A method for characterizing the pore structure of powder porous materials by liquid absorption and gas displacement

Abstract

The present invention relates to a method for characterizing the pore structure of a powdered porous material using the liquid imbibition and gas expulsion method. This method converts the powdered porous material into particles by adding or not adding a binder without affecting its microporous structure. This solves the problem of porous powders being unable to undergo the liquid imbibition and gas expulsion process properly, thereby enabling the liquid imbibition and gas expulsion method to be used to characterize the pore structure of porous powders.

Description

Technical Field

[0001] The invention relates to a method for characterizing the pore structure of a powder porous material by using a liquid absorption and gas displacement method, and belongs to the technical field of material structure characterization. Technical Background

[0002] Porous materials, due to their large specific surface area, controllable pore structure, and adjustable pore size, are widely used in gas and liquid purification and separation, catalysis, gas storage, supercapacitors, water treatment, and air purification. The performance of porous materials is closely related to their pore structure. Accurately characterizing their structure is crucial for their development and application.

[0003] Existing pore structure characterization methods such as mercury porosimetry, gas adsorption, and electron microscopy have their own defects when applied. For example, mercury porosimetry cannot be used to characterize micropores, electron microscopy can only observe local parts of the material, and the required instruments are expensive and have high requirements for testing conditions. When the gas adsorption method obtains the adsorption isotherm of ultramicropores at low temperature, it takes a long time to reach adsorption equilibrium, making it difficult to obtain a true adsorption isotherm and unable to obtain accurate ultramicropore structure information.

[0004] Due to the limitations of existing pore structure characterization methods, there is still a need to develop some new methods to describe the pore structure of porous materials. Patent CN101354333B proposes a method for evaluating the pore structure and performance of porous materials by pre-saturating the porous material with an adsorption gas probe at room temperature and pressure, then immersing the porous material in a predetermined liquid probe, and measuring the liquid absorption and degassing rate and the equilibrium liquid absorption and degassing volume. Patent CN105203440B uses the liquid absorption and degassing principle to determine the kinetic mechanism and gas selectivity coefficient K by fitting the liquid absorption and degassing curve using an adsorption kinetic model, and then judges the micropore volume, pore size and uniformity of the pore distribution of the carbon molecular sieve, and establishes a method for evaluating the pressure swing adsorption gas separation performance of the carbon molecular sieve. Patent CN108345766B establishes a kinetic equation controlled by micropore orifice diffusion and surface adsorption based on the rate control step of the liquid absorption and degassing process. The equation parameters can be used to judge the relative size of the micropore volume and pore size of the porous material. The porous materials characterized by the above-mentioned liquid absorption and degassing methods are all granular solids. When the porous materials are small in size and in powder form, the powdered porous materials often float on the surface of the liquid probe, resulting in the inability to carry out the liquid absorption and degassing process normally. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a method for characterizing the pore structure of powder porous materials based on the principle of liquid absorption and gas displacement.

[0006] The technical solution of the present invention:

[0007] A method for characterizing the pore structure of a powder porous material based on the principle of liquid absorption and gas displacement includes the following steps:

[0008] Step 1: Powder porous material molding:

[0009] For a powder porous material without self-adhesive ability: a binder is dissolved in a solvent to obtain a binder solution; the powder porous material and the binder solution are then mixed and stirred at room temperature for 2-3 hours to obtain a mixture; the obtained mixture is dried at 110-150° C. for 0.5-1 hour to remove part of the solvent, and then formed; and finally, treated at 230-290° C. for 2-4 hours to obtain a molded body having a lateral compressive strength greater than 100 N / cm; wherein the mass ratio of the binder to the powder porous material is 11:1-20:1, and the mass ratio of the solvent to the powder porous material is 1:1-2:1;

[0010] For powder porous materials with self-adhesive ability: pressurization at room temperature or heating and pressing is used to form a molded body with a lateral compressive strength greater than 100 N / cm.

[0011] Step 2: crushing and sieving the molded body obtained in step 1 to obtain 10-40 mesh molded porous material particles.

