Indispensable gutter layers in thin-film composite membranes for carbon capture

Industrial thin-film composite(TFC)membranes achieve superior gas separation properties from high-performance selective layer materials,while the success of membrane technology relies on high-performance gutter layers to achieve production scalability and low-cost manufacturing.However,the current literature predominantly focuses on the design of polymer architectures to obtain high permeability and selectivity,while the art of fabricating gutter layers is usually safeguarded by industrial manufacturers and appears lackluster to academic researchers.This is the first report aiming to provide a comprehensive and critical review of state-of-the-art gutter layer materials and their design and modification to enable TFC membranes with superior separation performance.We first elucidate the importance of the gutter layer on membrane performance through modeling and experimental results.Then various gutter layer materials used to obtain high-performance composite membranes are critically reviewed,and the strategies to improve their compatibility with the selective layer are highlighted,such as oxygen plasma treatment,polydopamine deposition,and surface grafting.Finally,we present the opportunities of the gutter layer design for practical applications.

Outstanding proton conductivity over wide temperature and humidity ranges and enhanced mechanical, thermal stabilities for surface-modified MIL-101-Cr-NH_(2)/Nafion composite membranes

High-performance proton exchange membranes are of great importance for fuel cells.Here,we have synthesized polycarboxylate plasticizer modified MIL-101-Cr-NH_(2)(PCP-MCN),a kind of hybrid metal-organic framework,which exhibits a superior proton conductivity.PCP-MCN nanoparticles are used as additives to fabricate PCP-MCN/Nafion composite membranes.Microstructures and characteristics of PCP-MCN and these membranes have been extensively investigated.Significant enhancement in proton conduction for PCP-MCN around 55℃ is interestingly found due to the thermal motion of the PCP molecular chains.Robust mechanical properties and higher thermal decomposition temperature of the composite membranes are directly ascribed to strong intermolecular interactions between PCP-MCN and Nafion side chains,i.e.,the formation of substantial acid–base pairs(-SO_(3)^(-)…^(+)H–NH-),which further improves compatibility between additive and Nafion matrix.At the same humidity and temperature condition,the water uptake of composite membranes significantly increases due to the incorporation of porous additives with abundant functional groups and thus less crystallinity degree in comparison to pristine Nafion.Proton conductivity(σ)over wide ranges of humidities(30-100%RH at 25℃)and temperatures(30-98℃ at 100%RH)for prepared membranes is measured.The s in PCPMCN/Nafion composite membranes is remarkably enhanced,i.e.0.245 S/cm for PCP-MCN-3wt.%/Nafion is twice that of Nafion membrane at 98℃ and 100%RH,because of the establishment of well-interconnected proton transport ionic water channels and perhaps faster protonation–deprotonation processes.The composite membranes possess weak humidity-dependence of proton transport and higher water uptake due to excellent water retention ability of PCP-MCN.In particular,when 3 wt.%PCP-MCN was added to Nafion,the power density of a single-cell fabricated with this composite membrane reaches impressively 0.480,1.098 W/cm^(2) under 40%RH,100%RH at 60℃,respectively,guaranteeing it to be a promising proton exchange membrane.

Preparation and Performance of Organically Modified Montmorillonite Composite Separation Membrane

A new composite separation membrane was developed by using organically modified montmorillonite(OMMT)as an additive.The effects of OMMT on the modification and properties of PVDF composite membranes were investigated.It is found that different kinds and amounts of OMMT into the casting solution can obviously change the pure water flux,separation performance and hydrophilicity of composite membrane in varying degrees.When the TA/PDA-MMT was 0.5 wt%,the pure water flux of the membrane reached the maximum,which was 584.7 L/(m^(2)·h),about 6 times that of the original membrane.The OMMT/PVDF composite membrane had good hydrophilicity and stability in the treatment of oily wastewater.The development of novel OMMT/PVDF composite membrane will provide a new idea for solving the problem of oily wastewater treatment.

