A method for treating acrylonitrile wastewater

Abstract

The invention discloses a method for treating acrylonitrile wastewater, including a pretreatment section, a wet oxidation section, and a deep treatment section; the acrylonitrile wastewater first removes calcium and magnesium hardness, enters a regulating tank after MVR concentration, is mixed with double membrane reflux liquid and a homogeneous catalyst in the regulating tank and pH is adjusted, is subjected to wet oxidation catalytic treatment after heat exchange, is cooled by a cooler, and is subjected to nanofiltration treatment, the nanofiltration concentrated water is partially refluxed to the regulating tank, and partially enters single membrane electrodialysis, and the nanofiltration produced water enters the deep treatment section; the single membrane electrodialysis mother liquor is returned to the regulating tank, and the anion liquid enters the deep treatment section, is treated by a biochemical unit, and finally reaches the discharge standard. In view of the characteristics of high COD, high nitrogen, high toxicity, and difficulty in degradation of acrylonitrile wastewater, the invention adopts a treatment process with homogeneous catalytic wet oxidation as the core, gives full play to the characteristics of high catalytic activity and strong treatment capacity of homogeneous catalytic wet oxidation, and finally achieves the discharge standard of acrylonitrile wastewater.

Description

Technical Field

[0001] The invention relates to a method for treating acrylonitrile wastewater, in particular to a method for treating acrylonitrile wastewater by utilizing homogeneous catalytic wet oxidation, and belongs to the technical field of wastewater treatment. Background Art

[0002] As an important chemical raw material, acrylonitrile is widely used in the production of nylon fiber, nitrile rubber, ABS / SAN resin, acrylamide, adiponitrile and ethylenediamine. In the process of producing acrylonitrile, about 1.5 tons of wastewater will be generated for every ton of acrylonitrile produced. Acrylonitrile is a cyanide substance with high toxicity. It can cause acute or chronic poisoning or even death if it enters the human body through the skin or inhalation. If it is discharged into the water, it will seriously endanger the activity and survival of microorganisms and cause disturbance of the aquatic ecosystem.

[0003] Incineration, biological and oxidation methods are usually used for acrylonitrile wastewater. Due to the presence of HCN, ammonium sulfate, etc. in acrylonitrile wastewater, it is difficult to burn completely in the incineration method, and a large amount of fuel needs to be added for combustion. The flue gas after combustion has problems such as cold pipe clogging, boiler corrosion, and tail gas treatment. In addition, the overall cost of this method is too high and the resource consumption is large. The cost of fuel alone is as high as 300 yuan / t of wastewater. The biological method can only treat low-concentration acrylonitrile wastewater. High-concentration acrylonitrile wastewater will seriously affect the survival of sludge microorganisms due to its high toxicity. Commonly used oxidation methods include ozone catalytic oxidation, electrocatalytic oxidation, photocatalysis, Fenton oxidation, wet oxidation, etc. Among them, electrocatalytic oxidation and photocatalysis are still limited by high treatment costs and are difficult to apply in industry. Fenton oxidation has problems such as complex operation, unstable hydrogen peroxide, and loss of iron ions. With the country's control of ozone pollutants, the application of ozone catalytic oxidation is also limited, and its treatment cost is also high.

[0004] Wet oxidation refers to the use of gaseous oxygen as an oxidant under high temperature (120-320°C) and high pressure (0.5-20MPa) conditions to oxidize and decompose organic matter in water into small molecular organic or inorganic matter. It has the characteristics of no secondary pollution and low treatment cost. Drawing on its wide application in alkaline slag wastewater, more and more scholars have begun to study wet oxidation technology to treat other difficult wastewaters. In order to improve its treatment effect and reduce its reaction temperature and pressure, the research focus is on catalytic wet oxidation.

[0005] CN201510274988.5 discloses a catalyst for catalytic wet oxidation of refractory organic wastewater, which is a "precious metal-transition metal-rare earth" composite catalyst, and the main component of the carrier FSC is alumina; CN201410340574.3 discloses a catalyst for catalytic wet oxidation treatment and a preparation method thereof, which has precious metal-non-precious metal nanoalloy as an active ingredient and activated carbon as a carrier; CN201510661575.2 discloses a multiphase wet oxidation catalyst, the components of which include a composite oxide carrier and a small amount of precious metal; CN201310621017.4 discloses a method for preparing a catalytic wet oxidation catalyst carrier, which has activated carbon as a core and amorphous silicon aluminum as a shell; CN201310130159.0 discloses a method for catalytic wet oxidation of ammonium sulfate-containing wastewater, and the heterogeneous catalyst used has zirconium oxide or alumina ceramic foam board as a carrier.

