New Types Of Membranes Research Articles

A COMPARISON OF GBR MEMBRANES

Introduction: Guided bone regeneration has become common practice among surgeons because it gives them the opportunity to place implants in bone defects or absorbed alveolar ridges. This fact raises the question which membrane should one use to achieve the best results. Purpose and Methods: The aim of this study is to present the most recent data around GBR membranes. The existing types of membranes will be compared for their ability to facilitate bone regeneration, their biocompatibility, and their clinical complications. Research for this study was done by evaluating papers of the last decade from the following online databases: PubMed, Medline, and Google Scholar. Finally, selected clinical cases will be presented. Results: Membranes are divided in two main categories resorbable (collagen, synthetic) and non-resorbable (ePTFE, Ti reinforced). It is quite challenging to compare clinical trials because they use different parameters for comparison such as selection criteria of the patients, the type of defect to be treated, the way of executing the treatment, the duration, the materials used and the evaluation criteria. As far as bone regeneration is concerned there seem to be no significant differences in bone level and density of newly formed bone between different types of membranes when used in combination with bone grafts. However, non-resorbable membranes are more likely to cause tissue dehiscence, become exposed to the oral environment and subsequently become infected. Also, there are new types of membranes being studied which aim to play an active role in bone regeneration with embedded active ingredients, but more research needs to be done. Conclusions: According to the most recent protocols the combination of bone grafts and collagen membranes is selected in most cases because it has less clinical complications.

PIM-1 as an organic filler to enhance CO2 separation performance of poly (arylene fluorene ether ketone)

PIM-1 and poly(arylene fluorene ether ketone) (Am-PAFEK) were synthesized by polycondensation. Their structures were characterized by 1H NMR and FT-IR spectral analyses. A series of flexible and transparent blend membranes were prepared by solution blending with different ratios of PIM-1 and Am-PAFEK. DSC and SEM analyses showed good compatibility between them. PIM-1 and Am-PAFEK in the blend membrane perform their respective functions. The former provides excellent permeability; the latter provides high selectivity for CO2. Addition of 20% Am-PAFEK into the blend membrane increased the gas separation selectivity of CO2/CH4 and CO2/N2 by 75% and 65%, respectively. The optimum separation performance was achieved with blend membrane with a CO2 permeability of 752.4 Barrer and a CO2/N2 selectivity ratio of 26.7, extremely close to the Robeson upper bound (2008). After 140-days aging test, the blend membranes still maintained above 70% CO2 permeability, indicating that it has good antiaging properties. Consequently, the new type of membranes have great potential in industrial applications.

Graphene Oxide Incorporated Forward Osmosis Membranes With Enhanced Desalination Performance and Chlorine Resistance.

In this work, grapheme oxide (GO) nano-sheets were synthesized and dispersed in the aqueous phase for the interfacial polymerization (IP) process to develop a new type of thin-film composite (TFC) membranes for forward osmosis (FO) applications. The effects of the GO concentrations on the membrane surfaces and cross-sectional morphologies and FO desalination performances of the as-prepared TFC membranes were investigated systematically. Compared with the control membrane, the optimal GO-incorporated TFC membrane displayed higher water flux, less specific reverse solute flux (SRSF) and lower structure parameter. Moreover, the optimized membrane showed 75.0 times higher chlorine resistance than the control membrane. In general, these new type of membranes could be an effective strategy to fabricate high-performance FO membranes with good desalination performance and chlorine resistance.

Preparation and investigations of ABPBI membrane for HT-PEMFC by immersion precipitation method

Poly(2,5-benzimidazole) (ABPBI) membranes were prepared by an easy and benign ‘immersion precipitation’ method; alleviating drawbacks of conventional solution casting method involving evaporation of the corrosive solvent. The importance of varying inherent viscosity on the properties of resulting membranes was investigated. The porous membranes formed by immersion precipitation method were analyzed for basic properties (water flux, porosity and dimensional analysis). Since the dense structure is required for their applicability for a fuel cell, through-porosity of the formed membranes was successfully eliminated using a unique shrinkage (~50%) property of ABPBI, initially, at 60 °C followed by at higher temperature. The correlation of membranes annealing temperature with the mechanical properties, phosphoric acid doping and proton conductivity was established. The present membranes exhibited high doping level (5.1 mol/RU), proton conductivity (0.083 S cm−1) and fuel cell performance. For comparison, solution casted membranes were prepared and analyzed. The OCP (0.91 V) and max power density (766 mW cm−2) are quite promising features of this new type of membranes.

