Determination And Analysis Of Phase Equilibrium And Physical Parameters For 1,4-Bis-(2-hydroxypropyl)-Piperazine-na~+ Aqueous Two-phase System

1,4-Bis-(2-hydroxypropyl)-piperazine(HPP)is a new type of renewable organic amine flue gas desulfurization agent.The impurity ions produced by flue gas and smoke dust are brought into HPP absorbent and accumulate continuously in recycling process.Heat stable salts(HSS)produced by the ions,especially SO42-oxidized from SO32-continuously during the desulfurization process,affect the regeneration and absorbability of HPP absorbent.In this paper,a new method and important basic parameters for the removal of HSS from the renewable organic amine desulfurizer system are provided by the separation of ions forming HSS from HPP absorbent using aqueous two-phase system(ATPS)method.At the temperatures of 30 ℃-50 ℃,the binodal curves for the ATPS composed of HPP-Na2SO4-H2O have been determined by the cloud point method and the liquid liquid phase equilibrium data of the ATPS has been measured by phase component analysis method.The binodal data and liquid liquid phase equilibrium data have been correlated by empirical equation and NRTL model respectively.Moreover,the surface tension,viscosity,density and refractive index of the conjugated top and bottom phase have been determined at different total concentration in the experimental temperature range.The results show that temperature has no significant effect upon the biphasic region,implying a small enthalpy contribution during phase separation.The correlation coefficients of Merchuk equation based on the weight analysis and the binodal data of ATPS are approximately 0.999 with only three equation parameters.The associated NRTL equation parameters meet the requirements of the practical calculation and engineering application,because the root-mean-square deviation(RMSD)and the average absolute deviation(AAD)of calculated and experimental values are lower than 2%and 1.5%respectively.The determination of binodal curves and liquid liquid equilibrium data for the HPP-Na2SO3-H2O ATPS has been taken by the cloud point method and phase component analysis method respectively at the temperatures of 30 ℃-50 ℃,and the correlation has been carried out by the empirical equation and the NRTL model respectively.Furthermore,the physical parameters of the conjugated two phase have been measured at different total concentration.Experimental results show that the phase diagram of HPP-Na2SO3-H2OATPS has little change with temperature at the experimental temperature,implying a small enthalpy contribution during phase separation.The empirical equation has high correlation coefficient for the correlation of the binodal data.Noteworthy,the correlation coefficients of phase diagram for HPP-Na2SO3-H2O and Merchuk equation are all greater than 0.999.The RMSD and AAD of calculated values of NRTL model and experimental values are lower than 2%and 1.7%,respectively.The effect of pH value and temperature on the stability of HPP-Na2SO4-H2O ATPS has been investigated.Furthermore,SO42-、NO3-、Cl-、K+、PO43-and 5O32-are selected to study the separation performance in the ATPS.The results of the analysis show that,the pH value of the HPP-Na2SO4-H2O phase disappearing decreases gradually with the increase of HPP concentration,and the pH value of the two phases disappearing decreases gradually with the increase of temperature in the same total concentration.The variation trend of distribution coefficient in the two phases with temperature is related to the spatial structure of ions,in which the anion distribution coefficient is influenced by the number of charges and the ion salting out capacity.The distribution coefficient of the above ions in the HPP-Na2SO4-H2O ATPS descends first and then changes indistinctly with the rising of the pH value.There is no obvious change in the distribution coefficient of K+ and Cl-when the pH value is greater than 9.50,and of NO3-and SO42-when the pH value is greater than 11.00.Because SO32-and PO43-are all moderately strong acid roots,the change of their distribution coefficients is related to the existence form in different pH values.In view of the application of HPP in the process of decarbonization,the phase diagram and liquid-liquid phase equilibrium data of the HPP-Na2CO3-H2O ATPS have been measured and related at the temperatures of 30 ℃-50 ℃.Meanwhile,admeasurement of ATPS physical parameters have been measured.The results show that the two phase region of the HPP-Na2CO3-H2O ATPS increases slightly with the temperature rising at the experimental temperatures,but small enthalpy contribution the influence phase separation.The empirical equation w1= exp(α+bw20.5+cw2+dw22)has high correlation coefficients to the binodal data,which are all higher than 0.999.The correlation between NRTL model and the three phase two-phase equilibrium data is very high with the the RMSD and AAD lower than 2%and 1.5%respectively.The associated NRTL equation parameters are applied in practical calculation and engineering application.