Science: Chemistry

Chlorine dioxide is a powerful, selective biocide. First discovered in 1811, its anti-microbial properties have been known since about 1900.

Chlorine dioxide has been used in the United States to disinfect public drinking water for more than 60 years. It also is used for a variety of sterilization, disinfection and decontamination purposes in the food, beverage and medical device industries.

Chlorine dioxide has attractive human- and ecological-toxicity profiles. Exposure does not pose chronic adverse health effects (e.g., cancer) nor does chlorine dioxide persist in the environment.

Chlorine dioxide is a relatively small, volatile and highly energetic molecule. Chlorine dioxide is almost never used commercially as a gas at high concentrations because of its instability; rather, it is generated at the point of use.

Chlorine dioxide gas has an intense greenish yellow color with a distinctive odor similar to that of chlorine. Chlorine dioxide is highly soluble in water but, unlike chlorine, chlorine dioxide does not react with water. It exists in aqueous solution as a dissolved gas.

Chlorine dioxide functions as a highly selective oxidant owing to unique, one-electron transfer mechanisms, wherein it attacks electron-rich centers in organic molecules and, in the process, is reduced to chlorite ion.

Because chlorine dioxide oxidizes but does not chlorinate, chlorinated organic by-products (e.g., THM, HAA, dioxins, furans) typically are not produced. Neither does chlorine dioxide produce appreciable amounts of aldehydes, ketones, ketoacids nor other problematic compounds associated with oxidation of organic matter by other, less selective means.

High-purity chlorine dioxide is less destructive/corrosive than chlorine to most materials, including stainless steel. In the presence of UV light, chlorine dioxide rapidly decomposes to form chlorine, oxygen and a variety of transient intermediate oxychlorine compounds which may be highly corrosive.

Chlorine dioxide’s unique properties permit it to be more effective than current oxidizing and non-oxidizing biocide technologies. Among its outstanding characteristics: (a) it remains a dissolved gas in water, thereby maintaining its biocidal activity under varied operating conditions, (b) it is effective over a wide pH range (4-10), remaining effective even where there are incoming stock pH swings, (c) it reacts selectively with organic compounds and does not form chlorinated organics (chloroform, bromoform, dioxins or trihalomethanes), all of which are coming under increasing regulatory pressure, (d) it reacts almost instantaneously to quickly provide effective biocidal control or remove undesirable contaminants, (e) at recommended use levels it does not create toxic by-products harmful to wildlife or the environment.

The GAS:SOLID™ system is an integrated arrangement of equipment and chemicals designed to produce high purity chlorine dioxide gas, on-site, at customers’ facilities. At the heart of the GAS:SOLID™ chlorine dioxide process is the reaction between chlorine gas and SAF-T-CHLOR™ thermally stable solid sodium chlorite.

Cl2 + 2NaClO2 -> 2ClO2 + 2NaCl

This reaction produces no by-products—just pure chlorine dioxide gas (in air or nitrogen), free of chlorite ion, chlorate ion, perchlorate ion or molecular chlorine.

GAS:SOLID™ systems deliver consistently pure chlorine dioxide over their entire operating range, without recalibration.