Bromine purification method

Abstract

The invention discloses a purification method of bromine, which comprises the following steps: continuously feeding crude bromine from the middle of a tower reactor, continuously feeding an aqueous solution containing bromine ions from the top of the tower reactor, and controlling the temperature of the tower reactor, so that chlorine in the bromine reacts with the aqueous solution containing the bromine ions in the tower, and purified bromine is extracted from the tower top. The tower reactor is adopted to purify bromine, continuous feeding and discharging are achieved, operation is easy, convenient and feasible, the purification efficiency is high, the chlorine content in bromine can be reduced to 0.01% or below, and the quality of bromine is improved to a large extent.

Description

Technical Field

[0001] The present invention relates to a method for purifying bromine, and in particular to a method for reducing the chloride ion content in bromine. Background Art

[0002] Bromine is an important industrial raw material. High-quality bromine is widely used in the pharmaceutical, new materials, pesticide, and other chemical industries. A key bromine quality indicator is its chlorine content. Only when the chlorine content is sufficiently low can high-quality downstream products be produced. The current mainstream bromine production process involves a displacement reaction between chlorine gas and brine or other aqueous solutions containing bromide ions. Bromine produced using chlorine gas contains chlorine. If the chlorine content is too high, chlorine will compete with bromine in the environment where bromine is used, affecting product yield and purity.

[0003] Currently, the industry standard for bromine, QB / T2021-2022, stipulates that the chlorine content requirement for premium-grade bromine is less than or equal to 0.03%, and the chlorine content requirement for first-grade bromine is less than or equal to 0.06%; the chemical reagent standard for bromine, GB / T1281-2011, stipulates that the chlorine content requirement for premium-grade bromine is less than or equal to 0.01%.

[0004] Currently, producing high-quality bromine, especially achieving a very low chlorine content, remains a challenge in the industry. This is because bromine and chlorine belong to the same halogen family of elements and have similar properties. Once the chlorine content in bromine drops to 0.06%, single methods such as distillation and extraction are unable to further reduce the chlorine content.

[0005] The article "New Process for Re-dechlorination of Bromine" introduces a method of adding primary acid to crude bromine, stirring it, and letting it stand for 2 days to reduce the chlorine content in bromine. Due to the high density and poor water solubility of bromine, the operation is difficult. It is difficult for bromine to form good contact and mass transfer with the primary acid, and the chlorine removal efficiency is low.

[0006] The article "Method for Refining Liquid Bromine" also introduces that although most of the free chlorine can be removed through two-stage distillation, it is still difficult to reach the standard of less than 0.01%, and other methods need to be adopted.

[0007] CN 102849682 A introduces a method for removing chlorine from crude bromine by contacting a reaction solution with crude bromine using a static mixer. However, due to the high density of bromine and its poor compatibility with water, the chlorine content in the crude bromine can only be reduced to below 0.045%. Summary of the Invention

[0008] To address the problem that the chlorine content in existing bromine is difficult to reduce to a very low level, the present invention provides a method for purifying bromine. This method is efficient and simple and can reduce the chlorine content in industrial bromine from a concentration of 0.1% or higher to below 0.01%.

[0009] The specific technical solutions of the present invention are as follows: A method for purifying bromine comprises: continuously feeding crude bromine from the middle of a tower reactor, and simultaneously continuously feeding an aqueous solution containing bromide ions from the top of the tower reactor, controlling the temperature of the tower reactor so that chlorine in the bromine reacts with the aqueous solution containing bromide ions in the tower, and extracting the purified bromine from the top of the tower.

[0010] The present invention uses a tower reactor, crude bromine is fed from the tower, and an aqueous solution containing bromide ions is fed from the top of the tower; the crude bromine and the aqueous solution containing bromide ions complete gas-liquid or liquid-liquid extraction interaction in the tower, chlorine in the bromine is consumed by the reaction, the purified bromine is extracted from the top of the tower, and the bromide ion solution is discharged from the bottom of the tower, thereby achieving purification and separation of bromine in the tower reactor.

[0011] Furthermore, the tower reactor is a packed tower, a plate tower or a spray tower, preferably a packed tower.

