Kinetics of short contact time coal liquefaction. Part II: Effect of nature of coal and solvent

Abstract

A bituminous coal (Powhatan No. 5 ) and a subbituminous coal (Belle Ayr) were liquefied in the presence of hydrogen donor solvents. Statistical analyses of the data showed that for contact times up to 10 min, the coal conversion, measured in terms of tetrahydrofuran solubles, was not significantly different for the two coals. However, the subbituminous coal gave more asphaltenes than the bituminous coal.The hydrogen-donating capacity of the solvent was varied by the addition of hydrogenated phenanthrene to SRC-I1 recycle solvent. The results indicated that there are two routes for the formation of oils from coal. One is by adduct formation giving asphaltenes and preasphaltenes, which in turn gives oils, and the other is direct oil formation from coal. The preferred route depends on the hydrogendonating capacity of the solvent, The kinetic model, proposed in Part I of this paper, is extended to account for the change in the donor capacity of the solvent. SCOPECoal liquefaction can be characterized as occurring in three stages, namely dissolution, hydrogen transfer, and hydrogenation. In each of these stages the nature of the solvent can affect the rate of reaction and the selectivity of the products. Solvent components which affect the behavior of coal liquefaction processes can be classified as hydrogen donors, hydrogen shuttlers, and components that aid in solubilization. Recent studies have shown that poor bydrogendonating solvents form adducts with coal to give insoluble products. This appears to occur to a lesser extent with good donor solvents. It is likely that for the case of good hydrogen donor solvents the formation of soluble products compensate for the adduct formation. Kinetic measurements at short contact times (up to 10 min) with solvents of varying hydrogen donor capacity have been made to provide a better understanding of the processes of liquefaction and adduct formation. CONCLUSIONS AND SIGNIFICANCEIn a stirred tank batch reactor, there appears to be no significant difference in the conversion of Powhatan No. 5 bituminous and Belle Ayr subbituminous coal to pentane and tetrahydrofuran (THF) solubles for contact times up to 10 min. More asphaltenes are recovered from the liquefaction of Belle Ayr coal than from that of Powhatan coal. Both the coals, when contacted with SRC-I1 recycle solvent, show an initial effective loss of solvent.The initial depletion of oils progressively decreases with an increase in the hydrogen-donating capacity of the solvent, indicating that the initial loss of solvent is independent of the nature of coal, but it is dependent on the hydrogen-donating capacity of the solvent. Oils can be formed either directly from coal or by an indirect route via asphaltenes and preasphaltenes through adduct formation. The latter results in an initial loss of solvent. The former route gains preference over the latter as the hydrogen-donating capacity of the solvent is increased. A single kinetic model entailing both direct and indirect routes is shown to adequately represent the data o...

Novel supports for coal liquefaction catalysts

“…m lt is clear that the addition of catalyst to the liquefaction reactor is advantageous, and it is not difficult to speculate as to why this is so. The insitu regeneration of hydrogen donor may be necessary to insure that free-radical coal fragments are quenched rapidly to prevent repolymerization (2,3), and it has been shown that good hydrogen donor capacity is essential to reduce solvent adduction (4)(5)(6). lt has been suggested that the catalyst may participate directly in the hydrogen transfer reactions between the hydrogen donor and the II coal fragments (7).…”