Gradient pore carbon molecular sieve material for ethylene / ethane adsorption separation as well as preparation method and application of gradient pore carbon molecular sieve material

Abstract

The invention relates to the technical field of chemical separation, and discloses a gradient pore carbon molecular sieve material for ethylene / ethane adsorption separation and a preparation method and application thereof. According to the preparation method, melamine foam is taken as a substrate material, an organic monomer is subjected to self-polymerization on the surface of the melamine foam to obtain a carbon-based compound, then the carbon-based compound is subjected to pyrolysis carbonization in a temperature range of 500-700 DEG C, the gradient pore carbon molecular sieve is prepared, and the process is simple in operation process and relatively low in cost. The synthesized carbon adsorbent is of an integral structure, has the pore channel characteristic of double-micropore gradient distribution, not only can realize ethylene / ethane high-selectivity adsorption separation, but also has the ethylene mass transfer diffusion rate obviously superior to that of a single-micropore carbon molecular sieve, and has important actual industrial application value in the field of ethylene adsorption separation.

Description

Technical Field

[0001] The invention belongs to the field of adsorption separation materials, and specifically relates to a preparation method and application of a gradient pore carbon molecular sieve material with high ethylene / ethane selectivity and fast equilibrium adsorption separation performance. Background Art

[0002] Ethylene is one of the organic chemical raw materials with the largest output and usage in the world. The polymerization products derived from it account for more than 75% of petrochemical products, and it occupies an important position in the chemical industry. According to statistics, my country's ethylene production capacity will reach 51.34 million tons / year in 2023, ranking among the top in the world. The main source of industrial ethylene is low-carbon alkanes or naphtha steam cracking, but ethane by-products will be produced simultaneously during the production process, thus affecting the ethylene polymerization process. Therefore, efficiently separating polymerization-grade ethylene from ethylene / ethane mixtures is an important and challenging task in the current petrochemical industry.

[0003] Ethylene and ethane belong to the C 2 Compound system, the two have very similar physical and chemical properties, and separation is difficult. At present, the industry mainly uses high-pressure and low-temperature distillation, but its separation energy consumption is high, the equipment is complex and the cost is high. In contrast, adsorption separation technology does not involve phase change and high temperature, and has the characteristics of low energy consumption, large operating flexibility, and equipment friendliness. The key to this technology lies in the adsorbent. Carbon materials have attracted widespread attention due to their advantages of developed pores, stable structure and easy regeneration. In 2023, Du and Xiao et al. reported a polydopamine-derived microporous carbon molecular sieve PDA-C900, which has good ethylene / ethane screening and separation performance. The ethylene adsorption capacity is 1.98 mmol / g at 298K and 1 bar, while ethane is almost not adsorbed (<0.1 mmol / g) (Nat. Commun., 2023, 14(1): 1197). Bao et al. reported a carbon molecular sieve C-Suc-750 with a microporosity of nearly 100%, and the kinetic adsorption selectivity of ethylene / ethane can reach 79.4 [patent number CN202111440994.5]. Lu et al. used a polymer of resorcinol-m-phenylenediamine-formaldehyde as a precursor to develop a nitrogen-doped carbon molecular sieve material d-CMS-3, with ethylene and ethane adsorption capacities of 1.52 and 0.14 mmol / g, respectively, at room temperature and pressure (Small, 2024, 20: 240196).

[0004] Although existing carbon molecular sieve materials have shown high ethylene / ethane adsorption selectivity, they usually contain only a single microporous channel, resulting in large internal diffusion resistance, low ethylene diffusion rate and actual bed utilization. In addition, the adsorbent is generally in powder form. Due to its fine particles and high packing density, it is easy to form a compact bed structure when filling the adsorption column, which may cause problems such as wear, column blockage and high pressure drop in the adsorption bed.

[0005] Based on this, the present invention proposes a method for preparing a gradient pore carbon molecular sieve material. First, melamine foam is used as a base material, organic monomers are self-polymerized on its surface to obtain a carbon-based composite, and then a step-by-step temperature-controlled pyrolysis is performed. The foam skeleton is pyrolyzed at high temperature to form The surface polymer is pyrolyzed to form The prepared gradient pore carbon material has an integral structure, in which the "diffusion-aided" large micropores can provide ethylene mass transfer diffusion channels, weaken the internal diffusion resistance, and thus increase the ethylene adsorption rate; the "screening type" ultra-micropores have precise molecular screening capabilities, through the matching effect between molecular size and pore size, only allow the adsorption of ethylene with a slightly smaller size (molecular size < pore size), while excluding ethane with a larger size (molecular size > pore size), thereby achieving highly selective adsorption and separation of ethylene / ethane. Summary of the invention

