A superhydrophobic molecular selector based on a porous organic cage, its preparation method and application

Abstract

This invention develops a superhydrophobic molecular selector based on a porous organic cage, its preparation method, and its application. The resulting superhydrophobic molecular selector (SMS-POC-1) has a superhydrophobic outer surface and an inner cavity with multiple ethane-selective functional sites, exhibiting excellent ethane adsorption capacity (97 cm⁻¹). 3 / g, 298K) and ethane / ethylene separation selectivity (S ads =2.40, 298 K), achieving a superior balance between ethane adsorption capacity and selectivity. Furthermore, SMS-POC-1 exhibited similar ethylene purification capabilities under both dry and humid conditions (60% RH), demonstrating the effectiveness of the present invention's SMS strategy in constructing moisture-resistant adsorbents. Therefore, this invention not only provides a general strategy for the design of moisture-resistant adsorption separation materials but also offers a promising candidate for potential applications in hydrocarbon separation.

Description

Technical Field

[0001] This invention belongs to the field of porous organic materials and separation technology, specifically relating to a superhydrophobic molecular selector based on a porous organic cage structure, which is used for the efficient separation of ethane and ethylene in dry and wet environments. Background Technology

[0002] Ethylene (C2H4) is an important raw material for the petrochemical industry and one of the world's most produced chemicals. The purity of ethylene needs to reach 99.95% or higher when producing certain chemicals.

[0003] Steam cracking is the primary industrial method for producing light olefins, including ethylene. However, this method typically does not directly yield high-purity ethylene (≥99.95%, polymer grade), as ethane is usually one of the main contaminants. This is because of the molecular size of ethane. and the molecular size of ethylene They are very similar and have similar physical properties. To produce commercial polymer-grade ethylene, further purification processes, such as cryogenic distillation, are usually required. However, this process is energy-intensive and costly.

[0004] Among potential alternatives to cryogenic distillation for hydrocarbon separation, selective adsorption has emerged as one of the most promising technologies due to its low energy consumption and low cost. In recent years, various organic framework materials, such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), porous organic polymers (POPs), and hydrogen-bonded organic frameworks (HOFs), have been widely used in hydrocarbon separation. Although most of these materials are superior to ethane in the selective adsorption of ethylene, the process still fails to achieve energy savings due to the need for an additional desorption step to obtain polymer-grade ethylene. Compared to ethylene selective adsorbents, ethane selective adsorbents can produce high-purity ethylene through a one-step breakthrough operation, avoiding the desorption step and thus achieving lower energy consumption and cost. However, current ethane selective adsorbents still suffer from drawbacks such as low ethane adsorption capacity, poor ethane / ethylene selectivity, poor stability, and severe competitive adsorption under humid conditions. Therefore, it is necessary to develop novel ethane selective adsorbents with high adsorption capacity and adsorption selectivity under actual humidity conditions.

[0005] However, designing moisture-resistant adsorbents with high ethane / ethylene separation performance is particularly challenging because most developed ethane-selective adsorbents inevitably consist of various hydrogen bond donors to introduce potential ethane-selective functional sites or facilitate the construction of the adsorbent framework. Therefore, these adsorbents typically exhibit strong hygroscopicity, leading to a decline in ethane / ethylene separation performance under humid conditions. Summary of the Invention

[0006] To address the problems in the background art, this invention proposes a novel strategy for constructing a "superhydrophobic molecular selector" (SMS) based on a porous organic cage (POC). The resulting SMS-POC-1 has a superhydrophobic outer surface and contains multiple ethane-selective functional sites in its inner cavity, thereby maintaining good ethane / ethylene separation performance in humid environments.

[0007] Based on the above description, the purpose of this invention is to provide an ethane-selective adsorbent capable of one-step purification of ethylene from an ethane-ethylene mixture in a real environment. This invention proposes for the first time a "superhydrophobic molecular selector" strategy based on a porous organic cage, aiming to solve the problem of limited performance in current ethane-ethylene separation under humid environments.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] The first objective of this invention is to provide a superhydrophobic molecular selector (SMS-POC-1) based on a porous organic cage, using tetraformylresorcinol-[4]arene and hydrazine hydrate as reactants, and methanol, chlorobenzene and other organic solvents as reaction solvents to obtain the target material, the structure of which is shown below:

[0010]

[0011] The structure is a [6+12] configuration, in which each cage consists of six aldehyde ligands and twelve amino ligands connected by covalent bonds.

