EXTRACTORSEXTRACTORS::

Liquid-liquid extraction has only become popular Liquid-liquid extraction has only become popular as a separations technique in the past thirty as a separations technique in the past thirty

years. In this time, liquid-liquid extractors have years. In this time, liquid-liquid extractors have become the separation equipment of choice for become the separation equipment of choice for

selected processesselected processes..

BASICSBASICS::The primary inlet and outlet streams of typical liquid-The primary inlet and outlet streams of typical liquid-

liquid extractor are shownliquid extractor are shown Droplet formation is the most common method of mass transfer. The droplets

are formed in either the heavy phase or the light phase so as to maximize surface area and solvent contact. Often LLE processes include a dispersion-coalescence cycle. Dispersion is the breaking up of the intact phase of liquid

into the droplets necessary for mass transfer. Coalescence is the coming together of the droplets into one mass and the cycle is incorporated through a

series of multiple dispersion and coalescence stages to enhance mass transfer. The picture below shows the dispersion of droplets that occurs in a liquid-liquid

extraction column.

Liquid – liquid extractionLiquid – liquid extraction

MIXER-SETTLERSMIXER-SETTLERS::

GENERAL INFORMATIONGENERAL INFORMATION::

Mixer-settler liquid-liquid extractors have two stages. In the Mixer-settler liquid-liquid extractors have two stages. In the mixing stage the immiscible solvent and the solute-carrying mixing stage the immiscible solvent and the solute-carrying

feed are brought into contact, droplets are formed by feed are brought into contact, droplets are formed by mixing, and the desired solute(s) are extracted by the mixing, and the desired solute(s) are extracted by the

solvent. To learn more about different mixer designs solvent. To learn more about different mixer designs see the see the MixersMixers section of this section of this

encyclopediaencyclopedia..In the settler the two liquid components do just that, they In the settler the two liquid components do just that, they

settle out into two phases. The heavier phase exits out the settle out into two phases. The heavier phase exits out the bottom of the settler and the lighter phase is drawn off the bottom of the settler and the lighter phase is drawn off the top. To learn more about different settler designs see the top. To learn more about different settler designs see the

Gravity SeparatorsGravity Separators section of this encyclopedia section of this encyclopedia..

EQUIPMENT DESIGNEQUIPMENT DESIGN::For most processes one mixer and one settler will For most processes one mixer and one settler will

not be enough to achieve effective separation. not be enough to achieve effective separation. Often a system is designed with several mixer-Often a system is designed with several mixer-

settler stages in series. Although the flow of the settler stages in series. Although the flow of the two liquid phases can two liquid phases can

be be countercurrentcountercurrent, , cocurrentcocurrent or or cross flowcross flow, solvent , solvent use is most inefficient in cross flow. The use is most inefficient in cross flow. The

transportation of the liquids from one stage to the transportation of the liquids from one stage to the next occurs either by gravity or using pumps. The next occurs either by gravity or using pumps. The schematic below shows a countercurrent system schematic below shows a countercurrent system

with three mixers and settlers in serieswith three mixers and settlers in series..

Mixer-settlerMixer-settler

USAGE EXAMPLESUSAGE EXAMPLES::

The mixer-settler system shown here is used in chemical The mixer-settler system shown here is used in chemical processing. Mixer-settler systems, became quite popular in processing. Mixer-settler systems, became quite popular in

the metals industry for their ability to handle high the metals industry for their ability to handle high throughputs that required long residence times. They have throughputs that required long residence times. They have

grown to find much use in several other processes, such as grown to find much use in several other processes, such as aromatic extraction and nuclear fuel processing. Shown aromatic extraction and nuclear fuel processing. Shown

below to the left is an example of a stainless steel 3-stage below to the left is an example of a stainless steel 3-stage mixer-settler liquid extractor. To the right is an example of mixer-settler liquid extractor. To the right is an example of

a mixer-settler with a tubular design used for glass, a mixer-settler with a tubular design used for glass, enamelled steel and other metallic materials with high enamelled steel and other metallic materials with high

operational pressuresoperational pressures..

