Vapor–Liquid Equilibria and Chemical Equilibria in the System (Formaldehyde + Water + Isoprenol)

Abstract

is an important intermediate in the chemical industry and is used, for example, in the production of various scent and flavor chemicals. Isoprenol is produced from aqueous formaldehyde and isobutene and is separated by distillation from mixtures containing formaldehyde, water, and isobutene in the process. As formaldehyde forms oligomers with both water and isoprenol, these mixtures are complex reacting systems, which are not easy to separate. Hence, for understanding and modeling the process, information on the vapor−liquid equilibria and the chemical equilibria in the system (formaldehyde + water + isoprenol) is essential. However, only very limited data on this system are available in the literature. Therefore, in the present work, vapor−liquid equilibria were measured in the following systems: system (water + isoprenol) at 20 and 90 kPa, system (formaldehyde + isoprenol) at 373 and 393 K, and system (formaldehyde + water + isoprenol) at 373 K. Furthermore, the chemical equilibria of the oligomerization reactions of formaldehyde and isoprenol were studied with 13 C-NMR spectroscopy at temperatures ranging from 283 to 353 K. The experimental data were used to extend a physico-chemical model of the system (formaldehyde + water) from the literature to include isoprenol.

Density of solutions of formaldehyde in water and alcohols

“…Stock solutions of (formaldehyde + water) and (formaldehyde + isoprenol) were prepared by dissolving paraformaldehyde powder in water or isoprenol at elevated temperatures as described in more detail elsewhere 19 . The overall formaldehyde mass fraction in these stock solutions was determined with a relative uncertainty of 2% by the Na 2 SO 3 titration method 3 using an OMNIS Titrator by Metrohm.…”

“…A correlation of the density of pure formaldehyde based on experimental data is available in the DIPPR database (version of May 2019) 34 . However, using this correlation yielded poor results in our calculations, which is not surprising, as formaldehyde is mainly bound in its oligomers with water and the alcohols 3,19 . Therefore, a separate correlation of the density of pure formaldehyde in systems of the type (formaldehyde + water + alcohol) was developed in the present work, which is given in Equation (): where and are model parameters.…”

“…The model can be extended to also include other alcohols than methanol, but this requires knowledge of the true species distribution in the solution, that is, the concentrations of all components including the formaldehyde oligomers in the chemical equilibrium must be known. This information is available for many practically relevant formaldehyde‐containing solutions, 18,19 but by far not for all. Other model parameters can be estimated using group‐contribution methods.…”

“…The alcohols that are presently included in the model are methanol, 1‐propanol, and isoprenol, but the model can easily be extended to also include other alcohols. 1‐propanol and isoprenol were chosen here besides methanol, as a chemical equilibrium model of the oligomerization reactions of formaldehyde with these alcohols is available, 18,19 which is needed for applying the model proposed by Ott 14…”

13C-NMR Spectroscopic Study of the Kinetics of Formaldehyde Oligomerization Reactions in the System (Formaldehyde + Water + Isoprenol)

“…Therefore, the reaction kinetics in solutions of (formaldehyde + isoprenol) and (formaldehyde + water + isoprenol) were studied at temperatures ranging from 282 to 333 K and at pH values ranging from 0.6 to 6.8 with quantitative 13 C-NMR spectroscopy. The experimental data were used to develop a kinetic model of the oligomerization reactions of formaldehyde with water and isoprenol that is consistent with the equilibrium model of Dyga et al 8 and the reaction kinetic model of Ott.…”