Production process for reducing nitrogen content in reagent-grade sulfuric acid

Abstract

The invention provides a production process for reducing the nitrogen content in reagent-grade sulfuric acid, and relates to the technical field of sulfuric acid. Comprising the following steps: adding urea solid powder into sulfuric acid at 55-65 DEG C according to the mass ratio of urea to sulfuric acid of (0.001-0.01): 100, and stirring until the urea solid powder is completely dissolved; s100, heating the mixture in the step S100 to 83-87 DEG C in a gradient manner, adding ammonium sulfate powder according to the mass ratio of ammonium sulfate to sulfuric acid of (0.05-0.1): 100 in the heating process, and stirring to react for 0.8-1.2 hours; performing reduced pressure distillation on the sulfuric acid after the reaction in the step S200 at 80-150 DEG C, introducing inert gas in a synchronous pulse manner for purging in the heating process, repeating for 2-3 times, and collecting a main fraction; treating tail gas. According to the method, the total nitrogen content and the content of NH4 < + > ions and NO3 <-> ions in the reagent-grade sulfuric acid are effectively reduced, the electronic-grade sulfuric acid is obtained, and the yield of the sulfuric acid can reach 97.5%.

Description

Technical Field

[0001] The present invention relates to the technical field of sulfuric acid impurity removal, and particularly to a production process for reducing the nitrogen content in reagent-grade sulfuric acid. Background Art

[0002] As a basic inorganic acid, sulfuric acid occupies an irreplaceable position in the modern industrial system. As one of the chemicals with the largest global production, the annual consumption of sulfuric acid is often used as an important indicator to measure a country's industrial development level. With the rapid development of high-tech industries, the demand for high-purity sulfuric acid has shown an explosive growth. Especially in strategic emerging industries such as semiconductor manufacturing, flat panel display, and new energy batteries, the purity of sulfuric acid is directly related to product quality and production yield.

[0003] In semiconductor manufacturing processes, sulfuric acid is widely used in key processes such as wafer cleaning and photoresist stripping. Taking advanced processes of 28 nanometers and below as an example, it is required that the total nitrogen content in sulfuric acid be controlled below 10 ppb, because nitrogen-containing impurities will react with the silicon wafer surface to form defects such as silicon nitride. Similarly, in the production of TFT-LCD panels, nitrogen-containing impurities will cause abnormalities in the liquid crystal alignment film; in the preparation process of lithium iron phosphate cathode materials, nitrides will cause problems such as battery self-discharge. However, in the current GB / T 625-2024 standard, the nitrate (calculated as N) index for extra pure sulfuric acid is 0.0001% (i.e., 1 ppm), which has a three-order-of-magnitude gap from the high-end demand.

[0004] Traditional distillation methods have good effects within the purity range of 99.9%, but face fundamental technical obstacles when it comes to reaching a purity of 99.9999% (6N) and above. This is mainly due to the special association system formed by nitrogen-containing compounds and sulfuric acid:

[0005] Nitrate association: NO3 - forms a [NO3·H2SO4] complex with H3SO4 + through hydrogen bonds, and its apparent boiling point rises to 330°C, almost overlapping with that of pure sulfuric acid (337°C).

[0006] Ammonium ion fixation: NH4 + reacts with HSO4 - to generate NH4HSO4, which is further converted into (NH4)2S2O7 in concentrated sulfuric acid, and its thermal decomposition temperature is as high as 350°C.

[0007] Nitrosyl compounds: Intermediate products such as HNOSO4 may be formed during the distillation process, which have extremely strong thermal stability.

[0008] To overcome this problem, several innovative solutions have emerged in recent years:

[0009] Molecular sieve coupled distillation technology: Special modified FAU zeolite molecular sieve is used to selectively adsorb nitrogen-containing species in the pre-purification stage. The SPS-100 system developed in Japan can reduce the initial nitrogen content from 50 ppm to below 100 ppb through a series connection of three molecular sieve towers.

[0010] Low-temperature plasma-assisted purification: Dielectric barrier discharge (DBD) plasma is introduced during the distillation process, and high-energy electrons are used to break the N-O / S bonds. Experimental data shows that at a power of 200 W and a frequency of 10 kHz, the nitrogen removal efficiency is increased by 3-4 orders of magnitude.

