Multistage Membrane Process Research Articles

Analysis and comparison of the membrane-cryogenic hybrid process and multistage membrane process for pre-combustion carbon capture based on the superstructure method

The feed in pre-combustion carbon capture has a high CO2 concentration and high pressure, which gives membrane technology and membrane-based hybrid technology a strong separation driving force. Because the membrane-cryogenic hybrid method can inexpensively achieve the high CO2 purity and recovery, it offers a novel approach in addition to traditional separation methods. Nevertheless, it is uncommon to consider the combination of membrane materials and processes. Furthermore, investigations comparing multistage membrane processes with membrane-cryogenic hybrid processes under identical conditions are lacking. Therefore, this paper establishes separately the membrane-cryogenic hybrid processes and multistage membrane process by the superstructure method, which considers the number of membrane stage, membrane material type, and operating parameters simultaneously. The optimal process structures for three-stage membrane, cryogenic-membrane process, and membrane-cryogenic process are investigated and compared. The influences of membrane price and electricity price on the CO2 capture cost are also investigated. Results shows that the CO2 capture cost of cryogenic + membrane process is the lowest (11.69 $/t CO2) of the studied processes at 96 % CO2 purity and 90 % CO2 recovery. The system structure of the cryogenic + membrane process varies with CO2 purity and recovery. Electricity price has a more important impact on the CO2 capture cost than membrane price under the optimized conditions.

Modeling and optimization of an integrated membrane – P/VSA separation process for CO2 removal from coal plant flue gas

This work presents a mathematical framework for the simulation and optimization of an integrated membrane – Pressure/Vacuum Swing Adsorption (P/VSA) process for CO2 removal from coal plant flue gas. The integrated process includes a membrane module in the first stage and a P/VSA unit in the second stage and it is optimized to minimize energy requirement for 95% and 90% total CO2 purity and recovery, respectively. Three membrane specifications, with CO2/N2 selectivity of 75, 50 and 25, and two adsorbents, zeolite 13X and MOF UTSA-16, are examined. The configuration which includes a membrane module with a CO2/N2 selectivity of 75 followed by a P/VSA unit with a UTSA-16 adsorbent leads to a minimum energy demand of 163 kWh/tn CO2, which is lower than the energy requirements of competitive CO2 separation processes, such as a two-stage P/VSA and multi-stage membrane processes. In addition, lowering the CO2/N2 selectivity from 75 to 50, leads to a minimum energy requirement of 177 kWh/tn CO2, which is still competitive to the other CO2 capture technologies. Furthermore, a comparison between different operating temperatures demonstrates that although a higher temperature increases the total energy demand, it has no impact on the optimal operating conditions and separation efficiency.

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.

Sustainability Enhancement of Fossil-Fueled Power Plants by Optimal Design and Operation of Membrane-Based CO2 Capture Process

Fossil-fueled power plants are a major source of carbon dioxide (CO2) emission and the membrane process is a promising technology for CO2 removal and mitigation. This study aims to develop optimal membrane-based carbon capture systems to enhance the sustainability of fossil-fuel power plants by reducing their energy consumption and operating costs. The multi-stage membrane process is numerically modeled using Aspen Custom Modeler based on the solution-diffusion mechanism and then the effects of important operating and design parameters are investigated. Multi-objective process optimization is then carried out by linking Aspen Plus with MATLAB and using an evolutionary technique to determine optimal operating and design conditions. The results show that, as the CO2 concentration in the feed gas increases, the CO2 capture cost significantly decreases and CO2 removal is enhanced, although the process energy demand slightly increases. The best possible trade-offs between objective functions are reported and analyzed, which confirm the considerable potential for improving the sustainability of the process. The CO2 capture cost and energy penalty of the process is as low as 13.1 $/tCO2 and 10% at optimal design and operating conditions. This study provides valuable insight into membrane separation and can be used by decision-makers for the sustainable improvement of fossil-fueled power plants.

Techno-Economic Optimization of Multistage Membrane Processes with Innovative Hollow Fiber Modules for the Production of High-Purity CO2 and CH4 from Different Sources.