[0006] The object of the present invention is to provide a method for preparing a gradient pore carbon molecular sieve material. The material synthesized by the method has a monolithic structure and has a pore characteristic of a double micropore gradient distribution, wherein the ultramicropore pore size is mainly concentrated between the molecular dynamics diameters of ethylene and ethane. When the material is applied to the adsorption separation of ethylene / ethane, high selectivity and rapid adsorption equilibrium can be achieved. To this end, the object of the present invention is achieved by the following technical solutions:

[0007] A method for preparing a gradient pore carbon molecular sieve material for ethylene / ethane adsorption separation, the present invention uses melamine foam as a base material, self-polymerizes an organic monomer on its surface to obtain a carbon-based composite, and then pyrolyzes and carbonizes the composite at a temperature range of 500 to 700°C to prepare a gradient pore carbon molecular sieve. Specifically, the following steps are included:

[0008] A method for preparing a gradient pore carbon molecular sieve material for ethylene / ethane adsorption separation, characterized in that it comprises the following steps:

[0009] S1. Cut the melamine foam into pieces, wash them thoroughly with ethanol, soak 4 pieces in 200 ml of deionized water, then add the nitrogen-containing organic monomer, disperse them by ultrasonic or stirring, and set aside;

[0010] S2. Weigh ammonium persulfate and dissolve it in deionized water to obtain solution A;

[0011] S3. Under sufficient stirring, solution A is added dropwise to the solution of step S1, and then the entire system is reacted at a temperature of 0 to 10° C. for 18 to 30 hours to obtain a black carbon precursor;

[0012] S4. The carbon precursor is washed and dried, placed in a temperature-controlled furnace, and heated to 500-700°C for pyrolysis and carbonization under the protection of an inert atmosphere through a step-by-step heating process. After naturally cooling to room temperature, a gradient pore carbon molecular sieve material is obtained.

[0013] Preferably, in step S1, the cutting is to cut the melamine foam into blocks of 5*2*2 cm3.

[0014] Preferably, in step S1, the nitrogen-containing organic monomer is one or more of pyrrole, aniline, dopamine and N-vinylpyrrolidone; and the concentration of the nitrogen-containing organic small molecule in deionized water is 0.00025-0.005 g / mL.

[0015] Preferably, in step S2, the concentration of ammonium persulfate in the solution A is 0.01 to 0.015 g / mL.

[0016] Preferably, in step S4, the inert atmosphere is argon, nitrogen or a mixture of the two gases in any ratio, and the flow rate is 20 to 80 mL / min.

[0017] Preferably, in step S4, the pyrolysis and carbonization reaction time is 1 to 3 hours.

[0018] Preferably, in step S4, the step-wise program heating process is: fast heating to 400°C at a heating rate of 5-20°C / min, and then slow heating to the target temperature at a rate of 1-2°C / min.

[0019] A gradient pore carbon molecular sieve material, which presents a monolithic structure at the macro level and a three-dimensional interpenetrating network skeleton at the micro level, and contains a gradient distributed pore structure, namely, "screening type" ultra-micropores and "diffusion-aiding" macro-micropores, wherein the pore size of the ultra-micropores is concentrated in The pore size distribution of macropores is within the range.

[0020] Preferably, the carbon molecular sieve material can achieve ethylene adsorption saturation within 3.5 min to 8.1 at 308 K and 0.5 bar.

[0021] A carbon molecular sieve material is used for the adsorption separation of ethylene / ethane mixed gas. The material can adsorb 2.2 mmol / g of ethylene and only 0.5 mmol / g of ethane at 298K and 1 bar.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] On the one hand, the traditional single microporous carbon molecular sieve has a deep and tortuous slit-type pore structure, the internal diffusion resistance of ethylene is large, and the adsorption equilibrium rate is slow. In contrast, the present invention provides a class of gradient pore carbon molecular sieve materials, in which ultra-micropores are used for ethylene / ethane molecular sieve identification, and large micropores provide ethylene mass transfer channels, reducing the internal diffusion resistance, thereby achieving synergistic optimization of ethylene / ethane adsorption selectivity and diffusion rate. On the other hand, in order to reduce the pressure drop of the adsorption bed in industry, it is usually necessary to use a binder to form and granulate the adsorbent. This method is very easy to block the pores, reduce the pore connectivity and ethylene mass transfer rate, and the present invention utilizes the inherent molding characteristics of commercial foams to directly construct an integral carbon frame without the use of any adhesive, thereby ensuring the connectivity between the pores. In addition, the carbon adsorbent developed by the present invention also has the advantages of stable structure and low cost, and has broad prospects for industrial separation applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the static adsorption isotherm of ethylene / ethane for the carbon molecular sieve prepared in Example 1 at 298K.