[0011] Supercritical fluid extraction: Supercritical CO2 is used as the extractant, and multi-stage countercurrent extraction of pre-distilled sulfuric acid is carried out at 25 MPa and 50 °C. Patents of BASF in Germany show that the selectivity coefficient of this method for nitrates can reach more than 500.

[0012] Electrochemical migration method: An electrodialysis system is constructed based on a Nafion membrane. Under the action of a strong electric field, the migration rate of nitrogen-containing ions is 20-30 times faster than that of SO4 2- and is particularly suitable for the removal of ammonium salts.

[0013] There is an urgent need to establish a grading standard system:

[0014] Industrial grade (≤1 ppm): Meeting the needs of traditional metallurgy and fertilizers; Electronic grade (≤100 ppb): Suitable for photovoltaic and ordinary PCB manufacturing; Ultra-pure grade (≤10 ppb): For advanced semiconductors and display panels; Cutting-edge grade (≤1 ppb): Used in the manufacturing of third-generation semiconductors and quantum devices.

[0015] With the rapid development of emerging industries such as 5G, artificial intelligence, and new energy vehicles, it is expected that the global market size of ultra-high purity sulfuric acid will exceed $5 billion by 2026. This demand is forcing the upgrading and transformation of basic chemical materials, and promoting the leap of sulfuric acid purification technology from traditional chemistry to precision manufacturing. Summary of the Invention

[0016] The present invention provides a production process for reducing the nitrogen content in reagent-grade sulfuric acid. By adopting gradient temperature rise in coordination with urea-ammonium sulfate chemical denitrification, and using vacuum distillation to synchronously purge nitrogen-containing gas compounds in sulfuric acid with inert gas pulses, the total nitrogen content, NH4 + ions and NO3 - ions in reagent-grade sulfuric acid are effectively reduced, and electronic-grade sulfuric acid is obtained, with a sulfuric acid yield of up to 97.5%.

[0017] A production process for reducing the nitrogen content in reagent-grade sulfuric acid includes the following steps:

[0018] S100. At 55 - 65 °C, in sulfuric acid, add solid urea powder in a mass ratio of urea to sulfuric acid of 0.001 - 0.01:100, and stir until completely dissolved.

[0019] S200. Gradually heat up the mixture in step S100 to 84 - 86 °C. During the heating process, add ammonium sulfate powder in a mass ratio of ammonium sulfate to sulfuric acid of 0.05 - 0.1:100, and stir and react for 0.8 - 1.2 h.

[0020] S300. The sulfuric acid after the reaction in step S200 is subjected to vacuum distillation at 80 - 150 °C. During the heating process, inert gas is pulsed and introduced for purging synchronously, and repeat 2 - 3 times, then collect the main distillate.

[0021] S400. Tail gas treatment.

[0022] In the present invention, ammonium sulfate is added to sulfuric acid, and ammonium nitrate is formed through an ion exchange reaction, and its thermal instability is utilized to achieve deep denitrification. However, single ammonium sulfate cannot completely remove the stable association formed by nitrogen compounds in sulfuric acid and sulfuric acid. Urea reacts with nitric acid in an acidic environment to generate N2, CO2 and H2O, completely destroying nitrogen oxides and producing no solid by-products; ammonium sulfate additionally provides NH4 + , which combines with the remaining NO3 - to form thermally unstable ammonium nitrate. Ammonium nitrate decomposes into N2O and H2O above 85 °C. Urea chemically reduces NO3 - , and ammonium sulfate reacts with NO3 - impurities in sulfuric acid to form ammonium nitrate, and nitrogen is removed through thermal decomposition, covering all forms of nitrogen-containing impurities. In addition, urea can inhibit the high-temperature decomposition of ammonium sulfate to release ammonia and avoid secondary pollution. The pulsed injection of inert gas destroys the gas-liquid equilibrium and promotes the overflow of gases such as N2O, NO and NO2, avoiding redissolution.

