U.S. patent application number 12/513030 was filed with the patent office on 2010-03-04 for process for producing metallic lithium.
This patent application is currently assigned to Santoku Corporation. Invention is credited to Hiroshi Miyamoto, Eiji Nakamura, Hiroaki Takata, Yukihiro Yokoyama.
Application Number | 20100051470 12/513030 |
Document ID | / |
Family ID | 39344325 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100051470 |
Kind Code |
A1 |
Nakamura; Eiji ; et
al. |
March 4, 2010 |
PROCESS FOR PRODUCING METALLIC LITHIUM
Abstract
Provided is a safe and efficient method for producing lithium
metal which facilitates efficient production of anhydrous lithium
chloride without corrosion of the system materials by chlorine gas
or molten lithium carbonate, and which allows production of lithium
metal by molten salt electrolysis of the produced anhydrous lithium
chloride as a raw material. The method includes the steps of (A)
contacting and reacting lithium carbonate and chlorine gas in a dry
process to produce anhydrous lithium chloride, and (B) subjecting
the raw material for electrolysis containing the anhydrous lithium
chloride to molten salt electrolysis under such conditions as to
produce lithium metal, wherein the chlorine gas generated by the
molten salt electrolysis in step (B) is used as the chlorine gas in
step (A) to continuously perform steps (A) and (B).
Inventors: |
Nakamura; Eiji; (Kobe-shi,
JP) ; Takata; Hiroaki; (Kobe-shi, JP) ;
Yokoyama; Yukihiro; (Kobe-shi, JP) ; Miyamoto;
Hiroshi; (Kobe-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
Santoku Corporation
Kobe-shi, Hyogo
JP
|
Family ID: |
39344325 |
Appl. No.: |
12/513030 |
Filed: |
November 2, 2007 |
PCT Filed: |
November 2, 2007 |
PCT NO: |
PCT/JP2007/071374 |
371 Date: |
May 29, 2009 |
Current U.S.
Class: |
205/407 |
Current CPC
Class: |
C01D 15/04 20130101;
C25C 3/02 20130101 |
Class at
Publication: |
205/407 |
International
Class: |
C25C 3/02 20060101
C25C003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 2, 2006 |
JP |
2006-298328 |
Claims
1. A method for producing lithium metal comprising the steps of:
(A) contacting and reacting lithium carbonate and chlorine gas in a
dry process to produce anhydrous lithium chloride; and (B)
subjecting a raw material for electrolysis comprising said
anhydrous lithium chloride obtained from step (A) to molten salt
electrolysis under such conditions as to produce lithium metal,
wherein chlorine gas generated by said molten salt electrolysis in
step (B) is used as said chlorine gas in step (A) to continuously
perform steps (A) and (B).
2. The method according to claim 1, wherein said contacting and
reacting in step (A) are carried out at a temperature of not lower
than 350.degree. C. and lower than 506.degree. C.
3. The method according to claim 1, wherein said lithium carbonate
is in the form of powder or granule prepared by granulating
powder.
4. The method according to claim 3, wherein D90 (particle size at
which cumulative volume fraction is 90%) of said lithium carbonate
in powder form is not more than 0.70 mm.
5. The method according to claim 3, wherein particle size
distribution of said lithium carbonate in granular form is in the
range of 0.1 to 5 mm.
6. The method according to claim 1, wherein said lithium carbonate
has a moisture content of not higher than 1 mass %.
7. The method according to claim 1, wherein said contacting and
reacting in step (A) are carried out under stirring.
8. The method according to claim 2, wherein said lithium carbonate
is in the form of powder or granule prepared by granulating
powder.
9. The method according to claim 2, wherein said lithium carbonate
has a moisture content of not higher than 1 mass %.
10. The method according to claim 3, wherein said lithium carbonate
has a moisture content of not higher than 1 mass %.
11. The method according to claim 4, wherein said lithium carbonate
has a moisture content of not higher than 1 mass %.
