Hierarchical pore structure carbon material, preparation method thereof and application of hierarchical pore structure carbon material in oil gas recovery

Abstract

The invention provides a hierarchical pore structure carbon material, a preparation method thereof and application of the hierarchical pore structure carbon material in oil gas recovery, and relates to the technical field of active adsorption. The carbon material disclosed by the invention is a nitrogen and oxygen doped hierarchical pore structure carbon material, the nitrogen doping amount of the carbon material is 1%-5%, and the oxygen doping amount of the carbon material is 0.5%-5%; the micropore rate is 50%-60%, and the average pore size is 0.5-20 nm. The benzene adsorption activity of the hierarchical pore structure carbon material is 295-332 mg / g, the benzene adsorption selectivity is 90%-93%, the adsorption retention rate is greater than or equal to 90%, the desorption temperature is low, the process can be simplified and the energy consumption can be reduced in oil gas adsorption and recovery, the regeneration efficiency is high, the applicability is strong, and the process efficiency of oil gas volatile gas recovery can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of active adsorption technology, specifically to a multi-level porous carbon material, its preparation method, and its application in oil and gas recovery. Background Technology

[0002] With the accelerating pace of industrialization, the volatilization of oil and gas generated during petroleum refining, storage, and transportation has become a significant source of environmental pollution and resource waste. Statistics show that oil and gas evaporation losses account for 0.5% to 3% of the total crude oil volume, and the volatilized oil and gas contain large amounts of volatile organic compounds (VOCs) (such as benzene compounds and alkanes), causing not only air pollution but also potential safety hazards (such as explosion risks). Existing technologies for adsorbing these volatile oil and gas include condensation, membrane separation, and adsorption, with adsorption being widely used due to its low cost and ease of operation.

[0003] Activated carbon is a commonly used adsorbent in adsorption methods, but traditional activated carbon suffers from problems such as low adsorption capacity, poor selectivity, and insufficient regeneration performance. Specifically, traditional activated carbon has a uniform pore size distribution (mainly micropores), resulting in significant differences in adsorption efficiency for different molecular weight components in oil and gas, especially for large molecular hydrocarbons (such as hydrocarbon compounds with more than 5 carbon atoms). In addition, after traditional activated carbon becomes saturated, it requires high-temperature (approximately 600~900°C) thermal regeneration or vacuum desorption, which is not only energy-intensive but may also lead to oxidation and deactivation of the activated carbon, and even pose a risk of combustion due to localized high temperatures. Because the surface of traditional activated carbon lacks polar groups, it has low adsorption selectivity for polar or weakly polar oil and gas molecules, which can easily lead to residual pollutants during desorption, affecting regeneration efficiency.

[0004] To improve the mass transfer efficiency of activated carbon adsorption, some studies have optimized the pore structure of activated carbon to simultaneously enhance the adsorption capacity for both small and large molecular hydrocarbons. For example, membrane separation and adsorption combined technology enhances the gas diffusion rate through hierarchical porous activated carbon. However, its preparation process is complex, and the selective adsorption problem cannot be solved when the proportion of mesopores (pore size of 2~50nm) is insufficient (<30%). At the same time, there is also a technical defect that although the carbon surface has high selectivity for non-polar hydrocarbons, it has insufficient adsorption capacity for polar components in mixed oil and gas. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention discloses a multi-level porous carbon material, its preparation method, and its application in oil and gas recovery. This invention aims to solve the technical problems of existing commercial activated carbon, which has a high proportion of micropores (pore size <2nm), high diffusion resistance to large molecular oil and gas (such as C6-C12 hydrocarbons), and weak selective adsorption capacity for polar / non-polar oil and gas molecules.

[0006] To achieve the above technical objectives, on the one hand, the present invention proposes a hierarchical porous carbon material, wherein the carbon material is a nitrogen-oxygen-doped hierarchical porous carbon material, wherein the nitrogen doping amount of the carbon material is 1%~5%, the oxygen doping amount is 0.5%~5%, the microporosity is 50%~60%, and the average pore size is 0.5~20nm.

[0007] In a further example of the present invention, the nitrogen doping amount of the carbon material is 1.2% to 4.7%, preferably 2.4% to 4.7%, and more preferably 4.7%.

[0008] In a further example of the present invention, the oxygen doping amount of the carbon material is 0.5% to 2.6%, preferably 1.1% to 2.6%, and more preferably 2.6%.

[0009] In a further example of the present invention, the microporosity of the carbon material is 57% to 60%, preferably 57.58% to 59.6%, and more preferably 59.6%.

[0010] In a further example of the present invention, the specific surface area of ​​the carbon material is 1500~1650 m². 2 / g, preferably 1610~1630m 2 / g, further optimized 1610m 2 / g.

