JPH0251658B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to ultrafiltration membranes. In particular, the present invention relates to a method for producing crack-free dry membranes with increased stability.

The manufacture and use of inorganic semipermeable membranes for ultrafiltration is well known in the art.
Most such inorganic membranes are advantageous in terms of resistance to temperature and solvent effects. In some cases, the membrane is molecularly permselective.
permselectivity) and ion exchange properties.
US Pat. No. 3,497,394 to Berger discloses an exchange membrane made by forcing a metal oxide gel into a porous support.

For practical applications of ultrafiltration membranes, high flux is an essential feature and it has been found that it is preferable to have a highly porous support and a thin micro membrane. Therefore, colloidal particles must not penetrate deeply into the filter body. However, in the dry inorganic semi-permeable membrane described in French _{patent no} . It is said that a thin film forms on the surface of the porous combined membrane-support formed from the suspension.

Ultrafiltration membranes should also have good mechanical and chemical stability for practical commercial applications. However, dewatering of ordinary granular membranes usually results in mud cracking, thereby causing the membrane to lose its semi-permeable properties. In preparing the surface of the support, the occurrence of cracks is of course acceptable. For example, Thomas U.S. Pat.
No. 3,926,799 describes a membrane support by coating a porous substrate with a zirconia slurry, drying the resulting composite and firing at high temperature to form a textured precoat. This method is not acceptable for the formation of the membrane itself, as it appears that large pores or cracks are formed. Ultrafiltration membranes that are susceptible to the formation of such cracks must be kept moist at all times. Such membranes include those taught by Trulson et al., U.S. Pat. Substantially uniform, continuous, adhesive, porous coatings of deposited and preformed aggregated inorganic metal oxide particles are described. The cohesive force of this type of membrane is due to relatively weak physical forces, and the cohesive force between the particles and the stability of the particulate membrane will be increased by dehydration of the metal oxide particles.
However, such dehydration has not been carried out in practice because the membrane must be kept constantly moist to prevent the formation of cracks that would destroy the semipermeability of the membrane.

Of course, increased mechanical and chemical stability are desirable properties for inorganic ultrafiltration membranes. Furthermore,
Increased flexibility may be achieved through the development of ultrafiltration membranes that do not need to be kept constantly wet. It is also clear that by eliminating that need, handling, transport and storage of the membrane will be facilitated.

It is therefore an object of the present invention to provide an improved ultrafiltration membrane.

Another object of the present invention is to provide a method for producing dry, crack-free inorganic ultrafiltration membranes.

Another object of the invention is to provide a crack-free, mechanically and chemically stable membrane.

Yet another object of the invention is to provide a stable, crack-free, dry ultrafiltration membrane with good permselectivity and flow properties.

In consideration of these and other objectives, it has been decided that the present invention has the following configuration.

That is, in the method for producing a dry inorganic ultrafiltration membrane, (a) a volatile liquid medium selected from the group consisting of alcohols and ketones, which is capable of drawing the membrane coating material into the membrane support; (b) applying an aqueous suspension of said coating material to said membrane support; and (c) volatilizing the so treated membrane of water and said liquid medium. a process for producing an essentially crack-free dry inorganic ultrafiltration membrane comprising exposing the microporous membrane support and the coating material to a temperature capable of removing said liquid medium from said microporous membrane support and said coating material, or dry inorganic ultrafiltration. A method for producing a membrane comprising: (a) carrying out an aqueous suspension of the coating material in a volatile liquid medium selected from the group consisting of alcohols and ketones, which is capable of drawing said coating material into the membrane support; (b) applying the resulting mixture to a microporous membrane support; (c) exposing the membrane so treated to a temperature capable of volatilizing water and said liquid medium; The above object is achieved by a method for producing an essentially crack-free dry mineral ultrafiltration membrane, which comprises removing the liquid medium from the porous membrane support and the membrane coating material.

The object of the invention is achieved by coating a microporous support with an inorganic membrane coating material in the presence of a volatile liquid capable of entrapping the coating material into the pores of the support. Desolvation of the suspension from the coating before complete removal of the volatile liquid results in shrinkage of the coating and subsequent filling of the voids resulting from such shrinkage with the coating material. . As a result, no cracks occur during desolvation of the coating material. The membrane thus produced is a dry, essentially crack-free, inorganic membrane with increased mechanical and chemical stability. A suspension of the coating material may be applied after applying the volatile liquid medium to the membrane support, or a coating material, preferably zirconia, mixed with a suitable volatile liquid may be applied to the membrane support. It's okay.

