A procedure is presented for designing supercritical gas extraction processes using a pure solvent fluid to effect the separation. The necessary conditions for the procedure to be applicable are the existence of crossover behavior and separable crossover pressures in the fluid phase mixture. Data are presented to support the existence of such phenomena in ternary systems, and an actual separation process has been designed and operated based upon the data. For systems exhibiting this behavior, process synthesis principles are developed to illustrate the evolution of a process flowsheet for the separation of a mixture into its pure components.

Table IV. Comparison of Experimental Solubilities of Ammonium Bromide and Ammonium Iodide in Liquid Ammonia with Literature Values solubility, wt % solute temp, °C lit.0 obsd6 dev, % ammonium bromide 9.2 69.3 (5) 69.29 -0.01 20.0 69.7 (5) 70.22 . +0.74 32.6 70.4 (5) 71.59 +1.70 53.6 71.2 (5) 72.34 +1.60 25 70.4 (3) 70.75 +0.50 ammonium iodide 2.5 77.2 (5) 77.17 -0.04 22.6 78.6 (5) 78.47 -0.17 44.2 80.0 (5) 79.34 -0.83 57.0 80.9 (5) 81.50 +0.74 25 78.7 (4) 78.64 -0.09 0 (5) Kendall's data; (3) and (4) Hunt's data. 6 Smoothed value from observed data.1 % with the data of Hunt (4) and Kendall (5). But the values of ammonium bromide in liquid ammonia at 32.6 and 53.6 °C were 1.7 and 1.6% larger than those of Kendall (5).No literature data have been available for mixtures of ammonium halides in liquid ammonia.The solubility curves against temperature are shown in Figure 2. The solubility of ammonium iodide is shown by a smoothed increasing curve. However, it was found that the solubilitytemperature curve for ammonium bromide and its mixture of ammonium iodide had a bend point on the solubility curve. With increasing weight ratio of ammonium iodide, the solubility increased and the bend point on the solubility curve gradually moved toward lower temperature. AcknowledgmentWe express our gratitude to Mr. A. Shimomura for his experimental work and Mr. A. Kurata for his useful suggestion.

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Models for gas separations with spiral‐wound membranes are developed and found to exhibit good agreement with experiments performed on N2/O2 mixtures. The two‐dimensional (2D) model can be accurately approximated by a one‐dimensional (1D) surrogate model when the spacer widths are chosen to make the channel pressure drops small. Subsequently, the separation of propane/propylene mixtures from the recycle purge stream of a polypropylene reactor is investigated. Assuming ideal gas is found to lead to significant overestimations in membrane stage cuts (sometimes more than 10%), an extent comparable to that associated with extrapolating constant olefin permeance from a low‐pressure condition. While olefin permeance can change significantly with pressure, using a constant‐permeance formulation can result in a small (< 2.5%) underprediction in stage cut if the value for the permeance is taken from the feed condition. Finally, membrane properties and costs necessary for a viable separation process are discussed.