U.S. patent application number 10/311747 was filed with the patent office on 2004-01-22 for method for making anhydrous sodium perchlorate.
Invention is credited to Bossoutrot, Jean-Michel.
Application Number | 20040011663 10/311747 |
Document ID | / |
Family ID | 8851439 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040011663 |
Kind Code |
A1 |
Bossoutrot, Jean-Michel |
January 22, 2004 |
Method for making anhydrous sodium perchlorate
Abstract
The invention concerns a method for making anhydrous sodium
perchlorate whereby an aqueous sodium perchlorate solution,
directly derived from electrolysis of an aqueous sodium chlorate
solution, is subjected to vacuum evaporation. The invention also
concerns anhydrous sodium perchlorate crystals which preserve good
pourability and methods for making them.
Inventors: |
Bossoutrot, Jean-Michel;
(F-69630 Chaponost, FR) |
Correspondence
Address: |
HUNTON & WILLIAMS
INTELLECTUAL PROPERTY DEPARTMENT
1900 K STREET, N.W.
SUITE 1200
WASHINGTON
DC
20006-1109
US
|
Family ID: |
8851439 |
Appl. No.: |
10/311747 |
Filed: |
July 21, 2003 |
PCT Filed: |
May 21, 2001 |
PCT NO: |
PCT/FR01/01553 |
Current U.S.
Class: |
205/474 |
Current CPC
Class: |
C01B 11/18 20130101;
C25B 1/28 20130101; C25B 15/08 20130101 |
Class at
Publication: |
205/474 |
International
Class: |
C25B 001/28 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 20, 2000 |
FR |
00/07847 |
Claims
1. Process for the manufacture of anhydrous sodium perchlorate,
according to which an aqueous sodium perchlorate solution,
originating directly from an electrolysis stage or from a
succession of individual electrolytic stages on an aqueous chlorate
solution of the said metal, is subjected to vacuum evaporation at a
temperature of between 52 and 75.degree. C., preferably of between
60 and 70.degree. C.
2. Process according to claim 1, characterized in that the absolute
pressure is between 1500 and 7000 Pa.
3. Process according to claim 1 or 2, characterized in that the
aqueous sodium perchlorate solution is chosen so that the anhydrous
sodium perchlorate can be isolated directly by crystallization.
4. Process according to claim 3, characterized in that the
composition of the aqueous sodium perchlorate solution lies within
the region of the NaClO.sub.4--NaClO.sub.3--H.sub.2O ternary
diagram delimited by the points: A: 58 g of NaClO.sub.3, 270 g of
NaClO.sub.4 B: 87 g of NaClO.sub.3, 295 g of NaClO.sub.4 C: 280 g
of NaClO.sub.4 D: 300 g of NaClO.sub.4 per 100 g of water.
5. Process according to any one of claims 1 to 4, characterized in
that, on conclusion of the evaporation stage, the suspension of the
anhydrous sodium perchlorate crystals is filtered and then the
crystals are optionally washed with water.
6. Process according to claim 5, characterized in that the
temperature of the aqueous wash liquor is between 55 and 80.degree.
C., preferably between 55 and 65.degree. C.
7. Process according to claim 5 or 6, characterized in that the
filtered anhydrous sodium perchlorate crystals are subsequently
subjected to a drying stage until a residual water content of less
than 0.1% by weight and preferably of less than or equal to 0.05%
by weight is obtained.
8. Process according to claim 5 or 6, characterized in that a
sufficient amount of finely divided silica is added to the filtered
anhydrous sodium perchlorate crystals.
9. Process according to claim 8, characterized in that the amount
of silica added is between 0.05 and 0.5% by weight with respect to
the anhydrous sodium perchlorate crystals.
10. Process according to claim 8 or 9, characterized in that the
silica is a hydrophobic silica.
11. Process according to any one of claims 8 to 10, characterized
in that the specific surface area of the silica is between 100 and
300 m.sup.2/g.
12. Anhydrous sodium perchlorate crystals which are capable of
being obtained according to any one of claims 7 to 11.
Description
[0001] The present invention relates to a process for the
manufacture of anhydrous sodium perchlorate.
[0002] It is known to manufacture sodium perchlorate by
electrolysis of an aqueous chlorate solution of the said metal in a
single electrolytic stage or a succession of individual
electrolytic stages. Reference may be made, on this subject, to
Patents EP 368 767, U.S. Pat. No. 3,518,180 and U.S. Pat. No.
3,475,301.
