S / N co-doped microporous carbon adsorbent as well as preparation method and application thereof

Abstract

The invention discloses an S / N co-doped microporous carbon adsorbent as well as a preparation method and application thereof, and belongs to the technical field of adsorbents. According to the method, firstly, melamine is utilized to enable waste polyvinyl chloride to be subjected to dechlorination reaction at room temperature to generate a microporous carbon material precursor, then decomposition and structural recombination of the microporous carbon material precursor are promoted through high-temperature pyrolysis, the generated local stress further increases the number of carbon defects, the carbon defects are in a high-energy state at high temperature, and the carbon defects are in a high-energy state at high temperature. And gas escape or further chemical reaction is easy to occur. Meanwhile, the activating agent is decomposed at high temperature and releases a large amount of small molecule gas to promote generation of carbon skeleton pores, and non-carbonizable PVC is converted into a high-value nitrogen-doped carbon material. And finally mixing thiourea, modifying the microporous carbon material by introducing a sulfur element, and further optimizing the polarity of the carbon surface by heteroatom doping, so that the CO2 adsorption performance is remarkably improved, and the sulfur-functionalized porous carbon adsorbent with high microporosity is constructed.

Description

Technical Field

[0001] The invention belongs to the technical field of adsorbents, and in particular relates to a S / N co-doped microporous carbon adsorbent and a preparation method and application thereof. Background Art

[0002] CCUS (Carbon Capture, Utilization and Storage) technology is an important means of emission reduction. It provides a feasible solution to climate change by capturing, utilizing and storing carbon dioxide. At present, the mainstream carbon dioxide capture technologies include chemical absorption, membrane separation technology, ionic liquid absorption and adsorption. Among these technologies, adsorption is regarded as a carbon capture technology with more development prospects due to its high chemical stability, high temperature resistance, good wear resistance, high selectivity for carbon dioxide, low heat capacity and flexible operation.

[0003] Porous carbon materials (PCs) have shown broad application potential in the field of adsorption materials due to their advantages such as low cost, simple preparation process, excellent stability, adjustable pore structure and modifiable surface properties. Studies have shown that micropores (pore size less than 1 nanometer) are the key factor affecting the carbon dioxide adsorption capacity of porous carbon materials, especially micropores with a pore size between 0.35nm and 0.7nm, which can significantly improve the adsorption performance of the material. In addition to adsorption performance, reducing the production cost of adsorbents is also an important direction to promote the large-scale application of carbon capture technology. The development of low-cost adsorbents will help reduce the operating costs of the overall carbon capture process.

[0004] On the other hand, the global plastic pollution problem is becoming increasingly serious. About 100 million tons of plastic products are produced each year, but only 9% are recycled, 12% are incinerated, and the remaining 79% are landfilled or directly discharged into the natural environment. Common types of plastics such as polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC) may take decades or even hundreds of years to completely degrade under natural conditions. The microplastics, toxic chemicals (such as bisphenol A and phthalates) and greenhouse gases (such as methane and carbon dioxide) produced during the degradation process will cause continuous harm to the ecological environment.

[0005] Therefore, how to provide an adsorbent preparation method that can not only solve the waste disposal problem but also significantly improve the adsorption performance of carbon capture adsorbents and reduce the research and development costs of carbon capture adsorbents is a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes a S / N co-doped microporous carbon adsorbent and a preparation method and application thereof.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing an S / N co-doped microporous carbon adsorbent, comprising the following steps:

[0009] Dissolve waste polyvinyl chloride in an organic solvent, then add melamine, and obtain a microporous carbon material precursor through grinding and washing; mix the microporous carbon material precursor with an activator and conduct a first calcination, then perform pickling, filtration, and drying to obtain a microporous carbon material; mix the microporous carbon material and thiourea and conduct a second calcination to obtain the S / N co-doped microporous carbon adsorbent.