Recent advances in multi-layer composite polymeric membranes for CO_2 separation: A review

The development of multilayer composite membranes for CO_2 separation has gained increasing attention due to the desire for energy efficient technologies. Multilayer composite membranes have many advantages, including the possibility to optimize membrane materials independently by layers according to their different functions and to reduce the overall transport resistance by using ultrathin selective layers, and less limitations on the material mechanical properties and processability. A comprehensive review is required to capture details of the progresses that have already been achieved in developing multilayer composite membranes with improved CO_2 separation performance in the past 15-20 years.In this review, various composite membrane preparation methods were compared, advances in composite membranes for CO_2/CH_4 separation,CO_2/N_2 and CO_2/H_2 separation were summarized with detailed data, and challenges facing for the CO_2 separation using composite membranes,such as aging, plasticization and long-term stability, were discussed. Finally the perspectives and future research directions for composite membranes were presented.

Substrate matters:The influences of substrate layers on the performances of thin-film composite reverse osmosis membranes

Thin-film composite(TFC) reverse osmosis(RO) membranes are playing the dominating role in desalination.Tremendous efforts have been put in the studies on the polyamide selective layers. However, the effect of the substrate layers is far less concerned. In this review, we summarize the works that consider the impacts of the substrates, including pore sizes, surface hydrophilicity, on the processes of interfacial polymerization and consequently on the morphologies of the active layers and on final RO performances of the composite membranes. All the works indicate that the pore sizes and surface hydrophilicity of the substrate evidently influence the RO performances of the composite membranes. Unfortunately, we find that the observations and understandings on the substrate effect are frequently varied from case to case because of the lack of substrates with uniform pores and surface chemistries. We suggest using track-etched membranes or anodized alumina membranes having relatively uniform pores and functionalizable pore walls as model substrates to elucidate the substrate effect.Moreover, we argue that homoporous membranes derived from block copolymers have the potential to be used as substrates for the large-scale production of high-performances TFC RO membranes.

Fabrication of high-performance PVA/PAN composite pervaporation membranes crosslinked by PMDA for wastewater desalination

The pyromellitic dianhydride（PMDA） crosslinked poly（vinyl alcohol）（PVA） was coated on top of the PAN ultrafiltration membrane to form a PVA/PAN composite PV membranes for wastewater desalination. The composite membranes have high application value in industrial wastewater treatment. By varying the membrane fabrication parameters including the weight percent（wt%） of the PMDA, the crosslink temperature and duration, membrane with the best desalination performance was obtained. The composite membrane with a 2-lm-thick PVA selective layer containing 20 wt% of PMDA and being crosslinked at 100 °C for 2 h showed the highest Na Cl rejection of 99.98% with a water flux of 32.26 L/（m^2 h）at 70 °C using the 35,000 ppm Na Cl aqueous solution as feed. FTIR spectroscopy, wide-angle X-ray diffraction, thermogravimetric analysis and scanning electron microscope have been used to characterize the structures and properties of both the crosslinked PVA dense films and PVA/PAN composite membranes. The effects of the concentrations of PMDA,the crosslinking time and temperature to the membrane water contact angle, swelling degree, salt rejection and water flux were systematically studied.

Ceramic Supported PDMS and PEGDA Composite Membranes for CO2 Separation

Composite membranes have attracted increasing attentions owing to their potential applications for CO2 separation. In this work, ceramic supported polydimethylsiloxane （PDMS） and poly （ethylene glycol） diacrylate （PEGDA） composite membranes were prepared. The microstructure and physicochemical properties of the compos- ite membranes were characterized. Preparation conditions were systematically optimized. The gas separation performance of the as-prepared membranes was studied by pure gas and binary gas permeation measurement of CO〉 N2 and H〉 Experiments showed that PDMS, as silicone rubber, exhibited larger permeance and lower separation factors. Conversely, PEGDA composite membrane presented smaller gas permeance but higher ideal selectivity for CO2/N2. Compared to the performance of those membranes using polymeric supports or freestanding membranes, the two kinds of ceramic supported composite membranes exhibited higher gas permeance and acceptable selectivity. Therefore, the ceramic supported composite membrane can be expected as a candidate for CO2 separation from light gases.

