Study Catalytic Degradation Of Lignin By Modified Molybdenum-based Sepiolite Catalyst

Depolymerization of lignin to produce high yield lignin oil is one of the prospective methods to achieve the sustainable and economic development for human society.Lignin,has a complicated cross-linking structure with the features of notorious inactive property and heterogeneous polymer.As a result,lignin is mostly regarded as a waste and normally burned as a low value fuel.According to relevant statistics,there is about 40-50 million tons of lignin produced from the pulp and paper industry every year.To date,multiply strategies have been devoted to effective conversion and depolymerization of lignin,including pyrolysis,hydrolysis,and hydrogenolysis.Among,catalytic hydrogenolysis has been studied extensively in recent years due to its effectiveness and feasibility for the conversion of lignin to liquid fuel or other high-value chemicals.Furthermore,the products obtained by this methodology have normally a high hydrogen/carbon ratio（H/C）,endowing it with significant underlying to be a fine liquid-fuel after upgrading.In this study,Mo/SEP（C-Mo/SEP）catalysts modified by different reductants（hydrogen,sodium borohydride）and alkali iron（Fe）were used to investigate the effect of modified Mo-seplolite catalyst on lignin catalytic depolymerization in supercritical ethanol medium.The properties of catalyst were analyzed by lignin conversion,lignin oil yield,petroleum ether soluble yield and solid yield.The effects of reduction modification and metal Fe modification on microstructure and properties of Mo/SEP were studied by means of N₂-adsorption-desorption,SEM,XRD,etc.The results showed that reduction treatment optimized the distribution of Mo⁵⁺species and B/L acid sites in The Mo/SEP catalyst.Under the supercritical condition,N-Mo/SEP catalyst carried out lignin depolymerization for 3 h under the atmosphere of 290 C N₂.The calorific value of lignin oil was 34.92 MJ/kg,which was slightly lower than that of 36.0 MJ/kg under C-Mo/SEP.The yield of lignin was the highest（112.0%）and that of petroleum ether soluble（PES）product（74.6%）over N-Mo/SEP catalyst.According to the results of gas chromatography-mass spectrometry,the possible reaction mechanism of lignin depolymerization catalyzed by N-Mo/SEP and H-Mo/SEP catalysts under supercritical conditions was proposed.For N-Mo/SEP catalysts,the synergistic effect of Mo⁵⁺and B/L acid sites promoted the cleavage of the C_aryl-OCH₃ bond,and the appropriate amount of acid promoted the alkylation reaction.As for the H-Mo/SEP catalyst,because it contains more inactive Mo⁴⁺species,a small amount of Mo⁵⁺active species and low acid quantity distribution,its ability to crack the C_aryl-OCH₃ bond is weak,and its ability to promote advanced alkylation reaction is also poor.Mo/SEP catalysts with different Mo and Fe contents（29Mo1Fe,27Mo3Fe,25Mo5Fe,23Mo7Fe,20Mo10Fe,15Mo15Fe）were prepared by impregnation method to explore the influence of load on the crystal structure of the catalyst and the active site on lignooil yield and specific monomer yield.