A carbon dioxide absorbent and a method of preparing the same

Abstract

The present disclosure relates to the technical field of carbon dioxide normal temperature capture materials, and particularly relates to a carbon dioxide absorbent and a preparation method thereof. The present disclosure provides a preparation method of a carbon dioxide absorbent, which comprises the following steps: dissolving a binder in water, adding lithium hydroxide powder and stirring to form a suspension slurry; adding a pore structure inducer to the suspension slurry and stirring to form a target slurry; performing freezing treatment on the target slurry, so that water in the target slurry forms an ice fiber template, thereby obtaining a lithium hydroxide frozen body; performing vacuum drying treatment on the lithium hydroxide frozen body, so that the ice fiber template sublimates, thereby obtaining a lithium hydroxide material with a three-dimensional network pore structure; and performing extrusion shaping treatment on the lithium hydroxide material with the three-dimensional network pore structure, thereby obtaining a carbon dioxide absorbent.

Description

Technical Field

[0001] This disclosure relates to the field of carbon dioxide capture materials at room temperature, and in particular to a carbon dioxide absorbent and its preparation method. Background Technology

[0002] With the increasing urgency of global carbon emission control, efficient carbon dioxide capture technology is key to achieving carbon emission reduction and carbon resource recycling. Lithium hydroxide (LiOH) can rapidly react with carbon dioxide at room temperature to form lithium carbonate, possessing advantages such as high theoretical capture capacity, low manufacturing cost, and stable reactivity. It is a core material for removing low-concentration carbon dioxide from confined spaces such as submarines and manned spacecraft.

[0003] However, direct use of powdered lithium hydroxide easily generates dust, causing material loss and pipeline blockage, posing safety hazards and high maintenance costs. While methods such as carrier immobilization or compression molding with binders (e.g., colloidal particles reported in related studies) have effectively reduced dust levels, the addition of binders and simple compression molding can clog or damage the internal pore structure of the absorbent, hindering carbon dioxide diffusion. This results in lithium hydroxide utilization rates far below theoretical values, and the adsorption rate tends to decay prematurely during periods of high utilization.

[0004] Currently, the utilization rate of lithium hydroxide in existing carbon dioxide absorbents is insufficient to meet the requirements for efficient capture. Summary of the Invention

[0005] The purpose of this disclosure is to provide a carbon dioxide absorbent and a method for preparing the same, so as to improve the utilization rate of lithium hydroxide in the carbon dioxide absorbent.

[0006] To achieve the above objectives, this disclosure provides the following technical solution:

[0007] In a first aspect, a method for preparing a carbon dioxide absorbent is provided, comprising: dissolving a binder in water, adding lithium hydroxide powder and stirring to form a suspension slurry; adding a pore structure inducing agent to the suspension slurry and stirring to form a target slurry; freezing the target slurry to form an ice fiber template in the water of the target slurry to obtain a lithium hydroxide cryogenic body; vacuum drying the lithium hydroxide cryogenic body to sublimate the ice fiber template to obtain a lithium hydroxide material with a three-dimensional network pore structure; and extruding and shaping the lithium hydroxide material with a three-dimensional network pore structure to obtain a carbon dioxide absorbent.

[0008] The aforementioned method for preparing carbon dioxide absorbent introduces a specific pore structure inducing the orderly arrangement of more pore structures within the absorbent, thereby increasing the proportion of micropores and mesopores in the material. Cryogenic pore-forming technology is employed to create more interconnected pore structures within the material. By combining the pore structure inducing agent with an ice fiber template for composite pore-forming, a three-dimensional network of hierarchical pores is constructed, ensuring that carbon dioxide (CO2) gas can diffuse into the material, making the chemical absorption of carbon dioxide more stable and avoiding premature decay of the absorption rate during the high utilization stage. Furthermore, this porous structure increases the reaction contact area, fully exposing the active sites of lithium hydroxide, significantly improving the effective utilization rate of lithium hydroxide, and making the overall capture capacity closer to the theoretical value. Additionally, by extruding and shaping the vacuum-dried lithium hydroxide material under a certain pressure, it acquires high strength, avoiding the safety hazards of powder in actual use.

[0009] In one embodiment, the target slurry is subjected to freezing treatment to form an ice fiber template with water in the target slurry, thereby obtaining a lithium hydroxide cryobody. This includes: transferring the target slurry into a mold, filling and sealing it, and then subjecting the target slurry to freezing treatment by contacting a low-temperature cold source to obtain the lithium hydroxide cryobody.

[0010] The embodiments disclosed herein achieve solidification and volume expansion of the slurry by freezing under confined space conditions, thereby generating internal pressure and controlling the tight and orderly stacking of the material at the microscale during the pore formation period, thus increasing the pore structure strength of the material.

[0011] In one embodiment, the freezing process takes 0.5-2 hours.

[0012] Here, a freezing time of 0.5 to 2 hours can ensure that the slurry is completely frozen, avoid local slack that could lead to breakage of the ice fiber template, improve pore connectivity, and shorten the reaction diffusion distance between carbon dioxide (CO2) and lithium hydroxide; it can also prevent excessive freezing time from causing pore structure deterioration and decreased absorption performance.

[0013] In one embodiment, the binder includes one or more of sodium carboxymethyl cellulose, polyvinyl alcohol, and microcrystalline cellulose.

