A ceramic diaphragm for separating waste lubricating oil and its preparation method

Abstract

The present invention relates to the technical field of ceramic diaphragms, and specifically discloses a ceramic diaphragm for separating waste lubricating oil and a preparation method thereof. The preparation method of the ceramic diaphragm for separating waste lubricating oil comprises: preparing pretreated silk protein nanofibers; mixing the pretreated silk protein nanofibers and hydroxyapatite powder, stirring, adding water, gelatin, sodium hexametaphosphate, ball milling, pouring into a mold, freeze drying, sintering, cooling, polishing the surface, and obtaining a ceramic substrate; calcining diatomaceous earth, cooling, adding anhydrous ethanol and water, stirring, adding triethylamine, stirring in a constant temperature water bath, filtering, washing, and drying to obtain pretreated diatomaceous earth; mixing water, γ-aminopropyltriethoxysilane, and polyethylene glycol, stirring, adding pretreated diatomaceous earth, stirring, immersing the ceramic substrate, drying, and curing to obtain a ceramic diaphragm for separating waste lubricating oil. The ceramic diaphragm for separating waste lubricating oil of the present invention can maintain adaptive uniform speed stability within a reasonable range.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic diaphragms, and particularly to a ceramic diaphragm for separating waste lubricating oil and a preparation method thereof. Background Art

[0002] In today's industrial field, the proper treatment and reuse of waste lubricating oil have become a key link in the process of sustainable development. Among them, ceramic diaphragms play an important role in the separation of waste lubricating oil. However, traditional ceramic diaphragms have exposed many defects that cannot be ignored in practical applications.

[0003] Firstly, the membrane flux of traditional ceramic diaphragms is often at an excessively high level and deviates from the reasonable range. In the actual operation of waste lubricating oil separation, an excessively high membrane flux is not beneficial. On the contrary, it will cause a series of adverse consequences. On the one hand, an excessively high membrane flux makes it difficult to achieve an ideal impurity retention effect. Various impurities contained in waste lubricating oil, such as metal particles, oxidation products, and colloids, cannot be effectively blocked on one side of the diaphragm due to the excessively high membrane flux, resulting in low purity of the separated lubricating oil and inability to meet subsequent reuse or emission standards. On the other hand, an excessively high flux will also damage the microstructure of the ceramic diaphragm itself. The strong fluid impact force and the rapid passage of impurities will deform or even rupture the pore structure of the diaphragm. In the long run, not only the service life of a single diaphragm is reduced, but also the stability of the entire separation system is greatly threatened. Frequent fault repairs and component replacements become normal, increasing the operating costs and time costs of enterprises.

[0004] Secondly, it is difficult for traditional ceramic diaphragms to achieve a uniform and stable membrane flux. During the continuous operation of waste lubricating oil separation, the membrane flux will show large fluctuations without any rules. This instability directly leads to the inability to stably and accurately control the separation process. For example, in an automated waste lubricating oil treatment production line, the fluctuations in membrane flux will cause the separation efficiency to be high or low, unable to operate stably according to the preset process parameters, thus affecting the coordinated operation of the entire production line, resulting in low production efficiency, uneven product quality, and also increasing energy waste and equipment wear.

[0005] Finally, when facing waste lubricating oils with different impurity contents and types, the traditional ceramic membranes show extremely poor adaptability in membrane flux. Waste lubricating oils have a wide range of sources and complex and variable compositions. There are significant differences in impurity content, impurity type, etc. among waste lubricating oils from different batches or sources. Due to the limitations of its structure and material properties, the traditional ceramic membrane cannot automatically adjust the membrane flux according to these changes. When treating waste lubricating oils with high impurity content or special impurity types, the membrane will quickly become blocked or be damaged due to being unable to withstand the pressure; conversely, when treating relatively "clean" waste lubricating oils, the treatment efficiency may be low due to the inability to increase the membrane flux. This makes it necessary to frequently adjust the treatment process or even replace the ceramic membrane for different waste lubricating oils in actual production, greatly increasing the complexity and cost of equipment maintenance, reducing the reliability and flexibility of the entire waste lubricating oil treatment system, and making it difficult to meet the large-scale and diverse waste lubricating oil treatment needs of modern industry.

[0006] In summary, the traditional ceramic membrane has significant deficiencies in the rationality, stability, and adaptability of membrane flux. There is an urgent need for an innovative ceramic membrane for waste lubricating oil separation and its preparation method to overcome the limitations of the existing technology, be able to perform separation operations flexibly, stably, and efficiently according to the actual situation of waste lubricating oil, and thus promote the further development and improvement of waste lubricating oil treatment technology. Summary of the Invention

[0007] The purpose of the present invention is to solve the deficiencies existing in the prior art and to propose a preparation method for a ceramic membrane for waste lubricating oil separation.

