chapter 2 - lle edited
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CHAPTER 2: LIQUID LIQUID EXTRACTION
CHAPTER / CONTENTDefinition & ApplicationLLE for Partially Miscible SolventLLE for Immiscible SolventLiquid liquid extraction equipment
LLE= Separation of constituents (solutes) of a liquid solution by contact with another insoluble liquid.
Solutes are separated based on their different solubilities in different liquid.
LLE= Separation process of the components of a liquid mixture by treatment with a solvent in which one or more desired components is soluble.
There are two requirements for liquid liquid extraction to be feasible:
component (s) to be removed from the feed must preferentially distribute in the solvent.
the feed and solvent phases must be substantially immiscibleDefinition & Application
The simplest LLE involves only a ternary (i.e 3 component system)
Important terms you need to know:
Feed-The solution which is to be extracted (denoted by component A)
Solvent-The liquid with which the feed is contacted(denoted by component C)
Diluent-Carrier liquid (denoted by component B) Extract-The solvent rich product of the operation Raffinate-The residual liquid from which solutes has been removed.Definition & Application
In some operations, the solutes are the desired product, hence the extract stream is the desirable stream. In other applications, the solutes my be contaminants that need to be removed, and in this instance the raffinate is the desirable product stream.
Extraction processes are well suited to the petroleum industry because of the need to separate heat sensitive liquid feeds according to chemical type (e.g aromatic, naphthenic) rather than by molecular weight or vapor pressure.
Major applications exist in the biochemical or pharmaceutical industry, where emphasis is on the separation of antibiotics and protein recovery.
In the inorganic chemical industry, they are used to recover high boiling components such as phosphoric acid, boric acid and sodium hydroxide from aqueous solution.Definition & Application
Extraction of nitrobenzene after reaction of HNO3 with toluene in H2SO4
Extraction of methylacrylate from organic solution with perchlorethylene
Extraction of benzylalcohol from a salt solution with toluene.
Removing of H2S from LPG with MDEA
Extraction of caprolactam from ammonium sulfate solution with benzene
Extraction of acrylic acid from wastewater with butanol
Removing residual alkalis from dichlorohydrazobenzene with waterDefinition & Application
Extraction of methanol from LPG with water
Extraction of chloroacetic acid from methylchloroacetate with water.Definition & Application The difference between LLE and distillation process in the separation of liquid mixtures:
LLE depends on solubilities between the liquid components and produces new solution which in turn has to be separated again, whereas;
Distillation depends on the differences in relative volatilities / vapor pressures of substances. Furthermore, it requires heat addition.
Definition & Application Advantages of LLE over distillation process:
Where distillation requires excessive amount of heat
Presence of azeotropes or low relative volatilities are involved ( value near unity and distillation cannot be used)
Removal of a component present in small concentrations, e.g hormones in animal oil.
Recovery of a high boiling point component present in small quantities in waste stream, e.g acetic acid from cellulose acetate.
Recovery of heat sensitive materials (e.g food) where low to moderate processing temperatures are needed. Thermal decomposition might occur.
Solvent recovery is easy and energy savings can be realized.
SINGLE STAGE CALCULATIONSMULTISTAGE COUNTER CURRENT SYSTEMLLE for Partially Miscible Solvent
Solvent and the solution are in contact with each other only once and thus the raffinate and extract are in equilibrium only once.
The solution normally binary solution containing solute (A) dissolved in a diluent or carrier (B). The extracting solvent can be either pure solvent C or may content little A. Raffinate (R) is the exiting phase rich in carrier (B) while extract is exiting phase rich in solvent (C).
When liquid solution mixed with solvent (C), an intermediate phase M momentarily forms as the light liquid moves through the heavy liquid in the form of bubbles. These bubbles provide a large surface area for contact between the solution and the solvent that speed up mass transfer process.
