Solar Thermal Energy-based High Purity CO2 Release from
Carbonate Sorbents
N.B. Nakkash1, Z. Wang2, G.F. Naterer3
1. Al-Nahrain University, Baghdad-Iraq
2. Clean Energy Research Laboratory, University of Ontario Institute of Technology,
Oshawa, Ontario, Canada, L1H 7K4
3. Faculty of Engineering and Applied Science, Memorial University of Newfoundland,
St. John’s, Newfoundland, Canada, A1B 3X5
Abstract
The increase of the carbon dioxide content in the atmosphere is a major cause
of concern in the conservation of nature and in saving the world from natural disaster
which follows atmospheric pollution. Reducing CO2 emissions for addressing climate
change becomes increasingly important as CO2 concentration in the atmosphere has
been increasing rapidly, although procedures and measures have been taken to
decrease or prevent the increase of carbon dioxide content in the atmosphere.
Recycling CO2 with hydrogen for the production of fuels rather than taking it as a waste
is a promising option for our future sustainability development. The subsequent release
of the CO2 after it is captured in a sorbent can be combined with a highly chemical bond
energy compound to produce biofuel. This requires a high purity of CO2 for the fuel
synthesis. This paper focuses on the high purity CO2 release from its sorbents after they
capture the CO2 emissions from an industrial plant.
Thermodynamic analysis is performed in this paper involving the enthalpy
changes, the total heat required for the sorbent decomposition at various temperatures,
and the maximum heat required by the decomposition with the release kinetics of
sorbents are also investigated theoretically.
The present work also concerns with experimentally studying the release of high
purity of CO2 from different carbonates such as MgCO3, NaHCO3, Na2CO3, CaCO3 and
KHCO3, using a direct concentrated solar thermal energy. Practically, a solar
experimental loop has been used in a solar solarium system to investigate the effects of
solar thermal energy and the radiation intensity on the chemical composition profile and
the amount of CO2 released at different temperatures, time intervals, and the total heat
required for decomposition of NaHCO3, KHCO3 and MgCO3 to release pure CO2, the
results were compared with the theoretical investigations.
Keywords: CO2 release, Solar Energy, Thermochemical cycle, Different sorbents
1
Introduction
concentration in the atmosphere in view
of
increasing
emissions
derived
distributed sources which account for
approximately half of the total emissions
[6]. Several separation techniques have
been proposed to capture CO2 from flue
gases, such as: Chemical absorption,
physical absorption, Physical adsorption,
Membrane technologies and Cryogenic
separation.
Carbon dioxide capture directly from
atmospheric air receives more attention
recently. The earliest record goes back
to 1940’s, when CO2 was absorbed from
the atmosphere in an experimental
packed tower unit using a caustic
solution to produce oxygen [6]. About
10 years ago the research of CO2
capture technologies has been driven by
the necessity for climate change
mitigation. Not all CO2 separation
techniques are suitable for separation of
a very dilute gas. The chemical
absorption with metal hydroxides as
sorbent shows potential to be a feasible
path towards CO2 capture from ambient
air besides organic capture [8, 9 -15].
Several studies have been done
regarding the feasibility of CO2 capture
from ambient air into a Ca(OH)2- or
NaOH-based solution [9-14]. Different
thermochemical
cycles
for
CO2
consuming
and
releasing
using
renewable energy sources have been
studied for Ca-based and Na-based [16
-19].
Solar energy is associated with
sustainability,
though
no
energy
conversion system comes without
environmental impacts, energy yield per
land area is typically lower than fossil
and nuclear energy. Solar energy is too
expensive to be competitive with fossil,
nuclear, and wind [20], but solar will
The atmospheric concentration of
carbon dioxide, the most critical
greenhouse gas, has increased from 280
ppm in the pre-industrial age to more
than 370 ppm, and is expected to
increase above 500 ppm by the end of
this century [1]. The increase of CO2 in
the atmosphere has been accompanied
by a rise in the global average annual
temperature by 0.8o C and a rise in
global average sea level by 200 mm
since 1870 [2].
This is due to
anthropogenic activities, particularly
burning of fossil fuels and land-use
changes, currently the combustion of
oil, natural gas and coal accounts for 88
% of the world’s supply of primary
energy [3]. Present strategies rely on
improving the efficiency in energy use,
on reducing fossil fuel consumption, and
on using renewable energy sources or
nuclear power plants. However, the
continuing increase of the world
population
together
with
the
concomitant
growth
in
energy
consumption
and
the
industrial
development in developed countries
conflict with the efforts to reduce
greenhouse gas emissions.
