Preparation method of in-situ hydrothermal biomass synergistic modified calcium-based absorbent

Abstract

The invention relates to a preparation method of an in-situ hydrothermal biomass synergistic modified calcium-based absorbent. The preparation method of the calcium-based absorbent comprises the following steps: 1) calcining a calcium-based raw material to obtain a raw material containing calcium oxide; 2) adding the raw material containing calcium oxide, biomass and water into a hydrothermal reaction kettle, and mixing to obtain mixed slurry; (3) carrying out in-situ hydrothermal reaction on the mixed slurry to obtain slurry; and 4) filtering the slurry to obtain a filter cake, drying the filter cake, and calcining to obtain the calcium-based absorbent. According to the method, the calcium-based absorbent is modified through the in-situ hydrothermal reaction of the cheap biomass, and the prepared calcium-based absorbent is fluffy in tissue, large in specific surface area, rich in mesopores, not prone to sintering inactivation and capable of being used for circularly absorbing greenhouse gas CO2 in flue gas for multiple times.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental pollution prevention and control and clean combustion, and particularly relates to a preparation method of an in-situ hydrothermal biomass co-modified calcium-based absorbent. Background Art

[0002] The technology of carbon dioxide capture, utilization and storage (CCS) is considered to be one of the most promising emission reduction technologies. This technology is to capture CO2 from large fixed carbon emission sources such as coal-fired power plants and cement plants, and then compress and transport the high-concentration CO2 to chemical plants for utilization or geological sequestration, so as to control the emission of CO2.

[0003] The technology of capturing carbon dioxide based on calcium looping is considered to be one of the most promising post-combustion CO2 capture technologies, which can be directly applied to conventional coal-fired power plants, cement plants, steel plants, etc. The principle is as follows: Flue gas containing 15-40% CO2 is introduced into a carbonation reactor, and the calcium-based absorbent absorbs CO2. Then, the carbonated product is transported to another calcination reactor with a higher temperature through a series of fluidized bed systems, and the calcium-based absorbent is regenerated. At the same time, high-concentration CO2 is obtained for compression, transportation and final geological sequestration; and the regenerated calcium-based absorbent is transported back to the carbonation reactor to capture CO2 in the flue gas. This technology has multiple advantages: 1. The precursor of the calcium-based absorbent is rich in reserves and low in price in nature; 2. It has superior chemical reaction kinetics characteristics in theory; 3. It has a relatively high CO2 absorption capacity in theory and can be recycled; 4. There is no need to reorganize the existing boiler units; 5. The cost is low and it has good commercial application prospects; 6. It is environmentally friendly and does not produce any secondary pollution.

[0004] However, the reaction activity of natural calcium-based absorbents is poor during the process of capturing carbon dioxide, and the conversion rate is low in actual use, which also causes large energy consumption in the production process. In order to improve the reaction activity of calcium-based absorbents, scholars have made a series of explorations, but materials with good performance often have a large preparation cost, and simple modification treatment is difficult to achieve high-efficiency carbon dioxide capture by materials.

[0005] In existing studies, various modification methods have different effects on improving the reactivity and cyclic stability of calcium-based sorbents, but there are certain problems and defects at present. For example, the cost of the sorbent has not been significantly reduced, or the preparation cycle of the sorbent is long and the process is complex, and even some cause secondary pollution. Organic acid modification has recently been considered as one of the promising modification methods for calcium-based sorbents. It reacts with calcium-based sorbents to form calcium organic acids or calcium-based complexes. After a simple heat treatment of these calcium organic acids or complexes, the organic acid functional groups decompose rapidly, and a modified calcium-based sorbent with a well-developed pore structure and loose texture can be formed.

[0006] Document 1 discloses a method for modifying CaO with ethanol. Although it reduces the decay rate of the carbonation conversion rate to a certain extent, CaO or CaCO3 itself does not react with ethanol and is not soluble in ethanol, and the interaction is small, and the improvement of the final carbon capture capacity is also insufficient.

[0007] Document 2 discloses a method for modifying limestone with pyroligneous acid. The modification with pyroligneous acid improves the microstructure of the adsorbent, such as pore size distribution and specific surface area, and then enhances the cyclic carbon capture capacity of limestone.

