A method for determining the upper limit of condensation of adsorbate gas molecules in a porous material by liquid imbibition gas displacement

Abstract

This invention relates to a method for determining the upper limit of adsorbate gas molecule aggregation in porous materials using a liquid-driven gas displacement method. Belonging to the field of materials characterization technology, it addresses at least one of the problems of existing technologies being unable to directly and effectively determine the pore size range in which adsorbate gas condenses within porous materials with complex pore size distributions at room temperature and pressure. The method of this invention is based on the liquid-driven gas displacement method. It uses liquid probe molecules with different molecular dynamic diameters to displace aggregated adsorbate gas molecules from the micropores of the porous material. The resulting displacement amounts are then compared, directly correlating the dynamic diameter of the liquid probe molecules with the upper limit of adsorbate gas molecule aggregation. By determining the aggregation upper limits of various adsorbate gas molecules in porous materials, the adjustment of the micropore structure of porous materials can be more targeted, thereby effectively improving their adsorption and separation performance.

Description

Technical Field

[0001] This invention relates to the field of materials characterization technology, and in particular to a method for determining the upper limit of adsorbate gas molecules in porous materials using a liquid-driven gas method. Background Technology

[0002] Porous materials, with their unique pore structures, have significant application value in adsorption separation, catalysis, and energy storage. Microporous materials (pore size <2 nm) significantly influence the adsorption and condensation behavior of gas molecules due to their high specific surface area and pore confinement effect. Clarifying the condensation state of adsorbate gas within the micropores of porous materials, especially the upper limit of the pore size at which condensation occurs, is crucial for understanding the pore structure and regulating material properties.

[0003] Currently, research on the condensation behavior of gases in porous materials mainly relies on two types of methods: experimental testing and theoretical calculation. Experimental methods include indirect testing (such as adsorption isotherms) and direct testing (such as visualization using micro / nanofluidic chips). However, the former is mostly limited to mesoporous materials with a single pore size and large dimensions, making it difficult to reflect the complex pore size distribution of porous materials. The latter is limited by micro / nano fabrication and imaging technologies, and cannot effectively detect condensation behavior at smaller scales (especially within the micropore range). Theoretical calculation methods (such as density functional theory and molecular simulations) can reveal interface effects and pore wall interactions at the molecular level, but they are usually based on ideal models and lack verification of material structure and experimental conditions, making it difficult to accurately correlate condensation behavior with pore size distribution.

[0004] Therefore, existing technologies still lack a method to directly and effectively determine the pore size range in which adsorbate gas condenses within micropores of porous materials with complex pore size distributions under normal temperature and pressure conditions. Summary of the Invention

[0005] In view of the above analysis, the present invention aims to provide a method for determining the upper limit of adsorbate gas molecules in porous materials by liquid-induced gas displacement, so as to solve at least one of the problems of existing technology being unable to directly and effectively determine the pore size range in which adsorbate gas condenses in porous materials with complex pore size distribution at room temperature and pressure.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for determining the upper limit of condensation of adsorbate gas molecules in porous materials using a liquid-induced gas displacement method, the method comprising the following steps: S1: Pre-treat the porous material to be tested under heating conditions to remove the water and gas impurities adsorbed in the pores of the porous material to be tested, and obtain the pre-treated porous material. S2: At a preset test temperature, the gas probe molecules to be tested are introduced into a container containing the pretreated porous material so that the pretreated porous material reaches saturation adsorption. S3: Use liquid probe molecules to displace gas probe molecules saturated and adsorbed in porous materials, and monitor the real-time pressure change in the container before and after the gas probe molecules are displaced. When the pressure fluctuation value is ≤0.05kPa / min and the duration is ≥5min, stop pressure acquisition and calculate the gas displacement amount at this time as the equilibrium gas displacement amount of liquid probe molecules. S4: Weigh the total mass of the container after processing in S3; S5: Replace with a liquid probe molecule with a larger dynamic diameter than the liquid probe molecule described in S3, and repeat S1~S4 to obtain test data corresponding to different times for liquid probe-gas probe molecules with different dynamic diameters. Calculate the gas driving amount of liquid probe molecules with different dynamic diameters at different times, and determine the upper limit of the pore size of the gas probe molecules to be tested condensing in the porous material.

[0007] Furthermore, in S1, the pretreatment is either purge desorption or vacuum desorption, and the pretreatment time is ≥120 min. The purge desorption uses the same gas as the gas probe molecules to be tested.

[0008] Furthermore, in S1, the heating temperature is 80~300℃, and different pretreatment temperatures are selected according to the porous material to be tested.

[0009] Furthermore, in S2, the pretreated porous material reaches saturation adsorption after the injection time of the gas probe molecules to be tested is ≥180 min.

