Optimizing carbon capture efficiency with direct capturing and amine: Insights from exegetic analysis

With climate change concerns on the rise, finding efficient and sustainable ways to separate carbon dioxide from industrial gas mixtures has become increasingly important. Membrane‐based gas separation technologies offer a promising solution due to their low energy consumption, low emissions, and ease of operation. In this study, we dug deep into theoretical energy consumption and practical optimization strategies for CO2 separation using such technologies. Our results showed that CO2 separation can be achieved with relatively low specific energy consumption, ranging from 0.09 to 0.27 MJe/kg CO2, depending on feed CO2 concentration. By conducting process simulations, we determined the optimal feed gas pressure and membrane surface area required to achieve a CO2 absorption ratio of 90% (mol). We also analyzed the effects of CO2 permeation and selectivity on energy consumption and membrane area, revealing that increasing both can significantly reduce energy consumption, albeit with more membrane surface area required. Using seepage flow circulation was found to be a particularly effective way to improve feed CO2 concentration and reduce energy consumption. To optimize and improve the capturing process, we conducted exergy analysis in each of the five stages of optimization, reporting Cooling Utilities (MW), Heating Utilities (MW), and Total Utilities (MW) for each step. Our results showed that in the optimal mode, Total Utilities (MW) were reported as 228.1, highlighting the potential of membrane‐based CO2 separation for carbon capture and storage applications. This study provides valuable insights and practical strategies for achieving efficient and sustainable CO2 separation.

significant attention as a means to reduce atmospheric carbon dioxide levels.Solvent-based carbon dioxide collection techniques have been extensively researched and developed to achieve this goal. 3However, recent advancements in gas separation membranes have shown promising results in achieving high CO 2 permeability, making membrane separation a potential new technology for direct air capture (DAC).The use of chemical process simulation, which has a long-standing history in industrial chemical process development and performance evaluation, has played a critical role in advancing research in this field. 4][7][8] Table 1 summarizes the key challenges associated with optimizing carbon capture efficiency, focusing on both DAC and amine-based postcombustion carbon capture using monoethanolamine (MEA) and methyldiethanolamine (MDEA).These challenges encompass various aspects, from energy requirements and costs to environmental risks and limitations in efficiency and capacity.Notably, DAC, a technology with significant potential for climate change mitigation, confronts issues, such as high energy demands and substantial costs.Environmental concerns arise due to the use of toxic solvents, underscoring the importance of ensuring safety and environmental protections in its implementation.On the other hand, amine-based postcombustion carbon capture, especially using MEA, faces challenges related to energy consumption and solvent characteristics.As carbon capture technologies are poised to play a crucial role in reducing atmospheric carbon dioxide levels, understanding and addressing these limitations are vital steps toward their effective deployment and sustainability.
As the threat of climate change continues to loom large, it is essential to explore all viable solutions, including the optimization of membrane-based gas separation technologies, to mitigate carbon emissions and secure a sustainable future. 16,17Aspen Plus is a widely utilized process simulation program that is employed for the purpose of designing, analyzing, and optimizing chemical processes. 18,19This software enables engineers and academics to create models and conduct T A B L E 1 limitations of optimizing carbon capture efficiency with direct capturing and amine monoethanolamine (MEA) and methyldiethanolamine: Insights from exegetic analysis.

Challenge Description Reference
High energy requirements for amine-based postcombustion capture Absorption and regeneration processes in amine-based postcombustion capture are energy-intensive, resulting in a high energy penalty.[6, 9]   Energy penalty in natural gas process plants Solvent regeneration and low CO 2 levels in flue gas contribute to a significant energy penalty in natural gas process plants.[8, 9]   Energy-intensive MEA solution regeneration Postcombustion capture with MEA solutions is energy-intensive due to MEA solution regeneration.Energy savings can be achieved through optimization.[10]   Safety risks in CO 2 -enhanced oil recovery Risks related to CO 2 -enhanced oil recovery include hazards from crude oil, liquid ammonia, and supercritical CO 2 , posing safety concerns during the process.[9, 11]   High costs of carbon capture and storage (CCS) technology The capture step in CCS technology is costly, and impurity separation further increases project costs.[12]   Limited deployment and technical challenges CCS technology is still in its demonstration phase and faces technical, economic, and commercial challenges, limiting its deployment.[13]   Health and safety risks Health and safety risks in CCS technology include human safety, water quality concerns, and questions about the permanence of carbon dioxide storage.[14]   Stakeholder management complexity Managing various stakeholders in CCS projects can be complex and opposition from certain groups can lead to project closures. [15]

Adsorbent development and diffusion limitations
Efficient and stable adsorbents for CO 2 capture and understanding their transport diffusion limitations are crucial for CCS technology development.Experimental data is limited.[12]   Exergy destruction Traditional combined cycle gas turbine systems suffer significant exergy destruction, with potential for efficiency improvements.[7]  simulations of diverse chemical processes, encompassing carbon capture, biomass gasification, pyrolysis, and other related processes.The program facilitates the execution of numerous tasks, including sensitivity analysis, optimization, and cost calculation.These functionalities offer significant contributions to the field of process optimization, energy efficiency, and exergy analysis across diverse applications.The integration of Aspen Plus with additional software tools, such as Matlab and Excel, serves to augment its functionalities and facilitate the modeling of unit processes that are not encompassed by the conventional Aspen Plus software packages. 20

| LITERATURE REVIEW
This study focuses on the optimization of the biogas upgrading process utilizing the chemical absorption method for CO 2 removal.The solvent used in this process is 2-amino-2-methyl-1-propanol (AMP).The simulations were conducted using Aspen Plus software.
