A method for treating nitrophenol nitration by-products in crude nitration products

Abstract

The present invention provides a method for treating nitrophenol nitration byproducts in a crude nitration product, the method comprising the following steps: (1) using DNT waste acid to concentrate salt washing wastewater and preparing a catalyst by an impregnation method; (2) mixing the crude nitration product, an additive, and the catalyst obtained in step (1) in a reactor to obtain a mixed system, and performing solid-liquid separation after the reaction to obtain an acidic solution; and (3) returning the acidic solution obtained in step (2) to the reactor in step (2) for washing, and then performing solid-liquid separation to obtain a crude nitric acid solution, a nitrate, and a spent catalyst. The method achieves resource utilization of nitric acid in the DNT waste acid concentrated salt wastewater and the crude nitrate product, while converting nitrophenol byproducts into small molecular substances such as CO2, CO, H2O, and NOx, thereby significantly reducing the generation of nitrophenol-containing wastewater.

Description

Technical Field

[0001] The invention belongs to the technical field of nitration product production and relates to a method for treating nitrophenol nitration by-products, in particular to a method for treating nitrophenol nitration by-products in a crude nitration product. Background Art

[0002] Nitrates are important chemical raw materials for the production of polyurethane materials, fuels, explosives, and other products. Industrially, nitrates are produced using mixed acid nitration processes, including adiabatic and isothermal nitration. During the nitration reaction, oxidation reactions inevitably generate nitrophenols. After the nitration reaction is complete, the nitrate and mixed acid are typically separated statically or centrifugally. The resulting crude nitration product still contains large amounts of nitric acid and nitrophenols. To obtain a qualified refined product, the crude nitration product is typically washed to remove byproducts. This process typically involves three steps: acid washing, alkaline washing, and neutral washing. The acid washing process removes nitric acid and sulfuric acid from the crude nitration product. The alkaline washing process typically uses ammonia, sodium carbonate solution, or sodium hydroxide solution under alkaline conditions to remove nitrophenols and the nitric acid and sulfuric acid involved. Finally, the neutral washing process involves washing the nitration product once more with water to obtain the refined nitration product.

[0003] The nitrophenols generated by the nitration reaction are removed during the alkaline washing process. Since nitrophenols have high biochemical toxicity, the industry generally adopts Fenton oxidation treatment or high-pressure thermal cracking process for industrial treatment, which has high treatment costs.

[0004] Numerous treatment processes have been developed within the industry for this wastewater. Patent CN 102516082A discloses a method for preparing nitrobenzene by reacting benzene with mixed acid and washing the crude nitrobenzene product. The method comprises the following steps: A) liquid-phase nitration of benzene with the mixed acid to obtain a crude nitrobenzene product containing water, excess acid, nitrobenzene, unreacted benzene, and nitrophenolic impurities; B) thorough mixing of aqueous ammonia and the crude nitrobenzene product in a reactor, where the nitrophenolic impurities in the crude product react with the aqueous ammonia to form ammonium nitrophenolate salts, thereby forming an aqueous phase containing ammonium nitrophenolate and an oily phase of nitrobenzene; C) separation of the aqueous phase containing ammonium nitrophenolate, and mixing this aqueous phase with coal and optional additives to form a coal-water slurry. This patent utilizes the wastewater from the nitrobenzene-ammonia washing to prepare the coal-water slurry, enabling efficient and environmentally friendly wastewater treatment. However, this process is limited by the gasification capacity of the coal-water slurry.

[0005] Patent CN 103359865A discloses an energy-saving and environmentally friendly method for treating nitration wastewater. The method comprises: nitrates and nitration neutralization wastewater from a neutralization reactor enter an oil-water separator. The nitrates in the lower layer of the oil-water separator are directed to a subsequent nitration process. The nitration neutralization wastewater in the upper layer of the oil-water separator enters a cooling tower for cooling and then enters a filter. Nitrophenolates crystallized from the nitration neutralization wastewater are recovered in the filter. The filtered mother liquor enters a heater and is heated to the neutralization temperature required by the neutralization reactor. The heated mother liquor, which contains sufficient alkali and a low phenol content, is neutralized with the acidic nitrates in a neutralization reactor. This patent recovers the nitrophenolates crystallized from the wastewater, achieving harmless wastewater treatment. However, the complex structure of nitrophenolates makes effective resource utilization difficult. Furthermore, nitrophenolates have poor thermal stability, making storage prone to safety accidents. Therefore, the safe and efficient treatment of nitrophenols is a key technical area of concern in the nitration industry.

[0006] In addition, during the DNT production process using the mixed acid method, the waste acid generated needs to be further concentrated. Due to the continuous corrosion of the equipment during the actual production process, the waste acid contains Fe, Cr, and Ni ions, which are continuously precipitated to form metal salts during the waste acid concentration process. These metal salts need to be stopped regularly for cleaning. The cleaning agent is generally ferrous sulfate solution or warm water. The generated cleaning wastewater contains a large amount of Fe, Cr, and Ni ions. This wastewater is generally discharged into the environment, causing environmental pollution and waste of resources.

