A method and system for wet oxidation treatment of tmaH waste solution

Abstract

The application relates to a TMAH waste liquid wet oxidation treatment method and system, which comprises the following steps: (1) firstly adding powdered activated carbon into the TMAH waste liquid, and stirring and reacting for 1-3 hours; (2) simultaneously adding the mixture obtained in the step (1) and H2O2 into a wet oxidation reactor to carry out wet oxidation treatment. Compared with the prior art, the application improves the total nitrogen removal rate, improves the selectivity of the conversion of TMAH oxidation and decomposition into the final product nitrogen, and reduces the treatment load for further removing total nitrogen from the oxidation liquid.

Description

TECHNICAL FIELD

[0001] The present application relates to sewage treatment, in particular to a wet oxidation treatment method and system for TMAH waste liquid. BACKGROUND

[0002] In the photoresist developing process of liquid crystal display screen and chip manufacturing, developing waste liquid is produced, and the main pollutant component in the waste liquid is tetramethylammonium hydroxide (TMAH), which is an organic nitrogen compound with strong alkalinity, corrosivity and toxicity.

[0003] The typical water quality of TMAH waste liquid is that the concentration of TMAH is 20000-23800 mg / L, the concentration of TOC is 10550-13000 mg / L, the concentration of TN is 3075-3700 mg / L, and the pH value is 13-14.

[0004] When the concentration of TMAH in the waste water is 200-2000 mg / L, it can be degraded by aerobic biochemical method or anaerobic biochemical method; when the concentration of TMAH in the waste water is more than 2000 mg / L, TMAH will have strong inhibitory and toxic effects on water treatment microorganisms. Therefore, when biochemical treatment process is used to treat TMAH waste liquid, it needs to be diluted by a high multiple, which leads to the increase of biochemical treatment scale. In addition, there are disadvantages such as long reaction time, large reactor area, unstable treatment effect, etc. in the degradation of TMAH by biochemical process.

[0005] Wet air oxidation (WAO) is a method for treating toxic, harmful and high-concentration organic waste water. It is a chemical process in which oxygen is used as an oxidizing agent to oxidize organic pollutants in waste water into CO2, H2O and small molecular organic matter under high temperature (125℃-320℃) and high pressure (0.5MPa-10MPa). In practical application, air is often used as the oxidizing agent because of its low price, safe use and mature pressurizing equipment.

[0006] Catalytic wet air oxidation (CWAO) is based on the wet air oxidation treatment process, by adding catalyst to reduce the activation energy of the reaction, so as to reduce the required temperature and pressure without reducing the treatment effect, improve the oxidation decomposition ability, shorten the reaction time, improve the reaction efficiency, and make the oxidation reaction can be carried out under more moderate conditions.

[0007] However, when the common wet oxidation or catalytic wet oxidation process is applied to the treatment of TMAH waste liquid, although the wet oxidation method has a high removal rate of TOC, most of the organic nitrogen in the waste liquid is not converted into nitrogen gas after the wet oxidation treatment, but a large amount of ammonia nitrogen and nitric acid nitrogen are generated, and the oxidation liquid still needs further denitrification treatment.

[0008] When a catalyst with high ammonia nitrogen conversion activity and excellent nitrogen gas selectivity is used, the ammonia nitrogen in the wastewater can be converted into nitrogen gas instead of nitric acid nitrogen by the catalytic wet oxidation method. A large number of studies have been conducted on the removal of ammonia nitrogen in wastewater by the catalytic wet oxidation method, and most of the studies focus on the development of high-efficiency heterogeneous catalysts. For example, the article "Catalyst Deactivation Problem in Catalytic Wet Oxidation Treatment of Wastewater", Chemical Engineering Progress, Vol. 23, No. 7, 2004, mainly studies heterogeneous catalysts including: 1) noble metal series represented by Ru, Rh, Pd, Pt, etc., 2) transition metal oxide series represented by Cu, 3) composite oxide series represented by Co / Ce and Mn / Ce, etc. However, it is found in actual application that the above-mentioned heterogeneous catalysts all have the problem of gradually decreasing activity and eventually leading to catalyst deactivation. The reasons for catalyst deactivation include dissolution of active components, carbon deposition caused by covering of catalyst active centers by reaction products, and changes in catalyst physical structure, etc. Therefore, if the heterogeneous catalytic wet oxidation method is used to treat TMAH waste liquid, the catalyst needs to be replaced frequently, thereby increasing the operating cost and the complexity of operation and maintenance. SUMMARY

[0009] The purpose of the present application is to overcome the defects of the prior art and provide a wet oxidation treatment method and system for TMAH waste liquid.

