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Characteristics of Alkali Nitrates Molten Salt-Promoted MgO as a Moderate-Temperature CO2 Absorbent
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Energy Procedia 158 Energy Procedia 00(2019) (2017)5776–5781 000–000 www.elsevier.com/locate/procedia
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Characteristics of Alkali Nitrates Molten Salt-Promoted MgO as a The 15th Symposium on District Heating and Cooling Characteristics ofInternational Alkali Nitrates Molten Salt-Promoted MgO as a Moderate-Temperature CO2 Absorbent Moderate-Temperature CO2 Absorbent Assessing the feasibility of using the heat demand-outdoor Chao Yuaa, Jing Dingaa , Weilong Wangaa , Xiaolan Weibb Yu , Jing , Weilong Wang , Xiaolan temperatureChao function forDing a long-term district heat Wei demand forecast School of Engineering, Sun Yat-Sen University, 132 Waihuan Dong Road, Guangzhou High Education Mega Center, Guangzhou 510006, PR * *
a
a China School of Engineering, Sun Yat-Sen University, 132 Waihuan Dong Road, Guangzhou High Education Mega Center, Guangzhou 510006, PR a,b,c a a b c c b School of Chemistry and Chemical Engineering South China University of Technology, Guangzhou 510640, PR China China b School of Chemistry and Chemical Engineering South China University of Technology, Guangzhou 510640, PR China a IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Abstract
I. Andrić
*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre
Abstract The process of carbon capture and sequestration has been proposed as a method of mitigating the build-up of greenhouse gases in The atmosphere. process of carbon capture and sequestration hasmolten been proposed as a method of mitigating the build-up greenhouse in the We report several alkali nitrates salts promoted MgO-based CO2 sorbent with of superior CO2 gases capture Abstract the atmosphere. several nitrates molten salts composition, promoted MgO-based COmelting with superior CO2 nitrates capture performance overWe thatreport of neat MgO.alkali The influence of chemical loading, and temperature of alkali 2 sorbent performance that neat MgO.and Theadsorption influencetemperatures of chemical composition, loading, and melting temperatureThe of alkali was evaluated systematically. MgO nitrates sample molten salts, over and of theofcalcination on CO2 capture District heating networks are commonly addressed inwt. the %, literature one of and the evaluated most effective for decreasing the systematically. The MgO sample molten salts, andmol% of the(LiNO calcination and adsorption temperatures on COas doped with 10 m.p.135°C,Opt) another kind ofsolutions molten salt composed of 2 capture was 3-NaNO 3-KNO 3,25-62-13 greenhouse gas emissions from the%, building sector.HITEC) These require high investments which returned heat doped mol% (LiNO wt. systems %, m.p.135°C,Opt) and another kindCO ofare molten saltthrough of -KNO10 wt. m.p.142°C, was demonstrated to possess the high (up tocomposed 13.52the mmol NaNO 3-NaNO 3-KNO 3,25-62-13 3with 3-NaNO 2 (7-53-40 2 uptake sales. Due the changed climate and building policies, heatthe induring the future could decrease, wt. %,conditions m.p.142°C, HITEC) wasrenovation demonstrated toevolution possess high CO (up to 13.52 mmol NaNO and3-KNO 10.53to mmol g2−1(7-53-40 respectively). The microstructural and morphological ofdemand samples CO was g−1 3-NaNO 2 uptake 2 adsorption −1 −1 prolonging the investment return period. gstudied and by 10.53 mmol g and respectively). microstructural and morphological of samples during CO2 adsorption was XRD, FTIR, SEM. TheThe loading of alkali nitrates molten salts evolution was believed to prevent the formation of a rigid The main scope of this paper isMgO to assess the feasibility using the heatdelivery demand – outdoor function forThe heat studied XRD, FTIR, and of SEM. The loading of provide alkaliofnitrates molten salts was believed to preventCO the formation ofmelting ademand rigid MgCO layer on the surface particles and a continuous of CO32‒ totemperature promote 3 by 2 capture. forecast. Theondistrict of Alvalade, located inand Lisbon (Portugal), used as of a case The district is consisted of 665 MgCO layer the is surface MgOfactor particles provide a continuous delivery CO32‒study. to promote CO2 capture. The melting point of3 molten salts also aof crucial in the improvement of COwas 2 uptake. buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district point of molten salts is also a crucial factor in the improvement of CO2 uptake. renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were Copyright © 2018 Elsevier Ltd. All rights reserved. ©compared 2019 The Authors. Published by Elsevier Ltd. with results from a dynamic heat demand model, previously developed and validated by the authors. th International Copyright © 2018 Elsevier Ltd. All rights reserved. Conference on Applied Selection and peer-review under responsibility of the scientific committee of the 10 This an open accessthat article under the CC BY-NC-ND (http://creativecommons.org/licenses/by-nc-nd/4.0/) th International Theisresults when only weather change is license considered, the marginofof the error10could be acceptable for someon applications Conference Applied Selection andshowed peer-review under responsibility of the scientific committee Energy (ICAE2018). Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Appliedrenovation Energy. (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing Energy (ICAE2018). scenarios,MgO, the error value increasedCO up2 absorbent, to 59.5% alkali (depending on the salt, weather and renovation scenarios combination considered). Keywords: moderate-temperature, nitrates molten mechanism The value of slope coefficient increased on average within molten the range of 3.8% up to 8% per decade, that corresponds to the Keywords: MgO, moderate-temperature, CO2 absorbent, alkali nitrates salt, mechanism decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel./fax: +86-020-3933-2320;
* E-mail address: [email protected](Weilong Wang) Corresponding author. Tel./fax: +86-020-3933-2320; Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected](Weilong Wang) 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection peer-review under responsibility the scientific 1876-6102and Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018).
