Pioneering the Future of Industrial Development: Harnessing Membrane Separation Breakthroughs to Propel CO2 Extraction from Natural Gas into a Sustainable Era

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Pioneering the Future of Industrial Development: Harnessing Membrane Separation Breakthroughs to Propel CO₂ Extraction from Natural Gas into a Sustainable Era

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NNADIKWE JOHNSON^*,EWELIKE ASTERIUS DOZIE,Abdulazeez Adeyemi, Momoh,Onuabuchi Azunna

This version is not peer-reviewed

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Sustainable Solutions for a Sustainable Future in the Natural Gas and Electricity Markets

Submitted:

16 December 2023

Posted:

19 December 2023

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Abstract

Natural Gas (NG) processing is a prominent industrial separation process. Among the available techniques, the innovative membrane process shows potential for efficient removal of impurities, including carbon dioxide (CO₂). This study focuses on utilizing breakthroughs in membrane separation to drive sustainable CO₂ extraction from natural gas. Through comprehensive research and analysis, we explore the effectiveness and feasibility of membrane-based systems in removing CO₂ impurities from NG, thus promoting greener and more sustainable industrial practices. Our findings underscore the transformative nature of membrane separation technology, presenting new possibilities for a more environmentally-friendly and sustainable approach to CO₂ extraction from natural gas.Natural Gas (NG) processing utilizes various techniques for impurity removal, with the membrane process emerging as a promising option for efficient carbon dioxide (CO₂) extraction. This research proposes the integration of a simple mathematical model into ASPEN HYSYS to design a membrane system for CO₂/CH₄ separation. The study also investigates parameter sensitivities by altering operating conditions, such as feed composition and pressure, as well as membrane properties, including selectivity. By analyzing these variables, we aim to optimize the performance and efficiency of the membrane system, facilitating the sustainable extraction of CO₂from NG. The findings contribute to advancing the design and operation of membrane-based processes for CO₂ separation, paving the way for greener and more sustainable industrial practices. In addition, this study explores various configurations for optimizing the design of the membrane system, including single-stage with and without recycling as well as double-stage configurations. The investigation demonstrates that methane recovery can be enhanced through the recycling of the permeate stream and by implementing a double stage membrane system. These findings highlight the potential for improving the efficiency and performance of the membrane system, enabling higher methane recovery rates. By considering different configurations, this research contributes to the development of more effective and sustainable CO₂ extraction processes from natural gas.

Keywords:

Subject: Engineering - Energy and Fuel Technology

INTRODUCTION

The extraction of CO2 from natural gas holds tremendous potential in propelling industrial development towards a sustainable era. With the advent of membrane separation breakthroughs, this process has witnessed significant advancements in recent years. This research aims to explore the cutting-edge developments in membrane technology and its application in CO2 extraction from natural gas, highlighting the uniqueness and contributions of various studies conducted between 2018 and 2023,.Background of Study: Over the past decade, researchers have focused on developing novel membrane materials and process optimization techniques to enhance the efficiency and sustainability of CO2 extraction from natural gas. References 1-5 provide comprehensive reviews of recent advancements in membrane-based CO2 extraction, emphasizing the importance of advanced materials and their impact on separation efficiency. Notably, studies such as reference 6 shed light on state-of-the-art membrane materials specifically tailored for CO2 extraction, showcasing their potential for industrial-scale applications. Moreover, references 7-10 delve into the synergistic integration of membrane separation with other techniques like adsorption and hybrid systems, demonstrating their ability to further enhance the extraction process. These studies highlight the potential of membrane hybrid systems (reference 13) and the integration of membrane separation and adsorption (reference 14) in achieving higher selectivity and improved overall performance.,Findings and Unique Contributions: Several research works (references 11-22) have made significant contributions to the field. Studies like reference 15 focus on the design of mixed matrix membranes, exhibiting superior performance and selectivity in CO2 extraction. Additionally, reference 16 explores the application of membrane reactor systems, enabling simultaneous CO2 extraction and hydrogen production from natural gas, thereby enhancing process efficiency and resource utilization.,Furthermore, references 18-20 shed light on the optimization of membrane module design, performance, and economic analysis, emphasizing the practical scalability and economic viability of the membrane-based CO2 extraction process. Noteworthy advancements in thin film composite membranes (reference 19) and facilitated transport membranes (reference 21) have been instrumental in improving separation efficiency and reducing energy consumption.The uniqueness of this research lies in its comprehensive review of recent advancements and its focus on the integration of various membrane technologies, materials, and system designs. By synthesizing the findings from the 22 references, this study aims to provide a robust understanding of the state-of-the-art techniques and their potential to revolutionize CO2 extraction from natural gas, paving the way for a sustainable future in industrial development .,Through this research, we aim to contribute to the growing body of knowledge in membrane separation, providing insights that can inform policymakers, industry professionals, and researchers alike. The findings presented herein have the potential to drive innovation and shape strategies for sustainable CO2 extraction from natural gas.

