Influence of Surface Oxides on Ethanol Regeneration of Spent Carbonaceous Adsorbents
EXPERIMENTAL Activated carbon (AC) and activated carbon fiber (ACF) that
Activated carbon (AC) was supplied by Calgon Co., Ltd., USA, and its adsorbed aromatic compounds were regenerated by ethanol. The BET surface area is 9.27 1 10 5 m 2 /kg. We used activated carbon fiber influence of their acidic surface oxides on ethanol regeneration (ACF) (A-15; Osaka Gas Co., Ltd., Japan), whose BET surface area is was studied based on the frontier orbital theory. It is found that the 1.5 1 10 6 m 2 /kg. We oxidized AC or ACF by use of HNO 3 aqueous regeneration efficiency can be correlated by the energy difference solution and prepared AC-OX1 or ACF-OX1 by 1.1 N HNO 3 and AC-OX2 between HOMO of aromatic compounds and LUMO of adsorbents by 6.6 N HNO 3 . The detailed procedure of oxidation and acidic surface
The regeneration efficiency is improved by oxidizing oxides formed on the carbons have been already reported (4, 7).
AC or ACF because the adsorptive interaction becomes weak as
To determine the performance of repeating ethanol regeneration of spent the energy difference ΓE H 0 E L Γ increases. The influence of the carbons, we conducted the following batch runs. In a 3 1 10 04 m 3 Erlenmyer flask with a screw cock, 2 1 10 04 kg of AC, AC-OX1, AC-OX2, ACF, or oxides on repeating ethanol regeneration of the carbons that ad-ACF-OX1 was contacted with 2 1 10 04 m 3 of aqueous solution containing sorbed p-cresol was then experimentally elucidated. Although the 500 ppm p-cresol. The flask was placed on a shaker and agitated at 308 K regeneration efficiency of oxidized AC or ACF is kept higher than for 21 h, and the amount of p-cresol adsorbed was determined from the that of original AC or ACF even after the 16th regeneration, the initial and final concentrations of adsorbate in the liquid phase.
oxidation has no practical use because the adsorption capacity is
The adsorbents were filtered from the solutions by use of 0.1 mm memdecreased by the oxidation. α§ 1997 Academic Press brane filter (Toyo Roshi Co., Ltd., Japan; NC) and were dried by N 2 at Key Words: ethanol regeneration; activated carbon; activated 413 K for 1 h. The N 2 flow rate was 1.7 1 10 06 m 3 / s. After the adsorbents carbon fiber; acidic surface oxide; liquid adsorption; aromatic comwere dried, p -cresol was desorbed by 2 1 10 04 m 3 of ethanol for 21 h in the 3 1 10 04 m 3 Erlenmyer flask. After ethanol was removed from the pound; frontier orbital theory; semiempirical MO calculation.
adsorbent by N 2 at 413 K for 1 h, the adsorbents regenerated were used for adsorption of p -cresol again. We repeated this cycle 16 times for AC, AC-OX1, AC-OX2, ACF, and ACF-OX1 and determined changes of the amount adsorbed q n and the ratio of amount adsorbed to the amount on virgin adsorbent q n /q 0 with regeneration cycle number n.