Chapter 6: Isothermal Reactor Design: Molar Flow Rates

Frequently Asked Questions (FAQs)

  1. When accounting for pressure drop in a membrane reactor, does the same method as we would use with a PFR apply?

    Yes,

  2. Why can't you write the membrane equations in terms of conversion X?

    Because you can't relate the concentration of the product diffusing out, CB, and X.

  3. Would there ever by a case in which a membrane reactor would be used for the reverse? I.e. if H2, for example, was used as a reactant in a reaction, would one ever want to run concentrated H2 along the sides of the reactor and let it diffuse into the reaction zone?

    Yes, especially when O2 is one of the reactants.

  4. In a membrane reactor, how can one quantify the equilibrium point on the graph of F vs. V?

    In this region (i.e. after the knee) the reaction is in equilibrium and the rate of removal of B is what limits the overall rate of reaction.

  5. How can you assume that a semi-batch system has constant density?

    Most liquids do not change density during the course of the reaction.

  6. Do we only use the form of the PBR design equation for membrane reactors (IMRCF)?

    NO!! The mole balance is

    The relationship between reactor volume and catalyst weight is

    Substituting for W

    Then

  7. Why do they use a batch reactor to determine k if they are going to be using CSTR in actual industrial process?

    Batch experiments are most always easier to take the necessary data to determine k.

  8. In what cases would you use the order of magnitude reaction times other than to check k values that you calculate?

    When you are short on time and want to get quick engineering estimates.

  9. At some of the polymer plants and refineries I've visited, a huge problem is fouling of the reactors. The plant workers would sometimes have to go into the reactors to break through the solids/sludge that adhere to the reactor walls. I imagine this solid build up leads to a drastic volume decrease. So, how do we take into account the change of volume and it's detrimental effect to conversion?

    Good point. It would change the volume; however, catalyst decay by fouling is usually more important. See Ch.10.

  10. Is rinsing the reactor with water after a batch ample cleaning, or are chemical cleans necessary in between batches?

    It depends, if there are no side reactions, a chemical clean is probably not necessary. Also the larger the reactor the greater the cleaning time.