Prediction of the vapor–liquid equilibrium of chemical reactive systems containing formaldehyde using the COSMO-RS method

• COSMO-RS was used to model complex chemical and phase equilibria.
• The behavior of poly(oxymethylene) glycol oligomers was modeled successfully.
• COSMO-RS enables predictions for compounds/mixtures when no data are available.
• TURBOMOLE was used to obtain the σ profiles of poly(oxymethylene) glycol oligomers.
• Intramolecular interactions and conformations were considered.

We herein present a quantum chemical method for predicting the thermodynamic properties of a reactive formaldehyde + water system. The TURBOMOLE program was used to obtain the σ profiles of poly(oxymethylene) glycol oligomers produced via a series of chemical reactions in aqueous solution. The conductor-like screening model for real solutions (COSMO-RS) method, in combination with chemical equilibrium constants and the mass balance equation obtained using MATLAB, was successfully used to calculate the activity coefficients of all compounds in the liquid. Based on NMR data from the literature along with the obtained activity coefficients, we modified the thermodynamic chemical equilibrium constant Kn∗ for glycol formation. Finally, we estimated the vapor–liquid equilibrium and distribution of oligomers (MGn, n ≥ 1) in the formaldehyde-water solution. The COSMO-RS method was thus proven to be an efficient tool to study formaldehyde-containing aqueous solutions, and can be used as a basis for other similar reactive systems.