SALT EFFECT ON VAPOUR-LIQUID EQUILIBRIUM FOR THE BINARY SYSTEM METHANOL+ETHYL ACETATE

SALT EFFECT ON VAPOUR-LIQUID EQUILIBRIUM FOR THE BINARY SYSTEM METHANOL+ETHYL ACETATE
A
Project Report on
SALT EFFECT ON VAPOUR-LIQUID EQUILIBRIUM
FOR THE BINARY SYSTEM
METHANOL+ETHYL ACETATE
In partial fulfillment of the requirements of
Bachelor of Technology (Chemical Engineering)
Submitted By
VAIBHAV KUMAR MEHRA (ROLL NO-10600034)
Session: 2009-10
Under the Guidance of
Dr. Pradip Rath
Department of Chemical Engineering
National Institute of Technology
Rourkela-769008
Orissa
National Institute of Technology
Rourkela
CERTIFICATE
This is to certify that that the work in this thesis report entitled “salt effect on Vapourliquid equilibrium for the binary system methanol +ethyl acetate” submitted by Vaibhav
Kumar Mehra in partial fulfillment of the requirements for the degree of Bachelor of
Technology in Chemical Engineering, National Institute of Technology Rourkela, Orissa,
an authentic work carried out by them under my supervision and guidance.
To the best of my knowledge the matter embodied in the thesis has not been
submitted to any other University /Institute for the award of any degree.
Date:
Prof. (Dr) Pradip Rath
Department of Chemical Engineering
National Institute of Technology,
Rourkela – 769008
i
ACKNOWLEDGEMENT
It is with a feeling of great pleasure that I express my sincere gratitude to Prof. Pradip
Rath for suggesting us the topic and his ready and able guidance, through out the course
of the project. I thank Prof. R.K SINGH and Prof. H.M Jena for acting as project coordinators.
I am thankful to the Department of Chemical Engineering for providing me
necessary instrument. I also thank the other staff members of my department for their
invaluable help and guidance.
Vaibhav Kumar Mehra
(Roll No. 10600034)
B. Tech Final Year
Chemical Engineering
ii
ABSTRACT
In the recent time many scientists and technologists have drawn their attention towards
the substitution of a solvent with a non-volatile solid salt in azeotropic distillation which
alters the relative volatility. But so far, experimentally, little advancement have been
made in this field. The salt effect on vapour-liquid equilibrium of the system:
Methanol(1) + Ethyl Acetate(2), for constant liquid composition and under the varied
concentrations of the two salts-Lithium Chloride(LiCl) and Lithium Bromide(LiBr) have
been reported in this present work.
To prefigure a suitable correlation, the salt effect data obtained experimentally is
analyzed. A primary estimation of salt effect on the vapour-liquid equilibrium of the
binary system has been presented. Salting-in and Salting-out phenomena are also
presented. Under the section of previous investigations and literature review, the history
and the development of the work done in this area has been reported along with the
vapour pressure measurements and VLE data for the boiling systems.
A modified othmer still, a bulb condenser, a magnetic stirrer-cum heater and a
glass thermometer forms the experimental setup and refractive index method has been
used for vapour composition analysis, with the help of a digital refractometer with the
prism temperature, maintained constant at 20°C i.e. nDt. Activity coefficient has been
calculated using the experimental data which is further used in determining theoretical
VLE data that can be further correlated with the experimental one to find thermodynamic
consistency.
The effect of two inorganic salts-lithium chloride and lithium bromide on the
vapor-liquid equilibria (VLE) has been investigated under the atmospheric conditions of
98.6 ± 0.03 kpa pressure. In the present study it has been found that the system forms a
minimum boiling azeotrope at 0.732 mole fraction of methanol at 62.6°C. The azeotrope
shifts from 0.732 to 0.629, 0,586, 0.472 and 0.471 by addition of 5%, 10%, 15% and 20%
of lithium chloride by weight of methanol respectively and to 0.774, 0,706, 0.682, 0.670
by the addition of 5%, 10%, 15% and 20% lithium bromide by weight of methanol
respectively. So this was concluded that by using both the salts at different concentrations
e.g. 5%, 10%, 15% and 20% by weight, there was a change in relative volatility in the
system and the salts were unable to eliminate the azeotrope of the system.
iii
CONTENTS
TITLE
PAGE-NO
Abstract
iii
List of figures
vi
List of Tables
viii
Nomenclature
X
Chapter 1
INTRODUCTION
1
1.1 Introduction
2-3
1.2 Applications
3-4
1.3 Effect of dissolved salt in boiling solution
5
1.4 Theories of Salt Effect
5
1.4.1 Electrostatic Effects
5
1.4.2 Van der Waals Forces
6
1.4.3 Solubility of Salts in Non-electrolyte
6
1.4.4 Hydration Theory
6-7
1.4.5 Internal Pressure
Chapter 2
LITERATURE REVIEW AND
PREVIOUS INVESTIGATIONS
7
8
2.1 Effect of Salt on Vapour-Liquid
Equilibrium
9-10
2.2 Theories and Literature Survey
10
2.3 Previous Investigations
10
2.4 List of some previous investigation
on salt effect on VLE
iv
11-15
Chapter 3
Chapter 4
Chapter 5
DETERMINATION OF VLE DATA
16
3.1 Experimental Determination of
Vapour-liquid equilibrium
17
3.1.1 Distillation Method
17
3.1.2 Circulation method
17
3.2 Othmers Still and its Modification
18
3.3 Procedure for Determination
of VLE Data
19
3.4 Method Analysis
21
TREATMENT OF VLE DATA
25
4.1 Computation of Vapour-Liquid
Equilibrium
26
4.2 Model-Dependent method
for Data Reduction
26
4.3 Models for excess Gibbs Energy
26
4.4 Local Composition Modes
28
4.5 Sample Calculation
31
4.6 Results and Discussion
32
CONCLUSION
62
REFERENCES
v
LIST OF FIGURES
Fig No.
Contents
Page-No.
1
Schematic diagram for circulating stills
17
2
Experimental Set-Up
22
3
VLE Apparatus (Still)
23
4
Refractometer
24
5
Plot of Refractive Index vs Mole Fraction
47
6
Vapour-Liquid Equilibrium Plot (0 % salt)
48
7
Vapour-Liquid Equilibrium Plot (Lithium Chloride)
49
8
Vapour-Liquid Equilibrium Plot (Lithium Bromide)
50
9
Y1 (experimental) vs Y1(theoretical) plot for LiCl
51
10
Y1(experimental) vs Y1(theoretical) plot for LiBr
52
11
T-X-Y PLOT (NO SALT)
53
12
T-X-Y PLOT (5% LITHIUM CHLORIDE)
54
13
T-X-Y PLOT (10% LITHIUM CHLORIDE)
55
14
T-X-Y PLOT (15% LITHIUM CHLORIDE)
56
vi
15
T-X-Y PLOT (20% LITHIUM CHLORIDE)
57
16
T-X-Y PLOT (5% LITHIUM BROMIDE)
58
17
T-X-Y PLOT (10% LITHIUM BROMIDE)
59
18
T-X-Y PLOT (15% LITHIUM BROMIDE)
60
19
T-X-Y PLOT (20% LITHIUM BROMIDE)
61
vii
LIST OF TABLES
Table No.
1
Contents
Data of the amount of Methanol and
Page No
20
Ethyl acetate added in ml
2
Data of the amount of salt added in gms
20
3
Physical properties of solvents used
21
4
Refractive Index Data (Lithium Chloride)
34
5
Refractive Index Data (Lithium Bromide)
35
6
Vapour-Liquid Equilibrium Data (Lithium Chloride)
36
7
Vapour-Liquid Equilibrium Data (Lithium Bromide)
37
8
Calculation of activity coefficient (No salt)
38
9
Calculation of theoretical activity coefficient
39
10
Activity Coefficient (Lithium Chloride)
40
11
Activity Coefficient (Lithium Bromide)
41
12
Calculated and Theoretical Vapour Composition
42
(Lithium Chloride)
viii
13
Calculated and Theoretical Vapour Composition
43
(Lithium Bromide)
14
Error Calculation (Lithium Chloride)
44
15
Error Calculation (Lithium Bromide)
45
ix
NOMENCLATURE
E
G = Excess Gibbs Energy
γi = Activity Coefficient for Component i
xi = Mole Fraction of Component i in liquid phase
yi = Mole Fraction of Component i in vapour Phase
Aij = Constants in Margules Equation
A'ij = Constants in Van Laar Equation
Λij = Constants in Wilson Equation
Τij = Constants in NRTL Equation
yi* = Theoretical vapour phase mole fraction of component i
xi* = Theoretical liquid phase mole fraction of component i
R = Ideal Gas Constant
T = Temperature (K)
Pisat = Saturated vapour pressure of component i
PT = Atmospheric Pressure (98.6 ± 0.03 kpa in Rourkela)
A, B, C = Antoine’s Equation Coefficients
i, j, k = Component Identification
ux = Refractive index
x
CHAPTER 1
INTRODUCTION
1
1.1 Introduction
Vapour-liquid equilibrium (VLE), is a condition where a liquid and its vapour (gas
phase) are in equilibrium with each other or more precisely a state where the rate of
evaporation equals the rate of condensation on a molecular level such that there is no
overall vapor-liquid inter-conversion.