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.552
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1. Introduction In pre-combustion applications (gasification or natural gas reforming), moderate-temperature (200–400 °C) CO2 capture with metal oxide absorbents, notably MgO, through a gas-solid reaction is an attractive approach based on thermodynamic considerations and competitive price. However, this promise is thwarted by slow kinetics, owing to the high reaction barrier arising from the strong lattice enthalpy of the solid metal oxide and diffusion resistance from the carbonate product layer [1-3]. While its capacity in theory is quite high (24.8 mmol·g −1), it has been demonstrated that the actual uptake of CO2 by pure MgO is really low (<1 mmol·g−1) due to slow kinetic reactivity [1, 4-6]. Various techniques have been proposed to improve the CO2 uptake by MgO, several selective and reversible MgO based materials with significantly improved CO2 adsorption performance have since been reported. Molten salts have been widely used as potential heat transfer (HT) and thermal energy storage (TES) media due to their low viscosity, low vapor pressure, high heat capacity and wide working temperature range etc. Molten salt consisted of sodium nitrate and potassium nitrate (60-40 wt.%, m.p.238°C, Solar Salt) has been used successfully as a heat transfer fluid (HTS) in solar central receiver (SCR) system like Solar Two central receiver project at temperature up to 565°C, another kind of molten salt composed of NaNO3-KNO3-NaNO2 (7-53-40 wt.%, m.p.142°C, HITEC) is being considered to substitute the solar salt because of its low melting point and high operation temperature up to 454°C for long period use, or 538°C for short period[7, 8]. We used these molten salts to modify the MgO adsorbent and obtained good results. We also optimized the ratio of LiNO3-NaNO3-KNO3 (LiNO3-NaNO3KNO3, 25-62-13 wt. %, m.p.135°C，Opt) in the loading of a commercially available MgO used in the preparation of the composites. 2. Experiment Methods 2.1. Sample Preparation All the salts including sodium nitrate, potassium nitrate and lithium nitrate were bought with A.R. grade and were used as-received without any further purification or pre-preparation, among the three components, sodium nitrate and potassium nitrate were dried in an oven at 120°C for 24 h, besides, because lithium nitrate is easy to be oxidized and easy to absorb moisture from the air if dried in an oven, so it is kept in glove box separately in an atmosphere of Argon [9]. The synthesis of alkali nitrates molten salts promoted MgO-based CO2 sorbents were carried out by a reported method[10] and was divided into three steps: firstly, a certain amount of nitrates salts and MgO powder were dissolved in 150 ml methanol and magnetic stirred for an hour to ensure a homogeneous mixture, the solution was placed in an oven held at 120°C for 4h, then cooled to ambient temperature until the samples solidified to a white mass. After that, the solidified samples were ground into powder using mechanical rolling, sealed and kept in desiccators. Before CO2 adsorption, all samples need calcined in the oven at 450 °C for 4 h to eliminate the effect of CO2 and H2O in the process of synthesis. 2.2. Sample Characterization X-ray power diffraction (XRD) patterns were taken on an Empyrean X-ray diffract meter using Cu Kα radiation. The XRD diffraction patterns were taken in the 2θ range of 10-80°at a scan speed of 1.2°min−1. Infrared (IR) spectra were recorded at room temperature on an EQUINOX55 spectrometer. The morphologies of the samples were characterized using scanning electron microscopy (SEM, JSM-6330F). 2.3. Evaluation of CO2 Adsorption Capacity Thermo-gravimetric analysis （TGA）was conducted with SDTA851e thermal analyser. The performances of carbon dioxide capture at 300-375°C and 1 bar was examined on the TGA/SDTA851e by a gravimetric method. The sequence was listed in detail as follows: Initially, all samples were heated up in pure nitrogen at a heating rate of
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10 °C /min –100 °C and kept for 30 min to remove gases inside. Then the temperature increased to 450°C, sustained for 60 mins to eliminate the effect of CO2 and H2O. High purity CO2 was introduced to the chamber to conduct adsorption process at 300-375°C for 4 h. The adsorption data of 300-375°C was collected with the aim of exploring the impact of temperature on CO2 adsorption. 3. Results and Discussion 3.1. CO2 Absorption Capacity Analysis