[0012] Furthermore, the height-to-diameter ratio of the tower reactor is greater than or equal to 20:1, such as 20:1, 25:1, 30:1, 35:1, 40:1, etc. The number of theoretical plates of the tower reactor is greater than or equal to 20, such as 20, 25, 30, 35, 40, etc.

[0013] Furthermore, the packing of the packed tower can be glass spring packing, ceramic ball ring, Raschig ring packing, etc.

[0014] Furthermore, the content of chloride ions in the crude bromine is less than or equal to 1 wt %.

[0015] Furthermore, the concentration of bromide ions in the bromide ion-containing aqueous solution is 1.0 to 15 wt %, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, and 15%.

[0016] Furthermore, the aqueous solution containing bromide ions can be selected from brine, sodium bromide aqueous solution or wastewater containing bromide ions. The wastewater containing bromide ions can be sodium bromide-containing wastewater generated by the agrochemical, petrochemical or pharmaceutical industries.

[0017] Furthermore, the crude bromine and the aqueous solution containing bromide ions are fed continuously, wherein the feed rate of the crude bromine is 10 to 100 g / min, for example, 10 g / min, 20 g / min, 30 g / min, 40 g / min, 50 g / min, 60 g / min, 70 g / min, 80 g / min, 90 g / min, and 100 g / min, and the feed rate of the aqueous solution containing bromide ions is 10 to 100 g / min, for example, 10 g / min, 20 g / min, 30 g / min, 40 g / min, 50 g / min, 60 g / min, 70 g / min, 80 g / min, 90 g / min, and 100 g / min. The feed rates of the crude bromine and the aqueous solution containing bromide ions may be the same or different.

[0018] Furthermore, the tower bottom temperature is controlled at 100-105°C, for example, 100°C, 101°C, 102°C, 103°C, 104°C, 105°C.

[0019] Furthermore, the gas extraction temperature at the top of the tower is controlled to be 75-100°C, for example, 75°C, 80°C, 85°C, 90°C, 95°C, or 100°C.

[0020] Furthermore, the tower reactor can be heated by a reboiler of the tower reactor. At the start of the reaction, an appropriate amount of aqueous solution containing bromide ions is first added to the tower reactor to form a bottom layer to ensure temperature control of the tower reactor.

[0021] Furthermore, the gas phase extracted from the top of the tower is condensed to obtain purified bromine, wherein the chloride ion content of the purified bromine is less than 0.01 wt%.

[0022] Furthermore, the gas phase at the top of the tower is preferably cooled by two-stage condensation, wherein the temperature of the first-stage condensation is 10-30°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, and the temperature of the second-stage condensation is 0-7°C, for example, 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C. The second-stage condensation can not only condense and collect bromine normally, but also has a better energy-saving advantage.

[0023] Furthermore, the bromine content in the bromide ion aqueous solution discharged from the bottom of the tower is less than 0.01 wt %.

[0024] Furthermore, if the chlorine content in the crude bromine is greater than 1 wt %, the chlorine content is first reduced to 1% or less by distillation, and then the method of the present invention is used to further reduce the chlorine content to less than 0.01%.

[0025] The present invention has the following beneficial effects: 1. Currently, most crude bromine purification methods rely on distillation, but the purification effect is poor. In particular, when the crude bromine contains only trace amounts of chlorine, it is difficult to obtain high-purity bromine simply by extraction. The present invention utilizes an extraction reaction combined with distillation to achieve purification of crude bromine with good purification effect.

[0026] 2. The present invention adopts a tower reactor to purify bromine, realizes continuous feeding and discharging, is simple, convenient and feasible to operate, has high purification efficiency, can reduce the chlorine content in bromine to below 0.01%, and greatly improves the quality of bromine. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 FIG. 4 is a process flow chart of the method for purifying bromine of the present invention.

