Ionic liquid graft modified chitosan blend membrane as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of an ionic liquid grafted and modified chitosan blended membrane and application of the ionic liquid grafted and modified chitosan blended membrane to removal of hydrogen sulfide in natural gas. The blend membrane is prepared by blending the chitosan grafted with the alkyl imidazole halide salt ionic liquid and the polyethylene glycol. Specifically, the ionic liquid is grafted to the chitosan through alkylation reaction of the ionic liquid and chitosan amino, so that the chitosan is endowed with water solubility and the gas permeability is improved; meanwhile, polyethylene glycol is introduced as a plasticizer, so that the separation performance of hydrogen sulfide is further optimized. The ionic liquid graft modified chitosan blend membrane has the advantages of simple preparation process, green and environment-friendly materials, good separation performance and the like, is suitable for selective removal of H2S in natural gas with different concentrations and compositions, and has a good industrial application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the preparation of ion liquid grafted modified chitosan blended membrane and its use for H2S removal in natural gas, belonging to the field of gas separation and purification in green chemical industry, specifically relates to the preparation of ion liquid grafted modified chitosan / polyethylene glycol blended membrane material and its use for selective removal of H2S in natural gas with different concentrations and compositions. BACKGROUND

[0002] One of the key steps in natural gas purification is to remove acidic impurities such as hydrogen sulfide (H2S) and carbon dioxide (CO2) from methane (CH4). Currently, amine absorbents are commonly used in industry to capture H2S and CO2, but this acid removal process has problems such as high initial investment, high operating energy consumption, etc., which is difficult to meet the demand of green and sustainable development. In contrast, membrane separation technology has the advantages of small investment, low energy consumption, high separation efficiency, and small land occupation, and has been widely concerned and applied in the field of natural gas purification. Polyimide (PI) and cellulose acetate (CA) membranes are typical cases of industrial decarbonization applications, in addition, polyurethane (PU) and polyether block amide (PEBA) membranes have also been reported for the selective separation of H2S, CO2 and CH4. However, these traditional polymer matrix membranes generally have limited permeation performance and unsatisfactory selectivity. For this reason, many new polymers with precisely designed structures have been reported, such as self-microporous polymer (PIMs) membranes and hexafluoro dianhydride-based (6FDA) PI membranes, which exceed the Robeson upper limit describing the trade-off relationship between H2S permeability and selectivity. Although high-performance polymer membranes have made significant progress in separation performance, they generally use non-renewable fossil resources as raw materials in the preparation process, and the extremely slow degradation rate poses a potential threat to the ecological environment and biological systems.

[0003] Chitosan (CS) is a natural alkaline polysaccharide that can be prepared by deacetylation of the second largest natural polymer chitin. It has the advantages of low cost, easy degradation, good film forming property and rich alkaline sites, so it can be considered as a sustainable acid gas separation membrane material. At present, two technical problems restrict the large-scale application of chitosan membranes in the field of gas separation. On the one hand, there are strong hydrogen bond networks between chitosan molecular chains, which leads to poor solution processability. Although the water solubility can be given by protonation with inorganic / organic acid, this method usually accompanies the sacrifice of alkaline sites and the reduction of film forming performance, and the use of organic acid (such as acetic acid) releases volatile organic compounds (VOCs), which will cause environmental pollution. On the other hand, the strong hydrogen bond network of chitosan will lead to high crystallinity, which hinders the gas permeation. In order to improve its gas permeation performance, methods such as water swelling treatment of chitosan, blending with polyether block amide and blending with ionic liquid have been reported (J. Membr. Sci., 2008, 323, 225-234; J. Membr. Sci., 2014, 469, 198-208; Chem. Commun., 2024, 60, 6443-6446), but there is still a lack of related reports on the use of chitosan membranes for H2S separation in natural gas.

