METHOD FOR PURIFYING HYDROGEN SULFIDE AND METHOD FOR PRODUCING LITHIUM SULFIDE

Abstract

A hydrogen sulfide purification method includes removing a lithium raw material by using a cyclone, from a mixed gas containing unreacted hydrogen sulfide and the lithium raw material which is generated in a process of producing lithium sulfide by a reaction of hydrogen sulfide and the lithium raw material.

Description

TECHNICAL FIELD

The present invention relates to a hydrogen sulfide purification method, a lithium sulfide production method, a hydrogen sulfide purification apparatus, and a lithium sulfide production apparatus.

BACKGROUND ART

Lithium sulfide (Li2S) is used as, for example, a solid electrolyte of a lithium secondary battery. As a lithium sulfide production method, for example, a production method of reacting lithium hydroxide or the like as a lithium raw material with hydrogen sulfide in a disk dryer (for example, see Patent Literature 1) is known.

A sulfurization reaction between the lithium raw material and a hydrogen sulfide gas can be represented by the following formulae (1) to (3), for example.

2LiOH+H₂S→Li₂S+2H₂O   (1)

Li₂CO₃+H₂S→Li₂S+H₂O+CO₂   (2)

Li₂O+H₂S→Li₂S+H₂O   (3)

Further, for sulfur recovery in which hydrogen sulfide is recovered as elemental sulfur, the Claus process is well known. In the Claus process, the hydrogen sulfide is partially combusted with air in a reaction furnace to generate a mixed gas containing 1 volume of sulfur dioxide per 2 volumes of hydrogen sulfide, the mixed gas is passed through a catalyst bed filled with a catalyst such as natural bauxite, activated alumina, or titanium dioxide to generate vaporous elemental sulfur, and the vaporous sulfur is recovered as molten sulfur by a cooling operation.

A reaction in the reaction furnace and the catalyst bed can be represented by the following formulae (i) and (ii).

Reaction furnace: 3H₂S+3/2O₂→2H₂S+SO₂+H₂O   (i)

Catalyst bed: 2H₂S+SO₂→3S+2H₂O   (ii)

CITATION LIST

Patent Literature

Patent Literature 1: JP2017-222567A

SUMMARY OF INVENTION

Technical Problem

However, in the sulfurization reaction represented by the formulae (1) to (3), when unreacted H₂S remaining without being involved in the sulfurization reaction is subjected to sulfur recovery by the Claus process, there is a problem that a Claus catalyst contributing to the reaction represented by the formula (ii) is poisoned.

As a result of studies by the present inventors, it has been found that the poisoning of the Claus catalyst is caused by the lithium raw material contained in the unreacted H₂S. For example, in the technique disclosed in Patent Literature 1, a particle diameter of the lithium raw material is adjusted to 0.1 mm or more and 1.5 mm or less from the viewpoint of reaction efficiency and the like, but such finely powdered particles are easily diffused into the unreacted H₂S in a disk dryer, and as a result, a finely powdered lithium raw material is mixed into the unreacted H₂S.

Further, when the finely powdered lithium raw material and moisture coexist, there is another problem that a metal pipe or the like is corroded.

Therefore, an object of the present invention is to provide a hydrogen sulfide purification method that can prevent poisoning of a Claus catalyst and preventing corrosion of a metal pipe during sulfur recovery using unreacted hydrogen sulfide which is generated in a process of producing lithium sulfide by a reaction of hydrogen sulfide and a lithium raw material.

Solution To Problem

The present invention is as follows.

• • (1) A hydrogen sulfide purification method including removing a lithium raw material by using a cyclone, from a mixed gas containing unreacted hydrogen sulfide and the lithium raw material which is generated in a process of producing lithium sulfide by a reaction of hydrogen sulfide and the lithium raw material.

An aspect of the present invention also provides a hydrogen sulfide purification method and a lithium sulfide production method described in the following (2) to (4).

• • (2) The hydrogen sulfide purification method according to (1), in which moisture in the mixed gas from which the lithium raw material has been removed is 10 mass % or less.
  • (3) A lithium sulfide production method including reacting hydrogen sulfide containing the hydrogen sulfide obtained by the hydrogen sulfide purification method according to (1) or (2) with a lithium raw material to produce lithium sulfide.
  • (4) A lithium sulfide production method including reacting a lithium raw material including the lithium raw material purified by the hydrogen sulfide purification method according to (1) or (2) with hydrogen sulfide to produce lithium sulfide.

