Liquid purification or separation – Filter – Supported – shaped or superimposed formed mediums
Patent
1995-01-17
1996-08-06
Spear, Frank
Liquid purification or separation
Filter
Supported, shaped or superimposed formed mediums
21050025, 21050026, B01D 7104
Patent
active
055430465
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an inorganic membrane for microfiltration, that consists of a macroporous inorganic support and an inorganic membrane layer with pores having a pore size typically between 0.01 .mu.m and 10 .mu.m, which membrane layer is connected rigidly to the inorganic support. The invention relates also to a process for production of such an inorganic membrane.
BACKGROUND OF THE INVENTION
A membrane consisting of a macroporous support and a membrane layer is a composite membrane. The macroporous support contributes in here to the mechanical strength of the total membrane. Whenever the membrane layer with a high pore density is deposited relatively thin in comparison to the mean pore size on a relatively thick support, a membrane with a high flux is obtained. In case the inorganic membrane layer as well as the inorganic support is made of suitable ceramic materials then the membrane will be chemically highly inert and will operate well at elevated temperatures.
From EP-A-0-144 097 a composite ceramic membrane is known having the above-mentioned characteristics. This ceramic membrane has a membrane layer that is formed by coating a porous support with a thin film by immersion in a stable sol of colloidal metal oxide (g -AlOOH) particles and then drying and heating the support, thus forming a macroporous membrane layer of metal oxide particles.
Such known inorganic membranes may display mechanical faults, like little fractures and `pinholes` with typical size 10 .mu.m to 100 .mu.m, which are relatively large in comparison to the mean pore size, typically 5 nm-5 .mu.m, thus reducing the separating characteristics.
Another intrinsic disadvantage of these membranes is the relatively large thickness of the membrane layer in comparison to the mean pore size, resulting in reduced flux characteristics of the membrane. In said patent publication the thickness of the membrane layer ranges from 50 to 1000 times the mean pore size of the membrane layer.
SUMMARY OF THE INVENTION
The present invention has as an object to provide an inorganic membrane with improved separating and flux characteristics. An other object is to provide an inorganic membrane particularly useful for biomedical filtration, in particular in solutions with vulnerable cells. Therefore, according to the invention an inorganic membrane for microfiltration is proposed, wherein the membrane consists of an inorganic macroporous support having a mean pore size in the range of 0.25 .mu.m-025 .mu.m, and an inorganic membrane layer being deposited and connected rigidly to a flattened surface of the macroporous support by means of a deposition method, whereby the pores of the membrane layer are perforations shaped as shallow channels square to the membrane layers, and are formed with a diameter in the range of 0.05-5 .mu.m by means of etching, said channels having a length at least smaller than ten times the diameter of the channels.
Good filtration results are obtained according to the invention with an inorganic membrane consisting of a porous support of alumina with mean pore size in the range 0.25-25 .mu.m and an inorganic membrane layer of silicon dioxide with channels of 0.05-5 .mu.m. In preference the support and the membrane layer are constituted from equivalent materials with the same inorganic components. An inorganic membrane is thus obtained applicable in a broad temperature range with a good cohesion between the support and the membrane layer. Because of the low length/diameter ratio of the channels an inorganic membrane with a high flux is obtained. In addition through this measure vulnerable cells have a minimum chance in being damaged during passing these channels.
The inorganic membrane may be produced by firstly depositing a suitable inorganic layer by chemical vapour deposition on the inorganic support, and secondly making perforations in this inorganic layer by means of a suitable etching process.
According to the invention an inorganic membrane is manufactured, in which the perforations in
REFERENCES:
patent: 3794174 (1974-02-01), Booman et al.
patent: 4923608 (1990-05-01), Flottmann et al.
By P. Sioshansi, "Medical Applications of Ion Beam Processes", Nuclear Instruments & Methods in Physics Research, Feb. 1987, pp. 204-208.
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