[0003] Thus, Patent EP 368 767 discloses a continuous process for
the manufacture of sodium perchlorate by electrolysis in a single
stage of an electrolyte (liquid comprising sodium chlorate and
sodium perchlorate in the dissolved state) kept uniform with a
stationary composition, which composition is chosen so that it can
directly deposit, by cooling, perchlorate crystals in a
monohydrate, dihydrate or anhydrous form.
[0004] It is also indicated that, on conclusion of the electrolysis
stage, the aqueous sodium perchlorate solution is crystallized by
cooling or evaporation of water.
[0005] In Example 2 of U.S. Pat. No. 3,518,180, the electrolytic
cell fed with a solution comprising 300 g/l of sodium chloride and
700 g/l of sodium perchlorate produces, at the outlet, a solution
comprising 80 g/l of sodium chlorate and 1100 g/l of sodium
perchlorate. After settling in an intermediate tank, this solution
is subsequently evaporated to result in a suspension of crystals
which is then centrifuged to give perchlorate crystals. No
information is given regarding the nature of the perchlorate or the
evaporation conditions.
[0006] Furthermore, the process for the manufacture of sodium
perchlorate by oxidation of sodium chlorate, disclosed in U.S. Pat.
No. 3,038,782, is carried out in the presence of lead dioxide in a
reaction medium comprising sulphuric acid. After the electrolysis
stage, the aqueous perchlorate solution is freed from lead-based
compounds by filtration at approximately 90-100.degree. C. and then
evaporated at 150.degree. C. and subsequently the concentrated
aqueous solution comprising 1.32 mol of sodium perchlorate, 2.96
mol of perchloric acid, 0.12 mol of sulphuric acid and 8.45 mol of
water is cooled to 25.degree. C. to give, after filtration, 0.92
mol of sodium perchlorate crystals accompanied by 0.08 mol of
perchloric acid and 0.15 mol of water. The perchloric acid is
subsequently removed by neutralization to finally give anhydrous
sodium perchlorate comprising approximately 3.3% by weight of
water, which, after drying at 105-100.degree. C., results in dry
anhydrous sodium perchlorate.
[0007] The Applicant Company has now found that the crystallization
of anhydrous sodium perchlorate under specific conditions makes it
possible to obtain crystals with a high degree of purity.
[0008] A first subject-matter of the present invention is a process
for the manufacture of anhydrous sodium perchlorate, according to
which an aqueous sodium perchlorate solution, originating directly
from an electrolysis stage or from a succession of individual
electrolytic stages on an aqueous chlorate solution of the said
metal, is subjected to vacuum evaporation at a temperature of
between 52 and 75.degree. C., preferably of between 60 and
70.degree. C. The absolute pressure is preferably between
approximately 1500 and 7000 Pa.
[0009] The aqueous sodium perchlorate solution is advantageously
chosen so that the anhydrous sodium perchlorate can be isolated
directly by crystallization, that is to say a solution which
deposits the anhydrous sodium perchlorate by evaporation of water
or by cooling; reference may be made, on this subject, to the work
published under the direction of Paul Pascal, Nouveau Trait de
Chimie Minrale [New Treatise on Inorganic Chemistry], 1966, Volume
II, Part 1, p. 353 and FIG. 37, which shows the
NaClO.sub.4--NaClO.sub.3--H.sub.2O ternary diagram.
[0010] The composition of this aqueous solution is preferably that
which lies within the region of the
NaClO.sub.4--NaClO.sub.3--H.sub.2O ternary diagram delimited by the
points: A: 58 g of NaClO.sub.3, 270 g of NaClO.sub.4; B: 87 g of
NaClO.sub.3, 295 g of NaClO.sub.4, C: 280 g of NaClO.sub.4 and D:
300 g of NaClO.sub.4 per 100 g of water.
[0011] The aqueous sodium perchlorate solution, originating from
the electrolysis of an aqueous sodium chlorate solution, can be
obtained by keeping the concentration of the sodium chlorate and of
the sodium perchlorate constant in the single electrolysis stage by
continuous addition of sodium chlorate and water simultaneously,
each in an amount equal respectively to the amount of sodium
chlorate and to the amount of water which, in the free state or in
the combined form, are withdrawn continuously from the said
stage.
[0012] Sodium bichromate can be added to the electrolytic solution
to inhibit cathodic side reactions, such as, for example, the
reduction of hypochlorite and chlorate ions.
[0013] The temperature of the electrolysis is generally between 40
and 90.degree. C. and the pH of the electrolytic solution is
between 6 and 10.
[0014] Platinum-based anodes are advantageously used.
[0015] After the evaporation stage, the suspension of anhydrous
sodium perchlorate crystals is filtered and then the crystals can
subsequently be washed with water to remove the residual
impurities.
