Experts in Chem-Feed and Water Treatment
ClO2: One Chemical – Multiple
Technologies of Generation
How to select the suitable equipment
Dr. rer. nat. Matthias Rothe
ProMinent ProMaqua GmbH
Maaßstraße 32/1, D-69123 Heidelberg
Tel. +49 (6221) 6489-0, Fax. +49 (6221) 6489-400
[email protected] www.promaqua.com
Properties of Chlorine Dioxide
Experts in Chem-Feed and Water Treatment
Cl
Cl
•O
O
O
O•
ƒ unpaired electron, considered to be a free radical:
high reactivity for oxidation and disinfection
ClO2 + e- €
ClO2- (Chlorite)
E0 = 0.95 V
ƒ soluble in water as a gas
- reactivity independent of pH
- able to penetrate cellular membranes
- able to kill and remove biofilm
ƒ yellow-green gas, cannot be stored or compressed,
has to be produced freshly on site
Product Mangement, Dr. Rothe, 04.09.07
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Selection Criteria for ClO2-Generators
Experts in Chem-Feed and Water Treatment
ƒ capacity
- small
< 1 kg/h
- medium 1 – 10 kg/h
- large
> 10 kg/h
ƒ precursor chemicals
- liquid chemicals
- liquid + gaseous chemicals (chlorine gas)
ƒ yield and chemical by-products
- chlorite and chlorate
- chlorinated organics
ƒ safety features
ƒ costs
- invest costs
- operating costs
Product Mangement, Dr. Rothe, 04.09.07
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Multiple Technologies to Generate ClO2
Experts in Chem-Feed and Water Treatment
Photochemical
Very Small (< 100 g/h)
Electrochemical
Medium (< 10 kg/h)
7,5% NaClO2 / 9% HCl
Small (< 2 kg/h)
25% NaClO2 / 31% HCl
Medium (< 10 kg/h)
Aqueous Cl2
Medium (< 10 kg/h)
Vapor phase Cl2
Large (> 10 kg/h)
Solid Matrix
Medium (< 10 kg/h)
(NaClO3 / H2O2 + H2SO4)
Mixed Phase (Gas/Water)
Large (> 10 kg/h)
3-Chemical Systems
(NaClO2/ NaOCl/ HCl)
Vapor Phase
Large (> 10 kg/h)
Low pH
Medium (< 10 kg/h)
1-Chemical
Systems (NaClO2)
2-Chemical Systems
(NaClO2 / HCl)
2-Chemical Systems
(NaClO2 / Cl2)
2-Chemical System
common practice in European drinking water treatment
Product Mangement, Dr. Rothe, 04.09.07
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Chlorite / Acid - Procedure
Experts in Chem-Feed and Water Treatment
chemicals:
sodium chlorite (NaClO2)
hydrochloric acid (HCl)
5 NaClO2 + 4 HCl 4 ClO2 + 5 NaCl + 2 H2O
ƒ > 90 % yield at 80 % conversion rate
ƒ chlorine-free solution of chlorine dioxide
ƒ precise and reliable technology due to dosage of liquids
- systems using metering pumps have a fast reactivity on
changes of the ClO2-demand and the backpressure of the
water to be treated
ƒ no handling of gas chlorine necessary
Product Mangement, Dr. Rothe, 04.09.07
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Chlorite / Acid - Procedure
Experts in Chem-Feed and Water Treatment
ClO2 to Process
Reactor
ƒ metering pumps with
flow control
ƒ pressurized system
avoiding development
of gas bubbles
ƒ best way to control the
capacity
ƒ eductor driven dosage
of the precursors with
flow meters
ƒ vacuum system
avoiding leakages
ƒ hardly controllable
HCl
water
NaClO2
9%
or 31 %
(at 25 %
Chlorite +
31 % HCl)
7,5 %
or 25 %
Product Mangement, Dr. Rothe, 04.09.07
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Why not Using Different Acids than HCl?