[0023] Principle of urea-ammonium sulfate synergistic denitrification: Ammonium sulfate dissociates into NH4 + in concentrated sulfuric acid, and sulfuric acid itself also dissociates into H + , HSO4 - or SO4 2- . The main ions in the system include NH4 + , NO3 - , H + , HSO4 - . Formation of ammonium nitrate: NH4 + +NO3 - ⇌NH4NO3. In reagent-grade sulfuric acid, the concentration of NO3 - is usually low, and by adding ammonium sulfate externally, the concentration of NH4 +The concentration promotes the equilibrium to shift to the right, generating ammonium nitrate; meanwhile, the strongly acidic environment provided by sulfuric acid inhibits the hydrolysis of NH4 + and is conducive to the combination of NH4 + and NO3 - . Ammonium nitrate is thermally unstable and easily decomposes above 80 °C. The decomposition products are N2O and H2O, which can overflow during the distillation process, thus achieving nitrogen removal; in addition, the strongly acidic environment of reagent-grade sulfuric acid can catalyze the decomposition of ammonium nitrate to generate nitric acid and ammonium bisulfate, and the generated nitric acid further decomposes into NO, NO2 and H2O, which are finally removed by distillation. Single ammonium sulfate has limited effect on removing complex nitro sulfuric acid. Urea hydrolyzes in an acidic condition to generate ammonium ions (NH4 + ) and cyanic acid (HCNO). Cyanic acid further reacts with nitric acid to generate nitrogen, carbon dioxide and water, which can completely remove nitrogen impurities without generating solid by-products.

[0024] In the present invention, through the synergistic effect of urea and ammonium sulfate, nitrogen in different valence states in sulfuric acid (NH4 + , NO3 - ) is converted into volatile gases. Vacuum distillation separates H2SO4 and nitrogen-containing gases through boiling point differences, and inert gas-assisted purge mass transfer carries away nitrogen-containing gases; chemical reduction solves dissolved NO3 - , physical distillation removes gaseous nitrides, and the synergistic effect of chemical reduction and physical distillation realizes effective nitrogen removal.

[0025] Furthermore, in step S100, the particle size of the urea powder is 50 - 100 microns; the stirring rate is 80 - 100 rpm, and the reaction time is 20 - 30 min.

[0026] Furthermore, in step S200, the gradient temperature increase includes: heating from 65 °C to 75 °C at a heating rate of 1 °C / min and holding for 10 min; heating from 75 °C to 85 °C at a heating rate of 0.5 °C / min and holding for 30 - 40 min.

[0027] Heating from 65 °C to 75 °C at a heating rate of 1 °C / min to avoid rapid temperature rise, which may cause rapid pyrolysis of urea; a heating rate of 0.5 °C / min promotes the full reaction of NH4 + and NO3 - to generate NH4NO3, and simultaneously initiates the decomposition of NH4NO3 to release N2O. Holding for 30 - 40 min to maintain the reaction equilibrium until the online detection of NO3 - ≤0.1 ppm, then stop the reaction.

[0028] Further, in step S200, when the temperature rises to 75°C, ammonium sulfate is added at a rate of 0.05 - 0.1 kg / min and added within 10 - 20 minutes, with a synchronous stirring rate of 80 - 100 rpm; the particle size of the ammonium sulfate is 50 - 100 μm.

[0029] Under the condition of 55 - 65°C, add urea first to avoid the direct reaction between urea and sulfuric acid at high temperature, then add ammonium sulfate at 75°C to prevent the premature decomposition of ammonium nitrate, and ensure the balance between the formation and decomposition of ammonium nitrate at 85°C to avoid boiling over.

[0030] Further, in step S300, the inert gas includes one or both of nitrogen and argon.

[0031] Further, in step S300, under normal pressure, under a pressure of 49.5 - 50.5 kPa, the inert gas pulses, and the initial fraction is collected at 80 - 100°C; under a pressure of 19.5 - 20.5 kPa, the inert gas pulses, and the main fraction is collected at 100 - 130°C; under a pressure of 4.8 - 5.2 kPa, the impurity fraction is collected at 130 - 150°C.

[0032] Lowering the pressure reduces the boiling point, preferentially removing the initial fraction of light components such as water and volatile HNO3; under moderately vacuum conditions, H2SO4 selectively volatilizes, and N2 and N2O are purged out by the inert gas, obtaining the high-purity H2SO4 main fraction; deep decompression forces the decomposition of hardly volatile impurities (HSO4NO2) or they remain at the bottom of the kettle.