The raffinate and extract are in equilibrium with each other. Single stage calculations
Single stage calculationsLiquid-Liquid Extractiony* (A)ys (A)Intermediate, MRaffinate phase, Rx* (A) Extract phase, ExM (A)FMass of feed solutionSMass of extracting solventEMass of extract phaseRMass of raffinate phaseMMass of intermediatexFMass fraction of A in FySMass fraction of A in SxMMass fraction of A in Mx*Equilibrium mass fractiony*Equilibrium mass fraction of A in Eof A in R
Note: Intermediate shown just for purpose of demonstration. Dont have to draw it when answering the questionFeed Solution, FxF (A) Extracting Solvent, S
In most single extraction, we are interested to determine the equilibrium composition and masses of raffinate and extract phases by using ternary phase diagram and simple material balances.
Using material balance, Single stage calculations Calculate the mass of intermediate M using total material balance: Eq. (1) Determine mass fraction of solute A in intermediate M using material balance for solute A : Eq. (2) Use both Eq. 1 and 2 to find xM value
On a right angle triangular diagram or equilateral triangular diagram for A-B-C system:Single stage calculations Locate point F (xF) and S (yS)
Draw a straight line from F to S
Using the calculated value of xM, locate point M (xM) on the FS line. Note that point M must be on FS line.
Draw a new tie line that pass through point M. This new tie line must take shape of the nearest given tie lines.
From the new tie line, you can locate point E and R and hence you can determine the composition of raffinate, R and extract, E that are in equilibrium.
Once you have determine composition of R and E, you can determine the masses of E and R using the material balance as follows:Single stage calculations Using the total material balance:Eq. (3) Using the material balance for solute A:Eq. (4) Solve those Eq 3 and 4 to determine the masses of E and R
Example 1Single stage calculations100 kg of a solution containing 0.4 mass fraction of ethylene glycol (EG) in water is to be extracted with equal mass of furfural 250C and 101 kPa. Using the ternary phase equilibrium diagram method, determine the followings: the composition of raffinate and extract phases
the mass of extract and raffinate
the percent glycol extracted Use the following equilibrium tie line to construct the ternary phase diagram
Furfural rich layerWater rich layer% EG% water% furfural% EG% water% furfural0.05.095.00.092.08.08.54.587.02.089.68.414.54.581.05.586.08.521.06.073.07.084.48.629.07.064.08.083.38.742.08.549.514.077.28.850.014.036.031.060.09.051.033.016.051.033.016.0
Solution 1Single stage calculations Calculate the mass of intermediate M using total material balance F = 100 kgS = 100 kgxF=0.4yS=0kg Determine mass fraction of solute A in intermediate M using material balance for solute A: Locate point F & S, draw line FS. Locate point xM on FS line. Draw new tie line that pass through point xM. From that tie line, locate point E and R hence you can determine the composition of R (x*) and E (y*) which is in equilibrium. From the graph, y* = 0.26, x* = 0.075 (Solution for point 1)
Single stage calculations Right angle methodFSMER
Single stage calculations Equilateral methodSMERF
Solution 1 (cont)Single stage calculations Using the total material balance Using the material balance for solute A: Eq. (i)Insert eq (i) into eq above Solution for point 2% of EG extracted = (Mass of EG in extract / Mass of EG in feed) x 100%% of EG extracted =Solution for point 3
Tutorial1. 12.5-2 (Textbook-page 832)A single stage extraction is performed in which 400kg of a solution containing 35 wt% acetic acid in water is contacted with 400 kg of pure isopropyl ether. By using equilateral diagram, determine the composition of raffinate and extract phases the mass of extract and raffinate the percent acetic acid extracted
Tutorial2. 12.5-4 (Textbook-page 832)A mixture weighing 1000kg contains 23.5 wt% acetone and 75.5 wt% water and is to be extracted by 500 kg methyl isobutyl ketone in a single stage extraction. By using equilateral diagram, determine the composition of raffinate and extract phases the mass of extract and raffinate the percent acetone extracted
Solvent and solution which flow opposite (countercurrent) to each other, come into contact more than once and mix on stages inside the reactor.
Normally numbering of the stages begin at the top down to the bottom. Thus the top most stage is named as stage 1, stage directly below stage 1 is stage 2 and so on. Multi stage counter current system
The analysis of multistage extraction can be performed using right angle or equilateral triangular diagram to determine the number of ideal stages req