What are true pressure distillation and reduced pressure boiling range?

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What are vacuum distillation and reduced-pressure boiling range? When distilling heavy petroleum products at atmospheric pressure, polymeric hydrocarbons begin to decompose when the distillation temperature reaches 360–380°C. Therefore, it is necessary to carry out distillation at a lower temperature. Since the energy required for molecules at the liquid surface to escape decreases as external pressure is reduced, lowering the external pressure can lower the boiling point of hydrocarbons. Thus, the distillation process carried out at a pressure lower than atmospheric pressure is called vacuum distillation. A set of data consisting of the percentage of distillates of petroleum products measured by vacuum distillation and their corresponding distillation temperatures is called the vacuum distillation range of petroleum products. The distillation temperature read under a certain residual pressure during vacuum distillation is usually converted to the temperature at 760 millimeters of mercury pressure using standard curves, calculation tables, or conversion charts, while the amount of distillate is expressed as a volume percentage (or weight percentage).