Patent ID: 8450507

Claim:
An integrated process for preparing trioxane from formaldehyde, comprising: a) feeding a feed stream A1 comprising formaldehyde and water and a recycle stream B3 comprising water as the main component and additionally formaldehyde and trioxane to a formaldehyde concentration unit and separating it into a formaldehyde-rich stream A2 and a stream A3 comprising at least 80% by weight of water; b) feeding a product stream C1 comprising trioxane, water and formaldehyde, a recycle stream E1 comprising trioxane, water, and formaldehyde, and optionally said stream A2 to a first low-pressure distillation column and distilling at a pressure of from 0.1 to 1.5 bar, and withdrawing a trioxane-enriched stream B1 comprising trioxane as a main component and additionally water and formaldehyde, a bottom draw stream B2 comprising at least 80% by weight of formaldehyde and water, and said recycle stream B3 as a side draw stream; c) feeding said bottom draw stream B2 and optionally said stream A2 to a trioxane synthesis reactor and reacting said streams to obtain said product stream C1; d) feeding said stream B1 to a medium-pressure distillation column and distilling at a pressure of from 1.0 to 3.0 bar to obtain a low boiler stream D1 comprising methanol, methylol, and methyl formate, and a stream D2 comprising predominantly trioxane and additionally formaldehyde and water; e) feeding said stream D2 to a high-pressure distillation column and distilling at a pressure of from 2.5 to 10.0 bar to obtain said recycle stream E1 and a product stream E2 comprising at least 80% by weight of trioxane; wherein said stream A2 is fed either to said low-pressure distillation column or said trioxane synthesis reactor or both.