VaporâLiquid Equilibrium and Physicochemical Properties of Novel

Article pubs.acs.org/jced

Vapor−Liquid Equilibrium and Physicochemical Properties of Novel Aqueous Blends of (2-Diethylaminoethanol + Piperazine) for CO2 Appropriation S. Adak and M. Kundu* Department of Chemical Engineering, National Institute of Technology, Rourkela, Orissa 769008, India S Supporting Information *

ABSTRACT: Equilibrium solubility of CO2 in aqueous blends of 0.23 mol/kg piperazine (PZ) + 0.92 mol/kg 2-diethylaminoethanol (DEAE), 0.52 mol/kg PZ + 2.08 mol/kg DEAE, 0.92 mol/kg PZ + 3.68 mol/kg DEAE, and 1.49 mol/kg PZ + 5.96 mol/kg DEAE in the low pressure region of 0.1−65 kPa and at temperatures of 303.15− 323.15 K is reported in the present article. A thermodynamic model is developed, which correlates the experimentally generated data on CO2 solubility in the newly proposed blend with an excellent agreement. Density and viscosity of DEAE + PZ + H2O have been measured at temperatures of 303.1−323.1 K and total amine mass percentage in all the blends are kept constant at 0.3. The mass % ratios of PZ/DEAE considered for measurements were 3:27, 6:24, 9:21, and 12:18. pKa of aqueous DEAE solution are reported in 298.15−333.15 K temperature range. Generated density data are correlated using Redlich−Kister equation, Grunberg and Nissan, and Gonzalez-Olmos, and Iglesias type models and viscosity data are correlated using Grunberg and Nissan model.

1. INTRODUCTION The world is predicted to be warmer at least 3 to 4 °C by 2100 due to greenhouse gas (GHG) emission, which would shift the present equilibrium in ecosystem regarding its food security, fresh water availability, forestation, and climate dynamics.1 CO2, the greenhouse gas concentration in the atmosphere, has increased primarily because of the anthropogenic activities like natural gas processing, coal-based power plant, steel and aluminum industry, and urban transportation exhausts. There has been an unequivocal conscience, in the Paris 2015 summit on global climate change toward a global low carbon transition and economy, conserving a sustainable development goal.1 Intended nationally determined contributions (INDCs) of various countries have pledged to reduce global warming, hence, to reduce emissions per capita to an extent of 9% by 2030.2 To keep pace with the world vision, fresh and extensive R&D initiatives across the globe in carbon capture and sequestration (CCS), and carbon capture and utilization (CCU) are imminent. Post combustion CO2 capture (PCC) has already initiated new dimensions in research related to gas treating deploying room temperature ionic liquids (ILs) and its mixture with alkanolamines,3−5 alkali metal salts of tertiary amino acids promoted with MEA for CO2 capture.6 Currently, chemical absorption in alkanolamine is the established postcombustion CO2 capture technology to be implemented commercially. However, solvent loss, high capital investment for absorbers and strippers, and high regeneration energy requirement of alkanolamines have necessitated still better solvent formulation suitable for large scale industrial process applications.7 The environmentally benign, lower regeneration energy consuming, degradation resistant, low vapor pressure, thermally and © XXXX American Chemical Society

chemically stable, less corrosive and nonfoaming alkanolamine formulation is among the current pursuit in gas treating research. Primary, secondary, tertiary alkanolamines and their blends have been used extensively for CO2 mitigation. Numerous blends of monoethanolamine (MEA) and diethanolamine with tertiary and sterically hindered alkanolamines like N-methyldiethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP), 2-amino-2-(hydroxymethyl)-1, and 3-propanediol (AHPD) are tested for their CO2 capture capacity. Some solvents have been proposed with multiple amine functionalities and among them, piperazine (PZ) has been in use as a promoter in treating coal based power plant flue gas.8−12 Use of PZ-promoted MDEA was disclosed through U.S. Patent (issued back in 198213). It is an established fact that PZ is more effective than the conventional activators like MEA and its major advantages are its high activity toward carbon dioxide and its formidable thermal as well as oxidative degradation resistance.13,14 Besides, PZ blends incur less solvent loss due to their low volatility.15 The effect of molecular structure and functional groups present in alkanolamine influences various characteristics including its CO2 absorption capacity, which may be defined in terms of steric hindrance/induction effect (+I effect) offered by the attached alkyl groups or amine basicity. In an effort to explore the potential; nonsterically hindered solvents incurring lower regeneration energy for CO2 capture, Singh et al. investigated the structure dependence of various primary amines including Received: October 3, 2016 Accepted: May 22, 2017

A

DOI: 10.1021/acs.jced.6b00856 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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diamines.16,17 In their persuasion, Bajpai and Mondal proposed a sterically unhindered diamine (2-aminoethyl) ethanolamine (AEEA) and its blends with DEA for efficient absorption of CO2.18 In a series of publications, Kumar and Kundu investigated on the same front reporting the equilibrium CO2 solubility of aqueous N-methyl-2-ethanolamine (MAE) and N-ethyl-ethanolamine (EAE) and their blends with MDEA and AMP.19−21 Machida et al.22 reported CO2 solubility in three types of tertiary diamines, N,N,N′,N′-tetramethylethylenediamine (C2-diamine), N,N,N′,N′-tetramethyl-1,3-diaminopropane (C3-diamine), and N,N,N′,N′-tetramethyl-1,6-diaminohexane (C6-diamine), and investigated the effect of alkyl chain length between the two amino groups in their CO2 solubility. The multiple amine functionalities might lead more CO2 molecules to be attached with a single solvent molecule. Chowdhury et al.23 studied VLE, gas scrubbing, and reaction calorimetry experiment on 24 different tertiary alkanolamine including MDEA. They identified seven solvents, which could be potentials. Among them, we have chosen 2-diethylaminoethanol (DEAE) for further study and it has been found to be a promising alternative to MDEA (Table 1) for CO2 capture.

computationally simple model using exhaustive reaction scheme of the CO2 + PZ + DEAE system. In order to interpolate confidently, the generated density and viscosity data are correlated applying various thermodynamic relations.

