Elucidation of Mechanism of Coal Liquefaction Using Tritium and ³⁵S Tracer Methods

Abstract

The reactivity of hydrogen in tetralin and in Taiheiyo coal in the presence of iron catalysts (pyrrhotite and iron pentacarbonyl (Fe(CO)5)) and sulfur were investigated using tritium and 35S tracer methods under liquefaction conditions. Coal liquefaction was performed for 30 min at an initial pressure of 5.9 MPa and a temperature of 400 °C in the presence of tetralin solvent and tritiated hydrogen, with and without a catalyst and 35S-labeled sulfur. The rate of coal conversion and the tritium distribution in coal were higher when Fe(CO)5 and sulfur were used than were obtained with conventional pyrrhotite. Further, the coal products obtained with the use of Fe(CO)5 and sulfur were lighter than those produced in the presence of added pyrrhotite. The results suggest that the catalyst derived from Fe(CO)5 and sulfur was successfully dispersed in the coal and directly acted on the coal to increase both the rate of coal conversion and the tritium transfer from the gas phase to the coal. The iron catalysts greatly promoted the hydrogen exchange between the gas phase and the tetralin solvent in the absence of coal. Part of the added sulfur participated in the sulfur exchange reaction with the pyrrhotite catalyst. The addition of sulfur increased the amount of hydrogen incorporated into the coal. This suggests that sulfur promoted the formation of tetralyl radicals during the hydrogen transfer from the solvent to the coal.

Clean liquid fuels from direct coal liquefaction: chemistry, catalysis, technological status and challenges

“…194 catalytic dissociation will increase the pool of available hydrogen within coal or the coal-solvent system and will be available for aromatic hydrogenation, the promotion of bond cleavage reactions, and radical stabilization. 84,[199][200][201][202][203] Molecular hydrogen can also influence the course of thermal C-C bond cleavage reactions by competing with donor hydrogen. Vernon studied C-C bond cleavage in the reaction of model compounds such as bibenzyl (C 6 H 5 CH 2 ) 2 and biphenyl (C 6 H 5 ) 2 at 450 C in the presence of tetralin, hydrogen or a mixture of these compounds.…”

Reactions of Tetralin with Tritiated Molecular Hydrogen on Pt/Al2O3, Pd/Al2O3, and Pt−Pd/Al2O3 Catalysts

“…As reported recently, tritium tracer methods are very effective for the quantitative tracing of hydrogen behavior of coal and tetralin during coal liquefaction in a batch reactor. − Further, tetralin is known to be a simple and good solvent in the coal liquefaction process and can be taken as a typical model compound representing the aromatic compounds in distillate fuels, especially in fcc-LCO. Recently, we reported that the hydrogen mobility of tetralin can be elucidated using a flow reactor .…”

Catalysis in Direct Coal Liquefaction

“…In addition to its role in the conversion of catalyst precursors into active metal sulfides, it promotes radical chain reactions between coal, solvent and molecular hydrogen [10,62,97,144] and under certain conditions even causes bond cleavages [145]. In addition to its role in the conversion of catalyst precursors into active metal sulfides, it promotes radical chain reactions between coal, solvent and molecular hydrogen [10,62,97,144] and under certain conditions even causes bond cleavages [145].…”