A treatment method for POSM production wastewater

Abstract

This application relates to the technical field of industrial production wastewater treatment, and specifically discloses a method for treating POSM production wastewater. The treatment method provided in this application is specifically as follows: Pretreatment converts heavy metal ions into precipitates, and the supernatant of ultrafiltration enters mild oxidation; wet catalytic oxidation; electrolytic oxidation is carried out under the condition that the current density is 1-10 A / dm 2 . The hydraulic retention time is 10-60 min; targeted adsorption is filled with microcrystalline materials, the liquid flow rate is 0.2-1 BV / H, and the adsorption temperature is 20-35 °C; the wastewater enters the MVR forced circulation system for evaporation, and is sent from the crystallization separator to the forced circulation heat exchanger through the forced circulation pump and then back to the crystallization separator; pyrolysis coupling. By adopting the above scheme to treat POSM wastewater, no mother liquor remains, the effluent COD is low and stable, and both condensate water and salt resources can be recycled, which not only realizes the reuse of resources, but also reduces the treatment cost.

Description

Technical Field

[0001] The present application relates to the technical field of industrial production wastewater treatment, and particularly relates to a method for treating POSM production wastewater. Background Art

[0002] The combined production process of propylene oxide and styrene (POSM) is to make propylene oxide, benzene and ethylene undergo a hydrogenation reaction under the action of a specific catalyst to generate intermediate products, and then through heating and cracking to finally obtain styrene and propane. This process is widely favored due to the flexible selection of catalysts, high product yield and safe and reliable operation.

[0003] The characteristic of the POSM co-production method is that it can co-produce two important organic chemical products, styrene and propylene oxide, and combines the endothermic reaction of ethylbenzene dehydrogenation and the exothermic reaction of propylene oxidation, saving energy and operating costs. The disadvantage of this method is that the reaction is complex and there are many by-products.

[0004] The main difficulties in the treatment of POSM production wastewater lie in its characteristics such as high salinity, high COD, high temperature, high alkalinity and biological toxicity. Comprehensive treatment of such high-concentration degradable organic wastewater has been highly regarded at home and abroad, and more stringent standards have been formulated. At present, incineration technology is mostly used to treat POSM production wastewater. Although this treatment process is relatively mature and has a high pollutant removal rate, the incineration of waste liquid will generate a large amount of nitrogen oxides and a large amount of waste salts. If these nitrogen oxides and waste salts are not properly treated, they will pollute the atmosphere and soil.

[0005] In the existing technical solutions, the invention patent CN 112624300 A discloses a method for treating wastewater in the production of propylene oxide, which includes contacting the wastewater with a wet oxidation heterogeneous catalyst to effectively reduce the COD in the wastewater for producing propylene oxide. Although this treatment method can reduce the COD in the propylene oxide wastewater, it cannot achieve the degree of condensate water reuse and salt reuse.

[0006] Therefore, it is very necessary to develop a more clean and non-secondary pollution, and economical and effective treatment technology. Summary of the Invention

[0007] In order to solve the above technical problems, the present application provides a method for treating POSM production wastewater.

[0008] The present application provides a method for treating POSM production wastewater, which specifically includes the following steps in sequence: pretreatment, wet catalytic oxidation, electrolytic oxidation, targeted adsorption, MVR, pyrolysis coupling;

[0009] (1) Pretreatment: The wastewater enters the regulation tank. After the water volume in the regulation tank is adjusted and the water quality is balanced, it reacts with the Na2S solution to convert heavy metal ions into precipitates. Then, after ultrafiltration, the clear liquid enters mild oxidation, and the intercepted concentrated liquid is centrifugally dewatered. The dewatered filter residue is transported out for disposal, and the centrifugate returns to the reaction section.

[0010] (2) Wet catalytic oxidation: The reaction temperature is 200°C - 300°C, the reaction pressure is 3 - 10 MPa, air or oxygen is used as the oxidant, the catalyst is one or more of copper-based, ruthenium-based, and cerium-based catalysts, the dosage of the catalyst is 0.5% - 5%, and the catalytic oxidation time is 2 - 4 h.

[0011] (3) Electrochemical oxidation: The material of the electrolysis device is selected from boron-doped diamond or graphene-coated titanium substrate. The temperature of the liquid in the electrochemical oxidation device is below 60°C, the current density is 1 - 10 A / dm 2 , and the hydraulic retention time is 10 - 60 min.

[0012] (4) Targeted adsorption: The targeted adsorption is filled with microcrystalline materials, the liquid flow rate is 0.2 - 1 BV / H, and the adsorption temperature is 20 - 35°C.

[0013] (5) MVR: The wastewater enters the MVR forced circulation system for evaporation. It is sent from the crystallization separator to the forced circulation heat exchanger by the forced circulation pump and then returns to the crystallization separator. The flow rate of the heat exchanger is 2 - 2.2 m / s.

[0014] (6) Pyrolysis: The wastewater enters the pyrolysis device, first passes through the drying section, and then enters the pyrolysis section.

[0015] In the wastewater treatment method provided by this application, step (1) is pretreatment: The wastewater from the combined production process of propylene oxide and styrene (POSM) first enters the regulation tank. After the water volume in the regulation tank is adjusted and the water quality is balanced, it then undergoes reaction precipitation to remove Cu 2+ , Cr 3+ , Mo 4+Heavy metal ions such as etc., and then through mild oxidation, while removing most of the organic matter in the wastewater, the pH value of the wastewater is reduced. Step (2) is wet catalytic oxidation, using air or oxygen as the oxidant, one or more of noble metals such as copper-based, ruthenium-based, palladium-based as the catalyst, and metal oxidant filler as the enhanced disperser to increase the contact area between oxygen and water and play a catalytic role at the same time. The wastewater is subjected to wet catalytic oxidation reaction under high temperature and high pressure to further remove the organic matter in the wastewater. Step (3) is electrolytic oxidation: under the action of an external electric field, through physical and chemical effects, the organic pollutants in the wastewater are further purified efficiently. Step (4) is targeted adsorption: through the huge specific surface area and adsorption characteristics of the microcrystalline adsorption material, the organic matter in the wastewater is adsorbed on the adsorption material to achieve the purpose of removing the organic pollutants in the wastewater. When the adsorption is saturated, the adsorption material is regenerated with alkali, and the regeneration liquid returns to the front end of wet catalytic oxidation. Step (5) is MVR: the water outlet of targeted adsorption enters the MVR system. In the MVR system, the secondary steam generated is compressed by a mechanical heat compressor, the temperature, pressure are increased, and the enthalpy is increased, and it is returned to be used as the heating heat source of the heating chamber of the evaporator to keep the feed liquid in a boiling state, thereby completing the evaporation and crystallization of the wastewater. The water vapor generated by evaporation is condensed into condensed water by a condensation device for reuse, and the mother liquor containing crystal salts enters a pyrolysis device to further remove organic matter. Step (6) is pyrolysis: first, the MVR mother liquor is dried at a low temperature to evaporate most of the water in it, and then pyrolyzed at a high temperature to further remove the organic matter in the salt, so that the crystal salt reaches the purity for recycling.