[0010] Furthermore, the flow rate of the gas probe molecule to be tested is 5~100 mL / min.

[0011] Furthermore, in S3, the liquid probe molecule that first displaces the gas probe molecules in the porous material with saturated adsorption is chosen to be water.

[0012] Furthermore, in S5, when the pressure fluctuation value of the monitored container is ≤0.05kPa / min and the duration is ≥5min, the displacement amount at this time is calculated as the liquid probe molecular equilibrium displacement amount. V e Replace with liquid probe molecules with larger kinetic diameters until the gas displacement is balanced. V e Stop replacing the liquid probe molecules when the concentration is ≤0.1 mL / g.

[0013] Furthermore, in S3 and S5, the displacement air volume is calculated using the following formula: ; in,V t Under standard conditions t The amount of gas displaced from the porous material sample at any given time, in mL / g; V s The volume of the container-contained, sealed space is expressed in mL. V l The volume of the liquid probe molecules injected into the container, in mL; V a The volume of the porous material sample skeleton is given in mL. P t for t The pressure above the liquid surface in the container at any given time, in kPa; P 0 represents the initial pressure in the container before liquid injection, in kPa; m represents the mass of the porous material sample to be tested, in g. T The experimental temperature is in K. T θ =273.15 K; P θ =101.3 kPa; η The liquid evaporation coefficient is used to eliminate data measurement bias caused by liquid probe evaporation, and is expressed as: ; in: P s ρ is the saturated vapor pressure at the experimental temperature, in kPa.

[0014] Furthermore, record when V e The molecular dynamics diameter of the liquid probe at ≤0.1 mL / g is r x The upper limit for the aggregation of the adsorbate gas molecules in the porous material is then determined to be... r x ±0.05 nm.

[0015] Furthermore, in S5, the replacement of the liquid probe molecule with a larger kinetic diameter specifically refers to: When replacing, select liquid probe molecules with similar kinetic diameters, and the difference in kinetic diameter between the replaced liquid probe molecule with a larger kinetic diameter and the replaced liquid probe molecule should not exceed 0.2 nm. The gas probe molecules include at least one of hydrogen, carbon dioxide, oxygen, argon, nitrogen, methane, and sulfur hexafluoride; The liquid probe molecule includes at least one of water, methanol, ethanol, isopropanol, benzene, ethyl acetate, cyclohexane, isooctane, and 1,3,5-triethylbenzene.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: This invention is based on the liquid-driven gas displacement method. It uses liquid probe molecules with different molecular dynamic diameters to displace condensed adsorbate gas molecules from the micropores of porous materials. The displacement amounts are then compared to directly correlate the dynamic diameter of the liquid probe molecules with the upper limit of adsorbate gas condensation. This invention focuses on the adsorption and condensation state of adsorbate gas molecules in the complex microporous structure of porous materials, directly measuring and comparing the range within which condensation can occur. This solves the problems of current experimental studies, which can only measure materials with large and singular pore sizes, and the lack of experimental data to verify theoretical calculations. By determining the upper limits of condensation of various adsorbate gas molecules in porous materials, the adjustment of the microporous structure of porous materials can be more targeted, thereby effectively improving their adsorption and separation performance.

[0017] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0018] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0019] Figure 1 This is a graph showing the liquid absorption and gas displacement curves of different liquid probe molecules in Example 1; Figure 2 This is a pore size distribution diagram of carbon molecular sieve based on the NLDFT model in Experiment Example 1; Figure 3 This is a diagram of the pore size distribution of activated carbon based on the NLDFT model in Experiment Example 1; Figure 4 This is a nitrogen density distribution diagram based on GCMC simulation in Experiment Example 2. Detailed Implementation

[0020] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0021] A specific embodiment of the present invention discloses a method for determining the upper limit of adsorbate gas molecules condensation in porous materials using a liquid-induced gas displacement method, the method comprising the following steps: S1: Pre-treat the porous material to be tested under heating conditions to remove the water and gas impurities adsorbed in the pores of the porous material to be tested, and obtain the pre-treated porous material. S2: At a preset test temperature, the gas probe molecules to be tested are introduced into a container containing the pretreated porous material so that the pretreated porous material reaches saturation adsorption. S3: Use liquid probe molecules to displace gas probe molecules saturated and adsorbed in porous materials, and monitor the real-time pressure change in the container before and after the gas probe molecules are displaced. When the pressure fluctuation value is ≤0.05kPa / min and the duration is ≥5min, stop pressure acquisition and calculate the gas displacement amount at this time as the equilibrium gas displacement amount of liquid probe molecules. S4: Weigh the total mass of the container after processing in S3; S5: Replace with a liquid probe molecule with a larger dynamic diameter than the liquid probe molecule described in S3, and repeat S1~S4 to obtain test data corresponding to different times for liquid probe-gas probe molecules with different dynamic diameters. Calculate the gas driving amount of liquid probe molecules with different dynamic diameters at different times, and determine the upper limit of the pore size of the gas probe molecules to be tested condensing in the porous material.

