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    • Levenspiel 3rd Edition - Problems Checklist
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  • Reactor Combinations for Single Reactions

    • Second Order Reaction in Two MFRs in Series Page
      Levenspiel3E-6-1
      A liquid reactant stream (1 mol/liter) passes through two mixed flow reactors in a series. The concentration of \(A\) in the exit of the first reactor is 0.5 mol/liter. Find the concentration in the exit stream of the second reactor. The reaction is second order with respect to \(A\) and, the volume of second reactor is twice that of first reactor i.e., \(V_2 = 2V_1\).
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    • Radioactive Reaction in Two MFRs in Series Page
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      Levenspiel3E-6-2
      Water containing a short-lived radioactive species flows continuously through a well-mixed holdup tank. This gives time for the radioactive material to decay into harmless waste. As it now operates, the activity of the exit stream is 1/7 of the feed stream. This is not bad, but we would like to lower it still more.

      One of our office secretaries suggests that we insert a baffle down the middle of the tank so that the holdup tank acts as two well-mixed tanks in series. What is the expected activity of the exit stream compared to the entering stream?
      1 / _________ of the feed stream (round off to 1 decimal place)

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    • MFR followed by PFR for Second Order Reaction Page
      Levenspiel3E-6-3
      An aqueous reactant stream (4 mol \(A\)/liter) passes through a mixed flow reactor followed by a plug flow reactor. Find the concentration at the exit of the plug flow reactor if in the mixed flow reactor \(C_A=1\) mol/liter. The reaction is second-order with respect to \(A\), and the volume of plug flow unit is three times that of the mixed flow unit.
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    • PFR Replacing Two MFR in Series Page
      Levenspiel3E-6-5
      Originally we had planned to lower the activity of a gas stream containing radioactive \(\ce{Xe}\text{-138}\) (half-life = 14 min) by having it pass through two holdup tanks in series, both well mixed and of such size that the mean residence time of gas is 2 weeks in each tank. It has been suggested that we replace the two tanks with a long tube (assume plug flow). What should be the mean residence time of gas in this tube for the same extent of radioactive decay?
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    • Radioactivity at the End of Two CSTRs in Series Page
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    • Kinetics from MFR Page
      Levenspiel3E-6-16
      Using a color indicator which shows when the concentration of \(A\) falls below 0.1 mol/liter, the following scheme is devised to explore the kinetics of the decomposition of \(A\). A feed of 0.6 mol \(A\)/liter is introduced into the first of the two mixed flow reactors in series, each having a volume of 400 cm3.  The color change occurs in the first reactor for a steady-state feed rate of 10 cm3/min, and in the second reactor for a steady-state feed rate of 50 cm3/min.
      1. Find the order of reaction (\(n\))
      2. What is the value of \(k\) in mol, liter, min units, where \(-r_A = kC_A^n\)?
        ______ \(\text{ (mol/liter)$^{1-n}$.min$^{-1}$}\) where \(n\) is the order of reaction, and \(C_A\) in mol/liter.
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    • Replacing CSTR with Two-Smaller CSTRs Page
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    • Autocatalytic Reaction in PFR / MFR / Combinations Page
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    • Recycle Reactor Page
      Levenspiel3E-6-9
      At present we have 90% conversion of a liquid feed (Order of reaction = 1, \(C_{A0} =10\) mol/liter) to our plug flow reactor with recycle of product, with recycle ratio (defined as ratio of volume of fluid returned to the reactor entrance to the volume leaving the system) of 2. If we shut off the recycle stream, how much will be the  processing rate of our feed relative to that with recycle,  to the same 90% conversion?
      __________ times the processing rate of feed with recycle (round off to 2 decimal places).
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    • Replacing MFRs with PFR Page
      1993-24-b-cre
      At present a first order, isothermal, liquid phase reaction is being conducted in a cascade of two equal sized mixed flow reactors to obtain 95% conversion. If this system is replaced by a plug flow reactor of the same total volume, what is the percentage increase in the production rate for the same conversion?
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    • First Order Reaction in CSTRs in Series Page
      2011-52-53-cre
      In an aqueous solution, reaction \(P\rightarrow Q\) occurs under isothermal conditions following first order kinetics. The feed rate is 500 cm3/min and concentration of \(P\) in the feed is \(1.5\times 10^{-4}\) mol/cm3. The reaction is carried out in a 5 litre CSTR. At steady state, 60% conversion is observed.
      1. The rate constant (in min-1) is ______ (0.06 / 0.15 / 0.21 / 0.28)
      2. The 5 litre CSTR is replaced by five CSTRs in series. If the capacity of each new CSTR is 1 litre, then the overall conversion (in %) is _____ (65 / 67 / 73 / 81)
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    • CSTRs in Series - First Order Reaction Page
      2000-2-16-cre
      The conversion for a first order liquid-phase reaction \(A \rightarrow B\) in a CSTR is 50%. If another CSTR of the same volume is connected in series, then the % conversion at the exit of the second reactor will be _______ (60 / 75 / 90 / 100)
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    • Arrangement of Reactors for Second Order Reaction Page
      2001-15-cre
      A CSTR and a PFR of equal volume \(V\) (each) are given for the conduct of a second order, isothermal, liquid phase reaction. The reactors are to be arranged sequentially (in series). Find the values of the conversion for the two possible reactor arrangements.
      \(A \stackrel{k}{\rightarrow} B \qquad k =1\) m3/(kmol.s) \(\qquad C_{A0}= 0.1\) kmol/(m3.s), and \(\tau\) = 5 s (for volume \(V\)).
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    • Reactors in Series - First Order Reaction Page
      1990-17-iii-cre
      An irreversible homogeneous liquid phase reaction \(A \rightarrow B + C\) is carried out in two isothermal flow reactors of 100 litre capacity each operating at 60\(^\circ \)C. Find the exit conversion (%) if both the reactors are operated in series, when
      1. both the reactors are ideal plug flow reactors. ____________
      2. an ideal plug flow reactor is followed by an ideal back-mix reactor.____________
      Additional Data:

      Feed rate = 20 litre/min; Feed concentration = 1 mol/litre; Rate constant = 0.5 min-1

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    • Reactors in Series - Second Order Reaction Page
      1999-17-cre
      An isothermal plug flow reactor is designed to give 80% conversion of \(A\) for a second-order liquid phase reaction \(A \rightarrow B\). Pure \(A\) at concentration 1 kmol/m\(^3\) is fed to the reactor at a flow rate of 5 m\(^3\)/h. The rate constant for the reaction at a specified operating temperature is 0.5 m\(^3\)/(kmol.h). When the reactor is actually operated based on this design, it was found that 30% of the initial reactor behaved as a well-mixed reactor while the remaining behaved as a plug flow reactor. Calculate the conversion (in %) obtained in such a reactor.
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    • Reactor Combinations for Minimum Volume Page
      2003-70-cre
      A liquid phase reaction is to be carried out under isothermal conditions. The reaction rate as a function of conversion has been determined experimentally and is shown in figure given below. What choice of reactor or combination of reactors will require the minimum overall reactor volume, if a conversion of 0.9 is desired?

      1. CSTR followed by a PFR
      2. PFR followed by a CSTR
      3. CSTR followed by a PFR followed by a CSTR
      4. PFR followed by a CSTR followed by a PFR
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