JP2018052771A - Bromine recovery apparatus and bromine recovery process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bromine recovery apparatus for recovering bromine present in bromine-containing air, and a bromine recovery process that uses the bromine recovery apparatus.SOLUTION: A bromine recovery apparatus is provided. In a bromine generation packed column of the apparatus, bromine present in an aqueous solution obtained by adding an oxidant to a bromide ion-containing aqueous solution is brought into contact with inert gas (such as air) for gasification. Thereafter, the bromine-containing gas is mixed with SOgas to give a hydrogen bromide-containing gas. The hydrogen bromide-containing gas is turned into an aqueous solution of hydrogen bromide and thereby bromine is separated and recovered. The bromine recovery apparatus comprises an outlet gas duct for discharging a gas within the apparatus; an oxidation reduction potential detector including a measuring electrode for measuring an oxidation reduction potential of a gas present in the gas duct, the measuring electrode being surrounded and covered by a material that exhibits liquid retainability and is selected from glass fibers, porous glass, porous sintered products, porous polymer resins and resin nets; and a SOgas control valve.SELECTED DRAWING: None

Description

  The present invention relates to a bromine recovery apparatus for recovering bromine from bromine-containing air and a bromine recovery method using the bromine recovery apparatus.

  The main industrial raw materials for bromine production are seawater, concentrated seawater, bittern, natural brine, etc., and bromine always exists as bromide ions in these aqueous solutions. A production method is generally employed in which bromide ions contained in these aqueous solutions are converted into bromine using an oxidizing agent such as chlorine and then bromine is separated and extracted from the aqueous solution (see, for example, Patent Document 1).

  The method of separating / extracting bromine from the aqueous solution is selected depending on the concentration of bromide ions contained in the aqueous solution, and in the case of a high concentration (for example, 1000 ppm (as bromine) or more), the required amount of steam is small. A method of collecting by direct steam distillation is adopted from an economic viewpoint. However, an aqueous solution containing a high concentration of bromide ions has a finite amount of resources, and there is a problem that resources are depleted as bromine is collected.

On the other hand, in the case of an aqueous solution containing low-concentration bromide ions such as seawater in which bromide ions are inexhaustible, the bromine is expelled into the air by contacting it with air in a packed tower after oxidation to bromine with chlorine. A method is used in which air is added to and mixed with a reducing agent such as sulfurous acid gas (hereinafter referred to as “SO ₂ gas”) or caustic soda (NaOH) and returned to a bromide ion-containing aqueous solution obtained by reducing and concentrating bromine. Since SO ₂ gas is more reactive than NaOH as a reducing agent, the apparatus can be made compact and the chemical cost is low, so the method using SO ₂ gas (SO ₂ method) is an economic advantage. Is expensive.

The chemical reaction formula for reducing and concentrating bromine by the SO ₂ method is shown below.

Br ₂ (bromine) + SO ₂ (sulfurous acid) + 2H ₂ O → 2HBr (hydrogen bromide) + H ₂ SO ₄ (sulfuric acid)

JP 2001-002402 A

In the production method for collecting bromine by the SO ₂ method, the required input amount of SO ₂ gas is determined by the amount of conversion from the raw material bromide ion-containing aqueous solution to bromine. Theoretically, bromine and SO ₂ gas react in equimolar amounts. Therefore, when the molar ratio SO ₂ / Br ₂ is less than 1, Br ₂ is not recovered, and when SO ₂ / Br ₂ is large, SO ₂ gas in the exhaust gas is reduced. Since this increases the cost of processing SO ₂ gas in the exhaust gas, it is preferable to input SO ₂ gas so that SO ₂ / Br ₂ = 1.0 to 1.3.