[0012] Step 3: The formed porous material particles obtained in step 2 are treated under vacuum conditions at 150-200°C for 6-10 hours to dry and fully degas. The particles are then placed in a sample cell of a liquid aspiration and degassing device. A gas probe is adsorbed until saturated under normal pressure and constant temperature conditions. A liquid probe is then injected to perform a liquid aspiration and degassing process. The pressure value in the sample cell that changes with time is simultaneously collected to obtain a liquid aspiration and degassing curve. The pore structure information of the porous material is obtained by analyzing the liquid aspiration and degassing curve. The liquid aspiration and degassing device described is the liquid aspiration and degassing device disclosed in patent CN101354333B.

[0013] The powder porous material without self-adhesive ability includes but is not limited to activated carbon, carbon molecular sieve, carbon nanotube, metal oxide and the like.

[0014] The powder porous material with self-bonding ability includes but is not limited to lignite, mesophase carbon microspheres, zeolite molecular sieves, etc.

[0015] The binder is polyvinylidene fluoride, polytetrafluoroethylene, polyethylene glycol, polyvinyl alcohol or carboxymethyl cellulose, preferably polyvinylidene fluoride. The molecular weight of the binder is above 10,000, preferably above 1,000,000.

[0016] The solvent includes but is not limited to N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide and the like.

[0017] The molding methods include but are not limited to sheet molding, extrusion molding, pelletizing molding, etc.

[0018] The gas probes include but are not limited to oxygen, nitrogen, argon, methane, carbon dioxide, sulfur hexafluoride and the like.

[0019] The liquid probe includes but is not limited to water, methanol, ethanol, isopropanol, cyclohexane, benzene, toluene and the like.

[0020] Principle of the present invention:

[0021] The liquid absorption and gas displacement method of the present invention is a new method for characterizing the pore structure of porous materials by measuring the amount of gas discharged when the porous material is immersed in a liquid probe and the relationship between the amount of gas discharged and the change of the gas amount over time at room temperature and pressure. At room temperature and pressure, most gases are in a supercritical state, and adsorption can only occur in the micropores of the porous material. For powder porous materials, the liquid absorption and gas displacement process can be carried out normally by converting the powder into particles without affecting the micropore structure. When the powder porous material has self-adhesive ability, preparing it into particles has no effect on the micropore structure. When the powder material itself does not have adhesive properties, a binder is used to bond it into particles. The selection of the binder follows the following principles: (1) the binder does not change the basic pore structure of the powder porous material, which is mainly the micropore structure; (2) the binder does not generate micropores; (3) the binder does not react with the gas probe or the liquid probe. The present invention prefers polyvinylidene fluoride (PVDF) with a molecular weight of over one million as a binder. Its large molecular size prevents it from entering micropores. During bonding, the molecules crosslink to form micron-sized macropores, thus preventing the microporous structure from being affected during the bonding process. When the binder dosage is sufficiently low, it primarily resides on the outer surface of the powder particles, preventing it from clogging the macropores and mesopores that serve as channels. PVDF is soluble only in a few highly polar solvents and does not react with the liquid probe used in the aspiration and degassing process.

[0022] The beneficial effects of the present invention are as follows: the present invention converts powder porous materials into particles without affecting their microporous structure, thereby solving the problem that powder porous materials cannot normally undergo the liquid absorption and gas expulsion process, thereby enabling the liquid absorption and gas expulsion method to be used to characterize the pore structure of powder porous materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 These are the water absorption and nitrogen displacement curves of commercial granular fruit shell-based activated carbon and shaped fruit shell-based activated carbon particles.

[0024] Figure 2 This is the SEM image of commercial granular fruit shell-based activated carbon.

[0025] Figure 3 This is the SEM image of the formed granular activated carbon.

[0026] Figure 4 The water absorption and nitrogen displacement curves of commercial granular coconut shell-based activated carbon and shaped coconut shell-based activated carbon granules.

[0027] Figure 5 The water absorption and nitrogen displacement curves of commercial granular coal-based activated carbon and shaped coal-based activated carbon particles.

[0028] Figure 6 These are the liquid absorption and gas displacement curves of commercial granular carbon molecular sieves and shaped carbon molecular sieve particles.

