Preparation method of supported catalytic filler and application thereof in waste acid concentration

Abstract

The application discloses a preparation method of a supported catalytic filler and application of the supported catalytic filler in waste acid concentration, and the supported catalytic filler takes silicon carbide as a carrier, takes ruthenium, iridium and iron metals as active components, and takes cyclodextrin as a modifier, and has the characteristics of high rectification efficiency, high organic matter decomposition efficiency, corrosion resistance and low density. In combination with the waste acid concentration method, the content of sulfuric acid and nitrobenzene substances in stripping waste water and sulfuric acid concentration waste water can be effectively reduced, a waste water treatment process is simplified, and the application has the advantages of good separation effect and simple treatment process.

Description

Technical Field

[0001] This invention belongs to the field of chemical waste acid treatment technology, specifically relating to a method for preparing a supported catalytic packing and its application in waste acid concentration. Background Technology

[0002] Toluene and nitric acid feedstocks are catalytically reacted with concentrated sulfuric acid to produce dinitrotoluene (DNT) and water. A large amount of waste dilute sulfuric acid is generated during the production process. The nitrated waste acid can be reused after removing impurities and concentrating. The nitrated waste acid contains impurities such as mononitrotoluene, dinitrotoluene, trinitrotoluene, nitric acid, nitrous acid, and nitrogen oxides. Among them, nitrobenzene substances have nitro groups with strong electrophilic groups, are chemically stable, and have poor biochemical properties, are difficult to degrade, and have high biological toxicity.

[0003] In industry, a common method for recycling dinitrotoluene nitration waste acid is steam stripping combined with sulfuric acid concentration. Patent CN102648152B uses direct steam to strip the nitration waste acid to remove nitric acid and nitrobenzene compounds. After vapor-phase condensation in the stripping tower, organic matter and wastewater are separated. The stripped waste acid is then introduced into a vacuum boiler for sulfuric acid concentration to obtain concentrated sulfuric acid. Due to limitations in packed distillation efficiency and sulfuric acid entrainment in the steam, both the stripping wastewater and the concentrated sulfuric acid wastewater contain a certain amount of sulfuric acid, leading to sulfuric acid loss. Furthermore, the toxic nitrobenzene compounds in the stripping wastewater and concentrated sulfuric acid wastewater require wastewater treatment before discharge. Patent CN1285514C mixes alkaline and acidic wastewater from dinitrotoluene washing with concentrated sulfuric acid wastewater and uses toluene extraction to recover nitrobenzene compounds from the wastewater. However, this method suffers from complex wastewater treatment processes, increased toluene impurities, and the risk of emulsification during extraction.

[0004] Therefore, existing methods for treating dinitrotoluene nitration waste acid still have significant limitations, including low distillation efficiency and complex processing procedures. Developing a method for treating dinitrotoluene nitration waste acid that offers good separation and a simple processing technology has become an urgent problem to be solved in the industry. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method for preparing supported catalytic packing and its application in waste acid concentration. The catalytic packing has the characteristics of high distillation efficiency, high organic matter decomposition efficiency, corrosion resistance, and low density. Combined with the waste acid concentration method of the present invention, it can effectively reduce the content of sulfuric acid and nitrobenzene substances in wastewater, simplify the wastewater treatment process, and has the advantages of good separation effect and simple treatment process.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a supported catalytic packing material includes the following steps:

[0008] 1) Carrier pretreatment: Grind the carrier into 100-200 mesh powder, put it into a muffle furnace, and calcine it in a nitrogen atmosphere at 900-1300℃ for 8-12 hours.

[0009] 2) Impregnation: Active component A, active component B, active component C, and pore-forming agent are added to the solvent and mixed to obtain the impregnation solution;

[0010] Add the carrier obtained in step 1) to the impregnation solution, adjust the pH to 7-9 with alkaline solution, impregnate for 8-12 hours, wash with ethanol and dry.

[0011] 3) Hydrothermal treatment: The impregnated carrier obtained in step 2) is mixed with a cyclodextrin aqueous solution and heated in a high-pressure hydrothermal reactor at 110-200℃ for 5-8 hours. The solid is separated and washed with ethanol.

[0012] 4) Molding: After hydrothermal treatment in step 4), the carrier and binder are stirred evenly to form a paste. The paste is added into a mold and extruded into a loose packing. After drying, it is placed in a muffle furnace and calcined in a nitrogen atmosphere at 800-1000℃ for 8-12 hours. It is then washed with ethanol and dried to constant weight to obtain the supported catalytic packing.

[0013] Preferably, the carrier in step 1) is silicon carbide and one or more of silicon powder, carbon powder, titanium dioxide, silicon dioxide, kaolin, and activated carbon, preferably, the proportion of silicon carbide is not less than 90 wt%.

[0014] Preferably, the active component A in step 2) is one or more of ruthenium trichloride, ruthenium acetylacetonate, or potassium ruthenate, and the amount of active component A added is 0.1% to 5% of the carrier mass;

[0015] Preferably, active component B is one or more of iridium chloroiridic acid, iridium chloride, iridium acetate, sodium iridium chloroiridate, ammonium iridium chloroiridate, potassium iridium chloroiridate, and iridium acetylacetonate, and the amount of active component B added is 0.1% to 5% of the carrier mass;

[0016] Preferably, the active component C is one or more of ferrous sulfate, ferrous acetate, ferrous nitrate, and ferrous chloride, and the amount of active component C added is 0.1% to 10% of the carrier mass;

[0017] Preferably, the porogen is one or more of polyquaternium-10, octadecyl diethanolamine and polyvinyl alcohol, and the amount of porogen added is 1 to 20% of the carrier mass;

[0018] Preferably, the solvent is one or more of water, methanol, ethanol, acetone, ethyl acetate, and chloroform, and the amount of solvent added is 100-300% of the carrier mass.

[0019] Preferably, the cyclodextrin in step 3) is one or more of α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin, and the amount of cyclodextrin added is 1 to 5% of the carrier mass;

[0020] Preferably, the adhesive in step 4) is one or more of polyvinyl butyral, polyvinyl alcohol, polyethylene glycol, and polyacrylate, and the amount of adhesive added is 5 to 10% of the carrier mass.

[0021] Preferably, the type of random packing in step 4) is one of Raschig rings, Pall rings, stepped rings, rectangular saddle rings, heterosaddle rings, conjugate rings, or cross septum rings, with a diameter of 6-80 mm and a thickness of 2-9 mm.

[0022] This invention also relates to the application of the above-mentioned supported catalytic packing in waste acid concentration.

