Measurements and modeling of high-pressure phase behavior of binary CO2–amides systems

High-pressure vapor–liquid equilibrium (VLE) data were measured for binary CO2–N,N-dimethylformamide, CO2–N,N-diethylformamide and CO2–N,N-dibutylformamide systems at various temperatures (318.2–398.2 K) and pressure up to 25 MPa. These CO2–N,N-dimethylformamide, CO2–N,N-diethylformamide and CO2–N,N-dibutylformamide systems exhibits type-I phase behavior, which is characterized by an uninterrupted critical mixture curve which has a maximum in pressure. The solubility of N,N-dimethylformamide, N,N-diethylformamide and N,N-dibutylformamide for the CO2–N,N-dimethylformamide, CO2–N,N-diethylformamide and CO2–N,N-dibutylformamide systems increases as the temperatures increases at constant pressure. The CO2–N,N-dimethylformamide, CO2–N,N-diethylformamide and CO2–N,N-dibutylformamide systems have continuous critical mixture curves that exhibit maximums in pressure at temperatures between the critical temperatures of CO2 and N,N-dimethylformamide, N,N-diethylformamide or N,N-dibutylformamide. Also, three phases were not observed of any of the systems studied. In each systems, the mixture critical point increases as the temperatures increases, and also the mixture critical pressure does as molecular weight increases. perimental results for CO2–N,N-dimethylformamide, CO2–N,N-diethylformamide and CO2–N,N-dibutylformamide systems is modeled using the Peng–Robinson equation of state. A good fit of the calculated data is obtained with the Peng–Robinson equation of state.