Sustainable Recovery of Dibutyl Terephthalate from Aromatic Polyester Waste via Solvothermal Alcoholysis

In this work, a series of homometallic and heterometallic aryloxides, including [M'6(sal-Me)6] (M'+ = Li+ (1), Na+ (2), K+ (3)), [M'(sal-Me)]n (M'+ = Rb+ (4), Cs+ (5)), [Mg2(sal-Et)4(EtOH)2] (6), [Zn4(sal-Me)8] (7), [Ca3(sal-Me)6(EtOH)2] (8), [M2M'2(sal-Me)6(X)x] (where M2+ = Mg2+ and M'+ = Li+ (9), Na+ (10), K+ (11); M2+ = Zn2+ and M'+ = Li+ (13), Na+ (14), K+ (15); or M2+ = Ca2+ and M'+ = Li+ (16), Na+ (17), K+ (18) with X = THF or MeOH and x = 0, 2, 4), [MgRb(μ-H2O)(sal-Me)3(H2O)0.5]n (12), [Mg4Na2(sal-Me)6(sal)2(THF)4] (19), [CaLi6(sal-Me)8] (20), [Ca4M'(μ5-OH)(sal-Et)8(EtOH)] (M'+ = Na+ (21), K+ (22)), [ZnLi2(sal-Me)4(THF)2] (23), and [ZnM'2(sal-R)4]n (for M' = Na and R = Et (24), M' = K and R = Me (25)), were investigated as catalysts for the chemical recycling of postconsumer poly(ethylene terephthalate) (PET) and poly(ethylene-co-isosorbide-co-1,4-cyclohexanedimethylene terephthalate) (PEICT) waste. The catalytic performance of metal aryloxides was evaluated in relation to their chemical composition, solid-state structures, and solution behavior, allowing general trends in the catalytic activity of alkali metal and divalent metal aryloxides (Mg2+, Ca2+, Zn2+) and their heterometallic combinations to be established. Key factors governing catalytic activity, reaction mechanisms, and the formation of reaction intermediates are also discussed.