Synthesis and application of a deep eutectic solvent as a green catalyst for use in oil esterification: DOE...

Area of Science:

• Green Chemistry
• Catalysis
• Materials Science

Background:

• Deep eutectic solvents (DESs) are emerging as sustainable alternatives to traditional solvents, aligning with green chemistry principles.
• DESs are formed by combining hydrogen-bond acceptors (HBAs) and hydrogen-bond donors (HBDs), resulting in liquids with unique physicochemical properties.
• The synthesis and characterization of novel DESs are crucial for expanding their applications in environmentally benign processes.

Purpose of the Study:

• To synthesize and characterize novel deep eutectic solvents (DESs) using tetrabutylammonium bromide as HBA and oxalic acid as HBD.
• To evaluate the physicochemical properties, electrochemical behavior, and toxicological profile of the synthesized DESs.
• To investigate the efficacy of the synthesized DES as a green catalyst for the esterification of used oil, optimizing reaction conditions and comparing its greenness with conventional methods.

Main Methods:

• Synthesis of DESs by combining tetrabutylammonium bromide (HBA) and oxalic acid (HBD) in varying molar ratios.
• Characterization using FT-IR and NMR spectroscopy; assessment of physicochemical and electrochemical properties.
• Cytotoxicity studies on 3T3 cell lines and antimicrobial activity tests against five microorganisms.
• Esterification of used oil using DES as a catalyst, optimized via Design of Experiments (DoE).
• Greenness evaluation using National Environmental Methods Index (NEMI), Analytical Procedure Index (GAPI), and Analytical Eco-Scale methods.

Main Results:

• Novel DESs were successfully synthesized and characterized, exhibiting no toxicity to 3T3 cell lines and no inhibition of microbial growth.
• The synthesized DES demonstrated significant potential as a green catalyst for used oil esterification, achieving 96.3% efficiency under optimized conditions (8.5 mL methanol, 0.5 g DES, 10 min reflux at 60 °C).
• Design of Experiments (DoE) analysis identified DES amount as the most significant variable, with statistically significant interactions between DES amount/reflux time and methanol volume/reflux time.
• Comparative greenness analysis indicated superior environmental performance of the DES-based esterification compared to traditional methods.

Conclusions:

• The synthesized DESs are eco-friendly, non-toxic, and biocompatible, making them suitable for sustainable chemical applications.
• The DES demonstrated high catalytic activity and efficiency in the esterification of used oil, offering a greener alternative to sulfuric acid.
• Optimization studies and greenness assessments confirm the viability of DESs as sustainable catalysts in industrial processes, contributing to waste valorization and reduced environmental impact.