Bar Feed Pressure Research Articles

Changing the conventional clarification method in metal sulfide precipitation by a membrane-based filtration process

The metal sulfide precipitation process is a widely studied technology used to recover metals or remove pollutants from different aqueous sources. However, the conventional clarification stage used to separate the generated precipitates cannot effectively remove them from recovered solutions. Taking this into account, the current study focuses on developing a new separation method applied in metal sulfide precipitates, based on a membrane filtration process. Different operating conditions and metal concentration in the feed solution were evaluated for the separation of copper sulfide precipitates formed from synthetic cyanide solutions in ceramic microfiltration membranes. Results showed attractive values of flux and copper recovery. Flux results ranged between 0.9 L/m2s and 1.2 L/m2s for copper concentrations above 500 mg/L, and copper recoveries resulted closer to 100% at the determined optimal operating conditions (4.5 pH, 120% NaHS stoichiometric dosage, and 2 bar feed pressure). These flux values decreased up to one order of magnitude for diluted copper concentrations, due to a change of aggregation capacity of precipitates. This study has demonstrated that the membrane filtration process can be a suitable alternative for the conventional gravitational clarification, promoting better performance results in terms of equipment capacity, metal recovery, and process safety.

Fabrication of novel polyethersulfone (PES) hybrid ultrafiltration membranes with superior permeability and antifouling properties using environmentally friendly sulfonated functionalized polydopamine nanofillers

Developing hybrid ultrafiltration (UF) membranes with high permeability and low fouling tendency is important for a wide range of wastewater treatment applications. Herein, we report the synthesis of novel environmental-friendly sulfonated functionalized polydopamine (SPDA) nanocomposite as a nanofiller for UF membranes. Firstly, mussel-inspired PDA nanoparticles (NPs) were synthesized based on oxidation and self-polymerization of dopamine monomer. PDANPsweresubsequentlysulfonatedwith3-mercapto-1-propanesulfonicacid(athiolwith –SO3H group)throughMichael's addition reaction to produce the SPDA nanofiller. Fourier transform infrared spectroscopy and zeta potential measurements verified the functionalization of the PDA. Hybrid UF membranes were then fabricated via the non-solvent-induced phase separation process (NIPS), using polyethersulfone (PES) as a matrix and SPDA nanofiller at different loading levels (0–4 wt%). The water contact angle values showed an increase in the hydrophilicity of the fabricated UF membranes. The water permeability and antifouling capability of the hybrid UF membranes were dependent on the nanofiller's loading quantity. At 1 bar feed pressure, the pure water flux of the 2 percent SPDA nanofiller membrane was 2.7 times higher than that of the pristine membrane. Foulant solutions have been used to determine the antifouling efficiency of the hybrid membranes using sodium alginate (SA), humic acid (HA) and bovine serum albumin (BSA). The antifouling properties of the PES membranes have been significantly improved by incorporating the SPDA nanofillers in accordance with the foulant rejection and flow recovery ratios. The results indicated that SPDA nanofillers have great potential to improve the permeability and antifouling properties of PES membranes.Capsule: High-flux and antifouling PES hybrid membranes fabricated using environmentally-friendly sulfonated functionalized polydopamine nanofillers.

Green Preparation of Thin Films of Polybenzimidazole on Flat and Hollow Fiber Supports: Application to Hydrogen Separation.

This work shows the preparation of thin films, with thickness from 70 nm to 1 μm, of meta-polybenzimidazole (m-PBI) on polyimide P84 supports. Ethanolic solutions of m-PBI were used to coat flat and hollow fiber supports of asymmetric P84 with m-PBI in a process where the coating and drying was performed at room temperature. A solution of NaOH in EtOH allowed the dissolution of the m-PBI powder, providing the perfect coating solution to build thin films of m-PBI without damaging the polymeric support. It also meant a green alternative, avoiding the use of toxic solvents, such as dimethylacetamide. The resulting membranes have been tested for the separation of H2 mixtures at high temperature at different setups to allow checking their reproducibility. With 100 nm thickness the membranes showed their best gas separation performance. For flat membranes at 180 °C and 3 bar feed pressure a H2 permeance of 48.5 GPU was obtained, with respective H2 /CO2 and H2 /N2 selectivities of 33.3 and 55.8. Besides, the hollow fibers under a feed pressure of 6 bar and tested at the same temperature showed near 90 GPU of H2 with a H2 /CO2 selectivity of 13.5 in the one-fiber module and over 39 GPU of H2 with a H2 /CO2 selectivity of 20.2 in the five-fiber module. Finally, the stability of the membranes was proved for 22 days at 180 °C.

