Note: Descriptions are shown in the official language in which they were submitted.
CA 02946017 2016-10-14
A METHOD FOR HYDROGEN PEROXIDE BASED CHLORINE DIOXIDE
PRODUCTION PROCESS WITH A VERTICAL GENERATOR
Description
Field
This invention relates to a method for hydrogen peroxide based chlorine
dioxide
production process with a vertical generator.
Background
Chlorine dioxide (C102) is a strong oxidizing agent that has been applicable
in medical
care, sterilization, and pulp bleaching and water treatment. Production
process for chlorine
dioxide can be categorized into electrolytic process and chemical process. The
electrolytic
process has certain advantages in environmental discharge, and low raw
material consumption,
yet requiring high investment for a complex system and maintenance,
sophisticated
requirement of operation and high energy consumption, which limits its
application.
Therefore, the chemical process dominants in the industry today. After years
of development
and research, the chemical process has been fully developed for dozens of
derivative methods.
The most applied method ¨ a methanol based process has multiple advantages
regarding the
product purity, low capital investment and convenient production. However,
various
byproducts are produced in the process e.g. methanol, formaldehyde and formic
acid, which
are toxic and bring drawbacks to the applications. For instance, chlorinated
organics can be
formed in bleaching process; or, carcinogens e.g. trichloromethane can be
formed in drinking
water treatment process. Another widely applied method is the hydrochloric
acid based
process. During this process, 1 mol of chlorine dioxide generated 0.5 mol
chlorine gas will
simultaneously be produced which requires further treatment. On the contrary,
the hydrogen
peroxide based process possesses an incomparable improvement that can generate
high
quality chlorine dioxide without chlorine and other hazardous gases or with
small amount of
chorine. Due to multiple advantages of the hydrogen peroxide based process,
e.g. raw material,
cost, and efficiency etc., the process shows bright prospects for the future.
However, the
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hydrogen peroxide based process generally use a multistage aeration generator
which gives
rise to a large amount of waste discharge and leads to environmental issues
during the
chlorine dioxide production.
Therefore, it becomes an urgent problem for eliminating or reducing
contaminative
discharges during the chlorine dioxide production process.
Summary of Invention
The technical issue to be solved by the current invention is to provide a
method for
hydrogen peroxide based chlorine dioxide production process with a vertical
generator, which
discharges no waste acid while producing high purity chlorine dioxide, with
neutral salt cake
and oxygen as the by-products, being clean and environmental-friendly.
This invention presents approaches to above technical issues as follows:
A method for hydrogen peroxide based chlorine dioxide production process with
a
vertical generator, characterized by consisting of a chlorine dioxide
generation section
constituted of a reboiler (3), an upper circulation piping (5), a generator
(21), a lower
circulation piping (22), a generator exhaust gas pipe (10), a generator
circulation pump (23),
an indirect cooler (19), an absorber (18), a generator vacuum pump (13) and
the related piping;
a salt cake filtration section constituted of a filter (7), a hydrocyclone
(8), a gas-liquid
separation tank (9), a filter vacuum pump (11), a salt cake feed pump (20) and
the related
piping; and a tail gas treatment section constituted of a tail gas scrubber
(14), a tail gas blower
(15) and the related piping.
A method for hydrogen peroxide based chlorine dioxide production process with
a
vertical generator, also characterized by the following process procedures:
1. Mix hydrogen peroxide and sodium chlorate solution in the piping before
feed into the
generator through a straight pipe in the header below the reboiler.
Concentrated sulfuric acid
flows to a throat in the outlet on the top of the reboiler and is diluted to
60wt%-65wt%
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concentration with deionized water before being injected into generator
circulation system.
Under the force of the generator circulation pump, the chemical raw materials
are mixed and
react sufficiently, producing chlorine dioxide, water, oxygen and neutral salt
cake under a
controlled low mother liquor acidity in the vertical generator as well as the
generator pressure,
the temperature and other process parameters maintained within a certain
range. The produced
C102 gas is released, while the remaining liquor and by-product settle to the
bottom of the
generator as generator liquor, which is circulated between the reboiler and
the generator
continuously by the circulation pump to mix and react with a continuous feed
of hydrogen
peroxide, NaC103 mixture and concentrated sulfuric acid, producing C102 gas
continuously.
