SO₂ Solubility In Aqueous Of N,N’-bis（2-hydroxypropyl） Piperazine Sulfate Solution

Piperazine organic amine was widely used in flue gas desulfurization (FGD) because of its high absorbtion selectivity of SO2, low loss of absorbent and no recontamination. In this work, the solubility of SO2 in aqueous solution of N,N’-bis(2-hydroxypropyl) piperazine (HPP) sulfate was measured and a modified Kent-Esienberg model was developed.Firstly, the solubility of low-concentration SO2 (the SO2 partial pressure range from 100 to 500 Pa) and desulfurization efficiency curve in HPP sulfate aqueous solution was measured. The results show that low temperature, high HPP concentration and partial pressure of SO2 were favorable for SO2 solubility. For example, the SO2 solubility decreases 0.064 mol/L (17.6%) with the temperature raising from 298 K to 303K at the condition of the HPP concentration (0.488 mol/L) and the constant SO2 partial pressure (102 Pa), while it increases 0.068 mol/L (26.1%) with the HPP concentration increasing from 0.754 mol/L to 1.005 mol/L at 328K and the constant SO2 partial pressure (103 Pa). The desulfurization efficiency curves show that the penetrating time decreases with temperature raising and HPP concentration reducing. Such as the penetrating time was 12h at 308K while 8h at 328K in 0.488 mol/L HPP sulfate aqueous solution. And it was 15h in 0.754 mol/L HPP sulfate aqueous solution and 19h in 1.005 mol/L HPP sulfate aqueous solution at 298K.Then the chemical reaction equilibrium, absorption phase equilibrium, as well as material equilibrium and charge conservation were investigated in SO2-HPP-H2SO4-H2O system. In this work, the Kent-Esienberg model was established based on the chemical reaction and physical absorption. The gas phase can be approximately regarded as ideal because the solubility data was measured under atmospheric pressure. And the liquid phase non-idealities were represented by pseudo-equilibrium constants. Additionally, the dissolution heat of SO2 into HPP sulfate aqueous solution was calculated by Gibbs-Duhem equation. The results indicate that the physical dissolution was the most important step, so Henry’s constant should be used as the pseudo-equilibrium constant in high-concentrationSO2 absorption (the SO2 partial pressure ranges from 7.50 to 101.12kPa). While in low-concentration SO2 absorption, the chemical reaction was the critical process, as a result the HPP secondary dissociation constant was selected to be the pseudo-equilibrium constant. The average relative error between the calculated values and the experiment were 5.7% for high-concentration and 3.2% for low-concentration SO2 solubility, which can satisfy the industrial application. Besides, the dissolution heat increases with absorption loading and temperature has little effect on it.