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:
𝑘𝐴𝑒
/
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