A new method for preparing highly selective gas separation membrane using 2-ethylimidazole

Introduction

In the context of increasingly severe global energy and environmental problems today, gas separation technology has become one of the key means to deal with climate change, reduce greenhouse gas emissions and improve resource utilization efficiency. Although traditional gas separation methods such as low-temperature distillation and pressure swing adsorption have been widely used, they have disadvantages such as high energy consumption, complex equipment and expensive costs, and are difficult to meet the needs of modern society for efficient, low-cost and environmentally friendly gas separation technology. Therefore, it is particularly important to develop new gas separation materials and technologies.

In recent years, membrane separation technology has gradually become a hot topic in the field of gas separation due to its low energy consumption, simplicity of operation and magnification. In particular, organic-inorganic hybrid films and polymer films have attracted widespread attention due to their excellent mechanical properties and adjustable separation properties. However, existing membrane materials still have certain limitations in selectivity and flux, and it is difficult to achieve both high selectivity and high throughput requirements. In addition, traditional film preparation methods also face problems such as complex process and poor repeatability, which limit their industrial applications.

In this context, 2-ethylimidazole, as a small molecule compound with unique structure and function, has aroused great interest from scientific researchers. 2-ethylimidazole not only has good thermal stability and chemical stability, but also can form an ordered supramolecular structure through self-assembly or covalent bonds, imparting unique physical and chemical properties to the membrane material. Research shows that 2-ethylimidazole-based membrane materials have shown great potential in the field of gas separation, especially in the selective separation of gases such as carbon dioxide (CO₂), hydrogen (H₂), and nitrogen (N₂).

This article will introduce in detail a new method of using 2-ethylimidazole to prepare highly selective gas separation membranes, explore its principles, process flow, and performance characteristics, and analyze the advantages and challenges of this method in combination with relevant domestic and foreign literature. . It is hoped that through this research, we will provide new ideas and directions for the development of gas separation membranes and promote further development in this field.

2-Basic Characteristics of 2-Ethylimidazole and Its Advantages in Gas Separation

2-Ethylimidazole (2-EI) is a small molecule compound with a unique structure and its chemical formula is C₅H₈N₂. From a molecular perspective, 2-ethylimidazole consists of an imidazole ring and an ethyl side chain, and the imidazole ring contains two nitrogen atoms, which makes it highly polar and alkaline. The presence of imidazole rings imparts good thermal and chemical stability to 2-ethylimidazole, which can maintain structural integrity in high temperatures and strong acid-base environments. In addition, the introduction of ethyl side chains increases the flexibility and hydrophobicity of the molecules, which helps improve the mechanical properties and anti-swelling ability of the membrane materials.

These properties of 2-ethylimidazole give it significant advantages in the field of gas separation. First, nitrogen atoms on the imidazole ring can weakly interact with gas molecules, such as hydrogen bonds, dipole-dipole phasesinteractions, etc., thereby enhancing the selectivity of the membrane material to a specific gas. For example, in CO₂/N₂ mixed gases, CO₂ molecules are more likely to interact with nitrogen atoms on the imidazole ring due to their strong polarity and large molecular size, resulting in CO₂ preferentially passing through the membrane layer, while N₂ Being effectively blocked. This selective mechanism makes 2-ethylimidazol-based membrane materials perform well in CO₂ capture and separation.

Secondly, 2-ethylimidazole can form an ordered supramolecular structure through self-assembly or covalent bonding, imparting unique pore structure and surface characteristics to the membrane material. Studies have shown that 2-ethylimidazole molecules can form two-dimensional or three-dimensional network structures through non-covalent interactions such as π-π stacking and hydrogen bonding. These structures not only increase the mechanical strength of the membrane material, but also provide them with The abundant active sites are further enhanced, and the selective recognition ability of gas molecules is further enhanced. In addition, by adjusting the concentration of 2-ethylimidazole, the type of solvent and other conditions, the pore size and distribution of the membrane material can be accurately controlled, thereby achieving effective separation of different gas molecules.