[0025] Figure 2 This is the dynamic adsorption curve of ethylene at 308K for the carbon molecular sieve prepared in Example 1.

[0026] Figure 3 This is an electron microscope image of the carbon molecular sieve material prepared in Example 1 (the inset is a macroscopic morphology image).

[0027] Figure 4 This is the static adsorption isotherm of ethylene / ethane for the carbon molecular sieve prepared in Example 2 at 298K.

[0028] Figure 5 This is the static adsorption isotherm of ethylene / ethane of the carbon molecular sieve material prepared in Comparative Example 7 at 298K. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

[0030] Example 1

[0031] First, commercial melamine foam was cut into 5×2×2cm3 squares and thoroughly cleaned with ethanol to remove surface impurities. Then, 4 pieces of foam were soaked in 200mL of deionized water, 1g of dopamine was added, and ultrasonic treatment was performed for 10 minutes to ensure uniform dispersion. 0.4g of ammonium persulfate was weighed and dissolved in 20mL of deionized water to prepare solution A. Under continuous stirring, solution A was added dropwise to the above mixture containing melamine foam and dopamine. Then, the entire system was placed in an environment of 7°C for reaction for 24 hours to obtain a black carbon precursor. The obtained precursor was then washed and dried, placed in a temperature-controlled furnace, and heated to 400°C at a rate of 5°C / min under the protection of an argon atmosphere, and then heated to 700°C at a rate of 2°C / min, and maintained at this temperature for 1 hour to complete the carbonization process. After the carbonization was completed, the material was allowed to cool naturally to room temperature to obtain carbon molecular sieve material #1.

[0032] In this example, the ethylene / ethane adsorption isotherm of carbon molecular sieve #1 was measured using a Tristar II 3020 gas adsorption instrument. The results are shown in Figure 1 The ethylene adsorption capacity of the material at 298K and 1 bar is 2.2 mmol / g, while the ethane adsorption capacity is only 0.5 mmol / g, indicating that the carbon molecular sieve in Example 1 has good separation selectivity for ethylene / ethane. The ethylene adsorption kinetic curve of carbon molecular sieve #1 at 308K and 0.5 bar was measured by gravimetric method, and the results are shown in Figure 2 As shown, it can be seen that the material can achieve ethylene adsorption saturation within 5.6 minutes, and the adsorption rate is fast. Then the pore size distribution of carbon molecular sieve #1 was measured, and the results showed that the material mainly contains The ultra-micropores and The SEM image of the test material shows that the carbon molecular sieve #1 presents a three-dimensional interpenetrating network framework, while it presents an integral structure at the macroscopic level.

[0033] Example 2

[0034] First, commercial melamine foam was cut into 5×2×2cm3 squares and thoroughly cleaned with ethanol to remove surface impurities. Then, 4 pieces of foam were soaked in 200mL deionized water, 0.6g dopamine was added, and ultrasonic treatment was performed for 10 minutes to ensure uniform dispersion. 0.3g of ammonium persulfate was weighed and dissolved in 20mL deionized water to prepare solution A. With continuous stirring, solution A was added dropwise to the above mixture containing melamine foam and dopamine. Then, the entire system was placed in an environment of 0°C for reaction for 20 hours to obtain a black carbon precursor. The precursor was then washed and dried, placed in a temperature-controlled furnace, and heated to 400°C at a rate of 5°C / min under the protection of an argon atmosphere, and then heated to 600°C at a rate of 1°C / min, and maintained at this temperature for 1 hour to complete the carbonization process. After the carbonization was completed, the material was allowed to cool naturally to room temperature to obtain carbon molecular sieve material #2. Figure 4 The ethylene / ethane adsorption isotherms of carbon molecular sieve #2 were displayed. The results showed that the ethylene adsorption capacity of the material at 298K and 1bar was 0.79mmol / g, while the ethane adsorption capacity was only 0.20mmol / g, indicating that carbon molecular sieve #2 has good separation selectivity for ethylene / ethane.

