A biochar particulate adsorbent for efficient CO2 capture, its preparation method and application

Abstract

The application discloses a kind of biochar granular adsorbent for high-efficiency capture of CO2 and its preparation method and application, it is related to the technical field of CO2 capture.A kind of preparation method of biochar granular adsorbent for high-efficiency capture of CO2, comprising the following steps: (1) wood lignocellulosic biomass powder and inorganic are uniformly mixed, and mixture is obtained;(2) the mixture is extruded into shape, and mixed granular is obtained, the average length of mixed granular is 10-50mm, and the average diameter is 5-15mm;(3) mixed granular is treated at 500-900 DEG C in the atmosphere of anaerobic or low oxygen, and constant temperature pyrolysis is obtained, and biochar granular adsorbent is obtained.The biochar granular adsorbent of the application has high CO2 adsorption performance and cycle stability simultaneously, the method of the application is simple, low in cost, widely available and widely applicable.

Description

Technical Field

[0001] This invention relates to the technical field of CO2 capture, and more particularly to a biochar particulate adsorbent for efficient CO2 capture, its preparation method, and its application. Background Technology

[0002] CO2 emissions primarily originate from the combustion of various fossil fuels. Existing CO2 capture technologies are mainly categorized into four types based on their stage in the combustion process: pre-combustion capture, chemical looping capture, oxy-fuel combustion, and post-combustion capture. Post-combustion capture refers to the separation and capture of CO2 in the flue gas after combustion. It does not affect existing combustion processes and is unaffected by the CO2 concentration in the flue gas, making it applicable to various complex situations while requiring relatively low investment. Therefore, it is considered the most promising CO2 capture technology. Post-combustion CO2 capture technologies include solvent absorption, cryogenic separation, membrane separation, and adsorption. Solid adsorbents are considered an ideal solution for post-combustion CO2 capture due to their low regeneration energy consumption, simple operation, low investment cost, fast adsorption rate, stable performance, strong regenerability, and relatively small environmental and health impact.

[0003] Currently, solid adsorbents can be broadly classified into physical adsorbents and chemical adsorbents. Porous physical adsorbents reduce the energy requirements for regeneration and typically have lower desorption costs. However, silica and molecular sieves, with their rapid adsorption / desorption kinetics, exhibit high humidity sensitivity, limiting their application. While MOFs possess excellent designability and sieving properties, their large-scale production and utilization costs remain prohibitively high at present. Carbon-based adsorbents offer advantages such as high stability and low precursor costs, but their irregular pore sizes result in lower selectivity and adsorption capacity. Chemical adsorbents generally do not require consideration of selectivity, but their strong chemical bond energies increase desorption costs. While amine-based solid adsorbents have solved the problems of high desorption energy and equipment corrosion associated with amine solutions, their adsorption rate and volatile toxicity still require further improvement. High-abundance, low-toxicity metal oxides possess strong thermal stability, but their desorption processes typically require high temperatures (>670K) and are energy-intensive, necessitating further development of this technology. Alkali metal solid adsorption offers high absorption capacity, low pollution, and good recycling performance; however, due to factors such as agglomeration during the reaction process, their conversion rate is usually only 40-60% of the theoretical value, and their inherent alkalinity easily causes equipment corrosion. Therefore, current physical and chemical absorption methods all have certain shortcomings. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a biochar particulate adsorbent for efficient CO2 capture, its preparation method, and its application. The biochar particulate adsorbent of this invention possesses both high adsorption performance and cycle stability. The method described in this invention is simple, low-cost, widely available, and has broad applicability.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a biochar particulate adsorbent for efficient CO2 capture, comprising the following steps:

[0007] (1) Mix lignocellulosic biomass and inorganic materials evenly to obtain a mixture, wherein the inorganic materials include potassium source, iron source and sodium source, and the mass ratio of potassium source, iron source and sodium source to biomass is (0.1-0.2):(0.02-0.05):(0-0.1):1;

[0008] (2) The mixture is extruded to form a mixed granule, wherein the average length of the mixed granule is 10-50 mm and the average diameter is 5-15 mm.