[0004] Therefore, the present application proposes a new strategy, that is, by alkylating reaction, imidazole halide ionic liquid is grafted to the amino group of chitosan, thereby giving chitosan water solubility and effectively improving the gas permeation performance; further introducing low molecular weight polyethylene glycol (PEG) as a plasticizer into the modified chitosan, which has good compatibility with the modified chitosan, to improve the toughness and H2S separation performance of the membrane. The prepared ionic liquid grafted modified chitosan blend membrane has a high reversible hydrogen bond interaction with H2S, so the H2S permeation coefficient is high and the selectivity is good. The blend membrane reported in the present application has the advantages of simple preparation process, green and environmentally friendly material, good separation performance, etc., and is suitable for selective removal of H2S in natural gas with different concentrations and compositions, and has good application potential. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the existing H2S gas separation membrane, and disclose a preparation method of ionic liquid grafted modified chitosan blend membrane and its use for selective removal of H2S in natural gas.

[0006] To achieve the above-mentioned goal, the present application adopts the following technical scheme:

[0007] The application relates to a preparation method and application of an ionic liquid grafted modified chitosan blended membrane, and the synthesis steps are as follows: ionic liquid is synthesized by quaternary ammonium reaction with alkyl imidazole and double-halogenated alkane as raw materials. The obtained ionic liquid is mixed with chitosan powder and polyethylene glycol in water according to a certain molar ratio to prepare a casting solution, and a homogeneous blended membrane is prepared by a solution casting method, which is used for separating H2S in natural gas with different concentrations. The structural formula of the ionic liquid and the polyethylene glycol, the ionic liquid synthesis equation and the chitosan grafting ionic liquid reaction equation are as follows.

[0008] The structural formula of the ionic liquid and the polyethylene glycol:

[0009]

[0010] The ionic liquid synthesis equation:

[0011]

[0012] The chitosan grafting ionic liquid reaction equation:

[0013]

[0014] In the structural formula of the ionic liquid, R1 is a linear alkyl group with 1-6 carbon atoms, n is a linear alkyl group with 2-7 carbon atoms, X is halogen including chlorine and bromine, and the polyethylene glycol includes but is not limited to ethylene glycol, diethylene glycol, polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600 and polyethylene glycol 1000.

[0015] Further, the preparation method of the ionic liquid grafted modified chitosan blended membrane in the method of the application comprises the following three steps.

[0016] (1) Preparation of ionic liquid: N-alkyl imidazole and double-halogenated alkane are dissolved in an organic solvent according to a certain proportion, stirred at a certain temperature for a certain time, after the reaction is completed, the organic solvent in the reaction system is removed by reduced pressure distillation, deionized water is added for dissolution, excess double-halogenated alkane is removed by phase separation, and the residual double-halogenated alkane is extracted by ethyl acetate three times, most of the water in the ionic liquid aqueous solution is removed under the condition of heating and reduced pressure, and finally dried under the condition of high temperature and vacuum, so that the ionic liquid is obtained.

[0017] (2) Preparation of ionic liquid grafted modified chitosan blended membrane casting solution: the synthesized ionic liquid is dissolved in water, then a certain mass of chitosan powder and polyethylene glycol are added, and the mixture is stirred at a certain temperature for a certain time, so that a clear and transparent casting solution is obtained. In this process, the alkylization reaction occurs between the ionic liquid and the amino group on the chitosan molecule, so that the grafting modification of the ionic liquid and the dissolution of the chitosan are realized.

[0018] (3) Preparation of ion liquid grafted modified chitosan blend membrane: the prepared casting solution was uniformly coated on the super flat glass dish, under certain temperature and humidity conditions, most of the solvent water was slowly volatilized, and then further dried at high temperature, thus the ion liquid modified chitosan blend membrane was obtained.