Fouling-resistant Composite Membranes for Separation of Oil-in-water Microemulsions

Fouling-resistant ceramic-supported polymer composite membranes were developed for removal of oil-in-water （O/W） mieroemulsions. The composite membranes were featured with an asymmetric three-layer structure, i.e., a porous ceramic membrane substrate, a polyvinylidene fluoride （PVDF） ultrafiltration sub-layer, and a polyamide/polyvinyl alcohol （PVA） composite thin top-layer. The PVDF polymer was east onto the tubular porous ceramic membranes with an immersion precipitation method, and the polyamide/PVA composite thin top-layer was fabricated with an inteffaeial polymerization method. The effects of the sub-layer composition and the recipe in the inteffaeial polymerization for fabricating the top-layer on the structure and performance of composite membranes were systematically investigated. The prepared composite membranes showed a good performance for treating the O/W microemulsions with a mean diameter of about 2.41μm. At the operating pressure of 0.4MPa, the hydraulic permeability remained steadily about 190L·m^-2·h^-1, the oil concentration in the permeate was less than 1.6mg·L^-1, and the oil rejection coefficient was always higher than 98.5% throughout the operation from the beginning.

STRUCTURE AND PROPERTIES OF COMPOSITE POLYURETHANE HOLLOW FIBER MEMBRANES

Composite polyurethane(PU)-SiO_2 hollow fiber membranes were successfully prepared via optimizing thetechnique of dry-jet wet spinning,and their pressure-responsibilities were confirmed by the relationships of pure water flux-transmembrane pressure(PWF-TP)for the first time.The origin for this phenomenon was analyzed on the basis of membranestructure and material characteristics.The effects of SiO_2 content on the structure and properties of membrane wereinvestigated.The experimental results indicated that SiO_2 in membrane created a great many interfacial micro-voids andplayed an important role in pressure-responsibility,PWF and rejection of membrane:with the increase of SiO_2 content,theability of membrane recovery weakened,PWF increased,and rejection decreased slightly.

Polymer/Ceramic Composite Membranes and Their Application in Pervaporation Process

Pervaporation(PV),as an environmental friendly and energy-saving separation technology,has been received increasing attention in recent years.This article reviews the preparation and application of macroporous ceramic-supported polymer composite pervaporation membranes.The separation materials of polymer/ceramic composite membranes presented here include hydrophobic polydimethylsiloxane(PDMS) and hydrophilic poly(vinyl alcohol)(PVA),chitosan(CS) and polyelectrolytes.The effects of ceramic support treatment,polymer solution properties,interfacial adhesion and incorporating or blending modification on the membrane structure and PV performance are discussed.Two in-situ characterization methods developed for polymer/ceramic composite membranes are also covered in the discussion.The applications of these composite membranes in pervaporation process are summarized as well,which contain the bio-fuels recovery,gasoline desulfuration and PV coupled proc-ess using PDMS/ceramic composite membrane,and dehydration of alcohols and esters using ceramic-supported PVA or PVA-CS composite membrane.Finally,a brief conclusion remark on polymer/ceramic composite mem-branes is given and possible future research is outlined.

Reducing active layer thickness of polyamide composite membranes using a covalent organic framework interlayer in interfacial polymerization