The objective was to devise enhanced process designs for the effective collection and sequestration of carbon dioxide (CO 2 ). 21Enhancing Carbon Dioxide Removal Efficiency from Coal-Fired Power Plants using MEA.The objective of this study was to reduce the energy consumption associated with the desorption process used for CO 2 absorption in coal-fired power plants.To do this, a solution containing 30 weight percent MEA was utilized as the solvent.The CO 2 collection mechanism was optimized by researchers through the utilization of Aspen Plus simulations. 22The enhancement of carbon capture efficiency through direct capturing and aminebased systems may be accomplished through a range of methodologies.A research was conducted to examine the process of CO 2 capture utilizing an amine resin called Lewatit R VP OC 1065.The investigation revealed that the structure of the resin aided the adsorption of CO 2 and H 2 O, resulting in the synthesis of carbamic acid through direct reactions catalyzed by amine and amine-H 2 O. 23 A separate investigation was conducted to examine the impact of amine composition, amine structure, pressure, and temperature on the effectiveness of CO 2 collection and the corrosion of carbon steels while employing amine-based solvents. 24A study was done to compare the efficiency, cost, and recirculation rate of amine solvents, namely MEA, diethanolamine (DEA), and MDEA, in removing CO 2 under various operating circumstances.The research conducted demonstrated that MEA showed considerable potential as a solvent in comparison to DEA and MDEA, since it displayed superior efficacy in removing CO 2 and was also determined to be the most cost-effective option.
The present work aimed to examine the vapor-phase functionalization of porous carbon fibers with amine functionalities for the purpose of CO 2 collection. 12The utilization of a combination of Al 2 O 3 and amine functionalization yielded rapid CO 2 sorption with enhanced capture efficacy.Conversely, direct functionalization caused a significant decrease in the surface area of the porous support and restricted gas exchange.
Mirza et al. 25 conducted a study to explore the feasibility of integrating vacuum membrane distillation (VMD) with DAC for sustainable combined water-CO 2 recovery.They examined four modules and found that the commercially available LiquiCel module and custommade hollow fiber module were the most durable.The LiquiCel and customized salinity modules exhibited a dissolved oxygen removal of 96.47%, 50.98%, 99.95%, and 71.58%, under the same operating conditions.
Wang et al. 26 developed and optimized a new microalgae-attached membrane photobioreactor (AM-PBR) based on a modified polyvinylidene difluoride (PVDF)/polyvinylpyrrolidone (PVP) composite membrane for direct carbon uptake from the air by microalgae.They found that the carbon deposition rate of the modified membrane was 18.61% higher than that of the original PVDF-based AM-PBR, and the best ratio of PVDF and PVP was 2:1 with a solution of 20% by weight.
Jiang et al. 27 explored electricity-to-gas conversion, which allows excess electricity to be converted to methane when CO 2 is present.Their research showed that a combination of hydrogenotrophic methanogenesis and hemostatogenesis-stoclastic pathway creates a microbial consortium of mesophilic culture.Meanwhile, Dai et al. 28 found that pressurized oxy-combustion is one of the most promising and efficient CO 2 -capturing technologies for coal-fired power plants.However, they highlighted the high partial pressure of sulfur oxides (SO x ) in flue gas pressure and recirculation, leading to corrosion and environmental hazards.Thus, they suggested designing dry desulfurization systems with high efficiency and low SO x emission.
Kosaka et al. 29 discussed carbon capture and utilization technologies, which require energy-intensive processes of CO 2 capture and separation before CO 2 catalytic conversion.In contrast, carbon capture and recycling (CCR) technologies using dual-functional materials directly convert low-concentration CO 2 in the flue gas or atmosphere to CH 4 or CO.They demonstrated a circulating fluidized bed approach to enable continuous CCR operation, resulting in high carbon adsorption efficiency (88%) and high H 2 conversion (85%) to produce mainly CH 4 (99% selectivity).Similarly, Zhang et al. 30 found that the direct biomass-fueled fluidized bed boiler power plant with carbon sequestration can MAJNOON ET AL.
| 4757 strongly support the goal of carbon neutrality.They developed multistage models of biomass combustion, steam generation, and turbine-heater-steam feedwater systems to illustrate the dynamic.In the pursuit of decarbonized hydrogen production, Nalbant Atak et al. 31 proposed a membrane reactor model that integrates CO 2 absorption and various plant components, such as compressors, boilers, burners, pumps, blowers, and mixers.Through theoretical analysis, they examined the potential of this system to produce high-grade hydrogen with complete CO 2 absorption to prevent harmful emissions.At simulation conditions of 773 K, 9 bar, and S/C = 1.3, the integrated membrane reactorbased system demonstrated an impressive thermal efficiency (based on lower heating value), methane conversion, and CO 2 efficiency of 51%, 67.22%, and 66%, respectively.Furthermore, the distribution of exergy degradation was reported as 49% for the burner, 36% for the boiler, 14% for the membrane reactor, and 1%.
