20220622 Exam Solution

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1 Chemical Processes and Technologies (Ing. Giorgia De Guido) Exam June 22nd, 2022 - Exercise: Solution Exercise no. 1 (of 2) A mixture of i- butane and n- butane is separated in the so -called “C4 splitter” (a standard trayed distillation column), which is operated at 9 bar. The mixture is available at its bubble -point temperature at the operating pressure o f the column and is characterized by a content [mol%] of i-butane as reported in the Data section below. The aim is to obtain a top product that contains 99 mol% i-butane and a bottom product that contains 98 mol% n-butane. Assuming an ideal thermodynamic behaviour for the system and a total molar flow rate of the feed stream as reported in the Data section below, please determine: 1. the total molar flow rate [kmol/h] of the distillate and bottom products and how much i-butane is recovered, respectively, in these two products; 2. the value of the average relative volatility, explaining how it was calculated; 3. whether it is possible to operate the distillation column with a reflux ratio (R) equal to 12. If it is possible to operate the column with the value of R given at the previous point, determine: 4. the number of theoretical stages needed to achieve the desired separation, respectively, for the upper (enriching) section and for the lower (stripping) section of the column; 5. the thermal duty (in kW) required at the top condenser. If it is not possible to operate the column with the value of R given at point 3, assume a reflux ratio equal to 1.2·Rmin and solve points 4 to 5. Data: Mole percentage of i-butane in the feed stream = 530.5 M+ [mol%] Molar flow rate of the feed stream = 6(6 27)100 3 M⋅−+ [kmol/h] where: M5 = fifth digit of student number from the left (Student number/matricola = XXXXXX) M6 =…