A device and method for treating caprolactam wastewater

Abstract

The application discloses a kind of caprolactam wastewater treatment device and method, the device includes: wet oxidation reactor, membrane filtration device, catalytic wet oxidation reactor, electrodialysis device and biochemical treatment device;Wet oxidation reactor is connected with membrane filtration device, membrane filtration device is connected with catalytic wet oxidation reactor, catalytic wet oxidation reactor is connected with electrodialysis device, and the water outlet of dilute chamber of electrodialysis device is connected with biochemical treatment device.Electrodialysis device can be replaced by membrane deamination device.The application further discloses a kind of caprolactam wastewater treatment method.The device of the application is simple, and processing capacity is large, green environmental protection, safe and reliable, and energy consumption is low.The method of the application is simple, and the removal rate of COD and ammonia nitrogen is high, and the biodegradability is good, without additional byproduct and three wastes, low in cost, suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to a wastewater treatment device and method, in particular to a caprolactam wastewater treatment device and method. BACKGROUND

[0002] Caprolactam, a white flaky solid material, has an oily touch, and the melting point is 69.3℃, which is one of the important raw materials of organic chemical industry, mainly used for the production of nylon-6 fiber and nylon-6 engineering plastics, and can also be used for drug synthesis. In recent years, with the rapid development and expansion of China's chemical industry, the demand for caprolactam in manufacturing, textile and medical device industries has been accelerated. From 2008 to 2018, the production of caprolactam in China increased from 299,700 tons to 2,826,000 tons, of which 31% was used for industrial manufacturing. The increase in raw material demand and the result of the improvement of self-production technology is the increase of caprolactam production capacity, and the amount of caprolactam wastewater is also increasing.

[0003] At present, the mainstream process of caprolactam production is cyclohexanone liquid phase ammonium oxime method. First, cyclohexanone, ammonia and hydrogen peroxide are used to generate cyclohexanone oxime under the action of titanium-silicon molecular sieve. Then, cyclohexanone oxime undergoes Beckmann rearrangement under the action of oleum to generate caprolactam sulfate. Caprolactam sulfate is neutralized with ammonia water to obtain crude caprolactam aqueous solution. Finally, the crude caprolactam aqueous solution is subjected to extraction, back extraction, ion exchange, hydrogenation, evaporation and distillation 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. If untreated high-concentration caprolactam wastewater is discharged into the natural environment, it will cause irreversible damage to the sustainable development of the ecological system, and even threaten human health. Therefore, exploring an economical and efficient method to treat caprolactam wastewater is the current primary goal.

[0004] In the method of treating caprolactam wastewater, biological method is widely used due to its low economic cost and no secondary pollution. However, this method is not only limited by the growth and metabolism of the organism itself, but also has high requirements for the water quality, which is difficult to meet the treatment demand of high-concentration wastewater. Some enterprises use incineration process for treatment, but the operation cost and disposal cost of the salt are very high, and the corrosion of the incinerator is serious due to the high content of ammonium sulfate. Therefore, the high-level oxidation technology with high treatment efficiency is applied. The treatment principle is to use free radicals with strong oxidation to attack macromolecular organic pollutants, so that they are decomposed into small molecular substances such as CO2 and H2O, so as to mineralize the organic matter and reduce the content of organic matter in wastewater.

[0005] Advanced oxidation methods include photocatalytic oxidation, Fenton oxidation and catalytic wet oxidation. Among them, catalytic wet oxidation (CWAO) technology is a representative of wastewater heat treatment technology, which uses oxidants to oxidize organic matter in wastewater into CO2 and water at high temperature and high pressure, so as to achieve the purpose of removing pollutants. However, due to the high COD content in caprolactam wastewater, the heat generated during the CWAO oxidation reaction causes the temperature in the reaction kettle to rise too much, making it difficult to safely control the temperature of the CWAO system, and a large amount of carbon black is produced, which can easily cause the heat exchanger and valve to be blocked, and the ammonia nitrogen in the produced water is very high, so the conventional CWAO process cannot be used for treatment.

[0006] CN115124183A discloses a caprolactam wastewater treatment system and method, which uses struvite crystallization and multi-stage biochemical combined process to treat caprolactam wastewater. However, the treatment process is very long, and the biodegradability of caprolactam wastewater is very poor, so the treatment effect is difficult to meet the standard.

[0007] CN114149140A discloses a caprolactam production wastewater treatment method, which uses anaerobic biochemical and ozone advanced oxidation combined process to treat caprolactam wastewater. However, the operation cost of ozone preparation is very high.

[0008] CN103708646A discloses a caprolactam industrial wastewater treatment method, which uses hydrogen peroxide and catalytic wet oxidation combined process to treat caprolactam wastewater. However, the pH value of the wastewater needs to be adjusted to 2 for reaction, which requires high acid corrosion resistance of the equipment, and consumes a large amount of expensive hydrogen peroxide, resulting in high operation cost.

[0009] In summary, it is urgent to find a simple, large-capacity, high-COD-and-ammonia-nitrogen-removal-rate, good-biodegradability, small-reaction-temperature-increase-and-safety-controllable, green, safe, and low-energy-consumption caprolactam wastewater treatment device and method without additional by-products and three wastes, with low cost and suitable for industrial production. SUMMARY

[0010] The technical problem to be solved by the present application is to overcome the above-mentioned defects in the prior art, and to provide a simple, large-capacity, green, safe, and low-energy-consumption caprolactam wastewater treatment device.

[0011] The further technical problem to be solved by the present application is to overcome the above-mentioned defects in the prior art, and to provide a simple, high-COD-and-ammonia-nitrogen-removal-rate, good-biodegradability, small-reaction-temperature-increase-and-safety-controllable, no additional by-products and three wastes, low-cost, and suitable for industrial production caprolactam wastewater treatment method.

