Ligands on Demand

As the next generation of nuclear reprocessing technologies edge toward industrial readiness, concerted efforts are needed to ensure their safety, predictability, robustness, and economic viability. Organic ligands are critical to the selectivity of nuclear reprocessing, current focus is on ligands and processes that can remove long-lived radiotoxic actinides. Amides and diamides are promising ligand classes for the removal of actinides due to their selectivity for the f-block elements, with N,N di (2 ethylhexyl)isobutyramide (DEHiBA) a popular monoamide for the extraction of uranium devoid of plutonium to overcome plutonium proliferation concerns. DEHiBA is of interest to the GANEX 1st cycle process, a replacement technology to PUREX, overcoming a number of weaknesses faced by this mature industrial process. Whilst tri-n-butyl phosphate (TBP) is the ligand employed in the PUREX process, TBP has other uses outside of the nuclear industry, these other uses improve the economic viability of TBP, whereas specialised ligands for nuclear reprocessing like DEHiBA are more novel with limited demand at present, resulting in high costs and thus creates a barrier to research.
This work utilises industry 4.0 (the integration of artificial intelligence and automation for manufacture, otherwise referred to as smart manufacturing) to efficiently optimise the manufacture of DEHiBA, focussing on cost reduction, sustainability improvements and production throughput. Ultimately reducing a cost barrier to research and implementation of this ligand for industrial application. Specifically, the methodology utilises flow chemistry, automation, online analysis, and machine-learning algorithms to automate the optimisation of chemical space, this methodology is also applicable to other relevant ligands like the diamides or variations of DEHiBA. Four synthetic routes were optimised in this work with litres of crude DEHiBA manufacture accessible for <£65 per litre at the time of publishing with a throughput of 15 kg L-1 h-1, with other synthetic conditions capable of >70 kg L-1 h-1. A purification route for the crude DEHiBA was devised and optimised to yield a product purity >99.9% in just two steps with a yield of 97% from start to end. The complete manufacture platform therefore requires at a minimum four pumps, one tubular reactor, two continuous stirred tank reactors and two coalescing separators to achieve this via two telescoped operations to yield pure DEHiBA on demand with >97% yield.
DEHiBA manufactured in this work was verified for its uranium extraction performance against literature and commercial sources, demonstrating comparable performance for the extraction of uranium(VI). The extraction of uranium(VI) was further investigated with DEHiBA, varying the ligand concentration and purity, the ratio of organic to aqueous phase and nitric acid concentration for the extraction of 0.10 M uranyl nitrate, demonstrating optimal performance with 5 M nitric acid and at least 10% extraction efficiency improvements when using 1.5 M DEHiBA instead of the typical 1.0 M DEHiBA associated with the GANEX process. A range of organic : aqueous phase ratios were also compared to see how the throughput of uranium affects the extraction efficiency of uranium(VI), identifying minimal extraction efficiency losses (5%) in exchange for a four-fold increase in throughput when using 1.5 M DEHiBA and 5 M nitric acid. These studies support the process intensification of uranium(VI) extraction with DEHiBA, comparing extraction efficiency and uranium throughput. Throughout these studies, temperature was identified to be an overlooked variable in the literature that requires future attention due to its influence on the exothermic extraction of uranium.