text 2016 06 29

Page 1

Andrea Landella POLITECNICO DI MILANO Industrial Organic Chemistry Exam Jun 29, 2016 A mixture of n-hexane, n-octane and n-decane (0.25, 0.6, 0.15 v/v), initially at 250 °C and 8 bar, is fed to an isothermal flash unit, where thermodynamic equilibrium conditions are reached. The flash is operated at 2 bar and 155 °C. The vapor phase can be described as an ideal mixture of ideal gases and the liquid mixture is ideal. The Poynting correction is assumed to be negligible. 1. Calculate the extent of vaporization and thermal duty of the flash (assume as positive the heat entering in the system) V-101 Q≠0 F, TF, PF, z V, y L, x Tfls Pfls RESULTS: Extent of vaporization Thermal Duty 2. Calculate amount and composition of the vapor and liquid streams leaving the flash unit. RESULTS: Liquid amount Vapor amount n-hexane n-octane n-decane Liquid composition Vapor composition 3. Evaluate the maximum temperature at which the flash can operate at 2 bar: RESULTS: temperature Andrea Landella POLITECNICO DI MILANO DATA Antoine’s equation (PVAP in bar, T in K) Ai Bi Ci log10 𝑃𝑉𝐴𝑃 = 𝐴𝑖 − 𝐵𝑖 𝑇 + 𝐶𝑖 n-hexane 4.00266 1171.530 -48.784 n-octane 4.04867 1355.126 -63.633 n-decane 4.07857 1501.268 -78.670 Thermodynamic properties 𝐶𝑝,𝐿𝐼𝑄 [J/mol/K] 𝐶𝑝,𝑉𝐴𝑃 [J/mol/K] ∆𝐻𝑒𝑣𝑎𝑝 [J/mol] 𝑃𝐶 [bar] 𝑇𝐶 [K] 𝜔 [−] n-hexane 195.6 143.3 31573 30.1 507.5 0.299 n-octane 255.7 175.9 41495 24.9 568.8 0.398 n-decane 313.3 233.1 51392 21.2 617.7 0.489 The heat capacities for the vapor and gas phase and the liquid densities can be considered constant. The enthalpies of vaporization are given at the flash temperature.