[0023] A method for concentrating waste acid includes the following steps:

[0024] 1) Stripping: The waste acid from the production of dinitrotoluene is fed into flash tank D1. The liquid phase from flash tank D1 enters the packing above stripping tower C1. The gas phase from flash tank D1 mixes with the gas phase from the top of tower C1 and is then condensed by stripping tower condenser E1. The condensed liquid phase is discharged as stripping wastewater. The bottom of tower C1 is stripped with direct steam. The liquid phase flowing out from the bottom of tower C1 is heated by stripping tower boiler D2. The gas phase evaporated by D2 is returned to the bottom of tower C1. The remaining liquid phase after being heated by stripping tower boiler D2 enters buffer tank D3.

[0025] 2) Primary sulfuric acid concentration: Waste acid from buffer tank D3 is stripped and pumped into primary sulfuric acid concentration boiler D4 by waste acid pump P1 for heating. The gas phase from D4 enters primary sulfuric acid collection tower C2. The circulating pump P2 of primary sulfuric acid collection tower returns part of the bottom liquid to the top of the tower for sulfuric acid collection, and the other part returns to buffer tank D3. The gas phase at the top of tower C2 is condensed by primary sulfuric acid collection tower condenser E2. The condensed liquid phase is discharged as sulfuric acid concentration wastewater.

[0026] 3) Secondary sulfuric acid concentration: Waste acid from the primary sulfuric acid concentration boiler D4 overflows to the secondary sulfuric acid concentration boiler D5 for heating. The gas phase from D5 enters the secondary sulfuric acid collection tower C3. The secondary sulfuric acid collection tower circulation pump P3 returns part of the bottom liquid to the top of the tower for sulfuric acid collection, and the other part returns to the buffer tank D3. The gas phase at the top of the C3 tower is condensed by the secondary sulfuric acid collection tower condenser E3. The condensed liquid phase is discharged as sulfuric acid concentration wastewater. Concentrated sulfuric acid is obtained from the outlet of the secondary sulfuric acid concentration boiler D5.

[0027] In this invention, the waste acid from the production of dinitrotoluene refers to the waste acid generated during the catalytic reaction of toluene and nitric acid with concentrated sulfuric acid to produce dinitrotoluene.

[0028] Preferably, the C1 theoretical plate number of the stripping tower in step 1) is 10-25, and a demister is installed at the top of the tower.

[0029] Preferably, the temperature of the stripping tower condenser E1 after condensation is 10-70℃.

[0030] Preferably, the direct steam pressure is 2-9 barG, and the direct steam flow rate is 0.05-0.2 times the flow rate of waste acid from the production of dinitrotoluene.

[0031] Preferably, the heating temperature of the stripping tower boiler D2 is 180-190℃ and the pressure is 20-40kPaA.

[0032] Preferably, the number of theoretical plates C2 in the primary sulfuric acid collection tower described in step 2) is 5 to 15, and a demister is installed at the top of the tower.

[0033] Preferably, the temperature after condensation in the primary sulfuric acid collection tower condenser E2 is 10-70℃.

[0034] Preferably, the flow rate of the liquid returned to the top of the column from the bottom is 0.1-0.5 times the flow rate of the waste acid from the production of dinitrotoluene.

[0035] Preferably, the heating temperature of the primary sulfuric acid concentration boiler D4 is 180-190℃, and the pressure is 1-10kPaA.

[0036] Preferably, the number of theoretical plates (C3) in the secondary sulfuric acid collection tower described in step 3) is 5 to 15, and a demister is installed at the top of the tower.

[0037] Preferably, the temperature of the condenser E3 in the secondary sulfuric acid collection tower after condensation is 10-70℃.

[0038] Preferably, the flow rate of the liquid returned to the top of the column from the bottom is 0.1-0.5 times the flow rate of the waste acid from the production of dinitrotoluene.

[0039] Preferably, the heating temperature of the secondary sulfuric acid concentration boiler D5 is 170-180℃, and the pressure is 1-10kPaA.

[0040] Preferably, the packing material for the stripping tower C1, the primary sulfuric acid collection tower C2, and the secondary sulfuric acid collection tower C3 is the supported catalytic packing material described above.

[0041] This invention utilizes a catalytic packing material prepared with ruthenium, iridium, and iron metals as active components and modified with cyclodextrin. On one hand, it features high distillation efficiency, corrosion resistance, and low density, improving the separation efficiency of sulfuric acid from water, nitrobenzenes, and nitrogen oxides, and reducing the amount of sulfuric acid entrained in stripping wastewater and concentrated sulfuric acid wastewater. On the other hand, the hydrophobic ends of the cyclodextrin on the packing surface facilitate the adsorption and enrichment of nitrobenzenes, promoting the catalytic oxidation of nitrobenzenes by the ruthenium, iridium, and iron metal active components, decomposing them into small molecules such as CO2, formic acid, and acetic acid. This effectively reduces nitrobenzene levels in stripping wastewater and concentrated sulfuric acid wastewater, eliminating the need for a toluene extraction process for organic matter recovery, thus simplifying the wastewater treatment process. Simultaneously, cyclodextrin has a binding effect, reducing the loss of active components. Furthermore, by adding packing material to the waste acid concentration and collection tower, forced circulation of the bottom liquid to the top of the tower captures sulfuric acid entrained in the gas phase, enhancing the separation efficiency of sulfuric acid and water, and extending the reaction time for the oxidation and decomposition of organic matter, further reducing the amount of sulfuric acid and nitrobenzenes in concentrated sulfuric acid wastewater.

[0042] The significant advantages of this invention are:

[0043] 1) The catalytic packing of the present invention has the characteristics of high distillation efficiency, high organic matter decomposition efficiency, corrosion resistance and low density. It can effectively reduce the content of sulfuric acid and nitrobenzene substances in stripping wastewater and sulfuric acid concentration wastewater, eliminating the need for organic matter recovery process and simplifying the wastewater treatment process.

[0044] 2) The sulfuric acid concentration and capture tower of the present invention uses packing to force the bottom liquid of the tower to circulate and capture the sulfuric acid entrained in the gas phase, thereby enhancing the separation efficiency of sulfuric acid and water, extending the reaction time of organic matter oxidation and decomposition, and further reducing the content of sulfuric acid and nitrobenzene substances in the sulfuric acid concentration wastewater. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of a waste acid concentration method according to the present invention.

