Process for the preparation of a reagent grade sulfuric acid with low nitrogen content

Abstract

The present application relates to the field of sulfuric acid preparation, and discloses a preparation process of reagent-grade sulfuric acid with low nitrogen content. The preparation process comprises the following steps: burning sulfur in a combustion furnace to generate a gas containing SO2, mixing the gas with ammonia, and then performing denitration under the action of a denitration catalyst, oxidizing under the action of an oxidation catalyst, and then evaporating in an SO3 evaporator to obtain a gas containing SO3, introducing the gas into an absorption tower to react with purified water, and finally introducing the gas into a degassing tower. The temperature of the burning is 700-820 DEG C, the denitration catalyst is a V2O5 / MnO2 composite, the molar content of V2O5 is 2-10% of the V2O5 / MnO2 composite, and the oxidation catalyst is a TiO2-Co composite. The process can effectively reduce the content of nitrogen-containing impurities in industrial sulfuric acid and improve the purity of the sulfuric acid by using the denitration catalyst and the oxidation catalyst, and reagent-grade sulfuric acid is prepared.

Description

Technical Field

[0001] This invention relates to the field of sulfuric acid preparation, and more specifically to a preparation process for reagent-grade sulfuric acid with low nitrogen content. Background Technology

[0002] In the wet process for producing industrial sulfuric acid, sulfur-containing raw materials typically undergo high-temperature combustion with hot air in an incinerator to generate sulfur dioxide. This process inevitably converts nitrogen from the air and nitrogen-containing impurities in the raw materials into various nitrogen oxide byproducts. These byproducts undergo subsequent conversions and condensation processes, resulting in a high nitrogen content in the produced sulfuric acid, which limits its application in semiconductors, precision chemistry, and high-end analysis. Patent CN120328490A discloses a production process for reducing the nitrogen content in reagent-grade sulfuric acid. This process utilizes gradient heating combined with urea-ammonium sulfate chemical denitrification, and employs vacuum distillation with simultaneous inert gas pulse purging to remove gaseous nitrogen compounds from the sulfuric acid. This effectively reduces the total nitrogen and NH4+ content in reagent-grade sulfuric acid. + Ions and NO3 - The content of ions. However, this process requires multiple heating, distillation and purging steps, which is cumbersome and energy-intensive. At the same time, if the added urea and ammonium sulfate do not react completely or are not removed, they may introduce new impurities.

[0003] Therefore, there is an urgent need for a preparation process of reagent-grade sulfuric acid with low nitrogen content. This process should be simple, easy to implement industrially, and should not only effectively reduce the nitrogen impurity content in industrial sulfuric acid, but also improve the purity of sulfuric acid. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of low nitrogen content and low purity of sulfuric acid in industrial sulfuric acid in the prior art, and to provide a preparation process for reagent-grade sulfuric acid with low nitrogen content. This process can effectively reduce the nitrogen content in industrial sulfuric acid and improve the purity of sulfuric acid by using a denitrification catalyst and an oxidation catalyst to prepare reagent-grade sulfuric acid.

[0005] To achieve the above objectives, the present invention provides a process for preparing reagent-grade sulfuric acid with low nitrogen content, the process comprising:

[0006] S1: Sulfur is placed in a combustion furnace and burned under the influence of combustion-supporting gas to generate SO2-containing gas;

[0007] S2: The SO2 gas obtained in step S1 is mixed with ammonia to obtain a mixed gas, which enters the denitrification unit for denitrification under the action of a denitrification catalyst to obtain denitrification products;

[0008] S3: The denitrification product obtained in step S2 enters the oxidation unit, is oxidized under the action of an oxidation catalyst, and then evaporates in an SO3 evaporator to obtain SO3-containing gas;

[0009] S4: The SO3-containing gas obtained in step S3 is passed into the absorption tower and reacted with purified water, then enters the degassing tower, whereby...

[0010] The combustion temperature described in step S1 is 700-820℃;

[0011] The denitrification catalyst is a V2O5 / MnO2 composite, wherein the molar content of V2O5 is 2-10% of the V2O5 / MnO2 composite.

[0012] The oxidation catalyst is a TiO2-Co complex.

