Thermodynamic Modeling for CO2 Absorption in ... - ACS Publications

Aug 5, 2010 - Influence of Gas Impurities on Thermodynamics of Amine Solutions. 1. ..... emission processes of N2O at the beginning of paddy field irr...
0 downloads 3 Views 442KB Size
Download PDF
Ind. Eng. Chem. Res. 2011, 50, 163–175

163

Thermodynamic Modeling for CO2 Absorption in Aqueous MDEA Solution with Electrolyte NRTL Model Ying Zhang AspenTech, Limited, Pudong, Shanghai 201203, People’s Republic of China

Chau-Chyun Chen* Aspen Technology, Inc., Burlington, Massachusetts 01803

Accurate modeling of thermodynamic properties for CO2 absorption in aqueous alkanolamine solutions is essential for the simulation and design of such CO2 capture processes. In this study, we use the Electrolyte Nonrandom Two-Liquid activity coefficient model to develop a rigorous and thermodynamically consistent representation for the MDEA-H2O-CO2 system. The vapor-liquid equilibrium (VLE), heat capacity, and excess enthalpy data for the binary aqueous amine system are used to determine the NRTL interaction parameters for the MDEA-H2O binary. The VLE, heat of absorption, heat capacity, and NMR spectroscopic data for the MDEA-H2O-CO2 ternary system are used to identify the NRTL interaction parameters for the molecule-electrolyte binaries and the previously unavailable standard-state properties of the amine ion, MDEA protonate. The calculated VLE, heat of absorption, heat capacity, and the species concentrations for the MDEA-H2O-CO2 system are compared favorably to experimental data. 1. Introduction CO2 capture by absorption with aqueous alkanolamines is considered an important technology to reduce CO2 emissions from fossil-fuel-fired power plants and to help alleviate global climate change.1 Methyldiethanolamine (MDEA), which is an alternative to monoethanolamine (MEA) for bulk CO2 removal, has the advantage of relatively low heat of reaction of CO2 with MDEA.2 To properly simulate and design the absorption/ stripping processes with MDEA-based aqueous solvents, it is essential to develop a sound process understanding of the transfer phenomena3 and accurate thermodynamic models4 to calculate the driving forces for heat and mass transfer. In other words, scalable simulation, design, and optimization of the CO2 capture processes start with modeling of the thermodynamic properties, specifically vapor-liquid equilibrium (VLE) and chemical reaction equilibrium, as well as calorimetric properties. Accurate modeling of thermodynamic properties requires availability of reliable experimental data. Earlier literature reviews5,6 suggested that, while there are extensive sets of experimental data available for the MDEA system, some of the published CO2 solubility data for the aqueous MDEA system may be questionable. The use of a thermodynamically consistent framework makes it possible to correlate available experimental data, to screen out questionable data, and to morph these diverse and disparate data into a useful and thermodynamically consistent form for process modeling and simulation. Excess Gibbs energy-based activity coefficient models provide a practical and rigorous thermodynamic framework to model thermodynamic properties of aqueous electrolyte systems, including aqueous alkanolamine systems for CO2 capture.4,7 For example, Austgen et al.8 and Posey9 applied the electrolyte NRTL model10-12 to correlate CO2 solubility in aqueous MDEA solution and other aqueous alkanolamines. Kuranov et al.,5 Kamps et al.,6 and Ermatchkov et al.13 used Pitzer’s equation14 to correlate the VLE data of the MDEA-H2O-CO2 system. * To whom correspondence should be addressed. Tel.: 781-221-6420. Fax: 781-221-6410. E-mail: [email protected].

Arcis et al.15 also fitted the VLE data with Pitzer’s equation and used the thermodynamic model to estimate the enthalpy of solution of CO2 in aqueous MDEA. Faramarzi et al.16 used the extended UNIQUAC model17 to represent VLE for CO2 absorption in aqueous MDEA, MEA, and mixtures of the two alkanolamines. Furthermore, they predicted the concentrations of the species in both MDEA and MEA solutions containing CO2 and in the case of MEA, compared to NMR spectroscopic measurements.18,19 In the present work, we expand the scope of the work of Austgen et al.8 and Posey9 to cover all thermodynamic properties. We use the 2009 version10 of the electrolyte NRTL model10-12 as the thermodynamic framework to correlate recently available experimental data for CO2 absorption in aqueous MDEA solution. Much new data for thermodynamic properties and calorimetric properties have become available in recent years, and they cover wider ranges of temperature, pressure, MDEA concentration, and CO2 loading. The binary NRTL parameters for MDEA-water binary are regressed from the binary VLE, excess enthalpy, and heat capacity data. The binary NRTL parameters for water-electrolyte pairs and MDEA-electrolyte pairs and the standard-state properties of protonated 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 thermodynamic representation for the MDEA-H2O-CO2 system over a broader range of conditions and give more reliable predictions over previous works. In conjunction with the use of the electrolyte NRTL model for the liquid-phase activity coefficients, we use the PC-SAFT20,21 equation of state (EOS) for the vapor-phase fugacity coefficients. While both PC-SAFT EOS and typical cubic EOS would give reliable fugacity calculations at low to medium pressures, we choose PC-SAFT for its ability to model vapor-phase fugacity coefficients at high pressures, which is an important consideration for modeling CO2 compression. The PC-SAFT parameters used in this model are given in Table 1. The parameters for water and CO2 are taken from the literature21 and the Aspen

10.1021/ie1006855  2011 American Chemical Society Published on Web 08/05/2010

164

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

Table 1. Parameters for PC-SAFT Equation of State MDEA

Table 2. Parameters of the Characteristic Volume for the Brelvi-O’Connell Modela

H2O

CO2 Aspen Databank22 2.5692

source

this work

segment number parameter, m segment energy parameter, ε segment size parameter, σ association energy parameter, εAB kAB

