A method for optimizing and adjusting the pore size of finished ceramic membranes

Abstract

The present invention discloses a method for optimizing and adjusting the pore size of a finished ceramic membrane, comprising: a) soaking a clean finished ceramic membrane after cleaning with deionized water until the membrane is saturated with water adsorption; b) drying the wet ceramic membrane saturated with water adsorption, and controlling the relative humidity of the ceramic membrane to be 5% to 90%; c) coating the ceramic membrane with a relative humidity of 5% to 90% with a polycarbosilane organic solution with a mass fraction of 1% to 10%; d) pyrolyzing the ceramic membrane coated with polycarbosilane. Experiments have shown that the present invention can not only make it easy to optimize the pore size of a certain existing finished ceramic membrane according to application needs, but also has a simple adjustment operation and is easy to achieve scale, which is of great value in improving and improving the filtration accuracy and interception capacity of the existing finished membrane, and is helpful for ceramic membrane manufacturers to expand a variety of ceramic membrane products.

Description

Technical Field

[0001] The invention relates to a method for optimizing and adjusting the pore size of a finished ceramic membrane, and belongs to the technical field of ceramic membranes. Background Art

[0002] Because membrane separation technology has a series of advantages such as high efficiency, low energy consumption, easy operation and environmental friendliness, it has been widely used in many fields such as food and pharmaceutical processing, seawater desalination, wastewater treatment, bioengineering, energy engineering, etc. Among many membrane materials, porous ceramic membrane materials have broad application prospects in the fields of normal temperature and high temperature filter devices, catalyst carriers and inorganic reaction separators due to their outstanding advantages such as good chemical stability, high mechanical strength, strong resistance to microbial contamination, high temperature resistance, high pressure backwashing and strong regeneration ability. In particular, silicon carbide ceramic membranes not only have the characteristics of high strength, high modulus, high temperature resistance and oxidation resistance, but also have the advantages of acid and alkali resistance, adjustable resistivity, resistance to microbial erosion, non-deformation of membrane pores, strong anti-pollution ability and easy cleaning. These advantages are unmatched by organic membranes and other ceramic membranes, making silicon carbide ceramic membranes have application prospects in many harsh environments. They are now widely used in industries such as petrochemicals, metallurgy and chemical industry, biopharmaceuticals, integrated circuits, etc. that are prone to produce various types of oily wastewater and acidic and alkaline wastewater, and have gradually become a very promising rising star in the membrane industry.

[0003] Because the membrane separation mechanism is a screening mechanism, the permeability and selectivity are directly related to the membrane pore size. For example, if the membrane pore size is too large, it will not be able to intercept and remove all pollutants. If the membrane pore size is reduced, the interception accuracy of pollutants will be significantly improved. Therefore, the membrane pore size will ultimately affect the application environment and field of the finished ceramic membrane. For example, microfiltration membranes with a pore size of approximately 0.1μm to 10μm are usually used for microbial removal, solid-liquid separation, oil / water emulsion separation, etc.; ultrafiltration membranes with a pore size of approximately 10nm to 100nm can be used to remove suspended solids, bacteria, some viruses, etc.; nanofiltration membranes with a pore size of approximately 1nm to 10nm can remove most organic molecules, almost all viruses and a series of salts; and reverse osmosis membranes with a pore size of approximately 0.1nm to 1nm can remove most minerals and monovalent ions in water.

[0004] However, current research mainly focuses on adjusting the ceramic membrane preparation process to prepare target ceramic membrane products with specific pore sizes. It is not possible to optimize and adjust the pore size of existing finished ceramic membranes according to application requirements, which limits the application range of finished ceramic membranes and makes it difficult for ceramic membrane manufacturers to expand their ceramic membrane products. Therefore, if a method can be developed to optimize the pore size of existing finished ceramic membranes, it will not only be of great value to improve the filtration accuracy and interception capacity of existing finished membranes, but also help ceramic membrane manufacturers to expand their various ceramic membrane products. Summary of the invention