[0012] The second aspect of this invention aims to provide a method for preparing a superhydrophobic molecular selector (SMS-POC-1) based on a porous organic cage, the synthetic route of which is as follows:

[0013]

[0014] The polymerization reaction used in the method of this invention is a Schiff base formation reaction.

[0015] The method for preparing a superhydrophobic molecular selector (SMS-POC-1) based on a porous organic cage according to the present invention comprises the following steps:

[0016] (1) First, dissolve the aldehyde ligand tetramethylresorcinol-[4]arene (RC4ACHO) in a reaction vessel containing the reaction solvent, and then disperse the amino ligand hydrazine hydrate (NH2-NH2·H2O) into the reaction vessel. Sonicate the reaction solution for 5-20 minutes to ensure that the solution is mixed evenly.

[0017] (2) React the sealed reaction vessel from step (1) at 80-120°C for 1-2 days;

[0018] (3) After cooling the reaction vessel from step (2) to room temperature, open it. Methanol vapor slowly diffuses into the mixture (4-7 days), and yellow blocky crystals precipitate at the bottom. Filter and wash with methanol multiple times; then allow to stand and exchange with methanol 6-8 times, replacing the methanol solvent with fresh methanol every 4-6 hours. Dry the obtained product under vacuum at 80-200°C for 4-24 hours to obtain a yellow solid powder, which is the superhydrophobic molecular selector based on a porous organic cage (SMS-POC-1) described in this invention.

[0019] Preferably, the reaction solvent in step (1) includes, but is not limited to, one or more of chlorobenzene, methanol, chloroform, and hydrazine hydrate.

[0020] Preferably, the molar ratio of aldehyde ligand to amino ligand is amino ligand: aldehyde ligand = (2-5):1. More preferably, it is 2:1.

[0021] Preferably, the reaction temperature is 100℃ and the heating time is 24 hours.

[0022] Preferably, the washing method in step (3) is as follows: after filtering the obtained product, wash it with methanol at 20-50°C 3-5 times.

[0023] The third aspect of this invention aims to provide an application of a superhydrophobic molecular selector based on a porous organic cage (SMS-POC-1), specifically, for one-step purification of ethylene from an ethane-ethylene mixture in a real environment (containing moisture).

[0024] Preferably, in the application of the present invention, the ethane / ethylene volume ratio is 50:50 or 10:90, the relative humidity is 0-60%RH, and the temperature is 298K.

[0025] Tests show that the material obtained in this invention (SMS-POC-1) has good thermal stability, moisture resistance, and porous properties: the material can be stable at nearly 350℃; the BET specific surface area can reach 1921 m². 2 / g; With a superhydrophobic outer surface and internal pores with multiple ethane-selective functional sites, it can be applied in many fields such as adsorption and separation, and is an excellent example of moisture-resistant adsorption and separation material.

[0026] Compared with existing technologies, the advantages of this invention are that SMS-POC-1 achieves a superior balance between ethane adsorption capacity and selectivity in humid environments through its superhydrophobic outer surface and the cavity of ethane-selective functional sites. SMS-POC-1 exhibits similar ethylene purification capabilities under both dry and humid conditions (60% RH), demonstrating its moisture resistance performance. Therefore, this invention provides a general strategy for the design of moisture-resistant adsorption separation materials and offers a promising candidate for hydrocarbon separation. Attached Figure Description

[0027] Figure 1 PXRD pattern of SMS-POC-1 synthesized in this invention;

[0028] Figure 2 The SMS-POC-1 synthesized in this invention 1 H NMR spectrum;

[0029] Figure 3 Thermogravimetric spectrum of SMS-POC-1 synthesized in this invention;

[0030] Figure 4 Infrared spectrum of SMS-POC-1 synthesized in this invention;

[0031] Figure 5 Nitrogen adsorption-desorption isotherm spectrum of SMS-POC-1 synthesized in this invention;

[0032] Figure 6 The single-component adsorption spectra of ethane and ethylene of the SMS-POC-1 synthesized in this invention at 298 K;

[0033] Figure 7 The IAST selectivity (ethane / ethylene = 1:1, 298 K) spectrum of SMS-POC-1 synthesized in this invention;

[0034] Figure 8 The breakthrough curve of SMS-POC-1 synthesized in this invention under dry / moist conditions at 298K;

[0035] Figure 9 The water contact angle spectrum of SMS-POC-1 synthesized in this invention; Detailed Implementation

