Gas Separation Technology Research Articles

Control of gas selectivity and permeability through COF-GO composite membranes for sustainable decarbonization and hydrogen production

A promising way to address modern environmental and energy supply challenges is via rapid implementation of decarbonization and hydrogen production technologies. Development of gas separation membranes with high selectivity and permeability is essential for these processes but is still a bottleneck. Our research focuses on achieving precise control of gas diffusion pathways through on-demand regulation of material interactions in thin composite membranes. We combine 2D covalent organic frameworks (COFs) and graphene oxide (GO) to create COF-GO composite membranes with desirable nanosheet stacking, controllable thicknesses and pathways for gases. By pH-assisted self-assembly, we fine-tune material interactions and achieve simultaneous enhancement of permeability and selectivity by increasing membrane thickness and regulating the interactions between COF and GO nanosheets by pH. At a thickness of 1.3 μm, the COF-GO membrane, assembled under pH 4, demonstrates good working characteristics for H2/CO2 equimolar mixture (at room temperature and 1 bar), with a H2 permeability of 366 Barrer, selectivity of 15.6, and long-term stability exceeding 200 h. This work paves the way for tailored, performing gas separation with long-term stability. It guides the unique 2D transport mechanism to be utilized under practical conditions. Our research offers a novel strategy for the design of composite membranes from two-dimensional (2D) materials for gas separation technologies. It contributes to sustainable decarbonization and hydrogen production solutions, bringing us closer to a greener, more environmentally friendly future.

An innovative gas management methodology based on PSA for efficient gas allocation and utilization in hybrid hydrogen network: Integrating process simulation, modeling, and machine learning

Pressure swing adsorption(PSA) based gas separation technology is widely applied in chemical industries, especially in hydrogen purification. Its complex mechanism and non-steady state feature restrict the separation performance adjustment and application on efficient gas utilization. Process simulation, machine learning and modelling combined innovating gas management methodology is proposed in this paper to perform accurate gas separation for natural gas based syngas mixture. VB script program is employed to drive Aspen adsorption simulation, and then classical and regression tree(CART), polynomial regression(PNR) and surrogate model are comprehensively used to perform machine learning. Consequently, the coefficient matrix is obtained to quantify the separation performance. This method holds the potential for broader application in refineries and SPCs hybrid hydrogen network, facilitating the comprehensive utilization of hydrogen containing gases. Case study results show this methodology can conserve natural gas and gas productivity by 21.3 %, as well as carbon emission by 8211.6 Nm3/h. This work highlights the promising application of digital twin technology within the chemical industry, showcasing how process simulation, machine learning, and modeling can collectively revolutionize gas management and resource conservation.

A review on recent advances of cellulose acetate membranes for gas separation.

This review thoroughly investigates the wide-ranging applications of cellulose-based materials, with a particular focus on their utility in gas separation processes. By focusing on cellulose acetate (CA), the review underscores its cost-effectiveness, robust mechanical attributes, and noteworthy CO2 solubility, positioning it as a frontrunner among polymeric gas separation membranes. The synthesis techniques for CA membranes are meticulously examined, and the discourse extends to polymeric blend membranes, underscoring their distinct advantages in gas separation applications. The exploration of advancements in CA-based mixed matrix membranes, particularly the incorporation of nanomaterials, sheds light on the significant versatility and potential improvements offered by composite materials. Fabrication techniques demonstrate exceptional gas separation performance, with selectivity values reaching up to 70.9 for CO2/CH4 and 84.1 for CO2/N2. CA/PEG (polyethylene glycol) and CA/MOF (metal-organic frameworks) demonstrated exceptional selectivity in composite membranes with favorable permeability, surpassing other composite CA membranes. Their selectivity with good permeability lies well above all the synthesised cellulose. As challenges in experimental scale separation emerge, the review seamlessly transitions to molecular simulations, emphasizing their crucial role in understanding molecular interactions and overcoming scalability issues. The significance of the review lies in addressing environmental concerns, optimizing membrane compositions, understanding molecular interactions, and bridging knowledge gaps, offering guidance for the sustainable evolution of CA-based materials in gas separation technologies.