The C102 gas produced in the generator is diluted by a large amount of water
vapors and
oxygen produced from the reactions, becoming gas mixture. The gas mixture
exits from the
generator exhaust pipe, passes through the intercooler, and then enters the
absorber to be
absorbed by chilled water and form C102 aqueous solution for delivery. The
reaction is as
below:
2NaC103+H2SO4 + 14202 ¨> 2C102 + 02+ 2H20+Na2SO4
2. With a continuous feeding of hydrogen peroxide and sodium chlorate mixture
and
concentrated sulfuric acid, reactions take place continuously. Along with the
continuous
generation of C102, there is a continuous crystallization of salt cake, the by-
product, inside the
generator. The salt cake feed pump (20) takes out part of the mother liquor
containing salt
cake crystals from the lower circulation piping (22) of the generator and
transfers them to the
hydrocyclone (8) to separate solids and liquid. Mother liquor that has gone
through the
separation, after joining with washing liquid from the filter (7) and the gas-
liquid separation
tank (9), flows to the lower circulation piping (22) of the generator, while
the filtrated neutral
salt cake crystals are transferred out of the system for utilization.
3. Tail gas from the system enters the tail gas scrubber (14) to be scrubbed
by chilled
water. Dilute chlorine dioxide solution obtained from this process returns to
the absorber (18),
and tail gas is discharged by the tail gas blower (15).
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It is preferred that the generator be a vertical generator.
It is preferred that hydrogen peroxide and sodium chlorate mix in pipeline
before being
introduced to generator circulation system through a straight pipe in the
header below the
boiler.
It is preferred that sulfuric acid be diluted to 60wt%-65wt% concentration by
deionized
water before being injected into the generator circulation system.
It is preferred that acidity of the mother liquor within the generator be
maintained at
2-5N.
It is preferred that temperature inside the generator be 60-80 C, maintaining
vacuum
conditions at a gauge pressure of -72 to -85kPa.
It is preferred that the mother liquor density inside the generator be 1.4 to
1.8g/cm3.
It is preferred that the sodium chlorate concentration inside the generator be
1.8 to
3 .3mo1/1.
Advantages and effects of the invention:
1. Hydrogen peroxide and sodium chlorate mix in the pipeline before being
introduced to
the generator circulation system to decrease the concentration of hydrogen
peroxide, which
prevents the situation where chlorine dioxide decomposes due to violent
reactions caused by
high concentration of hydrogen peroxide fed to the generator, improving
reaction efficiency
and safety.
2. High purity chlorine dioxide, with a chlorine content of 0.01 to 0.08 g/1
C102.
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3. No waste acid discharge from the chlorine dioxide production process.
4. By-product of the chlorine dioxide production process is a neutral salt
cake.
Description of the drawings
Fig. 1 shows the process flow diagram of the invention.
Where:
1. Sodium chlorate feed pipe; 2. Hydrogen peroxide feed pipe; 3. Reboiler; 4.
Sulfuric acid
feed pipe; 5. Upper circulation piping of the generator; 6. Salt cake outlet;
7. Filter; 8.
Hydrocyclone; 9. Gas-liquid separation tank; 10. Generator exhaust gas pipe;
11. Filter
vacuum pump; 12. Absorber chilled water feed pipe; 13. Generator vacuum pump;
14. Tail
gas scrubber; 15. Tail gas blower; 16. Scrubber chilled water feed pipe; 17.
Chlorine dioxide
transfer pipe; 18. Absorber; 19. Intercooler; 20. Salt cake feed pump; 21.
Generator; 22 Lower
circulation piping of the generator; 23. Generator circulation pump
Detailed description of embodiments
A further description of the method for hydrogen peroxide based chlorine
dioxide
production process with a vertical generator that this invention relates to is
given through the
examples below. The following examples are prescribed for illustrating the
technical
framework and characteristics of this invention with the intention to make the
details of the
invention understandable to those unfamiliar with it, while not meant to limit
the protection
scope of the invention. The protection scope shall cover any equivalent
transformation of or
embellishment to the spirit of this invention.
Example 1:
A method for hydrogen peroxide based chlorine dioxide production process with
a
CA 02946017 2016-10-14
vertical generator, characterized by the following: a chlorine dioxide
generation section, a salt
cake filtration section and a tail gas treatment section.
