Membrane Separation Processes Research Articles

Machine Learning for Polymer Design to Enhance Pervaporation-Based Organic Recovery.

Pervaporation (PV) is an effective membrane separation process for organic dehydration, recovery, and upgrading. However, it is crucial to improve membrane materials beyond the current permeability-selectivity trade-off. In this research, we introduce machine learning (ML) models to identify high-potential polymers, greatly improving the efficiency and reducing cost compared to conventional trial-and-error approach. We utilized the largest PV data set to date and incorporated polymer fingerprints and features, including membrane structure, operating conditions, and solute properties. Dimensionality reduction, missing data treatment, seed randomness, and data leakage management were employed to ensure model robustness. The optimized LightGBM models achieved RMSE of 0.447 and 0.360 for separation factor and total flux, respectively (logarithmic scale). Screening approximately 1 million hypothetical polymers with ML models resulted in identifying polymers with a predicted permeation separation index >30 and synthetic accessibility score <3.7 for acetic acid extraction. This study demonstrates the promise of ML to accelerate tailored membrane designs.

Recent Advancement in Emerging MXene-Based Photocatalytic Membrane for Revolutionizing Wastewater Treatment.

MXene-based photocatalytic membranes provide significant benefits for wastewater treatment by effectively combining membrane separation and photocatalytic degradation processes. MXene represents a pioneering 2D photocatalyst with a variable elemental composition, substantial surface area, abundant surface terminations, and exceptional photoelectric performance, offering significant advantages in producing high-performance photocatalytic membranes. In this review, an in-depth overview of the latest scientific progress in MXene-based photocatalytic membranes is provided. Initially, a brief introduction to the structure and photocatalytic capabilities of MXene is provided, highlighting their pivotal role in promoting the photocatalytic process. Subsequently, in pursuit of the optimal MXene-based photocatalytic membrane, critical factors such as the morphology, hydrophilicity, and stability of MXenes are meticulously taken into account. Various preparation strategies for MXene-based photocatalytic membranes, including blending, vacuum filtration, and dip coating, are also discussed. Furthermore, the application and mechanism of MXene-based photocatalytic membranes in micropollutant removal, oil-water separation, and antibacterial are examined. Lastly, the challenges in the development and practical application of MXene-based photocatalytic membranes, as well as their future research direction are delineated.

Understanding Fouling in an Industrial Biorefinery Membrane Separation Process by Feature-Oriented Data-Driven Modeling

Understanding Fouling in an Industrial Biorefinery Membrane Separation Process by Feature-Oriented Data-Driven Modeling

Continuous operation of nano-catalytic ozonation using membrane separation coupling system: influence factors and mechanism

The application of nano-catalysts in improving the ozonation removal efficiency for refractory organic compounds has been extensively investigated. However, cost-effective nano-catalysts separation remains a challenge. In this study, membrane separation processes were employed to separate nano-MgO catalysts from an ozonation system. A continuous nano-catalytic ozonation membrane separation (nCOMS) coupling system was successfully constructed for treating quinoline. The results showed that long hydraulic retention time (HRT) and high nano-MgO dosage could improve the quinolone removal efficiency but shorten operation cycles. At the optimal operation conditions of HRT=4 h and nano-MgO dosage=0.2 g/L, the nCOMS system achieved a stable quinoline removal efficiency of 85.2% for 240 min running with a transmembrane pressure lower than 10 kPa. The quinoline removal efficiency contribution for ozonation, catalysis and membrane separation was 57.1%, 24.9% and 18.0%, respectively. Compared to ozonation membrane separation system, the fouling rate index of the nCOMS system increased by 60% under optimal conditions, but the irreversible fouling was reduced to 28%. In addition, the nCOMS system exhibited reduced adverse effects of coexisting natural organic matter (NOM) on quinoline removal and membrane fouling. In conclusion, the nCOMS system demonstrated higher quinoline removal efficiency, lower irreversible fouling, and reduced adverse effect of coexisting NOM, thereby signifying its potential for practical applications in advanced treatment of industrial wastewater.