3.3044

Gross and Sadowski 21 1.0656

237.44 K

366.51 K

152.10 K

3.5975 Å

3.0007 Å

2.5637 Å

3709.9 K

2500.7 K

0K

0.066454 Å3

0.034868 Å3

0 Å3

2. Thermodynamic Framework 2.1. Chemical and Phase Equilibrium. CO2 solubility in aqueous amine solutions is determined by both its physical solubility and the chemical equilibrium for the aqueous phase reactions among CO2, water, and amines. 2.1.1. Physical Solubility. Physical solubility is the equilibrium between gaseous CO2 molecules and CO2 molecules in the aqueous amine solutions:

(1)

It can be expressed by Henry’s law: PyCO2φCO2 ) HCO2xCO2γ*CO2

(2)

where P is the system pressure, yCO2 the mole fraction of CO2 in the vapor phase, φCO2 the CO2 fugacity coefficient in the vapor phase, HCO2 the Henry’s law constant of CO2 in the mixed solvent of water and amine, xCO2 the equilibrium CO2 mole fraction in the liquid phase, and γ*CO2 the unsymmetric activity coefficient of CO2 in the mixed solvent of water and amine. The Henry’s constant in the mixed solvent can be calculated from those in the pure solvents:23

()

ln

Hi

γ∞i

)

∑x

A

ln

A

( ) HiA ∞ γiA

(3)

where Hi is the Henry’s constant of supercritical component i in the mixed solvent, HiA the Henry’s constant of supercritical component i in pure solvent A, γ∞i the infinite dilution activity coefficient of supercritical component i in the mixed solvent, ∞ the infinite dilution activity coefficient of supercritical γiA component i in pure solvent A, and xA the mole fraction of solvent A. We use wA in lieu of xA in eq 3 to weigh the contributions from different solvents.22 The parameter wA is calculated using eq 4: wA )

∞ 2/3 xA(ViA )

∑ x (V B

∞ 2/3 iB)

(4)

B

∞ ViA

parameter source V1,i V2,i

MDEA this work 0.369b 0

H2O

CO2

Brelvi and O’Connell 0.0464 0

24

Yan and Chen25 0.175 -3.38 × 10-4

a The Brelvi-O’Connell model has been described in ref 24. The correlation of the characteristic volume for the Brelvi-O’Connell 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 the characteristic volume for MDEA.

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

CO2(V) T CO2(l)

Characteristic Volume (m3/kmol)

represents the partial molar volume of supercritical Here, ∞ is component i at infinite dilution in pure solvent A. ViA 24 calculated from the Brelvi-O’Connell model with the charBO acteristic volume for the solute (VCO ) and solvent (VsBO), which 2 are listed in Table 2.

Table 3. Parameters for Henry’s Constant (Expressed in Units of Pa)a solute i solvent j source aij bij cij dij

CO2 H2O Yan and Chen25 91.344 -5876.0 -8.598 -0.012

CO2 MDEA this work 19.8933 -1072.7 0.0 0.0

a The correlation for Henry’s constant is given as follows: ln Hij ) aij + bij/T + cij ln T + dijT, where T is the temperature (given in Kelvin).

Henry’s law constants for CO2 with water and for CO2 with MDEA are required. The former has been extensively studied,25 although knowledge about the latter is relatively limited. Because it is not feasible to directly measure CO2 physical solubility in pure amines, because of the reactions between them, the common practice is to derive the CO2 physical solubility in amines from that of N2O for their analogy in molecular structure and, thus, in physical solubility as believed:26 HCO2,MDEA HN2O,MDEA

)

HCO2,water

(5)

HN2O,water

In 1992, Wang et al.27 reported the solubility of N2O in pure MDEA solvent as follows: -1312.7 HN2O,MDEA (kPa m3 kmol-1) ) (1.524 × 105) exp T (6)

(

)

Based on the work of Versteef and van Swaaij,28 we obtained the following two equations for the solubilities of N2O and CO2 in water: -2284 HN2O,water (kPa m3 kmol-1) ) (8.5470 × 106) exp T

(

) (7)

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

(

) (8)

We use eqs 5-8 to determine HCO2,MDEA and the parameters are summarized in Table 3. The Henry’s constant of CO2 in pure solvent A is corrected with the Poynting term for pressure:25

( RT1 ∫

HCO2,A(T, P) ) HCO2,A(T, po,l A ) exp

P

p◦,l A

)

∞ VCO dp 2,A

(9)

where HCO2,A(T,P) is the Henry’s constant of CO2 in pure solvent A at system temperature and pressure, HCO2,A(T,p°,l A ) the Henry’s constant of CO2 in pure solvent A at system temperature and ∞ the partial molar volume the solvent vapor pressure, and VCO 2,A

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

165

Table 4. Parameters for the Reference States Properties property

ig ∆fG298.15 (J/kmol)

ig ∆fH298.15 (J/kmol)

MDEA H2O CO2 H3O+ OHHCO3 CO23 MDEAH+

-1.6900 × 10 -2.2877 × 108 -3.9437 × 108

-3.8000 × 10 -2.4200 × 108 -3.9351 × 108

8

∞,aq ∆fG298.15 (J/kmol)

∞,aq ∆fH298.15 (J/kmol)

source

-2.8583 × 108 -2.2999 × 108 -6.9199 × 108 -6.7714 × 108 -5.1422 × 108 a

Aspen Databank22 Aspen Databank22 Aspen Databank22 Aspen Databank22 Wagman et al.29 Wagman et al.29 Wagman et al.29 this work

8

-2.3713 × 108 -1.5724 × 108 -5.8677 × 108 -5.2781 × 108 -2.5989 × 108 a

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 fit experimental data.

of CO2 at infinite dilution in pure solvent A calculated from the Brelvi-O’Connell model. At low pressures, the Poynting correction is almost unity and can be ignored. 2.1.2. Aqueous-Phase Chemical Equilibrium. The aqueousphase chemical reactions involved in the MDEA-water-CO2 system can be expressed as 2H2O T H3O+ + OH-

(10)

CO2 + 2H2O T H3O+ + HCO3

(11)

2+ HCO3 + H2O T H3O + CO3

(12)

MDEAH+ + H2O T H3O+ + MDEA

(13)

We calculate the equilibrium constants of the reaction from the reference-state Gibbs free energies of the participating components: -RT ln Kj ) ∆Goj (T)

