Preparation of Li4SiO4 Sorbents for Carbon Dioxide Capture via a

Nov 20, 2017 - *Telephone: +86-27-87542417-8503. ... The spray-dried sorbents exhibited both excellent CO2 capture capacity and cyclic stability durin...
0 downloads 4 Views 3MB Size
Download PDF
Article Cite This: Energy Fuels XXXX, XXX, XXX−XXX

pubs.acs.org/EF

Preparation of Li4SiO4 Sorbents for Carbon Dioxide Capture via a Spray-Drying Technique Yingchao Hu, Wenqiang Liu,* Zijian Zhou, and Yuandong Yang State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, Hubei 430074, People’s Republic of China ABSTRACT: Various synthesis methods, such as the combustion method, sol−gel method, impregnated suspension, precipitation, etc., have been previously proposed for the production of efficient Li4SiO4 sorbents. During these methods, the mixture of the precursors of Li and Si were usually dried through the oven, water bath, or oil bath, which are all energyconsuming and slow processes. To produce Li4SiO4 sorbents quickly and efficiently, the spray-drying technique was employed in this work. The spray-dried sorbents exhibited both excellent CO2 capture capacity and cyclic stability during the multiple cycles, indicating that the spray-drying method was effective for the preparation of efficient and durable Li4SiO4 sorbents for hightemperature CO2 removal. Especially, the sorbent using lithium tartrate as the Li source achieved a considerable first-cycle CO2 sorption capacity of ∼0.275 g of CO2/g of sorbent and still held the capacity of ∼0.248 at the 50th sorption/desorption cycle under the realistically low CO2 concentration of 15 vol %. The excellent performance of the sorbent was demonstrated to be attributed to the corresponding small crystallite size of Li4SiO4, high surface area, large pore volume, and rich porosity.

1. INTRODUCTION Global warming has gained worldwide attention, and since the 1950s, many unpredicted changes have been observed, including a warming atmosphere and ocean, diminishing amounts of snow and ice, and a rising sea level.1 These observed changes are believed to be closely related to the warming of the climate system. As a major anthropogenic greenhouse gas contributing to global warming, atmospheric carbon dioxide (CO2) has been rapidly enriched and reaches a high concentration of 407 ppm currently.2 CO2 derived from the burning of fossil fuels, especially coal combustion, which has produced various pollutions, such as harmful gases, particulate matter, and trace element pollutions,3−5 accounts for a considerable part of global warming. Therefore, postcombustion capture (PCC), as one of the technologies of carbon capture and sequestration (CCS), has been recognized as a promising approach to control the emission of CO2 into the atmosphere.6−11 Among the high-temperature PCC sorbents, Li4SiO4 is an excellent candidate for CO2 capture as a result of its sorption rate, sequestration capacity, cyclic durability, and wide sorption temperature.12−15 CO2 capture based on Li4SiO4 sorbents follows the reversible reaction: Li4SiO4 + CO2 ↔ Li2CO3 + Li2SiO3. In a typical Li4SiO4 looping system for CO2 removal, Li4SiO4 sorbents circulate between the sorption reactor and desorption reactor. An industrial exhaust gas stream containing CO2 (i.e., flue gas from a coal-fired power plant) flows through the sorption reactor, and CO2 is fixed by Li4SiO4 sorbents; thus, the gas stream free of CO2 is exhausted from the sorption reactor. The carbonated sorbents are circulated to the desorption reactor for regeneration. As a consequence, a high concentration of CO2 could be achieved in the outlet of the desorption reactor for the subsequent compression and sequestration. The regenerated sorbents are sent back to the sorption reactor for another cycle. Obviously, the CO2 sorption performance (such as the sorption rate, capacity, stability, etc.) of Li4SiO4 sorbents plays a key role © XXXX American Chemical Society

