A purification treatment process for pyrazolone production wastewater

Abstract

The present application belongs to the technical field of wastewater treatment, and particularly relates to a purification treatment process for pyrazolone production wastewater. The present application, in view of the characteristics of high COD, high total nitrogen, high salt and difficult biodegradation of the pyrazolone production wastewater, constructs a whole-process collaborative process of targeted pretreatment-resource recovery-mild detoxification-depth purification, efficiently recovers acetonitrile through composite extraction and pervaporation membrane separation, catalyzes alkaline hydrolysis through a magnesium-aluminum composite catalyst, mildly degrades heterocyclic compounds through ring-opening, and improves biodegradability. Photocatalysis and Fenton-like are combined to continuously generate hydroxyl radicals, deeply oxidize and mineralize refractory organic matter, modify the biological carbon to adsorb residual small molecules and chroma, and reduce the residual metal ion and secondary pollution risk. The oxidation-adsorption coupling strategy combines the strong degradation ability of advanced oxidation and the adsorption purification function of biological carbon, realizes the beneficial improvement of treatment efficiency, ensures that the wastewater meets the discharge standard, recovers resources to reduce costs, and has both environmental and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a purification process for pyrazolone production wastewater. Background Technology

[0002] Pyrazolone is an important intermediate in pesticides, pharmaceuticals, and dyes. Industrially, it is often prepared by condensation and cyclization of hydrazine with ketones / esters. The current mainstream process is the acetonitrile-assisted reaction method, which can improve selectivity and reduce impurities, but the wastewater after the reaction has the following characteristics:

[0003] Contains residual acetonitrile, pyrazolone intermediates, and by-product salts (sodium chloride / sodium sulfate);

[0004] High COD (8000~15000 mg / L), high total nitrogen, and deep color;

[0005] Poor biochemical susceptibility (B / C < 0.2), making it difficult to meet traditional biochemical standards;

[0006] Direct emissions cause severe pollution and waste resources from acetonitrile and salt separation.

[0007] Currently, the main methods for treating pyrazolone production wastewater include physicochemical and biological treatment methods. Physicochemical methods, such as extraction, distillation, and adsorption, can remove some organic matter, but often suffer from low resource recovery rates, high treatment costs, and the potential for secondary pollution. Biological treatment methods are widely studied due to their lower cost and environmental friendliness; however, the high-salt environment and complex heterocyclic compounds in pyrazolone wastewater strongly inhibit microorganisms, leading to low treatment efficiency and difficulty in achieving emission standards. To improve biodegradability, dilution pretreatment is often required, which not only increases the treatment scale and cost but also reduces the possibility of resource recovery. Furthermore, while advanced oxidation technologies can effectively degrade recalcitrant organic matter, they suffer from high oxidant consumption, high operating costs, incomplete mineralization, and the potential generation of toxic and harmful intermediate products, failing to meet increasingly stringent environmental protection requirements.

[0008] Therefore, developing an efficient, economical, and environmentally friendly wastewater treatment process for pyrazolone production to achieve deep removal of pollutants and effective resource recovery is an urgent problem to be solved in this field. Summary of the Invention

[0009] The purpose of this invention is to address existing problems by providing a purification process for pyrazolone production wastewater.

[0010] This invention is achieved through the following technical solution:

[0011] A purification process for pyrazolone production wastewater, wherein the wastewater is the mother liquor and washing wastewater generated during the condensation and ring-closure preparation of pyrazolone from methylhydrazine and ethyl acetoacetate in acetonitrile-coated solubilization, and the wastewater has a COD of 8000~35000 mg / L and a salt content of 5~20%, comprising the following steps:

[0012] S1. Pretreatment and targeted impurity removal:

[0013] After filtering and pH adjustment (5.5~6.5) of the wastewater, a two-stage countercurrent extraction was performed using a composite extractant to remove pyrazolone and hydrophobic byproducts from the wastewater, yielding the raffinate phase.

[0014] S2 and acetonitrile efficient recovery:

[0015] The raffinate obtained in step S1 is subjected to vacuum distillation and pervaporation membrane separation to recover acetonitrile; wherein, the vacuum distillation yields crude acetonitrile, and the bottom liquid of the vacuum distillation column enters the pervaporation unit for separation using a PDMS (polydimethylsiloxane) pervaporation membrane to remove acetonitrile content in the residue to ≤200mg / L.

[0016] S3, Gentle denitrification and detoxification:

[0017] The wastewater after acetonitrile removal is subjected to alkaline catalytic hydrolysis in the presence of a magnesium-aluminum composite catalyst to convert residual nitriles into organic acids and undergo ring-opening degradation of heterocyclic compounds, thereby improving the biodegradability of the wastewater. After the reaction, the catalyst is recovered by centrifugation and recycled.

[0018] S4. Volume reduction and concentration, and salt resource utilization:

[0019] The hydrolyzed wastewater is sequentially treated by ultrafiltration and nanofiltration. The nanofiltration concentrate is incorporated into step S5 for deep purification. The nanofiltration permeate is mechanically steam-compressed and evaporated to crystallize and obtain industrial-grade ammonium sulfate or ammonium chloride. The evaporation condensate is reused.

