1. JCCT
  2. Ch&ChT Vol. 19, No. 3, 2025
  3. Optimisation of the Extraction Process of Toluene and Humic Acid Extract from Brown Coal

Optimisation of the Extraction Process of Toluene and Humic Acid Extract from Brown Coal

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Denis Miroshnichenko1,2, Maryna Zhylina3,4,5, Oleksandr Bielov1, Liudmyla Lysenko1, Mykhailo Miroshnychenko1, Hennadii Omelianchuk1, Serhiy Pyshyev6, Jurijs Ozolins3
Affiliation: 
1 National Technical University Kharkiv Polytechnic Institute, 2 Kirpychova St., Kharkiv 61000, Ukraine 2 State Enterprise "Ukrainian State Research Institute for Carbochemistry (SE “UKHIN), 7 Vesnina St., Kharkiv 61023, Ukraine 3 Riga Technical University, Faculty of Natural Sciences and Technology, Institute of Biomaterials and Bioengineering, 3 K-1, Paula Valdena St., Riga LV-1048, Latvia 4 Institute of Agricultural Resources and Economics, Stende Research Centre, Dizzemes, Dizstende, Libagu parish, Talsu County, LV-3258, Latvia 5 Institute of Materials and Surface Engineering, Faculty of Natural Sciences and Technology at Riga Technical University, 7. P. Valdena St., Riga LV-1048, Latvia 6 Lviv Polytechnic National University, 12 S. Bandery St., Lviv 79013, Ukraine
DOI: 
https://doi.org/10.23939/chcht19.03.572
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Keywords: 
lignite
humic acids
toluene extract
bitumen A
extraction
optimization
Abstract: 
Lignite (brown coal) is a promising source of humic acids (HAs) and toluene-soluble extracts (bitumen "A"), which have applications as soil conditioners/biostimulants (HAs) and hydrophobic coatings or polymer additives (toluene extract). This study optimized their sequential extraction from Ukrainian lignite, evaluating yield trade-offs and structural properties. Four extraction variants were tested. Conventional toluene-first extraction (Variant 0) yielded the highest toluene extract (14.86 wt. %), but lower HAs (41.0 wt. %), while reversing the sequence (Variants 2–3) increased HA yields (47.39–51.70 wt. %) at the expense of toluene extract (1.79–5.28 wt.%). Structural analysis revealed toluene extracts had higher aromaticity (60.1–61.9% aromatic carbon) and molecular association (1.9–2.2) than HAs (48.5–60.3%; 1.6–2.0), reflecting their distinct chemistries. Alkaline pretreatment enhanced HA aromaticity but reduced toluene extract recovery. The findings enable tailored protocols for agricultural (HAs) or industrial (toluene extract) applications, supporting sustainable lignite valorization.
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