JP3334962B2 - Recovery method of sulfur dioxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering sulfur dioxide from flue gas as sulfur dioxide.

[0002]

2. Description of the Related Art In combustion of heavy oil and coal, sulfur dioxide is contained in combustion exhaust gas. Various methods for collecting sulfur dioxide in combustion exhaust gas have been studied from the viewpoint of environmental pollution prevention. For example, a method of neutralizing sulfur dioxide with lime milk and collecting it as gypsum is well known. Also, a sulfurous acid gas is absorbed by a sodium hydroxide aqueous solution or a sodium sulfate aqueous solution to form a sodium bisulfite aqueous solution, which is used in an electrodialysis apparatus in which a bipolar membrane and a cation exchange membrane are alternately arranged.
A method of producing a mixed aqueous solution of a sulfate and a sulfurous acid and an aqueous solution of a sulfite by supplying the mixture to both chambers has been proposed (Japanese Patent Publication No. 60-36811).

[0003]

However, in this method, the sulfurous acid discharged from the electrodialysis apparatus is obtained as a mixed aqueous solution with a sulfate, so that an operation for separating the sulfurous acid and the sulfate is required. Therefore, in the above-mentioned document, the mixed aqueous solution of sulfurous acid and sulfate obtained in this manner is supplied to an electrodialysis device using another bipolar membrane to perform separation.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present inventors have used an electrodialysis apparatus in which bipolar membranes and monovalent anion selective permeable membranes are alternately arranged. By combining the above, a method for recovering sulfur dioxide gas was found, and the present invention was proposed.

That is, the present invention provides an absorption step in which a sulfurous acid gas is absorbed into a sulfite aqueous solution to obtain a mixed aqueous solution of sulfite and bisulfite, and the mixed aqueous solution of sulfite and bisulfite is mixed with the bipolar membrane. An electrodialysis step in which an aqueous solution of sulfite and an aqueous solution of sulfite are supplied by supplying an electrodialysis apparatus having a selective anion-selective permeable membrane arranged alternately, and a sulfurous acid gas is separated from the aqueous solution of sulfite obtained in the electrodialysis step A method for recovering sulfur dioxide, comprising a gas-liquid separation step.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram illustrating the method of the present invention.
In the present invention, first, in the absorption step I, the flue gas 1 containing the sulfite gas and the aqueous sulfite solution 2 are supplied, and the sulfur dioxide gas in the exhaust gas is absorbed by the aqueous sulfite solution. The liquid that has absorbed the sulfurous acid gas becomes a mixed aqueous solution of a sulfite and a bisulfite. As a device used in the absorption step I, a known gas-liquid absorption device can be used without any limitation. For example, as the absorption device, a gas dispersion type absorption device such as a bubble stirring tank or a tray column, or a liquid dispersion type absorption device such as a spray tower or a packed tower can be used.

[0007] The mixed aqueous solution 2 of sulfite and bisulfite obtained in the absorption step I is sent to the electrodialysis step II. In the electrodialysis step II, as shown in FIG. 2, an electrodialysis apparatus in which bipolar membranes B and monovalent anion selectively permeable membranes A are alternately arranged is used. The bipolar membrane B is a composite ion exchange membrane having a structure in which a cation exchange membrane and an anion exchange membrane are laminated. As such a bipolar film, a known film can be used without any particular limitation. The following is known as a manufacturing method thereof. For example, a method of laminating a cation exchange membrane and an anion exchange membrane with a mixture of polyethyleneimine-epichlorohydrin and hardening and bonding the same (Japanese Patent Publication No. 32-3962), an ion exchange bond between the cation exchange membrane and the anion exchange membrane (Japanese Patent Publication No. 34-3961), a method in which a cation exchange membrane and an anion exchange membrane are coated with a fine powder of an ion exchange resin, or a paste mixture of an anion or cation exchange resin and a thermoplastic substance. Pressure bonding method (Japanese Patent Publication No. 35-14531), a method of applying a paste-like substance composed of vinylpyridine and an epoxy compound on the surface of a cation exchange membrane and irradiating it with a paste (Japanese Patent Publication No. 38-1983) No. 16633), ionizing radiation after adhering a sulfonic acid type polymer electrolyte and allylamine on the surface of an anion exchange membrane. Irradiation cross-linking method (Japanese Patent Publication No. 51-4113) and method of depositing a mixture of a dispersion system of an ion-exchange resin having an opposite charge and a base polymer on the surface of an ion-exchange membrane (JP-A-53-37190) ), A sheet of polyethylene film impregnated with styrene and divinylbenzene was sandwiched between stainless steel frames, one side was sulfonated, the sheet was removed, the remaining part was chloromethylated, and then aminated. (U.S. Pat. No. 3,562,139), and a method in which the interface between an anion exchange membrane and a cation exchange membrane is treated with an inorganic compound and the two membranes are joined (Japanese Patent Laid-Open No. 59-472).
No. 35).

