Page 104 - Advances in Eco-Fuels for a Sustainable Environment

Prospects of biodiesel feedstock as an effective ecofuel source and their challenges 77

nonedible fats include the blood and innards such as the liver and heart. Aside from
meat-processing facilities, animal fats can also be fetched from the collection and
processing of animal mortalities by rendering companies [51].

3.2.4 General prospective feedstock challenges

The biodiesel feedstocks are faced with some challenges that have limited their use on
a commercial scale. Some of those have been reported [1, 4], including:

(1) Collection from scattered locations, high dormancy, and problems in picking and
harvesting.
(2) Nonavailability of quality planting material or seeds, limited period of availability,
unreliable and improper marketing channels.
(3) Lack of postharvest technologies and their processing, nonremunerative prices, the wide
gap between potential and actual production, the absence of state incentives promoting bio-
diesel as fuel, and economics and cost-benefit ratio.
(4) Some of the costs of the nonedible oils cannot be obtained as they are currently not traded in
the open market [1].
(5) The high free fatty acid (FFA) content associated with nonedible oil, animal fats, and some
edible oils brings about increases in the production cost [1].
(6) A peculiar challenge associated with the use of poultry fat for biodiesel production is the
formation of precipitates in the blend with conventional diesel. The precipitate, a threat to
the diesel engine, is formed when stored at low temperatures such as 4°C [53].
(7) In general, animal fats do have a high viscosity (about 11–17 times higher than diesel fuel),
lower volatilities that cause the formation of deposits in engines due to incomplete com-
bustion, and incorrect vaporization characteristics. These problems are associated with
the large triglyceride molecule and its higher molecular mass [54].

3.3 Methods of oil extraction and their challenges

Four main methods of extraction with their benefits and challenges have been iden-
tified under this section. The methods include (i) mechanical extraction, (ii) chemical
extraction, (iii) enzymatic extraction, and (iv) supercritical fluid extraction. Before the
oil extraction takes place, seeds have to be dried. Seed can be either dried in the oven
(105°C) or sun dried for 3 weeks [7].

3.3.1 Mechanical extraction method
The most conventional technique of oil extraction is the mechanical press method
[7, 22, 55]. This method involves the use of either a manual ram press or an
engine-driven screw press. Studies have shown us that the engine-driven screw press
can extract 68%–80% of the oil while the ram presses only achieved 60%–65%
[7, 22]; however, the efficiency range of the engine-driven screw presses can be
broadened to 70%–80%. This broader range is due to the fact that seeds can be sub-
jected to a different number of extractions through the expeller. Up to three passes is