12. The method according to claim 5, wherein said lithium carbonate
has a moisture content of not higher than 1 mass %.
13. The method according to claim 8, wherein said lithium carbonate
has a moisture content of not higher than 1 mass %.
14. The method according to claim 2, wherein said contacting and
reacting in step (A) are carried out under stirring.
15. The method according to claim 3, wherein said contacting and
reacting in step (A) are carried out under stirring.
16. The method according to claim 4, wherein said contacting and
reacting in step (A) are carried out under stirring.
17. The method according to claim 5, wherein said contacting and
reacting in step (A) are carried out under stirring.
18. The method according to claim 6, wherein said contacting and
reacting in step (A) are carried out under stirring.
19. The method according to claim 8, wherein said contacting and
reacting in step (A) are carried out under stirring.
Description
FIELD OF ART
[0001] The present invention relates to a method for producing
lithium metal by molten salt electrolysis, in particular, a method
for producing lithium metal which allows continuous operation of
molten salt electrolysis along with the production of anhydrous
lithium chloride as a raw material for the electrolysis.
BACKGROUND ART
[0002] Anhydrous lithium chloride is used as a raw material in
molten salt electrolysis for production of lithium metal, or a
desiccant. As a method for producing anhydrous lithium chloride,
for example, Patent Publication 1 discloses reaction of lithium
hydroxide with hydrochloric acid for producing a high purity
product, and Patent Publication 2 discloses reaction of lithium
carbonate suspended in water with chlorine gas in the presence of
an iron-nickel catalyst.
[0003] Both of these methods inevitably include dehydrating and
drying of the resulting lithium chloride for obtaining anhydrous
lithium chloride, which requires additional costs for operation and
facility.
[0004] Patent Publication 3 discloses a method for producing
anhydrous lithium chloride by reacting chlorine gas with lithium
hydroxide. The raw material lithium hydroxide, which is strongly
alkaline, irritates eyes, skin, and mucosa, and is easily stirred
up when, in particular, the reaction is performed in a dry process,
which causes difficulties in handling and additional costs for
operation and facility.
[0005] When lithium carbonate in the form of molten salt, which is
highly corrosive to metal materials, is used in the production of
anhydrous lithium chloride, severe limitation is imposed on the
materials which may be used for the reaction vessel or piping
(Non-patent Publications 1 and 2). In addition, the heat resistance
of the reaction vessel should also be considered in view of the
high temperature of the molten salt. On the other hand, for the
production of anhydrous lithium chloride using chlorine gas, which
is also corrosive, there are hardly any metal materials that could
be used in the chlorine gas atmosphere beyond 500.degree. C.
Instead, ceramics and the like materials which withstand high
temperature, corrosive environment, need to be employed for the
reaction vessel and piping.
[0006] Molten salt electrolysis has been employed for producing
lithium metal, and attempts have conventionally been made to use
inexpensive lithium carbonate as a lithium source. However, lithium
carbonate is not in use in commercial production at present because
the graphite anode-consuming electrolytic reaction
(2Li.sub.2CO.sub.3+C.fwdarw.4Li+3CO.sub.2) is the main reaction,
and the lithium metal resulting from the electrolysis reacts with
lithium carbonate (Li.sub.2CO.sub.3+4Li.fwdarw.3Li.sub.2O+C) in the
electrolyte to obstruct continuous electrolysis.
[0007] In view of the above problems, it is the current practice to
produce lithium metal from anhydrous lithium chloride as a lithium
source by molten salt electrolysis.
[0008] Patent Publication 4 discloses a method of molten salt
electrolysis using anhydrous lithium chloride, wherein lithium
carbonate is introduced onto the surface of the bath around the
anode to cause the reaction
2Li.sub.2CO.sub.3+2Cl.sub.2.fwdarw.4LiCl+2CO.sub.2+O.sub.2, to
thereby generate anhydrous lithium chloride and allow continuous
electrolysis.
