Silvia Simone

Performance of PDMS membranes in pervaporation: effect of silicalite fillers and comparison with SBS membranes.

Laboratory-made silicalite filled PDMS membranes were tested by means of concentration and temperature influence on the membrane performance in removal of ethanol from ethanol/water mixtures. This allowed studying the applicability of solution-diffusion model in the transport mechanism description. Experiments were performed by varying the ethanol concentration in the feed and temperature. Two types of fillers were incorporated into the PDMS network: commercial zeolite silicalite (CBV 3002) and laboratory-made colloidal silicalite-1. Obtained results were then compared with data gathered for unfilled PDMS membranes to examine the effect of fillers incorporation. Moreover, the comparison with novel block co-polymer based porous and dense SBS membranes was done. It was found that the solution-diffusion model was a good representation of ethanol transport through both filled and unfilled PDMS membranes, whereas the water flux did not obey this model due to the swelling effects. Incorporation of the fillers increased membrane stability and improved the selectivity. Performance of the SBS membranes characterized by a dense structure was found to be similar to the performance of filled PDMS membranes.

Hollow Fiber Ultrafiltration Membranes from Poly(Vinyl Chloride): Preparation, Morphologies, and Properties

Hollow fiber poly(vinyl chloride) membranes were prepared by using the dry/wet spinning method. Cross-section, internal, and external surfaces of the hollow fibers structure were studied by SEM. The pore size and pore size distribution of the hollow fibers were measured by a PMI capillary flow porometer. UF experiments of pure water and aqueous solution of PVP K-90 were carried out. The effect of the PVC concentration on the hollow fibers mechanical properties was also investigated. It was found that the PVC fibers cross-sectional structure was affected by the polymer concentration in the dope solution. In particular, reduction of macrovoids size was observed when increasing PVC concentration from 15 to 19 wt%. The pore size distribution of the PVC hollow fibers was controlled by adjusting the PVC concentration. Indeed, an increase of PVC concentration up to 19 wt% leads to fibers with sharp pore size distribution (the 99% of pores is about 0.15 µm).The pure water permeation flux decreased from 162 to 128 (l/m2 · h · bar), while the solute separation performance increased from 82 to 97.5%, when increasing the PVC concentration. The elongation at break, the tensile strength, and the Youngs modulus of the PVC hollow fibers were improved with PVC concentration in dope solution.

ECTFE membranes produced by non-toxic diluents for organic solvent filtration separation

A new grade of ethylene-chlorotrifluoroethylene, low melting point HALAR® ECTFE (LMP ECTFE), was studied and used as a polymer for the preparation of solvent-resistant flat-sheet membranes. Among the different types of non-toxic solvents tested, di-ethyl adipate (DEA) was selected for preparing flat sheet membranes via thermally induced phase separation (TIPS). The morphology of the membranes has been analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Dense and porous membranes have been obtained and characterized by contact angle, pore size and porosity tests. Porous membranes showed an asymmetric structure made of a denser top-side and a spherulitic porous structure on the bottom side. Membrane resistance was studied using the dense membrane in contact with most aggressive organic solvents, such as polar protic, polar aprotic and non-polar solvents. The results suggest that the newly developed LMP ECTFE membranes are very promising candidates for organic solvent separation. Ultrafiltration (UF) and nanofiltration (NF) tests with alcohols and di-methyl formamide (DMF) demonstrated their solvent separation potential.

Clarification of Orange Press Liquors by PVDF Hollow Fiber Membranes

Press liquors are typical by-products of the citrus juice processing characterized by a high content of organic compounds and associated problems of environmental impact, which imply high treatment costs. However, these wastes contain a great number of health promoting substances, including fibers, carotenoids and phenolic compounds (mainly flavonoids), whose recovery against waste-destruction technologies is very attractive for new business opportunities. In this work, the clarification of orange press liquor by using microfiltration (MF) membranes is studied as a preliminary step to obtain a permeate stream enriched in antioxidant compounds which can be further processed to produce extracts of nutraceutical and/or pharmaceutical interest. MF poly(vinylidene fluoride) (PVDF) hollow fibers were prepared by the dry/wet spinning technique. A series of fibers was produced from the same polymeric dope, in order to investigate the effect of selected spinning parameters, i.e., bore fluid composition and flowrate, on their properties. The morphology of the produced fibers was analyzed by Scanning Electron Microscopy (SEM). Fibers were further characterized for their mechanical properties, porosity, bubble point, pore size distribution and pure water permeability (PWP). Some of the produced fibers exhibited high permeability (pure water permeability ~530 L/m2·h·bar), coupled to good mechanical resistance and pore size in the range of MF membranes. These fibers were selected and used for the clarification of press liquor from orange peel processing. In optimized operating conditions, the selected fibers produced steady-state fluxes of about 41 L/m2·h with rejections towards polyphenols and total antioxidant activity of 4.1% and 1.4%, respectively.

Novel Photocatalytic PVDF/Nano-TiO2 Hollow Fibers for Environmental Remediation

Polyvinylidene difluoride (PVDF) mixed matrix membranes loaded with inorganic TiO2 nanoparticles have received increasing attention in the last few years as self-cleaning membranes for possible application in wastewater treatment and seawater filtration. These novel membranes show increased hydrophilicity, stability and catalytic activity under UV-A irradiation. In this work, PVDF-TiO2 hollow fibers were prepared by employing new strategies for enhancing the stability of the TiO2 dispersion, reducing particle agglomeration and improving their distribution. The spinning conditions for producing ultrafiltration hollow fiber membranes from PVDF material and nano-TiO2 were investigated. Finally, the optimized fibers have been characterized and tested for methylene blue (MB) degradation in water and salty seawater, revealing good permeability, long-term stability under UV-A irradiation, and photo-catalytic activity in both test solutions.

Preparation and characterization of green polylactic acid (PLA) membranes for organic/organic separation by pervaporation

Membrane science, in the context of the growing attention towards the preservation and protection of the environment, has an emerging role as a very well-recognised eco-friendly technology. In order to meet the complete concept of sustainability, however, greener strategies still need to be put in place regarding the preparation of the membranes. Polylactic acid (PLA) green flat sheet membranes were prepared using ethyl lactate as a green solvent and water as a non-solvent, for the first time. The morphology, thickness, contact angle, mechanical properties, FTIR and degree of swelling were determined for studying the properties of the produced membranes. A systematic study was performed testing PLA membranes in pervaporation (PV) for the separation of methanol (MeOH)/methyl tert-butyl ether (MTBE) azeotropic mixture evaluating their performance by varying feed temperature and vacuum degree. The findings revealed that the membrane morphology changed from finger-like to spongy-like and finally to dense-like structure by acting on the evaporation time (ET) during the preparation with an improvement in the overall mechanical properties. The PLA dense membrane produced with an ET of 7xa0min was successfully tested in PV exhibiting a preferred permeation towards MeOH with a highest selectivity value of more than 75. An Arrhenius-type dependence between flux and temperature was found.Graphical Abstract

Tailoring PES membrane morphology and properties via selected preparation parameters

Abstract Polyethersulfone (PES) is among the most interesting materials for membranes preparation, thanks to its outstanding properties, coupled to compatibility with several additives and the facility to be solubilized in several solvents. In this work, flat sheet membranes were prepared by the non-solvent induced phase separation (NIPS) technique, using PES as polymer and polyvinyl pyrrolidone (PVP, 10 kDa) as additive. Preparation and casting conditions were varied and membranes with tailored morphology and properties were obtained. The main objective was to investigate the relationship between selected preparation conditions and membrane features. This may help to understand how to tailor membrane morphology and properties depending on the desired application.