Novel phase diagrams of aqueous two-phase systems based on 1,4-bis-(2-hydroxypropyl)-piperazine + Na2CO3 + H2O: Equilibrium data and correlation

Abstract

Aqueous two-phase system (ATPS) has been regarded as a potential method for removing heat-stable salts (HSS) in 1, 4-bis-(2-hydroxypropyl)-piperazine (HPP). In this work, the binodal and liquid-liquid equilibrium data of the HPP + Na2CO3 + H2O system have been determined by cloud point and phase component analysis methods at a series of temperatures. It is well revealed that the effect of temperature on the system presents minor variations in the biphasic region. The binodal data are fitted by polynomial and empirical equations, and NRTL model is employed for fitting the liquid-liquid equilibrium data. The results reveal that the binodal data is adequately correlated with the empirical equation, with a correlation coefficient R2 greater than 0.99 and standard deviations (SD) less than 0.02%. The NRTL model is in good accordance with the liquid-liquid equilibria data, with a relative root mean square deviations (RMSD) between the calculated and the experimental values are lower than 1.70%, and the average absolute deviations (AAD) are lower than 1.30%. Thereby, the parameters of equations and NRTL model are consistent with the actual calculation and engineering application requirements. The ATPS method for removing HSS is expected to be applied for other CO2 capture process using alcohol amines as absorbents.