N, s co-doped ultra-microporous carbon material, and preparation method and application thereof

Abstract

This invention discloses an N,S co-doped ultraporous carbon material, its preparation method, and its applications. The method involves synthesizing a precursor PS-3 via polymerization using 3-cyanopyridine and p-toluenesulfonic acid as raw materials. The precursor PS-3 is then subjected to high-temperature carbonization at different temperatures to obtain the N,S co-doped ultraporous carbon material with pore size. This invention eliminates the activation step, requiring only one reaction step, with mild reaction conditions and simple equipment. The ultraporous pores obtained in this invention have a pore size <0.6 nm, classifying them as ultraporous. This is mainly due to their lack of nitrogen adsorption but high carbon dioxide adsorption, indicating the presence of numerous ultraporous structures with pore sizes around 0.33 nm. The specific pore size and pore area were then determined using 195K carbon dioxide. Testing showed that the material can be used for ethane / ethylene adsorption separation, exhibiting excellent adsorption separation performance and a large adsorption ratio.

Description

Technical Field

[0001] This invention belongs to the field of functionalized ultraporous organic polymer preparation technology, specifically relating to an N,S co-doped ultraporous carbon material and its preparation method and application. Background Technology

[0002] Ethylene is one of the most important chemical raw materials in the petrochemical industry, widely used in the manufacture of various polymers and organic compounds. A key processing step in ethylene feedstock is the separation of C2H6 / C2H4 mixtures. Therefore, effectively improving the separation efficiency of C2H6 / C2H4 mixtures has become a major challenge in the industry. Adsorption separation technology utilizes differences in molecular geometry and physical properties, offering advantages such as energy saving and high efficiency. Carbon materials, as porous materials, show great promise and wide application in gas separation due to their rich properties, attracting attention for their high pore size, good stability, and high separation efficiency.

[0003] Currently reported ultraporous carbon materials are mostly prepared using biomass as a precursor, followed by high-temperature carbonization for the adsorption and separation performance of alkane / olefins. However, using biomass as a raw material for ultraporous carbon preparation presents several challenges. First, the variety of raw material sources leads to inconsistent performance. Second, published results show that materials obtained using biomass as a precursor exhibit low selectivity for C2H6 / C2H4. In contrast, obtaining carbon precursors through fixed chemical reactions offers advantages such as large-scale synthesis and good stability. Therefore, developing an ultraporous carbon material capable of achieving efficient C2H6 / C2H4 separation still presents significant room for improvement. Summary of the Invention

[0004] The purpose of this invention is to provide an N,S co-doped ultraporous carbon material, its preparation method, and its application. This method eliminates the activation step, requires only one reaction, has mild reaction conditions, and uses simple equipment. The prepared ultraporous carbon material has a high adsorption ratio for ethane / ethylene adsorption and separation.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing N,S co-doped ultraporous carbon material involves using 3-cyanopyridine and p-toluenesulfonic acid as raw materials to synthesize a precursor PS-3 via polymerization reaction, and then subjecting the precursor PS-3 to high-temperature carbonization at different temperatures to obtain an N,S co-doped ultraporous carbon material with pore size.

[0007] The structural formula of the precursor PS-3 is as follows:

[0008] Further, the specific steps are as follows:

[0009] S1. Mix 3-cyanopyridine and p-toluenesulfonic acid with anhydrous ethanol, and stir until 3-cyanopyridine and p-toluenesulfonic acid are completely dissolved to obtain homogeneous solution A and homogeneous solution B, respectively.

[0010] S2. Mix and stir the homogeneous solution A and homogeneous solution B obtained in step S1, and react at room temperature for 6-8 hours.

[0011] S3. Perform rotary evaporation on the reaction solution obtained in step S2, setting the rotary evaporation temperature to above 35°C, and stop rotary evaporation when the liquid is completely evaporated.

[0012] S4. Add the product obtained in step S3 to ethyl acetate and stir for more than 12 hours. The solution gradually changes from colorless to white suspension. Then filter to obtain white solid substance and dry to obtain precursor PS-3.

[0013] S5. Place the precursor PS-3 obtained in step S4 in a tube furnace, set the carbonization temperature to 600-800℃ and the carbonization time to 100-140min, and finally obtain PS-3-C.

[0014] Preferably, in step S1, the molar ratio between 3-cyanopyridine and p-toluenesulfonic acid is 1:1, and the concentrations of 3-cyanopyridine and p-toluenesulfonic acid in homogeneous solution A and homogeneous solution B are both 2.4 mol / L.

