A method for preparing a high-purity sodium bisulfite solution

Abstract

The application relates to the technical field of sodium bisulfite preparation, and provides a preparation method of high-purity sodium bisulfite solution, which comprises pre-purification, selective electrodialysis, reaction concentration, terminal filtration and sealed filling; a crude aqueous solution containing sodium bisulfite is sequentially subjected to precision filtration and Na-type iminodiacetic acid-based chelating porous membrane treatment under low-temperature and low-oxygen conditions; monovalent anion selective membranes and cation exchange membranes are used to make and migrate to a product chamber and to remain in a raw material chamber; high-purity sodium hydroxide is added into desulfate liquid, and then purified sulfur dioxide is introduced into the desulfate liquid through a hydrophobic porous membrane to perform reaction concentration; finally, terminal filtration and inert gas protection filling are performed. Through the technical scheme, the problems that it is difficult to synchronously remove sulfate and metal impurities by the existing method, evaporation and concentration are prone to cause oxidation, and the product stability is poor are solved.

Description

Technical Field

[0001] This invention relates to the field of sodium bisulfite preparation technology, and more specifically, to a method for preparing a high-purity sodium bisulfite solution. Background Technology

[0002] Sodium bisulfite is an inorganic compound with reducing and antioxidant properties, widely used in pharmaceuticals, food, fine chemicals, textiles, papermaking, and water treatment. Industrially, sodium bisulfite is typically prepared by absorbing sulfur dioxide with sodium hydroxide, sodium carbonate, or sodium sulfite. The main reactions are as follows: ; ; .

[0003] The prior art disclosed in application number CN90109976.7 discloses a method for first refining industrial sodium carbonate into sodium carbonate decahydrate, then dissolving it and introducing sulfur dioxide to prepare a high-purity sodium bisulfite solution. This method can reduce some impurities in the sodium carbonate raw material, but it cannot simultaneously solve the problem of metal ions and sulfate impurities introduced by the sulfur dioxide gas source, equipment, and process water.

[0004] CN101613118A discloses a method for preparing pharmaceutical-grade sodium bisulfite, which involves dissolving food-grade sodium bisulfite in water, followed by filtration, concentration, cooling crystallization, dehydration, and drying. This method requires high-grade sodium bisulfite as raw material, and during concentration and drying, bisulfite ions may be oxidized to sulfate ions, and solid sodium bisulfite may also be dehydrated and converted into sodium metabisulfite.

[0005] In addition, existing technologies also include a resource-based route for preparing sodium bisulfite solution using calcium sulfite, sulfuric acid, and sodium sulfate. This route can utilize flue gas desulfurization byproducts, but the raw material impurities are complex, and it introduces high levels of sulfate, calcium ions, and particulate matter into the reaction system, making it unsuitable for directly preparing high-purity products.

[0006] Sodium bisulfite aqueous solution readily undergoes the following oxidation reactions when exposed to air: .

[0007] Sodium bisulfate, generated by the oxidation reaction, appears as sulfate or bisulfate impurities in the system. Transition metals such as iron and copper may further catalyze the oxidation of bisulfite, leading to a further increase in sulfate content. Ordinary activated carbon, precision filtration, or cation exchange can only remove specific types of impurities and cannot effectively separate dissolved sulfate. Ordinary H-type strongly acidic cation exchange materials will also release hydrogen ions, causing sodium bisulfite to decompose and release sulfur dioxide.

[0008] Bisulfite is a monovalent anion, while sulfate is a divalent anion. Sodium bisulfite primarily functions as... Under acidic conditions, the difference in migration between monovalent and divalent anions can be utilized by using a monovalent anion-selective membrane to... and Moved to the product room, and Preferably, the solution should be kept in the feed chamber. However, if high-concentration sodium bisulfite solution is directly subjected to electrodialysis, concentration polarization, membrane fouling, and osmotic pressure will increase. Therefore, it is necessary to control the feed concentration, particulate matter, metal ions, temperature, pH, and dissolved oxygen before performing fractionated electrodialysis.

[0009] Increasing the concentration of sodium bisulfite through evaporation increases the risk of heat exposure and oxidation. If some of the sodium bisulfite is first reacted with high-purity sodium hydroxide to produce sodium sulfite, and then the sodium sulfite is used to absorb and purify sulfur dioxide, the overall reaction is equivalent to generating new sodium bisulfite into the system. ; ; The overall reaction is .

[0010] Based on the above, it is necessary to provide a method for preparing high-purity sodium bisulfite that does not rely on high-temperature evaporation and solid crystallization, and can simultaneously control the concentrations of sulfate, trace metals, particulate matter, dissolved oxygen, and product. Summary of the Invention

[0011] To overcome the above-mentioned defects, the present invention provides a method for preparing high-purity sodium bisulfite solution, which solves the problems in existing sodium bisulfite preparation methods, such as the difficulty in simultaneously removing sulfates and trace metals, the easy oxidation of bisulfite ions, the easy deterioration of products due to evaporation and concentration, and the easy conversion of solid products into sodium metabisulfite.

[0012] According to one aspect, at least one embodiment of the present invention provides a method for preparing a high-purity sodium bisulfite solution, comprising the following steps: (1) The sulfur dioxide absorption system is replaced with an inert gas until the oxygen volume fraction in the tail gas of the absorption system is not higher than 0.5%. At 5 to 20°C, the sulfur dioxide after demisting and precision filtration is absorbed by a sodium hydroxide aqueous solution with a mass fraction of 5% to 12%, and the pH at the end of the absorption is controlled to be 4.0 to 4.6 to obtain a crude aqueous solution with a sodium bisulfite mass fraction of 8% to 15%.

[0013] The temperature of the crude aqueous solution was controlled at 0–15℃, the pH was maintained at 4.0–4.6, and the dissolved oxygen content was controlled to be no higher than 0.5 mg / L under inert gas protection. The crude aqueous solution was then passed sequentially through a precision filter membrane with a pore size of 0.05–0.20 μm and a Na-type iminodiacetic acid chelated porous membrane to obtain a pre-purified solution.