[0020] S5, Deep Purification:

[0021] The nanofiltration concentrate obtained in step S4 is combined with the mechanical vapor recompression evaporation mother liquor, and then subjected to photocatalytic coupling Fenton oxidation and modified biochar fixed bed adsorption in sequence. The treated effluent meets the discharge or reuse standards.

[0022] Further, the composite extractant mentioned in step S1 is a mixture of tributyl phosphate and kerosene, with a volume ratio of 1:(3~5) and an extraction ratio (oil:water) of 1:(2~5).

[0023] Furthermore, the vacuum degree of the reduced pressure distillation described in step S2 is -0.06 to -0.08 MPa (gauge pressure), the number of theoretical plates is 25 to 30, and the reflux ratio is 1.5 to 2.5;

[0024] The pervaporation unit uses a PDMS (polydimethylsiloxane) pervaporation membrane, which can withstand a salt concentration of ≤25wt% and an operating temperature of 60~70℃.

[0025] Furthermore, the magnesium-aluminum composite catalyst mentioned in step S3 is MgO-Al2O3, with a crystal form of γ-Al2O3 supported on MgO, a particle size of 50~100μm, and an addition amount of 0.5~1g / L;

[0026] The magnesium-aluminum composite catalyst is prepared by co-precipitation method, specifically: magnesium salt and aluminum salt are mixed and dissolved at a Mg:Al molar ratio of 1:(2~3), ammonia water is added dropwise to adjust the pH to 9.0~10.0, the precipitate is aged, filtered, washed, dried, and calcined at 550~650℃ for 3~4h to obtain the catalyst.

[0027] The conditions for alkaline-catalyzed hydrolysis are: pH 11.0~12.0, reaction temperature 110~125℃, pressure 0.15~0.20MPa, and reaction time 60~80min.

[0028] Furthermore, the nanofiltration process described in step S4 uses a surface-modified alkali-resistant nanofiltration membrane with a molecular weight cutoff of 200~400 Da;

[0029] The mechanical vapor recompression evaporation uses a titanium alloy evaporator with an evaporation temperature of 70~85℃ and a vacuum degree of -0.07~-0.09MPa (gauge pressure).

[0030] Furthermore, in step S5, before entering the reactor, the photocatalytically coupled Fenton oxidation process involves adding a coagulant (polyaluminum chloride, dosage 50-80 mg / L) to the combined wastewater for homogenization pretreatment. The photocatalytically coupled Fenton oxidation process uses a g-C3N4 / modified TiO2 composite catalyst at a dosage of 0.3-0.8 g / L, H2O2 as the oxidant at a dosage of 500-800 mg / L, UV-C as the activation light source, and a reaction time of 30-40 min.

[0031] Furthermore, the preparation of the g-C3N4 / modified TiO2 composite catalyst includes the following steps:

[0032] (1) Mix urea and thiourea at a mass ratio of 9:1, place them in a covered crucible, calcine at 500~600℃ for 2.5~3.5h, with a heating rate of 5℃ / min, cool, ball mill, and pass through a 200-mesh sieve to obtain g-C3N4.

[0033] (2) Disperse the above g-C3N4 in an ethanol-water mixture (ethanol:water = 4:1) at a mass-to-volume ratio of 1g:(20~30)mL. After ultrasonic treatment for 30~40min, add tetrabutyl titanate (the amount added is 10~15% of the volume of the ethanol-water mixture), adjust the pH to 3.0~3.5 with dilute hydrochloric acid (mass fraction 5~10%), and stir in a water bath at 60℃ for 2~3h to obtain g-C3N4-TiO2 suspension;

[0034] (3) Add ethyl silicate (0.8-1.2% of the volume of the ethanol-water mixture) to the above suspension, adjust the pH to 8.5-9.0 with ammonia, stir at 40-50℃ for 1-3 hours to form a uniform SiO2 protective film, filter, wash with deionized water until neutral, dry at 75-85℃, and calcine at 400℃ for 2 hours.

[0035] Furthermore, the photocatalytic coupling Fenton oxidation uses an industrial-grade ultraviolet reactor. The reactor is a multi-lamp matrix arrangement with a lamp spacing of 15-20cm. A guide plate is installed inside the reactor, and the light penetration depth is 5-15cm.

[0036] Furthermore, the adsorbent of the modified biochar fixed bed in step S5 is corn cob-based modified char, with a space velocity of 1-2 h⁻¹. -1 .

[0037] Furthermore, the preparation of the corn cob-based modified char includes the following steps:

[0038] 1) Crush the corn cobs through a 10-20 mesh sieve, wash them with water to remove mud and sand, dry them at 100-110℃, and then place them in a tube furnace under N2 protection. Carbonize them at 400-500℃ for 2-3 hours with a heating rate of 6-10℃ / min. After natural cooling, corn cob-based raw biochar is obtained.

[0039] 2) Mix corn cob-based raw biochar with 10% NaOH solution at a solid-liquid ratio of 1:(4~6), soak at 75~85℃ for 2~3 hours, then filter and dry at 60~70℃;

[0040] 3) After drying, activate at 500~600℃ for 1~2h under N2 atmosphere. After activation, cool to room temperature, impregnate with 5% H2O2 solution at room temperature for 1~2h, wash with water until neutral, dry at 75~85℃, and sieve to 1~3mm to obtain corn cob-based modified biochar.