[0009] (3) The mixed and shaped particles are subjected to constant temperature pyrolysis at 500-900℃ in an oxygen-free or low-oxygen atmosphere to obtain biochar granular adsorbent.

[0010] This invention involves in-situ loading of environmentally friendly elements such as K, Fe, and Na into biomass waste, then preparing mixed and molded granules, and finally obtaining biochar granule adsorbents with highly efficient dispersion of active components and good cycle stability through a one-step pyrolysis process. This greatly simplifies the preparation process of traditional biochar granule adsorbents and has good economic benefits.

[0011] This invention utilizes biomass-loaded potassium, iron, and sodium sources, with clearly defined ratios of these sources to the biomass. This allows the active components (K, Fe, Na) to be efficiently dispersed directly within the porous biochar particle carrier in the form of nanocrystals during the preparation process. This effectively inhibits the aggregation and deactivation of the active components during CO2 adsorption-desorption, thus improving CO2 capture efficiency. If the ratios of the potassium, iron, and sodium sources to the biomass are outside the specified ranges, the active components cannot be uniformly dispersed in the biochar carrier, which can easily lead to deactivation during CO2 adsorption-desorption.

[0012] In this invention, the average length or average diameter of the mixed-formed particles is influenced by the biomass itself. If the length or diameter is too large, the internal structure of the biomass particles may be uneven, making them prone to cracking. Furthermore, since the mixed-formed particles require pyrolysis, excessive length or diameter can lead to slow combustion rates and low calorific values ​​due to heat transfer issues, resulting in uneven structure of the biochar granule adsorbent. Conversely, if the length or diameter is too small, it will reduce yield, increase energy consumption, and cause problems such as excessively fast combustion and blockage. Therefore, by controlling the average length and average diameter of the mixed-formed particles within the aforementioned range, this invention helps improve the uniformity of the internal structure of the mixed-formed particles, thereby giving the biochar granule adsorbent excellent adsorption performance.

[0013] In this invention, if the pyrolysis temperature is too low, the pyrolysis is insufficient, resulting in fewer micropores in the mixed and formed particles and poor adsorption performance; if the pyrolysis temperature is too high, the carbon yield decreases, pores collapse, and the volatilization of K and Na is accelerated. Therefore, this invention, by controlling the pyrolysis temperature, promotes the formation of particle pores, thereby improving the adsorption performance of the biochar granular adsorbent.

[0014] Preferably, in step (1), the mass ratio of lignocellulosic biomass to inorganic matter is 100:(5-30), and the molar ratio of potassium in the potassium source, iron in the iron source, and sodium in the sodium source is 1:(0.1-2):(0-10).

[0015] Preferably, the lignocellulosic biomass in step (1) includes at least one of wood flour, bark, straw, branches, Chinese medicine residue, fungal residue, and corn cob.

[0016] Preferably, the potassium source in step (1) is at least one of potassium oxide, potassium carbonate, potassium hydroxide, and potassium ferrate.

[0017] Preferably, the sodium source in step (1) is at least one of sodium oxide, sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0018] Preferably, the iron source in step (1) is at least one of iron oxide, iron carbonate, and potassium ferrate.

[0019] Preferably, the average particle size of the lignocellulosic biomass in step (1) is 0.15-8 mm, and the moisture content is 20-50 wt.%.

[0020] This invention breaks biomass down to less than 8mm, which is beneficial for subsequent granulation and pyrolysis processes.

[0021] Preferably, the total water content of the mixture in step (1) is less than 50%.

[0022] Because lignocellulosic biomass has a certain degree of hygroscopicity, when the total water content is less than 40%, the biomass can absorb this water. However, when the water content is greater than 40%, the absorbed water may not be evenly distributed during the mixing process, or even fail to be absorbed at all. Therefore, this invention controls the total water content of the mixture to be less than 40%, which is beneficial for the uniform mixing of biomass with potassium, iron, and sodium sources.

