Mechanism of catalytic gasification of coal char. Quarterly technical progress report No. 7, 1 April-30 June 1982
1982
The results of our experimental studies have led us to propose a char asification mechanism (Quarterly Report No. 6) in which the catalyst reacts chemically with the carbon and also with the oxidizing gas to transfer reactive oxygen from the gaseous reactant to the char. The oxygenated carbon structure then splits to yield CO, a major gasification product. Our efforts have been aimed at elucidating some mechanistic details of this scheme. Since transfer of electric charge between catalyst and char is a feature of the mechanism, we have measured the thermoelectric power (Seebeck effect) of catalyst-impregnated carbon wafers to identify the charge carrier type. The results show that, at steady state in an inert atmosphere, electron holes, probably in the carbon phase, are the majority charge carriers. However, during the initial interaction between the catalyst and the carbon, a transient condition exists in which the nature of the electrical transport process is not clear. To provide experimental support for a proposed thermal decarbonylation step in the production of CO from oxygenated carbon structures, we studied the decomposition of a polynuclear carbonyl compound (violanthrone) by temperature-programmed desorption/reaction (TPD/TPR) with and without the addition of catalyst. A significant yield of CO wasmore » measured in the temperature range 500 to 800 K, but later examination by field ionization mass spectrometry (FIMS) of the reactor residue after nearly complete gasification showed no fragments indicative of the loss of CO from the starting material. Further examination of the activation of sodium-chloride-impregnated carbon by steam pretreatment has confirmed the effect. The conditions used are far from optimal, however, and the chemical mechanism of the process is not understood.« less
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