[0011] In a further example of the present invention, the average pore size of the carbon material is 8-11 nm, preferably 8-9 nm, and more preferably 8.2-8.5 nm.

[0012] In a further example of the present invention, the specific surface area of ​​the carbon material is 1500~1650 m². 2 / g, preferably 1610~1630m 2 / g, further optimized 1610m 2 / g.

[0013] In a further example of the present invention, the benzene adsorption activity of the carbon material is 295~332 mg / g, the benzene adsorption selectivity is 90%~93%, the adsorption retention rate is ≥90%, and the desorption temperature is 100~150℃.

[0014] On the other hand, this invention proposes a method for preparing a hierarchical porous carbon material, which includes the following steps: S1, activated carbon and polyacrylonitrile are mixed and then impregnated in a pore-conditioning agent solution to obtain a primary precursor; S2, the primary precursor is activated with carbon dioxide to obtain the secondary precursor; S3, the secondary precursor is treated with nitrogen-oxygen dopants to obtain the hierarchical porous carbon material.

[0015] In a further example of the present invention, step S1 includes: grinding and sieving activated carbon and polyacrylonitrile, impregnating them in a pore conditioning agent solution, and then drying them to obtain the primary precursor.

[0016] In an optional example of the present invention, the activated carbon includes at least one of coal-based activated carbon, wood-based activated carbon, fruit shell activated carbon, synthetic resin activated carbon, and bamboo charcoal activated carbon.

[0017] In an optional example of the present invention, the mass ratio of activated carbon to acrylonitrile is 7:(2~5), preferably 7:(2~4), and more preferably 7:3.

[0018] In an optional example of the present invention, the activated carbon and the polyacrylonitrile are ground and then sieved to 50-100 mesh, preferably to 100 mesh.

[0019] In an optional example of the invention, the pore conditioning agent includes one or both of KOH or ZnCl2.

[0020] In an optional example of the present invention, the concentration of the pore conditioning agent solution is 0.15~0.9 mol / L, preferably 0.2~0.8 mol / L, and more preferably 0.5 mol / L; the impregnation time is 1~3.5 h, preferably 1~3 h, and more preferably 2 h.

[0021] In an optional example of the present invention, the drying operation in step S1 is carried out in a vacuum drying oven at a temperature of 60-90°C for 6-8 hours.

[0022] In a further example of the present invention, step S2 includes: heating the primary precursor to an activation temperature under an inert atmosphere, and then drying and activating it under an atmosphere containing carbon dioxide to obtain the secondary precursor.

[0023] In an optional example of the present invention, the heating rate of the primary precursor in step S2 under an inert atmosphere is 2~10℃ / min.

[0024] In an optional example of the present invention, the activation temperature of the primary precursor is 500~800°C.

[0025] In an optional example of the present invention, the carbon dioxide atmosphere is introduced at a rate of 10-60 mL / min and the activation time is 1-5 h.

[0026] In a further example of the present invention, step S3 includes: immersing the secondary precursor in a dopant solution for reflux treatment, and then annealing it to obtain the hierarchical porous carbon material.

[0027] In an optional example of the present invention, the dopant includes one or both of urea and ammonia.

[0028] In an optional example of the present invention, the dopant solution is an aqueous solution of the dopant with a concentration of 1.5 to 9 mol / L, preferably 2 to 8 mol / L, more preferably 5 to 8 mol / L, and even more preferably 8 mol / L.

[0029] In an optional example of the present invention, the temperature of the reflux operation is 75~85°C, preferably 80°C; the reflux time is 5~10h, preferably 10h.

[0030] In an optional example of the present invention, the annealing is carried out in an inert atmosphere at a temperature of 750~850°C, preferably 800°C.

[0031] On the other hand, the present invention proposes the application of the above-mentioned hierarchical porous carbon material or carbon material prepared by the above-mentioned method for preparing hierarchical porous carbon material in oil and gas recovery.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: The hierarchical porous carbon material of this invention is a nitrogen- and oxygen-doped carbon material. A suitable proportion of nitrogen doping enhances the adsorption of benzene compounds through electronic effects, while a suitable proportion of oxygen doping improves the oleophilicity of the carbon material through the action of oxygen groups (carboxyl groups, phenolic hydroxyl groups), thereby improving the selective adsorption performance for polar / non-polar oil and gas molecules. A microporosity controlled at 50%–60% provides a large specific surface area, and a corresponding mesoporosity controlled at 40%–50% promotes macromolecular transport, effectively reducing the diffusion resistance to large-molecule oil and gas (such as C6-C12 hydrocarbons), thus further improving adsorption selectivity. The benzene adsorption activity of the hierarchical porous carbon material of this invention is 295–332 mg / g, the benzene adsorption selectivity is 90%–93%, and the adsorption retention rate is ≥90%. Its low desorption temperature simplifies the process and reduces energy consumption in oil and gas adsorption and recovery. Furthermore, its high regeneration efficiency and strong applicability effectively improve the process efficiency of oil and gas volatile gas recovery.