[0023] Preferably, the average length of the mixed and molded particles in step (2) is 15-20 mm and the average diameter is 6-12 mm.

[0024] Preferably, the oxygen concentration in step (3) is less than 2.0%.

[0025] Preferably, the heat treatment temperature of the mixed and molded particles in step (3) is 600-700℃, and the heat treatment time is 10-300min.

[0026] Secondly, the present invention also provides a biochar particle adsorbent prepared by the above method, wherein the average diameter of the biochar particle adsorbent is 3-10 mm and the average length is 5-20 mm.

[0027] The biochar granular adsorbent of this invention has many pores on its surface, possesses a special microcrystalline structure, a huge specific surface area, a unique pore structure, and complex surface-active functional groups, and exhibits stable chemical properties.

[0028] Thirdly, the present invention also provides a device for CO2 capture, comprising several valves, a first adsorption-desorption tower, a second adsorption-desorption tower, a vacuum pump, a gas-liquid separator, a condensate pipe, and a vent pipe, wherein both the first adsorption-desorption tower and the second adsorption-desorption tower are filled with biochar granular adsorbent.

[0029] Preferably, the plurality of valves includes a first valve to a sixth valve.

[0030] Preferably, both the first adsorption tower and the second adsorption tower are connected to an inlet pipe and a vacuum pump, and the vacuum pump, gas-liquid separator, and condenser are connected in sequence; a first valve is provided at the connection between the first adsorption tower and the inlet pipe, and a fifth valve is provided at the connection between the first adsorption tower and the vacuum pump; a third valve is provided at the connection between the second adsorption tower and the inlet pipe, and a sixth valve is provided at the connection between the second adsorption tower and the vacuum pump; the first adsorption tower and the second adsorption tower are also provided with exhaust pipes, which are controlled by a second valve and a fourth valve, respectively.

[0031] Fourthly, the present invention also provides an application of the above-mentioned device in CO2 capture, comprising the following steps:

[0032] (1) First, fill the first adsorption-desorption tower and the second adsorption-desorption tower with biochar granules respectively. Then open the first valve, the second valve and the sixth valve, and close the third valve, the fourth valve and the fifth valve at the same time. Then, pass the mixed gas containing CO2 into the first adsorption-desorption tower through the gas pipe to carry out CO2 adsorption and capture operation, while controlling the temperature of the first adsorption-desorption tower to be less than 65℃.

[0033] (2) When the CO2 adsorption in the first adsorption tower is close to saturation, close the first valve, the second valve and the sixth valve, and open the third valve, the fourth valve and the fifth valve at the same time to switch the mixed gas containing CO2 to the second adsorption-desorption tower, and control the temperature of the second adsorption-desorption tower to be less than 65°C.

[0034] (3) While CO2 is being adsorbed and captured in the second adsorption-desorption tower, high-temperature flue gas or steam at 120-150°C is introduced into the first adsorption-desorption tower from the outside to carry out CO2 desorption and regeneration operation. The temperature of the first desorption tower is controlled at 100-200°C. The desorbed CO2 and water vapor are discharged from the first adsorption-desorption tower by a vacuum pump. Finally, after the condensate is removed by the gas-liquid separator, high-purity CO2 gas is obtained and discharged from the exhaust pipe.

[0035] (4) When the CO2 adsorption in the second adsorption-desorption tower is close to saturation, the mixed gas containing CO2 is switched back to the first adsorption-desorption tower to perform the same CO2 adsorption and capture operation as in step (1). At the same time, the second adsorption tower is desorbed and regenerated using the same desorption and regeneration operation as in step (3) and high-purity CO2 gas is discharged.

[0036] (5) Repeat steps (1) to (4) alternately to perform CO2 adsorption and capture and CO2 desorption and regeneration operations in the first adsorption tower and the second adsorption tower.

