Preparation Of 4-methylanisole By Electrocatalytical Degradation Of Aspen Lignin In Alkali Solution With Three-dimensional Electrode Reactor

This paper focused on the degradation of aspen lignin to small molecule compounds in alkaline solution with three-dimensional electrode reactor. A three-dimensional electrode system, containing a Pb/PbO₂ anode, stainless steel wire mesh cathode, the granular activated carbon（GAC） third electrode, was employed to electrochemical catalysis degradation of aspen lignin. The main product was 4-methylanisole, co-products such as vanillin, syringaldehyde, acetovanillone, styrene, toluene, 2,6-dimethoxy phenol and so on were also obtained. The chemical stability, crystalline structure, and electrochemical performance of the Pb/PbO₂ electrode in alkaline liquor were monitored and observed by SEM, XRD, and CV respectively. The element composition of aspen lignin was analyzed by elemental analyzer. The degradation products were separated and analyzed by some separation methods about distillation, thin-layer chromatography and column chromatography separation, and then confirmed by MS, ¹H NMR, ¹³ C NMR, finally quantified by GC. The influence of temperature, current density, raw material lignin concentration and degradation time on the degradation of lignin was investigated experimentally.The experimental results show that the effective catalyst thin layer on the surface of self–prepared Pb/PbO₂ electrodes was β-PbO₂ film. As the thin layer of β-PbO₂ film, the electrochemical performance of Pb/PbO₂ electrode was much better stable. The main products of lignin by electrochemical degradation were the aromatic derivatives. Among the different extraction agent, ethyl acetate performed better extraction effect than others for the main product 4-methylanisole. The optimum condition for electrocatalytic degradation of alkali lignin was obtained as following: current density 50mA/cm², raw material lignin concentration 40g/l, temperature 50°C, degradation time 2h, the concentration of 4-methylanisole 2.5958g/l. In addition to that, the reaction pathways of the oxidative cleavage and hydrogenation reduction of lignin were also discussed.