[0012] The technical scheme adopted by the present application to solve its technical problems is as follows: a caprolactam wastewater treatment device, comprising: a wet oxidation reactor, a membrane filtration device, a catalytic wet oxidation reactor, an electrodialysis device and a biochemical treatment device; the water outlet of the wet oxidation reactor is connected with the water inlet of the membrane filtration device, the water outlet of the membrane filtration device is connected with the water inlet of the catalytic wet oxidation reactor, the water outlet of the catalytic wet oxidation reactor is connected with the water inlet of the electrodialysis device, and the water outlet of the dilute chamber of the electrodialysis device is connected with the biochemical treatment device. The wet oxidation reactor pretreats the caprolactam wastewater to remove most of the COD in the wastewater, to achieve the purpose of preliminary degradation of harmful substances in the wastewater, and to produce carbon black substances at the same time; the membrane filtration device filters out the carbon black produced by the wet oxidation reactor; under high temperature and high pressure conditions, oxygen in the air can generate strong oxidizing •OH free radicals on the surface of the catalyst in the catalytic wet oxidation reactor, which can directly oxidize organic pollutants and N, S and other toxic substances into CO2 and H2O, N2, SO4 2- and other harmless substances. In this process, no solid waste is generated, and no secondary pollution waste gas such as dioxin, NO x , SO2 is generated. At the same time, the oxidation reaction heat can be fully utilized in the reaction process, achieving self-heating balance, good energy saving, high removal rate, low operating cost, strong adaptability, simple process, small occupied area and other characteristics; the water produced by the catalytic wet oxidation is further sent to the electrodialysis device to remove ammonia nitrogen in the wastewater; the water outlet of the dilute chamber of the electrodialysis device is sent to the biochemical treatment device, and the water outlet of the concentrated chamber is sent to the ammonium sulfate crystallization device to collect ammonium sulfate crystals or further ammonia neutralization.

[0013] The working process of the device is: first, the caprolactam wastewater is sent to the wet oxidation reactor for pretreatment to remove most of the COD in the wastewater, to achieve the purpose of preliminary degradation of harmful substances in the wastewater, and to produce carbon black substances at the same time; then, the wet oxidation reaction water is sent to the membrane filtration device to filter out solid substances such as carbon black; then, the wastewater filtrate is sent to the catalytic wet oxidation reactor, under the action of high temperature, high pressure, oxygen and catalyst, the COD and ammonia nitrogen in the wastewater are further removed, the water produced by the catalytic wet oxidation is further sent to the electrodialysis device to remove ammonia nitrogen in the wastewater, the water outlet of the dilute chamber of the electrodialysis device is sent to the biochemical treatment device, and the water outlet of the concentrated chamber is sent to the ammonium sulfate crystallization device to recover ammonium sulfate crystals or further ammonia neutralization.

[0014] Preferably, the electrodialysis device is replaced by a membrane ammonia removal device. The membrane ammonia removal device is used to remove ammonia nitrogen in the catalytic wet oxidation water, and the water produced by the membrane ammonia removal device is sent to the biochemical treatment device, and the acid absorption liquid absorbing ammonia nitrogen is sent to the absorption liquid circulating tank.

[0015] Preferably, the membrane ammonia removal device comprises: a filter, a pH adjusting tank, a cross-flow membrane contactor assembly, an absorption liquid preparation tank and an absorption liquid circulating tank.

[0016] Preferably, the filter is connected with the pH adjusting tank, the pH adjusting tank is connected with the wastewater inlet of the cross-flow membrane contactor assembly, the wastewater outlet of the cross-flow membrane contactor assembly is connected with the biochemical treatment device, the absorption liquid preparation tank is connected with the absorption liquid inlet of the cross-flow membrane contactor assembly, the absorption liquid outlet of the cross-flow membrane contactor assembly is connected with the absorption liquid inlet of the absorption liquid circulating tank, and the absorption liquid circulating tank is connected with the absorption liquid inlet of the cross-flow membrane contactor assembly.

[0017] The working process of the membrane deamination device is as follows: the water produced by the catalytic wet oxidation is first filtered by the filter to filter the suspended solids in the wastewater and prevent the blockage of the membrane holes of the cross-flow membrane, and then is sent to the pH adjusting tank to adjust the pH value to be alkaline and preheat the wastewater, and then is sent to the wastewater inlet of the tube side of the cross-flow membrane contactor assembly, while the prepared absorption liquid in the absorption liquid preparation tank is sent to the absorption liquid inlet of the shell side of the cross-flow membrane contactor assembly, after the deamination treatment, the wastewater is sent to the biochemical treatment device through the wastewater outlet of the cross-flow membrane contactor assembly, and the absorption liquid is sent to the absorption liquid circulating tank through the absorption liquid outlet of the cross-flow membrane contactor assembly, and the absorption liquid circulating tank circulates the absorption liquid to the absorption liquid inlet of the shell side of the cross-flow membrane contactor assembly, or the concentrated solution of ammonium sulfate after absorbing ammonia nitrogen is sent to the ammonium sulfate crystallization device.

[0018] Preferably, the concentrated solution outlet of the absorption liquid circulating tank in the membrane deamination device or the concentrated solution outlet of the thick chamber of the electrodialysis device is connected with the ammonium sulfate crystallization device. The concentrated solution of ammonium sulfate enriched with ammonia nitrogen is sent to the ammonium sulfate crystallization device for crystallization and recovery of ammonium sulfate.

[0019] Preferably, the bottom of the wet oxidation reactor is provided with a water inlet, and one side of the lower part is provided with an air inlet.

[0020] Preferably, heating devices are arranged in the wet oxidation reactor and the catalytic wet oxidation reactor.

[0021] Preferably, the filtering precision of the membrane filtration device is ≤5 μm. The membrane filtration device can filter the suspended solids in the wastewater to prevent the blockage of the catalyst and the valve in the subsequent catalytic wet oxidation reactor. A small amount of filtered concentrated solution is sent to the plate-and-frame filter press for treatment.

[0022] Preferably, the membrane in the membrane filtration device is an inorganic membrane.

[0023] Preferably, the inorganic membrane includes a metal membrane or a ceramic membrane.

[0024] Preferably, the catalytic wet oxidation reactor is provided with a catalyst frame for placing the catalyst.

[0025] Preferably, the electrodialysis membrane of the electrodialysis device is composed of multiple pairs of flat sheet membranes. 2 .

[0026] Preferably, the flat sheet membrane is a homogeneous membrane or a heterogeneous ion exchange membrane.

[0027] Preferably, the filter has a filtering accuracy of ≤5 μm.

