Mechanically-assisted catalytic depolymerization of polyolefins

Various heterogeneous catalysts have demonstrated promising conversion of polyolefins to small molecules. However, due to the highly entangled nature of commercial polyolefins, bulk polymer diffusion is very slow in the melt phase. Thus, catalytic conversion of macromolecules remains a slow process at moderate temperature (200-300 °C). The inability of polymer chains to access most of the catalyst active sites embedded in catalyst pores limits the overall catalyst effectiveness requiring supplemental methods of chain cleavage. We propose the use of mechanical scission via melt-phase flow fields as a plausible mechanism to assist in C-C bond scission. Using a model polyolefin, poly(ethylene-alt-propylene), mechanical forces present in a common batch reactor are shown to induce appreciable chain cleavage in the absence of an active catalyst. Further, mechanical scission is enhanced by exchanging the batch reactor for a twin-screw compounder capable of reaching torque ~10⁴ times higher than in batch. This system provides in situ “preprocessing” of polymer chains in tandem with a solid-acid catalyst to enhance depolymerization. Combining mechanical scission with catalytic reactions will increase efficiency of reactions, alleviate mass transfer constraints, and reduce energy demand.