[0006] The above patents all use heterogeneous catalytic wet oxidation, which has advantages in catalyst separation and recovery and metal loss, but is not necessarily applicable to wet oxidation processes. The paper "Industrial Application of Alkali Slag Moderated Wet Oxidation + SBR Treatment Technology" (2011) discloses the alkali slag moderated wet oxidation process of Fushun Petrochemical Research Institute. This process has been promoted and applied in 28 refining and chemical companies and is highly representative. The wet oxidation reactor used is a bubbling flow internal circulation reactor with an inner cylinder. If a heterogeneous catalyst is used in this reactor, its gas-liquid circulation will be seriously affected, and even the reactor and pipeline will be blocked. If a fixed bed method is used, it will bring greater gas resistance, which is more unfavorable for gas-liquid circulation, and the reaction rate will also be greatly reduced.

[0007] Homogeneous catalysis has no internal and external diffusion effect and high dispersion, so its catalytic efficiency is higher than heterogeneous catalysis, and the catalyst preparation is much simpler than heterogeneous catalyst. However, the biggest problem of homogeneous catalysis in wet oxidation is the loss of metal catalyst. At present, there are few studies in this direction. CN201210225873.3 provides a method for treating industrial wastewater by wet oxidation of homogeneous catalysis, in which a ring gear filler is arranged in a fixed bed reactor, and the homogeneous catalyst uses an iron-based catalyst, but the patent does not mention the loss of catalyst and the corresponding solution; CN201010513668.8 provides a method for treating ammonium sulfate wastewater in the production process of acrylonitrile, which uses a homogeneous transition metal or a heterogeneous noble metal catalyst, but also does not mention the problem of catalyst loss. Summary of the invention

[0008] In view of the above shortcomings, the present invention provides a method for treating acrylonitrile wastewater, which realizes efficient treatment and standard discharge of acrylonitrile wastewater by combining homogeneous catalysis and membrane technology, solves the difficult problems of high COD, high nitrogen, high toxicity and non-degradability of acrylonitrile wastewater, and at the same time solves the problem of catalyst loss in the homogeneous catalytic process, so that the catalyst can be recycled, the comprehensive operating cost is low, and the economy and practicality are strong.

[0009] In order to achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for treating acrylonitrile wastewater, comprising a pretreatment section, a wet oxidation section and a deep treatment section;

[0011] The pretreatment section includes a de-hardening tank, an MVR unit and an adjustment tank; the acrylonitrile wastewater first enters the de-hardening tank to remove calcium and magnesium hardness, and when the COD mass concentration in the wastewater is ≤30000 mg / L, the de-hardened wastewater enters the MVR unit for concentration, the condensate is reused, and the concentrated MVR concentrated water enters the adjustment tank, where it is mixed with the homogeneous catalyst and the wet oxidation section reflux liquid and the pH is adjusted; when the COD mass concentration in the wastewater is greater than 30000 mg / L, it directly enters the adjustment tank;

[0012] The wet oxidation section includes a heat exchange unit, a wet oxidation reactor, a cooler, nanofiltration and single membrane electrodialysis; the effluent from the regulating tank enters the heat exchange unit, and enters the wet oxidation reactor after heat exchange and temperature increase; the effluent from the wet oxidation reactor is cooled by the cooler after heat exchange in the heat exchange unit, and enters the nanofiltration for treatment, wherein part of the nanofiltration concentrated water flows back to the regulating tank, and part of it flows into the single membrane electrodialysis, and the nanofiltration produced water flows into the deep treatment section; the single membrane electrodialysis mother liquor flows back to the regulating tank and is mixed with the MVR concentrated water, and the anion liquid flows into the deep treatment section;

[0013] The deep treatment section includes a neutralization tank, a biochemical unit and an effluent monitoring tank; nanofiltration water and single membrane electrodialysis anion liquid enter the neutralization tank, enter the biochemical unit for treatment after pH adjustment, and then discharge to the effluent monitoring tank, and finally meet the discharge standards.

[0014] Furthermore, chemical agents are used in the de-hardening pool to remove hardness, preferably a combination of sodium hydroxide and sodium carbonate, wherein sodium hydroxide is added at 1 to 4 times the mass concentration of magnesium ions, and sodium carbonate is added at 1 to 3 times the mass concentration of calcium ions.

