High-Capacity Li4SiO4-Based CO2 Sorbents via a Facile Hydration

Subscriber access provided by UB + Fachbibliothek Chemie | (FU-Bibliothekssystem)

Article

High-Capacity Li4SiO4-based CO2 Sorbents via a Facile Hydration-NaCl Doping Technique Ke Wang, Wei Li, Zeguang Yin, Zhongyun Zhou, and Pengfei Zhao Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 20 May 2017 Downloaded from http://pubs.acs.org on May 20, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

High-Capacity Li4SiO4-based CO2 Sorbents via a Facile Hydration-NaCl Doping

2

Technique

3

Ke Wang, Wei Li, Zeguang Yin, Zhongyun Zhou, Pengfei Zhao*

4

School of Electrical and Power Engineering, China University of Mining and

5

Technology, Xuzhou 221116, China

6

Corresponding author:

7

Dr. Pengfei Zhao

8

School of Electrical and Power Engineering

9

China University of Mining and Technology

10

Xuzhou 221116, China

11

Fax: 86-516-83592000

12

E-mail: [email protected]

13

Abstract: A sodium chloride (NaCl) doping-hydration technique was used to modify

14

the structure of Li4SiO4 to improve its sorption properties at low CO2 concentration.

15

XRD, nitrogen adsorption, SEM, XPS, differential scanning calorimetry (DSC), and

16

thermogravimetric analyses were conducted to characterize the compositions, textural

17

characteristics, morphologies, chemical valence states, molten phases and adsorption

18

properties of the synthesized samples. Hydration and NaCl doping produced

19

synergistic effects. On one hand, a small particle size and large specific surface area

20

were obtained, significantly facilitating chemisorption processes. On the other hand,

21

co-doped sodium and chlorine induced molten phases when absorbing CO2,

22

noticeably decreasing CO2 diffusion resistance. Thus, the CO2 absorption rate and 1

ACS Paragon Plus Environment

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 36

1

uptake were remarkably improved. Different amounts of NaCl also greatly affected

2

the morphology and chemisorption properties of the sorbents. At the optimized NaCl

3

concentration, the sorbent only required 3 wt.% doping to attain a maximum sorption

4

capacity of up to 34.2 wt.%. Moreover, the high capacity was maintained after 10

5

sorption/desorption cycles.

6

1. Introduction

7

The increased anthropogenic emission of greenhouse gases, such as CO2, mainly

8

from fossil fuel combustion, is one of the major contributors to global warming.1-3

9

CO2 capture and sequestration (CCS) technologies provide effective and practical

10

solutions for nations who wish to both continue to consume fossil fuels and obtain

11

ambitious emission targets.4-7 However, current CCS technology using aqueous

12

amines has a large energy penalty.8 To address this problem, the removal of CO2 at

13

high temperatures utilizes calcium-based materials,9-15 and ceramic absorbents

14

can separate CO2 directly from hot flue gases and the sorption-enhanced steam

15

methane reforming (SESMR) process, thereby eliminating the cooling process and

16

significantly decreasing the operating costs. Among these candidate materials, lithium

17

orthosilicate (Li4SiO4) has been recognized as one of the most attractive sorbents for

18

its relatively large absorption capacity and reasonable durability.20-24

16-19

19

Common Li4SiO4 sorbents produced via solid-state reaction have very low

20

surface areas.25, 26 Due to the limited gas-solid contact, slow kinetics are presented.

21

Several superior synthetic methods, such as ball milling 27, impregnated precipitation

22

28-30

, sol–gel,

31-33

carbon coating

34, 35

and hydration,36 were proposed to increase the 2


Page 3 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

specific surface area of sorbents. Modified Li4SiO4 particles with larger surface areas

2

and smaller particle sizes attainted higher carbonation conversions (>90%) at 100%

3

CO2/700 °C compared to that of raw Li4SiO4. Unfortunately, under a realistic CO2

4

concentration of 15 vol.%, only half of the sorbents participate in CO2 uptake even

5

over long time periods (~120 min).34 Therefore, it is highly important to further

6

enhance the performance of Li4SiO4 at low CO2 partial pressure.

7

Based on the double-shell model,37 due to a dense and solid product layer (a

8

mixture of Li2CO3 and Li2SiO3) surrounding the unreacted core of Li4SiO4, the

9

absorption shifts from the rapid chemisorption controlled regime to the slow CO2

10

diffusion-controlled regime.38 Inferior CO2 absorption properties were thus obtained

11

within a given residence time in the reactor. Compared with a pure CO2 atmosphere,

12

the CO2 diffusion resistance at low CO2 partial pressure (i.e., flue gases is only 15

13

vol.%) was increased, considering the absorption temperature was decreased to

14

500-600 °C under a CO2 concentration of 15 vol.%.39,

15

doping alkali carbonates (Na2CO3 and K2CO3) into Li4SiO4 ceramics can significantly

16

reduce the diffusion resistance, thereby facilitating the removal of CO2. Zhang et al. 41

17

mixed K2CO3 with Li4SiO4 through a solid-state reaction route. The large and dense

18

K2CO3-doped Li4SiO4 particles show only a slightly improved absorption conversion

19

of 58% at 15 vol.% CO2. Seggiani et al.

20

mixtures to promote Li4SiO4. The addition of 30 wt.% Na2CO3 showed a noticeably

21

improved absorption conversion of 80%. Later, several reports proved that extremely

22

high sorption properties can be further achieved by controlling the morphology of the

42

40

It has been proven that

developed binary and ternary carbonate

3


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

Li4SiO4 precursor using synthetic routes. Yang et al. 43 introduced the organic lithium

2

impregnated suspension method to tailor Na2CO3-doped Li4SiO4 particles with

3

relatively smaller and larger surface areas. Under 15 vol.% CO2, 10 wt.%

4

Na2CO3-doped sorbents present a 90% absorption conversion. Subha et al.44 also

5

reported the high capacity (90% absorption conversion) of alkali carbonate-doped

6

Li4SiO4 nanorods made through a microwave sol–gel process. However, both

7

synthetic methods clearly suffer from expensive reagents or time-consuming steps.

