How is octane made

Information about your use of this website will be shared with Google and other third parties. Read our privacy policy. Start your engines! Simon Cotton looks into one of the few chemical names known well to the public: Octane. Octane is one of the few chemical names that is part of everyday life and is recognised by the public. When you stop at a garage to fill up your car, you usually see the octane rating of the fuel displayed on the pump, 95 or 97, but what does it mean?

To understand that, you have to go back nearly a century. In the early days of the automobile, knocking or pre-ignition was a real problem. In a petrol engine, the gaseous mixture of air and hydrocarbon fuel is injected into the cylinder as the piston is on its downstroke, then gets compressed as the piston moves up.

At a particular point, a sparking plug fires a spark that ignites the mixture, and the resultant hot gases create the power that forces the piston down, driving the engine and powering the wheels. More sophisticated engines had higher compression ratios — the fuel-air mixture was compressed more before it was ignited, but this also made it more likely that the mixture would pre-ignite, causing the engine to misfire — knocking — and lose power.

In the mids an American chemist named Russell Marker , working for the Ethyl Corporation, made a systematic study of the knocking characteristics of different hydrocarbons. At best they have a zig-zag chain of carbon atoms, with attached hydrogens, though at room temperature the chains will be flexing around. Anyway, heptane caused really bad knocking.

Next he chose what we call 2,2,4-trimethylpentane, which at that time was usually known as isooctane. Well, isomers are compounds with the same molecular formula but different structures.

For example, octane has lots of isomers, like these three, all variants on C 8 H 18 :. So, the term isomerisation means converting one isomer into another one. In the chemical industry this usually means converting a straight-chain octane into an isomer with more branches; these are valuable on account of their higher 'octane ratings'. First, you have to understand the engines in petrol-fuelled cars. Petrol engines are driven by the combustion of a mixture of a gaseous mixture of air and hydrocarbon fuel.

This mixture is injected into the cylinder as the piston is on its downstroke, then gets compressed as the piston moves up. At a particular point, a sparking plug fires a spark that ignites the mixture, forming a very hot mixture of carbon dioxide and steam, creating the power that forces the piston down, driving the engine and powering the wheels.

This gave more power, but it was also likely that the fuel-air mixture would pre-ignite, before it was sparked. This was the work of an American chemist called Russell Marker photo, right. He started with heptane, a seven-carbon molecule that was very similar to octane. Heptane caused really bad knocking, so next he tried 2,2,4-trimethylpentane, traditionally known as isooctane; it also has the formula C 8 H 18 so is an isomer of octane. This has a branched chain containing eight carbon atoms, but does not cause any knocking.

Mixtures were made with varying amounts of heptane and isooctane, so that their knocking characteristics could be studied. The higher the octane rating, the more the gas-air mixture can be compressed before it is ignited, and the more power you get when it burns. As a result, the Surgeon General temporarily suspended the production of leaded gasoline and convened a panel to investigate the potential dangers of lead use in gasoline.

Despite these warnings, the Surgeon General set a voluntary standard of lead content, which the refining industry successfully met for decades. It was not until the s, following extensive health research, that the devastating health impacts of low-level lead exposure were established.

The health impacts of lead exposure in children include anemia, behavioral disorders, low IQ, reading and learning disabilities, and nerve damage. In adults, lead exposure is associated with hypertension and cardiovascular disease. Prior to the lead phase-out in gasoline, the total amount of lead used in gasoline was over , tons per year. Congress passed the Clean Air Act in , setting in motion the formation of the EPA and, ultimately, the removal of lead from gasoline.

EPA estimates that between and , 68 million children were exposed to toxic levels of lead from leaded gasoline alone. The phase-out of lead from gasoline subsequently reduced the number of children with toxic levels of lead in their blood by 2 million individuals a year between and The EPA is formed and given the authority to regulate compounds that endanger human health. Lead damages the catalytic converters used in these new vehicles to control tailpipe emissions. Catalytic converters are still used in vehicles today.

Lead is still used in some aviation fuels. Thanks to coordinated efforts, lead is now absent from gasoline in most of the world. Following the lead phase-out in the United States, the oil refining industry chose to construct additional refining capacity to produce octane from other petroleum products, rather than from renewable sources such as ethanol.

RFG has an increased oxygenate content, which helps it burn more completely. As a result, RFG lowers the formation of ozone precursors and other air toxics during combustion.

Petroleum refiners were not required to use any particular oxygenate in RFG, but by the late s, a petroleum product, methyl tertiary butyl ether MTBE , was used in 87 percent of RFG due to its ease of transport and blending.

In the Midwest, ethanol was a more common component of RFG. Despite its success at reducing ozone precursors, MTBE was phased out of the gasoline pool due to concerns over its solubility in water, which resulted in the contamination of water resources in numerous states. Currently, 30 percent of gasoline sold in the United States is reformulated gasoline. Ethanol is providing the additional octane required by RFG. At the time, the U. The octane number is determined by comparing the characteristics of a gasoline to isooctane 2,2,4-trimethylpentane and heptane.

Isooctane is assigned an octane number of It is a highly branched compound that burns smoothly, with a little knock. On the other hand, heptane is given an octane rating of zero. It is an unbranched compound and knocks badly. Straight-run gasoline has an octane number of about Cracking, isomerization and other processes can be used to increase the octane rating of gasoline to about Anti-knock agents may be added to further increase the octane rating.

Tetraethyl lead, Pb C2H5 4, was one such agent, which was added to gas at the rate of up to 2. The switch to unleaded gasoline has required the addition of more expensive compounds, such as aromatics and highly branched alkanes, to maintain high octane numbers.

Gasoline pumps typically post octane numbers as an average of two different values. One value is the research octane number RON , which is determined with a test engine running at a low speed of rpm. The other value is the motor octane number MON , which is determined with a test engine running at a higher speed of rpm. If, for example, a gasoline has a RON of 98 and a MON of 90, then the posted octane number would be the average of the two values or High octane gasoline does not outperform regular octane gasoline in preventing engine deposits from forming, in removing them, or in cleaning the engine.

However modern high octane fuels may contain additional detergents to help protect high compression engines. Consumers should select the lowest octane grade at which the car's engine runs without knocking.