[0015] Preferably, in step S5, the carbonization temperature is set to one of 600℃, 700℃, and 800℃.

[0016] Preferably, in step S5, the carbonization temperature is set to 800°C.

[0017] Preferably, in step S5, nitrogen is pre-purged into the tube furnace for 30 minutes to purge air from the tube, the nitrogen atmosphere is stabilized at 10 ml / min, and the heating rate of the tube furnace is 10 °C / min.

[0018] Preferably, all stirring involved in the steps is magnetic stirring.

[0019] To achieve the above objectives, the present invention also provides N,S co-doped ultraporous carbon materials prepared by the above preparation method.

[0020] To achieve the above objectives, the present invention also provides the application of the N,S co-doped ultraporous carbon material prepared by the above preparation method in the adsorption and separation of ethane / ethylene.

[0021] The reaction route of this invention is as follows (carbonization temperature is 600℃):

[0022]

[0023] This invention yields N,S co-doped ultraporous materials through effective structural design and a simple synthesis method. The entire process involves reacting 3-cyanopyridine and p-toluenesulfonic acid as raw materials to obtain the precursor PS-3, followed by high-temperature carbonization to shrink the pores, resulting in pore structures with different pore sizes containing N and S elements. By specifically designing the material structure to contain abundant N and S elements, the formation of ultraporous pores is facilitated, ultimately leading to its application in the study of ethane / ethylene adsorption and separation performance.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) The preparation process of the present invention requires only one reaction, the reaction conditions are mild, and the equipment used is simple, which has broad prospects for industrialization and large-scale application.

[0026] (2) The process of this invention is simple. On the one hand, the raw materials are all chemical raw materials with stable sources; on the other hand, it eliminates the steps of activating the original materials and alkali etching, which greatly shortens the reaction time and cost.

[0027] (3) The carbon material prepared by the present invention does not adsorb nitrogen but has a high adsorption of carbon dioxide, thus it is determined that it has a large number of ultra-microporous structures with a pore size of about 0.33 nm. The specific pore size and pore area are then determined by carbon dioxide at 195 K. The test shows that this material can be used for the adsorption and separation of C2H4 / C2H6 with an adsorption ratio of up to 21.57, which has excellent adsorption and separation effect and is better than most of the reported high-selectivity carbon adsorbents for C2H4 / C2H6. Attached Figure Description

[0028] Figure 1 The 77K nitrogen isotherm adsorption curves of PS-3-C-600, PS-3-C-700, PS-3-C-800, PS-3-C-500 and PS-3-C-900 prepared in Examples 1-3 and Comparative Examples 1-2, respectively.

[0029] Figure 2 The 298K carbon dioxide isotherm adsorption curves of PS-3-C-600, PS-3-C-700, PS-3-C-800, PS-3-C-500, and PS-3-C-900 prepared in Examples 1-3 and Comparative Examples 1-2, respectively.

[0030] Figure 3 The XRD patterns of PS-3-C-600, PS-3-C-700, PS-3-C-800, PS-3-C-900 and precursor PS-3 prepared in Examples 1-3 and Comparative Example 2, respectively;

[0031] Figure 4Raman spectra of PS-3-C-600, PS-3-C-700, PS-3-C-800, and PS-3-C-900 prepared in Examples 1-3 and Comparative Example 2, respectively;

[0032] Figure 5 The 298K C2H6 / C2H4 isotherm adsorption curves of PS-3-C prepared in Examples 1-3 and Comparative Example 2 are shown, (a) PS-3-C-600, (b) PS-3-C-700, (c) PS-3-C-800, and (d) PS-3-C-900.

[0033] Figure 6 The 195K carbon dioxide isotherm adsorption curves of PS-3-C prepared in Examples 1-3 and Comparative Example 2 are shown below: (a) PS-3-C-600, (b) PS-3-C-700, (c) PS-3-C-800, and (d) PS-3-C-900.

[0034] Figure 7 The pore size distribution diagrams of PS-3-C prepared in Examples 1-3 and Comparative Example 2 are shown, (a) PS-3-C-600, (b) PS-3-C-700, (c) PS-3-C-800, and (d) PS-3-C-900.

[0035] Figure 8 The XPS spectrum of PS-3-C-800 prepared in Example 3 is shown below.

[0036] Figure 9 The XPS analysis results of the PS-3-C-800 prepared in Example 3 show the elemental peaks: (a) C, (b) O, (c) N, and (d) S. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to the embodiments.

[0038] In the following examples, unless otherwise stated, all reagents used are commercially available or obtained in accordance with known literature; the experimental methods are generally performed under standard conditions or conditions recommended by the manufacturer.

