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Патент USA US2116138

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May 3, 1938.
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2,116,138
‘Patented May 3, l938_
2,116,138 _
UNrrED STATES PATENT' OFFICE
2,116,138
APPARATUS FOR THE ELECTROLYTIC PRO
DUCTION OF CHROMIC ACID AND CAUSTIC
ALKALI
John W. Boss, Livingston, Mont., assignor to
Chromium Products Corporation, Livingston,
Mont., a corporation of Montana
Original application June 15, 1936, Serial No.
85,405. Divided and this application October
` 12, 1936, Serial No. 105,321
3 Claims.
The present invention relates to an improved
apparatus for the electrolytic production of
(Cl. 204-5)
cause of the precipitation of bases at the planeseparating the caustic soda solution from the
chromic acid and caustic alkali. This invention n impure acid solution. As the acid solution
underlies the caustic solution. these bases or
relates to an improvement in the apparatus de
sludges tend to settle lin the acid, -redissolve and
Iscribed in my Patent No. 2,055,962, and the pres
lent application is a division of my application reprecipitate at the plane of- separation.
This cyclic behavior lowers the efliciency of
Serial No. 85,405, flledJune 15, 1936.
'
the cell and requires an excessive ñow of caustic
`An object of the .present invention is to pro
soda solution to carry out the precipitates; it
' duce in a single cell pure chromic acid from a
also requires closer supervision of the cell‘to reg
10 soluble chromate salt.
A further object is to overcome the defect. ulate the removal of these precipitates. In the
caused by accumulation of sludge between the` present invention as applied to revivifying used
feed solution and the caustic alkali' solution in plating acid there is no contact between it and
the caustic solution. Instead the caustic alkali
v cells of this type as heretofore known.
l5
A further object is to revivify used chromium solution ñoats on one part of an alkali chromate
feed solution while an impure chromic acid solu
plating solutions.
Another object is to produce ina single cell tion iioats on another part of the feed solution.
The used plating acid is then mixed with pure
both crude and finished chromic acid.
Still another object is to provide means for chromic acid solution and floated on top of the
effecting more complete removal of basic sludge impure chromic acid solution. The alkali chro
from the cell than has been possible by other mate feed solution can be maintained neutral or
nearly so and bases precipitated at its contact
means.
.
With the foregoing and _other objects in view, surface with the crude acid solution do not tend
to redissolve but settle out towards the bottom
the invention will be more fully described here
25 inafter, and will be more particularly pointed- of the feed solution.
In the drawingy Ill designates the body of a
out in the claims appended hereto.
_ In the drawing, wherein like symbols refer to cell which may be formedl of glass, stoneware
-like ` or
corresponding parts throughout
the
15
`
20
25
or other suitable material resistant vto the corro
sive action of the solutions employed. 'I'he cell
several views.
Figure 1 is a central vertical `section of a cell ' I0 is divided longitudinally into two equal com 30
partments by a partition II which extends down
in operating condition, and
,
Figure 2 is a top plan view of a modiiication into the cell a substantial distance but stops
of the cell in which the feed pipes do not` lie in short of the bottom of the cell. As shown the
partition II extends about three-quarters of the
the same vertical plane.
35
This invention relates to a process and appa--> `way down into the cell. There are, therefore, 35
ratus for the electrolytic` production of chromic formed two side compartments I2 and I3 com
acid and of caustic alkali. In the prior art it municating at their lower ends to form a com
is customary to produce chromic acid (CrOs) mon chamber or compartment I4.
The cell II) is provided near the upper part -of
bythe action of anacid such as sulphuric on an
4.0 alkali chromate or dichromate such as sodium the compartment I2 with an overflow pipe Iii.> 40
chromate or dichromate. Separation of the A movable .sleeve I6 connects the pipe I5 to the
chromicl acid is accomplished by crystallization
and draining off the mother liquor containing
`
in solution other products of the reaction.
