Coalescence-selective filtration integrated oily wastewater treatment device and method based on wettability gradient

Abstract

The invention relates to a coalescence-selective filtration integrated oily wastewater treatment device and method based on wettability gradient, a separation device comprises a vertical coalescence channel, a horizontal oil channel and a horizontal water channel, a one-inlet two-outlet three-dimensional flow channel integrated structure is adopted, demulsification and separation processes are coupled in single equipment, and the equipment volume is reduced by 50%; oil-water spontaneous separation is achieved through the gravity-capillary force-wetting gradient triple coupling effect, external power is not needed, the system pressure drop benefit is smaller than 10 kPa through the wetting gradient design, energy loss is reduced, the oil content of outlet water is smaller than 5 mg / L and is superior to the GB31570-2015 standard, and the oil recovery rate is larger than 99%; a intractable emulsion containing a surfactant can be treated, and the limitation of a traditional chemical demulsifier is broken through; the invention provides a structure-function integrated design normal form, and provides a technical path for the development of compact separation equipment through geometric parameter optimization and extreme wettability material matching.

Description

Technical Field

[0001] The present invention relates to the technical field of special wettability oil-water separation devices, and in particular to a wettability gradient-based coalescence-selective filtration integrated oily wastewater treatment device and method. Background Art

[0002] Oily wastewater comes from a wide range of sources, primarily concentrated in the catering, food processing, petrochemical, metalworking, textile printing and dyeing, and leather industries. Discharging untreated oily wastewater not only poses serious environmental risks but also wastes oil and water resources. Traditional oily wastewater treatment processes primarily include gravity sedimentation, flotation, membrane separation, adsorption, biochemical separation, and chemical coagulation. These separation methods all have drawbacks. Oil droplets in oil-in-water emulsions form a kinetically stable system due to the synergistic effects of surface electrostatic repulsion, steric hindrance, and short-range hydration. Traditional demulsification techniques (such as chemical demulsification and centrifugal separation) struggle to destabilize this system. Specifically, these demulsification techniques include small oil droplet size (<10 μm) and low droplet coalescence efficiency (<60%). This is particularly true for stubborn surfactant-containing emulsions (such as Span 80-stabilized emulsions), with effluent oil concentrations typically exceeding 20 mg / L. Traditional coalescing materials (such as polypropylene fibers) are unable to disrupt the interfacial stabilization mechanism of micron-sized oil droplets due to their limited wettability. Existing technologies rely on the step-by-step operation of demulsifiers and separators, resulting in equipment redundancy, extended processes, and multiple energy conversion losses. Specifically, the step-by-step process requires multi-stage pumping, the traditional device has a high pressure drop, requires additional power drive, and increases operating costs; the equipment occupies a large area and is difficult to adapt to the needs of compact industrial scenarios.

[0003] For example, the aqueous oil removal device disclosed in patent CN202420310945.2 utilizes a series process consisting of a filter, a coalescer (containing an oleophilic coalescing filter element and a partitioning chamber), and a liquid separator. This process is said to be able to control the oil content of the treated aqueous phase and the water content of the recovered oil phase to below 15 ppm. However, current oil-in-water emulsion treatment technology has significant system limitations. Conventional oleophilic coalescing filters are inefficient at breaking up stubborn emulsions containing surfactants (such as Span 80 and SDS), particularly failing to overcome the interfacial stabilization mechanism of 10-50 μm micron oil droplets. This makes it difficult to maintain the effluent oil content below the 5 ppm emission / reuse standard. Its step-by-step process design leads to equipment redundancy, excessive pressure drop, and energy consumption. Furthermore, the lack of quantitative design tools to optimize coalescing time and equipment parameters makes it difficult to adapt to compactness requirements. The limited functionality of the materials leads to easy clogging and short lifespan of the filter elements, necessitating the addition of water-removing coalescing filters and an over-reliance on chemical demulsifiers, increasing maintenance costs and the risk of secondary contamination. The fundamental reason is that the interfacial stabilization mechanism of micron oil droplets has not been effectively overcome, and the lack of quantitative design tools has led to the inability to accurately optimize the agglomeration process and equipment, exacerbating the contradiction between equipment redundancy and compactness requirements.

