Preparation process and system of high-purity bromine

Abstract

The application provides a preparation process and system of high-purity bromine, and belongs to the technical field of bromine preparation; the preparation process comprises the steps of sodium bromide aqueous solution preparation, acid adjustment, chlorine oxidation and bromine blowing reaction, fractional condensation and chlorine removal treatment, continuous concentrated sulfuric acid dehydration treatment and product collection; in the chlorine oxidation and bromine blowing reaction step, the acidic sodium bromide raw material liquid is pumped into an oxidation and bromine blowing tower, chlorine is introduced, the molar ratio of chlorine to sodium bromide is 1.05-1.1:1, the reaction temperature is 60-80 DEG C, the gas-liquid contact time is 30-60 min, at the same time, air is introduced as a carrier gas, the carrier gas flow is 0.5-0.6 m 3 / h, the flow ratio of air to the acidic sodium bromide raw material liquid is 1:3, stripping is carried out, and bromine-containing mixed gas is obtained; the product obtained by the method and process has low chlorine ion and moisture content, high purity, and meets the use requirements of high-end fields such as bromine flame retardants.

Description

Technical Field

[0001] This invention belongs to the field of bromine preparation technology, specifically relating to a preparation process and system for high-purity bromine. Background Technology

[0002] Bromine is an important basic chemical raw material, widely used in brominated flame retardants such as brominated polystyrene and octabromoether, as well as in pharmaceuticals, pesticides, and dyes. Bromine flame retardants, in particular, have extremely high purity requirements for bromine, with chloride content ≤50ppm and moisture content ≤0.05%. If chloride and moisture exceed the standards, it will cause downstream flame retardant products to yellow and discolor, decrease thermal stability, and damage mechanical properties, seriously affecting product quality.

[0003] Currently, the industrial process commonly uses sodium bromide aqueous solution as raw material, hydrochloric acid to adjust the acidity, and chlorine to oxidize and blow bromine to produce bromine. The core principle is that under acidic conditions, chlorine reacts with sodium bromide in a redox reaction to produce elemental bromine, which is then obtained by stripping and condensing. However, this process has the following prominent drawbacks: 1. Excessive chloride content: After the reaction, the crude bromine is prone to carrying unreacted chlorine gas, hydrogen chloride and other chlorine-containing impurities, which are difficult to remove completely using traditional condensation processes. This results in the chloride content in the product far exceeding the downstream use standard, which directly affects the synthesis purity and stability of bromine-based flame retardants. Traditional condensation processes are single-stage condensation methods, typically employing a fixed low-temperature condensation (generally 5-15℃). A bromine-containing gas mixture (bromine, chlorine, hydrogen chloride, and water vapor) is directly passed into a single condenser. Low-temperature cooling condenses the bromine into liquid crude bromine, while the uncondensed tail gas is directly absorbed by an alkaline solution. However, bromine has a boiling point of 58.8℃, chlorine -34.6℃, and hydrogen chloride -85℃, representing a significant difference in boiling points. While traditional single-stage low-temperature condensation (5-15℃) can completely condense the bromine, it also causes some chlorine and hydrogen chloride to condense along with the water vapor, entraining them into the liquid crude bromine. Furthermore, single-stage condensation cannot achieve the separation effect of "bromine condensation and recovery, while chlorine-containing impurities remain in the tail gas." The simultaneous condensation of chlorine-containing impurities and bromine results in persistently high chloride ion content in the crude bromine (typically above 500 ppm), making complete removal difficult.

[0004] 2. Excessive moisture content: After condensation, crude bromine still contains a large amount of free water. Traditional dehydration methods (such as static stratification and single-stage concentrated sulfuric acid dehydration) are inefficient, incomplete, and difficult to achieve continuous production, resulting in excessive moisture content in the product and exacerbating the hydrolysis and yellowing problems of downstream flame retardant products.

[0005] In existing technologies, some companies have tried to improve purity by lowering the condensation temperature and increasing the number of concentrated sulfuric acid dehydration cycles. However, the former leads to an increase in the amount of chlorine entrained during condensation, further increasing the chloride content, while the latter makes continuous production impossible and increases the cost of waste acid treatment.

