Method for treating and recycling MTO (Methanol To Olefins) production wastewater

Abstract

The invention relates to the technical field of wastewater treatment, and particularly discloses a method for treating and recycling MTO (Methanol To Olefins) production wastewater. The invention provides a method for treating and recycling MTO (Methanol To Olefins) production wastewater. The method comprises the following steps: mild oxidation, wet catalytic oxidation, reaction precipitation, targeted adsorption, CFIC treatment and MVR (Mechanical Vapor Recompression) treatment. In the step of mild oxidation, air or oxygen is used as an oxidant, and mild oxidation is carried out on the MTO production wastewater at 140-200 DEG C and under the pressure of 0.5-1.5 MPa; according to the wet catalytic oxidation, air or oxygen serves as an oxidizing agent, one or more of a copper-based catalyst, a ruthenium-based catalyst, a palladium-based catalyst and a cerium-based catalyst serve as a catalyst, and wet catalytic oxidation is carried out at the temperature of 200-300 DEG C and the pressure of 3-10 MPa. According to the MTO production wastewater treatment and recycling method disclosed by the invention, the COD (Chemical Oxygen Demand) of the effluent of the MTO production wastewater can stably reach the standard, and most of salts in the wastewater can be recycled, so that the reutilization of resources is realized.

Description

Technical Field

[0001] This application relates to the technical field of wastewater treatment, and particularly to a method for treating and recycling MTO production wastewater. Background Art

[0002] The methanol-to-olefins technology (MTO), as a key chemical technology for converting methanol into olefins, has witnessed rapid development in China in recent years. However, with the large-scale application of the MTO process, the problem of a large amount of wastewater generated during its production has become increasingly prominent, which has become one of the key factors restricting the sustainable development of the industry. How to efficiently and economically treat such wastewater while maximizing the utilization of resources has become the focus of attention in the industry.

[0003] Currently, the treatment of MTO wastewater mainly adopts a combination of traditional physical-chemical and biological treatment methods. For example, large particulate suspensions are intercepted by a grille, and the water quality and quantity are balanced in an adjustment tank; suspended substances and some organic matters are removed by means of coagulation precipitation, air flotation, etc.; biochemical means such as the activated sludge method or the biofilm method are further used to degrade organic pollutants. In addition, in order to meet more stringent discharge standards, deep purification measures such as sand filtration, activated carbon adsorption, and even reverse osmosis are supplemented. Although the above methods can improve the water quality to a certain extent, there are still many deficiencies; for example, the existing MTO wastewater treatment processes generally have the problem that the effluent COD is difficult to stably meet the standard, especially in the case of dealing with high salinity and complex organic composition. At the same time, some treatment links are prone to generating surplus mother liquor, which will bring the risk of secondary pollution if not disposed of in a timely and proper manner. More importantly, traditional methods often ignore the potential for recycling salt resources in the wastewater, resulting in the waste of precious raw materials while increasing the overall operating cost.

[0004] Therefore, developing a treatment method that can not only stably treat MTO wastewater with high salinity and complex organic composition but also recover the salt in it for resource recycling is of great significance for the sustainable development of the methanol-to-olefins industry. Summary of the Invention

[0005] In order to overcome the problems that the existing MTO wastewater treatment process may have when treating MTO wastewater with high salinity and complex organic composition, such as the effluent COD being difficult to stably meet the standard, and the existence of secondary pollution or resource waste, this application provides a method for treating and recycling MTO production wastewater.

[0006] The method for treating and recycling MTO production wastewater provided by this application adopts the following technical solutions: A method for treating and recycling MTO production wastewater includes the following steps: mild oxidation, wet catalytic oxidation, reaction precipitation, targeted adsorption, CFIC treatment, and MVR treatment; The mild oxidation uses air or oxygen as the oxidant to conduct mild oxidation on the MTO production wastewater at 140 - 200°C and a pressure of 0.5 - 1.5 MPa; The wet catalytic oxidation uses air or oxygen as the oxidant and one or more of copper - based, ruthenium - based, palladium - based, and cerium - based catalysts as the catalyst to conduct wet catalytic oxidation at 200 - 300°C and a pressure of 3 - 10 MPa.