[0028] Among them: 1. Bromide ion aqueous solution, 2. Bromide ion aqueous solution metering pump, 3. Crude bromine, 4. Crude bromine metering pump, 5. Reboiler, 6. Tower reactor, 7. Exhaust bromide ion solution, 8. Primary heat exchanger, 9. Secondary heat exchanger, 10. Purified bromine, 11. Heat exchange medium inlet, 12. Heat exchange medium outlet. DETAILED DESCRIPTION

[0029] The following description of exemplary embodiments of the present invention includes various details to facilitate understanding, which should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for the sake of clarity and conciseness, descriptions of well-known functions, operations, and structures are omitted from the following description.

[0030] Unless otherwise defined, technical and scientific terms used in this specification have the same meanings as commonly understood by those skilled in the art. Although methods and materials similar or equivalent to those described herein can be used in experiments or applications, the present invention describes the materials and methods below. In the event of conflict, the present specification, including definitions, will control.

[0031] In the following examples and comparative examples, unless otherwise specified, the concentrations are all expressed in mass percentage.

[0032] Example 1 like Figure 1The following is a process flow diagram for our bromine purification process. The crude bromine contains 0.4% chloride. The bromide ion solution is sodium bromide wastewater from the agrochemical industry, with a bromide ion concentration of 6.0%. The tower reactor is a 2.0-meter-high packed tower with a height-to-diameter ratio of 40:1 and 30 theoretical plates. The tower is filled with glass spring packing with a 4 mm diameter and 0.5 mm glass fibers. The packed tower is first lined with water, and the temperatures at both the bottom and top of the tower are raised to 100°C via a reboiler. Crude bromine is then fed into the tower via a metering pump at a rate of 30g / min. Simultaneously, wastewater containing sodium bromide is fed into the tower from the top at a rate of 30g / min. The heated, vaporized bromine undergoes a gas-liquid mass transfer reaction with the flowing sodium bromide wastewater, removing the chlorine from the bromine by reacting with the bromide ions. The dechlorinated bromine vaporizes and evaporates from the top of the tower, sequentially entering the primary and secondary heat exchangers for cooling to produce purified bromine. The reacted wastewater is then discharged from the bottom of the tower. After the system stabilizes, the top temperature is maintained at 80°C. According to QB / T2021-2022 standards, the chloride ion content of the purified bromine is 0.006%, and the bromine content of the wastewater discharged from the bottom of the tower is 0.008%.

[0033] Example 2 The crude bromine contains 0.6% chloride. The bromide ion solution is sodium bromide wastewater from the agrochemical industry, with a bromide ion concentration of 6%. A 5.0-meter-tall packed tower reactor is used, with a height-to-diameter ratio of 40:1 and 30 theoretical plates. The packing consists of 4mm-diameter glass springs and 0.5mm-diameter glass fibers. The tower is initially lined with water, and the temperatures at both the bottom and top are raised to 100°C via a reboiler. Crude bromine is then fed into the tower via a metering pump at a rate of 5.0 kg / min. Simultaneously, sodium bromide wastewater is fed from the top of the tower at a rate of 5.0 kg / min. The heated, vaporized bromine reacts with the flowing sodium bromide wastewater, removing the chlorine from the bromine by reacting with the bromide ions. The dechlorinated bromine vaporizes and evaporates from the top of the tower, entering a primary heat exchanger and then a secondary heat exchanger for cooling to produce purified bromine. The reacted wastewater is then discharged from the bottom of the tower. After the system stabilized, the tower top temperature was maintained at 78°C. According to the QB / T2021-2022 standard, the chloride ion content in the purified bromine was 0.004%, and the bromine content in the wastewater discharged from the bottom of the tower was 0.009%.

[0034] Example 3 The crude bromine contains 0.4% chloride. The bromide-containing solution is sodium bromide wastewater from the agrochemical industry, with a bromide ion concentration of 6.0%. A 2.0-meter-tall packed tower reactor is used, with a height-to-diameter ratio of 40:1 and 30 theoretical plates. The tower is packed with 4mm-diameter glass springs and 0.5mm-diameter glass fibers. The tower is initially lined with water, and the temperatures at both the bottom and top are raised to 100°C via a reboiler. Crude bromine is then introduced into the tower via a metering pump at a rate of 30g / min. Simultaneously, sodium bromide wastewater is introduced from the top of the tower at a rate of 10g / min. The heated, vaporized bromine reacts with the flowing sodium bromide wastewater, removing the chlorine from the bromine by reacting with the bromide ions. The dechlorinated bromine vaporizes and evaporates from the top of the tower, entering a primary heat exchanger and then a secondary heat exchanger for cooling to produce purified bromine. The reacted wastewater is then discharged from the bottom of the tower. After the system stabilized, the tower top temperature was maintained at 80°C. According to QB / T2021-2022 standards, the chloride ion content of the purified bromine was 0.008%, and the bromine content in the wastewater discharged from the tower bottom was 0.009%. Reducing the sodium bromide solution feed rate increased the chloride content of the purified bromine.

