➢ Ternary System
➢ Most practical situations involving liquid-liquid equilibrium involve three or more components.
➢ Our attention is with three component systems. In this process, a solute is removed from a feed stream by contacting it with a solvent.
➢ The solute is quite soluble in the solvent, while the other component in the feed is less soluble.
Liquid-Liquid Equilibrium
➢ Terminology
➢ Solute ≡ Component (1)
➢ Original solvent ≡ Component (2)
➢ Extractive solvent ≡ Component (3)
➢ x1S, x2Sand x3S are the composition of the three components in (solvent rich phase) 1,2,3 respectively.
➢ x1R, x2R and x3R are the composition of the Three components in the (raffinate phase) 1,2,3 respectively.
Liquid-Liquid Equilibrium
Feed
(component +original solvent)
Extractive solvent
solvent-rich phase (x S1, x S1, x S1) Raffinate-rich phase
(x1R1, x2R1, x3R1)
➢ The solvent phase is rich in solvent and preferentially soaks up component 1 (the solute), which we are trying to separate from the other component in the feed (component 2, raffinate).
➢ The raffinate phase is the liquid phase which is rich in the component 2 (raffinate) and from which the solute (component 1) is being removed.
Liquid-Liquid Equilibrium
➢ The original feed is usually a mixture of solute (component 1) and raffinate (component 2).
➢ The solvent-rich phase contains mostly solvent (component 3) and solute (component 1) and only a small amount of raffinate (component 2)
➢ The raffinate-rich phase contains mostly solute (component 1) and raffinate (component 2), but also possibly some small amount of
Liquid-Liquid Equilibrium
➢ Triangular Diagrams
➢ Ternary systems are represented on two types of triangular diagrams:
1. Equilateral triangles
Liquid-Liquid Equilibrium
2. Right Triangles
Liquid-Liquid Equilibrium
Liquid-Liquid Equilibrium
(Solute)
Original solvent
Extractive solvent
.
Mixture [50% Acetic + 20 H2O + 30%vinyl acetate
b) Liquid-liquid Equilibrium tie lines (LLE Tie lines)
➢ Different chemical systems give different types of triangular diagrams.
Liquid-Liquid Equilibrium
➢ The phase boundary, called the solubility line, is the solid line. Within the two-phase region,
➢ liquid-liquid equilibrium lines (the dashed lines) connect compositions of the two phases that are in equilibrium with each other
➢ The left side of the phase boundary gives the compositions of the raffinate-rich liquid phase (xjR).
➢ The right side of the phase boundary gives the compositions of the solvent-rich liquid phase (xjS).
➢ The LLE tie-lines and the equilibrium phase boundary are normally found by laboratory experimentation.
➢ A mixture that has an overall composition inside the two-phase region will split into two liquid phases with compositions given at the two ends of the LLE tie-line.
Liquid-Liquid Equilibrium
➢ A conjugate line can be used to locate the tie-lines.
➢ From point A on-the left phase boundary, the other end of the tie-line is found by drawing a horizontal line to the conjugate line.
➢ A vertical line is then drawn from the point M intersection to the right phase boundary. The point of intersection of this line and the right phase boundary (point B in the figure) is the other end of the tie-line.
Liquid-Liquid Equilibrium
M
➢ As the system becomes richer in solute, the tie-lines get shorter and ultimately become just a point at the plait point P. Outside the two- phase region, a single, homogeneous liquid phase exists.
➢ Effect of Temperature on solubility
➢ Usually, the solubility increases as the temperature increases, for this reason, most liquid-liquid extraction systems operate at low temperatures and some times even require refrigeration.
➢ Pressure, on the other hand, has little effect on solubility.
Liquid-Liquid Equilibrium
Ekstraksi pada suhu yang rendah agar kurva dua komponen menjadi lebih luas
➢ if we specify only one concentration of one liquid phase, all the other concentrations can be immediately determined from the phase diagram
➢ For example, if we fix the concentration of component 1 in the raffinate-rich phase (x1R), we can read from the diagram:
1. The concentration of component 3 in the raffinate-rich phase (x3R), by using the left side of the solubility curve.
2. The concentrations of components 1 and 3 in the solvent-rich phase that is in equilibrium with the raffinate-rich phase, by going to the other end of the LLE tie-line. The concentrations x1S and x3S are read from the right side of the solubility curve.
Liquid-Liquid Equilibrium
Example: Thirty thousand kg/hr of a ternary mixture of 19 weight percent isopropyl alcohol (IPA), 41 weight percent toluene, and 40 weight percent water are fed into a, decanter operating at 25°C. the figure gives the LLE data for the system. Determine the compositions and flow rates of the two liquid streams leaving the decanter.
Liquid-Liquid Equilibrium
Raffinate
ekstrak
Liquid-Liquid Equilibrium
➢ The solvent-rich phase is 23 percent IPA and 74 percent water.
