|technology > separation techniques > crystallization|
sugar industry and in the dairy industry (where lactose is produced from cheese whey or casein whey).
Crystallisation (fractionation) is also used in the edible oil industry, to modify the properties of edible oils and fats.
vacuum pans in which the juice is boiled under vacuum in order to minimise the temperatures involved. The growth of the sucrose crystal only involves sucrose and water. The non-sugars contained in the sugar juice are not incorporated into the crystal structure, instead most of them remain in the liquid phase while some are released to the vapour phase. The sugar crystals are removed from the liquid phase by centrifugation.
cooling down the solution, crystallisation starts and the crystals begin to grow. The crystals are removed from the liquid phase by centrifugation. Depending on the required grade, further purification (refining) can take place by washing the crystals, or redissolving them and recrystallising them, followed by treatment with active carbon for the removal of any impurities.
melting components in the liquid phase change at different temperatures. This difference can be extended by using an organic solvent which has the effect of decreasing the viscosity and leading to better washing of the crystals.
heating point is typically 75°C for palm oil). The molten oil is then cooled and stirred to form crystal nuclei, and the temperature is maintained at a lower temperature to induce crystal growth (typically 12 hours at 28 - 30°C for palm oil). If a solvent is used, it is added to the molten oil prior to cooling. The mixtures containing the crystallised solids and the dissolved liquids are separated by filters. If a solvent is used, it is removed from the fractions by distillation.