[0006] Therefore, developing a high-purity bromine preparation process that can simultaneously reduce chloride and moisture content, achieve continuous production, and be adapted to the modification of existing equipment has become a technical problem that the industry urgently needs to solve. Summary of the Invention

[0007] The purpose of this invention is to provide a process and system for preparing high-purity bromine. Addressing the core pain points of high chloride and high moisture content in existing sodium bromide raw material bromine preparation processes, this invention optimizes the distillation and condensation process and the continuous dehydration process. Without changing the core oxidation and bromine blowing reaction system, it achieves efficient removal of chloride and moisture, producing high-purity bromine that meets the requirements of high-end fields such as bromine-based flame retardants. Furthermore, the process is continuous and easy to industrialize.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, a process for preparing high-purity bromine uses sodium bromide as raw material and employs a continuous process of "dissolving and adjusting acid → oxidizing and blowing bromine with chlorine gas → staged condensation to remove chlorine → continuous dehydration with concentrated sulfuric acid → finished product collection" to prepare high-purity bromine. The specific steps include: Step 1: Preparation and acid adjustment of sodium bromide aqueous solution Sodium bromide solid is added to a dissolving tank, deionized water is added, and the mixture is stirred to dissolve and obtain a sodium bromide aqueous solution with a mass concentration of 20%-35%. 35-37wt% hydrochloric acid solution is added dropwise to adjust the pH of the solution to 1-3, thus obtaining an acidic sodium bromide raw material solution. Preferably, the mass concentration of the sodium bromide aqueous solution is 27.8-33.3%; Preferably, the pH of the solution is adjusted to 1.5-2.

[0009] Step 2: Chlorine oxidation and bromine blowing reaction The acidic sodium bromide feedstock solution obtained in step 1 is pumped into an oxidative bromine blowing tower. Chlorine gas is introduced from the bottom of the oxidative bromine blowing tower. The molar ratio of chlorine gas to sodium bromide is controlled at 1.05-1.1:1, the reaction temperature is 60-80℃, and the gas-liquid contact time is 30-60 min. Preferably, the molar ratio of chlorine to sodium bromide is 1.08-1.1:1, the reaction temperature is 70-75℃, and the gas-liquid contact time is 45-50 min; Chlorine reacts with sodium bromide in a redox reaction to produce elemental bromine. The reaction equation is as follows: 2NaBr + Cl2 = 2NaCl + Br2↑ Simultaneously, air is introduced as a carrier gas through a stripping fan at the top of the bromine stripping tower, with a flow rate of 0.5-0.6 m³ / h. 3 The flow rate ratio of air to acidic sodium bromide feed solution is 1:3 per hour. The generated elemental bromine, unreacted trace amounts of chlorine gas, and water vapor are blown off together to obtain a bromine-containing mixed gas.

[0010] Step 3: Staged condensation dechlorination treatment The bromine-containing mixed gas obtained in step 2 is fed into a distillation and condensation system, which includes a distillation column, a primary condenser, and a secondary condenser connected in sequence. The flow rate entering the distillation column is controlled at 0.6-0.8 m³ / s. 3 The distillation column has a bottom temperature of 60-65℃ and a top temperature of 55-60℃, with a system pressure of atmospheric pressure and a reflux ratio of 1:2-3. The vapor phase collected from the top of the distillation column sequentially enters the primary condenser and then the secondary condenser, where a gradient temperature-controlled condensation method is used to remove chloride impurities. The condensate temperature of the primary condenser is 40-55℃. The vapor phase discharged from the primary condenser enters the secondary condenser, with a controlled flow rate of 0.10-0.15 m³ / h. 3 / h, pressure is controlled at atmospheric pressure, the condensate temperature of the secondary condenser is 5-15℃, the liquid crude bromine discharged from the primary condenser and the liquid phase discharged from the secondary condenser both enter the crude bromine intermediate tank, the liquid phase at the bottom of the distillation column merges into the crude bromine intermediate tank, and the gas phase after secondary condensation enters the tail gas treatment system. Preferably, the flow rate entering the distillation column is 0.7-0.8 m³ / s. 3 / h, the bottom temperature of the distillation column is 62-64℃, and the top temperature is 58-60℃; Preferably, the condensing temperature of the first-stage condenser is 48-52℃, and the flow rate of the gas phase discharged from the first-stage condenser into the second-stage condenser is 0.12-0.14 m³ / s. 3 / h, the temperature of the secondary condenser is 8-10℃; The liquid crude bromine discharged from the primary condenser has a chloride content of 100-200 ppm, a moisture content of 0.18-0.25%, and a purity of 99.2-99.5%. The liquid trace bromine discharged from the secondary condenser has a chloride content ≤80ppm, a moisture content ≤0.2%, and a purity ≥99.8%.

