Note: Descriptions are shown in the official language in which they were submitted.
~079~84
This invention relates to the production of chlorine
clioxide. More particularly, this invention relates to a process
for producing chlorine dioxide by the reaction of alkali metal
chlorate with sulfur dioxide.
It is known in the art to produce chlorine dioxide by
the reaction of sulfur dioxide and an aqueous solution containing
an alkali metal chlorate. Such processes as have been available,
however, have been less than totally satisfactory. For example,
the efficiency of operation and conversion, generally may be on the
order of about 58 percent. Increasing reactants, particularly alkali
metal chlorate results in unacceptable salt crystallization in the
reactor, particularly in the 10wer portions of columns utilized in
effecting the reaction wherein, e.g., sodium chlorate is fed in at
- the top of the column and gaseous sulfur dioxide diluted with nitrogen
is fed countercurrently.
It is an object of the present invention to provide a process
for the production of chlorine dioxide wherein the problems existant
with prior art techniques are obviated.
In accordance with the present invention, relatively low
concentration sodium chlorate is reacted countercurrently with a
reactive stream containing chlorine and sulfur dioxide in a packed
column.
When gaseous sulfur dioxide is brought into contact with
.
an aqueous solution of sodium chlorate, chlorine dioxide is produced
in accordance with the following equation.
3 2 2 4 2
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It has now been found that the production of ch10rine dioxide
may be efficiently effected by passing an aqueous solution of dilute
sodium chlorate of a concentration of from about 30 percent to up to
about the saturation point of sodium chlorate in water, in countercurrent
flow to diluted sulfur dioxide and gaseous chlorine in a packed column,
the sulfur dioxide fed at a rate of from about 1.25:1 to about 1.5:1,
based on the moles of sodium chlorate feed, and the gaseous chlorine fed
at a rate of from about 0.5:1 to about 0.75:1 on a molar basis, based on
the moles of sodium chlorate fed to the packed column reactor, the sulfur
dioxide gas being introduced into the bottom portion of the column and
the chlorine gas being introduced into the central portion of the column.
The sulfur dioxide may be fed to the reactor in any diluent
which is non-reactive under the conditions utilized, such as nitrogen.
While the percentage of dilution may vary greatly, it has been found that
15 percent sulfur dioxide in nitrogen functions in a preferred manner in
the present process.
Such process surprisingly results in approximately a 10-16 per-
cent increase in efficiency over reactions utilizing only sodium chlorate
and sulfur dioxide, and perm;ts of the use of sodium chlorate in rela-
tively low concentrations, on the order of about ~0 percent by weight,
obviating crystal formation and plugging of reaction apparatus during
prolonged periods of use.
While apparatus of any design suitable to effect the reaction
may be employed, it has been found that packed tower chlorine dioxide
generators having an inlet approximately halfway of the height of the
packed column for the introduction of gaseous chlorine are particularly
well suited for the reaction, with the sulfur dioxide inlet located near
the bottom of the column, an inlet near the top of the column for the
aqueous sodium chlorate feed, and the takeoff means for both the gaseous
and solid reaction products. Generally, the ratio of the height of the
tower to the diameter of the tower can be that found suitable
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to maximize the reaction; ratios of 24:1 to about 30:1 have been
found to be acceptable.
The reaction zone in the column lies upstream of the
gaseous chlorine inlet and is a relatively short zone. The re-
actants are fed at such rates as are necessary to develop andmaintain an acidity of from 9 to 10 normal in this zone. Pre-
ferably, the flow rates are adjusted so that the molar ratio of
sulfur dioxide to sodium chlorate is about 1.35:1 and the molar
ratio of chlorine to sodium chlorate is about 0.6:1.
The packing utilized in the reaction column can be any
commercially available packing of suitable material, such as
Raschig rings, verl saddles, glass beads or the like. Preferably,
Raschig rings or verl saddles are used.
The reaction is conducted at a temperature of about 60
degrees centigrade, with external cooling as required to maintain
the reaction zone at this temperature. The temperature of the
uppermost portion of the column generator is generally on the
order of about 20 to about 30 degrees centigrade, allowing for
the effective absorption of generated hydrogen chloride. The
lower portion of the column is increasingly cooler than 60 degrees
centigrade.
The reaction is conducted on a batch or continuous basis,
preferably on a continuous basis by proper adjustment of feed rates.
The selection of the rates, dependent upon the apparatus employed,
the rate of reaction desired, and the like, which selection will be
within the skills of those practitioners of the art.
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Examples 2-3 following are indicative of the results
achieved when reacting sodium chlorate and sulfur dioxide, without
chlorine, in producing chlorine dioxide.
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EXAMPLE 1
A glass column having a height of approximately 30 inches
and an inside diameter of one inch was packed with 1/8 inch diameter
glass helices, and pre-wetted with 40 percent aqueous sodium chlorate
solution. Aqueous 40 percent sodium chlorate flow was adjusted so
that 0.325 mole of sodium chlorate was utilized in the reaction.
