Cobalt hexammine salts, process for their preparation, and their use in carbon dioxide absorption

Abstract

The invention provides a hexammine cobalt salt and a preparation method thereof. The chemical formula of the hexammine cobalt salt is [Co (NH3) 6] [HSO4] [SO4]. The invention also provides an application of the carbon dioxide absorption liquid in carbon dioxide gas absorption, a carbon dioxide gas absorption liquid and a method for absorbing carbon dioxide gas. The invention also provides a crystalline clathrate compound of carbon dioxide and hexammine cobalt salt and a method for releasing carbon dioxide molecules from the clathrate compound.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon dioxide capture, and in particular to a hexaammine cobalt salt, a preparation method thereof, and use thereof in carbon dioxide absorption. Background Art

[0002] As one of the main components of greenhouse gases, the global atmospheric concentration of carbon dioxide is increasing year by year. In order to reduce carbon emissions, capturing and neutralizing carbon dioxide has become an important task in industrial production.

[0003] In the process of capturing carbon dioxide from flue gas in the coal-fired power industry, the application of chemical absorbents represented by organic amines has a long history. Typical organic amine absorbents are alcohol amines, such as monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), methylethanolamine (MDEA), etc. However, some long-standing unresolved problems limit the further widespread application of organic amine carbon dioxide chemical adsorbents in industry. Taking the MEA absorbent as an example, since the decomposition temperature of the compounds generated after its reaction with carbon dioxide is as high as 100°C or above, its regeneration requires a large amount of energy input. This reduces the economic feasibility of using it to capture carbon dioxide. In addition, the MEA solution is alkaline and easily corrodes the pipeline, which will further lead to additional production costs.

[0004] On the contrary, after other absorbents capture carbon dioxide, only very low energy input is required to release the absorbed carbon dioxide and achieve the regeneration of the absorbent. For example, in the formation process of combustible ice (i.e., natural gas hydrate) or carbon dioxide hydrate, carbon dioxide can be absorbed and only a small amount of energy is required to release carbon dioxide from it. However, the conditions for forming these hydrates are correspondingly very harsh. Moreover, due to the extremely low energy required to release carbon dioxide, these hydrates are very unstable at normal temperature and pressure. Therefore, these processes are difficult to be put into practical application in the field of carbon dioxide capture.

[0005] Therefore, there is an urgent need for a carbon dioxide absorbent that can achieve carbon dioxide absorption and desorption under moderate conditions, achieve stable storage of carbon dioxide at normal temperature and pressure, and has low corrosion to equipment. Summary of the invention

[0006] In one aspect, the present invention provides a hexaaminecobalt salt, wherein the chemical formula of the hexaaminecobalt salt is [Co(NH3)6][HSO4][SO4].

[0007] Preferably, the hexaammine cobalt salt is a crystal, and the space group of the crystal is: P212121; the unit cell parameters are: α=90°, β=90°, γ=90°, wherein the unit cell parameters are measured at 25°C.

[0008] Preferably, the five strongest 2θ peak positions of the powder X-ray diffraction spectrum of the hexaammine cobalt salt using a Cu target are at 13.48°, 14.70°, 21.02°, 23.36°, and 32.20°, wherein the powder X-ray diffraction spectrum is measured at 25°C.

[0009] In another aspect, the present invention provides a method for preparing the above-mentioned hexaammine cobalt salt, wherein the preparation method comprises:

[0010] Adding activated carbon as a catalyst and aqueous ammonia to an aqueous solution of cobalt (II) sulfate to form a complex of divalent cobalt and ammonia;

[0011] Add hydrogen peroxide to the solution to oxidize the divalent cobalt to trivalent;

[0012] removing activated carbon from the solution;

[0013] Add concentrated sulfuric acid to the solution to make it acidic;

[0014] concentrating the solution to form the hexaamminecobalt salt; and

[0015] The hexaamminecobalt salt is isolated.

[0016] Preferably, separating the hexaamminecobalt salt comprises:

[0017] washing and drying; and / or

[0018] Recrystallization.

[0019] In another aspect, the present invention provides use of the above-mentioned hexaamminecobalt salt in carbon dioxide gas absorption.

