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Dr. BASAVARAJ R J
Asst. Professor in Chemical Engineering
Students group ID: [email protected] V College of Engineering, Bengaluru-560 059
MODERN SEPARATION TECHNIQUES M.Tech- I Semester Chemical Engineering
MODERN SEPARATION TECHNIQUES
Faculty Name: Dr. Basavaraja R JSubject code : 14HCE153 IA Marks : 50
No. of Lecture Hours / Week : 04 Exam Hours : 03No. of Practical Hours / Week : --- No. of Tutorial : 02 Hours/ WeekTotal No. of Lecture Hours : 52 Exam Marks : 100
SYLLABUS
Introduction: Review of conventional processes, Recent advances in separation techniques based on size, surface properties, ionic properties and other special characteristics of substances, Process concept, Theory and equipment used in cross flow filtration, cross flow electro filtration, dualfunctional filter, Surface based solid -liquid separations involving a second liquid, Sirofloc filter.
• Separation can be defined as an operation by which a mixture is resolved in to its components.
• Separation processes play vital role in process industries.
• With out separation processes no industry can exist.
Separations are carried out based on differences in properties such as size, shape, mass, or chemical affinity between the constituents of a mixture, and are often classified according to the particular differences they use to achieve separation.
• Every Industrial Process is designed to produce economically a desired product from a variety of starting materials through a succession of treatment steps.
UPSTREAM PROCESS
Typical Chemical Process
IMPUTRITIES
RAW MATERIALS
CHEMICAL / BIOCHEMICAL TREATMENT
PURFIED
RAW MATERIAL
DOWN STREAM PROCESS
COMBINED PRODUCT
BY PRODUCT
PRODUCT
Physical Treatment before reaction step is required for preparing the raw material – upstream processing or pre treatment step.
The raw material undergo a number of physical treatment steps to put them in the form in which they can be treated chemically.
• Iron pyrites ore is dried in rotary kiln and ground to – 200 mesh for sulfur and sulfur dioxide production.
• Calcium carbide is pulverized for the production of acetylene.
• Phosphate rock ground for production of elemental phosphorous, phosphorous pentoxide and phosphoric acid.
Chemical Processes
• Lime stone is pulverized, classified, treated in flotation cell for the beneficiation of limestone.
• Clay and limestone are pulverized for cement manufacture.
• Rice bran is palletized before extraction
Separating
DeviceFeed
stream
Separating agent
Product stream
By product stream
Schematic representation of a Separation Process
• One or more feed with two or more species enter the unit
• Two or more products of different compositions leave the unit
• A separating agent is required for the separation– Energy separating agent
– Mass separating agent
•Often separating agents will cause formation of second
phase of matter.
•A separation is accomplished if the generated phase has a
different composition from the feed.
Primary Basis for Separation
• Any separation depends on the use of one or more differences in
properties of components
• Greater the differences in properties, easier is the separation by
that method
– Vapor Pressure-distillation
– Diffusivity and Solubility-reverse Osmosis
– Molecular Size-ultra Filtration
Separation factor
• Proposed as a measure of degree of separation obtainable for particular mixture and a separation technique
• For a binary mixture it is the ratio of the concentration ratio of A and B in one phase to that in other
αij = xi1 / xj1 = ki / kj
xi2 /xj2 ki- equilibrium ratio
• Vapour liquid system-relative volatility• liquid-liquid system-selectivity• unity-no separation possible• larger the value greater the separation• separation factor is quite large-separation possible in a single stage
Classification of Separation Processes
• Separation may be achieved by chemical, mechanical and
physical/diffusion methods
• Chemical method ordinarily destroys the original substance
and hence used rarely.
• The mechanical /Physical / Diffusion methods are further
classified as equilibrium separation process, rate governed
separation process and mechanical separation processes.
• Petroleum industry is one of the earlier examples
• Development of new separation processes and equipments helped the growth of antibiotic industry and nuclear industry
• Recent times challenging problems of separation have come in the field of waste treatment, pollution control, production of ultra pure fluids and food preservation.
• Beverages processing, production of pharmaceuticals, harmones, enzymes, vaccines and other biologicals.