Advantageous Effects of Invention

According to an aspect of the present invention, the lithium raw material is removed from the mixed gas containing the unreacted hydrogen sulfide and the lithium raw material during sulfur recovery using the unreacted hydrogen sulfide which is generated in a process of producing lithium sulfide by the reaction of the hydrogen sulfide and the lithium raw material. Therefore, it is possible to provide a hydrogen sulfide purification method capable of preventing poisoning of a Claus catalyst and preventing corrosion of a metal pipe.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a reaction tank for explaining a lithium sulfide producing process and a lithium sulfide generation unit.

FIG. 2 is a schematic view for explaining a process and an apparatus for recovering a mixed gas containing unreacted hydrogen sulfide and a lithium raw material and removing the lithium raw material to purify the hydrogen sulfide.

FIG. 3 is a schematic view for explaining a cyclone portion as a raw material separator.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in more detail.

A hydrogen sulfide purification method according to an aspect of the present invention includes removing a lithium raw material using a cyclone from a mixed gas containing unreacted hydrogen sulfide and the lithium raw material, which is generated in a process of producing lithium sulfide by a reaction of hydrogen sulfide and the lithium raw material.

A hydrogen sulfide purification apparatus for carrying out the hydrogen sulfide purification method according to one aspect of the present invention includes: a lithium sulfide generation unit configured to generate lithium sulfide by reacting hydrogen sulfide with a lithium raw material; a mixed gas recovery unit configured to recover a mixed gas containing unreacted hydrogen sulfide and a lithium raw material in the lithium sulfide generation unit; and a hydrogen sulfide purification unit configured to purify the hydrogen sulfide by removing the lithium raw material from the mixed gas using a cyclone.

As described above, a sulfurization reaction of the lithium raw material and a hydrogen sulfide gas is used for production of lithium sulfide, and the sulfurization reaction can be represented by the following formulae (1) to (3), for example. In the following formula (1), LiOH is described as the lithium raw material, but the present invention is not limited thereto.

2LiOH+H₂S→Li₂S+2H₂O   (1)

Li₂CO₃+H₂S→Li₂S+H₂O+CO₂   (2)

Li₂O+H₂S→Li₂S+H₂O   (3)

Here, in the mixed gas containing the unreacted hydrogen sulfide and the lithium raw material according to the present invention, the unreacted hydrogen sulfide means unreacted hydrogen sulfide which remains without being involved in the sulfurization reaction represented by the formulae (1) to (3). The lithium raw material means lithium sulfide (Li₂S) and other lithium compounds generated in the process of producing lithium sulfide.

Next, the process of producing lithium sulfide by the reaction of the hydrogen sulfide and the lithium raw material (a lithium sulfide producing process), and a lithium sulfide generation unit that generates lithium sulfide by a reaction of hydrogen sulfide and a lithium raw material will be described. The lithium sulfide producing process and the lithium sulfide generation unit are known, and examples thereof include those disclosed in JP2017-222567A (Patent Literature 1) and JP2016-150859A.

Specifically, in the lithium sulfide producing process and the lithium sulfide generation unit, a lithium raw material is continuously or discontinuously supplied into a heated reaction tank, and the lithium raw material is moved in a certain direction in the reaction tank. Further, in the lithium sulfide producing process and the lithium sulfide generation unit, a hydrogen sulfide gas is supplied into the reaction tank continuously or discontinuously, and the lithium raw material is reacted with the hydrogen sulfide gas to continuously or discontinuously produce lithium sulfide.

Hydrogen Sulfide

Hydrogen sulfide generally reacts with the lithium raw material as a hydrogen sulfide gas to generate lithium sulfide. The hydrogen sulfide gas may be a gas containing only hydrogen sulfide, or may be a gas containing hydrogen sulfide as a main component and other gas components. Here, the main component means a component having the largest content in the gas, and is, for example, 50 vol % or more. In an aspect of the present invention, in order to prevent rapid occurrence of the sulfurization reaction, for example, an inert gas may be mixed with the hydrogen sulfide gas to lower a partial pressure of the hydrogen sulfide.

From this viewpoint, a concentration of the hydrogen sulfide gas is preferably 10 vol % to 100 vol %. The concentration of the hydrogen sulfide gas of 100 vol % means a gas containing only the hydrogen sulfide gas, that is, a pure gas. The case where the concentration of the hydrogen sulfide gas is less than 100 vol % means a mixed gas of the hydrogen sulfide gas and an inert gas such as Ar or nitrogen or a reducing gas such as hydrogen.

From the viewpoint of appropriately maintaining a gas flow rate in the reaction tank while maintaining reactivity with the lithium raw material, the concentration of the hydrogen sulfide gas is preferably 10 vol % to 100 vol %, more preferably 20 vol % or more or 90 vol % or less, and particularly preferably 30 vol % or more or 80 vol % or less.

