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ZANCO Journal of Pure and Applied Sciences
The official scientific journal of Salahaddin University-Erbil
ZJPAS (2018), 30 (3); 73-78
http://dx.doi.org/10.21271/ZJPAS.30.3.8
Prediction the Solubility Data of Solid Solutes in Supercritical CO2 by Combined
Mendez-Santiago-Teja and Peng Robinson Equations of State.
1 Serwan Ibrahim Aljaff, 2Mohammed Jawdat Barzanjy, 3Arkan Jasim. Hadi
1Department of Petroleum and Chemical Engineering, College of Engineering, University of Salahaddin, Erbil, Kurdistan
Region, Iraq.
2Department of Mechanical and Mechatronic Engineering, College of Engineering, University of Salahaddin, Erbil,
Kurdistan Region, Iraq.
3 Chemical Engineering Department, Faculty of Engineering, Soran University, Soran, Kurdistan Region, Iraq.
1. INTRODUCTION
A supercritical fluid (SCF) is a
substance (liquid or gas) which is in a state
above its critical temperature (TC) and critical
pressure (PC). At this critical point, liquids and
gases coexist, and a supercritical fluid shows
unique properties that are different from those
of either liquids or gases under standard
conditions. It has the gaseous property of being
able to penetrate porous and fibrous solids and
the liquid property of being able to dissolve
materials into their components. The solvating
power of the SCF follows the changes in the
density (Goodship & Ogur, 2004). Over the last
years, supercritical fluid (SCF) extraction has
been demonstrated to be a useful technique to
develop different types of industrial processes.
These include applications in many fields,
among them, the pharmaceutical field for the
A R T I C L E I N F O
A B S T R A C T
Article History:
Received:26/03/2017
Accepted: 07/05/2018
Published:12/06/2018
The solubility data of twelve solid solutes extracted by supercritical CO2
(SCCO2) are predicted by combined Mendez-Santiago and Teja (Density base)
equation of state, with Peng Robinson (PVT base) Equation of state depending on
Microsoft® Excel 2010 software .Prediction of solubility data verse operation
pressure by Mendez-Santiago and Teja equation of state (MST-EoS) depended on
the compressibility factors that came from Peng-Robinson equation of state (PR-
EoS) at isothermal condition. The combined model (MST with PR-EoS) gave
accuracy better than 80% of the references data with enhancement ratio ranged
from 9% to 1300%. All of these comparisons built on absolute average relative
percent ratio values (AARDs %). The combined model compared with famous
equations of state like (PR, MST, Modified MST, Chrastil and Modified PR
EoSs) and passed to minimize the AARDs% values. Sometimes, the combined
model resulted errors more than the references, but this were only when the
extraction temperatures closed to the melting points of the solid solutes and
approached to the liquid state.
Keywords:
Phase Equilibria
Supercritical Extraction
PR-EoS
MST EoS;
Modeling.
*Corresponding Author:
Serwan I. Aljaff
serwan.abdulkhader
@su.edu.krd
74 Aljaff S. et al. /ZJPAS: 2018, 30(3): 73-78
extraction of biologically active ingredients,
the food-processing field for decaffeination and
extraction of essential oils and aroma materials
from spices, and the environmental protection
field for the removal of different pollutants
from wastes (Martnez et. al., 2009)
Measurement of reliable experimental
solubility in the supercritical region is not so
easy; moreover, it is time consuming as well as
expensive to bring into effect. Therefore, it is
necessary to find a convenient tool for
predicting the solubility of solid in supercritical
fluids. Until now, there are three main groups
of solubility models. The first group considers
the supercritical fluid as a compressed gas,
which includes the cubic equation of state
method, one fluid theory based on augmented
van der Waals. The second group is the
density-based correlations. The third group
looks upon the supercritical fluid as an
expanded liquid. The traditional methods in the
first group are efficient and widely used for
engineering calculations, but the necessary
parameters for solutes are often unavailable
especially for large and complex molecules.
The density-based models do not need critical
parameters for solid solutes and makes the
calculations simpler (Zhao et al., 2010).
(Garlapati G. and Madras G.,2010)
worked on the modeling of three
cholorophenols namely, 4-chlorophenol, 2, 4-
dichlorophenol, and 2, 4, 6-trichlorophenol in
SCCO2 in pressure range (8.8 to 15.8 MPa) at
temperatures 308 to 318K, and predicted the
data with MST EoS.
(Wang W. et al.,2009) predicted the
solubility of four diglycolic acid esters were
measured at high temperatures ranging from
(343 to 363) K and pressures from (11.8 to
19.7) MPa in supercritical carbon dioxide by
semi empirical relation derived from MST
EoS. (Murga R. et al.,2004) worked on two
phenolic compounds, 4-hydroxy-3,5-
dimethoxybenzoic acid (syringic acid) and 4-
hydroxy-3-methoxybenzoic acid (vanillic acid)
extraction by SCCO2, in pressure range (8.5 to
50)MPa at temperatures from 313 to 333K.PR-
EoS and MST-EoS were used to correlate the
experimental data but with Considering a
Linear Dependence between the Enhancement
Factor and the Density of the Solvent.
(Duarte A. R. C. et al.,2004) correlated
the Experimental solubility data of
flurbiprofenin in supercritical carbon dioxide in
the pressure range from (8.0 to 25.0) MPa, at
temperatures of (303.0, 313.0, and 323.0) K
with an empirical density-based Chrastil
model. In this work the data at temperature
303K had ignored because it out of
supercritical phase of CO2.
