Characterization of tar from the pyrolysis/gasification of refuse derived fuel: Influence of process parameters and catalysis

Two nickel-based catalysts were prepared and investigated in relation to their influence over aromatic compounds contained in tar from the pyrolysis-gasification of refuse derived fuel (RDF), using a two-stage reaction system. The results were compared with those obtained in experiments carried out using a bed of sand, both with steam and without steam. The condensed tar was analyzed for its polycyclic aromatic hydrocarbon (PAH) content using gas chromatography-mass spectrometry (GC-MS), size exclusion chromatography (SEC), and Fourier transform infrared spectroscopy (FTIR) techniques. It was found that, in the presence of Ni/α-Al ₂O ₃ catalysts, some of the PAHs from three to four rings were eliminated; however, some single-ring and two-ring compounds such as styrene and indene were identified. This was also inferred from the molecular mass data (SEC). The identified PAHs consisted mainly of naphthalene, biphenyl, acenaphthylene, fluorene, and phenanthrene, but other PAHs also were identified for example: methylnaphthalenes. The influence of catalyst type on the gas composition showed that, using a 10 wt % Ni/α-Al ₂O ₃ catalyst, ∼45 vol % of hydrogen was achieved, while the CH ₄ and C ₂-C ₄ concentrations were markedly reduced, compared with the 5 wt % Ni/α-Al ₂O ₃ catalyst, which gave similar results to those obtained with the sand bed under the same conditions. The presence of oxygenated compounds in the tar samples was compared at different gasification temperatures. The results showed the presence of oxygenated compounds such as catechols and alcohols at 600 °C, these compounds were reduced as the gasification temperature increased, while the concentration of aromatic compounds increased.