[0010] Technical principle: The present invention utilizes the dechlorination of waste polyvinyl chloride at room temperature and prepares an S / N co-doped microporous carbon adsorbent through activation doping, significantly improving the CO2 adsorption performance of the adsorbent through multiple reactions. Using melamine as an auxiliary agent, PVC undergoes a dechlorination reaction at room temperature, and a microporous carbon material precursor is successfully prepared. During the pyrolysis process, high-temperature catalysis promotes the decomposition and structural reorganization of the microporous carbon material precursor, and the resulting local stress further increases the number of carbon defects. Carbon defects are in a high-energy state at high temperatures and are prone to gas escape or further chemical reactions. At the same time, the activator will decompose at high temperatures and release a large amount of small-molecule gases, generating an expansion pressure when precipitating inside the carbon material, significantly promoting the formation of carbon skeleton pores, and converting the "non-carbonizable" PVC into a high-value nitrogen-doped carbon material. Finally, mix thiourea and modify the microporous carbon material by introducing sulfur elements, further optimize the carbon surface polarity through heteroatom doping, significantly improve the CO2 adsorption performance, and construct a highly microporous and sulfur-functionalized porous carbon adsorbent.

[0011] Further, the mass ratio of the waste polyvinyl chloride to melamine is 1.00∶1.50.

[0012] Further, the grinding time is 40 min.

[0013] Further, the mass ratio of the microporous carbon material precursor to the activator is 1.00∶2.40; the activator is potassium acetate.

[0014] Further, the temperature of the first calcination is 603.7 °C, the time is 103 min, and the heating rate to the first calcination temperature is 5 °C / min; the first calcination is carried out in a protective atmosphere.

[0015] Further, the pickling reagent is hydrochloric acid with a mass concentration of 3.58%.

[0016] Further, the mass ratio of the microporous carbon material to thiourea is 1.00∶2.14.

[0017] Further, the temperature of the second calcination is 573 °C, the time is 132.78 min, and the heating rate to the second calcination temperature is 5 °C / min; the second calcination is carried out in a protective atmosphere.

[0018] The present invention also provides an S / N co-doped microporous carbon adsorbent prepared by the preparation method according to the above technical solution.

[0019] The present invention also provides the application of the S / N co-doped microporous carbon adsorbent according to the above technical solution in CO2 capture.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects:

[0021] The present invention uses waste high-density polyvinyl chloride to dechlorinate at room temperature, and prepares an S / N co-doped microporous carbon adsorbent by activation doping. The CO2 adsorption performance of the adsorbent is significantly improved through multiple reactions. The pore size of the S / N co-doped microporous carbon adsorbent prepared by the present invention is mainly concentrated at 0.45 nm, and the proportion of the microporous specific surface area is as high as 72.9%, with excellent CO2 adsorption performance. At 25 °C and 1 bar, the CO2 adsorption capacity is as high as 3.76 mmol / g; in the dynamic adsorption experiment at 25 °C and simulating 15% CO2 flue gas, the adsorption capacity reaches 1.72 mmol / g. The present invention realizes the dechlorination of PVC plastics at room temperature and the efficient capture and reuse of CO2, provides important support for the development of environmentally friendly plastic treatment methods and low-cost, high-performance carbon capture technologies, provides a favorable reference for the high-value utilization of solid waste, and at the same time realizes efficient and low-cost CO2 capture, showing broad application prospects. Description of the Drawings

[0022] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0023] Figure 1 It is the process flow chart of the preparation method of the S / N co-doped microporous carbon adsorbent in Example 1;

[0024] Figure 2 It is the scanning electron microscope image of the PC-TU2.14 adsorbent prepared in Example 1, where the scale of a is 50 μm, the scale of b is 2 μm, the scale of c is 200 nm, and the scale of d is 200 nm;

[0025] Figure 3Element mapping diagrams of the PC-TU2.14 adsorbent prepared in Example 1, where a is a transmission electron microscope image, b is a superimposed diagram of the C, O, N, and S element distributions, c is the C element distribution diagram, d is the N element distribution diagram, e is the O element distribution diagram, and f is the S element distribution diagram;