[0014] Here, the selected sodium carboxymethyl cellulose, polyvinyl alcohol, and microcrystalline cellulose all possess good water solubility and are fully compatible with water (such as deionized water), pore structure inducers, and lithium hydroxide, preventing slurry agglomeration and ensuring the uniformity of the subsequent pore structure. The aforementioned binders have moderate bonding strength and do not decompose or volatilize during the freeze-sublimation process. They can stably support the three-dimensional pore structure without causing pore blockage due to excessive binder, ensuring high utilization of lithium hydroxide. Furthermore, the embodiments of this disclosure allow for the combined use of multiple binders, enabling flexible adjustment of the product's mechanical strength and permeability according to the application scenario, adapting to different needs such as confined spaces (e.g., submarines) and industrial trapping.

[0015] In one embodiment, dissolving the adhesive in water includes: dissolving the adhesive in deionized water preheated to 50-70°C.

[0016] This embodiment uses deionized water as a solvent, which avoids the reaction of impurities (metal ions, minerals) in ordinary water with lithium hydroxide to form impurity salts or block the pores, thus ensuring the interface modification effect of the pore structure inducing agent. Using a preheating temperature of 50-70°C accelerates the dissolution of the binder, shortens the process time, and avoids high-temperature hydrolysis of lithium hydroxide or breakage of binder molecular chains, ensuring slurry stability. Furthermore, preheated water improves the dispersion uniformity of lithium hydroxide powder, reduces particle agglomeration, and allows for more regular growth of the ice fiber template during freezing, ultimately improving the consistency of the pore structure and reducing product performance fluctuations.

[0017] In one embodiment, the pore structure inducing agent includes one or more of cocamidopropyl betaine and oleamidopropyl dimethyl betaine.

[0018] The cocamidopropyl betaine (CAPB) and oleamidopropyl dimethyl betaine (OAPB) selected in this embodiment are bipolar surfactants. They can form hydrogen bonds with water, binders, and lithium hydroxide through their hydrophilic ends, and induce the directional growth of ice fibers through self-assembly at their hydrophobic ends, thereby increasing the mesoporous content. These inducers exhibit high chemical stability, remaining non-volatile and non-decomposing during vacuum drying and extrusion molding, eliminating the need for additional removal steps. This simplifies the process, while the residual inducers sustainably maintain pore structure stability, preventing pore collapse. Furthermore, the two inducers can be used alone or in combination, adapting to different raw material ratios (e.g., CAPB for high lithium hydroxide content formulations, OAPB for high binder content formulations), flexibly controlling the pore ratio and optimizing carbon dioxide diffusion and adsorption performance.

[0019] In one embodiment, the method further includes preparing raw materials according to the following mass percentages in the target slurry: 25%-65% lithium hydroxide powder, 1%-10% binder, 0.5%-5% pore structure inducer, and the balance being deionized water.

[0020] Here, a lithium hydroxide content of 25%–65% achieves an optimal balance between capture capacity and pore space. For example, a content of 50%–65% can meet high capacity requirements, while a content of 25%–40% can improve pore richness and adapt to different capture scenarios. The aforementioned binder content of 1%–10% can balance mechanical strength and pore permeability, avoiding insufficient particle strength (<80%) due to too low a content, or pore blockage (utilization rate <85%) due to too high a content. The aforementioned pore structure inducer content of 0.5%–5% can precisely control the pore effect, avoiding a decrease in the proportion of mesopores due to too low a content, or abnormal slurry viscosity due to too high a content.

[0021] In one embodiment, adding a pore structure inducer to the suspension slurry and stirring includes: adding the pore structure inducer to the suspension slurry and performing vigorous mechanical stirring at a stirring rate of 200-800 rpm.

[0022] Here, vigorous mechanical stirring at 200-800 rpm generates strong shear force, which breaks up lithium hydroxide particle agglomerates, ensuring that the pore structure inducer is uniformly dispersed in the slurry. This results in a uniform adsorption layer forming on the surface of each lithium hydroxide particle, guaranteeing the consistency of pore induction. The stirring rate is matched to the slurry viscosity, avoiding both excessively low rates (<200 rpm) leading to uneven inducer dispersion and excessively high rates (>800 rpm) causing air bubbles to be trapped (forming blind pores after freezing), thus significantly reducing the pore defect rate. This vigorous stirring also promotes interfacial interactions between the inducer and other components, providing uniform guidance for the directional growth of ice fibers, increasing the specific surface area, and providing sufficient sites for CO2 reactions.

[0023] In one embodiment, before freezing the target slurry, the method further includes: allowing the target slurry to stand for 0.5-2 hours.

[0024] Here, allowing the 0.5 to 2 hours of settling time allows the tiny air bubbles entrained during stirring to escape completely, preventing them from freezing after freezing and forming irregular blind pores after sublimation. This ensures the continuity of the pores and improves the CO2 diffusion rate. By allowing the slurry to stand for a period of time, the components in the slurry can be further stabilized, the lithium hydroxide particles can settle evenly, the adsorption of the inducing molecule interface can be balanced, the ice fiber template can grow uniformly during freezing, and the unevenness of the product pore distribution can be greatly reduced.

[0025] In one embodiment, the lithium hydroxide cryobody is subjected to vacuum drying treatment, which includes: vacuum drying the lithium hydroxide cryobody for 12-36 hours under a pressure of less than 20 Pa.

