General Overview of Fuels:
I've chosen Ethanol, LPG, Natural Gas and Petrol (gasoline) for the purposes of this node, as they are largely representitive of the common fuels of today. It must be noted that because of the chemical properties of the hydrocarbons used in fuel production, methene can be turned into methane which can be turned into methanol and vice versa... this applies to most fuels.
Production of Fuels:
Fuels are produced both naturally and through controlled reactions in laboratories. Natural fuels
include fossil fuels (created by the burial of organisms under sediment, then applied pressure and heat),
the main type of which is petroleum. Petroleum deposits are drilled on land or under sea, and contain a
viscous crude oil, and natural gas.
Natural gas consists of four different alkanes which are in a gaseous state at room temperature, but
is 88-95% methane. The remaining 5-12% of the gas consists of the paraffin series (most which is
removed and compressed into liquid petroleum gas), and does not contain carbon monoxide. Natural gas
may be extracted straight from wells, and piped to households, or it may also be created through cracking.
Hydrocracking of the methane in natural gas creates methanol, which in turn care be converted by the
Mobil Process of catalytic dehydration into a high quality synthetic gasoline.
The rest of the petroleum is refined by fractional distillation, which is the separation of the
material into useful groups by utilising the boiling points of the various substances. The distilling tower is
heated from the bottom, and works on vapor rising, then condensing under bubble caps as it reaches the
level of temperature where it condenses back to liquid, so that gas is piped off the top of the tower, and
thick residue remains at the base.
Petrol (gasoline) consists of mainly hydrocarbon compounds C5-C10 with boiling points ranging
between 40 and 180ºC. As petrol (the main fuel of human transport) is in great demand, and that a lot of
unneeded petroleum remains in the higher fractions of the tower, these higher fractions of hydrocarbons
are often cracked into smaller hydrocarbons that are useful in petrol production.
Cracking normally occurs at very high temperatures, so the presence of a catalyst aids in cracking
the hydrocarbons at a lower temperature. An example (500ºC with Al2O3-SiO2 catalyst) is a 12-Carbon
hydrocarbon cracked into two smaller hydrocarbons:
C11H24 —> C9H20 + C2H4 (undecane —> nonane + ethene)
This process creates more liquid (at room temperature) hydrocarbons which can be used in the
manufacturing of petrol, which is mainly octane. The nonane is incorporated into petrol (which is of
higher quality, due to a cracked hydrocarbon’s tendency to create more branches, therefore making it
more suitable for use in engines), and the other product of the reaction, ethene can be hydrated into
Ethanol is also produced both naturally and artificially.
Ethanol is produced by fermentation of sugars by enzyme
action (from yeast cells), a form of anaerobic respiration.
As ethanol is toxic to the enzymes when over a concentration
of 10%, the alcohol must be distilled. This is not efficient for
industrial purposes, so ethanol is created by hydrating the
hydrocarbon ethene in the presence of an acid catalyst
(often phosphoric acid), an addition reaction at 330ºC with
steam and a pressure of 60 atmospheres. For example:
C2H4 + H2O(g) —catalyst—> C2H5OH
(ethene + water —————> ethanol)
Liquid Petroleum Gas is simply the creation (via cracking)
or extraction (from petroleum and natural gas by liquefying these
heavier gases based on boiling points) of the paraffin series
(alkanes C2-C4). These alkanes are bottled under pressure in
steel cylinders as liquids to be used for fuel when a centralised
gas supply is unavailable.
Properties of Fuels:
Petroleum based fuels are, in general, immiscible with water, and therefore insoluble, as they are
virtually non-polar. As they are less dense than water, they float on the surface of water. These properties
relate to their common use as fuels, as they can be stored in underground units without a risk of leaking
and contaminating the surrounding soil, as they are stored on top of a layer of water, and also help to
water-proof the container so that substances do not leak into the container.
They generally have low melting points and boiling points, so they can be stored under pressure
then changed to a gas (or atomised), which is useful for heating (eg cooking) and in car engines, which
are internal-combustion units that rely on atomised petrol being ignited.
When burnt in air, light hydrocarbon mixtures (eg petrol, natural gas and LPG) burn readily in
oxygen and can reach high temperatures (eg natural gas can burn at 1930°C), making them highly
suitable as fuels. The flames produced through combustion are relatively clean (becoming less so as the
hydrocarbon molecule chains increase in length), which indicates near-complete combustion. This
characteristic of these fuels is a factor that sees them used often, as less harmful by-products are produced.
Natural Gas and Liquid Petroleum Gas have low boiling points, meaning that they generally stay in
a gaseous state when released from their pressurised (or normal in the case of Natural Gas) containers
except in extreme cold. This property makes them suitable as fuels for portable heating. LPG is used as
fuel in paraffin stoves, as it can be taken into relatively extreme climates and still become a jet of fuel to
Through cracking and hydrocracking, it is possible to change the products of petroleum to different
fuels with relative ease, with the products of these reactions being higher quality fuels. This property, the
ability to branch, relates to their use as fuels, as fuels with more branches off the main chain release more
energy in combustion.
