Agile synthesis and automated, high-throughput evaluation of diglycolamides for liquid-liquid extraction of rare-earth elements

• Published in: Green chemistry : an international journal and green chemistry resource : GC Vol. 26; no. 12; pp. 7188 - 7197
• Main Authors: An, Lun, Yao, Yue, Hall, Tyler B, Zhao, Fu, Qi, Long
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 17.06.2024; Royal Society of Chemistry (RSC)
• Subjects: Amines; Automation; Clean energy; Climate change; Data acquisition; Energy conversion; Environmental impact; Global warming; Life cycle analysis; Life cycle assessment; Ligands; Liquid-liquid extraction; Rare earth elements; Substrates; Sustainable development; Sustainable production; Synthesis; Workflow
• ISSN: 1463-9262; 1463-9270
• DOI: 10.1039/d4gc01146e

Liquid-liquid extraction is one of the most scalable processes to produce rare-earth elements (REEs) from natural and recycled resources. Accelerating the research, development, and deployment (RD&D) of sustainable processes to manufacture REEs requires both facile synthesis of extractive ligands at scale and fast evaluation of process conditions. Here, we establish an integrated RD&D methodology comprised of agile ligand synthesis and automated high-throughput extraction studies. Using diglycolamides (DGAs) as an example, we first developed a method for DGA synthesis (scalable to 200 g) by directly coupling diglycolic acid and secondary amines via the solvent-free melt-amidation reaction. A substrate scope of the melt-amidation synthesis was demonstrated for 9 different DGAs with good yields (85-96%) and purities (88-96%) without any post-reaction workup or purification process. Life cycle assessment shows that our synthesis method outperforms the prior-art pathway in each environmental impact category, especially showing a 67% reduction in global warming potential. Furthermore, we investigate the structure-activity relationship of various alkyl-substituted DGAs using an automated, high-throughput workflow for liquid-liquid extraction, achieving over 180 runs in 48 hours. The acquired data enables the development of a promising flowsheet for separating light and heavy REEs. The integrated RD&D method of agile synthesis and automated, high-throughput extraction studies paves the way for future iterative development of sustainable production of REEs and other critical materials to meet the needs for clean energy transformation. The study presents a scalable and sustainable extraction method for rare earth, featuring a green, scalable synthesis of diglycolamides that reduces greenhouse gas emissions by 67% and a liquid-liquid extraction workflow.