WO2001018278A1

WO2001018278A1 - Method for producing a polysulfide

Info

Publication number: WO2001018278A1
Application number: PCT/JP2000/006034
Authority: WO
Inventors: Eiji Endoh; Tetsuji Shimohira; Tatsuya Andoh; Junji Tanaka; Keigo Watanabe
Original assignee: Kawasaki Kasei Chemicals Ltd.; Nippon Paper Industries Co., Ltd.
Priority date: 1999-09-06
Filing date: 2000-09-06
Publication date: 2001-03-15
Also published as: JP2001073180A; AU6871500A

Abstract

A method for producing a polysulfide by subjecting a solution containing a sulfide to electrolytic oxidation in an electrolytic bath (1,2) equipped with anode chambers (11, 21) having anodes (13, 23), cathode chambers (14, 24) having cathodes (15, 25), and diaphragms (16, 26) partitioning an anode chamber and a cathode chamber to, wherein conditions for electrolysis reaction are set depending upon the position in the direction of stream of a solution in the electrolytic bath. The method can be used for producing polysulfide sulfur in a high concentration while inhibiting the dissolution of an electrode material of an anode and the by-production of thiosulfate ion.

Description

Description Method for producing polysulfide Technical field

The present invention relates to a method for producing a polysulfide by electrolytic oxidation, and more particularly to a method for producing a polysulfide digest by electrolytically oxidizing a cooking liquor in a pulp production process. Background art

From the viewpoint of effective utilization of wood resources, increasing the yield of chemical pulp is an important issue. One of the technologies for increasing the yield of kraft pulp, the mainstream of chemical pulp, is the polysulfide digestion process.

The cooking liquor in the polysulfide cooking process is produced by oxidizing an alkaline aqueous solution containing sodium sulfide, a so-called white liquor, with molecular oxygen such as air in the presence of a catalyst such as activated carbon (for example, the following reaction formula 1). (See Japanese Patent Application Laid-Open (JP-A) No. 61-259754 and JP-A-53-92981). According to this method, it is possible to obtain a polysulfide cooking liquor having a conversion of about 60%, a selectivity of about 60%, and a sulfur polysulfide concentration of about 5 g L on a sulfide ion base. However, in this method, thiosulfate ions that do not contribute to cooking at all are produced as by-products due to side reactions (for example, the following reaction formulas 2 and 3), so that a cooking liquor containing a high concentration of sulfur polysulfide is produced with high selectivity. It was difficult.

4N a ₂ S + 0 ₂ + 2H ₂ 0 → 2Na ₂ S ₂ + 4Na OH (1)

2Na S + 20 ₂ + H ₂ 0 → Na ₂ S ₂ 0 ₃ + 2 NaOH (2) 2 Na ₂ S ₂ + 30 ₂ → 2 Na ₂ S ₂ 0 ₃ (3) where sulfur polysulfide refers Porisarufai Dosarufa (PS- S) and also called, for example, sulfur sodium polysulfide N a ₂ S oxidation state of _x 0, i.e. atoms - refers to sulfur (X 1) pieces minute. In this specification, sulfur (S _x ^2— sulfur equivalent to one atom) and sulfide (S ² —), which are equivalent to sulfur having an oxidation number of 12 in polysulfide ions, are collectively referred to in this specification. in will be expressed as N a ₂ S state sulfur. In this specification, the unit liter of capacity is represented by L. On the other hand, WO9500701 describes an electrolytic production method of a polysulfide cooking liquor. In this method, an anode obtained by coating an oxide of ruthenium, iridium, platinum, or palladium on a carrier is used as an anode. Specifically, a three-dimensional mesh electrode of a carrier in which a large number of expanded metals are combined is disclosed. WO 97/412125 describes an electrolytic production method of a polysulfide cooking liquor using a porous anode having at least a surface made of carbon. 0 / zm carbon fiber aggregate is used

Disclosure of the invention

The present invention uses an electrolytic cell having an anode chamber in which an anode is arranged, a force sword chamber in which a force sword is arranged, and a diaphragm for partitioning the anode chamber and a cathode chamber, and a sulfide is contained in the anode chamber. Provided is a method for producing a polysulfide by electrolytic oxidation while continuously flowing a solution containing the polysulfide, wherein the distribution of the electrolytic conditions is imparted in the flow direction of the solution in the electrolytic cell (2).

