DEPHENOLIZATION OF COAL TAR HEAVY FRACTIONS: A REAGENT - FREE METHOD FOR PHENOL RECOVERY

Abstract

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 phenol
fraction, 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.