ExamplesExamples::

disadvantagesdisadvantages

Large amounts of floor space requiredLarge amounts of floor space required..

Only systems with a few stages are economicalOnly systems with a few stages are economical. .

Large amounts of valuable material, such as Large amounts of valuable material, such as the solvent, are tied up during the processthe solvent, are tied up during the process..

Poor solvent conservationPoor solvent conservation..

ADVANTAGESADVANTAGES

Reliable scale up techniquesReliable scale up techniques..Can handle high flow ratesCan handle high flow rates..Ideal for processes with slow mass transferIdeal for processes with slow mass transfer..Intense mixing, resulting in small droplets for Intense mixing, resulting in small droplets for

good mass transfergood mass transfer

22( ( Spray ColumnSpray Column::

This set-up merely consists of an empty shell with This set-up merely consists of an empty shell with provisions at the end for introducing and removing provisions at the end for introducing and removing

the liquids. Its construction is the simplest but the liquids. Its construction is the simplest but suffers from low efficiency due to poor phase suffers from low efficiency due to poor phase contacting and excessive back-mixing in the contacting and excessive back-mixing in the

continuous phase. Because of their simple continuous phase. Because of their simple construction, spray columns are still used in the construction, spray columns are still used in the industry for simple operations such as washing industry for simple operations such as washing

and neutralizationand neutralization..

SPRAY - COLUMNSSPRAY - COLUMNS

Spray column liquid-liquid extractors are the Spray column liquid-liquid extractors are the simplest of the column designs. The dispersed simplest of the column designs. The dispersed

phase is introduced via a nozzle either at the top phase is introduced via a nozzle either at the top or the bottom of the column, depending on or the bottom of the column, depending on

whether the heavy phase or light phase is being whether the heavy phase or light phase is being dispersed. The continuous phase enters the dispersed. The continuous phase enters the

opposite end of the column, resulting in mass opposite end of the column, resulting in mass transfer through the vertical counter flow of the two transfer through the vertical counter flow of the two phases. There is no dispersion-coalescence cycle phases. There is no dispersion-coalescence cycle inside the column, resulting in very low efficiency inside the column, resulting in very low efficiency for spray columns. Spray columns work best for for spray columns. Spray columns work best for

fluids containing large suspended solidsfluids containing large suspended solids..

33((Packed columnPacked column:: liquid-liquid extractors are also similar to those liquid-liquid extractors are also similar to those

seen in other separations sections of this seen in other separations sections of this encyclopedia. The packing, which assists in encyclopedia. The packing, which assists in

droplet formation, can either be structured in a droplet formation, can either be structured in a mesh net or randomly placed in the column. mesh net or randomly placed in the column.

Dispersion is accomplished with a nozzle at the Dispersion is accomplished with a nozzle at the top or bottom of the column, depending on top or bottom of the column, depending on

whether the heavy or the light phase is being whether the heavy or the light phase is being dispersed. As in sieve tray columns, the internals dispersed. As in sieve tray columns, the internals

of the column need to be coated with the of the column need to be coated with the continuous phasecontinuous phase..

USAGE EXAMPLESUSAGE EXAMPLES::Non-agitated liquid-liquid Non-agitated liquid-liquid

extractors have found their niche extractors have found their niche in several different industries, in several different industries,

including the petrochemical and including the petrochemical and water desalting and purification water desalting and purification

industriesindustries..

PACKED – COLUMNPACKED – COLUMN

ADVANTAGESADVANTAGESSpray columns are inexpensiveSpray columns are inexpensive..Sieve tray columns can handle a very sizeable Sieve tray columns can handle a very sizeable

throughputthroughput..Sieve tray columns have had good success Sieve tray columns have had good success

with scale up procedureswith scale up procedures..Packed columns are highly efficient when only Packed columns are highly efficient when only

a few stages are neededa few stages are needed..