[0033] Further, the collection duration of the initial fraction is 10 - 15 min, the collection duration of the main fraction is 2 - 3 h, and the collection duration of the impurity fraction is 30 - 45 min.

[0034] Further, in step S300, under a pressure of 49.5 - 50.5 kPa, nitrogen pulses, with a ventilation time of 5 seconds and a gas cut-off time of 10 seconds, and this is cycled; under a pressure of 19.5 - 20.5 kPa, argon pulses, with a ventilation time of 3 seconds and a gas cut-off time of 15 seconds, and this is cycled; the gas flow rate is 0.5 - 1.0 L / min.

[0035] Further, the tail gas treatment includes the condensation and recovery of H2SO4 mist. Use -10°C ethylene glycol solution to condense and recover the H2SO4 mist, and combine the recovered H2SO4 mist with the main fraction.

[0036] Further, the tail gas treatment also includes using an alkali solution to absorb nitrogen oxides, and the alkali solution includes 8 - 10% NaOH and 4 - 6% H2O2.

[0037] Preparation of NaOH solution: Add about 800 L of deionized water into an alkali-resistant container, and slowly add NaOH particles (stirring rate ≤ 50 rpm); after complete dissolution, make up the water to 1 m³ and cool it to 25 °C. Addition of H2O2: Before use, inject H2O2 into the NaOH solution using a plastic pump, avoid metal contact, and stir and mix for 10 minutes (rotation speed 30 rpm).

[0038] H2O2 oxidizes to break through the limitation of the NO dissolution equilibrium, oxidizes the insoluble NO to NO2, and then is absorbed by the NaOH solution to generate sodium nitrite and sodium nitrate, realizing the solidification of nitrogen and avoiding air pollution. For N2O that is difficult to remove, a Cu-Zn catalyst bed layer (300 - 400 °C) can be added to decompose N2O into nitrogen and oxygen.

[0039] Advantages of the invention

[0040] In the present invention, through the synergistic action of urea and ammonium sulfate, nitrogen in different valence states in sulfuric acid (NH4 + 、NO3 - )is converted into volatile gases, and by setting a gradient temperature rise, the denitrification reaction is ensured to proceed efficiently. Then, through vacuum distillation, H2SO4 and nitrogen-containing gases are separated by boiling point difference, and inert gas is used to assist in purging and mass transfer to carry away the nitrogen-containing gases; the synergistic action of chemical reduction and physical distillation realizes efficient nitrogen removal, effectively reducing the total nitrogen content, NH4 + ion and NO3 - ion content in reagent-grade sulfuric acid to obtain electronic-grade sulfuric acid, and the sulfuric acid yield can reach 97.5%. Detailed implementation manners

[0041] Example 1

[0042] A production process for reducing the nitrogen content in reagent-grade sulfuric acid includes the following steps:

[0043] S100. At 60 °C, add 0.05 kg of urea solid powder with a particle size of 50 μm to 1000 kg of sulfuric acid, and stir at 90 rpm for 25 min until completely dissolved;

[0044] S200. Heat the mixture in step S100 from 65 °C to 75 °C at a heating rate of 1 °C / min; when the temperature reaches 75 °C, add 0.75 kg of ammonium sulfate powder with a particle size of 75 microns at a rate of 0.05 kg / min, stir at a rate of 80 rpm, and keep the temperature for 10 min; heat from 75 °C to 85 °C at a heating rate of 0.5 °C / min and keep the temperature for 35 min;

[0045] S300. Under normal pressure and a pressure of 50 kPa, nitrogen pulses are applied with a ventilation time of 5 seconds and a gas cutoff time of 10 seconds, cycling continuously. The initial distillate is collected at 80 - 100 °C for 12 minutes; under a pressure of 20 kPa, argon pulses are applied with a ventilation time of 3 seconds and a gas cutoff time of 15 seconds, cycling continuously. The main H2SO4 distillate is collected at 100 - 130 °C for 2 hours; under a pressure of 5 kPa, the impurity distillate is collected at 130 - 150 °C for 40 minutes; the gas flow rate is 0.8 L / min.

[0046] S400. Tail gas treatment: The H2SO4 mist is condensed and recovered. The -10 °C ethylene glycol solution is used to condense and recover the H2SO4 mist, and the recovered H2SO4 mist is combined with the main distillate; alkaline solution is used to absorb nitrogen oxides, and the alkaline solution includes 10% NaOH and 4% H2O2.

