KR20090047288A - Calcium based high temperature carbon dioxide absorbent - Google Patents

Abstract

The present invention relates to a high temperature carbon dioxide absorbent and a method for producing the same which are regenerated to absorb carbon dioxide selectively after absorbing carbon dioxide from a high temperature mixed gas in the range of 450 to 800 ^o C including carbon dioxide. . Specifically, calcium oxide (CaO) is used as a carbon dioxide absorbing active material, and calcium aluminate (Ca ₁₂ Al _{14) is used} as an additive to secure the carbon dioxide absorption capacity and the carbon dioxide diffusion path during repeated carbon dioxide absorption and regeneration of the absorbent. It relates to a high temperature carbon dioxide absorbent using O ₃₃ ) and a method for producing the same. The high temperature carbon dioxide absorbent produced by mixing, drying, heat treatment, and then hydrating, drying, and heat treatment to dissolve the precursors of calcium oxide and calcium aluminate in water to have a uniform composition has a very high absorption capacity of carbon dioxide. It is not only high, but also has excellent stability in repetitive absorption of carbon dioxide and regeneration of the absorbent. Accordingly, the present invention relates to a high temperature carbon dioxide absorbent having a high stability and high carbon dioxide absorption capacity in repeated absorption / regeneration as listed above and a method for producing the same.

Carbon dioxide, absorption, high temperature absorber, calcium oxide, calcium aluminate

Description

 Calcium based high temperature carbon dioxide absorbent

The present invention selectively absorbs carbon dioxide in a high temperature mixed gas in the range of 450 ~ 800 ^° C and then increase the temperature or wash with a gas other than carbon dioxide to remove the absorbed carbon dioxide in a state that can absorb the carbon dioxide again. It relates to a high temperature carbon dioxide absorbent to be regenerated and a method of manufacturing the same. Specifically, calcium oxide (CaO) is used as a carbon dioxide absorbing active material, and calcium aluminate (Ca ₁₂ Al _{14) is used} as an additive to secure the carbon dioxide absorption capacity and the carbon dioxide diffusion path during repeated carbon dioxide absorption and regeneration of the absorbent. It relates to a high temperature carbon dioxide absorbent using O ₃₃ ) and a method for producing the same.

The high temperature carbon dioxide absorbent is methane steam reforming reaction (CH ₄ + 2H ₂ O ↔ CO ₂ + 4H ₂ , reaction temperature 800 ~ 900 ^o C) or water gas reaction (CO + H ₂ O ↔ CO ₂ + H ₂ , reaction temperature 300 It is used together with the catalyst in the reactor at ~ 500 ^o C) to remove the carbon dioxide generated at high temperature simultaneously with the reaction, leading to the reaction equilibrium according to Le Chatelier's principle to increase the yield of the product. It can be used to produce high purity hydrogen with less energy than The process of using a reforming catalyst and a carbon dioxide selective adsorbent together in a reforming reaction to produce hydrogen from methane is called a sorption enhanced steam methane reforming process. The general reforming reaction to produce hydrogen from natural gas takes place under a nickel catalyst and the reaction mechanism is as follows.

* Steam methane reforming

CH ₄ (g) + 2H ₂ O (g) ↔ CO ₂ (g) + 4H ₂ (g) ΔH ₂₉₈ = 164.8 kJ / mol (1)

According to the principle of LeChatlier, in order to increase the yield of hydrogen in Reaction (1), the target product hydrogen is selectively permeated using a thin film of platinum to remove it from the reaction, or the partial pressure of carbon dioxide is reduced by using a CO ₂ selective absorbent. There is a way to lower it. In order to increase the yield of hydrogen by lowering the partial pressure of carbon dioxide using an absorbent, a calcium-based solid carbon dioxide absorbent is generally used. The carbon dioxide absorption reaction of calcium oxide is as follows.

* Carbon dioxide absorption reaction

CO ₂ (g) + CaO (s) ↔ CaCO ₃ (s) ΔH ₂₉₈ = -178.2 kJ / mol (2)

The carbon dioxide absorption of calcium oxide is a strong exothermic reaction and occurs rapidly in the temperature range of 450 to 800 ^o C. When reaction (1) and reaction (2) proceed simultaneously in the same space, carbon dioxide in the product of reaction (1) is solidified in the form of calcium carbonate by reaction (2). Accordingly, the equilibrium of reaction (1) is shifted in the direction of producing hydrogen and carbon dioxide, and the production yield of hydrogen during reaction (2) is significantly increased compared to the general reforming reaction. The simultaneous reaction of reaction (1) and reaction (2) is as follows.