[0007] In this application, by sequentially conducting mild oxidation, wet catalytic oxidation, reaction precipitation, targeted adsorption, CFIC treatment, and MVR treatment on the MTO production wastewater, the problem that the effluent COD in the existing treatment process is difficult to meet the standard can be effectively solved, and the salt in the wastewater can also be effectively recovered, achieving the purpose of resource recovery and utilization. Specifically, by conducting mild oxidation treatment on the MTO production wastewater, a part of the organic matter in the wastewater can be initially decomposed, reducing the load of subsequent treatment. Then, wet catalytic oxidation is carried out. Using the action of the catalyst, the refractory organic matter in the wastewater is further efficiently degraded under high - temperature and high - pressure conditions, and pollutants such as COD, TOC, and ammonia nitrogen in the high - concentration wastewater are oxidized and decomposed into CO 2 , N 2 and harmless components such as water, significantly reducing the COD value and simultaneously deodorizing, decolorizing, and disinfecting, so as to achieve the purpose of purification treatment. The treatment and reuse method of MTO production wastewater provided in this application can not only make the MTO effluent COD meet the standard, but also recover Na 2 SO 4 in the highly saline wastewater generated during the methanol - to - olefins production process, solve the problem of highly saline wastewater treatment, save the treatment cost, create economic value, and achieve the purpose of clean production and energy conservation and emission reduction.

[0008] Optionally, a fixed bed is arranged inside the device for wet catalytic oxidation. The fixed bed is filled with a catalyst with a particle size of φ4 - 10 mm, and the filling density is 1.0 - 1.5 g / mL; the amount of the active component in the catalyst accounts for 0.05 - 5% of the weight of the carrier.

[0009] Optionally, the amount of the active component in the catalyst accounts for 0.1 - 3% of the weight of the carrier.

[0010] In this application, the copper - based catalyst can be copper sulfate, its active component is Cu 2+ , and the carrier is alumina; the active component of the ruthenium - based catalyst is ruthenium metal, and the carrier is titanium dioxide; the active component of the palladium - based catalyst is palladium metal, and the carrier is titanium dioxide; the cerium - based catalyst can be a cerium - based alloy catalyst, its active component is cerium metal, and the carrier is titanium dioxide.

[0011] Optionally, the specific steps of the reaction precipitation are as follows: Add a sodium hydroxide solution with a mass concentration of 5-30% to the wastewater after wet catalytic oxidation to adjust the pH to 7-10, and stir and react at 50-200 rpm for 20-30 min; the effluent enters the inclined tube precipitation section for precipitation; the precipitate at the bottom of the precipitation section is sent to a centrifuge for centrifugation, the liquid returns to the reaction sedimentation tank, and the solid enters the dissolution tank for further treatment.

[0012] Optionally, the rotation speed of the centrifugation is 3000-5000 rpm, and the time is 10-30 min.

[0013] Optionally, the treatment method of the solid in the dissolution tank is as follows: Add dilute sulfuric acid with a concentration of 15% to 35% to the dissolution tank, stir at 50-200 rpm for 10-30 min to completely dissolve the copper hydroxide solid, and return the dissolved copper sulfate solution to the wet catalytic oxidation system to realize the recycling of the catalyst.

[0014] Optionally, the specific steps of the targeted adsorption are as follows: Adjust the pH of the supernatant from the reaction sedimentation tank to 3-5, and then send it to the targeted adsorption system for adsorption at a working flow rate of 10 BV / H, so that Cu 2+ remains on the adsorption column; the adsorbent model is CH-90Na.

[0015] Optionally, the targeted adsorption further includes: after adsorption saturation, first desorb with a 5% dilute sulfuric acid solution, the flow rate is 4-5 BV / H, and the time is 30-45 min; then backwash with pure water or soft water, the backwash flow rate is 5-10 BV / H, and the backwash time is 30 min; finally, transform with a 5% sodium hydroxide solution, the transformation flow rate is 4-5 BV / H, and the time is 30 min.

[0016] Optionally, the CFIC treatment includes anoxic treatment and aerobic treatment.