[0047] Example 2

[0048] A production process for reducing the nitrogen content in reagent-grade sulfuric acid, comprising the following steps:

[0049] S100. Under the condition of 55 °C, 0.01 kg of urea solid powder with a particle size of 100 μm is added to 1000 kg of sulfuric acid, and stirred at 80 rpm for 20 minutes until completely dissolved;

[0050] S200. The mixture in step S100 is heated from 65 °C to 75 °C at a heating rate of 1 °C / min; when the temperature reaches 75 °C, 0.5 kg of ammonium sulfate powder with a particle size of 100 microns is added at a rate of 0.05 kg / min, and the stirring rate is 100 rpm, and kept warm for 10 minutes; heated from 75 °C to 84 °C at a heating rate of 0.5 °C / min, and kept warm for 40 minutes;

[0051] S300. Under normal pressure and a pressure of 49.5 kPa, nitrogen pulses are applied with a ventilation time of 5 seconds and a gas cutoff time of 10 seconds, cycling continuously. The initial distillate is collected at 80 - 100 °C for 10 minutes; under a pressure of 20.5 kPa, argon pulses are applied with a ventilation time of 3 seconds and a gas cutoff time of 15 seconds, cycling continuously. The main H2SO4 distillate is collected at 100 - 130 °C for 2.5 hours; under a pressure of 4.8 kPa, the impurity distillate is collected at 130 - 150 °C for 45 minutes; the gas flow rate is 1.0 L / min.

[0052] S400. Tail gas treatment: The H2SO4 mist is condensed and recovered. The -10 °C ethylene glycol solution is used to condense and recover the H2SO4 mist, and the recovered H2SO4 mist is combined with the main distillate; alkaline solution is used to absorb nitrogen oxides, and the alkaline solution includes 8% NaOH and 6% H2O2.

[0053] Example 3

[0054] A production process for reducing the nitrogen content in reagent-grade sulfuric acid, comprising the following steps:

[0055] S100. At 65 °C, add 0.1 kg of urea solid powder with a particle size of 80 μm to 1000 kg of sulfuric acid, and stir at 100 rpm for 30 min until completely dissolved.

[0056] S200. Heat the mixture in step S100 from 65 °C to 75 °C at a heating rate of 1 °C / min. When the temperature reaches 75 °C, add 1.0 kg of ammonium sulfate powder with a particle size of 50 μm at a rate of 0.1 kg / min, stir at a rate of 90 rpm, and keep warm for 10 min. Heat from 75 °C to 85 °C at a heating rate of 0.5 °C / min and keep warm for 30 min.

[0057] S300. Under normal pressure and a pressure of 50 kPa, perform nitrogen pulsing, with a ventilation time of 5 s and a gas cutoff time of 10 s, and cycle. Collect the initial distillate at 80 - 100 °C for 15 min. Under a pressure of 20 kPa, perform argon pulsing, with a ventilation time of 3 s and a gas cutoff time of 15 s, and cycle. Collect the main H2SO4 distillate at 100 - 130 °C for 3 h. Under a pressure of 5 kPa, collect the impurity distillate at 130 - 150 °C for 30 min. The gas flow rate is 0.5 L / min.

[0058] S400. Tail gas treatment: Condense and recover the H2SO4 mist. Use -10 °C ethylene glycol solution to condense and recover the H2SO4 mist, and combine the recovered H2SO4 mist with the main distillate. Absorb nitrogen oxides with an alkali solution, and the alkali solution includes 9% NaOH and 5% H2O2.

[0059] Example 4

[0060] A production process for reducing the nitrogen content in reagent-grade sulfuric acid, comprising the following steps:

[0061] S100. At 62 °C, add 0.07 kg of urea solid powder with a particle size of 80 μm to 1000 kg of sulfuric acid, and stir at 85 rpm for 28 min until completely dissolved.

[0062] S200. Heat the mixture in step S100 from 65 °C to 75 °C at a heating rate of 1 °C / min. When the temperature reaches 75 °C, add 0.6 kg of ammonium sulfate powder with a particle size of 50 μm at a rate of 0.06 kg / min, stir at a rate of 100 rpm, and keep warm for 10 min. Heat from 75 °C to 86 °C at a heating rate of 0.5 °C / min and keep warm for 33 min.

