In situ analytical pyrolysis of coal macerals and solid bitumens by laser micropyrolysis GC-MS

Specific macerals in coals and distinct solid organic bitumens within limes tones from northern China were separately analysed in situ by laser micropy rolysis gas chromatography-mass spectrometry. The major pyrolysates from th e resinite and cutinite macerals included aromatic hydrocarbons such as alk ylnaphthalenes, alkylbenzenes, alkyltetralins (in the resinite) and alkylph enols (in the cutinite), and aliphatic hydrocarbons such as n-alk-1-enes, n -alkanes, pristane and phytane. The same classes of hydrocarbons were also detected in co-occurring vitrinites, including very similar relative distri butions of alkylnaphthalenes in the case of the resin-rich coal. Several ob served quantitative differences are consistent with previous molecular data from maceral concentrates. The qualitative similarity of the maceral data suggest (1) extensive assimilation of free hydrocarbons by all macerals wit hin the coals; or (2) inefficient targeting of the macerals by the laser, a lthough microscopic observation showed that the laser craters were generall y constrained within surface boundaries of the maceral. The organic composi tion of a solid bitumen within a Carboniferous limestone was characterised by a distinctive distribution of C-0-C-4 alkyldibenzofurans, as well as alk ylbenzenes, alkylnaphthalenes and a low molecular weight distribution of n- alk-1-enes and n-alkanes. These data suggest the solid bitumen comprises a strongly aromatic matrix with terrestrially-derived oxygen functionality an d alkyl linkages. The same aromatic and aliphatic hydrocarbon products were also detected in the morphologically homogenous carbonates hosting the sol id bitumens, indicating the presence of sub-microscopic organic moieties th roughout the limestone. (C) 2001 Elsevier Science B.V. All rights reserved.