* Water absorption reforming

CH ₄ (g) + 2H ₂ O (g) + CaO (s) ↔ 4H ₂ (g) + CaCO ₃ (s) ΔH ₂₉₈ = -13.4 kJ / mol (3)

Reaction (1) has high energy consumption due to strong endothermic reaction, but reaction (3) combined with reaction (2), which is a strong exothermic reaction, is a weak exothermic reaction. No energy is needed. In addition, it is possible to obtain a high hydrogen production rate at a lower temperature (about 450 ~ 800 ^° C) than the general steam methane reforming reaction, and has the advantage that the steam methane reforming and water gas conversion reaction can be carried out simultaneously in a single reactor. High-temperature carbon dioxide absorbers, such as calcium oxide, are reused after the carbon dioxide is absorbed and then regenerated to release carbon dioxide. At least two fixed-bed reactors are needed to continuously produce the product because of the need to continuously repeat the absorption and regeneration of carbon dioxide. And since carbon dioxide absorption reaction and regeneration is performed at high temperature (700 ~ 900 ^o C), the absorbent performance is generally lowered as the number of times of CO ₂ absorption / removal increases due to deterioration of absorbent properties due to repeated absorption / regeneration reactions. . Therefore, in order to commercialize the absorption-enriched steam reforming process, it is necessary to develop an absorbent that maintains carbon dioxide absorption performance in repeated absorption / regeneration reactions.

In general, high temperature dry carbon dioxide absorbents are in the form of metal oxides. Since carbon dioxide is an acidic gas, alkaline earth metal oxides are known to have an excellent ability to absorb carbon dioxide at high temperatures compared to other metal oxides. These metal oxides have different temperature ranges for absorbing and emitting carbon dioxide depending on the type of metal. Alkaline earth metal oxides, which absorb carbon dioxide above 450 ^o C, are typical of calcium oxide (CaO), and natural minerals containing calcium have been used for the study of high temperature carbon dioxide absorbers. Natural minerals used as high-temperature carbon dioxide absorbents include absorption enhancement using limestone (Han, C. and Harrison, DP, Chem. Eng. Sci., 1994, 49, 5875), and absorption enhancement for hydrogen production. There are many reforming reactions (Yi, KB and Harrison, DP, Ind. Eng. Chem. Res., 2004, 44, 6, 1665).

However, in the case of natural minerals, the carbon dioxide absorption capacity decreases rapidly as the number of reactions increases, which makes it difficult to apply to the actual process. In addition, sulfur compounds exist because a small amount of sulfur compounds are present in the minerals, which lowers the activity of the reforming catalyst. Expensive pretreatment for removal must be followed. Accordingly, many studies have been conducted to develop synthetic high temperature carbon dioxide absorbent which is inexpensive and has excellent performance. Lithium zirconate, lithium orthosilicate and artificial dolomite have been studied as synthetic high temperature carbon dioxide absorbents. Fan et al. Developed a calcium-based high temperature carbon dioxide absorbent and applied for a US patent in 2006 (US 2006/0093540 A1). In order to manufacture calcium oxide, Fan and the like dissolved solid calcium hydroxide in water, and then injected carbon dioxide to precipitate it in the form of calcium carbonate, which was dried and calcined again to increase the amount of carbon dioxide absorbed to the weight of calcium oxide by 70%. . This absorbent showed superior performance compared to natural calcium oxide, but it has a disadvantage in that the absorption time of carbon dioxide is continuously decreased in the carbon dioxide absorption / regeneration reaction repeated at high temperature and the absorption time must be increased to prevent this. Among the high temperature carbon dioxide absorbents developed to date, the high temperature absorbent which has the stability of absorption capacity according to the increase in the number of repetition of the absorption / regeneration reaction is a calcium-based high temperature carbon dioxide absorber using calcium aluminate as an additive (Li, Z., et al., Energy & Fuel, 2005, 19, 1447). The high-temperature carbon dioxide absorber manufactured by Li et al. Had a stable absorption capacity of at least 13 times of absorption and regeneration, and showed that the absorption capacity was maintained even when the regeneration temperature was increased to 850 ^o C. However, because the manufacturing method is a relatively simple method of inducing the swelling of the particles in the process of hydrating a part of the solid calcium oxide and forming calcium aluminate between the resulting gaps in the calcium oxide and calcium aluminate Having a composition, there is a limit to maximizing the utilization of calcium oxide.