[0026] Figure 4 N2 adsorption-desorption isotherm curves of the adsorbents prepared in Example 1 and Comparative Examples 1-3;

[0027] Figure 5 Pore size distribution diagrams from 0 to 100 nm of the adsorbents prepared in Example 1 and Comparative Examples 1-3 analyzed by the H-K method;

[0028] Figure 6 Pore size distribution diagrams from 0 to 1.6 nm of the adsorbents prepared in Example 1 and Comparative Examples 1-3 analyzed by the H-K method;

[0029] Figure 7 XRD diagrams of the adsorbents prepared in Example 1 and Comparative Examples 1-3;

[0030] Figure 8 Raman spectra diagrams of the adsorbents prepared in Example 1 and Comparative Examples 1-3;

[0031] Figure 9 Surface chemical composition and elemental chemical valence state analysis result diagrams of the adsorbents prepared in Example 1 and Comparative Examples 1-3;

[0032] Figure 10 N1s spectra diagrams of the adsorbents prepared in Example 1 and Comparative Examples 1-3;

[0033] Figure 11 C1s spectra diagrams of the adsorbents prepared in Example 1 and Comparative Examples 1-3;

[0034] Figure 12 S2p spectra diagrams of the adsorbents prepared in Example 1 and Comparative Examples 1-3;

[0035] Figure 13 Fixed bed adsorption device diagram for simulating 15% CO2 flue gas;

[0036] Figure 14 Breakthrough times of the adsorbents prepared in Example 1 and Comparative Examples 1-3 under simulated flue gas;

[0037] Figure 15 Comparison diagrams of CO2 adsorption amounts of the adsorbents prepared in Example 1 and Comparative Examples 1-3 under simulated flue gas;

[0038] Figure 16Adsorption performance results of the adsorbents prepared in Example 1 and Comparative Examples 1-3 under pure CO2 (0-0.15 bar) at 25 °C;

[0039] Figure 17 Adsorption performance results of the adsorbents prepared in Example 1 and Comparative Examples 1-3 under pure CO2 (0-1 bar) at 25 °C. Detailed implementation manners

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0042] The embodiment of the present invention provides a preparation method of an S / N co-doped microporous carbon adsorbent, including the following steps:

[0043] Dissolve waste polyvinyl chloride in an organic solvent, then add melamine, grind and wash to obtain a microporous carbon material precursor; mix the microporous carbon material precursor with an activator and perform a first calcination, then perform pickling, filtration, and drying to obtain a microporous carbon material (PC); mix the microporous carbon material and thiourea and perform a second calcination to obtain the S / N co-doped microporous carbon adsorbent.

[0044] In a preferred embodiment, the waste polyvinyl chloride is waste high-density polyvinyl chloride (PVC).

[0045] In a preferred embodiment, the organic solvent is dimethylformamide (DMF).

[0046] In a preferred embodiment, the mass ratio of the waste polyvinyl chloride to melamine (Mel) is 1.00:1.50. The lone pair electrons of the amino group in melamine attack the carbon atom of the C-Cl bond to form a transition state, form a hydrogen bond network with the oxygen-containing or nitrogen-containing groups (such as C=O or C-N) in the PVC chain, realize the release of HCl, generate a dechlorinated PVC chain, and form a three-dimensional cross-linked network, which inhibits the volatilization of the decomposition products of PVC during high-temperature carbonization and realizes room-temperature dechlorination. At the same time, using melamine for dechlorination also realizes the introduction of nitrogen atoms, which can enhance the surface basicity and polarity of the carbon material, thereby further strengthening the interaction between carbon dioxide molecules and the adsorbent surface.

[0047] In a preferred embodiment, the grinding time is 40 min.

[0048] In a preferred embodiment, the number of washing times is 6.

[0049] In a preferred embodiment, the mass ratio of the microporous carbon material precursor to the activator is 1.00∶2.40; the activator is potassium acetate (KAc). As an activator, potassium acetate can undergo a decomposition reaction under high-temperature conditions, releasing a large amount of small-molecule gases. When the small-molecule gases precipitate inside the carbon material, the generated expansion pressure promotes the formation of carbon framework pores and further improves the formation of the microporous structure.

