Wolfgang Lenk

Polyelectrolyte multilayer membranes for pervaporation separation of aqueous-organic mixtures

Abstract Composite membranes for pervaporation of water/alcohol mixtures were prepared by consecutive alternating adsorption of poly(acrylic acid) (polyanion) and poly(ethylenimine) (polycation) on a polyamide-6 substrate. The influence of preparation conditions on the pervaporation separation properties of polyelectrolyte multilayer composite membranes was studied. Variation of polyelectrolyte concentration of the dipping solution and adsorption time had only a minor effect on the membrane performance. On the other hand, high molecular weight polyelectrolytes had a high impact on membrane performance. A separation factor α of 2500 was observed for a membrane having four double layers. Best results were obtained when the adsorption temperature was raised from 25°C to 80°C A membrane with two double layers showed a separation factor α of 900.

Influence of thermal treatment on the pervaporation separation properties of polyamide-6 membranes

Abstract Integrally-skinned asymmetric polyamide-6 membranes were prepared by casting 15 wt.% solution of polymer in 85 wt.% formic acid onto a glass plate and precipitation in water at 4°C. The obtained membranes were dried for 1 h at different temperatures ranging from 25 to 140°C in air and from 25 to 200°C in vacuum, respectively. The pervaporation separation properties of such treated membranes were studied with binary water-2-propanol mixtures consisting of 5 to 95 wt.% water. The membranes showed water permselectivity over a wide range of the feed composition. Thereby the water permselectivity reached a maximum at low water contents in the feed mixture. The selectivity was improved by thermal treatment of the membranes at temperatures above the glass transition temperature T g of polyamide-6 (≈60°C). However, the permeate flux decreased with increasing drying temperature due to the removal of entrapped water from amorphous domains, the formation of new crystalline domains and the decrease of the pore size and of the specific surface area during the thermal treatment. These effects were confirmed by dsc measurements, X-ray scattering experiments and BET measurements.

Effect of Polyelectrolyte Complex Layers on the Separation Properties and the Fouling Behavior of Surface and Bulk Modified Membranes

The effect of polyelectrolyte complex layers on the separation and filtration properties and on the fouling behavior of surface and bulk modified membranes were studied using two different separation processes, namely pervaporation and microfiltration. Therefore two different membrane types were employed. The microfiltration tests were conducted using a commercially available polypropylene membrane (Celgard 2400). The pervaporation experiments were performed on a home-made polyamide-6 pervaporation membrane.

Modifizierung von Polyaramid-Ultrafiltrationsmembranen durch Elektronenbestrahlung

Die Bestrahlung von Polyaramid-Ultrafiltrationsmembranen (PA-UF-Membranen; NADIR® UF-PA-5) mit energiereichen Elektronen ergab im Energiedosisbereich von D≈150 bis 200 kGy eine Erhohung des Ruckhaltevermogens R von 93 auf 98%. Entgegen der ublichen Erfahrung trat dabei keine Reduzierung des Permeatfluswertes JPVP auf. Durch ζ-Potentialmessungen und IR-spektroskopische Untersuchungen konnte der Einbau von zusatzlichen Carboxygruppen durch die Bestrahlung nachgewiesen werden, die diesen Effekt im wesentlichen verursachen. Electron beam irradition of polyaramide ultrafiltration membranes (PA-UF membranes; NADIR® UF-PA-5) led to an increase of retention R from 93% to 98% in the applied dose range between 150 and 200 kGy. Contrary to common findings, no reduction of permeate flux JPVP was observed. The formation of carboxy groups caused by electron beam irradiation was confirmed by ζ-potential measurements and ATR-FTIR spectroscopic investigations.