Meanwhile, Sun et al. 32 discussed the challenges faced by natural gas (NG) plants that emit low concentrations (4%-5%) of CO 2 , presenting technical and economic hurdles for existing amine adsorption technology.However, high-temperature multiphase membranes operating on molten carbonate have emerged as a promising solution for CO 2 capture, separation, and conversion.With their great potential, these membranes could prove instrumental in addressing the current challenges faced by NG plants.
We have examined the diverse effects of neutrophil extracellular traps (NETs) in various contexts, shedding light on their significance in environmental pollution and health.The studies highlighted in Table 2 illustrate how NETs can have detrimental effects on wound healing when exposed to environmental pollutants, such as microplastics and di(2-ethyl)hexyl phthalate.These findings emphasize the importance of understanding the intricate interactions between NETs and external factors.Additionally, in the context of rheumatoid arthritis, the control of NET levels through a combination of diseasemodifying antirheumatic drugs and acupuncture therapy has shown promise in managing clinical symptoms, underlining the potential relevance of NETs in autoimmune diseases.Furthermore, in the realm of carbon capture efficiency, we explored two key approaches: amine-based absorbents and Direct Air Carbon Capture and Storage (DACCS).The study comparing different amine solvents reveals the promise of MEA as a solvent for CO 2 removal, while DACCS technologies demonstrate their potential for large-scale GHG removal, particularly in regions with low-carbon energy supplies and waste heat utilization.This table offers valuable insights into the multifaceted roles of NETs and the promising avenues for enhancing carbon capture efficiency.NETs, which comprise DNA, histones, and antimicrobial proteins, are emitted by neutrophils as a response to infections or inflammation.The intricate process of NET formation involves the activation of neutrophils through diverse stimuli.This activation leads to the decondensation of chromatin, citrullination of histones, the release of DNA, and the construction of web-like NET structures, primarily designed to ensnare and eradicate pathogens.Notably, while NETs play an indispensable role in innate immunity, they may also contribute to tissue damage and inflammation in conditions, such as sepsis and autoimmune disorders.[ 24, 37]   Abbreviations: DAS, disease activity score; DEA, diethanolamine; dsDNA, double-stranded DNA; GHG, greenhouse gas; MDEA, methyldiethanolamine; MEA, monoethanolamine; NET, neutrophil extracellular trap; NF-κB, Nuclear factor-kappa B; Wnt, wingless-type MMTV integration site family.
A comprehensive comprehension of the nuanced mechanisms governing NET formation assumes paramount importance in the development of therapeutic strategies aimed at modulating NETs in the context of these pathological conditions. 33,34ater demand is a significant challenge for both androgen receptor (AR) and bioenergy with carbon capture and storage (BECCS), exacerbating the already limited global water resources.According to Didas et al., 38 the water demand for AR and BECCS is estimated to be 315 and 220 m 3 /(year ton) of CO 2 , respectively.However, these values are overly optimistic, as they do not account for additional factors such as irrigation and the absence of explicit water conservation policies, which could potentially increase water consumption.On the other hand, electrochemical water splitting has a relatively small water requirement, and DAC's water requirement varies depending on the process used, but it still demands less water than AR or BECCS.
Several types of amines, such as polyethyleneamines, tetraethylenepentamine, or diethylenetriamine, have been developed and employed in DAC.To enhance their performance, amines have been impregnated with various supporting materials, typically silica or alumina.Nonetheless, alternatives such as activated carbon, polymer networks, or ion exchange resins have been used to support the oxide. 39Membrane separation is an increasingly important technology for capturing CO 2 , offering a more efficient, streamlined process with a smaller footprint compared to conventional methods.Despite its potential, large-scale membrane separation is still in its early stages, with only a few pilot plants operating at concentrated CO 2 emission points.However, improving gas permeation in membranes is key to reducing adsorption costs, as increasing selectivity alone is not sufficient.Unfortunately, due to the low partial pressure of CO 2 in the atmosphere, membrane-based DAC has never been considered a viable option. 40,41nnovative approaches, such as VMD, offer the potential for membrane technology to be integrated with DAC processes.Sanz-Pérez et al. 42 conducted experiments using four different VMD modules to test their ability to capture CO 2 from air at different feed temperatures, flow rates, CO 2 loadings, and vacuum pressures.Interestingly, their findings showed that some basic species were able to cross the membranes, with pH values of 10.87 and 10.37 for the custom and LiquiCel modules, respectively.These results demonstrate the potential of VMD as a sustainable water-CO 2 hybrid approach in DAC.
