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.

► VLE data of NH3 (aq) and NH3/PZ blends were measured at 20–40 °C.
► The effect of PZ on the volatility of aqueous ammonia was obtained.
► The activity coefficients of NH3 increased with addition of PZ to NH3 (aq).
► The eNRTL model is discussed and used to model the VLE results.
► The model predictions were in good agreement with the experimental data.