[0005] In view of the above problems and requirements in the prior art, an object of the present invention is to provide a method for optimizing and adjusting the pore size of a finished ceramic membrane.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0007] A method for optimizing and adjusting the pore size of a finished ceramic membrane comprises the following steps:

[0008] a) soaking the clean finished ceramic membrane in deionized water until the membrane is saturated with water;

[0009] b) drying the wet ceramic membrane saturated with water adsorption, and controlling the relative humidity of the ceramic membrane to be 5% to 90%; Where: m a It is the mass of the clean finished ceramic membrane before being soaked in water after cleaning; m b It is the mass of the clean finished ceramic membrane after cleaning when it is saturated with water; m c It is the mass of the wet ceramic membrane saturated with water adsorption after drying for a certain period of time;

[0010] c) coating a ceramic membrane having a relative humidity of 5% to 90% with a polycarbosilane organic solution having a mass fraction of 1% to 10%;

[0011] d) High-temperature cracking of the ceramic membrane coated with polycarbosilane, i.e., in an inert atmosphere, keeping the temperature at 900-1400° C. for 1-3 hours, with a heating rate of 1-10° C. / min, and cooling naturally or by program, with a program cooling rate of 1-10° C. / min.

[0012] In one embodiment, in step d), before the high temperature cracking, the ceramic membrane coated with polycarbosilane is first subjected to oxidative crosslinking in air at 170 to 300° C. for 1 to 3 hours.

[0013] In one embodiment, the finished ceramic membrane described in step a) refers to any ceramic membrane of various pore sizes among SiO2, ZrO2, Al2O3, TiO2, Si3N4 and SiC in the prior art.

[0014] In one embodiment, the drying temperature in step b) is 20-40°C.

[0015] In one embodiment, the polycarbosilane described in step c) is a commercially available product with Mw=1000-2000, density of 1.1-1.3 g / mL, and melting point of 79-84°C.

[0016] In one embodiment, the polycarbosilane organic solution in step c) refers to a solution obtained by dissolving polycarbosilane in any one of n-hexane, cyclohexane, benzene, toluene, xylene, trimethylbenzene, chlorotoluene and decalin as a solvent, or a mixture of two or more thereof.

[0017] In one embodiment, the coating in step c) is performed by a dipping and pulling coating method, an ultrasonic atomization spray coating method or a brush coating method.

[0018] In one embodiment, the inert atmosphere in step d) is a nitrogen atmosphere or an argon atmosphere.

[0019] Compared with the prior art, the present invention has the following significant beneficial effects:

[0020] Experiments have proved that the present invention achieves the optimization and adjustment of the pore size of existing large-pore finished ceramic membranes by creatively controlling the water absorption humidity of the finished ceramic membrane within a specific range, and then coating a certain amount of polycarbosilane organic solution, and then subjecting it to high-temperature pyrolysis or first subjecting it to oxidative cross-linking and then subjecting it to high-temperature pyrolysis. This not only makes it easy to optimize the pore size of a certain existing finished ceramic membrane according to application needs, but also makes the adjustment operation simple and easy to achieve scale. Therefore, the present invention is not only of great value in improving and improving the filtration accuracy and interception capacity of existing finished membranes, but also helps ceramic membrane manufacturers to expand a variety of ceramic membrane products. Compared with the prior art, the present invention has achieved significant progress and unexpected technical effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the pore size distribution diagram of Examples 2-4. DETAILED DESCRIPTION

[0022] The technical scheme of the present invention is further described in detail and completely in conjunction with specific embodiments. The finished ceramic membranes used in the following embodiments and comparative examples are all commercially available (such as: produced by Shandong Saili Ke Membrane Technology Co., Ltd.) silicon carbide ceramic membranes with an average pore size of 1000nm and a half-peak width of 472nm.

[0023] Example 1

[0024] a) soaking the clean finished ceramic membrane in deionized water until the membrane is saturated with water;

[0025] b) drying the wet ceramic membrane saturated with water adsorption at 30° C., and controlling the relative humidity of the ceramic membrane to be 5%;

[0026] c) coating the ceramic membrane at a relative humidity of 5% with a 1% by mass polycarbosilane n-hexane solution, using an immersion coating method;

[0027] d) After the coated ceramic membrane is naturally dried overnight, it is first oxidatively cross-linked in air at 250°C for 2 hours, and then placed in a high-temperature furnace with nitrogen or argon protective gas for high-temperature cracking: the high-temperature furnace is heated at a rate of 5°C / min, heated to 1000°C and then kept warm for 2 hours, and then programmed to cool down at a rate of 10°C / min.

