A method for regulating a single-stage microporous metal oil-water separation membrane with high permeability and high selectivity

Abstract

This invention discloses a method for controlling a single-stage microporous metal oil-water separation membrane with both high permeability and high selectivity, comprising the following steps: 1. Obtaining a phenomenological formula and empirical parameters a, b, and c through gradient experiments; 2. Deriving the minimum value of f based on the empirical parameters a, b, and c, thus obtaining the corresponding R / D; 3. Using the obtained R / D, obtaining a single-stage microporous metal oil-water separation membrane with both high permeability and high selectivity. This invention employs a structure-function integrated design for the single-stage microporous metal oil-water separation membrane, breaking the seesaw effect between high selectivity and high permeability, overcoming the flux bottleneck of nano-ceramic / micron-sized metal porous separation membranes, and proposing a phenomenological formula that provides a continuous quantitative description of the actual wetting state. The microporous membrane exhibits high strength, good mechanical durability, and no risk of coating peeling, accelerating the upgrading and optimization of metal oil-water separation membranes and providing technical support for cost reduction and efficiency improvement in industrial mixed fluid filtration.

Description

Technical Field

[0001] This invention belongs to the field of porous metal materials technology, specifically relating to a method for controlling a single-stage microporous metal oil-water separation membrane that combines high permeability and high selectivity. Background Technology

[0002] With rapid industrialization, crude oil and oily wastewater leaks are frequent, creating an urgent need for efficient and environmentally friendly oil-water separation membranes in industries such as petrochemicals, daily chemicals, biopharmaceuticals, textiles, leather, and metal processing. New membrane materials should possess high permeability (high permeability) to oil-water mixtures, and simultaneously high oil-water separation efficiency (selectivity).

[0003] On the one hand, according to Darcy's equation and its extensions, the flux of a liquid permeating a porous body is related to the pore structure; the larger the pore size and the higher the porosity, the better the "permeability." That is, the more pores per unit area, the larger the pore size, and the thinner the pore walls, the greater the fluid flux. On the other hand, numerous surface wettability studies qualitatively suggest that smaller pore sizes result in higher separation efficiency. Therefore, various nanoscale separation membranes with different pore sizes have been prepared to achieve high selectivity. This creates a trade-off effect, where permeation flux and separation accuracy are difficult to balance, limiting the application of porous metal separation membranes.

[0004] Because nanoporous metal separation membranes have very low permeation flux, many studies have adopted a "layered" approach. This involves a very thin nanoporous layer on the substrate surface to achieve high selectivity, while the substrate layer uses a large-pore, high-porosity micron-pore structure to achieve high permeability. Compared to nanoscale monolayer separation membranes, the asymmetric structure of the surface nanoporous layer and the substrate micron-pore layer in the "layered" structure can reduce transmembrane pressure, avoid deep pore blockage, and achieve higher permeation flux. Therefore, numerous studies have attempted to construct nanopores of various compositions, shapes, and sizes on porous metal substrates, such as patents with application numbers 202410525481.1, 202311152871.0, 202211183474.5, 202411041646.4, 202310757330.4, 201910439253.1, 201910737112.8, 202211589203.X, 202410862716.6, 202410985888.2, 202410735045.7, and 202410701476.1. However, the pore size of the nanoporous layer in the "layered" structure is extremely small. Currently, the smallest pore size of commercially available nanoceramic / micron-sized metal porous separation membranes can reach 50 nm, resulting in a maximum permeation flux that can only reach 70% of the theoretical flux limit, thus restricting further improvement in the permeation flux of porous metal separation membranes. Imparting high selectivity to the substrate micron-sized porous layer would break through the flux bottleneck of nanoceramic / micron-sized metal porous separation membranes. For example, patents with application numbers 202410701476.1, 202311025206.5, 202110922302.4, 202110178120.0, 202310727314.0, 202210990549.4, and 202410685233.3 prepare highly selective polymer coatings on the surface of the substrate micron-sized porous layer, enabling the single-layer microporous membrane to possess both high selectivity and high permeability. However, polymer coatings inevitably swell, deform, oxidize, degrade, corrode, or peel off during use, causing the selectivity of the membrane material to rapidly decline over time. In some cases, the separation membrane even needs to be replaced daily. The potential threat to water bodies posed by some fluorinated coatings also limits the application of this type of separation membrane.