[0011] Step 4: Continuous concentrated sulfuric acid dehydration treatment The crude bromine product from the intermediate crude bromine tank is pumped into a continuous concentrated sulfuric acid dehydration tower. Water is removed using a continuous counter-current contact dehydration method. The tower temperature is controlled at 25-35℃, the tower pressure at atmospheric pressure, and the gas-liquid contact time at 20-30 minutes. The tower is filled with corrosion-resistant polytetrafluoroethylene (PTFE) Pall rings. Concentrated sulfuric acid with a mass fraction ≥98% is continuously added to the top of the tower, with a mass ratio of concentrated sulfuric acid to crude bromine of 1:10-20. The bromine discharged from the bottom of the dehydration tower is filtered through a corrosion-resistant 0.5-0.7μm PTFE membrane filter to obtain dehydrated bromine. The waste sulfuric acid discharged from the top of the dehydration tower (mass fraction reduced to 90%-95%) is collected in a waste acid storage tank and can be recycled after concentration. Preferably, the mass ratio of concentrated sulfuric acid to crude bromine is 1:16-16.7; Preferably, the temperature inside the dehydration tower is 30-32℃, and the gas-liquid contact time is 28-35 min; Preferably, the mass fraction of the waste sulfuric acid is 92-93%; After dehydration, crude bromine carries micron-sized sulfuric acid mist droplets. A precision of 0.5-0.7μm can completely trap the acid mist without trapping liquid bromine. Crude bromine enters from the bottom of the dehydration tower and forms a countercurrent contact with concentrated sulfuric acid flowing down from the top. The concentrated sulfuric acid reacts with the free water in the crude bromine to generate fuming sulfuric acid, achieving rapid and thorough removal of moisture. If the precision is >1μm, acid mist penetration will cause the acidity and moisture content of the finished product to slightly exceed the standard. If the precision is <0.5μm, it is prone to clogging and cannot be used for continuous production.

[0012] Step 5: Finished Product Collection The high-purity bromine product obtained in step 4 is pumped into the finished product storage tank. The storage tank is equipped with a nitrogen protection device to prevent the bromine from oxidizing and deteriorating. On the other hand, a high-purity bromine preparation system for realizing the above process includes the following: The system comprises a dissolution and acid conditioning unit, an oxidation and bromine blowing unit, a staged condensation and dechlorination unit, a continuous dehydration unit, a finished product collection unit, and supporting tail gas treatment and waste acid recovery units, connected in sequence. The specific structure is as follows: 1. Dissolving and acid-adjusting unit: including a dissolving tank, with a sodium bromide inlet and a hydrochloric acid inlet at the top, and a raw material liquid outlet at the bottom; the tank is equipped with a stirring device and an online pH monitor. 2. Oxidative bromine blowing unit: including an oxidative bromine blowing tower, which has a chlorine gas inlet and a carrier gas inlet at the bottom, a bromine-containing mixed gas outlet at the top, a raw material liquid inlet in the middle, and a gas-liquid distributor and packing layer inside the tower; 3. Staged condensation and dechlorination unit: including a distillation column, a primary condenser, a secondary condenser, and a crude bromine intermediate tank; the feed inlet of the distillation column is connected to the mixed gas outlet of the oxidative bromine blowing column, the gas phase outlet at the top of the distillation column is connected to the gas inlet of the primary condenser, the liquid phase pipeline at the bottom of the distillation column is connected to the crude bromine intermediate tank, the liquid phase outlet of the primary condenser is connected to the crude bromine intermediate tank, the gas phase outlet is connected to the gas inlet of the secondary condenser, the liquid phase outlet of the secondary condenser is connected to the crude bromine intermediate tank, and the gas phase outlet is connected to the tail gas treatment unit; both the primary and secondary condensers are equipped with independent condensate temperature control systems; 4. Continuous dehydration unit: includes a continuous concentrated sulfuric acid dehydration tower, a concentrated sulfuric acid storage tank, and a corrosion-resistant filter. The dehydration tower has a concentrated sulfuric acid inlet at the top, a crude bromine inlet and a finished product outlet at the bottom, and a packing layer in the middle. The finished product outlet is connected to the corrosion-resistant filter. The concentrated sulfuric acid storage tank is connected to the concentrated sulfuric acid inlet of the dehydration tower through a metering pump. 5. Finished product collection unit: includes a finished product storage tank, which is connected to the outlet of a corrosion-resistant filter. The tank has a nitrogen inlet at the top and a finished product outlet at the bottom. 6. Supporting Units: The tail gas treatment unit includes an alkaline absorption tower for absorbing chlorine and hydrogen chloride tail gas; the waste acid recovery unit includes a waste acid storage tank and a concentrated sulfuric acid concentration device for recovering and recycling the waste sulfuric acid discharged from the dehydration tower.

