Design of lithium modified graphite phase carbon nitride material for CO2 capture and separation

Abstract

The invention relates to a design of a lithium modified graphite phase carbon nitride material for CO2 capture and separation. According to the material, lithium is anchored on a graphite phase carbon nitride matrix in the form of Li-N chemical bonds, rich CO2 adsorption sites are formed in pore channels of the graphite phase carbon nitride material, and the material is suitable for two adsorption separation working conditions, namely adsorption purification of high-efficiency single-component CO2 gas and selective separation of mixed gas with equal moles of CO2 / N2; and excellent adsorption and separation performance can be maintained in severe environments such as high temperature. The material can be widely applied to the field of CO2 tail gas separation, can effectively solve the problem of CO2 emission, and has important application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of CO2 physical gas adsorption and separation, and specifically relates to the design of a lithium-modified graphitic carbon nitride material for CO2 capture and separation. Background Art

[0002] With the rapid development of industrialization, the concentration of CO2 in the atmosphere has been continuously increasing, leading to increasingly severe environmental problems such as global warming. Carbon capture and storage technology is considered an effective means to reduce CO2 emissions from industrial sources. Among them, the adsorption separation method has attracted much attention due to its low energy consumption and simple operation. However, existing CO2 adsorption materials still face technical bottlenecks such as low adsorption capacity, poor selectivity, and insufficient cycle stability.

[0003] Traditional CO2 adsorption materials mainly include: (1) molecular sieve materials: Although they have a regular pore structure, they have the disadvantages of high humidity sensitivity and high regeneration energy consumption; (2) metal-organic frameworks: Although they show a high specific surface area and adjustable pore size, they have poor hydrothermal stability and high costs; (3) amino-functionalized materials: Although they have a strong chemical adsorption effect on CO2, the amino groups are easily degraded and have a limited service life.

[0004] Graphitic carbon nitride, as a new type of non-metallic polymer material, shows potential in the field of gas adsorption due to its rich surface nitrogen sites and good thermal stability. However, its intrinsic material has problems such as a small specific surface area and insufficient active sites, resulting in the difficulty of meeting the actual application requirements for CO2 adsorption capacity and selectivity. In recent years, modifying graphitic carbon nitride with metals has become a research hotspot. Among them, alkali metal lithium is considered one of the most potential modifying elements due to its unique electron donor characteristics and moderate ionic radius. Therefore, developing a lithium-modified graphitic carbon nitride material with high CO2 adsorption capacity, excellent selectivity, and good stability is of great significance for promoting the practical application of CO2 capture technology.

[0005] Based on the concept of molecular engineering, the present invention innovatively designs and develops a high-performance lithium-modified graphitic carbon nitride adsorption material. The CO2 capture and separation performance of the lithium-modified graphitic carbon nitride material under different temperature and pressure conditions is studied at the molecular level, providing innovative ideas and technical solutions for the development of a new generation of efficient and stable CO2 capture materials, and having important significance for promoting the practical application of carbon capture and storage technology. Summary of the Invention

[0006] The object of the present invention is to provide a novel graphitic carbon nitride material and its design method for CO2 capture and separation, which is applicable to the efficient separation of CO2 / N2 mixed gas in industrial flue gas. The present invention adopts a multi-scale calculation method, including: (1) constructing a graphitic carbon nitride material model using Materials Studio software; (2) performing lattice structure optimization and electronic property calculation through the VASP (Vienna Ab-initio Simulation Package) software package; (3) simulating the adsorption of single-component CO2 gas and the separation performance of CO2 / N2 equimolar mixed gas using the RASPA software package.

[0007] The present invention relates to the design of a novel graphitic carbon nitride material for CO2 capture and separation, specifically including the following content:

[0008] (1) The present invention designs a novel adsorbent material, which has rich porosity and gas adsorption active sites and can efficiently adsorb and separate CO2.

[0009] (2) The novel adsorbent material designed by the present invention is a graphite-like layered crystal structure formed by the formation of Li-N chemical bonds between lithium and the graphitic carbon nitride matrix.

[0010] (3) The novel adsorbent material provided by the present invention has high stability and repeatability and can maintain its adsorption and separation performance under harsh environments such as high temperature.

[0011] (4) The crystalline porous material designed by the present invention can be widely applied to the field of CO2 tail gas separation such as flue gas from coal-fired power plants, which has important environmental protection and economic significance.

[0012] In summary, the present invention provides a design of a novel graphitic carbon nitride material for CO2 capture and separation, which has the characteristics of high efficiency, stability and controllability, can effectively solve the CO2 emission problem, and has important application value.

