A solid-in-liquid composite adsorbent for carbon dioxide capture and a preparation method and application thereof

Abstract

This invention provides a solid-liquid composite adsorbent for carbon dioxide capture, its preparation method, and its application, specifically relating to the field of carbon dioxide capture materials technology. The solid-liquid composite adsorbent of this invention includes a shell and a core; the shell comprises hydrophobic SiO2 and hydrophobic modified biochar; the core is an acidic gas absorbent. This invention utilizes a unique solid-liquid structure to combine the high specific surface area and low corrosivity of the solid adsorbent with the high adsorption capacity and high selectivity of the acidic gas absorbent, thereby improving the adsorption capacity of the adsorbent; by using a hydrophobic solid particle shell to encapsulate the acidic gas absorbent core, the contact area between the acidic gas absorbent and the capture equipment is reduced, preventing corrosion of the equipment by the acidic gas absorbent. As shown in the examples, the solid-liquid composite adsorbent provided in this application has a CO2 adsorption capacity of 1.5–5 mmol / g.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide capture materials technology, specifically relating to a solid-liquid composite adsorbent for carbon dioxide capture, its preparation method, and its application. Background Technology

[0002] CO2 capture materials are materials capable of adsorbing and storing CO2. They are mainly used in CO2 capture, gas separation, and storage, and can be divided into liquid absorbents and solid adsorbents. Common liquid absorbents include organic amines, ammonia solutions, and ionic liquids, which utilize solution absorption for carbon capture. They have relatively high capture efficiency and good adaptability to flue gas, but the solvent regeneration process consumes a lot of energy, has poor thermal stability, and is corrosive to equipment. Solid adsorbents are more resistant to the high temperature of flue gas, have good chemical stability, low toxicity and low corrosivity, and low cost. However, they are not competitive in terms of adsorption capacity and are easily deactivated by water vapor in the flue gas.

[0003] To address the problems of liquid absorbents and solid adsorbents mentioned above, a solid-liquid composite adsorbent is proposed. Most existing solid-liquid composite adsorbents are solid-supported amine adsorbents, which require the use of binders, crosslinking agents, and template agents during preparation, followed by heat treatment. This process is time-consuming, uses expensive raw materials, and generates a large amount of toxic and harmful gases and liquids. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a solid-liquid composite adsorbent for carbon dioxide capture. The solid-liquid composite adsorbent provided by this invention has a large adsorption capacity for CO2, a fast adsorption rate, low corrosivity to equipment, and is simple and environmentally friendly to manufacture.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] This invention provides a solid-liquid composite adsorbent, comprising a shell and a core;

[0007] The outer shell comprises hydrophobic SiO2 and hydrophobic modified biochar;

[0008] The core is an acidic gas absorbent liquid.

[0009] Preferably, the content of hydrophobic SiO2 in the shell is ≥80wt% and <100wt%, and the content of hydrophobic modified biochar is >0 and ≤20wt%.

[0010] The hydrophobic SiO2 has a particle size of 3–15 nm; the hydrophobic modified biochar has a particle size of 10–23 μm.

[0011] Preferably, the mass ratio of the outer shell to the volume ratio of the core is 1g:8-12mL.

[0012] Preferably, the particle size of the solid-liquid composite adsorbent is 40–60 μm.

[0013] Preferably, the acidic gas absorbent liquid includes an alkaline absorbent liquid.

[0014] Preferably, the alkaline absorbent includes one or more of K2CO3 solution, organic amine and ammonia solution.

[0015] This invention also provides a method for preparing the solid-liquid composite adsorbent described in the above technical solution, comprising the following steps:

[0016] Hydrophobic SiO2, hydrophobic modified biochar, and acidic gas absorption liquid are stirred and mixed to obtain a solid-liquid composite adsorbent.

[0017] The stirring speed is 8000-15000 r / min.

[0018] Preferably, the mixing time is 120–180 s.