[0028] Preferably, the pH adjusting tank is provided with a heating device. The pH adjusting tank, the cross-flow membrane contactor assembly and the absorbent circulating tank in the deamination process are all sealed devices that can prevent ammonia from volatilizing.

[0029] Preferably, the cross-flow membrane contactor assembly is composed of one or more cross-flow membrane contactors connected in series. When multiple cross-flow membrane contactors are connected in series, the wastewater outlet of a previous cross-flow membrane contactor is connected to the wastewater inlet of a subsequent cross-flow membrane contactor, and the absorbent outlet of the previous cross-flow membrane contactor is connected to the absorbent inlet of the subsequent cross-flow membrane contactor.

[0030] Preferably, the wastewater inlet and outlet of the cross-flow membrane contactor are arranged on the tube side, the absorbent inlet and outlet of the cross-flow membrane contactor are arranged on the shell side, and the wastewater inlet and the absorbent inlet of the cross-flow membrane contactor and the wastewater outlet and the absorbent outlet of the cross-flow membrane contactor are respectively arranged at opposite ends of the cross-flow membrane contactor. This design enables the wastewater and the absorbent to form cross-flow contact on the membrane.

[0031] Preferably, the deamination membrane in the cross-flow membrane contactor comprises a hollow fiber polypropylene membrane, a polyvinylidene fluoride membrane or a polytetrafluoroethylene membrane, etc.

[0032] Preferably, the average pore size of the deamination membrane is 0.1-2.0 μm.

[0033] The technical solution adopted by the present application to solve the technical problems is as follows: a method for treating caprolactam wastewater, wherein the caprolactam wastewater is sent into a wet oxidation reactor for wet oxidation reaction, then sent into a membrane filtration device for filtration, the filtrate is sent into a catalytic wet oxidation reactor for catalytic wet oxidation reaction, finally, the catalytic wet oxidation product water is sent into an electrodialysis device or a membrane deamination device for deamination treatment to obtain wastewater that meets subsequent biochemical treatment. The present application realizes the removal of most of the COD in the wastewater through low-temperature and low-pressure WAO, further reduces the COD in the wastewater through CWAO after filtering carbon black, and finally realizes the removal of ammonia nitrogen through an electrodialysis device or a membrane deamination device, thereby comprehensively realizing the removal of COD and ammonia nitrogen in the wastewater to meet the subsequent biochemical treatment discharge.

[0034] Preferably, the initial COD concentration of the caprolactam wastewater is 50,000-200,000 mg / L, the total nitrogen is 8,000-28,000 mg / L, the initial ammonia nitrogen concentration is 5,000-20,000 mg / L, and BOD5 / COD≤0.1. The caprolactam wastewater is derived from caprolactam extraction residual liquid, benzene stripping wastewater and ion exchange regeneration wastewater generated in a caprolactam production device.

[0035] Preferably, the temperature of the wet oxidation reaction is 200-250°C, the pressure is 3-6 MPa, and the residence time is 0.5-2.0 h. After the wet oxidation reaction, the COD concentration of the produced water can be reduced to 10,000-30,000 mg / L, and the ammonia nitrogen concentration is 10,000-20,000 mg / L. Part of the total nitrogen is converted into ammonia nitrogen after the wet oxidation reaction, resulting in an increase in the ammonia nitrogen concentration.

[0036] Preferably, the transmembrane pressure difference of the filtration is 0.5-2.0 bar. The transmembrane pressure difference can provide a cost-effective driving force.

[0037] Preferably, the temperature of the catalytic wet oxidation reaction is 230-275°C, the pressure is 4.0-7.5 MPa, and the residence time is 0.5-2.0 h. After the catalytic wet oxidation reaction, the COD concentration of the produced water can be reduced to 0.2-10,000 mg / L, and the ammonia nitrogen concentration is 7,000-30,000 mg / L. Under the reaction conditions, the best removal effect can be achieved with lower energy consumption. Part of the total nitrogen is converted into ammonia nitrogen after the catalytic wet oxidation reaction, resulting in an increase in the ammonia nitrogen concentration.

[0038] Preferably, the catalyst used in the catalytic wet oxidation reaction includes a homogeneous catalyst and / or a heterogeneous catalyst.

[0039] Preferably, the dosage of the homogeneous catalyst is 50-300 mg / L (more preferably 80-240 mg / L) of the caprolactam wastewater, and the dosage of the heterogeneous catalyst is 0.1-1.2 h -1 Preferably, the volume space velocity of the heterogeneous catalyst is 0.1-1.2 h -1 Preferably, the volume space velocity of the heterogeneous catalyst is 0.1-1.2 h 3 Preferably, the volume space velocity of the heterogeneous catalyst is 0.1-1.2 h 3 Preferably, the volume space velocity of the heterogeneous catalyst is 0.1-1.2 h

[0040] Preferably, the homogeneous catalyst includes one or more of ferric chloride, ferrous sulfate, copper nitrate, copper chloride or manganese nitrate, and hydrates thereof. The produced water after the deamination treatment is subjected to precipitation treatment by using a precipitation tank, the pH value of the water is adjusted to be alkaline in the precipitation tank, and / or sulfide is added to recover metal ions in the homogeneous catalyst.

[0041] Preferably, the heterogeneous catalyst comprises manganese dioxide, iron oxide, copper oxide, cerium oxide or ruthenium oxide, and a mixture of two or more of their hydrates and the like. More preferably, the heterogeneous catalyst is a mixture of cerium oxide and ruthenium oxide with a mass ratio of 1:2-3. The average particle size of the heterogeneous catalyst is 5-20 mm.

[0042] Preferably, when using an electrodialysis device for the deamination treatment, the catalytic wet oxidation effluent is fed into the concentrated chamber and the dilute chamber of the electrodialysis device, respectively, for electrodialysis treatment.

[0043] Preferably, the flow ratio of the catalytic wet oxidation effluent fed into the concentrated chamber and the dilute chamber is 1:1-5.

[0044] Preferably, the voltage of the electrodialysis treatment is 1-2 V per pair of electrodialysis membranes.

