zhang 2011 thermodynamic modeling for co2 absorption in aqueous mdea solution with electrolyte nrtl...

Thermodynamic Modeling for CO2 Absorption in Aqueous MDEA Solution withElectrolyte NRTL Model

Ying ZhangAspenTech, Limited, Pudong, Shanghai 201203, Peoples Republic of ChinaChau-Chyun Chen*Aspen Technology, Inc., Burlington, Massachusetts 01803

Accurate modeling of thermodynamic properties for CO2 absorption in aqueous alkanolamine solutions isessential for the simulation and design of such CO2 capture processes. In this study, we use the ElectrolyteNonrandom Two-Liquid activity coefficient model to develop a rigorous and thermodynamically consistentrepresentation for the MDEA-H2O-CO2 system. The vapor-liquid equilibrium (VLE), heat capacity, andexcess enthalpy data for the binary aqueous amine system are used to determine the NRTL interactionparameters for the MDEA-H2O binary. The VLE, heat of absorption, heat capacity, and NMR spectroscopicdata for the MDEA-H2O-CO2 ternary system are used to identify the NRTL interaction parameters for themolecule-electrolyte binaries and the previously unavailable standard-state properties of the amine ion, MDEAprotonate. The calculated VLE, heat of absorption, heat capacity, and the species concentrations for theMDEA-H2O-CO2 system are compared favorably to experimental data.

1. Introduction

CO2 capture by absorption with aqueous alkanolamines isconsidered an important technology to reduce CO2 emissionsfrom fossil-fuel-fired power plants and to help alleviate globalclimate change.1 Methyldiethanolamine (MDEA), which is analternative to monoethanolamine (MEA) for bulk CO2 removal,has the advantage of relatively low heat of reaction of CO2 withMDEA.2 To properly simulate and design the absorption/stripping processes with MDEA-based aqueous solvents, it isessential to develop a sound process understanding of thetransfer phenomena3 and accurate thermodynamic models4 tocalculate the driving forces for heat and mass transfer. In otherwords, scalable simulation, design, and optimization of the CO2capture processes start with modeling of the thermodynamicproperties, specifically vapor-liquid equilibrium (VLE) andchemical reaction equilibrium, as well as calorimetric properties.

Accurate modeling of thermodynamic properties requiresavailability of reliable experimental data. Earlier literaturereviews5,6 suggested that, while there are extensive sets ofexperimental data available for the MDEA system, some of thepublished CO2 solubility data for the aqueous MDEA systemmay be questionable. The use of a thermodynamically consistentframework makes it possible to correlate available experimentaldata, to screen out questionable data, and to morph these diverseand disparate data into a useful and thermodynamically con-sistent form for process modeling and simulation.

Excess Gibbs energy-based activity coefficient models pro-vide a practical and rigorous thermodynamic framework tomodel thermodynamic properties of aqueous electrolyte systems,including aqueous alkanolamine systems for CO2 capture.4,7 Forexample, Austgen et al.8 and Posey9 applied the electrolyteNRTL model10-12 to correlate CO2 solubility in aqueous MDEAsolution and other aqueous alkanolamines. Kuranov et al.,5Kamps et al.,6 and Ermatchkov et al.13 used Pitzers equation14to correlate the VLE data of the MDEA-H2O-CO2 system.

Arcis et al.15 also fitted the VLE data with Pitzers equationand used the thermodynamic model to estimate the enthalpy ofsolution of CO2 in aqueous MDEA. Faramarzi et al.16 used theextended UNIQUAC model17 to represent VLE for CO2absorption in aqueous MDEA, MEA, and mixtures of the twoalkanolamines. Furthermore, they predicted the concentrationsof the species in both MDEA and MEA solutions containingCO2 and in the case of MEA, compared to NMR spectroscopicmeasurements.18,19

In the present work, we expand the scope of the work ofAustgen et al.8 and Posey9 to cover all thermodynamic proper-ties. We use the 2009 version10 of the electrolyte NRTLmodel10-12 as the thermodynamic framework to correlaterecently available experimental data for CO2 absorption inaqueous MDEA solution. Much new data for thermodynamicproperties and calorimetric properties have become availablein recent years, and they cover wider ranges of temperature,pressure, MDEA concentration, and CO2 loading. The binaryNRTL parameters for MDEA-water binary are regressed fromthe binary VLE, excess enthalpy, and heat capacity data. Thebinary NRTL parameters for water-electrolyte pairs andMDEA-electrolyte pairs and the standard-state properties ofprotonated MDEA ion are obtained by fitting to the ternary VLE,heat of absorption, heat capacity, and NMR spectroscopic data.This expanded model should provide a comprehensive thermo-dynamic representation for the MDEA-H2O-CO2 system overa broader range of conditions and give more reliable predictionsover previous works.

In conjunction with the use of the electrolyte NRTL modelfor the liquid-phase activity coefficients, we use the PC-SAFT20,21equation of state (EOS) for the vapor-phase fugacity coefficients.While both PC-SAFT EOS and typical cubic EOS would givereliable fugacity calculations at low to medium pressures, wechoose PC-SAFT for its ability to model vapor-phase fugacitycoefficients at high pressures, which is an important consider-ation for modeling CO2 compression. The PC-SAFT parametersused in this model are given in Table 1. The parameters forwater and CO2 are taken from the literature21 and the Aspen

* To whom correspondence should be addressed. Tel.: 781-221-6420.Fax: 781-221-6410. E-mail: [email protected].

Ind. Eng. Chem. Res. 2011, 50, 163175 163

10.1021/ie1006855 2011 American Chemical SocietyPublished on Web 08/05/2010

Databank.22 The parameters for MDEA are obtained from theregression of experimental data on vapor pressure, liquid density,and liquid heat capacity.

2. Thermodynamic Framework

2.1. Chemical and Phase Equilibrium. CO2 solubility inaqueous amine solutions is determined by both its physicalsolubility and the chemical equilibrium for the aqueous phasereactions among CO2, water, and amines.

2.1.1. Physical Solubility. Physical solubility is the equi-librium between gaseous CO2 molecules and CO2 molecules inthe aqueous amine solutions:

It can be expressed by Henrys law:

where P is the system pressure, yCO2 the mole fraction of CO2in the vapor phase, CO2 the CO2 fugacity coefficient in the vaporphase, HCO2 the Henrys law constant of CO2 in the mixedsolvent of water and amine, xCO2 the equilibrium CO2 molefraction in the liquid phase, and CO2* the unsymmetric activitycoefficient of CO2 in the mixed solvent of water and amine.

The Henrys constant in the mixed solvent can be calculatedfrom those in the pure solvents:23

where Hi is the Henrys constant of supercritical component iin the mixed solvent, HiA the Henrys constant of supercriticalcomponent i in pure solvent A, i the infinite dilution activitycoefficient of supercritical component i in the mixed solvent,iA the infinite dilution activity coefficient of supercriticalcomponent i in pure solvent A, and xA the mole fraction ofsolvent A.

We use wA in lieu of xA in eq 3 to weigh the contributionsfrom different solvents.22 The parameter wA is calculated usingeq 4:

Here, ViA represents the partial molar volume of supercriticalcomponent i at infinite dilution in pure solvent A. ViA iscalculated from the Brelvi-OConnell model24 with the char-acteristic volume for the solute (VCO2BO ) and solvent (VsBO), whichare listed in Table 2.

Henrys law constants for CO2 with water and for CO2 withMDEA are required. The former has been extensively studied,25although knowledge about the latter is relatively limited.Because it is not feasible to directly measure CO2 physicalsolubility in pure amines, because of the reactions between them,the common practice is to derive the CO2 physical solubility inamines from that of N2O for their analogy in molecular structureand, thus, in physical solubility as believed:26

In 1992, Wang et al.27 reported the solubility of N2O in pureMDEA solvent as follows:

Based on the work of Versteef and van Swaaij,28 we obtainedthe following two equations for the solubilities of N2O and CO2in water:

We use eqs 5-8 to determine HCO2,MDEA and the parametersare summarized in Table 3.