[0015] Furthermore, the operating temperature of the MVR unit is controlled below 150°C, and the concentration multiple is 2 to 5 times; the MVR unit concentrates the acrylonitrile wastewater, reduces the subsequent wet oxidation unit treatment load, and solves the problem of poor economic efficiency of low-concentration and high-flow wastewater treatment.

[0016] Furthermore, the heat exchange unit is composed of multiple heat exchangers, which perform heat exchange on the outlet water of the wet oxidation reactor and the outlet water of the regulating tank. The outlet water of the wet oxidation reactor goes through the tube side, and the outlet water of the regulating tank goes through the shell side. After multiple heat exchanges, the outlet water temperature of the regulating tank rises to 130-160°C, and the outlet water temperature of the wet oxidation reactor decreases to 45-75°C.

[0017] Furthermore, the homogeneous catalyst is a composite catalyst of precious metals and transition metals; the precious metal is selected from one or more of platinum, palladium, rhodium, silver and ruthenium, and the transition metal is selected from one or more of copper, iron, manganese, zinc and nickel, preferably a copper-palladium catalyst, and the mass percentage of precious metals in the homogeneous catalyst is 1% to 20%; the precious metals and transition metals exist in the form of metal salt compounds or complexes and are dissolved in the liquid phase.

[0018] Furthermore, the homogeneous catalyst is only added in large quantities when the device is started up, and is added according to the COD mass concentration and metal ion mass concentration ratio of 2000:1 to 2:1. During normal operation, it is appropriately supplemented according to the catalyst loss rate and the change in reaction liquid concentration.

[0019] Furthermore, the adjustment tank shown adds acid to adjust the pH to 2-6; the acid is hydrochloric acid or sulfuric acid, preferably hydrochloric acid;

[0020] Furthermore, the wet oxidation reactor is a bubbling flow inner circulation reactor in an inner cylinder, which uses gaseous oxygen (air) as an oxidant under high temperature and high pressure conditions to oxidize general organic matter in water into small molecular organic matter or inorganic matter; those skilled in the art should understand that acrylonitrile is an organic matter that is difficult to degrade, and wet oxidation alone has limited ability to remove acrylonitrile, but under the conditions of a catalyst, oxygen under high temperature and high pressure is more likely to undergo free radical reactions, and the decomposition and conversion capacity and reaction rate of acrylonitrile are greatly improved under the action of the strong oxidizing property of free radicals. On the other hand, homogeneous catalysts themselves have high activity and high selectivity, and their treatment of special pollutants is faster and more effective, and their easy loss problem is also solved by membrane technology.

[0021] Furthermore, the reaction temperature of the wet oxidation reactor is 150-300°C, the reaction pressure is 2MPa-10MPa, and the liquid space velocity is 0.25-4h -1 , the gas-liquid volume ratio is 20:1~500:1.

[0022] Furthermore, the cooling medium of the cooler is circulating water, which further cools the outlet water of the wet oxidation reactor to 25-40°C, meeting the temperature requirements of the subsequent nanofiltration membrane.

[0023] Furthermore, the nanofiltration water production rate is 60% to 85%, and the membrane pore size is between 1 and 3 nm. It can intercept the metals of the homogeneous catalyst, high-valent salts (such as sulfates, carbonates), macromolecular organic matter (relative molecular mass greater than 200), etc., and enter the concentrated water side after interception, wherein the metals of the homogeneous catalyst eventually flow back to the regulating tank, and after heat exchange and temperature increase, return to the wet oxidation reactor for recycling; the nanofiltration water production includes unreacted acrylonitrile, small molecular organic matter, monovalent salts and ammonia nitrogen.

[0024] Furthermore, 1% to 50% of the nanofiltration concentrate enters single membrane electrodialysis; the single membrane electrodialysis only uses anion membrane, and under the action of electrode drive and anion membrane, some high-valent anion salts such as sulfate and carbonate in the nanofiltration concentrate pass through the anion membrane into the concentrate side, and also include small molecular organic matter that is negative, and the cationic catalyst remains in the mother liquor and is reused again; those skilled in the art should understand that nanofiltration has no retention of monovalent ions such as sodium, potassium, and chlorine, but has a higher retention rate for divalent anions, and single membrane electrodialysis solves the problem of divalent anion enrichment very well, and does not cause the loss of metal catalysts, and adopts branch side line treatment, and its treatment cost is also low.

[0025] Furthermore, the neutralization tank is adjusted to pH 6 to 9 by adding alkali; the alkali is sodium hydroxide or potassium hydroxide;

[0026] Furthermore, the salt concentration of the influent of the biochemical unit should not exceed 5000 mg / L. When the influent salt concentration is too high, in order to ensure the treatment effect of the subsequent nitrification and denitrification bacteria, other low-salt wastewater dilution treatment should be used, preferably domestic sewage, steam stripping purified water and other wastewater, whose salt concentration, COD, etc. are relatively low.

