Treatment device and method for wet oxidation produced water of caprolactam wastewater

Abstract

The invention relates to a treatment device and method for wet oxidation produced water of caprolactam wastewater. The treatment device comprises a produced water collection tank, a membrane filtration device, an electrolysis device, a macroporous adsorption resin column and a chelating adsorption resin column. The treatment method comprises the following steps: (1) adjusting the pH value of the wet oxidation produced water of the caprolactam wastewater, and then carrying out membrane filtration concentration; (2) carrying out electrolytic treatment on the obtained concentrated water; (3) carrying out resin adsorption on the obtained electrolysis wastewater; and (4) carrying out advanced treatment on the obtained adsorption wastewater. The device disclosed by the invention is simple in structure, large in treatment capacity, free of additional byproducts and three wastes, green, environment-friendly, safe and reliable. The method is simple in process, high in COD removal rate, high in catalyst metal ion and ammonium sulfate recovery rate, high in ammonium sulfate purity and good in fresh water biodegradability, solves the problem of membrane pollution of a membrane filtration device caused by high-concentration metal ions in wastewater, improves the efficiency of an electrolysis device, is low in cost and is suitable for industrial production.

Description

Technical Field

[0001] The invention relates to a device and method for treating water produced by wet oxidation, and in particular to a device and method for treating water produced by wet oxidation of caprolactam wastewater. Background Art

[0002] At present, the mainstream process for caprolactam production is the cyclohexanone liquid phase ammonia oximation method, which first generates cyclohexanone oxime from cyclohexanone, ammonia and hydrogen peroxide under the action of titanium silicon molecular sieve, and then the cyclohexanone oxime undergoes Beckmann rearrangement under the action of fuming sulfuric acid to generate caprolactam sulfate, which is neutralized with ammonia water to obtain a crude caprolactam aqueous solution, and finally the crude caprolactam aqueous solution is subjected to extraction, stripping, ion exchange, hydrogenation, evaporation, distillation and other steps to obtain refined caprolactam. In a series of complex production processes, cyclohexanone, cyclohexanone oxime and other difficult-to-degrade byproducts are produced. Therefore, caprolactam wastewater has the characteristics of high oxygen consumption and high toxicity. The discharge of untreated high-concentration caprolactam wastewater into nature will cause irreversible damage to the sustainable development of the ecosystem and even threaten human life and health. Therefore, exploring an economical and efficient method to treat caprolactam wastewater is the current primary goal.

[0003] Catalytic wet oxidation (CWAO) technology is a representative of wastewater thermal treatment technology. It uses oxidants, copper, iron, manganese, nickel or cobalt catalysts under high temperature and high pressure to catalytically oxidize organic matter in wastewater into CO2 and water, thereby achieving the purpose of removing pollutants. However, caprolactam production wastewater generally has the characteristics of high COD content, high salt content, and complex composition. Although catalytic wet oxidation can make the COD removal rate reach more than 98%, the removal rate of ammonia nitrogen is low, and all total nitrogen is converted into ammonia nitrogen. It is also impossible to remove inorganic salts (mainly ammonium sulfate) in the solution. The treated wastewater contains a large amount of ammonium sulfate and has poor biodegradability. In addition, there is still a small amount of COD in the produced water that is difficult to remove and cannot be directly discharged, so further treatment is required.

[0004] In summary, it is urgent to find a treatment device for wet oxidation water production of caprolactam wastewater with simple structure, large processing capacity, no additional by-products and three wastes, green and environmentally friendly, safe and reliable, as well as a simple process, high COD removal rate, high catalyst metal ion and ammonium sulfate recovery rate, high ammonium sulfate purity, good fresh water biodegradability, and at the same time solve the membrane pollution problem of membrane filtration device caused by high concentration of metal ions in wastewater, and improve the efficiency of electrolysis device, low cost, and suitable for industrial production of caprolactam wastewater wet oxidation water treatment method. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a treatment device for wet oxidation water production of caprolactam wastewater which has a simple structure, large processing capacity, no additional by-products and three wastes, is green, environmentally friendly, safe and reliable.

[0006] The technical problem further to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method for treating wet oxidation water produced by caprolactam wastewater with simple process, high COD removal rate, high recovery rate of catalyst metal ions and ammonium sulfate, high purity of ammonium sulfate, and good biodegradability of fresh water. At the same time, the problem of membrane pollution of membrane filtration devices caused by high concentration of metal ions in wastewater is solved, and the efficiency of the electrolysis device is improved. The method has low cost and is suitable for industrial production of caprolactam wastewater.

[0007] The technical solution adopted by the present invention to solve its technical problems is as follows: a treatment device for wet oxidation water production of caprolactam wastewater, comprising a water production collection tank, a membrane filtration device, an electrolysis device, a macroporous adsorption resin column and a chelating adsorption resin column; the water outlet of the water production collection tank is connected to the water inlet of the membrane filtration device; the concentrated water outlet of the membrane filtration device is connected to the water inlet of the electrolysis device; the water outlet of the electrolysis device is connected to the lower water inlet of the macroporous resin column; the upper water outlet of the macroporous resin column is connected to the lower water inlet of the chelating resin column.

[0008] Preferably, the produced water collection tank is provided with a water inlet and a pH value adjusting device.

[0009] Preferably, the membrane filtration device is provided with a fresh water outlet.

[0010] Preferably, the membrane is a nanofiltration membrane or a reverse osmosis membrane. Further preferably, the membrane is a nanofiltration membrane. The reverse osmosis membrane has a high removal rate for ions and a high removal rate for COD, while the nanofiltration membrane has a better selective separation ability, with a pore size between 0.1 and 2.0 nm. The nanofiltration membrane is between ultrafiltration and reverse osmosis, and can screen out substances with a molecular weight of about 100 to 2000 Daltons through pore size screening and charge action. It can retain most of the ammonium sulfate in concentrated water, but basically does not retain COD, thereby producing low-salinity fresh water, thereby achieving the ideal fresh water filtration and ammonium sulfate recovery effect, and the advantages of the nanofiltration membrane include low operating pressure, low energy consumption, high flux and relatively low investment and maintenance costs.

[0011] Preferably, the pore size of the membrane is 0.1-2.0 nm.

[0012] Preferably, the membrane filtration device is arranged in series in one or two stages.

[0013] Preferably, when the membrane filtration device adopts a two-stage series arrangement, the water outlet of the water production collection tank is connected to the water inlet of the first membrane filtration device; the concentrate water outlet of the first membrane filtration device is connected to the water inlet of the second membrane filtration device; the concentrate water outlet of the second membrane filtration device is connected to the water inlet of the electrolysis device; and a reflux channel is provided between the concentrate water outlet of the second membrane filtration device and the water inlet of the second membrane filtration device.

[0014] Preferably, the electrolysis device is provided with an electrolytic cell, the electrolytic cell is provided with positive and negative electrodes, and the positive and negative electrodes of the power supply can interchange directions.

[0015] Preferably, the electrode distance between the positive and negative electrodes is 5 to 30 mm.

[0016] Preferably, the anode and cathode electrodes are graphite electrodes, metal Pt electrodes or titanium-based DSA electrodes.

[0017] Preferably, the electrolysis device is provided with a fresh water outlet.

[0018] Preferably, the aspect ratio of the resin filler of the macroporous adsorption resin column is 2.5 to 5.0: 1. Further preferably, the height of the resin filler is 0.5 to 50 m.

[0019] Preferably, the macroporous resin type includes one or more of a macroporous polymeric adsorption resin, a macroporous weakly acidic cation exchange resin or a macroporous strongly basic type I anion exchange resin.