The Henrys constant of CO2 in pure solvent A is correctedwith the Poynting term for pressure:25

where HCO2,A(T,P) is the Henrys constant of CO2 in pure solventA at system temperature and pressure, HCO2,A(T,pA,l) the Henrysconstant of CO2 in pure solvent A at system temperature andthe solvent vapor pressure, and VCO2,A the partial molar volume

Table 1. Parameters for PC-SAFT Equation of StateMDEA H2O CO2

source this work Gross andSadowski 21

AspenDatabank22

segment numberparameter, m

3.3044 1.0656 2.5692

segment energyparameter,

237.44 K 366.51 K 152.10 K

segment sizeparameter,

3.5975 3.0007 2.5637

association energyparameter, AB

3709.9 K 2500.7 K 0 K

kAB 0.066454 3 0.034868 3 0 3

CO2(V) T CO2(l) (1)

PyCO2CO2 ) HCO2xCO2CO2* (2)

ln(Hii) ) A xA ln(HiAiA ) (3)

wA )xA(ViA )2/3

B

xB(ViB )2/3(4)

Table 2. Parameters of the Characteristic Volume for theBrelvi-OConnell Modela

Characteristic Volume (m3/kmol)parameter MDEA H2O CO2

source this work Brelvi and OConnell 24 Yan and Chen25V1,i 0.369b 0.0464 0.175V2,i 0 0 -3.38 10-4a The Brelvi-OConnell model has been described in ref 24. The

correlation of the characteristic volume for the Brelvi-OConnell model(ViBO) is given as follows: ViBO ) V1,i + V2,iT, where T is the temperature(given in Kelvin). b Here, the critical volume was used as thecharacteristic volume for MDEA.

Table 3. Parameters for Henrys Constant (Expressed in Units of Pa)asolute i CO2 CO2solvent j H2O MDEAsource Yan and Chen25 this workaij 91.344 19.8933bij -5876.0 -1072.7cij -8.598 0.0dij -0.012 0.0

a The correlation for Henrys constant is given as follows: ln Hij ) aij+ bij/T + cij ln T + dijT, where T is the temperature (given in Kelvin).

HCO2,MDEAHN2O,MDEA

)HCO2,waterHN2O,water

(5)

HN2O,MDEA (kPa m3 kmol-1) ) (1.524 105) exp(-1312.7T )

(6)

HN2O,water (kPa m3 kmol-1) ) (8.5470 106) exp(-2284T )

(7)

HCO2,water (kPa m3 kmol-1) ) (2.8249 106) exp(-2044T )

(8)

HCO2,A(T, P) ) HCO2,A(T, pAo,l) exp( 1RT pA,lP VCO2,A dp) (9)

164 Ind. Eng. Chem. Res., Vol. 50, No. 1, 2011

of CO2 at infinite dilution in pure solvent A calculated fromthe Brelvi-OConnell model.

At low pressures, the Poynting correction is almost unity andcan be ignored.

2.1.2. Aqueous-Phase Chemical Equilibrium. The aqueous-phase chemical reactions involved in the MDEA-water-CO2system can be expressed as

We calculate the equilibrium constants of the reaction fromthe reference-state Gibbs free energies of the participatingcomponents:

where Kj is the equilibrium constant of reaction j, Gj(T) thereference-state Gibbs free energy change for reaction j attemperature T, R the universal gas constant, and T the systemtemperature.

For the aqueous phase reactions, the reference states chosenare pure liquid for the solvents (water and MDEA), and aqueousphase infinite dilution for the solutes (ionic and molecular).

The Gibbs free energy of solvents is calculated from that ofideal gas and the departure function:

where Gs(T) is the Gibbs free energy of solvent s at temperatureT, Gsig(T) the ideal gas Gibbs free energy of solvent s attemperature T, and Gsigfl(T) the Gibbs free energy departurefrom ideal gas to liquid at temperature T.

The Gibbs free energy of an ideal gas is calculated from theGibbs free energy of formation of an ideal gas at 298.15 K, theenthalpy of formation of an ideal gas at 298.15 K, and the idealgas heat capacity.

where Gsig(T) is the ideal gas Gibbs free energy of solvent s attemperature T, fGs,298.15ig the ideal gas Gibbs free energy offormation of solvent s at 298.15 K, fHs,298.15ig the ideal gasenthalpy of formation of solvent s at 298.15 K, and Cp,sig theideal gas heat capacity of solvent s.

The reference-state properties, fGs,298.15ig and fHs,298.15ig , areshown in Table 4. The ideal gas heat capacities are shown inTable 5. For water, the Gibbs free energy departure function isobtained from the ASME steam tables. For MDEA, thedeparture function is calculated from the PC-SAFT equationof state.

For molecular solute CO2, the Gibbs free energy in aqueousphase infinite dilution is calculated from Henrys law:

where Gi,aq(T) is the mole fraction scale aqueous-phase infinitedilution Gibbs free energy of solute i at temperature T, fGiig(T)the ideal gas Gibbs free energy of formation of solute i attemperature T, Hi,w the Henrys constant of solute i in water,and Pref the reference pressure.

For ionic species, the Gibbs free energy in aqueous-phaseinfinite dilution is calculated from the Gibbs free energy offormation in aqueous-phase infinite dilution at 298.15 K, theenthalpy of formation in aqueous-phase infinite dilution at298.15 K, and the heat capacity in aqueous-phase infinitedilution:

Here, Gi,aq(T) is the mole fraction scale aqueous-phase infinitedilution Gibbs free energy of solute i at temperature T, fGi,298.15,aqthe molality scale aqueous-phase infinite dilution Gibbs freeenergy of formation of solute i at 298.15 K, fHi,298.15,aq theaqueous phase infinite dilution enthalpy of formation of solutei at 298.15 K, and Cp,i,aq the aqueous-phase infinite dilution heatcapacity of solute i. The term RT ln (1000/Mw) is added because

Table 4. Parameters for the Reference States Propertiesproperty fG298.15ig (J/kmol) fH298.15ig (J/kmol) fG298.15,aq (J/kmol) fH298.15,aq (J/kmol) source

MDEA -1.6900 108 -3.8000 108 Aspen Databank22H2O -2.2877 108 -2.4200 108 Aspen Databank22CO2 -3.9437 108 -3.9351 108 Aspen Databank22H3O+ -2.3713 108 -2.8583 108 Aspen Databank22OH- -1.5724 108 -2.2999 108 Wagman et al.29HCO3- -5.8677 108 -6.9199 108 Wagman et al.29CO32- -5.2781 108 -6.7714 108 Wagman et al.29MDEAH+ -2.5989 108 a -5.1422 108 a this work

a The values of MDEAH+ are calculated from the chemical equilibrium constant in Kamps and Maurer,30 which are used as the initial guess to fitexperimental data.

2H2O T H3O+ + OH- (10)

CO2 + 2H2O T H3O+ + HCO3

- (11)

HCO3- + H2O T H3O

+ + CO32- (12)

MDEAH+ + H2O T H3O+ + MDEA (13)

-RT ln Kj ) Gjo(T) (14)

Gs(T) ) Gsig(T) + Gsigfl(T) (15)

Gsig(T) ) fHs,298.15ig + 298.15T Cp,sig dT - T (fHs,298.15ig - fGs,298.15ig298.15 + 298.15T Cp,sigT dT) (16)

Table 5. Parameters for Ideal Gas Heat CapacityHeat Capacity (J/(kmol K))

parameter MDEA H2O CO2

source this work Aspen Databank22 Aspen Databank22C1i 2.7303 104 3.3738 104 1.9795 104C2i 5.4087 102 -7.0176 7.3437 10C3i 0 2.7296 10-2 -5.6019 10-2C4i 0 -1.6647 10-5 1.7153 10-5C5i 0 4.2976 10-9 0C6i 0 -4.1696 10-13 0C7i 278 200 300C8i 397 3000 1088.6a The correlation for the ideal gas heat capacity is given as follows:

Cpig ) C1i + C2iT + C3iT2 + C4iT3 + C5iT4 + C6iT5, C7i < T < C8i, whereT is the temperature (given in Kelvin).