[0010] The present application can at least solve the following problems:

[0011] (1) The wet oxidation method is used to treat TMAH waste liquid, and no expensive heterogeneous fixed-bed catalyst is used, thereby reducing the equipment construction cost and operating cost, and facilitating the application and promotion of the method.

[0012] (2) The wet oxidation method is improved to improve the selectivity of the conversion of ammonia nitrogen, an intermediate product of TMAH degradation, to nitrogen gas, the final product, in the wet oxidation reaction process, to reduce the generation of nitric acid nitrogen or nitrous acid nitrogen, and to improve the total nitrogen removal rate.

[0013] The purpose of the present application can be achieved by the following technical solution: a wet oxidation treatment method for TMAH waste liquid, comprising the following steps:

[0014] (1) Firstly, powdered activated carbon (PAC) is added into the TMAH waste liquid and stirred for 1-3 hours; PAC has high porosity and specific surface area, and can provide a large number of reaction micro-interfaces in the wet oxidation reactor, so that TMAH and active oxygen can rapidly react in the rich pore channels. Moreover, the surface of PAC has a large number of oxygen-containing groups, which have adsorption capacity for the intermediate product NH3 in the TMAH degradation.

[0015] Further, the powdered activated carbon has a mesh size of 200-300 mesh.

[0016] Further, the powdered activated carbon has an iodine value of not less than 800 mg / g, preferably not less than 1000 mg / g.

[0017] Further, the powdered activated carbon has a dosage concentration of 500-1000 mg / L, preferably 1000 mg / L. If the PAC dosage concentration is too low, it cannot play a role in catalytic decomposition of H2O2, providing reaction micro-interfaces and accelerating the wet oxidation reaction speed. If the dosage concentration is too high, it may cause problems such as wear and blockage of high-pressure equipment such as wet oxidation reactors, heat exchangers, pressure reducing valves, etc.

[0018] (2) The mixture obtained in step (1) and H2O2 are simultaneously added into a wet oxidation reactor for wet oxidation treatment.

[0019] Further, the wet oxidation reactor has a reaction temperature of 255-265℃, a reaction pressure of 5.5-6.5 MPa, and a reaction time of 90-120 min.

[0020] Further, the H2O2 is added at a concentration of 2-3 times the TMAH concentration in the waste liquid, or at a concentration of 3.8-5.7 times the TOC concentration in the waste liquid.

[0021] In the wet oxidation reactor, PAC first catalytically decomposes H2O2 into O2, hydroxyl radicals (·OH), superoxide radicals and other active oxygen species, and then TMAH undergoes wet oxidation reaction with active oxygen at a certain reaction temperature and reaction pressure, and is decomposed into organic amine intermediates, which are further degraded into CO2, H2O and NH3. The intermediate product NH3 generated in the TMAH degradation is adsorbed onto the surface of PAC, activated by the active oxygen species on the surface of PAC, and then the intermediate species produced are subjected to surface catalytic oxidation reaction with the active oxygen species, and finally N2 is generated.

[0022]

[0023]

[0024]

[0025] NH3 + O· → NH· + H2O

[0026] NH· + O· → HNO·

[0027] NH· + HNO· → N2 + H2O

[0028] Further, the wet oxidation reactor inlet is provided with a set of heat exchangers, and the high-temperature oxidation liquid after wet oxidation treatment is used as a heat source to heat and raise the temperature of the waste liquid before oxidation.

[0029] The application also provides a system for implementing the wet oxidation treatment method of the TMAH waste liquid, which comprises a waste liquid tank, a waste liquid conveying pump, a low-pressure heat exchanger, a high-pressure pump, a multi-stage high-pressure heat exchanger, a heat conducting oil heat exchanger and a wet oxidation reactor connected in sequence, and the wet oxidation reactor is connected with a hydrogen peroxide storage tank.