[0019] Preferably, the N-alkyl imidazole required for the synthesis of the ion liquid specifically includes N-methyl imidazole, N-ethyl imidazole, N-propyl imidazole, N-butyl imidazole, N-pentyl imidazole, N-hexyl imidazole; the double-halogenated alkane specifically includes 1,2-dibromoethane, 1,3-dibromopropane, 1,4-dibromobutane, 1,5-dibromopentane, 1,6-dibromohexane, 1,7-dibromoheptane, 1,2-dichloroethane, 1,3-dichloropropane, 1,4-dichlorobutane, 1,5-dichloropentane, 1,6-dichlorohexane, 1,7-dichloroheptane; the molar ratio of N-alkyl imidazole and double-halogenated alkane is 1:5.

[0020] Preferably, the solvent required for the synthesis of the ion liquid is acetonitrile, acetone, ethyl acetate, anhydrous ethanol, anhydrous methanol, diethyl ether.

[0021] Preferably, the temperature required for the synthesis of the ion liquid is 20-100℃, and the time is 12-96h.

[0022] Preferably, the chitosan powder selected in the preparation process of the blend membrane has a molecular weight of 100-1000kDa and a degree of deacetylation of ≥90%, and the amount is 0.5-5wt.% of the solvent water, and the molar ratio of the ion liquid to chitosan monomer is 1:1.

[0023] Preferably, the polyethylene glycol selected in the preparation process of the blend membrane specifically includes but is not limited to ethylene glycol (EG), diethylene glycol (DEG), polyethylene glycol 200 (PEG200), polyethylene glycol 400 (PEG400), polyethylene glycol 600 (PEG600), polyethylene glycol 1000 (PEG1000), and the mass of the polyethylene glycol accounts for 0-60% of the total mass of the chitosan blend membrane, and the preparation temperature of the casting solution is 40-80℃, and the time is 12-48h.

[0024] Preferably, the solvent volatilization conditions in the preparation process of the blend membrane are 20-60℃ and a relative humidity of 30-50%, the drying temperature is 80-100℃, and the time is 12-48h, and the final application form of the blend membrane includes but is not limited to flat membrane, hollow fiber membrane and roll membrane.

[0025] Preferably, the pressure of the feed mixed gas containing H2S and CO2 is 0.1-5MPa, the volume concentration of H2S is 0-20%, the volume concentration of CO2 is 0-50%, and the separation temperature is 20-80℃.

[0026] Compared with the prior art, the present application has the following advantages:

[0027] (1) The present application introduces ionic liquid graft modification, which endows chitosan with water solubility and improves gas permeability, and the preparation process is simple and environmentally friendly.

[0028] (2) The present application further introduces polyethylene glycol to plasticize the ionic liquid modified chitosan membrane material, thereby improving the permeability and selectivity of H2S. The prepared modified chitosan blend membrane has a high reversible hydrogen bond interaction with H2S, and can effectively remove H2S from H2S / CO2 / CH4 mixed gas. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The figure is a photograph of the casting solution preparation process of the present application. Specifically, 0.39g [Brhmim]Br ionic liquid and 0.19g chitosan powder are dispersed in 10g solvent water, and an alkylation reaction occurs at 70°C, Figure 1 a is the initial state of the casting solution; Figure 1 b is the state of the casting solution after 2h of reaction; Figure 1 c is the state of the casting solution after 6h of reaction; Figure 1 d is the state of the casting solution after 12h of reaction.

[0030] Figure 2 The figure is a stress-strain graph of several typical ionic liquid modified chitosan blend membranes in the present application. Specifically, Figure 2 Curve a in the middle is the stress-strain curve of [Brhmim]Br-CS; curve b is the stress-strain curve of [Brhmim]Br-CS / PEG200-20%; curve c is the stress-strain curve of [Brhmim]Br-CS / PEG400-20%; curve d is the stress-strain curve of [Brhmim]Br-CS / PEG600-20%; and curve e is the stress-strain curve of [Brhmim]Br-CS / PEG200-40%.