After removing volatile liquids from the treated membrane, such as by air drying, the stability of the membrane is increased by baking to a desolvation temperature.

The ultrafiltration membrane of the present invention consists of a crack-free dry mineral coating fixed to a microporous membrane. The membrane has desirable mechanical and chemical stability, good physical cohesion, resistance to acid, alkali, soap and detergent cleaning and the ability to withstand ultrasonic stress and abrasion. Unlike conventional membranes that develop cracks that tend to destroy their permeability when dry, the membranes of the present invention remain essentially crack-free when dry, yet their Physical stability is actually improved by drying and calcination.

The method of the invention uses a volatile liquid medium that is miscible with the membrane coating suspension to incorporate the coating material into the membrane support and to desolventize the coating material. As a result of such desolvation, shrinkage of the coating material occurs and the voids created as a result of the shrinkage are subsequently filled by said coating material. Such action is possible by desolventizing the coating material before the liquid medium is completely removed, thus eliminating the microscopic effects caused by desolvation of the coating film, which is unavoidable in conventional methods. A crack-free ultrafiltration membrane can be obtained.

As a specific example of the method for preparing the ultrafiltration membrane according to the present invention, first, a microporous membrane support is prepared without using a solvate as the coating material (non-solvate).
solvating), ie, a volatile liquid medium that is non-solvating, yet capable of entraining the coating material into the support and desolvating the coating material, is applied to the membrane support. A suspension of coating material is then applied to the membrane support. After allowing excess suspension to drip off the surface of the membrane, the membrane so treated is exposed to a temperature capable of volatilizing the liquid medium, removing the liquid from the microporous membrane support and coating material. remove. As mentioned above, the treated membrane is then, if desired, calcined to a dehydration or desolvation temperature to increase the stability of the membrane by sintering the coating material. Application of the volatile liquid medium can be carried out by wetting the entire microporous support with the volatile liquid medium until the support is saturated. This usually takes only a short time, for example less than a minute. The support is then brought into contact with the coating material suspension on one surface while still in the wet state. This is also usually about 1 minute. If the porous support has a convenient tubular shape, it is generally preferred to position the support tube vertically to wet the inner surface. Conveniently, the suspension is fed through an opening at the bottom of the tubular support by gravity, injection device or vacuum method, thereby avoiding entrainment of air. Fill the tube to the top with the coating material suspension and replenish the suspension as the liquid is drawn into the porous support. The coating operation takes about 1 minute. When it is desired to process a large number of tubes at once, it is desirable to provide sufficient separation between the tubes to allow free volatilization of the volatile liquid medium. After the support has been coated as described above, excess suspension is allowed to drip off of it within a few seconds. The treated tube is air-dried or exposed to a temperature capable of volatilizing the liquid medium, while it is convenient to hold the tube vertically. Air drying typically takes about 1 hour.

In another embodiment, the coating material is directly dispersed in a liquid medium that is non-solvating to the coating material and capable of entrapping it into the support and desolventizing the coating material. The resulting mixture is applied to the membrane support. Excess suspension is drained from the membrane as in the previous embodiment, and the membrane is dried and, if desired, calcined at a desolvation temperature to increase membrane stability.

Desolvation of the coating material with a volatile liquid medium not only removes another liquid used to form a suspension of the coating material, as in the support pretreatment embodiment described above, but also removes the coating material. It is also possible to remove the hydration water that was associated with the process.

Removal of such water by conventional membrane drying and/or calcination dehydration results in shrinkage and cracking as discussed above. In later embodiments, the particles of coating material in the mixture are incorporated into the porous surface as the solvent evaporates. However, the thickness of the film increases with contact time and therefore the timing must be observed to prevent the film from becoming too thick.

