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Topic: Conceptual Clarification of CSTR Operation  (Read 5300 times)

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Offline ethylenediamine

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Conceptual Clarification of CSTR Operation
« on: September 24, 2006, 02:59:36 AM »
For a CSTR, why does a species balance not include the rate of consumption and generation by chemical reaction?

It says d(C_A* V)/dt = (C_a,in)Q_in - (C_a)Q + (r_A)V

"r" is defined as r = -kC_A.

But wouldn't it be possible for r = (-k_1)C_A + (k_-1)C_A, where (k_-1)C_A represents the rate of a reverse reaction?
« Last Edit: September 24, 2006, 02:05:25 PM by geodome »

Offline Donaldson Tan

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Re: Chemical Engineering
« Reply #1 on: September 24, 2006, 08:02:40 AM »
It says d(C_A* V)/dt = (C_a,in)Q_in - (C_a)Q + (r_A)V

"r" is defined as r = -kC_A.

I think you answered your own question.

rA is defined as the rate of formation of A per unit volume. The equation for rA depends on the nature of the chemical reaction.

The dynamic material balance for species A in a CSTR is given by:
VR(dCA/dt) =Fin.CA0 - Fout.CA + rA.VR where:
1. VR is the volume of the CSTR
2. CA0 is the concentration of A in the feed stream
3. F refers to the flowrate.
 
For an irreversible chemical reaction A -> B + C, rA = - rate of consumption of A = -k.CA since A is being consumed by the reaction.

For a reversible chemical reaction, A <-> B + C, rA = rate of generation - rate of consumption = kb.CB.CC - kf.CA
« Last Edit: September 24, 2006, 08:14:56 AM by geodome »
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