Sanz-Pérez et al. 42 explored a novel approach for hydrogen production that integrates carbon absorption via chemical absorption into thermal and combined power plants.Their research investigated various critical process parameters in a parametric study.The ratio between MDEA and PZ was identified as a key design parameter, affecting carbon adsorption efficiency and process energy demand.Fujikawa et al. 5 and Mirza et al. 43 found discrepancies in the liquid and gas temperature profiles between the two models due to different energy balance methods.However, the effect on mass transfer was negligible as the composition and flow rate of the outflow streams were almost identical.Rezaie and Rosen 44 calculated energy consumption, solvent consumption, capital, and operating costs for nine different configurations using the conductor-like Screening model for real solvents-based/Aspen method and the Aspen Economic Analyzer tool.They found that the most promising results were obtained during ionic liquid regeneration at 1 bar and at high absorption and regeneration temperatures, due to higher operating and equipment costs associated with vacuum and higher service cost related to heat transfer when the gap between both temperatures increases.
In the economic analysis of carbon absorption, Ishida et al. 45 compared four designs in terms of energy consumption, economy, methanol production rate, and carbon emission while maintaining gasifier performance conditions, sulfur content in synthesis gas, and stoichiometric number in the methanol synthesis reactor.The study also revealed that the process of coal to methanol using external hydrogen from an electrolysis plant to achieve higher production rates and low CO 2 emissions is currently not cost-effective due to the high cost of H 2 .
Zeman and Lackner 46 reviewed the current status and potential impact of a new approach for material screening and highlighted the challenges that limit its application.They thoroughly discussed the issues associated with data availability, model compatibility, and data reproducibility, and suggested new directions for the future of this field. 44,45he Kraft process has stood the test of time as an effective method for CO 2 capture from the air using caustic solutions.First used in the paper industry in 1884 to extract cellulose from wood, this process relies on the same principles of using and recycling sodium hydroxide solution for CO 2 absorption.Sodium hydroxide is a powerful binder for CO 2 and is just as effective as calcium hydroxide, but with an added advantage of the highly soluble carbonate formed in water.By reacting sodium carbonate with calcium hydroxide, calcium carbonate is precipitated and sodium hydroxide is regenerated in a process called castification. 46,47owever, the use of NaOH solution is limited to 1 mol/L due to the undesirable precipitation that occurs with higher concentrations of NaOH and calcium. 26alcium hydroxide, on the other hand, has been found to be highly efficient in exchanging carbonate ions from sodium to calcium, with a theoretical efficiency of 96%.Though experimental values have not yet reached efficiencies close to the theoretical limit, the process is still promising.The precipitated calcium carbonate is then separated and subjected to the aforementioned calcination process in a furnace to form lime (CaO) and carbon dioxide, which can be transported and compressed.To complete the cycle, the calcium hydroxide is regenerated by hydration in a slaker and reused.Figure 1 provides a schematic of this process. 48he results showed that the use of a new amine formulation, MEA-AMP blend, can significantly improve the energy efficiency of the carbon capture process.The blend exhibited a higher CO 2 loading capacity and lower regeneration energy requirements compared to traditional MEA.The exergy analysis also identified the most efficient operating conditions for the absorption and regeneration processes, resulting in a decrease in energy losses and an increase in the overall system efficiency.In addition to technological improvements, there has also been a growing interest in the integration of renewable energy sources into carbon capture systems.For instance, the use of solar energy for the regeneration of solvents has been investigated as a means of reducing the overall energy consumption of the carbon capture process.The integration of renewable energy sources with carbon capture systems has the potential to create a sustainable and cost-effective solution for reducing GHG emissions.Moreover, there is a need for the development of new materials and technologies that can capture CO 2 directly from the atmosphere.These technologies, known as DAC, have the potential to remove CO 2 emissions from the air on a large scale.Several DAC technologies are currently being developed and tested, including solid sorbents, liquid solvents, and membranes.However, these technologies are still in the early stages of development, and further research is needed to improve their efficiency and cost-effectiveness.In conclusion, the development of innovative technologies and the integration of renewable energy sources are crucial for improving the energy efficiency and cost-effectiveness of carbon capture systems.Exergy analysis and system simulation can play a key role in identifying and optimizing these technologies.Furthermore, the development of DAC technologies has the potential to revolutionize carbon capture and provide a sustainable solution for mitigating GHG emissions.

| THEORY
Exergy is a crucial concept in the study of thermodynamics, as it provides a measure of the usefulness of energy within a system. 50Unlike energy, which can exist in various forms, exergy represents the maximum work that can be extracted from a system or substance.This is because exergy takes into account the quality of the energy, as well as the system's thermodynamic state. 51he mathematical expression for exergy considers the difference between the energy of a system and its energy in a reference state, which is typically taken to be the F I G U R E 1 Design a process for direct air capture based on the Kraft process, which is often used in the pulp and paper industry.Figure adapted from the American Physical Society report on the direct absorption of CO 2 from air by chemicals. 49nvironment at a constant temperature and pressure.This difference, known as the availability or exergy potential, reflects the maximum useful work that can be obtained from the system. 51By analyzing the exergy of a system, engineers and scientists can identify areas of inefficiency and explore ways to improve energy utilization and overall system performance.Exergy is a measure of the quality or potential of energy to do work and is defined as the maximum work that can be obtained from a system or a substance.Mathematically, exergy can be expressed as follows 52 : • Exergy (E): Exergy represents the maximum work that can be extracted from a system or substance.It is a measure of the potential of energy to perform useful work.Exergy takes into account both the quality of the energy and the thermodynamic state of the system.• H: This represents the enthalpy of the system, denoted as H. Enthalpy is a thermodynamic property that combines the internal energy (U) of the system and the product of its pressure (P) and volume (V).It is a measure of the total energy content of the system.• H 0 : H 0 is the enthalpy of the system in a reference state.