[0046] Among them, C1 is the stripping tower, C2 is the primary sulfuric acid collection tower, C3 is the secondary sulfuric acid collection tower, D1 is the flash tank, D2 is the stripping tower boiler, D3 is the buffer tank, D4 is the primary sulfuric acid concentration boiler, D5 is the secondary sulfuric acid concentration boiler, E1 is the stripping tower condenser, E2 is the primary sulfuric acid collection tower condenser, E3 is the secondary sulfuric acid collection tower condenser, P1 is the waste acid pump after stripping, P2 is the primary sulfuric acid collection tower circulation pump, and P3 is the secondary sulfuric acid collection tower circulation pump. Detailed Implementation

[0047] To further disclose, and not limit, the present invention, the invention will be further described in detail below with reference to examples.

[0048] Sources of dinitrotoluene nitration waste acid:

[0049] In the following examples and comparative examples, the dinitrotoluene waste acid was from the same batch of waste acid from the dinitrotoluene (DNT) unit of Wanhua Chemical Group Co., Ltd. The dinitrotoluene waste acid contained 73.9% sulfuric acid, 0.7% nitric acid and nitrite, and 5381 mg / L of nitrobenzene compounds (mononitrotoluene, dinitrotoluene, and trinitrotoluene). The temperature before entering the flash tank D1 was 130°C.

[0050] Methods for evaluating the corrosion resistance of catalytic packing materials:

[0051] Prepare sulfuric acid aqueous solutions with concentrations of 10wt%, 45wt%, and 80wt%, and nitric acid aqueous solutions with concentrations of 1wt%, 5wt%, and 10wt%, respectively. Soak the catalytic packing material in the different solutions at 80℃ for 30 days and measure the weight loss rate before and after. If the weight loss rate is <0.1%, it is considered that there is basically no corrosion.

[0052] Preparation of silicon carbide supported catalyst packing:

[0053] Catalytic packing material A:

[0054] 100g of silicon carbide and 5g of carbon powder were ground into 120-mesh powder and placed in a muffle furnace, where they were calcined at 1100℃ under a nitrogen atmosphere for 9 hours. 3g of ruthenium trichloride, 2g of chloroiridium acid, 5g of ferrous sulfate, and 10g of polyquaternium-10 were added to 200g of methanol, and the mixture was used to obtain an impregnation solution. The calcined support was added to the impregnation solution, and the pH was adjusted to 8 with 10% NaOH solution. The solution was impregnated for 10 hours, washed with ethanol, and dried. The impregnated support was mixed with 30g of 10% γ-cyclodextrin aqueous solution and heated in a high-pressure hydrothermal autoclave at 170℃ for 7 hours. The solid was separated and washed with ethanol. After hydrothermal treatment, the carrier is stirred with 6g of polyvinyl butyral to form a paste. The paste is then added to a mold and extruded into Pall rings with a diameter of 25mm and a thickness of 4mm. After drying, the Pall rings are placed in a muffle furnace and calcined in a nitrogen atmosphere at 1000℃ for 10 hours. After washing with ethanol, the Pall rings are dried to constant weight to obtain catalytic packing A.

[0055] Catalytic packing material A has a density of 2.59 g / cm³. 3 According to the corrosion resistance assessment, the weight loss rate is <0.1%, indicating that there is basically no corrosion.

[0056] Catalytic packing material B:

[0057] 100g of silicon carbide and 5g of titanium dioxide were ground into 120-mesh powder and placed in a muffle furnace, where they were calcined at 1100℃ under a nitrogen atmosphere for 10 hours. 3g of ruthenium acetylacetonate, 2g of iridium chloride, 5g of ferrous acetate, and 10g of polyquaternium-10 were added to 200g of methanol, and the mixture was used to obtain an impregnation solution. The calcined support was added to the impregnation solution, and the pH was adjusted to 8 with 10% NaOH solution. The mixture was impregnated for 10 hours, washed with ethanol, and dried. The impregnated support was then mixed with 30g of 10% α-cyclodextrin and heated in a high-pressure hydrothermal autoclave at 170℃ for 8 hours. The solid was separated and washed with ethanol. After hydrothermal treatment, the carrier was stirred with 6g of polyvinyl butyral to form a paste. The paste was then added to a mold and extruded into Pall rings with a diameter of 25mm and a thickness of 4mm. After drying, the Pall rings were placed in a muffle furnace and calcined at 1000℃ in a nitrogen atmosphere for 10 hours. The mixture was then washed with ethanol and dried to constant weight to obtain catalytic packing B.

[0058] Catalytic packing material B has a density of 2.61 g / cm³. 3 According to the corrosion resistance assessment, the weight loss rate is <0.1%, indicating that there is basically no corrosion.

[0059] Catalytic packing material C:

[0060] 100g of silicon carbide and 8g of silicon dioxide were ground into 120-mesh powder and placed in a muffle furnace, where they were calcined at 1100℃ under a nitrogen atmosphere for 9 hours. 0.2g of potassium ruthenium chloride, 0.15g of iridium chloride, 0.2g of ferrous sulfate, and 10g of polyquaternium-10 were added to 200g of methanol and mixed to obtain an impregnation solution. The calcined carrier was added to the impregnation solution, and the pH was adjusted to 7 with 10% NaOH solution. The mixture was impregnated for 10 hours, washed with ethanol, and dried. The impregnated carrier was mixed with 15g of 10% γ-cyclodextrin and heated in a high-pressure hydrothermal autoclave at 120℃ for 7 hours. The solid was separated and washed with ethanol. After hydrothermal treatment, the carrier was stirred with 6g of polyvinyl alcohol to form a paste. The paste was then added to a mold and extruded into Raschig rings with a diameter of 50mm and a thickness of 5mm. After drying, the Raschig rings were placed in a muffle furnace and calcined in a nitrogen atmosphere at 1000℃ for 10 hours. After washing with ethanol, the mixture was dried to constant weight to obtain the catalyst packing C.

[0061] The carbon density of the catalytic packing material is 2.49 g / cm³. 3 According to the corrosion resistance assessment, the weight loss rate is <0.1%, indicating that there is basically no corrosion.

[0062] Catalytic packing material D:

[0063] 100g of silicon carbide and 8g of titanium dioxide were ground into 120-mesh powder and placed in a muffle furnace, where they were calcined for 9 hours at 1000℃ under a nitrogen atmosphere. 5g of ruthenium trichloride, 4g of chloroiridium acid, 8g of ferrous chloride, and 10g of polyquaternium-10 were added to 200g of methanol, and the mixture was used to obtain an impregnation solution. The calcined support was added to the impregnation solution, and the pH was adjusted to 7 with 10% NaOH solution. The mixture was impregnated for 10 hours, washed with ethanol, and dried. The impregnated support was then mixed with 45g of 10% γ-cyclodextrin and heated in a high-pressure hydrothermal autoclave at 200℃ for 7 hours. The solid was separated and washed with ethanol. After hydrothermal treatment, the carrier is mixed with 6g of polyvinyl alcohol to form a paste. The paste is then added to a mold and extruded into stepped rings with a diameter of 50mm and a thickness of 5mm. After drying, the rings are placed in a muffle furnace and calcined at 900℃ in a nitrogen atmosphere for 10 hours. The rings are then washed with ethanol and dried to constant weight to obtain catalytic packing D.

