Lewis Acidic Ionic Liquid [Bmim]FeCl4 as a High Efficient Catalyst for Methanolysis of Poly (lactic acid)

Abstract

Methanolysis of poly (lactic acid) (PLA) was studied using Lewis acidic ionic liquid [Bmim]FeCl₄ as a catalyst and the qualitative analysis indicated that the main product was methyl lactate. Compared with ionic liquid [Bmim]Cl, FeCl₃ and other traditional catalysts, the Lewis acidic ionic liquid showed much better catalytic activity in the methanolysis of PLA. Significantly, the conversion of PLA and the yield of methyl lactate were 99.3 and 94.6% respectively with low dosage of catalyst (the molar ratio of [Bmim]FeCl₄ to LA unit is 0.0025:1). The lewis acidic ionic liquid [Bmim]FeCl₄ could be recycled up to 6 times and FT-IR results showed that the spectrum of the reused catalyst was similar to that of the fresh one. Moreover, a possible mechanism of the methanolysis of PLA catalyzed by [Bmim]FeCl₄ was proposed. The kinetics of PLA methanolysis was also investigated under the optimum conditions and the results indicated that it was a first-order kinetic reaction with activation energy of 21.28 kJ mol⁻¹.

Graphical Abstract

The methanolysis of poly (lactic acid) (PLA) was studied using Lewis acidic ionic liquid [Bmim]Fe_xCl_3x+1 (x>1) as catalyst. The effects of reaction temperature, reaction time, ionic liquid dosage and methanol dosage on methanolysis results were examined. The reusability of ionic liquid in the methanolysis of PLA was investigated, and the results showed that it could be recycled up to 6 times with no apparent decrease in the conversion of PLA and yield of methyl lactate. The reaction mechanism and kinetics of PLA methanolysis catalyzed by [Bmim]Fe_xCl_3x+1 were also investigated. Moreover, a possible catalysis mechanism of the methanolysis of PLA was proposed.