[0026] Here, ice fiber can be directly sublimated in solid form at a pressure below 20 Pa, avoiding ice melting and filling the pores, preserving the three-dimensional network pore structure completely, and improving the pore retention rate, which is far greater than that under traditional high-temperature drying methods; a drying time of 12 to 36 hours can ensure that the ice fiber is completely sublimated without residual moisture, avoiding the deliquescence of lithium hydroxide or pore blockage, and improving storage stability; the low-temperature sublimation process does not damage the activity of the raw material and has a good retention rate of lithium hydroxide reactivity.

[0027] In one embodiment, the lithium hydroxide material with a three-dimensional mesh structure is subjected to extrusion shaping treatment, which includes: extruding and shaping the lithium hydroxide material with a three-dimensional mesh structure at a pressure of 0.5-3.0 MPa for 0.5-10 minutes.

[0028] Here, a pressure of 0.5–3.0 MPa allows lithium hydroxide material (bulk density 0.30–0.45 g / cm³) to be compacted to 0.4–0.6 g / cm³, achieving a particle strength of 85%–95%, meeting the anti-breakage requirements during transportation and filling, with a breakage rate of less than 15%. A setting time of 0.5–10 minutes releases internal stress in the material, preventing insufficient strength due to too short a setting time or decreased production efficiency due to too long a setting time. This low-to-medium pressure setting prevents pore collapse, minimizes the decrease in mesoporous content, maintains a high lithium hydroxide utilization rate, and achieves a balance between high mechanical strength and high absorption performance.

[0029] In one embodiment, the carbon dioxide absorbent has a thickness of 0.5-6.0 mm and a diameter of 1.5-2.0 mm.

[0030] Here, a diameter range of 1.5~2.0 mm can adapt to the filling needs of different equipment. The smaller diameter can reduce the diffusion distance of carbon dioxide (CO2), improve the absorption rate, and adapt to rapid capture in confined spaces. A thickness range of 0.5~6.0 mm can flexibly adapt to different scenarios. For example, a thickness of 0.5~2.0 mm is suitable for low-concentration, high-flow-rate CO2 capture, while a thickness of 3.0~6.0 mm is suitable for high-concentration, large-capacity capture, improving the capture capacity per unit volume. The upper limit of the above size can avoid a significant decrease in utilization due to excessive diffusion distance, while the lower limit of the above size can avoid the risk of dust due to excessively fine products, ensuring that the particle strength is ≥85% and there is no risk of dust spillage.

[0031] In one embodiment, the bulk density of the carbon dioxide absorbent is 0.4~0.6 g / cm3, and the particle strength is 85%~95%.

[0032] Here, a bulk density of 0.4~0.6 g / cm³ can balance capture capacity and air permeability, while the capture capacity does not decrease significantly; a particle strength of 85%~95% can ensure that the product is not easily broken during transportation and use, solving the safety hazards of traditional powdered lithium hydroxide and reducing equipment maintenance costs.

[0033] In one embodiment, the bulk density of the lithium hydroxide material having a three-dimensional mesh structure is 0.30-0.45 g / cm³.

[0034] In this embodiment, a bulk density of 0.30~0.45 g / cm³ can ensure mechanical strength on the one hand, and will not damage the core channel structure on the other hand, providing a clear indicator for the quality control of intermediate products. If the bulk density of the final product is not within the above range, the raw material ratio or process parameters can be adjusted in time to avoid the final product performance failing to meet the standards.

[0035] Secondly, a carbon dioxide absorbent is provided, the carbon dioxide absorbent having a porous structure, and the carbon dioxide absorbent is prepared by any one of the preparation methods described above. Its effects are described in the above preparation method description. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. These drawings are incorporated in and constitute a part of this specification. They illustrate embodiments conforming to this disclosure and, together with the specification, serve to explain the technical solutions of this disclosure. It should be understood that the following drawings only show some embodiments of this disclosure and should not be considered as limiting the scope. Those skilled in the art can obtain other related drawings based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart illustrating the preparation method of the carbon dioxide absorbent according to an embodiment of the present disclosure;

[0038] Figure 2 This is a SEM image of the carbon dioxide absorbent prepared in Example 3 of this disclosure after use;

[0039] Figure 3 The XRD pattern of the carbon dioxide absorbent according to the present disclosure after a carbon dioxide absorption test;

[0040] Figure 4 This is a schematic diagram of the change in carbon dioxide absorption rate over time. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. The components of the embodiments of this disclosure described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this disclosure provided in the accompanying drawings is not intended to limit the scope of the claimed disclosure, but merely represents selected embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

[0042] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0043] In this document, the term "and / or" merely describes a relationship, indicating that three relationships can exist. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Furthermore, the term "at least one" in this document means any combination of at least two of any one or more elements. For example, including at least one of A, B, and C can mean including any one or more elements selected from the set consisting of A, B, and C.

[0044] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0045] like Figure 1 As shown, a method for preparing a carbon dioxide absorbent is provided, comprising the following steps:

[0046] S101: Dissolve the binder in water, add lithium hydroxide (LiOH) powder and stir to form a suspension slurry.

[0047] Here, the raw materials are uniformly mixed through slurry preparation, while the dissolution of the binder provides viscous support for subsequent molding, preventing the structure from becoming loose after subsequent setting.

