Presented ByPresented By

Abhijit Das ID# 2007-1-70-052Abhijit Das ID# 2007-1-70-052

Md. Ruhul Amin ID# 2007-1-70-033Md. Ruhul Amin ID# 2007-1-70-033

Abu Rizve Al Hosaine ID# 2007-3-70-036Abu Rizve Al Hosaine ID# 2007-3-70-036

Mahmudul Alam ID# 2007-3-70-040Mahmudul Alam ID# 2007-3-70-040

Definition:Definition: Liquid-liquid extraction is an Liquid-liquid extraction is an

separation technique where an aqueous separation technique where an aqueous solution is usually brought into contact with solution is usually brought into contact with another organic solvent which are another organic solvent which are immiscible and transfer of one or more immiscible and transfer of one or more solutes into the solution. solutes into the solution.

Liquid-liquid extraction principlesLiquid-liquid extraction principles

This technique contains two phase:This technique contains two phase: 1. Feed phase (solution)1. Feed phase (solution)

2. Solvent phase (second phase)2. Solvent phase (second phase)Feed phase contains components which is to be Feed phase contains components which is to be extracted. Solvent phase is immiscible with feed phase extracted. Solvent phase is immiscible with feed phase but some of component is transferred from feed phase to but some of component is transferred from feed phase to the solvent phase.the solvent phase.After extraction the feed phase is called the raffinate (R) After extraction the feed phase is called the raffinate (R) and solvent phase is called the extract (E) . and solvent phase is called the extract (E) .

Theory:Theory:

According to partition law at constant temperature, a According to partition law at constant temperature, a solute distributes itself between two immiscible solute distributes itself between two immiscible solvents only in a particular ratio.solvents only in a particular ratio.

KKp p = C= Coo/ C/ Caqaq

Where,Where,KKp p is the partition coefficient is the partition coefficientCCo o is the concentration of the analyte in the organic is the concentration of the analyte in the organic

phase (Solvent)phase (Solvent)CCaq aq is concentration of the analyte in the aqerous phase is concentration of the analyte in the aqerous phase

(Feed)(Feed)

In liquid-liquid extraction two aspects are very In liquid-liquid extraction two aspects are very important:important:

a)a) Error due to the volume changeError due to the volume change the volumes of the two individual phases after the volumes of the two individual phases after

attainment of equilibrium may be appreciably attainment of equilibrium may be appreciably different in comparison to the initial volumes of different in comparison to the initial volumes of the solvents used.the solvents used.

b) Based on the appropriate partition coefficient of b) Based on the appropriate partition coefficient of an immiscible solvent pair it is possible to an immiscible solvent pair it is possible to calculate the ‘effectiveness of an extraction’calculate the ‘effectiveness of an extraction’

ffnn = ( K= ( Kp p VV11/ V/ V2 2 + 1)~+ 1)~nn

From the above equation it is quite evident that From the above equation it is quite evident that the fraction extracted is absolutely independent the fraction extracted is absolutely independent of the initial solute concentration.of the initial solute concentration.

Solvent selection criteriaSolvent selection criteriaMiscibility:Miscibility: Miscible solvents mixed together in all proportion Miscible solvents mixed together in all proportion

without forming two separate phase.without forming two separate phase. For instance, solvents that miscible with water For instance, solvents that miscible with water

include acetone, 1,4- dioxane, pyridine etc.include acetone, 1,4- dioxane, pyridine etc.

Density:Density: Mass per unit volume is known as density. Solvents Mass per unit volume is known as density. Solvents

that are more dense than water will form the lower that are more dense than water will form the lower layer of pair when mixed together, while solvents layer of pair when mixed together, while solvents that are less dense than water will form the upper that are less dense than water will form the upper layer on water.layer on water.

For instance, the density of chloroform is 1.4892 For instance, the density of chloroform is 1.4892 g/ml at 20*C. So, water would form the top layer in a g/ml at 20*C. So, water would form the top layer in a water-chloroform solvent pair.water-chloroform solvent pair.

