Method for producing diol

A method for producing a diol, comprising:

• a) supplying metaboric acid, a saturated aliphatic hydrocarbon and a reaction gas containing molecular oxygen to a reactor and performing liquid-phase oxidation of the saturated aliphatic hydrocarbon with the reaction gas containing molecular oxygen in the presence of metaboric acid to obtain a reaction liquid containing an oxide;
• b) esterifying the oxide to obtain a reaction liquid containing a borate compound;
• c) separating the reaction liquid containing a borate compound into an unreacted saturated aliphatic hydrocarbon and a distillation residue by distillation;
• d) separating the distillation residue into orthoboric acid and an organic layer by hydrolysis;
• e) separating the organic layer into an alkali aqueous solution layer and a crude alcohol layer by saponification with an alkali;
• and
• f) performing first distillation on the crude alcohol layer to remove a monoalcohol therefrom and obtain a residual liquid, and then performing second distillation on the residual liquid under conditions of a temperature of lower than 250° C. and a residence time of shorter than 60 minutes,
• wherein the second distillation is performed by a simple distillation or a molecular distillation,
• in a case where the second distillation is performed using the simple distiller, a thermal load parameter calculated by a product of the temperature in ° C. in the second distillation and the residence time in minutes is 5850 or less,
• in a case where the second distillation is performed using the molecular distiller, the thermal load parameter calculated by the product of the temperature in ° C. in the second distillation and the residence time in minutes is 615 or less.