2. EXPERIMENTATION 2.1. Materials. The solvents, namely, DEAE, MDEA, PZ, were used. Millipore water (having conductivity 1 × 10−7 Ω−1 cm−1 and surface tension 72 mN·m−1 at 298 K) after degasification was used for solution preparation. The total amine contents of the solutions were obtained on titration using standard HCl and methyl orange as indicator. The blended alkanolamine solutions were prepared using standardized single alkanolamine solutions. The structure of the amines, carbon dioxide gas along with their purity and sources is presented in Table 2. Table 2. Materials Used in This Work along with Their Properties and Sources

Table 1. Comparison in Selected Properties among MDEA and DEAE24

compound N-methyldiethanolamine (MDEA) 2-diethylaminoethanol (DEAE)

absorption rate g-CO2/L -solution/min

absorption amount g-CO2/L -solution

cyclic capacity g-CO2/L -solution

pKa values

1.56

55

24

8.65

2.49

94

32

10.01

The enhanced attribute of DEAE in comparison to MDEA is possibly due to its structure and spatial alignments of functional groups influencing the reaction path ways while reacted to CO2. The higher pKa value of DEAE (≥9.0) in comparison to MDEA (≥8.0) seems to dictate higher basicity, hence its better absorption capacity and rate toward CO2 in comparison to MDEA. The carbamate stability dictates the CO2 absorption capacity and the regeneration energy requirement of the solvent. Being a tertiary alkanolamine, DEAE does not form carbamate. Recently, Fu et al.24 have reported CO2 solubility in DEAE + PZ blends of varying DEAE and PZ concentration (three single and nine blends of DEAE) at 101 kPa CO2 pressure. Present study is aimed toward the measurement and correlation of the VLE data generated for aqueous blends of PZ + DEAE using a thermodynamic framework followed by its physicochemical property estimation, and correlation (which is essential in engineering design of gas treating equipment), and pKa value estimation (to characterize the DEAE as solvent). Apart from rate data, the generated VLE data might be significant in absorber design based on the proposed solvent. Prior to that, the stripping characteristics, degradation resistance, corrosion, and foaming tendency of the proposed DEAE blend are needed to be examined. Density and viscosity make important components of the design database required in gas treating equipment design. In the backdrop of rich and hierarchical models (in a sense of approximate to most rigorous description of thermodynamic phase equilibrium of aqueous (CO2 + alkanolamine) blends) already being developed, we preferred and proposed to use a

2.2. Measurement of pKa. The dissociation constant, (pKa), of DEAE is measured potentiometrically using pH meter (LABINDIA, PICO Sr. No-PH12341258) in the temperature range of 298.15−333.15 K and the solution temperature was controlled to an extent of ±0.05 K of the desired temperature using water recirculation temperature controller (Polyscience, U.S.A. model no. 9712). The procedure of pH measurement and estimation of pKa using the pH values was done according to Ali et al.25 Experimental results were compared with Ali et al.25 and are presented in Table 3. 2.3. Vapor−Liquid Equilibrium Measurement. Experimental Setup. The CO2 solubility in PZ + DEAE + H2O was Table 3. Comparison of the pKa of MDEA at 298.15− 333.15 K Measured in This Work with the Literature Values at 101.3 kPaa pKa temperature (K) 298.15 303.15 313.15 323.15 333.15 % AAD = 0.914

literature 8.57 8.50 8.31 8.24 8.07

25

this study 8.648 8.539 8.364 8.105 7.998

% AAD = |((pKaexp − pKaa)/pKaexp)| × 100. Standard uncertainties (u): u(T) = 0.05 K and u(pH) = 0.032

a

B



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Table 4. Comparison of CO2 Loading, α and CO2 Mass Fraction (w) in Aqueous 4.48 mol/kg MDEA + 1.12 mol/kg PZ Solutions (Solvent: H2O) at 303.15 and 323.15 K Measured in This Work at Different CO2 Partial Pressure (PCO2 (kPa)) with the Literature Valuesa 4.48 mol/kg MDEA + 1.12 mol/kg PZ literature27

this study

T/K

PCO2 (kPa)

α

w

T/K

PCO2 (KPa)

α

w

303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15

0.51 1.75 2.61 5.23 6.80 8.65 10.7 25.7 38.9 56.4 1.05 4.68 8.37 19.7 32.8 45.8 60.3 69.5 84.0 94.5

0.208 0.303 0.348 0.435 0.468 0.513 0.523 0.664 0.708 0.758 0.155 0.255 0.323 0.418 0.483 0.541 0.584 0.610 0.636 0.657

0.0305 0.0438 0.0500 0.0617 0.0661 0.0720 0.0733 0.0912 0.0967 0.1028 0.0229 0.0371 0.0465 0.0594 0.0680 0.0756 0.0811 0.0844 0.0877 0.0903

303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15

0.5 1.5 2.7 4.8 7.6 11.8 27.6 38.4 52.9

0.197 0.279 0.346 0.402 0.470 0.540 0.635 0.692 0.738

0.0289 0.0405 0.0497 0.0573 0.0663 0.0755 0.0876 0.0947 0.1003

323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15

1 5.4 8.2 20.8 32.3 45.9 59.8 71.9 85.3 97.3

0.149 0.278 0.324 0.430 0.973 0.544 0.594 0.632 0.649 0.668

0.0220 0.0403 0.0467 0.0610 0.1282 0.0760 0.0824 0.0872 0.0893 0.0917

a

Standard uncertainties (u): u(T) = 0.05 K, u(PCO2) = 0.021 kPa. Combined extended uncertainties U are u(b) = 0.01 mol/kg, U(α) = 0.026, U(w) = 0.0005 (95% level of confidence and coverage factor, k = 2). b = molal concentration (mol/kg).

During the absorption process occurring in the equilibrium vessel, the buffer vessel was kept isolated from the equilibrium vessel. The moles of CO2 dispatched from the buffer vessel was estimated using the final and initial pressure reading of the pressure transducer (Swagelok, model no. PTI-S-NA-10015AO-B) attached to the buffer vessel (u(P1) = 0.031 kPa). During the absorption, the equilibrium vessel liquid phase was stirred. The observed time to reach equilibrium was 1 h. The pressure transducer fitted to the equilibrium vessel (Swagelok, model no. PTI-S-NA-50-15AO-B, u(P2) = 0.021 kPa) showed the total vessel pressure (Pt). The equilibrium pressure (PCO2) was estimated to be the difference of the Pt and pv. The CO2 moles absorbed by the aqueous PZ + DEAE solution was estimated using moles of CO2 being dispatched from the buffer vessel and the moles of CO2 present in the vapor space of the equilibrium vessel at a specific equilibrium pressure (compressibility factor of the gas was considered in CO2 mole calculations as described by Park and Sandall (2001)26). CO2 loading is expressed as moles of CO2 absorbed per moles of DEAE + PZ at a specific equilibrium CO2 pressure. Successive runs at a specific temperature can be taken by repeating the whole procedure already stated. It is to be noted that successive readings on CO2 solubility will be at a higher CO2 pressure than the previous one because of the diminishing capacity of the solution. The experimental procedure for the VLE measurement using this setup has been validated by comparing the generated VLE data with the data presented by Derks et al.27 as presented in Table 4 and Figure 1 (CO2 partial pressure is expressed in log scale). CO2 solubility measured using aqueous 4.48 mol/kg MDEA + 1.12 mol/kg PZ blend at 303.15 and 323.15 K are in

