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A new nano CaO-based CO2 adsorbent preparedusing an adsorption phase technique

 ARTICLE  in  CHEMICAL ENGINEERING JOURNAL · FEBRUARY 2013

Impact Factor: 4.32 · DOI: 10.1016/j.cej.2012.11.095

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A new nano CaO-based CO2  adsorbent prepared using an adsorption

phase technique

Yan Wang a, Yanqing Zhu a,b, Sufang Wu a,c,⇑

a Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, PR Chinab Institute of Environmental and Municipal Engineering, North China University of Water Resources and Electric Power, Zhengzhou, Henan 450011, PR Chinac Zhejiang Provincial Engineering Research Center of Industrial Boiler and Furnace Flue Gas Pollution Control, Hangzhou 311202, PR China

h i g h l i g h t s

" Using ‘‘adsorption phase technique’’,

a coating layer of 4.5 nm–11.6 nm

was formed with the TiO2 content

increasing.

" TiO2 content played an important

role of CO2  adsorption durability.

" Compact factor between 0.8 and 1.3

was tested to relate the adsorption

stability.

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o

 Article history:Received 13 August 2012

Received in revised form19 November 2012

Accepted 21 November 2012

Available online 29 November 2012

Keywords:

CO2  adsorbent

Nano CaO

Adsorption phase technique

a b s t r a c t

This study describes for the first time micro-scale hydrolysis has been used in the adsorption phase toprepare a nano CaO-based CO2  adsorbent with a highly durable sorption capacity. The hydrolysis of 

Ti(OC4H9)4 to form TiO2 was used to prepare TiO2-coated nano CaCO3, which was then calcinated to pre-

pare a nano CaO-based CO2  adsorbent with a controlled coating layer. The coating compactness was

defined for the first time in this study to describe the mole ratio of Ti to Ca on the surface of the nano

CaCO3. The coating compactness and the durability of the sorption capacity of samples with varying

TiO2   content, hydrolysis temperature, and ester concentration were studied in detail. The properties of 

the reactive adsorption of the prepared nano CaO-based CO 2   adsorbents were tested using a thermo-

gravimetric analyzer. The results showed that, of the conditions tested, the TiO 2 content exerts the most

influence on the durability of the sorption capacity. The nano CaCO 3 that was coated with 10 wt.% TiO2

and prepared under 20 C, which has a corresponding coating compactness of 1.0, exhibited a much more

durable CO2 sorption capacity than the other prepared samples.

Crown Copyright    2012 Published by Elsevier B.V. All rights reserved.

1. Introduction

The capture of CO2  through the use of a CaO-based adsorbent

plays an important role in the efficient separation of CO2   from

combustion/gasification gases [1–3] and sorption-enhanced hydro-

gen production processes   [4–6]. This capture is based on the

reversible carbonation reaction of CaO [7]. CaO is a potential adsor-

bent because of its high reactive sorption capacity and the

abundance of its natural precursors, such as limestone (CaCO3)

[8] and dolomites (Ca, Mg(CO3)2)  [9,10]. However, the CaO-based

adsorbents exhibit a rapid decay in their absorption capacity dur-

ing multiple carbonation–calcination reaction cycles   [11]. It is

widely believed that the capacity decay is mainly due to the sinter-

ing of CaO and CaCO3 in the regeneration process [12], the physical

aggregation of the crystals, which leads to an increased particle

size, or the loss of porosity that is caused by the volume reduction

of the small pores [13].

Compared with natural adsorbents, nano CaCO3   has drawn

increasing attention [14–17] because of its higher reactive sorption

capacity, fast reaction rate and its significant improvement in the

durability of the adsorbent. However, because nano CaCO3  has a

high ratio surface area and a high surface energy, it aggregates

1385-8947/$ - see front matter Crown Copyright    2012 Published by Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.cej.2012.11.095

⇑ Corresponding author at: Department of Chemical and Biological Engineering,

Zhejiang University, Hangzhou 310027, PR China. Tel.: +86 571 87953138.

E-mail address: wsf@zju.edu.cn (S. Wu).