[0050] In a preferred embodiment, the temperature of the first calcination is 603.7 °C, the time is 103 min, and the heating rate to the first calcination temperature is 5 °C / min; the first calcination is carried out in a protective atmosphere; the protective atmosphere is nitrogen, and the flow rate of the nitrogen is 200 mL / min. The microporous carbon material precursor and the activator interact during the calcination process, and high-temperature catalysis promotes the decomposition and structural reorganization of polyvinyl chloride, forming more carbon defects in the initially generated derived carbon material; carrying out the first calcination under the above conditions helps the uniform mixing and full contact reaction of waste polyvinyl chloride and the activator.

[0051] In a preferred embodiment, the reagent for pickling is hydrochloric acid with a mass concentration of 3.58%; the volume of the hydrochloric acid is twice the volume of potassium acetate to completely remove the residual potassium acetate.

[0052] In a preferred embodiment, the mass ratio of the microporous carbon material to thiourea (TU) is 1.00∶2.14. As a dopant, thiourea is used to introduce sulfur elements. Sulfur atoms can replace some carbon atoms in the carbon framework and combine with carbon to form sulfur-containing groups (such as -SO3H, -C=S), enhancing the surface chemical activity. At the same time, the gases (such as H2S, SO2) generated by the decomposition of thiourea escape in the carbon framework, forming micropores and mesopores, and increasing the specific surface area of the carbon material.

[0053] In a preferred embodiment, the temperature of the second calcination is 573 °C, the time is 132.78 min, and the heating rate to the second calcination temperature is 5 °C / min; the second calcination is carried out in a protective atmosphere; the protective atmosphere is nitrogen, and the flow rate of the nitrogen is 200 mL / min.

[0054] The present invention also provides an S / N co-doped microporous carbon adsorbent prepared by the preparation method according to the above technical solution.

[0055] The pore size of the S / N co-doped microporous carbon adsorbent provided by the present invention is concentrated at 0.45 nm, and the proportion of the microporous specific surface area is as high as 72.9%, providing an excellent pore structure and rich adsorption active sites for the efficient capture of CO2.

[0056] The present invention also provides an application of the S / N co-doped microporous carbon adsorbent described in the above technical solution in the capture of CO2.

[0057] In the examples of the present invention, room temperature refers to "25 ± 2 °C".

[0058] Unless otherwise specified, the raw materials in the examples of the present invention are all obtained through commercial channels.

[0059] Example 1

[0060] A preparation method of an S / N co-doped microporous carbon adsorbent, the process flow is shown in Figure 1 , and the specific steps are as follows:

[0061] (1) Dissolve waste high-density polyvinyl chloride in DMF and stir for 1 h, then mix it with melamine in a mass ratio of 1.00:1.50 and grind for 40 min, wash 6 times to remove chlorine, and obtain a microporous carbon material precursor.

[0062] (2) Grind and mix the microporous carbon material precursor and potassium acetate evenly in a mass ratio of 1.00:2.40 to obtain a mixture; place the obtained mixture in a porcelain boat of a tube furnace, in a N2 flow of 200 mL / min, heat it to 603.7 °C at a rate of 5 °C / min and hold for 103 min, cool with the furnace temperature, then add the cooled product to hydrochloric acid with a mass concentration of 3.68% (the volume of hydrochloric acid is 2 times the volume of potassium acetate), stir thoroughly to completely remove the residual potassium acetate, filter by suction and dry at 100 °C to obtain a microporous carbon material PC.

[0063] (3) Mix and grind the microporous carbon material PC and thiourea in a mass ratio of 1.00:2.14, then place it in a porcelain boat of a tube furnace for the second calcination, in a N2 flow of 200 mL / min, heat it to 573 °C at a rate of 5 °C / min and hold for 132.78 min to obtain an S / N co-doped microporous carbon adsorbent, named PC-TU2.14.

[0064] Comparative Example 1

[0065] The microporous carbon material PC obtained in step (2) of Example 1.

