Coal hydrogen transfer from tetralin

The dialin donor solvents were also used directly in coal liquefaction studies. Inasmuch as details of coal structure are unknown, the present theory can only be tested in a qualitative way, as follows. First, if the liquefaction of coal occurs under kinetic control with hydrogen-transfer from the donor solvent involved in the rate-determining step, then we should expect the dialin donors to be more effective than the control solvent T.et-ralin (and also Dfecalin). This is suggested by the theory because the dialins possess higher energy HOMOs than Tetralin and... 

Mechanisms of the formation of the decal ins in the recovered solvent were based on their isotopic contents. The cis-Decalin-die had a greater protium content than the recovered Tetralin-di2-This suggested that hydrogen transfer from the coal to the tetralin is involved in the formation of cis-Decalin. 

In coal liquefaction, highly dispersed, disposable, catalysts are needed because maximal contact between coal and catalysts is essential. It is assumed that one of the roles of the coal liquefaction catalyst is to assist in the rehydrogenation of the donor solvent (e.g. tetralin) by facilitating the hydrogen transfer from the gas phase.36,37... 

Autoclave Results - Solvent Activity Test. The initial microautoclave work was done with tetralin and methylnaphtha-lene, using Indiana V bituminous coal (Table I). Base line data is shown in Figure 4. All three tests, Kinetic, SRT, and Equilibrium, show an increase in coal conversion with an increase in the concentration of tetralin. The Equilibrium Test shows the highest coal conversion of approximately 86 wt% of the MAF coal (based on the solubility in the tetrahydrofuran) at the 50% tetralin concentration. The Kinetic Test shows lower coal conversion. The hydrogen transferred to the coal from the tetralin in the Equilibrium Test at the 50 wt% tetralin feed concentration is approximately 0.5 wt% of the MAF coal. In the Kinetic Test 50 wt% tetralin feed concentration results in a much smaller transfer at the short reaction time of 10 minutes. 

Direct Liquefaction Kinetics Hydrogenation of coal in a slurry is a complex process, the mechanism of which is not fully understood. It is generaly believed that coal first decomposes in the solvent to form free raclicals which are then stabilized by extraction of hydrogen from hydroaromatic solvent molecules, such as tetralin. If the solvent does not possess sufficient hydrogen transfer capability, the free radicals can recombine (undergo retrograde reactions) to form heavy, nonliquid molecules. A greatly simplified model of the liquefaction process is shown below. 

The hydrogen transfer reaction will be a second-order process since the transfer reaction from the tetralin to the coal will not be an abundant process at the temperatures used here. 

All of these reactions presumably arise through free radical mechanisms. The abstraction of hydrogen from tetralin by coal to produce naphthalene is of course expected. What sets this reaction apart from the rest is the linear dependence of naphthalene yield on coal concentration. From the slope of the yield curve, we calculate that hydrogen was removed from tetralin in the amount of 2.5 wt. percent of the added coal. This is a reasonable amount of hydrogen to be transferred to coal under liquefaction conditions. However, we note a recent report on the decomposition of 1,2-diphenylethane in tetralin in which Benjamin states that over twice the amount of naphthalene required in the formation of toluene was produced (11). Presumably, the excess appears as molecular hydrogen. In the present case, we cannot rule out the possibility that some fraction of the naphthalene was produced by a similiar mechanism. 

Hydrogen donors labelled with deuterium, such as tetralin-and naphthalene-4 have also been used to study the reaction mechanism of the hydrogen transfer. Tetralin-(ii2 is rapidly substituted in the 1-position by hydrogen from coal. At a reaction temperature of 400 °C the deuterium content of the 1-position remains, after a reaction time of 15 min, relatively constant at 66%. The 2-position, however, participates much less in the exchange reaction. On the other hand, the deu-... 

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