Figure 1.1. CO2 uptake of different samples at 350°C
Figure 1.2. Adsorption ability of Opt at different temperatures
Fig. 1.1 summarizes the CO2 adsorption capacities of different sorbents at 1 bar and 350°C. Here, the proportions of the cations in the nitrates of Li-Na, Li-K and Na-K were fixed at 1:1. It shows that Opt has the largest CO2 adsorption uptake reaching 13.52mmolg-1. Fig. 1.2 illustrates the CO2 uptake performance of Opt at different temperatures. The highest uptake loading was recorded at 350°C. However, the lead time to initiate the transition to an accelerating regime was shorter and the adsorption speed was faster for lower temperatures. The sorption uptake sharply decreases to 6.9 mmolg-1 at 375°C. It can be speculated that the adsorption capacity will begin to decline when the temperature exceeds a certain value. The sorption kinetics also vary depending on temperature. 3.2. XRD and IR Analysis
Figure 2.1. XRD spectra of different samples before calcination
Figure 2.2. XRD spectra of different samples after calcination
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Figure 2.3. XRD spectra of different samples after adsorption
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Figure 2.4. FT-IR spectra of pure MgO and Opt
Figure 2.1-3 shows the X-ray diffraction (XRD) patterns of different samples. It can be seen that sorbents exhibit a distinct diffraction peak at 18.53 °, 37.98 °, 50.79 °,58.67°, 68.21° and 72.07 ° corresponding Mg (OH) 2 before calcination and 36.94°, 42.89°, 62.41°, 74.57° and 78.60°corresponding MgO after calcination respectively. The synthetic product was magnesium hydroxide mixed with alkali metal nitrates before calcination. Following calcination at 450 °C for 4 h, the magnesium hydroxide lost water to revert to MgO. The characteristic peaks of MgCO3 at 32.64°, 46.76°, 53.87°, and 78.60° are clearly observed after adsorption. Figure 2.4 shows the variations in the FT-IR spectra of pure MgO and Opt at different period. The peaks ascribed to the nitrate ion (NO3−) appeared at 1384 cm−1 and 825 cm−1[11], it is indicated that nitrate is not decomposed and does not participate in the whole process of calcining. After the reaction with CO2, three new strong peaks emerged at 1437 cm−1, 892 cm−1, and 749 cm−1, assigned to asymmetric stretch, out of plane bending, and in plane bending modes of the carbonate ion (CO 32−), indicating that the large amounts of carbonate ions were generated by the reaction with CO 2 [12-14]. 3.3. Morphology Analysis
Figure 3.1. TEM images of Opt before calcination (magnification of 25000)
Figure 3.2. TEM images of Opt after calcination(magnification of 18000)
Figure 3.3. TEM images of Opt after adsorption(magnification of 17000)
Figure 3.4. TEM images of Hitec before calcination(magnification of 18000)
Figure 3.5. TEM images of Hitec after calcination(magnification of 20000)
Figure 3.6. TEM images of Hitec after adsorption(magnification of 20000)
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To explore whether alkali nitrates molten salts promoted MgO-based CO2 sorbent synthesis successfully, the particle morphologies of the sorbents were examined via SEM at a magnification of around 20000×. Figure 3.1 and 3.4 show the sorbents are acicular and aggregation irregular with large particle size before calcination. The samples become homogeneous spherical materials, layered and stack together after calcination. The sorbents are mixture of Mg (OH) 2 and nitrate before the calcination on the basis of XRD analysis. The surface morphology of Mg (OH) 2 is related to the size of grain. Mg (OH) 2 is aggregated in a slice when the grain is large, which is a group growing together, so the particle size is very large and it is difficult to separate[15]. Following calcination at 450 °C for 4 h, the magnesium hydroxide lost water to revert to MgO. MgO is a porous spherical polymer with smaller particle size. MgO can be converted into crystal or formed MgO aggregates with sintered adhesion when the temperature of the calcination is high, forming a dead burning MgO or sintered MgO. 3.4. Relationship between Molten Salt Melting Point and Adsorption of CO2 Absorption
Figure 4.1. CO2 uptake by different samples at 350°C
Figure 4.2. CO2 uptake by different samples at 350°C