[0008] A preparation method for a ceramic membrane for waste lubricating oil separation includes the following steps:

[0009] S1. Disperse silk fibroin nanofibers in water, stir, adjust the pH value of the system, add epichlorohydrin, stir in a constant temperature water bath, filter, collect the precipitate, wash, and dry to obtain pretreated silk fibroin nanofibers;

[0010] S2. Mix the pretreated silk fibroin nanofibers and hydroxyapatite powder, stir, add water, gelatin, and sodium hexametaphosphate, ball mill, pour into a mold, freeze-dry, sinter, cool, and polish the surface to obtain a ceramic substrate;

[0011] S3. Calcinate diatomite, cool, add anhydrous ethanol and water, stir, add triethylamine, stir in a constant temperature water bath, filter, wash, and dry to obtain pretreated diatomite;

[0012] S4. Mix water, γ-aminopropyltriethoxysilane, and polyethylene glycol, stir, add the pretreated diatomite, stir, immerse the ceramic substrate, dry, and cure to obtain a ceramic membrane for waste lubricating oil separation.

[0013] Preferably, the weight ratio of silk fibroin nanofibers, epichlorohydrin, hydroxyapatite powder, gelatin, sodium hexametaphosphate, diatomite, absolute ethanol, triethylamine, γ-aminopropyltriethoxysilane, and polyethylene glycol is 3-5: 1.2-1.6: 50-55: 2.5-3.5: 0.3-0.5: 8-10: 40-50: 1.5-3: 0.3-0.5: 2-4.

[0014] Preferably, in step S1, after dispersing the silk fibroin nanofibers in deionized water, stirring is carried out for 20-30 min at a stirring speed of 250-350 rpm.

[0015] Preferably, in step S1, a sodium hydroxide solution with a concentration of 0.2-0.3 mol / L is used to adjust the pH value of the system to 10.5-11.

[0016] Preferably, in step S1, epichlorohydrin is added, and based on the total weight of epichlorohydrin, the addition rate of epichlorohydrin is 4-5% per minute.

[0017] Preferably, in step S1, the constant temperature water bath temperature is 40-45 °C, the constant temperature water bath stirring time is 4-6 h, and the constant temperature water bath stirring speed is 250-350 rpm.

[0018] Preferably, in step S1, the drying temperature is 60-65 °C and the drying time is 18-22 h.

[0019] Preferably, in step S2, after mixing the pretreated silk fibroin nanofibers and hydroxyapatite powder, stirring is carried out for 10-20 min at a stirring speed of 200-300 rpm.

[0020] Preferably, in step S2, ball milling is carried out by a planetary ball mill for 8-9 h at a ball milling speed of 200-300 rpm.

[0021] Preferably, in step S2, the temperature of freeze-drying is -45--50 °C and the time of freeze-drying is 36-40 h.

[0022] Preferably, in step S2, sintering is carried out by a high-temperature sintering furnace for 2-3 h at a sintering temperature of 1000-1100 °C.

[0023] Preferably, in step S3, the diatomite is calcined in a muffle furnace at a calcination temperature of 500-600 °C for 3-4 h.

[0024] Preferably, in step S3, absolute ethanol and water are added and then stirring is carried out for 0.5-1 h at a stirring speed of 350-450 rpm.

[0025] Preferably, in step S3, triethylamine is added, and based on the total weight of triethylamine, the addition rate of triethylamine is 1-2% per minute.

[0026] Preferably, in step S3, the temperature of the constant temperature water bath is 23-27 °C, the stirring time of the constant temperature water bath is 3-4 h, and the stirring speed of the constant temperature water bath is 200-300 rpm.

[0027] Preferably, in step S3, the drying temperature is 50-55 °C, and the drying time is 20-24 h.

[0028] Preferably, in step S4, water, γ-aminopropyltriethoxysilane, and polyethylene glycol are mixed and stirred. The stirring time is 20-30 min, and the stirring speed is 200-300 rpm.

[0029] Preferably, in step S4, pretreated diatomite is added and stirred. The stirring time is 0.5-1 h, and the stirring speed is 300-400 rpm.

[0030] Preferably, in step S4, the ceramic substrate is immersed at an immersion speed of 4-6 mm / min and an immersion time of 1-2 h.

[0031] Preferably, in step S4, the drying temperature is 58-62 °C, and the drying time is 1.5-2 h.

[0032] Preferably, in step S4, it is cured in a blast drying oven, and the curing time is 1-2 h.

[0033] A ceramic diaphragm for waste lubricating oil separation is made by using the preparation method of the ceramic diaphragm for waste lubricating oil separation described in any one of the above.

