Chemical Engineering Science 64 (2009) 1185 -- 1194
Contents lists available at ScienceDirect
Chemical Engineering Science
journal homepage: w w w . e l s e v i e r . c o m / l o c a t e / c e s
Absorption of carbon dioxide into aqueous solutions of piperazine activated
2-amino-2-methyl-1-propanol
Arunkumar Samanta, S.S. Bandyopadhyay ∗
Separation Science Laboratory, Cryogenic Engineering Centre, IIT Kharagpur, W.B. 721 302, India
A R T I C L E
I N F O
Article history:
Received 13 May 2008
Received in revised form 24 October 2008
Accepted 25 October 2008
Available online 7 November 2008
Keywords:
Absorption
Kinetics
Carbon dioxide
AMP
Piperazine
A B S T R A C T
In this work, new experimental data on the rate of absorption of CO2 into piperazine (PZ) activated aqueous solutions of 2-amino-2-methyl-1-propanol (AMP) are reported. The absorption experiments using a
wetted wall contactor have been carried out over the temperature range of 298–313 K and CO2 partial
pressure range of 2–14 kPa. PZ is used as a rate activator with a concentration ranging from 2 to 8 wt%,
keeping the total amine concentration in the solution at 30 wt%. The CO2 absorption into the aqueous
amine solutions is described by a combined mass transfer-reaction kinetics-equilibrium model, developed
according to Higbie's penetration theory. Parametric sensitivity analysis is done to determine the effects
of possible errors in the model parameters on the accuracy of the calculated CO2 absorption rates from
the model. The model predictions have been found to be in good agreement with the experimental
results of rates of absorption of CO2 into aqueous (PZ+AMP). The good agreement between the model
predicted rates and enhancement factors and the experimental results indicates that the combined mass
transfer-reaction kinetics-equilibrium model with the appropriate use of model parameters can effectively
represent CO2 mass transfer in PZ activated aqueous AMP solutions.
© 2008 Elsevier Ltd. All rights reserved.
1. Introduction
The removal of acid gas impurities, such as carbon dioxide (CO2 )
and hydrogen sulfide (H2 S), from natural gas, refinery off-gases,
synthesis gas and other industrial gases is an important operation
in industrial gas processing. Due to the need to exploit even poorer
quality natural gas, extensive research activities to develop less energy intensive efficient gas processing technologies are essential.
Improved solvents for gas sweetening with reduced cost will ensure the utilization of tertiary natural gas resources. Besides, growing environmental concerns today for global warming and climate
change have motivated extensive research activities towards developing more efficient and improved processes for CO2 capture from
stationary CO2 emission sources for economic CO2 sequestration.
Thus, besides CO2 removal from natural gas, improved processes for
CO2 capture from the flue gas streams of fossil fuel based power
plants are also essential today.
Aqueous alkanolamine solutions are widely used for the removal
of acid gas impurities from natural gas and industrial gas streams.
Industrially important alkanolamines for the regenerative chemical
∗ Corresponding author. Tel.: +91 3222 283580; fax: +91 3222 282258.
E-mail address: ssbandyo@hijli.iitkgp.ernet.in (S.S. Bandyopadhyay).
0009-2509/$ - see front matter © 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ces.2008.10.049
absorption processes are monoethanolamine (MEA), diethanolamine
(DEA), N-methyldiethanolamine (MDEA), and 2-amino-2-methyl-1propanol (AMP) (Kohl and Nielsen, 1997). Recently, mixing of alkanolamines, e.g., mixture of a primary (e.g., MEA) or secondary (e.g.,
DEA) alkanolamine with a tertiary alkanolamine (e.g., MDEA) is suggested to capitalize on the advantages of each amine. The blended
amine solvents combine the higher equilibrium capacity of the tertiary amine for CO2 with the higher CO2 reaction rate of the primary
or secondary amine (Chakravarty et al., 1985). The use of blended
amines in gas treatment brings about a significant improvement in
absorption capacity and absorption rate and a great saving in solvent regeneration energy requirement. Besides, it also offers the
advantage of setting the selectivity of the solvent toward CO2 by
judiciously mixing the amines in varying proportions which results
in an additional degree of freedom for achieving the desired separation to meet the required specification of the treated gas. As
with MDEA, the sterically hindered amine, AMP, also provides an
equilibrium CO2 capacity about twice that of any primary or secondary amine. Besides, similar to the CO2 -MDEA reaction product,
the ultimate product of the CO2 -AMP reaction is bicarbonate. Hence,
the regeneration energy requirement, when AMP is used as a component of a blended amine solvent, will be lower as in the case of
using MDEA. On the other hand, AMP offers an additional advantage
over MDEA particularly for CO2 removal, due to the fact that the
CO2 -AMP reaction rate is much faster than the CO2 -MDEA reaction
rate.
1186
A. Samanta, S.S. Bandyopadhyay / Chemical Engineering Science 64 (2009) 1185 -- 1194
More recently, there is an interest in using activated alkanolamine
solvents by employing a reaction rate accelerator e.g., piperazine
(PZ), in the aqueous alkanolamine solution. PZ activated aqueous
MDEA or AMP for CO2 removal take advantage of the high rate of
reaction of CO2 with the activating agent, e.g., PZ, combined with
the advantage of high CO2 loading capacity of MDEA or AMP and
relatively lower regeneration energy requirement. PZ is used as an
activator in the activated MDEA process of BASF (Appl et al., 1982)
and it is reported that PZ is more effective than the conventional
activators (Bishnoi and Rochelle, 2002). While PZ activated aqueous
AMP solutions, like PZ activated aqueous MDEA, can be highly efficient solvents for CO2 removal, published literature on this solvent
system is very limited. Seo and Hong (2000) experimentally studied the effect of PZ on the absorption of CO2 in aqueous solutions of
AMP at 303 and 313 K using a wetted-sphere contactor. They used
AMP concentrations in the range of 0.55–3.35 kmol m−3 along with
PZ concentrations of 0.058, 0.115, and 0.233 kmol m−3 . However,
they performed their experiments at relatively higher CO2 partial
pressure resulting in substantial depletion of PZ at the gas–liquid
interface. As a result, the kinetic data reported by them from their
absorption experiments appear to be incorrect (Bishnoi and Rochelle,
2000). The kinetics of the absorption of CO2 into aqueous solutions of
(AMP+PZ) were also investigated by Sun et al. (2005) using a wetted
wall contactor. They performed the absorption experiments over the
temperature range of 303–313 K and CO2 partial pressure range of
2.63–4.55 kPa using solutions containing 1.0–1.5 kmol m−3 AMP and
0.1–0.4 kmol m−3 PZ. A hybrid kinetic model, a second order reaction
for CO2 with PZ and a zwitterion reaction mechanism for CO2 with
AMP have been used by Sun et al. (2005) to interpret their results.