[0037] Preferably, before introducing the CO2-containing mixed gas in step (1), the CO2-containing mixed gas is first cooled to below 80°C.

[0038] The present invention first cools the CO2-containing mixed gas to below 80°C to further increase the CO2 adsorption capacity.

[0039] Preferably, the CO2-containing mixed gas in step (1) includes at least one of syngas, flue gas, and air.

[0040] Preferably, the CO2 concentration of the CO2-containing mixed gas in step (1) is 10 ppm to 100%, and more preferably the CO2 concentration range is 400 ppm to 80%.

[0041] Preferably, the humidity of the CO2-containing mixed gas in step (1) is 20-100%, more preferably 50-90%; and the CO2 adsorption and capture temperature is 20-60℃.

[0042] This invention improves the adsorption effect of CO2 by controlling the CO2 concentration and humidity in a CO2-containing mixed gas.

[0043] Preferably, the temperature of the desorption tower II in step (2) is 120-180℃.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] (1) This invention uses inexpensive inorganic materials containing potassium, sodium and iron as raw materials and adopts a process of first mixing and molding and then constant temperature catalytic pyrolysis. Not only are the raw materials readily available and inexpensive, but the active components are also efficiently dispersed in the porous biochar particle carrier in the form of nanocrystals during the preparation process, which greatly simplifies the preparation process of traditional biochar particle adsorbents and has good economic benefits.

[0046] (2) This invention fully utilizes the confinement effect of biochar carrier on the loaded metal active components, creating a novel structure with highly dispersed nanocrystals that can effectively inhibit the aggregation and deactivation of active components during CO2 adsorption-desorption. Hundreds of cyclic adsorption-desorption experiments show that the biochar granular adsorbent described in this invention can significantly increase the CO2 adsorption capacity at medium and low temperatures under various complex environments, and significantly reduce the CO2 desorption and regeneration temperature of the adsorbent, exhibiting high energy efficiency and low energy consumption; compared with traditional solid CO2 adsorption, it has better practical application value. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the preparation method of the biochar granular adsorbent described in this invention.

[0048] Figure 2 This is a schematic diagram of the CO2 capture system described in this invention.

[0049] Figure 3 This is a schematic diagram showing the CO2 adsorption amount after 9 adsorption-desorption cycles in Example 2 of the present invention. Detailed Implementation

[0050] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the scope of protection and implementation of the present invention are not limited thereto.

[0051] Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0052] Example 1

[0053] A method for preparing a biochar particulate adsorbent for efficient CO2 capture includes the following steps:

[0054] (1) Raw material pretreatment: First, the corn stalk raw material is mechanically crushed to an average particle size of 5mm to obtain corn stalk powder; then, the corn stalk powder, potassium carbonate powder and iron oxide powder are put into a pulverizer, and then pure water is added and mixed evenly to obtain a mixture; wherein, the total water content of the mixture is kept at 30%; the mass ratio of potassium carbonate, iron oxide and corn stalk powder is 0.2:0.05:1;

[0055] (2) Mixing and molding: First, add the mixed particles into a wet molding machine and extrude them to obtain mixed molding particles. Then, cut the mixed molding particles to an average length of 10 mm and an average diameter of 5 mm.

[0056] (3) Isothermal pyrolysis: The mixed and shaped granules are placed in a high-temperature rotary furnace at 500℃ and treated at high temperature for 5 hours with a heating rate of 10℃ / min. Isothermal pyrolysis is then performed under a N2 atmosphere. After the temperature control program is completed, the granules are fully cooled and removed, then ground to obtain cylindrical biochar granule adsorbent. A schematic diagram of the preparation method of the biochar granule adsorbent of this invention is shown below. Figure 1 As shown.

[0057] In this embodiment, the average diameter of the biochar granular adsorbent is 3 mm and the average length is 5 mm.

