text 2016 02 12

Pagina 1

Andrea Landella POLITECNICO DI MILANO Industrial Organic Chemistry Exam Feb 12, 2016 A mixture of n-hexane, n-octane and n-decane (0.4, 0.3, 0.3), initially at 220°C and 15 bar, is isoenthalpically expanded in a lamination valve and fed to an adiabatic flash unit, where thermodynamic equilibrium conditions are reached. The vapor phase can be described as an ideal mixture of ideal gases and the liquid mixture is ideal. V-101 Q=0 F, TF, PF, z V, y L, x Tfls Pfls The Poynting correction is assumed to be negligible. 1. Evaluate the state (liquid, vapor or liquid-vapor) of the feed stream; 2. Calculate the temperature and pressure of the flash, which are required to achieve an extent of vaporization equal to 30% ( = 0.30); RESULTS: Flash temperature Flash pressure 3. Calculate amount and composition of the vapor and liquid streams leaving the flash unit. RESULTS: n-hexane n-octane n-decane Liquid composition Vapor composition 4. By removing the hypothesis of negligible Poynting correction, evaluate the effect of the Poynting correction on the prediction of the temperature and pressure of the flash. RESULTS: Flash temperature Flash pressure 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 z 𝐶𝑝,𝐿𝐼𝑄 [J/mol/K] 𝐶𝑝,𝑉𝐴𝑃 [J/mol/K] ∆𝐻𝑒𝑣𝑎𝑝 [J/mol] 𝜌𝐿𝐼𝑄 [g/cm3] PM [kg/kmol] n-hexane 0.4 195.6 143.3 31573 0.659 86.18 n-octane 0.3 255.7 175.9 41495 0.703 114.23 n-decane 0.3 313.3 233.1 51392 0.730 142.29 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 normal (1 atm) boiling temperature for…