[0064] The density of the catalyst packing material is 2.47 g / cm³. 3 According to the corrosion resistance assessment, the weight loss rate is <0.1%, indicating that there is basically no corrosion.

[0065] Catalytic packing material E:

[0066] 100g of silicon carbide and 10g of activated carbon powder were ground into 120-mesh powder and placed in a muffle furnace, calcined at 1100℃ under a nitrogen atmosphere for 9 hours. 2g of ruthenium trichloride, 2g of iridium acetate, 8g of ferrous sulfate, and 15g of octadecyl diethanolamine were added to 200g of methanol, and the mixture was stirred to obtain an impregnation solution. The calcined carrier was added to the impregnation solution, the pH was adjusted to 9 with 10% NaOH solution, and the mixture was impregnated for 12 hours. The carrier was then washed with ethanol and dried. The impregnated carrier was mixed with 45g of 10% α-cyclodextrin and heated in a high-pressure hydrothermal autoclave at 200℃ for 7 hours. The solid was separated and washed with ethanol. After hydrothermal treatment, the carrier is stirred with 6g of polyethylene glycol to form a paste. The paste is then added to a mold and extruded into stepped rings with a diameter of 16mm and a thickness of 3mm. After drying, the rings are placed in a muffle furnace and calcined in a nitrogen atmosphere at 1000℃ for 10 hours. The rings are then washed with ethanol and dried to constant weight to obtain catalytic filler E.

[0067] The density of the catalytic packing material E is 2.68 g / cm³. 3 According to the corrosion resistance assessment, the weight loss rate is <0.1%, indicating that there is basically no corrosion.

[0068] Example 1:

[0069] The packing material for stripping tower C1, primary sulfuric acid collection tower C2, and secondary sulfuric acid collection tower C3 is catalytic packing material A.

[0070] Reference Figure 1As shown, 1000 kg / h of waste acid from the production of dinitrotoluene is fed into flash tank D1. The liquid phase from flash tank D1 enters the packing above stripper C1. The gas phase from flash tank D1 mixes with the gas phase from the top of C1 and is condensed by stripper condenser E1. The condensed liquid phase is discharged as stripping wastewater. The bottom of C1 is stripped with direct steam. The liquid phase flowing out from the bottom of C1 is heated by stripper boiler D2. The vapor phase evaporated by D2 returns to the bottom of C1. The remaining liquid phase after heating by stripper boiler D2 enters buffer tank D3. Stripper C1 has 20 theoretical plates and a demister is installed at the top. The temperature after condensation by stripper condenser E1 is 65℃. The direct steam pressure is 2 barG, the direct steam flow rate is 70 kg / h, and the heating temperature of stripper boiler D2 is 189℃ with a pressure of 28.5 kPaA.

[0071] Waste acid from buffer tank D3 is stripped and pumped by waste acid pump P1 into primary sulfuric acid concentration boiler D4 for heating. The gas phase from D4 enters primary sulfuric acid collection tower C2. The circulating pump P2 of the primary sulfuric acid collection tower returns a portion of the bottom liquid to the top of the tower for sulfuric acid collection, and the other portion returns to buffer tank D3. The gas phase at the top of tower C2 is condensed by condenser E2 of the primary sulfuric acid collection tower. The condensed liquid phase is discharged as concentrated sulfuric acid wastewater. The primary sulfuric acid collection tower C2 has a theoretical plate count of 8 and is equipped with a demister at the top. The temperature after condensation in condenser E2 is 38℃. The flow rate of the bottom liquid returning to the top of the tower is 500 kg / h. The heating temperature of the primary sulfuric acid concentration boiler D4 is 186℃, and the pressure is 9.5 kPaA.

[0072] Waste acid overflowing from the primary sulfuric acid concentration boiler D4 is heated in the secondary sulfuric acid concentration boiler D5. The gas phase from D5 enters the secondary sulfuric acid collection tower C3. The circulating pump P3 of the secondary sulfuric acid collection tower returns a portion of the bottom liquid to the top of the tower for sulfuric acid collection, and the other portion returns to the buffer tank D3. The gas phase at the top of the C3 tower is condensed in the secondary sulfuric acid collection tower condenser E3. The condensed liquid phase is discharged as sulfuric acid concentration wastewater. Concentrated sulfuric acid is obtained from the outlet of the secondary sulfuric acid concentration boiler D5. The secondary sulfuric acid collection tower C3 has a theoretical plate number of 8, and a demister is installed at the top. The condensate temperature in the secondary sulfuric acid collection tower condenser E3 is 12℃, the bottom liquid return flow rate is 500 kg / h, and the heating temperature of the secondary sulfuric acid concentration boiler D5 is 172℃, with a pressure of 2.2 kPaA.

[0073] Analysis revealed that the stripping wastewater contained 301 mg / L of sulfuric acid and 4.9 mg / L of nitrobenzene compounds, while the concentrated sulfuric acid wastewater contained 1624 mg / L of sulfuric acid and 0.5 mg / L of nitrobenzene compounds, with a concentrated sulfuric acid concentration of 93.8%.

[0074] Example 2:

[0075] The packing material for stripping tower C1, primary sulfuric acid collection tower C2, and secondary sulfuric acid collection tower C3 is catalytic packing material B.

[0076] Reference Figure 1 As shown, 1000 kg / h of waste acid from the production of dinitrotoluene is fed into flash tank D1. The liquid phase from flash tank D1 enters the packing above stripper C1. The gas phase from flash tank D1 mixes with the gas phase from the top of C1 and is condensed by stripper condenser E1. The condensed liquid phase is discharged as stripping wastewater. The bottom of C1 is stripped with direct steam. The liquid phase flowing out from the bottom of C1 is heated by stripper boiler D2. The vapor phase evaporated by D2 returns to the bottom of C1. The remaining liquid phase after heating by stripper boiler D2 enters buffer tank D3. Stripper C1 has 18 theoretical plates and a demister is installed at the top. The temperature after condensation by stripper condenser E1 is 65℃. The direct steam pressure is 2 barG, the direct steam flow rate is 70 kg / h, and the heating temperature of stripper boiler D2 is 189℃ with a pressure of 28.5 kPaA.