[0020] In another aspect, the present invention provides a carbon dioxide gas absorption liquid, wherein the absorption liquid comprises hexaamminecobalt (III) ions, hydrogen sulfate ions and sulfate ions.

[0021] Preferably, the absorption liquid is an aqueous solution of the hexaamminecobalt salt according to claim 1.

[0022] In another aspect, the present invention provides a method for absorbing carbon dioxide gas, wherein the method comprises:

[0023] The carbon dioxide gas is brought into contact with the above-mentioned carbon dioxide gas absorbing liquid to generate a crystalline inclusion compound of carbon dioxide and hexaammine cobalt salt to absorb the carbon dioxide gas.

[0024] In another aspect, the present invention provides a crystalline inclusion complex of carbon dioxide and hexaamminecobalt salt, characterized in that the crystalline inclusion complex comprises a [Co(NH3)6][HSO4][SO4] skeleton and carbon dioxide molecules included in the vacancies of the [Co(NH3)6][HSO4][SO4] skeleton.

[0025] In another aspect, the present invention provides a method for releasing carbon dioxide molecules from the above-mentioned crystalline inclusion compound, wherein the method comprises:

[0026] The crystalline inclusion compound is allowed to dissolve in water and release carbon dioxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the crystal structure of hexaamminecobalt salt [Co(NH3)6][HSO4][SO4] according to one embodiment of the present invention.

[0028] Figure 2 Shown are the measurement results of powder X-ray diffraction of the hexaamminecobalt salt according to one embodiment of the present invention.

[0029] Figure 3 is a schematic diagram of the crystal structure of a crystalline inclusion compound according to one embodiment of the present invention.

[0030] Figure 4 A powder X-ray diffraction pattern of a crystalline inclusion compound according to one embodiment of the present invention is shown.

[0031] Figure 5 Thermogravimetric analysis results of a crystalline inclusion compound according to one embodiment of the present invention are shown.

[0032] Figure 6 A graph showing pressure changes for multiple carbon dioxide absorption-desorption cycles of a hexaamminecobalt salt according to one embodiment of the present invention is shown. DETAILED DESCRIPTION

[0033] One of the objects of the present invention is to provide a carbon dioxide absorbent that can achieve carbon dioxide absorption and desorption under moderate conditions and can achieve stable storage of carbon dioxide at normal temperature and pressure.

[0034] The present invention uses an aqueous solution of a hexaammine cobalt salt to selectively react with carbon dioxide gas to form a crystalline inclusion compound to capture carbon dioxide. The crystalline inclusion compound is relatively stable when dry, but can be redissolved in water in an aqueous environment and release carbon dioxide gas, and can then be used to capture carbon dioxide again. Thus, the present invention realizes a carbon dioxide absorbing liquid that can capture carbon dioxide gently and can be regenerated with low energy consumption.

[0035] In one aspect, the present invention provides a hexaamminecobalt salt, wherein the chemical formula of the hexaamminecobalt salt is [Co(NH3)6][HSO4][SO4]. The hexaamminecobalt salt comprises hexaamminecobalt (III) ions, sulfate ions and hydrogen sulfate ions, and the molar ratio of the hexaamminecobalt (III) ions, sulfate ions and hydrogen sulfate ions is 1:1:1.

[0036] The hexaamminecobalt salt of the present invention is an ionic crystal. The cation hexaamminecobalt (III) ion of the ionic crystal is a hexacoordinated complex cation, and its chemical formula is [C o (NH3)6] 3+ , wherein the cobalt is trivalent cobalt (cobalt (III)). The anion of the ionic crystal is not a single anion, but contains sulfate ions and hydrogen sulfate ions at the same time. That is, the hexaammine cobalt salt is neither a pure orthosulfate nor a pure acid sulfate. As described below, the hexaammine cobalt salt containing sulfate ions and hydrogen sulfate ions at the same time, after being dissolved in water, provides an ionic environment that can interact with carbon dioxide molecules in water to form a crystalline inclusion complex.

