Filter material suitable for removing fine particles in MTO (Methanol To Olefins) wastewater as well as preparation method and application of filter material

Abstract

The invention relates to the technical field of chemical wastewater treatment, in particular to a filter material suitable for removing fine particles in MTO wastewater and a preparation method and application thereof.The filter material comprises a core function phase, the core function phase is refined quartz sand subjected to hydroxylation modification treatment, the mass percentage content of the quartz sand is not lower than 95%, and the core function phase is an organic phase; the particle size of the quartz sand is designed to be in single-stage distribution or two-stage gradient distribution; wherein the particle size of the quartz sand in single-stage distribution ranges from 1.0 mm to 2.0 mm; the quartz sand in two-stage gradient distribution comprises an upper layer with the particle size range of 0.3-0.5 mm and a lower layer with the particle size range of 1.0-2.0 mm; according to the invention, efficient targeted removal of submicron particles is realized, through surface hydroxylation modification of the refined quartz sand, electrostatic adsorption and surface binding capabilities of the filter material to fine catalyst particles are significantly improved, and the removal rate of particles of 0.5-5 [mu] m is stabilized at 92% or more; and the technical bottleneck that the traditional quartz sand filter material has low rejection rate on particles with the particle size of less than 3 microns is broken through.

Description

Technical Field

[0001] This invention relates to the field of chemical wastewater treatment technology, specifically to a filter media suitable for removing fine particles from MTO wastewater, its preparation method, and its application. Background Technology

[0002] Methanol-to-olefins (MTO) is a key technology in modern coal chemical or natural gas chemical processes, generating a large amount of process wastewater during production. This wastewater has a complex composition, containing not only dissolved organic matter but also, characteristically, a large amount of fine catalyst particles (mainly ranging from 0.5 to 10 μm in size) and trace amounts of oily contaminants that have escaped from the reaction-regeneration system. These fine particles have extremely high surface energy and are highly stable in water. If they are not effectively removed, they will lead to a series of serious environmental and production problems, including blockage of subsequent biological treatment units, loss of catalyst resources, and excessive suspended solids in the effluent.

[0003] Currently, one of the mainstream technologies for treating MTO wastewater containing fine catalyst particles and oil pollutants in industry is particle filtration technology with quartz sand as the core. However, due to the unique physicochemical properties of MTO wastewater, existing technical solutions have shortcomings in filter media design, treatment efficiency, and long-term operation: (1) Insufficient filter media retention accuracy: Quartz sand filter media with uniform particle size is generally used, and the removal rate of fine particles below 3μm is usually less than 70%; (2) Limited regeneration effect: Filter media regeneration mostly adopts a single water washing regeneration process, which is difficult to completely remove the pollution layer formed by oil coating, resulting in incomplete regeneration of filter media and affecting its long-term operational stability; (3) Filter media performance is not adapted to wastewater characteristics: The surface properties of filter media have not been specifically optimized for the enhanced particle stability of MTO wastewater at pH>8. Therefore, developing a special filter media and its supporting application technology that can efficiently target and remove fine catalyst particles from MTO wastewater, has anti-oil clogging ability, and is easy to regenerate efficiently has become a key technical problem that urgently needs to be solved in this field.

[0004] Chinese patent publication number CN107720872B discloses a purification device and method for wash water in an MTO (Mechanical Toll Collection) unit. This method uses a granular bed (such as anthracite) to filter and adsorb pollutants. Once the bed is saturated, it switches to using wash water as the backwash liquid and mixes it with low-pressure steam for fluidized regeneration. Although this method introduces steam to enhance the regeneration effect, the main regeneration medium is still liquid water. This water has insufficient shearing and peeling capacity for dense fouling layers formed by viscous oily pollutants, resulting in incomplete regeneration, low bed porosity recovery rate, and affecting the long-term recyclability and operational stability of the filter media.

