Vapor–liquid and chemical equilibria model for formaldehyde–trioxane–sulfuric acid–water mixtures

BACKGROUND Trioxane (C 3 H 6 O 3 ) is industrially produced from aqueous formaldehyde (HCHO) solutions through catalytic distillation catalyzed by sulfuric acid (H 2 SO 4 ). Optimizing industrial process of the synthesis and developing new catalysts require a reliable model for the vapor–liquid equilibria in reaction mixture HCHO–C 3 H 6 O 3 –H 2 SO 4 – H 2 O and a deep understanding of the role of H 2 SO 4 in the industrial production of trioxane. RESULTS Here the Maurer and co-workers's model and the LIFAC model along with their model parameters were invoked to develop such a model. The vapor–liquid equilibrium data in HCHO–C 3 H 6 O 3 –H 2 SO 4 –H 2 O and HCHO–salt–H 2 O were systematically measured and utilized to determine the newly introduced model parameters. The model thus-established provides a reliable method for calculating and predicting the vapor–liquid and chemical equilibria data in HCHO–C 3 H 6 O 3 –H 2 SO 4 – H 2 O and HCHO–salt–H 2 O. CONCLUSIONS The prediction results uncover that, in addition to its ability to accelerate the reaction, the catalyst H 2 SO 4 has strong abilities to increase the activity of ‘real’ reactant for trioxane synthesis and to promote the phase separation that is very important for drastically increasing the yield of trioxane, reducing the energy requirement for the trioxane synthesis, and decreasing the formation of the by-product formic acid. © 2019 Society of Chemical Industry