Degradation Of Lignin To2,6-bis（dimethylethyl）-4-methylphenol By Electrochemical Catalysis On Pb/PbO₂anode In Alkaline Solution

This paper presents a novel method for lignin degradation to2,6-bis（dimethylethyl）-4-methylphenol （BHT） by electrochemical catalysis on Pb/PbO₂anode in alkaline solution.The Pb/PbO₂electrode was prepared in this study by electrodeposition. The chemicalstability, crystalline structure, and electrochemical performance of the Pb/PbO₂electrode inalkaline liquor were monitored and observed by SEM, XRD, and CV. A three electrodesystem, containing a Pb/PbO₂anode, a copper cathode and a reference saturated calomelelectrode （SCE）, was employed to electrochemical catalysis degradation of lignin inalkaline solution. The degradation process was investigated by EIS and CV. The products oflignin degradation were separated with silica gel column chromatography, active carbon,and half-preparative liquid chromatograph respectively. The products were qualitativelyanalyzed using1H NMR spectra,13C NMR spectra, and GC-MS. The products werequalitatively and quantitatively measured by internal standard method on the gaschromatography instrument. The influence of current density, reaction time, and theconcentrations of lignin on the products of lignin degradation in alkaline liquor was studiedsuccessively. Then the un-reacted lignin residua were analyzed by FT-IR in comparisonwith the structure of raw material. At last, the influence of electrolysis on the total phenolscontent was studied furthermore, and the electrolysis conditions were optimized byResponse Surface Methodology.The experimental results show that, the thin layer on the surface of self–preparedPb/PbO₂electrodes consisted both of α-PbO2and β-PbO2film. As the thin layer of β-PbO2film, the Pb/PbO₂electrode was much better stable and higher electrochemical performance.The main products of lignin degradation by electrochemical catalysis on Pb/PbO₂anode inalkaline solution were BHT, vanillin, acetic acid and other unidentified compounds. Theoptimum condition for lignin degradation was reaction time3h, current density25mA/cm2and the concentrations of lignin80g/L, at which the BHT yield was up to maximum value5.59g/L. The maximum yield of total phenols content were obtained by Response SurfaceMethodology under the optimal operation conditions as follows: CuO/graphite/PTFEelectrode with6.93%dosages of CuO catalyst was used as auxiliary electrode, the currentdensity was26.30mA/cm2, and the concentrations of lignin were85.4g/L.