Membrane-based Gas Separation Processes Research Articles

Process performance maps for membrane-based CO2 separation using artificial neural networks

Membrane-based gas separation processes are currently being implemented at different scales for several industrial applications. The optimal design of such processes, which is of key importance for their large-scale commercial deployment, has been extensively studied through parametric analyses and optimisation procedures. Nevertheless, the applicability of such design methodologies is generally limited by the large computational time and effort they require. In this work, surrogate models based on artificial neural networks are developed to circumvent the lengthy optimisation of a one-stage and two-stage cascade membrane-based gas separation process. In 200 ms, the surrogate model generates a Pareto front that describes the optimal trade-off between the process specific electricity consumption and productivity based on given input data, i.e., membrane material properties, feed composition and separation target. Whereas the surrogate model is applicable to any binary gas mixture, here its features are illustrated by creating process performance maps for post-combustion CO2 capture. Such maps provide valuable insights on: (i) attainable gas separation regions in term of CO2 recovery and CO2 purity, and (ii) the impact of membrane material, feed composition and separation target on the Pareto fronts and the optimal operating conditions.

Polymeric nanocomposite membranes for gas separation: Performance, applications, restrictions and future perspectives

In recent decades, anthropogenic industrial-based activities (i.e., energy production and its conveyance) has led to the emission of deleterious greenhouse gases such as CO 2 , H 2 S, and NO 2 as an important environmental concern. Membrane-based gas separation processes have been currently of paramount attention in critical industrial applications such as purification, biogas recovery, water treatment, gas processing and H 2 recovery. Polymeric nanocomposite membranes (PNM) have illustrated indisputable potential of utilization to mitigate the release of gaseous pollutants to the ecosystem and reduce their hazardous environmental effects. Incorporation of novel nanoparticles including activated carbon, nanofibers and carbon nanotubes have revolutionized the efficiency of polymeric membranes for gas separation. This review paper aims to present disparate applications of polymeric nanocomposite membranes for mitigating the emission of toxic/acidic gases to environment. Moreover, performance, applications and challenges towards the use of nanocomposite membranes are reviewed comprehensively and future perspectives towards their development in industrial applications are recommended. Finally, prevalent nanocomposite membranes for the separation of various gaseous mixtures are presented.

Comparison of analytical film theory and a numerical model for predicting concentration polarisation in membrane gas separation

Accurate prediction of the concentration polarisation (CP) effect is very important in the design of an efficient membrane-based gas separation process. This study analyses the reliability of analytical film theory (FT) for evaluating the performance of gas separation membranes in terms of CP and flux. The analytical model is compared against a more rigorous numerical model developed by using Computational Fluid Dynamics (CFD) for various operating variables. The results show that the FT prediction is less accurate at high CP conditions when gas permeation through the membrane increases, due to higher permeance selectivity and pressure ratio. Hence, the results suggest that FT is not recommended for membranes with high permeance or high-pressure conditions. Given that the typical range of feed composition and temperature has little impact on fluid properties (i.e., gas diffusion coefficient, densities, and viscosities), the resulting CP does not vary much and hence both FT and CFD models predict a similar CP. The analysis also suggests that the FT model is more accurate in predicting CP in the region closer to the membrane entrance. Overall, the analytical film theory serves as a reliable approximation in membrane gas applications under low CP at high crossflow and low flux conditions.

Mixed-Matrix Ion Gel Membranes for Gas Separation

The potential of ionic liquid materials to improve membrane-based gas separation processes has been realized during the past few years, through the exploitation of diverse configurations, chemical functionalities, and properties. Nowadays, one of the most recent trends on this field is the development of mixed-matrix ion gels, an emerging family of ionic soft-solid materials, in which fillers are embedded into polymer/IL matrices. This review aims at presenting an overview on the latest developments and advances on ion gel membranes containing a third component, such as zeolites, metal organic frameworks, silica, graphene oxide, metal salts, and nanoparticles, for gas separation processes. We provide an analysis of this building system and highlight the diverse type of mixed-matrix ion gels hitherto reported, for which the impact of the different fillers on the ion gels’ overall properties is discussed in detail. The main challenges on their preparation, as well as their transport mechanism and how it can be influenced by the different fillers, are also addressed. Finally, technological aspects, perspectives, and opportunities to pursue this topic are discussed from a critical point of view.

