Chlorine dioxide generation process

The present invention is directed to a chlorine dioxide generation process. The Novel process of this invention utilizes concentrated hydrochloric acid solution reacted with concentrated sodium chlorite solution, without prior dilution of either reactant. Resulting in consistent high efficiency with respect to yield and chemical consumption.

FIELD OF THE INVENTION 
This invention relates to a chlorine dioxide generation process and is more 
particularly concerned with a procedure which utilizes a chlorite and 
hydrochloric acid. 
BACKGROUND 
Chlorine dioxide is utilized in a variety of processes including a large 
number of bactericidal applications, especially in the fields of water 
treatment and odor abatement. Its usage is continuing to grow for many 
reasons. Due to the unstable nature of gaseous chlorine dioxide when 
compressed it is necessary to produce chlorine dioxide on site rather than 
to produce it at a plant and ship it for useage when needed. The prior art 
processes involve the production of chlorine dioxide by the reaction of a 
chlorite with a diluted hydrochloric acid, followed by introduction into 
the water system to be treated. 
Procedures for the manufacture of chlorine dioxide which have been 
previously proposed, especially those utilizing the chlorite/hydrochloric 
acid process, require the use of elaborate generation equipment that 
includes means of diluting the hydrochloric acid or they involve the use 
of plant personnel to dilute the hydrochloric acid which is a hazardous 
undertaking. Often these procedures require the use of an additional 
catalyst such as Potasium Persulfate or Potasium Perborate adding to the 
expense, and also can contaminate the chlorine dioxide with unwanted 
by-products. Also they require the use of excessive amounts of 
hydrochloric acid from 200 to 325% in excess of the stoichiometric weight 
requirements; this also adds another unnecessary expense. Others also 
require the careful control of the reaction temperature, which makes the 
reaction difficult to control, and complicates the equipment necessary. 
We have found that all of these problems can be overcome, and that a 
superior method of generating chlorine dioxide in a safe manner may be 
achieved by utilization of the process of the present invention. 
It is therefore a principal object of this invention to provide a process 
for the preparation of chlorine dioxide which is relatively simple, is 
safe, uses commercially available chemicals in their concentrated form, 
requiring no pre-dilution, and achieves consistently high yields. 
Still another object of the present invention is to provide a process that 
requires only a chlorite and hydrochloric acid, and is not dependent on an 
expensive catalyst. 
Another object of the present invention is to provide a process for the 
production of chlorine dioxide which is very economical by requiring 
substantially less hydrochloric acid to obtain high yields. 
Still another object is to provide a process which is not dependent on 
elevation or control of temperature. 
Other objects will become apparent hereinafter. 
SUMMARY OF THE INVENTION 
In accordance with this invention there is provided a process for the 
preparation of chlorine dioxide that obtains consistently high yields by 
reacting a concentrated sodium chlorite solution with a concentrated 
hydrochloric acid solution in the absence of dilution water, producing 
four moles of chlorine dioxide for every five moles of sodium chlorite 
according to the following non-limiting equation: 
EQU 5NaClO.sub.2 +4HCL--ClO.sub.2 +5NaCl+2H.sub.2 O 
Thus 0.8 moles hydrochloric acid is needed per one mole of sodium chlorite 
for a stoichiometric reaction. 
DETAILED DESCRIPTION OF THE INVENTION 
The process of the present invention calls for concentrated from 6 molar to 
12 molar, preferably 10 molar, hydrochloric acid to be reacted undiluted 
with a concentrated from 0.7 molar to 3.49 molar, preferably 1.92 molar, 
solution of sodium chlorite. The 10 molar acid and the 1.92 molar chlorite 
are fed neat into a reactor on a continuous basis at regulated 
proportions. A ratio of 1 mole sodium chlorite to 0.92 mole hydrochloric 
acid is used. This is a 15% excess over the stoichiometric requirement. A 
reaction time of 20-30 minutes is adequate to proceed to completion. It is 
the use of 10 molar hydrochloric acid reacted undiluted that results in a 
100% conversion to chlorine dioxide, using only a 15% excess over the 
stoichiometric mole ratio. Current art uses from 2.48 to 3.4 moles of 
hydrochloric acid per 1 mole of sodium chlorite which is a 200 to 325% 
excess over the stoichiometric to obtain 85 to 100% yields. 
In one process by E. E. Bandi Lebensmit Hyg. 58:170 1967 a 0.91 molar 
solution of sodium chlorite and a 2.57 molar hydrochloric acid are reacted 
using a ratio of 2.48 moles hydrochloric acid per one mole of sodium 
chlorite. With careful control of temperature and proper mixing yields of 
90 to 100% are claimed. 
In another prior art process described by W. J. Masschelein in his book 
"Chlorine Dioxide", published by Ann Arbor Science 1979, a 3.3 molar 
solution of sodium chlorite and a 1.6 molar solution of hydrochloric acid 
are reacted using a ratio of 2.9 to 3.4 moles hydrochloric acid per one 
mole of sodium chlorite, a 95 to 100% yield results. 
In still another process Swiss Patent #481,839 and 498,045 a 1.28 molar 
solution of sodium chlorite and a 3.4 molar solution of hydrochloric acid 
are reacted using a mole ratio of 2.8 to 3.2 moles hydrochloric acid per 
one mole of sodium chlorite. This process also uses a catalyst and yields 
of 85 to 95% are obtained. 
The current state of the art teaches that concentrated hydrochloric acid 
and concentrated sodium chlorite cannot be reacted without prior dilution 
of the acid. However, we have found that the reaction is very safe and no 
explosion will result, and, that the acid required to reach a 90% yield or 
better is about one third the amount required to achieve these yields if 
acid pre-dilution is practiced. 
In a second embodiment of the present invention, it was found that the 
yield or conversion to chlorine dioxide will approach 100% if the 
hydrochloric acid is used at the stoichiometric ratio. More specifically, 
when the 10 molar hydrochloric acid was fed at a ratio of 1 mole of sodium 
chlorite to 0.8 moles of hydrochloric acid, a 95% yield was obtained. 
In another embodiment of the present invention it was found that a shorter 
reaction time would result from using a higher ratio of acid. By 
increasing the acid feed rate from 118% to 150% excess above the 
stoichiometric ratio the reaction time will decrease from 20-30 minutes to 
8-12 minutes and the yield remains at 100%.

