A brief description of chlorine dioxide process is presented for reference.


Developed in 1950 by Olin-Mathieson Chemical Corporation. This process generates
chlorine dioxide (ClO2) by the reduction of sodium chlorate (NaClO3) with sulfur dioxide
(SO2) in the presence of sulfuric acid (H2SO4).

Modified Mathieson

Sodium chloride (NaCI) is added in small amounts to the reactants in the primary
generator. The addition of NaCI improves the reduction efficiency of the chlorate and
increases generator capacity. Sodium chloride, up to 10% of weight of sodium chlorate,
is usually mixed with the sodium chlorate by the sodium chlorate supplier.


The Solvay process is essentially the same as the Mathieson system except methanol
(CH3OH) is used in place of SO2 as the reducing agent.


The Hoist process is a batch process similar to the Mathieson process. The significant
difference is the solution concentrations and the batch operations.


The kesting Day-Fenn, or Day-Kesting process utilizes hydrochloric acid (HCI) for
reduction of NaCIO3. This process is suitable for integration with an electrolytic plant
producing chlorate.


Sodium chlorate and sodium chlorite are reacted in strong acid to form chlorine dioxide.
This is the first of the "R" processes developed by Dr. Howard Rapson.


The R2 process is based on the use of NaCI for reducing the chlorate. No SO2 is used.
R2 solution, a mixture of NaCIO3 and NaCI, is added to the generator along with H2SO4.
Air is used for agitation and dilution of the chlorine dioxide gas. This process results in
increased formation of chlorine (Cl2), which must be absorbed (usually to form
hypochlorite (NaOCI) after the ClO2 absorption tower.


The NaCI and half the H2SO4 of the R2 process is replaced with hydrochloric acid (HCI).


The R3 process is a modified R2 process in which the reaction temperatures are
increased to boiling and concentrations strengthened to permit crystallization of sodium
sulfate (Na2SO4) in the reaction vessel. This process, trademarked R3 by Erco* and
SVP by Hooker**, is also referred to as the "effluent-free" process since the
by-product removed is crystalline Na2SO4. RS is a trade name of Erco, Ltd.

* Erco, subsequently known as Aibright & Wilson America, is now owned by Sterling
Chemical Co.

** Hooker Chemical Co., subsequently Oxidential Petroleum Co., now Eka-Nobel.


The NaCI and half of the H2SO4 of the R3 process is replaced with HCI.


The R5 process is basically the same as the R3 process except the NaCI and all of the
H2SO4 are replaced with HCI. HCI and NaCIO3 are the only feeds to the generator. The
by-product is crystalline NaCI suitable for reuse in chlorate manufacture.

Higher operating temperature and chemicals concentration differentiate the R5 process
from the R2 process, which has no crystalline by-product. The R5 process incorporates
technology developed by Dow Chemical Canada under Dow patents.


This is an "integrated" process designated as R6 by Erco and is used in conjunction with
an electrolytic plant producing NaCIO3. Other versions of the process are known as Lurgi
or Chemetics integrated process depending upon the vendor.


This process is a modification of the R3 process. In order to eliminate chlorine gas from
the exit stream, the chlorine bearing gas stream is reacted with S02 to form a mixed acid
of H2SO4 and HCI which are returned to the generator. The only by-product is anhydrous


Methanol is the reducing agent in the R8 process. The by-product is sodium
sesquisulfate [Na3H(S04)2], an acid salt. This salt requires neutralization with caustic
soda before recovery in the liquor system. This system is patented by Albright & Wilson


The R9 process is an extension of the R8 process in which the sodium sesquisulfate is
diluted with water and separated into caustic soda and sulfuric acid in a membrane cell.


The R1O process is another extension of the R8 process. The sodium sesquisulfate is
diluted with both water and methanol following removal of sodium sulfate in a second
filtration stage. The filtrate is returned to the generator. The process is patented by
Albright & Wilson Americas.

SVP Lite

This is another methanol based system similar to the R8 process. The main difference
is the acid strength in the generator. A patent is held by Eka-Nobel.


The SVP-HP system developed by Eka-Nobel is similar to SVP-Lite except uses
hydrogen peroxide instead of methanol for reduction of chlorate. This system is operated
under vacuum. The by-product is neutral sodium sulfate (Na2SO4).


Also utilizing hydrogen peroxide, this system is operated at atmospheric pressure. In
addition to producing Na2SO4 as a by-product, a spent acid stream is also discharged.


The Lurgi process is an integrated process in which an on site electrolytic process is used
for producing ClO2 from chlorine and water. Hydrogen produced is reacted with Cl2 to
form HCI, which in turn is used in the process. Additional Cl2 is required to provide
sufficient HCI for the process. The process is similar to the R6 and Chemetics systems.


The is also an integrated system for on site production of chlorine dioxide by electrolytic
process. This is similar to the R6 and Lurgi Systems.