[0009] Patent Publication 5 discloses a method of molten salt
electrolysis using anhydrous lithium chloride, wherein lithium
carbonate and charcoal or the like as a carbon source are
simultaneously introduced into the anode compartment to cause the
reaction 2Li.sub.2CO.sub.3+2Cl.sub.2+C.fwdarw.4LiCl+3CO.sub.2, to
thereby prevent consumption of the anode.
[0010] The methods disclosed in Patent Publications 4 and 5 do not
solve the problem of reaction between the lithium metal resulting
from electrolysis and lithium carbonate discussed above. Thus these
methods have difficulties in the control of carbonate concentration
and various problems in operation, such as declined current
efficiency, black powder foam, and short circuit.
[0011] Patent Publication 6 discloses a method including the steps
of extracting a part of a mixed molten salt of the electrolyte
containing anhydrous lithium chloride outside the electrolytic
cell, introducing the extracted molten salt into a chlorinating
furnace, adding lithium carbonate and a chlorinating agent thereto,
reacting the molten lithium carbonate and the chlorinating agent,
and returning the resulting anhydrous lithium chloride to the
electrolytic cell for use as a raw material. This method has
difficulties in controlling the concentration of the electrolyte,
requires circulation facilities, and is not practical in view of
safety.
[0012] Patent Publication 7 discloses an electrolysis method
wherein the anode compartment is separated from the cathode
compartment with a porous electrically nonconductive partition,
lithium carbonate is introduced into the anode compartment, and
only the lithium ions are delivered to the cathode compartment to
deposite lithium metal. This method requires a high temperature,
the current efficiency is low, and the corrosion resistance of the
nonconductive partition should be attended to.
Patent Publication 1: U.S. Pat. No. 4,980,136-A1
Patent Publication 2: RU-2116251-C1
[0013] Patent Publication 3: U.S. Pat. No. 2,968,526-A1 Patent
Publication 4: U.S. Pat. No. 3,344,049-A1
Patent Publication 5: JP-59-200731-A
Patent Publication 6: JP-1-152226-A
[0014] Patent Publication 7: U.S. Pat. No. 4,988,417-A1 Non-patent
Publication 1: "Youyuen Netsugijutsu no Kiso (Basics of Molten Salt
Thermal Technology)", written and edited by The Society of
Molten-Salt Thermal Technology, published by Agne Gijutsu Center
(1993), p 97 Non-patent Publication 2: "Youyuen no Ouyou
(Applications of Molten Salt)", written and edited by Yasuhiko ITO,
published by Industrial Publishing & Consulting, Inc. (2003), p
305
SUMMARY OF THE INVENTION
[0015] It is an object of the present invention to provide a safe
and efficient method for producing lithium metal which facilitates
efficient production of anhydrous lithium chloride without
corrosion of the system materials by chlorine gas or molten lithium
carbonate, which allows production of lithium metal by molten salt
electrolysis of the produced anhydrous lithiumchloride as a raw
material, and which utilizes chlorine gas generated by the molten
salt electrolysis for producing the raw material anhydrous lithium
chloride without discharging the chlorine gas outside the
system.
[0016] According to the present invention, there is provided a
method for producing lithium metal comprising the steps of:
[0017] (A) contacting and reacting lithium carbonate and chlorine
gas in a dry process to produce anhydrous lithium chloride; and
[0018] (B) subjecting a raw material for electrolysis comprising
said anhydrous lithium chloride obtained from step (A) to molten
salt electrolysis under such conditions as to produce lithium
metal;
[0019] wherein chlorine gas generated by said molten salt
electrolysis in step (B) is used as said chlorine gas in step (A)
to continuously perform steps (A) and (B).
[0020] According to the present invention, there is also provided a
method for producing anhydrous lithium chloride comprising the step
of:
[0021] (A) contacting and reacting lithium carbonate and chlorine
gas in a dry process.
