Hydrogasification mechanism

Because it requires many possible variables, such as temperature, pressure, the nature of chemical reaction, and the character of the solid surface, and because it incorporates many constants which require experimental evaluation, the general mathematical model to estimate the product gas distribution for different levels of carbon conversion can become exceedingly complicated. Practical application of this model is particularly difficult when a choice has to be made between reaction mechanisms, each of which can generate complex functions with a sufficient number of arbitrary constants to fit any given experimental curve. The purpose of the work discussed in this paper was to study the influence of temperature and the partial pressure of hydrogen and steam on the rate of steam-hydrogen and coal char reactions based on the previous pilot plant data obtained at IGT (10, 11) and to develop a correlation to estimate the performance of a hydrogasification reactor in terms of its product gas distribution for different levels of carbon conversion. 

In contrast to hydrogenation and oxidation reactions, much less is known about the ability of materials to effect the catalysis of hydrogasification reactions. Alkali carbonates, 1-10 wt % catalyze the hydrogasification of coals and cokes at 800°-900°C (6). The suggested mechanism is that adsorption of the alkalies by carbon prevents graphitization of the surface. Zinc and tin halides are effective hydrogasification catalysts. There is, however, little kinetic information on any of the catalyzed hydrogasification reactions. 

In contrast to homogeneous reactions, where activation enthalpies are independent of the extent of reaction, hydrogasification activation enthalpies are clearly a function of the extent of reaction. One mechanism postulated by a number of investigators is based on the carbon structures becoming more graphitic with increasing reaction. In the absence of any other information, the simplest function for AH (X) is a linear form... 

The apparent activation energy for the second stage hydrogasification of char has been reported to vary between 30 to kl Kcal/mol (UO, Zahradnik and Glenn (jj ) discussed the mechanism of methane formation in hydrogasification reaction and proposed an empirical rate expression for Pittsburg seam coal as follows ... 

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