Recent advancements in molecular separation of gases using microporous membrane systems: A comprehensive review on the applied liquid absorbents

Industrial-based molecular separation of detrimental gaseous molecules (especially CO2) from various mixtures using different types of chemical absorbents has been recently of paramount attention all around the world to mitigate their severe impacts on ecosystem such as acid rain and global warming. This paper aims to present a state-of-the-art review about the recent advancements in the molecular separation of CO2 applying hollow fiber membrane contactors (HFMCs). Additionally, all employed membrane materials for separating CO2 contaminant including polymeric membranes (PMs), microporous organic polymers (MOPs), fixed-site-carrier membranes (FSCMs), inorganic membranes (IMs), mixed matrix membranes (MMMs), and carbon molecular sieve membranes (CMSMs) are comprehensively discussed. Discussion about the most important operating challenges towards the separation of CO2 inside the HFMCs (i.e., mass transfer resistance and membrane pores wettability) is considered as another objective of this paper. Another aim of this paper is to classify the prevalent types of liquid absorbents and critically discuss the advantages and disadvantages of each group in the field of membrane-based gas separation process.

Evaluation of Flowsheet Design Approaches to Improve Energy Efficiency in Multistage Membrane Processes to Recover Helium

In pressure-driven membrane-based gas separation processes, the driving force-related cost (capital and operating costs) is one of the most significant cost components. To reduce this driving force...

A Robust Zeolitic Imidazolate Framework Membrane with High H2/CO2 Separation Performance under Hydrothermal Conditions

An upsurge in searching membranes with high selectivity, permeability, and stability, which have been considered to be promising in the membrane-based gas separation process, has received huge attentions in academia and industry. In this work, we demonstrated a new molecular sieving ZIF membrane, which has a unique mixed-ligand ZIF structure constructed by two bulk imidazolate linkers within the zeolite GIS topology, resulting in appropriate aperture size, strong affinity to CO2, exceptional thermal and chemical stabilities, and superhydrophobic properties. Benefited from these features, the resulting JUC-160 membrane indeed exhibited remarkable separation efficiency and stability, with excellent H2/CO2 selectivity of 26.3 and considerable H2 permeance of 9.75 × 10-7 mol m-2 s-1 Pa-1 under high temperature up to 200 °C. Furthermore, owing to its superhydrophobicity, the JUC-160 membrane could maintain its prominent separation performance even with the presence of steam.

Prediction of Gas and Liquid Solubility in Organic Polymers Based on the PR+COSMOSAC Equation of State

The predictive capability of gas and liquid solubility in organic polymers is examined based on the combination of the PR+COSMOSAC equation of state (EOS) and the COSMO-SAC liquid model through three different excess Gibbs free energy based mixing rules, modified Huron-Vidal (MHV1), Wong-Sandler (WS), and self-consistent mixing rule (SCMR). Using 81 binary systems consisting of 23 gas molecules and 22 polymers (81 data points) with temperatures ranging from 298 to 461 K, it is found that WS and SCMR can provide reasonable prediction accuracy (RMSE(log10 kH) = 0.746 and 1.725, respectively) for the Henry’s law parameter in polymers, while the MHV1 mixing rule results in a much larger error (RMSE (log10 kH) = 3.118) compared to experiment. The WS and SCMR, but not MHV1, provide a converged value of Henry’s law parameter of gas in polymers as the molecular weight of the polymer increases. We further propose a modification to the SCMR (mSCMR) that results in significant improvement in the solubility prediction in polymers (RMSE (log10 kH) = 0.305) and the binary vapor–liquid equilibrium for common molecules. In this new approach, referred to as PRCS/mSCMR/COSMOSAC, all species-dependent parameters are determined from quantum mechanical (QM) calculations, and no adjustable parameters are required for the gas–polymer binary pairs. We believe that this new method may provide useful assistance to the development of polymer membrane-based gas separation processes especially when experimental information is not yet available.

A novel tool for the modeling, simulation and costing of membrane based gas separation processes using Aspen HYSYS: Optimization of the CO2/CH4 separation process

A key tool called “MemCal” is developed to support the simulation of membrane-based gas separation processes using Aspen HYSYS. By integrating “MemCal” with the simulator, users can simulate complex multi-component/multi-stage processes, perform sensitivity studies, and utilize the default HYSYS features to cost and optimize processes. Industrially, “MemCal” can be used to simulate the separation of air, biogas, natural gas, olefins-paraffins and other gases. The CO2/CH4 binary mixture separation was demonstrated in this manuscript as the first and the simplest application of “MemCal”. The simulation of various multi-stage processes suggested that the treatment cost can be dropped by optimizing the separation load distribution among the stages. For CO2/CH4 separation, the simulations suggested that the optimized two-stage process plus recycle resulted in the least separation cost. The installation of a third stage for boosting hydrocarbons recovery was found unjustified when membranes equivalent to or better than cellulose acetate are adopted.

Gas Separation through Bilayer Silica, the Thinnest Possible Silica Membrane.