Fouling resistant, high flux, charge tunable hybrid ultrafiltration membranes using polymer chains grafted graphene oxide for NOM removal

The unprecedented performance of fouling resistant, high flux and high rejection hybrid ultrafiltration polysulfone membranes with charge tunable channels using functionalized polymer chains grafted graphene oxide (SPK-g-GO) nanosheets for natural organic matter removal from aqueous feed is herein reported. The novel SPK-g-GO nanosheets were first prepared by esterification reaction at 55 °C using hydroxylated sulfonated poly(ether ether ketone) and graphene oxide. Then, polysulfone blend hybrid membranes with charge tunable channels were produced via the non-solvent induced phase separation method and optimized by varying the SPK-g-GO concentration from 1 to 8 wt.% in the casting solution. The membranes were characterized using scanning electron microscopy, Raman spectroscopy, atomic force microscopy, surface zeta potential and contact angle measurements. The surface texture and hydrophilicity of the membranes were altered due to the incorporation of SPK-g-GO. The hybrid membrane’s water flux was highly dependent on the amount of SPK-g-GO incorporated within the membrane matrix. The maximum water flux (485.7 L m−2 h−1), obtained using the membrane with 4 wt.% SPK-g-GO, was almost 270% higher than that of the membrane without SPK-g-GO (181.1 L m−2 h−1). The fouling resistance and natural organic matter retention capabilities of the membranes were examined via UF tests of synthetic natural organic matter solution at 1 bar feed pressure and neutral pH. The hybrid membrane with 4 wt.% SPK-g-GO loading exhibited remarkable improvement over the pristine one, rejecting more than 86% of the and recovering ~90% of its initial water flux after washing with a stable retention rate during a long-term filtration test.

Cevap Yüzey Metodu Kullanılarak Keçiboynuzu Ekstraktında Bulunan D-Pinitolün Nanofiltrasyon Uygulamasıyla Zenginleştirilmesinin Optimize Edilmesi

Bu çalışmada keçiboynuzu ekstraktında bulunan D-pinitolün 1-5 kDa ayırma sınırı aralığında nanofiltreler kullanılarak zenginleştirilmesi amaçlanmıştır. Zenginleştirme aşamaları ekstraksiyon, durultma, adsorban uygulaması ve nanofiltrasyon uygulamalarından oluşmaktadır. Nanofiltrasyon uygulamasını optimize etmek amacıyla Box-Behnken Cevap Yüzey Metodu (CYM) kullanılmıştır. Son aşamada elde edilen ürünün saflık kontrolü için D-pinitol içeriği, şeker kompozisyonu, toplam fenolik madde (TFM), toplam kuru madde (TKM) ve mineral madde kompozisyonları kullanılmıştır. Ekstraktlarda en yüksek D-pinitol konsantrasyonuna 5 kDa ayırma sınırındaki nanofiltrasyonda, 3 bar besleme basıncı, 25°C besleme sıcaklığı ve %83,3 permeat oranı koşullarında ulaşılmıştır. Bu koşullarda elde edilen permeat akısının D-pinitol içeriği 10,48 g/L olarak belirlenmiştir. Çalışmada ayrıca nanofiltrasyon prosesi için basınç, sıcaklık ve permeat/retentat oranı değişkenlerine bağlı bir optimizasyon modeli oluşturulmuş ve farklı koşullara bağlı olarak ekstraktların D-pinitol konsantrasyonundaki değişim yüksek doğrulukla (R2=0,91) matematiksel olarak modellenmiştir. Bu modele bağlı olarak, keçiboynuzu ekstraktlarında en yüksek sakkaroz, TFM ve TKM miktarları D-pinitol konsantrasyonunun %8,7 olduğu koşulda belirlenmiştir.

High-Flux, Antifouling Hydrophilized Ultrafiltration Membranes with Tunable Charge Density Combining Sulfonated Poly(ether sulfone) and Aminated Graphene Oxide Nanohybrid.

