A polyimide resin having a hindered amine structure, a preparation method thereof, and application in gas separation membranes

Abstract

The present invention discloses a polyimide resin having a hindered amine structure, a preparation method thereof, and its application in gas separation membranes, belonging to the field of polyimide resins. The present invention prepares a novel polyimide resin having a hindered amine structure by reacting a specific isocyanate compound with a polyimide resin containing hydroxyl / thiol / amino functional groups. The preparation method of the present invention is easy to operate, has low production costs, and is highly versatile. The resulting product exhibits good CO2 separation capabilities and excellent heat resistance, and can be used for carbon capture in high-temperature flue gas. It has promising application prospects in industries such as metallurgy, chemical industry, building materials, machinery, and electric power.

Description

Technical Field

[0001] The present invention belongs to the field of polyimide resins, and in particular relates to a polyimide resin with a hindered amine structure, a preparation method thereof, and application in gas separation membranes. Background Art

[0002] Since the Industrial Revolution, humanity's continued growth in fossil energy consumption has led to an annual increase in global CO2 emissions, significantly exacerbating global warming. To combat climate change and reduce CO2 emissions, countries around the world are actively developing carbon capture and other carbon-negative technologies. Membrane separation technology, with its energy-saving and high efficiency, zero secondary pollution, simple operation, and low cost, offers promising carbon capture methods.

[0003] Since the hindered amine structure in the polyethylene amine membrane can undergo a reversible chemical reaction with CO2 to enhance the transmission process of CO2 within the membrane, it shows good application prospects in the field of carbon capture. The research group, the research group of He Wenshou at Ohio State University in the United States, and the research group of Wang Zhi in China all prepared CO2 separation membranes with PVAm as the main material, and carried out pilot tests to examine the long-term stability and impurity resistance of the membrane. Among them, the research group of He Wenshou N-methylated the commercial PVAm material into PVAm-CH3 through a step-by-step reduction amination reaction. Its CO2 permeability reached 445.7 Barrer and the CO2 / N2 selectivity was 70.3. However, due to the generally poor heat resistance of PVAm and its modified materials, thermal decomposition will occur around 150°C. The test temperatures currently available are generally concentrated in the range of 20 to 40°C, which is much lower than the temperature of exhaust gases emitted by industries such as metallurgy, chemical industry, building materials, machinery, and electric power (≥100°C). Summary of the Invention

[0004] The purpose of the present invention is to provide a polyimide resin with a hindered amine structure and its application in gas separation membranes, so as to overcome the problem that existing hindered amine separation membrane materials have poor CO2 separation capacity and heat resistance, and are difficult to cope with the high-temperature exhaust gas emitted by metallurgy, chemical industry, building materials and other industries.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned polyimide gas separation membrane with a hindered amine structure, wherein a polyimide gas separation membrane with a hindered amine structure is prepared by reacting a polyimide resin containing a reactive group with a specific isocyanate compound, thereby achieving long-term and efficient treatment of high-temperature flue gas.

[0006] The purpose of the present invention is achieved through the following solutions.

[0007] A polyimide resin with a hindered amine structure, the structural formula is as follows:

[0008]

[0009] Where X is

[0010] Y is

[0011] Z is One of the following;

[0012] R is

[0013] Preferably, the molecular weight of the polyimide resin having a hindered amine structure is 2,000 to 800,000.

[0014] Preferably, the

[0015] X is

[0016] Y is

[0017] Z is

[0018] R is

[0019] The method for preparing a polyimide resin having a hindered amine structure as described in any one of the above items comprises the following steps:

[0020] S1, dissolving a polyimide resin containing a reactive group in a polar organic solvent;

[0021] S2, after the polyimide resin in step S1 is completely dissolved, adding an isocyanate compound and a catalyst to react to obtain a polyimide resin having a hindered amine structure;

[0022] The structural formula of the polyimide resin containing reactive groups is

[0023]

[0024] Where X is

[0025] Y is

[0026] W is

[0027] The structural formula of the isocyanate compound is

[0028] Where R is

[0029] Preferably, the molecular weight of the polyimide resin containing reactive groups in step S1 is 1,000 to 500,000.

