Process for recycling hydrobromic acid and potassium sulfate by using diafenthiuron potassium bromide-containing wastewater and re-purifying

Abstract

The invention relates to the technical field of industrial wastewater treatment and resource recycling, in particular to a process for recycling hydrobromic acid and potassium sulfate and re-purifying by utilizing diafenthiuron potassium bromide-containing wastewater, which comprises the following steps: firstly, adjusting the pH value to 2.0-4.0, and carrying out reduced pressure distillation to obtain a potassium bromide concentrated solution; performing multi-stage counter-current extraction and impurity removal by using a specific composite extracting agent, and adding sulfuric acid to react to generate hydrobromic acid and potassium sulfate; adding an entrainer, distilling and rectifying to obtain more than or equal to 48% of hydrobromic acid, and crystallizing and centrifuging residual liquid to obtain more than or equal to 99% of potassium sulfate; after the terminal wastewater is treated, the COD (Chemical Oxygen Demand) removal rate is greater than or equal to 90 percent. The diafenthiuron potassium bromide-containing wastewater is treated under the conditions of precise temperature control, extraction and the like, so that more than or equal to 48% of hydrobromic acid and more than or equal to 99% of potassium sulfate are obtained, and bromine and potassium are recycled; through composite extraction and other treatments, the COD removal rate of the wastewater is greater than or equal to 90%, solvent closed-loop circulation, recycled solvent reuse and low-concentration hydrobromic acid fraction reflux are also constructed, the cost is reduced, the raw material utilization rate is improved, and the requirements of green chemical industry are met.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment and resource recycling technology, specifically a process for recovering hydrobromic acid and potassium sulfate from butyl ether urea-containing potassium bromide wastewater and then purifying them. Background Technology

[0002] Diethyl urea, a commonly used pesticide and acaricide, generates a large amount of wastewater containing potassium bromide during its production. This wastewater not only contains high concentrations of bromide and potassium ions, but also contains organic impurities such as phenols and tar. Direct discharge of this wastewater would result in a serious waste of valuable elements such as bromine and potassium, leading to low resource utilization and increased raw material costs for enterprises. Furthermore, the high levels of organic pollutants in the wastewater would significantly increase the COD value, far exceeding emission standards, causing serious pollution to water bodies, soil, and other ecological environments, which is inconsistent with current environmental protection policies.

[0003] Currently, the treatment of potassium bromide-containing wastewater from butyl urea mainly employs simple neutralization precipitation or direct evaporation concentration processes. The former can only remove some heavy metal impurities and cannot recover bromine and potassium elements, and the removal effect of organic pollutants is poor, requiring further treatment. Although the latter can initially enrich potassium bromide, the purity of the obtained potassium bromide product is low because it does not specifically remove phenolic and tar impurities, making it difficult to meet the requirements of industrial applications. Furthermore, the evaporation process has high energy consumption, and the solvent cannot be recovered, resulting in high treatment costs. At the same time, the residual organic waste liquid after distillation still poses an environmental emission risk.

[0004] Furthermore, existing processes lack effective solvent recycling mechanisms. Extractants and azeotropic agents used in the treatment process are mostly single-use, increasing material costs and generating new organic waste, which contradicts the industry's development trend of green chemistry and energy conservation and emission reduction. Therefore, developing a process that can recover high-value elements and deeply remove organic pollutants from potassium bromide-containing wastewater containing butyl ether urea, while also considering solvent recycling and reducing energy consumption and costs, has become a pressing technical challenge for butyl ether urea manufacturers. Summary of the Invention

[0005] Technical problems to be solved To address the aforementioned shortcomings of existing technologies, this invention treats potassium bromide-containing wastewater containing butyl ether urea by precisely controlling temperature and extraction conditions to obtain ≥48% hydrobromic acid and ≥99% potassium sulfate, thus realizing the resource utilization of potassium bromide. Through composite extraction and other treatments, the COD removal rate of the wastewater reaches ≥90%, meeting the standard. Furthermore, a closed-loop solvent recycling system is constructed, allowing for solvent recovery and reuse, and the low-concentration hydrobromic acid fraction is refluxed, reducing costs, improving raw material utilization, and meeting the requirements of green chemical engineering.