The selectively permeable monovalent anion membrane A used in the present invention is not particularly limited, and a known anion exchange membrane capable of selectively permeating only known monovalent anions can be used.
For example, a thin layer of a condensate of an aldehyde and a compound having at least one amino group in the aromatic nucleus on the surface of the anion exchange membrane and capable of condensing with an aldehyde group or a methylol group to form a resin having an improved cross-linking bond. Film (Japanese Patent Publication No. 36-1)
No. 5258), a membrane having a thin film of an organic low molecular electrolyte having a cation exchange group or a non-crosslinked linear polymer electrolyte on the surface of an anion exchange membrane (Japanese Patent Publication No. 45-199)
No. 80), a quaternary amination treatment of an ion-exchange membrane matrix in which some of the functional groups that can be converted to a strongly basic anion exchange group have been previously inactivated by a quaternary amino treatment, and then a peroxide solution Or a quaternary aminated film after contact with a peroxide solution (JP-B-56-47213).

[0009] The monovalent anion selective permeability is such that only a monovalent bisulfite ion is selectively permeated from a mixed aqueous solution of a sulfite and a bisulfite supplied to an electrodialyzer, and the divalent sulfite ion is selectively permeated. This is a property necessary to prevent light from passing through. Permeability coefficient of bisulfite ion and sulfite ion (P
^{SO3 (} _HSO3 ) is less than 0.5, preferably less than 0.1 in terms of separation efficiency.

The above-mentioned selective transmission coefficient is a value obtained as follows. 0.5N NaHSO ₃ and Na ₂ S
A 1: 1 mixture of O ₃ was placed on both sides of the monovalent anion permselective membrane and electrodialysis was performed at 5 A / dm ² for 40 minutes to permeate through the monovalent anion permselective membrane. It was determined from the amounts of HSO ₃ ^- and SO ₃ ^2- transferred to the opposite side by the following equation.

P ^SO3 _HSO3 = t _SO3 · C _HSO3 / t _HSO3 · C _SO3 (where t _SO3 is the current efficiency of SO ₃ ^2- of the monovalent anion selective permeable membrane, and t _HSO3 is the monovalent anion. HS of permselective membrane
The current efficiency, C _{HSO3 @} is HSO ₃ before electrodialysis ^{- -} O ₃ concentration of, C _SO3 denotes a SO ₃ ^{2-concentration} before electrodialysis. In the above electrodialyzer, the anode 11 and the cathode 12
An electrode used in the electrochemical industry such as water electrolysis and salt electrolysis is used without any limitation. For example, nickel, iron, lead, platinum or graphite can be suitably used as the anode material, and nickel, iron, stainless steel or platinum can be suitably used as the cathode material.

The type of anolyte supplied to the anode chamber can be appropriately selected according to the type of anode material. Preferred examples of these combinations are, for example, as follows. Examples include nickel or iron-sodium hydroxide aqueous solution, lead-sulfuric acid aqueous solution, platinum-sulfuric acid or sodium sulfate aqueous solution, and graphite-salt aqueous solution. Preferred combinations of the cathode material and the catholyte are as follows. Nickel, iron, or stainless steel-can include sodium hydroxide, sodium sulfate, or saline solutions.

