A method for preparing acid-modified calcium-based CO2 adsorbent microspheres

Abstract

The application discloses a preparation method of acid-modified calcium-based CO2 adsorbent pellets. The method comprises the following steps: mixing and stirring a metal precursor solution and a complexing agent solution to prepare a mixed solution; concentrating the mixed solution after reaction to obtain a concentrated sol liquid; drying the concentrated sol liquid to obtain a dry gel; calcining the dry gel at 600-700 DEG C to obtain a zirconium-doped modified calcium-based adsorbent raw powder; mixing the zirconium-doped modified calcium-based adsorbent raw powder with an acid-modifying reagent and water, and putting the mixture into a kneader to knead and stir for 10-30 min, extruding the mixture into a strip, polishing the strip at high speed to obtain spherical particles, and finally obtaining calcium-based CO2 adsorbent pellets. The obtained adsorbent pellets have high sintering resistance, high adsorption performance, high mass transfer characteristics, high crushing strength and high wear resistance, and the kilogram-level production of the calcium-based adsorbent is realized, so that the adsorbent pellets are suitable for the adsorption and separation of high-temperature CO2 in flue gas of a thermal power plant.

Description

Technical Field

[0001] This invention relates to a modification technology for adsorbent materials used for high-temperature carbon dioxide removal, specifically to a method for preparing acid-modified calcium-based CO2 adsorbent microspheres. Background Technology

[0002] Since the beginning of this century, countries around the world have attached great importance to the research and development of alternative and renewable energy sources. Even so, fossil fuels will continue to dominate in the coming decades. The excessive use of fossil fuels has increased atmospheric carbon dioxide levels, accelerated global warming and glacial melting, and other ecological problems. In the long run, this will seriously harm the environment upon which we depend for survival, making the control of carbon emissions an urgent matter.

[0003] In recent years, the recycling of CO2 using calcium oxide has attracted increasing attention. In this technology, calcium-based adsorbents, as a CO2 capture material, possess advantages such as wide availability of raw materials, low cost, fast adsorption rate, high adsorption capacity, environmental friendliness, and low toxicity. Especially for high-temperature flue gas emitted from coal-fired power plants, calcium-based adsorbents can be used to directly adsorb and separate CO2, thus reducing energy loss and lowering overall costs.

[0004] The adsorption mechanism of CO2 by calcium-based adsorbents is as follows: In this reversible process, CaO typically adsorbs CO2 and converts it into CaCO3 at temperatures exceeding 600°C. Subsequently, after heat treatment at even higher temperatures (usually above 800°C), the adsorbent is regenerated back into CaO, enabling reuse. Furthermore, calcium cycling technology can be applied to various fields, such as calcium-based chemical looping gasification, calcium cycle-methane dry reforming, adsorption-enhanced methane steam reforming, reverse water-gas shift conversion, and thermochemical energy storage in solar power plants, demonstrating broad application prospects.

[0005] However, during the multi-cycle CO2 adsorption / desorption process, due to the low Taman temperature (533℃) of CaCO3, calcium-based adsorbent crystals undergo agglomeration and sintering during the reversible transformation of CaCO3 and CaO. This leads to internal pore blockage, particle enlargement, and hinders CO2 diffusion, ultimately reducing the adsorbent's CO2 adsorption performance. Furthermore, solid adsorbents used industrially for CO2 adsorption are typically used in fluidized bed reactors. Under fluidized conditions, the poor compressive strength and wear resistance of calcium-based adsorbent particles gradually break down and wear, generating a large amount of powder. After multiple reaction cycles, significant adsorbent loss occurs, resulting in a decline in adsorption performance. These are the biggest obstacles restricting the commercial application of calcium-based adsorbents.

[0006] Studies have shown that introducing high-melting-point inert materials into the preparation of calcium-based adsorbents through chemical doping can effectively improve the thermal stability of the prepared samples, thereby reducing the occurrence of adsorbent agglomeration and sintering. Furthermore, modifying calcium-based adsorbents with suitable organic or inorganic acids can improve the structural characteristics of the adsorbent particles, such as CaO grain size, sample specific surface area, and pore volume, thus enhancing the adsorption performance and mechanical strength. In summary, inert material doping and acid modification can effectively improve the anti-sintering properties, CO2 adsorption performance, and mechanical strength of calcium-based adsorbents, thereby increasing their industrial application potential.

