Formation and chemical structure of preasphaltenes in short residence time coal hydrogenolysis

The formation and chemical structure of preasphaltenes in short residence time coal hydrogenolysis were investigated. In short residence time coal hydrogenolysis, preasphaltenes are the major product. The maximum yield for this parametric study was obtained under reaction conditions of 500 °C and 21 s. The formation of preasphaltenes reached the maximum value in the initial stage of the liquefaction reaction. As the liquefaction reaction continued, the deoxygenation of preasphaltenes proceeded. However, the decrease in aromatic atoms bound to the hydroxy, methoxy and oxygen atoms of the diphenyl ether group (Arz.sbnd;O) is small, and the ArO functionality still remains abundant in preasphaltenes. Preasphaltene-I is characterized by carbon aromaticity ( f a ) of 0.6–0.7, aromatic rings of from 1 to 3–5 per condensed aromatic ring system, 55–70% substitution of aromatic ring carbons and C 2–3 aliphatic substituents. The molecular weight ranges from 500 to 650, and is not much different from that of the asphaltenes. The f a values based on the Brown-Ladner method and on solid state CP/MAS 13C n.m.r. spectra data agree closely.