RU2440182C1 - Method of producing flat porous membrane from polyethersulfone - Google Patents

Abstract

FIELD: process engineering. ^ SUBSTANCE: invention relates to production of flat porous hydrophilic membrane from polyethersulfone with pore size varying from 0.1 to 1 mcm intended for fabrication of disk flat and cartridge corrugated filtration elements thereof. Proposed method exploits phase decomposition wherein precipitator treatment by vapors is executed in maintaining constant concentrations of saturated vapors of precipitator and solvent in climatic chamber. Precipitator vapors are produced from mix of water with aliphatic monohydroxy alcohol with carbon atom number varying from 1 to 3. ^ EFFECT: preventing formation of surface layers with lower porosity, and solvent evaporation in processing by precipitator vapors. ^ 10 cl, 8 dwg, 8 tbl, 8 ex

Description

Technical field

The invention relates to a technology for the production of a flat porous hydrophilic polyethersulfone membrane with a pore size of 0.1 to 1 μm by phase disintegration for the production of flat and cartridge-shaped pleated filter elements from it. Filter elements can be used for microfiltration of liquids in the pharmaceutical, microbiological, biochemical, food and other industries.

State of the art

In the global production of membranes, particular attention is paid to polysulfones (polyethersulfones, polyarylsulfones, polyphenylene sulfones). This is due to the sufficiently high chemical and mechanical strength of these polymers, their high glass transition temperature (200-220 ° C), and the ability to impart hydrophilic properties to membranes from these polymers. The main advantages of polyethersulfone membranes are as follows: mechanical strength; chemical and biological inertness; thermal stability, which allows you to repeatedly sterilize the filter elements in the places of their installation by a stream of sharp steam at temperatures up to 140 ° C.

It is known that most polymer membranes are made by the technology of phase decomposition of a polymer solution, which is implemented in practice by four methods: 1) phase decomposition induced by a non-solvent precipitator (non-solvent induced phase separation - NIPS); 2) phase decay induced by precipitating vapors (vapor induced phase separation - VIPS); 3) phase decomposition induced by evaporation of the solvent (evaporation induced phase separation - EIPS); 4) thermally induced phase separation TIPS [M. Ulbricht. Advanced functional polymer membranes. // Polymer 2006. V.47. Number 7. P.2217]. Most methods of manufacturing polysulfone and polyethersulfone membranes with pore sizes from 0.1 to 1 μm are based on the VIPS method and include the following stages: preparation of a homogeneous polymer solution by pouring it onto a substrate (metal, glass, etc.), exposure to steam precipitant (water), immersion in a precipitant solution, washing the membrane and then drying.

A known method of manufacturing a membrane from polysulfone, polyethersulfone, polyarylsulfone (US patent 6045899), in which before immersion in water, the treatment is carried out in a climatic chamber from 3 to 20 with steam with a relative humidity of 50 to 90% at 25 ° C. The membranes on the steam side have a skin layer with a pore size of 0.1 to 10 μm and a pore number of at least 15 per 1000 μm ² . A comparison of the structure of the skin layer in Fig. 1A, 2A of the patent and the structure of the surface layer of the claimed membrane shown in Fig.6 of the claimed invention shows how much higher surface porosity of the claimed membrane.

Closest to the claimed technical solution is a method of obtaining a microfiltration membrane with improved filtration properties (patent WO 2006.131290 A1), in accordance with which the polysulfone and polyethersulfone membrane is produced by the method of phase decomposition induced by vapor precipitator (VIPS). After treatment in a climate chamber with air having a humidity in the range of 40 to 65%, a skin layer with a low surface porosity also forms. A comparison of Fig. 4, 8 and 12 of the patent and FIG. 6 of the claimed invention also demonstrates a higher surface porosity of the claimed membrane.

A common disadvantage of the known methods is that as a result of evaporation of the solvent in the climate chamber, a skin layer with a low porosity forms on the membrane surface. Membranes with low surface porosity may have lower productivity due to local hydraulic resistance of the skin layer. Such membranes can have a shorter working life, since due to the wide distribution of contaminant particles in real filtered fluids, fasting of the mouths of a few even large pores of the skin layer can occur. In addition, during the manufacture of membranes by known methods, harmful solvent vapors may enter the atmosphere.