[0030] The TMAH waste liquid to be treated and the powdered activated carbon are simultaneously added into the waste liquid tank, and after stirring and mixing, the waste liquid is conveyed to the low-pressure heat exchanger by the waste liquid conveying pump, and after heating by the low-pressure heat exchanger, the temperature of the waste liquid is raised to 50-70 DEG C, and then the waste liquid is conveyed to the multi-stage high-pressure heat exchanger by the high-pressure pump, and after heat exchange, the temperature of the waste liquid is raised to 210-230 DEG C, and then the waste liquid is further heated to 255-265 DEG C by the heat conducting oil heat exchanger, and then the waste liquid is introduced into the wet oxidation reactor to react with H2O2 from the hydrogen peroxide storage tank, and the high-temperature oxidation liquid after treatment of the wet oxidation reactor is sequentially introduced into the multi-stage high-pressure heat exchanger and the low-pressure heat exchanger to exchange heat with the waste liquid to be treated, so that heat recovery is realized.

[0031] Further, the low-pressure heat exchanger and the multi-stage high-pressure heat exchanger are further provided with an automatic pressure reducing valve and a gas-liquid separator, after heat exchange with the waste liquid to be treated in the multi-stage high-pressure heat exchanger, the high-temperature oxidation liquid is reduced in pressure to 0.4-0.6 MPa by the automatic pressure reducing valve, and then separated by the gas-liquid separator, and the pressure is reduced to normal pressure, and the tail gas is discharged from the top of the gas-liquid separator, and the oxidation liquid in the lower part of the gas-liquid separator is conveyed to the low-pressure heat exchanger by an oxidation liquid conveying pump to exchange heat, and the oxidation liquid containing the powdered activated carbon discharged from the low-pressure heat exchanger is introduced into an activated carbon recovery device for recovery.

[0032] Further, the multi-stage high-pressure heat exchanger comprises two or more heat exchangers connected in series.

[0033] Compared with the prior art, the application has the following beneficial effects:

[0034] (1) PAC is first added into the TMAH waste liquid, and stirred and reacted for more than 60 min, and the high-concentration hydroxyl (OH -surface modification of PAC, OH - The pore wall of the activated carbon can be corroded, the impurities in the pores can be removed, the specific surface area and pore area of the activated carbon can be increased, and the affinity of the activated carbon to O2 and NH3 can be increased after the modification. - The affinity of the modified activated carbon to O2 and NH3 can be increased.

[0035] (2) The TMAH waste liquid after the reaction with the PAC is transported into a wet oxidation reactor, and H2O2 liquid medicine is also added into the wet oxidation reactor, the temperature of the wet oxidation reaction is controlled to be 255-265°C, the reaction pressure is controlled to be 5.5-6.5 MPa, and the reaction time is controlled to be 90-120 min. Under the reaction conditions, the TOC removal rate of the wet oxidation to the TMAH waste liquid is 82%-86.1%, and the TN removal rate is 75.0%-80.3%. Most of the TMAH in the waste liquid is removed and decomposed, and the main reaction products are CO2, H2O and N2.

[0036] (3) In the wet oxidation treatment, the oxidation heat of the TMAH waste liquid itself is preferably used to maintain the reaction temperature, and the specific method is that a set of heat exchangers are arranged at the inlet of the wet oxidation reactor, and the high-temperature oxidation liquid after the wet oxidation treatment is used as a heat source to heat and warm the waste liquid before the oxidation. The higher the concentration of the organic matter in the waste liquid, the higher the oxidation reaction heat generated. The insufficient heat can be supplemented by the external high-temperature heat-conducting oil.

[0037] When the concentration of TMAH in the waste liquid is low, such as less than 12000 mg / L, in order to fully utilize the oxidation heat of the waste liquid itself to maintain the reaction temperature and save the energy consumption of using external heat medium, the TMAH waste liquid can be concentrated before the wet oxidation treatment, and the concentration of TMAH in the waste liquid is concentrated to more than 20000 mg / L. Other high-concentration organic waste liquids (such as stripping liquid waste liquid) discharged by the liquid crystal panel factory can also be introduced to combine with the TMAH waste liquid for wet oxidation treatment, so as to realize efficient treatment of multiple high-concentration organic waste liquids.