(Coutsikos Ph. et al.,1997) used
modified PR-EoS to correlate the solubility
data of p-quinone (1,4-benzoquinone) and
9,10-anthraquinone at 308 K and 318 K in
supercritical carbon dioxide over a pressure
range of about (8.5-30) MPa.
In this work, the Mathematical model
calculations divided into two parts. The first
had done by PR-EoS which started the
calculations and continued up to finding out the
compressibility factors of each operation
pressure point, and then MST equation used
these compressibility factor values to estimate
and predict solid solute solubility data verse
pressures in and out of the references data.
2. MATERIALS AND METHODS
In this work, the solid solute solubility
data from the references correlated and
predicted by MST equation:
Where:
Where E is the enhancement factor. A
and B equation constants, ρ1 is supercritical
phase molar density in (mol.m-3), y2 solid
solubility mole fraction, P is operation pressure
in MPa , T system temperature in Kelvin and
75 Aljaff S. et al. /ZJPAS: 2018, 30(3): 73-78
Psub is solid sublimation pressure in MPa
(Garlapati and Madras ,2010).
Some literature preferred the modified MST
equation to exclude sublimation pressure as
follows (Hansen et al., 2001):
where:
Where the reference molar density is selected
to equal to (35492 mol.m-3 at 1 atm and -78 oC,
and this value is calculated from CO2 gas
density at 1 atm and -78 OC (1562 Kg/m3
divided by CO2 molecular weight) (Zhao et
al.,2010 and Caballero et al., 1991), and this
excluded the need of the sublimation pressures
values. Density of SCCO2 (molar density)
estimated by solving Z (compressibility factor)
cubic equation which based on PR-EOS for
each operation pressure (Green and Perry,
1973).
Z3 - (1 - B) Z2 + (A - 3B2 - 2B) Z -(AB - B2 -
B3) = 0
Where:
A = aP / (RT) 2, B = bP/RT and Z=PV/RT (a, b
are Peng –Robinson EoS parameters). The
molar density estimated by Z value from real
gas law (Martnez et. al., 2009):
ρ =P/ZRT
Finally, the data is compared with the
data of literatures depending on values of
average absolute relative deviation percent
(AARD %), where:
3. RESULTS AND DISCUSSION
The comparison of AARDs% of this work
results with references results had showed
positive impacts in most states, especially at
low temperatures, as it is obvious in the next
figures, but at high temperature more
deviations remarked . That may due to solid
solute mole fractions cancelation (it was too
low in comparison with SCCO2 mole fraction)
in PR-EoS and neglecting the solid solute
density from modified MST equation for the
same reason.
Figures (1, and 2), showed that the AARDs%
increased when the extraction temperature
increased; this may be because of the extraction
temperature was close to 4-chlorophenol and 2,
4 dichlorophenol melting point threshold (315
K) [12] and they were about to reach the
boundary of liquid phase.
76 Aljaff S. et al. /ZJPAS: 2018, 30(3): 73-78
Figure (3), had showed the same behavior for
2,4,6 trichlorophenol, although the solute
melting point is far (342k). Only at 318k this
work model generated a big AARD% in
comparison with the references. It is important
to be mentioned, that (Garlapati, et al., 2009)
recorded one AARD% value for each solute at
all extraction temperatures as average value,
but it is known, that the AARDs% value even
for same solute changes when the temperature
differs .
Figures (4 to 7), showed a good
agreement with this work model in comparison
with the references model for all states
excepted at 343k for both dinonyl-2,2'
oxidiacetate and diurdecyl-2,2' oxidiacetate,
although (Wang, et al.,2009) use semi
empirical relation.
77 Aljaff S. et al. /ZJPAS: 2018, 30(3): 73-78
In figures (8 and 9), the combined model
showed better results than each of MST and
PR-EoS at all temperatures except Vanillic acid
at 313k and by PR-EoS.
Figures (10, 11, and 12) showed perfect
agreement with this work model in all states,
although (Coutsikos, et al.,1997) used modified
PR-EoS which needs more physical properties
for phase equilibria calculation.
78 Aljaff S. et al. /ZJPAS: 2018, 30(3): 73-78
4. CONCLUSIONS
The combined model (MST with PR-EoS)
succeeded to predict twelve high molecular
weight hydrocarbon compounds better than
each of PR, MST, Modified MST, Chrastil
and Modified PR equations of state. Twenty-
five times out of thirty-one the combined
model proved its superiority for different
hydrocarbons at different temperatures. Simple
errors started to appear when the system
approached to melting point threshold of the
solid solutes (in comparison with the
references) as 4-chlorophenol at 313 ºC while
its melting point is 315ºC, but the errors still
simple in comparison with the references data.
For each solid solute when the
extraction temperature increased, AARD%
increased, and extracted solid solute mole
fraction increase. The reason was that, the solid
solute mole fraction is canceled from mixture
molar volume calculation by PR-EoS in the
first part and from mixture molar density
calculation by MST EoS as the second part of
the combined model due to trace amount
(<<<1%).
Also, taking CO2 gas molar density as a
reference molar density for the combined
model enhanced the prediction of solid solute
solubility data and minimizes the AARDs%.
This indicates that, for the molar density,
Supercritical CO2 behaves like gases.
Conflict of Interest
There is no conflict of interest.
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