[0077] Waste acid from buffer tank D3 is stripped and pumped by waste acid pump P1 into primary sulfuric acid concentration boiler D4 for heating. The gas phase from D4 enters primary sulfuric acid collection tower C2. The circulating pump P2 of the primary sulfuric acid collection tower returns a portion of the bottom liquid to the top of the tower for sulfuric acid collection, and the other portion returns to buffer tank D3. The gas phase at the top of tower C2 is condensed by primary sulfuric acid collection tower condenser E2. The condensed liquid phase is discharged as sulfuric acid concentration wastewater. Primary sulfuric acid collection tower C2 has a theoretical plate count of 8, and a demister is installed at the top. The temperature after condensation in primary sulfuric acid collection tower condenser E2 is 40℃. The flow rate of the bottom liquid returning to the top of the tower is 500 kg / h. The heating temperature of primary sulfuric acid concentration boiler D4 is 187℃, and the pressure is 10 kPaA.

[0078] Waste acid overflowing from the primary sulfuric acid concentration boiler D4 is heated in the secondary sulfuric acid concentration boiler D5. The gas phase from D5 enters the secondary sulfuric acid collection tower C3. The circulating pump P3 of the secondary sulfuric acid collection tower returns a portion of the bottom liquid to the top of the tower for sulfuric acid collection, and the other portion returns to the buffer tank D3. The gas phase at the top of the C3 tower is condensed in the secondary sulfuric acid collection tower condenser E3. The condensed liquid phase is discharged as sulfuric acid concentration wastewater. Concentrated sulfuric acid is obtained from the outlet of the secondary sulfuric acid concentration boiler D5. The secondary sulfuric acid collection tower C3 has a theoretical plate number of 5, and a demister is installed at the top. The condensate temperature in the secondary sulfuric acid collection tower condenser E3 is 30℃, the bottom liquid return flow rate is 500 kg / h, and the heating temperature of the secondary sulfuric acid concentration boiler D5 is 179℃, with a pressure of 3.1 kPaA.

[0079] Analysis revealed that the stripping wastewater contained 367 mg / L of sulfuric acid and 6.3 mg / L of nitrobenzene compounds, while the concentrated sulfuric acid wastewater contained 1352 mg / L of sulfuric acid and 0.7 mg / L of nitrobenzene compounds, with a concentrated sulfuric acid concentration of 93.5%.

[0080] Example 3:

[0081] The packing material for the stripping tower C1, the primary sulfuric acid collection tower C2, and the secondary sulfuric acid collection tower C3 is catalytic packing material C.

[0082] Reference Figure 1 As shown, 1000 kg / h of waste acid from the production of dinitrotoluene is fed into flash tank D1. The liquid phase from flash tank D1 enters the packing above stripper C1. The gas phase from flash tank D1 mixes with the gas phase from the top of C1 and is condensed by stripper condenser E1. The condensed liquid phase is discharged as stripping wastewater. The bottom of C1 is stripped with direct steam. The liquid phase flowing out from the bottom of C1 is heated by stripper boiler D2. The vapor phase evaporated by D2 returns to the bottom of C1. The remaining liquid phase after heating by stripper boiler D2 enters buffer tank D3. Stripper C1 has 15 theoretical plates and a demister is installed at the top. The temperature after condensation by stripper condenser E1 is 65℃. The direct steam pressure is 4 barG, the direct steam flow rate is 50 kg / h, and the heating temperature of stripper boiler D2 is 189℃ with a pressure of 28.5 kPaA.

[0083] Waste acid from buffer tank D3 is stripped and pumped by waste acid pump P1 into primary sulfuric acid concentration boiler D4 for heating. The gas phase from D4 enters primary sulfuric acid collection tower C2. The circulating pump P2 of the primary sulfuric acid collection tower returns a portion of the bottom liquid to the top of the tower for sulfuric acid collection, and the other portion returns to buffer tank D3. The gas phase at the top of tower C2 is condensed by primary sulfuric acid collection tower condenser E2. The condensed liquid phase is discharged as sulfuric acid concentration wastewater. Primary sulfuric acid collection tower C2 has a theoretical plate count of 5 and is equipped with a demister at the top. The temperature after condensation in primary sulfuric acid collection tower condenser E2 is 30℃. The flow rate of the bottom liquid returning to the top of the tower is 100 kg / h. The heating temperature of primary sulfuric acid concentration boiler D4 is 187℃, and the pressure is 10 kPaA.

[0084] Waste acid overflowing from the primary sulfuric acid concentration boiler D4 is heated in the secondary sulfuric acid concentration boiler D5. The gas phase from D5 enters the secondary sulfuric acid collection tower C3. The circulating pump P3 of the secondary sulfuric acid collection tower returns a portion of the bottom liquid to the top of the tower for sulfuric acid collection, and the other portion returns to the buffer tank D3. The gas phase at the top of C3 is condensed in the secondary sulfuric acid collection tower condenser E3. The condensed liquid phase is discharged as sulfuric acid concentration wastewater. Concentrated sulfuric acid is obtained from the outlet of the secondary sulfuric acid concentration boiler D5. The secondary sulfuric acid collection tower C3 has a theoretical plate number of 5, and a demister is installed at the top. The condensate temperature in the secondary sulfuric acid collection tower condenser E3 is 30℃, the bottom liquid return flow rate is 100 kg / h, and the heating temperature of the secondary sulfuric acid concentration boiler D5 is 179℃, with a pressure of 3.1 kPaA.

[0085] Analysis revealed that the stripping wastewater contained 684 mg / L of sulfuric acid and 13.2 mg / L of nitrobenzene compounds. The concentrated sulfuric acid wastewater contained 1517 mg / L of sulfuric acid and 1.8 mg / L of nitrobenzene compounds. The concentration of concentrated sulfuric acid was 93.2%.

[0086] Example 4:

[0087] The packing material for stripping tower C1, primary sulfuric acid collection tower C2, and secondary sulfuric acid collection tower C3 is catalytic packing material D.

[0088] Reference Figure 1 As shown, 1000 kg / h of waste acid from the production of dinitrotoluene is fed into flash tank D1. The liquid phase from flash tank D1 enters the packing above stripper C1. The gas phase from flash tank D1 mixes with the gas phase from the top of C1 and is condensed by stripper condenser E1. The condensed liquid phase is discharged as stripping wastewater. The bottom of C1 is stripped with direct steam. The liquid phase flowing out from the bottom of C1 is heated by stripper boiler D2. The vapor phase evaporated by D2 returns to the bottom of C1. The remaining liquid phase after heating by stripper boiler D2 enters buffer tank D3. Stripper C1 has a theoretical plate count of 25, a demister is installed at the top, the temperature after condensation in stripper condenser E1 is 60℃, the direct steam pressure is 4 barG, the direct steam flow rate is 200 kg / h, and the heating temperature in stripper boiler D2 is 189℃ with a pressure of 28.5 kPaA.

