Vapour liquid equilibria of carbon dioxide in dilute and concentrated aqueous solutions of piperazine at low to high pressure

This work presents new experimental results for carbon dioxide (CO2) solubility in aqueous piperazine (PZ) in the temperature range of (298–328) K and CO2 partial pressure of about (0.1–1500) kPa. The concentrations of the aqueous PZ were in the range of about (0.2–4.5) M. A thermodynamic model based on electrolyte nonrandom two-liquid (ENRTL) theory has been developed to correlate and predict the vapour–liquid equilibrium (VLE) of CO2 in aqueous PZ. The model predictions have been in good agreement with the experimental data of CO2 solubility in aqueous blends of this work as well as those reported in the literature. It is observed that, at low temperature (up to 333 K) and low PZ concentration, using regressed ENRTL interaction parameters and Henryʹs constant of CO2 in water is sufficient to predict VLE of CO2 in aqueous PZ. However, at high temperature and high PZ concentration, it is required to adjust Henryʹs law constant in aqueous solution of PZ for better prediction of CO2 partial pressure over aqueous PZ solution. The current model can also predict speciation, heat of absorption, pH of the loaded solution, and PZ volatility.