Changes in hydrogen utilization with temperature during direct coal liquefaction

A method for quantitative measurement of the hydrogen utilized in different modes of reaction has been applied to hydroliquefaction reactions at temperatures ranging from 375 to 450 °C. The analytical approach is capable of differentiating hydrogen utilized in hydrogenation reactions from that used in bond scission chemistry (hydrogenolysis). The hydrogenolysis reactions result in breakdown of the coal matrix, formation of light hydrocarbon gas and elimination of organic heteroatoms. The results indicate that in this small continuous reactor, operated at 13.8 MPa (2000 psig) H₂, little net chemical activity of hydrogen occurs at 375 °C. However, at 400 °C, the slurry has been hydrogenated significantly with little net hydrogen incorporation. At 450 °C comparable amounts of hydrogen are consumed in gas generation, heteroatom removal, hydrogenation and matrix breakdown, with large net hydrogen incorporation. These results indicate that at temperatures below the thermolysis threshold of 400 °C, significant internal hydrogen redistribution occurs in the slurry. At higher temperatures, a more conventional hydroliquefaction chemistry involving significant bond cleavage and aromatization is indicated. This approach to analysis of hydrogen utilization requires integration of a variety of analytical data. The uncertainties in these data and their impact on the resultant utilization profile are discussed.