GENESYS Manual and Automatic Chlorine Dioxide Systems
Two Chemical Generation Systems
- Chlorine Gas – Sodium Chlorite
This generation method, the most flexible and efficient method of generating chlorine dioxide, generates chlorine dioxide in a two step process. First, (equation 1), chlorine gas reacts with water to form hypochlorous acid (HOCl) and hydrochloric acid (HCl). These acids react (equation 2) with sodium chlorite to form chlorine dioxide, water, and sodium chloride (NaCl). The ratios of sodium chlorite and hypochlorous acid (chlorine) must be carefully controlled. Insufficient chlorine feed will result in a large amount of unreacted chlorite. Excess chlorine feed will result in the formation of sodium chlorate (NaClO3), which is the oxidation product of chlorine dioxide.
(1) Cl2 + H2O → HOCl + HCl
(2) 2NaClO2 + HOCl + HCl →2ClO2 + H2O + 2NaCl
Net: 2NaClO2 + Cl2→ 2ClO2 + 2NaCl
- Acid – Chlorite
The acid chlorite generation method is the simplest and easiest to operate generation chemistry. This method uses two chemical feeds and is simple reaction chemistry (equation 3). Instead of having to balance the amounts of sodium chlorite and hypochlorous acid, one merely has to provide sufficient hydrochloric acid. Excess acid does form undesirable reaction products. This ease of operation comes at the cost of chlorine dioxide yield. The theoretical conversion of sodium chlorite to chlorine dioxide is only 80%, while the chlorine-chlorite and acid-hypochlorite-chlorite reactions both have theoretical conversions of 100%.
(3) 5NaClO2 + 4HCl → 4ClO2 + 5NaCl + 2H2O
Three Chemical Generation Systems
- Acid-Hypochlorite-Chlorite
This is an alternative to chlorine-chlorite generation that is used when chlorine gas is not available. First (equation 4), sodium hypochlorite is combined with hydrochloric or other acid to form hypochlorous acid. Sodium chlorite is then added to this reaction mixture to produce chlorine dioxide (equation 5).
(4) NaOCl + HCl → HOCl + NaCl
(5) NaClO2 + HOCl + HCl → 2ClO2 + H2O + 2NaCl
Net: 2NaClO2 + NaOCl + 2HCl → 2ClO2 + H2O + 3NaCl
Since equations 2 and 5 are identical, the chlorine dioxide generation step is the same. Consequently, the typical operating conditions, yield, and purity for this method of generation are the same as for chlorine-chlorite generation. This method also shares the requirement of carefully balancing sodium chlorite and hypochlorous acid feeds, which is made more difficult by poor storage characteristics (rapid degradation) of sodium hypochlorite solutions.