[0058] A device for CO2 capture, such as Figure 2 As shown, it includes a first valve, a second valve, a third valve, a fourth valve, a fifth valve, a sixth valve, a first adsorption-desorption tower, a second adsorption-desorption tower, a vacuum pump, a gas-liquid separator, a condensate pipe, a vent pipe, and a high-temperature flue gas or steam inlet device. Both the first and second adsorption-desorption towers are filled with biochar granular adsorbent.

[0059] The first and second adsorption towers are both connected to an inlet pipe and a vacuum pump. The vacuum pump, gas-liquid separator, and condenser are connected in sequence. The first adsorption tower is equipped with a first valve at the connection with the inlet pipe and a fifth valve at the connection with the vacuum pump. The second adsorption tower is equipped with a third valve at the connection with the inlet pipe and a sixth valve at the connection with the vacuum pump. The first and second adsorption towers are also equipped with exhaust pipes, which are controlled by the second and fourth valves, respectively.

[0060] A CO2 capture process includes the following steps:

[0061] (1) First, the biochar granules adsorbent are loaded into the first adsorption-desorption tower and the second adsorption-desorption tower respectively. Then, the CO2 / N2 mixed gas (CO2 concentration of 10% and humidity of 80%) is cooled to below 80°C. Then, the first valve, the second valve and the sixth valve are opened, while the third valve, the fourth valve and the fifth valve are closed. The CO2 / N2 mixed gas is allowed to pass through the first adsorption-desorption tower of the tubular fixed bed filled with sufficient biochar granules adsorbent for CO2 adsorption and capture. The CO2 / N2 mixed gas is introduced along the gas pipe so that the mass ratio of CO2 to adsorbent is less than 10 mL / g·min. During the entire adsorption operation, a sufficient amount of circulating cooling water is always introduced into the shell of the first adsorption-desorption tower, while the temperature of the first adsorption-desorption tower is controlled to be less than 65°C.

[0062] (2) When the CO2 adsorption in the first adsorption tower is close to saturation, close the first valve, the second valve and the sixth valve, and open the third valve, the fourth valve and the fifth valve at the same time to switch the mixed gas containing CO2 to the second adsorption-desorption tower. At this time, the circulating cooling water is switched to the second adsorption-desorption tower simultaneously.

[0063] (3) While CO2 is being adsorbed and captured in the second adsorption-desorption tower, high-temperature flue gas at 120°C is introduced into the shell of the first adsorption-desorption tower from the outside to carry out CO2 desorption and regeneration operation. During the entire desorption and regeneration process, the temperature of the first adsorption-desorption tower is controlled at 120°C. The desorbed CO2 and water vapor are discharged from the first adsorption-desorption tower by a vacuum pump. Finally, after the condensate is removed by a gas-liquid separator, high-purity CO2 gas is obtained and discharged from the exhaust pipe.

[0064] (4) When the CO2 adsorption in the second adsorption-desorption tower is close to saturation, the mixed gas containing CO2 is switched back to the first adsorption-desorption tower to perform the same CO2 adsorption and capture operation as in step (1). At the same time, the second adsorption tower is desorbed and regenerated using the same desorption and regeneration operation as in step (3) and high-purity CO2 gas is discharged.

[0065] (5) Repeat steps (1) to (4) alternately to perform CO2 adsorption and capture and CO2 desorption and regeneration operations in the first adsorption tower and the second adsorption tower.

[0066] Example 2

[0067] The difference from Example 1 is that a method for preparing a biochar particulate adsorbent for efficient CO2 capture includes the following steps:

[0068] (1) Raw material pretreatment: First, the Chinese herbal medicine residue is mechanically crushed to an average particle size of 5 mm to obtain Chinese herbal medicine residue powder; then, the Chinese herbal medicine residue powder, potassium carbonate powder, iron oxide powder, and sodium carbonate powder are put into a pulverizer, and then pure water is added and mixed evenly to obtain a mixture; wherein, the total water content of the mixture is kept at 30%; the mass ratio of potassium carbonate, iron oxide, sodium carbonate, and Chinese herbal medicine residue powder is 0.13:0.02:0.05:1;

[0069] (2) Mixing and molding: First, add the mixed particles into a wet molding machine and extrude them to obtain mixed molding particles. Then, cut the mixed molding particles to an average length of 20 mm and an average diameter of 8 mm.