[0048] The aforementioned binders may include one or more of sodium carboxymethyl cellulose, polyvinyl alcohol, and microcrystalline cellulose. All three binders exhibit good water solubility (compatible with deionized water), moderate bond strength, and good chemical stability (does not undergo side reactions with LiOH). Furthermore, they do not decompose or volatilize during freeze-sublimation, providing stable support for the pore structure. These binders can be used alone or in combination. By combining binders (e.g., sodium carboxymethyl cellulose + polyvinyl alcohol), the viscosity, formability, and pore compatibility can be adjusted according to actual needs. For example, polyvinyl alcohol offers higher bond strength, while microcrystalline cellulose provides better air permeability; combining them can further optimize the product's mechanical strength and gas diffusion performance.

[0049] The three binders selected in this embodiment meet the molding requirements and work synergistically with the pore structure inducer to avoid pore blockage and ensure the utilization rate of LiOH.

[0050] In one embodiment, dissolving the adhesive in water may include dissolving the adhesive in deionized water preheated to 50-70°C.

[0051] Here, the low conductivity and high purity of deionized water prevent uneven local electrolyte concentration in the slurry, ensuring uniform growth of the ice fiber template during freezing and resulting in a consistent final pore structure. A temperature range of 50-70℃ accelerates binder dissolution (e.g., sodium carboxymethyl cellulose dissolves slowly at room temperature, but at 50-70℃, dissolution time can be shortened by more than 30%), while avoiding slight hydrolysis of LiOH or breakage of binder molecular chains at high temperatures (>70℃) (affecting the bonding effect). Preheating the deionized water raises the overall temperature of the slurry, resulting in more uniform dispersion of LiOH powder (reducing the probability of particle agglomeration), and creates a temperature difference with the subsequent freezing step, promoting rapid and orderly crystallization of the ice fibers.

[0052] S102: Add a pore structure inducer to the suspension slurry and stir to form the target slurry.

[0053] This step utilizes the interfacial modification effect of a pore structure inducer to pre-construct pore prototypes in the slurry, providing guidance for the orderly growth of ice fiber templates during the freezing stage. In other words, the inducer is not merely a filler, but rather regulates the slurry's microstructure through intermolecular forces, preventing disordered ice fiber growth during freezing and providing molecular guidance for the subsequent formation of a three-dimensional network of pores.

[0054] In one embodiment, the pore structure inducer includes one or more of cocamidopropyl betaine (CAPB) and oleamidopropyl dimethyl betaine (OAPB).

[0055] The aforementioned pore structure inducers exhibit hydrophilic ends that can form hydrogen bonds with water, binders, and LiOH, while their hydrophobic ends can self-assemble into microdomains. During freezing, these inducers guide the directional growth of ice fibers along these microdomains, ultimately forming a multi-level pore structure consisting of micropores, mesopores, and macropores. Furthermore, these pore structure inducers demonstrate good water solubility and high chemical stability, remaining non-volatile and non-decomposing during vacuum drying and extrusion molding, thus maintaining stable pore structure. CAPB exhibits higher pore induction efficiency (suitable for formulations with a high LiOH content), while OAPB offers better interfacial compatibility (suitable for formulations with a high binder content). When used in combination, the pore ratio (e.g., micropore / mesopore ratio) can be adjusted according to the raw material ratio to further optimize CO2 diffusion and adsorption performance.

[0056] Traditional pore-inducing agents (such as calcium carbonate and ammonium bicarbonate) need to be removed through subsequent acid washing and high-temperature decomposition, which may damage the pores or leave residual impurities. However, the two inducers specified in the embodiments of this disclosure do not need to be removed and can continue to play an interface modification role after they remain, which can ensure the stability of the pores and simplify the process.

[0057] In one embodiment, the method further includes preparing raw materials according to the following mass percentages in the target slurry: 25%-65% lithium hydroxide powder, 1%-10% binder, 0.5%-5% pore structure inducer, and the balance being deionized water.

[0058] The above-mentioned range of proportions is designed based on extensive experimental verification, which can ensure the consistency of product pore structure and absorption performance in different production batches, and meet the needs of industrial-scale production.

[0059] In one embodiment, adding a pore structure inducer to the suspension slurry and stirring may include: adding the pore structure inducer to the suspension slurry and performing vigorous mechanical stirring at a stirring rate of 200-800 rpm.

[0060] Unlike ordinary magnetic stirring, strong mechanical stirring can generate stronger shear force, breaking up LiOH particle agglomerates (especially after the addition of an inducer, the slurry viscosity increases slightly, requiring strong stirring to ensure uniform dispersion). Strong stirring can promote the uniform distribution of inducer molecules in the slurry, enabling the formation of an inducer adsorption layer on the surface of each LiOH particle. This provides uniform guidance for the directional growth of the ice fiber template during freezing, avoiding defects such as locally dense pores and locally non-porous areas.

[0061] The stirring speed range of 200-800 rpm can balance the dispersion effect and slurry stability. When the speed is <200 rpm, the inducer is unevenly dispersed (large differences in pore induction effect); when the speed is >800 rpm, air bubbles are easily entrained in the slurry (after freezing, irregular large pores are formed at the air bubble sites, destroying the three-dimensional network structure). In specific implementation, the stirring speed can be adjusted according to the slurry viscosity (for example, when the LiOH content is high and the viscosity is high, 600-800 rpm can be used; when the content is low and the viscosity is low, 200-400 rpm can be used) to ensure the homogeneity of the slurry.