[0035] Example 3

[0036] First, commercial melamine foam was cut into 5×2×2cm3 squares and thoroughly cleaned with ethanol to remove surface impurities. Then, 4 pieces of foam were soaked in 200mL of deionized water, 0.12g of aniline was added, and ultrasonication was performed for 10 minutes to make them evenly dispersed. 0.2g of ammonium persulfate was weighed and dissolved in 20mL of deionized water to prepare solution A. Under continuous stirring, solution A was added dropwise to the above mixture containing melamine foam and aniline. Then, the entire system was placed in an environment of 7°C for reaction for 24 hours to obtain a black carbon precursor. The obtained precursor was then washed and dried, placed in a temperature-controlled furnace, heated to 400°C at a rate of 8°C / min under the protection of an argon atmosphere, and then heated to 600°C at a rate of 1°C / min, and maintained at this temperature for 1 hour to complete the carbonization process. After the carbonization was completed, the material was allowed to cool naturally to room temperature to obtain carbon molecular sieve material #3. The ethylene adsorption kinetic curve of carbon molecular sieve #3 at 308K and 0.5bar was measured, and it was found that the material could reach adsorption equilibrium within 8.1min.

[0037] Example 4

[0038] First, commercial melamine foam was cut into 5×2×2cm3 squares and thoroughly cleaned with ethanol to remove surface impurities. Then, 4 pieces of foam were soaked in 200mL deionized water, 0.3g N-vinyl pyrrolidone was added, and ultrasonication was performed for 10 minutes to make them uniformly dispersed. 0.2g of ammonium persulfate was weighed and dissolved in 20mL deionized water to prepare solution A. Under continuous stirring, solution A was added dropwise to the above mixture containing melamine foam and aniline. Then, the entire system was placed in an environment of 10°C for reaction for 24 hours to obtain a black carbon precursor. The obtained precursor was then washed and dried, placed in a temperature-controlled furnace, heated to 400°C at a rate of 5°C / min under the protection of an argon atmosphere, and then heated to 700°C at a rate of 1°C / min, and maintained at this temperature for 1 hour to complete the carbonization process. After the carbonization was completed, the material was allowed to cool naturally to room temperature to obtain carbon molecular sieve adsorption material #4. By measuring the ethylene adsorption kinetic curve of carbon molecular sieve #4 at 308K and 0.5bar, it was found that the material can reach adsorption equilibrium within 3.5min.

[0039] Example 5

[0040] First, commercial melamine foam was cut into 5×2×2cm3 squares and thoroughly cleaned with ethanol to remove surface impurities. Then, 4 pieces of foam were soaked in 200mL deionized water, 0.16g aniline and 0.11g pyrrole, and ultrasonicated for 10 minutes to make them evenly dispersed. Then 0.3g of ammonium persulfate was weighed and dissolved in 20mL deionized water to prepare solution A. Under continuous stirring, solution A was added dropwise to the above mixture containing melamine foam and pyrrole. Then the entire system was placed in an environment of 7°C for reaction for 24 hours to obtain a black carbon precursor. The obtained precursor was then washed and dried, placed in a temperature-controlled furnace, heated to 400°C at a rate of 5°C / min under argon atmosphere protection, and then heated to 600°C at a rate of 1.5°C / min, and maintained at this temperature for 1 hour to complete the carbonization process. After the carbonization was completed, the material was allowed to cool naturally to room temperature to obtain carbon molecular sieve adsorption material #5. By measuring the ethylene adsorption kinetic curve of carbon molecular sieve #5 at 308K and 0.5bar, it was found that the material could reach adsorption equilibrium within 4.8min.

[0041] In order to further illustrate the superiority of the present application, the present application also provides the following comparative examples.

[0042] Comparative Example 6

[0043] Compared with Example 1, the difference of Comparative Example 6 is that melamine foam is not used as the base material. Dopamine is directly polymerized and then heated to 900°C at a rate of 5°C / min for carbonization for 1 hour under the protection of argon atmosphere to obtain comparative carbon molecular sieve #6. By testing the pore size distribution, it is found that the pore size of carbon molecular sieve #6 is between the kinetic diameters of ethylene and ethane, and ethylene / ethane screening separation can be achieved. However, the results of the kinetic adsorption experiment show that the material takes about 21 minutes to achieve ethylene adsorption equilibrium, indicating that the diffusion rate of ethylene molecules by a single microporous carbon molecular sieve is slow, further proving that the gradient pore carbon molecular sieve can significantly increase the ethylene adsorption rate.