8

We prepared a highly effective Li4SiO4 sorbent via a new NaCl doping and

9

hydration procedure. On one hand, the steam was used in the most of hydration

10

method.45, 46 Recently, we have developed the water-based hydration to significantly

11

improve the sorption capacity of Li4SiO4.36 On the other hand, Na2CO3 and K2CO3

12

are widely used in the synthesis of alkali-doped Li4SiO4 sorbents. This is the first time

13

that NaCl has been used as doping source. Moreover, the structure of NaCl-doped

14

sorbents was different from the cases of alkali carbonate-doped Li4SiO4. In

15

comparison to organic lithium impregnated suspension and microwave sol–gel, four

16

features are apparent. 1) Our approach is simple and cost effective. This method

17

involved one wet impregnation doping step. Moreover, NaCl is abundant and

18

inexpensive. 2) This synthetic procedure is an absolutely “green” procedure. Only

19

non-toxic NaCl solutions were used. 3) Our sorbents require only 3 wt.% NaCl

20

doping to reach a maximum absorption capacity of up to 34.2 wt.% (~96% absorption

21

conversion). 4) NaCl-water solutions are the main component of sea water, which

22

would benefit scalable applications. 4


Page 4 of 36

Page 5 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

2. Experimental

2

2.1. Sorbents

3

All synthetic raw materials were of analytical grade (from Aladdin Chemical

4

Reagent Co., Ltd.). Pure Lithium silicate (Li4SiO4) sorbents were synthesized by a

5

high-temperature solid-state reaction. For the preparation process, 4.7 g of lithium

6

nitrate (LiNO3) and 1.0 g of fumed silica (SiO2) were accurately weighed. After

7

sufficient mixing, the mixture was calcined at 800 °C for 4 h. The resulting powder

8

was called SS. Samples were prepared by a NaCl doping-hydration method as follows:

9

1 g of SS and 0.01~0.05 g of sodium chloride (NaCl) were placed in 200 ml of

10

deionized water. The mixture was stirred for 2 h at 80 °C and dried in a drier at

11

105 °C. Finally, the obtained powder was calcined again at 800 °C for 2 h. For

12

comparison, HC (via a water hydration-calcination method) sorbents were synthesized

13

by a similar method but without adding NaCl.

14

NaCl-doped Li4SiO4 absorbents were also synthesized using the traditional

15

solid-state reaction method. 4.7 g of LiNO3, 1.0 g of SiO2 and 0.03 g of NaCl were

16

accurately weighed and mixed, and then calcined at 800 °C for 4 h, and the resulting

17

sorbent was named SS-3Na.

18

All samples were named according to the following rules: the first half referred

19

to the preparation method (HC: hydration-calcination method and SS: solid-state

20

method) and the second half designated the mass ratio of NaCl/Li4SiO4. If the second

21

half is absent, the sample had no NaCl doping. For example, HC-3Na indicates that

22

the modified Li4SiO4 powders were synthesized by the hydration-calcination method 5


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

with 3 wt.% NaCl addition.

2

2.2 Characterization Methods

3

X-ray diffraction (XRD) was utilized to detect the phase composition of the

4

sorbents using a Bruker Model D8 Advance X-ray diffractometer. Scanning electron

5

microscopy (SEM) was performed to observe the morphology of these samples using

6

a Hitachi S-4800 field-emission microscope. N2 adsorption/desorption isotherms were

7

employed to analyze the specific BET surface area and BJH pore-size distribution

8

using a TriStar 3020 volumetric adsorption analyzer. The chemical valence states on

9

the surfaces of the samples were investigated using X-ray photoelectron spectroscopy

10

(XPS, Perkin-Elmer, PHI 5600). The data were calibrated using the adventitious C 1s

11

peak with a fixed value of 284.6 eV and analyzed using XPSPEAK41 processing

12

software. DSC analysis was performed in a Labsys Evo simultaneous thermal

13

thermogravimetric analyzer; the samples were dynamically heated from room

14

temperature to 1000 °C at a rate of 10 °C/min under a CO2 atmosphere with a flow

15

rate of 50 mL/min.

16

CO2 absorption properties were measured by a ZRY-1P thermogravimetric

17

analyzer (Techcomp Jingke Scientific Instrument Co., Ltd., Shanghai, China). A series

18

of sorbents was heat-treated from room temperature to 800 °C at a rate of 10 °C/min,

19

and the whole process was carried out under 15 vol.% CO2 in N2 (50 ml/min).

20

Additionally, the isothermal absorption properties were determined. The samples were

21

heated to a specified temperature under N2 atmosphere (50 ml/min), then the gas line

22

was immediately switched to 15 vol.% CO2 in N2 (50 ml/min), and the sample 6


Page 6 of 36

Page 7 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

maintained at the specified temperature for 120 min. For evaluating the cyclic

2

absorption properties, 10 absorption/desorption cycles were performed as follows:

3

CO2 absorption at 575 °C in a 50 ml/min CO2-N2 mixture containing 15 vol.% CO2

4

for 40 min and CO2 desorption at 700 °C in 50 ml/min pure N2 for 10 min.

5

3. Results and discussion

6

3.1. Different modified methods

7

After Li4SiO4 samples were synthesized using different methods, the samples

8

were characterized by XRD. As shown in Figure 1, the XRD peaks of SS and HC

9

were identified as Li4SiO4 crystalline phase, and no any second phase appeared. In

10

addition to the crystalline phase of Li4SiO4, the characteristic peaks of NaCl were

11

observed in both SS-3Na and HC-3Na. It seemed that the doping limit is less than 3

12

wt.%, which was confirmed by XRD and XPS results in the following section.

13

Furthermore, the diffraction peaks of HC and HC-3Na became much broader than

14

those observed in the samples synthesized by solid-state reaction.