[0013] Through the above technical solution, the preparation process of reagent-grade sulfuric acid with low nitrogen content provided by the present invention achieves the following beneficial effects:

[0014] In this invention, by selecting a V₂O₅ / MnO₂ composite as a denitrification catalyst and a TiO₂-Co composite as an oxidation catalyst, and by controlling the combustion temperature in step S1, the nitrogen-containing impurity content in industrial sulfuric acid can be effectively reduced, and the purity of the sulfuric acid can be improved, ultimately producing reagent-grade sulfuric acid. This reagent-grade sulfuric acid can be used for cleaning and etching semiconductor chips and silicon wafers for ultra-large-scale integrated circuits. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] This invention provides a process for preparing reagent-grade sulfuric acid with low nitrogen content, characterized in that the process includes:

[0017] S1: Sulfur is placed in a combustion furnace and burned under the influence of combustion-supporting gas to generate SO2-containing gas;

[0018] S2: The SO2 gas obtained in step S1 is mixed with ammonia to obtain a mixed gas, which enters the denitrification unit for denitrification under the action of a denitrification catalyst to obtain denitrification products;

[0019] S3: The denitrification product obtained in step S2 enters the oxidation unit, is oxidized under the action of an oxidation catalyst, and then evaporates in an SO3 evaporator to obtain SO3-containing gas;

[0020] S4: The SO3-containing gas obtained in step S3 is passed into the absorption tower and reacted with purified water, then enters the degassing tower, whereby...

[0021] The combustion temperature described in step S1 is 700-820℃.

[0022] The denitrification catalyst is a V2O5 / MnO2 composite, wherein the molar content of V2O5 is 2-10% of the V2O5 / MnO2 composite.

[0023] The oxidation catalyst is a TiO2-Co complex.

[0024] In this invention, when the combustion temperature meets the above-mentioned range, the generation of nitrogen oxide byproducts can be reduced; this invention uses a V2O5 / MnO2 composite as a denitrification catalyst to remove nitrogen oxides from the mixed gas, enabling it to exhibit good catalytic activity even at low temperatures; this invention uses a TiO2-Co composite as an oxidation catalyst to promote the oxidation of SO2 to SO3.

[0025] According to the present invention, preferably, when the mixed gas enters the denitrification unit, the flow rate of the mixed gas is 8000-20000 m³ / h.

[0026] More preferably, the flow rate of the mixed gas is 10,000-15,000 m³ / h.

[0027] In this invention, when the flow rate of the mixed gas meets the above-mentioned range, the catalytic effect of the denitrification catalyst can be further improved, and the nitrogen content of sulfuric acid can be reduced.

[0028] According to the present invention, preferably, the temperature of the denitrification unit is 280-320°C.

[0029] More preferably, the temperature of the denitrification unit is 290-310℃.

[0030] According to the present invention, preferably, the flow rate of the denitrification product entering the oxidation unit is 6000-15000 m³ / h.

[0031] More preferably, the flow rate of the denitrification product entering the oxidation unit is 10,000-13,000 m³ / h.

[0032] According to the present invention, preferably, the temperature of the oxidation unit is 300-400°C.

[0033] More preferably, the temperature of the oxidation unit is 320-350°C.

[0034] According to the present invention, preferably, the preparation method of the denitrification catalyst includes: placing a manganese salt in an alcohol solution, gelling it, evaporating it, and calcining it to obtain MnO2 powder; impregnating the MnO2 powder in a vanadate solution, and drying and calcining it.

[0035] According to the present invention, preferably, the manganese salt is selected from at least one of manganese chloride, manganese sulfate, manganese fluoride and manganese acetate, and more preferably manganese chloride.

[0036] According to the present invention, preferably, the alcohol solution is selected from at least one of methanol, ethanol, propanol and ethylene glycol.

[0037] According to the present invention, preferably, the evaporation temperature is 90-120°C.

[0038] According to the present invention, preferably, the vanadate is selected from at least one of ammonium metavanadate, sodium metavanadate, potassium metavanadate, sodium orthovanadate, ammonium orthovanadate, and ammonium pyrovanadate, more preferably at least one of ammonium metavanadate, sodium metavanadate, and potassium metavanadate.