[0066] Comparative Example 2

[0067] A preparation method of S / N co-doped microporous carbon adsorbent is the same as that of Example 1, except that in step (3), the microporous carbon material PC and thiourea are mixed and ground at a mass ratio of 1.00:1.00, and the obtained material is named PC-TU1.

[0068] Comparative Example 3

[0069] A preparation method of S / N co-doped microporous carbon adsorbent is the same as that of Example 1, except that in step (3), the microporous carbon material PC and thiourea are mixed and ground at a mass ratio of 1.00:3.00, and the obtained material is named PC-TU3.

[0070] 1. Structural Characterization

[0071] The morphology and structure of the PC-TU2.14 adsorbent prepared in Example 1 were observed by scanning electron microscopy (SEM; GeminiSEM300, ZEISS, Germany), and the results are shown in Figure 2 .

[0072] Figure 2 Fig. is the scanning electron micrograph of the PC-TU2.14 adsorbent prepared in Example 1, where the scale bar of a is 50 μm, the scale bar of b is 2 μm, the scale bar of c is 200 nm, and the scale bar of d is 200 nm. It can be seen from Figure 2 that the low-magnification SEM image (such as 50 μm) shows that the overall morphology of the adsorbent is irregular granular, the surface is rough, and there may be a porous structure. The high-magnification SEM (2 μm, 200 nm) images further reveal that the adsorbent has a rich microporous and mesoporous structure inside, and the pores are interconnected, providing more active sites for CO2 adsorption.

[0073] The element mapping characterization of the PC-TU2.14 adsorbent prepared in Example 1 was carried out by high-resolution transmission electron microscopy (HRTEM, JEM-2100F, JEOL, Japan) to analyze the types and spatial distribution characteristics of each element in the sample, and the results are shown in Figure 3 .

[0074] Figure 3 Fig. is the element mapping diagram of the PC-TU2.14 adsorbent prepared in Example 1, where a is the transmission electron micrograph, b is the superimposed diagram of the distributions of C, O, N, and S elements, c is the C element distribution diagram, d is the N element distribution diagram, e is the O element distribution diagram, and f is the S element distribution diagram. It can be seen from Figure 3 that the distributions of carbon, oxygen, nitrogen, and sulfur elements in the PC-TU2.14 adsorbent prepared in Example 1 are uniform.

[0075] The specific surface area and pore size distribution of the adsorbents prepared in Example 1 and Comparative Examples 1-3 were analyzed by N2 isothermal adsorption-desorption experiments, and the results are shown in Figure 4。

[0076] Figure 4 N2 adsorption-desorption isotherm curves of the adsorbents prepared in Example 1 and Comparative Examples 1-3. From Figure 4 it can be seen that in the low-pressure region (P / P0 < 0.1) and high-pressure region (0.9 < P / P0 < 1.0), the isotherms of all adsorbent samples rise rapidly, and there is a relatively slow rise in the medium-pressure region (0.1 < P / P0 < 0.9). According to the classification of the International Union of Pure and Applied Chemistry (IUPAC), this is relatively close to the characteristics of type II isotherms. In addition, PC (Comparative Example 1) has a low adsorption capacity at low P / P0 (<0.1), and the adsorption capacity rises smoothly at medium and high P / P0, indicating that it is mainly mesoporous / macroporous with a small proportion of micropores. PC-TU1 (Comparative Example 2) has a slightly higher adsorption capacity than PC at low P / P0, but the increase is limited, introducing a small amount of micropores. PC-TU2.14 (Example 1) and PC-TU3 (Comparative Example 3) have a significantly increased adsorption capacity at low P / P0 (<0.1), indicating an increase in the proportion of micropores, with a high specific surface area and a dense microporous network, providing abundant active sites for CO2 adsorption, which conforms to the characteristics of ultra-microporous materials. The adsorption capacity rises rapidly in the high-pressure region (0.9 < P / P0 < 1.0), forming a hierarchical pore structure of micropores-mesopores-macropores.