[0008] Document 3 discloses a method for modifying CaO-based sorbents with formic acid. Although the modification with formic acid solution improves the crystal structure of CaO, due to the low conversion rate of calcium formate, the treatment with gaseous formic acid fails to increase the carbon dioxide capacity of the adsorbent.

[0009] Document 4 discloses a method for modifying CaCO3 particles with acetic acid, which increases both the conversion rate and the porosity, but the problems of high price and high cost have still not been solved, and the process is rather cumbersome.

[0010] Document 5 discloses a method for modifying limestone with propionic acid. The modification with propionic acid enhances the CO2 capture reactivity and sulfation reactivity of calcium-based sorbents, and the formed sorbent has a good pore structure, but the cost is high and it cannot be recycled.

[0011] It can be seen that organic acid modification can improve the carbonation (CO2 capture) reactivity of calcium-based sorbents to a certain extent, but the preparation cost of the sorbent is still high. Moreover, the simple modification methods reported in the above documents have not yet achieved the ideal CO2 capture efficiency. Therefore, there is an urgent need to develop a method for obtaining high-performance calcium-based sorbents at low cost.

[0012] Literature 1: Li Y, Zhao C, Qu C, et al. CO2 Capture Using CaO Modified with Ethanol / Water Solution during Cyclic Calcination / Carbonation[J]. Chem Eng Technol, 2008, 31(2): 237–244.

[0013] Literature 2: Li Y, Sun R, Liu H, Lu C. Cyclic CO2 Capture Behavior of Limestone Modified with Pyroligneous Acid(PA) during Calcium Looping Cycles[J]. Ind Eng Chem Res, 2011, 50: 10222–10228.

[0014] Literature 3: Ridha FN, Manovic V, Wu Y, et al. Post-combustion CO2 capture by formic acid-modified CaO-based sorbents[J]. Int J Greenh Gas Control, 2013, 16: 21-28.

[0015] Literature 4: Imani M, Tahmasebpoor M, Sánchez-Jiménez PE, et al. Improvement in cyclic CO2 capture performance and fluidization behavior of eggshell-derived CaCO3 particles modified with acetic acid used in calcium looping process[J]. J CO2 Util, 65(2022), 102207.

[0016] Literature 5: Sun R, Li Y, Wu S, et al. Enhancement of CO2 capture capacity by modifying limestone with propionic acid[J]. Powder Technol, 2013, 233: 8-14. Summary of the Invention

[0017] Problems to be Solved by the Invention

[0018] In order to solve the technical problems existing in the prior art, the present invention provides a preparation method of a calcium-based absorbent, the calcium-based absorbent and its use. By using the preparation method of the calcium-based absorbent of the present invention, a calcium-based absorbent with a fluffy structure, a large specific surface area and rich mesopores can be prepared, which has a low cost, can be used for highly efficient capture of greenhouse gas CO2 in flue gas, and is not easily sintered and deactivated, and can be used for multiple cycle absorptions.

[0019] Solutions for Solving the Problems

[0020] [1] A preparation method of a calcium-based absorbent, which comprises the following steps:

[0021] Step 1) Calcining a calcium-based raw material to obtain a raw material containing calcium oxide;

[0022] Step 2) Adding the raw material containing calcium oxide, biomass and water into a hydrothermal reaction kettle for mixing to obtain a mixed slurry;

[0023] Step 3) Performing an in-situ hydrothermal reaction on the mixed slurry to obtain a slurry;

[0024] Step 4) Filtering the slurry to obtain a filter cake, drying the filter cake and then calcining to obtain a calcium-based absorbent.

[0025] [2] The preparation method according to [1], wherein, in the step 1), the calcium-based raw material is selected from one or more of quicklime, limestone, eggshells, snail shells or shells;

[0026] The raw material containing calcium oxide is a powder with a particle size of 20 μm to 2 mm.

[0027] [3] The preparation method according to [1] or [2], wherein, in the step 2), the biomass is cellulose, rice husk, wood chips or cotton stalks.

[0028] [4] The preparation method according to any one of [1] to [3], wherein, in the step 2), the mass ratio of the biomass to the raw material containing calcium oxide is 5:1 to 20:1.

