Nothing Special   »   [go: up one dir, main page]
Scribd Logo
Upload

Welcome to Scribd!

  • 29 views

    Q Q F F RT F Q P RT F Q P: Gas Phase Continious Reactors

    Uploaded by

    Sintu Mhlonyane
    For a gas phase reaction occurring in a continuous reactor: 1) The pressure will remain roughly the same as it is an open system, unlike a batch reactor where pressure increases. 2) The volumetric flowrate will change to compensate for changes in moles according to the ideal gas law. 3) The concentration of a reactant is influenced by changes in volumetric flowrate according to the given equation.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PDF, TXT or read online from Scribd

    Q Q F F RT F Q P RT F Q P: Gas Phase Continious Reactors

    Uploaded by

    Sintu Mhlonyane
    29 views4 pages
    For a gas phase reaction occurring in a continuous reactor: 1) The pressure will remain roughly the same as it is an open system, unlike a batch reactor where pressure increases. 2) The volumetric flowrate will change to compensate for changes in moles according to the ideal gas law. 3) The concentration of a reactant is influenced by changes in volumetric flowrate according to the given equation.

    Original Title

    Gas Continuous

    Copyright

    © Attribution Non-Commercial (BY-NC)

    Available Formats

    PDF, TXT or read online from Scribd

    Did you find this document useful?

    Is this content inappropriate?

    For a gas phase reaction occurring in a continuous reactor: 1) The pressure will remain roughly the same as it is an open system, unlike a batch reactor where pressure increases. 2) The volumetric flowrate will change to compensate for changes in moles according to the ideal gas law. 3) The concentration of a reactant is influenced by changes in volumetric flowrate according to the given equation.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    29 views4 pages

    Q Q F F RT F Q P RT F Q P: Gas Phase Continious Reactors

    Uploaded by

    Sintu Mhlonyane
    For a gas phase reaction occurring in a continuous reactor: 1) The pressure will remain roughly the same as it is an open system, unlike a batch reactor where pressure increases. 2) The volumetric flowrate will change to compensate for changes in moles according to the ideal gas law. 3) The concentration of a reactant is influenced by changes in volumetric flowrate according to the given equation.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    You are on page 1of 4

    GAS PHASE CONTINIOUS REACTORS

    Take the following gas phase reaction:

    A 10 B
    What will happen if this reaction occurs in a continuous reactor?

    Pin
    Should the pressure increase, like in a piston reactor?

    Pout?

    NO, NO NO! THIS IS NOT POSSIBLE IN A OPEN SYSTEM. Remember that pressure is the driving force for flow, so we need to have a pressure drop (due to frictional losses) over the reactor. In CKN we will assume that the losses is negligible, so the pressure will remain roughly the same. So how do we compensate for the change in moles? We return to the ideal gas law, our faithful friend for gas phase problems in CKN. The ideal gas law for isothermal flow systems will result in:

    PoQ = Ftot RTo Ftot Q = PoQo = Ftot o RTo Ftoto Qo


    The volumetric flowrate will alter!

    GAS PHASE CONTINIOUS REACTORS


    For a single reaction where we use conversion, it is easy to show (by using the stoicheometric table) that:

    Ftot Q = = 1+ x Ftoto Qo
    Similar to piston reactors, we need to realise that the concentration in a flow system is influenced by changes in volumetric flowrate.

    CA =

    F (1 x) FA FA (1 x) = C Ao = = Ao Q Q Ftot Qo (1 + x) (1 + x) o Ftoto

    This has a major effect on the reaction rate and should be incorporated into all mole balances. For a non-catalysed nth order reaction occurring in a PFR we will have:

    C Ao dx =k dV Qo

    n 1

    (1 x) n (1 + x) n

    Note that the form is not the same as that of the piston batch reactor:

    dx (1 x) n n 1 = kC Ao dt (1 + x) n 1
    Derive similar expressions for a CSTR and catalysed flow systems!

    GAS PHASE CONTINIOUS REACTORS


    For the Levenspiel plot, it is easier to work with conversion and to use V/FAo as the size indicator.

    1 ( rA ( x))

    x
    You should be able to prove to yourself that for a CSTR:

    1 V x = rA ( x) FAo
    And for a PFR:
    x 1 V = r ( x) dx FAo 0 A

    Very important to note that the rate is a function of , and therefore the Levenspiel plot is a function of the feed conditions. If the feed conditions are altered the whole shape of the Levenspiel plot needs to be altered.

    GAS PHASE CONTINIOUS REACTORS


    When opting for the multiple DE method (for multiple reactions this will be the only choice) one should determine the volumetric flowrate by summing all the molar flowrates. For the reaction A+2B C occurring in a non catalysed PFR we will have:

    F dFA = k A Q dV

    FB Q
    n

    FA dN B = 2k Q dt

    FB Q

    FA + FB + FC + FI Q = Qo F +F +F +F Bo Co I Ao

    You might also like