PRODUCTION OF BIODIESEL FROM COTTON SEED OIL USING AN HETEROGENOUS

CATALYST

BY

ABUGA CHRISTOPHER EMMANUEL

ENG1503475

A PROPOSAL SUBMITED TO THE DEPARTMENT OF CHEMICAL ENGINEERING

UNIVERSITY OF BENIN, EDO STATE

2020
 CHAPTER ONE

INTRODUCTION

1.1 Background to the Study

Due to the overdependence on fossil fuel as the major source of energy, there has been decline in
petroleum reserves since it is non-renewable. With the increase in population and energy
consuming processes and equipment, global energy demand is steadily increasing from year to
year (Asri et al. 2017) and as such, there is need for a shift from petroleum to renewable sources
of energy which will meet the required energy need. There is also a need to reduce the negative
impacts of fossil energy such as environmental degradation, increased global warming and
greenhouse gas emissions.

Biodiesel has shown excellent potential as an alternative to diesel fuel. It is a renewable and
biodegradable fuel which can be manufactured from any oil bearing seed or animal fat. It consists
of long chain alkyl esters and is made by chemically reacting lipids with an alcohol in the presence
of a catalyst to produce fatty acid methyl esters.

Biodiesel is currently the most important alternative diesel fuel in European Union (EU),
contributing to reduce the external dependence on fossil fuels and simultaneously the
environmental impacts of the transportation sector, since it emits substantially lower quantities of
most of the regulated pollutants compared to mineral diesel. However, biodiesel industry has some
significant difficulties. In particular, feedstock selection can have a profound impact on the
production process but also on food prices when food crops such as palm oil are diverted to energy
(Morais et al, 2010). The need for biodiesel production from non-edible oils is being studied in
order to limit the competition between food and fuel.

The pollution caused by the meat industry wastes increases with the growing annual meat
consumption. It may be reduced and more valuable products can be obtained by converting them
to useful products (1). Animal fat is part of the waste (by-product) from abattoirs and slaughter
houses, it can be channeled into energy production by being used as a feedstock for biodiesel
production. It reduces the cost of biodiesel, since it is a low cost feedstock, and finds use for the
waste from the meat industry.
Biodiesel can be produced in different ways but the most common method used is the
transesterification procedure. The animal fat undergoes a transesterification reaction with
methanol in the presence of a catalyst to yield fatty acid esters, otherwise known as biodiesel. The
transesterification reaction can be carried out under various reaction conditions such as molar
ratios, temperatures, reaction time and catalyst concentration. It can also be carried out in the
presence of different catalysts which could be homogeneous or heterogeneous, acid or alkali,
organic or inorganic and so on. It is important to find the optimum reaction conditions and the best
catalyst for the transesterification of a particular feed stock.

1.2 Problem Statement

Considerable attention has been given to biodiesel production as an alternative to fossil fuel.
However, as the biodiesel is produced from vegetable oils, there are concerns that biodiesel
feedstock may compete with food supply in the long run and cause increase in the prices of those
feedstock. Hence, the recent focus is to find non-edible sources of feedstock that can be used as
raw material for biodiesel production. It is also important to determine the optimum operating
conditions (such as catalyst amount, methanol/oil molar ratio, temperature and time) required for
the production of biodiesel in order to minimize the cost of production of biodiesel while
maximizing profits to give it an edge over petroleum diesel in terms of economics.

1.3 Aim and Objectives

The aim of this study is to optimize the production of biodiesel from cotton seed oil using response
surface methodology in the presence of a heterogeneous catalyst derived from animal waste.
The specific objectives of the study are:
1. To determine the physical and chemical analysis of cotton seed oil
2. To produce biodiesel via transesterification of cotton seed oil with methanol using modified
animal bones.
3. To carry out optimization of process variables using response surface methodology on
biodiesel production yield.
4. To characterize the biodiesel produced.
1.4 Scope of Study
The scope of this work will be limited to the transesterification of the cotton seed oil to produce
biodiesel and the characterization of feedstock and biodiesel. The effects of the process variable
will be studied using response surface methodology.

1.5 Relevance of the Study

Production of biodiesel will reduce dependence on non-renewable sources of energy and eradicate
the negative effects of petroleum diesel on the environment. Biodiesel from cotton seed oil will
limit the use of edible feedstock, thereby reducing increase in prices of the edible sources. It also
ensures appropriate use for cotton seed oil which otherwise, is a waste from the restaurant. The
potential environmental benefits of using biodiesel instead of petroleum derived diesel include a
reduction in the generation of greenhouse gases. It also has a very low Sulphur content thereby
reducing acid rain formation. Biodiesel is biodegradable and in the event of a fuel spill there are
fewer long-term environmental effects compared to fossil fuel based products (2). This study is
also essential because it aims to study the optimization of process variables on the production of
biodiesel in order to establish the optimum condition required for maximum conversion and
minimum cost.
 CHAPTER TWO

LITERATURE REVIEW

2.1 Biodiesel
Biodiesel is a liquid biofuel obtained by chemical processes from vegetable oils or animal fats
and an alcohol that can be used in diesel engines, alone or blended with diesel oil (3). ASTM
International (originally known as the American Society for Testing and Materials) defines
biodiesel as a mixture of long-chain monoalkylic esters from fatty acids obtained from renewable
resources, to be used in diesel engines.
It is a non-fossil alternative diesel fuel defined as the mono alkyl esters of long chain fatty acids
derived from vegetable oils or animal fat. It consists of long chain alkyl esters and is made by
reacting lipids with an alcohol, producing fatty acid esters.

Although, biodiesel contains very different compounds than petroleum derived diesel, it has
combustion properties very similar to petroleum diesel, including the energy content and cetane
ratings. This makes it a good alternative to petroleum diesel.

Biodiesel can either be used in its pure form (B100) or may be blended with petroleum diesel at
any concentration in most injection pump diesel engines.