15

The microstructural properties of samples obtained by different methods were

16

observed by SEM. As illustrated in Figure 2, the morphology of SS and SS-3Na

17

samples were relatively dense and large particles (~30 µm), which are consistent with

18

those produced in the solid state reaction. Although there are still some sintered

19

particles in the HC and HC-3Na sample, the size of most particles decreased to

20

approximately 2 µm. Apparently, the water-based hydration technique can effectively

21

reduce the particle size in pure and doped Li4SiO4 samples. In addition, the addition of

22

NaCl resulted in smaller particle size compared with both pure Li4SiO4 samples. 7


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

Figure 3a shows the dynamic curves for the four different samples in an

2

atmosphere of 15 vol.% CO2. Until the temperature reached 500 °C, the weight of SS

3

increased and reached the highest point of 1.8 wt.% at approximately 600 °C. With a

4

further increase in temperature, the quality of these samples began to decrease. HC

5

showed similar dynamic absorption characteristics but exhibited a slight higher

6

capacity (3.9 wt.%). Compared to a 100% CO2 atmosphere, the results highlighted the

7

lower absorption temperature and the poor performance of pure Li4SiO4 under

8

realistic CO2 conditions. It is also clear that the Li4SiO4 sorbent doped with NaCl

9

showed remarkably enhanced uptake of CO2 compared with the non-doped Li4SiO4

10

sorbent. The increased CO2 capture was more predominant in HC-3Na. Moreover, the

11

initial absorption temperature (approximately 400 °C) in the SS-3Na and HC-3Na

12

samples both became relatively lower. Similar observations were reported for

13

NaCO3-doped Li4SiO4.47

14

The absorption properties were further tested by isothermal absorption

15

experiments at 575 °C under 15 vol.% CO2. As shown in Figure 3b, the weight of the

16

SS sample increased slowly, and the final absorption amount was only 6.1 wt.%. HC

17

showed a slightly faster absorption rate, and its maximum absorption capacity reached

18

13.7 wt.%. SS-3Na achieved an even higher absorption rate and uptake of CO2.

19

Apparently, both hydration pretreatment and the NaCl doping process appear to

20

benefit the absorption properties. Due to the synergistic effect of hydration and NaCl

21

doping, HC-3Na displayed extraordinary CO2 absorption with the most rapid reaction

22

rate and the highest uptake (34.2 wt.%), which was over 5-fold more than that of SS. 8


Page 8 of 36

Page 9 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

The absorption performances of alkali carbonate-doped sorbents in the recent

2

literature are summarized in Table 1. The increased uptake of HC-3Na was also higher

3

than the highest reported capacity (~30.0 wt.%) of 10 wt.% Na2CO3-doped sorbents.

4

Moreover, our sorbents require a low amount of doping (3 wt.% NaCl) to reach their

5

maximum capacity.

6

3.2. Different amounts of dopant

7

The crystalline phases of the prepared sorbents doped with different amounts of

8

NaCl were determined using powder XRD. The pattern of the reference sample (HC)

9

is also provided. As shown in Figure 4, only Li4SiO4 peaks were observed in the XRD

10

patterns of HC. Besides Li4SiO4, no additional substances were detected in the

11

HC-1Na sorbent. The doped NaCl may be in the liquid state, as its relatively low

12

melting point (801 °C) 48 approaches the calcination temperature (800 °C). During the

13

preparation process, NaCl may have been incorporated into Li4SiO4 to form a solid

14

solution. However, when the doping content was increased to 3 wt.% or higher, the

15

diffraction peak of NaCl was identified, which suggested that its doping amount

16

exceeded the solubility limit. An impurity phase of Li2SiO3 was also observed in

17

HC-5Na. Mejı´a-Trejo et al.

18

higher Na-doping amounts.

47

has reported the appearance of Li2SiO3 in the case of

19

To further study the distribution of NaCl within the particle, XPS analysis of HC,

20

HC-1Na and HC-3Na were performed. As illustrated in Figure 5a, the Na doping

21

resulted in a change in the oxidation state of Li 1S. For pure Li4SiO4, the peak at 54.4

22

eV originated from the appearance of a LixSiOy phase.49 Previous studies 50, 51 showed 9


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 36

1

that metal oxide (COx or VOx) reacted with the lithium-based materials resulted in

2

higher binding energies. The peaks of the spectra in two NaCl-doped samples both

3

shift to higher binding energies, which can probably be attributed to doped with Na

4

doping. Similar to Li 1S, the O 1s spectra of the three samples are also provided the

5

evidence of changes in the oxidation state of Li4SiO4 introduced by Cl doping (Figure

6

5b). The O 1s component at ∼531.1 eV was mainly observed in HC, which matches

7

the O 1s signature obtained for Li4SiO4.52 It was reported that the presence of

8

carbonates with higher binding energies (~533.5 eV)

9

oxidation state. Interestingly, there is a similar shift of the O 1s data in HC-1Na and

10

HC-3Na, clearly proving that doped chlorine successfully substituted for the oxygen.

11

Based on XRD and XPS results, we can speculate that NaCl has entered the lithium

12

silicate lattice to form solid solution. Similar description was also be found in

13

Mejı´a-Trejo et al's work 47.

53

resulted in a change in the

14

The morphologies of the Li4SiO4 samples with different NaCl concentrations

15

were examined by SEM and are shown in Figure 6. HC presented two types of

16

particles. Most of the particles were large and dense, with a particle size of around 30

17

µm, having a polyhedral structure. Minor amounts of small aggregated particles were

18

also observed. It is evident that the presence of NaCl induces significant

19

morphological changes. Upon addition of only 1 wt.% NaCl, the surface was no

20

longer smooth. Some particles maintained their original morphology, while others

21

became smaller polymerized particles with an average size of 6 µm. As the NaCl

22

content was further increased to 3 wt.%, the remaining polyhedral structure 10


Page 11 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

completely disappeared. Instead, a raspberry-like structure consisting mainly of

2

regular micrometer-sized spheres was formed. These micrometer-sized spheres

3

seemed to decrease in size in HC-5Na. Similar to the case of NaCO3-doped Li4SiO4

4

sorbents

5

Li4SiO4 particles. As a result of this effect, these sorbents should have a higher surface

6

area. To confirm this hypothesis, N2 adsorption was used to examine the porous

7

nature of the doped sorbents. The BET specific surface area, pore volume, and

8

average pore diameter were calculated and listed in Table 2. Although the surface

9

areas and average pore volumes were low, they both grew as the addition of NaCl

10

47

, NaCl also appears to act as a physical barrier to control the growth of

increased.

