Continuous and Simultaneous CO2 Absorption, Calcium Extraction

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Continuous and simultaneous CO2 absorption, calcium extraction and production of calcium carbonate using ammonium nitrate Min-Gu Lee, Dongwoo Kang, Yunsung Yoo, Hoyong Jo, Ho-Jun Song, and Jinwon Park Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b02880 • Publication Date (Web): 26 Oct 2016 Downloaded from http://pubs.acs.org on October 30, 2016

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Industrial & Engineering Chemistry Research

Continuous and simultaneous CO2 absorption, calcium extraction and production of calcium carbonate using ammonium nitrate Min-Gu Lee1, Dongwoo Kang1, Yunsung Yoo1, Hoyong Jo1, Ho-Jun Song3, Jinwon Park12* 1

Department of Chemical and Biomolecular Engineering Yonsei University, Seoul, Republic of Korea 2

3

National Institute of Environmental Research, Incheon, Republic of Korea

Green Manufacturing 3Rs R&D Group, Korea Institute of Industrial Technology, Ulsan, Republic of Korea

*corresponding author: [email protected] Telephone: +82-2-2123-2763 Fax: +82-2-312-6401

Abstract CCU (Carbon Capture and Utilization) technology is receiving notable attention since CCS (Carbon Capture and Storage) technology has some limitations. Using solid waste or natural minerals, CO2 capture can be achieved through the wet absorption-based CCU technology. This research proposes a new and novel process through which simultaneous and continuous carbon dioxide absorption, calcium component extraction and production of calcium carbonate salt can be achieved. Also, recycling of the absorbent can be performed without requiring a thermal desorption step. The possibility of absorbent recovery was investigated and the crystal structure of produced calcium carbonate salt was proven to be vaterite. Based on the process, 0.566 tons of carbon dioxide was reduced per ton of CaO. The precipitated salt produced by carbonation reaction was determined to be vaterite by XRD analysis and SEM image. To summarize, a continuous process using NH4NO3 is thought to have potential for application in industry.

Keywords: Carbon dioxide, Calcium carbonate, Ammonium nitrate, Ca ion extraction

ACS Paragon Plus Environment


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1. Introduction 1.1 Research Background When greenhouse gases, including carbon dioxide, PFCs (perfluorocarbons), methane, nitrous oxide, and CFCs (chlorofluorocarbons), accumulate in the atmosphere, they make it hard for the earth to release terrestrial radiation. Of the 6 types of greenhouse gases designated in the Kyoto protocol, the amount of carbon dioxide gas in the environment is massive compared to the others.1 This is the reason why many nations and researchers are trying to reduce carbon dioxide emissions although its level of contribution to global warming is lower than other greenhouse gases. One of the main causes of the enormous amount of carbon dioxide emissions into the atmosphere is the use of fossil fuels such as coal, petroleum, and gases.2,3 The best way to reduce atmospheric carbon dioxide concentration is to reduce the amount of fossil fuels used.4 However, this is extremely difficult to achieve since most industrial facilities and power plants have been designed based on the use of fossil fuels. Hence, CCS (Carbon Capture and Storage) technologies have been developed and applied in many facilities globally.2,5,6 CCS technologies can be classified into more detailed categories, but one of the most widely used technologies is the wet absorption technique, which uses a liquid absorbent to capture carbon dioxide.7 In this method, a liquid absorbent such as amine, which shows high reactivity toward gaseous carbon dioxide, captures CO2 and is saturated at absorber. This CO2-rich amine is transported to a desorber and the captured carbon dioxide is separated from the absorbent liquid at a relatively high temperature. Then, the liquid absorbent is regenerated and this is transported to absorber comprising a continuous process. A representative absorbent is monoethanolamine (MEA), which reacts with carbon dioxide gas with a high reaction rate forming carbonate and carbamate ions.1,8 This is the main concept of conventional wet absorption CCS technology. However, due to the large amount of energy required to regenerate the absorbent, the total energy consumption of the continuous absorption-desorption process is high.8-10 To solve this problem, eliminating the desorption step has been investigated by many researchers. One potential method is separating dissolved carbon dioxide by forming precipitated salts through chemical conversion.9,11 When metal ions such as calcium ions are added to the CO2-rich MEA absorbent, ionic CO2 reacts with metal ions and


