JPS6256780B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adsorbent for bromine recovery containing a zeolite having a specific chemical composition, and a method for recovering bromine from an aqueous solution containing free bromine or a bromine-containing gas using the same.

Specifically, an adsorbent containing zeolite with a SiO ₂ /Al ₂ O ₃ molar ratio of 18 or more is brought into contact with an aqueous solution containing free bromine or a bromine-containing gas, and then the adsorbent is heated. The present invention provides a method for recovering bromine by desorbing bromine.

The main industrial raw materials for bromine production are seawater, concentrated seawater, bittern, natural citrus water, etc. In these raw material liquids, bromine always exists as a dilute solution of bromide. The industrial method for producing bromine consists of a step of oxidizing the bromine ions contained in these aqueous solutions with an oxidizing agent such as chlorine to liberate bromine, and a step of separating and collecting the free bromine from the aqueous solution.

Up to now, as methods for separating and collecting free bromine from an aqueous solution, 1) a method of forcing it out with air, and 2) a method of direct steam distillation have been carried out industrially.
These methods have advantages and disadvantages; for example, in the case of the former method, in which bromine is forced out with air, a means for separating it from air is required in order to extract bromine as a mixed gas with air. As this separation means, only bromine is captured using chemicals such as caustic soda, sodium bromide, and sulfur dioxide gas. Therefore, since it is necessary to recover the free bromine again, this method is only a means for concentration rather than a recovery method. The latter method of direct steam distillation requires a huge amount of steam to recover bromine. As mentioned above, these methods require a large amount of chemicals and energy, which currently account for a large proportion of the manufacturing cost.

On the other hand, a method for adsorbing free bromine onto a strongly basic anion exchange resin has been disclosed. That is, a method in which an aqueous solution containing free bromine is brought into contact with a strongly basic anion exchange resin to adsorb bromine, and an agent highly reactive with bromine, such as a mixed aqueous solution of caustic soda and sodium sulfite, is used to desorb bromine from the resin. (Japanese Patent No. 212506), a method using a sodium sulfite aqueous solution (U.S. Patent No. 3037845), or a method of directly recovering bromine by heating with steam (Japanese Patent Application Laid-open No. 1983-
59603, Japanese Unexamined Patent Publication No. 129804/1983), etc. Another method is to contact a bromine-containing gas with a porous strongly basic anion exchange resin to adsorb bromine, and to desorb and recover bromine by blowing steam into the bromine-adsorbed resin and heating it (Japanese Unexamined Patent Application Publication No. 1983-1999). 109201) has been disclosed. In this way, strongly basic anion exchange resins can adsorb free bromine contained in aqueous solutions or gases, but in methods that use chemicals as a desorption method, other methods are required to obtain the eluted bromine. It must be separated from the drug and recovered.

On the other hand, the method of thermal desorption with steam has the advantage of directly recovering bromine, but in general, strongly basic anion exchange resins have sufficient durability in terms of oxidation resistance and heat resistance due to their properties. However, especially in industrial applications, it is necessary to repeat adsorption and desorption operations, so it cannot be said to be a satisfactory adsorbent for use under these harsh conditions.

As a result of intensive studies to overcome the shortcomings of these known methods, the present inventors found that an adsorption method containing zeolite with a specific chemical composition that can directly recover bromine from an aqueous solution containing free bromine or a bromine-containing gas. We have developed a bromine recovery agent and a bromine recovery method using it. That is, in the present invention, the chemical composition has the general formula xM〓O・
Contains a zeolite represented by Al ₂ O ₃・ySiO ₂・ZH ₂ O (where M is a cation with a valence of n, x=0 to 2, y≧18, Z=0 or a positive number) An adsorbent for bromine recovery and an aqueous solution containing free bromine or a bromine-containing gas having a chemical composition of the general formula xM〓O・
Contains a zeolite represented by Al ₂ O ₃・ySiO ₂・ZH ₂ O (where M is a cation with a valence of n, x=0 to 2, y≧18, Z=0 or a positive number) The present invention was achieved by discovering that bromine can be easily desorbed and recovered by heating the adsorbent after contacting with the adsorbent.

According to the present invention, 1) Since chemicals such as caustic soda, sodium bromide, and sulfur dioxide gas are not used at all, raw material costs can be significantly reduced. 2) Very little energy is required to recover bromine. 3) In terms of oxidation resistance and heat resistance, it is an extremely stable and durable adsorbent, and is versatile enough to be used in both aqueous and gaseous environments as long as it contains free bromine. It has advantages such as being rich in minerals, and its industrial value is extremely large.

The present invention will be explained in detail below.