[0033] The method for preparing hierarchical porous carbon materials of this invention optimizes the hierarchical porous structure of the prepared carbon materials by combining pore regulators with carbon dioxide activation, significantly improving the diffusion rate of macromolecular hydrocarbons; and achieves nitrogen-oxygen dual doping by using dopants, further enhancing the selective adsorption of polar / nonpolar molecules. The method for preparing hierarchical porous carbon materials of this invention is simple to operate, and the prepared hierarchical porous carbon materials can be widely used for the adsorption and recovery of volatile organic compounds (VOCs) in gas stations, petrochemical industries, etc., and the preparation method of this invention has significant value for promotion and application. Attached Figure Description

[0034] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The image shows a scanning electron microscope image of the hierarchical porous carbon material prepared according to Example 1 of the present invention.

[0035] Figure 2 The XPS full spectrum results of the hierarchical porous carbon material of Example 1, and the carbon materials of Comparative Example 1 and Comparative Example 2 are shown. Detailed Implementation

[0036] To facilitate understanding of the present invention, a more comprehensive description will be provided below, along with preferred embodiments. However, it should be understood that these embodiments are merely for more detailed explanation and should not be construed as limiting the invention in any way, i.e., not intended to limit the scope of protection of the invention.

[0037] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0038] In a first aspect, the present invention proposes a hierarchical porous carbon material, wherein the carbon material is a nitrogen-oxygen doped hierarchical porous carbon material, wherein the nitrogen doping amount of the carbon material is 1%~5% and the oxygen doping amount is 0.5%~5%; the microporosity is 50%~60% and the average pore size is 0.5~20nm.

[0039] The hierarchical porous carbon material of this invention features a suitable ratio of nitrogen and oxygen doping, which effectively enhances its absorption activity for benzene compounds. Furthermore, targeted modification of the carbon material surface increases its oleophilicity through the action of oxygen groups (carboxyl and phenolic hydroxyl groups), resulting in a hierarchical porous carbon material with excellent selective adsorption energy for both polar and nonpolar oil and gas molecules. The microporosity of the carbon material is controlled at 50%–60%, providing a large specific surface area, while the corresponding mesoporosity is controlled at 40%–50%, promoting macromolecular transport and effectively reducing diffusion resistance to large oil and gas molecules (such as C6-C12 hydrocarbons), thus improving adsorption selectivity. The embodiments and comparative examples of this invention demonstrate the technical advantages of the hierarchical porous carbon material in terms of benzene absorption activity, selectivity, and adsorption capacity retention after 10 adsorption-desorption cycles.

[0040] As a further embodiment, the nitrogen doping content of the carbon material is 1.2% to 4.7%, preferably 2.4% to 4.7%, and more preferably 4.7%.

[0041] As a further embodiment, the oxygen doping content of the carbon material is 0.5% to 2.6%, preferably 1.1% to 2.6%, and even more preferably 2.6%.

[0042] As a further embodiment, the microporosity of the carbon material is 57%~60%, preferably 57.58%~59.6%, and even more preferably 59.6%. The hierarchical porous carbon material of the present invention does not contain macropores (pore size > 50 nm), and correspondingly has a mesoporosity of 40%~50%, preferably 40%~43%, even more preferably 40.4%~42.42%, and even more preferably 40.4%.

[0043] As a further embodiment, the specific surface area of ​​the carbon material is 1500~1650 m². 2 / g, preferably 1610~1630m 2 / g, further optimized 1610m 2 / g.

[0044] As a further embodiment, the average pore size of the carbon material is 8~11 nm, preferably 8~9 nm, and even more preferably 8.2~8.5 nm.

[0045] The embodiments and comparative examples of this invention demonstrate the selective adsorption performance of the hierarchical porous carbon materials of this invention for polar / nonpolar oil and gas molecules with different nitrogen doping amounts, oxygen doping amounts, microporosity, specific surface area, and average pore size.

[0046] As a further solution, based on a large amount of experimental data, it has been confirmed that the benzene adsorption activity of the hierarchical porous carbon material of the present invention is 295~332 mg / g, the benzene adsorption selectivity is 90%~93%, the adsorption retention rate is ≥90%, and its desorption temperature is 100~150℃, which is relatively low. It is especially suitable for the adsorption and recovery of volatile organic compounds (VOCs) in oil and gas recovery and has broad application prospects.