[0020] Preferably, the height-to-diameter ratio of the resin filler of the chelating resin column is 2.5 to 5.0: 1. Further preferably, the height of the resin filler is 0.5 to 50 m.

[0021] Preferably, the chelating resin type includes weakly acidic cation exchange resin, etc. Further preferably, the chelating resin includes Tulsimer® CH-90Na, SPC-90, etc.

[0022] Preferably, the chelating resin column is provided with an upper water outlet.

[0023] Preferably, a regulating valve is provided on the connecting pipeline of each component.

[0024] The working process of the device of the present invention is as follows: first, the wet oxidation water produced by the caprolactam wastewater stored in the produced water collection tank is adjusted in pH value by a pH value adjusting device, and then introduced from the water inlet of the membrane filtration device for membrane filtration, and then the concentrated water obtained by the membrane filtration is sent from the concentrated water outlet of the membrane filtration device to the water inlet of the electrolysis device, and the fresh water enters the biochemical system through the fresh water outlet of the membrane filtration device or is used for the regeneration of the cathode electrode in the electrolysis device; when the membrane filtration device adopts a two-stage series arrangement, the wet oxidation water produced by the caprolactam wastewater is sent from the first membrane to the water inlet of the electrolysis device. The concentrated water is introduced into the water inlet of the filtration device for membrane filtration, and the concentrated water is sent into the water inlet of the second membrane filtration device for membrane filtration. A part of the concentrated water is refluxed from the concentrated water outlet of the second membrane filtration device to the water inlet of the second membrane filtration device, and the remaining part is sent to the water inlet of the electrolysis device; in the electrolysis device, most of the catalyst metal ions in the concentrated water are reduced and deposited, and the COD substances are oxidized. The electrolytic wastewater is sent to the macroporous adsorption resin column from the lower water inlet of the macroporous resin column for resin adsorption to further remove COD, and then the adsorbed wastewater is discharged from the The lower water inlet of the chelating resin column is sent to the chelating adsorption resin column for deep treatment to further remove the residual catalyst metal ions. The ammonium sulfate in the obtained ammonium sulfate production water is highly concentrated and sent to the ammonium sulfate recovery system for evaporation and crystallization to obtain ammonium sulfate crystal byproduct; when the cathode electrode in the electrolysis device gains weight and needs to be regenerated, the positive and negative poles of the power supply are first swapped, and then the fresh water produced by the membrane filtration device is sent to the electrolysis device for reverse electrolysis treatment. After the original cathode electrode recovers its weight, the regenerated liquid containing catalyst metal ions is returned to the fresh water outlet. Back to the wet oxidation system; when the macroporous resin column needs to be regenerated, first use acidic gas to purge the bottom of the macroporous adsorption resin column, and then inject hot sodium hydroxide aqueous solution from the bottom. After cleaning, the cleaning liquid is returned to the wet oxidation system, and then cleaned from the bottom with clean water until the pH value is neutral, and the cleaning liquid is returned to the wet oxidation system; when the chelating resin column needs to be regenerated, use acid solution or alkaline solution, or both alternately, to rinse and desorb the adsorption saturated chelating resin from the bottom, and then adjust the pH value of the desorption liquid, and the desorption liquid is returned to the wet oxidation system.

[0025] The technical solution adopted by the present invention to further solve the technical problem is as follows: A method for treating water produced by wet oxidation of caprolactam wastewater comprises the following steps: (1) After adjusting the pH value of the wet oxidation water produced by caprolactam wastewater, the water is sent to a membrane filtration device for membrane filtration and concentration to obtain concentrated water and fresh water respectively; (2) sending the concentrated water obtained in step (1) into an electrolysis device for electrolysis treatment, wherein the cathode electrode precipitates the catalyst metal element, and the anode electrode releases oxygen to oxidize and decompose part of the COD to obtain electrolyzed wastewater; (3) feeding the electrolytic wastewater obtained in step (2) into a macroporous adsorption resin column from bottom to top for resin adsorption to remove COD and obtain adsorbed wastewater; (4) The adsorption wastewater obtained in step (3) is sent from bottom to top into a chelating adsorption resin column for deep treatment to remove the catalyst metal ions and obtain ammonium sulfate product water.

[0026] The inventive concept of the present invention is: the wet oxidation water produced by the caprolactam wastewater with a high ammonium sulfate salt content is first separated by a membrane to obtain concentrated water with a high salt content and fresh water with a low salt content. The fresh water can directly enter the biochemical system for further treatment, while there is still a small amount of COD and catalyst metal ions in the concentrated water, which will affect the normal operation of the ammonium sulfate recovery device to recover ammonium sulfate crystals through evaporation and crystallization. Therefore, the concentrated water needs to be electrolyzed by an electrolysis device before entering the recovery system. The cathode obtains electrons, and the catalyst metal ions are reduced and precipitated. The anode loses electrons to electrolyze water to produce oxygen, and part of the COD is oxidized and degraded. The macroporous adsorption resin further adsorbs and removes the COD, and the chelating resin deeply removes the catalyst metal ions.

[0027] Preferably, in step (1), the COD concentration of the wet oxidation water produced by the caprolactam wastewater is 50-2500ppm, the ammonia nitrogen concentration is 5000-15000ppm, the sulfate concentration is 30000-100000ppm, the content of catalyst metal ions is 10-400ppm, and the pH value is 2-8. The COD is chemical oxygen demand. The wet oxidation water produced by the caprolactam wastewater treated by the present invention is obtained by treating the caprolactam wastewater in a catalytic wet oxidation reaction system of a petrochemical plant.

[0028] Preferably, in step (1), the pH value is adjusted to 6.0-7.0. If the pH value is too low, the membrane performance will change, resulting in a reduced removal rate of the catalyst metal ions, and too low a pH value will also cause acid corrosion to the membrane filtration device material. The pH value is adjusted using ammonia water with a mass fraction of 10-30% or concentrated sulfuric acid with a mass fraction of 98%. Using ammonia water to adjust the pH value can make the ammonia nitrogen concentration in the wet oxidation water of caprolactam wastewater not less than 8000ppm, ensuring that the metal ions are complexed by high concentrations of ammonia nitrogen and are not easy to precipitate, thereby avoiding the problem of membrane pollution; adjusting to a suitable pH value avoids the formation of hydroxide precipitation of the catalyst metal ions due to too high a pH value, which causes the membrane to be blocked, and also avoids the formation of free ammonia volatilization of ammonia nitrogen when the pH value is higher than 7, thereby reducing the ammonia nitrogen removal rate of the membrane.

[0029] Preferably, in step (1), in the second stage of the single-stage or two-stage series membrane filtration device, the concentrated water pressure of the membrane filtration is 3.0-7.0 MPa, and in the first stage of the two-stage series membrane filtration device, the concentrated water pressure of the membrane filtration is 1.5-2.5 MPa. The purpose of membrane filtration is to achieve the concentration of ammonium sulfate, so that the conductivity is greatly improved. Under the pressure, fresh water can quickly pass through the membrane, while ammonium sulfate and catalyst ions are retained in the membrane concentrated water, so that the catalyst ions and ammonia nitrogen in the fresh water are removed, and the biodegradability is greatly improved.

[0030] Preferably, in step (1), the flow rate in a single membrane filtration device is 2 to 8 m 3 / h. The appropriate flow rate makes the membrane surface flow rate of the membrane module more balanced, avoiding membrane pollution caused by too low membrane surface flow rate and membrane damage caused by too high membrane surface flow rate.