The reference state is typically chosen as the environment at constant temperature (T 0 ) and pressure (P 0 ).H 0 represents the enthalpy of the system when it is in a state of equilibrium with this reference environment.• T 0 : T 0 is the temperature of the reference state, usually constant and equal to the environmental temperature.• S: S represents the entropy of the system, denoted as S.
Entropy is a measure of the system's disorder or randomness.It quantifies the degree of thermal energy dispersion in the system.• S 0 : S 0 is the entropy of the system in the reference state.It represents the entropy of the system when it is in equilibrium with the reference environment.
The mathematical expression for exergy (E) in Equation ( 1) calculates the difference between the enthalpy (H) of the system and the enthalpy in the reference state (H 0 ), adjusted by the product of the temperature difference (T − T 0 ) and the difference in entropy (S − S 0 ).This difference, known as the availability or exergy potential, represents the maximum useful work that can be obtained from the system.In the field of thermodynamics, the concept of exergy plays a crucial role in evaluating the maximum work that can be obtained from a system or substance.Exergy is mathematically expressed as the difference between the real enthalpy and the enthalpy of the reference state, multiplied by the ratio of the real entropy and the entropy of the reference state. 53This measure reflects the potential of energy to perform useful work, and is important for identifying the most efficient operating conditions and equipment for various thermodynamic processes.In thermodynamics, systems are broadly classified as closed (nonflow) or open (flow) systems, also known as control mass and control volume systems, respectively.In closed systems, only heat can be transferred across the system boundaries, whereas open systems allow for both heat and work transfer.The conservation equations for mass and energy and the nonconservative equations for entropy and exergy can be mathematically expressed for a control volume system undergoing a nonsteady flow process between two internal times t 1 and t 2 .These equations form the basis for analyzing the behavior of various thermodynamic processes and designing efficient systems. 54,55 Here, i and m represent the mass flow into and out of the system boundaries.For the mass flow m in the control volume of the time interval t 1 to t 2 : Here, ρ is the density of the material flowing along dA in time intervals t 1 and t 2 .V n is the normal velocity vector at the surface dA of material m.For a one-dimensional flow during which the velocity and mass on the control surface do not change: Flow exergy or open system is the sum of nonflow exergy and work exergy of current flow across system boundaries at reference pressure P 0 : So that  Exergy analysis associated with heat transfer at a location with temperature T. For a control mass, in a dead state with its initial state, as it heats or cools it causes heat transfer resulting in exergy transfer.Therefore, the heat transfer is based on the mass mQ.For the control volume, the exergy related to the thermal energy Q at temperature T can be expressed as follows for the initial states i and final states 56 : Exergy, like negentropy, has the ability to do maximum work, and as a result, maximum efficiency is possible only when all exergy is maintained.Gaggioli calls exergy efficiency real or real efficiency because it takes into account the nonideality of the process.Ibrahim and Rosen stated the general forms of energy efficiency and exergy for a steady state process as follows 31,57 : ) Two other forms of exergy efficiency for devices that work continuously can be as follows 58 : TaskEfficiency E E = .
In general, the exergy efficiency shows a clear picture of the energy content of the system based on its exergy content and isolates the inefficiencies associated with irreversibility.In addition, exergy efficiency measures the potential required for improvement.

| System introduction
The utilization of Aspen Plus simulations has been of great significance in the field of carbon capture research, including several applications, particularly in the realms of energy optimization and exergy analysis.The following are notable examples of Aspen Plus simulations employed in the field of carbon capture research.
The focus of this study was to enhance the economic effectiveness of a conventional CO 2 collecting mechanism deployed in Aspen HYSYS.Researchers conducted a sensitivity analysis utilizing data obtained from Fortum's waste incineration facility located in Norway.The objective of this investigation was to enhance key parameters, such as the height of the absorber packing, the effectiveness of CO 2 removal, and the lowest approach temperature for the lean/rich amine heat exchanger. 59The present study examines the viability of a carbon capture methodology that entails the absorption of carbon dioxide (CO 2 ) in water, resulting in its conversion into bicarbonate ions (HCO 3 ─).The converted carbon dioxide has the potential to be sequestered in oceanic reservoirs or in solid form.The utilization of Aspen Plus simulations was important in assessing the influence of enzyme catalyst carbonic anhydrase and pH modulation on the rate of carbon capture. 19The experimental simulation of the absorption and desorption columns, heat exchange, and recycling of water and amine has been accurately represented in the flow sheet illustrated in Figure 2. Operating conditions have been selected to reflect real-life scenarios, and where necessary, reasonable estimates have been employed for any unreported data required for the simulation.Aspen HYSYS, a chemical engineering software program, has been utilized for the modeling and simulation of the chemical processes in this study, with a total of Aspen HYSYS 11 used.This software is extensively used in numerous industries, including petrochemicals, refining, pharmaceuticals, and particularly in the oil and gas sector, for the design and optimization of process plants.To maintain accuracy, the carbon dioxide input flow rate to the system must not exceed 5%.Table 3 provides the pertinent information regarding the input flow to the system.Design variables for simulation work in a chemical or power plant can vary depending on the specific process or system being modeled.However, some common variables that are often considered include: 1. Flow rates: These are crucial in any plant simulation.