[0022] The method of this invention determines the upper limit of pore size at which adsorbate gas can condense within the micropores of porous materials under constrained conditions at room temperature and pressure. Based on the liquid-driven gas displacement method, liquid probe molecules with different molecular dynamic diameters are used to displace condensed adsorbate gas molecules from the micropores of porous materials. The displacement amounts are then compared to directly correlate the dynamic diameter of the liquid probe molecules with the upper limit of condensation of the adsorbate gas molecules. This invention focuses on the adsorption and condensation state of adsorbate gas molecules within the complex microporous structure of porous materials, directly measuring and comparing the range within which condensation can occur. This solves the problems of current experimental studies, which can only measure materials with large and singular pore sizes, and the lack of experimental data to verify theoretical calculations. By determining the upper limits of condensation of various adsorbate gas molecules in porous materials, the adjustment of the microporous structure of porous materials can be more targeted, thereby effectively improving their adsorption and separation performance.

[0023] It should be noted that the container used for adsorption and displacement in this invention is a liquid-suction and gas-driving device in the prior art, which can inject gas or liquid through a pipeline and control the entry and exit of gas or liquid through a valve. This invention will not elaborate further.

[0024] Specifically, in S1, the pretreatment is either purge desorption or vacuum desorption, and the pretreatment time is ≥120 min, for example, 120 min, 125 min, 130 min, 135 min, 140 min, 145 min, or 150 min. The purge desorption uses the same gas as the gas probe molecules to be tested. The purpose of the pretreatment is to remove adsorbed moisture and gaseous impurities from the pores of the porous material.

[0025] Specifically, the purging and desorption process uses the same gas as the probe gas to be tested, with a flow rate of 5~100 mL / min, for example, 5 mL / min, 10 mL / min, 15 mL / min, 20 mL / min, 25 mL / min, 30 mL / min, 35 mL / min, 40 mL / min, 45 mL / min, 50 mL / min, 55 mL / min, 60 mL / min, 65 mL / min, 70 mL / min, 75 mL / min, 80 mL / min, 85 mL / min, 90 mL / min, 95 mL / min, and 100 mL / min.

[0026] Specifically, the pressure of the vacuum desorption is 10. -3 ~ 10 -4 Pa.

[0027] Specifically, in S1, the heating temperature is 80~300℃, for example, 80℃, 100℃, 120℃, 140℃, 160℃, 180℃, 200℃, 220℃, 240℃, 260℃, 280℃, 300℃.

[0028] Preferably, different pretreatment temperatures are selected according to the porous material to be tested. For example, the pretreatment temperature for activated carbon is 100~150℃, the pretreatment temperature for carbon molecular sieve is 150~200℃, the pretreatment temperature for zeolite molecular sieve is 150~300℃, and the pretreatment temperature for carbon nanotubes is 100~150℃.

[0029] Specifically, in S1, the porous material to be tested has a microporous structure.

[0030] Preferably, the porous material to be tested includes at least one of activated carbon, carbon molecular sieve, zeolite molecular sieve, carbon nanotube, metal oxide and other porous materials.

[0031] Specifically, in S2, the pretreated porous material reaches saturation adsorption after the injection time of the gas probe molecules to be tested is ≥180 min.

[0032] Preferably, the flow rate of the gas probe molecule to be tested is 5~100 mL / min, for example, 5 mL / min, 10 mL / min, 15 mL / min, 20 mL / min, 25 mL / min, 30 mL / min, 35 mL / min, 40 mL / min, 45 mL / min, 50 mL / min, 55 mL / min, 60 mL / min, 65 mL / min, 70 mL / min, 75 mL / min, 80 mL / min, 85 mL / min, 90 mL / min, 95 mL / min, and 100 mL / min.

[0033] It should be noted that the gas probe molecules in this invention do not react with the porous material and liquid probe molecules, including at least one of hydrogen (kinetic diameter 0.28 nm), carbon dioxide (kinetic diameter 0.33 nm), argon (kinetic diameter 0.34 nm), oxygen (kinetic diameter 0.346 nm), nitrogen (kinetic diameter 0.364 nm), methane (kinetic diameter 0.38 nm), and sulfur hexafluoride (kinetic diameter 0.55 nm); the liquid probe molecules do not react with the tested porous material and gas probe molecules, and the liquid probe molecules include at least one of water (kinetic diameter 0.28 nm), methanol (kinetic diameter 0.38 nm), ethanol (kinetic diameter 0.47 nm), isopropanol (kinetic diameter 0.51 nm), ethyl acetate (kinetic diameter 0.55 nm), benzene (kinetic diameter 0.58 nm), cyclohexane (kinetic diameter 0.61 nm), isooctane (kinetic diameter 0.7 nm), and 1,3,5-triethylbenzene (kinetic diameter 0.84 nm).