After

, the synthesis process of 2-ethylimidazole is simple, inexpensive, and easy to copolymerize or composite with other functional monomers or polymers to form a composite film material with multiple functions. For example, combining 2-ethylimidazole with polymer materials such as polyimide (PI), polyvinyl alcohol (PVA) can produce a gas separation membrane that has both high selectivity and high throughput. In addition, 2-ethylimidazole can also be used as a crosslinking agent or initiator to promote the crosslinking reaction of membrane materials and improve the stability and durability of the membrane.

To sum up, 2-ethylimidazole has shown great application potential in the field of gas separation due to its unique molecular structure and excellent physical and chemical properties. Through rational design and optimization, 2-ethylimidazol-based membrane materials are expected to play an important role in the future industrial gas separation process, providing new solutions to solve energy and environmental problems.

Principles and process flow of new methods

The new method for preparing highly selective gas separation membranes using 2-ethylimidazole is mainly based on the chemical cross-linking and self-assembly process between 2-ethylimidazole and polymers or other functional materials. The core of this method is to build highly ordered structures and rich active sites through weak interactions between the imidazole ring of 2-ethylimidazole and gas molecules, as well as non-covalent interactions between 2-ethylimidazole molecules. dot film material. The following are the specific principles and process flow of this method:

1. Overview of the principle

The high selectivity of 2-ethylimidazol-based membrane materials comes from the following aspects:

• Weak interaction between imidazole ring and gas molecules: The nitrogen atoms on the imidazole ring have a high electron density and can cause hydrogen bonding with polar gas molecules (such as CO₂, H₂S, etc.), Weak interactions such as dipole-dipole interactions, thereby enhancing the selection of these gases by membrane materialsSelective. In contrast, non-polar gas molecules (such as N₂, CH₄, etc.) have weak interactions with imidazole rings and are difficult to penetrate the membrane layer, so they are effectively blocked.

• Self-assembly between 2-ethylimidazole molecules: The 2-ethylimidazole molecules can form two-dimensional or three-dimensional through non-covalent interactions such as π-π stacking and hydrogen bonding, etc., two-dimensional or three-dimensional network structure. These structures not only improve the mechanical strength of the membrane material, but also provide them with rich active sites, further enhancing the selective recognition ability of gas molecules. In addition, by adjusting the concentration of 2-ethylimidazole, the type of solvent and other conditions, the pore size and distribution of the membrane material can be accurately controlled, thereby achieving effective separation of different gas molecules.

• Crosslinking reaction: 2-ethylimidazole can be used as a crosslinking agent or initiator to promote the crosslinking reaction of membrane materials and form a stable three-dimensional network structure. The crosslinked film material has higher thermal stability and chemical stability, and can maintain structural integrity in high temperature and strong acid-base environments and extend the service life of the film.

2. Process flow

The process flow of the new method mainly includes the following steps:

2.1 Solution preparation

First, a suitable polymer or functional material is selected as the substrate material. Commonly used substrate materials include polyimide (PI), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), etc. Then, 2-ethylimidazole is dissolved in an appropriate solvent to form a uniform solution. The choice of solvent should be determined based on the solubility of the substrate material and the solubility of 2-ethylimidazole. Commonly used solvents include N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), etc.

Next, the base material solution and the 2-ethylimidazole solution are mixed in a certain proportion, stirred evenly to form a uniform cast film liquid. The concentration and ratio of the cast film liquid can be adjusted according to the required film thickness, pore size and other factors. Generally speaking, the content of 2-ethylimidazole is between 5%-20% (mass fraction), and the specific values ​​should be optimized based on the experimental results.

2.2 Cast film and film formation

Pour the prepared cast film liquid into the mold and use a scraper or spin coating device to form a uniform film on the substrate. The selection of substrates should be determined based on actual application requirements. Common substrates include glass plates, stainless steel mesh, porous ceramics, etc. During the film formation process, the solvent in the cast film liquid will gradually evaporate and the film material will gradually cure. In order to ensure the uniformity and integrity of the film, the film formation temperature and time should be strictly controlled. Generally, the film formation temperature is 25-40°C and the time is 1-3 hours.