45
Some of the disadvantages of such a process
are: That diillculty is encountered in removing
other acid radicals from the chromic acid; and
_that the alkali originally combined as chromate
take off I 1. The distance between the take oñ
I'l` and the overñow pipe I5 may be regulated
by means of the sleeve I 6 to alter the rate of
overflow from the compartment I2. Also lower 45
is not suitable for use in preparing new quan
down in the compartment I2 but yet a substan
tial distance above the bottom of the partition
II the cell I0 has a second overflow pipe I8
similarly _provided with a sleeve I9 and take ol!
2U. 1n the compartment I3 approximately op 50
posite to the overflow pipe I8 in the other com
tities of sodium chromate.
When a used plating solution is reviviiied ac
cording to the procedure taught in the applica
55 tions above mentioned some difñculty arises be
common compartment I4 and below the lower
edge >,of the partition II is placed another over 55
or dichromate appears as a salt such as sodium
50 sulphate.
This salt is not of much value and
partment, is placed an overflow pipe 2_I with
sleeve 22 and take ofi? 23.
At one side of the
2
2,116,138
flow tube 24 with sleeve 25 and take oil 26. An
anode 21 is suspended in the compartment I2
and a cathode 28 is suspended in the ‘compart
ment I3. The anode 21 may be made of lead
and the cathode 28 of iron, steel orcopper. It
will be noted that the. anode 21 is positioned in
the upper part of the compartment I2 at a re
gion approximately opposite the overflow pipe I5
while the cathode 28 is placed lower in the com
10 partment I3 approximately opposite the over
the plane of separation between it and the solu
tions floating above it moves downward toward
the partition II. It is, therefore, necessary to
replenish this solution to prevent mixing of the
_solutions in the other compartments» The so
dium chromate solution also tends to accumu
late some caustic soda. Some basic substances
such as aluminum, forming soluble compounds
with the caustic soda, may also accumulate in
this feed solution; In addition to this there is a
flow pipe 2|.
In the following description sodium chromate
sludge of insoluble basic materials which may
appear at the separation plane between «the
will be used as an example but it is to be under
stood that any alkali salt of chromic acid may
sodium chromate and the crude chromic acid.
This sludge is insoluble in the sodium chromate
15 be used. In filling the cell the compartment I4
is filled with a solution of sodium chromate of
specific gravity, for example, 1.450. This solu
tion is introduced through the feed pipe 29 and
the'solution is added until it fills the lower ends
20 of the side compartments I2 and I3. In the
compartment I3 on top of the sodium chromate
solution is floated a caustic soda solution of, for
example, specific gravity 1.200. This solution is
added through the supply pipe 30 to substantially
25 fill the compartment I3.
In the other side com'
partment I2 is floated flrst a crude chromic acid
solution of specific gravity, for example, 1.325.
This solution is added through the feed pipe 3|.
and eventually settles to the bottom of the cell 15
where it lies until such time as the cell may be
cleaned.
'
.
In operation of this cell it is of the utmost im
portance to maintain the planes of separation
between the various solutions. Thus, if the so 20
dium chromate feed solution be permitted to drop
below the lower edge of the partition II the solu-l
tions in the side compartments will mingle and
the contents of the cell destroyed.
If, on the
other hand, the sodium chromate solution be
allowed to rise as high as the anode 28 evolution
of gas will cause breaking of the plane of separa
tion between it and the caustic soda solution. In
the chamber I2 the sodium chromate solution
The amount of this solution must be such as to
30 extend from the top of the sodium chromate
must not rise higher than the feed pipe 3| and 30
solution to some point below the anode 21.. Fi- ’ the overflow opening I8, which are both situated
nally, on top of this crude chromicl acid solution
is floated a pure chromic acid solution of specific
gravity, for example, 1.200. This v,last solution
It will be
35 is added through its feed pipe 32.
necessary, of course, in adding these various
solutions to balance the heads of solutions in the
opposite chambers so as to prevent mixing be
neath the partition II. It is also necessary, as
40 soon as the solutions are added, that current be
passed between the electrodes so as to prevent
diffusion of the various solutions.
