The mutual impact of low-quality lignite and high-density polyethylene (HDPE) during open system pyrolysis was investigated, aiming to improve utilization of lignite with simultaneous treatment of HDPE waste. Pyrolysis of lignite, HDPE, and their mixture (mass ratio, 1:1) was performed at temperatures 400, 450, 500, 550, and 600 °C. Initial substrates and pyrolysis products were characterized by thermogravimetric analysis (TGA), gas chromatography–mass spectrometry (GC–MS), specific carbon isotope analysis of individual hydrocarbons (δ13C), Rock-Eval pyrolysis, and elemental analysis. The positive synergetic effect during co-pyrolysis of lignite/HDPE mixture was observed at temperatures ≥450 °C, with the greatest being at 500 °C. The highest yield of liquid co-pyrolysis products with a similar composition to that of crude oils is also noticed at 500 °C. The yields of liquid and gaseous products and quality of pyrolytic products obtained by co-pyrolysis of lignite/HDPE mixture are notably improved compared with pyrolysis of lignite alone. On the other hand, data obtained from pyrolysis of HDPE alone indicate that it cannot be concurrent to well-developed catalytic thermal processes for polymer recycling. However, concerning the huge amount of produced HDPE, at least part of this plastic material can be reused for advanced thermal treatment of lignite, particularly in countries where this low-rank coal represents the main source of energy.

The most prolific oil shale deposit in Serbia is located in the Aleksinac Basin and is assigned to the Lower Miocene. Depositional environments and hydrocarbon potential were assessed for the Aleksinac oil shale and coal layers through bulk geochemical, organic petrographical, biomarker, and carbon isotope data from core samples from a single well. Maturity parameters (vitrinite reflectance, T max , biomarker isomerisation ratios) prove that the organic matter (OM) is immature. A lower lacustrine oil shale sequence is comprised of alternating sandstone and clay-rich rocks and some thin coal beds, indicating strong variations in depositional environment. This stratum is covered with thick sandstone (50 m) terminated by the main 4 m thick coal seam that was deposited in a low-lying mire, as evidenced by high total sulfur and mineral matrix contents. The plant input was dominated by angiosperms. A relative rise in water level led to the drowning of the swamp and to the deposition of a 60 m thick upper oil shale in a lacustrine environment. The OM of the oil shale is dominated by kerogen Type I (lamalginite). Biomarker data suggest a stratified water column that likely formed due to differences in salinity. The stratified water column led to a strictly anoxic environment and photic zone euxinia in a mesosalinar, hydrologically closed lake, which enabled the accumulation of uncommonly high amounts of organic material (average TOC: 18.0 wt%) with excellent preservation (average HI: 743 mg HC/g TOC).

The influence of pyrolysis type on the shale oil generation and its composition was studied. Different methods such as Rock-Eval pyrolysis, thermogravimetric analysis (TGA) and pyrolysis in the open and closed systems were applied. Samples from the Upper layer of Aleksinac oil shale (Serbia) were used as a substrate and first time characterized in detail. The impact of kerogen content and type on the shale oil generation in different pyrolysis systems was also estimated. Majority of the analysed samples have total organic carbon content > 5 wt. % and contain oil prone kerogen types I and/or II. Therefore, they can be of particular interest for the pyrolytic processing. The thermal behaviour of analysed samples obtained by TGA is in agreement with Rock-Eval parameters. The pyrolysis of oil shale in the open system gives higher yield of shale oil than the pyrolysis in the closed system. The yield of hydrocarbons (HCs) in shale oil produced by the open pyrolysis system corresponds to an excellent source rock potential, while HCs yield from the closed system indicates a very good source rock potential. The kerogen content has a greater impact on the shale oil generation than kerogen type in the open pyrolysis system, while kerogen type plays a more important role on the generation of shale oil than the kerogen content in the closed system. The composition of the obtained shale oil showed certain undesirable features, due to the relatively high contents of olefinic HCs (open system) and polar compounds (closed system), which may require further treatment to be used.

This paper presents the first results of the geothermal evolution modeling in East Herzegovina based on vitrinite reflectance calculations and measurements. Modeling of burial and geothermal was performed using "SimpleMat" software with well known kinetic model of vitrinite reflectance - EASY % Ro. By fitting the calculated reflectance values with mean measured vitrinite reflectances, it was concluded that there was erosion of some 900 m in the area, and that first possible petroleum generation could have started some 100 Ma ago. According to final calibration model that includes additional thickness and subsequent erosion of Paleogene sequence, the Upper Triassic sediments should have maturity from 0.70 to 1.1 % Rr, Lower Jurassic from 0.62 to 0.70 % Rr, whereas Upper Cretaceous sediments should have values from 0.40 to 0.60 % Rr, which is in accordance with measured vitrinite reflectance in 23 samples. Assuming that beginning of oil window in the East Herzegovina correspond to the vitrinite reflectance of 0.50 % Rr, all analyzed Mesozoic samples are at the initial stage of catagenesis ("oil window"), while Cenozoic sediments are at the stage of diagenesis.

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