Method for recycling sodium sulfite from organic sulfuric acid waste liquid

Abstract

The invention relates to a method for recycling sodium sulfite from organic sulfuric acid waste liquid, which comprises the following steps: evaporating waste sulfuric acid to remove water and organic matters, adding sulfur, reacting to generate sulfur dioxide, absorbing by using sodium carbonate or sodium hydroxide to generate sodium sulfite crystals, washing, centrifuging and drying to obtain a sodium sulfite product. By adopting the technical scheme of the invention, the waste sulfuric acid can be subjected to efficient resource treatment and resource recycling, a large amount of sodium hydroxide required by acid-base neutralization is saved, and sulfur resources in the sulfuric acid and oxygen consumed by sulfur dioxide generated by sulfur reaction are saved.

Description

Technical Field

[0001] The invention relates to the technical field of hazardous waste resource recovery, in particular to a method for resource recovery of sodium sulfite from organic sulfuric acid waste liquid. Background Art

[0002] Industrial production processes generate large quantities of waste sulfuric acid containing water, organic matter, and salt. This is particularly true in chip manufacturing, where wafer etching and cleaning processes generate millions of tons of waste sulfuric acid annually (for example, a 12-inch wafer fab alone produces over 3,000 tons per month). The typical composition of this waste acid is: 10-20% H₂SO₄; 8-15% inorganic salts (such as Na₂SO₄ / CaSO₄); 1-5% organic matter (such as photoresist residue); and 60-80% H₂O. If this waste sulfuric acid is not promptly disposed of, it cannot be used in chip production. Currently, waste sulfuric acid is used for limited production of titanium dioxide, aluminum sulfate, and acid-base neutralization, and the neutralization method uses Ca(OH)2 to produce gypsum slag (containing organic matter ≤0.1%), which has high disposal costs and creates problems in hazardous waste transfer; the production and reuse of titanium dioxide requires an acid concentration ≥70%, and the chloride ion needs to be <100ppm (the actual chip waste acid Cl- ≥500ppm); thermal decomposition regeneration requires high-temperature cracking above 1200℃, energy consumption >800kWh / ton, and produces SO3 aerosol pollution.

[0003] The mainstream process for producing sodium sulfite is the sulfur combustion method. Patent publication number CN108217612A discloses a method for producing sodium sulfite. This method involves reacting sulfur with air to produce sulfur dioxide, which is then introduced into liquid caustic soda to produce sodium sulfite. The reaction equation is:

[0004] S+O2↑→SO2(combustion furnace); SO2+Na2CO3→Na2SO3+CO2↑(absorption tower)

[0005] The disadvantage is that the reaction not only consumes the oxygen in the air, but also requires 100% sulfur reaction, which wastes oxygen and sulfur resources. According to the calculation, the theoretical value of sulfur consumption is 0.5 tons per ton of product, but the actual consumption is 0.53-0.55 tons. The nitrogen-containing air in the exhaust leads to NO in the tail gas. x Generate (>200mg / m 3 ); Due to local oxidation caused by excessive O2, the product contains Na2SO4 impurities ≥0.3%.

[0006] The invention patent with foreign patent number JP2019059943A proposes the reaction of waste sulfuric acid with coke:

[0007] 2H2SO4+C→2SO2+CO2+2H2O

[0008] However, in actual operation, the reactor is clogged due to salt coking, and the mixing of CO2 with SO2 causes the absorption efficiency to drop by more than 30%. Summary of the Invention

[0009] The purpose of the present invention is to provide a method for resource recovery of sodium sulfite from organic sulfuric acid waste liquid, breaking through the technical bottleneck of the inability to efficiently recycle high-salt and high-organic waste sulfuric acid; eliminating the dual resource waste of sulfur and oxygen in the traditional sodium sulfite process; and building a closed-loop industrial chain for waste acid disposal and resource recovery in the chip manufacturing industry.

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] The method for recycling sodium sulfite from organic sulfuric acid waste liquid is characterized by comprising the following steps:

[0012] Step 1: Industrial organic waste sulfuric acid containing H2SO4 ≥ 10% enters the evaporator for reduced pressure evaporation, and water and volatile organic matter are condensed by the condenser and removed by vacuum pump to obtain concentrated acid with anhydrous and organic matter above the boiling point of sulfuric acid and a H2SO4 concentration of 60-95%;

[0013] Step 2: The concentrated acid is heated to 150-280°C in a reactor, and sulfur is added continuously in three batches using a sulfur feeder. The total molar amount of sulfur is 0.98-1.02 times the molar amount of H2SO4 in the concentrated acid, and SO2 gas is generated by reaction;

[0014] Step 3: The SO2 gas is passed into a sulfuric acid scrubber and washed with sulfuric acid having a concentration of ≥95%, and then subjected to a three-stage falling film absorption by spraying sodium hydroxide or sodium carbonate solution; the sodium bisulfite generated by the falling film absorption is then added to sodium carbonate to form a sodium sulfite solution;

[0015] Step 4 and 5: The sodium sulfite solution is crystallized in an Oslo crystallizer under controlled temperature. The crystals are centrifuged and dried in a dryer to obtain the finished sodium sulfite product.

