Stability & Decomposition
The property of hydrogen peroxide to decompose exothermally in the presence of certain catalytically acting impurities, with the formation of oxygen gas and water is very important for handling during storage as well as during chemical reaction. Decomposition is indicated by the development of gas and - with only slight removal of heat - by rise in temperature.
The stability of hydrogen peroxide solutions is influenced primarily by the temperature, the pH value, and above all by the presence of impurities with a decomposing effect.
An increase in the temperature promotes the decomposition as well as a higher pH value. For optimum stability, the pH range of pure hydrogen peroxide is below 4.5. Above pH 5, the decomposition increases sharply. Therefore, commercial solutions are generally adjusted to a pH value below 5.
The shelf life of hydrogen peroxide is negatively affected by impurities of every type even when some of these impurities are present in very low concentrations (ppm quantities). The decomposition can be induced homogeneously by dissolved ions with a catalytic effect. Heavy metals like iron, copper, manganese, nickel, and chromium are especially effective here. Hydrogen peroxide is also decomposed through the effect of light as well as by certain enzymes (catalase).
As a result of the stabilizers, which are usually added to our commercial grades in ppm amounts, our hydrogen peroxide is protected against unavoidable impact during handling and has an excellent shelf life. With normal handling and cool storage, and when the necessary precautionary measures are observed, the losses of hydrogen peroxide are very slight even during extended periods (years) of storage.
Evonik's peracetic acid products are sufficiently stabilized. If stored properly, they can be kept for an extended period of time without notable loss of content. However, if diluted with tap or other water, the stable commercial products will hydrolise and decompose rapidly.
Decomposition will be accelerated by higher temperatures and impurities, especially by heavy metals such as iron, copper and manganese. It is, therefore, advisable to store peracetic acid under cool conditions and, if dilution is necessary, to dilute it with appropriate water only immediately before the application.
During decomposition oxygen gas is formed. Often this reaction is responsible for the loss in content of insufficiently stabilized peracetic acid.
The hydrolysis of peracetic acid occurs whenever peracetic acid solutions are diluted. Acetic acid and hydrogen peroxide are the products of this hydrolysis. With any dilution of commercially available peracetic acid, a new equilibrium between peracetic acid, acetic acid, hydrogen peroxide and water will be established. Those products are neither storable nor transportable.