[0034] Beneficial effects:

[0035] In the present invention, silk fibroin nanofibers react with epichlorohydrin to graft specific groups, and then are compounded with hydroxyapatite powder by means of ball milling, sintering, etc. During this process, silk fibroin nanofibers interact with hydroxyapatite, and the special structure of the former combines with the crystal structure of the latter, optimizing the pore structure inside the ceramic substrate, reducing the irregularity of pores and the risk of blockage, making the flow resistance of waste lubricating oil decrease when passing through, so that the membrane flux speed is in a reasonable range and can "pass steadily at a constant speed", improving the stability and repeatability of the waste lubricating oil separation process, and also developing the unique application value of silk fibroin nanofibers in precisely regulating the membrane flux in the field of ceramic diaphragms.

[0036] In the present invention, diatomite is calcined and treated with triethylamine, and then mixed with polyethylene glycol and γ-aminopropyltriethoxysilane and coated on the surface of a ceramic substrate. Through operations such as impregnation, drying, and curing, the diatomite is tightly bonded to the ceramic substrate. On the basis of ensuring "uniform and stable", the "adaptive" membrane flux characteristics are further realized. When the working environment of waste lubricating oil changes, such as an increase in impurity content, the porous structure and surface properties of diatomite can respond to these changes. Specifically, the interaction between diatomite, the substrate, and polyethylene glycol will prompt the diaphragm to change the effective filtration area of the pores or the surface charge properties, prevent impurities from blocking the pores, and maintain the "adaptive uniform and stable" membrane flux within a reasonable range.

[0037] In practical applications, the membrane flux of the ceramic diaphragm is not the higher the better. Excessively high membrane flux will lead to poor impurity retention effect, damage the microstructure of the diaphragm, and affect the stability of the entire separation system in practical applications. Different from the limitation of "blindly pursuing high throughput" in traditional technologies that rely only on the inherent properties of a single material or a simple structure, the present invention enables the ceramic diaphragm to adapt to the treatment requirements of waste lubricating oils of different qualities. Even when the composition of the waste lubricating oil fluctuates greatly, it can still maintain a good separation effect, reduce the decline in treatment effect caused by differences in lubricating oil quality, and there is no need to frequently adjust the treatment process or replace the diaphragm, reducing the equipment maintenance cost and replacement frequency, further improving the stability and reliability of the entire waste lubricating oil treatment system, and extending the service life of the equipment. Specific embodiments

[0038] The following further explains the present invention in conjunction with specific embodiments.

[0039] Example 1

[0040] A preparation method of a ceramic diaphragm for separating waste lubricating oil includes the following steps:

[0041] S1. Disperse 30 g of silk fibroin nanofibers in 350 g of water, stir for 20 min at a stirring speed of 250 rpm, adjust the pH value of the system to 10.5 with a sodium hydroxide solution with a concentration of 0.2 mol / L, add 12 g of epichlorohydrin, based on the total weight of epichlorohydrin, the addition speed of epichlorohydrin is 4% per minute, stir in a 40°C constant temperature water bath for 4 h at a stirring speed of 250 rpm, filter, collect the precipitate, wash, and dry at 60°C for 18 h to obtain pretreated silk fibroin nanofibers;

[0042] S2. Mix the pretreated silk fibroin nanofibers with 500 g of hydroxyapatite powder, stir for 10 min at a stirring speed of 200 rpm, add 400 g of water, 25 g of gelatin, and 3 g of sodium hexametaphosphate, ball mill for 8 h using a planetary ball mill at a rotation speed of 200 rpm, pour into a mold, freeze-dry at -45 °C for 36 h, sinter for 2 h using a high-temperature sintering furnace at a sintering temperature of 1000 °C, cool, and polish the surface to obtain a ceramic substrate;

[0043] S3. Calcinate 80 g of diatomite in a muffle furnace at 500 °C for 3 h, cool, add 400 g of absolute ethanol and 50 g of water, stir for 0.5 h at a stirring speed of 350 rpm, add 15 g of triethylamine, with the total weight of triethylamine as the benchmark, the addition speed of triethylamine is 1% per minute, stir in a 23 °C constant temperature water bath for 3 h at a stirring speed of 200 rpm, filter, wash, and dry at 50 °C for 20 h to obtain pretreated diatomite;

[0044] S4. Mix 380 g of water, 3 g of γ-aminopropyltriethoxysilane, and 20 g of polyethylene glycol, stir for 20 min at a stirring speed of 200 rpm, add the pretreated diatomite, stir for 0.5 h at a stirring speed of 300 rpm, immerse the ceramic substrate at an immersion speed of 4 mm / min for 1 h, dry at 58 °C for 1.5 h, and cure for 1 h using a blast drying oven to obtain a ceramic membrane for waste lubricating oil separation.