2.1.1 Historical Development of Biodiesel

Rudolf diesel invented the diesel engine in the 1890s (4). By the time he showed his engine at the
world exhibition in Paris in 1900, his engine was running on 100% peanut oil (Owolabi et al.
2012). However, because cheap petroleum fuels were easily available, few people were interested
in alternatives (Pahl, 2015).
During World War II (1939-1945), when petroleum fuel supplies were interrupted, vegetable oil
was used as fuel by several countries. However, when the war ended and petroleum supplies were
again cheap and plentiful, vegetable oil fuel was forgotten.
The petroleum embargo of the 1970s caused many countries to look to vegetable oil as a possible
fuel but the viscosity (thickness) of the vegetable oil caused damage to the engines. Scientists then
conducted experiments to convert the vegetable oil into7 biodiesel. The word “biodiesel” was
probably first used in about 1984 (Van Gerpen, 2005).
The first biodiesel manufacturing plant specifically designed to produce fuel was started in 1985
at an agricultural college in Austria. Biodiesel was first manufactured commercially in 1991 in
Kansas City, Missouri (Van Gerpen, 2005).
The establishment and commercialization of biodiesel in many countries around the world has
triggered the development of standards to ensure and promise high quality of product and user
confidence. Two of the widely used biodiesel standards are ASTM D6751 (ASTM = American
Society for Testing and Materials) and the European standard EN14214 (Chitra, 2012).

2.1.2 Properties and Composition of Biodiesel

Biodiesel can be produced from various feed stocks, oils and fats of varying origin and quality.
The diesel produced from these different sources are of different qualities and therefore need to
meet the standard condition for biodiesel which is specified by ASTM D6751. The parameters
which define the quality of biodiesel include the following:

2.1.2.1 Density
Density is defined as the mass per unit volume of a substance, it is defined mathematically as:

𝑚
𝜌=
𝑣

The density of a material varies with temperature and pressure. Density is a very important fuel
property because it affects the mass of fuel injected into the combustion chamber, and thus air-fuel
ratio which affects the engine performance. Biodiesel density mainly depends on its ester content
and the remained quantity of alcohol, hence the density of biodiesel is affected mainly by the
feedstock used for the biodiesel production.

2.1.2.2 Specific Gravity

Specific gravity is the ratio of the density of a substance to the density of a reference substance.
The reference substance for liquids is water while that for gases is air. Mathematically, for a liquid,
the specific gravity (SG) is given as:

𝜌𝑙𝑖𝑞𝑢𝑖𝑑
𝑆𝐺 =
𝜌𝑤𝑎𝑡𝑒𝑟
2.1.2.3 Viscosity
The viscosity of a fluid is the measure of its resistance to gradual deformation by shear stress or
tensile stress. It can also be referred to as a measure of the fluid’s resistance to flow due to internal
friction. Kinematic viscosity is the measure of the inherent resistance of a fluid to flow when no
external force is exerted, except gravity, it is the ratio of the dynamic viscosity to its density.

Viscosity is an important property of biodiesel because it affects the engine fuel injection system
predominantly at low temperatures. A highly viscous fuel will result in poor fuel atomization,
incomplete combustion and carbon deposition on the injectors. High viscosity also leads to loss of
engine power, production of smoke and operational problems such as difficulty in engine starting,
unreliable ignition, and deterioration in thermal efficiency, therefore the viscosity of the biodiesel
must be low. Biodiesel is slightly more viscous than petroleum diesel but the values are close.
Viscosity is one of the main reasons vegetable oils are not used as fuels.

2.1.2.4 Flash Point

The flash point of a volatile material is the minimum temperature at which the material will ignite
(flash) on application of an ignition source. Flash point minimum temperatures are required for
proper safety and handling of fuels. The flash point of biodiesel is higher than that of petroleum
diesel, this makes it safe for transport purpose because high values of flash point decreases the risk
of fire.

Table 2. 1: Standard Specification for Diesel and Biodiesel

Fuel Property Diesel Biodiesel Unit

Fuel Standard ASTM D975 ASTM PS 121
Fuel composition C10-21HC* C12-22 Not applicable
Lower heating value 36.6x103 32.6x103 Calories
Kinematic 1.3-4.1 1.9-6 mm2/s
viscosity@40°C
 Specific gravity 0.85 0.88 No units
@15.5°C
Density @ 15°C 848 878 g/cm3
Carbon 87 77 Wt %
Hydrogen 13 12 Wt %
Sulphur 0.05 0.0-0.0024 Wt %
Boiling point (°C) 188-343 182-338 °C
Flash point 60-80 100-170 °C
Cloud point -15 to5 -3 to 12 °C
Pour point -35 to -15 -15 to 10 °C
Cetane number 40-55 48-65 Not applicable
Stoichiometric 15 13.8
air/fuel
(5)

2.1.3 Advantages and Limitations of Biodiesel

2.1.4.1 Advantages of Biodiesel
Due to having better properties than that of petroleum diesel itself, it can be concluded that the
search for biodiesel is indeed beneficial to mankind as it has many advantages as a substituent.
The advantages of biodiesel include:
1. Biodiesel is a renewable source of energy i.e. it has a continuous source of supply and it will
decrease the country’s dependence on imported petroleum (6).
2. Biodiesel is biodegradable and non-toxic. It degrades about four times faster than petroleum
diesel. This is enhanced by its oxygen content, higher than the oxygen content of mineral diesel
(Igbokwe and Nwafor, 2014).
3. Biodiesel has higher cetane number than petroleum diesel and therefore ignites faster.. Cetane
number is used as indicator to determine diesel fuel quality, especially the ignition quality. It
is to measure the readiness of the fuel to auto-ignite when injected into the engine (Igbokwe
and Nwafor, 2014).
4. Biodiesel does not contribute to global warming due to its closed carbon cycle. It reduces the
emission of greenhouse gases such as carbon monoxide (CO) and carbon dioxide (CO2). A life
cycle analysis of biodiesel showed that overall CO2 emissions were reduced by 78% compared
with petroleum-based diesel fuel (4).
5. Biodiesel contains less Sulphur and aromatics than diesel, which means lower Sulphur and
aromatic emissions (7).
6. It provides a market for excess production of vegetable oils and animal fats (4).
7. It has lubricating properties that lengthen the lifespan of engines (Chitra, 2012).
8. Higher combustion efficiency: Biodiesel is much less combustible, with a flash point greater
than 423 K compared to 350 K for petroleum-based diesel fuel (Demirbas and Balat, 2006).

