1. Introduction
CO2 is considered as one of the gases that causes the
greenhouse effect and changes in the weather conditions as one of the
most important pollutants in the atmosphere. Considering that the amount
of CO2 production increases day by day, it is important
to use an effective and economical way to absorb this gas. Chemical
absorption is one of the most commonly used methods for
CO2 absorption. One way that improves the absorption of
CO2, it is to mix an amine such as triethanolamine (TEA)
with a solvent such as piperazine whose solubility is more limited in
water and can act as an accelerator to increase the Co2mass transfer rate for amine systems. This absorbent solution has the
potential and the ability to take advantage of both solvents. The
process of chemical absorption by alkanolamine solutions is used to
sweeten gases containing combination of H2S and
CO2. Amines are obtained from the combination of alcohol
and ammonia. In TEA and N-methyl-ethanolamine, ammonia molecules are
directly attached to the nitrogen atom instead of hydrogen atoms, and
are called third-type amines.
In 2004, Yeon et al. studied an absorption reaction in a large
laboratory experiment of carbon dioxide absorption proces alkanolamine,
piperazine and TEA and kinetics. Absorption process was carried out in
range of 303-382 K and in a mixture of piperazine with 0.26 and 0.64
molar plus 0.38, 1.13 and 2.26 molar TEA. Also, the absorption rate was
obtained as a function of the partial pressure of carbon dioxide.
According to the results obtained in their research, the initial
concentration of adsorbent and the partial pressure of carbon dioxide
gas have increased the rate of absorption. Tounsi et al. (2005) measured
the new equilibrium data for CO2 in the diethanolamine
(DEA)+methanol (MeOH)+H2O system under temperature
conditions of 323.15 and 15.32 K, and pressure up to 10 MPa. They used
kinetic and mass balance methods to generate their solubility data. They
used kinetic and mass balance methods to generate their solubility data.
To fit the experimental data, they used the Kenneth-Eisenberg model to
have a good match. In 2008, Archane et al. measured the
CO2 solubility data in a mixture of
DEA+MeOH+H2O with a constant concentration of DEA of
30% by weight and a change in the concentration of methanol from 0 to
30% by weight at a temperature of 158.29 K. They saw low changes in the
balance of data by changing the concentration of methanol. Also, from
the equation of electrolyte state was used to model and calculate the
equilibrium properties of the system and to report new parameters. In
2008, You et al. studied the effect of
adding 2-amino-2-methyl-1-propanol (AMP) on CO2absorption by aqueous ammonia solution at 298 K. Experimental data are
not presented in the table and they graphically capture the adsorbent
efficiency in removing CO2 from an gas containing 15%
vol. CO2 and 85% vol N2. They showed
that the addition of AMP would reduce the evaporation of ammonia and, to
a certain extent, also increase the CO2 absorption
capacity. Yang et al. (2010) measured the solubility of
CO2 in an aqueous mixture of AMP and piperazine (as
activator) at 313-335 K and up to 139.9 kPa. The concentration of AMP in
the mixture of solvents was 26.8% and 17.9%, while the concentration
of piperazine was 12.9% and 4.3% by weight, respectively. They
observed that at constant temperature and constant concentration of
total amine, the solubility of CO2 increased with
increasing relative pressure. Also, at constant temperature and constant
AMP concentration, adding piperazine increased the solubility of
CO2. Schüler et al. (2012) reported the data on the
solubility of CO2 in a mixture of water and methanol at
298 K and 333 K at atmospheric pressure. They showed that the solubility
of CO2 increases with the increase in methanol amount in
the mixture, but at higher temperatures it decreases solubility. In
2013, Kariznovi et al. measured and predicted the density, viscosity,
and solubility of CO2 for various alcohols such as
methanol, ethanol, 1-propanol at 303.2 K and 323.2 K and pressure up to
6 MPa. They also observed that increasing the dissolution of
CO2 in alcohols has led to an increase in density and a
decrease in the viscosity of saturated fluid. Empirical solubility data
