A Study of the Reinforcement Effect of MWCNTs onto Polyimide Flat Sheet Membranes

Polyimides rank among the most heat-resistant polymers and find application in a variety of fields, including transportation, electronics, and membrane technology. The aim of this work is to study the structural, thermal, mechanical, and gas permeation properties of polyimide based nanocomposite membranes in flat sheet configuration. For this purpose, numerous advanced techniques such as atomic force microscopy (AFM), SEM, TEM, TGA, FT-IR, tensile strength, elongation test, and gas permeability measurements were carried out. In particular, BTDA–TDI/MDI (P84) co-polyimide was used as the matrix of the studied membranes, whereas multi-wall carbon nanotubes were employed as filler material at concentrations of up to 5 wt.% All studied films were prepared by the dry-cast process resulting in non-porous films of about 30–50 μm of thickness. An optimum filler concentration of 2 wt.% was estimated. At this concentration, both thermal and mechanical properties of the prepared membranes were improved, and the highest gas permeability values were also obtained. Finally, gas permeability experiments were carried out at 25, 50, and 100 ◦C with seven different pure gases. The results revealed that the uniform carbon nanotubes dispersion lead to enhanced gas permeation properties

Ceramic-Supported Alginate Adsorbent for the Removal of Heavy Metal Ions

Hybrid alginate/ceramic support sorbents have been developed by the physical imbibing of an alginic acid solution into silica pores and γ-alumina microspheres. The metal ion-binding capacity of the prepared hybrids was examined by means of batch Cd 2+ ion adsorption experiments. In addition, since the porous γ-alumina microspheres proved capable of retaining higher quantities of alginic acid than silica, they were chosen as a more appropriate substrate for the application of a chemical modification procedure. In this context, the aim was to develop hybrid sorbents with an enhanced stability and adsorption capacity obtained by grafting the bio-molecule onto the substrate. Such chemical modification included grafting two different types of silanes onto the external surface and pores of γ-alumina, followed by chemical bonding of the alginate with the characteristic groups of the silane molecules involved. Such chemically-prepared sorbents exhibited almost twice the Cd 2+ ion adsorption capacity of sorbents prepared by physical imbibing methods. The best uptake achieved in the present work was 1.44 mg Cd 2+ ion/g substrate. Moreover, the adsorption capacity per bonded alginate mass exceeded the capacity often reported in the literature for alginate beads

Geochemical modeling of mercury in coastal groundwater

The systematic analysis of groundwater in the Greek island of Skiathos revealed a seasonal increase of total mercury concentrations after the extensive groundwater abstraction during the busy and heavily touristic summer months. This contamination was accompanied by a corresponding increase of the chloride content of groundwater, attributed to seawater intrusion into the freshwater-depleted aquifer within mercury-rich bedrock. The effects of elevated concentrations of chloride anions in the mobilization of mercury and its speciation were addressed by geochemical equilibrium modeling, considering cinnabar (HgS) as the mineral source of mercury. Adsorption onto hydrous ferric oxide (Fe2O3·H2O) was a necessary ingredient of the geochemical model for bringing the calculated concentrations in agreement with field measurements, after optimization of the cinnabar/adsorbent mass ratio to a value of 4.9 × 10−8. The speciation of mercury was found to depend on the acidity and redox status as well as on the chloride content of groundwater. Mercury concentrations in the groundwater of Skiathos rise above the World Health Organization limit of 1 μg L−1 for a seawater intrusion higher than 3 %, with HgCl2 being the dominant species followed by HgClOH, HgCl3− and HgCl42−. The assumed concentration of dissolved organic matter in groundwater had a negligible impact on the mercury speciation and its mobilization by chloride

Cellulose-based carbon hollow fiber membranes for high-pressure mixed gas separations of CO2/CH4 and CO2/N2