Gi,aq(T) ) fGiig(T) + RT ln(Hi,wPref ) (17)

Gi,aq(T) ) fHi,298.15,aq + 298.15T Cp,i,aq dT - T (fHi,298.15,aq - fGi,298.15,aq298.15 + 298.15T Cp,i,aqT dT) + RT ln(1000Mw )

(18)

Ind. Eng. Chem. Res., Vol. 50, No. 1, 2011 165

fGi,298.15,aq , as reported in the literature, is based on molalityconcentration scale while Gi,aq is based on mole fraction scale.

The standard-state properties fGi,298.15,aq , fHi,298.15,aq , and Cp,i,aqare available in the literature for most ionic species, except thoseof MDEAH+. (See Tables 4 and 6.) We calculate the reference-state properties of the MDEAH+ ion from the experimentalequilibrium constant of eq 13, as reported in 1996 by Kampsand Maurer.30 The calculated fGi,298.15,aq and fHi,298.15,aq valuesare given in Table 4, and the calculated Cp,i,aq values are givenin Table 6. As will be shown later, we use these calculatedreference-state properties for MDEAH+ as part of the adjustableparameters in the fitting experimental data of thermodynamicproperties, including VLE, heat of solution, heat capacity, andspecies concentration from NMR spectra. Also given in Table6 are estimated values of Cp,i,aq for HCO3- and CO32-. They havebeen taken from the 1964 work of Criss and Cobble.31

2.2. Heat of Absorption and Heat Capacity. The CO2 heatof absorption in aqueous MDEA solutions can be derived froman enthalpy balance of the absorption process:

where Habs is the heat of absorption per mole of CO2, HFinallthe molar enthalpy of the final solution, HInitiall the molar enthalpyof the initial solution, HCO2

gthe molar enthalpy of gaseous CO2

absorbed, nFinal the number of moles of the final solution, nInitialthe number of moles of the initial solution, and nCO2 the numberof moles of CO2 absorbed.

There are two types of heat of absorption: integral heat ofabsorption and differential heat of absorption. The integral heatof absorption for a certain amine-H2O-CO2 system refers tothe heat effect per mole of CO2 during the CO2 loading of theamine solution increasing from zero to the final CO2 loadingvalue of that amine-H2O-CO2 system. The differential heatof absorption for an amine-H2O-CO2 system refers to the heateffect per mole of CO2 if a very small amount of CO2 is addedinto this amine-H2O-CO2 system.

For calculation of both types of heat of absorption, enthalpycalculations for the initial and final amine-H2O-CO2 systemsand for gaseous CO2 are required. The heat capacity of theMDEA-H2O-CO2 system can be calculated from the temper-ature derivative of enthalpy.

We use the following equation for liquid enthalpy:

Here, Hl is the molar enthalpy of the liquid mixture, Hwl themolar enthalpy of liquid water, Hsl the molar enthalpy of liquidnonaqueous solvent s, Hi,aq the molar enthalpy of solute i(molecular or ionic) in aqueous-phase infinite dilution, and Hexthe molar excess enthalpy. The terms xw, xs, and xi representthe mole fractions of water, nonaqueous solvent s, and solute i,respectively.

The liquid enthalpy of pure water is calculated from the idealgas model and the ASME Steam Tables EOS for enthalpydeparture:

where Hwl (T) is the liquid enthalpy of water at temperature T,fHw,298.15ig the ideal gas enthalpy of formation of water at 298.15K, Cp,wig the ideal-gas heat capacity of water, and Hwigfl(T,p)the enthalpy departure calculated from the ASME Steam TablesEOS.

Liquid enthalpy of the nonaqueous solvent s is calculatedfrom the ideal-gas enthalpy of formation at 298.15 K, the ideal-gas heat capacity, the vapor enthalpy departure, and the heat ofvaporization:

Here, Hsl(T) is the liquid enthalpy of solvent s at temperature T,fHs,298.15ig the ideal-gas enthalpy of formation of solvent s at298.15 K, Cp,sig the ideal-gas heat capacity of solvent s, HsV(T,p)the vapor enthalpy departure of solvent s, and vapHs(T) theheat of vaporization of solvent s.

The PC-SAFT EOS is used for the vapor enthalpy departureand the DIPPR heat of vaporization correlation is used for theheat of vaporization. Table 7 shows the DIPPR equation andthe correlation parameters for the heat of vaporization.

The enthalpies of ionic solutes in aqueous phase infinitedilution are calculated from the enthalpy of formation at 298.15K in aqueous-phase infinite dilution and the heat capacity inaqueous-phase infinite dilution:

where Hi,aq(T) is the enthalpy of solute i in aqueous-phaseinfinite dilution at temperature T, fHi,298.15,aq the enthalpy offormation of solute i in aqueous-phase infinite dilution at 298.15K, and Cp,i,aq the heat capacity of solute i in aqueous-phaseinfinite dilution.

Table 6. Parameters for Aqueous-Phase Infinite Dilution Heat Capacitya

Heat Capacity (J/(kmol K))parameter H3O+ OH- HCO3- CO32- MDEAH+

source Aspen Databank22 Aspen Databank22 Criss and Cobble31 Criss and Cobble31 this workC1 7.5291 104 -1.4845 105 -2.9260 104 b -3.9710 105 b 2.9900 105 b

a The aqueous-phase infinite dilution heat capacity is assumed to be constant (Cp,i,aq ) C1). b The Cp,i,aq value of MDEAH+ is calculated from thechemical equilibrium constant in Kamps and Maurer,30 which is used as the initial guess to fit experimental data. The Cp,i,aq values of HCO3- and CO32-are the average values of heat capacity between 298 K and 473 K (taken from Criss and Cobble31).

Habs )nFinalHFinal

l - nInitialHInitiall - nCO2HCO2

g

nCO2(19)

Hl ) xwHwl + xsHs

l + i

xiHi,aq + Hex (20)

Table 7. Parameters for Heat of Vaporization (Expressed in Unitsof J/kmol)a

component i MDEAsource this workC1i 9.7381 107C2i 4.6391 10-1C3i 0C4i 0C5i 0Tci 741.9b

a The DIPPR equation for the heat of vaporization is given as follows:vapHi ) C1i(1 - Tri)Z, where Z ) C2i + C3iTri + C4iTri2 + C5iTri3 andTri ) T/Tci (here, Tci is the critical temperature of component i). Thetemperatures are given in Kelvin. b The Tci value for MDEA is obtainedfrom Von Niederhausern et al.32

Hwl (T) ) fHw,298.15ig + 298.15T Cp,wig dT + Hwigfl(T, p) (21)

Hsl(T) ) fHs,298.15ig + 298.15T Cp,sig dT + HsV(T, p) - vapHs(T)

(22)

Hi,aq(T) ) fHi,298.15,aq + 298.15T Cp,i,aq dT (23)


Both fHi,298.15,aq and Cp,i,aq are also used in the calculation ofGibbs free energy of the solutes, thus impacting chemicalequilibrium calculations. In this study, fHi,298.15,aq and Cp,i,aq forMDEAH+ are determined by fitting to the experimental phaseequilibrium data, the heat of solution data, and the speciationdata, together with molality scale Gibbs free energy of formationat 298.15 K, fGi,298.15,aq , and NRTL interaction parameters.

The enthalpies of molecular solutes in aqueous phase infinitedilution are calculated from Henrys law:

Hi,aq(T) ) fHiig(T) - RT 2( ln Hi,wT ) (24)

where fHiig(T) is the ideal gas enthalpy of formation of solutei at temperature T, and Hi,w Henrys constant of solute i in water.

