Continuous hydrogenation of plastic wastes pyrolysis oil over used hydrotreatment catalysts

The continuous hydrogenation of refuse-derived fuel (RDF) pyrolysis oil using hydrotreating catalysts previously utilized in oil refineries is studied in this article. The hydrogenation of styrene and methyl-styrene, the primary gum precursors contributing to the low stability of the pyrolysis oil, is the main scope of the treatment. Experimental results demonstrate the catalyst's high activity at moderate temperatures, with partial hydrogenation of aromatic olefins prevailing over catalytic cracking and oligomerization. However, both undesired reactions result in coke formation, which gradually deactivates the catalyst. Deactivation studies reveal that the coke deposits on the refinery-used catalyst can even have positive effects on catalyst stability, blocking the alumina acid sites and even increasing the thermal stability of the active phase. Thermal regeneration of the catalysts also leads to active catalysts for the target reactions, but the stability of the catalyst is lower, with highest coke formation rates at low temperatures, and lower activity of the active phases at the highest studied temperatures. Results are analysed in terms of a deactivation kinetic modelling considering first-order for the main hydrogenations and second-order deactivation kinetics. • Continuous hydrogenation of RDF pyrolysis oil using spent NiMo catalysts. • Partial hydrogenation of aromatic olefins reducing gum formation trend. • Carbonaceous deposits of the used catalysts protect against further deactivation. • Deactivation effects are more important at lower temperatures. • Deactivation behaviour modelled considering second order deactivation kinetics.