Jan Schauer

Polymer anion-selective membranes for electrolytic splitting of water. Part II: Enhancement of ionic conductivity and performance under conditions of alkaline water electrolysis

An attempt was made to increase the ionic conductivity of novel, heterogeneous, anion-selective membranes by increasing the porosity of their surface skin. This was based on the addition of a water-soluble component, namely poly(ethylene-ran-propylene glycol), to an inert polymer matrix, based on low-density polyethylene, while mixing it with the ion-exchange particles. A series of membranes was prepared, consisting of 66 wt% of anion-exchange phase represented by a styrene-divinyl benzene copolymer matrix with quaternary ammonium functional groups and an inert polymer matrix in a mixture with variable amounts of water-soluble component added. The membranes were subsequently tested with respect to their morphology, mechanical properties, apparent ion-exchange capacity, ionic conductivity, and performance under conditions of alkaline water electrolysis. When added in the appropriate amount, the addition of a water-soluble component was found to improve the electrochemical properties of the resulting membrane efficiently, while at the same time not reducing its mechanical properties to below a critical level.

Ultrafiltration and microfiltration membranes in latex purification by diafiltration with suction

Operation conditions of diafiltration with suction in purification of poly(glycidyl) methacrylate latex from sodium tetraborate and emulsifier were studied in a batch process using ultrafiltration blend polysulfone/poly(vinylpyrrolidone) and microfiltration Synpor® membranes. Intensity of permeate suction was controlled by changing the pumping rate at fixed cross-sections of the inlet tubes in both the retentate and permeate lines. An optimum value of flow rate was determined for each membrane type to ensure the best purification efficiency. Operating at this flow rate prevented not only undesirable dilution of the latex with osmotic water but also ensured the highest membrane permeability to solutes without cake formation on the membrane surface. It was shown that 92% degree of latex purification could be obtained by 8-h suction diafiltration with Synpor membrane having the pore entrance sizes close to nanoparticle dimensions. The possibility of complete purification of GMA nanoparticles from impurities using the hybrid membrane process combining dialysis followed by suction diafiltration with microporous membranes, and ultrafiltration with an appropriate membrane is discussed.

The preparation of microporous membranes from blends of poly(2,6-dimethyl-1,4-phenylene oxide) and sulfonated poly(2,6-dimethyl-1,4-phenylene oxide)

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is a chemically resistant polymer and, therefore, an attractive material for the formation of membranes. However, membranes of unmodified PPO prepared by an immersion precipitation possess very low hydraulic permeabilities at the filtration processes. The membranes with higher hydraulic permeabilities can be prepared from sulfonated PPO and/or from blends of unsulfonated PPO and sulfonated PPO. In conclusion, the mechanism of the formation of membranes from blends of unsulfonated PPO and sulfonated PPO is suggested.

Crosslinked ultra-thin polyimide film as a gas separation layer for composite membranes

Abstract Composite membranes with an ultra-thin polyimide separation layer were prepared by two-dimensional UV crosslinking of Langmuir-Blodgett films of a salt of polyamic acid based on 4,4′-hexafluoroisopropylidenebis(phthalic anhydride) and 2-(methacryloyloxy)ethyl 3,5-diaminobenzoate on the argon/water interface and then its deposition onto the surface of a porous support and by subsequent thermal imidization. Separation factors for CO2/N2, α = 6.4, and for O2/N2, α = 2.4, at permeation rates of the order 10−6 cm3 (STP)/(cm2 s cm Hg) were reached.

Ultra-thin polyimide film as a gas-separation layer for composite membranes

Abstract Composite membranes with an ultra-thin polyimide separation layer have been prepared by the deposition of dimethylalkylammonium salt of polyamic acid on a poly(phenylene oxide) porous support layer by the Langmuir—Blodgett technique and subsequent thermal cyclization of the polyimide precursor. In spite of a relatively mild thermal treatment, complete cyclization was achieved as observed by Fourier transform infra-red spectroscopy. The composite membrane with polyimide ultra-thin separation layer exhibited a considerably high permeation rate, maintaining a good selectivity.

Comparison of different cells for resistance determination of freely standing polymer membranes developed for direct methanol fuel cell (DMFC) applications

Cation conductive membranes, especially highly proton conductive membranes, are of interest not only for chlor-alkali electrolysis but for polymer electrolyte fuel cells as well. The very challenge for electrochemical characterization in this case is the low specific resistance of the polymer required for such applications, which in turn makes membrane resistance measurement a non-trivial problem. We investigate the different possibilities to characterize such membranes. For that purpose, a series of membranes made from sulfonated poly (phenylene oxide) (SPPO, degree of sulfonation (DS) from 7% up to 40%) was prepared. Commercially available membranes Nafion 117 as a reference are investigated, too. This contribution summarizes our new results concerning impedance spectroscopy measurements, using different measuring cells.

