Abstract
As a country that is poor in petroleum yet rich in coal, it is significant for China to develop direct coal liquefaction (DCL) technology to relieve the pressure from petroleum shortages to guarantee national energy security. To improve the efficiency of the direct coal liquefaction process, scientists and researchers have made great contributions to studying and developing highly efficient hydrogen donor (H-donor) solvents. Nevertheless, the details of hydrogen donation and the transfer pathways of H-donor solvents are still unclear. The present work examined hydrogen donation and transfer pathways using a model H-donor solvent, tetralin, by density functional theory (DFT) calculation. The reaction condition and state of the solvent (gas or liquid) were considered, and the specific elementary reaction routes for hydrogen donation and transfer were calculated. In the DCL process, the dominant hydrogen donation mechanism was the concerted mechanism. The sequence of tetralin donating hydrogen atoms was α-H (C1–H) > δ-H (C4–H) > β-H (C2–H) > γ-H (C3–H). Compared to methyl, it was relatively hard for benzyl to obtain the first hydrogen atom from tetralin, while it was relatively easy to obtain the second and third hydrogen atoms from tetralin. Comparatively, it was easier for coal radicals to capture hydrogen atoms from the H-donor solvent than to obtain hydrogen atoms from hydrogen gas.
Highlights
Direct coal liquefaction (DCL) transforms solid coal to liquid fuels and chemicals, which is a clean and efficient technology for coal utilization [1]
As China is poor in petroleum yet rich in coal, it is vital to develop direct coal liquefaction to relieve the pressure from petroleum shortages, which would help guarantee national energy security and the rapid development of the national economy [2]
Coal (H/C atomic ratio ≈ 0.8) is converted to liquid fuels (H/C atomic ratio ≈ 2) by adding external hydrogen atoms to free radicals derived from coal pyrolysis during the DCL process [3]
Summary
Direct coal liquefaction (DCL) transforms solid coal to liquid fuels and chemicals, which is a clean and efficient technology for coal utilization [1]. There are two kinds of main hydrogen atom sources in DCL: hydrogen gas and hydrogen donor (H-donor) solvents [5,6,7]. Hydrogen gas is supposed to be the main hydrogen atom source in DCL [8,9]. In order to produce more liquid fuels, DCL processes traditionally operate at high hydrogen partial pressure (≥20 MPa). Under such a severe reaction condition, traditional DCL faces many challenges, such as Catalysts 2018, 8, 648; doi:10.3390/catal8120648 www.mdpi.com/journal/catalysts
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