More recently, Lin et al. (2008) studied the performance of microporous polyvinylidinefluoride hollow fiber membrane contactor using
the aqueous solutions of PZ and AMP as the solvents. Experimental
results showed that the CO2 absorption rate was much enhanced by
the addition of PZ promoter. However, there is no study reported
in the open literature to interpret the experimental absorption data
of CO2 in PZ activated aqueous AMP solutions using a numerically
solved coupled mass transfer-kinetics-equilibrium model that takes
into account all possible reversible reactions of CO2 -(AMP+PZ+H2 O).
In this work, the absorption of CO2 into PZ activated aqueous
AMP solutions has been studied experimentally and theoretically
at various temperatures, different relative compositions of AMP/PZ
in the solutions, and various CO2 partial pressures to gain better
understanding of the absorption of CO2 into PZ activated aqueous
alkanolamine solutions. Following the work of Hagewiesche et al.
(1995) and Mandal et al. (2001), the diffusion-reaction processes for
the chemical absorption of CO2 are modeled according to Higbie's
(1935) penetration theory with the assumption that all reactions are
reversible. Parametric sensitivity analysis has also been presented
using the mathematical model developed in this work to determine
the effects of possible errors in the important model parameters on
the accuracy of the calculated absorption rates and enhancement
factors from the model.
2. Model development
2.1. Reaction scheme and reaction mechanism
When CO2 is absorbed into an aqueous mixed amine solution of
AMP(R R R N, where R = C2 H2 (CH3 )2 OH and R = H) and PZ, the
following reactions may take place in the liquid phase:
Base-catalyzed hydration reaction:
K1 ,k21
CO2 + R R R N + H2 O ←→ R R R NH+ + HCO−
3
(1)
Formation of monocarbamate:
K2 ,k22
CO2 + PZ + H2 O ←→ PZCOO− + H3 O+
(2)
Formation of monocarbamate by PZ/AMP:
K3 ,k23
CO2 + R R R N + PZ ←→ PZCOO− + R R R NH+
(3)
Formation of dicarbamate:
K4 ,k24
CO2 + PZCOO− + H2 O ←→ PZ(COO− )2 + H3 O+
Formation of dicarbamate by
(4)
PZCOO− /AMP:
K5 ,k25
CO2 + R R R N + PZCOO− ←→ PZ(COO− )2 + R R R NH+
(5)
Formation of bicarbonate:
K6 ,k26
CO2 + OH− ←→ HCO−
3
(6)
Formation of carbonate:
K7
2−
+
HCO−
3 + H2 O ←→ CO3 + H3 O
(7)
Protonation of PZ:
K8
PZ + H3 O+ ←→ PZH+ + H2 O
(8)
Protonation of monocarbamate:
K9
PZCOO− + H3 O+ ←→ PZH+ COO− + H2 O
(9)
Protonation of AMP:
K10
R R R N + H3 O+ ←→ R R R NH+ + H2 O
(10)
Dissociation of water:
K11
2H2 O ←→ H3 O+ + OH−
(11)
Reactions (1)–(6) have finite reaction rates and are reversible. Reactions (7)–(11) are reversible and instantaneous with respect to mass
transfer and at equilibrium, since they involve only proton transfer.
In view of the very low carbamate stability constant of the
sterically hindered amine AMP (Sartori and Savage, 1983), the only
reaction of importance between CO2 and AMP is suggested to be
the formation of bicarbonate ion. Hence, bicarbonate ions may be
present in the solution in much larger amounts than the carbamate ions (Yih and Shen, 1988; Hagewiesche et al., 1995; Mandal
et al., 2001). Thus, the CO2 -AMP reaction, suggested to be similar
to that of CO2 -MDEA, may be represented by reaction (1), neglecting the formation of carbamate by AMP. The proposed mechanism
for the reaction between CO2 and PZ involves the formation of a
zwitterion followed by the deprotonation of the zwitterion by a
base to produce PZ-carbamate and protonated base (Bishnoi and
Rochelle, 2000; Derks et al., 2006; Samanta and Bandyopadhyay,
2007). Any base present in the solution may contribute to the deprotonation of the zwitterion (Caplow, 1968; Danckwerts, 1979).
The contribution of each base would depend on its concentration as well as how strong a base it is (Hagewiesche et al., 1995;
Bishnoi, 2000). Hence, the main contribution to the deprotonation of the zwitterion in an aqueous solution of a mixture of AMP
and PZ would come from PZ, AMP and to a lesser extent from
H2 O and OH− . The presence of significantly more AMP appears to
catalyze the reaction of CO2 and PZ to form carbamate and the
AMP deprotonation will dominate. In the case of PZ, formation of
zwitterion should be the rate-determining step, while the deprotonation step involves only a proton transfer and is considered
to be very fast. Reaction (2) represents the reaction between CO2
A. Samanta, S.S. Bandyopadhyay / Chemical Engineering Science 64 (2009) 1185 -- 1194
and PZ for producing carbamate (Bishnoi and Rochelle, 2000; Derks
et al., 2006; Samanta and Bandyopadhyay, 2007). The rate constant,
k22 , is considered the global rate coefficient for the formation of
zwitterion and zwitterion deprotonation (reaction (2)). Hence, this
representation does not rule out the possible formation of a zwitterion reaction intermediate. Also, the rate constant, k24 , is viewed
as the global rate coefficient for the formation of PZ-dicarbamate,
PZ(COO− )2 , by reaction (4). The third order rate constants, k23
and k25 , for AMP catalyzed PZ-carbamate (reaction (3)) and PZdicarbamate (reaction (5)) formations have been considered to
include the contribution of AMP in zwitterion deprotonation.
2.2. Bulk liquid equilibrium model
Liquid bulk concentrations of all chemical species must be known
in order to solve the diffusion-reaction model developed in this work.
The liquid bulk concentrations of all chemical species can be estimated from the initial concentration of AMP and PZ solution; the
initial CO2 loading, 1 , of the solution and the assumption that all
reactions are at equilibrium. The concentration of water is assumed
to remain constant because its concentration is much larger than the
concentration of other chemical species. Here, for convenience the
chemical species have been renamed as follows:
u3 = [R R R NH+ ]
u2 = [R R R N],
u1 = [CO2 ],
u4 = [HCO−
3 ],
u5 = [OH− ],
u7 = [H3 O+ ],
u8 = [PZ],
u10 = [PZCOO− ],
u9 = [PZH+ ]
u11 = [PZH+ COO− ]
−
u12 = [PZ(COO )2 ]
We have the following 12 equations for 12 liquid bulk concentrations:
AMP balance:
(12)
PZ balance:
(13)
CO2 balance:
u01 + u04 + u06 + u010 + u011 + 2u012 = 1 {[AMP]initial + [PZ]initial }
(14)
Electroneutrality balance:
+ u07
+ u09
− u04
− u05
− 2u06
− u010
− 2u012
=0
K4 =
K6 =
K7 =
K8 =
u07 u010
u01 u08
u07 u012
u01 u010
u04
u01 u05
u06 u07
u04
u09
u07 u08
K10 =
u03
(22)
u02 u07
K11 = u05 u07
(23)
The 12 simultaneous nonlinear algebraic equations (12)–(23)
have been solved using a subroutine called DNEQNF documented in
the IMSL Math/Library (Visual Numerics, Inc., 1994) in FORTRAN 90
for the 12 unknowns (u01 , . . . , u012 ) of the liquid bulk concentrations.
