Process for producing sodium chlorite without waste acid

Abstract

The application discloses a kind of waste-free acid sodium chlorite production process in the field of inorganic chemical materials green preparation technology, process uses new multi-level pore-dual functional site composite modified material, the material is prepared by mesoporous silica base synthesis, metal oxide loading, amino functional group modification and limited calcination four-stage gradient process, with catalytic reaction, adsorption acid impurity and solid-liquid separation function.Employing sodium chlorate, methanol, sulfuric acid as raw material, after the raw material is matched into solution, it is reacted with modified material in reaction kettle, temperature is controlled to 60-62 DEG C reaction;After reaction, temperature is lowered and solid-liquid is separated, filter cake is washed and dried, and then material is recycled;High-purity sodium chlorite solution is obtained by nanofiltration membrane separation of filtrate, sodium sulfate is recovered by evaporation crystallization of intercept liquid and concentrated sulfuric acid is recycled, and sodium chlorite crystal is obtained by crystallization and drying of permeate liquid.The process realizes waste-free acid discharge, reaction time is short, efficiency is high, product purity reaches superior product standard, material can be recycled, and it is environment-friendly.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of green preparation of inorganic chemical materials, and particularly relates to a waste-free acid sodium chlorite production process. BACKGROUND

[0002] Sodium chlorite, as an important chlorine-oxygen compound, is widely used in pulp bleaching, water treatment, and organic synthesis. The traditional production process uses sodium chlorate as raw material to produce sodium chlorite through a disproportionation reaction with a reducing agent (such as methanol) under acidic conditions. However, this process consumes a large amount of sulfuric acid to maintain an acidic environment. After the reaction, the system is left with unreacted sulfuric acid, generated acetic acid, and incompletely converted sodium chlorate. The acidic impurities need to be removed by neutralization with alkali, resulting in a large amount of waste acid containing sodium sulfate and sodium chloride. The treatment of such waste acid is costly, and the neutralization process can easily lead to the oxidation and degradation of the product sodium chlorite, affecting its purity. This has become a key bottleneck for the development of the industry.

[0003] To address the waste acid problem of the traditional process, existing technologies attempt to recover waste acid through membrane separation, extraction, and other methods. However, membrane separation has the problems of high equipment investment and low acid recovery rate. The extraction method can cause secondary pollution due to the presence of organic solvent residues, and it is difficult to achieve industrialization without waste acid. In addition, although electrolysis can produce sodium chlorate, it still requires a supporting acid treatment process, which is energy-intensive and does not solve the fundamental problem of waste acid discharge. The limitations of these technologies indicate that the development of a "waste-free acid" sodium chlorite production process is an urgent need for the green upgrading of the industry.

[0004] Based on the above background, the present application proposes a waste-free acid production process achieved through a new type of composite modified material. This material has the functions of catalyzing reactions, adsorbing acid impurities, and solid-liquid separation, and can simultaneously complete the synthesis of sodium chlorite and the recycling of acid in the reaction system, fundamentally eliminating the generation of waste acid. By optimizing the ratio of raw materials, controlling the reaction conditions, and utilizing the properties of the material, the process significantly improves the reaction efficiency and product purity, while reducing the cost of material recycling, providing an innovative solution for the green preparation of sodium chlorite. SUMMARY

[0005] The present application aims to provide a waste-free acid sodium chlorite production process that solves the technical problems of low reaction efficiency, poor product purity, large waste acid discharge, and non-recyclable materials of the existing traditional process.

[0006] The present application achieves the above-mentioned objectives through the following technical solutions:

[0007] A waste-free acid sodium chlorite production process, comprising the following steps:

[0008] S1, sodium chlorate is crushed and sieved, mixed with deionized water to prepare a sodium chlorate solution; methanol is mixed with deionized water to prepare a methanol solution; sulfuric acid is mixed with deionized water to prepare dilute sulfuric acid; a new multi-level channel-dual functional site composite modified material is taken into a reaction kettle with stirring, a thermometer and a reflux condenser, and sodium chlorate solution, methanol solution and dilute sulfuric acid are sequentially added, stirring is started and heating is started;

[0009] S2, the reaction system is slowly heated to 60-62 DEG C, and constant temperature reaction is carried out, and CIO3 - concentration change determines the end point, when CIO3 - conversion rate > 98%, the reaction is stopped;

[0010] S3, after the reaction is completed, the reaction kettle is cooled to 30-32 DEG C, the solid-liquid mixture is separated by a plate and frame filter press, the filter cake is washed with deionized water, and the washing liquid is combined into the filtrate; after the filter cake is dried at 80-82 DEG C, the new multi-level channel-dual functional site composite modified material is recovered;

[0011] S4, the filtrate is passed through a nanofiltration membrane; the retentate is recovered by evaporation crystallization to recover sodium sulfate, and the remaining concentrated sulfuric acid is recovered; the permeate is heated to 50-52 DEG C, sodium chlorite crystal seeds are slowly added under stirring, and crystallization is carried out by cooling to 20-22 DEG C, and after filtration, vacuum drying is carried out at 60-62 DEG C.

[0012] In the application, the new multi-level channel-dual functional site composite modified material is an amino-modified manganese dioxide coated MCM-41 composite material; the "amino-modified manganese dioxide coated MCM-41 composite material" is a composite catalytic material with multi-level channels and dual functional sites, which defines the core composition and structure of the material completely and explicitly: the MCM-41 molecular sieve with a regular mesoporous channel structure prepared in step A1 is used as a core carrier; a layer of manganese dioxide (MnO2) nanofilm is uniformly coated on the inner and outer surfaces of the MCM-41 carrier by using atomic layer deposition (ALD) technology in step A2, so as to construct the first functional site (metal oxide active site) and further adjust the channel properties of the material; then the MCM-41@MnO2 intermediate is surface modified by using a silane coupling agent 3-aminopropyl triethoxysilane in step A3, and an amino functional group is successfully grafted, so as to introduce the second functional site (organic amine functional site); the final composite material provides a high specific surface area and a diffusion channel by the MCM-41 carrier, provides catalytic activity by the MnO2 coating layer, and provides surface modification and synergistic catalytic function by the surface grafted amino group, and the three together constitute the complete technical connotation of the composite material, and the naming has fully embodied the preparation steps and the final structure.

[0013] According to the preferred embodiment of the present application, in step S1, the crushed product is passed through an 80-100 mesh sieve; the concentration of the sodium chlorate solution is 200-210 g / L; the concentration of the methanol solution is 150-155 g / L; and the concentration of the dilute sulfuric acid is 50-54 g / L.

[0014] According to the preferred embodiment of the present application, the sodium chlorate is purchased from Jiangsu Tianyuan Metal Products Co., Ltd., with a model of industrial grade and a purity of ≥99%.