Lithium Raw Material

The lithium raw material is a raw material serving as a lithium source of lithium sulfide, and examples thereof include lithium hydroxide, lithium carbonate, and lithium oxide. Among these, the lithium hydroxide is preferable from the viewpoint of causing a sulfurization reaction at a low temperature and having excellent stability.

Sulfurization Reaction

When the lithium raw material and the hydrogen sulfide gas supplied into the reaction tank are brought into contact with each other, a sulfurization reaction represented by the formulae (1) to (3) occurs, and lithium sulfide (Li₂S) as a main product and water (H₂O) as a by-product are generated.

When the lithium raw material is brought into contact with the hydrogen sulfide gas in a sufficiently heated state, the reaction further proceeds.

At this time, the lithium raw material is preferably heated to a temperature range in which the lithium raw material does not melt.

Reaction Tank

The reaction tank is a facility that provides a space in which the lithium raw material and the hydrogen sulfide gas react, and the shape and size thereof are not limited. An outer shape of the reaction tank is, for example, a rectangular parallelepiped shape, a cylindrical shape, or a polygonal columnar shape and is not limited. The reaction tank may include a stirrer that promotes the reaction of the lithium raw material and the hydrogen sulfide gas.

Heating of Reaction Tank

In the lithium sulfide producing process, it is preferable to heat an inside of the reaction tank, particularly a portion with which the lithium sulfide is in contact during movement, thereby heating the lithium raw material moving in the reaction tank. The lithium raw material in a sufficiently heated state can be brought into contact with the hydrogen sulfide gas to promote the sulfurization reaction.

FIG. 1 is a schematic view of a reaction tank 11 for explaining the lithium sulfide producing process and the lithium sulfide generation unit.

Regarding heating the reaction tank 11, as shown in FIG. 1, an intermediate region 13 of the reaction tank 11 as viewed in a moving direction of a lithium raw material 12 is preferably heated by a heating unit 14.

By heating in this manner, as shown in FIG. 1, in view of a positional relationship in the movement direction of the lithium raw material 12, the intermediate region 13 in the reaction tank 11 can be set as a region for directly heating the reaction tank 11, and both sides of the intermediate region 13, that is, an upstream region and a downstream region, specifically an inner wall surface of the reaction tank 11 in the regions can be set as a heating region in which a temperature is raised to 100° C. or higher. In FIG. 1, the left side is the upstream side, and the right side is the downstream side.

At this time, from the viewpoint of promoting the sulfurization reaction, the temperature of the inner wall surface of the reaction tank 11 in the intermediate region 13 is preferably 200° C. to 450° C., and particularly preferably 300° C. or higher or 450° C. or lower.

Since the temperature of the inner wall surface of the reaction tank 11 in the intermediate region 13 can be considered to be substantially the same as a temperature of the lithium raw material 12, the sulfurization reaction can be sufficiently promoted when the temperature of the inner wall surface of the reaction tank 11 in the intermediate region 13 is 200° C. to 450° C.

Supply of Lithium Raw Material Into Reaction Tank and Movement

In the lithium sulfide producing process and the lithium sulfide generation unit, as shown in FIG. 1, the lithium raw material 12 is continuously supplied into the reaction tank 11 and moved in a certain direction in the reaction tank 11.

In addition, the direction in which the lithium raw material 12 is moved in the reaction tank 11 is not limited, for example, a horizontal direction, a vertical direction, a rotation direction, a rotation axis direction, a length direction of the reaction tank 11, and the like. For example, as shown in FIG. 1, the lithium raw material 12 can be moved in the length direction of the reaction tank 11.

Supply of Hydrogen Sulfide Gas Into Reaction Tank and Movement

In the lithium sulfide producing process and the lithium sulfide generation unit in the embodiment shown in FIG. 1, hydrogen sulfide 15 is continuously supplied into the reaction tank 11.

In the lithium sulfide producing process and the lithium sulfide generation unit, as shown in FIG. 1, the hydrogen sulfide 15 is allowed to flow from downstream to upstream along a direction opposite to the movement direction of the lithium raw material 12 in the reaction tank 11.

In the lithium sulfide producing process and the lithium sulfide generation unit, a movement direction of the hydrogen sulfide 15 may be the same as the movement direction of the lithium raw material 12.

At this time, a flow rate of the hydrogen sulfide 15 in the reaction tank 11 is not limited.

Furthermore, in the lithium sulfide producing process and the lithium sulfide generation unit, as shown in FIG. 1, the hydrogen sulfide 15 is preferably supplied into the reaction tank 11 from downstream of a position where the lithium raw material 12 is supplied into the reaction tank 11 in the positional relationship in the movement direction of the lithium raw material 12.