[0006] Technical solution To achieve the above objectives, the present invention provides the following technical solution: A process for recovering and purifying hydrobromic acid and potassium sulfate from potassium bromide-containing wastewater containing butyl ether urea includes the following steps: S100, Pretreatment and Concentration Purification: The pH of the potassium bromide-containing wastewater was adjusted to 2.0-4.0 with dilute sulfuric acid, and then vacuum distilled under system pressure of -0.085 to -0.098 MPa and temperature of 40-70℃ to obtain potassium bromide concentrate; S200, Multi-stage countercurrent extraction for impurity removal: The potassium bromide concentrate is subjected to 3-4 stages of countercurrent extraction using a composite extractant composed of o-xylene and methyl isobutyl ketone in a volume ratio of 3:1 to 5:1. The extraction temperature is 35-55℃ and the extraction time is 25-45 minutes, resulting in the separation of a purified aqueous phase and an organic phase containing phenolic tar. S300, Sulfuric Acid Conversion and Reaction Control: Add sulfuric acid with a concentration of 50% to 98% to the purified aqueous phase in batches, controlling the total amount of sulfuric acid added to be 1.05 to 1.15 times the theoretical reaction amount. Under stirring and cooling circulation conditions, react at 20 to 50°C for 30 to 60 minutes to fully convert potassium bromide into hydrobromic acid and potassium sulfate. S400, Azeotropic distillation to separate hydrobromic acid: Add an azeotropic agent to the reaction solution obtained in step S300 and perform azeotropic distillation. The azeotropic agent is a mixed solvent of o-xylene and n-butanol with a volume ratio of 4:1. The azeotropic distillation is carried out at 115-135°C, and a water vapor mixture containing hydrobromic acid is continuously distilled out. S500, Hydrobromic Acid Distillation and Purification: The mixture of hydrobromic acid-containing water vapor obtained in step S400 is condensed and introduced into a packed distillation column. Continuous distillation is carried out under the conditions of a top temperature of 100-118℃, a bottom temperature of 120-135℃, and a reflux ratio of 3-8. Hydrobromic acid products with a concentration of not less than 48% are collected, and the low-concentration fraction is refluxed to the azeotropic distillation process. S600, potassium sulfate crystallization and efficient separation: Cool the azeotropic distillation residue to -5 to 5°C, add seed crystals to induce crystallization, and then centrifuge at a centrifugation rate of 2500 to 4000 rpm for 15 to 35 minutes to obtain potassium sulfate solid with a purity of not less than 99%; S700 Solvent Recovery and Recycling: The phenol-containing tar organic phase generated in step S200 is combined with the mother liquor after centrifugation in step S600, and vacuum distillation is carried out under system pressure of -0.090 to -0.099 MPa and temperature of 75 to 95℃ to separate and recover the organic solvent. Among them, o-xylene is recycled to step S200 or S400, and methyl isobutyl ketone and n-butanol are recycled to the corresponding processes after dehydration. S800 Terminal wastewater treatment: All process wastewater is collected and treated by ozone oxidation and activated carbon adsorption, with a COD removal rate of ≥90%, and discharged after meeting the emission standards.

[0007] Furthermore, the concentration of the dilute sulfuric acid in step S100 is 5% to 15%, and the pH is adjusted to 2.5 to 3.5.

[0008] Furthermore, in the multi-stage countercurrent extraction described in step S200, the volume ratio of extractant to concentrate in each stage is 0.5:1 to 1:1.

[0009] Furthermore, the method of adding sulfuric acid in batches as described in step S300 is as follows: first, add 60% to 70% of the total amount quickly, and then add the remaining part slowly dropwise, controlling the reaction temperature to not exceed 45°C.

[0010] Furthermore, the amount of azeotropic agent added in step S400 is 0.8 to 1.5 times the volume of the reaction liquid.

[0011] Furthermore, in step S500, the distillation column has a theoretical plate number of 15 to 25 and an operating pressure of atmospheric pressure or slightly negative pressure of -0.01 to -0.03 MPa.

[0012] Furthermore, the cooling crystallization described in step S600 adopts a programmed cooling method: first, the temperature is lowered to 10-15°C at a rate of 1-2°C / minute, and then held for 20-40 minutes for ripening, and then the temperature is lowered to the final temperature of -2-2°C at a rate of 0.5-1°C / minute.

[0013] Furthermore, the aqueous fraction obtained from solvent recovery in step S700 is subjected to adsorption and dehydration treatment using 3A molecular sieves, and the water content in the organic phase after dehydration is ≤0.1%.

[0014] Furthermore, in step S800, the ozone dosage for ozone oxidation treatment is 50–100 mg / L, and the space velocity of the activated carbon adsorption column is 2–4 h⁻¹.

[0015] Beneficial effects Compared with known public technologies, the technical solution provided by this invention has the following beneficial effects: I. This invention achieves high-value resource recovery and deep purification synergistic treatment of potassium bromide-containing wastewater from butyl urea. On the one hand, by precisely controlling the pretreatment concentration, multi-stage countercurrent extraction, and sulfuric acid conversion reaction conditions, it efficiently recovers hydrobromic acid with a concentration of not less than 48% and potassium sulfate products with a purity of not less than 99%, realizing the resource utilization of bromine and potassium elements in the wastewater and creating significant economic value. On the other hand, through impurity removal with composite extractants, azeotropic distillation separation, and terminal ozone-activated carbon combined treatment, the COD removal rate of the process wastewater is ≥90%, and the final effluent meets environmental protection standards, solving the pollution problem of butyl urea production wastewater and achieving dual benefits of resource recovery and environmental governance.