Generally, zeolite is a crystalline aluminosilicate, and its chemical composition is expressed by the following formula xM〓O.Al ₂ O _{3.ySiO 2.ZH 2} O, based on Al ₂ O ₃ .

(However, M means a cation with a valence of n, x,
y and Z are 0 or positive numbers, x is usually around 1, and y is 2
That's all. ) Although there are structural differences between zeolites, the type of zeolite is generally determined by the difference in y (ie, SiO ₂ /Al ₂ O ₃ molar ratio) among the above chemical compositions. Those with y of 2 are type A zeolites, those with y of 2.5 to 3.5 are type X zeolites, and those with y of 2.5 to 3.5 are type X zeolites.
5.5 is Y-type zeolite, 6-10 is L
It is classified into zeolites such as type zeolite, offretite, erionite, and ferrienite.
Also, for 10 or more, mordenite, ZSM-5, ZSM
-8, ZSM-11, ZSM-21, ZSM-34, ZSM-
35, there are many zeolites such as silicalite, and these zeolites have a wide range of 10 to 30 or 10 to ∞.
It is characterized in that it can have a SiO ₂ /Al ₂ O ₃ molar ratio.

Any zeolite can be used in the present invention as long as it has a SiO ₂ /Al ₂ O ₃ molar ratio of 18 or more.

Furthermore, it is of course possible to use zeolite which has been treated with hydrochloric acid to dissolve and remove Al so that the SiO ₂ /Al ₂ O ₃ molar ratio is 18 or more. Zeolites with a molecular weight of less than 18 do not adsorb bromine at all, or the amount of bromine adsorbed is small, making them impractical.

Zeolite with a SiO ₂ /Al ₂ O ₃ molar ratio of 18 or more exhibits its performance particularly in the coexistence of water. That is,
When water coexists with bromine-containing gas, SiO ₂ /Al ₂ O ₃
When the molar ratio is less than 18, almost no bromine is adsorbed on the zeolite. However, if the SiO ₂ /Al ₂ O ₃ molar ratio is 18 or more, bromine will be sufficiently adsorbed even if water coexists in the bromine-containing gas. When the SiO ₂ /Al ₂ O ₃ molar ratio is 40 or more, there is almost no influence of water. In particular, adsorption of free bromine in aqueous solutions is strongly affected by moisture.
The SiO ₂ /Al ₂ O ₃ molar ratio is preferably 40 or more.

Here, the cation [M] of the zeolite is usually an alkali metal or alkaline earth metal cation or a quaternary ammonium ion in the as-synthesized state, but it may be exchanged with another cation. Preferably it is H ion. To make H ion substitution type, quaternary ammonium ion type can be simply calcined, alkali metal or alkaline earth metal ion type can be made by contacting with mineral acid, or There is a method in which baking is performed after contacting with an aqueous solution containing ammonium ions.

The zeolite-containing adsorbent in the present invention includes those composed only of zeolite itself, but rather than using zeolite itself, that is, in the form of a powder, it is used as a columnar, spherical, or crushed shaped body. Good to use. A method of forming a molded body using a binder such as silica sol, alumina sol, or clay may be adopted as appropriate.

There are various aqueous solutions or bromine-containing gases containing free bromine. For example, aqueous solutions containing free bromine include solutions prepared by adding an oxidizing agent such as chlorine to seawater, concentrated seawater, bittern, natural citrus water, etc. to liberate bromine;
There are solutions in which bromine is absorbed by washing gas containing bromine with seawater, water, aqueous sodium bromide solution, etc. The bromine concentration of these solutions is not particularly limited, but
In order to carry out the method of the present invention more effectively, the bromine concentration is preferably 1 g/l or more.

On the other hand, bromine-containing gases include, for example, bromine-containing seawater, concentrated seawater, bittern, natural citrus water, etc., which are oxidized by blowing chlorine into them, and then forcing out the liberated bromine with air. Not only generated gases but also bromine-containing gases generated from processes in bromine utilization industries and any other bromine-containing gases are targeted. The bromine concentration of such bromine-containing gas varies; for example, in the case of the seawater method, the bromine concentration of the generated gas is extremely low, with a concentration of 0.7 to 0.8 mg/l.
In contrast, bittern, natural water, etc.
It can be as high as mg/l. In the case of these generated gases, the coexistence of moisture is unavoidable, but when the bromine concentration is extremely low, such as in the gases generated by the seawater method, the influence of moisture on bromine adsorption cannot be ignored. In that case, it is preferable to remove some moisture from the gas before bringing it into contact with the adsorbent of the present invention. Particularly preferably, the water vapor partial pressure in the bromine-containing gas is 5 mmHg or less. In the case of a gas with a high bromine concentration, moisture has little effect and removal of moisture is not necessary.