Membrane-based gas separation processes can address key challenges in energy and environment, but for many applications the permeance and selectivity of bulk membranes is insufficient for economical use. Theory and experiment indicate that permeance and selectivity can be increased by using two-dimensional materials with subnanometer pores as membranes. Motivated by experiments showing selective permeation of H2/CO mixtures through amorphous silica bilayers, here we perform a theoretical study of gas separation through silica bilayers. Using density functional theory calculations, we obtain geometries of crystalline free-standing silica bilayers (comprised of six-membered rings), as well as the seven-, eight-, and nine-membered rings that are observed in glassy silica bilayers, which arise due to Stone-Wales defects and vacancies. We then compute the potential energy barriers for gas passage through these various pore types for He, Ne, Ar, Kr, H2, N2, CO, and CO2 gases, and use the data to assess their capability for selective gas separation. Our calculations indicate that crystalline bilayer silica, which is less than a nanometer thick, can be a high-selectivity and high-permeance membrane material for 3He/4He, He/natural gas, and H2/CO separations.

On the optimal design of membrane-based gas separation processes

Gas-separation processes are of paramount importance for several industrial applications. In this context, membrane-based gas separation has a great innovation potential in term of limiting the energy consumption and simplifying the process operation and control. Much of the research in this field focused on parametric analyses or optimization procedures aimed at the investigation of some performance indicators, such as separation performance, energy consumption, membrane area. This work aims at developing a comprehensive method which provides criteria for the optimal design and operation of membrane gas separation processes. First, a parametric analysis is carried out, resulting in the definition of attainable regions for different process configurations and product specifications. Subsequently, a multi-objective optimization is carried out by employing a genetic algorithm that minimizes the compression energy and the required membrane area by selecting the optimal process layout, operating variables, and membrane materials.

Effect of coagulant bath on the gas permeation properties of cellulose acetate asymmetric membrane

Membrane based gas separation process technology has been recognized as one of the most efficient and advanced unit operation for gas separation. One of the problems in membrane gas separation is membrane performance. This paper explores the application of cellulose acetate (CA) membrane for natural gas purification and separation by improving its permeability and selectivity. The main interest in this research is to study the effect of quench medium on the gas separation performance towards its physical characteristics and gas separation performance of CA membrane. Cellulose acetate polymer was dissolved in n- methyl-2-pyrrolidone solvent and casted onto a glass plate using a pneumatically controlled casting system with fixed shear rate and solvent evaporation times. The parameter varied was the non-solvent used as quench medium during membrane post treatment that were methanol and n-hexane. The different quench media as post treatment affected the O2 and N2 gas permeation and O2/N2 selectivity as well as the tensile strength of the flat sheet asymmetric membrane. Combination of methanol and n-hexane as quench media gave the best result than the other steps. This solvent exchange step influenced the morphology by producing thin skin layer and thus gives better gas separation performance than other steps

Mathematical modelling of membrane gas separation using the finite difference method

Membrane gas separation has been recognized as the main technology that is used in chemical engineering for hydrogen recovery, air separation, natural gas sweetening, helium recovery, natural gas dehydration, and so on. Membrane-based gas separation processes have great potential for these industrial applications because of their environmental friendliness, energy efficiency and ease of scale up. Mathematical modelling of the membrane-based gas separation process can be useful to predict the performance of such separation processes. An improved mathematical model has been implemented in this research for the separation of a binary gas mixture using a membrane separator. The finite difference method (FDM) is applied to predict the membrane gas separation behaviour. The method is helpful as it involves the least effort and computational time because algebraic equations are used instead of differential equations. Different configurations, such as single stage and double stage, are used in this study. The results of the FDM simulation are compared with the simulation results of the model and the experimental data of several membrane systems.

Crystalline Nanoporous Materials Based on Poly(2,6‐dimethyl‐1,4‐phenylene)oxide

SummaryDifferent types of crystalline nanoporous materials (powders, films, aerogels) based on poly(2,6‐dimethyl‐1,4‐phenylene)oxide can be easily obtained depending on the preparation procedures. The nanoporous nature of the crystalline phase confers to these materials peculiar transport properties which make them particularly interesting for a potential use as a sorption medium to remove traces of pollutants from water and air or for membrane based gas separation processes. Different aspects relative to the structure and the transport properties of these new polymeric materials are described.

Modeling and simulation of sour gas membrane-absorption system: Influence of operational parameters on species removal

Membrane-based gas separation process is an effective method for separation of species from gas mixtures. Combination of membrane process with other separation methods such as absorption is an appropriate method for gas separation. One of applications of hybrid systems of membrane–absorption is sour gas sweetening. In this paper, the hollow fiber membrane contactor and amine solution are used for separation of CO 2 and H 2S from CO 2/H 2S/CH 4 gas mixture. Sour gas and amine solution enter the shell and fiber respectively. CO 2 and H 2S react with the amine solution. Reaction mechanism and equations for three phases of gas, liquid, and membrane are needed for modeling of this system. MATLAB software is used for simulation. The results show that concentrations of CO 2 and H 2S decrease in the beginning of the fiber. Liquid phase is controlling phase. Furthermore, pressure increase has a positive effect on separation.

