Effect of regeneration treatment with liquid water at high pressure and temperature on the characteristics of three commercial activated carbons

The regeneration of three commercial activated carbons by thermal desorption with liquid water at 320 degrees C and 150 atm, in the absence of oxygen, was investigated. The efficiency of this procedure was evaluated by measuring the rate and the amount of substance retained in successive cycles of adsorption-regeneration. The efficiency of the treatment was found to be very high. The study was conducted with the adsorption of two compounds differing greatly in their molecular sizes: phenol and an azo dye (direct red 79 C.I. 29065). In all three carbons a slight increase in the adsorptive power was observed with respect to the original carbons; this is attributed to the cleaning or opening of closed pores. The carbons exhausted with phenol showed the greatest difficulty in regenerating because part of the phenol may be chemically adsorbed. The effect of the treatment on the textural and chemical characteristics of the original carbons was also investigated using N-2 adsorption isotherms, mercury porosimetry, pycnometry, scanning electron microscopy and acid-base titration. The alterations found were not very significant, except for a slight increase in the true density, total pore volume and the acidity of the treated carbons. (C) 1999 Elsevier Science Ltd. All rights reserved.