[0031] Figure 3 The figure is a scanning electron microscope graph of a typical ionic liquid grafted chitosan blend membrane prepared in the present application. Specifically, Figure 3 a is a surface scanning electron microscope graph of [Brhmim]Br-CS / PEG200-40% membrane; Figure 3 b is a cross-sectional scanning electron microscope graph of [Brhmim]Br-CS / PEG200-40% membrane; Figure 3 c is a surface scanning electron microscope graph of [Clbpim]Cl-CS / PEG600-20% membrane; Figure 3 d is a cross-sectional scanning electron microscope graph of [Clbpim]Cl-CS / PEG600-20% membrane. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described below through specific embodiments.

[0033] Implementation Case 1

[0034] Dissolve 0.5 mol of 1,6-dibromohexane in 20 mL of acetone, add 0.1 mol of N-methylimidazole dropwise at room temperature, and heat to 40°C for 96 hours. After the reaction is complete, remove the acetone by vacuum distillation, add deionized water to dissolve, remove the excess 1,6-dibromohexane by phase separation, and extract the remaining 1,6-dibromohexane three times with ethyl acetate. Then, remove most of the water from the ionic liquid aqueous solution under heating and reduced pressure. Finally, dry under high temperature and vacuum conditions to obtain 1-bromohexyl-3-methylimidazolium bromide, denoted as [Brhmim]Br.

[0035] Implementation Case 2

[0036] Dissolve 0.5 mol of 1,4-dichlorobutane in 20 mL of anhydrous methanol, add 0.1 mol of N-propylimidazole dropwise at room temperature, and heat to 60°C for 48 hours. After the reaction is complete, remove the anhydrous methanol by distillation under reduced pressure, add deionized water to dissolve, remove the excess 1,4-dichlorobutane by phase separation, and extract the remaining 1,4-dichlorobutane three times with ethyl acetate. Then, remove most of the water from the ionic liquid aqueous solution under heating and reduced pressure, and finally dry under high temperature and vacuum conditions to obtain 1-chlorobutyl-3-propylimidazole chloride, denoted as [Clbpim]Cl.

[0037] Implementation Case 3

[0038] 1 mmol [Brhmim]Br was dissolved in 10 g of water, followed by the addition of 1 mmol of chitosan powder (based on monomer molar weight, degree of deacetylation 90%, Mw = 200,000 Da). The mixture was stirred vigorously at 70°C for 12 h to obtain a uniform and transparent casting solution. After cooling to room temperature, the casting solution was poured onto an ultra-flat glass dish. The solvent was then slowly evaporated in an environment of 50°C and 50% relative humidity. The mixture was then oven-dried at 80°C until the weight of the film remained unchanged. This yielded the ionic liquid-grafted chitosan blend film, designated [Brhmim]Br-CS. Photos of the casting solution preparation process are attached. Figure 1 The membrane stress-strain curve is shown in the attached Figure 2 As shown in a.

[0039] Implementation Case 4

[0040] Dissolve 1 mmol [Brhmim]Br in 10 g water, then add 1 mmol chitosan powder (90% deacetylation, Mw=200000 Da) and 20% of PEG200 of the total mass of the membrane, and stir vigorously at 70°C for 12 h to obtain a uniform transparent casting solution. After cooling to room temperature, the casting solution is poured on a super-flat glass dish, then slowly evaporate most of the solvent in an environment of 50°C and 50% relative humidity, and then oven-dried at 80°C until the weight of the membrane is constant, to obtain the ionic liquid grafted chitosan blend membrane, denoted as [Brhmim]Br-CS / PEG200-20%, where 20% is the total mass fraction of PEG200 in the membrane, and the stress-strain curve of the membrane is shown in Fig. 2b. Figure 2

[0041] Example 5

[0042] According to the membrane preparation method of Example 4, replace PEG200 with PEG400, to obtain the ionic liquid grafted chitosan blend membrane, denoted as [Brhmim]Br-CS / PEG400-20%, where 20% is the total mass fraction of PEG400 in the membrane, and the stress-strain curve of the membrane is shown in Fig. 2c. Figure 2