[0029] Figure 7 These are the water absorption and nitrogen displacement curves of commercial granular 5A molecular sieve and formed 5A molecular sieve particles. DETAILED DESCRIPTION

[0030] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0031] Comparative Example 1

[0032] A commercial granular fruit shell-based activated carbon was crushed and sieved to obtain a 10-20 mesh particle sample. After drying and degassing at 150°C in vacuum for 6 hours, a liquid absorption and gas displacement experiment was carried out using the liquid absorption and gas displacement device disclosed in patent CN101354333B. N2 was used as the gas probe and deionized water was used as the liquid probe. The liquid absorption and gas displacement curve was measured at 303.15K as shown in the following figure: Figure 1 As shown, the equilibrium purge volume is 5.67 mL / g.

[0033] Example 1

[0034] Step 1: Grind the commercial fruit shell-based activated carbon of 10-20 mesh in Comparative Example 1 to less than 100 mesh to obtain powdered activated carbon.

[0035] Step 2: Dissolve 1g of polyvinylidene fluoride in 16.5g of N,N-dimethylacetamide to obtain a clear binder solution. Add 11g of powdered activated carbon to the binder solution, achieving an activated carbon to binder ratio of 11:1 and a N,N-dimethylacetamide to activated carbon ratio of 1.5:1. Stir for 3 hours to ensure full contact between the activated carbon and binder. After mixing thoroughly, dry at 150°C for 0.5 hours.

[0036] Step 3: The dried activated carbon is pressed into shape using a powder tablet press at a pressure of 10 MPa.

[0037] Step 4: After forming, place it in a muffle furnace and treat it at a high temperature of 230°C for 4 hours. The lateral compressive strength of the formed body is 114.17N / cm.

[0038] Step 5: The treated activated carbon was crushed into 10-20 mesh, dried and degassed under vacuum at 150°C for 6 hours, and then the liquid absorption and gas displacement experiment was carried out using the liquid absorption and gas displacement device disclosed in patent CN101354333B. N2 was used as the gas probe and deionized water was used as the liquid probe. The liquid absorption and gas displacement curve was measured at 303.15K as shown in the figure below. Figure 1 As shown, the equilibrium purge volume is 5.65 mL / g.

[0039] Example 2

[0040] Step 1: Grind the commercial fruit shell-based activated carbon of 10-20 mesh in Comparative Example 1 to less than 100 mesh to obtain powdered activated carbon.

[0041] Step 2: Dissolve 1g of polyvinylidene fluoride in 12g of N,N-dimethylacetamide to obtain a clear binder solution. Add 12g of powdered activated carbon to the binder solution, achieving a 12:1 activated carbon to binder mass ratio and a 1:1 N,N-dimethylacetamide to activated carbon mass ratio. Stir for 2 hours to ensure full contact between the activated carbon and binder. Mix thoroughly and dry at 110°C for 1 hour.

[0042] Step 3: The dried activated carbon is pressed into shape using a powder tablet press at a pressure of 10 MPa.

[0043] Step 4: After forming, place it in a muffle furnace and treat it at a high temperature of 290°C for 2 hours. The lateral compressive strength of the formed body is 105.71N / cm.

[0044] Step 5: The treated activated carbon was crushed into 10-20 mesh, dried and degassed under vacuum at 150°C for 6 hours, and then the liquid absorption and gas displacement experiment was carried out using the liquid absorption and gas displacement device disclosed in patent CN101354333B. N2 was used as the gas probe and deionized water was used as the liquid probe. The liquid absorption and gas displacement curve was measured at 303.15K as shown in the figure below. Figure 1 As shown, the equilibrium purge volume is 5.67 mL / g.

[0045] Comparative Example 2

[0046] The pore structures of the 10-20 mesh activated carbons in Example 1, Example 2, and Comparative Example 1 were characterized using 77K nitrogen adsorption method, and the micropore volumes were 0.219 cm 3 / g, 0.218cm 3 / g, 0.220cm 3 A certain amount of polyvinylidene fluoride was dissolved and then added into deionized water, resulting in the precipitation of polyvinylidene fluoride into a membrane. The polyvinylidene fluoride membrane was characterized by nitrogen adsorption at 77K, and the results showed that there were no micropores in the polyvinylidene fluoride membrane.

