Synthesis of fluorinated extractants for metal extraction in supercritical CO2

Abstract

Waste electric and electronic equipment (WEEEs), also known as ‘e-waste’ is one of the world’s fastest growing waste stream. Current waste management practices such as hydrometallurgy require the use of toxic chemicals, and poor waste disposal methods are unable to cope with the exponential growth of e-waste. Furthermore, advancements in technology have resulted in more precious metals being used in modern-day electronics, causing e-waste to be referred to as an ‘urban mine’. The ultimate goal of this study is to determine the effectiveness of the Supercritical Fluid Extraction (SFE) technique, a green extraction technique that is capable of extracting targeted metal ions from e-waste. According to past literatures, fluorinated organics are able to dissolve significantly in supercritical carbon dioxide (scCO2), thus enhancing the recovery yield of metal ions. However, information on fluorinated chelating agents (i.e. β-diketone) are scarce and some of the chemicals are not commercially available. Therefore, in this study, we focused on synthesizing three types of fluorinated chelating agents that started from Diethyl malonate. The chemicals synthesized in the experiment were characterized by the Fourier-Transform Infrared (FTIR) spectroscopy and Nuclear Magnetic Resonance (NMR) analysis techniques. The FTIR analysis was used to identify the functional groups within the synthesized chemical. The degree of success was determined by the degree of similarity between the IR spectra of the synthesized chemical to the reference sample. The NMR analysis focused on the 1H NMR spectrum. Similar to the FTIR analysis, the degree of success is determined by the degree of similarity between the NMR spectra of the synthesized chemical to the reference sample. The NMR analysis was used to derive the purity and yield percentages of the synthesized chemicals. The results of the experiment in this study have shown that despite scaling up the experiment, the yield % and purity % of the chemical synthesized in scheme 1 were consistent. The consistent results despite the experiment scale-up indicate that the experiment for scheme 1 has high reproducibility. Additionally, the results from modifying the starting materials ratio into 1:1 showed a higher degree of similarity to the referenced sample according to the NMR and FTIR spectra of the synthesized chemical. The chemical synthesized from scheme 2 failed due to the presence of impurities.