[0019] Preferably, the hydrophobically modified biochar is silane coupling agent modified biochar, and the preparation method includes the following steps:

[0020] Biochar is mixed with an alkaline solution and activated to obtain activated biochar.

[0021] The activated biochar, silane coupling agent, and alcohol solvent are mixed and heated to modify the biochar, thus obtaining the hydrophobically modified biochar.

[0022] The present invention also provides the application of the solid-liquid composite adsorbent prepared by the preparation method described above in the capture of carbon dioxide.

[0023] This invention provides a solid-liquid composite adsorbent for carbon dioxide capture, comprising a shell and a core; the shell comprises hydrophobic SiO2 and hydrophobic modified biochar; the core is an acidic gas absorbent. This application utilizes a unique solid-liquid structure to combine the high specific surface area and low corrosivity of the solid adsorbent with the high adsorption capacity and selectivity of the acidic gas absorbent, thereby improving the adsorption capacity of the adsorbent; the hydrophobic solid particle shell encapsulates the acidic gas absorbent core, reducing the contact area between the acidic gas absorbent and the capture equipment, thus preventing corrosion of the equipment; the superhydrophobicity of SiO2 and modified biochar forms a self-correlated hydrophobic particle network, preventing the acidic gas absorbent droplets from agglomerating, further improving the adsorption capacity of the adsorbent. The solid-liquid composite adsorbent provided in this application has a CO2 adsorption capacity of 1.5–5 mmol / g and an absorption rate of 0.3–0.75 mol·min. -1 ·kg-1 .

[0024] The present invention also provides a method for preparing the above-mentioned solid-liquid composite adsorbent for carbon dioxide capture. The method is simple to prepare, conducive to industrial production, and the use of biochar as raw material can reduce costs and realize the resource utilization of biomass.

[0025] Furthermore, the solid-liquid composite adsorbent prepared in this application can completely desorb gases by disrupting the structure of the hydrophobic powder network that encapsulates small droplets, thus reversing it into hydrophobic powder and liquid solution, which has good development prospects; the micron-sized spheres of liquid encapsulated by solid particles are beneficial for transportation, avoiding dust and low corrosivity. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 Images of biochar before and after hydrophobic modification;

[0028] Figure 2 SEM images of biochar before and after hydrophobic modification;

[0029] Figure 3 The images show the physical samples of the composite adsorbents prepared in Examples 1-4 and Comparative Example 1.

[0030] Figure 4 The images show the microstructure of the composite adsorbents prepared in Examples 1-4 and Comparative Example 1.

[0031] Figure 5 This is a comparison chart of the carbon dioxide adsorption capacity of the composite adsorbents prepared in Examples 1-4 and Comparative Example 1. Detailed Implementation

[0032] This invention provides a solid-liquid composite adsorbent, comprising a shell and a core;

[0033] The outer shell comprises hydrophobic SiO2 and hydrophobic modified biochar;

[0034] The core is an acidic gas absorbent liquid.

[0035] In this invention, unless otherwise specified, all raw materials and equipment used are commercially available products well known in the art.

[0036] In this invention, the outer shell comprises hydrophobic SiO2 and hydrophobically modified biochar. The content of hydrophobic SiO2 in the outer shell is preferably ≥80 wt% and <100 wt%, more preferably 81–97 wt%, and even more preferably 83–95 wt%. The particle size of the hydrophobic SiO2 is preferably 3–15 nm, more preferably 5–10 nm. In a specific embodiment of this invention, the particle size of the hydrophobic SiO2 is 7 nm, and the specific surface area is 220 m². 2 / g, density is 0.06g / cm³ 3 In this invention, the content of hydrophobically modified biochar in the shell is preferably >0 and ≤20 wt%, more preferably 3-19 wt%, and even more preferably 5-17 wt%. The particle size of the hydrophobically modified biochar is preferably 10-23 μm, more preferably 12-20 μm, and even more preferably 15-18 μm; the density of the hydrophobically modified biochar is 0.14 g / cm³. 3 This invention mixes hydrophobic SiO2 and hydrophobically modified biochar, which increases the adsorption capacity of the composite adsorbent while reducing the amount of hydrophobic SiO2 used, thereby reducing costs and achieving the goal of biomass resource utilization. The presence of hydrophobic SiO2 improves the dispersibility of the hydrophobically modified biochar. However, the density and nanoparticle size of the hydrophobically modified biochar are larger than those of hydrophobic silica. Therefore, when the amount of hydrophobically modified biochar exceeds 20 wt%, the resulting adsorbent is unstable and prone to sedimentation, thus reducing the adsorption capacity.