[0045] Preferably, in the electrodialysis device, the flow rate of the catalytic wet oxidation effluent per m 2 The capacity of the electrodialysis membrane for treating wastewater is 3-12 L / h (more preferably 4-8 L / h).

[0046] Preferably, the effective area of each pair of electrodialysis membranes is 0.1-1.0 m 2 .

[0047] Preferably, when using a membrane deamination device for the deamination treatment, the catalytic wet oxidation effluent is first filtered, then the pH value is adjusted to alkaline, and preheated, and the treated catalytic wet oxidation effluent and the absorption solution are fed into the tube side and the shell side of the cross-flow membrane contactor of the membrane deamination device, respectively, for cross-flow absorption reaction.

[0048] Preferably, the pH value is adjusted to 11-13. By adjusting the pH value, the ammonia nitrogen in the wastewater can be maintained in the form of free ammonia, so that it can be overflowed in the form of gaseous ammonia.

[0049] Preferably, the pH value is adjusted by sodium hydroxide.

[0050] Preferably, the preheating is to 15-55°C (more preferably 40-50°C). By preheating, the ammonia can be quickly overflowed, and the deamination efficiency is improved.

[0051] Preferably, the absorption solution is a sulfuric acid solution, and the pH value of the sulfuric acid solution is 1-3.

[0052] Preferably, the flow ratio of the sulfuric acid solution to the wastewater is 1:2-15 (more preferably 1:3-10). By limiting the flow ratio, the control of the deamination rate of the wastewater and the neutralization degree of the sulfuric acid solution can be achieved.

[0053] Preferably, the residence time of the cross-flow absorption reaction is 0.5-3.0 h.

[0054] The beneficial effects of the present application are as follows:

[0055] (1) The device of the present application is simple, has large processing capacity, is green, safe and reliable, and has low energy consumption;

[0056] (2) The process of the present application is simple, and the removal rates of COD and ammonia nitrogen are as high as 98.76% and 99.86% respectively, the biodegradability index BOD5 / COD (B / C) of the produced water is greater than 0.3, and the concentrations of COD and ammonia nitrogen in the produced water meet the concentration requirements of the subsequent biochemical treatment section;

[0057] (3) Compared with Fenton and ozone catalytic oxidation processes, the method of the present application does not produce additional by-products and three wastes to form secondary pollution, and compared with the conventional CWAO process, the reaction process has small temperature rise and is safe and controllable, has low cost, and is suitable for industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 is a schematic diagram of the treatment device for caprolactam wastewater in embodiments 1 and 2 of the present application. DETAILED DESCRIPTION

[0059] The present application will be further described below in combination with embodiments and drawings.

[0060] The caprolactam wastewater 1 used in the embodiments and comparative examples of the present application is derived from caprolactam extraction residual liquid generated from a caprolactam production device of a certain factory, has an initial COD concentration of 157850 mg / L, a total nitrogen of 19000 mg / L, an initial ammonia nitrogen concentration of 7400 mg / L, and a B / C=0.01, and has extremely poor biodegradability; the caprolactam wastewater 2 is derived from benzene stripping wastewater and ion exchange regeneration wastewater of a certain factory, has an initial COD concentration of 108420 mg / L, a total nitrogen of 28000 mg / L, an initial ammonia nitrogen concentration of 16830 mg / L, and a B / C=0.008, and has extremely poor biodegradability.

[0061] The raw materials or chemical reagents used in the embodiments of the present application are obtained through conventional commercial channels unless otherwise specified.

[0062] The produced water COD concentration in the embodiments and comparative examples of the present application is detected by potassium dichromate method, and the ammonia nitrogen concentration is detected by Nessler's reagent spectrophotometry.

[0063] A treatment device for caprolactam wastewater embodiment 1 (containing an electrodialysis device)

[0064] As Figure 1As shown, the caprolactam wastewater treatment device comprises a wet oxidation reactor 1, a membrane filtration device 2, a catalytic wet oxidation reactor 3, an electrodialysis device 4 and a biochemical treatment device 6; the water outlet 102 of the wet oxidation reactor 1 is connected with the water inlet 201 of the membrane filtration device 2, the water outlet 202 of the membrane filtration device 2 is connected with the water inlet 301 of the catalytic wet oxidation reactor 3, the water outlet 302 of the catalytic wet oxidation reactor 3 is connected with the water inlet 401 of the electrodialysis device 4, and the dilute chamber water outlet 402 of the electrodialysis device 4 is connected with the biochemical treatment device 6;

[0065] The bottom of the wet oxidation reactor 1 is provided with a water inlet 101, and the lower side is provided with an air inlet 103; the lower side of the catalytic wet oxidation reactor 3 is provided with an air inlet 303; the wet oxidation reactor 1 and the catalytic wet oxidation reactor 3 are both provided with heating devices; the filtration precision of the membrane filtration device 2 is ≤5 μm; the membrane in the membrane filtration device 2 is an inorganic ceramic membrane; the catalytic wet oxidation reactor 3 is provided with a catalyst frame for placing catalysts; the electrodialysis membrane of the electrodialysis device 4 is composed of 400 pairs of flat membranes, and the effective area of each pair of flat membranes is 0.5 m 2 ; the flat membranes are heterogeneous ion exchange membranes.

[0066] The concentrated chamber water outlet 403 of the electrodialysis device 4 is connected with an ammonium sulfate crystallization device 7.

[0067] The working process of the device is as follows: first, the caprolactam wastewater is sent into the wet oxidation reactor 1 for pretreatment to remove most of the COD in the wastewater, so as to preliminarily degrade harmful substances in the wastewater, and at the same time, carbon black substances are generated; then, the wet oxidation water is sent into the membrane filtration device 2 to filter out solid substances such as carbon black; then, the wastewater filtrate is sent into the catalytic wet oxidation reactor 3, and under the action of high temperature, high pressure, oxygen and catalysts, the COD and ammonia nitrogen in the wastewater are further removed; the catalytic wet oxidation water is further sent into the electrodialysis device 4 to remove ammonia nitrogen in the wastewater; the water outlet of the dilute chamber of the electrodialysis device 4 is sent into the biochemical treatment device 6, and the water outlet of the concentrated chamber is sent into the ammonium sulfate crystallization device 7 to recover ammonium sulfate crystals or further perform ammonia neutralization.