[0013] Traditional processes typically employ a single low-temperature condensation temperature of 5-15℃. This temperature maximizes the condensation of elemental bromine and improves the recovery rate. However, it does not consider the entrainment of chlorine impurities, leading to excessive chloride content in crude bromine. Some companies have attempted to lower the condensation temperature to 0-5℃ in an effort to further improve the bromine recovery rate. However, this has resulted in more chlorine and hydrogen chloride being condensed with water vapor, further increasing the chloride content to over 800 ppm, failing to address the core problem. The boiling point of elemental bromine is 58.8℃, and the temperature needs to be lower than its boiling point; otherwise, elemental bromine will be lost with the tail gas, reducing the recovery rate. The condensation temperature of chlorine is about -34.6℃, and the condensation temperature of hydrogen chloride is about -85℃. The boiling points of both are much lower than that of elemental bromine, so the temperature needs to be higher than the high condensation temperature. However, if the temperature is too high, the bromine will not condense completely, and if the temperature is too low, chlorine and hydrogen chloride will be entrained and condensed, which will increase the chloride content. Finding a precise balance between "bromine recovery rate" and "chlorine removal effect" is not simply a matter of setting a low or high temperature.

[0014] This invention employs a dehydration tower packed with polytetrafluoroethylene (PTFE) Pall ring packing. This packing has a large specific surface area and high gas-liquid contact efficiency. It also utilizes a counter-current contact method where crude bromine enters from the bottom and concentrated sulfuric acid from the top, ensuring full contact between the two and preventing incomplete dehydration in certain areas, thus guaranteeing uniform moisture removal. The dehydration tower, pipelines, and filters are all lined with PTFE corrosion-resistant material or Hastelloy alloy, which can withstand the strong corrosion of concentrated sulfuric acid and bromine, with a service life of over 5 years, enabling long-term stable and continuous operation. Furthermore, a waste acid storage tank and a concentrated sulfuric acid concentration device are installed to concentrate the waste sulfuric acid (90-95% by mass) generated during dehydration to over 98%, allowing it to be reused in the dehydration process, achieving waste acid recycling, reducing pollution, and lowering production costs. A metering pump precisely controls the feed flow rates of concentrated sulfuric acid and crude bromine, and combined with an online monitoring device for the moisture content of crude bromine, the amount of concentrated sulfuric acid added is dynamically adjusted to ensure a stable ratio of 1:10-20, achieving continuous and stable dehydration.

