Page 227 - Advances in Eco-Fuels for a Sustainable Environment

Advances in bio-oil extraction from nonedible oil seeds and algal biomass 191

7.3.1 Seed preperation

Seeds are prepared for oil extraction by initially removing the outer layer of the fruit to
expose the kernel or seed, followed by drying of the kernel to the desired moisture con-
tent [29]. Further, seeds are separated from fruits and the separated seeds are sieved,
cleaned, andstoredatroomtemperature.Theseedsthatdonotdehiscearemechanically
cracked open. The seeds and kernels that are separated from various sources are dried
under the sun or in an oven at 30–0°C for 3–5days [30, 31].

7.3.2 Kernel or seed extraction
The first step to prepare seeds for oil extraction is to remove the outer layer of the fruits
to expose the kernel. To obtain the kernel for further processing, the seeds are cracked
open by using stompers or mallets. Because this step is the most time consuming,
the seeds can be cracked open in a bulk amount by using stompers and mallets in bulk
at a time [29].

7.3.3 Kernel or seed drying

The kernel or seeds are prepared in such a way that they contain the optimum moisture
content for high oil extraction. It has been observed that the kernel with around 15%
moisture content yields high oil by both mechanical and chemical extraction
methods [29]. Seeds have to be dried before they undergo the oil extraction procees,
and the process of seed drying is done carefully in a sieve tray drier by checking the
moisture content of the seed several times in a day so as to remove at the desired
dryness. The seeds are dried until the dry weights remain constant [29].

7.4 Extraction techniques

There are three main techniques that are available for the extraction of oil from a seed
or kernel: mechanical, chemical, or enzymatic. Apart from these widely used
methods, there are some other methods that are available that have been designed spe-
cifically for some sample types: accelerated solvent extraction (ASE), SFE, or
microwave-assisted extraction (MAE) [30].

7.4.1 Mechanical extraction
Oil extraction by mechanical expellers or presses is the most conventional method. In
this method, either a manual ram press or an engine-driven screw press is used for the
extraction of oil. It has been observed that the ram press can extract around 60%–65%
of oil while an engine-driven screw press can extract around 68%–80% of the avail-
able oil from seeds [30].
The design of the mechanical press is very important as it plays a crucial role in the
yield of oil. The yield can be increased by the pretreatment of the seeds by a cooking