Whenever a mixture of liquids is boiled, the composition of the vapor phase is
usually different from that in the liquid phase. For some mixtures there is a unique point
or rather composition where the liquid and vapor phases are identical, these kinds of
mixtures are known as the azeotropes. The azeotrope may have a boiling point higher
than the boiling point of the two pure liquids from which it is formed and are known as
maximum boiling point azeotrope or lower than the boiling point of the two pure liquids
from which it is formed and therefore referred as minimum boiling point azeotrope. In a
maximum boiling point azeotrope the intermolecular forces between different molecules
are stronger than the forces between either of the pure forces, whereas in a minimum
boiling point azeotrope the intermolecular forces between different molecules are weaker
than the forces between either of the pure forces. [24]
In many branches of science, the phase equilibrium thermodynamics is of
fundamental importance. In chemical engineering almost all the manufacturing processes
involve mass and energy transfer between phases. Processes such as: gas – liquid
absorption, adsorption, leaching, refrigeration, distillation, liquid – liquid extraction etc.
are some of important areas where mass transfer and heat transfer between phases are
taken very effectively into account to get desired result.
The separation of azeotropic systems (which have low relative volatility) is either
difficult or uneconomical, by using conventional methods like fractional distillation .To
overcome such difficulties in industries a third component is added in order to alter the
system properties. If the third component is liquid then in that case the molecules of the
liquid component forms an association or complex with the molecule of the less volatile
component of the feed as compared to that of the more thereby increasing the relative
volatility of the more volatile component and thus the azeotrope can be eliminated. This
process however requires an additional column to recover the separating agent from the
product stream. [20]
2
Due to this difficulty the solids salts are considered better than the liquid
separating agents as they produce a solvent-free extract and requires no other separating
column. The salt dissolved in a mixed solvent may affect the boiling point, the mutual
solubilities of the two liquid components, and the equilibrium vapour phase composition.
Generally, the ions of the dissolved salt tend to attract, the molecules of the more polar
component by the electrostatic field of the ions and thereby enriching the vapour
composition of the less polar solvent, in which the salt is less soluble.
If the dissolved salt associates, preferentially, with the molecules of one
component of the solvent compared with those of the other, then in that case one
component is "salted out" in respect to the other. In such a case, the activities and the
solubility relationship between the two volatile components of the liquid solution are
altered relative to each other in a manner which results in a change of composition of the
equilibrium vapour phase, even if no salt is present in the vapour phase.
Various predictive and correlative models were proposed to calculate the vapourliquid equilibrium of the mixed solvent-salt systems. The experimental data are correlated
using four models based on the local composition concept:
1-The electrolytic NRTL model of Mock et al. (1986)
2-The modified UNIQUAC model of Sander et al. (1986)
3-Modified Wilson and modified NRTL models of Tan (1985), Tan (1987) and Tan
(1990).
The results of correlation were compared with those obtained through data prediction
using the modified Wilson and the modified NRTL predictive models of Tan. The new
set of ion-solvent and salt-solvent interaction parameters obtained from the data
correlation with the extended UNIQUAC model of Sander et al. (1986) and salt-solvent
interaction parameters obtained from the data correlation with the electrolyte NRTL
model of Mock et al. (1986), would be a contribution to the database.[12,19]
1.2 Applications
Distillation in industries is mainly based on the fact that the composition of
vapour should be different from that of the liquid and side by side must have high relative
volatility with which it is in equilibrium. As discussed above, the effective and
3
economical separation of components for the system showing azeotrope formation is
done by extractive distillation and/or azeotropic distillation using salt as a third
component. Salt is neither vaporized nor condensed anywhere in the distillation process
and therefore has low energy requirements. This type of process using salt in extractive
distillation was first applied in

HIAG (Halz industries Acetin Geselleschoft) process; it was licensed by
DEGEUSSA and based on patents registered by Adolph Gorhan. [21]. HIAG
process used extractive distillation where 70/30 mixtures of the potassium and
sodium Acetate were used as separating agent. It produced around 99.8%
Ethanol, completely free from the separating agent and obtained directly from the
top of the column. This process had a lower capital investment and energy cost
than azeotropic distillation benzene is used as an agent.

Azeotropic distillation involving benzene was also the conventional process for
Isopropanol-water separation. The IHI (Ishika Wajima-Harima heavy Industries)
company in japan [13,15] was implementing a process for production of alcohol
from its aqueous solution the salt calcium chloride to break the azoetrope, by this
process the company is having a production capacity of 7300 tones per year
which further reducing the capital cost to 56% and an energy requirement to 45%
of that of the conventional benzene process.

The only large scale production by use of salt effect on extractive distillation in
North America was production of nitric acid from aqueous using magnesium
nitrate as separating agent.

In 1926 Othmer [4] developed a large-scale industrial process for Eastern Kodak,
which separated methanol from its aqueous azeotrope by extractive distillation
using strong calcium chloride, brine as separating agent. Rather than patenting
the process, Eastern decided instead, to have it remain as trade secret. He also
experimented with the use of salt as separating agent for the concentration of
acetic acid from its aqueous solution.
4
1.3 Effect of dissolved salt in boiling solution
A salt dissolved in a boiling solution of a binary system; there are several expected
effects which may occur. They are as follows

There is crossover in salt effect between salting- out and salting-in, as liquid
composition is increased, even though the salt is clearly more soluble in one of
the components of the binary system.

There is an enrichment of vapor composition through out, in the component in
which salt is less soluble than that of other.

There is a relatively large effect on vapor composition caused by a salt having
little difference in solubility between the components.
The overall effect is the net change in the relative volatility or shifting of the azeotropic
point or the elimination of the azeotrope, if the selection of the salt is proper [22].
1.4 Theories of Salt Effect
1.4.1 Electrostatic Effects - Debye and McAuley [1] were the first to treat salting out as
an electrostatic phenomenon. They considered the ion as a perfect sphere, they defined a
Helmholtz work function, ΔA, is equal to the difference in the work of charging and
discharging the ion in the media of dielectric constants say, D and D0, respectively, and
the work done against the potential due to the ionic atmosphere. They expressed the
activity coefficient of the non-electrolyte as a function of the ratio of charge to ionic
radius, the ion concentration, and the decrement in the dielectric constant of the aqueous
solution due to non-electrolyte. The equation of Debye and McAuley is based upon the
assumptions that the dielectric constant of the solution can be expressed as a linear
function of salt concentration and non-electrolyte concentration; salting out is due only to
alterations in the dielectric constant of the solution; and the solution is dilute in both nonelectrolyte and salt. Estimation of the ionic radius in solution is very difficult, especially
at moderate to high ion concentrations. The electrostatic theory gives fairly good results
for many dilute systems. However, it always predicts salting out and cannot account for
salting in [10].
5
1.4.2 Van der Waals Forces- Electrostatic attractions between ions and a neutral
molecule are to large extent short-range forces. Other short-range forces, such as
dispersion forces, may also be of considerable importance. Long and McDevit [6]
proposed the semi empirical equation
ln γ΄= A Σ (Zj)²Cj - BΣ aj Cj
………………………….(1.1)
Where,
A and B = empirical constants dependent upon both non-electrolyte and
electrolyte
aj = polarizability of ion j
Cj = molar concentration of ion of type j
Zj = valence of ion of type j
The first term in Equation 1 accounts for changes in the activity coefficient due to
electrostatic interactions; the second term reflects the effect of dispersion forces [10].
1.4.3 Solubility of Salts in Non-electrolyte- If a salt is more soluble in the nonelectrolyte than in water, salting in will occur. Glasstone [2] noted an increase in the
solubility of ethyl acetate in water when lithium and ammonium iodides were added.
