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Y. Cao et al.
7.2.1 Raw Oil for Bio-Lubricants Production
Lubricants consist of base oil and additives. Base oil can be divided into mineral oil,
synthetic oil, and bio-lubricant base oil. Unlike mineral oil and synthetic oil, bio-oil
is generally obtained from the modification of plant raw oil. For the bio-lubricants,
the raw oil is the oil extracted from seeds via a series of procedures. Therefore the
properties of raw oil are of great importance to bio-lubricant. In this section we will
introduce production methods of raw oil.
As vegetable oils are being engaged for industrial lubricants usage, the competition
between using oil as food or as industrial lubricants have prompted the search for nonedible oils as suitable raw material. Castor oil, a non-edible vegetable oil produced
from the seeds of castor plant, is one of the largest investigated oils for industrial
and automotive lubrication [3]. Relative to other vegetable oils, it has a good shelf
life and does not deteriorate unless subjected to excessive heat [27]. The castor oil is
characterized by high viscosity although this is unusual for a natural vegetable oil.
This behavior is largely due to hydrogen bond of its hydroxyl groups. With these
advantages, castor is mainly produced as a promising resource for bio-lubricants,
and the industrial production technology is developed. So we choose castor oil as an
example to illustrate the process of oil manufacture.
The extraction of oil from castor seed is by one or a combination of mechanical
pressing and solvent extraction. In mechanical pressing, the seeds are crushed and
then adjusted to low moisture content by warming in a steam-jacketed vessel. Thereafter, the crushed seeds are loaded into hydraulic presses and they are pressed by
mechanical means to extract oil. The oil from mechanical pressing has light color and
low content of free fatty acids. However, mechanical pressing will only remove about
45% of the oil while the remaining oil in the cake can be recovered only by solvent
extraction. In the solvent extraction method, the crushed seeds are extracted with
a solvent in a Soxhlet extractor or commercial extractor. Solvents used for extraction include heptane, hexane, and petroleum ethers [27]. The seeds can be extracted
after pretreatment. Conventional pretreatment may include dehulling, size reduction,
breaking, grinding, and thermal treatment (cooking) with the purpose of debilitating
the cell coats and preparing the material for optimal oil extraction.
7.2.1.1 Transportation
Castor seeds have a thin and crisp crust which makes seeds easy to break. Meanwhile,
the nutlet of castor is soft. Once the curst is broken, the nutlet will cohere with the
dust and it is difficult to separate them. Taking these into consideration, the seeds
should be transported into the factory after cleaning. To avoid the breaking of seeds
and tedious procedure, cleaning process is operated with the combination of hull
beater and double-layer aspirated plansifter. The aspirated plansifter provides both
high cleaning efficiency and low damage percentage. The size of castor seeds is
generally around 13, 8.5, and 6 mm, so the holes’ diameter of first layer should be
Y. Cao et al.
7.2.1 Raw Oil for Bio-Lubricants Production
Lubricants consist of base oil and additives. Base oil can be divided into mineral oil,
synthetic oil, and bio-lubricant base oil. Unlike mineral oil and synthetic oil, bio-oil
is generally obtained from the modification of plant raw oil. For the bio-lubricants,
the raw oil is the oil extracted from seeds via a series of procedures. Therefore the
properties of raw oil are of great importance to bio-lubricant. In this section we will
introduce production methods of raw oil.
As vegetable oils are being engaged for industrial lubricants usage, the competition
between using oil as food or as industrial lubricants have prompted the search for nonedible oils as suitable raw material. Castor oil, a non-edible vegetable oil produced
from the seeds of castor plant, is one of the largest investigated oils for industrial
and automotive lubrication [3]. Relative to other vegetable oils, it has a good shelf
life and does not deteriorate unless subjected to excessive heat [27]. The castor oil is
characterized by high viscosity although this is unusual for a natural vegetable oil.
This behavior is largely due to hydrogen bond of its hydroxyl groups. With these
advantages, castor is mainly produced as a promising resource for bio-lubricants,
and the industrial production technology is developed. So we choose castor oil as an
example to illustrate the process of oil manufacture.
The extraction of oil from castor seed is by one or a combination of mechanical
pressing and solvent extraction. In mechanical pressing, the seeds are crushed and
then adjusted to low moisture content by warming in a steam-jacketed vessel. Thereafter, the crushed seeds are loaded into hydraulic presses and they are pressed by
mechanical means to extract oil. The oil from mechanical pressing has light color and
low content of free fatty acids. However, mechanical pressing will only remove about
45% of the oil while the remaining oil in the cake can be recovered only by solvent
extraction. In the solvent extraction method, the crushed seeds are extracted with
a solvent in a Soxhlet extractor or commercial extractor. Solvents used for extraction include heptane, hexane, and petroleum ethers [27]. The seeds can be extracted
after pretreatment. Conventional pretreatment may include dehulling, size reduction,
breaking, grinding, and thermal treatment (cooking) with the purpose of debilitating
the cell coats and preparing the material for optimal oil extraction.
7.2.1.1 Transportation
Castor seeds have a thin and crisp crust which makes seeds easy to break. Meanwhile,
the nutlet of castor is soft. Once the curst is broken, the nutlet will cohere with the
dust and it is difficult to separate them. Taking these into consideration, the seeds
should be transported into the factory after cleaning. To avoid the breaking of seeds
and tedious procedure, cleaning process is operated with the combination of hull
beater and double-layer aspirated plansifter. The aspirated plansifter provides both
high cleaning efficiency and low damage percentage. The size of castor seeds is
generally around 13, 8.5, and 6 mm, so the holes’ diameter of first layer should be