In industrial processes, formaldehyde is mainly handled in aqueous solutions, which often contain methanol. In these solutions, formaldehyde forms predominantly adducts with the solvents.In aqueous solutions, methylene glycol and poly(oxymethylene) glycols are formed, in methanolic solutions hemiformal and poly(oxymethylene) hemiformals. As both the formation of poly-(oxymethylene) glycol and of poly(oxymethylene) hemiformal are slow compared to typical residence times in separation equipment, reliable information on kinetics of these reactions is essential for process design. Two independent methods were applied to obtain this information: NMR spectroscopy and high-resolution densimetry. The experiments were carried out at temperatures between 273 and 334 K and pH between 2 and 9. Both for poly(oxymethylene) glycol formation and poly(oxymethylene) hemiformal formation, the minimal reaction rate occurs between pH 3 and 5. At 293 K, the inverse rate constant 1/k at this minimum is about 6 min for poly(oxymethylene) glycol formation and about 110 h for poly(oxymethylene) hemiformal formation. The rate constants determined with NMR spectroscopy and densimetry generally agree well. Previously reported discrepancies between results from both methods are explained by the fact that rate constants of poly(oxymethylene) glycol formation depend strongly on the solvent water or deuterium oxide. Reaction kinetics of poly(oxymethylene) glycol and poly-(oxymethylene) hemiformal formation in the mixed-solvent system with water and methanol predicted from results obtained in the single-solvent systems are in good agreement with experimental data. is large Ocmg¿cfa % 650 at 293 K), the inverse reaction, the degradation of methylene glycol, is slow (at room temperature typically 1/&*mg « 1 min).

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Methylal (also known as dimethoxymethane and formaldehyde dimethyl acetal) is a side product of the production of polyacetal plastics from formaldehyde, which has to be removed in downstream processing. The design of the separation equipment requires a verified model for the vapor-liquid-phase equilibrium. New experimental results are presented for the vapor-liquid and liquid-liquid equilibrium of the ternary system (formaldehyde + water + methylal) and for the vapor-liquid equilibrium of the ternary system (formaldehyde + methanol + methylal) and of the quaternary system (formaldehyde + water + methanol + methylal). New experimental results and the literature data are compared with prediction results.

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Formaldehyde is one of the most important intermediate products of the chemical industry. Due to its high reactivity, it is commonly handled in aqueous or methanolic solutions. In these solutions, formaldehyde is dissolved chemically. Therefore, modeling thermodynamic properties of aqueous and methanolic formaldehyde-containing mixtures require the consideration of chemical reactions and physical effects. A recently published physico-chemical model (Maurer, 1986) for the description of vapor-liquid equilibria of these systems is tested and improved on the basis of about 140 new experimental data points for mixtures containing formaldehyde, water, methanol, and trioxane at temperatures between 320 and 380 K and pressures below 100 kPa. Improvements are achieved by fitting some of those binary interaction parameters, which formerly had to be estimated due to the lack of experimental data. The revised model is able to reliably predict vapor-liquid equilibria in multicomponent formaldehyde-containing mixtures.