PROCESS FEED AGENT PRODUCT PRINCIPLE EXAMPLE
EVAPORATION L H L+V DIFFERENCES IN VOLATILITY
CONCENTRATION OF SOLUTIONS
DISTILLATION L&OR V H L+V DIFFERENCES IN VOLATILITY
PETROLEUM PRODUCTS,ALCOHOL
ABSORPTION G L( NV) L+V PREFERENTIAL SOLUBILITY
RECOVERY OF CO2,SO2
STRIPPING L G(NC) L+V DIFFERENCES IN VOLATILITY
REMOVAL OF LIGHT HYDROCARBONS
LIQUID EXTRACTION
L L(IMM) L+L PREFERENTIAL SOLUBILITY
PENCILLIN RECOVERY
LEACHING OR WASHING
S L L+S PREFERENTIAL SOLUBILITY
RECOVERY OF MINERALS FROM ORE
CRYSTALLIZATION L H(REMOVAL)
L+S DIFFERENCES IN SOLUBILITY
SUGAR,CITRIC ACID
DRYING S H S+V DIFFERENCES IN VOLATILITY
FOOD DEHYDRATION
ADSORPTION G(OR)L S L(OR)G DIFFERENCES IN CHEMICAL AFFINITY
DRYING OF GASES,DECOLOURATION OF SOLNS.
ION EXCHANGE L S( RESIN) L+S ELECTRICAL CHARGE
+ADSORPTION
WATER SOFTENING
FREEZE DRYING FROZEN WATER
H S+V SUBLIMATION OF WATER
DEHYRATION OF FOOD
Equilibrium Processes
PROCESS FEED AGENT PRODUCT PRINCIPLE EXAMPLE
DIALYSIS L M SELECTIVE L+L DIFFERENCE IN DIFFUSIONAL RATE
ARTIFICIAL KIDNEY
ELECTRO DIALYSIS
L M +ELE.FIELD L+L DIFFERENCE IN IONIC MOBILITY
DESALINATION OF BRACKISH WATER
ULTRA FILTRATION
L+COLLOID
M+PRESSURE GRADIENT L+L DIFFERENCE IN PERMEABILITIES
PROTEIN CONCENTRATION
REVERSE OSMOSIS
L M+PRESSURE GRADIENT L+L DIFFERENCE IN COMBINED
SOLUBILITIUES AND DIFFUSIVITIES
IN MEMBRANES
DESALINATION OF SEA WATER
GAS PERMEATION
G M+PRESSURE GRADIENT G DIFFERENCE IN SOLUBILITIES AND
TRASPORT RATE THRO’MEMBRANES
GAS REVOCERY/ PURIFICATION OF HYDROGEN
THERMAL DIFFUSION
G(OR)L TEMP.GRADIENT G(OR) L DIFFERENCE IN RATE OF THERMAL
DIFFUSION
SEPARATION OF ISOTOPES
Rate Governed Processes
PROCESS FEED AGENT PRODUCT PRINCIPLE EXAMPLE
FILTRATION L+S FILTER MEDIUM+ PRESSURE
L+S SIZE Separation of Solids form Slurry
SETTLING L+S GRAVITY L+S DIFFERENCE IN DENSITY
Clarification of Solutions
CENTRIFUGING L+S(OR)L CENTRIFUGAL FORCE
L+S(OR)L DIFFERENCE IN DENSITY
Recovery of Insoluble Products
CYCLONE SEPARATION
G+S(OR)L INERTIAL FORCE
G+S(OR)L DIFFERENCE IN DENSITY
Recovery of Insoluble Products
ELECTROSTATIC PRECIPITATION
G+S(FINE ELECTRICAL FIELD
G+S CHARGE ON FINE SOLID PARTICLES
Dust Removal from Stack Gasses
Mechanical Processes
Electro-dialysis
At the cathode2e- + 2 H2O → H2 (g) + 2 OH-
while at the anodeH2O → 2 H+ + ½ O2 (g) + 2e- or 2 Cl- → Cl2 (g) + 2e-
Direct and Indirect methods
• Direct method:
Only energy is added or removed- Eg.Distillation , evaporation, crystallization-Product is obtained in a single stage.
• Indirect method :
Involves addition of foreign substance- Eg.Extraction , absorption, adsorption-Product is obtained in a second operation.
Choice of Separation Processes
The criteria for choice for recovery of products depends on
1. Nature of the Feed (Gas Liquid or Solid)
2. Concentration of Product in the Feed
3. Physical and Chemical Characteristics of the desired product
4. Impurities in the feed
5. Intended use of the product
6. The minimal acceptance standard of purity
7. Marketability of the product.
Selected Separation Processes
1. Filtration
2. Distillation
3. Extraction
4. Crystallization
5. Evaporation
6. Supercritical Extraction
7. Gel Electrophoresis
8. Chromatography Separations
9. Gel Filtration
10.Membrane Separation Processes
Distillation Removal of liquid mixtures in to their components by vaporization.
The property exploited is the relative volatility.
More the relative volatility between the components to be separated easier will be the separation.Less the relative volatility difficult will be the separation.
Azeotropic system.
Simple distillation, Continuous distillation, steam distillation, extractive distillation, azeotropic distillation.
Packed column distillation, plate column distillation.
