Super-hydrophobic molecular selector based on porous organic cage as well as preparation method and application of super-hydrophobic molecular selector

Abstract

The invention develops a super-hydrophobic molecular selector based on a porous organic cage as well as a preparation method and application thereof, the obtained super-hydrophobic molecular selector (SMS-POC-1) has a super-hydrophobic outer surface and an inner cavity with a plurality of ethane selective functional sites, shows excellent ethane adsorption capacity (97 cm < 3 > / g, 298K) and ethane / ethylene separation selectivity (Sads = 2.40, 298K), and can be used for preparing the super-hydrophobic molecular selector (SMS-POC-1). And the excellent balance between the ethane adsorption capacity and the selectivity is realized. In addition, the SMS-POC-1 shows similar ethylene purification capacity under dry and wet conditions (60% RH), which proves that the SMS strategy of the invention is effective in the aspect of construction of anti-moisture adsorbents. Therefore, the invention not only provides a general strategy for the design of a moisture-proof adsorption separation material, but also provides a promising candidate scheme for the potential application of hydrocarbon separation.

Description

Technical Field

[0001] The present invention belongs to the field of porous organic materials and separation technology, and specifically relates to an application technology of a super hydrophobic molecule selector based on a porous organic cage structure for efficiently separating ethane and ethylene in dry and wet environments. Background Art

[0002] Ethylene (C2H4) is an important raw material for the petrochemical industry and one of the most produced chemicals in the world. When producing certain chemicals, the purity of ethylene must reach above 99.95%.

[0003] Steam cracking is the main industrial process for producing light olefins (including ethylene). However, this process usually cannot directly obtain high-purity ethylene (≥99.95%, polymer grade), in which ethane is usually one of the main contaminants. Because the molecular size of ethane and the molecular size of ethylene The ethylene is very close to the ethylene and has 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 the potential alternatives to cryogenic distillation for hydrocarbon separation, selective adsorption has become one of the most promising technologies due to its low energy consumption and low cost. In recent years, a variety of 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 the field of hydrocarbon separation. Although most of these materials are superior to ethane in the selective adsorption of ethylene, this process still fails to achieve energy saving due to the need for an additional desorption step to obtain polymer-grade ethylene. Compared with ethylene-selective adsorbents, the process of ethane-selective adsorbents can produce high-purity ethylene in a one-step breakthrough operation, avoiding the desorption step, thereby achieving lower energy consumption and cost. However, current ethane-selective adsorbents still have disadvantages 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 new 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. As a result, these adsorbents usually have a strong tendency to absorb moisture, resulting in a decrease in ethane / ethylene separation performance under humid conditions. Summary of the invention

[0006] In order to solve the problems in the background technology, the present invention proposes a new strategy to construct a "superhydrophobic molecular selector" (SMS) based on porous organic cages (POC). The resulting SMS-POC-1 has a superhydrophobic outer surface and contains multiple ethane selective functional sites in the inner cavity, so that it can maintain good ethane / ethylene separation performance in a humid environment.

[0007] Based on the above description, the purpose of the present invention is to provide an ethane selective adsorbent that can purify ethylene from ethane and ethylene mixed gas in one step in a real environment. The present invention proposes for the first time a "superhydrophobic molecular selector" strategy based on porous organic cages, aiming to solve the current performance limitation of ethane and ethylene separation in humid environments.

[0008] In order to achieve the above-mentioned invention object, the present invention provides the following technical solutions:

[0009] The first aspect of the present invention aims to provide a super hydrophobic molecular selector (SMS-POC-1) based on a porous organic cage, using tetracarboxylresorcinol-[4]arene and hydrazine hydrate as reaction monomers and using an organic solvent such as methanol or chlorobenzene as a reaction solvent to obtain a target material, the structural formula of which is as follows:

[0010]

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

[0012] The second aspect of the present invention is to provide a method for preparing a super hydrophobic molecule selector (SMS-POC-1) based on a porous organic cage, the synthesis path of which is as follows:

[0013]

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

[0015] The preparation method of a super hydrophobic molecule selector (SMS-POC-1) based on a porous organic cage described in the present invention is prepared by the following steps:

[0016] (1) The aldehyde ligand tetracarboxylresorcinol-[4]arene (RC4ACHO) is first dissolved in a reaction vessel containing a reaction solvent, and then the amino ligand hydrazine hydrate (NH2-NH2·H2O) is dispersed into the reaction vessel, and the reaction solution is ultrasonicated for 5 to 20 minutes to ensure that the solution is evenly mixed;

[0017] (2) reacting the sealed reaction vessel of step (1) at 80 to 120° C. for 1 to 2 days;

[0018] (3) The reaction vessel of step (2) is cooled to room temperature and then opened, and methanol vapor is slowly diffused into the mixture (4 to 7 days), and yellow block crystals are precipitated at the bottom. Filter by suction, rinse and wash with methanol multiple times; then stand and exchange with methanol for 6 to 8 times, and filter and replace fresh methanol solvent every 4 to 6 hours. The obtained product is dried at 80 to 200 ° C under vacuum for 4 to 24 hours to obtain a yellow solid powder, which is the super hydrophobic molecule selector (SMS-POC-1) based on porous organic cages described in the present 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 the aldehyde ligand to the amino ligand is amino ligand:aldehyde ligand = (2-5):1, more preferably 2:1.

