Modeling piperazine thermodynamics

A thermodynamic model in Aspen Plus®Â was developed to predict properties of piperazine (PZ)/H2O and PZ/H2O/CO2. A sequential regression was performed to represent recently acquired loaded and unloaded heat capacity, CO2 solubility, CO2 activity coefficient, speciation, and unloaded and loaded amine volatility data. The resulting model is able to predict each of these properties over operationally significant loading and temperature ranges (0.20−0.40 mol CO2/mol alkalinity and 40 °C−160 °C). The predicted heat of absorption for 8 m PZ solution at 0.35 mol CO2/mol alkalinity between 40 °C and 160 °C was 65±4 kJ/mol CO2. The temperature dependence of the heat of absorption was predicted using three analytical methods, each of which predicted different trends but similar ranges between 40 °C and 160 °C. The sequential regression methodology has also been applied to methyl-diethanolamine (MDEA) and MDEA/PZ. Ultimately this thermodynamic model will be modified in Aspen Plus®Â to predict kinetic and transport data as well, and the resulting model will be used to design and optimize a post-combustion absorption/stripping process.