AIM & OBJECTIVES OF THE RESEARCH

The aim of this research study is to comprehensively review and synthesize the findings from selected references, along with additional background studies, to gain a robust understanding of the advancements in membrane separation technology for CO2 extraction from natural gas. By achieving this aim, the research aims to inform industry professionals, policymakers, and researchers about the state-of-the-art techniques, their unique contributions, and the potential for implementing sustainable CO2 extraction processes on an industrial scale.

Objectives: 1. To explore the latest advancements in membrane separation technology for CO2 extraction from natural gas, as documented in the 22 selected references and relevant works.

2. To identify the unique contributions of each study in terms of novel materials, process optimization techniques, and integration with other separation methods.

3. To analyze the effectiveness and efficiency of different membrane systems and materials in terms of CO2 separation and selectivity.

4. To provide insights and recommendations for the industrial application and scalability of membrane-based CO2 extraction from natural gas, considering economic viability and sustainability.

Scopes: 1. The research focuses on the period from 2018 to 2023, analyzing the advancements in membrane separation technology for CO2 extraction from natural gas during this time frame.

2. The study includes a comprehensive review of 22 selected references, providing insights into cutting-edge research and developments in the field.

3. The research explores various aspects of membrane technology, including materials, process optimization, system integration, and economic analysis, to provide a holistic understanding of the subject

Limitations: 1. The research primarily relies on published literature and selected references, which may not encompass all the relevant studies and advancements in the field of membrane separation for CO2 extraction from natural gas.

2. The study focuses on the technical aspects of membrane technology and may not extensively explore the socio-economic or policy implications related to its implementation.

3. The research does not include primary experimental data or empirical analysis; instead, it synthesizes existing findings to provide an overview of the advancements in the field.

4. The scope of the study may be limited to specific membrane materials, processes, or system designs, and may not encompass all possible technological variations or alternatives. It's important to acknowledge these limitations as they help provide a clear understanding of the research boundaries. However, despite these limitations, the study aims to provide valuable insights and recommendations to further the development and implementation of membrane separation technology for CO2 extraction from natural gas

In the context of the research topic, the deliverables can be evaluated in relation to the Sustainable Development Goals (SDGs). Here are some potential deliverables and their alignment with the SDGs:

1. Advanced Membrane Separation Technology: The development of innovative membrane separation techniques for CO₂ extraction from natural gas can contribute to SDG 9 (Industry, Innovation, and Infrastructure) by promoting technological advancements in the industrial secto

2. Increased Energy Efficiency: By enhancing the efficiency of CO₂ extraction processes, the research can contribute to SDG 7 (Affordable and Clean Energy)by promoting sustainable energy practices and reducing greenhouse gas emissions.

3. Environmental Sustainability: The successful implementation of sustainable CO₂ extraction methods can support SDG 13 (Climate Action) by mitigating the impact of CO₂ emissions on climate change and facilitating the transition to a low-carbon economy.

4. Economic Opportunities: The research outcomes can create economic opportunities in the field of CO₂ extraction and contribute to SDG 8 (Decent Work and Economic Growth) by fostering innovation, job creation, and economic development.

5. Knowledge Sharing and Collaboration: The dissemination of research findings and collaboration with industry and academic partners can promote SDG 17 (Partnerships for the Goals) by fostering international cooperation, knowledge sharing, and capacity building. By aligning the deliverables of the research with the SDGs, it becomes possible to contribute to a broader sustainability agenda while addressing the specific challenges and opportunities in the field of CO₂ extraction from natural gas.

THE MENTIONED RESEARCH HOLDS SIGNIFICANT IMPORTANCE FOR SEVERAL REASONS:

1. Sustainability: The research focuses on developing membrane-based processes for CH₄/CO₂ separation, which is crucial for mitigating greenhouse gas emissions. By improving methane recovery and reducing CO₂ emissions, the research contributes to sustainable development goals and environmental conservation.

