Exercise 05 Solution ENG

Pagina 1

1 Dipartimento di Chimica, Materiali e Ingegneria Chimica “Giulio Natta” POLITECNICO di MILANO Practical class (informatic laboratory) of Chemical Processes and Technologies (Prof. Stefania Moioli) 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 Material balances can be solved using the two recovery specifications for n -hexane (lk component) and n-heptane (hk component) assuming that n -pentane (light nonkey) is recovered in the distillate only and n-octane (heavy nonkey) is recovered in the bottoms only. The amount of each component in the top product stream and in the bottom product stream is reported, respectively, in Table 1 and in Table 2 (assuming F = 100 [kmol/h]). Table 1. Molar flow rate [kmol/h] of each component in the top product stream (D). i n-C5 n-C6 (lk) n-C7 (hk) n-C8 D∙xi,D [kmol/h] 4.00 39.20 0.50 0.00 Table 2. Molar flow rate [kmol/h] of each component in the bottom product stream (B). i n-C5 n-C6 (lk) n-C7 (hk) n-C8 B∙xi,B [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 (xi,D) and in the bottom product (xi,B). i n-C5 n-C6 (lk) n-C7 (hk) n-C8 xi,D [-] 0.091533 0.897025 0.011442 0.000000 xi,B [-] 0.000000 0.014210 0.879218 0.106572 2 The Fenske’s equation is used to determine Nmin. To use it, it is necessary to calculate 3 , , ,lk lk top lk bottom lk feed   =   , with the three relative (relative to the hk component) volatilities calculated at the following three temperatures (also the thermal conditions of the feed stream are considered since it is at its bubble point): • dew point temperature of the distillate product:…