to the looping system. Hence, for efficient CO2 removal, it is crucial to prepare Li4SiO4 with excellent sorption performance. In the previous literature, Li4SiO4 sorbents were conventionally synthesized via the basic solid-state reaction: 2Li2CO3 + SiO2 → Li4SiO4 + 2CO2, directly using Li2CO3 and SiO2 or other Si sources (e.g., diatomite, rice husk ash, and fly ash16−18). However, the Li4SiO4 powder derived this way usually presents poor microstructures with a low specific surface area and barren porosity.19 To overcome these problems, many other synthesis methods, including the combustion method, sol−gel method, impregnated suspension, precipitation, etc.,19−27 were employed. Most of these methods are able to produce Li4SiO4 sorbents with improved microstructures and better CO2 sorption performance compared to the sorbents from the solid-state reaction method. The general steps for most of these synthesis methods include four steps: (i) mixing the Li and Si sources with water or other solvents, (ii) using different approaches (e.g., physical stirring and ultrasonic agitation) to improve the dispersion of Li and Si sources, (iii) drying and evaporating the solution, suspension, or slurry, and (iv) calcining the dried powder to produce the final sorbents. The drying and evaporation step in the literature was usually achieved via an oven, water bath, or oil bath that is an energy-consuming and slow process. For example, during the water-based sol−gel approach, the formed gel was dried at 150 °C for 24 h to form a dry mixture of precursors.22,26 In the course of preparing Li4SiO4 sorbents via an impregnated suspension method,19 the precursor suspension was evaporated through the 100 °C oil bath until the dried Special Issue: 6th Sino-Australian Symposium on Advanced Coal and Biomass Utilisation Technologies Received: October 10, 2017 Revised: November 20, 2017 Published: November 20, 2017 A

DOI: 10.1021/acs.energyfuels.7b03051 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels

Figure 1. Schematic diagram of the spray-drying process. dryer (QFN-ZL-2). Finally, the dried powder was calcined at 900 °C in air for 4 h, and the ultimate Li4SiO4 powder was obtained after grinding and sieving (150−200 μm). The schematic diagram of the spray-drying process is shown in Figure 1. The suspension was pumped by a peristaltic pump and atomized though a two-fluid nozzle operated by the compressed air. The atomized droplets were quickly dried when contacting the hot air, forming the dried powder that was further separated and collected in the cyclone. The main operation parameters are an inlet temperature of 180 °C, a pumping rate of 24 mL/min, and a one-nozzle air injection of ∼10 L/min. The final sorbents were named LT, LB, and LA, representing the sorbents produced using the Li sources of lithium tartrate, lithium benzoate, and lithium acetate dehydrate, respectively. 2.2. CO2 Sorption Performance Tests. A ∼15 mg sample was employed for the CO2 sorption performance tests in a thermogravimetric analyzer (TGA, Pyris 1, PerkinElmer). Sorption was performed in the presence of 15 vol % CO2 at 550 °C (450, 500, and 600 °C), and desorption was conducted under pure N2 at 700 °C. The temperature ramp is set at 15 °C/min, and the total flow rate of the gas is 100 mL/min. The CO2 sorption capacity was characterized by Cn (grams of CO2 per gram of sorbent), as defined in eq 1

mixture was obtained. Besides, a concentration process at 120 °C by a hot plate was needed for the synthesis of Li4SiO4 sorbents via a glycine-assisted solution combustion technique.25 These drying methods are easily accessible and manageable in the laboratory but not suitable for the commercial production of Li4SiO4 sorbents as a result of the great time and energy consumption. Hence, it is necessary to reduce the energy consumption and increase the drying rate for these synthesis methods. The spray-drying technique, which is an industrial-scale method of rapid drying to transform solution, suspension, or slurry to dry powders, has already been widely applied in the food and pharmaceutical industries.28,29 During the spraydrying process, the solution, suspension, or slurry is pumped into a spray dryer, atomized by a nozzle with compressed air, and then quickly evaporated to form a dry powder in the hot chamber. The whole process is very fast and much more efficient than the conventional oven-drying, water bath, and oil bath processes. However, thus far, the application of the spraydrying technique to produce Li4SiO4 powder has received limited attention. The main objective of this study is to investigate whether the spray-drying technique is applicable to produce Li4SiO4 with excellent performance for high-temperature CO2 removal.

