DE4028356A1 - Open-pore polysulphone-amide micro:filtration membrane - by casting film from soln. contg. polymer, pptn. agent with air at 20 deg C or above, and coagulating in a pptn. bath - Google Patents

Abstract

(1) Open-pore polysulphone-amide microfiltration membrane (I) is produced by (a) casting a film from a soln. of polysulphone-amide (II) in a polar solvent, contg. a precipitating agent (III) for (II) and possibly a pore-former (IV) and a swelling agent (V), (b) passing air at 20 deg.C. or above over the film and (c) immersing it in a coagulating liq. which is miscible with the polar solvent but is a precipitating agent for (II). - The membrane (I) is claimed as such and has a continuous sponge structure with pore size 0.1-5 microns (increasing from one side to the other) and is wettable with water.

Description

The invention relates to a method for producing Polysulfonamide membranes for microfiltration and the membranes obtained by this method.

Membranes are referred to as microfilters Pore size range of about 0.1-10 microns include and mainly for the separation of particles and Microorganisms are used.

Membranes made of polysulfonamides, manufactured after Precipitation bath processes are known for reverse osmosis Desalination, 54 (1985) 207-217 a method for Manufacture of polyester fleece reinforced ultrafiltration  membranes described. The process is based on the Use of a polysulfonamide from the reaction of 4,4'- and 3,3'-diaminodiphenyl sulfone with terephthaloyl chloride in Dimethylacetamide (DMAc), the polymer concentration 13- Is 14% by weight. The membrane is in the way prepared that the casting solution applied to a nonwoven is exposed to the atmosphere on both sides for a certain time and then passed into a precipitation bath, where as Precipitation bath water is used, if necessary with a Addition of dimethylformamide (DMF).

By Liu Gouxin et al; Desalination 62 (1987) 239-249 described the manufacture of RO membranes from Solutions with 13-17% of an unspecified Polysulfonamids, 78-84% DMAc and calcium nitrate or Lithium chloride as an additive (3-5%) which also in the casting solution in the manufacture of The resulting calcium chloride is contained in the polymer. To one to get the necessary sponge structure for the RO membranes work at high polymer concentrations. This structure is also favored by a low one Precipitation bath temperature or the addition of some water to the Pouring solution to reduce the exchange of DMAc.

Desalination 62 (1987) 353-361 describes the structure of Polysulfonamide ultrafilters discussed. The membranes have an asymmetrical structure with a pronounced Finger structure in the lower layer. Also in Desalination, 62 pp. 221-232 are properties of RO and UF membranes described and also scanning electron micrographs of microfilters shown, which have a very rough structure, the  Recordings of the at least partial existence of a closed-pore cell structure suggest that in greatly reduced flow rate. In this However, publication will not provide any information about Properties, manufacture and pore size of the shown Microfilter made.

Another publication by the latter authors in Synth. Polym. Membr., Proc. Microsymp. Macromol, 29th, (1986), 213-218 are data on flow rate and Manufacturing process of polysulfonamide microfilters already structure described. The ones listed there Flow rate values are significantly lower than those commercially available microfilter. As a manufacturing process no precipitation bath process used, but a combination of Evaporation and precipitation using water vapor from the Gas phase, with a structure primarily due to the precipitation that occurs as a closed cell structure is described, which is only when removing the Residual solvent breaks up, certainly parts with closed-pore structure are preserved, as from the low flow rate can be removed.

A composition containing polysulfonamide with which microfilters can also be produced in the SU-A-20 52 798/05. Casting solutions are used, for the production of micro filters up to 15% Non-solvent (water or alcohol) for the polymer contain. The microfilters obtained there, over their Structure no details are given, point around the flow rate is 10 times lower than commonly used microfilters. this fact  indicates insufficient porosity or Surface porosity and one for microfilters serious disadvantage.

The object of the invention is To create microfiltration membranes that are preferred at static filtration are used, in which the filtering medium flows through the membrane, the Membrane acts as a depth filter. Convenient for this The operating mode is when the structure is as open as possible, d. H. the membrane has a high porosity, which in the Rule is reached when they have a so-called Has a sponge structure, that is, a structure in which the membrane matrix from an open, fine network of Polymer material is made. With this structure there is a maximum mechanical stability at maximum flow rate and good dirt retention capacity, whereby it is particularly advantageous if the membrane has asymmetrical sponge structure, in which the Pores from one side to the other steadily in size change so that the depth filtration particles to be separated according to their size in different areas of the membrane are held, if the Memnran from the side with the larger pores is flowed through, making a much higher Dirt holding capacity than with symmetrical membranes comparable pore size results. Furthermore, the Membranes have an improved flow rate because this is inversely proportional to the pore size, d. H. the The layer with the finest pores essentially determines the hydraulic resistance of the entire membrane, so that too when using the membrane in cross-flow mode, in which  the fine side of a membrane is flowed over tangentially Avoiding the formation of a covering layer, the application of the membrane advantages, preferably in an asymmetrical form. About that In addition, the membranes to be created according to the invention high requirements regarding the regularity of the Network are sufficient, because the Pore size distribution of the membrane results, the respective largest pores the retention capacity of the membrane Determine microorganisms and particles. The largest in each case Pores are usually created using the so-called Bubble point tests where the pressure is determined one completely with a certain liquid wet membrane allows air to pass through. The Membranes to be produced according to the invention should therefore be used for given flow rate a bubble point as high as possible have, the relation of bubble point to flow as with commonly used microfilters (Tab. 1) is.

