Liquid purification or separation – Filter – Supported – shaped or superimposed formed mediums
Reexamination Certificate
1999-09-27
2001-09-25
Kim, John (Department: 1723)
Liquid purification or separation
Filter
Supported, shaped or superimposed formed mediums
C210S483000, C210S488000, C210S489000, C210S500290, C210S500300, C210S500380, C210S500410, C210S500430, C210S504000, C210S505000, C210S506000, C210S508000
Reexamination Certificate
active
06293411
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns integral porous separation membranes supported on nonwoven polymeric supports such as are typically employed as filter media in conventional filtration modules for the filtration of fluids.
The term “porous separation membranes” is generally understood to refer to ultrafiltration and microfiltration membranes that have pores with diameters of about 0.001 to 0.1 &mgr;m and about 0.01 to 30 &mgr;m, respectively. Such membranes are conventionally fabricated from organic polymers, and are often brittle, with little capacity for mechanical loads. For increasing mechanical structural strength, porous membranes of organic polymers are supported with a wide variety of support materials such as woven material, knitted fabrics, non-woven materials, or films. The terms “integral” and “nonintegral” are differentiated by the type of bonding between the membrane and the support material.
The term “integral supported membranes,” refers to those wherein the still fluid permselective membrane material is brought into contact with the support material and the membrane is formed by the mutually interpenetrating bond formed between the permselective membrane and the support. The support then, to a certain extent, penetrates into the membrane or may even be entirely encapsulated by the membrane. The membrane can be reinforced on one or both sides.
In contradistinction, in the case of a non-supported membrane, the already cast permselective membrane is applied directly onto the support by, for instance, lamination or by an adhesive. From the viewpoints of production and applications, integral supported separation membranes are preferable.
The cost of the production of integral supported separation membranes is governed by the degree of increase of mechanical strength desired, but increased mechanical strength is typically attainable at the cost of loss of service life or filtration capacity, often up to some 40% and usually accompanied by a decrease in retention capability for the substances to be removed, all as compared to non-supported membranes. Such drawbacks are unacceptable in industrial applications.
Thus, the object of the invention is the provisions of integral supported membranes having longer service lifetimes, higher filtration capacity and improved retention capability. This object and others which will become apparent to one of ordinary skill are met by the present invention, which is summarized and described in detail below.
BRIEF SUMMARY OF THE INVENTION
The invention comprises the provision of integral supported porous separation membranes wherein the support for the permselective membrane is made of a mat or fleece of compacted non-woven fibers the mat exhibiting a basis weight of from about 20 to about 40 g/m
2
, a thickness from about 90 to about 170 &mgr;m and an air permeability of between about 1200 and about 2400 L/m
2
·s at a pressure of 0.002 bar.
Rather surprisingly, it has been discovered that the integrated supported membranes of the present invention exhibit a number of unexpected advantages at the same flux relative to integral supported membranes of the prior art. Membranes fabricated in accord with the present invention have improved retention capability, particularly for microorganisms, and can be monitored with greater safety for integrity, since they possess a bubble point some 40% higher and a rate of diffusion reduced by about a factor of 10 to 20. These advantages permit filtration equipment equipped with such supported membrane to be tested for integrity with greater safety, especially in sensitive filtration applications such as pharmaceuticals, biotechnicals, and in the food and beverage industries. Similar advantages are gained with filtration devices for medical and gene technology, where a higher degree of safety is paramount.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In a preferred embodiment of the invention, the non-woven material for the support comprises a multi-component or composite fiber, wherein the composite includes a first polymer and a second polymer such that the second polymer is present on at least a portion of the surface of the composite fibers and exhibits a glass transition temperature which is lower than the glass transition temperature of the first polymer.
In a further preferred embodiment, the composite non-woven fiber support is made out of a mat of fibers, wherein the core advantageously comprises a polymer having a higher glass transition temperature, for instance polypropylene, with an enveloping outside layer of a chemically resistant, thermoplastic polymer, such as polyethylene.
The permselective separation membrane itself may be formed from any polymer which is suitable for the formation of a porous membrane according phase inversion casting techniques, including solvent evaporation, coagulation bath and combinations of these processes. Particularly well-adapted to such procedures are membranes cast from polysulfones, polyethersulfones, polyamides, polyacrylamides, polyacrylnitriles, cellulose hydrates and cellulose esters. Particularly preferred are polyethersulfones, polyamides and the cellulosic esters cellulose acetate, cellulose nitrate and mixtures of the two.
The integral supported separation membranes of the invention can be fabricated into filters which are flat, pleated or tubular, and may even be used as a support material for additional membrane layers.
REFERENCES:
patent: 4340479 (1982-07-01), Pall
patent: 5108827 (1992-04-01), Gessner
patent: 5500167 (1996-03-01), Degen
patent: 5989432 (1999-11-01), Gildersleeve et al.
Chernoff Vilhauer McClung & Stenzel LLP
Kim John
Sartorius AG
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