Preparation of PET track-etched membranes for membrane distillation by photo-induced graft polymerization

New type of membranes with appropriate mechanical strength, thermal and chemical stability, high efficiency and hydrophobic surface are requisite for the development of membrane distillation (MD) applications. In this study hydrophobic track-etched membranes (TeMs) with pore size of 180 nm and thickness of 12 μm based on polyethylene terephthalate (PET) were prepared using photo-induced graft polymerization of silicon monomer such as triethoxyvinylsilane leading to increasing of contact angle up to 104°. The effect of monomers and additives concentration, time of grafting and aging on the surface morphology, pore size and contact angle were investigated by Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDX) and goniometric analysis. The performance of the membranes was evaluated using direct contact membrane distillation (DCMD) process. The results show maximum permeate flux of 700 g/m2·h and 180 g/m2 h (dT = 75 °C) during 24 h saline solution operation (15 and 30 g/l respectively) with efficiency up to 99.3%.

Highly permeable polymer separates gases

As college students prepare for the journey to school later this month, they’ll likely be packing comfy chairs and other precious finds tightly into their cars. In some situations, such as designing polymer membranes, tight packing is not the way to go, a study shows. By creating a polymer with molecular branches that pack inefficiently, researchers have made a potentially highly useful membrane (Nat. Mater. 2017, DOI: 10.1038/nmat4939). The exceptionally permeable material may lead to new types of membranes for large-scale separation of air gases, biogas purification, and carbon capture. Separating gases by passing them through membranes could be a low-cost, energy-saving alternative to other gas separation methods. For instance, cryogenic distillation chills air to ultralow temperatures to liquefy it, which is energy intensive, then separates the components by their boiling points. A few membrane-based techniques have been commercialized. But in general, polymer films are not very gas permeable, which

Description of the gas transport through dynamic liquid membrane

Abstract Recently we published a short communication about the gas separation by new type of membranes so called “dynamic liquid membranes” (DLM). The gas transport through water film was described by solution diffusion model commonly used for evaluation of the gas permeation through nonporous polymeric membranes; therefore this type of membranes is suitable for the separation of such systems where one of the components has high solubility in water. The separation ability of DLM based on thin water film for the binary mixtures of carbon dioxide and methane was investigated. Since direct measurement of permeate flux and its composition was not possible, we suggested three models for gas transport evaluation based on the use of simplifying assumptions. The obtained values of carbon dioxide permeate flux (permeance) from all models are very close, the highest difference is 6.3 mol % for feed composition 92 mol % CO2. Carbon dioxide flux is between 0.048 and 0.729 m3 m−2 h−1. The results of carbon dioxide permeation flux determined as difference between experimental values of the feed and retentate fluxes with permeate flux calculated using the Model 3 were in very good agreement.

Origins and Evolution of Inorganic-Based and MOF-Based Mixed-Matrix Membranes for Gas Separations

Gas separation for industrial, energy, and environmental applications requires low energy consumption and small footprint technology to minimize operating and capital costs for the processing of large volumes of gases. Among the separation methods currently being used, like distillation, amine scrubbing, and pressure and temperature swing adsorption, membrane-based gas separation has the potential to meet these demands. The key component, the membrane, must then be engineered to allow for high gas flux, high selectivity, and chemical and mechanical stability at the operating conditions of feed composition, pressure, and temperature. Among the new type of membranes studied that show promising results are the inorganic-based and the metal-organic framework-based mixed-matrix membranes (MOF-MMMs). A MOF is a unique material that offers the possibility of tuning the porosity of a membrane by introducing diffusional channels and forming a compatible interface with the polymer. This review details the origins of these membranes and their evolution since the first inorganic/polymer and MOF/polymer MMMs were reported in the open literature. The most significant advancements made in terms of materials, properties, and testing conditions are described in a chronological fashion.

Molecular Simulation Study of Gas Solubility and Diffusion in a Polymer-Boron Nitride Nanotube Composite.