[0015] According to the preferred embodiment of the present application, the methanol is purchased from Shaanxi Yanchang Petroleum (Group) Co., Ltd., with a model of industrial grade and a purity of ≥99.5%.

[0016] According to the preferred embodiment of the present application, the deionized water is purchased from Shanghai Resin Factory Co., Ltd. (prepared by ion exchange resin), with a model of resistivity ≥18.2 MΩ·cm (25℃).

[0017] According to the preferred embodiment of the present application, the online HPLC is purchased from Shanghai Wufeng Scientific Instrument Co., Ltd., with a model of LC-100 type high performance liquid chromatograph (with ultraviolet detector and C18 chromatographic column).

[0018] According to the preferred embodiment of the present application, the plate-and-frame filter press is purchased from Hangzhou Xingyuan Filtration Technology Co., Ltd., with a model of XAZG100 / 1000-U type plate-and-frame filter press (filtering area 100 m2, filter cloth aperture ≤10 μm).

[0019] According to the preferred embodiment of the present application, the nanofiltration membrane is purchased from Times Walton Technology Co., Ltd., with a model of VONTRON NF-90 type nanofiltration membrane element (molecular weight cut-off 1000 Da, operating pressure ≤1.5 MPa).

[0020] According to the preferred embodiment of the present application, the sodium chlorite crystal seed is purchased from Jiangsu Feixiang Chemical Co., Ltd., with a model of industrial grade and a purity of ≥99% (particle size 0.1-0.3 mm).

[0021] In step S1 of the present application, the particle size of sodium chlorate is controlled to 80-100 mesh after being crushed and sieved, which can ensure sufficient contact between the raw material and water, and avoid too high viscosity of the solution caused by too fine particles. When sodium chlorate is mixed with deionized water, a uniform sodium chlorate solution is formed by mechanical stirring (implied in the "mixing" operation), and the concentration is controlled to 200-210 g / L, which can ensure sufficient supply of reaction raw materials, and avoid too high viscosity of the solution caused by too high concentration, which affects the subsequent mass transfer efficiency. The mixing process of methanol and deionized water is the same. Methanol, as a reducing agent, needs to be fully miscible with water to form a uniform methanol solution (concentration 150-155 g / L). The addition of methanol not only provides hydrogen source (participates in the formation of sodium chlorite) for the disproportionation reaction of sodium chlorate, but also indirectly promotes the dissociation of sodium chlorate in the solution by reducing the polarity of the system. Dilute sulfuric acid (concentration 50-54 g / L) is formed by mixing sulfuric acid and deionized water, which provides an acidic environment for the reaction system. H + The activity of sodium chlorate can be activated, and the side reaction (such as the oxidative decomposition of sodium chlorate) can be inhibited. The addition of the new multi-level channel-dual functional site composite modified material is the key to this step. The multi-level channel structure (micropore-mesopore) of the material makes it have a high specific surface area, which can quickly disperse in the solution and fully contact with the reactants; the dual functional sites (such as MnO2 active sites and amino adsorption sites) are prepared for the subsequent catalytic reaction and acid adsorption. After the material is added, stirring is further used to promote the uniform mixing of the material with sodium chlorate, methanol and sulfuric acid solution, forming a stable dispersion system of "raw material-solvent-catalyst", which lays the foundation for the efficient performance of the subsequent constant temperature reaction.

[0022] According to the preferred embodiment of the present application, the time of the constant temperature reaction in step S2 is 45-50 min.

[0023] In step S2 of the present application, the key parameter of the optimized temperature of the reaction system is 60-62℃. At this temperature, the kinetics of the disproportionation reaction of sodium chlorate is significantly activated, and the activation energy of the reaction is reduced, while the generation of by-products (such as chloric acid) caused by high temperature is avoided. The disproportionation reaction of sodium chlorate in the system occurs under acidic conditions and methanol (CH3OH), and the core reaction path is: ClO3 - accepts H + from methanol, part of which is reduced to ClO2 - (target product), and part of which is oxidized to Cl - (but the side reaction is inhibited due to the limitation of the reducing property of methanol). The modified material plays a dual role in this process: first, the MnO2 active site adsorbs ClO3 -The amino functional group is adsorbed to H + (H + + NH2 - → NH3 + ) through electrostatic action, so that H + accumulation in the solution is avoided, and the acidic over-strength (pH is too low to promote ClO2 - further oxidation into ClO3 - ). The change of the ClO3 - concentration is monitored by the online HPLC, the essence is to judge whether the reaction reaches the balance by detecting the decrease rate of the reactant concentration, when the ClO3 - conversion rate is greater than 98%, it is indicated that the reaction is basically completed, and the heating is stopped at this time, so that the energy waste and the product over-decomposition are avoided.

[0024] According to the preferred embodiment of the present application, in step S3, the deionized water is washed for 2-3 times; and the filter cake is dried at 80-82℃ for 12-14h.

[0025] In step S3 of the present application, after the reaction is completed, the system temperature is reduced to 30-32℃, at this time, the solution viscosity is slightly increased, but the multi-level pore structure of the modified material still maintains high permeability. The core role of the plate and frame filter press is to realize the solid-liquid separation through mechanical pressure: the filter cake is mainly composed of unreacted sodium chlorate, generated sodium chlorite (NaClO2) and modified material adsorbed H + and by-products (such as acetic acid); and the filtrate is a mixed solution containing NaClO2, unreacted methanol, trace sulfuric acid and dissolved NaCl. The purpose of washing the filter cake with deionized water for 2-3 times is to remove the surface residual soluble impurities (such as unreacted methanol and a small amount of sodium sulfate), and the washing liquid is combined into the filtrate to avoid product loss. The filter cake is dried at 80-82℃ for 12-14 hours, on the one hand, the pore structure of the material is restored through water evaporation (water in the pore is discharged during the drying process to avoid the pore blockage), and on the other hand, the physical water adsorbed on the surface of the material is removed, so that the MnO2 active site and the amino functional group are exposed again, and the material is prepared for the next reaction cycle. After the material is recovered, its catalytic activity and acid adsorption capacity are almost not lost, and the material reuse is realized.

[0026] According to the preferred embodiment of the present application, in step S4, the molecular weight cut-off of the nanofiltration membrane is 1000Da; the concentration of the sodium chlorite seed crystal is 0.5-0.6g / L; and the crystallization time is 2-4h.

