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Production of Materials – Renewable Ethanol
9.2 Production of materials: 3. Renewable ethanol
3. Other resources, such as ethanol, are readily available from renewable resources
such as plants
Background: Much of our energy comes from chemicals formed millions of years
ago, e.g. coal and oil, which are termed fossil fuels. Research into alternative energy
sources continues, with interest in solar energy, tidal energy and so forth. Chemists
too are involved in this search and look to the chemicals in the biomass for renewable
sources of energy. As fossil fuel supplies are depleted, ethanol, obtained from
renewable
plant
resources,
will
be
of
increasing
importance.

Describe the dehydration of ethanol to ethylene and identify the need for a
catalyst in this process and the catalyst used.

Describe the addition of water to ethylene resulting in the production of ethanol
and identify the need for a catalyst in this process and the catalyst used.
The following information addresses the above two syllabus points together.
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Alcohols contain the hydroxy (-OH) functional group.
Alcohols are also known as alkanols.
Alcohols can be represented by the general formula ROH where ‘R’ represents
any alkyl group.
Alcohols are named by removing the ‘e’ on the hydrocarbon chain and adding the
ending ‘-ol’.
Alcohols can contain more than one –OH group and are named as ‘diols’ and
‘triols’ etc.
For example:
HO-CH2-CH2-OH is named 1,2-ethanediol
HO-CH2-CHOH-CH2-OH is named 1,2,3-propanetriol
NOTE: in these cases the ‘e’ is not dropped from the name.

Ethylene and ethanol are easily interchanged by addition of water (hydration) and
removal of water (dehydration). Catalysts such as sulfuric acid, phosphoric acid or
heated ceramic solids can be used to catalyse these dehydration and hydration
reactions.
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Production of Materials – Renewable Ethanol
NOTE:
1. The catalyst used in the hydration of ethene is and acid catalyst.
2. The catalyst used in the dehydration of ethanol to ethene is alumina or
mostly today porous ceramic catalysts are used with the ethanol vapour
being heated to 350C.
3. In a laboratory this reaction can be carried out using concentrated
sulfuric acid, as per the following equation:
Conc H2SO4
C2H5OH
C2H4(g) + H2O(g)
Additional background information
Countries rich in petroleum or natural gas, e.g. around the Persian Gulf, or
petroleum refining and cracking facilities, e.g. Singapore, can make ethanol by
hydration of ethylene.
Countries rich in land and climate suitable for growing crops that could be
used to produce ethanol, e.g. Brazil, can make ethylene by dehydration of
ethanol.
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Production of Materials – Renewable Ethanol


Process information from secondary sources such as molecular model kits,
digital technologies or computer simulations to model:
-
the addition of water to ethylene
the dehydration of ethanol

Perform this dot point using molecular model kits.
Describe and account for the many uses of ethanol as a solvent for polar and
non-polar substances.

Ethanol is used as a solvent in dissolving medicines and food flavourings and
colourings that do not dissolve easily in water. Once the non-polar material is
dissolved in the ethanol, water can be added to prepare a solution that is
mostly water.

The ethanol molecule has a water loving (hydrophilic) -OH group that helps it
dissolve polar molecules and ionic substances. The short, water fearing
(hydrophobic) hydrocarbon chain CH3CH2- can attract non-polar molecules.
Thus ethanol can dissolve both polar and non-polar substances.

Industrially and in consumer products, ethanol is the second most important
solvent after water. Ethanol is the least toxic of all the alcohols as it is
poisonous in moderate amounts rather than small amounts. Consumer products
listed as containing alcohol practically always contain ethanol as the alcohol.
Outline the use of ethanol as a fuel and explain why it can be called a renewable
resource.


Process information from secondary sources to summarise the use of ethanol as
an alternative car fuel, evaluating the success of current usage.
Assess the potential of ethanol as an alternative fuel and discuss the advantages
and disadvantages of its use.

Ethanol is considered a renewable fuel from the fact that is can be produced by
the fermentation of sugar cane. Sugar cane can be continuously grown.

Brazil (1970’s) was one of the first countries to produce ethanol from sugar
cane for use in cars as fuel. Today ¼ of Brazil’s cars use pure ethanol as their
fuel.

The remainder use a 20% ethanol blend.

Cars that use pure ethanol or a higher % blend require some modification.

Other countries are slowly introducing ethanol blends into their automotive
fuels.
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Production of Materials – Renewable Ethanol

Cars using pure ethanol or petrol-ethanol mixture release fewer pollutants,
particularly carbon monoxide.