Steam distillation.
Filtration :
Used for heterogeneous mixtures.
The general problem of the separation of solid particles from liquids can be solved by using a wide variety of methods, depending on the types of solids,the proportion of solid to liquid in the mixture,viscosity of the solution,and other factures.
In filtration,a pressure difference is setup that causes the fluid to flow through small holes in a screen or cloth which block the passage of large particle;these in turn,buildup on the cloth as a porous cake.
Different filtration includes
Batch filtration, continuous filtration, vacuum filtration, pressure filtration .
Extraction
Removal of active ingredient from mixture using a solvent.
Liquid-liquid extraction is also called as solvent extraction. Solid liquid extraction is called leaching.
Extraction and leaching exploits the differences in solubility of solutes in different solvents.The solubility is expressed as distribution coefficient or selectivity.
Used to recover heat sensitive material from solution.
Penicillin G is an antibiotic which is recovered from fermentation broths by counter current solvent extraction.
Two component system three component system.
Extract, raffinate.
Solutropic system.
Solvent extraction is a method for separating a substance from one or more others by using a solvent. It relies on variations in the solubilities of different compounds in different substances. In most cases, the substance to be extracted, which may be a solid, a liquid or a gas, is dissolved in a liquid, along with other substances, and a liquid solvent is used for the extraction — this is sometimes called liquid-liquid extraction.
The technique may also be applied to solid materials that contain compounds that need to be extracted. This method is widely used in industry, and in the laboratory for refining, isolating and purifying a variety of useful compounds.
Extraction
A solvent will be chosen that does not mix with the compound in which the substance of interest is currently dissolved, so that, when left undisturbed, they will form two separate layers, as with oil and water.
It is also important that the compound to be extracted should have greater solubility in the solvent that has been added, and that this should not dissolve any unwanted substances in the original mixture. Once added, the two liquids may be shaken together for a time then allowed to stand for a while, so that they separate out.
The choice of solvent to be used will depend on the chemical and physical properties of all the substances in the mixture. The process may need to be carried out in several stages, using different solvents.
Extraction
Liquid-liquid extraction (also known as solvent extraction) involves the separation of the constituents (solutes) of a liquid solution by contact with another insoluble liquid. Solutes are separated based on their different solubilities in different liquids. Separation is achieved when the substances constituting the original solution is transferred from the original solution to the other liquid solution.
The Figure showed a feed liquid (the "first" liquid) containing the desirable compound that is to be separated together with other compounds. Then an immiscible extraction liquid (the "second" liquid) is added and mixed with the feed liquid through agitation. The species re-distribute themselves between the 2 liquid phases. Agitation of the 2 phases is continued until equilibrium, and then agitation is stopped and the liquids are allowed to settle until both phases are clear. The 2 phases can then be separated.
Liquid-Liquid Extraction
Crystallization
Removal of solids from solutions by super saturating the
solution.
The super saturation may be carried out by cooling, by
vaporizing a portion of the solvent, adiabatic evaporation or by
adding a third component which will reduce the solubility of
solute.
Tank crystallizers, agitated batch crystallizers, continuous
crystallizers, vacuum crystallizers.
Evaporation
Removal of major portion of liquid from solution by boiling the
solution.
Major portion of solvents used in extraction are recovered by
evaporation.
Solution is heated in evaporators by using steam in calendrias.The
liquid evaporated is collected at the top ,condensed and collected if
vapor is the useful product.
The solution leaving at the bottom is a thick solution.
The solids enter with the solution dose not evaporate because they
do not have sufficient vapor pressure.
Economy, Single effect,multiple effect, once through, circulation
evaporators. Natural convection, forced convection.Climbing film
falling film evaporators,vapor recompression evaporators.
The liquid portion of the feed is divided in to two portions but the
the solid that enters goes only to the bottom stream.
Evaporation, Contd..
Super Critical Extraction
• The basic principle of SCE is that when the feed material is contacted with a supercritical fluid then the volatile substances will partition into the supercritical phase.
• After the dissolution of soluble material the supercritical fluid containing the dissolved substances is removed from the feed material.
• The extracted component is then completely separated from the SCF by means of a temperature and/or pressure change.
• The SCF is then recompressed to the extraction conditions and recycled.
Advantages of SCE
• Thermally labile compounds can be extracted with minimal damage as low temperatures can be employed by the extraction.
• Dissolving power of the SCF is controlled by pressure and/or temperature.
• SCF is easily recoverable from the extract due to its volatility.
• Non-toxic solvents leave no harmful residue.
• High boiling components are extracted at relatively low temperatures.
• Separations not possible by more traditional processes can sometimes be effected.
