Valorizing non-condensable pyrolysis gases from mixed plastic waste: A comprehensive parametric study of the cross-metathesis reaction for propylene production

This work focuses on the valorization of the non-condensable pyrolysis gases (NCPGs) derived from mixed plastic waste (MPW). A feedstock consisting of ethylene and 1-butene, primary constituents of NCPGs, was utilized for propylene production via cross-metathesis reaction. A comprehensive parametric study was performed on a series of xWO 3 /Al-MCM-41 catalysts. The effect of temperature, Si/Al ratio, WO 3 loading, residence time (W cat /F 0 ), feed ratio (ethylene/1-butene), and reactants partial pressure were investigated. Ex situ and in situ characterization techniques (XRD, Raman spectroscopy, TEM, BET, FT-IR (study of pyridine adsorption), TPO, TPR, and EXAFS) were applied to the fresh and used catalysts. Αluminum (Al) incorporation into the MCM-41 structure promoted both Lewis and Brønsted acidity, favoring the isomerization reaction of 1-butene to 2-butene. The tungsten oxo (W=O) species served as the precursor for the active site for propylene production through the cross-metathesis reaction. The 20 wt% WO 3 /Al-MCM-41 catalyst, with a Si/Al ratio of 30, attained a remarkable performance at 550 °C, 1 bar, W cat /F 0 = 117.4 kg Cat ·s·mol −1 and ethylene/1-butene = 4.5/1. Under these conditions, the ethylene and 1-butene conversions reached 28% and 97%, respectively, along with a C-based selectivity of 73% towards propylene. • Non-condensable pyrolysis gases (NCPGs) are a highly valuable output stream. • The catalytic metathesis of ethylene and 1-butene for propylene production was studied. • Incorporating Al into MCM-41 enhances acidity, key for the isomerization of 1-butene. • Excess ethylene/1-butene and longer residence time improved propylene selectivity. • The 20%WO 3 /Al-MCM-41(30) catalyst reached 73% propylene selectivity and 97% 1-butene conversion.