Gasoline

Gasoline

Chemistry of Petroleum

• Petroleum is composed of organic compounds containing Carbon and Hydrogen– Hydrocarbon Molecules

• CH4 Methane, the simplest Hydrocarbon

CH4 + 2 O2 2 H20 + CO2 + Energy

More Hydrocarbons

2 Carbon AtomsETHANE (C2H6)

3 Carbon AtomsPROPANE (C3H8)

4 Carbon AtomsBUTANE (C4H10)

And so on. Five Carbon Atoms give you PENTANE (C5H12)

Six Carbon Atoms give you HEXANE (C6H14) Seven give you HEPTANE (C7H16).

The World’s Favorite Hydrocarbon

Octane: Eight Carbons (C8H18). The main ingredient in gasoline

CnH2n+2

• Use the formula below to determine the number of Hydrogen Atoms busing the number of Carbon atoms (n).

Hydrocarbons

Chemistry of Petroleum

• Temperature and number of carbon atoms determine the form of petroleum

• At Ordinary surface temperatures: – Less than 5 Carbon atoms

• Gas

– 5 to 15 Carbon Atoms• Free-Flowing Liquids.• CRUDE OIL

– Greater than 15• Thick viscous liquids to waxy solids.

Crude Oil• Liquid petroleum recovered directly from the well

is called crude (unrefined or unprocessed) oil. • Crude oil is comprised of a mixture of

hydrocarbon molecules • Light (sweet) Crude

– low S impurities– Can easily be refined to gasoline– Produced in Nigeria, U.S. Gulf States, Canada 

• Heavy (sour) Crude – high S impurities– Difficult to refine to gasoline– Produced in Saudi Arabia, Mexico, Venezuela, Iraq

Petroleum Refining

• An oil refinery is an industrial plant where crude oil is processed and refined into more useful petroleum products.

Every barrel of crude oil can be refined into many products or fractions.

Crude Oil Fractions• Petroleum gas (1-4 Carbons)

– used for heating, cooking, making plastics

• Naphtha (8 Carbons)– dry cleaning solution; intermediate that will be

further processed to make gasoline

• Gasoline (8 Carbons)– motor fuel

• Kerosene (12 Carbons)– fuel for jet engines and tractors; starting

material for making other products

Crude Oil Fractions• Gas Oil or Diesel (16 Carbons)

– used for diesel fuel and heating oil; starting material for making other

• Lubricating Oil (36 Carbons)– used for motor oil, grease, other lubricants

• Heavy gas or Fuel oil (44 Carbons) – used for industrial fuel; starting material for

making other products

• Residuals (80 Carbons)– coke, asphalt, tar, waxes; starting material for

making other products

Components of a Refinery

Fractional Distillation

• The hydrocarbons in crude oil have different boiling points, according to the number of carbon atoms their molecules contain and how they are arranged.

• Fractional distillation uses the difference in boiling point to separate the hydrocarbons in crude oil.

• The fractionating column is cooler at the top than the bottom, so the vapors cool as they rise.

Fractional Distillation

Fractional Distillation

• Vapors condense onto a tray when they reach the part of the column which is cooler than their boiling point.

• As the last gases from the bottom of the column pass through the holes in a tray, any lighter hydrocarbons still in the condensed liquid are boiled off, and rise through the column.

Chemical Processing

• Very few of the components come out of the fractional distillation column ready for market.

• Many of them must be chemically processed to make other fractions.

– For example, only 40% of distilled crude oil is gasoline

• After distillation, one fraction can be changed into another by two methods of chemical processing: Cracking and Unification

Cracking

• Cracking breaks large chains into smaller chains.

• After various hydrocarbons are cracked into smaller hydrocarbons, the products go through another fractional distillation column to separate them.

Unification

• Unification combines smaller hydrocarbons into larger ones

• A reformer combines chains to make naphtha into gasoline.

• A significant by-product of this reaction is hydrogen gas, which is then either used for hydrocracking or sold.

Refineries and the Environment

• The refining process releases numerous different chemicals into the atmosphere; consequently, there are substantial air pollution emissions.

• Due to pollution problems there is strong pressure to prevent the development of new refineries, and no major refinery has been built in the U.S. since 1976.

• However, many existing refineries have been expanded during that time.

Illinois Refineries• Illinois leads the

Midwest in crude oil refining capacity with four refineries.

• About 5.2% of U.S. Petroleum is refined in Illinois and is mainly supplied by the Tar Sands on Canada.

Cost of Gasoline

• While it isn't represented in the diagram, some of the actual money you spend at the pump does go to the service station.

• Service stations add on a few cents per gallon.