11

Dynamic adsorption experiments were performed under 15 vol.% CO2 in N2. As

12

shown in Figure 7a, all sorbents absorbed CO2 and reached a peak at approximately

13

620 °C. It is also noted that the doped sorbents began to absorb CO2 at 400 °C, which

14

is 100 °C lower than the initial absorption temperature of HC. Apparently, the initial

15

absorption temperature appears to depend on the amount of NaCl addition. However,

16

the absorption rate and capacity of all modified Li4SiO4 samples were obviously

17

improved. Among them, HC-5Na exhibited better absorption performance with a

18

maximum absorption of 24.9 wt.%.

19

To further analyze the CO2 sorption performance, isothermal sorption

20

experiments were also performed at 575 °C (Figure 7b). Compared with HC, the CO2

21

sorption ability, including the reaction rate and maximum absorption, were

22

significantly enhanced by the addition of NaCl. In the initial reaction stage (0-15 min), 11


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

the steepest slope among the doped samples was also observed in HC-5Na. It seemed

2

that the further addition of dopants led to more rapid sorption, which is consistent

3

with the dynamic results (Figure 7a) and previous reports of Na2CO3-doped sorbents.

4

However, after 2 h of absorption, a slight reduction in the maximum absorption was

5

attained in HC-5Na compared to HC-3Na. The XRD spectrum (Figure 4) of HC-5Na

6

indicates the formation of some impurities that did not absorb CO2, which may be the

7

main reason for the reduction. Based on both dynamic and isothermal absorption, the

8

optimal additive ratio for the doped samples is 3 wt.% because HC-3Na presented the

9

highest maximum absorption capacity and a relatively faster reaction rate.

10

Combined with hydration and NaCl doping, HC-3Na remarkably improved the

11

CO2 absorption rate and uptake. On one hand, HC-3Na presented favorable structure

12

(a small particle size and large specific surface area), thereby significantly facilitating

13

chemisorption processes. On the other hand, additional tests were performed to

14

illustrate the role of NaCl in the adsorption process. Firstly, fresh HC-3Na sample was

15

subjected to adsorption experiments (575°C in 15% CO2 for 1 h) and the resulted

16

sample was designed as HC-3Na-a. Followed by desorption experiment (800°C in

17

100% N2 for 30 min) and the desorbed sample was named HC-3Na-b. Compared with

18

the case of HC-3Na, the XRD patterns (Figure 8) showed that the HC-3Na-a samples

19

mainly include Li2SiO3, Li2CO3 and a small amount of unreacted Li4SiO4. These

20

phases are also observed in other Li4SiO4-based sorbents. 33 However, the diffraction

21

peaks of NaCl disappeared. The XRD patterns of HC-3Na-b also confirmed the

22

disappearance of NaCl. Only the diffraction peaks of Li4SiO4 were identified. The 12


Page 12 of 36

Page 13 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

absence of NaCl in HC-3Na-a and HC-3Na-b was mainly attributed to the formation

2

of low temperature eutectic products (a mixture of NaCl and carbonates) involving in

3

the absorption process, which is supported by the phase diagram of NaCl–MCO3

4

system from FTsalt-FACT salt databases. More importantly, if there are eutectic on

5

the Li4SiO4 samples during CO2 absorption, exothermic behaviors would appear and

6

could be gauged by TG-DSC. As shown in Figure 9, compared with HC sample,

7

NaCl-doped sample with 10wt% NaCl doping had a clearly exothermic peak at

8

627 °C, providing the evidence of the formation of a eutectic phase in the dynamic

9

CO2 capture process. Both samples also exhibited strong exothermic peaks at high

10

temperatures, which are associated with desorption CO2. Obviously, the presence of

11

such a molten phase during absorption process resulted in the least CO2 diffusion

12

resistance.

13

3.3. Kinetic analysis and stability

14

To obtain kinetic information, the absorption isotherms of HC-3Na and HC were

15

monitored at different temperatures and fitted to the following double exponential

16

model 30, 38:

17

y=A exp-k1t + B exp-k2t + C

(1)

18

where y represents the CO2 absorption capacity; t is the time; A, B and C are the

19

pre-exponential factors; and k1 and k2 are the exponential constants indicating CO2

20

chemisorption directly over the Li4SiO4 particles and the diffusion rate kinetically

21

controlled by lithium ions, respectively.

22

Figure 10 shows the isotherms of HC-3Na and HC at 475, 525 and 575 °C. As 13


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 36

1

expected, the CO2 absorption capacity increased with increasing temperature. The

2

isothermal data were then fitted to the double exponential model, and the obtained

3

parameter values are presented in Tables 3 and 4. For two sorbents, the k2 values are

4

much smaller than those of k1, which indicates that lithium diffusion is the decisive

5

factor limiting the whole absorption process. These results are consistent with

6

previous reports

7

were larger than those of HC, suggesting that both chemisorption and lithium

8

diffusion were enhanced by NaCl doping. Such enhancements were attributed to the

9

higher surface area and smaller particle size in HC-3Na.

10 11

30, 38

. By comparison, the k1 and k2 values of the HC-3Na sorbent

Furthermore, the activation enthalpies were estimated using the Eyring model: ln(k/T)=-(∆H++ /R) (1/T) + ln E + ∆S++ /R

(2)

12

where k is the rate constant, T is the absolute temperature, E is the pre-exponential

13

factor, R is the gas constant and ∆H++ and ∆S++ are the activation enthalpy and entropy,

14

respectively. Figure 11 shows the plots of ln(k/T) versus 1/T for chemisorption and

15

diffusion. The activation enthalpy for the chemisorption process decreased from 30.97

16

to 26.13 kJ/mol upon NaCl addition, which means that chemisorption is less

17

dependent on temperature in the presence of NaCl. Furthermore, the chemisorption

18

period was increased while that of the CO2 diffusion processes was reduced (Table 5).

19

Therefore, the diffusion reaction enthalpy showed completely opposite behavior. The

20

∆H++values obtained were 83.54 and 90.48 kJ/mol for HC and HC-3Na, respectively.