Disclosure of invention

The technical problem to which the present invention is directed is to obtain membranes with maximum surface porosity and high strength, technological and operational characteristics. The technical result of the claimed invention is to increase the porosity and strength of the membranes, as well as reducing the emission of solvent vapor into the atmosphere.

To solve the problem, as well as to achieve the claimed technical result, a method for producing a flat porous membrane of polyethersulfone is proposed, which involves forming a polyethersulfone polymer solution in an aprotic polar solvent containing polyethylene glycol by applying it to a moving surface through the gap between the die of the die and the moving surface, processing the solution layer vapor precipitator, exposure in a precipitation bath, heat treatment, washing and drying the membrane. A distinctive feature of the proposed method is that the solution layer is treated with precipitating vapors at constant concentrations of saturated solvent and precipitating vapors, while the precipitating vapors are obtained from a mixture of water with an aliphatic monohydric alcohol with the number of carbon atoms from 1 to 3.

In addition, it is proposed to treat the solution layer with precipitating vapors at a temperature of from 20 to 30 ° C until the complete transverse shrinkage of the membrane.

In addition, it is proposed to use a polymer solution containing polyethersulfone with a weight average molecular weight of at least 46,000 in an amount of 10 to 20 wt.%.

In addition, it is proposed to use a polymer solution containing polyvinylpyrrolidone with a weight average molecular weight of at least 50,000 in an amount of up to 10 wt% as a hydrophilizing agent.

In addition, it is proposed to use a polymer solution containing an aprotic polar solvent in an amount of from 10 to 50 wt.%, While it is most optimal to use a polymer solution containing dimethylformamide in an amount of from 10 to 30 wt.%.

In addition, it is proposed to use a polymer solution containing polyethylene glycol with a number of carbon atoms from 8 to 20 as a blowing agent, in particular, a polymer solution containing polyethylene glycol-200 with a number of carbon atoms from 8 to 10 in an amount of at least 50 wt.% Or a polymer solution can be used containing polyethylene glycol-300 with a number of carbon atoms from 12 to 14 in an amount of at least 60 wt.% or a polymer solution containing polyethylene glycol-400 with a number of carbon atoms from 16 to 20 in an amount of at least 70 wt.%.

Processing the solution layer with precipitating vapors in a climate chamber at constant concentrations of saturated solvent and precipitating vapors, with the formation of precipitating vapors from a mixture of water with an aliphatic monohydric alcohol with the number of carbon atoms from 1 to 3, eliminates the evaporation of the solvent and thereby prevents the formation of surface layers with reduced porosity and durability.

The authors experimentally established that the presence in saturated vapors of the main precipitant - water of a certain amount of saturated vapors of a weaker precipitant - an aliphatic monohydric alcohol with the number of carbon atoms from 1 to 3 improves the quality of the membrane surface being treated (see Figs. 1-6).

Figure 1 shows an electron microscopic image of a chip near the upper surface, and figure 2 is a photograph of the upper surface of the membrane obtained in accordance with example 1, in which the upper surface of the membrane is treated with saturated vapors of isopropyl alcohol. When alcohol vapor is absorbed, having a surface tension coefficient much lower than the surface tension coefficient of the polymer solution, a defective layer forms on the upper surface of the membrane due to the Marangoni effect, distorting the porous structure of the membrane [Nachinkin O.I. Polymer microfilters. M .: Chemistry, 1985, p. 59]. In Fig. 1, it can be seen that the defective layer has a thickness of up to 10 μm and represents a vortex structure, as predicted by the Marangoni effect. Figure 2 clearly shows that the defective layer is cut with cracks, through which the porous structure characteristic of the membrane is visible. It is obvious that during filtration, the flow passing through the cracks of the defective layer can experience significant local hydraulic resistance.

Figure 3 shows an electron microscopic image of a chip near the upper surface, and figure 4 is a photograph of the upper surface of the membrane obtained in accordance with example 2, in which the upper surface of the membrane is treated with saturated water vapor. The surface to be treated has a less perturbed structure compared to the surface in FIG. 1, but the surface porosity is substantially less than the porosity in the membrane volume.

