PROCESS AND APPARATUS FOR SUPPLYING ALKALI CHLORATE AND ACID TO A REACTOR FOR PRODUCING CHLORINE DIOXIDE

PROCEDE ET APPAREILLAGE POUR ALIMENTER EN CHLORATE DE METAL ALCALIN ET EN ACIDE UN REACTEUR DESTINE A LA PRODUCTION DE DIOXYDE DE CHLORE

English Abstract

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ABSTRACT
To produce a gaseous mixture of chlorine dioxide
and chlorine, alkali chlorate solution is reacted with an
acid, such as hydrochloric acid, in a reactor that comprises
one or more reaction stages. The alkali chlorate solution
and the acid are first passed jointly through a mixing cham-
ber to form a mixed solution, which is supplied from the
mixing chamber to the uppermost reaction stage of the reactor.

Claims

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CLAIMS
1. A process of reacting an alkali chlorate
solution with an acid to produce a gaseous mixture of
chlorine dioxide and chlorine in a reactor that comprises
one or more reaction stages, which contain a mixed solution
that contains alkali chlorate and acid, characterized in
that the alkali chlorate solution and the acid are jointly
passed through a mixing chamber and a mixed solution is fed
from the mixing chamber into the uppermost reaction stage
of the reactor.
2. A reactor for reacting an alkali chlorate so-
lution with an acid to form a gaseous mixture of chlorine
dioxide and chlorine, which reactor comprises one or more
reaction stages, characterized in that a mixing chamber is
connected to the reactor and is provided with supply lines
for alkali chlorate solution and acid and with a liquid out-
let, which opens into the uppermost reaction stage of the
reactor.
3. A reactor according to claim 2, characte-
rized in that an annular chamber is provided between the mix-
ing chamber and one of the supply lines and surrounds the
other supply line and the annular chamber defines a liquid
passage leading to the mixing chamber.
4. A reactor according to claim 2 or 3, charac-
terized in that the mixing chamber flares conically toward
the reactor.