[0027] Furthermore, the biochemical unit adopts a combined process of A / O and post-denitrification; the A / O process has the A section in front and the O section in the back, the A section is mainly used to improve the biodegradability of wastewater and accelerate the biodegradation rate, the O section is mainly used for the removal of organic matter and the nitrification reaction of residual ammonia nitrogen, and the post-denitrification is used to remove total nitrogen and convert nitrate nitrogen and nitrite nitrogen into nitrogen gas for removal.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) In view of the characteristics of acrylonitrile wastewater, such as high COD, high nitrogen, high toxicity and difficulty in degradation, the present invention adopts a treatment process with homogeneous catalytic wet oxidation as the core, giving full play to the characteristics of high catalytic activity and strong treatment capacity of homogeneous catalytic wet oxidation, and finally achieving the discharge of acrylonitrile wastewater in compliance with the standards.

[0030] (2) The present invention solves the problem of catalyst loss in homogeneous catalytic wet oxidation by combining wet oxidation with membrane technologies such as nanofiltration membrane and electrodialysis single anion membrane, realizes the recycling of catalyst, and greatly reduces the cost of catalyst, especially precious metal catalyst.

[0031] (3) The method of the present invention solves the problem of poor economic efficiency in treating low-concentration, high-flow wastewater. The acrylonitrile wastewater is efficiently concentrated by the MVR unit, the temperature is raised by heat exchange before entering the reactor, and a catalyst is introduced into the wet oxidation reactor to increase the reaction rate and reduce the reaction temperature and pressure, thereby keeping the treatment cost of the entire wet oxidation process at a low level.

[0032] (4) The method of the present invention solves the problem of high salt content in wastewater after concentration and the scaling and clogging of reactors and process pipelines caused by it. The de-hardening tank first solves the impact of calcium and magnesium hardness of wastewater on subsequent membrane processes; two-stage nanofiltration removes most of the monovalent salts such as sodium chloride and potassium chloride in the wastewater, reducing the accumulation of salt during the wet oxidation cycle treatment process; single membrane electrodialysis removes most of the anionic salts in the wastewater, such as sulfates and carbonates, and achieves salt balance during the wet oxidation cycle treatment process.

[0033] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 . Flow chart of the treatment of acrylonitrile wastewater of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below in conjunction with specific examples. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples.

[0036] Example 1

[0037] use Figure 1 The process method shown treats acrylonitrile wastewater.

[0038] Process flow such as Figure 1As shown: the acrylonitrile wastewater first enters the de-hardening tank to remove the calcium and magnesium hardness, and then enters the MVR unit for concentration, the condensate is reused, and the concentrated concentrate enters the regulating tank, where it is mixed with the nanofiltration concentrate, the single membrane electrodialysis mother liquor, and the homogeneous catalyst, and acid is added for pH adjustment, and then enters the heat exchange unit, and heat-exchanges with the effluent of the wet oxidation reactor to increase the temperature before entering the wet oxidation reactor; the acrylonitrile wastewater is efficiently treated under the high temperature, high pressure and catalyst of the wet oxidation reactor, and the effluent is first cooled by heat exchange in the heat exchange unit, and then cooled by the cooler before entering the nanofiltration; most of the nanofiltration concentrate flows back to the regulating tank, and a small part enters the single membrane electrodialysis through the side line, the single membrane electrodialysis mother liquor is returned to the regulating tank, the anion liquid flows to the neutralization tank of the deep treatment section, and the nanofiltration produced water also flows to the neutralization tank; the effluent of the neutralization tank enters the biochemical unit, and the wastewater is deeply treated by the biochemical unit and then discharged to the effluent monitoring tank, and finally meets the discharge standards.

[0039] The water quality of a certain acrylonitrile wastewater is as follows: COD 11000mg / L, total salt content 5000mg / L, sulfate concentration 300mg / L, ammonia nitrogen 350mg / L, total nitrogen 1500mg / L, calcium ion concentration 100mg / L, magnesium ion concentration 50mg / L, pH 6, and wastewater flow rate 30t / h.

