Vapor–liquid equilibria of NH3 in (NH3 + H2O) and (NH3 + PZ + H2O) system

Volatility is an important issue for aqueous ammonia used as an absorbent for post-combustion CO2 capture. Vapor–liquid equilibrium (VLE) of NH3 in aqueous ammonia and aqueous blends of ammonia and piperazine (PZ) were measured at 20 °C, 30 °C and 40 °C. The experimental VLE results for NH3 cover the mole fraction ranges 2.5–15% NH3 (aq) in aqueous ammonia and 2.5–15% NH3 in the 0.4 M PZ blended solutions. Vapor pressures of NH3 for 5%, 10% and 15% NH3 (aq) were compared with available data in the literature. Activity coefficients for NH3 in NH3 (aq) and aqueous blends of NH3 + PZ were calculated and compared for different temperatures to obtain the effect of PZ on the volatility of aqueous ammonia. The eNRTL model was used to model the results and a comparison between model predictions and experimental data shows good agreement.