The routine solves a system of nonlinear equations using a modified Powell hybrid algorithm and a finite-difference approximation
to the Jacobian. This algorithm is a variation of Newton's method,
which uses a finite-difference approximation to the Jacobian and
takes precautions to avoid large step sizes or increasing residuals
(Visual Numerics, Inc., 1994; More et al., 1980). As finite-difference
approximation is used to estimate the Jacobian, double precision
calculation has been adopted in order to obtain an accurate Jacobian.
It has been found that the algorithm converged to solution even
when the initial guesses are not close to the solution (Aboudheir
et al., 2003; Samanta and Bandyopadhyay, 2007).
The mathematical model developed to interpret the experimental results of absorption of CO2 into aqueous solutions of AMP and
PZ is based on the concept of gas absorption accompanied by multiple reversible chemical reactions in a thin liquid film. It takes into
account the coupling between mass transfer, chemical equilibria and
chemical kinetics of all liquid phase chemical reactions. The mathematical model describing the diffusion-reaction processes consists
of partial differential equations formulated according to Eq. (24) for
the reactants and products present in the liquid phase:
j ui
j2 u = Di 2i +
i Ri
jt
jx
(24)
All reactions are numerically treated as reversible reactions with
finite rate, in which the reverse reaction rate constants are calculated
using the equilibrium constant of the corresponding reaction.
The rate equations of the finite rate reactions (Eqs. (1)–(6)) are
then given by Eqs. (25)–(30).
R1 = −k21 u1 u2 +
k21
u3 u4
K1
(25)
R2 = −k22 u1 u8 +
k22
u7 u10
K2
(26)
(15)
All reactions are in equilibria:
K2 =
(21)
u07 u010
i
u08 + u09 + u010 + u011 + u012 = [PZ]initial
u03
u011
2.3. Diffusion-reaction model
u6 = [CO2−
3 ]
u02 + u03 = [AMP]initial
K9 =
1187
k23
u3 u10
K3
(16)
R3 = −k23 u1 u2 u8 +
(17)
R4 = −k24 u1 u10 +
(18)
R5 = −k25 u1 u2 u10 +
(19)
(20)
R6 = −k26 u1 u5 +
k24
u12 u7
K4
k25
u3 u12
K5
k26
u4
K6
(27)
(28)
(29)
(30)
The following Eqs. (31)–(37), based on Eq. (24) govern the diffusion and reaction processes for CO2 absorption into an aqueous
solution containing AMP and PZ.
1188
A. Samanta, S.S. Bandyopadhyay / Chemical Engineering Science 64 (2009) 1185 -- 1194
CO2 balance:
6
ju1
j 2 u1 = D1
+
Ri
jt
jx2
(31)
i=1
Total carbon (from CO2 ) balance:
ju1 ju4 ju6 ju10 ju11
ju12
+
+
+
+
+2
jt
jt
jt
jt
jt
jt
j 2 u1
j2 u4
j 2 u6
j2 u10
= D1
+ D4
+ D6
+ D10
2
2
2
jx
jx
jx
jx2
2
2
j u11
j u12
+ D11
+ 2D12
jx2
jx2
(32)
(33)
−D1
(34)
(35)
dx
at x = 0 and t > 0
(44)
= kg (p1 − H1 u1 (0, t))
at x = 0 and t > 0
(45)
For negligible mass-transfer resistance in the gas phase, Eq. (45)
reduces to
(46)
Absorption rate and enhancement factor: The differential equations
are integrated from t = 0 to , the contact time, to obtain the concentration profile of CO2 in the liquid film. The time averaged absorption rate per unit interfacial area is obtained by Eq. (47) over
the contact time, .
R=−
j u1
(0, t) dt
0 jx
D1
(47)
For wetted wall contactor, the contact time, , is calculated using
=
(37)
K7 =
u6 u7
u4
(38)
K8 =
u9
u8 u7
(39)
K9 =
u11
u10 u7
(40)
u3
u2 u7
(41)
K11 = u5 u7
(42)
Thus, there are 12 partial differential–algebraic equations which can
be solved for the concentration profiles of the 12 chemical species
(u1 , . . . , u12 ) present in the aqueous solutions of (AMP+PZ).
2/3
2h 3 1/3 d
3 g
VL
(48)
The enhancement factor, E, defined as the ratio of the rate of absorption of a solute gas to that if there is no reaction, is given by
E=
Instantaneous reactions assumed to be at equilibrium:
K10 =
j u1
(36)
Electroneutrality Balance:
ju3 ju7 ju9 ju4 ju5
ju6 ju10
ju12
+
+
−
−
−2
−
−2
jt
jt
jt
jt
jt
jt
jt
jt
2
2
2
2
2
j u3
j u7
j u9
j u4
j u5
= D3
+ D7
+ D9
− D4
− D5
jx2
jx2
jx2
jx2
jx2
2
2
2
j u6
j u10
j u12
− 2D6
− D10
− 2D12
jx2
jx2
jx2
=0
u1 (0, t) = u∗1 = p1 /H1
Dicarbamate balance:
ju12
j2 u12
= D12
− R4 − R5
jt
jx2
(43)
For the volatile chemical species i = 1 (CO2 ), the mass-transfer rate
in the gas near the interface is equal to the mass-transfer rate in the
liquid near the interface:
Carbamate balance:
ju10 ju11
j2 u10
j2 u11
+
= D10
+ D11
− R2 − R3 + R4 + R5
2
jt
jt
jx
jx2
j ui
dx
Total PZ balance:
ju8 ju9 ju10 ju11 ju12
+
+
+
+
jt
jt
jt
jt
jt
j 2 u8
j2 u9
= D8
+ D9
jx2
jx2
2
j u10
j2 u11
j2 u12
+ D10
+ D11
+ D12
2
2
jx
jx
jx2
ui = u0i
Boundary conditions at gas–liquid interface (x = 0): At x = 0, the
fluxes of all non-volatile chemical species, i.e., i = 2,3, . . . ,12, are equal
to zero.