(14)

the where Kj is the equilibrium constant of reaction j, ∆G°(T) j reference-state Gibbs free energy change for reaction j at temperature T, R the universal gas constant, and T the system temperature. For the aqueous phase reactions, the reference states chosen are pure liquid for the solvents (water and MDEA), and aqueous phase infinite dilution for the solutes (ionic and molecular). The Gibbs free energy of solvents is calculated from that of ideal gas and the departure function: Gs(T) ) Gsig(T) + ∆Gsigfl(T)

(15)

where Gs(T) is the Gibbs free energy of solvent s at temperature T, Gsig(T) the ideal gas Gibbs free energy of solvent s at temperature T, and ∆Gsigfl(T) the Gibbs free energy departure from ideal gas to liquid at temperature T. The Gibbs free energy of an ideal gas is calculated from the Gibbs free energy of formation of an ideal gas at 298.15 K, the enthalpy of formation of an ideal gas at 298.15 K, and the ideal gas heat capacity. ig Gsig(T) ) ∆fHs,298.15 +

(

∫

T Cig dT 298.15 p,s ig ∆fGs,298.15

ig ∆fHs,298.15 298.15

+

-T×

)

ig Cp,s dT 298.15 T

∫

T

(16)

where Gsig(T) is the ideal gas Gibbs free energy of solvent s at ig the ideal gas Gibbs free energy of temperature T, ∆fGs,298.15 ig formation of solvent s at 298.15 K, ∆fHs,298.15 the ideal gas ig the enthalpy of formation of solvent s at 298.15 K, and Cp,s ideal gas heat capacity of solvent s.

Table 5. Parameters for Ideal Gas Heat Capacity Heat Capacity (J/(kmol K)) parameter source C1i C2i C3i C4i C5i C6i C7i C8i

MDEA this work 2.7303 × 104 5.4087 × 102 0 0 0 0 278 397

H2O

CO2 22

Aspen Databank 3.3738 × 104 -7.0176 2.7296 × 10-2 -1.6647 × 10-5 4.2976 × 10-9 -4.1696 × 10-13 200 3000

Aspen Databank22 1.9795 × 104 7.3437 × 10 -5.6019 × 10-2 1.7153 × 10-5 0 0 300 1088.6

a The correlation for the ideal gas heat capacity is given as follows: 2 3 4 5 Cig p ) C1i + C2iT + C3iT + C4iT + C5iT + C6iT , C7i < T < C8i, where T is the temperature (given in Kelvin).

ig ig and ∆fHs,298.15 , are The reference-state properties, ∆fGs,298.15 shown in Table 4. The ideal gas heat capacities are shown in Table 5. For water, the Gibbs free energy departure function is obtained from the ASME steam tables. For MDEA, the departure function is calculated from the PC-SAFT equation of state. For molecular solute CO2, the Gibbs free energy in aqueous phase infinite dilution is calculated from Henry’s law:

G∞,aq (T) ) ∆fGig i i (T) + RT ln

( ) Hi,w Pref

(17)

(T) is the mole fraction scale aqueous-phase infinite where G∞,aq i dilution Gibbs free energy of solute i at temperature T, ∆fGig i (T) the ideal gas Gibbs free energy of formation of solute i at temperature T, Hi,w the Henry’s constant of solute i in water, and Pref the reference pressure. For ionic species, the Gibbs free energy in aqueous-phase infinite dilution is calculated from the Gibbs free energy of formation in aqueous-phase infinite dilution at 298.15 K, the enthalpy of formation in aqueous-phase infinite dilution at 298.15 K, and the heat capacity in aqueous-phase infinite dilution: G∞,aq (T) ) ∆fH∞,aq i i,298.15 +

(

∫

T

298.15

∞,aq ∆fH∞,aq i,298.15 - ∆fGi,298.15 + 298.15

C∞,aq p,i dT - T ×

)

( )

C∞,aq p,i 1000 dT + RT ln 298.15 T Mw (18)

∫

T

(T) is the mole fraction scale aqueous-phase infinite Here, G∞,aq i dilution Gibbs free energy of solute i at temperature T, ∆fG∞,aq i,298.15 the molality scale aqueous-phase infinite dilution Gibbs free ∞,aq the energy of formation of solute i at 298.15 K, ∆fHi,298.15 aqueous phase infinite dilution enthalpy of formation of solute i at 298.15 K, and C∞,aq p,i the aqueous-phase infinite dilution heat capacity of solute i. The term RT ln (1000/Mw) is added because

166

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

Table 6. Parameters for Aqueous-Phase Infinite Dilution Heat Capacitya Heat Capacity (J/(kmol K)) parameter

H3O+

OH-

HCO3

CO23

MDEAH+

source C1

Aspen Databank22 7.5291 × 104

Aspen Databank22 -1.4845 × 105

Criss and Cobble31 -2.9260 × 104 b

Criss and Cobble31 -3.9710 × 105 b

this work 2.9900 × 105 b

∞,aq ∞,aq ) C1). b The Cp,i value of MDEAH+ is calculated from the The aqueous-phase infinite dilution heat capacity is assumed to be constant (Cp,i 30 ∞,aq 2values of HCOchemical equilibrium constant in Kamps and Maurer, which is used as the initial guess to fit experimental data. The Cp,i 3 and CO3 are the average values of heat capacity between 298 K and 473 K (taken from Criss and Cobble31). a

∞,aq ∆fGi,298.15 , as reported in the literature, is based on molality is based on mole fraction scale. concentration scale while G∞,aq i ∞,aq ∞,aq ∞,aq , ∆fHi,298.15 , and Cp,i The standard-state properties ∆fGi,298.15 are available in the literature for most ionic species, except those of MDEAH+. (See Tables 4 and 6.) We calculate the referencestate properties of the MDEAH+ ion from the experimental equilibrium constant of eq 13, as reported in 1996 by Kamps ∞,aq ∞,aq and ∆fHi,298.15 values and Maurer.30 The calculated ∆fGi,298.15 ∞,aq are given in Table 4, and the calculated Cp,i values are given in Table 6. As will be shown later, we use these calculated reference-state properties for MDEAH+ as part of the adjustable parameters in the fitting experimental data of thermodynamic properties, including VLE, heat of solution, heat capacity, and species concentration from NMR spectra. Also given in Table ∞,aq for HCO3- and CO32-. They have 6 are estimated values of Cp,i been taken from the 1964 work of Criss and Cobble.31 2.2. Heat of Absorption and Heat Capacity. The CO2 heat of absorption in aqueous MDEA solutions can be derived from an enthalpy balance of the absorption process:

∆Habs )

l l g - nInitialHInitial - nCO2HCO nFinalHFinal 2

nCO2

(19)

l where ∆Habs is the heat of absorption per mole of CO2, HFinal the molar enthalpy of the final solution, HlInitial the molar enthalpy g of the initial solution, HCO2 the molar enthalpy of gaseous CO2 absorbed, nFinal the number of moles of the final solution, nInitial the number of moles of the initial solution, and nCO2 the number of moles of CO2 absorbed. There are two types of heat of absorption: integral heat of absorption and differential heat of absorption. The integral heat of absorption for a certain amine-H2O-CO2 system refers to the heat effect per mole of CO2 during the CO2 loading of the amine solution increasing from zero to the final CO2 loading value of that amine-H2O-CO2 system. The differential heat of absorption for an amine-H2O-CO2 system refers to the heat effect per mole of CO2 if a very small amount of CO2 is added into this amine-H2O-CO2 system. For calculation of both types of heat of absorption, enthalpy calculations for the initial and final amine-H2O-CO2 systems and for gaseous CO2 are required. The heat capacity of the MDEA-H2O-CO2 system can be calculated from the temperature derivative of enthalpy. We use the following equation for liquid enthalpy:

Hl ) xwHwl + xsHsl +

∑xH i

∞,aq i

+ Hex

(20)

Table 7. Parameters for Heat of Vaporization (Expressed in Units of J/kmol)a component i source C1i C2i C3i C4i C5i Tci

MDEA this work 9.7381 × 107 4.6391 × 10-1 0 0 0 741.9b

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

The liquid enthalpy of pure water is calculated from the ideal gas model and the ASME Steam Tables EOS for enthalpy departure: ig Hwl (T) ) ∆fHw,298.15 +

∫

T

298.15

ig Cp,w dT + ∆Hwigfl(T, p)

(21)

where Hwl (T) is the liquid enthalpy of water at temperature T, ig the ideal gas enthalpy of formation of water at 298.15 ∆fHw,298.15 ig the ideal-gas heat capacity of water, and ∆Hwigfl(T,p) K, Cp,w the enthalpy departure calculated from the ASME Steam Tables EOS. Liquid enthalpy of the nonaqueous solvent s is calculated from the ideal-gas enthalpy of formation at 298.15 K, the idealgas heat capacity, the vapor enthalpy departure, and the heat of vaporization: ig Hls(T) ) ∆fHs,298.15 +

∫

T

298.15

ig Cp,s dT + ∆HVs (T, p) - ∆vapHs(T)

(22)

Here, Hsl(T) is the liquid enthalpy of solvent s at temperature T, ig the ideal-gas enthalpy of formation of solvent s at ∆fHs,298.15 298.15 K, Cigp,s the ideal-gas heat capacity of solvent s, ∆HVs (T,p) the vapor enthalpy departure of solvent s, and ∆vapHs(T) the heat of vaporization of solvent s. The PC-SAFT EOS is used for the vapor enthalpy departure and the DIPPR heat of vaporization correlation is used for the heat of vaporization. Table 7 shows the DIPPR equation and the correlation parameters for the heat of vaporization. The enthalpies of ionic solutes in aqueous phase infinite dilution are calculated from the enthalpy of formation at 298.15 K in aqueous-phase infinite dilution and the heat capacity in aqueous-phase infinite dilution:

i

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

H∞,aq (T) ) ∆fH∞,aq i i,298.15 +

∫

T

298.15

C∞,aq p,i dT

(23)

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

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

phase chemical equilibrium calculations, we choose the aqueousphase infinite dilution reference state for molecular solute CO2 and all ionic species. In applying the electrolyte NRTL model for liquid-phase activity coefficient calculations, the binary NRTL interaction parameters for molecule-molecule binary, molecule-electrolyte binary, and electrolyte-electrolyte binary systems are required. Here, electrolytes are defined as cation and anion pairs. In addition, solvent dielectric constants are needed to facilitate calculations of long-range ion-ion interaction contribution to activity coefficients. Table 8 shows the dielectric constant correlation used in this work for MDEA. Unless specified otherwise, all molecule-molecule binary parameters and electrolyte-electrolyte binary parameters are defaulted to zero. All molecule-electrolyte binary parameters are defaulted to (8,-4), average values of the parameters as reported for the electrolyte NRTL model.12 The nonrandomness factor (R) is fixed at 0.2. The calculated thermodynamic properties of the electrolyte solution are dominated by the binary NRTL parameters associated with the major species in the system. In other words, the binary parameters for the water-MDEA binary, the + 2water-(MDEAH+, HCO3 ) binary, the water-(MDEAH , CO3 ) + binary, and the MDEA-(MDEAH , HCO3 ) binary systems determine the calculated thermodynamic properties. These binary parameters, in turn, are identified from fitting to available experimental data.