It is reported that the temperature onset for the capture of CO 2 correlates with the melting point of the molten salt[16].It can be concluded from Figure 4.1-2 that the molten salt melting point affects the rate of adsorption and has little effect on CO2 adsorption capacity. The CO2 uptake is mainly determined by the composition of molten salt. 4. Conclusions In this study, various alkali nitrates molten salts promoted MgO-based CO2 sorbents were prepared, and their absorption performances for CO2 capture were investigated profoundly. The absorption capacity and rate were dramatically influenced by chemical composition, loading, melting temperature of alkali nitrates molten salts, and the calcination and adsorption temperatures. The MgO sample doped with 10 mol% (LiNO3-NaNO3-KNO3,25-62-13 wt. %, m.p.135°C,Opt) and another kind of molten salt composed of NaNO3-KNO3-NaNO2 (7-53-40 wt. %, m.p.142°C, HITEC) was demonstrated to possess the high CO2 uptake (up to 13.52 mmol g−1 and 10.53 mmol g−1 respectively) over that of neat MgO at 350 °C. The peculiar effects of alkali metal nitrates were attributed to the presence of a high concentration of oxide ions in the molten alkali metal nitrates that restricted the formation of rigid surface layers of unidentate carbonates and facilitated the generation of carbonate ions (CO32−), resulting in the rapid formation of MgCO3 and ease of regeneration of the particles at moderate temperatures. Acknowledgements This work was supported by the funding of Science and Technology Program of Guang Zhou (201510010248), Nature Science Foundation of China (51436009), Nature Science Foundation of China (U1507113), and Science and Technology Planning Project of Guang Dong Province (2015A010106006)
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References [1] Gregg SJ, Ramsay JD. Adsorption of carbon dioxide by magnesia studied by use of infrared and isotherm measurements. Journal of the Chemical Society A Inorganic Physical Theoretical. 1970:2784-7. [2] Glasser L, Jenkins HDB. Volume-Based Thermodynamics: A Prescription for Its Application and Usage in Approximation and Prediction of Thermodynamic Data. Journal of Chemical & Engineering Data. 2010;56:874-80. [3] Drese JH, Choi S, Lively RP, Koros WJ, Fauth DJ, Gray MML, et al. Synthesis–Structure–Property Relationships for Hyperbranched Aminosilica CO2 Adsorbents. Advanced Functional Materials. 2009;19:3821-32. [4] Fagerlund J, Highfield J, Zevenhoven R. Kinetics studies on wet and dry gas–solid carbonation of MgO and Mg(OH) 2 for CO 2 sequestration. Rsc Advances. 2012;2:10380-93. [5] Beruto D, Botter R, Searcy AW. Thermodynamics of two, two-dimensional phases formed by carbon dioxide chemisorption on magnesium oxide. Journal of Physical Chemistry. 2002;91:3578-81. [6] Philipp R, Fujimoto K. FTIR spectroscopic study of carbon dioxide adsorption/desorption on magnesia/calcium oxide catalysts. Journal of Physical Chemistry. 1992;96:9035-8. [7] Herrmann U, Kelly B, Price H. Two-tank molten salt storage for parabolic trough solar power plants. Energy. 2004;29:883-93. [8] Kearney D, Herrmann U, Nava P, Kelly B, Mahoney R, Pacheco J, et al. Assessment of a Molten Salt Heat Transfer Fluid in a Parabolic Trough Solar Field. Journal of Solar Energy Engineering. 2003;125:293-9. [9] Peng Q, Yang X, Ding J, Wei X, Yang J. Design of new molten salt thermal energy storage material for solar thermal power plant. Applied Energy. 2013;112:682-9. [10] Qin Q, Wang J, Zhou T, Zheng Q, Huang L, Zhang Y, et al. Impact of organic interlayer anions on the CO 2 adsorption performance of MgAl layered double hydroxides derived mixed oxides. Journal of Energy Chemistry. 2017;26:346-53. [11] S. S. Inorganic infrared and raman spectra. Journal of Molecular Structure. 1972;15:468-9. [12] Du H, Williams CT, Ebner AD, Ritter JA. In Situ FTIR Spectroscopic Analysis of Carbonate Transformations during Adsorption and Desorption of CO2 in K-Promoted HTlc. Chemistry of Materials. 2010;22:3519-26. [13] Ito T, Kobayashi H, Tashiro T. Boles of low-coordinated surface ions in adsorption of gases on MgO. IL Nuovo Cimento D. 1997;19:1695705. [14] Adler HH. Infrared absorption frequency trends for anhydrous normal carbonates. Amer. Mineral. 1963;48. [15] Li QJ, Liu HY, Lu HF, Zheng MZ, Xie J,Chen YF. Effect of pH value on the growth of magnesium hydroxide crystals. Journal of materials science and engineering. 2007;25:609-11. [16] Deng B, Chen Z, Gao M, Song Y, Zheng K, Tang J, et al. Molten salt CO2 capture and electro-transformation (MSCC-ET) into capacitive carbon at medium temperature: effect of the electrolyte composition. Faraday discussions. 2016;190:241-58.