Total AMP balance:
ju2 ju3
j 2 u2
j2 u3
+
= D2
+ D3
2
jt
jt
jx
jx2
The diffusion coefficients of various ionic species in solution are
assumed to be equal to that of PZ. This amounts to neglecting the
effect of electrostatic potential gradients on ion diffusion. The more
rigorous approach taking into account the electrostatic potential gradients with unequal diffusion coefficients of the ionic species requires much higher computation time with little influence on the
accuracies of the model calculated rates of absorption (Glasscock and
Rochelle, 1989; Hagewiesche et al., 1995; Rinker et al., 1996).
Initial and boundary conditions at x = ∞ : At t = 0 (for all x 0)
and at x = ∞ (for all t 0), the concentration of chemical species,
i = 1, . . . ,12, are equal to their liquid bulk concentrations, i.e.,
R
kL (u∗1 − u01 )
(49)
2.4. Method of solution
The suggested model consists of partial differential and algebraic
equations. The partial differential equations are transformed into ordinary differential equations in t by discretizing the spatial variable
x using method-of-lines. Equally spaced nodes are used to discretize
the spatial variable x. The typical number of nodes used in this work
is 450 and corresponding nodal spacings are of the order of 10−8 m.
The resulting system of ordinary differential equations coupled with
the nonlinear algebraic equations is solved by using the subroutine
DDASSL (Petzold, 1983; Brenan et al., 1989) in double precision FORTRAN 90 on a Pentium IV processor. The subroutine DDASSL uses
the backward-differentiation formulas of orders one through five in
a variable step integration mode to integrate the nonlinear systems
of differential/algebraic equations.
A. Samanta, S.S. Bandyopadhyay / Chemical Engineering Science 64 (2009) 1185 -- 1194
1189
Table 1
Physicochemical properties aqueous (AMP+PZ) solutions.
Mass
% AMP
Mass
% PZ
[AMP]
(kmol m−3 )
[PZ]
(kmol m−3 )
T (K)
28
28
28
28
25
25
25
25
22
22
22
22
30
2
2
2
2
5
5
5
5
8
8
8
8
0
0.23
0.23
0.23
0.23
0.58
0.58
0.58
0.58
0.94
0.94
0.94
0.94
0.0
3.14
3.14
3.14
3.14
2.81
2.81
2.81
2.81
2.49
2.49
2.49
2.49
3.33
298
303
308
313
298
303
308
313
298
303
308
313
313
a
a
a×103
(kg m−1 s)
H1 b
(kPa m3 kmol−1 )
D1 b×109
(m2 s−1 )
998.72
995.93
993.07
990.30
1000.9
998.41
995.61
992.67
1003.7
1001.0
998.2
995.0
988.44
3.737
3.005
2.524
2.060
3.879
3.123
2.591
2.119
4.063
3.312
2.708
2.235
2.043
3870
4226
4674
4949
3753
4088
4620
4888
3715
4044
4513
4829
4720c
0.62
0.73
0.90
1.17
0.58
0.72
0.82
1.05
0.55
0.67
0.75
0.95
1.46c
(kg m−3 )
Samanta and Bandyopadhyay (2006).
b
Estimated using N2 O analogy; this study.
c
Mandal et al. (2005).
3. Physicochemical properties
The densities and viscosities of the aqueous (AMP+PZ) have been
measured using standard procedures described earlier (Samanta and
Bandyopadhyay, 2006) and are presented in Table 1. The solubility
and diffusivity of CO2 in the aqueous amine and activated amine solutions containing 30 wt% total amine and with PZ concentrations of
2, 5 and 8 wt% are estimated in the temperature range of 298–313 K
using the N2 O-analogy method. The procedures were similar to that
discussed earlier by Samanta et al. (2007). Since CO2 reacts with
amines, physical solubility and diffusivity of CO2 in amine solutions
cannot be determined directly. As a result, one must use a nonreacting gas, e.g., nitrous oxide (N2 O) as a surrogate to CO2 in estimating the physical solubility and diffusivity of CO2 in these solvents.
Clarke (1964) proposed that N2 O, a molecule with similar molecular structure, molecular weight, and similar electronic configuration
as CO2 , could be used to represent CO2 behavior in reactive systems. It has been established by Laddha et al. (1981) that the ratios
of CO2 /N2 O physical solubilities and CO2 /N2 O diffusivities in water
and in several non-reacting organic solvents are constant. Hence, the
physical solubility and diffusivity of CO2 in solvents with which it
reacts can be determined by using these constant factors as shown
in Eqs. (50) and (51) for H1 and D1 .
H1 = HN2 O-amine
D1 = DN2 O-amine
HCO2 -water
HN2 O-water
DCO2 -water
DN2 O-water
ln k21 = 23.69 −
5176.49
T
(50)
(51)
2360.7
− 24.727 × 10−5 [MDEA]
T
(52)
(53)
The rate coefficients for the reactions of CO2 with aqueous
PZ were determined by these authors and presented elsewhere
(Samanta and Bandyopadhyay, 2007). The rate coefficients for reactions (2) and (4) were fitted as functions of temperature by the
following Arrhenius equations:
3.5 × 104 1
1
k22 = 5.8 × 104 exp −
−
(54)
R
T
298
3.55 × 104
k24 = 5.95 × 10 exp −
R
4
1
1
−
T
298
(55)
Values of the forward rate coefficient k26 of reaction (6) was
calculated using Eq. (56) presented by Pinsent et al. (1956) for the
temperature range of 273–313 K:
where HN2 O-amine and DN2 O-amine are the physical solubility and diffusivity of N2 O in the amine solution. This is known as “N2 O analogy”.
This analogy has been frequently used to estimate the physical solubility and diffusivity of CO2 in amine solvents (Laddha et al., 1981;
Haimour and Sandall, 1984; Versteeg and van Swaaij, 1988). The
estimated H1 and D1 values are presented in Table 1. The diffusion coefficients of chemical species in the liquid phase are also
needed for the model. The diffusion coefficients of the ionic species
have been assumed to be equal to that of PZ. The diffusion coefficients of PZ in solution have been estimated using the diffusion
coefficient of MDEA, corrected for the molecular weight by multiplying with a factor of 1.38. The diffusion coefficient of MDEA has
been calculated from Eq. (52) as given by Snijder et al. (1993):
ln DMDEA = −13.088 −
where [MDEA] is the concentration of MDEA in aqueous solution,
mol m−3 .
The reaction rate constant k21 for the reaction of CO2 with aqueous AMP (Eq. (1)) was calculated from the following correlation presented by Saha et al. (1995) over the temperature range 294–318 K:
log10 k26 = 13.635 −
2895
T
(56)
The values of the independent equilibrium constants have been
found out using reliable correlations and the dependent ones have
been estimated by appropriate combination of the independent equilibrium constants.
