Vapor-liquid equilibrium of monoethanolamine/piperazine/water at 35-70°C

The equilibrium partial pressures of monoethanolamine (MEA), piperazine (PZ), and water were measured in a stirred reactor with a recirculating vapor phase by FTIR analysis at 35 - 70 Celsius degrees. MEA and PZ volatility were measured in two separate pilot plant campaigns to capture CO₂ from flue gas under a range of absorber conditions. The laboratory data were regressed to determine NRTL binary interaction parameters that predicted the experimental points within 10 - 20%. It was proven that MEA volatility (0.45<MEA<0.55) is a viable concern in CO₂ capture processes from an economic, environmental, and overall health perspective. PZ, on the other hand, was not observed to be as volatile (0.06<PZ<0.08) as predicted by previous models and therefore volatility loss would not be a significant drawback for using it as a CO₂ capture solvent. Pilot plant results show an average MEA gas phase concentration at the absorber outlet to be approximately 45 ppm while the PZ concentrations averaged 6 ppm and 8 ppm at the absorber inlet and outlet, respectively.