[0030] Preferably, the organic solvent is a mixture of one or more of o-cresol, m-cresol, p-cresol, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,4-dioxane, tetrahydrofuran, and acetonitrile.

[0031] Preferably, the catalyst is a mixture of one or more of triethylamine, triethylenediamine, stannous octoate, dibutyltin dilaurate, lead octoate (24% Pb), cobalt octoate (6% Co), iron octoate (6% Fe), zinc naphthenate (14.5% Zn), and 1,4-diazabicyclo[2.2.2]octane.

[0032] Preferably, the amount of the catalyst used is 0.1 to 5 wt.% of the mass of the polyimide resin containing the reactive groups.

[0033] Preferably, the amount of the isocyanate compound used is 10 to 50 wt.% of the mass of the polyimide resin containing the reactive group.

[0034] Preferably, the reaction temperature is -10 to 100°C, more preferably 20 to 60°C.

[0035] Preferably, the reaction time is 1 to 48 hours, more preferably 2 to 24 hours.

[0036] Preferably, in step S2, after the reaction is complete, the reactant is poured into deionized water for precipitation and filtered; the precipitate is then washed with ethanol, filtered and dried to obtain a polyimide resin having a hindered amine structure.

[0037] A film, comprising any one of the above-mentioned polyimide resins having a hindered amine structure.

[0038] Preferably, the film is in the form of a flat membrane or a hollow fiber membrane.

[0039] More preferably, the thickness of the flat membrane is 1 to 200 μm; the outer diameter of the hollow fiber gas separation membrane is 200 to 500 μm, and the inner diameter is 150 to 350 μm.

[0040] Preferably, the film is a gas separation membrane for separating CO2.

[0041] Preferably, the film captures CO2 in air, industrial flue gas, natural gas or biogas.

[0042] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0043] 1. The preparation method of the present invention has the characteristics of easy operation, low production cost, strong versatility, etc. Polyimide resins containing hydroxyl, thiol and amino functional groups in their molecular structures are all suitable for this modification method.

[0044] 2. The polyimide resin film of the present invention can effectively improve the permeability coefficient and selectivity of the film to CO2.

[0045] 3. The hindered amine structure of the present invention is connected to the polyimide main chain through a chemical bond, which effectively avoids the overflow of the blended hindered amine adsorbent at a higher working pressure.

[0046] 4. The modification method of the present invention will not substantially reduce the heat resistance of the polyimide material, and the product can be used for a long time in high-temperature flue gas environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The synthetic route of the polyimide resin having a hindered amine structure in Examples 1-3 is shown.

[0048] Figure 2 The NMR spectra of the resins before and after modification of Comparative Examples 1-3 and Examples 1-3 are shown.

[0049] Figure 3 Graph showing the heat resistance of the films of Comparative Examples 1-3 before and after modification.

[0050] Figure 4 Graph showing the heat resistance of the films of Examples 1-3 before and after modification.

[0051] Figure 5 Graphs showing the mechanical properties of the films of Comparative Examples 1-3 and Examples 1-3 before and after modification.

[0052] Figure 6 Graphs showing the gas separation performance of the membranes of Comparative Examples 1-3 and Examples 1-3 before and after modification. DETAILED DESCRIPTION

[0053] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, 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 intended to limit the present invention.

[0054] Example 1

[0055] Step (1): First, dissolve 25g (0.2mol) of p-hydroxybenzaldehyde in 20mL of DMF. Then, add 50mL (0.4mol) of 2,6-dimethylaniline to a 250mL three-necked flask. Under N2 protection, add 20mL of concentrated hydrochloric acid dropwise. After the addition is complete, add the DMF solution of completely dissolved p-hydroxybenzaldehyde. Heat and reflux for 24h. After the reactants cool to room temperature, add NaOH solution and adjust the pH value of the system to 8. A pink solid precipitates. Filter the reactants and take the filter cake. Dissolve the reactants in methanol and add deionized water to precipitate. Filter the mixture, wash the filter cake three times with deionized water, and dry it to obtain 4-[bis(4-amino-3,5-dimethylphenyl)methyl]phenol (Compound I).