[0041] The present invention has the following advantages over the prior art:

[0042] 1. This invention addresses the characteristics of pyrazolone production wastewater, which is characterized by high COD, high total nitrogen, high salinity, and poor biodegradability. It constructs a synergistic process encompassing targeted pretreatment, resource recovery, mild detoxification, and deep purification. Through a combination of composite extraction and pervaporation membrane separation, not only is acetonitrile resources in the wastewater efficiently recovered, significantly reducing the load on subsequent treatment, but also, under the action of a magnesium-aluminum composite catalyst, ring-opening degradation of heterocyclic compounds is achieved under mild conditions through alkaline catalytic hot water hydrolysis. This effectively improves the biodegradability of the wastewater, laying a solid foundation for subsequent deep treatment.

[0043] 2. The combined use of photocatalysis and Fenton-like oxidation in this invention utilizes the synergistic effect of photogenerated electrons and hydrogen peroxide to continuously generate highly oxidizing hydroxyl radicals, achieving deep oxidation and mineralization of recalcitrant organic matter. Modified biochar, with its rich porous structure and surface functional groups, not only deeply adsorbs residual small-molecule organic matter and color, but also effectively reduces the residual concentration of metal ions such as aluminum and titanium in the effluent through its reducing and adsorption properties, thus reducing the risk of secondary pollution. This oxidation-adsorption coupling strategy integrates the strong degradation capabilities of advanced oxidation with the adsorption and purification functions of biochar, achieving a significant improvement in treatment efficiency.

[0044] 3. This invention not only achieves stable and compliant discharge of pyrazolone production wastewater, but also reduces raw material and wastewater treatment costs for enterprises through the recovery and utilization of resources such as acetonitrile, resulting in significant environmental and economic benefits. The overall process is stable and easy to operate, and the optimized combination of each unit ensures a good balance between treatment efficiency and operating costs, providing an efficient, economical, and sustainable solution for the treatment of high-concentration, recalcitrant chemical wastewater. Attached Figure Description

[0045] Figure 1 A comparison chart of COD removal rates for each embodiment and comparative example;

[0046] Figure 2 This is a comparison chart of the total nitrogen removal rates of various embodiments and comparative examples. Detailed Implementation

[0047] To further explain the present invention, the following specific embodiments are described.

[0048] Experimental materials

[0049] Table 1

[0050]

[0051] Note: Unless otherwise specified, the raw materials used in this invention are all from commercially available conventional products.

[0052] Example 1

[0053] A purification process for pyrazolone production wastewater, wherein the wastewater is the mother liquor and washing wastewater generated during the condensation and ring-closure preparation of pyrazolone from methylhydrazine and ethyl acetoacetate in acetonitrile-coated solubilization, comprising the following steps:

[0054] S1. Pretreatment and targeted impurity removal:

[0055] The wastewater was filtered, and the pH was adjusted to 5.5. Then, a two-stage countercurrent extraction was performed using a composite extractant to remove pyrazolone and hydrophobic byproducts from the wastewater, resulting in the raffinate phase.

[0056] The composite extractant is a mixture of tributyl phosphate and kerosene in a volume ratio of 1:3, and the extraction ratio (oil:water) is 1:2.

[0057] S2 and acetonitrile efficient recovery:

[0058] The raffinate obtained in step S1 is subjected to vacuum distillation and pervaporation membrane separation to recover acetonitrile. The vacuum distillation is carried out under a vacuum of -0.06 MPa, with 25 theoretical plates and a reflux ratio of 1.5. Crude acetonitrile is obtained from the vacuum distillation. The bottom liquid of the vacuum distillation column enters the pervaporation unit and is separated using a PDMS (polydimethylsiloxane) pervaporation membrane to remove acetonitrile from the residue to ≤200 mg / L. The PDMS (polydimethylsiloxane) pervaporation membrane can withstand a salt concentration of ≤25 wt% and an operating temperature of 60℃.

[0059] S3, Gentle denitrification and detoxification:

[0060] The wastewater after acetonitrile removal was subjected to alkaline catalytic hot hydrolysis in the presence of a magnesium-aluminum composite catalyst at pH 11.0, a reaction temperature of 110℃, a pressure of 0.15MPa, and a reaction time of 60min. This process converted residual nitriles into organic acids and degraded heterocyclic compounds through ring-opening, thereby improving the biodegradability of the wastewater. After the reaction, the catalyst was recovered by centrifugation and recycled.

[0061] The magnesium-aluminum composite catalyst is MgO-Al2O3, with a crystal form of γ-Al2O3 supported on MgO, a particle size of 50 μm, and an addition amount of 0.5 g / L;

[0062] The magnesium-aluminum composite catalyst was prepared by a co-precipitation method, specifically: magnesium salt and aluminum salt were mixed and dissolved at a Mg:Al molar ratio of 1:2, ammonia was added dropwise to adjust the pH to 9.0, the precipitate was aged, filtered, washed, dried, and calcined at 550℃ for 3 hours to obtain the catalyst.

[0063] S4. Volume reduction and concentration, and salt resource utilization:

[0064] The hydrolyzed wastewater is sequentially treated by ultrafiltration and nanofiltration (using a surface-modified alkali-resistant nanofiltration membrane with a molecular weight cutoff of 200~400 Da). The nanofiltration concentrate is incorporated into step S5 for deep purification. The nanofiltration permeate is subjected to mechanical steam recompression evaporation at a temperature of 70°C and a vacuum of -0.07 MPa to crystallize and obtain industrial-grade ammonium sulfate or ammonium chloride. The evaporation condensate is reused.