[0022] According to the method of the present invention, by means
of step (A), efficient production of anhydrous lithium chloride is
facilitated without causing corrosion of the system materials by
the chlorine gas and the molten lithium carbonate. Then by means of
step (B), lithium metal is produced by molten salt electrolysis of
the anhydrous lithium chloride obtained from step (A) as a raw
material, while the chlorine gas generated by the molten salt
electrolysis is used for producing the raw material anhydrous
lithium chloride without discharging the chlorine gas outside the
system. Thus the method of the present invention is excellently
safe and efficient in producing anhydrous lithium chloride and
lithium metal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a graph showing the relationship between the
reaction temperature and the chlorination ratio of the lithium
carbonate in powder form at various particle sizes (D90).
[0024] FIG. 2 is a sectional pattern diagram of an example of a
system that may be used for the production of anhydrous lithium
chloride in step (A) of the present invention.
[0025] FIG. 3 is a sectional pattern diagram of an example of a
system that may be used for practicing the method for producing
lithium metal according to the present invention.
PREFERRED EMBODIMENTS OF THE INVENTION
[0026] The present invention will now be explained in detail.
[0027] The method of the present invention includes step (A) of
contacting and reacting lithium carbonate and chlorine gas in a dry
process to produce anhydrous lithium chloride. This step (A) allows
efficient production of anhydrous lithium chloride, so that this
step alone may be a method for producing anhydrous lithium
chloride.
[0028] The reaction between the lithium carbonate and the chlorine
gas in step (A) is effected in a dry process, i.e., by contacting
solid lithium carbonate and chlorine gas without a solvent, such as
water. Chlorine gas generated by the molten salt electrolysis in
step (B) to be discussed later may be used here. When step (A)
alone is carried out to produce anhydrous lithium chloride,
chlorine gas supplied from a gas cylinder or the like may be
used.
[0029] The chlorine gas may preferably be at 100% concentration,
but may alternatively be mixed with inert gas, such as argon or
helium. The lithium carbonate may be in any form without
limitation, and preferably in the form of powder, which may further
be granulated.
[0030] The optimum particle size range of the powdered lithium
carbonate for efficient reaction with the chlorine gas in step (A)
was determined through an experiment. In the experiment, reactivity
of lithium carbonate powders having D90's of 0.02 to 0.82 mm with
chlorine gas was determined in the temperature range of 250 to
550.degree. C. D90 represents the particle size at which the
cumulative volume fraction is 90% as measured with a laser
diffraction particle size analyzer (Microtrac IISRA manufactured by
NIKKISO CO., LTD.).
[0031] A vertical furnace having a cylindrical alumina pipe of 50
mm inner diameter was used. A perforated alumina dish having 5 mm
diameter pores at not less than 50% porosity was disposed in the
soaking area in the cylindrical pipe, and an air permeable silica
cloth was placed on the dish. While argon gas was blown up into the
cylindrical pipe at 1.0 L/min, 10 g of lithium carbonate was placed
on the cloth and held in the pipe. When the soaking area in the
pipe reached the objective temperature, the argon gas was replaced
with chlorine gas (3N, 1.0 L/min), and held for 20 minutes. Then
the chlorine gas was replaced with argon gas, and the pipe was
cooled. When the temperature fell to 100 to 150.degree. C., the
reaction product of lithium carbonate and chlorine gas was taken
out, and the chlorination ratio was immediately determined.
According to "Kagaku Daijiten (Comprehensive Dictionary of
Chemistry)" (Kyoritsu Shuppan Co., Ltd., issued Mar. 30, 1960), the
solubility of anhydrous lithium chloride and lithium carbonate in
water is 67 g and 1.54 g, respectively, in 100 g of water at
0.degree. C., and 127.5 g and 0.73 g, respectively, in 100 g of
water at 100.degree. C. Based on this, 10 g of the product of
reaction with chlorine gas was dissolved in 50 g of water, and from
the weight of the collected precipitate, the chlorination ratio
from lithium carbonate to anhydrous lithium chloride was
calculated. The results are shown in FIG. 1.
