METHOD FOR SEPARATING TRIOXANE FROM A TRIOXANE/FORMALDEHYDE/WATER MIXTURE BY MEANS OF PRESSURE CHANGE RECTIFICATION

A process for removing trioxane from a use stream I of formaldehyde, trioxane and water, by a) providing a use stream I which comprises formaldehyde as the main component and trioxane and water as the secondary components, b) feeding the use stream I, a recycle stream V and a recycle stream VII which comprises formaldehyde as the main component and water and trioxane as the secondary components into a first distillation stage and distilling to obtain a stream II a steam III and formaldehyde as the and a steam X c) distilling the stream III, in a second distillation stage the pressure in the second distillation stage being from 0.1 to 15 bar higher than the pressure in the first distillation stage, to obtain a stream IV and the recycle stream V as the secondary components, d) feeding the stream X and if appropriate a stream IX into a third distillation stage and distilling at a pressure of from 1 to 10 bar to obtain a stream VI which consists substantially of water and a recycle stream VII which comprises formaldehyde as the main component and water and trioxane as the secondary components.