They represent the amount of material or energy flowing through a particular section of the plant.For instance, the mass flow rate of a liquid solvent in an air contactor or the NG flow rate feeding a combustor can be important variables in a chemical plant simulation.2. Heat duties: These represent the amount of heat that needs to be added or removed in a process.For example, in a heat exchanger, the heat duty can be a critical variable.It can be initially set with a guess value and then overwritten with the actual heat duty delivered by another component of the plant.3. Pressure drops: These are changes in pressure across a component or section of the plant.In some simulations, components like heat exchangers might be modeled with the assumption of "ideal" conditions, characterized by zero pressure drop.4. Performance parameters: These are specific to the component or process being modeled.For example, in an absorber block, there could be a high number of performance parameters that need to be considered.5. Chemical composition: The molar or mass composition of streams in the plant can be important variables.For instance, the molar composition of a liquid solution used to capture CO 2 in an air contactor can be a critical variable.6. Temperature: This is a crucial variable in many processes, especially those involving heat exchange.For instance, the outlet temperature of water in a heat exchanger can be a key variable.7. Control variables: These are variables that the system manipulates to achieve the desired output.For example, in a control system design for a propulsion plant, the choice of a suitable pitch/r.p.m. combination law, engine governor calibration, and the scantling of the shaft line can be important control variables.
These variables are typically defined as either import or export variables in the simulation.Import variables Initial simulation of the direct absorption system of the crane.
T A B L E 3 Input flow information to the system.

Stream name Air-in Vapor phase
Vapor/phase fraction are read from the simulation, while export variables are written to the simulation.It's important to note that the specific design variables needed can vary greatly depending on the specific plant and process being simulated.Therefore, a thorough understanding of the plant's operation and the simulation software being used is crucial.In the simulated system illustrated in Figure 2, two separator towers were included to model the absorption and desorption processes.The first tower, known as the Absorber, takes in two streams-one containing the input air with a percentage specified in Table 3, and the other containing the MEA solvent.The inlet solvent flow is composed of three parts that are connected to a mixer.The first section is the newly added solvent, followed by the water needed by the system, and finally the recovered solvent from the second tower. 60o accurately model the system, reasonable estimates were made for any data that was not reported.The input flow to the system, as specified in Table 4, was set to contain less than 5% carbon dioxide.
To accurately model the chemical processes involved in our system, we utilized the CHEMISTRY model with CHEMISTRY ID = MEA to simulate the electrolyte solution.Furthermore, two REACTION models, Absorber and Stripper, were created to represent the reactions occurring in the absorber and stripper towers, respectively.The Absorber and Stripper models were designed to operate in the temperature range of 303-353 and 353-393 K, respectively 61 (Table 5).
It is important to note that in the Absorber/ Stripper models, all reactions other than CO 2 with OH─ and CO 2 with MEAamine were assumed to be in chemical equilibrium.This approach helps to simplify the simulation process while still allowing us to accurately model the system's behavior.By incorporating these models into our simulation, we can effectively analyze the system's performance under various operating conditions and identify areas where improvements can be made.

| Model introduction
The oil and gas processing and refining sectors rely on equations of state such as the Peng-Robinson equation of state and the Soave-Redlich-Kwong equation of state.However, in the hydramine process, nonideal solutions like acid gases, hydrocarbon molecules, and alcohols create a nonideal chemical system that operates under high pressure.To model this system effectively, a chemical acid-solvent gas equation of state was developed based on the equation of state of public relations and the nonrandom dual solution activity coefficient model of the electrolyte.This equation considers the chemical properties of the amine solution and can accurately simulate CO 2 absorption and removal in the hydramine process. 62he hydramine process involves a reversible chemical reaction between hydramine solution and acid gas.By adjusting the temperature and pressure of the system, the hydramine-rich solution can be regenerated into the hydramine-lean solution to achieve a cyclic absorption and regeneration process.The choice of a suitable hydramine solution is critical to enhance decarburization efficiency.However, the concentration limit of most primary and secondary amine solutions is 15% and 30%, respectively, due to their volatility and corrosion effects, making selective recovery challenging.It is important to note that increasing the concentration of the amine solution can reduce equipment costs, but should not exceed the recommended limit to prevent corrosion.MDEA is a preferred solvent due to its low corrosion, low regeneration energy consumption, low solvent loss, and thermal and chemical stability. 63,64To accurately simulate the entire hydramine process, it is crucial to determine the absorption and regeneration tower parameters, such as the number of trays, working pressure, and tower top temperature, which are listed in Table 6.Keeping these parameters in accordance with the hydramine process under different designs is vital to facilitate design comparison and selection.