[0032] From FIG. 1, it is understood that high chlorination ratios
were achieved at reaction temperatures of 350.degree. C. or higher,
and that termination of the reaction in a dry process requires a
temperature below 506.degree. C., which is the eutectic temperature
of the raw material, lithium carbonate, and the product, anhydrous
lithium chloride. Accordingly, the temperature suitable for the
reaction is not lower than 350.degree. C. and lower than
506.degree. C., preferably not lower than 400.degree. C. and lower
than 506.degree. C. Incidentally, X-ray diffraction analysis of the
products produced at temperatures below 506.degree. C. detected
nothing other than lithium carbonate.
[0033] The D90 of the powdered lithium carbonate suitable for the
reaction may be not more than 0.70 mm, preferably not more than
0.40 mm, more preferably not more than 0.10 mm.
[0034] The reaction discussed above is performed in a solid system
without molten lithium carbonate being involved, and at a
temperature lower than 506.degree. C. Thus the problem of corrosion
of the apparatus may be avoided, and even stainless steel, which is
a general-purpose material, may be used for manufacturing the
system with sufficient corrosion resistance.
[0035] In step (A), the reaction of the lithium carbonate with the
chlorine gas may be effected in a fixed, moving, or fluidized bed,
and either in a continuous or batch system.
[0036] In a moving bed system, by blowing the chlorine gas into the
moving lithium carbonate as a counterflow, anhydrous lithium
chloride may be produced continuously as a moving bed, which may be
continuously drawn out or supplied to step (B) to be discussed
later.
[0037] For such a moving bed system, it is preferred to granulate
powdered lithium carbonate into granules of a uniform size and to
stir the reaction system, so that the contact between the lithium
carbonate and the chlorine gas is effected smoothly.
[0038] In step (A), continuous introduction of the lithium
carbonate, reaction with the chlorine gas, and recovery of the
resulting anhydrous lithium chloride may be achieved by stirring
the lithium carbonate in apparatus of a rotary kiln type while the
chlorine gas is blown in a counterflow, or by introducing the
lithium carbonate down into a vertical reaction vessel equipped
with stirring means while the chlorine gas is blown up in a
counterflow. In the latter case, hermetical sealing of the facility
may be secured more easily.
[0039] In the process of continuously introducing the powdered
lithium carbonate into such apparatus, lithium carbonate of a
smaller particle size is advantageous in view of the reaction
speed, but may cause declined air permeability to obstruct
introduction of the chlorine gas into the center of the lithium
carbonate bed, which may inhibit progress of the reaction. In order
to avoid this, investigation was made on the relationship between
the form of the lithium carbonate constituting the moving bed and
the ratio of chlorination with the chlorine gas, to reveal that it
was effective to granulate the lithium carbonate powder into
granules. The particle size distribution of the granulated lithium
carbonate may preferably be in the range of 0.1 to 5 mm. At less
than 0.1 mm, the effect of granulation may not be exhibited
sufficiently, and at more than 5 mm, not only the granulation per
se but also introduction of the chlorine gas into the center of the
resulting granules becomes hard. The particle size distribution may
be controlled by means of a sieve after the granulation.
[0040] The granulation may be carried out by self-granulation, such
as rolling, fluidized-bed, or stirring granulation, or by forced
granulation, such as loosening, compression, extrusion, or
dissolving granulation, among which extrusion granulation is
preferred. The granulation may be carried out with an organic
binder. In this case, the residual carbon will act as an additive
for reduction reaction. The binder may alternatively be water, and
then moisture needs to be removed sufficiently after the
granulation.
[0041] The moisture content of the lithium carbonate in powder or
granular form used as a raw material for step (A) may usually be
not higher than 1 mass %, preferably not higher than 0.3 mass %. At
higher moisture contents, the anhydrous lithium chloride powder
generated in step (A) may be agglomerated and solidified into bulks
as the temperature rises to some extent, even lower than the
melting point. The bulks may cause hanging or decline of gas
permeability in the reaction vessel, which may withhold the
progress of reaction at a low chlorination ratio.