[0014] Precision filter membranes are used to remove dust, corrosion products, colloids, and insoluble particles. Na-type iminodiacetic acid chelate porous membranes are used to remove metal ions such as Fe, Cu, Pb, Ca, and Mg. Using Na-type chelate porous membranes avoids the release of hydrogen ions into the sodium bisulfite solution by H-type exchange materials.

[0015] Preferably, the average pore size of the Na-type iminodiacetic acid chelated porous membrane is 0.1–1.0 μm, the iminodiacetic acid group exchange capacity is 0.6–1.8 mmol / g, and the empty bed contact time of the pre-purified solution in the chelated porous membrane is 2–10 min.

[0016] (2) Under the protection of 0-10℃ and inert gas, the pre-purified liquid is introduced into the feed chamber of an electrodialysis unit consisting of two or more stages connected in series. The electrodialysis unit is composed of alternating monovalent anion-selective membranes and cation exchange membranes.

[0017] An aqueous solution with a pH of 4.0–4.6 and a sodium bisulfite mass fraction of 0.5%–3.0% was used as the initial solution for the product chamber. Electrodialysis was performed at a current density of 5–20 mA / cm². Migrating through the cation exchange membrane to the product chamber, Migration to the product chamber via a monovalent anion-selective membrane, and... It should be reserved in the raw material room first.

[0018] When the mass fraction of sodium bisulfite in the product's internal solution reaches 22%–30%, and When the content is not higher than 100 mg / kg, electrodialysis is stopped to obtain desulfate solution.

[0019] Preferably, the electrodialysis unit comprises 2 to 4 stages of electrodialysis membrane stacks connected in series, with the electrode chambers of each stage isolated from the feed chamber and product chamber via electrode membranes. The linear velocity of the pre-purified solution on the membrane surface is 2 to 5 cm / s, the current density is 8 to 15 mA / cm², and the operating temperature is 3 to 7°C.

[0020] The sheet resistivity of the monovalent anion-selective membrane is preferably not higher than 8 Ω·cm². (The membrane contains 0.50 mol / L...) and 0.25 mol / L Furthermore, the test solution was an aqueous solution with a pH of 4.3, and the results were measured at 5°C and 10 mA / cm². Migration flux and The ratio of migration flux is preferably not less than 8:1.

[0021] (3) Under the protection of 5-15℃ and inert gas, add a high-purity sodium hydroxide aqueous solution with a mass fraction of 48%-52% to the desulfate solution.

[0022] The molar ratio of sodium hydroxide added to sodium bisulfite in the desulfate solution is 0.85:1 to 1.00:1, so that at least part of the sodium bisulfite is converted into sodium sulfite, thus obtaining a concentrated precursor solution.

[0023] The sodium hydroxide aqueous solution is preferably added in stages over a period of 30–90 minutes, with the temperature during the addition process kept below 15°C by jacket cooling. After the sodium hydroxide is completely added, the reaction continues for another 10–30 minutes. The pH of the concentrated precursor solution is preferably 7.5–9.0.

[0024] (4) The purified sulfur dioxide is introduced into the enrichment precursor solution through a hydrophobic porous membrane. The molar ratio of sulfur dioxide to sodium hydroxide added in step S3 is 0.95:1 to 1.05:1. The reaction is carried out at 5 to 20°C until the pH of the solution is 3.8 to 4.5, so that sodium sulfite is converted into sodium bisulfite, and a enrichment solution with a sodium bisulfite mass fraction of 33% to 42% is obtained.

[0025] The hydrophobic porous membrane is preferably a polytetrafluoroethylene hollow fiber membrane or a polyvinylidene fluoride hollow fiber membrane, with an average pore size of 0.05–0.30 μm. The purified sulfur dioxide flows on the gas phase side of the hydrophobic porous membrane, while the enriched precursor flows on the liquid phase side. The pressure on the gas phase side is 5–30 kPa higher than the pressure on the liquid phase side.

[0026] Introducing sulfur dioxide through a hydrophobic porous membrane can increase the gas-liquid mass transfer area and reduce local over-acidity, bubble entrainment, and sulfur dioxide escape caused by direct bubbling.

[0027] (5) Under the protection of inert gas, the concentrated liquid is passed through a terminal filter membrane with a pore size of 0.02 to 0.10 μm to obtain a high-purity sodium bisulfite aqueous solution, and then sealed and filled.

[0028] Nitrogen gas with an oxygen content not exceeding 10 ppm and a dew point not exceeding -30°C is preferably used as the inert gas. Before filling, the dissolved oxygen content of the product is controlled to be not higher than 0.3 mg / L, and the filling container is purged with nitrogen to ensure that the oxygen volume fraction in the top space of the filling container is not higher than 0.2%.

[0029] The obtained high-purity sodium bisulfite aqueous solution has a sodium bisulfite mass fraction of 33%–42%; the effective concentration based on dissolved solids is... The quality score should preferably be no less than 99.0%. The content is not higher than 100 mg / kg. The content is not higher than 50 mg / kg, the Fe content is not higher than 0.5 mg / kg, the Cu content is not higher than 0.1 mg / kg, the Pb content is not higher than 0.1 mg / kg, and the water-insoluble matter content is not higher than 10 mg / kg.

[0030] The beneficial effects of the embodiments of the present invention are as follows: 1. In this invention, removing particulate matter and trace metals before electrodialysis reduces membrane fouling and lowers the risk of metal-catalyzed bisulfite oxidation by Fe, Cu, and other metals; and maintaining the target anion primarily in a monovalent state at a pH of 4.0–4.6. Using monovalent anion selective membranes to make and Moved into the product room, and at the same time, the bivalent Priority is given to retaining the target salt and sulfate in the raw material chamber, thereby achieving the separation of the target salt and sulfate. At the same time, product transfer electrodialysis is used, so that the purified sodium bisulfite enters the product chamber, while particulate matter, colloids and retained sulfate remain in the raw material chamber, which helps to reduce cross-contamination in the product chamber.

