Catalytic glycolysis of polyethylene terephthalate (PET) by solvent-free mechanochemically synthesized MFe2O4 (M = Co, Ni, Cu and Zn) spinel

• MFe 2 O 4 (M = Co, Ni, Cu, and Zn) spinel has been successfully synthesized through solvent-free mechanochemical technique. • All catalysts were active for PET glycolysis and the catalytic activity was found to be correlated with the Lewis acid strength of M 2+ . • The Hansen Solubility Parameters (HSPs) of ZnFe 2 O 4 were the closest to the HSPs of PET, implying high compatibility between the two. • Although ZnFe 2 O 4 was the best catalyst in terms of catalytic activity, CoFe 2 O 4 was the best in terms of separation with an external magnet. • Magnetic CoFe 2 O 4 can be used for PET glycolysis for at least five times without significant activity loss. • Simulation by using Aspen Plus® software showed that scale-up is feasible. In the present study, the solvent-free mechanochemically synthesized MFe 2 O 4 (M = Co, Ni, Cu, and Zn) spinel was used as a catalyst for PET glycolysis. All catalysts were active for PET glycolysis to produce bis(2-hydroxyethyl) terephthalate (BHET) with the order of PET conversion of ZnFe 2 O 4 > CuFe 2 O 4 > CoFe 2 O 4 > NiFe 2 O 4 . The catalytic activity was correlated with the Lewis acid strength of the M 2+ in MFe 2 O 4 , i.e., a catalyst with strong Lewis acid exhibited high catalytic activity. Although CoFe 2 O 4 was the second-best catalyst among the four in terms of yield of BHET, it possessed the highest saturation magnetization, which is a great advantage for magnetic separation of the catalyst. The reaction over CoFe 2 O 4 exhibited apparent activation energy ( E a ) of 188 kJ mol −1 , and it was reusable for at least five times. Moreover, a simulation using Aspen Plus® software showed that scale-up is highly feasible.