[0037] The hexaammine cobalt salt of the present invention is a stable crystal at normal temperature and pressure, and is poorly soluble in water without disturbance. Disturbance refers to providing energy input, such as stirring, heating or radiation.

[0038] In one embodiment, the hexaammine cobalt salt is a crystal, and the space group of the crystal is: P212121; the unit cell parameters are: α = 90°, β = 90°, γ = 90°, wherein the unit cell parameters are measured at 25°C. The unit cell volume is The above crystal characteristics are measured from the single crystal X-ray diffraction pattern of the product of the embodiment of the present invention.

[0039] Figure 1 Schematic diagram of the crystal structure of hexaamminecobalt salt [Co(NH3)6][HSO4][SO4] according to one embodiment of the present invention, which shows the staggered arrangement of three ionic groups in the crystal.

[0040] In one embodiment, the five strongest 2θ peak positions of the powder X-ray diffraction spectrum of the hexaaminecobalt salt using a Cu target are at 13.48°, 14.70°, 21.02°, 23.36°, and 32.20°, wherein the powder X-ray diffraction spectrum is measured at 25°C. Figure 2 The measurement results of powder X-ray diffraction of hexaamine cobalt salt according to one embodiment of the present invention are shown. The powder X-ray diffraction results are consistent with the single crystal X-ray diffraction results, and are consistent with the results calculated based on the above lattice parameters.

[0041] The novel hexaamminecobalt salt of the present invention can be used for carbon dioxide absorption.

[0042] The present invention also provides a method for preparing the above-mentioned hexaammine cobalt salt, wherein the preparation method comprises:

[0043] Adding activated carbon as a catalyst and aqueous ammonia to an aqueous solution of cobalt (II) sulfate to form a complex of divalent cobalt and ammonia;

[0044] Add hydrogen peroxide to the solution to oxidize the divalent cobalt to trivalent;

[0045] removing activated carbon from the solution;

[0046] Add sulfuric acid to the solution to make it acidic;

[0047] concentrating the solution to form the hexaamminecobalt salt; and

[0048] The hexaamminecobalt salt is isolated.

[0049] First, a cobalt sulfate (II) aqueous solution is provided. The function of the cobalt sulfate (II) aqueous solution is to provide an aqueous environment, cobalt (II) ions and sulfate ions for the reaction. The concentration range of the cobalt sulfate (II) aqueous solution can be 0.1-0.5 g / mL. Preferably, the concentration range of the cobalt sulfate (II) aqueous solution is 0.2-0.3 g / mL. Too low a concentration will make the product difficult to extract, and too high a concentration will make the product difficult to purify.

[0050] Preferably, the aqueous solution of cobalt sulfate (II) is obtained by adding cobalt sulfate (II) into ultrapure water. The reason for selecting ultrapure water is to avoid other metal cations coordinating with ammonia to produce impurities. Cobalt sulfate (II) can be used in the form of hydrates, such as cobalt sulfate (II) heptahydrate.

[0051] Subsequently, activated carbon is added thereto. The function of the activated carbon is to act as a catalyst to catalyze the coordination of ammonia and cobalt to form a complex of divalent cobalt and ammonia. In order to promote the reaction, the added activated carbon is stirred until it is evenly dispersed. Preferably, the particle size range of the activated carbon is 200-600 mesh, preferably 300-500 mesh. If the particle size is too high, the dispersion is uneven and the catalytic activity is low. If the particle size is too low, it will not be easy to separate from the solution. Preferably, the dispersion concentration range of the activated carbon dispersed in water is 0.01-0.03g / mL. If the dispersion concentration is too high, it is not easy to disperse evenly in water. If the dispersion concentration is too low, the operability is poor. In a more preferred embodiment, activated carbon with a 400 mesh and a dispersion concentration of 0.015g / mL dispersed in water can be used.

[0052] Subsequently, aqueous ammonia is added. The function of aqueous ammonia is to coordinate with divalent cobalt. The molar concentration of aqueous ammonia is preferably 25%-30%. When the concentration is too low, the volume of aqueous ammonia required is large. When the concentration is too high, volatilization is serious and the operability is poor. In a more preferred embodiment, 30% concentrated aqueous ammonia can be used. In order to promote the reaction, stirring is maintained.