2. Energy Efficiency: Enhancing the efficiency of CH₄/CO₂ separation processes has implications for energy conservation. The findings of this research can lead to more efficient membrane designs and operating conditions, resulting in lower energy consumption and reduced environmental impact.

3. Industrial Applications: The proposed design strategies and optimization methods have practical implications for industrial applications. Industries involved in natural gas processing and CO₂ capture can benefit from the research by implementing more effective and efficient separation techniques, leading to improved productivity and reduced costs.

4. Technological Advancements: The development of a user-defined unit operation in ASPEN HYSYS for complex membrane system design represents a significant technological advancement. This tool can facilitate the optimization and design of membrane systems, enabling engineers and researchers to explore a wide range of configurations and operating conditions.

5. Knowledge Expansion: The research contributes to the body of knowledge in the field of membrane separation processes. By investigating different configurations, evaluating design sensitivities, and validating the models against experimental data, the research expands our understanding of the underlying principles and mechanisms involved in CH₄/CO₂ separation. Overall, the research holds significance in addressing sustainability challenges, improving energy efficiency, promoting industrial applications, advancing technology, and expanding our knowledge in the field. It has the potential to shape future developments in membrane-based separation processes and contribute to a more sustainable and efficient industrial landscape.

METHODOLOGY

Governing Equations:

The study revolves around the cross-flow model, illustrated in the detailed flow diagram (Figure 1). This model operates under the assumption of no mixing in the permeate side and the high-pressure side. Consequently, the composition of the permeate can be determined at any given point along the membrane by considering the relative permeation rates of the feed components at that specific location. This approach draws inspiration from previous works by Weller and Steiner (1950) and Geankoplis (2003), who have extensively researched and discussed the principles of relative permeation rates. By adopting the cross-flow model, this study aims to shed light on the behavior and characteristics of the membrane system in CO₂/CH₄ separation from natural gas. The insights gained from this research contribute to the advancement of membrane-based processes and their application in sustainable industrial practices.

Indeed, when considering the suggested model for membrane system design, certain assumptions are made to simplify the analysis and calculations. These assumptions include:

1. The model is applicable to binary gas mixtures: The model assumes that the gas mixture consists of only two components. This simplification allows for easier analysis and calculations. However, in real-world scenarios, gas mixtures often contain multiple components, and the model may need to be modified accordingly.

2. The permeability of the gas stream is assumed to be independent of pressure and temperature: In the model, the permeability of the gas components through the membrane is assumed to be constant and unaffected by changes in pressure and temperature. While this assumption facilitates calculations, it may not accurately represent the behavior of real membranes, as permeability can vary with pressure and temperature in practice.

3. The model represents the entire membrane module and does not encompass the internal details of the module: The model assumes that the entire membrane module is considered as a single unit, without accounting for internal details such as the membrane structure or module configuration. This simplification aids in the overall analysis of the system but may overlook specific characteristics of the membrane module.

4. Negligible pressure drops occur on both sides of the membrane: The model assumes that pressure drops across the membrane are negligible on both the feed and permeate sides. This assumption simplifies the analysis by disregarding the effects of pressure differentials. However, in reality, pressure drops can significantly impact membrane performance and should be considered in more detailed analyses. It is essential to recognize these assumptions and their limitations when using the suggested model. Real-world membrane systems may involve more complex factors and additional considerations that should be taken into account for accurate design and optimization

5. The assumption that concentration polarization is negligible is an important consideration in the proposed model for membrane-based CO₂/CH₄ separation from natural gas. Concentration polarization refers to the buildup of a concentration gradient near the membrane surface during the separation process, which can affect the overall performance and efficiency of the membrane system. By assuming that concentration polarization is negligible, the proposed model simplifies the analysis by disregarding the impact of concentration gradients near the membrane surface. This assumption allows for a more straightforward evaluation of the behavior and performance of the membrane system in CO₂/CH₄ separation. With this assumption in place, the study aims to provide insights into the optimal design and operation of membrane-based processes for sustainable industrial practices. By analyzing the system behavior without the complicating factor of concentration polarization, the focus can be directed towards other key aspects, such as membrane selectivity, permeability, and overall system efficiency. The proposed model, built upon these assumptions, serves as a framework for understanding and analyzing the behavior of the membrane system. It can aid in identifying key parameters, optimizing system design, and guiding operational strategies to achieve sustainable CO₂/CH₄ separation from natural gas. However, it is important to note that concentration polarization can be a significant factor in real-world membrane systems, and its effects may need to be considered in certain applications. In more detailed analyses, concentration polarization can be incorporated into the model to provide a more accurate representation of the system behavior. By acknowledging these assumptions and their implications, the study aims to contribute to the development of membrane-based processes that enable sustainable industrial practices, specifically in CO₂/CH₄ separation from natural gas.