[0077] The adsorption isotherm shows that PC-TU first adsorbs part of the gas at low pressure, mainly in the form of a monolayer. When the relative pressure reaches 0.97, the monolayer adsorption reaches saturation. As the pressure increases, the adsorption transitions from monolayer to multilayer. CO2 mainly adsorbs in a monolayer in most micropores. In smaller micropores, CO2 molecules adsorb on the pore surface in a monolayer and reach saturation, while in a few larger micropores, CO2 molecules first adsorb on the pore surface in a monolayer, and finally reach saturation as the relative pressure increases. This unique pore characteristic not only helps the rapid transmission of gas but also improves the adsorption efficiency.

[0078] The specific surface area, pore diameter, and pore volume of the adsorbents were measured by a high-throughput specific surface area and pore size analyzer (ASAP 2460, Micromeritics, USA); the specific surface area of the samples was calculated by the Brunauer-Emmett-Teller (BET) equation, the micropore specific surface area of the samples was calculated by the Thickness Plot (t-plot) equation, and the pore size distribution of the samples was calculated by the Horvath-Kawazoe (HK) equation. The results are shown in Table 1 and Figures 5-6 。

[0079] Figure 5 Pore size distribution diagrams from 0 to 100 nm of the adsorbents prepared in Example 1 and Comparative Examples 1-3 analyzed by the H-K method. Figure 6Pore size distribution diagrams of the adsorbents prepared in Example 1 and Comparative Examples 1-3 analyzed by the H-K method. From Figure 5 and 6 it can be seen that the pore size of PC-TU2.14 is mainly distributed at 0.45 nm, the pore size of PC is mainly distributed at 0.49 nm, the pore size of PC-TU1 is mainly distributed at 0.49 nm, while PC-TU3 has almost no pore size at this stage. The rich and regular microporous structure of PC-TU2.14 can provide more sites for CO2 adsorption.

[0080] Table 1 Specific surface area and pore distribution of the adsorbents prepared in Example 1 and Comparative Examples 1-3

[0081]

[0082]

[0083] As can be seen from Table 1, the average pore size of PC-TU2.14 prepared in Example 1 is 2.6220 nm, and the proportion of the microporous specific surface area is 72.9%, indicating that the adsorbent prepared in Example 1 contains a large number of microporous structures and also has mesoporous and macroporous structures.

[0084] The crystal structure of the adsorbent was determined by an X-ray diffractometer (XRD, SmartLAB9, Japan), and the results are shown in Figure 7 .

[0085] Figure 7 XRD patterns of the adsorbents prepared in Example 1 and Comparative Examples 1-3. From Figure 7 it can be seen that the peak angle of the adsorbent prepared in Example 1 near 2θ 24° is significantly broadened, indicating that its graphitization degree is lower and the structure is more disordered. This disordered structure brings more abundant amorphous carbon pores and defect sites, providing a large number of active sites for CO2 adsorption. From PC → PC-TU1 → PC-TU2.14 → PC-TU3, the (002) peak gradually broadens and the intensity weakens (even disappears), indicating that the activation / doping process significantly destroys the graphite ordered structure and forms an amorphous carbon skeleton, further confirming the structural advantages of PC-TU2.14 as a microporous carbon material and providing key support for its application in CO2 capture.

[0086] The molecular structure and amorphous properties of the adsorbent were determined by a Raman spectrometer (LabRAM HR Evolution, France), and the results are shown in Figure 8 .

[0087] Figure 8 Raman spectra of the adsorbents prepared in Example 1 and Comparative Examples 1-3. From Figure 8It can be seen that two broad bands are observed at 1350 cm -1 and 1588 cm -1 , corresponding to the D (amorphous carbon structure) band and the G (graphite structure) band respectively. The intensity ratio of the D band and the G band (ID / IG) reflects the degree of graphitization and defects in the prepared samples. The larger the value, the more defects, the more disordered the structure, and it promotes the formation of amorphous carbon structure, forming more CO2 adsorption sites. The ID / IG of the adsorbent prepared in Example 1 is 0.889, which indicates that more defects are generated at this ratio in the high-temperature activation reaction. PC-TU3 has the highest defect density due to the generation of additional defects caused by sulfur (S) doping. It is proved that sulfur doping plays an important role in causing material defects, and with the strengthening of the activation / doping process, the graphite ordered structure is further destroyed.