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Energyonline Procedia 00 (2018) 000–000 Available onlineatat www.sciencedirect.com Available www.sciencedirect.com Energy Procedia 00 (2018) 000–000
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Energy Procedia 158 Energy Procedia 00(2019) (2017)5776–5781 000–000 www.elsevier.com/locate/procedia
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Characteristics of Alkali Nitrates Molten Salt-Promoted MgO as a The 15th Symposium on District Heating and Cooling Characteristics ofInternational Alkali Nitrates Molten Salt-Promoted MgO as a Moderate-Temperature CO2 Absorbent Moderate-Temperature CO2 Absorbent Assessing the feasibility of using the heat demand-outdoor Chao Yuaa, Jing Dingaa , Weilong Wangaa , Xiaolan Weibb Yu , Jing , Weilong Wang , Xiaolan temperatureChao function forDing a long-term district heat Wei demand forecast School of Engineering, Sun Yat-Sen University, 132 Waihuan Dong Road, Guangzhou High Education Mega Center, Guangzhou 510006, PR * *
a
a China School of Engineering, Sun Yat-Sen University, 132 Waihuan Dong Road, Guangzhou High Education Mega Center, Guangzhou 510006, PR a,b,c a a b c c b School of Chemistry and Chemical Engineering South China University of Technology, Guangzhou 510640, PR China China b School of Chemistry and Chemical Engineering South China University of Technology, Guangzhou 510640, PR China a IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Abstract
I. Andrić
*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre
Abstract The process of carbon capture and sequestration has been proposed as a method of mitigating the build-up of greenhouse gases in The atmosphere. process of carbon capture and sequestration hasmolten been proposed as a method of mitigating the build-up greenhouse in the We report several alkali nitrates salts promoted MgO-based CO2 sorbent with of superior CO2 gases capture Abstract the atmosphere. several nitrates molten salts composition, promoted MgO-based COmelting with superior CO2 nitrates capture performance overWe thatreport of neat MgO.alkali The influence of chemical loading, and temperature of alkali 2 sorbent performance that neat MgO.and Theadsorption influencetemperatures of chemical composition, loading, and melting temperatureThe of alkali was evaluated systematically. MgO nitrates sample molten salts, over and of theofcalcination on CO2 capture District heating networks are commonly addressed inwt. the %, literature one of and the evaluated most effective for decreasing the systematically. The MgO sample molten salts, andmol% of the(LiNO calcination and adsorption temperatures on COas doped with 10 m.p.135°C,Opt) another kind ofsolutions molten salt composed of 2 capture was 3-NaNO 3-KNO 3,25-62-13 greenhouse gas emissions from the%, building sector.HITEC) These require high investments which returned heat doped mol% (LiNO wt. systems %, m.p.135°C,Opt) and another kindCO ofare molten saltthrough of -KNO10 wt. m.p.142°C, was demonstrated to possess the high (up tocomposed 13.52the mmol NaNO 3-NaNO 3-KNO 3,25-62-13 3with 3-NaNO 2 (7-53-40 2 uptake sales. Due the changed climate and building policies, heatthe induring the future could decrease, wt. %,conditions m.p.142°C, HITEC) wasrenovation demonstrated toevolution possess high CO (up to 13.52 mmol NaNO and3-KNO 10.53to mmol g2−1(7-53-40 respectively). The microstructural and morphological ofdemand samples CO was g−1 3-NaNO 2 uptake 2 adsorption −1 −1 prolonging the investment return period. gstudied and by 10.53 mmol g and respectively). microstructural and morphological of samples during CO2 adsorption was XRD, FTIR, SEM. TheThe loading of alkali nitrates molten salts evolution was believed to prevent the formation of a rigid The main scope of this paper isMgO to assess the feasibility using the heatdelivery demand – outdoor function forThe heat studied XRD, FTIR, and of SEM. The loading of provide alkaliofnitrates molten salts was believed to preventCO the formation ofmelting ademand rigid MgCO layer on the surface particles and a continuous of CO32‒ totemperature promote 3 by 2 capture. forecast. Theondistrict of Alvalade, located inand Lisbon (Portugal), used as of a case The district is consisted of 665 MgCO layer the is surface MgOfactor particles provide a continuous delivery CO32‒study. to promote CO2 capture. The melting point of3 molten salts also aof crucial in the improvement of COwas 2 uptake. buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district point of molten salts is also a crucial factor in the improvement of CO2 uptake. renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were Copyright © 2018 Elsevier Ltd. All rights reserved. ©compared 2019 The Authors. Published by Elsevier Ltd. with results from a dynamic heat demand model, previously developed and validated by the authors. th International Copyright © 2018 Elsevier Ltd. All rights reserved. Conference on Applied Selection and peer-review under responsibility of the scientific committee of the 10 This an open accessthat article under the CC BY-NC-ND (http://creativecommons.org/licenses/by-nc-nd/4.0/) th International Theisresults when only weather change is license considered, the marginofof the error10could be acceptable for someon applications Conference Applied Selection andshowed peer-review under responsibility of the scientific committee Energy (ICAE2018). Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Appliedrenovation Energy. (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing Energy (ICAE2018). scenarios,MgO, the error value increasedCO up2 absorbent, to 59.5% alkali (depending on the salt, weather and renovation scenarios combination considered). Keywords: moderate-temperature, nitrates molten mechanism The value of slope coefficient increased on average within molten the range of 3.8% up to 8% per decade, that corresponds to the Keywords: MgO, moderate-temperature, CO2 absorbent, alkali nitrates salt, mechanism decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel./fax: +86-020-3933-2320;
* E-mail address: [email protected](Weilong Wang) Corresponding author. Tel./fax: +86-020-3933-2320; Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected](Weilong Wang) 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection peer-review under responsibility the scientific 1876-6102and Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018).
