A method for preparing a carbon-based gas separation membrane

Abstract

The application provides a preparation method of a carbon-based gas separation membrane for CO2 separation. The method uses carbon quantum dots as a precursor, composites a small molecule compound, is dissolved in a certain solvent, is stirred uniformly, and is left to obtain a membrane liquid. Then a certain volume of the membrane liquid is coated on the surface of a gamma-Al2O3 carrier, is dried at room temperature, is treated in an oven, and is calcined in a tube furnace to obtain a carbon-based gas separation membrane which can be applied to CO2 separation. The method overcomes the disadvantages of traditional carbon molecular sieve membranes, such as using a complex high polymer as a precursor, a very high calcination temperature, and easy cracking and curling, the membrane preparation process is simpler, the raw materials are green and economical, the trade-off effect is overcome, and the separation performance is excellent.

Description

Technical Field

[0001] This invention belongs to the field of chemical separation, and specifically relates to a method for preparing a carbon-based gas separation membrane. Background Technology

[0002] Excessive emissions and improper use of the greenhouse gas CO2 have led to a series of climate problems, including global warming, glacial melting, and sea-level rise. Therefore, the capture and conversion of CO2 from flue gas is of paramount importance. Furthermore, pre-combustion capture of CO2 from natural gas is crucial for improving CH4 combustion efficiency, thus research on CO2 separation from natural gas has received widespread attention. Current CO2 separation technologies include cryogenic distillation, pressure swing adsorption, chemical absorption, and membrane separation. Among these, membrane separation technology has become a research hotspot due to its advantages of low energy consumption, simple equipment, small footprint, and low investment. To date, most membrane materials suitable for large-scale industrial applications are polymeric materials, which are easy to process, but they suffer from a significant trade-off effect in permeability and selectivity. Inorganic membranes, however, can overcome the Robinson's limit of membrane separation performance, making them a research focus. Carbon molecular sieve membranes, in particular, possess good thermal stability and pressure resistance, as well as selective sieving and adsorption of gas molecules, making them suitable for CO2 separation and promising for industrial applications. However, the preparation of carbon molecular sieve membranes generally requires high molecular polymer materials as precursors, and involves strict calcination and heating procedures and atmospheric conditions, and also suffers from problems such as high membrane brittleness and aging. Summary of the Invention

[0003] This invention aims to provide a method for preparing a carbon-based gas separation membrane and apply the carbon-based gas separation membrane to the separation of CO2. Compared with the traditional carbon molecular sieve membrane process, it simplifies the complicated preparation process of polymer precursors, reduces the calcination temperature under an inert atmosphere, and improves the problem of the membrane being brittle and easy to crack with the support of the carrier.

[0004] The present invention discloses a method for preparing a carbon-based gas separation membrane, specifically using carbon quantum dots as a precursor, compounding small molecule compounds to obtain a membrane solution, coating the membrane solution onto a carrier surface using a drop-coating or dip-coating method, and then drying and calcining to obtain a carbon-based gas separation membrane, which is applied to the efficient separation of CO2 in CO2 / CH4 and CO2 / N2. The carbon-based gas separation membrane prepared by this method differs from carbon molecular sieve membranes, which typically use high-molecular polymer materials as precursors; instead, it uses carbon quantum dots as a precursor, and its synthesis can utilize various environmentally friendly and inexpensive organic materials or biomass as raw materials.

[0005] The method described in this invention is used to prepare a carbon-based gas separation membrane. The surface of carbon quantum dots contains abundant functional groups (-COOH, -NH2, -OH, etc.), which can undergo cross-linking reactions with the groups of certain small molecule compounds. After post-treatment steps such as drying and calcination, this cross-linked structure is reorganized to obtain a carbon-based membrane with a porous structure and preferential adsorption of a certain gas, thereby realizing the separation and purification of specific components in a mixed gas.

[0006] The method described in this invention is used to prepare a carbon-based gas separation membrane. The structure of the carbon-based separation membrane is controlled by changing the ratio of carbon quantum dots to small molecule additives, the amount of membrane droplets added, the drying time, the calcination temperature, and the calcination time, so as to optimize its separation performance.