Chemical Engineering Journal 218 (2013) 39–45

Contents lists available at SciVerse ScienceDirect

Chemical Engineering Journal

j o u r n a l h o m e p a g e :   w w w . e l s e v i e r . c o m / l o c a t e / c e j

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more easily, which makes sintering a serious problem. Several

methods with varying degrees of success have been proposed to in-

crease the life cycle performance of CaO-based sorbents by pre-

venting the sintering of CaO. These methods include the

incorporation of inert materials, such as Al2O3   [18], SiO2  [19,20],

MgO [21,22], and CaTiO3   [14] through several chemical synthesis

and physical methods, the utilization of potentially sintering-resis-

tant calcium precursors [23,24], the hydration treatment of CaO to

regain its reactivity [25,26], and the development of high surface

area CaCO3  [27].

The addition of an inert material is a general way to modify the

nano adsorbent to obtain better durability. In previous studies, the

combination of an inert material and the adsorbent was usually

achieved through immediate wet mixing   [28], precipitation

[29,30] or surface coating [20]. The coating of a CaO-based adsor-

bent is an effective way to prevent sintering. The surface coating

material behaves as a partition wall that prevents the agglomera-

tion of CaO particles. Therefore, controlling the coating layer is

important for improving durability. However, previous research

on coating-modified CaO-based adsorbents has not reported the

proper preparation of a controlled coating layer  [14,20].

The adsorption phase technique  [31,32]   uses the adsorption

phase as a microreactor to coat the surface of the adsorbent. It is

a remarkable technique because the particle size is efficiently

and easily controlled. In this paper, the adsorption phase technique

was first used to prepare TiO2-coated nano calcium carbonate. A

controlled coating layer was obtained through the micro-scale

hydrolysis of Ti(OC4H9)4   in the adsorption phase. The effects of 

the TiO2  content, hydrolysis temperature, and ester concentration

on the CO2  adsorption performance and the relationship between

the durability and the nano calcium carbonate coating compact-

ness were studied.

2. Experimental

 2.1. Reagents and instruments

Nano CaCO3   (>95% purity) with a particle size of 70 nm with

water (Huzhou Ling Hua Ltd., China) was used as the CaO-based

sorbent precursor. Tetrabutyl titanate (Ti(OC4H9)4; Shanpu Shang-

hai Chemical Co. Ltd.) was used as the source of TiO2, and ethanol

(Wuxi Jingke Chemical Co. Ltd.) was used as the solvent. An A-type

zeolite (Sinopharm Chemical Reagent Co. Ltd.) was used to remove

the water from the nano CaCO3.

A thermo-gravimetric analyzer (TGA, Pyris1, Perkin-Elmer, USA)

was used for the reactive sorption capacity measurements. X-ray

photoelectron spectroscopy (XPS, VG ESCALAB MK II, UK) was used

to detect the type and relative content of the surface elements. The

morphology of the sorbent was investigated using a transmission

electron microscope (TEM, JEM-1200EX, USA).

 2.2. Preparation of TiO 2-coated nano CaCO 3 using an adsorption phasetechnique

An 18-g mass of aqueous nano CaCO3   was dispersed in dehy-

drated ethanol using an ultrasonic dispersion method to form a

suspension and then placed into heat-treated zeolite to dehydrate.

A clear dehydrated ethanol solution with a specific concentration

of Ti(OC4H9)4 was added dropwise into the dehydrated suspension

while stirring. After all of the solution was added, the solution was

stirred for an additional 1–2 h. The solids were collected by vac-

uum filtration, dried and then heat-treated at 500 C for 2 h until

the solid sample was obtained.

TiO2-coated nano CaCO3   samples with different TiO2  contents

can be obtained by changing the amount of n-butyl titanate. In

addition to the TiO2

  content, the hydrolysis temperature and the

concentration of the n-butyl titanate ethanol solution were also

varied to prepare the different samples. All of the sample prepara-

tion conditions are listed in Table 1.

The preparation method is based on the adsorption phase tech-

nique. The mechanism by which TiO2  is formed on the nano cal-

cium carbonate is shown in   Fig. 1. The nano CaCO3   with water

was dehydrated using zeolite, and only a thin layer of water on

the round surface of the nano CaCO3   particle was maintained.