[0047] Secondly, the present invention proposes a method for preparing a hierarchical porous carbon material, the method comprising the following steps: S1, mixing activated carbon with polyacrylonitrile and then impregnating it in a pore conditioning agent solution to obtain a primary precursor; S2, activating the primary precursor with carbon dioxide to obtain a secondary precursor; S3, treating the secondary precursor with a nitrogen-oxygen dopant to obtain the hierarchical porous carbon material.

[0048] The above technical solution uses activated carbon and polyacrylonitrile as raw materials. Through precursor optimization and activation process control, a hierarchical pore structure (micropore-mesopore synergy) is constructed to improve diffusion rate and adsorption capacity. Furthermore, nitrogen / oxygen doping modification enhances the surface polarity of the porous carbon, improving the selective adsorption of specific oils and gases. The embodiments and comparative examples of this invention demonstrate that the carbon material prepared by the method of this invention exhibits high benzene series absorption activity and selectivity, low desorption temperature, high oil and gas recovery efficiency, and low energy consumption, providing an efficient and sustainable solution for the field of oil and gas recovery.

[0049] As a further embodiment, step S1 includes: grinding and sieving activated carbon and polyacrylonitrile, impregnating them in a pore conditioning agent solution, and then drying them to obtain the primary precursor.

[0050] As some optional parameters, the activated carbon includes at least one of coal-based activated carbon, wood-based activated carbon, fruit shell activated carbon, synthetic resin activated carbon, and bamboo charcoal activated carbon, reflecting that the preparation method of the multi-level porous carbon material of the present invention has a wide range of raw material applicability. In actual operation, more economical and practical activated carbon can be selected as raw material as needed to reduce process costs.

[0051] As some optional parameters, the mass ratio of activated carbon to acrylonitrile is 7:(2~5), preferably 7:(2~4), and more preferably 7:3. The embodiments and comparative examples of the present invention show the preparation process using different mass ratios of activated carbon to acrylonitrile. A suitable mass ratio of activated carbon to acrylonitrile is beneficial to increasing the specific surface area of ​​the obtained carbon material and ultimately improving the adsorption activity of benzene series compounds of the carbon material.

[0052] As some optional parameters, the activated carbon and polyacrylonitrile are ground and then sieved to 50-100 mesh, preferably to 100 mesh. A suitable particle size helps to improve the impregnation efficiency of the pore conditioner solution.

[0053] As some optional parameters, the pore regulator includes one or both of KOH or ZnCl2. Embodiments of the present invention illustrate the process of preparing hierarchical porous carbon materials using different pore regulators.

[0054] As some optional parameters, the concentration of the pore conditioning agent solution is 0.15~0.9 mol / L, preferably 0.2~0.8 mol / L, and more preferably 0.5 mol / L; the immersion time is 1~3.5 h, preferably 1~3 h, and more preferably 2 h. In the embodiments and comparative examples of the present invention, the concentration of the pore conditioning agent solution was explored and optimized.

[0055] Understandably, the amount of pore-conditioning agent solution relative to the sieved activated carbon and polyacrylonitrile mixture in the impregnation operation in step S1 is not limited. It is sufficient to ensure that the sieved activated carbon and polyacrylonitrile mixture are in full contact with the load. In actual process, the sieved activated carbon and polyacrylonitrile mixture can be immersed in the pore-conditioning agent solution, and stirring can be used to promote full contact between the two. In an optional example of the present invention, the pore-conditioning agent solution can be recycled.

[0056] As some optional parameters, the pore conditioner solution is an aqueous solution of a pore conditioner.

[0057] As some optional parameters, the drying operation in step S1 is carried out in a vacuum drying oven at a temperature of 60~90℃ for 6~8 hours.

[0058] As a further embodiment, step S2 includes: heating the primary precursor to the activation temperature under an inert atmosphere, and then drying and activating it under an atmosphere containing carbon dioxide to obtain the secondary precursor.

[0059] As some optional parameters, the heating rate of the primary precursor in step S2 under an inert atmosphere is 2~10℃ / min. Optimizing the heating rate of the primary precursor can avoid local overheating and promote the formation of a hierarchical pore structure with more suitable pore size.

[0060] As some optional parameters, the activation temperature of the primary precursor is 500~800℃. At this activation temperature, the activation efficiency can be effectively improved and the pore size distribution can be adjusted.

[0061] As some optional parameters, in the atmosphere containing carbon dioxide, the carbon dioxide introduction rate is 10~60 mL / min and the activation time is 1~5 h, thereby improving the carbon dioxide activation efficiency and regulating the pore structure.

[0062] As a further embodiment, step S3 includes: immersing the secondary precursor in a dopant solution for reflux treatment, and then annealing it to obtain the hierarchical porous carbon material.