[0016] In step 1 of the above method, the evaporator has a reduced pressure evaporation vacuum of -0.08 to -0.095 MPa and a temperature of 80-95°C.

[0017] In step 2 of the above method, the reaction temperature during the continuous addition of sulfur is controlled between 180° C. and 280° C.

[0018] In step 3 of the above method, the gas flow rate of the sulfuric acid scrubber is 0.3-0.5 m / s, and the liquid-gas ratio is 3-5 L / Nm 3 , the washing acid circulation concentration is 90-98%.

[0019] The cooling rate during the crystallization process in step 4 of the above method is 0.8-1.5°C / min.

[0020] The beneficial effects of the present invention are:

[0021] The present invention reacts waste sulfuric acid with sulfur to generate sulfur dioxide, and the sulfur in the waste sulfuric acid is reduced to sulfur dioxide and utilized, thereby not only disposing of a large amount of waste sulfuric acid, but also saving a large amount of sodium hydroxide required for acid-base neutralization, and more importantly, saving the sulfur element resource in the sulfuric acid and the oxygen in the air that was originally required to consume when the sulfur reacted to generate sulfur dioxide.

[0022] The present invention removes water and volatile organic compounds by evaporation, then adds sulfur when heated to above 150°C to generate sulfur dioxide gas, achieving gas-liquid separation of the sulfur dioxide and waste sulfuric acid. The sulfur dioxide gas is then absorbed by sodium hydroxide or sodium carbonate to form sodium sulfite crystals. The crystals are then washed, centrifuged, and dried to obtain the sodium sulfite product. This invention not only solves the problem of waste acid disposal in the chip manufacturing industry, ensuring normal and stable production operations, but also recovers waste sulfuric acid to produce high-value sodium sulfite, achieving resource disposal and recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] refer to Figure 1 After evaporation, dehydration, and removal of volatile organic compounds, the present invention continuously adds sulfur in an amount equimolar to the sulfuric acid content when the temperature rises to above 150 degrees Celsius. The reaction generates sulfur dioxide gas, which is then vaporized from the waste sulfuric acid to achieve recovery and separation from the waste sulfuric acid. The sulfur dioxide gas is washed with sulfuric acid and then absorbed with sodium hydroxide or sodium carbonate to generate sodium sulfite crystals. The crystals are washed, centrifuged, and dried to obtain a sodium sulfite product. Specifically, the steps include:

[0026] Step 1: Pretreatment and evaporation concentration. Industrial organic waste sulfuric acid containing ≥10% H₂SO₄ is filtered to remove solid particles and then fed into an evaporator. It is evaporated and dehydrated at a vacuum of -0.08 to -0.095 MPa and a temperature of 80-95°C. Volatile organic compounds are simultaneously condensed and recovered. The VOCs condenser is constructed of a Hastelloy composite layer. The H₂SO₄ concentration at the concentration endpoint is controlled to be 60-95% (w / w), with a salt crystallinity ≤15%.

[0027] Step 2: Sulfur reduction reaction. Pump concentrated acid into the reactor. When the temperature reaches 150°C, sulfur is continuously added using a sulfur feeder with three radial sulfur feed ports. The total molar amount of sulfur, n(S), is n(0.98-1.02) × n(H2SO4). The stirring speed is 80-120 rpm, and the reaction time is 40-90 minutes. The SO2 generation rate is monitored in real time, and the reactor pressure is controlled at 0.15-0.25 MPa.

[0028] Continuous sulfur reduction in a specific temperature range of 150-280°C can achieve highly selective conversion of hexavalent sulfur to tetravalent sulfur in waste sulfuric acid. The reaction pathway is as follows:

[0029] Main reaction: 2H2SO4+S→3SO2↑+2H2O

[0030] Removal of organic impurities during low-temperature evaporation: Control reaction: R-COOH+H2SO4→CO+CO2↑+H2O

[0031] Thermal stability of salt ensures that Na2SO4+S→does not react

[0032] Analysis of the reaction principle: Sulfur acts as both a reducing agent and a reaction medium. Molten sulfur with a melting point of 119°C coats H2SO4 molecules to promote electron transfer; inorganic salts such as Na2SO4 form microcrystalline nuclei in the system, accelerating the precipitation of SO2 bubbles.

[0033] Step 3: SO2 gas stripping refining and alkali absorption crystallization.

[0034] The SO2 generated by the reaction enters the sulfuric acid scrubber to remove heavy metals such as As and Se; the SO2 concentration after refinement is ≥99.2% (v / v). The gas flow rate of the sulfuric acid scrubber is set to 0.3-0.5m / s, and the liquid-gas ratio is 3-5L / Nm 3 , the washing acid circulation concentration is 90-98%.