These iodides are more soluble in ethyl acetate than in water. The salting in may be due
to a preferential association of ions and non-electrolyte or of undissociated salt and nonelectrolyte, A general analysis of the salt effect indicates that salting out decreases with
rising dipole moment, that hydration effects are scalar for non-polar, but vector for polar
non-electrolytes, large ions cause small salting in due to hydrotropism; and salting in
results when a salt is more soluble in the non-electrolyte than in water [10].
1.4.4 Hydration Theory-The hydration theory was proposed by Rothmund [23].He
postulated that each salt ion binds a constant number of water molecules as a shell of
oriented water dipoles surrounding the ions, thereby decreasing the activity of the water
but having no effect on the remaining water or on the non-electrolyte . This "bound"
water is then unavailable as solvent for the non-electrolyte. The number of water
6
molecules so bound by each salt ion is called the hydration number of the ion.
Considering the wide variation in hydration numbers reported in the literature, it appears
that this concept permit only a qualitative estimate of the magnitude of the salt effect,
Mc.Devit [5] found this model is inadequate because it indicated the hydration number,
which should be independent of the species of non-electrolyte, which is not true. Also
this theory neither allowed the occurrence of salting-in nor did it correspond to the
observed ion order.
The hydration theory, however, has considerable success when it is applied to
aqueous solutions of non-electrolytes for potentially ion-sizeable polar non-electrolytes;
harned and owen have proposed the modified hydration theory. This theory explains the
differences in effects due to solutes and ions by assuming that each on orients water
molecules in a definite direction. If the orientation is favorable to the non-electrolyte
molecules, salting-in occurs; an unfavorable orientation reduces salting-out [22].
1.4.5 Internal Pressure- According to the internal pressure concept proposd by
Tammann and applied Mc.Devit and Long [5], the concentration in the total volume upon
the addition of salt to water can be thought of as a compression of the solvent. This
compression makes the introduction of a molecule of non-electrolyte more difficult, and
this result in salting-out. An increase in total volume upon the addition of a salt would
produce the counter effect known as salting-in.
Mc. Davit and Long [5] applying and internal pressure concept of Tammann to
non polar non-electrolytes, calculated the free energy of transfer of latter from pure to the
salt solution [22].
7
CHAPTER 2
LITERATURE REVIEW AND
PREVIOUS INVESTIGATIONS
8
2.1 Effect of Salt on Vapour-Liquid Equilibrium
The addition of a dissolved salt is generally known to further complicate the vapourliquid equilibrium relationships in a system of two volatile components, since the liquid
phase then becomes a concentrated solution of an electrolyte whose degree of
dissociation is a function of the relative proportions of the other two components. The
salt may affect the activities of the volatile components either through formation an
association complex or alternatively altering the structure of the binary solvent mixture.
Generally, the particles (molecules or ions or both) of dissolved salt tend to attract the
molecules of one component of the binary more strongly than those of the other, tending
to form association complexes preferentially, but not necessarily solely, with the former.
Usually, the added component is more likely to associate preferentially with the
chemically similar binary system (like associates with like), thus affecting the volatilities
of the two original components by differing amounts.
Electrostatic fields by preferential attraction of the salt ions would apply for the more
polar component of the binary solvent. Since the added agent is likely to complex to a
certain extent with both liquid components, the volatiles of both will most likely tend to
be lowered, but by differing amounts depending on how selective the agent is, if the
association preference of the salt is for the less volatile of the two liquid components,
then its volatility will be reduced by volatile component, resulting in an increase in the
value of relative volatility and enrichment of the equilibrium vapour in the more volatile
component. Also, the value of relative volatility will be decreased and the vapor
composition will be enriched in the less volatile component if the association preference
of the salt is for the more volatile component.
A general rule of thumb used often in Physical Chemistry states that like dissolves like.
That is, the things tend to be most soluble in those solvents with which they are most
similar to in terms of their molecular nature and structure. When like dissolves like is
coupled with like associated with like, the empirical rule of salt effect theory results
which predicts that the vapour phase will be enriched in that component of the binary
solvent in which the salt is less soluble. In other words, if the salt more soluble in the less
volatile component, the salt will increase the value of relative volatility. Conversely, if
9
the salt is more soluble in the more volatile component, relative volatility will be
decreased. In the former case, the more volatile component is said to be salted out by the
salt, and in the latter, to be salted-in. Previous experimental findings have tended to
support the above theory of salt effect as general.
Kablukov and Miller were amongst the first to study the ethanol water system
with various salts added. Gross and Halpern refined the liquid phase model relating salt
effect on vapor composition to association in the liquid phase. Empirically, it has been
concluded that the magnitude of salt effect on the activity coefficients of the volatile
components, for a given salt in a given system, will depend on the concentration of salt
present in solution, and on salt effect parameter (Further, Johnson and Furter)[3,8] which
is a function of such factors as degree of difference of solubility of the salt in the two
pure components, degree of dissociation of the alt in solution, ion charge, ion radius, and
others [22].
2.2 Theories and Literature Survey
One needs to be well versed with the basic thermodynamic properties and assumptions,
which directly or indirectly affect the vapour liquid equilibrium and inter conversion of
energies of the system before going into experimentation. Determination of the
thermodynamic properties of a fluid that cannot be measure directly necessitates relating
such properties to measurable quantities. The relationships formulated between the
thermodynamic properties and the measurable quantities facilitate for easier calculation
of the phase equilibrium for industrial practice. Some of the literature on different
experimental results and theories behind it are as follows.
2.3 PREVIOUS INVESTIGATIONS
Many authors have worked on the salt effect on vapour-liquid extraction system. It is
observed that the use of salt has proven advantageous. Although a relative few significant
advances and developments in this field is reported at experimental level. In this review
developments and trends are outlined with emphasis on existing correlation. The systems
with the results obtained by different authors are listed below.
10
2.4 LIST OF SOME PREVIOUS INVESTIGATION ON SALT EFFECT ON VLE
S.NO Reference
SYSTEM
SALT
USED
NaCl,
NH4Cl,
& AlCl3
CONCLUSIONS
1
Fawzi banat,
Sameer Al Aseh,
Jana Simandl effect of
dissolved
inorganic salts on
VLE.
Propionic
acid-Water
mixture
2
Tongfan Sun,
EthanolKerry R. Bullock, Water
Amyn S. TejaCorrelation and
prediction of salt
effects on vapor–
liquid
equilibrium in
alcohol–water–
salt systems
KI, NaCl,
CaCl2
A modified solvation model is
described for the correlation
and prediction of salt effects
on VLE in alcohol–water–salt
systems. The model
incorporates the Bromley
equation to calculate the water
activity, to describe alcohol–
salt interactions. The modified
solvation model yields results
that compare well with
experimental data and with
published models.
3
T.C.Tan,C.M.Chai, Water–
A.T.Tok, K.W. Ho Ethanol–2Propanol
-Prediction and
mixture
NaNO3,
NaCl, KCl
The vapour–liquid
equilibrium of water–ethanol–
2-propanol was
experimentally found to be
11
The VLE of the propionic
acid-water system under nosalt condition and in the
presence of four chloride salts
(NaCl, NH4Cl, CaCl2, AlCl3)
dissolved to various
concentrations were studied at
40 and 50.8°C. The chloride
salts used in this work have a
salting-out effect on propionic
acid in the following order:
AlCl3>/CaCl2>/NaCl>/NH4Cl.
The enhancement factor was
mainly dependent on the salt
type and concentration, rather
than on temperature.
Increasing salt concentration
led to the increase of saltingout of propionic acid.
Experimental data were well
correlated by the modified
Furter equation.
experimental
verification of
the salt effect on
the
vapour–liquid
equilibrium
affected by the addition of
NaNO3, NaCl, KCl or
CH3COOK. All these salts
salted-in water more than
ethanol and 2-propanol and all
except NaCl salted-in ethanol
relatively more than
2-propanol. These effects
were well predicted by Tan–
Wilson and Tan–NRTL
models
4
Shuzo Ohe,
Kimihiko
Yokoyama and
Shoichi
Nakamura
AcetoneMethanol
KI, NaCl,
MgCl2,
CaCl2
If the salt is more soluble in a
less volatile component, then
the relative volatility will be
raised, because of the lowered
vapor pressure of the less
volatile component. The salts
are more soluble in methanol,
the less volatile and thus
increasing relative volatility.
On the other hand, the salt
effect increases with
increasing solubility ratio of
salt in acetone to methanol at
the concentration from 60 to
100 mole %acetone.
