Investigating the Solubility of CO2 in the Solution of Aqueous K2CO3 Using Wilson-NRF Model

Document Type: Research Paper


1 M.S. Student, Department of Chemical Engineering, Ferdowsi University of Mashhad, Mashhad, Iran

2 Assistant Professor, Department of Chemical Engineering, Ferdowsi University of Mashhad, Mashhad, Iran



Hot potassium carbonate (PC) solution in comparison with amine solution had a decreased energy of regeneration and a high chemical solubility of . To present vapor and liquid equation (VLE) of this system and predict  solubility, the ion specific non-electrolyte Wilson-NRF local composition model (isNWN) was used in this study; the framework of this model was molecular. Therefore, it was suitable for both electrolyte and non-electrolyte solutions. The present research employed the NWN model and the Pitzer-Debye-Hückel theory in order to assess the contribution of the excess Gibbs energy of electrolyte solutions in a short and long range. The data of  solubility in water and the system of aqueous  were correlated in the model considering a temperature range of  and a pressure range of and . The average absolute error of ( ) and ( ) systems were  and  respectively. The results and comparisons with other models proved that the experimental data were exactly correlated in the model.


1. Introduction

The global climate is changing due to the continuous increase in the temperature of the earth, which is of great concern for the environment. The major reason for the global warming is the increasing production of  more than the nature can accept.  is increasingly released into the atmosphere through using fossil fuels and industrial processes (Višković et al., 2014). There are different methods available for the elimination of  from flue gases of power plants and gas streams. CO2 capture by using chemical absorption is a mature technology currently used (Zhenqi et al., 2012; Meihong et al., 2011; Zhao et al., 2012). Utilization of amine solution is the most popular method for chemical absorption (Afkhamipour et al., 2013; Austgen  et al., 1991; Dang et al., 2003; Sidi-Boumedine et al., 2004) . However, amines have some disadvantages; for instance, these solutions have shown excessive energy requirement for regeneration, easy degradation, and strong corrosion to equipment. Appropriate absorbers must have a fast reaction rate and a lower heat of regeneration. Hot potassium carbonate solution has a decreased energy of regeneration (Kohl et al., 1997) and a high chemical solubility of  (Todinca et al., 2007). An equilibrium thermodynamic model is required to anticipate the total pressure of the solution as well as the partial pressure of . Similar systems can be thermodynamically modeled through many available models to achieve acceptable simulation and optimization for a chemisorption process (Afkhamipour et al., 2013). These models can be categorized into three groups: 1) a state equation through phi-phi method as reported by Gubbins and Buttom (Button et al., 1999) and Huttenhuis et al. (Huttenhuis et al., 2008); 2) semi-empirical models such as the Kent-Eisenberg model (Kent et al., 1976) 3) excess Gibbs energy or gamma-phi method such as the works of Austgen et al. (Austgen et al., 1991) and Li and Mather (Li et al., 1998; Qian et al., 1995). This research has investigated the free energy of surplus Gibbs to demonstrate the systems VLE ( ) and ( ) through the thermodynamic modeling. In these systems, the local composition statement was used regarding the short-range contribution, and one of the Debye-Hückel (DH) equations was employed for long range electrostatic interactions (Zhao et al., 2000; Messnaoui et al., 2008). Haghtalab and Mazloumi (Haghtalab et al., 2009) applied Wilson-NRF model to electrolyte solutions, which were considered as an ion-pair. The model had a salt specific parameter as well as two adjustable parameters per each salt. However, Mazloumi (Mazloumi et al., 2015) had used this model using ion specific parameters for strong aqueous binary and ternary electrolytes. The results were highly correlated with the experimental data. The Wilson-NRF model was utilized as the thermodynamic model for non-electrolytes in the current work as presented in the study of Mazloumi (Mazloumi et al., 2015).

2. Thermodynamic framework

The  solubility and the other solute species quantity may be predicted by the thermodynamic modeling (Anderko et al., 2002). A few equations must be considered to model a system like potassium carbonate solution thermodynamically, and a thermodynamic approach should be utilized for the VLE calculations.

