Chitosan gel film containing carboxylic acid functionalized ionic liquid as well as preparation method and application of chitosan gel film

Abstract

The invention discloses a preparation method of a chitosan gel film containing carboxylic acid functionalized ionic liquid and application of the chitosan gel film to removal of H2S and CO2 in energy gas. Specifically, water is used as a solvent, dissolution of chitosan is promoted through the acid-base action between carboxylic acid functionalized ionic liquid and chitosan, and the chitosan gel film with the high ionic liquid content can be prepared after solvent volatilization and drying. By means of high gas affinity and plasticizing capacity of the ionic liquid, the chitosan gel membrane shows good H2S and CO2 separation performance and mechanical performance, and the used membrane can be dissolved and recycled by adding water, so that secondary utilization is realized. The chitosan gel membrane disclosed by the invention has the advantages of simple preparation process, greenness, low cost, excellent separation performance, recyclability and the like, and is expected to be applied to various industrial desulfurization and decarbonization processes.

Description

Technical Field

[0001] The present invention relates to the preparation of a chitosan gel membrane containing a carboxylic acid-functionalized ionic liquid and its use for the removal of H2S and CO2 from energy gases, belonging to the technical field of gas separation and purification in green chemical engineering. Specifically, it relates to the green preparation of a recyclable chitosan gel membrane material with a high ionic liquid content and its use for the removal of H2S and CO2 from energy gases with different concentrations. Background Art

[0002] Acidic gas impurities usually exist in energy gases such as natural gas and biogas, mainly hydrogen sulfide (H2S) with strong corrosivity and high toxicity and carbon dioxide (CO2) which is a greenhouse gas. The presence of acidic gases can cause problems such as equipment corrosion, catalyst poisoning, and a decrease in the calorific value of energy gas combustion. Moreover, H2S and CO2 are also important raw materials for producing high-value-added sulfur- or carbon-containing chemicals. Therefore, it is very necessary to remove H2S and CO2 from energy gases before entering the transmission pipeline. In recent years, membrane separation technology has gradually become an important industrial separation technology due to its advantages such as high separation efficiency, energy conservation and environmental protection, and low investment cost, especially in the field of gas separation. At present, some research reports have described the selective removal of H2S and CO2 from energy gases by means of membrane separation technology (for example, the methods reported in the following literature and patents: Nat. Mater., 2018, 17, 283-289; Sci. Adv., 2019, 5, eaaw5459; J. Membr. Sci., 2020, 593, 117430; J. Membr. Sci., 2024, 699, 122618; CN106554835A; CN111054225A; CN114072220, etc.). Although there have been certain breakthroughs in the material preparation and separation performance of the above-mentioned membrane materials, it is worth noting that these membrane materials have complex preparation processes, high raw material costs, and the treatment of waste membrane materials is also a thorny problem that needs to be solved.

[0003] Chitosan (CS) is a natural alkaline polysaccharide that is easily degradable. It can be obtained by deacetylating chitin, the second largest natural polymer. It has the advantages of low cost, high biocompatibility, and good film-forming properties. However, there are extremely strong hydrogen bond interactions within and between chitosan molecules, making it difficult to depolymerize and dissolve in conventional solvents, so its solution processability is poor. Only in a strongly acidic aqueous solution can chitosan dissolve after the amino groups on the molecular chain are protonated to form a polycationic electrolyte, but this method will lead to the loss of basic sites; on the other hand, the strong hydrogen bond interactions inside chitosan result in too high crystallinity of the film, which is not conducive to gas permeation. Ionic liquids (ILs) are a new generation of green solvents with extremely low vapor pressure, easily adjustable structure, high thermal stability, and excellent gas affinity. They have been widely used in acidic gas absorption and membrane separation, especially for H2S and CO2 gases (such as the methods reported in the following literature and patents: AIChE J., 2014, 60, 4232 - 4240; Chem. Eng. Sci., 2017, 173, 253 - 263; J. Membr. Sci., 2017, 543, 282 - 287; CN106554835A; CN108840311B; CN113019078B; CN115532039A, etc.). However, there is currently no research on using ionic liquids to simultaneously promote the dissolution of chitosan and modify chitosan membranes.