[0039] According to the present invention, preferably, the molar ratio of the vanadate to the MnO2 powder is 0.05-0.2:1.

[0040] More preferably, the molar ratio of the vanadate to the MnO2 powder is 0.08-0.15:1.

[0041] According to the present invention, preferably, the gelation time is 3-8 days.

[0042] More preferably, the gelation time is 4-6 days.

[0043] According to the present invention, preferably, the calcination includes calcining at 250-350°C for 0.5-1 h, followed by calcination at 550-650°C for 0.5-3 h.

[0044] According to the present invention, preferably, the calcination temperature is 550-700°C.

[0045] More preferably, the calcination temperature is 600-650℃.

[0046] According to the present invention, preferably, the preparation method of the oxidation catalyst includes: mixing an imidazole compound and a cobalt salt in the presence of a first solvent, heating and reacting the mixture, soaking it in a second solvent, drying it, adding titanium hydroxide, and then calcining it.

[0047] According to the present invention, preferably, the imidazole compound is selected from at least one of 2-methylimidazole, benzimidazole and 2-nitroimidazole.

[0048] More preferably, the imidazole compound is selected from 2-methylimidazole.

[0049] According to the present invention, preferably, the cobalt salt is selected from at least one of cobalt chloride, cobalt acetate, cobalt nitrate, cobalt carbonate, cobalt oxalate, and cobalt sulfate.

[0050] More preferably, the cobalt salt is selected from cobalt chloride and / or cobalt oxalate.

[0051] According to the present invention, preferably, the first solvent is at least one selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, formic acid and acetic acid.

[0052] According to the present invention, preferably, the first solvent is a mixture of N,N-dimethylformamide and formic acid.

[0053] More preferably, the volume ratio of N,N-dimethylformamide to formic acid is 1:1.

[0054] According to the present invention, preferably, the second solvent is selected from at least one of methanol, ethanol, propanol and ethylene glycol.

[0055] According to the present invention, preferably, the temperature of the heating reaction is 80-150°C.

[0056] More preferably, the temperature of the heating reaction is 100-120°C.

[0057] According to the present invention, preferably, the soaking time is 48-96 hours.

[0058] More preferably, the soaking time is 60-80 hours.

[0059] According to the present invention, preferably, the molar ratio of titanium hydroxide to cobalt salt is 0.005-0.03:1.

[0060] More preferably, the molar ratio of titanium hydroxide to cobalt salt is 0.01-0.02:1.

[0061] According to the present invention, preferably, the sulfur has a particle size of 50-80 micrometers.

[0062] More preferably, the sulfur has a particle size of 60-70 micrometers.

[0063] In this invention, when the particle size of sulfur meets the above-mentioned range, it can further promote more complete combustion of sulfur, while avoiding sulfur clogging the channel of the combustion furnace into the denitrification unit.

[0064] According to the present invention, preferably, the oxygen content in the combustion-supporting gas is 25-45 wt%.

[0065] More preferably, the oxygen content in the combustion-supporting gas is 30-40 wt%.

[0066] According to the present invention, preferably, the combustion time is 2-24 hours.

[0067] More preferably, the combustion time is 4-12 hours.

[0068] According to the present invention, preferably, the combustion furnace is connected to an external waste heat recovery device, which is connected to the liquid ammonia vaporizer and the SO3 vaporization chamber, thereby saving energy consumption in the preparation process.

[0069] The present invention does not impose any special restrictions on the structure of the SO3 evaporator. Preferably, the SO3 evaporator is a tower structure. In step S3, the denitrification product is converted into liquid SO3 under the action of an oxidation catalyst. The liquid SO3 enters the evaporator from the upper part of the equipment, the gaseous SO3 is discharged from the top, and the residual liquid is discharged from the bottom. The equipment can operate continuously and can remove most of the heavy component impurities such as residual sulfuric acid, nitrate, ammonium salt, and ash.

[0070] The present invention does not impose any special restrictions on the structure of the absorption tower. Preferably, the absorption tower is made of Q235 steel, lined with ultrapure PTFE, and equipped with an external demister, so as to better control the interference of sulfuric acid return on product quality.