Within the current climate emergency framework and in order to avoid the most severe consequences of global warming, membrane separation processes have become critical for the implementation of carbon capture, storage, and utilization technologies. Mixtures of CO2 and CH4 are relevant energy resources, and the design of innovative membranes specifically designed to improve their separation is a hot topic. This work investigated the potential of modified polydimethylsiloxane and ionic liquid–chitosan composite membranes for separation of CO2 and CH4 mixtures from different sources, such as biogas upgrading, natural gas sweetening, or CO2 enhanced oil recovery. The techno-economic optimization of multistage processes at a real industrial scale was carried out, paying special attention to the identification of the optimal configuration of the hollow fiber modules and the selection of the best membrane scheme. The results demonstrated that a high initial content of CH4 in the feed stream (like in the case of natural gas sweetening) might imply a great challenge for the separation performance, where only membranes with exceptional selectivity might achieve the requirements in a two-stage process. The effective lifetime of the membranes is a key parameter for the successful implementation of innovative membranes in order to avoid severe economic penalties due to excessively frequent membrane replacement. The scale of the process had a great influence on the economic competitiveness of the process, but large-scale installations can operate under competitive conditions with total costs below 0.050 US$ per m3 STP of treated feed gas.

Numerical Simulation and Optimization of 4-Component LDG Separation in the Steelmaking Industry Using Polysulfone Hollow Fiber Membranes.

A general finite element model and a new solution method were developed to simulate the permeances of Lintz Donawiz converter gas (LDG) components and the performance of a polysulfone membrane separation unit. The permeances at eight bars of CO, N2, and H2 in LDG simulated using the developed model equations employing the experimental mixed gas data were obtained by controlling the finite element numbers and comparing them with pure gas permeation data. At the optimal finite element numbers (s = 15, n = 1), the gas permeances under the mixed-gas condition were 6.3% (CO), 3.9% (N2), and 7.2% (H2) larger than those of the pure gases, On the other hand, the mixed-gas permeance of CO2 was 4.5% smaller than that of pure gas. These differences were attributed to the plasticization phenomenon of the polysulfone membrane used by CO2. The newly adopted solution method for the stiff nonlinear model functions enabled the simulation of the performance (in terms of gas recovery, concentration, and flow rate) of the first-stage membrane within two seconds under most gas flow conditions. The performance of a first-stage membrane unit separating LDG could be predicted by the developed model with a small error of <2.1%. These model and solution methods could be utilized effectively for simulating gas permeances of the membrane that is plasticized severely by the permeating gas and the separation performance of two- or multi-stage membrane processes.

Separation of nitrogen from methane by multi-stage membrane processes: Modeling, simulation, and cost estimation

This study focuses on the application of multi-stage membrane separation processes for the removal of nitrogen from natural gas. Reliable modeling and process simulation are essential for the analysis of the gas separation process. A mathematical model was developed using thermodynamic models, like lattice fluid (LF) and non-equilibrium lattice fluid (NELF), for gas sorption and transfer model for gas diffusion in the membrane. The proposed mass transfer model was validated with the experimental data for the gas solubility and permeability in various glassy and rubbery membranes. Then the proposed model was coupled with Aspen Plus software (Aspen Tech) for simulation of different proposed configurations of the multi-stage membrane processes. The performance of various gas separation configurations was investigated in terms of product purity, methane recovery, total capital investment, and total annual cost. The results indicated that the membranes with higher permeability had more suitable economic parameters. For example, the total annual cost for the AF1600 membrane was seven times the total annual cost value for the PTMSP membrane in the single-stage membrane separation process. It was observed that the methane purity of above 96 %mol and methane recovery of 90% could not be achieved by the single-stage process. However, the specified separation criteria can be achieved via the multi-stage membrane processes by two or three membranes. The best configuration was selected from various proposed configurations by evaluating the economic parameters.

Multi-stage gas separation process for separation of carbon dioxide from methane: Modeling, simulation, and economic analysis

The emphasis of this study is the use and comparison of the rubbery and glassy membranes in the multi-stage gas separation process for separation of the CO2/CH4 mixtures. For analysis of the gas separation processes, reliable modeling and simulation of the process are essential. Thermodynamic models of lattice fluid (LF) and non-equilibrium lattice fluid (NELF) were used to model the gas sorption in the rubbery and glass membranes, respectively, and a transfer model was employed to model the gas diffusion. The developed model was integrated with the Aspen Custom Modeler (ACM) of Aspen Plus software to simulate various proposed gas separation processes. The performance of single-stage and multi-stage processes was evaluated in terms of the CH4 recovery, product purity, total capital investment, and total annual cost. It was found that the membranes with higher permeability had more suitable economic parameters than the membranes with high CO2/CH4 selectivity. The results showed that the CH4 recovery of 99% and product purity of 98% could not be achieved by the single-stage process. However, the desired separation criteria can be met via the multi-stage membrane processes with two or three membranes. The best configuration was chosen from different configurations by examining the economic parameters.

