A report on Biodiesel Production from
Waste Cooking Oil (WCO)
DEPARTMENT OF CHEMICAL ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY ROURKELA
Submitted By:
Arvind Kushwha
116CH0105
Abstract
Waste cooking oil is not environmentally friendly to dispose, so the viable way in which this
problem can be dealt is by converting them into biodiesel. Biodiesel, defined as the monoalkyl
esters of vegetable oils or animal fats is an attractive alternative fuel. It is a low emission diesel
substitute made from renewable resources and waste lipid. The most common way to produce
biodiesel is through alkali-catalyzed transesterification process in which the triglyceride
component of oil reacts with alcohol in presence of catalyst. The unique properties of biodiesel
such as reduction in green house gas emissions, non-sulphur emissions, non particulate matter
pollutants, low toxicity and biodegradability makes it superior to fossil diesel fuel. The yield of
biodiesel depends on different transesterification parameters such as oil to alcohol molar ratio,
reaction time and temperature, type of catalysts used. This report summarizes in detail about the
optimum transesterification condition for the biodiesel production.
Introduction
With the depletion of the world’s petroleum reserves and the increasing environmental concerns,
there is a great demand for alternative sources of petroleum-based fuel, including diesel and
gasoline fuels. Biodiesel, a clean renewable fuel has recently been considered as the best
alternative for a diesel fuel substitution because it can be used in any compression ignition
engine without the need of modification..1 It can be produced from any material containing fatty
acids such as animal fats, edible and non-edible oils. More than 95% of biodiesel production
feed-stocks comes from edible oils since they are mainly produced in many regions and the
properties of biodiesel produced from these oils are much suitable to be used as diesel fuel
substitute.2 However, it may cause some problems such as the competition with the edible oil
market, which increases both the cost of edible oils and biodiesel. Moreover, it will promote
deforestation as more forests will be destroyed for the cultivation of edible oil bearing plants. In
order to prevent the food vs energy conflict, the researchers have narrowed themselves to noedible oils and waste cooking oil which are not suitable for human consumption. The use of
animal fats is limited as they contain more of saturated fatty acids and normally exist in solid
form at room temperature.3
The different technologies used for biodiesel production include: direct use by blending of raw
oils, micro-emulsions, thermal cracking and transesterification.4 Transesterification is the
reaction of lipid with an alcohol to form esters and a byproduct, glycerol. It consists of a
sequence of three consecutive reversible reactions. The first is the conversion of triglyceride to
diglycerides, followed by the conversion of diglycerides into monoglycerides, and finally
monoglycerides into glycerol, yielding one ester molecule from each glyceride at each step.5
These reactions proceed well in the presence of some homogeneous catalysts such as potassium
hydroxide, sodium hydroxide or sulfuric acid, or heterogeneous catalysts such as metal oxides or
carbonates.6 Depending upon the type of feedstock each catalyst has its own advantages and
disadvantages. The transesterification process is carried out at an average temperature of 50°C to
60°C, with an average reaction time of 2 hours.7 These parameters and yield percentage vary
according to the choice of alcohol and catalysts used.
Critical Analysis
Energy is the major fundamental requirement for human existence and as of now fossil fuels has
been serving the world. The entire dependence of mankind on these sources and their limited
availability has shifted the focus on alternative energy sources such as wind, geothermal and
biofuel. The major reason biodiesel has gained the popularity is that it can be used directly in the
diesel engine without any modification. The wide availability of feed-stocks for its production
and its degradability nature also contributes to its importance. However, the major barrier in its
commercialization is higher cost. The use of edible oils as raw material not only increases the
cost but also gives rise to food vs fuel crisis. A lot of research on non-edible oil and waste
cooking oil has shown prominent yield still their production is limited to only developed
countries like Canada, USA, Germany etc. Currently biodiesel is used in the form of blend with
conventional diesel, its direct use is still not in practice. Methanol is widely used alcohol in the
transesterification process while choice of catalyst varies depending on the acid value of feed oil.
Higher acid value oil requires the process to go through esterification and use of heterogeneous
catalyst is more preferable. While homogeneous catalysts have been found more beneficial for
low acid value oils because of their lower reaction temperature and higher conversion rate.
However, the major issue with homogeneous catalysts is that the biodiesel produced has to be
gone through washing process for the catalysts removal which cannot be recovered.
The yield of biodiesel can be increased and made cost effective by optimizing the parameters
like reaction temperature, oil to alcohol molar ratio, reaction time, type and concentration of
catalysts. As the transesterification process is reversible reaction, higher alcohol to oil ratio shifts
the reaction equilibrium to product side. The reactions constituent has to be properly agitated for
proper conversion. It has been observed that increasing the reaction temperature above 60°C
decreases the yield as methanol starts evaporating. Increasing the reaction time aids in the yield
of biodiesel. However, excessive use of catalyst only increases the cost and doesn’t impact
positively on the yield. The physical properties of biodiesel shows its density to be 87 g/𝑐𝑚3 at
15°C and kinematic viscosity as 1.9-6 𝑚𝑚2 /s. Too high viscosity is disadvantageous as injectors
do not perform properly. Biodiesel has higher lubricity than fossil diesel fuel which implies that
the diesel running with biodiesel will be less prone to wear and will last longer. Also, on the
basis of ignition quality biodiesel can be said to be better as they have higher cetane number than
fossil diesel.
Concluding Remarks and Future Perspective
Biodiesel is better than diesel fuel in terms of sulfur content, cetane number, aromatic content
and biodegradability. It has demonstrated a number of promising characteristics in applications
for combustion in compression-ignition engines including a reduction of exhaust emissions. It is
much less polluting than petroleum diesel, resulting in much lower emissions of almost every
pollutant. Use of waste cooking oil as a source for biodiesel production not only saves the
environment from being polluted but also helps in counteracting world’s energy crisis.
Promoting the use of biodiesel as potential fuel in diesel compression engine has tremendous
future aspects. It promotes the cultivation of energy crops which has ultimate environmental
benefits such as carbon capture and wildlife improvement. It also provides stable energy security
as the petroleum sources are declining and also their prices are continuously rising.
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