This chapter discusses how retrogressive reactions occur in catalytic liquefaction using dispersed Mo sulfide catalyst. Retrogressive reactions occur in coal liquefaction at 425–450° C in 25 mL reactors, even in the presence of dispersed Mo sulfide catalyst. By using H-donor solvent in catalytic runs at higher temperatures, the retrogressive reactions can be mitigated. Two approaches can be considered for improving the balance between thermal fragmentation(TF) and hydrogen available (HD): (1) modifying the rate of coal fragmentation at high temperatures by incorporating low-temperature coal pretreatment, temperature-staging, temperature-programming, and catalytic pretreatments and (2) increasing the hydrogen transfer capacity by using H-donor and hydrogen shuttler, in combination with hydrogenation catalyst under high pressure of hydrogen.
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