In the present invention, of the chambers divided by the bipolar membrane B and the monovalent anion selective permeable membrane A of the electrodialysis apparatus, the chamber where the bipolar membrane is located on the cathode side is defined as the alkali chamber 14 and the bipolar membrane. Is located at the anode side
Called 3. The mixed aqueous solution 15 of bisulfite and sulfite obtained in the absorption step I is supplied to the alkali chamber 14,
A sulfurous acid aqueous solution 16 is supplied to the acid chamber 13.

The mixed aqueous solution 1 supplied to the alkali chamber 14
Only the monovalent bisulfite ion in 5 selectively passes through the monovalent anion selective permeable membrane A and moves to the acid chamber 13, and the divalent sulfite ion remains in the alkali chamber 14.
In the acid chamber 13, the bisulfite ion reacts with the hydrogen ion supplied from the bipolar membrane B to generate sulfurous acid. This is shown in the reaction formula as follows.

HSO ₃ ⁻ + H ⁺ → H ₂ SO ₃ On the other hand, in the alkaline chamber 14, the remaining bisulfite ions that do not pass through the monovalent anion selectively permeable membrane A and the bipolar membrane B
Reacts with the hydroxide ions supplied from the reaction vessel to generate sulfite ions. This is shown in the reaction formula as follows.

HSO ₃ ⁻ + OH ⁻ → SO ₃ ² + H ₂ O Sulfite ions supplied as a mixed aqueous solution to the alkaline chamber 14 do not permeate into the acid chamber, and move to the acid chamber together with the supplied sulfite ions. The remaining amount of the remaining bisulfite ion and hydroxyl ion formed by the reaction of the hydroxide ion is recovered as the salt aqueous solution 18. The sulfurous acid generated in the acid chamber is recovered as an aqueous solution 17.

The method of electrodialysis in the present invention includes:
The acid chamber and the alkali chamber are provided with a liquid tank to be supplied to each chamber, and the liquid is circulated between the respective chambers and the liquid tank, or each liquid is supplied to the acid chamber and the alkali chamber in one pass. A method of supplying, a method of circulating one of the liquids in the acid chamber or the alkali chamber, and a method of using the other liquid in one pass, or the like can be arbitrarily adopted.

In the present invention, the cations constituting the sulfite and bisulfite are typically alkali metal ions such as sodium ion, potassium ion and lithium ion.
It may be a sulfonium ion or the like.

In the present invention, the above-mentioned electrodialysis step II
Is then sent to a gas-liquid separation step III to separate sulfurous acid gas. Part of the sulfurous acid gas has already been separated as a gas in the electrodialysis step II, and is discharged from the electrodialysis step in a gas-liquid mixed state. In the gas-liquid separation step III, this may be simply gas-liquid separated, or may be separated by generating a sulfurous acid gas dissolved in the aqueous sulfurous acid solution. Gas may be generated.

As the gas-liquid separation method used in the gas-liquid separation step III, a known method can be adopted. For example, a known diffusion device such as a plate tower or a packed tower can be used. Thus, the sulfurous acid gas 4 can be recovered.

In the present invention, the sulfite aqueous solution 5 obtained in the electrodialysis step II can be reused as the sulfurous acid gas absorbing solution in the absorption step I. Further, the aqueous sulfurous acid solution 3 ′ after the separation of the sulfurous acid gas 4 in the gas-liquid separation step III can be reused as the aqueous sulfurous acid solution supplied to the acid chamber in the electrodialysis step II.

[0022]

According to the present invention, sulfur dioxide contained in flue gas can be effectively recovered. The aqueous sulfurous acid solution separated in the gas-liquid separation step can be reused as a supply liquid to the acid chamber in the electrodialysis step, and the aqueous sulfite solution generated in the electrodialysis step can be reused as an absorbent in the absorption step. Available. Therefore, the components generated in each step of the present invention can be reused in other steps, and a closed system that does not generate waste when viewed as a whole step can be configured.

