Chlorine dioxide has been commercially used for bleaching pulp since the mid 1940s. It is usually produced on-site by reacting sodium chlorate with a reducing agent in an acidic solution. By varying the reducing agent and the acid solution, different byproducts are produced.
Speaking in broad categories, ClO2
is produced under atmospheric or vacuum conditions. Atmospheric processes, for example, are the Mathieson process and the HP-A® (Hydrogen Peroxide Atmospheric).
The vacuum process, introduced by Eka Chemicals, is referred to as the Single Vessel Process (SVP®). The first standard SVP® unit was installed in 1969. Today, the SVP chlorine cioxide process family consists of a number of similar processes, all performed with basically the same set-up equipment. The processes are distinguished by the use of different reducing agents for converting chlorate to chlorine dioxide and acids. The most common process is the SVP-LITE® process, which is based on the use of methanol, producing an elemental chlorine-free (ECF) product and usable byproducts with minimum waste.