Heterostructure engineered membranes based on two-dimensional bimetallic MOF for enhanced remediation of dye contaminated wastewater

As a heterogeneous Fenton-like catalyst, two-dimensional (2D) bimetallic MOF can be readily engineered into lamellar membranes which integrate precise separation and Fenton-like degradation to enhance the elimination of organic contaminants from wastewater by rational design of interlayer spacing and constituent units. In this work, a 2D FeNi-MOF is assembled with ultrathin graphitic carbon nitride (g-C3N4) spacers into heterostructure membranes for enhanced remediation of dye contaminated wastewater by synergistic promotion of membrane separation and Fenton-like processes. For the establishment of heterostructure, FeNi-MOF and g-C3N4 nanosheets are alternately arranged by the coordination bonds between bimetallic nodes and pyridinic N to create orderly laminar nanochannels. On the one hand, the heterostructure provides abundant water passages and fixes the membrane interlayer distance to 1.0–1.2 nm with the permeation flux of 47.8–110.1 L·m2·h−1·bar−1. On the other hand, the heterostructure can act as the Fenton-like mediator to expedite the cycle efficiency of Fe(III)/Fe(II) and Ni(II)/Ni(III). The synergistic promotion mechanism of membrane separation and Fenton-like processes is elaborated by simulating the molecular transport peculiarity through membrane nanochannels and the electron transfer efficiency between dual active centers. The contaminant molecules are trapped within the membrane by specific or non-specific channel-guest interaction with heterostructure nanochannels while the steadily generated radicals attack and degrade the confined contaminants, reaching the dye removal rate of approximately 99.0%. Anchoring between adjacent layers and bimetallic cycle reaction in confined fluid confer the stability and recyclability to the heterostructure membrane under wide-range pH and pressures, which are promising for the sustainable treatment of dye contaminated wastewater.

Feasibility study on the separation and purification of sinomenine hydrochloride from Caulis sinomenii solution based on membrane ultrafiltration technology

The traditional preparation of sinomenine hydrochloride (SH) requires more chloroform and the steps are cumbersome. The use of membrane separation technology can solve the above problems. In this study, Box-Behnken design (BBD) was used to optimize the membrane separation and purification process of SH based on single factor experiments of feed temperatures, diafiltration washing volume, and molecular weight cut-off (MWCO) ranges, the optimized evaluation index is the permeability of SH through the membrane. In addition, to evaluate the effectiveness of membrane separation, the recovery rate of chloroform and the purity of crude SH were compared between traditional separation and purification methods and membrane separation techniques. Finally, the precipitate after extraction was recovered. The optimal process conditions determined are feed temperature of 46 °C, diafiltration washing volume of 75%, and MWCO range of 1 kDa to 150Da. Compared with traditional methods, the implementation of membrane separation can increase the recovery rate of chloroform by 10%. The application of membrane separation technology not only makes the extraction solution clearer, but also reduces the demand for organic solvents during the extraction process. Therefore, this method represents a green and environmentally friendly separation and purification method.

MFI Zeolite Membranes and PV Separation of Isopropanol-Water Azeotropic Mixtures

Membrane separation process has become one of the emerging technologies that undergo a rapid growth since few decades. Pervaporation (PV) is one among the membrane separation processes which gained foremost interest in the chemical and allied industries. It is an effective and energy-efficient technology that carries out separations, which are difficult to achieve by conventional separation processes. Inorganic membranes such as zeolite membranes with uniform, molecular-sized pores, selective adsorption and molecular sieving action offer unique type of pervaporation membrane for a number of separation processes. This paper presents the role of MFI-zeolite membrane and its progress in the pervaporation process. The fundamental aspects of pervaporation over different types of membranes are reviewed and compared. The focus of this paper is on zeolite membrane synthesis, membrane characterization and pervaporation studies. The transport mechanism during pervaporation is discussed and the issues related with pervaporation are addressed. Innovation and future development of zeolite membrane in pervaporation are also presented.

