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

Abstract In this study, the densities of formaldehyde (FA) + water (H 2 O) binary systems with formaldehyde fractions ( x F A ) 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 x F A of 0.05–0.27 and x M e O H 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(CH 2 O) n H, MG n n  ≥ 1) and poly (oxymethylene) hemiformals (CH 3 O(CH 2 O) n H, HF n , n  ≥ 1) produced by the reactions of FA with H 2 O and MeOH, respectively. The densities and volumes of these unknown oligomers, MG n and HF n , were computed by the COSMO-RS method and were correlated with the polymerization degree, n , and temperature, T . Furthermore, the densities of the FA + H 2 O and FA + H 2 O + 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 + H 2 O and FA + H 2 O + MeOH systems were studied for the first time.