To ensure an accurate simulation of the hydramine process, the design parameters of the absorption tower and regeneration tower are crucial.The number of trays in the absorption tower is mainly determined by the CO 2 feed gas, and typically ranges from 14 to 20 trays.To optimize the absorption effect, we have set the number of trays in the hydramine absorption tower to 20.Similarly, the number of trays in the recovery tower is determined based on conventional design ranges, and the pressure, temperature, and other parameters of both towers are adjusted accordingly, as outlined in Table 3.It is important to note that during the simulation process, the calculation of the hull must be evaluated entirely to ensure accuracy. 63

| Model verification
To verify the accuracy of the simulation analysis, the one-step hydramine process and the one-step membrane module were checked using literature data and technical parameters summarized in Table 7.The one-step hydramine process for NG deacidification proposed by Wang et al. was investigated, and the simulated CO 2 content of the sweet gas was found to be quite close to the literature data with a relative deviation of less than 0.08%, confirming the accuracy of the simulation unit.
The one-step regeneration model was investigated based on processing parameters provided by an industrial company, and the simulation results showed that the relative deviations between the production rates and CO 2 contents of the permeate and high-pressure residual gases were within 5%, confirming the reliability of the newly established simulation unit. 65

| RESULTS
Using the thermodynamic principle, it calculated the theoretical energy consumption required for separating carbon dioxide from the gas mixture, using Equation ( 1) for an isothermal and isobaric process in an ideal gas state.This theoretical energy represents the minimum energy required to obtain pure carbon dioxide from the gas mixture.The objective of this study is to optimize the heat exchanger network.The Aspen Energy Analyzer is utilized for the purpose of examining the correlation between operating costs, equipment cost index, and the minimal temperature difference for heat transfer.The pinch point approach is employed in this study to assess the lowest temperature difference for heat transfer, taking into account the real heat transfer impact and the objective of lowering the overall investment in the project.
Figure 3 shows the results of our analysis, which demonstrate that the theoretical specific energy consumption for CO 2 separation is relatively low, ranging from 0.09 to 0.27 MJe/kg CO 2 , for feed CO 2 concentrations ranging from 0.6 to 0.024.Gas separation typically involves an entropy-driven process, whereas gas mixing is a spontaneous and irreversible process that generates entropy.The findings suggest that the energy consumption in a membrane-based process generally aligns with theoretical expectations.Interestingly, we found that as the feed CO 2 concentration increases, the specific energy consumption decreases significantly.This suggests that our model could be optimized for highly concentrated CO 2 feeds.
Further optimization of CO 2 separation with membrane technologies is possible, especially for lower CO 2 partial pressures.However, due to the low concentration of CO 2 in the feed and the high volume of the gas stream to be treated, the energy consumption will be very high.Therefore, practical solutions such as permeate flow circulation to increase the CO 2 concentration in the feed stream or multistage separation to reduce the irreversibility of the process can be implemented in addition to improving the performance of membrane materials.
To achieve a CO 2 absorption ratio of 90% (mol), process simulations were carried out to determine the required feed gas pressure and membrane area.CO 2 penetration and selectivity are key parameters affecting the energy consumption and membrane area in the gas separation process.The maximum permeability is about 10,000 bar with a maximum selectivity of 100, but composite membranes made of poly(vinyl alcohol) or poly(vinylamine) have shown higher selectivity, exceeding 100.
As shown in Figure 4, increasing CO 2 penetration can significantly reduce specific energy consumption and membrane surface area.Additionally, higher CO 2 selectivity leads to a decrease in specific energy consumption, but a larger membrane surface area is required.In conclusion, optimizing CO 2 separation with membrane technologies is promising, and implementing practical solutions along with improving membrane materials can help reduce energy consumption.
However, increasing the selectivity of the membrane material also means that more membrane surface area is required, which could result in higher costs.Thus, a continuous increase in selectivity may not significantly improve the separation performance.Additionally, if the operating point of the membrane process exceeds line 1.1, the membrane system may not be able to compete with MEA-based systems, but this is only when considering energy consumption.
One potential solution to reduce energy consumption is to implement a recycle flow to the feed, which can increase the CO 2 concentration and the partial pressure difference of CO 2 .This can improve the driving force for CO 2 transfer across the membrane, ultimately leading to lower energy consumption.Overall, the simulation results indicate that improving the selectivity and penetration of the membrane material can lead to significant reductions in energy consumption and membrane surface area (Figure 5).
In summary, it is clear that membrane technologies have the potential to significantly reduce energy consumption in CO 2 separation processes.However, to achieve this, further optimization is required, especially for lower CO 2 partial pressures.Permeate flow circulation and multistage separation are two practical solutions to reduce energy consumption, in addition to improving the performance of membrane materials.
Simulation results have shown that increasing CO 2 penetration and selectivity can lead to a reduction in specific energy consumption, but also requires more membrane surface area.In addition, the effect of permeate circulation ratio on energy consumption and membrane surface area has been investigated, with the conclusion that there is a limit to the benefits of circulation.
While the specific energy consumption of membranebased systems may not be as low as MEA-based absorption systems, membrane technologies have the advantage of improving the purity of CO 2 in the product to meet specific transportation and storage requirements.Therefore, understanding the state of energy consumption is crucial for the development and implementation of membrane technologies in CO 2 separation processes.