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.552
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1. Introduction In pre-combustion applications (gasification or natural gas reforming), moderate-temperature (200–400 °C) CO2 capture with metal oxide absorbents, notably MgO, through a gas-solid reaction is an attractive approach based on thermodynamic considerations and competitive price. However, this promise is thwarted by slow kinetics, owing to the high reaction barrier arising from the strong lattice enthalpy of the solid metal oxide and diffusion resistance from the carbonate product layer [1-3]. While its capacity in theory is quite high (24.8 mmol·g −1), it has been demonstrated that the actual uptake of CO2 by pure MgO is really low (<1 mmol·g−1) due to slow kinetic reactivity [1, 4-6]. Various techniques have been proposed to improve the CO2 uptake by MgO, several selective and reversible MgO based materials with significantly improved CO2 adsorption performance have since been reported. Molten salts have been widely used as potential heat transfer (HT) and thermal energy storage (TES) media due to their low viscosity, low vapor pressure, high heat capacity and wide working temperature range etc. Molten salt consisted of sodium nitrate and potassium nitrate (60-40 wt.%, m.p.238°C, Solar Salt) has been used successfully as a heat transfer fluid (HTS) in solar central receiver (SCR) system like Solar Two central receiver project at temperature up to 565°C, another kind of molten salt composed of NaNO3-KNO3-NaNO2 (7-53-40 wt.%, m.p.142°C, HITEC) is being considered to substitute the solar salt because of its low melting point and high operation temperature up to 454°C for long period use, or 538°C for short period[7, 8]. We used these molten salts to modify the MgO adsorbent and obtained good results. We also optimized the ratio of LiNO3-NaNO3-KNO3 (LiNO3-NaNO3KNO3, 25-62-13 wt. %, m.p.135°C，Opt) in the loading of a commercially available MgO used in the preparation of the composites. 2. Experiment Methods 2.1. Sample Preparation All the salts including sodium nitrate, potassium nitrate and lithium nitrate were bought with A.R. grade and were used as-received without any further purification or pre-preparation, among the three components, sodium nitrate and potassium nitrate were dried in an oven at 120°C for 24 h, besides, because lithium nitrate is easy to be oxidized and easy to absorb moisture from the air if dried in an oven, so it is kept in glove box separately in an atmosphere of Argon [9]. The synthesis of alkali nitrates molten salts promoted MgO-based CO2 sorbents were carried out by a reported method[10] and was divided into three steps: firstly, a certain amount of nitrates salts and MgO powder were dissolved in 150 ml methanol and magnetic stirred for an hour to ensure a homogeneous mixture, the solution was placed in an oven held at 120°C for 4h, then cooled to ambient temperature until the samples solidified to a white mass. After that, the solidified samples were ground into powder using mechanical rolling, sealed and kept in desiccators. Before CO2 adsorption, all samples need calcined in the oven at 450 °C for 4 h to eliminate the effect of CO2 and H2O in the process of synthesis. 2.2. Sample Characterization X-ray power diffraction (XRD) patterns were taken on an Empyrean X-ray diffract meter using Cu Kα radiation. The XRD diffraction patterns were taken in the 2θ range of 10-80°at a scan speed of 1.2°min−1. Infrared (IR) spectra were recorded at room temperature on an EQUINOX55 spectrometer. The morphologies of the samples were characterized using scanning electron microscopy (SEM, JSM-6330F). 2.3. Evaluation of CO2 Adsorption Capacity Thermo-gravimetric analysis （TGA）was conducted with SDTA851e thermal analyser. The performances of carbon dioxide capture at 300-375°C and 1 bar was examined on the TGA/SDTA851e by a gravimetric method. The sequence was listed in detail as follows: Initially, all samples were heated up in pure nitrogen at a heating rate of
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10 °C /min –100 °C and kept for 30 min to remove gases inside. Then the temperature increased to 450°C, sustained for 60 mins to eliminate the effect of CO2 and H2O. High purity CO2 was introduced to the chamber to conduct adsorption process at 300-375°C for 4 h. The adsorption data of 300-375°C was collected with the aim of exploring the impact of temperature on CO2 adsorption. 3. Results and Discussion 3.1. CO2 Absorption Capacity Analysis