[0016] II. This invention constructs a closed-loop solvent recycling system, which separates and recovers solvents such as o-xylene, methyl isobutyl ketone, and n-butanol from the phenol tar organic phase and centrifugal mother liquor under specific conditions through vacuum distillation. Among them, o-xylene can be directly reused in the extraction or azeotropic distillation process, and methyl isobutyl ketone and n-butanol can also be reused in the corresponding process after dehydration (water content ≤0.1%) by 3A molecular sieve, which greatly reduces the cost of solvent consumption. At the same time, the low-concentration fraction generated in the hydrobromic acid distillation process is returned to the azeotropic distillation process to further improve the utilization rate of raw materials. The overall process has low energy consumption and low material loss, which meets the requirements of green chemical production. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments thereof. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0018] I. Preparation of Process Raw Materials and Equipment (a) Raw material specifications Wastewater to be treated: Wastewater containing potassium bromide taken from the butyl urea production workshop. After testing, the wastewater contained potassium bromide at a mass concentration of 80-120 g / L, phenolic organic matter (mainly phenol) at a mass concentration of 5-12 g / L, COD at a value of 3500-5000 mg / L, pH at a value of 6.5-8.0, and the remainder was water and small amounts of impurities such as sodium chloride and sodium sulfate.

[0019] Chemical reagents: dilute sulfuric acid, concentration 5%–15%, used for pH adjustment; concentrated sulfuric acid, concentration 98%, used for potassium bromide conversion reaction; o-xylene, purity ≥99.0%, used as an extractant and azeotropic agent component; methyl isobutyl ketone, purity ≥98.5%, used as an extractant; n-butanol, purity ≥99.0%, used as an azeotropic agent component; potassium sulfate seed crystals, purity ≥99.0%, particle size 0.1–0.3 mm; 3A molecular sieve, particle size 3–5 mm, static water adsorption capacity ≥20%.

[0020] (II) Equipment Selection

[0021] Pretreatment system: 10m³ corrosion-resistant regulating tank, made of 316L stainless steel, equipped with an online pH monitor and a mechanical stirring device with a stirring speed of 150-200rpm; 5m³ vacuum distillation tower, made of 316L stainless steel, equipped with a horizontal spiral plate heat exchanger, a vacuum pump with an ultimate vacuum of ≤-0.099MPa, as well as a temperature control system and a liquid level control system.

[0022] Extraction system: 4-stage series mixing and clarification tanks, each with an effective volume of 1m³, made of 316L stainless steel. The mixing chamber is equipped with a high-speed stirrer with a stirring speed of 800-1200rpm, and the clarification chamber is equipped with baffles and a liquid level adjustment device; organic phase storage tank with a volume of 2m³, made of fiberglass; aqueous phase storage tank with a volume of 2m³, made of 316L stainless steel.

[0023] Conversion reaction system: 5m³ reactor, made of 316L stainless steel, equipped with a double-jacketed cooling system, the cooling medium of which is chilled brine, and the temperature can be controlled between 5 and 15℃; mechanical stirring device, stirring speed of 200 to 300 rpm; temperature sensor, accuracy ±0.5℃; and a 500L dropping funnel equipped with a flow control valve.

[0024] Azeotropic distillation system: 8m³ azeotropic distillation column, made of 316L stainless steel, filled with stainless steel corrugated packing with a specification of θ50mm and a specific surface area of ​​250m² / m³; the distillation column is equipped with a reboiler, the heat source is saturated steam, the pressure is 0.3~0.5MPa, a condenser, the cooling medium is circulating water, the temperature is 20~30℃, and a solvent metering tank with a volume of 1m³, made of fiberglass.

[0025] Distillation and purification system: 10m³ packed distillation column, made of 316L stainless steel, with 20 theoretical plates, filled with stainless steel wire mesh corrugated packing with a specification of θ70mm and a specific surface area of ​​350m² / m³; the distillation column is equipped with a top condenser, using chilled brine as the cooling medium at a temperature of 5-10℃; a bottom reboiler, using heat transfer oil as the heat source, with a temperature controllable between 130-150℃; a reflux ratio controller with an accuracy of ±0.1; a product storage tank with a volume of 5m³ made of 316L stainless steel; and a reflux tank with a volume of 1m³ made of 316L stainless steel.

[0026] Crystallization separation system: 5m³ crystallization tank, made of 316L stainless steel, equipped with a programmed cooling control system with an adjustable cooling rate of 0.1~2℃ / min, a mechanical stirring device with a stirring rate of 50~100rpm, and a temperature sensor with an accuracy of ±0.2℃; horizontal screw discharge centrifuge with a processing capacity of 1~2m³ / h, a drum diameter of 800mm, a maximum speed of 4000rpm, and made of 316L stainless steel; dryer, hot air circulation type, with a temperature controllable at 80~100℃ and an air volume of 500~800m³ / h.

[0027] Solvent recovery system: 5m³ vacuum distillation kettle, made of 316L stainless steel, equipped with a vacuum pump with an ultimate vacuum of ≤-0.099MPa; heat transfer oil heating system, with temperature controllable between 75 and 100℃; condenser, with circulating water as the cooling medium and a temperature of 20 to 30℃; 3A molecular sieve adsorption column, 500mm in diameter and 3000mm in height, made of carbon steel lined with rubber, with internal 3A molecular sieve packing; solvent storage tanks including a 2m³ o-xylene storage tank, a 1m³ methyl isobutyl ketone storage tank, and a 1m³ n-butanol storage tank, all made of fiberglass.