[0005] Therefore, an integrated structure-function design is needed to break away from the existing layered approach that relies on nanoporous layers to achieve selectivity and microporous substrate layers to achieve high "permeability". By optimizing the pore structure, the microporous substrate, which originally only undertook "permeability", is endowed with high selectivity, breaking the seesaw effect between high selectivity and high "permeability", and achieving a leapfrog improvement in the performance of metal oil-water separation membranes. Summary of the Invention

[0006] The technical problem this invention aims to solve is to address the shortcomings of the prior art by providing a method for controlling a single-stage microporous metal oil-water separation membrane that combines high permeability and high selectivity. This method proposes a unique structure-function integrated microporous membrane. First, based on gradient experimental results, a phenomenological formula for the selectivity of the single-stage microporous structure for oil droplets under target operating conditions is derived. Second, based on the formula, the optimal single-stage microporous pore structure with high selectivity is derived. Finally, the optimized microstructure is achieved using the same preparation techniques and raw materials, resulting in a single-stage microporous metal oil-water separation membrane that combines high permeability and high selectivity.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for controlling a single-stage microporous metal oil-water separation membrane with both high permeability and high selectivity, characterized in that the method includes the following steps:

[0008] Step 1: Gradient experiments were conducted on the raw materials using powder rolling technology assisted by a pore-forming agent to obtain multiple microporous membranes with different R / D values, where R and D are the pore wall thickness and pore size of the microporous membrane, respectively. Then, the wetting state of each microporous membrane was measured, and the results were substituted into the phenomenological formula: Calculations were performed, where f describes the thermodynamic stability of the intermediate wetting state in the fixed system, i.e. the selectivity of the microporous membrane to prevent oil droplets from passing through, and the values ​​of empirical parameters a, b and c were obtained.

[0009] Step 2: Substitute the values ​​of the empirical parameters a, b, and c obtained in Step 1 into the phenomenological formula to calculate the R / D value corresponding to the minimum value of f under the target working condition.

[0010] Step 3: Using the same raw materials as in Step 1, the ingredients are prepared with the R / D value obtained in Step 2, and then the powder rolling technology assisted by the pore-forming agent described in Step 1 is used to prepare a single-stage microporous metal oil-water separation membrane with both high permeability and high selectivity.

[0011] Based on the classical model of surface wettability, this invention has discovered the influence of microporous structure on surface wettability in a series of intermediate wetting states and proposed a theoretical model. In the classical wettability theory, the Cassie model describes the state of complete non-wetting on a rough surface, while the Wenzel model describes the state of complete wetting. The actual wetting state on the surface is usually between the two extreme states mentioned above. These intermediate wetting states are metastable, and there is no suitable theoretical formula to describe these actual intermediate wetting states. Their main parameters are also difficult to measure experimentally, resulting in a large deviation between the existing theory and the actual wetting state, which makes it difficult to guide the optimal design and active control of the performance of oil-water separation membranes.

[0012] This invention uses the morphological parameter R / D and experimentally determines relevant parameters to establish a phenomenological relationship between the single-stage microporous structure and the selectivity for oil droplets. This enables a continuous description of the intermediate wetting state under specific working conditions and provides a simple and easy-to-implement control method and theoretical basis for the design of single-stage microporous metal oil-water separation membranes.

[0013] In addition, this invention clarifies the existence of an optimal single-level micron-pore structure. According to the second law of thermodynamics, in a system formed by oil droplets, microporous membranes, and surrounding fluid, when the system remains constant—that is, when secondary variables such as liquid composition, viscosity, flow rate, pressure on the membrane surface, membrane material composition, oil droplet type and size, external temperature and pressure, pore shape on the microporous membrane surface, microporous membrane thickness, pore depth, and the ratio of connected to closed pores remain essentially constant—the system's free energy has a minimum value. The intermediate wetting state corresponding to this minimum value is the most stable. At this point, oil droplets are least likely to penetrate the microporous membrane, and the microporous membrane exhibits the highest selectivity for oil droplets. From another perspective, the larger the R / D ratio, the more stable the Cassie-Baxter state. However, due to the large proportion of solids at the mixing interface in contact with oil droplets in the system, the underwater static oil contact angle (USCA) decreases, weakening the selectivity for oil droplets. Conversely, when R / D increases, USCA increases, but the fluid pressure that the microporous membrane can withstand decreases. With slight disturbances in fluid pressure, oil droplets will penetrate the microporous membrane, leading to local contamination of the microporous membrane and thus affecting the separation efficiency. Based on the above principle analysis, this invention believes that for a stationary system under specific operating conditions, there should be an optimal structure for a single-level microporous structure.

[0014] From the perspective of improving the permeability of membrane materials, according to Darcy's formula and its extensions, the flux of liquid permeating a porous body is related to the pore structure. The larger the pore size and the higher the porosity, the greater the flux. From the actual process of fluid permeation of membrane materials, pore size and porosity represent the percentage of the membrane surface area that the fluid can enter when it comes into contact with the membrane material surface. That is, the more pores per unit area of ​​the membrane material, the larger the pore size, and the thinner the pore wall, the greater the fluid flux. Darcy's formula uses the permeation coefficient B to characterize the pore structure of the membrane material. The factors affecting B are quite complex and difficult to calculate theoretically, such as the pore size of the membrane material surface, the pore wall thickness, the number of pores per unit area, composition, membrane thickness, pore channel tortuosity, and pore wall roughness. Therefore, its specific value is usually determined experimentally. Since the value of B is a passively measured parameter, it is not easy to achieve active control of flux and optimal design of the microstructure of the membrane material.