[0043] Example 6

[0044] According to the membrane preparation method of Example 4, replace PEG200 with PEG600, to obtain the ionic liquid grafted chitosan blend membrane, denoted as [Brhmim]Br-CS / PEG600-20%, where 20% is the total mass fraction of PEG600 in the membrane, and the stress-strain curve of the membrane is shown in Fig. 2d. Figure 2

[0045] Example 7

[0046] According to the membrane preparation method of Example 4, the amount of PEG200 added is increased to 40% of the total mass of the membrane, to obtain the ionic liquid grafted chitosan blend membrane, denoted as [Brhmim]Br-CS / PEG200-40%, where 40% is the total mass fraction of PEG400 in the membrane, and the stress-strain curve of the membrane is shown in Fig. 2e. Figure 2 Figure 3

[0047] Example 8

[0048] ​​​​​Dissolve 1 mmol [Clbpim]Cl in 10 g water, then add 1 mmol chitosan powder (95% degree of deacetylation, Mw = 400000 Da) and 20% of the total mass of the film PEG600, and stir vigorously at 70°C for 12 h to obtain a homogeneous transparent casting solution. After cooling to room temperature, the casting solution is poured onto a super-flat glass dish, then slowly evaporate most of the solvent in an environment of 50°C and 50% relative humidity, and then oven-dry at 80°C until the weight of the film does not change. The ion liquid grafted chitosan blend film is obtained, denoted as [Clbpim]Cl-CS / PEG600-20%, where 20% is the total mass fraction of PEG600 in the film. The surface and cross-section scanning electron micrographs of the film are shown in Figures 3a and 3d. The ion liquid and the preparation method of the chitosan blend film used in the following examples are similar to Examples 1-2 and 3-8. Figure 3 c and 3d. The ion liquid and the preparation method of the chitosan blend film used in the following examples are similar to Examples 1-2 and 3-8.

[0049] Examples 9-14

[0050] The prepared ion liquid grafted chitosan blend film was tested for H2S and CO2 permeation coefficients in different concentrations of gas sources under certain test conditions, 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:

[0051]

[0052] The results of the above embodiments show that the ion liquid grafted chitosan blend film according to the present application has excellent acid gas permeability and high selectivity. In addition, the tensile properties of several typical ion liquid modified chitosan blend films are characterized, and it is proved that they have good mechanical properties; the morphology of the prepared ion liquid grafted chitosan blend film is uniform and smooth, and there are no obvious defects. Figure 2 The tensile properties of several typical ion liquid modified chitosan blend films are characterized, and it is proved that they have good mechanical properties; the morphology of the prepared ion liquid grafted chitosan blend film is uniform and smooth, and there are no obvious defects. Figure 3 The tensile properties of several typical ion liquid modified chitosan blend films are characterized, and it is proved that they have good mechanical properties; the morphology of the prepared ion liquid grafted chitosan blend film is uniform and smooth, and there are no obvious defects.

[0053] The above is only a preferred embodiment of the present application, and the protection scope of the present application is not limited to the above examples. Any technical solutions within the scope of the present application should be considered within the protection scope of the present application. It should be noted that some improvements and refinements without departing from the principles of the present application should be considered within the protection scope of the present application.