[0005] Chinese patent publication number CN114477488B discloses an apparatus and method for purifying MTO wastewater. Its core improvement lies in using hot nitrogen or air at 220-300℃ for high-temperature fluidized bed regeneration of saturated filter media, aiming to soften and remove oily contaminants through thermal energy. While this method enhances the regeneration process, the filter media used (such as quartz sand and anthracite) remain conventional and unmodified. It does not address the increased surface potential and enhanced stability of fine particles in MTO wastewater at pH > 8 by performing any hydrophilicization or charge modification on the filter media surface. Therefore, it fails to fundamentally improve the initial adsorption capacity and targeted capture ability of the filter media in alkaline environments, and the high-temperature regeneration process consumes a significant amount of energy.

[0006] In MTO wastewater treatment, existing filter media and related processes suffer from several key challenges, including insufficient precision in removing fine particles (especially submicron particles), low regeneration efficiency affecting long-term operational stability, and a failure to optimize the filter media surface to suit the physicochemical properties of the wastewater. Therefore, it is necessary to provide a filter media suitable for removing fine particles from MTO wastewater to overcome these technical bottlenecks. Summary of the Invention

[0007] The purpose of this invention is to provide a filter material, its preparation method, and its application suitable for removing fine particles from MTO wastewater in order to solve the above-mentioned problems and overcome the defects of the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, embodiments of the present invention provide a filter media suitable for the removal of fine particles from MTO wastewater, comprising a core functional phase, wherein the core functional phase is refined quartz sand that has undergone hydroxylation modification treatment, wherein the quartz sand contains... The mass percentage content is not less than 95%, and the particle size of the quartz sand is designed to be a single-level distribution or a two-level gradient distribution; Among them, the single-stage distribution of quartz sand has a particle size range of 1.0 to 2.0 mm; the two-stage gradient distribution of quartz sand includes an upper layer with a particle size range of 0.3 to 0.5 mm and a lower layer with a particle size range of 1.0 to 2.0 mm. The hydroxyl density on the surface of the quartz sand after hydroxylation modification is ≥1.2 mmol / g. The modified quartz sand surface can target and capture submicron-sized catalyst particles with hydroxyl-rich surfaces and weak positive charge in wastewater through electrostatic adsorption and hydrogen bonding.

[0009] In some embodiments of the first aspect, an auxiliary function phase is further included, which is combined with the core function phase; The auxiliary functional phase is a composite of nano-titanium dioxide modified with a silane coupling agent and diatomaceous earth, and the particle size of the auxiliary functional phase is 50 to 100 nm.

[0010] In some embodiments of the first aspect, the auxiliary functional phase comprises 0% to 5% by mass in the filter media; The mass percentage of the nano-titanium dioxide in the auxiliary functional phase is 0% to 5%; The mass of the silane coupling agent is 0% to 2.0% of the mass of the auxiliary functional phase.

[0011] In some embodiments of the first aspect, when the particle size of the quartz sand is designed to have a two-level gradient distribution, the bulk density of the quartz sand is 1.6 to 1.8 g / cm³, and the porosity increases from the lower layer to the upper layer; wherein the porosity of the lower layer is 35% to 45%, and the porosity of the upper layer is 40% to 50%.

[0012] Secondly, embodiments of this application also provide a method for preparing filter media suitable for removing fine particles from MTO wastewater, comprising the following steps: S1. Perform hydroxylation modification treatment by soaking the quartz sand in a 10% hydrochloric acid solution for 8 hours. S2. Wash the quartz sand treated in step S1 with deionized water until it is neutral. S3. Place the quartz sand treated in step S2 into a 5% sodium hydroxide solution and react at a constant temperature of 60°C for 4 hours. S4. Dry the refined quartz sand treated in step S3 at 105°C for 12 hours.

[0013] Thirdly, embodiments of this application also provide an application of filter media suitable for removing fine particles from MTO wastewater, comprising the following steps: S1. The filter material is loaded into the filter bed of the filtration device; S2. Control the pH value of the MTO wastewater to be treated to be 4.0 to 9.0, and filter it through the filter bed at a filtration flow rate of 8 to 20 m / h. S3. When the pressure difference of the filter bed reaches 0.3 MPa, the filter media is regenerated.