[0034] Specifically, in S3, the flow rate of the liquid probe molecule injected into the container is greater than 3.6 mL / s, and the injection time is ≥1 s.

[0035] Preferably, the injected liquid probe molecules are ensured to completely submerge the porous material sample. Simultaneously with the injection of liquid probe molecules, stirring is performed to ensure full contact between the liquid probe molecules and the porous material sample, eliminating the influence of outward diffusion of liquid and gas probe molecules. Pressure parameter acquisition is stopped when all adsorbed gas probe molecules within the pores of the porous material sample have been displaced, i.e., when the pressure inside the container no longer changes (typically defined as a pressure fluctuation of less than 0.05 kPa per minute). The pressure data acquisition time depends on the test sample and is typically no less than 50 minutes.

[0036] Preferably, in S3, the liquid probe molecule used to first displace the gas probe molecules in the porous material with saturated adsorption is water. Water has a relatively small kinetic diameter of 0.28 nm. In this invention, water with the smallest kinetic diameter is selected first for displacement, and then liquid probe molecules with larger kinetic diameters are replaced sequentially. The difference in kinetic diameter between the replaced liquid probe molecule with the larger kinetic diameter and the replaced liquid probe molecule does not exceed 0.2 nm.

[0037] It should be noted that in S4, the total mass includes the mass of the container, porous material, liquid probe molecules, and stirring rotor; in S5, the test data includes the real-time test pressure and the total mass of the container.

[0038] Specifically, in S5, when the pressure fluctuation value of the monitored container is ≤0.05kPa / min and the duration is ≥5min, the displacement of gas at this time is calculated as the liquid probe molecular equilibrium displacement of gas. V e Replace with liquid probe molecules with larger kinetic diameters until the gas displacement is balanced. V e Stop replacing the liquid probe molecules when the concentration is ≤0.1 mL / g.

[0039] Specifically, in S3 and S5, the displacement air volume is calculated using the following formula:

[0040] in, V t For standard conditions ( T θ =273.15 K, P θ =101.3 kPa) t The amount of gas displaced from the porous material sample at any given time, in mL / g; V s The volume of the container-contained, sealed space is expressed in mL. V l The volume of the liquid probe molecules injected into the container (calculated based on the mass and density of the liquid probe molecules), in mL; V a The volume of the porous material sample skeleton (calculated using the helium displacement method) is mL; P t for t The pressure above the liquid surface in the container at any given time, in kPa; P 0 represents the initial pressure in the container before liquid injection, in kPa; m represents the mass of the porous material sample to be tested, in g. T The experimental temperature is in K. ηThe liquid evaporation coefficient is used to eliminate data measurement bias caused by liquid probe evaporation, and is expressed as:

[0041] in: P s ρ is the saturated vapor pressure at the experimental temperature, in kPa.

[0042] It should be noted that, V l The mass of the liquid probe molecules is calculated based on their mass and density. The mass of the liquid probe molecules is obtained by subtracting the mass of the container, porous material, and stirring rotor from the total mass in S4, where the masses of the container, porous material, and stirring rotor are known.

[0043] Preferably, record when V e The molecular dynamics diameter of the liquid probe at ≤0.1 mL / g is r x The upper limit for the aggregation of the adsorbate gas molecules in the porous material is then determined to be... r x ±0.05nm.

[0044] Specifically, in S5, replacing the liquid probe molecule with one having a larger kinetic diameter means: When replacing the liquid probe molecule, select one with a similar kinetic diameter, and ensure that the difference in kinetic diameter between the replaced liquid probe molecule with a larger kinetic diameter and the replaced liquid probe molecule does not exceed 0.2 nm.

[0045] It should be noted that the principle upon which the method of this invention is based is as follows: Based on the relationship between the kinetic diameters of liquid probe molecules and gas probe molecules, the following two scenarios exist: (i) When the kinetic diameter of the liquid probe molecule is less than or equal to that of the gas probe molecule, the liquid probe molecule can displace all the gas probe molecules adsorbed in the pores of the porous material sample, resulting in a relatively large displacement capacity. (ii) When the kinetic diameter of the liquid probe molecule is greater than that of the gas probe molecule, the liquid probe molecule can only displace the gas probe molecules adsorbed in pores larger than its own molecular kinetic diameter, and the resulting displacement capacity is smaller compared to when the kinetic diameter of the liquid probe molecule is smaller than that of the gas probe molecule.