[0031] Preferably, in step (1), when a two-stage series membrane filtration device is used, 20-50% of the concentrate produced by the second membrane filtration device is refluxed to the second membrane filtration device. The use of a two-stage series membrane filtration device is conducive to reducing the amount of concentrate produced and making the flow rate on the membrane surface more balanced. The concentrate reflux can ensure that the flow rate of the membrane assembly in the membrane filtration device is between 2 and 8 m / s. 3 / h range to avoid membrane pollution caused by too low membrane surface flow rate.

[0032] Preferably, in step (1), the total yield of the fresh water is 50-90%. The yield of the fresh water is determined according to the concentration of ammonium sulfate in the raw water and the required ammonia nitrogen concentration in the fresh water. The higher the concentration of ammonium sulfate in the raw water or the lower the required ammonia nitrogen concentration in the fresh water, the lower the fresh water yield. The total yield of the concentrated water fed to the electrolysis device is 10-50%, and the concentrated water output is greatly concentrated, reducing the processing load of the subsequent electrolysis device, macroporous adsorption resin column and chelating resin column.

[0033] After the membrane filtration treatment in step (1), the COD concentration in the fresh water remains unchanged or increases, and ammonia nitrogen, sulfate and catalyst metal ions are efficiently removed, with ammonia nitrogen concentration of <1000ppm, sulfate concentration of <3500ppm, catalyst metal ion content of ≤1.0ppm, and pH value of 5.8-7.2; the COD concentration in the concentrated water remains unchanged or decreases, with ammonia nitrogen concentration of 20000-40000ppm, sulfate concentration of 60000-140000ppm, catalyst metal ion content of 20-4000ppm, and pH value of 5.8-7.2. The catalyst ions and ammonia nitrogen in the membrane filtered fresh water are removed, and the biodegradability is greatly improved. The ammonium sulfate in the membrane filtered concentrated water is concentrated, and the ammonium sulfate concentration is ≥80000ppm, so that the wastewater entering the electrolysis device has a high salt content and greatly improves the conductivity, ensuring a high current density in the electrolysis device, thereby improving the efficiency of the electrolysis device.

[0034] Preferably, in step (2), the voltage of the electrolysis treatment is 3 to 6 V, and the current density is 300 to 500 A / m 2 The concentrated water load treated per unit area of ​​the anode electrode is 0.05 to 0.15 m 3 / h / m 2 , the time is 2 to 5 hours. During the electrolysis process, the catalyst ions undergo a reduction reaction in the cathode area and are deposited, thereby achieving effective capture of the catalyst ions. The catalyst metal ion content of the electrolytic wastewater is below 300 ppm, which can greatly reduce the load of the chelating resin column adsorbing the catalyst metal ions; at the same time, COD undergoes oxidative decomposition in the anode area, effectively reducing its concentration to below 500 ppm, which can greatly reduce the load of the macroporous adsorption resin column adsorbing COD. The current density (A / m 2 ) = current (A) / area of ​​anode electrode (m 2 ); The concentrated water load treated per unit area of ​​the anode electrode (m 3 / h / m 2 ) = concentrated water volume (m 3 ) / electrolysis treatment time (h) / anode electrode area (m 2 ).

[0035] Preferably, in step (2), when the cathode electrode weight gain is ≥ 0.5 kg / m 2 When the cathode electrode is regenerated, the positive and negative poles of the power supply are first interchanged, and then the fresh water produced by the membrane filtration device is sent to the electrolysis device for reverse electrolysis treatment. After the weight of the original cathode electrode is restored, the regenerated liquid containing the catalyst metal ions is returned to the front of the wet oxidation system through the fresh water outlet. The conditions of the reverse electrolysis treatment are the same as those of the electrolysis treatment. By converting the original power cathode into the power anode, the catalyst metal element originally deposited on the cathode will be redissolved in the water due to oxidation and converted into the form of catalyst metal ions. The solution containing the catalyst metal ions can be circulated for catalytic wet oxidation process.

[0036] After the electrolytic treatment in step (2), the COD concentration in the electrolytic wastewater is ≤500ppm, the concentrations of ammonia nitrogen and sulfate ion do not change significantly, the content of catalyst metal ions is 5 to 300ppm, and the pH value is 6 to 7. The COD concentration of the electrolytic wastewater is below 500ppm, which can greatly reduce the load of COD adsorbed by the macroporous adsorption resin column, and the content of catalyst metal ions is below 300ppm, which can greatly reduce the load of catalyst metal ions adsorbed by the chelating resin column.

[0037] Preferably, in step (3), the flow rate of the electrolytic wastewater into the macroporous adsorption resin column is 2 to 4 BV / H. The macroporous adsorption resin is mainly used to remove COD in the electrolytic wastewater. The flow rate (BV / H) = electrolytic wastewater flow rate (m 3 / h) / resin filler volume (m 3 ).

[0038] After the resin adsorption treatment in step (3), the COD concentration in the adsorbed wastewater is ≤50ppm, which meets the requirements for entering the ammonium sulfate recovery device, and the concentrations of ammonia nitrogen and sulfate ion do not change significantly. The catalyst metal ion content is 5 to 300ppm, and the pH value is 6 to 7. The COD concentration in the adsorbed wastewater is ≤50ppm, which ensures that COD will not cause pollution to the chelating resin.

[0039] Preferably, in step (3), when the COD removal rate is ≤50%, the resin is cleaned and regenerated.

[0040] Preferably, in step (3), the cleaning and regeneration refers to: first, the bottom of the macroporous adsorption resin column is purged with acidic gas at a flow rate of 100-130 BV / H for 0.5-2.0 h, and then a sodium hydroxide aqueous solution at 60-80°C and a mass fraction of 10-25% is injected from the bottom at a flow rate of 2-4 BV / H. After cleaning for 1-2 h, the cleaning liquid is returned to the wet oxidation system, and then cleaned with clean water from the bottom at a flow rate of 2-4 BV / H until the pH value is neutral, and the cleaning liquid is returned to the wet oxidation system. As the amount of treated water increases, the resin adsorbent gradually approaches a saturated state, and a regeneration step must be implemented to restore its efficiency. The gas used for backwashing is preferably carbon dioxide and excess unused oxygen generated in the CWAO system, and backwashing can loosen attached pollutants. The sodium hydroxide aqueous solution can be preheated to 60-80°C in the heat exchanger (about 275°C) of the CWAO device. The regeneration liquid containing high concentration of COD and sodium hydroxide produced by regeneration is returned to the front-end process, mixed with the original wastewater and sent to the CWAO device for treatment.

[0041] Preferably, in step (4), the flow rate of the adsorption wastewater into the chelating adsorption resin column is 2 to 4 BV / H. The main function of the chelating resin for deep treatment is to recover the catalyst ions. There is still a small amount of catalyst ions remaining in the water produced by the macroporous adsorption resin, so it is necessary to use the chelating adsorption resin for deep purification. The flow rate (BV / H) = adsorption wastewater flow rate (m 3 / h) / resin filler volume (m 3 ).

[0042] After the deep treatment with the chelating resin in step (4), the COD concentration in the adsorbed wastewater is less than 50 ppm, the concentrations of ammonia nitrogen and sulfate ion have no significant changes, the catalyst metal ion content is less than 1.0 ppm, and the pH value is 6-7, so the wastewater can be sent to the ammonium sulfate recovery device.

[0043] Preferably, in step (4), when the removal rate of the catalyst metal ions is ≤90%, the resin is cleaned and regenerated.