[0007] Therefore, providing a method for efficiently and cost-effectively treating nitrophenols produced as by-products during the nitration reaction while realizing resource utilization of DNT waste acid concentration and cleaning wastewater has become one of the problems that need to be solved in this field. Summary of the Invention

[0008] In response to the shortcomings of the prior art, the present invention provides a method for treating nitrophenolic nitration byproducts in crude nitration products. This method achieves resource utilization of DNT waste acid concentrated salt wastewater and nitric acid in the crude nitration product, while also converting nitrophenolic byproducts into small molecules such as CO2, CO, H2O, and NOx, significantly reducing the generation of nitrophenol-containing wastewater.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for treating nitrophenol nitration by-products in a crude nitration product, the method comprising the following steps:

[0011] (1) Using DNT waste acid to concentrate salt washing wastewater, the catalyst was prepared by impregnation method;

[0012] (2) mixing the nitrated crude product, additives, and the catalyst obtained in step (1) in a reactor to obtain a mixed system, and performing solid-liquid separation after the reaction to obtain an acidic solution;

[0013] (3) returning the acidic solution obtained in step (2) to the reactor in step (2) for washing, and then performing solid-liquid separation to obtain a crude nitric acid solution, nitration products, and spent catalyst.

[0014] The DNT waste acid concentration and salt washing wastewater in step (1) of the present invention is generated during the production of dinitrotoluene (DNT). The waste acid generated during the DNT production process needs to be concentrated and reused. During the concentration process, metal ions (Fe, Cr, Ni) in the waste acid precipitate to form salts, which require regular cleaning. The cleaning process generates salt washing wastewater, which is a sulfate solution of the three metals Fe, Cr, and Ni.

[0015] The treatment method provided by the present invention uses DNT waste acid to concentrate the cleaning wastewater to prepare a catalyst, and the prepared catalyst is used to catalyze the oxidation reaction of nitrophenols in the nitration crude product with dilute nitric acid, so that the nitrophenols are decomposed into small molecular substances (oxalic acid, formic acid, acetic acid, NO X ) substances, thereby significantly reducing the content of nitrophenols in the crude nitration product, effectively reducing the amount of wastewater containing nitrophenols in the subsequent alkaline washing or ammonia washing process, and significantly reducing the cost of wastewater treatment. The diluted nitric acid after washing is further decomposed into small molecular acid substances to produce CO2, H2O, NO through ultrasonic treatment. X , achieving harmless treatment of nitrophenols, greatly reducing the generation of wastewater containing nitrophenolates in subsequent alkali washing or ammonia washing units, and significantly reducing wastewater treatment costs.

[0016] As a preferred technical solution of the present invention, the iron ion content in the DNT waste acid concentrated salt washing wastewater in step (1) is 3 to 10 wt%, for example, it can be 3 wt%, 5 wt%, 7 wt%, 9 wt% or 10 wt%, but is not limited to the listed values, and other values not listed within the numerical range are also applicable; the chromium ion content is 0.7 to 2.7 wt%, for example, it can be 0.7 wt%, 2 wt% or 2.7 wt%, but is not limited to the listed values, and other values not listed within the numerical range are also applicable; the nickel ion content is 0.4 to 2 wt%, for example, it can be 0.4 wt%, 1 wt% or 2 wt%, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0017] The metal ion content of the present invention is measured by Agilent 700 series ICP-OES, OES (atomic emission spectroscopy) test, wherein the wavelength of 259.4nm is iron ions, the wavelength of 267.7nm is chromium ions, and the wavelength of 231.6nm is nickel ions.

[0018] Preferably, the iron ions include Fe 2+ with Fe 3+ .

[0019] Preferably, the metal content in the catalyst of step (1) is 2 to 60 wt%, based on the total mass of the catalyst, for example, it can be 2 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt% or 60 wt%, but is not limited to the listed values, and other values not listed within the numerical range are also applicable; preferably, it is 5 to 32 wt%.

[0020] Preferably, the average particle size of the catalyst in step (1) is 5-15 μm, for example, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm or 15 μm, but is not limited to the listed values, and other values not listed within the numerical range are also applicable; preferably, it is 10-12 μm.

[0021] The catalyst of the present invention is used for catalytic oxidation of nitrophenols in a nitric acid environment to decompose them into oxalic acid, formic acid, acetic acid, NO X , thereby significantly reducing the content of nitrophenols in the crude nitration product.

[0022] Preferably, the catalyst preparation by the impregnation method in step (1) includes a loading process, a reduction process and an activation process performed sequentially.

[0023] Preferably, the loading process comprises impregnating the porous support with an impregnation liquid.

[0024] The present invention obtains a catalyst by using DNT waste acid concentrated cleaning wastewater containing three metals, Fe, Cr and Ni, to impregnate a porous carrier. The three metal elements Fe, Cr and Ni loaded on the catalyst are active components of the catalyst.

[0025] Preferably, during the impregnation process, the mass ratio of the porous support to the impregnation liquid is 1:(0.1-2) based on the pure metal in the impregnation liquid, for example, it can be 1:0.1, 1:0.5, 1:1, 1:1.5 or 1:2, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0026] Preferably, the impregnation solution comprises DNT waste acid concentrated salt washing wastewater and a complexing agent.

[0027] Preferably, the complexing agent includes any one of ethylenediaminetetraacetic acid, iminodiacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid or acetic acid, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of ethylenediaminetetraacetic acid and iminodiacetic acid, a combination of trans-1,2-cyclohexanediaminetetraacetic acid and acetic acid, a combination of ethylenediaminetetraacetic acid, iminodiacetic acid and trans-1,2-cyclohexanediaminetetraacetic acid, or a combination of ethylenediaminetetraacetic acid, iminodiacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid and acetic acid.

[0028] Preferably, the porous support comprises any one or a combination of at least two of silica, activated carbon or carbon black. Typical but non-limiting combinations include a combination of silica and activated carbon, a combination of silica and carbon black, a combination of activated carbon and carbon black, or a combination of silica, activated carbon and carbon black; preferably silica.