Table 1

Membranes that meet the above objectives are produced by the method of claim 1.  

Membranes are made from the known precipitation bath process Polysulfonamiden produced, so results at low Polymer held a so-called finger structure, which at Ultrafilter is quite desirable. A sponge structure was only with the methods according to the prior art Obtained polymer concentrations above 15 wt .-%, one Area in which none are sufficient for microfiltration membranes Adequate porosity can be achieved.

Surprisingly, it has been found that the inventive method when the selection of Systems pouring solution / precipitation bath takes place in such a way that the precipitation The polymer develops very quickly, the tendency to go out formation of a sponge structure increases. The polymer is there when dissolved in a polar organic solvent or the solution in which the polymer is obtained is preferred was used for the production of the casting solution, preferably DMAc or N-methylpyrrolidone (NMP) as Solvent for the production of the polymer and the Pouring solution can be used.

The polymer used is the process according to the invention preferably used a polysulfonamide available is by condensation of terephthaloyl chloride or Isophthaloyl chloride with 4,4'-diamino-diphenyl sulfone or 3,3'-diamino-diphenyl sulfone, but especially by Polycondensation of terephthalic acid chloride and 4,4'-dia mino-diphenyl sulfone, the concentration of the polymer in the casting solution preferably about 4-10%, especially however, it is preferably 5-7%. Through condensation of 4,4'-diaminodiphenyl sulfone and terephthalic acid chloride produced polymer is in the aforementioned SU-A- 20 52 798/05 page 3 (see example 1). The be preferred use of this polymer results from the outstanding  thermal properties (softening point = 383 ° C) and the good solvent resistance.

It has been shown that, for example, when using Formamide is used as a precipitant in the casting solution of water as a precipitation bath achieves this rapid precipitation becomes. Of course, other combinations of Precipitant in the casting solution and composition of the Precipitation bath part of this invention, insofar as they are the required properties of a rapid precipitation are sufficient. It is particularly advantageous to adjust the concentration To choose precipitants in the casting solution so that the precipitation point of the polysulfonamide is almost reached.

The concentration of the precipitant in the casting solution is approximately between 15% and 40%, particularly however, preferably between 20 and 30%.

Also useful for the formation of a sponge structure acts as a swelling agent for the polymer in the Casting solution, preferably dimethyl sulfoxide (DMSO) Is used. The concentration is expediently 0.1-20%, preferably 10-20%.

The formation of a sponge structure can also be promoted by the presence of a pore former, such as CaCl ₂ , in the casting solution, the concentration being 0.1-3.2%.

The precipitation bath preferably consists of water or a Water / formamide mixture or from a mixture of water and the solution and swelling used in the casting solution  medium, the temperature of the bath expediently in Range of 0-50 ° C, but preferably between 20-30 ° C is held.

If a casting solution according to the above Composition used by the precipitation bath method, result there are still membranes in which areas with Alternate sponge structure with finger structure areas (Ex. 1). An essential feature of the invention The procedure is that the casting solution film already drawn out a solution that the described above Has properties before immersion in the precipitation bath is treated with a stream of air of a certain temperature, which is then the membrane of the invention with a homogeneous continuous sponge structure results.

The treatment is carried out in such a way that, after being drawn out into a film, the casting solution is flowed over by an air stream at a temperature of 20 ° C. and above, preferably 20-100 ° C., and in particular 40-80 ° C., the air preferably in one Distance of 2-20 cm, in particular 5-15 cm, from the film flows out of one or more nozzles at a speed of preferably 10 to 60 m / s, the amount of air used preferably being in the range of 0.1-1.8 m ³ , in particular 0.2-0.8 m ³ , per m ^{2 of} membrane produced and the treatment time is preferably in the range of 1-20 s, in particular 2-10 s. The nozzles are selected according to their type and arrangement in such a way that the most uniform possible overflow of the film is ensured. Conventional dry compressed air is preferably used for the process, although a gas other than air, such as gaseous nitrogen, can also be used.

It has been shown that air treatment in the described way with casting solutions that are not after are composed of the teachings of this invention, not the desired result, namely a homogeneous Sponge structure, leads. (Ex. 2).