5
Ernesto Vercher,
A.Vicent
Orchill´es,Pablo
J. Miguel,
Vicenta
Gonz´alezAlfaro, Antoni
Mart´ınezAndreu-Isobaric
vapor–liquid
equilibria at 100
kPa
Acetone+
Methanol
Lithium
Nitrate
The addition of lithium nitrate
to acetone + methanol system
produces an important saltingout effect on the acetone, and
the azeotrope disappears at
salt mole fractions higher than
0.022. This effect is stronger
than that produced by sodium
iodide, sodium thiocyanate,
and calcium bromide on this
system.
6
A. Vicent
Orchill´es,
Vicenta
Gonz´alez-
copper(II)
chloride
The addition of copper(II)
chloride to 1-propanol +water
systems produces a salting-out
effect of the alcohol and the
1-propanol
+water
12
Alfaro,
Antoni
Mart´ınezAndreu-Isobaric
vapor–liquid
equilibria at 100
KPa
displacement of the azeotropic
point towards higher x1
values. This effect is smaller
than that observed for calcium
nitrate, calcium chloride,
lithium nitrate, or lithium
chloride on this system. On
the other hand, the minimum
non-azeotropic point also
changes with the salt content
but this variation is small and
does not depend, practically,
on the salt used.
7
Michael
Jo1decke, A
lvaro Pe´rezSalado Kamps,
and Gerd
Maurer-
Methanol+
water
NaCl
By increasing the
concentration of the salt in the
liquid (at constant temperature
and at constant salt-free
concentration of methanol in
that liquid), an increase in the
concentration of methanol in
the gaseous phase is
experimentally observed (i.e.,
methanol is “salted-out”, and
water is “salted-in”).
8
Maria C. Iliuta l,
Fernand C.
Thyrion
acetone+
methanol
Sodium
Thiocyanate,
NaI.
In the acetone-methanolNaSCN system, a crossover
effect between salting-in and
salting-out on acetone was
observed as in the case of NaI,
the transition from salting-in
to salting-out takes place at an
acetone mole fraction (saltfree basis) of about 0.3 for the
NaSCN and 0.2 for the NaI
system. In the case of NaSCN,
the azeotropic point can be
eliminated at a salt mole
fraction higher than 0.03. A
stronger salting-out effect and
a weaker salting-in effect on
acetone was observed in NaI
compared to NaSCN. An
apparent crossing point
between the dew point and the
13
bubble point curves was also
found for the acetonemethanol-NaSCN system, as
in the case of NaI.
9
A. S. Narayana,
Acetic
S. C. Naik, and P. Acid+Water
Rath -Salt Effect
in Isobaric
Vapor-Liquid
Equilibria
10
S. Abderafi and
T. Bounahmidi
Measurement and
estimation of
vapor–liquid
equilibrium for
industrial sugar
juice using the
Peng–Robinson
equation of state
Sucrose,
glucose,
fructose,
aspartic
acid,
glutamic
acid, acetic
acid, lactic
acid and
succinic
acid
KCI,
Na2SO4, and
K2SO4
Addition of KCI, Na2SO4, and
K2SO4 results in “salting out”
of acetic acid. Water-acetic
acid solutions containing salts
KCI and Na2SO4 above 80
and 91wt % water on salt-free
basis, respectively, form
azeotropes. An equation of the
type log (Ys/Y0) = KW fits
the data for the three salts
studied in this system. All the
three salts studied are found to
have salting out effect for
acetic acid in varying degrees.
NaOH and
KCl
In the present study, attention
is given to adapting the PR
EOS for industrial sugar
juices using the pseudo
component approach.
Industrial sugar juices were
considered as aqueous
solutions of sugar, amino acid,
carboxylic acid and ash. The
pseudo components
composition can be obtained
by analytical techniques
frequently used in sugar
industry. In future papers, the
PR EOS will be used to
predict other physical
properties of industrial sugar
juices and to simulate
evaporation process of a sugar
factory.
.
14
11
Motoyoshi
Hashitani and
Mitsuho Hiratasalt effect of
calcium chloride
in vapour-liquid
equilibrium of
alcohol-acetic
ester systems
Ethyl
acetate+
ethanol
Calcium
chloride
15
The increase of relative
volatility of acetic ester is
noticed when calcium
chloride is added in these
alcohol-acetic ester mixtures.
The azeotropic composition of
these mixtures shifts to the
higher acetic ester
composition. The addition of
calcium chloride is suggested
to be effective for the
separation of these alcoholacetic ester mixtures.
CHAPTER 3
16
DETERMINATION OF VLE
DATA
3.1 Experimental Determination of vapour-liquid Equilibrium
Various methods for direct determination of equilibrium data are as follows:
1. Distillation method
2. Circulation method
3. Static method
4. Bubble and Dew point method
5. Flow method
The present experimental setup is based on the circulation method, so the basic theme of
the setup and procedure the method is as follows.
3.1.1 Distillation Method
In this method, liquid is taken in the boiling flask and heated, as the composition of liquid
phase is constant, a small amount of liquid is considered for analysis. Condensation of the
vapour on the cold walls of distillation flask at the beginning of the experiment leads to
large number of errors, that‟s why this method is seldom used.
3.1.2 Circulation method
This method is the most commonly used, can easily be used both in the region of medium
and low pressure. Various equilibrium stills with simple circulation differ significantly in
their construction details but they all are based on a common principle.
B
A
.
Fig-1 Schematic diagram for circulating stills
17
Principle
As the vapors come out from the distillation flask „A‟ they pass through the vapour
conduit and after complete condensation collect in the receiver „B‟. The liquid flows
backward once the receiver is filled; a trap is generally inserted there to prevent the flow
of liquid from the distillation flask to the receiver. If the still is started with the receiver B
empty, at the instant at which it fills, its contents are richer in more volatile component
than that of the vapour phase over the boiling mixture in the distillation flask. Operating
further, the contents of the distillation flask become richer with more volatile component
and the receiver becomes poorer. This process continues till the steady state is obtained,
in which the compositions in both vessels no longer changes with time. Both
compositions are determined automatically.
According to the manner of circulation of the phases, these stills are classified into two
groups.
1. Still with circulation of the vapour phase.
2. Still with circulation of the vapour and liquid phase.
These stills with minor modifications have been used in the present experimental work.
3.2 Othmers Still and its Modification
Othmers still was designed and constructed D.F. Othmers [4] in 1928. The Still is made
of glass, so it is quite compact. Due to some faults and vulnerability, certain
modifications were made in the design and construction.
An improved version of othmers still was presented by Johnson and Futer [9] for
the salt effect studies. Fig-2 shows such equilibrium still. The modifications introduced
are
a) Flattening the bottom of still to facilitate the use of magnetic stirrer-cum plate heater.
b) Introduction of a thermowell or protector of thermometer, to prevent the accidental
knocking of the thermometer by the stirrer.
The still was lagged with two layers of the magnesia-asbestos covering the boiling
chamber from the liquid level to tire top of the neck [22].
18
3.3 Procedure for Determination of VLE Data
Apparatus and procedure
The still which was used in the present work had been designed to avoid and reduce
faults and errors. The still was thoroughly washed with water and then with methanol. It
was mounted over the hot plate magnetic stirrer. A condenser was mounted over the
condensate chamber. A magnetic stirrer was used for stirring thereby maintaining
homogeneity of the liquid to improve salt dissolution.
The main characteristic of the present design is that, the pot volume is much
higher than the liquid condensate volume and at steady state only a few drops of
condensate were collected and analyzed for the determination of the vapour composition.
Due to which the composition of the liquid prior to the addition of the salt could well be
taken as the equilibrium liquid composition without introducing appreciable error. The
still was charged with 200 ml of methanol and ethyl acetate mixture of desired
composition.