[0038] (4) Considering the potential for combustion and explosion accidents in high-pressure oxygen compressors during practical engineering applications, this invention uses H2O2 as the oxidant in the wet oxidation process of TMAH waste liquid. The role of H2O2 in the wet oxidation reaction is to decompose and generate O2, providing the active oxygen required for TMAH decomposition and NH3 oxidation. Simultaneously, the synergistic effect of PAC improves the decomposition efficiency of H2O2 and the oxidation efficiency of O2, as well as the selectivity of NH3 to N2 conversion. PAC has high porosity and specific surface area, providing a large number of reaction micro-interfaces within the wet oxidation reactor, allowing TMAH and active oxygen to react rapidly within its abundant pore channels. Furthermore, the PAC surface has abundant oxygen-containing groups, which adsorb the intermediate product NH3 from TMAH degradation, significantly improving the selectivity of the conversion of the intermediate product NH3 to the final product N2 during the wet oxidation process. Attached Figure Description

[0039] Figure 1 This is a diagram of the wet oxidation treatment system for TMAH waste liquid of the present invention.

[0040] The diagram is labeled as follows: 1-Waste liquid tank; 2-Waste liquid transfer pump; 3-Low-pressure heat exchanger; 4-High-pressure pump; 5-First-stage high-pressure heat exchanger; 6-Second-stage high-pressure heat exchanger; 7-Heat transfer oil heat exchanger; 8-Wet oxidation reactor; 9-Pressure reducing valve; 10-Gas-liquid separator; 11-Oxidation liquid transfer pump; 12-Activated carbon recovery device; 13-Hydrogen peroxide storage tank; 14-Hydrogen peroxide dosing pump. Detailed Implementation

[0041] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0042] Example

[0043] The flowchart of the wet oxidation unit for treating TMAH waste liquid is as follows: Figure 1 As shown, the system includes a waste liquid tank 1, a waste liquid transfer pump 2, a low-pressure heat exchanger 3, a high-pressure pump 4, and a multi-stage high-pressure heat exchanger (in this embodiment, a two-stage series high-pressure heat exchanger: a primary high-pressure heat exchanger 5 and a secondary high-pressure heat exchanger 6), a heat transfer oil heat exchanger 7, and a wet oxidation reactor 8, connected in sequence. The wet oxidation reactor 8 is connected to a hydrogen peroxide storage tank 13, and a hydrogen peroxide dosing pump 14 is installed on the connecting pipeline. An automatic pressure reducing valve 9 and a gas-liquid separator 10 are also provided between the low-pressure heat exchanger 3 and the multi-stage high-pressure heat exchanger. The material outlet of the wet oxidation reactor 8 returns to the secondary high-pressure heat exchanger 6, the primary high-pressure heat exchanger 5, the automatic pressure reducing valve 9, the gas-liquid separator 10, and the activated carbon recovery device 12 in sequence through pipelines.

[0044] The method for treating TMAH waste liquid using the above system includes the following steps:

[0045] 1. TMAH waste liquid enters waste liquid tank 1, and powdered activated carbon (PAC) is added to the tank simultaneously. A stirrer is installed inside the tank to ensure thorough contact between the PAC and the waste liquid, with a stirring time of no less than 60 minutes. The purpose of this process is to utilize the high concentration of hydroxide ions (OH-) in the TMAH waste liquid. - ), surface modification of PAC. OH - It can corrode the pore walls of activated carbon, remove impurities from the pores, and increase the specific surface area and pore area of ​​the activated carbon. In a wet oxidation reactor, it can provide a large number of reaction micro-interfaces, allowing TMAH and active oxygen to react rapidly within its abundant pore channels. Moreover, activated carbon can be corroded by OH... - After modification, it can increase the affinity for O2 and NH3 in the liquid phase.

[0046] 2. The mixture in waste liquid tank 1 is transported to low-pressure heat exchanger 3 by waste liquid transfer pump 2. The pump pressure is 0.25-0.3 MPa, and in this embodiment, it is 0.3 MPa. Inside low-pressure heat exchanger 3, the oxidized liquid separated by gas-liquid separator 10 is used as the heat medium to heat the waste liquid. Low-pressure heat exchanger 3 is a shell-and-tube heat exchanger, which can be used as a single unit or multiple units in series. The heat exchanger material is 304 stainless steel. In this embodiment, a single unit is used. The cold waste liquid flows through the tube side of low-pressure heat exchanger 3, entering from the top and exiting from the outlet on the other side of the top of low-pressure heat exchanger 3 after heat exchange. The hot oxidized liquid flows through the shell side, entering from the bottom and exiting from the outlet on the upper side wall of low-pressure heat exchanger 3 after heat exchange. After being heated by the low-pressure heat exchanger 3, the temperature of the cold material waste liquid increases from 20-25℃ to 50-70℃, while the temperature of the hot material oxidation liquid decreases from 85-95℃ to 40-50℃.