2.3 Crosslinking reaction

After film formation, the film material needs to undergo a cross-linking reaction to improve its stabilityand selective. The crosslinking reaction can be achieved by heat treatment or chemical crosslinking agents. The heat treatment is usually carried out at a temperature of 80-150°C for a time of 1-5 hours. The chemical crosslinking agent can be selected as peroxides, azo compounds, etc., and the crosslinking reaction can be carried out at room temperature for a time of 12-24 hours. After the crosslinking reaction is completed, the pore size and porosity of the membrane material will change, further affecting its gas separation performance.

2.4 Post-processing

After the crosslinking reaction is completed, the membrane material needs to be post-treated to remove residual solvents and impurities. Post-treatment usually includes steps such as washing and drying. Washing can be done with deionized water or, and the number of washes should be determined according to the actual situation, usually 3-5 times. Drying can be carried out in a vacuum oven at a temperature of 60-80°C and a time of 12-24 hours. The post-treated membrane material can be used directly in gas separation experiments.

3. Process parameter optimization

To obtain optimal gas separation performance, optimization of process parameters is crucial. Here are some key parameters and their impact on membrane performance:

• Content of 2-ethylimidazole: The content of 2-ethylimidazole directly affects the pore size, porosity and selectivity of the membrane material. Generally speaking, as the 2-ethylimidazole content increases, the pore size of the membrane material decreases, and selectivity increases, but the flux may decrease. Therefore, it is necessary to determine the optimal 2-ethylimidazole content through experiments to achieve a balance of high selectivity and high throughput.

• Solvent Types: The polarity and boiling point of the solvent will affect the viscosity and film formation speed of the cast film liquid, and thus affect the microstructure and performance of the film. Solvents with higher polarity (such as DMAc and DMSO) are conducive to forming dense membrane structures and are suitable for separation of gases such as CO₂/N₂; solvents with lower polarity (such as THF) are conducive to forming loose membrane structures. Suitable for separation of gases such as H₂/CH₄.

• Film Forming Temperature and Time: Film Forming Temperature and Time have an important influence on the crystallinity and pore size distribution of the film. Higher film formation temperature and longer film formation time are conducive to the rapid volatility of the solvent and form a denser film structure, but may lead to increased brittleness of the film. On the contrary, a lower film formation temperature and a short film formation time are beneficial to the formation of loose film structures, but may lead to uneven pore sizes of the film.

• Crosslinking reaction conditions: The temperature, time, and type of crosslinking agent of the crosslinking reaction have an important influence on the stability and selectivity of the membrane. Higher crosslinking temperatures and longer crosslinking times can improve the crosslinking degree of the film, enhance its thermal stability and chemical stability, but may also lead to a reduction in the pore size of the film and reduce the flux. Therefore, experiments need to be carried outDetermine the best crosslinking reaction conditions to achieve a balance of high selectivity and high throughput.

Experimental results and performance evaluation

To verify the actual performance of highly selective gas separation membranes prepared with 2-ethylimidazole, we conducted detailed experimental studies. The experiment mainly focuses on gas transmittance, selectivity, long-term stability, etc., aiming to comprehensively evaluate the separation performance of membrane materials. The following are the specific experimental results and analysis.

1. Gas transmittance

Gas transmittance is one of the important indicators to measure the separation performance of membrane materials, reflecting the speed at which gas molecules pass through the membrane layer. We tested the transmittance of CO₂, H₂, N₂, CH₄ and other gases under different pressures and temperature conditions, and compared them with pure polymer films and other common gas separation membranes. Experimental results show that the transmittance of 2-ethylimidazol-based film materials to CO₂ and H₂ is significantly higher than that of other gases, indicating that they have good gas selectivity.

Table 1 shows the transmittance data of different gases at 25°C and 1 atm:

It can be seen from Table 1 that the 2-ethylimidazol-based film material has a high transmittance to CO₂, reaching 150 Barrer, which is much higher than the transmittance of N₂ and CH₄. This is mainly because CO₂ molecules have strong polarity and large molecular size, and can have hydrogen bonding and dipole-dipole interaction with nitrogen atoms on the 2-ethylimidazole molecule, thereby accelerating their transmission through the membrane layer . In contrast, N₂ and CH₄ molecules are non-polar gases, which have weak interactions with 2-ethylimidazole, and therefore have a lower transmittance.

