Hydrogen peroxide is a strong oxidant with many valuable uses across a broad range of applications. The bleaching properties of hydrogen peroxide make it a useful tool to remove colour from wood pulp and textiles, whilst the fact that it breaks down into harmless water and oxygen mean it does not readily damage the environment.
What is hydrogen peroxide
Peroxide itself is a term used to describe any substance that contains a peroxide group where two oxygen atoms are bonded together or a peroxide anion is present in solution. These peroxide groups are unstable and break down to release oxygen, which is responsible for the bleaching action of peroxides. Hydrogen peroxide is simply water with an extra oxygen atom bonded as a peroxide group, which is why hydrogen peroxide has similar chemical properties to water, and why water is formed when the substance decomposes.
Commercial production of hydrogen peroxide
Hydrogen peroxide is produced in amounts exceeding 3 million tonnes annually, of which half of that production is used in bleaching wood pulp and paper. The rest finds use in chemical industries as an oxidant in certain industrial reactions, and in the textiles, cleaning and beauty industries.
The commercial synthesis of hydrogen peroxide occurs through a four step process called the anthraquinone process, utilising an organic molecule called 2-Ethyl-9,10-anthraquinone. This anthraquinone compound is dissolved in a polar and nonpolar solvent, forming what’s called the working solution and forms the basic tool for producing hydrogen peroxide.
Step 1 – Hydrogenation
The working solution is placed in an alumina hydrogenator with palladium as a catalyst at 45°C. When hydrogen gas is allowed to react with the solution it forms hydrogenated anthraquinones that act as a carrier for the hydrogen. The working solution must be carefully controlled to avoid the anthraquinone from becoming too hydrogenated, and the temperature and reaction conditions must be kept at optimum controlled rates to avoid this happening.
Step 2 – Filtration
Once the anthraquinone is hydrogenated, the palladium catalyst has to be filtered out or else it may react with the hydrogen peroxide once it is produced and cause it to decompose. As hydrogen peroxide decomposes through an exothermic reaction, it releases a lot of energy and in high concentrations can be dangerous and cause explosions.
Step 3 – Oxidation
In order to produce hydrogen peroxide, the hydrogenated anthraquinone that has been used as a carrier for the hydrogen now needs to be exposed to oxygen gas. This causes auto-oxidation to occur, and the anthraquinone and hydrogen peroxide become separate, allowing the anthraquinone to be reused and the hydrogen peroxide to be extracted.
Step 4 – Extraction
In order to extract the hydrogen peroxide, the working solution is pumped through a 35 metre tall extraction column along with water, ensuring that all of the solution is able to come into contact with the water. The water is siphoned off through the column as this occurs, with the hydrogen peroxide dissolved in this water.
After extraction, the anthraquinone is present in its original form and can be reused again, leading to a more environmentally friendly and sustainable reaction. This and hydrogen peroxide’s properties make it a valuable oxidant and bleaching agent that is less damaging to the environment than the chlorine bleaches that are also available.