Inorganic Membrane Materials Research Articles

Precise molecular sieving of ethylene from ethane using triptycene-derived submicroporous carbon membranes.

Replacement or debottlenecking of the extremely energy-intensive cryogenic distillation technology for the separation of ethylene from ethane has been a long-standing challenge. Membrane technology could be a desirable alternative with potentially lower energy consumption. However, the current key obstacle for industrial implementation of membrane technology is the low mixed-gas selectivity of polymeric, inorganic or hybrid membrane materials, arising from the similar sizes of ethylene (3.75 Å) and ethane (3.85 Å). Here we report precise molecular sieving and plasticization-resistant carbon membranes made by pyrolysing a shape-persistent three-dimensional triptycene-based ladder polymer of intrinsic microporosity with unparalleled mixed-gas performance for ethylene/ethane separation, with a selectivity of ~100 at 10 bar feed pressure, and with long-term continuous stability for 30 days demonstrated. These submicroporous carbon membranes offer opportunities for membrane technology in a wide range of notoriously difficult separation applications in the petrochemical and natural gas industry.

Efficient photochromic self-recovery behavior in Tm/Yb co-doped K0.5Na0.5NbO3 thick films

Photochromic (PC) materials have potential applications in the fields of memory, anti-counterfeiting due to their reversible writable/erasable properties. The common organic PC films are restricted during applications owing to the strict requirements of thermal stability and waterproof of devices. Additionally, most of the PC materials strongly rely on external conditions (irradiation/heat) to realize reversible PC regulations, which may cause irreversible damage to devices (reduce the performance and service life). Hence, it is imperative to develop new inorganic membrane materials with PC self-recovery behavior. Here, a novel strategy to achieve completely reversible PC regulation based on the K0.5Na0.5NbO3 (KNN) based thick films is reported. It is worth noting that the PC self-recovery behavior can be optimized via forming the inter-electronic-levels in the band gap via Tm/Yb co-doping in KNN, alleviating the barrier of carrier transition from valence band to conduction band and heightening the recombination efficiency of carriers. And the obtained thick films manifest a reversible PC self-recovery reaction within 6 min. This work is expected to provide the effective guidance for facilitating the further utilization of PC materials.

Research progress and prospect of membrane method in seawater/brine extraction of lithium

With the widespread promotion of new energy electric vehicles for lithium batteries worldwide, the demand for lithium is surging. And the industry chain of lithium is in the process of technological transformation and upgrading, the extraction of lithium from salt lake brine is becoming the main source. Comprehensively compare the precipitation method, adsorption method, calcining leaching method, extraction method, and other processes used in the extraction of lithium from brine, membrane separation is a high-efficiency and energy-saving separation and purification technology without phase change at room temperature, and it has become the most promising energy-saving and environmentally-friendly new technology in the lithium extraction industry. At present, the research on membrane processes with lithium separation effect mainly includes membrane-adsorption, membrane-solvent extraction and membrane-electrodialysis, etc. And membrane-electrodialysis technology has been successfully applied to extract lithium from salt lake brine in industry. However, the existing shortcomings of organic membranes, such as membrane blockage, organic matter dissolution loss, and environmental pollution, limit the promotion of membrane-electrodialysis in the lithium extraction industry. Inorganic ceramic membranes are divided into microfiltration, ultrafiltration and nanofiltration according to the pore size. The separation process is mainly based on the “physical screening” theory, and the inorganic ceramic membrane material has stable chemical structure, good mechanical properties, simple preparation process, high temperature resistance, uniform pore size, It has many advantages such as narrow pore size distribution range and long life. Therefore, the development of new inorganic membrane materials has attracted widespread attention from the academic community and has become a hot issue in the study of lithium extraction by membrane methods.

Do membrane filtration systems in drinking water treatment plants release nano/microplastics?

