liquid liquid extraction and flocculation
TRANSCRIPT
Liquid-Liquid Extraction And
FlocculationBy- Pradip Yadav
Ajay kumar
Afzal farooque
Contents
Introduction to Extraction
Principle and objective
Types of Liq-liq extraction and Equipments used
Applications
Introduction to Flocculation
Objective
Design of flocculator
Applications
.
Separation processes - general
Mechanical separations e.g. filtration of a solid from a suspension in a liquid, centrifugation, screening etc
Mass transfer operations e.g. distillation, extraction etc
Mass transfer operations – nature of interface between phases:
Gas-liquid contact e.g. absorption, evaporation, distillation etc
Liquid-liquid contact e.g. extraction
Liquid-solid contact e.g. crystallization, adsorption
Gas-solid contact e.g. adsorption, drying etc
.
Hierarchy of Separation Technologies
Physical SeparationsDecantation, Coalescing, Filtration, Demisting
EvaporationSingle Effect, Multiple Effect
DistillationSimple, Azeotropic, Extractive, Reactive
ExtractionSimple, Fractional, Reactive
AdsorptionPressure Swing, Temperature Swing
CrystallizationMelt, Solvent
MembranesMF, UF, NF, RO
Easy
Difficult
DifficultyDifficultyOf Of SeparationSeparation
Liquid-liquid extraction :It is a useful method to separate components (compounds) of a mixture
Let's see an example.
Suppose that you have a mixture of sugar in vegetable oil (it tastes sweet!) and you want to separate the sugar from the oil. You observe that the sugar particles are too tiny to filter and you suspect that the sugar is partially dissolved in the vegetable oil.
How about shaking the mixture with water
Will it separate the sugar from the oil? Sugar is much more soluble in water than in vegetable oil, and, as you know, water is immiscible (=not soluble) with oil.
Did you see the result? The water phase is the bottom layer and the oil phase is the top layer, because water is denser than oil.
*You have not shaken the mixture yet, so sugar is still in the oil phase.
By shaking the layers (phases) well, you increase the contact area between the two phases. The sugar will move to the phase in which it is most soluble: the water layer
Now the water phase tastes sweet,because the sugar is moved to the water phase upon shaking.**You extracted sugar from the oil with water.**In this example, water was the extraction solvent ;the original oil-sugar mixture was the solution to be extracted; and sugar was the compound extracted from one phase to another. Separating the two layers accomplishes the separation of the sugar from the vegetable oil
Partition Coefficient Kp (Distribution Coefficient Kd)
When a compound is shaken in a separatory funnel with two immiscible solvents, the compound will distribute itself between the two solvents.
Normally one solvent is water and the other solvent is a water-immiscible organic solvent.
Most organic compounds are more soluble in organic solvents, while some organic compounds are more soluble in water.
Here is the universal rule:
At a certain temperature, the ratio of concentrations of a solute in each solvent is always constant. And this ratio is called the distribution coefficient, K.
(when solvent1 and solvent2 are immiscible liquids
For example, Suppose the compound has a distribution coefficient K = 2 between solvent1 and solvent2
By convention the organic solvent is (1) and water is (2)
(1) If there are 30 particlesof compound , these aredistributed between equalvolumes of solvent1 and solvent2..
(2) If there are 300 particles of compound , the same distribution ratio is observed in solvents 1 and 2
(3) When you double the volume of solvent2 (i.e., 200 mL of solvent2 and 100 mL of solvent1),the 300 particles of compound distribute as shown
If you use a larger amount of extraction solvent, more solute is extracted
What happens if you extract twice with 100 mL of solvent2 ?In this case, the amount of extraction solvent is the same volume as was used in Figure 3, but the total volume is divided into two portions and you extract with each.
As seen previously, with 200 mL of solvent2 you extracted 240 particles of compound . One extraction with 200 mL gave a TOTAL of 240 particles
You still have 100 mL of solvent1, containing 100 particles. Now you add a second 100 mL volume of fresh solvent2. According to the distribution coefficient K=2, you can extract 67 more particles from the remaining solution
An additional 67 particles are extracted with the second portion of extraction solvent (solvent2).The total number of particles extracted from the first (200 particles) and second (67 particles) volumes of extraction solvent is 267.This is a greater number of particles than the single extraction (240 particles) using one 200 mL portion of solvent2!
It is more efficient to carry out two extractions with 1/2 volume of extraction solvent than one large volume!