[0068] A caprolactam wastewater treatment device embodiment 2 (containing a membrane ammonia removal device)

[0069] As Figure 1The difference between the present embodiment and embodiment 1 is that the electrodialysis device 4 is replaced by a membrane deamination device 5; the membrane deamination device 5 comprises a filter 501, a pH adjusting tank 502, a cross-flow membrane contactor assembly 503, an absorbent preparation tank 504 and an absorbent circulating tank 505; the filter 501 is connected with the pH adjusting tank 502, the pH adjusting tank 502 is connected with a wastewater inlet 5031 of the cross-flow membrane contactor assembly 503, a wastewater outlet 5032 of the cross-flow membrane contactor assembly 503 is connected with the biochemical treatment device 6, the absorbent preparation tank 504 is connected with an absorbent inlet 5033 of the cross-flow membrane contactor assembly 503, an absorbent outlet 5034 of the cross-flow membrane contactor assembly 503 is connected with an inlet 5051 of the absorbent circulating tank 505, and a circulating liquid port 5052 of the absorbent circulating tank 505 is connected with the absorbent inlet 5033 of the cross-flow membrane contactor assembly 503; the filter precision of the filter 501 is ≤5 μm; the pH adjusting tank 502 is provided with a heating device; the cross-flow membrane contactor assembly 503 is composed of two cross-flow membrane contactors connected in series, a wastewater outlet 5032 of a former cross-flow membrane contactor is connected with a wastewater inlet 5031 of a latter cross-flow membrane contactor, and an absorbent outlet 5034 of the former cross-flow membrane contactor is connected with an absorbent inlet 5033 of the latter cross-flow membrane contactor; the wastewater inlet 5031 and the wastewater outlet 5032 of the cross-flow membrane contactor are arranged on the tube side, the absorbent inlet 5033 and the absorbent outlet 5034 of the cross-flow membrane contactor are arranged on the shell side, and the wastewater inlet 5031 and the absorbent inlet 5033 of the cross-flow membrane contactor and the wastewater outlet 5032 and the absorbent outlet 5034 of the cross-flow membrane contactor are respectively oppositely arranged at two ends of the cross-flow membrane contactor; the deamination membrane of the cross-flow membrane contactor is a hollow fiber polypropylene membrane with an average pore size of 0.2 μm; the pH adjusting tank 502, the cross-flow membrane contactor assembly 503 and the absorbent circulating tank 504 are all sealed devices. The rest is the same as embodiment 1.

[0070] The concentrated liquid outlet 5053 of the absorbent circulating tank 505 in the membrane deamination device 5 is connected with the ammonium sulfate crystallization device 7.

[0071] The working process of the membrane deamination device 5 is as follows: the water produced by catalytic wet oxidation is first filtered by the filter 501 to filter the suspended solids in the wastewater and prevent the membrane holes of the cross-flow membrane from being blocked, and then is sent into the pH adjusting tank 502 to adjust the pH value to be alkaline, and the wastewater is preheated at the same time, and then is sent into the wastewater inlet 5031 of the tube side of the cross-flow membrane contactor assembly 503, and the prepared absorbent in the absorbent preparation tank 504 is sent into the absorbent inlet 5033 of the shell side of the cross-flow membrane contactor assembly 503, after deamination treatment, the wastewater is sent into the biochemical treatment device 6 through the wastewater outlet 5032 of the cross-flow membrane contactor assembly 503, and the absorbent is sent into the absorbent circulating tank 505 through the absorbent outlet 5034 of the cross-flow membrane contactor assembly 503, and the absorbent circulating tank 505 circulates the absorbent into the absorbent inlet 5033 of the shell side of the cross-flow membrane contactor assembly 503, or the concentrated ammonium sulfate solution after absorbing ammonia nitrogen is sent into the ammonium sulfate crystallization device 7.

[0072] A method for treating caprolactam wastewater

[0073] In the device of Example 1, the caprolactam wastewater 1 is sent into the wet oxidation reactor at a flow rate of 1 m 3 / h, and after wet oxidation reaction (residence time is 2 h) at 250℃ and 6 MPa, the wastewater is sent into the membrane filter device for filtration at a transmembrane pressure difference of 2 bar, and then the filtrate is sent into the catalytic wet oxidation reactor filled with 1 m 3 of heterogeneous catalyst (mixture of cerium oxide and ruthenium oxide with a mass ratio of 1:3, average particle size is 10 mm) for catalytic wet oxidation reaction (residence time is 1 h) at 260℃ and 7 MPa, and finally, the water produced by catalytic wet oxidation is sent into the concentrated chamber and the dilute chamber of the electrodialysis device for electrodialysis treatment (the flow rate ratio of the water in the concentrated chamber to the water in the dilute chamber is 1:3, the voltage is 2 V / pair of flat-plate membranes, the electrodialysis membrane of the electrodialysis device is composed of 400 pairs of flat-plate membranes, and the effective area of each pair of flat-plate membranes is 0.5 m 2 ), and the wastewater meeting the subsequent biochemical treatment is obtained.

[0074] It is detected that after wet oxidation reaction, the COD concentration of the produced water is reduced to 18938 mg / L, and the ammonia nitrogen concentration is 15242 mg / L; after catalytic wet oxidation reaction, the COD concentration of the produced water is reduced to 4969 mg / L, the ammonia nitrogen concentration is 12712 mg / L, the total nitrogen concentration is 13027 mg / L, and B / C=0.14; after electrodialysis treatment, the COD concentration of the final produced water is 2484 mg / L, the removal rate is 98.43%, the ammonia nitrogen concentration is reduced to 140 mg / L, the removal rate is 98.11%, the B / C of the produced water is increased to 0.43, the biodegradability is very good, and the COD and ammonia nitrogen concentrations in the produced water meet the concentration requirements of the subsequent biochemical treatment section.

[0075] A method for treating caprolactam wastewater

[0076] The difference between this embodiment and embodiment 1 is that the heterogeneous catalyst is replaced by a copper nitrate homogeneous catalyst, and the dosage of copper nitrate is 100 mg / L of caprolactam wastewater; the catalytic wet oxidation reactor is used to perform the catalytic wet oxidation reaction at 250℃ and 6.5 MPa (the residence time is 1.5 h). The produced water after the electrodialysis treatment is subjected to the precipitation treatment by using a precipitation tank, the pH value of the water is adjusted to be alkaline in the precipitation tank, and / or sulfide is added to recover the metal ions in the homogeneous catalyst. The rest is the same as embodiment 1.

