External Fields in Separation Processes: Thermal Diffusion, Electrolysis, Electrodialysis, and Electrophoresis

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▪ 6.0 Centrifugation (Studied in “Mechanical – Physical Separations”)
▪ 6.1 Thermal Diffusion
▪ 6.2 Electrolysis
▪ 6.3 Electro-dialysis
▪ 6.4 Electrophoresis

▪ External fields can take advantage of differing degrees of response of molecules and
ions to force fields.
▪ Special note: Filtration and Centrifugation are studied in Mechanical – Physical
Separations

▪ Thermal diffusion utilizes the transfer of heat across a thin liquid or gas to
accomplish isotope separation.
▪ The ESA → Thermal Gradient
▪ The process exploits the fact that the isotopes are either lighter and heavier.
▪ Expect a heavier stream and a lighter Stream.
▪ The molecules will diffuse towards the hot surface.

▪ The most common examples is 235U separation of isotopes.
▪ The lighter 235U gas molecules will diffuse toward a hot surface, and the heavier 238U gas
molecules will diffuse toward a cold surface.
▪ The S-50 plant at Oak Ridge, Tennessee was used during World War II to prepare feed
material for the EMIS process.
▪ It was abandoned in favor of gaseous diffusion.
▪ This process has been used to enhance separation of isotopes in permeation processes.
▪ Water contains 0.000149 atom fraction of deuterium.
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▪ Electrolysis is a technique that uses a direct electric current
(DC) to drive an otherwise non-spontaneous chemical reaction.
▪ The ESA → Electric Current
▪ Electrolysis is commercially important as a stage in the
separation of elements from naturally occurring sources such as
ores using an electrolytic cell.
▪ The voltage that is needed for electrolysis to occur is called the
decomposition potential.
▪ In many cases, a Membrane will be used
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▪ Electrolysis is extensively used in many
Manufacturing proceses.
▪ As a Separation Process:
▪ Chlorine
▪ Hydrogen-Oxygen Gas Production

▪ Membrane electrolysis is a process whereby both electrode
reactions
▪ the cathodic reduction
▪ the anodic oxidation
▪ Both are linked to the transport and transfer of charged ions.
▪ In membrane electrolysis:
▪ the electrode reaction is essential to the actual separation
process.

▪ The purpose of the membrane is to:
▪ separate the anode loop (anolyte) from the cathode loop (catholyte) by a fluid
▪ This avoids unwanted secondary reactions
▪ this combines the electrode reaction with a separation step or to isolate separately the products formed on the
electrode.

▪ In water electrolysis:
▪ such products may be in a gaseous form such as oxygen and hydrogen as well as the acids (H+) and bases
(OH-)
▪ These are formed on the electrode or the combination of gaseous chlorine and caustic soda solution and
hydrogen as in sodium chloride electrolysis

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▪ Check this video:
▪ https://www.youtube.com/watch?v=ueeHNwL5lSE
▪ Chlorin-Caustic Soda Production
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▪ In electrodialysis
▪ Cation-permeable AND anion-permeable membranes
carry a fixed charge
▪ This prevents migration of species of like charge.
▪ The main goal is to remove ions from solution:
▪ Decrease concentration of a solute
▪ Remove a solute completely
▪ Main focus is the SOLVENT/Solution

▪ It involves the migration of ions through ion-
exchange membranes in an applied electric field.
▪ The flux of an ion through the membrane is
dependent upon its charge, the bulk concentration
of the ion and its mass transport to the membrane
surface.
▪ In this way species can be removed from reaction
mixtures and waste streams thereby reducing the
need for costly disposal and purification.
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▪ Electrodialysis dates back to the early 1900s
▪ The GOAL → Electrodes and a direct current were used to increase
the rate of dialysis.
▪ Today:
▪ Electrodialysis refers to an electrolytic process for separating an
aqueous, electrolyte feed into:
▪ Concentrate
▪ Dilute / desalted water diluate
▪ ESA → Electric field AND ion-selective membranes

▪ There can be many sections which are
separated depending on the type of
membrane:
▪ Example four ion-selective membranes are of two
types arranged in an alternating-series pattern.
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▪ The cation-selective membranes (C) carry
a negative charge, and thus attract and
pass positively charged ions (cations),
while retarding negative ions (anions).
▪ The anion-selective membranes (A) carry
a positive charge that attracts and
permits passage of anions.