Figure 5 shows an electron microscopic image of the chip near the upper surface, and Fig.6 is a photograph of the upper surface of the membrane obtained in accordance with example 3, in which the upper surface of the membrane is treated with a mixture of saturated water vapor and isopropyl alcohol. It is seen that the surface porosity of the membrane corresponds to bulk porosity, and the surface structure has neither defective layers nor other distortions.

The technical result that can be obtained by carrying out the claimed invention is to increase the porosity and quality of the surface layer and, on this basis, increase the productivity and service life of the membrane obtained in accordance with the claimed method. In addition, the inventive method allows to minimize the emission of solvent vapor into the atmosphere.

Brief Description of the Drawings

Figure 1 - electron microscopic image of a chip near the upper layer of the membrane obtained by treatment with saturated vapors of isopropyl alcohol in accordance with example 1.

Figure 2 is an electron microscopic image of the upper layer of the membrane obtained by treatment with saturated vapors of isopropyl alcohol in accordance with example 1.

Figure 3 - electron microscopic image of a chip near the upper layer of the membrane obtained by treatment with saturated water vapor in accordance with example 2.

Figure 4 is an electron microscopic image of the upper layer of the membrane obtained by treatment with saturated water vapor in accordance with example 2.

Figure 5 is an electron microscopic photograph of a cleavage near the upper layer of the membrane obtained by treatment with saturated vapors of a mixture of water and isopropyl alcohol in accordance with example 3.

6 is an electron microscopic image of the upper layer of the membrane obtained by treatment with saturated vapors of a mixture of water and isopropyl alcohol in accordance with example 3.

7 is a schematic flow diagram of a pilot plant of continuous operation for the manufacture of membranes of the claimed method.

Fig - experimental curve "Multidiffusion" for example 3, which shows the algorithm for determining the pressure of the point of the bubble P _TP .

The implementation of the invention

The inventive method for producing a flat porous membrane of polyethersulfone implemented on a pilot scale. The following examples of the manufacture of the membrane were carried out on a pilot installation of continuous operation, the basic technological scheme of which is shown in Fig.7.

The starting components for the molding solution are prepared: powders of polyethersulfone and polyvinylpyrrolidone (if used) are combined and the mixture is dried at a temperature of 110-120 ° C for 2 hours or more until a constant weight is established. The aprotic polar solvent of qualification “hch” (dimethylformamide or n-methylpyrrolidone or dimethylacetamide) is mixed with a pore former polyethylene glycol with the number of carbon atoms from 8 to 20 (PEG-200 or PEG-300 or PEG-400 grades). The resulting mixture is filtered through a PTFE membrane with a filtration rating of 1 μm of a mixture of solvent and pore former - polyethylene glycol.

All components are combined in a working mixer and dissolved in a mixer (1) at a temperature of 30-40 ° C for 12 hours or more until the solution is completely homogenized. The resulting molding solution is degassed in a stopped stirrer during discharge - 0.5 atm for 1 hour or more until the bubbles are completely removed

The molding solution is fed through a filter (2), in which a stainless steel mesh with a filtration rating of 5 μm is installed, into the die (3). From the die, the molding solution is applied in the form of a liquid film with a thickness of 100 ± 50 μm onto the moving surface of the conveyor through the gap between the die of the die and the moving surface. The moving surface of the conveyor is a polymer or steel endless belt (4).

The liquid film passes through a climatic chamber (5), in which a temperature of 20 to 30 ° C is maintained. Air saturated with vapors of an aprotic polar solvent and precipitant — a mixture of water and an aliphatic monohydric alcohol with the number of carbon atoms from 1 to 3 — is fed into the climate chamber. Saturated vapors are created in the air supplied to the climate chamber by pre-sparging air through a solution containing solvent, water and alcohol. The residence time in the climate chamber is selected such that at the exit from the climate chamber complete transverse shrinkage of the formed membrane is completed.

After the climate chamber, the membrane is immersed in a precipitation bath with water (6), which has the same temperature as the vapors in the climate chamber. The membrane is removed from the conveyor in water and kept in water for at least 5 minutes. Next, the membrane is passed through a washing bath (7) with water heated to a temperature of 90 ° C; the residence time in this bath is also at least 5 minutes. Then the membrane is dried in the chamber (8) with hot air at a temperature of 140 ° C and wound into a roll.