Drinking water treatment plants (DWTPs) are thought to be able to remove many micropollutants including nanoplastics (NPs) and microplastics (MPs). However, few studies have focused on the water treatment process itself producing NPs and/or MPs. This paper discussed the possibility of releasing NPs and MPs from organic membranes in drinking water treatment plants. The effects of physical cleaning, chemical agents, mechanical stress, aging, and wear on the possibility of membrane breach during long-term use were analyzed. Further analysis based on membrane aging mechanisms and material properties revealed that the membrane filtration systems could release NPs/MPs to drinking water supply networks. Although the toxicity of membrane materials to human body needs further study, the action that should be taken to treat the release of NPs/MPs in DWTPs cannot be ignored: (1) in-depth study of the generation and release mechanisms of NPs/MPs; (2) reconsideration of membrane life cycle design; (3) determination of NPs/MPs concentration limits in drinking water through toxicity assessment; (4) accelerating development of biomembrane and inorganic membrane materials; and (5) unification of NPs/MPs sampling and testing standard. Accordingly, more research needs to be conducted to investigate the release of NPs and/or MPs from DWTPs.

Optimal process design of biogas upgrading membrane systems: Polymeric vs high performance inorganic membrane materials

Membrane separation is a key technology for biogas purification. Multistaged processes based on either cellulose acetate (CA) or polyimide (PI) materials are classically used for this application. In this study, a systematic process synthesis optimization is performed in order to identify the most cost effective solution for three different membrane materials (CA, PI and zeolite) and three different outlet pressure levels (5, 10 and 15 Bar). It is shown that a costly (i.e. 2000 EUR per square meter vs 50 for CA and PI) but high performance membrane material such a zeolite offers the best cost effective solution compared to commercially available polymeric membranes. Increasing the outlet pressure increases the purification cost. Two stages processes with recycling loops offer the best balance between purity, recovery, complexity and cost, whatever the outlet pressure level. The use of vacuum pumping is shown to improve the process economy, while expander and extra feed compression do not show an interest.

Membrane desalination technologies in water treatment: A review

Abstract One of the most pressing problems worldwide is inadequate access to potable water. Many technologies have been applied to address this through research to find robust but inexpensive methods of desalination that offer high fluxes and use less energy, while reducing chemical use and environmental impact. Membrane desalination technology is universally considered to solve water shortage problems due to its high efficiency and lower energy consumption than distillation methods. This review focuses on the desalination performance of membrane technologies with consideration of the effect of driving force, potential technologies, membrane types, flux, energy consumption and operating temperature, etc. Pressure driven membrane processes (MF, UF, NF, RO), and their fouling propensity and major drawbacks are discussed briefly. Membrane characteristics and the effects of operating conditions on desalination are also covered. Organic-hybrid and inorganic membrane materials can offer advantages, with high flux, good selectivity, and useful chemical and thermal resistance.

Preliminary study on gas separation performance of flat sheet mixed matrix (PVDF/Zeolite)

Membrane separation has attracted a lot of attention over the last years mainly due to its separation ability, operational capability and economical viability. Mixed matrix membrane (MMM) combines the superior transport and selectivity properties of inorganic membrane materials and the excellent fabrication properties of organic polymers. This emerging technology can be utilized to purify biogas which can be used in a variety of applications. In this study, flat sheet mixed matrix membranes were synthesized with different percentages of N-Mehtyl-2-pyrrolidone (NMP) as solvent, Polyvinylidene Fluoride (PVDF) as the polymer matrix and zeolite 4A as the dispersed fine particles, membrane A (80: 20: 0), membrane B (80: 18: 2), membrane C (80: 15: 5), and membrane D (75: 15: 10) respectively. The membranes were fabricated using dry/wet phase inversion method. The membrane’s performance in terms of permeability and selectivity was examined using the single gas permeation device. The general trend was that, the permeability of the two gases (CO2/CH4) decreased with the increase of the pressure (0.5, 1, 1.5) bar. Membrane D was found to be suitable to separate the pair gas (CO2/CH4) as the permeability was 65623.412, Barrer and 15587.508, Barrer respectively, and its selectivity for was 4.21 at 0.5 bar.