One of ethanol’s distinguishing properties that relates to its use as a fuel is its ability to be created
in different ways. It can be hydrated ethene, or produced through metabolic processes, making it both
versatile and renewable as a fuel resource. Ethanol, like its hydrocarbon counterparts, combusts relatively
cleanly, and when in a plentiful supply of oxygen, will produce little carbon monoxide (a toxic gas). It is
also miscible with other substances, and therefore is useful when used in conjunction with other fuels.
Liquid Petroleum Gas is sold commercially in pressurised canisters for barbecues, paraffin stoves
and patio heaters. As it
has been compressed into a liquid, this makes it easier to carry larger amounts of fuel around, as it is in a
smaller container, making it a useful fuel for more remote or outside locations.
Petrol is the most common fuel for cars with internal combustion engines. It is atomised
before being ignited in the car engine, and cracked fuels with many branches are an efficient fuel (as they
have a higher resistance to pre-ignition, or ignition of the fuel before it is supposed to ignite via a spark).
Petrol consists of a blend of medium hydrocarbons, and in colder weather, the blend is changed to more volatile hydrocarbons so that vaporisation can
be better achieved.
Ethanol, aside from its uses as a steriliser, solvent and intoxicating drink, is used in high-
compression internal combustion engines (as a transporting fuel, often mixed with another fuel such as
petrol) as the vapour is highly explosive when mixed with air. It is a suitable fuel for cars as it too has a
high resistance to pre-ignition.
Natural Gas is a fairly simple fuel, as it is generally extracted from Natural Gas wells and piped to
a central station before being piped to households to use in cooking and heating. It is a basic fuel that is
used commonly in eastern countries and in places with unreliable electricity supplies.
Interaction with People:
The main interaction of fuels with people is their use for their capabilities to release energy in the
form of heat. Fuels are utilised in cars, heating and cooking to the benefit of mankind. Jobs are created
by the giant petroleum and petrochemical industries, and the by-products of these industries are numerous
- from textiles to detergents to medicines.
Aside from the obvious interaction as a fuel, these organic molecules have serious effects and
repercussions on the people who utilise them. The products of combustion (apart from heat energy and
- Carbon dioxide - produced in a excess supply of air, a non-toxic gas
CH4 + 2O2 —> CO2 + 2H2O
- Carbon monoxide - produced in a limited supply of air, an extremely toxic gas which has an affinity for haemoglobin, and will create a stable compound with this, stopping oxygen from being transported around peoples’ bodies. This, if breathed in sufficient amounts, can cause death.
2CH4 + 3O2 —> 2CO + 4H2O
- Carbon - produced in very limited air supply, a black soot that can ruin equipment, such as engines.
Carbon monoxide, in particular, is a product of fuel that has a negative impact on people.
CH4 + O2 —> C + 2H2O
Lead is added to some petrols to reduce the risk of pre-ignition and make the internal combustion a
smoother reaction. To prevent the accumulation of lead (a heavy metal) in the engine, 1,2-dibromoethane
is added to the petrol, and lead bromide is formed. This is a volatile substance, and exits the car as
exhaust. Although this is useful for the engine, lead, which is a neurotoxin, is added to the atmosphere.
This lead, when inhaled, can damage both the brain and the nervous system, especially in young children. Generally, in many of today's Western countries, lead is not added to petrol, and has been replaced by methyl tert-buthyl ether. Petrol with MTBE is referred to as 'unleaded petrol'.
Smog produced by car exhausts reacting with sunlight (a photochemical reaction) is also a danger
to the health of people, as it increases the risk of both breathing problems (eg asthma) and infections that
affect airways (eg pneumonia).
Interaction with the Environment:
The products of the combustion and production of fuels are pollutants to the environment. Crude
oil (petroleum) contains amounts of Nitrogen and Sulfur, and these are released from the fractional
distillation tower as pollutants. These pollutants are integrated into acid rain, which can cause great
damage to ecosystems, water supplies and buildings.
Spills of oil from oil tankers in the ocean are very damaging to the environment because of the
density of the hydrocarbons in the oil. As these float on top of the water, beach communities as well as
birds and animals that live in or near the ocean are affected.
The carbon dioxide produced by combustion of fuels
plays a large part in the accumulation of greenhouse gases. CO2 is 50% of the greenhouse gases currently trapped in the
atmosphere of earth, and methane is 15%. These gases which
cannot be vented off into space create a blanket around the earth which contributes to the problem of
Drilling wells for petroleum and natural gas also destroys the habitats of many animals in countries
worldwide. These wells (in conjunction with pipe systems that stretch across continents) are aesthetically
displeasing, and disrupt wildlife.
Although fuels are of great use to mankind, they also have bad effects, not only on the users of the
fuels, but also on communities and ecosystems in the world around us.
Apatrix says: Coal, perhaps exotic stuff like rocket fuel, hydrogen peroxide... where are the rest of the fuels? Or stay with HCs and look for stuff like glucose. :)
Reply: The fuels I have gathered here a merely an example of fuels and their properties. For more detailed information, I would definitely suggest looking at specific writeups on each fuel type - there's much too much information to contain in one node!
The Hutchinson Encyclopedia; The Guinness Encyclopedia of Science; 3 Chemistry Text Books; BP - Petroleum Industry