We studied how petroleum gone through fractional distillation to obtian fuels for vehicles in A-Level Chemistry, but what impacts do they do to the environment?
Pollution from cars
nitrogen and oxygen are from the air; high temperatures are required to produce oxides of nitrogen (NOx)
N2 + O2 -> 2NO
- it is important to say CO is harmful to humans
- alcohols and ethers (oxygenates), since they have oxygen atoms in them, their combustion is more complete than the combustion of the corresponding alkane. Less CO and CxHy are produced.
energy density (Kj Kg-1) =
enthalpy of combustion (Kj mol-1) x no. moles in 1 Kg fuel (mol Kg-1)
Products and effects from pollutants from petrol:
Hydrocarbons (CxHy)
- incomplete combustion
- contribute to photochemical smog and respiratory problems
- reduced by catalytic converters and oxygenates (but increases CO2)
carbon monoxide (CO)
- incomplete combustion
- toxic to us
- reduced by catalytic converters and oxygenates (but increases CO2)
carbon dioxide (CO2)
- complete combustion of hydrocarbons
- global warming and greenhouse effect
- hydrogen is only alternative which doesn't produce CO2
nitrogen oxides (NOx)
- nitrogen and oxygen from air reacts at high temperatures from engine
- photochemical smog and respiratory problems and acid rain
- reduced by catalytic converters (CO2 is increased)
sulfur oxides (SOx)
- sulfur in petrol and oxygen from air react due to engine heat
- causes acid rain
- low sulfur petrol produced by desulphurisation
Alternative fuels:
diesel
- less CO produced and already sold
- but not sustainable
- produces more NOx and particulates
LPG or autogas
- less CO, CO2, CxHy, and NOx and engines easily converted
- not sustainable
- needs to be stored under pressure
Ethanol
- large amount of energy needed for cultivating sugar
- less CO, SO2, and NOx, also ethanol has a high octane number and CO2 absorbed during sugar cane growth
- its highly flammable
biodiesel
- waste plant and animal oils and fat, but uses fossil fuel energy for production
- plants absorbed CO2, less CO, CxHy, SO2 and particulates
- NOx emissions higher than diesel engine
hydrogen
- only entirely renewable if electricity for electrolysis to obtain hydrogen and oxygen is renewable
- water is the only product of combustion
- highly flammable and high pressure tank needed to store it as a liquid.
Drafted by Eunice (Chemistry)
References:
https://dieselnet.com/tech/diesel_combustion.php
https://www.encyclopedie-environnement.org/en/air-en/diesel-engines-and-wood-combustion-in-charge/
https://www.pnas.org/content/116/15/7192