used to dissolve the oil in the prepared oilseed or similar input and then recovered in
a desolventizing (evaporation) process and recycled for reuse in the process [3, 4].
Crude vegetable oil obtained at these facilities is then transferred to a refining
facility where it is prepared for human consumption or prepared for use in animal
feeds. Refining of edible oil is a process where free fatty acids are volatilized,
condensed, and recovered simultaneously with vacuum decoloring operation.
However, processes in vegetable oil refining, such as filter backwash, acidification of soap-stock, and washing of equipment, produce big amounts of wastewaters
[5]. These wastewaters have high chemical oxygen demand (COD), oil and grease
levels as well as elevated phosphorus and dissolved solids concentrations [6].
2 Refining
Crude oils are not usually considered to be edible before the removal of numerous
nonglyceride compounds through operations collectively known as refining. The
refining processes remove undesirable materials, such as phospholipids,
monoacylglycerols, diacylglycerols, free fatty acids, color and pigments, oxidized
materials, flavor components, trace metals, sulfur compounds, trace solvent residue,
and water, but may also remove valuable minor components which are antioxidants
and vitamins, such as carotenes and tocopherols. Unfortunately, some of the refining
operations are not very selective and remove some beneficial compounds along with
the targeted undesirable ones. However, some vegetable oils (e.g., olive, tallow, and
lard) have been consumed without refining.
Figure 8.2 shows a general diagram of the processing steps involved in the
refining of vegetable oils. There are two major types of refining: chemical and
physical. The major steps involved in chemical refining include degumming, neutralizing, bleaching, and deodorizing. Physical refining removes free fatty acids
(FFA) and flavors by distillation, to combine the steps of neutralization and deodorization into one operation.
Conventional chemical refining involves degumming for the removal of phospholipids, neutralization for the removal of FFA, and bleaching for decolorization
and deodorization. Water is added during degumming to hydrate any gums present
and the mixture is then centrifuged for separation. Non-hydratable gums are
removed using phosphoric or citric acid before water is added and separation takes
place in a centrifuge.
In physical refining, the crude oil is degummed and bleached and then steam
stripped to remove FFA, odor, and VOCs all in one step. This replaces chemical
reaction mode using an alkali (caustic soda) in chemical refining. A physical
pretreatment is used to achieve low phospholipid content by degumming and
using bleaching earth. Following this, FFA can be stripped from the physically
pretreated oil using steam distillation in a vacuum at temperatures of around 250
C
and refined by the oil flowing over a series of trays countercurrent to the flow of the
stripping steam [7]. Previous neutralization stages are eliminated because the
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D. Kaya and Y.-T. Hung
a desolventizing (evaporation) process and recycled for reuse in the process [3, 4].
Crude vegetable oil obtained at these facilities is then transferred to a refining
facility where it is prepared for human consumption or prepared for use in animal
feeds. Refining of edible oil is a process where free fatty acids are volatilized,
condensed, and recovered simultaneously with vacuum decoloring operation.
However, processes in vegetable oil refining, such as filter backwash, acidification of soap-stock, and washing of equipment, produce big amounts of wastewaters
[5]. These wastewaters have high chemical oxygen demand (COD), oil and grease
levels as well as elevated phosphorus and dissolved solids concentrations [6].
2 Refining
Crude oils are not usually considered to be edible before the removal of numerous
nonglyceride compounds through operations collectively known as refining. The
refining processes remove undesirable materials, such as phospholipids,
monoacylglycerols, diacylglycerols, free fatty acids, color and pigments, oxidized
materials, flavor components, trace metals, sulfur compounds, trace solvent residue,
and water, but may also remove valuable minor components which are antioxidants
and vitamins, such as carotenes and tocopherols. Unfortunately, some of the refining
operations are not very selective and remove some beneficial compounds along with
the targeted undesirable ones. However, some vegetable oils (e.g., olive, tallow, and
lard) have been consumed without refining.
Figure 8.2 shows a general diagram of the processing steps involved in the
refining of vegetable oils. There are two major types of refining: chemical and
physical. The major steps involved in chemical refining include degumming, neutralizing, bleaching, and deodorizing. Physical refining removes free fatty acids
(FFA) and flavors by distillation, to combine the steps of neutralization and deodorization into one operation.
Conventional chemical refining involves degumming for the removal of phospholipids, neutralization for the removal of FFA, and bleaching for decolorization
and deodorization. Water is added during degumming to hydrate any gums present
and the mixture is then centrifuged for separation. Non-hydratable gums are
removed using phosphoric or citric acid before water is added and separation takes
place in a centrifuge.
In physical refining, the crude oil is degummed and bleached and then steam
stripped to remove FFA, odor, and VOCs all in one step. This replaces chemical
reaction mode using an alkali (caustic soda) in chemical refining. A physical
pretreatment is used to achieve low phospholipid content by degumming and
using bleaching earth. Following this, FFA can be stripped from the physically
pretreated oil using steam distillation in a vacuum at temperatures of around 250
C
and refined by the oil flowing over a series of trays countercurrent to the flow of the
stripping steam [7]. Previous neutralization stages are eliminated because the
328
D. Kaya and Y.-T. Hung