[0028] The pore size distribution was measured using a mercury intrusion instrument, and it was found that after the above adjustment, the average pore size of the ceramic membrane was reduced from 1000nm to 680nm, and the porosity was 45%, thus achieving the optimized adjustment of the pore size of the finished silicon carbide ceramic membrane.

[0029] Example 2

[0030] a) soaking the clean finished ceramic membrane in deionized water until the membrane is saturated with water;

[0031] b) drying the wet ceramic membrane saturated with water adsorption at 30° C., and controlling the relative humidity of the ceramic membrane to be 35%;

[0032] c) coating the ceramic membrane at a relative humidity of 35% with a 1% by mass polycarbosilane n-hexane solution, using an immersion coating method;

[0033] d) After the coated ceramic membrane is naturally dried overnight, it is placed in a high-temperature furnace with nitrogen or argon protective gas for high-temperature cracking: the high-temperature furnace is heated at a rate of 5°C / min, heated to 1000°C and kept warm for 2 hours, and then cooled naturally after the insulation ends.

[0034] The pore size distribution was measured by mercury intrusion porosimeter, and it was found that after the above adjustment, the average pore size of the ceramic membrane decreased from 1000nm to 950nm. Although the pore size change was not obvious, the pore size distribution diagram (see Figure 1 It was found that after the above adjustment in this embodiment, nanopores less than 100 nm were generated on the surface of the ceramic membrane, so that the optimized and adjusted ceramic membrane could improve the retention effect of small particle size filter.

[0035] Example 3

[0036] a) soaking the clean finished ceramic membrane in deionized water until the membrane is saturated with water;

[0037] b) drying the wet ceramic membrane saturated with water adsorption at 30° C., and controlling the relative humidity of the ceramic membrane to be 35%;

[0038] c) coating the ceramic membrane at a relative humidity of 35% with a 5% by mass polycarbosilane n-hexane solution by a dipping and pulling coating method;

[0039] d) After the coated ceramic membrane is naturally dried overnight, it is placed in a high-temperature furnace with nitrogen or argon protective gas for high-temperature cracking: the high-temperature furnace is heated at a rate of 5°C / min, heated to 1000°C and kept warm for 2 hours, and then cooled naturally after the insulation ends.

[0040] The pore size distribution was measured by mercury intrusion porosimetry, and it was found that after the above adjustment, the average pore size of the ceramic membrane was reduced from 1000nm to 800nm, and the nanopores on the surface of the ceramic membrane disappeared (see Figure 1 shown).

[0041] Example 4

[0042] a) soaking the clean finished ceramic membrane in deionized water until the membrane is saturated with water;

[0043] b) drying the wet ceramic membrane saturated with water adsorption at 30° C., and controlling the relative humidity of the ceramic membrane to be 10%;

[0044] c) coating the ceramic membrane at a relative humidity of 10% with a 5% by mass polycarbosilane n-hexane solution, using an immersion coating method;

[0045] d) After the coated ceramic membrane is naturally dried overnight, it is placed in a high-temperature furnace with nitrogen or argon protective gas for high-temperature cracking: the high-temperature furnace is heated at a rate of 5°C / min, heated to 1000°C and kept warm for 2 hours, and then cooled naturally after the insulation ends.

[0046] The pore size distribution was measured by mercury intrusion porosimetry, and it was found that after the above adjustment, the average pore size of the ceramic membrane decreased from 1000nm to 920nm. Although the pore size change was not obvious, nanopores less than 100nm were generated on the surface of the ceramic membrane (see Figure 1 As shown), the optimized and adjusted ceramic membrane can improve the retention effect of small particle size filter.