[0042] Referring to FIG. 2, an example of a system in which step
(A) alone may be performed for producing anhydrous lithium chloride
will be explained.
[0043] FIG. 2 is a sectional pattern diagram of an example of a
system in which step (A) may be performed for producing anhydrous
lithium chloride. The system 10 includes a reaction vessel
(chlorinating furnace) 11 for contacting and reacting lithium
carbonate and chlorine gas in a dry process, a hopper 12 for
reserving therein lithium carbonate 12a as a raw material, and a
chlorine gas cylinder 13.
[0044] The reaction vessel 11 may be made of a material which is
resistant to corrosion by hot chlorine gas, for example, Inconel
(registered trademark), stainless steel, or mild steel lined with
ceramics, such as alumina, silica, or mullite.
[0045] The hopper 12 is equipped with a rotary valve 14 for
supplying the lithium carbonate into the reaction vessel 11, and is
connected from above to the reaction vessel 11. The chlorine gas
cylinder 13 is connected from below to the reaction vessel 11 via a
duct 15 made of, for example, stainless steel and equipped with a
valve 15a, for supplying the chlorine gas up into the reaction
vessel 11.
[0046] The reaction vessel 11 is provided with an electric furnace
16 arranged therearound for controlling the reaction temperature,
and a shaft 17a arranged therein having a plurality of stirring
bars 17b for effecting the reaction under stirring, with the shaft
17a being connected to an external motor 17c. The stirring bars 17b
may be of any shape, such as rod, plate, or vane, as long as the
stirring may be effected.
[0047] Below the reaction vessel 11, a stainless steel rotary valve
18 is disposed for discharging the generated anhydrous lithium
chloride out of the system. Above the reaction vessel 11, a duct 19
equipped with a valve 19a and a blower 19b is disposed for
discharging the carbon dioxide gas and oxygen gas generated by the
reaction out of the system. The duct 19 may be made of, for
example, stainless steel, nickel-based alloys, or vinyl
chloride.
[0048] Step (A) may be performed in the system 10 by supplying the
lithium carbonate 12a in the hopper 12 down into the reaction
vessel 11 while the chlorine gas from the chlorine gas cylinder 13
is supplied up into the reaction vessel 11, with the shaft 17a
being rotated by the motor 17c and the temperature inside the
reaction vessel 11 being controlled with the electric furnace 16,
to thereby mix and react the lithium carbonate 12a and the chlorine
gas under stirring.
[0049] Here, the lithium carbonate 12a contacts and reacts with the
chlorine gas in a counter flow manner in the reaction vessel 11,
and the resulting anhydrous lithium chloride is sequentially
discharged out of the system via the rotary valve 18. The supply
rate of the lithium carbonate 12a into the reaction vessel 11 is
controlled by the rotary valve 14, whereas the supply rate of the
chlorine gas is controlled by the valve 15a. Carbon dioxide gas and
oxygen gas resulting from the reaction in the reaction vessel 11
are sucked by the blower 19b with the discharge rate being
controlled with the valve 19a, and discharged out of the
system.
[0050] The method of the present invention includes step (B) of
subjecting the raw material for electrolysis including the
anhydrous lithium chloride obtained from step (A) to molten salt
electrolysis under such conditions as to produce lithium metal.
[0051] In step (B), the specific constructions of the electrolytic
cell, the electrodes, and the electrolyte, as well as the specific
operating conditions, such as cell voltage and current density, for
the molten salt electrolysis, are conventionally well known, and
may suitably be selected with reference to the conventional
methods. In the Examples to be discussed later, an example of the
conditions will be presented.
[0052] According to the method of the present invention, chlorine
gas is generated by the molten salt electrolysis in step (B). By
incorporating the generated chlorine gas as the chlorine gas used
in step (A), steps (A) and (B) may be carried out continuously.