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

[0022] Preferably, the washing method described in step (3) is: after suction filtering the obtained product, washing it with methanol at 20 to 50° C. for 3 to 5 times.

[0023] The third aspect of the present invention aims to provide an application of a super hydrophobic molecular selector (SMS-POC-1) based on a porous organic cage, 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 volume ratio of ethane / ethylene 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 by the present invention (SMS-POC-1) has good thermal stability, moisture resistance and porous properties: the material can be stable at nearly 350°C; the BET specific surface area can reach 1921m 2 / g; it has a super-hydrophobic outer surface and an inner cavity channel with multiple ethane selective functional sites, and can be used in many fields such as adsorption and separation. It is an excellent moisture-resistant adsorption and separation material.

[0026] Compared with the prior art, the present invention has the following beneficial effects: SMS-POC-1 can achieve a superior balance between ethane adsorption capacity and selectivity in a humid environment through its superhydrophobic outer surface and the inner cavity of the ethane selective functional site. SMS-POC-1 exhibits similar ethylene purification capabilities under dry and wet conditions (60% RH), demonstrating its moisture resistance performance. Therefore, the present invention provides a general strategy for the design of moisture-resistant adsorption separation materials and provides a promising candidate for hydrocarbon separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 : PXRD pattern of SMS-POC-1 synthesized in the present invention;

[0028] Figure 2 : The SMS-POC-1 synthesized by the present invention 1 H NMR spectrum;

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

[0030] Figure 4 : Infrared spectrum of SMS-POC-1 synthesized by the present invention;

[0031] Figure 5 : Nitrogen adsorption-desorption isotherm of SMS-POC-1 synthesized in the present invention;

[0032] Figure 6 : Single component adsorption spectrum of ethane and ethylene of SMS-POC-1 synthesized in the present invention at 298K;

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

[0034] Figure 8 : The penetration curve of SMS-POC-1 synthesized in the present invention under dry / humid conditions at 298K;

[0035] Fig. 9 : Water contact angle spectrum of SMS-POC-1 synthesized by the present invention; DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not limited to the present invention.

[0037] Example 1

[0038] 41 mg (0.05 mmol) of RC4ACHO and 16 mg (0.1 mmol) of 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, and cooled naturally after reacting for 24 hours. By slowly diffusing methanol vapor into the above mixture, yellow block crystals SMS-POC-1 (72% yield) were obtained. The crystals were first rinsed with methanol at 20 to 50 ° C for 3 to 5 times, and the washed product was exchanged with methanol solvent for 6 to 8 times, and fresh methanol solvent was replaced by suction every 4 to 6 hours. The obtained product was vacuum dried at 100 ° C for 12 hours to obtain the product SMS-POC-1 of the present invention.

[0039] Figure 1 The PXRD pattern of SMS-POC-1 synthesized by the present invention is shown. The results show that the prepared SMS-POC-1 has excellent crystallinity. The PXRD pattern obtained by the experiment is highly consistent with the XRD pattern obtained by single crystal analysis simulation, proving that a porous organic cage material with good crystallinity has been successfully synthesized.

[0040] Figure 2 Shown is the SMS-POC-1 synthesized by the present invention 1 The H NMR spectrum further confirmed that all hydrogen positions were consistent with the structural fragments.

[0041] Figure 3 The thermogravimetric spectrum of SMS-POC-1 synthesized in the present invention is shown. Thermogravimetric analysis shows that the thermal decomposition temperature of the material of the present invention is nearly 350° C., indicating that it has high thermal stability.

[0042] Figure 4 The infrared spectrum of SMS-POC-1 synthesized in the present invention is shown at 1620 cm -1 The peak is the characteristic absorption peak of -C=N- generated by Schiff base reaction. The characteristic absorption peaks of -NH2 and -CHO of the reaction monomers were not observed in the spectrum, indicating that the polymerization reaction has been completed and the reaction is very thorough.

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

[0044] Example 2

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

[0046] In order to evaluate the adsorption and separation performance of the SMS-POC-1 material synthesized in Example 1, the material was used as an adsorbent to conduct single-component adsorption experiments of ethane and ethylene at 298K. In the experiment, 80-100 mg of the adsorbent was taken and the adsorption temperature was set to 298K. The experimental results are shown in Figure 6 The test shows that under the conditions of 298K and 1 bar, the adsorption capacity of ethane is 97cm 3 / g, while the adsorption capacity of ethylene is 74cm 3 / g, which is lower than the adsorption of ethane by SMS-POC-1 under the same conditions. In addition, the ideal adsorption solution theory (IAST) was used to evaluate the adsorption selectivity of SMS-POC-1 for C2H6 / C2H4 (v / v=50 / 50) at 298K (S 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 shows that SMS-POC-1 has the characteristic of preferentially adsorbing ethane and is an ethane-selective organic porous adsorbent.

