A method for co-processing organic shellfish shell waste and synergistically preparing Ca-based CO2 adsorbents

Abstract

This invention belongs to the technical field of solid waste resource utilization and CO2 adsorption materials. It relates to a method for preparing a Ca-based CO2 adsorbent based on the synergistic treatment and enhanced efficiency of organic shellfish shell waste. The method involves pretreating the shellfish shell waste, followed by a second organic acid treatment to form a foam-like calcium-based intermediate with a unique morphology and porous, fluffy structure. This intermediate is then coated with organic acid and calcined to obtain the Ca-based CO2 adsorbent. The adsorbent has a temperature window of approximately 650–720°C and an adsorption gas flow rate of 50–120 mL / min. It achieves an adsorption capacity of 54.31% for various CO2 concentrations from 60% to 100%, and retains 41.15% of its adsorption capacity after six adsorption cycles. Furthermore, the main raw material of this invention is derived from solid waste shellfish shells, and the preparation method is low-cost and simple, exhibiting significant environmental benefits and industrialization prospects.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and CO2 adsorption material technology, and relates to a method for preparing Ca-based CO2 adsorbents based on the synergistic treatment and enhanced preparation of organic shellfish shell waste, which can be applied to CO2 adsorption under high temperature environment. Background Technology

[0002] With the development of global industrial technology, carbon emissions resulting from environmental pollution have become a common problem facing humanity. Especially in the current context, there is an urgent need to study the treatment of greenhouse gases such as carbon dioxide. The greenhouse effect caused by excessive carbon dioxide emissions seriously affects people's lives and production. This is an urgent problem that needs to be solved in the development of my country and other countries around the world. Among them, carbon capture, utilization, and storage (CCUS) is the most promising strategy to alleviate this important ecological problem of carbon emissions. Existing carbon dioxide capture methods mainly include membrane separation, absorption, and adsorption. Among them, absorption methods are energy-intensive and space-consuming; membrane separation methods are difficult to maintain and have a small processing range, and both of these methods heavily rely on the addition of chemical reagents to achieve carbon dioxide adsorption and desorption, which is not environmentally friendly. In contrast, among carbon dioxide capture methods, adsorption methods are favored by researchers due to their advantages such as low cost, high thermal and chemical stability, good wear resistance, high carbon dioxide loading capacity, and strong selectivity. As one of the mainstream carbon capture and storage technologies, CaO-based adsorption cycling has been widely studied due to its advantages such as readily available raw materials, safety and non-toxicity, large adsorption capacity, and wide applicability.

[0003] On the other hand, my country has a shellfish aquaculture area of ​​up to 1.20425 million hectares, resulting in a total shellfish production exceeding 14.58 million tons. However, the vast majority of these shells are not properly disposed of, causing widespread and significant land occupation, waste disposal, and air pollution problems. The hard mantle formed by the secretions of the glandular cells of these mollusks not only possesses unique structural characteristics, but similar shell materials also exhibit extremely high (approximately 96%) content of CaCO3 crystals and various metal and organic components, showing great potential for the preparation of CaO-based CO2 adsorbents.

[0004] Currently, the vast majority of CaO adsorbents are derived from further processing of mineral resources such as limestone. This leads to increased costs in mining and transportation. More importantly, the preparation process is accompanied by a large amount of CO2 emissions. Furthermore, pure CaO suffers from severe sintering problems in the high-temperature carbonation cycle reaction required to achieve maximum adsorption capacity, which seriously limits its application in industrial settings and is a key research issue at present.

[0005] Currently, the research and development of CO2 adsorbents focuses on preparing those with better adsorption performance, wider applications, and diversified utilization. For example, Chinese invention patent application CN117983015A discloses a method for preparing a carbon dioxide adsorbent material, whose effective adsorption components are mainly nickel / iron / zinc / magnesium 2,5-dihydroxyterephthalate with a MOF framework structure. However, with the improvement of performance, the preparation process of the adsorbent becomes more complex, and the construction of multiple metal elements leads to higher costs. Furthermore, the organic parts of the MOF framework are prone to decomposition at high temperatures, causing secondary pollution. Meanwhile, we have noticed that in the optimization of CaO-based materials, metal doping is often used to improve adsorption capacity and multiple recycling efficiency. For example, Chinese invention patent application CN106693880B discloses a calcium-based CO2 adsorbent and its preparation method, which uses Ca2MnO4 to optimize the material structure and enhance anti-sintering ability, but there is still room for improvement in overall adsorption capacity and stability.

[0006] Given the current situation, if a CO2 adsorbent with high adsorption efficiency and stability can be prepared, and the comprehensive utilization of seashell materials can be achieved using a "green preparation method", it would be an important direction with "environmental, economic and social" value in the current application of high-temperature carbonation cycle CO2 adsorption. Summary of the Invention

[0007] This invention aims to further improve Ca-based CO2 adsorbents while achieving green manufacturing. It provides a method for the synergistic and efficient preparation of Ca-based CO2 adsorbents based on the co-processing of organic shellfish waste. For the first time, it was discovered that under specific secondary organic acid treatment conditions, shellfish materials can form a uniquely morphological and porous, foam-like calcium-based intermediate. This intermediate is then coated with organic acid and calcined to prepare the Ca-based CO2 adsorbent. The adsorbent operates within a temperature window of approximately 650–720 °C, with an adsorption gas flow rate of 50–120 mL / min. It achieves an adsorption capacity of 54.31% for various CO2 concentrations from 60% to 100%, and retains 41.15% of its adsorption capacity after six adsorption cycles. Furthermore, the main raw material of this invention is derived from solid waste shellfish materials, and the preparation method is low-cost and simple, demonstrating significant environmental benefits and industrialization prospects.

[0008] To achieve the above objectives, the present invention employs a technical solution consisting of the following technical measures.

[0009] This invention provides a method for the synergistic treatment and enhanced preparation of Ca-based CO2 adsorbents based on organic shellfish shell waste, comprising the following steps:

[0010] (1) The shellfish waste is cleaned, sterilized, dried, and crushed into shellfish pieces with a particle size of no more than 1 cm;

[0011] (2) The shellfish pieces obtained in step (1) are immersed in an aqueous solution of organic acid with a mass concentration of 2-6 wt% and reacted under shaking conditions for 23-24 hours. After the time is up, the shellfish pieces are separated, washed and dried to obtain the first acid hydrolysis product. The first acid hydrolysis product is then immersed in an aqueous solution of organic acid with a mass concentration of 2-6 wt% and reacted again under shaking conditions for 23-24 hours. After the time is up, the shellfish pieces are separated, washed and dried to obtain the foam-like calcium-based intermediate.

[0012] The organic acid in the aqueous solution A is any one of acetic acid, propionic acid, citric acid, and lactic acid.