[0044] Preferably, in step (4), the cleaning regeneration refers to: using an acid solution with a mass concentration of 5 to 10% or an alkaline solution with a mass concentration of 5 to 10%, or both of them alternately, at a flow rate of 2 to 4 BV / H, to rinse and desorb the saturated chelating resin from the bottom for 1 to 2 hours, and then adjusting the pH value of the desorption liquid to 1 to 6, and the desorption liquid is returned to the wet oxidation system. With the continuous increase in the amount of treated water, the chelating resin has also reached its adsorption capacity limit, that is, close to saturation. In order to maintain the efficiency of the system, it must be regenerated regularly. The above operation is conducive to promoting the desorption of metal ions. More preferably, the acid solution is sulfuric acid and / or nitric acid, and the alkaline solution is an aqueous sodium hydroxide solution. The pH value is adjusted to avoid precipitation of catalyst metal ions.

[0045] The beneficial effects of the present invention are as follows: (1) The treatment device of the present invention has a simple structure, a large treatment capacity, no additional by-products and three wastes are generated, is green and environmentally friendly, safe and reliable, and solves the applicability problem of the equipment through the combination of multiple process equipment, and brings into play the best performance of each equipment; (2) The method of the present invention has a simple process, low cost, and is suitable for industrial production. The final removal rate of COD in concentrated water is as high as 95.4%, the electrolytic recovery rate of catalyst metal ions ((1-electrolytic wastewater content / concentrated water content)*100%) is as high as 96.8%, the total recovery rate of catalyst metal ions ((1-(fresh water content+ammonium sulfate production water content) / wet oxidation total water production)*100%) is as high as 99.8%, the ammonium sulfate recovery rate (actual output / theoretical output*100%) is as high as 85.0%, the purity is as high as 88.5%, and the fresh water has good biodegradability; the problem of membrane pollution of the membrane filtration device caused by high concentration of metal ions in wastewater and low metal ion removal rate is solved, the water production of membrane filtration concentrated water is reduced by the membrane filtration device, the processing load of subsequent processes is reduced, the efficiency of the electrolysis device is improved, COD and catalyst metal ions are removed or recovered by multi-stage treatment, so that the purity of ammonium sulfate in the obtained ammonium sulfate production water is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of a treatment device for wet oxidation water produced by caprolactam wastewater according to Examples 1 to 3 of the present invention; Figure 2It is a schematic diagram of a treatment device for wet oxidation water production of caprolactam wastewater according to Example 4 of the present invention; The reference numerals are as follows: 1. Produced water collection tank; 1-1. Water outlet of produced water collection tank; 1-2. Water inlet of produced water collection tank; 1-3. pH value adjustment device; 2. Membrane filtration device; 2-1. First membrane filtration device; 2-1-1. Water inlet of first membrane filtration device; 2-1-2. Concentrate water outlet of first membrane filtration device; 2-1-3. Fresh water outlet of first membrane filtration device; 2-2. Second membrane filtration device; 2-2-1. Water inlet of second membrane filtration device; 2-2-2. Concentrate water outlet of second membrane filtration device; 2-2-3. Fresh water outlet of second membrane filtration device; 3. Electrolysis device; 3-1. Water inlet of electrolysis device; 3-2. Water outlet of electrolysis device; 3-3. Electrolysis cell; 3-4. Cathode and cathode electrodes; 3-5. Power supply; 3-6. Fresh water outlet of electrolysis device; 4. Macroporous adsorption resin column; 4-1. Lower water inlet of the macroporous adsorption resin column; 4-2. Upper water outlet of the macroporous adsorption resin column; 5. Chelating adsorption resin column; 5-1. Lower water inlet of the chelating adsorption resin column; 5-2. Upper water outlet of the chelating adsorption resin column; 6. Regulating valve. DETAILED DESCRIPTION

[0047] The present invention will be further described below in conjunction with the embodiments and drawings.

[0048] The wet oxidation water produced by the caprolactam wastewater treated in the embodiments of the present invention and the comparative examples is derived from the caprolactam wastewater sent to a petrochemical plant for treatment in a catalytic wet oxidation reaction system; the raw materials or chemical reagents used in the embodiments of the present invention, unless otherwise specified, are obtained through conventional commercial channels.

[0049] The effluent COD concentration in the examples of the present invention and the comparative examples was detected by potassium dichromate method, and the ammonia nitrogen concentration was detected by Nessler's reagent spectrophotometry.

[0050] Example 1 like Figure 1As shown, a device for treating water produced by wet oxidation of caprolactam wastewater comprises a water production collection tank 1, a membrane filter device 2, an electrolysis device 3, a macroporous adsorption resin column 4 and a chelating adsorption resin column 5; the membrane filter device 2 is arranged in two stages in series, the water outlet 1-1 of the water production collection tank 1 is connected to the water inlet 2-1-1 of the first membrane filter device 2-1; the concentrated water outlet 2-1-2 of the first membrane filter device 2-1 is connected to the water inlet 2-2 of the second membrane filter device 2-2 -1 is connected; the concentrated water outlet 2-2-2 of the second membrane filtration device 2-2 is connected to the water inlet 3-1 of the electrolysis device 3; a reflux channel is provided between the concentrated water outlet 2-2-2 of the second membrane filtration device 2-2 and the water inlet 2-2-1 of the second membrane filtration device 2-2; the water outlet 3-2 of the electrolysis device 3 is connected to the lower water inlet 4-1 of the macroporous resin column 4; the upper water outlet 4-2 of the macroporous resin column 4 is connected to the lower water inlet 5-1 of the chelating resin column 5; The produced water collection tank 1 is provided with a water inlet 1-2 and a pH value adjusting device 1-3; the first membrane filtration device 2-1 and the second membrane filtration device 2-2 are both provided with fresh water outlets 2-1-3 and 2-2-3; the membrane is a nanofiltration membrane with a pore size of 0.7nm; the electrolysis device 3 is provided with an electrolytic cell 3-3, and the electrolytic cell 3-3 is provided with a positive and negative electrodes 3-4, and the positive and negative electrodes of the power supply 3-5 can interchange directions; the electrode spacing of the positive and negative electrodes 3-4 is 10mm, wherein the area of ​​the anode electrode is 5.5m 2 ; The anode and cathode electrodes 3-4 are both metal Pt electrodes; the electrolysis device 3 is provided with a fresh water outlet 3-6; the resin filler aspect ratio of the macroporous adsorption resin column 4 is 3:1, the resin filler height is 3m, and the macroporous resin type is a macroporous polymeric adsorption resin; the resin filler aspect ratio of the chelating resin column 5 is 3:1, the resin filler height is 3m, and the chelating resin type is a weakly acidic cation exchange resin Tulsimer® CH-90Na; the chelating resin column 5 is provided with an upper water outlet 5-2; and a regulating valve 6 is provided on the connecting pipelines of each component.

[0051] The working process of the device of the present invention is as follows: first, the pH value of the wet oxidation product water of the caprolactam wastewater stored in the product water collection tank 1 is adjusted by the pH value adjusting device 1-3, and then introduced from the water inlet 2-1-1 of the first membrane filtration device 2-1 for membrane filtration, and the obtained concentrated water is sent from the water inlet 2-2-1 of the second membrane filtration device 2-2 for membrane filtration, and a part of the obtained concentrated water is refluxed from the concentrated water outlet 2-2-2 of the second membrane filtration device 2-2 to the water inlet 2-2-1 of the second membrane filtration device 2-2, and the remaining part is sent to the electrolysis device 3 The fresh water enters the biochemical system or is used for regeneration of the cathode electrode 3-4 in the electrolysis device 3 through the fresh water outlet 2-1-3 and 2-2-3 of the first membrane filtration device 2-1 and the second membrane filtration device 2-2. In the electrolysis device 3, most of the catalyst metal ions in the concentrated water are reduced and deposited, while the COD substances are oxidized. The resulting electrolytic wastewater is sent from the lower water inlet 4-1 of the macroporous resin column 4 to the macroporous adsorption resin column 4 for resin adsorption to further remove COD. The adsorbed wastewater is then sent from the lower water inlet 5-1 of the chelating resin column 5 to the biochemical system or the cathode electrode 3-4 in the electrolysis device 3. The fresh water produced by the membrane filtration device 2 is sent to the electrolysis device 3 for reverse electrolysis treatment until the weight of the original cathode electrode 3-4 is restored, and the regeneration liquid containing the catalyst metal ions is discharged through the fresh water outlet 3-6. Return to the wet oxidation system; when the macroporous resin column 4 needs to be regenerated, the bottom of the macroporous adsorption resin column 4 is first purged with acidic gas, and then hot sodium hydroxide aqueous solution is injected from the bottom. After cleaning, the cleaning liquid is returned to the wet oxidation system, and then cleaned from the bottom with clean water until the pH value is neutral, and the cleaning liquid is returned to the wet oxidation system; when the chelating resin column 5 needs to be regenerated, the saturated chelating resin 5 is rinsed and desorbed from the bottom with acid solution or alkaline solution, or both are used alternately, and the pH value of the desorption liquid is adjusted, and the desorption liquid is returned to the wet oxidation system.

