Advances in research on hydrogenation saturation of polycyclic aromatic hydrocarbons in coal tar

Significance  Polycyclic aromatic hydrocarbons (PAHs), a predominant component in coal tar, can be used to produce jet fuels with high energy density and thermal stability through hydrogenation saturation. Based on the characteristics of the PAH hydrogenation process, this study proposed that primary challenges in PAH hydrogenation saturation include the resonance energy of PAHs themselves, the spatial site resistance of hydrogenation intermediates, and the competitive adsorption of feedstocks and intermediates on active sites in the catalysts.

Progress  Based on the review of research progress in catalysts for PAH hydrogenation saturation in recent years, this study analyzed the substantial factor influencing the catalyst performance, and key findings are as follows: (1) More hydrogenation active sites in catalysts can be obtained by increasing the dispersion of the active metal components in catalysts and reducing the sizes of metal particles in catalysts, with appropriate electron-deficient states of active metals in catalysts promoting the adsorption and activation of PAH molecules on the active sites and inhibiting the adverse effects caused by the competitive adsorption. (2) Catalyst carriers with abundant pore throats and mesopore structures (6‒8 nm) are favorable for the diffusion of PAHs and hydrogenation intermediates, thus reducing the adverse effects of hydrogenation intermediates' spatial site resistance on hydrogenation reactions. Meanwhile, these catalyst carriers can provide more reaction surfaces, thereby enhancing deep hydrogenation reactions. (3) The interactions between acidic suitable carriers and active components can promote the formation of suitable electron-deficient states of the active components. A summary of the thermodynamic and kinetic characteristics of the PAH hydrogenation saturation process revealed that the PAH hydrogenation reactions are exothermic and reversible, with the equilibrium constant and equilibrium conversion increasing with decreasing reaction temperature and increasing reaction pressure, the PAH diffusion intensifying with an increase in the reaction temperature, and the adsorption constant decreasing with an increase in the number of saturated rings.

Prospects  This study proposed suggestions for research on the design and adjustment of the active components and carriers of catalysts, along with the thermodynamics and kinetics of the PAH hydrogenation saturation process. The analyses and discussions of the hydrogenation saturation process of PAHs in coal tar and catalysts in this study will provide useful guidance for the efficient exploitation and utilization of tar-rich coal resources.