Excess enthalpy (Hex) is calculated from the activity coef-ficient model (i.e., the electrolyte NRTL model).

2.3. Activity Coefficients. Activity coefficients are requiredin phase equilibrium calculations, aqueous-phase chemicalequilibrium calculations, heat of absorption, liquid heat capacity,and liquid enthalpy calculations. The activity coefficient of acomponent in a liquid mixture is a function of temperature,pressure, mixture composition, and choice of reference state.In VLE calculations, we use the asymmetric mixed-solventreference state for the molecular solute CO2, and in aqueous-

phase chemical equilibrium calculations, we choose the aqueous-phase infinite dilution reference state for molecular solute CO2and all ionic species.

In applying the electrolyte NRTL model for liquid-phaseactivity coefficient calculations, the binary NRTL interactionparameters for molecule-molecule binary, molecule-electrolytebinary, and electrolyte-electrolyte binary systems are required.Here, electrolytes are defined as cation and anion pairs. Inaddition, solvent dielectric constants are needed to facilitatecalculations of long-range ion-ion interaction contribution toactivity coefficients. Table 8 shows the dielectric constantcorrelation used in this work for MDEA.

Unless specified otherwise, all molecule-molecule binaryparameters and electrolyte-electrolyte binary parameters aredefaulted to zero. All molecule-electrolyte binary parameters aredefaulted to (8,-4), average values of the parameters as reportedfor the electrolyte NRTL model.12 The nonrandomness factor (R)is fixed at 0.2. The calculated thermodynamic properties of theelectrolyte solution are dominated by the binary NRTL parametersassociated with the major species in the system. In otherwords, the binary parameters for the water-MDEA binary, thewater-(MDEAH+, HCO3-) binary, the water-(MDEAH+, CO32-)binary, and the MDEA-(MDEAH+, HCO3-) binary systemsdetermine the calculated thermodynamic properties. These binaryparameters, in turn, are identified from fitting to available experi-mental data.

3. Modelling Results

Table 9 summarizes the model parameters and sources ofthe parameters used in the thermodynamic model. Most of theparameters can be obtained from the literature. The remainingparameters are determined by fitting to the experimental data.

Table 8. Parameters for Dielectric Constanta

component i MDEAsource Aspen Databank22Ai 21.9957Bi 8992.68Ci 298.15

a The correlation for the dielectric constant is given as follows: i(T)) Ai + Bi[(1/T) - (1/Ci)], where T is the temperature (given in Kelvin).

Table 9. Parameters Estimated in Modelingparameter component source data used for regression

Antoine equation MDEA regression vapor pressure of MDEAvapH MDEA regression heat of vaporization of MDEA, calculated from the vapor

pressure using the Clausius-Clapeyron equationdielectric constant MDEA Aspen Databank22Henrys constant CO2 in H2O Yan and Chen25

CO2 in MDEA this workNRTL binary parameters CO2-H2O binary Yan and Chen25

MDEA-H2O binary regression VLE, excess enthalpy, and heat capacity for the MDEA-H2O binarymolecule-electrolyte binaries regression VLE, excess enthalpy, heat capacity, and species concentration from

NMR spectra for the MDEA-H2O-CO2 systemfG298.15ig H2O, MDEA, CO2 Aspen Databank22fH298.15

ig H2O, MDEA, CO2 Aspen Databank22Cpig H2O, CO2 Aspen Databank22

MDEA regression liquid heat capacity of MDEAfG298.15,aq H3O+, OH-, HCO3-, CO32- Aspen Databank

22

MDEAH+ regression VLE, excess enthalpy, heat capacity, and species concentration fromNMR spectra for the MDEA-H2O-CO2 system

fH298.15,aq H3O+, OH-, HCO3-, CO32- Aspen Databank22

MDEAH+ regression VLE, excess enthalpy, heat capacity, and species concentration fromNMR spectra for the MDEA-H2O-CO2 system

Cp,aq H3O+, OH- Aspen Databank22HCO3-, CO32- Criss and Cobble31MDEAH+ regression VLE, excess enthalpy, heat capacity, and species concentration from

NMR spectra for the MDEA-H2O-CO2 system

Table 10. Experimental Data Used in the Regression for Pure MDEAdata type temperature, T (K) pressure, P (kPa) data points average relative deviation, |Y/Y| (%) reference

vapor pressure 293-401 0.0006-1.48 26 1.5 Daubert et al.33vapor pressure 420-513 3.69-90.4 14 4.0 Noll et al.34vapor pressure 420-738 3.69-3985 23 2.9 VonNiederhausern et al.32liquid heat capacity 299-397 5 0.5 Maham et al.35liquid heat capacity 303-353 11 0.4 Chen et al.36liquid heat capacity 278-368 19 0.3 Zhang et al.37


3.1. MDEA. Extensive experimental vapor pressure data andliquid heat capacity data are available for MDEA. The data usedin the regression for MDEA and the correlation results aresummarized in Table 10.

Table 11 shows the Antoine equation parameters regressed fromthe recently available vapor pressure data.32-34 The heat ofvaporization (from 293 K to 473 K) generated with the regressedAntoine equation parameters through the Clausius-Clapeyronequation are used to determine the DIPPR heat of vaporizationequation parameters (shown in Table 7). The ideal-gas heat capacitycorrelation parameters are obtained by fitting to the liquid heatcapacity data35-37 (shown in Table 5). Table 10 shows the excellentcorrelation of the experimental data for vapor pressure, with anaverage relative deviation of

3.3. MDEA-H2O-CO2 System. Extensive VLE,5,6,8,13,45-64heat of absorption,65,66 heat capacity,67 and NMR spectro-scopic68 data of the ternary MDEA-H2O-CO2 system areavailable.

The terms fG298.15,aq , fH298.15,aq , and Cp,aq of MDEAH+ andthe binary NRTL parameters for major molecule-electrolytepairs are regressed from selected experimental data of theMDEA-H2O-CO2 system. Table 14 summarizes the VLE,5,6,13heat of absorption,65,66 heat capacity,67 and species concentra-tion68 data used to obtain these parameters.

Species concentration data from NMR spectra are very usefulto validate the model predictions for the species distribution inthe ternary system. Calculated heat of absorption of CO2 bythe MDEA solution also strongly depends on the speciesdistribution.

For VLE data, we choose the total pressure data of Kuranovet al.,5 Kamps et al.,6 and the CO2 partial pressure data ofErmatchkov et al.13 in the regression. Together, these data covertemperatures from 313 K to 413 K, pressures from 0.1 kPa to6000 kPa, MDEA mole fractions from 0.03 to 0.13, and CO2loadings from 0.003 to 1.32. The CO2 partial pressure data ofJou et al.45 also cover wide ranges for temperature, pressure,MDEA concentration, and CO2 loading. However, consideringthe reported inconsistency5,6,13 between these data45 and thoseof Kuranov et al.,5 Kamps et al.,6 and Ermatchkov et al.,13 wechoose to exclude the data of Jou et al.45 from the regression.The Jou et al. data45 and all other available literature VLEdata8,46-64 are used only for model validation.

The average relative deviations between the correlation resultsand the various experimental data are shown in Table 14. Theregressed parameters for the MDEA-H2O-CO2 system aresummarized in Table 15. As expected, the regressed values offG298.15,aq , fH298.15,aq , and Cp,aq for MDEAH+ in Table 15 arecomparably close to the estimated values reported in Tables 4and 6.