[0077] It is detected that, after the wet oxidation reaction, the COD concentration of the produced water is reduced to 18938 mg / L, and the ammonia nitrogen concentration is 15242 mg / L; after the catalytic wet oxidation reaction, the COD concentration of the produced water is reduced to 5385 mg / L, the ammonia nitrogen concentration is 12992 mg / L, and the total nitrogen concentration is 13891 mg / L; after the electrodialysis treatment, the COD concentration of the final produced water is 1953 mg / L, the removal rate is 98.76%, the ammonia nitrogen concentration is reduced to 147 mg / L, the removal rate is 98.01%, the B / C of the produced water is increased to 0.48, the biodegradability is very good, and the COD and ammonia nitrogen concentrations in the produced water meet the concentration requirements of the subsequent biochemical treatment section.

[0078] A method for treating caprolactam wastewater

[0079] In the device of embodiment 2, the caprolactam wastewater 2 is sent into the wet oxidation reactor at a flow rate of 0.8 m 3 / h, and after the wet oxidation reaction at 230℃ and 5 MPa (the residence time is 1 h), the wastewater is sent into the membrane filtration device to be filtered at a transmembrane pressure difference of 2 bar, and the filtrate is sent into the 1 m 3 long heterogeneous catalyst (a mixture of cerium oxide and ruthenium oxide with a mass ratio of 1:2, and the average particle size is 10 mm) to perform the catalytic wet oxidation reaction at 270℃ and 7 MPa (the residence time is 1.5 h), and finally, the catalytic wet oxidation produced water is sent into the membrane ammonia removal device to be treated. The catalytic wet oxidation produced water is first filtered, then the pH value is adjusted to 11 by using sodium hydroxide, and the temperature is preheated to 40℃, the treated catalytic wet oxidation produced water and the sulfuric acid solution (the pH value is 2) are respectively sent into the tube side and the shell side of the cross-flow membrane contactor of the membrane ammonia removal device to perform the cross-flow absorption reaction (the flow rate ratio of the sulfuric acid solution to the wastewater is 1:5, and the residence time is 2 h), and the wastewater meeting the subsequent biochemical treatment is obtained.

[0080] After the wet oxidation reaction, the COD concentration of the produced water was reduced to 26860 mg / L, and the ammonia nitrogen concentration was 16500 mg / L; after the catalytic wet oxidation reaction, the COD concentration of the produced water was reduced to 9370 mg / L, the ammonia nitrogen concentration was 24690 mg / L, and the total nitrogen concentration was 25104 mg / L; after the ammonia removal treatment by the membrane ammonia removal device, the COD concentration of the final produced water was 9582 mg / L (the slight increase in the COD concentration of the produced water after the membrane ammonia removal was due to the absorption of part of the water by sulfuric acid in the ammonia removal process), the removal rate was 91.16%, the ammonia nitrogen concentration was 98 mg / L, the removal rate was 99.42%, the B / C of the produced water was increased to 0.32, the biodegradability was very good, and the COD and ammonia nitrogen concentrations in the produced water met the concentration requirements of the subsequent biochemical treatment section.

[0081] A method for treating caprolactam wastewater

[0082] The difference between this example and example 3 is only that the residence time for the catalytic wet oxidation reaction is 2.0 h; in the ammonia removal treatment, the pH value is adjusted to 11.5 by sodium hydroxide, and the residence time for the cross-flow absorption reaction is 2.5 h. The rest is the same as in example 3.

[0083] After the wet oxidation reaction, the COD concentration of the produced water was reduced to 26860 mg / L, and the ammonia nitrogen concentration was 16500 mg / L; after the catalytic wet oxidation reaction, the COD concentration of the produced water was reduced to 6370 mg / L, the ammonia nitrogen concentration was 21475 mg / L, and the total nitrogen concentration was 21795 mg / L; after the ammonia removal treatment by the membrane ammonia removal device, the COD concentration of the final produced water was 6512 mg / L (the slight increase in the COD concentration of the produced water after the membrane ammonia removal was due to the absorption of part of the water by sulfuric acid in the ammonia removal process), the removal rate was 93.99%, the ammonia nitrogen concentration was 23 mg / L, the removal rate was 99.86%, the B / C of the produced water was increased to 0.34, the biodegradability was very good, and the COD and ammonia nitrogen concentrations in the produced water met the concentration requirements of the subsequent biochemical treatment section.

[0084] Comparative example 1-1

[0085] The difference between this comparative example and method example 1 is only that 1. the caprolactam wastewater 1 is directly sent into the catalytic wet oxidation reactor for catalytic wet oxidation reaction, the reaction temperature is 260-270°C, the pressure is 7 MPa, and the residence time is 3 h; the produced water is sent into the electrodialysis device for ammonia removal treatment (the flow ratio of the concentrated chamber water to the dilute chamber water is 1:3, and the voltage is 0.8 V / pair of membranes). The rest is the same as in method example 1.

[0086] The detection shows that, after the catalytic wet oxidation reaction, the COD concentration of the produced water is 25380 mg / L, the ammonia nitrogen concentration is 16210 mg / L, and the total nitrogen concentration is 17224 mg / L; after the treatment by the electrodialysis device, the COD concentration of the final produced water is 14537 mg / L, the removal rate is 90.79%, the ammonia nitrogen concentration is reduced to 4240 mg / L, the removal rate is 42.70%, the B / C of the produced water is increased to 0.22, but the biodegradability is still poor, and the COD and ammonia nitrogen concentrations of the produced water exceed the concentration requirements of the subsequent biochemical treatment section.

