Answer to the Letter to the Editor of the Chemical Engineering Journal by J. Kärger: Comment on the paper "Diffusion and adsorption selectivities of hydrocarbons over FCC catalysts" by A. M. Ávila, C. M. Bidabehere and U. Sedran in Chem. Eng. J. 132 (2007

CLAUDIA M. BIDABEHERE; ADOLFO ÁVILA; ULISES SEDRAN

CHEMICAL ENGINEERING JOURNAL

Elsevier

Lugar: Amsterdam; Año: 2008 vol. 145 p. 525 - 527

1385-8947

In a letter by Kärger [1] about our paper on the assessmentof the diffusivities in fluid catalytic cracking (FCC) catalysts [2],it is mentioned that diffusivities calculated by different methods(macroscopic in one case, or from pulsed field gradient (PFG) NMRtechnique in the other) are different. It is also pointed out that theresults of diffusivities for a given compound obtained from differentmacroscopic techniques are not explained satisfactorily. Bothfacts are true. We understand that the letter is not only a valuablecontribution to the field, considering its large and laboriousdata collection, but also an incentive for the search of a better comprehensionof the mechanisms controlling the FCC process. Mostimportantly, the differences observed should not hamper experimentswith macroscopic techniques nor lead to disregard resultssuspected of mass and/or heat transfer limitations. It is importantto recognize them as enriched by other type of information, andthat they become necessary as design tools. By these reasons, andconsidering that not too much can be added to the details depictedin Ref. [1], we believe it would be useful to clarify some issues,mainly pointing to a distinct approach in the interpretation of thedata.