Recent advances in the interfacial engineering of MOF-based mixed matrix membranes for gas separation.

The membrane process stands as a promising and transformative technology for efficient gas separation due to its high energy efficiency, operational simplicity, low environmental impact, and easy up-and-down scaling. Metal-organic framework (MOF)-polymer mixed matrix membranes (MMMs) combine MOFs' superior gas-separation performance with polymers' processing versatility, offering the opportunity to address the limitations of pure polymer or inorganic membranes for large-scale integration. However, the incompatibility between the rigid MOFs and flexible polymer chains poses a challenge in MOF MMM fabrication, which can cause issues such as MOF agglomeration, sedimentation, and interfacial defects, substantially weakening membrane separation efficiency and mechanical properties, particularly gas separation. This review focuses on engineering MMMs' interfaces, detailing recent strategies for reducing interfacial defects, improving MOF dispersion, and enhancing MOF loading. Advanced characterisation techniques for understanding membrane properties, specifically the MOF-polymer interface, are outlined. Lastly, it explores the remaining challenges in MMM research and outlines potential future research directions.

A mechanochemical process to capture and separate carbon dioxide from natural gas using boron nitride nanosheets.

Addressing climate change is a critical and pressing matter that requires immediate attention to mitigate its severe repercussions. In order to enhance the capture and separation of carbon dioxide from natural gas and nitrogen gas, it is imperative to develop new capture materials and more efficient storage processes. In this study, we introduce an innovative environmentally friendly storage and separation technique. Through a controlled mechanochemical process, a substantial amount of carbon dioxide (103.6 wt%) was successfully captured within boron nitride. This process also excels at effectively isolating carbon dioxide from a gas mixture containing natural gas (CH4) or nitrogen due to its superior adsorption selectivity for CO2 over the other two gases. The stored carbon dioxide can be released upon heating, and this procedure can be repeated several times (minimum four times), indicating a game changing process in CO2 gas capture and separation technology with the advantages of green, low cost and efficiency.

Advancements in defect engineering of two-dimensional nanomaterial-based membranes for enhanced gas separation.

The advent of two-dimensional nanomaterials, a revolutionary class of materials, is marked by their atomic-scale thickness, superior aspect ratios, robust mechanical attributes, and exceptional chemical stability. These materials, producible on a large scale, are emerging as the forefront candidates in the domain of membrane-based gas separation. The concept of defect engineering in 2D nanomaterials has introduced a novel approach in their application for membrane separation, offering an effective technique to augment the performance of these membranes. Nonetheless, the development of customized microstructures in gas separation membranes via defect engineering remains nascent. Hence, this review is designed to serve as a comprehensive guide for the application of defect engineering in 2D nanomaterial-based membranes. It delves into the most recent developments in this field, encompassing the synthesis methodologies of defective 2D nanomaterials and the mechanisms underlying gas transport. Special emphasis is placed on the utilization of defect-engineered 2D nanomaterial-based membranes in gas capture applications. Furthermore, the paper encapsulates the burgeoning challenges and prospective advancements in this area. In essence, defect engineering emerges as a promising avenue for enhancing the efficacy of 2D nanomaterial-based membranes in gas separation, offering significant potential for advancements in membrane-based gas separation technologies.

