Thermal Stability Of Membranes Research Articles

Investigating the Antibacterial Activity of Polymeric Membranes Fabricated with Aminated Graphene Oxide.

A novel, functionalized graphene oxide–based cellulose acetate membrane was fabricated using the phase inversion method to improve the membrane characteristics and performance. We studied the effect of aminated graphene oxide (NH2–GO) composite on the CA membrane characteristics and performance in terms of membrane chemistry, hydrophilicity, thermal and mechanical stability, permeation flux, and antibacterial activity. The results of contact angle and water flux indicate the improved hydrophilic behavior of composite membranes in comparison to that of the pure CA membrane. The AGO-3 membrane showed the highest water flux of about 153 Lm−2h−1. The addition of hydrophilic AGO additive in CA membranes enhanced the antibacterial activity of AGO–CA membranes, and the thermal stability of the resulting membrane also improved since it increases the Tg value in comparison to that of a pristine CA membrane. The aminated graphene oxide (NH2–GO) was, therefore, found to be a promising additive for the fabrication of composite membranes with potent applications in wastewater treatment.

TiO2 Nanoparticle Filler-Based Mixed-Matrix PES/CA Nanofiltration Membranes for Enhanced Desalination.

Mixed-matrix nanocomposite (PES/CA/PVP) membranes were fabricated for water desalination by incorporating varying amount of titanium dioxide nanoparticles (TiO2 NPs) ranging from 0 and 2 wt. %. Efficient dispersion of nanoparticles within polymeric membranes was achieved using the chemical precipitation method for uniform surface generation, and an asymmetric morphology was achieved via phase inversion method. Finally, membranes were characterized by Fourier Transform Infrared (FTIR) spectroscopy, Thermo Gravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), porosity and contact angle analysis. FTIR confirmed chemical composition of membranes in terms of polymers (PES/CA/PVP) and TiO2. TGA analysis confirmed an increase in thermal stability of membranes with the increase of TiO2 nanoparticles loading. The addition of TiO2 nanoparticles also resulted in an increase in porous structures due to an increase in mean pore size, as shown by SEM results. An increase in the hydrophilicity of the membranes was observed by increasing the concentration of TiO2 nanoparticles. The present study investigated pristine and mixed-matrix nanocomposite NF membrane performance while filtering a NaCl salt solution at varying concentration range (from 1 to 4 g/Lit 6 bar). The prepared membranes demonstrated significant improvement in water permeability and hydrophilicity. Further, to optimize the water flux and salt rejection, the concentration of Polyvinylpyrrolidone (PVP) was optimized along with TiO2 nanoparticles. Both the water flux and salt rejection of the fabricated membranes were observed to increase with an increase inTiO2 nanoparticles to 2 wt. % loading with optimized PVP concentration, which demonstrated the improved desalination performance of resultant membranes.

Preliminary study on fire risk of redox flow battery components

The redox flow battery (RFB) is one new kind of energy storage unit, which is used in electrochemical energy storage. However, the knowledge on its fire risk is very limited. Thus the fire risk of redox flow batteries was investigated using cone calorimeter and C80 calorimeter in this work. The combustion behaviors of RFB components are tested using cone calorimeter, whereas the thermal behaviors of the component materials, including bipolar plate, electrode frame, electrode and membrane, inside the RFBs are measured using C80 calorimeter. By comparing the results in two experiments, it is indicated that the main hazardous source of the fire is the electrode frame, followed by the bipolar plate. The thermal stability of membranes is the worst. The electrode is a non-flammable component with little fire risk. This analytical results can provide safety guide for both improvements of RFBs and large scale usage.