[0062] S103: The target slurry is subjected to freezing treatment, so that the water in the target slurry forms an ice fiber template, thereby obtaining a lithium hydroxide cryobody.

[0063] Here, the freezing and solidification properties of water are utilized to form a continuous ice fiber template, providing physical support for subsequent sublimation and pore formation. This is a key process in constructing three-dimensional interconnected channels. This step differs from traditional high-temperature drying and dehydration; freezing ensures water exists in the form of solid ice fibers, rather than being lost in a liquid state, thus preventing channel collapse during drying. Simultaneously, the fibrous structure of the ice fibers forms interconnected mass transfer channels, rather than isolated pores, providing pathways for CO2 diffusion.

[0064] In one embodiment, before freezing the target slurry, the method further includes: allowing the target slurry to stand for 0.5-2 hours.

[0065] Here, by allowing the target slurry to stand for 0.5-2 hours, air bubbles entrained during stirring (especially tiny bubbles generated by vigorous stirring) can rise and escape, preventing them from freezing in the ice fiber template after freezing and forming irregular blind pores (non-connected, affecting CO2 diffusion) after sublimation. Simultaneously, standing allows for further stabilization of the components in the slurry (e.g., uniform sedimentation of LiOH particles and equilibrium of inducing agent molecular interface adsorption), ensuring consistent ice fiber template growth during freezing and improving the uniformity of the pore structure. If the standing time is <0.5 hours, air bubbles may not completely escape, resulting in insufficient slurry stability and a certain defect rate in the pores after freezing; if the standing time is >2 hours, LiOH particles may excessively settle (leading to excessively high concentration at the bottom and low concentration at the top), resulting in uneven pore distribution in the final product and large fluctuations in LiOH utilization. During the standing process, the slurry should be kept sealed to prevent moisture evaporation and concentration changes. The standing process can be carried out at room temperature (20-25℃) without additional temperature control.

[0066] In one embodiment, the process of freezing the target slurry may specifically include: transferring the target slurry into a mold, filling it completely, and sealing it, then bringing the target slurry into contact with a low-temperature cold source for freezing treatment to obtain the lithium hydroxide cryogenic body. Optionally, the freezing treatment time is 0.5-2 hours.

[0067] The aforementioned low-temperature cold source can be liquid nitrogen or a freezerable cold stage. Selecting liquid nitrogen or a freezerable cold stage as the low-temperature cold source can quickly and uniformly freeze the slurry to form a continuous and controllable ice fiber template. This can ensure the stable formation of the three-dimensional mesh structure and avoid the introduction of impurities and the failure of material components, thereby improving the carbon dioxide absorption rate of the absorbent and the effective utilization rate of lithium hydroxide.

[0068] This method involves freezing under confined space conditions, limiting the molding space of the slurry, causing it to solidify and expand in volume, generating internal pressure. This controls the tight and orderly packing of material at the microscale during the pore formation period, increasing the strength of the material's pore structure and allowing ice fibers to grow directionally within fixed boundaries, resulting in a final product with a regular shape (e.g., sheet-like / cylindrical). Sealing also prevents moisture evaporation from the slurry during freezing, which could lead to increased concentration and abnormal ice fiber growth.

[0069] In practice, a sealed copper mold can be used. The mold material is preferably a metal with good thermal conductivity (such as copper or aluminum), which can accelerate the heat exchange between the slurry and the low-temperature cold source and ensure uniform freezing.

[0070] The freezing time range of 0.5-2 hours ensures that the slurry is completely frozen from the surface to the interior (avoiding localized ungluing that could lead to breakage of the ice fiber template), while preventing excessive freezing time (>2 hours) that could cause excessive ice fiber growth and decreased pore connectivity. In practice, the freezing time must be matched with the slurry thickness (e.g., 2 hours for a 6.0mm thick slurry, only 0.5 hours for a 0.5mm thick slurry) to ensure uniform freezing.

[0071] S104: The lithium hydroxide cryobody is subjected to vacuum drying treatment to sublimate the ice fiber template, thereby obtaining a lithium hydroxide material with a three-dimensional network pore structure.

[0072] This step achieves direct conversion of the solid-state ice fiber to a gaseous state through vacuum sublimation, avoiding the melting of ice which would cause the pores to be filled with slurry, thus fully preserving the three-dimensional network structure of the ice fiber template. Here, the core of vacuum drying is the low-temperature, water-free stage. Traditional heating drying can lead to slurry shrinkage and pore blockage, while this step achieves the unity of template removal and pore preservation through sublimation.

[0073] In one embodiment, vacuum drying of the lithium hydroxide cryobody may include: vacuum drying the lithium hydroxide cryobody for 12-36 hours under a pressure of less than 20 Pa.

[0074] Here, the lower the pressure, the faster the sublimation rate, but the cost of equipment must be balanced (the cost of vacuum equipment increases significantly when the pressure is <10 Pa). Therefore, a pressure below 20 Pa is the best choice after balancing sublimation efficiency and equipment cost. A drying time of 12-36 hours ensures complete sublimation of the ice fibers (avoiding residual moisture that could cause LiOH deliquescence or pore blockage). This time should also be matched to the slurry thickness and freezing degree. For example, a slurry with a thickness of 6.0 mm and a freezing time of 2 hours requires 36 hours of drying; a slurry with a thickness of 0.5 mm and a freezing time of 0.5 hours requires 12 hours of drying. During the drying process, the temperature can be moderately increased (≤30℃) to accelerate the sublimation rate, but excessively high temperatures should be avoided to prevent a decrease in LiOH activity or softening of the binder.