[0004] Therefore, the present invention reports a chitosan gel membrane containing a carboxylic acid-functionalized ionic liquid, its preparation method and uses. On the one hand, by means of the carboxylic acid-functionalized ionic liquid, the dissolution ability of chitosan in water is greatly improved, and the aqueous solution processability of chitosan is enhanced; on the other hand, the high affinity of the ionic liquid for H2S and CO2 is used to promote gas dissolution, and the plasticizing effect of the ionic liquid is used to reduce the crystallinity of the chitosan membrane, thereby enhancing gas diffusion. The prepared chitosan gel membrane containing a carboxylic acid-functionalized ionic liquid has the advantage of good H2S and CO2 separation performance, and the used membrane material can be dissolved and recovered by adding water to prepare a chitosan gel membrane again. The chitosan gel membrane based on the carboxylic acid-functionalized ionic liquid prepared by the present invention has outstanding advantages such as simple, green, low-cost preparation process, excellent separation performance, and renewable use. It can be used for the removal of H2S and CO2 from various gas sources and has good industrial application prospects. Summary of the Invention

[0005] The object of the present invention is to disclose a preparation method of a chitosan gel membrane containing a carboxylic acid-functionalized ionic liquid and its use for the removal of H2S and CO2 from energy gas in view of the deficiencies of the existing H2S membrane separation technology.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A carboxylic acid-functionalized ionic liquid chitosan gel membrane, its preparation method and use, characterized in that: using alkyl imidazole and halo-carboxylic acid as raw materials, preparing carboxylic acid-functionalized ionic liquid through quaternization reaction and ion exchange, mixing it with chitosan in water according to a certain stoichiometric ratio to prepare a casting solution, and finally preparing a self-supporting homogeneous membrane through the solution casting method for the removal of H2S and CO2 in energy gases with different concentrations. The carboxylic acid-functionalized ionic liquid has the following general structural formula:

[0008]

[0009] Wherein, R1 is a straight-chain alkyl group with 1 to 6 carbon atoms, n is a straight-chain or branched-chain alkyl group with 1 to 3 carbon atoms, and X is an anion commonly constituting ionic liquids, including but not limited to chloride ion, bromide ion, tetrafluoroborate ion, hexafluorophosphate ion, bis(trifluoromethanesulfonyl)imide ion, trifluoromethanesulfonate ion, thiocyanate ion, dicyanamide ion. The anion structures are as follows:

[0010]

[0011] Furthermore, the preparation method of the carboxylic acid-functionalized ionic liquid chitosan gel membrane in the method of the present invention includes the following three steps:

[0012] (1) Preparation of carboxylic acid-functionalized ionic liquid: Mix halo-carboxylic acid and N-alkyl imidazole in an organic solvent according to a certain ratio, stir and react at a certain temperature for a certain time, then stand and cool in an ice-water bath until a white solid precipitates, and filter to obtain a carboxylic acid-functionalized ionic liquid with a halogen ion as the anion. Further through ion exchange, a carboxylic acid-functionalized ionic liquid containing different anions can be obtained;

[0013] (2) Preparation of casting solution: Dissolve the carboxylic acid-functionalized ionic liquid in water, then add a certain amount of chitosan powder to the above aqueous solution, and continuously stir for a period of time under certain temperature conditions to obtain a transparent and uniform casting solution;

[0014] (3) Preparation of chitosan gel membrane: Spread the above casting solution on a flat glass, slowly volatilize most of the solvent water under certain temperature and humidity conditions, and then further dry at a high temperature until the weight of the membrane no longer changes, and a chitosan gel membrane containing carboxylic acid-functionalized ionic liquid can be obtained.