[0029] Preferably, the average particle size of the porous carrier is 5 to 15 μm, for example, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm or 15 μm, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0030] Preferably, the specific surface area of the porous carrier is 300 to 600 m 2 / g, for example, it can be 300m 2 / g、350m 2 / g, 400m 2 / g, 450m 2 / g、500m 2 / g、550m 2 / g or 600m 2 / g, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0031] Preferably, during the impregnation process, ammonia water is used to adjust the pH value to 8-12, for example, 8, 9, 10, 11 or 12, but it is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0032] Preferably, the immersion temperature is 25-35°C, for example, it can be 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C or 35°C, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0033] Preferably, the immersion time is 8 to 12 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0034] Preferably, ultrasonic treatment is used during the impregnation process.

[0035] Preferably, the frequency of the ultrasonic treatment is 28 to 40 kHz, for example, 28 kHz, 30 kHz, 35 kHz or 40 kHz, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0036] Preferably, the reducing agent used in the reduction process comprises hydrazine hydrate solution and / or hydrogen, preferably hydrazine hydrate solution.

[0037] Preferably, the concentration of the hydrazine hydrate solution is 50-60%, for example, 50%, 52%, 54%, 56%, 58% or 60%, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0038] Preferably, the reduction process lasts for 2 to 5 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0039] Preferably, the reduction process further includes filtering and washing in sequence.

[0040] Preferably, the activation process comprises: calcining the reduced catalyst precursor under an inert gas environment.

[0041] Preferably, the inert gas comprises any one or a combination of at least two of nitrogen, helium, argon or neon. Typical but non-limiting combinations include a combination of ammonia and helium, a combination of nitrogen and neon, a combination of nitrogen and argon, a combination of helium, argon and neon, or a combination of nitrogen, helium, argon and neon.

[0042] Preferably, the calcination temperature is 300-350°C, for example, 300°C, 310°C, 320°C, 330°C, 340°C or 350°C, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0043] Preferably, the calcination treatment time is 3 to 4 hours, for example, 3 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours or 4 hours, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0044] Preferably, the reactor in step (2) comprises a reactor.

[0045] Preferably, the additive in step (2) includes water or low-concentration nitric acid.

[0046] Preferably, the concentration of the low-concentration nitric acid is 0.1 to 5 wt%, for example, it can be 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt% or 5 wt%, but is not limited to the listed values, and other values not listed within the numerical range are also applicable; preferably, it is 0.1 to 2 wt%.

[0047] Preferably, the concentration of nitric acid in the mixed system in step (2) is 2 to 25%, for example, it can be 2%, 5%, 10%, 15%, 20% or 25%, but is not limited to the listed values. Other values not listed within the numerical range are also applicable; preferably, it is 5 to 20%.

[0048] Preferably, the concentration of the catalyst in the mixed system in step (2) is 1 to 5%, for example, it can be 1%, 2%, 3%, 4% or 5%, but is not limited to the listed values. Other values not listed within the numerical range are also applicable; preferably, it is 2 to 3%.

[0049] Preferably, the reaction in step (2) comprises a stirring reaction.

[0050] Preferably, the stirring reaction temperature is 30-90°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or 90°C, but is not limited to the listed values, and other values not listed within the numerical range are also applicable; preferably, it is 50-80°C.

[0051] Preferably, the stirring reaction time is 5 to 20 minutes, for example, 5 minutes, 8 minutes, 11 minutes, 14 minutes or 15 minutes, but is not limited to the listed values. Other values not listed within the numerical range are also applicable; preferably, it is 8 to 15 minutes.

[0052] Preferably, the washing in step (3) comprises countercurrent washing.

[0053] Preferably, the volume ratio of the acidic solution to the crude nitration product in the countercurrent washing is (0.5-2):1, for example, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1 or 2:1, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0054] Preferably, the countercurrent washing is performed 1 to 3 times, for example, 1 time, 2 times or 3 times.

[0055] Preferably, the temperature of the countercurrent washing is 30 to 90°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or 90°C, but is not limited to the listed values, and other values not listed within the numerical range are also applicable; preferably, it is 50 to 80°C.

[0056] Preferably, the residence time of the countercurrent washing is 5 to 20 minutes, for example, it can be 5 minutes, 8 minutes, 11 minutes, 14 minutes, 17 minutes or 20 minutes, but is not limited to the listed values. Other values not listed within the numerical range are also applicable; preferably, it is 8 to 15 minutes.

[0057] The purpose of the countercurrent washing of the present invention is to ensure that the nitrocresol is completely decomposed during the washing process, and the catalyst can be recycled during the washing process until the activity is lost.

[0058] Preferably, the treatment method further comprises sequentially performing ultrasonic treatment and concentrating on the crude nitric acid solution obtained in step (3);

[0059] Preferably, the concentrated nitric acid is used for nitration reaction.

[0060] Preferably, the frequency of the ultrasonic treatment is 25 to 30 kHz, for example, 25 kHz, 26 kHz, 27 kHz, 28 kHz, 29 kHz or 30 kHz, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0061] Preferably, the residence time of the ultrasonic treatment is 5 to 10 min, for example, 5 min, 5 min, 7 min, 8 min, 9 min or 10 min, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0062] Preferably, the temperature of the ultrasonic treatment is 60-80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0063] Preferably, the pressure of the ultrasonic treatment is 50-150 kPa, for example, 50 kPa, 70 kPa, 90 kPa, 110 kPa, 130 kPa or 150 kPa, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0064] The present invention uses ultrasonic cavitation to further decompose small molecular acids dissolved in the crude nitric acid solution into carbon dioxide and water, reducing the impurity content in the nitric acid solution. The nitric acid solution after ultrasonication is further concentrated and reused in the nitration reaction system, achieving the reuse of nitric acid resources and eliminating the generation of three wastes during the treatment process.