[0036] The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0037] Example 1

[0038] 41 mg (0.05 mmol) RC4ACHO and 16 mg (0.1 mmol) hydrazine hydrate were added to 5 mL of chlorobenzene. The mixture was sealed in a 20 mL high-pressure bottle, stirred, and heated to 100 °C. After reacting for 24 h, it was allowed to cool naturally. By slowly diffusing methanol vapor into the mixture, yellow blocky crystals of SMS-POC-1 (72% yield) were obtained. The crystals were first washed 3–5 times with methanol at 20–50 °C. The washed product was then allowed to stand with methanol solvent for 6–8 cycles, with fresh methanol solvent replaced every 4–6 h. The obtained product was dried under vacuum at 100 °C for 12 h to obtain the product of this invention, SMS-POC-1.

[0039] Figure 1 The PXRD pattern of the SMS-POC-1 synthesized in this invention is shown. The results indicate that the prepared SMS-POC-1 exhibits excellent crystallinity. The experimentally obtained PXRD pattern is in high agreement with the XRD pattern obtained through single-crystal analytical simulation, proving the successful synthesis of a porous organic cage material with good crystallinity.

[0040] Figure 2 The image shows the SMS-POC-1 synthesized according to the present invention. 1 The H NMR spectrum further confirmed that all hydrogen sites were consistent with the structural fragments.

[0041] Figure 3 The thermogravimetric analysis (TGA) of the SMS-POC-1 synthesized in this invention is shown. The TGA analysis indicates that the thermal decomposition temperature of the material is close to 350℃, indicating that it has high thermal stability.

[0042] Figure 4 The image shown is the infrared spectrum of SMS-POC-1 synthesized in this invention, located at 1620 cm⁻¹. -1 The peak is the characteristic absorption peak of -C=N- generated by the Schiff base reaction. No characteristic absorption peaks of the reactant monomers -NH2 and -CHO were observed in the spectrum, indicating that the polymerization reaction was complete and very thorough.

[0043] Figure 5 The figure shows the nitrogen adsorption-desorption isotherm of SMS-POC-1 synthesized in this invention. The BET specific surface area of ​​the material of this invention was calculated to be 1921 m². 2 / g.

[0044] Example 2

[0045] Single-component adsorption experiments of ethane and ethylene at 298 K

[0046] To evaluate the adsorption and separation performance of the SMS-POC-1 material synthesized in Example 1, single-component adsorption experiments of ethane and ethylene were conducted using this material as an adsorbent at 298 K. In the experiments, 80-100 mg of adsorbent was used, and the adsorption temperature was set to 298 K. The experimental results are as follows: Figure 6 As shown in the figure. Tests indicate that under the conditions of 298 K and 1 bar, the adsorption capacity of ethane is 97 cm⁻¹. 3 / g, while the adsorption capacity of ethylene is 74cm. 3 The adsorption capacity of SMS-POC-1 for ethane was lower than that of SMS-POC-1 under the same conditions. Furthermore, the ideal adsorption solution theory (IAST) was used to evaluate the adsorption selectivity (S) of SMS-POC-1 for C2H6 / C2H4 (v / v = 50 / 50) at 298 K. ads The results showed that it exhibited significant selectivity at low pressure, reaching 5.42 and 2.40 at low pressure and 1 bar, respectively (see...). Figure 7 This result indicates that SMS-POC-1 preferentially adsorbs ethane, making it an ethane-selective organic porous adsorbent.

[0047] Example 3

[0048] Penetration column adsorption-desorption experiment

[0049] To evaluate the actual separation effect of SMS-POC-1 on ethane and ethylene, a breakthrough test of an ethane-ethylene mixed gas was conducted using the adsorbent synthesized in Example 1. In this experiment, the volume ratio of ethane to ethylene was 50:50, and the breakthrough conditions were 298 K and 1 atm. Approximately 0.5 g of SMS-POC-1 was packed into a quartz tube with a diameter of 6 mm to form a fixed bed. Before the experiment, the mixture was first heated at 100 °C at a flow rate of 10 cm⁻¹. 3 ·min -1 The fixed bed was purged with helium at a constant flow rate for 1 hour. Then, after cooling to room temperature, the gas flow was adjusted to the desired ethane-ethylene gas mixture (C2H6:C2H4 = 1:1). Next, two breakthrough experiments were conducted, one under dry conditions and the other under 60% relative humidity. The composition of the outlet gas was continuously monitored using a mass spectrometer (BSD-Mass), and the test curves were obtained through software processing (see [link to test curve]). Figure 8 The test results show that ethylene preferentially permeates from the fixed bed, and the breakthrough curves are almost identical under both dry and humid conditions. This indicates that SMS-POC-1 retains excellent ethane selective adsorption performance even in humid environments, making it effective for one-step purification of polymer-grade ethylene.

