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The components of petroleum are separated by fractional distillation. Petroleum is heated to about 600°C and passed into a distillation column. Components with lower boiling points rise and are extracted from the upper parts of the column. Components with higher boiling points are extracted from the lower parts of the column.
Components are extracted in stages depending on their boiling points. For example, petroleum gas has a low boiling point, and hence it is extracted from the top of the column. Bitumen has a high boiling point, hence is extracted from the bottom of the column. Kerosene has a boiling point higher than petroleum gas but lower than bitumen, and hence it is extracted from the middle of the column.