The values of K2 , K4 and K9 were calculated from the following
correlations of Bishnoi (2000):
ln K2 = −29.31 −
5615
T
(57)
ln K4 = −30.78 −
5615
T
(58)
ln
1
K9
= −8.21 −
5286
T
(59)
Danckwerts and Sharma (1966) correlated the data for K7 over
the temperature range of 273–323 K with the following equation:
log10 K7 = 6.498 − 0.0238T −
2902.4
T
(60)
1190
A. Samanta, S.S. Bandyopadhyay / Chemical Engineering Science 64 (2009) 1185 -- 1194
Pagano et al. (1961) reported data for K8 according to the following equation:
4351
1
= −11.91 −
(61)
ln
K8
T
Data for K11 were reported by Posey (1996) for the temperature
range 273–523 K and were correlated according to the following
equation:
ln K11 = 132.899 −
13445.9
− 22.4773 ln T
T
(62)
Data for (K6 K11 ) were reported by Read (1975) for the temperature range 273–523 K and were correlated according to the following
equation:
log10 (K6 K11 ) = 179.648 + 0.019244T − 67.341 log10 T
7495.441
−
T
(63)
Value of K10 for aqueous AMP-PZ was calculated from the following
correlation reported by Silkenbäumer et al. (1998) for the temperature range 313–353 K:
ln(K10 K11 ) =
7261.78
− 22.4773 ln T + 142.58612
T
(64)
Reagent grade PZ ( > 99% pure) and AMP ( > 97% pure) were
obtained from E. Merck, Germany, and were used without further
purification. Distilled water degassed by prolonged boiling and
cooled to ambient temperature under vacuum, was used for preparing the amine solutions. The CO2 gas ( > 99.9% pure) and nitrogen
gas ( > 99.999% pure) were obtained from Chemtron Science Pvt.
Ltd., India.
A volumetric gas flow rate of about 180×10−6 m3 s−1 was used
throughout all runs using mass flow controllers (Sierra Instruments,
USA) for CO2 and N2 . Nitrogen gas was used as a diluent for CO2 to
obtain various desired partial pressures of CO2 . The liquid flow rate
was maintained at about 2×10−6 m3 s−1 by a precalibrated rotameter. The CO2 concentrations at the inlet and outlet of the wetted wall
contactor was determined with a HORIBA NDIR on-line CO2 analyzer
(Model: VA 3000, Japan) connected through its continuous sampling
unit (Model: HORIBA VS 3000, Japan). Liquid samples were collected
at the bottom of the absorption zone at fixed intervals after the absorption measurements reached steady state. The total CO2 content
of each liquid sample was determined by acidulating a known volume of the sample using 6 N HCl in a glass cell placed in a thermostated bath and accurately measuring the volume of the evolved
gas, as described earlier by Saha et al. (1995). The corresponding rate
of absorption of CO2 in the PZ activated AMP solvent was determined
from the liquid phase CO2 concentration.
4. Experimental
5. Results and discussion
A 2.81×10−2 m o.d. stainless-steel wetted wall contactor was used
for the absorption measurements. The apparatus and method are
similar to that described by Saha et al. (1995). Absorption measurements were performed at 298, 303, 308 and 313 K. The total pressure
in the absorption chamber was about 100 kPa with the CO2 partial
pressures in the range of 2–14 kPa. PZ concentrations in the activated aqueous AMP solutions were in the range of 2–8 wt%, while
the total amine concentration in the solution was kept at 30 wt%.
The temperature of absorption was controlled within ± 0.2 K of the
desired level with two circulator temperature controllers (JULABO
FP 55 and Julabo F 32, FRG).
Table 2 presents the measured rates and enhancement factors
for the absorption of CO2 into (28 mass% AMP+2 mass% PZ), (25
mass% AMP+5 mass% PZ) and (22 mass% AMP+8 mass% PZ) at 298,
303, 308 and 313 K and 30 wt% AMP at 313 K. As shown in Table 2
and Fig. 1, the addition of small amounts of PZ to an aqueous solution of AMP results in significant enhancement in the rates of
absorption. For example, for T = 313 K and CO2 partial pressure
of about 5 kPa, the enhancement factor for absorption in aqueous
solutions of 30 mass% AMP, (2 mass% PZ+28 mass% AMP), (5 mass%
PZ+25 mass% AMP), and (8 mass% PZ and 22 mass% AMP) are about
45.1, 150.1, 209.7 and 250.5, respectively. So, by replacing 2 mass%
Table 2
Experimental and model predicted results for the absorption of CO2 into aqueous (AMP+PZ) in the wetted wall contactor.
[AMP]
(kmol m−3 )
[PZ]
(kmol m−3 )
T (K)
3.14
3.14
3.14
3.14
3.14
3.14
3.14
2.81
2.81
2.81
2.81
2.81
2.81
2.81
2.49
2.49
2.49
2.49
2.49
2.49
2.49
3.326
3.326
3.326
0.23
0.23
0.23
0.23
0.23
0.23
0.23
0.58
0.58
0.58
0.58
0.58
0.58
0.58
0.94
0.94
0.94
0.94
0.94
0.94
0.94
0.0
0.0
0.0
298
303
308
313
313
313
313
298
303
308
313
313
313
313
298
303
308
313
313
313
313
313
313
313
p1 (kPa)
4.85
4.88
4.87
4.8
1.93
6.83
13.78
4.92
4.86
4.93
4.82
1.97
6.88
13.69
4.84
4.79
4.79
4.56
1.93
6.65
13.61
5.04
7.02
14.06
(s)
0.60
0.63
0.56
0.48
0.44
0.43
0.43
0.55
0.53
0.46
0.44
0.42
0.44
0.41
0.58
0.53
0.49
0.45
0.53
0.43
0.48
0.43
0.43
0.45
kL×105 (m s−1 )
3.64
3.83
4.52
5.57
5.82
5.87
5.88
3.66
4.18
4.78
5.51
5.64
5.50
5.70
3.46
4.03
4.43
5.20
4.77
5.28
5.00
6.56
6.61
6.46
Experimental results
Predicted results
R×106 (kmol m−2 s)
E
R×106 (kmol m−2 s)
E
6.33
7.080
7.34
8.11
4.8
12.30
20.60
8.84
9.75
10.70
11.40
5.84
15.38
27.80
10.20
10.70
11.75
12.30
6.70
17.10
31.60
3.16
3.98
8.14
138.9
159.9
155.7
150.1
211.4
151.7
125.8
184.5
196.4
210.0
209.7
257.0
198.7
174.0
226.1
224.4
249.7
250.5
351.7
235.3
224.3
45.1
40.5
42.3
5.83
6.15
6.98
8.46
3.98
11.57
19.15
7.70
8.85
9.72
11.60
5.21
16.17
29.48
8.90
9.93
10.92
12.21
5.49
16.79
32.3
2.91
3.74
7.51
128.0
138.9
148.1
156.5
175.3
142.7
116.9
160.7
178.2
190.7
213.4
229.3
208.9
184.5
197.3
208.2
232.0
248.7
288.2
231.0
227.4
41.6
38.0
39.0
A. Samanta, S.S. Bandyopadhyay / Chemical Engineering Science 64 (2009) 1185 -- 1194
Fig. 1. Effect of molar ratio of PZ/AMP on the enhancement of CO2 absorption into
aqueous solution of (AMP+PZ): , T = 313 K.
