Manufacture of a filtration membrane

Abstract

A filtration membrane made by a method that includes: a) selecting and preparing an organic polymer, such as a collodion; b) injecting a collodion into at least one channel of an extrusion die that also comprises an extrusion die core and at least one outlet; c) injecting an internal liquid into a hollow centering pin, the hollow centering pin comprising a channel positioned on the core of the extrusion die and also positioned at an axis of the outlet of the extrusion die; d) applying a holding film to the outlet of the extrusion die; e) unrolling the holding film onto a surface of at least one hollow fiber emerging from the outlet of the extrusion die; f) immersing the hollow fiber with the first holding film in a rinsing solution so as to obtain a flat hollow fiber filtration membrane; and ending the rinsing of the filtration membrane.

Description

TECHNICAL FIELD[0001]The present invention relates to the field of membrane filtration and more particularly to the manufacture of a hollow fiber filtration membrane associated with a support film.TECHNICAL BACKGROUND[0002]An important aspect of the manufacture of this type of membrane is related to the quality of the inner and outer surfaces of the hollow fibers and the fragility of the resulting membranes. Therefore, a method is usually used that includes particularly delicate steps in order to avoid mechanical stress and physical damage to the membranes.PRIOR ART[0003]The manufacture of organic membranes is based on the principles of phase separation (dry, wet, thermal) or foaming, and even irradiation followed by appropriate chemical treatment(s). The steps in manufacturing a membrane produced according to the principle of liquid-liquid phase separation are seemingly simple. But in reality, it is a complex process to manufacture a membrane because it is possible to obtain membra...

AI Technical Summary

Benefits of technology

The patent describes a method for making a filtration membrane that is cost-effective and reproducible. The membrane made using this method is strong and efficient. This invention solves the problems of previous methods for making filtration membranes.

Problems solved by technology

But in reality, it is a complex process to manufacture a membrane because it is possible to obtain membranes that perform very differently, from a same formulation (collodion).

When producing a hollow fiber through an extrusion spinneret, the surface state of the centering needle and, more importantly, the surface state of the extrusion orifice can cause the formation of major defects in its inner and outer surface.

In contrast, it has been noted that an even slightly degraded surface of the extrusion orifice can cause major defects in the outer surface of the fiber.

The presence of the slightest defect on the inner perimeter of the extrusion orifice of a spinneret can therefore significantly impact the quality of the surface of the nascent fiber.

In fact, the swelling which occurs in the nascent fiber increases the impact of existing defects on the perimeter of the extrusion orifice.

It is difficult to change the manufacturing conditions to minimize the impact of the surface state of the spinneret on the defects formed on the outer surface of the fiber.

Generally, the extrusion spinneret must be changed, which considerably increases the manufacturing cost of the membranes.

The outer surface of a hollow fiber or the active surface of a flat membrane is often damaged by the presence of scratches or burrs on the face of the advancement means which come into contact with them.

The membranes so produced have a semicrystalline structure, which can accelerate their aging and thereby limit their attraction.

Depending on the surface state of the rollers and on the draw conditions imposed, the fiber may suffer damage which can be very significant.

Observations made by scanning electron microscopy have shown that the outer surface of a fiber or the active surface of a flat membrane is very often damaged: indentations, marks, and tears are present on a regular basis.

These major defects affect the retention performance of membranes produced in this manner.

Experience has shown that these defects are the cause of accelerated chemical, mechanical, or thermal aging of membranes.

However, the presence of this dual filtration barrier results in poor hydraulic performance.

In addition, as previously indicated, the presence of numerous advancement means creates surface defects that can degrade the separation performance of the outer skin of the membrane.

This then results in the formation of hollow fibers which have attractive water permeabilities but poor selectivity performance.

Often these collodions also contain microgels which are the cause of many defects affecting selectivity and accelerating the chemical, thermal, and mechanical aging of the membranes so produced.

However, the spinning speeds are limited with such collodions.

To maintain production capacity, we must therefore increase the number of fibers produced in parallel, which intensifies spinning difficulties and gives rise to additional problems.

In addition, flat and hollow fiber membranes produced with an identical formulation did not provide the same hydraulic performance.

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