Use the Peng-Robinson equation (kij = 0) to determine the phase envelope of ethane n-heptane at compositions of xC7 = [0, 0.1, 0.2, 0.3, 0.5, 0.7, 0.9, 1.0]. Plot P versus T for each composition by performing bubble-pressure calculations to their terminal point and dew-temperature calculations until the temperature begins to decrease significantly and the pressure approaches its maximum. If necessary, close the phase envelope by starting at the last dew-temperature state and performing dew-pressure calculations until the temperature and pressure approach the terminus of the bubble-point curve. For each composition, mark the points where the bubble and dew curves meet with X’s. These X’s designate the “mixture critical points.” Connect the X’s with a dashed curve. The dashed curve is known as the critical locus of the mixture.