[0047] Example 5

[0048] a) soaking the clean finished ceramic membrane in deionized water until the membrane is saturated with water;

[0049] b) drying the wet ceramic membrane saturated with water adsorption at 30° C., and controlling the relative humidity of the ceramic membrane to be 85%;

[0050] c) coating the ceramic membrane at a relative humidity of 85% with a 5% by mass polycarbosilane n-hexane solution, using an immersion coating method;

[0051] d) After the coated ceramic membrane is naturally dried overnight, it is placed in a high-temperature furnace with nitrogen or argon protective gas for high-temperature cracking: the high-temperature furnace is heated at a rate of 5°C / min, heated to 1000°C and kept warm for 2 hours, and then cooled naturally after the insulation ends.

[0052] The pore size distribution was measured using a mercury intrusion meter, and it was found that after the above adjustment, the average pore size of the ceramic membrane was reduced from 1000nm to 850nm, which can achieve optimal adjustment of the pore size of the finished ceramic membrane.

[0053] Example 6

[0054] Investigate the effect of relative humidity on the pore size control of finished ceramic membranes:

[0055] The method described in Example 4 was adopted, except that the relative humidity of the ceramic membrane was changed (see Table 1 for details); then the average pore size of the adjusted ceramic membrane and the half-peak width representing the pore size distribution were measured. The specific test results are shown in Table 1 for details.

[0056] Table 1 Effect of relative humidity on the pore size control effect of finished ceramic membrane

[0057]

[0058] It can be seen from the results shown in Table 1 that: under the same conditions, as the relative humidity of the ceramic membrane before coating increases, the loading amount of polycarbosilane will decrease, and the regulating effect on reducing the pore size will be more significant; but if the relative humidity is too low or too high, the pore size regulation effect will not be obvious.

[0059] Example 7

[0060] Investigate the effect of the mass fraction of polycarbosilane on the pore size regulation of the finished ceramic membrane:

[0061] The method described in Example 4 was adopted, except that the mass fraction of polycarbosilane was changed (see Table 2 for details); then the average pore size of the adjusted ceramic membrane and the half-peak width representing the pore size distribution were measured. The specific test results are shown in Table 2 for details.

[0062] Table 2 Effect of the mass fraction of polycarbosilane on the pore size control effect of finished ceramic membrane

[0063]

[0064]

[0065] It can be seen from the results shown in Table 2 that: under the same conditions, as the mass fraction of the coated polycarbosilane increases, the loading amount of polycarbosilane will increase, and the regulating effect on reducing the pore size will be more significant; however, if the mass fraction of the coated polycarbosilane is too low (less than 1%) or too high (greater than 10%), the pore size regulation effect will not be obvious.

[0066] Example 8

[0067] Investigate the effect of pyrolysis temperature on the pore size control of finished ceramic membranes:

[0068] The method described in Example 4 was adopted, except that the cracking temperature was changed (see Table 3 for details); then the average pore size of the adjusted ceramic membrane and the half-peak width representing the pore size distribution were measured. The specific test results are shown in Table 3 for details.

[0069] Table 3 Effect of pyrolysis temperature on the pore size control effect of finished ceramic membrane

[0070]

[0071] From the results shown in Table 3, it can be seen that under the same conditions, as the pyrolysis temperature increases, the regulating effect on reducing the pore size becomes smaller, but the pore size distribution becomes narrower.

[0072] Example 9

[0073] Investigate the effect of oxidation cross-linking temperature on the pore size regulation of finished ceramic membranes:

[0074] The method described in Example 1 was adopted, except that the oxidation crosslinking temperature was changed (see Table 4 for details); then the average pore size of the adjusted ceramic membrane and the half-peak width characterizing the pore size distribution were measured. The specific test results are shown in Table 4 for details.

[0075] Table 4 Effect of oxidation cross-linking temperature on the pore size control effect of finished ceramic membrane

[0076] Relative humidity Crosslinking temperature / ℃ Cracking temperature / ℃ Average pore size / nm Half peak width / nm 60％ 170 1000 630 433 60％ 250 1000 500 370 60％ 300 1000 580 463

[0077] From the results shown in Table 4, it can be seen that under the same conditions, the optimal oxidation crosslinking temperature is 250°C, which can reduce the pore size by 50%, and the pore size distribution is narrow, and the adjustment effect is most significant.