[0015] The morphology parameter R / D proposed in this invention can characterize both the permeability and selectivity of the microporous membrane surface. As mentioned above, under specific operating conditions, R / D serves as the main variable, allowing for quantitative and active control of the microporous membrane surface wettability. Furthermore, from the perspective of filtration flux, the parameters describing the microstructure of the membrane material in Darcy's formula and its extensions are all empirical constants, requiring experimental determination and making it difficult to achieve active flux control. As mentioned above, under specific operating conditions, R / D serves as the main variable, allowing for quantitative and active control of the microporous membrane flux. The smaller the R / D, the greater the permeation flux; conversely, the larger the R / D, the smaller the flux and the worse the permeability. Therefore, R / D becomes a bridge connecting the theories of fluid motion and surface wettability, providing a simple and easy-to-implement control method and a quantitative theoretical basis for overcoming the seesaw effect between high selectivity and high permeability, and for preparing single-stage microporous metal oil-water separation membranes with both high permeability and high selectivity.

[0016] To simplify the model and facilitate active control of the morphology, the R / D parameter ignores the influence of the internal pore tortuosity coefficient of the membrane material on the flux. This is because, under specific operating conditions, when the raw material powder, preparation technology, and membrane material thickness remain constant, the influence of the internal pore tortuosity coefficient on the flux is not significant, according to the extended Darcy formula (pressure loss coefficient). That is, under the same operating conditions, the material composition, membrane thickness, and pore tortuosity coefficient of the gradient experiment and the optimal single-level micron-pore structure in this invention do not change significantly. In this case, the morphology parameter R / D becomes the main factor affecting the flux of the microporous membrane. However, infinitely increasing R / D to improve flux is not feasible, as an excessively high R / D can lead to lower mechanical properties of the microporous membrane, potential microcracks under long-term water flow impact, and even failure to sinter due to the collapse of the porous framework during preparation. Therefore, the selection of R / D should comprehensively consider permeability, selectivity, and the mechanical strength of the membrane material.

[0017] Considering the above factors, this invention conducts gradient experiments on powder rolling technology assisted by pore-forming agents on the raw materials. Substituting the experimental results into the phenomenological formula, the values ​​of empirical parameters a, b, and c are determined to obtain the phenomenological formula for the selectivity of oil droplets to the single-level microporous structure: The microporous structure is represented by the R / D ratio of the microporous membrane surface, where R and D are the pore wall thickness and pore size of the porous titanium separation membrane, respectively. This ratio characterizes both the permeability and selectivity of the microporous membrane surface. In the phenomenological formula, the empirical parameters a, b, and c depend on factors such as the thickness, pore depth, ratio of connected to closed pores of the microporous membrane, the shape of the pores on the microporous membrane surface, the surface tension between the microporous membrane, oil droplets, and the surrounding fluid, the size of the oil droplets, and the viscosity of the surrounding fluid, all within the target operating condition. For a specific operating condition, and when the raw material powder, preparation technology, and microporous membrane thickness remain constant, these secondary variables are usually fixed or change very little. Therefore, the empirical parameters a, b, and c can be simplified to their corresponding constants. Specifically, according to the second law of thermodynamics, the oil... The droplets, membrane material, and surrounding fluid environment can be considered as a whole as an energy system. Under specific operating conditions, the type and size of the oil droplets, the composition of the membrane material, and the composition, viscosity, temperature, and pressure on the membrane surface of the surrounding fluid remain essentially unchanged and can be regarded as constants, concentrated in the empirical parameters a, b, and c. Secondly, regarding the morphological characteristics of the microporous membrane, when the raw material powder, preparation technology, and thickness of the microporous membrane remain unchanged, the shape of the pores on the surface of the microporous membrane will not change significantly, and the depth of the pores inside the microporous membrane, the ratio of connected pores to closed pores will only fluctuate within a certain range and will not significantly affect the wetting state of the microporous membrane. Therefore, under specific operating conditions, the above two types of factors can be regarded as constants and concentrated in the empirical parameters a, b, and c. At this point, the intermediate wetting state of the system is mainly controlled by the morphology parameter R / D of the microporous membrane surface. When the operating conditions change, the type and size of the oil droplets, the composition of the membrane material, and the composition, viscosity, temperature, and pressure on the membrane surface of the surrounding fluid are different; or when the raw material powder, preparation technology, and thickness of the microporous membrane change, the pore structure characteristics of the microporous membrane surface and interior change. At this time, the empirical parameters a, b, and c also change accordingly. The theoretical relationship between the empirical parameters a, b, and c and the above-mentioned influencing factors is very complex and has not yet been revealed. The method of determining the empirical parameters through gradient experiments in this invention is more convenient and accurate, and can be extended to different operating conditions and application fields to obtain the corresponding empirical parameters a, b, and c.