The membranes of the present invention are formed from a suspension of inorganic refractory materials. Usually such inorganic refractory materials are in the form of oxides, such as metal oxides. especially
-A, -A, -B, -A, - as described in Berger U.S. Pat. No. 3,497,394.
Oxides of metals of the B, -B, -B and group and lanthanides and actinides can be used in practicing the invention. Zirconia is a particularly preferred coating material as it is known to be chemically inert to strong and weak acids, alkalis and solvents even at high temperatures, making it advantageous for practical commercial applications.

The finely dispersed colloidal oxides used in the present invention are usually solvated or hydrated or surface bearing hydroxyl groups. When deposited to form a filtration membrane, the cohesive forces that hold the membrane together are due to weak Juan der Waalska or very close hydrogen bonding. When heat treated to desolvation or dehydration temperature or sintering temperature, strong metal-
Oxygen-metal bonds are formed, thereby increasing the cohesive forces between the membrane coated particles. Unlike conventional wet particle membranes that cause microcracks due to shrinkage due to dehydration,
The present invention essentially solves the problem of shrinkage. This is because most of the dehydration of the particulate surface occurs through the use of the miscible dehydrating liquid during deposition of the membrane material. The desolvated particles have thus already shrunk and the coated particles continue to fill the voids created by the removal of the solvent. This prevents the formation of cracks later during the drying of the membrane, resulting in a heat-treated membrane that is microporous and consists mainly of dehydroxides without any cracks as observed. result.

The coated particles used are in a size range that forms a good semi-permeable filter. Typically such particles are in the range of about 5 mμ to about 10 μm, with a range of about 10 mμ to about 1 μm generally preferred for ultrafiltration purposes. It is generally preferred to formulate the dispersion in an aqueous medium for convenience in handling and good stability, although it will be appreciated that other liquid mediums may be used. If the suspension is applied after the volatile liquid medium has been applied to the support, the suspension itself must be miscible with the volatile liquid medium. If the vehicle used in the coating material dispersion is a volatile, non-solvating liquid that is compatible with the dispersion so as not to cause agglomeration of the dispersion, another embodiment may be used to separate the suspension and unsolvated liquids. Direct contact can be made with the treated microporous support.
However, as mentioned above, such a suspension will continue to coat the support substrate as long as it is in contact with the substrate, so the contact time must be carefully controlled in this embodiment. If the contact between the suspension and the support is unduly long, undesirable thicknesses will form. The thickness of the film is also influenced by the concentration of coated particles in the suspension. Depending on the type of coating material used, concentrations of about 0.5 to 20% by weight, based on the total weight of the suspension, are generally satisfactory, and concentrations of about 6% by weight generally form optimum coating thicknesses. preferable.
The membrane coating is generally less than 1 micron to about 20 microns thick.

The microporous support or substrate, like the membrane itself, should be comprised of a chemically and thermally resistant material. Sintered metal inorganic oxides such as metal oxides, carbon and graphite are examples of suitable substrate materials. The substrate should have a high porosity with a pore size capable of supporting the colloidal particles used to form the membrane coating. Therefore, it is generally desirable for the substrate to have a pore size of about 5 microns to about 40 microns and a pore volume of about 5 to about 60%. In particular, the substrate should have a pore volume of about 20% to about 40% and a pore size of about 100 mμ to about 2μ.

The microporous membrane support of the present invention is not limited to a particular shape. For example, the support may be flat, spiral, hollow fiber, or any other convenient shape;
Porous carbon tubes, whose tubular shape is generally preferred, have excellent resistance to chemicals and high temperatures and have been found to be particularly advantageous. When firing such a tube, care should be taken not to cause its oxidation or reduction of any metal oxide particles. Approximately 0.19
It has been found that carbon tubes with a porosity of ml/g and a peak in the pore size distribution at about 0.3 microns constitute a particularly preferred membrane support material. When coating a support, the direction of flow of the coating material suspension is water flow,
The flow may be from inside to outside or from outside to inside depending on various design factors such as pressure, etc.