So, let us suppose
Volume of methanol be „v‟ ml
So volume of ethyl acetate= „(200-v)‟ ml
If n is the mole fraction of methanol, then
ρm=density of methanol
ρe=density of ethyl acetate
Mm=molar mass of methanol
Me=molar mass of ethyl acetate
19
TABLE 1-Data of the amount of methanol and ethyl acetate added in ml
Mole fraction
Volume of
Volume of
of methanol
methanol (ml)
ethyl acetate
(ml)
0.1
8.84
191.16
0.2
18.85
181.15
0.3
30.28
169.72
0.4
43.45
156.55
0.5
58.78
141.22
0.6
76.89
123.11
0.7
98.55
101.45
0.8
124.96
75.04
0.9
157.89
42.11
TABLE 2- Data of the amount of salt added in gms
Weight of 5% of W in 10% of W 15% of W 20% of W
methanol
gms
in gms
in gms
in gms
6.9535
0.3477
0.6954
1.0431
1.3908
14.8305
0.7415
1.4830
2.2245
2.9660
23.8197
1.1909
2.3818
3.5727
4.7636
34.1782
1.7089
3.4178
5.1267
6.8356
46.2439
2.3122
4.6244
6.9366
9.2488
60.4848
3.0242
6.0484
9.0726
12.0968
77.5202
3.8760
7.7520
11.6280
15.5040
98.2951
4.9148
9.8296
14.7444
19.6592
124.2002
6.2100
12.4200
18.6300
24.8400
in gms. (W)
20
Now the set up is ready for operation at an atmospheric condition of 98.6±0.03 kpa,
pressure. The thermometer was introduced into the respective port as shown in the Fig 2.
The energy control switch regulator ensures continuous stirring and uniform heating. The
solution was heated for some time till the condensate was observed. Then again the
solution was allowed to heat at a milder heating than before till the steady state was
reached i.e. the temperature in the thermometer became constant. The solution is again
heated for about 30 minutes to ensure the attainment of equilibrium a few drops of
vapour sample were collected for analysis.
As the vapour sample withdrawn for analysis, is negligible, the original
composition of the liquid practically remains unchanged, which was taken as liquid phase
composition without including any substantial error.
TABLE 3 - Physical properties of solvents used
Components
Boiling Points in °C
Present
Refractive Index at
Specific Gravity
20°C
20°C
Literature* Present
work
Literature* Present
work
Literature*
work
Ethyl acetate
77.1
77
1.3689
1.3766
0.899
0.899
Methanol
64.7
64.7
1.3265
1.3302
0.790
0.790
* International critical Table
3.4 Method Analysis
The method of analysis of the vapour sample, which was considered to be completely
free from the dissolved salt, involved either the physical properties determination like
density measurement or refractive index measurement or instrumental method of analysis
like gas chromatography. However all the samples were measured by the refractive index
method. Using a digital refractometer whose prism temperature was maintained constant
at 20°C.
21
1. Boiling Chamber
2. Condensate Chamber
3. Bulb Condenser
4. Thermowell
5. Thermowell
6. Magnetic Bar
7. Three Way Stopcock
8. Capillary Tube
9. Salt Loading Port
10. Thermometer
22
VLE APPARATUS
Fig 3 - VLE Apparatus (Still)
23
REFRACTOMETER
Fig 4 -Refractometer
24
CHAPTER 4
TREATMENT OF VLE DATA
25
This chapter represents the analysis of the experimental work. The isobaric VLE data
determined and tabulated has been investigated. In this chapter we examine what can be
learned from the experiment. Consider the measurements of vapour-liquid equilibrium
data, from which activity coefficient correlations are derived.
4.1 Computation of Vapour-Liquid Equilibrium
Experimental VLE measurements contain some combination of the measurable variables
like temperature, pressure and vapour or liquid compositions. Static equilibrium stills, for
example may produce either P T x, P T y or P T w (weight of the component in system).
As all the important variables are not measurable, so they can be derived by computation.
However in re-circulating stills, all four variables are measurable but one of them can be
excluded for computation.
4.2 Model-Dependent method for Data Reduction
This method is applied for a reduction of P T x – equilibrium data, using model for the
excess Gibbs free energy as a function of composition. As a result model parameters are
obtained, and the composition of vapour phase can be calculated from the known
composition of other phase at any desired temperature or pressure within a valid range.
4.3 Models for excess Gibbs Energy
In general GE/RT is a function of T, P and composition, but for liquids at low to
moderate pressures it is a very weak function of P. Therefore the pressure dependence of
activity coefficient is usually neglected. Thus, for data at constant T:
GE/RT = g(x1, x2, x3…, xn) (const T)
The "Margules equation" is an example of this functionality, which is given by
ln γ1= x22[A12 + 2(A21-A12)x1]
……………(4.1)
ln γ2= x12[A21 + 2(A12-A21)x2]
…………...(4.2)
26
A number of other equations are in common use for correlation of activity
coefficients. For binary systems the function is represented by an equation is
GE/x1x2RT, which may be as a power series in x1;
GE/x1x2RT= a + bx1 +cx12 + …. (Const T)
As x2 = 1-x1 mole fraction x1 serves as the single independent variable. An equivalent
power series with certain advantages is known as Redlich/Kister expansion [7]
GE/x1x2RT= A + B(x1- x2) +C(x1- x2)2 +….
In application, different truncations of this series are appropriate and in each case specific
expressions for ln γ1 and ln γ2 are generated by the following equation.
ln γ1= [∂(nGE/RT)/ ∂ni]P, T, n j
…………… (4.3)
E
When A=B=C= ....=0, G /RT=0, ln γ1 =0, ln γ2=0, γ1=γ2=0, and the solution is ideal .
If B=C=…..=0, then
GE/x1x2RT = A
Where „A‟is a constant for the for a given temperature. Corresponding equations for
ln γ1 and ln γ2 are
ln γ1 = Ax22 and
ln γ2 = Ax12
Infinite-dilution values of the activity coefficient are ln γ1
If C =…. = 0 then
∞
∞
= ln γ1
=A
GE/x1x2RT= A + B(x1- x2) = A + B (2x1-1)
E
In this case G /x1x2RT is linear in x1. if we define A+B=A21 and A-B=A12, the
Margules equation obtained,
GE/x1x2RT= A21x1 + A12x2
…………….. (4.4)
Another well known equation results when the reciprocal expression is expressed as a
linear function of x1,
27
x1 x2 = A'+ B' (x1 - x2)
GE/RT
This may also be written as
x1 x2 = A'(x1 + x2) + B' (x1 - x2)
GE/RT
The new parameters are defined as A‟+ B' =1/ A‟12 and A' - B' =1/ A'21
so an equivalent form is obtained :
x1 x2 = x1/ A'21 + x2/ A'12
GE/RT
GE/x1x2RT = A'12 A'21
A'12 x1+ A'21 x2
………….. (4.5)
…………. (4.6)
The activity coefficient implied by this equation is
ln γ1 = A'12 ( 1+ A'12 x1 )-2 and ln γ2 = A'21 ( 1+ A'21 x2 )-2
A'21 x2
A'12 x1
These are known as van laar equations. When x1=0, ln γ1∞ = A'12 when x2=0,
ln γ2∞ = A'21
The Redlich/Kister expansion, the Margules equations, and the van laar equation are all
special cases of a general treatment of based on rational functions, i.e. on equations for
GE/x1x2RT given by ratios of polynomials. They provide great flexibility in the fitting of
VLE data for binary systems. However they have scant theoretical foundation, and
therefore fail to admit a rational basis for extension to multicomponent systems. [18]
4.4 Local Composition Modes
Theoretical developments in the molecular thermodynamics if liquid solution behavior is
often based on the concept of „local composition‟. Within a liquid solution, local
compositions, are different from the overall mixture composition, are presumed to
account for the short range order and non-random molecular orientations that results from
28
differences in molecular size and intermolecular forces. The concept was introduced by
G.M. Wilson in 1964 with publication of a model of solution behavior since known as the
Wilson equation [11]. The success of this equation is the correlation of VLE data
prompted the development of alternative local-composition models, most notably the
NRTL (Non Random Two Liquid) equation of Renon and Prausnitz [14]. And the
UNIQUAC (UNIversal QUAsi-Chemical) equation of Abrams and Prausnitz. [16]. A
further significant development, based on the UNIQUAC equation, is the UNIFAC
method [17]. in which activity coefficients are calculated from the contributions of the
various-groups making up the molecules of a solution.
The Wilson equation, like the Margules and van Laar equations, contains just two
parameters for a binary system (Λ12 and Λ21 ), and is written as
GE/RT = -x1 ln( x1 + x2 Λ12 ) - x2 ln(x2 + x1 Λ21 )
…….………(4.7)
ln γ1= - ln( x1 + x2 Λ12 ) + x2(
-
) ………….(4.8)
ln γ2= - ln( x2 + x1 Λ21 ) - x1(
-
)
…..……...(4.9)
For infinite dilution, these equations become:
ln γ1∞ = - ln Λ12 + 1 -
Λ21
and
ln γ2∞ = - ln Λ21 + 1 -
Λ12
….. (4.10) & (4.11)
Note that Λ12 and Λ21 must always be positive numbers.