[0039] Example 1

[0040] A method for preparing N,S co-doped ultraporous carbon materials, the specific steps of which are as follows:

[0041] S1. Mix 3-cyanopyridine (12 mmol, 1.2493 g) and p-toluenesulfonic acid (12 mmol, 2.2826 g) with 5 mL of anhydrous ethanol respectively, and stir until 3-cyanopyridine and p-toluenesulfonic acid are completely dissolved to obtain homogeneous solution A and homogeneous solution B respectively.

[0042] S2. Mix and stir the homogeneous solution A and homogeneous solution B obtained in step S1, and then place them in a magnetically stirred tube reactor at room temperature for 6 hours.

[0043] S3. After the reaction is complete, place the reaction solution obtained in step S2 in a rotary evaporator and evaporate it at 45°C. Stop evaporation when the liquid has been completely evaporated.

[0044] S4. Add the product obtained in step S3 to ethyl acetate and stir for more than 12 hours to ensure that the product is completely washed out. The solution gradually changes from colorless to white suspension. Then, filter to obtain white solid substance. To prevent loss from multiple transfers, place the white solid substance directly in a quartz boat and then dry it in an oven for 12 hours to obtain precursor PS-3.

[0045] S5. Place the precursor PS-3 obtained in step S4 in a tube furnace, maintain a stable nitrogen atmosphere at 10 ml / min, and raise the temperature of the tube furnace at 10℃ / min. After raising the temperature to the specified carbonization temperature (600℃), maintain the temperature for 120 min to carry out carbonization, and finally obtain PS-3-C-600.

[0046] Example 2

[0047] The difference between this embodiment and Example 1 is that the carbonization temperature in step S5 is 700°C, while the other processes remain the same as in Example 1, and the resulting product is named PS-3-C-700.

[0048] Example 3

[0049] The difference between this embodiment and Example 1 is that the carbonization temperature in step S5 is 800°C, while the other processes remain the same as in Example 1, and the resulting product is named PS-3-C-800.

[0050] Comparative Example 1

[0051] The difference between Comparative Example 1 and Example 1 is that the carbonization temperature in step S5 is 500°C, while the other processes are the same as in Example 1. The resulting product is named PS-3-C-500.

[0052] Comparative Example 2

[0053] The difference between Comparative Example 1 and Example 1 is that the carbonization temperature in step S5 is 900°C, while the other processes are the same as in Example 1. The product obtained is named PS-3-C-900.

[0054] The structural and compositional characterization results of the products prepared in the above examples and comparative examples are analyzed as follows:

[0055] from Figure 1 As can be seen, PS-3-C-500 exhibits a certain adsorption capacity for nitrogen at 77K, and the adsorption curve is of type II, indicating that the material is mainly composed of mesopores (pore size 2-50 nm), making C2H6 / C2H4 separation impossible. Therefore, this material will not be further analyzed for pore size or subjected to other characterizations and will be used as a control sample. Apart from this, the other materials showed no significant adsorption effect, indicating that the nitrogen uptake (N2) by these materials at 77K is negligible (<0.1 mmol / g).

[0056] from Figure 2 As can be seen from the figure, the material exhibits high adsorption capacity for carbon dioxide. Combined with the uniform lack of nitrogen adsorption shown in the figure, this indicates the presence of pores with a diameter of approximately 0.33 nm, i.e., ultramicropores (pore size < 0.6 nm). For the PS-3-CX material, the overall adsorption capacity for carbon dioxide increases with increasing carbonization temperature. This is mainly due to the formation of more refined micropores as the pyrolysis temperature further increases. However, when the temperature rises to a certain level, the carbon dioxide adsorption capacity decreases. This is because, with the continuous increase in temperature, some heat is used for the formation of graphitic carbon. Therefore, the formation of ultramicropores is mainly due to the shrinkage of existing pores caused by high temperatures. Compared with all materials, PS-3-C-800 has a significantly higher adsorption effect for carbon dioxide than other materials.

[0057] Figure 3 The degree of graphitization of the material was indicated, demonstrating that the prepared PS-3-CX were all amorphous structures. XRD analysis revealed two broad diffraction peaks at 20-23 / 44°, corresponding to the (002) and (100) planes of the graphite phase. With increasing temperature, the (002) peak shifted slightly to the right. According to the Bragg equation 2dsinθ=nλ, the higher the peak width, the smaller the interplanar spacing. This indicates that PS-3-C-800 has the smallest interplanar spacing, and the overall graphite structure is developing towards order. Furthermore, the peak at 44.0° on the (100) plane of the graphite phase did not change position, but it was stronger relative to the precursor PS-3, indicating a moderate increase in the size of the aromatic crystals.

