Study On Preparation Of Alkyl Lactates By Alcoholysis Of Poly(L-Lactic Acid)

The alcoholysis of poly(lactic acid) (PLA) was investigated using different catalysts. The effects of experimental parameters such as reaction temperature, reaction time, the amount of catalyst and dosages of alcohol on the alcoholysis reaction were examined in detail. The results showed that ferric chloride (FeCl3) was a good catalyst, and the optimized reaction conditions was reaction temperature 130 ℃, reaction time 4.0 h, n(alcohol):n(PLA)=5:1, catalyst FeCl3 used dosage 1.0% (molar ratio). The methanol, ethanol, n-propanol, isopropanol and butanol were used in the alcoholysis of PLA. Under the above conditions, the conversion of PLA reached 96.1%,95.3%,94.7%,85.1% or 92.9%, and the yield of alkyl lactates was 87.2%, 85.8%,84.6%,77.5% or 81.9%, respectively. The structure of obtained product was characterized by FT-IR. The reusable performances of FeCl3 was investigated, the results indicated that the FeCl3 could be reused up to 6 times without any significant decrease in the conversion of PLA and the yield of methyl lactate. The kinetics of the methanolysis of PLA was also studied. The results indicated that the methanolysis of PLA with FeCl3 was a first-order kinetic reaction with an activation energy of 32.41 kJ/mol. The reaction mechanism of PLA alcoholysis with FeCl3 was proposed.Otherwise, l-butyl-3-methylimidazolium-ferric chloride([Bmim]Cl-FeCl3) ionic liquid with different ferric chloride molar fractions were synthesized and used in the alcoholysis of PLA. The effects of the acidic properties of the ionic liquids, reaction temperature, reaction time, alcohol dosage and ionic liquid dosage on the alcoholysis reaction were investigated. It was shown that [Bmim]Cl-FeCl3 performed a good catalytic effect when the ferric chloride molar fraction x was 0.67, and the optimized reaction conditions was reaction temperature 120 ℃, reaction time 3.0 h, n(alcohol):n(PLA)=5:l, n([Bmim]Cl-FeCl3):n(PLA)=0.0025:1. The methanol, ethanol, n-propanol, isopropanol and butanol were used in the alcoholysis of PLA. Under the above conditions, the conversion of PLA reached 99.3%,98.4%,96.2%, 88.1% or 94.9%, and the yield of alkyl lactates was 94.6%,91.9%,90.6%,80.3% or 88.4%, respectively. The structure of obtained product was characterized by FT-IR. The ionic liquid could be recycled up to 6 times with no apparent decrease in the conversion of PLA and yield of methyl lactate. The kinetics of the reaction was also investigated. The results indicated that the methanolysis of PLA in the persence of [Bmim]Cl-FeCl3 was a first-order kinetic reaction with an activation energy of 21.28 kJ/mol. The reaction mechanism of PLA alcoholysis with ionic liquid [Bmim]Cl-FeCl3 was proposed.As a kind of functional ionic liquid, [Bmim]Cl-FeCl3 combines the advantages of both lewis acid FeCl3 and the ionic liquid. In the alcoholysis of PLA, [Bmim]Cl-FeCl3 performs a good catalytic activity at low temperature, which leads to a milder reaction conditions, such as shorter reaction time, better selectivity, higher product yield.To our knowledge, there is no report in literature about the study mentioned above.