Research On The Application Of In-situ Generation Of Ros With Oxygen Cathode To Depolymerize Lignin In Protic Ionic Liquid

Lignin is a natural biological resource with complex structure and abundant reserves.It is recognized as the most effective route to realize its value-added utilization by breaking specific chemical bonds to obtain small molecular aromatic compounds.Among them,with the help of electrochemical methods,the oxygen reduction reaction(ORR)continuously occurs on the surface of the cathode to generate reactive oxygen species(ROS),breaking the intramolecular bonds to achieve the degradation of lignin macromolecules,referred to as electrochemical oxygen cathode method to depolymerize lignin,has been proven to be a green efficient technical approach.Proton-based ionic liquids have the advantages of stabilizing ROS and selective generation of H2O2-type ROS.In this study,triethylamine hydrogen sulfate([HNEt3][HSO4])proton-based ionic liquids are selected as supporting electrolyte to explore the regulation of ORR in situ production of ROS and its effect on lignin model compounds and lignin depolymerization efficiency.Contents and results are as follows:(1)The electrochemical research methods are used to study the electrochemical behavior of ORR in protic ionic liquids and the qualitative and quantitative analysis of the main species that generate ROS in situ.Cyclic voltammetry(CV)and rotating ring disk electrode method(RRDE)confirmed that O2 had a 2-electron transfer reaction on the cathode in[HNEt3][HSO4]ionic liquid,and the active oxygen species are mainly HO2-/H2O2.The quantitative determination of in-situ generated H2O2 is realized by using Pt wire microelectrode in a constant potential system.(2)With the degradation of the model compound,and the ORR conditions for ROS production were optimized as:modified graphite felt cathode,30?,-1.2 V(vs Ag/Ag+).Based on the results of product extraction and analysis,it is speculated tha the degradation mechanism is:First,model compound will oxidize on the anode surface,lose electrons,and generate active molecules with C? positive ions,and then directly attacked by HO2-/H2O2 generated on the cathode surface,resulting in the cleavage of C?-C? bonds.The degradation rate of model compound can reach 60.5%after 4 h,and the selectivity of vanillin of the product can reach 76.3%.(3)The effect of depolymerization of actual lignin samples in proton-type ionic liquid by oxygen cathode method was explored.The determination method of lignin degradation in ionic liquids is established based on gravimetric method.The degradation rate of the lignin sample is determined to be 36.5%and the current efficiency is 74.1%at-1.2 V cathodic potential for 4 h.According to the above quantitative determination method of H2O2,the average utilization rate of H2O2 generated in situ is 40.3%.Finally,according to the difference about boiling point,a technical solution is proposed to achieve the recycling of ionic liquid by product extraction and condensation reflux.