[0058] According to I D / I G It can determine the degree of defect in the material. From Figure 4Overall, it can be seen that the degree of material defects decreases with increasing carbonization temperature. This is because, with the increase in temperature, some of the thermal energy is used for the growth of the graphene lattice, which is beneficial to the lower Ig. D / I G Compared to the PS-3-C-600, the PS-3-C-600 has a higher degree of defects because of SP. 2 Increase in the number of grain boundaries or sp 3 Increased hybridization leads to this.

[0059] By comparison Figure 5 The four images in the image show C2H4 (38.5 cm²) at 298K using a PS-3-C-600 at 1.0 bar. 3 / g) and C2H6 (35.91cm) 3 The molecules (c₂H₆, C₂H₄, C₂H₄) all exhibited significant co-adsorption, indicating that the material's pore size was greater than that of C₂H₆ (0.44 nm) and greater than that of C₂H₄ (0.42 nm), resulting in an adsorption ratio of C₂H₆:C₂H₄ = 1.07. PS-3-C-700 achieved an adsorption capacity of 45.8 cm⁻¹ for C₂H₄ at 298 K. 3 / g, the adsorption capacity of C2H6 is only 3.57cm. 3 The adsorption capacity of PS-3-C-700 was so high that it almost completely blocked the entry of C2H6 molecules, indicating the presence of narrow ultrapores in the carbon material. This allows for excellent molecular sieve selectivity in separating C2H4 (0.42 nm) and C2H6 (0.44 nm), with an adsorption ratio of C2H6:C2H4 of 12.8 at this point. With further increases in carbonization temperature, the separation effect of PS-3-C-800 on C2H4 (STP) continued to improve, with adsorption capacities of C2H4 (47.02 cm⁻¹) and C2H6 (0.44 nm) respectively. 3 / g) and C2H6 (2.18cm 3 The adsorption rate ( / g) indicates that the pores narrowed again, increasing the adsorption of C2H4 while decreasing the adsorption of C2H6 due to pore shrinkage. This is because high temperature promotes pore contraction, resulting in a more significant separation of the two gases. The adsorption ratio of C2H6:C2H4 in this sample is 21.57, achieving the optimal separation effect. PS-3-C-900 showed almost no adsorption of C2H4 (STP). This was mainly because the high temperature destroyed part of the pore structure, almost eliminating it, and the material exhibited significant repulsion towards alkanes and alkenes. Overall, PS-3-C-800 represents a carbon-based adsorbent capable of screening C2H4 from C2H6. The adsorption ratio of PS-3-C-800 for C2H4 / C2H6 reaches 21.57, which is superior to most reported highly selective carbon adsorbents for C2H4 / C2H6. Overall, the adsorption ratios are PS-3-C-800 > PS-3-C-700 > PS-3-C-600 > PS-3-C-900.

[0060] like Figure 6 As shown, based on the carbon dioxide adsorption capacity at 195K, all materials except PS-3-C-900 showed significant adsorption effects, and the adsorption capacities were similar, indicating that the specific surface areas of the materials were also similar.

[0061] from Figure 7 As can be seen, the pore size distribution of PS-3-C-600 is uneven, with pores around 0.39 nm and 0.5 nm present. The pore size distribution is not concentrated, and the pore size is larger than that of C2H4 and C2H6, which is consistent with the significant adsorption results of C2H4 / C2H6 at 298K. The pore sizes of PS-3-C-700 and PS-3-C-800 are similar, with pores concentrated at 0.41 nm, which is also consistent with the significant adsorption results of C2H4 / C2H6 at 298K, and can achieve effective separation between the two. PS-3-C-900 has negligible pore content due to pore destruction, so it has no adsorption effect, which is also consistent with the lack of significant adsorption results of C2H4 / C2H6 at 298K. The specific surface area, micropore area, and total pore area of ​​PS-3-C-600, PS-3-C-700, PS-3-C-800, and PS-3-C-900 prepared in Examples 1-3 and Comparative Example 2 are shown in Table 1 below:

[0062] Table 1 shows the specific surface area, micropore area, and total pore area of ​​PS-3-C prepared in Examples 1-3 and Comparative Example 2, respectively.