[0044] Comparative Example 7

[0045] Compared with Example 5, the difference of Comparative Example 7 is that the temperature is raised to 400°C at a rate of 5°C / min under argon atmosphere protection, and then raised to 900°C at a rate of 2°C / min for pyrolysis. The other conditions are the same as those of Example 5, thereby preparing comparative carbon molecular sieve material #7. The adsorption isotherm of ethylene / ethane is measured, as shown in FIG. Figure 5 As shown in the figure, it was found that the material had an ethylene adsorption capacity of 2.51 mmol / g at 298 K and 1 bar, while the ethane adsorption capacity was 2.76 mmol / g, which is an ethane selective adsorbent. This is because carbon molecular sieve #6 lacks ultra-micropores that can be used to screen and separate ethylene / ethane. When the foam skeleton is pyrolyzed at a higher temperature, more CO is released. 2 NH 3 , H 2 Reducing gases such as O produce a strong etching reaction on the carbon skeleton, resulting in the pore size being larger than the molecular size of ethylene and ethane, thus showing a co-adsorption phenomenon for the two gases.

[0046] It should be understood that the above detailed description of the technical solution of the present invention with the help of optimized embodiments is illustrative rather than restrictive, and it cannot be determined that the specific implementation methods of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, modifications to the technical solutions recorded in the embodiments, or equivalent replacement of some of the technical features therein, should be deemed to fall within the scope of patent protection determined by the claims submitted for the present invention.

[0047] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a gradient pore carbon molecular sieve material for ethylene / ethane adsorption separation, characterized in that: The following steps are involved: S1. Cut the melamine foam into pieces, wash them thoroughly with ethanol, soak them in deionized water, then add the nitrogen-containing organic monomer, disperse them by ultrasonic or stirring, and set aside; S2. Weigh ammonium persulfate and dissolve it in deionized water to obtain solution A; S3. Under sufficient stirring, solution A is added dropwise to the solution of step S1, and then the entire system is reacted at a temperature of 0 to 10° C. for 18 to 30 hours to obtain a black carbon precursor; S4. The carbon precursor is washed and dried, placed in a temperature-controlled furnace, and heated to 500-700°C for pyrolysis and carbonization under the protection of an inert atmosphere through a step-by-step heating process. After naturally cooling to room temperature, a gradient pore carbon molecular sieve material is obtained.

2. The method for preparing the gradient pore carbon molecular sieve material for ethylene / ethane adsorption separation according to claim 1, characterized in that: In step S1, the cutting is to cut the melamine foam into blocks of 5*2*2cm3.

3. The method for preparing the gradient pore carbon molecular sieve material for ethylene / ethane adsorption separation according to claim 1, characterized in that: In step S1, the nitrogen-containing organic monomer is one or more of pyrrole, aniline, dopamine and N-vinylpyrrolidone; and the concentration of the nitrogen-containing organic small molecule in deionized water is 0.00025-0.005 g / mL.

4. The method for preparing the gradient pore carbon molecular sieve material for ethylene / ethane adsorption separation according to claim 1, characterized in that: In step S2, the concentration of ammonium persulfate in the solution A is 0.01-0.02 g / mL.

5. The method for preparing the gradient pore carbon molecular sieve material for ethylene / ethane adsorption separation according to claim 1, characterized in that: In step S4, the inert atmosphere is argon, nitrogen or a mixture of the two gases in any ratio, and the flow rate is 20 to 80 mL / min.

6. The method for preparing the gradient pore carbon molecular sieve material for ethylene / ethane adsorption separation according to claim 1, characterized in that: In step S4, the pyrolysis and carbonization reaction time is 1 to 3 hours.

7. The method for preparing the gradient pore carbon molecular sieve material for ethylene / ethane adsorption separation according to claim 1, characterized in that: In step S4, the step-by-step program heating process is: fast heating to 400°C at a heating rate of 5-20°C / min, and then slow heating to the target temperature at a rate of 1-2°C / min.

8. A carbon molecular sieve material prepared by the method according to any one of claims 1 to 7, characterized in that: The material presents a monolithic structure at the macro level and a three-dimensional interpenetrating network skeleton at the micro level, and contains a gradient-distributed pore structure, namely, "screening-type" ultra-micropores and "diffusion-aiding" macro-micropores, wherein the pore sizes of the ultra-micropores are concentrated in The pore size distribution of macropores is within the range.

9. The carbon molecular sieve material according to claim 1, characterized in that: The carbon molecular sieve material achieves ethylene adsorption saturation within 3.5 to 8.1 minutes at 308K and 0.5 bar.

10. The carbon molecular sieve material according to claim 8 is used for the adsorption separation of ethylene / ethane mixed gas.

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