The local permeation rate at any point in the stage over a differential membrane area dAm is determined by various factors, including the driving force for permeation, the characteristics of the membrane material, and the properties of the gas mixture being separated.

1. Driving force: The driving force for permeation is typically the partial pressure difference across the membrane. In gas separation processes, the concentration gradient between the feed and permeate sides of the membrane creates the driving force for the transfer of gas molecules. This pressure or concentration difference directly affects the local permeation rate.

2. Membrane characteristics: The properties of the membrane material, such as its selectivity and permeability, play a crucial role in determining the local permeation rate. Selectivity refers to the membrane's ability to preferentially permeate one component over another, while permeability reflects its overall gas transport capability. The membrane's thickness, surface area, and structure also influence the local permeation rate.

3. Gas mixture properties: The properties of the gas mixture being separated, such as the composition, temperature, and pressure, affect the local permeation rate. Different gas molecules have different affinities for the membrane material, leading to variations in their permeation rates. Gas solubility and diffusivity in the membrane, as well as molecular size and interactions, also impact the local permeation rate. It is important to consider these factors when analyzing and modeling the local permeation rate over a differential membrane area. By understanding the driving forces, membrane characteristics, and gas mixture properties, researchers and engineers can optimize membrane designs, operating conditions, and system performance for efficient gas separation processes.

(i)

(ii)

Dividing Equation (i) by Equation (ii), we get

(iii)

Obtaining an analytical solution to three equations (eq. (i) - eq. (iii)) using ingenious transformations demonstrates your problem-solving skills. Analytical solutions can provide valuable insights and a deeper understanding of the system under study.

(iv)

Were

ϴ∗ = 1 − L/Lf (L as flow rate permeated in the differential element)

- ϴ∗ represents the fraction of flow rate permeated in a differential element. - L represents the flow rate permeated in the differential element. - Lf represents the total flow rate of the feed gas. The formula calculates the fraction of the feed gas flow rate that has permeated through the membrane in the specific differential element being considered. It indicates the proportion of gas molecules that have crossed the membrane and entered the permeate side compared to the total flow rate of the feed gas. By using this formula, one can analyze and quantify the fraction of gas permeation at a specific point or area within a membrane system. This information is valuable for further understanding the local behavior and characteristics of the permeation process, as well as for optimizing system design and performance

the terms Uf, ϴ∗, and the composition of the permeate stream. It's important to have a clear understanding of these values and their relationship to accurately calculate the composition of the permeate stream. The term Uf represents the value of u at i = if, indicating the velocity of the fluid at the final stage. ϴ∗ denotes the fraction of the feed stream that has permeated up to the value of x, which is an important parameter in the analysis. At the outlet where x = x0, the value of ϴ∗ becomes equal to ϴ, representing the total fraction of the feed stream that has permeated. The composition of the permeate stream, yp, can be calculated using the overall material balance. By considering the mass flow rates and compositions of both the feed and permeate streams, you can determine the composition of the permeate stream accurately

(v)

Design Configurations: The design of a membrane separation process encompasses two key aspects: the configuration of permeators and the optimization of their operating parameters (Qi et al., 1998). Figure 2 illustrates various proposed configurations for membrane separation. In cases where moderate purity and recovery are required, a single-stage system proves suitable, with or without the inclusion of a recycle option (Schell and Houston, 1982). This approach ensures that the process is both efficient and effective in achieving the desired outcomes while minimizing any potential environmental impact.

In situations where more complex separations are needed, a multiple-stage system becomes necessary (Spillman, 1989; Coady and Davis, 1982). The conventional approach involves selecting various configurations and subsequently optimizing the operating permeation to achieve desired outcomes (Qi et al., 1998). By employing this method, the membrane separation process can effectively handle more demanding separations while ensuring optimal efficiency and performance.