[0089] Waste acid from buffer tank D3 is stripped and pumped by waste acid pump P1 into primary sulfuric acid concentration boiler D4 for heating. The gas phase from D4 enters primary sulfuric acid collection tower C2. The circulating pump P2 of the primary sulfuric acid collection tower returns a portion of the bottom liquid to the top of the tower for sulfuric acid collection, and the other portion returns to buffer tank D3. The gas phase at the top of tower C2 is condensed by condenser E2 of the primary sulfuric acid collection tower. The condensed liquid phase is discharged as concentrated sulfuric acid wastewater. The primary sulfuric acid collection tower C2 has a theoretical plate count of 15 and is equipped with a demister at the top. The temperature after condensation in condenser E2 is 38℃. The flow rate of the bottom liquid returning to the top of the tower is 400 kg / h. The heating temperature of the primary sulfuric acid concentration boiler D4 is 186℃, and the pressure is 9.5 kPaA.

[0090] Waste acid overflowing from the primary sulfuric acid concentration boiler D4 is heated in the secondary sulfuric acid concentration boiler D5. The gas phase from D5 enters the secondary sulfuric acid collection tower C3. The circulating pump P3 of the secondary sulfuric acid collection tower returns a portion of the bottom liquid to the top of the tower for sulfuric acid collection, and the other portion returns to the buffer tank D3. The gas phase at the top of C3 is condensed in the secondary sulfuric acid collection tower condenser E3. The condensed liquid phase is discharged as sulfuric acid concentration wastewater. Concentrated sulfuric acid is obtained from the outlet of the secondary sulfuric acid concentration boiler D5. The secondary sulfuric acid collection tower C3 has a theoretical plate count of 10 and is equipped with a demister at the top. The condensate temperature in the secondary sulfuric acid collection tower condenser E3 is 12℃, the bottom liquid return flow rate is 400 kg / h, and the heating temperature of the secondary sulfuric acid concentration boiler D5 is 172℃, with a pressure of 2.2 kPaA.

[0091] Analysis revealed that the stripping wastewater contained 470 mg / L of sulfuric acid and 8.5 mg / L of nitrobenzene compounds, while the concentrated sulfuric acid wastewater contained 1490 mg / L of sulfuric acid and 1.1 mg / L of nitrobenzene compounds, with a concentrated sulfuric acid concentration of 93.4%.

[0092] Example 5:

[0093] The packing material for the stripping tower C1, the primary sulfuric acid collection tower C2, and the secondary sulfuric acid collection tower C3 is catalytic packing material E.

[0094] Reference Figure 1 As shown, 1000 kg / h of waste acid from the production of dinitrotoluene is fed into flash tank D1. The liquid phase from flash tank D1 enters the packing above stripping tower C1. The gas phase from flash tank D1 mixes with the gas phase from the top of tower C1 and is then condensed in stripping tower condenser E1. The condensed liquid phase is discharged as stripping wastewater. The bottom of tower C1 is stripped with direct steam. The liquid phase flowing out from the bottom of tower C1 is heated by stripping tower boiler D2. The vapor phase evaporated in D2 returns to the bottom of tower C1. The remaining liquid phase after heating by stripping tower boiler D2 enters buffer tank D3. Stripping tower C1 has a theoretical plate count of 25, a demister is installed at the top, the temperature after condensation in stripping tower condenser E1 is 70℃, the direct steam pressure is 2 barG, the direct steam flow rate is 100 kg / h, and the heating temperature in stripping tower boiler D2 is 189℃, with a pressure of 28.5 kPaA.

[0095] Waste acid from buffer tank D3 is stripped and pumped by waste acid pump P1 into primary sulfuric acid concentration boiler D4 for heating. The gas phase from D4 enters primary sulfuric acid collection tower C2. The circulating pump P2 of the primary sulfuric acid collection tower returns a portion of the bottom liquid to the top of the tower for sulfuric acid collection, and the other portion returns to buffer tank D3. The gas phase at the top of tower C2 is condensed by primary sulfuric acid collection tower condenser E2. The condensed liquid phase is discharged as sulfuric acid concentration wastewater. Primary sulfuric acid collection tower C2 has a theoretical plate count of 8, and a demister is installed at the top. The temperature after condensation in primary sulfuric acid collection tower condenser E2 is 30℃. The flow rate of the bottom liquid returning to the top of the tower is 100 kg / h. The heating temperature of primary sulfuric acid concentration boiler D4 is 186℃, and the pressure is 9.5 kPaA.

[0096] Waste acid overflowing from the primary sulfuric acid concentration boiler D4 is heated in the secondary sulfuric acid concentration boiler D5. The gas phase from D5 enters the secondary sulfuric acid collection tower C3. The circulating pump P3 of the secondary sulfuric acid collection tower returns a portion of the bottom liquid to the top of the tower for sulfuric acid collection, and the other portion returns to the buffer tank D3. The gas phase at the top of C3 is condensed in the secondary sulfuric acid collection tower condenser E3. The condensed liquid phase is discharged as sulfuric acid concentration wastewater. Concentrated sulfuric acid is obtained from the outlet of the secondary sulfuric acid concentration boiler D5. The secondary sulfuric acid collection tower C3 has a theoretical plate count of 10 and is equipped with a demister at the top. The condensate temperature in the secondary sulfuric acid collection tower condenser E3 is 20℃, the bottom liquid return flow rate to the top of the tower is 100 kg / h, and the heating temperature of the secondary sulfuric acid concentration boiler D5 is 172℃, with a pressure of 2.2 kPaA.

[0097] Analysis revealed that the stripping wastewater contained 511 mg / L of sulfuric acid and 9.7 mg / L of nitrobenzene compounds. The concentrated sulfuric acid wastewater contained 1069 mg / L of sulfuric acid and 0.9 mg / L of nitrobenzene compounds. The concentration of concentrated sulfuric acid was 93.1%.

[0098] Comparative Example 1:

[0099] The packing material for stripping tower C1, primary sulfuric acid collection tower C2, and secondary sulfuric acid collection tower C3 is ceramic Pall rings, with a diameter of 25 mm and a thickness of 4 mm.

