont’
Hydrogen removal in refineries, ammonia plants, and olefin
units.
Separation by Solid Agent
• Process that use solid mass-separating
agents.
• Solid normally in the form of a granular
material or packing. E.g: activated
carbon, aliminium oxide, silica gel, or
calcium aluminosilicate zeolite.
• Example of process: Adsorption,
Chromatography, & Ion Exchange.
Generalized downstream
processing
Bioseparation
Techniques
RIPP Scheme
• Liquid-solids separations (dewatering,
concentration, particle removing) @
Recovery
• Solute-solute separations (Isolation,
Purification)
• Solute-liquid separations (Polishing)
Bioseparation Techniques
Stage
Objective(s)
Recovery
• Remove or collect cells,
(separation of cell debris
insolubles)
• Reduce volume
Typical Unit
Operations
Filtration, sedimentation,
extraction, adsorption,
centrifugation
Isolation
• Remove materials having Extraction, adsorption,
properties widely different ultrafiltration,
from those of target
precipitation
product
• Reduce volume
Purification
• Remove remaining
impurities, which typically
are similar to those of
target product
Chromatography, affinity
methods, precipitation
Polishing
• Remove liquids
• Convert product to
crystalline form (not
always possible)
Drying, crystallization
Example of bioseparation
Separation and purification of intracellular
enzymes
fermentation
lyophilization
Cell removal and
concentration
Cell disruption
Removal of cell
debris
Protein
precipitation or
aqueous twophase extraction
dialysis
Solvent
precipitation
Chromatographic
purification
ultrafiltration
Rules of thumb
• Remove the most plentiful impurities first
• Remove the easiest-to-remove impurities
first
• Make the most difficult and expensive
separations last
• Select processes that make use of the
greatest differences in the properties of
the product and its impurities
• Select and sequence processes that
exploit different separation driving forces
Cyclodextrin
Remove the easiest-to-remove
impurities first: unused starch, linear
Remove the most plentifuldextrins,
impurities
glucose, maltose, etc
first: CD-agent complex
Select processes that make use of the
greatest differences in the properties of the
product and its impurities: decanol and CD
Make the most difficult and
expensive separations last:
CD crystals
Select and sequence processes
that exploit different separation
driving forces
Example 1
You have been given a task to purify the erythromycin antibiotic
from fermentation broth. The information on erythromycin is given
below. What do you think the most likely unit operations that
should be used for the isolation and purification of
erythromycin? Justify the reasons for the selection of the unit
operations.
Information on erythromycin
Formula
: C37H67NO13, Molecular weight
: 733.94
Form
: Salts with acids, Melting point : 56 °C
UV max
: 280 nm, pKa
: pH 8.8
Freely soluble in alcohols, acetone, chloroform, acetonitrile,
ethyl acetate. Moderately soluble in ether, ethylene
dichloride, amyl acetate. Hydrated crystals from water,
melting point 135-140 °C. Resolidifies with second melting
point 190-193 °C
Solution
Erthromycin has limited solubility in water but is
soluble in several solvents, including amyl
acetate. Since the solubility of amyl acetate is
low, isolation could be performed by a liquid-liquid
extraction of erythromycin using water-amyl
acetate system. For the extraction, it would be
desirable to raise the pH of the aqueous phase above
the pKa of erythromycin of 8.8, so that the secondary
amino group is converted from the positively charged
from the neutral free base form. For the purification step,
crystallization is a good choice, since hydrated crystals
have been obtained from water.
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