[0028] Terminal water treatment system: 5m³ ozone oxidation tower, made of fiberglass, equipped with an ozone generator with an output of 500-1000g / h and an ozone concentration of 80-120mg / L; an aeration device with titanium aeration heads and a pore size of 10-20μm; an activated carbon adsorption column with a diameter of 800mm and a height of 4000mm, made of carbon steel lined with rubber, containing granular activated carbon with a particle size of 2-4mm and an iodine adsorption value ≥1000mg / g; and a clear water storage tank with a volume of 10m³, made of fiberglass.

[0029] II. Specific Process Steps and Examples

[0030] Example 1 S100, Pretreatment and Concentration Purification The potassium bromide-containing wastewater containing butyl urea was pumped into a regulating tank. The wastewater had a potassium bromide concentration of 95 g / L, a phenol concentration of 8 g / L, and a COD of 4200 mg / L. Stirring was started at 180 rpm, and 10% dilute sulfuric acid was slowly added via a metering pump. The pH was monitored in real time and adjusted to 3.0. The regulated wastewater was then pumped into a vacuum distillation tower. The vacuum pump was started to stabilize the system pressure at -0.092 MPa, and the heating device was activated to control the tower temperature at 55°C for vacuum distillation concentration. During distillation, the distillation rate was controlled by a level control system. Distillation was stopped when the potassium bromide concentration at the bottom of the tower reached 350 g / L, yielding a potassium bromide concentrate with a volume of 27% of the original wastewater. The secondary vapor generated during distillation was condensed and collected in a terminal wastewater tank for further treatment.

[0031] S200, multi-stage countercurrent extraction for impurity removal The potassium bromide concentrate obtained from S100 was pumped into the first mixing chamber of a four-stage series mixing and clarification tank. Simultaneously, a composite extractant (o-xylene and methyl isobutyl ketone mixed at a volume ratio of 4:1) was pumped into the fourth mixing chamber at a volume ratio of 0.8:1 for each stage of extractant to concentrate. The stirring in each mixing chamber was turned on at a speed of 1000 rpm, the extraction temperature was controlled at 45℃, and the extraction time for each stage was 35 minutes. After extraction, the mixture was allowed to stand in the clarification chamber for 20 minutes to separate into layers. The purified aqueous phase was collected from the bottom of the first clarification chamber. The phenol concentration was ≤0.1 g / L and the COD was 380 mg / L. The organic phase containing phenol tar was collected from the top of the fourth clarification chamber with a phenol concentration of 28 g / L. The two phases were then pumped into their respective storage tanks.

[0032] S300, Sulfuric Acid Conversion and Reaction Control The purified aqueous phase obtained from S200 was pumped into the reactor, and the stirrer was started at a speed of 250 rpm. The jacket cooling system was activated to stabilize the temperature inside the reactor at 25℃. 98% concentrated sulfuric acid was added to the reactor in batches through a dropping funnel: first, 65% of the theoretical reaction amount (1.1 times the total sulfuric acid) was added quickly. The theoretical reaction amount was calculated based on the complete conversion of potassium bromide to hydrobromic acid, i.e., n(H2SO4):n(KBr)=1:2. During the addition, the stirring speed was kept constant, and the temperature was monitored in real time. When the temperature rose to 40℃, the addition rate was slowed down. The remaining 35% concentrated sulfuric acid was added slowly dropwise through the dropping funnel at a dropping rate of 5L / h, and the temperature inside the reactor was controlled not to exceed 45℃ throughout the process. After the addition was completed, the reaction was stirred for another 45 minutes to ensure that the potassium bromide was fully converted, resulting in a reaction solution containing hydrobromic acid and potassium sulfate. The conversion rate of potassium bromide was tested to be ≥99.5%.

[0033] S400, azeotropic distillation separation of hydrobromic acid The reaction solution obtained from S300 is pumped into an azeotropic distillation column. An azeotropic agent (a mixture of o-xylene and n-butanol at a volume ratio of 4:1) is added at a volume of 1.2 times the volume of the reaction solution. The reboiler is turned on, and saturated steam at 0.4 MPa is introduced for heating. The temperature inside the column is controlled at 125°C for azeotropic distillation. During the distillation process, a water vapor mixture containing hydrobromic acid escapes from the top of the column, is condensed by a condenser, and is collected in the rectification feed tank. When there is no obvious distillate at the top of the column (distillation rate ≤ 0.5 L / h), the azeotropic distillation is stopped. The remaining liquid at the bottom of the column is an aqueous solution of potassium sulfate with a potassium sulfate concentration of 420 g / L, which is pumped into a crystallization tank for further processing.

[0034] S500, purified by distillation of hydrobromic acid The condensate obtained from the S400 distillation column, containing 35% hydrobromic acid, is pumped into a packed distillation column. The top condenser is turned on, with the cooling medium temperature at 8°C, and the bottom reboiler is turned on, with the heat transfer oil temperature at 130°C. The operating pressure is controlled at atmospheric pressure, and the theoretical number of plates is 20. After the temperature inside the column stabilizes, the reflux ratio is adjusted to 5 for continuous distillation. The concentration of the top fraction is monitored in real time. When the top temperature stabilizes at 110°C, the top fraction is collected, yielding a hydrobromic acid product with a concentration of 49.2%. After testing, the purity is ≥99.8%, the impurity Cl⁻ content is ≤0.01%, and the SO₄²⁻ content is ≤0.005%. The low-concentration fraction (hydrobromic acid concentration <30%) generated during the distillation process is returned to the S400 azeotropic distillation column via a reflux pump to participate in azeotropic distillation again.