[0016] Furthermore, the present application can recover the main salts therein, such as Na2CO3 etc. Although the POSM co-production method has many by-products, they are all organic matters, and the content of inorganic salts is high and relatively pure. The technology of the present application adopts the coupling technology of pretreatment - wet catalytic oxidation - electrolytic oxidation - targeted adsorption - MVR - pyrolysis to fully remove the organic matter in the wastewater. First, the mild oxidation and wet catalytic oxidation in the pretreatment are used to remove most of the organic matter in the wastewater and degrade the macromolecular organic matter into small molecular organic matter. Secondly, the electrolytic oxidation is operated to further oxidize and decompose the organic matter in it into CO2 etc. and remove it. Then, through targeted adsorption, the small molecular organic matter in it is adsorbed on the surface or pores of the microcrystalline material, greatly removing the organic matter in the wastewater. Finally, through the MVR evaporation and pyrolysis technologies, the organic matter in the product salt is further removed sufficiently, so that the organic matter concentration of the product salt reaches the level for recycling. The technical solution of the present application not only solves the problem of salt disposal, but also can recover and create economic value.

[0017] Furthermore, the present application can recover the main water resources therein. Through pretreatment, wet catalytic oxidation, electrolytic oxidation, and targeted adsorption technologies, impurities such as organic matter, SS, ammonia nitrogen, and total nitrogen are removed, and then through MVR evaporation and condensation, the generated condensed water can meet the reuse standard, achieving the purposes of clean production and energy conservation and emission reduction.

[0018] Preferably, in the pretreatment step, the parameter conditions for the reaction with the Na2S solution are as follows: the stirring speed is 50 - 200 rpm, the reaction time is 20 - 30 min; the rotation speed of the centrifuge is 3000 - 5000 rpm, the wetted material is selected as 316L, and the centrifugation time is 10 - 30 min.

[0019] Ultrafiltration uses tubular ultrafiltration, with the inner diameter of the membrane tube being 5 - 8 mm, the length of the membrane tube being 3 - 4 m, the membrane pore size being 20 - 50 nm, and the membrane material being PVDF.

[0020] The reaction temperature of mild oxidation is 140°C - 200°C, the reaction pressure is 0.5 - 1.5 MPa, air or oxygen is used as the oxidant, and there is no catalyst.

[0021] Preferably, a fixed bed is provided inside the wet catalytic oxidation device, and metal oxidant fillers with a diameter of φ4 - 10 mm are filled as enhanced dispersers, with a packing density of 1.0 - 1.5 g / mL.

[0022] Preferably, in the electrolytic oxidation step, the electrolytic oxidation device includes a water inlet unit, an electrolytic oxidation unit, an exhaust gas treatment unit, and a water outlet unit; the water inlet unit includes a sewage pump, a water inlet tank, and an on-line conductivity meter; the electrolytic oxidation unit includes a water inlet pump, an oxidation tank, a direct current power supply, and a slag and liquid sedimentation tank; the exhaust gas treatment unit includes a draft fan, a scrubber, an alkali liquid storage tank, and a sedimentation tank; the water outlet unit includes a water outlet pump, a reflux pump, and an on-line detection device.

[0023] The electrolytic oxidation device is equipped with a cooling device, and the cooling device uses a shell-and-tube heat exchanger or a plate heat exchanger to ensure that the temperature of the liquid in the electrolytic device is lower than 60°C.

[0024] Preferably, in the targeted adsorption step, when the COD of the wastewater after adsorption is below 100 mg / L, it enters the MVR treatment system; when the COD of the wastewater after adsorption exceeds 100 mg / L, the microcrystalline material needs to be regenerated. During regeneration, fresh water and steam are introduced to heat the microcrystalline material adsorbent to above 100°C for regeneration, and then it is purged with steam above 150°C. The regenerated liquid after purging enters the wet catalytic oxidation system.

[0025] Preferably, in the targeted adsorption step, the preparation method of the microcrystalline adsorbent is specifically as follows:

[0026] Add 15 - 25 mol of silica, 0.7 - 1.5 mol of alumina, and 2 - 4 mol of aluminum hydroxide to 1 L of water, mix evenly, keep warm at 60 - 80 °C for 2 - 6 h to form a mixed solution; then crystallize at 120 - 140 °C for 10 - 12 h; then add 5 - 15 g of synergist and mix evenly; calcine at 600 - 800 °C for 12 - 15 h to obtain it.

[0027] The synergist is obtained by mixing bentonite and poly (lactic - glycolic acid) copolymer with a weight ratio of (1 - 3):(0.2 - 0.8).

[0028] Through multiple experiments, the applicant found that the microcrystalline adsorbent obtained by dispersing silica, alumina, and aluminum hydroxide with specific concentrations in water, crystallizing, and then calcining with a synergist as raw materials has unexpected effects in the wastewater treatment process.

[0029] In a specific embodiment, in the synergist, the weight ratio of the bentonite to the poly (lactic - glycolic acid) copolymer can be 1:0.2, 1:0.5, 1:0.8, 2:0.2, 2:0.5, 2:0.8, 3:0.2, 3:0.5, 3:0.8.

[0030] Through experimental analysis, it can be known that in this application, by using bentonite and poly (lactic - glycolic acid) copolymer with the above - mentioned weight ratio as the synergist as the raw material for preparing the microcrystalline adsorbent, the effect of wastewater treatment is further improved.

[0031] Preferably, in the MVR, the secondary steam generated by the steam compressor enters from the inlet of the heat exchanger, enters the crystallization separator along the shell - side of the heat exchanger, comes out from the top of the crystallization separator and then enters the scrubbing tower, absorbs the entrained foam in the scrubbing tower, and the secondary steam coming out of the scrubbing tower enters the steam compressor along the steam pipe; the temperature and pressure are increased in the steam compressor and then supplied to the forced - circulation evaporation for continuous use; the evaporation and crystallization of wastewater can be achieved without consuming additional steam throughout the process.