▪ Both types of membranes are impervious
to water.
▪ The net result:
▪ Both anions and cations are concentrated in
compartments:
▪ 2 and 4
▪ From which concentrate is withdrawn
▪ Ions are depleted in compartment 3
▪ From which the diluate is withdrawn.

▪ Compartment pressures are essentially
equal.
▪ Compartments 1 and 5:
▪ contain the anode and cathode (respectively)
▪ A direct-current voltage causes:
▪ current to flow through the cell by ionic
conduction
▪ from the cathode (right)
▪ to the anode (left)
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▪ Both electrodes are chemically neutral
metals
▪ Typically:
▪ Anode is stainless steel
▪ Cathode platinum- coated tantalum,
niobium, or titanium.
▪ The electrodes are neither:
▪ oxidized nor reduced.

▪ Electrodialysis:
▪ Production of table salt from seawater
▪ Concentration of brines from reverse osmosis
▪ Treatment of wastewater from electroplating
▪ De-mineralisation of cheese whey
▪ Production of ultrapure water for semiconductor industry

▪ Check out this video:
▪ https://www.youtube.com/watch?v=wcb8RFWa6BY
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▪ Electrophoresis (from the Greek "ηλεκτροφόρηση" meaning "to bear electrons")
▪ is the motion of dispersed particles relative to a fluid under the influence of a spatially
uniform electric field.
▪ ESA → Electric Field
▪ It involves the size- and charge-based separation of charged solutes that move in
response to an electric field applied across an electrophoretic medium.
▪ The Electrophoresis of a:
▪ positively charged particles (cations) → cataphoresis
▪ negatively charged particles (anions) → anaphoresis.
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▪ It commonly occurs in a gel matrix of synthetic or natural
polymer.
▪ It must be done in a developed in-place between parallel glass
plates or inside a silica capillary to minimize electro-osmosis and
resistive Joule heating.
▪ Common Examples:
▪ Agarose
▪ Polyacrylamide
▪ Starch → its high water content allows allows passage of large solutes
through their porous structures.

▪ Electrophoresis is widely used to separate and purify biomolecules:
▪ Proteins and Nucleic acids.

▪ Several electrophoretic modes are widely used to isolate and
concentrate biomolecules.
▪ They are distinguished by:
▪ Denaturants
▪ Matrix pH
▪ Electrolyte content relative to the direction of the applied field
gradient
▪ all of which influence the electrophoretic mobility of the
biomolecule.

▪ It can be used to exploit the different migration velocities of charged colloidal or suspended
species in an electric field.
▪ Positively charged species, such as
▪ Dyes, hydroxide sols, and colloids, migrate to the cathode
▪ Negatively charged particles:
▪ Such as most small, suspended particles go to the anode.
▪ By changing from an acidic to a basic condition:
▪ migration direction can be changed, particularly for proteins.
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▪ Electrophoresis is thus a versatile method for separating biochemicals.
▪ Chemical stains, fluorescence, immunological probes, and spectroscopy/spectrometry are
used to visualize and recover biomolecules distinguished by electrophoresis.

▪ 7.1 Leaching
▪ 7.2 Washing
▪ 7.3 Drying
▪ 7.4 Evaporation
▪ 7.5 Crystallization

▪ From beets to sugar
If you were to measure the time it takes to produce shimmering white sugar crystals
from a beet that had just been delivered from the field to the factory, you would be
surprised:
▪ On average, it takes less than eight hours.