When a solution containing sulfide ions is electrolytically oxidized by the galvanostatic method, when the oxidation proceeds and the concentration overpotential increases due to the decrease of sulfide ions in the solution, the anode potential shifts to a noble potential, As a result, problems such as formation of thiosulfate ions and dissolution of the anode in the electrode are likely to occur. In the present invention, the oxidation progresses in accordance with the progress of the oxidation of the anolyte by providing the distribution of the electrolytic conditions in the flow direction of the sulfide-containing solution (hereinafter referred to as anolyte) flowing through the anode compartment. When there is no oxidation, electrolysis can be performed under conditions that give priority to efficiency, and when oxidation has progressed, electrolysis can be performed under conditions that do not easily cause side reactions.

According to the study of the present inventor, when the average value of X of polysulfide ions (hereinafter referred to as average polysulfurization degree) exceeds 4, thiosulfate ions are produced as a by-product during electrolysis, and in the case of nickel anode. Easily dissolves anodic nickel

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is an explanatory diagram showing one example of an apparatus for implementing the present invention.

Explanation of reference numerals

1: upstream electrolytic cell

2: Downstream electrolyzer

1 1, 21: Anode chamber

1 2, 22: Anode current collector

1 3, 23: Anode

14, 24: Power Sword Room

1 5, 25: Power Sword

1 6, 26: best mode for carrying out the invention

To impart a distribution of electrolysis conditions in the flow direction of the anolyte in the electrolytic cell, specifically, two or more electrolytic cells are arranged in series in the flow of the solution, and the electric angle of the upstream electrolytic cell It is preferable that the conditions and the electrolysis conditions of the downstream electrolyzer be different because the electrolyzer has a simple structure and its operation is easily controlled. An electrolytic cell having a distribution of electrolysis conditions depending on the position in the electrolytic cell can be used alone or in combination with another electrolytic cell.

FIG. 1 shows an example of an apparatus for carrying out the present invention. In Fig. 1, polysulfide is produced by combining two electrolytic cells in series, such as an upstream electrolyzer (1) and a downstream electrolyzer (2). Each cell is composed of an anode chamber (11, 21), an anode current collector (12, 22), an anode (13, 23), a power sword chamber (14, 24), and a power sword. (15, 25) and a diaphragm (16, 26).

In the present invention, the electrolysis conditions to be changed in the flowing direction of the electrolytic solution include the following.

(Current density on anode surface)

Oxidation of sulfide ions is believed to occur at the anode surface. As the current density on the anode surface increases, the diffusion of polysulfide ions and Na ions generated on the electrode surface cannot catch up, and the difference between the composition of the solution on the electrode surface and the composition of the entire solution increases. It becomes.

If the oxidation of the solution has not progressed sufficiently, the composition of the solution on the anode surface remains within the range where the side reaction hardly occurs even if the current density on the anode surface is relatively high V. However, in a solution in which the oxidation of the solution has sufficiently proceeded, the composition of the solution on the anode surface is in a range where a side reaction is likely to occur.

On the other hand, when the current density on the anode surface is low, an anode having a larger surface area is required to produce the same amount of polysulfide, and the electrolytic cell becomes large.

Therefore, in the production method of the present invention, the distribution is provided so that the current density on the anode surface becomes lower toward the downstream side in the flowing direction of the solution in the electrolytic cell 內. For example, if there are two electrolytic cells, the current density at the anode surface of the upstream electrolytic cell is greater than the current density at the anode surface of the downstream electrolytic cell, and the anode surface of the upstream electrolytic cell current density 0 in. 0 0 5 to 2 0 k AZM are ^two der, such that the current density in § Roh once the surface of the electrolytic cell downstream is 0. 0 0 1~ 1 5 k AZ m 2 It is preferable to control.