[0053] Subsequently, hydrogen peroxide is added to the solution. The function of hydrogen peroxide is to oxidize divalent cobalt to trivalent cobalt. Preferably, hydrogen peroxide is added slowly to avoid excessive oxidation reaction causing the reaction solution to overflow the reactor. After adding hydrogen peroxide, the system can be heated and kept warm to speed up the reaction. For the preparation method of the present invention, it is usually sufficient to keep the temperature at room temperature or slightly above room temperature, for example, in the range of 25-60°C. Preferably, the temperature range is 40-60°C, and the insulation time range is 10-30 minutes.

[0054] Subsequently, the activated carbon is removed to avoid interfering with the subsequent salt crystallization process. The activated carbon can be removed by filtration. The mesh number of the filter is smaller than the carbon particle size. For example, a range of 100-200 mesh can be selected.

[0055] Subsequently, sulfuric acid is added to the solution to make the solution acidic. The function of sulfuric acid is to neutralize excess ammonia and further provide an acidic environment, thereby providing hydrogen ions and sulfate radicals. Preferably, concentrated sulfuric acid is used to avoid introducing more water due to the use of dilute sulfuric acid. Concentrated sulfuric acid with a molar concentration of more than 95%, preferably more than 98%, can be used. In order to promote the reaction, stir evenly.

[0056] Subsequently, the solution is concentrated to form the hexaamminecobalt salt. For example, after sufficient reaction, the solvent can be slowly evaporated so that a solid product appears in the solution. The inventors have found that in the above-mentioned acidic environment, in the process of evaporating the solvent, the solid product that first crystallizes and precipitates is the hexaamminecobalt salt of the present invention, which takes precedence over the sulfate of hexaamminecobalt or the hydrogen sulfate of hexaamminecobalt. The degree of solvent volatilization can be determined according to the content of each ion in the solution to ensure that the solid products are all the hexaamminecobalt salt of the present invention.

[0057] Finally, the hexaamminecobalt salt is separated, which can be separated by filtering, centrifuging, etc.

[0058] Preferably, in order to separate thoroughly (i.e., purify), separation of the hexaamine cobalt salt includes washing and drying, and / or recrystallization. The obtained solid or solid-liquid mixture mainly composed of solids is washed and dried to completely remove the residual components of the solution other than the solid product. Washing can be carried out using solvents that do not dissolve the hexaamine cobalt salt of the present invention (such as alcohols, such as ethanol), etc., to wash away the residual solution other than the hexaamine cobalt salt of the present invention. The drying temperature does not exceed 150°C to avoid product decomposition. The washing and drying process can be repeated several times, for example 2-3 times, to obtain higher purity.

[0059] The product can also be dissolved in water and then recrystallized for purification. The specific process of recrystallization is to disperse the crystals in ultrapure water to form a supersaturated system, heat the system (but below 150°C) until the crystals are completely dissolved, and then slowly cool down to precipitate single crystals of the product, remove the solution by filtering, and retain the recrystallized crystals. The recrystallization process can also be repeated several times to ensure the purity of the product, for example 2-3 times.

[0060] In the above reactions, the reactions can all be carried out under air atmosphere.

[0061] The above method can simply form the hexaamminecobalt salt of the present invention with relatively cheap raw materials and relatively mild reaction conditions.

[0062] The present invention also provides the use of the above-mentioned hexaamine cobalt salt in carbon dioxide gas absorption. The hexaamine cobalt salt of the present invention can be used in various occasions where carbon dioxide gas absorption is required. For example, it can be used to treat flue gas and absorb carbon dioxide therein. Typically, an aqueous solution of the hexaamine cobalt salt is prepared separately as a carbon dioxide absorption liquid. However, in a process in which there is a water body in contact with carbon dioxide, the hexaamine cobalt salt can also be directly added to the water body to achieve carbon dioxide absorption.