If you extract twice with 1/2 the volume, the extraction is more efficient than if you extract once with a full volume. Likewise, extraction three times with 1/3 the volume is even more efficient…. four times with 1/4 the volume is more efficient….five times with 1/5 the volume is more efficient…ad infinitum
The greater the number of small extractions, the greater the quantity of solute removed. However for maximum efficiency the rule of thumb is to extract three times with 1/3 volume
Did you get it? .....the concept of liquid-liquid extraction?
Liquid-liquid extraction is based on the transfer of a solute substance from one liquid phase into another liquid phase according to the solubility. Extraction becomes a very useful tool if you choose a suitable extraction solvent.You can use extraction to separate a substance selectively from a mixture, or to remove unwanted impurities from a solution. In the practical use, usually one phase is a water or water-based (aqueous) solution and the other an organic solvent which is immiscible with water.
The success of this method depends upon the difference in solubility of a compound in various solvents. For a given compound, solubility differences between solvents is quantified as the "distribution coefficient"
Basic principles
In liquid-liquid extraction, a soluble component (the solute) moves from one liquid phase to another. The two liquid phases must be either immiscible, or partially miscible.
usually isothermal and isobaric
can be done at low temperature (good for thermally fragile solutes, such as large organic molecules or biomolecules)
can be very difficult to achieve good contact between poorly miscible liquids (low stage efficiency)
extracting solvent is usually recycled, often by distillation (expensive and energy-intensive)
can be single stage (mixer-settler) or multistage (cascade)
Example - Penicillin G
6-aminopenicillanic acid (6-APA) is manufactured by GSK in Irvine. It is used to manufacture amoxicillin and ‘Augmentin’.
Fermentation products (penicillin G broth) are filtered (microfiltration) and extracted at low pH with amyl acetate or methyl isobutyl ketone. The penicillin G is then extracted further at a higher pH into an aqueous
phosphate buffer..
Immiscible liquids
e.g. water – chloroform
Consider a feed of water/acetone(solute).
K = mass fraction acetone in chloroform phase
mass fraction acetone in water phase
K = kg acetone/kg chloroform = y/x
kg acetone/kg waterK = 1.72
i.e. acetone is preferentially soluble in the chloroform phase
.
Partially miscible liquids
E.g. water – MIBK
Consider a solute acetone.
Need to use a triangular phase diagram to show equilibrium compositions of MIBK-acetone-water mixtures.
Characteristics are single phase and two phase regions, tie lines connecting equilibrium phase compositions in two phase region.
.
Triangular phase diagrams
Each apex of triangle represents 100% pure component
.
B
A S
P%A%S
%B
Extractants
The efficiency of a liquid liquid extraction can be enhanced by adding one or more extractants to the solvent phase. The extractant interacts with component I increasing the capacity of the solvent for i.To recover the solute from the extract phase the extractant-solute complex has to be degraded.
.
Choice of solvent
Factors to be considered: Selectivity Distribution coefficient Insolubility of solvent Recoverability of solute from solvent Density difference between liquid phases Interfacial tension Chemical reactivity Cost Viscosity, vapour pressure Flammability, toxicity
.
Selectivity:
β = (mass fraction B in E)/(mass fraction A in E)
(mass fraction B in R)/(mass fraction A in R)
β > 1
Distribution coefficient:K = y/x
Large values are desirable since less solvent is required for a given degree of extraction
Physical properties: Low viscosity
Low vapour pressure
Non-flammable (high flash point)
Non-toxic
.
Recoverability of solvent and solute: No azeotrope formed between solvent and solute
Mixtures should have a high relative volatility
Solvent should have a small latent heat of vaporization
Density: A density difference is required between the two phases.
Interfacial tension:The larger the interfacial tension between the two phases the
more readily coalescence of emulsions will occur to give two distinct liquid phases but the more difficult will be the dispersion of one liquid in the other to give efficient solute extraction.
Chemical reactivity:Solvent should be stable and inert..
Types of flow in LLE
When both phases are flowing: Co-current contact
Cross flow
Counter-current flow
.
