Rate constant of hydrogen transfer from H-donor solvents to coal radicals

Abstract

To investigate the sustainability of direct coal liquefaction, evaluating the hydrogen-donating activity of hydrogen-donor solvents (H-donors) is one of the critical parameters to determining the distribution and quality of liquid fuels. However, it is difficult to assess the capability of H-donors through experiments alone. Therefore, in this work, the density functional theory calculations and transition state theory were employed quantitatively to analyze the rate constants of hydrogen transfer from H-donors to coal radicals. Results indicated that hyperconjugation and ring strain play essential roles in the hydrogen-donating activity of H-donors. The hydrogen-donating activity is enhanced when the methyl group is substituted at the α position of tetralin. With the increase of alkyl substituents’ chain length, the hydrogen-donating activity of 1-ethyltetralin, 1-propyltetralin, and 1-butyltetralin are close but lower than that of 1-methyltetralin. The alkyl isomerization has a significant influence on the hydrogen-donating activity of H-donors. Due to a higher ring strain, the hydrogen-donating activity of H-donors containing five-membered saturated rings is lower than that of the hydrogenated aromatics with similar structures. Experimental data from the literature confirm the theoretical analysis.