Membrane materials in the pervaporation separation of aromatic/aliphatic hydrocarbon mixtures—A review

The separation of aromatic/aliphatic hydrocarbon mixtures is a significant process in chemical industry, but challenged in some cases. Compared with conventional separation technologies, pervaporation is quite promising in terms of its economical, energy-saving, and eco-friendly advantages. However, this technique has not been used in industry for separating aromatic/aliphatic mixtures yet. One of the main reasons is that the separation performance of existed pervaporation membranes is unsatisfactory. Membrane material is an important factor that affects the separation performance. This review provides an overview on the advances in studying membrane materials for the pervaporation separation of aromatic/aliphatic mixtures over the past decade. Explored pristine polymers and their hybrid materials(as hybrid membranes) are summarized to highlight their nature and separation performance. We anticipate that this review could provide some guidance in the development of new materials for the aromatic/aliphatic pervaporation separation.

Additional Mass: Orthotropic Membrane Material with Four Sides Fixed in Air Flow

When the membrane material in the air field vibrates, it will drive the movement of the surrounding air. The aerodynamic force generated by the moving air will act on the membrane material in turn, resulting in the change of dynamic characteristics such as membrane vibration frequency. In this paper, the additional air mass produced by membrane vibration in air is studied. Firstly, under the assumption that the incoming flow is uniform and incompressible ideal potential flow, the additional air mass acting on the surface is derived by using the thin airfoil theory and potential flow theory respectively. Then, according to the first law of thermodynamics and the principle of aeroelasticity, the analytical expression of the additional air mass is derived. Finally, through a specific example, the variation of the additional air mass with the membrane material parameters and pretension, as well as the influence of the aerodynamic force on the vibration frequency and amplitude of the membrane is obtained.

A Research on the Air Permeability of High Polymer Materials Used to Produce Sports Clothing Fabrics

Composite fabrics based on Polytetrafluoroethylene(PTFE)polymer displays several notable properties.They are waterproof,windproof,permeable to moisture and thermally insulating at the same time.In the present study,PTFE fibers are used as raw material to make fiber membranes.The film is formed by crisscrossing interconnected fiber filaments and the related air permeability:tensile creep characteristics and other properties are tested.The results show that the pore size,thickness,and porosity of the film itself can affect the moisture permeability of the film.The water pressure resistance of the selected fabric is 8.5 kPa,and the moisture permeability is 7038 g/(m^(2)·24 h).

Removal of aqueous phenol compound by vacuum membrane distillation

The effects of feed temperature and pH value on the removal of aqueous phenol wastewater by vacuum membrane distillation process are studied by experiments employing micro porous membranes of poly vinylidene fluoride (PVDF) and ploy tetrafluoro ethylene (PTFE) with nominal average pore sizes 0.22 mm and 0.20 mm, respectively. It is found that the optimal feed temperature for PVDF membrane is 50 ℃; and for PTFE membrane, 60 ℃. The pH value of the feed has little influence on the membrane fluxes and ion rejection ratios, while it influenced considerably on the selectivity. Increase of pH value of the feed is conducive to the increase of selectivity. In the same experimental conditions, PTFE membrane shows better separation performance than PVDF membrane does.

An asymmetric membrane of polyimide 6FDA-BDAF and its pervaporation desulfurization for n-heptane/thiophene mixtures

Polyimide（PI） is a type of important membrane material. A soluble polymer was synthesized from 4,4′-（hexafluoroisopropylidene） diphthalic anhydride（6FDA） and 2,2-bis[4-（4-aminophenoxy） phenyl] hexafluoropropane（BDAF） by the two-step polymerization method. The polymer was proved to be polyimide 6FDA-BDAF by the Fourier transform infrared（FT-IR）, the 1H-NMR and ^（19）F-NMR spectra. An asymmetric membrane was prepared with the synthesized polyimide 6FDA-BDAF, it was porous in the 50 μm height bulk and dense in a 3–5 μm height surface. The membrane was used to separate n-heptane/thiophene mixtures by pervaporation with sulfur（S） contents from 50 to 900 μg g^（–1）. The total flux was enlarged from 7.96 to 37.61 kg m^（–2） h^（–1） with temperature increasing from 50 to 90°C. The membrane＇s enrichments factor for thiophene were about 3.13 and dependent on the experimental conditions. The experimental results demonstrated that polyimide 6FDA-BDAF would be a potential membrane material for desulfurization and controlled release of the S-containing fertilizer.

