Amphiphilic composite foam material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of foam composite materials and application thereof in natural gas hydrates, and particularly relates to an amphiphilic composite foam material and a preparation method and application thereof. The preparation method of the amphiphilic composite foam material comprises the following steps: taking a precursor solution of polyimide and polytetrafluoroethylene as raw materials, foaming through an isocyanate method to obtain a polytetrafluoroethylene / polyimide foam material, and then carrying out alkali etching on the polytetrafluoroethylene / polyimide foam material to obtain the amphiphilic block type composite foam material. The preparation method of the amphiphilic composite foam material is low in raw material cost, simple in process, reliable in principle, high in recyclability and friendly to preparation environment, and the prepared foam material is stable in structure. The invention further provides application of the amphiphilic composite foam material in storage of the natural gas hydrate, and the amphiphilic structure distributed in a block mode can synergistically promote efficient and rapid generation of the natural gas hydrate.

Description

Technical Field

[0001] The invention belongs to the technical field of foam composite materials and their application in natural gas hydrates, and in particular relates to an amphiphilic composite foam material and a preparation method and application thereof. Background Art

[0002] As a clean energy, natural gas occupies an important position in the energy structure. However, the efficiency and safety issues in its storage and transportation have always been the key factors restricting its widespread application. Hydrate solid natural gas technology has attracted widespread attention in the field of natural gas storage and transportation due to its mild storage conditions, and is regarded as a strong candidate for the next generation of natural gas storage technology. Nevertheless, the slow characteristics of hydrate nucleation and growth kinetics and the relatively low gas storage capacity still limit the further application of this technology.

[0003] In the prior art, fixed beds have been widely studied for their large specific surface area and rich pores to enhance the nucleation and growth rate of hydrates. In particular, fixed bed materials such as metal foams, inorganic foams, organic foams, gels, and particle stacks have been shown to significantly improve the nucleation efficiency and growth rate of hydrates. There are currently two mainstream fixed bed material studies. On the one hand, the hydrophilic groups on the hydrophilic surface can promote the formation of hydrogen bond structures by water molecules to capture more methane molecules; on the other hand, the hydrophobic surface enhances hydrate nucleation by enhancing gas adsorption and promoting gas-liquid contact. However, the performance of hydrophilic and hydrophobic materials in hydrate formation is still relatively low. For polyimide foams with hydrophobic surfaces, hydrophilic -OH groups are generated on their surfaces by alkaline etching, thereby enhancing their interaction with water molecules. However, the improvement of the hydrate performance of polyimide foams is very limited only by hydrophilic surface modification.

[0004] Patent CN115873405A proposes a method for preparing an expanded graphite / polyimide foam material and its application. The multi-level pore structure effectively improves the mass transfer and heat transfer problems in the hydrate formation process, thereby increasing the formation rate of natural gas hydrates. However, the surface of the expanded graphite / polyimide foam system constructed is a hydrophobic surface, and its promoting effect in hydrate formation needs to be further improved. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the above-mentioned defects in the prior art and provide a method for preparing an amphiphilic composite foam material, which has low cost, simple process, reliable principle, high recyclability and environmentally friendly preparation.

[0006] The invention also provides a modified polytetrafluoroethylene / polyimide foam material, which has a hydrophilic and hydrophobic block structure and a stable structure and can be recycled for multiple times during the hydrate generation process.

[0007] The invention also provides the use of modified polytetrafluoroethylene / polyimide foam material in the storage of natural gas hydrates. The natural gas hydrates are formed quickly and have a high gas storage capacity.

[0008] The preparation method of the amphiphilic composite foam material of the present invention is as follows: the polytetrafluoroethylene / polyimide foam material is subjected to alkaline etching by vacuum extraction method, and the specific alkaline etching steps are as follows: the polytetrafluoroethylene / polyimide foam material is placed in a strong alkaline solution and soaked for 15-90 minutes, taken out for cleaning and drying, and the amphiphilic composite foam material is obtained. The cleaning is firstly performed by using clean water and ethanol for three times respectively. The drying temperature is 70°C and the drying time is 2-3 hours.

[0009] The strong base is one of sodium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide; the concentration of the strong base solution is 1.5-2.5 mol / L.