[0063] S300. At normal pressure and a pressure of 50.5 kPa, nitrogen pulses are applied. The gas is let in for 5 seconds and then cut off for 10 seconds, cycling continuously. The initial distillate is collected at 80 - 100 °C for 13 minutes. At a pressure of 19.5 kPa, argon pulses are applied. The gas is let in for 3 seconds and then cut off for 15 seconds, cycling continuously. The main H2SO4 distillate is collected at 100 - 130 °C for 2.8 hours. At a pressure of 5.2 kPa, the impurity distillate is collected at 130 - 150 °C for 30 minutes. The gas flow rate is 0.6 L / min.

[0064] S400. Tail gas treatment: The H2SO4 mist is condensed and recovered. The -10 °C ethylene glycol solution is used to condense and recover the H2SO4 mist, and the recovered H2SO4 mist is combined with the main distillate. Alkaline solution is used to absorb nitrogen oxides, and the alkaline solution includes 10% NaOH and 5% H2O2.

[0065] Comparative Example 1

[0066] A production process for reducing the nitrogen content in reagent-grade sulfuric acid includes the following steps:

[0067] S100. Heat the sulfuric acid from 65 °C to 75 °C at a heating rate of 1 °C / min. When the temperature reaches 75 °C, add 1.0 kg of ammonium sulfate powder with a particle size of 50 microns at a rate of 0.1 kg / min, with a stirring rate of 90 rpm, and keep the temperature for 10 minutes. Heat from 75 °C to 85 °C at a heating rate of 0.5 °C / min and keep the temperature for 30 minutes.

[0068] S200. At normal pressure and a pressure of 50 kPa, nitrogen pulses are applied. The gas is let in for 5 seconds and then cut off for 10 seconds, cycling continuously. The initial distillate is collected at 80 - 100 °C for 15 minutes. At a pressure of 20 kPa, argon pulses are applied. The gas is let in for 3 seconds and then cut off for 15 seconds, cycling continuously. The main H2SO4 distillate is collected at 100 - 130 °C for 3 hours. At a pressure of 5 kPa, the impurity distillate is collected at 130 - 150 °C for 30 minutes. The gas flow rate is 0.5 L / min.

[0069] S300. Tail gas treatment: The H2SO4 mist is condensed and recovered. The -10 °C ethylene glycol solution is used to condense and recover the H2SO4 mist, and the recovered H2SO4 mist is combined with the main distillate. Alkaline solution is used to absorb nitrogen oxides, and the alkaline solution includes 9% NaOH and 5% H2O2.

[0070] Comparative Example 2

[0071] A production process for reducing the nitrogen content in reagent-grade sulfuric acid includes the following steps:

[0072] S100. At 65 °C, add 0.1 kg of solid urea powder with a particle size of 80 μm to 1000 kg of sulfuric acid, and stir at 100 rpm for 30 min until completely dissolved;

[0073] S200. Directly heat the mixture in step S100 from 65 °C to 85 °C, add 1.0 kg of ammonium sulfate, and keep the temperature for 70 min;

[0074] S300. Under normal pressure and at a pressure of 50 kPa, pulse nitrogen, ventilate for 5 s and stop for 10 s, and cycle. Collect the initial distillate at 80 - 100 °C, and the collection time is 15 min; at a pressure of 20 kPa, pulse argon, ventilate for 3 s and stop for 15 s, and cycle. Collect the main sulfuric acid distillate at 100 - 130 °C, and the collection time is 3 h; at a pressure of 5 kPa, collect the impurity distillate at 130 - 150 °C, and the collection time is 30 min; the gas flow rate is 0.5 L / min.

[0075] S400. Tail gas treatment: Condense and recover the sulfuric acid mist. Use -10 °C ethylene glycol solution to condense and recover the sulfuric acid mist, and combine the recovered sulfuric acid mist with the main distillate; absorb nitrogen oxides with an alkali solution, and the alkali solution includes 9% NaOH and 5% H2O2.

