Thermal Regeneration of Granular Activated Carbons Using Inert Atmospheric Conditions

Abstract

Thermal regeneration is increasingly being used for the recovery of field-spent granular activated carbons (GAC) generated by the water treatment industry. Despite its commercial success, conventional methods using oxidising conditions (usually steam) are known to damage the porosity of the regenerated carbons, thus reducing their adsorption capacity and economic value. This paper presents a comparative investigation into the benefits of using inert conditions for the regeneration of field-spent GAC. For the purpose of this work, a sample of spent carbon was regenerated in nitrogen and in steam to different degrees of burn off. The resulting samples were analysed for their porosity and surface area characteristics using nitrogen gas adsorption, and for their aqueous adsorption capacities using phenol and methylene blue. Experimental results showed that steam was sightly more effective than nitrogen at regenerating the total micropore volume and BET surface area of the carbons. However, these benefits were largely counteracted by greater losses in the carbon yield and damage to the narrow microporosity. Carbons regenerated in nitrogen exhibited greater adsorption capacities for the adsorption of small molecular size compounds (phenol) from solution, while carbons regenerated in steam adsorbed larger molecular size compounds (methylene blue) more effectively. However, when product yields were taken into consideration, inert regeneration was found to produce significantly better results than steam regeneration. An optimum process temperature was determined to be 950 degrees C.

Recovery, concentration and purification of phenolic compounds by adsorption: A review

“…However, steam reactivation may reduce the adsorption capacity (Cabal et al, 2009) and causes greater carbon losses than nitrogen. Carbons regenerated under nitrogen exhibited greater adsorption capacities for smaller size molecules than steam regenerated ones (San Miguel et al, 2002). Temperature-programmed thermal desorption of model phenols adsorbed onto ACs is a technique used to study the surface composition, the binding states of volatile adsorbates and the desorption kinetics (Salvador and Merchán, 1996;Humayun et al, 1998;Nevskaia et al, 1999).…”

Biogas Cleaning: Activated Carbon Regeneration for H2S Removal

“…Catalytic oxidation is responsible of localized partial gasification of the carbon material. Partial destruction of narrow micropores and the formation of larger dimension pores occur [38]. This treatment is "harder" than nitrogen, but should guarantee better performances, since reactions with SO 2 or S previously adsorbed can occur.…”

“…This type of thermal regeneration is responsible for thermal decomposition of adsorbed matter, in this case H 2 S molecules, thermal cracking and desorption of decomposition products [38,39]. This treatment is a "soft" treatment, which causes minor damages to the narrow microporosity and a high recovery of the pore volume and surface area, responsible for physical adsorption, whose entity depends on regeneration temperature [37].…”

“…Considering to the literature studies [37,38], parameters were set for the regeneration tests: According to the literature, the gas flow rate does not affect the regeneration, while the most important parameter is the temperature and/or the regeneration time, as appropriate. Three different values were selected in order to understand how Rr changes with the temperature.…”

Novel decentralized greywater treatment system based on combined adsorption and electrochemical oxidation

“…Thermal regeneration of GAC is the most common alternative used at industrial scale. It involves a pyrolytic and oxidative stage, where saturated GAC is exposed to temperatures over 900ºC (Brown et al 2004a, Narbaitz and Cen 1994, San Miguel et al 2002. Regeneration efficiencies of this process are above 90%, however, it is a high energy consuming process (5.6-13.9 x 10 6 J kg C -1…”