Cn =

mCO2 m0

(1)

where Cn represents the mass of captured CO2 for per gram of sorbent at the end of the sorption process, mCO2 is the mass of captured CO2, and m0 means the initial mass of the sorbents. 2.3. Characterization Techniques. The phase compositions of the prepared sorbents are examined using PANalytical B.V. Empyrean X-ray diffraction equipped with a copper target with Cu Kα radiation (λ = 0.1542 nm). The specific surface area and pore size distributions were calculated by Brunauer−Emmett−Teller (BET) and Barrett− Joyner−Halenda (BJH) equations based on the N2 adsorption− desorption isotherms at 77 K using an accelerated surface area and porosimetry apparatus (ASAP2460, Micromeritics). In addition, the field emission scanning electron microscopy (FSEM, Nova NanoSEM 450, FEI, Inc.) was employed to observe the micromorphology of the sorbents.

2. EXPERIMENTAL SECTION 2.1. Materials and Sorbent Preparation. Three organic lithium precursors, including lithium tartrate (C4H4Li2O6, ≥99.0%, Adamas Reagent), lithium benzoate (C7H5LiO2, ≥99.0%, Aladdin), and lithium acetate dehydrate (C2H3O2Li·2H2O, ≥99.0%, Sinopharm), were selected as Li sources, and SiO2 sol (30%, Guangzhou Huixin Chemical Co., Ltd.) was used as the Si source. A predetermined amount of lithium precursor was first dissolved in deionized water, and then SiO2 sol was added to the solution to form a suspension. The molar ratio of Li/Si was controlled at 4.2:1. Subsequently, the formed suspension was quickly dried via a spray B

DOI: 10.1021/acs.energyfuels.7b03051 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels

3. RESULTS AND DISCUSSION 3.1. Analysis of the Prepared Sorbents. The phase compositions of the prepared sorbents were analyzed through the XRD curves, as shown in Figure 2. The results indicate that,

Figure 3. Pore size distributions of the prepared sorbents.

population of mesopores within 2−3 nm, while the distribution peaks of LA are mainly centered at larger pores (i.e., 4, 7, and 10 nm). In combination with the aforementioned surface area and pore volume of the sorbents, it seems that smaller pores contribute more to the specific surface area as well as the pore volume. In addition, the FSEM micromorphology of the fresh sorbents in Figure 4 also demonstrates that LT exhibits more porous structures than LB and LA. To conclude, the spray-dried Li4SiO4 sorbents employing different Li sources exhibit different characteristics. Among the prepared sorbents, the sorbent derived from LT shows the smallest crystallite size of Li4SiO4, highest BET surface area, largest pore volume, and richest porosity, but LA shows the opposite characteristics. Smaller grains and higher surface area and pore volume mean larger contact areas, which could greatly promote the proceeding of the sorption reaction. Besides, more porous morphology and richer porosity are also beneficial for CO2 molecules to diffuse into the internal part of the sorbent particles to react with Li4SiO4. 3.2. Optimization of the Operation Temperatures. The sorbents were subjected to the temperature-programmed sorption/desorption tests to determine the optimal sorption and desorption temperatures. The sorbents were heated from room temperature to 800 °C under a 15 vol % CO2 atmosphere at a ramp of 5 °C/min. It can be seen from Figure 5 that LT begins to sorb CO2 at ∼200 °C and then the sorption rate becomes much faster from ∼350 °C. The sorption for LB and LA begins at ∼350 °C, and all of the sorbents are regenerated beyond ∼560 °C. Therefore, the desorption temperature for the cyclic tests is selected at 700 °C, at which the carbonated sorbents could be fully regenerated. To find out the optimal sorption temperature, the sorbents were kept at 450, 500, 550, and 600 °C for isothermal sorption. Besides, the temperatureprogrammed sorption/desorption curves are also useful for the comparison of the sorption rates and capacity of the sorbents.30 It is clear to observe from Figure 5 that, under the same temperature-programmed conditions, LT apparently exhibits a faster sorption rate and higher sorption capacity. As for LB and LA, the initial sorption rate of LA is faster but soon surpassed by that of LB. A deeper comparison of kinetics and capacity was conducted in the subsequent discussions. Figure 6 gives the isothermal sorption performance of the sorbents at different sorption temperatures of 450, 500, 550, and 600 °C. As expected, no obvious sorption could be observed for all of the sorbents at 600 °C, where the desorption reaction dominates, as seen from Figure 5. The isotherms are mainly composed of two stages, a fast-increase stage followed by a slow stage, which is a typical phenomenon for gas−solid