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produces precipitated calcium carbonate (PCC) salts. Unlike previously stated conventional CCS technology, no desorption step is required and the precipitated calcium carbonate salt product can be utilized for various purposes such as in the cement, paper-making, and pharmaceutical industries.2,9 This is referred to as carbon capture and utilization (CCU), which has obvious merits compared to conventional CCS technology. However, one of the problems associated with CCU technology, which produces precipitated salts, is securing metal ions. For the CCU technology to be economically feasible, it is impossible to supply Ca2+ ion by mining minerals. One good alternative supply is industrial solid waste containing calcium components.12 There are many types of calcium-containing industrial solid wastes including waste concrete or cement, and steelmaking slags. However, to utilize the calcium ions contained in them, an extraction process is needed. Extraction of these wastes can be achieved by mixing them with some acidic substances.13,14 Many types of acids can be used, but if strong acids are used in the extraction step, the extracted products will also be acidic. When these extracted products are mixed with CO2-saturated absorbents, the yield of precipitated calcium carbonate salt is reduced due to the pH conditions and the potential for solution recycling is decreased. In order to avoid these problems, the extracting solvent should be weakly acidic and should not affect the absorption performance of the absorbents. Thus, a carbon capture and utilization approach considering the CO2 absorption performance, calcium ion extraction, PCC precipitation, possibility of solvent regeneration, and industrial requirements such as corrosiveness and cost should be developed.2 In this research, a 2 M ammonium nitrate solution (NH4NO3) was used as the absorbent and calcium oxide solid was assumed to be industrial waste. Calcium ions cannot be easily extracted under aqueous conditions. However, with an ammonium nitrate solution that is weakly acidic, calcium ions can be well extracted. Also, an ammonium nitrate solution mixed with calcium oxide solid is highly reactive toward carbon dioxide gas due to ammonium hydroxide formation during the absorption and precipitation steps. Also, after the precipitation step, ammonium nitrate can be recovered, which demonstrates the possibility of absorbent recycling. The detailed process mechanisms will be discussed below in the 1.2 Theoretical Background.



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1.2 Theoretical Background In Fig.1, schematic of the research including main concepts and each step were described. As seen the Fig.1, carbon dioxide capture. Ionization of the dissolved carbon dioxide, calcium ion extraction, and carbonation or carbon fixation can be achieved simultaneously using ammonia solvent. The final product was precipitated calcium carbonate and absorbent can be recycled without thermal desorption step which requires large amount of energy. Based on the Fig.1, it can be concluded that energy consumption can be greatly reduced. Simplified process were shown in fig.2. As stated above, carbon capture and utilization process considering some of important features were invented and absorbent recycle, precipitated calcium carbonate salt formation, and removing desorption step were achieved. Each and whole process are shown below: Step 1: Mixing ammonium nitrate solution with calcium oxide solid. Step 2: Carbon dioxide absorption into the solution at Step 1. Step 3: Separating precipitated calcium carbonate salt from the solution at Step 2. Step 4: Through Step 1 ~ 3, absorbent solution is regenerated and whole process is repeated.

This step notion can be shown with chemical reaction equation as follows. (Eqn. 1) 2NH4NO3(aq) + CaO(s) + H2O(l) → 2NH4OH(aq) + Ca(NO3)2(aq) (Eqn. 2) 2NH4OH(aq) + Ca(NO3)2(aq) + CO2(g) → (NH4)2CO3(aq) + Ca(NO3)2(aq) + H2O(l) (Eqn. 3) (NH4)2CO3(aq) + Ca(NO3)2(aq) → 2NH4NO3(aq) + CaCO3

As seen from Eqn. 1~3, precipitated calcium carbonate salt can be produced as well as absorbent


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regeneration without thermal desorption step can be possible. In Fig.2, simplified process is shown. Aqueous ammonium nitrate solution mixed with calcium oxide are used as absorbents. To simulate flue gas which produced from normal coal-fired power plant, 15 vol% of CO2 mixed with nitrogen gas was used. In the absorbent mixture, carbon dioxide absorption, extraction, and precipitation of final product occurred. Precipitated salts were filtrated to be analyzed. Without thermal desorption step, absorbent recycling was possible. To prove potential of this process, absorption performances and characteristics of each step and properties of precipitated calcium carbonate salts were investigated. To analyze absorption characteristics, gas analyzer was used to measure the concentration of carbon dioxide gas. And X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were used to investigate crystalline structure of PCC. Detailed methodology of experiments would be dealt in next section.