[0018] For intermediate wetting states that are difficult to describe theoretically, this phenomenological formula concentrates various minor variables that do not change significantly under specific operating conditions into empirical parameters a, b, and c, highlighting the main influencing parameter R / D. For the first time, it achieves a continuous quantitative description of intermediate wetting states. This phenomenological formula skips the complex principles and formula derivations of how various minor variables affect wetting states, and achieves a practical quantitative description of intermediate wetting states. It breaks the qualitative understanding that smaller pore sizes result in higher separation efficiency, and becomes the theoretical support for endowing single-stage microporous membranes with high selectivity for oil droplets.

[0019] f describes the thermodynamic stability of the intermediate wetting state in a fixed system, i.e., the selectivity of the microporous membrane to prevent oil droplets from passing through. The smaller the f value, the higher the selectivity of the microporous membrane to oil droplets, and the larger the f value, the lower the selectivity. The phenomenological formula proposed in this invention describes the wetting state of the oil-water-solid three-phase system and uses the f value to quantify the selectivity of the microporous membrane to oil droplets. The minimum value of f within the applicable range of the formula corresponds to the morphological parameter R / D, which describes the optimal selectivity that a single-stage microporous membrane can obtain when the composition of the oil-water mixture, the size of the oil droplets, the flow rate, and the temperature remain unchanged in the target working condition, and the material, thickness, and preparation technology of the microporous membrane remain unchanged, and the corresponding optimal single-stage micron pore structure.

[0020] Based on the phenomenological formula obtained in step one, this invention derives the R / D corresponding to the minimum f value. The optimal single-level microporous structure should satisfy the calculated R / D value. In the phenomenological formula of single-level microporous structure and oil droplet selectivity, the smaller the f value, the higher the microporous membrane selectivity. Under the target working conditions, when the oil-water mixture composition, oil droplet size, flow rate, and temperature remain unchanged, without changing the material, thickness, or preparation technology of the microporous membrane, the R / D corresponding to the minimum f value represents the optimal single-level microporous structure under the target working conditions, corresponding to the optimal selectivity that such microporous membranes can achieve.

[0021] Finally, the present invention uses the same raw materials as in step one, with the R / D value obtained in step two for batching, and then uses the powder rolling technology assisted by the pore-forming agent described in step one for preparation, to achieve the optimal single-level micron pore structure obtained in step two, and obtain a single-level microporous metal oil-water separation membrane with both high permeability and high selectivity.

[0022] Based on the classical model of surface wettability, this invention discovers an optimal wetting state for the selectivity of microporous membranes to oil droplets within a series of intermediate wetting states in a specific oil-water-solid three-phase system. In the phenomenological formula proposed in this invention, the minimum value of f describes this optimal state. Moreover, when the changes in minor variables are insignificant and can be considered constant, the morphology parameter R / D has a significant impact on the selectivity of the microporous membrane; fine-tuning the morphology can significantly improve the selectivity of the microporous membrane. Therefore, it is difficult to obtain the optimal single-level microporous structure through traditional trial-and-error iteration. This invention directly obtains this optimal structure through calculation, greatly accelerating the upgrading and optimization of metal oil-water separation membranes and providing simple and convenient technical support for cost reduction and efficiency improvement in industrial mixed fluid filtration.

[0023] The aforementioned method for controlling a single-stage microporous metal oil-water separation membrane with both high permeability and high selectivity is characterized in that the R / D value range in the gradient experiment described in step one is 0.59 < R / D < 1.36. To bypass the theoretical derivation of wetting states by various complex minor variables and achieve a practical description of specific working conditions, the phenomenological formula proposed in this invention has a limited applicable range. When this limited range is exceeded, the wetting state of the system formed by the oil droplets, microporous membrane, and surrounding fluid changes significantly beyond a critical value, and the phenomenological formula derived in this invention can no longer describe its wetting state. Therefore, during the determination of empirical parameters a, b, and c, the morphological parameter R / D value in the gradient experiment should all conform to the applicable range of the phenomenological formula, so that the measured empirical parameters can accurately and continuously describe each intermediate wetting state within the formula's applicable range.

[0024] The above-described method for controlling a single-stage microporous metal oil-water separation membrane that combines high permeability and high selectivity is characterized in that at least three microporous membranes with different R / D values ​​are prepared in the gradient experiment in step one. This invention ensures that the values ​​of empirical parameters a, b, and c can be obtained through subsequent calculations by controlling the number of microporous membranes with different R / D values ​​in the gradient experiment.

[0025] The above-described method for controlling a single-stage microporous metal oil-water separation membrane with both high permeability and high selectivity is characterized in that the method for detecting the wetting state in step one is as follows: 40 points are randomly selected on the surface of the microporous membrane, and the diameter of the inscribed circle of the pore and the minimum inscribed circle diameter of the surrounding pore walls are measured. The statistical average of the 40 measurements is taken as the morphological parameter of the microporous membrane. This invention ensures the accuracy of the data through controlled detection methods, guaranteeing that the final prepared single-stage microporous metal oil-water separation membrane possesses both high permeability and high selectivity.

