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lower FFAs followed by transesterification) process based on the FFA content. In a
two-step process, esterification plays a major role in limiting FFA content and
makes the oil with high FFA content useful to produce biodiesel.
Esterification of non-edible oils containing high FFA content is carried out using
concentrated sulfuric acid in a homogeneous form as a catalyst. However, homogeneous acid is usually nonrecyclable and inflicts severe environmental issues and
corrosion problems [9]. Besides, it was observed that a substantial amount of water
effluents is produced during the washing of homogeneously catalyzed biodiesel and
also exhibited a significant product (biodiesel) loss. A high cost of raw material (oil)
and all the above-highlighted disadvantages result in the addition of cost for biodiesel production in each stage which is responsible for high biodiesel price.
Certainly, the cost of biodiesel production can be lowered by using non-edible and
waste vegetable oils. However, the disadvantage of lower solubility between reactants and also environmental hazards involved in the conventional process can only
be mitigated using an effective process modification and (or) efficient catalyst.
1.1 Feedstock for Biodiesel Production
The common feedstock for biodiesel production involves various pure fatty acids
(palmitic, linoleic, stearic, linolenic, and oleic acids), edible oils (soybean, peanut,
rice bran, cottonseed, palm, and sunflower), and non-edible oils (waste vegetables,
Karanja, neem, Jatropha, polanga, rubber seed, mahua, palm fatty acid distillates,
algal). Biodiesel is typically made by reacting triglyceride (ester of three fatty acids
and glycerol molecule) present in vegetable oils with alcohol. High-quality biodiesel can also be produced by reacting pure fatty acids with alcohol [6, 10, 11].
However, generally complex heterogeneous blends of various fatty acids known as
vegetable oils are the preferable sources to produce biodiesel because of their low
cost than pure fatty acids. Usually, vegetable oils are categorized into two groups
such as edible and non-edible oils based on their composition, source, and application. Edible oils like palm, peanut, rice bran, soybean, and sunflower are widely
used to produce high-quality biodiesel. However, the widespread use of edible oils
for fuel may elevate the crisis of food against the comfort of fuel [12]. The use of
edible oils for biodiesel production increases the cost of biodiesel which also limits
its commercialization. Waste vegetable oils and non-edible oils like Karanja,
Jatropha, date seed, castor, rubber seed, mahua, some nontraditional seeds, and
algae oils are preferred sources to produce biodiesel. In general, non-edible and
waste vegetable oils contain a high amount of FFAs and water but later have an
advantage of no gum content in the oil. Thus, non-edible and waste vegetable oils
are low-quality oils which are mostly available at a lower cost, and using these oils
in biodiesel production lowers the cost of biodiesel to a substantial extent [13].
Therefore, non-edible oils and waste vegetable oils are the highly preferred feedstock to produce biodiesel, and their composition has been given in Table 1.
Catalytic and Non-Catalytic Methods for Biodiesel Production
lower FFAs followed by transesterification) process based on the FFA content. In a
two-step process, esterification plays a major role in limiting FFA content and
makes the oil with high FFA content useful to produce biodiesel.
Esterification of non-edible oils containing high FFA content is carried out using
concentrated sulfuric acid in a homogeneous form as a catalyst. However, homogeneous acid is usually nonrecyclable and inflicts severe environmental issues and
corrosion problems [9]. Besides, it was observed that a substantial amount of water
effluents is produced during the washing of homogeneously catalyzed biodiesel and
also exhibited a significant product (biodiesel) loss. A high cost of raw material (oil)
and all the above-highlighted disadvantages result in the addition of cost for biodiesel production in each stage which is responsible for high biodiesel price.
Certainly, the cost of biodiesel production can be lowered by using non-edible and
waste vegetable oils. However, the disadvantage of lower solubility between reactants and also environmental hazards involved in the conventional process can only
be mitigated using an effective process modification and (or) efficient catalyst.
1.1 Feedstock for Biodiesel Production
The common feedstock for biodiesel production involves various pure fatty acids
(palmitic, linoleic, stearic, linolenic, and oleic acids), edible oils (soybean, peanut,
rice bran, cottonseed, palm, and sunflower), and non-edible oils (waste vegetables,
Karanja, neem, Jatropha, polanga, rubber seed, mahua, palm fatty acid distillates,
algal). Biodiesel is typically made by reacting triglyceride (ester of three fatty acids
and glycerol molecule) present in vegetable oils with alcohol. High-quality biodiesel can also be produced by reacting pure fatty acids with alcohol [6, 10, 11].
However, generally complex heterogeneous blends of various fatty acids known as
vegetable oils are the preferable sources to produce biodiesel because of their low
cost than pure fatty acids. Usually, vegetable oils are categorized into two groups
such as edible and non-edible oils based on their composition, source, and application. Edible oils like palm, peanut, rice bran, soybean, and sunflower are widely
used to produce high-quality biodiesel. However, the widespread use of edible oils
for fuel may elevate the crisis of food against the comfort of fuel [12]. The use of
edible oils for biodiesel production increases the cost of biodiesel which also limits
its commercialization. Waste vegetable oils and non-edible oils like Karanja,
Jatropha, date seed, castor, rubber seed, mahua, some nontraditional seeds, and
algae oils are preferred sources to produce biodiesel. In general, non-edible and
waste vegetable oils contain a high amount of FFAs and water but later have an
advantage of no gum content in the oil. Thus, non-edible and waste vegetable oils
are low-quality oils which are mostly available at a lower cost, and using these oils
in biodiesel production lowers the cost of biodiesel to a substantial extent [13].
Therefore, non-edible oils and waste vegetable oils are the highly preferred feedstock to produce biodiesel, and their composition has been given in Table 1.
Catalytic and Non-Catalytic Methods for Biodiesel Production