2.1.4.2 Limitations of Biodiesel

Even if biodiesel has several advantages, its use also implies some disadvantages that should be
mentioned:

1. Agricultural feedstock is needed to produce biodiesel and at some times its availability
might be constrained due to its necessity to produce food. This may impose limits on the
production of biodiesel (7).
2. The kinematic viscosity of biodiesel is higher than that of diesel fuel.
3. Oxidation of biodiesel happens more easily than oxidation of diesel, so, when it is stored
for long periods some products that may be harmful to the vehicle components might be
produced (8).
4. A modified refueling infrastructure is needed to handle biodiesel, which adds to its total
cost (6).

2.2 Feedstock for Biodiesel Production

There are different types of suitable raw materials for biodiesel production. This includes many
types of vegetable oils and animal fats. Most of the raw materials used are first generation
feedstock which are edible. “Price and availability are important factors that determine different
types of feedstock used for biodiesel production from one region of the world to another”(9).
Edible feedstock should not be used as it will not be cost effective and it is not feasible to be used
in a larger scale. There will be fight over for sustainability and food for fuel production (10).

Table 2.2: List of Biodiesel Feedstock

Vegetable oils Non-edible oils Animal fats Other sources

Soybeans Almond Lard Bacteria
Rapeseed Babassu Tallow Algae
Canola Brassica carinata Poultry fat Fungi
Safflower cardunculus Fish oil Micro algae
Barley Jatropha curcas Tapenes
Coconut Jatropha nana Latexes
Copra Jojoba oil Cooking oil
Cotton seed Laurel (Yellow grease)
Groundnut Palm Microalgae
Oat Karang (Chlorellavulgaris)
Rice Tobacco seed
Sorghum Rubber seed
Wheat Rice bran
Winter rapeseed oil Sesame
Salmon oil
Source: (6)

The oils most used for worldwide biodiesel production are rapeseed (mainly in the European Union
countries), soybean (Argentina and the United States of America), palm (Asian and Central
American countries) and sunflower, although other oils are also used, including peanut, linseed,
safflower, used vegetable oils, and also animal fats. Methanol is the most frequently used alcohol
although ethanol can also be used. Since cost is the main concern in biodiesel production and
trading (mainly due to oil prices), the use of non-edible vegetable oils has been studied for several
years with good results (Jabbaria and Pesyanb 2017).
Besides its lower cost, another undeniable advantage of non-edible oils for biodiesel production
lies in the fact that no foodstuffs are spent to produce fuel. These and other reasons have led to
medium- and large-scale biodiesel production trials in several countries, using non-edible oils such
as castor oil, tung, cotton, jojoba and jatropha. Animal fats are also an interesting option, especially
in countries with plenty of livestock resources, although it is necessary to carry out preliminary
treatment since they are solid; furthermore, highly acidic grease from cattle, pork, poultry, and fish
can be used.
Microalgae appear to be a very important alternative for future biodiesel production due to their
very high oil yield; however, it must be taken into account that only some species are useful for
biofuel production. Although the properties of oils and fats used as raw materials may differ, the
properties of biodiesel must be the same, complying with the requirements set by international
standards.

2.2.1 Typical Oil Crops Useful for Biodiesel Production

The main characteristics of typical oil crops that have been found useful for biodiesel production
are summarized in the following paragraphs (Jabbaria and Pesyanb 2017).

2.2.1.1 Rapeseed and Canola

Rapeseed adapts well to low fertility soils, but with high sulfur content. With a high oil yield (40–
50%), it may be grown as a winter-cover crop, allows double cultivation and crop rotation.
It is the most important raw material for biodiesel production in the European Community.
However, there were technological limitations for sowing and harvesting in some Central and
South American countries, mainly due to the lack of adequate information about fertilization, seed
handling, and storage (the seeds are very small and require specialized agricultural machinery).
Moreover, low prices in comparison to wheat (its main competitor for crop rotation) and low
production per unit area have limited its use.
Rapeseed flour has high nutritional value, in comparison to soybean; it is used as a protein
supplement in cattle rations. Sometimes canola and rapeseed are considered to be synonymous;
canola (Canadian oil low acid) is the result of the genetic modification of rapeseed in the past 40
years, in Canada, to reduce the content of erucic acid and glucosinolates in rapeseed oil, which
causes inconvenience when used in animal and human consumption.
Canola oil is highly appreciated due to its high quality, and with olive oil, it is considered as one
of the best for cooking as it helps to reduce blood cholesterol levels.

2.2.1.2 Soybean
It is a legume originating in East Asia. Depending on environmental conditions and genetic
varieties, the plants show wide variations in height. Leading soybean producing countries are the
United States, Brazil, Argentina, China, and India.
Biodiesel production from soybean yields other valuable sub-products in addition to glycerin:
soybean meal and pellets (used as food for livestock) and flour (which have a high content of
lecithin, a protein). Grain yield varies between 2,000 and 4,000 kg/hectare. Since the seeds are
very rich in protein, oil content is around 18%.

2.2.1.3 Oil Palm

Oil palm is a tropical plant that reaches a height of 20–25 m with a life cycle of about 25 years.
Full production is reached 8 years after planting.
Two kinds of oil are obtained from the fruit: palm oil proper, from the pulp, and palm kernel oil,
from the nut of the fruit (after oil extraction, palm kernel cake is used as livestock food). Several
high oil-yield varieties have been developed. Indonesia and Malaysia are the leading producers.
International demand for palm oil has increased steadily during the past years, the oil being used
for cooking, and as a raw material for margarine production and as an additive for butter and
bakery products. It is important to remark that pure palm oil is semisolid at room temperature
(20–22oC), and in many applications is mixed with other vegetable oils, sometimes partially
hydrogenated.

2.2.1.4 Sunflower
Sunflower ‘‘seeds’’ are really a fruit, the inedible wall (husk) surrounding the seed that is in the
kernel. The great importance of sunflower lies in the excellent quality of the edible oil extracted
from its seeds. It is highly regarded from the point of view of nutritional quality, taste and flavor.
Moreover, after oil extraction, the remaining cake is used as a livestock feed. It must be noted that
sunflower oil has a very low content of linoleic acid, and therefore it may be stored for long
periods. Sunflower adapts well to adverse environmental conditions and does not require
specialized agricultural equipment and can be used for crop rotation with soybean and corn. Oil
yield of current hybrids is in the range 48–52%.

