Phase behavior measurement of the binary carbon dioxide–N,N-dimethylacetamide and carbon dioxide–N,N-diethylacetamide systems at high pressure

Pressure-composition isotherms are obtained for the carbon dioxide–N,N-dimethylacetamide (N,N-DMA) and for the carbon dioxide–N,N-diethylacetamide (N,N-DEA) systems at 40, 60, 80, and 100°C. These two carbon dioxide–polar solute systems have continuous critical mixture curves that exhibit maximums in pressure at temperatures between the critical temperatures of carbon dioxide and N,N-DMA or N,N-DEA. The experimental data are modeled using the multi-fluid-nonrandom lattice fluid (MF-NLF) equation of state. The coefficient of energy and volume parameters for each pure N,N-DMA or N,N-DEA is determined from a fit of the vapor pressure curve and saturated liquid densities. A good fit of the data is obtained with the MF-NLF equation using one adjustable mixture parameter that is temperature-independent, for the carbon dioxide–N,N-DMA and carbon dioxide–N,N-DEA systems.