2. Experimental Section 2.1 Materials Ammonium nitrate (NH4NO3, purity >99% mass fraction) was purchased from Sigma-Aldrich and used without further purification. The concentration of aqueous ammonium nitrate solution made using deionized water was 2 M. To measure the mass of the reagent, a balance with a precision of 0.0001 g was used. Calcium oxide (CaO, purity >99.5% mass fraction) and calcium nitrate (Ca(NO3)2, purity >99% mass fraction) were purchased from Alfa-Aesar and used without further purification. All of the experiments and preparation steps were carried out at a temperature of 298.15 K.

2.2 Experimental set-up and details 2.2.1 Extraction Experiments In this research, calcium oxide solid powder was assumed to be an industrial solid waste containing calcium components such as waste concrete or cement. In order to increase the reaction yield, it is important to extract calcium components as calcium ions using an extraction solvent, which is the 2 M ammonium nitrate solution. First, a 2 M aqueous ammonium nitrate solution was prepared. Ten grams



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of calcium oxide powder was mixed with 40 g of the 2 M aqueous ammonium nitrate solution. The solid/liquid ratio (S/L ratio) of the mixture was 0.2. This S/L ratio was determined considering the viscosity of the mixture and expected extraction yield. If the viscosity of the mixture is high, it is hard to stir the mixture. On the other hand, the extraction yield or efficiency is lower when the S/L ratio is low due to the low calcium source content. At a S/L ratio of 0.2, stirring of the mixture is not difficult and the extraction yield could be higher than that with a lower S/L ratio. The mixture was stirred for 3 hours and filtered using glass fiber filter paper with a pore size of 0.7 micrometers. After filtration, the concentration of calcium ions contained in the remaining solution was measured by ICP-OES (OPTIMA 8300, Perkin Elmer).

2.2.2 Carbon Dioxide Absorption and Precipitation Experiments Fig. 3 shows a schematic of the experimental apparatus. For the absorption experiment, 15 vol% carbon dioxide gas mixed with 85 vol% nitrogen gas was used. Since most CO2-emitting industrial facilities including coal-fired power plants emit flue gas with CO2 concentrations of 10-15 vol%, 15 vol% carbon dioxide gas was mixed with 85 vol% nitrogen. To maintain the exact amount of each gas, mass flow controllers (MFCs) controlled by a mass flow management (MFM) unit were used. The flow rates of carbon dioxide and nitrogen gas were 1,852 cc/min SLM (liter per minute at the standard state of gas) and 262 SCCM (cubic centimeter per minute at the standard state of gas), respectively. Before flowing the mixed gas into the reactor, high purity nitrogen gas was used to purge impurities which may have remained in the reactor. When the mixed gas is injected into the bottom of the reactor, the absorbent solution absorbs carbon dioxide gas and remaining gas will come out through the surface of the absorbent solution. This remaining gas is transported to the gas analyzer (Gas_master, Sensoronic), which recorded concentration data. When the gas analyzer indicates that the concentration of carbon dioxide gas in the remaining gas is 15 vol%, the absorption reaction was judged to be complete. Based on our hypothesis, the possibility of absorbent regeneration after carbonation was investigated by interpreting the CO2 loading data. Meanwhile, analysis of the


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produced precipitated calcium carbonate was performed. After mixing calcium oxide powder with the aqueous ammonium nitrate solution, CO2 was bubbled into the solution. Also, stirring speed was 400 rpm to promote mass transfer. Then, precipitated calcium carbonate salt was formed. After finishing bubbling when the gas analyzer indicated that the concentration of carbon dioxide gas was 15 vol%, the precipitated salt was separated from the mixed solution using a glass fiber filter with a pore size of 0.7 micrometers. The filtrated solution was then moved back to the reactor and carbon dioxide bubbling was performed again in order to investigate solvent regeneration. All of the absorption experiments were conducted under ambient pressure at 298.15 K. The separated PCC salts were dried in a heating oven for 72 hours at a temperature of 353.15 K. The dried PCC was evaluated by SEM (JSM-7001F, Jeol) and XRD (Ultima IV, Rigaku Corp., Japan) analysis.

