Unit 26

Environmental Problems associated with the use of fossil fuels

How air pollutants are formed?

By the incomplete combustion of fuels / petrol By the burning of impurities in fuels (such as

sulphur dioxide from sulphur impurities.)

Test for gases in car exhaust

Test for carbon dioxide Turns lime water milky. Test for carbon monoxide Turns citrated blood cherry red. Test for acidic gases Turns universal indicator red.

Air pollutants from car exhausts

Carbon monoxide – from the incomplete combustion of petrol.

Unburnt hydrocarbons – such as benzene, C6H6, which is carcinogenic / causing cancer.

Carbon particulates (black smokes) – unburnt carbon particles from the incomplete combustion of fuel

Too small to be filtered by the hairs in the nose. Causing serious lung diseases .

Air pollutants from car exhausts

Nitrogen oxides High temperature in the cylinders of the car

engine and electric sparks / lightening (thunderstorm)

Oxidation of nitrogen N2(g) + O2(g) 2NO(g) Oxidation of nitrogen oxide by air 2NO(g) + O2(g) 2NO2(g)

Nitrogen oxides

Poisonous gases Irritate and attack respiratory system Dissolving in rainwater to form acid rain. 2NO2(g) + H2O(l) HNO2(aq) + HNO3(aq)

Photochemical smog

Nitrogen oxides together with unburnt hydrocarbons produce photochemical smog.

Smog is poisonous.

Lead compounds

Tetraethyl lead – added to petrol for improving the burning of petrol

Lead compounds accumulate in our bodies. They have harmful effects on red blood cells and brain cells.

Pollutants from industry

From factories, power stations and incinerators Same as that from car exhausts With one more air pollutant (from the burning of

sulphur impurities) Sulphur dioxide

Sulphur dioxide

From the burning of coal or low grade petroleum From the waste gas of incinerators as rubbish (waste p

aper) contains sulphur compounds as impurities. Irritates the respiratory systems & affects the normal fu

nction of lungs Causes cancer and even death. SO2(g) + H2O(l) H2SO3(aq)

Acid rain

Is rainwater from non-polluted air acidic? pH 5.6 Carbon dioxide dissolves in rainwater to form c

arbonic acid. CO2(g) + H2O(l) H2CO3(aq)

Sulphur dioxide and nitrogen dioxide dissolve in rainwater to form acid rain.

Effect of acid rain

Harm to water lives– Acid rain makes rivers and lakes more acidic.

Harmful to water lives and even kills them.

Damage to forests– Forests seriously damaged by acid rain. Trees are

stunted. Leaves drop off and the trees die.

Effect of acid rain

Damage to metalwork– Speeding up the rate of corrosion of metals

Damage to building materials– Acid rain attacks buildings made up of limestone.

Greenhouse effect

Carbon dioxide in the atmosphere acts like glass of a greenhouse. It allows high energy radiation from the sun to penetrate the atmosphere and warms the Earth’s surface. The high energy radiation is re-radiated as infra-red radiation. However, the infra-red radiation is trapped by the atmosphere (carbon dioxide). The Earth is thus warmed up.

Greenhouse gases

Carbon dioxide, methane, nitrogen oxides, ozone and chlorofluorocarbons are greenhouse gases.

Ways to reduce the greenhouse effect (to reduce carbon dioxide emission)

Plant more trees Stop burning fossil fuels Stop cutting down trees.

Methods for reducing air pollution

Using unleaded petrol in cars.– For reducing the amount of lead compounds in air.

Methods for reducing air pollution

Installing catalytic converter in car exhaust system

It is a honeycomb structure. Installed in the exhaust system of cars. On structure, platinum and other transition

metal are deposited.

Catalytic converters

carbon monoxide (CO)nitrogen oxides (NOx)hydrocarbons (HC)

carbon dioxide (CO2)nitrogen (N2)water (H2O)

stainless steel case honeycomb-shapedsupport

Shortcoming of catalytic converters

Solid lead compounds deposit on the surface of catalyst and block the honeycomb.

Catalytic converters can only be fitted with motor-cars which are run on unleaded petrol.

How does catalytic converter work?

Nitrogen oxide reacts with carbon monoxide when they pass over the catalyst.

2NO(g) + 2CO(g) N2(g) + 2CO2(g) The carbon monoxide and unburnt hydrocarbo

ns are oxidized in the presence of catalyst to form harmless products.

2CO(g) + O2(g) 2CO2(g) 2C8H18(l) + 25O2(g) 16CO2(g) + 18H2O(l)

Using scrubbers in power stations

Removing up to 95% of carbon dioxide. Two methods of scrubbing

– Dry scrubbing– Wet scrubbing

Dry scrubbing

Powdered limestone (CaCO3) is blown into the combustion chamber where it decomposes.

CaCO3(S) CaO(s) + CO2(g) The calcium oxide reacts with sulphur dioxide t

o form calcium sulphite. CaO(s) + SO2(g) CaSO3(s) These products are washed away as a slurry –

a mixture of solids and water.

Using scrubbers in power stations

CaSO3 + SO2

coal

CaCO3

air

S+O2 SO2

CaO

water +CaO

waste slurr y

furnace

dry scrubbing wet scrubbing

CaSO3 slurry

Wet scrubbing

Sulphur dioxide is removed by the action of calcium oxide and water (I.e., calcium hydroxide solution).

CaO(s) + H2O(l) Ca(OH)2(aq)

Ca(OH)2(aq) + SO2(g) CaSO3(s)+ H2O(l)

By the electrostatic precipitators in industry

Removes 99% of the particulates.

e–

e–

e–

e–

50 000 V d.c.power supply

particulate

particulate-freegas flow

dirtygas flow

Key: represents particulate

+ –

Electrostatic precipitators

Dirty gases pass through a strong electric field. The particles become charged. The charged particles are then collected on

plates of opposite charge.

Role of Governemnt

Legislation Monitoring and investigating planning

Oil splliage

Petroleum is toxic and flammable. Pollutes beaches and spoils recreation resorts. Blocks the oxygen supply of water lives. Clogs the feathers of birds and prevents them f

rom flying abd swimming. Poisoned sea birds and fishes.

Cleaning up oil spillage

Using detergents to emulsify the oil.