Treatment method for high-COD aniline wastewater through cooperation of membrane-process graded concentration and double-effect evaporative crystallization

Abstract

The invention provides a treatment method for high-COD aniline wastewater through cooperation of membrane-process graded concentration and double-effect evaporative crystallization, which comprises the following treatment steps: S1, wastewater pretreatment: m-phenylenediamine wastewater enters a raw water temporary storage tank for temporary storage, and mechanical impurities are removed through a booster pump and a security filter; according to the process, the evaporation water amount is remarkably reduced through double-membrane method NF + RO gradient pre-concentration, and the treatment load of an evaporation system is reduced; secondary steam waste heat is utilized in double-effect evaporation, energy is saved by 50% compared with traditional single-effect evaporation, the total operation cost is reduced by 30%-40% in combination with the low energy consumption characteristic of a membrane method, meanwhile, m-phenylenediamine is efficiently recycled in the form of a crude product, the distilled water recycling rate exceeds 95%, a circular economy closed loop of'wastewater-resource-recycled water 'is formed, and the resource utilization rate is greatly increased.

Description

Technical Field

[0001] The present invention relates to the technical field of highly difficult industrial wastewater, and in particular to a treatment method for high-COD aniline wastewater by membrane-based graded concentration and synergistic double-effect evaporation and crystallization. Background Art

[0002] MPD (chemical formula: C6H8N2) is an important aromatic diamine compound. Due to its unique chemical properties (such as strong reactivity, alkalinity, and stability), it is widely used in various industrial fields such as the dye industry and reverse osmosis membrane production. MPD wastewater is characterized by high pollution and high COD. MPD (COD contribution value is as high as 1.6g / g) is biologically toxic. Traditional biochemical treatment methods are ineffective, and traditional single treatment processes are difficult to meet standards. Existing membrane treatment methods suffer from severe membrane fouling and difficult to handle concentrated liquids. Conventional evaporation and crystallization processes have high energy consumption and difficult-to-control operating costs. Existing technologies typically treat high-salt, high-organic wastewater using single membrane technologies (such as RO) or traditional evaporation processes, but these processes pose challenges such as membrane fouling, high energy consumption, and resource waste. This invention, for the first time, combines nanofiltration (NF) concentration and reduction with reverse osmosis (RO) advanced treatment and dual-effect evaporation and crystallization. By leveraging the synergistic effects of NF's selective retention (retaining m-phenylenediamine) and RO's efficient desalination (removing salt and small molecules), it addresses the challenge of single technologies being unable to treat high-organic wastewater. Summary of the Invention

[0003] (1) Technical problems solved In view of the shortcomings of the existing technology, the present invention provides a treatment method for high-COD aniline wastewater by membrane graded concentration synergistically with double-effect evaporation and crystallization, which solves the problem that a single technology cannot treat high-concentration organic wastewater.

[0004] (2) Technical solution To achieve the above objectives, the present invention is implemented through the following technical solution: a method for treating high-COD aniline wastewater by membrane-based graded concentration and synergistic double-effect evaporation and crystallization, characterized by comprising the following processing steps: S1. Wastewater pretreatment: The m-phenylenediamine wastewater is temporarily stored in the raw water buffer tank, and mechanical impurities are removed through a booster pump and a safety filter; S2, membrane graded concentration: (1) Primary membrane concentration: The wastewater is pressurized by a high-pressure pump and enters the primary membrane system, where it is circulated and concentrated to 1 / 4 of its original volume. The primary produced water is temporarily stored, and the concentrated water is returned to the raw water tank for circulated concentration. (2) Secondary membrane deep treatment: The primary produced water enters the secondary membrane system through the secondary booster pump and high-pressure pump. The secondary produced water meets the discharge standards and the concentrated water returns to the primary raw water tank; S3, double-effect evaporation crystallization: the first-stage concentrated liquid enters the double-effect evaporator, after the first-effect evaporation, it is transferred to the second effect to continue evaporation until the solution specific gravity is 1.1-1.2, to promote crystallization; S4, metaphenylenediamine recovery: After crystallization, the mixed liquid is separated by a centrifuge, the solid is the crude metaphenylenediamine, and the mother liquor is returned to the evaporator for recycling; S5. Distilled water reuse: If the condensed water produced by the above evaporation process meets the reuse standards, it can be directly reused instead of discharged.

[0005] Preferably, the S1 m-phenylenediamine wastewater has a high COD (32000 mg / l-48000 mg / l) and a concentration of 2.0%-3.0%.

[0006] Preferably, the primary membrane system in S2 adopts an anti-pollution nanofiltration membrane, and the secondary membrane system adopts an anti-pollution reverse osmosis membrane.

[0007] Preferably, the molecular weight cut-off of the nanofiltration membrane in S2 is ≤150Da, and the operating pressure is 2.0-4.0MPa.

[0008] Preferably, the nanofiltration membrane in S2 performs gradient pre-concentration to complete the reduction at a lower pressure.