measured in a stainless steel made equilibrium vessel. VLE measurements were performed at pressures of 0.1−60 kPa and temperatures of 303.1, 313.1, and 323.1 K. The VLE setup primarily consisted of two vessels, namely, buffer vessel and equilibrium vessel submerged in a temperature controlled water bath and already has been discussed elsewhere19 with pressure transducers being replaced by (Swagelok, model no. PTI-S-NA100-15AO-B) attached to the buffer vessel and (Swagelok, model no. PTI-S-NA-50-15AO-B) attached to the equilibrium vessel. Experimental Method. For an experimental run, the buffer and the equilibrium vessels were allowed to reach the temperature in equilibration with the constant temperature water bath (maintained using recirculation temperature controller, Polyscience, U.S.A. model no. 9712). Uncertainty in temperature measurement was 0.05 K. At a particular temperature, 8−9 measurements of equilibrium CO2 loading were made under varying equilibrium CO2 pressure. Both the vessels (buffer and the equilibrium) were evacuated simultaneously using vacuum pump (HINDVAC). After evacuation, the buffer vessel was isolated from the equilibrium vessel. The buffer vessel is capable of hailing at a total pressure of 1.5 to 2.5 times to that of the desired maximum CO2 partial pressure (to be maintained in the equilibrium vessel) and it is being filled up using pure CO2 gas cylinder. Twenty-five milliliters of freshly prepared PZ + DEAE + H2O solution with a specific DEAE/PZ composition was drawn into the equilibrium vessel through a buret fitted to the vessel. Afterward, the equilibrium vessel was fully vacuum-packed on the second evacuation and allowed to rest under solution vapor pressure (pv). The solution vapor pressure was recorded. The maximum error expected in the volume dispatched is estimated to be 0.05 mL. The CO2 gas from the buffer vessel was transferred to the equilibrium vessel. C



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viscometer. The viscometer containing the solution was kept in a constant temperature water bath (±0.05 K of the set temperature) using a water recirculation temperature controller (Polyscience, U.S.A. model no. 9712). Once the solution reached the desired temperature, time of flow of the solution was recorded. Each stated viscosity data was the average of three measurements with an uncertainty in measurement U(η) = 0.039 mPa cdts (at 95% level of confidence and coverage factor, k = 2). The experimental procedure for the viscosity measurement using Ostwald viscometer were validated by comparing the experimental viscosity data of aqueous 0.66, 1.10, and 1.70 mol/kg PZ solution with the literature value reported by Derks et al.27 and are presented in Table 6; the AAD in the viscosity measured were found to be 0.79%, 0.65%, and 2.94%, respectively.

Figure 1. Comparison of CO2 loading in aqueous 1.12 mol/kg PZ + 4.48 mol/kg MDEA solution with literature data at 303.15 and 323.15 K.

3. MATHEMATICAL MODELING 3.1. Thermodynamic Model for VLE of CO2 + PZ + DEAE + H2O Blend. When CO2 reacts with an aqueous solution of PZ+ DEAE blend, the following sets of reactions occur in the liquid phase

agreement with the data stated by Derks et al.27 Subsequently, CO2 solubility in PZ + DEAE+ H2O are measured at low pressure of 0.1−65 kPa and at temperatures of 303.15−323.15 K. The four different aqueous blends of 0.23 mol/kg PZ + 0.92 mol/kg DEAE, 0.52 mol/kg PZ + 2.08 mol/kg DEAE, 0.92 mol/kg PZ + 3.68 mol/kg DEAE, and 1.49 mol/kg PZ + 5.96 mol/kg DEAE are considered for experimentation keeping the PZ/DEAE mole ratio of 1:4. Total amine mass percentages in blends are ranging from 11.1 to 44.4. 2.4. Measurement of Density. The densities of PZ + DEAE+ H2O solutions were measured at temperatures of 303.15−323.15 K using a 25.18 mL Gay-Lussac pycnometer. The pycnometer containing the amine solution was immersed in a constant temperature water bath. The bath temperature was controlled within ±0.05 K of the set temperature with a water recirculation temperature controller (Polyscience, U.S.A. model no. 9712). Once the solution reached the set temperature, it was weighed to within ±0.0001 g with an analytical balance (Sartorius, model CPA225D). Each stated density is the average of three measurements. The uncertainty in the measured density was 0.076 kg/m3 at 95% level of confidence combined uncertainty; for coverage factor k = 2. The experimental procedure for the density measurement using pycnometer was validated by comparing the generated density data with the data stated by Derks et al.27 as presented in Table 5. The average absolute deviation (AAD) in the density measured for 0.66, 1.10, and 1.70 mol/kg PZ solution was found to be 0.024%, 0.023%, and 0.022%, respectively, in comparison to the measurement of Derks et al.27 2.5. Measurement of Viscosity. The viscosities of PZ + DEAE+ H2O solutions were measured using an Ostwald

HCO2

CO2 (g) ←→ ⎯ CO2 (aq)

(1)

K2

H 2O ↔ H+ + OH−

(2)

K3

DEAEH+ ↔ DEAE + H+

(3)

K4

CO2 + H 2O ↔ HCO3− + H+

(4)

K5

PZH+ ↔ PZ + H+

(5)

K6

HCO3− ↔ CO32 − + H+

(6)

K7

PZ + CO2 ↔ PZCOO− + H+

(7)

K8

PZCOO−H+ ↔ PZCOO− + H+

(8)

K9

PZCOO− + CO2 ↔ PZ(COO−)2 + H+

(9)

The equilibrium constants (K2−K9) for the above reactions are expressed as K 2 = [H+][OH−] K3 =

(10)

[DEAE][H+] [DEAEH+]

(11)