Claims

1. A method for preparing and using a chitosan blend membrane grafted with an ionic liquid, characterized in that: First, a quaternization reaction of dihalogenated alkanes and alkyl imidazoles was used to synthesize a halogenated alkyl imidazole halide ionic liquid. The obtained ionic liquid and chitosan powder were then dispersed in water. Subsequently, a certain amount of polyethylene glycol was added as a plasticizer. The ionic liquid and chitosan were reacted under heating and stirring conditions to prepare a uniform and transparent casting solution. Finally, a self-supporting homogeneous blend membrane was prepared by solution casting for the separation of hydrogen sulfide (H2S) in natural gas. The specific preparation method is as follows: (1) Preparation of ionic liquid: N-alkyl imidazole and dihalogenated alkane are dissolved in an organic solvent in a certain proportion, and the mixture is stirred at a certain temperature for a certain time. After the reaction is completed, the organic solvent in the reaction system is removed by distillation under reduced pressure, deionized water is added to dissolve the mixture, excess dihalogenated alkane is removed by phase separation, and the residual dihalogenated alkane is extracted three times with ethyl acetate. Most of the water in the ionic liquid aqueous solution is removed under heating and reduced pressure conditions, and finally, the ionic liquid is obtained by drying under high temperature vacuum conditions. (2) Preparation of ionic liquid grafted chitosan blend membrane casting solution: The synthesized ionic liquid is dissolved in water, followed by the addition of a certain amount of chitosan powder and polyethylene glycol. The mixture is stirred vigorously at a certain temperature for a period of time to obtain a clear and transparent casting solution. During this process, the ionic liquid undergoes an alkylation reaction with the amino groups on the chitosan molecules, achieving grafting modification of the chitosan and dissolution of the chitosan. (3) Preparation of chitosan blend membrane modified by ionic liquid grafting: The prepared casting liquid is evenly coated on an ultra-flat glass dish. Under certain temperature and humidity conditions, most of the solvent water is slowly evaporated, and then further dried at high temperature to obtain an ionic liquid-modified chitosan blend membrane.

2. The chitosan blend membrane grafted with an ionic liquid and modified according to claim 1, and its preparation method and use, characterized in that: The N-alkylimidazole as a raw material for synthesizing the ionic liquid specifically includes N-methylimidazole, N-ethylimidazole, N-propylimidazole, N-butylimidazole, N-pentylimidazole, and N-hexylimidazole; the dihalogenated alkanes specifically include 1,2-dibromoethane, 1,3-dibromopropane, 1,4-dibromobutane, 1,5-dibromopentane, 1,6-dibromohexane, 1,7-dibromoheptane, 1,2-dichloroethane, 1,3-dichloropropane, 1,4-dichlorobutane, 1,5-dichloropentane, 1,6-dichlorohexane, and 1,7-dichloroheptane; and the molar ratio of the N-alkylimidazole to the dihalogenated alkanes is 1:

5.

3. The chitosan blend membrane grafted with an ionic liquid and modified according to claim 1, and its preparation method and use, characterized in that: The organic solvent used in the synthesis of the ionic liquid is acetonitrile, acetone, ethyl acetate, anhydrous ethanol, anhydrous methanol and ether.

4. The chitosan blend membrane grafted with an ionic liquid and modified according to claim 1, and its preparation method and use, characterized in that: The ionic liquid synthesis temperature is 20-100° C., and the synthesis time is 12-96 hours.

5. The chitosan blend membrane grafted with an ionic liquid and modified according to claim 1, and its preparation method and use, characterized in that: The chitosan powder selected in the preparation process of the blended film 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 molar ratio of the ionic liquid to the chitosan monomer is 1:

1.

6. The chitosan blend membrane grafted with an ionic liquid and modified according to claim 1, and its preparation method and use, characterized in that: The polyethylene glycol selected in the preparation process of the blended membrane specifically includes but is not limited to ethylene glycol, diethylene glycol, polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, and polyethylene glycol 1000. The mass of polyethylene glycol accounts for 0-60% of the total mass of the chitosan blended membrane. The preparation temperature of the casting solution is 40-80°C and the time is 12-48h.

7. The chitosan blend membrane grafted with an ionic liquid and modified according to claim 1, and its preparation method and use, characterized in that: The solvent volatilization conditions in the preparation process of the blend membrane are 20-60°C, relative humidity is 30-50%, drying temperature is 80-100°C, and time is 12-48h, and the final application form of the blend membrane includes but is not limited to flat membrane, hollow fiber membrane and roll membrane.

8. The chitosan blend membrane grafted with an ionic liquid and modified according to claim 1, and its preparation method and use, characterized in that The feed pressure of the H2S / CO2 / CH4 mixed gas is 0.1-5 MPa, the concentration of H2S is 0-20 vol%, the concentration of CO2 is 0-50 vol%, and the separation temperature is 20-80°C.

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