[0026] The above-mentioned method for controlling a single-stage microporous metal oil-water separation membrane with both high permeability and high selectivity is characterized in that, during the sintering process of the pore-forming agent-assisted powder rolling technology described in steps one and three, both the upper and lower surfaces of the green sheet are fixed by pressure using smooth and flat ceramic sheets at a pressure of 0.2 MPa. This invention, by controlling the fixing method during the sintering process, limits the axial shrinkage deformation of the green sheet, reducing the pore structure deformation caused by surface shrinkage deformation of the single-stage microporous metal oil-water separation membrane.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. This invention adopts a structure-function integrated design scheme, simplifies various minor variables, clarifies the significant influence of the morphology parameter R / D on the selectivity of microporous membranes, obtains the optimal single-level micron pore structure through calculation, endows the substrate micron pore layer with high selectivity, breaks the seesaw effect between high selectivity and high permeability, overcomes the flux bottleneck of nano-ceramic / micron metal porous separation membranes, accelerates the upgrading and optimization of metal oil-water separation membranes, and provides simple and convenient technical support for cost reduction and efficiency improvement in industrial mixed fluid filtration.

[0029] 2. The phenomenological formula proposed in this invention is the first to achieve a continuous quantitative description of the intermediate wetting state. The actual wetting state is highly complex and difficult to describe theoretically due to the influence of various secondary variables, such as the thickness of the microporous membrane, pore depth, the ratio of connected to closed pores, the shape of the pores on the microporous membrane surface, the surface tension between the microporous membrane, oil droplets, and the surrounding fluid, the size of the oil droplets, and the viscosity and temperature of the surrounding fluid. This invention proposes that for specific working conditions, and when the raw material powder, preparation technology, and microporous membrane thickness remain constant, the complex influence principles and formulas of secondary variables can be skipped, and the focus can be placed on the phenomenological parameters a, b, and c. Within its applicable range, the phenomenological formula proposed in this invention quantifies the actual wetting state simply and practically, breaking the qualitative understanding that smaller pore sizes result in higher separation efficiency, and becoming the theoretical support for endowing single-stage microporous membranes with high selectivity for oil droplets.

[0030] 3. Compared with the layered multi-stage metal oil-water separation membrane, the single-stage microporous metal oil-water separation membrane has a simpler preparation process and is expected to achieve large-scale industrial application. The preparation process of the layered structure is complex and the technical cost is high, making it difficult to obtain a large-area, continuous and defect-free layered multi-stage metal oil-water separation membrane.

[0031] 4. Compared with the fragile layered structure of multi-stage metal oil-water separation membranes, the single-stage microporous metal oil-water separation membrane has higher strength and better mechanical durability. Multi-stage metal oil-water separation membranes are prone to cracking or layered structure detachment when faced with the impact of small solid particles in the mixed fluid, thus causing the oil-water separation efficiency to decrease rapidly.

[0032] 5. Various polymer-coated separation membranes used in this invention are prone to swelling, deformation, oxidative degradation, coating corrosion, or peeling during use. In contrast, single-stage microporous metal oil-water separation membranes exhibit higher strength and superior mechanical durability. They are less susceptible to cracking or porous structure detachment when subjected to impacts from small solid particles in the mixed fluid, eliminating the risks of swelling, deformation, oxidative degradation, coating corrosion, or peeling. They are widely applicable to industrial oily wastewater with high temperature, high salinity, strong acids, strong alkalis, and complex compositions. Furthermore, single-stage microporous metal oil-water separation membranes offer significant advantages in biopharmaceuticals and daily chemical industries, while the potential threat posed by existing fluorinated coatings to water bodies limits the application of polymer-coated separation membranes.

[0033] 6. This invention directly obtains the optimal structure through calculation, which greatly accelerates the upgrading and optimization of metal oil-water separation membranes, provides simple and convenient technical support for cost reduction and efficiency improvement in industrial mixed fluid filtration, and solves the problem that it is difficult to obtain the optimal single-stage micron pore structure through traditional trial and error iteration.

[0034] 7. The method of determining empirical parameters through gradient experiments in this invention is convenient and accurate, and can be extended to different working conditions and application fields.

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0036] Figure 1 This invention and the prior art present the design concept for a single-stage microporous metal oil-water separation membrane.

[0037] Figure 2 This is a SEM image of sample 1 obtained in Example 1 of the present invention.

[0038] Figure 3 This is a SEM image of sample 2 obtained in Example 1 of the present invention.

[0039] Figure 4 This is a SEM image of sample 3 obtained in Example 1 of the present invention.

[0040] Figure 5 This is a SEM image of sample 4 obtained in Example 1 of the present invention.

[0041] Figure 6 This is a tensile property diagram of sample 4 obtained in Example 1 of the present invention.

[0042] Figure 7 This is a diagram showing the bending performance of sample 4 obtained in Example 1 of the present invention.