[0009] Preferably, the first effect in S3 is heated by steam, and the second effect utilizes secondary steam, and the concentrated liquid after evaporation is crystallized to precipitate m-phenylenediamine.

[0010] Preferably, the second-effect evaporation temperature in S3 is controlled at 60-70°C.

[0011] (3) Beneficial effects The present invention provides a treatment method for high-COD aniline wastewater by membrane-based graded concentration combined with double-effect evaporation and crystallization. It has the following beneficial effects: 1. This process significantly reduces the amount of evaporated water and the processing load of the evaporation system through double-membrane NF+RO gradient pre-concentration. The double-effect evaporation utilizes the waste heat of secondary steam, saving 50% energy compared with traditional single-effect evaporation. Combined with the low energy consumption characteristics of the membrane method, the total operating cost is reduced by 30%-40%. At the same time, m-phenylenediamine is efficiently recovered in the form of crude product, and the distilled water reuse rate exceeds 95%, forming a circular economy closed loop of "wastewater → resources → reused water", which greatly improves resource utilization.

[0012] 2. This invention achieves a stable COD level of <500 mg / L in the effluent from the treatment process, meeting the indirect emission limit of the comprehensive sewage discharge standard and minimizing environmental pollution risks. The collaborative design of membrane concentration and evaporative crystallization overcomes the challenge of zero-discharge of high-COD wastewater. Crystallization separation technology avoids the generation of hazardous MPD waste, significantly enhancing environmental compliance. The overall process is highly efficient, economical, and sustainable, providing a viable industrialized path for the treatment of reverse osmosis membrane production wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is an overall flow chart of a treatment method for high-COD aniline wastewater using membrane-based graded concentration and synergistic double-effect evaporation and crystallization proposed by the present invention; Figure 2 The present invention provides a membrane fractionation concentration flow chart for a treatment method of high-COD aniline wastewater using membrane fractionation concentration in synergistic dual-effect evaporation and crystallization. DETAILED DESCRIPTION

[0014] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0015] Example: like Figure 1-2 As shown, the embodiment of the present invention provides a method for treating high-COD aniline wastewater by membrane graded concentration and synergistic double-effect evaporation crystallization, comprising the following treatment steps: S1. Wastewater pretreatment: The m-phenylenediamine wastewater is temporarily stored in the raw water buffer tank, and mechanical impurities are removed through a booster pump and a safety filter. The wastewater quality is: COD 38000mg / L, m-phenylenediamine concentration 2.5%, pH 9.5-10.

[0016] S2, membrane graded concentration: (1) Primary membrane concentration: The wastewater is pressurized by a high-pressure pump and enters the primary membrane system, where it is circulated and concentrated to 1 / 4 of its original volume. The primary produced water is temporarily stored, and the concentrated water is returned to the raw water tank for circulation; (2) Secondary membrane deep treatment: The primary produced water enters the secondary membrane system through the secondary booster pump and high-pressure pump. The secondary produced water meets the discharge standards and the concentrated water returns to the primary raw water tank. NF (retention rate > 85%) → (COD drops to below 8,000 mg / L) → RO (COD drops to below 500 mg / L).

[0017] S3. Double-effect evaporation and crystallization: The first-stage concentrated liquid enters the double-effect evaporator. After the first-effect evaporation, it is transferred to the second-effect evaporation to continue evaporation until the solution specific gravity is 1.1-1.2. The temperature is 5-15℃ for crystallization. The first-effect evaporation capacity is 0.3 t / h (steam consumption is 0.15 t / h), and the second-effect evaporation capacity is 0.2 t / h (steam consumption is 0.1 t / h). The crude MPD product is crystallized.

[0018] S4. MPD recovery: After crystallization, the mixed liquid is separated by a centrifuge, and the solid is the crude meta-phenylenediamine. The mother liquor is returned to the evaporator for recycling treatment; the income from the MPD crystal product offsets 30% of the cost.

[0019] S5. Distilled water reuse: If the above-mentioned secondary produced water meets the reuse standards, it can be directly reused instead of discharged.