[0070] (3) Constant temperature pyrolysis: The mixed and shaped particles are placed in a high-temperature rotary furnace at 700℃ and treated at high temperature for 5 hours. The heating rate is 10℃ / min. The constant temperature pyrolysis is carried out under N2 atmosphere. After the temperature control program is completed, the particles are cooled and taken out. After grinding, cylindrical biochar particles adsorbent are obtained.

[0071] In this embodiment, the average diameter of the biochar granular adsorbent is 8 mm and the average length is 10 mm.

[0072] Example 3

[0073] The difference from Example 2 is that a method for preparing a biochar particulate adsorbent for efficient CO2 capture includes the following steps:

[0074] (1) Raw material pretreatment: The corn stalk raw material is first mechanically crushed to an average particle size of 5mm to obtain corn stalk powder; then the corn stalk powder, potassium carbonate powder, iron oxide powder and sodium carbonate powder are put into a pulverizer, and then pure water is added and mixed evenly to obtain a mixture; wherein, the total water content of the mixture is kept at 30%, and the mass ratio of potassium carbonate, iron oxide, sodium carbonate and corn stalk powder is 0.1:0.05:0.1:1;

[0075] (2) Mixing and molding: First, add the mixed particles into a wet molding machine and extrude them to obtain mixed molding particles. Then, cut the mixed molding particles to an average length of 50 mm and an average diameter of 15 mm.

[0076] (3) Constant temperature pyrolysis: The mixed and shaped particles are placed in a high-temperature rotary furnace at 600℃ and treated at high temperature for 5 hours. The heating rate is 10℃ / min. The constant temperature pyrolysis is carried out under N2 atmosphere. After the temperature control program is completed, the particles are cooled and taken out. After grinding, cylindrical biochar particles adsorbent are obtained.

[0077] In this embodiment, the average diameter of the biochar granular adsorbent is 10 mm and the average length is 20 mm.

[0078] Example 4

[0079] The difference from Example 2 is that in the preparation method of a biochar particle adsorbent for efficient CO2 capture, the average length of the mixed and molded particles in step (2) is 15 mm and the average diameter is 6 mm.

[0080] Example 5

[0081] The difference from Example 2 is that in the preparation method of a biochar particle adsorbent for efficient CO2 capture, the average length of the mixed and molded particles in step (2) is 20 mm and the average diameter is 12 mm.

[0082] Example 6

[0083] The difference from Example 2 is that a CO2 capture process is used in step (1) where the CO2 concentration in the CO2 / N2 mixture is 20% and the humidity is 100%.

[0084] Example 7

[0085] The difference from Example 2 is that a CO2 capture process is used in step (1) where the CO2 concentration in the CO2 / N2 mixture is 10% and the humidity is 60%.

[0086] Comparative Example 1

[0087] The difference from Example 2 is that in the preparation method of a biochar particle adsorbent for efficient CO2 capture, the mass ratio of potassium carbonate, iron oxide, sodium carbonate and traditional Chinese medicine residue powder in step (1) is 0.05:0.01:0.1:1.

[0088] Comparative Example 2

[0089] The difference from Example 2 is that in the preparation method of a biochar particle adsorbent for efficient CO2 capture, the mass ratio of potassium carbonate, iron oxide, sodium carbonate and traditional Chinese medicine residue powder in step (1) is 0.3:0.1:0.1:1.

[0090] Comparative Example 3

[0091] The difference from Example 2 is that in the preparation method of a biochar particle adsorbent for efficient CO2 capture, the average length of the mixed and molded particles in step (2) is 5 mm and the average diameter is 1 mm.