[0063] The present invention also provides a carbon dioxide gas absorbent, wherein the carbon dioxide gas absorbent comprises the above-mentioned hexaammine cobalt salt. The above-mentioned hexaammine cobalt salt can be used as an effective ingredient in the carbon dioxide absorbent product. The hexaammine cobalt salt can also be used as an absorbent component in a multifunctional reagent and mixed with other reagents, as long as these reagents do not have a significant adverse effect on the absorption and desorption of carbon dioxide.

[0064] The present invention also provides a carbon dioxide gas absorption liquid, wherein the absorption liquid contains hexaamminecobalt (III) ions, hydrogen sulfate ions and sulfate ions. The solution with these three ions can be included with carbon dioxide molecules to form a crystalline inclusion compound of carbon dioxide and hexaamminecobalt salt, thereby fixing carbon dioxide. Preferably, the carbon dioxide gas absorption liquid is composed of water, hexaamminecobalt (III) ions, hydrogen sulfate ions and sulfate ions.

[0065] Preferably, the absorption liquid is an aqueous solution of the above-mentioned hexaammine cobalt salt. The aqueous solution of the hexaammine cobalt salt of the present invention is simple to prepare and conveniently provides ions in the required proportion.

[0066] The present invention provides a method for absorbing carbon dioxide gas, wherein the method comprises:

[0067] The carbon dioxide gas is brought into contact with the above-mentioned carbon dioxide gas absorbing liquid to generate a crystalline inclusion compound of carbon dioxide and hexaammine cobalt salt to absorb the carbon dioxide gas.

[0068] In one embodiment, carbon dioxide gas is contacted with the aqueous solution of the hexaamine cobalt salt of the present invention at room temperature under a carbon dioxide partial pressure of 142.6 kPa or more to generate a crystalline inclusion complex of carbon dioxide and the hexaamine cobalt salt. When the carbon dioxide partial pressure is too low, it may be difficult to form a significant amount of inclusion complex precipitation.

[0069] Without relying on any theory, when the aqueous solution of the hexaammine cobalt salt of the present invention contacts carbon dioxide, as carbon dioxide dissolves in water, the hexaammine cobalt salt in the solution will crystallize under the induction of carbon dioxide, and the carbon dioxide will be molecularly enclosed in the hydrogen bond cage of the hexaammine cobalt salt structure to form a crystalline carbon dioxide inclusion complex (CO2@[Co(NH3)6][HSO4][SO4]). In the inclusion complex, each mole of [Co(NH3)6][HSO4][SO4] can absorb one mole of carbon dioxide. Figure 3 The figure is a schematic diagram of the crystal structure of a crystalline inclusion compound according to an embodiment of the present invention. The crystalline inclusion compound is stable at room temperature and pressure, and can release high-purity carbon dioxide by dissolving in water, while regenerating an aqueous solution of hexaamminecobalt salt.

[0070] In order to form inclusion compound precipitation, the carbon dioxide partial pressure in the atmosphere must meet certain basic requirements. At 0°C and 25°C, the minimum partial pressure of carbon dioxide to form inclusion compounds is 58.2 and 142.6 kPa respectively. Increasing the carbon dioxide pressure can increase the conversion rate of hexaammine cobalt salt and carbon dioxide to form inclusion compound precipitation. The higher the temperature, the greater the required carbon dioxide partial pressure.

[0071] In order to achieve a higher reaction pressure, a reactor can be selected as the place where carbon dioxide reacts with hexaamminecobalt salt.

[0072] The present invention also provides a crystalline inclusion complex of carbon dioxide and hexaammine cobalt salt, wherein the crystalline inclusion complex comprises a [Co(NH3)6][HSO4][SO4] skeleton and carbon dioxide molecules included in the cavities of the [Co(NH3)6][HSO4][SO4] skeleton.

[0073] The present invention also provides a method for releasing carbon dioxide molecules from the above-mentioned crystalline inclusion compound, wherein the method comprises:

[0074] The crystalline inclusion compound is allowed to dissolve in water and release carbon dioxide.