[0007] The inventors have previously published related research reports and papers, including a doctoral dissertation by Guo Hongxia, "Study on Inert Component Doping and Structure-Activity Relationship of Calcium-Based CO2 Adsorbents" (Tianjin University, 2018), which reported the preparation of Zr-doped calcium-based adsorbents using the sol-gel method. The uniformly distributed CaZrO3 effectively inhibited the agglomeration of CaO crystals. Higher Zr doping content resulted in smaller nanoparticles of the adsorbent, with both mesopores and macropores coexisting, jointly promoting good adsorption performance. This work was a small-scale study, confirming the important role of the Zr component in the adsorbent sample. Furthermore, a master's thesis by Jiang Tao, "Scale-up Preparation and Molding Study of Calcium Oxide-Based CO2 Adsorbents" (Tianjin University, 2020), investigated the scale-up preparation of Zr-doped CaO-based CO2 adsorbent powder. The effects of Ca precursor concentration, citric acid dosage, gelation temperature and time, CO2 volume fraction during carbonation / calcination, and calcination temperature on the adsorption performance of the samples were investigated. The production of 4 kg / batch of adsorbent powder was successfully achieved. This section represents a preliminary scale-up study, determining the production process conditions for Zr-doped calcium-based adsorbent powder. However, the samples obtained in this work were all powdered calcium-based adsorbents, not granulated. Due to their relatively poor compressive strength and wear resistance, they cannot be directly used for industrial CO2 capture. Furthermore, the traditional extrusion-spheronization process typically damages the pore structure of the adsorbent particles, reducing the specific surface area and pore volume of the product, thus decreasing the adsorbent's adsorption performance. In addition, the extruder in this molding process is prone to clogging due to material flow, making it impossible to achieve large-scale production of small-diameter granules (below 0.5 mm). Therefore, improvements to the molding process are needed to meet practical application requirements. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of current technologies by providing a method for preparing acid-modified Zr-doped calcium-based CO2 adsorbent microspheres. Based on the achievement of kilogram-scale / batch production of calcium zirconium adsorbent powder, this method further investigates its molding and granulation process. Through spin granulation-spheronization, an appropriate amount of acid reagent is added during the molding process for modification, resulting in acid-modified Zr-doped calcium-based CO2 adsorbent microspheres with excellent adsorption performance and mechanical strength. This provides theoretical and technical support for the industrial production of calcium-based adsorbents. The adsorbent microspheres obtained by this invention possess high anti-sintering properties, high adsorption performance, high mass transfer characteristics, high crushing strength, and high wear resistance, and achieve kilogram-scale production of calcium-based adsorbents. They are suitable for the adsorption and separation of high-temperature CO2 in flue gas from thermal power plants.

[0009] The technical solution of this invention is as follows:

[0010] A method for preparing acid-modified calcium-based CO2 adsorbent microspheres, the method comprising the following steps:

[0011] 1) Prepare a mixed solution by mixing and stirring the metal precursor solution and the complexing agent solution;

[0012] The metal precursor solution comprises a calcium salt, a zirconium salt, and deionized water, with a molar ratio of calcium salt:zirconium salt = 15–40:1 and deionized water:(calcium salt + zirconium salt) = 10–40:1. The complexing agent solution comprises a complexing agent and deionized water, with a molar ratio of deionized water:complexing agent = 4–20:1 and a molar ratio of complexing agent:(calcium salt + zirconium salt) = 0.5:1–2:1. The complexing agent is citric acid.

[0013] 2) Stir the mixed solution continuously for 1 to 6 hours at a stirring speed of 100 to 300 rpm and a reaction temperature of 50 to 80°C;

[0014] 3) After the reaction is complete, the mixed solution is concentrated to 30-35% of its original volume by vacuum distillation to obtain a concentrated sol liquid;

[0015] 4) Place the concentrated sol into a forced-air drying oven and dry it at 100-120℃ for 8-12 hours to obtain a dry gel. Then grind the dry gel and place it in a muffle furnace and calcine it at 600-700℃ for 1-3 hours to obtain the zirconium-doped modified calcium-based adsorbent powder.

[0016] 5) The calcium-based adsorbent powder is first thoroughly mixed with water, then mixed with acid-modifying reagent, and then placed together in a kneader and kneaded for 10-30 minutes to obtain a mixture in the form of a pellet.

[0017] The mass ratio of zirconium-doped calcium-based adsorbent powder to acid-modifying reagent is 4:1 to 19:1; the mass ratio of zirconium-doped calcium-based adsorbent powder to deionized water is 0.5:1 to 1.5:1.

[0018] 6) The preform is placed in a spinning pellet mill and extruded at a speed of 20-40 rpm to obtain strips. The strips are then broken into rod-shaped particles with a length of 0.3-1 cm.

[0019] 7) The short rod-shaped particles are placed in a spherical mill and ground at a high speed of 500-1500 rpm to obtain spherical particles. The small spheres are air-dried naturally for 2-6 hours, then placed in a drying oven and dried at 100-140℃ for 1-2 hours. Finally, they are placed in a muffle furnace and calcined at 600-700℃ for 1-2 hours to obtain calcium-based adsorbent spheres.

