Depolymerization Of Polycarbonate In Ionic Liquids

Ionic liquids are described as green solvents in 21 st century.Effective depolymerization in ionic liquids could be accomplished under normal pressure and relatively low temperature.Recent studies on chemical recycling of polycarbonate(PC) and depolymerization in ionic liquids are summarized.The experiment was carried out in conventional glassware with the reaction medium of various ionic liquids,such as 1-hexyl-2-methylimidazolium trifluoromethanesulfonate([Hmim]CF₃SO₃),1-methylimidazolium hydrogen sulfate([mim]HSO₄),1-(3-sulfonic)butyl-3-metylimidazolium trifluoromethanesulfonate ([BMSIM]CF₃SO₃),1-hexyl-2-methylimidazolium hydrogen sulfate([Hmim]HSO₄) and 1-benzyl-3-methylimidazolium trifluoromethanesulfonate([Bzmim]CF₃SO₃), respectively.[Hmim]CF₃SO₃ was selected as the reaction medium,in which the PC was depolymerized effectively to biphenol A(BPA).The products were analyzed by Liquid Chromatography and Mass Spectrometry (LC-MS),Gas Chromatography and Mass Spectrometry(GC-MS), High-Performance Liquid Chromatography(HPLC),Gas Chromatography (GC),Fourier-transform Infrared Spectroscopy(FT-IR),respectively.Depolymerization of PC in ionic liquid([Hmim]CF₃SO₃) was experimentally studied under the conditions of temperature 130-210℃, reaction time 3-24h and ionic liquid content 4.0-20.0 g/gPC.The results indicated that the main product of depolymerization was BPA,while the content of DPC was so low.Yield of BPA increased with the increasing of temperature and reaction time.The yield of BPA was reached 84.4%at optimal conditions of temperature 170℃,reaction time 18h,and ionic liquid content 12.0 g/gPC.According to the distribution of depolymerization products and the energy of carbon chain,the main mechanism of deploymerization in ionic liquids was proposed.The depolymerizaiton of PC in ethylene glycol was studied for comparing with the depolymerization in ionic liquid.It was shown that the yield of BPA was 63.7%at the conditions of temperature 170℃,reaction time 15h,and ethylene glycol content 8.0 ml/gPC,respectively.Compared the efficiency of depolymerization in ILs with that in SCF studied by our team,effective depolymerization of PC in sub-supercritical methanol, methanol water co-solvents and ionic liquid can be reached,the yield of BPA were all above 80%.However,there are several problems in depolymerization in ILs,such as products separation,ILs recycling,the mechanism of depolymerizaiton and "green character" of ILs,etc.Further investigations on depolymerization of PC in ILs are a new challenge for us.