[0063] As some optional parameters, the dopant includes one or both of urea and ammonia. The embodiments of the present invention illustrate the preparation process of hierarchical porous carbon materials using different dopants.

[0064] As some optional parameters, the dopant solution is an aqueous solution of the dopant with a concentration of 1.5~9 mol / L, preferably 2~8 mol / L, more preferably 5~8 mol / L, and even more preferably 8 mol / L. The embodiments and comparative examples of the present invention have explored and optimized the concentration of the dopant solution.

[0065] As some optional parameters, the temperature of the reflow operation is 75~85℃, preferably 80℃; the reflow time is 5~10h, preferably 10h. Optimizing the reflow operation control conditions can accelerate the diffusion and penetration of dopants in the pores of activated carbon and promote the uniform distribution of dopants.

[0066] As some optional parameters, the annealing is carried out in an inert atmosphere at a temperature of 750~850℃, preferably 800℃. Controlling the annealing temperature can prevent oxidation and improve the stability of the dopant on the activated carbon.

[0067] It should be noted that the inert atmosphere described in this invention refers to a gaseous environment composed of gases that do not chemically interact with the reactants, such as a nitrogen atmosphere, or an atmosphere formed by gases of Group 0 elements in the periodic table (such as argon).

[0068] Thirdly, the present invention proposes the application of the above-mentioned hierarchical porous carbon material or the carbon material prepared by the above-mentioned hierarchical porous carbon material preparation method in oil and gas recovery.

[0069] The embodiments and comparative examples of this invention also illustrate the preparation process of multi-level porous carbon materials under specific working conditions. It should be noted that these working conditions are only preferred examples and do not limit the scope of protection of this invention.

[0070] Example 1 A method for preparing a hierarchical porous carbon material specifically includes the following steps: Step S1: Mix and grind 7g of activated carbon and 3g of polyacrylonitrile (PAN) in a mortar, sieve to 100 mesh, then immerse in 0.5mol / L KOH solution for 2h, followed by drying in a vacuum drying oven at 80℃ for 6h to obtain the primary precursor. Step S2: Place 5g of the primary precursor in a tube furnace, heat to 600℃ at 10℃ / min under a N2 protective atmosphere, then dry and activate under CO2 at 50mL / min for 2h to obtain the secondary precursor. Step S3: Immerse 5g of the secondary precursor in a 5mol / L urea solution, reflux at 80℃ for 10h, then anneal at 800℃ for 2h under a N2 atmosphere to obtain a nitrogen-oxygen-doped hierarchical porous carbon material.

[0071] Figure 1 The image shown is a scanning electron microscope image of the hierarchical porous carbon material fabricated in this embodiment. Figure 1 It can be observed that the surface of the hierarchical porous carbon material prepared in this embodiment exhibits a hierarchical pore structure including micropores and mesopores, combined with Figure 2 The successful doping of nitrogen and oxygen elements was confirmed in the study. Figure 2 The XPS full spectrum results of Example 1 are shown, based on which the nitrogen doping content can be determined to be 4.7% and the oxygen doping content to be 2.6%.

[0072] Comparative Example 1 A method for preparing a carbon material, the specific preparation process includes: mixing and grinding 7g of activated carbon and 3g of polyacrylonitrile (PAN) in a mortar, sieving to 100 mesh, and then drying in a vacuum drying oven at 80℃ for 6h to obtain activated carbon. Figure 2 The XPS full spectrum results of the carbon material prepared in this comparative example are shown.

[0073] Comparative Example 2 A method for preparing a carbon material, specifically comprising the following steps: Step S1, mixing and grinding 7g of activated carbon and 3g of polyacrylonitrile (PAN) in a mortar, sieving to 100 mesh, then immersing in 0.5mol / L KOH solution for 2h, followed by drying in a vacuum drying oven at 80℃ for 6h to obtain a first precursor. Step S2, placing 5g of precursor A3 in a tube furnace, heating to 600℃ at 10℃ / min under a N2 protective atmosphere, then drying and activating under CO2 at 50mL / min for 2h to obtain the carbon material. Figure 2 The XPS full spectrum results of the carbon material prepared in this comparative example are shown.

[0074] Comparative Example 3 A method for preparing a carbon material, the specific preparation process includes: Step S1, mixing and grinding 7g of activated carbon and 3g of polyacrylonitrile (PAN) in a mortar, sieving to 100 mesh, then immersing in 0.5mol / L KOH solution for 2h, followed by drying in a vacuum drying oven at 80℃ for 6h to obtain a first precursor. Step S2, placing 5g of the first precursor in a tube furnace, heating to 600℃ at 10℃ / min under a N2 protective atmosphere, then drying and activating under CO2 at 50mL / min for 2h to obtain a second precursor. Step S3, mixing 5g of the second precursor with ethylenediamine, refluxing at 80℃ for 60h, followed by annealing at 800℃ for 2h under a N2 atmosphere to obtain a nitrogen-doped carbon material.