'
When the electrodes are connected to a. suit
able source of direct current the pure chromic
acid solution loses basic ions to the impure solu
tion on which it floats while the crude solution
loses chromate ions to the solutions above it.
The pure solution thus tends to increase in
specific gravity while the impure solution loses
in specific gravity. In view of this fact, it is
necessary to regulate the specific gravity of the
crude solution in order to prevent mixing with
the pure solution as they tend to attain the same
specific gravities due to the operation of the cell.
The crude solution receives from the sodium
chromate solution underlying it, chromate ions
and loses to the underlying solution alkali or
basic ions. However, the crude solution loses
chromate ions to the pure solution above it at a
60 rate greater than the sodium chromate solution
supplies these ions to it. It is, therefore, neces
sary to replenish the crude chromic acid solution
from outside sources to maintain the supply of
chromate ions. Such a source of the crude acid
may be a simple cell such as described in my
above identified applications. The caustic soda
solution takes from the sodium chromate in the
lower compartment basic ions and the solution
in the compartment I3 increases both in volume
and in density requiringfdrawing off and regu
lating of the density in order to maintain the
plane of separation between it and the sodium
chromate solution underlying it.
at the mid point between the lower edge of the
partition I I and the anode 21. A rise above that
point would cause mixing of both feed and over
flow with the sodium chromate solution. Simi
larly the plane of separation between the plain
and crude chromic acid solutions must not 'drop
as low as the opening of the feed pipe 3| or the
opening of the overflow pipe I8 as this would
cause mixing of the two chromic acid solutions. 40
Also the plane between these acid solutions must
not rise as high as the anode 21 for here gas
evolution would destroy the plane of separation
between the solutions.
In view of the requirement for regulating these
pla‘nes of separation it will be seen to be necesi
sary that some means of observing the planes be
provided. 'I'hus the cells themselves may be
made of transparent material, for the various
chromate solutions are readily distinguishableby
color while the caustic Ísoda is similarly dis
tinguishable by its lack of color. An alternative
means of observing the planes is` to lower a’ glass
tube into the cell, close the .top and carefully
withdraw it from the cell. The solutions carried 55
in the glass tube will indicate by their color and
planes of separation the relation existing in the
cell between these solutions.
.
The most convenient way to operate this cell
and the way for which the cell illustrated is in
tended is a continuous operation. It will be
noted that the lower ends of the tubes 30, 3| and
32 are turned so as to direct the streams of in#
coming liquid away from the nearest plane _of
separation, the object being to avoid disturbing 65
this plane. The feed pipes and overflow pipes
are adjusted and connected with sources of solu
tion to promote flow of these solutions through
the cell to prevent a rise in specific gravity which
would tend to destroy the planes of separation. 70
The rate of overflow is adjusted by sliding the
take oil pipes in the sleeves so that more or less
` 'I'he sodium chromate feed solution decreases
pressure will be required to force solution out
of the cell.
75 in volume due to loss of its ions as described and
The feed pipe 29 for the common chamber I4
3
2,110,138
communicates with a source of sodium chromate
feed chamber.
solution of the desired specific gravity and the
supply is regulated to compensate for the rate of
cathode chamber is provided with anode or cath
ode and with the various feed and overflow pipes.
It is obvious that various changes and modifi
cations may be made in the details of construc
tion and design of the above specifically described
embodiment of this invention without departing
from the spirit thereof, such changes and modi»
flcations being restricted only by the scope of the
consumption of this -solution in the cell.
Also
if the operation of the cell is being impaired by
accumulation of insoluble impurities and by ac
cumulating caustic soda in this chamber the vol
ume of solution fed may be increased and the
excess carried off through the overflow pipe 24,
this having the effect of flushing the chamber I4
of these impurities.
In operating this cell to revivify fouled plated
solutions the cell is filled as described and the
fouled solution introduced through the pipe 32
15 into the purified chromic acid layer. As pointed
out above the‘chromic acid content of this puri
'ied layer will be increased by operation of the
i cell and the basic content will be decreased.