[0047] The results of Comparative Example 2 show that the micropore volume of the original granular activated carbon and the granular activated carbon after bonding is approximately equal, and the binder itself does not generate new micropores. Analyzing Comparative Example 1, Example 1, and Example 2, it can be concluded that the equilibrium gas displacement volume of the granular activated carbon after bonding is equal to that of the original granular activated carbon, indicating that the three have the same micropore volume. When the amount of binder used is small, the bonding process will not affect the micropore structure. This conclusion is consistent with the results of Comparative Example 2. Figure 2 and Figure 3 The SEM images show that the bonding process has no effect on the pore structure of activated carbon.

[0048] Comparative Example 3

[0049] A commercial granular coconut shell-based activated carbon was crushed and sieved to obtain a 20-30 mesh particle sample. After drying and degassing at 150°C in vacuum for 6 hours, a liquid absorption and gas displacement experiment was carried out using the liquid absorption and gas displacement device disclosed in patent CN101354333B. N2 was used as the gas probe and deionized water was used as the liquid probe. The liquid absorption and gas displacement curve was measured at 303.15K as shown in the following figure: Figure 4 As shown, the equilibrium purge volume is 5.36 mL / g.

[0050] Example 3

[0051] Step 1: Grind the 20-30 mesh commercial coconut shell-based activated carbon in Comparative Example 3 to less than 100 mesh to obtain powdered activated carbon.

[0052] Step 2: Dissolve 1g of polyvinylidene fluoride in 30g of N,N-dimethylacetamide to obtain a clear binder solution. Add 15g of powdered activated carbon to the binder solution, achieving a 15:1 activated carbon to binder mass ratio and a 2:1 N,N-dimethylacetamide to activated carbon mass ratio. Stir for 2.5 hours to ensure full contact between the activated carbon and binder. After mixing thoroughly, dry at 130°C for 0.75 hours.

[0053] Step 3: The dried activated carbon is pressed into shape using a powder tablet press at a pressure of 10 MPa.

[0054] Step 4: After forming, place it in a muffle furnace and treat it at high temperature at 260℃ for 3 hours. The lateral compressive strength of the formed body is 111.43N / cm.

[0055] Step 5: The treated activated carbon was crushed into 20-30 mesh, dried and degassed under vacuum at 150°C for 6 hours, and then the liquid absorption and gas displacement experiment was carried out using the liquid absorption and gas displacement device disclosed in patent CN101354333B. N2 was used as the gas probe and deionized water was used as the liquid probe. The liquid absorption and gas displacement curve was measured at 303.15K as shown in the figure below. Figure 4 As shown, the equilibrium purge volume is 5.35 mL / g.

[0056] Comparative Example 4

[0057] A commercial coal-based activated carbon was crushed and sieved to obtain 30-40 mesh granular activated carbon. After drying and degassing at 150°C in vacuum for 6 hours, a liquid absorption and gas displacement experiment was carried out using the liquid absorption and gas displacement device disclosed in patent CN101354333B. With N2 as the gas probe and deionized water as the liquid probe, the liquid absorption and gas displacement curve was measured at 303.15K. Figure 5 As shown, the equilibrium purge volume is 2.88 mL / g.

[0058] Example 4

[0059] Step 1: Grind the 30-40 mesh commercial coal-based activated carbon in Comparative Example 4 to less than 100 mesh to obtain powdered activated carbon.

[0060] Step 2: Dissolve 1g of polyvinylidene fluoride in 30g of N,N-dimethylacetamide to obtain a clear binder solution. Add 20g of powdered activated carbon to the binder solution, achieving a 20:1 activated carbon to binder mass ratio and a 1.5:1 N,N-dimethylacetamide to activated carbon mass ratio. Stir for 2 hours to ensure full contact between the activated carbon and binder. After mixing thoroughly, dry at 150°C for 0.5 hours.

[0061] Step 3: The dried activated carbon is pressed into shape using a powder tablet press at a pressure of 10 MPa.

[0062] Step 4: After forming, place it in a muffle furnace and treat it at a high temperature of 230°C for 4 hours. The lateral compressive strength of the formed body is 102.18N / cm.