Table 5. Comparison of the Density, ρ(kg/m3) of the Aqueous PZ Solutions (Solvent: H2O) of Different Concentration at 303.15−323.15 K Measured in This Work with the Literature Values at 101.3 kPaa ρ (kg/m3) temperature/K 303.15 313.15 323.15 % AAD

0.66 mol/kg aqueous PZ solution



literature27

literature27

this work

literature27

this work

999.58 995.73 991.34

1.0025 0.9985 0.9939 0.022%

1002.4 998.08 993.64

997.9 994.3 989.8 0.024%

this work 997.55 994.45 989.89

999.8 996.0 991.5 0.023%

% AAD = |((pexp − pa)/pexp)| × 100. Standard uncertainty u(T) = 0.05 K. Combined extended uncertainties (U): U(b) = 0.01 mol/kg, U(ρ) = 0.076 kg/m3, and U(P) = 1 kPa (95% level of confidence and coverage factor, k = 2). b = molal concentration (mol/kg).

a

D



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Table 6. Comparison of the Viscosity, η (mPa·s) Data of the Aqueous PZ Solutions (Solvent: H2O) of Different Concentration at 303.15−323.15 K Measured in This Work with the Literature Values at 101.3 kPaa η (mPa·s) 0.66 mol/kg aqueous PZ solution



temperature/K

literature27

this work

literature27

this work

literature27

this work

303.15 313.15 323.15 % AAD

0.980 0.787 0.650 0.79%

0.987 0.789 0.641

1.154 0.922 0.747 0.65%

1.169 0.916 0.747

1.402 1.091 0.876 2.94%

1.456 1.124 0.893

a % AAD = |((ηexp − ηa)/ηexp)| × 100. Standard uncertainty u(T) = 0.05 K. Combined extended uncertainty (U): U(b) = 0.01 mol/kg, U(ρ) = 0.076 kg/m3 and U(η) = 0.039 mPa·s and U(P) = 1 kPa (95% level of confidence and coverage factor, k = 2). b = molal concentration (mol/kg).

Table 7. Parameters Used for the Estimation of Equilibrium Constant and Henry’s Constanta K i /HCO2 = exp

a

( Ta + bi ln T + ciT + di) K (mol/kg), for i = 3, 5 i

i

parameter

ai

bi

ci

di

source

K2 K3 K4 K5 K6 K7 K8 K9 HCO2 (atm kg/mol)

−13445.9 −2.4569 −12092.1 0.133 −12431.7 9288.2 −3961.6 9288.2 −6789.04

−22.4773 15.7336 −36.7816 0.521 −35.4819 0 0 0 −11.4519

0 0 0 −0.0526 0 0 0 0 −0.010454

140.932 −112.3998 235.482 −0.091 220.067 −41.583 −13.041 −44.7 94.4914

Edwards et al.28 this work Edwards et al.28 Najibi and Maleki29 Bishnoi et al.14 Bishnoi et al.14 Bishnoi et al.14 Bishnoi et al.14 Edwards et al.28

Apart from K3 and K5, all the other equilibrium constants are mole fraction based.

K4 =

[HCO3−][H+] [CO2 ]

Charge balance = OH− + HCO3− + 2CO32 − + PZCOO− + 2PZ(COO−)2

[PZ][H+] K5 = [PZH+]

−

α([DEAE]t + [PZ]t ) = PZCOO− + PZCOO−H+ + PZ(COO−)2 + HCO3− + CO32 − + CO2

(14)

K9 =

(15)

)

[DEAE]t = DEAE + DEAEH+

+

(21)

PZ balance

(16)

[PZ]t = PZ + PZCOO− + PZCOO−H+ + PZ(COO−)2 + PZH+

+

[PZ(COO )2 ][H ] [PZCOO−][CO2 ]

(22)

For the [CO2 + PZ+ DEAE + H2O] system, eqs 10−17 and 19−22 have been reduced to a single seventh order polynomial equation in hydrogen ion concentration; [H+]. The CO2 loading (α) is estimated in terms of [H+], reaction equilibrium constants and Henry’s constant. (The model detailing is provided in SI.) In this work, vapor phase nonideality has been neglected and liquid phase nonideality has been lumped into selected equilibrium constants K3, K5, and K7. The adjustable equilibrium constants Ki is defined as

(17)

The concentration of CO2in the liquid phase is related to equilibrium CO2 pressure by Henry’s law PCO2 = HCO2[CO2 ]

mol of CO2 absorbed mol of PZ + mol of DEAE

(20)

DEAE balance

[PZCOO ][H ] K8 = [PZCOO−H+] −

(

where, α is the CO2 loading α =

+

[PZCOO ][H ] [PZ][CO2 ] −

(19)

CO2 balance

(13)

[CO32 −][H+] K6 = [HCO3−]

K7 =

H+ + DEAEH+ + PZH+

(12)

(18)

where HCO2 is Henry’s constant. Equilibrium and Henry’s constants defined above are temperature dependent and all of them except deprotonation constant of DEAE are adopted in the present work from open literature after appropriate conversion (Table 7). In addition to the above equations, the following equations are considered.

i i K i = Kd/l × K appa where i = 3, 5, 7

(23)

Out of these three equilibrium constants, K5l and K7l are taken from open literature and K3d is derived using the pKa value E



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PZ + DEAE + H2O blends

determined experimentally (Table 7). We assumed that apparent equilibrium constants (Kiappa) are the function of temperature, CO2 partial pressure, and amine concentration having the following form

n

ρm =

i=1

a ⎛ ⎞ a i = exp⎜a1 + 2 + 32 + b1 ln pCO + b2pCO + c1[DEAE] + c 2[PZ]⎟ K appa 2 2 ⎝ ⎠ T T

here ai, bi, and ci are fit parameter achieved by regression of our experimental data for the quaternary CO2 + PZ+ DEAE + H2O system (Table 8). The objective function to be minimized has been defined as Table 8. Estimated Parameters for Eq 24 K3appa

parameter

a1 −8.27080 a2 0.200508 a3 −0.111780 b1 −0.651920 b2 7.164433 c1 0.443596 c2 −0.56460 (AAD) % correlation = 7.42

(31)

i≠j

where Aij values are the binary interaction parameters. ρm is the measured density of the ternary mixture. A semiempirical model originally proposed by GonzalezOlmos and Iglesiasis also used to correlate the generated experimental data, which is expressed by eq 3230

(24)