It is desirable that the aqueous solution or bromine-containing gas (hereinafter referred to as bromine-containing fluid) containing free bromine be brought into contact with zeolite, which is an adsorbent, so as to obtain as high a bromine adsorption amount as possible. For example, a zeolite molded body is packed into an adsorption column to form a fixed bed, and a bromine-containing fluid is passed through this, or a bromine-containing fluid is supplied from the bottom of the packed column and an upward flow is applied to form a fluidized bed and contact is made. is good.
In the latter case, it is better to repeat the process two or more times. Adsorption is preferably carried out at a temperature below 60°C, preferably below 40°C. In the present invention, the contact time between the adsorbent and the bromine-containing fluid is
It varies depending on the liquid and the bromine concentration in the fluid, but
In any case, these are kept in contact for a sufficient amount of time to adsorb bromine in the fluid.

The zeolite-containing adsorbent of the present invention that has sufficiently adsorbed bromine can be prepared by thoroughly draining the fluid when the fluid is an aqueous solution, or by washing with a minimum amount of water if necessary and then draining the fluid, or by draining the fluid after washing with a minimum amount of water when the fluid is a gas. is fine as is,
The adsorbent thus treated may then be heated to desorb bromine.

As for the desorption method, if the zeolite-containing adsorbent is heated to 60°C or higher, bromine will be easily desorbed, and if it is condensed by cooling, it can be directly recovered as liquid bromine. As a heating method, any method may be used, such as bringing water vapor, heated air, etc. into direct contact with the zeolite-containing adsorbent, or performing external heating.

The desorbed zeolite-containing adsorbent can be used again as an adsorbent.

In the bromine recovery method of the present invention, by using a plurality of adsorbent layers in parallel, bromine adsorption and desorption operations can be performed sequentially using these layers, and bromine can be continuously recovered. By using the present invention, bromine can be recovered extremely easily compared to conventional methods.

This will be explained below using Examples and Comparative Examples.

Example 1 H-substituted ZSM-5 type (SiO ₂ /Al ₂ O ₃ molar ratio = 50)
A zeolite molded body (column shape with a diameter of 1.5 mm) was granulated and molded with 100 parts by weight of synthetic zeolite powder and 25 parts by weight of SiO ₂ sol (SiO ₂ equivalent) at 700°C in air for 1 hour.
The material that was fired for a period of time was used as an adsorbent. This adsorbent
50 g was packed into a column with an inner diameter of 2.3 cm. (referred to as an adsorption column) A bittern solution containing bromine at a concentration of 4.4 g/l was adjusted to pH 3.0 with sulfuric acid, and chlorine gas was blown in to liberate bromine (referred to as a stock solution).

This stock solution was passed through the top of the adsorption column at a flow rate of 500 ml/Hr. When the bromine concentration in the effluent at the adsorption column outlet became almost the same as the original solution, the flow of liquid was stopped, and the amount of bromine adsorbed was measured, and it was 97 mg・Br ₂ /
g. It was an adsorbent. Then pure water 100% at the same flow rate.
After washing by flushing ml, the liquid was thoroughly drained. 180
When external heating was performed to ℃ and a very small amount of air was blown in, 4.61 g of bromine was desorbed and recovered. Substantially no residual bromine was observed in the adsorbent.

Example 2 H-substituted mordenite type (SiO ₂ /Al ₂ O ₃ molar ratio =
20) Synthetic zeolite powder 100 parts by weight and _SiO2 sol 25
500 parts by weight (SiO ₂ equivalent) of granulated and molded zeolite molded bodies (column shape with a diameter of 1.5 mm) in air.
℃ for 1 hour and used as an adsorbent. 50 g of this adsorbent was packed into a column with an inner diameter of 2.6 cm. An aqueous solution containing 5.0 g/l of free bromine was added to the top of the adsorption column.
The liquid was passed through at a flow rate of ml/Hr. When the bromine concentration in the effluent at the adsorption column outlet became almost the same as the stock solution, the flow of liquid was stopped, and the amount of bromine adsorbed was measured.
Br ₂ /g adsorbent. After thoroughly draining the liquid and blowing heated air at 160℃, bromine was detected.
2.74g was detached and recovered.

Comparative Example 1 H-substituted mordenite type (SiO ₂ /Al ₂ O ₃ molar ratio =
15) Synthetic zeolite powder 100 parts by weight and SiO ₂ sol 25
500 parts by weight (SiO ₂ equivalent) of granulated and molded zeolite molded bodies (column shape with a diameter of 1.5 mm) in air.
℃ for 1 hour and used as an adsorbent. When an adsorption experiment was conducted on this adsorbent under exactly the same conditions as in Example 2, the amount of bromine adsorbed was only 5.2 mg・Br ₂ /
g. It was an adsorbent.