[0031] 2. In this invention, the concentration is achieved through a sodium hydroxide-sulfur dioxide reaction instead of high-temperature evaporation, which reduces heat exposure and air contact. The added sodium hydroxide and sulfur dioxide are ultimately converted into new sodium bisulfite, without introducing foreign cations. Introducing sulfur dioxide through a hydrophobic porous membrane helps control the gas-liquid mass transfer rate and reaction endpoint, reducing local over-acidity and sulfur dioxide escape.

[0032] 3. In this invention, the entire process operates under conditions of low temperature, low dissolved oxygen, and inert gas protection, which helps to inhibit the oxidation of bisulfite to sulfate and improve the stability of the product during production and filling. Detailed Implementation

[0033] The following embodiments are used to further illustrate the present invention, but do not constitute a limitation on the scope of protection of the present invention. Those skilled in the art can make proportional adjustments to the equipment scale, number of membrane modules, flow rate, and batch size without departing from the concept of the present invention.

[0034] Unless otherwise specified, all liquid percentages are by mass, all gas percentages are by volume, and ppm represents parts per million.

[0035] The process water is preferably high-purity water with a resistivity of not less than 10 MΩ·cm, and is deoxygenated with nitrogen until the dissolved oxygen is not higher than 0.3 mg / L before use.

[0036] In high-purity sodium hydroxide The preferred content is no higher than 0.05%. The content is not higher than 20 mg / kg, and the Fe content is not higher than 0.5 mg / kg.

[0037] The purity of purified sulfur dioxide is preferably not less than 99.9%, with an oxygen content not exceeding 20 ppm and a total metal impurity content not exceeding 0.1 mg / m³. Before entering the absorber or membrane contactor, the sulfur dioxide passes sequentially through a demister, a dryer, and a gas filter with a pore size not exceeding 0.01 μm.

[0038] Pipelines, tanks, and membrane housings that come into contact with materials are preferably made of PFA, PTFE, PVDF, fluorine-lined materials, or passivated 316L stainless steel that has been proven not to release metals into the product.

[0039] A commercially available Na-type iminodiacetic acid chelating membrane that meets the following parameters can be used, or it can be prepared according to the following method.

[0040] A porous PVDF membrane with an average pore size of 0.3 μm was used as the base membrane. The membrane was irradiated with an electron beam under a nitrogen atmosphere to an absorbed dose of 20–40 kGy. The irradiated base membrane was then placed in a methanol aqueous solution containing 10%–20% glycidyl methacrylate and grafted at 45–55 °C for 3–6 h. After washing away the unreacted monomers, the grafted membrane was placed in a 0.5–1.5 mol / L sodium iminodiacetate aqueous solution and reacted at 70–85 °C for 8–16 h to allow the epoxy groups to undergo a ring-opening reaction with the iminodiacetate groups.

[0041] After the reaction, the membrane was washed with high-purity water until the conductivity of the washing solution stabilized. Then, 2-4 bed volumes were treated with a 2%–5% high-purity sodium chloride aqueous solution to convert the chelating groups on the membrane to the Na form. Finally, the membrane was washed with deoxygenated high-purity water until… The content meets the process requirements.

[0042] The average pore size of the chelating membrane was determined by the bubble point method or the capillary flow pore size method, and the exchange capacity was determined by acid-base titration. The average pore size of the obtained membrane should be 0.1–1.0 μm, and the iminodiacetic acid group exchange capacity should be 0.6–1.8 mmol / g.

[0043] After the chelating membrane fails, it can be regenerated with 1%–3% high-purity hydrochloric acid, followed by sequential treatment with high-purity water, 1%–3% high-purity sodium hydroxide, 2%–5% high-purity sodium chloride aqueous solution, and deoxygenated high-purity water. Before the regenerated membrane comes into contact with the product again, the pH of the last wash solution should be confirmed. The metal content meets the requirements.

[0044] The monovalent anion-selective membrane to be evaluated was installed in a test electrodialysis unit with an effective membrane area of ​​100 cm². A feedstock containing 0.50 mol / L... and 0.25 mol / L Furthermore, a deoxygenated aqueous solution with a pH of 4.3 was added to the product side, and the solution contained 1.0% [amount missing]. Deoxygenated aqueous solution.

[0045] The system was run for 60 minutes at 5℃ under nitrogen protection and 10mA / cm², and the product side was measured. and The amount of substance added. Ion migration flux is calculated using the following formula: ; In the formula, Let be the migration flux of ion i. A represents the amount of substance added to the product-side ion i, A represents the effective membrane area, and t represents the running time.

[0046] / The migration selectivity coefficient β is calculated using the following formula: .

[0047] The monovalent anion-selective membrane used in this invention has a β value not higher than 0.15, preferably not higher than 0.125, that is... Migration flux and The ratio of migration flux is not less than 8:1.

[0048] The effective content of sodium bisulfite was determined by iodometric titration. The titration was performed immediately after sampling under nitrogen protection, according to... It reacts with I₂ in a 1:1 molar ratio and... Conversion.

[0049] and The determination was performed using ion chromatography. To prevent contamination after sampling... Caused by oxidation by air In case of a false increase, immediately add the sample to a deoxygenated formaldehyde stabilizing solution. A hydroxymethylsulfonate adduct is formed, which is then detected by ion chromatography.

[0050] Fe, Cu, Pb, Ca, and Mg were determined using ICP-MS or ICP-OES. Samples were completely oxidized with high-purity hydrogen peroxide in a sealed container, then acidified with ultrapure nitric acid before injection.

[0051] Water-insoluble matter was measured by filtering the sample through a pre-weighed 0.02 μm filter membrane, washing with deoxygenated high-purity water, and drying to constant weight.

