Recovery of Wilkinson's catalyst from polymer based matrix using carbon dioxide expanded methanol

Carbon dioxide-expanded methanol (CXM) is for the first time employed to recover Wilkinson's catalyst from the matrix of hydrogenated nitrile butadiene rubber (HNBR) using the chelating agent N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA). The effects of temperature and pressure on the extraction performance were carefully investigated over the temperature range of 40–100 °C and the pressure range of 20–20 MPa. Increasing temperature effectively increased the extraction rate and became less influential when temperature is above 80 °C. Increasing pressure over the different pressure ranges at 80 °C impacted the extraction rate differently. 6 MPa was considered as the optimal pressure at 80 °C. The rhodium residue was reduced from 700 to 222 ppm by a 5 h extraction at 6 MPa and 80 °C. An extraction mechanism was illustrated for interpreting the present extraction system and guiding the future work. This study establishes a technology platform for separating the expensive catalyst from the polymer matrix, using “green” CO2-expanded liquids.

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► For the first time, CO2-expanded methanol (CXM) was used to recover Wilkinson's catalyst from a hydrogenated nitrile butadiene rubber (HNBR) matrix with N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA) as chelatant.
► A high extraction ratio of 68 wt% with rhodium residue of 222 ppm was achieved after 5 h operation at the mild and optimal operational condition of 80 °C and 6 MPa.
► One extraction mechanism was proposed for the extraction of Wilkinson's catalyst from a polymer matrix using CXM and PMDETA.