[0088] X-ray photoelectron spectroscopy (XPS, EscaLab 250xi, USA) was used to further determine the chemical composition and functional groups of the adsorbent, and the results are shown in Figure 9 .

[0089] Figure 9 are the surface chemical composition and elemental chemical valence state analysis results diagrams of the adsorbents prepared in Example 1 and Comparative Examples 1-3. It can be seen from Figure 9 that with the increase of the thiourea doping amount, the intensities of the N1s and S2p peaks in the adsorbent gradually increase, verifying that thiourea can be used as an effective dopant. The O content of PC-TU2.14 is 14.72%, lower than that of PC (19.26%) and PC-TU3 (15.23%). The pore size distribution of PC-TU3 is more concentrated, but too high sulfur doping ratio (2.86%) may cause partial pore blockage, indicating that moderate sulfur doping can optimize the surface polarity and avoid the destruction of the pore structure caused by over-sulfuration.

[0090] Figure 10 is the N1s spectrogram of the adsorbents prepared in Example 1 and Comparative Examples 1-3. Figure 11 is the C1s spectrogram of the adsorbents prepared in Example 1 and Comparative Examples 1-3. Figure 12 is the S2p spectrogram of the adsorbents prepared in Example 1 and Comparative Examples 1-3. In PC-TU2.14, the ternary co-doping of O / N / S forms carboxyl-pyridine nitrogen-thiol synergistic sites, where the sulfur content (2.05%) and the functional group ratio (such as COOH 33.6%) achieve a balance between the micropore occupancy and the mass transfer channel, avoiding the decrease of mechanical strength caused by over-etching and significantly improving the CO2 adsorption affinity.

[0091] Based on the above characterization results, it can be confirmed that the microporous carbon material co-doped with S / N was synthesized in this invention. The pore size of this material is concentrated at 0.45 nm, and the proportion of the microporous specific surface area is as high as 72.9%. In the PC-TU2.14 adsorbent, the micropore-mesopore-macropore structure forms multilayer adsorption, providing abundant defect sites for CO2 adsorption. In addition, the presence of heteroatom functional groups enhances the Lewis acid sites and base sites in the carbon framework, thereby further promoting the interaction between PC-TU2.14 and CO2.

[0092] 2. CO2 Dynamic Adsorption Performance Test

[0093] Using a self-made fixed-bed adsorption device and a multifunctional dynamic adsorption instrument (GXH-3011, Huayun, China), the dynamic capture ability of the sample under the simulated conditions of a mixed gas (CO2 / N2 = 0.15 / 0.85) was measured. The experimental device is as Figure 13 shown. Before the adsorption experiment began, 0.2 g of the adsorbent sample was placed in the adsorption column of the tube furnace, and 0.2 g of quartz wool was stuffed above and below the sample for fixation. The temperature of the tube furnace was set at 120 °C, and high-purity N2 (27 mL / min) was introduced for desorption for 2 h to remove the small amount of water vapor and CO2 adsorbed in the sample. After the desorption was completed, when the tube furnace cooled to room temperature, the tube furnace was adjusted to 25 °C, and a mixed gas of CO2 15% / N2 85% (27 mL / min) was introduced for the adsorption experiment, and the outlet concentration was detected by an online CO2 analyzer. A blank control group was set up, with only 0.2 g of quantitative quartz wool added to the adsorption column of the tube furnace without adding the adsorbent. Each set of data was measured 3 times, and the uncertainty of the CO2 adsorption data was 2% or less to ensure the accuracy of the data.

