Voir nos articles sur ladsorption

One can use Dubinin-Radushkevich (D – R) isotherm and determine the β parameter, and on its basis estimate the value of the adsorption energy.

Dear Mohammad Saleheen

As mentioned by Mirosław Grzesik, the D-R model has a parameter analogous to adsorption energy. In addition, from isotherm experiments, you can find the thermodynamic parameters (delta(H°, S°, G°)) and isosteric heat of adsorption (delta(Hx)). However, if you would like to find a parameter analogous to Activation Energy (Ea), kinetic studies at different temperatures (different adsorption rates, k) would be performed.

Hope this helps.

Regards.

Thank you Drs. Mirosław Grzesik and Carlos Eduardo Rodrigues Barquilha . That helps.

- Mohammad

Carlos Eduardo Rodrigues Barquilha, What constants do you propose to determine the value of Ea, because I hope not so-called pseudo- ... -order rate constant, which are actually lumped parameters?

Dear Mirosław Grzesik

I honestly haven't calculated this parameter in my research yet, but I believe that the most appropriate would be to use some diffusivity coefficient. I can suggest some articles that discussed the activation energy in adsorption and ion exchange processes.

1. Inglezakisa and Zorpas (2012): doi: 10.1080/19443994.2012.669169

2. Saha and Chowdhury (2011): doi: 10.5772/13474

Dear Mohammad Saleheen, these articles can be helpful for you too.

Regards.

I would like to confirm something about the so called lumped parameter-pseudo kinetic constant. I know that the adsorption reaction is between the adsorbate ions and the surface active sites in the adsorbent internal/external surface(s). These surface sites are carbon atoms (if the adsorbent is activated carbon). If i want to determine the kinetic rate constant via differential kinetic analysis (initial rates method) using the batch reactor. Is it not okay to assume that the surface active sites have a much higher concentration comparative to the adsorbate ions (vary insignificantly during the adsorption reaction) so they can be lumped together with the kinetic rate constant resulting in the pseudo kinetic rate constant k' = kCs

A + S -> AS

Where, -Rads = k'Cads^n -intrinsic kinetics ignoring diffusion mass transport

n= reaction order

Cads- current adsorbate concentration

Cs= concentration of (carbon) surface active site(s)

Dear Carlos Eduardo Rodrigues Barquilha, If you haven't calculated (even though you're suggesting from some k), that's fine. If someone was calculating on k from eg PSO, that's his problem. If someone used Arrhenius eq. for diffusivity, that's his problem too. They obtained some numbers, but what is their meaning - nobody knows. Adsorption is a complex process, but the activation energy concerns an elementary process. Regards,

Dear Mirosław Grzesik

I agree with you. This is also true for the other thermodynamic parameters where different equilibrium constants (from Langmuir, Freundlich, Henry, partition...) are used to determine the thermodynamic equilibrium constant (Kc) and delta(H°, S°, G°), respectively, producing values completely different.

Adsorption is certainly a complex process.

Regards,

Dear Carlos,

I recommend the following reference: Liu, Y.; Is the Free Energy change of Adsortpion correctly calculated?, J. Chem. Eng. Data, 2009, 34, 1981-1985

Regards

application of D-R model

What does the D-R isotherm have to the activation energy? Adsorption energy is not the same as activation energy.