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An experimental study of hydrogen sulfide adsorption on a fixed bed for biogas purification is proposed. The adsorbent investigated was powdered hematite, synthesized by a wet-chemical precipitation method and further activated with copper (II) oxide, used both as produced and after pelletization with polyvinyl alcohol as a binder. The pelletization procedure aims at optimizing the mechanical properties of the pellet without reducing the specific surface area. The active substrate has been characterized in its chemical composition and physical properties by X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), thermogravimetric analysis (TGA) and N2 physisorption/desorption for the determination of surface area. Both powders and pellets have been tested as sorbents for biogas purification in a fixed bed of a steady-state adsorption column and the relevant breakthrough curves were determined for different operating conditions. The performance was critically analyzed and compared with that typical of other commercial sorbents based on zinc oxide or relying upon specific compounds supported on a chemically inert matrix (SulfaTreat&reg, ). The technique proposed may represent a cost-effective and sustainable alternative to commercial sorbents in conventional desulphurization processes.

Accounting for the wavelength- and source-dependent optical absorption properties of the abundant light-absorbing organic (brown) carbon (BrC) and the mixing state of atmospheric black carbon (BC) are essential to reduce the large uncertainty in aerosol radiative forcing. Estimation of BrC absorption online by subtraction is highly uncertain and may be biased if not decoupled from the potential BC absorption enhancement (lensing) due to non-refractory (organic and inorganic) coating acquisition.Here, the reported total particulate absorption is based on long-term, filter-based seven-wavelength Aethalometer (AE33 model) data, corrected for multiple scattering effects with Multi-Wavelength Absorbance Analyzer (5λ MWAA) measurements. Using ultraviolet-visible spectroscopy absorbance measurements along with particle size distributions obtained by a scanning mobility particle sizer, we have conducted Mie calculations to assess the importance of source-specific extractable particulate BrC (Moschos et al., 2018) versus BC absorption.For the species-specific optical closure, the wavelength dependence of bare BC absorption is estimated using MWAA measurements upon successive filter extractions to remove the influence of BrC/coatings. The lensing contribution, supported by observations from field-emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, is estimated at longer wavelengths using a refined proxy for the BC coating thickness. The approach is validated independently by applying a novel positive matrix factorization-based approach on the calibrated total AE33 absorption data.Based on the observational constraints established in this study, we demonstrate for various distinct case studies that the interplay between lensing and BrC absorption results in lower than expected BC absorption at shorter wavelengths. This indicates that the volume additivity assumption is not valid for particulate absorption by internally mixed heterogeneous atmospheric aerosol populations. These comprehensive experimental analyses verify the BC lensing suppression predicted for simplified core-shell structures containing moderately absorbing BrC (Lack & Cappa, 2010). The implications discussed in this work are relevant for co-emitted species from biomass burning or aged plumes with high BrC to BC mass/absorption ratio. ReferencesMoschos, V., Kumar, N. K., Daellenbach, K. R., Baltensperger, U., Prévôt, A. S. H., and El Haddad, I.: Source apportionment of brown carbon absorption by coupling ultraviolet-visible spectroscopy with aerosol mass spectrometry, Environ. Sci. Tech. Lett., 5, 302-308, https://doi.org/10.1021/acs.estlett.8b00118, 2018.Lack, D. A. and Cappa, C. D.: Impact of brown and clear carbon on light absorption enhancement, single scatter albedo and absorption wavelength dependence of black carbon, Atmos. Chem. Phys., 10, 4207–4220, https://doi.org/10.5194/acp-10-4207-2010, 2010.

Membrane distillation is a promising thermally driven separation process that can be used for water desalination. The primary requirement of this technique is the hydrophobicity of the membrane, so polymeric membranes are mainly used as the ceramic ones are intrinsically hydrophilic. In this work, in order to modify the water wettability, Al2O3 commercial tubular membranes with different pore sizes were functionalized using methyltrichlorosilane. The main aim of the work was to verify in depth the effects and the success of this hydrophobizing treatment. The effect of silanization on pore size and geometry was evaluated using scanning electron microscopy as well as gas permeation in order to highlight possible morphological changes in the membrane structure. No evident modification was detected. The hydrophobicity was assessed by measuring water contact angles which increased from about zero for the pristine supports up to 145° for the modified membranes. After treatment, the water entry pressures ranged between 0.7 and 2.1 bar. Further analyses were carried out in order to elucidate the amount of silicon grafted to the Al2O3 particles and its distribution. Finally, the modified membranes were tested in a vacuum membrane distillation plant at different temperatures (50, 70 and 90 °C) using as feed both deionized water and a highly concentrated NaCl solution (90 g/L). Very satisfactory performances were obtained. The permeate fluxes were comparable – or even higher – to those registered for a polypropylene membrane used as a reference. The separation properties were evaluated during the NaCl solution tests and were close to the full rejection of salt in any operating condition.