AMP with 2 mass% PZ, the enhancement factor increased by about
233%. Replacing an additional 3 mass% AMP with PZ increased the
enhancement factor by an additional 40%. A further replacement of
3 mass% AMP with an equal amount of PZ resulted in increasing the
enhancement factor by additional 20%.
The mathematical model has been used to predict the rates of absorption of CO2 into aqueous blends of PZ and AMP. For this system,
the rate constants, k23 and k25 , have been obtained by adjusting the
values of rate constants in the mathematical model until the predicted rates of absorption agreed with the experimentally measured
rates of absorption to within an average absolute deviation of 5% for
each temperature and for a particular concentration of the (AMP+PZ)
solution. It has been observed that, if reaction (3) is not considered,
the model under predicts the rate of absorption by about 36% compared with the measured rates for CO2 partial pressure above 5 kPa.
From this observation it appears that the role of AMP in proton transfer is also important. It is also observed that if reactions (4) and (5)
are not considered, the model under predicts the rate of absorption
by about 11% for CO2 partial pressure above 5 kPa. Thus, formation
of PZ-dicarbamate (reactions (4) and (5)) is also important in the
overall kinetics of CO2 -AMP-PZ. The estimated values of k23 and k25
for CO2 -(AMP+PZ+H2 O) have been correlated by the following the
Arrhenius equations (65) and (66).
1
7.2 × 104 1
4
k23 = 3.516 × 10 exp −
−
(65)
R
T
298
k25 = 1.836 × 104 exp −
7.6 × 104
R
1
1
−
T
298
(66)
The estimates of k23 from this work is plotted as function of temperature in Fig. 2.
The measured and model predicted rates of CO2 absorption are
compared in the parity plot shown in Fig. 3. The model predicted
rates of absorption for CO2 into (AMP+PZ+H2 O), as presented in Table
2 and Fig. 3, are in excellent agreement with the experimental results.
The average absolute deviation (AAD) between the experimental and
model results of rates of absorption of CO2 into aqueous (AMP+PZ)
is about 7.7%.
Typical calculated concentration profiles for absorption of CO2
into aqueous (25 mass% AMP+5 mass% PZ) are shown in Fig. 4. The
concentrations of AMP and PZ near the gas–liquid interface are lower
1191
Fig. 2. Arrhenius plot for k23 for (CO2 +AMP+PZ).
Fig. 3. Parity plot of model predicted rates and experimental rates of absorption of
CO2 into aqueous (AMP+PZ).
by about 4.08% and 30.24%, respectively, than their liquid bulk concentrations after a gas–liquid contact time of about 0.44 s. From this
observation, it appears that the assumption of fast pseudo-first reaction regime for absorption of CO2 in PZ activated AMP may not be
correct.
5.1. Parametric sensitivity analysis
Parametric sensitivity analysis has been performed using the
mathematical model developed in this study for the absorption
of CO2 into PZ activated AMP solution to examine the effects of
important parameters on the rates of absorption and to determine
the effects of possible inaccuracies in the values of the pertinent
model parameters on the accuracy of the calculated CO2 absorption rates from the model. The parameters considered for these
analyses are interfacial concentration of CO2 (CO2 partial pressure), Henry's law constant for CO2 , diffusion coefficients of CO2
1192
A. Samanta, S.S. Bandyopadhyay / Chemical Engineering Science 64 (2009) 1185 -- 1194
Fig. 4. Calculated concentration profile of species in the liquid film near the
gas–liquid interface at the end of the absorption length: [AMP] = 2.81 kmol m−3 ,
[PZ] = 0.58 kmol m−3 , T = 313 K, p1 = 4.82 kPa and = 0.44 s.
Fig. 6. The effect of errors in Henry's Law constant on the predicted rate of absorption
of CO2 into an aqueous (AMP+PZ) solution.
Fig. 5. Predicted enhancement factor for the absorption of CO2 into aqueous
(AMP+PZ) as a function of CO2 interfacial concentration.
Fig. 7. The effect of errors in the diffusion coefficient of CO2 on the predicted rate
of absorption of CO2 into an aqueous (AMP+PZ) solution.
in amine solution, and reaction rate constants, k23 . The parametric sensitivity analysis, presented in Figs. 5–9 has been performed for T = 313 K, [AMP] = 2.81 kmol m−3 , [PZ] = 0.58 kmol m−3 ,
p1 = 4.82 kPa, = 0.44 s. For Figs. 5–9, most of the required physicochemical and transport parameters have been taken from Tables
1 and 2 and reaction rate constants and other data are determined
from the correlations presented in Section 3.
Fig. 5 shows the effect of the CO2 interfacial concentration (i.e.,
CO2 partial pressure) on the enhancement factor. It is clear that the
enhancement factor at lower interfacial concentrations (i.e., lower
partial pressures) is greater than that at higher interfacial concentrations (i.e., higher partial pressures). This may be due to the fact
that as the CO2 interfacial concentration decreases, the contribution
of physical absorption to the overall absorption of CO2 decreases
and the contributions of the chemical reactions between CO2 and
(AMP+PZ+H2 O) increases.
Fig. 6 shows the effect of any possible errors in the value of
Henry's law constant of CO2 on the accuracy of the model pre-
dicted rate of absorption of CO2 into aqueous (AMP+PZ) solution.
Here, errors of −50% to +50% have been assumed in the value of the
Henry's law constant and the corresponding errors in the model calculated rate of absorption have been determined to be from +87.3%
to −32.6%. Hence, it is evident that the rate of absorption of CO2
in PZ activated amine is very sensitive to the value of Henry's law
constant. The reason may be due to the fact that it determines
the amount of CO2 that dissolves into the aqueous amine solution
for the given temperature, pressure and amine concentration. It is
therefore important to have accurate values of the Henry's law constant of CO2 in the (AMP+PZ) solution in order to accurately predict the rates of absorption of CO2 in aqueous (AMP+PZ) from the
model.
The effect of errors in the diffusion coefficient of CO2 in aqueous (AMP+PZ) on the predicted rate of absorption is shown in Fig. 7.