[0020] In step 1), the calcium salt is calcium nitrate; in step 1), the zirconium salt is zirconium nitrate.

[0021] In step 3), dense bubbles are generated on the surface of the concentrated solution, and the solution gradually changes from colorless to pale yellow.

[0022] In step 5), the acid-modifying reagent is one of nitric acid (purity 65-68%), acetic acid (purity ≥99%), or malonic acid (purity ≥99%).

[0023] In step 7), the particle size of the calcium-based adsorbent microspheres is 0.3 mm to 1.5 mm.

[0024] The amount of the metal calcium salt, metal zirconium salt and complexing agent in step 1), and the amount of calcium-based adsorbent powder in step 5) are in the range of hundreds of grams to tens of thousands of grams (100 to 10,000 g).

[0025] The essential features of this invention are:

[0026] In the current technology, Chinese patent document CN101961638B presents a method for synthesizing wear-resistant nano-calcium-based CO2 reactive adsorbents. This patent involves dispersing CaCO3 in water, adding aluminum sol and stirring, followed by spray granulation to obtain small spheres with a diameter of 20–250 μm, thus obtaining spherical calcium oxide-based CO2 adsorbents. The precursor materials used in this patent are only physically mixed, resulting in weak intermetallic interactions. Compared to the chemical doping modification method used in this invention, it is more difficult to effectively improve the cyclic CO2 adsorption stability of the prepared adsorbent.

[0027] Chinese patent document CN103962087B discloses a surface-coated modified nano-calcium-based CO2 adsorbent and its preparation method. The surface coating layer is a metal oxide, and the uniformity and thickness of the surface coating layer are controlled by an adsorption phase reaction method. This patent is simple to operate and easy to control in the small-scale preparation of the adsorbent. However, in the scale-up preparation process, due to the increased amount of raw materials, the mass and heat transfer of the various components of the material differs significantly from the small-scale test. Therefore, it becomes more difficult to adjust the uniformity and thickness of the coating layer using the aforementioned adsorption phase reaction method.

[0028] Chinese patent document CN106000301B discloses a method for preparing spherical calcium oxide-based CO2 adsorbents. This method involves combining sodium alginate with a calcium salt solution to obtain spherical calcium-based adsorbents with a particle size of 1.5 mm to 4 mm. This patent uses a syringe or peristaltic pump to drip the precursor solution into the calcium salt solution; however, this dripping method is inefficient and slow, making it unsuitable for the mass production of spherical adsorbents. In contrast, the spinning granulation-spheronization method used in this invention is more mature and can be used for the large-scale production of calcium-based adsorbent spheres.

[0029] Chinese patent document CN112275251A discloses a method for mass production of doped modified calcium-based CO2 adsorbent microspheres. This method synthesizes Al-doped calcium-based adsorbents through co-precipitation technology and extrusion-spheronization. It is a generally accepted fact in the literature that the adsorption performance of Al-modified calcium-based adsorbents is inferior to that of Zr-modified calcium-based adsorbents. While Al doping improves the thermal stability of the adsorbent, it is difficult to maintain a sustained decrease in CO2 adsorption capacity, limiting its industrial application prospects. Furthermore, in the extrusion-spheronization method used in that patent, the extruder is prone to clogging due to material flow issues, making it impossible to achieve large-scale production of small-diameter granules (below 0.5 mm). The spinning granulation-spheronization method used in this invention effectively solves this problem.

[0030] The aforementioned Chinese patent documents all focus on small-scale laboratory studies of calcium-based adsorbents. Even those including scale-up studies have significant limitations in their methods, and are still some distance from large-scale production. This invention, building upon the achievement of kilogram-level / batch production of calcium-based adsorbent powder, further utilizes an improved spinning granulation-spheronization technique to conduct acid modification studies on the adsorbent. This results in a product that, compared to the samples in the aforementioned patent documents, exhibits superior characteristics in CO2 adsorption capacity, cycle stability, wear rate, and crushing strength. Simultaneously, it provides a reference for the large-scale production of CaO-based adsorbents.