[0014] In some embodiments of the third aspect, the regeneration process employs a dual backflushing process involving both air and water, comprising the following steps: S1. Nitrogen gas is introduced into the bottom of the filter bed for backflushing, and the nitrogen flow rate is controlled to be 20 to 40 m / h for 5 minutes. S2. Hot water at a temperature not lower than 80°C is introduced into the bottom of the filter bed for backwashing, and the hot water flow rate is controlled at 15 to 20 m / h for 40 minutes.

[0015] The beneficial effects are: 1. This invention achieves highly efficient targeted removal of submicron particles. By modifying the surface of refined quartz sand with hydroxylation, the electrostatic adsorption and surface bonding ability of the filter media for fine catalyst particles is significantly improved. The removal rate of particles from 0.5 to 5 μm is consistently above 92%, breaking through the technical bottleneck of low retention rate of traditional quartz sand filter media for particles smaller than 3 μm. 2. This invention constructs an anti-oil synergistic purification system. The optional added composite auxiliary functional phase has both porous adsorption and photocatalytic properties, which can synergistically degrade trace oil pollutants during the filtration process, effectively alleviate the filter material clogging problem caused by oil contamination, and extend the filtration cycle. 3. By adopting a single-stage or two-stage gradient particle size design, combined with a controllable porosity distribution, a progressive interception mechanism from coarse filtration to fine filtration is formed, which not only improves the dirt holding capacity, but also reduces the rate of increase of bed pressure drop, ensuring the long-term stable operation of the system. 4. The dual backwashing and regeneration technology of air and water achieves efficient removal and cleaning of the fouling layer on the surface of the filter media through the synergistic effect of nitrogen shearing and hot water washing. The residual pollutant rate of the filter media after regeneration is less than 3%, which is significantly better than the effect of traditional single water backwashing or high temperature air regeneration. It also has lower energy consumption and safer operation. 5. This filter media and its application method can adapt to wastewater with pH values ​​ranging from 4.0 to 9.0. In particular, it addresses the challenge of increased particle stability in MTO wastewater under alkaline conditions. Through surface modification, it enhances the treatment efficiency over a wide pH range. The overall process has the advantages of long filter media life, high regeneration efficiency, and low operating costs, providing reliable technical support for the deep treatment and resource reuse of MTO wastewater. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This invention provides a flow chart for preparing filter media suitable for removing fine particles from MTO wastewater. Figure 2 The following are actual images of water samples of MTO wastewater before and after treatment with the composite filter media according to an embodiment of the present invention; Figure 3 The diagram shows the changes in inlet and outlet fine particulate matter concentrations during a 30-day long-term operation of the composite filter media provided in an embodiment of the present invention for treating a certain MTO quench water. Figure 4 The diagram shows the classification efficiency curves of the composite filter media provided in an embodiment of the present invention and the traditional quartz sand when treating MTO quench water, for particles in the 0.1-5.5 μm particle size range. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0019] It is important to emphasize that this invention addresses the core challenges in MTO reaction wastewater treatment, such as the low retention efficiency (generally less than 70%) of traditional quartz sand filter media for submicron-sized catalyst particles (0.5 to 5 μm), susceptibility to clogging by oil contaminants, and short operating cycles due to incomplete regeneration. This invention proposes a systematic solution. The technical concept of this invention is as follows: using high-purity refined quartz sand as the core, through precise particle size gradient design and high-density surface hydroxylation modification, a filter media substrate with both physical sieving and chemical adsorption functions is constructed to achieve highly efficient targeted capture of fine particles. Simultaneously, a silane coupling agent-modified nano-titanium dioxide and diatomaceous earth composite can be optionally introduced to form an auxiliary functional phase. Utilizing its porous adsorption and photocatalytic synergy, oil contaminants are degraded online, alleviating clogging at the source. Furthermore, a dual-backwash regeneration process is developed, using gas shearing and hot water washing to achieve deep regeneration and long-term recycling of the filter media.