[0032] The condensate after evaporation and crystallization enters the condensate reuse pool, and the concentrated liquid enters the pyrolysis device from the bottom of the salt leg.

[0033] When the evaporation capacity of the MVR forced - circulation evaporator drops by about 10%, drain the liquid in the forced - circulation evaporator to the pyrolysis device for further treatment.

[0034] Preferably, the parameter conditions of the MVR are: evaporation temperature is 85 - 100 °C, the pipe diameter of the heat exchanger is 32 mm×1.2 mm, the liquid flow rate in the tube - side of the heat exchanger is 2 - 2.2 m / s, the gas velocity in the crystallization separator < 6 m / s, the gas velocity at the compressor inlet is 25 m / s, and the gas velocity at the compressor outlet is 30 m / s.

[0035] Preferably, in the pyrolysis step, the temperature in the drying section is 100 - 200°C, the drying duration is 0.5 - 2 h, and the drying is carried out until the water content is 10% - 20%; the temperature in the pyrolysis section is 300 - 600°C, the pyrolysis duration is 0.5 - 2 h, and the COD content in the crystal salt after pyrolysis is lower than 30 mg / kg.

[0036] In a second aspect, the present application provides the application of the above treatment method in the treatment of POSM production wastewater.

[0037] In summary, the technical solution of the present application has the following effects:

[0038] The present application uses a combined technology of pretreatment - wet catalytic oxidation - electrolytic oxidation - targeted adsorption - MVR - pyrolysis to treat the wastewater from the combined production process of propylene oxide and styrene (POSM), solving the problems of difficult - to - treat secondary pollution, un - recyclable condensate water and salt resources in the existing treatment processes. The pretreatment - wet catalytic oxidation - electrolytic oxidation - targeted adsorption - MVR - pyrolysis technology in the present application not only does not produce difficult - to - treat secondary pollution, does not leave mother liquor, has low and stable effluent COD, but also enables the recycling of condensate water and salt resources. It not only realizes the reuse of resources but also reduces the treatment cost.

[0039] The targeted adsorption microcrystalline adsorbent of the present application imitates the microstructures of shells and corals. Through a multi - level pore structure, it significantly increases the surface area and the density of active sites, enhancing the selectivity and capture rate for specific pollutants; this structure not only improves the adsorption performance but also reduces the material usage. At the same time, the adsorbent has strong physical stability and chemical tolerance, ensuring the reliability of long - term use. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a process flow diagram of the treatment method for POSM production wastewater in the embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The following further describes the present application in detail with reference to examples, comparative examples and performance detection tests. These examples should not be construed as limiting the scope claimed by the present application. Examples Example 1

[0042] Example 1 provides a treatment method for POSM production wastewater.

[0043] The process flow diagram of the treatment method for POSM production wastewater in Example 1 is as Figure 1 shown, and specifically includes the following steps in sequence.

[0044] The wastewater in Example 1 comes from the POSM wastewater of a chemical company in Tianjin. The water volume is 40 t / h, the measured pH is 13.2, the COD is 118,000 mg / L, the total nitrogen is 200 mg / L, the TDS is 50,000 - 55,000 mg / L, and the Na2CO3 content is 25% - 30%.

[0045] (1)Pretreatment: The wastewater from the combined production process of propylene oxide and styrene (POSM) first enters the regulation tank. After the water volume is regulated and the water quality is balanced in the regulation tank, sodium sulfide is added in the reaction tank to form precipitates of heavy metal ions such as copper, chromium, and molybdenum. Then, solid-liquid separation is achieved by ultrafiltration membrane. The filtrate is then subjected to mild oxidation. The temperature of mild oxidation is 160 °C, the reaction pressure is 1 MPa, and air is used as the oxidant. The intercepted concentrated solution of ultrafiltration is centrifugally dehydrated. The dehydrated filter residue is transported out for disposal, and the centrifugate is returned to the reaction section.

[0046] The parameter conditions for the reaction of adding Na2S solution are: the stirring speed is 150 rpm, the reaction time is 25 min; the speed of the centrifuge is 4000 rpm, the wetted material is selected as 316L, and the centrifugation time is 20 min.

[0047] Tube ultrafiltration is used for ultrafiltration. The inner diameter of the membrane tube is 6 mm, the length of the membrane tube is 3 m, the membrane pore size is 35 nm, and the membrane material is PVDF.

[0048] The effluent COD is 35,026 mg / L, the total nitrogen is about 31 mg / L, and the TDS is about 51,016 mg / L.

[0049] (2)Wet catalytic oxidation: The reaction temperature of wet catalytic oxidation is 270 °C, the reaction pressure is 8 MPa. TiO2 fillers with a diameter of φ4 - 10 mm are filled as the catalyst fixed bed, and the packing density is 1.5 g / mL. Ruthenium is used as the catalyst, and the mass ratio of the catalyst to TiO2 filler is 1:100. Air is continuously introduced for catalytic oxidation for 2 h. The effluent COD is about 3602 mg / L, the total nitrogen is about 3.1 mg / L, the TDS is about 31,008 mg / L, and the Na2CO3 content accounts for about 88%.

[0050] (3)Electrolytic oxidation: The temperature of the electrolytic oxidation device is below 60 °C, the electrode material is selected as boron-doped diamond, and the current density is 5 A / dm 2 , and the hydraulic retention time of the electrolytic oxidation device is 25 min. After the wastewater is electrolytically oxidized, the effluent COD is about 1101 mg / L, the total nitrogen is about 2.5 mg / L, the TDS is about 30,123 mg / L, and the Na2CO3 content accounts for about 96%.

[0051] (4)Targeted adsorption: The targeted adsorption system consists of 6 towers in parallel. During normal operation, 5 towers are for adsorption and 1 tower is for regeneration. Each tower is filled with 40 m 3The microcrystalline adsorbent has a total filling volume of 240 m 3 , and the liquid flow rate is 0.2 BV / H. After one-time targeted adsorption (without regeneration), the COD of the effluent is 80.7 mg / L, the total nitrogen is about 0.25 mg / L, and the TDS is about 28,012 mg / L, among which the content of Na2CO3 accounts for about 99.6%.