[0007] This invention provides a method for preparing a carbon-based gas separation membrane, comprising the following steps:

[0008] (1) Add a certain mass of carbon quantum dots to the solvent and stir magnetically at room temperature for 3-24 hours until a colloidal dispersion is formed;

[0009] (2) Add a certain proportion of small molecule compounds to the carbon quantum dot colloid obtained in step (1), stir for 5-24 hours to allow it to undergo a cross-linking reaction, let it stand, and obtain the membrane solution for preparing carbon-based separation membrane.

[0010] (3) Coat the membrane solution obtained in step (2) onto the carrier, dry at room temperature for 1-3 days, put it in an oven and dry at 100-200℃ for 5-20 hours to obtain a pre-treated loaded membrane.

[0011] (4) The membrane obtained in step (3) is placed in a tube furnace, calcined in an inert atmosphere, and cooled to room temperature to obtain a carbon-based gas separation membrane for CO2 separation.

[0012] Based on the above preparation method, preferably, carbon quantum dots are synthesized using citric acid and ethylenediamine (molar ratio 1:1) as raw materials via a hydrothermal method. The reaction temperature is 150-200℃, and the hydrothermal time is 5-10 h. Specific synthesis methods can be found in relevant literature. The carbon quantum dot size is approximately 3-5 nm, and the concentration of the prepared carbon quantum dot colloid is 0.5-2.0 g / L. -1 .

[0013] Based on the above preparation method, preferably, the solvent in step (1) can be at least one of water, ethanol, methanol and ethylene glycol.

[0014] Based on the above preparation method, preferably, the small molecule compound in step (2) is generally a compound containing amino or imino groups, preferably triethylamine, dopamine or polyethyleneimine.

[0015] Based on the above preparation method, preferably, the mass ratio of carbon quantum dots to small molecule compounds in step (2) is 1-4:1.

[0016] Based on the above preparation method, preferably, the support in step (3) is a γ-Al2O3 support or an α-Al2O3 support, and the minimum pore size of the selected support is 5 nm.

[0017] Based on the above preparation method, preferably, the method of coating the membrane liquid onto the carrier in step (3) can be drop coating or dip-coating method, wherein the preferred ratio of the amount of membrane liquid added to the carrier is 0.1-1 mL: diameter 18 mm, and the optimal membrane preparation method is to drop 0.1-1 mL of membrane liquid onto the surface of a 5 nm-γ-Al2O3 carrier (diameter 18 mm, thickness 1 mm).

[0018] Based on the above preparation method, preferably, the inert atmosphere in step (4) is one of nitrogen, helium, or argon, and the heating rate is 0.5-2℃ / min. -1 The maximum calcination temperature is 300-450℃, the calcination time is 5-30h, and the carbon-based separation membrane for CO2 separation is finally obtained by programmed cooling or natural cooling.

[0019] The beneficial effects of this invention are:

[0020] (1) In this invention, carbon quantum dots are selected as the precursor for preparing carbon-based gas separation membranes. Carbon quantum dots are widely available and inexpensive raw materials and can be synthesized by a simple hydrothermal method. This reduces the complicated preparation process of polymer precursors for traditional carbon molecular sieve membranes and overcomes the disadvantages of easy cracking and curling. At the same time, the calcination temperature is also lower than the carbonization temperature of traditional carbon molecular sieve membranes. Therefore, the membrane preparation process is simpler and the raw materials used are greener and more economical.

[0021] (2) The carbon-based separation membrane prepared by the present invention uses γ-Al2O3 or α-Al2O3 as a carrier, which avoids the problem of brittleness and easy cracking of self-supporting carbon membranes, greatly improves the mechanical properties of the membrane, and significantly reduces the membrane thickness, increases the permeation of gas molecules, overcomes the trade-off effect, and has excellent separation performance. Attached Figure Description

[0022] Figure 1 The images show the SEM surface morphology (left) and cross-section (right) of the carbon-based gas separation membrane prepared under the condition of a carbon quantum dot to dopamine mass ratio of 2:1 as described in Example 3 of this invention. Detailed Implementation

[0023] The following embodiments will further illustrate the present invention, but are not intended to limit the invention.

