Presentation on theme: "Section B: Petroleum as an Energy Source"— Presentation transcript:
1Section B: Petroleum as an Energy Source Man has used oil for over 5000 yearsFirst drilled in 1859 in PAOil is used in almost every aspect of modern life: products, shipping, manufacturing, heating, transportation, etc
2B.1 Energy and Fossil Fuels: Overview Chemical energy, a form of Potential Energy, is stored in the bonds of compoundsIn an energy releasing chemical reaction bonds break and reactant atoms reorganize into new bondsResult has less chemical energy, but process released energy (heat and light)
3B.1 Energy and Fossil Fuels: Combustion of Methane Energy releasing reaction of burning methaneCH4 + 2 O2 CO2 + 2 H2O + energy2 Steps: Bond breaking, then bond making
4B.1 Energy and Fossil Fuels: Combustion Breaking bonds requires energy: endothermic change (increases chemical energy)energy + CH4 + 2 O2 C + 4 H + 4 OThe forming new bonds releases energy: exothermic change (decreases chemical energy [>])C + 4 H + 4 O CO2 + 2 H2O + energyOverall this is exothermic as more is released when reforming than is required to break bondsBurning methane:Show that the potential energy is at one point, goes up after bonds are broken, than goes lower than ever when bond making
5B.1 Energy and Fossil Fuels: Combustion (continued) Overall reaction maybe exothermic or endothermic:if more energy is added to break bonds than produced when bond making then endothermicopposite, like burning methane, is exothermicGenerally, if a reaction is endothermic, then the reverse reaction is exothermicActual “reaction mechanism” are more complex
6B.2 Energy Conversion Conversion makes energy more useful Hair dryer example: oil/potential - generate steam/thermal – spin turbine/kinetic - general electricity/electrical – transmit – thermal and kinetic in the hair dryer.Energy is not consumed, but changes form - Law of Conservation of EnergyBut some energy is lost to useful work.
7B.2 Energy Conversion (continued) Conversion of chemical energy into heat and then mechanical typically loses > 50%Minimizing conversion is essential to using fuel efficientlySolar cells (convert sunlight to electricity) and fuel cells (convert chemical energy to electricity) hold promise in adding efficiency of petroleum use.
8B.2 Energy Conversion – Automobile example Around 25% of the energy in gasoline contributes to powering the drive wheels.75% is lost into the environment, mostly in the form of heat: 33% lost through exhaust, 30% through engine cooling, 6% pumping combustion air, 3% due to piston ring friction, …Sample conversion in a car:Generator / alternator – mechanical energy to electricRear window defroster converts electrical to thermalEngine converts chemical to mechanical and thermalGasoline is potential energy.
9B.3 Combustion Lab: Background In this lab we measure how much thermal energy is released when burning a fuel.We burn a paraffin wax candle (long chain alkane) under a can of water and watch the water temperature increase.We will note the increase in temperature, while the mass of the candle decreases.
10B.3 Combustion Lab: Background Candle wax burning: (exothermic)C25H52(s) + 38 O2(g) 25 CO2 (g) + 26 H2O (g) + EParaffin wax Oxygen Carbon Dioxide water vapor ENERGY(Alkane) gas gas gasMore energy is liberated by forming bonds of the CO2 and H2O molecules than is required to break bonds of C25H52 and O2
11B.3 Combustion Lab: Background Specific heat capacity of a substance is the quantity of heat needed to raise the temperature of 1 gram of the substance by 1° C.The SHC of water is 4.2 J/(g·°C or joules per gram per degree Celsius).To raise the temperature of 10 g water from 25°C to 30°C: 4.2 J * 10 g * 5°C = 210 JA sixty watt light bulb requires 6,000 J for one minute
12B.3 Combustion Lab: Background Heat of combustion is the quantity of thermal energy given off when a certain amount of substance is burned.This is usually measured when :one gram orone mole (molar heat of combustion)of substance is burned.
13Hydrocarbon Table: Including Heat of Combustion BoilingShortHeat ofMolar Heat ofNamePoint (C)#CarbonformulaCombustion(kJ/g)(kJ/mol)Methane-1621CH455.6890Ethane-88.62C2H652.01560Propane-42.13C3H850.02200Butane-0.54C4H1049.32859Pentane36.15C5H1248.83510Hexane68.76C6H1448.24141Heptane98.47C7H16***4817Octane125.78C8H1847.85450
14B.3 Combustion Lab: Calculations Mass of water in grams = volume of water (100mL) * 1.0 g/mLTotal rise in temperature = final temperature – initial temperatureHeat = mass * Specific heat of substance (water – 4.2J/(g·°C)) * change in temp.Mass of burned wax = Mass of candle & card before burn – mass after burnHeat of combustion of paraffin = #3 / #4
15B.4 Using Heats of Combustion Hydrocarbon + Oxygen gas Carbon dioxide+Water+??Thermal energy??2 C2H6 + 7 O2 4 CO2 + 6 H2O kJ(see the table with heat of combustion entry for ethane-C2H6)Notice the table entry is for one mole, we have 2 here “2 C2H6” so we multiply by 2.12 g of octane would be:12 * 47.8kJ = 574 kJ
16B.5 Altering Fuels: Overview Due to changes in demand various fractions of hydrocarbons vary in price over time. E.G: the gasoline fraction demand is growing more quickly than other types, such as keroseneChemists and chemical engineers work innovate to maximize $ for crude oil, by maximizing the amount of the more valuable fractions while minimizing less valuable fractions of distillation.
17B.5 Altering Fuels: Cracking Due to cars becoming more popular in the early 1900’s chemists invented cracking.Cracking - larger hydrocarbons are broken into smaller ones. E.G: C16 => 2 C8s (kerosene into gasoline)Extra C1-4 are burned to feed the cracking process> 1/3 of all crude is cracked, and catalysts are used such as aluminosilicates for efficiency (< tempature)Gasoline is mostly straight chain, but branched chains burn better in engines – less knocking. E.G: 2,2,4-trimethylpentane isomer of octane is works well
18B.5 Altering Fuels: Octane Rating Isooctane (2,2,4-trimethylpentane) by definition is 100 octane, straight chain heptane is 0. Gas is rated this way. (> isooctane > octane rating, > heptane < octane rating)Prior to the mid-1970, lead, was added to gasoline to inexpensively increase the octane rating by more slowly burning straight chain gasoline molecules, but the lead was found to be harmful to the environment, so eliminated.
19B.5 Altering Fuels: Oxygenated Fuels A fuel with an oxygen atom – added to gasoline to raise octane rating, introduced when lead was removed. (burns cleaner due to the oxygen)Methanol (methyl alcohol, CH3OH): > octane rating and produced from natural gas, coal, corn or woodMTBE (116 octane rating), first used in ’70s as an octane booster then increased importance as an oxygenated additive. BUT is mixes readily with water, tastes bad, can be bad for you, and seeps into water from leaking tanks. (net: good for air, bad for water) Some states have eliminated the use, some others limiting use.MTHF (87 octane rating), is promising. Generated from renewable resources, also oxygenates fuelFor more on MTBE state usage see:
20B.5 Altering Fuels: Oxygenated Fuels (continued) Octane ratings can also be boosted by isomerization – convert straight chain hydrocarbon molecules to branched chainHydrocarbon vapor is heated with a catalyst to get branched chains.Branched C6H14 can be added to gasoline fractions (C5-12) to produce high-quality gasIsomerization and cracking add costs!