[0015] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. Completely resolve the problem of excessive chloride ions. This invention employs a gradient temperature-controlled staged condensation process. By precisely controlling the condensate temperature of the first-stage condenser (40-55℃), it utilizes the boiling point difference to achieve efficient separation of elemental bromine from chlorine and hydrogen chloride. Without the need for additional dechlorination equipment, the chloride content can be reduced from over 500ppm in existing processes to ≤50ppm, fully meeting the requirements for downstream brominated flame retardants. 2. Achieve deep and continuous moisture removal This invention abandons the traditional static stratification and single dehydration method and adopts a continuous concentrated sulfuric acid countercurrent dehydration process, which improves the dehydration efficiency by 3-5 times, reduces the moisture content from more than 0.5% in the existing process to ≤0.05%, and realizes continuous production, which is suitable for industrial-scale preparation needs. 3. Strong process compatibility and easy industrialization. The core oxidative bromine blowing reaction system of this invention is consistent with the existing process. Only the distillation and condensation system and the dehydration system need to be modified. There is no need to replace the core equipment. The cycle is short and it is suitable for upgrading existing bromine production enterprises. Among them, the distillation tower, as a pre-separation unit, is integrated between the oxidative bromine blowing and the first-stage condensation. No additional pressurization equipment is required. It relies on the waste heat of the gas phase at 60-75℃ to achieve atmospheric pressure distillation. The equipment modification is simple. Existing bromine production lines only need to add a small distillation tower to complete the upgrade. The modification investment is low. 4. Green and environmentally friendly, with high resource utilization rate Chlorine and hydrogen chloride in the exhaust gas are absorbed by alkaline solution and discharged in compliance with standards. Waste sulfuric acid can be recycled after concentration, which reduces pollutant emissions and raw material waste and is in line with the concept of green chemical production. 5. High product purity, suitable for high-end applications. The bromine product prepared by this invention has a chloride content of ≤50ppm, a moisture content of ≤0.05%, a purity of ≥99.95%, and a total recovery rate of ≥99.5%. When used in the production of high-end bromine-based flame retardants such as brominated polystyrene and octabromoether, it can effectively avoid problems such as yellowing and decreased thermal stability of the product, thereby improving the quality of downstream products. Detailed Implementation

[0016] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. The embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0017] Example 1: A preparation process for high-purity bromine (specifically for PA6 flame retardant) 1. Step 1: Preparation and acid adjustment of sodium bromide aqueous solution 10m 3 6.5 tons of deionized water were added to a dissolving tank, and 2.5 tons of sodium bromide solid were added. The mixture was stirred for 30 minutes until completely dissolved to obtain a sodium bromide aqueous solution with a mass concentration of 27.8%. 37wt% hydrochloric acid solution was added dropwise to adjust the pH of the solution to 2, thus obtaining an acidic sodium bromide raw material solution.

[0018] 2. Step 2: Chlorine oxidation and bromine blowing reaction The acidic sodium bromide feed solution obtained in step 1 was diluted with water at a concentration of 1.5 m³. 3 A chlorine gas flow rate of 0.12 kmol / h is pumped into the oxidative bromine blowing tower, and chlorine gas is introduced from the bottom of the tower. The chlorine gas flow rate is controlled at 0.12 kmol / h (chlorine to sodium bromide molar ratio 1.08:1). The reaction temperature is controlled at 70℃, the gas-liquid contact time is 45 min, and air is simultaneously introduced as a carrier gas at a flow rate of 0.5 m³ / h. 3 / h, stripping, to obtain a bromine-containing mixed gas.

[0019] 3. Step 3: Staged condensation dechlorination treatment The bromine-containing mixed gas obtained in step 2 is passed into the distillation and condensation system, with a flow rate of 0.7 m³ / s into the distillation column. 3 The distillation column has a bottom temperature of 62℃ and a top temperature of 58℃, a system pressure of atmospheric pressure, a reflux ratio of 1:2, a condensate temperature of 48℃ in the first-stage condenser, and a gas phase exiting the first-stage condenser entering the second-stage condenser at a flow rate of 0.12 m³ / h. 3 / h, pressure is atmospheric pressure, the condensate temperature of the secondary condenser is 10℃, the liquid phase discharged from the primary condenser and the secondary condenser both enter the crude bromine intermediate tank, the liquid phase at the bottom of the distillation column merges into the crude bromine intermediate tank, and the gas phase after secondary condensation enters the tail gas treatment system.