(Flow velocity in the anode room)

It is preferable to maintain the anolyte in a laminar flow region with a small flow velocity in order to reduce pressure loss. However, in a laminar flow, the anolyte in the anode chamber is not agitated, and in some cases, deposits tend to accumulate on the diaphragm facing the anode chamber, and the cell voltage increases with time and becomes chewy. On the other hand, when the anolyte flow rate is set to be large, there is an advantage that the anolyte near the surface of the diaphragm is agitated and deposits are less likely to collect. The average superficial velocity in the anode chamber is preferably 1 to 30 cmZ seconds. The flow rate of the catholyte is not limited, but is preferably determined according to the magnitude of the buoyancy of the generated gas. A more preferable range of the average superficial velocity in the anode chamber is 1 to 15 cm / sec, and a particularly preferable range is 2 to 10 cmZ seconds.

There are two electrolytic cells, and the flow rate of the anode liquid in the upstream electrolytic cell is smaller than the flow rate of the anode liquid in the downstream electrolytic cell, and the flow rate of the anode liquid in the upstream electrolytic cell is two. It is more preferable that the flow rate is 0.5 to 20 cmZ seconds and the flow rate of the anode liquid in the downstream electrolytic cell is 1 to 30 cmZ seconds. (Anode properties, etc.)

The material of the anode in the present invention is not particularly limited as long as it has oxidation resistance in an alkaline solution. Non-metals include carbon materials, metals include base metals such as nickel, konokoleto, and titanium, and alloys thereof. And noble metals such as platinum, gold and rhodium, and alloys or oxides thereof. Of these, in the case of base metals, nickel or nickel alloys have a higher potential for dissolving the oxides and forming oxides than the potential for forming the sulfur polysulfide and thiosulfate ions. In production, it has sufficient durability for practical use. The anode is preferably a porous body.

Specifically, when the number of electrolytic cells is two, the anode on the upstream side is a nickel porous body, and the anode on the downstream side is a carbon porous body, side reactions are suppressed to efficiently convert polysulfide. It is preferable because it can be obtained.

In the present invention, the surface area of the anode per unit volume of the anode chamber is preferably 500 to 2000 Om ² Zm ³ . Here, the volume of the anode chamber is the volume of a portion defined by the effective conducting surface of the diaphragm and the current collector plate of the anode. If the surface area of the anode is less than 50 O m ² / !!! ³ , the current density on the anode surface will increase and not only will it be easier to generate by-products such as thiosulfate ions, but also nickel etc. It is not preferable to use a base metal or an alloy thereof as an anode because an anode dissolution easily occurs. If the surface area of the anode is set to be larger than 2000 Om ² Xm ³ , the pressure loss of the liquid will increase, which may cause a problem in the electrolysis operation. The anode of the surface area per unit volume of the anode compartment, 1 0 0 0~ 1 0 0 0 O m 2 and even more preferably in the range of Zm ^3.

Further, the surface area of the anode is preferably ^{2 to 10} Om ² Zm ² per unit area of the diaphragm separating the anode chamber and the power source chamber. The surface area of the anode, and even more preferably unit area per 5~5 O n ^ Zm ² of the septum.

Specifically, the number of electrolytic cells is two, the anode surface area per unit area of the diaphragm of the upstream electrolytic cell is smaller than the anode surface area per unit area of the diaphragm of the downstream electrolytic cell, and The surface area of the upstream node is 2 to 100 m ² / m ² per unit area of the diaphragm, and the surface area of the downstream node is 1 O to 500 0 per unit area of the diaphragm. 0 m ² Z m ² is more preferable.

In the present invention, it is preferable to use a porous node having a physically continuous three-dimensional network structure. The network structure is a physically continuous structure, and may be continuously connected by welding or the like. Specifically, for example, in the case of a nickel anode material, porous nickel obtained by plating nickel on the skeleton of the foamed polymer material and then baking and removing the internal polymer material can be used.

In the case of a porous anode having a three-dimensional network structure, the pores formed by the network structure preferably have an average pore diameter of 0.1 to 5 mm. If the average pore diameter is larger than 5 mπι, the anode surface area cannot be increased, the current density on the anode surface will increase, and only the by-products such as thiosulfate ions will be easily generated. It is not preferable because anode dissolution tends to occur. If the average pore diameter of the pores is smaller than 0.1 mm, the pressure loss of the liquid increases, which may cause a problem in the electrolysis operation, which is not preferable. More preferably, the average pore size of the mesh of the anode is 0.2 to 2 mm.