Stage 1 Stage 2
1 2
1 2
Major Types of Extraction Equipment
Column Column ContactorsContactors
Mixer SettlersMixer SettlersCentrifugalCentrifugal
Used primarily in the metals industry due to: - Large flows - Intense mixing - Long Residence time - Corrosive fluids - History
Used primarily in thepharmaceutical industry due to: - Large flows - Intense mixing - Long Residence time - Corrosive fluids - History
StaticStatic AgitatedAgitated
SpraySpray PackedPacked TrayTray PulsedPulsed RotaryRotary
ReciprocatingReciprocating
Rarely used Used in: - Refining - Petrochemicals
Example: - Random - Structured - SMVPTM
Used in: - Refining - Petrochemicals
Example: - Sieve
Used in: - Nuclear - Inorganics - Chemicals
Example: - Packed - Tray - Disc & Donut
Example: - RDC - Scheibel
Example: - Karr
Used in: - Chemicals - Petrochemicals - Refining - Pharmaceutical
Extraction equipment
Batch:
mixer-settler
column:
separatory funnel
rotating-disk contactera. agitator; b. stator disk
single-stage:
Continuous:
Types:Simple Extraction Single Stage
A – 99
B – 0
C – 1
100
Feed (F)
A – 0
B – 50
C – 0
50
Solvent (S)
A – 0
B – 50
C – 0.8
50.8
Extract (E)
A – 99.0
B – 0
C – 0.2
99.2
Raffinate (R)
( )( ) ( )( ) 4.07.929950MF
SE
7.92
990.250
0.8
RaffinateinSoluteConc.
ExtractinSoluteConc.M
0.21.0
0.2
FeedinSolute
RaffinateinSoluteU
===
===
===Fraction Unextracted
Distribution Coefficient
Extraction Factor
Cross Flow Extraction
ARR11 RR22 RR33 RR44
C C C C
F + S = M1 R1 + S = M2 R2 + S = M3 R3 + S = M4
A + B
F
B + C B + C B + C B + C
E1 E2 E3 E4
R1R2
R3
R4
E1E2
E3
E4
M1
M2M3M4
B
A C
F
Countercurrent Flow Extraction
ARR11 RR22 RR33 RR44
A + B
F
B + CC
E1
E2
E3
E4B + C B + C
B + C
F + S = ME1 + R4 = MF + S = E1 + R4
F – E1 = R4 – S = ∆
Equations
C
R1
R2
R3
R4
E1
B
A
F
∆
M E2
E3E4
S
Countercurrent Extraction
B + C
A
C
A + BFeed (F)
Solvent (S)
Extract (E):Solute Rich Stream
Raffinate (R):Solute Lean Stream
Primary Interface
Continuous Phase
Dispersed Phase
Dilute fractional extraction
A common situation:
the feed contains two important solutes (A, B), and we want to separate them from each other.
Choose two solvents:
A prefers solvent 1 (“extract”)
B prefers solvent 2 (“raffinate”)
Kd,A = yA/xA > 1
Kd,B = yB/xB < 1
1
N
FzA
zB
solvent 1yA,N+1 = 0yB,N+1 = 0
solvent 2xA,0 = 0xB,0 = 0
extractyA,1
yB,1
raffinatexA,N
xB,N
E R
E
R
abso
rbin
g se
ctio
nst
rippi
ng s
ectio
n
Center-cut extraction
When there are 3 solutes: A, B and C,
and B is desired
(A and C may be > 1 component each)
solvent 1
solvent 2solvent 1+ A
solvent 2+ B + C solvent 3
solvent 2solvent 3+ B
solvent 2+ C
FzA, zB, zC
Requires two columns:• column 1 separates A from B+C• column 2 separates B from C
Requires three extracting solvents:
A prefers solvent 1 over solvent 2B, C prefer solvent 2 over solvent
1B prefers solvent 3 over solvent 2C prefers solvent 2 over solvent 3
Typical Applications
• Remove products and pollutants from dilute aqueous streams
• Wash polar compounds or acids/bases from organic streams
• Heat sensitive products
• Non-volatile materials
• Azeotropic and close boiling mixtures
• Alternative to high cost distillations
Extraction is Used in a Wide Variety of Industries
Chemical •Washing of acids/bases, polar compounds from organics
Pharmaceuticals • Recovery of active materials from fermentation broths• Purification of vitamin products
Effluent Treatment • Recovery of phenol, DMF, DMAC• Recovery of acetic acid from dilute solutions
Polymer Processing • Recovery of caprolactam for nylon manufacture• Separation of catalyst from reaction products
Petroleum • Lube oil quality improvement• Separation of aromatics/aliphatics (BTX)
Petrochemicals • Separation of olefins/parafins• Separation of structural isomers