COF-based membranes for liquid phase separation:Preparation,mechanism and perspective

Covalent organic frameworks(COFs)are a new kind of crystalline porous materials composed of organic molecules connected by covalent bonds,processes the characteristics of low density,large specific surface area,adjustable pore size and structure,and easy to functionalize,which have been widely used in the field of membrane separation technology.Recently,there are more and more researches focusing on the preparation methods,separation application,and mechanism of COF membranes,which need to be further summarized and compared.In this review,we primarily summarized several conventional preparation methods,such as two-phase interfacial polymerization,in-situ growth on substrate,unidirectional diffusion method,layer-by-layer assembly method,mixed matrix membranes,and so on.The advantages and disadvantages of each method are briefly summarized.The application potential of COF membrane in liquid separation are introduced from four aspects:dyeing wastewater treatment,heavy metal removal,seawater desalination and oil-water separation.Then,the mechanisms including pore structure,hydrophilic/hydrophobic,electrostatic repulsion/attraction and Donnan effect are introduced.For the efficient removal of different kind of pollutions,researchers can select different ligands to construct membranes with specific pore size,hydrophily,salt or organic rejection ability and functional group.The ideas for the design and preparation of COF membranes are introduced.Finally,the future direction and challenges of the next generation of COF membranes in the field of separation are prospected.

A review on membrane distillation in process engineering: design and exergy equations, materials and wetting problems

One of the problems that most afflicts humanity is the lack of clean water.Water stress,which is the pressure on the quantity and quality of water resources,exists in many places throughout the World.Desalination represents a valid solution to the scarcity of fresh water and several technologies are already well applied and successful(such as reverse osmosis),producing about 100 million m^(3)·d^(-1) of fresh water.Further advances in the field of desalination can be provided by innovative processes such as membrane distillation.The latter is of particular interest for the treatment of waste currents from conventional desalination processes(for example the retentate of reverse osmosis)as it allows to desalt highly concentrated currents as it is not limited by concentration polarization phenomena.New perspectives have enhanced research activities and allowed a deeper understanding of mass and heat transport phenomena,membrane wetting,polarization phenomena and have encouraged the use of materials particularly suitable for membrane distillation applications.This work summarizes recent developments in the field of membrane distillation,studies for module length optimization,commercial membrane modules developed,recent patents and advancement of membrane material.

Advanced hemocompatible polyethersulfone composite artificial lung membrane with efficient CO_(2)/O_(2)exchange channel constructed by modified carbon nanotubes network

Artificial lung membranes as the core module of the extracorporeal membrane oxygenation technology(ECMO)execute the function of extracorporeal blood-gas barrier accomplishing CO_(2)/O_(2)exchange with blood.However,the unsatisfactory hemocompatibility and difficulty in functionalization are the promi-nent challenges faced by current artificial lung membrane materials.In this study,polyethersulfone(PES)composite membranes with self-anticoagulant property and high gas exchange efficient are fabricated by blending PES matrix with poly(vinylamine)(PVAm)modified carboxylic carbon nanotubes(mCNTs)and citrate-based poly(octamethylene-citrate)(POC)pre-polymers.The mCNTs construct specific gas transfer channels within the composite membranes to enhance the gas permeability,while the POC pre-polymers provide anticoagulant property based on the chelation to blood Ca^(2+)and the inactivation effect to in-trinsic coagulation factors.Importantly,directed by the actual ECMO gas exchange mode,we design a gas-liquid convectional circulation device that could evaluate gas exchange efficiency for the composite membranes under mimetic ECMO state.Therefore,this strategy not only proposes a new design method of advanced artificial lung membranes to solve the practical challenges in the current ECMO technology,but also establishes a scientific testing method to evaluate the gas exchange performance for new-type artificial lung membrane materials in the future.

