Análise e simulação dos efeitos da variação de pressão e temperatura no teor de monômero residual em polímeros vinílicos em emulsão

Abstract

The residual monomer content is a concern in any chemical polymeric synthesis process as it is both a commercial specification and a storage safety parameter; since most reagents release large amounts of flammable vapors at room temperature. This care is even more restricted when working with polymers based on Vinyl Acetate, the so-called PVAs, widely used as additives in the paint, paper and high-performance adhesive industries. Vinyl Acetate has a low flash point (-8°C) and, therefore, requires actions that guarantee the presence of molecules in the aqueous phase to the detriment of the vapor phase, thus favoring the polymerization reaction. In general, in PVA syntheses, a longer reaction time is dedicated in order to guarantee that the monomer content reaches the specification, therefore increasing the cycle time of the process. In this work, NRTL, Wilson and UNIFAC thermodynamic models are used for the activity coefficient of the simplified Gamma – Phi equation in order to simulate an emulsion polymerization process in the Aspen Plus software and, subsequently, compare the results with real content data monomeric in the liquid phase obtained by gas chromatography (GC) during the reaction inside an isothermal semi-continuous reactor. After choosing the best model to represent the liquid-vapour balance in the reaction tank, sensitivity analyzes were performed in the simulation software itself to evaluate different thermodynamic operating conditions (temperature and pressure) in order to find specification pairs that reduce the reagent loss by evaporation and increase its conversion in the process. After the sensitivity analyses, it was found that an increase in the pressure and temperature set-points, within industrial safety limits, after the end of the feeding of the reagents to the vessel contributes to accelerating the consumption of monomer to the desired value and, therefore, they reduce the time required for the process. Furthermore, after analyzing the simulation results and comparing them with the gas chromatograph responses, it was noticed that the three models accurately report the process phenomena, with emphasis on the Wilson correlation, which showed the smallest deviation.