The present invention provides a high temperature carbon dioxide absorbent and a method for producing the same, which show a high carbon dioxide absorption in repeating the carbon dioxide absorption and the regeneration of the absorbent at a high temperature but do not reduce the CO ₂ absorption even after repeated absorption and regeneration.

Calcium oxide (CaO) is used as a carbon dioxide absorbing active material, and calcium aluminate (Ca ₁₂ Al ₁₄ O ₃₃ ) is used as an additive to secure the carbon dioxide absorption capacity and the carbon dioxide diffusion path during repeated carbon dioxide absorption and regeneration of the absorbent. Was used. In the process of artificially preparing calcium oxide, an alumina precursor that can be dissolved in water was added to prepare a carbon dioxide high temperature absorber having a perfectly uniform composition of calcium and alumina.

The present invention relates to a method for producing a high temperature carbon dioxide absorbent used in a process for improving the production of hydrogen by absorbing carbon dioxide at the same time in a steam reforming reaction using methane, ethanol, and naphtha or an aqueous reaction of carbon monoxide. Specifically, in the process of repeating carbon dioxide absorption and regeneration of the absorbent, calcium oxide is used as the carbon dioxide absorbing active material, and calcium aluminate is used as an additive to prevent the sintering of the absorbent and to secure the diffusion path of carbon dioxide. It relates to a manufacturing method. The method for preparing a high temperature carbon dioxide absorbent of the present invention selects precursors of calcium oxide and calcium aluminate as a material that can be dissolved in water, thereby realizing a uniform composition of calcium oxide and calcium aluminate, and thus, in a repeated absorption / regeneration process. It is a manufacturing method that can secure the stability of carbon dioxide absorption capacity and maximize the utilization of calcium oxide as an active substance.

The present invention relates to a method for preparing a high temperature carbon dioxide absorbent in the form of a mixture of calcium oxide (CaO) and calcium aluminate (Ca ₁₂ Al ₁₄ O ₃₃ ). Specifically, the precursor of calcium oxide can be dissolved in water such as calcium nitrate (Ca (NO ₃ ) ₂ H ₂ O), calcium acetate (CH ₃ COO) ₂ Ca), calcium chloride (CaCl ₂ ) Calcium-containing compounds or their hydrates are used, and as a precursor of calcium aluminate, containing a portion of the precursor of calcium oxide and aluminum which can be dissolved in water such as aluminum nitrate (Al (NO ₃ ) ₃ ). The compounds or their hydrates relate to methods of making hot carbon dioxide absorbents.

Preferably, the present invention is a method for preparing a high temperature carbon dioxide absorbent that absorbs carbon dioxide from a mixed gas containing carbon dioxide in the temperature range of 450 ^° C to 800 ^° C, a precursor of calcium oxide and a precursor of calcium aluminate After completely dissolving in distilled water, adding a dispersing agent and stirring while heating at a temperature range of 60-80 ^o C, the solution thus obtained is dried to obtain a mixed powder of calcium nitrate and aluminum nitrate, and then inert gas or Primary firing in an air atmosphere and at 400-600 ^° C. for 2-8 hours to form calcium oxide and calcium hydroxide, and a mixture of aluminum oxide and aluminum hydroxide, a mixture of calcium oxide and calcium hydroxide, and aluminum oxide and aluminum hydroxide Is crushed again to draw in an inert gas or air atmosphere. Comprising to 600 firing the second for 2 hours at a temperature of 1000 ^o C produce a mixture of calcium and calcium aluminate oxide, and hydrated and dispersed in distilled water, calcium and mixtures of calcium aluminate-oxide obtained in the second firing step Drying the hydrated sample in the third firing in an atmosphere of air or inert gas in the temperature range of 400-600 ^o C, and pulverizing the product obtained in the third firing step to air or in the temperature range of 600 to 1000 ^o C It provides a method for producing a high temperature carbon dioxide absorbent which is a mixture of calcium oxide and calcium aluminate, including the step of fourth firing in an atmosphere of inert gas.

The present invention is also a high temperature carbon dioxide absorbent prepared according to the method of the present invention described above, which absorbs carbon dioxide from a mixed gas containing carbon dioxide in the temperature range of 450 ^° C. to 800 ^° C., with 70-95% by weight of calcium oxide. It provides a high temperature carbon dioxide absorbent consisting of a homogeneous mixture of (CaO) and 5-30% by weight of calcium aluminate (Ca ₁₂ Al ₁₄ O ₃₃ ).