Figures 7 and 8 show that most of the total pressure data ofKuranov et al.5 and Kamps et al.6 are fitted within (20%.Figures 9-11 show the excellent correlation results for the totalpressure data for MDEA concentration from 2 m to 8 m, CO2loading from 0.11 to 1.32, temperature from 313 K to 413 K,and pressure up to 6000 kPa. Figures 12 and 13 show that mostof the CO2 partial pressure data of Ermatchkov et al.13 are fittedwithin (30%. Figure 12 suggests that there is a slight systematicdeviation that changes from negative to positive as the CO2loading increases. Figures 14-16 show the satisfactory cor-relation results for the CO2 partial pressure data for MDEAconcentration from 2 m to 8 m, CO2 loading from 0.003 to 0.78,temperature from 313 K to 393 K, and pressure from 0.1 kPa

Figure 3. Comparison of the experimental data from Kim et al.42(represented by symbols: (O) T ) 373 K, (4) T ) 353 K, (0) T ) 333 K,and () T ) 313 K) for the vapor composition of the MDEA-H2O binarysolution and the model results (represented by lines).

Figure 4. Comparison of the experimental data from Posey9 (representedby full symbols: (b) T ) 298 K, ([) T ) 342 K) and Maham et al.35,43(represented by empty symbols: (O) T ) 298 K, (4) T ) 313 K, (0) T )338 K) for excess enthalpy of the MDEA-H2O binary solution and themodel results (represented by lines).

Figure 5. Comparison of the experimental data from Chen et al.36(represented by symbols: (O) MDEA mole fraction ) 0.8, (4) MDEA molefraction ) 0.6, (0) MDEA mole fraction ) 0.4, and () MDEA molefraction ) 0.2) for heat capacity of the MDEA-H2O binary solution andthe model results (represented by lines).

Figure 6. Model predictions of water and MDEA activity coefficients at313, 353, and 393 K over the entire mole fraction range; solid lines representwater activity coefficients and dashed lines represent MDEA activitycoefficients.


to 70 kPa. The correlation results match the experimental datawell, except that the calculated CO2 pressure at 313 K is slighterhigher than the measured values for the 8 m MDEA solution athigh CO2 loading (see Figure 16). Upon further examination,we find that, under the same conditions, the predicted totalpressure matches the experimental data of Sidi-Boumedine etal.62 well.

Table 16 shows a comparison of model predictions andexperimental VLE data from numerous other sources notincluded in the regression. The results highlight the fact thatwe cannot match all the VLE data because the experimental

Table 14. Experimental Data Used in the Regression for the MDEA-H2O-CO2 System

data typetemperature,

T (K)pressure,P (kPa)

MDEAmole fraction CO2 loading

datapoints

average relativedeviation, |Y/Y| (%) reference

VLE, TPx, total pressure 313-413 70-5000 0.035-0.067 0-1.32 82 6.8 Kuranov et al.5VLE, TPx, total pressure 313-393 200-6000 0.126 0.13-1.15 23 10.5 Kamps et al.6VLE, TPx, CO2 pressure 313-393 0.1-70 0.033-0.132 0.003-0.78 101 17.7 Ermatchkov et al.13heat of solution 313-393 0.06 0.1-1.4 112 6.8 Mathonat65heat of solution 298 0.017-0.061 0.02-0.25 40 2.1 Carson et al.66heat capacity (isobaric) 298 0.061-0.185 0-0.64 39 3.0 Weiland et al.67species concentration 293-313 0.04 0.1-0.7 8 47.5 Jakobsen et al.68

Table 15. Regressed Parameters for the MDEA-H2O-CO2 System with r ) 0.2parameter component i component j value standard deviation

fG298.15,aq (J/kmol) MDEAH+ -2.5951 108 2.1986 105fH298.15

,aq (J/kmol) MDEAH+ -5.1093 108 5.8718 105Cp,aq (J/(kmol K)) MDEAH+ 3.3206 105 1.2799 104ij H2O (MDEAH+, HCO3-) 8.7170 0.2246ij (MDEAH+, HCO3-) H2O -4.2995 0.0836ij H2O (MDEAH+, CO32-) 10.4032 0.3676ij (MDEAH+, CO32-) H2O -4.9252 0.1248ij MDEA (MDEAH+, HCO3-) 5.2964 0.2746ij (MDEAH+, HCO3-) MDEA -0.8253 0.0685

Figure 7. Ratio of experimental total pressure to calculated total pressure,as a function of CO2 loading ((4) data from Kuranov et al.5 and (O) datafrom Kamps et al.6).

Figure 8. Parity plot for the MDEA-H2O-CO2 system total pressure:experiment versus model ((4) Kuranov et al.5 and (O) Kamps et al.6).

Figure 9. Comparison of the experimental data from Kuranov et al.5(represented by symbols: (O) T ) 413 K, (4) T ) 393 K, () T ) 373 K,(0) T ) 353 K, and (]) T ) 313 K) for total pressure of theMDEA-H2O-CO2 system and the model results (represented by lines);the MDEA concentration is 2 m.

Figure 10. Comparison of the experimental data from Kuranov et al.5(represented by symbols: (O) T ) 413 K, (4) T ) 393 K, () T ) 373 K,(0) T ) 353 K, and (]) T ) 313 K) for total pressure of theMDEA-H2O-CO2 system and the model results (represented by lines);the MDEA concentration is 4 m.


data from different sources can be inconsistent. With theexception of the data from Jou et al.,45 Silkenbaeumer et al.,56and Ali and Aroua,61 the model predictions are very satisfactory,with the average relative deviation on pressure (either totalpressure or CO2 partial pressure) in the range of 7%-80%. Itis particularly significant that the model predictions give anexcellent match with the recent data of Kamps et al.,60 Sidi-Boumedine et al.,62 and Mamum et al.63

Figure 17 shows the species distribution as a function of CO2loading for a 23 wt % MDEA solution at 293 K. The calculated

concentrations of the species are consistent with the experimentalNMR measurements from Jakobsen et al.68

Figure 11. Comparison of the experimental data from Kamps et al.6(represented by symbols: (O) T ) 393 K, (0) T ) 353 K, and (]) T ) 313K) for total pressure of the MDEA-H2O-CO2 system and the model results(represented by lines); the MDEA concentration is 8 m.

Figure 12. Rato of experimental CO2 partial pressure ((O) Ermatchkov etal.13) to calculated CO2 partial pressure (line), as a function of CO2 loading.

Figure 13. Parity plot for CO2 partial pressure of the MDEA-H2O-CO2system: experiment ((O) Ermatchkov et al.13) versus model (line).

Figure 14. Comparison of the experimental data for CO2 partial pressureof the MDEA-H2O-CO2 system and the model results; the MDEAconcentration is 2 m. Empty symbols are data from Ermatchkov et al.13((O) T ) 393 K, (0) T ) 353 K, (]) T ) 313 K), solid lines represent the2009 eNRTL model results, and dashed lines represent the 1986 eNRTLmodel results.




Figures 18-20 show comparisons of the model correlationsand the experimental data of Mathonat65 for the integral heatof CO2 absorption in aqueous MDEA solution at 313, 353, and393 K, respectively. The calculated values are in reasonableagreement with the experimental data. Also shown in Figures18-20 are the predicted differential heats of CO2 absorption.The integral heat and the differential heat overlap at low CO2loadings, and then diverge much at high CO2 loadings (i.e.,>0.8), where the differential heat decreases by >50%. We furthershow the computed integral heat of absorption as the sum ofthe various contributions from reactions 10-13, CO2 dissolution,and excess enthalpy.

where Habs is the integral heat of absorption per mole of CO2,Hi the standard heat of reaction for reaction i per mole ofkey component reacted, and ni the reaction extent of thereaction key component for reaction i when 1 mol CO2 isabsorbed.

The heat of CO2 dissolution (Hdissolution) is calculated as theenthalpy difference between 1 mol of CO2 in the vapor phaseand 1 mol of CO2 in aqueous-phase infinite dilution. Thecontribution of excess enthalpies (Hex) is computed as theexcess enthalpy difference between the final and initial com-positions of the solution per mole of CO2 absorbed.

