Benzonaphthothiophene: Molecular Indicators for Thermal Maturity

Abstract

Benzonaphthothiophenes (BNTs) were firmly identified in coals by comparison with retention indices reported in the literature. The thermodynamic stabilities of BNTs were calculated by quantum chemical computations, and their stability sequence is as follows:The BNT isomers are ubiquitous in coal samples from the Xihu Depression and the Ordos Basin. This study reveals the effects of thermal maturity on the distributions of BNTs in coals, where the relative abundances of [1,2]BNT and [2,3]BNT to [2,1]BNT were observed to be mainly controlled by thermal maturation conditions. Combining with theoretical calculations of thermodynamic stability, two benzonaphthothiophene maturity indicators, defined as, were proposed. Two preliminary calibrations of BNTR-1 and BNTR-2 against measured vitrinite reflectance (%Ro) were established, and the relationships are as follows: %Rc = 5.5 × BNTR-1/100 + 0.5 (%Ro >0.9) and %Rc = 15 × BNTR-2/100 + 0.5 (%Ro > 0.9), respectively. BNTR-1 and BNTR-2 have good correlations with the widely used molecular maturity parameters. The good correlations with vitrinite reflectance and maturity parameters suggest that BNTR-1 and BNTR-2 are useful indicators in evaluating the maturity for sedimentary organic matter at high levels of thermal stress. The accuracy of the BNT ratio ([2,1]BNT/ [1,2]BNT) must be kept in mind when it is used as a migration tracer of oil generated at a high thermal maturation stage. There is no clear trend for the absolute concentrations of BNTs with increasing pristane/phytane and gammacerane/C 30 hopane values, suggesting that the redox conditions and water salinity during deposition may have little influence on the generation of BNTs. This study can expand the understanding of the distribution and geochemical significance of complex sulfur-containing organic compounds in sedimentary organic matter.

Brown carbon absorptivity in fresh wildfire smoke: associations with volatility and chemical compound groups

“…The importance of molecular size in determining BrC light absorptivity can be highlighted size-exclusion chromatography measurements. [13][14][15][16] Online measurements of BrC using aerosol mass spectrometers have identied oxygenated organics, 8,17,18 nitroaromatics, [19][20][21] and low-volatility oxygenated organics 22 as dominant light-absorbing groups in different regions. The wide range of compounds observed in BrC across various studies underscores the complexity of BrC composition and emphasizes the need for a more holistic metric to relate BrC optical properties to chemical composition.…”