Disadvantages of SCE
• Elevated pressure required
• Compression of solvent requires elaborate recycling measures to reduce energy costs
• High capital investment for equipment
Distillation column
Str
ippi
ng s
ectio
n
Enr
ichi
ng s
ectio
n
FermenterSolid-liquid separation
Recovery
Recovery
Cell rupture
Purification
Purification
Cell debrisCell products
Cells
SupernatantExtra
cellularproducts
Intracellularproducts
Major process steps in Downstream processing in a typical Bioprocess Industry
• Media preparation-The formation of media to be used in culturing the process organism during the development of the inoculum and in the production fermenter.
• Sterilization_Sterilization of the medium, fermenter and ancillary equipment,development of Inocula for industrial fermentations.
• Production of active,pure culture in sufficient quantity to inoculate the production vessel.
• The growth of the organism in the production fermenter under optimum conditions for product formation.
Bio processes
• Preparation of reactants-upstream process
• Optimization of conditions in reactor to maximize process yield
• Recovery of product-down stream process
After successful fermentation or enzyme reactions, desired products must be separated and purified
This final step is commonly known as downstream processing or bioseparations.
This can account for up to 60 percent of the total production costs,excluding the cost of raw materials.
The fermentation products can be
The cells themselves (biomass)
Components within the fermentation broth
( extra cellular)
Those trapped in cells( intracellular)
Examples of Bio processing Products
Type Products
Cell itself Bakers yeast,single cell protein
Extra cellular Alcohols,organic acids,amino acids
Intracellular Recombinant DNA proteins
Bio separation processes make use of many separation techniques commonly used in chemical process industries
However, Bio separations have distinct characteristics which are not common in the traditional separations of chemical processes.
Some of the unique characteristics of bioseparation products are
The products are in dilute concentration in aqueous medium
The products are usually temperature sensitive
There is a great variety of products to be separated
The products can be intracellular,often as insoluble inclusion bodies
The physical and chemical properties of products are similar to contaminants
Extremely high purity and homogeneity may be needed for human health care
These characteristics of bioseparation products limit the use of many traditional separation technologies and also require the development of new methods
• The upstream and down stream processes are
mainly the separation processes.
• The separation processes accounts for 50-90% of
the capital investment
• Separation itself may be main function of an entire
process
Common downstream processes used in Bio processing are
Solid liquid separations – Filtration,centrifugation
Extraction and Leaching
Evaporation
Distillation
Crystallization
Adsorption
Drying
Cross flow filtration is different from dead end filtration in which the feed is passed through a membrane or bed, the solids being trapped in the filter and the filtrate being released at the other end. Cross-flow filtration gets its name because the majority of the feed flow travels tangentially across the surface of the filter, rather than into the filter.
Principle of cross flow filtration
Cross flow filtration
Advantages:•A higher overall liquid removal rate is achieved by the prevention of filter cake formation•Process feed remains in the form of a mobile slurry, suitable for further processing•Solids content of the product slurry may be varied over a wide range•It is possible to fractionate particles by size
In crossflow filtration, the feed is passed across the filter membrane (tangentially) at positive pressure relative to the permeate side. A proportion of the material which is smaller than the membrane pore size passes through the membrane as permeate or filtrate; everything else is retained on the feed side of the membrane as retentate.
With crossflow filtration the tangential motion of the bulk of the fluid across the membrane causes trapped particles on the filter surface to be rubbed off. This means that a crossflow filter can operate continuously at relatively high solids loads without blinding
Cross flow filtration
Crossflow filtration vs Dead-end filtration Filtration modes can be divided by crossflow filtration and dead-end filtration depending the flow direction on membrane surface.
In crossflow filtration, feed moves parallel to the filter medium to generate shear stress to scour the surface (Fig. 1a). Extra energy is required to generate crossflow, but cake layer thickness can be controlled. Pseudo steady-state may exist, where scouring effect and particle deposition find a balance and cake layer hardly grows. This filtration mode is particularly effective when feed water carries high level of foulants such as suspended solids and macromolecules. All MBR processes and most of wastewater filtrations are adapting crossflow modes.
In dead-end filtration, no crossflow exits and feed moves toward the filter medium. All the particles that can be filtered by filter settle on the filter surface. Since the filtration is not sustainable forever without removing accumulated solids, backwashing is performed periodically and/or filter medium is replaced. This filtration mode is particularly effective when feed water carries low level of foulants. Many surface water filtrations, pretreatment for seawater RO, and tertiary filtrations are adapting dead-end modes.
• Theory and equipment used in cross flow filtration
• cross flow electro filtration, dual functional filter
• Surface based solid -liquid separations involving a second liquid, Sirofloc filter.
Assignment
• surface properties, ionic properties and other special characteristics of substances used in se