➢ The overall compositions of the feed (z1 = 19 percent and z2 = 40 percent) are located on the diagram.
➢ The compositions of the two liquid phases are read off the diagram at the two ends of the LLE tie-line.
➢ The raffinate-rich phase is 14 percent IPA and 2 percent water (the rest being toluene).
komposisi dicari
dihubungkan dengan tie line
Solving the last two equations simultaneously gives S = 15833 kg/h
R = 14176 kg/h
IPA in = (30000)(0.19) = 5700 kg/h IPA out = S(0.23) + R(0.14)
= (15833)(0.23) + (14176)(0.14) = 5625 kg/h Total mass: 30000 = S + R
Water = (30000)(0.4) = S(0.74) + R(0.02)
Liquid-Liquid Equilibrium
The difference is due to the accuracy of reading composition from the diagram
Neraca massa komponen dari air Neraca massa total
Liquid-Liquid Extraction
➢ In liquid-liquid extraction, a liquid of two or more components to be separated is contacted with a second liquid phase, called the solvent, which is immiscible or partially miscible with one or more components of the liquid feed.
➢ The simplest liquid-liquid extraction involves only a ternary system. The feed consists of two miscible components, the carrier (C) and the solute (A). Solvent (S) is a pure component. Components (C,S) are at most only partially soluble in each other. Solute (A) is soluble in (C) and completely or partially soluble in S.
➢ During the extraction process, mass transfer of (A) from the feed to the solvent occurs, with less transfer of (C) to the solvent, or (S) to the feed.
Liquid-Liquid Extraction
➢ Liquid-liquid extraction is used to separate components in situations where:
1. Relative volatilities are quite close to unity ( < 1.1), making distillation very costly. (Distillation requires tall towers due to the existence of many trays, and high energy consumption because of high reflux ratios.)
e.g. A mixture of benzene and cyclohexane. The normal boiling points of these organics are 80.1°C and 80.7°C, respectively, making their separation by distillation impractical
2. Thermally sensitive components will not permit high enough temperatures to produce a vapor-liquid system at reasonable pressures (pressures greater than 10-50 mm Hg).
Liquid-Liquid Extraction
➢ EQUIPMENT
➢ Different mechanical devices are used in liquid-liquid extraction such as:
1. The simplest is a mixer/settler, or decanter, in which the two liquid phases are separated.
2. Plate towers, packed towers, and mechanically agitated mixers (rotating disk contactors)
➢ the number of stages tends to be much smaller than in distillation columns. This is due to the larger settling times required for liquid-liquid separation because of the small density differences between the liquid phases.
➢ Liquid-liquid extraction columns are sometimes operated in a pulsed mode.
Liquid-Liquid Extraction
Extractor/stripper process.
Liquid-Liquid Extraction
1. Mixer/ Settler
Horizontal gravity-settling vessel.
Mixing vessel with variable-speed turbine agitator
Liquid-Liquid Extraction
2. Spray column
Liquid-Liquid Extraction
Extract
3. Packed column
Single-section cascade
Two-section cascade
Dual solvent with two-section cascade
Liquid-Liquid Extraction
Liquid-Liquid Extraction
Liquid-Liquid Extraction
➢ GRAPHICAL MIXING RULES
If we have two streams that contain three components and mix them together.
Let one of these streams be stream A with flow rate FA (kg/h) and composition x1A, x2Aand x3A (weight fractions of components 1,2, and 3), and let the other be stream FB with corresponding composition x1B, x2B and x3B . The mixed stream leaving the mixer will have a flow rate FM and composition x1M, x2Mand x3M . A flow diagram is as follows:
FA
x1A, x2A , x3A
FB x1B, x2B , x3B
FM
x1M, x2M , x3M
Liquid-Liquid Extraction
➢ To determine the location of the mixture composition on a graph, since there are three components, only two coordinates are needed to completely specify the composition of any stream. We can use either right or equilateral triangular plots.
➢ If we use right-triangular plot. locate point A with coordinates (x1A, x2A) and point B with coordinates (x1B, x2B). The point M with coordinates (x1M, x2M) representing the mixture will lie some place on the graph.
Liquid-Liquid Extraction
➢ After mixing point M is supposed to lie on a straight line joining the A and B points. If we can show that the angles and in the figure are equal, then M must lie on a straight line between A and B.
➢ The total mass balance for the system is
➢ Component balances for components 1 and 2 are
and
(1)
(2)
(3)
Liquid-Liquid Extraction
➢ Rearranging these two equations, we obtain:
➢ Solving for the ratio FAIFB, we have:
or
Liquid-Liquid Extraction
➢ These two ratios are the tangents of the angles and , hence, tan
= tan . Therefore, = , and we have proven that the line AMB is a straight line.
➢ The coordinates of the point M can be solved for analytically by using equations (1), (2), and (3). Alternatively, M can be located graphically where the distance from the point A to the point M divided by the distance from the point M to the point B is equal to the ratio FB/FA.
