Zn-Acetate-Containing ionic liquid as highly active catalyst for fast and mild methanolysis of Poly(lactic acid)

Zn-acetate-containing ionic liquid (IL), 1-butyl-3-methylimidazolium acetate-promoted zinc acetate (2[Bmim][OAc]-Zn(OAc)2) was synthesized and used to catalyze the methanolysis of poly(lactic acid) (PLA). In this study, it was found that not only the methanolysis condition was milder compared with reported literatures, but also the high conversion of PLA and the yield of product methyl lactate were obtained when this Zn-acetate-containing IL was used as catalyst. The influences of technological parameters on PLA methanolysis were investigated and the optimum reaction conditions were obtained. Under the following conditions of catalyst (n[Bmim][OAc]:nZn(OAc)2 = 2.0:1, 0.04 g), n(CH3OH):n(PLA) = 5.0:1 and PLA (4.0 g) at 110 °C for 2.0 h, the PLA conversion and the methyl lactate yield were over 97% and 92%, respectively. Compared with the conventional ILs and other traditional catalysts, this Zn-acetate-containing IL exhibited excellent catalytic performance and the advantage of small dosage. The IL could be reused for 5 times, both FT-IR and TGA results indicated that the spectra of the reused IL were almost similar to those of the fresh one. Moreover, a possible mechanism of PLA methanolysis catalyzed by [Bmim][OAc]-Zn(OAc)2 was proposed through the experiments. The reaction kinetics was also investigated, and the results showed that it was a pseudo-first order kinetic reaction with an activation energy of 20.96 kJ/mol.