Errors of −50% to +50% have been introduced into the value of the
diffusion coefficient of CO2 , and the corresponding errors in the predicted rate of absorption has been determined to be from −27.6% to
A. Samanta, S.S. Bandyopadhyay / Chemical Engineering Science 64 (2009) 1185 -- 1194
1193
of −50% to +50% have been introduced into the value of k23 , and the
corresponding errors in the predicted rate of absorption have been
determined to be from −13.2% to +10.4%. Thus, for accuracy in the
calculated rate of absorption and enhancement factor, it is also important to have accurate values of the rate constant of the reaction
between CO2 and AMP in presence of PZ.
6. Conclusion
Fig. 8. The effect of errors in the diffusion coefficients of all liquid phase chemical
species on the predicted rate of absorption of CO2 into an aqueous (AMP+PZ) solution.
In this work, the absorption of CO2 into aqueous solutions of mixture of small amounts of PZ and much larger amounts of AMP was
studied experimentally and theoretically. Absorption measurement
over the temperature range of 298–313 K and CO2 partial pressure
range of 2–14 kPa were done using a wetted wall contactor. It has
been found that the addition of small amounts of PZ to an aqueous
solution of AMP, e.g., 2 wt% PZ in 28 wt% aqueous AMP, significantly
enhances the rate of absorption of CO2 and enhancement factor. A
comprehensive coupled mass transfer-reaction kinetics-equilibrium
model has been developed to describe absorption of CO2 into PZ activated aqueous AMP solutions incorporating all important reversible
reactions in the liquid phase. The model is validated by comparing
the model predicted rates of absorption and enhancement factors
with the experimental results of absorption of CO2 into aqueous
(AMP+PZ). New kinetic parameters, k23 and k25 , for the reactions of
CO2 with aqueous (AMP+PZ) have been obtained using the developed mathematical model and the measured absorption data of this
work. The model has also been used for parametric sensitivity analysis to determine the effects of various important parameters on the
rates of absorption and enhancement factors.
Notation
d
Di
E
h
H1
kL
p1
[PZ]
Fig. 9. The effect of errors in k23 on the predicted rate of absorption of CO2 into an
aqueous (AMP+PZ) solution.
+21.4%. Therefore, it is also important to have accurate values of the
diffusion coefficient of CO2 in aqueous (AMP+PZ) in order to predict
the rates of absorption from the model with good accuracy.
The effect of errors in the values of the diffusion coefficients of
all chemical species in the liquid phase except CO2 , on the predicted
rate of absorption has been shown in Fig. 8. Here, errors of −50% to
+50% have been considered in the values of these diffusion coefficients simultaneously, and the corresponding errors in the predicted
rate of absorption have been determined to be −5.3% to +2.3%. Hence,
it can be seen that relatively large errors in the values of the diffusion coefficients of all chemical species other than CO2 in the liquid
phase, are not likely to introduce significant errors in the predicted
rate of absorption. This observation justifies the assumption that the
diffusion coefficients of all ionic species in solution are equal to that
of PZ (Section 2.3).
Fig. 9 shows the effect of errors in the value of the rate constant, k23 (Eq. (3)) on the predicted rate of absorption. Here, errors
[PZ]initial
R
Ri
t
ui
ui 0
ui *
VG
VL
x
outer diameter of the wetted wall column, m
diffusion coefficient of species i in the aqueous solution, m2 s−1
enhancement factor for absorption of CO2
absorption length of the wetted wall column, m
Henry's law constant for CO2 , kPa m3 kmol−1
liquid-phase mass transfer coefficient for physical
absorption of a gas is defined as kL =2 D1 / , m s−1
partial pressure of CO2 in the gas phase, kPa
concentration of PZ in the aqueous solution,
kmol m−3
initial liquid bulk concentration of PZ, kmol m−3
average rate of absorption of CO2 per unit interfacial
area, kmol m−2 s−1
reaction rate expression for reaction i
independent time variable, s
concentration of species i in the liquid phase,
kmol m−3
initial liquid bulk concentration of species i,
kmol m−3
interfacial concentration of CO2 in the liquid,
kmol m−3
volumetric flow rate of gas, m3 s−1
volumetric flow rate of solution, m3 s−1
independent spatial variable, m
Greek letters
1
initial CO2 loading of the aqueous amine solution,
kmol CO2 , kmol total amine−1
1194
i
A. Samanta, S.S. Bandyopadhyay / Chemical Engineering Science 64 (2009) 1185 -- 1194
thickness of diffusion film, m
viscosity of the solution, kg m−1 s−1
stoichiometric factor
density of the solution, kg m−3
References
Aboudheir, A., Tontiwachwuthikul, P., Chakma, A., Idem, R., 2003. Kinetics of the
reactive absorption of carbon dioxide in high CO2 -loaded, concentrated aqueous
monoethanolamine solutions. Chemical Engineering Science 50, 1071–1079.
Appl, M., Wagner, U., Henrici, H.J., Kuessner, K., Volkamer, F., Ernst-Neust, N., 1982.
Removal of CO2 and/or H2 S and/or COS from gases containing these constituents.
US Patent 4336233.
Bishnoi, S., 2000. CO2 absorption and solution equilibrium in piperazine activated
methyldiethanolamine. Ph.D. Dissertation, The University of Texas at Austin.
Bishnoi, S., Rochelle, G.T., 2000. Absorption of carbon dioxide into aqueous
piperazine: reaction kinetics, mass transfer and solubility. Chemical Engineering
Science 55, 5531–5543.
Bishnoi, S., Rochelle, G.T., 2002. Absorption of carbon dioxide in aqueous
piperazine/methyldiethanolamine. A.I.Ch.E. Journal 48, 2788–2799.
Brenan, K.E., Campbell, S.L., Petzold, L.R., 1989. Numerical Solution of Initial-Value
Problems in Differential–Algebraic Equations. North-Holland, New York.
Caplow, M., 1968. Kinetics of carbamate formation and breakdown. Journal of
American Chemical Society 90, 6795–6803.
Chakravarty, T., Phukan, U.K., Weiland, R.H., 1985. Reaction of acid gases with
mixtures of amines. Chemical Engineering Progress 81, 32–36.
Clarke, J.K.A., 1964. Kinetics of absorption of carbon dioxide in monoethanolamine
solution at short contact times. Industrial and Engineering Chemistry
Fundamentals 3, 239–245.
Danckwerts, P.V., 1979. The reaction of CO2 with ethanolamines. Chemical
Engineering Science 34, 443–446.
Danckwerts, P.V., Sharma, M.M., 1966. The absorption of carbon dioxide into aqueous
amine solutions of alkalis and amines (with some notes on hydrogen sulphide
and carbonyl sulphide). The Chemical Engineer 10, CE244–CE280.
