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

Abstract

Precious metals, in particular Pd, have a wide range of applications in industry. Due to their scarcity, precious metals have to be recycled, preferably with green and energy-saving recycling processes. In this article, palladium extraction from an aluminosilicate-supported catalyst, containing about 2 wt% (weight%) of Pd (100% PdO), with supercritical CO2 (scCO2) assisted by complexing polymers is described. Two polymers, p(FDA)SH homopolymer and p(FDA-co-DPPS) copolymer (FDA: 1,1,2,2-tetrahydroperfluorodecyl acrylate; DPPS: 4-(diphenylphosphino)styrene), were tested with regards to their ability to extract palladium. Both polymers showed relatively low extraction conversions of approximately 18% and 30%, respectively. However, the addition of piperidine as activator for p(FDA-co-DPPS) allowed for an increase in the extraction conversion of up to 60%.

Recovery of Precious Metals: A Promising Process Using Supercritical Carbon Dioxide and CO2-Soluble Complexing Polymers for Palladium Extraction from Supported Catalysts

“…The presence of additives is, therefore, necessary. Recently, our group has proposed the use of scCO 2 -soluble metal-complexing copolymers to extract metals from solid matrices [21][22][23]. Even though some polymers such as siloxane [24,25] or vinylalkanoate-based [26,27] polymers are soluble in scCO 2 , they usually present some limitations.…”

“…To ensure a better solubility of the copolymers in scCO 2 and enable the use of lower CO 2 pressures, gradient copolymers were preferred to block copolymers [32]. The ability of two copolymers, poly(4-vinyl pyridine-co-1,1,2,2tetrahydroperfluorodecylacrylate) (P(4VP-co-FDA)) and poly(diphenylphosphinestyreneco-1,1,2,2-tetrahydroperfluorodecylacrylate) (P(DPPS-co-FDA)), to extract up to 50% of Pd from alumina-supported catalysts was demonstrated [21][22][23]33]. The use of molecular complexing additives, such as dithiocarbamates, beta-diketones, dithizone, and perfluorocarboxylic acids, is also possible and has been reported in the literature [34][35][36][37][38][39].…”

Synthesis and Phase Behavior of a Platform of CO2-Soluble Functional Gradient Copolymers Bearing Metal-Complexing Units

“…So far, different reports have shown the use of low molecular weight compounds, (e.g., dithiocarbamates, beta-diketones, dithizone, perfluorocarboxylic acids) which can act as complexing additives [16,[44][45][46][47][48][49][50][51]. Nevertheless, our group has reported in the last years the possibility to use scCO 2 -soluble metal-complexing polymers to extract metals from solid matrices, without dissolving or destroying the supports [52][53][54][55]. These polymers contain two different types of monomer units, namely CO 2 -philic monomer units ensuring a high solubility of the polymers in scCO 2 , and metal-complexing monomer units enabling binding to the metals.…”