▪ Juice extraction
The beets are:
▪ sliced into thin strips
▪ preheated in a cossette scalder
▪ sent to an extraction tower.
▪ Water at 70° Celsius is poured
through the device to extract the
sugar and produce raw juice.
▪ The used cosettes are dried by
means of screw presses and hot
air.
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▪ Juice purification
▪ A lime kiln is used to produce the
natural substances lime and
carbon dioxide, which are added
sequentially to the raw juice to
bind and precipitate out the non-
sugar impurities.
▪ A clear, thin juice with a sugar
content of about sixteen percent
remains.

▪ Evaporation
▪ The thin juice is concentrated by
heating to make a thick golden
brown juice with a sugar content
of about sixty-seven percent.

▪ Crystallization
▪ The thick juice is boiled until crystals are
formed, which are a glowing golden yellow
color because they are covered with syrup.
▪ The syrup is separated from the crystals in a
centrifuge.
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▪ Crystallization
▪ Hot water is used to rinse off any residual
syrup.
▪ The remaining sugar crystals are clear as
glass, and the light refracted from them is
white as snow.
▪ This sugar is dissolved and re-crystallized to
produce refined sugar – sugar that is
extremely pure.

▪ Converting
▪ The finished sugar is dried, cooled and stored in silos, and is subsequently withdrawn and further
processed or packed.
▪ Over eighty percent of the sugar is shipped to the converting industry, which uses it to make
confectioneries, beverages, baked goods, etc.
▪ Just under twenty percent of the sugar is converted to various types of household sugar and
packaged.

▪ Recycling
▪ All the by-products of this process are returned to the natural cycle.
▪ The pressed slices of sugar beet are used as animal feed.
▪ The Carbokalk (carbolic lime) that is a by-product of processing the juice is an excellent
fertilizer.

▪ Leaching →
▪ the process of extracting substances from a solid by dissolving them in a liquid
▪ Leaching is the process of a solute becoming detached or extracted from its
carrier substance by way of a solvent.
▪ Leaching (in metallurgy)
▪ is a process widely used in extractive industry.
▪ Here, ore is treated with chemicals to convert the valuable metals within into:
▪ soluble salts
▪ impurity remain insoluble.

▪ Technically an Extraction, since it:
▪ is a process of selectively removing a compound of interest from a
mixture using a solvent.
▪ The major difference between solid–liquid and liquid– liquid
systems:
▪ Difficulty of transporting the solid (often as slurry or a wet cake) from
stage to stage.
▪ For an extraction to be successful:
▪ the compound must be more soluble in the solvent than in the mixture.
▪ Additionally:
▪ the solvent and mixture must be immiscible
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▪ Making tea is a good example of extraction.
▪ Water is placed in contact with tea bags
▪ The "tea" is extracted from the tea leaves into
the water.
▪ This works because:
▪ the "tea" is soluble in water
▪ the leaves are not soluble
▪ A simple filtration process separates the solids vs.
aqueous material

▪ In Leaching, there are three substances which are required:
▪ a carrier
▪ a solute
▪ and a solvent
▪ As you can see, this is a partition between 2 binary systems
▪ (at least)
▪ The main property exploited here is solubility
▪ To promote rapid solute diffusion out of the solid and into the
liquid solvent, particle size of the solid is usually reduced.
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▪ Some other type of properties which may be exploited are:
▪ Particle size
▪ Solvent
▪ Temperature
▪ Agitation
▪ Surface area
▪ Homogeneity of the carrier and solute
▪ Microorganism activity
▪ Mineralogy
▪ Intermediate products
▪ Crystal structure

▪ Type of Operations:
▪ In the pharmaceutical, food, and natural product
industries:
▪ countercurrent solid transport is provided by complicated
mechanical devices.
▪ In adsorptive-bubble separation methods:
▪ surface-active material collects at solution interfaces.

