DE2236226B2 - Process for the production of semi-permeable asymmetrical capillary membranes - Google Patents

Description

meable layer of merobran in the capillary formed falls inside out.

The asymmetric capillary membranes according to the present invention suitably have one Inside diameter of about 0.2 to 2 mm. The semi-permeable, dense "layer" is on the inner wall of the capillaries, while the outside has a porous structure that serves as a support material. Because the semipermeable layer is on the inside of the capillaries, the new The solution to be filtered is applied from the inside to asymmetrical membrane capillaries.

They are self-supporting up to a hydrostatic pressure of about 50 atm. The breaking point depends on the inner radius of the capillary. The capillaries are used for e.g. B. in ultrafiltration or reverse osmosis to a bundle of about. 100 to 10,000 units combined. A The bundle can be about 20 to about 100 cm in length.

This arrangement has the opposite to the use of the known film or tubular membranes great advantage that no special support material is necessary and that a very large membrane surface can be accommodated at a certain volume unit. This makes the filtration units much easier and cheaper to manufacture.

The advantage over the known hollow fiber membranes is the far better control the excessive concentration. in laminar flow using input effects (H. Strathmann and B. K e i 1 i n, desalination 6, 179 [1969]). By acting on the membranes according to the invention from the inside, a defined Flow can be achieved on the membrane surface. By increasing the flow velocity Practically any high shear forces can be effective on the membrane surface and thus practically all particles or macromolecules deposited on the membrane surface are removed will. Increase in concentration or formation of precipitation on the membrane surface, which in the case of the membranes acted upon from the outside, a very Difficult problem can pose in this way largely avoided.

The capillaries can be made from practically all common

ίο plastics, which are otherwise also used for semi-permeable membranes come under control, be produced.

Example! for making the
asymmetrical scinupermeable membrane capillaries

A polymer suitable for the production of semipermeable membranes, ζ. Β Cellulose acetate, polyvinyl chloride or an aliphatic or aromatic polyamide is dissolved in a solvent suitable for the polymer in question in a concentration of about 5 to about 50%. The membrane capillaries are formed continuously by means of a special spinneret. It consists of a double capillary, on the outside of which the polymer solution flows down and inside which the precipitant, generally water, flows down. At the end of the nozzle, the precipitant comes into contact with the polymer solution, and the membrane layer is precipitated from the inside out. By choosing a suitable nozzle, both the inner and the outer diameter of the capillaries can be varied within limits between approximately 0.2 to 2 mm. Through the precipitation process from the inside out, the membrane gets its active semipermeable layer on the inside. The properties of the asymmetrical membranes in capillary form, namely their separation limits and tiltration current densities, can be varied within wide limits, just as in the case of membranes in film forms. You can

Tabel

solvent Precipitant Membrane properties rniraiions-
current density
at 30 atm
cm / sec polymer Dimethylacetamide + LiCl 5%
Dimethylformamide 4- LiCl 5%
N-methylpyrrolidone + LiCl 5% water
Formic acid
water
Formic acid
water
Formic acid Pore size
A. 2 to ⁴ 8-10
2 to 4 · 10- ⁴
5 to 9-10 ⁴
4 to 6-10- ⁴
0.5WsI-IO- ³
3 to 6 10- * Poly (m-phenylene
isophthalamide) 10 to 20% Formic acid water 4 to 10
3 to 6
4 to 8
3 to 6
4 to 8
3 to 6 2 to ⁴ 8-10 Poly (hexamethylene capricine)
amide) 10 to 35% Formic acid water 3 to 8 4 to 8 · 10 · ⁴ Pcily- (trimethylhexa-
methylene terephthalamide)
lOto25% Dimethyl sulfoxide
Dimethylformamide water
water 4 to 8 Ibis 9th IO- ^3rd
0.5 to 5 · 10- » Polyacrylonitrile 10 to 25% Tetrahydrofuran
Dimethylformamide water
water 5 to 15
4 to 10 0.5 to 5 · 10- »
0.5 to 8 · l0- ^a Polyvinyl chloride
10 to 25% acetone water
Ethanol 8 to 20
10 to 30 3 to 6 · ΙΟ- »
5 to ⁸ 9-10 Polymethyl methacrylate
10 to 20% 8 to 10
8 to 20

Forum greetings through the polyra content, through the Solvent and through the precipitation bath as well as the Fftll ' temperature vary within wide limits. By post-treatment of the precipitated capillary membranes can also have an additional influence on the term limit as well as the 4-point filtration current density and the mechanical stability can be achieved. The capillaries produced in this way can be adjusted to the desired Length z. B. of about. Cut 10 to about 100 cm, grouped into bundles of about 100 to 5000 units of about 0.1 to 10 square meters of membrane surface can be in series or can be connected in parallel, depending on the desired return flow and flow conditions. Of the hydrostatic pressure with which the new membranes can be operated in capillary form is through the mechanical strength of the KapUlaten is determined and limited in height to approx. 50 atö. By attitude The pore size of the membrane between about 3 and 500 Å can contain substances with a molecular weight from about 20 to 2,000,000 can be removed from a solution. Fractionation can also be used be carried out by connecting membranes of different pore sizes in the back. the Capillaries with an inner diameter of 0.2 to

ίο 2 mm can be made from all polymers that are soluble in a solvent. Some of the polymers particularly suitable for the production of the capillary membranes according to the invention, the associated solvents and precipitating agents and the filtration properties of the asymmetric membranes produced therefrom are listed in the table.