In this work, a new protocol was developed for creating charge-tuned, hydrophilic hybrid ultrafiltration (UF) membranes with high flux, rejection rate, and fouling resistance. The membranes were fabricated using a combination of sulfonated poly(ether sulfone) (SPES) and aminated graphene (GO-SiO2-NH2) nanohybrid via the non-solvent-induced phase separation (NIPS) method. The GO-SiO2-NH2 nanohybrid was first synthesized using GO nanosheets and 3-aminopropyl triethoxysilane (APTES) through the covalent condensation reaction at 80 °C and was thoroughly characterized. Then, 2-8 wt% of the nanohybrid was incorporated into the matrix of SPES for the fabrication of the hybrid membranes. The resulting membranes were characterized using an electrokinetic analyzer, a contact angle goniometer, and Raman, field emission scanning electron microscopy-energy-dispersive X-ray spectrometry (FESEM-EDX), and atomic force microscopy experiments. The porosity, charge density, and surface morphology were altered, and the hybrid membranes became more hydrophilic after the incorporation of the nanohybrid. The pure water flux of the hybrid membranes systematically increased with the loading amount of the nanohybrid. The pure water flux of the hybrid membrane containing 6 wt% GO-SiO2-NH2 nanohybrid at a 2 bar feed pressure was 537 L m-2 h-1, about 3-fold that of pristine membrane (186 L m-2 h-1). The fouling resistance of the hybrid membranes was evaluated and confirmed using several representative foulants, including bovine serum albumin, humic acid, sodium alginate, and a synthetic solution of natural organic matter (NOM). The fabricated membranes were capable of removing more than 97% of NOM, without a compromise of their rejection rate.

High-pressure CO2/CH4 separation of Zr-MOFs based mixed matrix membranes

The gas separation properties of 6FDA-DAM mixed matrix membranes (MMMs) with three types of zirconium-based metal organic framework nanoparticles (MOF NPs, ca. 40 nm) have been investigated up to 20 bar. Both NPs preparation and MMMs development were presented in an earlier publication that reported outstanding CO2/CH4 separation performances (50:50 vol% CO2/CH4 feed at 2 bar pressure difference, 35 °C) and this subsequent study is to demonstrate its usefulness to the natural gas separation application. In the current work, CO2/CH4 separation has been investigated at high pressure (2–20 bar feed pressure) with different CO2 content in the feed (10–50 vol%) in the temperature range 35–55 °C. Moreover, the plasticization, competitive sorption effects, and separation of the acid gas hydrogen sulfide (H2S) have been investigated in a ternary feed mixture of CO2:H2S:CH4 (vol% ratio of 30:5:65) at 20 bar and 35 °C. The incorporation of the Zr-MOFs in 6FDA-DAM enhances both CO2 permeability and CO2/CH4 selectivity of this polymer. These MMMs exhibit high stability under separation conditions relevant to an actual natural gas sweetening process. The presence of H2S does not induce plasticization but increases the total acid gas permeability, acid gas/CH4 selectivity and only causes reversible competitive sorption. The overall study suggests a large potential for 6FDA-DAM Zr-MOF MMMs to be applied in natural gas sweetening, with good performance and stability under the relevant process conditions.

Scalable One‐Step Gel Conversion Route to High‐Performance CHA Zeolite Hollow Fiber Membranes and Modules for CO2 Separation

Efficient separation of CO2 from other molecules such as CH4, N2, and hydrocarbons is a key problem in many energy production and greenhouse gas reduction schemes. Zeolite materials demonstrate attractive gas separation properties, but their industrial application as membranes in gas separation are elusive because of high cost and low reproducibility of conventional fabrication techniques. A facile method is demonstrated for the fabrication of high‐silica CHA zeolite membranes on low‐cost alumina hollow fiber substrates by a one‐step direct gel conversion method, along with a detailed characterization of the CHA hollow fiber membranes. To demonstrate the scalability of the method, 20 hollow fiber (710 μm OD and 390 μm ID) membranes are synthesized in the same batch and assembled into a module. Under dry conditions, the membranes show an excellent CO2 permeance up to 3500 GPU (1 Gas Permeation Unit = 3.348 × 10−10 mol m−2 s−1 Pa−1) and an excellent CO2 separation performance (e.g., CO2/CH4 separation factors up to 210 in the 1–7 bar feed pressure range). In addition, the membranes exhibit a considerable increase in CO2 selectivity under humid (saturated water vapor) conditions with moderate permeance drops. This study opens a promising new path for accelerated development of low‐cost zeolitic membranes for gas separation technology.