[0052] A method for treating water produced by wet oxidation of caprolactam wastewater comprises the following steps: (1) 5m 3 The wet oxidation water produced by caprolactam wastewater (COD concentration is 854ppm, ammonia nitrogen concentration is 10200ppm, sulfate concentration is 34285ppm, catalyst metal ion content is 223.4ppm, pH value is 5.7) is adjusted to pH 6.5 with ammonia water (mass fraction is 20%), and then sent to the two-stage series membrane filtration device. In the first membrane filtration device, the concentrated water pressure is 2.0MPa and the flow rate is 5m 3 / h (Fresh water discharge 2m 3 / h, concentrated water output 3m 3 / h), the concentrated water pressure of the second membrane filtration device is 5.0MPa and the flow rate is 3.8m 3 / h, membrane filtration and concentration are carried out, and 1.2m 3 / h, concentrated water output 2.6m 3 / h, 30.8% of the concentrated water produced by the second membrane filtration device is returned to the second membrane filtration device, and 3.2m 3 Fresh water and 1.8m 3 Concentrated water, the total yield of fresh water is 64%; (2) The 1.8 m 3 The concentrated water is sent to the electrolysis device and electrolyzed for 3 hours at a voltage of 5V and a current of 2200A. The cathode electrode precipitates the catalyst metal element, and the anode electrode releases oxygen to oxidize and decompose part of the COD to obtain electrolytic wastewater. (3) The electrolytic wastewater obtained in step (2) was passed through a flow rate of 8 m 3 / h is sent from bottom to top into a macroporous adsorption resin column (resin filler height-to-diameter ratio 3:1, resin filler height 3m) for resin adsorption to remove COD and obtain adsorbed wastewater; (4) The adsorption wastewater obtained in step (3) was transferred to the adsorption zone at a flow rate of 8 m 3 / h is sent from bottom to top into a chelating adsorption resin column (resin filler height-to-diameter ratio 3:1, resin filler height 3m) for deep treatment to remove catalyst metal ions and obtain ammonium sulfate product water.

[0053] After testing, after the membrane filtration treatment in step (1), the COD concentration in the fresh water was 986 ppm, which was slightly increased but could enter the biochemical system for further degradation. The ammonia nitrogen concentration was 542 ppm, the sulfate concentration was 1925 ppm, and the catalyst metal ion content was 0.45 ppm. In the concentrated water, the COD concentration was 603.1 ppm, the ammonia nitrogen concentration was 27700 ppm, and the sulfate concentration was 92231 ppm. It was inferred that the main component of the concentrated water was ammonium sulfate, and the catalyst metal ion content was 613.4 ppm. The pH value of the fresh water was 7.2, and the pH value of the concentrated water was 6.0, indicating that no obvious change in pH was caused during the treatment process.

[0054] According to the test, after the electrolytic treatment in step (2), the COD concentration in the electrolytic wastewater was 108 ppm, the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 21.26 ppm, the electrolytic recovery rate of the catalyst metal ion was 96.5%, and the pH value was 6.2.

[0055] After testing, after the resin adsorption treatment in step (3), the COD concentration in the adsorbed wastewater was 35.8 ppm, the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 20.32 ppm, and the pH value was 6.5.

[0056] After testing, after the deep treatment with chelating resin in step (4), 30.6 ppm of COD in the adsorbed wastewater was found (the final removal rate of COD in the concentrated water was 94.9%), the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 0.35 ppm, and the pH value was 6.4, which could be sent to the ammonium sulfate recovery device. The final ammonium sulfate recovery rate was 85.0%, and the ammonium sulfate purity was 80.3%.

[0057] In step (2), when the cathode electrode weight increases by ≥ 0.5 kg / m 2 When the cathode electrode is regenerated, the positive and negative poles of the power supply are first interchanged, and the fresh water produced by the membrane filtration device is sent to the electrolysis device for reverse electrolysis treatment. The conditions of the reverse electrolysis treatment are the same as those of the electrolysis treatment. After the original cathode electrode recovers its weight, the regenerated liquid containing the catalyst metal ions is returned to the wet oxidation system through the fresh water outlet.

[0058] In step (3), when the COD removal rate is ≤50%, the resin is cleaned and regenerated. First, the bottom of the macroporous adsorption resin column is purged with acidic gas (carbon dioxide produced in the CWAO system and excess unused oxygen) at 300m 3 / h flow rate for purging (the purged tail gas is sent to the gas treatment unit for further treatment) for 1.0h, and then the 85℃, 20% mass fraction sodium hydroxide aqueous solution preheated in the heat exchanger of the CWAO device is injected from the bottom at 8m 3 After cleaning for 1.0h at a flow rate of 8m / h, the cleaning liquid is returned to the wet oxidation system and then cleaned with water from the bottom at a flow rate of 8m / h. 3 / h cleaning until the pH value is neutral, and the cleaning liquid is returned to the wet oxidation system. The regeneration liquid containing high concentrations of COD and sodium hydroxide is returned to the front-end process and mixed with the original wastewater and sent to the CWAO device for treatment.

[0059] In step (4), when the removal rate of catalyst metal ions is ≤90%, the resin is cleaned and regenerated, and 20m 3 8% mass concentration of dilute sulfuric acid solution and 20m 3 A sodium hydroxide aqueous solution with a mass concentration of 8% is poured at a flow rate of 8m 3 / h, flush and desorb the saturated chelating resin from the bottom for 2.0h, then adjust the pH value of the desorption liquid to 6.0, and return the desorption liquid to the wet oxidation system.

[0060] In steps (1) to (4), the total recovery rate of catalyst metal ions was 99.8%.

[0061] Example 2 A device for treating water produced by wet oxidation of caprolactam wastewater, same as that in Example 1.