[0087] It can be known from the comparison between Example 1 and Comparative Example 1-1 that: since Comparative Example 1-1 does not perform the wet oxidation reaction for pretreatment of the wastewater, the removal effect of COD is greatly reduced, and it is difficult to perform subsequent treatment, and the reason is that: a lot of carbon black substances are produced in the catalytic wet oxidation process, which are attached to the surface of the catalyst to reduce the catalytic performance, so it is necessary to perform the wet oxidation pretreatment first and then perform the catalytic oxidation reaction; in the catalytic wet oxidation reactor, the reaction temperature is increased by 35℃ from the bottom to the top of the reactor, the temperature difference in the reactor is too large, and the temperature at the top of the reactor fluctuates by more than 10℃ with time, which is not conducive to the control of the temperature in the reactor, indicating that the wet oxidation pretreatment is not performed, which causes the temperature in the reactor to be difficult to control, and even the risk of temperature runaway; since the voltage in the electrodialysis device is only 0.8V / pair of membranes, the removal rates of COD and ammonia nitrogen by the electrodialysis are greatly reduced, and the B / C value is low due to the excessively high ammonia nitrogen.

[0088] Comparative Example 1-2

[0089] The difference between this comparative example and Method Example 1 is only that the produced water after the wet oxidation reaction is not filtered and directly enters the catalytic wet oxidation reactor. The rest is the same as Method Example 1.

[0090] The detection shows that, after the wet oxidation reaction, the COD concentration of the produced water is reduced to 18938 mg / L, and the ammonia nitrogen concentration is 15242 mg / L; after the catalytic wet oxidation reaction, the COD concentration of the produced water is 12470 mg / L, the ammonia nitrogen concentration is 15995 mg / L, the total nitrogen concentration is 17210 mg / L, and the B / C is 0.11; after the treatment by the electrodialysis device, the COD concentration of the final produced water is 7550 mg / L, the removal rate is 95.22%, the ammonia nitrogen concentration is reduced to 854 mg / L, the removal rate is 88.46%, the B / C of the produced water is increased to 0.30, the biodegradability is good, and the COD and ammonia nitrogen concentrations of the produced water meet the concentration requirements of the subsequent biochemical treatment section.

[0091] Comparing Example 1 with Comparative Examples 1-2, it can be seen that: since Comparative Examples 1-2 did not filter the carbon black produced by wet oxidation, the COD removal effect was significantly reduced. The reason is that: the wet oxidation reaction produces a lot of carbon black substances, which adhere to the surface of the catalyst that catalyzes the wet oxidation reaction, thereby reducing the catalytic performance; since the COD concentration entering the electrodialysis device is as high as 12470 mg / L, a large amount of organic matter easily adheres to the electrodialysis membrane, causing the rate of ion permeation through the electrodialysis membrane to slow down, resulting in a decrease in the removal rate of ammonia nitrogen and COD.

[0092] Comparative Example 2

[0093] In the apparatus of Example 2, caprolactam wastewater 2 was discharged at a flow rate of 0.8 m³ / s. 3 The solution is fed into a wet oxidation reactor at 195°C and 2.5 MPa for a wet oxidation reaction (residence time of 2 hours), then fed into a membrane filtration device for filtration at a transmembrane pressure difference of 2 bar. The filtrate is then fed into a 1m³ packing tank. 3 In a catalytic wet oxidation reactor using a heterogeneous catalyst (a mixture of cerium oxide and ruthenium oxide at a mass ratio of 1:2, with an average particle size of 10 mm), a catalytic wet oxidation reaction was carried out at 220 °C and 3 MPa (residence time of 3 h). Finally, the catalytic wet oxidation permeate was sent to a membrane deammoniation unit for deammoniation treatment. First, the catalytic wet oxidation permeate was filtered, then the pH value was adjusted to 10 with sodium hydroxide and preheated to 40 °C. The treated catalytic wet oxidation permeate and sulfuric acid solution (pH value of 4.3) were sent to the tube side and shell side of the cross-flow membrane contactor in the membrane deammoniation unit, respectively, for cross-flow absorption reaction (the flow ratio of sulfuric acid solution to wastewater was 1:5, and the residence time was 2 h), resulting in wastewater.

[0094] Testing revealed that after wet oxidation, the COD concentration of the permeate decreased to 34,420 mg / L, and the ammonia nitrogen concentration to 16,500 mg / L. After catalytic wet oxidation, the COD concentration decreased to 18,631 mg / L, and the ammonia nitrogen concentration to 25,890 mg / L. After ammonia removal by a membrane deammoniation unit, the final COD concentration of the permeate was 18,712 mg / L, with a removal rate of 82.74%, and the ammonia nitrogen concentration was 2,927 mg / L, with a removal rate of 82.61%. The B / C ratio of the permeate increased to 0.28, but the biodegradability was poor, and the COD and ammonia nitrogen concentrations in the permeate exceeded the concentration requirements of the subsequent biological treatment stage.

[0095] Comparing Method Example 3 with Comparative Example 2, it can be seen that: due to the decrease in the reaction temperature of WAO and CWAO in Comparative Example 2, the COD removal rate decreased; due to the fact that the pH value of the wastewater was only adjusted to 10 in the ammonia removal treatment and the pH value of the sulfuric acid absorption liquid was as high as 4.3, the ammonia nitrogen removal rate decreased significantly, and the B / C value was low due to the excessive ammonia nitrogen.

Claims

1. A process for the treatment of caprolactam wastewater, characterized by: The caprolactam wastewater is sent into a wet oxidation reactor, and after wet oxidation reaction, is sent into a membrane filtration device for filtration, and the filtrate is sent into a catalytic wet oxidation reactor for catalytic wet oxidation reaction, and finally, the catalytic wet oxidation product water is sent into an electrodialysis device or a membrane ammonia removal device for ammonia removal treatment to obtain wastewater meeting subsequent biochemical treatment; the initial COD concentration of the caprolactam wastewater is 50,000-200,000 mg / L, the total nitrogen is 8,000-28,000 mg / L, the initial ammonia nitrogen concentration is 50,000-200,000 mg / L, and BOD5 / COD≤0.1; the temperature of the wet oxidation reaction is 200-250 ℃, the pressure is 3-6 MPa, and the residence time is 0.5-2.0 h; the temperature of the catalytic wet oxidation reaction is 230-275 ℃, the pressure is 4.0-7.5 MPa, and the residence time is 0.5-2.0 h; when the electrodialysis device is used for ammonia removal treatment, the catalytic wet oxidation product water is sent into the concentration chamber and the dilute chamber of the electrodialysis device respectively for electrodialysis treatment; the flow ratio of the catalytic wet oxidation product water sent into the concentration chamber and the dilute chamber is 1:1-5; the voltage of the electrodialysis treatment is 1-2 V / pair of electrodialysis membranes; When the membrane ammonia removal device is used for ammonia removal treatment, the catalytic wet oxidation product water is first filtered, then the pH value is adjusted to alkaline, and the catalytic wet oxidation product water after treatment and the absorption liquid are sent into the tube side and the shell side of the cross-flow membrane contactor of the membrane ammonia removal device respectively for cross-flow absorption reaction; the absorption liquid is sulfuric acid solution, the pH value of the sulfuric acid solution is 1-3, the flow ratio of the sulfuric acid solution and the wastewater is 1:2-15, and the residence time of the cross-flow absorption reaction is 0.5-3.0 h.

