Multi-stage Membrane Research Articles

Fractionation of complex aromatic hydrocarbon mixtures using membrane cascades hybridized with distillation

Membrane-based separations are a promising technology to enable reductions in process intensity in chemical processing industries. However, membrane-based complex mixture fractionation is a nascent process, and these systems may require several membrane stages to achieve product specifications. Here, we highlight an example multi-stage fractionation process for complex aromatic hydrocarbon mixtures. Three separate hollow fiber membrane modules with varying hydrocarbon molecular weight cut offs were used for this experimental demonstration of a multi-stage membrane separation of a synthetic crude oil that is loosely based on the actual composition of light Permian oil. Moreover, the potential energy benefit of a traditional distillation combined with membrane cascade systems was investigated by combining a transport model based on the dry glass reference perturbation theory (DGRPT) and a process simulator. The work highlights that the heat energy duty of a distillation column can be reduced by more than 50 % when hybridized with a membrane cascade.

Air gap membrane distillation unit operated by thermoelectric module

Membrane Distillation (MD) is a promising and evolving technology with substantial potential for efficient freshwater production. However, most of the traditional MD systems typically incorporate several components, including a coolant chamber, coolant stream, coolant pump, chiller, and coolant lines. Eliminating these key components offers numerous benefits to MD systems. Therefore, this work presents an experimental investigation of a novel hybrid air gap membrane distillation (AGMD) unit coupled with thermoelectric modules (TEMs). The thermoelectric module acts as a heat pump by simultaneously providing both the heating and the cooling demands of the air gap membrane distillation unit. In the TEM-AGMD prototype, the hot surface of the TEM is deployed to heat the feed stream to be treated, while the cold side of the TEM is in close contact with the AGMD condensation plate, thereby eliminating the need for the cooling stream, coolant line, coolant pump, chiller, and coolant chamber. Thus, the investigated system exhibited fewer components and needed no pumping power for the cooling stream, resulting in a compact and an energy efficient membrane distillation (MD) system. Results from the experiment indicate that optimal system performance can be achieved by increasing the number of thermoelectric modules, implementing multi-stage membrane distillation, and intensifying the circulating feed flowrate. Furthermore, operating the thermoelectric modules at high power input boosts unit productivity but worsens the unit's specific energy consumption. Moreover, the proposed TEM-AGMD unit can achieve a minimal specific energy consumption of 962 kWh/m3. The proposed prototype boasts an easy design that enables outstanding water desalination with exceptional salt rejection and minimal power consumption. The combination of thermoelectric module with membrane distillation, capitalizing on recent advancements in MD technology, holds great promise for developing a hybrid system for decentralized water treatment and desalination.

Process design and optimization of membrane-based CO2 capture process with experimental performance data for a steam methane reforming hydrogen plant and a coal-fired power plant

Membrane-based separation is one of the promising next-generation carbon capture technologies. High degrees of freedom in process design for multi-stage membrane networks, make it difficult to fully understand the impact of network configuration on the economics of capture and separation performance. Furthermore, the optimality in process design is heavily influenced by the levels of membrane performance and the characteristics of feed gas. Membrane model utilized for the study is validated and tuned with 183 experimental data measured at various operating conditions, having 2.45 % of overall prediction error. The superstructure-based framework for the optimization of multi-stage membrane networks is used, with which design interactions between network configurations, flue gas characteristics and membrane performance are systematically investigated. Techno-economic analysis is embedded in the optimization framework, which performs rigorous trade-off between capital and operating costs, as well as allows simultaneous determination of optimal process network configuration and operating variables. Flue gas streams emitted from a coal-fired power plant and a steam methane reforming hydrogen production plant are selected as CO2 capture sources for the analysis of flue gas characteristics. Case study shows capture cost ranged from 30.2 $/tCO2 to 79.9 $/tCO2, depending on the network configuration and design specifications, and clearly improves our techno-economic understanding on the network configuration of membrane capture process. In addition, cryogenic-hybridized membrane capture process is examined and the optimal level of enriched CO2 stream concentration between membrane capture and cryogenic distillation processes is determined. Study suggests how network configuration of membrane capture process can impact capture cost.