[0040] The specific operating conditions for acrylonitrile wastewater treatment are as follows: the acrylonitrile wastewater first enters the de-hardening tank, and reagents are added according to the mass concentration of sodium hydroxide 120 mg / L and the mass concentration of sodium carbonate 300 mg / L. After clarification, the calcium ion concentration of the supernatant is reduced to below 10 mg / L, and the magnesium ion concentration is below 6 mg / L. Other factors remain unchanged, and the effluent enters the MVR unit; the concentration multiple of the MVR unit is 3, and the concentrations of COD, total salt content, sulfate, ammonia nitrogen, etc. will further increase after concentration. The flow rate is 10 t / h, the condensate COD is less than 50 mg / L, the total salt content is less than 200 mg / L, and the ammonia nitrogen is less than 8 mg / L , the flow rate is about 20t / h, which meets the direct discharge standard; the concentrated water from the MVR unit enters the regulating tank, where it is mixed with the secondary nanofiltration concentrated water, single membrane electrodialysis mother liquor, and homogeneous catalyst. After mixing, the flow rate becomes 12.5t / h, and hydrochloric acid is added at the same time to adjust the pH to 5.2; the homogeneous catalyst uses a palladium-copper composite catalyst. After mixing, the palladium metal ion concentration in the liquid is about 10mg / L, and the copper metal ion concentration is about 100mg / L. After heat exchange, the wastewater temperature of the effluent from the regulating tank rises to 150℃ and enters the wet oxidation reactor; the reaction temperature of the wet oxidation reactor is 180℃, the pressure is 3MPa, and the liquid space velocity is 2h -1, the gas-liquid volume ratio is 100:1; the wet oxidation effluent is cooled to 55°C by the heat exchange unit, and then cooled to 35°C by the cooler. The effluent enters the nanofiltration, the pore size of the nanofiltration membrane is 1nm, the water production rate is 74.4%, and the metal catalysts, sulfates, carbonates, macromolecular organic matter (excluding acrylonitrile) are intercepted and enter the concentrated water side. Most of the sodium, potassium, chloride ions, ammonia nitrogen, acrylonitrile, etc. pass through the nanofiltration membrane into the water production side; 43.7% of the nanofiltration concentrated water enters the single-mode electrodialysis treatment, and the remaining 56.3% is directly collected in the regulating tank The single-mode electrodialysis anion liquid flows to the lower neutralization tank, and the mother liquor flows to the regulating tank. Sodium hydroxide is added to the neutralization tank to adjust the pH to 6.5; the influent salt of the biochemical unit is relatively high. Considering the requirements of subsequent nitrification and denitrification microorganisms for salt, the stripping purified water is used as make-up water to dilute the salt; the biochemical unit adopts A / O process plus post-denitrification, and the final effluent COD is 44mg / L, the total salt content is 4590mg / L, the ammonia nitrogen is 2mg / L, and the total nitrogen is 14mg / L, which meets the external discharge standard and can be discharged from the effluent monitoring pool. The removal effect of each unit pollution factor is shown in Table 1, and the treatment efficiency of each unit is shown in Table 2.

[0041] Table 1

[0042]

[0043] Table 2

[0044]

[0045] It can be seen from this embodiment that the process method of the present invention realizes efficient operation of homogeneous catalytic wet oxidation. For the problems of high COD, high nitrogen, high toxicity, and difficulty in degradation of acrylonitrile wastewater, the COD removal rate of the wet oxidation unit of this embodiment is as high as 97.7%, and the total nitrogen removal rate is as high as 95.7%, and finally the acrylonitrile wastewater is discharged up to the standard. At the same time, through the combination with membrane technology, the loss problem of homogeneous catalyst is solved, and the recycling of catalyst is realized.

[0046] Example 2

[0047] use Figure 1 The process method shown treats acrylonitrile wastewater.

[0048] The water quality of a certain acrylonitrile wastewater is as follows: COD 38000mg / L, total salt content is 10000mg / L, sulfate ion concentration is 620mg / L, ammonia nitrogen is 800mg / L, total nitrogen is 5000mg / L, calcium ion concentration is 150mg / L, magnesium ion concentration is 80mg / L, and wastewater flow rate is 10t / h.