DISADVANTAGESDISADVANTAGES

Spray columns are very inefficientSpray columns are very inefficient..Sieve tray and packed columns can suffer from Sieve tray and packed columns can suffer from

solids pluggingsolids plugging..Packed columns have lower throughput due to Packed columns have lower throughput due to

the packingthe packing..Packed columns are hard to scale up Packed columns are hard to scale up

accuratelyaccurately..The initial dispersion is a concern packed The initial dispersion is a concern packed

columns, to avoid channelingcolumns, to avoid channeling

44((What is a baffle plateWhat is a baffle plate::

Baffle plates have many design uses in general in different Baffle plates have many design uses in general in different applications. However, the name pretty much describes its applications. However, the name pretty much describes its

intended function for the biggest part. It baffles air to create intended function for the biggest part. It baffles air to create the pressurized conditions required within your systems the pressurized conditions required within your systems

design for proper and distribution and flow rate through out design for proper and distribution and flow rate through out your system. Many baffles are adjustable and some are your system. Many baffles are adjustable and some are fixed. There are various reasons for that too. Air noise is fixed. There are various reasons for that too. Air noise is

also something that baffles are used to help alleviate noisy also something that baffles are used to help alleviate noisy type situations that may exist or have a potential to do sotype situations that may exist or have a potential to do so..

in your gas tank they dampen the movement of the fuel in your gas tank they dampen the movement of the fuel when you accelerate or decelerate as an examplewhen you accelerate or decelerate as an example

What are the functions What are the functions of baffle platesof baffle plates??

Baffle plates are mainly used as Baffle plates are mainly used as a steam separator i.e the a steam separator i.e the

mixture of steam of water gets mixture of steam of water gets separated when the water separated when the water

molecules struck the baffles and molecules struck the baffles and due to gravity they fall down andue to gravity they fall down an

What is a baffle plate forWhat is a baffle plate for??

Baffle plates have many design Baffle plates have many design uses in general in different uses in general in different applications. However, the applications. However, the

name pretty much describes its name pretty much describes its intended function for the intended function for the

biggest part. It bafflesbiggest part. It baffles. .

how to remove a baffle plate from how to remove a baffle plate from a wood heatera wood heater??

11. . Open the door or doors of the wood heater to Open the door or doors of the wood heater to locate the baffle plate near the top of the heater locate the baffle plate near the top of the heater

interior. 2. Push up on the front edge of the interior. 2. Push up on the front edge of the plate. 3. Tap the underside of theplate. 3. Tap the underside of the

    What is the use af What is the use af a baffle plate in the storage tanka baffle plate in the storage tank??  

To keep the liquid from sloshing aroundTo keep the liquid from sloshing around  

55((ROTATING DISC LIQUID-LIQUIDROTATING DISC LIQUID-LIQUIDEXTRACTION UNITEXTRACTION UNIT::

HIS Rotating Disc Liquid-Liquid Extraction Unit has been HIS Rotating Disc Liquid-Liquid Extraction Unit has been designed to demonstrate thedesigned to demonstrate the

basic principles of a liquid-liquid extraction process. When basic principles of a liquid-liquid extraction process. When separation by distillation is ineffective or veryseparation by distillation is ineffective or very

difficult, liquid-liquid extraction is one of the main alternatives to difficult, liquid-liquid extraction is one of the main alternatives to consider. Close boiling mixtures or substancesconsider. Close boiling mixtures or substances

that cannot withstand the temperature of distillation, even under that cannot withstand the temperature of distillation, even under a vacuum, may often be separated from impurities bya vacuum, may often be separated from impurities by

extraction, which utilizes chemical differences instead of vapor extraction, which utilizes chemical differences instead of vapor pressure differencespressure differences..

Separation by liquid-liquid extraction can be defined as the Separation by liquid-liquid extraction can be defined as the selective removal of one or more components eitherselective removal of one or more components either

from a homogeneous liquid mixture or from a solution, using a from a homogeneous liquid mixture or from a solution, using a second liquid or solvent, which is partially or whollysecond liquid or solvent, which is partially or wholly

immiscible with the firstimmiscible with the first..

