Removal of naphthalene by activated carbons from hot gas

The gasification of biomass and waste is a potentially high efficiency process for energy generation. However, the appropriate cleaning of the produced fuel gas is a major issue, in particular for tar removal. This study investigates the performance of three new-generation activated carbons, which are able to adsorb a wide spectrum of tars at high temperature, from 750 °C up to 900 °C. For this purpose, a laboratory-scale hot gas filtration apparatus was designed and set-up. Experimental tests were carried out with naphthalene as the reference tar compound. The selected activated carbons were tested under different conditions of temperature, test duration and naphthalene concentration. The procedure allows evaluating the contributions of adsorption and cracking phenomena on the overall tar removal efficiency. Complete naphthalene removal was obtained with two of the selected activated carbons, at 850 °C and 900 °C respectively. Simultaneously, a partial reforming of adsorbed naphthalene was observed, and molecular hydrogen was detected in the gas phase. Results were correlated to the differences in porosimetry and chemical surface of the selected activated carbons, as well as to those highlighted by Scanning Electronic Microscopy and X-ray analyses. Finally, a procedure for activated carbon regeneration by carbon dioxide is reported, together with results from preliminary tests.