Efficient separation of o-, m-, and p-cresols from simulated coal-based products using eco-friendly amine ionic liquids: Algae toxicity assessment, extraction, and mechanism exploration

Three cresol isomers (o-, m-, and p-cresols) derived from coal-based products are valuable compounds mainly used in the fine chemical and pharmaceutical industries. For the clean production of cresols without using strong acid and alkali aqueous solutions, liquid-liquid extraction was adopted, and four eco-friendly amine ionic liquids (AILs) were synthesized and characterized as extractants. The toxicity of AILs was evaluated using an algal toxicity assessment. The results showed that AILs can be considered practically nonharmful. The effects of stirring time, mAILs:m mixtures, extraction temperature, and initial content for extraction of cresols were investigated. The results showed that the AILs exhibited better performance for the extraction of the three cresol isomers. At the initial cresol content of mcresol:moil= 1:10, the AIL N,N,N ',N '-tetramethylguanidine acetate ([N-tmg] [Ac]) could extract cresols with an extraction efficiency of more than 97% under the optimal extraction conditions mAILs:m mixtures = 1:5, stirring time of 30 min, temperature of 25 degrees C. In addition, the intermolecular interactions were analyzed using quantum chemistry calculations. The results demonstrated that the hydrogen bonds (H-bonds) formed between the anions in the AILs and the phenolic hydroxyl groups of cresols were the major driving forces for the extraction of cresols. Finally, the reusability of the [N-tmg] [Ac] and [TEA] [Ac] AILs was explored, and the recovered AILs were confirmed by proton nuclear magnetic resonance (1H NMR) spectroscopy. Compared with traditional technologies that utilize strong acid and alkali aqueous solutions, the proposed method can avoid the discharge of acid and alkali wastewater, providing a promising route for the cleaner production of cresols from coal-based products.