Unsupported electrospun membrane for water desalination using direct contact membrane distillation

AbstractIn this project, an unsupported electrospun poly(vinylidene fluoride)‐co‐hexafluoropropylene (PVDF‐HFP) membrane was used for water desalination using direct contact membrane distillation (DCMD). The membrane was electrospun using a laboratory‐scale machine with multiple nozzles that was developed in‐house. Critical process parameters, including the applied voltage and polymer concentration, were optimized to obtain bead‐free electrospun membranes with fiber diameters less than 300 nm. To improve the membrane thermal stability and performance, the selected electrospun membrane was heat‐pressed at 160°C. The untreated and heat‐pressed membranes were tested in a DCMD setup at different feed temperatures (60, 70, and 80°C) and feed flow rates (0.4, 0.6, and 0.8 L/min), while maintaining the permeate temperature and flow rate at 20°C and 0.2 L/min, respectively. The modified electrospun membrane exhibited a very high permeate flux (>37.5 kg/m2/h) and a salt rejection rate of 99.99% at a feed temperature of 70°C. The performance of the heat‐pressed unsupported PVDF‐HFP electrospun membrane was nearly identical to a commercially available polytetrafluoroethylene (PTFE) supported membrane. These promising results demonstrate that relatively low‐cost electrospun membranes can be easily produced and successfully used in DCMD to minimize the capital cost and increase the energy efficiency of the process.

Pervaporative Desalination of Water Using Hydroxypropyl methylcellulose / Polyvinylpyrrolidone Blend Membranes

The pervaporation is a promising process to achieve highly efficient desalination performance. In this study, Hydroxypropyl methylcellulose (HPMC) and Polyvinylpyrrolidone (PVP) polymers were chosen in the synthesis of blend membranes and used for pervaporative desalination process. The chemical structure and thermal stability of membranes were analyzed by using Fourier-transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA), respectively. The effects of PVP ratio in membrane and operation temperature on the flux and salt rejection were examined. The highest separation efficiency was acquired as water flux of 4.86 kg/m2h and a salt rejection of 99.9% using 50 wt% PVP ratio at 40 °C. The obtained results show that HPMC/PVP blend membrane has a great potential for water desalination via pervaporation.

Preparation of hybrid membranes by incorporating hydrophilic UiO-66 nanoparticles for high-performance pervaporation dehydration of aprotic solvents

Hydrophilic UiO-66 crystals with superior water adsorption ability were synthesized and incorporated into the polyimide (PI) membrane for efficient aprotic solvent separation via pervaporation. The effect of the different UiO-66 addition in the pyromellitic dianhydride (PMDA)-2, 2-bis[4-(4-amlnophenoxy)phenyl]propane (BAPP)-based PI membrane on the membrane structure, thermal stability, surface hydrophilicity, solvent-resistant, and pervaporation performance was systematically studied. The UiO-66/PI hybrid membranes with small amount content (2 wt%) exhibited high hydrophilicity and excellent swelling resistance due to the superb dispersion benefiting from the excellent complexation of UiO-66 and PI chain. The effects of operational variables such as operating temperature and concentration of feed solution on the pervaporation separation performance of the hybrid membranes with different UiO-66 loadings were investigated. When the mass fraction of UiO-66 was 2 wt%, the hybrid membranes show the permeation flux of 109.7 and 57.1 g/(m2h) and separation factor of 34.1 and 133.9, respectively, for DMF/H2O and DMAc/H2O systems.

Numerical studies of sorption-enhanced glycerol steam reforming in a fluidized bed membrane reactor at low temperature

In order to improve the hydrogen production efficiency by glycerol steam reforming, a membrane-assisted fluidized bed reactor with carbon dioxide sorption is developed to enhance the reforming process. Low-temperature operation in a membrane reactor is necessary considering the thermal stability of membrane. In this work, the sorption-enhanced glycerol steam reforming process in a fluidized bed membrane reactor under the condition of low temperature is numerically investigated, where the hydrotalcite is employed as CO2 sorbents. The impact of operating pressure on the reforming performance is further evaluated. The results demonstrate that the integration of membrane hydrogen separation and CO2 sorption can effectively enhance the low-temperature glycerol reforming performance. The fuel conversion above 95% can be achieved under an elevated pressure.

Polymeric amine membrane materials for carbon dioxide (CO2)/methane (CH4) separation

AbstractCarbon dioxide separation from methane using membrane technology is getting attraction, and polymeric membranes are the most prominent polymer membrane materials. However, the existing polymeric membranes performance is inadequate due to trade‐off limitation open new windows to explore. Therefore, in this study, amine polymeric membrane (APM) has been fabricated by the addition of different concentration (5 wt.% and 15 wt.%) of diethanolamine (DEA). The developed amine polymeric membranes have been characterized in term of morphology and thermal analysis using field emission scanning electron microscope and thermogravimetric analyzer, respectively. The permeance and selectivity have been determined by using pure carbon dioxide (CO2) and methane (CH4). Also, the effect of amine concentration on permeance and selectivity has been studied. The results confirmed the symmetric and homogenous structure and thermal stability of membranes up to 490 °C. The maximum percent increase by the 15 wt.% addition of diethanolamine is 102.08 % at 10 bar pressure.