[0071] According to the present invention, preferably, the packing material of the absorption tower is ultrapure PFA Raschig rings, and the height of the absorption tower is 2-4 m.

[0072] According to the present invention, preferably, the absorption tower is connected to a circulating acid tank, and the circulating acid tank pumps low-concentration sulfuric acid into the absorption tower via a pump.

[0073] In this invention, the temperature and concentration of sulfuric acid after SO3 absorption in the absorption tower increase, and it flows back to the circulating acid tank by gravity. At the same time, a certain amount of purified water is added to the circulating acid tank to balance the concentration of the circulating absorption acid.

[0074] According to the present invention, preferably, step S4 further includes introducing ozone into the absorption tower, wherein the flow ratio of ozone to denitrification products is 0.01-0.2:1.

[0075] More preferably, the flow ratio of ozone to denitrification products is 0.1-0.15:1.

[0076] In this invention, ozone is introduced into the absorption tower to promote the conversion of SO2 into SO3 in the SO3-containing gas prepared in step S3, thereby improving the purity of sulfuric acid.

[0077] According to the present invention, preferably, in the packed tower structure of the degassing tower, the sulfuric acid obtained after the reaction of SO3-containing gas with purified water in step S4 enters from the top of the degassing tower and exits from the bottom, and the gas obtained after the reaction of SO3-containing gas with purified water in step S4 enters from the bottom of the degassing tower and exits from the top.

[0078] According to the present invention, preferably, the degassing tower and the acid receiving tank form an integrated tower-tank structure.

[0079] According to the present invention, preferably, the degassing tower contains a spray-type acid separator, wherein the spray density of the acid separator is 10-50 m³ / s. 3 / (m 2 ·h).

[0080] The present invention will be described in detail below with reference to the embodiments.

[0081] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0082] Preparation Example 1

[0083] (1) Manganese chloride was added dropwise to ethanol and gelled for 5 days to form a sol-gel. The gel was evaporated at 80°C until a dry gel was obtained. The dry gel was calcined at 300°C for 0.8 h and then calcined at 600°C for 2 h to obtain MnO2 powder.

[0084] (2) MnO2 powder was impregnated in oxalic acid solution of NH4VO3, wherein the molar ratio of vanadate to MnO2 powder was 0.1:1, the impregnation time was 3h, and then dried at 120℃ for 2h to obtain powder. The powder was placed in a muffle furnace and calcined at 600℃ for 4h to prepare denitrification catalyst-1 with a molar content of 4% V2O5.

[0085] Preparation Example 2

[0086] (1) Manganese chloride was added dropwise to ethanol and gelled for 5 days to form a sol-gel. The gel was evaporated at 80°C until a dry gel was obtained. The dry gel was calcined at 300°C for 0.8 h and then calcined at 600°C for 2 h to obtain MnO2 powder.

[0087] (2) MnO2 powder was impregnated in oxalic acid solution of NH4VO3, wherein the molar ratio of vanadate to MnO2 powder was 0.3:1, the impregnation time was 4h, and then dried at 120℃ for 2h to obtain powder. The powder was placed in a muffle furnace and calcined at 650℃ for 4h to prepare denitrification catalyst-2 with a molar content of V2O5 of 12%.

[0088] Preparation Example 3

[0089] 2-Methylimidazole was dissolved in a mixed solution of DMF and formic acid. After stirring for 30 min, cobalt chloride hexahydrate was added and stirred for another 30 min until the solid was completely dissolved. The mixed solution was transferred to a steel pressure reactor lined with polytetrafluoroethylene (PTFE). The volume ratio of DMF to formic acid was 1:1. The reaction temperature was 100 °C, and the reaction time was 48 h. The solid was centrifuged and soaked in methanol at room temperature for 72 h, with the methanol being replaced every 24 h. After soaking, it was vacuum dried at 100 °C. A titanium hydroxide solution was added, and the mixture was calcined at 600 °C. The molar ratio of titanium hydroxide to cobalt salt was 0.01:1. This yielded oxidation catalyst-1.