[0052] Dissolved oxygen was measured using an online dissolved oxygen meter with fluorescence method; pH was measured using a 25°C resistant meter. Measurement using a glass electrode.

[0053] The ratio of sodium bisulfite to dissolved solids is determined by effective... The content is calculated by normalizing it to the sum of all quantitatively determined soluble inorganic components in the same batch of samples. The same validated method should be consistently used in the official quality standard; product purity should not be estimated solely based on the amount of material fed.

[0054] Example 1, 1. Preparation of crude liquid Add nitrogen-deoxygenated high-purity water and high-purity sodium hydroxide to the sealed absorber to prepare 100 kg of an 8.0% sodium hydroxide aqueous solution. Replace the system with nitrogen until the oxygen volume fraction in the exhaust gas does not exceed 0.5%.

[0055] The absorbent temperature was controlled at 10℃, and high-purity sulfur dioxide, which had undergone demisting, drying, and 0.01μm filtration, was introduced. The absorbent was circulated through a membrane gas-liquid contactor using a circulating pump, and the sulfur dioxide intake was controlled to gradually decrease the liquid pH. Aeration was stopped when the pH (equivalent to 4.3 at 25℃). Based on the iodometric titration results, the resulting crude solution was diluted with deoxygenated high-purity water. The quality score has been adjusted to 12.0%.

[0056] 2. Pre-purification The crude liquid was cooled to 8°C and deoxygenated with nitrogen until the dissolved oxygen level was 0.3 mg / L. The crude liquid was then passed through a PVDF precision filter membrane with a pore size of 0.10 μm, and then through a Na-type iminodiacetic acid chelated porous membrane with an average pore size of 0.3 μm and an exchange capacity of 1.1 mmol / g.

[0057] The effective bed volume of the chelating membrane module is 10L, the liquid flow rate is controlled at 2L / min, and the corresponding empty bed contact time is 5min. Online pH and dissolved oxygen detection are set at the membrane module outlet to control the outlet liquid pH at 4.2-4.4 and the dissolved oxygen at no more than 0.5mg / L, thus obtaining the pre-purified liquid.

[0058] 3. Electrodialysis A three-stage series electrodialysis membrane stack is used, with each stage consisting of 10 membrane pairs. The effective area of ​​a single membrane is 0.5 m². The sheet resistivity of the monovalent anion-selective membrane is no higher than 8 Ω·cm². / The migration selectivity coefficient is no higher than 0.125.

[0059] Add pre-purified liquid to the raw material compartment, and add 10 kg of a 1.0% (w / w) solution with a pH of 4.3 to the product compartment. Initial liquid. The material temperature is controlled at 5℃, the membrane surface linear velocity at 3cm / s, and the current density at 10mA / cm², and nitrogen is used to maintain the oxygen volume fraction in the top space of each circulation tank at no more than 0.2%.

[0060] The electrode chamber uses an independently circulating electrode solution and is isolated from the material chamber by an electrode membrane. Sampling and testing of the product chamber are performed in stages. and When the solution in the product chamber reaches 42.0 kg, The quality score reached 28.0%, and Electrodialysis was stopped when the concentration of sulfate was not higher than 100 mg / kg, and desulfate solution was obtained.

[0061] 4. Increased concentration of the reaction 42.0 kg of desulfate solution contains Approximately 11.76 kg, corresponding to approximately 113.0 mol. According to NaOH and... With a molar ratio of 0.90:1, approximately 101.7 mol of NaOH needs to be added, which is approximately 4.07 kg of pure NaOH.

[0062] Under nitrogen protection at 10℃, 8.14 kg of a 50% (w / w) high-purity NaOH aqueous solution was added in three stages over 60 min. During the addition process, the material temperature was kept below 15℃ by jacket cooling. After the addition was complete, stirring continued for 20 min to obtain the concentrated precursor solution.

[0063] Make high purity The enrichment precursor solution is introduced through a PTFE hollow fiber membrane with an average pore size of 0.10 μm. The pressure on the gas phase side is controlled to be 15 kPa higher than that on the liquid phase side, and the liquid temperature is 10 °C. Approximately 6.52 kg of the precursor solution is introduced at a molar ratio of 1.00:1 to the added NaOH. The reaction endpoint was set at pH 4.2–4.4.

[0064] According to NaOH and Completely transformed Based on theoretical material balance calculations, the total mass of the material after concentration is approximately 56.66 kg, which is effective. The yield is approximately 22.34 kg, with a theoretical mass fraction of approximately 39.4%. This value is a theoretical material balance value; the actual product concentration should be based on the iodine titration results.

[0065] 5. Filtering and filling The concentrated solution was cooled to 8°C and passed through a terminal filter membrane with a pore size of 0.05 μm. The container was then filled with nitrogen gas containing no more than 10 ppm oxygen and a dew point no higher than -30°C, ensuring that the oxygen volume fraction in the top space of the container did not exceed 0.2%. The container was then sealed before filling.

[0066] Example 2 uses the same equipment and basic operations as Example 1, with the following differences: In crude liquid The mass fraction was 8.0%, the absorption temperature was 5℃, and the absorption endpoint pH was 4.6.

[0067] The precision filter membrane has a pore size of 0.05 μm; the Na-type chelate porous membrane has an average pore size of 0.1 μm, an exchange capacity of 0.6 mmol / g, and an empty bed contact time of 10 min.

[0068] The electrodialysis temperature was 3℃, the current density was 8mA / cm², the membrane surface linear velocity was 2cm / s, and the initial solution in the product chamber contained... The mass fraction is 0.5%.

[0069] 50.0 kg was obtained after electrodialysis. The desulfate solution has a mass fraction of 23.0%, in which... It is approximately 11.50 kg, which corresponds to approximately 110.5 mol.

[0070] According to NaOH and Add approximately 93.9 mol of NaOH at a molar ratio of 0.85:1, which is equivalent to adding approximately 7.51 kg of a 50% NaOH aqueous solution.