[0013] The advantages of the design and application of the lithium-modified graphitic carbon nitride (CN-Li) material for CO2 capture and separation provided by the present invention are as follows:

[0014] (1) The present invention adopts a multi-scale calculation method to establish a structure-activity relationship model between the material structure and CO2 adsorption performance at the molecular level, providing a reliable theoretical basis and technical guidance for experimental synthesis.

[0015] (2) The CN-Li material provided by the present invention has a highly controllable pore structure and adsorption active sites, can achieve the efficient separation of CO2 tail gas, and improve the separation efficiency.

[0016] (3) The separation process of the CN-Li material provided by the present invention does not require additional energy input, so the energy consumption cost can be reduced.

[0017] (4) The CO2 tail gas separation using the CN-Li material provided by the present invention can reduce carbon dioxide emissions and contribute to environmental protection.

[0018] (5) The CN-Li material provided by the present invention has high stability and recyclability, reducing costs and resource waste. Description of the Drawings

[0019] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. In the drawings:

[0020] Figure 1 is the structural configuration diagram of the lithium-modified graphitic carbon nitride material of the present invention;

[0021] Figure 2 is the adsorption performance of the lithium-modified graphitic carbon nitride material of the present invention for single-component CO2 and N2 gases under different temperature and pressure conditions;

[0022] Figure 3 is the selective adsorption performance of CO2 relative to N2 in the CO2 / N2 equimolar mixed gas by the lithium-modified graphitic carbon nitride material of the present invention;

[0023] Figure 4 is the radial distribution function of CO2 gas molecules in the lithium-modified graphitic carbon nitride material of the present invention;

[0024] Figure 5 is the isosteric heat of adsorption of CO2 and N2 in the lithium-modified graphitic carbon nitride material of the present invention under different temperature and pressure conditions;

[0025] Figure 6 is the summary of the working performance of the lithium-modified graphitic carbon nitride material of the present invention. Detailed Embodiments

[0026] The following further illustrates the present invention with specific embodiments, but the present invention is not limited to these embodiments.

[0027] Example 1: Construction of the lithium-modified graphitic carbon nitride material, and prediction and preliminary evaluation of the gas adsorption and separation performance of the lithium-modified graphitic carbon nitride material by the pore size

[0028] In this invention, a lithium-modified graphitic carbon nitride material model was designed using the Materials Studio software package. Considering the outstanding advantages of graphitic carbon nitride materials in the field of gas adsorption and separation: (1) High stability: It has good chemical and thermal stability and can adapt to various complex environments; (2) Strong adsorption force: Its unique porous structure and large specific surface area provide abundant gas adsorption sites; (3) High selectivity: It has a strong affinity for specific gas molecules, enabling efficient and precise separation; (4) Easy modification and regulation: The material properties can be adjusted to meet different gas adsorption and separation requirements. In addition, many studies have shown that introducing metal lithium ions as active sites into CO2 adsorbent materials can significantly improve the performance of the adsorbent materials. Therefore, this invention also considered the introduction of metal lithium ions to enhance the material's capture and separation performance. Using the Lewis acid-base theory, Li sites were anchored by forming Li-N coordination chemical bonds in the graphitic carbon nitride material ( Figure 1 ), and a graphitic carbon nitride material was constructed and named Li-CN-T. Next, the VASP software package was used to optimize the structural parameters of the constructed lithium-modified graphitic carbon nitride model (based on the theory that the smaller the energy, the more stable the structure, and the structure with the minimum energy and the most stable structure was obtained). Its main components are briefly described in Figure 1 : The structural size is 2.13×2.13×2.01 nm 3 ; the pore size is 0.54×0.67 nm 2 .

[0029] Example 2: Simulation and evaluation of the single-component gas (CO2, N2) adsorption performance of the constructed lithium-modified graphitic carbon nitride material at different temperatures and pressures

[0030] To analyze the gas adsorption performance of the material, we simulated and analyzed the adsorption isotherms of single-component gases (CO2, N2). The results showed that in the range of 0 - 1.0 bar, the adsorption amounts of CO2 and N2 both decreased with the increase in temperature. Under the condition of 1.0 bar, the CO2 and N2 adsorption amounts of CN-Li were in the order: CN-Li-273 K (17.43 mmol / g and 1.65 mmol / g) > CN-Li-298 K (16.05 mmol / g and 0.92 mmol / g) > CN-Li-333 K (13.13 mmol / g and 0.46 mmol / g) ( Figure 2 ). It can be seen that the adsorption amount of N2 is much lower than that of CO2, which means that the CN-Li material has good CO2 preferential selectivity. In addition, in the temperature range of 273 - 333 K, the change in temperature has little effect on the performance of the CN-Li material, indicating that the material has good application ability.