2.2.1.5 Peanut
The quality of peanut is strongly affected by weather conditions during the harvest. Peanuts are
mainly used for human consumption, in the manufacture of peanut butter, and as an ingredient for
confectionery and other processed foods. Peanuts of lower quality (including the rejects from the
confectionery industry) are used for oil production, which has a steady demand in the international
market. Peanut oil is used in blends for cooking and as a flavoring agent in the confectionery
industry. The flour left over, following oil extraction, is of high quality with high protein content;
in pellet form, it is used as a livestock feed.

2.2.1.6 Castor Seed

The castor oil plant grows in tropical climates, with temperatures in the range 20 – 30oC; it cannot
endure frost. It is important to note that once the seeds start germinating, the temperature must not
fall below 120C. The plant needs a warm and humid period in its vegetative phase and a dry season
for ripening and harvesting. It requires plenty of sunlight and adapts well to several varieties of
soils. The total rainfall during the growth cycle must be in the range 700–1,400 mm; although it is
resistant to drought, the castor oil plant needs at least 5 months of rain during the year. Castor oil
is a triglyceride, ricinolenic acid being the main constituent (about 90%). The oil is non-edible and
toxic owing to the presence of 1–5% of ricin, a toxic protein that can be removed by cold pressing
and filtering. The presence of hydroxyl groups in its molecules makes it unusually polar as
compared to other vegetable oils.

2.2.1.7 Cotton
Among non-foodstuffs, cotton is the most widely traded commodity. It is produced in more than
80 countries and distributed worldwide. After the harvest, it may be traded as raw cotton, fiber or
seeds. In cotton mills, fiber and seeds are separated from raw cotton. Cotton fiber is processed to
produce fabric and thread, for use in the textile industry. In addition, cotton oil and flour are
obtained from the seed; the latter is rich in protein and is used in livestock feed and after further
processing, for human consumption.

2.2.1.8 Jojoba
Although jojoba can survive extreme drought, it requires irrigation to achieve an economically
viable yield. Jojoba needs a warm climate, but a cold spell is necessary for the flowers to mature.
Rainfall must be very low during the harvest season (summer). The plant reaches its full
productivity 10 years after planting (Mutwakel et al, 2016). The oil from jojoba is mainly used in
the cosmetics industry; therefore, its market is quickly saturated.

2.2.1.9 Jatropha caucas

Jatropha curcas is a perennial shrub to small evergreen tree of up to 6 m height, adapted to all kinds
of soil and does not demand any special nutritive regime (Patil and Singh, 1991). It has been
introduced in Africa and Asia and is now cultivated worldwide. In India, it was believed to be
introduced by the Portuguese settlers during 16th century. It is a multipurpose, deciduous, small
tree, reported to be cultivated in drier regions of central and western parts of India. Recently, it has
also been introduced in the northern and southern states of India. The plant is widely distributed
and fits easily into agricultural system in the form of hedges, windbreak, and erosion barrier or as
a source of firewood (Paramathma et al., 2004). In recent years there are growing concerns about
the utility of J. curcas as a source of biofuel plantations in order to generate alternate source of
energy. This is mainly due to the suitability of oil derived from Jatropha seeds for biofuel purposes
(Paramathma et al., 2004). The oil contains 21.0% saturated fatty acids and 79.0% unsaturated
fatty acids (Bhasabutra and Sutiponpeibun, 1982). The quality of oil interms of its fatty acid
composition is very important. The current studies on the fatty acids distribution of Jatropha oil
and physicochemical properties of oil viz., specific gravity, refractive

2.2.1.10 Almond
Tropical almond (Terminalia catappa) is a large, spreading tree now distributed throughout the
tropics in coastal environments. The tree is tolerant of strong winds, salt spray, and moderately
high salinity in the root zone. It grows principally in freely drained, well aerated, sandy soils. The
species has traditionally been very important for coastal communities, providing a wide range of
non-wood products and services. It has a spreading, fibrous root system and plays a vital role in
coastline stabilization. It is widely planted throughout the tropics, especially along sandy
seashores, for shade, ornamental purposes, and edible nuts. The timber makes a useful and
decorative general-purpose hardwood and is well suited for conversion into furniture and interior
building timbers. Fruits are produced from about 3 years of age, and the nutritious, tasty seed
kernels may be eaten immediately after extraction. Tropical almond is easily propagated from seed,
and is fast growing and flourishes with minimal maintenance in suitable environments. Selected
cultivars of the species warrant wider commercial planting for joint production of timber and nuts.
The tree has a demonstrated potential to naturalize in coastal plant communities, but not to
adversely dominate such communities (Olatidoye et al., 2011). The productivity and marketing of
cultivars with large and/ or soft-shelled nuts needs to be assessed.

2.2.2 Properties, Composition and FFA Content of the Feedstock

The physical properties and chemical composition of the feedstock used in the transesterification
reaction determines the type of fatty acid methyl ester produced and therefore affects the property
of the biodiesel produced. The free fatty acid (FFA) content of the feedstock also affects the yield
of biodiesel. Reactants with low FFA content gives higher biodiesel yield than those with high
FFA content.

2.3 Methanol
Methanol (CH3OH), also known as methyl alcohol, is the simplest alcohol, being only a methyl
group (CH3) linked to a hydroxyl group (OH). Methanol was formerly produced by the
destructive distillation of wood, hence its name, wood alcohol. It is a light, volatile, colorless,
flammable liquid with a boiling point of 65ᵒC and a distinctive odor very similar to that of
ethanol (drinking alcohol).
Methanol and ethanol are common alcohols for transesterification reaction. Methanol has the
advantage of lower cost, and is therefore more common in use. Ethanol has the advantage of being
produced from renewable sources (bioethanol) but the commercial grade contains water, which
adversely affects reaction rate. Most of the commercial production of biodiesel employs methanol
producing FAME (11).

2.3.1 Properties of Methanol

1. Methanol is a flammable, colorless, volatile liquid
2. It is miscible in water, ethanol, ether, benzene and ketones
3. It burns with a non-luminous bluish flame
4. It is a highly polar substance
5. Methanol burns in air forming carbon dioxide and water

2.3.2 Manufacture of Methanol

There are several processes for manufacturing methanol but the most used process is the catalytic
reaction of carbon monoxide and hydrogen. The most widely used catalyst is a mixture of copper
and zinc oxides, supported on alumina.