[0017] In this application, the CFIC treatment is a multi-stage wastewater treatment. In a multi-stage wastewater treatment tank, biological fillers are installed, microorganisms multiply on the fillers, and a microporous aeration disk is used to supply air (dissolved oxygen) to the microorganisms in the tank. The multi-stage biological contact oxidation tank is mainly divided into an anoxic section and an aerobic section. In the anoxic section, under the condition of low dissolved oxygen, the sewage removes total nitrogen through denitrification. In the aerobic stage, under the condition of high dissolved oxygen, the sewage undergoes nitrification and oxidation. After sufficient treatment by the anoxic + aerobic CFIC, the ammonia nitrogen in the water is converted into nitrate nitrogen, and at the same time, the concentration of organic pollutants is greatly reduced. There is a reflux inside the nitrification and denitrification system, and the nitrate nitrogen generated in the nitrification system is refluxed to the denitrification system to be converted into nitrogen gas, reducing the total nitrogen in the treatment system. The CFIC treatment has the following characteristics: ① It can provide a large biological membrane area in a limited space, maintain a strong living condition for the habitat and growth of microorganisms, and maintain the total amount of useful organisms. ② Through sludge selection, the extracellular matrix produced by microorganisms with a certain activity is used as a carbon source, and NO 3- is used as the final electron acceptor, which can reduce the carbon source dosage by about 30%. ③ High treatment efficiency, strong nitrogen removal ability, long sludge age, strong impact resistance, simple operation control, simple maintenance, etc.

[0018] Optionally, in the MVR treatment step, 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 distillation kettle for continuous evaporation. When the moisture content is about 20%, the resulting miscellaneous salts are packed by a packing machine and transported out for disposal.

[0019] In summary, this application has the following beneficial effects: 1. In the method for treating and recycling MTO production wastewater provided by this application, through the combined treatment of mild oxidation and wet catalytic oxidation, the degradation efficiency of organic matter is significantly improved, ensuring that the effluent COD meets the standard stably, and effectively solving the problem that the effluent COD in the traditional process is difficult to meet the standard.

[0020] 2. The method for treating and recycling MTO production wastewater provided by this application can also recover Na 2 SO 4 from the highly saline wastewater generated in the methanol-to-olefins production process, solve the problem of treating highly saline wastewater, save the treatment cost, create economic value, and achieve the purpose of clean production and energy conservation and emission reduction.

[0021] 3. This application uses copper-based, ruthenium-based, palladium-based, and cerium-based catalysts. Not only is the recovered purity high, but it can also be continuously used as a catalyst in the wet catalytic oxidation section of the water treatment process, achieving the purpose of resource recycling.

[0022] 4. The CFIC (multi-stage biological treatment) technology adopted in this application can provide the best fixed-bed packing for the growth and reproduction of microorganisms, reduce the volume of the structure or improve the treatment capacity through a high sludge volume load, effectively disperse the water quality fluctuations of the influent through a high concentration of microorganisms and the attached growth mode, make the effluent stable, and the shock resistance is significantly higher than that of traditional activated sludge, and has a strong tolerance to toxic substances.

[0023] 5. The method for treating and recycling MTO production wastewater provided by this application can improve the clean production and environmental protection level of methanol to olefins, realize the closed-loop circulation of resources and energy in the wastewater treatment process, make the integrated utilization of resources more optimized, the product structure more reasonable, the environment more friendly, and the benefits more obvious. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a flow chart of the method for treating and recycling MTO production wastewater provided by this application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] This application provides a method for treating and recycling MTO production wastewater, as Figure 1 shown, which specifically includes the following steps: (1) Moderate oxidation: Feed the MTO production wastewater into the adjustment tank. After adjusting the water volume and balancing the water quality in the adjustment tank, use air or oxygen as the oxidant to carry out moderate oxidation at 140 - 200 °C and 0.5 - 1.5 MPa pressure, removing most of the organic matter in the wastewater while reducing the pH value of the wastewater; (2) Wet catalytic oxidation: Then feed the wastewater after moderate oxidation into a wet catalytic oxidation device equipped with a catalyst, use air or oxygen as the oxidant to carry out wet catalytic oxidation at 200 - 300 °C and 3 - 10 MPa pressure, oxidize and decompose pollutants such as COD, TOC, and ammonia nitrogen in the wastewater, and convert them into harmless components such as CO 2 、N 2 and water, etc., while deodorizing, decolorizing, and disinfecting, so as to achieve the purpose of purification treatment. Among them, a fixed bed is provided inside the wet catalytic oxidation device, and the fixed bed is filled with a catalyst of φ4 - 10 mm, and the filling density is 1.0 - 1.5 g / mL; the catalyst is selected from one or more of copper-based, ruthenium-based, palladium-based, cerium-based and other catalysts; the amount of the active component in the catalyst accounts for 0.05 - 5% of the weight of the carrier, preferably 0.1 - 3%; the catalytic oxidation time is 2 - 4 h; a fixed bed is provided inside the wet catalytic oxidation device, and a metal oxidant of φ4 - 10 mm is filled as a strengthening disperser, and the filling density is 1.0 - 1.5 g / mL to increase the contact area between oxygen and water and play a catalytic role at the same time.

