Unit 3 Section 2

Two types of cracking

Thermal, catalytic

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Conditions for thermal cracking

high temp ~ 1000 *C high pressure ~ 70 atm

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products of thermal cracking

lots of alkenes, useful for polymers

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Catalytic cracking contitions

zeolite catalyst (hydrated aluminosilicate) at slight pressure and high temp ~ 500*C

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products of catalytic cracking

mainly aromatic hydrocarbons and alkanes needed to produce motor fuels

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Pollution from burning fuels

nitrogen oxides, sulfur dioxide

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how is nitrogen monoxide produced

high pressure and temperature in car engine cause nitrogen and oxygen atoms from the air to reacct together.

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how does nitrogen monoxide react further

N2+O2-->2NO THEN 2NO + O2 --> 2NO2 (forms nitrogen dioxide)

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nitrogen oxides are

toxic and posonous molecules

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Engines dont always...

burn all the fuel molecules

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This leads to

some of the unburnt fuel molecules reacting with Nitrogen oxides in presence of sunlight to form ground level O3 (major component of smog)

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Problems with ground level ozone

irriates people's eyes, aggravates respiratory problems and even causes lung damage

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3 main pollutants from vehicle exhausts

nitrogen oxides, unburnt hydrocarbons, CO

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How does a catalytic converter work

very large surface areas to make sure that the harmful pollutants have the best chance of reacting to form less harmful chemicals

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How does catalytic converter remove unburnt hydrocarbons

e.g C3H8 + 5O2 ----> 3CO2 + 4H2O (just complete combustion)

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How does catalytic converter remove nitrogen oxides

2NO --> N2 + O2 and 2NO + 2CO ----> N2 + 2CO2

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sulfur dioxide does what when gets into atmosphere

dissolves in moisture and is converted into sulfuric acid (acid rain) same process occurs when Nitrogen dioxide goes into atmosphere (nitric acid)

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acid rain does what

destroys trees/vegeatation, and corrodes buildings and statues, and kills fish in lakes.

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How to remove SO2 from power station flue gases before gets into atmosphere

Powdered calcium carbonate or calcium oxide mixed with water to make alkaline slurry. when flue gases mix with alkaline slurry, harmless salt is formed (calcium sulfate) {CaO + SO2 --> CaSO3}

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Get Revising

Unit 3 Section 2

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