Kinetic unit problem in Aspen simulation of reactive distillation
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The original kinetic model obtained through experimental regression is of the form r=dx/dt=k1*xA*xB - k2*xC*xD. The unit of k is the reciprocal of time, 1/s. k=k0*exp(-E/RT), so the unit of k0 is also 1/s. When using Aspen for simulations, if the concentration basis is set to mole fraction, what is the unit of k0? Is it 1/s? Can I use my model parameters directly? In the Help file, I saw that the unit of k0 corresponding to the mole fraction is kmol/(s·m3)? How should it be converted? Thank you all! !
Check the built-in help files by yourself
This post was last edited by zhdw0906 on 2018-3-5 20:48: The unit issue of reaction rates in Aspen (Note: kgmole=kmol). The power law expression depends on the concentration basis you select in the Basis list box; the holdup basis is determined by the specifications in the RadFrac | Reactions | Holdups sheet, even in rate-based mode in RadFrac when the holdup value is determined by rate-based correlations or specifications. The basis is determined separately for each stage, and for stages where no holdup is specified, a mole basis is assumed. The units for the pre-exponential factor are as follows:
Hello, I have another question I’d like to ask. I now know that in Aspen simulations, the unit of the pre-exponential factor is kmol/(m3 s), but the unit of k obtained from my experimental regression is the reciprocal of time, namely 1/s; since k = k0*exp(-E/RT), the unit of k0 is also 1/s. How to convert k0 to kmol/(m3 s)? Thank you so much! !
It applies to first-order reactions, where the reaction rate r = k*c; here, r represents the rate per unit amount of catalyst (the amount of catalyst is expressed in Aspen terms as holdup), with the catalyst being measured in terms of mass in kg, or in terms of volume in m3； In the formula: the unit of is 1 ； The unit of c is ». That is, when expressed in terms of the catalyst mass, it is = km**; hence, km = ». When expressed in terms of the catalyst volume, it is = kv**, so kv = ». The relationship between these two pre-exponential factors is that km = *kv*. As for your question, I’m not quite sure, because the unit of k for a first-order reaction is », and from a purely conversion perspective, = *, with the meaning being *. So is this still a first-order reaction?