[0031] The beneficial effects of this invention are as follows:

[0032] 1) The acid-modified zirconium-doped calcium-based adsorbent produced by this invention has high industrial application prospects. Among many inert materials, the introduction of Zr species enables the synthesized adsorbent to exhibit superior CO2 capture ability. The Ca / Zr oxides contained therein, due to their high Tammann temperature, act as physical barriers between CaO particles, inhibiting the growth of CaO subcrystals and the melting of impurity micro-surfaces during calcination. Analysis of the Ca2p, Zr3d, and O1s photoelectron spectra of the synthesized sample shows that despite the formation of the CaZrO3 crystal phase, the binding energy of Ca2p does not change with the Zr doping content. On the one hand, the Zr3p1 / 2 peak is located at approximately 346.0 eV, overlapping with the Ca2p3 / 2 peak; on the other hand, Ca2p is not sensitive to the interaction between Ca and Zr. Conversely, with increasing Zr doping, the binding energies of Zr3d5 / 2 (approximately 181.5 eV) and Zr3d3 / 2 (approximately 184.0 eV) shift slightly upwards. This indicates an interaction between Ca and Zr and the formation of the CaZrO3 crystalline phase. Figure 1 The powder XRD pattern of zirconium-doped calcium-based adsorbent microspheres is shown. It can be seen that each sample contains the CaZrO3 crystalline phase, which has good thermal and chemical stability and a relatively low coefficient of thermal expansion. It can effectively alleviate the agglomeration and sintering of the adsorbent and improve the thermal stability of the calcium-based adsorbent in multiple adsorption / desorption cycles.

[0033] 2) This invention is the first to explore the molding and granulation of calcium-based adsorbent materials using spin granulation technology. Traditional screw extruders used in the extrusion method face many limitations when producing small-diameter particles, such as small extrusion surface, low extrusion pressure, easy material slippage, long material running time with the screw, high temperature, limited production, and low efficiency, especially in the case of small-orifice extrusion. The planetary roller spin granulator used in this invention features rollers that are tightly fitted to the extrusion screen, and the rollers' rotation and revolution speeds are consistent, eliminating slippage and achieving pure rolling friction. This results in high extrusion efficiency and enables high-volume production of small-diameter particles.

[0034] Furthermore, this invention is the first to use a tetrahedral toothed rolling disc for the spherical granulation of calcium-based adsorbent materials. The strip-shaped material obtained from the spin granulator rotates at high speed with the disc in a centrifugal rolling mill. Several forces act within the rolling mill: friction between the material and the disc, friction between the materials themselves, friction between the material and the cylinder wall, and the cutting force of the rolling teeth on the material. After being cut, the material undergoes both revolution and rotational tumbling motion under the action of these frictional forces, ultimately spheroidizing the strip-shaped particles into small spherical particles. Traditional truncated pyramidal toothed rolling discs are only suitable for materials with low moisture content, low viscosity, and no heat sensitivity, resulting in a narrow application range. In contrast, the tetrahedral toothed rolling disc used in this invention has strong cutting ability and a wide range of applications, effectively enabling the spherical granulation of high-viscosity, high-moisture calcium-based adsorbents.

[0035] 3) This invention is the first to propose using mass-produced (kilogram-level) zirconium-doped calcium-based adsorbent powder for spherical granulation. By employing a spin granulation-spheronization process, the type and amount of acid-modifying reagent were improved. For the first time, nitric acid and malonic acid were proposed as acid-modifying reagents for the mass preparation of calcium-based adsorbent microspheres, achieving beneficial results. As an organic acid, the addition of malonic acid improves the pore structure of the sample. When the mass ratio of calcium-based adsorbent powder to malonic acid is 4:1 to 19:1, the resulting calcium-based adsorbent microspheres possess a loose, porous structure and a large specific surface area, which is beneficial for CO2 diffusion and improves the adsorbent's chemical adsorption activity for CO2. Figure 2 The CO2 adsorption / desorption performance of the calcium-based adsorbent microspheres in Examples 1-4 was tested in a thermogravimetric reactor. The adsorption process was carried out at 650°C and 15 vol% CO2 / N2 for 30 min; the desorption process was carried out at 900°C and pure N2 atmosphere for 10 min. The product shown in Example 1, prepared by adding malonic acid, exhibited the best adsorption performance, with an initial CO2 adsorption capacity of 0.46 g CO2 / g adsorbent. After 16 CO2 adsorption / desorption cycles, its adsorption capacity still reached 0.41 g CO2 / g adsorbent, maintaining approximately 90% of the adsorption activity. Therefore, the calcium-based adsorbent microspheres synthesized according to this invention possess excellent CO2 adsorption performance and high overall thermal stability.