[0047] 3. After being heated by the low-pressure heat exchanger 3, the waste liquid is transported by the high-pressure pump 4 to the series-connected first-stage high-pressure heat exchanger 5 and second-stage high-pressure heat exchanger 6. The high-pressure pump delivers pressures of 5.5–6.5 MPa. Inside the high-pressure heat exchanger, the high-pressure oxidizing liquid flowing from the wet oxidation reactor 8 is used as the heat medium to further heat the waste liquid. The high-pressure heat exchanger is a shell-and-tube heat exchanger. In this embodiment, two units are designed in series, but three or more units can also be designed in series. The heat exchanger material is 2205 duplex steel or titanium; in this embodiment, 2205 duplex steel is used. In this embodiment, the cold waste liquid flows through the tube side, entering the heat exchanger from the top and exiting from the outlet on the other side of the top of the heat exchanger after heat exchange. The hot oxidizing liquid flows through the shell side, entering the low-pressure heat exchanger from the bottom and exiting from the outlet on the upper side wall of the heat exchanger after heat exchange. After being heated by the first-stage high-pressure heat exchanger 5 and the second-stage high-pressure heat exchanger 6, the temperature of the cold material waste liquid increases from 50-70℃ to 210-230℃, while the temperature of the hot material oxidation liquid decreases from 255-265℃ to 110-120℃.

[0048] 4、The waste liquid is heated by the high-pressure heat exchanger, and then enters the heat conduction oil heat exchanger 7 for further heating. The heat conduction oil is used as a heat medium to heat the waste liquid. The heat conduction oil heat exchanger is a shell-and-tube heat exchanger. In this embodiment, the cold material waste liquid flows through the tube side and enters the heat exchanger from the top. After heat exchange, the waste liquid flows out from the other side of the top of the heat exchanger. The heat medium heat conduction oil flows through the shell side and enters the low-pressure heat exchanger from the bottom. After heat exchange, the heat conduction oil flows out from the upper outlet of the side wall of the heat exchanger. The material of the tube side of the heat conduction oil heat exchanger 7 is 2205 duplex steel or titanium, and in this embodiment, it is 2205 duplex steel. The material of the shell side is carbon steel. After heating by the heat conduction oil heat exchanger 7, the temperature of the waste liquid increases from 210-230°C to 255-265°C. The heat conduction oil is heated in a cycle, and an external electric heating heat conduction oil furnace can be used to provide heat.

[0049] 5、The waste liquid is heated by the high-pressure heat exchanger, and then enters the heat conduction oil heat exchanger 7 for further heating. The heat conduction oil is used as a heat medium to heat the waste liquid. The heat conduction oil heat exchanger is a shell-and-tube heat exchanger. In this embodiment, the cold material waste liquid flows through the tube side and enters the heat exchanger from the top. After heat exchange, the waste liquid flows out from the other side of the top of the heat exchanger. The heat medium heat conduction oil flows through the shell side and enters the low-pressure heat exchanger from the bottom. After heat exchange, the heat conduction oil flows out from the upper outlet of the side wall of the heat exchanger. The material of the tube side of the heat conduction oil heat exchanger 7 is 2205 duplex steel or titanium, and in this embodiment, it is 2205 duplex steel. The material of the shell side is carbon steel. After heating by the heat conduction oil heat exchanger 7, the temperature of the waste liquid increases from 210-230°C to 255-265°C. The heat conduction oil is heated in a cycle, and an external electric heating heat conduction oil furnace can be used to provide heat.

[0050] In the wet oxidation reactor 8, the reaction temperature is controlled at 255-265°C, the reaction pressure is 5.5-6.5 MPa, and the reaction time is 90-120 min. The H2O2 entering the wet oxidation reactor 8 is rapidly decomposed into O2, hydroxyl radicals (·OH), superoxide radicals, and other active oxygen species. The TMAH in the waste liquid is oxidized and removed, and a large amount of oxidation heat is generated. In the case of using H2O2 as an oxidizing agent, the main products of TMAH decomposition are CO2, H2O, and N2, and the concentration of ammonia nitrogen or nitric acid nitrogen generated is low.