[0020] In a first aspect, the present invention provides a filter media suitable for the removal of fine particles from MTO wastewater, comprising a core functional phase and an auxiliary functional phase, wherein the auxiliary functional phase is composite with the core functional phase, and the core functional phase is refined quartz sand that has undergone hydroxylation modification. The mass percentage content is not less than 95%, and it has high chemical stability and mechanical strength. The particle size of the quartz sand is designed to be a single-stage distribution or a two-stage gradient distribution. In single-stage distribution, the particle size is uniform, generally suitable for scenarios with relatively stable water quality, not extremely high particle load, and less stringent requirements on the rate of pressure differential increase. In two-stage gradient distribution, the upper layer of fine sand ensures high-precision interception, while the lower layer of coarse sand intercepts a very small amount of large particles or flocs escaping from the upper layer; simultaneously, it serves as a support layer, preventing the upper fine sand from being lost during backwashing and ensuring uniform water and air distribution. Two-stage gradient distribution enables progressive interception, optimizes pressure drop, and forms a structure where porosity decreases from top to bottom and pore size increases from top to bottom. It is specifically designed for complex systems like MTO wastewater, which has high concentrations, wide particle size distributions, and especially contains a large number of submicron particles.

[0021] Among them, the single-stage distribution of quartz sand has a particle size range of 1.0 to 2.0 mm; the two-stage gradient distribution of quartz sand includes an upper layer with a particle size range of 0.3 to 0.5 mm and a lower layer with a particle size range of 1.0 to 2.0 mm. When the particle size of the quartz sand is designed with a two-stage gradient distribution, the bulk density of the quartz sand is 1.6 to 1.8 g / cm³, and the porosity increases from the bottom layer to the top layer; the porosity of the bottom layer is 35% to 45%, and the porosity of the top layer is 40% to 50%. This gradient pore structure is conducive to achieving step-by-step interception from coarse to fine, extending the filtration cycle, and reducing the rate of increase in bed pressure drop.

[0022] The hydroxyl density on the surface of the hydroxylated modified quartz sand is ≥1.2 mmol / g. The modified quartz sand surface can target and capture submicron-sized catalyst particles with hydroxyl-rich surfaces and weak positive charge in wastewater through electrostatic adsorption and hydrogen bonding.

[0023] The auxiliary functional phase is a composite of nano-titanium dioxide and diatomaceous earth, modified with a silane coupling agent, and has a particle size of 50 to 100 nm. Through the synergistic effect of photocatalytic degradation and porous physical adsorption, the auxiliary functional phase enhances the removal of trace oil pollutants from wastewater and alleviates the clogging of filter media pores by oil.

[0024] The auxiliary functional phase comprises 0% to 5% by mass in the filter media; the nano-titanium dioxide comprises 0% to 5% by mass in the auxiliary functional phase; and the silane coupling agent comprises 0% to 2.0% by mass of the auxiliary functional phase. Adjusting their contents optimizes the dispersibility and interfacial bonding strength of the composite. Diatomaceous earth is calcined at 500℃ for 2 hours, cooled, and then mixed with nano-titanium dioxide at a mass ratio of 3:1. 2% by mass of silane coupling agent KH-550 is added to this mixture, which is then placed in a high-speed mixer and stirred at 1500 r / min for 30 minutes to obtain a composite of nano-titanium dioxide and diatomaceous earth modified with silane coupling agent. Hydroxylated mono-distribution refined quartz sand is mixed with the auxiliary functional phase at a mass ratio of 97:3. The materials are placed in a mixing device and dry-mixed for 15 minutes until homogeneous, thus obtaining the mono-distribution composite filter media.

[0025] Using the above-mentioned single-stage distributed composite filter media, MTO quench water was treated with a pH of 6.8 and a suspended solids (SS) concentration of 145 mg / L. Fine catalyst particles with a particle size of less than 1 μm accounted for 22% of the total suspended solids, of which particles in the 0.5-1 μm range accounted for 15%. The filtration flow rate was controlled at 10 m / h.