Characteristics analysis of multi-channel ceramic membranes for dilute gas absorption in falling film operation

Capturing dilute gases has posed a significant challenge due to the extremely low mass transfer driving force associated with them. Falling film-based absorption using porous membranes emerges as a promising technology for gas separation, offering a substantial gas–liquid interface area while simultaneously eliminating mass transfer resistance within pores that is inherent in hydrophobic membrane-based absorption processes. In this study, we investigated the mass transfer performance of multi-channel ceramic membranes in falling film-based dilute CO2 absorption under various gas and liquid operating conditions. Experimental tests and computational fluid dynamics (CFD) simulations were conducted to examine the effects of pore size and geometrical configuration on the distribution of liquid and gas flows across different channels. Simulations indicated that the optimization of multi-channel ceramic membranes for the falling film-based dilute gas absorption should prioritize achieving a more rational distribution of gas–liquid flows. When the disparity between liquid and gas distribution in the outermost channels exceeded 40%, as opposed to cases where the difference was within 20%, there was a reduction of over 50% in mass transfer performance.

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

AbstractWith 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.

Ab initio modelling of transport phenomena in multi-component mixtures of rarefied gases

The direct simulation Monte Carlo method based on ab initio potentials is applied to model transport phenomena in binary, ternary and quaternary mixtures of noble gases. To this end, the Couette and Fourier problems are solved over the whole range of the rarefaction parameter spanning the near free-molecular, transitional, and slip flow regimes. Moreover, analytical solutions are obtained in the limits of the free-molecular and continuous medium regimes of flow. As a result, the shear stress, heat flux through multi-component mixtures, distributions of velocity, temperature, and mole fractions of each species are calculated as a function of the gas rarefaction. An analysis of these data points out the properties which are strongly affected by the chemical composition. It is found that the largest deviations of characteristics of mixtures from those of a single gas are observed for the binary mixture of helium and krypton, while their deviations for the ternary and quaternary mixtures are smaller. A temperature variation in a mixture leads to non-uniform distributions of chemical composition due to the thermal diffusion phenomenon. Such redistributions are analyzed in both problems and their effect on the heat and momentum transfer is evaluated. The reported results can be used to evaluate the main factors determining transport phenomena in practical applications such as vacuum systems, microfluidics, gas separation technology, space research etc.

Using a superstructure approach for techno-economic analysis of membrane processes

An intelligent optimization of multistage gas permeation layouts is required to achieve high product gas purities and high product recoveries at the same time in gas separation technologies. In this work, a superstructure-based mathematical model for the optimization of CO2 removal in three applications including post-combustion CO2 capture, natural gas sweetening and biogas upgrading is designed. A typical polymeric membrane prepared within the BIOCOMEM project, with high CO2 permeance, CO2/N2 selectivity of 25, and CO2/CH4 selectivity of 7.9 is studied to assess the potential of this membrane at a real industrial scale. Using a superstructure-based model, operating conditions, driving force distribution along each membrane stage, the use of feed compression and/or permeate vacuum, the number of stages and recycle options are simultaneously optimized. The techno-economic analysis of all three applications is then carried out and the most promising membrane-based process configuration was chosen. The multi-stage membrane process is investigated in terms of capture cost, energy consumption, and membrane area. The results revealed that high purity and recovery at a minimum cost could be achieved by the three-stage process in post-combustion CO2 capture and natural gas while in biogas upgrading the two-stage configuration exhibited the best performance. It was found that a reduction in capture cost to around 42 €/tCO2 is possible in post-combustion CO2 capture if membranes with a selectivity of 50 and the same permeation flow are developed.

Kinetic characterization of gas mixture separation by hydrate method with 1,3-dioxolane and multi-walled carbon nanotubes complex synergistic system