[0075] In one embodiment, the bulk density of the lithium hydroxide material having a three-dimensional mesh structure is 0.30-0.45 g / cm³.

[0076] Lithium hydroxide material with a three-dimensional network porous structure is an intermediate product after vacuum drying. The bulk density range of 0.30-0.45 g / cm³ for lithium hydroxide material with this structure directly reflects the abundance of the three-dimensional network porous structure. If the density is <0.30 g / cm³, it indicates excessively loose pores (large pores >40%), making it prone to collapse during subsequent extrusion and shaping. If the density is <0.30 g / cm³, it indicates that the pores are too porous (large pores account for >40%), making it prone to collapse during subsequent extrusion and shaping. This indicates an insufficient pore volume ratio (mesopores + micropores < 60%), resulting in a certain degree of decrease in the utilization rate of LiOH in the final product. During process implementation, if the density after drying exceeds 0.30-0.45 g / cm³, it can be corrected by adjusting the raw material ratio (e.g., increasing / decreasing the proportion of inducing agents) or freezing / drying parameters (e.g., adjusting the freezing rate and vacuum pressure) to ensure the final product performance meets standards.

[0077] The density of the intermediate product is 0.30-0.45 g / cm³. After subsequent extrusion and shaping, the density is increased to 0.4-0.6 g / cm³. The density increase is controlled within 20%-30%, which ensures mechanical strength without excessively compressing the pores, thus achieving a balance between pore retention and strength improvement.

[0078] S105: The lithium hydroxide material with a three-dimensional network structure is subjected to extrusion shaping to obtain a carbon dioxide absorbent.

[0079] This step, while preserving the three-dimensional channels, enhances the material's mechanical strength through moderate extrusion, avoiding dust generation in practical applications, and simultaneously fixing the product's shape (such as sheet or cylinder). This step balances the contradiction between channel richness and mechanical strength; traditional high-pressure molding destroys the channels, while this solution uses low-to-medium pressure molding, compacting only the material's surface and weak internal areas, thus preserving the core three-dimensional channel structure and achieving a balance between high utilization and low dust.

[0080] In one embodiment, the extrusion shaping process of the lithium hydroxide material with a three-dimensional mesh structure may include: extruding the lithium hydroxide material with a three-dimensional mesh structure under a pressure of 0.5-3.0 MPa for 0.5-10 minutes.

[0081] The aforementioned pressure range of 0.5-3.0 MPa allows lithium hydroxide material (bulk density 0.30-0.45 g / cm³) to be compacted to a bulk density of 0.4-0.6 g / cm³, achieving a particle strength of 85%-95%, while simultaneously preventing pore collapse caused by high pressure (>3.0 MPa) (the mesoporous proportion would decrease from over 50% to below 40%). In practical implementation, the pressure can be adjusted according to the product form; for example, 0.5-1.0 MPa can be used for sheet-like products (to avoid edge cracking), while 1.0-3.0 MPa can be used for cylindrical products (to ensure axial strength).

[0082] The aforementioned time range of 0.5-10 minutes allows for the release of internal stress in the material, ensuring structural stability and preventing insufficient strength (particle strength <80%) due to a setting time that is too short (<0.5 minutes) or decreased production efficiency (over 40% reduction in output per unit time) due to a setting time that is too long (>10 minutes). In practice, stepwise pressurization can be used during the setting process (e.g., pre-pressurizing at 0.5 MPa for 1 minute, then increasing to the target pressure) to further reduce pore damage and improve product consistency.

[0083] In this embodiment, the prepared carbon dioxide absorbent has a thickness of 0.5-6.0 mm and a diameter of 1.5-2.0 mm. The specific thickness can vary depending on the application scenario. For example, in confined spaces (such as submarines or spacecraft), a smaller diameter (1.5-2.0 mm) allows for filling small reaction vessels, and a thickness of 0.5-2.0 mm ensures a short CO2 diffusion distance (<3 mm) and a fast absorption rate. In industrial capture scenarios, a thickness of 3.0-6.0 mm increases the capture capacity per unit volume, adapts to large reaction towers, and reduces equipment size. Setting the upper limit of these dimensions (6.0 mm thickness, 2.0 mm diameter) avoids excessively long diffusion distances (>6 mm, resulting in decreased internal LiOH utilization); setting the lower limit (0.5 mm thickness, 1.5 mm diameter) avoids the risk of dust due to excessively fine product dimensions.

[0084] Experimental data show that products with a diameter of 1.5-2.0 mm and a thickness of 0.5-6.0 mm have a stable CO2 absorption capacity of 0.860-0.890 kg / kg LiOH. If the diameter is greater than 2.0 mm or the thickness is greater than 6.0 mm, the absorption capacity decreases.

[0085] In one embodiment, the bulk density of the carbon dioxide absorbent is 0.4~0.6 g / cm³. 3 The particle strength is 85%~95%.

[0086] The aforementioned density range balances capture capacity and permeability. When the density is <0.4 g / cm³, the product structure is loose (particle strength <80%), making it easily broken. When the density is >0.6 g / cm³, the proportion of pores decreases (mesoporous proportion <50%), CO2 diffusion is hindered, and LiOH utilization rate is <90%. Compared with traditional LiOH absorbents (bulk density 0.6-0.8 g / cm³), this density range significantly improves permeability without significantly reducing capture capacity, making it suitable for high-velocity CO2 capture scenarios.