Ceramic Membranes for the Separation of Carbon Dioxide—A Review

The separation and sequestration of CO2 produced from the combustion of fossil fuels is the need of the day to encounter ‘Greenhouse Effect’ and ‘Global Warming’. Again, it is quite important also for improving the calorific value of natural gas and for reutilization of flue gas. Membrane technology has the potential to play a crucial role in this regard. Compared to other traditional techniques for the separation and sequestering of CO2, membrane technology, particularly ceramic membrane, is still in relatively developing stage. But it has tremendous potential to emerge as a successful technology to meet the requirement in future. This article reviews previous works and recent achievements by different researchers on various CO2 selective ceramic membranes with reference to other type of membranes, like polymeric, hybrid and mixed matrix type. It also discusses various gas transport mechanism in membranes, different features of ceramic membranes, parameters that affect the gas separation in ceramic membranes, new generation ceramic and other types of membranes, industrial applications of membrane based gas separation process and future direction in membrane research.

Mesoporous germanium-rich chalcogenido frameworks with highly polarizable surfaces and relevance to gas separation

Mesoporous materials with tunable non-oxidic framework compositions can exhibit new kinds of functionality including internal surfaces with high polarizability. As the chemical and physical characteristics of the framework components can induce useful catalytic, absorption and optoelectronic features, the mesoporous structure can promote fast mass diffusion kinetics and size-selective transport of guest molecules. So far, synthetic efforts have resulted in mesoporous metal chalcogenides on using structure-directing moulds of soft or hard templates. These include ordered mesoporous II-VI semiconductors (such as CdS (refs 2,3), ZnS (ref. 4) and CdTe (ref. 5)). Recently, template-free synthetic routes for high-surface-area chalcogenide aerogels have been reported. Here, we describe a novel kind of porous materials based on germanium-rich chalcogenide networks and 'soft' highly polarizable surfaces. We demonstrate that these materials can exhibit excellent selectivity for separating hydrogen from carbon dioxide and methane. These highly polarizable mesoporous structures have important implications for membrane-based gas separation process technologies including hydrogen purification.

A general model for membrane-based separation processes

A separation process could be defined as a process that transforms a given mixture of chemicals into two or more compositionally distinct end-use products. One way to design these separation processes is to employ a model-based approach, where mathematical models that reliably predict the process behaviour will play an important role. In this paper, modelling of membrane-based processes for separation of gas and liquid mixtures are considered. Two general models, one for membrane-based liquid separation processes (with phase change) and another for membrane-based gas separation are presented. The separation processes covered are: membrane-based gas separation processes, pervaporation and various types of membrane distillation processes. The specific model for each type of membrane-based process is generated from the two general models by applying the specific system descriptions and the corresponding modelling assumptions. Analyses of the generated models, together with their validation and application in process design/analysis are highlighted through several case studies.

Medium-Pressure Clathrate Hydrate/Membrane Hybrid Process for Postcombustion Capture of Carbon Dioxide

This study presents a medium-pressure CO2 capture process based on hydrate crystallization in the presence of tetrahydrofuran (THF). THF reduces the incipient equilibrium hydrate formation conditions from a CO2/N2 gas mixture. Relevant thermodynamic data at 0.5, 1.0, and 1.5 mol % THF were obtained and reported. In addition, the kinetics of hydrate formation from the CO2/N2/ THF system as well as the CO2 recovery and separation efficiency were also determined experimentally at 273.75 K. The above data were utilized to develop the block flow diagram of the proposed process. The process involves three hydrate stages coupled with a membrane-based gas separation process. The there hydrate stages operate at 2.5 MPa and 273.75 K. This operating pressure is substantially less than the pressure required in the absence of THF and hence the compression costs are reduced from 75 to 53% of the power produced for a typical 500 MW power plant.

Polymeric Membranes for Natural Gas Conditioning

All raw natural gas needs conditioning. Polymeric membrane based gas separation processes, being cost and energy effective, environmentally friendly, as well as simple and versatile, have proven their potential as better alternatives to traditional processes for natural gas over the last three decades. In this article, the polymeric membrane based separation mechanisms for natural gas are analyzed. Two major membrane-based conditioning processes, acid gas removal from natural gas, and natural gas dehydration are presented. The current status, membrane material used, technological processes, limitations, and attractive approaches to overcome these limitations of these applications are discussed.