[0010] The method for preparing the polytetrafluoroethylene / polyimide foam material comprises the following steps:

[0011] 1) dissolving a polybasic aromatic anhydride in a polar solvent, adding an alcohol, heating and stirring, performing an esterification reaction, obtaining a carboxylate solution, cooling naturally to room temperature, obtaining a polyimide precursor solution, adding polytetrafluoroethylene particles and water to the polyimide precursor solution, mixing and stirring, obtaining a solution A; the alcohol is methanol;

[0012] 2) polyethylene glycol, water-soluble silicone oil, dibutyltin dilaurate, triethanolamine and isocyanate are mixed, and the mixture is stirred after ultrasonic treatment to obtain solution B;

[0013] 3) Solution A and Solution B are mixed and stirred, poured into a mold for foaming, and cured at high temperature to obtain a polytetrafluoroethylene / polyimide foam material.

[0014] Step 1) The mass ratio of the polyimide precursor solution to the polytetrafluoroethylene particles is (10:1)-(10:3); the mass ratio of the polyimide precursor solution to water is 5:2, and the water is deionized water.

[0015] Step 2) The raw materials of the solution are added according to the following weight proportions: 40-50 parts of polyethylene glycol, 40-50 parts of water-soluble silicone oil, 1-5 parts of dibutyltin dilaurate, 10-20 parts of triethanolamine, and 280-300 parts of isocyanate.

[0016] Step 3) The mass ratio of solution A to solution B is (2:1)-(3:1), the high temperature curing temperature is 160-200°C, and the curing time is 2-4h.

[0017] The polyvalent aromatic anhydride in step 1) is one of pyromellitic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride, and 3,3',4,4'-biphenyl tetracarboxylic anhydride; the polar solvent is N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide. The mass ratio of the solvent to 3,3',4,4'-benzophenone tetracarboxylic anhydride is 4:3-5:3; the molar ratio of 3,3',4,4'-benzophenone tetracarboxylic anhydride to alcohol is 1:2-1.2:2; the esterification reaction temperature is 60-70°C, and the esterification reaction time is 2-3h.

[0018] An amphiphilic composite foam material is prepared by the preparation method of the amphiphilic composite foam material, wherein the mass ratio of polytetrafluoroethylene to polyimide in the amphiphilic composite foam material is (1:2)-(3:2).

[0019] The application of the amphiphilic composite foam material, using the modified amphiphilic composite foam material for the rapid formation of natural gas hydrate, comprises the following steps:

[0020] 1) using a vacuum pumping method to replace the gas in the modified polytetrafluoroethylene / polyimide foam material with water, and controlling the water content of the modified polytetrafluoroethylene / polyimide foam material to 50%-75% by weighing and extrusion;

[0021] 2) placing the water-absorbed modified polytetrafluoroethylene / polyimide foam material into a high-pressure methane reactor, sealing it and placing it in a low-temperature constant temperature bath;

[0022] 3) When the temperature is constant at 0°C ± 0.2°C, open the methane cylinder to inflate the high-pressure reactor. After completion, close the methane cylinder, the hydrate reaction begins, and natural gas hydrate is generated.

[0023] Specifically, the application of the amphiphilic composite foam material comprises the following steps:

[0024] 1) dissolving a polybasic aromatic anhydride in a polar solvent, adding alcohols thereto, heating and stirring, performing an esterification reaction to obtain a carboxylate solution, cooling the solution naturally to room temperature to obtain a polyimide precursor solution, adding polytetrafluoroethylene particles and deionized water to the polyimide precursor solution, mixing and stirring to obtain a polytetrafluoroethylene / polyimide precursor solution (solution A);

[0025] 2) polyethylene glycol, water-soluble silicone oil, dibutyltin dilaurate, triethanolamine and isocyanate are mixed, and the mixture is stirred after ultrasonic treatment to obtain solution B;

[0026] 3) Solution A and solution B are mixed, stirred, poured into a mold for foaming, and then cured at high temperature to obtain a polytetrafluoroethylene / polyimide foam material.

[0027] 4) The polytetrafluoroethylene / polyimide foam material is subjected to alkaline etching, the polytetrafluoroethylene / polyimide foam material is immersed in a strong alkaline solution (sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide) by vacuum extraction, taken out, cleaned, and dried to obtain an amphiphilic composite foam material.