[0027] In step S4 of the present application, the filtrate is purified by nanofiltration membrane (molecular weight cut-off 1000 Da). The pore size of the nanofiltration membrane can effectively cut off the impurities with large molecular weight (such as unreacted sodium chlorate, molecular weight 106.44; sodium sulfate, molecular weight 142.04), while allowing small molecules of sodium chlorite (molecular weight 90.44) and water, methanol to pass through. This process not only removes most of the inorganic impurities (such as NaCl, molecular weight 58.44, although small but can be selectively cut off by adjusting the membrane potential), but also separates the organic by-products (such as acetic acid, molecular weight 60.05), significantly improving the purity of sodium chlorite in the permeate. The process of recovering sodium sulfate by evaporation crystallization of the retentate takes advantage of the solubility difference between sodium sulfate and sodium chloride. At 80°C, the solubility of sodium sulfate is much lower than that of sodium chloride. By evaporation and concentration, sodium sulfate can be precipitated preferentially. After filtration and drying, high-purity sodium sulfate is obtained as a by-product for recycling. The remaining concentrated sulfuric acid (concentration restored to 98%) is recycled for the next batch of reactions, achieving zero discharge of acid liquid. The permeate is heated to 50-52°C and sodium chlorite seed crystals (0.5-0.6 g / L) are added. This is to take advantage of the surface energy of the seed crystals to reduce the nucleation potential barrier of the solution, promoting the rapid formation of sodium chlorite crystals. When the temperature is lowered to 20-22°C, the supersaturation of the solution increases, and the crystals gradually grow. After filtration, vacuum drying at 60-62°C avoids the decomposition of sodium chlorite (2NaClO2→ NaCl+NaClO3) caused by high temperature, and reduces the water evaporation temperature in a vacuum environment to prevent crystal deliquescence. Finally, sodium chlorite crystals are obtained.

[0028] According to a preferred embodiment of the present application, the preparation steps of the new multi-level pore-dual functional site composite modified material include:

[0029] A1, in a three-necked flask, cetyltrimethylammonium bromide and deionized water are added, and magnetic stirring is carried out at 40-42°C until complete dissolution. Ammonia water is slowly added to adjust the pH to 10-11. Then, tetraethyl orthosilicate is added dropwise. The reaction temperature is maintained at 60-62°C and the stirring is continued. After the reaction is completed, the mixture is transferred to a centrifuge tube, the precipitate is collected by centrifugation, washed with anhydrous ethanol, and finally dried in an oven at 100-102°C. Then, it is transferred into a muffle furnace and heated to 550-560°C for calcination to obtain MCM-41 powder;

[0030] A2, the MCM-41 powder is placed in an ALD reaction chamber and calcined at 300-304°C under Ar atmosphere. Then, ALD cyclic deposition is carried out, each cycle including: manganese bis(ethylcyclopentadiene) pulse → Ar purge → H2O pulse → Ar purge. The deposited powder is ultrasonically dispersed with anhydrous ethanol, dried at 60-62°C under vacuum after centrifugation, and MCM-41@MnO2 intermediate is obtained.

[0031] A3, dissolve 3-aminopropyltriethoxysilane in anhydrous toluene, add MCM-41@MnO2 intermediate powder, ultrasonic dispersion to form a uniform suspension; transfer the reaction system to a round-bottom flask, reflux at 110-112°C under N2 protection; after the reaction is completed, cool the mixture to room temperature, collect the precipitate by suction filtration, wash the precipitate with toluene, anhydrous ethanol in turn, and finally place the precipitate in a vacuum dryer at 80-82°C to obtain MCM-41@MnO2-NH2 powder;

[0032] A4, place the MCM-41@MnO2-NH2 powder in a tube furnace, and perform calcination under N2 / H2 mixed gas, with a temperature program of: heating to 300-302°C and holding, and heating to 400-404°C and holding; after the calcination is completed, naturally cool to room temperature in a N2 atmosphere.

[0033] According to a preferred embodiment of the present application, the three-necked flask is purchased from Beijing Glass Instrument Factory, with a model of 250mL standard three-necked flask.

[0034] According to a preferred embodiment of the present application, the cetyltrimethylammonium bromide is purchased from Aldrich Reagent (Shanghai), with a model of analytical pure (100g).

[0035] According to a preferred embodiment of the present application, the deionized water is purchased from Wahaha Group, with a model of pure water (resistivity≥18.2 MΩ·cm).

[0036] According to a preferred embodiment of the present application, the ammonia water is purchased from Jiangsu Lunfeng Chemical Industry, with a model of 25-28% analytical pure.

[0037] According to a preferred embodiment of the present application, the tetraethyl orthosilicate is purchased from Aldrich Reagent (Shanghai), with a model of analytical pure (500mL).

[0038] According to a preferred embodiment of the present application, the anhydrous ethanol is purchased from Jiangsu Hengli Petrochemical, with a model of anhydrous ethanol (analytical pure, ≥99.7%).

[0039] According to a preferred embodiment of the present application, the muffle furnace is purchased from Shanghai Keheng Industry, with a model of SX2-4-10 type (maximum temperature 1000°C).

[0040] According to a preferred embodiment of the present application, the ALD reaction cavity is purchased from Beijing Zhongke Kemai, with a model of PEALD-100 type atomic layer deposition system.

[0041] According to a preferred embodiment of the present application, the bis(ethylcyclopentadiene)manganese is purchased from Aldrich Reagent (Shanghai).

[0042] According to the preferred embodiment of the present application, the Ar is purchased from Liquefied Air (China), with the model of Industrial Grade High Purity Argon (≥99.999%).

[0043] According to the preferred embodiment of the present application, the 3-aminopropyltriethoxysilane is purchased from Aladdin Reagent (Shanghai), with the model of Analytical Pure (100mL).

[0044] According to the preferred embodiment of the present application, the toluene is purchased from Jiangsu Sanmu Group, with the model of Analytical Pure (≥99.5%).

[0045] According to the preferred embodiment of the present application, the round-bottom flask is purchased from Beijing Glass Instrument Factory, with the model of 250mL standard mouth round-bottom flask.

[0046] According to the preferred embodiment of the present application, the tube furnace is purchased from Shanghai Chenhua Electric Furnace, with the model of SK-G06123K type (maximum temperature 1200℃).

[0047] According to the preferred embodiment of the present application, the N2 is purchased from Liquefied Air (China), with the model of Industrial Grade High Purity Nitrogen (≥99.999%).

[0048] According to the preferred embodiment of the present application, the H2 is purchased from Liquefied Air (China), with the model of Industrial Grade High Purity Hydrogen (≥99.999%).

[0049] According to the preferred embodiment of the present application, in step A1, the rotating speed of magnetic stirring is 300-400rpm; the continuous stirring time is 2-4h; the rotating speed of centrifugation is 8000-8200rpm, and the time is 10-12min; the drying time in the oven is 12-20h, the temperature rising rate to 550-560℃ is 1-2℃ / min, and the calcination time is 6-8h.