[0036] The addition of nitric acid, acetic acid, or malonic acid can ionize and release a large amount of H+ during the molding process of the adsorbent material. + Ions promote a chemical reaction between the adsorbent and CaO particles, resulting in a tight bond between the adsorbent particles. When the mass ratio of calcium-based adsorbent powder to nitric acid is 4:1 to 19:1, the uniformity of components in the calcium-based adsorbent spheres is effectively improved. The resulting adsorbent spheres exhibit higher single-particle crushing strength and better wear resistance, demonstrating significant advantages. Figure 3As can be seen, the single-particle crushing strength of the products shown in Examples 1 to 4 is better (tested 30 times respectively), with a minimum of 1.3N and a maximum of 1.93N. It has been reported that the minimum applicable particle strength in a fluidized bed reactor is 1N. Therefore, the calcium-based adsorbent microspheres synthesized according to the present invention all meet the practical application requirements. Figure 4 The wear resistance of the microsphere samples of Examples 1-4 in the brittleness tester is shown (tested at 1500 rpm and 3000 rpm respectively). Among them, the sample shown in Example 4 has better wear resistance, with a wear rate of 2.55 wt% after 1500 rpm and 3.62 wt% after 3000 rpm, indicating that this calcium-based adsorbent microsphere has excellent wear resistance.

[0037] Figure 5 Scanning electron microscope (SEM) images of the samples synthesized in Examples 1-4 are shown. Examples 1 and 2, obtained by adding malonic acid, exhibit a loose, porous structure and good sphericity. This indicates that malonic acid can act as a dispersant, effectively hindering the aggregation and sintering of adsorbent particles during the reaction. Therefore, adding an appropriate amount of malonic acid can improve the adsorption performance and thermal stability of calcium-based adsorbent microspheres. Examples 3 and 4, obtained by adding nitric acid, have a more compact structure compared to Examples 1 and 2. This may be due to the large amount of H₂ produced by nitric acid, a strong acid, during the molding process. + The ions react with CaO in an acid-base reaction, causing the skeleton of the adsorbent particles to dissolve and collapse. This results in a tighter bond between the adsorbent particles, which ultimately helps to improve the compressive strength and wear resistance of the adsorbent spheres. Attached Figure Description

[0038] Figure 1 The powder XRD patterns of the calcium-based CO2 adsorbent microspheres prepared in Examples 1-4 are shown below.

[0039] Figure 2 The results of CO2 adsorption capacity tests of the calcium-based CO2 adsorbent microspheres prepared in Examples 1-4 after 16 cycles in a thermogravimetric analyzer are shown.

[0040] Figure 3 The average single-particle crushing strength of the calcium-based CO2 adsorbent microspheres prepared in Examples 1-4 (tested 30 times each);

[0041] Figure 4 The calcium-based CO2 adsorbents prepared in Examples 1-4 were tested for friability performance (at 1500 rpm and 3000 rpm) using a friability tester.

[0042] Figure 5 SEM (scanning electron microscope) images of the calcium-based CO2 adsorbent microspheres prepared in Examples 1-4. Detailed Implementation

[0043] Example 1

[0044] 1) Dissolve 5 kg (30.5 mol) of calcium nitrate in 5 L of deionized water and 0.5 kg (1.5 mol) of zirconium nitrate in 1 L of deionized water. Mix the two solutions to obtain a metal precursor solution. Then, dissolve 3.5 kg of citric acid monohydrate (16.7 mol) in 2 L of deionized water to obtain a complexing agent solution. Mix the metal precursor solution and the complexing agent solution using the sol-gel method to prepare a dilute sol.

[0045] 2) The dilute sol was continuously stirred at a stirring speed of 200 rpm, a reaction temperature of 70℃, and a reaction time of 6 h. After the reaction was completed, the mixed solution was concentrated to 30% of its original volume by vacuum distillation to remove excess water and obtain concentrated sol liquid. The concentrated sol was placed in a drying oven and dried at 100℃ for 12 h to obtain dry gel. The dry gel was then ground to 60 mesh and calcined in a muffle furnace at 600℃ for 2 h to obtain zirconium-doped modified calcium-based adsorbent powder.

[0046] 3) Take 1 kg of the calcium-based adsorbent raw powder and weigh it with malonic acid (purity ≥99%) at a mass ratio of 19:1. Add an equal mass of deionized water to the raw powder and mix. Place the mixture in a kneader and knead for 20 minutes to obtain a lumpy blank. Then, place the blank in a spin pelletizer and extrude it at a speed of 30 rpm to obtain strips. Manually break the strips into short rod-shaped particles with a length of about 1 cm. Place the short rod-shaped particles in a spherical mill and grind them at a speed of 1000 rpm to obtain spherical particles. After air-drying the small spheres naturally for 3 hours, place them in a drying oven and dry them at 100℃ for 2 hours. Then, calcine them at 700℃ for 1 hour to finally obtain calcium-based adsorbent small spheres. Screen out the small spheres with a particle size of 0.3-0.6 mm as the test samples.