[0046] In the above scenario, when the obtained gas displacement is close to zero (≤0.1 mL / g), the corresponding liquid probe molecules cannot displace the gas probe molecules adsorbed in the pores of the porous material sample being tested. This is the equilibrium gas displacement. If the kinetic diameter of the liquid probe molecule exceeds the upper limit of condensation of the gas probe molecules in the pores, it indicates that the molecular kinetic diameter is slightly smaller than the kinetic diameter of its adjacent liquid probe molecule, and is close to the upper limit of condensation of the gas probe molecules under investigation in the pores. In other words, the upper limit of condensation of the gas probe molecules under investigation in the pores is near the kinetic diameter of the liquid probe molecule with the larger kinetic diameter.

[0047] During liquid-gas adsorption, liquid probe molecules need to enter pores larger than their own diameter to displace the gas probe molecules condensed within those pores. When the kinetic diameter of the gas probe molecules is close to the pore size, the gas probe molecules will condense under the superposition of potential energy from the surrounding pore walls. However, as the pore size increases, the force exerted by the pore walls on the gas probe molecules weakens to a certain extent, and the gas probe molecules no longer condense. Therefore, for a specific porous material-gas probe molecule system, there is an upper limit to the pore size at which adsorbed gas probe molecules can condense, and this upper limit is related to the size of the gas probe molecules. Obviously, the minimum pore size that gas probe molecules can enter in the porous material corresponds to its molecular kinetic diameter; therefore, the kinetic diameter of the gas probe molecules can be reasonably considered as the lower limit of the pore size at which condensation occurs. To assess the upper limit of gas probe molecules condensation in the pores of porous materials, this invention uses liquid probe molecules with different kinetic diameters to displace adsorbed and condensed gas probe molecules in the pores of porous materials. The liquid probe molecules that can displace condensed gas probe molecules have a kinetic diameter smaller than the upper limit of condensation pore size, while the liquid probe molecules that cannot displace condensed gas probe molecules have a kinetic diameter larger than the upper limit of condensation pore size. Thus, by accurately measuring the number of displaced gas probe molecules, the upper limit of the pore size at which gas probe molecules can condense in porous materials can be estimated based on the corresponding kinetic diameter of the liquid probe molecules.

[0048] The technical solution of the present invention will be further explained below with reference to specific embodiments. All raw materials involved in the present invention are commercially available or prepared using existing technical methods. The molecular dynamics diameter of the present invention refers to the effective diameter exhibited during collisions between molecules, and all of these are data known in the art.

[0049] Example 1 A method for determining the upper limit of condensation of adsorbate gas molecules in porous materials using a liquid-induced gas displacement method, the method comprising the following steps: S1: The porous material to be tested is crushed, sieved and dried. The porous material to be tested is then purged and desorbed at 160℃ with a flow rate of 50mL / min and a time of 150min to obtain the pretreated porous material. S2: At a preset test temperature, the gas probe molecules to be tested are introduced into a container containing the pretreated porous material. The injection flow rate of the gas probe molecules to be tested is 60 mL / min, and the injection time is ≥180 min, so that the pretreated porous material reaches saturated adsorption. S3: Displace gas probe molecules from saturated adsorbed porous materials using liquid probe molecules. The flow rate of the liquid probe molecules injected into the container is greater than 3.6 mL / s, and the injection time is ≥1s, ensuring that the injected liquid probe molecules can completely immerse the porous material sample. At the same time, monitor the real-time pressure change in the container before and after the gas probe molecules are displaced. When the pressure fluctuation value is ≤0.05kPa / min and the duration is ≥5min, stop the pressure acquisition and calculate the gas displacement amount at this time as the equilibrium gas displacement amount of the liquid probe molecules. S4: Weigh the total mass of the container after processing in S3; S5: Recover the porous material, replace it with a liquid probe molecule that is different from the one described in S3 and has a larger kinetic diameter, and repeat S1~S4 to obtain test data corresponding to different times for liquid probe-gas probe molecules with different kinetic diameters. Replace with liquid probe molecules with larger kinetic diameters until the gas displacement is reached. V t Stop replacing the liquid probe molecules when the concentration is ≤0.1 mL / g; S6: Calculate and compare the gas displacement corresponding to liquid probe molecules with different kinetic diameters based on the test data obtained in S5, so as to determine the upper limit of the pore size for the gas probe molecules to be tested to condense in the porous material.

[0050] The expression for the displacement volume is shown in equation (1): (1) in, V t For standard conditions ( T θ =273.15 K, P θ =101.3 kPa) t The amount of gas displaced from the porous material sample at any given time, in mL / g; V s Let be the volume of the constant-volume closed space formed by the containers, in mL; V l The volume of the liquid probe molecules injected into the container, in mL; V aThe volume of the porous material sample skeleton is given in mL. P t for t The pressure above the liquid surface in the container at any given time, in kPa; P 0 represents the initial pressure in the container before liquid injection, in kPa; m represents the mass of the porous material sample to be tested, in g. T The experimental temperature is in K. η The liquid evaporation coefficient is used to eliminate data measurement bias caused by liquid probe evaporation, and is expressed as:

[0051] in: P s ρ is the saturated vapor pressure at the experimental temperature, in kPa.

