W. Nijdam

Development and applications of very high flux microfiltration membranes

Inorganic microfiltration membranes with a pore size down to 0.1 ?m have been made using laser interference lithography and silicon micro machining technology. The membranes have an extremely small flow resistance due to a thickness smaller than the pore size, a high porosity and a very narrow pore size distribution. They are relatively insensible to fouling, because they have a smooth surface, short pore channels and because they can be operated in cross flow configuration at very low transmembrane pressures. Experiments with yeast cell filtration of beer show a minimal fouling tendency and a flux that is about 40 times higher than in conventional diatomaceous earth filtration. The uniform pore distribution makes the membranes suitable for many other applications like critical cell to cell separation, particle analysis systems, absolute filtrations and model experiments.

Ceramic microsieves: influence of perforation shape and distribution on flow resistance and membrane strength

Ceramic microsieves with slit-shaped perforations were compared to sieves with circular-shaped perforations, regarding flow resistance and membrane strength. Destructive tests show that the highest strength is obtained if the perforations are placed in a non-alternating pattern. Especially for slits, alternating patterns should be avoided as they make the structure unnecessarily flexible. The highest stress occurs at the edges of the membrane where it is attached to the support. Flexible structures bend stronger and therefore cause a higher stress at the edge, resulting in an easier rupture of the membrane. Our results show that ceramic microsieves with slits show a four to five-fold decrease in flow resistance for comparable strength related to sieves with circular pores.

Determination of particle-release conditions in microfiltration: a simple single-particle model tested on a model membrane

A simple single-particle model was developed for cross-flow microfiltration with microsieves. The model describes the cross-flow conditions required to release a trapped spherical particle from a circular pore. All equations are derived in a fully analytical way without any fitting parameters. For experimental verification of the model ultra-thin microsieves of uniform pore size and distribution were used. The release of trapped particles (polystyrene spheres and yeast cells) was determined by flux measurements as well as by in-line observation through a microscope. The results show that the model gives a fairly good indication of what cross-flow should be applied to keep the pores free for the conditions specified in this paper. In addition it provides us with a simple rule of thumb for the design of cross-flow modules for microsieves. It describes which geometrical demands have to be met to enable filtration without pore blocking, again for the conditions specified in this paper.

A hydrogen separation module based on wafer-scale micromachined palladium-silver alloy membranes

A thin but strong and defect free palladium-silver (Pd-Ag) alloy membrane is fabricated with a sequence of well-known thin film and micromachining techniques. A microfabrication process also creates a robust wafer-scale membrane module, which is easy to be integrated into a membrane holder to have gastight connections to the outer world. The microfabricated membranes have been tested to determine the mechanical strength, hydrogen permeability and hydrogen selectivity. The membranes have high mechanical strength and can withstand pressures up to 3 bars at room temperature. High flow rates of up to 3.6 mol H/sub 2//m/sup 2/.s have been measured with a minimal selectivity of 1500 for H/sub 2//He. The membranes survived operation at 450/spl deg/C, which is a temperature relevant for practical application in industry, for more than 1000 hours.

Fabrication and characterization of MEMS based wafer-scale palladium-silver alloy membranes for hydrogen separation and hydrogenation/dehydrogenation reactions

In this paper, a MEMS based wafer-scale palladium-silver alloy membrane (MWSPdAgM) is presented. This membrane has the potential to be used for hydrogen purification and other applications. A palladium-silver alloy layer (Pd-Ag) was prepared by co-sputtering. The thin Pd-Ag alloy has high hydrogen selectivity, high permeation rate as well as high mechanical and chemical stability. Typical flow rates of 0.5 mol H/sub 2//m/sup 2/.s have been measured with a minimal selectivity of 550 for H/sub 2//N/sub 2/. Anodic bonding of thick glass to silicon was used to package the membrane and create a very robust module. The membrane has high mechanical strength and can withstand pressures up to 4 bars at room temperature. The presented fabrication method allows the development of a module for industrial applications that consists of a stack with a large number of glass/membrane plates.

A microsieve for leukocyte depletion of erythrocyte concentrates

A new ultra thin filtration membrane has been used for leukocyte removal from erythrocyte concentrates. This filtration membrane, an Aquamarijn Microsieve(R), has a high pore density and a narrow pore size distribution and shows good separation behaviour. The low surface roughness of the microsieve will contribute to the biocompatibility and will reduce cell rupture, in particular hemolysis, during filtration. In this paper a brief overview of the effects that occur during filtration will be given. Also the results of the experiments of leukocyte removal from erythrocyte concentrates will be discussed.