Preparation Of Immobilized Ionic Liquids And Their Application In Alcoholysis Of Poly(Lactic Acid)

In recent years,with the rapid development of petrochemical industry,the production and consumption of bio-based material poly?lactic acid?have gradually increased,and brought serious environmental pollution and waste of resources.Immobilized ionic liquid?IL?,as a novel,environmental friendly catalyst,has the merits of both good catalytic activity of ionic liquids and the characteristics of easy of separation and recycling,which is expected to overcome equipment corrosion,environmental pollution and difficult to reuse for catalyst in traditional acid or base catalyst system,and can realize green and efficient chemical recycling of waste PLA.In this paper,different metal complex alkaline IL were prepared and used in the methanolysis of PLA,and the IL[Bmim][OAc]-Zn?OAc?₂ was selected as the best catalyst.The composition and structure were measured by infrared spectrum,nuclear magnetic resonance and high-resolution mass spectrum.The result indicated that the final product was the target IL.The[Bmim][OAc]-Zn?OAc?₂ was used for PLA methanolysis and obtained the optimum reaction conditions:reaction temperature 110?;reaction time 2 h;mass ratio of catalyst to PLA was 0.01:1 and molar ratio of methanol to PLA was 5:1.Under these conditions,the PLA conversion and the product yield were 97.2%and 92.3%,respectively.The product was characterized by gas chromatography and infrared spectrum,the results indicated that the final product was methyl lactate and the purity was over 99%.The reusability of catalyst showed that the IL could be reused 5 times without distinctly decrease in its catalytic activity.Moreover,the mechanism and kinetics of PLA methanolysis catalyzed by[Bmim][OAc]-Zn?OAc?₂ were also investigated,the results showed that the reaction was first-order with an activation energy of 20.96 kJ/mol.[Bmim][OAc]-Zn?OAc?₂ was immobilized on SBA-15 through immersion to give immobilized IL[Bmim][OAc]-Zn?OAc?₂/SBA-15.The composition and structure were measured by elemental analysis,X-ray diffraction,N₂ adsorption-desorption and scanning electron microscope.The results demonstrated that the IL was successfully immobilized on the inner and outer surface of carrier,and the ordered pore structure of SBA-15 was not destroyed.The[Bmim][OAc]-Zn?OAc?₂/SBA-15 was used for PLA methanolysis and the catalyst could be separated by simple filtration.The optimum reaction conditions were obtained as follows:reaction temperature 110?;reaction time 2 h;mass ratio of catalyst to PLA was 0.01:1 and molar ratio of methanol to PLA was 5:1.Under these conditions,the PLA conversion and the product yield were 97.6%and 92.4%,respectively.The product was characterized by gas chromatography and infrared spectrum,the results indicated that the final product was methyl lactate and the purity was over 99%.The reusability of immobilized IL showed that the catalytic activity was reduced significantly after 3 times consecutive use.In addition,the kinetics of PLA methanolysis catalyzed by[Bmim][OAc]-Zn?OAc?₂/SBA-15 were also investigated,the results indicated that the reaction was first-order with an activation energy of 36.62 kJ/mol.Metal complex alkaline IL modified with coupling agent was immobilized on SBA-15 by chemical bonding to obtain immobilized IL[tespmim][OAc]-Zn?OAc?₂/SBA-15.The composition and structure were measured by elemental analysis,X-ray diffraction,N₂adsorption-desorption and transmission electron microscope.The results indicated that the IL was successfully immobilized on the inner and outer surface of carrier,and the ordered pore structure of SBA-15 was not destroyed.The[tespmim][OAc]-Zn?OAc?₂/SBA-15 was used for PLA methanolysis,and the catalyst could be separated by simple filtration.The optimum reaction conditions were obtained as follows:reaction temperature 120?;reaction time 2 h;mass ratio of catalyst to PLA was 0.01:1 and molar ratio of methanol to PLA was 5:1.Under these conditions,the PLA conversion and the product yield were 98.6%and 92.8%,respectively.The product was characterized by gas chromatography and infrared spectrum,the results indicated that the final product was methyl lactate and the purity was over 99%.The reusability of catalyst showed that the catalyst could be reused 4times without significantly decrease in catalytic activity.Moreover,the kinetics of PLA methanolysis catalyzed by[tespmim][OAc]-Zn?OAc?₂/SBA-15 were also investigated,the results indicated that the reaction was first-order with an activation energy of 48.66 kJ/mol.For all we know,up to now there was no literature reported about the study mentioned above.