The Research Of Rare Earth Metals Catalysts Development And Their Applicantionon Lignin Depolymerization

Lignin is a kind of macromoleculepolymer consists of three phenylpropaneunits connected by C-O-C and C-C bonds.It is considered as a remarkable material with the potential to produce premium fuel as well as high-valued aromatic chemicals.However,compared with cellulose conversion,lignin conversion technology can be difficult.Lignin is a kind of polymer with compact structure which is resistant to chemicals.Furthermore,the re-polymerization phenomenon and low selectivity during reaction are two bottleneck problems for lignin conversion.Some methods such as lignin structure unit breaking,deoxygenation,benzene hydrogenation,dealkylation,methoxycanhave achieved effective lignin depolymerization results under mild condition.Rare earth metals have a unique electron clouds structure and have shown excellent transfer ability during catalytic reaction.Those metals have been used in petroleum cracking for several decades and showed remarkable catalytic cracking and hydrogenation effect.In this paper,a series of rare earth metals were developed and the applications of those catalysts in lignin depolymerization were systematically studied.Metals includingNi,Co and La were used to modify the catalyst Ce-MCM-41 following chemical reduction method.Those modified catalysts were characterized by TEM and used in alkali lignin Indulin AT depolymerization reactions.The result indicated that Ce,Ni,Co and Lawere uniform loaded on the channel of MCM-41.The particle size of Ce was about 5nm whilesizesof other metals were at 2?3nm.The ether extraction yield of lignin after catalytic depolymerized by Ce-MCM-41 is 19%.It was found that the optimized catalyst Ni/Ce-MCM-41 could effectively depolymerize lignin to 46.1%liquefied fuel under optimized reaction condition.All products obtained from lignin depolymerization catalyzed by four kinds of catalysts are the same,which were listed as 2-methoxy phenol,4-ethyl methyl guaiacol,4-ethyl-guaiacol and 4-propyl guaiacol.When the catalyst Ce-MCM-41 was used as catalyst,the highest yield product was 4-ethyl methyl guaiacol.When the catalyst Co/Ce-MCM-41,La/Ce-MCM-41,Ni/Ce-MCM-41 was used,the highest selectivity ofthe product 2-methoxy phenol was achieved.Two kinds of catalysts Ce-CNT together with La-CNT were synthesized by loading rare earth metal on carbon nanotube(CNT).Those two kinds of catalystswere used for commercial lignin BCL depolymerization under mild condition.The catalytic performances as well as catalysts stability were evaluated through depolymerization results.The fuel feature of liquefied lignin was measured by element analysis and calorific value test.The result suggested that Ce modified CNT showed small particles and uniform dispersion.The catalyst showed significant effect on lignin depolymerization under mild condition.The ethyl acetate extraction yield catalyzed by Ce-CNT reached to higher than 82%,better than La-CNT.The upgraded fuel after extraction presented low oxygen content as well as carbon-hydrogen ratio,and the calorific value is 26.3MJ/kg,much higher than raw lignin.A negligible activity lossofCe-CNTwas found after four times run,which showed good anti-carbon performance together with stability.On basis of the research above,a series of bi-functional catalysts using many hydrogenation metals Ni,Pd and Rucombined with Ce-CNT were developed.XRD and XPS were used to analyze metal values.The catalysts were used for raw biomass lignin as well as industrial lignin Indulin AT depolymerization.The result showed that the element Ce existed as CeO2 while element Ni always existed as zero value.During catalysts synthesis process,a high-performed catalyst Ni/Ce-CNT was synthesized when the mass ratio of PVP to metal was 1:1,reduction time was 5h.When Ni/Ce-CNT was used for raw lignin depolymerization,a high monophenols yield at 21.4%was achieved when the reaction condition was set at 300? for 2h in dioxane-water-1%HCl.During reaction process,Ni and Ce presented synergy effect.It was found that Ce had the effect on lignin bonds cracking while Ni showed effect on free radicals passivation and prevented products from re-polymerization.Ni/Ce-CNT showed good stability during the reaction.No obvious activation loss was observed after many cycles.A series of metallic-modified Ce-ZSM-5 catalysts were developed by hydrogen reduction method.Those catalysts were used in organosolve lignin as well as a series of lignin model compounds depolymerization.The result showed that the bi-functional catalyst Ru/Ce-ZSM-5 had remarkable effect on organosolve lignin depolymerization.The result of lignin model compounds depolymerization process indicated that Ce didn't show significant influence on ether bonds cleavage whileRu and Pd showed good effect on ether bond cracking as well as products hydrogenation.Therefore,a conclusion can be drawn that during lignin depolymerization reaction,rare earth metals showed major effect on C-Cbonds cleavage rather than ether bond cleavageIn this research,a series of composite metal catalysts with rare earth metals as core werw developed.The reaction mechanism of those catalysts in different catalytic systems were investigated,and an effective lignin conversion was achieved.