21

These results implied that the diffusion process became more dependent on

22

temperature upon NaCl doping due to the formation of a thicker layer associated with 14


Page 15 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

the enhanced CO2 uptake within a given residence time (2 h). Na2CO3-doped sorbents

2

also exhibited similar ∆H++ patterns dependent on the temperature.47

3

All of the above results suggest that the HC-3Na sample has the most excellent

4

absorption properties. Thus, the cyclic performance of the HC-3Na sorbent was

5

examined over 10 absorption/desorption cycles. As shown in Figure 12, there was no

6

significant deterioration in the total CO2 absorption capacity. The maximum uptake

7

was maintained at approximately 32.0 wt.% over 10 cycles. Figure 13 compare the

8

SEM images of fresh and cycled Li4SiO4 sorbent. The used sorbent maintained its

9

inherent morphology with raspberry-like structure. It has been reported that the

10

addition of alkali metals

11

temperatures, making the cycled particles less prone to sintering and resulting in good

12

regeneration properties.

13

4. Conclusions

37, 47

facilitates the regeneration of sorbent at lower

14

Li4SiO4 sorbents that are highly effective at low CO2 partial pressure were

15

prepared using a facile NaCl doping-hydration method. Both hydration pretreatment

16

and the NaCl doping process are beneficial to CO2 capture. Coupled with hydration

17

and NaCl doping, a small particle size and large specific surface area were obtained,

18

significantly facilitating chemisorption processes. At the same time, co-doped sodium

19

and chlorine induced a molten phase during CO2 absorption, resulting in the

20

decreased CO2 diffusion resistance. Therefore, the decreased the absorption

21

temperature, accelerated the absorption process, and enhanced the capacity were

22

achieved in HC-3Na. Different amounts of NaCl also greatly affected the morphology 15


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

and sorption characteristics of the Li4SiO4 sorbents. During the doping-hydration

2

process, the optimal additive ratio was 3 wt.%. Compared with HC, the chemisorption

3

and lithium diffusion processes were also improved, as evidenced by the kinetic

4

results. Moreover, HC-3Na maintained its good absorption performance over multiple

5

cycles. However, excessive NaCl (5 wt.%) led to the formation of impurities, which

6

decreased the maximum absorption.

7

Acknowledgement

8 9

This work was supported by financial supports from the Fundamental Research Funds for the Central Universities (2015XKMS054).

10

References

11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

(1) Hanak, D. P.; Anthony, E. J.; Manovic, V., A review of developments in pilot-plant testing and modelling of calcium looping process for CO2 capture from power generation systems. Energy Environ. Sci. 2015, 8 (8), 2199-2249. (2) Soofastaei, A.; Aminossadati, S. M.; Kizil, M. S.; Knights, P., A discrete-event model to simulate the effect of truck bunching due to payload variance on cycle time, hauled mine materials and fuel consumption. Int J Min Sci Technol. 2016, 26 (5), 745-752. (3) Blamey, J.; Anthony, E. J.; Wang, J.; Fennell, P. S., The calcium looping cycle for large-scale CO2 capture. Prog. Energy Combust. Sci. 2010, 36 (2), 260-279. (4) Soofastaei, A.; Aminossadati, S. M.; Kizil, M. S.; Knights, P., A comprehensive investigation of loading variance influence on fuel consumption and gas emissions in mine haulage operation. Int J Min Sci Technol. 2016, 26 (6), 995-1001. (5) Tan, Y.; Nookuea, W.; Li, H.; Thorin, E.; Yan, J., Property impacts on Carbon Capture and Storage (CCS) processes: A review. Energy Convers. Manage. 2016, 118, 204-222. (6) Rashidi, N. A.; Yusup, S., An overview of activated carbons utilization for the post-combustion carbon dioxide capture. Journal of Co2 Utilization 2016, 13, 1-16. (7) Quader, M. A.; Ahmed, S.; Dawal, S. Z.; Nukman, Y., Present needs, recent progress and future trends of energy-efficient Ultra-Low Carbon Dioxide (CO2) Steelmaking (ULCOS) program. Renewable & Sustainable Energy Reviews 2016, 55, 537-549. (8) El Hadri, N.; Quang, D. V.; Goetheer, E. L. V.; Abu Zahra, M. R. M., Aqueous amine solution characterization for post-combustion CO2 capture process. Appl. Energy 2017, 185, Part 2, 1433-1449. (9) Hu, Y.; Jia, Q.; Shan, S.; Li, S.; Jiang, L.; Wang, Y., Development of CaO-based sorbent doped with mineral rejects-bauxite-tailings in cyclic CO2 capture. J. Taiwan Inst. Chem. Eng. 2015, 46, 155-159. (10) Shan, S.; Ma, A.; Hu, Y.; Jia, Q.; Wang, Y.; Peng, J., Development of sintering-resistant 16