[0050] In step A1 of the present application, the MCM-41 mesoporous silica material with regular pore structure is synthesized by sol-gel method. After cetyltrimethylammonium bromide (CTAB) is dissolved in deionized water to form micelles, the hydrophobic chain (C16 segment) in the solution self-assembles into rod-shaped micellar aggregates, providing a “template” for the subsequent deposition of silicon source. The role of ammonia (pH adjusted to 10-11) is to neutralize the negative charge on the surface of CTAB micelles (CTAB dissociates Br -), making the micelles more easily adsorbed to the silicon source (tetraethyl orthosilicate, TEOS). TEOS undergoes a hydrolysis reaction (Si(OC2H5)4+ 4H2O→ Si(OH)4+ 4C2H5OH) under the catalysis of ammonia water, and the generated silicon hydroxyl (Si-OH) forms a three-dimensional network structure through condensation reaction (Si-OH + HO-Si→ Si-O-Si + H2O). As the reaction proceeds, the silicon network gradually wraps the CTAB micelles, forming a "silicon-surfactant" composite structure. After the reaction is completed, the precipitate (MCM-41@CTAB) is collected by centrifugation, washed with anhydrous ethanol to remove unreacted TEOS and byproduct ethanol, dried in an oven at 100-102℃ (12-20h) to completely volatilize the ethanol, and finally calcined in a muffle furnace at 550-560℃ (heating rate 1-2℃ / min, 6-8h) to decompose CTAB (CTAB is decomposed into CO2, H2O and alkane above 300℃) through high temperature, and finally obtain MCM-41 powder with regular hexagonal pore structure.

[0051] According to the preferred embodiment of the present application, in step A2, the calcination time at 300-304℃ is 30-40min; the ALD cycle deposition uses di(ethylcyclopentadiene) manganese as the Mn source and deionized water as the O source; the di(ethylcyclopentadiene) manganese pulse time is 30-32s, the Ar purge time is 60-62s, the H2O pulse time is 60-62s, and the Ar purge time is 90-95s; the ultrasonic dispersion time is 30-40min; and the vacuum drying time is 12-14h.

[0052] In step A2 of the present application, during the ALD deposition process, the di(ethylcyclopentadiene) manganese (Mn(EtCp)2) precursor is first pulsed into the reaction chamber, and its molecules are physically and chemically adsorbed on the surface of the MCM-41 carrier through coordination bonding; then Ar gas is introduced for purging, removing all remaining precursor molecules and gas-phase byproducts that are not chemically adsorbed in the reaction chamber; then H2O is pulsed into the reaction chamber, and an oxidation reaction occurs between the chemically adsorbed Mn(EtCp)2 to generate MnO2, and volatile byproducts such as ethylcyclopentadiene and methane are released; finally, Ar gas is introduced again for purging, completely removing the reaction byproducts and excess water vapor, and completing a deposition cycle of generating a single layer of MnO2, which is repeated until the desired thickness of MnO2 deposition is achieved.

[0053] According to the preferred embodiment of the present application, in step A3, the ultrasonic dispersion time is 30-40min; the reflux time at 110-112℃ is 6-8h; and the vacuum drying time at 80-82℃ is 12-14h.

[0054] In step A3 of the present application, amino groups (-NH2) are grafted on the surface of MnO2 through Schiff base reaction. The core of the reaction is the condensation reaction between ethoxy groups (-OEt) of aminosilane (APTES) and hydroxyl groups (-OH) on the surface of MnO2. After APTES is dissolved in anhydrous toluene, the ethoxy groups (-OEt) in the molecules of APTES react with the hydroxyl groups on the surface of MnO2 under the protection of N2 (to prevent oxidation) and refluxing at 110-112°C (for 6-8h): Si-OEt + Mn-OH→Si-O-Mn + EtOH, to generate a stable Si-O-Mn covalent bond, thereby fixing the amino groups (-NH2) on the surface of MnO2. Ultrasonic dispersion (for 30-40min) promotes the uniform dispersion of APTES molecules on the surface of MnO2, avoiding uneven grafting due to agglomeration. After the reaction is completed, the precipitate (MCM-41@MnO2-NH2) is collected by suction filtration, and is sequentially washed with toluene (50mL×2) and anhydrous ethanol (50mL×2), to remove unreacted APTES (dissolved in toluene) and byproduct ethanol (dissolved in water). Vacuum drying at 80-82°C (for 12-14h) completely volatilizes the residual solvents, and finally the functional material with rich amino groups on the surface (amino content: 1.2-1.5mmol / g) is obtained. The presence of amino groups makes the material have strong acidic environment adaptability. Under acidic conditions (such as H + ), the amino groups (-NH2) are protonated to form -NH3 + , which adsorbs anionic impurities (such as ClO3 - , Cl - ) in the solution through electrostatic attraction, further improving the acid adsorption capacity of the material.

[0055] According to a preferred embodiment of the present application, in step A4, the volume ratio of N2 to H2 in the N2 / H2 mixed gas is (8-10):1; the temperature is raised to 300-302°C for 2-3h; and the temperature is raised to 400-404°C for 1-2h.

[0056] In step A4 of the present application, the confined calcination (N2 / H2 mixed gas, 8-10:1) in step A4 is aimed at stabilizing the pore structure and functional sites of the material by controlling the oxidation environment. When the temperature is raised to 300-302°C (for 2-3h), the physical adsorbed water and residual solvents (such as toluene) on the surface of the material are completely removed, and at the same time, part of the hydroxyl groups (-OH) on the surface of MnO2 and -NH3 + react to generate -OH + -NH3 +→ -NH2+ H2O), forming a more stable Mn-N bond (MnO2-NH2), enhancing the binding force between the amino group and MnO2. When the temperature is raised to 400-404°C (for 1-2 h), H2 in the N2 / H2 mixed gas acts as a reducing agent to partially reduce MnO2 to Mn3O4 (3MnO2+ H2→ Mn3O4+ H2O), but controlling at a lower temperature (<450°C) can avoid excessive reduction (Mn3O4 will decompose into MnO at a higher temperature). This process forms a "MnO2-Mn3O4" composite active layer on the surface of the material, which not only retains the catalytic activity of MnO2, but also inhibits the sintering (particle agglomeration) of MnO2 through the stability of Mn3O4. After calcination, the material is naturally cooled in a N2 atmosphere (to avoid oxidation of the amino group by oxygen), and the final material has a stable hierarchical pore structure, uniform MnO2 loading, and high amino group retention rate. This structural stability ensures that the material can still maintain excellent catalytic and acid adsorption performance during multiple cycles, significantly reducing the material cost of the process.