[0004] For another example, patent CN202322946362.7 discloses an oil-water separation device, which is connected to an inlet pipe on the left side of the main tank body. The inlet pipe is used in combination with a spoiler to prevent the oil-water mixture from impacting the liquid surface when entering the tank body. A coalescer is installed inside the main tank body. After the oil-water mixture enters the main tank body, it first enters the coalescer through the growth of the liquid surface, and when passing through the coalescer from the inside to the outside, the coalescer can capture and gather water droplets mixed in the oil to produce larger water droplets. When the oil-water mixture enters the coalescer, since the density of water is greater than the density of oil, the water will naturally settle downward to form a water layer. In this process, the water droplets will be captured and gathered together to form larger water droplets, and since the density of water is greater than the density of oil, it is convenient to separate and stratify from the oil. The separated oil overflows into the oil drain trough as the liquid surface grows, and is then discharged from the oil drain port. The separated water enters the drainage trough and is then discharged from the drain port, effectively performing oil-water separation. The current coalescer device has the following technical bottlenecks: its working principle is based on the oil-water mixture penetrating the coalescing medium from the inside out. However, this design has three core limitations: 1) Insufficient adaptability of the separation mechanism - gravity separation is more suitable for oil-in-water emulsions (such as crude oil dehydration), but the treatment efficiency of water-in-oil emulsions (such as industrial oily wastewater) is significantly reduced, especially for micron-sized emulsified oil droplets (oil droplet size <50μm) and stubborn emulsions containing surfactants (such as Span80 / SDS system). It is completely ineffective because the oil droplets lack sufficient driving force for floating; 2) Structural optimization lacks theoretical support - the equipment separation efficiency is limited by the passive matching of the fluid residence time and the pore size of the coalescing medium. The performance defects need to be compensated by increasing the tank volume, resulting in significant redundant design of the equipment and a floor space requirement that exceeds 30% of the requirements of compact industrial scenarios; 3) There are inherent defects in the functional design - the coalescing medium relies only on a single lipophilic surface and does not establish a synergistic mechanism of wettability gradient and flow field enhancement. When treating high-viscosity oil products, the medium is more prone to medium blockage and needs to be frequently cleaned or replaced.

[0005] Therefore, developing a technology that has small oil droplet size, high stability, low operating cost, simple equipment and strong treatment capacity for emulsified oily wastewater is a technical problem that needs to be solved urgently. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the present invention provides an integrated oily wastewater treatment device and method based on wettability gradient coalescence and selective filtration. The vertical coalescence channel, horizontal oil channel, and horizontal water channel in the treatment device adopt a one-inlet and two-outlet three-dimensional flow channel integrated structure. The wetting gradient field of the vertical channel and the selective filtration of the horizontal channel work synergistically to solve the "demulsification-separation" step-by-step process problem; by setting a specific gradient wettability medium filling ratio and channel geometric parameters, the "wetting gradient force drive-flow field synergy" model is enhanced; the oil-water separation method defined by the present invention is based on a wetting gradient force-driven demulsification-separation coupling process, and is suitable for stubborn emulsions containing surfactants.

[0007] This invention successfully addresses the emulsion stability challenge by mathematically quantifying the time required for oil droplets to coalesce from an initial particle size to a target particle size. This model, for the first time, accurately correlates separation efficiency η ≥ 99.6% with device geometric parameters, replacing the traditional empirically driven trial-and-error design model. Based on this model, an integrated "coalescence-selective filtration" device was designed: A three-dimensional flow channel structure with a single inlet branching into two independent flow channels (one inlet, two outlets) integrates the vertical coalescence channel with the horizontal oil channel and horizontal water channel into a single device. Oil droplets are driven to migrate and coalesce directional-ly through a wetting gradient medium, and synchronized oil-water separation is achieved using super-hydrophilic underwater super-oleophobic quartz sand (horizontal water channel) and super-hydrophobic super-oleophilic quartz sand (horizontal oil channel). This device completely breaks through the limitations of traditional step-by-step processes, reducing the device volume by over 50% compared to traditional designs, lowering energy consumption and significantly improving its adaptability to compact industrial scenarios.

[0008] Specifically, the present invention provides an integrated coalescence-selective filtration oily wastewater treatment device based on wettability gradient, including a vertical coalescence channel, a horizontal oil channel, and a horizontal water channel, and adopts a one-inlet and two-outlet three-dimensional flow channel integrated structure. The process of completing the three steps of the demulsification tank, coalescer, and separator is integrated into a single device. The collaborative design of the vertical coalescence channel and the horizontal oil channel and horizontal water channel enables the demulsification-separation process to be completed synchronously. The present invention realizes the dynamic coupling of the two through the composite flow field design of vertical coalescence channel + horizontal dual channel. The triple coupling of gravity-capillary force-wetness gradient realizes energy self-supply and achieves separation with zero external power.

[0009] "Zero external power" specifically means that there is no active driving force in the separation process. The core steps of oil-water separation (demulsification, coalescence, and stratification) rely entirely on triple coupling, without the need for additional mechanical or chemical energy input. The density difference drives the oil to float and the gravity to sediment underwater. Extreme wettability materials (such as super-hydrophilic underwater super-oleophobic quartz sand) selectively adsorb water through the capillary effect. The asymmetric surface energy field (super-hydrophilic underwater super-oleophobic + super-hydrophobic super-oleophilic area) generates a directional driving force, and the wetting gradient force that drives the migration and coalescence of oil droplets can achieve oil-water separation by demulsification, coalescence, and stratification.

[0010] The vertical coalescence channel is filled with quartz sand of 40 to 120 mesh; the quartz sand is a gradient filled with superhydrophilic underwater superoleophobic quartz sand and superhydrophobic superoleophilic quartz sand in a volume ratio of 2:1 to 1:2. An asymmetric surface energy field is constructed, and the directional migration of oil droplets is driven by the wettability gradient force. This unbalanced force not only enhances the demulsification ability of the coalescer but also reduces head loss to promote the gradual coalescence and separation of oil droplets. Superhydrophilic underwater superoleophobic quartz sand can destabilize oil droplets and promote their detachment, reducing clogging, but too high a ratio can easily reduce coalescence efficiency. Superhydrophobic superoleophilic quartz sand preferentially adsorbs oil droplets, promoting their adhesion and coalescence, but may increase the risk of clogging in the coalescence bed. When superhydrophilic underwater superoleophobic quartz sand and superhydrophobic superoleophilic quartz sand are packed in a gradient volume ratio of 2:1 to 1:2, the wetting forces at the wettability interface enhance the probability of oil droplet coalescence, causing oil droplets to move away from the superhydrophilic interface and toward the superhydrophobic interface, significantly improving coalescence efficiency. Furthermore, the mixed design of superhydrophilic underwater superoleophobic quartz sand and superhydrophobic superoleophilic quartz sand plays an important role in reducing bed pressure drop. The superhydrophilic underwater superoleophobic quartz sand forms a continuous water film by adsorbing water molecules, while the superhydrophobic superoleophilic quartz sand forms a continuous oil film by adsorbing oil droplets. This dual-membrane structure effectively avoids the problem of pore blockage caused by liquid bridging in a single coalescing bed. The flow resistance of the continuous water phase is significantly reduced when passing through the water film on the surface of the superhydrophilic underwater superoleophobic quartz sand, thereby reducing the bed pressure drop.

[0011] At the same time, the wetting force generated by the wettability gradient between the super-hydrophilic underwater super-oleophobic quartz sand and the super-hydrophobic super-oleophilic quartz sand further promotes the migration of oil droplets to the super-hydrophobic super-oleophilic quartz sand surface, significantly improving the coalescence efficiency of oil droplets. This wetting force generated by the wettability gradient causes oil droplets in the liquid phase to move away from the super-hydrophilic interface and toward the super-hydrophobic interface, significantly increasing the probability of oil droplet wetting and coalescence.

[0012] Furthermore, the unbalanced force of the constructed asymmetric surface energy field combined with the laminar shear force of 0.1~0.5m / h in the vertical coalescence channel causes the oil droplets to undergo an "adsorption-collision-fusion" chain reaction, with the particle size increasing from 1-50μm to >500μm, and the demulsification efficiency exceeding 98%.

[0013] The horizontal oil and water channels have an aspect ratio of 4:1 to 3:1. The cross-sectional areas of both channels are equal, ensuring balanced flow. Design considerations: When the aspect ratio is greater than 4:1 to 3:1, the contact time between oil and water in the channel is prolonged; when the aspect ratio is less than 4:1 to 3:1, cumulative pressure drop leads to reduced flow.

[0014] Furthermore, the horizontal oil channel is filled with 40-120 mesh super-hydrophobic and super-oleophilic quartz sand, forming a low-adhesion oil film with a rolling angle of less than 5° and an oil recovery rate of >99%. The horizontal water channel is filled with 40-120 mesh super-hydrophilic underwater super-oleophobic quartz sand, which repels oil droplets through the hydration layer, achieves a contact angle of >150°, and an oil content of <5 mg / L in the effluent water. The gradient distribution of the super-hydrophobic and super-oleophilic quartz sand and the super-hydrophilic underwater super-oleophobic quartz sand creates a surface energy difference, generating an unbalanced force that drives the directional migration of oil droplets, i.e., a wetting gradient force drive.

[0015] Furthermore, the preparation steps of super hydrophilic underwater super oleophobic quartz sand are as follows: Step S1: Pour the piranha solution into a beaker containing quartz sand and react for 1.5-2.5 hours. Wash the quartz sand with deionized water and anhydrous ethanol three times respectively. Dry the washed quartz sand to obtain activated quartz sand. Step S2: adding anhydrous ethanol and ammonium hydroxide to ethyl orthosilicate, heating and stirring for 80 to 100 minutes; cooling to room temperature, adding the activated quartz sand prepared in step S1 to the cooled sol, stirring and mixing, washing the quartz sand with deionized water three times, and drying the washed quartz sand at 75 to 85° C. for 10 to 12 hours to obtain super-hydrophilic underwater super-oleophobic quartz sand.

[0016] Furthermore, step S1: slowly pouring the piranha solution into a beaker containing 190-210g of quartz sand (QS) and reacting it for 1.5-2.5 hours, washing the quartz sand with 500mL of deionized water and 500mL of anhydrous ethanol three times, each time for 10-20 minutes, and drying the washed quartz sand at 55-65°C for 5-7 hours to obtain activated quartz sand; the piranha solution is an acidic piranha solution, which is a mixture of 96%-98% concentrated sulfuric acid and 30% hydrogen peroxide in a volume ratio of 3:1.

[0017] Step S2: 90 wt.% anhydrous ethanol and 4 wt.% ammonium hydroxide (NH4OH) are slowly added to 6 wt.% ethyl orthosilicate, heated and stirred in a water bath at 65-75 ° C for 80-100 min, with a stirring rate of 400-600 rpm to ensure that TEOS is completely hydrolyzed to prepare a sol, and the sol is cooled to room temperature. 190-210 g of activated quartz sand prepared in step S1 is added to the cooled sol and stirred for 9-11 h; the quartz sand is washed with 500 mL of deionized water 3 times, each time for 10-20 min, and the washed quartz sand is dried at 75-85 ° C for 10-12 h to remove water and organic matter in the gel to obtain super hydrophilic underwater super oleophobic quartz sand.

[0018] Furthermore, the preparation steps of super hydrophobic and super oleophilic quartz sand are as follows: Superhydrophilic underwater superoleophobic quartz sand and a silane coupling agent were dispersed in n-heptane and stirred at 75-85°C for 9-10 hours. Then, the solution was centrifuged, the solid was collected and washed three times with 500-600 mL of n-heptane, and finally vacuum dried for 11-12 hours to obtain superhydrophobic and superoleophilic quartz sand.

[0019] Furthermore, 190–200 g of superhydrophilic underwater superoleophobic quartz sand and 3–5 mL of a silane coupling agent were dispersed in 190–210 mL of n-heptane and stirred at 75–85°C for 9–10 hours. The solution was then centrifuged, and the solids were collected and washed three times with 500–600 mL of n-heptane for 10–20 minutes each. Finally, the solids were vacuum-dried at 75–85°C for 11–12 hours to obtain the superhydrophobic and superoleophilic quartz sand.

[0020] Furthermore, the silane coupling agent is 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS).

[0021] Furthermore, the hydraulic retention time of oily wastewater in the vertical coalescence channel is: ; in: t is the hydraulic retention time of oily wastewater in the vertical coalescence channel, s; D 0 is the oil droplet size before coalescence, m; D is the oil droplet size after coalescence, m; k is the aggregation coefficient; m is the viscosity of the oil-water emulsion, Pa·s; c O is the surface tension of the oil, mN / m; i O is the static contact angle of oil on the superoleophobic quartz sand surface under superhydrophilic water, °; e is the porosity of quartz sand filling in horizontal oil channels and horizontal water channels, °; d O is the equivalent particle size of quartz sand in the horizontal oil channel, m; Furthermore, the quartz sand filling lengths in the horizontal oil channel and the horizontal water channel of the oil-water separation device are respectively: ; ; in: L O is the quartz sand filling length in the horizontal oil channel, m; L W is the filling length of quartz sand in the horizontal water channel, m; c O is the surface tension of the oil, mN / m; c W is the surface tension of water, mN / m; i O is the static contact angle of oil on the superoleophobic quartz sand surface under superhydrophilic water, °; i W is the static contact angle of water on the superhydrophobic and superoleophilic quartz sand surface, °; e is the porosity of the quartz sand filling in the horizontal oil channel and the horizontal water channel; α is the shape coefficient of quartz sand; d O is the equivalent particle size of quartz sand in the horizontal oil channel, m; d W is the equivalent particle size of quartz sand in the horizontal water channel, m; m O is the viscosity of diesel, mPa·s; m W is the viscosity of water, mPa·s; v O is the superficial velocity of oil in the horizontal oil channel, m / s; v W is the apparent velocity of water in the horizontal water channel, m / s.

[0022] The present invention also provides a method for separating oil and water using the aforementioned wettability gradient-based coalescence-selective filtration integrated oil-water separation device, comprising the following steps: The oily wastewater enters the vertical coalescence channel from the feed port, where the oil droplets coalesce under the wettability gradient formed by the super-hydrophilic underwater super-oleophobic quartz sand and the super-hydrophobic super-oleophilic quartz sand, and then enter the middle chamber. After the oily wastewater in the middle chamber flows into the horizontal oil channel, the water is intercepted by the capillary force of the superhydrophobic and superoleophilic quartz sand, and the oil flows out from the oil outlet after passing through the horizontal oil channel. The outflowing oil is recycled. After the oily wastewater in the middle chamber flows into the horizontal water channel, the oil is intercepted by the capillary force of the superhydrophilic underwater superoleophobic quartz sand. The water then flows out of the outlet after passing through the horizontal water channel; the oil content of the outlet water is <5 mg / L.

[0023] Compared with the prior art, the advantages and positive effects of the present invention are: 1. This invention uses a flow field-interface coupling design, that is, a one-inlet, two-outlet three-dimensional flow channel, through the coordination of a vertical coalescing channel and horizontal dual channels, to couple the demulsification and separation processes within a single device, reducing the device volume by 50%; 2. The present invention achieves spontaneous oil-water separation through the triple coupling of gravity, capillary force and wetting gradient, without the need for external power; 3. The wetting gradient design makes the system pressure drop less than 10kPa, significantly reducing energy loss; 4. The oil content of the effluent is less than 5mg / L, which is better than the GB31570-2015 standard; the oil recovery rate is greater than 99%; it can treat stubborn emulsions containing surfactants, such as 0.1% Span80 emulsion, breaking through the limitations of traditional chemical demulsifiers; 5. This invention reveals the coupling mechanism between oil droplet coalescence dynamics and selective filtration in a composite flow field, establishes a theoretical model of "wetting gradient force-flow field synergistic enhancement", and provides a new theoretical framework for emulsion separation. 6. This invention proposes a "structure-function" integrated design paradigm, which provides a technical path for the development of compact separation equipment by optimizing geometric parameters and matching them with extreme wettability materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the wettability gradient-based coalescence-selective filtration integrated oil-water separation device in Example 1; Figure 2 The effect of the vertical coalescence channel on the oil droplet size distribution of the diesel-in-water emulsion in Example 2: (a) Oil droplet size before coalescence; (b) Oil droplet size after coalescence; Figure 3 (a) water contact angle of the superhydrophilic underwater superoleophobic quartz sand in Example 2; (b) underwater diesel contact angle; Figure 4 (a) water contact angle; (b) oil contact angle of the superhydrophobic and superoleophilic quartz sand in Example 2; In the figure: 1-feed port; 2-vertical coalescing channel; 3-horizontal oil channel; 4-oil outlet; 5-horizontal water channel; 6-water outlet; 7-bracket; 8-intermediate chamber. DETAILED DESCRIPTION

[0025] The present invention can be better understood according to the following examples. However, it is easy for those skilled in the art to understand that the contents described in the examples are only used to illustrate the present invention, and should not and will not limit the present invention described in detail in the claims.

[0026] The technical solution of the present invention is further described below with reference to implementation cases.

[0027] Example 1 This embodiment provides an integrated oil-water separation device based on wettability gradient coalescence and selective filtration, such as Figure 1 As shown, it includes a feed inlet 1, a vertical coalescing channel 2, a horizontal oil channel 3, and a horizontal water channel 5. The vertical coalescing channel 2 is filled with 80-mesh quartz sand, and a bracket 7 is provided below the horizontal oil channel 3 and the horizontal water channel 5. The quartz sand is a superhydrophilic underwater superoleophobic and superhydrophobic superoleophilic quartz sand filled in a gradient manner with a volume ratio of 1:1 to construct an asymmetric surface energy field, and drive the directional migration of oil droplets through the wettability gradient force. The wettability gradient force can not only enhance the demulsification ability of the coalescer, but also reduce the head loss to promote the gradual coalescence and separation of oil droplets.

[0028] Example 2 This embodiment provides a method for separating oil and water using a wettability gradient-based coalescence-selective filtration integrated oil-water separation device according to embodiment 1, comprising the following steps: a diesel-in-water emulsion with a concentration of 1000 mg / L and an oil droplet size of 1 μm is introduced from a feed port 1 into a vertical coalescence channel 2, wherein the superficial flow velocity of the vertical coalescence channel 2 is 0.15 m / h; super-hydrophobic and super-oleophilic quartz sand in the vertical coalescence channel 2 adsorbs oil droplets and promotes their coalescence; super-hydrophilic sand adsorbs water droplets to form a continuous aqueous phase; and super-hydrophilic underwater super-hydrophobic sand adsorbs water droplets to form a continuous aqueous phase. The oily quartz sand preferentially absorbs water molecules while repelling oil droplets. Under the action of gravity and capillary pressure, the water forms a continuous water flow channel. After the water flows through the intermediate chamber 8, the water phase is discharged through the water outlet 6 of the horizontal water channel. The superhydrophobic and superoleophilic quartz sand preferentially absorbs oil droplets while repelling water molecules. Under the action of gravity and capillary pressure, the oil forms a continuous oil flow channel. The oil phase is discharged through the oil outlet 4 of the horizontal oil channel. Conventional ultraviolet spectrophotometry shows that the oil content of the outlet water is less than 5 mg / L, which is better than the GB31570-2015 standard.

[0029] The constructed asymmetric surface energy field combined with the laminar shear force of 0.15 m / h in the vertical coalescence channel causes the oil droplets to undergo an “adsorption-collision-fusion” chain reaction, e.g. Figure 2As shown in the figure, after being treated with the vertical coalescence channel, the oil droplet size distribution of the water-in-diesel emulsion changed significantly: the median particle size (Dx (50)) of the emulsion before coalescence was 1 μm, while the average particle size of the emulsion after coalescence increased to 500 μm. This rapid increase in particle size indicates that the emulsion has undergone significant coalescence, causing the system to transform from a stable emulsified state (emulsified oil) to an unstable dispersed state (dispersed oil). This phase transition destroys the stability of the emulsion and significantly reduces the specific surface area of ​​the oil-water interface, thereby weakening the barrier effect of the interfacial film. This change is conducive to the efficient separation of the oil and water phases by the horizontal oil channel and the horizontal water channel in the subsequent process, providing favorable conditions for the rapid stratification and collection of oil and water.

[0030] Particle size measurement method: The oil droplet size distribution in the emulsion was analyzed using a Malvern laser particle size analyzer (MASTERSIZER 3000, Malvern, England). The Malvern laser particle size analyzer was preheated and the 300RF lens was selected. The refractive index of the oil phase (1.44-1.48) and the refractive index of the water phase (1.33) were set. After measuring the background with pure water, 50-100 μL of sample was slowly added. The shading degree was controlled at 8-15%, and the circulating pump flow rate was maintained at 1000 rpm. Three consecutive measurements were performed, and the median particle size (Dx(50)) was recorded to ensure data stability.

[0031] The preparation steps of super hydrophilic underwater super oleophobic quartz sand are as follows: Step S1: Slowly pour 500 mL of piranha solution into a beaker containing 200 g of quartz sand (QS) and allow to react for 2 hours. Wash the quartz sand three times with 500 mL of deionized water and 500 mL of anhydrous ethanol, each for 15 minutes. Dry the washed quartz sand at 60°C for 6 hours to obtain activated quartz sand. The piranha solution is an acidic piranha solution composed of a mixture of 98% concentrated sulfuric acid and 30% hydrogen peroxide in a volume ratio of 3:1. Step S2: Slowly add 90 wt.% anhydrous ethanol and 4 wt.% ammonium hydroxide (NH4OH) to 6 wt.% tetraethyl orthosilicate. Heat and stir in a 70°C water bath for 80 minutes at a stirring rate of 500 rpm to ensure complete hydrolysis of TEOS to prepare a sol. The sol is cooled to room temperature. 200 g of activated quartz sand prepared in Step S1 is added to the cooled sol and stirred for 9 hours. The quartz sand is washed with 500 mL of deionized water three times for 15 minutes each time. The washed quartz sand is dried at 80°C for 12 hours to remove water and organic matter from the gel, thereby producing superhydrophilic underwater superoleophobic quartz sand.

[0032] The static contact angles of water and oil were measured using a video optical contact angle meter (OCA25, EastDefy, Germany). The hydrophobic sample to be tested was fixed horizontally on the test platform, and a 2 μL droplet of ultrapure water or diesel was accurately added using a microsyringe. The droplet image was captured in real time by a high-resolution CCD camera, and the Young-Laplace equation was used to fit the three-phase contact points to calculate the static contact angle value. Three different positions were selected for measurement for each sample, and the results were taken as the average ± standard deviation. Figure 3 As shown in the figure, the functionalized quartz sand achieves superoleophobicity (underwater oil contact angle of 150.4°) and superhydrophilicity (water contact angle of 0°) through the rough structure of nano-SiO2.

[0033] The separation efficiency and water flux of the horizontal water channel are calculated as follows: ; Where, is the water separation efficiency, and are the oil content in the outflow water of the horizontal water channel and the oil content in the oily wastewater in the intermediate chamber, mg / L. In this embodiment, ， , after calculation, .

[0034] ; Where, is the water flux, L·m -2 ·h -1 ; is the volume of water flowing out of the horizontal water channel, L; is the cross-sectional area of ​​the horizontal water channel, m 2 ; is the time required for water to completely pass through the horizontal water channel, h. In this embodiment, , , , after calculation, ; The separation efficiency is 99.6%.

[0035] The preparation steps of super hydrophobic and super oleophilic quartz sand are as follows: Silanization treatment: The super-hydrophilic underwater super-oleophobic quartz sand prepared above and 4 mL of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS) silane coupling agent were dispersed in 200 mL of n-heptane and stirred at 80 ° C for 9 hours. Then, the solution was centrifuged at 1500 rpm for 5 minutes, the solid was collected and washed 3 times with 500 mL of n-heptane, each time for 15 minutes. Finally, it was vacuum dried at 80 ° C for 11 hours to obtain super-hydrophobic and super-oleophilic quartz sand. Functionalized quartz sand is modified by nano-SiO2 rough structure + silane coupling agent molecular layer, such as Figure 4 As shown, super hydrophobicity (water contact angle of 154°) and super oleophilicity (oil contact angle of 0°) are achieved, with a separation efficiency of 99.05% and an oil flux of 1675 Lm -2 h -1 After 1000 cycles of testing, the water contact angle decayed by 2%.

[0036] The separation efficiency and oil flux of the horizontal oil channel are calculated as follows: ; Where, is the oil separation efficiency, and are the water content in the oil flowing out of the horizontal oil channel and the water content in the oily wastewater in the intermediate chamber, mg / L, respectively.

[0037] ; Where, is the oil flux, L·m -2 ·h -1 ; is the volume of oil flowing out of the horizontal oil channel, L; is the cross-sectional area of ​​the horizontal oil channel, m 2 ; is the time required for the oil to pass completely through the horizontal oil channel, h.

[0038] In this embodiment, the experimental data, , , ; , , , .

[0039] The contact angle decay is calculated as follows: ; Where, i W is the static contact angle of water on the super-hydrophobic and super-oleophilic quartz sand surface, i tIt is the static contact angle of water on the super-hydrophobic and super-oleophilic quartz sand surface after a certain period of time or under certain conditions.

[0040] The initial water contact angle of superhydrophobic and superoleophilic quartz sand is 154°. After 1000 cycles of testing, the water contact angle is 150.9°, with a decay rate of 2%.

[0041] The hydraulic retention time of oily wastewater in the vertical coalescing channel of the oil-water separation device is as follows: ; The quartz sand filling lengths in the horizontal oil channel and the horizontal water channel of the oil-water separator are respectively: ; ; in: t is the hydraulic retention time of oily wastewater in the vertical coalescence channel, s; L O is the quartz sand filling length in the horizontal oil channel, m; L W is the filling length of quartz sand in the horizontal water channel, m; D 0 is the oil droplet size before coalescence, taking 1×10 -6 m; D is the particle size of the oil droplets after coalescence, and 5×10 -4 m; k is the aggregation coefficient, which is taken as 0.35; m is the viscosity of the oil-water emulsion, 1.0 mPa·s; c O is the surface tension of the oil, 30 mN / m; c W is the surface tension of water, 72 mN / m; i O is the static contact angle of oil on the superoleophobic quartz sand surface under superhydrophilic water, which is 150.4°; i W is the static contact angle of water on the superhydrophobic and superoleophilic quartz sand surface, which is 154°; e is the porosity of the quartz sand filling in the horizontal oil channel and the horizontal water channel, which is taken as 0.43; αis the shape coefficient of quartz sand, which is taken as 0.78; d O is the equivalent particle size of quartz sand in the horizontal oil channel, which is 1.8×10 -4 m; d W is the equivalent particle size of quartz sand in the horizontal water channel, which is 1.8×10 -4 m; m O is the viscosity of diesel, which is 3 mPa·s; m W is the viscosity of water, taken as 1 mPa·s; v O is the superficial velocity of oil in the horizontal oil channel, which is 4.17×10 -5 m / s; v W is the apparent velocity of water in the horizontal water channel, which is 4.17×10 -5 m / s; Substitute the benchmark parameters: ; It can be seen that the 1 μm oil droplets coalesced to 500 μm within 30 minutes.

[0042] Substitute the benchmark parameters: ; ;

[0043] In summary, this embodiment achieves the following through a quantitative model: (1) Efficient coalescence: 1 μm oil droplets coalesce to 500 μm within 30 minutes, solving the problem of kinetic stability of oil-in-water emulsions.

[0044] (2) Compact design: The quartz sand filling length in the horizontal oil channel is precisely optimized to 0.12m, and the quartz sand filling length in the horizontal water channel is precisely optimized to 0.14m. While ensuring a separation efficiency of 99.6%, the equipment volume is reduced.

[0045] The core value of the formula Scientific Significance: This study, for the first time, established a quantitative kinetic model of oil droplet "directional migration-channel coalescence-two-phase separation" through the coordinated regulation of wettability gradient field and pore flow field, providing a theoretical foundation for the design of high-throughput oil-water separation systems. Engineering significance: Provides a parametric design tool for the "coagulation-filtration" integrated device, realizing closed-loop optimization from material properties → flow field control → geometric parameters, replacing the empirical trial and error mode.

[0046] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. An integrated oily wastewater treatment device based on wettability gradient coalescence and selective filtration, characterized in that: The treatment device includes a vertical coalescence channel, a horizontal oil channel, and a horizontal water channel, and adopts a one-inlet, two-outlet three-dimensional flow channel integrated structure; the oily wastewater is emulsified oil with an oil droplet size of less than 50 μm, and the apparent flow velocity of the vertical coalescence channel is 0.1~0.5 m / h; the vertical coalescence channel is filled with 40~120 mesh quartz sand, and the quartz sand is superhydrophilic underwater superoleophobic quartz sand and superhydrophobic superoleophilic quartz sand in a gradient filling volume ratio of 2:1~1:2; the channel aspect ratios of the horizontal oil channel and the horizontal water channel are both 4:1~3:

1.

