Gasification of brown coal and char with carbon dioxide in the presence of finely dispersed iron catalysts

Abstract

Gasification of brown coal and char with CO 2 using iron catalysts precipitated from an aqueous solution of FeCl 3 has been studied. When the pyrolyzed char is gasified in the temperature-programmed mode, the presence of the iron can lower the temperature giving the maximal rate of CO formation by 130–160 K, a larger lowering being observed at a higher loading in the range of ≤ 3 wt.% Fe. The specific rates of the isothermal gasification of iron-bearing chars at 1173 and 1223 K increase with increasing char conversion, resulting in complete gasification within a short reaction time. Comparison of the initial rates of uncatalyzed and catalyzed gasification reveals that iron addition can lower the reaction temperature by 120 K. Mössbauer spectra show that the precipitated iron exists as fine FeOOH particles, which are reduced mainly to Fe 3C on charring at 1123 K. Most of the Fe 3C is transformed into α-Fe and γ-Fe at the initial stage of gasification, and subsequently these species are oxidized to FeO and Fe 3O 4. The changes during gasification are discussed in terms of solid-gas and solid-solid reactions.