An anode having a three-dimensional network structure has a network structure composed of linear materials. The diameter of the filament material constituting the mesh is preferably 0.1 to 2 mm. A wire having a diameter of less than 0.01 mm is not preferable because it is extremely difficult to manufacture and the installation is not easy. If the diameter of the wire exceeds 2 mm, a large surface area of the anode cannot be obtained, the current density on the anode surface increases, and by-products such as thiosulfate are easily generated, which is not preferable. . It is particularly preferable that the diameter of the filament material constituting the mesh is 0.02 to 1 mm. A current is supplied to the anode through the anode current collector. As a material of the current collector, a material having excellent alkali resistance is preferable. For example, nickel, titanium, carbon, gold, platinum, stainless steel, and the like can be used. The surface of the current collector may be planar. The current may be supplied simply by mechanical contact with the anode, but it is preferable that the current is physically bonded by welding or the like.

(Current density per diaphragm area)

If in the present invention the electrolytic cell is two, the current density at the diaphragm surface of the upstream side of the electrolytic cell is 0. 5~ 2 0 k A / m 2, at the diaphragm surface of the downstream electrolyzer Current density is 0 - 1~ 1 5 k A / m 2 a and even Shi favored. If the current density at the diaphragm surface of the electrolytic cell on the upstream side is less than 0.5 kA / m ² , unnecessarily large electrolytic equipment is required, which is not preferable. If the current density on the diaphragm surface of the upstream electrolytic cell exceeds ²⁰ kA / m ² , the anodic potential becomes higher due to a decrease in sulfide ions in the solution and an increase in concentration overvoltage due to mass transfer. Potential, and as a result not only increases by-products such as thiosulfuric acid, sulfuric acid, and oxygen, but when a base metal such as nickel or an alloy thereof is used as the anode, the electrode may cause anode dissolution. It's good because there is.

When the current density on the diaphragm surface is lower than that of the upstream electrolytic cell, the sulfide can be selectively electrolyzed without shifting the anode potential to a noble potential. Preferred because it can be oxidized to produce polysulfides.

(Material of diaphragm)

It is preferable to use a cation exchange membrane as a diaphragm for partitioning the anode compartment and the cathode compartment. The cation exchange membrane guides the cations from the anode compartment to the force sword compartment, and impedes the transfer of sulfide and polysulfide ions. As the cation exchange membrane, a polymer membrane in which a cation exchange group such as a sulfonic acid group or a carboxylic acid group is introduced into a hydrocarbon-based or fluororesin-based polymer is preferable. If there is no problem in terms of alkali resistance or the like, a bipolar membrane or an anion exchange membrane can be used.

(Temperature)

It is also possible to change the temperature condition of the anode chamber between the upstream side and the downstream side. Preferably, the temperature of the anode compartment is in the range of 70 to 110 ° C. When the temperature of the anode chamber is lower than 70 ° C, not only the cell voltage increases, but also by-products are easily generated, and when a base metal such as nickel and their alloys are used as the anode, the anode melting is performed. Is not preferable because of the possibility that The upper temperature limit is practically limited by the material of the cell or diaphragm.

(Liquid Katsunari)

Further, in the present invention, in order to make the reaction on the downstream side easier, the distribution of the liquid composition is added in the flow direction of the solution in the electrolytic cell して by diluting or adding an acid or an alkali. Can be given.

(Cathode or cathode chamber)

The force sword material in the present invention is preferably an alkali resistant material. In addition to base metal-based materials such as nickel, Raney nickel, nickel sulfide, steel, and stainless steel, precious metals such as platinum, gold, and rhodium and alloys thereof. Can be used.

The force sword is used in the form of a single plate or a mesh, or a plurality of them in a multi-layer configuration. A three-dimensional electrode combining linear electrodes can also be used. As the electrolyzer, a two-chamber electrolyzer comprising one anode chamber and one force source chamber is used. Electrolyzers combining three or more rooms are also used. If multiple electrolytic cells are used, the force and anode can be arranged in a monopolar or bipolar configuration.