Carbonized cellulose -based hollow fiber membranes were prepared by dry-wet spinning phase inversion method, followed by carbonization and evaluated in terms of gas separation performance for CO2/N2 and CO2/CH4 mixtures, under flow conditions. Permeability and real selectivity were measured for both mentioned mixtures, in a temperature range of 25 °C to 60 °C, a differential pressure range of 8 bar(a) to 20 bar(a) and a CO2 concentration range from 5% v/v to 15% v/v. The highest yielding mixture selectivity values were 42 for CO2/N2 at 10% v/v CO2, 25 °C & 8 bar(a) and around 150 for CO2/CH4 at the same conditions, whereas the respective CO2 permeabilities were 110 and 45 Barrer. Additionally, experiments of varying head pressure, while maintaining differential pressure, transmembrane pressure, at 8 bar(a), have revealed that CO2/N2 separation factor can be further enhanced with real selectivity being raised to 55 and permeability to 180 at 20 bar head pressure. The same approach had negligible effect on CO2/CH4 separation. This is an important finding by taking into consideration that natural gas treatment, i.e. sweetening and purification processes, is energetically and economically convenient if it takes place under the conditions, where the NG stream is extracted from the wells, or after a decompression. Moreover, Process simulation indicates that a two-stage system using the developed carbon membranes is technologically feasible to produce 96% methane with a low methane loss of <4%. Further improving membrane gas permeance can significantly reduce the specific natural gas processing cost which is dominated by the membrane-related capital cost

Green chemistry-based fabrication of hollow fiber and flat sheet polyimide membranes for CO2/CH4 separation

In this work, the successful fabrication of polymeric hollow fiber (HF) and flat sheet (FS) membranes was examined by employing γ-butyrolactone (GBL)-a green and environmentally friendly solvent- for the polymer's dissolution following the principles of green chemistry and sustainability regarding the membrane preparation. In addition, the ternary phase diagram of the P84/GBL/water was constructed and the viscosity of dope solution was measured for different concentrations and temperatures. Their morphological characteristics of the prepared polyimide membranes were investigated through SEM analysis. CO2/CH4 separation measurements under continuous flow were performed to evaluate the efficiency of the membranes for a binary 10/90 vol.% CO2/CH4 gas mixture. The developed green HF and FS membranes exhibited comparable, and in some cases even superior, performance compared to membranes prepared using the conventional and highly toxic NMP solvent, making them highly promising candidates for CO2/CH4 separation, with a real mixture separation factor of ∼58

A study on natural clinoptilolite for CO₂/N₂ gas separation

<p>Based on its low cost and low water adsorption capacity, compared to synthetic zeolites (A-type, X-type and Y-type), natural, untreated clinoptilolite was examined as a potential adsorbent for a separation process targeting on removal of CO₂ from flue gas. Taking into consideration typical flue gas composition and temperature, adsorptive properties of binary CO₂/N₂ mixtures were tested in the temperature range of 268 to 403 K and compared with literature data. The results showed that CO₂ concentration, total pressure, and temperature strongly affect selectivity and working capacity, restricting the conditions under which the material could be used as an efficient adsorbent.</p

CO2/CH4 and He/N2 Separation Properties and Water Permeability Valuation of Mixed Matrix MWCNTs-Based Cellulose Acetate Flat Sheet Membranes: A Study of the Optimization of the Filler Material Dispersion Method

The main scope of this work is to develop nano-carbon-based mixed matrix celluloseacetate membranes (MMMs) for the potential use in both gas and liquid separation processes. Forthis purpose, a variety of mixed matrix membranes, consisting of cellulose acetate (CA) polymerand carbon nanotubes as additive material were prepared, characterized, and tested. Multi-walledcarbon nanotubes (MWCNTs) were used as filler material and diacetone alcohol (DAA) as solvent.The first main objective towards highly efficient composite membranes was the proper preparationof agglomerate-free MWCNTs dispersions. Rotor-stator system (RS) and ultrasonic sonotrode (USS)were used to achieve the nanofillers’ dispersion. In addition, the first results of the application of thethree-roll mill (TRM) technology in the filler dispersion achieved were promising. The filler material,MWCNTs, was characterized by scanning electron microscopy (SEM) and liquid nitrogen (LN2)adsorption-desorption isotherms at 77 K. The derivatives CA-based mixed matrix membranes werecharacterized by tensile strength and water contact angle measurements, impedance spectroscopy,gas permeability/selectivity measurements, and water permeability tests. The studied membranesprovide remarkable water permeation properties, 12–109 L/m2/h/bar, and also good separationfactors of carbon dioxide and helium separations. Specifically, a separation factor of 87 for 10%He/N2feed concentration and a selectivity value of 55.4 for 10% CO2/CH4feed concentrationwere achieved