EXTRACTION UNITEXTRACTION UNIT::The normal mode of operation is that the light phaseThe normal mode of operation is that the light phaseand heavy phase liquids are pumped counter currentlyand heavy phase liquids are pumped counter currentlyinto the extraction column. The heavy phase will enterinto the extraction column. The heavy phase will enterthe top of the column and flow downwards while thethe top of the column and flow downwards while thelight phase will enter the bottom of the column and flowlight phase will enter the bottom of the column and flowupwards due to density differences. Countercurrent flowupwards due to density differences. Countercurrent flowin the column and agitation of the two phases by thein the column and agitation of the two phases by therotating disc will cause the transfer of solute componentrotating disc will cause the transfer of solute componentfrom one phase (raffinate) to the other (extract). Thefrom one phase (raffinate) to the other (extract). Theraffinate will emerge at the bottom while the extract willraffinate will emerge at the bottom while the extract willemerge at the top of the extraction column. This liquid liquidemerge at the top of the extraction column. This liquid liquidextraction process is done in numerous continuousextraction process is done in numerous continuousstages throughout the column to give a higher degreestages throughout the column to give a higher degreeof separationof separation..

EXPERIMENTAL CAPABILITIESEXPERIMENTAL CAPABILITIES

Demonstration of liquid / liquid extractionDemonstration of liquid / liquid extractionexperiments using a rotating disc columnexperiments using a rotating disc column..Determination of the height equivalent theoreticalDetermination of the height equivalent theoreticalplates (HETP) and extraction efficiency for theplates (HETP) and extraction efficiency for thecolumncolumn..Investigatation on the effect of total feed flow ratesInvestigatation on the effect of total feed flow ratesto feed ratio on and solvent the column’s extractionto feed ratio on and solvent the column’s extraction

efficiencyefficiency..Investigatation on the effect of rotating disc speedsInvestigatation on the effect of rotating disc speedson the column’s extraction efficiencyon the column’s extraction efficiency..

TECHNICAL SPECIFICATIONSTECHNICAL SPECIFICATIONS

a) Rotating Disc Columna) Rotating Disc ColumnColumn diameter : DN 50Column diameter : DN 50Effective height : 2.0 mEffective height : 2.0 mNo. of discs : 40No. of discs : 40b) Stirrer Motorb) Stirrer MotorVariable speed motor with digital speed displayVariable speed motor with digital speed display..Speed range : 50 to 2000 rpmSpeed range : 50 to 2000 rpmMax. torque : 60 NcmMax. torque : 60 NcmPower : 130 WPower : 130 Wequipped with feed port, vent and drain valvesequipped with feed port, vent and drain valves..Capacity : 50 LCapacity : 50 LGraduations : 2 LGraduations : 2 Ld) Dosing Pumpsd) Dosing Pumpslength and stroke frequencylength and stroke frequency..Flow rate : up to 42 L/hrFlow rate : up to 42 L/hrPower : 0.25 kWPower : 0.25 kW..

66( ( AGITATEDAGITATED::Many agitated column designs Many agitated column designs 

are used for liquid-liquid are used for liquid-liquid extraction. Only a few of the extraction. Only a few of the more popular designs will be more popular designs will be 

explored in this sectionexplored in this section..

AGITATED - COLUMNAGITATED - COLUMN

GENERAL INFORMATIONGENERAL INFORMATION::

Agitated columns contain some type of Agitated columns contain some type of mechanical device to agitate the liquids as they mechanical device to agitate the liquids as they 

pass through the column. Rotating and pass through the column. Rotating and reciprocating mechanisms are the most reciprocating mechanisms are the most 

common methods for creating and maintaining common methods for creating and maintaining dispersion throughout the column. The diagram dispersion throughout the column. The diagram 

below to the right shows the interior of an below to the right shows the interior of an agitated column and the picture on the right is agitated column and the picture on the right is 

an agitator used in an extraction columnan agitator used in an extraction column..