[0065] Preferably, the concentrating comprises performing distillation in a distillation column.

[0066] Preferably, the feed plate in the distillation process is the 7th to 12th theoretical plates.

[0067] Preferably, the number of theoretical plates of the distillation tower is 16 to 25, for example, 16, 18, 20, 22 or 25, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0068] Preferably, the top temperature in the distillation is 60-80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0069] Preferably, the top pressure in the distillation is 25 to 35 kPaa, for example, 25 kPaa, 27 kPaa, 29 kPaa, 31 kPaa, 33 kPaa or 35 kPaa, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0070] Preferably, the reflux ratio in the distillation is 0.2 to 0.4, for example, 0.2, 0.24, 0.28, 0.32, 0.36 or 0.4, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0071] The present invention concentrates dilute nitric acid, and the high-concentration nitric acid obtained by concentration can be reused in the nitration reaction; the low-concentration nitric acid extracted from the top of the tower during the distillation process can be reused in step (2) of the treatment method of the present invention. Therefore, no waste liquid is generated in the treatment method provided by the present invention, and waste-free treatment is achieved.

[0072] As a preferred technical solution of the present invention, the method for treating nitrophenol nitration by-products in the crude nitration product provided by the present invention comprises the following steps:

[0073] (1) Using DNT waste acid to concentrate salt washing wastewater, a catalyst with an average particle size of 5-15 μm is prepared by an impregnation method; the metal content in the catalyst is 2-60 wt%;

[0074] The preparation method of the catalyst comprises the following steps:

[0075] (a) Mixing DNT waste acid concentrated salt washing wastewater and complexing agent to obtain impregnation solution, and then mixing the average particle size of 5 to 15 μm and the specific surface area of 300 to 600 m 2 / g porous carrier, adding ammonia water dropwise during stirring to adjust the pH value to 8-12, then ultrasonically treating at 28-40KHz at 25-35°C for 8-12h, and drying to obtain a solid powder;

[0076] Wherein, the ratio of the porous support to the impregnation solution is 1:(0.1-2) based on the pure metal in the impregnation solution;

[0077] (b) refluxing the solid powder obtained in step (2) under the action of a reducing agent for 2 to 5 hours, filtering and washing until neutral to obtain a catalyst precursor;

[0078] (c) calcining the catalyst precursor obtained in step (2) at a temperature of 300-350° C. under an inert gas atmosphere to obtain the catalyst;

[0079] (2) mixing the crude nitration product, the additive, and the catalyst obtained in step (1) in a reaction kettle to obtain a mixed system, stirring the reaction at 30 to 90° C. for 5 to 20 minutes, and then performing solid-liquid separation to obtain an acidic solution;

[0080] The concentration of nitric acid in the mixed system is 2-25%, and the concentration of the catalyst is 1-5%.

[0081] (3) returning the acidic solution obtained in step (2) to the reactor in step (2) for countercurrent washing 1 to 3 times, and then obtaining a crude nitric acid solution, a nitrated product, and a spent catalyst after solid-liquid separation;

[0082] The volume ratio of the acidic solution to the crude nitrated product in the countercurrent washing is (0.5-2):1; the temperature of the countercurrent washing is 30-90° C., and the residence time is 5-20 min;

[0083] (4) subjecting the crude nitric acid solution obtained in step (3) to ultrasonic treatment and then concentrating it in a distillation tower;

[0084] The ultrasonic treatment has a frequency of 25 to 30 kHz, a residence time of 5 to 10 min, a temperature of 60 to 80° C., and a pressure of 50 to 150 kPaa.

[0085] The concentrated nitric acid can be reused for nitration reaction; the number of theoretical plates in the distillation is 16 to 25, the tower top pressure is 25 to 35 kPa, and the reflux ratio is 0.2 to 0.4.

[0086] The numerical range described in the present invention includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values included in the range.

[0087] Compared with the prior art, the present invention has the following beneficial effects:

[0088] (1) The treatment method provided by the present invention realizes the resource utilization of metal elements in DNT waste acid concentrated wastewater and the harmless treatment of nitrophenols in nitration crude products, greatly reducing the generation of nitrophenol-containing wastewater;

[0089] (2) The treatment method provided by the present invention has low treatment cost and a simple, safe and environmentally friendly treatment process. DETAILED DESCRIPTION

[0090] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0091] The chemicals used to prepare the catalysts in the embodiments of the present invention were all from Sinopharm Chemical Reagent Co., Ltd. and were of analytical grade; the DNT waste acid concentrated salt washing wastewater (hereinafter referred to as wastewater) was from the DNT section of the TDI production unit of Wanhua Chemical Group Co., Ltd.

[0092] The raw materials involved in the embodiments of the present invention are crude nitrobenzene (crude MNB) and crude dinitrotoluene (crude DNT) produced by Wanhua Chemical Group Co., Ltd.