[0037] In this invention, the core is an acidic gas absorbent, which preferably includes an alkaline absorbent. The alkaline absorbent preferably includes one or more of K₂CO₃ solution, an organic amine, and an ammonia solution, wherein the organic amine is preferably monoethanolamine or N-methyldiethanolamine; the alkaline absorbent is more preferably a K₂CO₃ solution. In this invention, the concentration of the K₂CO₃ solution is preferably any concentration, more preferably 30–80 wt%. In a specific embodiment of this invention, the K₂CO₃ solution concentration is 50 wt%. In this invention, the acidic gas absorbent can adsorb carbon dioxide through a chemical reaction.

[0038] In this invention, the mass-to-volume ratio of the outer shell to the core is preferably 1g:8-12mL, more preferably 1g:9-11mL, and even more preferably 1g:10mL. If the mass-to-volume ratio of the outer shell to the core is too large, it will cause the solid phase to float; if it is too small, it will form a mousse-like substance, making the prepared composite adsorbent unstable. Different mass-to-volume ratios correspond to different particle sizes of hydrophobic SiO2. In this invention, the mass-to-volume ratio corresponds to a hydrophobic SiO2 particle size of 3-15nm. By controlling the mass-to-volume ratio, a stable solid-liquid composite adsorbent with good flowability is obtained.

[0039] In this invention, the particle size of the solid-liquid composite adsorbent is preferably 40-60 μm, more preferably 45-55 μm, and even more preferably 50 μm.

[0040] The solid-liquid composite adsorbent obtained in this invention contains up to 90%–97% liquid internally, appears as a white powder, and exhibits good flowability. The highly dispersed hydrophobic solid particle shell encapsulates the acidic gas absorbent liquid, breaking it into small droplets. Simultaneously, the superhydrophobicity of the shell forms a self-correlated network of hydrophobic particles, creating numerous voids between the micron-sized particles and providing channels for mass transfer between the micro-droplets and the external gas phase. The combined effects of hydrophobic SiO2, hydrophobically modified biochar, and the acidic gas absorbent enhance the adsorption capacity and rate of the composite adsorbent.

[0041] This invention also provides a method for preparing the solid-liquid composite adsorbent described in the above technical solution, comprising the following steps:

[0042] Hydrophobic SiO2, hydrophobic modified biochar, and acidic gas absorption liquid are stirred and mixed to obtain a solid-liquid composite adsorbent.

[0043] The stirring speed is 8000-15000 r / min.

[0044] In this invention, the preparation steps of the hydrophobically modified biochar preferably include:

[0045] Biochar is mixed with an alkaline solution and activated to obtain activated biochar.

[0046] The activated biochar, silane coupling agent, and alcohol solvent are mixed and heated to modify the biochar, thus obtaining the hydrophobically modified biochar.

[0047] This invention involves mixing biochar with an alkaline solution and activating it to obtain activated biochar.

[0048] In this invention, the biochar is preferably obtained by pyrolysis, and the pyrolysis temperature is preferably 450-600℃, more preferably 500℃.

[0049] In this invention, the alkaline solution is preferably a saturated KOH and / or NaOH aqueous solution, more preferably a saturated KOH aqueous solution. This invention does not have special requirements on the amount of alkaline solution used; complete soaking of the biochar is sufficient. This invention does not have special requirements on the mixing method; operations well known in the art are acceptable.