[0016] The Applicant Company has noticed that, when the aqueous
wash liquor is brought to a temperature of between 55 and
80.degree. C., preferably of between 55 and 65.degree. C., the
washed crystals are composed essentially of anhydrous sodium
perchlorate (devoid of sodium perchlorate monohydrate) and exhibit
good flowability. In addition, the degree of purity of the
anhydrous sodium perchlorate is improved.
[0017] The anhydrous sodium perchlorate crystals, thus filtered and
washed, generally comprise 1 to 2% by weight of water.
[0018] A simplified diagram of a specific embodiment of the
invention is given in FIG. 1. A crystallizer 1, fed with aqueous
sodium perchlorate solution originating directly from the
electrolysis of sodium chlorate 2, is placed under vacuum and then
heated to a temperature of between 52 and 75.degree. C. The
evaporated water 3 leaves the crystallizer and a suspension of
anhydrous sodium perchlorate crystals is withdrawn via 4. This
suspension is subsequently filtered in 5 and wet anhydrous sodium
perchlorate crystals are recovered in 6 and the filtrate is
recovered in 7. According to an alternative form, after filtering,
the anhydrous sodium perchlorate crystals can be washed with water
brought to a temperature of 55-80.degree. C.
[0019] According to another specific embodiment of the invention
(FIG. 2), a crystallizer 1 equipped with an elutriation leg 4 is
fed continuously with aqueous sodium perchlorate solution
originating directly from the electrolysis of sodium chlorate 2.
The crystallizer, placed under vacuum, is heated to and maintained
at a temperature of between 52 and 75.degree. C. The suspension of
the anhydrous sodium perchlorate crystals is subsequently withdrawn
in 5 and then filtered in 6.
[0020] The wet anhydrous sodium perchlorate crystals are recovered
in 7 and can optionally be washed. The aqueous filtration solution
8 can be recycled to the electrolysis and can optionally be
injected into the crystallizer in 9.
[0021] The choice of the throughput of the loop for recirculation
of the aqueous sodium perchlorate solution of the crystallizer and
that of the elutriation throughput injected in 9 make it possible,
by regulating the amount of water evaporated in 3, to obtain the
desired size of the crystals.
[0022] Another aim of the invention is the production of anhydrous
sodium perchlorate crystals which retain good flowability over
time. This aim can be achieved by subjecting the filtered (washed
or unwashed) anhydrous sodium perchlorate crystals to a drying
stage until a residual water content of less than 0.1% by weight
and preferably of less than or equal to 0.05% by weight is
obtained.
[0023] The drying stage can be carried out at a temperature of
between 60 and 150.degree. C. and for a period of time of between
10 minutes and 1 hour.
[0024] Fluidized bed drying is preferred and the temperature is
preferably between 100 and 150.degree. C. for a period of time of
between 15 and 45 minutes in a batchwise process.
[0025] It is also possible to operate with continuous drying.
[0026] The Applicant Company has also noticed that the addition of
a sufficient amount of finely divided silica to the filtered
(washed or unwashed) anhydrous perchlorate crystals, preferably the
crystals obtained after filtering and washing, makes it possible to
obtain anhydrous sodium perchlorate crystals which retain good
flowability over time.
[0027] These anhydrous perchlorate crystals have good flowability
even after storage for a few months.
[0028] The amount of silica charged generally depends on its
nature. An amount of silica of between 0.05 and 0.5% by weight with
respect to the anhydrous sodium perchlorate crystals has given
highly advantageous results.
[0029] Although it is possible to use silica with a hydrophilic
nature, it is generally preferable to use hydrophobic silica. The
specific surface area of the silica is advantageously between 100
and 300 m.sup.2/g.
[0030] The addition of the silica to the anhydrous sodium
perchlorate crystals can be easily carried out in a mixer, for
example a rotary mixer.
[0031] The present invention also relates to the anhydrous sodium
perchlorate crystals thus obtained.
Experimental Part
EXAMPLE 1
[0032] A crystallizer with a capacity of one litre is fed, with a
throughput of 300 cm.sup.3/h, with an aqueous solution comprising
1100 g/l of sodium perchlorate and 115 g/l of sodium chlorate
originating directly from a sodium chlorate electrolytic cell.
[0033] The crystallizer is placed under an absolute pressure of
5000 Pa and brought to and then maintained at a temperature of
65.degree. C. Under these conditions, to maintain a constant level
in the crystallizer, 70 g/h of water are evaporated and a
suspension is withdrawn comprising 20 to 30% by weight of anhydrous
sodium perchlorate crystals in the form of slightly agglomerated
rods with a size of 500.times.100 .mu.m.
[0034] The suspension is subsequently filtered and then the filter
residue is washed with water brought to 65.degree. C.