[0093] Example 1

[0094] This embodiment provides a method for treating nitrophenol nitration by-products in a crude nitration product, the method comprising the following steps:

[0095] (1) Using DNT waste acid to concentrate salt washing wastewater, an impregnation method was used to prepare a granular product with an average particle size of 11 μm and a specific surface area of 300 m 2 / g of catalyst; the metal content (Fe, Cr and Ni) in the catalyst is 30wt%; the iron ion concentration in the DNT waste acid concentrated salt washing wastewater is 3%, the chromium ion concentration is 0.7%, and the nickel ion concentration is 0.4%;

[0096] The preparation method of the catalyst comprises the following steps:

[0097] (a) 53.6 g of DNT waste acid concentrated salt washing wastewater, 19.91 g of EDTA and 300 g of deionized water were mixed to obtain an impregnation solution, and then 5.5 g of a 11 μm average particle size and a specific surface area of 300 m 2 / g silica carrier, adding 30wt% ammonia water dropwise during stirring to adjust the pH value to 8, and then ultrasonically treating at 28KHz at 25°C for 12h, and drying to obtain a solid powder;

[0098] (b) refluxing the solid powder obtained in step (2) under the action of a 50 wt% aqueous hydrazine hydrate solution for 2 h, filtering and washing until neutral to obtain a catalyst precursor;

[0099] (c) calcining the catalyst precursor obtained in step (2) at 300° C. for 4 h under a nitrogen atmosphere to obtain the catalyst;

[0100] (2) mixing crude DNT, low-concentration nitric acid with a nitric acid content of 0.1%, and the catalyst obtained in step (1) in a reaction kettle to obtain a mixed system, stirring and reacting at 69° C. for 8 minutes, and then performing solid-liquid separation to obtain an acidic solution;

[0101] The mass ratio of the crude DNT to low-concentration nitric acid is 4.5:1; the crude DNT has a nitric acid content of 3% and a nitrocresol content of 4200 ppm;

[0102] The concentration of nitric acid in the mixed system is 11.8%, and the concentration of the catalyst is 1%;

[0103] (3) returning the acidic solution obtained in step (2) to the reactor in step (2) for countercurrent washing once, and then obtaining a crude nitric acid solution, a nitrated product, and a spent catalyst after solid-liquid separation;

[0104] The volume ratio of the acidic solution to the crude nitrated product in the countercurrent washing is 1:1; the temperature of the countercurrent washing is 69° C., and the residence time is 8 minutes;

[0105] (4) subjecting the crude nitric acid solution obtained in step (3) to ultrasonic treatment and then concentrating it in a distillation tower;

[0106] The ultrasonic treatment was carried out at a frequency of 25 kHz, a residence time of 7 min, a temperature of 70°C and a pressure of 50 kPaa.

[0107] The concentration of the concentrated nitric acid is 44.4%, which can be reused in the nitration reaction; the number of theoretical plates in the distillation is 20, the tower top pressure is 32 kPa, and the reflux ratio is 0.34.

[0108] By adopting the treatment method provided in this embodiment, the nitrocresol content in the nitrated product is reduced to 2000 ppm after the countercurrent washing in step (3), and 52% of the nitrocresol is decomposed during the washing process.

[0109] During the distillation process, dilute nitric acid with a concentration of 0.1% is extracted from the top of the tower and can be reused in the stirring reaction described in step (2).

[0110] Example 2

[0111] This embodiment provides a method for treating nitrophenol nitration by-products in a crude nitration product, the method comprising the following steps:

[0112] (1) Using DNT waste acid to concentrate salt washing wastewater, an impregnation method was used to prepare a granular product with an average particle size of 8 μm and a specific surface area of 450 m 2 / g of catalyst; the metal content (Fe, Cr and Ni) in the catalyst is 10wt%; the iron ion concentration in the DNT waste acid concentrated salt washing wastewater is 5%, the chromium ion concentration is 2%, and the nickel ion concentration is 2%;

[0113] The preparation method of the catalyst comprises the following steps:

[0114] (a) 9.78 g of DNT waste acid concentrated salt washing wastewater, 4.98 g of CrDTA and 300 g of deionized water were mixed to obtain an impregnation solution, and then 8.8 g of a granular material with an average particle size of 8 μm and a specific surface area of 450 m 2 / g silica carrier, adding 50wt% ammonia water dropwise during stirring to adjust the pH value to 8.5, and then ultrasonically treating at 40KHz at 35°C for 10h, and drying to obtain a solid powder;

[0115] (b) refluxing the solid powder obtained in step (2) under the action of a 60 wt % hydrazine hydrate aqueous solution for 3 h, filtering and washing until neutral to obtain a catalyst precursor;

[0116] (c) calcining the catalyst precursor obtained in step (2) at 300° C. for 4 h under an argon atmosphere to obtain the catalyst;

[0117] (2) mixing crude DNT, low-concentration nitric acid with a nitric acid content of 1%, and the catalyst obtained in step (1) in a reaction kettle to obtain a mixed system, stirring and reacting at 60° C. for 5 minutes, and then performing solid-liquid separation to obtain an acidic solution;

[0118] The mass ratio of the crude DNT to low-concentration nitric acid is 3.2:1; the crude DNT has a nitric acid content of 3% and a nitrocresol content of 4400 ppm;

[0119] The concentration of nitric acid in the mixed system is 25%, and the concentration of the catalyst is 3%;

[0120] (3) returning the acidic solution obtained in step (2) to the reactor in step (2) for countercurrent washing three times, and then obtaining a crude nitric acid solution, a nitrated product, and a spent catalyst after solid-liquid separation;

[0121] The volume ratio of the acidic solution to the crude nitrated product in the countercurrent washing is 0.5:1; the temperature of the countercurrent washing is 60°C, and the residence time is 5 minutes;

[0122] (4) subjecting the crude nitric acid solution obtained in step (3) to ultrasonic treatment and then concentrating it in a distillation tower;

[0123] The ultrasonic treatment was carried out at a frequency of 30 kHz, a residence time of 5 min, a temperature of 65°C and a pressure of 150 kPaa.

[0124] The concentration of the concentrated nitric acid is 50%, and can be reused for nitration reaction; the number of theoretical plates in the rectification is 25, the tower top pressure is 25 kPa, and the reflux ratio is 0.3.