CO  2 H 2  CH 3OH

2.3.3 Uses of Methanol

1. Methanol is a key component in the production of biodiesel.
2. It is used as a feedstock to produce chemicals such as acetic acid and formaldehyde,
which in turn are used in products like adhesives, foams, plywood, solvents, paints and
explosives.
3. Methanol can be used on its own as a vehicle fuel or blended directly into gasoline to
produce a high-octane efficient fuel with lower emissions than conventional gasoline.
4. It is also used to produce methyl tertiary butyl ether (MTBE), a gasoline component
that improves air quality, and dimethyl ether (DME), a clean-burning fuel with similar
properties to propane.
5. Methanol is used as a feedstock for the plastics industry.
 6. It is also used as a solvent and as an antifreeze in pipelines and windshield washer fluid.

2.4 Methods of Biodiesel Production

Transformation of vegetable oils into biodiesel can be realized using four technologies:

1. Heating/pyrolysis
2. Dilution/blending
3. Micro-emulsion
4. Transesterification.

2.4.1 Pyrolysis
The pyrolysis refers to a chemical change caused by the application of thermal energy in the
absence of air or nitrogen. The liquid fractions of the thermally decomposed vegetable oils are
likely to approach diesel fuels. The pyrolyzate has a lower viscosity, flash point, and pour point
than diesel fuel and equivalent calorific values. The cetane number of the pyrolyzate is lower. The
pyrolyzed vegetable oils contain acceptable amounts of sulfur, water and sediments and give
acceptable copper corrosion values but unacceptable ash, carbon residual and pour point (12).

2.4.2 Dilution
The dilution of vegetable oils can be accomplished with such material as diesel fuels, solvent or
ethanol. Dilution results in the reduction of viscosity and density of vegetable oils. The addition
of 4% ethanol to diesel fuel increases the brake thermal efficiency, brake torque and brake power,
while decreasing the brake specific fuel consumption. Since the boiling point of ethanol is less
than that of diesel fuel, it could assist the development of the combustion process through an
unburned blend spray.

2.4.3 Micro-Emulsion
The formation of micro emulsion is one of the potential solutions for solving the problem of
vegetable oil viscosity. Micro-emulsions are defined as transparent, thermodynamically stable
colloidal dispersion. The droplet diameters in micro-emulsions range from 100 to 1000 Å. Micro-
emulsion can be made of vegetable oils with an ester and dispersant (co solvent), or of vegetable
oils, and alcohol and a surfactant and a cetane improver, with or without diesel fuels. All micro-
emulsions with butanol, hexanol and octanol met the maximum viscosity requirement for diesel
fuel. The 2-octanol was found to be an effective amphiphile in the micellar solubilization of
methanol in triolein and soybean oil.

2.4.4 Transesterification
Transesterification is the process of reacting a triglyceride (from an oil or fat) with an alcohol
(ethanol or methanol) to produce a fatty acid methyl ester (FAME). The reaction can be carried
out in the presence of a catalyst or

Among all these techniques, the transesterification is an extensive, convenient and the most
promising method for the reduction of viscosity, density and other properties of the straight
vegetable oils.

2.5 Transesterification
Biodiesel is most derived from a chemical reaction called transesterification. It is the chemical
conversion of oil to its corresponding fatty ester in the presence of a catalyst. The reaction converts
esters from long chain fatty acids into mono alkyl esters. Chemically, biodiesel is a fatty acid
methyl ester.
Transesterification is the reaction of a lipid with an alcohol to form esters and a byproduct, glycerol
(Gashaw and Lakachew, 2014). It is, in principle, the process of exchanging the organic group,
R’’ of an ester with the organic group R’ of an alcohol. These reactions are often catalyzed by the
addition of an acid or base catalyst.

Alcohol + ester different alcohol + different ester

Methanol and ethanol are used most frequently but methanol is preferred because of its low cost
and its physical and chemical advantages (polar and shortest chain alcohol).

2.5.1 Transesterification Reaction Mechanism

The overall reaction between a triglyceride and an alcohol is given by,
Triglyceride + 3 ROH ↔ Glycerol + 3 alkyl ester (i)
Reaction (i) is supposed to take place in three consecutive and reversible steps where triglycerides
are converted to diglycerides and then diglycerides are converted to monoglycerides followed by
the conversion of monoglycerides to glycerol. In each step, an ester is produced and thus three
ester molecules are produced from one molecule of triglycerides (Sharma and Singh, 2008).

Triglyceride + ROH ↔ Diglyceride + alkyl ester (ii)

Diglyceride + ROH ↔ Monoglyceride + alkyl ester (iii)

Monoglyceride + ROH ↔ Glycerol + alkyl ester (iv)

In the above equations, ROH represents an alcohol. From stoichiometry, 3 moles of alcohols are
required for each mole of triglyceride to produce 3 moles of alkyl ester (biodiesel). However, due
to the reversible nature of the reaction an excess of alcohol is always employed for reactions to
proceed in the forward direction. An alcohol to oil ratio of 6:1 is normally used in industrial
processes to obtain high alkyl ester yields. According to a study carried out by Meher et al., (2006),
molar ratios less than 6:1 caused incomplete reactions while molar ratios of 15:1 and above made
the separation of glycerin difficult and decreased the apparent yield of esters because a part of the
glycerol remained in the biodiesel phase. Akhihiero et al. (2013) reported the use of molar ratio
8:1 in the transesterification of jatropha seed oil.

In the transesterification mechanism, the carbonyl carbon of the starting ester (RCOOR 1)
undergoes nucleophilic attack by the incoming alkoxide (R2O−) to give a tetrahedral intermediate,
which either reverts to the starting material, or proceeds to the transesterified product (RCOOR 2).
The various species exist in equilibrium, and the product distribution depends on the relative
energies of the reactant and product.

2.5.2 Separation and Purification of Biodiesel

The biodiesel production process yields with it certain impurities and residues which are left in the
biodiesel produced. These impurities and residues could be detrimental to the combustion system
and, therefore, have to be removed. The table below shows some of the effects of impurities and
residues in biodiesel.

Table 2. 3 : Effects of Impurities in biodiesel on Diesel Engine Performance

Impurity Effects
FFAs Corrosion, low oxidation stability.
Hydrolysis
Water Hydrolysis (free fatty acid and alcohols formation), corrosion, bacteriological
growth (filter blockage).
Methanol Low values of density and viscosity, low flash point (transport, storage and use
problems).
Glycerides High viscosity, deposits in the injectors (carbon residue), crystallization.
Metals(soap, Deposit in the injectors, filter blockage (sulphated ashes), engine weakening,
catalyst)
Glycerol Settling problems, increased aldehyde and acrolein emissions
(5).