[0071] according to Approximately 6.02 kg of NaOH was added via a PVDF hollow fiber membrane at a molar ratio of 1.00:1. The reaction temperature was 5℃, and the final pH was 4.5.

[0072] Based on theoretical material balance, the final material mass is approximately 63.53 kg, effective It weighs approximately 21.27 kg, with a theoretical mass fraction of approximately 33.5%.

[0073] Example 3 uses the same basic operations as Example 1, with the following differences: In crude liquid The mass fraction was 15.0%, the absorption temperature was 20℃, and the absorption endpoint pH was 4.0.

[0074] The precision filter membrane has a pore size of 0.20 μm; the Na-type chelate porous membrane has an average pore size of 1.0 μm, an exchange capacity of 1.8 mmol / g, and an empty bed contact time of 2 min.

[0075] The electrodialysis system uses a four-stage tandem membrane stack, operating at 7°C, with a current density of 15 mA / cm², a membrane surface linear velocity of 5 cm / s, and the initial solution in the product chamber... The quality fraction is 3.0%.

[0076] 40.0 kg was obtained after electrodialysis. A desulfate solution with a mass fraction of 30.0%, wherein... It is approximately 12.00 kg, which corresponds to approximately 115.3 mol.

[0077] According to NaOH and Add approximately 103.8 mol of NaOH at a molar ratio of 0.90:1, which is equivalent to adding approximately 8.30 kg of a 50% NaOH aqueous solution.

[0078] according to Approximately 6.65 kg of NaOH was added via a PTFE hollow fiber membrane at a molar ratio of 1.00:1. The reaction temperature was 15℃, and the endpoint pH was 4.0.

[0079] Based on theoretical material balance, the final material mass is approximately 54.95 kg, effective It weighs approximately 22.80 kg, with a theoretical mass fraction of approximately 41.5%.

[0080] Example 4 illustrates the operation method of using 48% NaOH and continuous reaction concentration.

[0081] 60.0 kg of desulfate solution, obtained after pre-purification and three-stage electrodialysis, was added to a jacketed continuous circulation reactor. The desulfate solution contained... The mass fraction is 26.0%, containing Approximately 15.60 kg, corresponding to approximately 149.9 mol.

[0082] According to NaOH and With a molar ratio of 0.95:1, approximately 11.87 kg of a 48% (w / w) high-purity NaOH aqueous solution was added using a constant flow pump. The NaOH addition time was controlled at 90 min, the reaction temperature at 8–12 °C, and the reaction was continued to circulate for 20 min after addition.

[0083] according to With a molar ratio of 1.00:1 to NaOH, approximately 9.12 kg of high-purity NaOH will be used. The PVDF hollow fiber membrane with an average pore size of 0.20 μm was continuously introduced into the circulating liquid. The pressure on the gas phase side was 20 kPa higher than the pressure on the liquid phase side, and the pH at the final reaction point was controlled to be 4.2.

[0084] Based on theoretical material balance, the final material mass is approximately 80.99 kg, effective The volume was approximately 30.42 kg, with a theoretical mass fraction of approximately 37.6%. The resulting concentrated solution was filtered through a 0.02 μm terminal membrane and then filled under nitrogen protection.

[0085] Example 5 illustrates the method of mother liquor circulation and initial liquid circulation in the electrodialysis product chamber.

[0086] Take a portion of the qualified concentrate from the previous production batch before final filtration and dilute it with deoxygenated high-purity water to... With a mass fraction of 2.0% and a pH of 4.3, it was used as the initial solution for the next batch of electrodialysis products.

[0087] A portion of the residual liquid from the previous batch of electrodialysis feedstock is discharged from the system, and the remainder is mixed with the freshly prepared crude solution. Based on the content of the residual liquid in the feedstock chamber... , The reuse ratio is controlled based on the metal ion detection results, ensuring that the mixture entering the precision filtration stage... Not higher than 0.30%, Not higher than 0.10%.

[0088] When any batch of raw material chamber residual liquid or When the set value is exceeded, the emission ratio should be increased; it is not allowed to be based solely on pH or The concentration determines whether the mother liquor can be reused. This procedure is used to prevent the unlimited accumulation of non-target salts in the circulation system.

[0089] The crude solution was prepared according to Example 1 and subjected to 0.10 μm precision filtration, but without passing through a Na-type iminodiacetic acid chelated porous membrane, and directly subjected to three-stage electrodialysis, NaOH reaction concentration, and... Membrane contact reaction.

[0090] This comparative example is used to compare the Fe, Cu, and Pb contents in the pre-purified liquid and the final product with Example 1, under the same low-oxygen storage conditions. The increase in content was studied to evaluate the effect of chelation of metals on inhibiting metal catalytic oxidation.

[0091] Pre-purification was performed according to Example 1, replacing the monovalent anion-selective membrane with a common strong-base anion exchange membrane that does not have monovalent / divalent selectivity. The remaining electrodialysis conditions, concentration conditions, and filling conditions were the same as in Example 1.

[0092] This comparative example was used to determine the product's performance in a laboratory under ordinary anion exchange membrane conditions. and migration flux, / Migration selectivity coefficient and in the final product The content was used to evaluate the effect of monovalent anion-selective membranes.

[0093] Production was carried out according to Example 1, but nitrogen protection was not used in the absorption, pre-purification, electrodialysis, NaOH feeding and filling steps, the material was in contact with air and dissolved oxygen was not controlled.

[0094] This comparative example is used to compare dissolved oxygen levels in crude liquid, electrodialysis product liquid, concentrated liquid, and finished product. The content was determined, and a closed-storage stability test was conducted to evaluate the effect of hypoxia control on inhibition. The role of oxidation.

[0095] Pre-purification and electrodialysis were completed according to Example 1, omitting the addition of NaOH and... Membrane contact reaction. The desulfate solution is vacuum evaporated under an absolute pressure of 10–20 kPa and a liquid temperature of 45–60 °C until… The mass fraction reached the same range as in Example 1.