[0020] The liquid crude bromine discharged from the first-stage condenser has a chloride content of 150 ppm, a moisture content of 0.22%, and a purity of 99.3%. The liquid phase discharged from the secondary condenser has a chloride content of 72 ppm, a moisture content of 0.15%, and a purity of 99.86%.

[0021] 4. Step 4: Continuous concentrated sulfuric acid dehydration treatment Crude bromine from the intermediate crude bromine tank is pumped into a continuous concentrated sulfuric acid dehydration tower at a flow rate of 0.8 t / h. 98 wt% concentrated sulfuric acid (concentrated sulfuric acid to crude bromine mass ratio 1:16) is added at the top of the tower at a flow rate of 0.05 t / h. The temperature inside the dehydration tower is 30℃, the pressure is atmospheric pressure, and the gas-liquid contact time is 25 min. The tower is filled with polytetrafluoroethylene (PTFE) Pall ring packing. After countercurrent dehydration, the bromine discharged from the bottom is filtered through a corrosion-resistant filter with a 0.5 μm PTFE membrane core to obtain dehydrated bromine. The waste sulfuric acid discharged from the top of the dehydration tower (mass fraction reduced to 93%) is collected in a waste acid storage tank and can be recycled after concentration.

[0022] 5. Step 5: Finished Product Inspection and Collection The dehydrated bromine obtained in step 4 was pumped into a nitrogen-protected finished product storage tank and sampled for testing. The measured chloride content was 38 ppm, the moisture content was 0.03%, the bromine content was 99.95%, and the total recovery rate was 99.6%, which fully meets the bromine standard for the production of brominated polystyrene (for PA6 flame retardant).

[0023] Example 2: A preparation process for high-purity bromine (for octabromoether flame retardant). 1. Step 1: Preparation and acid adjustment of sodium bromide aqueous solution Add 6.0 tons of deionized water and 3.0 tons of sodium bromide solid to a 10 m³ dissolving tank, stir for 30 min until completely dissolved, and obtain a sodium bromide aqueous solution with a mass concentration of 33.3%. Add 36 wt% hydrochloric acid solution dropwise to adjust the pH of the solution to 1.5 to obtain an acidic sodium bromide raw material solution.

[0024] 2. Step 2: Chlorine oxidation and bromine blowing reaction The acidic sodium bromide feed solution obtained in step 1 was diluted with water at a concentration of 1.8 mJ. 3 A chlorine gas flow rate of 0.15 kmol / h is pumped into the oxidative bromine blowing tower, and chlorine gas is introduced from the bottom of the tower. The chlorine gas flow rate is controlled at 0.15 kmol / h (chlorine to sodium bromide molar ratio 1.1:1). The reaction temperature is controlled at 75℃, the gas-liquid contact time is 50 min, and air is simultaneously introduced as a carrier gas at a flow rate of 0.6 m³ / h. 3 / h, stripping, to obtain a bromine-containing mixed gas.

[0025] 3. Step 3: Staged condensation dechlorination treatment The bromine-containing mixed gas obtained in step 2 is passed into the distillation and condensation system, with a flow rate of 0.8 m³ / s into the distillation column. 3The distillation column has a bottom temperature of 64℃ and a top temperature of 60℃, a system pressure of atmospheric pressure, a reflux ratio of 1:3, a condensate temperature of 52℃ in the first-stage condenser, and a gas phase exiting the first-stage condenser entering the second-stage condenser at a flow rate of 0.14 m³ / h. 3 / h, pressure is atmospheric pressure, the condensate temperature of the secondary condenser is 8℃, the liquid phase discharged from the primary condenser and the secondary condenser both enter the crude bromine intermediate tank, the bottom liquid of the distillation column flows into the crude bromine intermediate tank, and the gas phase after secondary condensation enters the tail gas treatment system. The liquid crude bromine discharged from the primary condenser has a chloride content of 120 ppm, a moisture content of 0.20%, and a purity of 99.4%. The liquid phase discharged from the secondary condenser has a chloride content of 65 ppm, a moisture content of 0.11%, and a purity of 99.91%.