[0050] In this invention, the activation temperature is preferably 110–150°C, more preferably 120–140°C, and the activation time is preferably 30–60 h, more preferably 40–50 h. This invention improves the porosity of biochar and enhances its surface active sites through activation. During the activation process, a large number of micropores are introduced onto the surface of the biochar, thereby improving its adsorption performance.

[0051] In this invention, the activation process preferably further includes rinsing with water and drying. The washing method is not particularly important; any operation well-known in the art can be used, until the washing solution is neutral. Similarly, the drying method is not particularly important; any operation well-known in the art can be used until the activated biochar is completely dry.

[0052] After obtaining the activated biochar, the present invention mixes the activated biochar, silane coupling agent, and alcohol solvent, and then heats and modifies the mixture to obtain the hydrophobically modified biochar.

[0053] In this invention, the silane coupling agent is preferably dodecyltrimethoxysilane. The solid-liquid ratio of the activated biochar to the silane coupling agent is preferably 1-3 g:1 mL, more preferably 1.3-1.5 g:1 mL. In this invention, the alcohol solvent preferably includes ethanol; the volume ratio of the alcohol solvent to the silane coupling agent is preferably 9:1.

[0054] In this invention, the preferred temperature for the heat modification is 40–80°C, more preferably 55–65°C, and the preferred time is 2–6 hours, more preferably 3–5 hours. This invention does not have special requirements for the method of heat modification; any operation well-known in the art can be used. In a specific implementation of this invention, a water bath heating method is preferably used to heat the mixed solution of activated biochar, silane coupling agent, and ethanol.

[0055] In this invention, the heating modification preferably further includes allowing the resulting product system to stand, filter, wash, and dry to obtain the hydrophobic modified biochar. The standing time is preferably 3 hours. This invention does not have special requirements for the filtration method; any operation well-known in the art can be used. The washing is preferably performed using anhydrous ethanol, and the washing is repeated three times. The drying temperature is preferably 120–140°C, and the drying time is preferably 1–3 hours. This invention does not have special requirements for the drying method; any operation well-known in the art can be used. Specifically, this invention uses an oven for drying. This invention utilizes a silane coupling agent to modify activated biochar, grafting hydrophobic groups onto the surface of the activated biochar.

[0056] In this invention, the biochar’s affinity for CO2 adsorption is increased after activation and modification, while the biochar’s dispersibility and hydrophobicity are also increased.

[0057] The present invention does not have any special requirements on the order of adding the hydrophobic SiO2, hydrophobic modified biochar and acidic gas absorbent liquid; they can be added together.

[0058] In this invention, the stirring speed is 8000–15000 r / min, preferably 10000–12000 r / min, and the stirring time is preferably 120–180 s, more preferably 140–160 s. This invention utilizes the shear force of high-speed stirring to encapsulate the liquid with a solid, thereby obtaining a solid-liquid composite adsorbent.

[0059] This invention also provides the application of the solid-liquid composite adsorbent prepared by the preparation method described above in the capture of carbon dioxide. This invention does not impose special requirements on the method of application; any application method well-known in the art can be used. In an embodiment of this invention, the solid-liquid composite adsorbent is placed in an inert gas environment and kept at 25°C for 1 hour, and then carbon dioxide adsorption is carried out at this temperature.

[0060] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. The described embodiments are only some embodiments of the present invention, and not all embodiments. Any modifications, equivalent substitutions, improvements, etc., made to the embodiments of the present invention based on the technical essence and general principles of the present invention without creative effort should be within the protection scope of the present invention.

[0061] Preparation of hydrophobically modified biochar

[0062] Biochar was prepared from rice husks (distillers' grains) using a pyrolysis method at 500℃. The prepared biochar was soaked in a saturated KOH solution and kept at 130℃ for 48 hours. The solution was washed until neutral and then dried to obtain activated biochar. 3 mL of dodecyltrimethoxysilane was added to 97 mL of anhydrous ethanol, and the mixture was sonicated for 15 min. Then, 5 g of activated biochar was added, and the mixture was stirred in a 60℃ water bath for 4 hours. After standing for 3 hours, the mixture was filtered, washed three times with anhydrous ethanol, and dried in a 130℃ oven for 2 hours to obtain hydrophobically modified biochar.