• Gas prices mainly rise when there are changes in refining and the price of crude oil

Gasoline (4-Stroke) Engine

• Burns fuel and air in enclosed space producing hot gases

• Allows heat to flow from hot engine to cold outside air

• Converts some of this heat into useful work

• Example of a Heat Engine

Gasoline (4-Stroke) Engine

• The four strokes of the cycle are induction, compression, power, and exhaust. 

• Each corresponds to one full stroke of the piston, therefore the complete cycle requires two revolutions of the crankshaft to complete.

Induction Stroke

• During the induction stroke, the piston moves downward, drawing a fresh charge of vaporized fuel/air mixture.

• The carburetor mixes the fuel and air.

Compression Stroke• As the piston rises the

poppet valve is forced shut by the increased cylinder pressure. 

• Flywheel momentum drives the piston upward, compressing the fuel/air mixture.

• Compressed Fuel is easier to ignite.

Power Stroke

• At the top of the compression stroke the spark plug fires, igniting the compressed fuel. 

• As the fuel burns it expands, driving the piston downward.

• Chemical energy converted to thermal energy converted to mechanical energy.

Exhaust Stroke

• At the bottom of the power stroke, the exhaust valve is opened by the cam/lifter mechanism. 

• The upward stroke of the piston drives the exhausted fuel out of the cylinder.

Gasoline (4-Stroke) Engine

• Power stroke: heat in, work out

• Exhaust stroke: heat out

• Some of the extra work out is used during induction and compression

• Some heat lost to conduction and convection in and around the engine.

Gasoline and 4-stroke Engines

• A 4-stroke engine is designed to run on a refined mixture of hydrocarbons from C7–Heptane and C8–Octane.

• This mixture is called Gasoline

• C7 and C8 vaporize at temperatures below the boiling point of water. – That's why if you spill gasoline on the ground

it evaporates very quickly.

Octane Rating

• The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites.

• Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane

• Most gas stations offer three octane grades: – regular, usually 87 octane– mid-grade, usually 89 octane – premium usually 92 or 93.

• The ratings must be posted on bright yellow stickers on each gasoline pump.

Knocking• Knocking occurs when gas

ignites by compression rather than because of the spark from the spark plug.

• Problems– Annoying– Reduces efficiency– Damages engine

• Heptane handles compression very poorly

• Octane handles compression very well

Solutions to Knocking

• Increase the octane rating of the gasoline

• This costs $$$$$• Requires chemical

processing techniques to be done numerous times

• Almost impossible to refine 100% octane.

• Most car engines today are designed to run effectively on an octane rating of 87.

Gasoline Additives

• During WWI, it was discovered that you can add a chemical called tetraethyl lead to gasoline and significantly improve its octane rating.

• Lower octane grades of gasoline could be made usable by adding this chemical.

• This led to the widespread use of "ethyl" or "leaded" gasoline.

Tetraethyl Lead (TEL)• TEL was cheap to

manufacture.

• Most oil companies could process TEL at their refineries.

• This increased profits for the oil company.

• However…….

Tetraethyl Lead (TEL)

• Due to the combustion of TEL in gasoline, the Earth became covered in a thin layer of lead.

• Even glacial ice at the north pole recorded an alarming increase of lead during the mid to late 1900s.

Health Risks of TEL Exposure

Acute Exposure in Adults

• Blindness• Brain Damage• Kidney disease• Cancers• Death

Low Level Exposure in Children

• Lowered IQ• Reading and Learning

Disablities• Impaired hearing• Hyperactivity• Impaired Growth

Removal of TEL

• In the early 1970s, catalytic converters were required in vehicles by the Clean Air Act to reduce smog forming pollutants.

• Lead from gasoline additives clogs a catalytic converter.

Note: Leaded Gasoline was not phased out due to health concerns directly from the lead!

Removal of TEL

• Leaded gasoline was phased out in the United States staring in 1973 due to the Clean Air Act.

• Illegal to sell leaded gasoline for on-road vehicles as of January 1, 1996.

• Fuel containing lead may continue to be sold for off-road uses, including aircraft, racing cars, farm equipment, and marine engines until 2008

Most of the 7 million tons of lead burned in the gasoline in the United

States in the twentieth century remains --- in the soil, air, and water and in the bodies of living organisms.

Lead is Still a Problem

MTBE

• MTBE has been used in U.S. gasoline at low levels since 1979 to replace TEL to increase its octane rating and help prevent engine knocking.

• A hydrocarbon molecule that is created at a refinery from methanol. – Big money maker for petrochemical

companies

• Gasoline can contain as much as 10 percent to 15 percent MTBE.

MTBE Use and Releases

MTBE

• The main problem with MTBE is that it is thought to be carcinogenic and it mixes easily with water.

• If gasoline containing MTBE leaks from an underground tank at a gas station, it can get into groundwater and contaminate wells.

• Twenty seven states have passed laws to ban MTBE in certain areas.