[0015] Preferably, the halogenated carboxylic acids required for synthesizing the ionic liquid specifically include 2-chloroacetic acid, 2-chloropropionic acid, 3-chloropropionic acid, 2-chlorobutyric acid, 3-chlorobutyric acid, 4-chlorobutyric acid, 2-bromoacetic acid, 2-bromopropionic acid, 3-bromopropionic acid, 2-bromobutyric acid, 3-bromobutyric acid, and 4-bromobutyric acid. The N-alkylimidazoles specifically include N-methylimidazole, N-ethylimidazole, N-propylimidazole, N-butylimidazole, N-pentylimidazole, and N-hexylimidazole. The molar ratio of the halogenated carboxylic acid to the alkylimidazole is 1:1.

[0016] Preferably, the solvents required for synthesizing the ionic liquid are acetone, acetonitrile, tetrahydrofuran, ethyl acetate, absolute ethanol, absolute methanol, or their binary or ternary mixtures.

[0017] Preferably, the temperature required for synthesizing the ionic liquid is from room temperature to 100 °C, and the time is 12 to 48 h.

[0018] Preferably, the ion exchange method includes the resin method or the precipitation method, and the anions include, but are not limited to, chloride ions, bromide ions, tetrafluoroborate ions, hexafluorophosphate ions, bis(trifluoromethanesulfonyl)imide ions, trifluoromethanesulfonate ions, thiocyanate ions, and dicyanamide ions.

[0019] Preferably, the chitosan powder selected in the preparation process of the casting solution has a molecular weight of 100,000 to 1,000,000, a deacetylation degree of ≥90%, and a dosage of 0.5 to 5 wt.% of the solvent water. The dosage of the carboxylic acid-functionalized ionic liquid can be a single one or a mixture of two or more different ionic liquids, and its dosage is 0.5 to 10 times the molar amount of the chitosan monomer. The preparation temperature of the casting solution is 20 to 80 °C, and the time is 1 to 6 h.

[0020] Preferably, the solvent evaporation conditions in the preparation process of the gel film are 20 to 60 °C, the relative humidity is 30 to 50%, the drying temperature is 80 to 100 °C, and the time is 12 to 48 h. The final application forms of the gel film include, but are not limited to, flat membranes, hollow fiber membranes, and spiral wound membranes.

[0021] Preferably, the feed pressure of the mixed gas containing H2S and CO2 is 0.1 to 10 MPa, the volume concentration of H2S is 0 to 20%, the volume concentration of CO2 is 0 to 50%, and the separation temperature is from room temperature to 80 °C.

[0022] Preferably, the chitosan gel film can be recycled and reused. The recycling method is as follows: Mix the used chitosan gel film with water at a ratio of 1 g of film / 10 g of water, and a secondary recycled gel film sample can be re-prepared according to the methods and conditions for preparing the casting solution and the gel film described above.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] (1) The present invention uses carboxylic acid functionalized ionic liquid to greatly improve the water solubility of chitosan. Chitosan gel membranes with a high content of carboxylic acid functionalized ionic liquid can be prepared using water as a solvent. The membranes can be dissolved and recovered by adding water after use, thus achieving secondary membrane preparation. Therefore, the present invention has the advantages of a simple preparation process, greenness, and recyclability.

[0025] (2) The present invention uses carboxylic acid functionalized ionic liquid to modify chitosan. By virtue of the good interaction and plasticizing effect of the ionic liquid with H2S and CO2, the permeation of H2S and CO2 gases is enhanced. The prepared gel membrane has excellent H2S and CO2 separation performance and can effectively remove H2S and CO2 from the gas source. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Attached Figure 1 The following is a photo of a chitosan gel film containing a carboxyl functionalized ionic liquid prepared in the present invention and a scanning electron microscope image thereof. Specifically, Figure 1 a is the photograph of CS / [Cmmim]Br (1:1) membrane and its surface and cross-section scanning electron microscope images; Figure 1 b is the photograph of CS / [Cemim][Tf2N](1:4) membrane and its surface and cross-section scanning electron microscopy images; Figure 1 c is the photograph of CS / [Cemim][Tf2N] / [Cmmim]Cl (1:1.6:0.4) membrane and its surface and cross-section scanning electron microscopy images; Figure 1 d is a photograph of the CS / [Cmmim][Tf2N] / [Cmmim]Cl (1:1.6:0.4) membrane prepared by secondary recycling and its surface and cross-section scanning electron microscope images. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below through specific embodiments.