Rose Quality as Affected by Higher Air Temperatures Resulting from Poly-Tunnel Height in a Subtropical Region

Highlights Interior temperatures increased with decreasing poly-tunnel height. In subtropical regions, high interior temperatures of poly-tunnels could degrade quality of rose-cut flower. Stunted growth of rose plants because of higher temperatures could lead to mis-interpretations of nutrient deficiency. Abstract . High temperature is a major constraint to plant production in many regions of the world. Observations indicate that poly-tunnel structure design can influence interior temperature, and in turn determine the quality of cut flowers, including the length of the stems, the leaf biomass, and nutrient uptake. In this study, interior temperature and cut-flower quality of roses were assessed in five poly-tunnels with eave heights ranging from 2 to 4 m. Interior temperatures from 11:00-15:00 h in the hottest months of July and August were monitored. Rose (Rosa hybrida ‘Peach Avalanche’) was cultivated in these poly-tunnels with the same cultivation regimes. Higher interior temperatures were observed in poly-tunnels with lower eave heights. Leaf membrane thermal stability (MTS) values were negatively correlated with higher interior temperatures, indicating that the photosynthetic system of plant leaves was impaired. Stem length and mass were decreased with higher temperature by over 50%, while leaf biomass decreased by 25% in the poly-tunnel with eave height of 2 m in comparison with that of 4 m. Nitrogen concentration in plant leaves increased with higher temperature, whereas the patterns of other elements were not associated with different poly-tunnel eave heights. These results indicate that poly-tunnel interior high temperatures that were associated with lower eave heights are a major constraint for commercialized rose-cut flower production in this region, and improved design of poly-tunnels could increase production. Keywords: Cut flower, Membrane thermal stability, Stem length, Stem mass, Yunnan Province.

Thermal stability and dynamics of soft nanoparticle membranes: role of entropy, enthalpy and membrane compressibility.

Nanoparticle based ultra-thin membranes have been shown to have remarkable mechanical properties while also possessing novel electrical, optical or magnetic properties, which could be controlled by tailoring properties at the level of individual nanoparticles. Since in most cases the ultra-thin membranes are coupled to some substrates, the role of membrane-substrate interactions, apart from nanoparticle-nanoparticle interactions become very crucial in understanding their mechanical and thermal stability, as well as their plethora of applications. However, systematic studies in this direction have been conspicuously absent. Here we report thermal stability and the corresponding microscopic dynamics of polymer supported ultra-thin membranes comprising of self-assembled, ordered grains of polymer grafted nanoparticles having tunable mechanical properties. The initially ordered membranes show distinct pathways for temperature induced disordering depending on membrane flexibility as well as on interfacial entropic and enthalpic interactions with the underlying polymer thin film. We also observe contrasting temperature dependence of microscopic dynamics of these membranes depending on whether the graft polymer-substrate polymer interactions are predominantly entropic or enthalpic in nature. Our results suggest that apart from their varied applications, the soft nanoparticle-polymer hybrid membranes are a playground for rich physics involving subtle entropic and enthalpic effects along with the nanoparticles softness, which eventually determine their thermo-mechanical stability.

