Conceptual design of a crystallization-based trioxane production process

Trioxane, a cyclic trimer of formaldehyde, is an important intermediate that is mainly used as a source of water-free formaldehyde in chemical production processes. Different routes for the production of trioxane from aqueous formaldehyde solutions have been described in the literature, which all have in common that they are energy-intensive. In this work, the conceptual design of a new production process for trioxane is presented. It is a modification of a state-of-the-art pressure swing process from the literature, where the most critical distillation step is replaced with a crystallization. The new crystallization-based process and the pressure swing process were simulated in a consistent manner based on a well-established physico-chemical model for the ternary system (formaldehyde + water + trioxane). To obtain a sound basis for the description of the crystallization, solid–liquid equilibria in the ternary system, for which previously no data was available, were measured at conditions relevant for the process. A comparison of the two processes showed that the new crystallization-based process has a considerably reduced energy demand and much smaller recycle streams. Furthermore, it was found that the crystallization can be performed efficiently at temperatures well above 273 K. All this makes the new crystallization-based process an attractive candidate for trioxane production.