The NRTL equation, containing three parameters for a binary system, is
GE/ x1 x2RT =
……….(4.12)
ln γ1 = x22 [
…….(4.13)
ln γ2 = x12 [
.…….. (4.14)
29
Here,
G12 = exp(-ατ12)
G21= exp(-ατ21)
And
τ12= b12/RT
τ21= b21/RT
…….(4.15) & (4.16)
…...(4.17) & (4.18)
Where α, b12 and b21 , parameters specific to a particular pair of species, are independent
of composition and temperature. The infinite-dilution values of the activity coefficients
are given by the equations:
ln γ1∞ = τ21 + τ12 exp(-ατ12) and ln γ2∞ = τ12 + τ21 exp(-ατ21)
…(4.19) & (4.20)
The UNIQUAC equation and the UNIFAC method are models of greater complexity.
The local composition models have limited flexibility in the fitting of data, but
they are adequate for most engineering purposes. Moreover, they are implicitly
generalizable to multi component systems without introduction of any parameters beyond
those required to describe the constituent binary systems. For example, the Wilson
equation for multicomponent systems is:
GE/RT= -∑ xi ln ( ∑ xj Λij )
i
j
(4.21)
ln γi = 1- ln ( ∑ xj Λij ) - ∑ xk Λki / ∑ xj Λkj
j
k
(4.22)
j
Λij = 1 for i = j, etc. All indices refer to the same species, and summations are over all
species. For each ij pair there are two parameters, because Λij
Λji . For a ternary system
the three ij pairs are associated with the parameters Λ12 , Λ21 ; Λ13, Λ31 ; and Λ23, Λ32.
The temperature dependence of the parameters is given by:
Λij = Vj /Vi
(i
j)
……..(4.23)
Where Vj and Vi are the molar volumes at temperature T of pure liquids j and i, and aij is
a constant independent of composition and temperature. Thus the Wilson equation, like
all other local-composition models, has built into it approximate temperature dependence
for the parameters. Moreover, all parameters are found from data for binary (in contrast
30
to multi-component) systems. This makes parameter determination for the localcomposition models a task of manageable proportions [18].
4.5 SAMPLE CALCULATION
Calculation of activity coefficient
yi = xi γi pisat
at azeotropic condition
xi= yi
so, γi = PT / Pisat
Calculation of vapour phase
Using Antoine equation
log Pisat = A - B/( T+C)
…………….(4.24)
Replacement of activity coefficient to VLE Model
Margules equation
ln γ1* = x22[A12 + 2(A21-A12)x1]
…….(4.25)
ln γ2* = x12[A21 + 2(A12-A21)x2]
……(4.26)
γ1* and γ2* are theoretical values of activity coefficients derived from the experimental
values. The procedure is as follows
Methanol
A=7.8975
B=1474.08
C=229.13
Ethyl Acetate
A=7.0981
B=1238.71
C=217.10
Now, for different values of T we can calculate Pisat
31
Gibbs Energy
GE/RT= x1 ln γ1 + x2 ln γ2
……………..(4.27)
And by Margules equation method GE/x1x2RT= A21x1 + A12x2 ……(4.28)
Now ln γ1∞ = A12 and ln γ2∞ =A21 which are obtained by plotting curve ln γ1, ln γ2 vs x1
So now by putting the values of A12 and A21 the theoretical γ1* and γ2* can be found out
and thereby by the following relations theoretical vapour composition y1* and y2* can be
obtained.
y1*= x1 γ1 P1sat / (x1 γ1 P1sat + x2 γ2 P2sat)
………(4.29)
y2*= x2 γ2 P2sat / (x1 γ1 P1sat + x2 γ2 P2sat)
……….(4.30)
All the values given above have been calculated and tabulated [25].
4.6 Results and Discussion
The VLE data for the present binary system was obtained at atmospheric condition of
98.6 ± 0.03 kpa pressure.
In the present Methanol (1) Ethyl Acetate (2) system , it has been observed that
the system forms a minimum boiling azeotrope 0.732 mole fraction of methanol at
62.6°C. The salts which have been used to study the salt effect on the system are Lithium
Chloride and Lithium Bromide.
It has been found out that salting –in and salting-out of methanol has been seen in
the case of Lithium Bromide whereas during the study for the salt Lithium Chloride only
salting-in of methanol was observed. This is due to the changes of relative volatility of
the binary system with the solid salts. Apparently the salt effect increases as we increase
the concentration of salts as by the addition of salts like Lithium Chloride and Lithium
Bromide, it has been found that the azeotrope shifts but the azeotropy couldn‟t be
eliminated even with addition of higher concentrations of salts. The azeotrope shifts from
0.732 to 0.629, 0,586, 0.472 and 0.471 by addition of 5%, 10%, 15% and 20% of lithium
chloride salt respectively and to 0.774, 0,706, 0.682, 0.670 by the addition of 5%, 10%,
15% and 20% lithium bromide respectively. From this data it has been found that
Lithium Chloride is more effective than Lithium Bromide.
32
TABULATION
33
TABLE 4REFRACTIVE INDEX DATA
SYSTEM: METHANOL (1) + ETHYL ACETATE (2)
SALT: LITHIUM CHLORIDE
Liquid
composition
X1
Liquid
phase
refractive
index (on
salt free
basis)
Salt (0%)
Salt (5%)
ux
T
ux
0
1.3689
1.3689
77.1 1.3685
77.1 1.3685
0.1
1.3679
1.3635
70.5 1.3605
0.2
1.3655
1.3524
0.3
1.3622
0.4
Salt (15%)
Salt (10%)
T
ux
T
ux
T
77.1 1.3685
77.1
1.3685
77.1
70 1.3572
69.6 1.3535
69.5
1.3526
69.5
66.5 1.3521
65.9 1.3491
65.8 1.3471
65.9
1.3458
65.9
1.3510
63.7 1.3476
63.4 1.3484
63.4 1.3518
63.3
1.3510
63.5
1.3586
1.3494
62.8 1.3474
62.7 1.3512
62.7 1.3588
62.8
1.3586
62.7
0.5
1.3548
1.3489
62.0 1.3496
61.8 1.3540
61.8 1.3630
61.7
1.3632
61.7
0.6
1.3523
1.3481
62.7 1.3521
62.7 1.3548
62.7 1.3638
62.7
1.3642
62.9
0.7
1.3481
1.3476
62.4 1.3532
62.6 1.3527
62.8 1.3609
62.9
1.3616
62.9
0.8
1.3433
1.3462
62.5 1.3512
62.6 1.3472
63.0 1.3531
63.0
1.3540
63.1
0.9
1.3355
1.3403
62.8 1.3435
62.9 1.3385
63.2 1.3402
63.4
1.3410
63.4
1
1.3265
1.3263
64.7 1.3265
64.7 1.3265
64.7 1.3265
64.7
1.3265
64.7
34
T
ux
Salt
(20%)
TABLE 5REFRACTIVE INDEX DATA
SYSTEM: METHANOL (1) + ETHYL ACETATE (2)
SALT: LITHIUM BROMIDE
Liquid
composition
X1
Liquid
phase
refractive
index (on
salt free
basis)
0
1.3689
0.1
0.3
0.5
0.7
0.9
1
1.3679
1.3622
1.3548
1.3481
1.3355
1.3265
Salt (5%)
Salt (10%)
Salt (0%)
Salt (15%)
Salt
(20%)
ux
T
ux
T
ux
T
ux
T
ux
T
1.3689
77.1
1.3689
77.1
1.3689
77.1
1.3689