[0090] Example 1

[0091] S1: Sulfur with a particle size of 60 micrometers is placed in a combustion furnace and burned in air to generate a mixed gas containing SO2. The combustion furnace is connected to a waste heat recovery device, which is connected to a liquid ammonia vaporizer and an SO3 vaporization chamber. The oxygen content in the air is 32%, the combustion temperature is 780℃, and the combustion time is 6 hours.

[0092] S2: Liquid ammonia is vaporized in the liquid ammonia vaporizer and mixed with SO2 in a mixed gas. It then enters the denitrification unit and, under the action of denitrification catalyst-1, denitrification products are obtained. The flow rate of the mixed gas entering the denitrification unit is 12000 m³ / h, and the denitrification temperature is 300℃.

[0093] S3: The denitrification product obtained in step S2 enters the oxidation unit and obtains a product containing SO3 under the action of oxidation catalyst-1. The product is then indirectly heat-exchanged in the SO3 evaporator to obtain a gas containing SO3. The flow rate of the denitrification product entering the oxidation unit is 8000 m³ / h, the oxidation temperature is 320℃, the oxidation time is 4h, and the evaporation temperature of the SO3 evaporator is 150℃.

[0094] S4: The SO3-containing gas and ozone prepared in step S3 are introduced into an absorption tower. The absorption tower is connected to a circulating acid tank. The circulating acid tank pumps low-concentration sulfuric acid into the absorption tower. The SO3-containing gas reacts with the low-concentration sulfuric acid and water in the absorption tower, and then enters a degassing tower. The degassing tower contains a spray-type acid separator. After passing through a filtration unit, low-nitrogen reagent-grade sulfuric acid is obtained. The flow ratio of ozone to denitrification products is 0.15:1. In the degassing tower, the spray density of 99wt% sulfuric acid is 20m³. 3 / (m 2 ·h).

[0095] Example 2

[0096] S1: Sulfur with a particle size of 80 micrometers is placed in a combustion furnace and burned in air to generate a mixed gas containing SO2. The combustion furnace is connected to a waste heat recovery device, which is connected to a liquid ammonia vaporizer and an SO3 vaporization chamber. The oxygen content in the air is 32%, the combustion temperature is 800℃, and the combustion time is 6 hours.

[0097] S2: Liquid ammonia is vaporized in the liquid ammonia vaporizer and mixed with SO2 in a mixed gas. It then enters the denitrification unit and, under the action of denitrification catalyst-1, denitrification products are obtained. The flow rate of the mixed gas entering the denitrification unit is 15000 m³ / h, and the denitrification temperature is 300℃.

[0098] S3: The denitrification product obtained in step S2 enters the oxidation unit and obtains a product containing SO3 under the action of oxidation catalyst-1. The product is then indirectly heat-exchanged in the SO3 evaporator to obtain a gas containing SO3. The flow rate of the denitrification product entering the oxidation unit is 12000 m³ / h, the oxidation temperature is 380℃, the oxidation time is 6h, and the evaporation temperature of the SO3 evaporator is 150℃.

[0099] S4: The SO3-containing gas and ozone prepared in step S3 are introduced into an absorption tower. The absorption tower is connected to a circulating acid tank. The circulating acid tank pumps low-concentration sulfuric acid into the absorption tower. The SO3-containing gas reacts with the low-concentration sulfuric acid and water in the absorption tower, and then enters a degassing tower. The degassing tower contains a spray-type acid separator. After passing through a filtration unit, low-nitrogen reagent-grade sulfuric acid is obtained. The flow ratio of ozone to denitrification products is 0.1:1. In the degassing tower, the spray density of 99wt% sulfuric acid is 30m³. 3 / (m 2 ·h).

[0100] Example 3

[0101] S1: Sulfur with a particle size of 100 micrometers is placed in a combustion furnace and burned in air to generate a mixed gas containing SO2. The combustion furnace is connected to a waste heat recovery device, which is connected to a liquid ammonia vaporizer and an SO3 vaporization chamber. The oxygen content in the air is 32%, the combustion temperature is 850℃, and the combustion time is 8 hours.

[0102] S2: Liquid ammonia is vaporized in the liquid ammonia vaporizer and mixed with SO2 in a mixed gas. It then enters the denitrification unit and, under the action of denitrification catalyst-1, denitrification products are obtained. The flow rate of the mixed gas entering the denitrification unit is 23000 m³ / h, and the denitrification temperature is 350℃.