3. Result and Discussion 3.1 CO2 loading performance The performance of carbon dioxide absorption was investigated based on the CO2 loading curve. The concentration of the carbon dioxide contained in the gas that passed through the absorbent solution was measured by a gas analyzer. The concentration of carbon dioxide was measured every 30 seconds and the accumulated amount of CO2 was calculated by utilizing equation (4). Total CO2 loading (mol) =∑feed CO2 (mol/sec) X [(set-up CO2 gas concentration (%) – venting CO2 gas concentration (%))/15 %] X time (sec)

(Eqn.

4) As described below, steps (a), (b) and (c) were employed to develop the amounts of carbon dioxide adsorption.

(a): Curve (a) was used to investigate the CO2 absorption performance of NH4NO3 as is. As judged from the figure, a small amount of CO2 is absorbed in this step.



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(b): Curve (b) was used to investigate the CO2 absorption performance of the mixture of NH4NO3 and CaO. (c): Curve (c) was used to investigate the 2nd CO2 absorption performance of the mixture of NH4NO3 and CaO.

From curve (b), it can be indirectly stated that NH4NO3 and CaO form NH4OH and Ca(NO3)2. The amount of carbon dioxide absorbed into NH4OH is (a’). From Fig. 4, it can be determined that Ca(NO3)2 does not affect CO2 absorption when it is mixed with NH4OH due to its low absorption ability compared to NH4OH. This curve was obtained in the CO2 absorption experiment using a CaO solution with concentration of 1 M, which has the same amount of NO32- ions as the 2 M aqueous NH4NO3 solution. The amount of CO2 absorbed into 1 M Ca(NO3)2 is similar to that of water. The alpha value of CO2 absorption was 1.45 because NH4OH was produced and CO2 was absorbed in this mixture system. Compared to a 7 wt% NH4OH absorbent solution whose alpha value is 2.33, the absorption capacity was lower as it is thought that the presence of Ca(NO3)2 makes the absorbent performances lower because it is weakly acidic when dissolved in water. By comparing Fig. 4 and Fig. 5, NH4OH formation can be confirmed. After these steps, CaO was added into the solution which is saturated with carbon dioxide. As a result of CaO addition, precipitated calcium carbonate was produced and the precipitated solid was separated by filtration using glass filter paper. Also, the possibility of absorbent recycling was investigated using a filtered solution. The same amount of CaO was added to the separated absorbent solution and the CO2 absorption experiment was conducted using the same procedure. In this re-absorption experiment, the performance of CO2 absorption was similar to that of the first absorption. Also, it appeared that the loss of absorbent, which is important in absorbent recycling, was not meaningful in our experiments. In this research, the desorption step used in conventional CCS technology, which comprises 70 % of the total energy demand, was eliminated. From this point of view, a large amount of cost can be avoided compared to conventional CCS technology since this continuous process is conducted under ambient pressure and temperature conditions. Also, the produced precipitated calcium carbonate salt can improve the economic


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feasibility since it can be used for various purposes in many industries. Based on the results, this continuous process appears to have potential for application in industry and the absorption and conversion yields were also high.

3.2 Precipitation (Carbonation Yield) In this research, CaO powder was mixed with a NH4NO3 solution and carbon dioxide was bubbled into the mixture solution. In order to investigate the extraction yield of NH4NO3, CaO powder was mixed with a NH4NO3 solution and stirred for 24 hours. Using ICP-OES analysis, the ionic concentration was investigated The results are shown in Fig. 6. The extraction yield of NH4NO3 was lower than that of strong acids. However, the difference was small. Also, unlike strong acids which can affect CO2 absorption due to its higher acidity, NH4NO3 is thought to not have as strong of an impact on the absorption performance as strong acids. As shown in Table 1, the amount of carbon dioxide absorbed into 2 M NH4NO3 mixed with a 0.8 M CaO solution is expressed in terms of the number of moles of CO2. At the first absorption step, 0.5763 mol of carbon dioxide was absorbed, which is higher than values obtained with DEA and MDEA which are secondary and ternary amines, respectively. When comparing this value to that of MEA, which is a reference absorbent, similar absorption performance was obtained. Also, in order to investigate the amount of carbon fixation or carbonation, which is the purpose of this research, the conversion yield based on the amount of carbon dioxide absorbed was calculated. Equation (5) was used to calculate a conversion yield of 99.44%. Conversion yield % =

.∙

× 100

(Eqn. 5)

In other words, 0.5731 mol of absorbed carbon dioxide was converted into precipitated calcium carbonate salt, which is a satisfactory value. The amount of calcium carbonate precipitated is (b’) in Fig. 4. In the case of the carbonation reaction that occurs after CO2 absorption, a sufficient amount of reactive-state carbon dioxide was not secured compared to the amount of the added calcium component. However, for this research, carbon dioxide absorption and calcium component extraction



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occurred spontaneously and this may lead to dissolved carbon dioxide being converted into precipitated calcium carbonate salt. Considering this step and especially the amount of carbon dioxide converted to precipitated calcium carbonate salt, 0.566 ton of carbon dioxide per 1 ton of calcium oxide, which was assumed to be solid waste, was reduced through this process.