[0078] In addition, it should be noted that the finished ceramic membrane described in the above embodiment can be replaced by inorganic ceramic membranes of various pore sizes in the prior art, including but not limited to any one of SiO2, ZrO2, Al2O3, TiO2, Si3N4 and SiC; the n-hexane solution of polycarbosilane described in the above embodiment can also be a solution obtained by dissolving polycarbosilane in cyclohexane, benzene, toluene, xylene, trimethylbenzene, chlorotoluene and decahydronaphthalene or a mixture of two or more thereof as a solvent; the coating method is not limited to the immersion coating method, but can also be any one of the ultrasonic atomization spray coating method and the brush coating method.

[0079] From the above, it can be seen that the present invention creatively controls the water absorption humidity of the finished ceramic membrane within a specific range, and then coats a certain amount of polycarbosilane organic solution, and then undergoes high-temperature pyrolysis or first undergoes oxidative cross-linking and then high-temperature pyrolysis, thereby achieving the optimization and adjustment of the pore size of the existing large-pore finished ceramic membrane. This not only makes it easy to optimize the pore size of a certain existing finished ceramic membrane according to application needs, but also the adjustment operation is simple and easy to achieve scale. Therefore, the present invention is not only of great value in improving and improving the filtration accuracy and interception capacity of existing finished membranes, but also helps ceramic membrane manufacturers to achieve the expansion of a variety of ceramic membrane products. Compared with the prior art, the present invention has achieved significant progress and unexpected technical effects.

[0080] Finally, it should be pointed out that the above are only some preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above contents of the present invention all fall within the scope of protection of the present invention.

Claims

1. A method for optimizing and adjusting the pore size of a finished ceramic membrane, characterized in that: The steps include: a) soaking the clean finished ceramic membrane in deionized water until the membrane is saturated with water; b) drying the wet ceramic membrane saturated with water adsorption, and controlling the relative humidity of the ceramic membrane to be 5% to 90%; Where: m a It is the mass of the clean finished ceramic membrane before being soaked in water after cleaning; m b It is the mass of the clean finished ceramic membrane after cleaning when it is saturated with water; m c It is the mass of the wet ceramic membrane saturated with water adsorption after drying for a certain period of time; c) coating a ceramic membrane having a relative humidity of 5% to 90% with a polycarbosilane organic solution having a mass fraction of 1% to 10%; d) High-temperature cracking of the ceramic membrane coated with polycarbosilane, i.e., in an inert atmosphere, keeping the temperature at 900-1400° C. for 1-3 hours, with a heating rate of 1-10° C. / min, and cooling naturally or by program, with a program cooling rate of 1-10° C. / min.

2. The method according to claim 1, characterized in that: Step d), before the high temperature cracking, the ceramic membrane coated with polycarbosilane is first subjected to oxidative crosslinking in air at 170-300° C. for 1-3 hours.

3. The method according to claim 1, characterized in that: The finished ceramic membrane described in step a) refers to any ceramic membrane of SiO2, ZrO2, Al2O3, TiO2, Si3N4 and SiC with various pore sizes in the prior art.

4. The method according to claim 1, characterized in that: The drying temperature in step b) is 20-40°C.

5. The method according to claim 1, characterized in that: The polycarbosilane described in step c) is a commercially available product with Mw=1000-2000, density of 1.1-1.3 g / mL and melting point of 79-84°C.

6. The method according to claim 1, characterized in that: The polycarbosilane organic solution in step c) refers to a solution obtained by dissolving polycarbosilane in any one of n-hexane, cyclohexane, benzene, toluene, xylene, trimethylbenzene, chlorotoluene and decalin as a solvent, or a mixture of two or more thereof.

7. The method according to claim 1, characterized in that: The coating in step c) is carried out by dipping and pulling coating method, ultrasonic atomization spray coating method or brush coating method.

8. The method according to claim 1, characterized in that: The inert atmosphere in step d) is a nitrogen atmosphere or an argon atmosphere.

Images