(Electrolysis conditions)

When two electrolytic cells are used in the present invention, electrolysis is performed so that the conversion rate of sulfide in the solution is 10 to 72% in the upstream electrolytic cell, and sulfurization in the solution is performed in the downstream electrolytic cell. The electrolysis is preferably carried out so that the conversion of the product is 25 to 75%.

If the conversion of sulfide in the solution in the upstream electrolytic cell is less than 10%, the load on the downstream electrolytic cell becomes too large when trying to achieve a high sulfur polysulfide concentration, which is not preferable. . If the conversion of sulfide in the solution in the upstream electrolytic cell exceeds 72%, side reactions are likely to occur in the upstream electrolytic cell, which is not desirable. If the conversion rate of sulfur sulfide in the solution in the downstream electrolytic cell is less than 25%, the polysulfide concentration in the solution is undesirably low.

The anode potential, S ₂ ² _ as an oxidation product of sulfide ^{ions, S 2 ", S, S} 5 2 - polysulfide ions (S _x ²⁾ is produced, such as, to Chio sulfate ions do not byproduct Is preferably maintained.

The anolyte is a one-pass process (a process in which part of the anolyte exiting the electrolytic cell is circulated to the inlet of the electrolytic cell without flow) to produce a high-concentration sulfur polysulfide polysulfide digest. Is preferred. In the present invention, an alkali metal ion is preferable as the countercation of sulfide ions. As the alkali metal ion, sodium ion or sodium ion is preferable: The method of the present invention is suitable for a method of treating a white liquor or a green liquor in a pulp production process to obtain a polysulfide cooking liquor. It is particularly suitable for processing white liquor. When incorporating the polysulfide production process of the present invention into the pulp production process, at least a part of the white liquor is extracted, treated in the polysulfide production process of the present invention, and then supplied to the digestion process. The composition of white liquor, which is currently used for kraft pulp digestion, usually contains 2 to 6 mo1 ZL as alkali metal ions, of which 90% or more is sodium ion. Yes, the rest is almost power-real ions.

Anions are mainly composed of hydroxide ion, sulfide ion and carbonate ion, and also include sulfate ion, thiosulfate ion, chloride ion and sulfite ion. In addition, it contains trace components such as calcium, silicon, aluminum, phosphorus, magnesium, copper, manganese, and iron. When such white liquor is supplied to the anode chamber according to the present invention and electrolytic oxidation is performed, sulfide ions are oxidized to generate polysulfide ions. Along with this, metal ions move to the cathode chamber through the diaphragm.

When used in the pulp cooking process, the sulfur polysulfide strain in the solution obtained by electrolyzing white liquor (polysulfide cooking liquor) is 5 to 15 g, depending on the sulfide ion concentration in the white liquor. ZL is preferred. If the degree of sulfur polysulfide is less than 5 g / L, the effect of increasing the pulp yield during cooking may not be sufficiently obtained. When the concentration of sulfur polysulfide is higher than 15 g ZL, the pulp yield does not increase because the Na ₂ S form sulfur decreases. The Na ₂ S-form sulfur is preferably at least 10 g ZL.

Although various reactions can be selected for the reaction in the power source chamber, it is preferable to use a reaction in which hydrogen gas is generated from water. Alkali hydroxide is generated from the resulting hydroxide ions and alkali metal ions that have migrated from the anode compartment. The solution to be introduced into the cathode chamber is preferably a solution substantially consisting of water and an alkali metal hydroxide, and particularly preferably a solution consisting of water and a hydroxide of sodium or potassium. The concentration of the alkali metal hydroxide is not limited, but is, for example, 1 to 15 mo 1 L, and preferably 2 to 5 mo 1 / L. If a solution having an ionic strength lower than the ionic strength of the white liquor flowing through the anode chamber is used as a power source solution, it is possible to prevent insolubles from being deposited on the diaphragm. The generated hydrogen gas can be used as a fuel or as a raw material for hydrogen peroxide. The generated alkali hydroxide is Besides being used for pulp cooking, it can be used for pulp bleaching, especially since it has few impurities. Example