[0125] By adopting the treatment method provided in this embodiment, the nitrocresol content in the nitrated product is reduced to 1600 ppm after the countercurrent washing in step (3), and 63.6% of the nitrocresol is decomposed during the washing process.

[0126] During the distillation process, dilute nitric acid with a concentration of 1% is extracted from the top of the tower and can be reused in the stirring reaction described in step (2).

[0127] Example 3

[0128] This embodiment provides a method for treating nitrophenol nitration by-products in a crude nitration product, the method comprising the following steps:

[0129] (1) Using DNT waste acid to concentrate salt washing wastewater, an impregnation method was used to prepare a granular product with an average particle size of 15 μm and a specific surface area of 400 m 2 / g of catalyst; the metal content (Fe, Cr, Ni) in the catalyst is 5wt%; the iron ion concentration in the DNT waste acid concentrated salt washing wastewater is 10%, the chromium ion concentration is 2.7%, and the nickel ion concentration is 2%;

[0130] The preparation method of the catalyst comprises the following steps:

[0131] (a) 3.03 g of DNT waste acid concentrated salt washing wastewater, 1.55 g of EDTA and 300 g of deionized water were mixed to obtain an impregnation solution, and then 8.9 g of a 15 μm average particle size and a specific surface area of 400 m 2 / g activated carbon support, 30wt% ammonia water was added dropwise during stirring to adjust the pH value to 8, and then ultrasonicated at 34KHz at 30°C for 12h, and dried to obtain a solid powder;

[0132] (b) reducing the solid powder obtained in step (2) under reflux for 2 h in the presence of a 55 wt % aqueous hydrazine hydrate solution, and then filtering and washing until neutral to obtain a catalyst precursor;

[0133] (c) calcining the catalyst precursor obtained in step (2) at 350° C. for 3 h under a helium atmosphere to obtain the catalyst;

[0134] (2) mixing crude DNT, low-concentration nitric acid with a nitric acid content of 2%, and the catalyst obtained in step (1) in a reaction kettle to obtain a mixed system, stirring and reacting at 90° C. for 20 minutes, and then performing solid-liquid separation to obtain an acidic solution;

[0135] The mass ratio of the crude DNT to low-concentration nitric acid is 3.2:1; the crude DNT has a nitric acid content of 2% and a nitrocresol content of 3800 ppm;

[0136] The concentration of nitric acid in the mixed system is 10.2%, and the concentration of the catalyst is 5%;

[0137] (3) returning the acidic solution obtained in step (2) to the reactor in step (2) for countercurrent washing three times, and then obtaining a crude nitric acid solution, a nitrated product, and a spent catalyst after solid-liquid separation;

[0138] The volume ratio of the acidic solution to the crude nitrated product in the countercurrent washing is 2:1; the temperature of the countercurrent washing is 90°C, and the residence time is 20 minutes;

[0139] (4) subjecting the crude nitric acid solution obtained in step (3) to ultrasonic treatment and then concentrating it in a distillation tower;

[0140] The ultrasonic treatment was carried out at a frequency of 23 kHz, a residence time of 10 min, a temperature of 80°C, and a pressure of 75 kPaa.

[0141] The concentration of the concentrated nitric acid is 30%, and can be reused in the nitration reaction; the number of theoretical plates in the rectification is 16, the tower top pressure is 35 kPa, and the reflux ratio is 0.2.

[0142] By adopting the treatment method provided in this embodiment, the nitrocresol content in the nitrated product was reduced to 1800 ppm after the countercurrent washing in step (3), and 47.4% of the nitrocresol was decomposed during the washing process.

[0143] During the distillation process, the dilute nitric acid with a concentration of 5% is extracted from the top of the tower and can be reused in the stirring reaction described in step (2).

[0144] Example 4

[0145] This embodiment provides a method for treating nitrophenol nitration by-products in a crude nitration product, the method comprising the following steps:

[0146] (1) Using DNT waste acid to concentrate salt washing wastewater, an impregnation method was used to prepare a particle size of 5 μm and a specific surface area of 320 m 2 / g of catalyst; the metal content (Fe, Cr, Ni) in the catalyst is 2 wt%; the iron ion concentration in the DNT waste acid concentrated salt washing wastewater is 8%, the chromium ion concentration is 2%, and the nickel ion concentration is 2%;

[0147] The preparation method of the catalyst comprises the following steps:

[0148] (a) 1.47 g of DNT waste acid concentrated salt washing wastewater, 0.59 g of IDA and 300 g of deionized water were mixed to obtain an impregnation solution, and then 8.9 g of a 5 μm average particle size and a specific surface area of 320 m 2 / g of carbon black carrier, 10wt% ammonia water was added dropwise during stirring to adjust the pH value to 12, and then ultrasonicated at 34KHz at 25°C for 8h, and dried to obtain a solid powder;

[0149] (b) refluxing the solid powder obtained in step (2) under the action of a 55 wt% aqueous hydrazine hydrate solution for 5 h, filtering and washing until neutral to obtain a catalyst precursor;

[0150] (c) calcining the catalyst precursor obtained in step (2) at 330° C. for 3 h under a helium atmosphere to obtain the catalyst;

[0151] (2) mixing crude MNB, low-concentration nitric acid with a nitric acid content of 2%, and the catalyst obtained in step (1) in a reactor to obtain a mixed system, stirring and reacting at 30° C. for 10 minutes, and then performing solid-liquid separation to obtain an acidic solution;

[0152] The mass ratio of the crude DNT to low-concentration nitric acid is 3.2:1; the crude MNB has a nitric acid content of 0% and a nitrocresol content of 1700 ppm;