Carbon dioxide capture from air has
been known for a long time though its
application as a measure to control the
global atmospheric CO2 concentration
only emerged recently. Most CO2
capture technologies deal with the
decarbonization of fossil fuels prior to
combustion or with the separation of
CO2 from combustion flue gases [4-5].
According to Intergovernmental Panel
on Climate Change (IPCC) scenarios, air
remediation will become necessary for
achieving stabilization of the global CO2
2
most
likely
make
a
significant
contribution to the mix of energy
sources that will make up the long-term
future energy portfolio [21].
Solar derived energy follows two
paths from the source to the end-use:
direct (radiant energy), or indirect
(including wind, hydro, wave, tidal,
thermal the biomass cycle and
photovoltaic (P.V).
From the direct
usage and availability of natural
resources, the use of solar energy
appears very attractive. This is the
direct utilization of concentrated solar
radiation as the source of hightemperature process heat. The amount
of solar energy that can be collected is
only restricted by the size of the
concentrator system can achieve
radiation flux density greater than
2MW/m2, with process heat above
1500K [22, 23].
Solar reactors are classified into:
direct absorption which absorbs sunlight
directly on the reactor feed and indirect
uses an intermediate heat transfer fluid,
such as molten salts, or solid separator
wall between the receiver and the
reactor. The fluid or wall is directly
heated by solar energy and then
transfers the energy into the receiver.
Carbon dioxide can be utilized in
three major pathways: as a storage
medium for renewable energy, as a
feedstock for various chemicals and as a
solvent or working fluid the use of CO2
to convert solar energy into biomass
and to various renewable fuels. Instead
of releasing carbon dioxide to the
atmosphere it is trapped and utilized for
the preparation of other useful organic
compounds such as methanol and
dimethlyl ether by hydrogenation of CO2
to methanol with hydrogen produced
from thermochemical water splitting
with cupper-chlorine (Cu-Cl) cycle [24,
25].
The methanol produced at the clean
energy
producing
site
is
then
transported
to
a
mass
energy
consuming site where methanol is used
as a fuel and/or a chemical raw
material.
Thermodynamic Analysis
The thermodynamic analysis of solar
thermochemical cycles for the release of
CO2 from different sorbents NaHCO3,
KHCO3, MgCO3, Na2CO3 and CaCO3
have been studied. The equilibrium
composition of the pertinent reactions,
temperature requirements, and energy
balances are computed for various
operating conditions. The decomposition
reactions are endothermic reactions.
-For Sodium bicarbonate:
2NaHCO3s+Heat→Na2CO3s+CO2g+H2Og
∆Ho298.15K = 135.07 kJ/mol
The total theoretical heat required for
complete decomposition at 473K is
133,716J/mole; using the average heat
capacity of NaHCO3 the total heat
required to heat NaHCO3 is 19999
J/mol. Therefore, the total heat required
for heating and decomposition is
153,715
J/mol
(1874.575J/gram
NaHCO3).
-For Potassium bicarbonate:
2KHCO3(s) +Heat →K2CO3(s)+CO2(g) +H20(g)
∆Ho298.15K =138.748 kJ/mol
The total theoretical heat required for
complete decomposition at 423K is
8198.288J/mole; using the average heat
3
capacity of KHCO3 the total heat
required to heat KHCO3 is 10667.184
J/mol. Therefore the total heat required
for heating and decomposition is
18865.47 J/mol (188.6547 J/gram
KHCO3).
for heating and decomposition is
441,072 J/mol (4161J/gram Na2CO3).
Figures 1, 2, 3, 4 and 5 shows the effect
of changing the temperature on the
total heat required for heating and
decomposition of NaHCO3, KHCO3,
MgCO3 and CaCO3 and Na2CO3.
The mechanism of decomposition of
particles is gradually proceeds from the
outer surface of the particles is
gradually by
• Heat is transferred from the sun
by direct heating to the surface
of the tube then to the surface
of the decomposing particles.