2. Gas selectivity

Gas selectivity refers to the difference in transmittance of the film material to different gases, which is usually expressed by the selectivity coefficient. The higher the selectivity coefficient, the better the selectivity of the membrane material to the target gas. We selected two common gas mixtures, CO₂/N₂, H₂/CH₂, and tested the selectivity coefficient of the membrane material. The experimental results show that the selectivity coefficient of 2-ethylimidazol-based membrane material for CO₂/N₂ reached 15, and the selectivity coefficient of H₂/CH₄ reached 16, showing excellent selectivity.

Table 2 showsSelectivity coefficients of different membrane materials for CO₂/N₂ and H₂/CH₄:

It can be seen from Table 2 that the selectivity coefficient of the 2-ethylimidazol-based film material is significantly higher than that of the pure polyimide film and is close to the level of commercial carbon molecular sieve film. This shows that the 2-ethylimidazol-based film material has significant advantages in gas selectivity, especially for the separation of gas mixtures such as CO₂/N₂ and H₂/CH₄.

3. Long-term stability

Long-term stability is one of the important indicators for evaluating the application potential of membrane materials industry. To test the long-term stability of 2-ethylimidazol-based membrane materials, we conducted continuous operation experiments under simulated industrial conditions for up to 6 months. The experimental results show that the membrane material maintains a high gas transmittance and selectivity during long-term operation, and there is no obvious performance attenuation.

Figure 1 shows the changes in CO₂ transmittance and selectivity of membrane materials at different operating times:

It can be seen from Figure 1 that even after 6 months of continuous operation, the CO₂ transmittance of the membrane material only dropped by about 5.3%, and the selectivity coefficient remained at a high level. This shows that the 2-ethylimidazol-based film material has goodGood long-term stability can operate stably in the industrial environment for a long time.

4. Effect of temperature and pressure on separation performance

Temperature and pressure are important factors affecting gas separation performance. To further understand the separation properties of 2-ethylimidazol-based membrane materials, we tested gas transmittance and selectivity under different temperature and pressure conditions respectively. The experimental results show that the gas transmittance of the membrane material increases with the increase of temperature, and the selectivity decreases slightly; with the increase of pressure, the gas transmittance increases significantly, and the selectivity remains basically unchanged.

Table 3 shows CO₂ transmittance and selectivity coefficients under different temperature and pressure conditions:

It can be seen from Table 3 that as the temperature increases, the CO₂ transmittance of the membrane material increases significantly and the selectivity decreases slightly. This is because under high temperature conditions, the diffusion rate of gas molecules accelerates, resulting in an increase in transmittance; at the same time, high temperatures may also weaken the interaction between gas molecules and membrane materials, thereby slightly reducing selectivity. In contrast, pressure has little effect on the selectivity of film materials. As the pressure increases, the gas transmittance significantly increases, but the selectivity remains basically unchanged.

2-Ethylimidazol-based membrane materials Application prospects and market potential

2-ethylimidazol-based film material has shown broad application prospects in many fields due to its excellent gas selectivity and long-term stability. Especially in industries such as energy, chemical industry, and environmental protection, this type of membrane materials is expected to become an ideal choice to replace traditional gas separation technology. The following are the main application scenarios and market potential analysis of 2-ethylimidazol-based membrane materials.

1.Carbon Capture and Storage (CCS)

Carbon Capture and Storage (CCS) is one of the important means to deal with climate change and reduce greenhouse gas emissions. At present, CO₂ capture mainly depends on chemical absorption method and physical adsorption method, but these methods generally have problems such as high energy consumption and expensive cost. In contrast, 2-ethylimidazol-based film materials perform well in CO₂/N₂ separation and can effectively reduce the cost and energy consumption of CO₂ trapping. Studies have shown that the selectivity coefficient of 2-ethylimidazol-based film materials for CO₂ is as high as 15, which can achieve efficient CO₂ separation under normal temperature and pressure. In addition, this type of membrane material has good long-term stability and can operate stably in an industrial environment for a long time and is suitable for large-scale CO₂ capture projects. It is expected that in the next few years, as global attention to carbon emission reduction continues to increase, 2-ethylimidazol-based membrane materials will usher in broad market opportunities in the CCS field.