[0013] (3) Mix 4 g of the foam-like calcium-based intermediate obtained in step (2) with 40-80 mL of an organic acid aqueous solution B with a mass concentration of 5-10 wt%, stir and mix for 0.5-1 hour, then separate the solid product coated with organic acid, and calcine it in an inert gas atmosphere at 850-950 °C for 0.5-1.5 hours to prepare a Ca-based CO2 adsorbent;

[0014] The organic acid in the aqueous solution B is any one of acetic acid, propionic acid, citric acid, oxalic acid, and lactic acid.

[0015] In this paper, the shellfish waste mentioned in step (1) refers to typical solid waste from the shellfish aquaculture industry, including shells of common economic shellfish species, such as clams, mussels, abalone shells, and clam shells. Since this invention primarily utilizes calcium carbonate as the main component of shellfish shells, based on common knowledge, the calcium carbonate crystal forms in shellfish shells mainly include calcite and aragonite. Experiments in this invention have confirmed that shellfish shells with the above-mentioned main calcium carbonate crystal forms can all be used as raw materials for this invention, and all have relatively consistent technical contributions. Although clams and mussels collected from markets in Hainan / Chengdu are often selected in the following embodiments for the convenience of designing variable experiments and for ease of collection, this does not imply a limitation / specification of the shellfish waste described in this invention. Furthermore, the following embodiments verify that shellfish shells with calcite and aragonite as the main components can all be used to prepare Ca-based CO2 adsorbents and have relatively consistent technical contributions. Therefore, theoretically, the shellfish waste described in this invention can cover the shellfish waste of currently commercially available economic shellfish species.

[0016] Typically, the washing, sterilization, and drying of shellfish waste described in step (1) aims to remove residual impurities from the surface of the shellfish waste as much as possible, in order to facilitate controllability in the subsequent acid hydrolysis process. Those skilled in the art can process the shellfish waste according to the actual situation of the collected shellfish waste, referring to existing literature (such as literature on the resource recycling of shellfish waste).

[0017] In one of the preferred technical solutions, when the shell waste is the shell of a clam or mussel, the shell waste in step (1) is cleaned, sterilized and dried, and then roasted at a temperature of 200~220 ℃ for 23~24 hours after drying to completely remove the residual organic impurities on its surface.

[0018] Similarly, in step (1), the shells are crushed into pieces with a particle size of no more than 1 cm. This is also to ensure controllability in the subsequent acid hydrolysis process and to avoid the inability to separate the foam-like calcium-based intermediate consistent with the present invention due to insufficient acid hydrolysis. It should be noted that if the particle size of the shells is too small, excessive acid hydrolysis will cause the shell material, which is mainly composed of calcium carbonate, to transform into organic acid calcium and carbonate and completely dissolve in the organic acid system, thus failing to form a foam-like calcium-based intermediate, resulting in a decrease in yield. Therefore, it is more preferable to crush the shells into pieces with a particle size of 0.8 to 1 cm.

[0019] Typically, the oscillation conditions described in step (2) are conventional process operations to promote the acid hydrolysis reaction. Those skilled in the art can follow conventional principles to operate, such as using oscillation conditions with a frequency of 125~200 rpm.

[0020] Typically, in step (2), the shellfish pieces obtained in step (1) are immersed in an organic acid aqueous solution A with a mass concentration of 2-6 wt%, and the first acid hydrolysis product is immersed in an organic acid aqueous solution A with a mass concentration of 2-6 wt%. The ratio of shellfish pieces to organic acid aqueous solution A and the ratio of the first acid hydrolysis product to organic acid aqueous solution A both follow the principle of full acid hydrolysis, that is, ensuring that the loss of organic acid in organic acid aqueous solution A does not change significantly during the acid hydrolysis reaction. For example, when the shellfish pieces are 5 g, the organic acid aqueous solution A is at least 75 mL in both reactions, or organic acid aqueous solution A with a mass concentration of 2-6 wt% is added during the acid hydrolysis reaction.

[0021] It should be noted that in step (2), the shellfish blocks are acidified twice with an organic acid aqueous solution A at a mass concentration of 2-6 wt%. An unsuitable acid concentration may cause excessive dissolution or incomplete separation of the shellfish material, directly affecting the formation of the "bubble-like" structure of the subsequent foam-like calcium-based intermediate. In addition, in comparative experiments, the inventors also tried to combine the conditions of the two acidifications into a single acidification, but they were unable to prepare the foam-like calcium-based intermediate consistent with the present invention. This is presumably the reason why this microscopic morphology product has not been found in the literature to date.

[0022] The inventors conducted a certain analysis and research on the unique morphology of the foam-like calcium-based intermediate obtained in step (2). One hypothesis is that this is due to the precise control of the conditions in the two acid hydrolysis processes, in which the organic matter undergoes cross-linking and denaturation with calcite-type calcium carbonate. During this process, the long-chain structure of organic macromolecules and the multi-tube energy groups of organic acids form ionic bonds, coordinate bonds, and other multi-element cross-links with Ca-based ions, combined with the continuous entanglement of organic chains, forming an organic-inorganic composite network framework. Thus, a foam-like calcium-based intermediate with a "bubble-like" microstructure is obtained. However, in subsequent experiments to expand the selection of shellfish waste, the same foam-like calcium-based intermediate could also be prepared from shellfish shells containing non-calcite-type calcium carbonate, so its formation mechanism is currently unknown.

[0023] In contrast, inorganic acid systems lack long-chain structures and multi-functional groups, and are devoid of molecular entanglement and cross-linking. Furthermore, inorganic acids are mostly in ionic form and have high H+ content. + The strong ionization properties brought about by the concentration cause the calcium carbonate-based shell material to react rapidly in a very short time, resulting in the dissolution of the shell material. The kinetics are uncontrollable, and the products such as calcium chloride / calcium nitrate (if hydrochloric acid or nitric acid are used) are easily soluble. The system is completely liquefied, with no solid phase produced, thus making it impossible to form the characteristic "bubble-like" structure.

[0024] It should be noted that the selection of organic acids in organic acid aqueous solution A and organic acid aqueous solution B in steps (2) and (3) is limited, respectively. This is because actual experiments have shown that when the organic acid in organic acid aqueous solution A in step (2) is formic acid or oxalic acid, it is difficult or impossible (with extremely low yield) to prepare a foam-like calcium-based intermediate. This indicates that not all conventional organic acid selections are suitable for this invention, and the reason is currently unknown. Similarly, formic acid is not suitable for organic acid aqueous solution B in step (3), but oxalic acid can be selected.

[0025] In one of the preferred technical solutions, comparative experiments have shown that the organic acid aqueous solution A in step (2) is preferably an acetic acid aqueous solution with a mass concentration of 3 wt%, and the microstructure and yield of the foam-like calcium-based intermediate prepared using it are optimal.