[0075] Without being bound by any theory, the reaction equation for capturing carbon dioxide to form a crystalline inclusion compound and releasing carbon dioxide from the crystalline inclusion compound in the present invention can be as follows:

[0076]

[0077] The above absorption-desorption reaction of carbon dioxide is a reversible reaction. When the carbon dioxide partial pressure exceeds a critical value, the formation of a crystalline inclusion complex can be induced. The higher the partial pressure, the more the equilibrium shifts to the right. When the crystalline inclusion complex is placed in pure water, it partially dissolves and releases carbon dioxide. The equilibrium can be shifted to the left by applying a disturbance. A disturbance refers to the input of energy. Typical and convenient disturbances include stirring and heating. Other disturbances, such as radiation, can also be used.

[0078] When the disturbance is small, the rate at which the inclusion complex releases carbon dioxide may be slow. After a moderate disturbance, the inclusion complex dissolves significantly in water. Especially in an open container, the equilibrium can be shifted further to the left because the released carbon dioxide can continue to leave the system. The degree of disturbance can depend on the specific environment, such as the partial pressure of carbon dioxide in the atmosphere and the ionic environment in the water. Generally, the more severe the disturbance, the faster the inclusion complex dissolves and the faster the carbon dioxide is released.

[0079] By repeating the above method of forming a crystalline inclusion compound and releasing carbon dioxide, a carbon dioxide absorption-desorption cycle and repeated regeneration of the absorbent can be achieved.

[0080] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail in combination with the embodiments below. The following content is only an example and explanation of the concept of the present invention. The technicians in the relevant technical field make various modifications or supplements to the specific implementation cases described or replace them with similar methods. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all belong to the protection scope of the present invention.

[0081] Example 1

[0082] At room temperature, 22.4g of cobalt sulfate (II) heptahydrate is dissolved in 100mL of ultrapure water. 1.5g of activated carbon is added to the solution and stirred until uniformly dispersed. 60mL of 30% concentrated ammonia water is quickly added and stirred. After 40mL of hydrogen peroxide is slowly added, the system is heated to 50°C and maintained for 20 minutes, then filtered while hot. 20mL of concentrated sulfuric acid is added to the filtrate and stirred evenly. Most of the solvent is removed by heating and evaporation. The crude product is washed 3 times with 30mL of ethanol, dried and recrystallized twice in ultrapure water to obtain 5.0g of product. The appearance of the product is an orange-red transparent prismatic solid.

[0083] The product structure was analyzed by single crystal X-ray diffraction using a Mo target at 25°C using a Rigaku Oxford Diffraction diffractometer. The product molecular formula was [Co(NH3)6][HSO4][SO4] based on its single crystal X-ray diffraction pattern. The space group was P212121. The unit cell parameters were: α=90°, β=90°, γ=90°.

[0084] The powder sample was obtained by grinding the product after recrystallization, and then the powder X-ray diffraction measurement was performed at 25°C using a RigakuMiniFlex 600 diffractometer and a Cu target. Figure 2 As shown in Figure 2, the five strongest 2θ peaks are located at 14.70°, 23.36°, 13.48°, 21.02°, and 32.20°, which is consistent with the lattice structure calculated from the single crystal X-ray diffraction results.

[0085] Example 2

[0086] At room temperature, 1.118g of the hexaammine cobalt sulfate obtained in Example 1 is dissolved in 10mL ultrapure water to obtain a red clear solution. The solution is placed in an autoclave. The autoclave is purged with carbon dioxide to remove air, and the final reactor is filled with carbon dioxide gas at a pressure of 2MPa. After standing for 12 hours, the solution is carefully taken out from the autoclave, and solids are separated from the solution by filtration to obtain orange-red crystals. At -173 ° C (about 100K), using Rigaku Oxford Diffraction diffractometer, by using the single crystal X-ray diffraction analysis crystal structure of Mo target, it is calculated that the crystal is a hexaammine cobalt salt inclusion compound of carbon dioxide, and the molecular formula is: CO2@[Co(NH3)6][HSO4][SO4], and carbon dioxide is present in the cavity of [Co(NH3)6][HSO4][SO4] skeleton in molecular form. Figure 3 is a schematic diagram of the crystal structure of a crystalline inclusion compound according to one embodiment of the present invention.