[0052] When the pressure fluctuation of the monitored container is less than 0.05 kPa per minute, the calculated gas displacement is the liquid probe molecular equilibrium gas displacement. V e ,when V e The molecular dynamics diameter of the liquid probe at ≤0.1 mL / g is r x The upper limit for the aggregation of the adsorbate gas molecules in the porous material is then determined to be... r x ±0.05 nm.

[0053] In this embodiment, nitrogen gas (kinetic diameter 0.364 nm) was used as the adsorbate gas to be investigated, and a commercial carbon molecular sieve (Carbopol, Germany) was used. CarboTech Using German-produced BF185 carbon molecular sieve as the porous material, liquid-gas dispersive experiments were conducted through the above steps. The liquid probes selected were water (kinetic diameter 0.28 nm), ethanol (kinetic diameter 0.44 nm), isopropanol (kinetic diameter 0.47 nm), and cyclohexane (kinetic diameter 0.61 nm). At a test temperature of 30℃ and a pressure acquisition time of 2000 s, test data (gas dispersive curves) corresponding to different liquid probe-gas probe molecules at different times were obtained, i.e., liquid-gas dispersive curves. V t -t )like Figure 1 As shown, according to Figure 1 It can be seen that the equilibrium displacement rate obtained by different liquid probes ( V e The results are shown in Table 1.

[0054] in, V s =40mL, Vl =2mL, V a =0.75mL, P 0 = 103.3 kPa T θ =273.15 K, P θ =101.3 kPa, T =303.15K (30+273.15), when the test time is 2000s; water: P t =129.01 kPa, m =1.0025g, P s =4.242 kPa; Ethanol: P t =116.06 kPa, m =1g, P s =10.25 kPa; Isopropanol: P t =112.33 kPa, m =1.0011g, P s =8.199 kPa; Cyclohexane: P t =111.21 kPa, m =1.0008g, P s =12.8 kPa.

[0055] Table 1. Equilibrium gas displacement (mL / g) for different liquid probes

[0056] The table shows that the gas displacement decreases with increasing kinetic diameter of the liquid probe molecules. Water has the smallest kinetic diameter, smaller than that of nitrogen molecules, and can displace the gas adsorbed within the porous material. Ethanol, with a larger kinetic diameter than nitrogen, can only displace nitrogen adsorbed in pores with a diameter greater than 0.47 nm. In contrast, cyclohexane has a relatively large kinetic diameter and is hindered by the pore openings, preventing it from entering the pores and completing the gas displacement process, resulting in a small, almost zero, gas displacement. By comparison, the upper limit for nitrogen condensation in this type of carbon molecular sieve porous structure is 0.61 ± 0.05 nm.

[0057] Example 2 The method and the adsorbate gas to be investigated in this embodiment are the same as in Example 1, except that ZSM-5 zeolite molecular sieve (ZSM-5 type zeolite molecular sieve produced by Nankai University Catalyst Factory) is used as the porous material. The liquid-induced gas displacement experiment is conducted through the above steps. The pretreatment temperature is 200℃, and the liquid probes selected are water (kinetic diameter 0.28 nm), ethanol (kinetic diameter 0.47 nm), benzene (kinetic diameter 0.58 nm), and cyclohexane (kinetic diameter 0.61 nm). The gas displacement results obtained with different liquid probes at a test temperature of 30℃ are shown in Table 2. The results show the same trend as in Examples 1 and 2, that is, the gas displacement decreases with the increase of the kinetic diameter of the liquid probe molecules. By comparison, the upper limit of nitrogen condensation in the pore structure of this type of zeolite molecular sieve ZSM-5 is 0.61 ± 0.05 nm.

[0058] Table 2. Equilibrium gas displacement (mL / g) for different liquid probes

[0059] Example 3 The method in this embodiment is similar to that in Example 1, except that methane (kinetic diameter 0.378 nm) is used as the adsorbate gas to be investigated. Activated carbon (fruit shell activated carbon produced by Shanxi Xinhua Shengtan Carbon Manufacturing Co., Ltd.) is subjected to a liquid-induced gas displacement experiment through the above steps. The pretreatment temperature is 120℃, and the liquid probes selected are water (kinetic diameter 0.28 nm), benzene (kinetic diameter 0.58 nm), cyclohexane (kinetic diameter 0.61 nm), and isooctane (kinetic diameter 0.70 nm). The gas displacement results obtained with different liquid probes at a test temperature of 30℃ are shown in Table 3. The results show the same trend as in Example 1, that is, the gas displacement decreases with the increase of the kinetic diameter of the liquid probe molecules. By comparison, the upper limit of methane condensation in the pore structure of fruit shell activated carbon is 0.7 ± 0.05 nm.