The volatile liquid medium used to pretreat the microporous support is one that is non-solvating with the coating material and capable of incorporating the coating material into the support and desolvating the coating material. It should be. Such volatile liquids should therefore be miscible with the coating suspension medium so as to incorporate the coating material into the support. Such a liquid is approx.
Preferably, volatilization occurs at a convenient temperature of 15°C to about 100°C. Most ketones and alcohols are suitable pretreatment liquids, with acetone and methanol being the preferred liquids, with acetone being particularly preferred and highly suitable for use with aqueous suspensions of coating materials. If the coating material suspending medium is a volatile, nonsolvating liquid for the particles, the coating operation can be carried out directly without membrane support pretreatment;
The suspending medium serves to incorporate the coating material into the support and to desolventize the coating material particles. Methanol is a suitable suspending medium for use in this aspect of the invention and can be readily used as a suspending medium for the preferred zirconia coating material without pretreatment of the support substrate.

Exposure of the treated membrane to a temperature that allows the liquid medium to volatilize and be removed from the membrane support and coating material is facilitated by air drying in an atmosphere, i.e., from about 150°C to about 100°C. can be achieved. If high temperatures are required for long periods of time in the case of oxidizable materials such as carbon and metals, heating can be carried out in an inert atmosphere. The temperature should be above the desolvation or dehydration temperature. When firing to increase the stability of the film, it is advantageous to use temperatures above the temperature at which the particles sinter. Generally firing is about 25℃
Dehydration or desolvation temperatures will range from about 1500<0>C, particularly from about 60<0>C to about 1200<0>C. Firing temperatures in the range of about 400°C to about 600°C are preferred, with firing times on the order of 30 minutes. The furnace may be preheated to the desired temperature, or the temperature may be gradually increased while the membrane and support remain in place. The temperature is usually gradually increased to the desired maximum temperature and held there for about 10 minutes to 2 hours.

The fired membranes, especially the zirconia membranes, prepared in accordance with the present invention retain their coatings even after being subjected to cyclic cleaning with acidic, basic, detergent and soap washes, as well as after being subjected to abrasion and ultrasonic testing. It has been found that On the other hand, the conventional wet membranes described above have been found to only partially retain in acidic, basic and detergent cycle cleaning. Conventional membrane coatings have been found to delaminate when subjected to cyclic soap washing and abrasion and ultrasonic testing. The membrane of the present invention exhibits good repellency when dry, whereas the conventional wet membrane had poor repellency when dry.
A stable hydrated zirconia coating is permanently attached to the membrane of the present invention due to its excellent stability, giving it ultrafiltration properties that can be used to extract low molecular weight macromolecules. . The invention is further illustrated by the following examples.

Example 1 Length 63.5cm, inner diameter 6mm, outer diameter 10mm, porosity
A 0.185 cm ³ /g microporous carbon tube was used as the membrane support. 75% of the pores were between 0.1 mμ and 1.0 mμ, and the peak of the distribution was at about 0.3 mμ. 0.025 of tube
cm ³ /g was about 2 to about 10 mμ pores. The air permeation rate through the tube was approximately 1500 cm ³ /min at 25° C. and 0.68 atmospheric pressure difference. The water flow rate was measured at 38° C. and 6.8 atm at approximately 200 ml/min. The tube was tilted with one end facing down, and sufficient acetone was introduced through the top opening to fill the tube, and acetone was replenished when the liquid level dropped due to absorption. When saturated in about 30 seconds, the acetone was dripped from the tube. The zirconia suspension was then rapidly injected through the bottom cork until the tube was full. The tube was held vertically for 1 minute to ensure that the suspension level was continuously maintained at the top spout, after which time the suspension was allowed to drip out of the tube. Next, while keeping the tube vertical,
Air dry for an hour. Then fired in a furnace i.e. 25℃
The temperature was increased to 650° C. in about 15 minutes and maintained at that temperature for an additional 15 minutes. The coating suspension was 6% by weight per unit volume of an aqueous suspension of zirconia (88%) stabilized with ittria (12%). The particle surface area is approximately 45cm ² /g, and the aggregate diameter is 0.1-1.0μ.
It was hot. The coated tube was found to have about 1.7 mg/cm ² of zirconia on the carbon tube. The ultrafiltration membrane thus obtained was washed with circulating water for 10 minutes, and then
20 min in 0.5% oxalic acid, then 10 min in 0.1 M NaOH
After rinsing for 1 minute and a final rinse with water for 10 minutes, inspection revealed that an essentially crack-free membrane coating remained intact. 25 of coated pipe
200 mm (1 inch) piece folded and half filled with water
ml beaker for 15 minutes at about 70 watts.
The coating remained intact as well in ultrasonic testing with an ultrasonic stress of 10 ⁴ cps. 4.2Kg/ ^cm2
After measuring a water flow rate (flux) of 8.48 m ³ /m ² /day {173 gfd (gallons/ft ² /day)} at (60 psi) and 40°C, Texaco C cutting oil was applied to the membrane as feed. Using an aqueous emulsion of 1% soluble oil, 4.2Kg/cm ² (60psi), 8.48m ³ /
Tested at a flow rate of 173 gtd (m ² /day) and a circulation rate of 2.5 gpm (11.5 gpm). The removal rate of emulsified oil by turbidimetry was 99.5%. Concentration was carried out until an oil concentration of 5% was reached. The flow rate at this point was 60 psi, 40°C, 11.3/min (2.5 gpm) circulation.
It was 8.18m ³ /m ² /day (167gfd). The removal rate of emulsified oil by turbidimetry was 99.7%. Another zirconia membrane of the same type and prepared by the same method was stained.
Tested using Ficoll 400M, a hydrolyzed starch with a molecular weight of 400,000. Removal rates better than 99% were observed.