[0087] The powdered sample was obtained by grinding and subjected to powder X-ray diffraction measurement at 25°C using a Rigaku MiniFlex 600 diffractometer with a Cu target. Figure 4 As shown in Figure 2, the five strongest 2θ peaks are located at 15.08°, 19.70°, 23.16°, 24.78°, and 31.82°, which is consistent with the lattice structure calculated from the single crystal X-ray diffraction results.

[0088] The conversion rate of the hexaammine cobalt salt to form a clathrate is calculated by the mass difference before and after the solution absorbs carbon dioxide. Specifically, the calculation formula of the conversion rate is:

[0089]

[0090] According to the measurement results, the conversion rate at a reaction pressure of 2 MPa was calculated to be 65.0%. Unconverted hexaamminecobalt salt still existed in the solution.

[0091] As can be seen from Example 2, without relying on any theory, when the aqueous solution of the hexaaminecobalt salt of the present invention comes into contact with carbon dioxide gas, the carbon dioxide dissolved in the water can induce the crystallization of the hexaaminecobalt salt, and the carbon dioxide molecules can be embedded in the hydrogen bond framework in the hexaaminecobalt salt structure to form a crystalline inclusion complex and precipitate out from the solution.

[0092] Example 3

[0093] The preparation was carried out in the same manner as in Example 2, except that the pressure was controlled at 0.5 MPa. The conversion rate obtained was 25.6%.

[0094] Example 4

[0095] The preparation was carried out in the same manner as in Example 2, but the pressure was controlled to be 1.5 MPa, and the conversion rate obtained was 59.58%

[0096] Example 5

[0097] The preparation was carried out in the same manner as in Example 2, but the pressure was controlled at 2.5 MPa, and the conversion rate obtained was 83.45%

[0098] Example 6

[0099] Thermogravimetric analysis experiments were carried out on the prepared CO2@[Co(NH3)6][HSO4][SO4] crystalline inclusion complex. Figure 5 The results of thermogravimetric analysis of the crystalline inclusion compound are shown. The results show that the sample has no obvious mass loss before 135°C, and the sample is stable and does not decompose before this temperature. That is, at room temperature and pressure, the dried crystalline inclusion compound of the present invention is quite stable. Therefore, it can be used for room temperature storage and transportation of carbon dioxide.

[0100] Example 7

[0101] 5mL of saturated [Co(NH3)6][HSO4][SO4] aqueous solution at 25°C was placed in a 60mL reactor, and then CO2 was charged into the reactor to a pressure of 1MPa. Next, the system temperature was controlled to change between 0-30°, and the pressure change in the process was recorded with a digital pressure recorder to examine the circulation performance of the hexaammine cobalt salt aqueous solution. First, the system temperature was brought to 30°C. At this time, part of the CO2 in the reactor entered the aqueous solution to form a crystalline inclusion complex, and the system pressure dropped. As the reaction gradually reached equilibrium, the system pressure gradually stabilized. When the system pressure changed by less than 0.1kPa for 5 consecutive minutes, it was considered to have reached equilibrium, and the equilibrium pressure was recorded. The equilibrium pressure is about 975kPa. Subsequently, the system was cooled to 0°C, and the pressure change over time was recorded. When the temperature dropped, more crystalline inclusion complexes were formed and the system pressure dropped. After the temperature stabilized at 0°C, as the reaction gradually reached equilibrium again, the system pressure gradually stabilized. When the system pressure changed by less than 0.1kPa for 5 consecutive minutes, it was considered to have reached equilibrium, and the equilibrium pressure was recorded. The equilibrium pressure is 868 kPa. Then, the temperature is raised to 30°C again, and the next cycle of cooling test and monitoring is started. Figure 6 The graph shows the change of system pressure over time due to the absorption of carbon dioxide caused by the temperature drop in the five cycles of the hexaammine cobalt salt of the present invention. Figure 6 As shown, the equilibrium pressure remains unchanged after 5 cycles. The solution after the last cycle is taken out to remove the solvent, and the X-ray diffraction results of the recrystallized solid powder are shown in the figure, which is consistent with that before the cycle. The above results show that the absorption-desorption process of carbon dioxide by the hexaamine cobalt salt is a completely reversible process, and the conversion rate of the inclusion complex can be affected by temperature and carbon dioxide partial pressure. In general, absorption and desorption can be carried out under moderate conditions near room temperature.

