Study On Preparation Of Woody Biomass Hydro-liquefaction Catalysts And Catalytic Performance

The depletion of fossil resources?coal,petroleum and natural gas?,which are the base of rapid human development,is a serious threat to human development and national strategic security.Large quantities of fossil energy were used every year in the world,which seriously damaged the environment?acid rain,dust,global warming,etc.?.Therefore,seeking a green,renewable and resource-rich alternative energy is necessary.Every year,biomass produced by green plants via photosynthesis is about 10 times of the energy consumption of the people in the world.Biomass resources also have the advantages of low ash,renewable,carbon neutral and so on.Hence,biomass will be the sources of energy and chemicals in the future.Biomass hydro-liquefaction is one of the most important ways to convert biomass into liquid fuels and chemicals efficiently.The key scientific problem of biomass hydro-liquefaction is to develop an efficient and stable catalyst.Sawdust hydro-liquefaction in the absence of catalyst was performed in five solvents,i.e.,cyclohexane,toluene,methanol,ethanol,and isopropanol.The results show that the conversion yield of sawdust when isopropanol as solvent is the highest,whereas the yield of bio-oil when liquefied in methanol is the highest.High sawdust conversion and bio-oil yield are obtained when liquefied in ethanol.A total of 42 compounds with high content were identified from the bio-oil by gas chromatography/mass spectrometry?GC/MS?.Main compounds in bio-oil obtained in cyclohexane and toluene are phenolics.Some esters appear in bio-oil obtained in methanol and ethanol.Ethanol is determined as solvent for sawdust hydro-liquefaction since it is easy to be produced from biomass by fermentation.Three supports with different pore structure,i.e.,SiO₂,Al₂O₃ and ZSM-5-SBA-15?meso-microporous molecular sieve?,were prepared.Taking ammonium paramolybdate,and ammonium tetrathiomethacrylate as precursor,MoO₂/SiO₂,MoS₂/SiO₂,MoS₂/Al₂O₃and MoS₂/ZSM-5-SBA-15 catalysts were prepared by incipient impregnation.The supports and catalysts were characterized by N₂ adsorption-desorption,pyridine adsorption infrared spectroscopy?Py-IR?,X-ray diffraction?XRD?,scanning electron microscopy/energy dispersive spectroscopy?SEM/EDS?and transmission electron microscopy?TEM?.The bio-oil yields of 49.97 and 52.01%were obtained when MoO₃/SiO₂ and MoS₂/SiO₂ was used as catalyst,respectively,indicating that MoS₂ had a better catalytic effect.In order to investigate the effect of the supports on catalytic effect,sawdust hydro-liquefaction over MoS₂/SiO₂,MoS₂/Al₂O₃,and MoS₂/ZSM-5-SBA-15?with Si/Al ratio of 20,30,and 40?were carried out.The results show that ZSM-5-SBA-15 with a Si/Al ratio of 30 has the highest catalytic activity.The optimum conditions are as follows:reaction time 40 min,reaction temperature 320 ?,sawdust/catalyst=10:1,initial H₂ pressure of 6 MPa.The bio-oil yield under optimum conditions was 60.74%.After treated in water at 320 ? for 24h,the catalytic activity of MoS₂/ZSM-5-SBA-15 is not significantly changed,indicating that the catalyst is stable.Five MoO₂ catalyst supported on SiO₂,Al₂O₃,ZSM-5,SAPO-11,and ZSM-5-SBA-15-30was prepared from MoO₃ reduction by H₂.MoO₂/SiO₂ catalyst has a highest catalytic activity,and bio-oil yield is 58.6%.The preparation method of MoO₂/SiO₂ by oxidation of ammonium tetrathiate molybdate was proposed for the first time.MoO₂/SiO₂ was analyzed by XRD,SEM,TEM and EDS mapping.The results show that the average particle size of MoO₂ is about 74.6 nm,and MoO₂ is well dispersed.When the initial H₂ pressure was 2MPa,the bio-oil yield was 60.01%,which is obviously higher than that of MoO₂/SiO₂catalyst?58.6%?prepared by H₂ reduction method.When the initial H₂ pressure increased to6 MPa,the bio-oil yield was 72.3%.GC/MS analysis showed that the relative content of phenolics in bio-oil was the highest,reaching 43%,and the relative content of ethyl esters was about 29%.There were still many unidentified compounds by GC/MS.MoO₂/Mo₂C-R catalyst with dual active components was prepared by H₂ reduction of MoO₃/C at high temperature.The bio-oil yield obtained over this catalyst was 56.86%.In order to obtain higher bio-oil yield,MoO₂/Mo₂C-R catalyst was modified by Fe,Co,Ni,La,and Ce for the first time.The effect of the amount of modifier on catalytic activity were investigated.The results show that the effect of Ce is better than that of the other four modifiers.When the molar ratio of Ce/Mo was 0.20,the yield of ethanol-soluble matter and total bio-oil reached 55.68%and 64.28%,respectively.Twenty-two long-chain fatty acid ethyl esters,two alkanols,four amides,four lignin derivatives?p-di?2,6-dimethoxyphenolyl?compound?,four xanthone compounds,three cellulose derivatives,and some unknown group components were enriched.Three pure?ethyl 16-hydroxy-hexadecanoate,ethyl 18-hydroxyoctadec-8-enoate and diethyl octadec-9-enedioate?were isolated.The oxidation products of sawdust liquefaction residue are mainly fatty acids and benzene polycarboxylic acids.The presence of mellitic acid in the oxidation product proved at the molecular level that the sawdust was polymerized during the hydro-liquefaction process,and a larger condensed aromatic ring structure was formed.