[0024] Comparative Example 1

[0025] Preparation of pure carbon quantum dot film: 0.024 g of hydrothermally synthesized carbon quantum dots [Zhu S, Meng Q, Wang L, et al. Highly Photoluminescent Carbon Dots for Multicolor Patterning, Sensors, and Bioimaging[J]. Angewandte Chemie International Edition, 2013, 125(14): 4045-4049.] were dispersed in 20 mL of deionized water and stirred for 3 h to obtain 1.2 g L -1 A carbon quantum dot colloidal dispersion system was prepared. 0.5 mL of the carbon quantum dot colloid was drop-coated onto a blank 5 nm γ-Al₂O₃ support (18 mm diameter, 1 mm thickness) at room temperature. After drying at room temperature for one day, the membrane was placed in a 150 °C oven for 10 h and then cooled to room temperature. The membrane was then calcined under Ar gas at 1 °C for 1 min. -1 Heat to 350℃, hold for 5 hours, then reduce temperature by 1℃ / min. -1 The carbon-based gas separation membrane was obtained by cooling to room temperature. The prepared carbon-based gas separation membrane was sealed in a membrane module, and the CO2 permeation rate measured at room temperature reached 1.53 × 10⁻⁶. -7 molm -2 s -1 Pa -1 The separation selectivity for CO2 / CH4 was 2.37.

[0026] Comparative Example 2

[0027] Preparation of pure dopamine membrane: Weigh 0.024 g of dopamine hydrochloride and dissolve it in 20 mL of deionized water. Stir for 3 h to obtain 1.2 g L. -1 A 0.5 mL solution of dopamine was drop-coated onto a blank 5 nm γ-Al₂O₃ support (18 mm in diameter, 1 mm thick) at room temperature. After drying at room temperature for 1 day, the membrane was dried in a 150 °C oven for 10 h and then cooled to room temperature. The resulting dopamine membrane was sealed in a membrane module, and the CO₂ permeate at room temperature was measured to be 7.12 × 10⁻⁶. -7 mol m -2 s -1 Pa -1 The separation selectivity for CO2 / CH4 was 0.88.

[0028] Example 1

[0029] 0.024 g of hydrothermally synthesized carbon quantum dots [Zhu S, Meng Q, Wang L, et al. Highly Photoluminescent Carbon Dots for Multicolor Patterning, Sensors, and Bioimaging[J]. Angewandte Chemie International Edition, 2013, 125(14):4045-4049.] were dispersed in 20 mL of deionized water and stirred for 3 h to obtain 1.2 g L. -1 A carbon quantum dot colloidal dispersion system was prepared. Then, controlling the mass ratio of carbon quantum dots to small molecule compounds at 1:1, triethylamine, dopamine, polyvinyl alcohol, and polyethyleneimine were added to the carbon quantum dot colloid, and the mixture was stirred for 10 hours to ensure homogeneity. After standing, a membrane solution was obtained. 0.5 mL of the membrane solution was drop-coated onto the surface of a blank 5 nm-γ-Al₂O₃ support (18 mm in diameter, 1 mm thick) at room temperature. After drying at room temperature for 1 day, the membrane was placed in a 150 °C forced-air drying oven for 10 hours and then cooled to room temperature. The membrane was then calcined under an Ar atmosphere at 1 °C for 1 minute. -1 Heat to 350℃, hold for 5 hours, then reduce temperature by 1℃ / min. -1 The carbon-based gas separation membrane was obtained by cooling to room temperature. The prepared carbon-based gas separation membrane was sealed in a membrane module, and the CO2 permeation and CO2 / CH4 separation selectivity were measured at room temperature, as shown in Table 1.

