1/2026
Ru/Al2O3 catalyst-assisted processing of waste silane-grafted cross-linked polyethylene
Waste crosslinked polyethylene (XLPE) can be a source of valuable hydrocarbons for further use. XLPE is widely used material which – unlike polyethylene – is very stable both chemically and mechanically. Therefore, its waste is difficult to process. A very promising way is slow pyrolysis catalyzed by ruthenium (Ru/Al2O3) which allows the conversion of waste into hydrocarbons via degradation of rigid chemical structure of cross-linked material. High hydrocarbon yields (91–92 wt.%) were achieved by slow pyrolysis without or with catalyst, but significant changes in the composition of resulting gas and oil were found with the Ru/Al₂O₃ catalyst. To reveal the possibilities of using this catalyst for processing of XLPE at a relatively lower final temperature (max. 480 °C, mostly 450–470 °C), an effect of the catalyst on degradation of XLPE structure and related rheological properties of XLPE melt was investigated. It was found that the activation energy of degradation decreases significantly in the presence of the catalyst and the degradation is greatly facilitated by Ru/Al2O3 at the defect sites of the XLPE structure (the tertiary carbons). By the catalyst, the torque for XLPE melt and the its shear viscosity are significantly reduced already at 250 °C. Thus, Ru/Al2O3 catalyst, even in very small amounts (1 wt.% Ru), significantly promotes the degradation of XLPE structure and reduces the solid pyrolysis residue. This finding greatly facilitates the processing of waste XLPE. The catalytic mechanism of action of Ru is outlined and the equations for the XLPE cleavage are given. The main product of processing, pyrolysis oil, can be used as a clean heating fuel, or oil for further use, or a source of solvents, liquid and solid hydrocarbons, especially paraffin.