[0043] Figure 8 The images show the physical samples of sample 4 obtained in Example 1 of this invention before and after the bending performance test. Detailed Implementation

[0044] Figure 1 This invention and the prior art represent the design concept of a single-stage microporous metal oil-water separation membrane. Figure 1 Figure a on the left shows that, according to existing technology, smaller pore sizes lead to higher separation efficiency. Therefore, various nanoscale separation membranes have been prepared to achieve high selectivity. However, this creates a seesaw effect where it is difficult to balance permeation flux and separation accuracy, limiting the application of porous metal separation membranes. Figure 1Figure b in the middle shows that existing technologies believe a layered approach is used to achieve high selectivity through a very thin layer of nanoporous structure on the substrate surface, while the substrate layer uses a large-pore, high-porosity microporous structure to achieve high permeability. This very thin nanoporous structure is usually achieved through a polymer coating. However, polymer coatings inevitably swell, deform, oxidize, degrade, corrode, or peel off during use, causing the selectivity of the membrane material to rapidly decline over time. In some cases, the separation membrane even needs to be replaced daily. Figure 1 Figure c on the right shows that this invention breaks away from the existing layered approach of relying on nanoporous layers to achieve selectivity and microporous layers on the substrate to achieve high permeability. By optimizing the pore structure, it endows the microporous substrate, which originally only served permeability, with high selectivity, thus overcoming the seesaw effect between high selectivity and high permeability and achieving a leapfrog improvement in the performance of metal oil-water separation membranes.

[0045] Example 1

[0046] In this implementation, for the target working conditions, a high-temperature resistant and corrosion-resistant porous titanium metal oil-water separation membrane is specifically required. The existing preparation process is powder rolling technology assisted by a pore-forming agent, and the raw materials are titanium powder with a particle size of 40μm to 45μm and NH3HCO3 pore-forming agent with a particle size of 45μm to 58μm.

[0047] This embodiment includes the following steps:

[0048] Step 1: A gradient experiment was conducted using pore-forming agent-assisted powder rolling technology to mix titanium powder with a particle size of 40μm to 45μm and NH3HCO3 pore-forming agent with a particle size of 45μm to 58μm. The details are as follows:

[0049] (1) Gradient Experiment 1:

[0050] The design gradient experiment 1 had an R / D ratio of 0.8. Therefore, based on previous experience, 55% titanium powder and 45% pore-forming agent were uniformly mixed, and the mixture was powder rolled to obtain a 0.8 mm thick blank sheet. Then, smooth and flat ceramic sheets were used to fix both sides of the blank sheet under a pressure of 0.2 MPa, followed by vacuum sintering at 850℃ for 2 hours, with a vacuum degree not exceeding 9.0 × 10⁻⁶. -2 Pa, microporous membrane sample 1 was obtained;

[0051] Forty points were randomly selected on the surface of sample 1, and the diameter of the inscribed circle of the aperture and the minimum inscribed circle diameter of the surrounding aperture wall were measured. The statistical average of the 40 measurements was then obtained. 49.9μm The diameter is 61.9 μm, and the morphology coefficient R / D of sample 1 was measured to be 0.81. Figure 2As shown, the morphology coefficients of gradient experiment one satisfy the applicable range of the phenomenological formula, and the empirical parameters a, b, and c measured accordingly can accurately and continuously describe each intermediate wetting state.

[0052] Sample 1 was ultrasonically cleaned in acetone, ethanol, methanol and deionized water for 5 min to 10 min respectively. After cleaning, sample 1 was always placed in still deionized water to eliminate the influence of air impurity adsorption. The test showed that the wetting state of the separation membrane conformed to the application range of the phenomenological formula, and it was superhydrophilic / underwater superoleophobic. Its underwater oil contact angle (oil phase is dichloromethane) was 143°±0.25°, f was 0.30, and porosity was 54.9%.

[0053] (2) Gradient Experiment 2:

[0054] The design of gradient experiment two had an R / D ratio of 1.0. Therefore, based on previous experience, 70% titanium powder and 30% pore-forming agent were uniformly mixed, and the mixture was powder rolled to obtain a 0.8 mm thick blank sheet. Then, smooth and flat ceramic sheets were used to fix both sides of the blank sheet under a pressure of 0.2 MPa, followed by vacuum sintering at 850℃ for 2 hours, with a vacuum degree not exceeding 9.0 × 10⁻⁶. -2 Pa, yielding microporous membrane sample 2;

[0055] Forty points were randomly selected on the surface of sample 2, and the diameter of the inscribed circle of the aperture and the minimum inscribed circle diameter of the surrounding aperture wall were measured. The statistical average of the 40 measurements was then obtained. 49.9μm The diameter is 50.4 μm, and the morphology coefficient R / D of sample 2 was measured to be 1.02. Figure 3 As shown, the morphology coefficients of gradient experiment 2 satisfy the applicable range of the phenomenological formula, and the empirical parameters a, b, and c measured accordingly can accurately and continuously describe each intermediate wetting state.

