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The equilibrium behaviors of two-phase liquid−liquid systems composed of poly(ethylene glycol) (PEG) 1500 or 4000 + sodium sulfite + water were experimentally determined at temperatures of (288.15, 298.15, 308.15, and 318.15) K. The effects of the molecular weight of PEG and the temperature on the phase separation were studied. The binodal curves were fitted to an empirical equation that correlates the concentrations of PEG 1500 or 4000 and sodium sulfite, and the coefficients for the different temperatures were estimated. The tie-line compositions were estimated and correlated using the Othmer−Tobias and Bancroft equations, and the parameters are reported. The liquid−liquid equilibrium (LLE) experimental data obtained were wellcorrelated to the activity coefficients of the non-random two-liquid (NRTL) and UNIversal QUAsiChemical (UNIQUAC) models, and the mean deviations were less than 0.36 % and 0.31%, respectively.

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Um algoritmo geral para resolver problemas inversos lineares e não lineares, baseado em redes neurais recursivas, é discutido neste trabalho. O procedimento será aplicado a problemas físico-químicos modelados por equações integrais, diferenciais e de autovalor. As aplicações são discutidas em espectroscopia de aniquilação de pósitrons, cinética química e espectroscopia vibracional. O método é robusto com relação a erros nas condições iniciais ou em dados experimentais. A presente abordagem é simples, numericamente estável e tem uma grande aplicabilidade.A general algorithm to solve linear and nonlinear inverse problems, based on recursive neural networks, is discussed in this work. The procedure will be applied to physical chemical problems modeled by integral, differential and eigenvalue equations. Representative applications discussed are in positron lifetime spectroscopy, chemical kinetics and vibrational spectroscopy. The method is robust with respect to errors in the initial condition or in the experimental data. The present approach is simple, numerically stable and has a broad range of applicability.

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