▪ If the (very thin) surface layer is collected:
▪ partial solute removal from the solution is achieved.
▪ In ore flotation processes:
▪ solid particles migrate through a liquid and attach to rising
gas bubbles
▪ This allows a floating out of solution.
▪ When leaching is rapid, it can be accomplished in one
stage.
▪ However, the leached solid will retain surface liquid that
contains solute.
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▪ Leaching of large solids can be very slow because of
small solid diffusivities.
▪ It is common to reduce size of the solids by:
▪ crushing, grinding, flaking, slicing, etc.
▪ Solids are contacted with solvent by:
▪ either percolation or immersion.
▪ To recover solute in the extract, it is desirable to add one or more washing stages in a
countercurrent arrangement.

▪ When operating under Stages:
▪ Effluents from a leaching stage are essentially solids-free liquid
▪ They are called the overflow, and wet solids, the underflow.
▪ To reduce the concentration of solute in the liquid portion of the underflow:
▪ leaching is often accompanied by countercurrent-flow washing stages.

▪ The combined process produces:
▪ A final overflow
▪ referred to as extract, which contains some of the solvent and most of the solute
▪ A final underflow
▪ the extracted or leached solids, which are wet with almost pure solvent.
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▪ Ideally:
▪ the soluble solids are perfectly separated from the insoluble solids
▪ BUT solvent is distributed to both products.
▪ Therefore, additional processing of the extract and the leached solids is necessary
to recover solvent for recycle.

▪ Go back to the Case Study
▪ Identify the Extraction Process
▪ Is this liq-liq or solid-liq?
▪ Why do we have a slicer?
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▪ Basket Extractor.
▪ Continuous Operator

▪ Perforated Belt Extractor

▪ Industrial applications of leaching include:
▪ REMOVALS:
▪ Removal of copper from ore using sulfuric acid
▪ Removal of caffeine from green coffee beans using supercritical CO2
▪ RECOVERIES:
▪ Recovery of proteins and other natural products from bacterial cells.
▪ Recovery of gold from ore using sodium-cyanide solution
▪ EXTRACTIONS:
▪ Extraction of sugar from sugar beets using hot water
▪ Extraction of tannin from tree bark using water

www.ChemicalEngineeringGuy.com https://demonstrations.wolfram.com/CountercurrentLeachingOfOilFromMeal/

▪ Washing is the process of selectively removing unwanted compounds from a mixture
using a solvent.
▪ For a washing to be successful:
▪ the unwanted materials must be more soluble in the solvent than in the mixture.
▪ Additionally, the solvent and mixture must be immiscible.
▪ Immiscible solvents are not soluble in each other and form two layers when mixed.
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▪ The washing of clothes is a good example.
▪ Dirty clothes are placed in water.
▪ The dirt, the unwanted material, is removed leaving the
clothes, what we are interest in, behind.
▪ This works because the dirt is soluble in the water and
clothes are not.

▪ When:
▪ leaching is very rapid as with small particles containing very soluble solutes
▪ or when leaching has already been completed
▪ or when solids are formed by chemical reactions in a solution
▪ We have to:
▪ counter-currently wash the solids to reduce the solute concentration in the liquid adhering
to the solids.
▪ This can be accomplished in a series of:
▪ gravity thickeners
▪ or centrifugal thickeners, called hydroclones
▪ Note that they must be arranged for countercurrent flow of the underflows and
overflows.

