Efficient recovery of spent catalysts in PAO production via annular drainage hydrocyclone: a sustainable approach for fluorinated waste reduction

Abstract

Polyalphaolefins (PAOs) serve as the base stock for nearly 50 % of the world's premium lubricants, yet their production generates a substantial volume of fluorinated spent catalysts. Achieving source separation and minimizing these catalysts is critical for the sustainable and clean production of PAOs. In this study, an annular drainage hydrocyclone (AH) was designed for the separation and recovery of fluorine-containing spent catalyst in the PAO production process. The inherent trade-off between inlet velocity, droplet fragmentation, and short-circuiting in conventional hydrocyclones has been effectively resolved. The enhanced separation mechanism of self-regulation of the short-circuit flow of the AH was revealed through numerical simulation. The adaptability of the AH under varying oil-phase viscosities and water-phase contents was validated through bench-scale experiments, followed by industrial pilot-scale verification. The results showed that the short-circuit flow of the AH was reduced by 94.8 % (down to 0.4 %) compared with the conventional hydrocyclone. The AH exhibits superior separation capability and lower energy consumption under both multi-moisture content and high-viscosity two-phase mixture conditions. Results from industrial-scale trials indicated a 33.5 % enhancement in catalyst separation efficiency compared with the existing process. Accompanied by a 54.5 % reduction in fluorinated catalyst emissions per ton of PAO product and a 98.1 % decrease in energy consumption. This work lays the foundation for the industrial application of AH in liquid-phase catalyst recovery and energy-efficient process intensification in the petrochemical sector.