77.1
1.3689
77.1
1.3635
70.5
1.3618
70.5
1.3566
70.4
1.3535
70.2
1.3523
70
1.3510
63.7
1.3427
65.9
1.3393
65.9
1.3380
65.9
1.3357
65.8
1.3489
62.0
1.3412
63.1
1.3410
64.3
1.3406
64.8
1.3398
65.3
1.3476
62.4
1.3451
64
1.3468
63.9
1.3478
63.1
1.3492
64.3
1.3403
62.8
1.335
62.6
1.3368
63
1.3412
64.3
1.3426
65
1.3265
64.7
1.3265
64.7
1.3265
64.7
1.3265
64.7
1.3265
64.7
35
TABLE 6VAPOUR EQUILIBRIUM DATA
SYSTEM: METHANOL (1) + ETHYL ACETATE (2)
SALT: LITHIUM CHLORIDE
Serial
no
Liquid
composition
X1
Vapour Phase Composition
Salt (0%)
Salt
(5%)
Salt
(10%)
Salt
(15%)
Salt
(20%)
Y1
Y1
Y1
Y1
Y1
1
0
0.000
0.000
0.000
0.000
0.000
2
0.1
0.287
0.389
0.494
0.600
0.625
3
0.2
0.631
0.640
0.713
0.759
0.786
4
0.3
0.667
0.747
0.730
0.647
0.668
5
0.4
0.706
0.752
0.660
0.447
0.453
6
0.5
0.718
0.702
0.586
0.306
0.299
7
0.6
0.736
0.639
0.564
0.278
0.262
8
0.7
0.747
0.610
0.622
0.377
0.353
9
0.8
0.778
0.662
0.757
0.613
0.587
10
0.9
0.889
0.832
0.917
0.890
0.877
11
1
1.000
1.000
1.000
1.000
1.000
36
TABLE 7VAPOUR EQUILIBRIUM DATA
SYSTEM: METHANOL (1) + ETHYL ACETATE (2)
SALT: LITHIUM BROMIDE
Serial
no
Liquid
composition
X1
Vapour Phase Composition
Y1(0%
Salt)
Y1(5%
Salt)
Y1(10%
Salt)
Y1(15%
Salt)
Y1(20%
Salt)
1
0
0.000
0.000
0.000
0.000
0.000
2
0.1
0.287
0.340
0.488
0.563
0.590
3
0.3
0.667
0.775
0.833
0.855
0.891
4
0.5
0.718
0.801
0.804
0.811
0.825
5
0.7
0.747
0.733
0.701
0.682
0.654
6
0.9
0.889
0.901
0.844
0.801
0.777
7
1
1.000
1.000
1.000
1.000
1.000
37
TABLE 8CALCULATION OF ACTIVITY CO-EFFICIENT
SYSTEM: METHANOL (1) + ETHYL ACETATE (2)
NO SALT
γ1
γ2
ln γ1
80.52
2.245
0.970
0.809
-0.030
109.57
70.66
2.839
0.645
1.044
-0.439
63.7
97.87
63.76
2.240
0.737
0.807
-0.305
0.4
62.8
94.12
61.54
1.850
0.786
0.615
-0.241
5
0.5
62
90.77
59.57
1.560
0.935
0.445
-0.067
6
0.6
62.7
93.70
61.30
1.292
1.061
0.256
0.060
7
0.7
62.4
92.44
60.56
1.140
1.371
0.131
0.316
8
0.8
62.5
92.86
60.80
1.033
1.801
0.033
0.588
9
0.9
62.8
94.12
61.54
1.035
1.785
0.034
0.579
Serial
no
(X1)
T
P1
P2
1
0.1
70.5
126.28
2
0.2
66.5
3
0.3
4
38
ln γ2
TABLE 9CALCULATION OF THEORITICAL ACTIVITY CO-EFFICIENT
SYSTEM: METHANOL (1) + ETHYL ACETATE (2)
NO SALT A12=-0.36,A21=0.66
Serial
no
γ1*
ln(γ1*)
γ2*
ln(γ2*)
Liquid
composition
(X1)
∆G/RTX1X2
0.1
8.053
0.881
-0.126
0.988
-0.012
0.2
4.669
1.031
0.031
0.962
-0.039
0.3
2.252
1.131
0.123
0.933
-0.069
0.4
1.136
1.178
0.164
0.914
-0.090
0.5
0.755
1.179
0.165
0.914
-0.090
0.6
0.576
1.148
0.138
0.945
-0.056
0.7
1.239
1.101
0.096
1.024
0.024
0.8
2.983
1.052
0.051
1.175
0.161
0.9
5.833
1.015
0.015
1.447
0.369
1
2
3
4
5
6
7
8
9
39
TABLE 10ACTIVITY CO-EFFICIENT
SYSTEM: METHANOL (1) + ETHYL ACETATE (2)
LITHIUM CHLORIDE
(X1)
5% Salt
10% Salt
15% Salt
20% Salt
γ1
γ2
γ1*
γ2*
γ1
γ2
γ1*
γ2*
γ1
γ2
γ1*
γ2*
γ1
γ2
γ 1*
γ2*
0.1
3.087
0.845
0.848
0.983
3.976
0.709
0.829
0.981
4.850
0.561
0.729
0.975
5.049
0.527
0.707
0.973
0.2
2.947
0.643
1.067
0.944
3.296
0.514
1.063
0.940
3.496
0.430
1.026
0.919
3.623
0.381
1.015
0.914
2.543
0.566
1.221
0.904
2.485
0.603
1.231
0.896
2.211
0.793
1.259
0.860
2.263
0.740
1.263
0.852
0.4
1.981
0.664
1.293
0.878
1.739
0.911
1.311
0.868
1.170
1.479
1.383
0.819
1.192
1.468
1.397
0.808
0.5
1.540
0.996
1.290
0.880
1.286
1.382
1.310
0.869
0.674
2.328
1.394
0.815
0.659
2.352
1.412
0.803
1.121
1.453
1.236
0.929
0.990
1.753
1.253
0.920
0.489
2.904
1.325
0.869
0.456
2.944
1.341
0.857
0.7
0.922
2.101
1.158
1.051
0.932
2.019
1.169
1.048
0.562
3.318
1.218
1.020
0.526
3.446
1.228
1.012
0.8
0.875
2.734
1.081
1.298
0.983
1.936
1.086
1.312
0.796
3.079
1.110
1.351
0.759
3.274
1.116
1.356
0.965
2.681
1.023
1.783
1.050
1.305
1.024
1.839
1.010
1.716
1.031
2.073
0.995
1.932
1.032
2.121
0.3
0.6
0.9
40
TABLE 11ACTIVITY CO-EFFICIENT
SYSTEM: METHANOL (1) + ETHYL ACETATE (2)
LITHIUM BROMIDE
(X1)
5% Salt
10% Salt
15% Salt
20% Salt
γ1
γ2
γ1*
γ2*
γ1
γ2
γ1*
γ2*
γ1
γ2
γ1*
γ2*
γ1
γ2
γ1*
γ2*
2.656
0.899
0.937
0.993
3.825
0.699
0.918
0.989
4.443
0.600
0.902
0.987
4.687
0.567
0.887
0.986
2.381
0.458
1.082
0.961
2.559
0.340
1.148
0.940
2.626
0.295
1.179
0.929
2.748
0.223
1.202
0.919
1.657
0.630
1.105
0.951
1.580
0.593
1.182
0.928
1.562
0.561
1.221
0.914
1.557
0.510
1.252
0.903
1.042
1.361
1.059
1.020
1.001
1.530
1.100
1.044
1.008
1.679
1.120
1.052
0.918
1.744
1.137
1.057
1.059
1.600
1.009
1.255
0.974
2.481
1.015
1.470
0.875
3.009
1.017
1.584
0.825
3.285
1.020
1.677
0.1
0.3
0.5
0.7
0.9
41
TABLE 12CALCULATED AND THEORITICAL VAPOUR COMPOSITION
SYSTEM: METHANOL (1) + ETHYL ACETATE (2)
LITHIUM CHLORIDE
X1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Vapour compositionY1 (experimental)
Vapour compositionY1 (theoretical)
0%
salt
5%
salt
10%
salt
15%
salt
20%
salt
0%
salt
5%
salt
10%
salt
15%
salt
20%
salt
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.287
0.389
0.494
0.600
0.625
0.134
0.131
0.128
0.115
0.112
0.631
0.640
0.713
0.759
0.786
0.294
0.304
0.304
0.302
0.301
0.667
0.747
0.730
0.647
0.668
0.444
0.470
0.474
0.490
0.494
0.706
0.752
0.660
0.447
0.453
0.568
0.600
0.606
0.633
0.638
0.718
0.702
0.586
0.306
0.299
0.663
0.691
0.696
0.723
0.728
0.736
0.639
0.564
0.278
0.262
0.736
0.753
0.757
0.778
0.782
0.747
0.610
0.622
0.377
0.353
0.793
0.797
0.799
0.810
0.812
0.778
0.662
0.757
0.613
0.587
0.845
0.836
0.835
0.834
0.834
0.889
0.832
0.917
0.890
0.877
0.906
0.888
0.885
0.873
0.870
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
42
TABLE 13CALCULATED AND THEORITICAL VAPOUR COMPOSITION
SYSTEM: METHANOL (1) + ETHYL ACETATE (2)
LITHIUM BROMIDE
X1
Vapour compositionY1 (experimental)
Vapour compositionY1 (theoretical)
0%
salt
5%
salt
10%
salt
15%
salt
20%
salt
0%
salt
5%
salt
10%
salt
15%
salt
20%
salt
0
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.1
0.287
0.340
0.488
0.563
0.590
0.134
0.141
0.139
0.137
0.135
0.3
0.667
0.775
0.833
0.855
0.891
0.444
0.427
0.448
0.457
0.464
0.5
0.718
0.801
0.804
0.811
0.825
0.663
0.640
0.662
0.673
0.682
0.7
0.747
0.733
0.701
0.682
0.654
0.793
0.788
0.791
0.792
0.794
0.9
0.889
0.901
0.844
0.801
