Biofuels as Potentia: A Case Study

Biofuels 1
Chemistry- Research assignment
Name:
College:

Biofuels 2
Abstract
For a long time, biofuels have been explored and utilized as an alternative source of fuel,
however in small scale. Despite the rising popularity of these fuels, their sustainability has
been questioned regarding food versus fuel trade-off and land use. This research seeks to
examine the viability of ethanol-based biofuels as potential superiors to fossil fuels in terms
of energy output capabilities and greenhouse gas emission, especially carbon (iv) oxide.
Different types of feedstock for ethanol production are examined and compared in terms of
their energy content. Based on the gathered information, reasonable conclusions are drawn
and recommendations for improvement put forward.

Biofuels 3
Introduction
The preference of biofuels over other energy sources such as fossil fuels is driven by a wide
range of policy objectives (Kern, Kivimaa, Rogge, & Rosenow, 2018). Most importantly,
they have low greenhouse gas emissions which is a great advantage especially in this age
when environmental conservation is a major concern. Besides, biofuels are renewable energy
sources hence provide a significant contribution towards a sustainable transport sector
especially when combined with electric vehicles. In aviation, heavy freight, and marine
transport, bio-energy has been considered as the reasonable alternative to fossil fuels
regarding greenhouse gas emissions (De Baan, Alkemade, & Koellner, 2012). Despite the
myriad opportunities and interests for biofuels, plant construction is slowing down. This can
be partly attributed to the growing concern about sustainability of these energy sources with
respect to food and land use (Araújo, Mahajan, Kerr, & Silva, 2017).
Claim
Biofuels are more efficient and have less environmental impact than fossil fuels.
Research question
Is the combustion of ethanol-based biofuels (sugarcane) more efficient than standard fossil
fuels (petroleum) in terms of energy output (enthalpy) and carbon dioxide (CO2) emissions?
Rationale
In order to understand and appreciate how bioenergy contributes to the mitigation of climate
change, it’s important to carry out comparisons between conventional fuel sources such as
petroleum and alternative sources such as ethanol-based fuels. An investigation into the

Biofuels 4
energy output and corresponding carbon (iv) oxide emissions for different types of fuels is
necessary to determine the best fuel sources to be adopted for the development of a
sustainable transport system and other energy requirements.
Background
The economic status of developing countries as well as their growth is largely determined by
sources of energy and their utilization (Grammelis, 2016). In 2013, the Statistical Review of
World Energy estimated that the primary energy sources consisted of natural gas at 23.7 %,
coal at 30 % and petroleum at 32.9 % which amounted to 87 % share for fossil fuels
(Muktham, K. Bhargava, Bankupalli, & S. Ball, 2016). Modern day activities ranging from
cooking to transportation are highly dependent on fossil fuels. The figure below shows world
energy consumption by fuel type. It can be observed that oil, natural gas and coal
consumption greatly overshadow the consumption of renewable energy sources combined.
Figure 1: World energy consumption by fuel type
http://www.bp.com/en/global/corporate/energy-economics/statistical-review-of-world-
energy.html

Biofuels 5
The standard molar enthalpy of combustion of ethanol is about -1366.8 kJ/mol. This is the
heat amount released on completely burning a mole of ethanol at the standard state conditions
of 25 degree Celsius and a pressure of 1 atm. This is significantly lower than that of gasoline
(octane) which is approximately -5460 kJ/mol. Therefore, the burning of gasoline releases
more energy compared to ethanol. However, in terms of CO2 emission, ethanol reduces
emissions by about 34 % on average compared to octane. This is because the carbon (iv)
oxide emitted during the burning of ethanol is reused by the growing of feedstocks for
ethanol production. Compared to pure gasoline, ethanol and other fuels obtained from its
mixture with gasoline have higher levels of octane and therefore have lower emissions.
However, ethanol and its derivatives have higher ground-level emissions which result from
fuel tanks and other dispensing apparatus. The table below shows the CO2 emissions for
different fuel types.
The chart below shows the CO2 contributions for different types of fuels at different stages of
fuel production. The chart shows that, the carbon (iv) oxide emissions associated with the
production of biofuels is very low compared to the CO2 emissions associated with the
production of fossil fuels such as diesesl.

Biofuels 6
It is important to note that emission from ethanol is controversial and depends on whether
indirect impacts on land use are considered in calculations.
Analysis and interpretation
Worldwide, the most commonly used renewable biofuel for transport is ethanol-based
(Grammelis, 2016). This, depending on the type of feedstock, gives up to 80 % savings over
fossil fuels in terms of greenhouse gas emission (Muktham, K. Bhargava, Bankupalli, & S.
Ball, 2016). The production of bioethanol can be achieved via the use of three major raw
materials (Muktham, K. Bhargava, Bankupalli, & S. Ball, 2016):
i) Starch containing feedstock: these include corn, wheat and cassava
Feedstock Starch content, % w/w
Corn meal 70.8
Wheat 53-57

Biofuels 7
Cassava 76-81
Table 1: Starch content for different types of starch-based feedstock
html.scirp.org/file/_3-2210171_1.htm
ii) Sucrose containing feedstock: these include sugar beet and sugarcane
Feedstock Sucrose content, % w/w
Sugarcane 31.8
Sugar beet juice 16.5
Sweet sorghum stalks 67.4
Table 2: Sucrose content for different types of sucrose-based feedstock
html.scirp.org/file/_3-2210171_1.htm
iii) Cellulose containing feedstock: for example wood, straw and grass
Figure 2: Ethanol yield per tonne of feedstock

Biofuels 8
https://www.ambientediritto.it/dottrina/Politiche%20energetiche%20ambientali/politiche
%20e.a/img_food_crops/img11.jpg
The figure above shows quantity of ethanol in litres produced per tonne of different types of
feedstock. It is observed that the quantity of ethanol produced from Corn (which accounts for
the largest percentage of raw materials for ethanol production in the US) much greater than
the quantity of ethanol produced from both sugarcane used in Brazil and sugar beet used in
France.
In terms of energy densities, biofuels have significantly lower energy compared to fossil fuels
such as gasoline. This means that, biofuels are generally less efficient compared to fossil
fuels as a larger fuel quantity is necessary to supply the same amount of energy. The graph
above shows the comparison of the energy densities for different fuel types. As the graph
shows, the energy density for ethanol is only 25 MJ/kg compared to that of gasoline at 47
MJ/kg.
Types of ethanol-based biofuels
Corn-based biofuel

Biofuels 9
The chemical formula of ethanol is the same regardless of the method used or the substance
from which it is derived. Corn-based ethanol has been in use in the transport sector for a long
time although the industry has been applied only in small scale (Hood, Teoh, Devaiah, &
Vicuna Requesens, 2013). However, this has changed recently and the modern industry has
grown to a point of integration into any country’s supply of transport fuel. In the US ethanol
is commonly produced from starch based substances, usually corn (How Corn is processed to
Make Ethanol). A single grain of corn has several parts including the endosperm and the
pericarp. The endosperm consists mainly of starch which is the main energy storage for the
corn and thus can be extracted to produce fuel (Mosier, 2015). Starch is made up of units of
D-glucose which have an impact on the yield of ethanol (Mosier, 2015). The process of
converting starch is more labour intensive compared to the use of sugar.
Steps
This is the first step in the multi-step process of converting starch from corn into ethanol.
There are two methods of milling: dry and wet milling. Wet milling involves breaking down
the corn kernels into starch by heating them in an acidic solution of sulphur (Lee, Yangcheng,
Cheng, & Jane, 2015). The starch is then isolated and can be used to in ethanol manufacture.
Dry milling offers a simpler process and its main products are ethanol and carbon dioxide.
The steps involved in dry milling include:
Grinding
This process involves hammering the corn into smaller particles. This is done to break the
corn’s outer coating which increases the starch’s area of contact with enzymes in the
chemical reactions to follow. After grounding, a solution called slurry is formed by mixing
the corn with hot water (Lee, Yangcheng, Cheng, & Jane, 2015).

Biofuels 10
Liquefaction
In this stage, the starch in the slurry interacts with water molecules forming a viscous
suspension. Liquefaction is a partial hydrolysis process that breaks down long chain starch
molecules into smaller chains (Wang, Han, Dunn, Cai, & Elgowainy, 2015).
Saccharification
This is a process where the starch is hydrolysed further to produce glucose monomers.
Glucoamylase is used as an enzyme in this process. The hydrolysis reaction can be
represented by the following chemical reaction:
(C6 H10 O5)n +nH2 O H+ 393 K nC6 H 12 O6
The optimum conditions for this reaction include: a pH of about 4.5 which is acidic and a
temperature in the range of 55 – 65 ℃ (Lee, Yangcheng, Cheng, & Jane, 2015)
Fermentation
This is the final step in the conversion of starch to ethanol. The optimal conditions for this
step include a temperature between 30 and 32 ℃. In this reaction, the mole yield of ethanol
and carbon (iv) oxide is twice that of the glucose. The equation is shown below:
C6 H12 O6 → 2C2 H5 OH +2 CO2
Glucose ethanol
A significant percentage of the glucose (90-95 %) turns into ethanol. The overall equation
can be written as follows:

Biofuels 11
(C6 H10 O5)x →C6 H12 O6 →2 C2 H5 OH +2CO2
Starch glucose ethanol
Sugarcane-based biofuel
Sugars such as sugarcane, molasses and sugar beet which are primarily made up of glucose or
sucrose provide an alternative source of ethanol. Brazil is considered among the world’s
major producers of biofuel utilizing ethanol produced from sugarcane (Basso, Basso, Gallo,
& Basso, 2015). The first step is sugarcane harvesting after which sugar is extracted. The
sugarcane is cut into smaller pieces and milled with water producing a juice from which
sucrose is extracted (O'Hara, 2016). Fermentation is then carried out using yeast and other
nutrients to keep the yeast growing. Since fermentation is an exothermic reaction, cooling is
necessary to keep the conditions optimal for fermentation.
Enthalpy of ethanol-based biofuels
To find ethanol’s enthalpy of combustion we proceed as follows:
The following chemical equation represents the complete combustion of ethanol:
C2 H5 OH +3 O2 → 2 CO2 +3 H2 O+heat
Where one mole of ethanol combines with 3 moles of oxygen to give 2 moles of carbon (iv)
oxide, 3 moles of water and energy in form of heat.
Chemical bond Energy (kJ/mol)
H-H 432
C-H 413
C-C 347

Biofuels 12
O-H 467
C=C 614
N-N 160
O-O 146
Table 3: Average bond energies
https://www.slideshare.net/mrtangextrahelp/tang-06-bond-energy-17729639
On the reactants side, the broken bonds are:
1 C-C bond (348 kJ/mol)
5 C-H bonds (2065 kJ/mol)
3 O=O bonds (1485 kJ/mol)
1 C=O bond (799 kJ/mol)
Total = 348+2065+1485+799 = 4697 kJ/mol
On the products side the formed bonds are:
6 H-O bonds (-2778 kJ/mol)
4 C=O bonds (-3196 kJ/mol)
Total = -2778 – 3196 = -5974 kJ/mol
Therefore, ∆ H =−5974+ 4697=−1277 kJ /mol
1 mol of ethanol = (12*2)+(6*1)+(16) = 46 g
This corresponds to approximately 28 kJ/g of ethanol burned.
Comparison of the energy content of fuels
Fuel H/C ratio Energy content
(kJ/g)
CO2 emitted
(mol/1000 kJ)
Hydrogen - 120 -

Biofuels 13
Gas 4:1 51.6 1.2
Petroleum 2:1 43.6 1.6
Coal 1:1 39.3 2.0
Ethanol 3:1 27.3 1.6
Table 4: The energy content of various fuels
https://www.wou.edu/las/physci/GS361/Energy_From_Fossil_Fuels.htm
The chart above shows the energy density of various fuel types in comparison with ethanol
It is evident from the above data that the level of unsaturation rises down the table from
natural gas to coal. The quantity of carbon (iv) oxide emission also increases with the
increasing degree of unsaturation. The energy quantity released is dependent on the ratio of
hydrogen to carbon in the hydrocarbon chain. The greater the number of hydrogens per
carbon atom the higher the energy released during combustion (Ghenai, 2011).
The hydrocarbons in petroleum are highly unsaturated. In the estimation of energy content,
the molecule is considered to have multiple –CH2- units. However, petroleum still contains
aromatic molecules depending on the petroleum distillate (Ghenai, 2011). For instance,
gasoline has an energy value of approximately 48.1 kJ/g because it has a smaller fraction of
aromatics compared to crude oil which has an energy value of approximately 45.2 kJ/g.

Biofuels 14
Coal is mainly made up of hydrocarbons said to be aromatic. The true average energy
produced by burning a gram of coal is less than the provided value because coal has
considerable quantities of minerals and H2O (Ghenai, 2011). For instance, soft lignite coal
has energy value in the range of 17-21 kJ/g while anthracite which is a hard coal has higher
energy value in the range of 29-33 kJ/g.
CO2 emissions
The above graph shows the carbon (iv) emissions per m3 for different fuel types. This graph
clearly shows that fossil fuels have the highest emissions while biofuels have comparatively
lower emissions. It is important to note that CO2 emission levels are also dependent on the
type of feedstock used in the production of ethanol. The table below shows a comparison
between CO2 emissions for ethanol production in Brazil from sugarcane and the US from
corn. The data indicates that the overall carbon (iv) oxide emission from sugarcane feedstock
is significantly lower compared to that from corn.

Biofuels 15
Gasoline
Gasoline has the chemical formula C8H18 which is the chemical formula for octane
(Coronado, De Carvalho, & Silveira, 2009). It has a density of about 0.75 t/m3. The
stoichiometric equation for the combustion of gasoline in air is:
C8 H18 +12.5 O2+ 47 N2 → 8 CO2+ 9 H2 O+47 N2
The relative formula mass of gasoline is 144 g. from the chemical equation above, 144 g of
gasoline produce 352 g of carbon (iv) oxide. This corresponds to 352 tons of carbon (iv)
oxide per 152 m3 of gasoline. This is equivalent to about 2.316 ton of carbon (iv) oxide per
m3 of gasoline.
Ethanol
Ethyl alcohol has the chemical formula C2H5OH and it has a density of 0.79 t/m3 (Coronado,
De Carvalho, & Silveira, 2009). The stoichiometric equation of the combustion of ethanol in
air is:
C2 H5 OH +3 O2 +11.28 N 2 → 2CO2+3 H2 O+11.28 N 2

Biofuels 16
The mass of ethanol is 46 g as calculated before. Therefore, from the above equation, 46 g of
ethanol produce 88 g of carbon (iv) oxide. Considering the density of ethanol, this
corresponds to 88 tons of carbon (iv) oxide per 58.23 m3 of ethanol. This is equivalent to
about 1.511 tons of carbon (iv) oxide per m3 of ethanol.
Diesel
Petroleum diesel has the chemical formula C12H26 with a density of about 0.864 t/m3
(Coronado, De Carvalho, & Silveira, 2009). The stoichiometric equation of the combustion of
diesel in air is:
C12 H26+18.5O2 +69.56 N2 →12 CO2 +13 H2 O+69.56 N2
The mass of diesel from the given chemical formula is: (12*12)+(1*26) = 170 g. The mass of
the emitted CO2 is: 12(12+16*2) = 528 g.
Therefore, the combustion of 170 g of diesel produces 528 g of CO2. This corresponds to
approximately 528 tons of CO2 per 196.76 m3 of diesel considering the given density of
diesel. This is equivalent to about 2.683 tons of CO2 per m3 of diesel.
The above results clearly show that ethanol has the lowest carbon (iv) oxide emission at
1.511 tons of carbon (iv) oxide per m3 of ethanol while diesel has the highest emission at
2.683 tons of CO2 per m3 of diesel.
Conclusion and evaluation
Evaluation

Biofuels 17
The information and data obtained from various sources appears to be consistent expect for
several variations. For instance, different sources give different values for the average bond
energies. However, these differences are considerably small and do not affect our ability to
carry out comparisons of the different energy sources. From the gathered data and
corresponding computations, it is evident that the energy content of ethanol-based fuels is
significantly lower compared to that of fossil fuels. Natural gas has energy content of about
5.7 kJ/g which almost twice that of ethanol at 27.3 kJ/mol. Of the four energy sources
compared, ethanol has the least energy content.
In terms of CO2 emissions, ethanol does prove to be superior over all the fossil fuels, except
natural gas. There have been claims that greenhouse gas emissions from ethanol-based fuels
can exceed those due to gasoline considering environmental effects in the scenario of
lifecycle assessment. On the other hand, biofuels have been shown to reduce greenhouse gas
emissions by 60 % to 94 % compared to fossil fuels.
Conclusion
From the gathered information and data, the overall energy output for ethanol-based fuels is
lower compared to that from fossil fuels. However, ethanol-based fuels are generally superior
in terms of CO2 emissions. It is impossible to fully support the question because according to
the data, it contains conflicting statements. Biofuels have better performance than fossil fuels
in terms of CO2 emission but their energy content is significantly lower compared to that of
fossil fuels.
Recommendation
Currently, the production and utilization of biofuels is highly concentrated in a few regions,
especially the developed countries. However, in order to achieve the common goal of a