Page 16 of 36

Page 17 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

CaO-based sorbent derived from eggshells and bauxite tailings for cyclic CO2 capture. Environ. Pollut. 2016, 208, 546-552. (11) Zhao, P.; Sun, J.; Li, Y.; Wang, K.; Yin, Z.; Zhou, Z.; Su, Z., Synthesis of Efficient CaO Sorbents for CO2 Capture Using a Simple Organometallic Calcium-Based Carbon Template Route. Energy Fuels 2016. (12) Wang, K.; Hu, X.; Zhao, P.; Yin, Z., Natural dolomite modified with carbon coating for cyclic high-temperature CO2 capture. Appl. Energy 2016, 165, 14-21. (13) He, Z.; Li, Y.; Ma, X.; Zhang, W.; Chi, C.; Wang, Z., Influence of steam in carbonation stage on CO2 capture by Ca-based industrial waste during calcium looping cycles. Int. J. Hydrogen Energy 2016, 41 (7), 4296-4304. (14) Xu, Y.; Luo, C.; Zheng, Y.; Ding, H.; Zhang, L., Macropore-Stabilized Limestone Sorbents Prepared by the Simultaneous Hydration-Impregnation Method for High-Temperature CO2 Capture. Energy Fuels 2016, 30 (4), 3219-3226. (15) Cruz-Hernandez, A.; Alcantar-Vazquez, B.; Arenas, J.; Pfeiffer, H., Structural and microstructural analysis of different CaO-NiO composites and their application as CO2 or CO-O-2 captors. Reaction Kinetics Mechanisms and Catalysis 2016, 119 (2), 445-455. (16) Alcantar-Vazquez, B.; Duan, Y.; Pfeiffer, H., CO Oxidation and Subsequent CO2 Chemisorption on Alkaline Zirconates: Li2ZrO3 and Na2ZrO3. Ind. Eng. Chem. Res. 2016, 55 (37), 9880-9886. (17) Lara-Garcia, H.; Alcantar-Vazquez, B.; Duan, Y.; Pfeiffer, H., CO Chemical Capture on Lithium Cuprate, Through a Consecutive CO Oxidation and Chemisorption Bifunctional Process. J. Phys. Chem. C 2016, 120 (7), 3798-3806. (18) Diaz-Herrera, P. R.; Ramirez-Moreno, M. J.; Pfeiffer, H., The effects of high-pressure on the chemisorption process of CO2 on lithium oxosilicate (Li8SiO6). Chem. Eng. J. 2015, 264, 10-15. (19) Teresa Flores-Martinez, M.; Pfeiffer, H., CO2 chemisorption and cyclability analyses in -Li5AlO4: effects of Na2CO3 and K2CO3 addition. Greenhouse Gases-Science and Technology 2015, 5 (6), 802-811. (20) Wang, K.; Zhao, P.; Guo, X.; Li, Y.; Han, D.; Chao, Y., Enhancement of reactivity in Li4SiO4-based sorbents from the nano-sized rice husk ash for high-temperature CO2 capture. Energy Convers. Manage. 2014, 81, 447-454. (21) Chen, X.; Xiong, Z.; Qin, Y.; Gong, B.; Tian, C.; Zhao, Y.; Zhang, J.; Zheng, C., High-temperature CO2 sorption by Ca-doped Li4SiO4 sorbents. Int. J. Hydrogen Energy 2016, 41 (30), 13077-13085. (22) Xiang, M.; Zhang, Y.; Hong, M.; Liu, S.; Zhang, Y.; Liu, H.; Gu, C., CO2 absorption properties of Ti- and Na-doped porous Li4SiO4 prepared by a sol-gel process. J. Mater. Sci. 2015, 50 (13), 4698-4706. (23) Nair, B. N.; Burwood, R. P.; Goh, V. J.; Nakagawa, K.; Yamaguchi, T., Lithium based ceramic materials and membranes for high temperature CO2 separation. Prog. Mater Sci. 2009, 54 (5), 511-541. (24) Shan, S.; Jia, Q.; Jiang, L.; Li, Q.; Wang, Y.; Peng, J., Novel Li4SiO4-based sorbents from diatomite for high temperature CO2 capture. Ceram. Int. 2013, 39 (5), 5437-5441. (25) Kim, H.; Jang, H. D.; Choi, M., Facile synthesis of macroporous Li4SiO4 with remarkably enhanced CO2 adsorption kinetics. Chem. Eng. J. 2015, 280, 132-137. (26) Xu, H.; Cheng, W.; Jin, X.; Wang, G.; Lu, H.; Wang, H.; Chen, D.; Fan, B.; Hou, T.; Zhang, R., Effect of the Particle Size of Quartz Powder on the Synthesis and CO2 Absorption Properties of Li4SiO4 at High Temperature. Ind. Eng. Chem. Res. 2013, 52 (5), 1886-1891. (27) Romero-Ibarra, I. C.; Ortiz-Landeros, J.; Pfeiffer, H., Microstructural and CO2 chemisorption 17