Figure 2. XRD curves of the prepared sorbents.

within the 2θ range of 15−65°, the diffraction peaks assigned to Li4SiO4 were detected for all of the prepared sorbents, while the phase of Li2SiO3 was observed for LT, LB, and LA probably as a result of the uneven dispersion of Li and Si during the spraydrying process. On the basis of the XRD patterns, the crystallite size of Li4SiO4, which plays an important role in the gas−solid reaction, was calculated via the Scherrer equation as follows: D=

Kλ β cos θ

(2)

where D is the crystallite size of Li4SiO4 and K, λ, β, and θ mean the Scherrer constant, X-ray wavelength, full width at half maximum (fwhm), and Bragg angle, respectively. The results of the crystallite size are given in Table 1, and it is clear to see that the crystallite sizes of Li4SiO4 for these three Table 1. Crystallite Size of Li4SiO4, Specific BET Surface Area, and Pore Volume of the Sorbents sorbent

crystallite size of Li4SiO4 (nm)

surface area (m2/g)

pore volume (cm3/g)

LT LB LA

46.99 59.56 64.62

4.68 2.33 1.40

0.010 0.007 0.002

sorbents are of nanoscale. The crystallite size of Li4SiO4 for LT is 46.99 nm, while it is increased to 59.56 and 64.62 nm for LB and LA, respectively. The crystallite size exerts an important influence on the contact areas for the sorbents and CO2, which can be reflected in the specific surface area (see Table 1). The sorbent using LT as the Li source exhibits the highest BET surface area of 4.68 m2/g. For LB, the surface area is about 2.33, but the surface area of LA is only 1.40 m2/g. Similarly, LT possesses the largest pore volume of 0.010 cm3/g, whereas LA exhibits the smallest pore volume. It is generally accepted that the sorbent with a smaller crystallite size and larger surface area (also pore volume) for the gas−solid reaction probably exhibits better CO2 sorption performance. The pore size distributions of the sorbents, as presented in Figure 3, indicate that LT displays a bimodal distribution pattern, and the pore sizes of LB and LA are of trimodal distributions. It is obvious that LT and LB have a high C

DOI: 10.1021/acs.energyfuels.7b03051 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels

Figure 4. FSEM micromorphology of fresh (a) LT, (b) LB, and (c) LA.

also clear to see that, at the end of the 120 min isothermal sorption, every sorbent tested at 550 °C possesses the highest CO2 sorption capacity and the sorbents at 500 and 450 °C take the second and third places, respectively. With regard to the sorption kinetics, the sorbents at lower temperatures (i.e., 450 and 500 °C) present relatively faster sorption rates than themselves tested at 550 °C at the beginning of the isothermal sorption, but soon the rates at 450 and 500 °C are surpassed by that at 550 °C. In general, 550 °C is a better sorption temperature than the other selected test temperatures for the current spray-dried Li4SiO4 sorbents. To directly compare the performance of the different sorbents, the isotherms at 550 °C for the sorbents are plotted in the last image of Figure 6. It can be seen that LT stands out among the tested sorbents in both the kinetics and capacity, which is mainly due to its smallest crystallite size, highest surface area, and richest porosity. In addition, the initial sorption rate of LA is faster than that of LB, whereas LB exhibits the higher capacity after 120 min of sorption. To summarize, for the efficient CO2 sorption, 550 and 700 °C are designed as the sorption and regeneration temperatures, respectively, for the subsequent cyclic CO2 sorption/desorption tests.