Incorporation of CoIII acetylacetonate and SNW-1 nanoparticles to tailor O2/N2 separation performance of mixed-matrix membrane

Mixed-matrix membranes containing a porous organic framework (SNW-1 nanoparticles) and a cobalt-based complex (Co(acac)3) were fabricated using the solution-casting technique for potential applications in O2/N2 separation. The mixed-matrix membranes did not show any appreciable defects. In the following mixture gas permeation testing conducted with a binary mixture composed of 21% O2 and 79% N2 at 1 bar feed pressure and 35 °C, the mixed-matrix membranes containing SNW-1 nanoparticles showed an enhanced O2 permeability, whereas Co(acac)3 improved the O2/N2 selectivity. Hence, with a combination of both nanoparticles and a Cobalt complex in a polymer matrix, a clear synergistic enhancement in O2/N2 separation properties was reported, in which O2 permeability and O2/N2 selectivity were escalated by 33% and 18%, respectively. Solubility-diffusivity analysis in the mixed-matrix membranes revealed that SNW-1 and Co(acac)3 can improve O2 diffusivity and O2 solubility, respectively, resulting in an enhancement of both O2 permeability and O2/N2 selectivity for membranes containing both the nanoparticles and the cobalt complex. Future efforts will be focused on developing asymmetric hollow fiber membranes with thin skin layer comprising both SNW-1 and Co(acac)3.

Membrane module for pilot scale oxygen production

An oxygen transport membrane module capable of total 596 Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) membranes was constructed and tested under various capacities. The module is designed to operate with up to 20 bar feed pressure and a vacuum on the permeate side. The separation performance was tested with of up to 96 membranes tubes. A maximum oxygen purity of 98.9% was obtained and a maximum oxygen flux of 2.8 ml cm−2 min−1 was measured under a feed pressure of 10 bar. The maximum permeate oxygen flow rate achieved was 22 l min−1. The performance is lower than expected, for which an inhomogeneous module temperature and suboptimal flow distribution can be accounted for, as CFD simulations show. A lot of membrane breakages occurred during operation. Some reasons for that could be identified and the module could be optimized throughout the 2 years of testing. Within that time, three long term tests were performed and a maximum continuous operational time of 1800 h was achieved.

Concatenation of carbonaceous nanofillers for mixed matrix membrane development

Two different carbonaceous nanofillers, carbon nanofiber (CNF) and graphene oxide (GO) were synergistically incorporated into glassy poly (2,6-dimethyl-1,4-phenylene oxide) (PPOdm) polymer to synthesize a novel mixed matrix membrane (MMM) for CO2/CH4 separation. The combined effect of binary filler on the filler dispersion and gas separation performance of resultant membrane were analysed. The binary filler-based MMM rendered homogenous filler dispersion quality, as compared to single filler-based MMM. The CNF particles dispersed in between GO nanosheets, inhibited the restacking of GO whilst the strong steric effect imposed by GO nanosheets improved the dispersion of CNF particles in the polymer matrix. The optimum gas separation performance was recorded at 2 wt% CNF/3 wt% GO loading with ideal CO2/CH4 selectivity of 59.70 and CO2 permeability of 62.32 Barrer at 3.5 bar feed pressure. The CNF particles with smooth wall and larger diameter allowed gases to diffuse through faster by creating a gas pathway and eventually improved the gas permeability. Meanwhile, GO nanosheets with surface hydroxyl and carboxyl groups facilitated the transport mechanism of CO2 molecules, acted as a selective barrier and rendered high selectivity. Therefore, both permeability and selectivity of resultant membrane were enhanced.

The Gas Permeation Characteristics of Ternary Component Mixed Matrix Membranes Prepared Using ZIF-8 with a Large Range of Average Particle Size

ZIF-8 crystals with average particle sizes of 14, 23, 65, 144, and 262 nm were synthesized to prepare poly(ether sulfone) based mixed matrix membranes with 10 and 20% loading. The membranes were characterized by measuring single gas permeabilities of H2, CO2, and CH4 at 35 °C with pressures from 3 to 15 bar. The separation performance of PES/pNA/ZIF-8 (10%) with 23 nm crystals was also investigated by separating CO2/CH4 mixtures at 3 and 10 bar. The single gas permeabilities decreased with increasing particle size of ZIF-8; however, the ideal selectivities depended on the ZIF-8 content of membranes. A significant improvement was obtained in the membrane performance when 23 nm ZIF-8 particles loaded PES/pNA(4%)/ZIF-8(10%) MMM. This membrane had a CO2/CH4 selectivitiy of 56.2 and permeability of 1.54 Barrer in the separation of 50% CO2–50% and CH4 mixture at 35 °C and 10 bar feed pressure.