[0065] S5, Deep Purification:

[0066] The nanofiltration concentrate obtained in step S4 is combined with the mechanical vapor recompression evaporation mother liquor, and a coagulant aid (polyaluminum chloride, dosage 50 mg / L) is added for homogenization pretreatment. Then, photocatalytic coupling Fenton oxidation and modified biochar fixed bed adsorption are carried out in sequence. The treated effluent meets the discharge or reuse standards.

[0067] The photocatalytic coupling Fenton oxidation uses a g-C3N4 / modified TiO2 composite catalyst with a dosage of 0.3 g / L, H2O2 as the oxidant with a dosage of 500 mg / L, UV-C as the activation light source, and a reaction time of 30 min.

[0068] The preparation of the g-C3N4 / modified TiO2 composite catalyst includes the following steps:

[0069] (1) Mix urea and thiourea at a mass ratio of 9:1, place them in a covered crucible, calcine at 500℃ for 2.5h, with a heating rate of 5℃ / min, cool, ball mill, and pass through a 200-mesh sieve to obtain g-C3N4.

[0070] (2) Disperse the above g-C3N4 in an ethanol-water mixture (ethanol:water = 4:1) at a mass-volume ratio of 1g:20mL. After ultrasonic treatment for 30min, add tetrabutyl titanate (10% of the volume of the ethanol-water mixture), adjust the pH to 3.0 with dilute hydrochloric acid (5% by mass), and stir in a water bath at 60℃ for 2h to obtain g-C3N4-TiO2 suspension;

[0071] (3) Add ethyl silicate (0.8% of the volume of ethanol-water mixture) to the above suspension, adjust the pH to 8.5 with ammonia, stir at 40°C for 1 hour to form a uniform SiO2 protective film, filter, wash with deionized water until neutral, dry at 75°C, and calcine at 400°C for 2 hours.

[0072] The adsorbent in the modified biochar fixed bed is corn cob-based modified char, with a space velocity of 1 h⁻¹. -1 ;

[0073] The preparation of the corn cob-based modified char includes the following steps:

[0074] 1) The corn cobs were crushed and passed through a 10-mesh sieve, washed with water to remove mud and sand, dried at 100℃, and then placed in a tube furnace under N2 protection. The carbonization was carried out at 400℃ for 2 hours with a heating rate of 6℃ / min. After natural cooling, corn cob-based raw biochar was obtained.

[0075] 2) Mix corn cob-based raw biochar with 10% NaOH solution at a solid-liquid ratio of 1:4, soak at 75℃ for 2 hours, then filter and dry at 60℃;

[0076] 3) After drying, activate at 500℃ for 1 hour under N2 atmosphere. After activation, cool to room temperature, impregnate with 5% H2O2 solution at room temperature for 1 hour, wash with water until neutral, dry at 75℃, and sieve to 1~3 mm to obtain corn cob-based modified biochar.

[0077] Example 2

[0078] A purification process for pyrazolone production wastewater, wherein the wastewater is the mother liquor and washing wastewater generated during the condensation and ring-closure preparation of pyrazolone from methylhydrazine and ethyl acetoacetate in acetonitrile-coated solubilization, comprising the following steps:

[0079] S1. Pretreatment and targeted impurity removal:

[0080] The wastewater was filtered and the pH was adjusted to 6.0. A two-stage countercurrent extraction was performed using a composite extractant to remove pyrazolone and hydrophobic byproducts from the wastewater, yielding the raffinate phase.

[0081] The composite extractant is a mixture of tributyl phosphate and kerosene in a volume ratio of 1:4, and the extraction ratio (oil:water) is 1:3.5.

[0082] S2 and acetonitrile efficient recovery:

[0083] The raffinate obtained in step S1 is subjected to vacuum distillation and pervaporation membrane separation to recover acetonitrile. The vacuum distillation is carried out at a vacuum degree of -0.07 MPa, with 28 theoretical plates and a reflux ratio of 2. Crude acetonitrile is obtained from the vacuum distillation. The bottom liquid of the vacuum distillation column enters the pervaporation unit and is separated using a PDMS (polydimethylsiloxane) pervaporation membrane to remove acetonitrile from the residue to ≤200 mg / L. The PDMS (polydimethylsiloxane) pervaporation membrane can withstand a salt concentration of ≤25 wt% and an operating temperature of 65℃.

[0084] S3, Gentle denitrification and detoxification:

[0085] The wastewater after acetonitrile removal was subjected to alkaline catalytic hot hydrolysis in the presence of a magnesium-aluminum composite catalyst at pH 11.5, a reaction temperature of 120℃, a pressure of 0.18MPa, and a reaction time of 70min. This process converted residual nitriles into organic acids and degraded heterocyclic compounds through ring-opening, thereby improving the biodegradability of the wastewater. After the reaction, the catalyst was recovered by centrifugation and recycled.

[0086] The magnesium-aluminum composite catalyst is MgO-Al2O3, with a crystal form of γ-Al2O3 supported on MgO, a particle size of 80 μm, and an addition amount of 0.8 g / L;

[0087] The magnesium-aluminum composite catalyst was prepared by a co-precipitation method, specifically: magnesium salt and aluminum salt were mixed and dissolved at a Mg:Al molar ratio of 1:2.5, ammonia was added dropwise to adjust the pH to 9.5, the precipitate was aged, filtered, washed, dried, and calcined at 600℃ for 3.5h to obtain the catalyst.

