Conceptual Design and Development of an Environment-Friendly Process for Simultaneous Extraction of Phenol and Naphthalene Compounds from Tar

Low-rank coal tar contains abundant phenolic compounds. Phenol extraction with ethanolamine is a promising alternative to the traditional method of caustic washing, which can cause serious environmental problems. However, the content of neutral oil, which primarily contains naphthalene compounds, in the phenolic compounds extracted via the ethanolamine method exceeds the Chinese metallurgical industry standard, limiting the industrial application of phenol extraction with ethanolamine. Herein, a conceptual process involving ethanolamine extraction, azeotropic distillation, and crystallization is proposed to reduce the neutral oil content. Naphthalene compounds were effectively separated from phenolic compounds as ethanolamine and naphthalene compounds form the minimum azeotrope. Thereafter, naphthalene compounds were separated from ethanolamine via crystallization. Ultimately, naphthalene compounds and phenolic compounds were simultaneously obtained as products. The separation characteristics of the new process were comprehensively analyzed, and key process parameters were optimized through experiments and simulations. The proposed process can overcome not only the secondary pollution caused by the caustic washing method but also the high neutral oil content of conventional organic solvent extraction methods. Thus, the proposed novel process has good industrial application prospects.