THERMAL-DESORPTION OF GALLIC ACID FROM ACTIVATED CARBON SURFACES

The thermal regeneration processes of two spent activated carbons from olive stones loaded with gallic acid (3, 4,5-trihydroxybenzoic acid) have been studied by differential thermogravimetry (DTG) and by mass s pectrometric temperature-programmed desorption (TPD-MS). The samples w ere heated to 1250 K in an inert gas flow both dry and wet. The percen tage of gallic acid removed with regard to the amount adsorbed is betw een 70 and 80% and it depends on the activation degree of the carbon s ample which affects the activated carbon-gallic acid interactions. At low temperatures a fraction of physisorbed gallic acid is released as heavy compounds and the rest is transformed to chemisorbed. Between 40 0 and 800 K the process is dominated by the decomposition of the chemi sorbed garlic acid into CO2, H2O and CO. At temperatures higher than 8 00 K, ring condensation reactions take place. The presence of water in the regeneration atmosphere enhances the transformation of physisorbe d to chemisorbed gallic acid, degrades a fraction of the heavy compoun ds leaving the carbon surface to lighter compounds and gasifies the ac tivated carbon up to 0.5% burn-off.