Chemical Processes and Bioethanol Production

This assignment covers various aspects of chemical processes, including hydrocarbon cracking, ethane as a feedstock, and the production of buta-1,3-diene. It also delves into bioethanol production, discussing the use of corn fermentation, fossil fuel energy consumption, and the comparison of ethanol with gasoline in terms of price and environmental impact. The assignment provides detailed explanations, examples, and calculations to support its findings.

SECTION A
Solution
Q1ai) standard enthalpy of combustion of ethanol
ii)
b) C2H5OH + 3O2 => 2CO2 + 3H2O
∆ H0combustion = ∑ ∆ H0(reactant bonds) - ∑ ∆ H0(product bonds)
∆ H0 = [5∆ H0C-H + ∆ H0C-C + ∆ H0C-O + ∆ H0O-H] – [4∆ H0C = O + 6∆ H0O-H]
∆ H0combustion = [5*413 + 347 + 336 + 464] – [4*805 + 6*464]
∆ H0combustion = 3212 – 6004
= -2792 kJ/mol
The experimental combustion enthalpy change is lower than the standard enthalpy of combustion
due to heat being lost to the surrounding environment, the metal equipment used absorbs heat, or
either inaccurate measurements may also results to lower enthalpy of combustion
c)
C6H12O6 => C2H5OH
C6H12O6 + 6O2 => 6CO2 + 6H2O ….(i)
C2H5OH + 3O2 => 2CO2 + 3H2O ….(ii)
C6H12O6 => 2C2H5OH + 2CO2

(i)=> 2* (ii)
C6H12O6 => 2C2H5OH + 2CO2
∆ H =∆ H 1 - 2∆ H 2
= -2808 – 2(-1368)
= -2808 + 2736
= -72 kJ/mol
Q2)
Q2a) the production of sugar for fuel releases much of carbon dioxide into the atmosphere, since
when the fuel burns it releases into the atmosphere just the amount of carbon dioxide that the
sugar plant took to make the sugar in the first place, as compared to the production of oil for fuel
Combustion for sugar for fuel
C12H22O11 + 12O2 => 12CO2 + 11H2O
ii) The production of sugar for food has same production of carbon dioxide to the atmosphere as
producing sugar for fuel, since the carbon dioxide intake and output remain balance.
b) Harvesting by hand does not involve fuel engine that burn to produce carbon dioxide, hence it
will effectively and efficiently reduce extra carbon dioxide emission to the atmosphere.
c) CH3CH2OH + 3O2 => 2CO2 + 3H2O
for 1 mole of ethanol we obtain 2 mole of CO2
1 tonne = 1000000 g
Mole = 1000000
46 =21739.130435moles
Using mole ratio of 1 : 2
Mole of CO2 = 2 ( 21739.130435 moles ¿
= 43478.26087 moles
Mass = moles * molar mass
= 43478.26087 * 44

= 1913043. 4783 g
= 1913043.4783
1000000
= 1.9130 tonnes
Q3a) is a process of combining or mixing a substance with oxygen
Oxygenate hydrocarbons has less energy content because during combustion process the oxygen in the
molecule burs first, hence giving off less heat or enthalpy
b) This is due to insufficient or incomplete combustion of fuel
Incomplete combustion of diesel
2C12H23 + 47O2 => 24CO + 23H2O
c) Since it is oxygenated this allows its complete combustion to results only in production of
carbon dioxide as a product rather than carbon monoxide
d) Increase level of carbon monoxide reduces the amount of oxygen carried by haemoglobin
around the body in red blood cells, resulting in vital organs such as brain, nervous tissues and
heart not to receive enough oxygen to work properly.
Similarly, emission of carbon monoxide to the atmosphere reacts with hydroxyl radicals hence
reducing their abundance; these further causes an increase to the lifetimes of strong greenhouse
gases like methane, therefore carbon monoxide indirectly increase global warming
Q4a) oil
The fermentation of corn requires energy from the burning fossils fuels, this fossil fuels are
majorly classified as coal, natural gas, crude oil, oil was precisely what was being used because
the Brazil had discovered its own off-shore reserves of oil
b) pure ethanol = 30% less per litre of petrol
Price of petrol per litre = $2
Price per litre of ethanol = 100−30
100 ∗$ 2
= $1.4

c) the price of foodstuff is rising up since most of the lands that were used to grow the foodstuff
crops are now being converted to corn crops fars, this definitely decreases the sufficient supply
of foodstuff hence the price directly shoot up because of this shortage.
d) Bioethanol being renewable fuel is reducing greenhouse gases emission by about 60% relative
to gasoline; similarly, it uses low percentage of about 30% of energy, resulting to lower fuel
economy when operating a vehicle, at the same time it has higher octane number which provides
increasing power performance.
SECTION B
Q1a) hydrocarbon
This is organic compounds made up of carbon and hydrogen
Cracking
Is process where long chain hydrocarbons are broken down into simpler molecules, such as light
hydrocarbon by breaking of carbon – carbon bonds in the precursors.
b) Bond of carbon – carbon is easily broken than carbon – hydrogen because the bond length of
Carbon – carbon is longer than that of carbon – hydrogen, therefore the hydrogen radii is smaller,
so more energy is needed on C- H for atomization of the effective nuclear change on the bonded
pair of electrons will be greater
Q2a) Ethane
b)
i. Composition of the feedstock
Example a higher proportion of ethane to other products is formed from ethane and
propane than from other feedstock

ii. The severity of condition used, that is the temperature of reactor furnance time taken for
the reactant to flow through it.
This means that the condition chosen for the furnace temperature and the flow rate of the
heated reactants depend on the products that are needed
Q3)
b) Aromatic
Are hydrocarbon wit sigma bonds and delocalized pi electrons between carbons atom forming a
circle
c) Naphtha is produced during fraction distillation of crude oil, where the fraction will distill out
after distillation of kerosene and before distillation of Gasoline (petrol)
d) 11 to 18
Q4a) C2H6 (g) => C2H4 (g) + H2 (g) ∆ H +138 kJ/mol
b) % yield = molar mass of ethene
molar mass of ethane∗100
= 28
30∗100

= 93.3%
c) Since it involves breaking down further the hydrocarbon already broken down until the point
where there is production of a stable hydrocarbon
Q5) cracking of Naphtha will also produce higher percentage of C4 compounds which lead to
surplus of buta-1, 3-diene
b) Using Ethane feedstock
c)
d) CH2CHCHCH2 +2 H2 => CH3CH2CH2CH3
e) Recycling of butane from buta-1, 3- diene will help in production of more isomers of butanes