[0045] Example 2

[0046] A preparation method of a ceramic membrane for waste lubricating oil separation, comprising the following steps:

[0047] S1. Disperse 50 g of silk fibroin nanofibers in 400 g of water, stir for 30 min at a stirring speed of 350 rpm, adjust the pH value of the system to 11 using a sodium hydroxide solution with a concentration of 0.3 mol / L, add 16 g of epichlorohydrin, with the total weight of epichlorohydrin as the benchmark, the addition speed of epichlorohydrin is 5% per minute, stir in a 45 °C constant temperature water bath for 6 h at a stirring speed of 350 rpm, filter, collect the precipitate, wash, and dry at 65 °C for 22 h to obtain pretreated silk fibroin nanofibers;

[0048] S2. Mix the pretreated silk fibroin nanofibers with 550 g of hydroxyapatite powder, stir for 20 min at a stirring speed of 300 rpm, add 500 g of water, 35 g of gelatin, and 5 g of sodium hexametaphosphate, ball mill for 9 h using a planetary ball mill at a rotation speed of 300 rpm, pour into a mold, freeze-dry at -50 °C for 40 h, sinter for 3 h using a high-temperature sintering furnace at a sintering temperature of 1100 °C, cool, and polish the surface to obtain a ceramic substrate;

[0049] S3. Calcinate 100 g of diatomite in a muffle furnace at 600 °C for 4 h, cool it, add 500 g of absolute ethanol and 80 g of water, stir for 1 h at a stirring speed of 450 rpm, add 30 g of triethylamine, and based on the total weight of triethylamine, the addition rate of triethylamine is 2% per minute. Stir in a constant temperature water bath at 27 °C for 4 h at a stirring speed of 300 rpm, filter, wash, and dry at 55 °C for 24 h to obtain pretreated diatomite;

[0050] S4. Mix 400 g of water, 5 g of γ-aminopropyltriethoxysilane, and 40 g of polyethylene glycol, stir for 30 min at a stirring speed of 300 rpm, add the pretreated diatomite, stir for 1 h at a stirring speed of 400 rpm, immerse the ceramic substrate at an immersion speed of 6 mm / min for 2 h, dry at 62 °C for 2 h, and cure in a blast drying oven for 2 h to obtain a ceramic diaphragm for waste lubricating oil separation.

[0051] Example 3

[0052] A preparation method of a ceramic diaphragm for waste lubricating oil separation, comprising the following steps:

[0053] S1. Disperse 35 g of silk fibroin nanofibers in 360 g of water, stir for 22 min at a stirring speed of 270 rpm, adjust the pH value of the system to 10.6 using a sodium hydroxide solution with a concentration of 0.22 mol / L, add 13 g of epichlorohydrin, and based on the total weight of epichlorohydrin, the addition rate of epichlorohydrin is 4.2% per minute. Stir in a constant temperature water bath at 41 °C for 4.5 h at a stirring speed of 270 rpm, filter, collect the precipitate, wash, and dry at 61 °C for 19 h to obtain pretreated silk fibroin nanofibers;

[0054] S2. Mix the pretreated silk fibroin nanofibers with 510 g of hydroxyapatite powder, stir for 12 min at a stirring speed of 220 rpm, add 420 g of water, 27 g of gelatin, and 3.5 g of sodium hexametaphosphate, ball mill for 8.2 h at a rotation speed of 220 rpm using a planetary ball mill, pour into a mold, freeze-dry at -46 °C for 37 h, sinter in a high-temperature sintering furnace for 2.2 h at a sintering temperature of 1020 °C, cool, and polish the surface to obtain a ceramic substrate;

[0055] S3. Calcinate 85 g of diatomite in a muffle furnace at 520 °C for 3.2 h, cool it, add 420 g of absolute ethanol and 60 g of water, stir for 0.6 h at a stirring speed of 370 rpm, add 18 g of triethylamine, and based on the total weight of triethylamine, the addition rate of triethylamine is 1.2% per minute. Stir in a constant temperature water bath at 24 °C for 3.2 h at a stirring speed of 220 rpm, filter, wash, and dry at 51 °C for 21 h to obtain pretreated diatomite;

[0056] S4. Mix 385 g of water, 3.5 g of γ-aminopropyltriethoxysilane, and 25 g of polyethylene glycol, stir for 22 min at a stirring speed of 220 rpm, add the pretreated diatomaceous earth, stir for 0.6 h at a stirring speed of 320 rpm, immerse the ceramic substrate at an immersion speed of 4.5 mm / min for 1.2 h, dry at 59 °C for 1.6 h, and cure for 1.2 h in a forced-air drying oven to obtain a ceramic diaphragm for waste lubricating oil separation.

[0057] Example 4

[0058] A method for preparing a ceramic diaphragm for waste lubricating oil separation, comprising the following steps:

[0059] S1. Disperse 45 g of silk fibroin nanofibers in 390 g of water, stir for 28 min at a stirring speed of 330 rpm, adjust the pH value of the system to 10.9 using a sodium hydroxide solution with a concentration of 0.28 mol / L, add 15 g of epichlorohydrin, and based on the total weight of epichlorohydrin, the addition rate of epichlorohydrin is 4.8% per minute, stir in a constant-temperature water bath at 44 °C for 5.5 h at a stirring speed of 330 rpm, filter, collect the precipitate, wash, and dry at 64 °C for 21 h to obtain pretreated silk fibroin nanofibers.

