Promising polymer-assisted extraction of palladium from supported catalysts in supercritical carbon dioxide

Abstract

Precious metals, in particular palladium (Pd), have a wide range of daily applications, from automotive catalysts to fine chemistry production. Nevertheless, these metals are relatively rare and highly expensive, considering their massive industrial utilization. In the last decades, different recycling methods have been explored. Nowadays, the most applied methods, namely pyro-and/or hydrometallurgy, involve energy-intensive processes and/or the generation of large amounts of effluents to be treated. Thus, the development of a more sustainable recycling process of precious metals is highly desirable. In the present work, we introduce a sustainable process based on the use of a green solvent, supercritical CO2, operated under mild conditions (P = 25 MPa and T = 40 °C). The extraction process is possible thanks to the addition of CO2-soluble complexing polymers bearing pyridine units. The proposed method leads to the extraction of more than 70% of Pd from an aluminosilica-supported catalyst.

Supercritical CO2 Extraction of Palladium Oxide from an Aluminosilicate-Supported Catalyst Enhanced by a Combination of Complexing Polymers and Piperidine

“…Herein, the potential of the scCO 2 extraction procedure and the influence of the extraction parameters on the extraction conversion and yield are investigated. Promising extraction conversions and yields would show that, combined with previous results [ 17 , 18 ], the scCO 2 polymer-assisted extraction process can be applied to a wide range of materials.…”

“…The p(FDA- co -DPPS) copolymer, activated in situ with piperidine, led to good extraction conversions of approximately 60% at 40 °C and 25 MPa. These results show that a pretreatment of the catalyst Cat D is not required to achieve promising extraction conversions, with extraction results from a non-optimized process already comparable to those achieved with a pretreatment of the catalyst [ 17 ]. Through the use of the right combination of complexing polymers and piperidine, as well as the fine-tuning of extraction conditions, the harmful waste streams generated during pretreatment of the catalyst with chlorine can be eliminated.…”

“…It is a pristine Pd/aluminosilicate (2.083 wt% Pd; 100% PdO) catalyst. The detailed characterization of this catalyst is provided in the Supporting Information (SI-Chapter 2) [ 17 , 33 ].…”

“…Recently, our group published an article regarding the polymer-assisted extraction of Pd in scCO 2 from an aluminosilicate-supported catalyst (catalyst Cat D, 2 wt% Pd in the form of PdO (100%)), as well as from pretreated versions of this catalyst [ 17 ]. In one case, the catalyst was reduced by H 2 before extraction (the reduction led to a catalyst composition of Pd 0 (79%), with a minor amount of PdO (21%)); in the other case, the catalyst was reduced by H 2 , and afterwards oxidized with Cl 2 (the oxidation led to a catalyst composition of Na 2 PdCl 4 (85%), with a minor amount of PdO (15%)).…”

Performance Parameters of Inductively Coupled Plasma Optical Emission Spectrometry and Graphite Furnace Atomic Absorption Spectrometry Techniques for Pd and Pt Determination in Automotive Catalysts

“…To improve efficiency of hydrometallurgical process, microwave-assisted leaching and cloud point extraction were also used [ 12 ]. Alternatively, green methods based on extraction using chelating agents were developed [ 13 , 14 ]. The efficient recovery and purification of Pd and Pt from spent catalyst is economically desirable.…”