Literature Review on the Hydrolysis of Vegetable Oil to Fatty Acids for Biofuel Production

Biofuels 1
Literature review on the hydrolysis of vegetable oil to fatty acids FOR BIOFUEL
PRODUCTION
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Biofuels 2
Introduction
The potential of the use of biofuel as an alternative renewable energy source has
drawn much attention across the globe. In view of its advantages, biofuel can replace fossil
fuels such as petroleum and natural gas in most applications (Jebur, 2017). Concerns about
the unsustainability of conventional sources of energy including environmental degradation
and their depletion have made it necessary to seek for alternative sources of energy. Biofuels
such as biodiesel can be generated from vegetable oils and animal fats. According to
Demirbas, and Karslioglu (2010), vegetable oils can be modified or processed using four
major methods to use them as biofuel. These methods include thermal cracking also known
as pyrolysis, blending or dilution with hydrocarbons, transesterification, and emulsification.
Factors such as the reaction temperature, presence of catalysts, the ratio of the moles of
glycerides to alcohol, the water content of fats or oils, and the reaction time affect
transesterification reactions. However, the use of biofuels faces a challenge due to its high
cost compared to conventional energy sources such as diesel. The high price of the feedstocks
used in biofuel production partly accounts for the high cost of biofuel. The feedstocks used in
the production of biofuels include edible vegetable oils such as coconut and soybean, non-
edible vegetable oils such as castor and neem as well as animal fats. However, the use of
edible vegetable oils raises a sustainability problem as a result of competition with food
sources. Waste cooking oils provide ideal feedstocks while at the same time solving the
problem of environmental degradation.
Conversion of vegetable oils into diesel fuels

Biofuels 3
The use of vegetable oils as biofuels requires the improvement of their properties
through the reduction of viscosity, changing their cold flow properties and increasing their
volatilities. According to Ilham and Saka (2010), viscosity is the main property that affects
the use of vegetable oils as fuels. The most commonly used method is transesterification.
Another common path for the production of biofuel is the hydrolysis of vegetable oils
followed by methyl esterification reaction. Hydrolysis is the process that splits large fat or oil
molecules into smaller ones. It can be performed using catalytic or non-catalytic methods.
The catalysts employed include lipase, acid or alkaline-based catalysts (Zahan, and Kano
2018). If the acid-based catalytic method is used, free fatty acids react with methanol in the
methyl esterification process at the boiling point of methanol. It is also possible to process
methyl esterification at higher reaction pressure in a non-catalytic reaction using supercritical
methanol at a temperature of about 350 °C.
Biofuel can be generated through transesterification by the use of enzymatic, alkali or
acid catalysts. Alkali and acid catalysts offer two major advantages over their enzymatic
counterparts. These include low cost and lower reaction time. Therefore, the production of
better quality biofuel and higher yields can be achieved by the use of alkali catalysts.
However, this process requires high grade feedstocks due to its sensitivity to foreign bodies
in the oils. A transesterification process involving two steps has also been studied with the
aim to improve the quality of the biofuel. The first step in this process is the esterification of
the oil using acid catalysts. The second step involves alkali-catalyzed transesterification.
However, this method faces several drawbacks which makes it unsuitable. These include low
yields and the necessity of high temperatures. The use of supercritical methanol in
transesterification without using catalysts has also been sought as an alternative process. This
method has the ability to produce higher yields and can handle highly impure feedstocks. A
major disadvantage associated with this method is its high cost. This is because it requires