QUESTION

A feed consisting mixture of hydrocarbons according to the composition shown in Table 2 is to be separated by distillation at atmospheric pressure. The recovery of n-heptane in the distillate is 99.1% and 98.7% n-octane is recovered at the bottom. The system is operating with partial reboiler and total condenser and the feed introduced to the tower at a saturated vapour condition. The K value for the component can be determined from the DePriester Chart.

a) If the K value for the heavy key component is 0.7 at the average temperature of the column, determine the temperature and minimum number of stages at total reflux. (Hint: You can use the average temperature for all calculations involve in the shortcut method)

b) Determine the number of theoretical stages and the location of feed tray at the operating reflux ratio R of 1.5 Rmin

c) How will the separation differ if the reflux ratio is decrease to 1.2 Rmin? What will happened to the number of stages required and why?

Table 2: The flowrate of components in feed stream Feed (kmol/h) n-pentane 11.8 n-hexane 4 n-heptane 11.3 n-octane 7.7 n-nonane 10.4