COF-anchored design of nanoporous graphene membranes for ultrafast and selective organic separation

Nanoporous graphene has attracted extensive attention as a type of disruptive membrane materials for organic separation. However, the fabrication of an ideal graphene membrane with high permeability and selectivity remains challenging due to the inevitable non-selective defects. Here, a strategy based on synergetic effect of graphene membranes and covalent organic framework (COF) nanounits is developed. Atomically thin nanoporous graphene provides high solvent flux and stability. To prevent the leakage from inevitable non-selective pores in graphene without sacrificing flux, porous COF nanounits are directly anchored at the defective sites. The fabricated membranes exhibit record-high solvent flux of 49.81 L m−2 h−1 (1–2 orders of magnitude higher than that of state-of-the-art membranes), and relatively low reverse solute flux of 1.69 g m−2 h−1 in organic solvent forward osmosis (OSFO) process. The strategy we proposed gives dramatic impetus to the development of OSFO and other membrane separation processes.

Defect Engineering in GO Membranes - Tailoring Size and Oxidation Degree of Nanosheet for Enhanced Pore Channels.

Graphene Oxide (GO) membrane has been extensively applied in the field of water purification and membrane separation processes. While the solute molecule transport in GO membranes encompasses interlayer channels, edge defects, and in-plane crack-like holes, the significance of edge defects or crack-like pores in ultrathin membranes is often overlooked. In our study, we focused on the construction of short-range channel GO membranes with varied defect structures by modulating the transverse size of the porous nanosheets. GO nanosheets with different sizes were procured through high-energy γ-irradiation combined with centrifugation. Notably, the large-sized porous GO nanosheets (L-pGO) exhibit a consistent structure, and numerous in-plane defects. In contrast, the smaller counterparts (S-pGO) present a fewer in-plane defects. The performance metrics revealed that L-pGO exhibited a water flux of 849.25 L m-2 h-1 bar-1, while S-pGO demonstrated nearly 100 % dye rejection capacity. These findings underscore the potential of defect engineering as a powerful strategy to enhance the efficiency of two-dimensional membranes.

Theory of expansion and compression of polymeric materials: Implications for membrane solvent flow under compaction

We extend the classical Flory-Rehner theory for the expansion and compression of porous materials such as cross-linked polymer networks and membranes. The theory includes volume exclusion, affinity with the solvent, and finite stretching of the polymer chains. We also modify this equilibrium theory, which applies to equal expansion of a material in all directions, to the situation where a material can only expand in a single direction, as is the case when a thin polymer layer is tightly bound to a support structure. We further extend this equilibrium model to the case where a pressure is applied across a thin polymer layer, such as a membrane, and liquid flows across the membrane. The theory describes how in the direction of liquid flow the membrane is increasingly compacted and becomes less porous, and this effect increases when the applied pressure goes up. We present results of example calculations for a thick membrane showing significant changes in compaction across its thickness, and a thin membrane where compaction due to flow is minor. Lastly, we model the dynamics of the change in size of a porous material in time after a step change in the solvent-polymer attraction parameter, which may be relevant, for instance, when the attraction parameter is highly temperature-dependent, and we change the temperature. The developed theory has direct implications for pressure-driven membrane separation processes ranging from reverse osmosis to organic solvent nanofiltration.