0.777
0.906
0.917
0.905
0.899
0.894
1
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
43
TABLE 14ERROR CALCULATION
SYSTEM: METHANOL (1) + ETHYL ACETATE (2)
LITHIUM CHLORIDE
Liquid
composition
(X1)
% ERROR= [ (Y1 (exp) ‒ Y2 (theo))/ Y1 (exp) ] * 100
0% SALT
5% SALT
10% SALT
15% SALT
20% SALT
53.31%
66.32%
74.09%
80.83%
82.08%
53.41%
52.50%
57.36%
60.21%
61.70%
33.43%
37.08%
35.07%
24.27%
26.05%
19.55%
20.21%
08.18%
41.61%
40.84%
7.66%
1.57%
18.77%
76.27%
83.48%
0.14%
17.84%
34.22%
79.86%
88.47%
6.16%
30.66%
28.46%
14.85%
70.03%
8.61%
26.28%
10.30%
36.05%
42.08%
1.91%
6.73%
3.49%
1.91%
0.80%
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
44
TABLE 15ERROR CALCULATION
SYSTEM: METHANOL (1) + ETHYL ACETATE (2)
LITHIUM BROMIDE
Liquid
composition
(X1)
% ERROR= [ (Y1 (exp) ‒ Y2 (theo))/ Y1 (exp) ] * 100
0% SALT
5% SALT
10% SALT
15% SALT
20% SALT
0.1
53.31%
58.52%
71.51%
75.66%
77.11%
33.43%
44.90%
46.21%
46.54%
47.92%
1.91%
20.09%
17.66%
1.70%
17.33%
6.16%
0.75%
1.28%
1.61%
2.14%
7.66%
0.17%
0.72%
1.22%
1.50%
0.3
0.5
0.7
0.9
45
GRAPHS
46
Fig 5 - Plot of Refractive Index vs Mole Fraction of methanol
47
Fig 6 - Vapour-Liquid Equilibrium Plot (0 % salt)
48
Fig 7 - Vapour-Liquid Equilibrium Plot (Lithium Chloride)
49
Fig 8 - Vapour-Liquid Equilibrium Plot (Lithium Bromide)
50
Fig 9 - Y1(experimental) vs Y1(theoretical) plot for LiCl
51
Fig 10 - Y1(experimental) vs Y1(theoretical) plot for LiBr
52
Fig 11 - T-X-Y PLOT (NO SALT)
53
Fig 12 - T-X-Y PLOT (5% LITHIUM CHLORIDE)
54
Fig 13 - T-X-Y PLOT (10% LITHIUM CHLORIDE)
55
Fig 14 - T-X-Y PLOT (15% LITHIUM CHLORIDE)
56
Fig 15 - T-X-Y PLOT (20% LITHIUM CHLORIDE)
57
Fig 16 - T-X-Y PLOT (5% LITHIUM BROMIDE)
58
Fig 17 - T-X-Y PLOT (10% LITHIUM BROMIDE)
59
Fig 18 - T-X-Y PLOT (15% LITHIUM BROMIDE)
60
Fig 19 - T-X-Y PLOT (20% LITHIUM BROMIDE)
61
CHAPTER 5
CONCLUSION
62
In this present study the effect of solid salts on the Vapour-Liquid equilibrium
relationship of a non-aqueous binary system i.e.
System: Ethyl Acetate (1) –Methanol (2) (with Salts: Lithium Chloride and Lithium
Bromide) at an atmospheric pressure of 98.6 ± 0.03 kpa has been investigated.
It is concluded that the thermodynamic behavior of the system was significantly
modified by the salts. It was also concluded that by using Lithium Chloride and Lithium
Bromide at different concentrations e.g. 5%, 10%, 15%, and 20% by weight of methanol
for the system Methanol (1) and Ethyl Acetate (2), there was a change in relative
volatility in the system but the azeotropy of the system couldn‟t be eliminated.
The acetate group in the solution is in excess, which might have resulted in the
increase of liberation of ethyl acetate to the vapor phase. Another reason could be the
degree of dissociation of the salt at different composition of the liquid phase. At lower
concentration of methanol it might be difficult for the solvent to dissociate the salt, but as
the concentration of methanol increases, more and more salt is dissolved holding back
this solvent group to give a salting in effect. Or else the liquid-liquid interaction might
have not allowed the methanol to be potentially active enough to dissociate the salt in the
methanol lean region, but as the methanol concentration increased with decrease in ethyl
acetate concentration the opposite phenomenon was observed.
The calculation of the deviation of the experimental and the calculated data has
been done as per the proposed method outlined. [22]
63
REFERENCES
1.
Debye, P., McAuley, J., Physik. Z. 26, 22 (1925).
2.
Glasstone, S., Pound, A. J., J . Chem. Soc. 127, 2660 (1925).
3.
P Gross and O. Halpern., J. Chem. Phys, 2, 184 (1934) and 2, 188 (1934)
4.
D.F Othmer., Ind. Engineering. Chem. Annual, Ed., 20, 763 (1948)
5.
F.A Long and W.F. Nc.Devit, J . Am Chem. Soc.74 , 1773 (1952)
6.
Long, F. A McDevit, W. F Chem. Revs. 51, 119 (1952).
7.
O.Redlich, A.T. Kister, and C.E. Turnquist, Chem. Eng. Progr. Symp. Ser. No. 2,
vol. 48, 49-61(1952)
8.
P Gross and F. kahn Mohatsh., Chem 86, 371 (1955)
9.
Johnson, A.I. Ward, D.M. and Furter, W.F. Can. K. Technol, 34, 429 (1957)
10.
J. M. Prausnitz and J. H. Targovnik “Salt Effects in Aqueous Vapor-Liquid
Equilibria” Industrial and Engineering Chemistry, VOL. 3, NO.2 (1958).
11.
G.M. Wilson, J. Am. Chem. Soc ., vol. 86, 127-130 (1964)
12.
W. F. Furter and R.A Cook “Salt Effect in distillation: A Literature Review” Int.
J. Heat Mass Transfer. Vol 10, pages 23-36. (1966)
13.
Ishika Wajima- Heavy industries co ltd. Tokyo, Japan Appl, 97, Apr, 14 (1967)
14.
H. Renon and J.M. Prausnitz, AIChE J., vol. 14, p. 135-144 (1968)
15.
Ohe, S., Japan, Chemical Oqarterly, 4(2), 20, 763 (1968)
16.
D.S. Abrams and J.M. Prausnitz, AIChE j., vol. 21, 116-128 (1975)
17.
UNIQUAC Functional-group Activity Coefficients; proposed by Aa. Freenslund,
R.L. Jones, and J.M. Prausnitz, AIChE J., vol.21, 1086-1099 (1975)
18.
H.C. Van Ness and M.M. Abbott, Classical Thermodynamics of Nonelectrolyte
Solutions: With Application to Phase Equilibria, Sec. 5-7, McGraw-Hill, New
York (1982)
19.
Maria C. Iliuta l, Fernand C. Thyrion “Salt effects on vapour-liquid equilibrium of
acetone- methanol System”, Fluid Phase Equilibria vol. 121, pages 235-252,
(1996)
20.
P Rath, S C Naik “Prediction of Salt Effect in Vapour-liquid Equilibria of System
Ethyl Acetate-ethanol at Atmospheric Pressure” IE (I) Journal.CH Vol 84, March
2004
64
21.
A Gorhan U.S. Patent 1,210,792 (1917)
22.
Swayambhuba Misra ,”studies on effect of Salt on Vapour –Liquid Equilibrium of
a binary system”,M-Tech thesis, submitted to the Chemical Engineering
Department, NIT Rourkela (2005)
23.
V.Rothmund ., Loslichkeit Uno Loslichkeitsbeein – Flusug.
24.
http://www.utc.edu/Faculty/Tom-Rybolt/371LAB/ExptLV.pdf
25.
J.M. Smith, H.C. Van Ness, M.M. Abbott adapted by B.I. Bhatt, Introduction to
Chemical Engineering Thermodynamics 7th edition.
65
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