[0092] Comparative Example 4

[0093] The difference from Example 2 is that in the preparation method of a biochar particle adsorbent for efficient CO2 capture, the average length of the mixed and molded particles in step (2) is 40 mm and the average diameter is 20 mm.

[0094] Comparative Example 5

[0095] The difference from Example 2 is that in the preparation method of a biochar particle adsorbent for efficient CO2 capture, the pyrolysis temperature of the mixed and molded particles in step (3) is 300°C.

[0096] Comparative Example 6

[0097] The difference from Example 2 is that in the preparation method of a biochar particle adsorbent for efficient CO2 capture, the pyrolysis temperature of the mixed and molded particles in step (3) is 1000℃.

[0098] experiment

[0099] 1. Determination of CO2 adsorption capacity: For flow rates less than 200 mL / min, online monitoring was performed using gas chromatography; for flow rates greater than 200 mL / min, real-time monitoring was performed using an infrared carbon dioxide detector.

[0100] 2. Determination of cycle stability: 1.0 g of the above-mentioned biochar granular adsorbent was placed in a fixed bed and a CO2 / N2 mixture with a humidity of 60% (CO2 concentration of 10%) was introduced at 60℃ at a rate of 50 mL / min. After adsorption saturation, the temperature was raised to 200℃ for desorption. After holding for one hour, the temperature was lowered to 60℃ and adsorption was carried out again.

[0101] The experimental results are shown in Table 1.

[0102] Table 1

[0103]

[0104] According to Table 1, comparing Comparative Examples 1-2 with Example 2, it can be seen that when the ratios of potassium, iron, and sodium sources to biomass are outside the range defined in this invention, the CO2 adsorption capacity is lower than in Example 2, and after multiple cycles, the CO2 adsorption capacity decreases significantly. This indicates that when the ratios of potassium, iron, and sodium sources to biomass are inappropriate, the active components cannot be uniformly dispersed in the biochar carrier, leading to easy deactivation of the active components during CO2 adsorption-desorption. Therefore, by limiting the range of ratios of potassium, iron, and sodium sources to biomass, this invention is beneficial to improving the adsorption performance and cycle stability of biochar granular adsorbents.

[0105] Comparing Comparative Examples 3-4 with Example 2, it can be seen that when the average length and average diameter of the mixed-formed particles are too large or too small, the CO2 adsorption capacity is lower than that of Example 2, and the CO2 adsorption capacity also decreases significantly after multiple cycles. Therefore, by controlling the average length and average diameter of the mixed-formed particles within the range defined in this invention, it is beneficial to improve the uniformity of the internal structure of the mixed-formed particles, thereby enabling the biochar granular adsorbent to have excellent adsorption performance.

[0106] Comparisons of Comparative Examples 5-6 with Example 2 show that both excessively low and excessively high pyrolysis temperatures negatively impact the performance and cycle stability of the biochar granular adsorbent. Therefore, this invention, by controlling the pyrolysis temperature range, effectively improves the adsorption performance of the biochar granular adsorbent.

[0107] According to Example 2 and Figure 3 It can be seen that after 9 cycles, the CO2 adsorption capacity remained stable at above 2.2 mmol / g, indicating that the biochar granular adsorbent described in this invention has both high adsorption performance and cycle stability.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a biochar granular adsorbent for efficient CO2 capture, characterized in that, Includes the following steps: (1) Mix lignocellulosic biomass and inorganic matter evenly to obtain a mixture, wherein the inorganic matter includes potassium source, iron source and sodium source, the mass ratio of lignocellulosic biomass to inorganic matter is 100:(5-30), and the molar ratio of potassium in potassium source, iron in iron source and sodium in sodium source is 1:(0.1-2):(0-10); (2) The mixture is extruded to obtain mixed granules, wherein the average length of the mixed granules is 15-20 mm and the average diameter is 6-12 mm. (3) The mixed and shaped particles are subjected to constant temperature pyrolysis at 500-900℃ in an oxygen-free or low-oxygen atmosphere to obtain biochar particle adsorbent.

