Advances in Ma terials Physics and Che mist ry, 2012, 2, 240-243
doi:10.4236/ampc.2012.24B061 Published Online December 2012 (htt p://www.SciRP.org/journal/ampc)
Experimental Studies on the Influence of HCO3- on Absorption
and Desorption of CO2 from Ammonia Solution
Shaojian Jiang, Wei Zhong, Rui Peng, Yong Jiang, Jun Zha ng
School of Energy Science and Engineering, Central South University, Changsha, China
Received 2012
ABSTRACT
With aqueous ammonia in the process of CO2 absorption and desorption to join sodium bicarbonate, the influence of HCO3- on CO 2
absorption and desorption from ammonia solution was investigated through the experimental analysis of the desorption quantity of
CO2, desorption rate, CO2 loading and the absorption rate. The experimental results showed that, in experimental conditions, The
desorption rate decreased gr adually with increasing ammonia concentrations. The desorption rate increased 12%, 17%, 19% and
28.8% when 1 mol/L of ammonia solution is added in 0.1 mol/L, 0.3 mol/L, 0.5 mol/L and 1 mol/L of sodium bicarbonate. The
higher concentration of ammonium bicarbonate solution which was added sodium bicarbonate，the more observably the effect of
CO2 desorption was promoted. The absorption rate had dropped when absorption process added 0.3 mol/L sodium bicarbonate, the
CO2 loadin g was a little change.
Keywords: Ammonia Desorption; the Desorption Rate; CO2 Absorption;CO2 Loading
1. Introduction
As the rapid development of modern industry, a large number
of the use of fossil fuels leads to increased CO2 emissions, and
CO2 is climate change and the main cause of global warming.
Therefore, carbon capture and storage (CCS) projects have
been reported[1]. The chemical absorption capture of CO2 has
been studied and widely used as a reliable and cost-efficient
method for CO2 because of its characteristics such as higher
absorption rate, higher CO2 recovery rate, no absorbent degra-
tion and lower desorption energy requirement, etc[2]. The tra-
ditional chemical absorption methods include alcohol amine
solution, alkali solution, aqueous alkanolamine solution, etc.
Among the m, MEA, as a r epresen tative of the alco hol amine i s
the most traditional absorbent[3], it is used in industry early in
the 19 th century. However, because its higher desorption en-
gy, amine degradation by O2, SO2 in flue gas which induces a
high absorbent makeup rate and high equipment corrosion
rate[ 4], o n the actual plant there is still a limit used in decarbu-
rization. Compared with MEA, aqueous ammonia which has
higher CO2 load ing capacity (g C O2 absorbed per g absorbent),
no corrosion problem, no absorbent degradation problem, lower
desorption energy[5,6], and the ability to capture all three major
acid gases(S O 2, NOX, CO2), is becoming a hot research 7].
It has been concluded that the maximum CO2 removal effi-
ciency by NH3 absorbent can achieve 95% and the major pro-
duced from the Aqua Ammonia Process including ammonium
bicarbonate and ammonium carbonate etc[8]. Due to the
process is reversible, therefore, a way to heat its bicarbonate
salts to desorb the solution is used to make sorbent recycling.
The process to CO2 desorption which is not desorbed com-
pletely has resulted in absorption capacity is reduced. Liu
Fang[9] researched the p rocess of CO2 desorption from ammo-
nium bicarbonate, Zeng Qing[10] studied the characteristics of
CO2 desorption from Carbonated ammonia solution, which
showed that desorption rate was influenced by temperature,
CO2 loading. Houping Huang[11] investigated a method to
regenerate ammonia so as to allow for the ammonia scrubbing
technique to be practical in the capture of CO2 that a weakly
basic io n-exchange resin co ntaining amine functional groups is
used. How to improve the desorption rate, and in the process of
absorption recycling, keep the CO2 loading capacity the same
are a key research d irection.
Research h as shown that[12], with the increasing of the con-
ntration of bicarbonate ions, CO2 is easier to release from the
solution. This paper studied the influence of HCO3- (put NaH-
CO3 into solution as a additives) on CO2 absorption and de-
sorption from ammonia solution which keep the concentration
of NH4+ the same and change the solution of HCO3- concentra-
on.