[0103] S3: The denitrification product obtained in step S2 enters the oxidation unit and obtains a product containing SO3 under the action of oxidation catalyst-1. The product is then indirectly heat-exchanged in the SO3 evaporator to obtain a gas containing SO3. The flow rate of the denitrification product entering the oxidation unit is 20000 m³ / h, the oxidation temperature is 380℃, the oxidation time is 6h, and the evaporation temperature of the SO3 evaporator is 150℃.

[0104] S4: The SO3-containing gas and ozone prepared in step S3 are introduced into an absorption tower. The absorption tower is connected to a circulating acid tank. The circulating acid tank pumps low-concentration sulfuric acid into the absorption tower. The SO3-containing gas reacts with the low-concentration sulfuric acid and water in the absorption tower, and then enters a degassing tower. The degassing tower contains a spray-type acid separator. After passing through a filtration unit, low-nitrogen reagent-grade sulfuric acid is obtained. The flow ratio of ozone to denitrification products is 0.1:1. In the degassing tower, the spray density of 99wt% sulfuric acid is 8m³ / h. 3 / (m 2 ·h).

[0105] Example 4

[0106] S1: Sulfur with a particle size of 60 micrometers is placed in a combustion furnace and burned in air to generate a mixed gas containing SO2. The combustion furnace is connected to a waste heat recovery device, which is connected to a liquid ammonia vaporizer and an SO3 vaporization chamber. The oxygen content in the air is 32%, the combustion temperature is 780℃, and the combustion time is 6 hours.

[0107] S2: Liquid ammonia is vaporized in the liquid ammonia vaporizer and mixed with SO2 in a mixed gas. It then enters the denitrification unit and, under the action of denitrification catalyst-1, denitrification products are obtained. The flow rate of the mixed gas entering the denitrification unit is 12000 m³ / h, and the denitrification temperature is 300℃.

[0108] S3: The denitrification product obtained in step S2 enters the oxidation unit and obtains a product containing SO3 under the action of oxidation catalyst-1. The product is then indirectly heat-exchanged in the SO3 evaporator to obtain a gas containing SO3. The flow rate of the denitrification product entering the oxidation unit is 8000 m³ / h, the oxidation temperature is 320℃, the oxidation time is 4h, and the evaporation temperature of the SO3 evaporator is 150℃.

[0109] S4: The SO3-containing gas obtained in step S3 is passed into an absorption tower connected to a circulating acid tank. The circulating acid tank pumps low-concentration sulfuric acid into the absorption tower. The SO3-containing gas reacts with the low-concentration sulfuric acid and water within the absorption tower, and then enters a degassing tower containing a spray-type acid separator. After passing through a filtration unit, low-nitrogen reagent-grade sulfuric acid is obtained. In the degassing tower, the spray density of 99 wt% sulfuric acid is 20 m³ / s. 3 / (m 2 ·h).

[0110] Comparative Example 1

[0111] Concentrated sulfuric acid was prepared according to the method of Example 1, except that denitrification catalyst-2 was used instead of denitrification catalyst-1 in step S2.

[0112] Comparative Example 2

[0113] Concentrated sulfuric acid was prepared according to the method of Example 1, except that in step S1, the combustion temperature was 1200°C.

[0114] Test Example 1

[0115] The concentrated sulfuric acid prepared in the examples and comparative examples was tested for sulfuric acid mass fraction and nitrogen content. The test results are shown in Table 1.

[0116] The method for determining the mass fraction of sulfuric acid in concentrated sulfuric acid is in accordance with GB / T 534-2024.

[0117] The nitrogen content of concentrated sulfuric acid was determined by spectrophotometry.

[0118] Table 1

[0119] Nitrogen content (wt%) Sulfuric acid mass fraction (wt%) Example 1 ≤0.001 99.2 Example 2 ≤0.001 99.0 Example 3 0.005 98.6 Example 4 0.01 98.2 Comparative Example 1 0.3 93.5 Comparative Example 2 0.1 94.3

[0120] According to the data in Table 1, this invention, by selecting a V₂O₅ / MnO₂ composite as the denitrification catalyst, a TiO₂-Co composite as the oxidation catalyst, and lowering the combustion temperature in step S1, can prepare reagent-grade sulfuric acid with a nitrogen content ≤0.01wt% and a sulfuric acid mass fraction ≥98.2wt%. As can be seen from Example 4, introducing ozone into the absorption tower can improve the purity of sulfuric acid.