We study the possibility of using polymer composites made of a polymer and boron nitride nanotubes (BNNTs) as a new type of membranes for gas separation. The polymer used is amorphous poly(ether imide) (PEI), and zigzag BNNTs are used to generate the composites with the PEI. The solubilities and self-diffusivities of CO2 and CH4 in the PEI and its composites with the BNNTs are calculated by molecular dynamics (MD) simulations. The molecular models of the PEI and its composites with the BNNTs are generated using energy minimization and MD simulation, and the Universal Force Field is used to represent the interactions between all the atoms. The morhology of the composites are characterized and are compared with that of PEI. The accuracy of the computations is tested by calculating the gases' solubilities and self-diffsivities in the pure PEI and comparing them with the experimental data. Good agreement is obtained with the data. The computed diffusivities and solubilities in the polymer-BNNTs composites are much larger than those in the pure polymer, which are attributed to the changes that the BNNTs induce in the polymer composite's free-volume distribution. As the mechanical properties of the polymer-BNNTs composites are superior over those of the pure PEI, their use as a membrane for gas separation offers distinct advantages over the pure polymer. We also demonstrate that, calculating the diffusion coefficients with MD simulations in the NPT ensemble, as opposed to the common practice of utilizing the NVT ensemble, leads to much more accurate results.

Separation of gas mixtures by new type of membranes – Dynamic liquid membranes

Abstract The selectivity and permeability of membrane material determines the efficiency of the gas separation process. To prepare a stable high selective and high permeable membrane and, in addition, also cheap, is the dream of most scientists dealing with the membrane technology. We proposed to investigate the gas separation by a completely new type of membranes possessing both; high selectivity and high gas permeability. Our preliminary results are very promising. We are able to prepare a very cheap and very thin liquid film with high separation performance of test CO2/CH4 mixture. A next curiosity of the new type of membranes is the continuous regeneration of the liquid film during the separation process. Based on this fact, we named the liquid film “dynamic liquid membrane” (DLM).

Dry–wet phase inversion block copolymer membranes with a minimum evaporation step from NMP/THF mixtures

Block copolymer (BCP) membranes are a very promising new type of membranes, but often have a difficult fabrication method that involves a long evaporation step prior to phase inversion. In this work, we study new novel BCP phase inversion recipes for the fabrication of asymmetric membranes with a thin, ordered isoporous selective layer on top of a highly interconnected porous support layer. A key aim is to shorten the evaporation time while simultaneously allowing the formation of even thinner selective top layers. Asymmetric membranes were fabricated via the combination of polystyrene-block-poly(4-vinyl pyridine) self-assembly, solvent evaporation and liquid induced phase separation. Using a solvent mixture of THF and NMP, a selective top layer of just 60nm thick was formed with an ordered honeycomb-like pore structure. The formed structure depended on several parameters, such as THF/NMP ratio, polymer concentration of the polymer solution and the duration of solvent evaporation. When a high THF/NMP ratio was used (more THF than NMP) the solvent evaporation step could be reduced to only 1s, a clear advantage when considering scale up of this approach. The THF/NMP ratio also influenced the morphology of the support layer, which translated into a variety of permeabilities (270–1320Lm−2h−1bar−1). Filtration experiments showed that the different top layer structures result in different filtration performance, with more ordered pores resulting in more selective filtration.

Challenges in Commercializing Biomimetic Membranes.

The discovery of selective water channel proteins—aquaporins—has prompted growing interest in using these proteins, as the building blocks for designing new types of membranes. However, as with any other new and potentially disruptive technology, barriers for successful market entry exist. One category includes customer-related barriers, which can be influenced to some extent. Another category includes market-technical-related barriers, which can be very difficult to overcome by an organization/company aiming at successfully introducing their innovation on the market—in particular if both the organization and the technology are at early stages. Often, one faces barriers from both these categories at the same time, which makes it necessary to gain insight of the particular market when introducing a new innovative product. In this review we present the basic concepts and discuss some of these barriers and challenges associated with introducing biomimetic aquaporin membranes. These include technical issues in membrane production and product testing. Then we discuss possible business models for introducing new technologies in general, followed by a presentation of beach-head market segments relevant for biomimetic aquaporin membranes.

Behavior of ionic species in sulfonated PEI using DFT simulations: A study to determine ionic conductivity

Compared with internal combustion engines, PEMFC are able to operate without polluting emissions. Increasing the operating temperature of the FC above 100 °C is one of the major objectives in this field as it would facilitate the commercial development of electric vehicles powered by fuel cells. To achieve this objective, it is important to develop new types of membranes to replace Nafion®. The poly (ether imide) sulfonated are presented as a new alternative in order to use as an electrolyte in PEMFC. In this work, DFT theory has been used to study the interaction between ionic species charged of hydrogen as hydroxyl ((OH)−) or hydronium ((H3O)+) and sulfonated poly (ether imide). The analysis of molecular reactivity through frontier MO (HOMO and LUMO) allows determine the mechanism of ionic conductivity which takes place over the polymeric membrane. This study is addressed to improve the efficient of PEM fuel cells.