[0028] The application of the amphiphilic composite foam material: using the amphiphilic composite foam material for the rapid formation of natural gas hydrates specifically comprises the following steps:

[0029] 1) The amphiphilic composite foam material is subjected to vacuum evacuation, the gas in the foam is replaced with water, and the water content of the modified polytetrafluoroethylene / polyimide foam material is measured by weighing and extrusion;

[0030] 2) placing the water-absorbed amphiphilic composite foam material into a high-pressure methane reactor with a pressure range of 0-15 MPa, sealing it and placing it in a low-temperature thermostatic bath (TMS8028);

[0031] 3) When the temperature is constant at 0°C ± 0.2°C, open the methane cylinder to inflate the high-pressure reactor. After completion, close the methane cylinder, the hydrate reaction begins, and natural gas hydrate is generated.

[0032] The preparation method of the amphiphilic composite foam material of the present invention comprises compounding polytetrafluoroethylene particles with polyimide foam and performing alkaline etching treatment. On the one hand, the polytetrafluoroethylene / polyimide foam material is prepared by introducing polytetrafluoroethylene particles, and the amount of polytetrafluoroethylene particles is controlled to adjust the surface hydrophobicity of the polytetrafluoroethylene / polyimide foam material; on the other hand, the skeleton of the polytetrafluoroethylene / polyimide foam material is treated with alkaline by using a NaOH solution, and the etching time of the NaOH solution is controlled to adjust the surface hydrophilicity of the polytetrafluoroethylene / polyimide foam material. The present invention combines the introduction of polytetrafluoroethylene particles with the surface alkaline etching method to jointly construct the amphiphilic composite foam material.

[0033] The polyimide foam skeleton of the present invention is alkali-etched and hydrolyzed to expose the polytetrafluoroethylene material, and the surface hydrophilic and hydrophobic block structure is realized on the surface of the polyimide foam. The hydrolysis degree of the polyimide foam is regulated by the etching time, and the hydrophilicity and hydrophobicity of the foam surface are controlled. The different promotion mechanisms of the amphiphilic materials on hydrates are combined to solve the problems of slow nucleation and low gas storage capacity in the hydrate reaction process.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The modified polytetrafluoroethylene / polyimide foam material prepared by the method of the present invention is an amphiphilic composite foam material, wherein: the hydrophobic segment can provide a gas transmission channel, promote gas-liquid contact, provide more reaction sites to strengthen the nucleation of hydrates, and shorten the induction time of the reaction; the hydrophilic segment allows more hydrate cages to be formed inside the fixed bed, captures more methane molecules, and increases the gas storage capacity; the synergistic effect of the hydrophilic and hydrophobic surfaces promotes the efficient generation of natural gas hydrates.

[0036] (2) The amphiphilic composite foam material of the present invention has a stable structure and can be recycled multiple times during the hydrate formation process.

[0037] (3) The amphiphilic composite foam material prepared by the present invention is used for the rapid formation of natural gas hydrates, which has low cost, simple process, reliable principle, high recyclability, and environmentally friendly preparation, providing a feasible solution for the rapid formation of natural gas hydrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the SEM image of the amphiphilic composite foam material prepared in Example 1.

[0039] Figure 2 This is the SEM image of the amphiphilic composite foam material prepared in Example 2.

[0040] Figure 3 This is the SEM image of the amphiphilic composite foam material prepared in Example 3.

[0041] Figure 4 The reaction equation of the polytetrafluoroethylene / polyimide foam material prepared by the present invention after being etched with sodium hydroxide, a is the first step of hydrolysis, and b is the second step of hydrolysis.

[0042] Figure 5 FTIR graphs of the foam materials prepared in Example 1 and Comparative Example 1.

[0043] Figure 6 Schematic diagram of the performance curves of the amphiphilic composite foam materials prepared in Example 1, Example 2, and Example 3 during the hydrate formation process.

[0044] Figure 7 The amphiphilic composite foam material prepared in Example 4 was recycled three times under the same conditions, which is a schematic diagram of the cyclic performance curve during the hydrate formation process.

[0045] Figure 8 Schematic diagram of the performance curves of the foam materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 during the hydrate formation process.

[0046] Fig. 9Schematic diagram of the performance curves of the foam materials prepared in Example 1 and Comparative Example 3 during the hydrate formation process.

[0047] Fig.10 Schematic diagram of the amphiphilic composite foam material prepared in Example 1. DETAILED DESCRIPTION

[0048] The present invention will be further described below in conjunction with specific embodiments.