[0087] Accordingly, this disclosure provides a carbon dioxide absorbent having a porous structure, which is prepared by the above-described preparation method.

[0088] The following experiments further illustrate some of the implementation methods of this disclosure.

[0089] Example 1

[0090] 25.0 g of sodium carboxymethyl cellulose was dissolved in 185.0 g of deionized water heated to 60°C. Then, 285.0 g of lithium hydroxide powder was added, and the mixture was vigorously stirred at 600 rpm until homogeneous, yielding a white suspension. Subsequently, 5.0 g of CAPB was dissolved in the white suspension and vigorously stirred at 600 rpm until homogeneous, yielding the target slurry. The target slurry was transferred to a sealable copper mold, filled and sealed, and allowed to stand for 1 h. The mold was then placed on a cold plate and frozen for 1 h to allow the slurry to fully solidify. The frozen sample was quickly transferred to a vacuum dryer and dried for 24 h. The resulting lithium hydroxide material was removed and placed in a tablet press mold. It was pressed at 0.6 MPa for 1 min to form tablets with a diameter of 1.5 mm and a thickness of 2 mm, thus obtaining the carbon dioxide absorbent product of this embodiment.

[0091] Example 2

[0092] 35.0 g of sodium carboxymethyl cellulose was dissolved in 180.0 g of deionized water heated to 70°C. Then, 275.0 g of lithium hydroxide powder was added, and the mixture was vigorously stirred at 600 rpm until homogeneous, yielding a white suspension. Subsequently, 10.0 g of OAPB was dissolved in the above white suspension, and the mixture was vigorously stirred at 600 rpm until homogeneous, yielding the target slurry. The target slurry was transferred to a sealable copper mold, filled and sealed, and allowed to stand for 1 h. The mold was then placed on a cold plate and frozen for 1.5 h to allow the slurry to fully solidify. The frozen sample was quickly transferred to a vacuum dryer and dried for 30 h. The resulting lithium hydroxide material was removed, placed in a tablet press mold, and pressed at 0.8 MPa for 1 min to form tablets with a diameter of 1.5 mm and a thickness of 2 mm, thus obtaining the carbon dioxide absorbent product of this embodiment.

[0093] Example 3

[0094] 35.0 g of sodium carboxymethyl cellulose was dissolved in 145.0 g of deionized water heated to 60°C. Then, 315.0 g of lithium hydroxide powder was added, and the mixture was stirred vigorously at 600 rpm until homogeneous, yielding a white suspension. Subsequently, 5.0 g of CAPB was dissolved in the white suspension, and the mixture was stirred vigorously at 600 rpm until homogeneous, yielding the target slurry. The target slurry was transferred to a sealable copper mold, filled and sealed, and allowed to stand for 1 h. The mold was then placed on a cold plate and frozen for 1 h to allow the slurry to fully solidify. The frozen sample was quickly transferred to a vacuum dryer and dried for 28 h. The resulting lithium hydroxide material was removed and placed in a tablet press mold. The tablets were pressed at 0.5 MPa for 1 min to form tablets with a diameter of 2 mm and a height of 3 mm, yielding the carbon dioxide absorbent product of this embodiment.

[0095] like Figure 2 The image shown is a scanning electron microscope (SEM) image of the carbon dioxide absorbent prepared in Example 3 after use, which shows that it has a porous structure.

[0096] like Figure 3 The X-ray diffraction pattern (XRD) shown shows that after the carbon dioxide absorption experiment, most of the lithium hydroxide in the carbon dioxide absorbent reacted with carbon dioxide to become lithium carbonate, with only a very small portion of unused lithium hydroxide remaining.

[0097] Comparative Example 1

[0098] 35.0 g of sodium carboxymethyl cellulose was dissolved in 150.0 g of deionized water heated to 60°C. Then, 315.0 g of lithium hydroxide powder was added, and the mixture was vigorously stirred at 600 rpm until homogeneous to obtain the target slurry. The target slurry was extruded into tablets with a diameter of 2 mm and a height of 3 mm. The tablets were then placed in an 80°C vacuum drying oven for drying until a constant weight was achieved, yielding a carbon dioxide absorbent product as a comparative example.

[0099] The pore structure parameters of the carbon dioxide absorbents prepared in Example 3 and Comparative Example 1 are shown in Table 1 below:

[0100] Table 1

[0101]

[0102] As can be seen from the pore structure data of the examples and comparative examples in the table above, compared with the traditional drying method, Example 3 of this disclosure uses a pore structure inducing agent-assisted ice fiber template method to introduce a multi-level pore structure inside the absorbent, increasing its specific surface area. The specific surface area of ​​Example 3 is 1.71 times that of the comparative example, providing more surface reaction sites for carbon dioxide absorption. In addition, the pore composition of Example 3 is mainly mesopores (2-50 nm), accounting for 55.4%, with the addition of micropores (less than 2 nm) and macropores (greater than 50 nm). The number of mesopores and micropores is significantly higher than that of the comparative example (49.9% and 10.4%, respectively). The large number of mesopores in the absorbent constitutes a continuous mass transfer network, serving as a fast diffusion channel for carbon dioxide molecules. Micropores provide a large number of highly efficient adsorption sites, and an appropriate amount of macropores support a stable framework. This efficient synergistic structure can promote the dispersion and contact of carbon dioxide in the carbon dioxide absorbent, thereby achieving a faster carbon dioxide absorption rate and extremely high lithium hydroxide utilization.

