Adsorption processes in rapid equilibrium

Chromatography Modeling
2

Dear Chaoying,

I have moved you questions to a new topic, as they are not strictly related to your original question and might be relevant for a broader audience.

  1. Your k_a and k_d values are quite high. Try decreasing them by orders of magnitude and you should see the expected result. For large values, the adsorption process is not rate limiting and increasing them even further makes no difference. The results will be practically identical with what you get for IS_KINETIC=0.

  2. This is an apparent paradox. Setting \frac{dq}{dt}=0 in the isotherm equation means that c and q are always in equilibrium. However, molecules of course still migrate between the mobile and stationary phases. Hence, the term with \frac{dq}{dt} needs to stay in the mass balance equation.

  3. This actually follows from the previous point. You can use the mentioned trick if using IS_KINETIC=0 and wanting to know \frac{dq}{dt} for the mass balance. However, CADET solves the resulting differential-algebraic equations (DAE) in a different and numerically more efficient way.

I hope this helps.

Best regards
Eric

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