A method for preparing a carbon molecular sieve membrane for efficient separation of ethylene and ethane

Abstract

The application belongs to the technical field of membrane preparation and application, and discloses a preparation method of a carbon molecular sieve membrane for efficient separation of ethylene and ethane. The carbon molecular sieve membrane for efficient separation of ethylene and ethane takes polyimide containing a benzoxazole unit as a precursor material, and is carbonized after being doped with sulfur-containing substances to form a film. After carbonization, transition metal silver ions are introduced to form metal coordination complex bonds with sulfur-containing units in the membrane, thereby improving the loading amount of the transition metal silver ions, promoting the transfer of ethylene in the membrane, and improving the separation performance of ethylene and ethane. The application introduces sulfur-containing substances to complex with transition metals, greatly improves the loading amount of the transition metals, and greatly improves the separation effect of ethylene and ethane. The application has a wide application prospect in the field of ethylene and ethane separation.

Description

TECHNICAL FIELD

[0001] The application discloses a preparation method of a carbon molecular sieve membrane for efficient separation of ethylene and ethane, and belongs to the technical field of membrane preparation and application. BACKGROUND

[0002] Ethylene is the core of the petrochemical industry, and the world annual production thereof is as high as 116 MMt, however, about 40% of ethylene in China needs to be imported every year, so the separation technology of olefin and alkane has important practical significance. At present, traditional ethylene-ethane separation technologies, such as low-temperature rectification, have problems such as high energy consumption, large equipment investment and complex process. Membrane separation is a high-efficiency gas separation technology based on the difference in permeation rate, and the process does not involve phase change, and has advantages such as low energy consumption, high efficiency, small land occupation and simple operation. However, due to the similar molecular kinetic diameters and other property parameters of ethylene and ethane, the traditional polymer membrane cannot effectively separate the ethylene-ethane system, and the polymer membrane for separating ethylene and ethane has the disadvantages of low ethylene permeability and small selectivity, which are described in detail in Membrane Science and Technology, Vol. 23, No. 4, 2003, pp. 123-140.

[0003] In recent years, carbon molecular sieve membranes have been continuously researched and developed, and have high permeability, and the membrane pore size can be easily controlled by precursor materials and carbonization environment and temperature. However, the carbon molecular membrane still has the disadvantage of poor selectivity for ethylene-ethane separation. Details are described in Chemical Engineering, Vol. 67, No. 10, 2016, pp. 4225-4230. In order to make up for the shortcomings of the carbon molecular membrane, the application proposes an anchoring transition metal ion strategy containing a sulfur unit, forms a metal active site, constructs a strong π complexation between the metal ion and the ethylene host-guest, improves the separation coefficient of ethylene-ethane, and adjusts the pore size and distribution of the carbon molecular sieve membrane to improve the separation performance of ethylene and ethane. SUMMARY

[0004] In view of the performance deficiency of the existing carbon molecular sieve membrane for separating ethylene and ethane, the application provides a carbon molecular sieve membrane for efficient separation of ethylene and ethane and a preparation method thereof.

[0005] In order to achieve the above-mentioned purpose, the application provides a carbon molecular sieve membrane for efficient separation of ethylene and ethane and a preparation method thereof, which uses a polyimide containing a benzoxazole unit as a precursor material, and performs film formation by doping a sulfur-containing substance, and then carbonizes. After carbonization, transition metal ions are introduced into the membrane to increase the loading amount of silver ions, promote the transfer of ethylene in the membrane, and thus improve the separation performance of ethylene and ethane.

[0006] The technical scheme of the application is as follows:

[0007] A preparation method of a carbon molecular sieve membrane for efficient separation of ethylene and ethane, the steps are as follows:

[0008] (1) Preparation of precursor film material: the polymer A containing benzoxazole unit and the polymer B containing sulfur are dissolved in solvent A, after stirring for a period of time, the solution is poured on a glass plate after standing and defoaming, and then dried at a certain temperature and dried under vacuum to obtain the precursor film;

[0009] (2) Preparation of carbon molecular sieve membrane: the precursor film is placed in a tube furnace, and protective gas A is introduced, and carbonization is carried out at a certain temperature for a certain time, and then the carbon molecular sieve membrane is obtained after natural cooling to room temperature.

[0010] (3) Preparation of carbon molecular sieve membrane loaded with transition metal: a certain mass of carbon molecular sieve membrane is placed in a certain mass of transition metal-containing substance A dissolved in solvent B, stirred for a period of time, then taken out, and then dried at a certain temperature to obtain the carbon molecular sieve membrane loaded with transition metal.

