Method for preparing 1,3,5-trioxane

1. A method of preparing 1,3,5-trioxane using a distillation apparatus comprising a reactor 10 , a distillation tower 20 , and a decanter 30 , wherein the distillation tower 20 comprises a distillation unit 21 and an extraction unit 22 within the tower,

said method comprising

preparing 1,3,5-trioxane-containing vapor from formaldehyde in the reactor 10 ;

distilling the 1,3,5-trioxane-containing vapor in the distillation unit 21 ;

introducing the distilled 1,3,5-trioxane-containing vapor into the extraction unit 22 and subjecting the distilled 1,3,5-trioxane-containing vapor to an extraction with an organic solvent to produce a vapor phase and a liquid phase, said organic solvent being capable of being azeotropically boiled with water;

wherein the liquid phase is introduced into the decanter 30 where the liquid phase is separated into a water phase (a) and an oil phase (b); and

wherein the water phase (a) is separated into a first water phase (a 1 ) refluxed into the distillation unit 21 and a second water phase (a 2 ) refluxed into the extraction unit 22 .

2. The method of preparing 1,3,5-trioxane according to claim 1 , wherein the vapor phase in the extraction unit 22 contains water and a part of the water (f) is refluxed into the top of the distillation tower 20 and the remaining of the water (e) is discharged to the outside of the distillation tower 20 , and wherein a ratio (f)/(e) is 1.0 or more; and

wherein ratio of the second water phase (a 2 ) refluxed into the extraction unit 22 to the water (f) refluxed into the top of the distillation tower 20 is 2.0 or more.

3. The method of preparing 1,3,5-trioxane according to claim 1 , wherein the vapor phase and the liquid phase in the extraction unit 22 contain formaldehyde and the concentration of the formaldehyde in the extraction unit 22 is 50 wt % or less of the total weight of the vapor phase and the liquid phase in the extraction unit 22 .