[0026] (3) Reaction precipitation: Add a sodium hydroxide solution with a mass concentration of 5 - 30% to the wastewater after wet catalytic oxidation to adjust the pH to 7 - 10, and stir and react for 20 - 30 min at 50 - 200 rpm; the effluent enters the inclined tube precipitation section, and the precipitation time is 1 h; send the precipitate at the bottom of the precipitation section to a centrifuge and centrifuge for 10 - 30 min at a speed of 3000 - 5000 rpm, the liquid returns to the reaction sedimentation tank, and the solid enters the dissolution tank; add dilute sulfuric acid with a concentration of 15% - 35% to the dissolution tank, stir at 50 - 200 rpm for 10 - 30 min to completely dissolve the copper hydroxide solid, and return the dissolved copper sulfate solution to the wet catalytic oxidation system to realize the recycling of the catalyst.

[0027] (4) Targeted adsorption: Adjust the pH of the supernatant from the reaction sedimentation tank to 3 - 5, and then send it to the targeted adsorption system for adsorption at a working flow rate of 10 BV / H to make Cu 2+ remain on the adsorption column; the adsorbent model is CH-90Na, and the saturated adsorption capacity is about 50 g / L; when the adsorption is saturated, first desorb with a 5% dilute sulfuric acid solution at a flow rate of 4 - 5 BV / H for 30 - 45 min; then backwash with pure water or soft water at a backwash flow rate of 5 - 10 BV / H for 30 min; finally, transform with a 5% sodium hydroxide solution at a transformation flow rate of 4 - 5 BV / H for 30 min; the acid and alkali are recycled, when the acidity of the desorption liquid is less than 1%, it is discharged to the reaction tank to recover the copper in it; when the sodium hydroxide concentration is lower than 1%, supplement sodium hydroxide and continue to use.

[0028] (5) CFIC treatment: Set biological fillers in the multi-stage wastewater treatment tank (CFIC), breed microorganisms on the fillers, and provide air (dissolved oxygen) to the microorganisms in the tank through microporous aeration discs; send the effluent from targeted adsorption into the CFIC system for sufficient anoxic + aerobic treatment.

[0029] (6) MVR treatment: The effluent from CFIC 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 in the heat exchanger is 2 - 2.2 m / s. The secondary steam generated by the steam compressor enters from the air 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 enters the scrubbing tower, and the secondary steam coming out of the scrubbing tower enters the steam compressor along the steam pipe. Temperature rise and pressure increase are completed in the steam compressor, and then it is supplied for forced circulation evaporation and continued use. The condensate after evaporation and crystallization enters the condensate reuse tank, the concentrated liquid enters the centrifuge from the bottom of the salt leg, solid-liquid separation is achieved under the action of the centrifuge, the salt coming out is packed by the packing machine to become product salt, and the mother liquor after centrifugation enters the concentrated liquid tank.

[0030] The raw materials, reagents, solvents, etc. used in this application can all be obtained through commercial purchase.

[0031] The following further elaborates on this application in conjunction with examples, performance detection tests, and description of the drawings. Example 1

[0032] Example 1 uses a method for treating and recycling MTO production wastewater to treat the MTO production wastewater of a certain methanol-to-olefins (MTO) plant in Tianjin. The water volume is 140 t / h, and the measured pH is 13 - 14, the COD is 10300 mg / L, the TDS is 45000 - 50000 mg / L, and the Na 2 SO 4 content is 40 - 50%.

[0033] The above treatment method specifically includes the following steps: (1) Mild oxidation: Feed the MTO production wastewater into the adjustment tank. After adjusting the water volume and equalizing the water quality in the adjustment tank, use air as the oxidant to carry out mild oxidation at 150 °C and 1 MPa pressure; the COD of the effluent is about 4100 mg / L, and the pH drops to 4 - 5.

[0034] (2) Wet catalytic oxidation: Then feed the wastewater after mild oxidation into a wet catalytic oxidation device equipped with CuSO 4 catalyst. The filling density of the CuSO 4 catalyst in the fixed bed is 1.3 g / mL; the amount of the active ingredient (Cu 4 ) in the CuSO 2+ catalyst accounts for 1.5% of the weight of the carrier (aluminum oxide); then continuously introduce air as the oxidant and carry out wet catalytic oxidation for 2 h at 270 °C and 8 MPa pressure; the COD of the effluent is about 600 mg / L, the pH is about 6, the TDS is about 62000 mg / L, and the Na 2 SO 4 content is about 55%.