[0026] In one of the preferred technical solutions, the organic acid in step (3) is preferably citric acid. Comparative experiments revealed that when the organic acid in step (3) is citric acid, the resulting Ca-based CO2 adsorbent exhibits significantly improved porous structure, redox properties, and surface acid-base properties, demonstrating surprisingly good adsorption performance. Furthermore, its tactile feel is significantly different from that of adsorbents prepared using other organic acids. Comparative experiments showed a clear difference between the preferred organic acids in steps (2) and (3), which indirectly indicates that the technical purpose, principle, and effect of the organic acids used in steps (2) and (3) are different.

[0027] Typically, the roasting process described in step (3) includes process parameters such as heating rate, which can be carried out according to conventional roasting process methods, for example, heating rate of 5~10 ℃ / min.

[0028] In this document, the separation, washing, drying, stirring and other processes all follow the conventional principles of chemical processes, and those skilled in the art can perform the specific operations based on common knowledge.

[0029] During the project initiation process related to this invention, the inventors aimed to find a more economical and efficient process for CO2 adsorbents that could achieve comprehensive utilization of solid waste. After preliminary research, shellfish shells were chosen as raw materials to prepare CaO-based CO2 adsorbents, as most of the raw materials can be selected from many common economic shellfish species for co-processing and reuse of waste. During the experiment, it was unexpectedly discovered that due to the special structure and main components of the aforementioned shellfish waste, a foam-like calcium-based intermediate with a "bubble-like" microstructure was formed during the continuous two-stage acid hydrolysis treatment with organic acids. This intermediate was then coated with organic acids and calcined to prepare a Ca-based CO2 adsorbent. Compared to commercially available CaCO3 or limestone-derived CaO-based CO2 adsorbents, this adsorbent exhibited better activity in terms of adsorption capacity and multiple carbonation cycles. This is because the continuous organic acid treatment caused the stable structure of the shellfish shells to undergo denaturation and optimization, resulting in better textural properties. This allowed the active sites of the system to be fully protected and efficiently utilized. Furthermore, the abundant functional groups and some impurities in the shellfish shells promoted synergistic effects, further enhancing the CO2 adsorption performance of the adsorbent.

[0030] This unexpected discovery greatly enhances the practical application value of the CO2 adsorbent prepared from shellfish waste using this invention under the concept of "green synthesis and waste-to-waste treatment," and provides a new way to reuse the aforementioned solid waste.

[0031] Furthermore, in the selection of organic acids for subsequent organic acid coating, comparative experiments unexpectedly revealed that when citric acid was selected as the organic acid, the prepared Ca-based CO2 adsorbent exhibited significantly better adsorption performance, achieving unexpected technical results.

[0032] The CO2 adsorbent finally prepared by the above technical solution has an adsorption capacity of more than 54% for carbon dioxide with a concentration of 60-100% in simulated flue gas, under the conditions of a temperature window of 650-720 ℃ and a gas velocity of 50-120 mL / min. After 6 adsorption cycles, it still retains about 41% of the adsorption capacity, with a decay rate of about 23%.

[0033] The present invention has the following beneficial effects:

[0034] 1. This invention provides a method for the synergistic treatment and enhanced preparation of Ca-based CO2 adsorbents based on organic shell waste. It is the first discovery that under specific secondary organic acid treatment conditions, shell materials can form foam-like calcium-based intermediates with unique morphology and porous and fluffy structure. The Ca-based CO2 adsorbent is then prepared by organic acid coating and calcination.

[0035] 2. The Ca-based CO2 adsorbent prepared by this invention can achieve an adsorption capacity of 54.31% under various CO2 concentration conditions of 60-100% within a temperature window of approximately 650-720 °C and an adsorption gas flow rate of 50-120 mL / min. Furthermore, it retains 41.15% of its adsorption capacity after 6 adsorption cycles, with a decay rate of approximately 23%. It is particularly suitable for high-temperature carbonation CO2 adsorption applications, such as the adsorption of carbon dioxide emitted from high-temperature processes in industries like enhanced methane reforming for hydrogen production and solar energy storage, as well as for in-situ reaction treatment of chemical processes.

[0036] 3. This invention discloses a method for the synergistic treatment and enhanced preparation of Ca-based CO2 adsorbents based on organic shellfish waste. It utilizes only common solid wastes available on the market, such as clam shells and mussel shells, which are economically valuable shellfish with low resource utilization and limited treatment methods. Therefore, these materials are widely available and inexpensive. Furthermore, compared to the limestone raw materials often used in the preparation of traditional CaO-based adsorbents, the preparation process is "green and zero-carbon." Other organic reagents used are also conventional chemical reagents, resulting in a significant reduction in overall raw material costs compared to commercially available materials. Compared to lithium-based and zirconium-based adsorbents on the market, this method offers better adsorption cycle efficiency and lower costs, demonstrating not only significant environmental benefits but also promising market application prospects.

[0037] 4. The preparation method of the present invention has the characteristics of low cost and process steps suitable for continuous production, and has the prospect of industrial production. Attached Figure Description

[0038] Figure 1 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Example 1 of the present invention at a constant temperature of 650℃ under a CO2 concentration of 120 mL / min.

[0039] Figure 2 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Example 1 of the present invention at a constant temperature of 650℃ under a CO2 concentration of 60 mL / min.

[0040] Figure 3 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Example 1 of the present invention under varying temperature adsorption conditions from room temperature to 1000 °C at a CO2 concentration of 100 mL / min.

[0041] Figure 4 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Example 1 of the present invention under a cyclic adsorption experiment (6 times) at a CO2 concentration of 60 mL / min.

[0042] Figure 5 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Example 1 of the present invention under a cyclic adsorption experiment (20 times) at a CO2 concentration of 60 mL / min.

[0043] Figure 6 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Example 2 of the present invention under varying temperature adsorption conditions from room temperature to 1000 °C at a CO2 concentration of 100 mL / min.

[0044] Figure 7 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Example 2 of the present invention under a cyclic adsorption experiment (6 times) at a CO2 concentration of 60 mL / min.

[0045] Figure 8 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Example 3 of the present invention under varying temperatures from room temperature to 1000 ℃ at a CO2 concentration of 100 mL / min.

[0046] Figure 9 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Comparative Example 1 of the present invention, under a CO2 concentration of 120 mL / min and a constant temperature adsorption experiment at 650℃.

[0047] Figure 10 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Comparative Example 1 of the present invention under varying temperature adsorption conditions from room temperature to 1000℃ at a CO2 concentration of 100 mL / min.

[0048] Figure 11 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Comparative Example 1 of the present invention under a CO2 concentration of 60 mL / min for cyclic adsorption experiments (6 times).

[0049] Figure 12 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Comparative Example 1 of the present invention under a CO2 concentration of 60 mL / min for 20 cycles of adsorption.

[0050] Figure 13 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Comparative Example 2 of the present invention, under a CO2 concentration of 120 mL / min and a constant temperature adsorption experiment at 650℃.

[0051] Figure 14 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Comparative Example 2 of the present invention, under a CO2 concentration of 60 mL / min and a constant temperature of 650℃.

