A new approach to quantify the microporosity of activated carbons by analysing the N2/77 K and CO2/273 K adsorption data by the simplex flexible method
✍ Scribed by A. Marcilla-Gomis; A.N. García-Cortés; J.M. Martín-Martínez
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 815 KB
- Volume
- 34
- Category
- Article
- ISSN
- 0008-6223
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✦ Synopsis
A mathematical model has been applied to N,/77 K and CO*/273 K adsorption isotherms for a series of activated carbons prepared by carbonising olive stones in N, and then activating them in COz to six different levels of burn-off in the range 8-80%. Narrow and wide micropore volumes of activated carbons were calculated from the Dubinin-Radushkevich and Dubinin-Astakhov equations considering one, two and three micropore size distributions in each sample, and allowing a variation of the micropore volume and characteristic energy of each distribution with the burn-off. The flexible simplex method was applied to obtain the parameters of each distribution in the mathematical model. Generally, it was found that increasing the number of micropore size distributions above two did not significantly improve fits. Each isotherm was fitted using six parameters at most. However, various constraints were imposed, and the parameters were estimated from each isotherm using non-linear, leastsquares regression analysis. The results obtained confirm the valuable use of COJ273 K adsorption to quantify the narrow microporosity of activated carbons. Differences between NJ77 K and CO,/273 K adsorption in microporous activated carbons were due to the wide microporosity.
An agreement between microbore volumes-obtained from COJ273 K adsorption and that corresponding to one of the two distributions of microuores obtained from N,/77 K adsorotion was obtained. The Dubinin-Radushkevich equation was more 'successful than the Dubinin-Astakhov equation in the quantification of the microporosity with N-J77 K and CO,/273 K. On the other hand, the exponent n of the Dubinin-Astakhov equation was better correlated with the burn-off of the carbons than with the parameter i3.