▪ Combined feed to the thickener consists of:
▪ feed solids or underflow from an adjacent thickener, together with fresh solvent or
overflow from an adjacent thickener.
▪ The thickener must first thoroughly mix liquid and solids.
▪ Then, a uniform concentration of solute in the liquid is obtained
▪ Then, it must produce:
▪ an overflow free of solids
▪ an underflow with as high a fraction of solids as possible.
▪ A thickener consists of a
▪ large-diameter
▪ shallow tank
▪ a flat/slightly conical bottom.
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▪ The combined feed enters the tank near the center by means of a feed launder that
discharges into a feed well.
▪ Settling and sedimentation of solid particles occur by gravity due to a solid particle
density that is greater than the liquid density.
▪ In essence:
▪ solids flow downward
▪ liquid flows upward.
▪ Around the upper, inner periphery of the tank:
▪ Overflow launder or weir for continuously removing clarified liquid.
▪ Solids settling to the tank bottom are moved inward toward a thick sludge discharge
by a slowly rotating motor-driven rake.
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▪ Gravity Thickener

▪ Thickeners as large as 100 m in diameter and 3.5 m high have been constructed.
▪ In large thickeners, rakes revolve at about 2 rpm.
▪ Residence times of solids and liquids in a gravity thickener are often large (minutes
or hours) and
▪ These are sufficient to provide adequate residence time for mass transfer and
mixing when small particles are involved.
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▪ the hydroclone is a better fit when:
▪ long residence times are not needed
▪ the overflow need not be perfectly clear of solids

▪ The FEED:
▪ pressurized feed slurry enters tangentially
▪ This creates, by centrifugal force, a downward-spiraling motion.
▪ Higher-density, suspended solids are
▪ by preference, driven to the wall
▪ This becomes conical as it extends downward
▪ The OUTLET:
▪ It is then discharged as a thickened slurry at the hydroclone bottom.
▪ The liquid, which is forced to move inward and upward as a spiraling vortex
▪ It exits from a vortex-finder pipe extending downward from the closed hydroclone top to a
location just below feed entry.
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▪ Comparison:
▪ Washing vs. Leaching (Here, extraction)
▪ https://www.youtube.com/watch?v=nUESTbOJSFE

▪ A common manufacturing step is drying
▪ Since many chemicals are processed wet but sold as dry solids
▪ The term drying also describes a gas mixture in which a condensable
vapor (i.e. water vapor) is removed from a non-condensable gas
(i.e. air) by cooling
▪ Although the only requirement is:
▪ that the vapor pressure of the liquid to be evaporated from the solid be
higher than its partial pressure in the gas stream
▪ This Section deals only with drying operations that produce solid
(dry) products.
▪ ESA → Heat
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▪ External conditions as:
▪ Temperature
▪ Humidity
▪ Air flow
▪ Degree of solid subdivision
▪ Drying rate
▪ Internal diffusion conditions must be considered as well:
▪ Capillary flow
▪ Equilibrium moisture content
▪ Heat sensitivity

▪ It is important to note that:
▪ solid, liquid, and vapor phases coexist in drying.
▪ This is a challenge for the equipment-design.
▪ The dryer design and operation represents a complex problem.
▪ Procedures are difficult to devise
▪ Equipment size may be controlled by heat transfer rather than MT
▪ NOTE:
▪ Technically, this could be a Heat Transfer Unit as well…
▪ Use a psychrometric charts are key:
▪ adiabatic-saturation temp.
▪ wet-bulb temperature

▪ Drying can be expensive:
▪ especially when large amounts of water, with its high heat of vaporization
▪ Water and energy conservation measures, and advances in equipment design have
broadened.
▪ The use of pre-feed dewatering operations by mechanical means, which also
diminish the length of drying cycles are:
▪ Expression
▪ Gravity, vacuum, or pressure filtration
▪ Settling
▪ Centrifugation
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▪ Heat must be transferred to the material being dried:
A. By convection from a hot gas in contact with the material
B. By conduction from a hot, solid surface in contact with the material;
C. By radiation from a hot gas or surface
D. By heat generation within the material by:
▪ dielectric, radio frequency, or microwave heating

▪ Industrial Equipment
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▪ Rolling Bed Dryer