[0063] Example 1

[0064] Weigh 9.6g of hydrophobic SiO2 (Evonik Degussa (China), R812S), 0.4g of hydrophobic modified biochar and 100g of 50wt% K2CO3 solution into a high-speed stirring cup and stir at 12000r / min for 120s to obtain a composite adsorbent.

[0065] Example 2

[0066] Weigh 9.2g of hydrophobic SiO2, 0.8g of hydrophobic modified biochar and 100g of 50wt% K2CO3 solution into a high-speed stirring cup and stir at 12000r / min for 120s to obtain a composite adsorbent.

[0067] Example 3

[0068] Weigh 8.8g of hydrophobic SiO2, 1.2g of hydrophobic modified biochar and 100g of 50wt% K2CO3 solution into a high-speed stirring cup and stir at 12000r / min for 120s to obtain a composite adsorbent.

[0069] Example 4

[0070] Weigh 8.4g of hydrophobic SiO2, 1.6g of hydrophobic modified biochar and 100g of 50wt% K2CO3 solution into a high-speed stirring cup and stir at 12000r / min for 120s to obtain a composite adsorbent.

[0071] Comparative Example 1

[0072] Weigh 10g of hydrophobic SiO2 and 100g of 50wt% K2CO3 solution into a high-speed stirring cup, stir at 12000r / min for 120s to obtain a composite adsorbent.

[0073] Comparative Example 2

[0074] Weigh 7.6g of hydrophobic SiO2, 2.4g of hydrophobic modified biochar and 100g of 50wt% K2CO3 solution into a high-speed stirring cup and stir at 12000r / min for 120s to obtain a composite adsorbent.

[0075] Comparative Example 3

[0076] Weigh 8.4g of hydrophobic SiO2, 1.6g of biochar and 100g of 50wt% K2CO3 solution into a high-speed stirring cup and stir at 12000r / min for 120s to obtain a composite adsorbent.

[0077] The adsorption capacity and rate of the prepared composite adsorbent were tested. The specific procedure was as follows: 15 mg of sample was taken and adsorbed under a N2 atmosphere (25 mL / min). -1 The sample was heated to 25°C and held for 1 hour, then CO2 adsorption was performed at 25°C for 30 minutes. The adsorption capacity of the composite adsorbent was measured using a simultaneous thermal analyzer, and calculated based on the weight change of the adsorbent in the sample.

[0078] Table 1. Results of CO2 adsorption capacity tests in Examples 1-4 and Comparative Examples 1-3

[0079] Adsorption capacity (mmol / g) <![CDATA[Absorption rate (mol·min -1 ·kg -1 )]]> Example 1 2.82 0.42 Example 2 3.39 0.57 Example 3 4.43 0.66 Example 4 4.91 0.71 Comparative Example 1 1.49 0.30 Comparative Example 2 4.04 0.68 Comparative Example 3 3.22 0.45

[0080] Figure 5 Table 1 shows a comparison of the carbon dioxide adsorption capacities of the composite adsorbents prepared in Examples 1-4 and Comparative Example 1 (1 corresponds to Comparative Example 1, 2-5 correspond to Examples 1-4 respectively). From Table 1 and... Figure 5 As can be seen, the adsorption performance of the solid-liquid composite adsorbent prepared using pure hydrophobic SiO2 (Comparative Example 1) is significantly lower than that of the solid-liquid composite adsorbent obtained by adding hydrophobically modified biochar. From Examples 1-4 and Comparative Example 2, it is evident that the adsorption performance of the composite adsorbent increases with the increase of the amount of hydrophobically modified biochar. However, when the amount of hydrophobically modified biochar increases to over 20 wt%, the adsorption performance of the composite adsorbent decreases. This is because excessive addition of hydrophobically modified biochar leads to instability in the formed adsorbent. Comparative Example 3 shows that when using unmodified biochar to prepare the solid-liquid composite adsorbent, the adsorption performance is low. This is because the obtained solid-liquid composite adsorbent is prone to agglomeration and sedimentation, resulting in poor dispersibility and affecting the performance of the composite adsorbent.