[0088] S4. Volume reduction and concentration, and salt resource utilization:

[0089] The hydrolyzed wastewater is sequentially treated by ultrafiltration and nanofiltration (using a surface-modified alkali-resistant nanofiltration membrane with a molecular weight cutoff of 200~400 Da). The nanofiltration concentrate is incorporated into step S5 for deep purification. The nanofiltration permeate is subjected to mechanical steam recompression evaporation at a temperature of 75°C and a vacuum of -0.08 MPa. Industrial-grade ammonium sulfate or ammonium chloride is obtained by crystallization, and the evaporation condensate is reused.

[0090] S5, Deep Purification:

[0091] The nanofiltration concentrate obtained in step S4 is combined with the mechanical vapor recompression evaporation mother liquor, and a coagulant aid (polyaluminum chloride, dosage 60 mg / L) is added for homogenization pretreatment. Then, photocatalytic coupling Fenton oxidation and modified biochar fixed bed adsorption are carried out in sequence. The treated effluent meets the discharge or reuse standards.

[0092] The photocatalytic coupling Fenton oxidation uses a g-C3N4 / modified TiO2 composite catalyst with a dosage of 0.5 g / L, H2O2 as the oxidant with a dosage of 600 mg / L, UV-C as the activation light source, and a reaction time of 35 min.

[0093] The preparation of the g-C3N4 / modified TiO2 composite catalyst includes the following steps:

[0094] (1) Mix urea and thiourea at a mass ratio of 9:1, place them in a covered crucible, calcine at 550℃ for 3h, with a heating rate of 5℃ / min, cool, ball mill, and pass through a 200-mesh sieve to obtain g-C3N4.

[0095] (2) Disperse the above g-C3N4 in an ethanol-water mixture (ethanol:water = 4:1) at a mass-volume ratio of 1g:25mL. After ultrasonic treatment for 35min, add tetrabutyl titanate (12% of the volume of the ethanol-water mixture), adjust the pH to 3.2 with dilute hydrochloric acid (mass fraction 8%), and stir in a water bath at 60℃ for 2.5h to obtain g-C3N4-TiO2 suspension;

[0096] (3) Add ethyl silicate (1% of the volume of ethanol-water mixture) to the above suspension, adjust the pH to 8.8 with ammonia, stir at 45°C for 2 hours to form a uniform SiO2 protective film, filter, wash with deionized water until neutral, dry at 80°C, and calcine at 400°C for 2 hours.

[0097] The adsorbent in the modified biochar fixed bed is corn cob-based modified biochar, with a space velocity of 1.5 h⁻¹. -1 ;

[0098] The preparation of the corn cob-based modified char includes the following steps:

[0099] 1) The corn cobs were crushed and passed through a 10-mesh sieve, washed with water to remove mud and sand, dried at 105℃, and then placed in a tube furnace under N2 protection. The carbonization was carried out at 450℃ for 2.5 hours with a heating rate of 8℃ / min. After natural cooling, corn cob-based raw biochar was obtained.

[0100] 2) Mix corn cob-based raw biochar with 10% NaOH solution at a solid-liquid ratio of 1:5, soak at 80℃ for 2.5h, then filter and dry at 65℃;

[0101] 3) After drying, activate at 550℃ for 1.5h under N2 atmosphere, cool to room temperature after activation, impregnate with 5% H2O2 solution at room temperature for 1.5h, wash with water until neutral, dry at 80℃, and sieve to 2mm to obtain corn cob-based modified biochar.

[0102] Example 3

[0103] A purification process for pyrazolone production wastewater, wherein the wastewater is the mother liquor and washing wastewater generated during the condensation and ring-closure preparation of pyrazolone from methylhydrazine and ethyl acetoacetate in acetonitrile-coated solubilization, comprising the following steps:

[0104] S1. Pretreatment and targeted impurity removal:

[0105] The wastewater was filtered and the pH was adjusted to 6.5. A two-stage countercurrent extraction was performed using a composite extractant to remove pyrazolone and hydrophobic byproducts from the wastewater, yielding the raffinate phase.

[0106] The composite extractant is a mixture of tributyl phosphate and kerosene in a volume ratio of 1:5, and the extraction ratio (oil:water) is 1:5.

[0107] S2 and acetonitrile efficient recovery:

[0108] The raffinate obtained in step S1 is subjected to vacuum distillation and pervaporation membrane separation to recover acetonitrile. The vacuum distillation is carried out under a vacuum of -0.08 MPa, with 30 theoretical plates and a reflux ratio of 2.5. Crude acetonitrile is obtained from the vacuum distillation. The bottom liquid of the vacuum distillation column enters the pervaporation unit and is separated using a PDMS (polydimethylsiloxane) pervaporation membrane to remove acetonitrile from the residue to ≤200 mg / L. The PDMS (polydimethylsiloxane) pervaporation membrane can withstand a salt concentration of ≤25 wt% and an operating temperature of 70℃.