That is, the chlorine gas generated by the molten salt electrolysis
in step (B) is used in carrying out step (A) to generate anhydrous
lithium chloride, which is in turn used in supplementing the
electrolyte, which decreases with the progress of the electrolysis
in step (B). In this way, steps (A) and (B) may be performed
continuously. Here, given that lithium carbonate having the lithium
weight equivalent to that of the anhydrous lithium chloride to be
electrolyzed in step (B) is converted to anhydrous lithium chloride
in step (A), which is then used as the raw material for the
electrolysis in step (B), nominal electrolysis of lithium carbonate
is achieved.
[0053] Yet the reaction occurred in the electrolytic cell is
practically chloride electrolysis, so that problems encountered in
the conventional carbonate electrolysis may be eliminated, such as
anode consumption, black powder foam, and decline of yield due to
reaction of the resulting lithium metal and lithium carbonate. In
addition, use of inexpensive lithium carbonate as the raw material
makes the method remarkably cost effective.
[0054] In the electrolysis operation, production control may
require adjustment of the electrolytic current. The present system
may flexibly respond to the change in operation by employing, as a
part of the anhydrous lithium chloride to be supplemented to the
system, anhydrous lithium chloride that has been prepared by a dry
or wet method outside the electrolytic system, or by introducing
additional chlorine gas from outside the electrolytic system to
produce more anhydrous lithium chloride than that is consumed in
the electrolysis.
[0055] In terms of the chlorine gas, the present invention allows
in principle to form a closed system, so that costs for
environmental protection may be reduced. The continuous
electrolysis allows safe and efficient production of lithium metal
without discharging the chlorine gas outside the system.
[0056] In the method for producing lithium metal according to the
present invention, the anhydrous lithium chloride prepared in a dry
process in step (A) is used as the raw material anhydrous lithium
chloride for the electrolysis. When commercially available,
ordinary anhydrous lithium chloride is used in the electrolysis,
moisture is introduced into the electrolytic cell to cause
generation of hydrogen gas, which leads to small explosion or
abnormal combustion. Thus problems exist in safety, stability, and
production efficiency of the electrolysis operation. On the
contrary, the anhydrous lithium chloride prepared in step (A) of
the present invention has an extremely low moisture content, and
accordingly the electrolysis may be effected without the drawbacks
mentioned above.
[0057] Referring to FIG. 3, an example of a system with which the
method of the present invention may be performed by continuously
carrying out steps (A) and (B), will now be discussed below. In the
following, members already appeared in FIG. 2 are referred to by
the same numbers as in FIG. 2, and further discussion is
eliminated.
[0058] FIG. 3 is a sectional pattern diagram of an example of a
system that may be used for continuously carrying out steps (A) and
(B) to produce lithium metal. The system 20 is basically composed
of the system 10 for carrying out step (A) as discussed with
reference to FIG. 2, and a cell for lithium electrolysis 21
connected thereto. The system 10 has been modified by replacing the
chlorine gas cylinder 13 with a chlorine gas transfer line 22
connecting the lower portion of the reaction vessel 11 and the cell
for lithium electrolysis 21, and by providing a transfer line 23
made of stainless steel for transferring the anhydrous lithium
chloride generated in the reaction vessel 11 to the cell for
lithium electrolysis 21 via a rotary valve 18. Other members of the
system 10 are the same as shown in FIG. 2.
[0059] Referring to FIG. 3, the cell for lithium electrolysis 21
may be a generally used Downs-type cell or a conversion thereof.
The cell 21 is equipped with a graphite electrode as an anode 24
and an iron electrode as a cathode 25, and electrolyte 26 is
introduced therein.
[0060] Steps (A) and (B) may be carried out continuously in the
system 20 by producing anhydrous lithium chloride in the reaction
vessel 11 as in the system 10, supplying the anhydrous lithium
chloride through the rotary valve 18 and transfer line 23 into the
electrolyte 26 in the cell for lithium electrolysis 21, and
effecting electrolysis. For the continuous operation of steps (A)
and (B), as the chlorine gas to be used in the reaction in the
reaction vessel 11, the chlorine gas generated by the molten salt
electrolysis in the cell for lithium electrolysis 21 is transferred
to the reaction vessel 11 through the chlorine gas transfer line 22
during the reaction.
