Solubility data for Nitrous Oxide (N2O) and Carbon dioxide (CO2) in Piperazine (PZ) and a new eNRTL model
Ardi Hartono, Rafiq Ahmad, Shahla Gondal, Hallvard F. Svendsen
Abstract
A new set of VLE data for low and medium pressures and data for N2O solubility in aqueous piperazine (PZ) solutions are provided as function of temperature and CO2 loading. Together with VLE data from literature, these data were used for parameter fitting in an eNRTL model for the CO2/water/PZ system in a sequential procedure from pure PZ via the binary water/PZ and to the ternary CO2/water/PZ system. New Antoine parameters and new binary interaction parameters are proposed. The NRTL model predicts well the VLE data, the SLE data, the calorimetric data and the activity coefficient of PZ. The two dissociation constants for PZ and PZH+ were refitted from literature data and used in the ternary parameter fitting. The eNRTL model predicts well the ternary data, for PCO2 (AARD = 22.8%), for PT (AARD = 20.9%) and N2O solubility (AARD 4.7 %), The volatility of PZ as function of concentration, temperature and loading is also well predicted at high concentrations of PZ but under-prediction was seen at low concentrations. Good predictions were also obtained for the heat of reaction of the PZ/H2O/CO2 system with the most significant contributions from piperazine protonation up to a loading of 0.4, PZCO2− formation up to loading about 0.6 and zwitterion formation up to loading 1. Dicarbamate and bicarbonate are formed but play minor roles. Above loading 1 mole CO2/ mole PZ, only the heat of CO2 dissolution plays an important role in the total heat of reaction.