In the transition to cleaner energy sources, low-carbon energy gases are expected to dominate fuel consumption. Hydrate-based gas separation technology is poised to play a key role in the decarbonization pathway for energy gases with high CO2 content. However, the current hydrate gas separation method faces challenges, including a long induction period, slow growth rate, and low separation efficiency. In light of these challenges, this paper investigates the kinetics of CH4/CO2 gas mixture hydrate formation and its separation efficiency in 1,3-dioxolane (DIOX) and multi-walled carbon nanotubes (MWCNTs). The experimental results showed that both DIOX and MWCNTs, when used in low concentrations, had a certain thermodynamic promotion effect, with DIOX showing a superior performance. DIOX outperforms MWCNTs in terms of gas consumption and induction time. whereas MWCNTs was superior to DIOX in terms of growth rate, and the purification rate at the same concentration could be increased by 32.66 %∼234.43 % compared with the DIOX system. Subsequently, this paper further investigated the effect of 300 ppm DIOX complexed with different concentrations of MWCNTs on hydrate formation and separation efficiency. DIOX was found to occupy the main promotional role in this complex system, retaining the growth acceleration stage in the DIOX system. When compounded with 200 ppm MWCNTs, the T90 time was shortened by 28.78 %∼59.29 %, and the purification rate could be increased by 86.4 % compared with a single 300 ppm DIOX system. This work provides guidance on the use and compounding of thermodynamic and kinetic promoters and aids hydrate technology where faster hydrate growth rates and more efficient gas mixture separation are required.

Improving gas separation performances of poly(furfuryl alcohol)-based carbon molecular sieve membrane by tuning furan ring opening and membrane structures

Carbon molecular sieve membranes (CMSMs) have exhibited significant potential in gas separation applications, particularly in the realm of hydrogen and carbon dioxide separation. Poly(furfuryl alcohol) (PFA) represents a cost-efficient and sustainable precursor utilized in the synthesis of CMSMs. Nonetheless, PFA-based CMSMs have exhibited suboptimal performance and frequently necessitate supplementary supporting layers. In the present investigation, we have explored various acids as catalysts for the in-situ self-polymerization of PFA. Our findings reveal that PFA membrane catalyzed by sulfuric acid exhibits the most favorable performance, yielding a hydrogen permeability of 1394.4 Barrer and a H2/CH4 selectivity of 404.1. These values exceed the Robeson upper limits established in 2019. The enhanced gas separation performance of the sulfuric acid catalyzed PFA-based CMSM could be attributed to the increased furan ring opening and higher polymerization degree achieved through this catalytic process. Furthermore, our investigation delved into the addition of poly(styrene-co-acrylonitrile) (SAN) into the PFA membrane, yielding a CMSM featuring both dense and porous layers. With the addition of 6 wt% SAN in PFA membrane, the resulting CMSM exhibited a hydrogen permeability of 3126.4 Barrer, underscoring the potential for high-performance CMSMs made from the economical PFA precursor. The optimization of the PFA polymerization process and the incorporation of SAN, hold the promise of further elevating the performance of PFA-based CMSMs, and these advancements will substantially contribute to the advancement of sustainable and efficient gas separation technologies.

Emerging Trends in Metal-Organic Frameworks for Gas Separation and Storage

This research paper explores the rapidly evolving landscape of Metal-Organic Frameworks (MOFs) in the context of gas separation and storage. In an era characterized by growing energy demands and environmental concerns, the efficient and sustainable management of gases such as carbon dioxide, methane, and hydrogen is of paramount importance. MOFs, with their tunable structures and exceptional surface areas, have emerged as promising candidates to address these challenges. The introduction provides an overview of the critical role MOFs play in revolutionizing gas separation and storage technologies. By synthesizing an extensive body of literature, the literature review outlines the historical context, highlighting the steady progression of MOFs from theoretical constructs to practical applications. It underscores knowledge gaps and highlights emerging trends, setting the stage for this research. The methods section details the experimental approaches employed, encompassing MOF synthesis, characterization techniques, and comprehensive testing methodologies. The results section presents compelling data demonstrating the performance of various MOFs in gas separation and storage scenarios. These results reveal the remarkable adsorption capacities and selectivity of MOFs, providing insights into their practicality. The discussion delves into the implications of these findings, illuminating how MOFs can redefine the landscape of gas separation and storage. Recognizing limitations and challenges, we propose potential research directions and applications. In conclusion, this paper underscores the transformative potential of MOFs in addressing pressing global issues related to energy and the environment. By offering efficient and sustainable solutions for gas separation and storage, MOFs can pave the way for a cleaner and more sustainable future.