[0029] [5] The preparation method according to any one of [1] to [4], wherein, in the step 3), the temperature of the in-situ hydrothermal reaction is 150 °C to 280 °C; the time of the in-situ hydrothermal reaction is 12 to 20 hours; the pressure of the in-situ hydrothermal reaction is 2 to 10 MPa.

[0030] [6] The preparation method according to any one of [1] to [5], wherein, in step 4), the drying temperature is 100°C to 150°C; the calcination temperature is 700°C to 900°C.

[0031] [7] The preparation method according to any one of [1] to [6], further comprising the following steps:

[0032] Step 5) Grind and screen the calcium-based absorbent obtained in step 4) so that the particle size of the calcium-based absorbent does not exceed 0.3 mm.

[0033] [8] The preparation method according to any one of [1] to [7], wherein, in step 2), magnesium oxide is optionally doped in the mixed slurry.

[0034] [9] A calcium-based absorbent, which is a calcium-based absorbent obtained by the preparation method according to any one of [1] to [8].

[0035]

[10] Use of the calcium-based absorbent according to [9] for absorbing carbon dioxide.

[0036] Effects of the Invention

[0037] The preparation method of the calcium-based absorbent of the present invention makes biomass be converted into bio-oil rich in organic acids through a hydrothermal reaction system of high temperature and high pressure. The bio-oil in-situ modifies the calcium-based absorbent, and a calcium-based absorbent with fluffy structure, large specific surface area and rich mesopores is prepared. It is not easy to sinter and deactivate, can be used for multiple cycle absorptions, is environmentally friendly, has low cost and rich raw materials. The calcium-based absorbent of the present invention can be used for highly efficient capture of greenhouse gas CO2 in flue gas. When recycled more than 33 times, it can still maintain a CO2 capture performance more than 470% higher than that of the unmodified material, and the effect is remarkable. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the preparation of the modified calcium-based absorbent.

[0039] A. Preparation method of traditional pyrolysis tar (baking condensate) modified calcium-based adsorbent;

[0040] B. Preparation method of the calcium-based adsorbent in Example 1 of the present invention.

[0041] Figure 2 Carbon capture performance test diagrams of calcium-based absorbent 1, calcium-based absorbent-pair 1 and calcium-based absorbent-pair 2 after 33 cycles under mild calcium cycle and / or severe calcium cycle conditions.

[0042] Figure 3Performance test chart of calcium-based absorbents prepared at different in-situ hydrothermal reaction temperatures in Example 2 of the present invention after 33 cycles of carbon capture.

[0043] Figure 4 Performance test chart of calcium-based absorbents prepared under different in-situ hydrothermal reaction pressures in Example 3 of the present invention after 33 cycles of carbon capture.

[0044] Figure 5 Performance test chart of calcium-based absorbents prepared by adding different doping substances in Example 4 of the present invention after 33 cycles of carbon capture.

[0045] Figure 6 SEM diagrams of samples of calcium-based absorbent 3-2 and calcium-based absorbent-dui1 of the present invention after the first calcination and 33 cycles.

[0046] A. After the first calcination of calcium-based absorbent-dui1;

[0047] B. After the first calcination of calcium-based absorbent 3-2;

[0048] C. After 33 cycles of calcium-based absorbent-dui1;

[0049] D. After 33 cycles of calcium-based absorbent 3-2.

[0050] Figure 7 XRD test charts of samples of calcium-based absorbent 3-2 and calcium-based absorbent-dui1 of the present invention after the first calcination and 33 cycles.

[0051] A. After the first calcination of calcium-based absorbent-dui1;

[0052] B. After 33 cycles of calcium-based absorbent-dui1;

[0053] C. After the first calcination of calcium-based absorbent 3-2;

[0054] D. After 33 cycles of calcium-based absorbent 3-2. Detailed implementation manners

[0055] The following will detail various exemplary embodiments, features, and aspects of the present invention. The special term "exemplary" here means "serving as an example, embodiment, or illustrative". Any embodiment described as "exemplary" here does not necessarily have to be construed as superior or better than other embodiments.

[0056] In addition, to better illustrate the present invention, numerous specific details are given in the following detailed implementation manners. Those skilled in the art should understand that the present invention can also be implemented without certain specific details. In other instances, methods, means, equipment, and steps well-known to those skilled in the art are not described in detail to highlight the gist of the present invention.