[0035] (3) Reaction precipitation: Add 3.5 t / h of sodium hydroxide solution with a mass concentration of 30% to the wastewater after wet catalytic oxidation, adjust the pH to 8, and stir and react for 30 min at 100 rpm; the effluent enters the inclined tube precipitation section, and the precipitation time is 1 h; about 55 t / h of Cu(OH) 2 sludge and about 20 g / L of SS are generated in the precipitation section. Send the sludge at the bottom of the precipitation section to a centrifuge and centrifuge for 20 min at a speed of 4000 rpm. The liquid returns to the reaction sedimentation tank, and Cu(OH) 2 with a moisture content of 20% is produced.Approximately 1.4 t / h of solid enters the dissolution tank; 3.5 t / h of dilute sulfuric acid with a concentration of 30% is added to the dissolution tank, and it is stirred at 100 rpm for 20 min to completely dissolve the copper hydroxide solid, and the dissolved copper sulfate solution is returned to the wet catalytic oxidation system to realize the recycling of the catalyst.

[0036] (4) Targeted adsorption: The pH of the supernatant from the reaction sedimentation tank is adjusted to 3 - 5 with 10% dilute sulfuric acid, and then it is sent to the targeted adsorption system for adsorption at a working flow rate of 10 BV / H, so that Cu 2+ remains on the adsorption column; no copper ions are detected in the effluent from the column, and the COD is about 580 mg / L. The targeted adsorption of 80 BV of wastewater reaches saturation, and 4 BV of dilute sulfuric acid is required for desorption. The obtained copper-containing solution is blue-green, and the regeneration liquid from the targeted adsorption returns to the front-end reaction sedimentation.

[0037] (5) CFIC treatment: Biological fillers are set in the multi-stage wastewater treatment tank (CFIC), microorganisms are propagated on the fillers, and air (dissolved oxygen) is provided to the microorganisms in the tank through microporous aeration discs; the effluent from the targeted adsorption is sent to the CFIC system for sufficient anoxic + aerobic treatment. After treatment, the COD of the effluent is 88 mg / L, the pH value is 6 - 8, the TDS is about 61000 mg / L, and the content of Na 2 SO 4 is about 56%.

[0038] (6) MVR treatment: The effluent from CFIC enters the MVR forced circulation system for treatment. The design parameters of MVR are as follows: evaporation temperature 85 - 100 °C, the outer diameter × thickness of the heat exchanger tube 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 crystal separator is < 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.

[0039] After the above treatment, 5.0 t / h of Na 2 SO 4 salt with a moisture content of 20% is produced, and the purity of Na 2 SO 4 is above 99%. 6.1 t / h of miscellaneous salt with a moisture content of 20% is produced, and the miscellaneous salt is transported out for disposal. 136 t / h of condensate water is produced, with a COD of about 18 mg / L, chloride ions < 1 mg / L, sulfate radicals about 60 mg / L, and TDS less than 200 mg / L, meeting the standard of "Quality of Reclaimed Water for Industrial Use in Urban Areas" (GB / T 19923 - 2005). Example 2

[0040] Example 2 uses a method for treating and recycling MTO production wastewater to treat the MTO production wastewater of a certain methanol-to-olefins (MTO) plant in Shaanxi. The water volume is 75 t / h, the measured pH is 12 - 13, the COD is 25000 mg / L, the TDS is 45000 - 50000 mg / L, and the content of Na 2 SO 4 is 50 - 60%.

[0041] The above treatment method specifically includes the following steps: (1) Moderate oxidation: Feed the MTO production wastewater into the adjustment tank. After adjusting the water volume and balancing the water quality in the adjustment tank, use air as the oxidant to carry out moderate oxidation at 160 °C and 1 MPa pressure; the COD of the effluent is about 10000 mg / L, and the pH drops to 4 - 5.