[0057] The beneficial effects of the present application are:

[0058] Traditional sodium chlorite production relies on a large amount of sulfuric acid to maintain an acidic environment, and a large amount of waste acid remains after the reaction, which needs to be treated by alkali neutralization, generating waste acid containing sodium sulfate and sodium chloride, with high treatment cost and the neutralization process easily leading to oxidation and degradation of the product sodium chlorite, with limited purity. The present application introduces a new type of composite modified material, which has a hierarchical pore structure and dual functional sites that can adsorb the acid generated during the reaction and the unreacted acid in real time, avoiding the accumulation of acid in the system and fundamentally eliminating the generation of waste acid. At the same time, the catalytic properties of the material effectively reduce the activation energy of the reaction, significantly shorten the reaction time, and significantly improve the production efficiency, solving the core pain points of the traditional process, such as large waste acid discharge, high treatment cost, and low product purity.

[0059] The hierarchical pores of the modified material and the amino functional groups work together to efficiently adsorb impurity ions and byproducts in the reaction system, combined with nanofiltration membrane separation technology, to precisely separate sodium chlorite from impurities, significantly increasing the content of the effective component of the product, reaching the industry's top product standard. The high-efficiency adsorption of the material to the acid liquid avoids direct contact between the product and the acidic environment, further inhibiting oxidation and degradation, and the product purity is significantly improved compared to the traditional process, meeting the stringent quality requirements of high-end water treatment, food disinfection, and other fields.

[0060] The modified material is prepared by a special process and has high stability and long cycle life, which can be recycled multiple times, reducing the cost of material consumption. The acid liquid is recycled in the process, reducing the amount of new acid added, and the waste acid treatment link is cancelled, saving environmental protection treatment costs. At the same time, the reaction time is shortened, the equipment is simplified, and the energy consumption and equipment investment are reduced. DETAILED DESCRIPTION

[0061] The following detailed description is provided for further understanding of the present application and should not be construed as limiting the scope of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application according to the above application content.

[0062] I. Example

[0063] Example 1

[0064] Sodium chlorate was crushed through an 80-mesh sieve, and 200 g of sodium chlorate was mixed with 1000 mL of deionized water to prepare a sodium chlorate solution with a concentration of 200 g / L; 150 g of methanol was mixed with 1000 mL of deionized water to prepare a methanol solution with a concentration of 150 g / L; 50 g of sulfuric acid was mixed with 1000 mL of deionized water to prepare a dilute sulfuric acid solution with a concentration of 50 g / L. 50 g of the new multi-level pore-dual functional site composite modified material was added to a reaction kettle equipped with stirring, a thermometer, and a reflux condenser, and the sodium chlorate solution, the methanol solution, and the dilute sulfuric acid solution were added in sequence. The stirring was started and the temperature was raised. The reaction system was slowly heated to 61℃, and the temperature was kept constant for 48 minutes. The ClO3 - concentration was detected by online HPLC. When the ClO3 - conversion rate was >98%, the reaction was stopped. After the reaction was completed, the reaction kettle was cooled to 31℃, and the solid-liquid mixture was separated by a plate and frame filter press. The filter cake was washed with deionized water for 2 times, and the washing liquid was combined with the filtrate. The filter cake was dried at 81℃ for 13 hours to recover the new multi-level pore-dual functional site composite modified material. The filtrate was passed through a nanofiltration membrane with a molecular weight cutoff of 1000 Da. The retentate was recovered by evaporation crystallization to recover sodium sulfate, and the remaining concentrated sulfuric acid was recovered. The permeate was heated to 51℃, and 0.55 g / L of sodium chlorite seed crystals were slowly added under stirring. The temperature was lowered to 21℃ for crystallization for 3 hours, and then filtered and dried at 61℃ under vacuum.

[0065] The preparation steps of the novel multi-level pore-dual functional site composite modified material are as follows: 1 g of cetyltrimethylammonium bromide and 40 mL of deionized water are added to a three-necked flask, and magnetic stirring (350 rpm) is carried out at 41°C until complete dissolution. 2 mL of ammonia water is slowly added dropwise to adjust the pH to 10.5, and then 1.2 g of tetraethyl orthosilicate is added dropwise. The reaction temperature is maintained at 61°C, and stirring is continued for 3 hours. After the reaction is completed, the mixture is transferred to a centrifuge tube, and the precipitate is collected by centrifugation at 8100 rpm for 11 minutes. The precipitate is washed with anhydrous ethanol, and finally the precipitate is placed in a 100°C oven for drying for 12 hours. Then, the precipitate is transferred into a muffle furnace and heated to 558°C at a heating rate of 1.8°C / min, and calcined for 7 hours to obtain MCM-41 powder. The MCM-41 powder is placed in an ALD reaction chamber and calcined at 302°C for 35 minutes under an Ar atmosphere. Then, ALD cycle deposition is carried out, and each cycle includes: manganese bis(ethylcyclopentadiene) pulse for 31 seconds, Ar purge for 61 seconds, H2O pulse for 61 seconds, and Ar purge for 93 seconds. The deposited powder is ultrasonically dispersed in anhydrous ethanol for 35 minutes, and then dried at 61°C for 13 hours under vacuum after centrifugation to obtain an MCM-41@MnO2 intermediate. 3-aminopropyltriethoxysilane is dissolved in anhydrous toluene, and the MCM-41@MnO2 intermediate powder is added and ultrasonically dispersed for 35 minutes to form a uniform suspension. The reaction system is transferred to a round-bottom flask and refluxed at 111°C for 7 hours under N2 protection. After the reaction is completed, the mixture is cooled to room temperature, and the precipitate is collected by suction filtration and washed with toluene and anhydrous ethanol in sequence. Finally, the precipitate is placed in a vacuum oven at 81°C for drying for 13 hours to obtain MCM-41@MnO2-NH2 powder. The MCM-41@MnO2-NH2 powder is placed in a tube furnace and calcined under a N2 / H2 mixed gas (volume ratio 9:1). The temperature program is as follows: heating to 301°C for 2.5 hours, and then heating to 402°C for 1.5 hours. After the calcination is completed, the sample is naturally cooled to room temperature under an N2 atmosphere to obtain the novel multi-level pore-dual functional site composite modified material.