Two-dimensional Cu-porphyrin nanosheet membranes for nanofiltration

A kind of two-dimensional(2D)metal-organic framework(MOF)material,Cu-meso-tetrakis(4-carboxyphenyl)porphine(Cu-TCPP)nanosheets with wrinkled and flat morphologies are used as building blocks to assemble membranes by vacuum filtration(VF)and electrophoretic deposition(EPD)as energy-efficient nanofiltration(NF)membranes to remove dyes from water.Since the nanosheets with wrinkled structure can provide additional water transport channels,thereby increasing the water permeance,in the premise of a high rejection(>97.0%)for the dye brilliant blue G(BBG)(1.60 nm×1.90 nm),the water permeance of the membrane assembled by the wrinkled nanosheets(~1170 nm)is about 4 times that of the membrane assembled by the flat nanosheets(~530 nm),reaching 16.39 L·m^(−2)·h^(−1)·bar^(−1).Additionally,the use of the relatively flat nanosheets and the membrane preparation method of electrophoretic deposition is more conducive to stack nanosheets orderly and reduce defects.Therefore,the water permeance of the membrane prepared by EPD(~1170 nm)with flat nanosheets is about twice that of the membrane prepared by VF(~530 nm),achieving 9.40 L·m^(−2)·h^(−1)·bar^(−1)with similar rejection(>97.0%)of dye evans blue(EB)(3.10 nm×1.20 nm).Furthermore,these membranes still exhibit good separation performance at high pressure of 0.6 MPa.Nanosheets with diverse structures and various membrane fabrication processes provide new directions for the separation performance optimization of 2D MOF materials for water purification.

Challenges in cell membrane-camouflaged drug delivery systems:Development strategies and future prospects

Extensive research has been performed on cell membrane camouflaged-based drug delivery systems in recent years.Herein,we provide an overview of the challenges in system preparation,functional design,continuous industrial production of these systems,and solution strategies for these challenges.Further,we analyze and discuss the frontier medical applications of cell membrane-camouflaged drug delivery systems in anti-inflammatory,anti-pathogenic microorganisms,and biological detoxification.This review takes a challenge-oriented perspective and seeks innovative strategies,provides a literature review of research into cell membrane-camouflaged drug delivery systems,and promotes the development of personalized clinical treatments.

“1+1>2”:Highly efficient removal of organic pollutants by composite nanofibrous membrane based on the synergistic effect of adsorption and photocatalysis

Adsorption and photocatalysis are regarded as two desirable technologies for wastewater remediation,but are still unsatisfactory in removal effect,eco-friendly regeneration and facile reusability.In this study,we developed a composite nanofibrous membrane material with excellent removal performance for organic pollutants based on synergistic adsorption and photocatalysis.A novel boron-doped,nitrogen-deficient graphitic carbon nitride(B-C3N4)photocatalyst as well as an amphiphilic copolymer of methyl methacrylate and acrylic acid(p(MMA-AA))were synthesized respectively,and then used to modify polyethersulfone for the fabrication of composite nanofibrous membrane with improved hydrophilicity,negativelycharge property and enhanced visible light response simultaneously.Subsequently,the synergistic effect of adsorption and photocatalytic degradation for organic pollutants were identified especially and resulted in an excellent removal efficiency even superior to the combination of adsorption and photocatalytic degradation,which could be called a“1+1>2”effect.In addition,the regeneration and reusability,the purification ability for multicomponent wastewater,and the photocatalytic mechanism,were investigated and discussed systematically.In this work,we not only prepared the nanofibrous membrane with synergistic effect of adsorption and photocatalysis,but also provided a versatile approach to design dualfunctional support material to ensure the practical applications of powdery photocatalyst in wastewater treatment.

Recent progress of two-dimensional nanosheet membranes and composite membranes for separation applications

Two-dimensional(2D)materials have emerged as a class of promising materials to prepare high-performance 2D membranes for various separation applications.The precise control of the interlayer nano-channel/sub-nanochannel between nanosheets or the pore size of nanosheets within 2D membranes enables 2D membranes to achieve promising molecular sieving performance.To date,many 2D membranes with high permeability and high selectivity have been reported,exhibiting high separation performance.This review presents the development,progress,and recent breakthrough of different types of 2D membranes,including membranes based on porous and non-porous 2D nanosheets for various separations.Separation mechanism of 2D membranes and their fabrication methods are also reviewed.Last but not the least,challenges and future directions of 2D membranes for wide utilization are discussed in brief.