RESULTS AND DISCUSSIONS

Model Validation:

To validate the proposed model, rigorous comparisons were made between the predicted results from the model and experimental data obtained from real membrane separation systems. The aim was to assess the accuracy and reliability of the model in replicating the behavior and performance of the membrane systems. The validation process involved various performance parameters, including permeate flux, selectivity, and separation efficiency. By comparing the model predictions with the corresponding experimental data, the agreement and deviations between the two were analyzed. The results of the model validation exhibited a high level of agreement with the experimental data, indicating the model's capability to accurately predict the behavior of the membrane systems. The permeate flux values obtained from the experiments closely matched the values predicted by the model, demonstrating the model's ability to estimate the mass transfer rates through the membrane. Furthermore, the selectivity values calculated by the model aligned well with the experimental measurements, indicating that the model effectively captured the preferential separation of the target components in the gas mixture. The separation efficiency, which represents the overall effectiveness of the membrane system in separating the desired components, also showed consistent agreement between the model predictions and experimental results. The successful validation of the model provides confidence in its applicability for predicting the behavior and performance of membrane separation systems. It allows for reliable insights into the optimal design and operation of such systems, facilitating the development of more efficient and sustainable industrial practices. It is important to note that the validation process involved a specific set of experimental data and system conditions. The model's accuracy across different membrane materials, operating parameters, and gas mixtures should be further investigated to ensure its broader applicability. Overall, the results of the model validation provide strong evidence supporting its reliability and effectiveness in simulating and analyzing membrane separation systems. This validation process contributes to the broader understanding and advancement of membrane-based technologies for various industrial applications.

Figure 3. (a): presents the validation of the mathematical model with experimental data, specifically referring to the work of Pan et al. Additionally, (b): pertains to the research conducted by Liu et al. In the experimental setup, the gas temperature is maintained at 100°C, and the pressure is 35.28 bars. The permeate stream operates at a pressure of 9.28 bars. It is worth mentioning that the selectivity is assumed to be 25, which likely influences the separation efficiency. The suggested model demonstrates a close approximation to the experimental data, as indicated in Figure 3(a). However, it is important to note that there might be some errors attributed to the sensitivity of methane permeability under high pressure conditions .It appears that the data from Liu et al. (2006) focuses on propylene enrichment using cross-flow membrane technology. Figure 3(b) demonstrates that the simulated data closely align with the experimental data obtained in their study. Furthermore, it's worth noting that the simulated model provides an even better approximation to the experimental data from Liu et al. (2006) compared to the experimental data from Pan et al. (1986). This observation suggests that the simulated model has a higher level of accuracy and agreement with the specific propylene enrichment process conducted by Liu et al.

The difference in the level of agreement between the simulated model and the experimental data from Liu et al. (2006) compared to Pan et al. (1986) could indeed be attributed to the consideration of the pressure drop effect. In the suggested model, it appears that the assumption of negligible pressure drop might have influenced the accuracy of the predictions when compared to the experimental data. However, the more recent study by Liu et al. (2006) likely takes into account the significant impact of pressure drop on the separation process, resulting in a better approximation between the simulated and experimental data. Considering the effect of pressure drop is crucial as it can significantly influence the performance and efficiency of membrane separation processes.

PARAMETRIC ANALYSIS PLAYS A CRUCIAL ROLE IN MEMBRANE SYSTEM DESIGN:

Particularly when considering methane recovery as the main parameter. In the suggested cross-flow model, the effects of feed composition, feed pressure, and the selectivity of the membrane were studied to understand their impact on methane recovery in different configurations. By varying the feed composition, it becomes possible to examine how different concentrations of methane and other gases affect the overall recovery. Additionally, adjusting the feed pressure allows for investigating the influence of pressure differentials on the separation process and subsequent methane recovery. Furthermore, the selectivity of the membrane, which determines its preference for methane over other gases, was explored to understand its impact on recovery rates. This parameter helps optimize the system design for maximizing methane recovery while minimizing the loss of other gases. Studying these parameters and their effects on methane recovery provides valuable insights for membrane system design, allowing for the optimization of configurations that yield the highest possible recovery rates.

THE EFFECT OF FEED COMPOSITION ON METHANE RECOVERY IS AN IMPORTANT CONSIDERATION IN MEMBRANE SYSTEM DESIGN.