Surface modification effect of carbon molecular sieve (CMS) on the morphology and separation performance of mixed matrix membranes

The lack of interfacial adhesion between the polymer and inorganic phases in mixed matrix membranes (MMMs) imposes a serious challenge. This study is focused on the improvement of polymer-filler adhesion via surface modification of carbon molecular sieve (CMS) by nitric acid (HNO3) oxidation process. The bare CMS and oxidized CMS based mixed matrix membranes fabricated by the solvent evaporation method. Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses confirmed the oxidation of CMS surface. An improved morphology and interfacial adhesion were observed in Polysulfone (PSU)/Ox-CMS MMMs as deduced by field emission scanning electron microscope analysis. Thermal stability of the developed membrane has been confirmed by Thermogravimetric analysis (TGA). Raman spectroscopy is carried out to evaluate the homogeneity of the filler distribution in the polymer phase. Gas separation performance of the synthesized MMMs has revealed the positive effects of surface modification of CMS particles with HNO3 oxidation on CO2/CH4 selectivity of the developed MMMs. A slight reduction in CO2 permeability (2–5%) observed in ox-CMS based MMMs. PSU/oxidized-CMS MMM with 30 wt % CMS loading has shown a superior performance (CO2 permeability = 3.91 barrer and CO2/CH4 selectivity = 65.92) which is approaching the Robeson upper bound limit. These highly selective membranes have a high potential in membrane-based CO2 separation applications.

Average Conformation of Branched Chain Lipid PGP-Me That Accounts for the Thermal Stability and High-Salinity Resistance of Archaeal Membranes.

The average conformation of the methyl-branched chains of archaeal lipid phosphatidyl glycerophosphate methyl ester (PGP-Me) was examined in a hydrated bilayer membrane based on the 2H nuclear magnetic resonance (NMR) of enantioselectively 2H-labeled compounds that were totally synthesized for the first time in this study. The NMR results in combination with molecular dynamics simulations revealed that the PGP-Me chain appeared to exhibit behavior different from that of typical membrane lipids such as dimyristoylphosphatidylcholine (DMPC). The C-C bonds of the PGP-Me chain adopt alternative parallel and tilted orientations to the membrane normal as opposed to a DMPC chain where all of the C-C bonds tilt in the same way on average. This characteristic orientation causes the intertwining of PGP-Me chains, which plays an important role in the excellent thermal and high-salinity stabilities of archaeal lipid bilayers and membrane proteins.

Bipyridine-based polybenzimidazole membranes with outstanding hydrogen fuel cell performance at high temperature and non-humidifying conditions

We describe the synthesis of bipyridine-based polybenzimidazole (Bipy-PBI) polymers with various molecular weights (MWs), and used their membranes for fuel cell (FC) applications to reveal the influence of the polymer MWs on the membrane casting, acid-doping level, thermal stability, mechanical properties, and proton conductivity. Bipy-PBI polymers with different MWs ranging from 48 to 141 kDa were successfully obtained. The mechanical properties clearly illustrated the importance of controlling the polymer MWs to fabricate flexible membranes with a sufficient mechanical strength for FC applications. Notably, a 36% increase in the membrane conductivity was obtained for Bipy-PBI compared to PBI of similar MW, thanks to the Bipy-PBI polymer structure which provided additional nitrogen atoms for the potential loading of acid molecules. The conductivity value of the highest MW Bipy-PBI at 120 °C provided a 0.037 S/cm with a146% increase in conductivity compared to the low MW Bipy-PBI. Notably, a 32% increase in the power density was recorded when using the highest MW-based Bipy-PBI membrane electrode assembly. This ratio is remarkable for the membrane effect on the FC performance at high operating temperatures and non-humidifying conditions.

One-Step Bark-Like Imitated Polypropylene (PP)/Polycarbonate (PC) Nanofibrous Meltblown Membrane for Efficient Particulate Matter Removal.

A bark-like imitated polypr opylene (PP)/polycarbonate (PC) nanofibrous membrane was constructed by one-step meltblown technique for efficient particulate matter (PM) removal. The effects of PC content (0%, 1%, 3%, 5%, and 7%) on membrane thermal stability, microscopic characteristics, filtration performance, hydrophilicity, and water vapor transmission were investigated. The results demonstrated that using facile design of incompatibility and viscosity difference between PC and PP polymers decreases average fiber diameter, creating a bark-like groove appearance and increasing surface potential, making a new PP/PC membrane with high filtration performance. The resultant PP/PC membrane had finer average fiber diameter of 0.63 μm, which was nearly 89.41% lower than PP membranes (5.95 μm), and its quality factor (0.036 Pa−1) was nearly 2.12 times than that of PP membranes (0.017 Pa−1) with the die hole diameter of 0.5 mm. This fabrication technique of a special meltblown filter membrane saves the cost of die retrofitting and post-processing, which provides an innovative method for particulate efficient removal of high efficient filters.