[0049] The raw materials and reagents used in the following examples and comparative examples are all commercially available products. The particle size of the polytetrafluoroethylene particles is 1 μm-5 μm. The content is the mass content, and the weight parts are all in the same unit of mass.

[0050] Example 1

[0051] The amphiphilic composite foam material prepared in this embodiment has a mass ratio of polytetrafluoroethylene to polyimide of 2:1, and an etching time of 60 min using a 2 mol / L NaOH solution. The preparation method thereof comprises the following steps:

[0052] 1) Dissolve 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride in N,N-dimethylformamide, add methanol thereto, heat and stir, carry out esterification reaction at 60°C for 2h to obtain a carboxylate ester solution, and cool naturally to room temperature to obtain a polyimide foam material precursor solution. The mass ratio of N,N-dimethylformamide to 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride is 5:3, and the molar ratio of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride to alcohol is 1:2.

[0053] Add polytetrafluoroethylene particles and deionized water to the polyimide precursor solution, mix and stir to obtain a polytetrafluoroethylene / polyimide precursor solution (solution A), wherein the mass ratio of the polyimide precursor solution to polytetrafluoroethylene is 10:2, and the mass ratio of the polyimide precursor solution to deionized water is 5:2.

[0054] Polyethylene glycol, water-soluble silicone oil, dibutyltin dilaurate, triethanolamine and isocyanate are mixed, and stirred after ultrasonic treatment to obtain solution B; the weight proportions of the components in solution B are: 40 parts of polyethylene glycol, 40 parts of water-soluble silicone oil, 1 part of dibutyltin dilaurate, 10 parts of triethanolamine, and 280 parts of isocyanate.

[0055] 2) Solution A and solution B were mixed in a mass ratio of 2:1, poured into a mold for foaming, and then high-temperature cured at 180° C. for 3 h to obtain a polytetrafluoroethylene / polyimide foam material.

[0056] 3) The foam was immersed in a NaOH solution by vacuum extraction for 60 min, the foam was taken out and washed three times with water and ethanol respectively, and dried at 70°C for 2 h to obtain an amphiphilic composite foam material, the SEM image of which is shown in FIG. Figure 1 As shown, the FTIR diagram is Figure 5 shown.

[0057] Example 2

[0058] The amphiphilic composite foam material prepared in this embodiment has a mass ratio of polytetrafluoroethylene to polyimide of 1:1, and an etching time of 15 min using a 1.5 mol / L NaOH solution. The preparation method thereof comprises the following steps:

[0059] 1) 3,3',4,4'-benzophenone tetracarboxylic dianhydride was dissolved in N,N-dimethylformamide, methanol was added thereto, the temperature was raised and stirred, and an esterification reaction was carried out at 60°C for 2 hours to obtain a carboxylate ester solution, which was naturally cooled to room temperature to obtain a solution A. The mass ratio of N,N-dimethylformamide to 3,3',4,4'-benzophenone tetracarboxylic dianhydride was 5:3, and the molar ratio of 3,3',4,4'-benzophenone tetracarboxylic dianhydride to alcohol was 1:2.

[0060] Add polytetrafluoroethylene particles and deionized water to the polyimide precursor solution, mix and stir to obtain a polytetrafluoroethylene / polyimide precursor solution (solution A), wherein the mass ratio of the polyimide precursor solution to polytetrafluoroethylene is 10:1, and the mass ratio of the polyimide precursor solution to deionized water is 5:2.

[0061] Polyethylene glycol, water-soluble silicone oil, dibutyltin dilaurate, triethanolamine and isocyanate are mixed, and stirred after ultrasonic treatment to obtain solution B; the weight proportions of the components in solution B are: 50 parts of polyethylene glycol, 50 parts of water-soluble silicone oil, 5 parts of dibutyltin dilaurate, 20 parts of triethanolamine, and 300 parts of isocyanate.

[0062] 2) Solution A and solution B were mixed in a mass ratio of 2:1, poured into a mold for foaming, and then high-temperature cured at 180° C. for 3 h to obtain a polytetrafluoroethylene / polyimide foam material.

[0063] 3) The foam was immersed in a NaOH solution by vacuum extraction for 15 min, the foam was taken out and washed three times with water and ethanol respectively, and dried at 70°C for 2.5 h to obtain an amphiphilic composite foam material, the SEM image of which is shown in FIG. Figure 2 shown.