Design and multi-objective optimization of hybrid process of membrane separation and electrochemical hydrogen pump for hydrogen production from biogas

A new hybrid process for hydrogen (H2) production that including membrane separation, electrochemical hydrogen pump (EHP) and steam methane reforming (SMR) was proposed. Firstly, the combination of two different membranes (PEO-CA) is applied to upgrade the biogas and capture CO2. Secondly, to avoid the toxic effect of CO on the EHP catalyst and, more importantly, to improve the H2 purity, the reforming reaction module is supplemented with water gas shift after the SMR. Finally, EHP is used to achieve high purity hydrogen. Simultaneously, the heat and power integration are considered to improve system efficiency. Sensitivity analysis, maximal information coefficient method and response surface methodology are applied to establish the correlation between objectives and parameters. Then, the second generation multi-objective non-dominated genetic algorithm (NSGA-II) is utilized to achieve minimum levelized cost of hydrogen (LCoH) and carbon emission per unit of hydrogen (ECO2). The optimized LCoH is 2.72 $/kgH2, and the ECO2 is 3.24 kgCO2e. Multi-stage membrane carbon capture process enhances CH4 conversion in SMR. The application of EHP reduces energy consumption and enhances hydrogen yield compared to PSA. The innovative use of membrane is hybridized with EHP to achieve the system intensification. The new hybrid process has a significant advantage in terms of ECO2 (37.45% reduction), although the price is higher compared to conventional biogas-to-hydrogen processes. Thus the new process is a promising low-carbon hydrogen production process from biogas.

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.

Biogas upgrading to biomethane with zeolite membranes: Separation performance and economic analysis

Biogas represents an important renewable source alternative to fossil fuels, which can significantly contribute to the reduction of global warming and the gradual decarbonisation. In this work, the purification of CH4 and CO2 from a biogas mixture was investigated using DD3R zeolite membrane modules, as a possible solution to replace the traditional techniques at higher environmental impact (i.e., solvent absorption and cryogenic distillation). Multistage membrane configurations operating at 25°C and 30 bar were proposed and explored to get highly pure biomethane (concentration of 98 %) and carbon dioxide (concentration of 99.5 %), imposing a recovery of both the species higher than 90 %. Then, an economic analysis was carried out, evaluating the economic potential of each configuration as a function of several parameters, such as membrane module cost, biomethane selling price, CO2 permeance, CO2/CH4 selectivity, feed flow rate and pressure. The multistage schemes were found to be promising in a wide range of zeolite membrane module cost (i.e., up to 2000 $/m2), providing positive values of the economic potential, due to the good recovery of both the components, which produced high revenues. The increment of the CO2 permeance and, especially, of the feed flow rate (i.e., plant size) allowed for a more profitable process. In particular, if feed flow rate increased from 100 to 1000 Nm3/h, the economic potential would grow of about 12 times, from 113 to 1370 thousand dollars per year. Hence, this preliminary economic assessment showed that zeolite membranes can be successfully used in biogas treatment to get pure CH4 and CO2. Such an analysis can be applied to any membrane materials, once permeance and selectivity are fixed.

Economic and operational assessment of solar-assisted hybrid carbon capture system for combined cycle power plants

The paper presents a post-combustion CO2 capture process which involves two configurations for enhancing the CO2 separation driving force in the conventional amine-based Carbon Capture System (CCS): a multi-stage membrane module for selective exhaust gas recirculation (SEGR case) and the combination of turbine exhaust gas recirculation with SEGR (EGR + SEGR case). Furthermore, the stripper reboiler in both configurations is integrated with a parabolic trough solar collector field with a 4-h thermal energy storage to provide the required thermal duty for solvent regeneration. Various system components are designed, simulated, and integrated with an economic model to evaluate the system's techno-economic performance across a wide range of loads. The results show that the proposed designs have efficient part-load performance although efficiency degradation is inevitable during partial-loads. A stable supply of solar thermal energy results during the partial operation of NGCC even during night. The EGR + SEGR case represents the case with the lowest levelized cost of electricity and CO2 avoided cost, 81.43 $/MWh and 101.66 $/tonneCO2, among the CCS-equipped designs, which highlight the advantages of this design over baseline and SEGR case. The proposed hybrid system shows promise for significantly decarbonizing fossil-fuel power plants and increasing power sector flexibility.

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.

