Gas separation: apparatus – Apparatus for selective diffusion of gases – Plural layers
Patent
1996-05-10
1998-05-19
Spitzer, Robert
Gas separation: apparatus
Apparatus for selective diffusion of gases
Plural layers
96 8, 96 13, 55524, 55DIG5, B01D 5322
Patent
active
057530149
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a membrane filter comprising a membrane provided with pores having a pore size typically between 5 nm and 50 .mu.m. The present invention further relates to a method of manufacturing such a membrane filter and to a membrane of the kind applied in such a membrane filter as well as various utilizations thereof.
BACKGROUND OF THE INVENTION
A membrane filter of the type described in the opening paragraph is frequently used for microfiltration, ultrafiltration, gas separation and catalysis and is known from a European Patent Application with publication number 325.752. The known micro filtration membrane filter comprises a layer of a polymer, glass or ceramics which has been provided with pores by means of a laser. The pores are formed by burning perforations in the layer with a pulsated KrF-Excimer-laser. Relatively small pores, having a size of about 0.5 .mu.m, are formed by means of crossing interference line patterns. In that case the pores are formed at the junctions of the interference lines.
These known membrane filters however are mechanically relatively weak and will foul relatively easily which will prevent them from achieving a very high flow rate or flux. In order to filtrate with a high flow rate the membrane should be made as thin as possible in which case the known membrane filter will not be capable any more to withstand the mechanical forces exerted on it during filtration.
Moreover the known membrane filter suffers from a relatively poor bio-compatibility rendering it practically unsuitable for medical purposes. Further the manufacturing of the known filter will be rather sensitive to process fluctuations as the adjustment of the laser apparatus is very critical with respect to the thickness of the membrane layer, the material of the membrane layer, the light intensity and the like. As a consequence the size of the individual pores will strongly depend on variations in the thickness of the layer, temperature fluctuations, laser energy stability and so on, which makes it hard, if not impossible, to form a filter with a sharp, well defined pore size distribution over a large membrane surface.
SUMMARY OF THE INVENTION
It is an object of the present invention to circumvent these disadvantages by providing for a membrane filter of the type described in the opening paragraph which is mechanically comparatively strong, highly bio-compatible and features a sharp, well defined pore size distribution. The present invention further provides for a method by which such an improved filter may readily be manufactured.
A membrane filter of the type described in the opening paragraph is according to the invention characterized in that said membrane comprises a substantially flat layer of substantially uniform thickness and in that the surface of said layer is substantially void of any protrusions or any other irregularities. The uniform thickness of the membrane of the filter according to the invention gives the filter a homogeneous lateral stress distribution over a large area. As a result, it will not, or at least less, give rise to lateral stress concentrations during operation, contrary to the known filter, which comprises a membrane which suffers from considerable thickness variation and in which mechanical stress moreover will tend to concentrate in the depressed portions between adjacent pores. Accordingly the filter of the present invention will be considerably less prone to breakage or other destruction during operation and, as a consequence, can be made considerably thinner facilitating an enhanced flow rate. In this respect proper results were obtained with a specific embodiment of the membrane filter according to the invention which is characterized in that the membrane has a thickness between 20 nm and 5 .mu.m with a thickness uniformity ranging from 10 nm to 100 nm respectively. Due to its thickness uniformity this membrane filter has proven to withstand the forces exerted on it during filtration even at comparatively large flux. To e
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