2. Experiment
2.1. Theory
The desorption reaction of CO2 into ammonia solution can be
described as the following equations (1), (2), (3). it is shown
the lowest enthalpy of dissociation for CO2 release from (1).
Ammonium carbonate can be further dissociated to release
more CO2, but at higher cost per mole CO2 desorbed. Therefore,
in the process of the most favorable desorption is to transfer
ammonium carbonate solution from the absorber and use it as
CO2 absorbent, as shown in (7). Moreover, it can reduce the
NH3 escape.
2NH4HCO3(aq)
⇔
(NH4)2CO3(aq)+CO2(g)+H2O(l) (1)
NH4HCO3(aq)
⇔
NH3(aq)+CO2(g)+H2O(l) (2)
(NH4)2CO3(aq)
⇔
2NH3(aq)+CO2(g)+H2O(l) (3)
For abso rpti on react ion ,it is typical ch emical reacti on p rocess
as following equations (4), (5) ,(6), (7).

S. J. JIAN G ET AL.
241
CO2+2NH3
→
NH2COONH4 (4)
NH2COONH4+H2O
⇔
NH3+NH4HCO3 (5)
NH3+NH4HCO3
⇔
(NH4)2CO3 (6)
(NH4)2CO3+CO2+H2O
⇔
2NH4HCO3 (7)
2.2. The Experiment Sy stem
The experiments were divided into desorption and absorption
process. The schematic diagrams for desorption process were
represented in Figure 1. It was experimented with ammonium
bicarbonate solution preparation simulation of the practical
absorbent, through the adjustment of ammonium bicarbonate
solution concentration and adding additives way to control
simulation absorbent. The desorption solution was controlled
the temperature by water-bath pot. CO2 gas was purged the
entire system before the start of the experiment.Then the solu-
tion was stirred by the magnetic s tirrer. Th e gas was analysed by
CO2 Analyzer through a mixture of gas es from desorp tion after
pickling bottle and desiccating agent. In the process of desorp-
tion, the temperature controlled in 60℃~99℃. The desorption
rate is tested at 99℃.
The experimental system for studying CO2 absorption is
showed in the schematic diagram of Figure 2. The simulated
flue gas consisted of 14 vol.% CO2 and 86 vol.% Air. The
temperatu re of the gases was 20℃，and the flow controlled by
mess flow controlled which was 80 m3/h. The temperature of
the absorber was controlled in 40 ~ 50℃, and the flow was
1450 L/h(liquid/gas is about 18 L/m3). The pressure of the
whole experiment process was close to 1 atmosphere. In the
experimental process, flue gas was flowing through absorption
tower continuously and absorber was recycling. After the ab-
sorption th e gas was analysed by CO2 anal yzer.
3. Result and Discussion
3.1. CO2 Desorptio n C haracteri st i c s in Ammonium
Bicarbo nate Solution
Experiments of 100 mL ammonium bicarbonate solution was
heated which th e concentr ations were 1 mol/L, 1.5 mol/L and 2
mol / L. F ro m 55 ℃ solution had been heated to a constant tem-
perature when water-bath water was boiling. The desorption
process was end when CO2 analyzer show flow velocity was
zero. Desorption started quickly when the solution was decom-
posed and a large number of small bubb les were emerged . With
the rise of temperature, the bubbles on the surface of liquid
level were becoming bigger, and bubbles was rising quickly as
well as they burst. Finally, the bubbles become less and less. It
was shown that CO2 desorption from the method of ammonia
absorber was obvious effective and with good reproducibility.
Typical CO2 desorption curve of Ammonium bicarbonate
solution changing with temperature rules was shown in Figure
3. With the r ise o f temperat ur e, CO2 desorption speeded rapidly,
when th e temperature r eached 8 5℃, CO2 desorption speed was
about to the biggest, and the amount of CO2 desorption in-
creased quickly. It was closed to the best desorption tempera-
ture of 87.5℃ which Liu Fang [13] confirmed in the desorp-
tion of the ammonia method of absorbent. With the temperature
rise further, the concentration of HCO3- reduced gradually so
that little CO2 desorbed out, desorption speed was reduced. As
the in creasing con centrat ion of HCO3-, the higher concentration
of desorption solution could desorb more over CO2. The final
desorption rates of 1 mol/L, 1.5 mol/L, 2 mol/L of ammonium
bicarbonate solution were 57%, 54% and 48%, it was shown
that the higher the concentration of solution was, CO2 desorp-
tion rate gradually reduced. Because the concentration of
HCO3- reduced and CO32- increased, leading to inhibit the reac-
tion (1).
