An investigation of the bituminous coal dissolution phenomena has been undertaken in order to develop information which would be useful in the design and scale-up considerations for a commercial liquefaction plant. The experimental data of this study were derived from pilot plants using various coal liquefaction processes. The data were analyzed in order to better understand the phenomena which occur in the preheater and reactor sections during the liquefaction of coal. Two different stages were found to exist in the coal dissolution reactions. In the initial stage of coal dissolution, a first-order reaction scheme is proposed, whereby coal undergoes a fast thermal reaction producing preasphaltene as the predominant product. Conversion for this reaction is calculated based on the amount of pyridine solubles formed. The rate coefficient for this stage is found to follow an Arrhenius type temperature dependence with an activation energy of 48 approx. 55 Kcal/g-mole. In the second stage of coal dissolution, a slower first-order rate expression is proposed in which the preasphaltene is converted to benzene solubles with subsequent rehydrogenation of the coal-derived solvent. A semi-empirical correlation for the dissolution rate coefficient in the second stage reaction is presented, which reasonably accounts for the effects of temperature, hydrogen partial pressure and of particular importance - reactor hydrodynamics. However, the rate coefficient was found to be practically independent of coal particle size. Finally, the rate of hydrogen absorption during coal dissolution is modeled by assuming that the gas and liquid phases are in equilibrium at the interface. The overall gas absorption coefficient was found to be a function of superficial gas velocity.
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