[0031] Example 3: Simulation evaluation of the selective adsorption performance of CO2 relative to N2 in an equimolar mixture of CO2 / N2 gas by the constructed lithium-modified graphitic carbon nitride material

[0032] In the actual working environment, the working environment of the adsorption material is relatively complex and cannot be a single-component gas environment. Therefore, the present invention simulated the selectivity of the lithium-modified graphitic carbon nitride material for CO2 relative to N2 under different conditions in the mixed components. The results show that in the range of 0 - 1.0 bar, the selectivity of CO2 over N2 decreases significantly with the increase in temperature. At 1.0 bar and 273 K, the selectivity of CO2 / N2 in CN-Li is as high as 1770; at 1.0 bar and 333 K, the selectivity of CO2 / N2 decreases significantly to 281( Figure 3 ). This is because as the temperature increases, the molecular motion intensifies, which will more significantly affect the interaction between the framework and CO2, and the adsorption amount of CO2 decreases faster, resulting in a significant decrease in selectivity. Overall, the selective adsorption performance of the CN-Li material for CO2 relative to N2 is still at a relatively high level.

[0033] Example 4: Simulation evaluation of the radial distribution function of CO2 gas molecules in the constructed lithium-modified graphitic carbon nitride material

[0034] To further study the influence of temperature change on the adsorption distribution of CO2 gas molecules, the radial distribution function of CO2 molecules at different temperatures was analyzed( Figure 4 ). The results show that at different temperatures, the CO2 adsorption peaks all appear at similar positions, which is because it is the same structure, indicating from the side that the change in temperature does not cause a significant change in the structure of the material. Therefore, CN-Li has good structural stability; at each adsorption peak, the peak intensity decreases with the increase in temperature, indicating that the aggregation degree of CO2 around Li decreases, which is mainly due to the intensification of the motion of CO2 molecules caused by the increase in temperature.

[0035] Example 5: Simulation evaluation of the isosteric adsorption heat of CO2 and N2 in the constructed lithium-modified graphitic carbon nitride material under different temperature and pressure conditions

[0036] To further study the influence law of temperature change on the adsorption performance of CO2 and N2, the isosteric adsorption heat of gas molecules at different temperatures and pressures was analyzed( Figure 5)。The results show that in the range of 0 - 1.0 bar, the adsorption heats of CO2 and N2 both show a decreasing trend with the increase of temperature. Under the condition of 1.0 bar, the order of the adsorption heats of CO2 and N2 for CN-Li is: CN-Li-273 K (52.26 and 18.61 kJ / mol) > CN-Li-298 K (48.31 and 18.35 kJ / mol) > CN-Li-333 K (44.34 and 18.24 kJ / mol). This indicates that there is a strong interaction between CO2 and the material, meaning that the CO2 molecules are relatively stable after adsorption on the material surface and are not easily desorbed, which is suitable for application scenarios requiring long-term stable adsorption. In addition, with the increase of temperature, the adsorption heat of CO2 decreases more significantly, indicating that temperature has a more significant impact on the interaction between the framework and CO2.

Claims

1. Design of a lithium-modified graphitic carbon nitride material for CO2 capture and separation, characterized in that The material is a graphite-like layered crystal structure formed by the formation of Li-N chemical bonds between lithium and graphitic carbon nitride matrix, with abundant pores and Lewis adsorption active sites, and has selective adsorption ability for CO2 gas.

2. The lithium-modified graphite-phase carbon nitride material according to claim 1, characterized in that The material is labeled as CN-Li-T, where T represents the test treatment temperature.

3. The lithium-modified graphitic carbon nitride material according to claim 1, characterized in that It is applicable to the following two adsorption and separation working conditions: (1) Adsorption purification of single-component CO2 gas; (2) Selective separation of equimolar mixed gas of CO2 / N2.

4. The lithium-modified graphitic carbon nitride material according to claim 1, wherein The crystalline porous material can maintain its adsorption and separation performance under harsh environments such as high temperature.

5. The lithium-modified graphitic carbon nitride material according to claims 1-4, characterized in that The material is widely applicable to the capture and separation of CO2 in flue gas of coal-fired power plants, tail gas of natural gas purification, and waste gas of industrial kilns, and has important environmental protection and economic significance.

Images