[0035] The refined SO2 is passed into a three-stage falling film absorption tower in series, and is countercurrently contacted with a 20-30% sodium hydroxide or sodium carbonate solution; the falling film absorption tower uses 316L stainless steel corrugated packing with a specific surface area of ​​250m 2 / m 3 The absorption liquid endpoint pH is controlled to be 7.0-8.5 and the temperature is below 100°C.

[0036] Step 4: The saturated sodium sulfite solution is fed into an Oslo crystallizer and cooled at a rate of 0.8-1.5°C / min for crystallization. The Oslo crystallizer is equipped with an online particle size analyzer. The slurry is centrifuged at 2000-3000 rpm and washed with ultrapure water until the conductivity is ≤50 μS / cm. The product is then dried at a temperature of 110-120°C and a discharge temperature of ≤60°C. After drying, the finished product is obtained.

[0037] The present invention is mainly used for the treatment of chip etching waste acid. The raw material is waste acid from a 12-inch wafer factory. The main components are H2SO4 18.2%, Na2SO4 14.7%, isopropyl alcohol 1.8%, and water 65.3%. It is evaporated to H2SO4 = 68.5% under a vacuum of -0.09MPa. The isopropyl alcohol-water azeotrope is collected in a VOCs recovery tank. The concentrated acid is pumped into a 5m 3 The reactor was heated to 180℃ and sulfur was continuously added using a sulfur feeder to generate SO21072Nm 3 (purity 99.3%), no heavy metals were detected after washing with 98% sulfuric acid; SO2 was absorbed by 20% sodium carbonate solution, and the crystallization end point pH was controlled to be 7.2; after centrifugation, the crystals were washed three times with ultrapure water and dried at 120°C to obtain sodium sulfite.

[0038] The present invention can also be applied to the treatment of pesticide waste acid. Because it contains benzene series, benzene ring organic matter is prone to coking during the evaporation stage. Before evaporation, 0.5% H2O2 (hydrogen peroxide) is added to oxidize and degrade the benzene series. The sulfur reaction temperature is raised to 280°C to destroy residual organic matter. The SO2 is then absorbed by passing it through a 30% sodium hydroxide solution. Using the present invention's technical solution, the SO2 yield reaches 98.6%, and the product's organic carbon content is ≤0.002%.

[0039] In summary, the resource utilization rate is greatly improved by adopting the technical solution of the present invention. The comparison is shown in Table 1.

[0040] Table 1 Resource utilization comparison table

[0041] index Traditional crafts The present invention Improvement Sulfur utilization rate 76％ 95.2％ +25.3％ Sulfur consumption per unit 0.53t / t 0.16t / t 69.8% reduction Oxygen consumption <![CDATA[280Nm 3 / t]]> 0 100％

[0042] The above is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for recycling sodium sulfite from organic sulfuric acid waste liquid, characterized in that: The following steps are involved: Step 1: Industrial organic waste sulfuric acid containing H2SO4 ≥ 10% enters the evaporator for reduced pressure evaporation, and water and volatile organic matter are condensed by the condenser and removed by vacuum pump to obtain concentrated acid with H2SO4 concentration of 60-95%; Step 2: The concentrated acid is heated to 150-280°C in a reactor, and sulfur is added using a sulfur feeder. The total molar amount of sulfur is 0.98-1.02 times the molar amount of H2SO4 in the concentrated acid, and SO2 gas is generated by reaction; Step 3: SO2 gas is passed into a sulfuric acid scrubber and washed with sulfuric acid having a concentration of ≥95%, and then subjected to falling film absorption by spraying sodium carbonate or sodium hydroxide solution; sodium bisulfite generated by falling film absorption is then added to sodium carbonate to form a sodium sulfite solution; Step 4: The sodium sulfite solution is crystallized in an Oslo crystallizer under controlled temperature, and the crystals are centrifuged and dried in a dryer to obtain the finished sodium sulfite product.

2. The method for recycling sodium sulfite from organic sulfuric acid waste liquid according to claim 1, wherein In step 1, the evaporator is subjected to reduced pressure evaporation at a vacuum degree of -0.08 to -0.095 MPa and a temperature of 80-95°C.

3. The method for recycling sodium sulfite from organic sulfuric acid waste liquid according to claim 1, wherein: The temperature range for continuous addition of sulfur in step 2 is 180-280°C.

4. The method for recycling sodium sulfite from organic sulfuric acid waste liquid according to claim 1, wherein: The gas flow rate of the sulfuric acid scrubber in step 3 is 0.3-0.5m / s, and the liquid-gas ratio is 3-5L / Nm 3 , the washing acid circulation concentration is 90-98%.

5. The method for recycling sodium sulfite from organic sulfuric acid waste liquid according to claim 1, wherein: The cooling rate during the crystallization process of step 4 is 0.8-1.5°C / min.

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