When an ethanol solution of tetrabutyl titanate was added drop-

wise into the dehydrated suspension, the Ti(OC4H9)4   spread to

the water layer and quickly hydrolyzed. Different operating condi-

tions resulted in different distributions of TiO2 on the surface of the

nano CaCO3  and different compact factors.

 2.3. Compactness definition and characterization test 

The compact factor C  is defined in Eq. (1) to quantify the coating

compactness. This factor is the relative molar content ratio of the

coating material (titanium) and the material to be coated (calcium)

on the surface of the nano CaCO3. It describes the coating status

and, in this paper, represents the dispersion of TiO2  on the surface

of the nano CaCO3.

 Table 1

Preparation conditions of samples.

Sample Nos. 1 2 3 4 5 6 7 8 9 10 11 12 13 14

TiO2

 content/wt.% 0 5 6.5 8 10 12 15 20 10 10 10 10 10 10

T /C 11.5 15 15 12.5 14.5 12 12.5 0 20 40 70 22 22

Ester concentration/wt.% 9.6 9.6 9.6 9.6 9.6 9.6 9.6 9.6 9.6 9.6 9.6 5 17.5

Fig. 1.   Mechanism image of ester hydrolysis of adsorption phase reaction.

40   Y. Wang et al. / Chemical Engineering Journal 218 (2013) 39–45

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C  ¼ nTi

nCa

;   ð1Þ

In Eq. (1),  n  refers to the molar number of elements.

Based on the locations of the characteristic lines that appear in

the XPS energy spectrum, the types of elements that are found on

the surface can be identified. The XPS energy spectrum of sample

No. 5 is shown in  Fig. 2. The elements Ti, Ca, C, and O were ob-

served on the surface. Once a specific energy region of Ti and Ca

are chosen for further scanning, a single element spectrum is ob-

tained, as shown in Fig. 3a and b. The photoelectron line intensity

(photoelectron peak area) reflects the number of atomic levels;

thus, we can obtain the relative molar content of the surface ele-

ments. The compact factor can be calculated from the following

equation based on the Atomic Sensitivity Factor (ASF) method:

C  ¼  nTi

nCa

¼   I Ti=S Ti

I Ca=S Ca

;   ð2Þ

where I  is the peak area of the XPS test data fitting and S  is the sen-

sitivity factor, which is related to the element and equipment used

(in this instrument,  S Ti = 1.1 and S Ca = 0.71).

 2.4. Sorption capacity test method

The cyclic CO2  sorption capacity was measured with a thermo-

gravimetric analyzer. The tests were conducted under carbonation,

with a CO2  partial pressure of 0.02 MPa in N2  at 600 C for 10 min,

and calcination in N2   at atmospheric pressure and 725 C for

10 min. The temperature was increased at a rate of 15 C/min

and decreased at a rate of 40 C/min. The cyclic CO2 sorption capac-

ity tests were also conducted in a fixed bed reactor. We used the

reactive sorption capacity to analyze the reaction of CaO with

CO2. The reactive sorption capacity and decay ratio were calculated

according to the following equations:

Reactive sorption capacity ¼  CO2   sorption amount

The mass of CaO in adsorbent

ð g CO2= g CaOÞ;   ð3Þ

Decay ratio ¼ðSC Þ1 ðSC Þn

ðSC Þ1

100%;   ð4Þ

where (SC )1   is the reactive sorption capacity of the first run and(SC )n  is the reactive sorption capacity of the  nth run.

3. Results and discussion

 3.1. Effects of TiO 2  content on the durability of the CO 2 adsorption

cycles

To investigate the effect of the TiO2 content on the cyclic perfor-

mance, seven samples (from No. 2 to No. 8) with different TiO2

mass fractions of 5%, 6.5%, 8%, 10%, 12%, 15%, and 20% were pre-pared. The TEM images of several typical samples are shown in

Fig. 4.

As shown in Fig. 4, the more dispersed nano calcium carbonate

particles were lighter in color.1 The formation of the TiO2   layer

darkened the colors of the edges. As the TiO2   content increases,

the thickness and distribution of the dark parts become more obvi-

ous. The samples with 5% and 10% TiO2  showed a thin layer and a

partial coating around the edges of the particles. The sample with

20% TiO2  showed a thick and almost complete coating around the

edges of the particles. The thickness of the coating layer ranged

from 4.5 nm to 11.6 nm as the TiO2  content increased from 5% to

20%.