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...

Downstream separation and purification of bio-based alpha-ketoglutaric acid from post-fermentation broth using a multi-stage membrane process

In this study, a multi-stage membrane process, assisted by vacuum evaporation and crystallization, for recovery of bio-based alpha-ketoglutaric acid from the actual post-fermentation broth was designed and investigated. In the first part of this study, pre-treatment of crude fermentation broth (centrifugation-ultrafiltration-nanofiltration) was carried out to remove biomass, proteins, sugars, part of inorganic ions and color compounds. The commercial ceramic UF membrane (15 kDa) and nanofiltration ceramic membrane (200 Da or 450 Da) were applied. Electrodialysis with a bipolar membrane was proposed for separation of ionic compounds and simultaneous electro-acidification to the acid form. During bipolar membrane electrodialysis carried out under acidic conditions, it was possible to remove close to 90 % of alpha-ketoglutaric acid. Moreover, the migration of other acids present in the fermentation broth (lactic and acetic) was significantly limited. The calculated specific energy consumption was low and equal to 0.6 kW h/kg. The final purification using crystallization assisted vacuum evaporation allowed obtaining alpha-ketoglutaric acid in solid form. Analysis of the final product showed that the proposed method of alpha-ketoglutaric acid recovery gives the acid of high purity equal to 94.8 %. Furthermore, the presented results have practical relevance and may in future be the basis for the development of separation technologies of alpha-ketoglutaric acid from the fermentation broth on industrial scale.

No-mixing-loss design of a multistage membrane carbon capture process for off-gas in thermal power plants

Carbon capture and storage (CCS) is a promising method for limiting the effects of global warming. A multistage membrane process is needed to capture and recover high-purity CO2 from off-gas with low CO2 concentrations in thermal power plants. In this study, a simple design method based on the “no-mixing-loss” concept was suggested. The performance of the process could be improved by avoiding mixing loss and the optimization process was simplified using a reduced number of optimization parameters. The feed and permeate pressure, and the design criteria of CO2 concentration at the retentate side in each section were considered as decision variables for optimizing the process with a target purity of 95% and a target recovery of 90%. Three-, five-, and seven-stage processes were designed and evaluated in terms of energy consumption and capture cost. In addition, a well-designed inner cooling system in the pressure units enhanced compressor efficiency and contributed to the reduction in energy consumption and costs.

Polymeric membrane materials for nitrogen production from air: A process synthesis study

Nitrogen production from air by membrane gas separation processes is a mature technology which is applied in numerous industrial sectors (chemical, food, aeronautics, space..). Depending on the nitrogen purity requirements (typically between 90 and 99.9%), single stage or multistage membrane process configurations are used. A very large number of advanced membrane materials have been recently reported, showing increasing permeability and/or selectivity for air separation applications (i.e. trade-off limits of dense polymeric materials for the O2/N2 gas pair) compared to the commercially available membranes. The interest of these new materials in terms of nitrogen production cost and their impact in terms of process configuration are reported through a process synthesis study. Based on a tailor made optimization methodology and program, the production cost and associated optimal process configuration are first identified for two standard O2/N2 separation membranes at four different levels of N2 purity (90, 95, 99, 99.9%). The same strategy is then performed with advanced trade-off membrane materials, with the possibility to combine different materials in multistaged systems. The impact in terms of nitrogen production cost for the different purities and the corresponding optimal membrane materials and process configurations are discussed. Surprisingly, a medium membrane selectivity combined to a high permeability is shown to systematically offer the best set of performances, for mono or multistaged systems. Vacuum operation and recycling loops are shown to generate lower N2 production costs.

Optimization of multistage olefin/paraffin membrane separation processes through rigorous modeling

AbstractIn this work, we explore the capabilities of an NLP optimization model to determine the viability of facilitated transport membrane processes intended to replace traditional distillation currently employed for propane/propylene separation. An NLP optimization model for multistage membrane processes has been formulated, introducing the mathematical description of the facilitated transport mechanisms in the PVDF‐HFP/BMImBF4/AgBF4 membranes previously developed by our research group. For the first time, a simultaneous optimization of the process and the membrane material (i.e., carrier concentration) has been performed, thanks to the implementation of the governing equations for the fixed site and mobile carrier mechanisms. Once the model is solved in GAMS it returns the optimal membrane area, carrier loading and permeate pressure of each stage based on Net Present Value Cost (NPVC) minimization. Different process flow sheets were evaluated and the results show prominent reductions on NPVC for facilitated transport multistage processes when compared to distillation.

