2006-07-25 03:26:53 · 5 answers · asked by Jitendra P 1 in Science & Mathematics ➔ Chemistry
nothing is currently added to gasoline as an octane improver - (anti knock additive). It is now built into the gasoline blend stocks. Things like aromatics do have high octane rating (you know that R+M/2 thing on the pump - its a measure of the fuels ability to knock) However, aromatics are limited in gasoline in many areas in the EU and in North America. Olefins have high octane and are a good source of octane in gasoline - as are iso-paraffins. Refineries have special unit to produce blendstocks with both of those (FCC and Alkylation Units), as well as aromatic blendstocks (Reformer).
Ethanol is not added to increase octane, contrary to popular beliefs. It is added to introduce alcohol into the gasoline for cleaner burning fuel. Ethanols road octane is 116, so it does indeed provide a bump in road octane, however it was not until the EPA mandated the use of ethanol that refiners were required to add ~10% volume.
It used to be products containing lead like tetra-ethyl-lead (TEL). But those are toxic. Also some maganese compounds bump octane up too. Due to the health and environmental impacts - these are only used in very limited/specialize gasolines - like racing gas for NASCAR and the like, and can not be used in on-road/driving to the store vehicles in the EU and most of NA.
Refineries DO NOT reblend extra benzene into gasoline for octane improvement. Benzene is far more valuable as a solvent than as an octane improver. Rarely will a refinery require additional octane improvement - they rely upon good blends of the base stocks. In fact, benzene concentrations in gasoline have been reduced significantly over the past 25 years.
2006-07-25 16:13:56 · answer #1 · answered by imabiggles 2 · 0⤊ 0⤋
New anti-knock (read "octane boost") compounds added to petrol :
1. Nothing - Petrol is reformulated in the refinery to give "natural" octane improvement. Requires catalytic reformer and isomerization unit.
2. TEL/ tetra-ethyl-lead - No longer used [EPA]
3. MTBE (methyl tert-butyl ether) - No longer used [EPA]
4. Iron picrate - unstable! Used as a "detonation enhancer" - scary!
5. Ferrocene - iron cyclopentadienyl - (Plutocene) Assoc. Octel's replacement for TEL. Used in some countries/not in others. 33mg/lt equiv to about 2 octane points on std 90RON gasoline.
6. MMT - Methylcyclopentadienyl Manganese Tricarbonyl - Forte 104, etc, etc. - Another lead replacement.
7. Ethanol (Absolute) at 10 - 20%.
There are others - but these are probably the most common
2006-07-25 19:41:04 · answer #2 · answered by Bruce H 3 · 0⤊ 0⤋
Used to be lead tetra ethyl but now it is reblended with benzene. Now here is a question for you.... If lead was taken out of petrol and benzene added ... which is the safer???
2006-07-25 03:31:04 · answer #3 · answered by andyoptic 4 · 0⤊ 0⤋
Lead
2006-07-25 03:31:03 · answer #4 · answered by bala 1 · 0⤊ 0⤋
It used to be lead, but now it's aromatic hydrocarbons like benzene or just straight ethanol.
2006-07-25 03:29:29 · answer #5 · answered by Brian L 7 · 0⤊ 0⤋