1 reply to this topic

Hi,
I'm an energy and environmental student designing an absorption column removing CO2 using 15% MEA at 40oC. I have not studied chemical engineering in depth as I am not studying a pure chemical engineering degree, and i'm struggling with drawing an equilibrium curve. I know that i need to find the mole ratio of CO2 to amine for Y, however the graph has partial pressure for the Y axis. I know that I need to find Pinert by Patm-PCO2 then find the number of moles, then mole ratio.

First Qu- The graph looks as though it has a log scale on the Y axis. Do I need to change this?

Second Qu- Do I need to divide by the pressure I require in my column as ?

I've attached the graph I have drawn using the data from Gas purification (Kohl, Arthur L.; Nielsen, Richard B. © 1997 Elsevier ) as the graph from the book is not too clear on the attachment, any guidelines to reach the desired X/Y graph would be much appreciated.

Thankyou

Attached Files

•  equilibrium_graph.doc   115KB   44 downloads

[MrShorty]

1Qu: I don't know that you "need" to change it -- it depends on exactly what you are trying to do with the graph. For example, on your Excel graph, everything below a mole ratio of about 0.6 essentially reads as 0 psia, which you know is wrong. If it were important to be able to actually read values off of the graph, then I would say it will be easier to read them using a log scale on the y-axis.

2Qu: I didn't quite understand this question. It appears to me you are wanting to "convert" the partial pressure of CO2 vs. liquid composition data you are given to get actual vapor compositions (specifically the molar ratio of CO2 to MEA). Whenever I've done these kind of calculations, I've used the relation Ptotal=sum(partial pressures of each component), y(each component)=partialpressure(each component)/Ptotal. The key piece of information you seem to be missing is the partial pressures of MEA and water and any inerts. You haven't described the context for the calculation/homework assignment, so it's hard for me to know how they expect you to obtain these values, but your question seems pretty simple, once you have all the partial pressures.