[0035] S600, potassium sulfate crystallization and efficient separation Potassium sulfate seed crystals were added to the potassium sulfate aqueous solution obtained from S400 at a concentration of 0.5% of the solution mass. The crystallization tank was stirred at a speed of 80 rpm, and the programmed cooling system was started: first, the temperature was lowered to 12°C at a rate of 1.5°C / min and maintained for 30 minutes; then, the temperature was lowered to 0°C at a rate of 0.8°C / min and maintained for 2 hours for crystallization. After crystallization, the slurry was pumped into a horizontal screw discharge centrifuge, and the centrifugation speed was controlled at 3200 rpm for 25 minutes. The solid obtained by centrifugation was dried in a hot air dryer at a temperature of 90°C and an air volume of 600 m³ / h for 2 hours to obtain potassium sulfate solid product. The purity was tested to be 99.3%, the moisture content was ≤0.5%, the impurity Cl⁻ content was ≤0.02%, and the SO₄²⁻ content was ≥52.0%. The centrifugation mother liquor was pumped into the solvent recovery system for further processing.

[0036] S700, Solvent Recovery and Recycling The phenol-containing tar organic phase obtained from S200 was combined with the centrifuged mother liquor obtained from S600 and pumped into a vacuum distillation kettle. The vacuum pump was started to stabilize the system pressure at -0.095 MPa, and the heat transfer oil heating system was turned on to control the kettle temperature at 85℃ for vacuum distillation. During the distillation process, the fractions were collected sequentially: when the fraction temperature was 65-70℃, the o-xylene fraction (purity ≥99.0%) was collected and pumped into the o-xylene storage tank for reuse in S200 extraction or S400 azeotropic distillation; when the fraction temperature was 75-80℃, the methyl isobutylene fraction was collected. Ketone fraction (purity ≥98.5%); when the fraction temperature is 90-95℃, collect n-butanol fraction (purity ≥99.0%); combine methyl isobutyl ketone and n-butanol fractions and pump them into a 3A molecular sieve adsorption column, control the flow rate at 1.5 m³ / h, and perform adsorption dehydration for 4 hours. After testing, the water content in the organic phase after dehydration is 0.08%, and pump them into the corresponding storage tanks for reuse in S200 extraction or S400 azeotropic distillation; the phenol-containing tar remaining at the bottom of the distillation vessel, with a phenol concentration ≥80%, is collected and entrusted to a professional unit for treatment.

[0037] S800, Terminal Wastewater Treatment The secondary condensate from S100 distillation, wastewater from S700 distillation, and other wastewater generated during the process, such as equipment cleaning water and floor washing water, were collected in the terminal wastewater tank. The COD of the wastewater was measured to be 1200 mg / L. The wastewater was then pumped into an ozone oxidation tower, the ozone generator was turned on, the ozone dosage was controlled at 80 mg / L, the aeration rate was 2 m³ / h, and the oxidation treatment lasted for 2 hours. After oxidation, the wastewater was pumped into an activated carbon adsorption column, and the space velocity was controlled at 3 h⁻¹ for adsorption treatment. The treated wastewater COD was measured to be 95 mg / L, and the COD removal rate was 92.1%. All indicators met the Class I discharge standard of the "Integrated Wastewater Discharge Standard" (GB8978-1996) and were directly discharged.

[0038] Example 2 S100, Pretreatment and Concentration Purification

[0039] The potassium bromide-containing wastewater containing butyl urea was pumped into a conditioning tank. The wastewater had a potassium bromide concentration of 82 g / L, a phenol concentration of 6 g / L, and a COD of 3600 mg / L. Stirring was started at a speed of 160 rpm, and 8% dilute sulfuric acid was added to adjust the pH to 2.5. The conditioned wastewater was then pumped into a vacuum distillation tower. The control system pressure was set at -0.088 MPa, and the tower temperature was set at 48°C for vacuum distillation. When the potassium bromide concentration at the bottom of the tower reached 320 g / L, distillation was stopped, yielding a potassium bromide concentrate with a volume of 26% of the original wastewater. The secondary steam condensate was collected in the terminal wastewater tank.

[0040] S200, multi-stage countercurrent extraction for impurity removal

[0041] A three-stage series mixing and clarification tank was used. The composite extractant was a mixture of o-xylene and methyl isobutyl ketone at a volume ratio of 3.5:1. The volume ratio of extractant to concentrate in each stage was 0.6:1. The extraction temperature was 40℃ and the extraction time for each stage was 30 minutes. After separation, the purified aqueous phase (phenol concentration ≤0.08g / L, COD=320mg / L) and the phenol-containing organic phase were collected.