Ammonia removal from aquaculture wastewater by high flux and high rejection polysulfone/cellulose acetate blend membrane

Polysulfone (PSf)/cellulose acetate (CA) blend membranes with different compositions (100/0, 90/10, 85/15, 80/20, 75/25 and 70/30) were prepared and characterized for removal of low concentration ammonia (1–10 mg/L) from aquaculture wastewater. The performance of prepared membranes in terms of pure water flux and ammonia removal percentage was analyzed by different experimental variables such as blend membrane compositions, ammonia concentration in feed tank (1, 5 and 10 mg/L) and membrane thickness (80 and 100 µm). The permeability of prepared membranes was examined by pure water flux measurement in feed pressure range of 1–3 bar. The contact angle measurement indicates that the hydrophilicity of PSf/CA blend membranes is enhanced by increasing the CA concentration in the casting solution. This increment improves the pure water flux of blend membranes. The ammonia removal by PSf/CA 80/20 (80 µm) was 79%, 99% and 92% from feed solutions containing 1, 5 and 10 mg/L of ammonia, respectively. The ammonia removal from feed solution containing 1 mg/L of ammonia is improved from 79 to 95% (at 2 bar feed pressure) by increasing the thickness of PSf/CA (80/20) membrane from 80 to 100 µm.

Highly thin film nanocomposite membrane based metal organic complexes for brackish water desalination

Recently metal organic frameworks MOFs incorporated thin film composite membranes had great attention in separation processes due enhancement porosity with excellent selectivity.In this work, binary and ternary complexes as a green metal organic framework were successfully prepared using carboxymethyl cellulose as a cluster organic linker. The two types of MOFs were embedded with different loading amount in the selective layer through interfacial polymerization. The prepared meso-fillers MOFs were characterized by SEM, FTIR and EDX. Also the membranes were characterized by SEM and separation assessments. The Results showed that the optimum loading MOFs was 0.1 wt%. Both binary complex MOF1 and ternary complex MOF2 were enhanced the performance of the membrane and the impact was depended on the MOFs loading amount. At the optimum MOFs loading amount 0.1 wt.%, the permeate flux increased from 30 LMH to 36 and 41 LMH, for the neat membrane, MOF1 and MOF2 membranes respectively. As well NaCl rejection was significantly affected and improved by embedding these MOFs, where NaCl rejection increased from 69% to 93% and 97% for neat membrane, MOF1 and MOF2 membranes respectively to 7000 ppm of NaCl at 5 bar feed pressure. The prepared membranes based MOF1 and MOF2 with 0.1 wt.% were tested for 60 days to confirm the stability of polyamide layer and their performance properties. The cubic like structure for the polyamide layer was observed by SEM images for 0.1% ternary complexes filled membrane so this study demonstrates that the MOFs based membrane is a promising technology on the laboratory mode for water desalination.

Carbon membranes for oxygen enriched air – Part I: Synthesis, performance and preventive regeneration

Abstract Chemisorption of oxygen on the active sites of carbon layers limits the use of carbon membranes in air separation application. A novel online electrical regeneration method was applied to prevent the active sites on carbon surface to be reacting with O2 while the membrane was in operation. This method reduced the aging effect and the membrane showed relative stable performance with only 20% loss in O2 permeability and 28% increase in O2/N2 selectivity, over the period of 135 days using various feeds containing H2S, n-Hexane and CO2-CH4 gas. The carbon membranes reported here were produced at the pilot-scale facility by the carbonization of regenerated cellulose under optimized conditions to achieve good air separation properties. The permeation properties of the membranes were tested by single gas separation experiments at 5 bar feed pressure (50 mbar permeate) and temperature range 20–68 °C. It was observed that O2 permeability is increasing exponentially with increase in operating temperature without significant loss in the O2/N2 selectivity. The O2 permeability of 10 Barrer (1 Barrer = 2.736E − 09 m3(STP)m/m2 bar h) with O2/N2 selectivity of 19 was achieved at 68 °C. Thermal (80 °C), chemical (propylene) and online-electrical (10 V DC) regeneration approaches were studied to lessen the aging effect on carbon membranes.