[0060] S2. Mix the pretreated silk fibroin nanofibers with 540 g of hydroxyapatite powder, stir for 18 min at a stirring speed of 280 rpm, add 480 g of water, 32 g of gelatin, and 4.5 g of sodium hexametaphosphate, ball-mill for 8.8 h at a rotational speed of 280 rpm using a planetary ball mill, pour into a mold, freeze-dry at -49 °C for 39 h, sinter in a high-temperature sintering furnace for 2.8 h at a sintering temperature of 1080 °C, cool, and polish the surface to obtain a ceramic substrate.

[0061] S3. Calcinate 95 g of diatomaceous earth in a muffle furnace at 580 °C for 3.8 h, cool, add 480 g of absolute ethanol and 70 g of water, stir for 0.9 h at a stirring speed of 430 rpm, add 27 g of triethylamine, and based on the total weight of triethylamine, the addition rate of triethylamine is 1.8% per minute, stir in a constant-temperature water bath at 26 °C for 3.8 h at a stirring speed of 280 rpm, filter, wash, and dry at 54 °C for 23 h to obtain pretreated diatomaceous earth.

[0062] S4. Mix 395 g of water, 4.5 g of γ-aminopropyltriethoxysilane, and 35 g of polyethylene glycol, stir for 28 min at a stirring speed of 280 rpm, add the pretreated diatomaceous earth, stir for 0.9 h at a stirring speed of 380 rpm, immerse the ceramic substrate at an immersion speed of 5.5 mm / min for 1.8 h, dry at 61 °C for 1.9 h, and cure for 1.8 h in a forced-air drying oven to obtain a ceramic diaphragm for waste lubricating oil separation.

[0063] Example 5

[0064] A preparation method of a ceramic diaphragm for waste lubricating oil separation, comprising the following steps:

[0065] S1. Disperse 40 g of silk fibroin nanofibers in 370 g of water, stir for 25 min at a stirring speed of 300 rpm, adjust the pH value of the system to 10.7 using a sodium hydroxide solution with a concentration of 0.25 mol / L, add 14 g of epichlorohydrin. Based on the total weight of epichlorohydrin, the addition rate of epichlorohydrin is 4.5% per minute. Stir in a constant temperature water bath at 42°C for 5 h at a stirring speed of 300 rpm, filter, collect the precipitate, wash, and dry at 62°C for 20 h to obtain pretreated silk fibroin nanofibers;

[0066] S2. Mix the pretreated silk fibroin nanofibers with 520 g of hydroxyapatite powder, stir for 15 min at a stirring speed of 250 rpm, add 450 g of water, 30 g of gelatin, and 4 g of sodium hexametaphosphate. Ball mill for 8.5 h at a rotation speed of 250 rpm using a planetary ball mill, pour into a mold, freeze-dry at -47°C for 38 h, sinter in a high-temperature sintering furnace for 2.5 h at a sintering temperature of 1050°C, cool, and polish the surface to obtain a ceramic substrate;

[0067] S3. Calcinate 90 g of diatomite in a muffle furnace at 550°C for 3.5 h, cool, add 450 g of absolute ethanol and 65 g of water, stir for 0.7 h at a stirring speed of 400 rpm, add 22 g of triethylamine. Based on the total weight of triethylamine, the addition rate of triethylamine is 1.5% per minute. Stir in a constant temperature water bath at 25°C for 3.5 h at a stirring speed of 250 rpm, filter, wash, and dry at 52°C for 22 h to obtain pretreated diatomite;

[0068] S4. Mix 390 g of water, 4 g of γ-aminopropyltriethoxysilane, and 30 g of polyethylene glycol, stir for 25 min at a stirring speed of 250 rpm, add the pretreated diatomite, stir for 0.7 h at a stirring speed of 350 rpm, immerse the ceramic substrate at an immersion speed of 5 mm / min for 1.5 h, dry at 60°C for 1.7 h, and cure in a blast drying oven for 1.5 h to obtain a ceramic diaphragm for waste lubricating oil separation.