Figure 1. Diagram of the apparatus to measure CO2 desorption
from ammonium bicarbonate solution:(1) CO2 Gas,(2) Mass flow
controller,(3) Magnetic Stirrer(4) Pickling,(5) De sicca ting Agent, (6 )
CO2 Analyzer.
Figure 2. Schematic diagram of experimental setup of CO2 and
aqueous ammonia absorption: (1) CO2 Cylinder,(2) Mass Flow
Controller, (3) Air compressor, (4)Gas Compound,(5) CO2 Absor-
ber, (6)Reservoir,(7) Pump,(8) CO 2 Analyzer.
6080 100
0
100
200
1mol
1.5m ol
2m ol
6080 100
0
1000
2000
1m ol
1.5m ol
2m ol
CO
2 desorption speed(m3.h-1)
CO
2 desorption amount
(mL)
T (℃ )
Figure 3. Typica l CO2 desorption curve of ammonium bicarbonat.

S. J. JIAN G ET AL.
242
3.2. The Influence on the Desorpt ion of Ammonium
Bicar bonate Solution w ithin Sodiu m Bic arbonate
The Figure 3 showed the higher the concentration of ammo-
um bicarbonate solution was, CO2 desorption rate gradually
reduced. The following experiments were conducted. Sodium
bicarbonate was added into the ammonium bicarbonate solution
to ch ange the co ncentrat ion of HCO3- and ensure NH4+ concen-
tration under the condition of invariable, to investigate HCO3-
to the effect o f CO2 desorption. 100 mL, 1mol/L of ammonium
bicarbonate was added 0.1 mol/L, 0.3 mol/L, 0.5 mol/L and
1mol/L of sodium bicarbonate to study its CO2 desorption cha-
racteristics. The desorption of 1mol/L ammonium bicarbonate
solution as a function of sodium bicarbonate concentrati on was
shown in Figure 4.
The CO2 desorption quantity and rate were increased by
adding sodium bicarbonate and intensified with higher concen-
tration of sodium bicarbonate.The desorption rate was 58% for
the solution of 1 mol/L ammonium bicarbonate solution.The
CO2 desorption rate with ammonium bicarbonate solution add-
ing 0, 0.1 mol/L, 0.3 mol/L, 0.5 mol/L and 1 mol/L of sodium
bicarbonate solutions were 58%, 65%, 68%, 69%, 74%, respec-
tively,the efficiencies were increased 12%, 17%, 19% and
28.8%. The sodium bicarbonate solutions of 0.1~0.3 mol/L into
1mol/L ammonium bicarbonate solution afforded the greatest
rate of increased desorption.Over 0.3 mol/L the rate was slow.
According to the chemical reaction kinetics,it was supposed to
make positive reaction for desorption to make the amount of
CO2 desorption increased when the concentration of HCO3-
continued to increase. The higher concentration of sodium bi-
carbonate which was weakly alkaline salt was,the degree of
hydrolysis was more and more small. Meanwhile, it's inhibit
effect to the NH4HCO3 ionization and makes the growth of
desorption amount.
3.3. The Influence of the Desorption of Different
Concentration of Ammonium Bicarbonate
Solution within So di um Bicarbona te
CO2 desorption characteristics for 1 mol/L, 1.5 mol/L, 2 mol/L,
2.5 mol/L of ammonium bicarbonate solution were investigated
which was joined 0.3 mol/L of sodium bicarbonate. The de-
sorption of different concentration of ammonium bicarbonate
solution as a function of sodium bicarbonate concentration was
shown in Figure 5. The increasing desorption amount with
increasing concentration expressed on approximate linear rela-
tionship. Nevertheless, the result that the higher the concentra-
tion of solution was, CO2 desorption rate gradually reduced had
been con firmed i n Figure 3. the quantity of CO2 desorption and
the concentration had an inverse proportion relation.When
adding sodium bicarbonate, CO2 desorption rate increased and
the higher concentration of ammonium bicarbonate solution the
better effect of the CO2 desorption rate bringing about by in-
troducing HCO3-, and the speed reduction of desorption rate
slowed down. Compared with 1.5 mol/L,plus 0.3 mol/L sodium
bicarbonate into 2 mol/L of ammonium bicarbonate solution
had only declined 3.2%. Add 2 mol/L of sodium bicarbonate
ammonium bicarbonate solution of the CO2 desorption rate than
only 1.5 mol/L declined 3.2%. This shown that the higher con-
centration of absorbent plus sodium bicarbonate, the more ob-
servably the effect o f CO2 desorption was promoted.