[0030] Table 1:

[0031]

[0032] Example 2

[0033] 0.024 g of hydrothermally synthesized carbon quantum dots [Zhu S, Meng Q, Wang L, et al. Highly Photoluminescent Carbon Dots for Multicolor Patterning, Sensors, and Bioimaging[J]. Angewandte Chemie International Edition, 2013, 125(14):4045-4049.] were dispersed in 20 mL of deionized water and stirred for 3 h to obtain 1.2 g L. -1 Aqueous dispersion of carbon quantum dots. Since carbon quantum dots have low solubility in ethanol, 0.0024 g of carbon quantum dots were dispersed in 20 mL of ethanol, yielding 0.12 g L. -1An ethanol dispersion system of carbon quantum dots was prepared. The mass ratio of carbon quantum dots to dopamine was controlled at 1:1. Dopamine was added to both the aqueous and ethanol dispersion systems of carbon quantum dots, and the mixture was stirred for 10 hours to ensure homogeneity. After standing, a membrane solution was obtained. 0.5 mL of the membrane solution was drop-coated onto a blank 5 nm γ-Al₂O₃ support (18 mm diameter, 1 mm thickness) at room temperature. After drying at room temperature for one day, the membrane was placed in a 150 °C oven for 10 hours and then cooled to room temperature. The membrane was then calcined under an Ar atmosphere at 1 °C for 1 minute. -1 Heat to 350℃, hold for 5 hours, then reduce temperature by 1℃ / min. -1 The temperature was lowered to room temperature to obtain a carbon-based gas separation membrane. The prepared carbon-based gas separation membrane was sealed in a membrane module, and the CO2 permeation and CO2 / CH4 separation selectivity were measured at room temperature, as shown in Table 2.

[0034] Table 2:

[0035]

[0036]

[0037] Example 3

[0038] 0.024 g of hydrothermally synthesized carbon quantum dots [Zhu S, Meng Q, Wang L, et al. Highly Photoluminescent Carbon Dots for Multicolor Patterning, Sensors, and Bioimaging[J]. Angewandte Chemie International Edition, 2013, 125(14):4045-4049.] were dispersed in 20 mL of deionized water and stirred for 3 h to obtain 1.2 g L. -1 A carbon quantum dot colloidal dispersion system was prepared. Dopamine was added to the carbon quantum dot colloid at mass ratios of 1:1, 2:1, and 4:1, and stirred for 10 hours to ensure homogeneity. The mixture was then allowed to stand to obtain a membrane solution. 0.5 mL of the membrane solution was drop-coated onto a blank 5 nm γ-Al₂O₃ support (18 mm diameter, 1 mm thickness) at room temperature. After drying at room temperature for one day, the membrane was dried in a 150 °C oven for 10 hours and then cooled to room temperature. The membrane was then calcined under an Ar atmosphere at 1 °C for 1 minute. -1 Heat to 350℃, hold for 5 hours, then reduce temperature by 1℃ / min. -1 The carbon-based gas separation membrane was obtained by cooling to room temperature. The prepared carbon-based gas separation membrane was sealed in a membrane module, and the CO2 permeation and CO2 / CH4 separation selectivity were measured at room temperature, as shown in Table 3.

[0039] Table 3:

[0040]

[0041] Example 4

[0042] 0.024 g of hydrothermally synthesized carbon quantum dots [Zhu S, Meng Q, Wang L, et al. Highly Photoluminescent Carbon Dots for Multicolor Patterning, Sensors, and Bioimaging[J]. Angewandte Chemie International Edition, 2013, 125(14):4045-4049.] were dispersed in 20 mL of deionized water and stirred for 3 h to obtain 1.2 g L. -1 A carbon quantum dot colloidal dispersion system was prepared. Dopamine was added to the carbon quantum dot colloid while maintaining a carbon quantum dot to dopamine mass ratio of 2:1. The mixture was stirred for 10 hours to ensure homogeneity. After standing, a membrane solution was obtained. 0.5 mL of the membrane solution was drop-coated onto a blank 5 nm γ-Al₂O₃ support (18 mm diameter, 1 mm thickness) at room temperature. After drying at room temperature for one day, the membrane was placed in a 150 °C oven for 10 hours and then cooled to room temperature. The membrane was then calcined under an Ar atmosphere at 1 °C for 1 minute. -1 The temperatures were sequentially increased to 250℃, 300℃, 350℃, 400℃, and 450℃, held for 5 hours, and then decreased by 1℃ / min. -1 The carbon-based gas separation membrane was obtained by cooling to room temperature. The prepared carbon-based gas separation membrane was sealed in a membrane module, and the CO2 permeation and CO2 / CH4 separation selectivity were measured at room temperature, as shown in Table 4.

