Spectroelectrochemical Studies Of Lignin Model Compounds Oxidation Mechanism

Biomass as the only carbon-containing renewable energy has become a hotspot in the current research.In particular,lignin is the only component of lignocellulosic biomass containing aromatic structures,which contain a variety of complex bonds.Dissolved lignin or phenolic bio-crude can be obtained by lignin depolymerization or liquefaction process to interrupt bonds.Thus,they will be the potential raw materials for bio-fuels,bio-chemicals and biological materials.The complicated lignin structure poses a challenge for the valorization of lignin,and if it is possible to understand the breakage of various types in lignin,it will provide a significant value for the conversion of lignin into high value-added chemicals.Electrochemical oxidation of lignin has the advantages of strong oxidation capacity,no need to add specific catalyst and the small reagent consumption,controllable dosage,etc.,which is in line with the concept of green environmental protection.Therefore,we intend to apply electrochemistry into lignin oxidation.However,since the conventional electrochemical techniques can not detect and distinguish intermediate products generated during the oxidation of lignin,the way of bond fracture during the process of reaction and possible electron transfer paths,only a hypothetical reaction mechanism can be proposed.To solve this problem,we propose spectroelectrochemistry to study the electrochemical oxidation of lignin in organic solvent and ionic liquids.For the study of reaction mechanisms,such an in-situ detection technique will provide much more straightforward evidences.Main contents of this dissertation are shown as follows:1.Production of high efficiency vibration infrared spectroscopy electrochemical analysis device.At present,electrochemical reaction cells suitable for commercial spectrometer is very few and not available for the requirements of spectroelectrochemical measurements under the condition of ionic liquids.The relevant reaction analysis device is the necessary condition for the smooth development of this subject.In order to promote this subject,a sandwich structured spectroelectrochemical cell with a thin layer design has been especially developed.2.The electrochemical oxidation mechanisms of lignin model compounds in acetonitrile and ionic liquids were studied by using in situ infrared spectroscopy,by means of a spectroelectrochemistry technique.The changes of in situ infrared spectra during the electrochemical oxidation reaction were used to identify resulted intermediates and final products,and thus accurately infer the reaction pathways and mechanisms.In order to confirm the correctness of the proposed mechanism,three substrates with similar structure of the selected lignin model compound were also investigated.Finally,the solvent effect on the oxidation mechanism of lignin model compounds was also addressed.