3.4. Sodium Bicarbonate of CO2 Absorption Effect
Using ammonia method to absorb CO2, the absorbent circulated
after desorption. When plus sodium bicarbonate,it had an in-
uence on the absorption process.Carbon dioxide absorption
rates for 5% ammonia solution and plus 0.3 mol/L sodium bi-
carbonate were measured in the experiment equipment(Figure
2). For each amine concentration about CO2 loadings were
tested. The experimental results were represented in Figure 6.
Ammonia solution had an great effect on absorbing CO2, the
CO2 absorption capacity reduced with increasing CO2 loading.
When added sodium bicarbonate, the absorption rate decreased.
0.00.5 1.0
1200
1300
1400
1500
1600
1700
CO
2
desorption amount(m L )
CO
2
desorption rate(% )
the concentration of sodium bicarbonate(m ol/L )
CO
2
desorption amount(m L )
0.50
0.55
0.60
0.65
0.70
0.75
0.80
CO
2
desorption rate(% )
Figure 4. The desorption of ammonium bicarbonate solution as a
function of sodium bicarbonate concentration.
1.0 1.5 2.0 2.5
1000
1500
2000
2500
3000
3500
4000
the concentration of NH
4HCO3
( mol.L-1 )
CO2 desorption amount(m L)
1.0 1.5 2.0 2.5
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
NH
4
HCO
3
NH
4
HCO
3
+0.3mol/L NaHCO
3
CO2 desorption amount(% )
Figure 5. The desorption of different concentration of ammonium
bicarbo nate solution as a function of sodium bicarbonate
concentration.

S. J. JIAN G ET AL.
243
0.0 0.1 0.2 0.3 0.40.5 0.6
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
CO2 absoption rate(% )
CO2 loading ( mol.mol-1 )
NH3(Aq)5%
NH3(Aq)5%+0.3mol/LNaHCO3
Figure 6. CO2 removal efficiency lines in aqueous ammonia and
aqueous am mon ia within sodium bicarbonate.
There was so much free ammonia in low CO2 loading in the
early stage th at carbamate( NH2COO-) was th e main species[1 4].
Meanwhile, the concentration of carbamate increased with in-
creasing CO2 loadi ng. Moreo ver, Carb amate an d carbonate ions
would be gradually converted to bicarbonate io ns as increasin g
absorbed amount of CO2 in ammonia solution(Eq. 5) after a
certain time. The process was inhibited by adding sodium bi-
carbonate and leading to the drop of the CO2 absorption rate.
While by changing the operation conditions, as well as the ab-
sorption tower structure could be improved the absorption rate.
Along with the absorption process, the absorption rate re-
duced gradually with increasing CO2 loading, and the CO2
loading capacity reduced when added sodium bicarbonate, but
the speed reduction of CO2 loading slowed down.Respectively,
the concentration of free ammonia decreased rapidly,while the
speed reduction of that slowed down. The concentration of
NH4+ remained the same in whole solution, for the same ab-
sorption effect, CO2 loading changed a little.
4. Conclusion
1) Using ammonia method had an good effect on CO2 ab-
sorption and desorption. High concentration of absorbent could
also have lower rates of desorption.
2) Sodium bicarbonate as additives, could greatly improve
the CO2 desorption rate, with the increasing of the concentra-
tion of HCO3-, the speed reduction of CO2 desorption rate
slowed down.
3) For different concentration of absorbent, the higher
concentration of absorbent plus sodium bicarbonate,the more
obser vably the effect of CO2 desorption was promoted.
The absorption process joined sodium bicarbonate, the ab-
sorptio n rate had reduced, C O 2 load ing changed a little.
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