Catalytic Degradation And Reaction Pathway Of Lignin Model Compound In Aqueous Solution By Heterogeneous Catalyts

Fe2O3/γ-Al2O3 heterogeneous catalysts were prepared by ultrasound impregnation method and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption (BET). The process of catalytic oxidation for treatment of guaiacol with H2O2 as oxidant in the presence of Fe2O3/γ-Al2O3 catalyst was investigated. The catalyst activity was evaluated by the removal of the guaiacol. The effects of different factors on the activity of Fe2O3/γ-Al2O3 were investigated, respectively. The optimum preparation methods for catalysts with the best performance were as follows:15 wt.% of the iron loading, roast 4h under the temperature of 550℃. Under the best of reaction conditions for oxidation of 100 mg/L guaiacol, initial pH 6.1, T=70℃,6 g/L catalyst, 0.0305 mol/L(1.5Qth) hydrogen peroxide,85% of guaiacol removal is achieved in 80min.Fe2O3/γ-Al2O3 catalysts were modified by ultrasound impregnating other trace elements. The stability and activity of modified catalysts is improved obviously, due to the increase of active components dispersion. The modified catalysts also were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption (BET). Under the conditions:100 mg/L guaiacol, initial pH 6.1, T=70℃,4 g/L catalyst,0.0204 mol/L(1.0 Qth) hydrogen peroxide,97% of guaiacol removal is achieved in 40min.The catalysts stability were investigated. The catalytic activity of Fe2O3/γ-Al2O3 catalyst was decreased after five recycle times and the removal of the guaiacol is decreased from 85%to 70%, iron dissolution was increased from 0.44 mg/L to 0.8 mg/L. Under the same conditions, the removal of the guaiacol was decreased from 97%to 87% and iron dissolution was significantly decreased from 0.25 mg/L to 0.2 mg/L for modified catalysts.Based on the HPLC-MS and GC-MS results, the intermediates and the degradation pathways of guaiacol were studied. The results showed that the main 6 intermediates are catechol,3,3’-dimethoxy-4,4’-dihydroxybiphenyl,3-methoxy-catechol,2-methoxy resorcinol,2-methoxy hydroquinone, and 4-methoxy catechol. The degradation pathway of guaiacol were included electrophilic substitution, coupling reaction and so on. The intermediates were oxidized to quinones firstly, then were further degraded into acid formic acid, acetic acid and oxalic acid, and ultimately were degraded into CO2 and H2O.