Mixtures of potassium sulphate and iron sulphate as catalysts for water vapour gasification of carbon: 3. Chemsitry of the in situ activation of the catalyst

Abstract

Previously it was shown that certain mixtures of K 2SO 4 and FeSO 4 were excellent raw materials for catalytic water vapour gasification of carbon. It was suggested from the results that the iron salt catalyses the reduction of K 2SO 4 to K as the main catalyticly active species of gasification. This paper is concentrated on this activation process. Using TGA, DTA, ESCA, EPMA and visual observations of the melting behaviour after or during treatment of varying K 2SO 4 FeSO 4 mixtures in H 2 and H 2 H 2O atmospheres it is found that elemental iron is formed in an early stage during heating up. This then catalyses the reduction of K 2SO 4 to K 2S, which is readily hydrolysed by water vapour to liquid KOH. K 2SO 4 and K 2S form an intermediate eutectic ( m. p. = 610 °C), which favours wettability of the carbon surface and hydrolysis of K 2S. As well as FeSO 4 any iron salts can be used that are easily reduced to elemental iron in the gasification atmosphere. A general reaction scheme, including activation and catalytic gasification, is proposed. The activation of K 2SO 4 to catalytically active KOH can be described as follows: Fe- saltγFe3 K 2 SO 4 + 8 Feγ3 K 2 S + 4 Fe 2 O 3 Fe 2 O 3 + 3 H 2 γ 2 Fe + 3 H 2 O K 2 S + H 2 OγKHS+ KOH KHS + H 2 OγKOH + H 2 S