Biomimetic aquaporin membranes coming of age

Membrane processes have been widely used for water purification because of their high stability, efficiency, low energy requirement and ease of operation. Traditional desalting membranes are mostly dense polymeric films with a “trade off” effect between permeability and selectivity. Biological membranes, on the other hand, can perform transport in some cases with exceptional flux and rejection properties. In particular the discovery of selective water channel proteins – aquaporins – has prompted interest in using these proteins as building blocks for new types of membranes. The major challenge in developing an aquaporin-based membrane technology stems from the fact that the aquaporin protein spans a membrane only a few nanometers thick. Such ultrathin membranes will not be able to withstand any substantial pressures, nor being industrially scalable without supporting structures. Incorporating aquaporin proteins into compatible materials, while ensuring membrane performance, scalability, and cost-effective production, is crucial for a successful technology development. Since the first suggestions for using aquaporins in membrane technology appeared around ten years ago, two main approaches have been suggested based on planar membranes and vesicles respectively. Here we summarize the essentials of aquaporin protein function and review the latest progress in this fascinating area of membrane research and development.

Mechanisms of Gas Permeation through Single Layer Graphene Membranes

Graphene has enormous potential as a unique molecular barrier material with atomic layer thickness, enabling new types of membranes for separation and manipulation. However, the conventional analysis of diffusive transport through a membrane fails in the case of single layer graphene (SLG) and other 2D atomically thin membranes. In this work, analytical expressions are derived for gas permeation through such atomically thin membranes in various limits of gas diffusion, surface adsorption, or pore translocation as the rate-limiting step. Gas permeation can proceed via direct gas-phase interaction with the pore, or interaction via the adsorbed phase on the membrane exterior surface. A series of van der Waals force fields allows for the estimation of the energy barriers present for various types of graphene nanopores. These analytical models will assist in the understanding of molecular dynamics and experimental studies of such membranes.

Synthesis of polymer electrolyte membranes based on poly(norbornene)s functionalized with pendant difluoroalkyl sulfonic acids

A novel difluoroalkanesulfonyl fluoride monomer, 2-(bicyclo[2.2.1]hept-5-en-2-yl)-1,1-difluoro-2- methoxypropane-1-sulfonyl fluoride, was synthesized in two steps. Nucleophilic addition of 2-acetyl-5-norbornene with difluoromethyl 2-pyridyl sulfone, followed by methylation with methyl trifluoromethanesulfonate produced substituted difluoromethyl 2-pyridyl sulfone. Removal of the pyridyl group with KOH/MeOH, and fluorination with Selectfluor afforded the desired monomer. Novel poly(norbornene)s containing pendent difluoroalkanesulfonic acids were synthesized by copolymerization of varying molar ratios of norbornene with difluoroalkanesulfonyl fluoride monomer by ring opening metathesis polymerization (ROMP) using Grubbs second-generation catalyst, followed by hydrolyzing under basic condition and treatment with aqueous HCl. Room temperature proton conductivity (12?49 mS/cm) was observed with these new type of membranes.

Nanofiber-based polyelectrolytes as novel membranes for fuel cell applications

Partially sulfonated poly(ether sulfone) (SPES) was prepared and electrospun to bead-free nanofibers. The obtained data from solution conductivity measurements and scanning electron microscopy illustrated that sulfonation leads to a drastic increase in polymer solution conductivity and a considerable decrease in nanofiber diameter and a narrower diameter distribution. The new types of membranes were fabricated using Nafion-filled electrospun mats. The porous SPES nanofibrous membranes were impregnated with appropriate amount of Nafion solution. After a good pore-filling, an excess amount of Nafion solution was used to form a uniform top layer (SPES-N-N). Another bilayer polyelectrolyte membrane was prepared by direct electrospinning of SPES nanofibers on Nafion112 membrane's surface and followed by impregnation of Nafion solution into the pores of electrospun SPES (SPES-N-N112). The membranes were characterized by methanol permeability, proton conductivity, oxidative/hydrolytic stability as well as single cell direct methanol fuel cell (DMFC) performance tests. The proton to methanol selectivity of the SPES nanofiber-based bilayer membranes is about 53,680 and 45,500Sscm−3 for SPES-N-N and SPES-N-N112 in comparison with 28,300 and 40,500Sscm−3 for Nafion112 and Nafion117, respectively. The single cell DMFC performance results revealed that the SPES nanofiber-based bilayer membranes have higher electrochemical performance than Nafion112 and Nafion117 membranes especially in elevated methanol concentration. The results showed that the fabricated bilayer membranes can be used as a promising polyelectrolyte membrane for fuel cell applications.