[0100] Reference Figure 1 As shown, 1000 kg / h of waste acid from the production of dinitrotoluene is fed into flash tank D1. The liquid phase from flash tank D1 enters the packing above stripping tower C1. The gas phase from flash tank D1 mixes with the gas phase from the top of the tower and is condensed in stripping tower condenser E1. The condensed liquid phase is discharged as stripping wastewater. The bottom of tower C1 is stripped with direct steam. The liquid phase flowing out from the bottom of tower C1 is heated by stripping tower boiler D2. The vapor phase evaporated in D2 returns to the bottom of tower C1. The remaining liquid phase after heating by stripping tower boiler D2 enters buffer tank D3. Stripping tower C1 has a theoretical plate count of 20, a demister is installed at the top, the temperature after condensation in stripping tower condenser E1 is 65℃, the direct steam pressure is 2 barG, the direct steam flow rate is 70 kg / h, and the heating temperature in stripping tower boiler D2 is 189℃, with a pressure of 28.5 kPaA.

[0101] Waste acid from buffer tank D3 is stripped and pumped by waste acid pump P1 into primary sulfuric acid concentration boiler D4 for heating. The gas phase from D4 enters primary sulfuric acid collection tower C2. The circulating pump P2 of the primary sulfuric acid collection tower returns a portion of the bottom liquid to the top of the tower for sulfuric acid collection, and the other portion returns to buffer tank D3. The gas phase at the top of tower C2 is condensed by condenser E2 of the primary sulfuric acid collection tower. The condensed liquid phase is discharged as concentrated sulfuric acid wastewater. The primary sulfuric acid collection tower C2 has a theoretical plate count of 8 and is equipped with a demister at the top. The temperature after condensation in condenser E2 is 38℃. The flow rate of the bottom liquid returning to the top of the tower is 500 kg / h. The heating temperature of the primary sulfuric acid concentration boiler D4 is 186℃, and the pressure is 9.5 kPaA.

[0102] Waste acid overflowing from the primary sulfuric acid concentration boiler D4 is heated in the secondary sulfuric acid concentration boiler D5. The gas phase from D5 enters the secondary sulfuric acid collection tower C3. The circulating pump P3 of the secondary sulfuric acid collection tower returns a portion of the bottom liquid to the top of the tower for sulfuric acid collection, and the other portion returns to the buffer tank D3. The gas phase at the top of the C3 tower is condensed in the secondary sulfuric acid collection tower condenser E3. The condensed liquid phase is discharged as sulfuric acid concentration wastewater. Concentrated sulfuric acid is obtained from the outlet of the secondary sulfuric acid concentration boiler D5. The secondary sulfuric acid collection tower C3 has a theoretical plate number of 8, and a demister is installed at the top. The condensate temperature in the secondary sulfuric acid collection tower condenser E3 is 12℃, the bottom liquid return flow rate is 500 kg / h, and the heating temperature of the secondary sulfuric acid concentration boiler D5 is 172℃, with a pressure of 2.2 kPaA.

[0103] Analysis revealed that the stripping wastewater contained 2672 mg / L of sulfuric acid and 1161 mg / L of nitrobenzene compounds. The concentrated sulfuric acid wastewater contained 7683 mg / L of sulfuric acid and 9.4 mg / L of nitrobenzene compounds. The concentration of concentrated sulfuric acid was 93.3%.

[0104] Comparative Example 2:

[0105] The packing material for stripping tower C1 is ceramic Raschig rings, with a diameter of 50 mm and a thickness of 5 mm. The primary sulfuric acid trapping tower C2 and the secondary sulfuric acid trapping tower C3 are not equipped with packing material.

[0106] Reference Figure 1As shown, 1000 kg / h of waste acid from the production of dinitrotoluene is fed into flash tank D1. The liquid phase from flash tank D1 enters the packing above stripper C1. The gas phase from flash tank D1 mixes with the gas phase from the top of C1 and is condensed by stripper condenser E1. The condensed liquid phase is discharged as stripping wastewater. The bottom of C1 is stripped with direct steam. The liquid phase flowing out from the bottom of C1 is heated by stripper boiler D2. The vapor phase evaporated by D2 returns to the bottom of C1. The remaining liquid phase after heating by stripper boiler D2 enters buffer tank D3. Stripper C1 has 18 theoretical plates and a demister is installed at the top. The temperature after condensation by stripper condenser E1 is 65℃. The direct steam pressure is 2 barG, the direct steam flow rate is 70 kg / h, and the heating temperature of stripper boiler D2 is 189℃ with a pressure of 28.5 kPaA.

[0107] Waste acid from buffer tank D3 is stripped and pumped by waste acid pump P1 into primary sulfuric acid concentration boiler D4 for heating. The gas phase from D4 enters primary sulfuric acid collection tower C2. The circulating pump P2 of the primary sulfuric acid collection tower returns part of the bottom liquid to the top of the tower for sulfuric acid collection, and the other part returns to buffer tank D3. The gas phase at the top of tower C2 is condensed by primary sulfuric acid collection tower condenser E2. The condensed liquid phase is discharged as sulfuric acid concentration wastewater. A demister is installed at the top of primary sulfuric acid collection tower C2. The temperature after condensation by primary sulfuric acid collection tower condenser E2 is 40℃. The flow rate of bottom liquid returning to the top of the tower is 500 kg / h. The heating temperature of primary sulfuric acid concentration boiler D4 is 187℃ and the pressure is 10 kPaA.

[0108] Waste acid overflowing from the primary sulfuric acid concentration boiler D4 is heated in the secondary sulfuric acid concentration boiler D5. The gaseous phase from D5 enters the secondary sulfuric acid collection tower C3. The circulating pump P3 returns a portion of the bottom liquid to the top of the tower for sulfuric acid collection, and the remaining portion returns to the buffer tank D3. The gaseous phase at the top of tower C3 is condensed in the secondary sulfuric acid collection tower condenser E3. The condensed liquid is discharged as concentrated sulfuric acid wastewater. Concentrated sulfuric acid is obtained from the outlet of the secondary sulfuric acid concentration boiler D5. A demister is installed at the top of the secondary sulfuric acid collection tower C3. The condensate temperature in the secondary sulfuric acid collection tower condenser E3 is 30℃, and the bottom liquid return flow rate is 500 kg / h. The heating temperature of the secondary sulfuric acid concentration boiler D5 is 179℃, and the pressure is 3.1 kPa.

[0109] Analysis revealed that the stripping wastewater contained 2481 mg / L of sulfuric acid and 1301 mg / L of nitrobenzene compounds. The concentrated sulfuric acid wastewater contained 11032 mg / L of sulfuric acid and 21.6 mg / L of nitrobenzene compounds. The concentration of concentrated sulfuric acid was 93.2%.

