Fuels Flashcards
what are the fossil fuels
coal, oil and natural gas
what are non-renewable resources
those that are used faster than they can be replaced
why are fossil fuels non-renewable
reserves of fossil fuels are limited and could eventually be exhausted
what are fossil fuels
non-renewable fuels that are derived from plant or animal matter
process of coal formation
- plants that die in ancient wetlands are only partially decomposed due to anaerobic and acidic conditions, forming peat
- Peat is buried under layers of sediment due to rising sea levels. the buried peat is subjected to heat and pressure
- After millions of years of heat and pressure, coal is formed
4.Coal is mined from the ground to be combusted in power plants for electricity
what is coal composed of
primarily carbon (and water)
“crude”
not refined
distillation
boiling to evaporate and then condensing into a liquid
coal burning reaction
C(s) + O2(g) = CO2 (g) (+ 32KJg-1)
what happens as we go down the layers of coal
the water content decreases and carbon content increases which results in the increase of energy content of the coal
why does less water in coal result in a higher energy conetnt
less water is needed to be vaporised, therefore the amount of heat released is greater
why does energy content increase with coal content in carbon
the more heat is released when is it burned
what is the overall efficiency of a coal-fired power station and why
30-40%, energy is lost in each step of the process (the more energy transformations, the less efficient the process)
steps in the formation of oil and natural gas
- ancient sea animals and plants die and their bodies fall to the sea floor, where anaerobic conditions prevent complete decomposition 2. plant and animal remains are covered by layers of sediment and subjected to heat and pressure over millions of years 3. after millions of years, oil and gas deposits are formed
natural gas
composed of mainly methane together with small amounts of ethane and propane, (water, sulfur, carbon dioxide and nitrogen may be present)
equation of the combustion of methane (natural gas)
CH4(g) + 2O2(g) = CO2(g) + 2H2O (l)
where is natural gas found
natural gas deposits are often found trapped above crude oil, once a well is sunk into the deposit, the natural gas flows to the surface
crude oil
a thick, sticky black liquid which is composed of a complex mixture of lots of different hydrocarbon compounds of different sizes
where is crude oil found
in pourous rock (under the ground and under the sea)
why is crude oil a finite resource?
it is being used up much faster than it is being formed
how is crude oil converted into a useable form
it must be fractionally distilled and then cracked to obtain useful fuels such as petrol
how are componenets of crude oil sepearted during fractional distillation
each fraction consists of groups of hydrocarbons of similar chain lengths, these molecules therefore have similar properties and boiling points
petrodiesel
a fraction of crude oil that cintains slightly longer molecules than those in petrol
why is petrodiesel an undesirable fuel
when petrodiesel is contaminated with sulfur and nitrogen, it is burned and it produces sulfuric acid and nitric oxide, which have many negative effects on the environment
biofuels
renewable resources that are derived from plants which can be easily grown and harvested
why are biofuels carbon neutral
plants initially remove CO2 from the atmosphere which is then releasesd when burning the biofuels, hence there is no net increase in the amount of CO2 in the atmosphere
why are biofuels relastically not carbon neutral
energy is required to farm, fertilise and transport biofuels
how is biogas produced
when organic materials decays in anaerobic conditions and a micture of gas is produced, composed of mainly methane and carbon dioxide
how is biogas produced (steps)
- organic matter used as a fertiliser (containing carbohydrates) for crops
- anaerobic bacteria decompose the organic waste
- CH4 is burnt for heating, cooking or electricity
euqation for the formation of biogas
C6H12O6 (s) = 3CO2 (g) + 3CH4 (g)
bioethanol
dervied from plant materials which contains many carbohydrates, the plant material is combined with water and anaerobic bacteria whcih ferment glucose to produce ethanol and CO2
how is bioethanol produced
via fermentation
fermentation process
sugar or starch is dissolved in water and yeast is added, the mixture is then fermented between 15–35 degrees celcius in the absence of oxygen for few days. various enzymes/microorganisms catalyse or facilicate the reactions involved
equation for fermentation
C6H12O6(aq) = 2C2H5OH(aq) + 3CO2(g)
how is glucose produced from carbohydrates
the carbohydrates are pulped with water, a process that involves blending the biomass in water to break up the cell or plant structures. various enzymes are then added to the mixture to break the carbohydrate down into glucose
what is the formation of carbohrates into glucose called
pre-treatment
how does the level of pre-treatment change
the stronger the bonding in the carbohydrate feedstock the greater the pre-treatment required to ensure the enzymes are effective
why is forest waste difficult to produce bioethanol
cellulose is abundent in forest waste but difficult to process as the hydrogen bonds holding the cellulose molecules together are relatively strong
distillation
occurs after fermentation, uses different boiling points of liquids to seperate them (water has a higher boiling point than ethanol)
why is distillation required
are fermentation a dilute ethanol solution is produced which must be seperated from the reaction mixture to be useful as a fuel
bioethanol is comparison to petrol
can damage engines, has 62% energy content of petrol
biodiesel
made from vegtable oils and animal fats which are composed of triglycerides, used primarily as a transport fuel
triglycerides
three fatty acid residues, each bonded to a glycerol molecule via an ester group
how are triglycerides converted to biodeisel
via transesterification
transesterification
a reaction between a triglyceride and methanol to produce biodeisel and glycerol in the presence of a ctalyst (KOH)
what does the structure of a triglyceride depend on
the plant/ animal used as a source (saturated = animals, unsaturated = plants)
saturated esters
conatin only single C-C bonds, the fatty acid chain is straight, which allows the molecules to pack closely together to form a solid and room temp
unsaturATED ESTERS
contain the presence of a double carbon bond, this causes a kink in the fatty acid chain, preventing the molecules from packing in closely together, hence they are liquids at room temp (as dispersion forces are weakened between neighbouring molecules)