Multi-stage membrane integrated system to achieving low-mixed-salt-discharge of high-salinity mining wastewater: System design and experimental validation

Minimizing the release of highly saline mine wastewater is crucial in order to meet the zero liquid discharge requirement of the coal chemical industry. However, the inorganic salts produced, such as NaCl and Na2SO4, have low value and are difficult to consume locally, particularly in western China. Therefore, this study proposes the multi-stage membrane integrated system with the aim of achieving low discharge of mixed salts in high-salinity mining wastewater. Two different combinations of reverse osmosis (RO), nanofiltration (NF), electrodialysis (ED), and bipolar membrane electrodialysis (BMED) are proposed for the integrated system, specifically designed for treating Bulianta coal mining wastewater ZLD projects in Inner Mongolia, western China. To compare the effectiveness of these combinations, experimental tests were conducted using ED to concentrate pure solutions of NaCl and Na2SO4 separately. The results indicated that, in terms of energy consumption for transferring the same charge across the membrane, Na2SO4 solution was more suitable to be concentrated than NaCl solution under low feed concentration (cation concentration<1.0 M) in ED, and the corresponding energy saving to transfer on unit charge significantly decreased from 6.15 × 10−3 kWh/mol charge to 1.60 × 10−4 kWh/mol when cation concentration ranged from 0.2 M to 1.0 M. Then, the production of acid and base in BMED was experimentally investigated using Na2SO4 solution and a mixed solution of NaCl and Na2SO4. Results revealed that the energy consumption decreased from 150.62 Wh/[H++OH-]mol to 97.88 Wh/[H++OH-]mol when the Na2SO4 solution increased from 0.2 M to 1.4 M, meanwhile the energy consumption for mixed solution of NaCl and Na2SO4 is strongly related to the mole ratio of Na2SO4 to NaCl. Thus, the utilization of NF membranes with high selectivity for Na2SO4 over NaCl in the NF stage, combined with high feed concentrations in the ED stage, is crucial for achieving lower energy consumption in BMED. Based on experimental results and analyses, the NF concentrate is more effectively treated in ED and BMED when dealing with mining wastewater with a high mole ratio of Na2SO4 to NaCl (>1).

Eat your beets: Conversion of polysaccharides into oligosaccharides for enhanced bioactivity

Bioactive oligosaccharides with the potential to improve human health, especially in modulating gut microbiota via prebiotic activity, are available from few natural sources. This work uses polysaccharide oxidative cleavage to generate oligosaccharides from beet pulp, an agroindustry by-product. A scalable membrane filtration approach was applied to purify the oligosaccharides for subsequent in vitro functional testing. The combined use of nano-LC/Chip Q-TOF MS and UHPLC/QqQ MS allowed the evaluation of the oligosaccharide profile and their monosaccharide complexity. A final product containing roughly 40 g of oligosaccharide was obtained from 475 g of carbohydrates. Microbiological bioactivity assays indicated that the product obtained herein stimulated desirable commensal gut bacteria. This rapid, reproducible, and scalable method represents a breakthrough in the food industry for generating potential prebiotic ingredients from common plant by-products at scale. Industrial relevanceThis work proposes an innovative technology based on polysaccharide oxidative cleavage and multi-stage membrane purification to produce potential prebiotic oligosaccharides from renewable sources. It also provides critical information to evidence the prebiotic potential of the newly generated oligosaccharides on the growth promotion ability of representative probiotic strains of bifidobacteria and lactobacilli.

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.

Model-Based Optimization of Multi-Stage Nanofiltration Using the Solution-Diffusion–Electromigration Model

Nanofiltration is well suited to separate monovalent ions from multivalent ions, such as the separation of Li+ and Mg2+ from seawater, a potential lithium source for the production of lithium-ion batteries. To the best of our knowledge, there is no existing work on the optimization of a multi-stage membrane plant that differentiates between different ions and that is based on a validated transport model. This study presents a method for modeling predefined membrane interconnections using discretization along the membrane length and across the membrane thickness. The solution-diffusion–electromigration model was used as the transport model in a fundamental membrane flowsheet, and the model was employed to optimize a given flowsheet with a flexible objective function. The methodology was evaluated for three distinct separation tasks, and optimized operating points were found. These show that permeances and feed concentrations might cause negative rejections and positive rejections (especially for bivalent ions) depending on the ions’ properties and fluxes, thereby allowing for a favorable separation between the ions of different valence at optimized conditions. In an application-based case study for the separation of Li+ and Mg2+ from seawater, the method showed that under optimal conditions, the mol-based ratio of Mg2+/Li+ can be reduced from 2383 to 2.8 in three membrane stages.