To implement the invention on an industrial scale, as the starting components of the polymer (molding) solution take:

Polyethersulfone:

- Solvay brand Radel H-3000 with a weight average molecular weight of 77600;

- Solvay brand Radel H-1000 with a weight average molecular weight of 57300;

- BASF brand Ultrason E 6020 P with a weight average molecular weight of more than 46,000.

Polyvinylpyrrolidone:

- Acros Organics K30 brand with a weight average molecular weight of 50,000;

- Acros Organics K90 brand with a weight average molecular weight of 1200000. Desalinated water according to GOST 6709-72 is used for installation and membrane testing.

For testing membranes that are poorly wetted in water, absolute isopropyl alcohol is taken in accordance with GOST 9805-84.

The porous structure of the membranes is examined using a scanning scanning electron microscope. Membranes are chipped in liquid nitrogen and a ~ 10 nm thick gold layer is sprayed onto them using a JFS-1100 ion sputtering device. Electron microscopy is carried out on a Quanta Inspect S microscope at a voltage of 30 kV.

Membrane water productivity is determined by measuring the time that a certain volume of liquid flows through a membrane sample of 250 × 250 mm (effective area 625 cm) at a pressure drop of 1 atm and a temperature of 293 K and is expressed in units of [m ³ / (m ² · h · atm )].

The pressure of the bubble point is determined on a 250 × 250 mm membrane sample (effective area 625 cm ² ) using a SartoCheck-3 device (Sartorius AG, Germany) in the Multidiffusion mode (flow measurement range 0.1-150 ml / min at drops pressure up to 6 atm). On Fig shows the experimental curve "Multidiffusion" for example 3, which shows the algorithm for determining the pressure of the point of the bubble P _TP . This pressure corresponds to the punching of the maximum pores by air, which is expressed in the deviation of the air flow from the initial straight line, which characterizes the true diffusion flow through the membrane, all pores of which are filled with water.

The value of the pressure of the point of the bubble P _TP corresponds to the maximum pore diameter D _MAX calculated by the Laplace formula:

where D _MAX - pore diameter, m;

σ is the surface tension of the wetting water, N / m;

θ is the wetting angle;

R _TP - pressure, Pa.

The water wetting angle of polyethersulfone membranes containing more than 5% polyvinylpyrrolidone, θ = 71 ± 1 ° [N. Wang, T. Yu, C. Zhao, and Q. Du. Improvement of Hydrophilicity and Blood Compatibility on Polyethersulfone Membrane by Adding Polyvinylpyrrolidone. Fibers and Polymers 2009, 10, No. 1. P.1]. The result is a Laplace formula for a polyethersulfone membrane moistened with water.

Example 1

A molding solution of the composition shown in table 1 is prepared, a layer with a thickness of 100 μm is applied to the conveyor belt and processed in a climatic chamber according to the mode shown in table 1.

Table 1 The composition of the solution and the processing conditions in the climate chamber The composition of the solution (C is the concentration in percent, relative to the total weight of the solution) Processing conditions in the climate chamber Component Substance, brand FROM, % The composition of the vapor phase Time temperature Membrane polymer Polyethersulfone Ultrason E 6020P 14.3 A mixture of saturated vapors of isopropyl alcohol and a solvent 20 min, 20 ° C Hydrophilizing component Polyvinylpyrrolidone K90 0.7 Solvent N-methylpyrrolidone 21.25 Blowing agent PEG-200 63.75

The resulting membrane is hydrophilic (spontaneously wetted in water), has a bubble point pressure of 2.7 atm and a water capacity of 9 m ³ / (m ² · h · atm).

Example 2

A molding solution of the composition shown in table 2 is prepared, a layer with a thickness of 100 μm is applied to the conveyor belt and processed in a climatic chamber according to the mode shown in table 2.

table 2 The composition of the solution and the processing conditions in the climate chamber The composition of the solution (C is the concentration in percent, relative to the total weight of the solution) Processing conditions in the climate chamber Component Substance, brand FROM, % The composition of the vapor phase Time temperature Membrane polymer Polyethersulfone Ultrason E 6020P 14.3 A mixture of saturated water vapor and solvent 15 min, 20 ° C Hydrophilizing component Polyvinylpyrrolidone K90 0.7 Solvent N-methylpyrrolidone 21.25 Blowing agent PEG-200 63.75

The resulting membrane is hydrophilic (spontaneously wetted in water), has a bubble point pressure of 3.7 atm and a water capacity of 14 m ³ / (m ² · h · atm).