Figure 5. Temperature-programmed sorption/desorption tests for the sorbents (15 vol % CO2 and 5 °C/min).

reaction. The sorption occurs immediately when CO 2 molecules reach the surface of the sorbent particle, corresponding to the chemical-reaction-controlled stage (fast-increase stage). Then, the diffusion of CO2 through the product layer that is previously formed during the chemical-reactioncontrolled stage plays the dominant role, leading to the decrease of sorption rates in the diffusion-controlled stage. It is

Figure 6. Isothermal sorption performance at different temperatures under 15 vol % CO2. D

DOI: 10.1021/acs.energyfuels.7b03051 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels

Figure 7. CO2 sorption capacity of multiple sorption/desorption cycles for the spray-dried sorbents (sorption, 550 °C, 30 min, and 15 vol % CO2; desorption: 700 °C, 10 min, and N2).

Figure 8. Performance of LT during the extended operation cycles (sorption, 550 °C, 30 min, and 15 vol % CO2; desorption, 700 °C, 10 min, and N2).

3.3. Multiple Sorption/Desorption Tests. To be practically applied for high-temperature CO2 removal, Li4SiO4 sorbents are required to possess good reactivity during multiple sorption/desorption cycles, which is one of the key criteria to evaluate the performance of CO2 sorbents. Hence, the cyclic CO2 sorption performance of the sorbents was tested with 30 min of sorption under 15 vol % CO2 at 550 °C and 10 min of desorption under pure N2 at 700 °C. It is observed from Figure 7 that LT shows the first-cycle capacity of as high as 0.274 g of CO2/g of sorbent, almost stabilizing in the next cycle. The capacity of LB and LA increases with cycles at first and then becomes stable, remaining at 0.251 and 0.215 g of CO2/g of sorbent after 20 cycles, respectively. Figure 7 also summarizes the 30 min sorption capacity of the three sorbents. It is obvious that the spray-dried Li4SiO4 sorbent using LT as the Li source exhibits the highest CO2 sorption capacity during the multiple cycles compared to the other sorbents. Furthermore, the LBderived sorbent also presents good cyclic CO2 sorption performance, while LA as the Li source performs not as well

as LB. The overall CO2 sorption performance of the prepared sorbents is in the following sequence: LT > LB > LA, as expected, the ranking of which is the same as those of specific BET surface area and pore volume and is contrary to that of the crystallite size characterized in the previous section. Besides, the overall cyclic performance is also positively related to the richness of the porosity of the sorbents as observed from the pore size distributions and FSEM micromorphology (Figures 3 and 4). This suggests that decreasing the crystallite size of Li4SiO4, enhancing the surface area and pore volume of the sorbents, and enriching the porosity are effective approaches to promote the CO2 sorption performance of Li4SiO4 sorbents. The cyclic stability during the long series of sorption/ desorption cycles is significant for an excellent sorbent because good stability means less replenishment of fresh sorbents into the looping systems. Therefore, extended operation cycles were conducted for the selected sorbent (LT) to identify the stability, and the results are provided in Figure 8. It is shown that the CO2 sorption capacity of LT at the first cycle reaches E

DOI: 10.1021/acs.energyfuels.7b03051 Energy Fuels XXXX, XXX, XXX−XXX

Energy & Fuels

■

∼0.275 g of CO2/g of sorbent and almost stabilizes during the first 20 cycles. Then, the capacity slowly decays with the increase of cycle numbers, still remaining at a high level of ∼0.248 g of CO2/g of sorbent over a long series of 50 sorption/ desorption cycles. This implies that the spray-dried Li4SiO4 sorbent, using LT as the Li source, owns good stability during the multiple cycles. The capacity of the currently spray-dried sorbent is comparable to that of the Li4SiO4 sorbent using similar raw materials but different drying methods in the previous literature.19 Besides, the variations of the sorption rates during the long cycles were also compared, as shown in Figure 9. It is seen that, with the increase of the cycle number,

ACKNOWLEDGMENTS This study was funded by the National Natural Science Foundation of China (Grant 51776083). The support from the Analytical and Testing Center at the Huazhong University of Science and Technology is sincerely acknowledged.