The operation procedures of the invention are shown as follows:
1) Sodium chlorate from sodium chlorate feed pipe (1) at 600g/1 concentration
mixes with
hydrogen peroxide from hydrogen peroxide feed pipe (2) at 60wt% concentration
in the
sodium chlorate feed pipe (1), before introduced to the generator circulation
system through a
straight pipe in the header below the reboiler (3). Concentrated sulfuric acid
from sulfuric acid
feed pipe (4) at 98wt% concentration flows to a throat in the outlet on the
top of the reboiler
(3) and is diluted to 60wt%-65wt% concentration with deionized water before
being injected
into the generator circulation system. Under the force of the generator
circulation pump (23),
the chemical raw materials are mixed and react sufficiently, producing
chlorine dioxide, water,
oxygen and neutral salt cake under controlled conditions inside the vertical
generator (21)
with a mother liquor acidity of 2 - 5N, a gauge pressure of -72 to -85kPa, a
temperature of
60 C - 80 C, a mother liquor density of 1.4 - 1.8g/cm3 and a sodium chlorate
solution
concentration of 1.8 - 3.3mo1/1. The produced C102 gas is released, while the
remaining
liquor and by-product settle to the bottom of the generator (21) as generator
liquor, which is
circulated between the reboiler (3) and the generator (21) continuously by the
circulation
pump (23) to mix and react with constant feed of hydrogen peroxide, sodium
chlorate mixture
and concentrated sulfuric acid, producing C102 gas continuously. The C102 gas
produced in
the generator (21) is diluted inside the generator (21) by a large amount of
steam evaporated
and oxygen produced from the reactions, becoming gas mixture. The gas mixture
exits from
the generator exhaust pipe (10), passes through the indirect cooler (19), and
then enters the
absorber (18) to be absorbed by chilled water from absorber chilled water feed
pipe (12) and
form C102 aqueous solution for delivery via chlorine dioxide transfer pipe
(17). While
generating vacuum in the generator (21), generator vacuum pump (13) also pumps
tail gas in
the absorber (18) to the tail gas scrubber (14).
2) With the continuous feeding of hydrogen peroxide and sodium chlorate
mixture and
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concentrated sulfuric acid, reactions take place ceaselessly. Along with the
continuous
generation of C102, there is a continuous crystallization of salt cake, the by-
product, inside the
generator (21). The salt cake feed pump (20) takes out part of the mother
liquor containing
salt cake crystals from the lower circulation piping (22) of the generator and
transfers them to
the hydrocyclone (8) to separate solids and liquid. Mother liquor passes
through the
separation, after joining with washing liquid from the filter (7) and the gas-
liquid separation
tank (9), flowing to the lower circulation piping (22) of the generator, while
the filtrated
neutral salt cake crystals are transferred out of the system from salt cake
outlet (6) for
utilization. While generating vacuum inside the filter (7), the filter vacuum
pump (11) also
pumps tail gas in the salt cake treatment section to the tail gas scrubber
(14).
3) Tail gas from the system enters the tail gas scrubber (14) to be scrubbed
by 5 C - 7 C
chilled water from scrubber chilled water feed pipe (16). Dilute chlorine
dioxide solution
obtained from this process returns to the absorber (18), and tail gas is
discharged by the tail
gas blower (15).
Example 2:
It is a method for hydrogen peroxide based chlorine dioxide production process
with a
vertical generator. The feature is that the process is consisted of chlorine
dioxide generation,
salt cake filtration and tail gas treatment.
The process of the invention is as following.
1) The 650g/1 concentration sodium chlorate solution from chlorate feed pipe
(1) and the
50wt% concentration hydrogen peroxide solution from hydrogen peroxide feed
pipe (2) are
mixed in the chlorate feed pipe (1). Then the mixed liquor flows into the
generator circulation
system from the pipe header of the bottom reboiler (3). The 96wt%
concentration sulfuric acid
from sulfuric acid feed pipe (4) flows to the nozzle at the top of the
reboiler (3). The sulfuric
acid is diluted to 60wt%-65wt% with deionized water and then injected into the
generator
circulation system. The chemical raw material is mixed by the generator
circulation pump (23)
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and reacts in the process, acidity of mother liquor is 2-5N, vacuum degree is -
72 - -85kPa,
temperature is 60 C-80 C, the density of the mother liquor is 1.4-1.8g/cm3 and
the
concentration of sodium chlorate is 1.8-3.3mol/L in the vertical generator
(21). The reaction
outcome is chlorine dioxide, water, oxygen and neutral salt cake. The chlorine
dioxide is
generated, the reaction remains in liquid and the by-product is precipitated
down to the
bottom of generator (21) and becomes the generator solution. The solution is
circulated
between the reboiler (3) and the generator (21). The liquid continuously mixes
with the fed
hydrogen peroxide, sodium chlorate and sulfuric acid, which generates chlorine
dioxide gas.
The chlorine dioxide from the generator (21) is diluted by the steam and
oxygen gas produced
in the generator (21), the mixed gas is exhausted from the generator exhaust
pipe (10). After
indirect cooler (19) the exhaust gas then enters absorber (18), is absorbed by
chilled water
from the chilled water feed pipe (12). The chlorine dioxide solution is
produced. The solution
is sent out from chlorine dioxide transfer pipe (17). The generator vacuum
pump (13)
generates vacuum in the generator (21) and pumps the tail gas from the
absorber (18) to the
scrubber (14).
