Coal easily reacted with CrO3 in aqueous solution, while CrO3 was reduced to Cr2O3 at the temperature of coal pyrolysis. In hydrocracking of coal treated with CrO3, coal was hydrocracked to more liquefied products under reducing temperature from CrO3 to Cr2O3. In present report, hydrocracking of Yubari residue treated with CrO3 was carried out from repetition to repetition at the same conditions, and the activity of chromium oxide catalyst formed by the reduction of CrO3 was estimated. HS (hexane soluble fraction) yield linearly increased up to four times and then slowly increased continuously with increasing number of reaction. Especially, BS (hexane insoluble-benzene soluble fraction) linearly increased with more number of reaction.
Not a large difference was observed in the average structures of liquefied products from parent coal and CrO3 treated coal, while 1H-NMR spectra of HS were largely affected by the number of reaction.
These results indicated that activity of chromium oxide catalyst was kept constant during of 1-8th reactions.