[0064] Example 3

[0065] The amphiphilic composite foam material prepared in this embodiment has a mass ratio of polytetrafluoroethylene to polyimide of 2:3, and an etching time of 90 min using a 2.0 mol / L NaOH solution. The preparation method thereof comprises the following steps:

[0066] 1) 3,3',4,4'-benzophenone tetracarboxylic dianhydride was dissolved in N,N-dimethylformamide, methanol was added thereto, the temperature was raised and stirred, and an esterification reaction was carried out at 60°C for 2 hours to obtain a carboxylate ester solution, which was naturally cooled to room temperature to obtain a solution A. The mass ratio of N,N-dimethylformamide to 3,3',4,4'-benzophenone tetracarboxylic dianhydride was 5:3, and the molar ratio of 3,3',4,4'-benzophenone tetracarboxylic dianhydride to alcohol was 1:2.

[0067] Add polytetrafluoroethylene particles and deionized water to the polyimide precursor solution, mix and stir to obtain a polytetrafluoroethylene / polyimide precursor solution (solution A), wherein the mass ratio of the polyimide precursor solution to polytetrafluoroethylene is 10:3, and the mass ratio of the polyimide precursor solution to deionized water is 5:2.

[0068] Polyethylene glycol, water-soluble silicone oil, dibutyltin dilaurate, triethanolamine and isocyanate are mixed, and stirred after ultrasonic treatment to obtain solution B; the weight proportions of the components in solution B are: 45 parts of polyethylene glycol, 45 parts of water-soluble silicone oil, 3 parts of dibutyltin dilaurate, 15 parts of triethanolamine, and 290 parts of isocyanate.

[0069] 2) Solution A and solution B were mixed in a mass ratio of 2:1, poured into a mold for foaming, and then high-temperature cured at 180° C. for 3 h to obtain a polytetrafluoroethylene / polyimide foam material.

[0070] 3) The foam was immersed in a NaOH solution by vacuum extraction for 90 min, the polytetrafluoroethylene / polyimide foam was taken out and washed with water and ethanol three times respectively, and dried at 70°C for 3 h to obtain an amphiphilic composite foam material, the SEM image of which is shown in FIG. Figure 3 shown.

[0071] Comparative Example 1

[0072] This comparative example uses a polyimide foam material, and its preparation method is the same as step 1) and step 2) of Example 1, specifically comprising the following steps:

[0073] 1) 3,3',4,4'-benzophenone tetracarboxylic dianhydride was dissolved in N,N-dimethylformamide, methanol was added thereto, the temperature was raised and stirred, and an esterification reaction was carried out at 60°C for 2 hours to obtain a carboxylate ester solution, which was naturally cooled to room temperature to obtain a solution A. The mass ratio of N,N-dimethylformamide to 3,3',4,4'-benzophenone tetracarboxylic dianhydride was 5:3, and the molar ratio of 3,3',4,4'-benzophenone tetracarboxylic dianhydride to alcohol was 1:2.

[0074] Deionized water was added to the polyimide precursor solution, and the mixture was mixed and stirred to obtain a polyimide precursor solution (solution A), wherein the mass ratio of the polyimide precursor solution to the deionized water was 5:2.

[0075] Polyethylene glycol, water-soluble silicone oil, dibutyltin dilaurate, triethanolamine and isocyanate are mixed, and stirred after ultrasonic treatment to obtain solution B; the weight proportions of the components in solution B are: 40 parts of polyethylene glycol, 40 parts of water-soluble silicone oil, 1 part of dibutyltin dilaurate, 10 parts of triethanolamine, and 280 parts of isocyanate.

[0076] 2) Solution A and solution B were mixed in a mass ratio of 2:1, poured into a mold for foaming, and then cured at 180°C for 3 hours to obtain a polyimide foam material. The FTIR image is as follows: Figure 5 shown.

[0077] Comparative Example 2

[0078] This comparative example uses polytetrafluoroethylene particles (PTFE), which are washed with deionized water and dried for later use.