Polyamide(PA)-based thin-film composite membranes exhibit enormous potential in water purification,owing to their facile fabrication,decent performance and desirable stability.However,the thick PA active layer with high transport resistance from the conventional interfacial polymerization hampers their applications.The controllable fabrication of a thin PA active layer is essential for high separation efficiency but still challenging.Herein,a covalent organic framework TpPa-1 interlayer was firstly deposited on a polyethersulfone(PES)substrate to reduce the thickness of PA active layer in interfacial polymerization.The abundant pores of TpPa-1 increase the local concentration of amine monomers by adsorbing piperazine molecules,while hydrogen bonds between hydrophilic groups of TpPa-1 and piperazine molecules slow down their diffusion rate.Arising from those synergetic effects,the PA active layer is effectively reduced from 200 nm to 120 nm.By optimizing TpPa-1 interlayer and PA active layer,the water flux of resultant membranes can reach 171.35 L·m^-2·h^-1·MPa^-1,which increased by 125.4%compared with PA/PES membranes,while the rejection rates of sodium sulfate and dyes solution remained more than 90%and 99%,respectively.Our strategy may stimulate rational design of ultrathin PA-based nanofiltration membranes with high performances.

Proton-Exchange Sulfonated Poly （ether ether ketone） （SPEEK）/SiOx-S Composite Membranes in Direct Methanol Fuel Cells

A sulfonated poly（ether ether ketone） （SPEEK） membrane with a fairly high degree of sulfonation （DS） can swell excessively and even dissolve at high temperature. To solve these problems, insolvable functionalized silica powder with sulfonic acid groups （SiOx-S） was added into the SPEEK matrix （DS = 55.1%） to prepare SPEEK/ SiOx-S composite membranes. The decrease in both the swelling degree and the methanol permeability of the membranes was a dose-dependent result of addition of the SiOx-S powder. Pure SPEEK membrane swelled 52.6% at 80℃, whereas the SPEEK/SiOx-S （15%, by mass） membrane swelled only 27.3% at the same temperature. From room temperature to 80℃, all SPEEK/SPEEK/SiOx-S composite membranes had methanol permeability of about one order of magnitude lower than that ofNafion115. Compared with pure SPEEK membranes, the addition of the SiOx-S powder not only leads to higher proton conductivity, but also increases the dimensional stability at higher temperatures, and greater proton conductivity can be achieved at higher temperature. The SPEEK/SiO4-S （20%, by mass） membrane could withstand temperature up to 145℃, at which in 100% relative humidity （RH） its proton conductivity exceeded slightly that of Nafion 1 15 membrane and reached 0.17 S·cm^-1, while pure SPEEK membrane dissolved at 90℃. The SPEEK/SiOx-S composite membranes are promising for use in direct methanol fuel cells because of their good dimensional stability, high proton conductivity, and low methanol permeability.

Separation of Sulfur/Gasoline Mixture with Polydimethylsiloxane/ Polyetherimide Composite Membranes by Pervaporatlon

Worldwide environment has resulted in a limit on the sulfur content of gasoline.It is urgent to investigate the desulfurization of gasoline.The polydimethylsiloxane(PDMS)/polyetherimide(PEI)composite membranes were prepared by casting a PDMS solution onto porous PEI substrates and characterized by scanning electron microscope(SEM).The membranes were used for sulfur removal from gasoline by pervaporation.The effects of feed temperature,sulfur content in the feed and PDMS layer thickness on membrane performance were investigated,and an activation energy of permeation was obtained.Experimental results indicated that higher feed temperature yielded higher total flux and lower sulfur enrichment factor.The total flux varied little with the increase of sulfur content in the feed,but the sulfur enrichment factor first increased with the amount of thiophene added into the gasoline,and then the variation was little.The increase of PDMS layer thickness resulted in a smaller flux but a larger sulfur enrichment factor.The result indicates that the PDMS/PEI composite membranes are promising for desulfurization by pervaporation.