The reactive sorption capacity test results are shown in  Fig. 5.

The sample marked 0% was not coated with TiO2. The initial reac-

tive sorption capacity of each sample was high, decayed rapidly in

the initial five to six cycles, and then decayed slowly. After 30 cy-

cles of carbonation–calcination, the reactive sorption capacity of 

most samples remained at a relatively stable value; this was true

for all samples except the samples with 5% and 6.5% TiO2, which

continued to decay. The non-TiO2  coated sample continued to de-

cay with a lower reactive sorption capacity than the other samples,

which indicates that the coating operation improved the durability

of the sorption capacity. A few samples, such as those with 10% and

12% TiO2, showed an increase in the CO2 reactive sorption capacity

after 20 cycles. We conjecture that this phenomenon is caused by

self-reactivation  [14,33]. An additional 30 cycles of carbonation–

calcination of the 10% TiO2 sample were run after the initial 30 cy-

cles. The sorption capacity was almost stable after the 40th run, as

shown in Fig. 6.The results of the BET surface area measurements on samples 1

and 5 before and after several runs are shown in Table 2. As shown

in the results, after 12 runs, the surface area and the average pore

size of sample No. 5, which was coated with TiO2, were maintained

at almost constant levels, whereas those of sample No. 1 decreased.

This finding indicates that the TiO2 coating may provide a partition

wall that prevents the agglomeration of the CaO particles and thus

improves the durability of the reaction sorption capacity of the

coated samples.

Fig. 7   shows the effect of the TiO2   content on the sorption

capacity in the 1st and the 30th runs. With increasing TiO2 content,

the sorption capacity of the initial sorbent decreased and that of 

the sample in the 30th run first increased and then decreased. In

the first run, the increasing content of the coating material led toa reduction in the relative content of CaO, which reduces the num-

ber of CO2  adsorption sites and decreases the CO2  sorption capac-

ity. As the cycles of adsorption and desorption progressed, the

activity of CaO decreased, and thus, the sorption capacity de-

creased. When the TiO2 content was greater than 8%, the decay ra-

tio was smaller, which meant that the durability was improved.

Taking into account the sorption capacity, a TiO2   content in the

range of 8–10% was considered to be optimal. Among those values,

after 30 cycles, the sample with 10% TiO2  had the highest sorption

capacity, with a value of 0.404 g of CO2/g of CaO, and the lowest

decay ratio at 28.3%, which results in the best adsorption

0 100 200 300 400 500 600 700 800 900 1000

   I  n   t  e  n  s

   i   t  y   (  a .  u .   )

Binding Energy (eV)

C1s

O1sO KVV

Ca2p3/2&1/2

Ca2s

Ti2p3/2&1/2

Ca LMM

Ti2s

Ti LMM

Fig. 2.  XPS full spectrum scan of TiO2  coated CaO-based adsorbent.

1 For interpretation of color in Fig. 4, the reader is referred to the web version of this article.

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performance. In S.F. Wu’s research, the reactive sorption capacityof TiO2/CaCO3 was 4.2 mol/kg after 40 runs, which was 14.3% lower

than that of sample No. 5.

 3.2. Effects of hydrolysis conditions on the durability of the CO 2

adsorption cycles

Because the n-butyl titanate hydrolysis reaction is a fast reac-

tion, the hydrolysis conditions have a great impact on the reaction

rate, which in turn affects the formation and growth of the coating

layer. Hydrolysis temperatures varying from 0 C to 70 C and ester

concentrations in the range of 5–17.5% were studied in this section.

Fig. 8 shows the CO2  reactive sorption capacities of the adsor-

bent samples No. 5 and 9–12, which were prepared under different

temperatures. As shown in the figure, the different hydrolysis tem-peratures had little influence on the reactive sorption capacity of 

the initial cycles. As the cycles progressed, the impact of the tem-perature became apparent. The sorption capacities of the samples

prepared under 40 C and70 C temperature conditions were grad-

ually reduced; these were not as stable as the other three samples,

which were prepared under temperatures in the range of 0–20 C.