[0049] The specific operating conditions for the treatment of acrylonitrile wastewater are as follows: the acrylonitrile wastewater first enters a de-hardening tank, and reagents are added according to a sodium hydroxide mass concentration of 150 mg / L and a sodium carbonate mass concentration of 400 mg / L. After clarification, the calcium ion concentration of the supernatant is reduced to below 8 mg / L, and the magnesium ion concentration is below 5 mg / L, and the others remain unchanged; since the COD concentration of acrylonitrile wastewater is greater than 30,000 mg / L, the effluent from the de-hardening tank directly enters the regulating tank through a bypass line, and is mixed with secondary nanofiltration concentrated water, single membrane electrodialysis mother liquor, and homogeneous catalyst in the regulating tank. After mixing, the flow rate becomes 12.5 t / h, and hydrochloric acid is added at the same time to adjust the pH to 5; the homogeneous catalyst adopts a palladium-copper composite catalyst. After mixing, the palladium metal ion concentration in the liquid is about 10 mg / L, and the copper metal ion concentration is about 125 mg / L. After heat exchange, the effluent from the regulating tank is heated to 155°C and enters the wet oxidation reactor; the reaction temperature of the wet oxidation reactor is 190°C, the pressure is 3 MPa, and the liquid space velocity is 2 h -1 , the gas-liquid volume ratio is 100:1; the wet oxidation effluent is cooled to 50°C by the heat exchange unit, and then cooled to 35°C by the cooler. The effluent enters the nanofiltration, the nanofiltration membrane pore size is 1nm, the water production rate is 76%, the metal catalyst, sulfate, carbonate, macromolecular organic matter (excluding acrylonitrile), etc. are intercepted and enter the concentrated water side, and most of the sodium, potassium, chloride ions, ammonia nitrogen, acrylonitrile, etc. pass through the nanofiltration membrane into the water production side; 33.3% of the nanofiltration concentrated water enters the single-mode electrodialysis treatment, and the remaining 66.7% is directly collected in the regulating tank. The single-mode electrodialysis anion liquid flows to the neutralization tank, and the mother liquor flows to the regulating tank. Sodium hydroxide is added to the neutralization tank to adjust the pH to 6.5; the influent salt of the biochemical unit is relatively high. Considering the requirements of subsequent nitrification and denitrification microorganisms for salt, domestic sewage is used as make-up water for salt dilution; the biochemical unit adopts A / O process plus post-denitrification, and the final effluent COD is 46mg / L, and the total salt content is 3820 mg / L, ammonia nitrogen is 3mg / L, and total nitrogen is 15mg / L, which meets the discharge standard and can be discharged from the effluent monitoring pool. The removal effect of each unit pollution factor is shown in Table 3, and the treatment efficiency of each unit is shown in Table 4.

[0050] Table 3

[0051]

[0052] Table 4

[0053]

[0054] It can be seen from this embodiment that the process method of the present invention can treat acrylonitrile wastewater of different concentrations, and ultimately achieves the discharge of acrylonitrile wastewater in accordance with various indicators by adjusting the process (by-line), the amount of catalyst added, the nanofiltration water production rate, the amount of low brine blending, and other methods.

[0055] Example 3

[0056] The water quality of the treated acrylonitrile wastewater is the same as that in Example 2, and the process route, implementation steps, and reaction parameters are also the same as those in Example 2, except that the catalyst is replaced by a palladium iron catalyst, and the pH of the regulating tank is adjusted to 3.5, and the pH of the deep treatment stage is adjusted back to 6.5, as shown in Table 5 for details.

[0057] Table 5

[0058]

[0059] It can be seen from this example that when the palladium-iron composite catalyst is used with the same dosage, the COD removal rate of the homogeneous catalytic wet oxidation is slightly higher than that of Example 2, but the total nitrogen removal rate is reduced to 91.5%.

[0060] Example 4

[0061] The water quality of the treated acrylonitrile wastewater is the same as that in Example 2, and the process route, implementation steps, and reaction parameters are also the same as those in Example 2, except that the type of catalyst is different, as shown in Table 6.

[0062] Table 6

[0063]

[0064] It can be seen from this example that when the palladium-nickel composite catalyst is used with the same dosage, the COD removal rate of the homogeneous catalytic wet oxidation is reduced to 93.2% and the total nitrogen removal rate is reduced to 86.5% compared with Example 2.

[0065] Example 5

[0066] The water quality of the treated acrylonitrile wastewater is the same as that in Example 2, and the process route, implementation steps, and reaction parameters are also the same as those in Example 2, except that the type of catalyst is different, as shown in Table 7.

[0067] Table 7

[0068]

[0069] It can be seen from this embodiment that by using a rhodium-copper composite catalyst with the dosage unchanged, the COD removal rate and the total nitrogen removal rate of the homogeneous catalytic wet oxidation are further improved compared with Example 2, but the improvement is limited. Considering the price of the precious metal rhodium, it is recommended to give priority to the use of palladium-copper catalyst based on comprehensive considerations.

[0070] Example 6

[0071] The water quality of the treated acrylonitrile wastewater is the same as that in Example 2, and the process route, implementation steps, and reaction parameters are also the same as those in Example 2, except that the type of catalyst is different, as shown in Table 8.