[0076] Comparative Example 3

[0077] A production process for reducing the nitrogen content in reagent-grade sulfuric acid, comprising the following steps:

[0078] S100. At 65 °C, add 0.1 kg of solid urea powder with a particle size of 80 μm to 1000 kg of sulfuric acid, and stir at 100 rpm for 30 min until completely dissolved;

[0079] S200. Heat the mixture in step S100 from 65 °C to 75 °C at a heating rate of 1 °C / min; when the temperature reaches 75 °C, add 1.0 kg of ammonium sulfate powder with a particle size of 50 microns at a rate of 0.1 kg / min, stir at a rate of 90 rpm, and keep the temperature for 10 min; heat from 75 °C to 85 °C at a heating rate of 0.5 °C / min, and keep the temperature for 30 min;

[0080] S300. Under normal pressure and at a pressure of 50 kPa, collect the initial distillate at 80 - 100 °C, and the collection time is 15 min; at a pressure of 20 kPa, collect the main sulfuric acid distillate at 100 - 130 °C, and the collection time is 3 h; at a pressure of 5 kPa, collect the impurity distillate at 130 - 150 °C, and the collection time is 30 min; nitrogen is passed throughout the process, and the gas flow rate is 1 L / min.

[0081] S400, Tail Gas Treatment: Condensation and Recovery of H2SO4 Mist. Use -10°C ethylene glycol solution to condense and recover H2SO4 mist, and combine the recovered H2SO4 mist with the main fraction; use alkali solution to absorb nitrogen oxides, and the alkali solution includes 9% NaOH and 5% H2O2.

[0082] The reagent-grade sulfuric acid was denitrified using the production processes of Examples 1-4, and the results are shown in Table 1.

[0083] Table 1 Results of Denitrifying Reagent-Grade Sulfuric Acid Using the Production Processes of Examples 1-4

[0084] Index Example 1 Example 2 Example 3 Example 4 Total Nitrogen (ppm) 0.018 0.020 0.025 0.021 <![CDATA[NO3 - (ppm)]]> 0.008 0.010 0.0012 0.009 <![CDATA[NH4 + (ppm)]]> 0.0015 0.0018 0.0020 0.0021 Conductivity (μS / cm) 0.35 0.38 0.42 0.40 <![CDATA[H2SO4 yield (%)]]> 97.5 97.1 96.8 96.2

[0085] As shown in Table 1, in Examples 1-4, urea-ammonium sulfate synergistic chemical denitrification was used, and the denitrification reaction was carried out with gradient temperature increase. The gaseous nitrogen-containing compounds were removed by vacuum distillation and synchronous inert gas pulse purge. The total nitrogen contents in the obtained sulfuric acid were 0.018 ppm, 0.020 ppm, 0.025 ppm, and 0.021 ppm respectively, all lower than 0.03 ppm; the contents of NO3 - in the sulfuric acid were 0.008 ppm, 0.010 ppm, 0.0012 ppm, and 0.009 ppm respectively, all lower than 0.01 ppm, and the conductivities were 0.35 μS / cm, 0.38 μS / cm, 0.42 μS / cm, and 0.40 μS / cm respectively, all lower than 0.5 μS / cm. This shows that using the production process of the present invention to denitrify reagent-grade sulfuric acid can achieve efficient denitrification, can obtain electronic-grade sulfuric acid, and the sulfuric acid yield in the production process is higher than 96.2%.

[0086] The reagent-grade sulfuric acid was denitrified using the production processes of Example 3 and Comparative Examples 1-3, and the results are shown in Table 2.

[0087] Table 2 Results of Denitrifying Reagent-Grade Sulfuric Acid Using the Production Processes of Example 3 and Comparative Examples 1-3

[0088] Index Total Nitrogen (ppm) <![CDATA[NO3 - (ppm)]]> <![CDATA[NH4 + (ppm)]]> Conductivity (μS / cm) Yield (%) Example 3 0.025 0.0012 0.0020 0.42 96.8 Comparative Example 1 (without urea) 0.15 0.13 0.02 1.2 95.0 Comparative Example 2 (without gradient temperature increase) 0.57 0.05 0.50 0.8 96.1 Comparative Example 3 (without pulse purge) 0.08 0.03 0.03 0.6 93.7

