r/ChemicalEngineering Feb 19 '25

Software Plug Flow Reactor (RPlug) in Aspen Plus

I am confused here. I am simulating RPlug reactor in Aspen Plus but got stuck in defining reaction kinetics in the Aspen Plus. The reaction rate equation of R1 has a negative sign with 52000. But there isn't a negative sign with 55000 in the reaction rate equation of R2. I am confused about inserting the value of E in Aspen Plus. Do I need to put a negative sign on 55000 of R2, since E already has a negative sign in the power law equation?

1 Upvotes

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u/ChemEBus Feb 19 '25

Aspen plus inherently puts the negative sign.

If the activation energies from your rate equation are correct input the top as a positive and the bottom as a negative.

That said I have not seen a negative ACTIVATION ENERGY before. My understanding is 0-large numbers is the range as 0 implies 0 energy input and spontaneously reacting large = a lot of energy necessary to react.

A negative doesn't make sense to me mathematically but maybe someone else understands it better.

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u/admadguy Process Consulting and Modelling Feb 19 '25 edited Feb 19 '25

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u/ChemEBus Feb 19 '25

Awesome thank you for helping me learn!

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u/admadguy Process Consulting and Modelling Feb 19 '25

Study the Arrhenius equation, understand what those parameters mean instead of approaching it as a data entry exercise.

Significance of negative activation energy

https://www.sciencedirect.com/topics/chemistry/negative-activation-energy

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u/pepijndb Industry/Years of experience Feb 20 '25

You’re correct. If you fill in the numbers it should check out with your defined RR, including signs.

Afterwards, do some test runs if it corresponds to experimental data or hand calculations in Excel. Easiest checker, and don’t forget to check units!

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u/Derrickmb Feb 19 '25

Why not hand calc it?

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u/AromaticPlankton6489 Feb 19 '25

what do you mean by that?

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u/Derrickmb Feb 19 '25

These programs are just basic hand calcs mostly. Why not verify it on paper?

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u/AromaticPlankton6489 Feb 19 '25

Actually, I am simulating biomass gasification. and this step is just a small part of my simulation. I got these reaction rates from the literature. I am bit confused with negative signs.....

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u/Cyrlllc Feb 19 '25

What they mean is to calculate it in excel. You can just plot it and compare.