Food Industry • Decaffeination of coffee and tea• Separation of essential oils (flavors and fragrances)
Metals Industry • Copper production• Recovery of rare earth elements
Inorganic Chemicals • Purification of phosphoric acid
Nuclear Industry • Purification of uranium
Removal of Phenol from Wastewater
ppb Phenol
Extra
ction
Extra
ction
Raffin
ate R
affinate
Strip
pin
gS
tripp
ing
So
lvent
So
lvent
Reco
very
Reco
very
Wastewater Feed
0.1 – 8 % Phenol
Raffinate
RecycledSolvent
Extract
PhenolBiological TreatmentBiological Treatment
OrOr
Carbon AdsorptionCarbon Adsorption
< 1 ppm Phenol
Recovery of Acetic Acid from WaterUsing a Low Boiling Solvent
Aqueous Feed
20 - 40 % Acetic Acid
Typical Solvents: Ethyl Acetate Butyl Acetate
Extra
ction
Extra
ction
Raffin
ate R
affinate
Strip
pin
gS
tripp
ing
So
lvent
So
lvent
Reco
very
Reco
very
Raffinate
RecycledSolvent
Extract
Acetic AcidAqueous Raffinate
Recovery of Carboxylic Acids from WastewaterUsing a High Boiling Point Solvent
Extra
ction
Extra
ction
De
hyd
ration
De
hyd
ration
So
lvent
So
lvent
Reco
very
Reco
very
Water Feed
0.1 – 5 % Mixed Acids
Acetic Acid99%+ Purity
Recovered SolventRecovered Solvent
Clean UpClean Up
Acid
A
cid
Reco
very
Reco
very
Formic Acid99%+ PurityWater
Raffinate< 1,000 ppb Mixed Acids
Series Extraction
Extra
ctor #1
Extra
ctor #1
Extra
ctor #2
Extra
ctor #2
Feed
A + B
Extract
B + C
Solvent 1
C Solvent 2
D
ProductB + D
RaffinateA
Extractor 1 & 2 May Differ By: - Temperature - pH - Solvent
Recovery of Caprolactam
Feed From
ReactionSection
Lacta
m O
il Ext.
Lacta
m O
il Ext.
AQ Waste to AQ Waste to DischargeDischarge
Am
. Sulph
ate Ext.
Am
. Sulph
ate Ext.
Am. Sulph. Am. Sulph. Waste to Waste to DischargeDischarge
Re
-Extra
ction
Re
-Extra
ction
Lactam Oil to Lactam Oil to RecoveryRecovery
WaterLactam Oil Phase65 – 70% Caprolactam
Ammonium Sulphate Phase2 – 3% Caprolactam
Extract
RaffinateSolvent
Phosphoric Acid Purification via Extraction
Extra
ction
Extra
ction
Raffinate to Raffinate to DisposalDisposal
Scru
b E
xtractionS
crub
Extraction
Re
-Extra
ction
Re
-Extra
ction
Phosphoric Phosphoric Acid to Acid to RecoveryRecovery
Water
Solvent
Phosphate Phosphate Rock DigesterRock DigesterHCLHCL
Feed
Recycle
Scrub Solve.
Extraction of Flavors andAromas
Oil Essential Extract
Extra
ction
Extra
ction
So
lvent 1
S
olven
t 1
Distilla
tionD
istillation
Aqueous Alcohol
So
lvent 2
S
olven
t 2
Distilla
tionD
istillation
Essential Oil
Hydrocarbon
Typical Products: Orange Oil Lemon Oil Peppermint Oil Cinnamon Oil
Separation of StructuralIsomers
Typical Applications: m. p. - Cresol Xylenols 2 , 6 - Lutidine 3 , 4 - Picoline
So
lvent 1
S
olven
t 1
Distilla
tionD
istillation
So
lvent 2
S
olven
t 2
Distilla
tionD
istillation
Extra
ction
Extra
ction
Mixed
IsomerFeed
Isomer 1
Extra
ction
Extra
ction
Isomer 2
pH Adjust(Optional)
Reflux
Solvent 1 Recycle Solvent 2 Recycle
AqueousRaffinate
AqueousRecycle
pH Adjust(Optional)
Choice of separation process
Factors to be considered:
Feasibility
Product value
Cost
Product quality
selectivity
.
What is Coagulation?
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Coagulation is the destabilization of colloids by addition of chemicals that neutralize the negative charges
The chemicals are known as coagulants, usually higher valence cationic salts (Al3+, Fe3+ etc.)
Coagulation is essentially a chemical process
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- - - - - -
-
- - - - -
- -
- - - - - -
-
- - - - -
What is Flocculation?
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Flocculation is the agglomeration of destabilized particles into a large size particles known as flocs which can be effectively removed by sedimentation or flotation.