[0011] The solvent A is one or a mixture of two or more of N, N-dimethylformamide, N, N-dimethylacetamide, tetrahydrofuran, and dimethyl sulfoxide;

[0012] The protective gas A is one or a mixture of two or more of nitrogen, argon, and CO2;

[0013] The transition metal substance A is one or a mixture of two or more of silver nitrate, copper nitrate, ferrous sulfate, silver sulfate, aluminum nitrate, aluminum sulfate, and silver tetrafluoroborate;

[0014] The solvent B is one or a mixture of two or more of methanol, ethanol, and propanol;

[0015] The polymer A is polyimide and / or polyamide;

[0016] The sulfur-containing polymer B is one or a mixture of two or more of polysulfone, polyether sulfone, and polyphenylene sulfide;

[0017] The ratio of polyimide to sulfur-containing substance in step (1) is 1:0.01-0.8;

[0018] The stirring time of the casting solution in step (1) is 8-72 h;

[0019] The drying temperature of the film in step (1) is 60-150 o C;

[0020] The carbonization temperature in step (2) is 500-1000 o C, and the carbonization time is 0.5-10 h;

[0021] The ratio of transition metal-containing substance to carbon molecular sieve membrane in step (3) is 0.1-60 % by mass; the mass concentration of the transition metal-containing substance is 1.0-50.0%;

[0022] The stirring time in step (3) is 2-48 h;

[0023] The drying temperature of the transition metal loaded carbon molecular sieve membrane in step (3) is 50-120 o C.

[0024] Compared with the prior art, the present application has the beneficial effects that: compared with other carbon molecular sieve membranes, the present application improves the loading of transition metal through the mutual coordination complexation between the sulfur-containing substance and the transition metal, and improves the permeability of ethylene through the mutual π complexation between the transition metal and ethylene, thereby greatly improving the separation capacity of ethylene and ethane, and the preparation method is simple, the effect is obvious, and the like. DETAILED DESCRIPTION

[0025] The specific embodiments of the present application will be further described below in combination with the technical solutions.

[0026] The preparation method of the polyimide used in the present application is as follows: 0.45 g of 6FAP and 0.5332 g of 6FDA are dissolved in 8 ml of N-methyl pyrrolidone under the environment of nitrogen and ice water bath, about 5 hours later, the reactor is taken out from the ice water bath and kept at room temperature for 24 h. 0.25 ml of pyridine and 1.6 ml of acetic anhydride are added to the reactor for chemical imidization. The solution is stirred at room temperature for 24 h, and finally the product is washed with methanol and water for multiple times, and vacuum dried at 80 o C for 24 h. Then the material is heated to 380 o C for 2 h and naturally cooled to form a polyimide material containing benzoxazole units.

[0027] The method used for the gas separation performance test in the present application is the constant volume pressure change method, the test temperature is 35 o C, and the test pressure is 0.2 MPa.

[0028] Comparative Example 1: 0.5 g of polyimide is dissolved in 10 ml of NMP, stirred at room temperature for 72 h. After standing for 48 h, the solution is poured onto a glass plate, dried at 105 o C, and then dried in a vacuum drying oven at 130 o C for 24 h.

[0029] About 0.8 g of the obtained membrane is taken into a tube furnace, argon gas is introduced as a protective gas, heated to 600 o C and kept for 5.0 h, and then naturally cooled to obtain the carbon molecular sieve membrane of Comparative Example 1.

[0030] Comparative Example 2: 0.5 g of polyimide and 0.25 g of polyether ether ketone were dissolved in 10 ml of NMP, and stirred at room temperature for 72 h. After standing for 48 h to remove bubbles, the solution was poured onto a glass plate, and dried at 105 o Cand then dried at 130 o Cfor 24 h in a vacuum drying oven.

[0031] About 0.8 g of the obtained membrane was put into a tube furnace, nitrogen was introduced as a protective gas, and the temperature was raised to 600 o Cand maintained for 5.0 h, and then naturally cooled to obtain the carbon molecular sieve membrane of Comparative Example 2.

[0032] Example 1: 2.0 g of polyimide was dissolved in 50 ml of DMAc, and stirred at room temperature for 48 h. After standing for 72 h to remove bubbles, the solution was poured onto a glass plate, and dried at 80 o Cand then dried at 120 o Cfor 48 h in a vacuum drying oven.

[0033] About 1.0 g of the obtained membrane was put into a tube furnace, carbon dioxide was introduced as a protective gas, and the temperature was raised to 800 o Cand maintained for 5.0 h, and then naturally cooled.