[0062] A method for treating water produced by wet oxidation of caprolactam wastewater comprises the following steps: (1) 5m 3 The wet oxidation water produced by caprolactam wastewater (COD concentration is 765ppm, ammonia nitrogen concentration is 9530ppm, sulfate concentration is 33680ppm, catalyst metal ion content is 208.3ppm, pH value is 5.6) is adjusted to pH 6.4 with ammonia water (mass fraction is 20%), and then sent to the two-stage series membrane filtration device. The concentrated water pressure in the first membrane filtration device is 1.7MPa and the flow rate is 5m 3 / h (Fresh water discharge 2m 3 / h, concentrated water output 3m 3 / h), the concentrated water pressure of the second membrane filtration device is 4.5MPa and the flow rate is 4.0m 3 / h, membrane filtration and concentration are carried out, and fresh water is discharged at 1.5m 3 / h, concentrated water output 2.5m 3 / h, 40% of the concentrated water produced by the second membrane filtration device is returned to the second membrane filtration device, and 3.5m 3 Fresh water and 1.5m 3 Concentrated water, the total yield of fresh water is 70%; (2) The 1.5 m 3 The concentrated water is sent to the electrolysis device and electrolyzed for 4 hours at a voltage of 4V and a current of 1800A. The cathode electrode precipitates the catalyst metal element, and the anode electrode releases oxygen to oxidize and decompose part of the COD to obtain electrolytic wastewater. (3) The electrolytic wastewater obtained in step (2) was passed through a flow rate of 7 m 3 / h is sent from bottom to top into a macroporous adsorption resin column (resin filler height-to-diameter ratio 3:1, resin filler height 3m) for resin adsorption to remove COD and obtain adsorbed wastewater; (4) The adsorption wastewater obtained in step (3) was transferred to a 3 / h is sent from bottom to top into a chelating adsorption resin column (resin filler height-to-diameter ratio 3:1, resin filler height 3m) for deep treatment to remove catalyst metal ions and obtain ammonium sulfate product water.

[0063] After testing, after the membrane filtration treatment in step (1), the COD concentration in the fresh water was 872 ppm, which was slightly increased but could enter the biochemical system for further degradation. The ammonia nitrogen concentration was 463 ppm, the sulfate concentration was 1637 ppm, and the catalyst metal ion content was 0.9 ppm. In the concentrated water, the COD concentration was 518.6 ppm, the ammonia nitrogen concentration was 31020 ppm, and the sulfate concentration was 107564 ppm. It was inferred that the main component of the concentrated water was ammonium sulfate, and the catalyst metal ion content was 682.35 ppm. The pH value of the fresh water was 6.9, and the pH value of the concentrated water was 6.2, indicating that no obvious change in pH was caused during the treatment process.

[0064] After testing, after the electrolytic treatment in step (2), the COD concentration in the electrolytic wastewater was 132 ppm, the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 26.04 ppm, the electrolytic recovery rate of the catalyst metal ion was 96.2%, and the pH was 6.0.

[0065] After testing, after the resin adsorption treatment in step (3), the COD concentration in the adsorbed wastewater was 40.2 ppm, the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 23.18 ppm, and the pH was 6.6.

[0066] After testing, after the deep treatment with chelating resin in step (4), the COD concentration in the adsorbed wastewater was 35.6 ppm (the final removal rate of COD in the concentrated water was 93.1%), the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 0.78 ppm, and the pH value was 6.4, which could be sent to the ammonium sulfate recovery device. The final ammonium sulfate recovery rate was 80.0%, and the ammonium sulfate purity was 78.2%.

[0067] In step (2), when the cathode electrode weight increases by ≥ 0.5 kg / m 2 When the cathode electrode is regenerated, the positive and negative poles of the power supply are first interchanged, and the fresh water produced by the membrane filtration device is sent to the electrolysis device for reverse electrolysis treatment. The conditions of the reverse electrolysis treatment are the same as those of the electrolysis treatment. After the original cathode electrode recovers its weight, the regenerated liquid containing the catalyst metal ions is returned to the wet oxidation system through the fresh water outlet.

[0068] In step (3), when the COD removal rate is ≤50%, the resin is cleaned and regenerated, and the specific method is the same as that in Example 1.

[0069] In step (4), when the removal rate of the catalyst metal ions is ≤90%, the resin is cleaned and regenerated, and the specific method is the same as that in Example 1.

[0070] In steps (1) to (4), the total recovery rate of catalyst metal ions was 99.6%.

[0071] Example 3 A device for treating water produced by wet oxidation of caprolactam wastewater, same as that in Example 1.

[0072] A method for treating water produced by wet oxidation of caprolactam wastewater comprises the following steps: (1) 5m 3 The wet oxidation water produced by caprolactam wastewater (COD concentration is 955ppm, ammonia nitrogen concentration is 9032ppm, sulfate concentration is 31260ppm, catalyst metal ion content is 198.3ppm, pH value is 5.8) is adjusted to pH 7.0 with ammonia water (mass fraction is 20%), and then sent to the two-stage series membrane filtration device. The concentrated water pressure in the first membrane filtration device is 1.7MPa and the flow rate is 5m 3 / h (Fresh water discharge 2m 3 / h, concentrated water output 3m 3 / h), the concentrated water pressure of the second membrane filtration device is 4.5MPa and the flow rate is 4.0m 3 / h, membrane filtration and concentration are carried out, and fresh water is discharged at 1.5m 3 / h, concentrated water output 2.5m 3 / h, 40% of the concentrated water produced by the second membrane filtration device is returned to the second membrane filtration device, and 3.5m 3 Fresh water and 1.5m 3 Concentrated water, the total yield of fresh water is 70%; (2) The 1.5 m 3 The concentrated water is sent to the electrolysis device and electrolyzed for 2 hours at a voltage of 6V and a current of 2600A. The cathode electrode precipitates the catalyst metal element, and the anode electrode releases oxygen to oxidize and decompose part of the COD to obtain electrolytic wastewater. (3) The electrolytic wastewater obtained in step (2) was discharged at a flow rate of 9 m 3 / h is sent from bottom to top into a macroporous adsorption resin column (resin filler height-to-diameter ratio 3:1, resin filler height 3m) for resin adsorption to remove COD and obtain adsorbed wastewater; (4) The adsorption wastewater obtained in step (3) was transferred to a 3 / h is sent from bottom to top into a chelating adsorption resin column (resin filler height-to-diameter ratio 3:1, resin filler height 3m) for deep treatment to remove catalyst metal ions and obtain ammonium sulfate product water.

[0073] After testing, after the membrane filtration treatment in step (1), the COD concentration in the fresh water was 1040 ppm, which was slightly increased but could enter the biochemical system for further degradation. The ammonia nitrogen concentration was 386 ppm, the sulfate concentration was 1568 ppm, and the catalyst metal ion content was 0.56 ppm. In the concentrated water, the COD concentration was 742.6 ppm, the ammonia nitrogen concentration was 28400 ppm, and the sulfate concentration was 102013 ppm. It was inferred that the main component of the concentrated water was ammonium sulfate, and the catalyst metal ion content was 631.12 ppm. The pH value of the fresh water was 6.8, and the pH value of the concentrated water was 5.9, indicating that no obvious change in pH was caused during the treatment process.

[0074] After testing, after the electrolytic treatment in step (2), the COD concentration in the electrolytic wastewater was 220 ppm, the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 20.23 ppm, the electrolytic recovery rate of the catalyst metal ion was 96.8%, and the pH was 6.5.

[0075] After testing, after the resin adsorption treatment in step (3), the COD concentration in the adsorbed wastewater was 39.5 ppm, the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 19.33 ppm, and the pH was 6.3.

[0076] After testing, after the deep treatment with chelating resin in step (4), the COD concentration in the adsorbed wastewater was 34.3 ppm (the final removal rate of COD in the concentrated water was 95.4%), the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 0.82 ppm, and the pH value was 6.4, which could be sent to the ammonium sulfate recovery device. The final ammonium sulfate recovery rate was 81.2%, and the ammonium sulfate purity was 88.5%.

[0077] In step (2), when the cathode electrode weight increases by ≥ 0.5 kg / m 2 When the cathode electrode is regenerated, the positive and negative poles of the power supply are first interchanged, and the fresh water produced by the membrane filtration device is sent to the electrolysis device for reverse electrolysis treatment. The conditions of the reverse electrolysis treatment are the same as those of the electrolysis treatment. After the original cathode electrode recovers its weight, the regenerated liquid containing the catalyst metal ions is returned to the wet oxidation system through the fresh water outlet.