• Heat is then conducted from the
reaction interface to the newly
formed layer of solid particle
• If the temperature at the reaction
interface is high enough, the
heat causes the decomposition
of solid
• The CO2 produced migrates away
from the reaction interface,
during the diffusion of CO2
through the solid particle, the
CO2 is heated to the same
temperature at the surface
• The CO2 migrates away from the
surface to the environment
The rate of decomposition with
temperature can be expressed using
Arrhenices equation
-For Magnesium carbonate:
MgCO3 + Heat → MgO(s) + CO2(g)
∆Ho298.15K =116.926 kJ/mol
The total theoretical heat required for
complete decomposition at 673K is
110,594 J/mole, using the average heat
capacity of MgCO3 the total heat
required to heat MgCO3 is 42,895 J/mol.
Therefore the total heat required for
heating and decomposition is 153,444
J/mol (1820J/gram MgCO3).
-For calcium carbonate:
CaCO3+Heat → CaO(s) + CO2(g) + H2O(g)
∆Ho298.15K = 178.301 kJ/mol
The total theoretical heat required for
complete decomposition at 1173K is
162,902 J/mole, using the average heat
capacity of CaCO3 the total heat
required to heat CaCO3 is 112,339
J/mol. Therefore the total heat required
for heating and decomposition is
275,241
J/mol
(2750.205J/gram
CaCO3).
-For sodium carbonate:
dX
-Ea
------ = A Exp (-------)
(1)
dt
RT
dX/dtis rate of reaction(decomposition)
Na2CO3 + Heat → Na2O(s) + CO2(g)
∆Ho298.15K = 319.382 kJ/mol
The total theoretical heat required for
complete decomposition at 1100K is
287,080 J/mole, using the average heat
capacity of CaCO3 the total heat
required to heat CaCO3 is 153992
J/mol. Therefore the total heat required
-Ea
k=AExp(------)
RT
4
(2)
Lnk=lnA – Ea/RT
(3)
Subs. 11 into 9
k1
Ea
1
1
Ln ------ = - ------- ( ----- - ------)
k2
R
T2
T1
Where k is the specific rate constant
dX
---- = k f(X)
dt
(dX/dt)
k= ---------f(X)
Substitute (5) into (3)
(dX/dt)
Ea
ln --------= lnA - ------f(X)
RT
(4)
Experimental Work
(5)
Experimentation was carried out by a
solar experimental loop consists of a
solar solarium system that provides
direct concentrated solar thermal energy
to heat the endothermic reactions in the
present work. The solar solarium system
consists of standard Glass-Double
Glazing clear/clear of dimensions
(118.745cmx90.805cm)
with
a
o
maximum working temperature 1000 C
used to investigate the effect of
radiation on the decomposition of
carbonates to release pure CO2.
The intensity of radiation was
measured
using
pyranometer
(LABQUEST
MINI
vernier),
the
pyranometer is type of dinometer used
to measure broad band solar irradiance
on a planar surface and is a sensor that
is designed to measure the solar
radiation flux density (W/m2) with time
from a field of view 180o.
K- Type Omega thermocouples have
been used to measure the temperature
of the sample in the tube and the
outside temperature at the surface of
the tube during heating with time. Also,
a thermal Imaging Camera (PI connect)
was utilized to measure the surface
temperature of the tube with time.
Figure (6) shows the direct solar
solarium system used in the present
work.
(6)
X at any particular time was calculate
from mass at time or temperature
Wi –Wt
X=---------Wi
(7)
Differentiate
dX
dWt/dt
------ = --------dt
Wi
(8)
Wi is mass of sample initially and Wt is
mass of sample at any time
From equation 2
Ea
Ln k1 = - --------- +lnA
RT1
Ea
Ln k2 = - --------- +lnA
RT2
Ea
lnA= lnk2 + ------RT2
(12)
(9)
(10)
(11)
5
MgCO3, NaHCO3, and KHCO3 have
been studied experimentally using the
direct solar solarium system to release
pure CO2, analytical balance model
Mettler Toledo PB3002-S DeltaRange
was utilized to measure the mass of the
samples and tubes before, during and
after the experiments at different time
interval.
Calibration of the balance was
conducted each time the balance was
operated using the internal calibration
mass and automatic self-calibration.
range of 423-493K and the % yield of
KHCO3 is 72.75% and 78.47%
respectively. Figures (14, 16) show that
the amounts of pure CO2 released
increases as the time of decomposition
increases and the total heat required to
release CO2 at the temperature of
KHCO3
decomposition
423K
is
50kJ/mole CO2.
