Pressure distillation ethylene/ethane fractionator

A distillation process has been set up to separate an ethylene-ethane mixture as shown in Fig. P4.94. The product stream will consist of 98% ethylene and it is desired to recover 97% of the ethylene in the feed. The feed, 1000 lb per hour of 35% ethylene, enters the preheater as a subcooled liquid (temperature = — 100 F, pressure = 250 psia). The feed experiences a 20 F temperature rise before it enters the still. The heat capacity of liquid ethane may be considered to be constant and equal to 0.65 Btu/(lb)(°F) and the heat capacity of ethylene may be considered to be constant and equal to 0.55 Btu/(lb)("F). Heat capacities and saturation temperatures of mixtures may be determined on a weight fraction basis. An optimum reflux ratio of 6.1 lb reflux/lb product has been previously determined and will be used. Operating pressure in the still will be 250 psia. Additional data are as follows ... 

II. Pressure effects—Changing split. Suppose we want to split between the C2 and the C3 conpounds (ethane and ethylene are in distillate and ever54hing else in bottoms). Change the value for distillate flow rate in Aspen Plus to achieve this. Operate at pressure of 15 atmospheres. Use the same settings as previously. Run Aspen Plus. Compare the temperature in the condenser to the tenperature in run I.c. (also at 15 atm). What can you conclude Report distillate and bottoms mole fractions and temperatures. 

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