Hydroconversion of waste polyethylene plastics under mild conditions using mechanically mixed bifunctional catalysts: Impact of metal-acid balance and proximity

Abstract

The disposal of non-biodegradable waste polyolefin plastics poses a serious environmental threat, highlighting the need for cleaner and more efficient thermochemical recycling technologies. This study introduces a scalable mechanical method to synthesize a metal-acid bifunctional catalyst. The mechanical ball milling process not only exposes more acidic sites but also enhances metal-acid proximity without blocking the pores. By varying the metal-acid balance (MAB) through different mixing ratios, we achieved higher yields and selectivity for soluble products at the optimal MAB level. Under mild conditions (250°C) for 8 h, polyethylene (PE) is efficiently converted into liquid phase iso-paraffins with an isomer selectivity of up to 56 % in the diesel and aviation kerosene fractions (C₁₁-C₁₈). This research underscores the importance of the accessibility of acidic sites to long-chain macromolecules, metal-acid site distance, and their balance in the hydrocracking of PE. It provides valuable theoretical insights and catalytic strategies for converting waste PE plastics into high-value fuel fractions.