Comparative Example 2 Y-type zeolite powder (SiO ₂ /Al ₂ O ₃ molar ratio =
5.2) _Zeolite molded _{body ( diameter}
The adsorbent was prepared by baking a 1.5 mm columnar material in air at 500°C for 1 hour. Example 2 for this adsorbent
When an adsorption experiment was conducted under exactly the same conditions, the amount of bromine adsorbed was only 2.2 mg·Br ₂ /g·adsorbent.

_{Example 3 Zeolite compact (} A column (1.5 mm in diameter) calcined in air at 700°C for 1 hour was used as an adsorbent.

100 g of this adsorbent was packed into a column with an inner diameter of 2.6 cm, and a mixed gas of bromine and air with a bromine concentration of 80 mg/g was bubbled through the top. When the bromine concentration of the column outlet gas reached approximately 80 mg/l, ventilation was stopped and the amount of bromine adsorbed was measured, and it was found to be 190 mg.Br ₂ /g.adsorbent.
Subsequently, this column was externally heated to 130°C and a very small amount of air was blown into it, and 19.0 g of bromine was desorbed.

Example 4 20 g of the same adsorbent as in Example 3 was packed into a column with an inner diameter of 1.5 cm. Seawater containing bromine compounds at a concentration of 65 mg/l was adjusted to pH 3.0 with sulfuric acid and chlorine gas was blown in to liberate bromine. Press out the bromine with air and heat to 20℃
Bromine concentration with moisture at saturated steam pressure at
0.8 mg/l of generated gas was obtained. This gas was passed through the top of the column at a flow rate of 700 ml/min.
When the bromine concentration in the column outlet gas reached approximately 0.8 mg/l, the ventilation was stopped and the amount of bromine adsorbed was measured.
It was 69 mg・Br ₂ /g・adsorbent. in this column
When heated air at 180°C was blown into the reactor, 1.38g of bromine was desorbed.

Example 5 An adsorption operation was performed in the same manner as in Example 4. However, the generated gas was brought into contact with a 55 wt% H ₂ SO ₄ aqueous solution in advance and then vented into the adsorption column. Bromine adsorption amount is 141
mg・Br ₂ /g・adsorbent. When the column was externally heated to 130°C and a very small amount of air was blown in, 2.82 g of bromine was desorbed.

Example 6 H-substituted mordenite type (SiO ₂ /Al ₂ O ₃ molar ratio =
20) Synthetic zeolite powder 100 parts by weight and _SiO2 sol 25
500 parts by weight (SiO ₂ equivalent) of granulated and molded zeolite molded bodies (column shape with a diameter of 1.5 mm) in air.
℃ for 1 hour and used as an adsorbent.

100 g of this adsorbent was packed into a column with an inner diameter of 2.6 cm, and a bromine/air mixed gas having a bromine concentration of 100 mg/l was bubbled through the top. When the bromine concentration of the column outlet gas reached approximately 100 mg/l, ventilation was stopped and the amount of bromine adsorbed was measured, and it was found to be 114 mg.Br ₂ /g.adsorbent. When air was blown into hot water at 70°C and a gas containing water at a saturated vapor pressure of 70°C was directly blown into this adsorption column, 10.8 g of bromine was desorbed. The desorption rate was 93%.

Comparative Example 3 H-substituted mordenite type (SiO ₂ /Al ₂ O ₃ molar ratio =
15) Synthetic zeolite powder 100 parts by weight and SiO ₂ sol 25
500 parts by weight (SiO ₂ equivalent) of granulated and molded zeolite molded bodies (column shape with a diameter of 1.5 mm) in air.
℃ for 1 hour and used as an adsorbent.

Pack 20g of this adsorbent into a column with an inner diameter of 1.5cm,
When adsorption operation was performed under the same conditions as in Example 4,
The amount of bromine adsorbed was only 2.1 mg·Br ₂ /g·adsorbent.

Claims (1)

[Claims] 1. The chemical composition has the general formula xM _2/o O・Al ₂ O ₃・
ySiO ₂ ZH ₂ O (where M is a cation with a valence of n,
x=0 to 2, y≧18, Z=0 or a positive number)
An adsorbent for bromine recovery containing a zeolite represented by: 2 An aqueous solution containing free bromine or a bromine-containing gas with a chemical composition of the general formula xM _2/o O・Al ₂ O ₃・
ySiO ₂ ZH ₂ O (where M is a cation with a valence of n,
x=0 to 2, y≧18, Z=0 or a positive number)
A method for recovering bromine, which comprises contacting with an adsorbent containing a zeolite represented by the formula, and then heating the adsorbent to desorb bromine.