[0042] S300, Sulfuric Acid Conversion and Reaction Control

[0043] Add 98% concentrated sulfuric acid to the purified aqueous phase. The total amount added is 1.08 times the theoretical reaction amount. First, add 60% quickly, and then add the remaining 40% slowly dropwise. Control the reaction temperature to not exceed 42℃ and the reaction time to 40 minutes. The potassium bromide conversion rate is ≥99.4%.

[0044] S400, azeotropic distillation separation of hydrobromic acid

[0045] The amount of azeotropic agent added is 1.0 times the volume of the reaction liquid. The temperature inside the column is controlled at 120℃ to carry out azeotropic distillation, and the condensate is collected for further distillation.

[0046] S500, purified by distillation of hydrobromic acid

[0047] The operating pressure was controlled at -0.02 MPa, the theoretical number of plates was 18, the reflux ratio was 4, and after distillation, a hydrobromic acid product with a concentration of 48.5% (purity ≥99.7%) was obtained.

[0048] S600, potassium sulfate crystallization and efficient separation

[0049] The cooling parameters were as follows: first, the temperature was lowered to 13℃ at a rate of 1.2℃ / min and kept at this temperature for 25 minutes; then, the temperature was lowered to -1℃ at a rate of 0.6℃ / min and kept at this temperature for 1.5 hours to crystallize; the centrifugation rate was 3000 rpm and the centrifugation time was 20 minutes; after drying, potassium sulfate solid product (purity 99.1%) was obtained.

[0050] S700, Solvent Recovery and Recycling

[0051] Vacuum distillation parameters: system pressure -0.092MPa, reactor temperature 80℃. After collecting each solvent fraction, it is dehydrated by adsorption of 3A molecular sieve (water content ≤0.09%) and reused in the corresponding process.

[0052] S800, Terminal Wastewater Treatment

[0053] The ozone dosage was 70 mg / L, the activated carbon adsorption space velocity was 2.5 h⁻¹, and the COD of the treated wastewater was 88 mg / L, with a COD removal rate of 92.8%, meeting the discharge standards.

[0054] Example 3 S100, Pretreatment and Concentration Purification

[0055] The potassium bromide-containing wastewater containing butyl urea was pumped into a regulating tank. The wastewater had a potassium bromide concentration of 115 g / L, a phenol concentration of 10 g / L, and a COD of 4800 mg / L. Stirring was started at a speed of 200 rpm, and 12% dilute sulfuric acid was added to adjust the pH to 3.5. The regulated wastewater was then pumped into a vacuum distillation tower. The control system pressure was set at -0.095 MPa, and the tower temperature was set at 65°C for vacuum distillation. When the potassium bromide concentration at the bottom of the tower reached 380 g / L, distillation was stopped, yielding a potassium bromide concentrate with a volume of 30% of the original wastewater. The secondary steam condensate was collected in the terminal wastewater tank.

[0056] S200, multi-stage countercurrent extraction for impurity removal A four-stage series mixing and clarification tank was used. The composite extractant was a mixture of o-xylene and methyl isobutyl ketone at a volume ratio of 4.5:1. The volume ratio of extractant to concentrate in each stage was 1.0:1. The extraction temperature was 50℃ and the extraction time for each stage was 40 minutes. After separation, the purified aqueous phase (phenol concentration ≤0.12g / L, COD=420mg / L) and the phenol-containing organic phase were collected.

[0057] S300, Sulfuric Acid Conversion and Reaction Control Add 98% concentrated sulfuric acid to the purified aqueous phase. The total amount added is 1.12 times the theoretical reaction amount. First, add 70% quickly, and then add the remaining 30% slowly dropwise. Control the reaction temperature to not exceed 45℃ and the reaction time to 50 minutes. The potassium bromide conversion rate is ≥99.6%.

[0058] S400, azeotropic distillation separation of hydrobromic acid The amount of azeotropic agent added is 1.4 times the volume of the reaction liquid. The temperature inside the column is controlled at 130℃ to carry out azeotropic distillation, and the condensate is collected for further distillation.

[0059] S500, purified by distillation of hydrobromic acid The operating pressure was controlled at -0.03 MPa, the theoretical number of plates was 22, the reflux ratio was 7, and after distillation, a hydrobromic acid product with a concentration of 49.8% (purity ≥99.9%) was obtained.

[0060] S600, potassium sulfate crystallization and efficient separation The cooling parameters were as follows: first, the temperature was lowered to 14℃ at a rate of 1.8℃ / min and kept at this temperature for 35 minutes; then, the temperature was lowered to 1℃ at a rate of 0.9℃ / min and kept at this temperature for 2.5 hours for crystallization; the centrifugation rate was 3800 rpm and the centrifugation time was 30 minutes. After drying, potassium sulfate solid product (purity 99.5%) was obtained.

[0061] S700, Solvent Recovery and Recycling Vacuum distillation parameters: system pressure -0.098MPa, reactor temperature 90℃. After collecting each solvent fraction, it is dehydrated by adsorption of 3A molecular sieve (water content ≤0.07%) and reused in the corresponding process.

[0062] S800, Terminal Wastewater Treatment The ozone dosage was 90 mg / L, the activated carbon adsorption space velocity was 3.5 h⁻¹, and the COD of the treated wastewater was 102 mg / L, with a COD removal rate of 91.7%, meeting the discharge standards.