[0023]

【Example】

Example 1 A sulfur dioxide gas was absorbed by supplying a sodium sulfite aqueous solution by using a grid packed tower in an absorption process to obtain a sulfur dioxide gas absorption liquid. The resulting solution contains Na ₂ SO ₃ 50
g / l, 200 g / l NaHSO ₃ .

As an electrodialysis tank, electricity _divided into an acid chamber and an alkali chamber by a bipolar membrane Neosepta BP-1 membrane manufactured by Tokuyama Soda Co., Ltd. and a monovalent anion selectively permeable membrane Neosceptor ACS (P ^SO3 _{HSO 3} = 0.1). A dialysis tank (manufactured by Tokuyama Soda Co., Ltd., effective membrane area ² dm ² ) was used. In the alkaline chamber, 50 g / l of Na ₂ SO ₃ which is a sulfurous acid gas absorbing solution, NaH
An aqueous solution containing 200 g / l of SO ₃ , 5 g of sulfurous acid in the acid chamber
/ L aqueous solution, and the film surface speed is 6 cm / sec.
c, operated at an average current density of 5 A / dm ² . as a result,
180 g / l Na ₂ SO ₃ , NaHSO ₃
An aqueous solution containing 3.1 g / l was obtained. An aqueous solution containing 56.6 g / l of sulfurous acid and 1.5 g / l of Na ₂ SO ₃ was obtained from the acid chamber.

Next, the sulfurous acid aqueous solution obtained from the acid chamber was supplied to a stripping device using a packed tower to release the sulfurous acid gas. After separating the sulfurous acid gas, a 5 g / l aqueous solution of sulfurous acid was obtained. This aqueous solution of sulfurous acid was supplied to the acid chamber of the electrodialyzer. On the other hand, N obtained from the alkaline chamber of the electrodialysis device
an aqueous solution containing a ₂ SO ₃ 180g / l, the NaHSO ₃ 3.1 g / l was fed into the grid packed tower as an absorbing solution for performing the absorption of sulfur dioxide in the absorption process.

[Brief description of the drawings]

FIG. 1 is a schematic view of a method for recovering sulfur dioxide gas of the present invention.

FIG. 2 is a diagram schematically showing one configuration example of an electrodialysis device used in the present invention.

[Explanation of symbols]

 Reference Signs List A Anion exchange membrane B Bipolar membrane I Absorption step II Electrodialysis step III Gas-liquid separation step 1 Smoke containing sulfur dioxide gas 2 Mixed aqueous solution of bisulfite and sulfite 3, 3 'sulfurous acid aqueous solution 4 Sulfite gas 5 Sulfite Aqueous solution 6 Smoke exhaust 11 Anode 12 Cathode 13 Acid chamber 14 Alkaline chamber 15 Mixed aqueous solution of bisulfite and sulfite 16 Sulfite aqueous solution 17 Sulfite aqueous solution 18 Sulfite aqueous solution

──────────────────────────────────────────────────続 き Continuation of front page (51) Int.Cl. ⁷ Identification code FI C02F 1/46 ZAB B01D 53/34 125R 1/469 C02F 1/46 103 C25B 1/22 (56) References JP-A-49- 58082 (JP, A) JP-A-51-93783 (JP, A) JP-A-52-5689 (JP, A) JP-A-7-31842 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C01B 17/60 B01D 53/34 ZAB C25B 1/22

Claims (1)

(57) [Claims] An absorption step of absorbing sulfurous acid gas into an aqueous sulfite solution to obtain a mixed aqueous solution of sulfite and bisulfite,
An electrodialysis process in which a mixed aqueous solution of sulfite and bisulfite is supplied to an electrodialysis apparatus in which bipolar membranes and monovalent anion selective permeable membranes are alternately arranged to produce an aqueous sulfite solution and an aqueous sulfite solution A gas-liquid separation step of separating a sulfurous acid gas from the aqueous sulfurous acid solution obtained in the electrodialysis step.