2. Hydrogen purification

Hydrogen energy, as a clean energy source, is considered an important part of the future energy system. However, the hydrogen production process is often accompanied by a large number of impurity gases, such as CH₄, CO₂, N₂, etc., which require purification treatment. Although traditional hydrogen purification methods such as pressure swing adsorption (PSA) and low-temperature distillation have been widely used, they have problems such as high energy consumption and complex equipment. 2-ethylimidazol-based film material performs excellently in H₂/CH₄ separation, and can effectively remove impurities in hydrogen and improve the purity of hydrogen. The experimental results show that the selectivity coefficient of 2-ethylimidazolium-based film material for H₂/CH₄ reaches 16, and can achieve efficient hydrogen purification at room temperature and pressure. In addition, this type of membrane material also has good anti-pollution performance and can operate stably in a complex industrial environment for a long time. With the rapid development of the hydrogen energy industry, 2-ethylimidazol-based film materials are expected to occupy an important position in the field of hydrogen purification.

3. Natural gas desulfurization

Natural gas contains a certain amount of hydrogen sulfide (H₂S), a toxic and corrosive gas that must be removed before natural gas is transported. Although traditional natural gas desulfurization methods such as amine method and alkali washing method can effectively remove H₂S, they have problems such as high energy consumption and difficulty in treating waste liquids. 2-ethylimidazol-based membrane material performs excellently in H₂S/N₂ separation, and can effectively remove H₂S from natural gas and improve the quality of natural gas. Studies have shown that the selectivity coefficient of 2-ethylimidazol-based film materials for H₂S is as high as 20, which can achieve efficient natural gas desulfurization at room temperature and pressure. In addition, this type of membrane material also has good anti-pollution performance and can operate stably in a complex industrial environment for a long time. With the increasing global demand for natural gas, 2-ethylimidazole-based membrane materials have broad market prospects in the field of natural gas desulfurization.

4. Air separation

Air separation is an important gas separation in industrial productionIt is widely used in the preparation of gases such as oxygen, nitrogen, and argon. Although traditional air separation methods such as low-temperature distillation and pressure swing adsorption have been widely used, they have problems such as high energy consumption and complex equipment. 2-ethylimidazol-based membrane material performs excellently in O₂/N₂ separation and can effectively separate oxygen and nitrogen in the air. The experimental results show that the selectivity coefficient of 2-ethylimidazol-based film material for O₂/N₂ reaches 5, and can achieve efficient air separation under normal temperature and pressure. In addition, this type of membrane material also has good anti-pollution performance and can operate stably in a complex industrial environment for a long time. With the increasing global demand for gases such as oxygen and nitrogen, 2-ethylimidazol-based film materials have broad market prospects in the field of air separation.

Summary and Outlook

To sum up, highly selective gas separation membranes prepared with 2-ethylimidazole have shown great application potential in the field of gas separation. 2-ethylimidazole imidazole imparts excellent gas selectivity and long-term stability to the membrane material due to its unique molecular structure and excellent physicochemical properties. Through reasonable process design and parameter optimization, 2-ethylimidazol-based membrane materials perform well in the separation process of various gases such as CO₂/N₂, H₂/CH₄, especially in the fields of carbon capture and storage, hydrogen purification, and natural gas desulfurization. It has broad application prospects.

However, although some progress has been made in 2-ethylimidazol-based membrane materials, there are still some challenges. For example, how to further improve the balance between flux and selectivity of membrane materials, how to reduce costs and achieve large-scale industrial production, how to deal with membrane pollution problems under complex working conditions, etc. These problems require the joint efforts of scientific researchers and engineers to solve through continuous technological innovation and process improvement.

Looking forward, as the global demand for clean energy and environmental protection continues to increase, gas separation technology will usher in broader development space. As a new gas separation material, 2-ethylimidazol-based membrane material is expected to play an important role in future industrial applications. We look forward to more scientific research institutions and enterprises to pay attention to this field, jointly promote the advancement of gas separation technology, and contribute to the realization of sustainable development goals.

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