Integral PVA-PES Composite Membranes by Surface Segregation Method for Pervaporation Dehydration of Ethanol

A facile surface segregation method was utilized to fabricate poly（vinyl alcohol）-polyethersulfone （PVA-PES） composite membranes. PVA and PES were first dissolved in dimethyl sulfoxide （DMSO）, then casted on a glass plate and immersed in a coagulation bath. During the phase inversion process in coagulation bath, PVA spontaneously segregated to the polymer solution/coagulation bath interface. The enriched PVA on the surface was further crosslinked by glutaraldehyde. Scanning electron microscopy （SEM）, X-ray photoelectron spectroscopy （XPS） and energy dispersive spectrometer （EDS） confirmed the integral and asymmetric membrane structure with a dense PVA-enriched surface and a porous PES-enriched support, as well as the surface enrichment of PVA. The coverage fraction of the membrane surtace by PVA reacned up to 86.8% when me PVA content m me membrane recipe was 16.7% （by mass）. The water contact angle decreased with the increase of PVA content. The effect of coagulation bath type on membrane structure was analyzed. The membrane pervaporation performance was evaluated by varying the PVA content, the annealing temperature, feed concentration and operation temperature. The membrane exhibited a fairly good ethanol dehydration capacity and long-term operational stability.

Enhancing Structural Stability and Pervaporation Performance of Composite Membranes by Coating Gelatin onto Hydrophilically Modified Support Layer

The interfacial compatibility of composite membrane is an important factor to its structural stability, andseparation performance. In this study, poly （ether sulfone） （PES） support layer was first hydrophilically modified with poly（vinyl alcohol） （PVA） via surface segregation during the phase inversion process. Gelatin （GE） was then cast on the PVA-modified PES support layer as the active layer followed by crosslinking to fabricate composite membranes for ethanol dehydration. The enrichment of PVA on the surface of support layer improved interfacial compatibility of the as-prepared GE/PVA-PES composite membrane. The water contact angle measurement and X-ray photoelectron spectroscopy （XPS） data confirmed the surface segregation of PVA with a surface coverage density of -80%. T-peel test showed that the maxima/force to separate the support layer and the active layer was enhanced by 3 times compared with the GE/PES membrane. The effects of PVA content in the support layer, crosslinking of GE active layer and operating parameters on the pervaporative dehydration performance were investigated. The operational stability of the composite membrane was tested by immersing the membrane in ethanol aqueous solution for a period of time. Stable pervaporation performance for dehydration of 90% ethanol solution was obtained for GE/PVA-PES membrane with a separation factor of -60 and a permeation flux of -1910 g.m^-2.h1 without peeling over 28 days immersion.

CO2/CH4 separation using inside coated thin film composite hollow fiber membranes prepared by interfacial polymerization

Carbon dioxide(CO_2) is greenhouse gas which originates primarily as a main combustion product of biogas and landfill gas. To separate this gas, an inside coated thin film composite(TFC) hollow fiber membrane was developed by interfacial polymerization between 1,3–cyclohexanebis–methylamine(CHMA) and trimesoyl chloride(TMC). ATR-FTIR, SEM and AFM were used to characterize the active thin layer formed inside the PSf hollow fiber. The separation behavior of the CHMA-TMC/PSf membrane was scrutinized by studying various effects like feed gas pressure and temperature. Furthermore, the influence of CHMA concentration and TMC concentration on membrane morphology and performance were investigated. As a result, it was found that mutually the CHMA concentration and TMC concentration play key roles in determining membrane morphology and performance. Moreover, the CHMA-TMC/PSf composite membrane showed good CO_2/CH_4 separation performance. For CO_2/CH_4 mixture gas(30/70 by volume) test, the membrane(PD1 prepared by CHMA 1.0% and TMC 0.5%) showed a CO_2 permeance of 25 GPU and the best CO_2/CH_4 selectivity of 28 at stage cut of 0.1. The high CO_2/CH_4 separation performance of CHMA-TMC/PSf thin film composite membrane was mostly accredited to the thin film thickness and the properties of binary amino groups.

SEPARATION OF PROPANE FROM PROPANE/NITROGEN MIXTURES USING PDMS COMPOSITE MEMBRANES BY VAPOR PERMEATION

This study deals with polydimethylsiloxane(PDMS)/polyvinylidene fluoride(PVDF) composite membranes for propane separation from propane/nitrogen mixtures,which is relevant to the recovery of propane in petroleum and chemical industry.The surface and cross-section morphology of PDMS/PVDF composite membranes was observed by scanning electron microscope(SEM).The surface morphology of PDMS/PVDF composite membranes is very dense.There are three layers,the thin dense top layer,finger-like porous middle layer and s...