[0028] Implementation Case 1

[0029] Dissolve 0.1 mol of 2-bromoacetic acid in 25 mL of acetonitrile, add an equal mole of N-methylimidazole dropwise at room temperature, then raise the temperature to 90°C, and vigorously stir the reaction under reflux for 24 hours. After the reaction is completed, place the reaction system in an ice-water bath to precipitate a white solid, which is filtered, washed with a small amount of acetonitrile, and dried in a vacuum oven at 60°C to obtain 1-carboxymethyl-3-methylimidazolium bromide, denoted as [Cmmim]Br.

[0030] Implementation Case 2

[0031] Dissolve 0.1 mol of 4-chlorobutyric acid in 25 mL of acetone, dropwise add an equimolar amount of N-ethylimidazole at room temperature, then heat up to 70 °C, and vigorously stir the reaction under reflux conditions for 48 h. After the reaction is completed, let the reaction system stand in an ice-water bath to precipitate white solid, filter and wash with a small amount of acetone, and then dry in a vacuum oven at 60 °C to obtain 1-carboxypropyl-3-ethylimidazolium chloride, denoted as [Cpeim]Cl.

[0032] Example 3

[0033] Perform ion exchange between 1-carboxymethyl-3-methylimidazolium bromide and lithium bis(trifluoromethanesulfonyl)imide in water. After the reaction is completed, centrifuge to separate the phases. Wash the lower phase twice with deionized water and then dry in a vacuum oven at 60 °C to obtain 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, denoted as [Cmmim][Tf2N].

[0034] Example 4

[0035] Dissolve 1-carboxymethyl-3-butylimidazolium chloride in water to prepare an aqueous solution. Use a peristaltic pump to transport and flow this aqueous solution through a packed column filled with a sufficient amount of tetrafluoroborate anion exchange resin to cause ion exchange between chloride ions and tetrafluoroborate ions. Collect the effluent at the bottom of the column, remove the solvent, and then dry in a vacuum oven at 60 °C to obtain 1-carboxymethyl-3-butylimidazolium tetrafluoroborate, denoted as [Cmbim][BF4].

[0036] Example 5

[0037] Dissolve 1 mmol of [Cmmim]Br in 10 g of water, add 1 mmol of chitosan powder (calculated based on the molar amount of monomers, deacetylation degree 90%, M W = 200000 Da), and continuously stir at 70 °C for 6 h to obtain a clear and homogeneous casting solution. After cooling to room temperature, pour the casting solution onto a super-flat glass dish, and then let most of the water slowly evaporate in a constant-temperature oven at 40 °C and 40% relative humidity. Then dry in an 80 °C oven until the weight of the film no longer changes to obtain the chitosan gel film containing carboxylic acid-functionalized ionic liquid as described above, denoted as CS / [Cmmim]Br (1:1), where 1:1 is the molar ratio of chitosan to [Cmmim]Br. The film photo and its scanning electron micrograph are shown in Attachment Figure 1 as shown in Fig. a.

[0038] Example 6

[0039] Dissolve 4 mmol of [Cemim][Tf2N] in 10 g of water, add 1 mmol of chitosan powder (calculated based on the molar amount of monomers, deacetylation degree 95%, M W(with a molecular weight of 200,000 Da), and continuously stirred at 70 °C for 6 h to obtain a clear and homogeneous casting solution. After cooling to room temperature, the casting solution was cast on a super-flat glass petri dish, and then most of the water was slowly volatilized in an incubator at 40 °C and 40% relative humidity, and then dried in an oven at 80 °C until the weight of the film no longer changed, thus obtaining the chitosan gel film containing carboxylic acid-functionalized ionic liquid, denoted as CS / [Cemim][Tf2N] (1:4), where 1:4 is the molar ratio of chitosan to [Cemim][Tf2N]. The film photograph and its scanning electron micrograph are shown in Appendix Figure 1 as shown in Fig. b.