[0047] Example 3

[0048] Through-column adsorption-desorption experiment

[0049] In order to evaluate the actual separation effect of SMS-POC-1 on ethane and ethylene, the penetration test of ethane-ethylene mixed gas was carried out using the adsorbent synthesized in Example 1. In this experiment, the volume ratio of ethane to ethylene was 50:50, and the penetration conditions were 298K and 1atm. About 0.5g of SMS-POC-1 was loaded into a quartz tube with a diameter of 6mm to form a fixed bed. Before the experiment, the adsorbent was first heated at 100℃ with a 10cm 3 ·min -1 The fixed bed was purged with a helium flow rate of 1000 g for 1 hour. Then, the gas was cooled to room temperature and the gas flow was adjusted to the desired ethane and ethylene gas mixture (C2H6:C2H4=1:1). Next, two breakthrough experiments were performed under dry conditions and 60% relative humidity conditions, respectively. The composition of the outlet gas was continuously monitored by a mass spectrometer (BSD-Mass), and the test curve was obtained by software processing (see Figure 8 ). The test results show that ethylene preferentially penetrates from the fixed bed, and the breakthrough curves are almost the same under dry and wet conditions. This result shows that SMS-POC-1 still has excellent ethane selective adsorption performance in a wet environment and can be effectively used for one-step purification of polymer-grade ethylene.

[0050] Example 4

[0051] By changing the ratio of reactants in the above Example 1, in Example 4, amino ligand: aldehyde ligand = 3:1, and keeping other factors unchanged, SMS-POC-1, the same material as that in Example 1, was obtained, and the properties of the product obtained were basically the same as those in Example 1.

[0052] Example 5

[0053] The reaction temperature in the above-mentioned Example 1 was changed. In Example 5, the reaction temperature was 120° C., and other parameters remained unchanged. The same material SMS-POC-1 as that in Example 1 was obtained, and the properties of the product obtained were basically consistent with those of Example 1.

[0054] In summary, the present invention uses tetracarboxylic resorcinol-[4]arene (RC4ACHO) and hydrazine hydrate (NH2-NH2·H2O) as reaction monomers, and combines solvothermal method and diffusion method to synthesize a superhydrophobic molecular selector (SMS-POC-1) with high specific surface area, moisture resistance, and ethane selectivity. The obtained SMS-POC-1 has superhydrophobic characteristics ( Fig. 9 ), achieving an excellent balance between ethane adsorption capacity and selectivity under humid conditions. This confirms the effectiveness of the SMS strategy proposed in the present invention in constructing moisture-resistant adsorbents.

[0055] As described above, for those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and technical concepts of the present invention, and all these changes and modifications belong to the protection scope of the appended claims of the present invention.

Claims

1. A super-hydrophobic molecule selector based on a porous organic cage, the structural formula of which is shown below: The structure is a [6+12] configuration, in which each cage is composed of six aldehyde ligands and twelve amino ligands connected by covalent bonds.

2. The method for preparing the super-hydrophobic molecule selector based on porous organic cage according to claim 1, wherein the steps are as follows: The aldehyde ligand and the amino ligand are dissolved in a reaction solvent in a certain molar ratio, and after being evenly mixed, the reaction solution is transferred to a pressure bottle and sealed; the pressure bottle is heated to a certain temperature and maintained for a period of time. After the reaction is completed, the mixture is allowed to cool naturally to room temperature; then, methanol vapor is slowly diffused into the mixture to achieve a crystallization process; the obtained block crystals are filtered, washed, solvent exchanged, vacuum dried, etc. to obtain the target product.

3. The method for preparing a super-hydrophobic molecule selector based on a porous organic cage according to claim 2, characterized in that: The aldehyde ligand is tetracarboxylic acid resorcinol-[4]arene RC4ACHO, and the amino ligand is hydrazine hydrate NH2-NH2·H2O.

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

5. The method for preparing a super-hydrophobic molecule selector based on a porous organic cage according to claim 2, characterized in that: The reaction solvent includes, but is not limited to, one or more of chlorobenzene, methanol, chloroform, and hydrazine hydrate.

6. The method for preparing a super-hydrophobic molecule selector based on a porous organic cage according to claim 2, characterized in that: The reaction temperature used is: 80-120°C.

7. The method for preparing a super-hydrophobic molecule selector based on a porous organic cage according to claim 2, characterized in that: The washing method is as follows: after the obtained product is filtered, it is rinsed with methanol at 20-50°C for 3-5 times.

8. The method for preparing a super-hydrophobic molecule selector based on a porous organic cage according to claim 2, characterized in that: The solvent exchange method is as follows: the washed product is statically exchanged with methanol solvent for 6 to 8 times, and fresh methanol solvent is replaced by suction filtration every 4 to 6 hours.

9. The use of the super-hydrophobic molecule selector based on porous organic cages according to claim 1, characterized in that: Used for one-step purification of ethylene from ethane / ethylene mixture in a real humid environment.

10. The use of the super-hydrophobic molecule selector based on porous organic cages according to claim 9, 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 298K.

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