[0035] Example 4 Crude bromine was purified in the manner of Example 3, except that crude bromine was fed into the tower at a rate of 100 g / min via a metering pump; and simultaneously, sodium bromide-containing wastewater from the agrochemical industry with a bromide ion concentration of 6.0% was fed into the tower from the top at a rate of 10 g / min.

[0036] According to the QB / T2021-2022 standard, the chloride ion content in the purified bromine is 0.01%, and the bromine content in the bromide ion solution discharged from the bottom of the tower is 0.01%.

[0037] Comparative Example 1 The crude bromine was purified in the manner of Example 3, except that a 2.0-meter-high empty tower was selected as the tower reactor, no packing was installed in the tower, the height-to-diameter ratio of the packed tower was 40:1, and the number of theoretical plates was 1.

[0038] According to QB / T2021-2022 standards, the chloride ion content of the purified bromine was 0.38%, and the bromine content of the bromide ion solution discharged from the bottom of the tower was 0.008%. This shows that after removing the packing from the tower, the gas-liquid exchange between the bromine gas and the sodium bromide-containing wastewater was poor, and the chlorine removal effect of the separated bromine was poor.

[0039] Comparative Example 2 The crude bromine was purified in the same manner as in Example 3, except that the crude bromine was fed into the tower at a rate of 30 g / min via a metering pump; and simultaneously, sodium bromide-containing wastewater was fed into the tower from the top at a rate of 2 g / min.

[0040] According to QB / T2021-2022 standards, the chloride ion content of the purified bromine is 0.10%, and the bromide ion solution discharged from the bottom of the tower contains 0.01%. This shows that even after reducing the feed rate of sodium bromide-containing wastewater, the chloride content of the purified bromine cannot be reduced to below 0.1%, resulting in poor purification results.

Claims

1. A method for purifying bromine, characterized in that: The crude bromine is continuously fed from the middle of the tower reactor, and the aqueous solution containing bromide ions is continuously fed from the top of the tower reactor. The temperature of the tower reactor is controlled so that the chlorine in the bromine reacts with the aqueous solution containing bromide ions in the tower, and the purified bromine is extracted from the top of the tower.

2. The purification method according to claim 1, wherein: The tower reactor is a packed tower, a plate tower or a spray tower.

3. The purification method according to claim 1 or 2, wherein: The tower reactor has a height-to-diameter ratio greater than or equal to 20:1, and a theoretical plate number greater than or equal to 20.

4. The purification method according to claim 2, wherein: The packing of the packed tower is glass spring packing, ceramic ball ring or Raschig ring packing.

5. The purification method according to claim 1, wherein: The content of chloride ions in the crude bromine is less than or equal to 1wt%.

6. The purification method according to claim 1, wherein: The concentration of bromide ions in the bromide ion-containing aqueous solution is 1.0 to 15 wt %.

7. The purification method according to claim 1, wherein: The aqueous solution containing bromide ions is brine, sodium bromide aqueous solution or wastewater containing bromide ions.

8. The purification method according to claim 1, wherein: The feed rate of crude bromine is 10~100g / min, and the feed rate of the aqueous solution containing bromide ions is 10~100g / min.

9. The purification method according to claim 1, wherein: The temperature at the bottom of the tower is controlled at 100-105°C, and the gas phase extraction temperature at the top of the tower is 75-100°C.

10. The purification method according to claim 1, wherein: The gas phase withdrawn from the top of the tower is condensed to obtain purified bromine; preferably, the chloride ion content in the purified bromine is less than 0.01 wt%.

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