The results in Figures 18-20 show that the heat of absorptionis dominated by MDEAH+ dissociation and excess enthalpy.In addition, CO2 dissolution is important near room temperature,whereas CO2 dissociation becomes more important at highertemperatures.

Figure 21 shows a comparison of the model correlations andthe experimental data of Weiland et al.67 for heat capacity ofthe MDEA-H2O-CO2 system. The model results are consistentwith the data.

To show the impact of the different versions of theelectrolyte NRTL model to the model results, we performVLE predictions with the same model parameter values givenin Table 15 with the 1986 version of the electrolyte NRTL

Table 16. Comparison between Experimental Data and Model Predictions for Total Pressure or CO2 Partial Pressure of the MDEA-H2O-CO2System

source data points temperature, T (K) pressure, P (kPa) MDEA concentration CO2 loading |P/P|a (%)Jou et al.45 118 298-393 0.001-6000 0.044-0.128 0.0004-1.68 204Chakma and Meisen46 76 373-473 100-5000 0.03-0.12 0.01-0.95 31.5Maddox et al.47 99 310-388 20-6000 0.02-0.04 0.17-1.51 21.1Austgen et al.8 14 313 0.005-100 0.045-0.13 0.003-0.67 32.2MacGregor and Mather48 5 313 1-4000 0.04 0.12-1.2 22.1Jou et al.49 37 313-373 0.004-260 0.07 0.002-0.80 37.5Dawodu and Meisen50 12 373-393 160-4000 0.12 0.09-0.8 13.3Liu et al.51 16 303-363 20-350 0.09 0.09-0.85 28.5Mathonat et al.52 9 313-393 2000-10000 0.06 0.5-1.3 57.4Rho et al.53 103 323-373 0.1-268 0.008-0.31 0.006-0.68 78.7Baek and Yoon54 12 313 1-2000 0.06 0.12-1.13 53.6Rogers et al.55 34 313-323 0.00007-1 0.04-0.13 0.0002-0.12 27.1Silkenbaeumer et al.56 11 313 12-4000 0.07 0.2-1.3 135Xu et al.57 65 328-363 4-800 0.07-0.13 0.04-0.9 20.2Lemoine et al.58 13 298 0.02-1.64 0.04 0.02-0.26 11.9Bishnoi and Rochelle59 3 313 0.1-0.7 0.13 0.01-0.03 17.9Kamps et al.60 5 313 80-5000 0.03 1.06-1.41 8.9Ali and Aroua61 15 313-353 0.08-100 0.04 0.05-0.8 495Sidi-Boumedine et al.62 103 298-348 2.7-4500 0.05-0.11 0.008-1.30 7.7Mamun et al.63 34 328-358 66-813 0.12 0.17-0.81 6.5Dicko et al.64 5 323 6-434 0.12 0.1-0.9 48.5

a Experimental pressure expressed either as total pressure or CO2 partial pressure.

Figure 17. Comparison of the experimental data for species concentrationin MDEA-H2O-CO2 and the model results at T ) 293 K. MDEAconcentration is 23 wt %. Symbols represent experimental data fromJakobsen et al.68 ((O) MDEA, (4) HCO3-, (0) MDEAH+, () CO32-, (])CO2); lines represent model results ((s) MDEA, (- - -) HCO3-, (- -)MDEAH+, (- -) CO32-, and ( ) CO2.

Habs ) i)1

k

niHi + Hdissolution + Hex (25)

Figure 18. Integral CO2 heat of absorption in 30 wt % MDEA aqueoussolution at 313 K. Symbols (0) represent experimental data from Matho-nat;65 lines represent model results ((s) integral heat of absorption,(- -) differential heat of absorption, ( ) contribution of reactions,(- -) contribution of CO2 dissolution, (- - -) contribution of excessenthalpies).


model.11 Figures 14-16 show that the two versions of themodel yield practically identical results at low MDEA

concentrations. The difference increases slightly with increas-ing MDEA concentration.

4. Conclusion

To support process modeling and simulation of the CO2capture process with MDEA, the electrolyte NRTL model hasbeen successfully applied to correlate the available experimentaldata on thermodynamic properties of the MDEA-H2O-CO2system. The model has been validated for predictions of vapor-liquid equilibrium (VLE), heat capacity, and CO2 heat ofabsorption of the MDEA-H2O-CO2 system with temperaturesfrom 313 K to 393 K, MDEA concentrations up to 8 m (50wt %), and CO2 loadings up to 1.32. This model should providea comprehensive thermodynamic property representation for theMDEA-H2O-CO2 system over a broader range of conditionsand give more-reliable predictions than those from previousworks.

Acknowledgment

The authors thank Huiling Que and Joseph DeVincentis fortheir support in preparing the manuscript.

Literature Cited

(1) Zhang, Y.; Chen, H.; Chen, C.-C.; Plaza, J. M.; Dugas, R.; Rochelle,G. T. Rate-Based Process Modeling Study of CO2 Capture with AqueousMonoethanolamine Solution. Ind. Eng. Chem. Res. 2009, 48, 92339246.

(2) Kohl. A. L.; Riesenfeld, F. C. Gas Purification, 4th ed.; GulfPublishing: Houston, TX, 1985.

(3) Taylor, R.; Krishna, R.; Kooijman, H. Real-World Modeling ofDistillation. Chem. Eng. Prog. 2003, 99, 2839.

(4) Chen, C.-C.; Mathias, P. M. Applied Thermodynamics for ProcessModeling. AIChE J. 2002, 48, 194200.

(5) Kuranov, G.; Rumpf, B.; Smirnova, N. A.; Maurer, G. Solubility ofSingle Gases Carbon Dioxide and Hydrogen Sulfide in Aqueous Solutionsof N-Methyldiethanolamine in the Temperature Range 313-413 K atPressures up to 5 MPa. Ind. Eng. Chem. Res. 1996, 35, 19591966.

(6) Kamps, A . P.-S.; Balaban, A.; Jodecke, M.; Kuranov, G.; Smirnova,N. A.; Maurer, G. Solubility of Single Gases Carbon Dioxide and HydrogenSulfide in Aqueous Solutions of N-Methyldiethanolamine at Temperaturesfrom 313 to 393 K and Pressures up to 7.6 MPa: New Experimental Dataand Model Extension. Ind. Eng. Chem. Res. 2001, 40, 696706.

(7) Chen, C.-C. Toward Development of Activity Coefficient Modelsfor Process and Product Design of Complex Chemical Systems. Fluid PhaseEquilib. 2006, 241, 103112.

(8) Austgen, D. M.; Rochelle, G. T.; Chen, C.-C. Model of Vapor-Liquid Equilibria for Aqueous Acid Gas-Alkanolamine Systems. 2.Representation of H2S and CO2 Solubility in Aqueous MDEA and CO2Solubility in Aqueous Mixtures of MDEA with MEA or DEA. Ind. Eng.Chem. Res. 1991, 30, 543555.

(9) Posey, M. L. Thermodynamic Model for Acid Gas Loaded AqueousAlkanolamine Solutions, Ph.D. Thesis, University of Texas at Austin, Austin,TX, 1996.

(10) Song, Y.; Chen, C.-C. Symmetric Electrolyte Nonrandom Two-Liquid Activity Coefficient Model. Ind. Eng. Chem. Res. 2009, 48, 77887797.

(11) Chen, C.-C.; Evans, L. B. A Local Composition Model for theExcess Gibbs Energy of Aqueous Electrolyte Systems. AIChE J. 1986, 32,444454.

(12) Chen, C.-C.; Britt, H. I.; Boston, J. F.; Evans, L. B. LocalComposition Model for Excess Gibbs Energy of Electrolyte Systems. PartI: Single Solvent, Single Completely Dissociated Electrolyte Systems. AIChEJ. 1982, 28, 588596.

(13) Ermatchkov, V.; Kamps, A . P.-S.; Maurer, G. Solubility of CarbonDioxide in Aqueous Solutions of N-Methyldiethanolamine in the Low GasLoading Region. Ind. Eng. Chem. Res. 2006, 45, 60816091.