Description

2123033
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The present invention relates to a p~cess of react:ing
an alkali chlorate solution with an acid to produce a ga-
seous mixture of chlorine dioxide and chlorine in a reactor
that comprises one or more reaction stages, which contain a
mixed solution that contains alkali chlorate and acid, and
to a reactor for carrying out that process.
That process and associated reactors ~ve been
disclosed in U.S. Patent 4,85l,l98 and the corresponding
European Patent 0 227 l8l, in DE-A-37 l9 878, and in U.S. Pa-
tent 4,938,944 and the corresponding European Patent 0 345 863.
Said reactors contain a plurality of superposed gas-permeable
plates, each of which defines a reaction stage. Stripping
air is passed through the reaction stages from below and ser-
ves to carry out of the reactor the gaseous C102, which still
contains C12, so that the occurrence of an explosive concen-
tration of chlorine dioxide will be prevented. The alkalichlorate solution may have been produced, e.g., by an elec-
trolysis.
The alkali chlorate is usually reacted with hy-
drochloric acid in the following reactions:
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2123033
-- 2 --
NaClO3 + 2 HCI --> ClO2 + 1/2 C12 ~ NaCl + H20 (1)
NaClO3 + 6 HCI --> 3 Cl2 + NaCl + 3 H20 (2)
It is important that the side reaction (2), in which no ClO2
is formed, should be suppressed as far as possible. It is an
object of the invention to achieve this in a manner which is
- as safe as possible.
In the process described first herei`nbefore that
object is accomplished in accordance with the invention in
that the alkali chlorate solution and the acid are jointly
passed through a mixing chamber and a mixed solution is fed
from the mixing chamber into the uppermost reaction stage of
the reactor. Because the acid consisting usually of hydro-
chloric acid and the alkali chlorate solution will react with
each other only slowly, the reaction rate will distinctly be
increased by the controlled mixing in the mixing chamber.
Different local acid concentrations will be avoided so that
the formation of Cl2 will be decreased. This will result in
a considerable improvement of the efficiency of the reactor.
The reactor for carrying out the process com-
prises a mixing chamber that is provided with lines for sup-
plying alkali chlorate solution and acid and the liquid out-
let of the mixing chamber opens into the uppermos~ reaction
stage of the reactor. The reactor is usually provided with
only one mixing chamber so that the expenditure for the means
for supplying chlorate and acid is minimized. In contrast,
known reactors comprise a large number of lines for supplying
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acid in order to ensure that the acid will be distributed
as uniformly as possible in the mixed solution in the re-
action stages.
Further features of the process and apparatus
will be explained with reference to the drawing, in which
Figure 1 is a schematic longitudinal sectional
view showing the reactor and
Figure 2 is a schematic longitudinal sectional
view showing an embodiment of the mixing means.
Figure 1 shows only the uppermost reaction
stage 1 of the reactor and the associated plate 2, which has
the shape of an inverted funnel and is provided with a cen-
tral gas duct 3 and a gas-conducting cap 4, which is spaced
The liquid level above the plate 2 is shown by the dotted line 5.
above the duct./The liquid flows off downwardly through the
overflow pipe 6. A plurality of superposed reaction stages
are usually provided. The reactor and its internal fixtures
are usually made of titanium.
A purging gas, such as air, is fed through line
8 to the lowermost reaction stage and rises through the gas
duct 3 and the space between the duct 3 and the cap 4, as
is indicated by the curved arrows 9. Together with the strip-
ping gas, C102-containing gaseous products are discharged
from the reactor through the opening 10. The lowermost region
in the reactor is constituted by a reboiling chamber 11, -
which from the overflow line 12 receives spent solution
coming from above. The solution is heated to its boiling
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point by heating means 13 and leaves the chamber 11 through
the outlet 14. Vapors are discharged through line 14a.
Alkali chlorate solution is supplied through
line 15 and first enters the mixing means 16, where it is
mixed at least in part with hydrochloric acid coming from
the line 17. Details of the ejectorlike mixing means are
shown in Figure 2. The mixing means shown in Figure 2 com-
prise a conical ~ixing chamber 18, through which the mixed
liquid flow in the direction indicated by the arrow l9.
Through the outlet 20 the liquid enters the uppermost re-
action stage l of the reactor. The outlet 20 is disposed be-
low the liquid level 5 a small distance above the plate 2;
see Figure l.
The acid is supplied through line 17 and first
enters an annular chamber 21, which surrounds the conically
constricted end of the line 15. The acid flows through an
annular gap 22 into the mixing chamber 18 and while it is
mixed with the chlorate solution coming from the line 15
flows to the reaction stage l. In most cases the mixing cham-
ber 18 has a length of about 20 to 80 cm so that the begin-
ning reaction of the chlorate with the acid will not give
rise to trouble. The velocity of flow in the mixing chamber
18 is usually in the range from l to 3 m/s and the volume
ratio of the chlorate and HCI solutions which are supplied
is in most cases between 2 : l and 4 : l. The mixing means 16
may be made, e.g., of polytetrafluoroethylene.
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Example
A reactor as shown in Figure 1, which comprises
6 reaction stages and is 3.8 m in diameter, is used to pro-
duce 1440 kg C102 per hour. The mixing means 16 shown in
Figure 2 are supplied with 5 m3/h hydrochloric acid containig
370 9 HCI per liter and with 12.3 m3/h of an aqueous sodium
chlorate solution which contains 500 9 NaC103 per liter.
The acid and the chlorate solution are at a temperature of
40C and the pressure in line 15 is 3 bars and in line 17 is
0.6 bars. The mixing chamber 18 has a length of 35 cm, a
smallest inside diameter of 1.4 cm and a largest inside dia-
meter of 5.5 cm. Purging air at a rate of 1800 sm3/h (sm3 =
standard cubic meter) is supplied to the reactor through
line 8. Together with the ClO2 and the purging air, Cl2 at a
rate of 315 sm3/h is discharged from the reactor.
If the mixing means 16 are omitted and the lines
15 and 17 extend directly into the reactor whereas the con-
ditions are the same in other respects, only 1250 kg C102
in conjunction with 350 sm3 C12 will be procuded per hour~
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Representative Drawing