Alberto Claudio Habert

Membrane formation mechanism based on precipitation kinetics and membrane morphology : flat and hollow fiber polysulfone membranes

Abstract Membrane formation from poly(bisphenol-A sulfone)/poly(vinyl pyrrolidone)/dimethylacetamide/water systems by phase inversion process using immersion–precipitation technique was investigated. The initial precipitation rate was determined from light transmission experiments and the membranes morphologies were observed by scanning electron microscopy (SEM). These results were used to explain an observed oscillatory behavior in macrovoid occurrence, as well as to identify the region where spinodal demixing dominates the early stages of the phase inversion process. It is proposed as a qualitative model dividing the solution in three different layers during the polymer solution mass exchange with the coagulation bath. Each layer is associated with different precipitation kinetics leading to distinct morphologies. The model assumes that the macrovoids development is a function of the resistances created by precipitation kinetics of former layers.

Removal of aromatics from multicomponent organic mixtures by pervaporation using polyurethane membranes: experimental and modeling

Polyurethane (PU) dense membranes were used in the separation of binary and multicomponent aromatic/aliphatic mixtures by pervaporation. The PU membranes found to be selective towards aromatics in all systems studied. Both, swelling of polymer matrix and the permeate flux increase with aromatic weight fraction in the feed. The highest selectivity was achieved with benzene/n-hexane mixture in the whole feed composition range. The permeation of the organics through the PU membrane was modeled based on the sorption–diffusion mechanism. The sorption equilibrium was calculated using Flory–Huggins (FH) or UNIQUAC equations and Stefan–Maxwell (SM) equations were used to describe the transport inside the membrane matrix. A correction was introduced in the diffusion coefficients of the permeating species to take into account the polymer matrix plasticization. The experimental and predict data showed a good agreement, indicating that the PU membrane are useful to reduce the aromatic content of industrial solvent by pervaporation process.

New insights in the removal of diluted volatile organic compounds from dilute aqueous solution by pervaporation process

The present work aimed the mass transfer investigation in the removal of organic contaminants from water by the pervaporation process. The terpolymer ethene-propene-diene (EPDM) was used as the selective elastomer. Two classes of model organic solutes were chosen: chlorinated hydrocarbons (trichloroethylene, dichloromethane and trichloromethane) and aromatic ones (toluene, phenol and aniline). Pervaporation tests were carried out using dense and composite membranes with different thickness, solute concentrations and feed flow velocities at room temperature. The liquid boundary layer resistance (i.e., concentration polarization phenomenon) was observed for all solutes. The resistance-in-series model was used to determine liquid and polymer phase resistances. The results obtained indicate that the model would be better written considering the chemical potential gradient as driving force, in order to take into account affinity between water and the organic solutes, as well as their interactions with the polymer selective layer. The rational activity coefficients of the solutes in the polymer phase were determined by inverse gas chromatography (IGC) and related to the mass transfer coefficient in the polymer phase.

Surface modification of porous polymeric membranes by RF-plasma treatment

Abstract Polymeric membranes can be modified by surface treatment with glow discharge created by non-polymerizable gases, with low power radio-frequency (rf) plasma. The purpose of this work is to study the influence of the exposure time, the supplied power and the nature of the gas on the permeability of the treated membranes. Asymmetric porous substrates of polysulfone (PSf) were used and their surfaces were modified with inorganic gas plasma (ammonia). Three rf power levels, respectively 5, 10 and 15 W were used. Treatment time ranged from 1 to 50 min. The chemical and structural characterization of the membranes before and after the surface modification was done by means of Atomic Force Microscopy (AFM), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The permeated flow of pure gases (N 2 and CO 2 ) was measured using conventional gas permeation cell at room temperature.

Hollow fibre modules for orange juice aroma recovery using pervaporation

The use of poly (dimethyl siloxane) PDMS hollow fibres was investigated in orange juice aroma recovery. Modules for pervaporation were designed and built for this purpose, scrutinized with binary ester-water feeds and compared to other module geometries using experimental enrichment factors and mass transfer coefficient values. Operational variables tested for the aroma separation included feed flow rate and aroma feed concentration. Further experimental runs were carried out with an industrial multicomponent feed consisting of an aqueous orange juice by-product. The results show the good potential of the modules for dilute aroma recovery.

Membrane for processing tropical fruit juice

In the present work, membrane processing was investigated in order to clarify and to recover aroma from tropical fruit juices. Pineapple and passion fruit juices were selected. Pervaporation experiments were also carried out with binary synthetic aqueous solutions of typical aroma components. Experimental and simulation results indicated that olefin pervaporation membranes presented a good performance due to its low water permeability and high enrichment factor to the components of aroma from the investigated synthetic solutions, as well as the single strength and the clarified fruit juices.

Surface Modification of Polymeric Materials by Plasma Treatment

Low-temperature plasma treatment has been used in the last years as a useful tool to modify the surface properties of different materials, in special of polymers. In the present work low temperature plasma was used to treat the surface of asymmetric porous substrates of polysulfone (PSf) membranes. The main purpose of this work was to study the influence of the exposure time and the power supplied to argon plasma on the permeability properties of the membranes. Three rf power levels, respectively 5, 10 and 15 W were used. Treatment time ranged from 1 to 50 min. Reduction of single gas permeability was observed with Ar plasma treatments at low energy bombardment (5 W) and short exposure time (20 min). Higher power and/or higher plasma exposition time causes a degradation process begins. The chemical and structural characterization of the membranes before and after the surface modification was done by AFM, SEM and XPS.

Preparation and morphological characterization of polyurethane/polyethersulfone composite membranes

This work investigated the preparation of composite membranes by simultaneous casting of polyurethane and polyethersulfone solutions, to form the top and the support layers, respectively. These membranes are intended to be used for propylene/propane separation. Polyvinylpyrrolidone was used as an additive in the corresponding solution to obtain a support with low transport resistance. The synthesis conditions were related to the morphology of the resulting membranes. Polyurethane concentration, nature of the solvent and exposure time before immersion into the precipitation bath were primarily investigated, in addition to the influence of additives, such as lithium nitrate and formamide.

Polymeric membranes containing silver salts for propylene/propane separation

The separation of olefin/paraffin mixtures is one of the most important processes of the chemical industry. This separation is typically carried out by distillation, which is an energy and capital intensive process. One promising alternative is the use of facilitated transport membranes, which contain specific carrier agents in the polymer matrix that interact reversibly with the double bond in the olefin molecule, promoting the simultaneous increase of its permeability and selectivity. In this study, polyurethane (PU) membranes were prepared using two different silver salts (triflate and hexafluorantimonate). The membranes were structurally characterized and their performance for the separation of propylene/propane mixtures was evaluated. The results of the characterization analyses indicated that the triflate salt was the most efficient carrier agent. The membranes containing this salt showed the best performance, reaching an ideal selectivity of 10 and propylene permeability of 188 Barrer.

Dual-layer hollow fibers for gas separation processes produced by quadruple spinning

ABSTRACT A novel quadruple spinneret to produce dual-layer hollow fiber membranes by simultaneous spinning of two polymer solutions, using the dual precipitation bath technique is proposed. Hollow fibers aimed at gas separation processes were prepared in extrusion system specifically designed and built for this purpose. A polyurethane polymer was selected as the selective layer (outer-layer), while polyethersulfone was defined as the support (inner-layer). Activated carbon powder was added into the PU solution for further improvement of the transport properties. The hollow fibers showed good adhesion between the polymer layers and a defect-free selective layer. Representative results include a CO2/N2 selectivity of 43.