Hydrophilic Composite Polybutylene Terephthalate/Polyvinyl Alcohol Membranes Prepared by Electrospinning

A hydrophilic composite polybutylene terephthalate(PBT)/polyvinyl alcohol(PVA)membrane with great potential applications in biological filtration has been investigated in this research.The composite membranes were fabricated by electrospinning with PBT meltblown nonwovens as the receiving substrate.These membranes have higher strength than the conventional single layer electrospinning membrane,smaller pore diameter than the common meltblown PBT nonwovens,good hydrophilicity,and high water flux.The flux of the composite membrane was 5.97×10^(3) L/(m^(2)·h)for 5%(mass fraction)glucose solution,which was higher than that of the commercial blood filtration membranes.The optimal process for preparing PBT/PVA composite membranes was obtained by orthogonal experiments.In general,the preparation process is simple and easy to control.

High-permeance crosslinked PTMSP thin-film composite membranes as supports for CO_2 selective layer formation

In the development of the composite gas separation membranes for post-combustion CO_2 capture, little attention is focused on the optimization of the membrane supports, which satisfy the conditions of this technology. The primary requirements to the membrane supports are concerned with their high CO_2 permeance. In this work, the membrane supports with desired characteristics were developed as high-permeance gas separation thin film composite(TFC) membranes with the thin defect-free layer from the crosslinked highly permeable polymer, poly[1-(trimethylsilyl)-1-propyne](PTMSP). This layer is insoluble in chloroform and can be used as a gutter layer for the further deposition of the CO_2-selective materials from the organic solvents. Crosslinking of PTMSP was performed using polyethyleneimine(PEI) and poly(ethyleneglycol) diglycidyl ether(PEGDGE) as crosslinking agents. Optimal concentrations of PEI in PTMSP and PEGDGE in methanol were selected in order to diminish the undesirable effect on the final membrane gas transport characteristics. The conditions of the kiss-coating technique for the deposition of the thin defect-free PTMSP-based layer, namely, composition of the casting solution and the speed of movement of the porous commercial microfiltration-grade support, were optimized. The procedure of post-treatment with alcohols and alcohol solutions was shown to be crucial for the improvement of gas permeance of the membranes with the crosslinked PTMSP layer having thickness ranging within 1-2.5 μm. The claimed membranes showed the following characteristics: CO_2 permeance is equal to 50—54 m^3(STP)/(m^2 h bar)(18,500—20,000 GPU), ideal CO_2/N_2 selectivity is 3.6-3.7, and their selective layers are insoluble in chloroform. Thus, the developed highpermeance TFC membranes are considered as a promising supports for further modification by enhanced CO_2 selective layer formation.

Preparation and properties of metal-PVA composite hydrophilic ultrafiltration membranes

Metal-polyvinyl alcohol(PVA) composite ultrafiltration membranes were prepared by coating a certain concentration of PVA solution on metallic fiber sintered membranes. The effects of preparation conditions, such as the coating solution concentration, sequence and times of coating, and heat-treatment on the properties of the composite membranes were studied. The results show that the hole diameter of the composite membrane decreases with the increase of the concentration of PVA, the hole diameter of composite membrane is different when the sequence of coating is different. When the higher concentration of PVA solution is used to coat the metallic membrane for the first time and the other smaller one for the second time, the hole diameter of the composite membrane is relatively small, compared with that of the composite membrane made by the smaller concentration of PVA solution for the first time and the other higher one for the second time. The holes of the composite membrane contract and the stability of the membrane is improved by heat treatment. When metal-PVA composite hydrophilic membranes are used to treat the oil/water emulsion with the concentration of 1 000 mg·L -1 , the retention is from 80% to 90%, and the permeate flux is from 15 L·m -2 ·h -1 to 40 L·m -2 ·h -1 at pressure of 0.2 to 0.3 MPa.