2.5.3 Phase Separation

This involves the separation of the glycerin layer from the ester layer. This process occurs naturally
especially when methanol or absolute ethanol is used as a reacting partner in alkaline-catalyzed
transesterification process since the glycerol has a higher density than the ester formed and
therefore settles to the bottom. It can be quite a slow process (around 3 hours for complete
separation) and, therefore, to facilitate the separation, centrifugation has been suggested though it
is not economical. Other means of facilitating the phase separation includes the addition of water.
The addition of hexane and extra glycerol to the reaction mixture has also been proved to be helpful
(5).

2.5.4 Purification of Biodiesel

Once phase separation has been achieved, the purification of the ester phase is necessary to ensure
that the biodiesel meet specifications. After the phase separation of glycerol, the biodiesel still has
an excessive amount of soaps, aggressive pH, catalyst, FFAs, water, methanol, glycerides and
other impurities. These substances, if not reduced to their minimum, will have effects on the
biodiesel. There are various means of removing the impurities mentioned that are left in the ester
phase after transesterification.

Raw biodiesel must be refined and one of the most common approaches is water washing, in which
clean water is passed through the biodiesel. Water is an excellent medium for neutralizing residual
catalyst, as well as removing residual methanol and glycerol (13). In the water washing process, a
certain amount of water mostly is added to the biodiesel and this is allowed to settle. As the water
passes through the ester phase, it attaches to the impurities such as MG, DG, TG, catalyst etc. Once
settled, the contaminated water is drained off together with the impurities. This process continues
until clear water is obtained. Once all the water is removed, the remaining biodiesel is dried and
ready for final quality check. Traces of glycerol are removed by water or acid washing solutions
(Karaosmanoglu et al., 1996).

Free fatty acids (FFA) are removed by distilling the ester phase making use of the fact that the
boiling points of methyl esters are generally 30 oC to 50oC lower than the FFAs. Methanol is
removed by heating the ester phase to a temperature of 70oC.

Partial glycerides (MG, DG) can be removed from the ester phase by converting them into
triglyceride which can then be separated from the methyl ester product. This is done by adding an
extra alkaline catalyst to the ester phase and the reaction is heated to about 100 oC (Klok et al.,
1990). In the process, the glycerols and the partial glycerides react with the methyl esters and thus
are converted to triglycerides which were then reintroduced into the transesterification reactor
together with new oils

Catalysts are generally removed by using an adsorbent such as bleaching earth (Wimmer, 1991),
and also by the use of silica gel or magnesium silicate (Cooke, 2004). The method employed to
purify biodiesel depends on the manufacturers and also the scale of the biodiesel produced.

2.6 Factors Affecting Transesterification Reaction

Once the reaction is known, the conditions in which it happens should be determined. The
parameters that will affect the reaction to a higher extent are:

1. Reaction Temperature
2. Reaction time
3. Molar Ratio (Alcohol to Oil ratio)
4. Catalyst Concentration
5. Mixing Intensity
6. Type of catalyst
7. Properties and Composition of the Feedstock

2.6.1 Reaction Temperature

Temperature values for the transesterification reaction vary depending on the literature source. It
is well known that higher temperatures speed up the reaction and shorten the reaction time. Apart
from that, higher temperatures usually mean obtaining higher ester yields (Rashid and Anwar,
2008). However; It should also be noted that if the reaction temperature is higher than the boiling
point of the alcohol, it will evaporate, resulting in a lower yield (Sharma et al, 2008). It is also an
accepted fact that usually the optimum temperatures for the transesterification range between 50
and 60ºC, depending on the kind of oil to be processed (Leung et al., 2010).
2.6.2 Reaction Time
The reaction time clearly influences the outcome of the reaction, since the conversion rate
increases with the reaction time (Maa and Hannab, 1999). If the reaction time is not long enough
the ester yield will be low, therefore, part of the oil will be unreacted.

2.6.3 Methanol/Oil Molar Ratio

This is one of the most important factors that can affect the ester yield. It is related to the type of
catalyst used, depending on that, the optimum value for the process can be obtained. Higher molar
ratios give a higher ester yield in a shorter time. Usually, when using acid catalysts higher molar
ratios are needed, probably because the use of acid catalysts is related to oils with high FFA content
(Maa and Hannab, 1999).

2.6.4 Catalyst Concentration

This parameter is highly affected by the kind of catalyst used, different catalysts will require
different concentrations. Even if they belong to the same group (as in the case of potassium
hydroxide and sodium hydroxide), different concentrations will be necessary to attain the same
yields. Therefore, the optimum value for every catalyst will have to be determined by titration. If
the amount of catalyst is higher than the optimum, there will be a decrease in the yield of methyl
esters due to the formation of soap in presence of high amount of catalysts, which apart from
lowering the yield increases the viscosity of the reactants (Rashid and Anwar, 2008).

2.6.5 Mixing
It has been observed that during the transesterification reaction, the reactants initially form a two
phase liquid system. To achieve perfect contact between the reagent and oil during
transesterification, they are mixed together. The mixing effect has been found to play a significant
role in the slow rate of reaction. Mixing is mandatory for the reaction to take place. Without
mixing, the reaction only occurs in the interface between the methanol and the oil and it is very
slow to be viable. Therefore, a mixing device is needed in the reactor used for the process (Rashid
and Anwar, 2008).
2.6.6 Type of Catalyst
The type of catalyst used for a transesterification reaction affects the reaction. There are different
classes of catalyst and they include homogeneous and heterogeneous catalysts, acid and base
catalysts, organic and inorganic catalysts.