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

analyses of Li4SiO4: Effect of surface modification by the ball milling process. Thermochim. Acta 2013, 567, 118-124. (28) Yang, X.; Liu, W.; Sun, J.; Hu, Y.; Wang, W.; Chen, H.; Zhang, Y.; Li, X.; Xu, M., Preparation of Novel Li4SiO4 Sorbents with Superior Performance at Low CO2 Concentration. ChemSusChem 2016, 9 (13), 1607-1613. (29) Shan, S.; Li, S.; Jia, Q.; Jiang, L.; Wang, Y.; Peng, J., Impregnation Precipitation Preparation and Kinetic Analysis of Li4SiO4-Based Sorbents with Fast CO2 Adsorption Rate. Ind. Eng. Chem. Res. 2013, 52 (21), 6941-6945. (30) Venegas, M. J.; Fregoso-Israel, E.; Escamilla, R.; Pfeiffer, H., Kinetic and Reaction Mechanism of CO2 Sorption on Li4SiO4:Study of the Particle Size Effect. Ind. Eng. Chem. Res. 2007, 46 (8), 2407-2412. (31) Wang, K.; Wang, X.; Zhao, P.; Guo, X., High-Temperature Capture of CO2 on Lithium-Based Sorbents Prepared by a Water-Based Sol-Gel Technique. Chem. Eng. Technol. 2014, 37 (9), 1552-1558. (32) Quddus, M. R.; Chowdhury, M. B. I.; de Lasa, H. I., Non-isothermal kinetic study of CO2 sorption and desorption using a fluidizable Li4SiO4. Chem. Eng. J. 2015, 260, 347-356. (33) Subha, P. V.; Nair, B. N.; Hareesh, P.; Mohamed, A. P.; Yamaguchi, T.; Warrier, K. G. K.; Hareesh, U. S., Enhanced CO2 absorption kinetics in lithium silicate platelets synthesized by a sol-gel approach. J. Mater. Chem. A 2014, 2 (32), 12792-12798. (34) Wang, K.; Zhou, Z.; Zhao, P.; Yin, Z.; Su, Z.; Sun, J., Synthesis of a highly efficient Li4SiO4 ceramic modified with a gluconic acid-based carbon coating for high-temperature CO2 capture. Appl. Energy 2016, 183, 1418-1427. (35) Wang, K.; Yin, Z.; Zhao, P., Synthesis of macroporous Li4SiO4 via a citric acid-based sol–gel route coupled with carbon coating and its CO2 chemisorption properties. Ceram. Int. 2016, 42 (2, Part B), 2990-2999. (36) Yin, Z.; Wang, K.; Zhao, P.; Tang, X., Enhanced CO2 Chemisorption Properties of Li4SO4, Using a Water Hydration-Calcination Technique. Ind. Eng. Chem. Res. 2016, 55 (4), 1142-1146. (37) Ida, J. i.; Lin, Y. S., Mechanism of High-Temperature CO2 Sorption on Lithium Zirconate. Environ. Sci. Technol. 2003, 37 (9), 1999-2004. (38) Zhang, Q.; Han, D. Y.; Liu, Y.; Ye, Q.; Zhu, Z. B., Analysis of CO2 Sorption/Desorption Kinetic Behaviors and Reaction Mechanisms on Li4SiO4. AlChE J. 2013, 59 (3), 901-911. (39) Seggiani, M.; Puccini, M.; Vitolo, S., High-temperature and low concentration CO2 sorption on Li4SiO4 based sorbents: Study of the used silica and doping method effects. Int. J. Greenhouse Gas Control 2011, 5 (4), 741-748. (40) K. Essaki; Kato, M., Influence of temperature and CO2 concentration on the CO2 absorption properties of lithium silicate pellets. J. Mater. Sci. 2005, 40, 5017-5019. (41) Zhang, Q.; Shen, C.; Zhang, S.; Wu, Y., Steam methane reforming reaction enhanced by a novel K2CO3-Doped Li4SiO4 sorbent: Investigations on the sorbent and catalyst coupling behaviors and sorbent regeneration strategy. Int. J. Hydrogen Energy 2016, 41 (8), 4831-4842. (42) Seggiani, M.; Puccini, M.; Vitolo, S., Alkali promoted lithium orthosilicate for CO2 capture at high temperature and low concentration. Int. J. Greenhouse Gas Control 2013, 17, 25-31. (43) Yang, X.; Liu, W.; Sun, J.; Hu, Y.; Wang, W.; Chen, H.; Zhang, Y.; Li, X.; Xu, M., Alkali-Doped Lithium Orthosilicate Sorbents for Carbon Dioxide Capture. Chemsuschem 2016, 9 (17), 2480-2487. (44) Subha, P. V.; Nair, B. N.; Mohamed, A. P.; Anilkumar, G. M.; Warrier, K. G. K.; Yamaguchi, T.; Hareesh, U. S., Morphologically and compositionally tuned lithium silicate nanorods as 18


Page 18 of 36

Page 19 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

high-performance carbon dioxide sorbents. J. Mater. Chem. A 2016, 4 (43), 16928-16935. (45) Zhang, S.; Zhang, Q.; Wang, H.; Ni, Y.; Zhu, Z., Absorption behaviors study on doped Li4SiO4 under a humidified atmosphere with low CO2 concentration. Int. J. Hydrogen Energy 2014, 39 (31), 17913-17920. (46) Ortiz-Landeros, J.; Martinez-dlCruz, L.; Gomez-Yanez, C.; Pfeiffer, H., Towards understanding the thermoanalysis of water sorption on lithium orthosilicate (Li4SiO4). Thermochim. Acta 2011, 515 (1-2), 73-78. (47) Meja-Trejo, V. L.; Fregoso-Israel, E.; Pfeiffer, H., Textural, Structural, and CO2 Chemisorption Effects Produced on the Lithium Orthosilicate by Its Doping with Sodium (Li4-xNaxSiO4). Chem. Mater. 2008, 20 (22), 7171-7176. (48) Drebushchak, V. A.; Ogienko, A. G.; Yunoshev, A. S., Metastable eutectic melting in the NaCl-H2O system. Thermochim. Acta 2017, 647, 94-100. (49) Radvanyi, E.; De Vito, E.; Porcher, W.; Larbi, S. J. S., An XPS/AES comparative study of the surface behaviour of nano-silicon anodes for Li-ion batteries. J. Anal. At. Spectrom. 2014, 29 (6), 1120-1131. (50) Verdier, S.; El Ouatani, L.; Dedryvere, R.; Bonhomme, F.; Biensan, P.; Gonbeau, D., XPS study on Al2O3- and AlPO4-coated LiCoO2 cathode material for high-capacity li ion batteries. J. Electrochem. Soc. 2007, 154 (12), A1088-A1099. (51) Nordlinder, S.; Augustsson, A.; Schmitt, T.; Guo, J. H.; Duda, L. C.; Nordgren, J.; Gustafsson, T.; Edstrom, K., Redox Behavior of vanadium oxide nanotubes as studied by X-ray photoelectron spectroscopy and soft X-ray absorption spectroscopy. Chem. Mater. 2003, 15 (16), 3227-3232. (52) Philippe, B.; Dedryvere, R.; Allouche, J.; Lindgren, F.; Gorgoi, M.; Rensmo, H.; Gonbeau, D.; Edstrom, K., Nanosilicon Electrodes for Lithium-Ion Batteries: Interfacial Mechanisms Studied by Hard and Soft X-ray Photoelectron Spectroscopy. Chem. Mater. 2012, 24 (6), 1107-1115. (53) Philippe, B.; Dedryvere, R.; Gorgoi, M.; Rensmo, H.; Gonbeau, D.; Edstrom, K., Role of the LiPF6 Salt for the Long-Term Stability of Silicon Electrodes in Li-Ion Batteries - A Photoelectron Spectroscopy Study. Chem. Mater. 2013, 25 (3), 394-404.

28 29

19


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

Figure captions:

2

Figure 1. XRD patterns of the Li4SiO4 samples synthesized by different modified

3

methods. Only the peaks corresponding to phases different from Li4SiO4 were

4

labeled.

5

Figure 2. SEM images of the Li4SiO4 samples: (a) SS, (b) HC, (c) SS-3Na, and (d)

6

HC-3Na.

7

Figure 3. CO2 absorption properties of the Li4SiO4 sorbents: (a) dynamic

8

thermograms in the range of 80-800 °C and (b) isothermal analyses at 575 °C.