3.3 Crystal structure (XRD and SEM) Under normal conditions, calcium carbonate salt exists in the form of hexagonal β-CaCO3 (calcite). There are other types of calcium carbonate other than calcite including orthorhombic λ-CaCO3 (aragonite) and µ-CaCO3 (vaterite). Calcite and aragonite can be formed in nature and the most stable state is calcite. Due to its highest stability, calcite is prevalent in most cases as a product of a carbonation reaction. As shown Fig. 7 and Fig. 8, Based on the experiments conducted in this research, precipitated calcium carbonate salt was formed as a result of the carbonation reaction and XRD and SEM analyses were performed in order to investigate its properties. In the XRD analysis, an acceleration voltage of 40 kV was used and the 2-theta range was 20 to 80 degrees. Compared to the reference, most of the peaks indicate that the vaterite is prevalent in the final mixture. Also, in the SEM analysis, a similar result was observed. While calcite and aragonite have orthorhombic shapes, vaterite has a spherical shape. Based on the SEM images and XRD results, the crystal structure of the precipitated calcium carbonate was vaterite. This is due to abundant amount of ammonium ions in the mixture solution which makes it hard for vaterite to be turned into calcite. The cost of vaterite is higher than that of calcite and it is thus thought to have a higher value than calcite. This can improve the economic feasibility of the suggested process since cost of vaterite is higher than calcite. Also, the total energy demand or total cost can be reduced since each step is conducted under ambient pressure and temperature without demanding a high amount of energy.

Conclusion This new and novel process is suggested based on the results of this research. In order to confirm


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simultaneous extraction where absorption and precipitation are possible, CaO powder was mixed with NH4NO3 and absorption experiments were conducted. Simulation gas which is assumed exhaust gas was mixture of 15 % carbon dioxide and 85 % nitrogen gas. Compared to an ammonium hydroxide solution, which is a carbon dioxide absorbent, the performance of CO2 absorption using our system is similar. Additionally, At the first absorption step, the amount of absorption was 0.5763 mol of CO2 after extracting calcium cation from CaO. Also, in order to investigate the possibility of solvent recycling, a 2nd absorption experiment was conducted. Absorbent recycling was confirmed and its absorption performance was satisfactory. The carbon dioxide absorption capacity of the recycled absorbent was similar to that of fresh absorbent and the performance was also satisfactory compared to that of absorbent used in commercial CCS technology. A considerable amount of carbon dioxide was converted to precipitated calcium carbonate salt, 0.566 tons of carbon dioxide per ton of calcium oxide. The calcium carbonate salt produced exists in the form of vaterite, as proved by XRD and SEM analyses. In future work, real industrial solid waste will be used and the purity of precipitated calcium carbonate will be investigated.