Ion-fuelled L-Phenylalanine controlled pumping by hybrid membrane materials

We report organic–inorganic membrane materials for controlled translocation of ion-pairs along directional conduction pathways. The supramolecular/sol–gel combined procedure has been realised in two steps. First, the self-organization properties of 3-(ureidoarene)propyltriethoxysilane compound, 1 in aprotic solvents were determined, revealing the formation of supramolecular oligomers, in the self-assembly step. They led in a second sol–gel transcription step to hybrid membrane materials. Then, the transport of organic molecules of variable charge, like L-Phenylalanine can be directionally tuned, via ion-fuelled membrane polarization phenomena. Using this strategy, the transport of the cationic, zwitterionic and anionic forms of the L-Phenylalanine can be controlled and directionally oriented from the feed to strip phase and vice versa.

Synthesis and characterization of hybrid organic–inorganic materials based on sulphonated polyamideimide and silica

The preparation of hybrid organic–inorganic membrane materials based on a sulphonated polyamideimide resin and silica filler has been studied. The method allows the sol–gel process to proceed in the presence of a high molecular weight polyamideimide, resulting in well dispersed silica nanoparticles (<50 nm) within the polymer matrix with chemical bonding between the organic and inorganic phases. Tetraethoxysilane (TEOS) was used as the silica precursor and the organosilicate networks were bonded to the polymer matrix via a coupling agent aminopropyltriethoxysilane (APTrEOS). The structure and properties of these hybrid materials were characterized via a range of techniques including FTIR, TGA, DSC, SEM and contact angle analysis. It was found that the compatibility between organic and inorganic phases has been greatly enhanced by the incorporation of APTrEOS. The thermal stability and hydrophilic properties of hybrid materials have also been significantly improved.

Ion transport in nanocomposites

Successive analysis of interface defect formation and its implications for the ionic conductivity was carried out for ionically conducting nanocomposites that hold much significance for technological applications. It was shown that the most efficient way to prepare such composites is through the use of nanosized particles. A review was made of the current state of research on inorganic composites and hybrid membrane materials that are already in use in alternative power engineering.

Alkali cation-π aromatic conduction pathways in self-organized hybrid membranes

We report new hybrid organic–inorganic membrane materials in which alkali cations are envisioned to diffuse along cation-π aromatic conduction pathways. The hierarchical generation of functional hybrid membrane materials has been realised in two steps. First, the self-assembling properties of 3-(ureidoarene)propyltriethoxysilane compounds in aprotic solvents were determined, revealing the formation of supramolecular oligomers. They led in a second sol– gel transcription step to self-organized hybrid membrane materials at nanoscopic scale. Finally they have been tested in dialysis transport experiments. The transport selectivity through self-organized membranes is due to the interaction of the partially hydrated ions with the hydrophilic or hydrophobic pathways within the matrix of the membrane. This interaction is governed by the energetic balance between the dehydration free energy and the binding energy of cation-π interaction with the aromatic moieties.

New approaches in the design of ceramic and hybrid membranes

This paper describes approaches developed for the preparation and also the characterization of innovative inorganic or hybrid membrane materials. Soft chemistry routes, sol–gel methods and plasma-enhanced chemical vapour deposition (PECVD) are used to get tailor-made layers with different architectures. The infiltrated composite membranes are first examined. They exhibit a good thermo-mechanical resistance, a low sensitivity to the presence of defects, a relatively high flow resistance and are attractive for catalytic contactor applications. Preliminary results on supported ceramic membranes with a hierarchical porosity are then presented. Finally, examples are given to illustrate the interest of the PECVD route and of plasma post-treatments for preparing very thin hybrid separative layers.

Molecular Modeling Study of the Permeability−Selectivity Trade-off in Polymeric and Microporous Membranes

A permeability−selectivity trade-off is observed in kinetic (diffusion-based) separations, such as oxygen/nitrogen, on polymeric and inorganic microporous membrane materials. Some materials are inherently better than others in the trade-off, but the molecular-level reasons are not clear. In this paper, we employed a molecular modeling approach to study the oxygen/nitrogen separation and provide insight into optimizing the pore characteristics (geometry, material of construction) for separation performance. The pore models were abstract, with features representative of different microporous or polymeric materials. They comprised three-dimensional atomistic models of unidirectional pores with diameters <5 A; various aspects of the pore geometry and material of construction were varied. Oxygen and nitrogen were modeled as rigid dimers, and the Lennard-Jones (LJ) potential was used to model the gas−pore site interactions. Free energy calculations and transition-state theory were used to predict the permeation...