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FLOCCULATION Conti…Flocculation, in the field of chemistry, is a process wherein colloids come out of suspension in the form of floc or flake; either spontaneously or due to the addition of a clarifying agent. The action differs fromprecipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually dissolved in a solution. In the flocculated system, there is no formation of a cake, since all the flocs are in the suspension.Examples - milk, blood, seawater
Mechanisms 1-perikinetic: collisions from Brownian motion. Thermal activity or Brownian motion is responsible for colloid collisions in the case of perikinetic flocculation. Smoluchowski theory can be used to predict rate of reduction of particle (colloid) number with time. 2-orthokinetic: induced collisions through stirring.In this case there is an external mixing source which promotes particle-particle contact.
Flocculants should have the following properties They must react rapidly with the cells. They must be non-toxic. They should not alter the chemical
constituents of the cell. They should have a minimum cohesive power
in order to allow for effective subsequent water removal by filtration.
Neither high acidity nor high alkalinity should result from their addition.
They should be effective in small amounts and be low in cost.
They should preferably be washable for reuse.
Coagulation and flocculation aim
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04/08/15.t 50
Why flocculation? Various sizes of particles in raw water
Particle diameter (mm) Type Settling velocity
10 Pebble 0.73 m/s
1 Course sand 0.23 m/s
0.1 Fine sand 0.6 m/min
0.01 Silt 8.6 m/d
0.00010.0001 (10 micron)(10 micron) Large colloidsLarge colloids 0.3 m/y0.3 m/y
0.000001 (1 nano)0.000001 (1 nano) Small colloidsSmall colloids 3 m/million y3 m/million y
Particle diameter (mm) Type Settling velocity
10 Pebble 0.73 m/s
1 Course sand 0.23 m/s
0.1 Fine sand 0.6 m/min
0.01 Silt 8.6 m/d
0.00010.0001 (10 micron)(10 micron) Large colloidsLarge colloids 0.3 m/y0.3 m/y
0.000001 (1 nano)0.000001 (1 nano) Small colloidsSmall colloids 3 m/million y3 m/million y
Colloids – so small: gravity settling not possible
G r
a v
I t
y s
e t
t l I
n g
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Colloid Stability
------------
Repulsion
Colloid - A Colloid - B
Colloids have a net negative surface charge
Electrostatic force prevents them from agglomeration
Brownian motion keeps the colloids in suspension
H2O
Colloid
Impossible to remove colloids by gravity settling
Colloidal interaction
04/08/15water treatment 52
Charge reduction
04/08/15water treatment 53
Colloid Destabilization
Colloids can be destabilized by charge neutralization
Positively charges ions (Na+, Mg2+, Al3+, Fe3+ etc.) neutralize the colloidal negative charges and thus destabilize them.
With destabilization, colloids aggregate in size and start to settle
04/08/15water treatment 54
Floc formation with polymers
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Cross flow Flocculator (sectional view)
Plan (top view)
Tra
nsv
erse
pad
dle
L
H
W
Mechanical Flocculator
04/08/15.
57
Hydraulic Flocculation
• Horizontally baffled tank
Plan view (horizontal flow)
• Vertically baffled tank
LIsometric View (vertical flow)
L
W
H
The water flows horizontally. The baffle walls help to create turbulence and thus facilitate mixing
The water flows vertically. The baffle walls help to create turbulence and thus facilitate mixing
Applications:
Surface chemistry:
In colloid chemistry, flocculation refers to the process by which fine particulates are caused to clump together into a floc. The floc may then float to the top of the liquid (creaming),settle to the bottom of the liquid (sedimentation), or be readily filtered from the liquid.
Physical chemistry:
For emulsions, flocculation describes clustering of individual dispersed droplets together, whereby the individual droplets do not lose their identity.[5] Flocculation is thus the initial step leading to further aging of the emulsion (droplet coalescence and the ultimate separation of the phases).(1993) Flocculation is used in mineral dressing
Civil engineering/earth sciences:
In civil engineering, and in the earth sciences, flocculation is a condition in which clays, polymers or other small charged particles become attached and form a fragile structure, a floc.
.
Appli…
Water treatment:
Flocculation and sedimentation are widely employed in the purification of drinking water as well as sewage treatment, storm-water treatment and treatment of other industrial wastewater streams.
Biology:
In biology, flocculation refers to the asexual aggregation of microorganisms.
Cheese production:
Flocculation is widely employed to measure the progress of curd formation while in the initial stages of making many cheeses to determine how long the curds must set
.
Paul Ashall 2007