| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for carry out azeotropic distillation while enhancing separation efficiency or lowering energy consumption. SOLUTION: The subject to be distilled containing two substances of a lower boiling-point substance (hereafter called 'low boiling-point substance') and a higher boiling-point substance (hereafter called 'high boiling-point substance') is distilled azeotropically using an entrainer capable of forming an azeotropic mixture with at least any one of the two substances. The azeotropic distillation is carried out by (1) feeding the subject to be distilled to an azeotropic distillation column from at least two feed ports different in height, (2), feeding the distilled portion having low concentration of the low boiling-point substance of the subject from the lower feed port among the two feed ports and the distilled portion having high concentration of the low boiling-point substance from the higher feed port and by (3) extracting at least three fractions different in boiling-point as the distillates of the azeotropic distillation column, namely, extracting the lowest boiling point fraction from the top part of the azeotropic distillation column, the highest boiling-point fraction from the bottom part and the intermediate fraction from the middle stage.
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