REMOVAL OF DRUGS FROM AQUEOUS MATRIXES USING A REVERSE OSMOSIS MEMBRANE

Pollution of water bodies by micropollutants is a problem of growing concern, especially regarding contamination with drug residues and metabolites. The presence of these substances in surface waters is related to deleterious consequences for the population and the environment. The incorrect disposal of drug residues and the low efficiency of conventional water treatment methods require the use of alternative methods, such as the use of membrane separation processes for the treatment of effluents. The present study aimed to evaluate the efficiency of a reverse osmosis membrane for the removal of ibuprofen and diclofenac sodium from an aqueous matrix. For this, permeation tests were performed with aqueous solutions of diclofenac and ibuprofen at a concentration of 10 mg∙L-1, alone and together. The hydraulic permeability of the membrane and the drug rejection efficiency were evaluated. The presence of drugs in the solution had little influence on the hydraulic permeability of the membrane. The minimum removal efficiency of both substances was greater than 98.5 %, generating a permeate stream practically free of drugs, whether evaluated separately or in the same solution. These results indicate the operational robustness of the membrane since neither the permeability nor the rejection were altered by the fact that we have the two drugs combined, in addition to demonstrating the potential use of reverse osmosis as a treatment method for the removal of residues and traces of drugs and other difficult-to-treat organic substances in aqueous matrices.

Plasmonic titanium nitride-based membranes for solar-driven domestic wastewater distillation treatment

Membrane separation processes have emerged as efficient wastewater treatment technologies due to their reduced footprint, sustainability, cost-effectiveness, ease of operation, high filtration selectivity, and compliance with end-user requirements. Especially solar-driven membrane distillation, known for its low energy requirements and high pollutant rejection rates, has gained prominence as a potential wastewater treatment process that does not need external thermal energy input for water treatment. Herein, we demonstrate plasmonic titanium nitride nanoparticle-incorporated polymeric membranes for the solar-driven membrane distillation of domestic laundry wastewater, specifically focusing on SDBS (sodium dodecylbenzene sulfonate) surfactant removal. Under solar illumination, the plasmonic element within the polymeric matrix enables a localized heating effect driven by photothermal conversion in the proximity of the surface of distillation membranes, thereby producing a vapor pressure enough for water distillation across the hydrophobic membranes. The fabricated photothermal mixed matrix membranes showed incremental distillation flux and derived energy efficiency with the loading of titanium nitride nanoparticles under light illumination, reaching up to 0.47 kg/m2h and 29.79 %, respectively. The rejection rate against SDBS achieved up to 99 %. We also verified that its distinctive surface photothermal heating effect is associated with enhanced plasmonic absorption, surface thermal conductivity, and improved interfacial heat transfer of the membranes in the presence of plasmonic elements. The photothermal membranes proved that the permeate produced by photothermal distillation of real laundry wastewater fulfilled all required parameters for safe use as irrigation water, demonstrating its practical feasibility and viability of solar-driven distillation for domestic wastewater treatment and reuse.

Impact of Concentration Polarization Phenomena on Gas Separation Processes with High-Performance Zeolite Membranes: Experiments vs. Simulations.

Polarization phenomena play a key role in membrane separation processes but remain largely unexplored for gas separations, where the mass transfer resistance is most often limited to the membrane. This assumption, which is commonly used today for the simulation of membrane gas separations, has to be reconsidered when high-performance materials, showing a very high permeance and/or selectivity, are used. In this study, a series of steady-state separation performances experimentally obtained on CO2/CH4 mixtures with a zeolite membrane are compared to the predictions of a dedicated 1D approach, recently derived and validated through CFD simulations. Polarization effects are shown to generate a significant negative impact on the separation performances, both in terms of the productivity and separation efficiency. The 1D model predictions, based on pure gas permeance data and without any adjustable parameters, are in very good agreement with the experimental data. This fast and efficient modeling approach can easily be implemented in simulation or process synthesis programs for the rigorous evaluation of membrane gas separation processes, when high-performance materials are used.