[0060] Table 3. Equilibrium gas displacement (mL / g) for different liquid probes

[0061] Example 4 The method and the adsorbate gas to be investigated in this embodiment are similar to those in Example 3, except that multi-walled carbon nanotubes (produced by Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.) are used as the porous material. The liquid-induced gas displacement experiment is conducted through the above steps. The pretreatment temperature is 120℃, and the liquid probes selected are water (kinetic diameter 0.28 nm), ethanol (kinetic diameter 0.47 nm), cyclohexane (kinetic diameter 0.61 nm), and isooctane (kinetic diameter 0.70 nm). The gas displacement results obtained with different liquid probes at a test temperature of 30℃ are shown in Table 4. The results show the same trend as in Examples 1, 2, and 3, that is, the gas displacement decreases as the kinetic diameter of the liquid probe molecules increases.

[0062] By comparison, the upper limit of methane condensation in the pore structure of multi-walled carbon nanotubes is found to be 0.70 ± 0.05 nm.

[0063] Table 4. Equilibrium gas displacement (mL / g) for different liquid probes

[0064] Comparative Example 1 The method and the gas to be adsorbed in this comparative example are similar to those in Example 1, except that γ-Al₂O₃ (pore size 2-3 nm) is used as the porous material. The liquid-induced gas displacement experiment was conducted using the above steps at a test temperature of 25°C. Water (0.28 nm) was chosen as the liquid probe, and the resulting gas displacement was 0.02 mL / g, which is relatively small, meaning that very little gas can be displaced by the liquid entering the pores. This is because γ-Al₂O₃ is a mesoporous material with a pore size between 2 and 3 nm. A larger pore size is not conducive to gas condensation within the pores, therefore this method is suitable for microporous materials.

[0065] Experimental Example 1 This experimental example uses the carbon molecular sieve and activated carbon used in Examples 1 and 3 as test samples. The adsorption isotherm under nitrogen adsorption conditions at 77 K was analyzed using nonlocal density functional theory (NLDFT). The pore size distribution and cumulative pore volume of the obtained samples are shown below. Figure 2 and Figure 3 As shown in the figure, the carbon molecular sieve sample is mainly composed of micropores and macropores, while the activated carbon is mainly composed of micropores, with micropores accounting for more than 90% of the total pore volume. This indicates that the sample itself has abundant microporous structure and good adsorption capacity.

[0066] The present invention has also conducted the above-described experiments on other embodiments, and the results are basically the same. Due to space limitations, they will not be listed one by one.

[0067] Experimental Example 2 verifies the reliability and accuracy of the method of the present invention. This experimental example utilizes the existing giant canonical Monte Carlo (GCMC) method to simulate the adsorption state density distribution of nitrogen gas within ultramicropores, such as... Figure 4 As shown, within the pore size range of 0.4 nm to 1 nm, the density exhibits a trend of first increasing and then decreasing. When the pore size is too small, molecules can only exist in a confined manner, resulting in a small adsorption capacity and thus a low density. When the pore size is 0.5 nm, the adsorption potential fields of the two pore walls superimpose, forming a stronger adsorption potential well, thereby adsorbing more nitrogen molecules. The molecules can form a tight packing and are strongly influenced by the potential energy of the pore walls, resulting in the highest density and easier aggregation. As the pore size further increases, the superposition of potential fields weakens, the adsorption capacity gradually decreases, the density gradually decreases, and the possibility of aggregation also gradually decreases. When the pore size is greater than 0.9 nm, the density change tends to level off, thus the upper limit of aggregation may be between 0.5 and 0.9 nm.

[0068] The upper limit of nitrogen condensation calculated using the method of Example 1 of the present invention is 0.61±0.05 nm, which is exactly in the range of 0.5~0.9 nm, demonstrating the accuracy and reliability of the method of the present invention.