'I'hese actions then purify fouled plating acid
20 when it is introduced into the finished chromic
In such a case each anode and
following claims:
What is claimed isz-
10
_
“1. A cell for electrolytic production of chromic
acid and caustic alkali consisting in a cell body,
a vertical partition extending partly down into
the body dividing said body into an anode and a
cathode chamber communicating at their lower
ends with a common chamber, the cathode cham
ber adaptedto receive a caustic alkali product
solution, said anode chamber adapted to receive
a chromic acid product solution in the upper part 20
acid layer. Since the cell is most conveniently
operated by maintaining continuous flow of so
lution, a portion of the overflow from the pipe
floating on an impure chromic acid solution in
|5_ is adjusted in specific gravity and returned
acid solution both floating on an alkali chromate
25 to the cell through the feed pipe 32 along with a
portion of the fouled acid to be purified. The
portion of overflow which is not adjusted and
returned is taken as product solution to be used
in a chromium plating bath or for the recovery of
30 chromic acid. In a similar manner a portion of
the caustic soda solution removed through the
overflow pipe 2| may be adjusted and returned
through the feed pipe 30 while the remaining
portion of the overflow maybe withdrawn as
caustic soda product solution.
Basic substances removed from .the floating
purified chromic acid layer in chamber I2 will be
found as in insoluble mud in the feed solution
in chamber Il of the cell.
‘
By a selection of the proper sizes of cells and
40
current values, an acid making cell as herein de
scribed can be operated to treat solution from
chromium plating cells so that the efficiency of
the plating operation is maintained and the
45 chromium content of the plating bath held con
stant.
‘
In operating the _cell it has been found that
a current density of about 30 amperes per square
foot of area of anode and of cathode chamber
50 section works well.
Referring to Figure 2 a modification in the
location of overflow pipes is seen.v In this form
the upper overflow pipes i5' and 2|' are located
near one end of the cell while the lower overflow
55 pipes I8' and 24' are located near the opposite
end of the cell. In other respects the construc
tion is the same. The location of these overflow
pipes, as well as the location of the feed pipes
is subject to variation in a horizontal plane, the
60 only requirement being that the vertical position
of their outlets conform with the requirements of
solution position.
It Will also be apparent that the cell is not
limited to the structure shown with regard to the
65 number of anode and cathode chambers but that
any> desired number of these upper chambers
may be provided communicating with a lower
the lower `part of said anode chamber, said cath
ode chamber solution and said impure chromic
feed solution in said common chamber, an anode ‘
in the upper part of the anode chamber in the
region of the product solution, .a cathode in the
cathode chamber, supply pipes in the region of
each of the solutions, and removal pipes in the
30
region of each of the solutions.
2. A cell for electrolytic production of chromic
acid and caustic alkali consisting in a cell body,
a vertical _partition extending partly down into
the body dividing said body into an anode and
a cathode chamber communicating at their lower 35
ends with a common chamber, the cathode cham
ber adapted to receive a caustic alkali solution,
the anode chamber adapted to receive a chromic
acid solution, said cathode chamber solution and
‘said anode chamber solution floating on an alkali
chromate feed solution in said common chamber,
an anode in the anode chamber, a cathode in
the cathode chamber, supply pipes in the region
of each of the solutions, removal pipes in the
region of each of the solutions, and means for
varying the rate of flow in the said removal pipes.
3. A cell for electrolytic production of chromic
acid and caustic alkali consisting in a cell body,
a vertical partition extending partly down into
the body dividing said body into an anode and 50
a cathode chamber communicating at their lower
ends with a common chamber, the cathode cham~
ber adapted to receive a caustic alkali product
solution, said anode chamber adapted to receive
a chromic acid product solution in the upper part
floating on an impure chromic acid solution in
the lower part of said anode chamber, said cath
ode chamber solution and said impure chromic
acid solution both floating on an alkali chromate
feed solution in said common chamber, an anode
in the upper part of the anode chamber in the
region of _the product solution, a cathode in the
cathode chamber, separate supply means for each
of said solutions, and separate removal means
65
for each of said solutions.
JOHN _W. Boss.
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