The precursor of calcium oxide used in the present invention is a calcium compound or a hydrate thereof selected from the group consisting of calcium acetate, calcium nitrate, calcium chloride and mixtures thereof that can be dissolved in water.

The precursor of calcium aluminate used in the present invention is a calcium compound selected from the group consisting of calcium acetate, calcium nitrate, calcium chloride and mixtures thereof, and aluminum nitrate, aluminum hydroxy chloride, aluminum acetate which can be dissolved in water. Aluminum compounds selected from the group consisting of or mixtures of hydrates thereof.

Specific manufacturing process of the high temperature carbon dioxide absorbent of the present invention is as follows.

First, the precursor of calcium oxide and the precursor of calcium aluminate are completely dissolved in distilled water, and a dispersing agent such as isopropyl alcohol (IPA) is added, and then preferably in a temperature range of 60 to 80 ^° C. ^o Stir for 1-5 hours, preferably 2 hours while heating at C. The solution thus obtained is dried using a spray dryer or a drying oven to obtain a powder. The dried sample is obtained in a very uniform mixture of calcium nitrate and aluminum nitrate. The powder obtained is calcined and then calcined in an inert gas or air atmosphere and at 400-600 ^° C., preferably at 500 ^° C. for 2-8 hours to decompose and remove the nitrate and then cooled. Through this firing process, calcium nitrate and aluminum nitrate are present as a mixture of calcium oxide and calcium hydroxide, and aluminum oxide and aluminum hydroxide. The calcined sample is again milled and calcined in an inert gas or air atmosphere and for 2 hours at a temperature range of 600 to 1000 ^o C, preferably 900 ^o C and then cooled. During the firing process at high temperature, the sample is obtained as a mixture of calcium oxide and calcium aluminate according to the stoichiometric ratio. The samples thus obtained were sintered in a complete liquid phase and then calcined. In order to smoothly transfer the gas phase, it is necessary to lower the density of the sample, so that the obtained sample is dispersed again in distilled water and stirred at 75 ^° C. for 1-5 hours, preferably 2 hours. During this hydration, the calcium oxide is converted back to calcium hydroxide, increasing the spacing of the compressed particles. The hydrated sample is obtained by using a spray dryer or a drying oven to obtain dried powder, which is calcined, cooled and pulverized in an air or inert gas atmosphere at a temperature in the range of 400-600 ^o C, preferably 500 ^o C. The pulverized powder is again calcined and cooled in an atmosphere of air or inert gas at a temperature range of 600 to 1000 ^° C., preferably 900 ^° C. The high temperature carbon dioxide absorbent thus obtained is used to absorb high temperature carbon dioxide through grinding and molding.

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto.

Example

compare Example  One

Sample Name: HTA1

1. 20 g of calcium oxide (Aldrich) was added to 100 ml of isopropyl alcohol and 600 ml of distilled water and stirred in a 1 liter volume beaker.

2. The mixture was heated to 75 ^° C. and stirred for 1 hour.

3. The solution stirred in Process 2 was placed in a drying oven and left at 120 ^° C. for 20 hours.

4. The dried powder obtained in step 3 was collected, put back into a heating furnace, heated to 500 ^° C. for 1 hour 30 minutes, and calcined for 3 hours in an air atmosphere.

5. The calcined sample was slowly cooled, pulverized and put back into a heating furnace, heated to 900 ^° C. for 2 hours, and calcined for 2 hours in an air atmosphere to generate sample HTA1.

Measurement of carbon dioxide absorption ratio by carbon dioxide absorption / regeneration using thermogravimetric analyzer

50 mg of a high temperature carbon dioxide absorbent prepared in a thermogravimetric analyzer (TA Instruments, Q50) was added and heated to 100 ^° C. for 1 hour and 10 minutes while flowing helium at 100 ml / min, and then maintained at isothermal. At isothermal, helium and carbon dioxide were absorbed for 60 minutes while flowing 30 ml / min and 70 ml / min, respectively, and the absorbent was regenerated while flowing helium at 100 ml / min for 30 minutes. Whenever the composition of the gas changes, record the weight change of the sample over time. The weight change was recorded by converting the sample into an Absorption ratio of the sample (moles of calcium oxide contained in the number of moles of carbon dioxide absorbed in 1 g of the absorbent / 1 g of the absorbent × 100). This sample shows the expansion of pores by simply hydrating pure calcium oxide, which shows 70% carbon dioxide absorption in the initial absorption / regeneration cycle and shows high utilization of calcium oxide, but shows a rapid decrease in the absorption ratio as the number of cycles increases. . This is caused by the decrease in the diffusion path of carbon dioxide as small particles are sintered to form larger particles as the number of absorption / regeneration cycles increases.