Zeolite templated carbon: Preparation, characterization and performance as filler material in co-polyimide membranes for CO2/CH4 separation

Zeolite templated carbon (ZTC), a structurally unique carbon material was used as new fillers for the preparation of composite polymeric membrane derived from BTDA-TDI/MDI (P84) co-polyimide. The thermal stability of membrane, the structure evolution, morphology and topology, as well as gas separation performance of modified membranes were investigated. Zeolite-Y, a hard template for ZTC, was synthesized via hydrothermal method. The ZTC was synthesized via impregnation of sucrose as carbon precursor into zeolite pore and followed by carbonization at 800°C. The zeolite template was removed through acid treatment to obtain ZTC, which was used as fillers for membrane preparation. The membrane was prepared using P84 co-polyimide as membrane precursor via phase inversion process. Synthesized materials were characterized using SEM, XRD, N2 adsorption-desorption isotherm and TEM. The thermal stability of membrane was improved by the addition of ZTC. As the result of ZTC loading into P84 co-polyimide membrane, the gas permeability of CO2 increased thirty-four times, as well as the CO2/CH4 selectivity boosted from 0.76 to 5.23. The ordered pore structure in ZTC plays important role in increasing the permeability and selectivity performances of the P84 co-polyimide membrane.

Improving the Gas-Separation Properties of PVAc-Zeolite 4A Mixed-Matrix Membranes through Nano-Sizing and Silanation of the Zeolite.

Mixed-matrix membranes containing synthesised nano-sized zeolite 4A and PVAc were fabricated to investigate the effect of zeolite loading on membrane morphology, polymer-filler interaction, thermal stability and gas separation properties. SEM studies revealed that, although the membranes with 40 wt % nano-sized zeolite particles were distributed uniformly through the polymer matrix without voids, the membranes with 15 wt % zeolite loading showed agglomeration. With increasing zeolite content, the thermal stability improved, the permeability decreased and the selectivity increased. The effect of silanation on dispersion of 15 wt % zeolite 4A nanoparticles through PVAc was investigated by post-synthesis modification of the zeolite with 3-Aminopropyl(diethoxy)methylsilane. Modification of the nanoparticles improved their dispersion in PVAc, resulting in higher thermal stability than the corresponding unmodified zeolite membrane. Modification also decreased the rigidity of the membrane. Partial pore blockage of the modified zeolite nanoparticles after silanation caused a further decrease in permeability, compared to the 15 wt % unmodified zeolite membrane.

Preparation and characterization of styrene-butadiene-styrene membrane incorporated with graphene nanosheets for pervaporative removal of 1,2,4-trimethylbenzene from water.

In the present study, novel styrene-butadiene-styrene (SBS) membranes were prepared by the addition of graphene (Gr) nanosheets to the casting solution and were utilized in the pervaporative separation of a dilute solution of 1,2,4-trimethylbenzene (1,2,4-TMB) as a volatile organic compound (VOC) in water. Several characterizations such as field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), mechanical tensile test, and determination of water contact angle and swelling degree were conducted to investigate the properties of the prepared membranes. The results showed that with the addition of Gr the membrane thermal stability and hydrophobicity were increased while there was an optimum Gr loading to achieve the highest elastic modulus and tensile strength. Moreover, it was found that by increasing the Gr concentration up to 0.5 wt. %, the separation factor and pervaporation separation index (PSI) were increased by 250% and 43% compared to pure SBS membrane and reached 930 and 545 kg/m2h, respectively.

