Research On Selective Oxidative Of Biomass Catalyzed By Metalloporphyrins

Since fossil resources (oil, coal, natural gas, etc.) are non-renewable and their pricecontinues to rise, the availability of fossil resources will decline constantly in the long-termperspective. Therefore, in order to reduce the rate of consumption of non-renewable fossilresources, we must find the new solutions. Although there are lots of renewable resourceswhich can be used to replace fossil resources, such as wind, water, nuclear fusion and fission,solar, etc. However, based on the sustainable transformation of industrial materials, such aschemical industry, industrial biotechnology and fuel, depend on the biomass resources,especially vegetable biomass resources. Thus, this paper intends to aim at transferringbiomass feedstocks from renewable resources in low-value into high-value chemicals, usingmetalloporphyrin as a catalyst for the selective catalytic oxidation of biomass feedstocks andpreparing the high value-added chemicals (aromatic aldehydes) so as to propose the theoryof catalytic oxidation of preparing high value aromatic aldehydes from biomass feedstock.The improved Adler’s method was used to prepare tetraphenylporphyrin. In order toimprove the water-solubility, the tetraphenylporphyrin was sulfonated into tetrakis-(4-sulfophenyl) porphyrin (TPPS4), and then synthesized into the corresponding tetra-(4-sulfophenyl) metalloporphyrin with the reaction of four kinds of metal salt (Co+2, Ni+2, Cu+2,and Zn2+). The catalytic oxidation effect of degrading the enzymolysis of corn stover ligninusing these metalloporphyrins has the following order: Co(TPPS4)>Cu(TPPS4)>Ni(TPPS4)>Zn(TPPS4). Selective catalytic oxidation products of degrading the enzymolysis of corn stoverlignin are mainly hydroxybenzaldehyde, vanillin and syringaldehyde, which are highvalue-added. Choosing Co(TPPS4) as catalyst, the optimal reaction conditions are:180min,150℃, Co(TPPS4) in an amount of0.1000g, H2O2as oxidant in an amount of0.5mL. Underthese conditions, the catalytic oxidation of lignin from corn stover degradation cansimultaneously obtain5.50%of p-hydroxybenzaldehyde,4.68%of vanillin and2.66%syringaldehyde, the total yield of three aromatic aldehydes is nearly five times as much as theone without catalyst. Therefore, the method of selective catalytic oxidation by usingmetalloporphyrin catalysts to prepare high-value chemicals (aromatic aldehydes) frombiomass feedstock is feasible.Co(TPPS4) was regarded as catalyst, TCI non-alkaline lignin, black liquor alkaline lignin,lignosulfonate and bamboo alkaline lignin were as feedstock. According to the results ofselectively catalytic oxidation degradation of the lignin, alkaline lignin (TCI non-alkalinelignin, black liquor alkaline lignin, and bamboo alkaline lignin) can be degraded to produce high value-added aromatic aldehyde compounds by catalytic oxidation in Co(TPPS4)/H2O2system, and the content of products accord with the composition of alkaline lignin. But, underthe same reaction conditions, the reactivity of alkali lignin was not as good as enzymolysis ofcorn stover lignin. That is the reason that2,6-dimethoxy-4-vinylphenol was presence in theproducts from alkaline lignin catalytic oxidation. Although the reactivity of alkali lignin wasnot as good as enzymolysis of corn stover lignin, but it still can be concluded that alkali lignincontains its base unit (p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol) by catalyticoxidation in Co(TPPS4)/H2O2system. Comparing with the method of alkaline nitrobenzeneoxidation, the method of measuring lignin unit structure was greener and more environmentalby Co(TPPS4)/H2O2system. At the same time, because lignosulfonate contains a largenumber of sulfonic acid group, which resulted in increased space steric hindrance, finally theproducts didn’t conform to the raw material composition, so lignosulfonate was not fullycatalytic oxidation degraded by Co(TPPS4)/H2O2system.Bio-oil can be separated into three parts, including low-boiling fraction (low-boilingorganic acids, alcohols, ketones, etc.), crude saccharide (mainly levoglucosan), and heavyfraction (guaiacol,2-methoxy-4-methylphenol, etc.). According to the special properties ofthese separated three parts, respectively, the further upgrading will be more reasonable andeffective. We proposed the conversion of heavy fraction of bio-oil (HFBO) to producevaluable aromatic aldehydes by an environmentally friendly method,metalloporphyrins/(H2O2) system catalytic oxidation. High value-added aromatic aldehydeswere selectively produced from heavy fraction of bio-oil in a catalytic oxidation process usingCo(TPPS4) as catalyst.4.57wt.%vanillin and1.58wt.%syringaldehyde were obtained fromcatalytic oxidation of HFBO.Ferulic acid,4-ethyl guaiacol, H-type and G-type polymer were selected to be lignin andheavy fraction of bio-oil model compounds. The model compounds were degradation inmetalloporphyrins/H2O2system to simulate the real lignin and HFBO catalytic oxidationprocess. A possible mechanism of lignin and HFBO oxidation using Co(TPPS4)/H2O2wasproposed by the research of model compounds. Cleavage of β-O-4bonds was the majorpathway that H-type and G-type polymer degraded to produce4-vinylphenolics.[(TPPS4)Co=O]+can transfer the oxygen atom to double bonds of4-vinylphenolics, andforming aromatic aldehyde or phenyl ethyl ketone compounds. The few aromatic aldehydecould be further oxidized to aromatic acid. The results also indicated that unsaturated sidechain of aromatic compounds were apt to produce aromatic aldehydes by catalytic oxidationin Co(TPPS4)/H2O2system. In order to improve the repeated performance of the catalyst, a sulfonic acid phenyl in Co(TPPS4) transformed into a carboxylic acid phenyl, and forming Co(TPPS3C), and thenCo(TPPS3C) was immobilized on the magnetic Fe3O4@SiO2with amino modified (FS). FSand FS-Co(TPPS3C) were characterized by FT-IR, UV, SEM, XRD and VSM. Enzymolysiscorn straw lignin was considered as raw material, Co(TPPS4) can be reused for three times atmost, and catalytic oxidation effect declined gradually. However, FS-Co(TPPS3C) byimmobilized showed high catalytic activity and stability in the recycling experiments. Theimmobilized FS-Co(TPPS3C) was better dispersed in water phase，because of the existence ofsulfonic acid group, which can also enhance the stability of the metalloporphyrin, and keepefficient catalytic activity of the metalloporphyrin. The method of magnetic separation canrealize the rapid and simple separation, and then recycling of catalyst, effectively avoid thecatalyst recycling and complexed operation.