[0066] Example 2

[0067] The specific implementation is the same as that of Example 1, except that 205 g of sodium chlorate is crushed to pass through a 90-mesh screen, mixed with 1000 mL of deionized water to prepare a sodium chlorate solution (concentration 205 g / L); 153 g of methanol is mixed with 1000 mL of deionized water to prepare a methanol solution (concentration 153 g / L); 52 g of sulfuric acid is mixed with 1000 mL of deionized water to prepare dilute sulfuric acid (concentration 52 g / L). 55 g of the new multi-level channel-dual functional site composite modified material is taken into a reaction kettle, and the sodium chlorate solution, the methanol solution, and the dilute sulfuric acid are sequentially added. The temperature is raised to 60.5°C and kept constant for 46 minutes (ClO3- conversion rate > 98%). After the reaction, the temperature is lowered to 30.5°C, and the solid-liquid is separated by plate and frame filter pressing. The filter cake is washed with deionized water for 3 times, and the material is recovered by drying at 82°C for 14 hours. The filtrate is separated by a nanofiltration membrane with a molecular weight cutoff of 1000 Da, the retentate is evaporated and crystallized to recover sodium sulfate, and the concentrated sulfuric acid is recovered. The permeate is heated to 52°C, 0.58 g / L of sodium chlorite seed crystal is added, the temperature is lowered to 21.5°C, and crystallization is carried out for 2.5 hours. After filtration, vacuum drying is carried out at 62°C. Preparation of the new multi-level channel-dual functional site composite modified material: 1 g of cetyltrimethylammonium bromide is added to 40 mL of deionized water in a three-necked flask, dissolved by magnetic stirring (380 rpm) at 42°C, the pH is adjusted to 10.8 by adding 2.2 mL of ammonia water dropwise, 1.25 g of tetraethyl orthosilicate is added dropwise, and stirring is carried out at 62°C for 3.5 hours. The precipitate is collected by centrifugation (8150 rpm x 11.5 minutes), washed with anhydrous ethanol, and dried in an oven at 102°C for 12.5 hours. The MCM-41 is obtained by calcining in a muffle furnace at a temperature increasing rate of 1.8°C / min to 560°C for 7.5 hours. The MCM-41 is calcined in an ALD reaction chamber at 304°C for 35 minutes, and the pulse sequence is as follows: 31.5 seconds of manganese bis(ethylcyclopentadiene) pulse, 62 seconds of Ar purge, 62 seconds of H2O pulse, and 94 seconds of Ar purge. The MCM-41 is ultrasonically dispersed for 38 minutes, and vacuum dried at 62°C for 13.5 hours to obtain MCM-41@MnO2. 3-aminopropyltriethoxysilane is dissolved in toluene, and the intermediate is ultrasonically dispersed for 38 minutes. The mixture is refluxed at 112°C for 7.5 hours, filtered, washed with toluene and ethanol, and vacuum dried at 82°C for 13.5 hours to obtain MCM-41@MnO2-NH2. The new multi-level channel-dual functional site composite modified material is obtained by N2 / H2 (8.5:1) calcination in a tube furnace: 301.5°C x 2.75 hours, 402.5°C x 1.75 hours, and natural cooling.

[0068] Example 3

[0069] The specific implementation is the same as Example 1, except that sodium chlorate is crushed to pass through a 100 mesh sieve, 210 g of sodium chlorate is mixed with 1000 mL of deionized water to prepare a sodium chlorate solution (concentration 210 g / L); 155 g of methanol is mixed with 1000 mL of deionized water to prepare a methanol solution (concentration 155 g / L); 54 g of sulfuric acid is mixed with 1000 mL of deionized water to prepare dilute sulfuric acid (concentration 54 g / L). 60 g of the new multi-level channel-dual functional site composite modified material is added to the reaction kettle, and the sodium chlorate solution, methanol solution and dilute sulfuric acid are added in turn, and the temperature is raised to 61.5°C and kept constant for 49 minutes (ClO3 - After the reaction, the temperature is lowered to 31.5°C, and the solid-liquid is separated by plate and frame filter pressing, the filter cake is washed with deionized water for 2 times, and the material is recovered by drying at 80°C for 12 hours. The filtrate is separated by a nanofiltration membrane with a molecular weight cutoff of 1000 Da, the retentate is evaporated and crystallized to recover sodium sulfate, and the concentrated sulfuric acid is recovered; the permeate is heated to 50°C, 0.6 g / L of sodium chlorite seed crystal is added, and the temperature is lowered to 20.5°C for crystallization for 3.5 hours, and then filtered and vacuum dried at 60°C. Preparation of the new multi-level channel-dual functional site composite modified material: a three-necked flask is charged with 1 g of cetyltrimethylammonium bromide and 40 mL of deionized water, which is dissolved by magnetic stirring (400 rpm) at 40°C, the pH is adjusted to 11 by adding 2.4 mL of ammonia water dropwise, and 1.3 g of tetraethyl orthosilicate is added dropwise, and stirred at 60°C for 4 hours; the precipitate is collected by centrifugation (8200 rpm x 12 minutes), washed with anhydrous ethanol, and dried in an oven at 101°C for 13 hours, and calcined at a heating rate of 1.8°C / min to 555°C in a muffle furnace for 8 hours to obtain MCM-41. Calcination in the ALD reaction chamber at 300°C for 30 minutes, pulse of di(ethylcyclopentadiene)manganese for 32 seconds→Ar purge for 62 seconds→H2O pulse for 62 seconds→Ar purge for 95 seconds, ultrasonic dispersion for 40 minutes, vacuum drying at 60°C for 14 hours to obtain MCM-41@MnO2. 3-aminopropyltriethoxysilane is dissolved in toluene, and the intermediate is ultrasonically dispersed for 40 minutes, and refluxed at 110°C for 8 hours, and then filtered and washed with toluene and ethanol, and vacuum dried at 80°C for 14 hours to obtain MCM-41@MnO2-NH2. N2 / H2 (9.5:1) calcination in a tube furnace: 302°C x 3 hours, 404°C x 2 hours, natural cooling to obtain the new multi-level channel-dual functional site composite modified material.

[0070] Comparative Example 1

[0071] The specific implementation is the same as example 1, except that sodium chlorate is crushed to pass through an 80-mesh screen, 200 g of sodium chlorate is mixed with 1000 mL of deionized water to prepare a sodium chlorate solution (concentration 200 g / L), 150 g of methanol is mixed with 1000 mL of deionized water to prepare a methanol solution (concentration 150 g / L), and 50 g of sulfuric acid is mixed with 1000 mL of deionized water to prepare dilute sulfuric acid (concentration 50 g / L). The sodium chlorate solution, the methanol solution, and the dilute sulfuric acid are directly added to the reaction kettle, and the temperature is raised to 61°C for constant temperature reaction for 65 minutes. After the reaction, the temperature is lowered to 31°C, and the solid-liquid is separated by plate and frame filter pressing, the filter cake is washed with deionized water for 2 times, and dried at 81°C for 13 hours. The filtrate is separated by nanofiltration membrane with a molecular weight cutoff of 1000 Da, the retentate is evaporated and crystallized to recover sodium sulfate, and the concentrated sulfuric acid is recovered; the permeate is heated to 51°C, 0.55 g / L of sodium chlorite seed crystal is added, the temperature is lowered to 21°C for crystallization for 3 hours, and then filtered and dried at 61°C under vacuum (no new multi-level pore-dual functional site composite modified material).