Kiappa

∑ xiρi + ∑ Aijxixj

i=N

ρ=

Where i = 3, 5, 7 in

∑ (Cix1i + Bi x2i)

(32)

i=0

j=Q

Ci =

K5appa

K7appa

0.14214 −0.07904 0.195172 −1.29266 −0.03256 0.011549 −0.06742

−0.73305 0.039892 −0.00163 0.528321 −0.59927 −1.25874 −0.21559

2 N ⎛ 1 ⎞ ⎡ (αi ,exp − αi ,cal) ⎤ ⎥ F = ⎜ ⎟∑ ⎢ ⎝ N ⎠ ⎢⎣ αi ,exp ⎥⎦ i=1

∑ CijT J (33)

j=0

j=Q

Bi =

∑ BijT j (34)

j=0

where x1 is the mole fraction of component/species 1 and x2 is the mole fraction of component/species 2 in the blended solutions. Cij and Bij are polynomial coefficients which are dependent on temperature T. 3.3. Correlation for Viscosity of PZ + DEAE + H2O Blend. The viscosity data of the ternary mixture are correlated using the Grunberg and Nissan type30 type of expression (eq 35)

(25)

Here N is the total number of measurements taken during experiment (190 data points), αi,exp is the experimental CO2 loading, and αi,cal is the calculated CO2 loading. 3.2. Correlation for Density of PZ + DEAE + H2O Blend. The excess molar volume is correlated by using the Redlich−Kister (R-K) equation

ln(ηm /mPa ·s) = x1x 2G12 + x 2x3G23 + x1x 2G31

(35)

G12, G23, and G31 are temperature-dependent pair interaction parameters as expressed by eq 36 Gij = a + b(T /K ) + c(T /K )2

(36)

n

V E jk /ml ·mol−1 = xjxk ∑ Ai (xj − xk)i i=0

4. RESULTS AND DISCUSSION 4.1. pKa of DEAE. The AAD in the generated pKa data for MDEA solution is found to be 0.91%, compared to the data stated by Ali et al.25 Experimentally obtained pKa data of DEAE at temperatures of 298.15−333.15 K are presented in Table 9

(26)

where, Ai values are interaction parameters and functions of temperature Ai = a + b(T /K ) + c(T /K )2

(27)

Table 9. pKa of the DEAE over 298.15−333.15 Ka

The excess molar volume of the ternary mixture is defined by eq 28 and is calculated by eq 29 E

E

E

V = V12 + V13 + V23 V E = Vm −

∑ xiVi 0

E

(28) (29)

where Vm is the molar volume of the liquid mixture (ternary) and Voi is the pure component molar volume in the mixture at the system temperature. The experimentally obtained molar volume of the liquid mixture is calculated by eq 30 Vm =

∑

xiMi ρm

a

temperature (K)

pKa

298.15 303.15 313.15 323.15 333.15

9.851 9.780 9.604 9.370 9.104

Standard uncertainty (u): u(T) = 0.05 K, and u(pH) = 0.032.

and they are further used for getting thermodynamic equilibrium constant of deprotonation of DEAE. 4.2. VLE of CO2 + PZ + DEAE + H2O Blend. CO2 solubility in aqueous blends of 0.23 mol/kg PZ + 0.92 mol/kg DEAE, 0.52 mol/kg PZ + 2.08 mol/kg DEAE, 0.92 mol/kg PZ + 3.68 mol/kg DEAE, and 1.49 mol/kg PZ + 5.96 mol/kg DEAE) have been measured at low pressure of 0.1−60 kPa at temperatures of 303.15−323.15 K and are presented in Table 10. The relative compositions of DEAE and PZ in the blends were not chosen randomly. The PZ/DEAE mole ratio was kept constant in various DEAE + PZ blends, because

(30)

where Mi is the molar mass of pure component i, ρm is the measured density of the ternary mixture, and xi is the mole fraction of component i. By equating eq 29 and eq 30, one can obtain the Ai values. A Grunberg and Nissan type30 model as expressed by eq 31 is used to correlate the density measurements of F



Article

Table 10. Experimental CO2 Loading, αexp, Calculated CO2 Loading, αcal, and CO2 Mass Fraction (w) in Four Different Aqueous Blends of PZ + DEAE (Solvent: H2O) at Different Temperature and CO2 Partial Pressure, PCO2(kPa) δ = |((αexp − αcal)/αexp| × 100a T/K 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15

PCO2 (KPa)

αexp

w

0.92 mol/kg DEAE + 0.23 mol/k PZ 0.2 0.0116 0.262 0.5 0.0180 0.409 0.7 0.0219 0.498 0.9 0.0248 0.566 1.4 0.0289 0.664 2.2 0.0319 0.735 4.3 0.0349 0.807 8.7 0.0375 0.868 14.5 0.0393 0.911 20.2 0.0401 0.932 26.1 0.0409 0.951 33.3 0.0414 0.962 44.3 0.0417 0.969 0.3 0.0110 0.249 0.4 0.0142 0.321 0.5 0.0175 0.396 0.9 0.0217 0.494 1.5 0.0255 0.582 2.7 0.0291 0.667 5.5 0.0326 0.750 8.5 0.0350 0.808 15.2 0.0372 0.860 20.3 0.0382 0.885 30.6 0.0394 0.914 40.7 0.0399 0.926 53.2 0.0401 0.932 0.4 0.0118 0.265 0.7 0.0155 0.351 1 0.0193 0.438 1.7 0.0225 0.514 2.7 0.0255 0.583 4.5 0.0286 0.656 7.1 0.0309 0.710 12.4 0.0344 0.794 20.3 0.0375 0.868 28.4 0.0388 0.899 35.2 0.0393 0.911 44.3 0.0398 0.923 61 0.0405 0.941 2.08 mol/kg DEAE + 0.52 mol/kg PZ 0.1 0.0195 0.224 0.3 0.0291 0.337 0.6 0.0365 0.427 1 0.0438 0.516 1.6 0.0511 0.607 3.5 0.0573 0.684 6.2 0.0620 0.744 11.4 0.0649 0.782 19.5 0.0686 0.829 26 0.0696 0.842 34 0.0715 0.868 42 0.0725 0.881 49.1 0.0735 0.893 59.2 0.0741 0.902 0.4 0.0166 0.190