Example 2 A membrane was prepared according to the procedure of Example 1, except that the acetone pretreatment was omitted. A suspension was prepared by diluting 1 volume of a 30% aqueous zirconia suspension to a total volume of 5 volumes with methanol. Using the measurement method and conditions described in Example 1, the following results were obtained with the crack-free membrane of the invention: water flow rate - 8.82 ^m3 / ^m2 /day (180 gfd), 1% oil. flow rate at the initial feed concentration of −8.67 m ³ /m ² /day (177 gfd),
Removal rate: 99.8%, flow rate after concentrating to 5% oil -
6.71m ³ /m ² /day (137gfd), removal rate 99.8%.

Example 3 Except that an alumina tube was used as the membrane support,
A calcined zirconia membrane was prepared as described in Example 1. The tube exhibited an initial water wet bubble point pressure of 1.55 Kg/cm ² (22 psi) in air. Performance under the same conditions and procedures as described in Example 1 using the 1% cutting oil was as follows. Distribution velocity - ^16.7m3 / ^m2 /day (340gfd), removal rate 98.4
%.

Example 4 Maximum firing furnace temperature was 1100°C for 1 hour in nitrogen atmosphere
A zirconia film was prepared on a carbon tube in the same manner as in Example 1, except that: Performance under the conditions and procedures of Example 1 was as follows. Water flow rate 15.0 m ³ /m ² /day (306 gfd), flow rate for 1% oil 13.3 m ³ /m ² /day (272 gfd), removal rate 99.4%.

Example 5 The procedure of Example 1 was again used. However, the coating suspension was made using 5% tantalum oxide. The particles are
It had an initial surface area of 5.14 m ² /g and was ground in ceramic balls at PH4 for 72 hours. The performance under the conditions and procedures of Example 1 was as follows. Water flow rate -
12.6 m ³ /m ² /day (258 gfd), flow rate for 1% oil - 9.8 m ³ /m ² /day (200 gfd), removal rate 96%.

Depending on other uses of the ultrafiltration membrane of the present invention,
Various embodiments are provided. For example, Example 1
A zirconia component can be prepared using methyl ethyl ketone as the pretreatment volatile liquid according to the procedure described in 2006, or a zirconia component can also be prepared using the same procedure, but with silica instead of zirconia and a silica film coating. You can also do that. In other applications, zirconia membranes can be fabricated on a variety of porous support materials, such as porous sintered metal tubes, fiberglass tubes, paper tubes, and the like.

The ultrafiltration membrane of the present invention represents a significant advance in the art in its various aspects. Besides exhibiting good flow rates and removal rates, the membrane can withstand chemicals, detergents, and extreme PH values and temperatures, and has better stability than previously available granular membranes. By providing these advantages in a dry, crack-free membrane, the present invention overcomes various limitations and limitations hitherto encountered and improves the accessibility to handling, storage, and application of inorganic ultrafiltration membranes. This will increase significantly.