[0043] Table 4:

[0044]

[0045] Example 5

[0046] 0.024 g of hydrothermally synthesized carbon quantum dots [Zhu S, Meng Q, Wang L, et al. Highly Photoluminescent Carbon Dots for Multicolor Patterning, Sensors, and Bioimaging[J]. Angewandte Chemie International Edition, 2013, 125(14):4045-4049.] were dispersed in 20 mL of deionized water and stirred for 3 h to obtain 1.2 g L. -1 A carbon quantum dot colloidal dispersion system was prepared. Dopamine was added to the carbon quantum dot colloid while maintaining a carbon quantum dot to dopamine mass ratio of 2:1. The mixture was stirred for 10 hours to ensure homogeneity. After standing, a membrane solution was obtained. 0.1 mL, 0.3 mL, and 0.5 mL of the membrane solution were drop-coated onto a blank 5 nm γ-Al₂O₃ support (18 mm diameter, 1 mm thickness) at room temperature. After drying at room temperature for one day, the membrane was placed in a 150 °C oven for 10 hours and then cooled to room temperature. The membrane was then calcined under an Ar atmosphere at 1 °C for 1 minute. -1 Heat to 350℃, hold for 5 hours, then reduce temperature by 1℃ / min. -1 The carbon-based gas separation membrane was obtained by cooling to room temperature. The prepared carbon-based gas separation membrane was sealed in a membrane module, and the CO2 permeation and CO2 / CH4 separation selectivity were measured at room temperature, as shown in Table 5.

[0047] Table 5:

[0048]

[0049] Many examples can be listed above. The applicant’s extensive experimental data proves that as long as it is within the scope of the technical solution of this invention, a carbon-based gas separation membrane that can be used to separate CO2 can be successfully prepared by this method.

Claims

1. A method for preparing a carbon-based gas separation membrane for CO2 separation, characterized in that, Includes the following steps: (1) Disperse carbon quantum dots in a solvent and stir for 3-24 hours to form a colloidal dispersion system; (2) Add small molecule compounds to the carbon quantum dot colloid obtained in step (1), stir for 5-24 hours, let stand, and obtain the membrane solution for preparing carbon-based separation membrane; (3) Coat the membrane solution obtained in step (2) onto the surface of the carrier, dry at room temperature for 1-3 days, put it in an oven and dry at 100-200℃ for 5-20 hours to obtain a pre-treated membrane. (4) The membrane obtained in step (3) is calcined in an inert atmosphere and cooled to room temperature to obtain a carbon-based gas separation membrane; The small molecule additive mentioned in step (2) is a compound containing amino or imino groups; The support mentioned in step (3) is a γ-Al2O3 or α-Al2O3 support; The inert atmosphere in step (4) is one of nitrogen, helium, or argon, and the heating rate is 0.5-2℃ / min. -1 The roasting temperature is 250-450℃ and the roasting time is 5-30h.

2. The preparation method according to claim 1, characterized in that, The concentration of the prepared carbon quantum dot colloid was 0.5-2.0 g / L. -1 .

3. The preparation method according to claim 1, characterized in that, The small molecule additive mentioned in step (2) is triethylamine, dopamine or polyethyleneimine.

4. The preparation method according to claim 1, characterized in that, The mass ratio of carbon quantum dots to small molecule compounds in step (2) is 1-4:

1.

5. The preparation method according to claim 1, characterized in that, In step (3), the membrane solution can be coated onto the carrier by either drop coating or dip-coating.

6. The preparation method according to claim 1, characterized in that, The solvent mentioned in step (1) is at least one of water, ethanol, methanol and ethylene glycol.

7. The preparation method according to claim 1, characterized in that, The carbon quantum dots have a size of 3-5 nm.

Images