[0094] Figure 14 is the breakthrough time of the adsorbents prepared in Example 1 and Comparative Examples 1-3 under simulated flue gas. From Figure 14 it can be seen that the breakthrough time of the PC-TU2.14 adsorbent (Example 1) doped with twice the amount of thiourea is longer than that of other samples (Comparative Examples 1-3). The longer the breakthrough time, the higher the corresponding CO2 dynamic adsorption capacity.

[0095] Figure 15 is a comparison chart of the CO2 adsorption capacities of the adsorbents prepared in Example 1 and Comparative Examples 1-3 under simulated flue gas. From Figure 15 it can be seen that the adsorption capacity of Example 1 is higher than that of the other samples, being 1.72 mmol / g.

[0096] 3. CO2 BET Static Adsorption Performance Test

[0097] The CO2 adsorption capacity of the adsorbents prepared in Example 1 and Comparative Examples 1-3 was evaluated using Autosorb-iQ / ASAP 2460 at 25 °C in the pressure ranges of 0 - 0.15 bar and 0 - 1 bar. The results are shown in Figures 16-17 .

[0098] Figure 16 Figure showing the adsorption performance results of the adsorbents prepared in Example 1 and Comparative Examples 1-3 under pure CO2 (0 - 0.15 bar) conditions at 25 °C. Figure 17 Figure showing the adsorption performance results of the adsorbents prepared in Example 1 and Comparative Examples 1-3 under pure CO2 (0 - 1 bar) conditions at 25 °C. From Figure 16 and Figure 17 it can be seen that the CO2 adsorption amount of the PC-TU2.14 adsorbent prepared in Example 1 is the most significant, reaching an adsorption amount of 1.76 mmol / g at 25 °C and 0.15 bar, and an adsorption amount of 3.76 mmol / g at 25 °C and 1 bar. The adsorption amount of PC-TU2.14 is higher than that of polyvinyl chloride-derived microporous carbon PC (Comparative Example 1), verifying that thiourea doping can effectively improve the CO2 adsorption capacity of polyvinyl chloride-derived carbon materials.

[0099] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for preparing a S / N co-doped microporous carbon adsorbent, characterized in that: The following steps are involved: Dissolving waste polyvinyl chloride in an organic solvent, then adding melamine, grinding and washing, to obtain a microporous carbon material precursor; The microporous carbon material precursor is mixed with an activator and then first calcined, and then acid-washed, filtered and dried to obtain a microporous carbon material; The microporous carbon material and thiourea are mixed and then subjected to a second calcination to obtain the S / N co-doped microporous carbon adsorbent.

2. The method for preparing the S / N co-doped microporous carbon adsorbent according to claim 1, characterized in that: The mass ratio of the waste polyvinyl chloride to melamine is 1.00:1.

50.

3. The method for preparing the S / N co-doped microporous carbon adsorbent according to claim 1, characterized in that: The grinding time is 40 min.

4. The method for preparing the S / N co-doped microporous carbon adsorbent according to claim 1, characterized in that: The mass ratio of the microporous carbon material precursor to the activator is 1.00:2.40; the activator is potassium acetate.

5. The method for preparing the S / N co-doped microporous carbon adsorbent according to claim 1, characterized in that: The temperature of the first calcination is 603.7° C., the time is 103 min, and the rate of heating to the first calcination temperature is 5° C. / min; the first calcination is carried out in a protective atmosphere.

6. The method for preparing the S / N co-doped microporous carbon adsorbent according to claim 1, characterized in that: The pickling reagent is hydrochloric acid with a mass concentration of 3.58%.

7. The method for preparing the S / N co-doped microporous carbon adsorbent according to claim 1, characterized in that: The mass ratio of the microporous carbon material to thiourea is 1.00:2.

14.

8. The method for preparing the S / N co-doped microporous carbon adsorbent according to claim 1, characterized in that: The temperature of the second calcination is 573° C., the time is 132.78 min, and the rate of heating to the second calcination temperature is 5° C. / min; the second calcination is carried out in a protective atmosphere.

9. A S / N co-doped microporous carbon adsorbent, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 8.

10. Use of the S / N co-doped microporous carbon adsorbent as claimed in claim 9 in capturing CO2.

Images