The Chemical Kinetics of the Hydrogenation of Coal Extract Solutions

Abstract

The chemical kinetics of the hydrogenation of coal extract solutions have been studied in a semi-continuous stirred tank reactor with slurried catalyst. The reactor system and experimental programme were designed so that many of the process variables affecting the rate of hydrogenation of coal extract solutions and suspected reaction intermediates could be investigated. These variables included reaction time, temperature, pressure, catalyst loading and coal concentration and their effects on hydrofining, catalyst deactivation and product composition were also studied. The results showed that at the catalyst loadings generally employed, the rate limiting steps were chemical reaction on the catalyst surface and mass transfer from the gas-liquid interface into the bulk liquid. The overall reaction was found to be first order with respect to coal material remaining, the rate constant showing an Arrhenius temperature dependence giving a high apparent activation energy. The kinetics could be adequately described in terms of a series of distillation fractions of different boiling range. On this basis, a scheme has been proposed for the reactions involved in the hydrogenation of coal extract solution. The rate constants for each. Step in the scheme were determined and a mathematical model was developed. The yields predicted by the model were in good agreement with the experimental results. It was also shown that the reaction scheme was applicable to the hydrogenation of coal extract solutions in other reactor systems.