The optimization and improvement of the absorption process were carried out in five stages, each involving exergy analysis and the reporting of Cooling Utilities (MW), Heating Utilities (MW), and Total Utilities (MW). Figure 6 illustrates that state 5 represents the initial state of the system, while state 1 denotes the final state after achieving maximum improvement.
Table 8 summarizes the results.Theoretical energy consumption for CO 2 separation is relatively low, ranging from 0.09 to 0.27 MJe/kg CO 2 .However, specific energy consumption tends to follow a similar curve for a membrane process, but decreases significantly as the feed CO 2 concentration increases.Membrane technologies can be further optimized through improvements in membrane materials or through the use of permeate flow circulation or multistage separation for lower CO 2 partial pressures.Process simulations are crucial in determining the required feed gas pressure and membrane area to achieve a 90% CO 2 absorption ratio, with CO 2 selectivity and penetration being critical parameters.Composite membranes made of poly (vinyl alcohol) or poly(vinylamine) exhibit high selectivity (>100), reducing specific energy consumption and membrane surface area.Increasing permeate circulation ratio F I G U R E Effect of permeability turnover ratio on energy consumption and membrane surface area.
improves CO 2 purity, benefiting CO 2 transport and storage.However, even with a two-step process with higher CO 2 permeability and high CO 2 /N 2 selectivity, specific energy consumption remains high at 1.7-1.8MJe/kg CO 2 , which is almost the upper limit for reported polymer membranes.

| CONCLUSION
In this study, we conducted a comprehensive analysis of CO 2 separation using membrane technology, with a primary focus on optimizing the energy efficiency of the process.Our findings demonstrate that the specific energy consumption required for this process is relatively low, falling within the range of 0.09-0.27MJe/kg CO 2 .Importantly, further potential for optimization exists, especially in scenarios with lower CO 2 partial pressures, which holds significant promise for further reducing energy consumption.Through our process simulations, we determined the critical parameters of feed gas pressure and membrane surface area required to achieve a CO 2 absorption ratio of 90% (mol).Additionally, we thoroughly examined the impact of CO 2 permeation and selectivity on energy consumption and membrane surface area.Notably, our study revealed that the utilization of recycle flow to the feed can significantly enhance the CO 2 concentration of the feed, leading to a potential reduction in energy consumption by increasing the partial pressure difference of CO 2 .To optimize the purification process further, we employed the pinch analysis approach to enhance the heat exchanger network.This in-depth analysis aimed at achieving the optimal matching between the logistics of the heat exchanger and the thermodynamic objective of minimizing energy consumption.Furthermore, we effectively addressed the issue of nonuniform energy flow throughout the heat exchanger network, resulting in improved system efficiency.In conclusion, all objectives of optimization were successfully achieved.Economic assessment in the energy sector plays a pivotal role in guiding Total utilities (MW) 6.9 Abbreviations: PVA, polyvinyl alcohol; PVAm, polyvinyl amine.
decisions and investments.It involves evaluating the costs and benefits associated with various energy technologies, approaches, and policies.Our analysis focuses on reducing expenses related to renewable technologies and enhancing their competitiveness in comparison to conventional fossil fuels.This encompasses cost reductions in manufacturing renewable energy components, integrating these technologies into the energy grid, and developing energy-efficient appliances and systems for consumers.Moreover, we underscore the significance of enhancing the resilience and security of the energy system through investments in infrastructure and cybersecurity This includes the development of energy-efficient materials and technologies for buildings and the industrial sector to curtail energy wastage and gain a competitive edge in the global battery industry.Additionally, our emphasis extends to strengthening the market for renewable fuels, advancements in CCS/ utilization, and enhancing safety measures in nuclear energy utilization.Throughout all these areas, our economic analysis not only assesses costs but also evaluates the substantial benefits that extend beyond direct economic gains to encompass broader societal advantages, including reduced GHG emissions and improved public health.Furthermore, we conducted an optimization of the absorption process in five stages, accompanied by a comprehensive exergy analysis to evaluate the cooling and heating equipment required for each stage.The proposed optimization approach demonstrated remarkable success in substantially reducing energy consumption within the CO 2 separation process, exemplified by significant reductions in cooling and heating systems.In summary, this study has provided valuable insights into the design and optimization of membrane-based CO 2 separation processes.By reducing environmental impacts and contributing to the development of sustainable energy systems, we move closer to achieving a more promising and sustainable future.

F
I G U R E 3 Specific energy consumption.Conditions: one-stage.F I G U R E 4 Effect of CO 2 selectivity on energy consumption and membrane area E is the specific energy consumption and A is the membrane area.

F I G R E 6
Exergy analysis of the simulation after each optimization.T A B L E 8 Results in a nutshell.
Comparison of the effects of NETs.
2 removal, with the highest GHG removal potential in countries with low-carbon electricity supply and waste heat usage.
T A B L E 6 Key parameters of the absorption tower and the recovery tower.Summary of model verification data.Bold values in the table suggest that the simulation model is a powerful tool for predicting the performance and environmental impact of CO 2 capture processes. Note: