Biofuel Technology: Current Design Principles, Feedstocks Analysis,
Environment Impact and Future Growth
Bocheng Ouyang
1,*
, Yiling Deng
2,a
, Wuqiang Yang
3,b
and Jiaxi Yang
4,c
1
School of Engineering, Pennsylvania State University,University Park, U.S.A.
2
Roedean School, Roedean Way,Brighton, U.K.
3
Peninsula Catholic High School,Virginia 23601 U.S.A.
4
Qingdao No.2 Middle School,Shandong, China
Keywords: Biofuel, Starch-Based Feedstock, Corn: Fermentation, Dry-Grinding, Wet-Milling, Transesterification.
Abstract: This work aims to analysis the advance and disseminate knowledge in all the biofuel-related areas. The biofuel
has been researched and developed in the last two decades. Newly emerged theories and techniques has
prompted the progress of the biofuel commercial application. In this work, the histories of the development
of the biofuels were researched. The physical principle of biofuel reaction was discussed. The two major
feedstocks of producing biofuel and their cultivation technologies were discussed. The major methods of
producing the biofuels including hydrolysis, fermentation, and transesterification were introduced. This work
also analyses the economic and environmental impact of biofuel application.
1 INTRODUCTION
Biofuels, as the name implies, are fuels derived from
biomass, including crops, herbs, and other materials.
The two most common types of biofuels in use today
are ethanol and biodiesel, both of which represent the
first generation of biofuel technology. Today, fossil
fuels are still the main fuel used in most countries, but
it is recognized that fossil energy sources are limited,
and the diminishing availability of fossil fuel
resources is causing prices to skyrocket, and sooner
or later fossil fuels will be depleted, leading to the
creation of renewable energy sources, of which
biofuels are one. While fossil fuels usually take
millions of years to form, biofuels are any
hydrocarbon fuel produced from organic matter in a
short time.
2 PHYSICAL PRINCIPLES
In order to efficiently and economically produce and
apply biofuel, the physical principles of the biofuel
must be understood, which are also true for other
types of fuel.
2.1 Chemical Reactions
Generally, the released energy of the biofuel comes
from the chemical reaction. Chemical reaction, by
definition, is a process that involves rearrangement of
the molecular or ionic structure of a substance.
The rearrangement of the molecule is exhibited by
the breaking of original bonds and formation of the
new bonds. The net energy difference of the
rearrangement is required to be absorbed from or
released to the environment in a form such as internal
energy. Chemical reactions can be investigated and
represented by two different components: reaction
thermodynamics and reaction kinetics.
2.2 Reaction Thermodynamics
Reaction thermodynamics is defined as the system
needing either to absorb or to release energy to the
surrounding environment to proceed the reaction.
Endothermic reactions require absorbing energy (net
input) while the exothermic reactions result in
releasing energy (net output) (Ott, Bevan J.; Boerio-
Goates, Juliana 2000). To examine the
thermodynamic properties of a biofuel, most biofuel
will be observed under steady-state conditions during
the chemical equilibrium. To characterize the
thermodynamic entity, Gibbs free energy was
680
Ouyang, B., Deng, Y., Yang, W. and Yang, J.
Biofuel Technology: Current Design Principles, Feedstocks Analysis, Environment Impact and Future Growth.
DOI: 10.5220/0011254900003443
In Proceedings of the 4th International Conference on Biomedical Engineering and Bioinformatics (ICBEB 2022), pages 680-685
ISBN: 978-989-758-595-1
Copyright
c
2022 by SCITEPRESS Science and Technology Publications, Lda. All rights reserved
introduced, which was named after the nineteenth-
century scientist Willard Gibbs. The Gibbs free
energy was commonly presented by the following
form:
∆𝐺 ∆𝐻  𝑇∆𝑆 1
where the G represents Gibbs free energy, H
represents enthalpy, T represents temperature, and S
represents entropy. A negative Gibbs free energy
indicates that the reaction is spontaneous process and
proceeds in the forward direction of the reaction,
while a positive Gibbs free energy indicates that the
reaction is a non-spontaneous process (Li, Khanal
2017). In the equation, enthalpy and entropy can
usually be calculated by the thermodynamics
properties of the reactant and product by the
following equations.
∆𝐻

∆𝐻
,
∆𝐻
,
2
∆𝑆 ∆𝑆

∆𝑆

3
2.3 Reaction Kinetics
Reaction kinetics is another important field to study
for determining the physical properties of biofuels
and their related reaction. Instead of determining the
spontaneity of the reaction by thermodynamic study,
kinetics study determines the rate of process of the
reaction (Hoff, J. H. van't (Jacobus Henricus van't);
Cohen, Ernst; Ewan, Thomas 1896). To simplify the
kinetics study of the reaction, most biochemical
reactions were assumed to occur in an isothermal
environment to preserve the biological activity of the
microbial community. To determine the rate of the
reaction, rate constant k was introduced and can be
represented by the following expression:
𝑘𝐴𝑒
/
4
where the k is the first-order rate constant of the
reaction, A is the Arrhenius constant, E is the
activation energy of the reaction, R is the gas
constant, and T is the temperature. The rate constant,
or the specific rate constant, is the proportionality
constant in the equation that expresses the
relationship between the rate of a chemical reaction
and the concentrations of the reacting substances. By
specifying the rate constant, the reaction rate can be
deducted and represent by the following expression:
𝑟
𝑘𝐶
𝐶
𝐶
5
where the C is the concentration of each component
and. The exponents x, y, and z correlate with the
stoichiometric number of each component according
to the chemical equilibrium in most cases.
3 TECHNOLOGY
IMPLEMENTATION
In order to effectively produce biofuel, raw materials
or so-called feedstocks are also an important field to
study. Based on different bio-properties, the major
categories of feedstocks are starch-based, oilseed-
based, lignocellulose-based, and algae-based
feedstocks. This article will focus on the major and
massive production feedstocks: starch based.
3.1 Starch-based Feedstock
Starch-based feedstocks are grown and cultivated for
food and feed supply. The major crops of Starch-
based feedstocks are cereals (such as wheat, rice,
maize, oat, barley, rye, millet, and sorghum) and
starchy roots (such as potatoes and yams). Based on
the data collecting by FAOSTAT (Etipbioenergy EU,
2012), the total global starch product is around 3.07
billion metric tons at current. Approximately 6% of
the starch production is used for biofuel production,
and the major biofuel product from the starch
feedstock is bioethanol (40%). Corn is the major
cereal crop that produces about 98% bioethanol.
3.2 Corn
This article will use corn as an example of starch-
based feedstock to specify the technical implements
during biofuel production.
Figure 1: Percentage Components of Corn.
Cron was an original tropical plane only after
centuries of modification, cron was well adapted to
and effectively grown at temperature climates.
Globally, the U.S. is the largest corn producer
providing 35% production, followed by China (21%)
and Brazil (8%). For bioethanol production, Yellow
dent corn (Zeamays var. indentata) is the commonly
Biofuel Technology: Current Design Principles, Feedstocks Analysis, Environment Impact and Future Growth
681
used corn at present. Figure 1. illustrates the profile
of the corn and its composition.
3.3 Growth Cycle of Corn
After selecting cultivars, the corn will be planted to
absorb water and nutrients in the endosperm. The
growth cycle of corn was typically divided into three
stages: emergence, vegetative and reproductive. The
VEG stage is further designated numerically to
represent the highest leaf and visible collar. Such
numerical designation is also applied to the REP
stage representing kernel development. Figure 2.
illustrates the corresponding observation of each
stage.
3.4 Growing Degree Day
Environmental temperature is an important factor
influencing Plant growth. Most plants including corn
can only grow at a temperature above their base
temperature, while the growth rate of the plant
generally increases with the increasing temperature
with sufficient light, water, and nutrients. However, a
ceiling temperature exists for most plants, and the
growth rate will decrease as the temperature reaches
the ceiling temperature. The growing degree day
(GDD) was introduced to reflect the accumulated
heat of a given period of time and predict the plant
growth rate (Prentice, I. Colin et al 1992). Following
expression is the calculation of ht GDD and the
prediction of the GDD for corn growth:
Figure 2: Growth Stage of Corn.
3.5
Bioethanol from Starch-based
Feedstock
To produce bioethanol, two types of processes, wet
milling and dry milling, have been designed and
developed. Both of the processes were able to utilize
the starch-based feedstock to produce while
simultaneously produce co-products.
3.5.1 Fermentation Process
In the fermentation process, the essential step is
hydrolysis since starch-based feedstock cannot be
directly fermented by yeast directly. The upstream
feedstock of starch will be cooked at a high
temperature (90-100℃) with the enzyme alpha-
amylase for gelatinization and liquefaction, which is
able to dissociate the intermolecular bond of starch
feedstock and breaks down to the long-chain
molecule. Then, the liquified feedstock will be
cooked at a low temperature (55℃) to proceed the
saccharification. In most cases, the saccharification
process can be proceeded prior to the fermentation or
simultaneously with the fermentation (Li, Khanal
2017). Recently, a newly designed and developed
enzymes, STARGEN, commence its industry
operation, allowing the starch hydrolysis process to
occur at a low temperature and targeting to reduce the
energy consumption of the fermentation.
3.5.2 Wet Milling and Dry Milling
Figure 3: Flow Diagram of Dry Milling.
ICBEB 2022 - The International Conference on Biomedical Engineering and Bioinformatics
682
As aforementioned, two different types of technical
(wet milling and dry milling) were applied. The
following process flow diagrams indicate two typical
fermentation processes of using corn as the starch-
based feedstock.
Figure 4: Flow Diagram of Wet Milling.
The dry milling or dry grind technique is the
major method of producing bioethanol production.
During the dry milling, the whole corn kernel was
ground and mixed with water and enzymes forming a
mash. After gelatinization and liquefaction, the mash
was cooled and mix with more enzymes to proceed
with saccharification and fermentation (Stock 2000).
Figure 3 shows the process of the dry milling.
Instead of grinding corn kernel directly, the wet
milling process allows the corn to steep for 48 hours
and separate into different parts. The germ of the
kernel can be further separated into fiber, starch, and
gluten by processing slurry separation. The wet
milling process produces multiple high value-added
co-products, while also enables “food and fuel”
production. Figure 4 shows the process of the wet
milling.
4 TYPICAL SYSTEM
DESCRIPTION
4.1 Bioethanol
Bioethanol is mainly derived from star-based and
sugar-based and lignocellulose-based natural
materials, such as wheat starch and crops. The
ethanol is produced through several processes, firstly,
those carbohydrates will convert into sugars by
hydrolysis process, those feedstocks would be cooked
under high temperature of 90-100℃. And then, under
the action of microorganism and carbon dioxide,
usually yeast, the feedstock is being fermented at a
low temperature of 55 ℃ which turn into a liquid that
contains ethanol. Finally, the liquid is going to be
refining into high purity bioethanol through
distillation and dehydration.
Figure 5: Production of ethanol with starch-based materials.
Biofuel Technology: Current Design Principles, Feedstocks Analysis, Environment Impact and Future Growth
683
However, for lignocellulose-based feedstock, the
production process and condition required is different
compare to starch-based and sugar-based materials.
Pretreatment is used to prepare the lignocellulosic
material for enzymatic hydrolyses of cellulose and
hemicelluloses to generate fermentable sugars,
including physical, chemical, and biological
pretreatments. Firstly, chemical pretreatment is used
through alkaline hydrolysis at high temperature of
100-170℃.Or physical pretreatment is used,
including process of mechanical communication,
steam explosion (160-260℃), ammonia fiber
explosion (around 100℃) and pyrolysis (over
220℃), or biological pretreatment. After this,
enzymatic hydrolysis converts cellulose and
hemicellulose into glucose and pentose respectively
under the condition of pH 4.8 and temperature 45-
50℃.finally, ferment and distillation the feedstock to
get bioethanol. Figure 5 and 6 indicates the process
of the production of the ethanol via starch-based
materials and lignocellulos-based materials.
Figure 6: Production of ethanol with lignocellulos-based
materials.
4.2 Biodiesel
The feedstock used to produce biodiesel has two
generations, the first generation uses animal fat and
oils from vegetables. Those oils need pretreatments
like degumming, deacidification, bleaching, and
dehydration, the use of pretreatment depends on the
compositions of the materials. Degumming is used to
remove phosphatides from most feedstock;
deacidification is used to remove free fatty acids;
bleaching is used to remove pigments and trace
metals and reduce oxidation; and finally, dehydration
is to remove water from oil or fats, as it is toxic to
transesterification and can affect the efficiency of
biodiesel conversion.
After pretreatment, is the process called
transesterification which can produce glycerin and
biodiesel by using alcohol as reactants, methanol is
commonly used in this process as it is cheaper and
easier to find compared to ethanol. And to separate
glycerin and biodiesel, settling, filtration and
decantation are used to find crude glycerin and crude
biodiesel. To increase the quality of biodiesel, it can
be done through refining.
5 ENVIRONMENTAL IMPACT
The production and use of biofuels can also release
air pollutants other than greenhouse gases that can
affect people and their surroundings. Air pollutants
from biofuels include carbon monoxide, sulfur
dioxide, nitrogen oxides, and ozone; these pollutants
have a variety of effects, including damage to human
health (e.g., cardiovascular disease, and respiratory
irritation) and to the environment (e.g., reduced
visibility, water, and soil acidification, and crop
damage).
Increased biofuel production will dramatically
increase water use, measured at some locations where
corn irrigation or production facilities draw water
from depleted groundwater sources. In some large
corn grain ethanol-producing countries, agricultural
irrigation has been increasing, resulting in
competition for freshwater with other uses (USDA
Foreign Agricultural Service 2018).
Figure 7: Production of biodiesel with first generation
feedstock.
ICBEB 2022 - The International Conference on Biomedical Engineering and Bioinformatics
684
6 ECONOMICS OF BIOFUEL
6.1 Introduction
Biofuel production is constantly developed
worldwide. In the U.S., ethanol production has three
times more than 5 years ago, from 2.8 billion gallons
in 2003 to over 9 billion gallons in 2008. Moreover,
Brazil produces secondly around the world with
approximately 5 billion gallons in 2007.
Biodiesel production is also growing rapidly from
25 million gallons in 2004 to 700 million gallons in
2008 in the U.S, which lays a solid foundation of
maintain the increased demand of renewable energy
in the market. However, recently, markets for fuels
and feedstocks fluctuate dramatically. The prices of
Petroleum have increased from $20 per barrel in 2002
to $140 per barrel in 2008.
6.2 Corn Ethanol
As forementioned, Drys-grind and wet-milling are
two methods of producing ethanol. In the U.S., dry-
grind methods are applied to more than 80% of
ethanol production. The advantage of applying the
dry-grind method is the relatively low capital cost,
which more eco-friendly for most plants. Dry-grind
plants produce ethanol and animal feed. Wet millings,
by contrast, are able to further produce value-added
co-products. Thus, ethanol yields from dry-grind
processes are higher. Table 1 lists the cost of each
typical item of the ethanol production.
Table 1: Ethanol production cost in USDA 2002.
US average
2002 1998
Feedstock costs
($/gal)
0.8030 0.8151
By-porduct credit
($/gal)
-0.2580 -0.2806
Net feedstock
cost
(
$/
g
al
)
0.5450 0.5345
Operating cost
($/gal)
0.4124 0.4171
Total cost ($/gal)
0.9574 0.9516
7 CONCLUSIONS
In conclusion, this work discussed the
thermodynamic principles of biofuels and identified
four major feedstocks of biofuel production.
Focusing on the starch-based feedstocks, the work
introduced the cultivation of corn, which is the major
source of the starched-based feedstock. The process
of the fermentation of the corn was researched. The
typical processes of the biofuel via different
feedstock were introduced and illustrated by a flow
diagram. The economy and commercial application
of the biofuels were also analyzed and concluded as
a sustainable and growing market. In the foreseeable
future, the biofeul will continuely and increasely
replace the current fossil fuels and serves as an
important role in reducing global carbon emmsion
and enviromental impacts.
ACKNOWLEDGEMENTS
We thank Professor Nasr Ghoniem for the full
educational support. Thanks to Mr. Kai Jiang for
holding discussions and providing helpful feedback
and comments.
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