Hi,
the ACT isotherm is currently only available on the dev branch of CADET-Process. Information on how to install this, can be found in our Contributor’s guide.
Best
Johannes
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I am already able to successfully use the ACT model in CADET-Process. Thank you very much.
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May I ask approximately how long does it take you to run this simulation? I’m trying to inverse fit three different components according to the ACT isotherm and it takes a very long time compared to other models.
I didn’t know you are using it for a multicomponent system. In a multicomponent system some combinations of \eta and pka for your components would cause very complex behaviors because of simultaneous changes of q_{app} and K_{app} and competitive binding, which can easily lead to displacement front (strong binder kicks off weaker binder), sequential adsorption (one fraction binds, release and then re-binds or displaced), multiple traveling fronts for the same component (split peaks). All these behaviors are very challenging to solve numerically. Normally these behaviors are seen when you have close pka and very different \eta between components.
I am still working on better ways to address this issue. Before that, one simple trick is to: rather than solving for one three component system, solve for three one component system. Define three sub systems for each component and solve them separately, combine the results and fit to your data. Note that one downside is that you have to assume there is no competitive binding anymore and will lose the model’s capability to solve complex displacement behaviors. However, if your system is something like monomer, HMW and LMW and the chromatogram looks normal, then this should be a valid assumption since HMW and LMW are low in percentages.
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Hey, thanks for your speedy reply. Yeah, but that’s exactly the problem, is that my chromatogram doesn’t look like a ‘normal’ chromatogram per se.
From several experiments we know that there is a lot of competition that leads to displacement of one of the species. Also the percentages of LMW and HMW are not so low, specially the HMW which makes up around 35% of the whole load composition.
I have done what you suggest, which is to fit them all individually, but then the prediction is not accurate since it lacks the competitive behavior. Anyway, thanks a lot for your reply. I would be very interested if you do more work regarding this topic!
The system might simply be numerically challenging to solve accurately due to stiffness or related effects. Have you tried solving the binding model in rapid-equilibrium and/or changing the time solver tolerances?
Hello, it can be. How could I do that? I’m using Cadet Process
Hi Sasha,
rapid-equilibrium vs kinetic binding is controlled by the field is_kinetic, see e.g. CADETProcess.processModel.Langmuir — CADET-Process 0.11.1 documentation
Time integration parameters are documented here, most important here are relTol and absTol, try to increase them.
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Hello, I’ve followed your suggestion and still with only a two component system the time it takes to process increases exponentially. With one component I would say takes around 1 minute or so and with 2 components even the whole afternoon nothing happens. I’ve tried increasing the tolerances as per your suggestion but still nothing. Could I share my code for you to test it?
Do you have an .h5 file? I should be able to take a look.
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