2) The hydrogen peroxide and sodium chlorate mixed while sulfuric acid is
continuously
added. The chlorine dioxide generated with by-product salt cake is
crystallizing in the
generator (21), the salt cake feed pump (20) sucks out the salt cake from the
generator lower
circulation pipe (22) and sends it to the hydrocyclone separator (8) for solid-
liquid separation.
The separated mother liquor and the liquid from the filter (7) and washing
liquid from
gas-liquid separation tank (9) are mixed before flow back to the generator
lower circulation
pipe (22). The filtered neutral salt cake crystal is discharged from the salt
cake outlet (6) and
sent to other plants. The filter vacuum pump (11) generates vacuum in the
filter (7) and sucks
out the tail gas in the salt cake treatment process to the tail gas scrubber
(14).
3) The system produced tail gas enters the tail gas scrubber (14) and scrubbed
by 5 C -
7 C chilled water from scrubber chilled water dosing pipe (16). The obtained
diluted chlorine
dioxide solution flows back to the absorber (18), the tail gas is pumped out
by the tail gas
blower (15).
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Example 3:
It is a method for hydrogen peroxide based chlorine dioxide production process
with a
vertical generator. The feature is that the process is consisted of chlorine
dioxide generation,
salt cake filtration and tail gas treatment.
The process of the invention is as following.
1) 700g/1 concentration sodium chlorate solution from the chlorate feed pipe
(1) and the
27.5wt% concentration hydrogen peroxide solution from the hydrogen peroxide
feed pipe (2)
is mixed in the chlorate feed pipe (1). Then the mixed liquid flows into the
generator
circulation system from the pipe header of bottom reboiler (3). The 93wt%
concentration
sulfuric acid from sulfuric acid feed pipe (4) flows to the nozzle at the top
of the reboiler (3).
The sulfuric acid is diluted to 60wt%-65t% with deionized water and injected
into the
generator circulation system. The chemical raw material is mixed by the
generator circulation
pump (23) and reaction occurs. The acidity of the mother liquor is 2-5N,
vacuum degree is
-72 - -85kPa, temperature is 60 C -80 C, the density of the mother liquor is
1.4-1.8g/cm3 and
the sodium chlorate concentration is 1.8-3.3mol/L in the vertical generator
(21).The reaction
outcome is chlorine dioxide, water, oxygen and neutral salt cake. Chlorine
dioxide is
generated, the reaction remained in liquid and the by-product is precipitated
down to the
bottom of the generator (21) and become the generator solution. The solution
is circulated
between the reboiler (3) and the generator (21). The liquid is continuously
mixed with the fed
hydrogen peroxide, sodium chlorate and sulfuric acid, which generates chlorine
dioxide gas.
The chlorine dioxide gas from the generator (21) is diluted by the steam and
oxygen gas
produced in the generator (21), and the mixed gas is exhausted from the
generator exhaust
pipe (10). After indirect cooler (19), the mixed gas enters the absorber (18),
absorbed by
chilled water from the chilled water dosing pipe (12) and produced a chlorine
dioxide solution.
The solution is sent out from the chlorine dioxide transfer pipe (17). The
generator vacuum
pump (13) generates vacuum in the generator (21) and pumps the tail gas from
the absorber
(18) to the tail gas scrubber (14).
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2) Hydrogen peroxide and sodium chlorate are mixed while the sulfuric acid is
continuously added in the process. As chlorine dioxide is generated in the
system, a
by-product salt cake is crystallized in the generator (21), the salt cake feed
pump (20) sucks
out the salt cake from the generator lower circulation pipe (22) and send to
the hydrocyclone
separator (8) for solid-liquid separation. The separated mother liquor and the
liquid from the
filter (7) and the washing liquid from the gas-liquid separation tank (9) are
mixed and flow
back to the generator lower circulation pipe (22). The filtered neutral salt
cake crystal is
discharged from the salt cake outlet (6) and is sent to other plants. The
filter vacuum pump
(11) generates vacuum in the filter (7) and pumps out the tail gas in salt
cake treatment
process to the tail gas scrubber (14).
3) Tail gas from the system enters the tail gas scrubber (14), is processed
with 5-7 C
chilled water from the chilled water feed pipe (16) of the scrubber, forms a
dilute chlorine
dioxide solution which flows back to the absorber (18), while the remaining
tail gas is blown
out by the tail gas blower (15).