[0052] Among them, the preparation method of the microcrystalline adsorbent is specifically as follows:

[0053] Add 20 mol of silica, 1 mol of alumina, and 3 mol of aluminum hydroxide to 1 L of water, mix evenly, keep warm at 70 °C for 4 h to form a mixed solution; then crystallize at 130 °C for 11 h; then add 10 g of synergist and mix evenly; place it in a calciner at 700 °C and calcine for 13 h to obtain it;

[0054] The synergist is obtained by mixing bentonite (model YD-223, product number MR-3, 180-325 mesh; purchased from Tianjin Yandong Mineral Products Co., Ltd.) and poly(lactic-co-glycolic acid) copolymer (product number S24482, performance parameters: molecular weight: 10,000 - 20,000, PLGA 65:35, carboxyl-terminated; purchased from Shanghai Yuanye Bio-Technology Co., Ltd.) in a weight ratio of 2:0.5.

[0055] (5)MVR: The wastewater enters the MVR forced circulation system for evaporation, and is sent from the crystallization separator to the forced circulation heat exchanger through the forced circulation pump and then back to the crystallization separator. The flow rate of the heat exchanger is 2.1 m / s.

[0056] The secondary steam generated by the steam compressor enters from the inlet of the heat exchanger, enters the crystallization separator along the shell side of the heat exchanger, comes out from the top of the crystallization separator and then enters the scrubbing tower, where the entrained foam is absorbed. The secondary steam coming out of the scrubbing tower enters the steam compressor along the steam pipe; it is heated and pressurized in the steam compressor and then supplied for continuous use in the forced circulation evaporation; the evaporation and crystallization of the wastewater can be achieved without consuming additional steam throughout the process.

[0057] The condensate after evaporation and crystallization enters the condensate reuse pool, and the concentrated liquid enters the pyrolysis device from the bottom of the salt leg.

[0058] When the evaporation capacity of the MVR forced circulation evaporator drops by about 10%, the liquid in the forced circulation evaporator is drained into the pyrolysis device for further treatment.

[0059] The parameter conditions of MVR are: evaporation temperature is 95 °C, the pipe diameter size of the heat exchanger is 32 mm × 1.2 mm, the liquid flow rate of the tube side of the heat exchanger is 2.1 m / s, the gas velocity of the crystallization separator < 6 m / s, the gas velocity at the inlet of the compressor is 25 m / s, and the gas velocity at the outlet of the compressor is 30 m / s.

[0060] Produce about 5.7 t / h of Na2CO3 concentrated solution with a solid content of 20%, where the purity of Na2CO3 is above 99.6%. Produce about 35.3 t / h of condensed water with a pH of 6 - 8, COD below 20 mg / L, and TDS below 50 mg / L, meeting the standard of "Quality of Reclaimed Water for Industrial Use in Urban Areas" (GB / T 19923 - 2005).

[0061] (6)Pyrolysis: The 20% Na2CO3 concentrated solution first enters the drying section. The temperature of the drying section is 150 °C, and the drying duration is 1 h until the water content reaches 10%. Then it enters the pyrolysis section. The temperature of the pyrolysis section is 450 °C, and the pyrolysis duration is 1 h. After the steam generated from drying and pyrolysis is recovered by heat, the generated condensed water is recycled. After pyrolysis, about 1.14 t / h of crystal salt with a COD below 30 mg / kg and a purity above 99.9% is produced, meeting the standard for salt to meet the reuse standard. Example 2

[0062] Example 2 provides a method for treating POSM production wastewater.

[0063] The method for treating POSM production wastewater in Example 2 specifically includes the following steps in sequence.

[0064] The wastewater in Example 2 comes from the POSM wastewater of a petrochemical company in Guangxi, with a water volume of 7.5 t / h. The measured pH is 13, COD is 200000 mg / L, total nitrogen is 242 mg / L, TDS is 55000 - 60000 mg / L, and the Na2CO3 content is 35%.

[0065] (1)Pretreatment: The wastewater from the combined production process of propylene oxide and styrene (POSM) first enters the regulation tank. After the water volume is regulated and the water quality is balanced in the regulation tank, sodium sulfide is added in the reaction tank to form precipitates of heavy metal ions such as copper, chromium, and molybdenum. Then solid - liquid separation is achieved using an ultrafiltration membrane. The filtrate undergoes mild oxidation. The temperature of mild oxidation is 200 °C, the reaction pressure is 1 MPa, and air is used as the oxidant. The retained concentrated solution of ultrafiltration is centrifugally dewatered. The dewatered filter residue is transported out for disposal, and the centrifugate returns to the reaction section.

[0066] The parameter conditions for the reaction of adding the Na2S solution are: the stirring speed is 150 rpm, the reaction time is 25 min; the speed of the centrifuge is 4000 rpm, the wetted material is selected as 316L, and the centrifugation time is 20 min.

[0067] The ultrafiltration uses tubular ultrafiltration. The inner diameter of the membrane tube is 6 mm, the length of the membrane tube is 3 m, the membrane pore size is 35 nm, and the membrane material is PVDF.

[0068] The effluent COD is approximately 61007 mg / L, total nitrogen is approximately 36 mg / L, and TDS is approximately 56009 mg / L.

[0069] (2) Wet catalytic oxidation: The temperature of wet catalytic oxidation is 280 °C, the pressure is 9 MPa, TiO2 fillers with a diameter of φ4 - 10 mm are filled as the catalyst fixed bed, the packing density is 1.5 g / mL, ruthenium is used as the catalyst, and the mass ratio of the catalyst to the TiO2 filler is 1:100. Air is continuously introduced and catalytic oxidation is carried out for 2 h.

[0070] The effluent COD is approximately 5701 mg / L, total nitrogen is approximately 3.6 mg / L, TDS is approximately 33106 mg / L, and the Na2CO3 content accounts for approximately 90%.

[0071] (3) Electrochemical oxidation: The temperature of the electrochemical oxidation device is below 60 °C, the electrode material is boron-doped diamond, and the current density is 5 A / dm 2 , and the hydraulic retention time of the electrochemical oxidation device is 25 min.

[0072] After the wastewater is electrochemically oxidized, the effluent COD is approximately 1402 mg / L, total nitrogen is approximately 2.9 mg / L, TDS is approximately 31107 mg / L, and the Na2CO3 content accounts for approximately 97%.

[0073] Among them, the electrochemical oxidation device includes an inlet unit, an electrochemical oxidation unit, an exhaust gas treatment unit, and an effluent unit; the inlet unit includes a sewage pump, an inlet tank, and an on-line conductivity meter; the electrochemical oxidation unit includes a feed pump, an oxidation tank, a direct current power supply, and a slag and liquid sedimentation tank; the exhaust gas treatment unit includes a draft fan, a scrubber, an alkali liquor storage tank, and a sedimentation tank; the effluent unit includes an effluent pump, a reflux pump, and an on-line detection device.