[0075] Comparative Example 4 A method for preparing a carbon material, specifically comprising the following steps: Step S1, mixing and grinding 7g of activated carbon and 3g of polyacrylonitrile (PAN) in a mortar, sieving to 100 mesh, then immersing in 0.5mol / L KOH solution for 2h, followed by drying in a vacuum drying oven at 80℃ for 6h to obtain a first precursor. Step S2, placing 5g of the first precursor in a tube furnace, heating to 600℃ at 10℃ / min under a N2 protective atmosphere, then drying and activating under CO2 at 50mL / min for 2h to obtain a second precursor. Step S3, annealing 5g of the second precursor at 100℃ for 2h under an O2 atmosphere to obtain an oxygen-doped carbon material.

[0076] Comparative Example 5 A method for preparing a carbon material, the specific preparation process includes: Step S1, mixing and grinding 7g of activated carbon and 3g of polyacrylonitrile (PAN) in a mortar, sieving to 100 mesh, then immersing it in 0.5mol / L KOH solution for 2h, followed by drying in a vacuum drying oven at 80℃ for 6h to obtain a first precursor. Step S2, placing 5g of the first precursor in a tube furnace, heating to 600℃ at 10℃ / min under a N2 protective atmosphere, then drying and activating under CO2 at 50mL / min for 2h to obtain a second precursor. Step S3, immersing 5g of the second precursor in a 5mol / L thiol solution, refluxing at 80℃ for 6h, followed by annealing at 800℃ for 2h under a N2 atmosphere to obtain a sulfur-doped carbon material.

[0077] This invention also tested the microporosity, specific surface area, and average pore size of the hierarchical porous carbon material prepared in Example 1 and the carbon materials prepared in Comparative Examples 1-5; and used these carbon materials as adsorbents to test the benzene adsorption activity and selectivity of different carbon materials. Selectivity refers to the adsorption selectivity of the adsorbent material for a mixture of benzene and n-hexane gas; the test results are shown in Table 1. The microporosity, specific surface area, and average pore size of the carbon materials were measured using the nitrogen adsorption-desorption method; the benzene adsorption activity and selectivity were measured using an adsorption breakthrough experiment.

[0078] Table 1

[0079] Combined with Table 1 Figure 2 It can be verified that, compared with the conventional activated carbon Comparative Example 1 and the undoped Comparative Example 2, the hierarchical pore structure controlled by impregnation with pore regulator and activation with carbon dioxide in Example 1 results in a larger specific surface area of ​​the prepared hierarchical pore structure carbon material. The proportion of micropores (average particle size <2nm) reaches 50%~60%, while the proportion of mesopores reaches 40%~50%, which promotes macromolecular transport. Its benzene adsorption activity is improved by 14%~52% compared with Comparative Example 1 and Comparative Example 2, and the selectivity is improved by 7%~34%. The high selectivity for benzene / n-hexane shows its preferential adsorption capacity for aromatic hydrocarbons.

[0080] Compared to Comparative Examples 3 and 4, which were doped with nitrogen and oxygen respectively, Example 1 enhanced the adsorption performance (electronic effect) of benzene compounds by nitrogen doping based on hierarchical pore structure control, and improved the lipophilicity by combining the doping of oxygen groups (carboxyl groups, phenolic hydroxyl groups). Specifically, the benzene adsorption activity of Example 1 was increased by 7%~19% and the selectivity was increased by 2%~11% compared with Comparative Examples 3 and 4. Example 1 had a better effect on oil and gas recovery.

[0081] Compared to Comparative Example 5, which was doped with sulfur, Example 1 exhibited higher benzene adsorption performance, and its selectivity and cycle stability were significantly better than those of Comparative Example 5, which confirmed that Example 1 of the present invention, through the regulation of hierarchical pore structure and the doping of specific elements, enabled the carbon material to have excellent selectivity for polar / nonpolar oil and gas molecules and good adsorption performance for oil and gas volatiles.

[0082] This invention also tested the desorption temperature and cycling stability (adsorption retention rate) of the hierarchical porous carbon material prepared in Example 1 and the carbon materials prepared in Comparative Examples 1-5. The test results are shown in Table 2. The desorption temperature is the lowest temperature required for gas or liquid molecules adsorbed in the pores of activated carbon to detach from the activated carbon surface and be released into the surrounding environment during adsorption. The specific test method is temperature programmed desorption (TPD). Cyclic stability is used to characterize the ability of carbon materials to maintain their adsorption performance after multiple adsorption and desorption (or adsorption-regeneration) cycles. This invention tested the adsorption retention rate of different carbon materials for 10 cycles using the adsorption breakthrough test method.