[0057] Unless otherwise specified, the units used in this specification are all international standard units, and the numerical values and numerical ranges appearing in the present invention should be understood to include the systematic errors inevitable in industrial production.

[0058] In this specification, the meaning expressed by "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0059] In this specification, the "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc. mentioned refer to the specific elements (e.g., features, structures, properties, and / or characteristics) related to the embodiment, which are included in at least one of the embodiments described herein, and may or may not exist in other embodiments. Additionally, it should be understood that the elements can be combined in various embodiments in any suitable manner.

[0060] In this specification, the numerical range expressed by "numerical value A to numerical value B" refers to the range including the endpoint numerical values A and B.

[0061] The present invention provides a preparation method of a calcium-based absorbent, which comprises the following steps:

[0062] Step 1) Calcining a calcium-based raw material to obtain a raw material containing calcium oxide;

[0063] Step 2) Adding the raw material containing calcium oxide, biomass, and water into a hydrothermal reaction kettle for mixing to obtain a mixed slurry;

[0064] Step 3) Performing an in-situ hydrothermal reaction on the mixed slurry to obtain a slurry;

[0065] Step 4) Filtering the slurry to obtain a filter cake, drying the filter cake and then calcining it to obtain a calcium-based absorbent.

[0066] The calcium-based raw material is a natural material mainly composed of calcium carbonate or calcium oxide. The calcium-based raw material is calcined to obtain a raw material containing calcium oxide, and the involved reaction formula is CaCO3→CaO+CO2↑. Preferably, the mass fraction of calcium carbonate in the calcium-based raw material is greater than 80%. <X

[0067] According to the preparation method of the present invention, in step 1), the calcium-based raw material is selected from one or more of quicklime, limestone, eggshells, snail shells, or oyster shells.

[0068] According to the preparation method of the present invention, in step 1), the calcination temperature is 700°C to 1100°C.

[0069] According to the preparation method of the present invention, in step 1), the raw material containing calcium oxide is a powder with a particle size of 20 μm to 2 mm.

[0070] According to the preparation method of the present invention, in step 2), the biomass is cellulose, rice husk, wood chips or cotton stalks.

[0071] According to the preparation method of the present invention, in step 2), the mass ratio of the biomass to the raw material containing calcium oxide is 5:1 to 20:1, for example, it can be 6:1, 8:1, 10:1, 12:1, 14:1, 16:1, 18:1, etc.

[0072] Within this mass ratio range, the calcium-based absorbent can be effectively modified, and the resulting calcium-based absorbent can maintain good absorption performance even after multiple cycles of use. If the mass ratio is too low, the modification will be insufficient, and the change degree of the pore structure on the material surface is relatively low; if the mass ratio is too high, more biomass is used, and the energy consumption of the process will also increase.

[0073] According to the preparation method of the present invention, in step 2), magnesium oxide can be doped in the mixed slurry to further improve the cyclic carbon capture ability of the in-situ hydrothermal biomass synergistically modified calcium-based absorbent.

[0074] According to the preparation method of the present invention, in step 2), the mass ratio of the doping substance to the raw material containing calcium oxide is 1:5 to 1:10, for example, it can be 1:6, 1:7, 1:8, 1:9, etc.

[0075] The raw material containing calcium oxide, biomass and water are encapsulated in a hydrothermal reaction kettle. In the high-temperature and high-pressure hydrothermal reaction system, the biomass is hydrothermally converted into biochar and bio-oil rich in organic acids. Under the action of the raw material containing calcium oxide (acid-base neutralization reaction), the hydrothermal conversion of the biomass proceeds in the direction of hydrothermal liquefaction (Le Chatelier's principle), breaking through the conversion equilibrium curve to generate a higher yield of organic acids; at the same time, the raw material containing calcium oxide forms a complex organic acid calcium complex under the in-situ synergistic modification of the bio-oil.

[0076] According to the preparation method of the present invention, in step 3), the temperature of the in-situ hydrothermal reaction is 150°C to 280°C, for example, it can be 160°C, 180°C, 200°C, 220°C, 240°C, 260°C, 270°C, 275°C, etc. If the temperature is too low, the reaction is not sufficient, resulting in insufficient modification and insignificant effect; if the temperature is too high, the energy consumption is large, and the in-situ hydrothermal reaction proceeds in the direction of generating biochar, reducing the modification effect.