[0072] Table 8

[0073]

[0074] It can be seen from this example that when a platinum-copper composite catalyst is used with the same dosage, the COD removal rate of the homogeneous catalytic wet oxidation is reduced to 96.2% and the total nitrogen removal rate is reduced to 77.5% compared with Example 2.

[0075] Example 7

[0076] The water quality of the treated acrylonitrile wastewater is the same as that in Example 2, and the process route, implementation steps, and reaction parameters are also the same as those in Example 2, except that the catalyst is replaced by a platinum-iron catalyst, and the pH of the regulating tank in the wet oxidation section is adjusted to 3.6, and the pH of the deep treatment section is adjusted back to 6.4, as shown in Table 9 for details.

[0077] Table 9

[0078]

[0079] It can be seen from this example that when the platinum-iron composite catalyst is used instead, the COD removal rate of the homogeneous catalytic wet oxidation is close to that of Example 2, but the total nitrogen removal rate decreases significantly.

[0080] Example 8

[0081] The water quality of the treated acrylonitrile wastewater is the same as that in Example 2, and the process route, implementation steps, and reaction parameters are also the same as those in Example 2, except that the catalyst is replaced by a platinum-iron catalyst, and the dosage is increased. At the same time, the pH of the regulating tank in the wet oxidation section is adjusted to 3.3, and the pH of the deep treatment section is adjusted back to 6.5, as shown in Table 10 for details.

[0082] Table 10

[0083]

[0084] It can be seen from this example that when a platinum-iron composite catalyst is used, the dosage is increased compared with Example 7, and the corresponding homogeneous catalytic wet oxidation COD removal rate is as high as 99.1%, which exceeds Example 2, but the total nitrogen removal rate is not improved.

[0085] Comparative Example 1

[0086] The water quality of the treated acrylonitrile wastewater is the same as that in Example 2, and the process route, implementation steps, and reaction parameters are also the same as those in Example 2, but no precious metal catalyst is added, and only a transition metal catalyst is added, as shown in Table 11 for details.

[0087] Table 11

[0088]

[0089] It can be seen from this comparative example that without adding precious metal catalysts and only adding copper metal catalysts, the COD removal rate and total nitrogen removal rate of homogeneous catalytic wet oxidation decreased significantly, the COD removal rate was only 68.1%, and the total nitrogen removal rate was only 65.5%.

[0090] Comparative Example 2

[0091] The water quality of the treated acrylonitrile wastewater is the same as that in Example 2, and the process route, implementation steps, and reaction parameters are also the same as those in Example 2, but no precious metal catalyst is added, and only a transition metal catalyst is added, as shown in Table 12 for details.

[0092] Table 12

[0093]

[0094] It can be seen from this comparative example that no precious metal catalyst is added, only copper metal catalyst is added. Compared with comparative example 1, the copper metal dosage is increased to 200 mg / L. It can be seen that the homogeneous catalytic wet oxidation COD removal rate and total nitrogen removal rate are significantly improved, but there is still a certain gap with Example 2.

[0095] Comparative Example 3

[0096] The water quality of the treated acrylonitrile wastewater is the same as that in Example 2, and the process route, implementation steps, and reaction parameters are also the same as those in Example 2. Neither the precious metal catalyst nor the transition metal catalyst is added. See Table 13 for details.

[0097] Table 13

[0098]

[0099] It can be seen from this comparative example that without adding a catalyst and using conventional wet oxidation, the reaction conditions are the same as those in Example 2, and the final COD removal rate is only 33.2%, and the total nitrogen removal rate is only 11.5%.