[0081] Figure 1 The images show biochar before and after hydrophobic modification, with the left image showing the biochar before modification and the right image showing the biochar after modification. Figure 2 The images show SEM images of biochar before and after hydrophobic modification, with the left image showing the biochar before modification and the right image showing the biochar after modification. Figure 1 As can be seen, the hydrophobic modification significantly improves the dispersibility of biochar and makes the particles finer, making it less prone to aggregation and moisture absorption during the subsequent preparation of solid-liquid composite adsorbents. Figure 2 As can be seen, activation and modification alter the surface properties of rice husk char, reducing the total number of pores and decreasing the pore volume, while still retaining some pores for carbon dioxide adsorption. However, activation with KOH and modification with silane coupling agents can increase the adsorption affinity of biochar for CO2, while also increasing its dispersibility and hydrophobicity, which is beneficial for subsequent incorporation into the shell of composite adsorbents.

[0082] Figure 3 The images show physical pictures of the composite adsorbents prepared in Examples 1-4 and Comparative Example 1, where 1 corresponds to Comparative Example 1, and 2-5 correspond to Examples 1-4, respectively. Figure 3 It can be seen that the stability of the composite adsorbent decreases with the increase of hydrophobic modified biochar dosage.

[0083] Figure 4 The images show the microstructures of the composite adsorbents prepared in Examples 1-4 and Comparative Example 1, where 1 corresponds to Comparative Example 1, and 2-5 correspond to Examples 1-4, respectively. Figure 4As can be seen, the solid-liquid structure mainly relies on the superhydrophobicity of silica to form a self-correlated hydrophobic SiO2 particle network, preventing droplet aggregation. The addition of hydrophobically modified silica increases the adsorption capacity of the composite adsorbent for carbon dioxide, and the presence of hydrophobic silica improves the dispersibility of rice husk charcoal.

[0084] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a solid-liquid composite adsorbent, wherein the solid-liquid composite adsorbent comprises a shell and a core; the shell comprises hydrophobic SiO2 and hydrophobic modified biochar; and the core is an acidic gas absorption liquid; The content of hydrophobic SiO2 in the shell is ≥80wt% and <100wt%, and the content of hydrophobic modified biochar is >0 and ≤20wt%; the particle size of the hydrophobic SiO2 is 3~15nm; the particle size of the hydrophobic modified biochar is 10~23μm. The mass ratio of the outer shell to the volume ratio of the core is 1g:8~12mL; The particle size of the solid-liquid composite adsorbent is 40~60μm; The acidic gas absorbent includes an alkaline absorbent; The alkaline absorption solution includes one or more of K2CO3 solution, organic amine and ammonia solution; Its features are, The preparation method of the solid-liquid composite adsorbent includes the following steps: Hydrophobic SiO2, hydrophobic modified biochar, and acidic gas absorption liquid are stirred and mixed to obtain a solid-liquid composite adsorbent. The stirring speed is 8000~15000 r / min.

2. The preparation method according to claim 1, characterized in that, The mixing time is 120~180s.

3. The preparation method according to claim 1, characterized in that, The hydrophobically modified biochar is a silane coupling agent modified biochar, and the preparation method includes the following steps: Biochar is mixed with an alkaline solution and activated to obtain activated biochar. The activated biochar, silane coupling agent, and alcohol solvent are mixed and heated to obtain the hydrophobically modified biochar.

4. The application of the solid-liquid composite adsorbent prepared by the preparation method according to any one of claims 1 to 3 in the capture of carbon dioxide.

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