[0051] The wet oxidation reactor is a vertical cylinder reactor, which can be a single reactor or two or more reactors in series. The material of the reactor is 2205 duplex steel or titanium, and in this embodiment, it is a single reactor of 2205 duplex steel. The top of the wet oxidation reactor is equipped with a burst membrane and a safety valve, and is provided with online monitoring instruments such as a thermometer and a pressure sensor.

[0052] 6、The high-temperature oxidation liquid treated by the wet oxidation reactor flows into the secondary high-pressure heat exchanger 6 and the primary high-pressure heat exchanger 5 in sequence, and exchanges heat with the waste liquid to be treated in the high-pressure heat exchanger to realize heat recovery.

[0053] 7、The oxidation liquid flowing out of the primary high-pressure heat exchanger 5 has a pressure of 5.2-6.2 MPa, which is reduced to 0.4-0.6 MPa by using an automatic pressure reducing valve 9.

[0054] 8. The oxidized liquid after pressure reduction enters a gas-liquid separator 10. In the gas-liquid separator, the pressure of the oxidized liquid is reduced to normal pressure, and tail gas generated is discharged from the top of the gas-liquid separator, transported through a pipeline to an external tail gas cooling tower and tail gas purification device for treatment and discharge. The oxidized liquid at the lower part of the gas-liquid separator is transported to the low-pressure heat exchanger 3 through an oxidized liquid transport pump 11 to exchange heat with the waste liquid to be treated, so as to realize waste heat recovery.

[0055] 9. The oxidized liquid flowing out of the low-pressure heat exchanger contains PAC, and an activated carbon recovery device 12 is arranged to recover the PAC. In the embodiment, the activated carbon recovery device is a cyclone separator, which separates most of the PAC from the oxidized liquid through rotary centrifugal action. The separated liquid containing PAC flows out from the bottom of the separator and is returned to the waste liquid tank for repeated use. The separated oxidized liquid flows out from the top of the separator and is discharged into a factory waste water station to be combined with other waste water for further treatment. The recovery rate of the activated carbon recovery device is about 60% to 80%, and fresh PAC can be supplemented in the waste liquid tank to maintain the PAC concentration in the waste liquid at 500 to 1000 mg / L.

[0056] The TMAH waste liquid discharged from a liquid crystal panel factory is taken as the treatment object to illustrate the treatment effect of the embodiment. The pH value of the TMAH waste liquid to be treated is 13.19, and the TOC and TN concentrations are 11280 mg / L and 3180 mg / L respectively. The treatment condition parameters and the oxidized liquid water quality data of the embodiment are shown in Table 2.

[0057] As can be seen from the data of conditions 1 to 7 in Table 2, the TOC removal rate is 82.0% to 86.1% and the TN removal rate is 74.7% to 80.3% when the TMAH waste liquid is treated by the wet oxidation method of the embodiment.

[0058] Air is taken as the oxidant for the comparative example, i.e. air is input as the oxidant in the feed pipeline of the wet oxidation reactor 8, the reaction temperature is 260°C, the reaction pressure is 6.0 MPa, no powdered activated carbon is added, and the other conditions are the same as in the embodiment. When the reaction time is 60 min, 90 min and 120 min respectively, the oxidized liquid water quality is shown in Table 1.

[0059] Table 1 Oxidized liquid water quality after wet oxidation treatment of TMAH waste liquid

[0060]

[0061] As can be seen from the data in Table 1, the TOC and TN concentrations of the oxidized liquid gradually decrease with the increase of the wet oxidation reaction time. After 120 min of wet oxidation reaction, the TOC removal rate is 81.1% and the TN removal rate is 41.2%, and the reaction products mainly include CO2, H2O, NH4 + and NO3 -Although the wet oxidation method has a high removal rate of TOC, the organic nitrogen in the waste liquid is not mostly converted into nitrogen gas after the wet oxidation treatment, but a large amount of ammonia nitrogen and nitric acid nitrogen is generated, and the oxidation liquid still needs further denitrification treatment.

[0062] Although the increase in the TOC removal rate of the wet oxidation method of the present application is not large, the TN removal rate is greatly increased.