[Comparative example]

Nickel plate as anode current collector, nickel foam as anode (Celmet, trade name, manufactured by Sumitomo Electric Industries, Ltd., 10 OmmX 2 OmmX 5 mm, average pore diameter of pores formed by the mesh structure of foam 0 8.3 mm), a two-chamber electrolytic cell was assembled using a mesh-shaped Ra-nickel electrode as a force source and a fluororesin cation exchange membrane (Flemion, manufactured by Asahi Glass Co., Ltd.) as a diaphragm. The anode compartment is 100 Omm high, 2 Omm wide and 5 mm thick, and the cathode compartment is 100 Omm high, 2 Omm wide and 5 mm thick, and the effective area of the diaphragm is 200 cm. ^{Was 2} . The nickel foam used as the anode was bonded to the nickel plate of the anode current collector by electric welding. The electrolytic cell was assembled by pressing the diaphragm against the anode side with the cathode from the cathode chamber side.

The physical properties and electrolytic conditions of the anode are as follows.

Anode thickness: 5mm,

Anode surface area per anode chamber volume: 3 1 2 5 m ² / χ ',

Anode surface area to diaphragm area: 12.5 m ² / m ² ,

Anode chamber porosity: 95%,

Anode liquid superficial tower speed: 2 cmZ seconds,

Electrolysis temperature: 85 ° C,

Current density at the diaphragm: 6 k A / m ² ₀

As anolyte, model white liquor _{(N a 2 S: 1 6} g / L sulfur atom terms, N a OH: 9 0 g / L, N a 2 C0 3: 3 4 g / L) was prepared, an anode The solution was fed at a flow rate of 12 OmLZ (superficial velocity 2 cmZ seconds) while being introduced from the lower side of the chamber and withdrawn upward. As the power source solution, a 3 N NaOH aqueous solution was used, and the solution was fed from the lower side of the cathode chamber at a flow rate of 80 mL / min, and sent out while being drawn out to the upper side. Heat exchangers are installed on both the anode side and the force source side to raise the temperature of the anode and catholyte solutions to the cells. I introduced it.

A constant current electrolysis was performed at a current of 12 OA (current density at the diaphragm: 6 kA / m ² ), a polysulfide digest was synthesized from the model white liquor, the cell voltage was measured, and the solution was sampled immediately after electrolysis. Then, sulfur polysulfide, Na ₂ S form sulfur and thiosulfate ion in the solution were analyzed and quantified.

During the electrolysis operation, except that nickel was eluted, the only products were sulfur polysulfide and thiosulfate, so the current efficiency and selectivity were determined to be A (g ZL) when the generated sulfur polysulfide concentration was A (g ZL). When the thiosulfate ion concentration is B (g / L) in terms of sulfur atom, it is defined as follows.

Current efficiency = (A / (A + 2B)) X I 00%,

Selectivity = [A / (A + B)] X I 00%.

The quantitative values of the concentrations of various sulfur compounds and the cell voltage were as follows. The composition of the polysulfide cooking liquor was 9. O gZL for sulfur polysulfide and 6.5 gZL for Na ₂ S-form sulfur; the thiosulfate ion was 0.50 gZL in terms of sulfur atoms. The average value of X of the polysulfide ion (S _x ² ) is 2.4, and the current efficiency is 90%, assuming no nickel elution, and the selectivity is 95%. %.

The average cell voltage was constant at 1.2-1.5 V. Attach a lugine tube near the anode, 10 cm above the bottom of the electrolyzer, at the center, and 10 cm below the top of the electrolyzer, and anode at 25 ° C for the saturated reference electrode. The electrode potential was measured. At the bottom of the cell, the voltage was -0.1 V, at the center it was +0.2 V, and at the top it was +0.5 V. Next, after a 24-hour test, the cell was disassembled and examined for the dissolution of the anode. As a result, it was found that the nickel anode at the top of the electrolytic cell was partially dissolved.