[0077] According to the preparation method of the present invention, in step 3), the time of the in-situ hydrothermal reaction is 12 to 20 hours. For example, it can be 14 hours, 16 hours, 18 hours, etc. If the time is too short, the modification will be insufficient and the pore structure will not be excellent enough; if the time is too long, the physical properties of the absorbent will be poor, reducing the use effect of the absorbent.

[0078] According to the preparation method of the present invention, in step 3), the pressure of the in-situ hydrothermal reaction is 2 to 10 MPa. For example, it can be 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, etc. Too low pressure will affect the efficiency of hydrothermal biomass conversion; too high pressure will cause the in-situ hydrothermal reaction to proceed in the direction of generating biochar, reducing the modification effect.

[0079] According to the preparation method of the present invention, in step 4), the drying temperature is 100°C to 150°C. For example, it can be 110°C, 120°C, 130°C, 140°C, etc.

[0080] According to the preparation method of the present invention, in step 4), the calcination temperature is 700°C to 900°C. For example, it can be 750°C, 800°C, 850°C, etc. This calcination temperature can completely burn and remove the organic complex, and the pore structure can be retained, and a calcium-based absorbent with a fluffy structure, a large specific surface area, and rich mesopores can be obtained.

[0081] According to the preparation method of the present invention, in step 4), the calcination time is 2 to 4 hours.

[0082] According to the preparation method of the present invention, it further includes the following steps:

[0083] Step 5) Grind and screen the calcium-based absorbent obtained in step 4) so that the particle size of the calcium-based absorbent does not exceed 0.3 mm.

[0084] The present invention also provides a calcium-based absorbent, which is the calcium-based absorbent obtained according to the preparation method of the present invention.

[0085] The present invention also provides a use of the calcium-based absorbent according to the present invention for absorbing carbon dioxide.

[0086] Taking the absorption of carbon dioxide as an example, the calcium-based absorbent of the present invention shows a significant improvement in carbon dioxide absorption capacity during multiple cyclic reactions, especially obvious in easily available natural materials. Taking the natural material of eggshell as an example, the carbon capture capacity is 0.053 g-CO2 / g-calcium-based absorbent after 33 cycles, while the in-situ hydrothermal biomass co-modified calcium-based absorbent under the optimal conditions can still maintain at 0.253 g-CO2 / g-calcium-based absorbent, which is 4.7 times higher. The calcium-based absorbent prepared in the present invention has rich pores, good porous structure and excellent anti-sintering performance, and can maintain a stable pore structure of macropores during high-temperature cycling. This structure can effectively slow down high-temperature sintering, thereby maintaining its high adsorption activity and enabling the calcium-based absorbent to have excellent cyclic absorption characteristics.

[0087] Embodiment

[0088] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0089] Example 1

[0090] Figure 1 (B) in the present invention is a schematic diagram for the preparation of the in-situ hydrothermal biomass co-modified calcium-based absorbent. Example 1 is carried out according to the Figure 1 device and steps shown in (B).

[0091] Using eggshell as the calcium-based raw material, the calcium-based raw material is calcined at 900 °C for 2 h to obtain a raw material containing calcium oxide; 1 g of the raw material containing calcium oxide and 8 g of cellulose powder are put into a hydrothermal reaction kettle and mixed to obtain a mixed slurry; the mixed slurry is subjected to in-situ hydrothermal reaction, the temperature of the in-situ hydrothermal reaction is 275 °C, the pressure of the in-situ hydrothermal reaction is 5 MPa, and the time of the in-situ hydrothermal reaction is 16 hours to obtain a slurry; the slurry is filtered to obtain a filter cake, and after the filter cake is dried at 120 °C for 12 h, it is calcined at 800 °C for 2 h in a muffle furnace to obtain calcium-based absorbent 1 (denoted as HT-5MPa / 275 °C).

[0092] Comparative Example 1

[0093] The eggshell is calcined at 900 °C for 2 h to obtain a raw material containing calcium oxide, and calcium-based absorbent-dui 1 (denoted as RawEggshell) is obtained.