In general, the sorption capacity of the sample prepared under

40 C was higher than that of the sample prepared under 70 C.

Thus, a lower temperature is relatively favorable, and a tempera-

ture range of 0–20 C is optimal.

The reactant concentration of butyl titanate dissolved in the

ethanol solution also had some impact on the adsorption perfor-

mance of the adsorbent.   Fig. 9   shows the CO2   reactive sorption

capacities of the adsorbent samples Nos. 10, 13, and 14, which

were prepared under the different ester concentrations of 5%,

9.6%, and 17.5%, respectively. As the cycles progressed, when theester concentration was 17.5%, the sorption capacity gradually

Fig. 4.  TEM images of samples with different TiO2 content. (a) Non-TiO2 coated nano CaCO3 (sample No. 1), (b) 5% TiO2 (sample No. 2), (c) 10% TiO2 (sample No. 5), (d) 20%

TiO2 (sample No. 8).

340 342 344 346 348 350 352 354 356 358

0

100

200

300

400

500

600 scanning curve of Ca2p

 FittedCurves

 FittedCurves

   I  n   t  e

  n  s   i   t  y   (  a .  u .   )

Binding Energy (eV)

454 456 458 460 462 464 466 468 470

0

100

200

300

400

500

600 scanning curve of Ti2p

 FittedCurves

 FittedCurves

   I  n   t  e

  n  s   i   t  y   (  a .  u .   )

Binding Energy (eV)

a b

Fig. 3.  XPS spectra of element (a) Ca, (b) Ti.

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decayed and did not reach a steady state even after 30 cycles. In

contrast, when the ester concentration was relatively low, the

sorption capacity was basically stable after only 10 cycles.

 3.3. Compactness and durability

The adsorption performance of the novel adsorbent was corre-

lated with the compactness of the coating layer. The compact fac-

tors of the TiO2 coating layers of samples with different adsorptionperformances are shown in Table 3.

0 5 10 15 20

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

  1st run

 30th run

  r  e  a  c   t   i  v  e  s  o  r  p   t   i  o  n  c  a  p  a  c   i   t  y   (  g   C   O

   2   /  g   C  a   O   )

TiO2 content/%

Fig. 7.  Effect of TiO2 content on sorption capacity of 1st and 30th run.

0 5 10 15 20 25 30

0.1

0.2

0.3

0.4

0.5

0.6

  r  e  a  c   t   i  v  e

  s  o  r  p   t   i  o  n  c  a  p  a  c   i   t  y   (  g   C   O

   2   /  g   C  a   O   )

number of cycles

Fig. 8.   CO2  reactive sorption capacity of sample Nos. 5, and 9–12 prepared under

different temperatures varying from 0 C to 70 C.

0 5 10 15 20 25 30

0.1

0.2

0.3

0.4

0.5

0.6

  r  e  a  c   t   i  v  e  s  o  r  p   t   i  o  n  c  a  p  a  c   i   t  y   (  g   C   O

   2

   /  g   C  a   O   )

number of cycles

 5%

 9.6%

 17.5%

Fig. 9.   CO2 reactive sorption capacity of sample Nos. 10, and 13,14 prepared underdifferent ester concentrations of 5–17.5%.

0 10 20 30 40 50 60

0.0

0.1

0.2

0.3

0.4

0.5

0.6

  r  e  a  c   t   i  v  e  s

  o  r  p   t   i  o  n  c  a  p  a  c   i   t  y   (  g   C   O

   2   /  g   C  a   O   )

number of cycles

 10%TiO2

 0%TiO2

Fig. 6.   CO2   reactive sorption capacity of sample No. 5.

 Table 2

BET analytic results of samples 1 and 5 before and after several runs.