[0102] The above examples illustrate that the synthesis method of the hexaammine cobalt salt of the present invention is simple and has strong thermal stability, can selectively capture carbon dioxide and recycle it, and the energy input of the regeneration process is low; the synthesized carbon dioxide inclusion compound is not easy to decompose in the air, and is convenient for transportation and storage. In addition, the carbon dioxide absorption system is weakly acidic and much less corrosive than alcohol amine absorbents. Thus, low-energy-consumption and high-selectivity carbon dioxide capture is achieved by forming inclusion compound precipitation in an aqueous solution, which at least partially solves the problems of high energy consumption and equipment corrosion in carbon dioxide capture technology.

[0103] More specifically, the beneficial effects of the present invention include but are not limited to:

[0104] 1. The hexaammine cobalt salt of the present invention has strong stability, acid and alkali resistance, can be repeatedly recycled, and has low corrosiveness;

[0105] 2. The carbon dioxide separated by the method of the present invention has extremely high purity;

[0106] 3. The regeneration process of the method of the present invention has low energy consumption;

[0107] 4. The carbon dioxide crystalline inclusion compound synthesized by the present invention has good crystallinity, high stability, and is easy to store and transport.

[0108] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A hexaammine cobalt salt, characterized in that The chemical formula of the hexaamminecobalt salt is [Co(NH3)6][HSO4][SO4].

2. The hexaammine cobalt salt according to claim 1, characterized in that The hexaammine cobalt salt is a crystal, and the space group of the crystal is: P212121; the unit cell parameters are: α=90°, β=90°, γ=90°, wherein the unit cell parameters are measured at 25°C.

3. The hexaammine cobalt salt according to claim 1, characterized in that The five strongest 2θ peak positions of the powder X-ray diffraction spectrum of the hexaamminecobalt salt using a Cu target are at 13.48°, 14.70°, 21.02°, 23.36°, and 32.20°, wherein the powder X-ray diffraction spectrum is measured at 25°C.

4. A method for preparing the hexaammine cobalt salt according to claim 1, characterized in that: The preparation method comprises: Adding activated carbon as a catalyst and aqueous ammonia to an aqueous solution of cobalt (II) sulfate to form a complex of divalent cobalt and ammonia; Add hydrogen peroxide to the solution to oxidize the divalent cobalt to trivalent; removing activated carbon from the solution; Add concentrated sulfuric acid to the solution to make it acidic; concentrating the solution to form the hexaamminecobalt salt; and The hexaamminecobalt salt is isolated.

5. The preparation method according to claim 4, characterized in that: Separating the hexaamminecobalt salt comprises: washing and drying; and / or Recrystallization.

6. Use of the hexaammine cobalt salt according to claim 1 in carbon dioxide gas absorption.

7. A carbon dioxide gas absorbing liquid, characterized in that: The absorption liquid contains hexaaminecobalt (III) ions, hydrogen sulfate ions and sulfate ions.

8. The carbon dioxide gas absorbing liquid according to claim 7, characterized in that: The absorption liquid is an aqueous solution of the hexaamminecobalt salt according to claim 1.

9. A method for absorbing carbon dioxide gas, characterized in that: The method comprises: The carbon dioxide gas is brought into contact with the carbon dioxide gas absorbing liquid according to claim 7 to generate a crystalline inclusion compound of carbon dioxide and hexaamminecobalt salt to absorb the carbon dioxide gas.

10. A crystalline inclusion compound of carbon dioxide and hexaammine cobalt salt, characterized in that: The crystalline inclusion compound comprises a [Co(NH3)6][HSO4][SO4] framework and carbon dioxide molecules included in the cavities of the [Co(NH3)6][HSO4][SO4] framework.

11. A method for releasing carbon dioxide molecules from the crystalline inclusion compound according to claim 10, characterized in that: The method comprises: The crystalline inclusion compound is allowed to dissolve in water and release carbon dioxide.

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