Chapter 12 - Chapter 12 12.1 Petroleum is a complex mixture...

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Chapter 12 12.1 Petroleum is a complex mixture of alkanes, cycloalkanes, alkenes, and aromatic hydrocarbons formed from the remains of plants and animals from millions of years ago Distillation can separate substances that have different boiling points from liquid mixtures and solutions Petroleum contains thousands of different hydrocarbons and their separation as individual pure compounds is neither economically feasible nor necessary. Instead, petroleum refining uses fractional distillation to separate petroleum into petroleum fractions Separation is possible because the boiling point increase as the number of carbon atoms increases: Larger hydrocarbon molecules (larger number of electrons and greater polarizability) have greater noncovalent intermolecular forces and higher boiling points than smaller ones Octane number – A gasoline is a measure of its ability to burn efficiently in an internal combustion engine A typical automobile engine uses the gasoline fraction of refined petroleum – a mixture of C 5 to C 12 hydrocarbons used primarily as motor fuels. This hydrocarbon mixture contains relatively small molecules and has a fairly high autoignition temperature, the temperature at which the liquid hydrocarbon will ignite and burn without a source of ignition Heptane does not burn smoothly and is arbitrarily assigned an octane number of 0, whereas 2,2,4-trimethylpentane burns smoothly and is assigned an octane number of 100 Straight-chain alkanes are less thermally stable and burn less smoothly than branched- chain alkanes The octane number of a gasoline can be increased either by increasing the percentage of branched-chain and aromatic hydrocarbon components or by adding octane enhancers In addition to fractional distillation, petroleum refining also includes converting the components of various fractions into more economically important products through catalytic cracking and catalytic reforming
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Catalytic cracking – Uses a catalyst, high temperatures, and pressure to break long-chain hydrocarbons into shorter-chain hydrocarbons that include alkanes and alkenes, many in the gasoline range Catalyst – A substance that increases the rate of a chemical reaction without being consumed as a reactant would be Catalytic reforming – Converts straight-chain hydrocarbons to branched-chain hydrocarbons and aromatics (Used to increase the octane rating of gasoline) Catalytic reforming converts a high percentage of straight-run gasoline, kerosene, and light oil fractions into a mixture of aromatic hydrocarbons including benzene, toluene, and xylenes Oxygenated gasoline – A blend of gasoline to which organic compounds that contains oxygen, such as methanol, ethanol, and tertiary –butyl alcohol, have been added Reformulated gasoline (RFG) – Oxygenated gasoline that contains a lower percentage of aromatic hydrocarbons and has a lower volatility than ordinary
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This note was uploaded on 09/21/2011 for the course CHE 131 taught by Professor Kerber during the Fall '08 term at SUNY Stony Brook.

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Chapter 12 - Chapter 12 12.1 Petroleum is a complex mixture...

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