CHE 354-002 Spring 2015
Final Exam
This exam is closed book and notes. This exam is worth a total of 100 points. The individual point values are listed to the left of each question. Additional paper is available from the instructor. A sheet of equations that you may need is attached. You have 150 minutes to complete the exam. Partial credit is available, so SHOW ALL WORK.
( 15 pts.) 1) To study the kinetics of an enzyme-catalyzed reaction, the enzyme was incubated with its
substrate and the reaction rate was measured. Additionally, the enzyme and substrate were incubated with three different types of inhibitors (in three separate reactions). The experimental data was linearized on the Lineweaver-Burk plot below. Indicate which of the lines below represents the case with no inhibitor and name the type of inhibitor in the other three cases.
a)
b)
c)
d)
e) Calculate the KM and vmax for the enzyme reaction above.
f) If the enzyme reaction is run in a batch reactor (CS0 = 30 mmol/L) without inhibitors present, how long will it take to reach a conversion of 95%?
( 15 pts.) 2) The elementary reaction A + B → D is to be carried out to obtain a desired product (D). The rate constant for this reaction is k1 = 150*exp(-5,000/T). Unfortunately, under conditions required for the reaction to occur, species B also undergoes a second-order decomposition to form. an undesired product, B → 2U, with ru = k2 CB(2), and k2 = 300*exp(-2,000/T).
a) What is the instantaneous selectivity for this system (SD/U)? Your answer must be simplified as much as possible.
b) Assuming this is a liquid-phase reaction, describe two different reactor systems (draw a
schematic AND describe with words) and operating conditions you would use to maximize the selectivity to D.
( 15 pts.) 3) Consider the set of liquid phase, elementary series reactions to be carried out in a 10 dm3 batch reactor. The reaction occurs at 300K, where k1 = 0.6 h-1 and k2 = 0.25 h-1 . The reaction starts with 4 mol/dm3 pure A.
a) Sketch a plot of the concentrations of each species versus time. You don’t have to be exact, just give the shape of each curve.
b) How long will it take to reach a maximum concentration of B?
c) Assuming the answer to part (b) is 2.5 h (this may or may not be correct), calculate CA, CB, and CC at that time.
(25 pts.) 4) The irreversible, elementary gas-phase reaction A + B → C + D takes place in an isothermal (T = 400K) packed bed reactor with pressure drop. Calculate the conversion exiting the reactor.
CA0 = 1 mol/dm3, CB0 = 2 mol/dm3, νo = 5 dm3/min, kA(400K) = 0.25 dm6/mol·min, α = 0.03 kg-1, W = 30 kg
Repeat for the case in which there is no pressure drop (α = 0).
Explain any difference (or lack thereof) between the two answers above.
(20 pts.) 5) The exothermic, liquid-phase reaction A → B + C is carried out in a 50 dm3 CSTR with a cooling coil. The feed stream is equimolar in A and B (CA0 = 5 mol/dm3 and νo = 2 dm3/min) and enters the reactor at 300 K. To avoid boiling of the liquid, the temperature in the reactor cannot exceed 350 K. Assume shaft work is negligible. Ethylene glycol enters the cooling coil at 270 K with a very high flow rate. CPA = CPB = CPC = 50 cal/mol·K, Ea = 15,000 cal/mol,
ΔHoRx = -10,000 cal/mol, U = 50 cal/ft2·min·K, kA(300 K) = 0.02 dm3/mol·min.
a) What is the maximum conversion that you could obtain in this system?
b) What surface area must your cooling coil have to maintain the conversion in part (a)?
( 10 pts.) 6) The reaction in problem 6, A → B + C, is to be carried out in a PFR with a co-current heat exchanger instead of the CSTR. Set up the equations that you would need to solve for conversion AND to plot and analyze the reactor and coolant temperatures as a function of PFR volume. Include all equations that you would need to enter into Polymath except for explicit equations defining constants or initial and final conditions.