Claims (1)

[Scope of Claims] 1. A method for producing a dry inorganic ultrafiltration membrane, comprising: (a) a volatile liquid medium selected from the group consisting of alcohols and ketones, which draws a membrane coating material into a membrane support; (b) applying an aqueous suspension of said coating material to said membrane support; and (c) subjecting the so treated membrane to water and said membrane support. A method for producing an essentially crack-free dry inorganic ultrafiltration membrane comprising exposing the liquid medium to a temperature capable of volatilizing the liquid medium and removing the liquid medium from the microporous membrane support and the coating material. 2. A method according to claim 1, in which a suspension of coating material is applied to one side of the membrane support. 3. The method according to claim 1, which comprises heat treating the film at a temperature of 25°C to 1500°C. 4. The method according to claim 3, wherein the temperature is 60°C to 1200°C. 5. The method according to claim 4, wherein the temperature is 400°C to 600°C. 6. The method of claim 1, wherein the coating material comprises zirconia. 7 The membrane support has a pore size of 50 nm to 40 μm and 5%
Claim 1 having a pore volume of ~60%
The method described in section. 8. The method according to claim 7, wherein the membrane support comprises a porous carbon tube. 9. The method of claim 7, wherein the membrane support comprises a chemically and thermally durable material. 10. The method according to claim 3 or 7, wherein the coating material is made of zirconia and the membrane support is made of a porous carbon tube. 11. The method according to claim 4, wherein the coating material comprises zirconia and the membrane support comprises a porous carbon tube. 12. After draining off the excess suspension from the surface of the membrane support, the volatile liquid medium applied in step (a) is removed by air drying the treated membrane at a temperature between 15°C and 100°C. A method according to any one of claims 1 to 5, 7 and 9, characterized in that: 13. The method of claim 12, wherein the coating material comprises zirconia. 14. The method according to claim 13, wherein the zirconia has a particle size of 5 nm to 10 μm. 15. The method according to claim 14, wherein the particle size is 10 nm to 1 μm. 16. A method according to any one of claims 1 to 15, wherein the volatile liquid medium comprises an alcohol or a ketone that volatilizes at a temperature of 15°C to 100°C. 17. The method of claim 16, wherein the volatile liquid medium comprises acetone. 18. The method of claim 16, wherein the volatile liquid medium comprises methanol. 19. The method of claim 12, wherein the support comprises a porous carbon tube and the coating material is coated on the inner surface of the tube. 20 A method for producing a dry inorganic ultrafiltration membrane, comprising: (a) dispersing an aqueous suspension of a coating material in a volatile liquid medium selected from the group consisting of alcohols and ketones; (b) applying the resulting mixture to a microporous membrane support; and (c) making the membrane thus treated capable of volatilizing water and said liquid medium. A method of making an essentially crack-free dry inorganic ultrafiltration membrane comprising exposing to temperature to remove the liquid medium from the microporous membrane support and the membrane coating material. 21. The method of claim 20, wherein the mixture is applied to one side of the membrane support. 22. The method of claim 20, comprising heat treating the film at a temperature of 25°C to 1500°C. 23. The method according to claim 22, wherein the temperature is 60°C to 1200°C. 24. The method according to claim 23, wherein the temperature is 400°C to 600°C. 25. The method of claim 20, wherein the coating material comprises zirconia. 26 The membrane support has a pore size of 50 nm to 40 μm and a
% to 60% pore volume. 27. The method according to claim 26, wherein the membrane support comprises a porous carbon tube. 28. The method of claim 26, wherein the membrane support comprises a chemically and thermally resistant material. 29. The method according to claim 22 or 26, wherein the coating material comprises zirconia and the membrane support comprises a porous carbon tube. 30. The method according to claim 23, wherein the coating material comprises zirconia and the membrane support comprises a porous carbon tube. 31. The method of claim 25, wherein the zirconia has a particle size of 5 nm to 10 μm. 32. The method according to claim 31, wherein the particle size is 10 nm to 1 μm. 33. A method according to any one of claims 20 to 32, wherein the volatile liquid medium comprises an alcohol or ketone that volatilizes at a temperature of 15°C to 100°C. 34. The method of claim 33, wherein the volatile liquid medium comprises acetone. 35. The method of claim 33, wherein the volatile liquid medium comprises methanol. 36. A method according to any one of claims 20 to 35, wherein the support comprises a porous carbon tube and the coating material is coated on the inner surface of the tube.