Sample BET surface area (m2/g) Average pore size (nm)

No. 1 No. 5 No. 1 No. 5

Fresh 5.90 20.76 20.80 19.14

After 12 runs 4.35 10.92 18.42 12.42

After 20 runs 3.33 10.33 16.60 13.18

0 5 1 0 1 5 2 0 2 5 3 0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

  r  e  a  c   t   i  v  e  s  o  r  p   t   i  o  n  c  a  p  a

  c   i   t  y   (  g   C   O

   2   /  g   C  a   O   )

number of cycles

 0% 5%

 6.5% 8%

 10% 12%

 15% 20%

Fig. 5.   CO2   reactive sorption capacity of sample Nos. 1–8 with different TiO2

content (carbonation: CO2   partial pressure of 0.02 MPa at 600 C for 10 min, and

calcination with an atmospheric pressure in N2  at 725 C for 10 min).

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The TiO2 content and the compact factor both increased in sam-

ples Nos. 2, 4, 7, and 8. It is easy to understand that an increased

TiO2  content indicates that more TiO2  is gathered on the surface

of the nano calcium carbonate. Thus, the relative content of tita-

nium to calcium on the surface was greater. The hydrolysis tem-

perature is critical for the control of the reaction kinetics that

determines the formation rate and the growth pattern of TiO2,

which results in the dispersion of TiO2  on the surface of the nano

calcium carbonate. Higher temperatures were conducive to thegrowth of the Ti(OH)4  precipitate crystal, which led to an inferior

dispersion of TiO2  and thus a smaller compact factor.

As shown in Fig. 10, the sorption capacity in the 30th run first

increases and then decreases with increasing compact factor. A

compact factor in the range of 0.8–1.3 resulted in a small decay

ratio and a high sorption capacity in the 30th run; this range was

thus regarded as an optimal range of   C . When   C   was less than

0.85, the sorption capacity decayed the most throughout the 30-

cycles because the coating layer was not dense and the distribution

of the coating material on the surface was not uniform. Thus, this

coating was not able to prevent the agglomeration of the CaCO3

or the sintering of the nano particles. When  C  was greater than

1.3, the coating layer was uniform and sufficiently dense. For

example, the compact factor of sample 8 was 1.89, and the sorptioncapacity of this sample gradually stabilized after the first few ini-

tial cycles of decay. However, the increase in the coating material

content led to a reduction in the relative content of CaO, which

greatly reduced the overall sorption capacity of the sorbent.

There were two main factors that affected the compact factor C :

the coating content and the operating conditions, which include

the temperature and the concentration used in the preparation of 

the absorbent. The coating content mainly determined the coating

thickness, whereas the operating conditions regulated the coating

uniformity. When the coating material content was constant, both

the sorption capacity and the durability of the sorbent prepared at

a low temperature and a low reactant concentration were im-

proved probably because these conditions reduce the reaction rate,

thus making the coating material on the surface of the nanocalcium carbonate distribute more evenly. In addition, when the

compact factor was close to 1.0, the compactness was considered

to be improved.

4. Conclusion

The application of an adsorption phase technique for the prep-

aration of a TiO2-coated nano-CaO based CO2  adsorbent with high

durability and a controlled coating layer was introduced in thisstudy. A coating layer of 4.5–11.6 nm was formed with increasing

TiO2   content. The TiO2  coating can prevent the sintering of nano

CaCO3  during multiple carbonation/calcination cycles. Among the

TiO2  content, the hydrolysis temperature, and the ester concentra-

tion, the TiO2 content has the most effect on the durability of resul-

tant absorbent for CO2   adsorption. The optimal content of TiO2

ranges from 8% to 12%. The optimal hydrolysis conditions included

a relatively low temperature in the range of 0–20 C and a low

reactant concentration of 5–10 wt.%. The compact factor is a

quantitative description of the status of the TiO2   coating layer

and differs when the TiO2-coated nano-CaCO3   is prepared under

different conditions. When the compact factor is between 0.9 and

1.3, the compactness is considered to be optimal because the

adsorption stability of these samples is the best of the samplestested.

 Acknowledgments

The National Natural Science Foundation of China is thanked for

its financial support (20876142). Kimberly Braches from McMaster

University is also acknowledged for her editing assistance.

 Appendix A. Supplementary material

Supplementary data associated with this article can be found, in

the online version, at  http://dx.doi.org/10.1016/j.cej.2012.11.095.

References

[1] D.A. Green, B.S. Turk, R.P. Gupta, J.W. Portzer, W. McMichael, D. Harrison,

Capture of carbon dioxide from flue gas using solid regenerable sorbents, Int. J.