▪ Rotatory Dryers
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▪ Drying is widely used to remove moisture from:
▪ crystalline particles of inorganic salts and organic compounds to produce a free-flowing
product;
▪ biological materials
▪ Such as foods
▪ pharmaceuticals
▪ detergents;
▪ lumber, paper, and fiber products;
▪ dyestuffs;
▪ solid catalysts;
▪ milk;
▪ films and coatings,
▪ products where high water content entails excessive transportation and distribution costs.
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▪ Rotatory Dryed:
▪ https://www.dailymotion.com/video/x32p9k9
▪ Fluidized Bed Dryer
▪ https://www.youtube.com/watch?v=hSSCGXXgIVQ

▪ Evaporation, is defined as:
▪ the transfer of volatile components of a liquid into a gas by heat transfer.
▪ Applications include:
▪ Humidification*
▪ Air conditioning
▪ Concentration of aqueous solutions
▪ For our Separation Process Course, the latter is the one of interest
▪ NOTE: Evaporation is also commonly referred as a Heat Transfer Operation
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▪ Before crystallizing an inorganic solute from an aqueous
solution:
▪ it is customary to bring the solute concentration close to
saturation.
▪ This is accomplished by evaporating water in an evaporator.
▪ It is also used to concentrate solutions even when the solute
is not subsequently crystallized:
▪ Solutions of sodium hydroxide
▪ Industrial acids
▪ Bulk Chemical
▪ Food & Beverages

▪ When the vapor formed is essentially pure:
▪ there is no mass-transfer resistance in the vapor.
▪ When the liquid is agitated:
▪ mass transfer is sufficiently rapid
▪ We can assume that the rate of solvent evaporation is related to:
▪ The rate of heat transfer from the
▪ Evaporators differ in configuration and degree of liquid agitation.
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▪ Evaporator types:
▪ (a) Horizontal-tube
▪ (b) Vertical-tube
▪ (c) Long-tube vertical
▪ (d) Forced circulation
▪ (e) Falling Film

▪ a) Horizontal-tube evaporator.
▪ Consists of a horizontal cylindrical vessel
▪ It is equipped in the lower section with a horizontal bundle of tubes
▪ Inside of these steam condenses and outside of which the solution to
be concentrated boils.
▪ Agitation is provided only by the movement of the bubbles leaving
the evaporator as vapor.
▪ This type of unit is suitable only for low-viscosity solutions that do
not deposit scale on the heat-transfer surfaces.
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▪ (b) Short-vertical-tube evaporator.
▪ It differs significantly from the horizontal-tube evaporator.
▪ The tube bundle is arranged vertically
▪ In this arrangement:
▪ the solution goes inside the tubes and steam condensing outside.
▪ Boiling inside the tubes causes the solution to circulate.
▪ This provides additional agitation and higher heat-transfer
coefficients.
▪ This type of evaporator is not suitable for very viscous solutions.

▪ (c) Long-vertical-tube evaporator.
▪ The tubes are much longer.
▪ This lengthening the vertical tubes provides:
▪ a separate vapor–liquid disengagement chamber
▪ A higher liquid velocity can be achieved
▪ An even higher heat-transfer coefficient.

▪ (d) Forced-circulation evaporator.
▪ To handle very viscous solutions:
▪ a pump is used to force the solution upward through relatively short
tubes
▪ As the name implies, it requires external Energy / Shaft Work

▪ (e) Falling-film evaporator.
▪ It is popular for concentrating heat-sensitive solutions such as fruit juices.
▪ The solution enters at the top
▪ It then flows as a film down the inside walls of the tubes.
▪ Concentrate and vapor produced are separated at the bottom.
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▪ a) Horizontal-tube evaporator.

▪ (b) Short-vertical-tube evaporator.

▪ (c) Long-vertical-tube evaporator.