[0089] In Comparative Examples 1-3, the process parameters in Example 3 were changed respectively, and the results are shown in Table 2. In Comparative Example 1, only ammonium sulfate was used for chemical denitrification without using urea, resulting in incomplete reduction of NO3 - and the content of NO3 - in the sulfuric acid was as high as 0.13 ppm, which was 10 times that of Comparative Example 3, indicating that the synergistic effect of urea-ammonium sulfate in Example 3 significantly reduced the total nitrogen content. In Comparative Example 2, the temperature was directly raised to 85°C and then ammonium sulfate was added, resulting in the thermal decomposition of ammonium sulfate, and the content of NH4 +The residual rate reaches 0.5 ppm, which is 250 times that of Comparative Example 3, indicating that the gradient heating in Example 3 can effectively avoid the residue of NH4 + ; in Comparative Example 3, nitrogen was directly blown throughout the vacuum distillation process, and nitrogen could not effectively desorb N2O, resulting in the total nitrogen content being 3 times that of Comparative Example 3, indicating that the pulse purge in Example 3 can effectively reduce entrainment loss and improve the yield of sulfuric acid. In summary, it shows that the production process of the present invention can efficiently denitrify reagent-grade sulfuric acid.

Claims

1. A production process for reducing the nitrogen content in reagent-grade sulfuric acid, characterized in that, It includes the following steps: S100: Under the condition of 55~65°C, add solid urea powder into sulfuric acid at a mass ratio of urea to sulfuric acid of 0.001~0.01:100, and stir until completely dissolved; S200: Gradually heat up the mixture in step S100 to 84~86°C. During the heating process, add ammonium sulfate powder at a mass ratio of ammonium sulfate to sulfuric acid of 0.05~0.1:100, and stir and react for 0.8~1.2 h; S300: Carry out vacuum distillation on the sulfuric acid after the reaction in step S200 at 80~150°C. During the heating process, synchronously pulse inert gas for purging, repeat 2~3 times, and collect the main fraction; S400: Tail gas treatment.

2. The production process according to claim 1, characterized in that, In step S100, the particle size of the urea powder is 50~100 microns; the stirring rate is 80~100 rpm, and the reaction time is 20~30 min.

3. The production process according to claim 1, characterized in that, In step S200, the gradient heating includes: heating from 65°C to 75°C at a heating rate of 1°C / min and keeping warm for 8~12 min; heating from 75°C to 85°C at a heating rate of 0.5°C / min and keeping warm for 30~40 min.

4. The production process according to claim 3, characterized in that, In step S200, when the temperature rises to 73~75°C, add ammonium sulfate at a rate of 0.05~0.1 kg / min, add it up within 10~20 minutes, and the stirring rate is 80~100 rpm; the particle size of the ammonium sulfate is 50~100 μm.

5. The production process according to claim 1, characterized in that, In step S300, the inert gas includes one or both of nitrogen and argon.

6. The production process according to claim 5, wherein In step S300, under normal pressure, at a pressure of 49.5~50.5 kPa, pulse the inert gas, and collect the initial fraction at 80~100°C; At a pressure of 19.5~20.5 kPa, pulse the inert gas, and collect the main fraction at 100~130°C; at a pressure of 4.8~5.2 kPa, collect the impurity fraction at 130~150°C.

7. The production process according to claim 6, characterized in that, The collection duration of the initial fraction is 10~15 min, the collection duration of the main fraction is 2~3 h, and the collection duration of the impurity fraction is 30~45 min.

8. The production process according to claim 6, characterized in that, In step S300, at a pressure of 49.5~50.5 kPa, pulse nitrogen, ventilate for 5 seconds, cut off the gas for 10 seconds, and cycle; at a pressure of 19.5~20.5 kPa, pulse argon, ventilate for 3 seconds, cut off the gas for 15 seconds, and cycle; the gas flow rate is 0.5~1.0 L / min.

9. The production process according to claim 1, characterized in that, The tail gas treatment includes the condensation and recovery of H2SO4 mist. Use -10°C ethylene glycol solution to condense and recover H2SO4 mist, and merge the recovered H2SO4 mist with the main fraction.

10. The production process according to claim 9, wherein, The tail gas treatment further includes absorbing nitrogen oxides with an alkali solution, and the alkali solution includes 8-10% NaOH and 4-6% H2O 2。