I am having trouble reproducing an example from "elementary principles of chemical processes" by Felder and Roussau (dehydrogenation of ethanol to ethanal and hydrogen at 400 degC in an adiabatic reactor (30% conversion of ethanol)).. The equillibrium conversion is 81% but the adiabatic temperature is 371 degC while the book gets an adiabatic temperature of 145 degC with only 30% conversion? I checked that the inlet enthalpy and standard heat of reaction are the same for the calculations.. I noticed that some of the reported values in the "result" page of the equillibrium reactor does not have the correct units and wonder whether there is a bug in the calculation? (initial and final Gibbs free Energy is reported in kj/kg, while when you hover with the mouse over the reactor it is shown in kW with same value, outlet temperature is reported as 25 degC (despite outlet stream having a 371 degC temperature), and the reaction extent is also wrong IMO..).
Is there something I am missing??
Lastly I think a great feature in the equillibrium or conversion reactor would be specifying a reaction extent or conversion percentage.
Hi Daniel. Yes the reaction is endothermic (69,11 kJ/mol).
The conversion extent reported by the equillibrium reactor is off by a factor of 100 compared to my school teaching (mol compound out - mol compound in)/stoeff coeff..
I will try to calculate it with spreadsheet tomorrow...
Br
Michael
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The data would fit more nicely if the conversion was off with a factor 10 (approx 8% conversion).. That would give an adiabatic temperature closer to 345 degC acc. to the calculations in the book compared to 371 degC from DWSIM....
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Found the issue. You must change the reaction basis to "Fugacity", as "Activity" should be used only for liquid phase reactions. After this change, you should get a conversion of 24.8% and outlet temperature of approximately 234 C.
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Thanks for the solution but were can I set the reaction basis? Is it exposed in the mac UI? I cant find it anywhere.... I did select the reaction to be in the vapor phase which I suppose would select it to use fugacities?
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Hi Daniel. Is there any way to manipulate the xml from an xml editor? I have not worked with compressed xml files before.. Is there any particular reason for choosing compressed xml (besides the file size)? Br Michael
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The dwxmz file is a renamed zip file. You can extract the xml, work on it, then compress with zip and rename it back to dwxmz. No particular reason except for the file size, XML is text so it is heavily compressible.
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Hi Everyone.
I am having trouble reproducing an example from "elementary principles of chemical processes" by Felder and Roussau (dehydrogenation of ethanol to ethanal and hydrogen at 400 degC in an adiabatic reactor (30% conversion of ethanol)).. The equillibrium conversion is 81% but the adiabatic temperature is 371 degC while the book gets an adiabatic temperature of 145 degC with only 30% conversion? I checked that the inlet enthalpy and standard heat of reaction are the same for the calculations.. I noticed that some of the reported values in the "result" page of the equillibrium reactor does not have the correct units and wonder whether there is a bug in the calculation? (initial and final Gibbs free Energy is reported in kj/kg, while when you hover with the mouse over the reactor it is shown in kW with same value, outlet temperature is reported as 25 degC (despite outlet stream having a 371 degC temperature), and the reaction extent is also wrong IMO..).
Is there something I am missing??
Lastly I think a great feature in the equillibrium or conversion reactor would be specifying a reaction extent or conversion percentage.
I am using the newest DWSIM for Mac 6 update 5.
I have attached the file
Br Michael
So in the book the reaction is endothermic?
Regarding the display units for gibbs energy, that's all that it is, wrong units being displayed. The equilibrium reactor calculation is correct.
Last edit: Daniel Medeiros 2020-07-14
The conversion reactor does exactly what you need, it lets you to specify a fixed conversion value for the base compound.
Hi Daniel. Yes the reaction is endothermic (69,11 kJ/mol).
The conversion extent reported by the equillibrium reactor is off by a factor of 100 compared to my school teaching (mol compound out - mol compound in)/stoeff coeff..
I will try to calculate it with spreadsheet tomorrow...
Br
Michael
The data would fit more nicely if the conversion was off with a factor 10 (approx 8% conversion).. That would give an adiabatic temperature closer to 345 degC acc. to the calculations in the book compared to 371 degC from DWSIM....
Found the issue. You must change the reaction basis to "Fugacity", as "Activity" should be used only for liquid phase reactions. After this change, you should get a conversion of 24.8% and outlet temperature of approximately 234 C.
Hi Daniel.
Thanks for the solution but were can I set the reaction basis? Is it exposed in the mac UI? I cant find it anywhere.... I did select the reaction to be in the vapor phase which I suppose would select it to use fugacities?
I forgot to expose this option in the cross-platform UI... sorry!
Until the next release you can run this updated file.
Last edit: Daniel Medeiros 2020-07-15
Hi Daniel. Is there any way to manipulate the xml from an xml editor? I have not worked with compressed xml files before.. Is there any particular reason for choosing compressed xml (besides the file size)? Br Michael
The dwxmz file is a renamed zip file. You can extract the xml, work on it, then compress with zip and rename it back to dwxmz. No particular reason except for the file size, XML is text so it is heavily compressible.