Conversion Of Macromolecular Lignin And Natural Oil By Catalyst Design

With the aggravation of the energy crisis,biomass energy which is the only storable and.transportable organic carbon resource with its abundant storage has aroused people's great attention.It is also regarded as the fourth energy system next to coal,petroleum and natural.gas.Effective utilization of biomass and oil is still one of the hot topic for researchers,as they are two of the most important biomass resources.In this paper,starting with the analysis of catalyst and catalyst system,the influence of the catalyst composition and physicochemical properties on the conversion of biomass and oil were studied.One-pot conversion of lignin to cycloalkanes had be accomplished with 100%selectivity,and high selective?>95%?transformation of stearic acid and coconut oil to fatty alcohols had also been achieved.A facile and effective method was reported for preparation of bio-jet fuel through co-activation between biomass and oil.The thesis was mainly explained in three parts:?1?Direct Production of Naphthenes and Paraffins from lignin? The use of lignin as a fuel and chemical precursor had aroused great concern,but the technique for lignin deconstruction need an urgent breakthrough.This section presented a novel and simple method for the conversion of lignin to the naphthenes and paraffins?predominantly C₆-Cg?at 300? and 6 MPa H₂ using amorphous silica-alumina oxides supported with Ni nanoclusters as catalyst.? The results showed that the key factor of depolymerization and further hydrodeoxygenation of lignin is to select the appropriate solvent and active sites under appropriate conditions.Although lignin has a better dispersion in polar solvents such as ethylene glycol,ethanol,and 1,4-dioxane,the major products were phenol compounds and the conversion of lignin was low.The optimum solvent for lignin depolymerization was a nonpolar solvent-dodecane which offered a large fraction of cyclohexanes/alkanes,meanwhile as the solvent was dodecane,the separation step of the solvent and the product was avoided.? The results of the effect of the deposition time,the Ni particle size,the reduction temperature and the acid content of the catalyst showed that the metallic properties of Ni loading,size distribution,and dispersion as well as the acidic features of Bronsted and Lewis acid sites and the synergy of metal and acid sites on the silica alumina support can greatly influence the activity of lignin depolymerization.The catalysts with larger external specific surface,small Ni nanoparticle size,stronger Br???nsted acidity was more suitable for the conversion of lignin.? The study of mechanism of the transformation of macromolecular lignin showed that the first step of conversion of lignin on Ni/ASA is that Ni nanoclusters cleave the exposed external C-O-C linkages of the lignin macromolecule to form phenolic oligomers?rate:0.58 g·g-1·h-1?.Then the multi-steps of C-O cleavage on phenolic oligomers follow?rate:0.13 g·g-1·h-1?.Finally after multi-steps of demethoxygenation?rate:20.6 g·g-1·h-1?,hydrogenation,and dehydration,guaiacol and syringol derivatives are converted to target cycloalkanes?rate:27.8 g·g-1·h-1?.Duing those steps,the rate-determining step was the cleavage of phenolic oligomers.?2?Design the macroporous-mesoporous Ni-based catalysts for the conversion of lignin to cycloalkanes? Although porous materials had got great achievement in the conversion of small molecule compounds,the application for macromolecules transformation still needs an urgent breakthrough.After carefully study the influence of the pore structure of the catalyst on the lignin depolymerization,the Ni supported on the ASA with macroporous-mesoporous was perpared as the catalyst.The gradual conversion of lignin was accomplished through depolymerization of lignin and phenolic oligomers with Ni particles in macropores,while the depolymerization and hydrodeoxygenation of phenolic polymers and monomers were in mesopores.Although the ratio of