Biofuels 18
sustainable future, it is necessary to roll out programs worldwide to adopt biofuels because
they have proved capable of significantly cutting greenhouse gas emissions if carefully
exploited.
References
7.3.2 How Corn is Processed to Make Ethanol. (n.d.). Retrieved from https://www.e-
education.psu.edu/egee439/node/673
Araújo, K., Mahajan, D., Kerr, R., & Silva, M. D. (2017). Global Biofuels at the Crossroads:
An Overview of Technical, Policy, and Investment Complexities in the Sustainability
of Biofuel Development. Agriculture, 7(4), 32. doi:10.3390/agriculture7040032
Basso, T., Basso, T., Gallo, C., & Basso, L. (2015). Towards the Production of Second
Generation Ethanol From Sugarcane Bagasse in Brazil. Sugarcane as Biofuel
Feedstock, 67-77. doi:10.1201/b18460-6
Coronado, C. R., De Carvalho, J. A., & Silveira, J. L. (2009). Biodiesel CO2 emissions: A
comparison with the main fuels in the Brazilian market. Fuel Processing
Technology, 90(2), 204-211. doi:10.1016/j.fuproc.2008.09.006
De Baan, L., Alkemade, R., & Koellner, T. (2012). Land use impacts on biodiversity in
LCA: a global approach. The International Journal of Life Cycle Assessment, 18(6),
1216-1230. doi:10.1007/s11367-012-0412-0
Ghenai, C. (2011). Combustion and Emissions Characteristics of Biodiesel
Fuels. Renewable Energy - Trends and Applications. doi:10.5772/26261
Grammelis, P. (2016). Energy, Transportation and Global Warming. Basingstoke, England:
Springer.

Biofuels 19
Hood, E. E., Teoh, K., Devaiah, S. P., & Vicuna Requesens, D. (2013). Biomass biomass
Crops for Biofuels and Bio-based Products biomass crops crops for biofuels and bio-
based products. Sustainable Food Production, 250-279. doi:10.1007/978-1-4614-
5797-8_170
Kern, F., Kivimaa, P., Rogge, K., & Rosenow, J. (2018). Policy mixes for sustainable energy
transitions. Transitions in Energy Efficiency and Demand, 215-234.
doi:10.4324/9781351127264-12
Lee, C. J., Yangcheng, H., Cheng, J. J., & Jane, J. (2015). Starch characterization and
ethanol production of duckweed and corn kernel. Starch - Stärke, 68(3-4), 348-354.
doi:10.1002/star.201500126
Mosier, N. S. (2015). Cellulosic Ethanol—Biofuel Beyond Corn. Bioenergy, 193-197.
doi:10.1016/b978-0-12-407909-0.00012-2
Muktham, R., K. Bhargava, S., Bankupalli, S., & S. Ball, A. (2016). A Review on
1^st and 2^nd Generation Bioethanol Production-Recent
Progress. Journal of Sustainable Bioenergy Systems, 06(03), 72-92.
doi:10.4236/jsbs.2016.63008
O'Hara, I. M. (2016). The sugarcane industry, biofuel, and bioproduct
perspectives. Sugarcane-Based Biofuels and Bioproducts, 1-22.
doi:10.1002/9781118719862.ch1
Tang 06 bond energy. (2013, March 26). Retrieved from
https://www.slideshare.net/mrtangextrahelp/tang-06-bond-energy-17729639
Wang, M., Han, J., Dunn, J., Cai, H., & Elgowainy, A. (2015). Well-to-Wheels Energy Use
and Greenhouse Gas Emissions of Ethanol From Corn, Sugarcane, and Cellulosic
Biomass for US Use: Well-to-Wheels Energy Use and Greenhouse Gas Emissions of

Biofuels 20
Ethanol From Corn, Sugarcane, and Cellulosic Biomass for US Use. Efficiency and
Sustainability in Biofuel Production, 249-279. doi:10.1201/b18466-13