This study aims to address the limited understanding of wash oil degradation in benzene units by analysing changes in the composition and properties of fresh and operating oils from different manufacturers. The findings will provide insights into the degradation pathways and stability of these oils. Gas chromatography/mass spectrometry was used to analyse the provided samples, and the dynamic viscosity of the oils was determined using a Brookfield LV DV2T rotational viscometer. During operation, the “heavy” oil (HO) becomes less volatile, while the ”light” oil (LO) becomes slightly more volatile. The viscosity of the HO increases 1.25 times during operation. The LO is characterised by a higher total concentration of alkyl derivatives (48 wt.% compared to 44 wt.% for the HO). LO is enriched with naphthalene and indene, while HO loses 1- and 2-methylnaphthalenes and shows an increase in the concentrations of dibenzofuran, fluorene, anthracene, and phenanthrene. The oxidation products of LO include oxidised alkyl groups, while HO shows oxidised non-substituted hydrocarbons. The practical value of such studies lies in guiding the selection of fresh oil under current operating conditions. LO is more resistant to degradation as an absorbent than heavier wash oil.

The classical dephenolization process of the heavy fraction of coal tar involves alkaline washing to produce sodium phenolate, followed by carbon dioxide decomposition to yield crude phenols and a soda solution. The soda solution is causticized with lime, generating lime sludge contaminated with phenols - a significant environmental concern. This study explores phenol extraction technologies leveraging phenolic acidity and molecular polarity to address these limitations. A novel method for dephenolizing coal tar heavy fractions without alkali was developed, yielding wash oil suitable for capturing benzene hydrocarbons with a phenol content of 0.7 - 1.0 %. This process eliminates aqueous phenolate generation, producing a hydrocarbon residue with a composition resembling the phenolfraction, achieving a reagent-free, waste-free methodology. The proposed method employs sodium phenolate solutions with optimized sodium hydroxide concentrations to ensure minimal phenol content in oil and control impurities in the phenolate solution, maintaining non-phenolic impurities at 15 - 20 %. This reduces neutral component loss and contamination, achieved by neutralizing phenols with a 27 % NaOH solution. Additionally, methyl tert - butyl ether (MTBE) was validated as a suitable organic solvent for phenol extraction from aqueous solutions. This integrated approach simplifies the technological process while aligning the composition of neutral oil with the phenolic fraction obtained during coal tar fractionation, presenting a sustainable solution for phenol recovery and wash oil purification.

The present research deals with forecasting the potential content of humic acids (HA) in Ukrainian lignite based on the coal’s physicochemical characteristics. The focus is on developing an experimental–statistical model that considers moisture content, volatile matter yield, and calorific value of lignite. The development of the humic acid yield’s dependence on some lignite parameters is based on both original research data and literature sources. Humic acids were extracted using alkaline solutions, and HA content was calculated for various lignite deposits in Ukraine. The adequacy check of the model showed a relative prediction error of up to 12%, indicating good agreement between the model and experimental data. The highest potential yield of humic acids was recorded for lignite from the Dnipropetrovsk region (Dnieper-Donets Basin), amounting to 53–56 wt.%. The presented results demonstrate the feasibility of using mathematical forecasting to assess the industrial potential of humic acid production from lignite.

The possibility of considering coal pitch as a material suitable for research modeling the processes of thermochemical transformations of the plastic mass of coal carbonization and their interaction with the solid carbon phase is analyzed. The possibilities of controlling the properties of coal pitch and blast furnace coke during its production with the help of aprotic acid additives in the presence of a co-catalyst are shown.

Coal tar wash oil degradation during industrial benzene recovery alters both the absorbent’s performance and the liquid-phase rheology. This study introduces an integrated rheological and quantum-chemical framework to evaluate the non-ideal flow behavior of light and heavy wash oils (fresh and operational) diluted with 0–30 vol.% benzene. Compositional changes were monitored via GC–MS, while viscosity non-ideality was quantified using relative viscosity deviations (η_%) and characteristic empirical parameters (φ_1max). Quantum-chemical calculations revealed stronger interactions between benzene and the polycyclic aromatic and heterocyclic compounds enriched in heavy operating oil, consistent with a lower (φ_1max) for heavy oil (0.23) compared to light oil (0.34–0.37). This multi-method approach provides a sensitive, phenomenological diagnostic probe for monitoring absorbent degradation, supporting operational decisions regarding wash oil regeneration or replacement in industrial scrubbing units.