The amount of conversion depends on fluctuations in natural factors such as fluctuations in bromide ion concentration due to rainfall of raw material aqueous solution and changes in conversion rate due to liquid temperature of raw material aqueous solution (yield increases as temperature rises), chlorine content, inert gas (air ) It is not constant due to fluctuations in operating factors such as quantity and gas-liquid contact efficiency (soil contamination status). Accordingly, it is necessary to appropriately monitor bromine in the exhaust gas at the outlet of the bromine recovery device and control the appropriate amount of SO ₂ gas input.

Currently, there are oxidant meters (I ₂ release / absorbance measurement), infrared spectrophotometers (FT-IR), etc. as this gas analyzer, but they are expensive and a technology for completely removing mist in the measurement gas. In addition to the technical problems, it is a precision instrument, and thus maintenance work for maintaining functions, running costs, etc. are generated.

An object of the present invention is to provide a production method for recovering bromine by controlling SO ₂ gas using a general-purpose, inexpensive and highly responsive instrument without using these expensive gas analyzers. is there.

  In light of the above circumstances, the present inventors have intensively studied a low-cost, general-purpose instrument that is highly responsive, and as a result, have studied the use conditions of the oxidation-reduction potentiometer used in solution measurement. Thus, it was found that bromine in the gas can be detected.

The apparatus of the present invention is attached to a flow rate control valve 11 for introducing SO ₂ gas 10 into bromine-containing air 5 obtained from the bromine generation packed tower 1, bromine recovery device 6, and bromine recovery device gas outlet. The mist eliminator 7, the oxidation-reduction potential detector 9, the subtraction unit 15 for processing the oxidation-reduction potential data, and the proportional integration adjuster 18 are included.

  The oxidation-reduction potential detector 9 uses a liquid-containing substance such as glass fiber, porous glass, porous sintered body, porous polymer resin, resin net around the measurement electrode, and has a thickness of 3 to 25 mm. It is covered with. This is because the coating is moistened with dilute sulfuric acid mist (hereinafter referred to as “mist”) contained in a trace amount in the bromine recovery device outlet gas 21 which is saturated with water, and the bromine in the bromine recovery device outlet gas 21 is absorbed. It is to do. When the thickness of the covering increases, the responsiveness deteriorates, and when the covering is thinned, the potential becomes unstable.

  Hereinafter, an embodiment of the redox potential detector will be described in more detail with reference to FIG.

  In FIG. 2, reference numeral 23 is a glass tube, 24 is a tube-shaped oxidation-reduction potential response portion formed integrally with a part of the glass tube 23, and 25 is a saturated KCl solution filled in the glass tube 23, for example. An internal electrolyte 26, which is an internal electrode provided so as to adhere to the oxidation-reduction potential response portion 24 in the internal electrolyte 25, is made of, for example, platinum.

  27 is a covering made of a substance having high water retention, and covers the glass tube 23 so as to surround at least the oxidation-reduction potential response portion 24, and is fixed with a band 28. Can be impregnated. As a result, the gas sample is brought into contact with the gas absorption liquid over a wide area, the change in the oxidation-reduction potential is made sensitive by the oxidation-reduction potential response portion 24, which is detected by the internal electrode 26, and the oxidation-reduction of the gas sample The potential can be measured with high reliability.

  Since the redox potential response portion 24 is in contact with the gas absorption liquid and the gas sample that has passed through the covering 27 is introduced to the entire contact portion, the response characteristics are extremely good, and the low concentration gas sample Can be measured quickly and accurately.

  If the mist of the bromine recovery device outlet gas 21 becomes excessive, the gas absorption liquid impregnated in the covering 27 is renewed too quickly, and it becomes difficult to detect the absorbed bromine at the internal electrode 26. On the contrary, if there is no mist, it becomes dry and the potential measurement with the redox potential detector 9 becomes impossible. Therefore, in order to obtain an appropriate amount of mist, the mist capture rate in the mist eliminator 7 attached to the bromine recovery device outlet gas duct is preferably 90 to 99.9%. The eliminator 7 used is composed of a filament and has an aperture ratio of 30 to 99%, preferably 60 to 98%. The mist capture ratio can be adjusted to the above range by setting the thickness of the filament. . However, even when the mist is completely removed and becomes mist-free, the potential can be measured by spraying a certain amount of water on the internal electrode 26 of the oxidation-reduction potential detector 9.