Model-based optimization of multistage ultrafiltration/diafiltration for recovery of canola protein

The ultrafiltration/diafiltration (UF/DF) process is a crucial step in the canola protein isolation process from rapeseed meal. The process involves using a multi-stage membrane system to separate components of the mixture. As diafiltration dilutes the feed stream in the ultrafiltration system, a large amount of diafiltration water is required. Reducing the diafiltrate for sustainability reasons can be done by carefully selecting process variables or using recycle streams. However, finding the optimum process variables can be a meticulous process if performed experimentally or via trial and error. In this study, we performed an optimization using a mechanistic model integrated with a genetic algorithm to aid in finding an optimum combination of process variables. The mechanistic ultrafiltration model was derived by taking into account transport phenomena within the filtration system. Parameters were characterized experimentally in term of viscosity coefficient, membrane resistance, cake porosity, aggregate diameter equivalent, and material compressibility factors. Using the mechanistic model-based optimization in combination with actual experimental values, the performance of a four-stage UF/DF system could already be improved despite fixing the configuration, albeit at the cost of a reduction in purity. Further improvement could be achieved by using recycle streams. The optimized system achieved a diafiltrate reduction of up to 79%, an increase of purity of up to 31%, and an increase of dry matter content of up to 18%, while maintaining the product purity of the reference set-up.

Pressure-driven membrane nutrient preconcentration for down-stream electrochemical struvite recovery

Nutrient recovery from wastewater is a sustainable solution to combat the harmful release of nutrients to the environment. Here, we investigate nutrient recovery from wastewater by pre-concentration of wastewater nutrients using pressure-driven membranes prior to downstream electrochemical nutrient precipitation. When using electrochemical struvite precipitation, a higher nutrient concentration leads to a higher precipitation efficiency. Therefore, we investigate the performance of commercial nanofiltration (NF) and reverse osmosis (RO) membranes with different polymer chemistry and molecular weight cut-offs (MWCO) and discuss the membrane selection based on design goals and wastewater compositions for maximum nutrient recovery efficiency. Our results indicated that the Alfa membrane, a polyamide thin film composite (PA-TFC) NF membrane with 300 Da MWCO has the highest concentration factor in phosphorus (P) preconcentration among all the membranes studied due to the high flux and removal efficiency. BW30LE (PA-TFC, 100 Da), Synder (PA-TFC, 100–250 Da) and NF90 (PA-TFC, 200–400 Da) achieved a high concentration factor for nitrogen (N) recovery. NF90 and Synder NF membranes are able to achieve a nitrogen concentration factor similar to BW30LE RO membrane at much lower energy consumption. A multistage membrane system design is suggested using the selected membranes for effective nutrient recovery. Life cycle assessment (LCA) was conducted to characterize the environmental impact of the multistage membrane nutrient recovery system. Among the different process configurations of the selected membranes, key trends included: 1) environmental impacts across most categories increased as the number of membranes increased, and 2) as the amount of fertilizer substitute that could be produced in a given configuration increased, total environmental impacts decreased with some exceptions.

Hybrid multi-stage flash (MSF) and membrane distillation (MD) desalination system for energy saving and brine minimization

A hybrid multi-stage flash and multi-stage membrane distillation system for freshwater recovery from the rejected MSF brine is studied. The proposed system reduces environmental impact through reducing the rate of rejected brine, desalination energy and product cost. This is achieved by utilizing the energy rejected from the brine heater to heat a portion of MSF reject that is fed into the MD system since MD systems operate at relatively low temperature and are tolerant to high salinity input. The system includes a multi-stage MD system with a capacity ranging from 75 to 200 m3/day that help in reducing brine volume as model novelty. MD energy is supplied from the condensate leaving MSF brine heater. The effect of MD feed inlet temperature on the performance of stand-alone MD and hybrid MSF-MD systems is investigated for various layouts of the integrated system. Performance of the proposed system is quantified in terms of productivity, MD gained output ratio (GOR), specific electric energy consumption (SEEC), freshwater recovery rate (RR) and water cost. The hybrid MSF-MD system can be used for rejected brine reduction. Parallel feed – parallel coolant integrated arrangement provides the best performance among other configurations, with a productivity, RR, GOR, and SEEC of 218.3 m3/day, 3.544 %, 0.921 and 1.107 kWh/m3, respectively for the MD system. Additionally, the hybrid MSF-MD system yielded about 30,098m3/day, 57.544 %, and 8.583 in productivity, RR and GOR, respectively. MD freshwater cost is reduced by 70 % - 90 % compared to the conventional MD system with an independent energy supply.

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.