The following examples are given to illustrate the process of the present 
invention but are not to be construed as limiting the invention thereto. 
EXAMPLES 
Example I 
A 1.92 molar solution of sodium chlorite was fed into the bottom of a 
packed reaction column at the rate of 112.2 ccm or 19.5 gms per minute. 
Hydrochloric acid 10 molar was fed neat also into the bottom of the 
reaction column, at a rate of 20.5 ccm or 7.3 gms/minute, this feed rate 
corresponding to 15% excess hydrochloric acid above the stoichiometric 
ratio of 1 mole sodium chlorite per 0.8 mole hydrochloric acid. The actual 
ratio would be 1 mole sodium chlorite to 0.92 mole hydrochloric acid. The 
generator was run for 60 minutes to insure a continuous, operational, 
equalibrium. Chlorine dioxide was taken out of the top of the generator 
over flow after being diluted with tap water. Test were made on a 
spectophotometer at 360 NM and showed a 100% conversion of the 
stoichiometric chlorine dioxide. 
Example II 
A 1.92 molar solution of sodium chlorite was fed into the bottom of a 
packed reaction column at the rate of 110.4 ccm (19.2 gms/min.). 
Hydrochloric acid 10 molar was also fed into the bottom of the above 
mentioned column at the rate of 17.6 ccm, (6.27 gms/min.), this ratio 
corresponding to the stoichiometric ratio of 1 mole of sodium chlorite to 
0.8 mole hydrochloric acid. 
The generator was allowed to run for 60 minutes for a continuous, stable, 
operation. The chlorine dioxide was diluted with tap water and run on a 
Turner Spectophotometer at 360 nanometers. The results showed a 95% 
conversion to chlorine dioxide of the stoichiometric 4 moles chlorine 
dioxide to 5 moles sodium chlorite. 
Example III 
A 1.92 molar solution of sodium chlorite was fed into the bottom of a 
packed reaction column at the rate of 315 ccm or 54.8 gms/min. 
hydrochloric acid 10 molar was fed neat into the opposite side of the 
reaction column at the rate of 107.2 ccm or 38.2 gms/min. This feed rate 
corresponding to a 118% excess of hydrochloric acid above the 
stoichiometric ratio of 1 mole sodium chlorite to 0.8 mole hydrochloric 
acid. The actual mole ratio would be 1 mole sodium chlorite to 1.75 moles 
hydrochloric acid. The generator was run for 30 minutes to insure a stable 
continuous operation. The chlorine dioxide exiting out the top of 
generator was diluted with tap water and measured on a Turner 
Spectophotometer at 360 NM. The results showed a 100% conversion to 
chlorine dioxide. 
PROCESS TECHNOLOGY 
As has been indicated, the general reaction of sodium chlorite and 
hydrochloric acid is known to the art. The advance of this invention is 
seen to be the reaction of concentrated 10 molar hydrochloric acid 
solution with concentrated sodium chlorite solution removed from the 
dilution or possibly quenching effect of water. By using this process a 
dramatic decrease in the hydrochloric acid requirement results. 
Temperature control and/or the need of a catalyst are eliminated, the 
yield of chlorine dioxide is very high, and the elimination of a costly 
acid dilution procedure is accomplished. 
Since certain changes may be made in the above process without departing 
from the scope of the invention herein involved, it is intended therefore 
that all matter contained in the above description shall be interpreted as 
illustrative and not in a limiting sense.