Environ. Technol. Manage. 4 (2004) 53–67.

[2] J.C. Abanades, E.J. Anthony,D.Y. Lu, C. Salvador, D. Alvarez, Capture of CO2 from

combustion gases in a fluidized bed of CaO, AIChE J. 50 (2004) 1614–1622.

[3] H. Gupta, L.S. Fan, Carbonation–calcination cycle using high reactivity calcium

oxide for carbon dioxide separation from flue gas, Ind. Eng. Chem. Res. 41

(2002) 4035–4042.

[4] J.R. Hufton, S. Mayorga, S. Sircar, Sorption-enhanced reaction process for

hydrogen production, AIChE J. 45 (1999) 248–256.

[5] C. Han, D.P. Harrison, Simultaneous shift reaction and carbon dioxide

separation for the direct production of hydrogen, Chem. Eng. Sci. 49 (1994)

5875–5883.

[6] S.F. Wu, L.B. Li, Y.Q. Zhu, X.Q. Wang, A micro-sphere catalyst complex with

nano CaCO3 precursor for hydrogen production used in ReSER process, Eng. Sci.

8 (2010) 22–26.

[7] A. Silaban, D.P. Harrison, High temperature capture of carbon dioxide:characteristics of the reversible reaction between CaO(s) and CO2(g), Chem.

Eng. Commun. 137 (1995) 177–190.

[8] P.S. Fennell, R. Pacciani, J.S. Dennis, J.F. Davidson, A.N. Hayhurst, The effects of 

repeated cycles of calcination and carbonation on a variety of different

limestones, as measured in a hot fluidized bed of sand, Energy Fuels 21 (2007)

2072–2081.

[9] Z.X. Chen, H.S. Song, M. Portillo, C.J. Lim, J.R. Grace, E.J. Anthony, Long-term

calcination/carbonation cycling and thermal pretreatment for CO2  capture by

limestone and dolomite, Energy Fuels 23 (2009) 1437–1444.

[10] S. Dobner, L. Sterns, R.A. Graff, A.M. Squires, Cyclic calcination and

recarbonation of calcined dolomite, Ind. Eng. Chem. Process Des. Dev. 16

(1977) 479–486.

[11] J.C. Abanades, D. Alvarez, Conversion limits in the reaction of CO2  with lime,

Energy Fuels 17 (2003) 308–315.

[12] P. Sun,J.R. Grace, C.J. Lim,E.J. Anthony,The effect of CaO sintering on cyclicCO2

capture in energy systems, AIChE J. 53 (2007) 2432–2442.

[13] D. Alvarez, J.C. Abanades, Determination of the critical product layer thickness

in the reaction of CaO with CO2, Ind. Eng. Chem. Res. 44 (2005) 5608–5615.

[14] S.F. Wu, Y.Q. Zhu, Behavior of CaTiO3/nano-CaO as a CO2   reactive adsorbent,Ind. Eng. Chem. Res. 49 (2010) 2701–2706.

 Table 3

The compact factors of TiO2  coating layer under different experimental conditions.

Sample Nos. 2 4 7 8 10 11 12

C    0.81 1.31 1.52 1.89 1.03 1.09 0.77

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.00.1

0.2

0.3

0.4

0.5

0.6

0.7

 1st run sorption capacity 30th run sorption capacity

  r  e  a  c   t   i  v  e  s  o  r  p   t   i  o  n  c  a  p  a  c   i   t  y   (  g   C   O

   2   /  g   C  a   O   )

compact factor 

0

20

40

60

80

 decay ratio of 30th run

   d  e  c  a  y  r  a   t   i  o   (   %   )

Fig. 10.  The relationship between compact factor and the 30th sorption capacity

and decay ratio.

44   Y. Wang et al. / Chemical Engineering Journal 218 (2013) 39–45

8/15/2019 2013-CEJ- Wang Yan- a new nano.pdf

http://slidepdf.com/reader/full/2013-cej-wang-yan-a-new-nanopdf 8/8

[15] S.F. Wu, Q.H. Li, J.N. Kim, K.B. Yi, Properties of a nano CaO/Al2O3  CO2 sorbent,

Ind. Eng. Chem. Res. 47 (2008) 180–184.