[0069] Comparative Example 1

[0070] The difference between Comparative Example 1 and Example 5 is that "silk fibroin nanofibers" are not added;

[0071] A preparation method of a ceramic diaphragm, comprising the following steps:

[0072] S1. Mix 520 g of hydroxyapatite powder, 450 g of water, 30 g of gelatin, and 4 g of sodium hexametaphosphate, stir for 15 min at a stirring speed of 250 rpm, ball mill for 8.5 h using a planetary ball mill at a rotational speed of 250 rpm, pour into a mold, freeze-dry at -47 °C for 38 h, sinter for 2.5 h using a high-temperature sintering furnace at a sintering temperature of 1050 °C, cool, and polish the surface to obtain a ceramic substrate;

[0073] S2. Calcinate 90 g of diatomite in a muffle furnace at 550 °C for 3.5 h, cool, add 450 g of absolute ethanol and 65 g of water, stir for 0.7 h at a stirring speed of 400 rpm, add 22 g of triethylamine, based on the total weight of triethylamine, the addition rate of triethylamine is 1.5% per minute, stir in a 25 °C constant temperature water bath for 3.5 h at a stirring speed of 250 rpm, filter, wash, and dry at 52 °C for 22 h to obtain pretreated diatomite;

[0074] S3. Mix 390 g of water, 4 g of γ-aminopropyltriethoxysilane, and 30 g of polyethylene glycol, stir for 25 min at a stirring speed of 250 rpm, add the pretreated diatomite, stir for 0.7 h at a stirring speed of 350 rpm, immerse the ceramic substrate at an immersion speed of 5 mm / min for 1.5 h, dry at 60 °C for 1.7 h, and cure for 1.5 h using a blast drying oven to obtain a ceramic separator.

[0075] Comparative Example 2

[0076] The difference between Comparative Example 2 and Example 5 is that the pretreated silk fibroin nanofibers in step S2 are replaced with silk fibroin nanofibers;

[0077] A method for preparing a ceramic separator, comprising the following steps:

[0078] S1. Mix 40 g of silk fibroin nanofibers and 520 g of hydroxyapatite powder, stir for 15 min at a stirring speed of 250 rpm, add 450 g of water, 30 g of gelatin, and 4 g of sodium hexametaphosphate, ball mill for 8.5 h using a planetary ball mill at a rotational speed of 250 rpm, pour into a mold, freeze-dry at -47 °C for 38 h, sinter for 2.5 h using a high-temperature sintering furnace at a sintering temperature of 1050 °C, cool, and polish the surface to obtain a ceramic substrate;

[0079] S2. Calcinate 90 g of diatomite in a muffle furnace at 550 °C for 3.5 h, cool, add 450 g of absolute ethanol and 65 g of water, stir for 0.7 h at a stirring speed of 400 rpm, add 22 g of triethylamine, based on the total weight of triethylamine, the addition rate of triethylamine is 1.5% per minute, stir in a 25 °C constant temperature water bath for 3.5 h at a stirring speed of 250 rpm, filter, wash, and dry at 52 °C for 22 h to obtain pretreated diatomite;

[0080] S3. Mix 390 g of water, 4 g of γ-aminopropyltriethoxysilane, and 30 g of polyethylene glycol, stir for 25 min at a stirring speed of 250 rpm, add pretreated diatomaceous earth, stir for 0.7 h at a stirring speed of 350 rpm, immerse the ceramic substrate at an immersion speed of 5 mm / min for 1.5 h, dry at 60 °C for 1.7 h, and cure for 1.5 h in a forced-air drying oven to obtain a ceramic separator.

[0081] Comparative Example 3

[0082] The difference between Comparative Example 3 and Example 5 is that "diatomaceous earth" is not added;

[0083] A method for preparing a ceramic separator, comprising the following steps:

[0084] S1. Disperse 40 g of silk fibroin nanofibers in 370 g of water, stir for 25 min at a stirring speed of 300 rpm, adjust the pH value of the system to 10.7 with a sodium hydroxide solution having a concentration of 0.25 mol / L, add 14 g of epichlorohydrin, and based on the total weight of epichlorohydrin, the addition rate of epichlorohydrin is 4.5% per minute, stir in a 42 °C constant-temperature water bath for 5 h at a stirring speed of 300 rpm, filter, collect the precipitate, wash, and dry at 62 °C for 20 h to obtain pretreated silk fibroin nanofibers;

[0085] S2. Mix the pretreated silk fibroin nanofibers and 520 g of hydroxyapatite powder, stir for 15 min at a stirring speed of 250 rpm, add 450 g of water, 30 g of gelatin, and 4 g of sodium hexametaphosphate, ball-mill for 8.5 h at a rotation speed of 250 rpm using a planetary ball mill, pour into a mold, freeze-dry at -47 °C for 38 h, sinter in a high-temperature sintering furnace for 2.5 h at a sintering temperature of 1050 °C, cool, and polish the surface to obtain a ceramic substrate;

[0086] S3. Mix 390 g of water, 4 g of γ-aminopropyltriethoxysilane, and 30 g of polyethylene glycol, stir for 25 min at a stirring speed of 250 rpm, immerse the ceramic substrate at an immersion speed of 5 mm / min for 1.5 h, dry at 60 °C for 1.7 h, and cure for 1.5 h in a forced-air drying oven to obtain a ceramic separator.