Development of novel sub-ambient membrane systems for energy-efficient post-combustion CO2 capture

A substantial increase in CO2/N2 selectivity of the membrane under sub-ambient temperature conditions allows the design of CO2 capture processes in an energy-efficient and cost-effective manner. An innovative sub-ambient temperature membrane process is proposed in this study for the separation of CO2 from power plant flue gases, in which the high membrane selectivity is strategically utilized with the aid of a simple, external refrigeration cycle. In the new membrane process, a sweeping-integrated single membrane module integrated with a purification column is sufficient to achieve a high purity of 99.9% CO2 product with 90% CO2 recovery. Process optimization is utilized to determine cost-effective operating conditions and appropriate membrane configurations. The optimized sub-ambient temperature membrane process is shown to reduce the overall CO2 capture cost by 13% as well reducing the parasitic load by 16%, compared to a conventional multi-stage membrane process operated at ambient temperature conditions. The sensitivities of CO2 capture cost and energy with respect to key design variables such as pressure ratio, membrane performance (i.e. CO2 permeance and CO2/N2 selectivity) and CO2 recovery are investigated to provide conceptual insights and design guidelines for developing efficient membrane processes for the capture of CO2.

Automated process design and optimization of membrane-based CO2 capture for a coal-based power plant

A systematic optimization framework is proposed with the aim to automate the design of multi-stage membrane processes for CO2 capture from flue gas of a coal-fired power plant. This framework utilizes a superstructure approach to determine the optimal configuration of membrane systems and identify the most appropriate operating conditions in a holistic manner. Certain design specifications are satisfied through the use of penalty functions which are used in a Genetic Algorithm (GA) optimization method employed to identify design solutions at or near to the global optimal point. Sensitivity analysis is used to analyze multi-stage membrane designs to understand the effects of different structural and operating parameters on the economics of membrane-based carbon capture. As part of a case study the proposed design framework is applied to design membrane processes for the capture of CO2 from a 600 MWe coal-fired power plant. Fixed membrane permeance and selectivity values are used to analyze sensitivities with respect to costing and structural design parameters. Additionally, the Robeson upper bound correlation between CO2 permeance and CO2/N2 selectivity is used within this framework to identify the optimal membrane properties which give economical separation of CO2 and N2. It is found that membranes having at least 4000 GPU CO2 permeance and over 50 of CO2/N2 selectivity with a commercial available module gave the optimal performance and would be a good guideline for future membrane material development. Also, if different membrane properties are used in each stage (in a multi-stage configuration) then using a higher CO2 permeance for the first stage (e.g. 6000 GPU CO2 permeance and CO2/N2 selectivity of 40) and higher selectivity membranes are used for subsequent downstream membrane stages (e.g. 1334 GPU CO2 permeance and CO2/N2 selectivity of 72) helps to reduce the electricity consumption and product purity which can reduce the overall cost of CO2 capture.

Optimization model for the design and feasibility analysis of membrane-based gas separation systems for CO2 enhanced coal bed methane (CO2-ECBM) applications

The purpose of this study is the development of an optimization model to design a coal bed methane (CBM) gas separation system using a multi stage membrane process. The proposed model is formulated using a nonlinear programming (NLP) technique and includes maximizing the total profit as the objective function, along with several constraints to fulfill the design specification under various scenarios. Using the proposed model, we can (i) identify the optimal system configuration and operation strategies such as the required membrane area, the number of stages, recycle strategies, and utility consumption; and (ii) analyze the cost contribution and major cost drivers that have effects on the system configuration and economics. We also investigate the sensitivity of major parameters, including the composition of the raw CBM feed and CH4 market price on the process configurations and operation strategies that affect the overall economics of the CBM production system.