[0052] Figure 15 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Comparative Example 2 of the present invention under varying temperature adsorption conditions from room temperature to 1000 °C at a CO2 concentration of 100 mL / min.

[0053] Figure 16 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Comparative Example 2 of the present invention under a CO2 concentration of 60 mL / min for cyclic adsorption experiments (6 times).

[0054] Figure 17 This is an adsorption capacity curve of the Ca-based CO2 adsorbent prepared in Comparative Example 3 of the present invention, under a CO2 concentration of 120 mL / min and a constant temperature adsorption experiment at 650℃.

[0055] Figure 18 This is a SEM image of the foam-like calcium-based intermediate obtained in step (2) of Example 1 of the present invention. It shows abundant foamy aggregates and a loose, porous structure.

[0056] Figure 19 This is a photograph of the final sample of the Ca-based CO2 adsorbent prepared in Comparative Example 1 of this invention.

[0057] Figure 20 This is a photograph of Comparative Example 4 of the present invention, showing that the shell fragments of a shellfish almost completely dissolved under a single acid hydrolysis condition.

[0058] Figure 21 These are photographs documenting step (2) of Embodiment 1 of the present invention. From left to right, the photographs show the shellfish pieces just immersed in a 3 wt% acetic acid aqueous solution, the first acid hydrolysis product after washing, and the first acid hydrolysis product after immersion in a 3 wt% acetic acid aqueous solution for 6 hours. Detailed Implementation

[0059] To further understand the present invention, preferred embodiments are described below with reference to examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. Those skilled in the art can refer to the content of this document to appropriately improve the process parameters. In particular, it should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the scope of the present invention. The methods and applications of the present invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate changes and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present invention to realize and apply the technology of the present invention. Although it is believed that those skilled in the art will fully understand the following terms, the following definitions are set forth to help illustrate the subject matter disclosed in the present invention.

[0060] This invention provides a method for the synergistic treatment and enhanced preparation of Ca-based CO2 adsorbents based on organic shellfish shell waste, comprising the following steps:

[0061] (1) The shellfish waste is cleaned, sterilized, dried, and crushed into shellfish pieces with a particle size of no more than 1 cm;

[0062] (2) The shellfish pieces obtained in step (1) are immersed in an aqueous solution of organic acid with a mass concentration of 2-6 wt% and reacted under shaking conditions for 23-24 hours. After the time is up, the shellfish pieces are separated, washed and dried to obtain the first acid hydrolysis product. The first acid hydrolysis product is then immersed in an aqueous solution of organic acid with a mass concentration of 2-6 wt% and reacted again under shaking conditions for 23-24 hours. After the time is up, the shellfish pieces are separated, washed and dried to obtain the foam-like calcium-based intermediate.

[0063] The organic acid in the aqueous solution A is any one of acetic acid, propionic acid, citric acid, and lactic acid.

[0064] (3) Mix 4 g of the foam-like calcium-based intermediate obtained in step (2) with 40-80 mL of an organic acid aqueous solution B with a mass concentration of 5-10 wt%, stir and mix for 0.5-1 hour, then separate the solid product coated with organic acid, and calcine it in an inert gas atmosphere at 850-950 °C for 0.5-1.5 hours to prepare a Ca-based CO2 adsorbent;

[0065] The organic acid in the aqueous solution B is any one of acetic acid, propionic acid, citric acid, oxalic acid, and lactic acid.

[0066] In this paper, the shellfish waste mentioned in step (1) refers to typical solid waste from the shellfish aquaculture industry, including shells of common economic shellfish species, such as clams, mussels, abalone shells, and clam shells. Since this invention primarily utilizes calcium carbonate as the main component of shellfish shells, based on common knowledge, the calcium carbonate crystal forms in shellfish shells mainly include calcite and aragonite. Experiments in this invention have confirmed that shellfish shells with the above-mentioned main calcium carbonate crystal forms can all be used as raw materials for this invention, and all have relatively consistent technical contributions. Although clams and mussels collected from markets in Hainan / Chengdu are often selected in the following embodiments for the convenience of designing variable experiments and for ease of collection, this does not imply a limitation / specification of the shellfish waste described in this invention. Furthermore, the following embodiments verify that shellfish shells with calcite and aragonite as the main components can all be used to prepare Ca-based CO2 adsorbents and have relatively consistent technical contributions. Therefore, theoretically, the shellfish waste described in this invention can cover the shellfish waste of currently commercially available economic shellfish species.

[0067] Typically, the washing, sterilization, and drying of shellfish waste described in step (1) aims to remove residual impurities from the surface of the shellfish waste as much as possible, in order to facilitate controllability in the subsequent acid hydrolysis process. Those skilled in the art can process the shellfish waste according to the actual situation of the collected shellfish waste, referring to existing literature (such as literature on the resource recycling of shellfish waste).

[0068] In one preferred embodiment, when the shell waste is the shell of a clam or mussel, the shell waste in step (1) is cleaned, sterilized, and dried, and then roasted at a temperature of 200~220 ℃ for 23~24 hours after drying to completely remove residual organic impurities on its surface.

[0069] Similarly, in step (1), the shells are crushed into pieces with a particle size of no more than 1 cm. This is also to ensure controllability in the subsequent acid hydrolysis process and to avoid the inability to separate the foam-like calcium-based intermediate consistent with the present invention due to insufficient acid hydrolysis. It should be noted that if the particle size of the shells is too small, excessive acid hydrolysis will cause the shell material, which is mainly composed of calcium carbonate, to transform into organic acid calcium and carbonate and completely dissolve in the organic acid system, thus failing to form a foam-like calcium-based intermediate, resulting in a decrease in yield. Therefore, in one preferred embodiment, it is more preferable to crush the shells into pieces with a particle size of 0.8 to 1 cm.

[0070] Typically, the oscillation conditions described in step (2) are conventional process operations that promote acid hydrolysis. Those skilled in the art can follow conventional principles to operate the process. In one embodiment, for example, an oscillation condition with a frequency of 125~200 rpm is used.

[0071] Typically, in step (2), the shellfish pieces obtained in step (1) are immersed in an organic acid aqueous solution A with a mass concentration of 2-6 wt%, and the first acid hydrolysis product is immersed in an organic acid aqueous solution A with a mass concentration of 2-6 wt%. The ratio of shellfish pieces to organic acid aqueous solution A and the ratio of the first acid hydrolysis product to organic acid aqueous solution A both follow the principle of sufficient acid hydrolysis, that is, ensuring that the loss of organic acid in organic acid aqueous solution A does not change significantly during the acid hydrolysis reaction. In one embodiment, for example, when the shellfish pieces are 5 g, the organic acid aqueous solution A is at least 75 mL in both reactions, or organic acid aqueous solution A with a mass concentration of 2-6 wt% is added during the acid hydrolysis reaction.

[0072] In one embodiment, the mass concentration of the organic acid aqueous solution A in step (2) is 2 to 6 wt%, for example 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, or any range or point value between them.