[0056] Sample 2 was ultrasonically cleaned in acetone, ethanol, methanol and deionized water for 5 min to 10 min respectively. After cleaning, sample 2 was always placed in still deionized water to eliminate the influence of air impurity adsorption. The test showed that the wetting state of the separation membrane conformed to the application range of the phenomenological formula, and it was superhydrophilic / underwater superoleophobic. Its underwater oil contact angle (oil phase is dichloromethane) was 150°±0.25°, f was 0.21, and porosity was 45%.

[0057] (3) Gradient Experiment 3

[0058] The design of gradient experiment 3 has an R / D ratio of 1.2. Therefore, based on previous experience, 60% by mass of titanium powder and 40% by mass of pore-forming agent are uniformly mixed. The mixture is then powder rolled to obtain a 0.8 mm thick green sheet. Both sides of the green sheet are then fixed with smooth, flat ceramic sheets under a pressure of 0.2 MPa and vacuum sintered at 850℃ for 2 hours, with a vacuum degree not exceeding 9.0 × 10⁻⁶. -2 Pa, yielding microporous membrane sample 3;

[0059] Forty points were randomly selected on the surface of sample 3, and the diameter of the inscribed circle of the aperture and the minimum inscribed circle diameter of the surrounding aperture wall were measured. The statistical average of the 40 measurements was then obtained. 57.7μm The diameter is 44.9 μm, and the morphology coefficient R / D of sample 3 was measured to be 1.285. Figure 4 As shown, the morphology coefficients of gradient experiment three satisfy the applicable range of the phenomenological formula, and the empirical parameters a, b, and c measured accordingly can accurately and continuously describe each intermediate wetting state.

[0060] Sample 3 was ultrasonically cleaned in acetone, ethanol, methanol and deionized water for 5 min to 10 min respectively. After cleaning, sample 3 was always placed in still deionized water to eliminate the influence of air impurity adsorption. The test showed that the wetting state of the separation membrane conformed to the application range of the phenomenological formula, and it was superhydrophilic / underwater superoleophobic. Its underwater oil contact angle (oil phase is dichloromethane) was 123.5°±0.25°, f was 0.68, and porosity was 42.8%.

[0061] In summary, the test results of each gradient experiment are shown in Table 1.

[0062] Table 1

[0063] R / D f Porosity / % Gradient Experiment 1 0.81 0.30 54.9 Gradient Experiment 2 1.02 0.21 45.0 Gradient Experiment 3 1.285 0.68 42.8

[0064] From the perspective of permeability, the smaller the R / D ratio, the larger the pore size on the membrane surface, the thinner the pore walls, and the more pores per unit area, the greater the membrane permeation flux, the higher the porosity, and the better the permeability.

[0065] From the perspective of selectivity, the above results show that there is no linear relationship between the morphology coefficient R / D and the parameter f describing the permeability of the separation membrane, but rather the phenomenological formula proposed in this invention. Among them, the sample in gradient experiment 2 has the smallest f value, the largest underwater oil contact angle, and the best selectivity for non-permeable oil droplets. The sample in gradient experiment 3 has the largest f value, the smallest underwater oil contact angle, and the worst selectivity for non-permeable oil droplets.

[0066] Substituting the test results of the above gradient experiment into the phenomenological formula: Calculations yielded a = 4.7, b = -9.0, and c = 4.5.

[0067] Step 2: Substitute the values ​​of the empirical parameters a, b, and c obtained in Step 1 into the phenomenological formula to perform calculations, and obtain... When the first derivative equals 0, the corresponding f = 0.19 is the minimum value in the entire applicable range. The R / D = 0.96 corresponding to the minimum value of f under the target working condition is obtained. When R / D = 0.96, f reaches its minimum value. At this time, the actual wetting state of the microporous membrane is optimal for the selectivity of oil droplets. R / D = 0.96 represents the optimal single-level microporous structure under the target working condition. The gradient experiment results show that when the changes of each minor variable are not significant and can be regarded as constant, the influence of the morphology parameter R / D on f is very significant. Fine adjustment of R / D can significantly improve the selectivity of the microporous membrane.

[0068] Step 3: Using the same raw materials as in Step 1, and with an R / D ratio of 0.96 obtained in Step 2, the mixture is prepared using the powder rolling technique assisted by the pore-forming agent described in Step 1. A 0.8 mm thick green sheet is obtained through powder rolling. Then, both sides of the green sheet are fixed with smooth, flat ceramic sheets under a pressure of 0.2 MPa and vacuum sintered at 850℃ for 2 hours, with a vacuum degree not exceeding 9.0 × 10⁻⁶. -2 Pa, yielding microporous membrane sample 4.

[0069] Forty points were randomly selected on the surface of sample 4, and the diameter of the inscribed circle of the hole and the minimum inscribed circle diameter of the surrounding hole wall were measured. The statistical average of the 40 measurements was taken to obtain the result. 58.6μm The thickness is 60.7 μm, and the morphology coefficient R / D of sample 4 was measured to be 0.97. Figure 5 As shown, the morphology coefficients satisfy the applicable range of the phenomenological formula, and the empirical parameters a, b, and c measured accordingly can accurately and continuously describe each intermediate wetting state.