Flat sheet membranes made of polyvinyldene fluoride (PVDF) were prepared via nonsolvent induced phase separation (NIPS). The focus of this work was concentrated on the effect of the support structure and material on the morphology and on the distillation performance of the final membranes. To this end, various membranes were prepared casting a uniform polymer solution film on six commercial non-woven tissues and on three thin nets, characterized by different materials and morphologies, and then immersing them in an ethanol coagulation bath. FE-SEM analysis was widely exploited to evaluate both the surface and cross section structure of membranes. The different interactions between the dope solution and the support materials as well as the different extent of mutual entanglement were found to be key parameters in the membrane preparation, governing both the overall porosity and pore size.

Polyvinylidene fluoride (PVDF) was used for membrane preparation using the nonsolvent induced phase separation (NIPS). In this paper, the effect of the polymer concentration in the dope solution and the nonsolvent bath composition is widely investigated. In particular, the effect of increasing concentrations of ethanol in the coagulation bath on the morphology and characteristics of the membranes, as well as on their performance in membrane distillation of pure water and a brine was evaluated. FESEM analysis, coupled with contact angle determination highlighted different coagulation paths that allowed to obtain superhydrophobic membranes at higher ethanol concentrations. Moreover, the polymer concentration had major effects on the overall porosity and pore size of the membrane. By tuning the membrane preparation conditions, it was possible to obtain membranes that showed great distillate flux as well as a complete salt rejection during the vacuum membrane distillation tests.

This paper deals with the preparation of novel polytetrafluoroethylene (PTFE) membranes from an aqueous dispersion of fluorinated polymer and a pore forming agent (PFA) sintered onto the outer surface of a porous tubular support. Different membranes were obtained by varying the ratio between PTFE and PFA in the starting dispersion as well as the number of dispersion layers sintered on the support. Membranes were characterized through scanning electron microscopy and gas–liquid displacement porosimetry. Distillation tests of the membrane were carried out on a laboratory scale unit fed with a NaCl solution. The characteristics and performance of the membranes were compared with those of commercial porous PTFE tubulets.

In order to satisfy the future energy demands, the development of alternative sources of energy is currently object of interest. Among all the possibilities, biogas is a renewable methane-based fuel obtainable by anaerobic digestion of different types of raw materials, including waste-waters. This gas product contains relevant amounts of methane (CH4), carbon dioxide (CO2) with traces of other compounds and, to be used, it needs to be purified from the components responsible of a decreasing in the combustion efficiency. On the upgrading process, the CO2 removal is necessary to respect the Wobbe Index specification and it can be realized by various technologies in different devices. Among all the current techniques, CO2-absorption into physical or chemical solvents in packed towers is commonly applied, but the use of gas-liquid membrane contactors represents an innovative alternative. In particular the second ones are characterized by various operational advantages, such as independent gas/liquid control, optimal load of the absorbent, no entrainment, flooding or foaming and modular and very compact devices. In this work a polypropylene hollow fiber membrane contactor was used to investigate the CO2-absorption from a model gas mixture into aqueous solutions of monoethanolamine (MEA), piperazine (PZ), methyildiethanolamine (MDEA) and their mixtures. The effect of reagent type and concentration was studied as well as the influence of temperature and gas composition. Experimental results show the high reactivity of MEA and PZ, capable of increasing the absorption rate in MDEA-based solvents, characterized by large loading capacity and easiness of regeneration.

In this study, electrically conductive microporous layers (MPLs) were prepared through the phase inversion technique by coagulation in a water bath of a mixture of either poly(vinylidene fluoride) or sulfonated poly(vinylidene fluoride) and graphite and carbon black as electrically-conductive fillers (ECFs). The novel gas diffusion layers (GDL) were obtained by casting the MPLs on a wet proof carbon cloth. Poly(vinylidene fluoride) (PVDF), due to its excellent chemical stability, thermal resistance and hydrophobic character was proposed in place of the more expensive and less processable PTFE. Moreover, sulfonated poly(vinylidene fluoride) (PVDFS, 1.9% sulfonation degree) it was investigated as binding agent in order to obtain MPLs with improved characteristics especially in view of the possibility of preparation of gas diffusion electrodes (GDEs) by the deposition of electro-active catalysts. MPLs morphology, water contact angle, electrical resistance, and through-plane air permeability were carefully examined. The PVDF and PVDFS MPLs were assembled with a catalysts coated Nafion membrane and the performance of the resulting membrane electrode assemblies were compared in a fuel cell fed with air and hydrogen. While electrical resistance of MPLs was slightly influenced by the different preparation conditions, the air permeability considerably increased by switching the solvent from N-methyl-2-pyrrolidone (NMP) to dimethyl sulfoxide (DMSO) and by increasing the air exposure time of the composite film after casting as confirmed by the morphological analysis through scanning electron microscopy. As an indication of the MPLs performance, at the operating current density of 0.60 A cm−2, the single cell voltage of the proton exchange membrane fuel cell (PEMFC) was enhanced from about 0.43 to 0.5 V for PVDF based MPLs to about 0.60 V of PVDFS based MPL. The use of the phase inversion technique open several possibilities to tailor the MPL structure to specific fuel cell applications and moreover offers a more straightforward and scalable preparation method.