[0087] Comparative Example 4

[0088] The difference between Comparative Example 4 and Example 5 is that the pretreated diatomaceous earth in step S4 is replaced with diatomaceous earth;

[0089] A method for preparing a ceramic separator, comprising the following steps:

[0090] S1. Disperse 40 g of silk fibroin nanofibers in 370 g of water, stir for 25 min at a stirring speed of 300 rpm, adjust the pH value of the system to 10.7 using a sodium hydroxide solution with a concentration of 0.25 mol / L, add 14 g of epichlorohydrin. Based on the total weight of epichlorohydrin, the addition rate of epichlorohydrin is 4.5% per minute. Stir in a 42°C constant temperature water bath for 5 h at a stirring speed of 300 rpm, filter, collect the precipitate, wash it, and dry it at 62°C for 20 h to obtain pretreated silk fibroin nanofibers;

[0091] S2. Mix the pretreated silk fibroin nanofibers with 520 g of hydroxyapatite powder, stir for 15 min at a stirring speed of 250 rpm, add 450 g of water, 30 g of gelatin, and 4 g of sodium hexametaphosphate, ball mill for 8.5 h using a planetary ball mill at a rotation speed of 250 rpm, pour it into a mold, freeze-dry at -47°C for 38 h, sinter it in a high-temperature sintering furnace for 2.5 h at a sintering temperature of 1050°C, cool it, and polish the surface to obtain a ceramic substrate;

[0092] S3. Mix 390 g of water, 4 g of γ-aminopropyltriethoxysilane, and 30 g of polyethylene glycol, stir for 25 min at a stirring speed of 250 rpm, add 90 g of diatomite, stir for 0.7 h at a stirring speed of 350 rpm, immerse the ceramic substrate at an immersion speed of 5 mm / min for 1.5 h, dry it at 60°C for 1.7 h, and cure it in a forced-air drying oven for 1.5 h to obtain a ceramic separator.

[0093] Performance Test

[0094] Membrane Flux: Test the membrane flux of the ceramic separators prepared in the above-mentioned various examples and comparative examples according to GB / T 39717-2020. The results are shown in Table 1 below.

[0095] Flux Standard Deviation: Test the flux standard deviation of the ceramic separators prepared in the above-mentioned various examples and comparative examples according to GB / T 39717-2020. The results are shown in Table 1 below.

[0096] Flux Change Rate before and after Impurity Content Change: Pour waste lubricating oil with low impurity and high impurity content into the liquid inlet container respectively; turn on the liquid inlet pump to make the waste lubricating oil pass through the ceramic separator. After stable liquid outlet, record the data. The results are shown in Table 1 below.

[0097] Calculation Formula:

[0098] J is the membrane flux;

[0099] V is the volume of waste lubricating oil passing through;

[0100] A is the effective filtration area of the ceramic separator;

[0101] t is the time.

[0102] (2)

[0103] ΔJ is the flux change rate before and after the change in impurity content;

[0104] J 1 is the waste lubricating oil flux with high impurity content;

[0105] J 0 is the waste lubricating oil flux with low impurity content;

[0106] Table 1 Performance test results

[0107]

[0108] Data analysis:

[0109] From the data of Examples 1-5 in Table 1, it can be seen that the ceramic diaphragm for waste lubricating oil separation prepared by the present invention has obvious advantages in the parameter results of "membrane flux", "flux standard deviation", and "flux change rate before and after the change in impurity content". First of all, the membrane flux can reach 181.25 (L / (m 2 ·h)), and the flux standard deviation can reach 2.85 (L / (m 2 ·h)), indicating that it maintains good uniform stability within a reasonable range of membrane flux. At the same time, the flux change rate before and after the change in impurity content can reach -5.16%, which shows that it can maintain good self-adaptability in the face of changes in impurity content, has obvious advantages in the actual application of waste lubricating oil separation, can better adapt to the treatment requirements of waste lubricating oils of different qualities, improve the separation efficiency and stability, reduce the equipment maintenance cost, extend the service life of the diaphragm, and promote the development of waste lubricating oil treatment technology.

[0110] From the data of Example 5 and Comparative Examples 1 and 2 in Table 1, it can be seen that adding silk fibroin nanofibers and activating them significantly improves the "uniform and stable" performance of the membrane flux and enhances its "self-adaptive" ability. This is mainly because silk fibroin nanofibers themselves have a large specific surface area, which can provide more active sites for the adsorption and separation of waste lubricating oil, helping to improve the separation efficiency. At the same time, silk fibroin nanofibers have a certain flexibility and strength, which can play a reinforcing role in the ceramic diaphragm, helping to maintain the structural integrity of the diaphragm when it is subjected to external forces, avoiding cracks or breakages due to brittleness, and thus maintaining stable filtration performance; then, continue to graft active groups onto the silk fibroin nanofibers, and then during the composite process with hydroxyapatite, the pore structure inside the ceramic substrate is further optimized, reducing the irregularity and clogging risk of the pores, making the flow resistance of the waste lubricating oil decrease when passing through, the membrane flux can be stabilized within a reasonable range and maintain better uniform stability, and in the face of changes in impurity content, the diaphragm can also maintain good self-adaptability by virtue of its stable structure.

