Experimental studies and molecular modelling of catalytic steam gasification of brown coal containing iron species

• Published in: Fuel (Guildford) 2012-03, Vol.93, p.404-414
• Main Authors: Domazetis, G., James, B.D., Liesegang, J., Raoarun, M., Kuiper, M., Potter, I.D., Oehme, D.
• Format: Article
• Language: English
• Subjects: Applied sciences; Catalysis; Catalysts; Catalytic brown coal steam gasification; Combustion; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fuels; Gasification; Iron; Modelling; Molecular modelling; Reaction mechanisms; Weight loss
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2011.09.001

► XPS data of catalytic steam gasification of char shows oxygen from steam is distributed as inorganic and organic. ► Higher loadings of polynuclear iron hydroxyl-species lead to greater conversion of char substrate. ► QM-SE molecular modelling data are consistent with experimental results. ► Concerted reaction mechanisms are energetically favoured over discreet mechanisms. The paper presents experimental data of catalytic steam gasification of brown coal containing aqua-iron species, and the chemical mechanism(s) at a molecular level. Experimental techniques provided weight loss from catalysed reaction of char with steam of 17wt% at 800°C and 40wt% at 900°C, over 15min, on a dry ash free basis (daf). Inorganic and organic oxygen, identified using XPS in the char samples, was derived from reactions with steam. High yields of H2 resulted from catalysed reactions between char and steam. Semi-empirical (SE) quantum molecular modelling using MOPAC, of reaction routes for high temperature pyrolysis and steam gasification, provided results consistent with experimental data for weight loss, iron species, and the distribution of inorganic and organic oxygen in char samples after reaction with steam. The catalysis mechanism(s) that have been examined are considered to be a hybrid of organometallic and heterogeneous chemistry, involving iron hydride species that precede H2 formation; oxygen insertion into [Fe–C–] to form [Fe–O–C–] followed by elimination of CO, creating another [Fe–C] site to continue the catalytic cycle. SE modelling indicates concerted reactions were more energetically favoured. Initial results from molecular dynamics (MD) show a higher concentration of H2O molecules about the active site [Fe–C].