2. The wettability gradient-based coalescence-selective filtration integrated oily wastewater treatment device according to claim 1, characterized in that: The horizontal oil channel is filled with 40-120 mesh super-hydrophobic and super-oleophilic quartz sand, and the horizontal water channel is filled with 40-120 mesh super-hydrophilic underwater super-oleophobic quartz sand.

3. The wettability gradient-based coalescence-selective filtration integrated oily wastewater treatment device according to claim 2, characterized in that: The preparation steps of super hydrophilic underwater super oleophobic quartz sand are as follows: Step S1: Pour the piranha solution into a beaker containing quartz sand and react for 1.5-2.5 hours. Wash the quartz sand with deionized water and anhydrous ethanol three times respectively. Dry the washed quartz sand to obtain activated quartz sand. Step S2: adding anhydrous ethanol and ammonium hydroxide to ethyl orthosilicate, heating and stirring for 80 to 100 minutes; cooling to room temperature, adding the activated quartz sand prepared in step S1 to the cooled sol, stirring and mixing, washing the quartz sand with deionized water three times, and drying the washed quartz sand at 75 to 85° C. for 10 to 12 hours to obtain super-hydrophilic underwater super-oleophobic quartz sand.

4. The wettability gradient-based coalescence-selective filtration integrated oily wastewater treatment device according to claim 2, characterized in that: The preparation steps of super hydrophobic and super oleophilic quartz sand are as follows: Superhydrophilic underwater superoleophobic quartz sand and a silane coupling agent were dispersed in n-heptane and stirred at 75-85°C for 9-10 hours. Then, the solution was centrifuged, the solid was collected and washed three times with 500-600 mL of n-heptane, and finally vacuum dried for 11-12 hours to obtain superhydrophobic and superoleophilic quartz sand.

5. The wettability gradient-based coalescence-selective filtration integrated oily wastewater treatment device according to claim 1, characterized in that: The hydraulic retention time of oily wastewater in the vertical coalescence channel is: ； in: t is the hydraulic retention time of oily wastewater in the vertical coalescence channel, s; D 0 is the oil droplet size before coalescence, m; D is the oil droplet size after coalescence, m; k is the aggregation coefficient; μ is the viscosity of the oil-water emulsion, Pa·s; γ O is the surface tension of the oil, mN / m; θ O is the static contact angle of oil on the superoleophobic quartz sand surface under superhydrophilic water, °; ε is the porosity of quartz sand filling in horizontal oil channels and horizontal water channels, °; d O is the equivalent particle size of quartz sand in the horizontal oil channel, m.

6. The wettability gradient-based coalescence-selective filtration integrated oily wastewater treatment device according to claim 1, characterized in that: The quartz sand filling lengths in the horizontal oil channel and the horizontal water channel are respectively: ； ； in: L O is the quartz sand filling length in the horizontal oil channel, m; L W is the filling length of quartz sand in the horizontal water channel, m; γ O is the surface tension of the oil, mN / m; γ W is the surface tension of water, mN / m; θ O is the static contact angle of oil on the superoleophobic quartz sand surface under superhydrophilic water, °; θ W is the static contact angle of water on the superhydrophobic and superoleophilic quartz sand surface, °; ε is the porosity of the quartz sand filling in the horizontal oil channel and the horizontal water channel; α is the shape coefficient of quartz sand; d O is the equivalent particle size of quartz sand in the horizontal oil channel, m; d W is the equivalent particle size of quartz sand in the horizontal water channel, m; μ O is the viscosity of diesel, mPa·s; μ W is the viscosity of water, mPa·s; v O is the superficial velocity of oil in the horizontal oil channel, m / s; v W is the apparent velocity of water in the horizontal water channel, m / s.

7. The method for separating oily wastewater using the wettability gradient-based coalescence-selective filtration integrated oily wastewater treatment device according to any one of claims 1 to 6, characterized in that: The following steps are involved: The oily wastewater enters the vertical coalescence channel from the feed port, where the oil droplets coalesce under the wettability gradient formed by the super-hydrophilic underwater super-oleophobic quartz sand and the super-hydrophobic super-oleophilic quartz sand, and then enter the middle chamber. After the oily wastewater in the middle chamber flows into the horizontal oil channel, the water is intercepted by the capillary force of the superhydrophobic and superoleophilic quartz sand, and the oil flows out from the oil outlet after passing through the horizontal oil channel. The outflowing oil is recycled. After the oily wastewater in the middle chamber flows into the horizontal water channel, the oil is intercepted by the capillary force of the superhydrophilic underwater superoleophobic quartz sand. The water then flows out of the outlet after passing through the horizontal water channel; the oil content of the outlet water is <5 mg / L.

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