In the method of the present invention, the oxidation-reduction potential of the bromine recovery apparatus outlet gas 21 is preferably set to 400 to 550 mV (set oxidation-reduction potential 16). The set oxidation-reduction potential 16 and the oxidation-reduction potential measured by the oxidation-reduction potential detector 9 are used. A valve open / close command 19 obtained by taking the oxidation-reduction potential deviation 17 from the potential 14 by the subtractor 15 and calculating the oxidation-reduction potential deviation 17 by the proportional integration controller 18 is transmitted to the SO ₂ gas flow control valve 11. It is.

According to the present invention, a general purpose, inexpensive and highly responsive instrument is used to control SO ₂ gas from seawater or the like where infinite amounts of bromide ions exist without using an expensive gas analyzer. Can be recovered.

It is a manufacturing flow which shows one Embodiment of the bromine collection | recovery apparatus of this invention. It is a principal part longitudinal cross-sectional view which shows one Embodiment of the oxidation reduction potential detector of this invention. 6 is a production flow diagram of Example 4. FIG. It is a graph which shows the correlation of the gas composition obtained in Example 4, and oxidation-reduction potential.

Example 1
100% relative humidity air containing mist composed of 10% sulfuric acid aqueous solution is used as a carrier gas, Br ₂ gas is 104.9 v-ppm, SO ₂ gas is 0.2 v-ppm, and a mixed gas having a gas linear velocity of 2.5 m It was 716 mV when it was made to distribute | circulate in piping at / second and the oxidation-reduction potential was measured with the gas measuring electrode (glass fiber coating | coated, thickness 10mm) of this invention.

Example 2
A 100% relative humidity air containing mist composed of 10% sulfuric acid aqueous solution is used as a carrier gas, a mixed gas containing Br ₂ gas at 0.3 v-ppm and SO ₂ gas at 2.0 v-ppm is a gas linear velocity of 2.5 m. The redox potential was measured with the gas measurement electrode of the present invention (glass fiber coating, thickness 10 mm) and was 559 mV.

Example 3
A gas having a relative humidity of 100% containing mist composed of a 10% sulfuric acid aqueous solution is used as a carrier gas, and a gas having an SO ₂ gas of 15.3 v-ppm is circulated in a pipe at a gas linear velocity of 2.5 m / sec. When the redox potential was measured with a gas measuring electrode (glass fiber coating, thickness 10 mm), it was 413 mV.

Comparative Example 1
100% relative humidity air containing mist composed of 10% sulfuric acid aqueous solution is used as a carrier gas, Br ₂ gas is 104.9 v-ppm, SO ₂ gas is 0.2 v-ppm, and the gas linear velocity is 2.5 m. When the redox potential was measured with a redox electrode not coated with glass fiber, the indicated value was unstable and the redox potential could not be measured.

Comparative Example 2
Air having a relative humidity of 50% is used as a carrier gas, and a mixed gas having Br ₂ gas of 104.9 v-ppm and SO ₂ gas of 0.2 v-ppm is circulated in the pipe at a gas linear velocity of 2.5 m / sec. When the oxidation-reduction potential was measured with the gas measuring electrode of the present invention (glass fiber coating, thickness 10 mm), the responsiveness was poor and the indicated value was unstable, and the oxidation-reduction potential could not be measured.

  The above results are summarized in the table below. The oxidation-reduction potential of gas can be measured by the method of the present invention, and the bromine concentration in gas can be measured.