[0050] Example 4

[0051] By changing the reactant ratio in Example 1 above, in Example 4, the ratio of amino ligand to aldehyde ligand is 3:1, while other parameters remain unchanged, resulting in the same material SMS-POC-1 as described in Example 1, with properties essentially consistent with the product obtained in Example 1.

[0052] Example 5

[0053] By changing the reaction temperature in Example 1 above, in Example 5 the reaction temperature is 120°C, while other parameters remain unchanged, and the same material SMS-POC-1 as described in Example 1 is obtained, with the properties of the product obtained in Example 1 being basically consistent.

[0054] In summary, this invention synthesizes a superhydrophobic molecular selector (SMS-POC-1) with high specific surface area, moisture resistance, and ethane selectivity using tetraformylresorcinol-[4]arene (RC4ACHO) and hydrazine hydrate (NH2-NH2·H2O) as reactants, combined with solvothermal and diffusion methods. The obtained SMS-POC-1 exhibits superhydrophobic characteristics ( Figure 9 This study achieved a superior balance between ethane adsorption capacity and selectivity under humid conditions, demonstrating the effectiveness of the proposed SMS strategy in constructing moisture-resistant adsorbents.

[0055] As described above, those skilled in the art can make various other corresponding changes and modifications based on the technical solutions and concepts of this invention, and all such changes and modifications fall within the protection scope of the appended claims of this invention.

Claims

1. A method for the preparation of a porous organic cage-based superhydrophobic molecular selector, characterized in that, The aldehyde ligand and the amino ligand are dissolved in a reaction solvent in a certain molar ratio, mixed uniformly, and then transferred to a pressure bottle and sealed; the pressure bottle is heated to a certain temperature for a period of time, and after the reaction is completed, the mixture is allowed to cool to room temperature naturally; then, methanol vapor is slowly diffused into the mixture to achieve the crystallization process; the obtained block crystal is filtered, washed, solvent exchanged, and vacuum dried to obtain the target product, whose structural formula is shown in the following figure: ； The structure is a [6 + 12] configuration, wherein each cage is composed of six aldehyde ligands and twelve amino ligands connected by covalent bonds.

2. The method for preparing a porous organic cage-based superhydrophobic molecular selector according to claim 1, characterized in that, The aldehyde ligand is tetracarboxyresorcinol-[4]arene RC4ACHO, and the amino ligand is hydrazine hydrate NH2-NH2·H2O.

3. The method for preparing a porous organic cage-based superhydrophobic molecular selector according to claim 1, characterized in that, The molar ratio of the aldehyde ligand to the amino ligand is aldehyde ligand:amino ligand = 1:(2-5).

4. The method for preparing a porous organic cage-based superhydrophobic molecular selector according to claim 2, characterized in that, The reaction solvent is one or more of chlorobenzene, methanol, chloroform, and hydrazine hydrate.

5. The method of claim 1, wherein the porous organic cage-based superhydrophobic molecular sifter is prepared by the steps of: The reaction temperature used is 80-120°C.

6. The method of claim 1, wherein the porous organic cage-based superhydrophobic molecular sifter is prepared by the steps of: The washing method is that after the obtained product is suction filtered, it is washed with 20-50°C methanol for 3-5 times.

7. The method for preparing a superhydrophobic molecular selector based on a porous organic cage according to claim 1, characterized in that, The solvent exchange method is that the obtained product after washing is placed in methanol solvent for 6-8 times, and fresh methanol solvent is replaced every 4-6 hours.

8. A porous organic cage-based superhydrophobic molecular selector, characterized in that, The structure is a [6 + 12] configuration, wherein each cage is composed of six aldehyde ligands and twelve amino ligands connected by covalent bonds. ； For purifying ethylene from ethane / ethylene mixed gas in a real moisture-containing environment in one step.

9. Use of the porous organic cage-based superhydrophobic molecular siever according to claim 8, characterized in that, The volume ratio of ethane / ethylene is 50:50 or 10:90, the relative humidity is 0-60% RH, and the temperature is 298 K.

10. Use of a porous organic cage-based superhydrophobic molecular selector according to claim 9, characterized in that, ​

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