Radical liquefaction products

Figures 2 and 3 contain yield curves for naphthalene and 1-methylindan as a function of reaction time for tetralin and tetralin plus coal, pyrite, or asphaltene. The asphaltene was a homogenized mixture of several samples isolated from coal liquefaction products during other work in our laboratory (9). This asphaltene sample contained essentially a negligible ash content (<0.1%). Therefore, it contains many organic structures similiar to those found in coal, but unlike coal, its reactions will be free of any complicating factors due to mineral matter. The yields of naphthalene and 1-methylindan are greater in the presence of asphaltene than in its absence, although not quite as high as in the presence of coal. This is additional evidence that these two products arise mainly from reactions associated with the presence of the organic portion of coaly matter. These reactions are quite likely free radical in nature.

Nature of the Free Radicals in Coals, Pyrolyzed Coals, Solvent-Refined Coal, and Coal Liquefaction Products... 

It has been proposed (17) that the portion of coal which is mobile under liquefaction conditions, contributes to the stabilization of thermally-generated radicals. Thus, coals which are highly fluid or contain large contents of extractable material might be expected to provide hydrogen and thus promote conversion. Collins has reported that vitrinite is a better donor of hydrogen than is Tetralin (20). Our own measurements of the aromatic content and elemental analyses of the coals (16,21) (or coal products) before and after conversion at short time are insufficient to confirm or deny the supposition that coal acts as its own H-donor even at short times. 

Characterization of the stable radicals present in coals, pyrolyzed coals, and liquefaction and other coal conversion products is a necessary first step toward elucidating the role of radicals in coal liquefaction. Electron... 

Mastral et al.23,24 have also investigated the effect of the main components present in tyres (carbon black, styrene-butadiene copolymer and polybutadiene) on the liquefaction of coal. Coprocessing of coal and carbon black confirmed the catalytic role of the latter, as it promotes hydrocracking reactions leading mainly to the formation of gaseous products. The addition of SBR to coal improves the yield of gases, oil and asphalt fractions, even at relatively low temperatures (350-375 °C). It is proposed that SBR favours the stabilization of the radicals involved in the process through alkylation reactions... 

In a study of short contact time coal liquefaction (109), in which major product fractions were examined with respect to their structure as well as their composition, the (nominal) high-molecular-weight product fractions of two similar subbituminous coals were found to possess radically different formal structures (cf. structure 6) one showed 73% and 60%, and the other showed 26% and H. 18%. Significantly, both fractions were deemed to closely resemble their respective precursor coals but to be slightly more aromatized than they. 

In the liquefaction step, the remaining cellulose is cleaved by the free radicals obtained from the H2 and C02to give a variety of products. 

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