[0079] Comparative Example 3

[0080] This comparative example uses a hydrophilic polyimide foam material, and its preparation method is the same as step 1) and step 2) of Example 1, and the etching time of 2 mol / L NaOH solution is 60 min, specifically comprising the following steps:

[0081] 1) 3,3',4,4'-benzophenone tetracarboxylic dianhydride was dissolved in N,N-dimethylformamide, methanol was added thereto, the temperature was raised and stirred, and an esterification reaction was carried out at 60°C for 2 hours to obtain a carboxylate ester solution, which was naturally cooled to room temperature to obtain a solution A. The mass ratio of N,N-dimethylformamide to 3,3',4,4'-benzophenone tetracarboxylic dianhydride was 5:3, and the molar ratio of 3,3',4,4'-benzophenone tetracarboxylic dianhydride to alcohol was 1:2.

[0082] Deionized water was added to the polyimide precursor solution, and the mixture was mixed and stirred to obtain a polyimide precursor solution (solution A), wherein the mass ratio of the polyimide precursor solution to the deionized water was 5:2.

[0083] Polyethylene glycol, water-soluble silicone oil, dibutyltin dilaurate, triethanolamine and isocyanate are mixed, and stirred after ultrasonic treatment to obtain solution B; the weight proportions of the components in solution B are: 40 parts of polyethylene glycol, 40 parts of water-soluble silicone oil, 1 part of dibutyltin dilaurate, 10 parts of triethanolamine, and 280 parts of isocyanate.

[0084] 2) Solution A and solution B were mixed in a mass ratio of 2:1, poured into a mold for foaming, and then high-temperature cured at 180° C. for 3 h to obtain a polyimide foam material.

[0085] 3) The foam was immersed in a NaOH solution by vacuum extraction for 60 minutes, the foam was washed three times with water and ethanol respectively, and dried at 70° C. for 3 hours to obtain a hydrophilic polyimide foam composite material.

[0086] test:

[0087] The materials of the above-mentioned embodiment and comparative example are used for the rapid formation of natural gas hydrates, and the steps are as follows:

[0088] 1) The material to be tested is subjected to vacuum evacuation method, the gas inside the fixed bed is replaced with water, the material absorbs water until saturated, and the water content is controlled at 50-75% by weighing and extrusion method;

[0089] 2) Place the material into a stainless steel high-pressure reactor, seal it and place it in a low-temperature constant temperature bath;

[0090] 3) When the temperature is constant at 0°C ± 0.2°C, open the methane cylinder to inflate the high-pressure reactor. After completion, close the methane cylinder, the hydrate reaction begins, and natural gas hydrate is generated.

[0091] Among them, the gas storage multiple of methane hydrate is defined as the volume of methane stored per unit volume of hydrate under standard conditions. The calculation formula for the gas storage multiple of methane hydrate at time t is:

[0092]

[0093] Where P0, V0, and T0 are the pressure, gas volume, and temperature at the initial moment, respectively. t 、T t are the pressure and temperature at any time of the reaction; N represents the amount of methane consumed at time t; N0 is the amount of methane at time 0; V mg is the molar volume of the gas; V w is the initial volume of the reaction solution, V mw is the molar volume of the reaction solution. R is the universal gas constant; Z is the compressibility factor; ΔV is the difference in molar volumes between water and methane hydrate, which is equal to 4.6 cm 3 / mol. The experimental data are shown in Table 1.

[0094] Example 4

[0095] In addition, the sample prepared in Example 1 was used to carry out the hydrate experiment in the above test. After each experiment, the equipment was disassembled, the sample was taken out, washed with deionized water three times, and dried in a constant temperature oven. Then, the material was subjected to three natural gas hydrate formation experiments, which were marked as Example 4-1, Example 4-2, and Example 4-3 respectively.

[0096] Example 5

[0097] The amphiphilic composite foam material prepared in this embodiment has a mass ratio of polytetrafluoroethylene to polyimide of 2:1, and an etching time of 60 min using a 2.0 mol / L KOH solution. The preparation method thereof comprises the following steps:

[0098] 1) Dissolve 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride in N,N-dimethylformamide, add methanol thereto, heat and stir, carry out esterification reaction at 60°C for 2h to obtain a carboxylate ester solution, and cool naturally to room temperature to obtain a polyimide foam material precursor solution. The mass ratio of N,N-dimethylformamide to 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride is 5:3, and the molar ratio of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride to alcohol is 1:2.