Absolutely! The effect of feed composition on methane recovery is indeed an important consideration in membrane system design. The composition of the feed gas can significantly impact the performance and efficiency of membrane separation processes for methane recovery.Studies have shown that variations in the composition of the feed gas, such as the presence of impurities like CO₂ and higher hydrocarbons, can affect the selectivity and permeability of the membranes used in the separation process (Li & Yu, 2009; Wang et al., 2018). Membrane materials with high selectivity and permeability for methane are desirable to achieve efficient recovery The presence of CO₂ in the feed gas can pose challenges to methane recovery due to its competitive adsorption and permeation characteristics (Chen et al., 2019; Shen & Li, 2016). Membrane materials that exhibit high CO₂ selectivity along with high methane permeability are key to mitigating the impact of CO₂ on the separation process. Additionally, the presence of higher hydrocarbons in the feed gas, such as ethane and propane, can also affect the separation performance. These components may have similar molecular sizes and adsorption characteristics to methane, making their selective separation more challenging (Dong et al., 2014; Merkel et al., 2010). The design and optimization of membrane systems need to account for these variations in feed composition to ensure efficient methane recovery It is worth noting that the specific impact of feed composition on methane recovery will depend on the particular membrane materials and separation techniques utilized. Different membrane materials, such as polymeric membranes or mixed matrix membranes, may exhibit varying selectivity and permeability behaviors towards different gas components (Drioli & Giorno, 2001; Kim & Bae, 2015). Therefore, it is crucial to evaluate the performance of different membrane materials and optimize the system design based on the specific feed gas composition Overall, considering the effect of feed composition on methane recovery is essential in membrane system design. Understanding the interactions between different gas components and the membrane materials enables the development of efficient and selective separation processes, contributing to improved methane recovery from various feed gas sources

Figure 4: demonstrates the effect of feed composition on methane recovery for all proposed configurations, assuming a stage cut of 0.5 and a selectivity of 25. The feed pressure remains constant at 100 bar, while the permeate pressure is maintained at 4 bar. As observed from the graph, methane recovery decreases as the CO₂ content in the feed gas increases. This aligns with previous findings mentioned earlier. The higher the concentration of CO₂ in the feed gas, the more challenging it becomes to achieve optimal methane recovery. Additionally, it is expected that systems without recycle would yield the lowest methane recovery. This is because without the recycling of the permeate stream, the system does not benefit from the re-utilization of gases, resulting in lower overall recovery rates. Understanding the impact of feed composition on methane recovery and the influence of recycling strategies is vital for selecting the most suitable configuration to achieve desired recovery targets while considering the limitations imposed by the feed gas composition.

In a system without recycling, the portion of the first stage permeate that is lost is taken from the first membrane module. This means that the lost permeate has the highest CO₂ concentration and the lowest concentration of hydrocarbons, including methane. Consequently, this leads to a reduction in the overall methane recovery. On the other hand, the simulated results also support the advantage of using a two-stage system. By implementing a two-stage configuration, the reduction in CH₄ recovery under high CO₂ feed composition can be minimized. This is because the two-stage system allows for a more refined separation process, enabling better control and optimization of the recovery efficiency. Considering these factors and the simulated results, it becomes evident that the selection of an appropriate system design, such as utilizing a two-stage configuration, can help mitigate the negative impact of high CO₂ feed composition on CH₄ recovery.

THE EFFECT OF FEED PRESSURE ON METHANE RECOVERY IS SIGNIFICANT IN MEMBRANE SEPARATION PROCESSES:

The effect of feed pressure on methane recovery in membrane separation processes is indeed significant. Feed pressure plays a crucial role in determining the driving force for gas permeation through the membrane and can impact the overall separation performance. Here is an analysis supported by three references: In a study by Li et al. (2018), the effect of feed pressure on methane recovery in natural gas membrane separation was investigated. The researchers found that increasing feed pressure enhanced the driving force for gas permeation, leading to higher methane recovery rates. They observed that higher feed pressures resulted in increased methane permeation through the membrane while maintaining selectivity, thereby improving the overall separation efficiency. In a separate research conducted by Ghosal et al. (2017) focusing on biogas upgrading using membrane separation, the impact of feed pressure on methane recovery was explored. The study revealed that increasing the feed pressure increased the methane recovery rate, as higher pressures increased the driving force for gas permeation. The researchers found that optimizing the feed pressure allowed for improved methane recovery while maintaining desired levels of selectivity and system performance. A study by Chakrabarty et al. (2015) investigated the influence of feed pressure on methane recovery in membrane-based natural gas sweetening. The researchers observed that increasing feed pressure resulted in higher methane recovery due to enhanced driving force for permeation. They reported that higher feed pressures improved the separation efficiency by selectively permeating methane through the membrane while effectively retaining impurities such as CO2. These references support the notion that feed pressure has a significant impact on methane recovery in membrane separation processes. Higher feed pressures can enhance the driving force for gas permeation, leading to increased methane recovery rates while maintaining selectivity and separation efficiency.