▪ (d) Forced-circulation evaporator.
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▪ (e) Falling Film Evaporators

▪ Drying is widely used to remove moisture from:
▪ Bulk Chemical Production
▪ Removal of water / Concentration
▪ Food & Beverage Industries
▪ Concentration of materials
▪ pharmaceuticals
▪ Paper, and fiber products
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▪ Falling Film Evaporator:
▪ https://www.youtube.com/watch?v=N7iIzKA5xh8
▪ Black Liquor Evaporator:
▪ https://www.youtube.com/watch?v=K_v4eFjCEGw
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www.ChemicalEngineeringGuy.com https://demonstrations.wolfram.com/MultipleEffectEvaporationOfSugarSolution/

▪ Physical Phenomena Overview:
▪ Crystallization is the process by which a solid forms:
▪ where the atoms or molecules are highly organized
▪ Its structure is called a crystal
▪ Typically forms of Crystallization:
▪ precipitating from a solution
▪ Freezing
▪ Deposition directly from a gas (rare)
▪ Attributes of the resulting crystal depend largely on factors such as:
▪ Temperature
▪ Pressure
▪ Time
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▪ Crystallization is a purification step
▪ the conditions must be such that impurities do not
precipitate with the product.
▪ Crystallization occurs in two major steps.
▪ The first is nucleation:
▪ the appearance of a crystalline phase from either a
super-cooled liquid or a supersaturated solvent.
▪ The second step is known as crystal growth
▪ which is the increase in the size of particles and
leads to a crystal state.
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▪ In solution crystallization:
▪ the mixture, which includes a solvent, is cooled and/or the solvent is evaporated.
▪ In melt crystallization:
▪ two or more soluble species are separated by partial freezing.

▪ Crystallization is a solid–fluid separation in which crystalline
particles are formed from a homogeneous fluid phase.
▪ Ideally, crystals are pure chemicals
▪ Typically, they are obtained in a high yield with a desirable shape
▪ For formation of organic crystals, organic solvents such as:
▪ acetic acid, ethyl acetate, methanol, ethanol, acetone, ethyl ether,
chlorinated hydrocarbons, benzene, and petroleum fractions.
▪ For aqueous or organic solutions, crystallization is effected by:
▪ cooling a solution
▪ evaporating the solvent
▪ or a combination of the two.
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▪ Process Overview:
▪ Crystallization is a liquid-solid mass transfer operation
▪ Here, the solid crystals are formed
▪ They must be precipitated from solution or melt.
▪ In such separation:
▪ the substance being crystallized diffuses from liquid to solid phase
▪ It then interacts with the solid surface where the crystals grow.

▪ Many of the impurities present in the solution are discarded during crystallization so
that the product is obtained in relatively purer form.
▪ Crystallization has been traditionally known to be the best and the cheapest
method for:
▪ obtaining pure solids from impure solutions
▪ They achieve desirable properties such as:
▪ Flow-ability
▪ Handling
▪ packaging characteristics
▪ attractive appearances
▪ Particle properties like crystal structure, crystal size distribution, polymorphism are
vital
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▪ Agitated Batch Crystallizer
▪ Swenson–Walker Crystallizer
▪ Circulating Liquor Crystallizers
▪ Circulating Magma Crystallizers
▪ Melt Crystallization
▪ Suspension Based Melt Crystallization
▪ Progressive Freezing Crystallization

▪ Agitated Batch Crystallizer
▪ Swenson–Walker Crystallizer
▪ Circulating Liquor Crystallizers
▪ Circulating Magma Crystallizers
▪ Melt Crystallization
▪ Suspension Based Melt Crystallization
▪ Progressive Freezing Crystallization
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▪ Crystallization is one of the oldest known separation operations
▪ Some common applications:
▪ Recovery of sodium chloride as salt crystals from water
▪ Recovery of sugar crystals
▪ Ammonium sulphate & sodium chromate
▪ Organic and inorganic compounds are marketed as crystals.
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www.ChemicalEngineeringGuy.com https://demonstrations.wolfram.com/EvaporativeCrystallizationWithRecycle/

External Fields in Separation Processes: Thermal Diffusion, Electrolysis, Electrodialysis, and Electrophoresis

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