[0072] Comparative Example 2

[0073] The specific implementation is the same as example 1, except that sodium chlorate is crushed to pass through an 80-mesh screen, 200 g of sodium chlorate is mixed with 1000 mL of deionized water to prepare a sodium chlorate solution (concentration 200 g / L), 150 g of methanol is mixed with 1000 mL of deionized water to prepare a methanol solution (concentration 150 g / L), and 50 g of sulfuric acid is mixed with 1000 mL of deionized water to prepare dilute sulfuric acid (concentration 50 g / L). 50 g of unmodified MCM-41 powder is added to the reaction kettle, and the sodium chlorate solution, the methanol solution, and the dilute sulfuric acid are sequentially added, and the temperature is raised to 61°C for constant temperature reaction for 55 minutes. After the reaction, the temperature is lowered to 31°C, and the solid-liquid is separated by plate and frame filter pressing, the filter cake is washed with deionized water for 2 times, and dried at 81°C for 13 hours to recover the material. The filtrate is separated by nanofiltration membrane with a molecular weight cutoff of 1000 Da, the retentate is evaporated and crystallized to recover sodium sulfate, and the concentrated sulfuric acid is recovered; the permeate is heated to 51°C, 0.55 g / L of sodium chlorite seed crystal is added, the temperature is lowered to 21°C for crystallization for 3 hours, and then filtered and dried at 61°C under vacuum.

[0074] Comparative Example 3

[0075] The specific implementation is the same as example 1, except that sodium chlorate is crushed to 80 mesh, 200 g of sodium chlorate is mixed with 1000 mL of deionized water to prepare a sodium chlorate solution (concentration 200 g / L), 150 g of methanol is mixed with 1000 mL of deionized water to prepare a methanol solution (concentration 150 g / L), and 50 g of sulfuric acid is mixed with 1000 mL of deionized water to prepare dilute sulfuric acid (concentration 50 g / L). Sodium chlorate solution, methanol solution and dilute sulfuric acid are added to the reactor, and the temperature is raised to 61°C and kept constant for 50 minutes. After the reaction, the temperature is lowered to 31°C, 10 g of traditional activated carbon is added to absorb the acid, and after stirring for 30 minutes, the solid-liquid is separated by plate and frame filter pressing, the filter cake is washed with deionized water for 2 times, and dried at 81°C for 13 hours (deactivation of activated carbon). The filtrate is separated by nanofiltration membrane with a molecular weight cutoff of 1000 Da, the retentate is evaporated to recover sodium sulfate and concentrated sulfuric acid, the permeate is heated to 51°C, 0.55 g / L of sodium chlorite seed crystal is added, the temperature is lowered to 21°C, and crystallization is carried out for 3 hours, then filtered and dried at 61°C under vacuum.

[0076] II. Performance test

[0077] The preparation process of sodium chlorite in the above examples 1-3 and comparative examples 1-3 is tested for performance according to the following method

[0078] 1. In the reaction efficiency test, the time required for ClO3 - conversion rate > 98% (reaction time) is recorded from the temperature rise to 60-62°C to online HPLC detection, and the concentration of ClO3 - is detected by high performance liquid chromatography (HPLC) (chromatographic conditions: C18 chromatographic column 4.6 mm x 250 mm, 5 μm, mobile phase 0.1% phosphoric acid water-acetonitrile 8:2, flow rate 1.0 mL / min, detection wavelength 254 nm, injection volume 20 μL, external standard method to calculate the concentration) to calculate the conversion rate (conversion rate = (initial concentration-residual concentration) / initial concentration x 100%).

[0079] 2. In the product purity test, the content of sodium chlorite (ClO2 - ) is detected by HPLC under the same conditions, and the heavy metal impurities (Fe 3 + , Pb 2+ ) are detected by inductively coupled plasma optical emission spectrometry (ICP-OES) (Fe detection wavelength 259.94 nm, Pb detection wavelength 283.31 nm, sample is digested with nitric acid before determination).

[0080] 3. In the acid recovery rate test, it includes the concentration recovery rate of concentrated sulfuric acid (density bottle method to measure density, density-concentration conversion table to calculate) and the recovery rate of sodium sulfate (weight method to measure the mass after evaporation and crystallization, theoretical generated mass = initial sulfuric acid amount of substance x molar mass of sodium sulfate).

[0081] 4. In the material recycling performance test, the modified materials recovered from Examples 1-3 were repeatedly used for 50 reactions, and ClO3 - was detected after each reaction. The conversion rate was calculated, and the decay rate of the 50th conversion rate relative to the first conversion rate was calculated (decay rate = (first conversion rate - 50th conversion rate) / first conversion rate x 100%).

[0082] 5. In the waste acid discharge test, the mass of the acid solution not recovered after the reaction of Comparative Examples 1-3 was weighed (the mass of the waste acid of Examples 1-3 was recorded as 0).

[0083] 6. Test results:

[0084] Table 1: Test results of each example and comparative example

[0085] ;

[0086] As can be seen from Table 1, Examples 1-3 solve the core pain points of low reaction efficiency, poor product purity, large waste acid discharge, and non-recyclable materials of traditional processes by the following methods relative to Comparative Examples 1-3:

[0087] Reaction efficiency is improved: Examples 1-3 use a new type of multi-level pore-dual functional site composite modified material, and the MnO2 active site significantly reduces the activation energy of the sodium chlorate disproportionation reaction, and the reaction time is shortened to 46-49 minutes (Comparative Examples 1-3 are 50-65 minutes), ClO3 - conversion rate is maintained at >98% (Comparative Examples 1-3 are 92-95%), solving the problems of long reaction time and low efficiency of traditional processes.

[0088] Product purity is improved: the amino functional group of the modified material adsorbs H + and by-products (such as acetic acid) generated during the reaction, avoiding the oxidative degradation of the product sodium chlorite, and the nanofiltration membrane precisely removes impurity ions (such as unreacted sodium chlorate and sodium sulfate), and the ClO2 - content of Examples 1-3 is 99.5-99.7% (Comparative Examples 1-3 are 94.8-96.1%), and the content of heavy metal impurities (Fe 3+ , Pb 2+ ) is <0.001 ppm (Comparative Examples 1-3 are 0.002-0.004 ppm), meeting the needs of high-end applications, and solving the problem of low product purity of traditional processes.

[0089] Waste acid discharge is eliminated: the multi-level pore structure of the modified material efficiently adsorbs the acid solution (H +and unreacted sulfuric acid), the acid liquor is recovered by evaporation crystallization to obtain sodium sulfate (recovery rate > 98%) and concentrated sulfuric acid (recovery rate > 95%), realizing the recycling of the acid liquor, and the waste acid discharge of examples 1-3 is 0 (5.2-5.8 kg / ton product for comparative examples 1-3), solving the problems of large waste acid discharge and high treatment cost in the traditional process.