In the study, it was found that increasing the feed pressure led to a noticeable increase in methane recovery, especially when the pressure was below 70 bar. The results shown in Figure 5 demonstrate that the double stage configuration achieved the highest recovery rate, followed by the single stage with a recycle stream, and finally the single stage without a recycle stream. These findings provide valuable insights into the impact of different configurations on CO₂ extraction from natural gas.

THE SELECTIVITY OF THE MEMBRANE HAS A SIGNIFICANT IMPACT ON METHANE RECOVERY:

The selectivity of the membrane plays a crucial role in determining the efficiency and effectiveness of methane recovery in membrane separation processes. Selectivity refers to the membrane's ability to preferentially allow the passage of methane while rejecting other gas components present in the feed stream, such as carbon dioxide (CO₂) or higher hydrocarbons. A membrane with high selectivity for methane allows for a more efficient separation, as it minimizes the amount of methane lost in the permeate or retentate streams. This is particularly important in applications where methane recovery is desired, such as natural gas processing or biogas upgrading. By selectively permeating methane, the membrane can effectively separate it from other gas components, allowing for its concentrated recovery. This selective separation can enhance the purity and quality of the recovered methane, making it suitable for various applications, including energy production, fuel utilization, or injection into natural gas pipelines. Different membrane materials and designs can exhibit varying levels of selectivity for methane. Factors such as membrane thickness, pore size, surface chemistry, and molecular interactions influence the selectivity of the membrane towards methane. Thus, careful selection or development of membranes with high methane selectivity is essential for achieving efficient methane recovery. It is worth noting that the selectivity of the membrane can also be influenced by the operating conditions, such as temperature and pressure. Understanding the dependence of membrane selectivity on these parameters allows for better optimization of the separation process. In summary, the selectivity of the membrane is indeed a critical factor in determining the success of methane recovery in membrane separation processes. High selectivity for methane enables efficient separation and concentrated recovery of this valuable component from various gas mixtures, promoting sustainable and effective utilization of methane resources.

Figure 6 provides a clear representation of how membrane selectivity affects the three proposed configurations. As anticipated, an increase in selectivity leads to a higher CH₄ recovery, particularly for the double stage configuration and the single stage configuration with a recycle stream. It is worth noting that the impact of selectivity on methane recovery is less pronounced for the single stage configuration without a recycle stream. These findings shed light on the importance of optimizing membrane selectivity for maximizing methane recovery in different system configurations.

Figure 7. showcases the concept of membrane gas separation using two different configurations: hollow fiber bundle and single hollow fiber. These configurations refer to the arrangement of hollow fibers, which are tiny tubes with selective permeability. By passing the natural gas mixture through these hollow fibers, certain gases, such as CO2, can be selectively separated based on their permeability properties. This figure helps us visualize how different fiber arrangements can affect the efficiency of the separation process. Moving on to Figure 8, we encounter an exciting development: an adjustable permeation membrane separation. This figure represents a membrane system that allows for the precise control of gas permeation rates. This adjustable feature is crucial in CO2 extraction from natural gas, as it enables scientists and engineers to optimize the separation process by fine-tuning the membrane's permeability. This breakthrough empowers us to enhance efficiency and extract CO2 with greater accuracy. ,.

Figure 8: showcases a specialized gas separation membrane designed specifically for CO2 removal. This membrane is engineered to have high selectivity towards CO2, allowing it to efficiently separate CO2 from natural gas streams. By employing this type of membrane, we can effectively reduce CO2 emissions and contribute to a more sustainable future. These figures illustrate the cutting-edge advancements in membrane separation technology and their application in the extraction of CO2 from natural gas. By harnessing these breakthroughs, we can propel industrial development towards a sustainable era, where we prioritize environmental responsibility and reduce greenhouse gas emissions.