[0063] Moreover, after the treatment by the method of the present application, the composition of the residual total nitrogen in the oxidation liquid is mainly organic nitrogen of organic amine which is not completely oxidized and decomposed or is not sufficiently oxidized and decomposed. Taking the working condition 6 in Table 2 as an example, the ammonia nitrogen accounts for 21.2% of the total nitrogen, the nitrate nitrogen (the sum of nitrate nitrogen and nitrite nitrogen) accounts for 0.9% of the total nitrogen, and the inorganic nitrogen (the sum of ammonia nitrogen, nitrate nitrogen and nitrite nitrogen) accounts for 22.1% of the total nitrogen, indicating that the existing form of nitrogen in the oxidation liquid is mainly organic nitrogen. In the working condition III in Table 1, the ammonia nitrogen accounts for 46.8% of the total nitrogen, the nitrate nitrogen accounts for 20.4% of the total nitrogen, and the inorganic nitrogen accounts for 67.3% of the total nitrogen, indicating that the existing form of nitrogen in the oxidation liquid is mainly inorganic nitrogen. The above comparison shows that the wet oxidation treatment method of the present application can improve the selectivity of the organic nitrogen to the final product N2 during the oxidation and decomposition of TMAH, thereby reducing the treatment load for further removal of total nitrogen.

[0064] In addition, by comparing the data of the working condition 2 and the working condition 8 in Table 2 (see Table 3 for comparison data), when H2O2 is used as the oxidant for the wet oxidation treatment of the TMAH waste liquid, the addition of PAC can improve the TOC removal rate and the TN removal rate. Moreover, the addition of PAC is also helpful to improve the selectivity of the organic nitrogen to the final product N2 during the oxidation and decomposition of TMAH. This is mainly because the PAC surface has a large number of oxygen-containing groups and has adsorption capacity for the NH3 intermediate product of TMAH degradation, and on the large number of reaction micro interfaces provided by the PAC, the adsorbed NH3 is oxidized to N2 by active oxygen species.

[0065] Table 3 Comparison of wet oxidation treatment effects with and without PAC

[0066] Case 2: PAC was added Case 8: No PAC was added TOC removal rate (%) 85.1 81.1 TN removal rate (%) 81.1 69.9 NH3-N / TN in the oxidation liquid (%) 22.4 34.8％ NO in the oxidation solution x - N / TN (%) 3.1％ 2.3％ Inorganic nitrogen in oxidation liquid / TN (%) 25.5％ 37.1％

[0067] According to the data of condition 9 in Table 2, when the wet oxidation reaction is carried out at a temperature of 220℃ and a pressure of 3.6MPa, although the H2O2 as oxidant and the addition of PAC are adopted, the removal rates of TOC and TN of the TMAH waste liquid by the wet oxidation are only 52.0% and 32.7% respectively, which are far lower than the removal rates of TOC and TN of the TMAH waste liquid by the wet oxidation in the conditions 1-7 of the embodiment of the present application. It is shown that the reaction temperature and the reaction pressure have great influence on the treatment effect of the TMAH waste liquid by the wet oxidation, and the low reaction temperature is not enough to cause the oxidation and decomposition of the TMAH.

[0068] According to the data of condition 10 in Table 2, when the wet oxidation reaction is carried out at a temperature of 280℃ and a pressure of 7.2MPa, the removal rates of TOC and TN of the TMAH waste liquid reach 94.2% and 88.0% respectively, which shows that the oxidation and decomposition of the TMAH can be more thorough when the reaction temperature is higher than 260℃ and is further increased. Considering that more energy consumption is needed to maintain the reaction temperature of 280℃ and the reaction pressure of 7.2MPa, and the pressure resistance of the equipment such as the heat exchanger, the wet oxidation reactor and the conveying pipeline is higher when the reaction pressure of 7.2MPa is maintained, the present application proposes that the suitable reaction temperature and pressure for treating the TMAH waste liquid by the wet oxidation process are 255-265℃ and 5.5-6.5MPa respectively.

[0069] Table 2: Treatment effects of each reaction condition of the embodiment and the comparative example

[0070]

[0071]

[0072] It can be seen that when the TMAH waste liquid is treated by the traditional wet oxidation process, the problems of low removal rate of total nitrogen and poor selectivity of the organic nitrogen in the waste water to the final product nitrogen exist. The wet oxidation waste water treatment process is improved in the present application, the H2O2 is used as the oxidant, and the surface-modified powder activated carbon is added in the treatment material, and the improved wet oxidation process is applied to the treatment of the TMAH waste liquid, and the remarkable effects are obtained, i.e. the removal rate of total nitrogen is improved, and the selectivity of the oxidation and decomposition of the TMAH to the final product nitrogen is improved, and the treatment load of the further removal of total nitrogen of the oxidation liquid is reduced.

