Application Of Chromatographic And Static Methods For Characterizing Of Active Carbons Porosity
APPLICATION OF CHROMATOGRAPHIC AND STATIC METHODS FOR CHARACTERIZING OF ACTIVE CARBONS POROSITY
H. Grajek, S. Neffe
Military University of Technology, Institute of Chemistry,
00-908 Warsaw, Kaliski str. 2, Poland
Carbon adsorbents (particularly activated carbons) are widely used in the pollution adsorption instalations from gas and liquid phase. In order to explain the adsorption processes proceeding on activated carbons the knowledge of the adsorption isotherms and thermodynamic functions as well as the determination of their porous structure is required\’. The following samples of Filtrasorb 400 activated carbon (Calgon Corp., USA) were used in the study: (i) virgin commercial adsorbent (denoted as F4W), (ii) virgin commercial adsorbent deashed by Korver\’s method (denoted as F4D), (iii) virgin commercial adsorbent deashed by Korver\’s method and oxidized with concentrated НМОз (denoted as F4DO). The content of oxygen functional groups of acidic character was determined by the method of neutralization with bases of various strengths, according to Boehm method2, while the amount of basic groups was estimated by the method of neutralization with hydrochloric acid. The results are summarized in Table 1.
Table 1. Concentration of acidic and basic groups
Sample
Acidic grou
)s; mmol/g
Basic groups; mmol/g
-COOH
-соос
>С-ОН
>с=о
F4
0.000
0.000
0.015
0.222
0.552
F4D
0.000
0.035
0.168
0.189
0.305
F4DO
0.713
0.221
0.419
0.367
0.151
The removal of mineral impurities from the 14 sample did not significantly change the chemical properties of the surface sample but the oxidizing process did.
The adsorption characteristics of the active carbons studied were calculated on the benzene adsorption isotherms data, which were determined gravimetrically at 293 К, and chromatographically at 553K. Parameters characterizing the tested samples: Wo - the micropore volume, Eo - the characteristic energy of adsorption, and Sy - the micropore walls surface are listed in Table 2.
Table 2. Parameters characterizing of the tested samples calculated on the basis of benzene adsorption isotherms determined at 293K (statically) and at 553K (chromatographically).
Parameter
Determination method
Sample
F4
F4D
F4DO
Wo cm\’Vg Statically
0.43
0.40
0.37
С h romatograph ical ly
0.45
0.50
0.43
Eo U/mol
Statically
20.4
21.1
22.3
Chromatograph ical ly
25.8
25.0
25.8
Sg m\’/g
Statically
705
680
670
Chromatographically
990
950
950
Taking into account results presented in the Table 2 one may said that the values of parameters calculated from the statically determined adsorption isotherm of benzene are lower in comparison with the magnitudes calculated from the chromatographically determined ones.
The observed differences in the values of adsorption parameters obtained from statical and chromatographical measurements may be explained as the result of increasing ofintrapore diffusivity of adsorbate at higher temperature. The diffusion effects have significant influence on the resulting quantities, particularly in the case of microporous active carbons. Therefore, the quantities determined by the chromatographic method represent some effective values.
Acknowledgments
This work was partly supported by the Polish State Committee for Scientific Research, Grant No. 3 T09B 036 16, and WAT/WIC/PBS 167/2000.
References
1. Grajek, H., Witkiewicz, Z., Jankowska, H., and Swiatkowski, A., Adsorption Science & Technology, 1999, 17, 1
2. Boehm, H.P„ Carbon, 1994, 32, 759
Related articles::