αcal

δ

0.241 0.421 0.504 0.561 0.644 0.704 0.771 0.848 0.901 0.929 0.947 0.961 0.976 0.260 0.310 0.357 0.497 0.606 0.691 0.756 0.793 0.854 0.887 0.929 0.952 0.969 0.263 0.372 0.456 0.576 0.654 0.711 0.746 0.784 0.824 0.859 0.882 0.907 0.937

8.25 3.17 1.23 0.86 2.98 4.20 4.44 2.34 1.04 0.27 0.34 0.10 0.71 4.46 3.30 9.76 0.64 4.19 3.58 0.76 1.90 0.70 0.24 1.63 2.81 3.95 0.81 5.86 4.29 12.05 12.32 8.47 5.16 1.34 5.07 4.44 3.19 1.67 0.41

0.149 0.227 0.347 0.464 0.565 0.678 0.727 0.776 0.826 0.854 0.879 0.896 0.909 0.922 0.229

33.79 32.67 18.63 9.94 6.80 0.94 2.30 0.79 0.32 1.42 1.28 1.72 1.69 2.21 20.50

Table 10. continued T/K 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15

G

PCO2 (KPa)

αexp

w

2.08 mol/kg DEAE + 0.52 0.6 0.0232 0.8 0.0301 1.1 0.0364 2 0.0453 3.6 0.0512 5.5 0.0546 8.6 0.0591 12.4 0.0614 19.8 0.0639 24.1 0.0658 33.2 0.0676 42.2 0.0693 54.3 0.0702 0.4 0.0147 0.6 0.0212 0.9 0.0275 1.4 0.0348 2.1 0.0405 3.7 0.0464 5.4 0.0503 7.3 0.0538 9.6 0.0562 14.6 0.0597 19 0.0617 24.2 0.0636 30.9 0.0648 38.5 0.0665 51.6 0.0685 3.68 mol/kg DEAE + 0.92 0.1 0.0158 0.2 0.0250 0.3 0.0344 0.4 0.0428 0.6 0.0495 0.9 0.0583 1.3 0.0650 1.9 0.0708 2.6 0.0762 4.1 0.0820 7 0.0878 11.8 0.0929 18.1 0.0976 25.7 0.1003 34.3 0.1027 46.3 0.1044 64.2 0.1065 0.3 0.0149 0.4 0.0220 0.6 0.0295 0.9 0.0389 1.3 0.0475 1.7 0.0550 2.3 0.0615 3.4 0.0681 5.1 0.0742 7.1 0.0786 11.1 0.0836 16.5 0.0881 23.9 0.0918

αcal

mol/kg PZ 0.267 0.292 0.350 0.350 0.426 0.421 0.534 0.553 0.608 0.648 0.651 0.694 0.707 0.731 0.737 0.758 0.769 0.795 0.793 0.813 0.817 0.845 0.839 0.870 0.851 0.894 0.168 0.199 0.244 0.248 0.318 0.318 0.406 0.414 0.475 0.505 0.548 0.611 0.597 0.661 0.640 0.692 0.671 0.715 0.715 0.743 0.741 0.760 0.765 0.775 0.781 0.792 0.803 0.809 0.828 0.833 mol/kg PZ 0.120 0.136 0.191 0.158 0.266 0.183 0.334 0.210 0.389 0.265 0.462 0.341 0.519 0.422 0.569 0.506 0.616 0.567 0.667 0.636 0.718 0.689 0.764 0.723 0.807 0.746 0.832 0.767 0.854 0.788 0.870 0.812 0.890 0.840 0.113 0.164 0.168 0.184 0.227 0.225 0.302 0.287 0.372 0.360 0.434 0.419 0.489 0.485 0.545 0.562 0.598 0.625 0.637 0.664 0.681 0.703 0.721 0.730 0.754 0.751

δ 9.44 0.15 0.97 3.62 6.51 6.51 3.40 2.81 3.35 2.58 3.47 3.66 5.11 18.07 1.58 0.07 1.91 6.33 11.42 10.73 8.12 6.50 3.96 2.59 1.35 1.35 0.69 0.60 13.23 17.23 31.15 37.09 31.79 26.30 18.71 11.02 7.95 4.70 4.00 5.30 7.48 7.72 7.70 6.67 5.69 45.13 9.19 0.76 4.83 3.24 3.63 0.74 3.13 4.61 4.18 3.30 1.23 0.39



Article

Table 10. continued T/K 313.15 313.15 313.15 313.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15

PCO2 (KPa)

Table 10. continued αexp

3.68 mol/kg DEAE + 0.92 30.9 0.0940 37.2 0.0956 45.7 0.0974 57.6 0.0990 0.2 0.0117 0.4 0.0180 0.6 0.0253 0.8 0.0310 1.1 0.0384 1.4 0.0430 2.2 0.0534 2.9 0.0587 4 0.0636 5.2 0.0683 6.8 0.0727 8.7 0.0765 10.6 0.0793 13.9 0.0831 17.5 0.0860 22.2 0.0890 27.5 0.0911 35.1 0.0936 43.7 0.0963 59.1 0.0990 5.96 mol/kg DEAE + 1.49 0.3 0.0197 0.4 0.0279 0.5 0.0363 0.7 0.0457 0.9 0.0538 1.1 0.0615 1.4 0.0676 1.8 0.0755 2.5 0.0835 3.3 0.0897 4.3 0.0951 5.7 0.1004 8.2 0.1062 10.3 0.1113 14.6 0.1144 22.2 0.1196 31.8 0.1232 40.7 0.1253 49.5 0.1273 62 0.1292 0.4 0.0185 0.6 0.0284 0.8 0.0376 1.2 0.0477 1.6 0.0565 2.1 0.0643 2.8 0.0715 3.6 0.0776 5.5 0.0876 7 0.0934 9.5 0.1001 14.2 0.1073 20.1 0.1133 26.4 0.1175

w

αcal

mol/kg PZ 0.774 0.765 0.789 0.775 0.805 0.787 0.820 0.801 0.088 0.139 0.137 0.165 0.194 0.196 0.239 0.227 0.298 0.275 0.335 0.318 0.421 0.414 0.465 0.474 0.507 0.539 0.547 0.584 0.585 0.623 0.618 0.653 0.643 0.673 0.676 0.696 0.702 0.713 0.729 0.728 0.748 0.739 0.771 0.751 0.795 0.759 0.820 0.768 mol/kg PZ 0.112 0.154 0.160 0.169 0.210 0.185 0.267 0.218 0.317 0.252 0.365 0.285 0.404 0.331 0.455 0.384 0.508 0.456 0.549 0.515 0.586 0.566 0.622 0.610 0.662 0.656 0.698 0.678 0.720 0.706 0.757 0.730 0.783 0.744 0.798 0.752 0.813 0.756 0.827 0.760 0.105 0.154 0.163 0.177 0.218 0.202 0.279 0.254 0.334 0.302 0.383 0.356 0.429 0.417 0.469 0.471 0.535 0.554 0.574 0.593 0.620 0.635 0.670 0.676 0.712 0.703 0.742 0.720