2.1. Standard state

The equilibrium of the system was defined through chemical potential. In this condition, each component of all the phases should have equal chemical potential values. These values of solvent (water) in an aqueous system can be defined by a mole fraction-symmetrical equation (Afkhamipour et al., 2013):



In which,  is the standard chemical potential of pure water.  also represents symmetrical water activation coefficient, and  is the water mole fraction;  stands for absolute temperature, and  is the universal gas constant. The chemical potential values of the solute in the system is calculated by the following equation:



2.2. Chemical equilibrium

The chemical reactions of the liquid phase must be taken into consideration for speciation calculations. The ionic complex species are produced when  reacts with PC in an aqueous solution. The subsequent reactions are given by:







The stoichiometric technique was utilized in this study to create the calculation. This technique was correctly investigated by several researchers (Al-Rashed et al., 2012; Cullinane et al., 2002).

Equation 6 calculates the chemical equilibrium constant,

Afkhamipour, M. and Mofarahi, M., Comparison of Rate-based and Equilibrium-stage Models of a Packed Column for Post-combustion CO2 Capture Using 2-Amino-2-Methyl-1-Propanol (AMP) Solution, International Journal of Greenhouse Gas Control, Vol. 15, p. 186-199, 2013.

Al-Rashed, O. A. and Sami H. A., Modeling the Solubility of CO2 and H2S in DEA–MDEA Alkanolamine Solutions Using the Electrolyte–UNIQUAC Model, Separation and Purification Technology, Vol. 94, p. 71-83, 2012.

Anderko, A. P. W. and Marshall, R., Electrolyte Solutions: from Thermodynamic and Transport Property Models to the Simulation of Industrial Processes, Fluid Phase Equilibria, Vol. 194, p. 123-142, 2009.

Austgen, D. M., Gary, T. R., and Chau, C. C., Model of Vapor-liquid Equilibria for Aqueous Acid Gas-alkanolamine Systems 2: Representation of Hydrogen Sulfide and Carbon Dioxide Solubility in Aqueous MDEA and Carbon Dioxide Solubility in Aqueous Mixtures of MDEA With MEA or DEA, Industrial & Engineering Chemistry Research, Vol. 30, No. 3, p. 543-555, 1991.

Bamberger, A., Sieder, G., and Maurer, G., High-pressure (Vapor+ Liquid) Equilibrium in Binary Mixtures of (Carbon Dioxide + Water or Acetic Acid) at Temperatures from 313 to 353 K, The Journal of Supercritical Fluids, Vol. 17, No. 2, p. 97-110, 2000.

Boumedine, S., Réda., Horstmann, S., Fischer, K., Provost, E., Fürst, W., and Gmehling, E., Experimental Determination of Carbon Dioxide Solubility Data in Aqueous Alkanolamine Solutions, Fluid Phase Equilibria, Vol. 218, No. 1, p. 85-94, 2004.

Button, J. K. and Gubbins, K. E., SAFT Prediction of Vapor-liquid Equilibria of Mixtures Containing Carbon Dioxide and Aqueous Monoethanolamine or Diethanolamine, Fluid Phase Equilibria, Vol. 158, p. 175-181, 1999.

Cullinane, J. T. and Gary T. R., Thermodynamics of Aqueous Potassium Carbonate, Piperazine, and Carbon Dioxide, Fluid Phase Equilibria, Vol. 227, No. 2, p. 197-213,2005.

Cullinane, J. T., Carbon Dioxide Absorption in Aqueous Mixtures of Potassium Carbonate and Piperazine, Ph.D. Diss, University of Texas at Austin, 2002.

Dang, H. and Gary T. R., CO2 Absorption Rate and Solubility in Monoethanolamine/Piperazine/Water, Separation Science and Technology, Vol. 38, No. 2, p. 337-357, 2003.

Fosbøl, P. L., Bjørn M. M., and Kaj, T., Solids Modeling and Capture Simulation of Piperazine in Potassium Solvents, Energy Procedia, Vol. 37, p. 844-859, 2013.

Kamps, P.S., Meyer A. E., Rumpf, B., and Maurer, G., Solubility of CO2 in Aqueous Solutions of KCl and in Aqueous Solutions of K2CO3, Journal of Chemical & Engineering, Vol. 52, No. 3, p. 817-832, 2007.

Kenneth, P. S. and Li, Y. G., Thermodynamics of Aqueous Sodium Chloride to 823 K and 1 kilobar (100 MPa), Proceedings of the National Academy of Sciences, Vol. 80, No. 24, p. 7689-7693, 1983.

Kent, R. L. and Eisenberg, B., Hydrocarb Process, Vol. 55, p. 87-90, 1976.

Kohl, A. L. and Richard N., Gas Purification, Gulf Professional Publishing, 1997.