9

Figure 4. XRD patterns of the original and modified Li4SiO4 samples. Only the peaks

10

corresponding to phases different from Li4SiO4 were labeled.

11

Figure 5. XPS spectra of samples: (a) Li 1s spectra; (d) O 1s spectra.

12

Figure 6. SEM images of the Li4SiO4 samples: (a) HC, (b) HC-1Na, (c) HC-3Na, and

13

(d) HC-5Na.

14


15

thermograms in the range of 80-800 °C and (b) chemisorption isothermal analyses at

16

575 °C.

17

Figure 8. Comparison of XRD patterns among different samples: (a) after carbonation

18

and (b) after calcination. Only the peaks corresponding to phases different from

19

Li4SiO4 were labeled.

20

Figure 9. DSC analysis of the HC and HC-10Na samples during in the range of

21

400-800 °C in pure CO2.

22

Figure10. Kinetic analysis of two Li4SiO4 sorbents: (a) HC-3Na and (b) HC. 20


Page 20 of 36

Page 21 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

Figure 11. Eyring plots for the two different processes of chemisorption (k1) and

2

diffusion (k2) for HC and HC-3Na.

3

Figure 12. Cyclic performance of the HC-3Na sample during 10 cycles of

4

sorption/desorption.

5

Figure 13. Comparison of SEM images of the Li4SiO4 samples (a) HC-3Na and (b)

6

used HC-3Na after 10 cycles.

7 8 9

21


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2

Figure 1. XRD patterns of the Li4SiO4 samples synthesized by different modified

3

methods. Only the peaks corresponding to phases different from Li4SiO4 were

4

labeled.

5

22


Page 22 of 36

Page 23 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(a)

(b)

(c)

(d)

1

2 3

Figure 2. SEM images of the Li4SiO4 samples: (a) SS, (b) HC, (c) SS-3Na, and (d)

4

HC-3Na.

5 6

23


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(b)

(a)

1 2


3

thermograms in the range of 80-800 °C and (b) isothermal analyses at 575 °C.

24


Page 24 of 36

Page 25 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

(a)

2 3

Figure 4. XRD patterns of the original and modified Li4SiO4 samples. Only the peaks

4

corresponding to phases different from Li4SiO4 were labeled.

5 6 7 8 9 10 11 12 13 14 15 16

25


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2

Figure 5. XPS spectra of samples: (a) Li 1s spectra; (d) O 1s spectra.

3 4 5 6 7 8 9 10 11 12 13 14

26


Page 26 of 36

Page 27 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(a)

(b)

(c)

(d)

1

2 3

Figure 6. SEM images of the Li4SiO4 samples: (a) HC, (b) HC-1Na, (c) HC-3Na, and

4

(d) HC-5Na.

5 6

27


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

(b)

1 2


3

thermograms in the range of 80-800 °C and (b) chemisorption isothermal analyses at

4

575 °C.

5

28


Page 28 of 36

Page 29 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1 2

Figure 8. Comparison of XRD patterns among different samples: (a) after carbonation

3

and

4

Li4SiO4 were labeled.

(b) after calcination. Only the peaks corresponding to phases different from

5 6 7 8 9 10 11 12 13 14 15 16

29


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2 3

Figure 9. DSC analysis of the HC and HC-10Na samples during in the range of 400-800 °C in pure CO2.

4 5 6

30


Page 30 of 36

Page 31 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(b)

(a)

1 2

Figure 10. Kinetic analysis of two Li4SiO4 sorbents: (a) HC-3Na and (b) HC.

3

31


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2

Figure 11. Eyring plots for the two different processes of chemisorption (k1) and

3

diffusion (k2) for HC and HC-3Na.

4

32


Page 32 of 36

Page 33 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1 2

Figure 12. Cyclic performance of the HC-3Na sample during 10 cycles of

3

sorption/desorption.

4 5

33


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

(b)

1 2

Figure 13. Comparison of SEM images of the Li4SiO4 samples (a) HC-3Na and (b)

3

used HC-3Na after 10 cycles.

4 5

34


Page 34 of 36

Page 35 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1

Table 1. Comparing the absorption performance of doped-Li4SiO4 sorbents from

2

published literature Temperature (°C)

Ref.

60

600

[42]

15

120

550

[43]

15

120

550

[43]

Dopants

Amount (wt.%)

Uptake (wt.%)

CO2 concentration (vol.%)

Alkali carbonates

~16.7

~30

15

Na2CO3

10

~30

K2CO3

5

~28

Time (min)

3 4

5 6

Table 2. N2 adsorption results of the Li4SiO4 sorbents Samples

Surface area (m2/g)

Pore volume (cm3/g)

Pore diameter (nm)

HC HC-1Na HC-3Na HC-5Na

1.56 2.13 2.61 2.79

9.78×10-3 1.47×10-2 1.48×10-2 1.51×10-2

5.56 5.53 5.49 5.43

Table 3. Kinetic parameters obtained from the isotherms of HC sorbent. T [°C]

k1 [s-1]

k2 [s-1]

A

B

C

R

475 525 575

9.82×10-4 1.31×10-3 2.01×10-3

6.33×10-5 1.30×10-4 3.52×10-4

-2.15 -4.41 4.03

-13.99 -16.34 -19.07

115.83 120.02 115.18

0.9998 0.9997 0.9999

7 8

Table 4. Kinetic parameters obtained from the isotherms of HC-3Na sorbent. T [°C] 475 525 575

k1 [s-1]

k2 [s-1] -3

4.18×10 5.51×10-3 7.78×10-3

-4

2.42×10 5.19×10-4 1.54×10-3

A

B

C

R

-7.99 -8.61 16.06

-13.75 -13.81 -48.25

120.83 121.60 133.86

0.9997 0.9885 0.9994

9 10 11 35


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

Page 36 of 36

Table 5 Different stages of the absorption process. Temperature (°C) Name

575

Time (min) HC

Chemisorption

Lithium diffusion

0.5

119.5

HC-3Na

14.5

115.5

2

36


High-Capacity Li4SiO4-Based CO2 Sorbents via a Facile Hydration

Recommend Documents