Abstract
Hydrocracking reactivities of Point of Ayr coal liquefaction extracts prepared by several different liquefaction routes have been compared. Structural changes have been assessed by size exclusion chromatography (s.e.c.), u.v.-fluorescence (u.v.-f.) spectroscopy and t.g.a.-based boiling point determinations. In line with relatively short residence times of products in the reaction zone during the liquefaction stage, the extract prepared in the flowing solvent reactor (FSR) gave the largest molecular mass (MM) distribution and the greatest shift to smaller MMs during hydrocracking. The greater reactivity of this extract reflects that of material freshly released from the coal, with a minimum of thermal degradation. The use of primary coal extracts appear useful in providing a common baseline for the assessment of hydrocracking potentials of extracts from different coals. The order of hydrocracking reactivities of >450°C b.p. material contained in the set of extract samples was: FSR > mini-bomb (10 min) > pilot plant > mini bomb (60 min). For all samples, significant conversion of > 450°C b.p. material to lower-boiling fractions took place during the first 30 min; the slow-down in conversion with time appears at least partially due to a reduction in the reactivity of the extracts. The results suggest that high-boiling materials (> 450°C) in the coal extracts progressively tend to become less reactive and more resistant to further breakdown, due to loss of reactive groups such as alkyl side chains and hydroxyl groups and also possibly due to structural shifts of larger-MM material to stabler molecular configurations. Observed differences in hydrocracking reactivities of extracts from the same coal prepared under different reaction conditions highlight the need to consider the effects of secondary reactions during the coal extraction stage in assessing hydrocracking reactivities of coal extracts.
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