[0153] The concentration of nitric acid in the mixed system is 2%, and the concentration of the catalyst is 3%;

[0154] (3) returning the acidic solution obtained in step (2) to the reactor in step (2) for countercurrent washing four times, and then obtaining a crude nitric acid solution, a nitrated product, and a spent catalyst after solid-liquid separation;

[0155] The volume ratio of the acidic solution to the crude nitrated product in the countercurrent washing is 1:1; the temperature of the countercurrent washing is 30°C, and the residence time is 10 minutes;

[0156] (4) subjecting the crude nitric acid solution obtained in step (3) to ultrasonic treatment and then concentrating it in a distillation tower;

[0157] The ultrasonic treatment was carried out at a frequency of 25 kHz, a residence time of 8 min, a temperature of 60°C and a pressure of 75 kPaa.

[0158] The concentration of the concentrated nitric acid is 35%, and can be reused in the nitration reaction; the number of theoretical plates in the rectification is 18, the tower top pressure is 30 kPa, and the reflux ratio is 0.4.

[0159] By adopting the treatment method provided in this embodiment, the nitrocresol content in the nitrated product is reduced to 850 ppm after the countercurrent washing in step (3), and 50% of the nitrocresol is decomposed during the washing process.

[0160] During the distillation process, dilute nitric acid with a concentration of 2% is extracted from the top of the tower and can be reused in the stirring reaction described in step (2).

[0161] Example 5

[0162] This embodiment provides a method for treating nitrophenol nitration by-products in a crude nitration product. The difference between the treatment method and Example 1 is that:

[0163] In this embodiment, the average particle size of the catalyst carrier in step (a) is changed to 18 μm and the specific surface area is 200 m 2 / g; further, the average particle size of the catalyst is correspondingly corrected to 18 μm and the specific surface area is 200 m 2 / g.

[0164] By adopting the treatment method provided in this embodiment, the nitrocresol content in the nitrated product is reduced to 3000 ppm after the countercurrent washing in step (3), and 28.6% of the nitrocresol is decomposed during the washing process.

[0165] Example 6

[0166] This embodiment provides a method for treating nitrophenol nitration by-products in a crude nitration product. The difference between the treatment method and Example 1 is that:

[0167] In this example, the catalyst concentration in the mixed system in step (2) is changed to 7%.

[0168] By adopting the treatment method provided in this embodiment, the nitrocresol content in the nitrate is reduced to 2100 ppm after the countercurrent washing in step (3), and 50% of the nitrocresol is decomposed during the washing process.

[0169] Comparative Example 1

[0170] This comparative example provides a method for treating nitrophenol nitration by-products in a crude nitration product. The difference between the treatment method and Example 1 is that:

[0171] The catalyst described in step (2) was omitted in this comparative example.

[0172] By adopting the treatment method provided in this comparative example, the nitrocresol content in the obtained nitrate is 4000 ppm, and there is basically no decomposition.

[0173] Comparative Example 2

[0174] This comparative example provides a method for treating nitrophenol nitration by-products in a crude nitration product. The difference between the treatment method and Example 1 is that:

[0175] In this comparative example, the catalyst described in step (2) is replaced with DNT waste acid concentrated salt washing wastewater of the same mass, wherein the DNT waste acid concentrated salt washing wastewater has an iron ion concentration of 3%, a chromium ion concentration of 1%, and a nickel ion concentration of 1%.

[0176] By adopting the treatment method provided in this comparative example, the nitrocresol content in the obtained nitrate is 2500 ppm.

[0177] Comparative Example 3

[0178] This comparative example provides a method for treating nitrophenol nitration by-products in a crude nitration product. The difference between the treatment method and Example 1 is that:

[0179] In this comparative example, the DNT waste acid concentrated salt washing wastewater in the catalyst preparation process of step (1) is replaced with a sodium sulfate solution, wherein the sodium ion concentration of the ferric sulfate solution is 4%.

[0180] By adopting the treatment method provided in this comparative example, the nitrocresol content in the obtained nitrate is 4100 ppm.

[0181] In summary, the method for treating nitrophenol nitration by-products in crude nitration products provided by the present invention realizes the resource utilization of DNT waste acid concentrated salt wastewater and nitric acid in crude nitration products, and at the same time converts nitrophenol by-products into small molecular substances such as CO2, CO, H2O, NOx, etc., thereby greatly reducing the generation of nitrophenol-containing wastewater.

[0182] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for treating nitrophenol nitration by-products in a crude nitration product, characterized in that: The processing method comprises the following steps: (1) using DNT waste acid to concentrate salt washing wastewater and preparing a catalyst by an impregnation method; the impregnation method for preparing the catalyst includes a loading process, a reduction process, and an activation process performed in sequence; the loading process is to impregnate a porous carrier with an impregnation liquid; The reducing agent used in the reduction process is hydrazine hydrate solution and / or hydrogen; The impregnation liquid is DNT waste acid concentrated salt washing wastewater and a complexing agent; The activation process includes: calcining the reduced catalyst precursor under an inert gas environment; (2) mixing the crude nitration product, an additive, and the catalyst obtained in step (1) in a reactor to obtain a mixed system, and performing solid-liquid separation after the reaction to obtain an acidic solution; the additive in step (2) is low-concentration nitric acid; and the concentration of the low-concentration nitric acid is 0.1 to 5 wt%; (3) returning the acidic solution obtained in step (2) to the reactor in step (2) for washing, and then performing solid-liquid separation to obtain a crude nitric acid solution, nitration products, and spent catalyst.