New proton conducting hybrid membranes for HT-PEMFC systems based on polysiloxanes and SO 3H-functionalized mesoporous Si-MCM-41 particles

For increased efficiency of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFC), new types of membranes have to be developed. This approach has been realized by preparing hybrid membranes containing SO 3H-functionalized mesoporous Si-MCM-41 as hydrophilic inorganic modifier in a polysiloxane matrix exhibiting sulfonic acid groups and basic heterocyclic groups like benzimidazole. The proton conductivity of sulfonated particles was modelled on the atomic scale in order to understand the influence of the density of sulfonic acid groups and of the presence of water molecules. The different hybrid membranes are characterized concerning their thermal stability, water uptake, and proton conductivity. Whereas the proton conductivity of well-established, but expensive and at >120 °C not long-time stable Nafion membranes continuously decreases with increasing temperature, the polysiloxane membranes, which suffer from a low-proton conductivity at around 100 °C, recover at about 120 °C due to intrinsic proton transport. At 180 °C the pure polysiloxane shows a proton conductivity which is only one order of magnitude lower than that of Nafion. Moreover, if the polysiloxane membrane contains additionally 10 wt.% of an SO 3H-modified Si-MCM-41, the proton conductivity of such hybrid membrane at temperatures >180 °C and low relative humidity <10% is higher than that of Nafion membranes by a factor of 10.

Two new types of copolymer membranes controlling clonidine zero-order release

Two new types of membranes were synthesized by UV curing in our laboratory. The first type of membrane was made of three monomers: 2-hydroxy-3-phenoxypropylacrylate(A), 4-hydroxybutyl acrylate(B), and 2-methyl-2-nitropropyl methacrylate(C1). The second type of membrane was made of the same monomers A and B, and 2-butoxyethyl methacrylate(C2). Permeation properties of clonidine releasing through two new types of copolymer membranes were studied. The effects of the ratios of monomers, the thicknesses of membranes, and the concentration of clonidine on the permeation rates were studied. It was found that both copolymer membranes could control clonidine zero-order release. The permeation rates of the first optimized membrane were linearly dependent on the square root of the drug concentration. The permeation rates of the second optimized membrane had no significant difference when the concentration of clonidine varied in the range of 3.0–5.0 mg mL−1. Furthermore, both optimized membranes were characterized by FTIR, DSC, and SEM. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Nanofiltration and calcium sulfate limitation for top brine temperature in Gulf desalination plants

All MSF desalination plants have been operated at a top brine temperature below 120°C. That is because of sulfate scaling phenomena, which usually occurs when the temperature is higher than 120°C. This type of scaling is hard scale that cannot be removed easily by chemical or mechanical cleaning. In the recent years desalination technology has created a new type of membranes that can overcome sulfate scaling. These new type of membranes is a nanofiltration membrane (NF). NF membranes have the ability to remove the sulfate and calcium ions in seawater feed, as a result the risk for sulfate scaling is eliminated. This paper mainly aims to study the scaling potential of CaCO 3, CaSO 4, BaSO 4, SrS0 4, silica and CaF at different productivity with a nanofiltration product water and compare it with the scaling potential of normal seawater. This paper also studies the maximum possible percentage inhibition for CaSO 4 using nanofiltration product water, if this water is used as a feed for a MSF unit. Acidification process has been also tried at different dosing to increase the % inhibition for CaCO 3 scaling. The result indicated a great percentage inhibition for CaSO 4 scale using a nanofiltration membrane. The inhibition reached 99.1% at 35% productivity and decreased to about 96.98% at 75% productivity without addition of any antiscalant or chemicals. The result also show a low prevention for CaCO 3 scaling started from 23.41 % inhibition at 10% productivity and decrease to about 5.3% at 75% productivity. Also for all other scaling constitutes, a great scaling inhibition was found — about 97.7% for BaS0 4, 99.8% for SrSO 4 scaling and 94.86% inhibition for CaF scaling at 50% conversion. This study proved the reliability of a nanofltration system in preventing all types of scaling in the Gulf seawater, which can be considered as a revolution in the MSF plants when applied at high operation temperature.