2.7 Catalysts in transesterification process

Catalysts play a significant role in the transesterification reaction. Catalyst types and
concentrations are very important for achieving an optimal process (Issariyakul et al., 2014).
Catalysts are usually used in the production of biodiesel to improve the reaction rate and yield
(Tariq et al., 2012). Catalytic activity is a function of its specific surface area, base strength and
base site concentration. In general, a good catalyst must have several qualities (i.e. not be
deactivated by water, be stable, be activated at low temperature and have high selectivity) (Rafaat
et al., 2010). The selection of a catalyst depends on the amount of FFA in the feedstock while
using WVO (Issariyakul et al., 2014). To achieve biodiesel that is economically feasible, the
development of active and cheap catalysts for effective transesterification of different kinds of
feedstock is absolutely necessary (Atadashi et al., 2013).
There are three different types of catalysts that can be employed in the transesterification process
of biodiesel: acid catalysts, base catalysts and biocatalyst (Figure 2.1) (Pathak, 2015).
Figure 2. 1: Classification of catalyst (adapted from Pathak, 2015)

Recently, there have been significant advancements in biodiesel production from homogeneous
catalysts to heterogeneous catalysts due to their high performance in the production quality and
efficiency (Pathak, 2015).

2.7.1 Homogeneous acid and base catalysts

Homogeneous catalysts are conventionally used in commercial biodiesel production processes.
The homogeneously-catalysed process often offers a reaction yield higher than 97% in short period
of time (10min-2h) with a reaction temperature between 25°C and 70°C (Issariyakul et al., 2014).
Homogeneous catalysts are catalysts that exist in the same phase as the reactants and are limited
to quality of the feedstock being anhydrous and acid value lower than 1mg of KOH/g of oil in the
transesterification process (Chouhan et al., 2011). These catalysts can either be acidic (H2SO4,
HCl, H3PO4 etc) or alkaline (NaOH, KOH, CH3ONa, CH3OK). They are associated with a number
of disadvantages including the formation of soap during biodiesel processes with FFA higher than
0.5%, corrosion of the equipment, high energy consumption resulting in an increase in capital
equipment cost, difficult separation of glycerol from methyl ester which leads to formation of
emulsion, and increases in viscosity (Atadashi et al., 2012). Others disadvantages include
consumption of catalyst with water content higher than 0.3% resulting in low reaction yield,
difficult recovery of glycerol due to the solubility of catalyst, the need for excessive methanol,
long reaction time, high temperature requirement, high catalyst loading and catalyst toxicity
(Christopher et al., 2014). Metal alkoxides (CH3ONa and CH3OK) are more active even at lower
molar concentration but they are more expensive than alkaline metal hydroxide (NaOH and KOH);
thus their low price makes them preferable as catalysts as they can render a high conversion of oil
simply by increasing the catalyst concentration (Atadashi et al., 2012).
The most commonly used homogeneous catalysts are basic catalysts, as they are 4000 times faster
than homogeneous acid catalysts (Deshmane and Adewuyi, 2013). These catalysts require high
quality feedstock and give high conversions of TG at short reaction times. However, these have
been shown to be sensitive to water and FFA content in feedstock, leading to soap formation,
reduction of catalysts, and performance and separation problems (Christopher et al., 2014). During
homogeneously-catalysed transesterification the glycerol produced is of low quality and requires
distillation for purification (Chouhan et al., 2011).
Homogeneous acid catalysts such as H2SO4 can be used to transesterify oil with high FFA and
water content; however, the process is slower than reactions mediated by homogeneous basic
catalysts. This is less attractive for industrial purposes but can be used
in the esterification step, which converts FFA to TG. Marchetti (2012) and Zhang et al.
(2003) showed biodiesel production from waste oil characterized by an acid concentration of
1.5-3.5mol%, with excess methanol in the presence of H 2SO4, at a high molar ratio of 50:1, and a
temperature of 80°C. A 97% conversion was reached at a reaction time of 10h. The ability of a
homogeneous acid catalyst to act as an esterification reagent and play a solvent role in the process
can mediate esterification and transesterification processes to occur in a single stage. Studies have
shown that two-stage transesterification is more advantageous: no acid waste treatment, low
equipment cost, and easy recovery of catalyst as compared to the limitation of a single step process
(Talebian-kiakalaieh et al., 2013,).

2.7.2 Heterogeneous base catalysts (metal oxide)

Presently, there are several heterogeneous-base catalysts available for biodiesel production.
These include CaO, CaZrO3, Al2O3 - SnO, Li/MgO, Al2O3/KI, KOH/Al2O3, KOH/Nay and
alumina/silicate supported K2CO3 (Shu et al., 2010).
Base-catalyzed transesterification is associated with faster rates and greater yield as compared to
the acid-catalyzed processes (Christopher et al., 2014). These catalysts are classified into six
categories according to Hattori’s classification for solid base catalyst:
1. Single metal oxide
2. Mixed metal oxide
3. supported alkali
4. Alkaline earth metals,
5. Hydrotalcites
6. Organic base solids.
The most commonly used are single metal oxides (Lee et al., 2009).
Reaction rates in single metal oxides depend directly on the basicity of the oxide, especially of the
strong base site. There are a variety of single metal oxides — including magnesium oxide (MgO),
calcium oxide (CaO) and strontium oxide (SrO) — that have been employed as catalysts for the
transesterification of biodiesel (Supper et al., 1999; Sharma et al., 2011). Liu et al. (2008) used
SrO metal oxide as a catalyst for transesterification of soybean oil after calcination of SrCO3 at
1200°C for 5h. A 95% yield was obtained at 65°C, 3wt% catalyst and 12:1 molar ratio methanol-
to-alcohol.
From the economic and ecological point of view, CaO is the most popular and promising metal
oxide applied for biodiesel synthesis due to its low cost, excellent catalytic properties, high basic
strength (H_=26.5), minor toxicity, and low environmental impact due to its low solubility in
methanol and high availability (Table 2.10) (Suppes et al., 2001; Liu et al., 2008; Lee et al., 2009;
Navajas et al., 2012; Deshmane & Adewuyi, 2013; Rezaei et al., 2013; Tang et al., 2013). The use
of CaO as a heterogeneous catalyst has been around for many years as it can be produced from
numerous sources: chicken eggshell, mollusk shell, bones, golden apple snail shell, mussel shell,
oyster shell, meretrix venus shell and mud crab shell (Boey et al., 2011; Jazie et al., 2013).

