Investigation of the pyrolytic liberation of molecular nitrogen from Palaeozoic sedimentary rocks

Open-system non-isothermal pyrolysis up to 1,200 degrees C in combination with elemental analysis was used to study the thermal liberation of molecular nitrogen (N-2) from sedimentary rocks and kerogen concentrates of Palaeozoic age from the Central European Basin system and an Eocene shale ( Liaohe Basin, China) with a high content (36%) of ammonium feldspar ( buddingtonite). The N/C-org ( atomic) ratios of the kerogen concentrates ranged from 0.005 to 0.014, which represents the range commonly observed for coals. Bulk N/C-org ratios of the Palaeozoic shales extended from 0.035 to 0.108, indicating the presence of significant amounts of inorganic nitrogen. Namurian A and A-B (CnA; CnA-B) samples typically exhibited the earliest onset of N2 generation with intense, characteristic peaks around 600 degrees C. N-2 liberation from the buddingtonite-rich sample occurred at higher temperatures, with a broad peak around 700 degrees C. Pyrograms of the kerogen concentrates showed no or strongly reduced N-2 generation in the 500 - 700 degrees C range. On- line isotope-specific analysis of the pyrolytically liberated N-2 on one sample revealed a variability of similar to 10 parts per thousand in the delta N-15 values and a steady increase in delta N-15 with temperature during the main phase of N-2 generation.