Table 8. Parameters for Dielectric Constant component i source Ai Bi Ci

MDEA Aspen Databank22 21.9957 8992.68 298.15

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

∞,aq ∞,aq Both ∆fHi,298.15 and Cp,i are also used in the calculation of Gibbs free energy of the solutes, thus impacting chemical ∞,aq ∞,aq and Cp,i for equilibrium calculations. In this study, ∆fHi,298.15 + MDEAH are determined by fitting to the experimental phase equilibrium data, the heat of solution data, and the speciation data, together with molality scale Gibbs free energy of formation ∞,aq , and NRTL interaction parameters. at 298.15 K, ∆fGi,298.15 The enthalpies of molecular solutes in aqueous phase infinite dilution are calculated from Henry’s law:

(

2 (T) ) ∆fHig H∞,aq i i (T) - RT

∂ ln Hi,w ∂T

)

167

(24)

where ∆fHig i (T) is the ideal gas enthalpy of formation of solute i at temperature T, and Hi,w Henry’s constant of solute i in water. Excess enthalpy (Hex) is calculated from the activity coefficient model (i.e., the electrolyte NRTL model). 2.3. Activity Coefficients. Activity coefficients are required in phase equilibrium calculations, aqueous-phase chemical equilibrium calculations, heat of absorption, liquid heat capacity, and liquid enthalpy calculations. The activity coefficient of a component 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-solvent reference state for the molecular solute CO2, and in aqueous-

3. Modelling Results Table 9 summarizes the model parameters and sources of the parameters used in the thermodynamic model. Most of the parameters can be obtained from the literature. The remaining parameters are determined by fitting to the experimental data.

Table 9. Parameters Estimated in Modeling parameter

component

source

Antoine equation ∆vapH

MDEA MDEA

regression regression

dielectric constant Henry’s constant

MDEA CO2 in H2O CO2 in MDEA CO2-H2O binary MDEA-H2O binary molecule-electrolyte binaries

Aspen Databank22 Yan and Chen25 this work Yan and Chen25 regression regression

H2O, MDEA, CO2 H2O, MDEA, CO2 H2O, CO2 MDEA 2H3O+, OH-, HCO3 , CO3 MDEAH+

Aspen Databank22 Aspen Databank22 Aspen Databank22 regression Aspen Databank22 regression

∞,aq ∆fH298.15

2H3O+, OH-, HCO3 , CO3 MDEAH+

Aspen Databank22 regression

C∞,aq p

H3O+, OH2HCO3 , CO3 MDEAH+

Aspen Databank22 Criss and Cobble31 regression

NRTL binary parameters

ig ∆fG298.15 ig ∆fH298.15 Cig p ∞,aq ∆fG298.15

data used for regression vapor pressure of MDEA heat of vaporization of MDEA, calculated from the vapor pressure using the Clausius-Clapeyron equation

VLE, excess enthalpy, and heat capacity for the MDEA-H2O binary VLE, excess enthalpy, heat capacity, and species concentration from NMR spectra for the MDEA-H2O-CO2 system

liquid heat capacity of MDEA VLE, excess enthalpy, heat capacity, and species concentration from NMR spectra for the MDEA-H2O-CO2 system VLE, excess enthalpy, heat capacity, and species concentration from NMR spectra for the MDEA-H2O-CO2 system 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 MDEA data type

temperature, T (K)

pressure, P (kPa)

data points

average relative deviation, |∆Y/Y| (%)

reference

vapor pressure vapor pressure vapor pressure liquid heat capacity liquid heat capacity liquid heat capacity

293-401 420-513 420-738 299-397 303-353 278-368

0.0006-1.48 3.69-90.4 3.69-3985

26 14 23 5 11 19

1.5 4.0 2.9 0.5 0.4 0.3

Daubert et al.33 Noll et al.34 VonNiederhausern et al.32 Maham et al.35 Chen et al.36 Zhang et al.37

168

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

Table 11. Antoine Equation Parameters for Pure MDEAa parameter

component i

value

C1i C2i C3i C4i

MDEA MDEA MDEA MDEA

1.2276 × 102 -1.3253 × 104 -1.3839 × 10 3.20 × 10-6

a The correlation for the Antoine equation is given as follows: ln Pi*,l ) C1i + C2i/T + C3i ln T + C4iT2, where T is the temperature (given in Kelvin).

3.1. MDEA. Extensive experimental vapor pressure data and liquid heat capacity data are available for MDEA. The data used in the regression for MDEA and the correlation results are summarized in Table 10. Table 11 shows the Antoine equation parameters regressed from the recently available vapor pressure data.32-34 The heat of vaporization (from 293 K to 473 K) generated with the regressed Antoine equation parameters through the Clausius-Clapeyron equation are used to determine the DIPPR heat of vaporization equation parameters (shown in Table 7). The ideal-gas heat capacity correlation parameters are obtained by fitting to the liquid heat capacity data35-37 (shown in Table 5). Table 10 shows the excellent correlation of the experimental data for vapor pressure, with an average relative deviation of 50%. We further show the computed integral heat of absorption as the sum of the various contributions from reactions 10-13, CO2 dissolution, and excess enthalpy. k

∆Habs )

∑ ∆n ∆H° + ∆H i

i

dissolution

+ ∆Hex

(25)

i)1

where ∆Habs is the integral heat of absorption per mole of CO2, ∆H°i the standard heat of reaction for reaction i per mole of key component reacted, and ∆ni the reaction extent of the reaction key component for reaction i when 1 mol CO2 is absorbed.

Figure 18. Integral CO2 heat of absorption in 30 wt % MDEA aqueous solution at 313 K. Symbols (0) represent experimental data from Mathonat;65 lines represent model results ((s) integral heat of absorption, (- · · -) differential heat of absorption, ( · · · ) contribution of reactions, (- · -) contribution of CO2 dissolution, (- - -) contribution of excess enthalpies).

The heat of CO2 dissolution (∆Hdissolution) is calculated as the enthalpy difference between 1 mol of CO2 in the vapor phase and 1 mol of CO2 in aqueous-phase infinite dilution. The contribution of excess enthalpies (∆Hex) is computed as the excess enthalpy difference between the final and initial compositions of the solution per mole of CO2 absorbed. The results in Figures 18-20 show that the heat of absorption is dominated by MDEAH+ dissociation and excess enthalpy. In addition, CO2 dissolution is important near room temperature, whereas CO2 dissociation becomes more important at higher temperatures. Figure 21 shows a comparison of the model correlations and the experimental data of Weiland et al.67 for heat capacity of the MDEA-H2O-CO2 system. The model results are consistent with the data. To show the impact of the different versions of the electrolyte NRTL model to the model results, we perform VLE predictions with the same model parameter values given in Table 15 with the 1986 version of the electrolyte NRTL

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

173

concentrations. The difference increases slightly with increasing MDEA concentration. 4. Conclusion

Figure 19. Integral CO2 heat of absorption in 30 wt % MDEA aqueous solution at 353 K. Symbols (4) represent experimental data from Mathonat;65 lines represent model results ((s) integral heat of absorption, (- · · -) differential overall absorption heat, ( · · · ) contribution of reactions, (- · -) contribution of CO2 dissolution, (- - -) contribution of excess enthalpies).