[0047] The calcium-based adsorbent microspheres synthesized in this embodiment were tested for CO2 adsorption performance in a thermogravimetric reactor. The adsorption process was carried out at 650°C and 15 vol% CO2 / N2 for 30 min; the desorption process was carried out at 900°C and in a pure N2 atmosphere for 10 min. Figure 2 As shown, the initial CO2 adsorption capacity of the sample in Example 1 was 0.46 g CO2 / g adsorbent, and after 16 cycles, the adsorption capacity was 0.41 g CO2 / g adsorbent, exhibiting good overall stability. It was the best-performing adsorbent among the samples synthesized in Examples 1-4. Single-particle crushing strength was tested in a particle strength testing machine, as shown... Figure 3 As shown, the average single-particle crushing strength of the sample in Example 1 was 1.33 N; the abrasion resistance was tested in a brittleness tester, as shown... Figure 4As shown, the wear rate of the sample ball was 3.78 wt% after 1500 revolutions and 5.49 wt% after 3000 revolutions.

[0048] Example 2

[0049] 1) The amounts of metal precursor, complexing agent, and deionized water used in this embodiment are the same as in Example 1);

[0050] 2) The suspension was continuously stirred at a stirring speed of 250 rpm, a reaction temperature of 60℃, and a reaction time of 3 h. After the reaction was completed, the mixed solution was concentrated to 30% of its original volume by vacuum distillation to remove excess water and obtain a concentrated sol liquid. The concentrated sol was placed in a drying oven and dried at 120℃ for 8 h to obtain a dry gel. The dry gel was then ground to 60 mesh and calcined in a muffle furnace at 700℃ for 2 h to obtain the zirconium-doped modified calcium-based adsorbent powder.

[0051] 3) In this embodiment, except that the mass ratio of calcium-based adsorbent powder to malonic acid is 9:1, the other steps are the same as those in embodiment 1);

[0052] The calcium-based adsorbent microspheres synthesized in this embodiment were tested for CO2 adsorption performance in a thermogravimetric reactor. The test conditions were the same as those described in Example 1. Figure 2 As shown, the initial CO2 adsorption capacity of the sample in Example 2 was 0.45 g CO2 / g adsorbent, and after 16 cycles, the adsorption capacity was 0.39 g CO2 / g adsorbent, indicating good overall stability. Single-particle crushing strength was tested in a particle strength testing machine, as shown... Figure 3 As shown, the average single-particle crushing strength of the sample in Example 2 was 1.3 N; the abrasion resistance was tested in a brittleness tester, as shown... Figure 4 As shown, the wear rate of the sample ball was 5.34 wt% after 1500 revolutions and 8.56 wt% after 3000 revolutions.

[0053] Example 3

[0054] 1) Dissolve 14 kg (85.4 mol) of calcium nitrate in 11 L of deionized water and 1 kg (3.0 mol) of zirconium nitrate in 2 L of deionized water. Mix the two solutions to obtain a metal precursor solution. Then, dissolve 20 kg (95.2 mol) of citric acid in 10 L of deionized water to obtain a complexing agent solution. Mix the metal precursor solution and the complexing agent solution using the sol-gel method to prepare a dilute sol.

[0055] 2) The dilute sol was continuously stirred at a stirring speed of 300 rpm, a reaction temperature of 75°C, and a reaction time of 4 h. After the reaction was completed, the mixed solution was concentrated to 35% of its original volume by vacuum distillation to remove excess water and obtain concentrated sol liquid. The concentrated sol was placed in a drying oven and dried at 120°C for 12 h to obtain a dry gel. The dry gel was then ground to 60 mesh and calcined in a muffle furnace at 700°C for 2 h to obtain zirconium-doped modified calcium-based adsorbent powder.

[0056] 3) Take 2 kg of the calcium-based adsorbent powder and weigh it with nitric acid at a mass ratio of 19:1. Add deionized water and mix (the mass ratio of deionized water to powder is 6:4). Place the mixture in a kneader and knead for 30 minutes to obtain a lumpy blank. Then, place the blank in a spin pelletizer and extrude it at a speed of 35 rpm to obtain strips. Manually break the strips into short rod-shaped particles with a length of about 1 cm. Place the short rod-shaped particles in a spherical mill and grind them at a speed of 1500 rpm to obtain spherical particles. After air-drying the small spheres naturally for 6 hours, place them in a drying oven and dry them at 120℃ for 2 hours. Then, calcine them at 700℃ for 2 hours to finally obtain calcium-based adsorbent spheres. Screen out the spheres with a particle size of 0.3-0.6 mm as the test samples.

