Effect of Contacting Method

FIGURE 1.7 KOH versus NaOH activation comparison. Nj adsorption isotherms at 77 K for chemically activated MWCNT (redrawn from Raymundo-Pinero, E., Azais, P., Cacciaguerra, T., Cazorla-Amords, D., Linares-Solano, A., and Beguin, F. Carbon 43(4) 786-795, 2005) (a) MWCNT prepared at450°C and (b) MWCNT prepared at 600°C. 

The importance of the size of precursor and activating agent for porosity development of samples prepared by physical mixing has been analyzed. The decrease in the carbonaceous precursor particle size produces some inCTease in the final porosity. As an example, the decrease in the particle size from 2 to 0.6 mm leads to an ino-ease in porosity that could be up to 10% for a bituminous coal. Regarding the activating agent size, comparison between an anthracite activated with hydroxide lentils or powder hydroxide shows no meaningful porosity difference. 

FIGURE 1.8 Comparison of the microporosity of samples prepared by impregnation using different drying times. Activating agent NaOH (redrawn from Lillo-Rodenas, M.A., Lozano-Castelld, D., Cazorla-Amoros, D., and Linares-Solano, A. Carbon 39(5) 751-759, 2001. With permission). 

According to these results, and many others published in the literature [20,23,35,38-44,49-97], to increase the adsorption capacity of an AC high hydroxide/carbon ratios need to be used. However, in addition to the increase in surface area and micropore volume, it is also important to analyze the effect on the MPSD. Eigure 1.11 presents the MPSD calculated by applying the Dubinin-Stoeckli (DS) equation [10,11] to the N2 adsorption data. The higher the KOH/anthracite ratio, the wider the pore size distribution and the higher the mean pore size. These MPSD curves agree with what can be deduced from the difference in the micropore volumes calculated from N2 and CO2 adsorption data. 

FIGURE 1.9 Nj adsorption isotherms of samples prepared by chemical activation using either physical mixing or impregnation with a hydroxide/anthracite ratio of 3/1 (weight) (a) KOH and (b) NaOH. 

---