VLE Modeling of Aqueous Solutions of Unloaded and Loaded Hydroxides of Lithium, Sodium and Potassium Shahla Gondal, Muhammad Usman, Juliana G.M.S. Monteiro, Hallvard F. Svendsen, Hanna Knuutila 8th Trondheim Conference on CO 2 Capture, Transport and Storage (TCCS-8) 16 - 18 June 2015
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VLE Modeling of Aqueous Solutions of Unloaded and Loaded Hydroxides of Lithium, Sodium and Potassium Shahla Gondal, Muhammad Usman, Juliana G.M.S. Monteiro,
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VLE Modeling of Aqueous Solutions of Unloaded and Loaded Hydroxides of
Lithium, Sodium and Potassium
Shahla Gondal, Muhammad Usman, Juliana G.M.S. Monteiro, Hallvard F. Svendsen, Hanna Knuutila
8th Trondheim Conference on CO2 Capture, Transport and Storage (TCCS-8) 16 - 18 June 2015
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Contents Introduction
VLE and Apparent Henry’s Law Constant Modeling Electrolyte-Non Random Two Liquid (e-NRTL) Model Parameter fitting in the (e-NRTL) Model
Experimental data used for modeling Experimental data used for Equilibrium modeling of Li+
Experimental data used for Equilibrium modeling of Na+
Experimental data used for Equilibrium modeling of K+
The Equilibrium Model Constants used in the Model
Results Parity plots Summary of the Statistics of Results
Conclusions
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Introduction
The process of absorption of carbon dioxide (CO2) into aqueous hydroxide and carbonate (loaded hydroxide) solutions has regained great interest during the last decade;
Firstly, the reaction between carbon dioxide and hydroxide ions resulting in production of bicarbonate and carbonate is of special interest as it occurs in all alkaline solutions
Secondly, these solutions do not degrade and are environment friendly as compared to organic solvents used for carbon capture
Promotion of bicarbonate formation, by e.g. carbonic anhydrase can make these systems more reactive
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VLE and Apparent Henry’s Law Constant Modeling For the designing of an absorption column and/or stripper in the CO2 capture
system, we need to predict;
The composition of vapor and liquid phases in the columns The temperature and pressure profiles in the columns Energy requirements for stripping
An equilibrium model gives a reasonable representation of the system behavior
The equilibrium model needs modeling of both the Vapor-Liquid-Equilibrium (VLE) and the Henry’s Law constant
In this work, experimental data for VLE and the Henry’s law constant are regressed simultaneously
The activities calculated by using this model would be consistent with the Henry’s law constant
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The e-NRTL (Electrolyte-Non Random Two Liquid ) Model
The predictive equilibrium model must include corrections for non-idealities in both liquid and vapor phases
Accurate calculation of activities of involved species over a wide range of temperatures, pressures and concentrations are required
The e-NRTL model provides a general framework with which experimental data of electrolyte systems can be satisfactorily represented with binary parameters only
The e-NRTL model has been used successfully to model many important industrial electrolyte systems, among which are the hot carbonate CO2 removal system, the sour water stripper system, and flue gas desulfurization
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Parameter fitting in the e-NRTL Model The e-NRTL is an excess Gibbs energy model and has a large number of
parameters which need to be fitted using experimental data
For parameter fitting in the e-NRTL model, particle swarm optimization (PSO) algorithm proposed by Kennedy, 1995 and Pinto et al.,2013 was employed
The temperature dependent energy parameters were modelled as:
Common H2O-CO2 parameters were fixed as ASPEN Plus default values
Molecule-Salt pair parameters involving, Li+, Na+ and K+ cations were obtained by regression of the experimental data
Since the e-NRTL is a local composition model, the interaction parameters estimated in this work are valid regardless of the composition of the solvent
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Reference
, , , *Conc. as LiOH
[wt. % ]
*Loading[mol CO2/mol Li+]
Temp.[°C]
No. of data
points
Vapor pressure of water over LiOH solutions, [kPa](Aseyev, 1999) and This study (Ebulliometric data) 0.58 – 462.4 0.25 – 10 0 0 – 150 43
Partial pressure of CO2 over CO2-Li2CO3-LiHCO3 equilibrium solutions, [kPa]
(Walker et al., 1927) 0.03 – 0.04 0.013–0.96 0.51 – 0.92 25 – 37 27**N2O solubility in terms of apparent Henry’s law constant, [kPa.m3/mol]
Experimental data used for equilibrium modeling of Li+
* The concentrations of Li2CO3 solutions are recalculated as LiOH solutions with 0.5 loading
[mol CO2/mol Li+]. **The physical solubility for CO2 was calculated from N2O solubility data
by using N2O analogy.