2.7.2.1 Animal bone and Calcium Oxide

The first information pertaining to the use of animal bone and CaO as catalyst with oil in the
production of biodiesel was reported by Peterson and Scarrah in 1984 (Boey et al., 2011). Rezaei
et al. (2013) used waste mussel shell to produce biodiesel after calcination at 950°C. The catalyst
was found to be effective, resulting in a 98% yield, at a temperature of 60°C, a 24:1 molar ratio
methanol-to-oil and 12wt% catalyst loading. Viriya-Empikul et al. (2009) calcined waste shells of
egg, golden apple snail, and Venus meretrix at 800°C to produce CaO catalysts for biodiesel using
palm oil. The results showed that all catalysts gave high biodiesel production, as > 90% yields
were obtained in 2h. Liu et al. (2011) used calcined river snail shell as catalyst with soybean oil.
A 98% yield was obtained at 65°C, 3wt% catalyst loading at 9:1 methanol molar ratio within 3h.
When further transesterification work on CaO was conducted by Boro et al. (2011) using a solid
oxide catalyst derived from waste shell of Turbinilla Striatula with mustard oil, a 93.3% yield was
achieved at 65±5°C by employing 3wt% catalyst with 9:1 methanol-to-oil ratio within 6h.
Catalyst activity of CaO can be improved by employing thermal activation treatment and washing
such as calcination to remove the surface carbonate and hydroxyl group (Chouhan et al., 2011).

2.8 Optimisation of biodiesel production

Biodiesel production yield optimisation can be assessed using statistical analysis design expert
software (e.g. Mini Tab, Design-Expert Stat-Ease 6.0.8, Design Expert 9). There are different
approaches — response surface method (RSM), factorial design, fractional factorial, crossed and
mixture design — used to discuss and explain the production yield generated from the experiment
(Bezerra et al., 2008; Omar et al., 2011; Wan et al., 2011).
Two are explained below:
Fractional factorial: This is used to estimate main effect, interaction and screening of many
factors to find significant few. This factorial can be irregular, general, D-optimal, placket Burman
or Taguchi OA (Omar et al., 2011).
Response surface methodology: This is used to investigate the influence of the reaction parameters
of the process, to predict the optimum process condition, as well as to minimise the number of
experiments. These properties may be determined by using different approaches: central
composition design (CCD), Box-behnken, 3-level factorial, hybrid, 1-factor, pentagonal,
hexagonal, D-Optimal, distance-based, modified distance, user-defined and historical data
(Bezerra et al., 2008; Wan et al., 2011).
In this present study, response surface methodology (RSM) was applied for data analysis with
CCD technique tool to achieve optimum purity and yield of biodiesel production. This also was
used to determine which variables have an impact on the response interest. The choice of the design
technique was due to its ability to give multiple responses and its ability to use more than three
factorial levels as compared to Box-behnken, which uses fewer than three levels of factorial.
2.8.1 Response surface method (RSM)
RSM is simple, based on a linear function, and is the most frequently used method for statistical
analyses in the optimisation of biodiesel (14). The aim of RSM is to explain the interaction effects
among process variables obtained from experimental data to construct a 3-D response surface and
contour plot following a regression model. This experimental design methodology offers not only
an efficient way of assessing uncertainty but also provides inference with minimum number of
simulations. There are two major classes of RSM: Central Composite design (CCD) and Box-
behnken design. These two methods have different structures. Before applying RSM, it is
important to choose an experimental design that would define which experiment should be carried
out in the study area(14).

2.8.2 Box-behnken design

Each numerical factor is varied over three levels and has fewer runs than three level factorials. The
factors are placed at one of the three spaced value coded as -1, 0, 1 and the design must fit a
quadratic model (Figure 2.2). The ball is located inside the box defined by a wire frame that is
composed of the edges of the box. This method does not need many central points because the
points on the outside are closer to the middle. The Box-behnken design has limited capability to
orthogonal blocking as compared to CCD and is used for large number of variables.

Figure 2. 2: Profile of Box-behnken design at three levels (adapted from Bezerra et al. 2008)

Nakatami et al. (2009) used combusted oyster shell as catalyst for transesterification of soybean.
The reaction condition was optimised using factorial design. Results showed that the time (5h) and
catalyst concentration (2.5wt%) were the most important factors affecting biodiesel purity (98%
conversion). Rezaei et al. (2013), using Box-behnken design to evaluate the effects of calcination,
temperature, catalyst concentration and methanol-to-oil molar ratio on the purity and yield of
produced biodiesel, found that this method was effective with 100% purity and 94.5% yield at 24:1
methanol/oil ratio and 2wt% catalyst concentration. It was also observed that molar ratio and
catalyst loading were the most important factors in the production of biodiesel. Su et al. (2013)
used Box-behnken design to investigate the reaction factors affecting FFA conversion from
esterification of enzyme hydrolysed FFA and methanol. The effects of reaction time, reaction
temperature, methanol to FFA ratio and hydrolysed concentration were investigated: all factors
were significant with an interval of 99.9%.

2.8.3 Central composite design (CCD)

CCD is a standard RSM design tool used to study transesterification reaction parameters and
predict the variables. CCD is suitable for sequential experiments and fit a quadratic surface, which
usually works well for process optimisation (Jazie et al., 2013). In CCD, all the corner points lay
on the surface by using a ball, as shown in Figure 2.7. Each number of factors is varied over five
levels: plus and minus alpha (axial point), plus and minus one (factorial point) and centre point.
CCD design performs a more detailed design as compared to Box-behnken design (Rezaei et al.,
2013).

Figure 2. 3: Central composite design profile with three inputs

Omar et al. (2011) studied the interactions of process variables using the CCD method to predict
the optimum process conditions for FAME. By applying RSM, CaO catalyst performance was
investigated. The results gave a good prediction at a high confidence level of 95% CCD with full
24 factorial designs. Jazei et al. (2013) used RSM with a CCD tool resulting in a quadratic
polynomial equation. Omar and Amin (2011) employed RSM to study the interaction of methanol-
to-oil ratio, reaction temperature, reaction time, catalyst loading and FFA conversion using CCD
by applying 24 full factorial design in the production of biodiesel from waste cooking palm oil
with Sr/ZrO2. Boey et al. (2011) applied mud crab shell as catalyst in biodiesel production and
performed a statistical analysis using CCD. Based on the experimental and predicted results, the
most important factors affecting biodiesel yield were catalyst concentration, reaction temperature
and methanol-to-oil molar ratio, with a 93% yield. Based on the aforementioned studies, the
parameters selected for optimization in this current study are temperature, oil-to-methanol ratio
and catalyst loading.

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