[0109] S3, Gentle denitrification and detoxification:

[0110] The wastewater after acetonitrile removal was subjected to alkaline catalytic hot hydrolysis in the presence of a magnesium-aluminum composite catalyst at pH 12.0, a reaction temperature of 125℃, a pressure of 0.20 MPa, and a reaction time of 80 min. This process converted residual nitriles into organic acids, causing ring-opening degradation of heterocyclic compounds and improving the biodegradability of the wastewater. After the reaction, the catalyst was recovered by centrifugation and recycled.

[0111] The magnesium-aluminum composite catalyst is MgO-Al2O3, with a crystal form of γ-Al2O3 supported on MgO, a particle size of 100 μm, and an addition amount of 1 g / L;

[0112] The magnesium-aluminum composite catalyst was prepared by a co-precipitation method, specifically as follows: magnesium salt and aluminum salt were mixed and dissolved at a Mg:Al molar ratio of 1:3, ammonia was added dropwise to adjust the pH to 10.0, the precipitate was aged, filtered, washed, dried, and calcined at 650℃ for 4 hours to obtain the catalyst.

[0113] S4. Volume reduction and concentration, and salt resource utilization:

[0114] The hydrolyzed wastewater is sequentially treated by ultrafiltration and nanofiltration (using a surface-modified alkali-resistant nanofiltration membrane with a molecular weight cutoff of 200~400 Da). The nanofiltration concentrate is incorporated into step S5 for deep purification. The nanofiltration permeate is subjected to mechanical steam recompression evaporation at a temperature of 85°C and a vacuum of -0.09 MPa. Industrial-grade ammonium sulfate or ammonium chloride is obtained by crystallization, and the evaporation condensate is reused.

[0115] S5, Deep Purification:

[0116] The nanofiltration concentrate obtained in step S4 is combined with the mechanical vapor recompression evaporation mother liquor, and a coagulant aid (polyaluminum chloride, dosage 80 mg / L) is added for homogenization pretreatment. Then, photocatalytic coupling Fenton oxidation and modified biochar fixed bed adsorption are carried out in sequence. The treated effluent meets the discharge or reuse standards.

[0117] The photocatalytic coupling Fenton oxidation uses a g-C3N4 / modified TiO2 composite catalyst with a dosage of 0.8 g / L, H2O2 as the oxidant with a dosage of 800 mg / L, UV-C as the activation light source, and a reaction time of 40 min.

[0118] The preparation of the g-C3N4 / modified TiO2 composite catalyst includes the following steps:

[0119] (1) Mix urea and thiourea at a mass ratio of 9:1, place them in a covered crucible, calcine at 600℃ for 3.5h, with a heating rate of 5℃ / min, cool, ball mill, and pass through a 200-mesh sieve to obtain g-C3N4.

[0120] (2) Disperse the above g-C3N4 in an ethanol-water mixture (ethanol:water = 4:1) at a mass-volume ratio of 1g:30mL. After ultrasonic treatment for 40min, add tetrabutyl titanate (15% of the volume of the ethanol-water mixture) dropwise. Adjust the pH to 3.5 with dilute hydrochloric acid (10% by mass). Stir in a water bath at 60℃ for 3h to obtain g-C3N4-TiO2 suspension.

[0121] (3) Add ethyl silicate (1.2% of the volume of ethanol-water mixture) to the above suspension, adjust the pH to 9.0 with ammonia, stir at 50°C for 3 hours to form a uniform SiO2 protective film, filter, wash with deionized water until neutral, dry at 85°C, and calcine at 400°C for 2 hours.

[0122] The adsorbent in the modified biochar fixed bed is corn cob-based modified char, with a space velocity of 2 h⁻¹. -1 ;

[0123] The preparation of the corn cob-based modified char includes the following steps:

[0124] 1) The corn cobs were crushed and passed through a 20-mesh sieve, washed with water to remove mud and sand, dried at 110℃, and then placed in a tube furnace under N2 protection. The carbonization was carried out at 500℃ for 3 hours with a heating rate of 10℃ / min. After natural cooling, corn cob-based raw biochar was obtained.

[0125] 2) Mix corn cob-based raw biochar with 10% NaOH solution at a solid-liquid ratio of 1:6, soak at 85℃ for 3 hours, then filter and dry at 70℃;

[0126] 3) After drying, activate at 600℃ for 2 hours under N2 atmosphere. After activation, cool to room temperature, impregnate with 5% H2O2 solution at room temperature for 2 hours, wash with water until neutral, dry at 85℃, and sieve to 3 mm to obtain corn cob-based modified biochar.

[0127] Comparative Example 1

[0128] Compared with Example 2, Comparative Example 1 omits the composite extraction in step S1 and directly proceeds to vacuum distillation. Other steps and parameters are the same as in Example 2.

[0129] Comparative Example 2

[0130] Compared with Example 2, Comparative Example 2 only uses vacuum distillation in step S2 and does not perform pervaporation membrane separation. The other steps and parameters are the same as in Example 2.

[0131] Comparative Example 3

[0132] Compared with Example 2, Comparative Example 3 omits the magnesium-aluminum composite catalyst in step S3, while the other steps and parameters are the same as in Example 2.

[0133] Comparative Example 4

[0134] Compared with Example 2, Comparative Example 4 only uses photocatalysis in step S5, without photocatalytic coupling of Fenton oxidation and modified biochar fixed-bed adsorption. Other steps and parameters are the same as in Example 2.