[0073] It should be noted that in step (2), the shellfish blocks are acidified twice with an organic acid aqueous solution A at a mass concentration of 2-6 wt%. An unsuitable acid concentration may cause excessive dissolution or incomplete separation of the shellfish material, directly affecting the formation of the "bubble-like" structure of the subsequent foam-like calcium-based intermediate. In addition, in comparative experiments, the inventors also tried to combine the conditions of the two acidifications into a single acidification, but they were unable to prepare the foam-like calcium-based intermediate consistent with the present invention. This is presumably the reason why this microscopic morphology product has not been found in the literature to date.

[0074] The inventors conducted a certain analysis and research on the unique morphology of the foam-like calcium-based intermediate obtained in step (2). One hypothesis is that this is due to the precise control of the conditions in the two acid hydrolysis processes, in which the organic matter undergoes cross-linking and denaturation with calcite-type calcium carbonate. During this process, the long-chain structure of organic macromolecules and the multi-tube energy groups of organic acids form ionic bonds, coordinate bonds, and other multi-element cross-links with Ca-based ions, combined with the continuous entanglement of organic chains, forming an organic-inorganic composite network framework. Thus, a foam-like calcium-based intermediate with a "bubble-like" microstructure is obtained. However, in subsequent experiments to expand the selection of shellfish waste, the same foam-like calcium-based intermediate could also be prepared from shellfish shells containing non-calcite-type calcium carbonate, so its formation mechanism is currently unknown.

[0075] In contrast, inorganic acid systems lack long-chain structures and multi-functional groups, and are devoid of molecular entanglement and cross-linking. Furthermore, inorganic acids are mostly in ionic form and have high H+ content. +The strong ionization properties brought about by the concentration cause the calcium carbonate-based shell material to react rapidly in a very short time, resulting in the dissolution of the shell material. The kinetics are uncontrollable, and the products such as calcium chloride / calcium nitrate (if hydrochloric acid or nitric acid are used) are easily soluble. The system is completely liquefied, with no solid phase produced, thus making it impossible to form the characteristic "bubble-like" structure.

[0076] It should be noted that the selection of organic acids in organic acid aqueous solution A and organic acid aqueous solution B in steps (2) and (3) is limited, respectively. This is because actual experiments have shown that when the organic acid in organic acid aqueous solution A in step (2) is formic acid or oxalic acid, it is difficult or impossible (with extremely low yield) to prepare a foam-like calcium-based intermediate. This indicates that not all conventional organic acid selections are suitable for this invention, and the reason is currently unknown. Similarly, formic acid is not suitable for organic acid aqueous solution B in step (3), but oxalic acid can be selected.

[0077] In one preferred embodiment, comparative experiments have shown that the organic acid aqueous solution A in step (2) is preferably an acetic acid aqueous solution with a mass concentration of 3 wt%, and the microstructure and yield of the foam-like calcium-based intermediate prepared using it are optimal.

[0078] In one of the preferred embodiments, the organic acid in step (3) is preferably citric acid. Comparative experiments revealed that when the organic acid in step (3) is citric acid, the resulting Ca-based CO2 adsorbent exhibits significantly improved porous structure, redox properties, and surface acid-base properties, demonstrating surprisingly good adsorption performance. Furthermore, its tactile feel is significantly different from that of adsorbents prepared with other organic acids. Comparative experiments showed a clear difference between the preferred organic acids in steps (2) and (3), which indirectly indicates that the technical purpose, principle, and effect of the organic acids used in steps (2) and (3) are different.

[0079] In one embodiment, the organic acid aqueous solution B in step (3) is 40-80 mL, for example, 40 mL, 42 mL, 44 mL, 46 mL, 48 mL, 50 mL, 52 mL, 54 mL, 56 mL, 58 mL, 60 mL, 62 mL, 64 mL, 66 mL, 68 mL, 70 mL, 72 mL, 74 mL, 76 mL, 78 mL, 80 mL or any range or point value between them; the mass concentration of the organic acid aqueous solution B is 5-10 wt%, for example, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, 10 wt% or any range or point value between them.

[0080] In one embodiment, the roasting treatment in step (3) is 850~950 °C, for example 850 °C, 860 °C, 870 °C, 880 °C, 890 °C, 900 °C, 910 °C, 920 °C, 930 °C, 940 °C, 950 °C or any range or point value therebetween; the roasting treatment is 0.5~1.5 hours, for example 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours or any range or point value therebetween.

[0081] Typically, the roasting process described in step (3) includes process parameters such as heating rate, which can be carried out according to the conventional roasting process. In one embodiment, the heating rate is 5~10 ℃ / min, for example 5 ℃ / min, 6 ℃ / min, 7 ℃ / min, 8 ℃ / min, 9 ℃ / min, 10 ℃ / min or any range or point value between them.

[0082] In this document, the separation, washing, drying, stirring and other processes all follow the conventional principles of chemical processes, and those skilled in the art can perform the specific operations based on common knowledge.

[0083] During the project initiation process related to this invention, the inventors aimed to find a more economical and efficient process for CO2 adsorbents that could achieve comprehensive utilization of solid waste. After preliminary research, shellfish shells were chosen as raw materials to prepare CaO-based CO2 adsorbents, as most of the raw materials can be selected from many common economic shellfish species for co-processing and reuse of waste. During the experiment, it was unexpectedly discovered that due to the special structure and main components of the aforementioned shellfish waste, a foam-like calcium-based intermediate with a "bubble-like" microstructure was formed during the continuous two-stage acid hydrolysis treatment with organic acids. This intermediate was then coated with organic acids and calcined to prepare a Ca-based CO2 adsorbent. Compared to commercially available CaCO3 or limestone-derived CaO-based CO2 adsorbents, this adsorbent exhibited better activity in terms of adsorption capacity and multiple carbonation cycles. This is because the continuous organic acid treatment caused the stable structure of the shellfish shells to undergo denaturation and optimization, resulting in better textural properties. This allowed the active sites of the system to be fully protected and efficiently utilized. Furthermore, the abundant functional groups and some impurities in the shellfish shells promoted synergistic effects, further enhancing the CO2 adsorption performance of the adsorbent.

[0084] This unexpected discovery greatly enhances the practical application value of the CO2 adsorbent prepared from shellfish waste using this invention under the concept of "green synthesis and waste-to-waste treatment," and provides a new way to reuse the aforementioned solid waste.

[0085] Furthermore, in the selection of organic acids for subsequent organic acid coating, comparative experiments unexpectedly revealed that when citric acid was selected as the organic acid, the prepared Ca-based CO2 adsorbent exhibited significantly better adsorption performance, achieving unexpected technical results.

[0086] The CO2 adsorbent finally prepared by the above technical solution has an adsorption capacity of more than 54% for carbon dioxide with a concentration of 60-100% in simulated flue gas, under the conditions of a temperature window of 650-720 ℃ and a gas velocity of 50-120 mL / min. After 6 adsorption cycles, it still retains about 41% of the adsorption capacity, with a decay rate of about 23%.