2. The processing method according to claim 1, characterized in that The iron ion content of the DNT waste acid concentrated salt washing wastewater in step (1) is 3-10wt%, the chromium ion content is 0.7-2.7wt%, and the nickel ion content is 0.4-2wt%.

3. The processing method according to claim 2, characterized in that The iron ion is Fe 2+ with Fe 3+ .

4. The processing method according to claim 1, characterized in that The metal content in the catalyst in step (1) is 2 to 60 wt % based on the total mass of the catalyst.

5. The processing method according to claim 4, characterized in that: The metal content in the catalyst in step (1) is 5 to 32 wt % based on the total mass of the catalyst.

6. The processing method according to claim 1, characterized in that The average particle size of the catalyst in step (1) is 5-15 μm.

7. The processing method according to claim 6, characterized in that The average particle size of the catalyst in step (1) is 10-12 μm.

8. The processing method according to claim 1, characterized in that During the impregnation process, the mass ratio of the porous support to the impregnation solution is 1:(0.1-2) based on the pure metal in the impregnation solution.

9. The processing method according to claim 1, characterized in that: The complexing agent is any one of ethylenediaminetetraacetic acid, iminodiacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid or acetic acid, or a combination of at least two thereof.

10. The processing method according to claim 1, characterized in that: The porous carrier is any one of silicon dioxide, activated carbon or carbon black, or a combination of at least two of them.

11. The processing method according to claim 1, characterized in that: The average particle size of the porous carrier is 5 to 15 μm.

12. The processing method according to claim 1, characterized in that: The specific surface area of the porous carrier is 300 to 600 m 2 / g.

13. The processing method according to claim 1, characterized in that: During the soaking process, ammonia water is used to adjust the pH value to 8-12.

14. The processing method according to claim 1, characterized in that The immersion temperature is 25-35°C.

15. The processing method according to claim 1, characterized in that The immersion time is 8 to 12 hours.

16. The processing method according to claim 1, characterized in that Ultrasonic treatment is used during the impregnation process.

17. The processing method according to claim 16, characterized in that: The frequency of the ultrasonic treatment is 28-40 KHz.

18. The processing method according to claim 1, characterized in that The reducing agent used in the reduction process is hydrazine hydrate solution.

19. The processing method according to claim 1, characterized in that The concentration of the hydrazine hydrate solution is 50-60%.

20. The processing method according to claim 1, characterized in that The reduction process takes 2 to 5 hours.

21. The processing method according to claim 1, characterized in that The reduction process further includes filtering and washing in sequence.

22. The processing method according to claim 1, characterized in that The inert gas is any one of nitrogen, helium, argon or neon, or a combination of at least two of them.

23. The processing method according to claim 1, characterized in that The temperature of the calcination treatment is 300-350°C.

24. The processing method according to claim 1, characterized in that The calcination time is 3 to 4 hours.

25. The processing method according to any one of claims 1 to 24, characterized in that: The reactor in step (2) includes a reaction kettle.

26. The processing method according to claim 1, characterized in that The concentration of the low-concentration nitric acid is 0.1-2 wt %.

27. The processing method according to claim 1, characterized in that The concentration of nitric acid in the mixed system in step (2) is 2-25%.

28. The processing method according to claim 27, characterized in that The concentration of nitric acid in the mixed system in step (2) is 5-20%.

29. The processing method according to claim 1, characterized in that The concentration of the catalyst in the mixed system in step (2) is 1-5%.

30. The processing method according to claim 29, characterized in that The concentration of the catalyst in the mixed system in step (2) is 2-3%.

31. The processing method according to claim 1, characterized in that The reaction in step (2) includes a stirring reaction.

32. The processing method according to claim 31, characterized in that The temperature of the stirring reaction is 30-90°C.

33. The processing method according to claim 32, characterized in that The temperature of the stirring reaction is 50-80°C.

34. The processing method according to claim 31, characterized in that The stirring reaction time is 5 to 20 minutes.

35. The processing method according to claim 34, characterized in that The stirring reaction time is 8 to 15 minutes.

36. The processing method according to any one of claims 1 to 24, characterized in that The washing in step (3) includes countercurrent washing.

37. The processing method according to claim 36, characterized in that The volume ratio of the acidic solution to the nitrated crude product in the countercurrent washing is (0.5-2):

1.

38. The processing method according to claim 36, characterized in that The countercurrent washing is performed 1 to 3 times.

39. The processing method according to claim 36, characterized in that The temperature of the countercurrent washing is 30-90°C.

40. The processing method according to claim 39, characterized in that The temperature of the countercurrent washing is 50-80°C.

41. The processing method according to claim 36, characterized in that The residence time of the countercurrent washing is 5 to 20 minutes.

42. The processing method according to claim 41, characterized in that The residence time of the countercurrent washing is 8 to 15 minutes.

43. The processing method according to any one of claims 1 to 7, characterized in that The treatment method further comprises sequentially performing ultrasonic treatment and concentrating on the crude nitric acid solution obtained in step (3).

44. The processing method according to claim 43, characterized in that The concentrated nitric acid is used for nitration reaction.

45. The processing method according to claim 43, characterized in that The frequency of the ultrasonic treatment is 25-30 kHz.

46. The processing method according to claim 43, characterized in that The residence time of the ultrasonic treatment is 5 to 10 minutes.

47. The processing method according to claim 43, characterized in that The temperature of the ultrasonic treatment is 60-80°C.

48. The processing method according to claim 43, characterized in that The pressure of the ultrasonic treatment is 50-150 kPa.

49. The processing method according to claim 43, characterized in that The concentration includes performing rectification in a rectification column.