[0070] Sample 4 was ultrasonically cleaned sequentially in acetone, ethanol, methanol, and deionized water for 5-10 minutes each. After cleaning, sample 4 was always placed in still deionized water to eliminate the influence of air impurity adsorption. The test results showed that the wetting state of the separation membrane conformed to the application range of the phenomenological formula, exhibiting superhydrophilic / underwater superoleophobic properties. Its underwater oil contact angle (oil phase is dichloromethane) was 151.5°±0.25°, f was 0.18, and the porosity was 52.1%.

[0071] Sample 4 was subjected to mechanical durability testing, see Figure 6 , Figure 7 and Figure 8 , Figure 6The top left image shows sample 4 undergoing a tensile test, and the bottom image shows the shape of sample 4 undergoing the tensile test. Figure 7 The image in the lower right corner shows sample 4 undergoing a bending performance test. Figure 8 The upper middle side shows sample 4 before the bending performance test, and the lower side shows sample 4 after the bending performance test. Figure 6 and Figure 7 As can be seen from the results, the tensile strength and flexural strength can reach up to 135.7 MPa and 66.4 MPa, respectively, with very small corresponding strains. The results are shown in Table 2. The single-stage microporous metal oil-water separation membrane of sample 4 has higher strength, better mechanical durability, and is not easily deformed. In contrast, the fragile layered structure of the surface of the multi-stage metal oil-water separation membrane in the prior art is prone to cracking or delamination when faced with the impact of small solid particles in the mixed fluid, resulting in a rapid decline in oil-water separation efficiency. Moreover, various polymer-coated separation membranes are prone to swelling and deformation during use, which leads to changes in surface morphology and affects wettability and separation efficiency. It has been reported that the deformation of superhydrophilic polymer sponge has reached 55% at 0.2 MPa.

[0072] Table 2

[0073] Strength / MPa strain / % Tensile test 135.7 1.8 Bending test 66.4 6.0

[0074] To ensure that the minor variables (composition, thickness, pore depth, ratio of connected to closed pores, and shape of pores on the microporous membrane surface, etc.) do not change significantly, the raw material powder used in each gradient experiment and verification experiment in this embodiment is the same powder from the same batch, the microporous membrane thickness is 0.8mm±0.02mm, the preparation process such as rolling speed, roll gap, hopper powder feeding, vacuum degree and sintering regime are all unchanged, and the tests are conducted in the same test environment and on the same equipment. The test conditions such as oil droplet composition, oil droplet size, deionized water composition, liquid viscosity, fluid temperature and pressure are all the same, and the samples are always placed in still deionized water after washing to eliminate the influence of air impurity adsorption.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for regulating a single-stage microporous metal oil-water separation membrane with high permeability and high selectivity, characterized in that, The method comprises the following steps: Step one, gradient experiment is carried out on raw materials by using powder rolling technology with pore-forming agent, and a plurality of microporous membranes with different R / D values are obtained, wherein R and D are the pore wall thickness and pore size of the microporous membrane respectively, then the plurality of microporous membranes are respectively subjected to wet state detection, and then the detection results are substituted into the phenomenological formula: The calculation is carried out, wherein f describes the thermodynamic stability of the intermediate wet state in the fixed system, that is, the selectivity of the microporous membrane to the oil droplets, and the values of the empirical parameters a, b and c are obtained; Step two, according to the values of the empirical parameters a, b and c obtained in step one, substituting into the phenomenological formula to calculate the R / D value corresponding to the minimum f value under the target working condition; Step three, using the same raw materials as in step one, the R / D value obtained in step two is used for batching, and then the powder rolling technology assisted by the pore forming agent described in step one is used for preparation, to obtain a single-stage microporous metal oil-water separation membrane with high permeability and high selectivity.

2. The method according to claim 1, wherein the single-stage microporous metal oil-water separation membrane with high permeability and high selectivity is characterized in that, The R / D value in the gradient experiment in step one is in the range of 0.59 3. The method of claim 1, wherein the single-stage microporous metal oil-water separation membrane has high permeability and high selectivity. In step one, at least three microporous membranes with different R / D values are prepared in the gradient experiment.

4. The method of claim 1, wherein the single-stage microporous metal oil-water separation membrane has high permeability and high selectivity. The method for detecting the wetting state in step one is: randomly selecting 40 point positions on the surface of the microporous membrane, measuring the diameter of the inscribed circle of the pore size and the minimum diameter of the inscribed circle of the peripheral pore wall, and taking the statistical average of the above 40 measurement values as the morphology parameter of the microporous membrane.

5. The method of claim 1, wherein the single-stage microporous metal oil-water separation membrane has high permeability and high selectivity. In the sintering process of the powder rolling technology assisted by the pore forming agent in step one and step three, smooth ceramic sheets are used to press and fix the upper and lower surfaces of the blank sheet, and the pressure is 0.2 MPa.

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