[0056] Step (2): 50 mL of m-cresol, 25 mL of toluene, 3.2222 g (0.01 mol) of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3.4647 g (0.01 mol) of 4-[bis(4-amino-3,5-dimethylphenyl)methyl]phenol, and 0.1 g of isoquinoline were added to a 250 mL three-necked flask in sequence. After reflux and dehydration at 120° C. for 6 h, the mixture was heated to 180° C. for 12 h to obtain a polyimide solution. This polycondensation process was always carried out in a nitrogen atmosphere. The polyimide solution was cooled to 80° C. and then slowly poured into anhydrous ethanol to precipitate a white fibrous polyimide. The polyimide was washed with ethanol several times and then dried to obtain a PI-C polyimide resin.

[0057] Step (3): 2.5310 g of PI-C polyimide resin was dissolved in 25 mL of DMSO at 40°C. After complete dissolution, 20 μL of dibutyltin dilaurate and 8 μL of triethylamine were added, stirred evenly, and 2 mL of isopropyl isocyanate was added dropwise. After the addition was complete, the reaction was continued for 2 h. After completion of the reaction, the mixture was poured into deionized water to precipitate, filtered, washed with anhydrous ethanol, and the filter cake was filtered again and dried to obtain PI-CN resin.

[0058] Step (4): PI-CN resin was dissolved in DMF to prepare a 25 wt.% casting solution, and a film was applied using a film applicator to form a film approximately 20 μm thick. The film was then placed in a vacuum oven and the solvent was removed according to a heating program of 80°C / 2 h → 120°C / 2 h → 160°C / 2 h → 180°C / 1 h → 200°C / 1 h. After cooling to room temperature, the glass plate was placed in deionized water to allow the film to automatically peel off, and then oven-dried to obtain a PI-CN film.

[0059] Example 2

[0060] Step (1): same as in Example 1

[0061] Step (2): 3.2222 g (0.01 mol) of 3,3',4,4'-benzophenonetetracarboxylic dianhydride was replaced with 3.1021 g (0.01 mol) of 4,4'-biphenyl ether dianhydride. The remaining steps were the same to obtain PI-O resin.

[0062] Step (3): Take 2.4828 g of PI-O resin and follow the same steps as above to obtain PI-ON resin. Step (4): Follow the same steps as above to obtain PI-ON film.

[0063] Example 3

[0064] Step (1): same as in Example 1

[0065] Step (2): 3.2222 g (0.01 mol) of 3,3',4,4'-benzophenonetetracarboxylic dianhydride was replaced with 4.4424 g (0.01 mol) of hexafluorodianhydride. The remaining steps were the same to obtain PI-F resin.

[0066] Step (3): Take 3.3962g of PI-F resin and follow the same steps to obtain PI-FN resin.

[0067] Step (4): The steps are the same to obtain a PI-FN film.

[0068] Comparative Example 1

[0069] The steps are the same as those in Example 1, except that step (3) is not performed, to obtain a PI-C film.

[0070] Comparative Example 2

[0071] The steps are the same as those in Example 2, except that step (3) is not performed, and a PI-O film is obtained.

[0072] Comparative Example 3

[0073] The steps are consistent with those in Example 3, except that step (3) is not performed, and a PI-F film is obtained.

[0074] Test Example:

[0075] (1) Nuclear magnetic resonance test of the resin obtained in the comparative example and the embodiment:

[0076] The results were determined using a 600M superconducting nuclear magnetic resonance spectrometer, and the solvent was DMSO (deuterated).

[0077] according to Figure 2 , NMR test results show that the modified resin was successfully synthesized.

