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.

Coke gas is a valuable fuel for metallurgical plants and a promising energy technology raw material, particularly for hydrogen energy. Absorption oil is used for gas purification, its prevention from thickening is an important task, so it is necessary to clarify the factors and mechanism of oil density increase in the process of its operation. For this purpose, the similarity and difference of products of oil polymerization in factory conditions with artificial polymerization of a separate fraction were established. Petrographic studies have shown that oil deposits in industrial equipment are represented by polymer-like material (94 %) with inclusions of coal particles (4 %). The results of infrared (IR) spectroscopy indicate certain similarities in the structure of substances and the presence of functional groups, which gives reason to believe that oligomerization products of absorbing oil components are present in the polymers of the benzene compartment, in the solid sediments and in the artificially obtained indene coumarone resin. It is shown that ammonia promotes the separation of ferrocyanide precipitates from the absorbing oil.

The quality of coal tar wash oil plays a key role in industrial processes for the absorption of benzene hydrocarbons from coke oven gas, and oil stability as well as resistance to polymerisation and corrosive oxidation processes are important aspects for ensuring efficient system operation. To ensure low oil consumption, it is necessary to suppress oxidative degradation processes. In this study, the effects of the phenolics of coal tar and its fractions on the antioxidant properties of the absorption oil were investigated. The results showed that phenols are effective oxidation inhibitors, promoting the formation of a protective film on the metal surface and reducing the corrosion rate of carbon steel from 0.56 to 0.33 mm year -1. A particularly strong protective effect was observed when the anthracene fraction of phenolic compounds was used, which possesses slightly reduced acidity with respect to low-molecular-weight phenols. This result can be explained by the weakening of the strength of the intermolecular interactions between phenolic compounds and pyridine bases. This reduces the negative effect of a decrease in the antioxidant abilities of phenols and increases the antioxidant effect of phenols in the anthracene fraction. The addition of various phenolic derivatives to the working absorbing oil did not have a significant effect on the viscosity or flow characteristics of the oils under study. The introduction of phenolic derivatives into the working oil did not change its coke-forming properties. The introduction of the N,N-dimethylformamide additive into coal tar wash oil did not lead to a decrease in coking properties but slightly decreased the viscosity of the working oil. In general, the obtained results are arguments in favour of the inexpediency of phenol extraction from coal tar wash oil to reduce its consumption due to oxidative processes of thickening.