Abstract: The invention relates to an integrated process for preparing trioxane from formaldehyde in which, in a first step, a stream A1 comprising water and formaldehyde and a recycle stream B2 consisting substantially of water and formaldehyde are fed to a trioxane synthesis reactor in which the formaldehyde is converted to trioxane to obtain a product stream A2 comprising trioxane, water and formaldehyde. Stream A2 and a recycle stream D1 comprising trioxane, water and formaldehyde are fed to a first distillation column and distilled at a pressure in the range from 0.1 to 2.5 bar to obtain a stream B1 enriched in trioxane, and the stream B2 consisting substantially of water and formaldehyde. Stream B1 is fed to a second distillation column and distilled at a pressure in the range from 0.2 to 17.5 bar to obtain a product stream C2 consisting substantially of trioxane, and a stream C1 comprising trioxane, water and formaldehyde.

Abstract: The invention relates to an integrated process for preparing trioxane from formaldehyde, comprising the steps of: a) a stream A1 comprising water and formaldehyde and a recycle stream B2 consisting substantially of water and formaldehyde are fed to a trioxane synthesis reactor and allowed to react to obtain a product stream A2 comprising trioxane, water and formaldehyde; b) stream A2 is fed to a first low-pressure distillation column and distilled at a pressure of from 0.1 to 2.5 bar to obtain a stream B1 enriched in trioxane and additionally comprising water and formaldehyde, and the recycle stream B2 consisting substantially of formaldehyde and water; c) stream B1 and a recycle stream D1 comprising trioxane, water and formaldehyde are fed to a second low-pressure distillation column and distilled at a pressure of from 0.1 to 2.

Abstract: A process for removing trioxane from a mixture I of formaldehyde, trioxane and water, by a) distilling the mixture I in a first distillation stage at a pressure of from 0.1 to 2 bar to obtain a stream II which comprises formaldehyde and a stream III which comprises predominantly trioxane and additionally water and formaldehyde, b) mixing the stream III with a recycle stream VII which comprises predominantly trioxane and additionally water and formaldehyde to obtain a stream IIIa which comprises predominantly trioxane and additionally water and formaldehyde, c) distilling the stream IIIa, if appropriate after removing low boilers from the stream III or IIIa in a further distillation stage, in a second distillation stage at a pressure of from 0.2 to 10 bar, the pressure in the second distillation stage being at least 0.

Abstract: Process for preparing high-concentration gaseous formaldehyde having a molar CH2O:H2O ratio of ?0.6 from an aqueous formaldehyde solution by evaporation of at least part of the solution, in which the aqueous formaldehyde solution is heated to a vaporization temperature T and the gas phase formed is taken off, wherein the evaporation temperature T obeys the relationship: T[° C.]?T?min[° C.] where T?min(c)=A+B×(c/100)+C×(c/100)2+D×(c/100)3 and A=+68.759, B=+124.77, C=?12.851, D=?10.095, where c is the instantaneous CH2O content of the aqueous formaldehyde solution during the evaporation in percent by weight and is from 20 to 99% by weight.

Abstract: Method of stabilizing high-concentration formaldehyde solutions having a CH2O content of >70% by weight against precipitation of solids, which comprises heating the high-concentration formaldehyde solution at a heating rate of at least 5° C./min to a temperature of from 80° C. to 200° C. immediately after it has been prepared and storing it at a temperature in this range.