lignin to catalyst was as high as 4:0.5?highest value in the references is 2:1?,the one-pot transformation of lignin to cycloalkanes was achieved in high efficiency?rate:0.48 g·g-1·h-1?.? HBEA-2 with intercrystalline mesopores?5-10 nm?was synthesized through alkali treatment while HBEA-3 with intracrystalline mesopores?8nm?was gained according to soft template synthesis.After loading with nickel particles through deposition-precipitation methods,these two catalysts were compared with flat-plate Ni/HBEA-1 and open-type Ni/ASA-1,in order to study the influence of structure on the depolymerization of lignin.It showed that as macromolecular lignin and phenolic oligomers can hardly enter the mesopores which are relatively small,the liquid yield with Ni/HBEA-2?40%?and Ni/HEBA-3?41%?were higher than Ni/HBEA-1?35%?,but still lower than open type Ni/ASA-1?46%?.? The ASA catalyst with macroporous?3 and 6 pm?and mesoporous?23 nm?was designed as a "nanoreactor" to realize the stepwise transformation of macromolecular lignin?2-10?m?in the pore,which still maintained a good activity under the condition of high ratio of lignin to catalyst?4:0.5?,The conversion of lignin was 42.8%and the selectivity of cycloalkanes was 100%,the conversion rate of macromolecular lignin was 0.48 g·g-1·h-1.Meanwhile the conversion of lignin on tranditional Ni/ASA was only 25.4%and 3.5%phenol compounds was found in the products,the conversion rate of macromolecular lignin was 0.14 g·g-1 ·h-1.? A new route for prepare bio-jet fuel by the co-activation of cycloalkanes and oils in the absence of hydrogen was proposed.Using cycloalkanes to provide the hydrogen for the hydrogenation of oil to solve the problem of hydrogen consumption problems,while cycloalkanes will convert to aromatic hydrocarbons to improve the energy density of bio-jet fuel,Thus avoid the adding aromatic processing steps of Traditional preparation process of bio-jet fuel?Finally,we successfully achieved the co-activation of cycloalkanes and Palm oil without the presence of hydrogen,20.84%naphthenes,19.36%paraffins and 59.79%aromatics was obtained.The content of bio-jet fuel components?C8-C18?was 78.4%.The physical and chemical characteristic of products meets the requirements of bio-jet fuel.?3?Design the RuSn bimetallic nanoclusters catalysts for the conversion of oils to fatty alcohols? Transformation of natural lipid to green bio-chemicals attracts great attention.An active catalyst of Ru₃Sn₇ nanoclusters on SiO₂ support was developed for quantitative conversion of coconut oil to fatty alcohols in dodecane at conditions?240?,4 MPa H₂?,both conversion and selectivity are more than 95%.? Among the tested single supported metals of Ru,Sn,Pt,Pd,Ni,Co,and their combinations,RuSn exhibited the highest hydrogenation capability.Assisted with the characterization of XRD patterns,IR of adsorbed CO,and TPR-H₂,the catalytic tests confirmed that the proper Ru/Sn ratio of 3/7?forming the most abundant Ru₃Sn₇ clusters as active species?on the SiO₂ support enabled the highest hydrogenation rate?2.45 g·g-1·h-1?,while suppressing the ester formation?side-reaction?on the Srn₂/SiO₂ species with a rate of 0.31 g·g-1·h-1.This founding was intrinsically different to the previously reported recognition that Ru…O=Sn was the active site for hydrogenation.To control the preferable compositions of Ru₃Sn₇ active sites on the SiO₂ support,a reduction temperature should be adjusted at around 460?.A higher reduction temperature allowed Sn/SiO₂ formation,which can catalyze the ester formation with a rate of 0.88 g·g-1·h-1.? The density function theory calculations showed that Ru₃Sn₇ nanoclusters had the lowest formation energy of-21.2 kJ·mol-1·atom-1 compared to Ru₁Sn₂ and Ru₂Sn₃.Meanwhile,the calculation result that the much lowered energy barrier?81.0 kJ·mol-1?for acid hydrogenation over Ru₃Sn₇?111?than that over Ru?0001??123.5 kJ·mol-1?indicated that the.Ru₃Sn₇ alloy had a higher activity than Ru for hydrogenation of acids,perfectly agreeing with the experimental results.