[0135] Comparative Example 5

[0136] Comparative Example 5 is the same as Example 2, except that the photocatalytic coupling Fenton oxidation treatment is omitted in step S5. Other steps and parameters are the same as in Example 2.

[0137] Comparative Example 6

[0138] Comparative Example 6 is the same as Example 2, except that the modified biochar fixed-bed adsorption treatment is omitted in step S5, and the other steps and parameters are the same as in Example 2.

[0139] 1. Experimental testing

[0140] Basic water quality parameters for the test: COD = 18000 mg / L, total nitrogen = 3200 mg / L, acetonitrile = 8500 mg / L, salinity = 12%, B / C = 0.15.

[0141] Test metrics:

[0142] COD: HJ 828-2017 Dichromate method;

[0143] Total nitrogen: HJ 636-2012 Alkaline potassium persulfate digestion ultraviolet spectrophotometric method;

[0144] Acetonitrile content: GC-FID gas chromatography (HJ HJ 788-2016);

[0145] B / C: BODS were measured using the dilution and inoculation method (HJ 505-2009), and the ratio was calculated.

[0146] Effluent compliance: GB 8978-1996 "Integrated Wastewater Discharge Standard" Class III standard.

[0147] 2. Test Results

[0148] Test results as follows Figure 1 , Figure 2 As shown in Table 2 below.

[0149] Table 2

[0150]

[0151] Depend on Figure 1 , Figure 2 As shown in Table 2, Examples 1-3 all consistently met the standards, with Example 2 being the best, exhibiting the highest removal rate, lowest acetonitrile residue, and the best biodegradability. Compared to Example 2, Comparative Example 1, which did not involve extraction, showed a significant decrease in COD and total nitrogen removal rates, and exceeded the acetonitrile residue standard. This was due to the failure to remove pyrazolone and hydrophobic byproducts, resulting in a sharp increase in distillation load, aggravated membrane fouling, and a sudden drop in acetonitrile separation efficiency.

[0152] In Comparative Example 2, without pervaporation, acetonitrile residue exceeded 200 mg / L, leading to an increased hydrolysis load. This is because vacuum distillation cannot separate low-concentration acetonitrile-water azeotropes. PDMS pervaporation is a necessary step for deep removal of acetonitrile.

[0153] Comparative Example 3, without magnesium and aluminum catalyst, showed a priority in improving biodegradability, but the heterocyclic ring opening was incomplete. This is because MgO-Al2O3 provides basic sites and catalytic activity, and the efficiency of nitrile conversion and heterocyclic degradation is significantly reduced without catalyst.

[0154] Comparative Example 4 lacked coupled oxidation and biochar, resulting in residual recalcitrant organic matter and substandard effluent. This is because photocatalysis alone has limited effect, and coupled Fenton-like enhanced oxidation and modified biochar deep adsorption are key to achieving the standard.

[0155] Comparative Example 5 used only biochar without photocatalytic Fenton, resulting in a significantly lower removal rate and substandard effluent. This is because biochar can only adsorb some organic matter and cannot oxidize and decompose heterocyclic compounds, nitrile degradation intermediates, or mineralize recalcitrant pollutants. This indicates that photocatalytically coupled Fenton is an essential unit for oxidative destruction.

[0156] Comparative Example 6 only used photocatalytic Fenton oxidation without the use of biochar. Even after oxidation, small-molecule, recalcitrant organic matter and color-causing substances remained, failing to meet standards. This is because advanced oxidation cannot achieve 100% mineralization. Modified biochar provides deep adsorption and decolorization. Oxidation alone cannot meet emission standards, indicating that the combined use of photocatalytic Fenton oxidation and modified biochar is essential for deep purification.

[0157] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A purification process for pyrazolone production wastewater, wherein the wastewater is the mother liquor and washing wastewater generated during the condensation and ring-closure preparation of pyrazolone from methylhydrazine and ethyl acetoacetate in acetonitrile-coated solubilization, characterized in that... Includes the following steps: S1. Pretreatment and targeted impurity removal: After filtering and pH adjustment of the wastewater, a two-stage countercurrent extraction was performed using a composite extractant to remove pyrazolone and hydrophobic byproducts from the wastewater, yielding the raffinate phase. S2 and acetonitrile efficient recovery: The raffinate obtained in step S1 is subjected to vacuum distillation and pervaporation membrane separation to recover acetonitrile; wherein, the vacuum distillation yields crude acetonitrile, and the bottom liquid of the vacuum distillation column enters the pervaporation unit for separation using a PDMS (polydimethylsiloxane) pervaporation membrane to remove acetonitrile content in the residue to ≤200mg / L. S3, Gentle denitrification and detoxification: The wastewater after acetonitrile removal is subjected to alkaline catalytic hydrolysis in the presence of a magnesium-aluminum composite catalyst to convert residual nitriles into organic acids and undergo ring-opening degradation of heterocyclic compounds. S4. Volume reduction and concentration, and salt resource utilization: The hydrolyzed wastewater is treated sequentially by ultrafiltration and nanofiltration. The nanofiltration permeate is mechanically steam-compressed and evaporated to crystallize industrial-grade ammonium sulfate or ammonium chloride. The evaporation condensate is then reused. S5, Deep Purification: The nanofiltration concentrate obtained in step S4 is combined with the mechanical vapor recompression evaporation mother liquor, and then subjected to photocatalytic coupling Fenton oxidation and modified biochar fixed bed adsorption in sequence. The treated effluent meets the discharge or reuse standards.