Purification of polymer nanoparticles by diafiltration with polysulfone/hydrophilic polymer blend membranes

Abstract The separation ability of new UF membranes based on blends of polysulfone (PS) with hydrophilic polymers (HP) was investigated in purification of polymer nanoparticle latices prepared by seeded emulsion polymerization. Low molecular weight components (emulsifier, salts, initiator) used in the synthesis of both glycidyl methacrylate (GMA) and sulfonated (SSS) nanoparticles as well as monomer residues were separated from nanoparticles of colloidal size (70–100 nm) by diafiltration using a three-compartment through-flow cell equipped with two membranes. In contrast to traditional pressure-driven diafiltration, this process is carried out under vacuum. The efficiency of new membranes and some commercial membranes were compared in the purification of nanoparticles. The influence of the nature of HP and structural characteristics of the skin layer of UF PS/HP membranes on their permeability to components of latex emulsions was estimated. The structure parameters of the skin membrane layer varied in the intervals: 1–7 nm (average diameter of pores), 0.6–49.2×10 10 (pore density) and 0.1–0.88% (relative surface porosity). For each type of membrane, an optimum correlation between the structure membrane parameters was found for ensuring the maximum permeate flux and purification degree of nanoparticle emulsions. It was shown that 95–98% and 85–89% purification degrees of GMA and SSS nanoparticle emulsions can be achieved by 6 h diafiltration with some UF blend PS/PVP membranes.

Electrochemical characterization of ionically conductive polymer membranes

Cation conductive membranes, especially highly proton conductive membranes, are of interest not only for chlor-alkali electrolysis but for polymer electrolyte fuel cells as well. The very challenge for electrochemical characterization in this case is the low specific resistance of the polymer required for such applications, which in turn makes resistance measurements a non-trivial problem. We investigate the different possibilities to characterize such membranes. The present part of our work deals with the adequate conditioning and equilibration of membranes designed especially for direct methanol fuel cell applications, with the measurement of the conductivity and with the determination of apparent transport numbers in the membrane. The usefulness of the respective leaching investigations, impedance spectroscopy measurements and concentration potential measurements for the case of membranes made from sulfonated poly(phenylene oxide) is discussed.

Polyurethane pervaporation membranes

Polyurethane membranes were prepared by the reaction of toluene-2,4-diisocyanate with hydroxy-terminated oligomers. Oligomers were either liquid polybutadiene (MW 3000) or propylene oxide-based polyethers (MW 420 and 4800). The prepared membranes were used in pervaporation of binary mixtures of water/ethanol, water/dioxane and ethanol/toluene, respectively. Polyurethanes with linking segments formed predominantly by high-molecular-weight oligomers (MW 3000 or 4800) were rubbery materials, while hard glassy membranes were obtained if the linking segments comprised high amounts of a polyether with MW 420. In pervaporation, all glassy membranes preferably transported small molecules of the feed mixture. In case a rubbery membrane was used in pervaporation in the presence of one feed component with a high affinity to the linking segments, the membrane preferentially transported this component. Durch Reaktion von Toluol-2,4-diisocyanat mit hydroxy-terminierten Oligomeren wurden Polyurethan-Membranen hergestellt. Die Oligomeren waren entweder flussiges Polybutadien (MW 3000) oder Polyether auf der Basis von Propylenoxid (MW 420 und 4800). Die Membranen wurden fur die Pervaporation der binaren Mischungen Wasser/Ethanol, Wasser/Dioxan und Ethanol/Toluol verwendet. Die Polyurethane mit Verbindungssegmenten hauptsachlich aus hochmolekularen Oligomeren (MW 3000 oder 4800) waren kautschukartige Materialien, wahrend bei Verwendung von Vernetzern mit einem hohen Anteil an Polyether mit MW 420 harte, glasartige Membranen erzielt wurden. Bei der Pervaporation transportierten die glasartigen Membranen bevorzugt kleine Molekule. Die kautschukartigen Membranen transportierten bei Anwesenheit einer Komponente in der Vorlage mit einer hohen Affinitat zu den verbindenden Segmenten hauptsachlich diese Komponente.