[0040] Example 7

[0041] Dissolve 1.6 mmol of [Cemim][Tf2N] and 0.4 mmol of [Cmmim]Cl in 10 g of water, add 1 mmol of chitosan powder (in terms of monomer molar amount, with a degree of deacetylation of 90%, M W = 200,000 Da), and continuously stir at 70 °C for 6 h to obtain a clear and homogeneous casting solution. After cooling to room temperature, the casting solution was cast on a super-flat glass dish, and then most of the water was slowly volatilized in an incubator at 40 °C and 40% relative humidity, and then dried in an oven at 80 °C until the weight of the film no longer changed, thus obtaining the chitosan gel film containing carboxylic acid-functionalized ionic liquid, denoted as CS / [Cemim][Tf2N] / [Cmmim]Cl (1:1.6:0.4), where 1:1.6:0.4 is the molar ratio of chitosan, [Cemim][Tf2N], and [Cmmim]Cl. The film photograph and its scanning electron micrograph are shown in Appendix Figure 1 as shown in Fig. c. The preparation methods of the carboxylic acid-functionalized ionic liquid and the chitosan gel film used in the following examples are similar to those in Examples 1-4 and 5-7.

[0042] Examples 8-15

[0043] Under certain test conditions, the permeability coefficients of H2S and CO2 in the freshly prepared chitosan gel film in gas sources with different concentrations were measured and the selectivity was calculated (the test method can refer to J. Membr. Sci., 2024, 699, 122618). The specific results are shown in the following table:

[0044]

[0045] Example 16

[0046] Select the gel film that has been used for 100 h in Example 13. Mix the film material with water at a ratio of 1 g of film / 10 g of water, and place it under stirring at 70 °C until a homogeneous and transparent casting solution is formed. Then, prepare the recycled chitosan gel film containing carboxylic acid-functionalized ionic liquid according to the methods in Examples 5-7. The film photos and their scanning electron microscope images are shown in Appendix Figure 1 as shown in

[0047] Examples 17-21

[0048] According to the test methods in Examples 8-15, measure the permeation coefficients of H2S and CO2 in the recycled chitosan gel film described in Example 16 in gas sources with different concentrations under certain test conditions, and calculate the selectivity (Example 17). The continuous test-recovery cycle test was carried out 5 times in total. The results of the last 4 times refer to Examples 18-21. The results show that this type of chitosan gel film has good recycling performance.

[0049]

[0050] The above are only the preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above-mentioned examples. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several improvements and refinements made without departing from the principle of the present invention should be regarded as within the protection scope of the present invention.

Claims

1. A chitosan gel film containing a carboxylic acid-functionalized ionic liquid, and a preparation method and use thereof, characterized in that: Using alkylimidazole and halo-carboxylic acid as raw materials, carboxylic acid-functionalized ionic liquids are prepared through quaternization reaction and ion exchange. They are mixed with chitosan in water according to a certain stoichiometric ratio to prepare a casting solution, and finally a self-supporting homogeneous membrane is prepared by the solution casting method for the removal of H2S and CO2 in energy gas; The specific preparation method is as follows: (1) Preparation of carboxylic acid-functionalized ionic liquid: Mix halo-carboxylic acid and N-alkylimidazole in an organic solvent in a certain proportion, stir and react at a certain temperature for a certain time, then let it stand and cool in an ice-water bath until a white solid precipitates, and filter to obtain a carboxylic acid-functionalized ionic liquid with a halogen ion as the anion. Further through ion exchange, carboxylic acid-functionalized ionic liquids with different anions can be obtained; (2) Preparation of casting solution: Dissolve the carboxylic acid-functionalized ionic liquid in water, then add a certain amount of chitosan powder to the above aqueous solution, and continuously stir for a period of time under certain temperature conditions to obtain a transparent and uniform casting solution; (3) Preparation of chitosan gel membrane: Coat the above casting solution on a flat glass, slowly volatilize most of the solvent water under certain temperature and humidity conditions, and then further dry at a high temperature until the weight of the membrane no longer changes, and a chitosan gel membrane containing carboxylic acid-functionalized ionic liquid can be obtained.

