Chemical Engineering - Chemical Reaction Engineering and Applied Chemical Kinetics

Full exam

CRE – 28.09.15 - Exam C 1 096116 Chemical Reaction Engineering 28 September 2015 Family name _________________________________________________ First name _________________________________________________ ID number _________________________________________________ Signature _________________________________________________ Please, consider that the sum of percentages of proposed exercises (5) is equal to 110%. This means that the maximum mark you can reach is 33. Remember to write on the top of each sheet you submit: your name, ID number, and signature. Use of mobile phones and internet connection is not allowed. 1. Second order reaction in a CSTR (25%) The following second-order liquid-phase reaction is taking place in a CSTR: ������������+������������→2������������+������������ A and B are fed to the reactor at rates of 3 mol/min and 1 mol/min respectively at a temperature of 300 K. The total volumetric flow rate is 5 l/min. Specific heats (in J/mol/K) of A, B, C and D are 125, 100, 130 and 135 respectively. The reactor is jacketed by water at a temperature of 40°C. The overall heat transfer coefficient has been estimated at 200 J/m2/s/K, while the heat transfer area is 0.5 m2. Mixing is ensured through an agitator, which contributes a work of 10 kW to the reactor. The heats of formation of A, B, C and D (at 298 K) are -45 kJ/mol, -30 kJ/mol, -50 kJ/mol and -60 kJ/mol respectively. The rate constant at 300 K is 0.1 l/mol/min and the activation energy is 30,000 J/mol. Find the steady-state temperature in the reactor for 90% consumption of the limiting reactant. Find the volume of the reactor to achieve this conversion. 2. Consecutive reactions in a batch reactor (20%) The following liquid-phase consecutive reaction is taking place in a constant volume batch reactor. ������������ ������������1→������������ ������������2→������������ The first reaction is first order and the second reaction is zero order. a) Determine the concentrations of A, B and C as functions of time. b) If at time t=0 only A and B are present (with concentrations equal to 1 mol/l and 0.2 mol/l, respectively), what is the concentration of species C after 10 min? Assume that ������������1= 0.0001 ������������−1 and ������������2= 0.2 ������������������������������������ ������������3 ������������. 3. First-order reversible reaction in a CSTR (15%) A first-order reversible liquid phase reaction is carried out in a CSTR at 450°C, with the initial concentration of A being equal to 2 mol/l . CRE – 28.09.15 - Exam C 2 ������������↔ ������������ Following parameters are given: ⎩ ⎪ ⎨ ⎪ ⎧ ������������������������ ������������=40 ������������ ������������������������������������ ������������ ������������������������ ������������=40 ������������ ������������������������������������ ������������ ∆������������ 27°������������ =−80 ������������ ������������ ������������������������������������ � ������������������������������������(27 °������������)=2∙10 9 ������������(327°������������ )=1 ℎ������������ −1 ������������=30,000 ������������/������������������������������������ Determine the res idence time in the reactor for 75 % equilibrium conversion . 4. First-order reaction in a packed bed reactor (30%) TA first-order, gas-phase reaction ������������→������������ is performed in a PBR at 500 K and 20 atm. Feed rate is 10 mol/s containing 20% A and the rest inerts. The PBR is packed with 8 mm-diameter spherical porous particles. The intrinsic reaction rate is ������������ ′= ������������������������ ������������, where ������������=3.75 ������������ ������������������������ ������������������������������������ ������������. Bulk density of the catalyst is 2.3 kg/l . The diffusivity is 0.1 cm2/s. The pressure drop parameter is found to be ������������=9.8∙10 −4 ������������������������ −1. a) What is the value of the internal effectiveness factor? What does it signify? b) How much catalyst (kg) is required to obtain a conversion of 75% in the reactor? c) Find the pressure at the exit of the reactor. 5. PFR followed by a CSTR (20%) A reversible reaction ������������↔������������ is taking place in a PFR. The equilibrium constant (in terms of concentrations) is 2 The conversion which is obtained is 40% of equilibrium conversion. A CSTR of equal size is placed downstream of the PFR (PFR-CSTR) to increase conversion. What is the total conversion in the reactor sequence with this arrangement?