Catalytic Fast Pyrolysis of Tar-Rich Coal with a Bauxite Residue for Upgrading High-Value Products: Product Distribution and Kinetic Analysis.

Fast pyrolysis technology can reduce the secondary reactions, improve the volatile product yield, and reduce the semicoke yield. Still, the high proportion of heavy tar components affects the development of fast pyrolysis industrialization. Therefore, this paper put forward a catalytic upgrading method of coal based on the solid waste bauxite residue (BR) as a catalyst. This study investigated the impact of varying particle sizes of pulverized coal and the addition of the BR catalyst on the product distribution and kinetics of coal fast pyrolysis. The results found that the tar yield was the highest at 600 °C when the particle size of pulverized coal was 75-150 µm, which was 19.44%. In the range of 550-650 °C, the relative content of benzene and toluene xylene (BTX) in liquid products increased with the temperature. With the increase of the proportion of the BR catalyst, the yield of semicoke in coal pyrolysis products increased, the yield of the gas phase also increased, and the yield of the liquid phase decreased.

Thermodynamic Analysis of In Situ Underground Pyrolysis of Tar-Rich Coal: Primary Reactions.

In situ underground pyrolysis of tar-rich coal is significant for alleviating the scarcity of oil and gas resources and realizing the green and efficient development and utilization of coal in China. Tar-rich coal is often subjected to high axial pressure, surrounding pressure, and pore pressure in the in situ underground pyrolysis environment. Consequently, laboratory simulation conditions are difficult to meet the actual needs. This paper conducts a thermodynamic study of the pyrolysis characteristics of tar-rich coal under an in situ environment. Typical thermodynamic functions of tar-rich coal, including the standard enthalpy of formation, standard formation Gibbs free energy, and standard entropy, were determined. Ten representative primary reactions were constructed with typical tar-rich coal pyrolysis oil components as a guide. The Gibbs free energy and equilibrium constant change laws of the above reactions were analyzed for pyrolysis temperatures from 200 to 800 °C and pyrolysis pressures from atmospheric pressure to 10 MPa. The results showed that the standard enthalpy of formation of tar-rich coal was -72.27 kJ·mol-1, the standard entropy was -37.79 J·mol-1·K-1, and the standard formation Gibbs free energy was -60.01 kJ·mol-1. When the reaction pressure increased from atmospheric pressure to 10 MPa, the thermodynamically feasible initial temperature fractions of the primary reaction of tar-rich coal pyrolysis all showed different degrees of increase. In the underground environment, the initial temperature of the primary reaction of in situ underground pyrolysis of tar-rich coal moves to a higher-temperature gradient to some extent, so the adjustment of the reaction temperature and pressure could guide the directional regulation of the in situ underground pyrolysis products of tar-rich coal.

Thermodynamic Analysis on In Situ Underground Pyrolysis of Tar-Rich Coal: Secondary Reactions.

To develop the in situ underground pyrolysis process of tar-rich coal more scientifically, the effect of temperature and pressure on the distribution of pyrolysis products should be clarified. This paper selected the typical components in five distillates of light tar, phenol tar, naphthalene tar, washing tar, and anthracene tar as the main reaction products. 32 typical secondary reactions were constructed. Based on the thermodynamic analysis strategy, the variation of the Gibbs free energy and equilibrium constant of secondary reactions was investigated. The results showed that pressure mainly affected the reaction characteristics of molecule-increasing reactions. The Gibbs free energy value of the molecule-increasing reactions increased with increasing pressure. The trend that the reaction could proceed spontaneously gradually weakened. The initial temperature of some reactions that could proceed spontaneously would need to increase by dozens or even hundreds of degrees. Due to the influence of formation pressure, the generation of related components of light tar, naphthalene tar, washing tar, and anthracene tar would be inhibited to varying degrees in the in situ underground pyrolysis process. The secondary reactions related to phenol tar were equimolecular reactions, which were almost unaffected by stratal pressure. Axial pressure and confining pressure of different coal seam depths should be considered in the process of in situ underground pyrolysis.