Retracted: High Efficiency Compound Vacuum Oil Gas Separation Technology Based on Integrated Oil Filter of Ultra-High Voltage Transformer

Retracted: High Efficiency Compound Vacuum Oil Gas Separation Technology Based on Integrated Oil Filter of Ultra-High Voltage Transformer

Enhancing Supercapacitive Swing Adsorption of CO2 with Advanced Activated Carbon Electrodes

AbstractGlobal warming due to anthropogenic CO2 emissions argues for the rapid development of efficient carbon capture technologies. Supercapacitive swing adsorption (SSA) is a gas separation technology that relies on the reversible charge and discharge of supercapacitor electrodes to absorb and desorb CO2 highly selectively and reversibly. However, thus far SSA only showed low sorption capacity, and slow sorption kinetics. Herein, it is shown that the sorption capacity can be substantially increased via the use of carbons with a higher specific capacitance. The highest gravimetric sorption capacity is measured with electrodes made from garlic‐roots derived activated carbon valuing 273 mmol kg−1 having a specific capacitance of 257 F g−1. In addition, the overall adsorption rate and productivity are improved. Cycling the electrodes for over 100 h showed highly reproducible, reversible CO2 adsorption and desorption behavior. A preliminary technoeconomic and sensitivity analysis is provided to demonstrate the potential of SSA for commercial applications.

Metal-organic framework-based mixed matrix membranes for gas separation: Recent advances and opportunities

The demand for carbon dioxide (CO2) emission mitigation has driven the scientific community to develop a viable strategy. Gas separation technology are considered as the most promising and effective carbon capture approach. The utility of mixed-matrix membranes (MMMs) for selective gas separation has prompted a paradigm shift from conventional methods towards more efficient and sustainable processes. Metal-organic frameworks (MOFs), with high porosity, surface area, and structural tunability, are identified as suitable fillers in MMMs. Their application in carbon capture and gas separation processes could significantly reduce greenhouse gas emissions while maintain cost-effectiveness. Herein, this review presents the latest scientific and technological advancements in several types of representative MOF fillers, including Zeolitic Imidazolate Frameworks (ZIFs), Materials of Institute Lavoisier (MILs), University of Oslo (UiO), and Hong Kong University of Science and Technology (HKUST-1). It also highlights the current challenges associated with MOF fillers and outlines potential research opportunities for future improvements in the performance of MOF-based MMMs.

Impact of concentration polarization on membrane gas separation processes: From 1D modelling to detailed CFD simulations

Membranes are one key technology for gas separation. Current design methodologies make use of a 1D set of mass balance equations with membrane taken as the only mass transfer resistance (no concentration polarization hypothesis). This strategy has however to be reconsidered with emerging high-performance membrane materials. Accordingly, a rigorous CFD simulation approach is developed in order to correctly compute their separation efficiency. The results reveal that, compared to CFD, in the presence of concentration polarization, 1D models largely overestimate the separation performance of high-performing membranes. Based on a generic modelling of mass transfer in the gas phase under concentration polarization, a novel 1D modified approach is reported, showing similar predictions compared to CFD simulations, but offering very fast computations. This strategy is of interest for the simple and systematic design of membrane gas separation processes, including process synthesis approaches.

Nanocomposite polymer blend membrane molecularly re-engineered with 2D metal-organic framework nanosheets for efficient membrane CO2 capture