[0073] The present application can also be applied to the treatment of other waste water containing high concentration of organic nitrogen.

Claims

1. A method for wet oxidation treatment of TMAH waste liquid, characterized by, It comprises the following steps: (1) first add powdered activated carbon in TMAH waste liquid, stirring reaction 1~3h; the powdered activated carbon is added at a concentration of 500~1000mg / L; (2) the mixture obtained in step (1) and H2O2 are simultaneously added into a wet oxidation reactor for wet oxidation treatment, the reaction temperature of the wet oxidation reactor is 255~265℃, the reaction pressure is 5.5~6.5MPa, the reaction time is 90~120min, and the H2O2 is added at a concentration of 2~3 times the TMAH concentration in the waste liquid or 3.8~5.7 times the TOC concentration in the waste liquid.

2. The TMAH waste liquid wet oxidation treatment method according to claim 1, characterized by, The powdered activated carbon has a mesh size of 200~300.

3. The method of claim 1, wherein the TMAH waste solution is treated by the wet oxidation process. The powdered activated carbon has an iodine value of not less than 800mg / g.

4. The TMAH waste liquid wet oxidation treatment method according to claim 3, characterized by, The powdered activated carbon has an iodine value of not less than 1000mg / g.

5. The method of claim 1, wherein the TMAH waste solution is treated by the wet oxidation process. The wet oxidation reactor inlet is provided with a set of heat exchangers, and the high-temperature oxidation liquid after wet oxidation treatment is used as a heat source to heat and warm the waste liquid before oxidation.

6. A system for carrying out the wet oxidation treatment method of TMAH waste liquid according to any one of claims 1 to 5, characterized by, It comprises a waste liquid tank (1), a waste liquid conveying pump (2), a low-pressure heat exchanger (3), a high-pressure pump (4), a multi-stage high-pressure heat exchanger, a heat conducting oil heat exchanger (7), and a wet oxidation reactor (8) connected in sequence, and the wet oxidation reactor (8) is connected with a hydrogen peroxide storage tank (13). The TMAH waste liquid to be treated and the powdered activated carbon are simultaneously added into the waste liquid tank (1), stirred and mixed, then conveyed to the low-pressure heat exchanger (3) by the waste liquid conveying pump (2), heated by the low-pressure heat exchanger (3), and the waste liquid temperature is raised to 50~70℃, then conveyed to the multi-stage high-pressure heat exchanger by the high-pressure pump (4), and the waste liquid temperature is raised to 210~230℃ after heat exchange, further heated to 255~265℃ by the heat conducting oil heat exchanger (7), then enters the wet oxidation reactor (8) and reacts with H2O2 from the hydrogen peroxide storage tank, and the high-temperature oxidation liquid after treatment of the wet oxidation reactor (8) flows into the multi-stage high-pressure heat exchanger and the low-pressure heat exchanger (3) in sequence, and exchanges heat with the waste liquid to be treated to realize heat recovery.

7. The system of claim 6, wherein, The low-pressure heat exchanger (3) and the multi-stage high-pressure heat exchanger are further provided with an automatic pressure reducing valve (9) and a gas-liquid separator (10), the high-temperature oxidation liquid exchanges heat with the waste liquid to be treated in the multi-stage high-pressure heat exchanger, then its pressure is reduced to 0.4~0.6MPa by the automatic pressure reducing valve (9), then separated by the gas-liquid separator (10), the pressure is reduced to normal pressure, the tail gas flows out from the top of the gas-liquid separator (10), and the oxidation liquid in the lower part of the gas-liquid separator (10) is conveyed to the low-pressure heat exchanger (3) by the oxidation liquid conveying pump (11) for heat exchange, and the oxidation liquid containing powdered activated carbon flowing out of the low-pressure heat exchanger (3) enters the activated carbon recovery device (12) for recovery.

8. The system of claim 6, wherein, The multi-stage high-pressure heat exchanger comprises two or more heat exchangers connected in series.

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