[0035] After filtering, the anhydrous sodium perchlorate crystals
comprise 0.8% by weight of sodium chlorate and, after washing, the
sodium chlorate content in the crystals is less than 0.2%.
[0036] Residual water is present at approximately 2% by weight.
EXAMPLE 2
[0037] A 20 m.sup.3 crystallizer, maintained under an absolute
pressure of 4000 Pa and at a temperature of 65.degree. C., is
continuously fed, via the recirculation loop, with an aqueous
sodium perchlorate solution originating from a stage of
electrolysis of sodium chlorate and comprising 1110 g/l of
perchlorate and 124 g/l of chlorate.
[0038] The throughputs for feeding with aqueous sodium perchlorate
solution, for evaporating water and for withdrawing suspension via
the elutriation leg are adjusted so as to obtain a level of solids
of approximately 15% by weight in the crystallizer and 30% by
weight in the elutriation leg.
[0039] The composition of the aqueous solution in the crystallizer
is 295 g of sodium perchlorate and 34 g of sodium chlorate per 100
g of water.
[0040] A residence time of the solid in the crystallizer of 5 to 6
h and that of the liquid of approximately 10 h makes it possible to
produce approximately 1.2 t/h of dry anhydrous sodium
perchlorate.
[0041] The suspension withdrawn from the elutriation leg is
subsequently filtered and then the filtered residue is washed with
water brought to 65.degree. C. The Cr.sup.3+ content in the
crystals after filtering is 7 ppm and, after washing, this content
is reduced to less than 1 ppm.
[0042] The chlorate (ClO.sub.3.sup.-) content present in the
crystals after filtering is 0.3% by weight and that after washing
is less than 0.05% by weight.
[0043] The residual water content in the washed crystals is
approximately 1 to 1.5% by weight.
[0044] The anhydrous sodium perchlorate crystals have a particle
size of 800 .mu.m in the elutriation leg.
EXAMPLE 3
[0045] The processing is carried out as described in Example 2 but
with an aqueous wash liquor brought to 35.degree. C. The result of
this is that the crystals set solid during the washing, which even
results in the filtration device becoming blocked.
EXAMPLE 4
[0046] The processing is carried out as in Example 1 but while
maintaining the crystallizer at 32.degree. C. and at an absolute
pressure of 500 Pa. Under these conditions, sodium perchlorate
monohydrate crystals are obtained.
EXAMPLE 5
[0047] 700 g of anhydrous sodium perchlorate crystals originating
from Example 1 are introduced into a fluidized bed maintained at
140.degree. C. After 40 minutes, the residual water content is only
0.05% by weight. This product retains very good flowability after
storage for one month.
EXAMPLE 6
[0048] Drying is carried out under the same conditions as those
described in Example 5 but with 50 kg of anhydrous sodium
perchlorate crystals originating from Example 2.
[0049] A residual water content of approximately 0.05% by weight is
obtained.
EXAMPLES 7-11
[0050] 50 kg of sodium perchlorate crystals prepared according to
Example 2 are charged to a rotary mixer, they are then stirred for
1 hour and then silica is added over 10 to 15 minutes. Stirring is
maintained for 30 to 40 minutes after the addition.
[0051] Finally, the resulting solid is packaged in a polyethylene
bag and then enclosed in a 50 kg keg for 6 months.
[0052] After 3 or 6 months, on opening the keg, the solid retains
perfect flowability (see Table I).
EXAMPLE 12
[0053] The sodium perchlorate crystals prepared according to
Example 2 and bagged up directly, then enclosed in a keg, set solid
after storage for three months.
EXAMPLE 13
[0054] The processing is carried out as in Example 7 except that,
instead of the silica, 200 ppm of triethanolamine, in the form of
an aqueous solution prepared beforehand by dissolution of 10 g in
150 g of water, are added over 10 to 15 minutes.
[0055] After opening the keg after storage for three months, the
solid has set solid.
EXAMPLE 14
[0056] The processing is carried out as described in Example 13
except that 200 ppm of sodium dodecyl sulphate are added instead of
triethanolamine.
[0057] After storage for three months, it is observed, on opening
the keg, that the product has set solid.
1TABLE I Amount Storage time Example Silica % by weight (months)
Observations 7 Degussa C600 0.3 3 Very good flowability " 0.3 6 " 8
" 0.2 3 " " 0.2 6 " 9 " 0.05 3 Very good flowability but a few
lumps in the keg 10 Degussa D22S 0.2 3 " " 0.2 6 " 11 " 0.05 3
Surface crust- ing and lumps in the keg " 0.05 6 "
* * * * *