fuels Flashcards
definition of fuel
a chemical substance which has chemical energy stored in its bonds which can be used to release energy
define peak oil
consumer demand exceeds what is available in terms of energy
what are the two types of fuel?
renewable and non-renewable
what is renewable fuel?
- infinite in supply
- replenished in a shorter period of time
what is a non-renewable fuel?
- finite in supply
- originate from dead organic matter that requires 10^6 years to sediment/deposit and therefore it takes a long time to replace
what are the non-renewables?
coal, natural gas, crude oil
what does coal originate from? where is it found? what makes each type different?
- organic matter that takes many years to form
- mined from underground where there are different types all varying in %C
peat
- 60% carbon
- 25KJg-1
brown coal
- 70% carbon
- 30KJg-1
black coal
- 70% carbon
- 35KJg-1
why do the coals differ?
lower down (black coal) has more pressure, less H2O and increased temperature this increases % of carbon and so more energy is released
what is the reaction when coal burns?
C(s) + O2(g)—-> CO2(g)
how is energy made from coal?
- water is heated by coal
- steam moves at Hugh pressure to move a turbine
- steam is condensed and heads back to the water heater or to cool the cooling tower
- generater collects energy as electricity from the turbine and makes power
where is energy lost in coal burning? how much remains?
- 10% lost as heat
- 5% lost in various ways in the plant
- 50% lost as heat in steam from the cooling tower
- 35% remains
what is natural gas made of?
- mostly CH4 methane
- some ethane and propane
where is natural gas located?
- gas reservoirs between layers of rock
- where they mine for petroleum
- where they mine for coal because natural gas can bind to the surface of coal. this generates CSG (coal seam gas)
- trappen in shale rock
how is natural gas extracted?
fracking
how does fracking work?
- water, sand and chemical agents are injected at high pressure into a well under ground
- forces open fissures in shale from where the gas can flow to be collected
what environmental problems are there with fracking?
- geological instability
- chemicals may get in water supplies etc.
how is crude oil formed? what is it composed of? where from?
- decomposition of dead matter
- composed of different sized hydrocarbons (different fractions) C1 to C >100
- under seabed
what is fractional distillation? how does it work?
used varying boiling temps of hydrocarbons to seperate them.
- large hydrocarbons have greater BP because of more dispersion forces
- increased dispersion forces means that more energy is needed to overcome the bonds between the molecules of crude oil
- fractioning column starts really hot (400) and those that will not boil run out.
- decreases in temp
- when the fraction condense, they are collected in the bubble cap
what are the renewable fuels?
bio gas, bioethanol, biodiesel
define biofuel
uses plant matter but can also use dead animal matter
what is biogas?
natural gas made from living matter
how is biogas made?
- rotting manure and vegetable waste that has carbohydrates
- is broken down in anaerobic conditions (no oxygen) with microbes to make CO2 gas and CH4 gas
what is used to make bioethanol?
polysaccharides in plants
how are polysaccharides made?
- photosynthesis
- 6CO2 + 6H2O —> C6H12O6(aq) + 6O2
- makes glucose a monosaccharide
- condensation polymerisation joins glucoses to make polysaccharide (starch or cellulose)
step 1 of making bioethanol
crush, mill the plant to release CHOs needed. enzymes and water (helps CHOs breakdown- hydrolysis) and high temp (increase rate of reaction)
step 2 of making bioethanol
CHOs are released and digested and we have lost of monosaccharides. temp is dropped to 32 (op temp) and yeast enzyme added
- fermentation reaction then occurs in anaerobic conditions
fermentation: C6H12O6 —> (yeast at 32) 2C2H5OH(l) +2CO2 - ethanol is slightly polar because of OH and not to many Cs to over power
- ethanol can be written CH3CH2OH
in step 2 of bioethanol making carbon dioxide is made- ways to fix?
- feed into crops
- sold to carbonate drinks
step 3 of making bioethanol
- purify and isolate ethanol through steam distillation
- achieves ethanol purity of 99.7%
step 4 of bioethanol. issue?
- petrol (NRF) is spiked with bioethanol to increase longevity of petrol
- E5 5% ethanol
- E10 10% ethanol
- ethanol (1360KJmol-1) produces less energy than petrol (5460KJmol-1)
advantage of combusting bioethanol over petrol
2 mol CO2 made for 1 mol of bioethanol
8 mol CO2 for 1 mol octane
what is the equation for producing biodiesel
transesterification:
triglyceride —-> (strong base or alcohol) glycerol + 3 biodiesel molecules
what does the strong base or alcohol do in the production of biodiesel? use CH3OH
CH3O against the O and H against the C=O break apart the ester link
how is palm oil made?
chemist requires the fatty acid (3 from one fat molecule)
how does the name of a biodiesel change?
the reactant used changes the name chemically it will alter
what does the ester link do?
gives biodiesel all its chemical and physical properties
when C>4 in combustion what happens to oxygen?
becomes a gas
advantages of biofuels
- uses less NRFs as transport fuel. however in industry and agriculture NRF are still used
- biofuels are carbon neutral. the amount of carbon dioxide released in equal to the amount of CO2 fixed by the plant in photosynthesis. there is no net increase in CO2
disadvantages of biofuels
- crops for fuel rather than crops for food (ethics)
- machinery run on NRF
- transport vehicles run on NRF
- soil erosion and decreased quality
- loss of food farming land, loss of habitat if obtaining new cropping land
- costly
what is petrodiesel made of?
75% hydrocarbons (mostly dodecane C12H26) and 25% aromatic compounds (naphthaline)
- dodecane: alkane (single C-C bonds), dispersion forces
- naphthalene: cylindrical structure, C=C bonds, dispersion forces
what is biodiesel? comparison
compound that contains an ester link that is electronegative
what factors need to be considered for vehicle transport fuels?
- flow through engine
- provide efficient energy
energy content (amount of energy per quantity) KJ-1 biodiesel and petrodiesel
- 41
- 48
energy density
- density: mass of a specific volume
- amount of energy released by set volume KJL-1
biodiesel, petrodiesel
- 36
- 40
viscosity (CST)
- resistance to flow
- 4.9
- 2.5
cloud point
- min temp that fuel solidifies
biodiesel, petrodiesel
- -3-15 (because of dipole dipole bonds due to electronegativity)
- -15 to 5
biodiesel is hydroscopic. what does this mean? how does this compare to petrodiesel?
- absorbs H2O and attracts it
- degrades quickly so storage is important this may compromise flow
- petrodiesel is hydrophobic