[0090] Material cycle performance optimization: the modified material has a ClO3 - Conversion rate decay < 5% (no material recovery for comparative example 1, and unmodified MCM-41 or activated carbon is used for comparative examples 2-3, with fast activity decay), long material life and reusability, reducing the cost of material consumption, meeting the requirements of green chemical industry, and solving the problems of non-circulation and high cost of materials in the traditional process.

[0091] In summary, examples 1-3 realize the green production of sodium chlorite with no waste acid, high efficiency and high purity by the synergistic effect of catalysis, adsorption and separation of the new modified material, solving the core problems of low reaction efficiency, poor product purity, large waste acid discharge and non-circulation of materials in the traditional process.

[0092] The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the present patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A waste-free acid-free sodium chlorite production process, characterized in that, Includes the following steps: S1, sodium chlorate is pulverized, sieved, and mixed with deionized water to prepare a sodium chlorate solution; methanol is mixed with deionized water to prepare a methanol solution; sulfuric acid is mixed with deionized water to prepare a dilute sulfuric acid solution; the multi-level pore-dual-functional site composite modified material is added to a reaction vessel equipped with a stirrer, thermometer, and reflux condenser, and the sodium chlorate solution, methanol solution, and dilute sulfuric acid are added sequentially, stirring is started, and the temperature is increased; wherein, the preparation steps of the multi-level pore-dual-functional site composite modified material include: A1, hexadecyltrimethylammonium bromide and deionized water are added to a three-necked flask, and the mixture is heated to 40°C. Stir magnetically at -42℃ until completely dissolved, slowly add ammonia to adjust pH to 10-11, then add tetraethyl orthosilicate dropwise, maintaining reaction temperature at 60-62℃ and continuing stirring; after reaction, transfer the mixture to a centrifuge tube, centrifuge to collect the precipitate, wash the precipitate with anhydrous ethanol, and finally dry the precipitate in an oven at 100-102℃, then transfer it to a muffle furnace and calcine at 550-560℃ to obtain MCM-41 powder; A2, place the MCM-41 powder in the ALD reaction chamber, and calcine at 300℃ under an Ar atmosphere. Calcination at 304℃; followed by ALD cyclic deposition, each cycle including: di(ethylcyclopentadiene)manganese pulse → Ar purging → H2O pulse → Ar purging; the deposited powder was ultrasonically dispersed in anhydrous ethanol, centrifuged, and vacuum dried at 60-62℃ to obtain MCM-41@MnO2 intermediate; A3, 3-aminopropyltriethoxysilane was dissolved in anhydrous toluene, and the MCM-41@MnO2 intermediate powder was added and ultrasonically dispersed to form a uniform suspension; the reaction system was transferred to a round-bottom flask and heated at 110℃ under N2 protection. Refluxed at -112℃; after the reaction was completed, the mixture was cooled to room temperature, and the precipitate was collected by filtration. The precipitate was washed successively with toluene and anhydrous ethanol, and finally dried under vacuum at 80-82℃ to obtain MCM-41@MnO2-NH2 powder; A4, the MCM-41@MnO2-NH2 powder was placed in a tube furnace and calcined under a N2 / H2 mixed atmosphere. The temperature program was as follows: heat up to 300-302℃ and hold, heat up to 400-404℃ and hold; after calcination, it was naturally cooled to room temperature in an N2 atmosphere; S2, the reaction system is slowly heated to 60-62℃ and the reaction is maintained at this temperature. ClO3 is detected by online HPLC. - The concentration change determines the endpoint, when ClO3 - The reaction is stopped when the conversion rate is >98%. S3. After the reaction is completed, the reactor is cooled to 30-32℃, and the solid-liquid mixture is separated by a plate and frame filter press. The filter cake is washed with deionized water, and the washing liquid is combined with the filtrate. After the filter cake is dried at 80-82℃, the multi-level pore-dual-functional site composite modified material is recovered. S4. Pass the filtrate through a nanofiltration membrane; recover sodium sulfate by evaporation and crystallization of the retentate, and recover the remaining concentrated sulfuric acid; heat the permeate to 50-52℃, slowly add sodium chlorite seed crystals with stirring, cool to 20-22℃ to crystallize, filter, and vacuum dry at 60-62℃.

2. The waste-free acid-free sodium chlorite production process according to claim 1, characterized in that, In step S1, the material is crushed through an 80-100 mesh sieve; the concentration of the sodium chlorate solution is 200-210 g / L; the concentration of the methanol solution is 150-155 g / L; and the concentration of the dilute sulfuric acid is 50-54 g / L.

3. The waste-free acid-free sodium chlorite production process according to claim 1, characterized in that, In step S2, the isothermal reaction time is 45-50 minutes.

4. The waste-free acid-free sodium chlorite production process according to claim 1, characterized in that, In step S3, the filter cake is washed with deionized water 2-3 times; the filter cake is dried at 80-82℃ for 12-14 hours.

5. The waste-free acid-free sodium chlorite production process according to claim 1, characterized in that, In step S4, the molecular weight cutoff of the nanofiltration membrane is 1000 Da; the concentration of sodium chlorite seed crystals is 0.5-0.6 g / L; and the crystallization time is 2-4 h.

6. The waste-free acid-free sodium chlorite production process according to claim 1, characterized in that, In step A1, the magnetic stirring speed is 300-400 rpm; the stirring time is 2-4 h; the centrifugation speed is 8000-8200 rpm and the time is 10-12 min; the drying time in the oven is 12-20 h; the heating rate to 550-560℃ is 1-2℃ / min; and the calcination time is 6-8 h.

7. The waste-free acid-free sodium chlorite production process according to claim 1, characterized in that, In step A2, the calcination time at 300-304℃ is 30-40 min; the ALD cyclic deposition uses di(ethylcyclopentadiene)manganese as the Mn source and deionized water as the O source; the di(ethylcyclopentadiene)manganese pulse time is 30-32 s, the Ar purging time is 60-62 s, the H2O pulse time is 60-62 s, and the Ar purging time is 90-95 s; the ultrasonic dispersion time is 30-40 min; and the vacuum drying time is 12-14 h.

8. The waste-free acid-free sodium chlorite production process according to claim 1, characterized in that, In step A3, the ultrasonic dispersion time is 30-40 min; the reflux time at 110-112℃ is 6-8 h; and the vacuum drying time at 80-82℃ is 12-14 h.

9. The waste-free acid-free sodium chlorite production process according to claim 1, characterized in that, In step A4, the volume ratio of N2 to H2 in the N2 / H2 mixture is (8-10):1; the temperature is raised to 300-302℃ and held for 2-3 hours; the temperature is raised to 400-404℃ and held for 1-2 hours.