Performance study of multistage membrane and hybrid distillation processes for propylene/propane separation

This article investigates the separation performance and energy efficiency of multistage membrane and hybrid processes for the separation of propane/propylene mixtures compared with the conventional distillation process. To satisfy the separation objective of 0.996 mol/mol (99.6 mol%) C3H6 purity and 97 % C3H6 separation recovery ratio, a detailed parametric study for the multistage membrane and hybrid process systems was described. For this purpose, the effects of operating conditions and process configurations on separation performance have been evaluated using a counter‐current flow model. The numerical model using a single‐stage membrane was validated with published experimental data for the membrane system, and the model was then applied to multistage membrane and hybrid processes. The optimum variables that satisfy the targeted purity and recovery ratio were examined using the multistage membrane at a given selectivity and pressure ratio. The energy consumption of several hybrid configurations for the separation of propane/propylene mixtures was investigated with conventional distillation.

A mathematical model for zeolite membrane module performance and its use for techno-economic evaluation of improved energy efficiency hybrid membrane-distillation processes for butane isomer separations

The aim of this work is to develop enabling tools that can assess the potential of zeolite membranes for industrial applications. The specific objectives are: (1) Develop a detailed mathematical model of a zeolite membrane separation process for accurate performance prediction under industrial conditions, and (2) Perform conceptual process design and techno-economic evaluation of the overall process for an application specific flowsheet. To this end, a detailed mathematical model, based on the real adsorption solution (RAS) theory and the Maxwell-Stefan formulation for transport was developed to describe permeation through a zeolite membrane. Effects like support resistances to transport, use of sweep gas and concentration polarization were included. The model is further applied to study butane isomer separation using a MFI-type zeolite membrane. A comparison of steady state flux and separation factor predicted by the model with the experimentally determined values suggests that the permeation in the real membranes is lower than that for the zeolite crystals. This lower permeance is attributed to the microstructural defects and suggests that there is a considerable scope of improvement in the performance of current state-of-the-art real MFI membranes. It is shown that up to a 10-fold increase in permeance through the membrane is practical, beyond which the external resistance starts to dominate. Furthermore, the detailed zeolite membrane model is integrated into a process level simulation, to evaluate the membrane performance in industrial settings, and a techno-economic analysis is also performed to this end. While single stage membrane process does not achieve the target purity and multi-stage membrane process requires prohibitively large area, a hybrid membrane/distillation process is found to be energy efficient and economically attractive.

Attainability and minimum energy of multiple-stage cascade membrane systems

Process design and simulation of multi-stage membrane systems have been widely studied in many gas separation systems. However, general guidelines have not been developed yet for the attainability and the minimum energy consumption of a multi-stage membrane system. Such information is important for conceptual process design and thus it is the topic of this work. Using a well-mixed membrane model, it was determined that the attainability curve of multi-stage systems is defined by the pressure ratio and membrane selectivity. Using the constant recycle ratio scheme, the recycle ratio can shift the attainability behavior between single-stage and multi-stage membrane systems. When the recycle ratio is zero, all of the multi-stage membrane processes will decay to a single-stage membrane process. When the recycle ratio approaches infinity, the required selectivity and pressure ratio reach their absolute minimum values, which have a simple relationship with that of a single-stage membrane process, as follows: Sn=S1, γn=γ1, where n is the number of stages. The minimum energy consumption of a multi-stage membrane process is primarily determined by the membrane selectivity and recycle ratio. A low recycle ratio can significantly reduce the required membrane selectivity without substantial energy penalty. The energy envelope curve can provide a guideline from an energy perspective to determine the minimum required membrane selectivity in membrane process designs to compete with conventional separation processes, such as distillation.

Effectiveness of membranes and hybrid membrane processes in comparison with absorption using amines for post-combustion CO2 capture

The effectiveness of membrane processes and feasibility of hybrid processes combining membrane permeation and conventional amine absorption processes were investigated for post-combustion CO2 capture. The traditional MEA process uses a substantial amount of thermal energy at the stripper reboiler when CO2 concentration increases. Questions are sometimes raised if the membranes can compete with amine absorption for post-combustion CO2 capture. Although both processes have their own advantages, can a hybrid process for post-combustion CO2 capture be yielded combining membranes and amine absorption with cost/performance advantages? Several single stage and multi-stage membrane process configurations were simulated for a target capture requirement aiming at possible application in enhanced oil recovery. It was shown that membrane processes offer the lowest energy penalty for post-combustion CO2 capture and are likely to expand as more and more CO2 selective membranes are developed. A comparison of energy perspective for the CO2 capture processes studied was drawn, and it was shown that the energy requirements of the hybrid processes are less than conventional MEA processes. The total energy penalty of the hybrid processes decreases as more share of CO2 is removed by the membranes.