Rolf-Dieter Behling

Molecular sieving effect of the zeolite-filled silicone rubber membranes in gas permeation

Abstract Composite membranes, consisting of a highly hydrophobic zeolite, silicalite-1, and PDMS polymer were prepared. Distinct gas permeation effects have been found for these membrane types. A new parameter, the facilitation ratio of zeolite, was introduced to characterize the function of silicalite in the membrane. Using this parameter it was confirmed that silicalite played an important role in the molecular transport and that the altered permeabilities and selectivities were a result of the molecular sieving effect of the silicalite.

Preparation and characterization of thin-film zeolite–PDMS composite membranes☆

Abstract Thin-film zeolite filled PDMS composite membranes, as thin as 3μm, have been prepared. Two criteria are essential for the successful preparation of these membranes: (a) application of ultrafine silicalite crystallites (0.2–0.5 μm) and (b) prepolymerization of the suspension comprising silicalite, two-component polydimethylsiloxane (PDMS) polymer, and isooctane. The separation properties of the composite membrane were characterized by pervaporation and gas permeation. High flux and high selectivity were observed in the pervaporation of aqueous ethanol solution. Composite membranes, having a silicalite to PDMS ratio (ws/wp) of 3.3, give a selectivity of 34 for separating ethanol from water, while the flux remains 150 g/m2-hr, at 22°C. The composite membranes also show improved performance in gas permeation, e.g. for separating O2 from N2. Optimization experiments provide suitable conditions and compositions for the preparation of the membranes. Employing PDMS concentrations in the 3.5–4.0 wt.% range and silicalite to PDMS ratios from 1.5 to 3.3, highly-selective composite membranes can be fabricated with high reproducibility.

Ceramic zeolite composite membranes.: Preparation, characterization and gas permeation

Abstract Ceramic zeolite composite membranes, comprising a ceramic substrate and a dense pure zeolite thin layer on the surface of the substrate, have been developed by in-situ synthesis. The zeolite thin layer has been shown by X-ray diffraction, SEM and optical microscopy to have a pure zeolite phase, in which individual zeolite crystallites have intergrown in three dimensions into a polycrystal zeolite thin disc. The nitrogen permeability of these composite membranes, after calcination, reaches 1–4 m 3 /m 2 -hr-bar at room temperature. The ideal selectivities are 2.81 for He over N 2 and 47.7 for N 2 over n-butane, which are far beyond the range of Knudsen diffusion. After improvement of the preparation procedure the membrane even shows a selectivity of 6.2 for n-butane over i-butane. Combined effects of “shape-selectivity” of the zeolite and capillary condensation of the non-zeolite pores are considered to be responsible for the high selectivities.

Nitrate removal of drinking water by means of catalytically active membranes

The reduction of nitrate to nitrogen in aqueous solutions by means of catalytically active membranes has been investigated. A heterogeneous catalyst (Pd/Cu) has been incorporated in a microporous polyetherimide membrane. After saturation with hydrogen nitrate containing water was filtered through these membranes. The nitrate reduction was studied as a function of pH, volume flow and temperature. It could be demonstrated that the catalyst remained active in the polymer matrix. The calculated activation energy for nitrate reduction is indicating that the reaction is dominated by mass transfer and diffusion.

Dehydration of organic compounds with SYMPLEX composite membranes

Abstract The SYMPLEX composite membrane is based on the complexing reaction of poly-ions. The reaction of polyanion and polycation gives a water insoluble membrane with low mechanical stability. In order to improve the mechanical behaviour, composite membranes were prepared in situ on a microporous, chemical resistant support. These membranes have been investigated for the dehydration of organic compounds by pervaporation. SYMPLEX composite membranes are well Suited to dehydration processes by pervaporation of higher alcohols and other organic compounds. Selectivities up to 20 000 and a water flux of 1.6 kg/h m2 for the dehydration of alcohols at water feed concentrations above 2 wt% could be obtained. Below these concentrations a decrease in selectivity could be observed, if n-alcohols such as methanol or ethanol which are very similar to water, are to be dehydrated. With other organic compounds such as ketones or amines, a high selectivity and flux could also be detected. High concentrations of strong bases in the feed destroyed the selective layer and in some cases the support, too.