[0074] (4) Targeted adsorption: The targeted adsorption system consists of 3 towers in parallel. During normal operation, 2 towers are for adsorption and 1 tower is for regeneration. Each tower is filled with 18 m 3 of microcrystalline adsorbent (the preparation method is the same as that in Example 1), the total filling amount is 60 m 3 , and the liquid flow rate is 0.21 BV / H.

[0075] After targeted adsorption once, the effluent COD is lower than 85.6 mg / L, total nitrogen is approximately 0.58 mg / L, TDS is approximately 31007 mg / L, and the Na2CO3 content accounts for approximately 99.7%.

[0076] (5) MVR: The wastewater enters the MVR forced circulation system for evaporation, and is sent from the crystallization separator to the forced circulation heat exchanger by the forced circulation pump and then returns to the crystallization separator, and the flow rate of the heat exchanger is 2.1 m / s.

[0077] The secondary steam generated by the steam compressor enters from the inlet of the heat exchanger, flows along the shell side of the heat exchanger into the crystallization separator, exits from the top of the crystallization separator and then enters the scrubbing tower, where the entrained foam is absorbed. The secondary steam exiting the scrubbing tower flows along the steam pipe into the steam compressor; it is heated and pressurized in the steam compressor and then supplied to the forced circulation evaporation for continued use; the entire process can achieve the evaporation and crystallization of wastewater without consuming additional steam.

[0078] The condensate after evaporation and crystallization enters the condensate reuse tank, and the concentrated liquid enters the pyrolysis device from the bottom of the salt leg.

[0079] When the evaporation capacity of the MVR forced circulation evaporator drops by about 10%, the liquid in the forced circulation evaporator is drained into the pyrolysis device for further treatment.

[0080] The parameter conditions of MVR are as follows: the evaporation temperature is 95 °C, the pipe diameter size of the heat exchanger is 32 mm × 1.2 mm, the liquid flow rate in the tube side of the heat exchanger is 2.1 m / s, the gas velocity in the crystallization separator < 6 m / s, the gas velocity at the compressor inlet is 25 m / s, and the gas velocity at the compressor outlet is 30 m / s.

[0081] About 1.25 t / h of Na2CO3 concentrated liquid with a solid content of 20% is produced, and the purity of Na2CO3 is above 99.7%. About 6.41 t / h of condensate is produced, with a pH of 6 - 8, a COD of about 19 mg / L, and a TDS lower than 50 mg / L, meeting the standard of "Quality of Reclaimed Water for Industrial Use in Urban Areas" (GB / T 19923 - 2005).

[0082] (6) Pyrolysis: The 20% Na2CO3 concentrated liquid first enters the drying section, where the temperature is 150 °C and the drying duration is 1 h until the moisture content reaches 10%; then it enters the pyrolysis section, where the temperature is 450 °C and the pyrolysis duration is 1 h. The steam generated during drying and pyrolysis is recovered by heat, and the generated condensate is recycled. After pyrolysis, about 0.25 t / h of crystal salt with a COD lower than 30 mg / kg and a purity above 99.9% is produced, meeting the standard for salt to meet the reuse standard. Example 3

[0083] Example 3 provides a method for treating POSM production wastewater.

[0084] The wastewater in this example is the same as that in Example 1.

[0085] The difference between the method for treating POSM production wastewater in this example and that in Example 1 is that in step (4), the preparation method of the microcrystalline adsorbent is different, which is specifically as follows.

[0086] Targeted adsorption: The targeted adsorption system consists of 6 towers in parallel. During normal operation, 5 towers are for adsorption and 1 tower is for regeneration. Each tower is filled with 40 m 3 of microcrystalline adsorbent, and the total filling volume is 240 m 3 . The liquid flow rate is 0.2 BV / H. After one-time targeted adsorption, the COD of the effluent is 192.1 mg / L. When the COD of the adsorbed wastewater exceeds 100 mg / L, the microcrystalline material needs to be regenerated. During regeneration, fresh water and steam are introduced to heat the microcrystalline material adsorbent to above 100 °C for regeneration, and then it is purged with steam above 150 °C. The regenerated liquid after purging enters the front-end wet catalytic oxidation CWO treatment system. After two-time targeted adsorption, the COD of the effluent is 99.8 mg / L, the total nitrogen is about 0.65 mg / L, the TDS is about 31745 mg / L, and the content of Na2CO3 accounts for about 99.6%.

[0087] Among them, the preparation method of the microcrystalline adsorbent is specifically as follows:

[0088] Add 20 mol of silicon dioxide, 1 mol of alumina, and 3 mol of aluminum hydroxide to 1 L of water, mix evenly, keep it at 70 °C for 4 h to form a mixed solution; then crystallize it at 130 °C for 11 h; calcine it at 700 °C for 13 h to obtain it. Example 4

[0089] Example 4 provides a method for treating POSM production wastewater.

[0090] The wastewater in this example is the same as that in Example 1.

[0091] The difference between the method for treating POSM production wastewater in this example and that in Example 1 is that the preparation method of the microcrystalline adsorbent in step (4) is different, which is specifically as follows.

[0092] Targeted adsorption: The targeted adsorption system consists of 6 towers in parallel. During normal operation, 5 towers are for adsorption and 1 tower is for regeneration. Each tower is filled with 40 m 3 of microcrystalline adsorbent, and the total filling volume is 240 m 3 . The liquid flow rate is 0.2 BV / H. After one-time targeted adsorption, the COD of the effluent is 130.8 mg / L. When the COD of the adsorbed wastewater exceeds 100 mg / L, the microcrystalline material needs to be regenerated. During regeneration, fresh water and steam are introduced to heat the microcrystalline material adsorbent to above 100 °C for regeneration, and then it is purged with steam above 150 °C. The regenerated liquid after purging enters the front-end wet catalytic oxidation CWO treatment system. After two-time targeted adsorption, the COD of the effluent is 91.3 mg / L, the total nitrogen is about 0.37 mg / L, the TDS is about 29519 mg / L, and the content of Na2CO3 accounts for about 99.5%.