[0099] Add polytetrafluoroethylene particles and deionized water to the polyimide precursor solution, mix and stir to obtain a polytetrafluoroethylene / polyimide precursor solution (solution A), wherein the mass ratio of the polyimide precursor solution to polytetrafluoroethylene is 10:2, and the mass ratio of the polyimide precursor solution to deionized water is 5:2.

[0100] Polyethylene glycol, water-soluble silicone oil, dibutyltin dilaurate, triethanolamine and isocyanate are mixed, and stirred after ultrasonic treatment to obtain solution B; the weight proportions of the components in solution B are: 40 parts of polyethylene glycol, 40 parts of water-soluble silicone oil, 1 part of dibutyltin dilaurate, 10 parts of triethanolamine, and 280 parts of isocyanate.

[0101] 2) Solution A and solution B were mixed in a mass ratio of 2:1, poured into a mold for foaming, and then high-temperature cured at 180° C. for 3 h to obtain a polytetrafluoroethylene / polyimide foam material.

[0102] 3) The foam was immersed in a KOH solution by vacuum extraction for 60 minutes, the foam was taken out and washed three times with clean water and ethanol respectively, and dried at 70° C. for 2 hours to obtain an amphiphilic composite foam material.

[0103] Table 1 Natural gas hydrate formation test data

[0104] project Reaction status Induction time (min) Gas storage multiple (V / V) Example 1 reaction 0 149 Example 2 reaction 0 127 Example 3 reaction 30 119 Example 4-1 reaction 0 149 Example 4-2 reaction 0 147 Example 4-3 reaction 0 145 Example 5 reaction 26 137 Comparative Example 1 reaction - 20 Comparative Example 2 No reaction - - Comparative Example 3 reaction 300 147

[0105] Figure 1 The results show that the amphiphilic composite foam material has a micron-pore structure formed by a polyimide skeleton, which is the main structure of the fixed bed. Figure 2 and Figure 3 It shows that the polyimide skeleton of the foam material is uniformly loaded with polytetrafluoroethylene particles. After being etched with NaOH solution, the surface roughness of the foam material increases, and a large number of polytetrafluoroethylene particles are exposed on the polyimide skeleton, forming a surface hydrophilic and hydrophobic block fixed bed. Figure 6 As shown, it is demonstrated that the hydrate of the amphiphilic material prepared by the present invention has strong storage performance.

[0106] Figure 4 This is the mechanism of alkaline etching reaction. Taking sodium hydroxide as an example, it reacts with amide groups to hydrolyze. In the first step, the amide groups are hydrolyzed into -COOH and -NH- (such as Figure 4 a), then the second step - COOH and Na + The reaction generates -COONa (such as Figure 4 b) Alkali treatment can increase a large number of carbon-oxygen functional groups on the surface of the polyimide foam, thereby improving the hydrophilic properties of the polyimide foam surface.

[0107] Figure 5 It shows that the polyimide skeleton has a very obvious characteristic peak at 1780cm -1 (C=O asymmetric stretch), 1720cm -1 (C=O symmetrical stretch), 1370cm -1 (CN stretch) and 720cm -1 (C=O bend). 1780cm of polyimide after acid-base treatment -1 、1720cm -1 The characteristic peak gradually weakened, 1370cm -1 The characteristic peak gradually shifted to 1418 cm -1 (The vibration of -OH and -C=O in the carboxyl group is formed), indicating that the polyimide structure is converted into an amino acid structure after alkali treatment.

[0108] Depend on Figure 8 As can be seen from the data in Table 1, Comparative Example 1 uses only polyimide foam material, and the gas storage multiple is 20V / V, and Comparative Example 2 uses only polytetrafluoroethylene particles, and no natural gas hydrate is generated; while the amphiphilic composite foam materials in Examples 1 to 3 of the present invention can effectively promote the formation of hydrates, and the gas storage multiple is as high as 119-149V / V.

[0109] like Fig. 9As shown, compared with Example 3, the introduction of the hydrophobic segment (polytetrafluoroethylene particles) in Example 1 of the present invention has a significant effect on the formation of hydrates. In particular, when the mass ratio of polytetrafluoroethylene: polyimide in the composite foam material prepared by the present invention is 2:1, excellent hydrated gas storage performance can be achieved. The reason is that the hydrophobic segment material is not introduced in Comparative Example 3, resulting in weak gas-liquid contact ability inside the fixed bed, fewer nucleation sites, and prolonged induction time of the reaction. Compared with Example 1, the introduction of the hydrophobic segment material strengthens the nucleation process inside the fixed bed, and the hydrate performance is significantly improved.