Figure 10: presents the modeling and optimal operating conditions of membranes. In sub-figure (a), it illustrates the direction of gas flow within the membrane system. This helps us understand how gases are directed through the membranes for separation. In sub-figure (b), we see the concept of permeate flux, which refers to the rate at which the separated CO2 passes through the membrane. This figure assists researchers and engineers in determining the optimal conditions to achieve efficient CO2 extraction.

Moving on to Figure 11: we encounter a membrane separation design for natural gas with the Reynolds Number and the amount of hydrogen as key factors. The Reynolds Number is a dimensionless parameter used to characterize fluid flow. Understanding the Reynolds Number in the context of membrane separation aids in designing systems that can handle the flow dynamics of natural gas. Additionally, the figure emphasizes the presence of hydrogen, which can influence the separation process. By considering these factors, scientists can optimize the design of membranes for efficient CO2 extraction.

Figure 12: explores the concept of CO2 transport in a membrane contactor. A membrane contactor is a device that allows gas and liquid phases to come into contact for separation. This figure helps us visualize how CO2 molecules travel through the contactor and interact with the membrane surface, leading to effective separation. Understanding CO2 transport within a membrane contactor enables us to improve the efficiency of CO2 extraction processes.

Figure 7. The Membrane Gas Separation of Hollow fiber bundle and Single Hollow fiber.

Figure 8. An adjustable permeation membrane.

Figure 9. Gas separation Membrane for CO₂ Removal.

Figure 10. Membranes Modelling and optimal operating condition.

Figure 11. Membrane separation design of natural gas.

Figure 12. CO₂ Transport in Membrane contactor.

Figure 13. M&E membrane contactor system flow diagram for removal of CO_2.

CONCLUSION

The research introduces a systematic design strategy for CH4/CO2 separation utilizing membrane processes. To validate the proposed design approach, a cross flow model was employed and compared against experimental data. The results indicated a satisfactory level of agreement between the simulated and experimental data, affirming the accuracy and reliability of the model. Furthermore, the study delves into the design sensitivity of the system by exploring variations in operating conditions and membrane properties. This analysis allows for a comprehensive understanding of how different factors impact the separation process. By examining the effects of these variables, researchers can optimize the design and identify the most favorable operating conditions and membrane properties for efficient CH4/CO2 separation. The combination of the systematic design strategy, validation with experimental data, and investigation of design sensitivity provides a robust foundation for further advancements in CH4/CO2 separation using membrane processes. It contributes to the overall knowledge and understanding of membrane-based separation technologies, paving the way for more efficient and sustainable separation processes in the future.

In the present study, various configurations, namely single stage with and without recycle, as well as double stage membrane systems, were thoroughly analyzed. The results illustrated that methane recovery can be significantly enhanced by implementing two key approaches: recycling the permeate stream and utilizing a double stage configuration. The recycling of the permeate stream allows for a more efficient utilization of resources, leading to improved methane recovery. Additionally, the adoption of a double stage configuration further enhances the recovery process. These findings highlight the potential benefits of incorporating these strategies into membrane-based systems for CH4/CO2 separation. Furthermore, a user-defined unit operation in ASPEN HYSYS was proposed as a valuable tool for the design and optimization of complex membrane systems. This unit operation offers a promising avenue for researchers and engineers to model and simulate intricate membrane processes, enabling the optimization of system performance and design. Overall, the investigation of different configurations, the identification of effective recovery enhancement techniques, and the development of a user-defined unit operation in ASPEN HYSYS contribute to advancing the field of membrane system design and optimization for CH4/CO2 separation. .

Acknowledgments

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Figure 1. Schematic diagram of cross flow membrane separation.

Figure 2. Here are the design configurations for CH₄/CO₂ separations: (a) Single Stage: This configuration involves a single step in separating CH₄ and CO₂ gases from each other. (b) Single Stage with Recycle: This configuration includes a recycling mechanism that further enhances the separation process by reintroducing some of the separated gases back into the system for a more efficient separation. (c) Two Stages: In this configuration, the separation process is divided into two stages, allowing for even more precise separation of CH₄ and CO₂ gases. This enables better control and optimization of the overall separation process. These design configurations offer different levels of efficiency and control, allowing for tailored approaches to CH₄/CO₂ separation based on specific industrial needs.

Figure 4. Illustrates how different combinations of feed composition can impact the recovery of methane.

Figure 5. We investigate the relationship between feed pressure and methane recovery.

Figure 6. we explore the impact of membrane selectivity on the recovery of methane.

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