In the positional relationship in the movement direction of the lithium raw material 12, a supply position of the hydrogen sulfide 15 may be provided in the heating region (upstream) or the intermediate region 13.

Exhaust

In the lithium sulfide producing process and the lithium sulfide generation unit, as shown in FIG. 1, water vapor (H₂O) and carbon dioxide (CO₂), which are by-products generated by the sulfurization reaction, and further unreacted hydrogen sulfide gas and the like are exhausted 17 to an outside of the reaction tank 11.

The exhausted unreacted hydrogen sulfide gas can be recovered as elemental sulfur by the Claus process. However, as described above, the exhausted unreacted hydrogen sulfide gas contains a finely powdered lithium raw material, and thus there are problems that the lithium raw material poisons the Claus catalyst and corrodes a metal pipe and the like when the lithium raw material exists together with moisture.

Therefore, an aspect of the present invention includes a process and an apparatus for recovering a mixed gas containing unreacted hydrogen sulfide and a lithium raw material and removing the lithium raw material to purify hydrogen sulfide. Specific methods and means will be described below.

Recovery of Lithium Sulfide

As shown in FIG. 1, the lithium sulfide (Li₂S), which is a main product generated by the sulfurization reaction, is preferably moved to downstream and recovered in a lithium sulfide recovery tank 18.

When the lithium sulfide (Li₂S) is recovered and stored in the lithium sulfide recovery tank 18, a temperature of an inner wall surface of the lithium sulfide recovery tank 18 is preferably heated to 100° C. or higher.

The water as a reaction by-product is condensed in the lithium sulfide recovery tank 18, and the lithium sulfide as a reaction product reacts with the condensed water to generate lithium hydroxide, which may reduce the purity of the lithium sulfide. On the other hand, if the inner wall surface of the lithium sulfide recovery tank 18 is heated as described above, the moisture in the lithium sulfide recovery tank 18 can be gasified so that the moisture no longer exists as water (liquid). Furthermore, the moisture in the lithium sulfide recovery tank 18 can be volatilized, and thus it is possible to prevent the recovered lithium sulfide from aggregating or adhering to the inner wall surface of the lithium sulfide recovery tank 18.

Furthermore, an inert gas may be supplied into the lithium sulfide recovery tank 18. Accordingly, the moisture can be discharged to the outside of the lithium sulfide recovery tank 18 together with the inert gas.

Next, the process and the apparatus for recovering a mixed gas containing unreacted hydrogen sulfide and a lithium raw material and removing the lithium raw material to purify hydrogen sulfide according to an aspect of the present invention will be described.

FIG. 2 is a schematic view for explaining the process and the apparatus for recovering a mixed gas containing unreacted hydrogen sulfide and a lithium raw material and removing the lithium raw material to purify hydrogen sulfide.

In FIG. 2, the mixed gas containing the unreacted hydrogen sulfide gas and the lithium raw material exhausted by the lithium sulfide producing process and the lithium sulfide generation unit described in FIG. 1 is recovered in a raw material separator 10, the lithium raw material is removed from the mixed gas by the hydrogen sulfide purification unit provided in the raw material separator 10, and thereby the hydrogen sulfide is purified.

FIG. 3 is a schematic view for explaining the hydrogen sulfide purification unit provided in the raw material separator 10.

In FIG. 3, a cyclone 104 as the raw material separator 10 mainly includes a mixed gas introduction port 102 and a gas exhaust port 116 for exhausting purified hydrogen sulfide gas. A recovered lithium raw material 108 is discharged via a storage tank (not shown). The gas exhaust port 116 may have a demister.

Next, an operation will be described.

A mixed gas 101 containing the unreacted hydrogen sulfide gas and the lithium raw material exhausted by the lithium sulfide producing process and the lithium sulfide generation unit described in FIG. 1 is introduced into the raw material separator 10 from the mixed gas introduction port 102.

Since the mixed gas 101 contains moisture, a temperature of the mixed gas is preferably adjusted to 100° C. to 220° C., and more preferably adjusted to 140° C. to 180° C. By setting the temperature of the mixed gas to 100° C. or higher, condensation of moisture in the raw material separator 10 can be prevented, and by setting the temperature of the mixed gas to 220° C. or lower, the cost of components of the raw material separator 10 can be reduced.

In the cyclone 104, the recovered lithium raw material 108 and hydrogen sulfide gas 118 are separated using gravity and centrifugal force. A diameter of the mixed gas introduction port 102 is preferably smaller than a diameter of the gas exhaust port 116. That is, a linear velocity of the mixed gas 101 at the introduction port 102 is preferably larger than a linear velocity of the hydrogen sulfide gas 118 at the gas exhaust port 116.