[0096] This comparative example is used to compare the two concentration methods. growth, effective Yield, Exhaust gas volume and unit product energy consumption were used to evaluate the effect of low-temperature reaction enrichment relative to evaporation concentration.

[0097] The NaOH was added according to Example 1, but without using a hydrophobic porous membrane, and the same amount of substance was added. The enriched precursor solution is added directly by bubbling through a single-hole or multi-hole gas distributor, and the overall reaction endpoint pH is controlled to be the same as in Example 1.

[0098] This comparative example is used to compare the lowest local pH during the reaction process. The effects of exhaust gas concentration, time required to reach the reaction endpoint, and product composition uniformity were evaluated to assess the role of the hydrophobic porous membrane gas-liquid contact mode.

[0099] High-purity NaOH was directly added to the crude solution, which had not undergone precise filtration, chelation to remove metals, or electrodialysis treatment, and then... The reaction is concentrated; only after concentration are precision filtration, chelation membrane treatment and electrodialysis carried out in sequence.

[0100] This comparative example is used to compare membrane fouling rate, electrodialysis voltage change, and metal removal rate. The removal rate and product loss were measured to verify whether the sequence of steps, "pre-purification and electrodialysis followed by reaction concentration," produced a synergistic effect.

[0101] Table 1 shows the detection results of the crude sodium bisulfite aqueous solution and its subsequent precision filtration and Na-type iminodiacetic acid chelated porous membrane in each embodiment.

[0102] Table 1. Pre-purification results of Examples 1-5

[0103] As can be seen from the data in Table 1, precision filtration and Na-type iminodiacetic acid chelated porous membranes are mainly used to remove insoluble particles and metallic impurities such as Fe, Cu, and Pb, and are effective for removing dissolved particles. There was no significant removal effect. In Example 1, the Fe content decreased from 4.62 mg / kg to 0.11 mg / kg, with a removal rate of approximately 97.6%; the Fe removal rates in other examples were also higher than 94%.

[0104] This pre-purification step reduces metallic impurities in the final product and minimizes the impact of Fe and Cu on... It catalyzes oxidation and reduces the risk of particulate contamination and metal deposition in subsequent electrodialysis membrane stacks.

[0105] Product transfer type single-price selective electrodialysis was performed according to the temperature, current density, membrane surface linear velocity and membrane stack number specified in Examples 1 to 5. The results are shown in Table 2.

[0106] Table 2 Electrodialysis results of Examples 1-5

[0107] As can be seen from the data in Table 2, in Examples 1 to 5 / The migration flux ratios ranged from 13.2:1 to 21.4:1, all higher than the defined 8:1. / The migration selectivity coefficients ranged from 0.047 to 0.076, all below 0.15.

[0108] This indicates that the target anion is mainly maintained in a monovalent state under pH conditions of 4.0–4.6. And by using a monovalent anion-selective membrane, it can... and Prioritize access to the product room while suppressing divalent [products / products]. Enter the product room. Product rooms in each embodiment. The content is 39-78 mg / kg, less than 100 mg / kg.

[0109] Example 2 uses a lower current density and a lower raw material concentration, The migration flux and current efficiency are relatively low. Example 3 uses a higher current density and a higher feed concentration. The migration flux is high, but The migration rate also increases accordingly. This indicates that current density, feed concentration, and membrane surface velocity need to be controlled together.

[0110] The test results of the concentrated liquid obtained in each embodiment after terminal filtration and low-oxygen sealed filling are shown in Table 3.

[0111] Table 3 Final product results of Examples 1-5

[0112] The results in Table 3 show that all embodiments were able to obtain An aqueous solution with a mass fraction of 33%–42% has an effective concentration of solids. The content is 99.18% to 99.52%. The content is 58–92 mg / kg, the Fe content is 0.07–0.14 mg / kg, the Cu content is 0.012–0.022 mg / kg, the Pb content is not higher than 0.008 mg / kg, and the water-insoluble matter content is 2.8–8.4 mg / kg.

[0113] Example 1 achieves a good balance in purity, impurity control, yield, and energy consumption. Example 2 uses a lower current density and a lower initial concentration, resulting in a relatively lower final concentration and yield. Example 3 uses a higher operating load, resulting in a higher final concentration, but... and The content increased slightly. Example 5 employed controlled mother liquor recycling, which was expected to have a higher yield and lower energy consumption, but... and The fact that the amount is closer to the upper limit indicates that mandatory discharge conditions must be set for the reuse of mother liquor.

[0114] Comparative Examples 1-6 used the same detection method as Example 1. The results are shown in Table 4.

[0115] Table 4 Final product results of Comparative Examples 1–6

[0116] In Comparative Example 1, omitting the Na-type chelating porous membrane resulted in an increase in Fe, Cu, and Pb concentrations in the final product to 3.12 mg / kg, 0.38 mg / kg, and 0.14 mg / kg, respectively. The concentration reached 145 mg / kg. This indicates that the chelating membrane not only performs the function of metal purification, but is also expected to reduce the subsequent formation of sulfate by removing catalytically oxidized metal ions.

[0117] Comparative Example 2 uses a common anion exchange membrane, and the product contains... The concentration reached 1220 mg / kg, significantly higher than the 58 mg / kg in Example 1. This indicates that ordinary anion exchange membranes cannot effectively suppress divalent anions. Migrating to the product room, monovalent anion-selective membranes are the key to achieving this. and Key technical features of separation.

[0118] Comparative Example 3 did not employ low-oxygen protection; its products contained... Reaching 860mg / kg, The overall yield decreased to 86.4%. This indicates that oxygen in the air can cause problems during absorption, electrodialysis, reaction concentration, and filling. Oxidation, low dissolved oxygen, and nitrogen protection play an important role in maintaining the effective content of the product.

