Chapter 12 Notes

Chapter 12 Notes - John W Moore Conrad L Stanitski Peter C...

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John W. Moore Conrad L. Stanitski Peter C. Jurs www.cengage.com/chemistry/moore Chapter 12 Fuels, Organic Chemicals and Polymers
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Petroleum Petroleum is a complex mixture of: • alkanes • cycloalkanes • alkenes • aromatic hydrocarbons Its composition and color vary with origin. Crude oil is extracted from the earth and must be refined (separated into different fractions).
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Fractional Distillation Simple mixtures can be separated by distillation. e.g. Cyclohexane and toluene. b.p. = 81 C b.p. = 111 C
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Petroleum components are gases, liquids and solids. Petroleum Refining Fractional distillation Partially separates complex mixtures into components with narrow boiling- point ranges. One fraction from petroleum: • Gasoline (boiling range: 20-200 C) composed of C 5 -C 12 hydrocarbons.
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Fractional distillation of petroleum Petroleum Refining
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Octane Number Hydrocarbons can autoignite: • Burn without a spark when T T autoignition • As P increases, T autoignition falls. Gasoline is compressed before spark ignition. • If it ignites before the spark, the engine “knocks”.
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Octane Number Regular gasoline is 87 octane: • 87% i -octane + 13% n -heptane. • or many other mixtures… In general: straight-chain < branched aromatic. Octane number rates a fuel’s ability to burn smoothly. • A scale defined by two fuels: 0 = n -heptane (low T autoignition ) 100 = i -octane (high T autoignition ) Chemical Octane n -octane -20 n -hexane 25 n -pentane 62 1-pentene 91 benzene 106 methanol 107 ethanol 108 t -butyl alcohol 113 toluene 118 n -heptane 0 i -octane 100
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Larger hydrocarbons can be “cracked”: C 16 H 34 C 8 H 16 + C 8 H 18 • Changes kerosene fraction into gasoline. • Alkenes have high octane numbers. • Alkenes are polymer starting materials. Catalyst pressure & heat alkane alkene alkane Catalytic Cracking
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Catalytic Reforming Converts small straight-chains into branched or aromatic hydrocarbons This produces better fuel. n -pentane (62 octane) 2-methylbutane (94 octane) CH 3 CH 2 CH 2 CH 2 CH 3 CH 3 CHCH 2 CH 3 catalyst CH 3 | C 5 H 12 C 5 H 12
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Catalytic Reforming
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Octane Enhancers Octane enhancers are added to increase octane numbers. Before catalytic converters were added to exhausts: • Tetraethyl lead, Pb(C 2 H 5 ) 4 • Had to be discontinued (poisons Pt-catalysts) • Removal improved public health (Pb is a health hazard) Current octane enhancers • Toluene t- butyl alcohol • Methanol • Ethanol
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High-CO areas must use oxygenated gasoline. • Contain > 2.7% O (by mass). • Extra O promotes complete combustion. Oxygenated & Reformulated Gas High-O 3 areas must use reformulated gasoline. • Less volatile • Atmospheric hydrocarbons promote O 3 formation. • Reformulated gas is also oxygenated.
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Car exhausts are much cleaner, but… …the number of cars keeps growing.
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This note was uploaded on 01/27/2012 for the course CH 1213 taught by Professor Xia during the Spring '07 term at Mississippi State.

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Chapter 12 Notes - John W Moore Conrad L Stanitski Peter C...

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