[0026] 4. Step 4: Continuous concentrated sulfuric acid dehydration treatment Crude bromine from the intermediate crude bromine tank is pumped into a continuous concentrated sulfuric acid dehydration tower at a flow rate of 1.0 t / h. 98 wt% concentrated sulfuric acid (concentrated sulfuric acid to crude bromine mass ratio 1:16.7) is added at the top of the tower at a flow rate of 0.06 t / h. The temperature inside the dehydration tower is 32℃, the pressure inside the tower is atmospheric pressure, the gas-liquid contact time is 28 min, and the tower is filled with polytetrafluoroethylene Pall ring packing. After countercurrent contact dehydration, the bromine discharged from the bottom is filtered through a corrosion-resistant filter with a 0.7 μm polytetrafluoroethylene membrane to obtain dehydrated bromine. The waste sulfuric acid discharged from the top of the dehydration tower (mass fraction reduced to 92%) is collected in a waste acid storage tank and can be recycled after concentration.

[0027] 5. Step 5: Finished Product Inspection and Collection The dehydrated bromine obtained in step 4 was pumped into a nitrogen-protected finished product storage tank and sampled for testing. The chloride content was 29 ppm, the moisture content was 0.02%, the bromine content was 99.97%, and the total recovery rate was 99.7%, which meets the stringent requirements for bromine used in the production of octabromoether high-end flame retardants.

[0028] Single-factor analysis experiment 1. Comparison Experiment of Primary Condensation Temperature Experimental conditions: same flow rate of bromine-containing mixed gas (0.7 m³ / s). 3 The parameters were: feed temperature (70℃), system pressure (0.1MPa), and condensate temperature of the first-stage condenser were changed while the rest remained unchanged. Offline detection of crude bromine in the liquid phase of the first-stage condenser was performed, excluding trace bromine recovery in the second-stage condenser. The results are shown in the table below:

[0029] Experimental data show that when the temperature of the primary condensate is controlled at 40-55℃, the crude bromine chloride content can be controlled at 100-200ppm, and the bromine recovery rate is maintained above 96.5%, achieving the optimal balance between dechlorination effect and recovery rate. Beyond this range, either chloride content exceeds the standard or the recovery rate decreases, further verifying the rationality and necessity of this temperature range.

[0030] 2. Comparison Experiment of Secondary Condensation Temperature Experimental conditions: the same first-stage condensate exhaust gas flow rate (0.12m³ / h). 3 The experiment involved adjusting the exhaust gas composition ( / h) and only changing the condensate temperature of the secondary condenser while keeping other parameters unchanged. The experimental results are shown in the table below.

[0031] Experimental data show that when the temperature of the secondary condensate is controlled between 5-15℃, the recovery rate of trace bromine can be maintained above 97.3%, and the chloride and moisture content of the recovered bromine meets the requirements of the subsequent dehydration process, while the energy consumption is reasonable. Outside this range, either the recovery is incomplete (temperature > 15℃) or the energy consumption is too high and the moisture content is too high (temperature < 5℃), which verifies the rationality of this temperature range.

[0032] 3. Comparative Experiment of Continuous Concentrated Sulfuric Acid Dehydration Treatment Experimental conditions: crude bromine moisture content 0.2%, processing capacity 0.8 t / h, other parameters unchanged. Experimental results are as follows: (1) Comparison experiment of feeding position

[0033] (2) Comparison experiment of the mass ratio of concentrated sulfuric acid to crude bromine

[0034] (3) Comparison experiment of filler types

[0035] Experimental conclusion: Using a counter-current feeding method with concentrated sulfuric acid fed from the top and crude bromine fed from the bottom, controlling the mass ratio at 1:10-20, and selecting polytetrafluoroethylene Pall rings as packing material can achieve the best dehydration effect while taking into account cost and equipment lifespan.

