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Chemistry 101 H Petroleum Chapter 7 - Petroleum This presentation was created by Professor Carl H. Snyder Chemistry Department University of Miami Coral Gables, FL 33124 [email protected] Copyright 2004 by Carl H. Snyder, University of Miami. All rights reserved. Petroleum + Distillation = Gasoline Petroleum comes from two Latin words: petrus (rock) + oleum (oil). Petroleum consists principally of various hydrocarbons that can be separated from each other by distillation. A Typical Cylinder The Four-Stroke Internal Combustion Engine Energy released through the combustion of gasoline (petroleum hydrocarbons) powers the four-stroke internal combustion engine. Stroke 1 Intake Stroke Intake valve open; exhaust valve closed Piston moves downward Gasoline-air mixture drawn into the cylinder 1 Stroke 2 Compression Stroke Both valves closed Piston moves upward Gasoline-air mixture compressed Stroke 4 Exhaust Stroke Exhaust valve is open; intake valve is closed Piston moves upward Gases resulting from combustion are moved out of the cylinder, out of the car, into the atmosphere. The Volatility of Hydrocarbons - Chain Length - For unbranched hydrocarbons, the shorter the hydrocarbon chain, the lower the boiling point. Stroke 3 Power Stroke Both valves closed Piston moves downward Combustion of gasoline-air mixture releases energy that moves the piston downward. A Summary Intake stroke Compression stroke Power stroke Exhaust stroke The Volatility of Hydrocarbons - Branching - For hydrocarbons of the same carbon-content, the greater the degree of branching, the lower the boiling point. 2 Compression Ratio The compression ratio is one of the factors that affects knocking. Knocking Knocking results from preignition or irregular ignition of the gas-air mixture. Octane Rating Octane Ratings at the Gasoline Pump Difference in tendencies to produce knocking. Deriving Octane Numbers 2,2,4-trimethylpentane and hetpane Mixtures of the two are used to determine octane ratings. Research vs. Motor Cruising along the highway or zooming away from a stop light? 3 A Solution To A Problem Of The 1920s - Leaded Gasoline Adding 1 teaspoon of tetraethyllead to a gallon of gasoline raises the gasoline’s octane number by about 10 points. A Solution To A Problem Of The 1990s - Beyond Lead Lead is toxic to humans and inactivates catalytic converters. Lead can be replaced by octane enhancers. MTBE (methyl tert-butyl ether) is a leading oxygenate and octane enhancer. MTBE (Methyl tert-Butyl Ether) Disadvantage: Potential for polluting undergroiund water supplies. "The state of California has determined that the use of this chemical presents a significant risk to the environment." A Solution To A Problem Of The 1970s - The Catalytic Converter Unburned hydrocarbons in exhaust gases contribute to air pollution known as smog. The catalyst of the catalytic converter helps oxidize these hydrocarbons to CO2 and H2O. MTBE (Methyl tert-Butyl Ether) Advantages: Octane enhancer Oxygenate A Solution to the Problems Presented by Tetraethyllead, MTBE, and Other Additives - Petroleum Refining Octane ratings can be increased by improved methods of petroleum refining. Converting crude oil to refined gasoline and other commercial products by: Distillation Catalytic Cracking Reforming - Isomerization Reforming - Cyclization Reforming - Aromatization 4 Distillation - The Process Distillation At The Refinery A liquid is heated to boiling The vapors are separated from the liquid The vapors are cooled The condensed, purified, distilled liquid is collected. Refinery distillation separates the crude oil into its various hydrocarbon fractions. Distilled Fractions Catalytic Cracking - Definition Catalytic Cracking - Example Catalytic Reforming 5 Reforming - Isomerization Isomerization converts straight-chain hydrocarbons to branched-chain hydrocarbons. Isomerization increases the octane rating of the hydrocarbons. Reforming - Aromatization Reforming - Cyclization Cyclization converts acyclic hydrocarbons into cyclic hydrocarbons. Cyclization paves the way for aromatization. Alternative Fuels Liquified Petroleum Gas (LPG) Compressed Natural Gas Ethanol Methanol Electricity Fuel Cells Aromatization converts nonaromatic, cyclic hydrocarbons into aromatic hydrocarbons. Aromatization increases the octane rating of hydrocarbons. Advantages and disadvantages of each. A Fuel Cell The combination of H2 and O2 in a fuel cell can provide energy where fossil fuels can’t be used, as in space capsules. End - Chapter 7 6