[0026] In this embodiment, during a 24-hour continuous operation cycle, the total removal rate of suspended solids (SS) reached 86.2%, with an average SS concentration of approximately 20 mg / L in the effluent. Specifically, the removal rate for fine particles with a diameter of 0.5-1 μm increased from less than 70% with traditional quartz sand filter media to 78%. Filtration was stopped when the filter bed pressure differential reached 0.3 MPa, and the filter media was regenerated using a dual backwashing process. After backwashing and regeneration, the filter media's dirt-holding capacity recovered to 91%. The results indicate that, while maintaining the core hydroxylation modification, even with a single-stage distribution, the filter media performance significantly surpasses traditional technologies (removal rate <70%), demonstrating the universality of the core invention. However, compared to the two-stage gradient distribution scheme, a 48-hour cycle showed a removal rate of 94.5%, effluent SS <8 mg / L, submicron particle removal rate of 88%, and a recovery rate of 97%.

[0027] Secondly, the present invention provides a method for preparing filter media suitable for removing fine particles from MTO wastewater, comprising the following steps: S1. Hydroxylation modification treatment is carried out. Natural quartz sand is selected, crushed by jaw crusher and ball milled, and then a single component with a particle size of 1.0–2.0 mm is obtained by passing it through a grading sieve. The quartz sand is soaked in a 10% hydrochloric acid solution for 8 hours to remove surface impurities and metal ions. S2. Wash the quartz sand treated in step S1 with deionized water until it is neutral. S3. The quartz sand treated in step S2 is placed in a 5% sodium hydroxide solution and reacted at 60°C for 4 hours to introduce high-density hydroxyl groups on the surface. S4. The refined quartz sand treated in step S3 is dried at 105°C for 12 hours to obtain hydroxylated modified refined quartz sand.

[0028] Thirdly, the present invention provides an application of filter media suitable for the removal of fine particles from MTO wastewater, comprising the following steps: S1. Fill the filter media into the filter bed of the filtration device; S2. Control the pH value of the MTO wastewater to be treated to be 4.0 to 9.0, and filter it through the filter bed at a filtration flow rate of 8 to 20 m / h. S3. Monitor the filter bed pressure difference in real time. When the filter bed pressure difference reaches 0.3MPa, stop filtration and regenerate the filter media.

[0029] The regeneration process employs a dual backflushing process involving both air and water, and includes the following steps: S1. Introduce nitrogen into the bottom of the filter bed for backflushing. Control the nitrogen flow rate to be 20 to 40 m / h and the duration to be 5 minutes. Use the gas shear force to initially loosen and peel off the surface dirt layer. S2. Introduce hot water at a temperature not lower than 80℃ into the bottom of the filter bed for backflushing, controlling the hot water flow rate at 15 to 20 m / h for 40 minutes. Through the combined action of thermodynamics and fluid shearing, the adhering oil and fine particles are thoroughly removed.

[0030] After filtration, the removal rate of fine catalyst particles with a particle size of 0.5 to 5 μm in the wastewater is no less than 92%, achieving efficient and stable removal of submicron-sized particles. After filtration, the suspended solids (SS) content of the wastewater can be stably reduced to below 10 mg / L, meeting the standards for subsequent treatment or reuse.

[0031] Appendix to this invention specification Figure 3 The horizontal axis represents continuous operating time (in hours), and the vertical axis represents the concentration of fine particulate matter in the inlet and outlet water samples at the corresponding time (in mg / L). As shown in the curves, the inlet particulate matter concentration fluctuates throughout the entire operating cycle, while the effluent concentration remains consistently low and stable. This indicates that the composite filter media possesses a continuous and efficient capacity for retaining fine particulate matter during long-term operation, without significant performance degradation or penetration. This verifies its excellent anti-fouling properties and operational stability in MTO quench water treatment.