[0034] About 0.2 g of the sulfur-containing carbon molecular sieve membrane was added to 50 mL of a 25.0 wt% silver tetrafluoroborate propanol solution, stirred for 12 h, and then taken out and stood, 120 o Cvacuum drying to obtain a silver-loaded carbon molecular sieve membrane.

[0035] Example 2: 2.0 g of polyimide and 1.2 g of polyether sulfone were dissolved in 40 ml of DMF, and stirred at room temperature for 24 h. After standing for 12 h to remove bubbles, the solution was poured onto a glass plate, and dried at 100 o Cand then dried at 120 o Cfor 24 h in a vacuum drying oven.

[0036] About 1.0 g of the obtained membrane was put into a tube furnace, argon was introduced as a protective gas, and the temperature was raised to 700 o Cand maintained for 2.0 h, and then naturally cooled to obtain a sulfur-containing carbon molecular sieve membrane.

[0037] About 0.5 g of the sulfur-containing carbon molecular sieve membrane was added to 200 mL of a 10.0 wt% silver nitrate ethanol solution, stirred for 24 h, and then taken out and stood, 80 o Cvacuum drying to obtain a silver-loaded carbon molecular sieve membrane.

[0038] Example 3: 2.0 g of polyimide and 0.4 g of polyether sulfone were dissolved in 50 ml of DMAc, and stirred at room temperature for 12 h. After standing for 48 h, the solution was poured onto a glass plate, and dried at 80 o C 150 °C for 2 h, and then at 200 °C for 2 h. o C 150 °C for 2 h, and then at 200 °C for 2 h.

[0039] About 0.8 g of the obtained membrane was put into a tube furnace, argon gas was introduced as a protective gas, and the temperature was raised to 600 o C and maintained for 9 h, and then naturally cooled to obtain a sulfur-containing carbon molecular sieve membrane.

[0040] About 0.5 g of the sulfur-containing carbon molecular sieve membrane was added to 100 mL of a 40.0 wt% silver sulfate methanol solution, and stirred for 48 h. After being taken out and standing, 120 o C vacuum drying to obtain a silver-containing loaded carbon molecular sieve membrane.

[0041] Table 1 is the gas permeability and selectivity of the gas separation membranes prepared in the control examples and the examples

[0042]

Claims

1. A method for producing a carbon molecular sieve membrane for efficient separation of ethylene and ethane, characterized by, The steps are as follows: (1) Preparation of precursor film material: a polymer A containing benzoxazole unit and a sulfur-containing polymer B are dissolved in a solvent A according to a mass ratio of 1:0.01-0.8, and after being stirred uniformly, the solution is poured onto a glass plate after being deaerated by standing, and then is pre-dried and dried under vacuum to obtain a precursor film; wherein the polymer A containing benzoxazole unit is a polyimide and / or a polyamide; the sulfur-containing polymer B is one of a polysulfone, a polyether sulfone, and a polyphenylene sulfide, or a mixture of two or more thereof; (2) Carbon molecular sieve membrane preparation: the precursor membrane is placed in a tube furnace, and protective gas A is introduced, and carbonization is carried out at a carbonization temperature of 500-1000 o C for 0.5-10 h, and then naturally cooled to room temperature to obtain a carbon molecular sieve membrane; (3) Preparation of carbon molecular sieve membrane loaded with transition metal: a transition metal substance A is dissolved in a solvent B to obtain a solution of the transition metal substance A with a mass concentration of 1.0-50.0%; the carbon molecular sieve membrane is stirred in the solution of the transition metal substance A for a period of time, and then is taken out and dried to obtain a carbon molecular sieve membrane loaded with the transition metal.

2. The preparation method according to claim 1, characterized in that, in step (1), the solvent A is one of N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, and dimethyl sulfoxide, or a mixture of two or more thereof.

3. The preparation method according to claim 1, characterized in that, in step (1), the stirring time is 8-72 h; The temperature of pre-drying and drying under vacuum conditions is 60-150 o C.

4. The preparation method according to claim 1, characterized in that, in step (2), the protective gas A is one of nitrogen, argon, and CO2, or a mixture of two or more thereof.

5. The preparation method according to claim 1, characterized in that, in step (3), the transition metal substance A is one of silver nitrate, copper nitrate, ferrous sulfate, silver sulfate, aluminum nitrate, aluminum sulfate, and silver tetrafluoroborate, or a mixture of two or more thereof; the solvent B is one of methanol, ethanol, and propanol, or a mixture of two or more thereof.

6. The preparation method according to claim 1, characterized in that, in step (3), the mass ratio of the transition metal substance A to the carbon molecular sieve membrane is 0.1-60 %; the stirring time is 2-48 h; Drying temperature is 50-120 o C.

Images