[0094] Comparative Example 2

[0095] Figure 1Figure (A) is a schematic diagram for the preparation of a traditional pyrolysis tar (baking condensate) modified calcium-based absorbent. Comparative Example 2 was carried out according to Figure 1 the device and steps shown in (A) of

[0096] Eggshells were used as the calcium-based raw material. The calcium-based raw material was calcined at 900 °C for 2 h to obtain a raw material containing calcium oxide. Rice husks were put into a pyrolysis reactor and pyrolyzed at 220 °C to obtain tar; the generated tar was used to modify the above-mentioned raw material containing calcium oxide to obtain a slurry; the slurry was filtered to obtain a filter cake, and the filter cake was dried at 120 °C for 12 h and then calcined in a muffle furnace at 800 °C for 2 h to obtain a calcium-based absorbent - Pair 2 (denoted as TC-Eggshell).

[0097] Calcium-Loop Carbon Capture Test

[0098] CO2 cyclic capture experiments were carried out in a thermogravimetric reactor:

[0099] Mild calcium cycle: 1) Carbonation (15% CO2, reaction temperature 650 °C, CaO + CO2 → CaCO3); 2) Regeneration (N2, reaction temperature 850 °C, CaCO3 → CaO + CO2).

[0100] Severe calcium cycle: 1) Carbonation (15% CO2, reaction temperature 650 °C, CaO + CO2 → CaCO3); 2) Regeneration (80% CO2 / N2, reaction temperature 900 °C, CaCO3 → CaO + CO2).

[0101] The calcium-based absorbent 1 was tested under mild calcium cycle carbon capture conditions for 33 cycles, corresponding to Figure 2 the first curve (from top to bottom) in Figure 2 ; the calcium-based absorbent 1 was tested under severe calcium cycle carbon capture conditions for 33 cycles, corresponding to Figure 2 the second curve (from top to bottom) in Figure 2 ; the calcium-based absorbent - Pair 2 was tested under severe calcium cycle carbon capture conditions for 33 cycles, corresponding to Figure 2 the third curve (from top to bottom) in

[0102] From Figure 2 it can be seen that the carbon capture ability of the calcium-based absorbent 1 after 33 cycles of mild and / or severe calcium cycle is significantly better than that of the calcium-based absorbent - Pair 1 and the calcium-based absorbent - Pair 2.

[0103] Example 2

[0104] Using the same preparation method as in Example 1, the temperature of the in-situ hydrothermal reaction was changed to 180 °C and 225 °C, and calcium-based absorbents 2-1 (denoted as HT-5MPa / 180 °C) and calcium-based absorbent 2-2 (denoted as HT-5MPa / 225 °C) were obtained respectively.

[0105] Calcium-Loop Carbon Capture Test

[0106] The calcium-based absorbent 1, calcium-based absorbent 2-1, calcium-based absorbent 2-2, and calcium-based absorbent-pair 1 were subjected to a CO2 cyclic capture experiment in a thermogravimetric reactor, tested under severe calcium cycle carbon capture conditions, and uniformly cycled 33 times. The results are as Figure 3 shown. It can be seen from the figure that the optimal temperature of the in-situ hydrothermal reaction is 275 °C.

[0107] Example 3

[0108] Using the same preparation method as in Example 1, the pressure of the in-situ hydrothermal reaction was changed to 3 MPa and 8 MPa, and calcium-based absorbents 3-1 (denoted as HT-3MPa / 275 °C) and calcium-based absorbent 3-2 (denoted as HT-8MPa / 275 °C) were obtained respectively.

[0109] Calcium-Loop Carbon Capture Test

[0110] The calcium-based absorbent 1, calcium-based absorbent 3-1, calcium-based absorbent 3-2, and calcium-based absorbent-pair 1 were subjected to a CO2 cyclic capture experiment in a thermogravimetric reactor, tested under severe calcium cycle carbon capture conditions, and uniformly cycled 33 times. The results are as Figure 4 shown.

[0111] It can be seen from the figure that the optimal pressure of the in-situ hydrothermal reaction is 8 MPa. The carbon capture capacity of calcium-based absorbent-pair 1 after 33 cycles is 0.053 g-CO2 / g-calcium-based absorbent, while the calcium-based absorbent 3-2 can still maintain at 0.253 g-CO2 / g-calcium-based absorbent after 33 cycles, which is increased by 4.7 times.