[0093] Among them, the preparation method of the microcrystalline adsorbent is specifically as follows:

[0094] Add 20 mol of silica, 1 mol of alumina, and 3 mol of aluminum hydroxide into 1 L of water, mix evenly, keep warm at 70 °C for 4 h to form a mixed solution; then crystallize at 130 °C for 11 h; then add 10 g of synergist and mix evenly; place it in a calciner at 700 °C and calcine for 13 h to obtain it.

[0095] The synergist is obtained by mixing bentonite (model YD-223, product number MR-3, 180-325 mesh; purchased from Tianjin Yandong Mineral Products Co., Ltd.) and poly (lactic-co-glycolic acid) copolymer (product number S24436, performance parameters: molecular weight: 10,000 - 20,000, PLGA 50:50, carboxyl-terminated) in a weight ratio of 2:0.5. Example 5

[0096] Example 5 provides a method for treating POSM production wastewater.

[0097] The wastewater in this example is the same as that in Example 1.

[0098] The difference between the method for treating POSM production wastewater in this example and that in Example 1 is that the preparation method of the microcrystalline adsorbent in step (4) is different, which is specifically as follows.

[0099] Targeted adsorption: The targeted adsorption system consists of 6 towers in parallel. During normal operation, 5 towers are for adsorption and 1 tower is for regeneration. Each tower is filled with 40 m 3 of microcrystalline adsorbent, and the total filling amount is 240 m 3 . The liquid flow rate is 0.2 BV / H. After targeted adsorption once, the effluent COD is 132.9 mg / L. When the COD of the adsorbed wastewater exceeds 100 mg / L, the microcrystalline material needs to be regenerated. During regeneration, fresh water and steam are introduced to heat the microcrystalline material adsorbent to above 100 °C to regenerate it, and then it is purged with steam above 150 °C. The regenerated liquid after purging enters the front-end wet catalytic oxidation CWO treatment system. After targeted adsorption twice, the effluent COD is 89.3 mg / L, the total nitrogen is about 0.49 mg / L, the TDS is about 29,918 mg / L, and the content of Na2CO3 accounts for about 99.7%.

[0100] Among them, the preparation method of the microcrystalline adsorbent is specifically as follows:

[0101] Add 20 mol of silica, 1 mol of alumina, and 3 mol of aluminum hydroxide into 1 L of water, mix evenly, keep warm at 70 °C for 4 h to form a mixed solution; then crystallize at 130 °C for 11 h; then add 10 g of synergist and mix evenly; place it in a calciner at 700 °C and calcine for 13 h to obtain it.

[0102] The synergist is obtained by mixing bentonite (model YD-223, product number MR-3, 180-325 mesh; purchased from Tianjin Yandong Mineral Products Co., Ltd.) and poly(lactic-co-glycolic acid) copolymer (product number S24479, performance parameters: molecular weight: 10,000 - 20,000, PLGA 75:25, carboxyl-terminated) in a weight ratio of 2:0.5. Example 6

[0103] Example 6 provides a method for treating POSM production wastewater.

[0104] The wastewater in this example is the same as that in Example 1.

[0105] The difference between the method for treating POSM production wastewater in this example and that in Example 1 is that: the preparation method of the microcrystalline adsorbent in step (4) is different, which is specifically as follows.

[0106] Targeted adsorption: The targeted adsorption system consists of 6 towers in parallel. During normal operation, 5 towers are for adsorption and 1 tower is for regeneration. Each tower is filled with 40 m 3 of microcrystalline adsorbent, and the total filling amount is 240 m 3 . The liquid flow rate is 0.2 BV / H. After one-time targeted adsorption, the effluent COD is 121.1 mg / L. When the COD of the adsorbed wastewater exceeds 100 mg / L, the microcrystalline material needs to be regenerated. During regeneration, fresh water and steam are introduced to heat the microcrystalline material adsorbent to above 100 °C for regeneration, and then purged with steam above 150 °C. The regenerated liquid after purging enters the front-end wet catalytic oxidation CWO treatment system. After two-time targeted adsorption, the effluent COD is 96.3 mg / L, the total nitrogen is about 0.48 mg / L, the TDS is about 28913 mg / L, and the content of Na2CO3 accounts for about 99.6%.

[0107] Among them, the specific preparation method of the microcrystalline adsorbent is as follows:

[0108] 20 mol of silicon dioxide, 1 mol of alumina, and 3 mol of aluminum hydroxide are added to 1 L of water, mixed evenly, kept at 70 °C for 4 h to form a mixed solution; then crystallized at 130 °C for 11 h; then 10 g of synergist is added and mixed evenly; calcined at 700 °C for 13 h to obtain;

[0109] The synergist is obtained by mixing bentonite (model YD-223, product number MR-3, 180-325 mesh; purchased from Tianjin Yandong Mineral Products Co., Ltd.) and poly(lactic-co-glycolic acid) copolymer (product number S33142, performance parameters: molecular weight: 10,000 - 20,000, PLGA 65:35, hydroxyl-terminated) in a weight ratio of 2:0.5. Example 7

[0110] Example 7 provides a method for treating POSM production wastewater.

[0111] The wastewater in this example is the same as that in Example 1.

[0112] The difference between the method for treating POSM production wastewater in this example and that in Example 1 is that the preparation method of the microcrystalline adsorbent in step (4) is different, which is specifically as follows.

[0113] Targeted adsorption: The targeted adsorption system consists of 6 towers in parallel. During normal operation, 5 towers are for adsorption and 1 tower is for regeneration. Each tower is filled with 40 m 3 of microcrystalline adsorbent, and the total filling amount is 240 m 3 , and the liquid flow rate is 0.2 BV / H. After one-time targeted adsorption, the COD of the effluent is 142.1 mg / L. When the COD of the adsorbed wastewater exceeds 100 mg / L, the microcrystalline material needs to be regenerated. During regeneration, fresh water and steam are introduced to heat the microcrystalline material adsorbent to above 100 °C for regeneration, and then purged with steam above 150 °C. The regenerated liquid after purging enters the front-end wet catalytic oxidation CWO treatment system. After two-time targeted adsorption, the COD of the effluent is 96.1 mg / L, the total nitrogen is about 0.58 mg / L, the TDS is about 29731 mg / L, and the content of Na2CO3 accounts for about 99.6%.