Carboxylated Carbon Nanotubes/Polyethersulfone Hollow Fiber Mixed Matrix Membranes: Development and Characterization for Enhanced Gas Separation Performance

ABSTRACTCarboxylated carbon nanotubes (C or cCNTs) were incorporated in polyethersulfone hollow fiber membranes (P HFMs) to improve the gas separation performance, i.e., pure gas permeability and ideal gas selectivity. The developed CP HFMs showed the remarkable improvement in thermal stability and mechanical strength as compared to that of the pristine P HFMs. The pure gas permeability of CO2, CH4, O2, and N2 gases for the HFMs were measured at 3 bar feed pressure and room temperature. It was observed that the presence of cCNTs in HFMs significantly improved the CO2 and O2 permeability for CP HFMs by 10.8-and 11.7- fold, respectively, as compared to that measured for P HFMs. Furthermore, the ideal gas selectivity for CO2/CH4, O2/N2, and CO2/N2 gas pairs for CP HFMs was also remarkably enhanced by almost 8.6-, 10.7-and 9.9-times, respectively, as compared to that measured for P HFMs. CP HFMs exhibited gas separation performance better than or comparable to that of the literature-reported CNTs-based membranes. Remarkably, the gas separation performance of CP HFMs crossed Robeson’s 2008 upper bound curve for O2/N2 gas-pair and was almost closer to the upper bound curves drawn by Robeson in 2008 for CO2/CH4 and CO2/N2 gas pairs. The improved separation performance can be attributed to the presence of cCNTs in HFMs. Thus, the results obtained in this study clearly showed that the CP HFMs can potentially be used as a membrane material for the industrially relevant gas separations.

Enhanced gas separation performance of 6FDA-DAM based mixed matrix membranes by incorporating MOF UiO-66 and its derivatives

Functionalization and post-synthetic modification (PSM) of metal-organic frameworks (MOFs) are two important routes to obtain MOFs with full potential in mixed matrix membrane (MMM) fabrication. We synthesized UiO-66 and two derivatives UiO-66-NH2 and UiO-66-NH-COCH3 with less than 50 nm particle size. The CO2 uptakes at 10 bar in the two functionalized UiO-66s were improved by 44% and 58%, respectively, with respect to the pristine solid. The MOF nanoparticles were incorporated into the highly permeable polymer 6FDA-DAM, making MMMs with 5–24 wt% particle loadings. All fillers and membranes were characterized accordingly, and their gas separation performances were evaluated by feeding CO2/CH4 equimolar mixtures at 2 bar pressure difference at 35 °C. CO2 permeability (PCO2) of pristine 6FDA-DAM (PCO2 = 997 ± 48 Barrer, αCO2/CH4 = 29 ± 3) increased by 92% with 20 wt% UiO-66 loading, while maintaining the CO2/CH4 selectivity. Improvements of 23% and 27% were observed for PCO2 with the same 20 wt% loading of UiO-66-NH2 and UiO-66-NH-COCH3, respectively. The αCO2/CH4 was improved up to 16% using both functionalized UiO-66 type MOFs. The best separation performance in this work was obtained with 14 wt% UiO-66 MMM (PCO2 = 1912 ± 115 Barrer, αCO2/CH4 = 31 ± 1), 16 wt% UiO-66-NH2 MMM (PCO2 = 1223 ± 23 Barrer, αCO2/CH4 = 30 ± 1) and 16 wt% UiO-66-NH-COCH3 MMM (PCO2 = 1263 ± 42 Barrer, αCO2/CH4 = 33 ± 1) at 2 bar feed pressure difference. The measurement was also conducted with various binary compositions (CO2 = 10 – 90%), both at low and high pressures up to 40 bar at 35 °C, showing no pressure-related CO2-induced plasticization. The atomistic modelling for the MOF/polymer interface was consistent with a moderate MOF surface coverage by 6FDA-DAM which did not play a detrimental role in the membrane performance.