Derks, P.W.J., Kleingeld, C., van Aken, C., Hogendoorn, J.A., Versteeg, G.F., 2006.
Kinetics of absorption of carbon dioxide in aqueous piperazine solutions.
Chemical Engineering Science 61, 6837–6854.
Glasscock, D.A., Rochelle, G.T., 1989. Numerical simulation of theories for gas
absorption with chemical reaction. A.I.Ch.E. Journal 35, 1271–1281.
Hagewiesche, D.P., Ashour, S.S., Al-Ghawas, H.A., Sandall, O.C., 1995. Absorption
of carbon dioxide into aqueous blends of monoethanolamine and Nmethyldiethanolamine. Chemical Engineering Science 50, 1071–1079.
Haimour, N., Sandall, O.C., 1984. Absorption of carbon dioxide into aqueous
methyldiethanolamine. Chemical Engineering Science 39, 1791–1796.
Higbie, R., 1935. The rate of absorption of a pure gas into a still liquid during short
periods of exposure. Transactions of the American Institute Chemical Engineers
31, 365–389.
Kohl, A.L., Nielsen, R.B., 1997. Gas Purification. fifth ed. Gulf Publishing Company,
Houston.
Laddha, S.S., Diaz, J.M., Danckwerts, P.V., 1981. The nitrous oxide analogy: the
solubilities of carbon dioxide and nitrous oxide in aqueous solutions of organic
compounds. Chemical Engineering Science 36, 228–229.
Lin, S.-H., Chiang, P.-C., Hsieh, C.-F., Li, M.-H., Tung, K.-L., 2008. Absorption of
carbon dioxide by the absorbent composed of piperazine and 2-amino-2-methyl1-propanol in PVDF membrane contactor. Journal of the Chinese Institute of
Chemical Engineers 39, 13–21.
Mandal, B.P., Biswas, A.K., Bandyopadhyay, S.S., 2001. Removal of carbon dioxide
by absorption in mixed amines: modeling of absorption in aqueous MDEA/MEA
and AMP/MEA solutions. Chemical Engineering Science 56, 6217–6224.
Mandal,
B.P.,
Kundu,
M.,
Bandyopadhyay,
S.S.,
2005.
Physical
solubility and diffusivity of N2 O and CO2 into aqueous solutions of (2-amino-2methyl-1-propanol+monoethaolamine)
and (N-methyldiethanolamine+monoethanolamine). Journal of Chemical and
Engineering Data 50, 352–358.
More, J., Garbow, B., Hillstrom, K., 1980. User Guide for MINPACK-1. Argonne National
Labs Report ANL-80-74, Illinois.
Pagano, J.M., Goldberg, D.E., Fernelius, W.C., 1961. A thermodynamic study
of homopiperazine, piperazine, and N-(2-aminoethyl)-piperazine and their
complexes with copper(II) ion. Journal of Physical Chemistry 65, 1062–1064.
Petzold, L.R., 1983. A Description of DASSL: A Differential/Algebraic System Solver
in Scientific Computing. North-Holland, Amsterdam. pp. 65–68.
Pinsent, B.R.W., Pearson, L., Roughton, F.J.W., 1956. The kinetics of combination of
carbon dioxide with hydroxide ions. Transactions of the Faraday Society 52,
1512–1520.
Posey, M.L., 1996. Thermodynamic model for acid gas loaded aqueous alkanolamine
solutions. Ph.D. Dissertation, The University of Texas at Austin.
Read, A.J., 1975. The first ionization constant of carbonic acid from 25 to 250 ◦ C and
to 2000 bar. Journal of Solution Chemistry 4, 53–70.
Rinker, E.B., Ashour, S.S., Sandall, O.C., 1996. Kinetics and modeling of carbon dioxide
absorption into aqueous solutions of diethanolamine. Industrial and Engineering
Chemistry Research 35, 1107–1114.
Saha, A.K., Bandyopadhyay, S.S., Biswas, A.K., 1995. Kinetics of absorption of CO2
into aqueous solutions of 2-amino-2-methyl-1-propanol. Chemical Engineering
Science 50, 3587–3598.
Samanta, A., Bandyopadhyay, S.S., 2006. Density and viscosity of aqueous solutions
of piperazine and (2-amino-2-methyl-1-propanol+piperazine) from 298 to 333 K.
Journal of Chemical and Engineering Data 51, 467–470.
Samanta, A., Bandyopadhyay, S.S., 2007. Kinetics and modeling of carbon dioxide
adsorption into aqueous solutions of piperazine. Chemical Engineering Science
62, 7312–7319.
Samanta, A., Roy, S., Bandyopadhyay, S.S., 2007. Physical solubility and
diffusivity of N2 O and CO2 in aqueous solutions of piperazine and (NMethyldiethanolamine+piperazine). Journal of Chemical and Engineering Data,
1381–1385.
Sartori, G., Savage, D.W., 1983. Sterically hindered amines for CO2 removal from
gases. Industrial and Engineering Chemistry Fundamentals 22, 239–249.
Seo, D.J., Hong, W.H., 2000. Effect of piperazine on the kinetics of carbon dioxide with
aqueous solutions of 2-amino-2-methyl-1-propanol and piperazine. Industrial
and Engineering Chemistry Research 39, 2062–2067.
Silkenbäumer, D., Rumpf, B., Lichtenthaler, R.N., 1998. Solubility of carbon
dioxide in aqueous solutions of 2-amino-2-methyl-1-propanol and Nmethyldiethanolamine and their mixtures in the temperature range from 313 to
353 K and pressure up to 2.7 MPa. Industrial and Engineering Chemistry Research
37, 3133–3141.
Snijder, D.E., te Riele, M.J.M., Versteeg, G.F., van Swaaij, W.P.M., 1993. Diffusion
coefficients of several aqueous alkanolamine solutions. Journal of Chemical and
Engineering Data 38, 475–480.
Sun, W.-C., Yong, C.-B., Li, M.-H., 2005. Kinetics of the absorption of carbon dioxide
into mixed aqueous solutions of 2-amino-2-methyl-1-propanol and piperazine.
Chemical Engineering Science 60, 503–516.
Versteeg, G.F., van Swaaij, W.P.M., 1988. Solubility and diffusivity of acid gases (CO2 ,
N2 O) in aqueous alkanolamine solutions. Journal of Chemical and Engineering
Data 33, 29–34.
Visual Numerics Inc., 1994. IMSL MATH/LIBRARY: FORTRAN Subroutines for
Mathematical Applications. Visual Numerics Inc., Texas.
Yih, S.-M., Shen, K.-P., 1988. Kinetics of carbon dioxide reaction with sterically
hindered 2-amino-2-methyl-1-propanol aqueous solutions. Industrial and
Engineering Chemistry Research 27, 2237–2241.