[0063] <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Micropore area (cm 3 / g)]]> <![CDATA[Total pore area (cm 3 / g)]]> PS-3-C-600 386.09 0.171 0.210 PS-3-C-700 376.09 0.170 0.186 PS-3-C-800 416.66 0.184 0.211 PS-3-C-900 3.95 -0.003 0.008

[0064] Figure 8 Table 2 shows the XPS total spectrum and elemental content of the PS-3-C-800 carbon material. Analysis of the XPS total spectrum and the table indicates that the material is co-doped with N and S elements. The vertical axis represents the content of each element, showing that after high-temperature carbonization, the proportions of S, N, and O elements significantly decreased, while the proportion of C element significantly increased, demonstrating the significant impact of the high-temperature carbonization process on the carbon content.

[0065] Table 2 Elemental composition of each material analyzed by XPS

[0066] sample C％ N％ O％ S％ PS-3-C-800 92.17 2.29 4.36 1.18

[0067] Figure 9 Comparative analysis charts of C1s(a), O 1s(b), N1s(c), and S2p(d) for the carbon material PS-3-C-800. Based on... Figure 9 (b) indicates that after high-temperature carbonization, the OS peak in the material decreases due to a significant reduction in the amount of O. According to... Figure 9(d) indicates that after high-temperature carbonization, the SO peak in the material decreases due to the reduction of S element, while the SC peak rises significantly. This is due to the transformation of SO to SC during the carbonization process. According to Figure 9 (c) indicates that after carbonization, some pyrrole-N in the material is converted to pyridine-N. In addition, the graphite-N content increases significantly, which is due to the partial conversion of pyrrole-N to graphitic nitrogen N during pyrolysis. According to... Figure 9 (a) indicates that the CC peak rises with increasing temperature, indicating that the CC content in the material increases. Secondly, with the decrease of O, CO gradually transforms into other bonds. The above analysis proves the influence of high-temperature carbonization on functional group transformation and the content before and after carbonization.

Claims

1. A method for preparing N,S co-doped ultraporous carbon materials, characterized in that, The precursor PS-3 was synthesized by polymerization reaction using 3-cyanopyridine and p-toluenesulfonic acid as raw materials. Then, the precursor PS-3 was subjected to high-temperature carbonization at different temperatures to obtain N,S co-doped microporous carbon materials with pore size. The structural formula of the precursor PS-3 is as follows:

2. The method for preparing an N,S co-doped ultraporous carbon material according to claim 1, characterized in that, The specific steps are as follows: S1. Mix 3-cyanopyridine and p-toluenesulfonic acid with anhydrous ethanol, and stir until 3-cyanopyridine and p-toluenesulfonic acid are completely dissolved to obtain homogeneous solution A and homogeneous solution B, respectively. S2. Mix and stir the homogeneous solution A and homogeneous solution B obtained in step S1, and react at room temperature for 6-8 hours. S3. Perform rotary evaporation on the reaction solution obtained in step S2, setting the rotary evaporation temperature to above 35°C, and stop rotary evaporation when the liquid is completely evaporated. S4. Add the product obtained in step S3 to ethyl acetate and stir for more than 12 hours. The solution gradually changes from colorless to white suspension. Then filter to obtain white solid substance and dry to obtain precursor PS-3. S5. Place the precursor PS-3 obtained in step S4 in a tube furnace, set the carbonization temperature to 600-800℃ and the carbonization time to 100-140min, and finally obtain PS-3-C.

3. The method for preparing an N,S co-doped ultraporous carbon material according to claim 2, characterized in that, In step S1, the molar ratio between 3-cyanopyridine and p-toluenesulfonic acid is 1:1, and the concentrations of 3-cyanopyridine and p-toluenesulfonic acid in homogeneous solution A and homogeneous solution B are both 2.4 mol / L.

4. A method for preparing an N,S co-doped ultraporous carbon material according to claim 2 or 3, characterized in that, In step S5, the carbonization temperature is set to one of 600℃, 700℃, or 800℃.

5. The method for preparing an N,S co-doped ultraporous carbon material according to claim 4, characterized in that, In step S5, the carbonization temperature is set to 800℃.

6. A method for preparing an N,S co-doped ultraporous carbon material according to claim 2 or 3, characterized in that, In step S5, nitrogen is purged into the tube furnace for 30 minutes to purge air from the tube, and the nitrogen atmosphere is stabilized at 10 ml / min. The heating rate of the tube furnace is 10 °C / min.

7. A method for preparing an N,S co-doped ultraporous carbon material according to claim 2 or 3, characterized in that, All stirring involved in the steps is done using magnetic stirring.

8. The N,S co-doped ultraporous carbon material prepared by the preparation method according to any one of claims 1-7.

9. The application of the N,S co-doped ultraporous carbon material as described in claim 8 in the adsorption and separation of ethane / ethylene.

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