Example 3

A molding solution of the composition shown in table 3 is prepared, a layer with a thickness of 100 μm is applied to the conveyor belt and processed in a climatic chamber according to the mode shown in table 3.

Table 3 The composition of the solution and the processing conditions in the climate chamber The composition of the solution (C is the concentration in percent, relative to the total weight of the solution) Processing conditions in the climate chamber Component Substance, brand FROM,% The composition of the vapor phase Time temperature Membrane polymer Polyethersulfone Ultrason E 6020P 14.3 A mixture of saturated water vapor, isopropyl alcohol and a solvent 15 min, 20 ° C Hydrophilizing component Polyvinylpyrrolidone K90 0.7 Solvent N-methylpyrrolidone 21.25 Blowing agent PEG-200 63.75

The resulting membrane is hydrophilic (spontaneously wetted in water), has a bubble point pressure of 4.2 atm and a water capacity of 11 m ³ / (m ² · h · atm).

The pressure of the bubble point P _TP = 4.5 atm corresponds to the maximum pore size according to formula (2), equal to D _MAX = 0.21 μm

Example 4

A molding solution of the composition shown in table 4 is prepared, a layer with a thickness of 100 μm is applied to the conveyor belt and processed in a climatic chamber according to the mode shown in table 4.

Table 4 The composition of the solution and the processing conditions in the climate chamber The composition of the solution (C is the concentration in percent, relative to the total weight of the solution) Processing conditions in the climate chamber Component Substance, brand FROM, % The composition of the vapor phase Time temperature Membrane polymer Polyethersulfone Ultrason E 6020P fourteen A mixture of saturated water vapor, ethyl alcohol and a solvent 25 min, 20 ° C Hydrophilizing component - - Solvent Dimethylformamide 12.9 Blowing agent PEG-400 73.1

The resulting membrane is partially wetted in water, so the pressure of the bubble point is determined by isopropyl alcohol, and it is 1.1 atm. Water productivity is equal to 18 m ³ / (m ^{2 ·} · h · atm).

Example 5

A molding solution of the composition shown in table 5 is prepared, a layer with a thickness of 150 μm is applied to the conveyor belt and processed in a climatic chamber according to the mode shown in table 5.

Table 5 The composition of the solution and the processing conditions in the climate chamber The composition of the solution (C is the concentration in percent, relative to the total weight of the solution) Processing conditions in the climate chamber Component Substance, brand FROM, % The composition of the vapor phase Time temperature Membrane polymer Polyethersulfone Ultrason E 6020P 11.4 Mixture of water vapor, propyl alcohol and solvent 15 min, 30 ° C Hydrophilizing component Polyvinylpyrrolidone K90 0.6 Solvent Dimethylformamide 17.6 Blowing agent PEG-300 70.4

The resulting membrane is hydrophilic (spontaneously wetted in water), has a bubble point pressure of 1.0 atm and a water capacity of 100 m ³ / (m ² · h · atm).

The pressure of the bubble point P _TP = 1.0 atm corresponds to the maximum pore size according to formula (2), equal to D _MAX = 0.94 μm

Example 6

A molding solution of the composition shown in table 6 is prepared, a layer with a thickness of 50 μm is applied to the conveyor belt and processed in a climatic chamber according to the mode shown in table 6.

Table 6 The composition of the solution and the processing conditions in the climate chamber The composition of the solution (C is the concentration in percent, relative to the total weight of the solution) Processing conditions in the climate chamber Component Substance, brand FROM, % The composition of the vapor phase Time temperature Membrane polymer Polyethersulfone Radel N-3000 19.5 A mixture of saturated water vapor, isopropyl alcohol and a solvent 10 min, 30 ° C Hydrophilizing component Polyvinylpyrrolidone K90 0.5 Solvent Dimethylformamide 32 Blowing agent PEG-200 48

The resulting membrane is hydrophilic (spontaneously wetted in water). The pressure of the bubble point on the water is more than 6 atm; therefore, it is measured by isopropyl alcohol and amounts to 2.8 atm. Water productivity is 3 m ³ / (m ² · h · atm).