[0111] From the data of Example 5 and Comparative Examples 3 and 4 in Table 1, it can be seen that adding diatomite and treating it significantly improves the "uniform and stable" performance of the membrane flux and enhances its "self-adaptive" ability. This is because diatomite itself has a rich microporous and mesoporous structure, which can serve as a molecular sieving channel. According to the size differences between impurity molecules and lubricating oil molecules, it allows lubricating oil molecules to pass through smoothly while retaining larger impurity molecules, achieving the preliminary separation of waste lubricating oil. At the same time, diatomite has good chemical stability, which can ensure the stability of the entire diaphragm system; further, grafting groups such as amino and alkyl groups onto the surface of diatomite optimizes its surface properties, enhances its affinity with non-polar components in waste lubricating oil, improves the separation selectivity, and helps to maintain the stability of the membrane flux. At the same time, the reactive active sites provided by the amino group enhance the binding force with the ceramic substrate and polyethylene glycol, optimizing the structural integrity and stability of the diaphragm, keeping the membrane flux within a reasonable range, and when the impurity content changes, through the response of its porous structure and surface properties, the diaphragm changes the effective filtration area of the pores or the surface charge properties, so as to maintain the relative stability of the membrane flux and exhibit good self-adaptability.

[0112] Those of ordinary skill in the art should understand that: the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a ceramic diaphragm for separating waste lubricating oil, characterized in that: The steps include: S1, dispersing silk protein nanofibers in water, stirring, adjusting the pH value of the system, adding epichlorohydrin, stirring in a constant temperature water bath, filtering, collecting precipitates, washing, and drying to obtain pretreated silk protein nanofibers; S2, mixing the pretreated silk protein nanofibers and hydroxyapatite powder, stirring, adding water, gelatin, and sodium hexametaphosphate, ball milling, pouring into a mold, freeze drying, sintering, cooling, and polishing the surface to obtain a ceramic substrate; S3, calcining the diatomaceous earth, cooling, adding anhydrous ethanol and water, stirring, adding triethylamine, stirring in a constant temperature water bath, filtering, washing, and drying to obtain pretreated diatomaceous earth; S4, mixing water, γ-aminopropyltriethoxysilane and polyethylene glycol, stirring, adding pretreated diatomaceous earth, stirring, immersing the ceramic substrate, drying, and curing to obtain a ceramic diaphragm for separating waste lubricating oil.

2. The method for preparing the ceramic diaphragm for separating waste lubricating oil according to claim 1, characterized in that: The weight ratio of silk protein nanofiber, epichlorohydrin, hydroxyapatite powder, gelatin, sodium hexametaphosphate, diatomaceous earth, anhydrous ethanol, triethylamine, γ-aminopropyltriethoxysilane and polyethylene glycol is 3-5:1.2-1.6:50-55:2.5-3.5:0.3-0.5:8-10:40-50:1.5-3:0.3-0.5:2-4.

3. The method for preparing the ceramic diaphragm for separating waste lubricating oil according to claim 1, characterized in that: In step S1, a sodium hydroxide solution with a concentration of 0.2-0.3 mol / L is used to adjust the pH value of the system to 10.5-11.

4. The method for preparing the ceramic diaphragm for separating waste lubricating oil according to claim 1, characterized in that: In step S1, epichlorohydrin is added at a rate of 4-5% per minute based on the total weight of epichlorohydrin.

5. The method for preparing the ceramic diaphragm for separating waste lubricating oil according to claim 1, characterized in that: In step S2, the freeze-drying temperature is -45--50°C, and the freeze-drying time is 36-40 hours.

6. The method for preparing the ceramic diaphragm for separating waste lubricating oil according to claim 1, characterized in that: In step S3, diatomaceous earth is calcined in a muffle furnace at a calcination temperature of 500-600° C. for 3-4 hours.

7. The method for preparing the ceramic diaphragm for separating waste lubricating oil according to claim 1, characterized in that: In step S3, triethylamine is added at a rate of 1-2% per minute based on the total weight of the triethylamine.

8. The method for preparing the ceramic diaphragm for separating waste lubricating oil according to claim 1, characterized in that: In step S4, the ceramic substrate is immersed at a speed of 4-6 mm / min and a dipping time of 1-2 h.

9. The method for preparing the ceramic diaphragm for separating waste lubricating oil according to claim 1, characterized in that: In step S4, the material is cured in a blast drying oven for 1-2 hours.

10. A ceramic diaphragm for separating waste lubricating oil, characterized in that: The waste lubricating oil separation ceramic diaphragm is manufactured by the preparation method of any one of claims 1 to 9.

Images