FTIR characteristics of charcoal with different combustion degrees as an indication of the genesis by and their significances for formation of fusinite in coal

Fourier transform infrared spectroscopy (FTIR), as a non-destructive method, is widely used for the identification of compounds and the characterization of molecular structures. In order to characterize the changes in the chemical structure of charcoal under different combustion temperatures, and thus to provide a theoretical basis for the formation of fusinite in coal, plant samples (charcoal) from modern wildfires with different degrees of combustion were selected to quantify their chemical structures using FTIR. The results shown that the sample reflectance was positively proportional to the combustion temperature. The sample No. 1 with maximum combustion temperature had the highest degree of combustion, which was measured to reach 518 ℃. The aromatic structure was dominated by tri-substituted benzene rings in all samples except the highest combustion sample No. 1, but dehydrocondensation occurred with increasing combustion temperature, resulting in a reduction of tri-substituted content of benzene rings to 20.5%. The tetra-substituted content was elevated due to dehydroaromatization of the naphthenic structure, while the change in the penta-substituted content was related to the cyclization of aliphatic chain and the decarboxylation of benzene ring. With the increase of combustion temperature, the CC content gradually increased due to the formation of aromatic hydrocarbons or the shedding of molecular side chains after dehydrogenation of cycloalkanes, reached 32% in the sample No. 1. The content of C－O first decreased and then increased. In the sample No. 1, the content of alkyl ether and aryl ether was the lowest, and the content of phenolic hydroxyl group was the highest, which may be the generation of phenolic substances by thermal breakage of ether bond under high temperature combustion. The CO content increased and then decreased to as low as 5.6% in the sample No. 1, which was due to the poor stability of the bond. Due to the influence of combustion temperature, the content of fatty substances varied greatly, with an overall gradual increase in methylene content, a decrease in methyl group, and an increase in branching degree. There were five types of hydrogen bonds in the samples, with ether-oxygen hydrogen bonds predominating in samples affected by low temperature (>55%). Cyclic hydrogen bonds and hydroxyl-N hydrogen bonds appeared in sample No. 1, while the content of ether-oxygen hydrogen bonds decreased significantly to 13.2%, which was attributed to the reduction of oxygen-containing functional groups caused by the increasing temperature. Comparison of reflectance and FTIR characteristics of fusinite in coal revealed that the characteristics of fusinite (semifusinite) in coal were very similar to those of charcoal, which might be produced mainly by wildfires. These changes indicated the effect of combustion temperature on the chemical structure in charcoal, reflecting the process of organic molecular structure changed with temperature in charcoal, and providing a theoretical basis for the evolution of organic matter and the formation of fusinite in coal

Evidence of widespread wildfires in a coal seam from the middle Permian of the North China Basin

The North China Basin is the largest coal-bearing basin in China, and has an areal extent of 800,000 km2. We analyzed 138 coal samples and in situ pillar coal samples of the middle Permian from this basin by macropetrography, microscope, scanning electron microscope, gas chromatography, and gas chromatography–mass spectrometer in order to study wildfires. High contents of inertinite (charcoal) and natural coke particles observed in coal samples indicate that vegetation in precursor mires and peats of the middle Permian coal from north China was exposed to far-ranging wildfires. In addition, high-molecular-weight polycyclic aromatic hydrocarbons were detected in the coal samples. These aromatic compounds were formed under high temperatures and provide further evidence of wildfire. These wildfires would have discharged significant CO and CO2 gases into the atmosphere and affected the paleoclimate and paleoecosystem

Geminal Brønsted Acid Ionic Liquids as Catalysts for the Mannich Reaction in Water

Quaternary ammonium geminal Brønsted acid ionic liquids (GBAILs) based on zwitterionic 1,2-bis[N-methyl-N-(3-sulfopropyl)-alkylammonium]ethane (where the carbon number of the alkyl chain is 4, 8, 10, 12, 14, 16, or 18) and p-toluenesulfonic acid monohydrate were synthesized. The catalytic ionic liquids were applied in three-component Mannich reactions with an aldehyde, ketone, and amine at 25 °C in water. The effects of the type and amount of catalyst and reaction time as well as the scope of the reaction were investigated. Results showed that GBAIL-C14 has excellent catalytic activity and fair reusability. The catalytic procedure was simple, and the catalyst could be recycled seven times via a simple separation process without noticeable decreases in catalytic activity