The investigation on the sorption and desorption of benzene and phenanthrene on the heated shale was carried out. The shale samples were thermally treated under different temperature ranging from 250 to 500o C to create a series of shale kerogen with differences in maturation. The original and heated shale samples were characterized by modern instrumental methods and were used as sorbents for the sorption/desorption experiments. As the treatment temperature increases, the maturation degree of the shale kerogen is elevated gradually. And the H/C, O/C atomic ratio and the percentages of aliphatic carbon and carbonyl carbon decrease, while the aromaticity and the reflectance index of vitrinite increase.  Nonlinear sorption isotherms of benzene and phenanthrene were observed. As the maturation degree of the kerogen increases, the isothermal nonlinearity increases whereas the sorption capacities and maximum micropore sorption volumes increase initially and then decrease. The maximum micropore volumes of benzene are higher than those of phenanthrene. The above phenomena can be satisfactorily explained by the molecular sieve effect during the hole-filling process and the changes in the micropore volume and its size distribution, which were caused by the change in the kerogen structure during the thermal maturation. The desorption isotherms of benzene on the kerogen samples exhibit hysteresis, and the kerogen samples of higher maturity show lower hysteretic index than those of lower maturation do. This is probably associated with the rigid structure in the higher maturated kerogen samples, which is hard to be swelled. The maximum micropore volumes of phenanthrene and benzene on the kerogen samples account for 23-46% and 36-65% of the maximum sorption volumes, respectively, displaying the importance of micropore filling mechanism for the sorption of hydrophobic organic compound on NOM.

Benzene and phenanthrene sorption mechanism on thermally stimulated kerogen

243rd National Meeting (2012)

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