Structure and pyrolysis behavior of the organic matter in two fractions of Yilan oil shale

Oil shale has been pyrolyzed for shale oil in industry to alleviate the shortage of petroleum in many countries. Some oil shales appear non-uniform in colour, suggesting different ash content and/or organic structure distribution throughout their deposition. This paper takes Yilan oil shale as the raw material to identify the structure and pyrolysis behaviour of the organic matter in fractions of different colour. The oil shale is separated into two parts by a heavy liquid flotation method and then subjected to acid treatments. The heavy part is gray and termed as YL-G-OM, while the light part is black and termed as YL-B-OM. These parts are characterized by proximate and ultimate analyses and 13C-nuclear magnetic resonance. Pyrolysis experiments are carried out in a TG-MS and a fixed-bed tubular reactor. The liquid product from the tubular reactor is analyzed by GC-MS and simulated distillation. Results indicate that the H/C ratios of YL-G-OM and YL-B-OM are 1.21 and 0.95, respectively. In comparison with YL-B-OM, YL-G-OM contains more aliphatic carbon and less aromatic carbon, and has a longer methylene chain and a lower condensation degree, which results in more liquid product and C2-C3 gas during pyrolysis. The yields of liquid product are 46.1 and 35.6% on daf basis for YL-G-OM and YL-B-OM, respectively. The liquid products of both samples contain about 80% heavy fractions including those trapped in the GC column, vacuum residue and vacuum gas oil, as well as some diesel (12.5-17.0%) and a little gasoline (3.3-4.3%). Co-pyrolysis of YL-G-OM and YL-B-OM shows a synergetic effect at temperatures between 425 and 460 °C, which promotes formation of liquid product and reduces the phenolic content in shale oil. The synergetic effect may be attributed to reduced condensation of radical fragments generated by bond cleavage of organic matter.