[0119] Comparative Example 4 uses vacuum evaporation concentration, and the product contains... The concentration reached 470 mg / kg, the total yield decreased to 85.9%, and the energy consumption reached 2.84 kWh / kg (100% concentration). This is significantly higher than the 1.08 kWh / kg in Example 1. (Note: This likely refers to a specific concentration of kWh / kg.) Low-temperature reaction concentration can avoid the thermal oxidation and high energy consumption caused by evaporation and concentration.

[0120] Comparative Example 5 uses the direct bubbling method for addition. final product The yield was 118 mg / kg, and the overall yield was 89.0%, both worse than in Example 1. This indicates that the membrane contactor can improve... Utilization rate and reaction uniformity, reducing local over-acidity and escape.

[0121] Comparative Example 6 changed the operation order, first concentrating and then purifying, and the water-insoluble matter in the product reached 24.0 mg / kg. The concentration reached 310 mg / kg, but the overall yield was only 82.6%, while energy consumption increased. This indicates that performing precision filtration, chelation to remove metals, and monovalent selective electrodialysis before reaction concentration is beneficial in reducing membrane fouling and losses from high-concentration solution treatment.

[0122] The results of the sulfur dioxide mass transfer process in Example 1 and Comparative Example 5 are shown in Table 5.

[0123] Table 5 Comparison of membrane contact and direct bubbling results

[0124] As shown in Table 5, the direct bubbling method has a shorter reaction time, but the lowest local pH drops to 2.68, and the exhaust gas... The concentration increased significantly, and the relative standard deviation of the concentration at different sampling points was also large. Although the reaction time was slightly prolonged by using a hydrophobic porous membrane, The utilization rate reached 99.1%, and the lowest local pH and product uniformity were improved.

[0125] The products obtained from Examples 1, 4, 1, 3, and 4 were stored in sealed containers at 25±2°C under light-protected conditions. The products from the Examples were stored in containers purged with nitrogen, while the container in Comparative Example 3 retained air at the top. The results are shown in Table 6.

[0126] Table 6 Product Storage Stability Results

[0127] As can be seen from the results in Table 6, the effective purity of Example 1 decreased from 99.52% to 99.35% after 90 days of storage. Increased from 58 mg / kg to 91 mg / kg; Example 4: After 90 days of storage The concentration was 98 mg / kg. Both groups were expected to remain within the defined mass range.

[0128] Comparative Example 1, omitting the chelating membrane, after 90 days of storage The increase to 1120 mg / kg indicates that residual Fe and Cu may catalyze [the reaction]. Oxidation. Comparative Example 3, without low-oxygen protection, showed an effective purity decrease to 94.58% after 90 days of storage. The concentration increased to 2920 mg / kg, indicating that oxygen was the primary factor leading to product deterioration during storage. Comparative Example 4, which involved evaporation and concentration, already had a high oxidative load during production, resulting in significant deterioration after storage. It will rise further.

[0129] As can be expected from the above results, the various technical steps of the present invention are not simply parallel and independent of each other, but rather constitute a synergistic relationship according to the laws of impurity formation and transport: Precision filtration first removes particulate matter, reducing the fouling load on subsequent chelating membranes and electrodialysis membranes.

[0130] Na-type iminodiacetic acid chelated porous membrane without introducing Removing Fe, Cu, and Pb under suitable conditions improves metal purity while reducing metal catalysis. Oxidation.

[0131] The pH of the pre-purified solution was maintained at 4.0–4.6 to ensure that the target component was mainly in monovalent form. It exists, and then utilizes a monovalent anion-selective membrane with divalent... Perform migration and separation.

[0132] After removing sulfates and metals, then use... The reaction concentration method can avoid membrane fouling, concentration polarization and simultaneous concentration of impurities caused by directly processing high-concentration crude liquid.

[0133] Hydrophobic porous membranes make Uniformly introduced into the liquid phase, reducing localized over-acidity caused by direct bubbling. Escape and uneven composition.

[0134] Low temperature, low dissolved oxygen, nitrogen protection, and low-oxygen filling work together to inhibit oxidation during production and storage. Oxidation.

[0135] Therefore, the present invention is expected to be able to obtain [the desired product] without employing high-temperature evaporation and solid crystallization. Mass fraction of 33%–42%, effective in solids Not less than 99.0%, A high-purity sodium bisulfite aqueous solution with a concentration not exceeding 100 mg / kg and a low trace metal content.

[0136] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a high-purity sodium bisulfite solution, comprising absorbing sulfur dioxide with a sodium-containing alkaline absorbent to prepare a crude aqueous solution containing sodium bisulfite, characterized in that, Includes the following steps: (1) The temperature of the crude aqueous solution is controlled at 0-15℃, its pH is adjusted to 4.0-4.6, and its dissolved oxygen content is controlled to be no higher than 0.5mg / L under inert gas protection, so that the mass fraction of sodium bisulfite in the crude aqueous solution is 8%-15%; the crude aqueous solution is passed through a precision filter membrane with a pore size of 0.05-0.20μm and a Na-type iminodiacetic acid chelated porous membrane in sequence to obtain a pre-purified solution; (2) Under conditions of 0–10°C and inert gas protection, the pre-purified liquid is introduced into the raw material chamber of an electrodialysis unit consisting of two or more stages connected in series. The electrodialysis unit is composed of alternating monovalent anion-selective membranes and cation exchange membranes. An aqueous solution with a pH of 4.0–4.6 and a sodium bisulfite mass fraction of 0.5%–3.0% is used as the initial liquid in the product chamber. Electrodialysis is performed at a current density of 5–20 mA / cm². and Selective migration from the raw material chamber to the product chamber, and causing Preferably retain it in the raw material chamber until the sodium bisulfite mass fraction of the solution in the product chamber reaches 22%–30%. The content is not higher than 100 mg / kg, and a desulfate solution is obtained; (3) Under the protection of 5-15℃ and inert gas, add a high-purity sodium hydroxide aqueous solution with a mass fraction of 48%-52% to the desulfate solution. The molar ratio of the added sodium hydroxide to the sodium bisulfite in the desulfate solution is 0.85:1-1.00:1, so that at least part of the sodium bisulfite is converted into sodium sulfite, and a concentrated precursor solution is obtained. (4) The purified sulfur dioxide is introduced into the enriched precursor solution through a hydrophobic porous membrane. The molar ratio of the sulfur dioxide introduced to the sodium hydroxide added in step (3) is 0.95:1 to 1.05:

