I have collected the CO2 adsorption isotherms at two different temperatures and also at different pressures. Now i would need to calculate the heat of adsorption for any pressure. Any suggestion? Do I have to use the Van 't Hoff equation?
Thank you in advance for your help!
Hi,
If you are using Quantachrome instrument, then there is provision for calculating the heat of adsorption in software itself. You just need to use the CO2 sorption data collected at two diff temp and you will get the result. you don't need to do it manually. But you can do it manually also. The discussion in the above shared link will give you enough insight about the calculation of Qst. If you need help, please feel free to ask or you can send me your data (qps file), i can fit the data in software and send the result to you (if you are using the Quantachrome instrument).
regards
raeesh
Hi Noemi,
To calculate thermodynamic data for any adsorption system, one must have adsorption data of the system for at least 3 temperatures. Then use the Van’t Hoff equation:
Ln Kd = (delta So/R) - (delta Ho/R)* 1/T
A plot of Ln Kd versus 1/T (in kelvin) will give you a gradient equals to (delta Ho/R). Since R =8.3145 Jmol-1K-1, then delta Ho can be evaluated. Similarly the intecept of the graph is equal to delta So/R. therefore delta So can be evaluated
Then delta Go can also be evaluated from the equation
delta Go= deltaHo - T delta So .
I hope this helps, but if it is not clear let me know and I will try to clarify things.
All the best.
Zaynab Aly
We can use Van't Hoff Equation but it's better if you generate isotherm curves at more than two temperatures.
In the case of sorption problem is a little different , determined by isosteric heat of adsorption (qst). I enclose a slide from the presentation of unfamiliar author.
Best regards
Andrzej
Dr Zaynab Aly, you're right, the problem being what it is Kd, or just become Langmuir? I think so, because the temperature range is very small. Best regards
Andrzej
Hi there,
I think I did not make myself clear.
Calculate the distribution coefficient (Kd) of an ion between an aqueous and a solid phase was obtained from the following equation:
Kd (mL/g) = (Co-Ce)/Ce * (V/M)
Then calculate Kd at different temperatures followed by the Van’t Hoff equation:
Ln Kd = (delta So/R) - (delta Ho/R)* 1/T
A plot of Ln Kd versus 1/T (in kelvin) will give you a gradient equals to (delta Ho/R). Since R =8.3145 Jmol-1K-1, then delta Ho can be evaluated. Similarly the intecept of the graph is equal to delta So/R. therefore delta So can be evaluated
Then delta Go can also be evaluated from the equation
delta Go= deltaHo - T delta So .
I hope this helps. All the best.
Check out my paper :
Z. Aly and V. Luca, “Uranium extraction from aqueous solution using dried and pyrolyzed tea and coffee wastes”, J. Radioanaly. Nucl. Chem., Volume 295, issue 2, (2013) pages 889-900. DOI: 10.1007/s10967-012-1851-6.
Dear Aly, it's OK. In my opinion, there is a difference in the surface adsorption of CO2 from sorption in solutions. Sample publication attached. A,
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