Figure 1.1. CO2 uptake of different samples at 350°C
Figure 1.2. Adsorption ability of Opt at different temperatures
Fig. 1.1 summarizes the CO2 adsorption capacities of different sorbents at 1 bar and 350°C. Here, the proportions of the cations in the nitrates of Li-Na, Li-K and Na-K were fixed at 1:1. It shows that Opt has the largest CO2 adsorption uptake reaching 13.52mmolg-1. Fig. 1.2 illustrates the CO2 uptake performance of Opt at different temperatures. The highest uptake loading was recorded at 350°C. However, the lead time to initiate the transition to an accelerating regime was shorter and the adsorption speed was faster for lower temperatures. The sorption uptake sharply decreases to 6.9 mmolg-1 at 375°C. It can be speculated that the adsorption capacity will begin to decline when the temperature exceeds a certain value. The sorption kinetics also vary depending on temperature. 3.2. XRD and IR Analysis
Figure 2.1. XRD spectra of different samples before calcination
Figure 2.2. XRD spectra of different samples after calcination
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Figure 2.3. XRD spectra of different samples after adsorption
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Figure 2.4. FT-IR spectra of pure MgO and Opt
Figure 2.1-3 shows the X-ray diffraction (XRD) patterns of different samples. It can be seen that sorbents exhibit a distinct diffraction peak at 18.53 °, 37.98 °, 50.79 °,58.67°, 68.21° and 72.07 ° corresponding Mg (OH) 2 before calcination and 36.94°, 42.89°, 62.41°, 74.57° and 78.60°corresponding MgO after calcination respectively. The synthetic product was magnesium hydroxide mixed with alkali metal nitrates before calcination. Following calcination at 450 °C for 4 h, the magnesium hydroxide lost water to revert to MgO. The characteristic peaks of MgCO3 at 32.64°, 46.76°, 53.87°, and 78.60° are clearly observed after adsorption. Figure 2.4 shows the variations in the FT-IR spectra of pure MgO and Opt at different period. The peaks ascribed to the nitrate ion (NO3−) appeared at 1384 cm−1 and 825 cm−1[11], it is indicated that nitrate is not decomposed and does not participate in the whole process of calcining. After the reaction with CO2, three new strong peaks emerged at 1437 cm−1, 892 cm−1, and 749 cm−1, assigned to asymmetric stretch, out of plane bending, and in plane bending modes of the carbonate ion (CO 32−), indicating that the large amounts of carbonate ions were generated by the reaction with CO 2 [12-14]. 3.3. Morphology Analysis
Figure 3.1. TEM images of Opt before calcination (magnification of 25000)
Figure 3.2. TEM images of Opt after calcination(magnification of 18000)
Figure 3.3. TEM images of Opt after adsorption(magnification of 17000)
Figure 3.4. TEM images of Hitec before calcination(magnification of 18000)
Figure 3.5. TEM images of Hitec after calcination(magnification of 20000)
Figure 3.6. TEM images of Hitec after adsorption(magnification of 20000)
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To explore whether alkali nitrates molten salts promoted MgO-based CO2 sorbent synthesis successfully, the particle morphologies of the sorbents were examined via SEM at a magnification of around 20000×. Figure 3.1 and 3.4 show the sorbents are acicular and aggregation irregular with large particle size before calcination. The samples become homogeneous spherical materials, layered and stack together after calcination. The sorbents are mixture of Mg (OH) 2 and nitrate before the calcination on the basis of XRD analysis. The surface morphology of Mg (OH) 2 is related to the size of grain. Mg (OH) 2 is aggregated in a slice when the grain is large, which is a group growing together, so the particle size is very large and it is difficult to separate[15]. Following calcination at 450 °C for 4 h, the magnesium hydroxide lost water to revert to MgO. MgO is a porous spherical polymer with smaller particle size. MgO can be converted into crystal or formed MgO aggregates with sintered adhesion when the temperature of the calcination is high, forming a dead burning MgO or sintered MgO. 3.4. Relationship between Molten Salt Melting Point and Adsorption of CO2 Absorption
Figure 4.1. CO2 uptake by different samples at 350°C
Figure 4.2. CO2 uptake by different samples at 350°C
