REMOVAL OF TRIOXANE FROM A TRIOXANE/FORMALDEHYDE/WATER MIXTURE BY MEANS OF PRESSURE-SWING RECTIFICATION

The invention relates to a method for separating trioxane from an inlet f low (I) consisting of formaldehyde, trioxane and water. Said method consists in a) preparing an inlet flow (I), which contains formaldehyde as the main component and trioxane and water as auxiliary components, b) feeding the inl et flow (I), a return flow (V) and a return flow (VII), containing formaldeh yde as the main component and trioxane and water auxiliary components, into a first distillation step and distilling it at a pressure of between 0.1 to 2.5 bars, thus enabling a flow (II), which contains formaldehyde as the main component and water as the auxiliary component, and a flow (III), which con tains trioxane as the main component and water and formaldehyde as the auxil iary components, and a flow (X), which contains water, trioxane and formalde hyde to be obtained, c) distilling the flow (III), optionally after separati ng materials at a low-boiling point from the flow (III) in a low-boiling sep aration step and in a second distillation step at a pressure of between 0.2 to 17. 5 bars, whereby the pressure in the second distillation step is 0.1 t o 15 bars higher that the pressure in the first distillation step. A flow (I V) is obtained which is essentially made of trioxane, and also a return flow (V), which contains trioxane as the main component and water and formaldehy de as the auxiliary components, d) feeding the flow (X) and optionally a flo w (IX), which contains water as the main component, into a third distillatio n step and distilling it at a pressure of between 1 to 10 bars, whereby a fl ow (VI), which is essentially made of water, and a return flow (VII), which contains formaldehyde as the main component and water and trioxane as the au xiliary components, are obtained.