[Example 1 ]

Two electrolytic cells equivalent to those of the comparative example were prepared except that the height of the anode chamber was 50 Omm, the height of the power sword chamber was 500 mm, the width was 20 mm, and the thickness was 5 mm. These are arranged in two stages in the height direction, and a model white liquor equivalent to that of the comparative example is prepared as an anolyte, and introduced from below the anode chamber of the lower electrolytic cell (this is called an upstream electrolytic cell). Then pull out to the top This was introduced from the lower part of the anode chamber of the upper electrolytic cell (this is called the downstream electrolytic cell), and it was sent at a flow rate of 12 OmLZ (superficial velocity 2 cniZ seconds) while extracting it upward. As in the comparative example, a 3 N NaOH aqueous solution was used as the power source solution, and it was separately introduced from the lower side of the power source chamber of the upstream electrolytic cell and the downstream electrolytic cell at a flow rate of 80 mLZ and extracted upward. While feeding.

Current 8 OA on the upstream side electrolysis cell (current density 8 k AZM ² in septum), a constant current electrolysis with electric current 4 OA (current density 4 k AZM ² at diaphragm) each on the downstream side electrolyzer Then, a polysulfide cooking liquor was synthesized. As in the above comparative example, the cell voltage and anode potential of each electrolytic cell were measured, and the liquid coming out of the downstream electrolytic cell was sampled, and sulfur polysulfide, Na ₂ S-type sulfur, and thiosulfate ions in the solution were measured. Was analyzed and quantified.

The quantitative values of the concentrations of various sulfur compounds and the cell voltage were as follows. The composition of the polysulfide cooking liquor was 9.4 gL for sulfur polysulfide, 6.3 g / L for Na ₂ S form sulfur, and 0.30 gZL for added thiosulfate ion in terms of sulfur atoms. The average value of X of the polysulfide ion (S _x ² —) is 2.5, and the current efficiency during that time is 94%, assuming that nickel is not eluted. 97%.

The average cell voltage of the upstream electrolyzer was constant at 1.5 to 1.8 V. Attach a lugine tube near the anode at 5 cm above the bottom of the electrolytic sodium carbonate, at the center, and 5 cm below the top of the electrolytic cell, and place the anode on a 25 ° C saturated sweet copper reference electrode. As a result of measuring the electrode potential of the electrode, it was found to be 0.01 V at the bottom of the electrolytic cell, +0.05 V at the center, and +0.15 V at the top. The average cell voltage of the downstream electrolyzer is constant at 1.0 to 1.2 V, and as in the case of the upstream electrolyzer, a luggage tube was placed and the anode electrode potential was measured. It was 0.20V, 10V at the center and 0.14V at the top.

Next, after the 24-hour test, the cell was disassembled and the presence or absence of dissolution of the anode was investigated. As a result, it was found that dissolution of nickel anode did not occur in both the upstream electrolytic cell and the downstream electrolytic cell.

[Example 2] Using the two-stage electrolytic cell used in Example 1 and changing the electrolytic current in the upstream electrolytic cell and the downstream electrolytic cell as follows, under the same operating conditions as in Example 1, Manufactured.

That is, an electric current of 10 OA (current density of 10 kA / m ² at the diaphragm) is supplied to the upstream electrolytic cell, and a current of 2 OA (current density of 2 kΑΖιη ² at the diaphragm) is supplied to the downstream electrolytic cell. A polysulfite digestion solution was synthesized by performing constant current electrolysis, and the cell voltage and anode potential of each electrolytic cell were measured, and the solution immediately after the two-stage electrolysis was sampled, as in the comparative example. Sulfur polysulfide, Na ₂ S form sulfur, and thiosulfate ion were analyzed and quantified.

Quantitative values of the concentrations of various sulfur compounds and cell voltages were as follows. The composition of the polysulfide cooking liquor was 9.6 gZL for sulfur polysulfide, 6.2 gZL for Na ₂ S-form sulfur, and 0.20 gZL for added thiosulfate ions in terms of sulfur atoms. The average value of X of the polysulfide ion (S-) is 2.5, and the current efficiency during that period is 96%, assuming no nickel elution, and the selectivity is 98%. there were.