It is reported that the temperature onset for the capture of CO 2 correlates with the melting point of the molten salt[16].It can be concluded from Figure 4.1-2 that the molten salt melting point affects the rate of adsorption and has little effect on CO2 adsorption capacity. The CO2 uptake is mainly determined by the composition of molten salt. 4. Conclusions In this study, various alkali nitrates molten salts promoted MgO-based CO2 sorbents were prepared, and their absorption performances for CO2 capture were investigated profoundly. The absorption capacity and rate were dramatically influenced by chemical composition, loading, melting temperature of alkali nitrates molten salts, and the calcination and adsorption temperatures. The MgO sample doped with 10 mol% (LiNO3-NaNO3-KNO3,25-62-13 wt. %, m.p.135°C,Opt) and another kind of molten salt composed of NaNO3-KNO3-NaNO2 (7-53-40 wt. %, m.p.142°C, HITEC) was demonstrated to possess the high CO2 uptake (up to 13.52 mmol g−1 and 10.53 mmol g−1 respectively) over that of neat MgO at 350 °C. The peculiar effects of alkali metal nitrates were attributed to the presence of a high concentration of oxide ions in the molten alkali metal nitrates that restricted the formation of rigid surface layers of unidentate carbonates and facilitated the generation of carbonate ions (CO32−), resulting in the rapid formation of MgCO3 and ease of regeneration of the particles at moderate temperatures. Acknowledgements This work was supported by the funding of Science and Technology Program of Guang Zhou (201510010248), Nature Science Foundation of China (51436009), Nature Science Foundation of China (U1507113), and Science and Technology Planning Project of Guang Dong Province (2015A010106006)
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References [1] Gregg SJ, Ramsay JD. Adsorption of carbon dioxide by magnesia studied by use of infrared and isotherm measurements. Journal of the Chemical Society A Inorganic Physical Theoretical. 1970:2784-7. [2] Glasser L, Jenkins HDB. Volume-Based Thermodynamics: A Prescription for Its Application and Usage in Approximation and Prediction of Thermodynamic Data. Journal of Chemical & Engineering Data. 2010;56:874-80. [3] Drese JH, Choi S, Lively RP, Koros WJ, Fauth DJ, Gray MML, et al. Synthesis–Structure–Property Relationships for Hyperbranched Aminosilica CO2 Adsorbents. Advanced Functional Materials. 2009;19:3821-32. [4] Fagerlund J, Highfield J, Zevenhoven R. Kinetics studies on wet and dry gas–solid carbonation of MgO and Mg(OH) 2 for CO 2 sequestration. Rsc Advances. 2012;2:10380-93. [5] Beruto D, Botter R, Searcy AW. Thermodynamics of two, two-dimensional phases formed by carbon dioxide chemisorption on magnesium oxide. Journal of Physical Chemistry. 2002;91:3578-81. [6] Philipp R, Fujimoto K. FTIR spectroscopic study of carbon dioxide adsorption/desorption on magnesia/calcium oxide catalysts. Journal of Physical Chemistry. 1992;96:9035-8. [7] Herrmann U, Kelly B, Price H. Two-tank molten salt storage for parabolic trough solar power plants. Energy. 2004;29:883-93. [8] Kearney D, Herrmann U, Nava P, Kelly B, Mahoney R, Pacheco J, et al. Assessment of a Molten Salt Heat Transfer Fluid in a Parabolic Trough Solar Field. Journal of Solar Energy Engineering. 2003;125:293-9. [9] Peng Q, Yang X, Ding J, Wei X, Yang J. Design of new molten salt thermal energy storage material for solar thermal power plant. Applied Energy. 2013;112:682-9. [10] Qin Q, Wang J, Zhou T, Zheng Q, Huang L, Zhang Y, et al. Impact of organic interlayer anions on the CO 2 adsorption performance of MgAl layered double hydroxides derived mixed oxides. Journal of Energy Chemistry. 2017;26:346-53. [11] S. S. Inorganic infrared and raman spectra. Journal of Molecular Structure. 1972;15:468-9. [12] Du H, Williams CT, Ebner AD, Ritter JA. In Situ FTIR Spectroscopic Analysis of Carbonate Transformations during Adsorption and Desorption of CO2 in K-Promoted HTlc. Chemistry of Materials. 2010;22:3519-26. [13] Ito T, Kobayashi H, Tashiro T. Boles of low-coordinated surface ions in adsorption of gases on MgO. IL Nuovo Cimento D. 1997;19:1695705. [14] Adler HH. Infrared absorption frequency trends for anhydrous normal carbonates. Amer. Mineral. 1963;48. [15] Li QJ, Liu HY, Lu HF, Zheng MZ, Xie J,Chen YF. Effect of pH value on the growth of magnesium hydroxide crystals. Journal of materials science and engineering. 2007;25:609-11. [16] Deng B, Chen Z, Gao M, Song Y, Zheng K, Tang J, et al. Molten salt CO2 capture and electro-transformation (MSCC-ET) into capacitive carbon at medium temperature: effect of the electrolyte composition. Faraday discussions. 2016;190:241-58.