[0087] The present application will be further explained in detail below with reference to embodiments. However, those skilled in the art should understand that these embodiments are provided for illustrative purposes only and are not intended to limit the present application.

[0088] Example

[0089] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the scope of this application. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all commercially available conventional products. This application should not be construed as being limited to the specific embodiments described.

[0090] 1. Raw materials

[0091] Shellfish waste was collected from markets in Hainan and Chengdu. The main chemical components of shellfish from several typical species were characterized and analyzed using X-ray fluorescence spectrometry (XRF). The results are shown in Tables 1-3.

[0092] Table 1. XRF analysis of major elements in clam shells

[0093]

[0094] Table 2. XRF analysis of major elements in abalone shells

[0095]

[0096] Table 3. XRF analysis of major elements in mussel shells

[0097]

[0098] The reagents used are shown in Table 4 below:

[0099] Table 4. Main reagents and gases required for the experiment

[0100]

[0101] 2. Preparation method

[0102] (1) The shellfish waste is cleaned, sterilized, dried at 80 °C for 24 hours, then placed in a muffle furnace and roasted at 200 °C for 24 hours, and then crushed into shellfish pieces with a particle size of about 0.8~1 cm.

[0103] (2) Immerse 5 g of the shellfish obtained in step (1) in 75 ml of an organic acid aqueous solution A with a mass concentration of 2-6 wt%, and react for 24 hours under shaking at 160 rpm. After the time is up, separate, wash and dry to obtain the first acid hydrolysis product. Then immerse the obtained first acid hydrolysis product in 75 ml of an organic acid aqueous solution A with a mass concentration of 2-6 wt%, and react again for 24 hours under shaking at 160 rpm. After the time is up, filter and separate, wash with ethanol and deionized water multiple times, and vacuum dry to obtain a foam-like calcium-based intermediate.

[0104] (3) Mix 4 g of the foam-like calcium-based intermediate obtained in step (2) with 40 mL of organic acid aqueous solution B with a mass concentration of 10 wt%, stir and mix for 1 hour, then separate the solid product coated with organic acid, and calcine it at 920 ℃ for 1 hour under an inert gas atmosphere at a heating rate of 10 ℃ / min to prepare Ca-based CO2 adsorbent.

[0105] 3. Testing Methods

[0106] The CO2 adsorbent samples prepared were tested for CO2 adsorption performance, including isothermal adsorption experiments, temperature-switching adsorption experiments, and cyclic adsorption experiments. The main body used a thermogravimetric analyzer (TA SQT-600) to detect the sample mass. The gas mixing system used high-purity CO2 and high-purity N2 to simulate flue gas through an electronic flow meter. The test flow rate was 20~200 mL / min, and the test sample weight was 10~20 mg.

[0107] The CO2 adsorption capacity is calculated as follows:

[0108]

[0109] In the formula, W represents the CO2 adsorption capacity of the sample, % (g / g); m represents the sample mass after maximum adsorption, g; and m0 represents the initial sample mass, g.

[0110] In the cyclic adsorption experiment, the adsorption temperature was set to 650 ℃ for 45 min, and the desorption temperature was set to 900 ℃ for 5 min.

[0111] Example 1

[0112] Example 1 is based on the steps in “2. Preparation method” above. In step (1), the shellfish waste is selected as clam shell. In step (2), the organic acid aqueous solution A is an acetic acid aqueous solution with a mass concentration of 3 wt%. In step (3), the organic acid aqueous solution B is an citric acid aqueous solution with a mass concentration of 10 wt%. The Ca-based CO2 adsorbent obtained in the end is used as a sample for testing.

[0113] like Figure 18 As shown, SEM images of the foam-like calcium-based intermediate prepared in step (2) are displayed; Figure 19 The image shown is a photograph of the final Ca-based CO2 adsorbent sample.

[0114] The prepared Ca-based CO2 adsorbent sample was ground and sieved, and particles with a particle size range of 60-80 mesh were selected. The adsorption performance and cyclic adsorption stability of CO2 in simulated flue gas were tested in a CO2 adsorption activity evaluation device, specifically including:

[0115] Isothermal adsorption experiment: Weigh 10 mg of sample, maintain a constant experimental temperature of 650 ℃, CO2 concentration of 100%, and gas flow rate of 120 mL / min. The CO2 adsorption capacity curve is shown in the appendix of the instruction manual. Figure 1 The CO2 adsorption capacity curve at a gas flow rate of 60 mL / min is shown in the appendix of the instruction manual. Figure 2 .

[0116] Temperature-switching adsorption experiment: Weigh 10 mg of sample, raise the experimental temperature from room temperature to 1000 ℃ at a rate of 10 ℃ / min, simulate flue gas CO2 concentration of 100%, and gas flow rate of 100 mL / min. The temperature-switching adsorption curve of this sample is shown in the appendix to the instruction manual. Figure 3 .

[0117] Cyclic adsorption experiment: Weigh 10 mg of sample and, under a nitrogen atmosphere, raise the temperature from room temperature to 900 °C at a rate of 10 °C / min and hold for 5 min. Then, lower the temperature to 650 °C at a rate of 30 °C / min while switching to a CO2 atmosphere. Maintain the temperature for 50 min, then switch back to a nitrogen atmosphere and raise the temperature to 900 °C to regenerate the adsorbent for 5 min. Subsequent experiments were conducted under cyclic conditions within the temperature range of 650–900 °C. The adsorption capacity curve for the cyclic adsorption experiment (6 cycles) under the condition that the sample adsorbs a gas flow rate of 100 mL / min is shown in the appendix of the instruction manual. Figure 4 The adsorption capacity curves for the cyclic adsorption experiment (20 cycles) under the condition of an adsorbed gas flow rate of 60 mL / min are shown in the appendix of the instruction manual. Figure 5 .

[0118] Example 2

[0119] Example 2 is based on the steps in “2. Preparation method” above. In step (1), the shellfish waste is selected as clam shell. In step (2), the organic acid aqueous solution A is an acetic acid aqueous solution with a mass concentration of 3 wt%. In step (3), the organic acid aqueous solution B is a lactic acid aqueous solution with a mass concentration of 10 wt%. The Ca-based CO2 adsorbent obtained in the end is used as a sample for testing.

[0120] The prepared Ca-based CO2 adsorbent sample was ground and sieved, and particles with a particle size range of 60-80 mesh were selected. The adsorption performance and cyclic adsorption stability of CO2 in simulated flue gas were tested in a CO2 adsorption activity evaluation device, specifically including:

[0121] Isothermal adsorption experiment: Weigh 10 mg of sample, maintain a constant experimental temperature of 650 ℃, CO2 concentration of 100%, and gas flow rate of 120 mL / min. The CO2 adsorption capacity curve is shown in the appendix of the instruction manual. Figure 6 .