[0032] Appendix to this invention specification Figure 4The diagram shows the classification efficiency curves of the composite filter media provided by this invention and traditional quartz sand in treating MTO quench water with particle sizes ranging from 0.1 to 5.5 μm. The horizontal axis represents particle size (unit: μm), and the vertical axis represents the classification removal efficiency (%) for the corresponding particle size. The curve comparison shows that, within the particle size range, the overall classification efficiency of the composite filter media is significantly better than that of traditional quartz sand, especially in the removal range of fine particles below 0.5 μm. This indicates that the composite filter media has a significant advantage in retaining submicron-sized particles and is suitable for the efficient separation of fine particulate pollutants in MTO quench water.

[0033] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A filter media suitable for removing fine particles from MTO wastewater, characterized in that: It includes a core functional phase, wherein the core functional phase is refined quartz sand that has undergone hydroxylation modification, and the quartz sand contains... The mass percentage content is not less than 95%, and the particle size of the quartz sand is designed to be a single-level distribution or a two-level gradient distribution; Among them, the single-stage distribution of quartz sand has a particle size range of 1.0 to 2.0 mm; the two-stage gradient distribution of quartz sand includes an upper layer with a particle size range of 0.3 to 0.5 mm and a lower layer with a particle size range of 1.0 to 2.0 mm. The hydroxyl density on the surface of the quartz sand after hydroxylation modification is ≥1.2 mmol / g. The modified quartz sand surface can target and capture submicron-sized catalyst particles with hydroxyl-rich surfaces and weak positive charge in wastewater through electrostatic adsorption and hydrogen bonding.

2. The filter media for removing fine particles from MTO wastewater according to claim 1, characterized in that: It also includes auxiliary function phases, which are combined with the core function phases; The auxiliary functional phase is a composite of nano-titanium dioxide modified with a silane coupling agent and diatomaceous earth, and the particle size of the auxiliary functional phase is 50 to 100 nm.

3. The filter media for removing fine particles from MTO wastewater according to claim 2, characterized in that: The auxiliary functional phase in the filter media has a mass percentage content of 0% to 5%; The mass percentage of the nano-titanium dioxide in the auxiliary functional phase is 0% to 5%; The mass of the silane coupling agent is 0% to 2.0% of the mass of the auxiliary functional phase.

4. The filter media for removing fine particles from MTO wastewater according to claim 1, characterized in that: When the particle size of the quartz sand is designed to have a two-stage gradient distribution, the bulk density of the quartz sand is 1.6 to 1.8 g / cm³, and the porosity increases from the lower layer to the upper layer; wherein the porosity of the lower layer is 35% to 45%, and the porosity of the upper layer is 40% to 50%.

5. A method for preparing filter media suitable for removing fine particles from MTO wastewater, using the filter media according to any one of claims 1-4, characterized in that: Includes the following steps: S1. Perform hydroxylation modification treatment by soaking the quartz sand in a 10% hydrochloric acid solution for 8 hours. S2. Wash the quartz sand treated in step S1 with deionized water until it is neutral. S3. Place the quartz sand treated in step S2 into a 5% sodium hydroxide solution and react at a constant temperature of 60°C for 4 hours. S4. Dry the refined quartz sand treated in step S3 at 105°C for 12 hours.

6. An application of a filter media suitable for removing fine particles from MTO wastewater, using the filter media according to any one of claims 1-4, characterized in that, Includes the following steps: S1. The filter material is loaded into the filter bed of the filtration device; S2. Control the pH value of the MTO wastewater to be treated to be 4.0 to 9.0, and filter it through the filter bed at a filtration flow rate of 8 to 20 m / h. S3. When the pressure difference of the filter bed reaches 0.3 MPa, the filter media is regenerated.

7. The application of the filter media for removing fine particles from MTO wastewater according to claim 6, characterized in that: The regeneration process employs a dual backflushing process involving both air and water, and includes the following steps: S1. Nitrogen gas is introduced into the bottom of the filter bed for backflushing, and the nitrogen flow rate is controlled to be 20 to 40 m / h for 5 minutes. S2. Hot water at a temperature not lower than 80°C is introduced into the bottom of the filter bed for backwashing, and the hot water flow rate is controlled at 15 to 20 m / h for 40 minutes.

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