[16] N.H. Florin, A.T. Harris, Reactivity of CaO derived from nano-sized CaCO3

particles through multiple CO2 capture-and-release cycles, Chem. Eng. Sci. 64

(2009) 187–191.

[17] S.F. Wu, P.Q. Lan, A kinetic model of nano-CaO reactions with CO2  in a sorption

complex catalyst, AIChE J. 58 (2012) 1570–1577.

[18] Z.S. Li, N.S. Cai, Y.Y. Huang, H.J. Han, Synthesis, experimental studies, and

analysis of a new calcium-vased carbon dioxide absorbent, Energy Fuels 19

(2005) 1447–1452.

[19] R. Wu, S.F. Wu, Performance of nano-CaCO3   coated with SiO2   on CO2

adsorption at high temperature, CIESC J. 57 (2006) 1722–1726.

[20] Q. Shi, S.F. Wu, Properties of SiO2   coated nano SiO2/CaCO3   sorbents by

precipitation method, CIESC J. 60 (2009) 507–513.

[21] L.Y. Li, D.L. King, Z.M. Nie, C. Howard, Magnesia-stabilized calcium oxide

absorbents with improved durability for high temperature CO2   capture, Ind.

Eng. Chem. Res. 48 (2009) 10604–10613.

[22] J.C. Mabry, K. Mondal, Magnesian calcite sorbent for carbon dioxide capture,

Environ. Technol. 32 (2011) 55–67.

[23] H. Lu, A. Khan, P.G. Smirniotis, Relationship between structural properties and

CO2   capture performance of CaO based sorbents obtained from different

organometallic precursors, Ind. Eng. Chem. Res. 47 (2008) 6216–6220.

[24] W.Q. Liu, N.W.L. Low, B. Feng, G.X. Wang, J.C. Diniz da Costa, Calcium

precursors for the production of CaO sorbents for multicycle CO2   capture,

Environ. Sci. Technol. 44 (2009) 841–847.

[25] B.V. Materic, C. Sheppard, S.I. Smedley, Effect of repeated steam hydration

reactivation on CaO-based sorbents for CO2 capture, Environ. Sci. Technol. 44

(2010) 9496–9501.

[26] V. Manovic, E.J. Anthony, Steam reactivation of spent CaO-based sorbent for

multiple CO2  capture cycles, Environ. Sci. Technol. 41 (2007) 1420–1425.

[27] N.H. Florin, A.T. Harris, Screening CaO-based sorbents for CO2   capture in

biomass gasifiers, Energy Fuels 22 (2008) 2734–2742.

[28] W.Q. Liu, B. Feng, Y.Q. Wu, G.X. Wang, J. Barry, J.C. Diniz da Costa, Synthesis of 

sintering-resistant sorbents for CO2  capture, Environ. Sci. Technol. 44 (2010)

3093–3097.

[29] R. Filitz, A.M. Kierzkowska, M. Broda, C.R. Muller, Highly efficient CO2

sorbents: Development of synthetic, calcium-rich dolomites, Environ. Sci.

Technol. 46 (2012) 559–565.

[30] J. Park, K.B. Yi, Effects of preparation method on cyclic stability and CO2

absorption capacity of synthetic CaO–MgO absorbent for sorption-enhanced

hydrogen production, Int. J. Hydrogen Energy 37 (2012) 95–102.

[31] X. Jiang, T. Wang, Preparation of TiO2 nanoparticles on different SiO2 supports

by the adsorption phase technique, J. Am. Ceram. Soc. 91 (2008)

46–50.

[32] H. Deng, X. Jiang, Preparation of CuO–Ag/SiO2 nano-composites via adsorption

phase reaction technique, Chin. J. Inorg. Chem. 27 (2011) 119–124.

[33] V. Manovic, E.J. Anthony, Thermal activation of CaO-based sorbent and self-

reactivation during CO2   capture looping cycles, Environ. Sci. Technol. 42

(2008) 4170–4174.

Y. Wang et al. / Chemical Engineering Journal 218 (2013) 39–45   45