Electrodeionization for Wastewater Reuse in Petrochemical Plants

This study investigated a hybrid membrane and electro-membrane separation process for producing demineralized water from tertiary petrochemical effluent, reusing it as feeding water for high-pressure boilers for steam generation. The effluents were treated in a pilot plant with a 1 m3 h−1 capacity by using a hybrid process of ultrafiltration (UF), reverse osmosis (RO), and electrodeionization (EDI). The physicochemical parameters of interest and maximum limits in industrial water were pre-determined by the industries. Operating parameters such as flow rate, pressure, percentage of recovery, and electric current were monitored, along with the frequency of chemical cleaning. The UF and RO systems operated with average permeate fluxes of 17 ± 4.06 L h−1 m−2 and 20.1 ± 1.9 L h−1 m−2, respectively. Under optimal operating conditions (flow rate of 600 L h−1, voltage of 22.2 ± 0.7 V, and electric current of 1.3 A), EDI produced high-quality water with an average electrical conductivity of 0.22 μS cm−1. Thus, the industrial water produced reached the quality required for reuse as make-up water for high-pressure boilers in the petrochemical industry. In addition, the specific energy consumption; the use of chemicals, spare materials, equipment; and labor costs were determined to support the technical feasibility study for implementing an industrial plant with a 90 m3 h−1 producing capacity. This resulted in a cost of USD 0.64 per cubic meter of demineralized water produced, a cost similar to values reported in the literature.

Review of Hybrid Membrane Distillation Systems.

Membrane distillation (MD) is an attractive separation process that can work with heat sources with low temperature differences and is less sensitive to concentration polarization and membrane fouling than other pressure-driven membrane separation processes, thus allowing it to use low-grade thermal energy, which is helpful to decrease the consumption of energy, treat concentrated solutions, and improve water recovery rate. This paper provides a review of the integration of MD with waste heat and renewable energy, such as solar radiation, salt-gradient solar ponds, and geothermal energy, for desalination. In addition, MD hybrids with pressure-retarded osmosis (PRO), multi-effect distillation (MED), reverse osmosis (RO), crystallization, forward osmosis (FO), and bioreactors to dispose of concentrated solutions are also comprehensively summarized. A critical analysis of the hybrid MD systems will be helpful for the research and development of MD technology and will promote its application. Eventually, a possible research direction for MD is suggested.

Evaluation of Field Applicability of Sewage Treated with an Electrochemical Floatation System Coupled with a Separation Membrane Process

An electrochemical floatation system (EFS)-based sewage-treatment process that applied a dimensionally stable anode (DSA) was developed to secure treated sewage water from sewage-treatment plants for reuse. The DSA was fabricated at a temperature of 673–923 K by dispersing a low quantity of activated carbon on a titanium plate coated with mixed metal oxides (Pt, Re, Pd, Re, and Ir) to a thickness of 5 μm. The average size of the bubbles generated through the DSA of the EFS was 20–40 μm, thus confirming microbubble generation. An efficiency assessment of a titanium-based DSA confirmed metal oxide activity through the removal of Escherichia coli (100%) and total organic carbon (TOC; 48.83%) at a reaction time shorter than 10 min and a low current density (19.6 A/m2). During the long-term operation of the EFS with the separation membrane process, the average removal efficiency was 94.7%, 90.0%, 96.1%, 90.9%, and 98.0% for suspended solids, biochemical oxygen demand, TOC, total nitrogen, and total phosphorous, respectively. Coliforms were not detected. Overall, our EFS coupled with the separation membrane process produced high-quality recycled water that could be used for various purposes according to the water-quality standards for different applications.

Analysis of the Techno-Economic Competitiveness of a Three-Stage Membrane Separation Process for Biogas Upgrading Using a Biopolymer-Based Mixed-Matrix Membrane

Analysis of the Techno-Economic Competitiveness of a Three-Stage Membrane Separation Process for Biogas Upgrading Using a Biopolymer-Based Mixed-Matrix Membrane

Highly Flexible and Self‐Standing Covalent Organic Framework–Metal–Organic Framework (COF–MOF) Composite Crystalline Porous Material (CPM) Membrane for Molecular Separation

