Liquid purification or separation – Filter – Supported – shaped or superimposed formed mediums
Patent
1985-12-06
1988-06-07
Sever, Frank
Liquid purification or separation
Filter
Supported, shaped or superimposed formed mediums
21050025, B01D 1300
Patent
active
047494875
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a semi-permeable membrane having improved transmission properties (i.e. flux) useful inter alia for the industrial desalting of molasses or milk whey by ultrafiltration.
PRIOR ART
Ultrafiltration is used industrially for the recovery of valuable macro-molecular products, such as proteins, fats and viruses, for example in the recovery of protein from cheese whey. Alternatively, ultrafiltration may be used in depollution applications, such as the removal of soluble oil from industrial waste effluents.
Classical filtration is limited to the retention of particles is sizes greater than 1 to 10 microns. Typical biofilters have a pore size of about 0.1 to 1 micron (10,000 angstrom) and can be used in connection with a filter aid (such as titanium oxide or alumina) which block the large pores of the biofilter to form a dynamic membrane. The filter aid simply rests on the surface of the biofilter and is not attached in any way. Without this, the pore size produced is too large for ultrafiltration applications. Membranes for biofiltration have been developed for particles as small as 0.08 microns (800 angstrom). Below these dimensions ultrafiltration membranes retain molecules with diameters as low as 10 angstrom through a molecular sieve mechanism which in many respects is analogous to filtration. Typical ultrafiltration membranes have pore dimensions in the range 10 to 200 angstrom.
Conventional ultrafiltration membranes have generally been formed of polymers, such as polyamides, polycarbonates and polysulphones. Generally, the ultrafiltration membranes will be either in the form of flat sheet or tubular membranes, or in the form of hollow fibres. However, the use of such organic polymeric systems suffers from a number of disadvantages.
Firstly, the polymeric ultrafiltration membranes are chemically sensitive to extremes of pH and tend to be dissolved by a number of solvents. Since the manufacturing techniques generally involve phase inversion using a solution of the polymer, it is difficult to provide polymers which are sufficiently soluble to allow for ease of manufacture but are resistant to commonly encountered industrial solvents.
More recently ceramic membranes have been developed to give high chemical and temperature resistance. However, these membranes suffer from the same disadvantage as other known membranes, as follows.
Secondly, the total pore area of known ultrafiltration membranes is generally less than 10% of the total membrane surface area. In fact, most commercially available ultrafiltration membranes at present on the market have a pore area less than 0.1% of the total membrane surface. Such low porosity limits the flux of liquid which can pass through the membrane. It is possible to increase the flux by increasing the pressure differential across the membrane, but the maximum flux is limited in use by the build up of a layer of the separated macro-molecular species on the membrane. To minimise this build up, the membrane is subjected to a high rate of cross flow (i.e. a high shear rate) of the liquid being filtered. Despite their low porosity, modern membranes have a flux which is limited even at high shear rates by the formation of a layer of separated species at high pressure.
AIM OF THE INVENTION
It is an object of the present invention to mitigate this problem and provide a semi-permeable membrane of higher porosity with surface properties leading to enhanced flux, and of good chemical resistance.
SUMMARY OF THE INVENTION
Broadly, the present invention resides in the provision of a microskin having special properties on a macroporous substrate, such as a conventional biofilter.
Thus, in one aspect the present invention provides a semi-permeable membrane, which comprises a macroporous substrate having a microporous microskin permanently deposited thereon, the microskin having a surface of Fractal geometry.
Another aspect of the invention provides a method of preparing a semi-permeable membrane, which comprises: having a surfac
REFERENCES:
patent: 4414111 (1983-11-01), Iwaisako et al.
Sever Frank
Syrinx Research Pty. Ltd.
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