Factors that affect the palm oil fractionation process
Factors that affect the palm oil crystallization process include oil composition, homogeneous polycrystals and cooling conditions.
(1) Oil composition: Palm oil contains 4% to 8% triglycerides, which will form a eutectic mixture with triglycerides, thereby reducing the solid content and slowing down the crystallization rate of oil. The monoglyceride content in palm oil is less than 1%, so it has no significant impact on the palm oil crystallization process.
(2) Polycrystalline The triglycerides of palm oil are polycrystalline, so they have different crystal forms, namely α-type, β’-type and β-type crystals. The stability and melting point of these crystal forms increase in sequence. When palm oil is cooled, α-form crystals are first obtained, and then converted into β’-form and β-form crystals in sequence. In order to obtain a good separation effect, it is hoped to obtain β’ and β-type crystals during the crystallization process, because the β’-type crystals are large and hard, which is conducive to subsequent filtration and separation.
(3) Cooling rate The cooling rate will affect the formation of crystal nuclei and the growth of crystals. When the temperature is low enough (32~36°C), saturated glyceryl esters will crystallize. These crystals serve as nuclei for further crystallization of low-melting point glycerides to form large crystals. Slow cooling rate and appropriate stirring rate are necessary conditions to obtain ideal crystals.
The first step in dry fractionation of palm oil is crystallization below 10°C. The liquid component is used as a substitute in frying, cooking and salad oils or is being further fractionated. With the further development of single-stage palm oil fractionation technology, there is an increasing tendency to perform double or triple fractions of palm oil to produce fractions with specific characteristics, such as high iodine value super oleic acid (iv > 65) and extra-hard palm stearin and intermediate components.
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