[0083] Table 2

[0084] As shown in Table 2, compared to the carbon materials in Comparative Examples 1-5, the hierarchical porous carbon material in Example 1 can be desorbed and regenerated at approximately 100°C after adsorption saturation, and still maintains an adsorption rate of ≥90% after 10 cycles. Therefore, applying the hierarchical porous carbon material of this invention to oil and gas recovery not only simplifies the operation process and reduces energy consumption, but also has the advantages of high regeneration efficiency and strong applicability, effectively improving the process efficiency of oil and gas volatile gas recovery.

[0085] Example 2 Based on the preparation method of the hierarchical porous carbon material shown in Example 1, this example explores and optimizes the mass ratio of activated carbon to PAN in step S1. Specifically, the parameters and conditions for the preparation method of the hierarchical porous carbon material in this example are the same as those in Example 1, except that the pore regulator used in step S1 is ZnCl2, and a different mass ratio of activated carbon to PAN is used in step S1. The specific parameter control is shown in Table 3.

[0086] This embodiment also tested the microporosity, specific surface area, average pore size, nitrogen doping amount, oxygen doping amount of the prepared hierarchical porous carbon material, as well as its benzene adsorption activity, selectivity and 10-cycle stability when used for the adsorption and recovery of volatile oil and gas. The specific test results are shown in Table 3.

[0087] Table 3

[0088] As can be verified from Table 3, controlling the mass ratio of activated carbon to polyacrylonitrile is beneficial to increasing the specific surface area of ​​the prepared carbon material and controlling the doping amount of nitrogen and oxygen, thereby exhibiting better benzene adsorption performance and selectivity in the adsorption of volatile oil and gas, and improving the adsorption capacity retention performance of the carbon material in the recycling test. In the preparation method of the hierarchical porous carbon material of the present invention, the mass ratio of activated carbon to polyacrylonitrile can be selected as 7:(2~5), preferably 7:(2~4), and more preferably 7:3.

[0089] Example 3 Based on the preparation method of the hierarchical porous carbon material shown in Example 1, this example explores and optimizes the concentration of the pore conditioner in step S1. Specifically, the parameters and conditions for the preparation method of the hierarchical porous carbon material in this example are the same as those in Example 1, except that a different concentration of pore conditioner is used in step S1. Specific parameter control is shown in Table 4. This example tests the microporosity, specific surface area, and average pore size of the prepared hierarchical porous carbon material, as well as its benzene adsorption activity, selectivity, and stability after 10 cycles in the adsorption and recovery of volatile oil and gas. Specific test results are shown in Table 4.

[0090] Table 4

[0091] As can be confirmed by Table 4, in step S1 of the method for preparing the hierarchical porous carbon material of the present invention, the optimization of the pore-conditioning agent solution concentration and impregnation time can be combined with carbon dioxide activation in step S2 to regulate the hierarchical porous structure, thereby improving the adsorption performance of the obtained carbon material. The concentration of the pore-conditioning agent can be selected as 0.15~0.9 mol / L, preferably 0.2~0.8 mol / L, more preferably 0.5 mol / L, and the impregnation time can be selected as 1~3.5 h, preferably 1~3 h, more preferably 2 h.

[0092] Example 4 Based on the preparation method of the hierarchical porous carbon material shown in Example 1, this example explores and optimizes the dopant concentration in step S3. Specifically, the parameters and conditions for the preparation method of the hierarchical porous carbon material in this example are the same as those in Example 1, except that different types and concentrations of dopant are used to impregnate the secondary precursor in step S3. Specific parameter control is shown in Table 5. This example also tests the nitrogen doping amount and oxygen doping amount of the prepared hierarchical porous carbon material, as well as its benzene adsorption activity, selectivity, and 10-cycle stability in the adsorption and recovery of volatile oil and gas. Specific test results are shown in Table 5.

[0093] Table 5

[0094] As can be confirmed by Table 5, in step S3 of the method for preparing hierarchical porous carbon materials of the present invention, the optimization of the dopant concentration can control the nitrogen and oxygen doping amounts of the prepared hierarchical porous carbon materials. Appropriate nitrogen and oxygen doping amounts can promote improved adsorption performance of benzene compounds, enhance oleophilicity, and increase selectivity. Optionally, the concentration of the dopant is 1.5~9 mol / L, preferably 2~8 mol / L, more preferably 5~8 mol / L, and even more preferably 8 mol / L.