■

REFERENCES

(1) Pachauri, R. K.; Allen, M. R.; Barros, V. R.; Broome, J.; Cramer, W.; Christ, R.; Church, J. A.; Clarke, L.; Dahe, Q.; Dasgupta, P. Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change; Intergovernmental Panel on Climate Change (IPCC): Geneva, Switzerland, 2014. (2) Global Monitoring Division (GMD), Earth System Research Laboratory (ESRL), National Oceanic and Atmospheric Administration (NOAA). Trends in Atmospheric Carbon Dioxide: Globally Averaged Marine Surface Monthly Mean Data; GMD, ESRL, NOAA: Boulder, CO, 2017; http://www.esrl.noaa.gov/gmd/ccgg/trends/ global.html (accessed Aug 17, 2017). (3) Xu, M.; Yu, D.; Yao, H.; Liu, X.; Qiao, Y. Coal combustiongenerated aerosols: Formation and properties. Proc. Combust. Inst. 2011, 33 (1), 1681−1697. (4) Luo, G.; Yao, H.; Xu, M.; Gupta, R.; Xu, Z. Identifying modes of occurrence of mercury in coal by temperature programmed pyrolysis. Proc. Combust. Inst. 2011, 33 (2), 2763−2769. (5) Xu, M.; Qiao, Y.; Zheng, C.; Li, L.; Liu, J. Modeling of homogeneous mercury speciation using detailed chemical kinetics. Combust. Flame 2003, 132 (1−2), 208−218. (6) Samanta, A.; Zhao, A.; Shimizu, G. K. H.; Sarkar, P.; Gupta, R. Post-combustion CO2 capture using solid sorbents: A review. Ind. Eng. Chem. Res. 2012, 51 (4), 1438−1463. (7) Hu, Y.; Liu, W.; Sun, J.; Yang, X.; Zhou, Z.; Zhang, Y.; Xu, M. High temperature CO2 capture on novel Yb2O3-supported CaO-based sorbents. Energy Fuels 2016, 30 (8), 6606−6613. (8) 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. (9) Hu, Y.; Liu, W.; Wang, W.; Sun, J.; Yang, X.; Chen, H.; Xu, M. Investigation of novel naturally occurring manganocalcite for CO2 capture under oxy-fuel calcination. Chem. Eng. J. 2016, 296, 412−419. (10) Hu, Y.; Liu, W.; Chen, H.; Zhou, Z.; Wang, W.; Sun, J.; Yang, X.; Li, X.; Xu, M. Screening of inert solid supports for CaO-based sorbents for high temperature CO2 capture. Fuel 2016, 181, 199−206. (11) Hu, Y.; Liu, W.; Sun, J.; Li, M.; Yang, X.; Zhang, Y.; Liu, X.; Xu, M. Structurally improved CaO-based sorbent by organic acids for high temperature CO2 capture. Fuel 2016, 167, 17−24. (12) 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. (13) Kato, M.; Yoshikawa, S.; Nakagawa, K. Carbon dioxide absorption by lithium orthosilicate in a wide range of temperature and carbon dioxide concentrations. J. Mater. Sci. Lett. 2002, 21 (6), 485−487. (14) Wang, K.; Zhou, Z.; Zhao, P.; Yin, Z.; Su, Z.; Sun, J. Molten sodium-fluoride-promoted high-performance Li4SiO4-based CO2 sorbents at low CO2 concentrations. Appl. Energy 2017, 204, 403−412. (15) Wang, K.; Yin, Z.; Zhao, P.; Zhou, Z.; Su, Z.; Sun, J. Development of metallic element-stabilized Li4SiO4 sorbents for cyclic CO2 capture. Int. J. Hydrogen Energy 2017, 42 (7), 4224−4232. (16) 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. (17) Wang, K.; Guo, X.; Zhao, P.; Wang, F.; Zheng, C. High temperature capture of CO2 on lithium-based sorbents from rice husk ash. J. Hazard. Mater. 2011, 189 (1−2), 301−307.