So is essential for the inventive method Combination of a system of coordinated Pouring solution and precipitation bath with the pretreatment explained immersion in the precipitation bath. Only this combination leads to the open-pore membranes according to the invention with a homogeneous sponge structure.

The pore size of the membrane is based on that used Air volume, the temperature of the air and the concentration of the Polymers set in the casting solution, the achievable pore size range after the resulting inventive method in membranes generally lies between 0.1 and 5 µ.

The process is preferably carried out continuously.

It is also advantageous to use the membrane according to the invention a reinforcement made of fabric or non-woven material to manufacture for subsequent processing steps and the use to improve the mechanical properties.

Examples

For Examples 1-6, a polysulfonamide solution prepared by condensation of 4,4′-diaminodiphenyl sulfone and terephthaloyl chloride was directly prepared using the method given in SU-A-20 52 798/05, Example 1, with 12% polymers and 3.6% CaCl _{2 used} in DMAc. For example 7, the polysulfonamide was precipitated from the above solution with water, dried in vacuo at 130 ° C. for 60 h and used for the preparation of the casting solution.

Example 1

A solution containing 6% polysulfonamide, 48.9% DMAc, 16.5% DMSO, 27% FA and 1.6% CaCl ₂ is drawn out on a glass plate to form a 150 μm thick film, 10 s in air kept at room temperature and coagulated in water at 20 ° C and rinsed thoroughly with RO water. The membrane had a sponge structure, but was interrupted by large finger-like vacuoles (see Fig. 1).

Example 2

A solution containing 6.2% polysulfonamide, 78.6% DMAc, 2.1% CaCl ₂ and 13.1% water is drawn out on a glass plate to form a 150 μm thick film, 10 s with 0.5 m ³ / m ² compressed air at 20 ° C from a distance of 10 cm at an angle of 45 ° and a nozzle outlet speed of 24 m / s treated and coagulated in water at 20 ° C and thoroughly rinsed with RO water. The resulting membrane had a pronounced finger structure ( Fig. 2).

Example 3

A solution containing 6% polysulfonamide, 48.9% DMAc, 16.5% DMSO, 27% FA and 1.6% CaCl ₂ is drawn out on a glass plate to form a 150 μm thick film, 10 s with 0, 5 m ³ / m ^{2 of} compressed air at 20 ° C from a distance of 10 cm at an angle of 45 ° and a nozzle exit speed of 24 m / s treated and coagulated in water of 20 ° C and thoroughly rinsed with RO water. The resulting membrane had a continuous sponge structure, a bubble point of 1.0 bar and a flow rate of 120 ml / cm ² min bar.

Example 4

A solution containing 6% polysulfonamide, 48.9% DMAc, 16.5% DMSO, 27% FA and 1.6% CaCl ₂ is drawn out on a rotating stainless steel drum to form a 150 µm thick film, 6.3 s with 0.74 m ³ / m ^{2 of} air at a temperature of 64 ° C from a distance of 10 cm at an angle of 45 ° and a nozzle outlet speed of 25.8 m / s treated and then coagulated with water at 21 ° C. The resulting membrane had a continuous, strongly asymmetrical sponge structure; the water flow was 34.3 ml / cm ² min bar and the bubble point measured with water was 1.5 bar ( Fig. 3).

Example 5

A solution containing 6% polysulfonamide, 48.9% DMAc, 16.5% DMSO, 27% FA and 1.6% CaCl ₂ is drawn out on a rotating stainless steel drum to form a 150 μm thick film, 3.6 s treated with 0.44 m ³ / m ^{2 of} air at a temperature of 64 ° C from a distance of 10 cm at an angle of 45 ° and a nozzle exit speed of 25.8 m / s and then coagulated with water at 21 ° C. The resulting membrane had a continuous, strongly asymmetrical sponge structure; the water flow was 32.0 ml / cm ² min bar and the bubble point measured with water was 3.2 bar ( Fig. 4).

Example 6

A solution containing 6% polysulfonamide, 48.9% DMAc, 16.5% DMSO, 27% FA and 1.6% CaCl ₂ is drawn out on a rotating stainless steel drum to form a 150 μm thick film, 2.3 s treated with 0.27 m ³ / m ^{2 of} air at a temperature of 64 ° C from a distance of 10 cm at an angle of 45 ° and a nozzle outlet speed of 25.8 m / s and then coagulated with water at 21 ° C. The resulting membrane had a continuous, slightly asymmetrical sponge structure; the water flow was 26.6 ml / cm ² min bar and the bubble point measured with water was 3.7 bar ( Fig. 5)

Example 7

A solution containing 6% polysulfonamide, 50.5% NMP, 16.5% DMSO and 27% FA is drawn out on a glass plate to form a 150 μm thick film, 10 s with 0.5 m ³ / m ^{2 of} compressed air 20 ° C and a nozzle outlet speed of 24 m / s treated and coagulated in water of 20 ° C and rinsed thoroughly with RO water. The resulting membrane had a continuous sponge structure; the water flow was 35.8 ml / cm ² min bar and the bubble point measured with water was 1.4 bar.