The average cell voltage of the upstream electrolytic cell was constant at 1.8 to 2.0 V. The anode electrode potential was measured. The voltage was +0.01 V at the bottom of the cell, +0.01 V at the center, and +0.18 V at the top. The average cell voltage of the downstream electrolyzer is constant at 0.8 to 1.0 V, and as in the case of the upstream electrolyzer, a luggage tube was placed and the anode electrode potential was measured. 30V, -0.2V at the center and -0.2V at the top.

Next, after the 24-hour test, the cell was disassembled and the presence or absence of dissolution of the anode was investigated. As a result, it was found that dissolution of nickel oxide did not occur in both the upstream electrolytic cell and the downstream electrolytic cell. Industrial applicability

The present invention provides a method for obtaining a high concentration of sulfur polysulfide from a sulfide ion in a solution by an electrolysis method. Produce high selectivity and low power with extremely low production The purpose is to: Another object of the present invention is to provide a method capable of producing a polysulfide cooking liquor under conditions of low pressure loss in the electrolysis operation.

In the production method of the present invention, while preventing the anode material of the electrode material used for the anode from being dissolved, by-products of thiosulfate ions are extremely small, and the cooking liquor containing a high concentration of sulfur polysulfide is maintained at a high selectivity and high. It can be manufactured with current efficiency. By using the polysulfide cooking liquor thus obtained for cooking, the pulp yield can be effectively increased.

Claims

The scope of the claims

1. An electrolytic chamber having an anode chamber in which an anode is arranged, a force-sword chamber in which a force sword is arranged, and a diaphragm separating the anode chamber and the cathode chamber, and a solution containing sulfuric acid is continuously supplied to the anode chamber. A method for producing polysulfide by subjecting it to electrolytic oxidation while flowing into a cell, wherein the distribution of electrolytic conditions is imparted in the flow direction of the solution in the electrolytic cell (2).

2. The method according to claim 1, wherein two or more electrolytic cells are arranged in series in the flow of the sulfide-containing solution, and the electrolytic conditions of the upstream electrolytic cell and the electrolytic cells of the downstream electrolytic cell are different. Method for producing polysulfide.

3. There are two electrolyzers, the current density on the anode surface of the upstream electrolyzer is greater than the current density on the anode surface of the downstream electrolyzer, and the upstream electrolyzer current density 0 at the anode surface. 0 0 5 to 2 0 k AZM is ^2, claim 2 current density at the anode surface of the electrolytic cell of the lower stream side is 0. 0 0 1 to 1 5 k AZM ² A method for producing the polysulfide according to the above.

4. There are two electrolyzers, and electrolysis is performed so that the conversion ratio of sulfide in the solution is 10 to 72% in the upstream electrolyzer, and the electrolysis is performed in the solution in the downstream electrolyzer. 4. The method for producing a polysulfide according to claim 2, wherein the electrolysis is performed so that the conversion of the sulfide is 25 to 75%.

5. There are two electrolytic cells, the anode surface area per unit area of the upstream electrolytic cell diaphragm is smaller than the anode surface area per unit area of the downstream electrolytic cell diaphragm, and The surface area is 2 to 100 m ² / m ² per unit area of the diaphragm, and the surface area of the downstream anode is 10 to 500 O m ² / m ² per unit area of the diaphragm. 4. The method for producing polysulfide according to 1.

6. There are two electrolyzers, and the flow rate of the sulfide-containing solution in the upstream electrolyzer is smaller than the flow rate of the sulfide-containing solution in the downstream electrolyzer, and the upstream electrolysis is performed. The flow rate of the sulfide-containing solution in the cell is 0.5 to 20 cmZ seconds, and the flow rate of the sulfide-containing solution in the downstream electrolytic cell is 1 to 30 cmZ seconds. Item 2-5, the method for producing a polysulfide according to item 1.

7. The method for producing a polysulfide according to any one of claims 2 to 6, wherein there are two electrolytic cells, the anode on the upstream side is a porous nickel body, and the anode on the downstream side is a porous carbon body.

8. The method for producing a polysulfide according to claim 1, wherein the surface of the anode is nickel or a nickel alloy containing 50% by weight or more of nickel.