Figure 9. CO2 sorption rates of LT at different cycles.

the fast sorption (chemical-reaction-controlled) stage lasts for a shorter time, resulting in the decrease of the sorption capacity. However, the sorbent displays similar kinetics in the first limited minutes at different cycles. Even at the 50th cycle, the CO2 sorption rate is still as fast as that of the fresh sorbent, which is of great importance for the sorbent to maintain stability over multiple cycles.

4. CONCLUSION Li4SiO4 sorbents were prepared via a spray-drying technique using different Li sources of LT, LB, and LA. The results showed that all of the sorbents exhibit excellent cyclic CO2 sorption performance. Especially, the Li4SiO4 sorbent derived from LT performed the best among the sorbents, exhibiting both high CO2 sorption capacity and good cyclic stability during the multiple sorption/desorption cycles. It is also demonstrated in this study that the small crystallite size of Li4SiO4, high specific surface area, large pore volume, and rich porosity are responsible for the outstanding CO2 sorption performance of the sorbent. The excellent performance of the spray-dried sorbent, i.e., high capacity, fast sorption rate, and good stability, indicates that the spray drying is an effective technique for the production of Li4SiO4 sorbents for efficient high-temperature CO2 removal.

■

Article

AUTHOR INFORMATION

Corresponding Author

*Telephone: +86-27-87542417-8503. Fax: +86-27-87545526. E-mail: [email protected]. ORCID

Wenqiang Liu: 0000-0002-4300-5894 Notes

The authors declare no competing financial interest. F

DOI: 10.1021/acs.energyfuels.7b03051 Energy Fuels XXXX, XXX, XXX−XXX

Article

Energy & Fuels (18) Olivares-Marín, M.; Drage, T.; Maroto-Valer, M. M. Novel lithium-based sorbents from fly ashes for CO2 capture at high temperatures. Int. J. Greenhouse Gas Control 2010, 4 (4), 623−629. (19) 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. (20) Bretado, M. E.; Guzmán Velderrain, V.; Lardizábal Gutiérrez, D.; Collins-Martínez, V.; Ortiz, A. L. A new synthesis route to Li4SiO4 as CO2 catalytic/sorbent. Catal. Today 2005, 107−108 (0), 863−867. (21) Cruz, D.; Bulbulian, S. Synthesis of Li4SiO4 by a modified combustion method. J. Am. Ceram. Soc. 2005, 88 (7), 1720−1724. (22) Wu, X.; Wen, Z.; Xu, X.; Wang, X.; Lin, J. Synthesis and characterization of Li4SiO4 nano-powders by a water-based sol−gel process. J. Nucl. Mater. 2009, 392 (3), 471−475. (23) 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. (24) Carella, E.; Hernandez, M. T. High lithium content silicates: A comparative study between four routes of synthesis. Ceram. Int. 2014, 40 (7, Part A), 9499−9508. (25) Rao, G. J.; Mazumder, R.; Bhattacharyya, S.; Chaudhuri, P. Synthesis, CO2 absorption property and densification of Li4SiO4 powder by glycine-nitrate solution combustion method and its comparison with solid state method. J. Alloys Compd. 2017, 725, 461−471. (26) 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. (27) 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. (28) Goula, A. M.; Adamopoulos, K. G. A new technique for spray drying orange juice concentrate. Innovative Food Sci. Emerging Technol. 2010, 11 (2), 342−351. (29) Chegini, G.; Ghobadian, B. Effect of spray-drying conditions on physical properties of orange juice powder. Drying Technol. 2005, 23 (3), 657−668. (30) Chowdhury, M. B. I.; Quddus, M. R.; deLasa, H. I. CO2 capture with a novel solid fluidizable sorbent: Thermodynamics and Temperature Programmed Carbonation−Decarbonation. Chem. Eng. J. 2013, 232, 139−148.

G

DOI: 10.1021/acs.energyfuels.7b03051 Energy Fuels XXXX, XXX, XXX−XXX