Removal of glycerol from biodiesel using multi-stage microfiltration membrane system: industrial scale process simulation

Abstract Biodiesel purification is one of the most important downstream processes in biodiesel industries. The removal of glycerol from crude biodiesel is commonly conducted by an extraction method using water, however this method results in a vast amount of wastewater and needs a lot of energy. In this study, microfiltration membrane was used to remove glycerol from biodiesel, and a process simulation was carried out for an industrial scale biodiesel purification plant using a microfiltration membrane system. The microfiltration experiment using a simulated feed solution of biodiesel containing glycerol and water showed that the membrane process produced purified biodiesel that met the international standards. The result of the process simulation of a multi-stage membrane system showed that the membrane area could be minimized by optimizing the concentration factor of every stage with the aid of a computer program that was written in Phyton programming language with Visual Studio Code. The overall productivity of a single stage membrane system was the same with that of the multi-stage system, however the single stage system required a larger membrane area. To produce 750 m3 day−1 of purified biodiesel, a multi-stage membrane system consisting of 10 membrane modules required a total membrane area of 1515 m2 that was 57% smaller compared to the single stage system consisting of one membrane module. This membrane area reduction was equivalent to a reduction of the total capital cost of 30%. Based on the analysis of the total capital cost, it was found that the optimum number of stages was 4 since it showed a minimum value of the total capital cost with a membrane area of 1620 m2 that was equivalent to the reduction of the total capital cost of 34%. The result of this simulation showed that the multi-stage microfiltration membrane has great potential to replace the conventional method in biodiesel industries.

Optimization-based technoeconomic comparison of multi-stage membrane distillation configurations for hypersaline produced water desalination

Unconventional oil and gas production raises concerns regarding sustainable management of high salinity wastewaters generated in this process. Membrane distillation (MD) is a thermal desalination process capable of treating hypersaline brines such as produced water. The low single pass recovery in MD systems operated in a single stage requires a large recycle stream to achieve the desired recovery, resulting in high energy consumption and operating cost. Multistage configurations in continuous recirculation operation mode offer the potential to reduce the energy intensity of MD systems. However, rigorous analysis is needed to assess the performance of MD configurations when operating in multi-stage mode. We present an optimization-based comparison of economic and energetic performance for five configurations of MD (including DCMD, AGMD, PGMD, CGMD, and VMD) operating in multi-stage continuous recirculation mode. Our findings demonstrate that multistage operation reduces the treatment cost and energy intensity of all MD configurations compared to single stage MD, with the greatest benefit for VMD and PGMD. AGMD with five stages outperforms other configurations with 3.58 $/m3feed treatment cost, followed by VMD, CGMD, DCMD, and PGMD with 3.8, 4.2, 5.4, and 9.06 $/m3feed treatment costs corresponding to twelve, eight, eight, and sixteen stages, respectively.

Membrane-assisted natural gas liquids recovery: Process systems engineering aspects, challenges, and prospects

Membrane-based natural gas liquid (NGL) recovery processes are still far from their large-scale applications owing to communication gaps among academic researchers and industry practitioners. A comprehensive process systems engineering (PSE) assessment of membrane-based NGL recovery processes is required to determine their commercial suitability. This PSE-based review presents the technical and economic aspects of standalone and integrated membrane processes. Literature review shows that polymeric membranes (e.g., cellulose acetate) are primarily evaluated in NGL recovery processes despite their low separation efficiencies. So far, multiple multistage membrane models with standalone and integrated designs have been suggested by analyzing different configurations to improve separation efficiency. In standalone processes, cellulose acetate membrane modules with high selectivity ratio can improve methane recovery by up to 100%. Absorption or cryogenic integrated processes exhibit high methane recovery (up to 99%) but demonstrate high energy consumption. The integrated absorption–membrane process is more capital cost intensive (i.e., 0.41 m$) than the cryogenic–membrane process (0.39 m$). Furthermore, in this review, the key challenges encountered by membrane processes and related issues are identified to improve their commercial viability by capitalizing on their maximum potential benefits. The major challenges associated with membrane processes constitute the lack of rigorous multistage membrane models and inflexibility in product purity and recovery. The policy implications and future directions suggest that owing to the growing demand for NGLs, membranes that can sustain varying natural gas compositions and conditions may be required. This PSE assessment will help process engineers and policymakers to improve natural gas supply chain economics.

A review of multistage membrane filtration approaches for enhanced efficiency during concentration and fractionation of milk and whey

This review considers the impact of combining discrete membrane filtration configurations in a multistage or sequential configuration to improve processing performance, energy efficiency and component selectivity in dairy processes. The review focuses on the impact of multistage membrane filtration on (i) concentration processes, through the examination of fouling accumulation and its impact on flux and energy efficiency, and (ii) fractionation processes, whereby the yield/purity of dairy components is assessed. Observations from single‐stage and batch microfiltration, ultrafiltration, nanofiltration and reverse osmosis processes reported in the literature are compared to the continuous multistage filtration processes common in commercial dairy installations.