Solubility: Solubility:

Immiscible solvents are often soluble in each Immiscible solvents are often soluble in each other and become mutually saturated when other and become mutually saturated when mixed with each other.mixed with each other.

For instance, 1.6% of the dichloromethane For instance, 1.6% of the dichloromethane (solvent) is soluble in water. In contrast, water is (solvent) is soluble in water. In contrast, water is 0.24% soluble in dichloromethane. 0.24% soluble in dichloromethane.

Factors influence solvent extraction:Factors influence solvent extraction:Effect of temperatureEffect of temperature The effect of temperature on the partition coefficient can be The effect of temperature on the partition coefficient can be

estimated from its effect on the solubilities of the solvents. estimated from its effect on the solubilities of the solvents.

Effect ofEffect of PPHH on extractionon extraction The neutral and ionic forms may not have the same The neutral and ionic forms may not have the same

identical partition coefficients in a second solvent; identical partition coefficients in a second solvent; therefore, the quantity of a substance being extracted therefore, the quantity of a substance being extracted solely depends upon the position of the acid-base solely depends upon the position of the acid-base equilibrium and ultimately upon the equilibrium and ultimately upon the PPHH of the solution.of the solution.

EmulsionEmulsion Emulsion may be defined as a dispersed system Emulsion may be defined as a dispersed system

containing more than one immiscible liquid phase. containing more than one immiscible liquid phase. Emulsion formation makes the separation of the Emulsion formation makes the separation of the two phases difficult.two phases difficult.

Factor causes slow-coalescence emulsionFactor causes slow-coalescence emulsiona)a) Finely divided powders of albumin, gelatin and Finely divided powders of albumin, gelatin and

natural gums have a tendency to coat the droplets natural gums have a tendency to coat the droplets formed in an emulsion which ultimately prevent formed in an emulsion which ultimately prevent them from coalescing.them from coalescing.

b)b) Surfactants decrease the interfacial tension Surfactants decrease the interfacial tension between the two immiscible liquids.between the two immiscible liquids.

c)c) Ionic species get absorbed at the interface of two Ionic species get absorbed at the interface of two immiscible layers resulting in the formation of a immiscible layers resulting in the formation of a net charge on the droplets. net charge on the droplets.

Prevention of emulsion formation:Prevention of emulsion formation:1)1) Employing a sufficiently large liquid-liquid interface Employing a sufficiently large liquid-liquid interface

provides a good extraction.provides a good extraction.2)2) Removal of insoluble materials before carrying out Removal of insoluble materials before carrying out

the extraction process.the extraction process.3)3) Using solvent pairs that have a large density Using solvent pairs that have a large density

difference. difference. 4)4) Avoid high pH ranges (basic) at the time of Avoid high pH ranges (basic) at the time of

extraction from water to avoid emulsification.extraction from water to avoid emulsification.5)5) Using adsorbent such as alumina, silica gel etc to Using adsorbent such as alumina, silica gel etc to

avoid anion exchangers. avoid anion exchangers.

Process of breaking of an emulsion Process of breaking of an emulsion (Coalescence)(Coalescence)

a)a) Mechanical meansMechanical meansb)b) CentrifugationCentrifugationc)c) Addition of monovalent Addition of monovalent d)d) Ethanol or higher alcoholEthanol or higher alcohole)e) Silicone deforming agentSilicone deforming agentf)f) Sudden cooling of emulsionSudden cooling of emulsiong)g) Altering the ratio of solventsAltering the ratio of solventsh)h) Thin-bed of an adsorbentThin-bed of an adsorbent

AdvantagesAdvantages

1. Ease to perform.1. Ease to perform.2. Not much time consuming.2. Not much time consuming.3. Decreased volumes of solvent.3. Decreased volumes of solvent.4. Superior ability to concentrate the 4. Superior ability to concentrate the analytes.analytes.

DisadvantageDisadvantage

Those substance which are not soluable in Those substance which are not soluable in solvent are not applicable in liquid-liquid solvent are not applicable in liquid-liquid extration processextration process