2. The purification treatment process for pyrazolone production wastewater according to claim 1, characterized in that, The composite extractant mentioned in step S1 is a mixture of tributyl phosphate and kerosene, with a volume ratio of 1:(3~5) and an extraction ratio of 1:(2~5).

3. The purification treatment process for pyrazolone production wastewater according to claim 1, characterized in that, The vacuum degree of the reduced pressure distillation described in step S2 is -0.06 to -0.08 MPa, the number of theoretical plates is 25 to 30, and the reflux ratio is 1.5 to 2.

5. The pervaporation unit uses a PDMS (polydimethylsiloxane) pervaporation membrane, and the operating temperature is 60~70℃.

4. The purification treatment process for pyrazolone production wastewater according to claim 1, characterized in that, The magnesium-aluminum composite catalyst mentioned in step S3 is MgO-Al2O3, with a crystal form of γ-Al2O3 supported on MgO, a particle size of 50~100μm, and an addition amount of 0.5~1g / L; The magnesium-aluminum composite catalyst is prepared by co-precipitation method, specifically: magnesium salt and aluminum salt are mixed and dissolved at a Mg:Al molar ratio of 1:(2~3), ammonia water is added dropwise to adjust the pH to 9.0~10.0, the precipitate is aged, filtered, washed, dried, and calcined at 550~650℃ for 3~4h to obtain the catalyst. The conditions for alkaline-catalyzed hydrolysis are: pH 11.0~12.0, reaction temperature 110~125℃, pressure 0.15~0.20MPa, and reaction time 60~80min.

5. The purification treatment process for pyrazolone production wastewater according to claim 1, characterized in that, The nanofiltration process described in step S4 uses a surface-modified alkali-resistant nanofiltration membrane with a molecular weight cutoff of 200-400 Da. The mechanical vapor recompression evaporation uses a titanium alloy evaporator with an evaporation temperature of 70~85℃ and a vacuum degree of -0.07~-0.09MPa.

6. The purification treatment process for pyrazolone production wastewater according to claim 1, characterized in that, Before entering the reactor, the photocatalytically coupled Fenton oxidation process described in step S5 involves adding a coagulant aid to the combined wastewater for homogenization pretreatment. The photocatalytically coupled Fenton oxidation process uses a g-C3N4 / modified TiO2 composite catalyst with a dosage of 0.3~0.8 g / L, H2O2 as the oxidant with a dosage of 500~800 mg / L, UV-C as the activation light source, and a reaction time of 30~40 min.

7. The purification treatment process for pyrazolone production wastewater according to claim 6, characterized in that, The preparation of the g-C3N4 / modified TiO2 composite catalyst includes the following steps: (1) Mix urea and thiourea at a mass ratio of 9:1, place them in a covered crucible, calcine at 500~600℃ for 2.5~3.5h, with a heating rate of 5℃ / min, cool, ball mill, and pass through a 200-mesh sieve to obtain g-C3N4. (2) Disperse the above g-C3N4 in an ethanol-water mixture at a mass-volume ratio of 1g:(20~30)mL, sonicate for 30~40min, add tetrabutyl titanate, adjust the pH to 3.0~3.5 with dilute hydrochloric acid, stir in a water bath at 60℃ for 2~3h to obtain g-C3N4-TiO2 suspension; (3) Add ethyl silicate to the above suspension, adjust the pH to 8.5~9.0 with ammonia, stir at 40~50℃ for 1~3h to form a uniform SiO2 protective film, filter, wash with deionized water until neutral, dry at 75~85℃, and calcine at 400℃ for 2h.

8. The purification treatment process for pyrazolone production wastewater according to claim 1, characterized in that, The photocatalytic coupling Fenton oxidation uses an industrial-grade ultraviolet reactor. The reactor is a multi-lamp matrix arrangement with a lamp spacing of 15-20cm. The reactor is equipped with a guide plate, and the light penetration depth is 5-15cm.

9. The purification treatment process for pyrazolone production wastewater according to claim 1, characterized in that, The adsorbent in the modified biochar fixed bed described in step S5 is corn cob-based modified char, with a space velocity of 1-2 h⁻¹. -1 .

10. The purification treatment process for pyrazolone production wastewater according to claim 9, characterized in that, The preparation of the corn cob-based modified char includes the following steps: 1) Crush the corn cobs through a 10-20 mesh sieve, wash them with water to remove mud and sand, dry them at 100-110℃, and then place them in a tube furnace under N2 protection. Carbonize them at 400-500℃ for 2-3 hours with a heating rate of 6-10℃ / min. After natural cooling, corn cob-based raw biochar is obtained. 2) Mix corn cob-based raw biochar with 10% NaOH solution at a solid-liquid ratio of 1:(4~6), soak at 75~85℃ for 2~3 hours, then filter and dry at 60~70℃; 3) After drying, activate at 500~600℃ for 1~2h under N2 atmosphere. After activation, cool to room temperature, impregnate with 5% H2O2 solution at room temperature for 1~2h, wash with water until neutral, dry at 75~85℃, and sieve to 1~3mm to obtain corn cob-based modified biochar.

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