[0095] It should be noted that the above description is a further detailed explanation of the present invention in conjunction with specific embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple improvements can be made without departing from the concept of the present invention, and all such improvements should be considered to fall within the scope of protection of the present invention.

Claims

1. A hierarchically porous carbon material, characterized in that, The carbon material is a nitrogen-oxygen doped multi-level pore structure carbon material, the nitrogen doping amount of the carbon material is 1% to 5%, the oxygen doping amount is 0.5% to 5%, the micropore rate is 50% to 60%, and the average pore diameter is 0.5 to 20 nm.

2. The hierarchical porous carbon material according to claim 1, characterized in that, The nitrogen doping amount of the carbon material is 1.2% to 4.7%, preferably 2.4% to 4.7%; And / or, the oxygen doping amount of the carbon material is 0.5% to 2.6%, preferably 1.1% to 2.6%; And / or, the micropore rate of the carbon material is 57% to 60%, preferably 57.58% to 59.6%; And / or, the average pore diameter of the carbon material is 8 to 11 nm, preferably 8 to 9 nm; and / or the specific surface area of the carbon material is 1500 to 1650 m 2 / g, preferably 1610 to 1630 m 2 / g; And / or, the benzene adsorption activity of the carbon material is 295 to 332 mg / g, the benzene adsorption selectivity is 90% to 93%, the adsorption retention rate is ≥90%, and the desorption temperature is 100 to 150°C.

3. A method for producing a carbon material having a hierarchical pore structure, characterized by, The method comprises the following steps: S1, after mixing the activated carbon and polyacrylonitrile, the mixture is immersed in a pore adjuster solution to obtain a primary precursor; S2, the primary precursor is activated by carbon dioxide to obtain a secondary precursor; S3, the secondary precursor is treated by a nitrogen-oxygen dopant to obtain the multi-level pore structure carbon material.

4. The method for producing a carbon material with a hierarchical pore structure according to claim 3, characterized by, The step S1 comprises: after grinding and sieving the activated carbon and polyacrylonitrile, the mixture is immersed in a pore adjuster solution, and then dried to obtain the primary precursor.

5. The method for producing a carbon material with a hierarchical pore structure according to claim 4, wherein The step S1 meets one or more of the following conditions: (1) the activated carbon comprises at least one of coal-based activated carbon, wood-based activated carbon, shell-based activated carbon, synthetic resin-based activated carbon, and bamboo charcoal-based activated carbon; (2) the mass ratio of the activated carbon to polyacrylonitrile is 7:(2 to 5), preferably 7:(2 to 4); (3) after grinding the activated carbon and polyacrylonitrile, the mixture is sieved to 50 to 100 mesh, preferably 100 mesh; (4) the pore adjuster comprises one or both of KOH and ZnCl2; (5) the concentration of the pore adjuster solution is 0.15 to 0.9 mol / L, preferably 0.2 to 0.8 mol / L; the immersion time is 1 to 3.5 h, preferably 1 to 3 h; (6) the drying operation is performed in a vacuum drying oven, the drying temperature is 60 to 90°C, and the drying time is 6 to 8 h.

6. The method for producing a carbon material with a hierarchical pore structure according to claim 3, wherein The step S2 comprises: heating the primary precursor to an activation temperature under an inert atmosphere, and then performing dry activation under an atmosphere containing carbon dioxide to obtain the secondary precursor.

7. The method for producing a carbon material with a hierarchical pore structure according to claim 6, wherein The step S2 meets one or more of the following conditions: (1) the heating rate of the primary precursor under the inert atmosphere is 2 to 10°C / min; (2) the activation temperature of the primary precursor is 500 to 800°C; (3) in the atmosphere containing carbon dioxide, the carbon dioxide flow rate is 10 to 60 mL / min, and the activation time is 1 to 5 h.

8. The method for producing a carbon material with a hierarchical pore structure according to claim 3, wherein The step S3 comprises: immersing the secondary precursor in a dopant solution for reflux treatment, and then annealing to obtain the multi-level pore structure carbon material.

9. The method for producing a carbon material with a hierarchical pore structure according to claim 8, wherein The step S3 meets one or more of the following conditions: (1) the dopant comprises one or both of urea and ammonia water; (2) the dopant solution is an aqueous solution of the dopant, and the concentration of the dopant solution is 1.5-9 mol / L, preferably 2-8 mol / L; (3) the temperature of the reflux operation is 75-85℃, preferably 80℃; the reflux time is 5-10 h, preferably 10 h; (4) the annealing is performed in an inert atmosphere, and the annealing temperature is 750-850℃, preferably 800℃.

10. Use of the carbon material with a hierarchical pore structure according to claim 1 or 2 or the carbon material prepared by the method according to any one of claims 3-9 in oil and gas recovery.

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