Exercise 06 Solution ENG

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Assignment #6: Results Multicomponent distillation a) Number of ideal trays required to recover 98% of n -hexane and 1% of n -heptane in the top product stream Assuming F = 100 [kmol/h], the amount of each component in the top product stream and in the bottom product stream is reported in Table 1 and in Table 2. Table 1. Molar flow rate of each component in the top product stream. i nC5 nC6 (lk) nC7 (hk) nC8 D·xD,i [kmol/h] 4.00 39.20 0.50 0.00 Table 2. Molar flow rate of each component in the bottom product stream. i nC5 nC6 (lk) nC7 (hk) nC8 B·xB,i [kmol/h] 0.00 0.80 49.50 6.00 The corresponding compositions (in terms of mole fractions) are summarized in Table 3. Table 3. Mole fractions of each component in the top product (xD,i) and in the bottom product (xB,i). i nC5 nC6 (lk) nC7 (hk) nC8 xD,i [-] 0.091533 0.897025 0.011442 0 xB,i [-] 0 0.014210 0.879218 0.106572 From the Fenske correlation, Nmin = 9.35 (𝛼̅lk = 2.4788). From the two Underwood minimum-reflux equations, θ =1.49 and Rmin = 1.34. The number of ideal stages can be calculate d by using the Gilliland graphical correlation, or alternatively:  the Eduljee equation: ϕ(N) = 0.43  N = 18;  the Molokanov equation: ϕ(N) = 0.44  N = 18. Thus, the number of ideal trays required to perform the desired separation is 17. b) Thermal power required at the reboiler of the column ( RQ ) cQ = 1068 [KW]; RQ = 1103 [KW].