2. A chitosan gel film containing a carboxylic acid-functionalized ionic liquid, its preparation method and use according to claim 1, characterized in that, The halo-carboxylic acids required for the synthesis of ionic liquids specifically include 2-chloroacetic acid, 2-chloropropionic acid, 3-chloropropionic acid, 2-chlorobutyric acid, 3-chlorobutyric acid, 4-chlorobutyric acid, 2-bromoacetic acid, 2-bromopropionic acid, 3-bromopropionic acid, 2-bromobutyric acid, 3-bromobutyric acid, 4-bromobutyric acid. The N-alkylimidazoles specifically include N-methylimidazole, N-ethylimidazole, N-propylimidazole, N-butylimidazole, N-pentylimidazole, N-hexylimidazole. The molar ratio of halo-carboxylic acid to alkylimidazole is 1:

1.

3. A chitosan gel film containing a carboxylic acid-functionalized ionic liquid, its preparation method and uses according to claim 1, characterized in that, The solvents required for the synthesis of ionic liquids are acetone, acetonitrile, tetrahydrofuran, ethyl acetate, absolute ethanol, absolute methanol or their binary or ternary mixtures.

4. A chitosan gel film containing a carboxylic acid-functionalized ionic liquid, and a preparation method and use thereof according to claim 1, characterized in that, The temperature required for the synthesis of ionic liquids is from room temperature to 100 °C, and the time is 12 - 48 h.

5. A chitosan gel film containing a carboxylic acid-functionalized ionic liquid, a preparation method and a use thereof according to claim 1, characterized in that The ion exchange methods include resin method or precipitation method, and the anions include but are not limited to chloride ion, bromide ion, tetrafluoroborate ion, hexafluorophosphate ion, bis(trifluoromethanesulfonyl)imide ion, trifluoromethanesulfonate ion, thiocyanate ion, dicyanamide ion.

6. A chitosan gel film containing a carboxylic acid-functionalized ionic liquid, its preparation method and use according to claim 1, characterized in that, For the chitosan powder selected in the preparation process of the casting solution, its molecular weight is 100,000 - 1,000,000, the degree of deacetylation is ≥90%, and the dosage is 0.5 - 5 wt.% of the solvent water. The carboxylic acid-functionalized ionic liquid can be a single one or a mixture of two or more different ionic liquids, and its dosage is 0.5 - 10 times the molar amount of chitosan monomer. The preparation temperature of the casting solution is 20 - 80 °C, and the time is 1 - 6 h.

7. A chitosan gel film containing a carboxylic acid-functionalized ionic liquid, its preparation method and use according to claim 1, characterized in that, The solvent volatilization conditions in the preparation process of the gel membrane are 20 - 60 °C, the relative humidity is 30 - 50%, the drying temperature is 80 - 100 °C, and the time is 12 - 48 h. And the final application forms of this gel membrane include but are not limited to flat membranes, hollow fiber membranes and spiral wound membranes.

8. A chitosan gel film containing a carboxylic acid-functionalized ionic liquid, its preparation method and use according to claim 1, characterized in that The feed pressure of the mixed gas containing H2S and CO2 is 0.1 - 10 MPa, the volume concentration of H2S is 0 - 20%, the volume concentration of CO2 is 0 - 50%, and the separation temperature is from room temperature to 80 °C.

9. A chitosan gel film containing a carboxylic acid-functionalized ionic liquid, its preparation method and use according to claim 1, characterized in that The chitosan gel membrane can be recycled and reused. The recycling method is as follows: Mix the used chitosan gel membrane with water at a ratio of 1 g of membrane / 10 g of water, and the second-recovered gel membrane sample can be prepared again according to the methods and conditions described in Claims 6 and 7.

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