Claims

1. A method for treating acrylonitrile wastewater, comprising a pretreatment section, a wet oxidation section and a deep treatment section; The pretreatment section includes a de-hardening tank, an MVR unit and an adjustment tank; the acrylonitrile wastewater first enters the de-hardening tank to remove calcium and magnesium hardness, and when the COD mass concentration in the wastewater is ≤30000 mg / L, the de-hardened wastewater enters the MVR unit for concentration, the condensate is reused, and the concentrated MVR concentrated water enters the adjustment tank, where it is mixed with the homogeneous catalyst and the wet oxidation section reflux liquid and the pH is adjusted; when the COD mass concentration in the wastewater is greater than 30000 mg / L, it directly enters the adjustment tank; The wet oxidation section includes a heat exchange unit, a wet oxidation reactor, a cooler, nanofiltration and single membrane electrodialysis; the effluent from the regulating tank enters the heat exchange unit, and enters the wet oxidation reactor after heat exchange and temperature increase; the effluent from the wet oxidation reactor is cooled by the cooler after heat exchange in the heat exchange unit, and enters the nanofiltration for treatment, wherein part of the nanofiltration concentrated water flows back to the regulating tank, and part of it flows into the single membrane electrodialysis, and the nanofiltration produced water flows into the deep treatment section; the single membrane electrodialysis mother liquor flows back to the regulating tank and is mixed with the MVR concentrated water, and the anion liquid flows into the deep treatment section; The deep treatment section includes a neutralization tank, a biochemical unit and an effluent monitoring tank; the nanofiltration water and the single membrane electrodialysis anion liquid enter the neutralization tank, enter the biochemical unit for treatment after pH adjustment, and then discharge to the effluent monitoring tank, and finally meet the discharge standards; in, The homogeneous catalyst is a composite catalyst of precious metal and transition metal; the precious metal is selected from one or more of platinum, palladium, rhodium, silver and ruthenium, and the transition metal is selected from one or more of copper, iron, manganese, zinc and nickel, and the mass percentage of the precious metal in the homogeneous catalyst is 1% to 20%; the precious metal and the transition metal exist in the form of metal salt compounds or complexes and are dissolved in the liquid phase; The nanofiltration water production rate is 60% to 85%, the membrane pore size is between 1 and 3 nm, and the metals, high-valent salts, and macromolecular organic matter of the homogeneous catalyst are intercepted and enter the concentrated water side after interception; The single membrane electrodialysis adopts anionic membrane. Under the action of electrode drive and anionic membrane, high-valent anionic salts and negative small molecular organic matter in the nanofiltration concentrated water pass through the anionic membrane into the concentrated water side, and the cationic catalyst remains in the mother liquor and is reused.

2. The method according to claim 1, characterized in that In the de-hardening pool, a combination of sodium hydroxide and sodium carbonate is used to remove hardness. Sodium hydroxide is added at 1 to 4 times the mass concentration of magnesium ions, and sodium carbonate is added at 1 to 3 times the mass concentration of calcium ions.

3. The method according to claim 2, characterized in that The operating temperature of the MVR unit is controlled below 150° C., and the concentration multiple is 2 to 5 times.

4. The method according to claim 1, characterized in that The heat exchange unit is composed of a plurality of heat exchangers, and performs heat exchange on the outlet water of the wet oxidation reactor and the outlet water of the regulating tank. The outlet water of the wet oxidation reactor goes through the tube side, and the outlet water of the regulating tank goes through the shell side.

5. The method according to claim 4, characterized in that The heat exchange unit raises the outlet water temperature of the regulating tank to 130-160°C and reduces the outlet water temperature of the wet oxidation reactor to 45-75°C.

6. The method according to claim 1, characterized in that The adjusting tank is added with acid to adjust the pH to 2-6, and the acid is hydrochloric acid or sulfuric acid.

7. The method according to claim 1, characterized in that The homogeneous catalyst is a copper-palladium catalyst.

8. The method according to claim 1, characterized in that The homogeneous catalyst is added according to the COD mass concentration and metal ion mass concentration ratio of 2000:1 to 2:1, and is supplemented during operation according to the catalyst loss rate and the change in reaction liquid concentration.

9. The method according to claim 1, characterized in that: The wet oxidation reactor is a bubbling flow internal circulation reactor with an inner cylinder, which uses oxygen as an oxidant to oxidize general organic matter in water into small molecular organic matter or inorganic matter.

10. The method according to claim 9, characterized in that The reaction temperature of the wet oxidation reactor is 150-300°C, the reaction pressure is 2MPa-10MPa, and the liquid space velocity is 0.25-4h -1 , the gas-liquid volume ratio is 20:1~500:

1.

11. The method according to claim 1, characterized in that: The cooling medium of the cooler is circulating water, which further cools the outlet water of the wet oxidation reactor to a temperature of 25-40°C.

12. The method according to claim 1, characterized in that 1% to 50% of the nanofiltration concentrated water enters the single membrane electrodialysis.

13. The method according to claim 1, characterized in that The pH of the neutralization tank is adjusted to 6-9 by adding alkali; the alkali is sodium hydroxide or potassium hydroxide.

14. The method according to claim 1, characterized in that The salt concentration of the biochemical unit influent does not exceed 5000 mg / L.

15. The method according to claim 1, characterized in that The biochemical unit adopts an A / O and post-denitrification combined process; the A / O process has the A section in the front and the O section in the back.

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