[0057] This embodiment achieved the production of 3 kg / batch of calcium-based adsorbent powder (the powder yield in Examples 1 and 2 was 1 kg). Due to the scale-up effect, the CO2 adsorption performance of the prepared adsorbent spheres decreased to some extent compared with Examples 1 and 2 (e.g., Figure 2 (As shown), but the overall stability is better, and the crushing strength of a single particle increased by 35% and 31% compared with Examples 1 and 2, respectively, showing higher compressive strength. The calcium-based adsorbent microspheres synthesized in this example were tested for CO2 adsorption performance in a thermogravimetric reactor. The test conditions were the same as those described in Example 1. Figure 2 As shown, the initial CO2 adsorption capacity of the sample in Example 3 was 0.41 g CO2 / g adsorbent, and after 16 cycles, the adsorption capacity was 0.37 g CO2 / g adsorbent, indicating good overall stability. Single-particle crushing strength was tested in a particle strength testing machine, as shown... Figure 3 As shown, the average single-particle crushing strength of the sample in Example 3 was 1.75 N; the abrasion resistance was tested in a brittleness tester, as shown... Figure 4 As shown, the wear rate of the sample ball was 4.69 wt% after 1500 revolutions and 6.15 wt% after 3000 revolutions.

[0058] Example 4

[0059] 1) The amounts of metal precursor, complexing agent, and deionized water used in this embodiment are the same as in Example 3);

[0060] 2) The experimental steps in this embodiment are the same as those in embodiment 3);

[0061] 3) In this embodiment, except that the mass ratio of calcium-based adsorbent powder to nitric acid is 9:1, the other steps are the same as those in embodiment 3).

[0062] The calcium-based adsorbent microspheres synthesized in this embodiment were tested for CO2 adsorption performance in a thermogravimetric reactor. The test conditions were the same as those described in Example 1. Figure 2 As shown, the initial CO2 adsorption capacity of the sample in Example 3 was 0.40 g CO2 / g adsorbent, and after 16 cycles, the adsorption capacity was 0.36 g CO2 / g adsorbent, indicating good overall stability. Single-particle crushing strength was tested in a particle strength testing machine, as shown... Figure 3 As shown, the average single-particle crushing strength of the sample in Example 4 was 1.93 N; the abrasion resistance was tested in a brittleness tester, as shown... Figure 4 As shown, the wear rate of the sample microspheres was 1.55 wt% after 1500 revolutions and 2.62 wt% after 3000 revolutions. Compared with Examples 1-3, the adsorbent microspheres synthesized in this example exhibited the best crushing strength and wear resistance.

[0063] This invention marks the first time that zirconium-doped calcium-based adsorbent powder produced at the kilogram-scale has been mass-produced using spin granulation technology. It also represents the first time that malonic acid and nitric acid have been used as acidic reagents in the modification of adsorbent materials, achieving promising results. The spin granulation process enables large-scale production of small-diameter particles, effectively improving the production efficiency of adsorbent pellets. The presence of the zirconium component acts as a physical barrier, preventing the aggregation and sintering of adsorbent particles, thus improving its multi-cycle thermal stability. Malonic acid, as an organic acid, introduces a large number of organic groups, reacting with calcium precursors to form organic calcium salts. During calcination, the organic calcium salts decompose into CaCO3 and organic matter. Further calcination of CaCO3 produces CaO, while the organic matter decomposes, releasing a large amount of gas, thereby improving the pore structure of the adsorbent, increasing its specific surface area, and ultimately enhancing its CO2 adsorption capacity. Nitric acid, as a strong inorganic acid, introduces a large amount of H+. + It reacts chemically with CaO / CaCO3, causing the adsorbent particle skeleton to dissolve and collapse, making the sample particle structure more compact and further improving its mechanical strength. Under the action of the above-mentioned acid-modified reagent, the adsorption capacity, compressive strength, wear resistance and production efficiency of the adsorbent spheres can be effectively improved.

[0064] From the above examples, we can conclude that:

[0065] (1) In this invention, an acid-modifying reagent is added as a molding aid during the molding and granulation of the batch-prepared raw powder. Under the modification effect of the acid reagent, the pore structure of the calcium-based adsorbent microspheres can be adjusted, improving their compressive strength and wear resistance, while the microsphere samples retain high CO2 adsorption performance. During the molding process, the calcium-based adsorbent material is granulated by spin pressing, realizing large-scale production of small-diameter particles (below 0.5 mm), effectively improving the production efficiency of adsorbent microspheres.

[0066] (2) In previous research, the performance of the adsorbent in laboratory-scale tests was good, but it was limited to the preparation of raw powder and did not explore the granulation process, making it impossible to mass-produce and meet the needs of industrialization. Therefore, the inventors conducted further experimental research to achieve mass production of granulated particles. Since the mass production of calcium-based adsorbent granules is not simply a matter of scaling up the small-scale test, it is also necessary to further optimize the specific preparation conditions to reduce the negative impact of the "process scale-up effect" and make the entire process more in line with industrial applications. In the process of scale-up preparation of adsorbent raw powder, this invention explored and optimized the relevant process conditions (the optimized conditions are reflected in steps 5) to 7) above), and finally completed the production of kilogram-level / batch adsorbent pellets (in other related papers and patents surveyed, the yield was almost always in the gram level / batch, or the specific yield was not specified).