Figures (17, 19) reveal the fraction
decomposition of MgCO3 increases with
time for 0.45gram and 0.49gram
MgCO3. The time required for complete
decomposition is 125min for 0.45g
MgCO3 and 133min for o.49g MgCO3
for decomposition temperature range of
673-750K. The pure CO2 released from
the decomposition of MgCO3 is
increased with time of decomposition
Figures 18 and 20. The total heat
required to release CO2 at the
temperature of MgCO3 decomposition
673K is 171.5kJ/mole CO2.
The radiant heat flux for the
decomposition of NaHCO3, KHCO3 and
MgCO3 is 380±10W/m2 measured in a
solarium room by a pyranometer, the
value is low compared with the intensity
of sunlight at the earth’s surface of
985.7W/m2 this is due to losses of the
radiant heat flux in the solarium room.
The thermal behaviour and the
kinetics of decomposition of carbonate
sorbents NaHCO3, KHCO3 and MgCO3
have been investigated from the
experimental results using Arrhenius
equation applied to solid – state
reactions. For the decomposition of
NaHCO3 at temperature above 500K the
activation energy is 30.43kJ/mole and
for KHCO3 at temperature interval 423495K is 44kJ/mole. For the temperature
interval 730-750K the activation energy
for MgCO3 is 117kJ/mole.
Results and Discussion
Figures 7, 9 and 11 show the
fractional decomposition profile of
NaHCO3 increases with increasing the
time of decomposition of NaHCO3. The
total time required for complete
decomposition decreases with amounts
of NaHCO3. Therefore, for decomposing
1.22gram NaHCO3 the time required for
complete decomposition is 67min
decreasing the amounts of NaHCO3 to
1.18gram and 1.15gram NaHCO3 the
total time required is 62min and 38min
respectively and the % yield of NaHCO3
is 90-99%. Figures 8, 10 and 12 show
that the amounts of pure CO2 released
increases with time at the temperature
range of decomposition 473-523K, the
total heat required to release CO2 at the
temperature of decomposition of
NaHCO3 473K is 349kJ/mole CO2.
The fractional decomposition profile of
KHCO3 with time is shown in Figures
(13, 15) as the time of decomposition
increases the fraction decomposition
increases. The total time required for
complete decomposition of 1.02gram
KHCO3 is 58min and for 1.11gram is
62min for decomposition temperature
6
Conclusion
6- Intergovernmental
Panel
on
Climate Change (IPCC) Fourth
Assessment
Report:
Climate
Change (2007).
7- Spector N., Dodge B.. Removal of
carbon dioxide from atmospheric
air. Trans.Am. Inst. Chem. Engrs.
42 (1946) 827-848.
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balance of CO2 capture from
ambient
air.
Environ.
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Capturing carbon dioxide from air.
In Proceedings of the First
National Conference on Carbon
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(2001).
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Stolaroff. Climate strategy with
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Change 74(1-3) (2006) 17–45.
11- Stolaroff J., Keith D, Lowry G..
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A direct solar energy has been used
to release high purity CO2 from different
carbonate sorbents after capturing the
CO2 emissions from industrial plants.
In the present work different
sorbents have been used the fractional
decomposition and the amounts of pure
CO2 released from each sorbent is
increased with time of decomposition at
different ranges of temperature of
decomposition. The released of the pure
CO2 can be recycled as a renewable
source of energy.
The
percentage
errors
between
theoretical and experimental results of
the amounts of pure CO2 released from
the different sorbents used are 5% for
NaHCO3, 20% for KHCO3 and 10% for
MgCO3.
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Symbols
A
Ea
k
R
t
T1
Wi
Wt
X
8
Notations
Pre-exponential factor (sec -1)
Activation energy (kJ/mol)
Specific rate constant (sec -1)
Gas constant (J/mole.K)
Time (min)
Temperature (K)
Initial mass of sample (gram)
Mass of sample at time t(gram)
Fraction decomposition
Figure 1: Total heat required for heating and decomposition of NaHCO3
Figure 2: Total heat required for heating and decomposition of KHCO3
9
Figure 3: Total heat required for heating and decomposition of MgCO3
Figure 4: Total heat required for heating and decomposition of CaCO3
10
Figure 5: Total heat required for heating and decomposition of Na2CO3
Figure 6: Solar solarium system
11
Fractional decomposition profileof
NaHCO3
Fractional decomposition profile of
NaHCO3
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
13
0.05
23
32
44
56
62
76
Time (min.)