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Experimental data used for equilibrium modeling of Na+
Reference
, , , *Conc. as NaOH
[wt. % ]
*Loading[mol CO2/mol Na+]
Temp.[°C]
No. of data
points
Vapor pressure of water over NaOH and Na2CO3 solutions, [kPa](Don and Robert, 2008), (Knuutila et al., 2010a), (Don and Robert, 2008) and (Taylor, 1955)
0.587 – 190.65 4.8 – 37.5 0 20 – 105 169
Partial pressure of CO2 over CO2-Na2CO3-NaHCO3 equilibrium solutions, [kPa](Walker et al., 1927), (Hertz et al., 1970), (Mai and Babb, 1955), (Ellis, 1959) and (Knuutila et al., 2010a)
0.031 – 108.9 0.02 – 9.8 0.55 – 0.98 20 –197 165
Total pressure for CO2 solubility in NaOH solutions at high pressures, [kPa]
(Rumpf et al., 1998) and (Lucile et al., 2012) 12.7– 10163 3.69 – 3.84 0 – 2.11 20 – 160 102
Partial pressure of CO2 for CO2 solubility in *NaHCO3 solutions at high pressures, [kPa](Gao et al., 1997), (Wong et al., 2005) and (Han et al., 2011)
100 – 57600 0.2 – 4.2 1.04 – 10.28 5 – 130 148
**N2O solubility in terms of apparent Henry’s law constant, [kPa.m3/mol](Knuutila et al., 2010b) and (Gondal et al., 2015) 4.29– 75.56 0.4 – 16.5 0 - 0.5 25 – 80 62
*The concentrations of Na2CO3 solutions are recalculated as NaOH solutions with 0.5 loading [mol CO2/mol Na+] and those of NaHCO3 solutions are recalculated
as NaOH solutions with 1 loading [mol CO2/mol Na+]. **The physical solubility for CO2 was calculated from N2O solubility data by using N2O analogy.
Reference
, , , *Conc. as KOH
[wt. % ]
*Loading[mol CO2/mol K+]
Temp.[°C]
No. of data
points
Total pressure above aqueous solutions of *K2CO3 and CO2, [kPa](Pérez-Salado Kamps et al., 2007) 267.2 – 9237 4.61 – 16.55 0.84 – 2.29 40 – 120 41
Total pressure over CO2-K2CO3-KHCO3 equilibrium solutions, [kPa](Tosh et al., 1959) 23.86 – 979.1 17.34 – 37.2 0.5 – 0.89 70 – 140 148
Partial pressure of CO2 over CO2-K2CO3-KHCO3 equilibrium solutions, [kPa](Walker et al., 1927) , (Tosh et al., 1959), (
Park et al., 1997) and (Jo et al., 2012)0.03 – 2230 0.03 – 37.2 0.5 – 1.01 25 – 120 217
**N2O solubility in terms of apparent Henry’s law constant, [kPa.m3/mol](Gondal et al., 2015) and (Knuutila et al., 2010b) 4.2– 39.65 0.5 – 26.93 0 - 0.5 25 – 80 43