compare Example  2

Sample Name: HTA2

1.4.4 g of solid oxide powder (CaO) and 1.5 g of aluminum hydroxy chloride (Al ₂ (OH) ₅ Cl.2H ₂ O) are added to 100 ml of isopropyl alcohol and 600 ml of distilled water and stirred in a 1 liter volume beaker. It was.

2. The mixture was heated to 75 ^° C. and stirred for 1 hour.

3. The solution stirred in Process 2 was placed in a drying oven and left at 120 ^° C. for 20 hours.

4. The dried powder obtained in step 3 was collected, put back into a heating furnace, heated to 500 ^° C. for 1 hour 30 minutes, and calcined for 3 hours in an air atmosphere.

5. The calcined sample was slowly cooled, pulverized, put back into a heating furnace, heated to 900 ^° C. for 2 hours, and calcined for 2 hours in an air atmosphere to generate sample HTA2.

Measurement of carbon dioxide absorption ratio by carbon dioxide absorption / regeneration using thermogravimetric analyzer

The experiment was conducted under the same conditions as in Comparative Example 1, and the results are shown in FIG. 2. Unlike the results of HTA 1 shown in Comparative Example 1, the sample showed no decrease in absorption ratio during 50 or more absorption and regeneration cycles. At the beginning of the absorption / regeneration cycle, the absorption ratio starts at about 60% and the 65th cycle is shown at the fifth cycle. In addition, the absorption ratio stabilized at 62% as the cycle number of absorption / regeneration was further increased. The absorption ratio of 62% corresponds to 0.37 g in terms of the weight of carbon dioxide that can be absorbed per gram of absorbent.

Example  One

Sample name: HTA3

1. Calcium nitrate hydrate _{(Ca (NO 3) 2 ·} 4H 2 O) 20g and the aluminum hydroxy chloride _{(Al 2 (OH) 5 Cl} · 2H 2 O) 1.5g of distilled water and isopropyl alcohol, 100 ml and 600 ml Into and stirred in a 1 liter volume beaker to produce a mixture.

2. The mixture was heated to 75 ^° C. and stirred for 1 hour.

3. The solution stirred in Process 2 was placed in a drying oven and left at 120 ^° C. for 20 hours.

4. The dried powder obtained in step 3 was collected, put back into a heating furnace, heated to 500 ^° C. for 1 hour 30 minutes, and calcined for 3 hours in an air atmosphere.

5. The calcined sample was slowly cooled, pulverized and put back into a heating furnace, heated to 900 ^° C. for 2 hours, and calcined for 2 hours in an air atmosphere.

6. The sample calcined in step 5 was added to 100 ml of isopropyl alcohol and 600 ml of distilled water and stirred in a 1 L volume beaker to form a mixture.

7. Repeat step 2 to step 5 to generate a sample HTA3.

Measurement of carbon dioxide absorption ratio by carbon dioxide absorption / regeneration using thermogravimetric analyzer

The experiment was conducted under the same conditions as in Comparative Example 1, and the results are shown in FIG. 3. This sample showed very similar results to that of HTA 2 shown in Comparative Example 2. However, the maximum carbon dioxide absorption ratio was 65% for HTA 2 but increased to 82.6% for HTA 3, and 79.1% even after the carbon dioxide absorption ratio was stabilized as the number of cycles increased, resulting in the results obtained using HTA 2 of Comparative Example 2. The performance was significantly improved.

Calcium aluminate prevents the sintering of calcium oxide and contributes to securing the diffusion path of carbon dioxide while calcium oxide repeats absorption / regeneration. As shown in Comparative Example 2, the formation of calcium aluminate between the gaps of very small particles generated in the process of hydrating calcium oxide to calcium hydroxide ensures the stability of the carbon dioxide absorption capacity in repeated absorption / regeneration.