[0063] Step 5: The treated activated carbon was crushed into 30-40 mesh, dried and degassed under vacuum at 150°C for 6 hours, and then the liquid absorption and gas displacement experiment was carried out using the liquid absorption and gas displacement device disclosed in patent CN101354333B. N2 was used as the gas probe and deionized water was used as the liquid probe. The liquid absorption and gas displacement curve was measured at 303.15K as shown in the figure below. Figure 5 As shown, the equilibrium purge volume is 2.90 mL / g.

[0064] By analyzing Example 1, Example 3 and Example 4, it can be found that the relationship between the micropore volume sizes is: fruit shell-based activated carbon > coconut shell-based activated carbon > coal-based activated carbon.

[0065] Comparative Example 5

[0066] A commercial carbon molecular sieve was crushed and sieved to obtain a 10-20 mesh particle sample. After drying and degassing at 180°C in vacuum for 7 hours, a liquid absorption and gas displacement experiment was carried out using the liquid absorption and gas displacement device disclosed in patent CN101354333B. O2 was used as the gas probe and deionized water was used as the liquid probe. The liquid absorption and gas displacement curve was measured at 303.15K as shown in the following figure: Figure 6 As shown, the equilibrium purge volume is 6.27 mL / g.

[0067] Comparative Example 6

[0068] The liquid probe in Comparative Example 5 was changed to anhydrous ethanol, and other conditions were the same as those in Comparative Example 5. The liquid absorption and gas displacement curves were measured at 303.15K. Figure 6 As shown, the equilibrium purge volume is 0.87 mL / g.

[0069] Example 5

[0070] Step 1: crush the 10-20 mesh commercial carbon molecular sieve in Comparative Example 5 to less than 100 mesh to obtain powdered carbon molecular sieve.

[0071] Step 2: Dissolve 1g of polyvinylidene fluoride in 22.5g of N-methylpyrrolidone to obtain a clear binder solution. Add 15g of powdered carbon molecular sieve to the binder solution, achieving a carbon molecular sieve to binder mass ratio of 15:1 and a N-methylpyrrolidone to carbon molecular sieve mass ratio of 1.5:1. Stir for 2h to ensure full contact between the carbon molecular sieve and binder. Mix thoroughly and dry at 150°C for 0.5h.

[0072] Step 3: The dried carbon molecular sieve is pressed into shape using a powder tablet press at a pressure of 10 MPa.

[0073] Step 4: After forming, place it in a muffle furnace and treat it at a high temperature of 230°C for 4 hours. The lateral compressive strength of the formed body is 115.88N / cm.

[0074] Step 5: The treated activated carbon was crushed into 10-20 mesh, dried and degassed under vacuum at 180°C for 7 hours, and then the liquid absorption and gas displacement experiment was carried out using the liquid absorption and gas displacement device disclosed in patent CN101354333B. O2 was used as the gas probe and anhydrous ethanol was used as the liquid probe. The liquid absorption and gas displacement curve was measured at 303.15K as shown in the figure below. Figure 6 As shown, the equilibrium purge volume is 0.88 mL / g.

[0075] The kinetic diameter of a water molecule is 0.28 nm, and the kinetic diameter of an ethanol molecule is 0.47 nm. Since liquid molecules can only enter pores larger than their molecular size, analysis of Example 5 and Comparative Example 5 shows that the pore size distribution of the micropores in the carbon molecular sieve is: mainly distributed below 0.47 nm, with only a small amount of micropores distributed above 0.47 nm.

[0076] Comparative Example 7

[0077] A commercial granular 4A molecular sieve was crushed and sieved to obtain a 10-20 mesh particle sample. After drying and degassing at 200°C in vacuum for 10 hours, a liquid aspiration and gas displacement experiment was conducted using the liquid aspiration and gas displacement device disclosed in patent CN101354333B. With N2 as the gas probe and deionized water as the liquid probe, the liquid aspiration and gas displacement curve was measured at 303.15K. Figure 7 As shown, the equilibrium purge volume is 5.74 mL / g.