[0103] Below, under the same experimental conditions, the absorbent samples prepared in Examples 1-3 and Comparative Example 1 were subjected to carbon dioxide absorption performance tests to evaluate their carbon dioxide absorption rate and lithium hydroxide utilization rate.

[0104] The specific experimental steps for absorption performance are as follows:

[0105] (1) First, turn on the temperature and humidity controller to make the temperature and humidity in the sealed room reach the set value (25℃, 60%) and remain stable for at least 30 minutes. During the entire test, keep the temperature and humidity in the sealed room constant.

[0106] (2) Then, carbon dioxide gas is introduced into the sealed chamber and the two circulating fans in the chamber are started. The CO2 concentration in the sealed chamber is controlled by the flow rate to reach 0.7%. After the gas intake is stopped, the reading of the carbon dioxide detector in the sealed chamber is observed. When the carbon dioxide concentration value does not change significantly within 5 minutes, the carbon dioxide concentration in the sealed chamber is considered to be stable. The testing equipment is then turned on to continuously monitor the carbon dioxide concentration in the sealed chamber.

[0107] (3) Place a certain mass of lithium hydroxide material into a box that can be connected to a sealed chamber, close the box and seal it, and send the carbon dioxide absorbent into the sealed chamber.

[0108] (4) After adding lithium hydroxide material, start timing. Observe and record the reading of the carbon dioxide detector every 60 minutes until the detector reading is basically constant. Plot the carbon dioxide absorption rate-time curve, as shown below. Figure 4 As shown.

[0109] (5) Finally, quickly remove the carbon dioxide absorbent, weigh it, and record the weight of the sample after absorbing carbon dioxide.

[0110] The experimental data are shown in Table 2 below:

[0111] Table 2

[0112]

[0113] As shown in Table 2 above, the utilization rate of lithium hydroxide, the carbon dioxide absorbent disclosed in this invention, is significantly higher than that of the comparative example. (See Appendix...) Figure 1 In the adsorption tests of Example 3 and Comparative Example 1, the sample of Example 3 showed a faster carbon dioxide absorption rate and a higher carbon dioxide absorption rate, proving that the three-dimensional network of pores constructed by the synergistic effect of the ice fiber template and the pore structure inducer not only increased the contact area of ​​the reaction and achieved extremely high lithium hydroxide utilization, but also achieved stable carbon dioxide absorption and avoided premature decay of the carbon dioxide absorption rate in the high utilization stage.

[0114] Finally, it should be noted that the above-described embodiments are merely specific implementations of this disclosure, used to illustrate the technical solutions of this disclosure, and not to limit it. The protection scope of this disclosure is not limited thereto. Although this disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the scope of the technology disclosed in this disclosure; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this disclosure, and should all be covered within the protection scope of this disclosure. Therefore, the protection scope of this disclosure should be determined by the protection scope of the claims.

Claims

1. A method for producing a carbon dioxide absorbent, characterized by, Includes the following steps: The binder is dissolved in deionized water preheated to 50-70°C, and lithium hydroxide powder is added and stirred to form a suspension slurry; the binder includes one or more of sodium carboxymethyl cellulose, polyvinyl alcohol and microcrystalline cellulose; A pore structure inducer is added to the suspension slurry and the mixture is vigorously mechanically stirred at a stirring rate of 200-800 rpm to form the target slurry; the pore structure inducer includes one or more of cocamidopropyl betaine and oleamidopropyl dimethyl betaine; After the target slurry is left to stand for 0.5-2 hours, it is transferred to a mold, filled and sealed, and then brought into contact with a low-temperature cold source for freezing treatment. This causes the water in the target slurry to form an ice fiber template, resulting in a lithium hydroxide cryogenic body. The freezing treatment time is 0.5-2 hours. Under pressure conditions below 20 Pa, the lithium hydroxide cryobody is subjected to vacuum drying for 12-36 hours to sublimate the ice fiber template, thereby obtaining a lithium hydroxide material with a three-dimensional network pore structure. The lithium hydroxide material with a three-dimensional network structure is extruded and shaped under a pressure of 0.5-3.0 MPa for 0.5-10 minutes to obtain a carbon dioxide absorbent. The method further includes preparing raw materials according to the following mass percentages in the target slurry: The lithium hydroxide powder has a mass percentage of 25%-65%, the binder has a mass percentage of 1%-10%, the pore structure inducing agent has a mass percentage of 0.5%-5%, and the balance is deionized water.

2. The method of claim 1, wherein, The carbon dioxide absorbent has a thickness of 0.5-6.0 mm and a diameter of 1.5-2.0 mm.

3. The method of claim 1, wherein, The bulk density of the carbon dioxide absorbent is 0.4-0.6 g / cm 3 The particle strength is 85-95%.

4. The method of claim 1, wherein, The bulk density of the lithium hydroxide material with a three-dimensional mesh structure is 0.30-0.45 g / cm³.

5. A carbon dioxide absorbent, characterized by, The carbon dioxide absorbent has a porous structure and is prepared by the preparation method according to any one of claims 1 to 4.

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