[0042] (2) Wet catalytic oxidation: Then feed the wastewater after moderate oxidation into a wet catalytic oxidation device equipped with CuSO 4 catalyst. The packing density of the CuSO 4 catalyst in the fixed bed is 1.3 g / mL; the amount of the active ingredient (Cu 4 ) in the CuSO 2+ catalyst accounts for 2% of the weight of the carrier (aluminum oxide); then continuously introduce air as the oxidant to carry out wet catalytic oxidation for 2 h at 270 °C and 8 MPa pressure; the COD of the effluent is about 1400 mg / L, the pH is about 6, the TDS is about 78000 mg / L, and the content of Na 2 SO 4 is about 72%.

[0043] (3) Reaction precipitation: Add 31 t / h of a 30% sodium hydroxide solution to the wastewater after wet catalytic oxidation, adjust the pH to 8, and stir and react at 100 rpm for 30 min; the effluent enters the inclined tube precipitation section. The diameter of the inclined tube is 100 mm, the thickness is not less than 1 mm, and the material is PP material. The precipitation time is 1 h; about 31 t / h of Cu(OH) 2 sludge and about 40 g / L of SS are generated in the precipitation section. Send the sludge at the bottom of the precipitation section to a centrifuge and centrifuge at a speed of 4000 rpm for 20 min. The liquid returns to the reaction sedimentation tank, and about 1.5 t / h of Cu(OH) 2 solid with a moisture content of 20% enters the dissolution tank; add 3.9 t / h of 30% dilute sulfuric acid to the dissolution tank and stir at 100 rpm for 20 min to completely dissolve the copper hydroxide solid, and return the dissolved copper sulfate solution to the wet catalytic oxidation system to realize the recycling of the catalyst.

[0044] (4) Targeted adsorption: The pH of the supernatant from the reaction sedimentation tank was adjusted to 3 - 5 with 10% dilute sulfuric acid, and then it was sent to the targeted adsorption system for adsorption at a working flow rate of 10 BV / H to retain Cu 2+ on the adsorption column; copper ions were not detected in the effluent from the column, and the COD was approximately 1300 mg / L. The targeted adsorption reached saturation after treating 80 BV of wastewater, and 4 BV of dilute sulfuric acid was required for desorption. The resulting copper-containing solution was bluish-green, and the regeneration liquid from the targeted adsorption was returned to the front-end reaction sedimentation.

[0045] (5) CFIC treatment: After the effluent from the targeted adsorption was fully treated in the multi-stage wastewater treatment tank (CFIC), the COD of the effluent was 200 mg / L, the pH value was 6 - 8, the TDS was approximately 76000 mg / L, and the content of Na 2 SO 4 was approximately 72%.

[0046] (6) MVR treatment: The effluent from CFIC entered the MVR forced circulation system for treatment. The design parameters of MVR were as follows: evaporation temperature 85 - 100 °C, heat exchanger pipe diameter (outer diameter × thickness) 32 mm × 1.2 mm, liquid flow rate in the tube side of the heat exchanger 2 - 2.2 m / s, gas velocity in the crystal separator < 6 m / s, gas velocity at the compressor inlet 25 m / s, and gas velocity at the compressor outlet 30 m / s.

[0047] After the above treatment, 2.1 t / h of Na 2 SO 4 salt with a moisture content of 20% was produced, and the purity of Na 2 SO 4 was above 99%. 5.6 t / h of miscellaneous salt with a moisture content of 20% was produced, and the miscellaneous salt was transported out for disposal. 75.2 t / h of condensate water was produced, with COD approximately 41 mg / L, chloride ions < 1 mg / L, sulfate radicals approximately 98 mg / L, and TDS below 250 mg / L, meeting the standard of "Quality of Reclaimed Water for Industrial Use in Urban Areas" (GB / T 19923 - 2005). Examples 3 - 6

[0048] Examples 3 - 6 respectively provide a method for treating and recycling MTO production wastewater.

[0049] The differences between the above examples and Example 1 are as follows: the percentage of the active ingredient in the catalyst accounting for the weight of the carrier is shown in Table 1 below.

[0050] Table 1 Percentage of the active ingredient in the catalyst accounting for the weight of the carrier in the treatment and recycling methods of Examples 3 - 6

[0051] The methods provided in Examples 3 - 6 were respectively used to treat the methanol - to - olefins (MTO) production wastewater in Tianjin. After the above treatment, the obtained Na with a water content of 20% 2 SO 4 salt, the yield of miscellaneous salts with a water content of 20%, and the yield of condensate water are shown in Table 2 below together with the indicators.