Li, Y. G. and Alan E. M., Correlation and Prediction of the Solubility of CO2 and H2S in an Aqueous Solution of 2-Piperidineethanol and Sulfolane, Industrial & Engineering Chemistry Research, Vol. 37, No. 8, p. 3098-3104, 1998.

Li, Y. G. and Alan, E. M., Correlation and Prediction of the Solubility of Carbon Dioxide in a Mixed Alkanolamine Solution, Industrial & Engineering Chemistry Research, Vol. 33, No. 8, p. 2006-2015, 1994.

Li, Z., Mingzhe, D., Shuliang, L., and Liming, D., Densities and Solubilities for Binary Systems of Carbon Dioxide + Water and Carbon Dioxide+ Brine at 59 C and Pressures to 29 MPa, Journal of Chemical & Engineering, Vol. 49, No. 4, p. 1026-1031, 2004.

Mazloumi, S. H., Representation of Activity and Osmotic Coefficients of Electrolyte Solutions Using Non-electrolyte Wilson-NRF Model with Ion-specific Parameters, Fluid Phase Equilibria, Vol. 388, p. 31-36, 2015.

Meihong, W., Lawal, A., Stephenson, P., Sidders, J., and Ramshaw, C., Post-combustion CO2 Capture with Chemical Absorption: A State-of-the-art Review, Chemical Engineering Research and Design, Vol. 89, No. 9, p. 1609-1624, 2011.

Messnaoui, B., Ouiazzane, S., Bouhaouss, A., and Bounahmidi, T., A Modified Electrolyte-UNIQUAC Model for Computing the Activity Coefficient and Phase Diagrams of Electrolytes Systems CALPHAD, Vol. 32, No. 3, p. 566-576, 2008.

Moore, R. C., Robetyum E. M., and Joonasim, M. S., Solubility of Potassium Carbonate in Water Between 384 and 529 K Measured Using the Synthetic Method, Journal of Chemical & Engineering, Vol. 42, No. 6, p. 1078-1081, 1997.

Posey, M. L. and Gary T. R., A Thermodynamic Model of Methyldiethanolamine-CO2-H2S-Water, Industrial & Engineering Chemistry Research, Vol. 36, No. 9, p. 3944-3953, 1997.

Qian, W., Li, Y. G., and Mather, A. E., Correlation and Prediction of The Solubility of CO2 and H2S in an Aqueous Solution of Methyldiethanolamine and Sulfolane, Industrial & Engineering Chemistry Research, Vol. 34, No. 7, p. 2545-2550, 1995.

Teodor, T., Tănasie, C., Pröll, T., and Căta, A., Absorption with Chemical Reaction: Evaluation of Rate Promoters Effect on CO2 Absorption in Hot Potassium Carbonate Solutions, Computer Aided Chemical Engineering, Vol. 24, p. 1065-1070, 2007.

Tosh, J. S., Field, J. H., Benson, H. E., and Haynes, W. P., Equilibrium Study of The System Potassium Carbonate, Potassium Bicarbonate, Carbon Dioxide, and Water, No. BM-RI-5484, Bureau of Mines, Pittsburgh, Pa.(USA), 1959.

Valtz, A., Chapoy, A., Coquelet, C., Paricaud, P., and Dominique, R., Vapor–liquid Equilibria in the Carbon Dioxide–water System, Measurement and Modeling from 278.2 to 318.2 K, Fluid Phase Equilibria, Vol. 226, p. 333-344, 2004.

Višković, A., Franki, V., and Valentić, V., CCS (Carbon Capture and Storage) Investment Possibility in South East Europe: A Case Study for Croatia, Energy, Vol. 70, p. 325-337, 2014.

Zhao, E., Bingtao., Yaxin, S., Wenwen, T., Leilei, Li., and Yuanchang, P., Post-combustion CO2 Capture by Aqueous Ammonia: A State-of-the-art Review, International Journal of Greenhouse Gas Control, Vol. 9, p. 355-371, 2012.

Zhao, E., Ming, Y., Sauvé, R. E., and Khoshkbarchi, M. K., Extension of the Wilson Model to Electrolyte Solutions, Fluid Phase Equilibria, Vol. 173, No. 2, p. 161-175, 2000.

Zhenqi, N., Yincheng, G., Qing, Z., and Wenyi, L., Experimental Studies and Rate-based Process Simulations of CO2 Absorption with Aqueous Ammonia Solutions, Industrial & Engineering Chemistry Research, Vol. 51, No. 14, p. 5309-5319, 2012.