2. The method for preparing the biochar granular adsorbent as described in claim 1, characterized in that, The total water content of the mixture in step (1) is less than 50%.

3. The method for preparing the biochar granular adsorbent as described in claim 1, characterized in that, Step (1) includes at least one of (a) to (c): (a) The potassium source is at least one of potassium oxide, potassium carbonate, potassium hydroxide, and potassium ferrate; (b) The sodium source is at least one of sodium oxide, sodium carbonate, sodium bicarbonate, and sodium hydroxide; (c) The iron source is at least one of iron oxide, iron carbonate, and potassium ferrate.

4. The biochar granular adsorbent prepared by the preparation method according to any one of claims 1-3, characterized in that, The average diameter of the biochar granular adsorbent is 3-10 mm and the average length is 5-20 mm.

5. A device for CO2 capture, characterized in that, It includes several valves, a first adsorption-desorption tower, a second adsorption-desorption tower, a vacuum pump, a gas-liquid separator, a condensate pipe, and a vent pipe. Both the first adsorption-desorption tower and the second adsorption-desorption tower are filled with the biochar granular adsorbent as described in claim 4.

6. The device as described in claim 5, characterized in that, The valves include valves one through six.

7. The device as described in claim 5, characterized in that, Both the first and second adsorption-desorption towers are connected to an inlet pipe and a vacuum pump. The vacuum pump, gas-liquid separator, and condenser are connected in sequence. The first adsorption-desorption tower is equipped with a first valve at the connection with the inlet pipe and a fifth valve at the connection with the vacuum pump. The second adsorption-desorption tower is equipped with a third valve at the connection with the inlet pipe and a sixth valve at the connection with the vacuum pump. The first and second adsorption-desorption towers are also equipped with exhaust pipes, which are controlled by a second valve and a fourth valve, respectively.

8. The application of the device as described in claim 7 in CO2 capture, characterized in that, Includes the following steps: (1) First, fill the first adsorption-desorption tower and the second adsorption-desorption tower with biochar granules respectively. Then open the first valve, the second valve and the sixth valve, and close the third valve, the fourth valve and the fifth valve at the same time. Then, pass the mixed gas containing CO2 into the first adsorption-desorption tower through the gas pipe to carry out CO2 adsorption and capture operation, while controlling the temperature of the first adsorption-desorption tower to be less than 65°C. (2) When the CO2 adsorption in the first adsorption-desorption tower is close to saturation, close the first valve, the second valve and the sixth valve, and open the third valve, the fourth valve and the fifth valve at the same time to switch the mixed gas containing CO2 to the second adsorption-desorption tower, and control the temperature of the second adsorption-desorption tower to be less than 65°C. (3) While CO2 is being adsorbed and captured in the second adsorption-desorption tower, high-temperature flue gas or steam at 120-150°C is introduced into the first adsorption-desorption tower from the outside to carry out CO2 desorption and regeneration operation. The temperature of the first adsorption-desorption tower is controlled at 100-200°C. The desorbed CO2 and water vapor are discharged from the first adsorption-desorption tower by a vacuum pump. Finally, after the condensate is removed by the gas-liquid separator, high-purity CO2 gas is obtained and discharged from the exhaust pipe. (4) When the CO2 adsorption in the second adsorption-desorption tower is close to saturation, the mixed gas containing CO2 is switched back to the first adsorption-desorption tower to perform the same CO2 adsorption and capture operation as in step (1). At the same time, the second adsorption-desorption tower is desorbed and regenerated using the same desorption and regeneration operation as in step (3) and high-purity CO2 gas is discharged. (5) Repeat steps (1) to (4) alternately to perform CO2 adsorption capture and CO2 desorption regeneration operations in the first adsorption-desorption tower and the second adsorption-desorption tower.

9. The application of the device as described in claim 8 in CO2 capture, characterized in that, In step (1), the CO2 concentration in the CO2-containing mixed gas is 10ppm~100%, and the humidity is 20-100%.

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