[0078] (2) Molecular weight determination of the resins obtained in the comparative examples and examples:

[0079] The determination was performed using gel permeation chromatography, with DMF as the eluent at a flow rate of 1 mL / min.

[0080] Table 1 GPC test results of the resins obtained in the comparative examples and examples

[0081]

[0082] (3) Thickness of the films obtained in the comparative examples and examples:

[0083] Table 2 Thickness test results of the films obtained in the comparative examples and the examples

[0084]

[0085] (4) Mechanical properties test of the films obtained in the comparative examples and examples:

[0086] The measurement was carried out using an electronic universal testing machine with an effective sample length of 30 mm and a tensile rate of 2 mm / min.

[0087] according to Figure 5 The tensile test results show that the addition of large steric groups will increase the molecular weight spacing, which in turn leads to a decrease in tensile strength. However, the difference before and after modification is not large, and the tensile strength exceeds 60MPa, which can meet the actual needs of gas separation.

[0088] (5) Heat resistance test of the films obtained in the comparative examples and examples:

[0089] The measurement was performed using a thermogravimetric analyzer under a N2 atmosphere at a heating rate of 10 K / min.

[0090] according to Figure 3 、 Figure 4 The thermogravimetric test results show that the samples T d5％ All of them exceed 400℃ and have good thermal stability.

[0091] (6) Gas separation performance test of the films obtained in the comparative examples and examples:

[0092] The test pressure is 0.5MPa and the test temperature is 35℃.

[0093] The modified membrane has improved CO2 permeability and selectivity (see Figure 6 ).

Claims

1. A polyimide resin having a hindered amine structure, characterized in that: The structural formula is as follows: Where X is Y is Z is One of the following; R is 2. The polyimide resin having a hindered amine structure according to claim 1, wherein The molecular weight of the polyimide resin having a hindered amine structure is 2,000 to 800,000.

3. The polyimide resin having a hindered amine structure according to claim 2, characterized in that: described X is Y is Z is R is 4. A method for preparing a polyimide resin having a hindered amine structure according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, dissolving a polyimide resin containing a reactive group in a polar organic solvent; S2, after the polyimide resin in step S1 is completely dissolved, adding an isocyanate compound and a catalyst to react to obtain a polyimide resin having a hindered amine structure; the structural formula of the polyimide resin containing a reactive group is Where X is Y is W is The structural formula of the isocyanate compound is Where R is 5. The method for preparing a polyimide resin having a hindered amine structure according to claim 4, wherein: The organic solvent is a mixture of one or more of o-cresol, m-cresol, p-cresol, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,4-dioxane, tetrahydrofuran, and acetonitrile; The catalyst is a mixture of one or more of triethylamine, triethylenediamine, stannous octoate, dibutyltin dilaurate, lead octoate, cobalt octoate, iron octoate, zinc naphthenate, tetraisobutyl titanate, and 1,4-diazabicyclo[2.2.2]octane; The amount of the catalyst used is 0.1 to 5 wt.% of the mass of the polyimide resin containing the reactive group; the amount of the isocyanate compound used is 10 to 50 wt.% of the mass of the polyimide resin containing the reactive group.

6. The method for preparing a polyimide resin having a hindered amine structure according to claim 4, wherein: The reaction temperature is -10 to 100° C., and the reaction time is 1 to 48 hours.

7. The method for preparing a polyimide resin having a hindered amine structure according to claim 4, wherein: In step S2, after the reaction is complete, the reactant is poured into deionized water for precipitation and filtered; the precipitate is then washed with ethanol, filtered and dried to obtain a polyimide resin having a hindered amine structure.

8. A film, characterized in that The film comprises a polyimide resin having a hindered amine structure as claimed in any one of claims 1 to 3.

9. A film according to claim 8, characterized in that: The film is a gas separation membrane used for separating CO2.

10. A film according to claim 8, characterized in that: The membrane captures CO2 from air, industrial flue gas, natural gas or biogas.

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