δ

T/K

1.24 1.75 2.20 2.34 58.12 20.89 1.08 4.61 7.84 4.83 1.79 1.96 6.29 6.84 6.46 5.67 4.62 3.06 1.56 0.25 1.12 2.68 4.45 6.32

313.15 313.15 313.15 313.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15

PCO2 (KPa)

αexp

w

5.96 mol/kg DEAE + 1.49 34.7 0.1213 42.4 0.1237 50.4 0.1258 60.1 0.1277 0.5 0.0169 0.8 0.0269 1.2 0.0363 1.7 0.0454 2.7 0.0537 5 0.0692 6.5 0.0750 8.4 0.0805 11.1 0.0880 14.7 0.0937 18.8 0.0991 25.5 0.1053 31.9 0.1095 43 0.1144 51.5 0.1169 59.1 0.1190

αcal

mol/kg PZ 0.769 0.733 0.787 0.739 0.802 0.743 0.816 0.743 0.096 0.152 0.154 0.179 0.210 0.217 0.265 0.265 0.316 0.349 0.414 0.478 0.452 0.528 0.488 0.572 0.538 0.612 0.576 0.645 0.613 0.668 0.656 0.692 0.685 0.704 0.720 0.715 0.738 0.717 0.753 0.714

δ 4.73 6.05 7.40 8.98 58.24 15.63 3.09 0.10 10.32 15.48 17.02 17.33 13.71 12.05 9.12 5.44 2.88 0.63 2.79 5.10

a

Standard uncertainties (u): u(T) = 0.05, u(PCO2) = 0.021 kPa. Combined extended uncertainties (U): U(b) = 0.01 mol/kg, U(α) = 0.026, U(w) = 0.0005 (95% level of confidence and coverage factor, k = 2). b = molal concentration (mol/kg)/

37.08 5.32 12.07 18.30 20.50 21.99 18.21 15.64 10.18 6.13 3.54 1.89 0.92 2.83 2.02 3.61 4.93 5.74 6.93 8.18 46.95 8.74 7.23 9.19 9.66 7.10 2.72 0.49 3.67 3.33 2.44 0.95 1.17 2.90

PZ was used as a rate promoter only. Generated solubility data are correlated using a nonactivity based model neglecting the nonideality of the vapor phase. The proposed model uses apparent equilibrium constants considering exhaustive reaction scheme of the CO2 + PZ + DEAE system. The experimentally obtained CO2 loading are compared with the model predicted loading revealing average absolute deviation of 7.42% for the blends. Figure 2 shows the parity between the experimental

Figure 2. Parity between the experimental and model predicted CO2 loading for the aqueous 0.23 mol/kg PZ + 0.92 mol/kg DEAE solution at various temperatures.

CO2 loading to that of model predicted ones for the aqueous 0.23 mol/kg PZ + 0.92 mol/kg DEAE solution at temperatures of 303.15−323.15 K. Figure 3 shows the effect of variation of temperature of 303.15−323.15 K on CO2 loading in aqueous 0.52 mol/kg PZ + 2.08 mol/kg DEAE solution (here, CO2 partial pressure being expressed in log scale). It states the decrease of CO2 solubility with increasing temperature. H



Article

Table 11. Density of PZ (1) + DEAE (2) + H2O (3) System at Various Temperature and Relative Amine Composition at 101.3 kPaa ρ (kg/m3) temperature/K w1/w2 3:27 6:24 9:21 12:18

303.15 986.91 991.09 994.56 998.10

308.15 983.63 987.21 990.94 994.75

313.15 980.20 984.10 987.91 991.58

318.15 976.82 980.84 984.53 988.30

323.15 973.80 977.53 981.37 985.06

a

w1 and w2 are the mass fraction of PZ and DEAE, respectively. Standard uncertainty: u(T) = 0.05 K. Combined extended uncertainties (U): U(w) = 0.001, U(ρ) = 0.076 kg/m3 and U(P) = 1 kPa (95% level of confidence and coverage factor, k = 2).

Figure 3. Effect of temperature on CO2 loading in aqueous 0.52 mol/kg PZ + 2.08 mol/kg DEAE solution.

Table 12. Ternary Redlich-Kister Parameters (Eq 26) for the PZ (1) + DEAE (2) + H2O (3) System

Figure 4 shows the experimental and predicted CO2 loading in various aqueous DEAE + PZ blends at 313.15 K, revealing

estimated (R-K) parameters: PZ (1) + DEAE (2) + H2O (3) parameters

value a b c a b c a b c

A0

A1

A2

(AAD) % correlation

0.0725 −0.2292 0.0053 −0.0755 −0.1506 0.0088 0.0750 −0.2064 0.0042 0.045%

measured and correlated density for PZ + DEAE + H2O systems. A Grunberg and Nissan type model as expressed by eq 31 correlates the density data of PZ + DEAE + H2O system with correlation deviations of 0.075%. The temperaturedependent Nissan parameters of the ternary system are reported in Table 13. The Nissan type equation correlates

Figure 4. Comparison of experimental and model predicted CO2 loading in four different aqueous PZ + DEAE blended solution at 313.15 K. (Symbol represents the experimental data and line represents the model predicted data for a specific blend.)

agreement with the model. DEAE is a high capacity solvent showing a CO2 loading of above 0.8 at a very low partial pressure of about 60 kPa in its various blends with PZ. It is also evident from Figure 4 that at a particular temperature constant PZ/DEAE mole ratio (1:4) and CO2 partial pressure, CO2 loading increases with a decrease in DEAE and PZ concentration in the blend (here, CO2 partial pressure being expressed in log scale). Because the deprotonation of amine becomes facile in the dilute solution of amine resulting in higher CO2 loading by the solvent. Thermal power plant flue gas is a huge CO2 source at nearly atmospheric pressure (3−15 volume percent of the flue gas is CO2). The proposed PZ + DEAE blend may be a proper choice to treat the flue gas because of its high absorption capacity at comparatively lower CO2 partial pressure. 4.3. Density of PZ + DEAE + H2O Blend. Experimental density data obtained for the PZ (1) + DEAE (2) + H2O (3) blends are presented in Table 11, where the total amine mass percentage is kept constant at 30. It is revealed that density of the blended solutions falls as the temperature rises and with declining Piperazine concentration in the blends. A set of temperature-dependent R-K parameters for the ternary system PZ (1) + DEAE (2) + H2O (3) are developed showing correlation deviation of 0.045% and are presented in the Table 12. There is an AAD % of 0.085 between the

