Green Chemistry

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.

For details:

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

Lun An a, Yue Yao b, Tyler B. Hall a, Fu Zhao b,c, Long Qi a

a. U.S. DOE Ames National Laboratory, Iowa State University, Ames, Iowa 50011, USA
b. School of Environmental and Ecological Engineering, Purdue University, West Lafayette, IN 47907, USA
c. School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, USA

DOI: https://doi.org/10.1039/D4GC01146E

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