[0078] Example 6

[0079] The 10-20 mesh 5A molecular sieve particles in Comparative Example 7 were crushed to less than 100 mesh to obtain powdered 5A molecular sieve. The powdered 5A molecular sieve was pressed into a mold under a pressure of 10 MPa using a powder tablet press. The molded body had a lateral compressive strength of 123.21 N / cm. The molded body was then crushed into 10-20 mesh, dried and degassed under vacuum at 200°C for 10 hours, and then a liquid absorption and gas displacement experiment was conducted using the liquid absorption and gas displacement device disclosed in patent CN101354333B. N2 was used as the gas probe and deionized water was used as the liquid probe. The liquid absorption and gas displacement curve was measured at 303.15K as shown in FIG. Figure 7 As shown, the equilibrium purge volume is 5.72 mL / g.

Claims

1. A method for characterizing the pore structure of powder porous materials based on the principle of liquid absorption and gas displacement, characterized in that: The steps include: Step 1: Powder porous material molding: For a powder porous material without self-adhesive ability: a binder is dissolved in a solvent to obtain a binder solution; the powder porous material and the binder solution are then mixed and stirred at room temperature for 2-3 hours to obtain a mixture; the obtained mixture is dried at 110-150°C for 0.5-1 hour to remove part of the solvent, and then formed; and finally, treated at 230-290°C for 2-4 hours to obtain a formed body having a lateral compressive strength greater than 100 N / cm; The mass ratio of the binder to the powder porous material is 11:1-20:1, and the mass ratio of the solvent to the powder porous material is 1:1-2:1; For powder porous materials with self-adhesive ability: use normal temperature pressurization or heated pressurization to form a molded body with a lateral compressive strength greater than 100N / cm; Step 2: crushing and sieving the molded body obtained in step 1 to obtain 10-40 mesh molded porous material particles; Step 3: The formed porous material particles obtained in step 2 are treated under vacuum conditions at 150-200°C for 6-10 hours to dry and fully degas, and then placed in a sample cell of a liquid aspiration and degassing device. The gas probe is adsorbed to saturation under normal pressure and constant temperature conditions, and then a liquid probe is injected to perform a liquid aspiration and degassing process. At the same time, the pressure value in the sample cell that changes with time is collected to obtain a liquid aspiration and degassing curve, and the pore structure information of the porous material is obtained by analyzing the liquid aspiration and degassing curve; The selection of the binder follows the following principles: the binder does not change the basic pore structure of the powder porous material, that is, the microporous structure; the binder does not generate micropores; the binder does not react with the gas probe or the liquid probe.

2. The method for characterizing the pore structure of powder porous materials based on the principle of liquid absorption and gas displacement according to claim 1, characterized in that: The powder porous material without self-adhesive ability is activated carbon, carbon molecular sieve, carbon nanotube or metal oxide; the powder porous material with self-adhesive ability is lignite, mesophase carbon microspheres or zeolite molecular sieve.

3. A method for characterizing the pore structure of powder porous materials based on the principle of liquid absorption and gas displacement according to claim 1 or 2, characterized in that: The binder is polyvinylidene fluoride, polytetrafluoroethylene, polyethylene glycol, polyvinyl alcohol or carboxymethyl cellulose, and the molecular weight of the binder is above 10,000.

4. The method for characterizing the pore structure of powder porous materials based on the principle of liquid absorption and gas displacement according to claim 3, characterized in that: The molecular weight of the binder is above 1 million.

5. The method for characterizing the pore structure of powder porous materials based on the principle of liquid absorption and gas displacement according to claim 1, 2 or 4, characterized in that: The solvent is N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide.

6. A method for characterizing the pore structure of a powder porous material based on the principle of liquid absorption and gas displacement according to claim 1, 2 or 4, characterized in that: The molding method is tablet molding, extrusion molding or pelletizing molding.

7. A method for characterizing the pore structure of a powder porous material based on the principle of liquid absorption and gas displacement according to claim 1, 2 or 4, characterized in that: The gas probe is oxygen, nitrogen, argon, methane, carbon dioxide or sulfur hexafluoride.

8. The method for characterizing the pore structure of powder porous materials based on the principle of liquid absorption and gas displacement according to claim 1, 2 or 4, characterized in that: The liquid probe is water, methanol, ethanol, isopropanol, cyclohexane, benzene or toluene.

Images