Cold gas propulsion microthruster for feed gas utilization in micro satellites

Micro spacecraft, which have gained huge popularity in the last decade, are termed as “CubeSats”, a well-known class of small satellites. The fast growing functionality and popularity of CubeSats have helped researchers push technology demonstration towards efficient performance and reliability needed for commercial and governmental applications. Keeping in mind the increasing space debris, dependence of satellite life on fuel, and the use of fossil fuels as propellants, recent efforts are being made to develop a cold gas propellant-based (CGP) micro propulsion system. The CGP system has various merits, namely, non-toxicity, easy to use, and low leakage concerns over other propulsion systems. Liquid propellant-based propulsion requires a liquid feed system, which uses pressurized gas (such as helium, argon and nitrogen) to pressure-feed liquid to the combustion or vaporization chamber so as to produce thrust. But once the liquid propellant is depleted, the pressurized gas is unusable while the system runs out of fuel. Thus, the proposed CGP system being studied, apart from being used as a normal cold gas propulsion system, also offers the advantage of being used as a propulsion system for a liquid fueled system, in the event the liquid fuel runs out. The present work reports on cold gas micro thruster development, utilization of feed gas in a liquid fueled thruster, and the experimental study on the CGP system in simulated vacuum conditions and under a range of pressure conditions. Pressure in the pressure feed gas system for a 1–50 kg category of satellites varies from 4 to 8 bar depending on the mission requirement. The pressure reduces as the liquid propellant gets exhausted. The experimental results are used to validate a computational fluid dynamics model of the system. Thrust values are obtained between the micro to milli-Newton range so as to fulfil the requirements of attitude and station keeping for CubeSats in the 1–50 kg dry mass range. Under vacuum conditions, we obtained thrust values of 0.8 mN at 1 bar feed pressure to 2.24 mN at 4 bar feed pressure. These thrust values are nearly twice those achieved for sea level tests for the corresponding feed pressure. Furthermore, the parameters such as Mach number, velocity vector, pressure, temperature, specific impulse, and nozzle efficiency are studied and reported for atmospheric and vacuum conditions.

Preparation and characterization of novel polyimide/functionalized ZnO bionanocomposite for gas separation and study of their antibacterial activity

In the present investigation novel Polyimide/functionalized ZnO (PI/ZnO) bionanocomposites containing amino acid (Methionine) and benzimidazole pendent groups with different amounts of modified ZnO nanoparticles (ZnO NPs) were successfully prepared through ultrasonic irradiation technique. Due to the high surface energy and tendency for agglomeration, the surface ZnO NPs was modified by a coupling agent as 3- methacryloxypropyl-trimethoxysilane (MPS) to form MPS-ZnO nanoparticles. The ultrasonic irradiation effectively changes the rheology and the glass transition temperature and the crystallinity of the composite polymer. PI/ZnO nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). TEM analysis showed that the modified ZnO nanoparticles were homogeneously dispersed in polymer matrix. The TGA results of PI/ZnO nanocomposites showed that the thermal stability is obviously improved the presence of MPS-ZnO NPs in comparison with the pure PI and that this increase is higher when the NP content increases. The permeabilities of pure H2, CH4, O2, and N2 gases through prepared membranes were determined at room temperature (25 °C) and 20 bar feed pressure. The membranes having 20% ZnO showed higher values of H2 permeability, and H2/CH4 and H2/N2 ideal selectivities (the ratio of pair gas permeabilities) compared with other membranes. The antibacterial activity of bionanocomposite films was tested against gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) and gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). Further, it was observed that antibacterial activity of the resulting hybrid biofilms showed somewhat higher for gram-positive bacteria compared to gram-negative bacteria.

Highly CO2 Selective Microporous Metal-Imidazolate Framework-Based Mixed Matrix Membranes.

Microporous metal-imidazolate framework (MMIF), a highly CO2 selective MOF, was incoporated into a polymeric membrane for separation of CO2 from CH4 and N2 for the first time. MMIF nanoparticles of 50-200 nm were synthesized using the sonication method and dispersed into Matrimid, a commercial polyimide, with MOF loading of 10% and 20% by weight to fabricate mixed matrix membranes (MMMs). Morphology, thermal behavior, and glass transition temperature of the membranes were characterized, and single and mixed gas permeation measurements at 35 °C and 4 bar feed pressure were carried out to reveal their separation performance. Both 10% and 20% MMIF containing Matrimid membranes exhibited enhanced gas permeabilities for all three gases. Contrary to expectations, ideal selectivity of membranes was not improved possibly due to the flexible framework of MMIF. On the other hand, mixed gas permeability measurements showed significant improvement in CO2/CH4 separation factor by 130% and CO2/N2 separation factor by 79% due to competitive adsorption favoring CO2.