1. The reaction is carried out at 5 to 20°C until the pH of the solution is 3.8 to 4.5, so that the sodium sulfite is converted into sodium bisulfite, and a enriched solution with a sodium bisulfite mass fraction of 33% to 42% is obtained. (5) Under the protection of inert gas, the concentrated liquid is passed through a terminal filter membrane with a pore size of 0.02 to 0.10 μm to obtain a high-purity sodium bisulfite aqueous solution, and the high-purity sodium bisulfite aqueous solution is sealed and filled.

2. The method for preparing a high-purity sodium bisulfite solution according to claim 1, characterized in that, The crude aqueous solution in step (1) is prepared by the following method: An inert gas is used to replace the sulfur dioxide absorption system until the oxygen volume fraction in the tail gas of the absorption system is no higher than 0.5%. At 5–20°C, a sodium hydroxide aqueous solution with a mass fraction of 5%–12% absorbs the sulfur dioxide that has been demisted and finely filtered. The pH at the end of the absorption is controlled to be 4.0–4.6, resulting in a crude aqueous solution with a sodium bisulfite mass fraction of 8%–15%.

3. The method for preparing a high-purity sodium bisulfite solution according to claim 2, characterized in that, The resistivity of the water used to prepare the sodium-containing alkaline absorbent solution is not less than 10 MΩ·cm, and the sodium hydroxide contains... The content is not higher than 0.05% by mass, the Cl⁻ content is not higher than 20 mg / kg, and the Fe content is not higher than 0.5 mg / kg; the purity of the sulfur dioxide is not lower than 99.9% by volume, wherein the oxygen content is not higher than 20 ppm, and the total amount of metal impurities is not higher than 0.1 mg / m³.

4. The method for preparing a high-purity sodium bisulfite solution according to claim 1, characterized in that, The average pore size of the Na-type iminodiacetic acid chelate porous membrane in step (1) is 0.1-1.0 μm, and the exchange capacity of the iminodiacetic acid group is 0.6-1.8 mmol / g. The empty bed contact time of the pre-purified liquid through the Na-type iminodiacetic acid chelate porous membrane is 2-10 min. Before use, the Na-type iminodiacetic acid chelate porous membrane is pretreated with high-purity water, sodium chloride aqueous solution with a mass fraction of 2%-5%, and deoxygenated high-purity water in sequence.

5. The method for preparing a high-purity sodium bisulfite solution according to claim 1, characterized in that, The electrodialysis unit in step (2) includes 2 to 4 electrodialysis membrane stacks connected in series. The electrode chambers of each electrodialysis membrane stack are isolated from the raw material chamber and the product chamber by electrode membranes. The linear velocity of the pre-purified liquid on the membrane surface is 2 to 5 cm / s, the current density of the electrodialysis membrane stack is 8 to 15 mA / cm², and the operating temperature is 3 to 7°C.

6. The method for preparing a high-purity sodium bisulfite solution according to claim 1, characterized in that, The sheet resistivity of the monovalent anion-selective membrane in step (2) is no higher than 8 Ω·cm²; with 0.50 mol / L and 0.25 mol / L Furthermore, the pH value was measured using an aqueous solution of 4.3 at 5°C and 10 mA / cm². Migration flux and The ratio of migration flux is not less than 8:

1.

7. The method for preparing a high-purity sodium bisulfite solution according to claim 1, characterized in that, In step (3), the high-purity sodium hydroxide aqueous solution is added in stages, and the addition time is controlled to be 30-90 min. The temperature of the desulfate solution is kept below 15°C during the addition process by cooling. After the sodium hydroxide is added, the reaction continues for 10-30 min to obtain a concentrated precursor solution with a pH of 7.5-9.

0.

8. The method for preparing a high-purity sodium bisulfite solution according to claim 1, characterized in that, The hydrophobic porous membrane in step (4) is a polytetrafluoroethylene hollow fiber membrane or a polyvinylidene fluoride hollow fiber membrane, and the average pore size of the hydrophobic porous membrane is 0.05 to 0.30 μm; the purified sulfur dioxide flows on the gas phase side of the hydrophobic porous membrane, and the enrichment precursor liquid flows on the liquid phase side of the hydrophobic porous membrane, with the gas phase pressure being 5 to 30 kPa higher than the liquid phase pressure.

9. The method for preparing a high-purity sodium bisulfite solution according to claim 1, characterized in that, In steps (1) to (5), nitrogen with an oxygen content of no more than 10 ppm and a dew point of no more than -30°C is used as the inert gas; the dissolved oxygen content of the high-purity sodium bisulfite aqueous solution before filling is no more than 0.3 mg / L, the filling container is replaced with nitrogen, and the oxygen volume fraction in the top space of the filling container is no more than 0.2%.

10. The method for preparing a high-purity sodium bisulfite solution according to claim 1, characterized in that, The sodium bisulfite aqueous solution obtained in step (5) has a sodium bisulfite mass fraction of 33%–42%; after deducting water, the sodium bisulfite mass fraction is determined by iodometric titration. The mass fraction of dissolved solids shall not be less than 99.0%. The content is not higher than 100 mg / kg. The content is not higher than 50 mg / kg, the Fe content is not higher than 0.5 mg / kg, the Cu content is not higher than 0.1 mg / kg, the Pb content is not higher than 0.1 mg / kg, and the water-insoluble matter content is not higher than 10 mg / kg.

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