Segmented coalescence system based on wettability gradient

Abstract

The invention provides a segmented coalescence system based on wettability gradient. The system comprises a storage tank, a segmented coalescer and a gravity separation tank, the segmented coalescer is composed of a plurality of layers of coalescence beds, a gravity separation area is clamped between every two layers of coalescence beds, through the wettability gradient design, the interface energy synergistic effect and optimized fluid dynamic characteristics are fully utilized, the separation efficiency reaches up to 98.50%, and the separation effect is good. The mixing design of the super-hydrophilic sand and the super-hydrophobic sand obviously enhances the wetting and coalescence efficiency of oil drops, the particle size gradient design realizes segmented coalescence of the oil drops, the lower layer of small-particle-size sand is demulsified and coalesces small oil drops, the upper layer of large-particle-size sand promotes combination of large oil drops, and the continuous water film and oil film structure effectively avoids the problem of pore channel blockage. And the bed pressure drop is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of oil-water treatment, and in particular to a segmented coalescence system based on wettability gradient. Background Art

[0002] Oil-water mixtures are widely present in daily life, industrial production processes, and frequent oil spills. They are complex in composition and difficult to handle. Such mixtures usually appear as oil-in-water or water-in-oil emulsions, in which tiny droplets have high stability and are prone to a series of problems such as equipment corrosion, material oxidation, safety hazards, and environmental pollution. It is particularly noteworthy that after oil pollutants enter the water body, they may be absorbed by aquatic organisms through the food chain, thereby posing a potential risk to human health. Therefore, the development of efficient and sustainable oil-water separation technology to achieve effective separation and purification of the mixture has become an important direction of current research.

[0003] In recent years, the rapid development of bionics and interface science has brought new opportunities for the design of functional materials, especially in the fields of oil-water separation, self-cleaning, air purification and liquid transmission. Materials with special wettability have shown great potential. Compared with traditional separation technologies (such as in-situ combustion, centrifugal separation, flotation, adsorption and chemical coagulation), bionic materials (such as metal mesh, foam, textiles, aerogels, etc.) have attracted widespread attention due to their efficient separation ability and environmentally friendly properties. However, the pore size of existing materials is generally large, and it is difficult to effectively intercept tiny oil droplets (less than 10μm in diameter) in oil-water emulsions stabilized by surfactants. These oil droplets have extremely high stability due to the encapsulation of surfactants. Although the "particle size screening" mechanism can be used to reduce the pore size of the material to improve the interception effect of tiny oil droplets, this method often leads to a significant decrease in filtration flux and high energy consumption. At the same time, the micron or nanometer pores are easily blocked by pollutants, which affects the long-term operation stability of the material.

[0004] In order to meet the above challenges, researchers have begun to explore oil-water separation technology based on particle coalescence beds in recent years. This type of technology can achieve high separation efficiency while maintaining high flux by designing coalescence beds with tortuous channel structures. However, despite certain progress in the separation of oil-in-water emulsions, the separation of surfactant-stabilized water-in-oil emulsions still faces great difficulties. The stability of water-in-oil emulsions stems from the synergistic effects of electrostatic repulsion, steric hindrance and short-range hydration. It is difficult to achieve complete demulsification by relying solely on simple physical attraction or repulsion mechanisms, which leads to relatively low separation efficiency of traditional cumulative coalescence beds.

[0005] At present, coalescers with demulsification ability and oil penetration ability from hydrophilic surface to hydrophobic surface under capillary effect have been developed for separation of water-in-oil emulsions. However, most of the current studies adopt uniform particle size and single-layer design, which fails to fully utilize the synergistic effect of particle size classification and wettability coupling, resulting in limited separation efficiency. In addition, existing coalescers often face the problem of excessive pressure drop in the clinical layer under high-throughput conditions, which limits their application in practical engineering.

[0006] For example, the prior art CN202420115604.X discloses a high-efficiency oily wastewater filtration coalescer. This technical solution mainly relies on physical filtration and coalescence, and does not propose a solution to the stability problem of water-in-oil emulsions. For surfactant-stabilized water-in-oil emulsions (such as motor oil, diesel, rapeseed oil, etc.), the separation efficiency is limited, especially the treatment effect on nano-scale oil droplets (0.1-10μm) is not explicitly mentioned. In this patent, the surface flow rate of the filter element is ≤0.001m / s, the initial pressure difference is ≤2KPa, and the allowable working pressure difference is ≤60KPa. Although this low flow rate design reduces energy consumption, it may lead to large head loss under high-throughput conditions. There is no explicit mention of the optimized design of head loss, which increases operating energy consumption under high-throughput conditions.

[0007] The prior art CN202420310945.2 discloses an aqueous phase oil removal device, which mainly relies on physical filtration and coagulation. The operating parameters are not clearly mentioned, and it lacks adaptability to different operating conditions (such as flow rate, oil droplet size, oil concentration, etc.). It does not propose a breakthrough solution to the complex stability problem of water-in-oil emulsions, and has deficiencies in separation efficiency, high-throughput adaptability and engineering application potential.

[0008] Therefore, developing a new technology that can effectively destroy the stability of oil-in-water emulsions and achieve efficient separation has become the focus of current research. Summary of the invention

[0009] In order to solve the above technical problems, the present invention aims to provide an efficient and stable oil-water separation system to solve the problem that the oil-in-water emulsion in the prior art is strong in stability and difficult to completely demulsify and separate due to electrostatic repulsion, steric hindrance and short-range hydration. The present invention solves the technical problem that the traditional particle agglomerator has low agglomeration efficiency due to the uniform particle size and single-layer design, fails to fully utilize the synergistic effect of particle size classification and wettability coupling, and has limited separation efficiency.

[0010] The present invention optimizes the particle size ratio of super-hydrophilic underwater super-oil-repellent sand and super-hydrophobic super-oil-wet sand in a mixed particle agglomeration bed, reduces pressure drop, reduces head loss, and designs a segmented agglomerator consisting of an agglomeration bed with a multi-level particle size gradient distribution to achieve segmented agglomeration of oil droplets, thereby improving oil-water separation efficiency and promoting its engineering application.

[0011] The present invention combines a segmented coalescer and a gravity separation tank, utilizes the synergistic effect of wettability gradient and interface energy, and thus significantly improves separation efficiency and reduces operating costs and clogging risks.

[0012] Specifically, the present invention provides a staged coalescence system based on wettability gradient, the coalescence system comprising a storage tank, a staged coalescer and a gravity separation tank; the staged coalescer is composed of several layers of coalescence beds, and a gravity separation zone is sandwiched between each layer of coalescence beds.

[0013] Furthermore, the storage tank stores the oil-in-water emulsion to be treated, and the oil is selected from one of engine oil, diesel, rapeseed oil and hexadecane.

[0014] Furthermore, the oil concentration is 100-500 mg / L, and the median diameter of the oil droplets is 0.1-10 μm.

[0015] Furthermore, each layer of the agglomeration bed is formed by mixing super-hydrophilic underwater super-oil-repellent sand and super-hydrophobic super-oil-philic sand.

[0016] The thickness of each agglomeration bed is 5-7 cm.

[0017] The mixed volume ratio of superhydrophilic underwater superoil-repellent sand and superhydrophobic superoil-philic sand is 1:1.

[0018] That is, the particle size ratio of super hydrophilic sand to super hydrophobic sand is 1:2.

[0019] Super hydrophilic underwater super oil-repellent sand forms a continuous water film by adsorbing water molecules, promoting water phase adsorption and oil droplet destabilization. Super hydrophobic super oil-repellent sand forms a continuous oil film by adsorbing oil droplets, enhancing the probability of oil droplet aggregation.

[0020] There is a large Lewis acid-base interfacial energy between the superhydrophobic sand and the oil interface, and the synergistic effect of the wettability gradient and interfacial energy significantly improves the wetting and agglomeration efficiency of the oil droplets.

[0021] Furthermore, the preparation steps of the super-hydrophilic underwater super-oil-repellent sand are as follows:

[0022] Step S1: ultrasonically clean the quartz sand and then dry it to obtain pretreated quartz sand;

[0023] Step S2: adding dopamine and polyethyleneimine into Tris-HCl buffer to prepare a polydopamine solution;

[0024] Step S3: adding silica nanoparticles to the polydopamine solution and sonicating;

[0025] Step S4: adding the quartz sand prepared in step S1, collecting the precipitate, and obtaining a super-hydrophilic underwater super-oleophobic SiO 2 @PDA-QS.

[0026] Furthermore, the preparation steps of the super hydrophobic and super oil-philic sand are as follows:

[0027] (1) SiO 2 @PDA-QS and silane coupling agent (N-(2-aminoethyl)-3-aminopropyltriethoxysilane) were dispersed in n-heptane;

[0028] (2) centrifuging the solution to collect the solid and washing it;

[0029] (3) After drying, super hydrophobic and super oleophilic AEAOS-SiO 2 @PDA-QS.

[0030] Furthermore, the specific preparation steps of the super-hydrophilic underwater super-oil-repellent sand are as follows:

[0031] Step S1: 190-210 g of quartz sand is ultrasonically cleaned with 500 ml of ethanol and 500 ml of deionized water for 3 times, with an ultrasonic intensity of 20-50 kHz, and each time for 15-20 min, and then placed in an oven at 75-85° C. and dried for 12 h to obtain pretreated quartz sand for use;

[0032] Step S2: adding 0.4-0.6 g dopamine (DA) and 0.4-0.6 g polyethyleneimine (PEI) into 30 mL Tris-HCl buffer (50-60 mmol / L, pH=8-10), and ultrasonically dispersing for 20-25 min to obtain a polydopamine (PDA) solution, with an ultrasonic intensity of 20-50 kHz;

[0033] Step S3: Add 2.5-3.5 g of silicon dioxide (SiO 2 ) nanoparticles, magnetically stirred at 500-600 rpm for 15-20 min and sonicated for 20-25 min to obtain a uniform suspension, with an ultrasound intensity of 20-50 kHz;

[0034] Step S4: Add 190-210g of the quartz sand prepared in step S1, stir at 20-25°C for 5-6h, the stirring speed is 700-900rpm, centrifuge the solution 1-2 times, the rotation speed is 1900-2100rpm, collect the precipitate, then wash it three times with 500ml of methanol and vacuum dry it at 75-85°C for 10-12h to obtain super hydrophilic underwater super oleophobic SiO 2 @PDA-QS.

[0035] Furthermore, the preparation steps of the super hydrophobic and super oil-philic sand are as follows:

[0036] (1) 190-210gSiO 2@PDA-QS and 4-6 mL of silane coupling agent (N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AEAOS)) were dispersed in 190-210 mL of n-heptane and stirred at 75-85 °C for 10-12 h at a stirring speed of 500-600 rpm;

[0037] (2) centrifuging the solution 1-2 times at 1900-2100 rpm, collecting the solid and washing it three times with 500 ml of n-heptane;

[0038] (3) Drying under vacuum at 80 °C for 12 h to obtain super hydrophobic and super oleophilic AEAOS-SiO 2 @PDA-QS.

[0039] Furthermore, the agglomeration beds in the segmented agglomerator are arranged layer by layer from bottom to top, and the size gradient of the mixed particles of the super-hydrophilic underwater super-oil-repellent sand and the super-hydrophobic super-oil-repellent sand in the agglomeration bed gradually increases from bottom to top.

[0040] Furthermore, when the agglomeration bed in the segmented agglomerator has 5 layers, from bottom to top, the first layer: the super hydrophilic sand particle size is 159-161 mesh, and the super hydrophobic sand particle size is 79-81 mesh.

[0041] The second layer: super hydrophilic sand particle size is 79-81 mesh, super hydrophobic sand particle size is 39-41 mesh.

[0042] The third layer: super hydrophilic sand particle size is 39-41 mesh, super hydrophobic sand particle size is 19-21 mesh.

[0043] The 4th layer: super hydrophilic sand particle size 19-21 mesh, super hydrophobic sand particle size 9-11 mesh.

[0044] The fifth layer: super hydrophilic sand particle size 9-11 mesh, super hydrophobic sand particle size 4-6 mesh.

[0045] The small-particle sand in the lower layer provides a large specific surface area, which promotes the demulsification and coalescence of tiny oil droplets. The large-particle sand in the upper layer reduces the surface velocity, promotes the coalescence of large oil droplets and reduces the risk of clogging.

[0046] The mixed design of super-hydrophilic sand and super-hydrophobic sand promotes the migration of oil droplets to the surface of super-hydrophobic sand through the wetting force generated by the wettability gradient, which significantly improves the coalescence efficiency of oil droplets. When the continuous water phase passes through the water film on the surface of super-hydrophilic sand, the flow resistance is significantly reduced, reducing the bed pressure drop.

[0047] Furthermore, the thickness of the gravity separation tank is 9-11 cm; the emulsion is allowed to stand in the gravity separation tank for 30-40 minutes.

[0048] Through gravity separation, large-size oil droplets are promoted to float and form a network oil film, which further coalesces small oil droplets and further separates the coalesced large oil droplets and the water phase.

[0049] Oil droplet coalescence mechanism in the segmented coalescer:

[0050] In the segmented coalescer based on wettability gradient, the mixed coalescing bed of superhydrophilic sand and superhydrophobic sand significantly enhances the coalescence efficiency of oil droplets in water-in-oil emulsion through the synergistic effect of wettability difference and interfacial energy. From the perspective of interfacial energy, the superhydrophobic sand and oil interface have a strong affinity for oil droplets due to the larger Lewis acid-base interfacial energy, which improves the wetting and coalescence efficiency of oil droplets. This wettability gradient and interfacial tension difference can effectively destroy the stability of water-in-oil emulsion and promote the adhesion and coalescence of oil droplets. It is worth noting that when the particle size ratio of superhydrophilic sand to superhydrophobic sand is 1:2, the increased specific surface area of ​​small-size superhydrophilic sand promotes the adsorption of water phase and destabilization of oil droplets; large-size superhydrophobic sand provides larger pores, which is conducive to the coalescence and growth of oil droplets, further enhancing the performance of the coalescing bed.

[0051] The design of gradually increasing the particle size of quartz sand from bottom to top in the coalescing bed optimizes the step-by-step coalescence process of oil droplets. The lower small-particle sand layer effectively demulsifies and coalesces small oil droplets, and the upper large-particle sand layer promotes the coalescence and growth of oil droplets through the larger pore size. This design improves the coalescence efficiency and optimizes the fluid dynamics. Specifically, the larger pore size between the upper large-particle quartz sand provides more space and longer residence time for oil droplets, allowing the oil droplets to fully collide, coalesce and form larger-particle oil droplets. Large-particle oil droplets have a higher floating speed in the gravity separation zone, making it easier to achieve oil-water separation. This design significantly enhances the coalescence efficiency and provides a guarantee for efficient oil-water separation.

[0052] The thickness and spacing design of the coalescing bed play a key role in the coalescing efficiency of oil droplets, which can be further analyzed from the perspective of interfacial energy. The increase in the thickness of the coalescing bed provides more opportunities for oil droplets to contact the surface of the superhydrophobic sand, thereby utilizing its low surface energy polar component to enhance the adhesion and coalescence of oil droplets. The design of the spacing of the coalescing bed also has an important influence on the coalescing performance of oil droplets. The space in the coalescing bed structure is equivalent to a gravity separation zone. The floating speed of large-size oil droplets is higher than that of small-size oil droplets, resulting in the gradual accumulation of oil droplets at the bottom of the upper coalescing bed and the formation of a reticular oil film. The main interface energy between oils is Lewis acid-base energy. Under the action of concentration polarization effect, small-size oil droplets are intercepted and further coalesced through collision.

[0053] In addition, the mixed design of superhydrophilic sand and superhydrophobic sand plays an important role in reducing the bed pressure drop, and this effect can also be explained from the perspective of interfacial energy. Superhydrophilic sand forms a continuous water film by adsorbing water molecules, while superhydrophobic sand forms a continuous oil film by adsorbing oil droplets. This double-membrane structure effectively avoids the problem of pore blockage caused by the liquid bridge phenomenon in a single coalescence bed. When the continuous water phase passes through the water film on the surface of the superhydrophilic sand, the flow resistance is significantly reduced, thereby reducing the bed pressure drop. At the same time, the wetting force generated by the wettability gradient between superhydrophilic sand and superhydrophobic sand further promotes the migration of oil droplets to the surface of superhydrophobic sand, significantly improving the coalescence efficiency of oil droplets. The wetting force generated by this wettability gradient makes the oil droplet particles in the liquid phase tend to move away from the superhydrophilic interface and close to the superhydrophobic interface, thereby significantly increasing the probability of wetting and coalescence of oil droplets.

[0054] Compared with the existing technology, the present invention has the following significant beneficial effects:

[0055] The segmented coalescence system for efficiently separating oil-in-water emulsions provided by the present invention is particularly suitable for the separation of surfactant-stabilized oil-in-water emulsions (such as motor oil, diesel, rapeseed oil, hexadecane, etc.). By mixing super-hydrophilic underwater super-oleophobic quartz sand with super-hydrophobic super-oleophilic quartz sand, utilizing the coupling effect of two media with opposite wettability and the optimized design of particle size gradient distribution, a segmented coalescer based on wettability gradient is constructed, which can realize segmented coalescence of oil droplets and efficient separation of oil-in-water emulsions. That is, the segmented coalescence system of the present invention achieves a separation efficiency of up to 98.50% through wettability gradient design, interfacial energy synergistic effect and optimized fluid dynamic characteristics, and has a significant treatment effect on nano-scale oil droplets (0.1-10μm), and the median particle size of the outlet oil droplets can reach 500-600μm.

[0056] Technical advantages: High-efficiency separation: The present invention makes full use of the synergistic effect of interfacial energy and optimized fluid dynamics through wettability gradient design, and the separation efficiency is as high as 98.5%. Wettability gradient and interfacial energy synergistic effect: The mixed design of super-hydrophilic sand and super-hydrophobic sand significantly enhances the wetting and agglomeration efficiency of oil droplets. Segmented agglomeration optimization: The particle size gradient design realizes the segmented agglomeration of oil droplets. The small-particle sand in the lower layer demulsifies and agglomerates small oil droplets, and the large-particle sand in the upper layer promotes the merging of large oil droplets. Low clogging risk: The continuous water film and oil film structure effectively avoids the problem of pore blockage and reduces the bed pressure drop.

[0057] The present invention optimizes the particle size ratio of super-hydrophilic sand and super-hydrophobic sand in the mixed particle agglomeration bed to reduce head loss, and designs a coalescer consisting of a coalescing bed with a multi-level particle size gradient distribution to achieve segmented coalescence of oil droplets, thereby improving the oil-water separation efficiency and promoting its engineering application.

[0058] The present invention has a running speed of 1-5 m / h, which reduces energy consumption while ensuring efficient separation.

[0059] The surface of the super-hydrophilic underwater super-oleophobic quartz sand is wrapped by water, and the surface of the super-hydrophobic super-oleophilic quartz sand is wrapped by oil, thereby forming a continuous water film and oil film channel. Water can flow with the water film, and oil can flow with the oil film, reducing flow resistance. The present invention effectively avoids the problem of channel blockage and reduces the bed pressure drop through the design of continuous water film and oil film structure. The particle size gradient design of the multi-layer coalescing bed further reduces the risk of blockage. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is a schematic diagram of the segmented coalescence system of the present invention;

[0061] Figure 2 is a graph of the median diameter of oil droplets in the original diesel-in-water emulsion in the embodiment, Dx(50)=1 μm;

[0062] Figure 3 is the median particle size diagram of the oil droplets in the water in the embodiment, Dx(50) = 504 μm;

[0063] Among them, 1-gravity separation tank; 2-oil outlet; 3-water outlet; 4-segmented coalescer; 5-gravity separation zone 4; 6-gravity separation zone 3; 7-gravity separation zone 2; 8-gravity separation zone 1; 9-coalescing bed 5; 10-coalescing bed 4; 11-coalescing bed 3; 12-coalescing bed 2; 13-coalescing bed 1; 14-peristaltic pump; 15-flow meter; 16-agitator; 17-storage tank; 18-water-in-oil emulsion. DETAILED DESCRIPTION

[0064] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0065] The technical solution of the present invention is further explained below in conjunction with implementation cases.

[0066] Example

[0067] This embodiment provides a staged coalescence system based on wettability gradient, such as Figure 1As shown, the agglomerator includes a storage tank 17, a segmented agglomerator 4 and a gravity separation tank 1; the segmented agglomerator 4 is composed of 5 layers of agglomerator beds, namely a first layer of agglomerator bed 13, a second layer of agglomerator bed 12, a third layer of agglomerator bed 11, a fourth layer of agglomerator bed 10, and a fifth layer of agglomerator bed 9, and gravity separation zones are sandwiched between each layer of the agglomerator beds, namely a first gravity separation zone 8, a second gravity separation zone 7, a third gravity separation zone 6, and a fourth gravity separation zone 5.

[0068] The storage tank stores the water-in-oil emulsion to be treated, and the oil is diesel. The oil concentration is 500 mg / L, and the median particle size of the oil droplets is 1 μm. Each layer of the agglomeration bed is mixed with super-hydrophilic underwater super-oil-repellent sand and super-hydrophobic super-oil-wet sand. The thickness of each layer of the agglomeration bed is 6 cm. The mixed volume ratio of super-hydrophilic underwater super-oil-repellent sand and super-hydrophobic super-oil-wet sand is 1:1. The particle size ratio of super-hydrophilic underwater super-oil-repellent sand to super-hydrophobic super-oil-wet sand is 1:2.

[0069] The preparation steps of the super-hydrophilic underwater super-oil-repellent sand are as follows:

[0070] Step S1: 200 g of quartz sand was ultrasonically cleaned with 500 ml of ethanol and 500 ml of deionized water for 3 times, with an ultrasonic intensity of 30 kHz and each time for 20 min, and then placed in an oven at 80° C. and dried for 12 h to obtain pretreated quartz sand for use;

[0071] Step S2: adding 0.5 g dopamine and 0.5 g polyethyleneimine into 30 mL Tris-HCl buffer (50 mmol / L, pH=9), and ultrasonically dispersing for 20 min to prepare a polydopamine (PDA) solution at an ultrasonic intensity of 30 kHz;

[0072] Step S3: Add 3 g of silica nanoparticles (SiO 2 NPs), magnetically stirred at 500 rpm for 15 min and sonicated for 20 min to obtain a uniform suspension, with an ultrasonic intensity of 30 kHz;

[0073] Step S4: Add 200 g of the quartz sand prepared in step S1 to the suspension, stir at 20 ° C for 5 h (800 rpm), centrifuge the solution once at a speed of 2000 rpm, collect the precipitate, wash it three times with 500 ml of methanol and vacuum dry it at 80 ° C for 12 h to obtain super hydrophilic underwater super oleophobic SiO 2 @PDA-QS.

[0074] The preparation steps of the super hydrophobic and super oil-philic sand are as follows:

[0075] (1) 200gSiO 2@PDA-QS and 5 mL of silane coupling agent (N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AEAOS)) were dispersed in n-heptane (200 mL) and stirred at 80 °C for 12 h (500 rpm);

[0076] (2) centrifuging the solution once at 2000 rpm, collecting the solid and washing it three times with 500 ml of n-heptane;

[0077] (3) Drying under vacuum at 80 °C for 12 h to obtain super hydrophobic and super oleophilic AEAOS-SiO 2 @PDA-QS.

[0078] The super hydrophilic sand particle size in the first layer of agglomeration bed 13 is 160 mesh, and the super hydrophobic sand particle size is 80 mesh; the super hydrophilic sand particle size in the second layer of agglomeration bed 12 is 80 mesh, and the super hydrophobic sand particle size is 40 mesh; the super hydrophilic sand particle size in the third layer of agglomeration bed 11 is 40 mesh, and the super hydrophobic sand particle size is 20 mesh; the super hydrophilic sand particle size in the fourth layer of agglomeration bed 10 is 20 mesh, and the super hydrophobic sand particle size is 10 mesh; the super hydrophilic sand particle size in the fifth layer of agglomeration bed 9 is 10 mesh, and the super hydrophobic sand particle size is 5 mesh.

[0079] The thickness of the gravity separation zone is 10 cm. After the emulsion has been allowed to stand in the gravity separation tank for 30 minutes, the oil concentration in the water at the bottom of the separation zone is measured.

[0080] (1) Separation efficiency:

[0081] The separation efficiency (η, %) of the oil / water emulsion in the coalescer is calculated according to formula (1):

[0082]

[0083] In the formula, C filtrate and C feed are the oil concentrations of the inlet and outlet water of the oil-in-water emulsion (mg / L); C feed =500mg / L; C filtrate =75mg / L; η=98.50%.

[0084] (2) The median particle size of the effluent oil droplets was determined by laser particle size analyzer (MASTERSIZER3000, Malvern, England).

[0085] (3) The present invention optimizes the particle size ratio of super-hydrophilic sand and super-hydrophobic sand in the mixed particle agglomeration bed to reduce head loss and enhance the agglomeration performance of the agglomerator:

[0086] Pressure drop (ΔP) is the pressure change before and after the water-in-oil emulsion flows through the coalescing bed, and is an indicator for evaluating the energy consumption in the coalescing bed oil removal process. The lower the pressure drop, the lower the energy required in the coalescing bed oil removal process.

[0087] ΔP=ρgΔh (2)

[0088] Where ρ is the density of water (1000kg / m 3 ); g is the acceleration due to gravity (9.81 m / s 2 );Δh is the height difference of the liquid level between the inlet and outlet interfaces (m).

[0089] In order to evaluate the performance of the mixed particle agglomeration bed, the oil-water separation capacity and energy consumption indicators need to be considered comprehensively.

[0090] The mass factor is calculated according to formula (3). The larger the value, the better the agglomeration performance of the mixed particle agglomeration bed.

[0091]

[0092] Where QF is the quality factor, kPa -1 ; ΔP is the pressure drop, kPa.

[0093] The separation efficiency of the invention is as high as 98.50%, and the treatment effect on nano-scale oil droplets (1 μm) is remarkable, and the median particle size of the effluent oil droplets can reach 504 μm.

[0094] The present invention optimizes the particle size ratio of superhydrophilic sand and superhydrophobic sand in a mixed particle agglomeration bed to reduce head loss and improve agglomeration performance, and designs a agglomerator consisting of an agglomeration bed with a multi-level particle size gradient distribution to achieve segmented agglomeration of oil droplets, thereby improving oil-water separation efficiency and promoting its engineering application.

[0095] Effect of the mixing ratio of superhydrophilic / superhydrophobic quartz sand in coalescing bed on oil-water separation performance:

[0096] Under the conditions of flow rate of 1m / h and diesel-in-water concentration of 500mg / L, the effect of volume mixing ratio of superhydrophilic underwater superoleophobic quartz sand and superhydrophobic superoleophilic quartz sand on oil-water separation performance:

[0097] At 1:0, the quality factor is 0.14; η = 86.28%; median particle size: Dx(50) = 289 μm

[0098] When the ratio is 2:1, the quality factor is 0.19; η = 92.68%; median particle size: Dx(50) = 390 μm

[0099] At 1:1, the quality factor is 0.32; η = 98.50%; median particle size: Dx(50) = 504 μm

[0100] When 1:2, the quality factor is 0.15; η = 88.03%; median particle size: Dx(50) = 313 μm

[0101] At 0:1, the quality factor is 0.11; η = 80.06%; median particle size: Dx(50) = 215 μm

[0102] When the superhydrophilic / superhydrophobic quartz sand mixing ratio is 1:0, the median particle size of the effluent oil droplets is 289μm, and the separation efficiency is 86.28%; when the mixing ratio is 0:1, the median particle size of the effluent oil droplets is only 215μm, and the separation efficiency is 80.06%. This is because superhydrophilic sand can destroy the stability of oil droplets and promote oil droplet detachment, reducing clogging, but too high a ratio can easily reduce the agglomeration efficiency; superhydrophobic sand preferentially adsorbs oil droplets, which can promote oil droplet adhesion and agglomeration, but may increase the risk of agglomeration bed clogging. When the mixing ratio is 1:1, the quality factor reaches a maximum of 0.32Kpa -1 , the highest separation efficiency is 98.50%, indicating that the wetting force existing at the two wettability interfaces enhances the probability of oil droplet coalescence, and the oil droplets tend to move away from the superhydrophilic interface and close to the superhydrophobic interface, which significantly improves the coalescence efficiency. That is, the operating speed of the present invention is 1m / h, which reduces energy consumption while ensuring efficient separation.

[0103] Effect of particle size ratio of super-hydrophilic / super-hydrophobic quartz sand in coalesced bed on oil-water separation performance:

[0104] Under the conditions of flow rate of 1m / h and diesel-in-water concentration of 500mg / L, the effect of particle size ratio of superhydrophilic underwater superoleophobic quartz sand and superhydrophobic superoleophilic quartz sand on oil-water separation performance:

[0105] When the ratio is 3:1, the quality factor is 0.15; η = 82.33%; median particle size: Dx(50) = 240 μm

[0106] At 2:1, the quality factor is 0.19; η = 90.94%; median particle size: Dx(50) = 359 μm

[0107] At 1:1, the quality factor is 0.21; η = 93.26%; median particle size: Dx(50) = 401 μm

[0108] At 1:2, the quality factor is 0.32; η = 98.50%; median particle size: Dx(50) = 504 μm

[0109] When 1:3, the quality factor is 0.18; η = 88.03%; median particle size: Dx(50) = 313 μm

[0110] When the particle size ratio is 1:2 (160 / 80 mesh), the maximum particle size of the oil droplets in the water is 504 μm, the separation efficiency is the highest (98.50%), and the quality factor is the best (0.32 Kpa -1). This is because the increase in the specific surface area of ​​the super-hydrophilic sand will promote the adsorption of the water phase and the destabilization of the oil droplets. At the same time, the smaller pores will increase the contact opportunities between the small oil droplets and the surface of the coalescing bed. When the particle size ratio is 2:1 (80 / 160 mesh), the particle size of the oil droplets in the water is 359μm, and the separation efficiency is 90.94%. The increased specific surface area of ​​the super-hydrophobic sand is difficult to destroy the stability of the water-in-oil emulsion. The particle size ratio of 1:1 (160 / 160 mesh) forms a uniform pore structure, the particle size of the oil droplets in the water is 401μm, and the separation efficiency is 93.26%, but the specific surface area is reduced, which reduces the contact efficiency between the oil droplets and the surface of the coalescing bed. Although the non-uniform pore structure formed by the non-uniform particle size ratio (1:3 or 3:1) may increase the chance of collision, the uneven distribution of the fluid will affect the separation efficiency.

[0111] Effect of flow rate on oil-water separation performance:

[0112] When the flow rate is 1m / h, the quality factor is 0.32; η=98.50%; median particle size: Dx(50)=504μmWhen the flow rate is 2m / h, the quality factor is 0.21; η=94.08%; median particle size: Dx(50)=416μmWhen the flow rate is 3m / h, the quality factor is 0.20; η=92.56%; median particle size: Dx(50)=388μmWhen the flow rate is 4m / h, the quality factor is 0.19; η=91.05%; median particle size: Dx(50)=356μmWhen the flow rate is 5m / h, the quality factor is 0.18; η=90.24%; median particle size: Dx(50)=313μm

[0113] When the flow rate increases from 1m / h to 5m / h, the median particle size of the oil droplets in the outlet water decreases from 444μm to 313μm, and the oil-water separation efficiency decreases from 96.05% to 90.24%. This is because low flow rates prolong the residence time of the water-in-oil emulsion in the coalescer, increase the chance of oil droplet collision, and promote coalescence; high flow rates have the opposite effect. When the apparent flow rate increases from 1m / h to 5m / h, the quality factor increases from 0.25Kpa -1 Down to 0.18Kpa -1 , mainly the increase of pressure drop and the decrease of separation efficiency.

[0114] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A stepwise coalescence system based on wettability gradient, characterized in that: The agglomeration system comprises a storage tank, a segmented agglomerator and a gravity separation tank; the segmented agglomerator is composed of a plurality of layers of agglomeration beds, and a gravity separation zone is sandwiched between each layer of the agglomeration beds.

2. The wettability gradient-based segmented coalescence system according to claim 1, characterized in that: The storage tank stores the oil-in-water emulsion to be treated, and the oil is selected from one of engine oil, diesel, rapeseed oil and hexadecane.

3. The wettability gradient-based segmented coalescence system according to claim 2, characterized in that: The oil concentration is 100-500 mg / L, and the median diameter of the oil droplets is 0.1-10 μm.

4. The wettability gradient-based segmented coalescence system according to claim 1, characterized in that: Each layer of agglomeration bed is composed of a mixture of superhydrophilic underwater superoil-repellent sand and superhydrophobic superoil-repellent sand.

5. The wettability gradient-based segmented coalescence system according to claim 4, characterized in that: The preparation steps of the super-hydrophilic underwater super-oil-repellent sand are as follows: Step S1: ultrasonically clean the quartz sand and then dry it to obtain pretreated quartz sand; Step S2: adding dopamine and polyethyleneimine into Tris-HCl buffer to prepare a polydopamine solution; Step S3: adding silica nanoparticles to the polydopamine solution and sonicating; Step S4: adding the quartz sand prepared in step S1, collecting the precipitate, and obtaining superhydrophilic underwater superoleophobic SiO2@PDA-QS.

6. The wettability gradient-based segmented coalescence system according to claim 4, characterized in that: The preparation steps of the super hydrophobic and super oil-philic sand are as follows: (1) Dispersing SiO2@PDA-QS and silane coupling agent (N-(2-aminoethyl)-3-aminopropyltriethoxysilane) in n-heptane; (2) centrifuging the solution to collect the solid and washing it; (3) After drying, superhydrophobic and superoleophilic AEAOS-SiO2@PDA-QS was obtained.

7. The wettability gradient-based segmented coalescence system according to claim 5, characterized in that: The specific preparation steps of the super-hydrophilic underwater super-oil-repellent sand are as follows: Step S1: 190-210 g of quartz sand is ultrasonically cleaned with 500 ml of ethanol and 500 ml of deionized water for 3 times, with an ultrasonic intensity of 20-50 kHz, and each time for 15-20 min, and then placed in an oven at 75-85° C. and dried for 12 h to obtain pretreated quartz sand for use; Step S2: adding 0.4-0.6 g dopamine and 0.4-0.6 g polyethyleneimine into 30 mL Tris-HCl buffer, and performing ultrasonic dispersion for 20-25 min to prepare a polydopamine solution, with an ultrasonic intensity of 20-50 kHz; Step S3: adding 2.5-3.5 g of silica nanoparticles to the polydopamine solution, magnetically stirring at 500-600 rpm for 15-20 min and ultrasonicating for 20-25 min to obtain a uniform suspension, with an ultrasonic intensity of 20-50 kHz; Step S4: Add 190-210 g of the quartz sand prepared in step S1, stir at 20-25 ° C for 5-6 h, centrifuge the solution 1-2 times at a speed of 1900-2100 rpm, collect the precipitate, and then wash it three times with 500 ml of methanol and vacuum dry it at 75-85 ° C for 10-12 h to obtain super hydrophilic underwater super oleophobic SiO2@PDA-QS.

8. The wettability gradient-based segmented coalescence system according to claim 6, characterized in that: The preparation steps of the super hydrophobic and super oil-philic sand are as follows: (1) Disperse 190-210 g SiO2@PDA-QS and 4-6 mL silane coupling agent (N-(2-aminoethyl)-3-aminopropyltriethoxysilane) in 190-210 mL n-heptane and stir at 75-85 °C for 10-12 h; (2) centrifuging the solution 1-2 times at 1900-2100 rpm, collecting the solid and washing it three times with 500 ml of n-heptane; (3) After vacuum drying at 80 °C for 12 h, superhydrophobic and superoleophilic AEAOS-SiO2@PDA-QS was obtained.

9. The wettability gradient-based segmented coalescence system according to claim 1, characterized in that: The agglomeration beds in the segmented agglomerator are arranged layer by layer from bottom to top, and the size gradient of the mixed particles of the super-hydrophilic underwater super-oil-repellent sand and the super-hydrophobic super-oil-repellent sand in the agglomeration bed gradually increases from bottom to top.

10. The wettability gradient-based segmented coalescence system according to claim 1, characterized in that: The thickness of the gravity separation tank is 9-11 cm; the emulsion is allowed to stand in the gravity separation tank for 30-40 minutes.

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