[0114] Among them, the specific preparation method of the microcrystalline adsorbent is as follows:

[0115] Add 20 mol of silica, 1 mol of alumina, and 3 mol of aluminum hydroxide to 1 L of water, mix evenly, keep warm at 70 °C for 4 h to form a mixed solution; then crystallize at 130 °C for 11 h; then add 10 g of synergist and mix evenly; calcine at 700 °C for 13 h to obtain;

[0116] The synergist is obtained by mixing bentonite (model YD-223, product number MR-3, 180-325 mesh; purchased from Tianjin Yandong Mineral Products Co., Ltd.) and poly(lactic-co-glycolic acid) copolymer (product number S33143, performance parameters: molecular weight: 10,000 - 20,000 PLGA 65:35, ester-terminated) with a weight ratio of 2:0.5. Example 8

[0117] Example 8 provides a method for treating POSM production wastewater.

[0118] The wastewater in this example is the same as that in Example 1.

[0119] The difference between the method for treating POSM production wastewater in this example and that in Example 1 is that the preparation method of the microcrystalline adsorbent in step (4) is different, which is specifically as follows.

[0120] Targeted adsorption: The targeted adsorption system consists of 6 towers in parallel. During normal operation, 5 towers are for adsorption and 1 tower is for regeneration. Each tower is filled with 40 m 3 of microcrystalline adsorbent, and the total filling volume is 240 m 3 , and the liquid flow rate is 0.2 BV / H. After one-time targeted adsorption, the COD of the effluent is 119.4 mg / L. When the COD of the adsorbed wastewater exceeds 100 mg / L, the microcrystalline material needs to be regenerated. During regeneration, fresh water and steam are introduced to heat the microcrystalline material adsorbent to above 100 °C for regeneration, and then it is purged with steam above 150 °C. The regenerated liquid after purging enters the front-end wet catalytic oxidation CWO treatment system. After two-time targeted adsorption, the COD of the effluent is 89.3 mg / L, the total nitrogen is about 0.51 mg / L, and the TDS is about 29210 mg / L, among which the content of Na2CO3 accounts for about 99.6%.

[0121] Among them, the preparation method of the microcrystalline adsorbent is specifically as follows:

[0122] Add 20 mol of silicon dioxide, 1 mol of alumina, and 3 mol of aluminum hydroxide to 1 L of water, mix evenly, keep warm at 70 °C for 4 h to form a mixed solution; then crystallize at 130 °C for 11 h; then add 10 g of synergist and mix evenly; calcine at 700 °C for 13 h to obtain it;

[0123] The synergist is obtained by mixing bentonite (model YD-223, product number MR-3, 180-325 mesh; purchased from Tianjin Yandong Mineral Products Co., Ltd.) and poly(lactic-co-glycolic acid) copolymer (product number S24482, performance parameters: molecular weight: 10,000 - 20,000, PLGA 65:35, carboxyl-terminated) with a weight ratio of 0.5:2. Example 9

[0124] Example 9 provides a method for treating POSM production wastewater.

[0125] The wastewater in this example is the same as that in Example 1.

[0126] The difference between the method for treating POSM production wastewater in this example and that in Example 1 is that the preparation method of the microcrystalline adsorbent in step (4) is different, which is specifically as follows.

[0127] Targeted adsorption: The targeted adsorption system consists of 6 towers in parallel. During normal operation, 5 towers are for adsorption and 1 tower is for regeneration. Each tower is filled with 40 m 3 of microcrystalline adsorbent, and the total filling volume is 240 m 3, the flow rate of the liquid is 0.2 BV / H. After one-time targeted adsorption (without regeneration), the COD of the effluent is 79.9 mg / L, the total nitrogen is about 0.26 mg / L, the TDS is about 28422 mg / L, and the content of Na2CO3 accounts for about 99.6%.

[0128] Among them, the preparation method of the microcrystalline adsorbent is specifically as follows:

[0129] Add 20 mol of silica, 1 mol of alumina, and 3 mol of aluminum hydroxide to 1 L of water, mix evenly, keep warm at 70 °C for 4 h to form a mixed solution; then crystallize at 130 °C for 11 h; then add 10 g of synergist and mix evenly; place it in a furnace at 700 °C and calcine for 13 h to obtain it;

[0130] The synergist is obtained by mixing bentonite (model YD-223, product number MR-3, 180-325 mesh; purchased from Tianjin Yandong Mineral Products Co., Ltd.) and poly(lactic-co-glycolic acid) copolymer (product number S24482, performance parameters: molecular weight: 10,000 - 20,000 PLGA 65:35, carboxyl-terminated; purchased from Shanghai Yuanye Bio-Technology Co., Ltd.) with a weight ratio of 1:0.8. Example 10

[0131] Example 10 provides a method for treating POSM production wastewater.

[0132] The wastewater in this example is the same as that in Example 1.

[0133] The difference between the method for treating POSM production wastewater in this example and that in Example 1 is that the preparation method of the microcrystalline adsorbent in step (4) is different, which is specifically as follows.

[0134] Targeted adsorption: The targeted adsorption system consists of 6 towers in parallel. During normal operation, 5 towers are for adsorption and 1 tower is for regeneration. Each tower is filled with 40 m 3 of microcrystalline adsorbent, and the total filling amount is 240 m 3 , the flow rate of the liquid is 0.2 BV / H. After one-time targeted adsorption (without regeneration), the COD of the effluent is 81.8 mg / L, the total nitrogen is about 0.28 mg / L, the TDS is about 28183 mg / L, and the content of Na2CO3 accounts for about 99.6%.

[0135] Among them, the preparation method of the microcrystalline adsorbent is specifically as follows:

[0136] Add 20 mol of silica, 1 mol of alumina, and 3 mol of aluminum hydroxide to 1 L of water, mix evenly, keep warm at 70 °C for 4 h to form a mixed solution; then crystallize at 130 °C for 11 h; then add 10 g of synergist and mix evenly; place it in a furnace at 700 °C and calcine for 13 h to obtain it;

[0137] The synergist is obtained by mixing bentonite (model YD-223, product number MR-3, 180-325 mesh; purchased from Tianjin Yandong Mineral Products Co., Ltd.) and poly(lactic-co-glycolic acid) (product number S24482, performance parameters: molecular weight: 10,000 - 20,000, PLGA 65:35, carboxyl-terminated; purchased from Shanghai Yuanye Bio-Technology Co., Ltd.) in a weight ratio of 3:0.2.

[0138] Although the present invention has been described in detail above with general descriptions and specific embodiments, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of the present invention claimed.