Table 13. Parameters of Grunberg and Nissan type model (Eq 31) for PZ (1) + DEAE (2) + H2O (3) System estimated Nissan parameters: PZ (1) + DEAE (2) + H2O (3) parameters A12

A13

A23

(AAD)% correlation


0.0034 0.5375 −0.0017 0.0369 −5.700e−4 1.705e−6 0.0680 6.571e−4 −5.745e−6 0.075%

the generated data more precisely than in comparison to the R-K equation. The density data of PZ + DEAE + H2O system is also correlated using Gonzalez-Olmos and Iglesias equation showing a correlation deviation of 0.082%. The temperaturedependent polynomial coefficients (Cij and Bij) of eq 32 are presented in Table 14. Parity among all the measured and correlated density data are presented in Figure 5 for the PZ + DEAE + H2O system. I



Article

Table 14. Gonzalez-Olmos and Iglesias model parameters (Eq 32) for PZ (1) + DEAE (2) + H2O (3) system

Table 16. Estimated Parameters of Eq 35 for PZ (1) + DEAE (2) + H2O (3) System

estimated Gonzalez-Olmos and Iglesias model parameters: PZ (1) + DEAE (2) + H2O (3) C00 = 3.24 × 104 C10 = 4.94 × 104 C20 = −7.32 × 106 B00 = 3.24 × 104 B10 = −2.34 × 105 B20 = −6.66 × 106 (AAD) % correlation

C01 = 0.0035 C11 = 0.0067 C21 = 3.01 × 104 B01 = 0.0035 B11 = −0.0049 B21 = −4.46 × 104

estimated Nissan parameters for viscosity: (PZ (1) + DEAE (2) + H2O (3)) parameter

C02 = 5.511 × 106 C12 = −2.80 × 104 C22 = −2.45 × 1054 B02 = −3.54 × 106 B12 = −3.34 × 104 B22 = −8.03 × 106 0.082%

G12

G13

G23

(AAD) % correlation


1.227e−4 0.0185 0.0015 0.0031 0.4762 −0.0014 0.0038 0.5534 −0.0016 1.09%

Figure 5. Parity between the experimental and correlated density data in aqueous PZ + DEAE solution at 313.15 K.

4.4. Viscosity of PZ + DEAE + H2O Blend. Experimental viscosity data for the PZ (1) + DEAE (2) + H2O (3) blends at temperatures of 303.15−323.15 K are presented in Table 15,

Figure 6. Parity plot for the experimental and correlated viscosity data in aqueous PZ + DEAE solution.

Table 15. Viscosity for PZ (1) + DEAE (2) + H2O (3) System at Various Temperature and Relative Amine Composition at 101.3 kPaa

5. CONCLUSIONS Present work has been an endeavor to characterize a potential solvent PZ + DEAE for CO2 capture. This article provides the measurements on CO2 solubility in aqueous PZ + DEAE blends with several amine blends at low CO2 pressure and in the temperature range suitable for absorption. The data generated are correlated using a computationally simple approximate model (with apparent equilibrium constants) with minimal correlation deviation. The equilibrium constant for deprotonation of DEAE has been estimated using the experimentally determined pKa of the DEAE over 298.15−333.15 K. It appears from the open literature and our own experimentation that PZ + DEAE blends appear to be better than PZ + MDEA with respect to their CO2 absorption capacity even at low CO2 partial pressures and expected to be faster in reaction with CO2. Density and viscosity measurements of PZ + DEAE+ H2O at temperatures of 303.15−323.15 K considering the PZ/DEAE mass percentage ratios of 3:27, 6:24, 9:21, and 12:18 are also reported. Generated density data have been correlated using various thermodynamic models. The correlated density and viscosity data with respect to temperature and relative amine compositions reveal estimable agreement with the experimental data for the PZ + DEAE blend. The generated density and viscosity data may be an important append to engineering database for gas treating equipment design. Rate studies, degradation resistance, biodegradability, corrosion behavior, foaming tendency, and coabsorption capacity for SO2, and NOx are to be done in detail before claiming the proposed blend as an alternative to PZ + MDEA and as a

η (mPa·s) temperature/K w1/w2 3:27 6:24 9:21 12:18

303.15 3.234 3.337 3.577 3.6108

308.15 2.784 2.940 3.131 3.172

313.15 2.363 2.540 2.667 2.774

318.15 2.046 2.263 2.364 2.418

323.15 1.841 1.956 2.035 2.178

a

w1 and w2 are the mass fraction of PZ and DEAE, respectively. Standard uncertainty u(T) = 0.05 K. Combined extended uncertainty (U): U(w) = 0.001, U(ρ) = 0.076 kg/m3, and U(η) = 0.039 mPa·s and U(P) = 1 kPa (95% level of confidence and coverage factor, k = 2).

and the total amine mass percentage is kept constant at 30.0 (with “wi” as the mass percentage of individual amines present in the solutions (w1 + w2 = 30)). The generated viscosity of the ternary mixtures are correlated using the Grunberg and Nissan type of expression (eq 35) with correlation deviations of 1.09% for PZ (1) + DEAE (2) + H2O (3) systems. The temperaturedependent fitting parameters of eq 36 for the aforesaid system are reported in Table 16. It is evident that viscosity of the solution increases as the temperature decreases and Piperazine concentration in the blend solution increases. Parity plot among all the measured and correlated viscosity data is presented in Figure 6 for PZ + DEAE + H2O system, showing good agreement among experimental and predicted data. J



Article

potential one, especially, in treating flue gas from a coal-based thermal power plant.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.6b00856. Additional mathematical modeling (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: 0661-2462999. ORCID

M. Kundu: 0000-0001-9897-3094 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge ministry of human resource and development (MHRD), Government of India for financially supporting this work. We also acknowledge “the somber concern being raised in several forums regarding GHG emission and its post effects” as our motivation behind the present work.

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REFERENCES

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