[0069] The same experiments were also conducted on other embodiments of the present invention, and the results were basically the same. Due to space limitations, they will not be listed one by one.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the upper limit of adsorbate gas molecules condensation in porous materials using a liquid-induced gas displacement method, characterized in that, The method includes the following steps: S1: Pre-treat the porous material to be tested under heating conditions to remove the adsorbed moisture and gas impurities in the pores of the porous material to be tested, and obtain the pre-treated porous material. S2: At a preset test temperature, the gas probe molecules to be tested are introduced into a container containing the pretreated porous material so that the pretreated porous material reaches saturation adsorption. S3: Use liquid probe molecules to displace gas probe molecules saturated and adsorbed in porous materials, and monitor the real-time pressure change in the container before and after the gas probe molecules are displaced. When the pressure fluctuation value is ≤0.05kPa / min and the duration is ≥5min, stop pressure acquisition and calculate the gas displacement amount at this time as the equilibrium gas displacement amount of liquid probe molecules. S4: Weigh the total mass of the container after processing in S3; S5: Replace with a liquid probe molecule with a larger dynamic diameter than the liquid probe molecule described in S3, and repeat S1~S4 to obtain test data corresponding to different times for liquid probe-gas probe molecules with different dynamic diameters. Calculate the gas driving amount of liquid probe molecules with different dynamic diameters at different times, and determine the upper limit of the pore size of the gas probe molecules to be tested condensing in the porous material.

2. The method for determining the upper limit of adsorbate gas molecule condensation in porous materials by liquid-induced gas displacement method according to claim 1, characterized in that, In S1, the pretreatment is either purge desorption or vacuum desorption, and the pretreatment time is ≥120 min. The purge desorption uses the same gas as the gas probe molecules to be tested.

3. The method for determining the upper limit of adsorbate gas molecule condensation in porous materials by liquid-induced gas displacement method according to claim 1, characterized in that, In S1, the heating temperature is 80~300℃.

4. The method for determining the upper limit of adsorbate gas molecules condensation in porous materials by liquid-induced gas displacement according to any one of claims 1-3, characterized in that, In S2, the pretreated porous material reaches saturated adsorption after the injection time of the gas probe molecules to be tested is ≥180 min.

5. The method for determining the upper limit of adsorbate gas molecule condensation in porous materials by liquid-induced gas displacement method according to claim 4, characterized in that, The flow rate of the gas probe molecule to be tested is 5~100 mL / min.

6. The method for determining the upper limit of adsorbate gas molecules condensation in porous materials by liquid-induced gas displacement according to any one of claims 1-3, characterized in that, In S3, the liquid probe molecule chosen to replace the gas probe molecules in the porous material that was first saturated with adsorption is water.

7. The method for determining the upper limit of adsorbate gas molecules condensation in porous materials using liquid-induced gas displacement as described in claim 1, characterized in that, In S5, when the pressure fluctuation value of the monitored container is ≤0.05kPa / min and the duration is ≥5min, the displacement amount at this time is calculated as the liquid probe molecular equilibrium displacement amount. V e Replace with liquid probe molecules with larger kinetic diameters until the gas displacement is balanced. V e Stop replacing the liquid probe molecules when the concentration is ≤0.1 mL / g.

8. The method for determining the upper limit of adsorbate gas molecules condensation in porous materials by liquid-induced gas displacement according to claim 1 or 7, characterized in that, In S3 and S5, the displacement air volume is calculated using the following formula: ； in, V t Under standard conditions t The amount of gas displaced from the porous material sample at any given time, in mL / g; V s The volume of the container-contained, sealed space is expressed in mL. V l The volume of the liquid probe molecules injected into the container, in mL; V a The volume of the porous material sample skeleton is given in mL. P t for t The pressure above the liquid surface in the container at any given time, in kPa; P 0 represents the initial pressure in the container before liquid injection, in kPa; m represents the mass of the porous material sample to be tested, in g. T The experimental temperature is in K. T θ =273.15 K; P θ =101.3 kPa; η The liquid evaporation coefficient is used to eliminate data measurement bias caused by liquid probe evaporation, and is expressed as: ； in: P s ρ is the saturated vapor pressure at the experimental temperature, in kPa.

9. The method for determining the upper limit of adsorbate gas molecules condensation in porous materials using liquid-induced gas displacement as described in claim 8, characterized in that, Record the balanced displacement volume V e The molecular dynamics diameter of the liquid probe at ≤0.1 mL / g is r x The upper limit for the aggregation of the adsorbate gas molecules in the porous material is then determined to be... r x ±0.05 nm.

10. The method for determining the upper limit of adsorbate gas molecules condensation in porous materials using a liquid-driven gas displacement method according to claim 1, characterized in that, In S5, the replacement of the liquid probe molecule with a larger kinetic diameter specifically refers to: When replacing, select liquid probe molecules with similar kinetic diameters, and the difference in kinetic diameter between the replaced liquid probe molecule with a larger kinetic diameter and the replaced liquid probe molecule should not exceed 0.2 nm. The gas probe molecules include at least one of hydrogen, carbon dioxide, oxygen, argon, nitrogen, methane, and sulfur hexafluoride; The liquid probe molecule includes at least one of water, methanol, ethanol, isopropanol, benzene, ethyl acetate, cyclohexane, isooctane, and 1,3,5-triethylbenzene.

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