[0078] In step (3), when the COD removal rate is ≤50%, the resin is cleaned and regenerated, and the specific method is the same as that in Example 1.

[0079] In step (4), when the removal rate of the catalyst metal ions is ≤90%, the resin is cleaned and regenerated, and the specific method is the same as that in Example 1.

[0080] In steps (1) to (4), the total recovery rate of catalyst metal ions was 99.7%.

[0081] Example 4 like Figure 2 As shown, the device for treating water produced by wet oxidation of caprolactam wastewater in the embodiment of the present invention is different from that in the first embodiment only in that: the membrane filter device 2 is arranged in one section, i.e., the first membrane filter device 2-1, the water outlet 1-1 of the produced water collection tank 1 is connected to the water inlet 2-1-1 of the first membrane filter device 2-1; the concentrated water outlet 2-1-2 of the first membrane filter device 2-1 is connected to the water inlet 3-1 of the electrolysis device 3. The rest is the same as in the first embodiment.

[0082] The working process of the device of the embodiment of the present invention is different from that of the embodiment 1 only in that: the pH value of the wet oxidation produced water of the caprolactam wastewater stored in the produced water collection tank 1 is first adjusted by the pH value adjusting device 1-3, and then introduced from the water inlet 2-1-1 of the first membrane filtration device 2-1 for membrane filtration, and the obtained concentrated water is sent to the water inlet 3-1 of the electrolysis device 3 from the concentrated water outlet 2-1-2 of the first membrane filtration device 2-1, and the fresh water enters the biochemical system through the fresh water outlet 2-1-3 of the first membrane filtration device 2-1 or is used for regeneration of the cathode electrode 3-4 in the electrolysis device 3. The rest is the same as the embodiment 1.

[0083] The difference between the method for treating the wet oxidation water produced by caprolactam wastewater in the embodiment of the present invention and that in embodiment 1 is that: in step (1), 5 m 3 The wet oxidation water of caprolactam wastewater (COD concentration of 854ppm, ammonia nitrogen concentration of 10200ppm, sulfate concentration of 34285ppm, catalyst metal ion content of 223.4ppm, pH value of 5.7) was adjusted to pH 6.5 with ammonia water (mass fraction of 20%) and then sent to the first membrane filtration device. The concentrated water pressure in the first membrane filtration device was 5.0MPa and the flow rate was 5.0m 3 / h, membrane filtration and concentration were performed to obtain 3.2m 3 Fresh water and 1.8m 3 The total yield of concentrated water and fresh water is 64%.

[0084] After testing, after the membrane filtration treatment in step (1), the COD concentration in the fresh water was 1042.6 ppm, which was slightly increased but could enter the biochemical system for further degradation. The ammonia nitrogen concentration was 612.8 ppm, the sulfate concentration was 2746.3 ppm, and the catalyst metal ion content was 0.55 ppm. In the concentrated water, the COD concentration was 522.3 ppm, the ammonia nitrogen concentration was 26233 ppm, and the sulfate concentration was 90542 ppm. It was inferred that the main component of the concentrated water was ammonium sulfate, and the catalyst metal ion content was 605.4 ppm. The pH value of the fresh water was 7.0, and the pH value of the concentrated water was 6.3, indicating that no obvious change in pH was caused during the treatment process.

[0085] After testing, after the electrolytic treatment in step (2), the COD concentration in the electrolytic wastewater was 112 ppm, the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 20.30 ppm, the electrolytic recovery rate of the catalyst metal ion was 96.6%, and the pH value was 6.2.

[0086] After testing, after the resin adsorption treatment in step (3), the COD concentration in the adsorbed wastewater was 31.3 ppm, the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 19.22 ppm, and the pH value was 6.6.

[0087] After testing, after the deep treatment with chelating resin in step (4), the COD in the adsorbed wastewater was 29.8ppm (the final removal rate of COD in the concentrated water was 94.3%), the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 0.48ppm, the pH value was 6.5, and it could be sent to the ammonium sulfate recovery device. The final ammonium sulfate recovery rate was 83.0%, and the ammonium sulfate purity was 81.6%.

[0088] In step (2), when the cathode electrode weight increases by ≥ 0.5 kg / m 2 When the cathode electrode is regenerated, the positive and negative poles of the power supply are first interchanged, and the fresh water produced by the membrane filtration device is sent to the electrolysis device for reverse electrolysis treatment. The conditions of the reverse electrolysis treatment are the same as those of the electrolysis treatment. After the original cathode electrode recovers its weight, the regenerated liquid containing the catalyst metal ions is returned to the wet oxidation system through the fresh water outlet.

[0089] In step (3), when the COD removal rate is ≤50%, the resin is cleaned and regenerated, and the specific method is the same as that in Example 1.

[0090] In step (4), when the removal rate of the catalyst metal ions is ≤90%, the resin is cleaned and regenerated, and the specific method is the same as that in Example 1.

[0091] In steps (1) to (4), the total recovery rate of catalyst metal ions was 99.8%.

[0092] Comparative Example 1 (1) Same as step (1) in Example 3 of the present invention; (2) The concentrated water obtained in step (1) was flowed at a rate of 9 m 3 / h is circulated from bottom to top and sent into a macroporous adsorption resin column (resin filler height-to-diameter ratio 3:1, resin filler height 3m) for resin adsorption to obtain adsorbed wastewater; (3) The adsorption wastewater obtained in step (2) was transferred to a 3 / h is circulated from bottom to top and sent into the chelating adsorption resin column (resin filler height-to-diameter ratio 3:1, resin filler height 3m) for deep treatment to obtain chelated wastewater; (4) The 1.5m 3 The chelated wastewater is sent to the electrolysis device and electrolyzed for 2 hours at a voltage of 6V and a current of 2600A to obtain ammonium sulfate water.

[0093] After testing, after the membrane filtration treatment in step (1), the COD concentration in the fresh water was 1040 ppm, which was slightly increased but could enter the biochemical system for further degradation. The ammonia nitrogen concentration was 386 ppm, the sulfate concentration was 1568 ppm, and the catalyst metal ion content was 0.56 ppm. In the concentrated water, the COD concentration was 742.6 ppm, the ammonia nitrogen concentration was 28400 ppm, and the sulfate concentration was 102013 ppm. It was inferred that the main component of the concentrated water was ammonium sulfate, and the catalyst metal ion content was 631.12 ppm. The pH value of the fresh water was 6.8, and the pH value of the concentrated water was 5.9, indicating that no obvious change in pH was caused during the treatment process.

[0094] After testing, after the resin adsorption treatment in step (2), the COD concentration in the adsorbed wastewater was 152 ppm, the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 581.22 ppm, and the pH was 6.5.

[0095] After testing, after the deep treatment with the chelating resin in step (3), the COD concentration in the adsorbed wastewater was 128 ppm, the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 25.81 ppm, and the pH value was 6.1.

[0096] After testing, after the electrolysis treatment in step (4), the COD concentration in the electrolytic wastewater was 102ppm, the concentrations of ammonia nitrogen and sulfate ion did not change significantly, the catalyst metal ion content was 15.43ppm, the electrolysis recovery rate of the catalyst metal ion was only 40.2%, and the pH was 6.5. Due to the high COD and catalyst ion content, it could not be sent to the ammonium sulfate recovery device. The final ammonium sulfate recovery rate was 79.2%, and the ammonium sulfate purity was 85.9%.

[0097] In steps (1) to (4), the total recovery rate of catalyst metal ions was 97.5%.