Example 7

A molding solution of the composition shown in table 7 is prepared, a layer with a thickness of 100 μm is applied to the conveyor belt and processed in a climatic chamber according to the mode shown in table 7.

Table 7 The composition of the solution and the processing conditions in the climate chamber The composition of the solution (C is the concentration in percent, relative to the total weight of the solution) Processing conditions in the climate chamber Component Substance, brand FROM, % The composition of the vapor phase Time temperature Membrane polymer Polyethersulfone Radel N-3000 12.4 A mixture of saturated water vapor, isopropyl alcohol and a solvent 30 min, 20 ° C Hydrophilizing component Polyvinylpyrrolidone K30 0.6 Solvent Dimethylformamide 13.05 Blowing agent PEG-400 73.95

The resulting membrane is hydrophilic (spontaneously wetted in water), has a bubble point pressure of 2.5 atm and a water capacity of 30 m ³ / m ² · h · atm.

Example 8

A molding solution of the composition shown in table 8 is prepared, a layer with a thickness of 100 μm is applied to the conveyor belt and processed in a climatic chamber according to the mode shown in table 8.

Table 8 The composition of the solution and the processing conditions in the climate chamber The composition of the solution (C is the concentration in percent, relative to the total weight of the solution) Processing conditions in the climate chamber Component Substance, brand FROM, % The composition of the vapor phase Time temperature Membrane polymer Polyethersulfone Radel H-1000 11.6 Mixture of water vapor, propyl alcohol and solvent 15 min, 30 ° C Hydrophilizing component Polyvinylpyrrolidone K30 0.4 Solvent Dimethylformamide 13.2 Blowing agent PEG-400 74.8

The resulting membrane is hydrophilic (spontaneously wetted in water), has a bubble point pressure of 1.8 atm and a water capacity of 55 m ³ / (m ² · h · atm).

Claims (10)

1. A method of producing a flat porous membrane of polyethersulfone, comprising forming by applying a polymer solution of polyethersulfone in an aprotic polar solvent containing polyethylene glycol onto a moving surface through the gap between the die of the die and the moving surface, processing the solution layer with precipitating vapor, holding in a precipitation bath, heat treatment, washing and drying the membrane, characterized in that the treatment of the solution layer with vapor of the precipitant is carried out at constant concentrations of saturated vapor solution a precipitating agent and a precipitant, while the precipitating vapors are obtained from a mixture of water with an aliphatic monohydric alcohol with the number of carbon atoms from 1 to 3. 2. The method according to claim 1, characterized in that the treatment of the solution layer with vapor of the precipitant is carried out at a temperature of from 20 to 30 ° C until the complete transverse shrinkage of the membrane. 3. The method according to claim 1, characterized in that they use a polymer solution containing polyethersulfone with a weight average molecular weight of at least 46,000 in an amount of from 10 to 20 wt.%. 4. The method according to claim 1, characterized in that a polymer solution containing polyvinylpyrrolidone with a weight average molecular weight of at least 50,000 in an amount of up to 10 wt.% Is used as a hydrophilizing agent. 5. The method according to claim 1, characterized in that they use a polymer solution containing an aprotic polar solvent in an amount of from 10 to 50 wt.%. 6. The method according to claim 5, characterized in that they use a polymer solution containing dimethylformamide in an amount of from 10 to 30 wt.%. 7. The method according to claim 1, characterized in that a polymer solution containing polyethylene glycol with a number of carbon atoms from 8 to 20 is used as a blowing agent. 8. The method according to claim 7, characterized in that they use a polymer solution containing polyethylene glycol-200 with the number of carbon atoms from 8 to 10 in an amount of at least 50 wt.%. 9. The method according to claim 7, characterized in that they use a polymer solution containing polyethylene glycol-300 with the number of carbon atoms from 12 to 14 in an amount of at least 60 wt.%. 10. The method according to claim 7, characterized in that they use a polymer solution containing polyethylene glycol-400 with the number of carbon atoms from 16 to 20 in an amount of at least 70 wt.%.

Images