[0036] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0037] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for preparing high-purity bromine, characterized in that, This includes steps such as preparation and acid adjustment of sodium bromide aqueous solution, chlorine oxidation and bromine blowing reaction, staged condensation dechlorination treatment, continuous concentrated sulfuric acid dehydration treatment, and finished product collection. The steps for preparing and adjusting the pH of the sodium bromide aqueous solution include adding hydrochloric acid solution to the sodium bromide aqueous solution and adjusting the pH of the solution to 1-3 to obtain an acidic sodium bromide raw material solution. The sodium bromide aqueous solution has a mass fraction of 20-35%; The chlorine-oxidative bromine blowing reaction step is as follows: acidic sodium bromide feedstock solution is pumped into the oxidative bromine blowing tower, chlorine gas is introduced, the molar ratio of chlorine gas to sodium bromide is 1.05-1.1:1, the reaction temperature is 60-80℃, the gas-liquid contact time is 30-60 min, and air is introduced as a carrier gas at a flow rate of 0.5-0.6 m³ / min. 3 / h, the flow ratio of air to acidic sodium bromide feed solution is 1:3, stripping to obtain a bromine-containing mixed gas; In the staged condensation and dechlorination process, the condensate temperature of the first-stage condenser is 40-55℃, and the condensate temperature of the second-stage condenser is 5-15℃.

2. The preparation process of high-purity bromine according to claim 1, characterized in that, The staged condensation and dechlorination step involves introducing a bromine-containing mixed gas into a distillation condensation system. This system includes a distillation column, a primary condenser, and a secondary condenser connected in sequence. The flow rate entering the distillation column is controlled to be 0.6-0.8 m³ / s. 3 The distillation column has a bottom temperature of 60-65℃ and a top temperature of 55-60℃, with a system pressure of atmospheric pressure and a reflux ratio of 1:2-3. The vapor phase collected from the top of the distillation column sequentially enters the primary condenser and then the secondary condenser, where a gradient temperature-controlled condensation method is used to remove chloride impurities. The condensate temperature of the primary condenser is 40-55℃. The vapor phase discharged from the primary condenser enters the secondary condenser, with a controlled flow rate of 0.10-0.15 m³ / h. 3 / h, pressure controlled at atmospheric pressure, the condensate temperature of the secondary condenser is 5-15℃, the liquid crude bromine discharged from the primary condenser and the liquid phase discharged from the secondary condenser both enter the crude bromine intermediate tank, the liquid phase at the bottom of the distillation column merges into the crude bromine intermediate tank, and the gas phase after secondary condensation enters the tail gas treatment system.

3. The preparation process of high-purity bromine according to claim 1, characterized in that, The continuous concentrated sulfuric acid dehydration process involves pumping the crude bromine product from the intermediate crude bromine tank into a continuous concentrated sulfuric acid dehydration tower. A continuous countercurrent contact dehydration method is used to remove moisture. The tower temperature is controlled at 25-35℃, the tower pressure at atmospheric pressure, and the gas-liquid contact time is 20-30 minutes. The tower is filled with corrosion-resistant polytetrafluoroethylene (PTFE) Pall rings. Concentrated sulfuric acid with a mass fraction ≥98% is continuously added to the top of the tower, with a mass ratio of concentrated sulfuric acid to crude bromine of 1:10-20. The bromine discharged from the bottom of the dehydration tower is filtered through a corrosion-resistant 0.5-0.7μm PTFE membrane filter to obtain dehydrated bromine.

4. The preparation process of high-purity bromine according to claim 1, characterized in that, The finished product collection step involves pumping high-purity bromine into a finished product storage tank, which is equipped with a nitrogen protection device to prevent bromine from oxidizing and deteriorating.

5. A system for implementing the preparation process of high-purity bromine according to any one of claims 1-4, characterized in that, It includes a dissolution and acid conditioning unit, an oxidation and bromine blowing unit, a staged condensation and dechlorination unit, a continuous dehydration unit, and a finished product collection unit; the staged condensation and dechlorination unit includes a primary condenser and a secondary condenser with independent temperature control systems; the continuous dehydration unit includes a continuous concentrated sulfuric acid dehydration tower, a concentrated sulfuric acid storage tank, and a corrosion-resistant filter, and the dehydration tower adopts a counter-current contact structure.

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