less unsaturation produce biodiesel with better heating value and vice versa
(Karmakar et al. 2010).
Acid value, also called neutralization number or acid number or acidity, is defined
as the milligramme of potassium hydroxide that is required to neutralize 1 g of oil or
fat. AV is a measure of number of carboxylic acid groups present in triglycerides.
During transesterification, AV decreases because of breakage of long chains, and
free fatty acids (FFAs) form soap and water with alkali, which should be removed
during purification (Karmakar et al. 2010).
Moisture content is the quantity of water present in the feedstocks. The presence
of moisture content should be kept at a minimum value of less than 0.5%. At reaction
temperature, water hydrolyses triglycerides to form FFAs which interfere in the
transesterification reaction by forming soap with alkali. The presence of moisture
content more than 1% also affects the yield of biodiesel in manifold. The moisture
could be removed by heating the oil between 60 and 80
C which breaks emulsion
formed between water and oil (Karmakar et al. 2010).
Calorific value, also called heat value or energy content, is defined as the quantity
of heat produced during combustion at constant pressure of 1 atm and temperature of
0
C. The calorific value of feedstock directly influences the energy content of
biodiesel. Fatty acid composition and calorific value are related in a fact that the
feedstocks with more saturation possess high calorific value (Karmakar et al. 2010).
Titre measures the solidification point of a mixture of fatty acids present in a
feedstock. Measurement of titre is important because transesterification is a liquidphase reaction. Feedstocks with high titre consume more energy for heating, which
leads to an increase in the production cost of biodiesel. Feedstocks between 30 and
45
C are used for biodiesel production (Karmakar et al. 2010).
Impurities are the presence of filterable or insoluble solids present in the feedstocks. Non-triglycerides are also considered as impurities. Impurities include bone
fragments, gums, food substances, sand, debris, seed particles, etc. Feedstock should
be filtered to remove impurities. Unsaponifiables are organic substances which do
not form soap with alkali. Unsaponifiables include higher alcohols, hydrocarbons,
waxes, sterols, etc. Unsaponifiables may be removed by water washing or by
refining (Karmakar et al. 2010).
6.3.2 Type of Alcohol
In transesterification, feedstock (oil or fat) reacts with an alcohol to produce biodiesel and glycerol. Feedstock is a limiting reactant, and alcohol is an excess reactant.
Alcohols may be primary or secondary or tertiary and linear or branched monohydric
organic compounds. Methanol, ethanol, propanol, butanol, isopropanol, t-butanol,
etc. are attempted to produce biodiesel. Methanol is the common acyl acceptor and
member of lower alcohol. Lower alcohols have lower boiling point which reduces
the energy consumption and decreases production cost of biodiesel (Table 6.1).
Also, short-chain alcohols afford more conversion than long-chain alcohols at the
134
S. Sivamani et al.
(Karmakar et al. 2010).
Acid value, also called neutralization number or acid number or acidity, is defined
as the milligramme of potassium hydroxide that is required to neutralize 1 g of oil or
fat. AV is a measure of number of carboxylic acid groups present in triglycerides.
During transesterification, AV decreases because of breakage of long chains, and
free fatty acids (FFAs) form soap and water with alkali, which should be removed
during purification (Karmakar et al. 2010).
Moisture content is the quantity of water present in the feedstocks. The presence
of moisture content should be kept at a minimum value of less than 0.5%. At reaction
temperature, water hydrolyses triglycerides to form FFAs which interfere in the
transesterification reaction by forming soap with alkali. The presence of moisture
content more than 1% also affects the yield of biodiesel in manifold. The moisture
could be removed by heating the oil between 60 and 80
C which breaks emulsion
formed between water and oil (Karmakar et al. 2010).
Calorific value, also called heat value or energy content, is defined as the quantity
of heat produced during combustion at constant pressure of 1 atm and temperature of
0
C. The calorific value of feedstock directly influences the energy content of
biodiesel. Fatty acid composition and calorific value are related in a fact that the
feedstocks with more saturation possess high calorific value (Karmakar et al. 2010).
Titre measures the solidification point of a mixture of fatty acids present in a
feedstock. Measurement of titre is important because transesterification is a liquidphase reaction. Feedstocks with high titre consume more energy for heating, which
leads to an increase in the production cost of biodiesel. Feedstocks between 30 and
45
C are used for biodiesel production (Karmakar et al. 2010).
Impurities are the presence of filterable or insoluble solids present in the feedstocks. Non-triglycerides are also considered as impurities. Impurities include bone
fragments, gums, food substances, sand, debris, seed particles, etc. Feedstock should
be filtered to remove impurities. Unsaponifiables are organic substances which do
not form soap with alkali. Unsaponifiables include higher alcohols, hydrocarbons,
waxes, sterols, etc. Unsaponifiables may be removed by water washing or by
refining (Karmakar et al. 2010).
6.3.2 Type of Alcohol
In transesterification, feedstock (oil or fat) reacts with an alcohol to produce biodiesel and glycerol. Feedstock is a limiting reactant, and alcohol is an excess reactant.
Alcohols may be primary or secondary or tertiary and linear or branched monohydric
organic compounds. Methanol, ethanol, propanol, butanol, isopropanol, t-butanol,
etc. are attempted to produce biodiesel. Methanol is the common acyl acceptor and
member of lower alcohol. Lower alcohols have lower boiling point which reduces
the energy consumption and decreases production cost of biodiesel (Table 6.1).
Also, short-chain alcohols afford more conversion than long-chain alcohols at the
134
S. Sivamani et al.