One mole of octane requires more oxygen to burn than one mole of ethanol.
Therefore, octane is more likely than ethanol to undergo incomplete
combustion and produce carbon monoxide and soot as pollutants.
C2H5OH + 3O2
2C8H18(g) + 25O2

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--> 2CO2 + 3H2O
16CO2(g) + 18H2O(l)
While there is little difference in the amount of energy released when 1 mole
of ethanol (683kJ) compared to octane (688kJ) combusted, there is a
significant difference, as shown by the equations, in the amount of CO2
produced.
It is argued that ethanol releases back into the atmosphere, CO2 that had been
captured earlier by plants, whereas, fossil fuels are dup up and burnt. There it
is said that ethanol as a fuel is carbon neutral.

Petrol does not usually completely combust. Hence, this emits the products of
incomplete combustion into the atmosphere. The combustion of ethanol
reduces these emissions and consequently alleviates problems, such as health
issues and is also an economic additive to petrol.

One problem of using ethanol from sugar cane is that it takes energy to grow
and harvest the crops, distil the ethanol and transport it to market. When these
costs are taken into account there may be little economic advantage.

To produce the sugar cane required for fermentation large areas of arable
farmland are needed. This could restrict food production in some countries.
The future . . .
Distillation of the aqueous ethanol product (96% ethanol and 4% water) to
obtain almost pure ethanol can take half as much energy as that released when
the ethanol is burnt. Distillation is being replaced by low energy methods such
as passing the aqueous ethanol through special zeolite filters that act as
molecular sieves. The more polar water molecules are strongly attracted to
polar parts of the zeolite while the less polar ethanol passes through thus
separating pure ethanol.
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Production of Materials – Renewable Ethanol


Describe conditions under which fermentation of sugars is promoted.
Summarise the chemistry of the fermentation process.

Present information from secondary sources by writing a balanced equation for
the fermentation of glucose to ethanol.

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Fermentation is the process where carbohydrates are converted to ethanol and
carbon dioxide.
Carbohydrates are usually in the form of glucose, sucrose or starch.
The fermentation process depends on the presence of micro-organisms called
yeasts. The yeast produce enzymes that catalyse the conversion of sugars to
ethanol.
The conversion of glucose to ethanol and carbon dioxide has the following
equation:
yeast
C6H12O6(aq)
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2CH3CH2OH(aq) + 2CO2(g) + heat
Ethanol in beer is made from barley, in which barley seeds are broken down
into fermentable sugars.
Ethanol in wine comes from the sugars in grape juice.
Under normal conditions the fermentation can proceed until the ethanol
concentration reaches about 15% by volume. At this concentration the yeast
can no longer survive and the fermentation process ceases.
Because the process is exothermic it is usually conducted under carefully
controlled temperature conditions.
The fermentation of sugars to ethanol is promoted by the following conditions:
- The sugars being in solution (involving mashing of grain or fruit if
necessary).
- The presence of yeast (which contains certain enzymes).
- A temperature of approximately 37°C (blood temperature).
- The exclusion of air, which provides low oxygen concentrations.
- Once the concentration of ethanol reaches 14-15% by volume, the yeast
can no longer survive, and the fermentation process stops.
Define the molar heat of combustion of a compound and calculate the value for
ethanol from first-hand data.

The molar heat of combustion of a substance is the heat liberated when one
mole of the substance undergoes complete combustion with oxygen at a
constant pressure of one atmosphere with the final products being carbon
dioxide and water.
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Production of Materials – Renewable Ethanol

Process information from secondary sources to summarise the processes
involved in the industrial production of ethanol from sugar cane.
The main steps in converting sugar cane to ethanol are:
1. The sugar cane crop is grown and then cut down ready for fermentation.
2. Crushed sugar cane is placed in fermentation tanks where bacteria act on it
and, over time, produce a crude form of ethanol.
3. The impure/crude ethanol is transferred to distillation stills where it is
heated until it vapourises. The vapour rises into the neck where it cools and
condenses to pure liquid ethanol. (Extracted from Excel HSC Chemistry)
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Production of Materials – Renewable Ethanol

Identify the IUPAC nomenclature for straight-chained alkanols from C1 to C8.
Alkanol
Condensed Structural
Formula
Structural Formula
Methanol
Ethanol
Propanol
1-propanol
Propan-1-ol
Butanol
1-butanol
Pentanol
1-pentanol
Hexanol
1-hexanol
Heptanol
1-heptanol
Octanol
1-octanol

The above alkanols are called primary alcohols. That is the functional –OH
group on a terminal (end) carbon.
 Secondary alkanols are where the functional –OH group is attached to a
carbon that is attached to two other carbons, e.g. propan-2-ol.
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Production of Materials – Renewable Ethanol

Tertiary alkanols are where the functional –OH group is attached to a
carbon that is attached to three other carbons., e.g 2-methyl-2-propanol

Solve problems, plan and perform a first-hand investigation to carry out the
fermentation of glucose and monitor mass changes.

Identify data sources, choose resources and perform a first-hand investigation
to determine and compare heats of combustion of at least three liquid alkanols
per gram and per mole.
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