Claims

1. A method for treating POSM production wastewater, characterized in that: Specifically, the following steps are carried out in sequence: pretreatment, wet catalytic oxidation, electrolytic oxidation, targeted adsorption, MVR, and thermal decomposition coupling; (1) Pretreatment: The wastewater enters the regulating tank, and after the water volume is adjusted and the water quality is balanced in the regulating tank, the heavy metal ions are converted into precipitates through the reaction of Na2S solution; then after ultrafiltration, the clear liquid enters the mild oxidation, and the retained concentrated liquid is centrifuged for dehydration. The dehydrated filter residue is transported out for disposal, and the centrifuged liquid returns to the reaction section; (2) Wet catalytic oxidation: the reaction temperature is 200℃~300℃, the reaction pressure is 3~10MPa, and air or oxygen is used as the oxidant; the wet catalytic oxidation device is equipped with a fixed bed, filled with φ4~10mm metal oxidant filler as an enhanced disperser, with a filling density of 1.0~1.5g / mL, and the catalyst is one or more of copper, ruthenium, and cerium catalysts. The catalyst dosage is 0.5%~5%, and the catalytic oxidation time is 2~4h; (3) Electrolytic oxidation: The material of the electrolytic oxidation device is selected from diamond doped with boron or titanium substrate coated with graphene. The temperature of the liquid in the electrolytic oxidation device is lower than 60°C, and the current density is 1~10A / dm 2 , hydraulic retention time is 10~60min; (4) Targeted adsorption: Targeted adsorption is filled with microcrystalline materials, the liquid flow rate is 0.2~1BV / H, and the adsorption temperature is 20~35℃; the preparation method of the microcrystalline adsorbent used in the microcrystalline material is as follows: Add 15-25 mol of silicon dioxide, 0.7-1.5 mol of aluminum oxide, and 2-4 mol of aluminum hydroxide into 1 L of water, mix well, and keep warm at 60-80°C for 2-6 hours to form a mixed solution; then crystallize at 120-140°C for 10-12 hours; then add 5-15 g of a synergist, mix well; and calcine at 600-800°C for 12-15 hours to obtain the product; The synergist is obtained by mixing bentonite and polylactic acid glycolic acid copolymer in a weight ratio of (1-3): (0.2-0.8); the performance parameters of the polylactic acid glycolic acid copolymer are: molecular weight: 10,000-20,000 PLGA, the monomer molar ratio of lactic acid to glycolic acid is 65:35, and carboxyl end-capping; (5) MVR: The wastewater enters the MVR forced circulation system for evaporation, and is pumped from the crystallizer to the forced circulation heat exchanger through a forced circulation pump and then returns to the crystallizer. The flow rate of the heat exchanger is 2-2.2 m / s; (6) Pyrolysis: The MVR mother liquor enters the pyrolysis device, first passes through the drying section, and then enters the pyrolysis section.

2. The method for treating POSM production wastewater according to claim 1, characterized in that: In the pretreatment step, the parameters of the reaction of adding Na2S solution are as follows: the stirring speed is 50-200 rpm, the reaction time is 20-30 min; the speed of the centrifuge is 3000-5000 rpm, the contact material is 316L, and the centrifugation time is 10-30 min; The ultrafiltration adopts tubular ultrafiltration, the inner diameter of the membrane tube is 5~8mm, the length of the membrane tube is 3~4m, the membrane pore size is 20~50nm, and the membrane material is PVDF; The reaction temperature of moderate oxidation is 140℃~200℃, the reaction pressure is 0.5~1.5MPa, air or oxygen is used as the oxidant, and there is no catalyst.

3. The method for treating POSM production wastewater according to claim 1, characterized in that: In the electrolytic oxidation step, the electrolytic oxidation device includes a water inlet unit, an electrolytic oxidation unit, a waste gas treatment unit, and a water outlet unit; the water inlet unit includes a sewage pump, a water inlet tank, and an online conductivity meter; the electrolytic oxidation unit includes a water inlet pump, an oxidation tank, a direct current, and a slag liquid sedimentation tank; the waste gas treatment unit includes an induced draft fan, a washing tower, an alkali solution storage tank, and a sludge tank; the water outlet unit includes a water outlet pump, a reflux pump, and an online detection device; The electrolytic oxidation device is equipped with a cooling device, which adopts a shell-and-tube heat exchanger or a plate heat exchanger to ensure that the temperature of the liquid in the electrolytic device is lower than 60°C.

4. The method for treating POSM production wastewater according to claim 1, characterized in that: In the targeted adsorption step, when the COD of the wastewater after adsorption is below 100 mg / L, it enters the MVR treatment system; when the COD of the wastewater after adsorption exceeds 100 mg / L, the microcrystalline material needs to be regenerated. During regeneration, fresh water and steam are introduced to heat the microcrystalline material adsorbent to above 100°C to regenerate it, and then it is purged with steam above 150°C. The regenerated liquid after purging enters the wet catalytic oxidation system.

5. The method for treating POSM production wastewater according to claim 1, characterized in that: In the MVR, the secondary steam generated by the steam compressor enters from the air inlet of the heat exchanger, enters the crystallizer along the shell side of the heat exchanger, and enters the scrubber after exiting from the top of the crystallizer. The entrained foam is absorbed in the scrubber, and the secondary steam from the scrubber enters the steam compressor along the steam pipe; the temperature and pressure are increased in the steam compressor, and then the forced circulation evaporation is continued; the whole process does not require the consumption of additional steam, and the evaporation and crystallization of the wastewater can be achieved; The condensate after evaporation and crystallization enters the condensate reuse pool, and the concentrated liquid enters the pyrolysis device from the bottom of the salt leg; When the evaporation capacity of the MVR forced circulation evaporator drops by about 10%, the liquid in the forced circulation evaporator is discharged to the pyrolysis device for further processing.

6. The method for treating POSM production wastewater according to claim 1, characterized in that: The parameter conditions of the MVR are: evaporation temperature is 85-100°C, heat exchanger tube diameter size is 32mm×1.2mm, heat exchanger tube liquid flow rate is 2-2.2m / s, crystal separator gas speed is <6m / s, compressor inlet gas speed is 25m / s, compressor outlet gas speed is 30m / s.

7. The method for treating POSM production wastewater according to claim 1, characterized in that: In the pyrolysis step, the temperature of the drying section is 100-200°C, the drying time is 0.5-2h, and the moisture content is dried to 10%-20%; the temperature of the pyrolysis section is 300-600°C, the pyrolysis time is 0.5-2h, and the COD content in the crystalline salt after pyrolysis is less than 30mg / kg.

8. Application of the treatment method according to any one of claims 1 to 7 in the treatment of POSM production wastewater.

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