Claims (1)

beats. 30,000 to 40,000 such hollow filaments are grouped together in a bundle Process for the production of semipermeable apparatus for ultrafiltration or the reverse asymmetrical capillary membranes are used for ultra-osmosis. The use of this hollow Filtration from the solution of a suitable poly thread has the advantage that it is up to a relatively high mers are self-supporting in a pressure for the polymer in question, so no support material suitable solvents through a precipitation reaction- need more, tion, characterized in that one knows hollow fibers with symmetrical and asymmetrical one the polymer solution through one of a metric structure. With the asymmetrically opened double capillaries existing spinneret in the io built hollow filament membranes that previously only made Extruded way that you have made on the outside of the cellulose acetate is located Double capillaries the polymer solution and in their so-called "active layer", d. H. the real one The inside allows the precipitant to flow down, the semipermeable membrane, on the outside of the through the precipitation hollow filament at the exit of the nozzle. These hollow filaments must therefore always be of medium with the polymer solution in contact 15 exposed to the outside with the solution to be filtered and so be the semi-permeable membrane layer in the. That is with considerable disadvantages formed capillary falls from the inside out. Control of the excessive concentration on the Connected membrane surface. It is extremely difficult rig, in a tightly packed bundle of fibers the upper 20 surface of each individual fiber optimally to flow. It The invention relates to a method of making comes to lean in general of semipermeable capillary membranes, which controlled a single fiber and therefore too poorly controlled have an asymmetrical structure in such a way that flow conditions on the thread surfaces, its semi-permeable, dense layer on the inside, especially when filtering macromolecular ones the capillary is located and that the outside of a 25 or colloidally dissolved particle occurs often an exporous one Has structure that only serves as a support layer. Treme excessive concentration on, and abfil-For a successful implementation z. B. the trated substances fall in on the surface of the thread Ultrafiltration and reverse osmosis is made in the form of a layer of gel. This is crucial Use of highly effective semi-permeable meme effect on the entire filtration process, are of great importance. 30 Once the The membranes should have a sharp cut-off point for the osmotic pressure of the starting solution at the membrane, so that molecules of a certain type and surface area increases, and if there is a deposition The size is quantitatively retained by particles on the membrane's surface while they completely pass all other filtration flow densities and partly also through permit. The filtration rate should, with secondary membrane formation mentioned 35, influence the separation's own low hydrostatic pressures as high as possible in the original membrane, because this increases the investment and energy costs, not only increases the operating costs, costs are decisively influenced. The mem- but it also becomes the whole separation process Branches should also have good chemical and mechanical properties. niche stability in order to have a good constancy of the 40 asymmetrical hollow fiber membranes of this type Filtration speed and a high life are z. B. in German Offenlegungsschrift 2137 338 guarantee duration. described. These have semipermeable membranes The so-called asymmetrical membranes, which are the shape of cylindrical tubes that are made in at generally in the form of foils and tubes pre-treated, symmetrical memmite in a certain way a diameter of 1 to 3 cm produced 45 branched skins in a cumbersome manner as tubular meet the stated requirements. already largely; but is the subject of U.S. Patent 3,583,907 for practical use must these membranes, which are almost exclusively through a dialysis machine in which a plurality of a precipitation or phase inversion reaction produced capillary membranes in stretched form below on a porous support material such as porous 50 retaining the original length or below Plastic, stoneware or metal plates or pipes easily stretched during the filtration in one be applied. The membrane support material provides housing that is held together. According to the information often a significant proportion of the total price of FiI- in the description it is symmetrical tration system. Also the ratio of meme-capillary membranes. The combustion surface to the apparatus volume is un- 55 The object of the present invention is advantageous and increases the investment costs. In the case of the apparatus, through a precipitation reaction from a polyture With these membranes, asymmetrical, semipermeable hollow fiber centration superelevations also easily occur on, which can only be produced by applying membranes for ultrafiltration For example, a turbulent flow parallel to its application, the post-membrane described above can be reduced. 60 parts can be avoided. In order to meet these technical and economic difficulties, this object is achieved according to the invention. To solve the problems with the known film membranes that the polymer solution is through one of one avoid, semipermeable double capillaries have been used in the existing spinneret in recent years Membranes in the form of fine hollow filaments extruded in such a way that one on the outside of the Developed diameters of around 0.02 to 0.2 mm. 6g double capillaries the polymer solution and in their The wall of the hollow filament is the actual interior which allows the precipitant to flow down, whereby Membrane daif. These hollow filaments ^ Membfanen are one at the exit of the nozzle the precipitant with the from the outside with the solution to be filtered * brings polymer solution into contact and thus the semi-perfect