Hollow-fiber membrane module

Liquid purification or separation – Casing divided by membrane into sections having inlet – Each section having inlet

Reexamination Certificate

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Details

C210S321600, C210S321610, C210S321830, C210S500230, C210S500360, C210S500380, C210S500390

Reexamination Certificate

active

06623637

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a hollow fiber membrane module to be used in industrial fields such as the semiconductor industry, food processing industry, pharmaceutical industry, and medical industry and to a method for the production thereof. More particularly, this invention relates to a hollow fiber membrane module which is suitable for a use requiring a smaller decline in flow volume of a fluid between the initial stage and the latter stage of filtration.
Generally, a hollow fiber membrane module is formed by causing a hollow fiber membrane wound on a bobbin to be rewound on a rewinding jig having a polygonal cross section. One side of a coil formed of a multiplicity of hollow fiber membranes rewound on the jig is then cut, thereby giving rise to a membrane bundle. The openings in the opposite terminal parts of the membrane bundle are stoppered in a straight form or in a looped form lest the interiors of the membranes of the bundle be invaded by a potting resin. Thereafter, the stoppered portions are potted, thereby completing sealed parts (as disclosed in JP-B-07-106,302, for example).
As another hollow fiber membrane module, the construction of a membrane bundle obtained by using hollow fiber membranes as wefts, knitting the wefts across warps after the fashion of a textile to produce a sheet, and rolling the sheet of fabric around itself has been proposed. The construction of a membrane bundle obtained by rolling the aforementioned sheet of fabric around itself with a mesh interposed between the superposed plies of the roll has also been known (as disclosed in JP-A-62-57, 965, for example).
These hollow fiber yarn bundles open in at least one terminal part of membrane bundle, and a diaphragm adapted to prevent the fluids flowing inside and outside the hollow fiber membranes from mingling with each other is disposed in the opening. This diaphragm uses an adhesive agent of thermosetting resin such as epoxy, urethane, or silicone rubber. These thermosetting resins have low initial viscosity, are suitable for the purpose of immersion-solidifying or injection-solidifying a permselective membrane or a microporous membrane which has small rigidity, and are particularly optimum for a membranous material of the shape of a hollow fiber.
When such a thermosetting resin is utilized for the technique of potting hollow fiber membranes, a large number of hollow fiber membranes are uniformly dispersed at the potting position, and the thermosetting resin fills the gaps between the hollow fiber membranes. If the thermosetting resin increases in viscosity, it will no longer be able to fill the gaps between the hollow fiber membranes or produce a fully satisfactory sealed state.
As the potting resin for filling the gaps between the hollow fiber membranes, therefore, a thermosetting resin which has low viscosity is used in particular. Such is the true state of the prior art.
When the hollow fiber membrane bundle having the straight shape or looped shape mentioned above is subjected to vertical filtration, however, the efficiency of filtration gradually degrades by clogging. It is known that the degree of the consequent degradation of flow volume, when rated is based on a fixed membrane area, decreases in proportion as the number of membranes decreases and the length of membrane increases.
In this case, the increase in membrane length requires the length of the module to be increased and, as a result, entails a disadvantage of making incorporation of modules in a given device difficult. An attempt to have long hollow fibers accommodated in a short module case causes breakage of fibers and inevitably adds to the number of hours of work for accommodation. Since the conventional hollow fiber membranes individually allow a large degree of freedom and easily induce relevant fluids to drift, they make it difficult for materials in a fluid to transfer through the membrane, and prevent the membrane from effectively achieving filtration efficiency.
The specification of a plain coil of the sheet of textile mentioned above embraces a device for preventing the drift by the intervention of a mesh. However, since this device adds to the number of component members, results in increased costs, and enhances the chance of yielding an extracted matter from the materials themselves which are required by the module in the existing state, the number of component members of the module is preferred to be as small as permissible.
As the potting resin for the hollow fiber membrane, a thermosetting resin having low viscosity is used as mentioned above. In the semiconductor industry, the materials for semiconductors have been in need of chemical resistance, with the gradual rise in the degree of integration of semiconductors as a contributory factor. Thus, the module relevant herein ought to adopt, as the potting material, a thermoplastic resin which is identical or similar to the thermoplastic resin for a hollow fiber membrane. Incidentally, the thermoplastic resin generally has a high melting temperature and exhibits high viscosity at that temperature and burdens the potting technique with various problems yet to be solved.
A thermoplastic resin favors adoption of the immersion or injection potting because it has high viscosity and consequently makes adoption of the centrifugal potting difficult. In this case, since hollow fiber membranes themselves have a small amount of rigidity and inevitably yield to the pressure of insertion into the thermoplastic resin or the pressure of injection of the resin, they are partly distributed unevenly and are unevenly dispersed in the terminal parts of membranes. Since this unevenness prevents sufficient filling of the gaps between the hollow fiber membranes with the potting resin, the membranes allow communication between the primary side and the secondary side to the extent of inevitably impairing the filtering function thereof.
When the method of crushing (for example, by thermosetting resin, thermoplastic resin, thermal deposition, or shearing) is carried out for stoppering membranes in advance of the adoption of the immersion or injection potting technique, this method results in degrading the operational efficiency because the hollow fiber membranes which have undergone the stoppering treatment no longer allow effective potting unless they are separated one by one.
The problem further arises that the terminal parts of the hollow fiber membranes generate voids which are bubbles of vacuum, unless the thermoplastic resin is deprived of strain by shrinkage before it is allowed to set. The hollow fiber membranes generally are subjected to centrifugal cooling after they have undergone the potting treatment. This cooling, however, brings the problem of adding to the number of component steps of the process.
SUMMARY OF THE INVENTION
This invention has been perfected in view of a diligent study initiated as a result of the true state of prior art described above. It has for an object thereof the provision of a compact hollow fiber membrane module, which precludes the occurrence of defective potting by failing to completely fill the gaps between the hollow fiber membrane with a resin, obviates the necessity for a stoppering step, further obviates the necessity for a step of removing voids occurring during the course of solidification, avoids the possibility of inducing fluids inside and outside the hollow fiber membrane to drift, effects material transfer in fluids through a membrane with high efficiency, and allows accommodation of long hollow fiber membranes in a short module. It is particularly directed at providing a hollow fiber membrane module which is endowed with enhanced efficiency of filtration and consequently adapted for use in the field of semiconductor industry calling for resistance to chemicals, for example.
To accomplish the object mentioned above, this invention provides a hollow fiber membrane module which is obtained by cheese-winding a plurality of layers of permselective hollow fiber membranes made of thermoplastic resin, thereby forming

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