4. Antioxidants and their purpose
• A molecule that inhibits the oxidation of other molecules
• They are used as fuel additives when creating fuel blends
5. AH! What is this ? Looks
like an oil gum. What
should I do now ?
6. Use antioxidants! Dummy!
• Oxidation reactions can produce free radicals leading to chain reactions
• Antioxidants terminate the chain reactions by disrupting radical intermediates
• Antioxidants prevent gumming in gasoline (IC Engines)
• Antioxidants deactivate metals (that cause oxidation) present in fuels
• Antioxidants prevent decomposition of lubricant base stocks
7. Substituted phenols and derivatives of phenylenediamine – Common antioxidants used to
inhibit gum formation in gasoline
8. Oxidation of lubricating oils
• Lubricating oils, when poured into engines, go under oxidation in air due to
numerous factors including
• Heat
• High Pressure
• Presence of metals (oxidizing agents)
9. How antioxidants work ?
• Oxidation takes place in three steps
• Initiation
• Propagation
• Termination
• The antioxidant part
10. Some common fuel antioxidant additives
• N,N′-Disalicylidene-1,2-propanediamine
• A metal deactivating compound in motor oils
• 2,4-Dimethyl-6-tert-butylphenol
• An anti-gumming agent
11. References
• Dr. Neil Canter (ed.), Use of antioxidants in automotive lubricants, Tribology and
Lubrication Technology, September 2008. – www.stle.org
• http://www.howstuffworks.com/5-symptoms-of-oil-deposits.htm#page=0
• http://en.wikipedia.org/wiki/Category:Fuel_antioxidants
Editor's Notes
Taking an example of an automotive lubricant,
Oxidation occurs through a three-step process known as initiation, propagation and termination. In the initiation stage, one of the external factors causes a free radical (or unpaired electron) to be generated in one of the organic species (R) that is part of the lubricant. This process involves breaking a bond with a hydrogen atom and is shown in equation.The free radical is a highly reactive species that can react with oxygen to form a peroxide radical that can generate additional radicals through reaction with more components in the lubricant. This step shown in equation (2) is known as propagation and leads to further decomposition of the lubricant.Eventually two of the radical species combine and form a stable compound. This is designated as the termination step because it removes free radicals from the system, as shown in equation (3).Antioxidants react with free radicals to form stable species and disrupt the degradation process shown above. The antioxidant inhibits oxidation by reacting with chain propagating free radicals to form stable molecules. The reaction showing how free radicals are eliminated by primary antioxidants is shown in equation (4). The “antioxidant” moiety is a stabilized free radical that does not react with any other species.
Trace metals in fuels catalyze oxidation reactions, which degrade the fuels. Metal deactivators form stable complexes with the metals, so their catalytic activity is lost. While N,N′-disalicylidene-1,2-propanediamine forms stable chelate complexes with many metals including copper, iron, chromium, and nickel, it is the coordination with copper that makes it a popular choice as a fuel additive.Copper has the highest catalytic activity in fuel, and N,N′-disalicylidene-1,2-propanediamine forms a highly stable complex with the metal.2,4-Dimethyl-6-tert-butylphenol is an alkylatedphenol used industrially as an antioxidant, e.g. to prevent gumming in fuels,