Reference

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option. Energy 2005, 30, 2318-2333. (6) Harrison, B.; Carbon capture and sequestration versus carbon capture utilization and storage for enhanced oil recovery. Acta Geotech 2014, 9, 29-38. (7) Yang, Z. Zhen.; He, L. N.; Gao, J.; Liu, A. H.; Yu, B.; Carbon dioxide utilization with C–N bond formation: carbon dioxide capture and subsequent conversion. Energy Environ. Sci. 2012, 5 (5), 66026639. (8) Kang, D.; Park, S.; Jo, H.; Park, J.; Carbon fixation using calcium oxide by an aqueous approach at moderate conditions. Chem. Eng. J. 2014, 248, 200-207. (9) Park, S.; Lee, M.; Park, J.; CO2 (carbon dioxide) fixation by applying new chemical absorptionprecipitation methods. Energy 2013, 59, 737-742. (10) Ma, S.; Song, H.; Wang, M.; Yang, J.; Zang, B.; Research on mechanism of ammonia escaping and control in the process of CO2 capture using ammonia solution. Chem. Eng. Res. Des. 2013, 91 (7) 1327-1334. (11) Yeh, J. T.; Resnik, K. P.; Rygle, K.; Pennline, H. W.; Semi-batch absorption and regeneration studies for CO2 capture by aqueous ammonia. Fuel Process. Technol. 2005, 86, 1533-1546. (12) Sanna, A.; Dri, M.; Maroto-Valer, M.; Carbon dioxide capture and storage by pH swing aqueous mineralization using a mixture of ammonium salts and antigorite source. Fuel 2013, 114, 151-16. (13) Katsuyama, Y.; Yamasaki, A.; Iizuka, A.; Fujii, M.; Kumagai, K.; Yanagisawa, Y.; Development of a process for producing high-purity calcium carbonate (CaCO3) from waste cement using pressurized CO2. Environ Prog. 2005, 24, 162-170. (14) Wang, X.; Maroto‐Valer, M.; Integration of CO2 capture and mineral carbonation by using recyclable ammonium salts. ChemSusChem 2011, 4 (9), 1291-1300.


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ACKNOWLEDGEMENT

This work was supported by the Human Resources Program in Energy Technology of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea. (No. 20154010200810) This research was supported by Global Ph.D. Fellowship Program through the National Research Foundation

of Korea (NRF)

funded by the Ministry of Education (NRF-

2014H1A2A1021595)



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Fig 1. Schematics of the simultaneous process


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Fig 2. Simplified process map for the simultaneous process using ammonium nitrate and calcium oxide.



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Fig 3. The schematic diagram of apparatus for absorption and carbonation experiments


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Fig 4. CO2 loading curve for each step: (a) for CO2 loading into 2 M ammonium nitrate solution, (b) for 2 M ammonium nitrate mixed with 0.8 mol calcium oxide powder, (c) for 2nd absorption step after absorbent regeneration by precipitation of calcium carbonate salts.



2.5

Amount of CO2 absorbed (mol CO2 / L solution)

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CO2 loading in 2M CaO(aq) CO2 loading in 2M NH4NO3 + 0.8 mol CaO

2.0

1.5

1.0

0.5

0.0 0

50

100

150

200

Operation Time (min) Fig 5. Comparison of CO2 loading for 2 M Calcium oxide solution and 2 M ammonium nitrate solution mixed with 0.8 mol calcium oxide powder.


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2M Hydrochloric acid

2M Nitric acid

2M Ammonium nitrate

2M Ammonia solution

0

5000

10000

15000

20000

25000

Fig 6. Extraction efficiency of some ammonium salts


30000

35000


1000 Calcite Reference Vaterite Reference Aragonite Reference CaCO3 formed in 2 M NH4NO3(aq) + 0.8 mol CaO

800

600

Intensity

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400

200

0

-200 20

30

40

50

60

Fig 7. Result of XRD analysis for the precipitated salts.


70

80

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Fig 8. SEM images of the precipitated salts: (a) particles at magnitude of 1.0K, (b) a particle at magnitude of 15K.



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Table 1. The amount of CO2 absorption, desorption and conversion yield with other references. The amount of Absorbent

Calcium Source

30 wt% MEA1)

5)

The amount of 6)

Conversion

CO2 absorbed

CO2 converted

Yield7)

0.7924

0.6706

84.63

0.3983

0.1733

43.51

Note

D. Kang et 30 wt% DEA2)

20 wt% CaO(aq) 100ml

al. (2013)

30 wt% MDEA3)

0.1833

0.0322

17.56

0.5763

0.5731

99.44

This 2 M NH4NO3(aq) + 0.8 mol CaO

research

1)

400 ml of aqueous 30 wt% MEA solution was used as absorbent. 400 ml of aqueous 30 wt% DEA solution was used as absorbent. 400 ml of aqueous 30 wt% MDEA solution was used as absorbent. 4) 400 ml of aqueous 2 N NH4NO3 mixed with 0.8 mol CaO powder was used as absorbent. 5) The unit of the amount of CO2 absorbed was expressed in (mol). 6) The unit of the amount of CO2 converted was expressed in (mol). 7) The unit of conversion yield was expressed in (%). 8) 400 ml of aqueous 30 wt% MEA solution was used as absorbent. 2)


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Abstract Graphics


Continuous and Simultaneous CO2 Absorption, Calcium Extraction

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