Determinação de dados experimentais de equilíbrio de fases para sistemas aquosos eletrolíticos contendo monoetileno glicol e modelagem a partir da teoria de soluções

Abstract

Throughout the regeneration process of monoethylene glycol (MEG), this compound is in mixtures with water and/or dissolved salts (mostly sodium chloride). Hence, it is essential to monitor the composition of the streams throughout the process in order to avoid the precipitation of salts in the pipelines and guarantee the product specification, MEG. To study the vapour-liquid equilibrium (VLE) of the water + MEG + NaCl ternary system under MEG regeneration conditions (from 300 to 1000 mbar and temperatures up to 413.15 K), experiments were performed using a modified Othmer ebulliometer. To determine the systems compositions in the ebulliometer it was also necessary experimental data of density and electrical conductivity, submitted to thermodynamic modelling using the ideal solution theory. The density and conductivity correlations of the data allowed to relate these properties to the system composition, guaranteeing complete data (P,T,x,y) in the ELV experiments. The system ELV data were then correlated using the UNIQUAC model, with the principle of maximum likelihood, where six parameters were adjusted. The density and electrical conductivity calculations of the system showed average and maximum errors of 0.00037 and 0.00213 g/cm³ in density and 0.615 and 3.776 mS/cm in conductivity, respectively. With the ELV model, absolute mean deviations of the vapor molar fraction were obtained: Δy = 0.0072 for the water + MEG system and Δy = 0.0099 for the ternary water + MEG + NaCl, indicating thermodynamic consistency.