To support process modeling and simulation of the CO2 capture process with MDEA, the electrolyte NRTL model has been successfully applied to correlate the available experimental data on thermodynamic properties of the MDEA-H2O-CO2 system. The model has been validated for predictions of vaporliquid equilibrium (VLE), heat capacity, and CO2 heat of absorption of the MDEA-H2O-CO2 system with temperatures from 313 K to 393 K, MDEA concentrations up to 8 m (∼50 wt %), and CO2 loadings up to 1.32. This model should provide a comprehensive thermodynamic property representation for the MDEA-H2O-CO2 system over a broader range of conditions and give more-reliable predictions than those from previous works. Acknowledgment The authors thank Huiling Que and Joseph DeVincentis for their support in preparing the manuscript. Literature Cited

Figure 20. Integral CO2 heat of absorption in 30 wt % MDEA aqueous solution at 393 K. Symbols (O) represent experimental data from Mathonat;65 lines represent model results ((s) integral heat of absorption, (- · · -) differential heat of absorption, ( · · · ) contribution of reactions, (- · -) contribution of CO2 dissolution, (- - -) contribution of excess enthalpies).

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

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

(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 Aqueous Monoethanolamine Solution. Ind. Eng. Chem. Res. 2009, 48, 9233–9246. (2) Kohl. A. L.; Riesenfeld, F. C. Gas Purification, 4th ed.; Gulf Publishing: Houston, TX, 1985. (3) Taylor, R.; Krishna, R.; Kooijman, H. Real-World Modeling of Distillation. Chem. Eng. Prog. 2003, 99, 28–39. (4) Chen, C.-C.; Mathias, P. M. Applied Thermodynamics for Process Modeling. AIChE J. 2002, 48, 194–200. (5) Kuranov, G.; Rumpf, B.; Smirnova, N. A.; Maurer, G. Solubility of Single Gases Carbon Dioxide and Hydrogen Sulfide in Aqueous Solutions of N-Methyldiethanolamine in the Temperature Range 313-413 K at Pressures up to 5 MPa. Ind. Eng. Chem. Res. 1996, 35, 1959–1966. ´ . P.-S.; Balaban, A.; Jo¨decke, M.; Kuranov, G.; Smirnova, (6) Kamps, A N. A.; Maurer, G. Solubility of Single Gases Carbon Dioxide and Hydrogen Sulfide in Aqueous Solutions of N-Methyldiethanolamine at Temperatures from 313 to 393 K and Pressures up to 7.6 MPa: New Experimental Data and Model Extension. Ind. Eng. Chem. Res. 2001, 40, 696–706. (7) Chen, C.-C. Toward Development of Activity Coefficient Models for Process and Product Design of Complex Chemical Systems. Fluid Phase Equilib. 2006, 241, 103–112. (8) Austgen, D. M.; Rochelle, G. T.; Chen, C.-C. Model of VaporLiquid Equilibria for Aqueous Acid Gas-Alkanolamine Systems. 2. Representation of H2S and CO2 Solubility in Aqueous MDEA and CO2 Solubility in Aqueous Mixtures of MDEA with MEA or DEA. Ind. Eng. Chem. Res. 1991, 30, 543–555. (9) Posey, M. L. Thermodynamic Model for Acid Gas Loaded Aqueous Alkanolamine Solutions, Ph.D. Thesis, University of Texas at Austin, Austin, TX, 1996. (10) Song, Y.; Chen, C.-C. Symmetric Electrolyte Nonrandom TwoLiquid Activity Coefficient Model. Ind. Eng. Chem. Res. 2009, 48, 7788– 7797. (11) Chen, C.-C.; Evans, L. B. A Local Composition Model for the Excess Gibbs Energy of Aqueous Electrolyte Systems. AIChE J. 1986, 32, 444–454. (12) Chen, C.-C.; Britt, H. I.; Boston, J. F.; Evans, L. B. Local Composition Model for Excess Gibbs Energy of Electrolyte Systems. Part I: Single Solvent, Single Completely Dissociated Electrolyte Systems. AIChE J. 1982, 28, 588–596. ´ . P.-S.; Maurer, G. Solubility of Carbon (13) Ermatchkov, V.; Kamps, A Dioxide in Aqueous Solutions of N-Methyldiethanolamine in the Low Gas Loading Region. Ind. Eng. Chem. Res. 2006, 45, 6081–6091. (14) Pitzer, K. S. Thermodynamics of Electrolytes. I. Theoretical Basis and General Equations. J. Phys. Chem. 1973, 77, 268–277.