EXAMPLES
[0061] The present invention will now be explained in more detail
with reference to Production Example and Example, which are not
intended to restrict the present invention.
Production Example 1
[0062] Using the system 10 shown in FIG. 2, anhydrous lithium
chloride was produced according to the following process.
[0063] Lithium carbonate in powder form of D90=0.04 mm was
provided, kneaded with water, and granulated in an extrusion
granulator. The granulated powder was dried to the moisture content
of 0.3 mass %, to thereby obtain lithium carbonate 12a in granular
form having the particle size distribution in the range of 0.8 to
1.2 mm.
[0064] Next, the lithium carbonate 12a was chlorinated with 3N
chlorine gas supplied from the chlorine gas cylinder 13. The
reaction vessel 11 was heated with the electric furnace 16 to
create an area of 400.degree. C. to 500.degree. C. over about 1000
mm, wherein the chlorinating reaction was effected. The velocity of
the moving bed was adjusted so that the residence time of the
lithium carbonate 12a in this temperature area was not shorter than
2 hours. During the reaction, the supply rate of the lithium
carbonate 12a from the hopper 12 was 3.5 kg/h in average, and the
discharge rate of the anhydrous lithium chloride was 3.9 kg/h in
average. By the operation for five days, 460 kg of anhydrous
lithium chloride was recovered.
[0065] In the reaction mentioned above, the exhaust gas from the
reaction vessel 11 was mainly composed of carbon dioxide and oxygen
gases. The chlorination ratio from the carbonate to the chloride
was maintained over 95%. Only slight hanging was occurred in the
reaction vessel 11, and continuous operation was permitted. The
resulting anhydrous lithium chloride had a moisture content of less
than 0.1 mass %.
Example 1
[0066] In the system 20 shown in FIG. 3, anhydrous lithium chloride
was produced in accordance with the following process.
[0067] The lithium carbonate 12a was produced in the same way as in
Production Example 1.
[0068] In the cell for lithium electrolysis 21 in the system 20,
molten salt electrolysis was performed at the current of 10 kA and
at the temperature of 460.degree. C., using an electrolyte composed
of 35 to 45 mass % lithium chloride and 55 to 65 mass % potassium
chloride, as the electrolyte 26. Production Example 1 was followed,
except that the chlorine gas generated by the electrolysis was
transferred to the reaction vessel 11 through the chlorine gas
transfer line 22, and the chlorination reaction of the lithium
carbonate 12a was carried out with the velocity of the moving bed
being adjusted so that the residence time of the lithium carbonate
12a in the area at 400.degree. C. to 500.degree. C. was not shorter
than 4 hours. During the reaction, the supply rate of the lithium
carbonate 12a from the hopper 12 was 11.5 kg/h in average, the
discharge rate of the anhydrous lithium chloride was 12.9 kg/h in
average, and 2.1 kg/h in average of lithium metal was recovered
from the cell for lithium electrolysis 21.
[0069] The exhaust gas mainly detected from the reaction vessel 11
was carbon dioxide and oxygen gases, and the chlorination ratio
from the carbonate to the chloride was maintained over 95%. Only
slight hanging was occurred in the reaction vessel 11, and
continuous operation was permitted. The electrolysis in the cell
for lithium electrolysis 21 was effected in the same way as the
ordinary chloride electrolysis, the formation of black powder foam,
which is characteristic of direct electrolysis of carbonate, was
not observed, and remarkable consumption of the anode 24 (graphite
anode) was not observed.
[0070] By this electrolysis for three months, 4.5 t of lithium
metal was produced at the current efficiency of 89% and the working
ratio of 92%. The obtained lithium metal was used as an anode foil
of lithium primary battery, with no problem being observed.
* * * * *