[0110] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for waste acid concentration, comprising the following steps: 1) stripping: waste acid from dinitrotoluene production is fed into a flash tank D1, the liquid phase of the flash tank D1 enters the packing above a stripping column C1, the gas phase of the flash tank D1 is mixed with the overhead gas phase of C1 and then condensed by a stripping column condenser E1, the condensed liquid phase is discharged as stripping waste water, the bottom of C1 is stripped by direct steam, the liquid phase flowing out of the bottom of C1 is heated by a stripping column boiler D2, the gas phase evaporated from D2 is returned to the bottom of C1, and the remaining liquid phase after heating by the stripping column boiler D2 enters a buffer tank D3; 2) primary sulfuric acid concentration: the waste acid in the buffer tank D3 is pumped by a waste acid pump P1 into a primary sulfuric acid concentration boiler D4 for heating, the gas phase of D4 enters a primary sulfuric acid capture column C2, a part of the liquid in the bottom of C2 is returned to the overhead to capture sulfuric acid by a primary sulfuric acid capture column circulating pump P2, and the other part is returned to the buffer tank D3, the overhead gas phase of C2 is condensed by a primary sulfuric acid capture column condenser E2, and the condensed liquid phase is discharged as sulfuric acid concentration waste water; 3) secondary sulfuric acid concentration: the waste acid overflowing from the primary sulfuric acid concentration boiler D4 is fed into a secondary sulfuric acid concentration boiler D5 for heating, the gas phase of D5 enters a secondary sulfuric acid capture column C3, a part of the liquid in the bottom of C3 is returned to the overhead to capture sulfuric acid by a secondary sulfuric acid capture column circulating pump P3, and the other part is returned to the buffer tank D3, the overhead gas phase of C3 is condensed by a secondary sulfuric acid capture column condenser E3, and the condensed liquid phase is discharged as sulfuric acid concentration waste water, and concentrated sulfuric acid is obtained at the outlet of the secondary sulfuric acid concentration boiler D5; wherein the packing of the stripping column C1, the primary sulfuric acid capture column C2 and the secondary sulfuric acid capture column C3 is a supported catalytic packing, and the preparation method of the supported catalytic packing comprises the following steps: (1) carrier pretreatment: calcining the carrier; (2) impregnation: active component A, active component B, active component C and pore former are added into a solvent respectively, a mixed solution is obtained after mixing, the carrier obtained in step (1) is added into the mixed solution, the PH value is adjusted to 7-9 by using lye, and impregnation is performed; wherein the active component A is one or more of ruthenium trichloride, ruthenium acetylacetone or potassium chlororuthenate, the addition amount of the active component A is 0.1%-5% of the mass of the carrier; the active component B is one or more of chloroiridic acid, iridium chloride, iridium acetate, sodium chloroiridate, ammonium chloroiridate, potassium chloroiridate or iridium acetylacetone, the addition amount of the active component B is 0.1%-5% of the mass of the carrier; and the active component C is one or more of ferrous sulfate, ferrous acetate, ferrous nitrate or ferrous chloride, the addition amount of the active component C is 0.1%-10% of the mass of the carrier; (3) hydrothermal treatment: the impregnated carrier obtained in step (2) is mixed with an aqueous cyclodextrin solution, heated in a hydrothermal kettle, and the solid is separated; (4) molding: the hydrothermally treated carrier obtained in step (3) is uniformly stirred with a binder to form a paste, the paste is added into a mold to be extruded into loose packing, dried and then calcined in a muffle furnace to obtain the supported catalytic packing.

2. The method of claim 1, wherein, The theoretical plate number of the stripping column C1 in step 1) is 10-25; The temperature after condensation of the stripping column condenser E1 is 10-70℃; The direct steam pressure is 2-9 barG, and the direct steam flow is 0.05-0.2 times the flow of the dinitrotoluene production waste acid; The heating temperature of the stripping column boiler D2 is 180-190℃, and the pressure is 20-40 kPaA.

3. The method of claim 1, wherein, The theoretical plate number of the primary sulfuric acid trapping tower C2 is 5-15; The condensation temperature of the condenser E2 of the primary sulfuric acid trapping tower is 10-70℃; The flow of the tower bottom liquid returned to the top is 0.1-0.5 times the flow of the dinitrotoluene production waste acid; The heating temperature of the primary sulfuric acid concentration boiler D4 is 180-190℃, and the pressure is 1-10 kPaA.

4. The method of claim 1, wherein, The theoretical plate number of the secondary sulfuric acid trapping tower C3 is 5-15; The condensation temperature of the condenser E3 of the secondary sulfuric acid trapping tower is 10-70℃; The flow of the tower bottom liquid returned to the top is 0.1-0.5 times the flow of the dinitrotoluene production waste acid; The heating temperature of the secondary sulfuric acid concentration boiler D5 is 170-180℃, and the pressure is 1-10 kPaA.

5. The method of claim 1, wherein, The carrier in step (1) is silicon carbide and optionally one or more of silicon powder, carbon powder, titanium dioxide, silicon dioxide, kaolin, and activated carbon.

6. The method of claim 5, wherein, The carrier in step (1), wherein the proportion of silicon carbide is not less than 90wt%.

7. The method of claim 1, wherein, In step (1), the carrier is ground into a 100-200 mesh powder and calcined at 900-1300℃ in a nitrogen atmosphere for 8-12h.

8. The method of claim 1, wherein, In step (2), the pore-forming agent is one or more of polyquaternary ammonium salt-10, octadecyl diethanolamine, and polyvinyl alcohol, and the pore-forming agent is added in an amount of 1-20% of the mass of the carrier.

9. The method of claim 1, wherein, In step (3), the cyclodextrin is one or more of α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin, and the cyclodextrin is added in an amount of 1-5% of the mass of the carrier.

10. The method of claim 9, wherein, In step (3), heating is performed in a high-pressure hydrothermal kettle at 110-200℃ for 5-8h.

11. The method of claim 1, wherein, In step (4), the binder is one or more of polyvinyl butyral, polyvinyl alcohol, polyethylene glycol, and polyacrylate, and the binder is added in an amount of 5-10% of the mass of the carrier.

12. The method of claim 1, wherein, In step (4), the type of the random packing is one of Raschig rings, Pall rings, stepped rings, rectangular saddle rings, hetero-saddle rings, conjugate rings, and cross baffle rings, with a diameter of 6-80mm and a thickness of 2-9mm.

13. The method of claim 1, wherein, In step (4), calcination is performed at 800-1000℃ in a nitrogen atmosphere for 8-12h.

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