The results of Examples 8 to 29 are shown below in Shown in tabular form. The manufacture of the membranes followed after an essentially standardized work regulation, below for Examples 14 and 16 is reproduced:

Example 14

A solution of 5% poly-4,4-diphenylsulfone terephthalamide, 15% water, 1.8% LiCl is coagulated in a precipitation bath (60% dime thylacetamide in water) with a pretreatment time of 13 s. Coagulation is carried out with a poly propylene (PP) reinforcement. Performance data of the membrane obtained for water: 10 200 1 xm ^-2 × h ^-1 at p = 1 bar; Bubble point Pmax = 3.2.

Example 16

A solution of 5% poly-4,4-diphenylsulfone terephthalamide, 15% water, 1.8% LiCl is coagulated in a precipitation bath (60% dime thylacetamide in water) with a pretreatment time of 6 s. Coagulation is carried out with a polypropylene (PP) reinforcement. Performance data of the membrane obtained for water: 12,000 1 xm ^-2 × h ^-1 at p = 1 bar; Bubblepoint Pmax = 4.0.

Examples 8 to 29, table

Claims (16)

1. A process for producing an open-pore polysulfonamide microfiltration membrane, characterized in that
that a casting solution consisting of a solution of a polysulfonamide in a polar solvent, a precipitant for the polymer, optionally a pore former and a swelling agent is formed into a film,
subjecting this film to a treatment which consists in overflowing the film with air at a temperature of 20 ° C. and above before immersing it in the precipitation bath,
and then coagulates it with a liquid that is miscible with the polar organic solvent but is a precipitant for the polysulfonamide. 2. The method according to claim 1, characterized in that the polysulfonamide used is available through Condensation of terephthaloyl chloride or isophthal oyl chloride with 4,4'-diaminodiphenyl sulfone or 3,3'- Diaminodiphenyl sulfone. 3. The method according to claims 1 to 2, characterized records that the film is immersed in the Precipitation bath with air at a temperature of 20 ° C to Overflow 100 ° C. 4. The method according to claim 3, characterized in that the air is allowed to act on the film at a distance of 2 to 20 cm from the film at a speed of 10 to 60 m / s from one or more nozzles, the amount of air used is in the range of 0.1 to 1.8 m ³ / m ^{2 of} membrane produced and the treatment time is in the range of 1 to 20 s. 5. The method according to claims 1 to 4, characterized records that it is carried out continuously. 6. The method according to claims 1 to 5, characterized records that as a solvent dimethylacetamide or N-methylpyrrolidone can be used. 7. The method according to claims 1 to 6, characterized records that as a swelling agent in the casting solution Dime thylsulfoxide is used. 8. The method according to claims 1 to 7, characterized records that the concentration of the swelling agent in the Casting solution in the range of 0.1 to 20 wt .-%, in particular which is in the range of 10 to 20 wt .-%. 9. The method according to claims 1 to 8, characterized records that as a precipitant in the casting solution formamide is used. 10. The method according to claims 1 to 9, characterized records that the concentration of the precipitant in the loading ranging from 15 to 40 wt .-%, especially in the range of 20 to 30 wt .-% is kept. 11. The method according to claims 1 to 10, characterized records that the casting solution used has a pore contains artist. 12. The method according to claims 1 to 11, characterized records that the pore former in a concentration from 0.1 to 3.2% by weight is used.   13. The method according to claim 1, characterized in that a casting solution or a precipitation bath is used with the following compositions: Casting solution:
5 to 7 parts by weight of poly-4,4-diphenylsulfone terephthalamide,
15 to 20 parts by weight of water, polyfunctional organic alcohols with at least 2 OH groups or mixtures thereof
0.5 to 3.9 parts by weight of pore former,
78.4 to 71.2 parts by weight of solvent;
45 to 60 wt .-% dimethylacetamide (DMAc) in water, or
40 to 70% by weight of water, polyfunctional organic alcohols with at least 2 OH groups or mixtures thereof in dimethylacetamide,
the duration of treatment is 6 to 13 s. 14. Open-pore polysulfonamide microfiltration membrane, characterized in that
that it is produced with a method according to one of the preceding claims,
has a continuous sponge structure and
has a pore size in the range from 0.1 to 5 μm, the pore size continuously increasing from one side to the other, and
is wettable with water. 15. Membrane according to claim 13, characterized in that it is reinforced with fleece or fabric.   16. Use of a membrane according to one of claims 14 or 15 for microfiltration.