174

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

(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, 783–789. (16) Faramarzi, L.; Kontogeorgis, G. M.; Thomsen, K.; Stenby, E. H. Extended UNIQUAC Model for Thermodynamic Modeling of CO2 Absorption in Aqueous Alkanolamine Solutions. Fluid Phase Equilib. 2009, 282, 121–132. (17) Thomsen, K.; Rasmussen, P. Modeling of Vapor-Liquid-Solid Equilibrium in Gas-Aqueous Electrolyte Systems. Chem. Eng. Sci. 1999, 54, 1787–1802. (18) Bo¨ttinger, W.; Maiwald, M.; Hasse, H. Online NMR Spectroscopic Study of Species Distribution in MEA-H2O-CO2 and DEA-H2O-CO2. Fluid Phase Equilib. 2008, 263, 131–143. (19) Hilliard, M. A Predictive Thermodynamic Model for an Aqueous Blend of Potassium Carbonate, Piperazine, and Monoethanolamine for Carbon Dioxide, Ph.D. Dissertation, University of Texas at Austin, Austin, TX, 2008. (20) Gross, J.; Sadowski, G. Perturbed-Chain SAFT: An Equation of State Based on a Perturbation Theory for Chain Molecules. Ind. Eng. Chem. Res. 2001, 40, 1244–1260. (21) Gross, J.; Sadowski, G. Application of the Perturbed-Chain SAFT Equation of State to Associating Systems. Ind. Eng. Chem. Res. 2002, 41, 5510–5515. (22) Aspen Physical Property System, V7.2; Aspen Technology, Inc.: Burlington, MA, 2010. (23) Van Ness, H. C.; Abbott, M. M. Vapor-Liquid Equilibrium: Part VI. Standard State Fugacities for Supercritical Components. AIChE J. 1979, 25, 645–653. (24) Brelvi, S. W.; O’Connell, J. P. Corresponding States Correlations for Liquid Compressibility and Partial Molar Volumes of Gases at Infinite Dilution in Liquids. AIChE J. 1972, 18, 1239–1243. (25) Yan, Y.-Z.; Chen, C.-C. Thermodynamic Modeling of CO2 Solubility in Aqueous Solutions of NaCl and Na2SO4. Submitted to J. Supercrit. Fluids. (26) Clarke, J. K. A. Kinetics of Absorption of Carbon Dioxide in Monoethanolamine Solutions at Short Contact Times. Ind. Eng. Chem. Fundam. 1964, 3, 239–245. (27) Wang, Y. W.; Xu, S.; Otto, F. D.; Mather, A. E. Solubility of N2O in Alkanolamines and in Mixed Solvents. Chem. Eng. J. 1992, 48, 31–40. (28) Versteeg, G. F.; Van Swaaij, W. P. M. Solubility and Diffusivity of Acid Gases (CO2, N2O) in Aqueous Alkanolamine Solutions. J. Chem. Eng. Data 1988, 33, 29–34. (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 of chemical thermodynamic properties. Selected values for inorganic and C1 and C2 organic substances in SI units. J. Phys. Chem. Ref. Data 1982, 11 (Supplement No. 2), pp 2-38 and 2-83. ´ . P.-S.; Maurer, G. Dissociation Constant of N-Meth(30) Kamps, A yldiethanolamine in Aqueous Solution at Temperatures from 278 to 368 K. J. Chem. Eng. Data 1996, 41, 1505–1513. (31) Criss, C. M.; Cobble, J. W. The Thermodynamic Properties of High Temperature Aqueous Solutions. V. The Calculation of Ionic Heat Capacities up to 200°. Entropies and Heat Capacities above 200°. J. Am. Chem. Soc. 1964, 86, 5390–5393. (32) Von Niederhausern, D. M.; Wilson, G. M.; Giles, N. F. Critical Point and Vapor Pressure Measurements for 17 Compounds by a Low Residence Time Flow Method. J. Chem. Eng. Data 2006, 51, 1990–1995. (33) Daubert, T. E.; Hutchison, G. Vapor Pressure of 18 Pure Industrial Chemicals. AIChE Symp. Ser. 1990, 86, 93–114. (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, 105–120. (35) Maham, Y.; Mather, A. E.; Hepler, L. G. Excess Molar Enthalpies of (Water + Alkanolamine) Systems and Some Thermodynamic Calculations. J. Chem. Eng. Data 1997, 42, 988–992. (36) Chen, Y.-J.; Shih, T.-W.; Li, M.-H. Heat Capacity of Aqueous Mixtures of Monoethanolamine with N-Methyldiethanolamine. J. Chem. Eng. Data 2001, 46, 51–55. (37) Zhang, K.; Hawrylak, B.; Palepu, R.; Tremaine, P. R. Thermodynamics of Aqueous Amines: Excess Molar Heat Capacities, Volumes, and Expansibilities of (Water + Methyldiethanolamine (MDEA)) and (Water + 2-Amino-2-methyl-1-propanol (AMP)). J. Chem. Thermodyn. 2002, 34, 679–710. (38) AI-Ghawas, H. A.; Hagewiesche, D. P.; Ruiz-Ibanez, G.; Sandall, O. C. Physicochemical Properties Important for Carbon Dioxide Absorption in Aqueous Methyldiethanolamine. J. Chem. Eng. Data 1989, 34, 385– 391.