実施例４
図３に示した装置において、臭素イオンが６０ｍｇ／Ｌの海水に硫酸を添加し、ｐＨ３．５とした。この海水に塩素ガスを臭素イオンに対して１．１倍当量加えて酸化し、この水溶液に臭素発生用充填塔にて５５倍当量の空気を導入し、臭素含有空気を得た。この臭素含有空気に多孔管からＳＯ_２ガスを添加した後、ガス出口部に開口率８０％の折れ板式ミストエリミネーターを取付けた臭素回収装置（充填塔）に導入して、臭素を回収した。

Example 4
In the apparatus shown in FIG. 3, sulfuric acid was added to seawater having a bromine ion of 60 mg / L to adjust the pH to 3.5. This seawater was oxidized by adding 1.1 times equivalent of chlorine gas to bromine ions, and 55 times equivalent of air was introduced into this aqueous solution in a packed tower for bromine generation to obtain bromine-containing air. After adding SO ₂ gas from the perforated tube to this bromine-containing air, the bromine was recovered by introducing it into a bromine recovery device (packed tower) in which a bent plate type mist eliminator having an opening ratio of 80% was attached to the gas outlet.

After passing through the mist eliminator, the gas measuring electrode of the present invention (glass fiber coating, thickness 10 mm) was attached, the gas composition was measured by changing the amount of SO ₂ gas added, and the relationship between the gas composition and the oxidation-reduction potential was examined. As a result, it was found that there is a correlation between the gas composition and the oxidation-reduction potential, and it is possible to grasp the appropriate amount of SO ₂ gas injection by measuring the oxidation-reduction potential.

  According to the present invention, bromine can be recovered from seawater or the like in which bromide ions are inexhaustible.

1 Bromine generation packed tower 2 Air 3 Bromide ion-containing aqueous solution (seawater, etc.)
4 Chlorine 5 Bromine-containing air 6 Bromine recovery device 7 Mist eliminator 8 Recovery liquid circulation pump 9 Redox potential detector 10 SO ₂ (sulfurous acid) gas 11 SO ₂ gas flow control valve 12 Make-up water 13 Bromine recovery liquid (reduction concentration)
14 Measurement redox potential 15 Subtractor 16 Set redox potential 17 Redox potential deviation 18 Proportional integral regulator 19 Valve open / close command 20 Bromine recovery device outlet gas duct 21 Bromine recovery device outlet gas 22 Exhaust gas cleaning tower 23 Glass tube 24 Redox potential Response unit 25 Internal electrolyte 26 Internal electrode 27 Cover 28 Fixing band 29 Redox potential display panel 30 SO ₂ gas blown porous pipe

Claims (4)

An oxidizing agent is added to an aqueous solution containing bromide ions, and bromine in the obtained aqueous solution is gasified by bringing it into contact with an inert gas in a bromine generation packed tower, and then SO ₂ gas is mixed with the bromine-containing gas. A bromine recovery device for obtaining a hydrogen bromide-containing gas, converting hydrogen bromide from the hydrogen bromide-containing gas into an aqueous solution and separating and recovering bromine, the bromine recovery device outlet gas duct for discharging the gas in the device, The measurement electrode for measuring the oxidation-reduction potential of the gas in the gas duct is covered with a liquid-containing substance selected from glass fiber, porous glass, porous sintered body, porous polymer resin, and resin net. A bromine recovery apparatus comprising a redox potential detector and an SO ₂ gas control valve. The bromine recovery apparatus according to claim 1, wherein the bromine recovery apparatus outlet gas duct is provided with an eliminator having an opening ratio of 30 to 99% constituted by a filament. The redox potential detector connected to the bromine recovery unit outlet gas duct takes the redox potential deviation between the redox potential of the bromine recovery unit outlet gas and the set redox potential with a subtractor, and the redox potential deviation is proportionally integrated. vessel with bromine recovery apparatus according to claim 1 or 2 the valve switching command found by arithmetic processing, characterized in that it comprises means for transmitting the SO ₂ gas control valve. Using the bromine recovery apparatus according to any one of claims 1 to 3, the SO ₂ gas addition amount is controlled so that the oxidation-reduction potential detected by the oxidation-reduction potential detector is 400 to 550 mV. Bromine recovery method.

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