Experts in Chem-Feed and Water Treatment
ƒ chloride of hydrochloric acid is required to achieve a conversion
rate of 80 %
5 NaClO2 + 5 HCl
HClO2 +
HCl
2 HOCl + 4 HClO2
5 HClO2 + 5 NaCl
2 HOCl
4 ClO2 + 2 HCl + 2 H2O
ƒ without chloride the conversion rate is 50 % and chlorate
is generated as a by-product
8 NaClO2 + 4 H2SO4
4 HClO2
2 HOCl + 4 HClO2
Product Mangement, Dr. Rothe, 04.09.07
8 HClO2 + 4 Na2SO4
2 HOCl + 2 HClO3
4 ClO2 + 2 HCl + 2 H2O
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Typical ClO2–Concentrations
water:
0,05-2 ppm
ClO2
Experts in Chem-Feed and Water Treatment
bypass:
200-1000 ppm
ClO2
reactor:
20.000 ppm
ClO2
Product Mangement, Dr. Rothe, 04.09.07
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Chlorite / Chlorine - Procedure
Experts in Chem-Feed and Water Treatment
chemicals:
sodium chlorite (NaClO2)
gas chlorine (Cl2)
2 NaClO2 + Cl2 2 ClO2 + 2 NaCl
ƒ 100 % conversion rate; > 90 % yield, if the gas
chlorine dosing system is perfectly trimmed
ƒ no chlorine-free solution of chlorine dioxide
- chlorinated by-products are not excluded
ƒ intermediate storage of the ClO2-solution required at fast
changes of the ClO2-demand and the backpressure of the
water to be treated
ƒ additional safety requirements for handling of gas chlorine
Product Mangement, Dr. Rothe, 04.09.07
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Chlorite / Chlorine - Procedure
Experts in Chem-Feed and Water Treatment
ClO2 to Process
Reactor
ƒ 1.) eductor driven dosage of gas
chlorine into water
ƒ 2.) metering pump driven
dosage of chlorite
ƒ pressurized system avoiding
development of gas bubbles
ƒ precise control of gas and water
flow required
ƒ capacity hardly controllable
gas chlorine
NaClO2
25 %
water
Product Mangement, Dr. Rothe, 04.09.07
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Chlorate / Peroxide - Procedure: Purate®
Experts in Chem-Feed and Water Treatment
chemicals: sodium chlorate (NaClO2)
hydrogen peroxide (H2O2)
sulphuric acid (H2SO4)
pre-blended Purate®
2 NaClO3 + H2O2 + H2SO4 % 2 ClO2 + O2 + Na2SO4 + 2 H2O
ƒ > 95 % yield at 100 % conversion rate
ƒ chlorine-free solution of chlorine dioxide
ƒ mixed phase reaction due to the generation of oxygen
ƒ small reactors due to high reaction speed
ƒ patented procedure
- joint venture between Eka-chemicals and ProMinent
ƒ most economical generation of chlorine dioxide
Product Mangement, Dr. Rothe, 04.09.07
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ProMinent Purate® - Procedure
Experts in Chem-Feed and Water Treatment
flow meter
by-pass water
PLC
Siemens S7
eductor
reaktor
vacuum
monitor
metering pump
H2SO4 78 %
Product Mangement, Dr. Rothe, 04.09.07
metering pump
Purate
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Yield and Chemical By-Products
Experts in Chem-Feed and Water Treatment
ƒ optimum relation between the precursor chemicals
- not enough acid at chlorite/acid- and Purate-procedure:
chlorite and chlorate as by-products
- not enough chlorine at chlorite/chlorine-procedure:
chlorite as by-product
ƒ optimum reactor design and capacity adjustment
- reactor hydraulics to achieve perfect mixing of the precursors
- reactor volume to achieve sufficient reaction time and to avoid
decomposition of ClO2 into chlorate
ƒ optimum reaction temperature
- too cold conditions require longer reaction time
ƒ side-reactions with components of the water to be treated
- reaction between ClO2 and e.g. iron generates chlorite
- has nothing to do with the generator’s yield!
Product Mangement, Dr. Rothe, 04.09.07
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Safety Standards and Approvals
Experts in Chem-Feed and Water Treatment
ƒ DVGW working sheets W 224 and W 226
(DVGW = German registered association for gas and water)
- worldwide unique standards for design and operation of
chlorine dioxide generators
• quality, concentration, and stoichiometric relation of the
precursor chemicals
• dosage and surveillance of the precursors
• control of any water flow required for generation and
dosage
• general safety features of the reactors
• general features of the generator’s controller
• general features of the ClO2-dosage and its surveillance
ƒ German drinking water regulation stipulate compliance
of W 224 and W 624, but no approval or certification
Product Mangement, Dr. Rothe, 04.09.07
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Operating Costs
Experts in Chem-Feed and Water Treatment
chlorite/acid: 1 kg NaOCl2 25 % + 1 kg HCl 31 %
1,50 €
+
0,50 €
134 g ClO2
2,00 €
1 kg ClO2 costs approx. 15,- €
chlorite/chlorine: 1 kg NaOCl2 25 % + 0,25 kg Cl2
1,50 €
+
0,20 €
167 g ClO2
1,70 €
1 kg ClO2 costs approx. 10,- €
Purate:
1 kg Purate + 1 kg H2SO4 98 %
1,20 €
+
0,20 €
284 g ClO2
1,40 €
1 kg ClO2 costs approx. 5,- €
Product Mangement, Dr. Rothe, 04.09.07
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„Stabilized“ Chlorine Dioxide
Experts in Chem-Feed and Water Treatment
ƒ stabilized chlorine dioxide doesn‘t exist!
ƒ mostly contains 5 % sodium chlorite or hypochlorite
solution instead of chlorine dioxide
ƒ please, have a look into the safety data sheet, where you
will find the real chemical classification
Product Mangement, Dr. Rothe, 04.09.07
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Thank you for your attention
Experts in Chem-Feed and Water Treatment
Any question?