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Y. Cao et al.
residue than the filter cloth. Before the filtration, there is no need to remove the
dregs thoroughly from the oil, as appropriate amount of big-diameter residues can
prevent the filtration equipment from being bunged up. After the filtration, the filtrate
can go on next process without further refined filtration. Dregs are beneficial to the
separation during the alkali refining process.
7.2.1.6 Extraction
There are two difficulties in the extraction process. The first one is that compared with
other oils, the castor oil is more difficult to lixiviate when using ordinary conditions,
as the existence of hydroxyl group in the molecule results in high polarity and viscosity. The other one is that castor cake has a strong tackiness and poor permeability,
which lead to the difficulties in the solvent leaching and desolventizing. The key to
solve these two problems is increasing extraction temperature and unchocking the
blockings. To ensure the temperature of the cake is above 60 °C, the delivery system
should be equipped with a heat insulation layer. The solvent preheater should preheat to 55 °C. The pipelines that transport miscella should be equipped with heating
jacket, ensuring the extraction temperature is 57–60 °C at which the castor oil has
a good solubility and low viscosity. Meanwhile, countermeasures should be taken
to prevent the blocking of the extractor and desolventizer. Combining these measures with other technical means, such as prolonging time of extraction and reducing
the height of the castor cake, the residual oil ratio of castor could be controlled
under 1%.
7.2.1.7 Desolvation
To assure the airflow channel unobstructed, there should be a pre-desolvation in
desolventizer toaster and the thickness of the bed material should be decreased. It
is of great importance for desolvation to intensify internal heat transfer, as this can
avoid the oilseed meal absorbing water and clotting with each other.
7.2.1.8 Refinement
During vegetable oils’ production, it is usual to refine the crude oil obtained from
either mechanical pressing or solvent extraction. The main aim of refining is to
remove impurities (e.g., colloidal matter, free fatty acid, and coloring matter) and
other undesirable constituents, thus making the oil more resistant to deterioration
during storage. Refining includes (a) removing solid and colloidal matter by settling
and filtration, (b) neutralizing the free fatty acid by alkali, (c) removing colored matter
by bleaching, and (d) deodorizing by treatment with steam at high temperature and
low pressure. The general method of refining used for edible oils is applicable to
castor oil [27]. But the condition for the refinement is harsher than other oils as a
Y. Cao et al.
residue than the filter cloth. Before the filtration, there is no need to remove the
dregs thoroughly from the oil, as appropriate amount of big-diameter residues can
prevent the filtration equipment from being bunged up. After the filtration, the filtrate
can go on next process without further refined filtration. Dregs are beneficial to the
separation during the alkali refining process.
7.2.1.6 Extraction
There are two difficulties in the extraction process. The first one is that compared with
other oils, the castor oil is more difficult to lixiviate when using ordinary conditions,
as the existence of hydroxyl group in the molecule results in high polarity and viscosity. The other one is that castor cake has a strong tackiness and poor permeability,
which lead to the difficulties in the solvent leaching and desolventizing. The key to
solve these two problems is increasing extraction temperature and unchocking the
blockings. To ensure the temperature of the cake is above 60 °C, the delivery system
should be equipped with a heat insulation layer. The solvent preheater should preheat to 55 °C. The pipelines that transport miscella should be equipped with heating
jacket, ensuring the extraction temperature is 57–60 °C at which the castor oil has
a good solubility and low viscosity. Meanwhile, countermeasures should be taken
to prevent the blocking of the extractor and desolventizer. Combining these measures with other technical means, such as prolonging time of extraction and reducing
the height of the castor cake, the residual oil ratio of castor could be controlled
under 1%.
7.2.1.7 Desolvation
To assure the airflow channel unobstructed, there should be a pre-desolvation in
desolventizer toaster and the thickness of the bed material should be decreased. It
is of great importance for desolvation to intensify internal heat transfer, as this can
avoid the oilseed meal absorbing water and clotting with each other.
7.2.1.8 Refinement
During vegetable oils’ production, it is usual to refine the crude oil obtained from
either mechanical pressing or solvent extraction. The main aim of refining is to
remove impurities (e.g., colloidal matter, free fatty acid, and coloring matter) and
other undesirable constituents, thus making the oil more resistant to deterioration
during storage. Refining includes (a) removing solid and colloidal matter by settling
and filtration, (b) neutralizing the free fatty acid by alkali, (c) removing colored matter
by bleaching, and (d) deodorizing by treatment with steam at high temperature and
low pressure. The general method of refining used for edible oils is applicable to
castor oil [27]. But the condition for the refinement is harsher than other oils as a