Imidazolium-based deep eutectic solvents with multiple interaction sites for enhanced carbazole separation from...

Area of Science:

• Chemical Engineering
• Materials Science
• Environmental Science

Background:

• Carbazole is a valuable heterocyclic compound often found in industrial byproducts like anthracene slag.
• Current extraction methods lack selectivity, leading to low purity of recovered carbazole.
• Efficient separation is crucial for resource recovery and mitigating environmental pollution from industrial waste.

Purpose of the Study:

• To design and synthesize novel weakly basic bifunctionalized deep eutectic solvents (DESs) for selective carbazole extraction.
• To evaluate the extraction performance, including efficiency, partition coefficient, and selectivity, of the synthesized DESs.
• To elucidate the mechanism of selective carbazole separation using spectroscopic and computational methods.

Main Methods:

• Synthesis of six weakly basic bifunctionalized DESs by combining sulfonic acids (benzenesulfonic acid and p-toluenesulfonic acid) with imidazoles (imidazole, 2-methylimidazole, 2-ethylimidazole).
• Experimental evaluation of carbazole extraction from anthracene slag using the synthesized DESs.
• Characterization of DES stability through regeneration cycles.
• Analysis of separation mechanisms using proton nuclear magnetic resonance (¹H NMR) and density functional theory (DFT) calculations.

Main Results:

• Extraction performance positively correlated with the substituent chain length of the DES.
• DESs containing p-toluenesulfonic acid (PTSA) showed higher extraction efficiency than those with benzenesulfonic acid (BSA).
• The optimal DES, [3EIm:PTSA], achieved 84.3% carbazole extraction efficiency, a partition coefficient of 6.2, and a selectivity coefficient of 22.1.
• Single-step extraction using [3EIm:PTSA] yielded 86.7% carbazole purity and 74.5% yield.
• The DES demonstrated stability over five regeneration cycles.

Conclusions:

• Weakly basic bifunctionalized DESs, particularly [3EIm:PTSA], offer a highly efficient and selective method for carbazole recovery from anthracene slag.
• The synergistic effect of hydrogen bonding between the sulfonic acid group and imidazole ring in the DES facilitates specific carbazole recognition.
• This approach provides a sustainable and environmentally friendly strategy for valorizing industrial byproducts and recovering valuable heterocyclic compounds.