As the demister, a known demister can be used, and the demister is not particularly limited. For example, examples thereof include a member in which a three-dimensional mesh structure made of a metal wire, a resin, a glass fiber, or the like is laminated for several layers to form a mat shape in order to increase a contact surface with a fluid while maintaining a small pressure loss.

The purified hydrogen sulfide gas 118 was accommodated in a purified hydrogen sulfide gas accommodation unit (not shown) provided outside the raw material separator 10 via the gas exhaust port 116. A moisture concentration of the purified hydrogen sulfide gas 118 is preferably 10 mass % or less, and more preferably 8 mass % or less.

The purified hydrogen sulfide gas and the recovered lithium raw material can be supplied to the lithium sulfide generation unit as shown in FIG. 2 and reused in the lithium sulfide producing process. In the lithium sulfide producing process, only the purified hydrogen sulfide gas and the recovered lithium raw material may be used, or a new hydrogen sulfide gas or lithium raw material may be additionally mixed and used.

Therefore, according to another aspect of the present invention, provided is a lithium sulfide production apparatus including: a lithium sulfide generation unit configured to generate lithium sulfide by reacting hydrogen sulfide with a lithium raw material; a mixed gas recovery unit configured to recover a mixed gas containing unreacted hydrogen sulfide and a lithium raw material in the lithium sulfide generation unit; a hydrogen sulfide purification unit configured to purify hydrogen sulfide by removing the lithium raw material from the mixed gas; and a hydrogen sulfide supply unit configured to supply the hydrogen sulfide obtained by the hydrogen sulfide purification unit to the lithium sulfide generation unit.

Alternatively, the present invention provides a lithium sulfide production apparatus including: a lithium sulfide generation unit configured to generate lithium sulfide by reacting hydrogen sulfide with a lithium raw material; a mixed gas recovery unit configured to recover a mixed gas containing unreacted hydrogen sulfide and a lithium raw material in the lithium sulfide generation unit; a hydrogen sulfide purification unit configured to purify hydrogen sulfide by removing the lithium raw material from the mixed gas; and a lithium raw material supply unit configured to supply the lithium raw material recovered by the hydrogen sulfide purification unit to the lithium sulfide generation unit.

Although various embodiments have been described above with reference to the drawings, it is needless to say that the present invention is not limited to such examples. It is obvious for a person skilled in the art that various modifications and variations can be made within the category described in the scope of claims and it is understood that such modifications and variations naturally belong to the technical scope of the present invention. Further, the components described in the above embodiment may be combined in any manner without departing from the spirit of the invention.

The present application is based on a Japanese Patent Application (No. 2022-128251) filed on Aug. 10, 2022, contents of which are incorporated herein by reference.

REFERENCE SIGNS LIST

• • 10 raw material separator
  • 11 reaction tank
  • 12 lithium raw material
  • 13 intermediate region
  • 14 heating unit
  • 15 hydrogen sulfide
  • 17 exhaust
  • 18 lithium sulfide recovery tank
  • 101 mixed gas
  • 102 mixed gas introduction port
  • 104 cyclone
  • 108 recovered lithium raw material
  • 116 gas exhaust port
  • 118 hydrogen sulfide gas

Claims

1. A hydrogen sulfide purification method comprising removing a lithium raw material by using a cyclone, from a mixed gas comprising unreacted hydrogen sulfide and the lithium raw material which is generated in a process of producing lithium sulfide by a reaction of hydrogen sulfide and the lithium raw material.

2. The hydrogen sulfide purification method according to claim 1, wherein moisture in the mixed gas from which the lithium raw material has been removed is 10 mass % or less.

3. A lithium sulfide production method comprising reacting hydrogen sulfide comprising the hydrogen sulfide obtained by the hydrogen sulfide purification method according to claim 1 with a lithium raw material to produce lithium sulfide.

4. A lithium sulfide production method comprising reacting a lithium raw material comprising the lithium raw material purified by the hydrogen sulfide purification method according to claim 1 with hydrogen sulfide to produce lithium sulfide.

5. A lithium sulfide production method comprising reacting hydrogen sulfide comprising the hydrogen sulfide obtained by the hydrogen sulfide purification method according to claim 2 with a lithium raw material to produce lithium sulfide.

6. A lithium sulfide production method comprising reacting a lithium raw material comprising the lithium raw material purified by the hydrogen sulfide purification method according to claim 2 with hydrogen sulfide to produce lithium sulfide.