(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. Data 1992, 37, 239–242. (40) Xu, S.; Qing, S.; Zhen, Z.; Zhang, C.; Carroll, J. Vapor Pressure Measurements of Aqueous N-Methyldiethanolamine Solutions. Fluid Phase Equilib. 1991, 67, 197–201. (41) Voutsas, E.; Vrachnos, A.; Magoulas, K. Measurement and Thermodynamic Modeling of the Phase Equilibrium of Aqueous N-Methyldiethanolamine Solutions. Fluid Phase Equilib. 2004, 224, 193– 197. (42) Kim, I.; Svendsen, H. F.; Børresen, E. Ebulliometric Determination of Vapor-Liquid Equilibria for Pure Water, Monoethanolamine, NMethyldiethanolamine, 3-(Methylamino)-propylamine, and Their Binary and Ternary Solutions. J. Chem. Eng. Data 2008, 53, 2521–2531. (43) Maham, Y.; Mather, A. E.; Mathonat, C. Excess properties of (alkyldiethanolamine + H2O) mixtures at temperatures from (298.15 to 338.15) K. J. Chem. Thermodyn. 2000, 32, 229–236. (44) Chiu, L.-F.; Li, M.-H. Heat Capacity of Alkanolamine Aqueous Solutions. J. Chem. Eng. Data 1999, 44, 1396–1401. (45) Jou, F. Y.; Mather, A. E.; Otto, F. D. Solubility of H2S and CO2 in Aqueous Methyldiethanolamine Solution. Ind. Eng. Chem. Process Des. DeV. 1982, 21, 539–544. (46) Chakma, A.; Meisen, A. Solubility of CO2 in Aqueous Methyldiethanolamine and N,N-Bis(hydroxyethl)piperazine Solutions. Ind. Eng. Chem. Res. 1987, 26, 2461–2466. (47) Maddox, R. N.; Bhairi, A. H.; Diers, J. R.; Thomas, P. A. Equilibrium Solubility of Carbon Dioxide or Hydrogen Sulfide in Aqueous Solutions of Monoethanolamine, Diglycolamine, Diethanolamine and Methyldiethanolamine. GPA Res. Rep. 1987, 1–47. (48) MacGregor, R. J.; Mather, A. E. Equilibrium Solubility of H2S and CO2 and Their Mixtures in a Mixed Solvent. Can. J. Chem. Eng. 1991, 69, 1357–1366. (49) Jou, F. Y.; Carroll, J. J.; Mather, A. E.; Otto, F. D. The Solubility of Carbon Dioxide and Hydrogen Sulfide in a 35 wt % Aqueous Solution Methyldiethanolamine. Can. J. Chem. Eng. 1993, 71, 264–268. (50) Dawodu, O. F.; Meisen, A. Solubility of Carbon Dioxide in Aqueous Mixtures of Alkanolamines. J. Chem. Eng. Data 1994, 39, 548–552. (51) Liu, H.; Xu, G.; Zhang, C.; Wu, Y. Solubilities of Carbon Dioxide in Aqueous Activated Methyldiethanolamine Solutions. Huadong Ligong Daxue Xuebao 1999, 25, 242–246. (52) Mathonat, C.; Majer, V.; Mather, A. E.; Grolier, J.-P. E. Enthalpies of Absorption and Solubility of CO2 in Aqueous Solutions of Methyldiethanolamine. Fluid Phase Equilib. 1997, 140, 171–182. (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, 1161–1164. (54) Baek, J.-I.; Yoon, J.-H. Solubility of Carbon Dioxide in Aqueous Solutions of 2-Amino-2-Methyl-1,3-Propanediol. J. Chem. Eng. Data 1998, 43, 635–637. (55) Rogers, W. J.; Bullin, J. A.; Davison, R. R. FTIR Measurements of Acid-Gas-Methyldiethanolamine Systems. AIChE J. 1998, 44, 2423– 2430. (56) Silkenba¨umer, D.; Rumpf, B.; Lichtenthaler, R. N. Solubility of Carbon Dioxide in Aqueous Solutions of 2-Amino-2-methyl-1-propanol and N-Methyldiethanolamine and Their Mixtures in the Temperature Range from 313 to 353 K and Pressures up to 2.7 MPa. Ind. Eng. Chem. Res. 1998, 37, 3133–3141. (57) Xu, G.-W.; Zhang, C.-F.; Qin, S.-J.; Gao, W.-H.; Liu, H.-B. GasLiquid Equilibrium in a CO2-MDEA-H2O System and the Effect on Piperazine on It. Ind. Eng. Chem. Res. 1998, 37, 1473–1477. (58) Lemoine, B.; Li, Y.-G.; Cadours, R.; Bouallou, C.; Richon, D. Partial Vapor Pressure of CO2 and H2S over Aqueous Methyldiethanolamine Solutions. Fluid Phase Equilib. 2000, 172, 261–277. (59) Bishnoi, S.; Rochelle, G. T. Thermodynamics of PiperazineMethyldiethanolamine-Water-Carbon Dioxide. Ind. Eng. Chem. Res. 2002, 41, 604–612. ´ . P.-S.; Rumpf, B.; Maurer, G.; Anoufrikov, Y.; Kuranov, (60) Kamps, A G.; Smirnova., N. A. Solubility of CO2 in H2O + N-Methyldiethanolamine + (H2SO4 or Na2SO4). AIChE J. 2002, 48, 168–177. (61) Ali, B. S.; Aroua, M. K. Effect of Piperazine on CO2 loading in Aqueous Solutions of MDEA at Low Pressure. Int. J. Thermophys. 2004, 25, 1863–1870. (62) Sidi-Boumedine, R.; Horstmann, S.; Fischer, K.; Provost, E.; Fu¨rst, W.; Gmehling, J. Experimental Determination of Carbon Dioxide Solubility Data in Aqueous Alkanolamine Solutions. Fluid Phase Equilib. 2004, 218, 85–94. (63) Ma’mun, S.; Nilsen, R.; Svendsen, H. F.; Juliussen, O. Solubility of Carbon Dioxide in 30 mass% Monoethanolamine and 50 mass% Methyldiethanolamine Solutions. J. Chem. Eng. Data 2005, 50, 630–634.

Ind. Eng. Chem. Res., Vol. 50, No. 1, 2011 (64) Dicko, M.; Coquelet, C.; Jarne, C.; Northrop, S.; Richon, D. Acid Gases Partial Pressures above a 50 wt% Aqueous Methyldiethanolamine Solution: Experimental Work and Modeling. Fluid Phase Equilib. 2010, 289, 99–109. (65) Mathonat, C. Calorimetrie de me´lange, a ecoulement, a temperatures et pressions elevees. Application a l’etude de l’elimination du dioxide de carbone a l’aide de solutions aqueuses d’alcanolamines, Universite Blaise Pascal, Paris, 1995, p 265. (66) Carson, J. K.; Marsh, K. N.; Mather, A. E. Enthalpy of Solution of Carbon Dioxide in (Water + Monoethanolamine, or Diethanolamine, or N-Methyldiethanolamine) and (Water + Monoethanolamine + N-Methyldiethanolamine) at T ) 298.15 K. J. Chem. Thermodyn. 2000, 32, 1285– 1296.

175

(67) Weiland, R. H.; Dingman, J. C.; Cronin, D. B. Heat capacity of Aqueous Monoethanolamine, Diethanolamine, N-Methyldiethanolamine, and N-Methyldiethanolamine-Based Blends with Carbon Dioxide. J. Chem. Eng. Data 1997, 42, 1004–1006. (68) Jakobsen, J. P.; Krane, J.; Svendsen, H. F. Liquid-Phase Composition Determination in CO2-H2O-Alkanolamine Systems: An NMR Study. Ind. Eng. Chem. Res. 2005, 44, 9894–9903.

ReceiVed for reView March 19, 2010 ReVised manuscript receiVed June 25, 2010 Accepted July 12, 2010 IE1006855