Immediately, sulfur dioxide addition was initiated (15 percent,
diluted with nitrogen) to a total feed of 0.55 mole, the rate of
addition such as to control the reaction zone approximately midway
the height of the column. Under these operating conditions, the
acid effluent was colorless in the lower portion of the column
reactor, indicating complete utilization of the sodium chlorate.
The temperature of the hot or reaction zone was approximately 60
degrees centigrade and was approximately 3 inches long.
On achiev;ng equilibrium conditions, the gas stream
emanating from the column reactor was continuously scrubbed with
a solution of caustic and hydrogen peroxide, converting all chlorine
dioxide generated to sodium chlorite and chlorine and hydrogen chloride
into sodium chloride, for analytical purposes, with acid effluent
collected analyzed for acidity and chlorate content.
Under these operating conditions, with a sulfur dioxide;
sodium chlorate ratio of 1.57:1, 0.208 mole of chlorine dioxide and
0.01 mole of chlorine were produced with an efficiency of 58.5 percent.
No chlorate was noted in the acid effluent, with 0.80 mole of acid
therein. Salt formation in the bottom of the column produced plugging
of the lower column.
EXAMPLE 2
Utilizing the operating conditions of Example l, with
0.88 mole sulfur dioxide and 0.570 mole sodium chlorate feed
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(S02:NaCl03=1.54:1) analysis indicated a process efficiency of 54.4
percent, with 0.370 mole chlorine dioxide produced and with complete
utilization of the sodium chlorate. Plugging of the lower portion
of the reaction column again occurred.
EXAMPLE 3
-
Utilizing the apparatus and operating conditions of Example
1, with 0.82 mole sulfur dioxide and 0.672 mole sodium chlorate feed
(S02:NaC103=1.34:1), analysis indicated a process efficiency of 61.8
percent on a yield of 0.418 mole chlorine dioxide and complete utili-
zation of the sodium chlorate. Again5 plugging of the lower portion
of the reaction zone column occurred.
The following examples serve to illustrate the process of
the present invention.
EXAMPLE 4
Utilizing the process conditions of Example 1, with the
exception that the apparatus included a chlorine inlet approximately
midway the length of the reaction column, with a 0.82 mole sulfur
dioxide, 0.559 mole sodium chlorate and 0.51 mole gaseous chlorine
feed (S02:NaC103=1.46:1; C12:NaC103=1.1:1), analysis indicated a
2Q 73.3 percent process efficiency on a yield of 0.410 mole chlorine
dioxide and complete utilization of the sodium chlorate. No plugging
of the reaction column was noted.
EXAMPLE 5
Utilizing the apparatus and operating conditions of Example
4 with 0.75 mole sulfur dioxide, 0.460 mole sodium chlorate and 0.21
mole chlorine feed (S02:NaC103=1.63:1; C12:NaC13=2.2:1), analysis
indicated a 72.5 percent process efficiency on a yield of 0.335 mole
chlorine dioxide and complete utilization of sodium chlorate. No
plugging of the reaction column was noted.
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EXAMPLE 6
Utilizing the apparatus and operating conditions of Example
4, with 0.86 mole sulfur dioxide, 0.570 mole sodium chlorate and 0.27
Mole chlorine feed (S02:NaCl03-1.52:1; C12:NaC103=2.1:1) analysis
Indicated a 69 percent process efficiency on a yield of 0.390 mole
chlorine dioxide and complete utilization of sodium chlorate. No
plugging of the reaction column was noted.
EXAMPLE 7
Utilizing the apparatus and operating conditions of Example
4. with a feed of 0.89 mole sulfur dioxide, 0.725 mole sodium chlorate
and 0.14 mole chlorine (S02:NaC103=1.27:1; C12:NaC103=5.2:1) analysis
indicated a 73.4 percent process efficiency on a yield of 0.532 mole
chlorine dioxide and complete utilization of sodium chlorate. No
plugging of the reaction column was noted.
EXAMPLE 8
Utilizing the apparatus and operating conditions of Example
4, with a feed of 0.82 mole sulfur dioxide, 0.670 mole sodium chlorate
and 0.13 mole chlorine (S02:NaC103=1.21:1; C12:NaCl03=5.1:1) analysis
indicated a 73.6 percent process efficiency on a yield of 0.494 mole
chlorine dioxide and complete utilization of the sodium chlorate. No
plugging of the reaction column.
It is readily seen from the above Examples 1-3 that, in order
to produce one pound of chlorine dioxide, 2.4 pounds of sulfur dioxide
and 2.7 pounds of sodium chlorate are required. In accordance with
Examples 4-8, which serve to illustrate the process of the present
invention, only 1.6 pounds of sulfur dioxide, 2.1 pounds of sodium
chlorate and 0.3 pound of chlorine are required to produce one pound
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of chlorine dioxide, with no plugging of the reaction apparatus.
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