(14) Pitzer, K. S. Thermodynamics of Electrolytes. I. Theoretical Basisand General Equations. J. Phys. Chem. 1973, 77, 268277.

Figure 19. Integral CO2 heat of absorption in 30 wt % MDEA aqueoussolution at 353 K. Symbols (4) represent experimental data from Matho-nat;65 lines represent model results ((s) integral heat of absorption,(- -) differential overall absorption heat, ( ) contribution ofreactions, (- -) contribution of CO2 dissolution, (- - -) contributionof excess enthalpies).

Figure 20. Integral CO2 heat of absorption in 30 wt % MDEA aqueoussolution at 393 K. Symbols (O) represent experimental data from Matho-nat;65 lines represent model results ((s) integral heat of absorption,(- -) differential heat of absorption, ( ) contribution of reactions,(- -) contribution of CO2 dissolution, (- - -) contribution of excessenthalpies).

Figure 21. Comparison of the experimental data for heat capacity of theMDEA-H2O-CO2 system and the model results at T ) 298 K. Symbolsrepresent experimental data from Weiland et al.67 ((O) 60 wt % MDEA,(4) 50 wt % MDEA, (0) 40 wt % MDEA, and (]) 30 wt % MDEA); linesrepresent model results.


(15) Arcis, H.; Rodier, L.; Karine, B.-B.; Coxam, J.-Y. Modeling of(Vapor + Liquid) Equilibrium and Enthalpy of Solution of Carbon Dioxide(CO2) in Aqueous Methyldiethanolamine (MDEA) Solutions. J. Chem.Thermodyn. 2009, 41, 783789.

(16) Faramarzi, L.; Kontogeorgis, G. M.; Thomsen, K.; Stenby, E. H.Extended UNIQUAC Model for Thermodynamic Modeling of CO2 Absorp-tion in Aqueous Alkanolamine Solutions. Fluid Phase Equilib. 2009, 282,121132.

(17) Thomsen, K.; Rasmussen, P. Modeling of Vapor-Liquid-SolidEquilibrium in Gas-Aqueous Electrolyte Systems. Chem. Eng. Sci. 1999,54, 17871802.

(18) Bottinger, W.; Maiwald, M.; Hasse, H. Online NMR SpectroscopicStudy of Species Distribution in MEA-H2O-CO2 and DEA-H2O-CO2.Fluid Phase Equilib. 2008, 263, 131143.

(19) Hilliard, M. A Predictive Thermodynamic Model for an AqueousBlend of Potassium Carbonate, Piperazine, and Monoethanolamine forCarbon Dioxide, Ph.D. Dissertation, University of Texas at Austin, Austin,TX, 2008.

(20) Gross, J.; Sadowski, G. Perturbed-Chain SAFT: An Equation ofState Based on a Perturbation Theory for Chain Molecules. Ind. Eng. Chem.Res. 2001, 40, 12441260.

(21) Gross, J.; Sadowski, G. Application of the Perturbed-Chain SAFTEquation of State to Associating Systems. Ind. Eng. Chem. Res. 2002, 41,55105515.

(22) Aspen Physical Property System, V7.2; Aspen Technology, Inc.:Burlington, MA, 2010.

(23) Van Ness, H. C.; Abbott, M. M. Vapor-Liquid Equilibrium: PartVI. Standard State Fugacities for Supercritical Components. AIChE J. 1979,25, 645653.

(24) Brelvi, S. W.; OConnell, J. P. Corresponding States Correlationsfor Liquid Compressibility and Partial Molar Volumes of Gases at InfiniteDilution in Liquids. AIChE J. 1972, 18, 12391243.

(25) Yan, Y.-Z.; Chen, C.-C. Thermodynamic Modeling of CO2 Solubil-ity in Aqueous Solutions of NaCl and Na2SO4. Submitted to J. Supercrit.Fluids.

(26) Clarke, J. K. A. Kinetics of Absorption of Carbon Dioxide inMonoethanolamine Solutions at Short Contact Times. Ind. Eng. Chem.Fundam. 1964, 3, 239245.

(27) Wang, Y. W.; Xu, S.; Otto, F. D.; Mather, A. E. Solubility of N2Oin Alkanolamines and in Mixed Solvents. Chem. Eng. J. 1992, 48, 3140.

(28) Versteeg, G. F.; Van Swaaij, W. P. M. Solubility and Diffusivityof Acid Gases (CO2, N2O) in Aqueous Alkanolamine Solutions. J. Chem.Eng. Data 1988, 33, 2934.

(29) Wagman, D. D.; Evans, W. H.; Parker, V. B.; Schumm, R. H.;Halow, I.; Bailey, S. M.; Churney, K. L.; Nuttall, R. L. The NBS tables ofchemical thermodynamic properties. Selected values for inorganic and C1and C2 organic substances in SI units. J. Phys. Chem. Ref. Data 1982, 11(Supplement No. 2), pp 2-38 and 2-83.

(30) Kamps, A . P.-S.; Maurer, G. Dissociation Constant of N-Meth-yldiethanolamine in Aqueous Solution at Temperatures from 278 to 368K. J. Chem. Eng. Data 1996, 41, 15051513.

(31) Criss, C. M.; Cobble, J. W. The Thermodynamic Properties of HighTemperature Aqueous Solutions. V. The Calculation of Ionic Heat Capacitiesup to 200. Entropies and Heat Capacities above 200. J. Am. Chem. Soc.1964, 86, 53905393.

(32) Von Niederhausern, D. M.; Wilson, G. M.; Giles, N. F. CriticalPoint and Vapor Pressure Measurements for 17 Compounds by a LowResidence Time Flow Method. J. Chem. Eng. Data 2006, 51, 19901995.

(33) Daubert, T. E.; Hutchison, G. Vapor Pressure of 18 Pure IndustrialChemicals. AIChE Symp. Ser. 1990, 86, 93114.

(34) Noll, O.; Valtz, A.; Richon, D.; Getachew-Sawaya, T.; Mokbel, I.;Jose, J. Vapor Pressures and Liquid Densities of N-Methylethanolamine,Diethanolamine, and N-Methyldiethanolamine. ELDATA: Int. Electron. J.Phys.-Chem. Data 1998, 4, 105120.

(35) Maham, Y.; Mather, A. E.; Hepler, L. G. Excess Molar Enthalpiesof (Water + Alkanolamine) Systems and Some Thermodynamic Calcula-tions. J. Chem. Eng. Data 1997, 42, 988992.

(36) Chen, Y.-J.; Shih, T.-W.; Li, M.-H. Heat Capacity of AqueousMixtures of Monoethanolamine with N-Methyldiethanolamine. J. Chem.Eng. Data 2001, 46, 5155.

(37) Zhang, K.; Hawrylak, B.; Palepu, R.; Tremaine, P. R. Thermody-namics of Aqueous Amines: Excess Molar Heat Capacities, Volumes, andExpansibilities of (Water + Methyldiethanolamine (MDEA)) and (Water+ 2-Amino-2-methyl-1-propanol (AMP)). J. Chem. Thermodyn. 2002, 34,679710.

(38) AI-Ghawas, H. A.; Hagewiesche, D. P.; Ruiz-Ibanez, G.; Sandall,O. C. Physicochemical Properties Important for Carbon Dioxide Absorptionin Aqueous Methyldiethanolamine. J. Chem. Eng. Data 1989, 34, 385391.

(39) DiGuilio, R. M.; Lee, R. J.; Schaeffer, S. T.; Brasher, L. L.; Teja,A. S. Densities and Viscosities of the Ethanolamines. J. Chem. Eng. Data1992, 37, 239242.

(40) Xu, S.; Qing, S.; Zhen, Z.; Zhang, C.; Carroll, J. Vapor PressureMeasurements of Aqueous N-Methyldiethanolamine Solutions. Fluid PhaseEquilib. 1991, 67, 197201.