[0052] Table 2 Results of treating MTO production wastewater by the treatment and reuse methods provided in Examples 3 - 6

[0053] According to the test results in Table 3, it can be seen that the treatment and reuse method of MTO production wastewater provided in Examples 3 - 6 of the present application can, on the one hand, efficiently recover the salts in the MTO production wastewater, and on the other hand, can effectively reduce the COD in the MTO production wastewater, making the treated wastewater meet the standard of "Quality of Reclaimed Water for Industrial Use in Urban Areas" (GB / T 19923 - 2005). Further comparison found that the yields of Na 2 SO 4 salt and miscellaneous salts obtained in Examples 1, 4 - 5 are higher, and the COD content in the condensate water can be as low as below 30 mg / L, and the sulfate ion content can be as low as below 70 mg / L. It shows that further controlling the amount of the active component in the catalyst within the range of 0.1 - 3% of the weight of the carrier in the present application has a better treatment effect on MTO production wastewater.

[0054] Although the present invention has been described in detail with general descriptions and specific embodiments above, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, the modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A method for treating and reusing MTO production wastewater, characterized in that: The following steps are involved: Mild oxidation, wet catalytic oxidation, reactive precipitation, targeted adsorption, CFIC treatment and MVR treatment; The moderate oxidation is to use air or oxygen as an oxidant to moderately oxidize the MTO production wastewater at 140-200°C and 0.5-1.5MPa pressure; The wet catalytic oxidation uses air or oxygen as an oxidant and one or more of copper, ruthenium, palladium and cerium catalysts as a catalyst, and is carried out at 200-300° C. and 3-10 MPa pressure.

2. The method for treating and reusing MTO production wastewater according to claim 1, characterized in that: The wet catalytic oxidation device is provided with a fixed bed, which is filled with a catalyst of φ4-10 mm and a filling density of 1.0-1.5 g / mL; the amount of active ingredients in the catalyst accounts for 0.05-5% of the weight of the carrier.

3. The method for treating and reusing MTO production wastewater according to claim 2, characterized in that: The amount of active components in the catalyst accounts for 0.1-3% of the weight of the carrier.

4. The method for treating and reusing MTO production wastewater according to claim 1, characterized in that: The specific steps of the reaction precipitation are: adding a sodium hydroxide solution with a mass concentration of 5-30% to the wastewater after wet catalytic oxidation to adjust the pH to 7-10, and stirring the reaction at 50-200rpm for 20-30min; the effluent enters the inclined tube sedimentation section for sedimentation; the sediment at the bottom of the sedimentation section is sent to a centrifuge for centrifugation, the liquid returns to the reaction sedimentation tank, and the solid enters the dissolution tank for further treatment.

5. The method for treating and reusing MTO production wastewater according to claim 4, characterized in that: The centrifugal speed is 3000-5000 rpm and the time is 10-30 min.

6. The method for treating and reusing MTO production wastewater according to claim 4, characterized in that: The method for treating the solid in the dissolving tank is as follows: adding dilute sulfuric acid with a concentration of 15% to 35% to the dissolving tank, stirring at 50-200 rpm for 10-30 minutes to completely dissolve the copper hydroxide solid, and returning the dissolved copper sulfate solution to the wet catalytic oxidation system to achieve catalyst recovery.

7. The method for treating and reusing MTO production wastewater according to claim 1, characterized in that: The specific steps of the targeted adsorption are: adjusting the pH of the supernatant from the reaction sedimentation tank to 3-5, and then sending it to the targeted adsorption system at a working flow rate of 10BV / H for adsorption, so that Cu 2+ Remain on the adsorption column; the adsorbent model is CH-90Na.

8. The method for treating and reusing MTO production wastewater according to claim 1, characterized in that: The targeted adsorption also includes: when the adsorption is saturated, firstly analyzing with a 5% dilute sulfuric acid solution, the flow rate is 4-5BV / H, and the time is 30-45min; then backwashing with pure water or soft water, the backwashing flow rate is 5-10BV / H, and the backwashing time is 30min; finally, transformation with a 5% sodium hydroxide solution, the transformation flow rate is 4-5BV / H, and the time is 30min.

9. The method for treating and reusing MTO production wastewater according to claim 1, characterized in that: The CFIC treatment includes anoxic treatment and aerobic treatment.

10. The method for treating and reusing MTO production wastewater according to claim 1, characterized in that: In the MVR treatment step, 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 distillation kettle for further evaporation. When the water content is about 20%, the resulting impurities are packaged by a packaging machine and transported for disposal.

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