(Invited) U.S. DOE Early-Stage Alkaline Membrane Fuel Cell R&D

The U.S. Department of Energy (DOE) supports research, development, and demonstration of fuel cell technologies for transportation, stationary, and crosscutting applications. Applied, early-stage fuel cell research and development (R&D) efforts predominantly focus on stack materials and components to achieve low-cost, high performance fuel cell systems, and include longer term technologies, such as alkaline membrane fuel cells (AMFCs). More favorable oxygen reduction kinetics and increased platinum group metal (PGM)-free catalyst stability at high pH conditions have invigorated interest in alkaline membrane fuel cells as an alternative to polymer electrolyte membrane fuel cells (PEMFCs), on which fuel cell electric vehicles currently available for retail sale are based. The catalyst accounts for >40% of the projected high-volume stack cost in PEMFC electric vehicles, owing largely to the inclusion of PGMs [1]. Achieving cost competitiveness with internal combustion engine vehicles could be expedited by eliminating PGM-based catalysts; AMFCs offer a promising route for successfully incorporating state of the art PGM-free catalysts into membrane electrode assemblies (MEAs). In addition, improved alkaline exchange membranes (AEMs) have crosscut benefits to applications beyond fuel cells, including electrolysis for hydrogen production and reversible fuel cells. Alkaline membrane R&D is targeted to increase conductivity over a wider range of operating temperature and relative humidity and to increase membrane mechanical, chemical, and thermal stability with diminished fuel crossover. In 2016, an expert-led workshop on AEMs was convened by the DOE based on intense interest in the field [2]. There was consensus on the need for AEM-specific standardized protocols and testing and for further improvement in MEA performance. Furthermore, the profound lack of readily available, stable AEMs or ionomers for high pH MEAs must be addressed in order to expand entry into the field and foster more rapid progress in AMFC development. In order to increase coordination in the polymer electrolyte membrane community (including AEMs) to accelerate R&D success in fuel cells and other devices (electrolyzers, redox flow batteries, etc.), the FCTO has recently organized the National Laboratory-led Membranes Working Group. Stable, conductive polymer materials and durable hydrogen oxidation catalysts are key to realizing commercially relevant AMFCs. This presentation will highlight recent advancements in AMFCs in the DOE R&D portfolio include increasing performance and durability in perfluorinated and hydrocarbon-based ionomers, increasing cation group stability, diminishing catalyst deactivation due to ionomer-catalyst interaction, and PGM-free MEA performance of 350 mW/cm2. This presentation will also provide an outlook on future activities.

Evaluation of cryo-treatment in the luminescent properties of PVDF/Eu2O3 composite obtained by using buriti oil as additive

Polymeric matrices containing luminescent particles find many applications like temperature sensor platforms. However, it is important to understand the impact of the particle immobilization on the polymer structural and optical properties in order to optimize its performance. Therefore, in this study, a new luminescent polymeric composite was fabricated by combining poly (vinylidene fluoride) (PVDF), buriti oil (BO) and Eu2O3 particles, evaluating the membrane luminescent properties before and after a cryo-treatment with liquid N2 in order to enhance the Eu(III) emission. Also, the influence of Eu2O3 particles and BO in the polymer structural, thermal, morphological and optical properties was evaluated. The composite membranes with bandgap lying between 5.60 and 5.90 eV were obtained as γ-PVDF phase after being dried at 100 °C, with spheroidal particles connected by necks. The PVDF membranes are very stable till temperatures as high as 370 °C, and the Eu2O3 particle addition increases the membrane thermal stability while the BO decreases the PVDF stability. The cryo-treatment with N2 increases the PVDF crystallinity, leading to the PVDF particles agglomeration. The PVDF/BO/Eu2O3 membrane exhibited the characteristic red emission from Eu(III) along with an unexpected BO emission. Finally, after the cryo-treatment, the Eu3+ emission increases while the BO emission vanishes, and due to this temperature sensitivity, the system shows potential to be applied in temperature sensor platforms.

Improved proton conductivity and methanol permeability of PVA-based proton exchange membranes using diphenylamine-4-sulfonic acid sodium salt and silica nanoparticles

ABSTRACTA novel series of PVA/DPA-4-SASS/SiO2 composite membranes were fabricated and characterized in the present study. Compared to the neat PVA, water uptake, proton conductivity, and ion exchange capacity of the membranes were enhanced. The membrane containing 5 Wt. % of SiO2 nanoparticles and 80 Wt. % of the DPA-4-SASS showed the highest values of water uptake, proton conductivity (1.5 × 10−1 S/cm) and ion exchange capacity (1.47 mmol/g). The results also indicated that methanol permeability was decreased by increasing the DPA-4-SASS content in the hybrid membranes. Thermal stability and mechanical properties of the cross-linked membranes were also improved.