[0110] From the data of Examples 4-1, 4-2 and 4-3, it can be seen that the hydration gas storage multiple of the amphiphilic composite foam material prepared by the present invention is maintained within a reasonable range of 145-149 V / V after multiple cycles of use. Figure 7 and Fig.10 The final product of the present invention is shown to be porous and highly tough sponge-like, indicating that the composite material has excellent recyclability.

Claims

1. A method for preparing an amphiphilic composite foam material, characterized in that: The polytetrafluoroethylene / polyimide foam material is subjected to alkaline etching by a vacuum extraction method. The specific alkaline etching steps are: the polytetrafluoroethylene / polyimide foam material is immersed in a strong alkaline solution for 15-90 minutes, taken out for cleaning and drying to obtain an amphiphilic composite foam material.

2. The method for preparing the amphiphilic composite foam material according to claim 1, characterized in that: The strong base is one of sodium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide; the concentration of the strong base solution is 1.5-2.5 mol / L.

3. The method for preparing the amphiphilic composite foam material according to claim 1, characterized in that: The method for preparing the polytetrafluoroethylene / polyimide foam material comprises the following steps: 1) dissolving a polybasic aromatic anhydride in a polar solvent, adding alcohols, heating and stirring, performing an esterification reaction, obtaining a carboxylate solution, cooling naturally to room temperature, obtaining a polyimide precursor solution, adding polytetrafluoroethylene particles and water to the polyimide precursor solution, mixing and stirring, obtaining a solution A; 2) polyethylene glycol, water-soluble silicone oil, dibutyltin dilaurate, triethanolamine and isocyanate are mixed, and the mixture is stirred after ultrasonic treatment to obtain solution B; 3) Solution A and Solution B are mixed and stirred, poured into a mold for foaming, and cured at high temperature to obtain a polytetrafluoroethylene / polyimide foam material.

4. The method for preparing the amphiphilic composite foam material according to claim 3, characterized in that: Step 1) The mass ratio of the polyimide precursor solution to the polytetrafluoroethylene particles is (10:1)-(10:3); the mass ratio of the polyimide precursor solution to water is 5:

2.

5. The method for preparing the amphiphilic composite foam material according to claim 3, characterized in that: Step 2) The raw materials of the solution are added according to the following weight proportions: 40-50 parts of polyethylene glycol, 40-50 parts of water-soluble silicone oil, 1-5 parts of dibutyltin dilaurate, 10-20 parts of triethanolamine, and 280-300 parts of isocyanate.

6. The method for preparing the amphiphilic composite foam material according to claim 3, characterized in that: Step 3) The mass ratio of solution A to solution B is (2:1)-(3:1), the high temperature curing temperature is 160-200°C, and the curing time is 2-4h.

7. The method for preparing the amphiphilic composite foam material according to claim 3, characterized in that: The polybasic aromatic anhydride in step 1) is one of pyromellitic dianhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride and 3,3′,4,4′-biphenyl tetracarboxylic dianhydride; the polar solvent is N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide.

8. A biphilic composite foam material, characterized in that: The amphiphilic composite foam material is prepared by the preparation method of the amphiphilic composite foam material according to any one of claims 1 to 7, wherein the mass ratio of polytetrafluoroethylene to polyimide in the amphiphilic composite foam material is (1:2)-(3:2).

9. An application of the amphiphilic composite foam material according to claim 8, characterized in that: Modified amphiphilic syntactic foams were used for the formation of natural gas hydrates.

10. The use of the amphiphilic composite foam material according to claim 9, characterized in that: The following steps are involved: 1) using a vacuum pumping method to replace the gas in the modified polytetrafluoroethylene / polyimide foam material with water, and controlling the water content of the modified polytetrafluoroethylene / polyimide foam material to 50%-75% by weighing and extrusion; 2) placing the modified polytetrafluoroethylene / polyimide foam material after absorbing water into a high-pressure methane reactor, sealing it and placing it in a low-temperature constant temperature bath; 3) When the temperature is constant at 0°C ± 0.2°C, open the methane cylinder to inflate the high-pressure reactor. After completion, close the methane cylinder, the hydrate reaction begins, and natural gas hydrate is generated.

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