[0067] (3) Currently, there is no information on the mass production of zirconium-doped calcium-based adsorbent granules. This invention achieves the production of adsorbent microspheres at the kilogram / batch level, and the resulting product exhibits good CO2 adsorption performance. Furthermore, the raw adsorbent powder cannot be directly used for industrial CO2 capture; it needs to be granulated. To improve the pore structure and mechanical strength of the granulated adsorbent microspheres, this invention incorporates acid-modifying reagents and conducts a systematic and comprehensive investigation to determine the optimal molding aid formulation. The above research provides theoretical and technical support for the industrial production of calcium-based adsorbents.

[0068] (4) Due to the loose and porous structure of the zirconium-doped calcium-based adsorbent powder prepared by the sol-gel method, it has a relatively low bulk density, which can differ from that of commercial calcium oxide or modified calcium oxide prepared by the co-precipitation method by up to 5 times, a significant difference. The low powder density easily leads to uneven distribution during mixing with the acid-modifying reagent, hindering uniform dispersion and negatively impacting the granulation process, ultimately harming the sample's performance. To address this issue, the zirconium-doped calcium-based adsorbent powder can be mixed with an appropriate amount of deionized water (molar ratio 1:1) to allow CaO to first form Ca(OH)₂. This effectively increases the powder density of the adsorbent by 2 to 3 times, enabling better uniform mixing with the acid-modifying reagent.

[0069] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing acid-modified calcium-based CO2 adsorbent microspheres, characterized in that... The method includes the following steps: 1) Prepare a mixed solution by mixing and stirring the metal precursor solution and the complexing agent solution; The metal precursor solution comprises a calcium salt, a zirconium salt, and deionized water, with a molar ratio of calcium salt:zirconium salt = 15~40:1 and deionized water:(calcium salt + zirconium salt) = 10~40:

1. The complexing agent solution comprises a complexing agent and deionized water, with a molar ratio of deionized water:complexing agent = 4~20:1 and a molar ratio of complexing agent:(calcium salt + zirconium salt) = 0.5:1~2:

1. The complexing agent is citric acid. 2) Stir the mixed solution continuously for 1 to 6 hours at a stirring speed of 100 to 300 rpm and a reaction temperature of 50 to 80°C; 3) After the reaction is complete, the mixed solution is concentrated to 30-35% of its original volume by vacuum distillation to obtain a concentrated sol liquid; 4) Place the concentrated sol into a forced-air drying oven and dry it at 100~120℃ for 8~12h to obtain a dry gel. Then grind the dry gel and place it in a muffle furnace and calcine it at 600~700℃ for 1~3h to obtain the zirconium-doped modified calcium-based adsorbent powder. 5) The calcium-based adsorbent powder is first thoroughly mixed with water, then mixed with acid-modifying reagent, and then placed together in a kneader and kneaded for 10-30 minutes to obtain a mixture in the form of a pellet. The mass ratio of zirconium-doped calcium-based adsorbent powder to acid-modifying reagent is 4:1 to 19:1; the mass ratio of zirconium-doped calcium-based adsorbent powder to deionized water is 0.5:1 to 1.5:

1. 6) The preform is placed in a spinning pellet mill and extruded at a speed of 20-40 rpm to obtain strips. The strips are then broken into rod-shaped particles with a length of 0.3-1 cm. 7) The rod-shaped particles are placed in a spherical mill and ground at high speed to obtain spherical particles. The small spherical particles are naturally air-dried for 2-6 hours, then placed in a drying oven and dried at 100-140℃ for 1-2 hours. They are then placed in a muffle furnace and calcined at 600-700℃ for 1-2 hours to finally obtain calcium-based CO2 adsorbent small spheres. In step 1), the calcium salt is calcium nitrate; in step 1), the zirconium salt is zirconium nitrate. In step 5), the acid-modifying reagent is one of nitric acid, acetic acid, or malonic acid. The amount of the calcium salt, zirconium salt and complexing agent in step 1), and the calcium-based adsorbent powder in step 5) is in the range of hundreds of grams to tens of thousands of grams.

2. The method for preparing acid-modified calcium-based CO2 adsorbent microspheres as described in claim 1, characterized in that the particle size of the calcium-based adsorbent microspheres in step 7) is 0.3 mm to 1.5 mm.

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