and saturated fluid density data were predicted by two EOSs of PR and
SRK. Their modeling results showed that both state equations in this
range of pressure and temperature are in good agreement with the
experimental data, but the saturation fluid density calculated by the
SRK equation of state was much better than the PR equation of state. In
2013, Kim et al. examined the absorption of carbon dioxide in laboratory
by using different alkanolamines and compared the results of each. They
were able to measure the solubility of carbon dioxide in alkanolamines
at temperatures of 313, 333, and 353 K. The results of this study showed
that the amount of heat of absorption is directly related to the heat
required for absorbent recovery, and also depends on the type of amine
and the amount of carbon dioxide. In 2014, Murshid et al. also measured
the solubility of CO2 in aqueous solution of AMP+
piperazine at two different temperatures of 303.15, 333.15 and various
concentrations. Their measurements were carried out at pressure range of
5-60 bar and found that adding piperazine to the AMP aqueous solution
increased the loading rate at high pressures. It also evaluated the
effect of pressure on the solubility, while solubility decreases with
increasing temperature. In 2014 Haghtalab et al. using a high pressure
chamber, the equilibrium data of CO2 solubility in
aqueous solution DIPA+AMP+PZ at K 313.15, 328.15 and 343.15 K and
measured the pressure range 1-40 bar. They also obtained empirical data
on the solubility of CO2 in dual aqueous solution of
diisopropanolamine (DIPA)+AMP and DIPA+ piperazine in the above
conditions. They subjected the results to partial CO2pressure versus acid gas loading (mol CO2/mol Amine).
They observed that the combination of AMP- piperazine as an activator
increases CO2 loading, which means that the absorption
of CO2 in a DIPA aqueous solution increases. They also
provided another work for the MDEA+AMP+PZ system in 2015 in the same
conditions, and reported that piperazine in aqueous solutions of
alkanolamines led to a slight variation in CO2 pressure
versus CO2 loading, and with increasing pressure, the
absorption of CO2 equilibrium increases and with
decreasing temperature, the absorption of CO2 in the
mixture of alkanolamines decreases. Shokohi et al. (2015) measured the
solubility of CO2 in a mixture of aqueous solution of
AMP+MDEA with different weight percentages, and temperatures of 313.13,
333.15, and 353.15 K up to a pressure of 2.5 MPa. They reported that the
solubility of CO2 decreases with increasing temperature,
while increasing with increasing pressure. Addition of AMP can also
improve the loading capacity of the MDEA. In 2015, Al-Salem conducted a
study on the removal of carbon dioxide from the exhaust gas from Kuwait
refineries using a mixture of several amines. This research was
conducted to identify and provide an appropriate method for reducing the
pollution of the Kuwaiti oil industry. In 2016, Arentte investigated the
absorption of carbon dioxide economically by activated charcoal with the
aim of providing a model for comparing the use of new and renewable
energies and carbon dioxide absorption methods. In 2016, Chu et al.
examined absorption of carbon dioxide with monoethanol amine. In this
study, they simulated numerical modeling of a full absorbed tower to
remove carbon dioxide from monoethanolamine gas and compared their
results with laboratory values and other simulation results. Then,
this absorption column was used for the industrial scale used and the
effect of operational pressure and tower height was studied on the
carbon dioxide mass transfer and energy consumption. The results showed
that optimal operating pressure is atmospheric pressure and the optimal
height of the absorbed columns in this work is about 8 meters. For the
minimum energy consumption, the surface area per unit volume and the
porosity of fill materials should be as large as possible.
In this research, a general model is proposed to calculate the carbon
dioxide solubility in amine solutions, which will be used the CPA
equation of state to predict the properties of the system. Finally, the
results and outputs of the simulated model, which include the amount of
CO2 solubility in this system and in different
conditions, will be compared with and verified by the laboratory data in
the articles.