Thermodynamic modelling of the nature of speciation and phase behaviour of binary and ternary mixtures of formaldehyde, water and methanol

Formaldehyde is a highly reactive chemical that is usually sold and processed in the form of aqueous solutions, with methanol added for stability. In these solutions, formaldehyde reacts with the solvents to form a variety of reaction products, including oligomers. These chemical reactions can occur in the liquid and vapour phases and have a significant influence on the properties of formaldehyde-containing solutions. Of particular interest to industrial applications is the prediction of the vapour-liquid equilibria (VLE) in formaldehyde solutions, considering the chemical reactions. We use the SAFT-gamma Mie group-contribution (GC) equation of state to obtain the fluid-phase behaviour of binary and ternary mixtures of formaldehyde with water and methanol. The oligomerisation reactions taking place in aqueous and methanolic solutions of formaldehyde are modelled implicitly using a physical approach, which is possible within the SAFT-gamma Mie framework by adding association (reactive) sites that mediate the formation of the reaction products. Using this approach, the nature of the chemical speciation in formaldehyde + water, formaldehyde + methanol and formaldehyde + water + methanol mixtures is studied. A new group, CH2O, characterising formaldehyde within the SAFT-gamma Mie GC approach, is developed. Experimental data for the VLE in binary mixtures of formaldehyde + water and formaldehyde + methanol are used to obtain the optimal unlike interaction parameters between the corresponding SAFT-? Mie groups. The newly developed parameters are used to predict the VLE of ternary formaldehyde + water + methanol mixtures for a wide range of temperatures and pressures, with excellent agreement to experimental data. Additionally, the SAFT-gamma Mie approach is shown to provide accurate predictions of the distribution of reaction species (oligomers) in binary and ternary mixtures containing formaldehyde. [GRAPHICS] .

Automated summary

This passage discusses the properties of formaldehyde and the influence of its chemical reactions on formaldehyde solutions, with a focus on predicting the vapor-liquid equilibria (VLE) in such solutions. The SAFT-gamma Mie group-contribution (GC) equation of state is used to model the behavior of formaldehyde mixtures with water and methanol, considering the implicit oligomerization reactions. The approach shows good agreement with experimental data and accurately predicts the VLE of ternary formaldehyde + water + methanol mixtures.