Distillation method

A distillation method, comprising:

• a supplying step of supplying a batch type distillation column with a liquid that is a process fluid;
• a pressure-temperature increasing step of increasing pressure and temperature of a fluid, used to heat the liquid, with a compressor and supplying the fluid to a reboiler;
• a heating step of exchanging heat in the reboiler between the liquid, which has been supplied to the distillation column, and the fluid, which has been increased in pressure and temperature, to heat the liquid and acquire overhead vapor and to condense the fluid;
• a condensing step of delivering the overhead vapor heated in the heating step to a condenser and condensing the overhead vapor into a condensate through heat exchange;
• a distillate removing step that removes the condensate;
• and
• a discharged liquid removing step that removes residual liquid from the distillation column,
• wherein the fluid holds condensation heat of the overhead vapor, is increased in pressure and temperature by the compressor, and then transfers the condensation heat to the liquid and condenses in the reboiler, and
• a pressure-regulating step that regulates pressure of the distillation column to distill the liquid with heat generated by a heat pump operated over a narrower temperature rising range in the pressure-temperature increasing step.