(41) Voutsas, E.; Vrachnos, A.; Magoulas, K. Measurement andThermodynamic Modeling of the Phase Equilibrium of AqueousN-Methyldiethanolamine Solutions. Fluid Phase Equilib. 2004, 224, 193197.

(42) Kim, I.; Svendsen, H. F.; Brresen, E. Ebulliometric Determinationof Vapor-Liquid Equilibria for Pure Water, Monoethanolamine, N-Methyldiethanolamine, 3-(Methylamino)-propylamine, and Their Binary andTernary Solutions. J. Chem. Eng. Data 2008, 53, 25212531.

(43) Maham, Y.; Mather, A. E.; Mathonat, C. Excess properties of(alkyldiethanolamine + H2O) mixtures at temperatures from (298.15 to338.15) K. J. Chem. Thermodyn. 2000, 32, 229236.

(44) Chiu, L.-F.; Li, M.-H. Heat Capacity of Alkanolamine AqueousSolutions. J. Chem. Eng. Data 1999, 44, 13961401.

(45) Jou, F. Y.; Mather, A. E.; Otto, F. D. Solubility of H2S and CO2 inAqueous Methyldiethanolamine Solution. Ind. Eng. Chem. Process Des.DeV. 1982, 21, 539544.

(46) Chakma, A.; Meisen, A. Solubility of CO2 in Aqueous Methyldi-ethanolamine and N,N-Bis(hydroxyethl)piperazine Solutions. Ind. Eng.Chem. Res. 1987, 26, 24612466.

(47) Maddox, R. N.; Bhairi, A. H.; Diers, J. R.; Thomas, P. A.Equilibrium Solubility of Carbon Dioxide or Hydrogen Sulfide in AqueousSolutions of Monoethanolamine, Diglycolamine, Diethanolamine and Me-thyldiethanolamine. GPA Res. Rep. 1987, 147.

(48) MacGregor, R. J.; Mather, A. E. Equilibrium Solubility of H2S andCO2 and Their Mixtures in a Mixed Solvent. Can. J. Chem. Eng. 1991, 69,13571366.

(49) Jou, F. Y.; Carroll, J. J.; Mather, A. E.; Otto, F. D. The Solubilityof Carbon Dioxide and Hydrogen Sulfide in a 35 wt % Aqueous SolutionMethyldiethanolamine. Can. J. Chem. Eng. 1993, 71, 264268.

(50) Dawodu, O. F.; Meisen, A. Solubility of Carbon Dioxide in AqueousMixtures of Alkanolamines. J. Chem. Eng. Data 1994, 39, 548552.

(51) Liu, H.; Xu, G.; Zhang, C.; Wu, Y. Solubilities of Carbon Dioxidein Aqueous Activated Methyldiethanolamine Solutions. Huadong LigongDaxue Xuebao 1999, 25, 242246.

(52) Mathonat, C.; Majer, V.; Mather, A. E.; Grolier, J.-P. E. Enthalpiesof Absorption and Solubility of CO2 in Aqueous Solutions of Methyldi-ethanolamine. Fluid Phase Equilib. 1997, 140, 171182.

(53) Rho, S.-W.; Yoo, K.-P.; Lee, J. S.; Nam, S. C.; Son, J. E.; Min,B.-M. Solubility of CO2 in Aqueous Methyldiethanolamine Solutions.J. Chem. Eng. Data 1997, 42, 11611164.

(54) Baek, J.-I.; Yoon, J.-H. Solubility of Carbon Dioxide in AqueousSolutions of 2-Amino-2-Methyl-1,3-Propanediol. J. Chem. Eng. Data 1998,43, 635637.

(55) Rogers, W. J.; Bullin, J. A.; Davison, R. R. FTIR Measurementsof Acid-Gas-Methyldiethanolamine Systems. AIChE J. 1998, 44, 24232430.

(56) Silkenbaumer, D.; Rumpf, B.; Lichtenthaler, R. N. Solubility ofCarbon Dioxide in Aqueous Solutions of 2-Amino-2-methyl-1-propanol andN-Methyldiethanolamine and Their Mixtures in the Temperature Range from313 to 353 K and Pressures up to 2.7 MPa. Ind. Eng. Chem. Res. 1998, 37,31333141.

(57) Xu, G.-W.; Zhang, C.-F.; Qin, S.-J.; Gao, W.-H.; Liu, H.-B. Gas-Liquid Equilibrium in a CO2-MDEA-H2O System and the Effect onPiperazine on It. Ind. Eng. Chem. Res. 1998, 37, 14731477.

(58) Lemoine, B.; Li, Y.-G.; Cadours, R.; Bouallou, C.; Richon, D.Partial Vapor Pressure of CO2 and H2S over Aqueous MethyldiethanolamineSolutions. Fluid Phase Equilib. 2000, 172, 261277.

(59) Bishnoi, S.; Rochelle, G. T. Thermodynamics of Piperazine-Methyldiethanolamine-Water-Carbon Dioxide. Ind. Eng. Chem. Res. 2002,41, 604612.

(60) Kamps, A . P.-S.; Rumpf, B.; Maurer, G.; Anoufrikov, Y.; Kuranov,G.; Smirnova., N. A. Solubility of CO2 in H2O + N-Methyldiethanolamine+ (H2SO4 or Na2SO4). AIChE J. 2002, 48, 168177.

(61) Ali, B. S.; Aroua, M. K. Effect of Piperazine on CO2 loading inAqueous Solutions of MDEA at Low Pressure. Int. J. Thermophys. 2004,25, 18631870.

(62) Sidi-Boumedine, R.; Horstmann, S.; Fischer, K.; Provost, E.; Furst,W.; Gmehling, J. Experimental Determination of Carbon Dioxide SolubilityData in Aqueous Alkanolamine Solutions. Fluid Phase Equilib. 2004, 218,8594.

(63) Mamun, S.; Nilsen, R.; Svendsen, H. F.; Juliussen, O. Solubility ofCarbon Dioxide in 30 mass% Monoethanolamine and 50 mass% Methyldi-ethanolamine Solutions. J. Chem. Eng. Data 2005, 50, 630634.


(64) Dicko, M.; Coquelet, C.; Jarne, C.; Northrop, S.; Richon, D. AcidGases Partial Pressures above a 50 wt% Aqueous MethyldiethanolamineSolution: Experimental Work and Modeling. Fluid Phase Equilib. 2010,289, 99109.

(65) Mathonat, C. Calorimetrie de melange, a ecoulement, a temperatureset pressions elevees. Application a letude de lelimination du dioxide decarbone a laide de solutions aqueuses dalcanolamines, Universite BlaisePascal, Paris, 1995, p 265.

(66) Carson, J. K.; Marsh, K. N.; Mather, A. E. Enthalpy of Solution ofCarbon Dioxide in (Water + Monoethanolamine, or Diethanolamine, orN-Methyldiethanolamine) and (Water + Monoethanolamine + N-Meth-yldiethanolamine) at T ) 298.15 K. J. Chem. Thermodyn. 2000, 32, 12851296.

(67) Weiland, R. H.; Dingman, J. C.; Cronin, D. B. Heat capacity ofAqueous Monoethanolamine, Diethanolamine, N-Methyldiethanolamine, andN-Methyldiethanolamine-Based Blends with Carbon Dioxide. J. Chem. Eng.Data 1997, 42, 10041006.

(68) Jakobsen, J. P.; Krane, J.; Svendsen, H. F. Liquid-Phase Composi-tion Determination in CO2-H2O-Alkanolamine Systems: An NMR Study.Ind. Eng. Chem. Res. 2005, 44, 98949903.

ReceiVed for reView March 19, 2010ReVised manuscript receiVed June 25, 2010

Accepted July 12, 2010

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zhang 2011 thermodynamic modeling for co2 absorption in aqueous mdea solution with electrolyte nrtl...

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