2. The method of treating caprolactam wastewater according to claim 1, characterized in that: The filtered transmembrane pressure difference is 0.5-2.0 bar; the catalyst used in the catalytic wet oxidation reaction includes a homogeneous catalyst and / or a heterogeneous catalyst; the homogeneous catalyst is added in an amount of 50-300 mg / L of caprolactam wastewater, the heterogeneous catalyst is used according to a volume space velocity of 0.1-1.2 h -1 The loading is carried out; the homogeneous catalyst includes one or more of ferric chloride, ferrous sulfate, copper nitrate, copper chloride or manganese nitrate, and hydrates thereof; the heterogeneous catalyst includes a mixture of two or more of manganese dioxide, iron oxide, copper oxide, cerium oxide or ruthenium oxide, and hydrates thereof.

3. The method of treating caprolactam wastewater according to claim 1 or 2, characterized in that: In the electrodialysis unit, each m 2 The electrodialysis membrane can treat wastewater at a capacity of 3 to 12 L / h; the effective area of each pair of electrodialysis membranes is 0.1 to 1.0 m 2 .

4. The method of treating caprolactam wastewater according to claim 1 or 2, characterized in that: When the membrane ammonia removal device is used for ammonia removal treatment, the pH value is adjusted to 11-13; the pH value is adjusted by sodium hydroxide; and the preheating temperature is 15-55 ℃.

5. An apparatus for treating caprolactam wastewater by the method according to any one of claims 1 to 4, characterized by Comprise: a wet oxidation reactor, a membrane filtration device, a catalytic wet oxidation reactor, an electrodialysis device and a biochemical treatment device; the water outlet of the wet oxidation reactor is connected with the water inlet of the membrane filtration device, the water outlet of the membrane filtration device is connected with the water inlet of the catalytic wet oxidation reactor, the water outlet of the catalytic wet oxidation reactor is connected with the water inlet of the electrodialysis device, and the water outlet of the dilute chamber of the electrodialysis device is connected with the biochemical treatment device.

6. The apparatus for treating caprolactam wastewater according to claim 5, characterized by: The electrodialysis device is replaced by a membrane ammonia removal device; the membrane ammonia removal device comprises a filter, a pH adjusting tank, a cross-flow membrane contactor assembly, an absorption liquid preparation tank and an absorption liquid circulating tank; the filter is connected with the pH adjusting tank, the pH adjusting tank is connected with the wastewater inlet of the cross-flow membrane contactor assembly, the wastewater outlet of the cross-flow membrane contactor assembly is connected with the biochemical treatment device, the absorption liquid preparation tank is connected with the absorption liquid inlet of the cross-flow membrane contactor assembly, the absorption liquid outlet of the cross-flow membrane contactor assembly is connected with the liquid inlet of the absorption liquid circulating tank, and the circulating liquid outlet of the absorption liquid circulating tank is connected with the absorption liquid inlet of the cross-flow membrane contactor assembly.

7. The apparatus for treating caprolactam wastewater according to claim 5 or 6, characterized by: The concentrated water outlet of the electrodialysis device or the concentrated liquid outlet of the absorption liquid circulating tank in the membrane deamination device is connected with the ammonium sulfate crystallization device.

8. The apparatus for treating caprolactam wastewater according to claim 5 or 6, characterized by: The bottom of the wet oxidation reactor is provided with a water inlet, and one side of the lower part is provided with an air inlet; one side of the lower part of the catalytic wet oxidation reactor is provided with an air inlet; heating devices are arranged in the wet oxidation reactor and the catalytic wet oxidation reactor; the filtering precision of the membrane filtration device is ≤5μm; the membrane in the membrane filtration device is an inorganic membrane; the inorganic membrane includes a metal membrane or a ceramic membrane; a catalyst frame for placing a catalyst is arranged in the catalytic wet oxidation reactor; the electrodialysis membrane of the electrodialysis device is composed of multiple pairs of flat sheet membranes; the flat sheet membranes are homogeneous membranes or heterogeneous ion exchange membranes.

9. The apparatus for treating caprolactam wastewater according to claim 6, characterized by: The filtering precision of the filter is ≤5μm; a heating device is arranged in the pH adjusting tank; the cross-flow membrane contactor assembly is composed of one or more cross-flow membrane contactors connected in series; when multiple cross-flow membrane contactors are connected in series, the wastewater outlet of a previous cross-flow membrane contactor is connected with the wastewater inlet of a subsequent cross-flow membrane contactor, and the absorption liquid outlet of the previous cross-flow membrane contactor is connected with the absorption liquid inlet of the subsequent cross-flow membrane contactor; the wastewater inlet and outlet of the cross-flow membrane contactor are arranged on the tube side, the absorption liquid inlet and outlet of the cross-flow membrane contactor are arranged on the shell side, and the wastewater inlet and the absorption liquid inlet of the cross-flow membrane contactor and the wastewater outlet and the absorption liquid outlet of the cross-flow membrane contactor are respectively arranged opposite to each other at two ends of the cross-flow membrane contactor; the deamination membrane in the cross-flow membrane contactor includes a hollow fiber polypropylene membrane, a polyvinylidene fluoride membrane or a polytetrafluoroethylene membrane; the average pore size of the deamination membrane is 0.1-2.0μm.

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