[0063] III. Verification and Explanation of Process Effects (a) Product quality inspection results The quality of the hydrobromic acid and potassium sulfate products obtained in the above three examples was tested, and the results are shown in the table below: Product Indicators Example 1 Example 2 Example 3 Industry standard requirements Hydrobromic acid concentration (%) 49.2 48.5 49.8 ≥48.0 Hydrobromic acid purity (%) 99.8 99.7 99.9 ≥99.5 Cl⁻ content (%) in hydrobromic acid 0.008 0.009 0.006 ≤0.010 <![CDATA[Content of SO4²⁻ in hydrobromic acid (%)]]> 0.004 0.005 0.003 ≤0.005 Potassium sulfate purity (%) 99.3 99.1 99.5 ≥99.0 Moisture content of potassium sulfate (%) 0.4 0.5 0.3 ≤0.5 Cl⁻ content (%) in potassium sulfate 0.018 0.019 0.015 ≤0.020 <![CDATA[Content of SO4²⁻ in potassium sulfate (%)]]> 52.2 52.1 52.3 ≥52.0 As shown in the table above, the hydrobromic acid obtained by the process of this invention has a concentration of no less than 48.5% and a purity of no less than 99.7%, with impurity content far below industry standards; the potassium sulfate has a purity of no less than 99.1%, and the moisture and impurity content meet the quality requirements of industrial-grade potassium sulfate. The products can be directly used in chemical, pharmaceutical and other fields to achieve efficient resource recovery.

[0064] (II) Verification of process environmental protection indicators The COD values ​​and removal rates of the terminal wastewater before and after treatment in the three examples were measured, and the results are shown in the table below: project Example 1 Example 2 Example 3 GB8978-1996 Class I Standard COD (mg / L) of wastewater before treatment 1200 1050 1320 / COD (mg / L) of treated wastewater 95 88 102 ≤100 COD removal rate (%) 92.1 92.8 91.7 ≥90.0 As shown in the table above, the process of this invention, through the combination of ozone oxidation and activated carbon adsorption, achieves a COD removal rate of over 91% for the terminal wastewater, and the COD value of the treated wastewater is below 100 mg / L, fully meeting the Class I discharge standard of the "Integrated Wastewater Discharge Standard" (GB8978-1996), effectively solving the pollution problem of potassium bromide-containing wastewater containing butyl urea.

[0065] (III) Instructions for Controlling Key Process Parameters S100 pH adjustment: If the pH is below 2.0, the corrosiveness of the wastewater will increase, which will aggravate the wear and tear on the equipment; if the pH is above 4.0, potassium bromide will easily react with impurities to form precipitates during the concentration process, which will affect the subsequent extraction effect. Therefore, the preferred pH is 2.5 to 3.5.

[0066] S200 extractant ratio: When the volume ratio of o-xylene to methyl isobutyl ketone is less than 3:1, the extraction efficiency for phenols decreases; when it is greater than 5:1, the viscosity of the extractant increases and the separation speed slows down, so 3:1 to 5:1 is preferred; when the volume ratio of each stage extractant to concentrate is less than 0.5:1, the extraction is insufficient; when it is greater than 1:1, the amount of extractant used is too large, increasing the recovery cost, so 0.5:1 to 1:1 is preferred.

[0067] S300 sulfuric acid addition amount: When it is less than 1.05 times the theoretical reaction amount, potassium bromide conversion is incomplete; when it is more than 1.15 times, excess sulfuric acid will increase the difficulty of subsequent separation. Therefore, 1.05 to 1.15 times is preferred. Adding it in batches can avoid the loss of hydrobromic acid due to excessive local temperature and ensure that the reaction proceeds smoothly.

[0068] S400 azeotropic agent dosage: When it is less than 0.8 times the volume of the reaction liquid, the azeotropic effect is not good and the hydrobromic acid separation is incomplete; when it is more than 1.5 times, it will increase the distillation energy consumption and solvent recovery burden, so 0.8 to 1.5 times is preferred.

[0069] S600 programmed cooling: First, rapidly cooling to 10-15℃ can promote crystal nucleus formation, and holding the temperature for ripening can make the crystals grow evenly; then slowly cooling to -2-2℃ can improve the potassium sulfate crystallization rate, avoid crystal agglomeration, and ensure the centrifugal separation effect.

[0070] In summary, the process of this invention achieves resource utilization and compliant discharge of potassium bromide-containing wastewater by precisely controlling the parameters of each stage. The product quality is stable, the environmental indicators are excellent, and the economic benefits are significant, making it suitable for large-scale industrial production.