[0122] Cyclic adsorption experiment: Weigh 10 mg of sample and, under a nitrogen atmosphere, raise the temperature from room temperature to 900 °C at a rate of 10 °C / min and hold for 5 min. Then, lower the temperature to 650 °C at a rate of 30 °C / min while switching to a CO2 atmosphere. Maintain the temperature for 50 min, then switch back to a nitrogen atmosphere and raise the temperature to 900 °C to regenerate the adsorbent for 5 min. Subsequent experiments were conducted under cyclic conditions within the temperature range of 650–900 °C. The adsorption capacity curve for the cyclic adsorption experiment (6 cycles) under the condition that the sample adsorbs a gas flow rate of 100 mL / min is shown in the appendix of the instruction manual. Figure 7 .

[0123] Example 3

[0124] Example 3 is based on the steps in "2. Preparation method" above. In step (1), the shellfish waste is selected as clam shell. In step (2), the organic acid aqueous solution A is an acetic acid aqueous solution with a mass concentration of 3 wt%. In step (3), the organic acid aqueous solution B is an oxalic acid solution with a mass concentration of 10 wt%. The Ca-based CO2 adsorbent prepared in the end is used as a sample for testing.

[0125] The prepared Ca-based CO2 adsorbent sample was ground and sieved, and particles with a particle size range of 60-80 mesh were selected. The adsorption performance and cyclic adsorption stability of CO2 in simulated flue gas were tested in a CO2 adsorption activity evaluation device, specifically including:

[0126] Isothermal adsorption experiment: Weigh 10 mg of sample, maintain a constant experimental temperature of 650 ℃, CO2 concentration of 100%, and gas flow rate of 120 mL / min. The CO2 adsorption capacity curve is shown in the appendix of the instruction manual. Figure 8 .

[0127] In Examples 1-3, Ca-based CO2 adsorbents were prepared by coating with different organic acids. Among them, Example 1 showed surprising adsorption performance, and its texture was also significantly different from those prepared by other organic acids.

[0128] Example 4

[0129] Example 4 follows the steps of Example 1, but uses an aqueous solution of acetic acid with a mass concentration of 5 wt% in step (2). It forms a gradient comparison experiment with Example 1, Comparative Example 6 and Comparative Example 7. Both Example 1 and Example 4 can successfully prepare foam-like calcium-based intermediates, but the yields are different. Example 1 has the best yield.

[0130] Examples 5-7

[0131] Examples 5-7 all follow the steps of Example 1, but in step (2), the organic acid aqueous solution A is a 3 wt% propionic acid aqueous solution, a citric acid aqueous solution, and a lactic acid aqueous solution, respectively, forming a single variable comparison experiment. All of them can successfully prepare foam-like calcium-based intermediates, but the yields are different, with Example 1 having the best yield.

[0132] In addition, abalone shells and mussel shells were used as shellfish waste in experiments according to Examples 1-7, and foam-like calcium-based intermediates and Ca-based CO2 adsorbents were successfully prepared in both cases.

[0133] Comparative Example 1

[0134] Comparative Example 1 uses commercially available anhydrous calcium carbonate (CaCO3) as a comparison. Referring to step (3) of “2. Preparation Method” above, 4 g of anhydrous calcium carbonate was used to replace the foam-like calcium-based intermediate. The organic acid aqueous solution B was a citric acid aqueous solution with a mass concentration of 10 wt%. The Ca-based CO2 adsorbent was prepared as a sample for testing.

[0135] The prepared Ca-based CO2 adsorbent sample was ground and sieved, and particles with a particle size range of 60-80 mesh were selected. The adsorption performance and cyclic adsorption stability of CO2 in simulated flue gas were tested in a CO2 adsorption activity evaluation device, specifically including:

[0136] Isothermal adsorption experiment: Weigh 10 mg of sample, maintain a constant experimental temperature of 650 ℃, CO2 concentration of 100%, and gas flow rate of 120 mL / min. The CO2 adsorption capacity curve is shown in the appendix of the instruction manual. Figure 9 .

[0137] Temperature-switching adsorption experiment: Weigh 10 mg of sample, raise the experimental temperature from room temperature to 1000 ℃ at a rate of 10 ℃ / min, simulate flue gas CO2 concentration of 100%, and gas flow rate of 100 mL / min. The temperature-switching adsorption curve of this sample is shown in the appendix to the instruction manual. Figure 10 .

[0138] Cyclic adsorption experiment: Weigh 10 mg of sample and, under a nitrogen atmosphere, raise the temperature from room temperature to 900 °C at a rate of 10 °C / min and hold for 5 min. Then, lower the temperature to 650 °C at a rate of 30 °C / min while switching to a CO2 atmosphere. Maintain the temperature for 50 min, then switch back to a nitrogen atmosphere and raise the temperature to 900 °C to regenerate the adsorbent for 5 min. Subsequent experiments were conducted under cyclic conditions within the temperature range of 650–900 °C. The adsorption capacity curve for the cyclic adsorption experiment (6 cycles) under the condition that the sample adsorbs a gas flow rate of 100 mL / min is shown in the appendix of the instruction manual. Figure 11 The adsorption capacity curves for the cyclic adsorption experiment (20 cycles) under the condition of an adsorbed gas flow rate of 60 mL / min are shown in the appendix of the instruction manual. Figure 12 .

[0139] It is evident that, although the Ca-based CO2 adsorbent prepared using native calcium carbonate in Comparative Example 1 initially exhibited a higher CO2 adsorption capacity than the sample in Example 1 during the cyclic adsorption experiment, the adsorption capacity decreased significantly, and its overall adsorption performance was inferior to that of the sample in Example 1.

[0140] Comparative Example 2

[0141] Comparative Example 2 refers to steps (1) to (2) of “2. Preparation Method” above. In step (1), the shellfish waste was selected as clam shell. In step (2), the organic acid aqueous solution A was an acetic acid aqueous solution with a mass concentration of 3 wt%. However, after obtaining the foam-like calcium-based intermediate, 5 g of the foam-like calcium-based intermediate was directly heated to 920 ℃ for 1 hour under an inert gas atmosphere at a heating rate of 10 ℃ / min. Finally, the Ca-based CO2 adsorbent was prepared as a sample for testing.

[0142] The prepared Ca-based CO2 adsorbent sample was ground and sieved, and particles with a particle size range of 60-80 mesh were selected. The adsorption performance and cyclic adsorption stability of CO2 in simulated flue gas were tested in a CO2 adsorption activity evaluation device, specifically including:

[0143] Isothermal adsorption experiment: Weigh 10 mg of sample, maintain a constant experimental temperature of 650 ℃, CO2 concentration of 100%, and gas flow rate of 120 mL / min. The CO2 adsorption capacity curve is shown in the appendix of the instruction manual. Figure 13 The CO2 adsorption capacity curve at a gas flow rate of 60 mL / min is shown in the appendix of the instruction manual. Figure 14 .