[0098] It can be seen from the comparative examples of the present invention that if the electrolytic treatment and the resin adsorption are exchanged, the final COD concentration of the produced water is above 100 ppm, and the metal ion concentration is still relatively high. This is because after the resin adsorption, the COD and metal ion concentrations are reduced to a certain extent, resulting in a slower electrolytic reaction, and the electrolytic treatment is more sensitive to higher concentrations of COD or metal ions. In addition, since the resin adsorption treatment is first performed when the COD and metal ion concentrations are high, it is easy to cause the resin to be deactivated faster, resulting in a higher cleaning frequency, increased consumption of cleaning alkali solution, and not conducive to the recycling of metal ions. However, the method of the present invention performs electrolysis first, which will greatly reduce the frequency of resin cleaning, and the regeneration of the electrode only requires a reverse operation, which will not increase additional costs.

Claims

1. A device for treating water produced by wet oxidation of caprolactam wastewater, characterized in that: It includes a produced water collection tank, a membrane filtration device, an electrolysis device, a macroporous adsorption resin column and a chelating adsorption resin column; the water outlet of the produced water collection tank is connected to the water inlet of the membrane filtration device; the concentrated water outlet of the membrane filtration device is connected to the water inlet of the electrolysis device; the water outlet of the electrolysis device is connected to the lower water inlet of the macroporous resin column; the upper water outlet of the macroporous resin column is connected to the lower water inlet of the chelating resin column.

2. The device for treating water produced by wet oxidation of caprolactam wastewater according to claim 1, characterized in that: The produced water collection tank is provided with a water inlet and a pH value adjusting device; the membrane filtration device is provided with a fresh water outlet; the membrane is a nanofiltration membrane or a reverse osmosis membrane; the pore size of the membrane is 0.1-2.0 nm.

3. The device for treating water produced by wet oxidation of caprolactam wastewater according to claim 1 or 2, characterized in that: The membrane filtration device is arranged in series in one or two stages; when the membrane filtration device is arranged in series in two stages, the outlet of the produced water collection tank is connected to the water inlet of the first membrane filtration device; the concentrate water outlet of the first membrane filtration device is connected to the water inlet of the second membrane filtration device; the concentrate water outlet of the second membrane filtration device is connected to the water inlet of the electrolysis device; a reflux channel is provided between the concentrate water outlet of the second membrane filtration device and the water inlet of the second membrane filtration device.

4. The device for treating water produced by wet oxidation of caprolactam wastewater according to any one of claims 1 to 3, characterized in that: The electrolysis device is provided with an electrolytic cell, in which positive and negative electrodes are provided, and the positive and negative electrodes of the power supply can interchange directions; the electrode spacing between the positive and negative electrodes is 5 to 30 mm; the positive and negative electrodes are graphite electrodes, metal Pt electrodes or titanium-based DSA electrodes; and the electrolysis device is provided with a fresh water outlet.

5. The device for treating water produced by wet oxidation of caprolactam wastewater according to any one of claims 1 to 4, characterized in that: The height-to-diameter ratio of the resin filler of the macroporous adsorption resin column is 2.5-5.0:1; the macroporous resin type includes one or more of macroporous polymeric adsorption resin, macroporous weakly acidic cation exchange resin or macroporous strongly basic type I anion exchange resin; the height-to-diameter ratio of the resin filler of the chelating resin column is 2.5-5.0:1; the chelating resin type includes weakly acidic cation exchange resin; the chelating resin column is provided with an upper water outlet; and a regulating valve is provided on the connecting pipelines of each component.

6. A method for treating water produced by wet oxidation of caprolactam wastewater based on the treatment device according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) After adjusting the pH value of the wet oxidation water produced by caprolactam wastewater, the water is sent to a membrane filtration device for membrane filtration and concentration to obtain concentrated water and fresh water respectively; (2) sending the concentrated water obtained in step (1) into an electrolysis device for electrolysis treatment, wherein the cathode electrode precipitates the catalyst metal element, and the anode electrode releases oxygen to oxidize and decompose part of the COD to obtain electrolyzed wastewater; (3) feeding the electrolytic wastewater obtained in step (2) into a macroporous adsorption resin column from bottom to top for resin adsorption to remove COD and obtain adsorbed wastewater; (4) The adsorption wastewater obtained in step (3) is sent from bottom to top into a chelating adsorption resin column for deep treatment to remove the catalyst metal ions and obtain ammonium sulfate production water.

7. The method for treating water produced by wet oxidation of caprolactam wastewater according to claim 6, characterized in that: In step (1), the COD concentration of the wet oxidation water produced by the caprolactam wastewater is 50-2500ppm, the ammonia nitrogen concentration is 5000-15000ppm, the sulfate concentration is 30000-100000ppm, the catalyst metal ion content is 10-400ppm, and the pH value is 2-8; the pH value is adjusted to 6.0-7.0; in the second stage of the single-stage or two-stage series membrane filtration device, the concentrated water pressure of the membrane filtration is 3.0-7.0MPa, and in the first stage of the two-stage series membrane filtration device, the concentrated water pressure of the membrane filtration is 1.5-2.5MPa; the flow rate in a single membrane filtration device is 2-8m 3 / h; when using two-stage series membrane filtration devices, 20-50% of the concentrated water produced by the second membrane filtration device is refluxed to the second membrane filtration device; the total yield of the fresh water is 50-90%.

8. The method for treating water produced by wet oxidation of caprolactam wastewater according to claim 6 or 7, characterized in that: In step (2), the voltage of the electrolysis treatment is 3-6V, and the current density is 300-500A / m 2 The concentrated water load treated per unit area of ​​the anode electrode is 0.05 to 0.15 m 3 / h / m 2 , time is 2 to 5 hours; when the cathode electrode weight increase is ≥ 0.5kg / m 2 To regenerate the cathode electrode, first swap the positive and negative poles of the power supply, then send the fresh water produced by the membrane filtration device to the electrolysis device for reverse electrolysis. After the original cathode electrode recovers its weight, the regenerated liquid containing catalyst metal ions is returned to the wet oxidation system through the fresh water outlet.

9. The method for treating water produced by wet oxidation of caprolactam wastewater according to any one of claims 6 to 8, characterized in that: In step (3), the flow rate of the electrolytic wastewater into the macroporous adsorption resin column is 2 to 4 BV / H; when the COD removal rate is ≤50%, the resin is cleaned and regenerated; the cleaning and regeneration refers to: first, the bottom of the macroporous adsorption resin column is purged with acidic gas at a flow rate of 100 to 130 BV / H for 0.5 to 2.0 h, and then a sodium hydroxide aqueous solution of 60 to 80°C and a mass fraction of 10 to 25% is injected from the bottom at a flow rate of 2 to 4 BV / H. After cleaning for 1 to 2 h, the cleaning liquid is returned to the wet oxidation system, and then cleaned with clean water from the bottom at a flow rate of 2 to 4 BV / H until the pH value is neutral, and the cleaning liquid is returned to the wet oxidation system.

10. The method for treating water produced by wet oxidation of caprolactam wastewater according to any one of claims 6 to 9, characterized in that: In step (4), the flow rate of the adsorbed wastewater into the chelating adsorption resin column is 2 to 4 BV / H; when the removal rate of the catalyst metal ions is ≤90%, the resin is cleaned and regenerated; the cleaning and regeneration refers to: using an acid solution with a mass concentration of 5 to 10% or an alkaline solution with a mass concentration of 5 to 10%, or alternating between the two, at a flow rate of 2 to 4 BV / H, to wash and desorb the adsorption saturated chelating resin from the bottom for 1 to 2 hours, and then adjusting the pH value of the desorption liquid to 1 to 6, and the desorption liquid is returned to the wet oxidation system.

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