The Hydrophobization of Active Carbons

Abstract

Three methods for the hydrophobization of active carbons (ACs) have been investigated, i.e. chemical modification, heat treatment under the influence of a ultrahigh frequency electromagnetic field and heat treatment under the influence of a low-frequency electromagnetic field. It is shown that methods involving physical modification are more preferable with the adsorbability of water on the treated AC over the relative pressure range 0.3 to 0.5 being decreased relative to the initial AC.

Effects of micropore size and chemical nature of the surface of carbon adsorbents on the adsorption isotherms of water vapor

“…The experimental adsorption isotherms presented in Fig. 1 can be described by equa tion (2). The exponent n decreases from eight to four with the increasing micropore size and this is likely due to both an increase in the nonuniformity of the microporous struc ture upon the deep activation of AC and to a lower con centration of water molecules in large pores.…”

“…The char acteristic energies of benzene vapor decrease in parallel to an increase in the micropore size. Taking into account that the Dubinin-Radushkevich (DR) equation 8 is a spe cial case of the Dubinin-Astakhov equation (2) with n = 2, we can compare the characteristic energies of ben zene vapor adsorption calculated according the DR equa tion with the characteristic energies of water adsorption determined according to equation (2). Let us designate the calculated ratio E Н 2 О /E -0 as β Н 2 О .…”

“…As can be seen in Table 2, the β Н 2 О values remain constant and equal to 0.057±0.007. Since β Н 2 О is constant for all the AC, it is possibile to substitute the characteristic energies of the benzene adsorption to equation (2) and to find the P/P s values for θ. Hence, we can construct the adsorption iso therms of water vapor.…”

“…[1][2][3][4][5] It is known 2 that the micropores are filled at increasingly higher pressures when the concentration of the primary adsorption sites (PAS) decreases, for example, during sur face hydrophobization. At the same time, the micropore volume is filled at lower pressures when the PAS concen tration is increased, particularly during CA oxidation.…”

“…Calculated(1,2) and experimental (1´, 2´) adsorption isotherms of water vapor on AC with micropore volume of 0.36 (1, 1´) and 1.28(2, 2´) …”