Membranes for solubility-based gas separation applications

The use of membranes in gas separations has grown at a very rapid pace in recent times. One particularly interesting application of gas separation with membranes is the removal of dilute heavy organics from light gas streams such as the removal of solvents from the exhaust of different process industries. For such applications separations are achieved using the solubility-selective mode in which preferential permeation of the heavier organic molecules is desired. This article aims to review some of the recent advancements in the field of membranes for solubility-based gas separations. The development of different inorganic, polymeric and hybrid membrane materials in light of the opportunities and challenges are presented.

Pervaporation of Aqueous Organic Acid Solutions by Porous Ceramic Membranes

Porous silica, silica-zirconia and silica-titania membranes were prepared by the sol-gel techniques for separation of aqueous solutions of organic acids (acetic acid and propionic acid) by pervaporation at 50–100°C and at normal boiling points. Applying the hot coating procedures with the colloidal sols prepared in different concentrations (different particle sizes), a quite thin porous silica layer active for separation was formed on a porous α-alumina cylindrical substrate.A fresh porous silica membrane showed a long time-dependency of several hours in the pervaporation performance before reaching a steady state due to the formation of silanol groups on the pore surface. Because of its small thickness less than about 0.5 μm quite large water fluxes of about 300 mol·m–2·h–1 were observed with a separation factor higher than several hundreds at around 73 mol% of acetic acid (10 wt% water) at 100°C, for example. Stability tests of the porous ceramic membranes were performed in aqueous organic acid solutions to find that silica and silica-titania membranes were quite stable in an aqueous solution of organic acid of concentration higher than about 20 mol% acid. Silica-zirconia membranes, on the other hand, were not stable in aqueous organic acid solutions of high concentration. The membrane stability is discussed on the observed solubility of inorganic membrane materials. Furthermore, separation and permeation mechanisms were discussed based on a simple pore model for pervaporation proposed previously to give good coincidence between observed and simulated results.

Membrane Ozonation in Wastewater Treatment

AbstractThe utilization of porous membranes in mass transfer processes of gaseous ozone to water was investigated. With this approach a direct control of the interface between gas and liquid is possible. Furthermore it prevents foam formation in the presence of surfactant pollution, which constitutes a problem in conventional ozonation methods. Different organic and inorganic membrane materials and geometrical arrangements were utilized and ozone transfer under varied experimental conditions was determined. Typical transfer rates obtained in the experiments were 10 g ozone per membrane square meter and hour, but under optimized conditions higher values were possible. A theoretical model was successfully applied to the results obtained. A peculiarity of the method is its inherent ozone dose control in relation to the volume flow of water.

Inorganic membranes and solid state sciences

Abstract The latest developments in inorganic membranes are closely related to recent advances in solid state science. Sol–gel processing, plasma-enhanced chemical vapor deposition and hydrothermal synthesis are methods that can be used for inorganic membrane preparation. Innovative concepts from material science (templating effect, nanophase materials, growing of continuous zeolite layers, hybrid organic–inorganic materials) have been applied by our group to the preparation of inorganic membrane materials. Sol–gel-derived nanophase ceramic membranes are presented with current applications in nanofiltration and catalytic membrane reactors. Silica membranes with an ordered porosity, due to liquid crystal phase templating effect, are described with potential application in pervaporation. Defect-free and thermally stable zeolite membranes can be obtained through an original synthesis method, in which zeolite crystals are grown inside the pores of a support. Hybrid organic–inorganic materials with permselective properties for gas separation and facilitated transport of solutes in liquid media, have been successfully adapted to membrane applications. Potential membrane developments offered by CVD deposition techniques are also illustrated through several examples related to the preparation of purely inorganic and hybrid organic–inorganic membrane materials.