[0071] 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 the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for recovering hydrobromic acid and potassium sulfate from potassium bromide-containing wastewater containing butyl ether urea, and for subsequent purification, characterized in that, The process includes the following steps: S100, Pretreatment and Concentration Purification: The pH of the potassium bromide-containing wastewater was adjusted to 2.0–4.0 with dilute sulfuric acid, and then vacuum distilled under system pressure of -0.085 to -0.098 MPa and temperature of 40 to 70℃ to obtain potassium bromide concentrate; S200, Multi-stage countercurrent extraction for impurity removal: The potassium bromide concentrate is subjected to 3-4 stages of countercurrent extraction using a composite extractant composed of o-xylene and methyl isobutyl ketone in a volume ratio of 3:1 to 5:

1. The extraction temperature is 35-55℃ and the extraction time is 25-45 minutes, resulting in the separation of a purified aqueous phase and an organic phase containing phenolic tar. S300, Sulfuric Acid Conversion and Reaction Control: Add sulfuric acid with a concentration of 50% to 98% to the purified aqueous phase in batches, controlling the total amount of sulfuric acid added to be 1.05 to 1.15 times the theoretical reaction amount. Under stirring and cooling circulation conditions, react at 20 to 50°C for 30 to 60 minutes to fully convert potassium bromide into hydrobromic acid and potassium sulfate. S400, Azeotropic distillation to separate hydrobromic acid: Add an azeotropic agent to the reaction solution obtained in step S300 and perform azeotropic distillation. The azeotropic agent is a mixed solvent of o-xylene and n-butanol with a volume ratio of 4:

1. The azeotropic distillation is carried out at 115-135°C, and a water vapor mixture containing hydrobromic acid is continuously distilled out. S500, Hydrobromic Acid Distillation and Purification: The mixture of hydrobromic acid-containing water vapor obtained in step S400 is condensed and introduced into a packed distillation column. Continuous distillation is carried out under the conditions of a top temperature of 100-118℃, a bottom temperature of 120-135℃, and a reflux ratio of 3-8. Hydrobromic acid products with a concentration of not less than 48% are collected, and the low-concentration fraction is refluxed to the azeotropic distillation process. S600, potassium sulfate crystallization and efficient separation: Cool the azeotropic distillation residue to -5 to 5°C, add seed crystals to induce crystallization, and then centrifuge at a centrifugation rate of 2500 to 4000 rpm for 15 to 35 minutes to obtain potassium sulfate solid with a purity of not less than 99%; S700 Solvent Recovery and Recycling: The phenol-containing tar organic phase generated in step S200 is combined with the mother liquor after centrifugation in step S600, and vacuum distillation is carried out under system pressure of -0.090 to -0.099 MPa and temperature of 75 to 95℃ to separate and recover the organic solvent. Among them, o-xylene is recycled to step S200 or S400, and methyl isobutyl ketone and n-butanol are recycled to the corresponding processes after dehydration. S800 Terminal wastewater treatment: All process wastewater is collected and treated by ozone oxidation and activated carbon adsorption, with a COD removal rate of ≥90%, and discharged after meeting the emission standards.

2. The process for recovering hydrobromic acid and potassium sulfate from potassium bromide-containing wastewater using butyl ether urea according to claim 1, characterized in that, The concentration of the dilute sulfuric acid in step S100 is 5% to 15%, and the pH is adjusted to 2.5 to 3.

5.

3. The process for recovering hydrobromic acid and potassium sulfate from potassium bromide-containing wastewater using butyl ether urea according to claim 1, characterized in that, In the multi-stage countercurrent extraction described in step S200, the volume ratio of extractant to concentrate in each stage is 0.5:1 to 1:

1.

4. The process for recovering hydrobromic acid and potassium sulfate from potassium bromide-containing wastewater using butyl ether urea according to claim 1, characterized in that, The method of adding sulfuric acid in batches as described in step S300 is as follows: first, add 60% to 70% of the total amount quickly, and then add the remaining part slowly dropwise, controlling the reaction temperature to not exceed 45°C.

5. The process for recovering hydrobromic acid and potassium sulfate from potassium bromide-containing wastewater using butyl ether urea according to claim 1, characterized in that, The amount of azeotropic agent added in step S400 is 0.8 to 1.5 times the volume of the reaction liquid.

6. The process for recovering hydrobromic acid and potassium sulfate from potassium bromide-containing wastewater using butyl ether urea according to claim 1, characterized in that, The theoretical number of plates in the distillation column described in step S500 is 15 to 25, and the operating pressure is atmospheric pressure or slightly negative pressure of -0.01 to -0.03 MPa.

7. The process for recovering hydrobromic acid and potassium sulfate from potassium bromide-containing wastewater using butyl ether urea according to claim 1, characterized in that, The cooling crystallization described in step S600 adopts a programmed cooling method: first, the temperature is lowered to 10-15°C at a rate of 1-2°C / minute, and then held for 20-40 minutes for ripening. Finally, the temperature is lowered to the final temperature of -2-2°C at a rate of 0.5-1°C / minute.

8. The process for recovering hydrobromic acid and potassium sulfate from potassium bromide-containing wastewater using butyl ether urea according to claim 1, characterized in that, The aqueous fraction obtained from solvent recovery in step S700 is dehydrated by adsorption using 3A molecular sieves, and the water content in the organic phase after dehydration is ≤0.1%.

9. The process for recovering hydrobromic acid and potassium sulfate from potassium bromide-containing wastewater using butyl ether urea according to claim 1, characterized in that, In step S800, the ozone dosage for ozone oxidation treatment is 50–100 mg / L, and the space velocity of the activated carbon adsorption column is 2–4 h⁻¹.