Fuel- commercial fuel, rocket fuel, and biodiesel
Fuel-
commercial fuel, rocket fuel, and biodiesel
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A fuel is any substance that burns and form various kind of
energy like heat.
During the mid-eighteenth century, the discovery of the
steam engine, which converts the chemical energy latent in fuels to mechanical
energy, ushered in the Industrial Revolution.
Today fuels not only heat our homes and move our cars but
are necessary for every facet of modern technology.
For example, fuels
generate the electricity required for our modern computing and communications
technologies, and they propel the rocket engines that make possible our
explorations of outer space.
Foods as
Fuels
The body generates energy from food by the same overall
process as combustion, so the overall enthalpy change is the same as the heat
of combustion, which can be determined in a calorimeter. You can get some idea
of the energy available from carbohydrate foods by looking at a typical one,
glucose (C6H12O6). The thermochemical equation for the combustion of glucose is
C6H12O6(s) 6O2(g) → 6CO2(g) 6H2O(l) ; H° = 2803 kJ
Fossil
Fuels
All of the fossil fuels in existence today were created millions
of years ago when aquatic plants and animals were buried and compressed by
layers of sediment at the bottoms of swamps and seas. Over time this organic
matter was converted by bacterial decay and pressure to petroleum (oil), gas,
and coal
C (graphite) + O2 (g) → CO2 (g); H = 393.5 kJ
Natural gas and petroleum together account for nearly
three-quarters of the fossil fuels consumed per year. They are very convenient
fluid fuels, being easily transportable and having no ash. Purified natural gas
is primarily methane, CH4, but it also contains small amounts of ethane, C2H6;
propane, C3H8; and butane, C4H10. We would expect the fuel values of natural
gas to be close to that of the heat of combustion of methane:
CH4 (g)+ 2O2 (g)→ CO2 (g) + 2H2O(g); H = 802 kJ
This value of H is equivalent to 50.1 kJ per gram of fuel.
Petroleum is a very complicated mixture of compounds.
Gasoline, which is obtained from petroleum by chemical and
physical processes, contains many different hydrocarbons (compounds of carbon
and hydrogen). One such hydrocarbon is octane, C8H18. The combustion of octane
evolves 5074 kJ of heat per mole.
C8H18(l) + 2 2 5 O2(g) →8CO2(g) + 9H2O(g); H = 5074 kJ
The major problem with petroleum and natural gas as fuels is
their relatively short supply. It has been estimated that petroleum supplies
will be 80% depleted by about the year 2030.
Natural-gas supplies may be depleted even sooner. Coal
supplies, on the other hand, are sufficient to last several more centuries.
This abundance has spurred much research into developing commercial methods for
converting coal to more easily handled liquid and gaseous fuels. Most of these
methods begin by converting coal to carbon monoxide, CO. One way involves the
water–gas reaction.
Rocket
Fuels
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Rockets are self-contained missiles propelled by the
ejection of gases from an orifice. Usually, these are hot gases propelled from
the rocket by the reaction of a fuel with an oxidizer.
Rockets are believed to have originated with the
Chinese—perhaps before the thirteenth century, which is when they began to
appear in Europe. However, it was not until the twentieth century that rocket
propulsion began to be studied seriously, and since World War II rockets have
become major weapons. Space exploration with satellites propelled by rocket
engines began in 1957 with the Russian satellite Sputnik I.
Today weather and communications satellites are regularly
put into orbit about the earth using rocket engines. One of the factors
determining which fuel and oxidizer to use is the mass of the fuel and oxidizer
required. We have already seen that natural gas and gasoline have higher fuel
values per gram than coal.
The difference is caused by the higher hydrogen content of
natural gas and gasoline. Hydrogen is the element of the lowest density, and at
the same time, it reacts exothermically with oxygen to give water. You might
expect hydrogen and oxygen to be an ideal fuel–oxidizer combination. The thermochemical
equation for the combustion of hydrogen is
H2 (g) + 1 2 O2 (g) → H2O(g); H° = 242 kJ
Biodiesel
“Biodiesel is a form of diesel fuel derived from plants
or animals and consisting of long-chain fatty acid esters. It is typically made
by chemically reacting lipids such as animal fat (tallow), soybean oil, or some
other vegetable oil with alcohol, producing a methyl, ethyl, or propyl ester by
the process of Trans esterification.”
Biodiesel is meant to be used in standard diesel engines and
is thus distinct from the vegetable and waste oils used in fuel-converted
diesel engines. Biodiesel can be used alone or blended with petro-diesel in any
proportion. Biodiesel blends can also be used as heating oil.
“Biodiesel production by homogeneous alkali
catalysis was simulated in PRO/II ® from crude soybean oil and crude palm oil
at industrial level, with ethanol. Actual compositions were assumed and
thermodynamic properties were estimated by a group contribution method.
The main effluents
from biodiesel production are streams rich in unreacted oil, water, ethanol,
and glycerine.
Some alternatives to the treatment of these effluents
were proposed, including hydrous or anhydrous ethanol production, production,
and recycling of pure glycerol,
and unreacted oil recycling. An economic evaluation was done to find out the
potential of each treatment possibility. It was demonstrated that, in the case
of Brazil in mid-2014, it was not profitable to produce biodiesel from these
oilseeds and ethanol without tax reductions or subsidies, but it is possible to
reduce production costs and biodiesel prices with effluents treatment,
generating more economical and sustainable plants.”
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