Regarding the RCSTR reactor, how is the input pre-exponential factor k converted to SI units?
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Dear experts, I’m new to Aspen. When simulating a reaction in an RCSTR reactor, I found the kinetic data for that reaction, namely the pre-exponential factor A and the activation energy E0. However, when entering these kinetic parameters, the pre-exponential factor k needs to be converted into SI units. But does the pre-exponential factor even have units? Also, how to convert to SI units?
The pre-exponential factor, also known as the frequency factor, has the same units as the unit of reaction rate; it determines the nature of the reaction. The previous answer was incorrect; thank you to those who pointed this out. I’m sorry for that, sorry… This post was last edited by zl128117 on 2009-3-26 at 15:19
Don’t mislead people; k = Aexp(-E/RT). k has units, and the frequency factor A is a parameter related to the number of collisions between reactant molecules per unit time and per unit volume, so it certainly has units as well.
Well, thanks to the two people before me! After thinking about it again, my question should be this: In an RCSTR reactor, when entering the kinetic parameters, how should the value of K in the equation kinitic factor = K(T/T0)exp((E/R)(1/T-1/T0)) be handled? Is this K exactly the pre-exponential factor A found in the kinetic parameters we refer to?
The factor in an RCSTR is the reaction rate constant; that formula is the modified Arrhenius equation. In the original Arrhenius equation, the assumption that the activation energy E and the pre-exponential factor A are independent of temperature is an approximation. Within the experimental temperature range, when A and E do not change much, the Arrhenius method is highly applicable. However, when making extrapolations over a wider temperature range, the Arrhenius formula needs to be modified. The modified Arrhenius equation has different activation energies and pre-exponential factors across various temperature ranges. The pre-exponential factor you find should be k in the modified Arrhenius equation; because when it can be assumed that the pre-exponential factor is independent of temperature, then n in the equation equals 0, and only k remains. As for T0 in the exponent, my understanding is that it is used to adjust the activation energy E. Therefore, the pre-exponential factor obtained should indeed be k in the modified Arrhenius equation.