ExamplesExamples  

EQUIPMENT DESIGNEQUIPMENT DESIGN::

Baffled mixing segments are common to all baffled Baffled mixing segments are common to all baffled column extractors. Turbine impellers rotate between a column extractors. Turbine impellers rotate between a set of baffles, creating several mixing zones along the set of baffles, creating several mixing zones along the column length. The mixed liquids move to the outside column length. The mixed liquids move to the outside sets of stator baffles, where they can separate out and sets of stator baffles, where they can separate out and move up or down to the next stage. The baffles help move up or down to the next stage. The baffles help reduce axial mixing, creating several mixing zones to reduce axial mixing, creating several mixing zones to 

increase mass transfer. The Schreiber and the increase mass transfer. The Schreiber and the Oldshue-Rushton columns are common baffled Oldshue-Rushton columns are common baffled 

designsdesigns..

Rotating diskRotating disk

Rotating Disk Contactors (RDC) and Asymmetric Rotating Disk Rotating Disk Contactors (RDC) and Asymmetric Rotating Disk Contactors (ARDC) are another type of agitated column Contactors (ARDC) are another type of agitated column

extractors. The ARDC seen in the animation is characterized by extractors. The ARDC seen in the animation is characterized by the off-center rotating shaftthe off-center rotating shaft..

The heavy phase enters the top of the extractor and mixes with The heavy phase enters the top of the extractor and mixes with the light phase in the top mixing region, composed of a rotating the light phase in the top mixing region, composed of a rotating

disk. The two phases then enter the external settling stage, disk. The two phases then enter the external settling stage, where they separate. The heavy phase then travels down to the where they separate. The heavy phase then travels down to the

next mixing region. This mixing-settling action continues down next mixing region. This mixing-settling action continues down the length of the column. Individual mixing regionsthe length of the column. Individual mixing regions

Rotating diskRotating disk

are separated by baffles, and the are separated by baffles, and the mixing and settling regions by a stator. mixing and settling regions by a stator.

A stator is a portion of a cylinder that A stator is a portion of a cylinder that separates the two regions while separates the two regions while

allowing transport between the twoallowing transport between the two..

USAGE EXAMPLESUSAGE EXAMPLES

Agitated column liquid-liquid extractors are Agitated column liquid-liquid extractors are used to purify water by extracting out impurities used to purify water by extracting out impurities

such as acetic acid and acetonesuch as acetic acid and acetone..Agitated extractors are also used in Agitated extractors are also used in

biotechnical and environmental industries. The biotechnical and environmental industries. The picture below shows an extractor in a plant. picture below shows an extractor in a plant.

The column below has the ability to adjust the The column below has the ability to adjust the cross-sectional area and the agitator speed, cross-sectional area and the agitator speed,

which can optimize droplet size. This flexibility which can optimize droplet size. This flexibility allows the column to maximize efficiencyallows the column to maximize efficiency..

AGITATED - COLUMNAGITATED - COLUMN

DISADVANTAGESDISADVANTAGES

Repair of internal mechanical Repair of internal mechanical parts can cause process delaysparts can cause process delays..

ADVANTAGESADVANTAGES

Mechanical parts result in good dispersionMechanical parts result in good dispersion..Little axial mixing compared to non-agitated Little axial mixing compared to non-agitated

columnscolumns..Karr column extractors can handle higher Karr column extractors can handle higher

throughputs than other agitated columnsthroughputs than other agitated columns..

Pulse - columnPulse - column

DISADVANTAGESDISADVANTAGES

Packing in packed column hinders flowPacking in packed column hinders flowMore expensive than non-agitated columnsMore expensive than non-agitated columns

ADVANTAGESADVANTAGES

Increases efficiency two foldIncreases efficiency two foldNo internal mechanical parts makes repairs No internal mechanical parts makes repairs

easyeasy