Membrane gas separation technology is an energy-efficient alternative to the traditional industrial processes for CO2 capture towards the mitigation of global warming. To overcome the inherent performance trade-off behavior of polymeric membranes, many nanoarchitectures have been incorporated for developing high-performance mixed matrix membranes. Yet, a successful nanocomposite membrane design remains challenging, especially for CO2 capture, because of polymer-filler incompatibility and interfacial defects. Herein, 2D Cu-TCPP nanosheets were synthesized and incorporated into Pebax/Poly (ethylene glycol) methyl ether acrylate (PEGMEA) blends to design MMMs with exceptional CO2/N2 separation performance. This synergistic polymer blend after crosslinking, offers a highly accommodating and robust matrix environment for the homogenous distribution of nanosheets. Cu-TCPP particles were also produced as 3D nanoflowers to probe their morphological effect on gas transport. The finely dispersed 2D nanosheets expanded the free volume of the resultant nanocomposite membranes, leading to a significantly enhanced CO2 permeability of up to 1183 Barrer which was 93% higher than the neat polymers, while they also increased the transport pathway tortuosity that contributes to a very high CO2/N2 selectivity of 57.6 at a loading of merely 0.1 wt%. Not only do such separation performances surpassed the Robeson upper bound by a large margin and outcompeted many existing advanced MMM designs, but they also remained stable after long-term operations. By carefully elucidating the gas transport tuning effect of 2D metal-organic framework nanosheets in nanocomposite membranes, this work could help broaden their applicability for other environmentally important molecular separations.

The Enhancement of CO2 and CH4 Capture on Activated Carbon with Different Degrees of Burn-Off and Surface Chemistry.

Activated carbon derived from longan seeds in our laboratory and commercial activated carbon are used to investigate the adsorption of methane (CH4) and carbon dioxide (CO2). The adsorption capacity for activated carbon from longan seeds is greater than commercial activated carbon due to the greater BET area and micropore volume. Increasing the degree of burn-off can enhance the adsorption of CO2 at 273 K from 4 mmol/g to 4.2 and 4.8 mmol/g at 1000 mbar without burn-off, to 19 and 26% with burn-off, respectively. This is because an increase in the degree of burn-off increases the surface chemistry or concentration of functional groups. In the investigation of the effect of the hydroxyl group on the adsorption of CO2 and CH4 at 273 K, it is found that the maximum adsorption capacity of CO2 at 5000 mbar is about 6.4 and 8 mmol/g for cases without and with hydroxyl groups contained on the carbon surfaces. The opposite behavior can be observed in the case of methane, this is due to the stronger electrostatic interaction between the hydroxyl group and carbon dioxide. The simulation results obtained from a Monte Carlo simulation method can be used to support the mechanism in this investigation. Iron oxide is added on carbon surfaces with different concentrations to reveal the effects of ferric compounds on the adsorption of CO2. Iron at a concentration of about 1% on the surface can improve the adsorption capacity. However, excessive amounts of iron led to a limited adsorption capacity. The simulation result shows similar findings to the experimental data. The findings of this study will contribute to the progress of gas separation technologies, paving the way for long-term solutions to climate change and greenhouse gas emissions.

Defect Engineering of MOF‐Based Membrane for Gas Separation

AbstractMetal–organic frameworks (MOFs) are highly versatile materials that have been identified as promising candidates for membrane‐based gas separation applications due to their uniformly narrow pore windows and virtually unlimited structural and chemical features. Defect engineering of MOFs has opened new opportunities for manipulating MOF structures, providing a simple yet efficient approach for enhancing membrane separation. However, the utilization of this strategy to tailor membrane microstructures and enhance separation performance is still in its infancy. Thus, this summary aims to provide a guideline for tailoring defective MOF‐based membranes. Recent developments in defect engineering of MOF‐based membranes will be discussed, including the synthesis strategies for defective MOFs, the effects of defects on the gas adsorption properties, gas transport mechanisms, and recently reported defective MOF‐based membranes. Furthermore, the emerging challenges and future prospects will be outlined. Overall, defect engineering offers an exciting opportunity to improve the performance of MOF‐based gas membranes. However, there is still a long way to go to fully understand the influence of defects on MOF properties and optimize the design of MOF‐based membranes for specific gas separation applications. Nonetheless, continued research in this field holds great promise for the development of next‐generation membrane‐based gas separation technologies.