n-Butyric, iso-butyric, n-valeric and iso-valeric esters of hydroxypropylcellulose were synthesized. Their behaviors, in terms of cholesteric structure, glass (Tg) and anisotropic-isotropic (Ti) transition temperatures are compared to results in the literature. A 6–8 month time period from sample preparation has no influence on the cholesteric phase characteristics. Six binary blends may be formed from the four esters. They show only a Tg value at each composition, which suggests a good miscibility among the components. However, positive deviation of linearity of Tg vs. composition varies from one pair to another. Analysis of the absorption curves in UV-vis spectra show that three pairs form a single cholesteric helix containing both components while other three give a only nematic phase. Colors changing from red to violet are shown for blends of n-butyric and iso-butyric esters at different weight ratio. Copyright © 2003 John Wiley & Sons, Ltd.

In this paper, solid blends of HPC/PVP obtained by polymerization in situ of NVP are analyzed. These blends retain the initial organization of HPC in NVP in terms of liquid crystalline structure and banded texture. It is also demonstrated that the banded texture may be stabilized with respect to thermal cycles by crosslinking the samples.

Results of an interlaboratory comparison on size characterization of SiO2 airborne nanoparticles using on-line and off-line measurement techniques are discussed. This study was performed in the framework of Technical Working Area (TWA) 34 - "Properties of Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS) in the project no. 3 "Techniques for characterizing size distribution of airborne nanoparticles". Two types of nano-aerosols, consisting of (1) one population of nanoparticles with a mean diameter between 30.3 and 39.0 nm and (2) two populations of non-agglomerated nanoparticles with mean diameters between, respectively, 36.2-46.6 nm and 80.2-89.8 nm, were generated for characterization measurements. Scanning mobility particle size spectrometers (SMPS) were used for on-line measurements of size distributions of the produced nano-aerosols. Transmission electron microscopy, scanning electron microscopy, and atomic force microscopy were used as off-line measurement techniques for nanoparticles characterization. Samples were deposited on appropriate supports such as grids, filters, and mica plates by electrostatic precipitation and a filtration technique using SMPS controlled generation upstream. The results of the main size distribution parameters (mean and mode diameters), obtained from several laboratories, were compared based on metrological approaches including metrological traceability, calibration, and evaluation of the measurement uncertainty. Internationally harmonized measurement procedures for airborne SiO2 nanoparticles characterization are proposed. © 2013 Springer Science+Business Media Dordrecht.

Novel proton exchange membranes have been prepared by in synthesis functionalization of a polyurethane matrix with a sulfonic group containing chain terminals. The synthesis procedure was based on the use of two polyethylene glycols with nominal molecular weight of 300 and 1 k and 4,4′ dicyclohexylmethane diisocyanate in presence of the sodium salt of isethionic acid as a donor of the sulfonic group. Glycerol was added in order to improve by reticulation the stability of the cast films. The membranes were characterized in terms of swelling, morphology, methanol permeability, proton conductivity, and ion exchange capacity. The best H2/air cell performance was achieved at 80 °C with a maximum power density of 16.9 mW/cm2 at a voltage of about 0.35 V. Polyurethane based ionomeric membranes have proved to be interesting candidates for proton exchange membrane fuel cells (PEMFC) applications.

The aim of this work was to offer a state-of-the-art critical survey for characterizing airborne nano- and microparticles by means of electron microscopy (EM) techniques and to highlight advantages and limits of different possible operation modes. Procedures of collection and sample preparation are revisited and improved to analyse airborne particles deposited on filtering membranes by using various sampling methods. Three kinds of electron microscopes are used to this end: scanning electron microscope (SEM), field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). Following and extending previous studies, we optimized procedures by varying both the sample collection/preparation and the operational parameters of the microscopes. In particular, we diversified the sampling methods applied, using ad hoc filters as well as common filters for standard gravimetric measures. This approach enabled us to achieve a simple and clean procedure allowing direct SEM or TEM observation of the collected particulate matter.