AbstractCrystalline porous materials (CPMs), including covalent organic frameworks (COFs) and metal–organic frameworks (MOFs), are promising materials for advanced separation technologies. However, the challenge of transforming nanoscale CPMs into large‐area functional membranes hinders their application in the membrane separation process. Herein, a self‐standing pure COF (TpPa‐1) nanofiber membrane with high crystallinity, good flexibility, excellent mechanical properties, and scalability is prepared using an electrospinning process and polymer sacrificial template strategy. Subsequently, the COF nanofiber membrane is innovatively used to replace traditional inorganic discs, metal meshes, and polymer membranes as porous supports, and the COF–MOF composite CPM membrane is prepared through the tailorable and confined growth of zeolite imidazolium salt frame‐8 (ZIF‐8) on the surface of the COF membrane and in the gaps of the COF nanofibers. The COF–MOF composite membrane exhibits excellent permeability and significantly enhances separation selectivity for organic dyes. Moreover, MOF and COF form an interpenetrating network structure, and their similar chemical properties improve the interfacial stability between the two phases, giving the COF–MOF composite membrane good long‐term separation performance. This is the first self‐standing composite CPM membrane with excellent molecular sieving performance, which provides new insights into the design of high‐performance and robust composite membranes.

Biofouling control of reverse osmosis membrane using free ammonia as a cleaning agent

Reverse osmosis (RO) is an important and widely-used membrane separation process for water recycling. However, biofouling is extensively considered a major problem for RO membranes due to the biofilm formation on the membrane surfaces. This study proposed and demonstrated a novel and sustainable chemical cleaning approach using a free ammonia (FA) solution for the removal of biofouling on RO membranes. The feasibility of FA solution for biofouling removal was investigated through a series of lab-scale soak cleaning tests and cross-flow cleaning tests on four fouled RO membranes (M1-M4) collected from municipal wastewater recycling plants. In soak cleaning tests on M1, FA concentrations of 65–560 mg NH3–N/L (pH = 8.9) can remove adenosine triphosphate (ATP) by 32–75 %, remove proteins by 18–47 % and remove polysaccharides by 31–74 %, which was up to 3.4 times of the removals by using NaOH solution under the same pH. FA solution of 310–560 mg NH3–N/L (pH = 8.9) even showed higher removals than NaOH solution with a higher pH of 11. In the cross-flow cleaning tests on M2-M4, FA solution of 310–560 mg NH3–N/L (pH = 8.9) removed the ATP by 82–100 %, removed proteins by 58–87 % and removed polysaccharides by 68–100 % in the fouling layers and increased the permeability by 8–16 %. Such cleaning effects in cross-flow tests were also positively correlated (R > 0.9, p < 0.05). Compared to the conventional anti-biofouling agent of NaOH solution (pH = 11), FA solution (310–560 mg NH3–N/L) showed significantly better cleaning performance. A high FA concentration of 560 NH3–N/L (pH = 8.9) could achieve comparable cleaning effect to 1 % EDTA solution (pH = 10). Additionally, increasing the frequency of cleaning or using a higher concentration of FA solution for biofouling removal will be more advantageous to prolong the membranes’ lifespan. The findings provide a promising alternative to using FA as a cost-effective and environmentally friendly solution for cleaning biofouling on RO membranes.

Advancing Faba Bean Protein Purification Using Membrane Technology: Current State and Future Perspectives

Plant-based proteins are gaining popularity because of their appeal to vegetarians and vegans, alignment with scientific and regulatory recommendations, and the environmental impact associated with livestock production. Several techniques are employed for the separation, isolation, and purification of plant-based proteins including membrane-based separation, diafiltration, centrifugation, chromatography, electrophoresis, micellar precipitation, and isoelectric precipitation. Despite decades of application, these techniques still have some limitations such as scale-up challenges, high solvent consumption, chemical/biological disposal, and the possibility of protein loss during precipitation or elution. Membrane separation processes are the most effective purification/concentration technology in the production of plant-based protein isolates and concentrates due to their selective separation, simple operational conditions, and easy automation. Membrane separation processes yielded products with higher protein content compared to isoelectric precipitation, and all concentrates presented good functional properties with expected variability among different legumes. This review critically focuses on the membrane technology advances and challenges for the purification of plant-based protein isolates. This study also highlights the plant-based diet trend, the market, composition, and the protein isolate of the faba bean, in addition to the emerging technologies for the elimination of antinutritional compounds.