[0121] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A process for preparing reagent-grade sulfuric acid with low nitrogen content, characterized in that, The process includes: S1: Sulfur is placed in a combustion furnace and burned under the influence of combustion-supporting gas to generate SO2-containing gas; S2: The SO2 gas obtained in step S1 is mixed with ammonia to obtain a mixed gas, which enters the denitrification unit for denitrification under the action of a denitrification catalyst to obtain denitrification products; S3: The denitrification product obtained in step S2 enters the oxidation unit, is oxidized under the action of an oxidation catalyst, and then evaporates in an SO3 evaporator to obtain SO3-containing gas; S4: The SO3-containing gas obtained in step S3 is passed into the absorption tower and reacted with purified water, then enters the degassing tower, whereby... The combustion temperature in S1 is 700-780℃; The denitrification catalyst is a V2O5 / MnO2 composite, wherein the molar content of V2O5 is 2-10% of the V2O5 / MnO2 composite. The oxidation catalyst is a TiO2-Co complex; The reagent-grade sulfuric acid contains ≤0.01 wt% nitrogen. The preparation method of the oxidation catalyst includes: mixing an imidazole compound and a cobalt salt in the presence of a first solvent, heating and reacting the mixture, soaking it in a second solvent, drying it, adding a solution of titanium hydroxide, and then calcining it. S4 also includes introducing ozone into the absorption tower, wherein the flow rate ratio of ozone to denitrification products is 0.01-0.2:

1.

2. The preparation process according to claim 1, wherein, When the mixed gas enters the denitrification unit, the flow rate of the mixed gas is 8000-20000 m³ / h; The temperature of the denitrification unit is 280-320℃; The flow rate of the denitrification products entering the oxidation unit is 6000-15000 m³ / h; The temperature of the oxidation unit is 300-400℃.

3. The preparation process according to claim 1 or 2, wherein, The preparation method of the denitrification catalyst includes: placing manganese salt in an alcohol solution, gelling it, evaporating it, and calcining it to obtain MnO2 powder; impregnating the MnO2 powder in a vanadate solution, and drying and calcining it.

4. The preparation process according to claim 3, wherein, The manganese salt is selected from at least one of manganese chloride, manganese sulfate, manganese fluoride, and manganese acetate; The vanadate is selected from at least one of ammonium metavanadate, sodium metavanadate, potassium metavanadate, sodium orthovanadate, ammonium orthovanadate, and ammonium pyrovanadate. The molar ratio of vanadate to MnO2 powder is 0.05-0.2:1; The gelation time is 3-8 days; The calcination includes calcining at 250-350℃ for 0.5-1h, followed by calcination at 550-650℃ for 0.5-3h. The roasting temperature is 550-700℃.

5. The preparation process according to claim 1, wherein, The imidazole compound is selected from at least one of 2-methylimidazolium, benzimidazole and 2-nitroimidazolium; The cobalt salt is selected from at least one of cobalt chloride, cobalt acetate, cobalt nitrate, cobalt carbonate, cobalt oxalate, and cobalt sulfate; The first solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, formic acid, and acetic acid; The second solvent is selected from at least one of methanol, ethanol, propanol, and ethylene glycol; The molar ratio of titanium hydroxide to cobalt salt is 0.005-0.03:

1.

6. The preparation process according to claim 1, wherein, The sulfur has a particle size of 50-80 micrometers; The oxygen content in the combustion-supporting gas is 25-45 wt%. The combustion time is 4-12 hours.

7. The preparation process according to claim 1, wherein, The absorption tower is connected to a circulating acid tank, and the circulating acid tank pumps low-concentration sulfuric acid into the absorption tower via a pump.

8. The preparation process according to claim 1, wherein, The degassing tower contains a spray-type acid separator, the spray density of which is 10-50 m³ / h. 3 / (m 2 ·h).