[0020] The COD of the m-phenylenediamine wastewater in S1 is high, with a concentration of 2.0%-3.0%. The primary membrane system in S2 uses a nanofiltration membrane, and the secondary membrane system uses a reverse osmosis membrane. The molecular weight cutoff of the nanofiltration membrane in S2 is ≤150Da, and the operating pressure is 2.0-4.0MPa. The first effect in S3 is steam-heated, and the second effect uses secondary steam. The concentrated liquid after evaporation is crystallized to precipitate MPD. The second-effect evaporation temperature in S3 is controlled at 50-70℃. Pre-concentration: Using a pollution-resistant nanofiltration membrane (NF90), the selectivity of nanofiltration is utilized to concentrate organic matter, while simultaneously allowing some small-molecule organic matter to pass through to reduce operating pressure, thereby achieving high-fold concentration at relatively low pressure, concentrating the MPD to 10% (COD = 140,000 mg / l). The secondary membrane system uses a reverse osmosis membrane (BWFR) to deeply intercept the small-molecule organic matter remaining in the primary produced water (retention rate > 95%), ensuring the COD concentration of the produced water is less than 500 mg / L, which is directly reused in the production line, reducing fresh water consumption. Gradient evaporation: First-effect evaporation: control the temperature at 60-65℃ and the vacuum degree at -0.07 MPa, and give priority to evaporating water to concentrate it; Second-effect evaporation: using the first-effect secondary steam heating, the temperature is reduced to 50-55 ° C, the vacuum degree is -0.08 MPa, and the m-phenylenediamine solution is further concentrated to promote its supersaturated crystallization; Crystal seed induction technology: After concentrating to a specific gravity of 1.2, the product is discharged and cooled to below 15°C before MPD seed crystals (particle size 50-100 μm) are added to reduce the crystallization energy barrier, avoid fine crystal formation, and improve the crude product purity (from 90% to 95%). Dynamic control of concentrated liquid: After double-effect evaporation and concentration, the concentration of the solution in the evaporator is monitored by an online hydrometer. When the specific gravity is greater than 1.2, the discharge pump is triggered to discharge part of the concentrated liquid to the crystallization system for further processing, avoiding crystallization in the evaporator and clogging the evaporator, while improving the purity of the crystals.

[0021] Membrane system self-cleaning design: A pulse backwash module is integrated into the nanofiltration membrane unit (frequency: 2 times / day, pressure: 0.3MPa), combined with a citric acid + EDTA compound cleaning agent, to extend the membrane life to more than 2 years (compared to 1 year with traditional processes); PLC+IoT monitoring: PLC collects parameters such as membrane flux, evaporator temperature, and centrifuge speed in real time, and uses algorithms to dynamically adjust pump speed and steam volume to ensure a system energy efficiency ratio (COP) greater than 4.5, a 30% improvement over traditional processes. Cascade utilization of waste heat: The evaporated condensed water (50-60℃) is preheated to raw water (25℃→40℃) through a plate heat exchanger, reducing the energy consumption of water heating in the membrane system and reducing overall steam consumption by 15%.

[0022] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for treating high-COD aniline wastewater by membrane graded concentration and synergistic double-effect evaporation crystallization, characterized in that: The following processing steps are included: S1. Wastewater pretreatment: The m-phenylenediamine wastewater is temporarily stored in the raw water buffer tank, and mechanical impurities are removed through a booster pump and a safety filter; S2, membrane graded concentration: (1) Primary membrane concentration: The wastewater is pressurized by a high-pressure pump and enters the primary membrane system, where it is circulated and concentrated to 1 / 4 of its original volume. The primary produced water is temporarily stored, and the concentrated water is returned to the raw water tank for circulated concentration. (2) Secondary membrane deep treatment: The primary produced water enters the secondary membrane system through the secondary booster pump and high-pressure pump. The secondary produced water meets the discharge standards and the concentrated water returns to the primary raw water tank; S3, double-effect evaporation crystallization: the first-stage concentrated liquid enters the double-effect evaporator, after the first-effect evaporation, it is transferred to the second effect to continue evaporation until the solution specific gravity is 1.1-1.2, to promote crystallization; S4, metaphenylenediamine recovery: After crystallization, the mixed liquid is separated by a centrifuge, the solid is the crude metaphenylenediamine, and the mother liquor is returned to the evaporator for recycling; S5. Distilled water reuse: If the condensed water produced by the above evaporation process meets the reuse standards, it can be directly reused instead of discharged.

2. The method for treating high-COD aniline wastewater by membrane fractionation concentration and synergistic double-effect evaporation crystallization according to claim 1, characterized in that: The S1 m-phenylenediamine wastewater has a high COD (32,000 mg / l-48,000 mg / l) and a concentration of 2.0%-3.0%.

3. The method for treating high-COD aniline wastewater by membrane fractionation concentration and synergistic double-effect evaporation crystallization according to claim 1, characterized in that: In the S2, the primary membrane system adopts an anti-pollution nanofiltration membrane, and the secondary membrane system adopts an anti-pollution reverse osmosis membrane.

4. The method for treating high-COD aniline wastewater by membrane graded concentration and synergistic double-effect evaporation crystallization according to claim 1, characterized in that: The molecular weight cut-off of the nanofiltration membrane in S2 is ≤150Da, and the operating pressure is 2.0-4.0MPa.

5. The method for treating high-COD aniline wastewater by membrane graded concentration and synergistic double-effect evaporation crystallization according to claim 1, characterized in that: The nanofiltration membrane in S2 performs gradient pre-concentration and completes the reduction at a lower pressure.

6. The method for treating high-COD aniline wastewater by membrane fractionation concentration and synergistic double-effect evaporation crystallization according to claim 1, characterized in that: In the S3, the first effect is heated by steam, and the second effect utilizes secondary steam. The concentrated liquid after evaporation is crystallized to precipitate m-phenylenediamine.

7. The method for treating high-COD aniline wastewater by membrane fractionation concentration and synergistic double-effect evaporation crystallization according to claim 1, characterized in that: The second-effect evaporation temperature in S3 is controlled at 60-70°C.

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