Density, excess molar volume, and COSMO-RS study of reactive aqueous solutions containing formaldehyde

In this study, the densities of formaldehyde (FA) + water (H2O) binary systems with formaldehyde fractions (xFA) of 0.05-0.27 at temperatures (T) of 293.15, 298.15, and 313.15 K were measured at 0.1 MPa, as well as those of a formaldehyde + water + methanol (MeOH) ternary system with xFA of 0.05-0.27 and xMeOH of 0.09-0.64. A thermodynamic model was combined with the conductor-like screening model for real solvents (COSMO-RS) coupled with a chemical reaction equilibrium and mass balance to describe the species distribution in the above solutions containing poly (oxymethylene) glycols ((HO(CH2O)nH, MGnn ≥ 1) and poly (oxymethylene) hemiformals (CH3O(CH2O)nH, HFn, n ≥ 1) produced by the reactions of FA with H2O and MeOH, respectively. The densities and volumes of these unknown oligomers, MGn and HFn, were computed by the COSMO-RS method and were correlated with the polymerization degree, n, and temperature, T. Furthermore, the densities of the FA + H2O and FA + H2O + MeOH solutions were calculated based on the species distribution and COSMO-RS simulations, which reproduced the experimental data well. Finally, the excess molar volumes of the FA + H2O and FA + H2O + MeOH systems were studied for the first time.