Fate of Char Nitrogen in Catalytic Gasification - Formation of Alkali Cyanate

The object of this work was to determine whether inorganic catalysts would react with char nitrogen to form cyanate during catalytic gasification. The formation of volatile nitrogen compounds during gasification was not studied. Gasification studies with black liquor, a wood-based biomass fuel from the pulping process, have shown that organic char nitrogen is converted into the inorganic compound cyanate during char conversion. The purpose of this work was to determine whether cyanate formation could be seen during catalytic gasification of other fuels loaded with different alkali metal and alkaline-earth metal salts with varying amounts, thus also gaining a better understanding of cyanate formation in black liquor conversion. The catalyst-loaded fuels were pyrolyzed for 10 s to form a char and then gasified at different temperatures in a 13% CO2 in N-2 atmosphere. The nitrogen contents of the untreated fuel samples, pyrolyzed fuel samples, and catalyst-loaded fuel samples after pyrolysis and gasification were analyzed with two different methods. The results showed that more nitrogen is volatilized from biomass samples than from fossil fuel samples and also that the catalyst loading has no clear effect on the amount of nitrogen remaining in the chars after pyrolysis. The residues remaining after gasification were analyzed for cyanate with ion chromatography. The alkali metal salts K2CO3, Na2CO3, and K2SO4 showed catalytic activity in conversion of char nitrogen to cyanate, while KO and CaCO3 did not show any catalytic activity toward cyanate formation. Less char nitrogen was converted to cyanate for coal than for peat and bark during gasification. This indicates that the form of the organically bound nitrogen in the fuel has an impact on cyanate formation.