[0112] Example 4

[0113] Using the same preparation method as that of calcium-based absorbent 3-2, magnesium oxide or copper oxide was doped in the mixed slurry, and the raw materials containing calcium oxide were fed according to the mass ratio of doped substance: raw material containing calcium oxide = 1:8, and calcium-based absorbents 4-1 (denoted as HT-Mg / Eggshell) and calcium-based absorbent 4-2 (denoted as HT-Cu / Eggshell) were obtained respectively.

[0114] Calcium-Loop Carbon Capture Test

[0115] The calcium-based absorbents 3-2, 4-1, 4-2, and -pair 1 were subjected to CO2 cyclic capture experiments in a thermogravimetric reactor, tested under harsh calcium-looping carbon capture conditions, and cycled 33 times uniformly. The results are as Figure 5 shown. It can be seen from the figure that Mg doping can further improve the cyclic carbon capture ability of the calcium-based absorbent, while Cu doping is not conducive to the cyclic carbon capture of the calcium-based absorbent.

[0116] Scanning Electron Microscope (SEM) Test

[0117] The micro-morphologies of the samples of calcium-based absorbent -pair 1 and calcium-based absorbent 3-2 after the first calcination and 33 cycles were observed respectively. The results are as Figure 6 shown. Figure 6 (A)-(D) of

[0118] X-Ray Diffraction (XRD) Test

[0119] are the SEM images of calcium-based absorbent -pair 1 after the first calcination, calcium-based absorbent 3-2 after the first calcination, calcium-based absorbent -pair 1 after 33 cycles, and calcium-based absorbent 3-2 after 33 cycles respectively. It can be seen from the figure that calcium-based absorbent 3-2 has a rich pore structure and can maintain a stable mesoporous structure at high temperature cyclic reactions. This structure can effectively slow down sintering deactivation, thereby maintaining a high adsorption activity and making the calcium-based absorbent have excellent cyclic absorption characteristics. Figure 7 shown. Figure 7 (A)-(D) of

[0120] It should be noted that although the technical solutions of the present invention are introduced by specific examples, those skilled in the art can understand that the present invention should not be limited thereto.

[0121] The embodiments of the present invention have been described above. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other ordinary skilled in the art in this technical field to understand the disclosed embodiments.

Claims

1. A preparation method of a calcium-based absorbent, characterized in that, It includes the following steps: Step 1) Calcining the calcium-based raw material to obtain a raw material containing calcium oxide; Step 2) Adding the raw material containing calcium oxide, biomass and water into a hydrothermal reactor for mixing to obtain a mixed slurry; Step 3) Conducting an in-situ hydrothermal reaction on the mixed slurry to obtain a slurry; Step 4) Filtering the slurry to obtain a filter cake, drying the filter cake and then calcining it to obtain a calcium-based absorbent.

2. The preparation method according to claim 1, wherein In the said Step 1), the calcium-based raw material is selected from one or more of quicklime, limestone, eggshells, snail shells or shells; The raw material containing calcium oxide is a powder with a particle size of 20μm to 2mm.

3. The preparation method according to claim 1 or 2, wherein In the said Step 2), the biomass is cellulose, rice husk, wood chips or cotton stalks.

4. The preparation method according to any one of claims 1-3, wherein, In the said Step 2), the mass ratio of the biomass to the raw material containing calcium oxide is 5:1 to 20:

1.

5. The preparation method according to any one of claims 1-4, wherein, In the said Step 3), the temperature of the in-situ hydrothermal reaction is 150°C to 280°C; the time of the in-situ hydrothermal reaction is 12 to 20 hours; the pressure of the in-situ hydrothermal reaction is 2 to 10MPa.

6. The preparation method according to any one of claims 1-5, wherein, In the said Step 4), the drying temperature is 100°C to 150°C; the calcining temperature is 700°C to 900°C.

7. The preparation method according to any one of claims 1-6 further includes the following steps: Step 5) Grinding and screening the calcium-based absorbent obtained in Step 4) to make the particle size of the calcium-based absorbent not exceed 0.3mm.

8. The preparation method according to any one of claims 1-7, in the said Step 2), optionally doping magnesium oxide in the mixed slurry.

9. A calcium-based absorbent, which is the calcium-based absorbent obtained by the preparation method according to any one of claims 1-8.

10. Use of the calcium-based absorbent according to claim 9 for absorbing carbon dioxide.

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