[0144] Temperature-switching adsorption experiment: Weigh 10 mg of sample, raise the experimental temperature from room temperature to 1000 ℃ at a rate of 10 ℃ / min, simulate flue gas CO2 concentration of 100%, and gas flow rate of 100 mL / min. The temperature-switching adsorption curve of this sample is shown in the appendix to the instruction manual. Figure 15 .

[0145] Cyclic adsorption experiment: Weigh 10 mg of sample and, under a nitrogen atmosphere, raise the temperature from room temperature to 900 °C at a rate of 10 °C / min and hold for 5 min. Then, lower the temperature to 650 °C at a rate of 30 °C / min while switching to a CO2 atmosphere. Maintain the temperature for 50 min, then switch back to a nitrogen atmosphere and raise the temperature to 900 °C to regenerate the adsorbent for 5 min. Subsequent experiments were conducted under cyclic conditions within the temperature range of 650–900 °C. The adsorption capacity curve for the cyclic adsorption experiment (6 cycles) under the condition that the sample adsorbs a gas flow rate of 100 mL / min is shown in the appendix of the instruction manual. Figure 16 .

[0146] Comparative Example 3

[0147] Comparative Example 3 refers to step (1) of “2. Preparation Method” above. In step (1), the shellfish waste is selected as clam shell, but the obtained 5 g shell block is directly heated to 920 ℃ for 1 hour in an inert gas atmosphere at a heating rate of 10 ℃ / min to prepare Ca-based CO2 adsorbent as a sample for testing.

[0148] The prepared Ca-based CO2 adsorbent sample was ground and sieved, and particles with a particle size range of 60-80 mesh were selected. The adsorption performance and cyclic adsorption stability of CO2 in simulated flue gas were tested in a CO2 adsorption activity evaluation device, specifically including:

[0149] Isothermal adsorption experiment: Weigh 10 mg of sample, maintain a constant experimental temperature of 650 ℃, CO2 concentration of 100%, and gas flow rate of 120 mL / min. The CO2 adsorption capacity curve is shown in the appendix of the instruction manual. Figure 17 .

[0150] Comparative Example 4

[0151] Comparative Example 4 was prepared according to step (1) of "2. Preparation Method" above. In step (1), the shellfish waste was selected as clam shells, but the obtained 5 g shell pieces were immersed in 150 ml of 3 wt% acetic acid aqueous solution and reacted for 48 hours under shaking conditions at 160 rpm. Figure 20 As shown, the shell fragments of the shellfish almost completely dissolved, making it difficult to collect the solid products after washing.

[0152] In contrast, such as Figure 21 As shown, in Example 1, solid products can still be observed during step (2).

[0153] Comparative Example 5

[0154] Comparative Example 5 refers to steps (1) to (2) of “2. Preparation Method” above. In step (1), shellfish waste was selected as shellfish. In step (2), the organic acid aqueous solution A was a formic acid aqueous solution with a mass concentration of 3 wt%. However, during the first acid hydrolysis, it was observed that the reaction in the flask was violent and the bubbles were obvious. After 6 hours of shaking reaction, almost no shell material could be observed in the flask. It was completely dissolved in the organic solution. After the first shaking was completed, no solid material could be filtered to obtain any solid material, and foam-like calcium-based intermediate could not be prepared.

[0155] However, when the organic acid aqueous solution A in step (2) is an oxalic acid aqueous solution with a mass concentration of 3 wt%, although a solid product can be obtained in step (2), the success rate and yield of preparing the foam-like calcium-based intermediate are extremely low.

[0156] Comparative Example 6

[0157] Comparative Example 6 follows the steps of Example 1, but in step (2), the organic acid aqueous solution A is an acetic acid aqueous solution with a mass concentration of 1 wt%, forming a gradient comparison experiment with Example 1, Example 4 and Comparative Example 7. However, neither Comparative Example 6 nor Comparative Example 7 can prepare a foam-like calcium-based intermediate. In Comparative Example 6, the final result of step (2) is a shellfish block with etching marks on the surface.

[0158] Comparative Example 7

[0159] Comparative Example 7 follows the steps of Example 1, but in step (2), the organic acid aqueous solution A is an acetic acid aqueous solution with a mass concentration of 10 wt%, forming a gradient comparison experiment with Example 1, Example 4 and Comparative Example 6. However, neither Comparative Example 6 nor Comparative Example 7 can prepare a foam-like calcium-based intermediate. In Comparative Example 7, the shellfish completely dissolves in step (2).

[0160] Comparative Example 8

[0161] Comparative Example 8 was prepared according to the steps of Example 1, but in step (3), the organic acid aqueous solution B was a formic acid aqueous solution with a mass concentration of 10 wt%. The Ca-based CO2 adsorbent was finally prepared as a sample for testing and it was found that its CO2 adsorption capacity was significantly inferior to that of Examples 1-3 and Comparative Example 1.

[0162] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for synergistically preparing Ca-based CO2 sorbents based on organic shellfish shell waste, characterized in that Includes the following steps: (1) The shellfish waste is cleaned, sterilized, dried, and crushed into shellfish pieces with a particle size of no more than 1 cm; (2) The shellfish pieces obtained in step (1) are immersed in an aqueous solution of organic acid with a mass concentration of 2-6 wt% and reacted under shaking conditions for 23-24 hours. After the time is up, the shellfish pieces are separated, washed and dried to obtain the first acid hydrolysis product. The first acid hydrolysis product is then immersed in an aqueous solution of organic acid with a mass concentration of 2-6 wt% and reacted again under shaking conditions for 23-24 hours. After the time is up, the shellfish pieces are separated, washed and dried to obtain the foam-like calcium-based intermediate. The organic acid in the aqueous solution A is any one of acetic acid, propionic acid, citric acid, and lactic acid. (3) Mix 4 g of the foam-like calcium-based intermediate obtained in step (2) with 40-80 mL of an organic acid aqueous solution B with a mass concentration of 5-10 wt%, stir and mix for 0.5-1 hour, then separate the solid product coated with organic acid, and calcine it in an inert gas atmosphere at 850-950 °C for 0.5-1.5 hours to prepare a Ca-based CO2 adsorbent; The organic acid in the aqueous solution B is any one of acetic acid, propionic acid, citric acid, oxalic acid, and lactic acid.

2. The method of claim 1, wherein: In step (1), the shellfish waste is cleaned, sterilized, and dried, and then roasted at a temperature of 200-220 ℃ for 23-24 hours.

3. The method of claim 1, wherein: In step (1), the shells are crushed into shell fragments with a particle size of 0.8~1 cm.

4. The method of claim 1, wherein: The organic acid aqueous solution A mentioned in step (2) is an acetic acid aqueous solution with a mass concentration of 3 wt%.

5. The method according to claim 1, characterized in that: The organic acid mentioned in step (3) is citric acid.

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