0
16
35
52
67
70
90
Figure 9. Fractional decomposition of NaHCO3
with time of 1.18gram NaHCO3 input
exposed to a radiant heat flux of
380±10W/m2 in a solarium room
Time (min.)
gram CO2 released from
NaHCO3
gram CO2 released from NaHCO3
Figure 7. Fractional decomposition of NaHCO3
with time of 1.22gram NaHCO3 input
exposed to a radiant heat flux of
380±10W/m2 in a solarium room
0.35
0.3
0.25
0.2
0.15
0.3
0.25
0.2
0.15
0.1
0.05
0
13 23 32 44 56 62 76
Time (min.)
0.1
0.05
Figure 10. CO2 released from NaHCO3 with
time of 1.18gram NaHCO3 input
exposed to a radiant heat flux of
380±10W/m2 in a solarium room
0
16
35
52
67
70
90
Time (min.)
Figure 8. CO2 released from NaHCO3 with time
of 1.22gram NaHCO3 input exposed
to a radiant heat flux of 380±10W/m2
in a solarium room
12
Fractional decomposition of KHCO3
Fractional decomposition profile
NaHCO3
0.4
0.3
0.2
0.1
0
5
10
16
24
31
38
Time (min.)
0.25
0.2
0.15
0.1
0.05
0
11 21 29 36 47 50 58 67
Time (min.)
Figure 13. Fractional decomposition of KHCO3
with time of 1.02gram KHCO3 input
exposed to a radiant heat flux of
380±10W/m2 in a solarium room
0.35
0.3
gram CO2 released from KHCO3
gram CO2 released from NaHCO3
Figure 11.Fractional decomposition of NaHCO3
with time of 1.15gram NaHCO3
input exposed to a radiant heat flux
of 380±10W/m2 in a solarium room
0.25
0.2
0.15
0.1
0.05
0
5
10
16
24
31
38
Time (min.)
0.2
0.15
0.1
0.05
0
11
21
29
36
47
50
58
Time (min.)
Figure 12. CO2 released from NaHCO3 with
time of 1.15gram NaHCO3 input
exposed to a radiant heat flux of
380±10W/m2 in a solarium room
Figure 14. CO2 released from KHCO3 with
time of 1.02gram KHCO3 input
exposed to a radiant heat flux of
380±10W/m2 in a solarium room
13
67
Fractional decomposition profile of
MgCO3
Fractional decomposition profile of
KHCO3
0.3
0.25
0.2
0.15
0.1
0.05
0
5 10 18 31 37 49 57 62 74
Time (min.)
22 33 52 69 75 85 102120123128
Figure 15. Fractional decomposition of KHCO3
with time of 1.11gram KHCO3 input
exposed to a radiant heat flux of
380±10W/m2 in a solarium room
Time (min.)
Figure 17. Fractional decomposition of MgCO3
with time of 0.45gram MgCO3 input
exposed to a radiant heat flux of
380±10W/m2 in a solarium room
0.25
0.2
gram CO2 released from MgCO3
gram CO2 release from KHCO3
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0.15
0.1
0.05
0
5 10 18 31 37 49 57 62 74
Time (min.)
Figure 16. CO2 released from KHCO3 with
time of 1.11gram KHCO3 input
exposed to a radiant heat flux of
380±10W/m2 in a solarium room
0.25
0.2
0.15
0.1
0.05
0
22 33 52 69 75 85 102120123128
Time (min.)
Figure 18. CO2 released from MgCO3 with
time of 0.45gram MgCO3 input
exposed to a radiant heat flux of
380±10W/m2 in a solarium room
14
Fractional decomposition profile
MgCO3
0.5
0.4
0.3
0.2
0.1
0
26 45 48 55 62 79 91 130133139
Time (min)
Figure 19. Fractional decomposition of MgCO3
with time of 0.49gram MgCO3 input
exposed to a radiant heat flux of
380±10W/m2 in a solarium room
gram CO2 released from MgCO3
0.25
0.2
0.15
0.1
0.05
0
26 45 48 55 62 79 91 130133139
Time (min)
Figure 20. CO2 released from MgCO3 with
time of 0.49gram MgCO3 input
exposed to a radiant heat flux of
380±10W/m2 in a solarium room
15