X-ray diffraction analysis results of HTA2 and HTA3 are shown in FIG. 4 to compare the structure of the products according to the preparation method. Peaks of calcium oxide and calcium aluminate were observed in both diffractograms of HTA2 and HTA3. However, the peaks of calcium aluminate exhibited in HTA2 were significantly higher than those in HTA3, indicating that the calcium aluminate contained in HTA3 was very small and uniformly dispersed. In addition, the peaks of calcium oxide contained in HTA2 and HTA3 are in different order of intensity. In other words, the peak of the calcium oxide shown in HTA2 was the largest peak at 37.4 ^o and had the same structure as the pure calcium oxide, but HTA3 showed the largest peak at 29.8 ^o , indicating that the crystal structure of calcium oxide was modified. This structural change is believed to have influenced calcium alumina crystal formation in the process of simultaneously forming calcium aluminate and calcium oxide formed after mixing in a very uniform state in the liquid phase.

Starting in the liquid phase as in Example 1 to induce uniform mixing of calcium oxide and calcium aluminate, and then repeat the hydration process to secure the diffusion path of carbon dioxide absorbed carbon dioxide in the repeated cycle of absorption / regeneration In addition to ensuring the stability of the carbon dioxide absorption ratio can be increased by more than 25%.

Figure 1 shows the results obtained by performing repeated carbon dioxide absorption / regeneration in a thermogravimetric analyzer using a sample (HTA1) obtained by hydrating and heat treatment of calcium oxide.

Figure 2 shows the results obtained by performing a repeated carbon dioxide absorption / regeneration in a thermogravimetric analyzer using a sample (HTA2) obtained by adding an alumina precursor while hydrating calcium oxide, dried, heat treatment.

Figure 3 is obtained by repeatedly performing carbon dioxide absorption / regeneration in a thermogravimetric analyzer using a sample obtained by dissolving, drying, and heat-treating the calcium precursor and the alumina precursor simultaneously (HTA3). The results are shown.

4 shows the X-ray diffraction diagrams of HTA2 and HTA3.

Claims (7)

As a method of manufacturing a high temperature carbon dioxide absorbent that absorbs carbon dioxide from a mixed gas containing carbon dioxide in the temperature range of 450 ^° C to 800 ^° C, Completely dissolving the precursor of calcium oxide and the precursor of calcium aluminate in distilled water, adding a dispersant, and stirring with heating at a temperature in the range of 60-80 ^° C., The solution thus obtained was dried to obtain a mixed powder of calcium nitrate and aluminum nitrate, and then first calcined in an inert gas or air atmosphere at 400-600 ^o C for 2-8 hours to obtain calcium oxide, calcium hydroxide and aluminum oxide. Forming a mixture of and aluminum hydroxide, Calcium oxide, calcium hydroxide, and a mixture of aluminum oxide and aluminum hydroxide are pulverized again to secondary calcining in an inert gas or air atmosphere for 2 hours in a temperature range of 600 to 1000 ^o C to form a mixture of calcium oxide and calcium aluminate. Steps, Dispersing the mixture of calcium oxide and calcium aluminate obtained in the secondary firing step in distilled water to hydrate and drying the hydrated sample to tertiary firing in an atmosphere of air or inert gas in the temperature range of 400-600 ^o C, and A method of preparing a high temperature carbon dioxide absorbent, which is a mixture of calcium oxide and calcium aluminate, comprising pulverizing the product obtained in the third firing step and fourth firing in an atmosphere of air or an inert gas in a temperature range of 600 to 1000 ^° C. . The method according to claim 1, wherein the precursor of calcium oxide is a calcium compound selected from the group consisting of calcium acetate, calcium nitrate, calcium chloride and mixtures thereof or hydrates thereof which can be dissolved in water. The method of claim 1, wherein the precursor of calcium aluminate is a calcium compound selected from the group consisting of calcium acetate, calcium nitrate, calcium chloride and mixtures thereof, aluminum nitrate, aluminum hydroxy chloride, aluminum acetate that can be dissolved in water. And a mixture of aluminum compounds or hydrates thereof selected from the group consisting of: The method of claim 1 wherein the dispersant is isopropyl alcohol (IPA). The process of claim 1 wherein the first and third firings are carried out at 500 ^° C. The process of claim 1 wherein the second and fourth firings are performed at 900 ^° C. A high temperature carbon dioxide absorbent prepared by the method according to claim 1 and absorbing carbon dioxide from a mixed gas containing carbon dioxide in the temperature range of 450 ^° C. to 800 ^° C., comprising 70-95% by weight of calcium oxide (CaO) and High temperature carbon dioxide absorbent consisting of a homogeneous mixture of 5-30% by weight of calcium aluminate (Ca ₁₂ Al ₁₄ O ₃₃ ).

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